Environmental Protection Review Report – Darlington Nuclear Generating Station

Executive summary

This EPR report was written by CNSC staff as a stand-alone document, describing the scientific and evidence-based findings from CNSC staff’s review of Ontario Power Generation’s (OPG’s) environmental protection measures. The periodic EPR report provides an assessment of documents related to the Darlington Nuclear Site (DN site), which consists of the Darlington Nuclear Generating Station (DNGS) and the Darlington Waste Management Facility (DWMF).

The DN site is located within the lands and waters of the Michi Saagiig Anishinaabeg, the Gunshot Treaty (1787-88), the Williams Treaties (1923), and the Williams Treaties First Nations Settlement Agreement (2018). Under its current power reactor operating licence, PROL 13.01/2025, OPG is permitted to operate the DNGS units for power production. Under the waste facility operating licence, WFOL-W4-355.00/2033, OPG is also permitted to operate the DWMF. This EPR does not encompass the proposed Darlington New Nuclear Project or the licences to prepare a site, the applications to modify the licence to prepare a site or the application for a licence to construct.

CNSC staff’s EPR report focuses on items that are of Indigenous, public, and regulatory interest, such as potential environmental releases from normal operations, as well as the risk of releases of radiological nuclear and hazardous (non-radiological) substances to the receiving environment, valued ecosystem components (VECs) and species at risk. CNSC staff also endeavour to focus on items related to Indigenous Nations and communities Rights, values and culture, when information is shared with the CNSC.

This EPR report includes CNSC staff’s assessment of documents submitted by the licensee to CNSC staff from 2016 to 2023 and the results of CNSC staff’s compliance activities, including the following:

engagement with Indigenous Nations and communities
regulatory oversight activities
the results of OPG’s environmental monitoring, as reported in the environmental monitoring program reports
OPG’s 2020 environmental risk assessment for the DN site
OPG’s 2021 preliminary decommissioning plan for the DN site
the results of the CNSC’s Independent Environmental Monitoring Program
the results from other environmental and groundwater monitoring programs and/or health studies (including studies completed by other levels of government) in proximity to the DN site

Based on their assessment and evaluation of OPG’s documentation and data, CNSC staff have found that the potential risks from nuclear and hazardous releases to the atmospheric, terrestrial, aquatic and human environments from the DN site are low to negligible, and that any releases are at levels similar to natural background. Furthermore, human health is not impacted by operations at the DN site and the health outcomes are indistinguishable from health outcomes found in the general public. CNSC staff have also found that OPG continues to implement and maintain effective environmental protection measures that meet regulatory requirements and adequately protect the environment and the health and safety of persons. CNSC staff will continue to verify OPG’s environmental protection programs through ongoing licensing and compliance activities.

CNSC staff’s findings from this report may inform recommendations to the Commission in future licensing and regulatory decisions, as well as inform CNSC staff’s ongoing and future compliance verification activities. CNSC staff’s findings do not represent the Commission’s conclusions. The Commission’s decision-making will be informed by submissions from CNSC staff, the licensee, Indigenous Nations and communities, and the public, as well as through any interventions made during public hearings on Commission proceedings.

A pamphlet of this EPR report with a public friendly summary is available in Appendix A of this report. OPG also makes many summary documents, including reports containing environmental data, available on OPG’s website. References used throughout this document are available upon request and requests can be sent to er-ee@cnsc-ccsn.gc.ca.

1.0 Introduction

1.1 Purpose

The Canadian Nuclear Safety Commission (CNSC) conducts environmental protection reviews (EPRs) for all nuclear facilities with potential interactions with the environment, in accordance with its mandate under the Nuclear Safety and Control Act (NSCA) ^{Footnote 1}. CNSC staff assess the environmental and health effects of nuclear facilities and/or activities during every phase of a facility’s lifecycle. As shown in figure 1.1, an EPR is a science-based environmental technical assessment conducted by CNSC staff to support the CNSC’s mandate for the protection of the environment and human health and safety, as set out in the NSCA. The fulfillment of other aspects of the CNSC’s mandate is met through other regulatory oversight activities and is outside the scope of this report. Each EPR report is typically conducted every 5 years and is informed by the licensee’s environmental protection (EP) program and documentation submitted by the licensee as per regulatory reporting requirements.

As per the CNSC’s Indigenous Knowledge Policy Framework ^{Footnote 2}, the CNSC recognizes the importance of considering and including Indigenous Knowledge in all aspects of its regulatory processes, including EPRs. CNSC staff are committed to working directly with Indigenous Nations and communities and knowledge holders on integrating their knowledge, values, land use information, and perspectives in the CNSC’s EPR reports, where appropriate and when shared with the licensee and the CNSC.

The purpose of this EPR is to report the outcome of CNSC staff’s assessment of the Ontario Power Generation Inc. (OPG)’s EP measures and CNSC staff’s health science and environmental compliance activities for the Darlington Nuclear Site (DN site) – operations at both the Darlington Nuclear Generating Station (DNGS) and the Darlington Waste Management Facility (DWMF). This review serves to assess whether OPG’s EP measures at the DN site meet regulatory requirements and adequately protects the environment and health and safety of persons.

While this EPR focuses on the EP measures of the DN site from 2016-2023, it should be noted that in May 2024, OPG submitted a licence application to renew the power reactor operating licence from December 1, 2025 to November 30, 2055 ^{Footnote 3}. CNSC staff has prepared this EPR to inform the licensing decision of the Commission.

Overview of the interactions between the CNSC’s environmental protection review framework and the licensee’s environmental protection measures. — **Figure 1.1: Environmental protection review framework**

CNSC staff’s findings may inform recommendations to the Commission in future licensing and regulatory decision making, as well as inform CNSC staff’s ongoing and future compliance verification activities.

CNSC staff’s findings do not represent the Commission’s conclusions. The Commission is an independent, quasi-judicial administrative tribunal and court of record. The Commission’s conclusions and decisions are informed by information submitted by the applicant or licensee, the CNSC staff, Indigenous Nations and communities, and the public, as well as through any interventions made during public hearings on Commission proceedings.

EPR reports are prepared to thoroughly document CNSC staff’s technical assessment relating to a licensee’s EP measures and are posted online for information and transparency. Posting EPR reports online, separately from the documents drafted during the licensing process, allows interested Indigenous Nations and communities and members of the public additional time to review information related to EP prior to any licensing hearings or Commission decisions. CNSC staff may use the EPR reports as reference material when engaging with interested Indigenous Nations and communities, members of the public and interested stakeholders. To assist with outreach and engagement for the DN site, a pamphlet of this EPR report with a public friendly summary is available in Appendix A of this report.

This EPR report is informed by documentation and information submitted by OPG, compliance activities completed by CNSC staff from 2016 to 2023, and other sources, such as:

engagement with Indigenous Nations and communities (section 1.2)
regulatory oversight activities (section 2.0)
CNSC staff’s review of OPG’s 2021 Nuclear Site preliminary decommissioning plan (PDP) ^{Footnote 4} and the 2021 preliminary decommissioning plan for the Darlington Waste Management Facility ^{Footnote 5} (section 2.2)
CNSC staff’s review of OPG’s environmental and groundwater monitoring program results for Darlington from 2016 to 2023 ^{Footnote 6} ^{Footnote 7} ^{Footnote 8} ^{Footnote 9} ^{Footnote 10} ^{Footnote 11} ^{Footnote 12} ^{Footnote 13} ^{Footnote 14} ^{Footnote 15} ^{Footnote 16} ^{Footnote 17} ^{Footnote 18} ^{Footnote 19} ^{Footnote 20}
data from studies related to assessments conducted for facilities and activities on the DN site (section 3.0)
results of the CNSC’s Independent Environmental Monitoring Program (IEMP), including discussions with Indigenous Nations and communities (section 4.0)
health studies with relevance to the DN site (section 5.0)
data from other environmental monitoring programs (EMPs) in proximity to the DN site (section 6.0)

This EPR report focuses on topics related to the facilities’ environmental performance, including atmospheric (emission) and liquid (effluent) releases to the environment, and the potential transfer of constituents of potential concern (COPCs) through key environmental pathways and associated potential exposures and/or effects on valued ecosystem components (VECs), including human and non-human biota. VECs refer to environmental, biophysical or human features that may be impacted by a project. The value of a component relates not only to its role in the ecosystem, but also to the value people place on it (for example, it may have scientific, social, cultural, economic, historical, archaeological or aesthetic importance). The focus of this report is on radiological nuclear and hazardous substances associated with licensed activities undertaken at the DN site, with additional information provided on other topics of Indigenous, public and regulatory interest. CNSC staff also present information on relevant regional environmental and health monitoring, including studies conducted by the CNSC or other governmental organizations.

1.2 Facility overview

This section provides general information on the DN site, including a description of the site location and a basic history of site activities and licensing. This information is intended to provide context for later sections of this report, which discuss completed and ongoing environmental and associated regulatory oversight activities.

1.2.1 Site description

The DN is located within the lands and waters of the Michi Saagiig Anishinaabeg, the Gunshot Treaty (1787-88), the Williams Treaties (1923), and the Williams Treaties First Nations Settlement Agreement (2018). The facilities are located in the Municipality of Clarington, Ontario, (formerly the township of Darlington) on the north shore of Lake Ontario. The DN site is located approximately 5 kilometres (km) southwest of the community of Bowmanville, 10 km east-southeast of the City of Oshawa, and 70 km east of Toronto. The DN site is 485 hectares (ha) in area, with additional water lot areas extending into Lake Ontario to accommodate structures and features associated with the DNGS. The DN site lands are bounded by Highway 401 and Energy Drive West to the north and Lake Ontario to the south. To the west, the DN site is bounded by Solina Road and agricultural land. The St. Mary’s Cement Bowmanville plant occupies the land east of the DN site.

The DN site is owned and operated by the licensee, OPG. DNGS and the DWMF operate under separate licences issued by the Commission to OPG. This EPR Report includes CNSC staff’s assessment of the EP measures at both the DWMF and DNGS and does not encompass the proposed Darlington New Nuclear Project (DNNP) as this EPR report is meant to encompass the ongoing operations at the Darlington Nuclear site under the existing power reactor and waste facility operating licences.

The DN site houses the following nuclear facilities (figure 1.2):

The DNGS, comprising 4 CANada Deuterium Uranium (CANDU) reactors and associated infrastructure and equipment
The Tritium Removal Facility (TRF), where tritium is extracted from tritiated heavy water
The DNNP lands
The DWMF, located in a separate protected area to the east of the DNGS

The DN site also includes a visitor information centre, a Hydro One switching station (which connects DNGS to the Hydro One transmission corridor), technical and administrative support facilities and security facilities.

Aerial overview of the Darlington Nuclear Site, including the DNGS, DWMF and proposed DNNP Site. — **Figure 1.2: Aerial view of the Darlington Nuclear Site**

1.2.2 Facility operations

The DNGS began operating in 1990, and the DWMF became operational in 2008. Under the power reactor operating licence for the DNGS, OPG possesses and uses nuclear substances and associated equipment to generate power. Under the waste facility operating licence for the DWMF, OPG operates the waste management facility and associated activities to manage waste generated from the DNGS.

1.2.2.1 Darlington Nuclear Generating Station

The DNGS consists of 4 CANDU pressurized heavy water nuclear reactor units and auxiliary systems that support their operation and the production of electricity. As of the writing of this report, two reactor units are in operation (Units 2 and 3), and two reactor units (Units 1 and 4) are undergoing refurbishment and life extension.

The DN site comprises many buildings of various sizes with a wide range of functions (see figure 1.2). An overview of the main features is described in table 1.1.

Table 1.1: Description of the Darlington Nuclear Generating Station’s main components
Component	Definition
Reactor building	Reactor buildings contain 4 reactor vaults, a reactor auxiliary bay, steam generators and a containment envelope. The reactor vault contains the reactor core and assembly and the reactivity control devices. The reactor auxiliary bay contains the reactor auxiliary and secondary circuits for low temperature, pressure and radioactivity levels around each vault. The containment envelope encompasses the 4 reactor vaults, the fueling duct connected to each vault and a pressure relief duct which connects the fueling ducts to the vacuum building that condenses any releases of radioactive steam and prevents release outside of the station.
Primary Heat Transport and Generator Systems	The primary heat transport systems cool the reactor by circulating pressurized heavy water through the reactor fuel channels. The heat is transferred to light water through steam generators.
Powerhouse Building holding the Secondary Heat Transport and Turbine-Generator Systems	The Powerhouse holds four turbine halls, four auxiliary bays and a central service area as well as the secondary heat transport and turbine generator systems. The secondary heat transport system moves steam produced into the steam generators using heat from the primary heat transport system. This system rotates the turbines and attached generators to rotate and generate power.
Heavy Water Management Building	The heavy water management building comprises of the heavy water supply, collection and transfer, cleanup and upgrading and the vapour recovery and resin handling systems. This system circulates heavy water through the reactor vessel, separately from the primary heat transport system.
Tritium Removal Facility	The Tritium Removal Facility houses the processes which remove tritium from the heavy water. Once extracted, the tritium is stored in stainless steel containers within a concrete vault.
Fuelling Facilities Auxiliary Areas	The fuelling facilities auxiliary areas, which store new fuel and two irradiated fuel bays, are located at each end of the station. Irradiated fuel bays are used to store and cool used fuel bundles. The used fuel bundles are stored in these fuel bays for at least 10 years before transferring to the DWMF.
Forebay, intake channel and discharge channels	The intake channels draw condenser cooling water (CCW) from the forebay into each unit. After the CCW is used in the condensers, the CCW is discharged into Lake Ontario through the drainage channel.

1.2.2.2 Darlington Waste Management Facility

The DWMF is located within its own fenced protected area and consists of 2 in-service storage buildings (each designed to house dry storage containers (DSCs)) and a DSC processing building. The DSC processing facility is used to prepare DSCs for storage. The used fuel Storage Buildings #1 and #2 provide interim site storage for the used fuel bundles of the DNGS until a disposal site for used fuel bundles becomes operational. Both DSC Storage Buildings #1 and #2 have the capacity to hold up to 500 DSCs, equivalent to roughly 9 years of operation for the DNGS.

The Retube Waste Storage Building (RWSB) stores intermediate-level wastes from the Darlington Refurbishment Project. The low-level and intermediate-level radioactive waste that is produced from the DN site is transferred to the Western Waste Management Facility (WWMF) located on the Bruce Nuclear Generating Station site in Tiverton, Ontario.

Table 1.2 defines the key structural components of the DWMF.

Table 1.2: Description of the Darlington Waste Management Facility’s main components
Component	Definition
Dry storage container	A free-standing reinforced concrete container with an inner steel liner and an outer steel shell that is designed and constructed to safely transfer and store dry used fuel on-site.
Processing building	A secured building where empty dry storage containers are prepared before being sent to the DNGS for used fuel loading, and where loaded dry storage containers are processed before being transferred to storage buildings. Processing activities include welding, painting and testing. The processing building also includes an amenities area with utility rooms, offices, washrooms, a lunch room and other supporting facilities.
Dry storage container transporter	A specially designed multi-wheeled vehicle for the transfer of dry storage containers between the DNGS’s irradiated fuel bays and the processing building, and from the processing building to storage buildings.
Retube Waste Storage Building	The retube waste storage building has the capacity to hold 490 dry storage modules containing intermediate level waste.

2.0 Regulatory oversight

The CNSC regulates nuclear facilities and activities in Canada to protect the environment and the health and safety of persons in a manner that is consistent with applicable legislation and regulations, environmental policies and Canada’s international obligations. The CNSC assesses the effects of nuclear facilities and activities on human health and the environment during every phase of a facility’s lifecycle. This section of the EPR report discusses the CNSC’s regulatory oversight of OPG’s EP measures for the DN site.

To meet the CNSC’s regulatory requirements and according to the licensing basis for the DN site, OPG is responsible for implementing and maintaining EP measures that identify, control and (where necessary) monitor releases of nuclear and hazardous substances and their potential effects on human health and the environment. These EP measures must comply with, or have implementation plans in place to comply with, the regulatory requirements found in OPG’s licence and licence condition handbook (LCH). The relevant regulatory requirements for OPG’s DN site are outlined in this section of the report.

2.1 Environmental protection reviews and assessments

To date, 3 federal environmental assessments (EAs) and 2 EPRs (including this one) have been carried out for the DN site, as indicated in table 2.1. Subsection 2.1.1 provides a description of the EAs conducted under the Canadian Environmental Assessment Act (CEAA 1992) ^{Footnote 21} predecessor to the Canadian Environmental Assessment Act, 2012 (CEAA 2012) ^{Footnote 22}. Subsection 2.1.3 provides information on the EPRs conducted for the DN site. In 2019, the Impact Assessment Act (IAA) ^{Footnote 23} came into force, replacing CEAA 2012. OPG’s current activities at the DN site do not require an impact assessment under the IAA’s Physical Activities Regulations ^{Footnote 24}. The purpose of an assessment under any of these pieces of legislation is to identify the possible impacts of a proposed project or activity and to determine whether those effects can be adequately mitigated to protect the environment and the health and safety of persons.

Table 2.1: Federal environmental assessments for the Darlington Nuclear Site
Project	Regime	EA start date	EA decision date	EA follow-up monitoring program
Construction of the Darlington Used Fuel Dry Storage Facility	CEAA 1992	September 18, 2001	November 7, 2003	Completed
Darlington New Nuclear Project	CEAA 1992	May 17, 2007	May 8, 2012 April 22, 2024*	Yes
Refurbishment and Continued Operation of DNGS	CEAA 1992	June 24, 2011	March 14, 2013	Updated through the Integrated Implementation Plan

*The CNSC Commission determined that the new technology proposed by OPG is not fundamentally different from the technologies assessed in the original EA and a new EA would not be required ^{Footnote 25}.

2.1.1 Environmental assessments completed under Canadian Environmental Assessment Act

Environmental assessments help guide the decision-making process. Historical and ongoing EAs as well as follow-up monitoring programs are reviewed by CNSC staff. CNSC staff acknowledge that these environmental assessments listed below occurred prior to the re-affirmation of the Williams Treaties First Nations harvesting Rights as part of the 2018 Williams Treaties First Nations Settlement Agreement. CNSC staff are committed to working with the Williams Treaties First Nations with the goal of considering and reflecting their views, perspectives and knowledge in the ongoing oversight on the DN.

2.1.1.1 Construction of the Darlington Used Fuel Dry Storage Facility

In 2001, OPG communicated its intent to construct and operate a used fuel dry storage facility (UFDSF) at the DNGS, renamed to DWMF upon construction. The proposed UFDSF project involved the construction of the UFDSF facility, preparation of DSCs for storage, and placement and monitoring of the DSCs in the storage building. CNSC staff determined that OPG’s proposal required a screening-level EA under CEAA 1992 ^{Footnote 26}, before the CNSC could consider OPG’s application under the NSCA. In November 2003, following the Commission’s consideration of the EA screening report ^{Footnote 27} written by CNSC staff, the Commission concluded in the Reasons for Decision that the project was not likely to cause significant adverse environmental effects if the mitigation measures identified in the EA screening report were taken ^{Footnote 28}.

The EA process identified the need for an EA follow-up monitoring program (FUMP) ^{Footnote 29}, which was deemed complete by CNSC staff in 2012 ^{Footnote 30}. Please note that OPG refers to FUMPs as an Environmental Monitoring and Environmental Assessment Follow-Up.

2.1.1.2 Darlington New Nuclear Project

In 2007, an EA was initiated under the CEAA 1992 for the proposed Darlington New Nuclear Project. This project encompassed the site preparation and eventual construction and operation of up to four additional nuclear reactors within the DN site. The Federal Minister of Environment referred the EA for the project to a joint review panel (JRP) for assessment ^{Footnote 31}.In 2011, the JRP submitted its EA Report to the Minister of the Environment, concluding that the “proposed project was not likely to cause significant adverse effects provided the mitigation measures proposed and commitments made by OPG and the Panel’s recommendations are implemented” ^{Footnote 31}. In May 2012, the Government of Canada accepted the intent of all of the JRP’s recommendations. In August 2012, the JRP, as a panel of the Commission issued a 10-year site preparation licence for DNNP. This licence was renewed in 2022.

In December 2021, OPG announced its selection of the General Electric Hitachi BWRX-300 reactor for deployment at the DNNP site and applied for a licence to construct in October 2022. In April 2024, the Commission determined following a public hearing in January 2024 that the EA decision made by the JRP in 2011 ^{Footnote 31} remains applicable to OPG’s selected reactor technology and a new environmental assessment is not required ^{Footnote 25}.

A complete project timeline for the Darlington New Nuclear Project can be found on the CNSC’s website: Darlington New Nuclear Project timeline (cnsc-ccsn.gc.ca)

2.1.1.3 Refurbishment and Continued Operation of DNGS

In 2011, an EA was conducted under the CEAA 1992 for the DNGS Refurbishment and Continued Operation Project ^{Footnote 32}. The purpose of the project being to refurbish the DNGS to allow it to continue to operate until approximately 2055. The principle works and activities within the scope of the proposed project included the construction of the RWSB and other supporting buildings, the transportation of low and intermediate-level radioactive waste to an off-site management DWMF, and the refurbishment of the CANDU reactors. In 2012, the Commission issued the Record of Proceedings and Decision ^{Footnote 33} and concluded that the proposed project was not likely to cause significant adverse effects.

2.1.2 Current environmental assessment follow-up monitoring program

EA follow-up monitoring programs are designed to validate the predicted environmental effects and the effectiveness of mitigation measures. The CNSC ensures that EA FUMPs that are within the CNSC’s mandate are incorporated into licensing and compliance activities.

2.1.2.1 Darlington New Nuclear Project

As required by CEAA 1992, the CNSC, with the Fisheries and Oceans Canada (DFO) and Transport Canada as Responsible Authorities, required that OPG establish and implement an EA FUMP ^{Footnote 34}. To meet this requirement, as well as other JRP recommendations accepted by the Government of Canada in the EA, OPG has created DNNP Commitments with associated deliverables.

As part of the DNNP Commitment D-P-12.1, which addresses the EA FUMP, OPG has provided an overall EA FUMP ^{Footnote 35}, as well as specific methodology reports covering a variety of environmental components; tracked through the completion of DNNP Deliverables D-P-12.2 through D-P-12.9 ^{Footnote 36}. In the Commission’s Record of Decision on the Determination of Applicability of Darlington New Nuclear Project Environmental Assessment to OPG’s Chosen Reactor Technology, the Commission outlined the following recommendations related to the EA FUMP:

“The Commission also recommends that in the OPG development and implementation of its EA follow-up program, OPG incorporate, to the extent possible, engagement with the Williams Treaties First Nations and the Métis Nation of Ontario on applicable items (e.g., measures to offset the loss of bank swallows nesting habitat), Indigenous Knowledge, and land use information and data in the program. The Commission expects that CNSC staff continues to support the Williams Treaties First Nations to gather traditional Indigenous Knowledge and land use information and data.”

2.1.2.2 FUMP for the Refurbishment and Continued Operation of DNGS ^{Footnote 37}

In the Record of Proceedings and Decision ^{Footnote 33}, an EA FUMP was required for the Darlington B Refurbishment and Continued Operation project. OPG developed an EA FUMP in consultation with the CNSC, ECCC and DFO and the public and Indigenous Nations were invited to review the program through a 30-day consultation period ^{Footnote 38}. The actions to be completed for the FUMP and the schedule for implementation and reporting are captured in the Integrated Implementation Plan (IIP) ^{Footnote 39}. OPG continues to provide periodic updates on the status of the EA FUMP to the CNSC through the IIP process.

2.1.3 Previous environmental protection review completed under the Nuclear Safety and Control Act

2.1.3.1 Darlington Nuclear Generating Station Licence Renewal

In 2015, OPG applied for a 10-year licence to renew its DNGS Operating Licence. An EA under the NSCA was conducted for the licence application ^{Footnote 40}. CNSC staff concluded that OPG has and would continue to make adequate provision for the protection of the environment and the health of persons. A two-part public Commission hearing on the licence application was held in August and November 2015 and the Commission approved OPG’s application ^{Footnote 41}.

In May 2024, OPG submitted a licence application to renew the power reactor operating licence from December 1, 2025 to November 30, 2055 ^{Footnote 3}. The Commission will hold a two-part public hearing in 2025. CNSC staff have prepared this EPR report to inform the licensing decision of the Commission.

2.1.3.2 Darlington Waste Management Facility Licence Renewal

In 2021, OPG applied for a 10-year licence to renew its DWMF Operating Licence. An EPR under the NSCA was conducted for the licence application ^{Footnote 42}. CNSC staff concluded that OPG has and would continue to make adequate provision for the protection of the environment and the health of persons. A public Commission hearing on the licence application was held in January 2023 and the Commission approved OPG’s application to renew the license until April 30, 2033 ^{Footnote 43}.

2.2 Planned end-state

The following section provides high-level information on the currently planned end-state of the DN site following decommissioning activities. This section is informed by OPG’s PDP for the DN site. The PDP is important to consider as part of CNSC staff’s ongoing oversight for the assessment of environmental and health effects of nuclear facilities and activities.

A PDP is required to be developed by the licensee and submitted to the CNSC for review and acceptance as early as possible in the facility’s lifecycle or the conduct of the licensed activities. The PDP is progressively updated, where needed, to reflect the appropriate level of detail required for the respective licensed activities. The PDP is developed for planning purposes only and the associated cost estimate is used to set aside dedicated decommissioning funding in the form of a financial guarantee. The PDP does not authorize decommissioning and does not provide sufficient details for the assessment of environmental impacts during decommissioning. Prior to the commencement of any decommissioning activities and to support an application for a licence to decommission, a detailed decommissioning plan is required to be developed by the licensee and submitted to the CNSC for review and acceptance.

PDPs for nuclear facilities are updated by the licensee at least every 5 years, considering notable changes relevant to decommissioning, or as requested by the CNSC. The decommissioning strategy and end-state objectives for the DN site are documented in the Darlington Nuclear Site preliminary decommissioning plan ^{Footnote 5} and the preliminary decommissioning plan for the Darlington Waste Management Facility ^{Footnote 4}.

OPG’s PDP assumes that the reactor units will be shut down between 2050 to 2056 and the DNGS will be dismantled once decommissioning is approved. A deferred decommissioning strategy has been planned and flexibility is built into the process to cater to the final decision OPG may make with respect to shutdown dates. The DWMF will remain in operation after shutdown of the DNGS reactors and is expected to continue receiving, processing, and storing DSCs during stabilization and storage with surveillance, until all the fuel has been removed. This PDP is the proposed plan for decommissioning the DNGS and since it also addresses the interfaces of the DNGS with the DWMF, which is also located on the DN site, it is referred to as the site PDP. The purpose of the PDP is to define the areas to be decommissioned and the sequence of the principal decommissioning work for the DNGS. The PDP also demonstrates that decommissioning is feasible with existing technology, and it provides a basis for estimating the cost of decommissioning. The PDP describes the final end-state after dismantling, demolition and site restoration, which notes that the site will be free of industrial and nuclear hazards.

In January 2022, OPG submitted the updated DN site PDP. CNSC staff have reviewed the PDP and provided comments and requests to which OPG is required to respond. An updated DN site PDP is expected in 2027. It should be noted that OPG submitted an application to extend the commercial operation date of the DNGS from December 1, 2025 to November 30, 2055 ^{Footnote 3}. This application is currently under review by CNSC staff and will require a Commission hearing for decision. Should the Commission grant a licence extension, OPG will be required to submit a revised PDP, including additional decommissioning activities and associated costs for the licence extension.

2.3 Environmental regulatory framework and protection measures

The CNSC has a comprehensive EP regulatory framework which includes the protection of people and the environment and considers both nuclear and hazardous substances, as well as physical stressors (such as noise). Public dose is included in the EP framework. The focus of this section of the EPR report is on the EP regulatory framework and the status of OPG’s environmental protection program (EPP) for the DN site. The results from OPG’s EPP are detailed in section 3.0 of this report.

OPG’s EPP for the DN site was designed and implemented in accordance with REGDOC-2.9.1, Environmental Protection: Environmental Principles, Assessments and Protection Measures (2017) ^{Footnote 44}, as well as the CSA Group’s environmental protection standards listed below. The implementation status for these documents is shown in table 2.2. The EPP includes derived release limits (DRLs) and public dose modelling.

Table 2.2: Status of environmental protection measures to implement regulatory documents and standards
Regulatory document or standard	Status
CSA N288.0-22, Environmental management of nuclear facilities: Common requirements of the CSA N288 series of Standards ^{Footnote 45}	Implemented
CSA N288.1-14, Guidelines for calculating derived release limits for radioactive material in airborne and liquid effluents for normal operation of nuclear facilities ^{Footnote 46}	Implemented
CSA N288.1-20, Guidelines for modelling radionuclide environmental transport, fate, and exposure associated with the normal operation of nuclear facilities ^{Footnote 47}	To be implemented following submissions of revised DRLs (2028)
CSA N288.4-19, Environmental monitoring programs at nuclear facilities and uranium mines and mills ^{Footnote 48}	Implemented
CSA N288.5-22, Effluent and emissions monitoring programs at nuclear facilities ^{Footnote 49}	Implemented
CSA N288.6-12, Environmental risk assessment at Class I Nuclear facilities and uranium mines and mills ^{Footnote 50}	Implemented
CSA N288.6-22, Environmental risk assessments at nuclear facilities and uranium mines and mills ^{Footnote 51}	To be implemented November 30, 2026
CSA N288.7-15, Groundwater protection programs at Class 1 nuclear facilities and uranium mines and mills ^{Footnote 52}	Implemented
CSA N288.7-22, Groundwater protection and monitoring programs for nuclear facilities and uranium mines and mills ^{Footnote 53}	Implementation Plan to be submitted by December 2, 2024
CSA N288.8-17, Establishing and implementing action levels for releases to the environment from nuclear facilities ^{Footnote 54}	Implemented
CNSC REGDOC-2.9.1, Environmental Protection: Environmental Principles, Assessments and Protection Measures, version 1.1 (2017) ^{Footnote 44}	Implemented

CNSC staff confirm that OPG has implemented programs that are following the relevant EP regulatory documents and standards or has implementation plans in place.

Licensees are also required to regularly report on the results of their EPPs. Reporting requirements are specified in REGDOC-3.1.1, Reporting Requirements for Nuclear Power Plants ^{Footnote 55}, REGDOC-3.1.2 Reporting Requirements, Volume I: Non-Power Reactor Class I Nuclear Facilities and Uranium Mines and Mills ^{Footnote 56}, the Radiation Protection Regulations ^{Footnote 57} (e.g., for action level (AL) or dose limit exceedances), the licensees’ approved programs and manuals, and the LCH ^{Footnote 58}.

OPG is required to submit quarterly safety performance indicator reports, annual reports on environmental protection for the NGS and quarterly reports and annual compliance reports as per REGDOC-3.1.1 ^{Footnote 55} and REGDOC-3.1.2 ^{Footnote 56}. These reports are reviewed by CNSC staff for compliance and verification, as well as trending. OPG publishes several of these reports on its website, such as web page Regulatory reporting - OPG ^{Footnote 59}.

CNSC staff regularly report on licensee performance to the Commission for activities conducted at the DN site. For example, CNSC staff's regulatory oversight reports (RORs) are a standard mechanism for updating the Commission, Indigenous Nations and communities, and the public on the operation and regulatory performance of licensed facilities. Previous RORs are available on the CNSC regulatory oversight reports web page ^{Footnote 60}. CNSC staff may also report to the Commission on significant events, such as unplanned releases to the environment, through an event initial report.

2.3.1 Environmental protection measures

To meet the CNSC’s regulatory requirements under REGDOC-2.9.1 (2017) ^{Footnote 44}, OPG is responsible for implementing and maintaining EP measures that identify, control and monitor releases of radioactive nuclear and hazardous substances from the DN site, as well as the effects of these substances on human health and the environment. EP measures are an important component of the overall requirement of licensees to make adequate provisions to protect the environment and the health of persons.

This subsection and the following ones under section 2.3 summarize OPG’s EPP for the DN site and the status of each specific EP measure, relative to the requirements or guidance outlined in the latest regulatory document or CSA Group standard. Section 3.0 of this EPR report summarizes the results of these programs or measures against relevant regulatory limits and environmental quality objectives or guidelines, and discusses, where applicable, any interesting trends.

OPG is required to implement an environmental management system (EMS) that conforms to REGDOC-2.9.1 (2017) ^{Footnote 44} and to submit an EPP for the DN site. OPG’s EPP includes the following components to meet the requirements and guidance as outlined in REGDOC-2.9.1 (2017) ^{Footnote 44}:

EMS (subsection 2.3.2)
environmental risk assessment (ERA) (subsection 2.3.3)
effluent and emissions control and monitoring (section 2.3.5)
- derived release limits and operating release limits
- air emissions and liquid effluent monitoring
environmental monitoring program (EMP) (section 2.3.6)
- ambient air monitoring
- fruits and vegetables monitoring
- animal feed monitoring
- eggs and poultry monitoring
- milk monitoring
- soil and sand monitoring
- surface water monitoring (lake and water supply plants)
- well water monitoring
- groundwater monitoring
- sediment monitoring
- fish monitoring

Section 3.0 of this EPR report summarizes the results of these programs or measures against relevant regulatory limits and environmental quality objectives or guidelines, and discusses, where applicable, any notable trends.

2.3.2 Environmental management system

An EMS refers to the management of an organization’s environmental policies, programs and procedures in a comprehensive, systematic, planned, and documented manner. It includes the organizational structure as well as the planning and resources to develop, implement and maintain an EP policy. The EMS serves as a management tool to integrate all of a licensee’s EP measures in a documented, managed and auditable process in order to:

identify and manage non-compliances and corrective actions within the activities through internal and external inspections and audits
summarize and report on the performance of these activities both internally (licensee management) and externally (Indigenous Nations and communities, the public, interested stakeholders, and the Commission)
train personnel involved in these activities
ensure the availability of resources (that is, qualified personnel, organizational infrastructure, technology and financial resources)
define and delegate roles, responsibilities, and authorities essential to effective management

OPG has established and implemented a corporate EMS for the DN site in accordance with REGDOC-2.9.1 (2017) ^{Footnote 44} and is also registered and certified under the International Organization for Standardization (ISO) standard 14001:2015 (a standard that helps an organization achieve the intended outcomes of its EMS). CNSC staff review OPG’s annual internal audits; management reviews; and environmental goals, targets and objectives to ensure compliance with REGDOC-2.9.1 (2017). While the CNSC does not consider ISO 14001 certification as part of the criteria for meeting the requirements of REGDOC-2.9.1, the results of these third-party audits are reviewed by CNSC staff as part of the compliance program. CNSC staff also review the status of OPG’s annual goals, targets and objectives and the implementation of the EMS as part of their review of the annual reports on EP.

The results of these reviews demonstrate that OPG’s EMS for the DN site meets the CNSC requirements as outlined in REGDOC-2.9.1 (2017) ^{Footnote 44}. The implementation of the EMS ensures that OPG continues to improve environmental performance at the DN site.

2.3.3 Environmental risk assessment

An ERA of nuclear facilities is a systematic process used by licensees to identify, quantify and characterize the risk posed by contaminants and physical stressors in the environment on human and other biological receptors, including the magnitude and extent of the potential effects associated with a facility. The ERA serves as the basis for the development of site-specific EP measures and the results from the ERA updates determine whether the facility’s effluent monitoring and EMP are effective. The results of these programs, in turn, inform and refine future revisions of the ERA.

In March 2021, OPG submitted their 2020 Environmental Risk Assessment for the DN site ^{Footnote 61} (2020 ERA) in accordance with the requirements set out in CSA N288.6-12 ^{Footnote 50}, and REGDOC 2.9.1 ^{Footnote 44} which stipulates that licensees must review and revise their ERA every 5 years. OPG’s ERA submission is site-wide and encompassed the entirety of the DN site, including the DWMF. The DN site-wide 2020 ERA included an ecological risk assessment (EcoRA) and a human health risk assessment (HHRA) for nuclear and hazardous contaminants and physical stressors. The 2020 ERA included risks associated with the DN site, which includes the DNGS and DWMF, based on effluent and environmental monitoring data for the period between 2016 to 2019.

The ERA was performed in a stepwise manner, as follows:

quantify the releases (of COPCs) to the environment from current (see section 3.1) and future activities
identify the environmental interactions of the current and expected releases of COPCs, and COPC exposure pathways in the environment
identify predicted COPC exposure for ecological and human receptors
identify potential effects to receptors
- quantify the releases (of COPCs) to the environment from current (see section 3.1) and future activities
- identify the environmental interactions of the current and expected releases of COPCs, and COPC exposure pathways in the environment
- identify predicted COPC exposure for ecological and human receptors
- identify potential effects to receptors
- determine whether the environment and health and safety of persons is and will continue to be protected

CNSC staff reviewed the 2020 site-wide ERA and required additional information in order to verify whether the ERA was compliant with requirements in REGDOC 2.9.1 and CSA N288.6 ^{Footnote 62}. In October 2021, OPG submitted a revised ERA report, taking into consideration CNSC staff comments ^{Footnote 63}. CNSC staff reviewed OPG’s revised ERA and found it to be compliant with CSA N288.6-12 ^{Footnote 50}.

OPG’s findings from the revised 2020 ERA are summarized in table 2.3 below. CNSC staff reviewed the revised ERA and have found that no new risks have emerged since the previous ERA and that unreasonable risks to human health and the environment attributable to DNGS and DWMF operations are unlikely.

The findings of the revised 2020 ERA are summarized in table 2.3. Adverse effects to ecological and human health due to releases of COPCs to the air and water from the DN site were found to be negligible.

Table 2.3: Summary of environmental risk assessment findings for the Darlington Nuclear Site ^{Footnote 63}
Type	Members of the public	Aquatic and terrestrial biota
Radiological	The annual dose to the critical receptor was well below the public dose limit and there were no concerns	There were no exceedances of the radiation dose benchmarks for ecological receptors.
Hazardous	There are negligible releases of hazardous COPCs from the facility. No adverse impacts expected on members of the public.	There are negligible releases of hazardous COPCs from the facility. However, concentrations of certain metals in soil, in a localized area were above the soil quality criteria. However, no adverse population level impacts expected on aquatic and terrestrial biota.
Physical stressors*	There are no adverse impacts expected from physical stressors associated with operations at the facility.	There are no adverse impacts on biota expected from physical stressors associated with operations at the facility.

2.3.4 Effluent and emissions control and monitoring

Controls on environmental releases are established to provide protection to the environment and to respect the principles of sustainable development and pollution prevention. The effluent and emissions prevention and control measures are established based on industry best practice, the application of optimization of protection (such as in design) and of as low as reasonably achievable (ALARA) principles, the Canadian Council of Ministers of the Environment (CCME) guidelines, and results of the licensee’s ERAs.

OPG has controls in place to minimize airborne emissions and waterborne effluents for radiological and non-radiological COPCs, and to ensure that releases are within regulatory limits and ALARA.

OPG has implemented an effluent and emission monitoring program in compliance with REGDOC-2.9.1 (2017) ^{Footnote 44} and the relevant standards, including CSA N288.5-22, Effluent and emissions monitoring programs at nuclear facilities ^{Footnote 49} and CSA N288.0-22, Environmental management of nuclear facilities: Common requirements of the CSA N288 series of Standards ^{Footnote 45}. This program contains DRLs and ALs. The DRLs represent the maximum acceptable level of emitted contaminants from the processes at the DN site and are derived from the dose limit for members of the public (that is, 1 millisievert [mSv] per year). In addition, the DN site has established ALs that serve as an early warning of potential loss of control of the EPP.

Based on compliance activities, CNSC staff have found that the effluent and emission monitoring program currently in place for the DN site continues to protect human health and the environment.

2.3.5 Environmental monitoring program

The CNSC requires each licensee to design and implement an EMP that is specific to the monitoring and assessment requirements of the licensed facility and its surrounding environment. The program is required to:

measure contaminants in the environmental media surrounding the facility or site
determine the effects, if any, of the facility or site operations on people and the environment
serve as a secondary support to effluent and emission monitoring programs to demonstrate the effectiveness of emission controls

More specifically, the program must gather the necessary environmental data to calculate the public dose and demonstrate compliance with the public dose limit found in the Radiation Protection Regulations ^{Footnote 64} of 1 mSv per year. The program design must also address the potential environmental interactions identified at the facility or site. Radionuclides are the major focus at the DN site, though hazardous substances environmental compliance approval (ECA) are included within monitoring activities associated with liquid discharges and air emissions. OPG’s EMP for the DN site consists of the following components:

ambient air monitoring
fruits and vegetables monitoring
animal feed monitoring
eggs and poultry monitoring
milk monitoring
soil and sand monitoring
surface water (lake and water supply plants)
well water monitoring
groundwater monitoring
sediment monitoring
fish monitoring

Monitoring frequency and parameters are specified in OPG EMP reports ^{Footnote 59}. The sampling locations are shown on the map below figure 2.1.

OPG is required to maintain its EMP to comply with REGDOC-2.9.1 (2017) ^{Footnote 44} and relevant standards, including CSA N288.4-19, Environmental monitoring programs at nuclear facilities and uranium mines and mills ^{Footnote 48} and CSA N288.0-22, Environmental management of nuclear facilities: Common requirements of the CSA N288 series of Standards ^{Footnote 45}.

Based on compliance activities and technical assessments, CNSC staff have found that OPG is compliant with REGDOC-2.9.1 (2017) ^{Footnote 44} and continues to implement and maintain an effective EMP for the DN site that adequately protects the environment and the health and safety of persons.

Aerial overview of environmental monitoring program sampling locations for the Darlington Nuclear Site. — **Figure 2.1: Darlington Nuclear Site Environment Monitoring Program sampling locations ^{Footnote 10}**

2.4 Requirements under other federal or provincial regulations

A core element of the CNSC’s requirement for an EMS is the identification of all regulatory requirements applicable to the facility, whether pursuant to the NSCA or other federal or provincial legislation. The EMS must ensure that programs are in place to respect these requirements.

2.4.1 Greenhouse gas emissions

While there is a range of broadly applicable federal environmental regulations (for example, petroleum products storage tanks, environmental emergency regulations), the management of greenhouse gas (GHG) emissions has been identified as a national priority.

Under the federal Canadian Environmental Protection Act, 1999 (CEPA 1999) ^{Footnote 65}, OPG is required to monitor and report on GHG emissions. Facilities that emit more than the emission reporting threshold (that is, 10,000 tonnes of CO2 equivalent) on an annual basis must report their GHG emissions to ECCC. In the case of the DN, site CO₂ releases remained below the reporting threshold from 2019 to 2023 ^{Footnote 6} ^{Footnote 7} ^{Footnote 8} ^{Footnote 9} ^{Footnote 10}.

The CNSC maintains a collaborative working relationship with ECCC through a formal memorandum of understanding (MOU) ^{Footnote 66}, which includes a notification protocol. An exceedance of the GHG emissions reporting threshold would be included under this notification protocol. This ensures that a coordinated regulatory approach is achieved to meet all federal requirements associated with EP, including GHGs.

2.4.2 Ozone depleting substances

In accordance with the Federal Halocarbon Regulations, 2022 ^{Footnote 67}, OPG is required to provide a semi-annual halocarbon release report to ECCC on the release of halocarbons of an amount greater than 10 kilograms (kg) but less than 100 kg from any system, container or equipment at the DN site. In the event of a release that surpasses 100 kg, OPG would be required to report the releases to ECCC within 24 hours and ECCC would inform the CNSC through the notification protocol of the CNSC-ECCC MOU. OPG would then be required to submit a follow-up report to ECCC within 30 days of the release detailing the circumstances leading to the release and the corrective and preventive actions taken to prevent a reoccurrence.

OPG has reports as required the information needed for the DN site for the assessed period (2019–2023).

2.4.3 Sulphur dioxide emissions

Under the authority of CEPA 1999 ^{Footnote 65}, OPG is also required to estimate the total sulphur dioxide (SO₂) emissions from the DN site and report to the National Pollutant Release Inventory (NPRI), provided that the reporting requirements are met. The sulphur dioxide emissions at the DN site remained below the NPRI reporting threshold for the assessed period (2019–2023). OPG is still reporting its sulphur dioxide releases in its annual environmental monitoring report ^{Footnote 6} ^{Footnote 7} ^{Footnote 8} ^{Footnote 9} ^{Footnote 10}.

2.4.4 Other environmental compliance approvals

Non-radiological liquid effluent is monitored in accordance with the provincial ECA requirements. Non-radiological liquid effluent from the radioactive liquid waste management system must comply with ECA requirements. COPCs not addressed by the ECA are assessed through the ERA to determine whether they merit additional regulatory oversight.

Non-radiological airborne emissions are required to be in compliance with provincial regulation O. Reg. 419/05 ^{Footnote 68}, which is met by complying with the ECA for Air and Noise. OPG did not report any non-compliances for its ECA. An Emissions Summary and Dispersion Modelling report is used to document and maintain compliance with O. Reg. 419/05 ^{Footnote 68}.

2.4.5 Fisheries Act Authorization

In October 2023, DFO and the CNSC signed a revised MOU outlining areas for cooperation and administration of the Fisheries Act ^{Footnote 69}, which aims to conserve and protect fish and fish habitat across Canada.

The CNSC-DFO MOU focuses on sections 34 and 35 of the Fisheries Act, which state that no person shall carry on any work, undertaking or activity that could cause the death of fish and/or harmful alteration, disruption or destruction of fish habitat, unless the Minister of DFO issues a Fisheries Act Authorization (FAA). This authorization, if granted, includes terms and conditions to avoid, mitigate, offset (that is, counterbalance impacts) and monitor the impacts on fish and fish habitat resulting from a specific project.

2.5 Canadian Nuclear Safety Commission and federal partners consideration of climate change

The CNSC’s regulatory framework requires licensees and proponents to consider climate change primarily through requirements related to EAs and safety assessments. These assessments take place throughout the licensing lifecycle as part of the licence application, licence renewal and periodic safety review (PSR) process.

CNSC staff’s consideration of climate change during these assessments may include examining whether climate change is considered in the analysis of external hazards and environmental parameters such as meteorological and hydrological parameters used in the design, evaluation and upgrade of a nuclear facility, and whether a licensee has applied the defence-in-depth principle in its design with sufficient safety margin.

Specifically, climate change considerations are included in the following mechanisms in the regulatory framework:

Environmental assessment

Previously under CEAA 2012 and currently under the IAA, proponents must assess the climate change impact on a project itself and thereby the surrounding environment, over the lifetime of the facility. As noted in section 2.1, the DN site has undergone numerous EAs that have demonstrated that, with mitigation measures implemented, climate change, as well as the anticipated increases in the magnitude and frequency of external hazards due to climate change, would not likely have impact on the project that would lead to residual adverse effect. The most recent EAs ^{Footnote 32} ^{Footnote 70} ^{Footnote 71} for the DN site conducted in 2007 and 2011 assessed the impact of climate change and are discussed further in Section 3.2.7.

Periodic safety reviews

Licensees for nuclear power plants are required to conduct PSRs to evaluate the design, condition and operation of the facility. Probabilistic Safety Assessment (PSA), as one of the safety factors evaluated in the PSR, includes analysis of external hazards, such as flooding, and their impact on a facility. As part of the 5-year cyclical review process, CNSC staff review the PSA and ensure that up-to-date hazard information is included.

In OPG’s latest hazard analysis report ^{Footnote 72}, flood hazards (including probable maximum flood due to a combination of probable maximum precipitation (PMP), 1:100 year lake level and storm surge) were screened out from additional probabilistic safety assessment, indicating that risk due to external flood hazards is low.

Environmental risk assessment

As described further in section 2.3.3, an ERA (updated in a 5-year review cycle) evaluates risk posed by contaminants and physical stressors to the environment under normal operating conditions, taking into consideration recent monitoring data (including meteorological parameters) and new scientific knowledge. The latest ERA update ^{Footnote 63} graphically evaluated the monthly variability of temperature and precipitation, as well as the annual prevailing wind distribution, based on latest monitoring data. Thermal plume monitoring results were presented and OPG demonstrated that it is unlikely there are any effects arising from the thermal plume in the lake for juvenile or adult stages of any fish species. CNSC staff will continue to assess potential thermal impacts to aquatic receptors from site discharges keeping in mind any environmental changes due to climate change.

CNSC and ECCC collaboration

The CNSC and ECCC have an MOU ^{Footnote 66} in place that includes collaboration related to climate change. For example, ECCC contributes expertise on projection of climate change and estimations of extreme rainfall intensity-duration-frequency curve and probable maximum precipitation (PMP) for various sites to CNSC staff. This informs CNSC staff’s technical reviews.

ECCC also has the mandate to monitor and provide meteorological data to Canadians, to conduct scientific research regarding the mechanism and effects of climate change, and to develop science-based guidance on assessment of climate change for application when projects are subject to federal impact assessments. The Strategic Assessment of Climate Change guidance ^{Footnote 73} includes specific guidance on net zero plans, calculation of GHG emissions/intensity and resiliency.

Further information on how the CNSC assesses the impacts of climate change on nuclear safety in Canada can be found at Climate Change Impact Considerations.

3.0 Status of the environment

This section provides a summary of the status of the environment around the DN site. It starts with a description of the nuclear and hazardous releases to the environment (section 3.1), followed by a description of the environment surrounding the DN site and an assessment of any potential effects on the different components of the environment as a result of exposure to these contaminants (section 3.2).

CNSC staff regularly review the potential effects on environmental components through annual reporting requirements and compliance verification activities, as detailed in other areas of this report. This information is reported to the Commission in the sections on EP in licensing commission member documents and annual RORs. The EMP reports submitted by OPG for the DN site are made publicly available and can be viewed on OPG’s website: Regulatory reporting - OPG ^{Footnote 59}.

3.1 Releases to the environment

Radioactive nuclear and hazardous substances that have the potential to cause an adverse effects to ecological or human receptors are identified as COPCs. The ways in which COPCs could find their way to the different receptors considered by the ERA are called “exposure pathways.”

Figure 3.1 illustrates a conceptual model of the environment around a nuclear site to show the relationship between releases (airborne emissions or waterborne effluent) and human and ecological receptors. This graphic is meant to provide an overall conceptual model of the releases, exposure pathways and receptors for the DN site and thus should not be interpreted as a complete depiction of the DN site and its surrounding environment.

Releases from the DWMF are significantly lower than those from the DNGS, and so emissions from the DWMF should be considered as a small fraction of the overall emissions and releases from the DN site. The specific releases and COPCs associated with the DN site are explained in detail in the following subsections.

Conceptual exposure pathways for atmospheric and aquatic releases to the environment from the DN Site. — **Figure 3.1: Conceptual model of the environment around the Darlington Nuclear Site**

3.1.1 Licensed release limits

OPG uses DRLs and ALs, approved by the CNSC, to control radiological effluent and emission releases from the site as discussed in section 2.3.5. A DRL for a given radionuclide is the release rate that would cause an individual of the most highly exposed group to receive a dose equal to the regulatory annual dose limit of 1 mSv.

3.1.2 Airborne emissions

OPG controls and monitors airborne emissions from the DN site to the environment under its effluent monitoring program. This program is based on CSA N288.5-22, Effluent and emissions monitoring programs at nuclear facilities ^{Footnote 49} and includes monitoring of both nuclear and hazardous emissions.

3.1.2.1 DN site radiological airborne releases

As part of OPG’s effluent monitoring program, releases to the atmosphere are collected and are routinely analyzed for tritium, elemental tritium, carbon-14 (C-14), iodine-131 (I-131), noble gases and particulates. The results are compared against DRLs developed by OPG and approved by the CNSC to ensure release limits to the environment will not exceed the annual regulatory public dose limit of 1 mSv. As shown in table 3.1, the average radiological emissions from the DN site remain at a very small fraction of the DRLs.

Table 3.1: Annual airborne releases from the Darlington Nuclear Site compared with applicable derived release limits (2019 – 2023) ^{Footnote 6} ^{Footnote 7} ^{Footnote 8} ^{Footnote 9} ^{Footnote 10}
Parameter (Bq/yr)	2019	2020	2021	2022	2023	DRLs ^{Footnote 58}
Tritium oxide	2.0x10¹⁴	1.9x10¹⁴	2.6x10¹⁴	2.2x10¹⁴	5.3x10¹⁴	3.91x10¹⁶
Elemental tritium*	2.5x10¹³	1.5x10¹³	1.7x10¹³	9.2x10¹³	1.3x10¹⁵	6.26x10¹⁷
Noble gas**	5.0x10¹³	2.4x10¹³	2.7x10¹³	2.2x10¹³	4.4x10¹³	3.46x10¹⁶
Iodine-131	1.4x10⁸	1.5x10⁸	1.5x10⁸	1.4x10⁸	1.2x10⁸	1.74x10¹²
Particulate gross beta-gamma	2.6x10⁷	3.1x10⁷	2.0x10⁷	2.9x10⁷	2.8x10⁷	5.51x10¹¹
Carbon-14	9.7x10¹¹	8.3x10¹¹	1.2x10¹²	1.2x10¹²	1.1x10¹²	7.68x10¹⁴

* Emissions from Darlington Tritium Removal Facility
** Airborne noble gas emission units are in becquerel- Mega electron-volt (Bq-MeV)

3.1.2.2 DWMF radiological airborne releases

Under normal operating conditions, radiological airborne releases are unlikely to occur during transfer and storage of sealed and welded DSCs at the DWMF. However, there is a small potential for airborne emissions at the DWMF resulting from DSC processing operations, such as welding and vacuum drying. The DSC processing building has a dedicated High Efficiency Particulate Air (HEPA) air filtered active ventilation system. Airborne particulate contamination, if present, would be effectively removed by the HEPA filters in the active ventilation system. Past PWMF, WWMF and DWMF operating experience demonstrates that particulate emissions in exhaust from DSC processing operations have been typically below the Minimum Detectable Activity. OPG website, under regulatory reporting ^{Footnote 74}

3.1.2.3 DN site non-radiological releases

The main sources of non-radiological releases at the DN site are the standby diesel generators onsite. These sources release small quantities of carbon monoxide, nitrogen oxides, sulphur dioxide. In addition, hydrazine, morpholine and ammonia are used in the feedwater system to prevent corrosion and are released in small quantities through controlled venting. Ozone-depleting substances are used in refrigeration systems, leaks are minimized through routine maintenance of equipment and inspections.

Non-radiological air emissions from the DN site are controlled in accordance with provincial ECA requirements. Dispersion modelling was used to predict the maximum concentrations of COPCs at the property line of the DN site. OPG did not report any ECA non-compliances to the provincial regulator or the CNSC on during the 2019-2023 period.

3.1.2.4 DWMF non-radiological releases

The potential for airborne hazardous substance releases at the DWMF is negligible. Paint touch-up operations for the DSCs involve a minimal amount of paint quantities and paint aerosols from the paint bays, which are removed through filters before exhausting into the active ventilation system. Welding fumes from DSC seal-welding operations are also exhausted through the HEPA filtered active ventilation system. The emissions from the welding operations are also negligible.

3.1.2.5 Findings

Based on CNSC staff’s review of the results of the air emissions monitoring program at the DN site, CNSC staff have found that OPG’s air emissions to the environment from the DN site have remained below the CNSC-approved licence limits throughout the reporting period (2019 to 2023). CNSC staff confirm that OPG continues to provide adequate protection of people and the environment from air emissions.

3.1.3 Waterborne effluent

OPG controls and monitors liquid (waterborne) effluent from the DN site to the environment under its implementation of the effluent monitoring program. This program is based on CSA N288.5-22, Effluent and emissions monitoring programs at nuclear facilities ^{Footnote 49} and includes monitoring of radiological and hazardous releases.

The DN site is located on the north shore of Lake Ontario. Waterborne effluent from the DN site is discharged into the CCW system through either the intake forebay or directly into the CCW discharge duct. The two exceptions are effluent from the domestic sewage system which goes to the Courtice Water Pollution Control Plant, and stormwater which is discharged to Lake Ontario through the storm sewers or drainage swales/creeks.

3.1.3.1 Active Drainage System

The active drainage system collects active (radiological) effluent waste from the drains in the reactor building, the Reactor Auxiliary Bay, the Central Service Area, the Fuelling Facilities Auxiliary Areas, the chemical laboratory sink, the Heavy Water Management Building, and the Tritium Removal Facility. The active liquid waste is directed to the receiving tanks of the radioactive liquid waste management system. The activity in the liquid waste may include tritium, carbon-14, gross alpha and gross beta-gamma (such as cesium-134, cesium-137, cobalt-60 (Co-60) or strontium-90). The active drainage system includes filters and ion exchange columns to purify the waste. After treatment the waste is sampled and chemically analyzed to ensure it meets radioactive and chemical limits prior to discharge. The treatment can also include the addition of sodium bicarbonate and calcium bicarbonate for hardness adjustment and potassium hydroxide for pH adjustment, if required. Radioactivity monitors on the discharge piping automatically stop discharge flow if the detected activity is above specified limits.

3.1.3.2 Inactive Drainage System

Building effluents from inactive areas in all four units, and from the Central Service Area, are collected and combined in a common header prior to discharging to two lagoons (each approximately 4000 m³) operated in series. Forced aeration occurs in the first lagoon to promote mixing and reaction between air and low levels of hydrazine. The effluent from the first lagoon overflows to the second lagoon, which allows sufficient retention time for settling. The lagoon water eventually discharges to the Forebay, to be circulated with CCW and eventually discharged.

3.1.3.3 Stormwater Management System

The Stormwater Management System, or Yard Drainage System, collects storm runoff from the entire DN site and discharges to Lake Ontario either directly through the storm sewer drainage system or through drainage swales/creeks/retention pond via culverts which eventually discharge to the Lake. Stormwater and foundation drainage is regulated by the Ministry of Environment, Conservation and Parks (MECP) under the Environmental Protection Act ^{Footnote 75} and the Ontario Water Resources Act ^{Footnote 76}. Site stormwater works are under the site ECA No. 0585-D4KP24 for industrial sewage works ^{Footnote 77}. The stormwater works are designed as per the ECA requirement to ensure that stormwater is properly managed to prevent erosion, flooding, and degradation of receiving water bodies. In the case that the stormwater discharge at the facility were to exceed a provincial limit, OPG would be required to report this exceedance to the CNSC as required under REGDOC-3.2.1, Public Information and Disclosure ^{Footnote 78}. To date, the CNSC has not received any reports of exceedances for stormwater discharge at the DN.

As part of OPG’s effluent monitoring program, samples of waterborne effluent are collected and routinely analyzed for tritium, carbon-14 and gross beta/gamma. As per table 3.2, the annual radiological waterborne releases from the DN site remain a very small fraction of the licensed DRLs. From 2019 to 2023 there have been no DRL (regulatory limit) exceedances.

Table 3.2: Annual waterborne releases from the Darlington Nuclear Site compared with applicable release limits (2019 – 2023) ^{Footnote 6} ^{Footnote 7} ^{Footnote 8} ^{Footnote 9} ^{Footnote 10}
Parameter (Bq/yr)	2019	2020	2021	2022	2023	DRL ^{Footnote 58}
Tritium oxide	1.0x10¹⁴	1.2x10¹⁴	1.9x10¹⁴	2.0x10¹⁴	2.7x10¹⁴	6.36x10¹⁸
Gross beta/gamma	2.3x10¹⁰	2.5x10¹⁰	1.6x10¹⁰	9.3x10⁹	1.7x10¹⁰	3.47x10¹³
Carbon-14	3.8x10⁸	3.8x10⁸	1.9x10⁹	9.7x10⁸	2.2x10⁸	6.97x10¹⁴

3.1.3.4 Findings

CNSC staff have found that OPG’s reported liquid effluent discharged to Lake Ontario from the DN site remained below the CNSC’s approved licence limits throughout the reporting period 2019 to 2023.

CNSC staff are satisfied that OPG is taking the appropriate measures at the DN site, as mentioned above, to effectively control and reduce concentrations and loadings of nuclear and hazardous substances in waterborne effluent.

3.2 Environmental effects assessment

This section presents an overview of the assessment of predicted effects from licensed activities on the environment and the health and safety of persons. CNSC staff reviewed OPG’s assessment of current and predicted effects on the environment and health and safety of persons due to licensed activities included in the ERA (see subsection 2.3.3) for the DN site.

To inform this section of the report, CNSC staff reviewed OPG’s 2020 ERA ^{Footnote 61} ^{Footnote 63}, as well as annual reports submitted between 2016 and 2022 inclusively ^{Footnote 9} ^{Footnote 10} ^{Footnote 11} ^{Footnote 12} ^{Footnote 13} ^{Footnote 14} ^{Footnote 15} ^{Footnote 16} ^{Footnote 17} ^{Footnote 18} ^{Footnote 19} ^{Footnote 20} ^{Footnote 79} ^{Footnote 80}.

While CNSC staff conducted a review for all environmental components, only a selection of components is presented in detail in the following subsections. The environmental components were selected based on regulatory requirements, facility type, and geographic context; some were also included because they have historically been of interest to the Commission, Indigenous Nations and communities and the public.

3.2.1 Atmospheric environment

An assessment of the atmospheric environment requires OPG to characterize both the meteorological conditions and the ambient air quality at the DN site.

3.2.1.1 Meteorological conditions

Meteorological conditions, such as temperature, wind speed, wind direction, and precipitation are monitored to assess the extent of the atmospheric dispersion of contaminants emitted to the atmosphere and the rates of contaminant deposition. Meteorological information is also used to determine predominant wind directions, which are used to identify critical receptor locations from the air pathway. Meteorological data were collected from stations within the site, and in local and regional areas, such as the Bowmanville climate station.

The DN site is in southern Ontario on the north shore of Lake Ontario. In Southern Ontario, the climate is influenced by the Great Lakes which results in uniform precipitation amounts year-round, delayed spring and autumn, and moderate temperatures in winter and summer.

3.2.1.2 Ambient air quality

Radiological

Samples of air are collected to monitor the environment around the DN site. These samples are analyzed for tritiated water (HTO), C-14, and noble gases (argon-41, xenon-133, xenon-135 and iridium-192) and the results are used in the calculation of public dose. Background samples are also collected for the dose calculations.

There are six active tritium-in-air samplers (measuring HTO) around the DN site which are collected and analyzed monthly. The background concentration of HTO in air is measured at Nanticoke, Ontario which is considered to be far from the influence of nuclear stations. The levels of HTO observed in the environment depend on station emissions, wind direction, wind speed, ambient humidity and seasonal variations. Fluctuations from year to year are expected even if site HTO emissions remain similar. There were no statistically significant trends over the past 10 years, and the highest annual average for HTO in air was in 2023 which was 5.0 Bq/m³ ^{Footnote 9}. In 2023, HTO in air measured at Nanticoke was <0.1 Bq/m³. The annual average HTO in air measured at the background location in recent years has been at or below the active sampler detection limit

Carbon-14 in air is monitored at four boundary locations for the DN site. Samples are analyzed after each quarter. There were no statistically significant trends over the past 10 years, and the highest annual average for Carbon-14 in air in 2022 was 240 Bq/kg-C (see details in Section 3.2.6.1 for information on the risks) ^{Footnote 4}. Carbon-14 is naturally occurring in the environment but is also a by-product of past nuclear weapons testing from the early 1960s. Carbon-14 background concentrations around the world are decreasing as weapons test carbon-14 levels naturally decay over time. The annual average carbon-14 in air concentration observed at the Nanticoke EMP background location in 2022 was 205 Bq/kg-C ^{Footnote 9}.

External gamma radiation doses from noble gases and iridium-192 are measured using sodium iodide spectrometers set up around DN site. There are 8 detectors around the DN site that monitor the dose rate continuously. Natural background dose has been subtracted from noble gas detector results. The annual boundary average noble gas dose rate is estimated from the monthly data from each detector. The DN boundary average dose rates for Ar-41, Xe-133, Xe-135, and Ir-192 are typically below the detection limits ^{Footnote 9}.

Chemicals in air

The main sources of atmospheric emissions result from boiler chemical emissions and fuel combustion. Boiler treatment chemicals including hydrazine, morpholine and degradation products are used within the feedwater system to prevent corrosion in the boilers. These chemicals are released to the atmosphere through controlled boiler venting. Combustion emissions result from the Auxiliary Heating Steam Facility, Standby Generators, Emergency Power Generators, and minor sources. These systems release carbon monoxide, nitrogen oxides, sulphur dioxide, suspended particulate matter, trace volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs).

As part of their 2020 ERA, OPG reviewed the results of the 2016-2019 Emission Summary and Dispersion Modelling Reports (ESDM). All modelled contaminants remained below the criteria for air quality from 2016 to 2019 ^{Footnote 63}. The estimated maximum 1-hour (hr) nitrogen oxides (NO_x) concentration at the property line was 526 micrograms per cubic metre (μg/m³), exceeding the 1-hr ambient air quality criteria (AAQC) of 400 μg/m³. This exceedance occurred in 2016, when a standby generator operated for up to 75 hrs during testing. This is a rare event as normally the standby generators operate within the 60 hr per annum limit, and in all years other than 2016, the modelled maximum Point of Impingement (POI)* values for NO_x are all below the AAQC. Since there was an occurrence where NO_x exceeded criteria, NO_x was carried forward as an air COPC as part of their ERA.

*A POI is the point at which a contaminant contacts the ground or a building

Physical Stressors

Physical stressors, such as noise, are relevant to both human receptors and ecological receptors. The noise environment of the DN site is one of an urban setting and is influenced by several noise sources including the DNGS, traffic on Highway 401, traffic on local roads, Canadian National rail line and local industry (e.g., St. Mary’s Cement Plant). OPG conducted an acoustic assessment in support of the DNNP in 2018/2019 ^{Footnote 81}. Results of the monitoring determined that the DNGS is not audible above other noise sources at the receptor locations (figure 3.2). Noise impacts both at the point of reference locations and baseline close to the DN site are mainly attributed to traffic from highway 401. Partial influence was also noted from local traffic volume and operation of the DNGS, St. Mary’s Cement and Durham York Energy Center. These findings are consistent with those determined by Specialist in Energy Nuclear Environmental Services (SENES) in a previous acoustic assessment conducted in 2008 ^{Footnote 82}. It is therefore not expected that the noise generated by DN site activities is having a distinguishable effect on human receptors near the DN site.

Aerial overview of noise monitoring locations at residential receptors of the DN Site. — **Figure 3.2: Locations of residential receptors potentially exposed to noise from DN site**

3.2.1.3 Findings

CNSC staff evaluated the environmental monitoring data and the 2020 ERA and concluded that OPG’s reported measurements of nuclear and hazardous substance contaminants in the atmospheric environment from the DN site have remained within expected trends. OPG continues to provide adequate protection of people and the environment from atmospheric releases, including noise. OPG initiated an NOx monitoring study at the DN site in late 2021. The first year of data will be summarized and assessed by CNSC staff in the upcoming DN ERA Addendum report.

3.2.2 Terrestrial environment

An assessment of potential effects on terrestrial biota at the DN site and the surrounding area involves characterizing the local habitat and species (including considering federal and provincial species at risk) and assessing the possibility of their exposure to nuclear and hazardous substances, as well as physical stressors that may be disruptive to ecological receptors.

The DN site-wide assessment ^{Footnote 63} was divided into polygons (AB,C,D, and E), generally consistent with the previous DNGS EcoRA ^{Footnote 83}, with modifications to Polygon E to assess the DNNP lands separately from the existing DNGS. The assessment polygons are shown in figure 3.3. Exposure of the terrestrial biota to COPCs in soil would likely occur through direct contact and/or uptake/ingestion of foods/prey contaminated with soil. Therefore, soil quality in each of the polygons was assessed from the perspective of environmental risk.

3.2.2.1 Radiological

The primary transport pathway for radiological COPCs to soil is through deposition from air. Airborne effluent releases of certain radionuclides such as elemental tritium (HT) and noble gases are not expected to partition to soil. For all of the polygons assessed at the DN site, the radiological dose from soil concentrations of C-14, Co-60, Cs-134, Cs-137, HTO and I-131 are predicted to be well below the UNSCEAR ^{Footnote 82} ^{Footnote 83} radiation benchmark of 2.4 mGy/day for terrestrial biota. The maximum radiological dose to vegetation (grass in Polygon E) from exposure to soil was estimated to be 0.0004 mGy/day, while the maximum dose to the earthworm and the eastern cottontail (occupancy factor for both =1) was estimated to be 0.0002 mGy/day, for both species. These values are well below the UNSCEAR radiation benchmark of 2.4 mGy per day for terrestrial biota ^{Footnote 84} ^{Footnote 85}. Therefore, there was negligible radiological risk to terrestrial organisms from exposure to soil.

For the DWMF, the maximum dose rate to any ecological VC residing in proximity (that is, within 5 m) of the facility was estimated to be 0.024 mGy/day, assuming full capacity of the facility. This is also well below the UNSCEAR ^{Footnote 84} ^{Footnote 85} radiation benchmark of 2.4 mGy/day for terrestrial biota. From 2016 to 2019, the average measured dose rate at the DWMF property boundary was 0.002 mGy/day, while the average measured dose rate at the retube waste storage building (RWSB) perimeter was 0.0014 mGy/ day.

Aerial overview of ecological risk assessment areas of the DN Site. — **Figure 3.3: Area of assessment for the ecological risk assessment ^{Footnote 83}**

3.2.2.2 Hazardous

The 2020 DN site-wide ERA also evaluated environmental monitoring data available since 2016 to determine if potential changes in non-radiological soil quality would modify or alter the risk to the terrestrial environment ^{Footnote 63}. These data were collected as part of an updated baseline monitoring program to support the DNNP site preparation licence renewal in 2019. To determine whether any non-radiological COPCs may pose a risk to ecological receptors, the soil concentrations of COPCs were screened against ecological screening benchmarks published by MECP ^{Footnote 86} based either on protection of plants and soil organisms or protection of birds and mammals. Also consulted, were CCME Soil Quality Guidelines for Environmental Health and the Interim Canadian Soil Quality Criteria ^{Footnote 87}.

For all polygons, except Polygon E, the target hazard quotient (HQ) of 1 was not exceeded for all terrestrial biota. In Polygon C, while strontium was the principal COPC, the HQ of 1 was not exceeded and thus, no risks were predicted for biota For polygon E there were exceedances (i.e. HQ > 1) for arsenic, cobalt, copper, lead, molybdenum, nickel, and zinc concentration benchmarks for earthworm as well as exceedances (HQ >1) for arsenic, cobalt, copper, lead, molybdenum, nickel, tin, and zinc concentration benchmarks for terrestrial plants. The HQ target of 1 was also exceeded for copper, lead, selenium, and zinc for terrestrial birds, and for arsenic, cadmium, copper, molybdenum, selenium and zinc for terrestrial mammals.

It was determined that Polygon E, where all of the exceedances of metals were recorded is a localized area with a prevalence of soils impacted by industrial activities such as but not limited to yard waste and building materials storage. Predicted risks of metals in soil in Polygon E are summarized in table 3.3. Overall, however, it can be concluded that there is a low potential for risk to terrestrial biota from contaminated soils in Polygon E. Given that it is a localized area, and most fauna move around, population level impacts on terrestrial biota are not expected. Regardless, as a part of risk management of this area, OPG has commissioned a soil characterization study in 2021. Results of this study will be included in an upcoming DN ERA Addendum report to be expected in late September 2024 and will be used to determine next steps for management of soil from this area.

Table 3.3: Predicted risks (HQ >1) of chemical COPCs/metals in soil to terrestrial organisms in Polygon E ^{Footnote 63}
COPC	Earthworm	Terrestrial plants	Eastern cottontail	Meadow vole	Common shrew	Raccoon	White-tailed deer	Terrestrial birds (bank swallow, yellow warbler)
Arsenic							-	-
Cadmium	-	-	-	-		-	-	-
Chromium	-	-	-	-	-	-	-	-
Cobalt			-	-	-	-	-	-
Copper						-
Cyanide (free)	-	-	-	-	-	-	-	-
Iron	-	-	-	-	-	-	-	-
Lead			-	-		-	-
Molybdenum			-	-		-	-	-
Nickel			-	-		-	-	-
PHC-F4	-	-	-	-		-	-	-
Selenium	-		-	-			-
Sodium	-	-	-	-	-	-	-	-
Strontium	-	-	-	-	-	-	-	-
Tin	-		-	-	-	-	-	-
Zinc			-	-		-	-

3.2.2.3 Terrestrial habitat and species

OPG has implemented an extensive biodiversity program at the DN site, which encompasses the DNGS and the DWMF. The biodiversity program at the DN site was first implemented in 1997 and annual biodiversity monitoring program reports are produced for the site ^{Footnote 88} ^{Footnote 89} ^{Footnote 90} ^{Footnote 91} ^{Footnote 92} ^{Footnote 93} ^{Footnote 94} ^{Footnote 95} ^{Footnote 96}. The purpose of the program is to aid in protecting ecologically significant areas, rebuilding damaged habitats, and recovering at-risk species in Ontario habitats. The DN site has achieved Wildlife Habitat Council conservation certification, which is a program that certifies ecosystem restoration efforts in support of overall biodiversity enhancement and conservation efforts ^{Footnote 97}.

The DN site is home to a number of terrestrial flora and fauna (see table 3.4), some of which have also been designated as species of special concern under the federal Species at Risk Act (SARA) ^{Footnote 98} or under the Province of Ontario’s Endangered Species Act ^{Footnote 99}. A number of terrestrial species at risk have been identified within the DN site study area during the 2011 to 2019 time period, including Monarch, Bank Swallow, Barn Swallow, Bobolink, Eastern Meadowlark, Wood Thrush, Canada Warbler, Little Brown Myotis, Northern Myotis, and Butternut. These species at risk were not selected as VCs, but each of these species was considered by reference to a representative species already assessed in the EcoRA. A list of terrestrial species which were selected as VCs is shown in table 3.5.

For the assessment of risks to terrestrial VCs, assessment endpoints, which are attributes that should be protected, were considered for each of the VC ^{Footnote 100}. Consistent with CSA N288.6 ^{Footnote 51}, the assessment endpoint for all receptors (other than species at risk) in the EcoRA was population abundance. The assessment endpoint for the species at risk was the individual, given that effects on even a few individuals of the species at risk would be unacceptable.

Table 3.4: Terrestrial species located/present at the Darlington Site Study Area
Invertebrates	Terrestrial Birds
Dragonflies Earthworms Monarch Butterflies^** (Caterpillars)	American Robin Bank Swallow^* Song Sparrow Yellow Warbler Marsh Wren Swamp Swallow House Wren Barn Swallow^* Tree Swallow Mourning Dove Downy Woodpecker Eastern Wood-Pewee^* Willow Flycatcher Great Crested Flycatcher Eastern Meadowlark^* Canada Warbler^*	Eastern Kingbird Black-capped Chickadee Grey Catbird Cedar Waxwing American Redstart Common Yellowthroat Savannah Sparrow Red-winged Blackbird Common Grackle American Goldfinch American Crow Red-eyed Vireo Olive-sided Flycatcher^* Bobolink^* Wood Thrush^*
Terrestrial Plants
Canada Blue Joint Sugar Maple Butternut Tree^**
Terrestrial Mammals
Eastern Cottontail Meadow Vole White-tailed Deer Common Shrew Raccoon Red Fox Short-tailed Weasel Deer Mouse Little Brown Myotis (bat)^ Northern Myotis (bat)^

^*Species of special concern under federal SARA ^{Footnote 96}

^**Endangered under federal SARA ^{Footnote 96}

^***Threatened under SARA ^{Footnote 96}

The VCs were selected to represent each major plant and animal group, reflecting the main ecological exposure pathways, feeding habits and habitats at or around the site. In making the selection, species that were ecologically similar to other species and could be represented by another species, were not selected in order to reduce redundancy in the exposure calculations.

Table 3.5: Terrestrial species selected as valued ecosystem components at the Darlington Site Study Area
Species considered	Major plant or animal group	Importance	Ecological significance	Exposed to and/or sensitive to receptor
Earthworms	Soil-dwelling detritivore	Present on site	Food source for ecological receptors	Exposed to airborne emissions through soil
Canada Blue Joint	Grasses	Present on site	Food source for terrestrial animals	Exposed to airborne emissions through soil and atmospheric deposition
Sugar Maple	Deciduous tree	Present on site	Important element in woodland community	Exposed to airborne emissions through soil and atmospheric deposition
American Robin	Ground feeding insectivore	Present on site	On-site breeder, common to upland community	Exposed to airborne emissions through food (terrestrial invertebrates) and soil
Bank Swallow	Aerial insectivore	Present on site	Breeds along Lake Ontario shoreline. Threatened species on both the federal and provincial level	Exposed to airborne emissions through food (terrestrial invertebrates) and soil
Song Sparrow	Tree/shrub feeding insectivore	Present on site	On-site breeder, common to upland successional habitat	Exposed to airborne emissions through food (terrestrial invertebrates) and soil
Yellow Warbler	Tree/shrub feeding insectivore	Present on site	On-site breeder, common to upland successional habitat	Exposed to airborne emissions through food (terrestrial invertebrates) and soil
Eastern Cottontail	Mammalian herbivore	Present on site	Common to upland habitat	Exposed to airborne emissions through food (plants) and soil
Meadow Vole	Mammalian herbivore	Present on site	On-site breeder, year-round presence, common to upland habitat, common prey	Exposed to airborne emissions through food (plants) and soil
White-tailed Deer	Mammalian herbivore	Present on site	Common to upland habitat	Exposed to airborne emissions through food (plants) and soil
Common Shrew	Mammalian insectivore	Present on site	Common in similar habitats to the site	Exposed to airborne emissions through food (plants) and soil
Raccoon	Mammalian omnivore	Present on site	Common to upland habitat	Exposed to airborne emissions through food and soil
Red Fox	Mammalian carnivore	Present on site	Common to upland habitat	Exposed to airborne emissions through food (small mammals) and soil
Short Tailed Weasel	Mammalian carnivore	Present on site	Common to upland habitat	Exposed to airborne emissions through food (small mammals) and soil

Terrestrial species at risk

In Ontario, the following legislation applies to species at risk: the provincial Endangered Species Act 2007 ^{Footnote 99} which stipulates/compiles a Species at Risk in Ontario List (SARO List) under O. Reg. 230/08 ^{Footnote 101}; and the federal Species at Risk Act ^{Footnote 98}. To comply with these laws, and as part of their 2020 ERA ^{Footnote 61}, OPG conducted a number of wildlife surveys from 2011 to 2019 to identify the species at risk potentially present on or around the DN site study area. Table 3.6 lists the terrestrial species at risk that were identified as potentially present around the DNGS and the DWMF, and that were assessed in the 2020 ERA. To be conservative, if a species was listed as threatened or endangered by either COSEWIC, SARA, or SARO, it was included for assessment. It should be noted that, as general prohibitions under SARA do not apply to species of special concern, and the CSA N288.6 did not specify species of Special Concern as ecologically significant, these species were not listed in table 3.6.

Exposure models for specific assessment of these species are typically lacking. Therefore, most of these species were assessed by reference to surrogate species already selected as VCs for the EcoRA (see table 3.5). Detailed justifications for selections of each of the surrogate species based on habitat, diet, and ecological niche considerations are presented in table 3.6.

Table 3.6: Surrogate species for Identified Species at Risk with Threatened or Endangered Status
Species at Risk (Common and Scientific name)	SARA (federally listed)	COSEWIC (federally listed)	SARO (provincially listed)	Surrogate Species	Last Observed
Terrestrial Invertebrates
Monarch butterfly Danaus plexippus	-	Endangered	-	Earthworm (Lumbricus terrestris)	2019
Plants
Butternut Tree (Juglans cinerea)	Endangered	Endangered	Endangered	Sugar Maple (Acer saccharum)	2019
Birds
Bank Swallow (Riparia riparia)	Threatened	Threatened	Threatened	Bank Swallow (Riparia riparia)	2019
Barn Swallow (Hirundo rustica)	Threatened	Threatened	Threatened	Bank Swallow (Riparia riparia)	2019
Bobolink (Dolichinyx oryzivorus)	Threatened	Threatened	Threatened	American Robin (Turdus migratorius)	2019
Canada Warbler (Cardellina canadensis)	Threatened	Threatened	-	Bank Swallow (Riparia riparia)	2011
Eastern Meadowlark (Strunella magna)	Threatened	Threatened	Threatened	American Robin (Turdus migratorius)	2019
Wood Thrush (Hylocichla mustelina)	Threatened	Threatened	-	American Robin (Turdus migratorius)	2015
Mammals
Little Brown Myotis (Myotis lucifugus)	Endangered	Endangered	Endangered	Common Shrew (Sorex cinereus)	2018
Northern Myotis (Myotis septentrionalis)	Endangered	Endangered	Endangered	Common Shrew (Sorex cinereus)	2018

Notes:

Bird species that were potentially breeding on-site were included. Least Bittern and Olive-Sider Flycatcher were not identified as species that were breeding on-site per surveys completed by Beacon Environmental ^{Footnote 96}; therefore, not included in this table.
Only bat species that are roosting on-site were included.
The federal and provincial status of species on site may change. The status of these species was last verified in August 2020 from COSEWIC, federal SARA Schedule 1 Status, and provincial SARO (MECP).
Species with Special Concern Status were not included in this table, as the general prohibitions under SARA did not apply to Species of Special Concern, and the CSA N288.6 did not specify this status as ecologically significant.

None of these species at risk are known to reside in or frequently visit the area within or immediately surrounding the DNGS or DWMF site; specifically, Polygon E, where COPCs in the soil could pose a risk to individuals. It can be concluded that, there is low potential for risk to these species (except for plant species) given that they are generally rare and move around, thereby reducing exposure to COPCs on-site. The risk to plants in this area is localized and does not impact wider plant community at the DN site

Two butternut trees, a plant species at risk, were observed at the DN site during field investigations in 2019 of which one was diseased with fungal canker and determined to be non-retainable. The other individual, however, was assessed to be retainable ^{Footnote 102}. There were no additional specimens found in the vicinity of the existing butternut tree. This species at risk (assessed through a surrogate species) was determined to be not at risk from operations at the DNGS or the DWMF.

ERA predictions

OPG selected a total of 14 terrestrial receptors for the assessment based on knowledge of the DNGS and DWMF sites and its surrounding environment and relevant field observations (see table 3.5). The 10 species at risk identified as potentially occurring in the area (see table 3.6) were also included as terrestrial receptors, and assessed using surrogate species, with the exception of bank swallows. The selected terrestrial receptors listed in table 3.5 reflect a variety of diets or feeding habits, cover a variety of trophic levels, and are representative of the potential species present in the area.

Exposure to Radiological Nuclear Substances

The potential radiological effects to ecological receptors were assessed by comparing the estimated radiation dose received by each ecological receptor from radiological COPCs through all applicable pathways (namely external and internal exposure due to radionuclides in air, soil, water, sediment, and gamma radiation) to the recommended benchmark values (that is, dose limits to non-human biota).

The overall radiation dose to all terrestrial VECs in all Polygons, which included all internal and external doses from all exposure pathways, was significantly below the radiological dose benchmarks recommended in CSA 288.6-12 ^{Footnote 50}, that is, 100 µGy/h (2.4 mGy/d) for terrestrial receptors. This result indicates no potential for adverse effects and no need for further detailed assessment.

Exposure to Hazardous substances

In all of the terrestrial Polygons, except Polygon E, the HQs were well below 1, indicating negligible risk from hazardous COPCs to terrestrial organisms, including species at risk. In Polygon E, however, there were a number of exceedences of the HQ of 1, as shown in table 3.7. Specifically, the HQ for zinc and copper was exceeded for most of the terrestrial VCs, whereas chromium, iron, sodium, strontium, PHC F4 and cyanide did not pose a risk to all of the VECs assessed. Also, given that the potential risk to some of the terrestrial biota is localized to Polygon E, and most fauna move around, population level impacts on terrestrial biota at the DNGS and the DWMF are not expected. The risk to terrestrial plants in this area is localized and do not impact the wider plant community.

Exposure to physical stressors

While physical stressors are not subject to a formal screening process, it is recommended in the CSA N288.6 that thermal stressors, and entrainment and impingement should be assessed for aquatic biota (see section 3.2.3, Aquatic Environment), due to their widely recognized concern at nuclear power plants. However, other physical stressors in the terrestrial environment such as noise, wildlife strikes with vehicles, and bird/bat strikes on buildings were not evaluated further based on the negligible impacts expected from these stressors on wildlife at the DN site. This was supported by survey and monitoring studies done at the DN site.

Terrestrial environment monitoring

While the ERA did not recommend specific terrestrial environmental monitoring, as a risk management best practice, it was recommended that a soil characterization study of the yard waste and building materials storage area in Polygon E should be undertaken by OPG. OPG commissioned a soil characterization study in 2021. Results of this study will be included in an upcoming DN ERA Addendum report to be expected in late September 2024. The results of the soil characterization study will inform the next steps for management of soil from this area.

3.2.2.4 Findings

The most recent assessment of potential effects on terrestrial biota near the DN site was provided in the 2020 ERA ^{Footnote 63}. As discussed in section 2.3.3, the ERA fully complied with the requirements of CSA N288.6-12 ^{Footnote 50} and incorporated recent environmental monitoring data.

Based on the review of OPG’s 2020 ERA and the results of the EMP for the DN site, CNSC staff have found that the terrestrial environment remains protected from nuclear and hazardous releases, as well as physical stressors from the DN site. Although there are some localized areas of soil contamination, the risk to terrestrial receptors is considered low, and OPG has committed to further evaluation in order to inform next steps for management of soil in this area.

Table 3.7: Potential risks (HQ >1) of chemical COPCs/metals terrestrial biota in Polygon E (adapted from OPG, 2021)
	Earthworm	American Robin	Bank Swallow	Song Swallow	Yellow Warbler	Terrestrial Plants	Eastern Cottontail	Meadow Vole	White-tailed Deer	Common Shrew	Racoon	Red Fox	Short-tailed Weasel
Arsenic		-	-	-	-				-			-	-
Cadmium	-	-	-	-	-	-	-	-	-		-	-	-
Chromium	-	-	-	-	-	-	-	-	-	-	-	-	-
Cobalt		-	-	-	-		-	-	-	-	-	-	-
Copper												-	-
Iron		-	-	-	-	-	-	-	-	-	-	-	-
Lead							-	-	-			-	-
Molybdenum		-	-	-	-		-	-	-			-	-
Nickel		-	-	-	-		-	-	-			-	-
Selenium	-					-	-	-	-	-	-	-	-
Sodium	-	-	-	-	-	-	-	-	-	-	-	-	-
Strontium	-	-	-	-	-	-	-	-	-	-	-	-	-
Tin	-	-	-	-	-	-	-	-	-	-	-	-	-
Zinc
PHC F4	-	-	-	-	-	-	-	-	-	-	-	-	-
Cyanide	-	-	-	-	-	-	-	-	-	-	-	-	-

3.2.3 Aquatic environment

An assessment of potential effects on aquatic biota at the DN site and the surrounding area involves characterizing the local habitat and species (including considering federal and provincial species at risk) and assessing the possibility of their exposure to nuclear and hazardous substances, as well as physical stressors that may be disruptive to ecological receptors.

3.2.3.1 Surface water quality

The DN site is located on the north shore of Lake Ontario. There is very little net flow along the northern shore of Lake Ontario, however the current in the nearshore region is overall easterly and is influenced by brief patterns of strong winds. Water withdrawal from the DNGS intake results in some localized effects, such as fish impingement as well as egg and larvae entrainment at the water intake. The discharge of cooling water also results in a thermal plume that can potentially affect localized fish populations. These effects are discussed more under the physical stressors section (section 3.2.2.3) of this report.

All waterborne effluent from DN is discharged into the CCW system either via the intake forebay or directly into the CCW discharge duct. The only exception is effluent from the domestic sewage system which is routed to the Courtice Water Pollution Control Plant, and stormwater which is discharged to Lake Ontario through storm sewers or drainage swales/creeks. The surface water screening performed by OPG in the 2020 ERA was based primarily on measurements of chemical COPCs in Lake Ontario water, as well as Coot’s Pond and Treefrog Pond water. In addition, measured concentrations of chemical parameters in the CCW discharges from 2016 to 2019, and measured concentrations of chemical parameters in stormwater discharges to Lake Ontario in 2019 were screened to ensure that the list of chemical COPCs was complete.

Hazardous

Lake Ontario

Lake water samples were collected in 2019 to support DNNP site preparation licence renewal ^{Footnote 103}. The maximum measured concentration for total aluminum in Lake Ontario (142 μg/L) exceeded the Canadian Drinking Water Quality Guideline (100 μg/L) ^{Footnote 104}, however the maximum dissolved aluminum concentration (21 μg/L) was below the Provincial Water Quality Objective (PWQO) ^{Footnote 105} screening criteria (75 μg/L in dissolved phase). The dissolved phase of aluminum is expected to be more bioavailable and toxic than aluminum in the suspended phase, therefore as the dissolved aluminum did not exceed its screening criteria aluminum was not carried forward as a chemical COPC for ecological health.

The maximum concentrations of a few biological parameters, including total coliforms, fecal coliforms, and Escherichia coli exceeded their selected screening criteria (which were the lake water background concentrations). Available screening criteria include PWQO values, which were developed for the protection of recreational water uses, rather than ecological health. There are no established regulatory or toxicity benchmarks for coliforms for the protection of ecological health, as coliforms are not relevant to ecological health. Therefore, although these biological parameters have higher concentrations than the lake water background values, these biological parameters were not assessed further as COPCs for quantitative assessment.

The maximum concentrations of major ions (calcium, magnesium, potassium) exceeded the selected screening criteria (the Lake Ontario background concentrations). There is no evidence of adverse health effects from these major ions in drinking water ^{Footnote 106}, and were essentially non-toxic for environmental biota, therefore calcium, magnesium, and potassium were not carried forward as COPCs for further assessment in the EcoRA.

In addition, the maximum field pH value observed in Lake Ontario (9.21) was beyond the range of selected screening criteria. Similarly, the maximum concentrations of total suspended solids, total ammonia, un-ionized ammonia, barium, and zinc exceeded the selected screening criteria, and therefore were carried forward as COPCs for further assessment in the EcoRA.

The maximum measured concentration of phosphorus exceeded its ecological screening criteria. Phosphorus presents in the aquatic environment as phosphate, where it acts as a nutrient rather than a toxicant. The interim PWQO guideline was set to avoid nuisance concentrations of algae in lakes and is not relevant to ecological health, therefore phosphorus was not considered a COPC for ecological health.

Liquid effluent

Information from 2016 to 2019 on the concentrations of COPCs in liquid effluents was assessed by OPG to aid in COPC selection. The final discharge released from the CCW duct was assessed for this screening. In addition, effluent released from the CCW duct is diluted in Lake Ontario through the diffuser, therefore, the initial mixing zone in Lake Ontario represents a maximum potential exposure for ecological receptors. Effluent quality results were converted to estimated concentrations in the mixing zone using a dilution factor of 7 at the diffuser, which is representative of the dilution provided by the diffuser. Estimated mixing zone concentrations from 2016 to 2019 were screened against the same screening criteria as the lake water samples.

As part of the ECA requirements, the effluent from the CCW is sampled and analyzed for compliance with effluent limits for unionized ammonia, hydrazine, morpholine, pH, and total residual chlorine (TRC). ECCC has developed a Federal Environmental Quality Guideline (FEQG) for hydrazine of 2.6 μg/L for fresh water ^{Footnote 107}. The maximum observed hydrazine concentration (6 μg/L) at the CCW duct was above the screening level of 2.6 μg/L. Similarly, the maximum measured morpholine and TRC concentrations in the CCW were greater than their respective screening criteria. However, the estimated maximum mixing zone concentrations for hydrazine, morpholine, and TRC were all below their selected screening criteria, therefore these parameters were not carried forward for further assessment in the EcoRA. Since the pH in effluent was within the range of the CCME guideline (pH range 6.5 to 9), pH was not carried forward as a COPC from the effluent screening.

Effluent monitoring is also required under the Ontario Provincial Environmental Compliance Approval, and the parameters measured in the radioactive liquid waste (RLW) and water treatment plant (WTP) effluents include phosphorus, total suspended solids (TSS), zinc, iron, oil and grease, and aluminum. Mixing zone calculations were conducted to obtain expected concentrations of COPCs in the CCW based on effluent discharge to the CCW from the RLW and the WTP and were based on a worst-case scenario, assuming effluent was discharged at the limits within the ECA. The calculated CCW concentrations, as well as the estimated mixing zone concentrations were compared against the ecological health screening criteria and were found to be well below these limits.

Based on the above there were no COPCs carried forward for further assessment in the EcoRA from the ECA effluent screening.

Stormwater

The Stormwater Management System, or Yard Drainage System, collects storm runoff from the entire DN site and discharges to Lake Ontario, either directly through the storm sewer drainage system, or through drainage swales/creeks via culverts which eventually discharge to Lake Ontario.

Stormwater chemical analyses from 2019 were compiled and maximum concentrations from this dataset were converted to equivalent loadings to Lake Ontario using the maximum measured peak flow rates at the time of sampling (except for temperature, conductivity and pH, for which the maximum values measured in stormwater were directly used for screening). These equivalent loadings were then converted to estimated Lake Ontario concentrations in a nearshore mixing zone. The estimated Lake Ontario concentrations were then screened against the same ecological screening benchmarks used in the lake water screening.

While the minimum pH value was within the MECP regulated range (6.5 to 8.5), the greatest pH value observed in the stormwater was 8.97, beyond the MECP pH range, however within the CCME water quality objective for pH for freshwater biota (6.5 to 9). Since the maximum measured pH was less than the CCME upper bound, and the stormwater would be diluted in Lake Ontario, pH was not considered further for assessment in the EcoRA.

The maximum estimated concentration of both total and dissolved barium in the lake water exceeded the selected screening criteria, therefore barium was carried forward for further assessment as a chemical COPC for lake water in the EcoRA. The maximum estimated barium concentration in lake water due to stormwater was 4.3 μg/L, which was lower than the maximum observed concentration of barium in Lake Ontario during the 2019 sampling events, which was 32.3 μg/L. Since measured barium concentrations in lake water are higher than those estimated from stormwater in Lake Ontario, the exposure assessment focused on measured barium concentrations in lake water as a conservative approach.

None of the polychlorinated biphenyls (PCBs) compounds were detected in the stormwater samples, therefore PCBs were not considered chemical COPCs for further assessment in the EcoRA. There are no regulatory or toxicity benchmarks for PCBs in surface water and PCBs do not partition to water due to their low solubility.

The concentration of oil and grease were also analyzed in the 2019 stormwater sampling event. The oil and grease test has been largely replaced by testing for petroleum hydrocarbons (PHCs). As the maximum estimated concentrations of the PHC compounds and fractions in lake water were well below their screening criteria, this parameter was not carried forward as a COPC for further assessment in the EcoRA.

Pond Water

Surface water samples were collected from Coot’s Pond (in Polygon AB) and Treefrog Pond (in Polygon D) and the data were assessed in the 2009 EcoRA ^{Footnote 83}. These ponds are not exposed to liquid effluent from DN, but Coot’s Pond is exposed to stormwater runoff from the construction landfill. The ponds are also expected to be exposed to chemical contaminants in air, which could be deposited in surface water after release to the atmosphere from DN. A screening of the available data from the 2009 EcoRA ^{Footnote 83} was conducted in the 2016 ERA ^{Footnote 108}. In 2019, Ecometrix performed environmental studies to support the DNNP site preparation licence renewal. Quarterly surface water samples were collected from both Coot’s Pond and Treefrog Pond ^{Footnote 103}. Parameters analyzed in this study included most chemicals that partition to water of those modelled by OPG in air. A screening of available data from the 2019 environmental study was conducted to determine if any COPCs could be present in surface water in either of these ponds. This screening used the same criteria as the other surface water screenings for ecological health

The maximum concentration of a few major ions, including calcium, magnesium, and potassium exceeded the screening criteria in both Coot’s Pond and Treefrog Pond. These major ions are not considered as toxicants for environmental receptors, therefore they were not carried forward as COPCs for pond water.

For Coot’s Pond, pH, total and unionized ammonia, barium and iron exceeded the screening criteria and were identified as COPCs. For Treefrog Pond, total ammonia, barium and iron exceeded their selected screening criteria, and were identified as chemical COPCs.

The maximum concentrations of a few biological parameters, including total coliforms, fecal coliforms, and Escherichia coli exceeded their selected screening criteria in both Coot’s Pond and Treefrog Pond. Available screening criteria include PWQO values, which were developed for the protection of recreational water uses, rather than ecological health ^{Footnote 109}. There are no established regulatory or toxicity benchmarks for coliforms for the protection of ecological health, and these parameters are not relevant to ecological health, therefore these biological parameters were not carried forward as COPCs for this EcoRA.

The maximum concentration for total aluminum in Coot’s Pond water was 369 μg/L, which exceeded its CWQG screening criterion. However, the maximum analyzed concentration for dissolved aluminum (in a filtered sample) was 25 μg/L, which was below the selected criterion (PWQO value) of 75 μg/L. As the dissolved aluminum was analyzed and did not exceed its screening criteria, aluminum was not carried forward as a chemical COPC for ecological health.

The maximum measured concentration of phosphorus in both ponds exceeded their ecological screening benchmark. Phosphorus exists in the environment as phosphate, where it acts as a nutrient rather than a toxicant, therefore phosphorus was not considered a COPC for ecological health.

Radiological

The liquid effluent radionuclide groups that are used for DRL calculation and public dose calculation at the DN site are HTO, mixed beta-gamma emitting radionuclides (gross beta-gamma), carbon-14 as dissolved carbonate/bicarbonate (C-14), and mixed alpha emitting radionuclides (gross alpha). Liquid effluent is monitored for radionuclides. Over the period from 2016 to 2019, dose contribution from gross alpha activities in water were at least two orders of magnitude less than all other radionuclide groups. As such, the contribution of gross alpha to total radioactive emissions is considered to be minimal. Gross alpha was therefore not considered to be a COPC for the EcoRA.

The following radiological stressors measured in the aquatic environment were used in the assessment of ecological health, for Lake Ontario and for the on-Site ponds:

C-14, which is released to both air and surface water by reactor operations at the DN site;
Co-60, which represents gross beta-gamma released to the atmosphere by the DN site;
Cs-134, which represent gross beta-gamma emissions released to surface water in liquid effluent from the DN site;
HT, which is released to the atmosphere by the TRF and in very small amounts from the powerhouse at the DN site;
HTO, which is released to both air and water by the reactor operations at the DN site; and
I-131, which was included for consistency with other EcoRAs conducted for the DN site and is not expected to be a primary contributor to radiological dose for ecological VCs.

3.2.3.2 Sediment quality

Sediment in Lake Ontario was characterized as part of the baseline data collection for the ecological risk assessment in the DNNP EA ^{Footnote 82}. From 2016 to 2019, two additional sampling studies were carried out. In 2018, a sediment characterization study consisted of two sampling events at the Darlington Harbour area and near-shore locations immediately west of the Darlington Harbour. In 2019, sediment samples were collected at the Lake Ontario near-shore and off-shore to support DNNP site preparation licence renewal. The updated 2018 to 2019 sediment data were screened against relevant screening criteria to select chemical COPCs for the EcoRA.

Hazardous

Lake Ontario Sediment

Lake Ontario in the vicinity of the DN site is not a depositional environment, therefore any chemical parameters in sediments in Lake Ontario due to DN’s influence are likely to be due to liquid effluents, and screening of Lake Ontario water and liquid effluents for COPCs are expected to be protective of aquatic life. However, the sediment monitoring data were also screened by OPG as an additional line of evidence for the selection of COPCs.

Some nutrients, metals, and PHCs exceeded their selected criteria (total Kjeldahl nitrogen (TKN), phosphorus, cesium, strontium, and PHC F3 fraction). Several PAHs also exceeded their Canadian Sediment Quality Guidelines (CSQG) (benzo(a)pyrene, chrysene, dibenzo(a,h) anthracene, phenanthrene, and pyrene). Among parameters that exceeded the screening criteria, the elevated TKN and phosphorus are likely due to agricultural inputs into Lake Ontario, and not due to DNGS operations. The above-mentioned nutrient, metal, PHC, and PAH parameters with exceedances were assessed as chemical COPCs for further assessment in the EcoRA.

The maximum concentration of calcium in lake sediment also exceeded the selected screening criterion, which was derived from the background calcium concentration in Lake Ontario sediment. Calcium is a natural component of sediment and not a toxicant to ecological life, therefore it was not assessed as a chemical COPC for further assessment in the EcoRA.

The detection limits of a few PCBs and pesticides (including heptachlor, aroclor 1016, aroclor 1248, aroclor 1260), and total PCBs are higher than their selected screening criteria, therefore making it difficult to deduce if there are any true exceedances. All PCB concentrations in the 2018 to 2019 sampling events were below detection indicating low PCB levels. There is no known source of PCBs at the DN site since PCBs were banned in the late 1970s, well before DNGS was constructed, therefore these parameters were not assessed further as chemical COPCs in sediment as they were below detection limits and most likely not present or a risk to receptors.

Pond Sediment

The on-site ponds, including Coot’s Pond and Treefrog Pond, are depositional environments. Other than stormwater runoff, these ponds do not receive liquid effluents from DN, so the only potential transport pathway for COPCs from DN to these ponds is through airborne deposition of air emissions from operations at the DN site. Among the contaminants that OPG modelled in air, NO_x were defined as chemical COPCs in air. NO_x is unlikely to deposit on surface water and partition to sediments. None of the other modelled contaminants in air were at concentrations of concern, so potential deposition of these chemicals to the ponds was not expected to lead to environmental risks.

During the 2019 environmental studies to support DNNP site preparation licence renewal ^{Footnote 103}, sediment samples were collected at Coot’s Pond and Treefrog Pond and the monitoring results were screened against selected screening criteria protective of ecological health. As Lake Ontario background concentrations were not appropriate to represent the background in the ponds, parameters without regulatory and toxicological benchmarks were screened against the upper range of crustal abundance in the United States ^{Footnote 110}.

For Coot’s Pond, TKN, total organic carbon (TOC), phosphorus, cadmium, chromium, copper, iron, manganese, nickel, vanadium, and zinc were carried forward as chemical COPCs in sediment. For Treefrog Pond, TKN, TOC, phosphorus, cadmium, copper, selenium, and vanadium were carried forward as chemical COPCs for ecological health in sediment.

Both Coot’s Pond and Treefrog Pond are nutrient enriched, as there were elevated concentrations of ammonia and phosphorus in pond water. Therefore, exceedances of TKN, TOC and phosphorus are likely due to agricultural runoff rather than operations at the DN site.

Radiological

Since the primary pathway for radionuclides to be transported to Lake Ontario sediment is through partitioning from liquid effluents, the same radionuclides were selected for sediment as were selected for surface water. This is conservative, since Lake Ontario in the vicinity of DN is not a depositional environment, and COPCs are unlikely to accumulate in lake sediment.

Coot’s Pond and Treefrog Pond are depositional environments, and these ponds do not receive liquid discharge from DNGS, therefore the main input of radiological contaminants is from airborne deposition from DN emissions and subsequent partitioning to sediment. While gross-beta gamma released to surface water is represented by Cs-134, sediment data are available for Cs-137 and Co-60 as well, therefore they have been included as COPCs and are evaluated in the exposure assessment.

The final list of radionuclides for both Lake Ontario and pond sediment was C-14, Cs-134, Cs-137+, Co-60, HTO, and I-131.

3.2.3.3 Aquatic habitat and species

Aquatic habitat

Aquatic habitat at the DN site includes tributary watercourses and ponds on the DN site, and the adjacent areas of Lake Ontario. Aquatic habitats support a variety of aquatic plant and animal communities and may include periphyton, phytoplankton, benthic invertebrates, zooplankton and fishes. Aquatic macrophytes are included as part of the vegetation communities section. The key aquatic features on the DN site include the main branch of Darlington Creek and the intermittent upper portions of tributaries to Darlington Creek, the artificially constructed Dragonfly, Treefrog and Polliwog Ponds, the intermittent upper portion of a tributary to Lake Ontario at the eastern toe of the Northwest Landfill Area slope, and Coot’s Pond (a stormwater runoff and settling pond that lies south of the construction waste landfill).

The artificially constructed ponds (Dragonfly, Treefrog and Polliwog Ponds) and the intermittent tributaries to Darlington Creek and Lake Ontario do not support fish and are not considered direct fish habitat.

Aquatic species

More than 90 fish species are known to inhabit Lake Ontario, almost all of which use the nearshore waters for spawning, rearing, feeding and migration. Although the community is diverse, fish density tends to be low. Fish community studies conducted near the DN site indicated that the fish species commonly present included alewife (Alosa pseudoharengus), round goby (Neogobius melanostomus), round whitefish (Prosopium cylindraceum), lake trout (Salvelinus namaycush), Spottail Shiner (Notropis hudsonius), White Sucker (Catostomus commersonii), brown trout (Salmo trutta), walleye (Sander vitreus), rainbow smelt (Osmerus mordax), and salmonid species. The nearshore environment of Lake Ontario is characterized by hard substrates and is a high energy environment. Therefore, it supports a limited density and diversity of benthic invertebrates, which are mainly found in shallow areas. Invasive zebra mussels (Dreissena polymorpha), and quagga mussels (Dreissena bugensis), have colonized the nearshore area of Lake Ontario and influence local benthic habitat and productivity. In 2016 and 2018, all the mussels identified were quagga mussels, which has essentially replaced zebra mussel in the nearshore environment of Lake Ontario.

Darlington Creek near the DN site supports a warmwater fish community. Historical data compiled for the creek confirmed the presence of ten species between 1998 to 2009 (common carp [Cyprinus carpio], white sucker, brook stickleback [Culaea inconstans], pumpkinseed [Lepomis gibbosus], bluntnose minnow [Pimephales notatus], fathead minnow [Pimephales promelas], blacknose dace [Rhinichthys obtusus], longnose dace [Rhinichthys cataractae], creek chub [Semotilus atromaculatus], and rainbow trout [Oncorhynchus mykiss]). The intermittent tributaries to Darlington Creek on the DN site lack permanent aquatic habitat and do not support fish and are often dry. Their primary habitat function is the conveyance of water and nutrients to downstream habitats.

Coot’s Pond is a stormwater runoff and settling pond. Coot’s Pond was intended to be fish-free to encourage amphibian production, however Northern Redbelly Dace has become established in the pond. Northern Redbelly Dace are common inhabitants of wetlands and beaver ponds. The pond was inhabited by emergent and submergent aquatic vegetation, and habitat quality is sufficient to support a wide array of benthic invertebrates. Coots Pond has emergent and submerged aquatic vegetation and possesses wetland and open-water pond habitats. Giant Bur-reed dominates an area on the west side of Coot’s Pond.

Treefrog, Polliwog and Dragonfly ponds are small wetland ponds that are not well connected to on-site watercourses and do not support fish. Dragonfly and Polliwog Ponds have been observed to dry up completely during summer, while Treefrog Pond remains wet.

The main exposure pathway for the aquatic community is through direct contact with water and sediment at the DN site outfall. As indicated in section 3.2.2 Terrestrial environment, some terrestrial species (such as riparian birds and mammals, amphibians and reptiles) were assessed as aquatic species for the purpose of the radiological and non-radiological exposure assessments.

Aquatic species at risk

In Ontario, the following legislation applies to species at risk: the provincial Endangered Species Act ^{Footnote 99} and the federal SARA ^{Footnote 98}. Four fish species at risk, with a provincial or federal ranking of special concern, threatened, endangered or extinct were recorded at the DN site (American eel, Atlantic salmon, lake sturgeon, and deepwater sculpin). However, lake sturgeon has not been observed since 1998 and is considered no longer present in the area. Atlantic salmon were observed within the area as recently as 2019; however, Atlantic salmon found in Lake Ontario are likely individuals from the Lake Ontario Atlantic Salmon Restoration Program and are not considered individuals of the native Lake Ontario Population. American eel was observed in impingement monitoring programs and is therefore considered in the ERA. An entrainment study at DNGS in 2015-2016 found nine deepwater sculpin larvae and estimated 724, 746 larvae are entrained annually. One deepwater sculpin larva was collected from larval tows in 2018. Data from bottom trawl surveys conducted from 1996 through to 2016 suggest that deepwater sculpin populations in Lake Ontario have recovered and current densities and biomass may be similar to those of other Great Lakes.

Table 3.8: Status of aquatic species at risk present around the DN site
Species	SARA status ^{Footnote 98}	SARO status ^{Footnote 99}
Fish
American Eel	Threatened	Endangered
Lake Sturgeon	Threatened	Endangered
Atlantic Salmon	Extinct (2010)	Not listed
Deepwater Sculpin	Special Concern	Not at Risk

ERA predictions

The most recent assessment of potential effects on aquatic biota near the DN site was provided in the 2020 ERA ^{Footnote 62}. As discussed in subsection 2.3.3, the ERA fully complied with the requirements of CSA N288.6-12, Environmental risk assessments at Class I nuclear facilities and uranium mines and mills ^{Footnote 50} and incorporated recent environmental monitoring data.

OPG selected a total of 14 aquatic receptors for the assessment based on knowledge of the DN site and its surrounding environment, and relevant field observations. The chosen aquatic receptors include the categories of benthic invertebrates, aquatic plants, amphibians and reptiles, benthic fish, pelagic fish, riparian birds and riparian mammals. The chosen ecological receptors reflect a variety of diets or feeding habits, cover a variety of trophic levels, and are representative of the potential species present in the area and include species identified as important to Indigenous Nations and communities.

Exposure to nuclear substances

The potential radiological effects on ecological receptors were assessed by comparing the estimated radiation dose received by each ecological receptor from radiological COPCs through all applicable pathways (namely external and internal exposure due to radionuclides in air, soil, water, sediment, and gamma radiation) to the recommended benchmark values (that is, dose limits to non-human biota).

The overall radiation dose, which included all internal and external doses from all exposure pathways, were significantly below the radiological dose benchmarks recommended in CSA 288.6-12 ^{Footnote 50} (that is, 400 µGy/h or 9.6 mGy/d for aquatic receptors). This result indicates negligible potential for adverse effects and no need for further detailed assessment.

Exposure to hazardous substances

The potential hazardous effects on ecological receptors were assessed by comparing the estimated exposure concentration received by each ecological receptor from hazardous COPCs through all applicable pathways (namely exposure to hazardous contaminants in air, soil, lichen, vegetation, water, sediment, benthic invertebrates, phytoplankton, zooplankton and aquatic vegetation) to the recommended benchmark values (that is, toxicity reference values for non-human biota). Benchmarks were then compared against exposure levels for aquatic and riparian receptors to calculate a HQ, which is the ratio of the concentration of the COPC (in surface water or sediment) to the most conservative toxicological benchmarks. A HQ that is ≤ 1, meaning the concentration of COPCs in surface water or sediment is less than or equal to the benchmark, indicates there is no potential risk to aquatic or riparian receptors from exposure. The interpretation of HQ results also takes into consideration the distribution of areas with a HQ>1, the mobility and home range of the affected receptor, and whether the exposure point concentrations can be attributed to DN operations.

Lake Ontario

There was no exceedance of the HQ target of 1 for riparian birds in Lake Ontario, and there are no mammals considered as ecological receptors in this polygon.

Maximum surface water concentrations for the site study area in Lake Ontario exceeded the benchmarks for ammonia for fish, however the upper confidence limit of the mean (UCLM) water concentration did not exceed the fish benchmark. Fish are more mobile, therefore using the UCLM for HQ water concentrations for ammonia are more representative of fish exposure than maximum concentrations. In addition, the elevated ammonia concentration in Lake Ontario is not likely resulting from the DN operations, therefore fish are not at toxicological risk from DN operations.

Maximum sediment concentrations for Lake Ontario exceeded the sediment benchmark for TKN for benthic invertebrates. Both the maximum and the UCLM sediment concentration of phosphorus exceeded the sediment benchmark. Since benthic invertebrates cannot move around a few benthic invertebrates may experience prolonged exposure at the maximum, therefore assessing the risk using the maximum sediment concentrations is appropriate. No significant risk is expected from TKN, phosphorus, and PHC F3 in the sediment for benthic invertebrates, however there is uncertainty surrounding the risk associated with TKN and phosphorus. There is evident input of agricultural runoff in Lake Ontario in the area, and these two parameters are not likely elevated due to operation at DN. In addition, there is no available benchmark for PHC F3 in sediment for benthic invertebrates. Sediment in Lake Ontario is transient, and the invertebrate community is mainly epifaunal. This suggests that the sediment exposure pathway is unlikely to be the primary exposure route for benthic invertebrates in Lake Ontario.

Cesium and strontium were identified as sediment COPCs as they exceeded the upper limit background concentrations in Lake Ontario sediment. There is no available benchmark for cesium and strontium for aquatic and riparian ecological receptors. However, the maximum concentrations of these two elements fall within the range of background concentrations for data collected from the continental USA ^{Footnote 110} between 0.25-25 mg/kg and 5-3000 mg/kg for cesium and strontium, respectively, therefore cesium and strontium are not likely to cause toxic effects on ecological receptors in Lake Ontario.

Toxic effects of PHCs are not expected for birds. While, toxicity reference values are not available for PHC F3 and PAH compounds (including benzo(a)pyrene, chrysene, dibenzo(a,h)anthracene, phenanthrene, and pyrene) for birds, these compounds are readily metabolized by vertebrates, and are not anticipated to accumulate in birds and mammals, especially at environmental concentrations ^{Footnote 111}. The major pathway for riparian birds to be exposed to PAHs is through ingestion of benthic invertebrates and sediment. The maximum PAH concentrations in the Lake Ontario site study area exceeded the CCME sediment quality guideline during one sampling event at Darlington Harbour, however no exceedances were identified in all other sampling events. As the Lake Ontario sediment is not depositional, and the invertebrate community is mainly epifaunal, the risk for riparian birds to be exposed to toxic level of PAHs is very low.

No adverse effects from pH are expected in Lake Ontario. The UCLM pH measured in Lake Ontario was 8.4 and although the maximum pH observed (9.2) exceeded the MECP water quality objective and the CCME water quality objective, the area is considered to be productive. This is evident from the DNNP EA ^{Footnote 82} and recent aquatic community studies ^{Footnote 103} ^{Footnote 112}, which document diverse populations of fish, phytoplankton and zooplankton, as well as benthic invertebrates.

Since the American eel is a species at risk, the assessment endpoint is the health of the individual. The fish benchmarks were exceeded for maximum water concentrations of ammonia, but not for UCLM water concentrations. Since fish are mobile, the UCLM water concentration is more appropriate than the maximum for assessment of toxicological risk to the American eel. The American eel is not at toxicological risk from DN operations.

Ponds

In Coot’s Pond (Polygon AB), maximum ammonia (un-ionized) concentrations in surface water exceeded the fish (northern redbelly dace) and turtle/frog benchmarks. Maximum and UCLM sediment concentrations in Coot’s Pond exceeded the sediment target benchmarks for TKN, TOC, cadmium, chromium, copper, iron, manganese, nickel, phosphorus, vanadium, and zinc for benthic invertebrates. There was no exceedance of the HQ target of 1 for birds and mammals.

The UCLM pH measured at Coot’s Pond was 9.0 and the aquatic environment is productive, so no adverse effects from pH are expected at Coot’s Pond. Although the maximum pH observed in Coot’s Pond (9.6) exceeded the MECP wand CCME water quality objective for pH, the productive nature of Coot’s Pond is evident from recent biodiversity studies ^{Footnote 102} ^{Footnote 112}.

Although potential risks were identified to aquatic receptors at Coot’s Pond from a number of COPCs, the source of these COPCs in Coot’s Pond is not the result of emissions from the DN site but is attributable to the pond having been designed as a settling pond for stormwater runoff, and to being adjacent to a licensed landfill section of the site. OPG has an ECA for the landfill and conducts and reports on quarterly monitoring and semi-annual inspections. There is no pathway from DN liquid effluent to Coot’s Pond. There is potential for DN air emissions to deposit at the pond, however the chemical signature in Coot’s Pond is characteristic of landfill runoff. The elevated TKN, TOC, ammonia and phosphorus concentrations in the sediment also suggest agricultural inputs in Coot’s Pond.

The maximum concentrations of strontium in soil in the Coot’s Pond area falls within the range of background concentrations for the continental USA ^{Footnote 110}. Strontium competes with calcium but it does not have a toxic effect on bone in chicks. Since there were no data to determine strontium benchmarks for birds, the mammal benchmark was used as a surrogate, and there were no exceedances.

Adverse health effects for birds and mammals are not expected from elevated levels of iron in surface water and sediment. Iron is generally present in surface water as salts in its trivalent form (Fe³⁺) when the pH is above 7 ^{Footnote 113} and is therefore not in a bioavailable form. In the sediment, iron is mainly present in the form of particulates, and is not bioavailable. Absorption of iron in the body (mammals and birds) is regulated, and very little is metabolised.

No risks were identified to ecological receptors in the Treefrog Pond area. Where data were available, the HQ target of 1 was not exceeded for aquatic and terrestrial biota in Polygon D.

Exposure to physical stressors

Impingement

Impingement of fish and entrainment of fish eggs and larvae within the DN site occurs from the use of lake water for CCW. Owing to intake design refinements and its later construction date, DN employs a more advanced intake structure which impinges fewer fish than at Pickering Nuclear Generating Station. Fish impingement sampling was conducted at the DN site May 2010 and April 2011. Thirteen fish species were observed, with alewife and round goby representing 97% of the counts and biomass. The estimated annual total was 274,931 fish impinged and 2,362 kg of fish biomass. Impinged American eels were reported to the Ministry of Natural Resources and Forestry (MNRF) annually as a condition of the Endangered Species Act (ESA) permit. From 2016 to 2019, the number of incidental impinged American eel at DNGS was reported at 13 (April 2016 - March 2017), 24 (April 2017- March 2018), 5 (April 2018 - March 2019), and 0 (April 2019 - March 2020).

As recommended in CSA N288.6-12 ^{Footnote 50}, various “equivalent loss” metrics can be calculated from the counts of fish impinged. These metrics include equivalent age 1, equivalent fishery yield, and production foregone and are more relevant to describing the effect on fish population than the raw counts. Equivalent age 1 values were calculated by OPG for most fish species. Production foregone was calculated for most fish species and represent the loss of future biomass due to the foregone growth of the fish taken at the station. The production foregone over all species considered was 905 kg, mainly from alewife, round goby and rainbow smelt. Adding this to the biomass of fish lost at the time of impingement (2355 kg) a total biomass loss of 3260 kg was calculated. Lost fishery yield was calculated only for species with commercial or recreational fisheries. This metric represents the loss of future fishery yield (expressed as biomass) that will not be harvested as a result of fish taken at the station. The lost fishery yield was 89 kg and consisted almost exclusively of rainbow smelt.

The alewife population in Lake Ontario in 2009 was estimated at 134 million age 1 and older fish, with a biomass of 5298 metric tonnes ^{Footnote 114}. The take of alewife at DN in 2010-2011 was equivalent to 56,515 age 1 fish, or 0.04% of the population. The total biomass lost, including production foregone, was 1571 kg, or 0.03% of the population biomass. These losses are considered to be negligible.

The rainbow smelt population in Lake Ontario in 2009 was estimated at 311 million age 1 and older fish, with a biomass of 1714 metric tonnes ^{Footnote 114}. The take of rainbow smelt at DN in 2010-2011 was 5857 fish, or 0.002% of the population. The total biomass lost, including production foregone, was 145 kg, or 0.008% of the population biomass. These losses are also considered to be negligible.

The invasive round goby has increased rapidly in Lake Ontario since appearing in 2002, with a concurrent decline in the native benthic prey species such as the slimy sculpin ^{Footnote 115}. Based on bottom trawl surveys on the U.S. side of the lake, round goby density was approximately 0.03/m², with a biomass of 0.2 g/m² ^{Footnote 115}. For a lake area of 18,960 km², Lake Ontario may contain around 568 million round goby, and a biomass of around 3.8 million kg. The take of round goby at DN in 2010-2011 was 151,510 fish, or 0.27% of the population. The total biomass lost, including production foregone, was 1,515 kg, or 0.04% of the population. These losses are considered to be negligible.

Overall, fish losses due to impingement at DN were considered negligible when considering the Lake Ontario populations of the impinged organisms. OPG has a DFO Fisheries Authorization for the impingement and entrainment of fish at DNGS and OPG will continue to meet the conditions of the Fisheries Act Authorization, which includes conducting two years of impingement monitoring at DNGS in 2024 and 2025. Note that the DFO Fisheries Act Authorization does not allow for impingement and entrainment of federal species at risk (SARA Schedule 1) and provides conditions for monitoring and reporting should a SARA Schedule 1 species become impinged or entrained. Impingement and entrainment of provincial species at risk (SARO) is covered under the ESA and associated regulations.

Entrainment

Fish egg/larvae entrainment sampling was conducted in 2004 (June - August), 2006 (March - September) ^{Footnote 116}, 2010, and 2015/2016. The most recent sampling effort was a follow up program to the EA for DN refurbishment and continued operation, where more intensive studies of fish (eggs and larvae) and macro benthic invertebrate entrainment were completed. The estimated annual entrainment was comprised of 94,482,521 eggs and 10,983,411 larvae. This number was higher than the 2004 and 2006 studies, likely because of the more robust sampling method used. The estimated annual biomass lost to entrainment in the 2015/2016 study was 589 kg, comprised mainly of round goby, walleye, and deepwater sculpin. Walleye was the only entrained species subject to fishing and the lost fishery yield for walleye was 149 kg. Deepwater sculpin is a species of special concern under the federal SARA and although its larvae were entrained, no eggs were captured in the 2015/2016 study. It was noted that the deepwater sculpin population in Lake Ontario is recovering ^{Footnote 117} and may be near its carrying capacity in Lake Ontario ^{Footnote 118}.

Overall, losses from fish entrainment were considered too low to measurably affect Lake Ontario fish populations ^{Footnote 103}. Benthic invertebrates were entrained in all months of the study period with a total of approximately 22,301 individuals collected. The estimated annual entrainment of benthic invertebrates was 1,548,288,043, with the highest numbers entrained for Echinogammarus and other amphipods (91% of the benthic invertebrate total). From the 2016 epifauna and infauna sampling, it was shown that the benthic invertebrate community in the vicinity of the DNGS does not differ from communities in the reference location in a manner that reflects a station-related effect, therefore, entrainment at the DNGS is not considered to be negatively impacting local benthic invertebrate populations. OPG will continue to meet the conditions of the Fisheries Act Authorization, which includes conducting entrainment monitoring at DNGS in 2024 and 2025.

Thermal plume

No adverse thermal effects have been demonstrated and none are anticipated based on numerous thermal effects monitoring studies and survival-to-hatch modelling predictions conducted by OPG ^{Footnote 119}. Following the DN Refurbishment EA, an assessment of thermal effects from the warm cooling water discharged by DN was conducted in 2011 and 2012 at 31 locations in and around the discharge as well at reference locations. These data indicate that a temperature difference (ΔT) of 3°C between ambient lake temperatures and thermal plume temperatures is a rare occurrence within the mixing zone of the plume, and never occurs outside this zone.

Round Whitefish has been the species of focus for the thermal assessment as it is known to be particularly sensitive to water temperature changes during spawning and larval development and is expected to be present in the diffuser area from January through March. The assessment of Round Whitefish is considered representative and protective of most coldwater fish species. An optimal temperature range for Round Whitefish embryos survival has been assessed to be 1°C to 5°C ^{Footnote 120}, with hatch timing and size-at-hatch strongly influenced by average incubation temperatures, and very low survival-to-hatch at 10°C ^{Footnote 121}. In 2014 the CANDU Owners Group (COG) funded new studies of Round Whitefish embryo survival using a naturally varying base temperature. The COG study found that a reduction to 90% survival required a temperature difference within the plume (i.e. ΔT) of 3.7°C above ambient ^{Footnote 122}. In a more recent 2017 COG study, a ΔT of 3°C between plume and ambient lake temperatures was recommended as a conservative benchmark for Round Whitefish, lower than the previously suggested ΔT of 3.7°C ^{Footnote 123}. The ΔT values around the DN diffuser are well below this level. Round Whitefish survival for any sequence of temperatures measured over the embryonic period can be predicted using a survival-to-hatch model developed by OPG in conjunction with ECCC and CNSC using COG data. The predicted survival using measured data over the winter of 2011-2012 was greater than 95%. The largest predicted survival loss (as compared to the average survival at reference locations) was 1.1%, which is well below the 10% threshold for moderate risk of population-level effects warranting mitigation used by the CNSC in the Darlington Refurbishment EA.

In 2016, OPG with the assistance from Professor M. Pandey at the University of Waterloo, developed a hybrid thermal response model for early development of Round Whitefish to be included in the monitoring plan for the DNGS thermal study in 2017-2018 ^{Footnote 124}. Additional model development was performed and predicted an average incubation temperature (corresponding to a 90% probability of survival) of 6.3°C. Based on the result, a conservative temperature threshold of 6.0°C was applied as an action level in a follow-up thermal plume monitoring study conducted during the winter 2017-2018 during a refurbishment outage. If the average temperature between December 1^st and March 31^st increases above 6.0°C at the DN ADCP reference station, then the survival model would be used to determine the actual survival loss relative to the 2011-2012 average reference temperature. The average winter temperatures during this monitoring season were cooler than in 2011-2012 and were all lower than 6.0°C. Consistent with the previous monitoring event in 2011-2012, elevated plume temperatures were observed relative to reference locations during the period of early and late Round Whitefish embryo development, however temperature differences in the plume were well below the thermal benchmark ΔT of 3°C above ambient. Therefore, it was concluded that there was low risk of adverse effects to Round Whitefish due to the thermal plume.

Maximum weekly average temperatures (MWATs) calculated from measured temperatures within the vicinity of the DN thermal discharge were also compared to MWAT thermal benchmark criteria for other fish species known to occur in the area, including emerald shiner, Alewife, White Sucker and Lake Trout. The MWAT thermal benchmark criteria are species-specific values below which thermal conditions are considered suitable, either for growth of juveniles and adults, or for embryonic development ^{Footnote 125}. The measured MWATs did not exceed any of the relevant MWAT thermal benchmark criteria ^{Footnote 126}. It was concluded that no effects are expected on local fishes due to the influence of the DN thermal discharge ^{Footnote 83} ^{Footnote 127}.

3.2.3.4 Aquatic environment monitoring

As part of the site’s EMP, OPG regularly collects and analyzes radionuclide concentrations in municipal drinking water, well water, lake water, fish, beach sand and sediment around the DN site. These data can be found in OPG’s annual compliance reports, which are assessed by CNSC staff and provide a comprehensive understanding of the aquatic environment surrounding the facility. Radionuclide concentrations in samples confirm that radionuclide concentrations are within expected trends, and therefore, human and ecological receptors near the facility are protected.

3.2.3.5 Findings

Based on the review of OPG’s ERA and the results of the environmental program for the DN site, CNSC staff have found that the aquatic environment remains protected from nuclear and hazardous releases from the DN site, as well as from physical stressors. Although there were some exceedances of HQs for aquatic receptors, these exceedances were considered to be low risk as the interpretation of HQ results takes into consideration the distribution of areas with HQ>1, the mobility and home range of the affected receptor, and whether the exposure point concentrations can be attributed to DN operations.

3.2.4 Hydrogeological environment

Assessment of the impacts on the hydrogeological environment consists of characterizing the baseline hydrogeological environment, in identifying potential onsite sources of groundwater contamination, determining the extent of contamination (if any) which could lead to an exposure pathway to human and/or non-human receptors, and determining the significance of any exposure from this pathway. Additionally, this assessment evaluated the effectiveness of current control measures in place in protecting the environment.

Groundwater protection is an element of the overall EP measures at the DN site. OPG has developed a groundwater monitoring program based on several focused area site assessment over many years. In 2012, a comprehensive Groundwater Monitoring Program Design was developed, which was gradually modified over the years.

In 2020, as part of OPG’s implementation of CSA Standard N288.7-15, Groundwater protection programs at Class I nuclear facilities and uranium mines and mills ^{Footnote 52}, OPG established a Groundwater Protection Program (GWPP) that includes a Groundwater Monitoring program (GWMP) ^{Footnote 128} ^{Footnote 129}, based on existing groundwater monitoring wells. The purpose of the GWPP is to minimize or prevent releases to and effects on groundwater, as well as to confirm that adequate measures are in place to control and/or monitor these releases ^{Footnote 130}. The GWMP serves to provide timely indication of unusual or unforeseen groundwater conditions that may require corrective action or additional monitoring.

This section summarizes the hydrogeological conditions at the DN site, as well as the project’s effects on groundwater quality and quantity.

3.2.4.1 Description of existing environment

The DN site is situated on the north shore of Lake Ontario between the Oak Ridges Moraine to the north and the Lake Ontario shoreline to the south. The Oak Ridges Moraine consists of interbedded layers of glacial till and sand and gravel and is a major source of groundwater recharge. The Iroquois Plain is situated south of the moraine and extends 8 to 12 km to Lake Ontario, and is largely underlain by glacial till, shoreline deposits, and glaciolacustrine deposits. The site generally consists of fill materials at surface followed (from top to bottom) by an upper till, interglacial deposits (grey silt or fine sand), and a lower till, on top of shale or limestone bedrock. Groundwater flow at the DN site is divided into three (3) main layers consisting of compacted sands and gravels (construction fill) which form the shallow overburden groundwater system, the interglacial deposits, and shallow bedrock groundwater system. Till units with relatively lower hydraulic conductivities act as aquitards, or confining layers, and restrict groundwater movement. Groundwater flow in these units is expected to be primarily vertically downward. Alternately, interglacial deposits between till units have moderate hydraulic conductivities and act as aquifers and transmit groundwater.

Groundwater flows from north to south towards Lake Ontario (as shown in figure 3.4) except for the northeast portion of the site which flows toward Darlington Creek and then to Lake Ontario. Groundwater flow in the shallow overburden is downward, whereas flow in the bedrock unit is predominantly upward, which serves to mitigate contaminant migration under the site in this unit. Groundwater flow in the protected area of the DN facility is complex, influenced not only by the general horizontal gradient towards the lake, but also by infrastructure features which include deep building excavations and dewatering activities. As can be observed by the westward flow of groundwater toward the reactor buildings in figure 3.4, the combined presence of these infrastructure features creates a hydraulic sink, meaning that groundwater within the station’s area of influence discharges into the subdrainage systems (i.e., travels inwards) rather than towards the shoreline. This also suggests a slight alteration of groundwater flow pattern, which has been observed from 2013 to 2016 along with a lowering of groundwater levels, began to recover in 2017. Groundwater has since returned to previous levels as a result of discontinued dewatering activities ^{Footnote 131}. All effluent collected through drainage systems is analyzed (and treated if necessary) to ensure it meets radiological and non-radiological limits prior to discharge to Lake Ontario.

Groundwater elevation contours and inferred flow at DN Site. — **Figure 3.4: Groundwater flow regime at the Darlington Nuclear Site**

Controlled area and site perimeter monitoring well locations of the DN Site. — **Figure 3.5: Monitoring locations – controlled area and site perimeter monitoring wells**

3.2.4.2 Groundwater quantity and quality

As discussed in the 2020 ERA ^{Footnote 61}, the potential for exposure of human and ecological receptors to COPCs through groundwater pathways associated with the DN facility includes discharge into Lake Ontario at the site boundary, as well as deposition of airborne radionuclides through soil. Both pathways are monitored as part of the GWMP, as well as the EMP. Direct exposure is not considered as groundwater is not used as a source of drinking water on the DN site and is not considered potable. Groundwater is monitored for radiological and non-radiological contaminants from onsite monitoring wells (figure 3.5) before it migrates off-site, ultimately toward Lake Ontario. Groundwater sample collection frequencies range from quarterly to biennially for up to 141 ^{Footnote 128}, most of which are near the reactor buildings. OPG collects the following data from various onsite monitoring wells:

groundwater levels in select monitoring wells;
tritium in groundwater downgradient of the DNGS Powerhouse, active liquid waste (ALW) treatment and collection system, heavy water management building (HWMB), TRF and building effluent lagoon;
PHCs including benzene/toluene/ethylbenzene/xylenes (BTEX) downgradient of the emergency power service/emergency power generator (EPS/EPG), fuel management systems, standby generator fuel management system and auxiliary heating steam facility;
tritium in perimeter monitoring wells to establish tritium concentrations surrounding the DN site (“upgradient perimeter wells”), and tritium and PHC, including BTEX, concentrations at the Lake Ontario shoreline (“end-use wells”).
monitor groundwater flow conditions and quality during the site preparation phase as well as the future phases of the DNNP.

The monitoring data for groundwater levels confirm that groundwater in all three hydro-stratigraphic units flow toward Lake Ontario. Water levels in the overburden and shallow bedrock units have remained consistent with historical values and do not indicate any significant changes. Groundwater levels in the Protected Area are the same as or marginally below the lake level, with the minimal level reported at the Forebay channel, representing possible inward flow caused by the hydraulic influence of the subsurface drains and sumps.

At the DN site, tritium concentration trends over time at monitored locations show that, in most cases, concentrations have remained nearly constant or decreased, which indicates stable or improved environmental performance. Elevated concentrations of tritium were previously observed in the vicinity of Unit 0 due to the 2009 injection water storage tank (IWST) D₂O spill. Tritium from the spill is migrating towards the westerly end of the forebay. With continuous drainage of groundwater into the Forebay water, tritium concentration in the area has declined substantially due to dilution and there is no adverse impact on human health and the environment resulting from the 2009 event.

In a few cases, tritium concentrations at certain locations in the Protected Area near the powerhouse (south of powerhouse – Units 3 and 4) fluctuated from a historical level of approximately 300 Bq/L -600 Bq/L to a peak of approximately 1000 Bq/L, and then declined with time, during the 2018 – 2022 period. In EPG fuel management building area, tritium in water table was observed to increase to 2,000 Bq/L in 2018, followed by a continuous decrease to historical range of 600 Bq/L. This has been interpreted as the result of a small component of groundwater influenced by the IWST tritium release migrating west towards the EPG area.

These unexpected increases were predominantly observed in shallow hydrostratigraphic units, reported to CNSC staff and addressed through detailed assessments as well as corrective actions, where necessary. There was no potential for adverse off-site impacts to humans or the environment, given that groundwater in the Protected Area is hydraulically contained on-site by the subsurface drains and sumps associated with the reactor buildings – this is demonstrated by groundwater elevation data, as well as the contaminant fate and transport model developed for the DN site ^{Footnote 132}. Additionally, this is confirmed by groundwater monitoring, which over the past five years (2018-2022) demonstrates that no exceedances of the screening criterion for the protection of human health and aquatic life (i.e., 1 × 10⁸ Bq/L tritium ^{Footnote 129}), have been observed in perimeter wells at the DN site. Although water on-site is not considered potable, monitoring data over the past five years also demonstrates that there have been no exceedances of the 7,000 Bq/L drinking water quality standard identified by Health Canada ^{Footnote 133} and the province of Ontario ^{Footnote 134} in perimeter wells at the DN site. Tritium concentrations within the perimeter wells are stable and within historical ranges. Control area wells generally exhibit similar concentration of tritium to site boundary wells irrespective of their closer proximity to the reactors.

Most groundwater quality results were non-detectable with respect to PHCs and BTEX. Detectable concentrations of PHCs were found in the south vicinity of the Unit 2 in hydraulic units representing shallow bedrock. This was interpreted as naturally occurring hydrocarbons in the petroliferous calcareous shale, and thus not considered as COPCs. Concentrations of PHCs remain below detection limits and thus below provincial groundwater quality standards (e.g., province of Ontario ^{Footnote 134}) at any shoreline wells. Where detected, concentrations of PHCs and BTEX met the MECP Table 3 Site Conditions Standards for PHCs and BTEX ^{Footnote 134}.

3.2.4.3 Findings

Based on a review of the ERA and the results from OPG’s GWMP and EMP, CNSC staff conclude that OPG’s reported radiological and non-radiological releases of COPCs to groundwater from the site perimeter concentrations have remained low and there are minimal adverse effects on groundwater quantity or quality from the DN site. While elevated concentrations of tritium are observed in monitoring wells in the protected area, these are effectively contained due to the hydraulic influence of subsurface drains and sumps. CNSC staff continually review results from the ERA, GWMP and EMP to ensure that the conclusion of no adverse effects remains valid.

3.2.5 Human environment

An assessment of the human environment at the DN site involves identifying representative persons located within or in proximity to the site and determining whether they could be exposed to nuclear or hazardous COPCs, such as through breathing the air; being on the land; drinking and swimming in surface water; and eating plants, fish and wildlife from the DN site area. Representative persons are those individuals who, because of their location and habits, are likely to receive the highest exposures to nuclear or hazardous substances from a particular source and, therefore, potentially have their health impacted by these exposures. In general, human receptors may be exposed to contaminants through 4 primary routes: dermal (skin), inhalation, incidental ingestion (soil), and ingestion of food and water.

OPG’s revised 2020 ERA ^{Footnote 63} included a HHRA to assess the risk to humans from both nuclear and hazardous substances released from activities at the DN site. The 7 potential critical groups were:

urban residents (Oshawa/Courtice, Bowmanville, West/East Beach)
agricultural farm
dairy farm
rural resident
industrial/commercial workers
sport fisher
camper

These groups were used for the exposure assessment for both radiological and non-radiological COPCs. Indigenous peoples were considered in the selection of receptors for the HHRA. Information from engagement with Indigenous communities, councils and organizations gathered during preparation of the DN Refurbishment EA showed no evidence suggesting use of lands, water or resources for traditional purposes within the Local Study Area. It is possible that a few individuals may carry out these activities in a very limited fashion. However, these activities would be restricted by the urbanization, population density, and preponderance of private land in the area. Based on this, it was concluded that any influence from the DN site on the health of Indigenous peoples was likely to be bounded by the assessment of other potential critical groups located much closer to the DN site who consume foods local to DN as part of their diet.

To illustrate, the agricultural farm receptor obtains a large fraction of their annual fruit, vegetables, and animal produce locally within 1.5 km from the DN site. These receptors also obtain their water supply mostly from wells and use it for drinking, bathing, irrigation and livestock watering. While there may be dietary differences such as more wild game in the Indigenous diet, and more farm produce in the farm diet, both groups will have high local fractions, and overall dietary intakes will be similar. However, the atmospheric dispersion factor from DN to the nearest Indigenous community is orders of magnitude lower than that to the nearest farm receptor. Therefore, it is expected that Indigenous communities would receive doses that are far lower than doses received by the potential critical groups currently assessed in the ERA.

3.2.5.1 Exposure to nuclear substances

The CNSC’s Radiation Protection Regulations ^{Footnote 64} prescribe radiation dose limits to protect workers, the public, and Indigenous Nations and communities from exposure to radiation from licensed activities. Doses are either monitored by direct measurement or by estimation of the quantities and concentrations of any nuclear substance released as a result of the licensed activities. The annual effective dose limit for a member of the public is 1 mSv per year.

The DN site emits nuclear (and hazardous) substances into air and water during normal course of operations. The following exposure pathways were considered to assess doses to human receptors from radiological COPCs:

inhalation of air and external exposure to air
ingestion of water and external exposure to surface water
incidental ingestion of soil and beach sand
external exposure to soil and beach sand
ingestion of food

The air- and water-borne radiological COPCs selected for the assessment of human health included: C-14, Co-60, Cs-134, HT, HTO, noble gases (argon-41, xenon-133 xenon-135), and mixed fission product radioiodines.

For the radiological exposure assessment, exposure point concentrations (EPCs) were either based on measured data from OPG’s EMP reports or modelled from emissions data.

The radiological HHRA presents a summary of the annual doses to the three most exposed critical groups from 2016 to 2019 (Table 3.9). The critical receptor groups considered included: the dairy farms, the (agricultural) farms, and the West/East beach residents. For each receptor group, three age classes were assessed: infant, child, adult. Radiological dose calculations to human receptors were calculated using annual average measured and modelled concentrations in environmental media. The annual average doses during 2016 - 2019 for the critical receptors ranged from 0.1 to 0.8 microsieverts (µSv). The primary radionuclide pathways contributing to this total dose were inhalation and ingestion of HTO in air and in water, plants, and animal products; external exposure to noble gases; and ingestion of C-14 in plants and animal products. These dose estimates remained at most approximately 0.08% of the regulatory public dose limit of 1 mSv/year (1,000 µSv/year) and at most approximately 0.06% of the dose from background radiation (1.4 mSv/a) in the vicinity of the DN Site. Demonstration that these critical groups are protected implies that other receptor groups near the DN site with anticipated lower exposure are also protected.

Table 3.9: Summary of highest estimated public doses from 2016 to 2019 for the DN site ^{Footnote 63}
Effective Dose to Critical Group (µSv/a)
Public dose limit (µSv)	2016	2017	2018	2019
1,000	0.6	0.7	0.8	0.4

3.2.5.2 Exposure to hazardous substances

In OPG’s HHRA ^{Footnote 63} for the DN site, the exposure pathways for chemical COPCs were selected to be consistent with the radiological exposure pathways, with some incomplete pathways detailed further below. Based on the results of the COPC screening, the human exposure assessment was performed for the inhalation pathway for nitrogen oxides (NO_x), and the drinking water and fish ingestion pathway for hydrazine, lithium and zirconium. The following exposure pathways were considered:

air inhalation and external exposure to air
ingestion of surface water
ingestion of aquatic animals

Human exposure to non-radiological contaminants in off-site soil was considered unlikely as any airborne releases from the DN site and subsequent off-site deposition of non-radiological particulates (metals) would be lost against the background soil levels. On-site workers, contractors, and visitors may potentially be exposed to on-site soil; however, these exposures would be considered and controlled through OPG’s on-site Health and Safety Management System Program. With respect to groundwater, there are no groundwater supply wells downgradient of potential source areas on the DN site. As such, concentrations of potential chemical stressors in off-site drinking water wells would not be influenced by the DN site. Ingestion of terrestrial plants (forage and plant produce) and terrestrial animals were not considered complete pathways in the exposure assessment to human receptors for non-radiological COPCs. Dermal absorption of chemical COPCs was considered to be minimal in comparison to drinking water ingestion, and so determined to be an incomplete exposure pathway.

For the waterborne non-radiological COPCs, EPCs were screened based on CCW data from OPG’s ECA from 2016 to 2019 (hydrazine), and Lake Ontario water samples collected at the DN site in 2019 (hydrazine, lithium and zirconium). For the airborne non-radiological COPCs, annual exposure at the potential critical group locations was based on NO_x release rates reported in OPG’s 2016 to 2019 ESDM reports and dispersion factors.

For the risk characterization, potential risks to human receptors were characterized quantitatively in terms of HQs for non-carcinogens (NOx) and incremental lifetime cancer risks (ILCRs) for potential carcinogens (hydrazine). Consistent with CSA N288.6-12 ^{Footnote 50}, the acceptable risk levels are less than 0.2 for non-cancer risk (HQ) and less than a cancer risk of 10^-6 (ILCR).

For air inhalation exposures, the estimated HQs of potential non-carcinogenic effects attributed to NO_x were below 0.2 for the potential critical receptor groups based on modelled annual average air concentrations. Short-term (1-hr) HQs were also determined for the sport fisher based on the 1-hr NO_x concentrations at the DN property boundary in 2016 (526 μg/m³) and in 2018/2019 (205 μg/m³). The short-term HQs were 4.65 and 1.8, respectively. Short-term HQs could not be calculated for the other receptor groups as short-term concentrations or dispersion factors were not available in the ESDM reports. The sport fisher is the closest receptor to the property boundary (i.e., fishing at the DN outfall). Since the other potential critical groups are farther away, it is anticipated that the HQs for the other receptors will be lower than that for the sport fisher. Regardless, an air quality monitoring study was initiated in 2021 at the DN site will be used to refine future risk estimates. The first year of data will be included in an DN ERA Addendum report expected in late September 2024.

With respect to surface water ingestion exposures, maximum measured and upper confidence limit on the arithmetic mean (UCLM) concentrations in lake water and maximum and mean measured concentrations in CCW effluent were diluted using dilution factors in order to estimate exposure point concentrations for the COPCs. The estimated HQs for lithium and zirconium were below 0.2 for all human receptors. For hydrazine, the risk for hydrazine was determined to be below the acceptable cancer risk level of 10^-6 for all human receptors based on the UCLM hydrazine concentrations, either measured in the CCW or lake water. When based on the maximum hydrazine concentrations in the CCW, on the other hand, the ILCRs exceeded 10^-6 (for the Oshawa/Courtice and Bowmanville urban residents, and camper receptors). However, maximum concentrations are not considered representative of long-term exposure and results should be interpreted based on the UCLM. As such, adverse effects to humans due to lithium, zirconium or hydrazine originating from the DN site via surface water ingestion are not expected.

Since several human receptors are potentially exposed to chemical COPCs through fish ingestion, the fish tissue concentrations for hydrazine, lithium and zirconium were estimated using bioaccumulation factors (BAFs) and dose calculations were done based on maximum and mean concentrations of hydrazine measured in the CCW. Estimated maximum and UCLM HQs for lithium and zirconium were below 0.2 for all receptors. As such, adverse effects to humans due to ingestion of lithium and zirconium in fish from the DN area are not expected. For hydrazine, the risks were below the acceptable risk level of 10^-6 based on UCLM concentrations of hydrazine in fish. In comparison, if based on maximum concentrations of hydrazine in fish, the risk would be above the acceptable cancer risk level of 10^-6 for the sport fisher and camper receptors. However, as previously mentioned, the maximum is not considered representative of long-term exposure, and results should be interpreted based instead on the UCLM. As such, adverse effects on humans due to hydrazine originating from the DN site through fish ingestion are not expected.

Physical stressors

Noise is the only physical stressor associated with the DN site that is of potential concern to human receptors. Based on an acoustic assessment, it was determined that noise generated by DN site activities would not be expected to have a distinguishable effect on human receptors located near the DN site (Sec. 3.2.1.2).

3.2.5.3 Findings

Based on assessments conducted for the DN site, including the review of the revised 2020 ERA ^{Footnote 63}, CNSC staff have found that impacts on the human environment from nuclear and hazardous substances released from the DN site are unlikely, and that people living and working near the facility remain protected.

3.2.6 Cumulative effects

The Government of Canada continues to work to add, gather, enhance and make publicly available the data and information needed to support understanding and consideration of cumulative effects on ecosystems, society and the economy, and associated effects on health and well-being. The nature and scope of cumulative effects considered varies depending on the specific statute ^{Footnote 135}. Potential cumulative effects are assessed at the EA stage for projects, however a formal cumulative effects assessment is not a requirement within CNSC staff’s assessments for EPRs as it is not a requirement under the NSCA or other regulatory documents. Nonetheless, CNSC staff’s assessments do consider the accumulation of COPCs within the environment because of the facility or activity through the cyclical nature of ERAs, the monitoring data in annual reports, data from the IEMP, and results from any regional monitoring programs and health studies.

Licensees are required to meet onsite, and near-field monitoring requirements associated with their provincial approvals and the federal regulations, including full life-cycle requirements. These programs focus on single operations with scheduled reports on performance submitted to the regulators. These activities are further supplemented by the CNSC’s IEMP activities (see section 4.0), which focus on local areas where Indigenous Nations and communities and members of the public could reasonably be expected to conduct recreational or traditional activities (that is, off-site accessible areas).

The Government of Canada’s overarching plan for cumulative effects is available through the About cumulative effects page.

3.2.7 Climate change considerations

As indicated in section 2.3, potential impacts of climate change on the DN site have been evaluated in the previous EAs and hazard analysis. A summary of projected climate change, assessment of potential impact of climate change, as well as regulator review is presented in this section.

3.2.7.1 Relevant Potential Changes in Climate in Ontario

CNSC staff consider the latest scientific information related to climate change to inform our regulatory oversight and technical reviews.

Scientific information that is considered includes the following reports:

Canada’s Changing Climate Report ^{Footnote 136} and its supplement ^{Footnote 137}, predicts that increases in global mean temperature could result in numerous impacts in Canada, such as increasing severity of heatwaves, drought and wildfires, changing annual and winter precipitation, as well as increasing frequency and magnitude of daily extreme precipitation events.
The State of the Great Lakes 2022 Report ^{Footnote 138} provides Great Lakes (including Lake Ontario) specific climate trend information. Key findings in this regard are as follows:
- Long term water temperature trends in Lake Ontario could not be assessed due to uncertainties in the data. However, it is concluded that there was a slight increasing trend of approximately 0.03°C per year in the lower Great Lakes (Lake Erie and Lake Ontario) from 1980 to 2020.
- Based on the 1950 to 2020 annual and seasonal total precipitation data for Lake Ontario, there is a slight increase of 2.3% per decade in the winter, 3.1% per decade in the summer, 4.5% per decade in the fall, and 2.7% per decade in annual precipitation overall.
- Based on the 1918 to 2020 lake water level data, Lake Ontario water level has been unchanging, i.e., no statistically significant trend (increasing or decreasing) exists.
- Based on maximum ice cover data, spanning from 1973 to 2020, there has been a decreasing trend of 0.24% per year. However, the 30-year trend (that is, 1990-2020) is showing an increase of 0.04% per year in ice cover for Lake Ontario.
The State of Climate Change Science in the Great Lakes Basin: A Focus on Climatological, Hydrologic and Ecological Effects ^{Footnote 139} synthesizes the state of climate change impacts in the Great Lakes basin and indicates that, over the last 60 years (1950-2010), the Great Lakes basin has experienced an increase in average annual air temperatures between 0.8-2.0°C, with this warming trend projected to continue.
Lake Ontario Shoreline Management Plan ^{Footnote 140} discusses climate change impacts on future coastal hazards. For the region surrounding DN site, the wave energy in Lake Ontario is projected to increase by about 20% towards the end of the century under a high emission scenario (RCP 8.5), which could lead to increase in future erosion rate by 20% in the absence of appropriate shoreline protection ^{Footnote 140}.

3.2.7.2 Darlington Nuclear Site Sensitivities to Changes in Climate

As per the 2011 EA ^{Footnote 71} and 2013 EA Screening Report ^{Footnote 32}, OPG plans to continue the operation of DNGS Units 1-4 to 2055 and the placement of reactors into end of life shutdown state is estimated to start in 2048 and be completed by 2085. These reports discussed the potential effects of climate change on activities related to the Continued Operation Phase of the project for the DNGS.

In the 2011 EAs, the physical structures and systems (Power Block, Ancillary Facilities, Breakwater, Condenser Cooling Water Systems, Stormwater Management System and Electric Power Systems) have been evaluated against climate parameters and assessed for potential sensitivity ^{Footnote 32}. The climate change parameters that were considered in the 2011 EAs to have a potential interaction with the physical structures and systems are:

Precipitation: annual precipitation is projected to increase (20% increase in annual precipitation across the Great Lakes Basin by 2080s under the highest emission scenario ^{Footnote 139}, and extreme precipitation is also projected to increase over the 21^st century).
Frequency and severity of extreme weather events: storms, not exclusively precipitation events (e.g., lightning, tornadoes, hurricanes) are expected to be more severe and occur more frequently– for example, more frequent extreme rainfall events are projected.
Lake Ontario water temperature: water temperatures are expected to increase (0.9 to 6.7°C increase in surface water temperature by the 2080s ^{Footnote 140}) due to warmer air temperatures.
Lake Ontario water level: lower surface water levels of lakes are expected or projected, especially toward the end of this century (although low confidence). Recent study ^{Footnote 141} however show the average lake water level to remain constant in agreement with ^{Footnote 138} although more extreme highs and lows are possible in the future. Regardless, it must be noted that the level of Lake Ontario is regulated for navigation purposes.

Other climate parameters were considered by OPG ^{Footnote 71} to have insignificant interactions with the site physical structures and systems and were found not to affect operations. These parameters include evaporation, soil moisture, and groundwater.

3.2.7.3 Evaluation of Climate Related Impacts

The climate parameter-physical structures or systems interactions identified as having a possible effect have been further evaluated in the 2011 EA ^{Footnote 71} and Hazard Screening Analysis ^{Footnote 72} for the DN site. The interactions deemed as warranting further evaluation were assessed to determine: (a) the sensitivity of the project physical structures or systems to the climate parameters; and (b) the risk level of any impact to the public or the environment. A summary of these analysis (interactions showing medium risk), as well as the review by CNSC staff, are described below.

Stormwater Management System

The effect of exceeding the design capacity of the stormwater system because of an increase in the frequency and/or severity of extreme precipitation events may include overflow of the system and some localized soil erosion. However, there will be no adverse effects to any structures or equipment at the DNGS nor any risk to the public or the environment as a result of a stormwater system overflow.

Further, any localized soil erosion from the stormwater system is easily repairable as part of the ongoing maintenance program. If the regional storm event, design storm used to size stormwater management system, is redefined, OPG will re-evaluate the stormwater management system and make appropriate modifications.

As part of the adaptive management strategy requirements for the DNGS, the physical structures and systems that could be affected by a change in environmental parameters (e.g., Stormwater Management System), due to changing climate, are monitored and modifications implemented, if required.

External Flooding Hazard

OPG have conducted analysis of flooding hazard due to different mechanisms or sources of flooding, including surface runoff resulting from PMP falling directly on the site, nearby streams and rivers, coastal flooding due to potential high lake levels combined with storm surge, wind waves, seiche (source of flooding in enclosed or semi-enclosed bodies of water), tsunami, and other causes ^{Footnote 72}. The probable maximum flood (PMF) is used for flood hazard assessment at DN site and is based on a combination of PMP, a 1:100-year lake level (75.60 m) and storm surge (0.75 m). It should be noted that the water level in Lake Ontario is regulated between a high still-water level of 75.6 m and a low still-water level of 73.9 m ^{Footnote 71}. The PMP is based on Ontario Ministry of Natural Resources and Forestry technical guidelines ^{Footnote 142}, and represents a 12-hour precipitation, equivalent to 420 mm of total rainfall, with 51% in the 6^th hour, based on Table A.2 and A.4 of Appendix A ^{Footnote 142}. This PMF has a very low probability of occurrence or exceedance, with an estimated return period of 1 in 1,000,000 years ^{Footnote 72} ^{Footnote 143} that is expected to bound potential effects of climate change. The hazard screening analysis ^{Footnote 72} and probabilistic safety analysis ^{Footnote 144} demonstrate that potential impact of flooding hazard at DN site is not significant.

3.2.7.4 Findings

The climate change parameters that may have an interaction with the DN site’s physical structures, systems and components include precipitation, extreme weather events and Lake Ontario water temperature and water level.

CNSC staff have reviewed the climate change impact assessment as reported in previous environmental assessment reports for the DN site and compared the climate change parameters used in those reports with the latest projection ^{Footnote 136} ^{Footnote 137} ^{Footnote 138}. In addition, CNSC staff review information relevant to climate change resiliency through the cyclical submissions of hazard analysis reports related to safety analysis, and environmental risk assessments.

CNSC staff concludes that, despite possible changes to the climate in the future, the effect of climate change parameters on physical structure, systems and components, and the associated risk to either the public or the environment, is expected to be low. CNSC staff notes facilities specific (e.g., DNGS) climate change resilience assessment based on most up to date localized historical observations and climate model projection data and up-to-date technical guides ^{Footnote 145} to further reaffirm low impact of climate change at DN site.

4.0 Canadian Nuclear Safety Commission Independent Environmental Monitoring Program

The CNSC has implemented its Independent Environmental Monitoring Program as an additional verification that Indigenous Nations and communities, the public and the environment around licensed nuclear facilities are protected. It is separate from, but complementary to, the CNSC’s ongoing compliance verification program. CNSC staff findings are supported by IEMP sampling, along with the licensee EP data and ERA predictions. The IEMP involves taking samples from publicly accessible areas around the facilities and analyzing the quantity of nuclear and hazardous contaminant substances in those samples. CNSC staff collect the samples and send them to the CNSC’s laboratory for testing and analysis. The CNSC provides opportunities and funding for Indigenous Nations and communities that have an interest in the CNSC-regulated facilities to participate in IEMP sampling campaigns conducted in their traditional and/or treaty territories.

CNSC staff conducted IEMP sampling around the DN site in 2014, 2015, 2017, 2021 and 2023. Indigenous Nations and communities were contacted and engaged by CNSC staff ahead of the development of the site-specific sampling plan.

In 2023, the most recent IEMP sampling campaign, CNSC staff collected the following samples in publicly accessible areas outside the perimeter of the DN site:

air (3 locations)
water (4 locations)
vegetation (5 locations)
soil and sand (8 locations)
food (1 locations)

Samples were analyzed by qualified laboratory specialists in the CNSC’s Ottawa laboratory. Using appropriate protocols, CNSC staff measured radionuclides, such as gross alpha, gross beta, and tritium in samples. CNSC staff also measured hazardous substances in the water samples, such as hydrazine, aluminum, and zinc. These hazardous substances were included in the IEMP sampling campaign at the DN site following a request by the Commission at the 2015 Darlington Renewal Hearing ^{Footnote 146}.

Figure 4.1 provides an overview of the sampling locations for the 2023 IEMP sampling campaign around the DN site. The IEMP results are published on the CNSC’s IEMP web page ^{Footnote 147}.

Overview of the sampling locations for the 2023 IEMP sampling campaign at the DN Site. — **Figure 4.1: Overview of the 2023 sampling locations ^{Footnote 148}**

4.1 Indigenous participation in the Independent Environmental Monitoring Program

It is a priority for the CNSC that IEMP sampling reflects Indigenous land use, values, and knowledge, where possible. In addition to routine IEMP sampling activities, in 2023, the CNSC engaged with 3 First Nations who have Aboriginal and Treaty rights in the area of the DN Site: Mississaugas of Scugog Island First Nation (MSIFN), Curve Lake First Nation (CLFN), and Hiawatha First Nation (HFN).

In 2023, in advance of the IEMP sampling campaign at DN site, notification emails were sent to Williams Treaties First Nations, who have Aboriginal and Treaty Rights where the DN site is located as well as the Indigenous Nations and communities who have expressed interest in the DN site, inviting suggestions for species of interest, VCs, or potential sampling locations where traditional practices and activities may take place.

In 2023, the CNSC met with MSIFN, CLFN, and HFN. These meetings provided CNSC staff with the opportunity to collaborate with Indigenous Nations and communities, to learn about their individual histories and cultures, and to address questions related to the operations at OPG’s DN site. The following sections summarize CNSC staff`s collaboration with each Indigenous Nation and community ahead of and during the 2023 sampling campaign.

4.1.1 Sampling with the Mississaugas of Scugog Island First Nation

The Mississaugas of Scugog Island First Nation reviewed the sampling plan in early 2023 and provided comments on species and locations of importance. CNSC staff considered MSIFN’s comments in the IEMP sampling plan, however the specific species and locations could not be incorporated as they were located with the DN fence line, which is beyond the scope of the program. Three representatives from MSIFN joined the sampling team in the field in September 2023 and worked with CNSC staff to collect water, vegetation, and soil samples. The sampling team and MSIFN representatives discussed the IEMP and walked through techniques for sampling air, water, and soil, as well as packaging and chain of custody procedures.

4.1.2 Sampling with Curve Lake First Nation and Hiawatha First Nation

Representatives from Curve Lake First Nation and Hiawatha First Nation joined the CNSC field team to collect samples. CNSC staff started by explaining the program to CLFN and HFN representatives, as well as chain of custody procedures for the collected samples. CNSC staff then walked CLFN and HFN representatives through the air sampling process and equipment. CLFN and HFN representatives assisted in the collection of water, vegetation, sand, and soil samples. During the sampling campaign, CLFN and HFN representatives requested that CNSC staff test manoomin (wild rice) harvested from Chemong Lake east of CLFN and shared the spiritual and cultural importance of manoomin to their communities. CNSC field team members prepared a sample kit and walked participants through the instructions on how to get the manoomin sample packaged and sent to the lab. CNSC staff note that the manoomin sample was not from the edible portion of the plant, due to the timing of when it was harvested. CLFN and HFN have expressed their appreciation for the opportunity to sample manoomin and HFN is looking forward to bringing CNSC staff to collect manoomin samples near their community in the future. The CNSC is committed to working with Curve Lake First Nation and Hiawatha First Nation to ensure that the IEMP reflects their Indigenous traditional knowledge, land use and values, where possible.

4.2 Summary of Results

The levels of radioactivity measured in soil, sediment, water and vegetation were below available guidelines and CNSC screening levels. CNSC screening levels are based on conservative assumptions about the exposure that would result in a dose of 0.1 mSv per year (one-tenth of the regulatory public dose limit of 1 mSv per year). Results for all campaigns are published on the CNSC’s IEMP web page ^{Footnote 147}.

The CNSC’s IEMP in 2023 results are consistent with the results submitted by OPG, supporting the CNSC’s assessment that the licensee’s EP program is effective. The results add to the body of evidence that people and the environment in the vicinity of the DN site are protected and that there are no anticipated health impacts.

5.0 Health studies

The following section draws from the results of regional health studies, and national and international reports and publications to provide additional confidence that the health of people living near or working at the DN site in southern Ontario is protected from CNSC licensed activities.

The Durham Region Health Unit works collaboratively with the office of the Medical Officer of Health and other government and non-governmental health service providers to directly monitor the health of people living near the DN site. In regional health studies, disease rates around the facility are compared to similar populations to detect any potential health outcomes that may be of concern.

To complement the CNSC’s regulatory oversight, CNSC staff continuously work toward strengthening relationships with the various health units and offices. CNSC staff also keep abreast of any new publications and data related to the health of populations living near, or working at, licensed nuclear facilities. Lastly, CNSC staff, at times, conduct health studies on select populations through their research on the effects of low dose (and low dose-rate) exposures. In addition to community information, Canadian and international publications are discussed below. For additional information on health studies related to nuclear facilities, visit the CNSC’s web page on Health Studies ^{Footnote 149} ^{Footnote 147}.

5.1 Population and community health studies and reports

The Municipality of Clarington is located in southeast Durham Region, bordering Oshawa, Scugog, and the county of Northumberland. Clarington is divided into 7 Health Neighbourhoods, ranging in population size from 9,000 to 15,800 as of 2016 (last update). The neighbourhoods of Darlington and Clarke are rural communities, with the remaining 5 classified as urban (see all 7 community profiles ^{Footnote 150}. Information about this region is captured by the Durham Regional Health Unit and, more broadly, by the statistics reported by Cancer Care Ontario.

5.1.1 Durham Region Health Department

The Durham Region Health Department (DRHD) routinely monitors the health status of Durham Region using health indicators and health data from sources such as hospitals and laboratories, among other record-storing facilities and databases.

5.1.1.1 Darlington neighbourhood profile

The Darlington neighbourhood profile ^{Footnote 150} breaks down socio-demographic information, as well as certain health indicators such as general health (including chronic and infectious disease rates), child health, and, health behaviours (such as smoking, immunization and cancer screening). The reported statistics were compared with the statistics for Durham Region and for Ontario, and were found to be similar overall. Some diseases were more prevalent while others were less prevalent, which is consistent with the natural fluctuation of disease.

Specifically, the Darlington health profile indicates that in 2016 (last update):

the prevalence of asthma in children (16.4%) was similar to Durham Region and Ontario
the prevalence of diabetes (8.9%) was lower compared with Durham Region and Ontario
the prevalence of lung disease, including chronic obstructive pulmonary disease (COPD), (10.6%) was similar to Durham Region and higher than Ontario
the prevalence of hypertension (high blood pressure) (20.8%) was lower compared with Durham Region and similar to Ontario

5.1.1.2 Determinants of health

Determinants of health are an important consideration in the overall health status of an individual, community, or population. These include a range of personal, social, economic, and environmental factors, such as income and social status, social support networks, education, employment and working conditions, personal health practices, health services, culture, among others. Through the Health Neighbourhoods initiative, the DRHD has identified seven Priority Neighbourhoods in Durham Region ^{Footnote 151}. These communities have many health challenges, as shown by their rates and rankings on a variety of indicators and require added focus to build on health and well-being. The Priority Neighbourhoods are Downtown Ajax, Downtown Whitby, Lakeview (Oshawa), Gibb West (Oshawa), Downtown Oshawa, Central Park (Oshawa) and Beatrice North (Oshawa). These neighbourhoods have the lowest income levels of the 50 Health Neighbourhoods in Durham Region, which is an important determinant of health as people with higher incomes tend to have better physical and mental health. Smoking (adults), cardiovascular disease hospitalization (ages 45-64), and hepatitis C rates are also elevated, and life expectancy for males is lower in these neighbourhoods. None of the identified Priority Neighbourhoods are located in the municipality of Clarington.

5.1.1.3 Mortality and cancer data

The DRHD publishes regional health reports specific to mortality (last updated in 2017) ^{Footnote 152}. In 2012, the average life expectancy in Durham Region was 80.9 years for males, and 84.5 years for females. On average, there were 3,500 deaths per year among Durham Region residents between 2008 and 2012. Ischemic heart disease (heart attacks) was the leading cause of death in Durham Region and Ontario from 2010 to 2012. Lung cancer and dementia (including Alzheimer’s disease) were the second and third. These three causes accounted for nearly a third of deaths in Durham Region. Disease rates between males and females were comparable.

The DRHD also publishes a dashboard with cancer data for Durham Region (last updated in 2022) ^{Footnote 153}. Between 2010 and 2018 there were 31,763 newly diagnosed cases of cancer and 10,795 cancer deaths among Durham Region residents. For that same time frame, there was a significant decrease in the incidence of lung, prostate, colorectal, bladder and ovarian cancers. There was a decrease in cancer mortality from lung and colorectal cancer, and an increase in cancer mortality from liver cancer. The most common cancers were breast (females) and prostate (males), lung, and colorectal, accounting for almost half of new cancer cases. This is similar to Ontario and Canadian rates ^{Footnote 154} ^{Footnote 155}. Cancer incidence rates were similar among Durham Region residents for most cancer sites; however, prostate, thyroid, melanoma and lung cancer rates were higher than overall Ontario rates, while colorectal cancer rates were lower than the provincial rates ^{Footnote 153}. Similarly, cancer mortality rates were comparable among Durham Region residents for most cancer sites; however, bladder, breast, lung and non-Hodgkin Lymphoma rates were higher than Ontario rates as a whole, while colorectal and liver cancer rates were lower than Ontario rates. These findings are consistent with natural fluctuation of disease, which is influenced by many factors and determinants of health, including socio-demographic and lifestyle (e.g., smoking, alcohol consumption, overweight/obesity, etc.).

5.1.2 Cancer Care Ontario

Cancer Care Ontario is the Government of Ontario’s principal cancer advisor, with a mandate to equip health professionals, organizations and policy makers with up-to-date cancer knowledge and tools to prevent cancer and deliver high-quality patient care.

5.1.2.1 Ontario Cancer Profiles

Cancer Care Ontario, through its Ontario Cancer Profiles ^{Footnote 156}, provides interactive map-based dashboards that display key public health indicators including cancer incidence, mortality, and risk factors by Public Health Unit (PHU). Information is also presented by Local Integration Health Network (LIHN); however, given its larger geographical area, this section will present PHU data. Cancer incidence and mortality trends are typically considered over long periods of time. For the longest and most recently reported period of 2014 to 2018, for all cancer types combined, Durham Region had incidence rates higher than the Ontario average, but cancer deaths similar to those of Ontario. Compared to the Ontario average, Durham Region had higher incidence rates of melanoma, prostate (males), lung and thyroid cancer, whereas rates of non-Hodgkin lymphoma and colorectal cancer were lower. While some incidence rates are higher in Durham Region than in Ontario, they are comparable to other geographically/demographically similar regions without nuclear sites (e.g., Niagara and Ottawa).

Incidence rates of different cancer types often vary by region and are influenced by many factors, including socio-demographic and lifestyle (e.g., overdue cancer screening, high alcohol intake, smoking and excess body weight/obesity). For the most recent reported period of 2018-2020, the DRDH had smoking and alcohol intake rates similar to, and overweight/obesity rates higher than Ontario. It is recognized that the opportunity to be healthy is not the same for everyone, and is affected by personal, social, economic and environmental factors. The DRHD supports the reduction of health inequalities across Durham Region and offers a wide range of health-enhancing programs ^{Footnote 157}.

5.1.2.2 Health status of Indigenous Peoples

Health status data for Indigenous Peoples are not reported separately by the DRHD. Although there is no cancer data specific to Indigenous Peoples in Durham Region, a 2017 report on cancer in First Nations people in Ontario ^{Footnote 158} has shown that First Nations people living in Ontario had a higher incidence of lung cancer in females, and of colorectal, kidney, cervical and liver cancers than other people in Ontario over a 20-year period (1991-2010) ^{Footnote 159}. Cancer mortality was also significantly higher in First Nations people than in other people in Ontario.

5.1.2.3 Primary factors that influence cancer and other diseases

In general, the incidence of cancer and other diseases are influenced by socio-demographic factors, the availability of early detection and screening, and the prevalence of risk and protective factors. Risk factors for cancer development include unhealthy behaviours (such as smoking, poor diet, alcohol use, physical inactivity), previous treatments, exposure to certain environmental and occupational carcinogens (such as ultraviolet rays, radon, asbestos, fine particulate matter), medical conditions and infectious agents (such as human papillomavirus), non-modifiable factors (such as family history) and genetic predispositions ^{Footnote 155}.

5.1.3 Findings

The review of health reports is an important aspect of ensuring that the health of people living near nuclear facilities is protected. The regional and community health reports and dashboards indicate that cancer incidence and mortality rates, and the prevalence of health indicators and risk factors related to cancer, are largely consistent with those of the population of Ontario as a whole.

5.2 Current scientific understanding of radiation health effects

The current scientific knowledge about the sources, effects and risks of ionizing radiation is reviewed and published by the international experts that make up the UNSCEAR ^{Footnote 160}. This information comes from population studies, animal and cell studies, and clinical investigations. These studies build the foundation of knowledge about the relationship between radiation exposure and health effects, such as cancer. This knowledge, in turn, informs the recommendations of the International Commission on Radiological Protection (ICRP) ^{Footnote 161}, which focuses on establishing a robust radiation protection framework, to protect human health and the environment.

5.2.1 Canadian studies of radiation health effects

Epidemiological studies involving the DN site provide insight on populations living near or working at the DN site. The levels of exposure in local area residents and workers are low, and there is no evidence of adverse health effects resulting from past and present nuclear operations or activities in the region. These findings are consistent with the select important Canadian and international studies of radiation effects on human health in similar populations, described below.

5.2.1.1 Radiation Exposure and Cancer Incidence (1990 to 2008) Around Nuclear Power Plants in Ontario, Canada

In 2013, the CNSC conducted a study on radiation exposure and cancer incidence around Ontario nuclear power plants. The RADICON study determined the radiation doses to members of the public living within 25 km of the Pickering, Darlington, and Bruce nuclear power plants, and compared cancer cases among this subset of the population with cases among the general population of Ontario from 1990 to 2008 ^{Footnote 162}.

The main findings were that there was no consistent pattern of cancer and no evidence of childhood leukemia clusters around the three Ontario nuclear power plants. Some types of cancer were higher than expected, but others were lower or similar. Variations in all cancers combined and radiosensitive cancers were within the natural variation of cancer in Ontario.

5.2.1.2 Verifying Canadian Nuclear Energy Worker Radiation Risk: A Reanalysis of Cancer Mortality in Canadian Nuclear Energy Workers (1957–1994)

In 2011, the CNSC published a study entitled Verifying Canadian Nuclear Energy Worker Radiation Risk: A Reanalysis of Cancer Mortality in Canadian Nuclear Energy Workers (1957–1994) ^{Footnote 163}. CNSC staff also published this work in the scientific literature ^{Footnote 164}. An analysis of 42,228 Canadian nuclear workers (including workers employed by DNGS) provided no evidence of increased risk of cancer mortality between 1964 and 1994. Canadian workers had lower all-cause and solid cancer mortality compared with the general Canadian population.

5.2.2 International studies of radiation health effects

The epidemiological evidence of radiation-related health effects comes from several main research populations. These populations include the lifespan studies of atomic bomb survivors ^{Footnote 165} ^{Footnote 166} ^{Footnote 167} ^{Footnote 168}, people involved in the Chernobyl disaster ^{Footnote 169} ^{Footnote 170}, patients treated with radiotherapy for cancer and non-cancer diseases ^{Footnote 171}, and miners exposed to radon and radon decay products ^{Footnote 172} ^{Footnote 173}.

5.2.2.1 International Nuclear Worker Study

The largest and most relevant study is the International Nuclear Worker Study (INWORKS), a multinational cohort study that assessed cancer risk from 1943 to 2005 in 308,297 workers from the nuclear industry in France, the United Kingdom and the United States ^{Footnote 174} ^{Footnote 175} ^{Footnote 176} ^{Footnote 177} ^{Footnote 178}. According to the 2023 INWORKS study ^{Footnote 178}, the risk of radiation-induced solid cancer mortality resulting from chronic exposure to low doses of radiation may be slightly higher than previously reported. The study supports a linear association between prolonged low dose external exposure to ionizing radiation and solid cancer mortality. These findings are consistent with the LSS, as well as the use of the linear non-threshold model that underpins the system of radiological protection and informs the CNSC regulatory dose limits.

The major findings consistent within all these studies are:

Excess risk of cancer increases as radiation dose increases.
Statistically significant population effects are typically observed at doses above approximately 100 mSv (either acutely or chronically exposed).
At doses of 100 mSv (received acutely or chronically), the risk of developing cancer increases by approximately 0.5% above background cancer risk, which in Canada is approximately 45% ^{Footnote 179}, resulting in a total risk of 45.5%.

Importantly, the absence of statistically significant data does not indicate the absence of risk. To put these findings into perspective, for most nuclear energy workers from the facility, lifetime dose would fall under 100 mSv, given the average effective dose received is less than 5 mSv per year (2.8 mSv in 2023) [REF]. In comparison, members of the public living near DN site have typically received annual incremental doses less than 0.001 mSv per year (0.0007 mSv in 2023), resulting in negligible lifetime doses.

Doses to workers and members of the public from the operation of nuclear facilities are in addition to the average natural background radiation in Canada of 1.8 mSv per year, which varies regionally from around 1 to 4 mSv per year ^{Footnote 168}.

5.2.3 Findings

The existing body of knowledge on various populations is used by CNSC staff to help determine the health and safety of workers and persons living near the DN site, in the absence of substantial population-specific studies with radiation exposure data.

Experts worldwide study radiation health effects to provide objective scientific evidence, which supports licensee environmental and radiation protection programs, ensuring that workers and members of the public are protected. The current international understanding is that low doses of radiation are associated with low risks to health, indiscernible from the natural variation of disease. CNSC staff are confident that those living near, and working at, any nuclear facility in Canada are adequately protected.

5.3 Summary of health studies

Reviewing and conducting health studies and reports are important to help ensure the protection of people living near or working at nuclear facilities. Population and community health studies and reports indicate that cancer incidence and mortality rates, as well as the prevalence of specific health indicators and risk factors related to cancer, are largely consistent between populations around the DN site and the population of Ontario as a whole.

Health discrepancies are observed between Indigenous Peoples and other people in Ontario due in large part to the inequities they have faced historically and continue facing presently. Public health authorities can help improve these outcomes through policies and initiatives informed by holistic population health studies focusing on Indigenous health and wellbeing.

The current understanding of the risks associated with radiation exposures is supported by the publications by international agencies like UNSCEAR and the ICRP, as well as academics and researchers worldwide. Very low exposures of radiation (like those experienced by Durham Region residents and DN site employees) result in very low risks to health, indiscernible from the natural variation of disease.

In conclusion, the health studies and reports presented in this section provide a snapshot of the health of people living near the DN site. Based on CNSC staff’s assessment of radiation and environmental exposures from the facility and available health data, CNSC staff are not aware of, and do not expect any adverse health outcomes attributable to the operation of the DN site.

6.0 Other environmental monitoring programs

Several monitoring programs are carried out by other levels or bodies of government, and are reviewed by CNSC staff to confirm that the environment and the health and safety of persons around the facility in question are protected. A summary of the findings of these programs is provided below.

6.1 National Pollutant Release Inventory

ECCC operates the NPRI ^{Footnote 180}, which is Canada’s public inventory of pollutant releases, disposals, and transfers, tracking over 320 pollutants from over 7,000 facilities across the country. Reporting facilities include factories that manufacture a variety of goods; mines; oil and gas operations; power plants; and sewage treatment plants. Information that is collected includes:

releases from facilities to air, water, or land
disposals at facilities or other locations
transfers to other locations for treatment and recycling
facilities’ activities, locations, and contacts
pollution prevention plans and activities

CNSC staff conducted a search of the NPRI database, reviewed the data for the DN site (in other words, the DNGS), and did not notice any trends or unusual results. It is worth noting that radionuclides are not included in the inventory of pollutants in the NPRI database. However, the CNSC receives radionuclide loadings from CNSC licensees through other means, such as annual and quarterly reports. This information has been used in this report, but the complete dataset is available for download on the CNSC’s Open Government Portal ^{Footnote 181}.

6.2 Drinking Water Surveillance Program

The Drinking Water Surveillance Program (DWSP) ^{Footnote 182} provides water quality information for selected municipal drinking water systems for scientific and research purposes through the monitoring of analytes, including organic, inorganic and radiological parameters (such as, tritium, gross alpha and gross beta). The water supply plants in the DWSP in closest proximity to the DN site include, Bowmanville WTP, Newcastle WTP, Oshawa WTP, Whitby WTP, Ajax WTP.

The most recent dataset from the DWSP is for 2020. Radioactivity levels were measured for both Lake Ontario intake waters (raw) and water treated at the drinking water plant (treated water). In 2020, the results show that tritium, gross alpha and gross beta radioactivity levels have all been well below their respective drinking water standard or screening levels. The detailed data are available on the Drinking Water Surveillance Program website.

6.3 Ontario Ministry of Labour, Training and Skills Development Ontario Reactor Surveillance Program

The objective of the Ontario Reactor Surveillance Program (ORSP) ^{Footnote 183} is to establish, operate and maintain a radiological surveillance network to assess radiological concentrations around designated major nuclear facilities in the province. The ORSP monitors the air, water and food around nuclear power plants for radioactivity. The purpose of the ORSP is to assure the public living and working in the vicinity of nuclear facilities that their health, safety, welfare and property are not affected by emissions from nuclear facilities.

The ORSP’s core surveillance focuses on air and drinking water, with the most recently posted dataset from 2020. For the DN site, air is monitored at 8 locations and water is monitored at 5 locations within the Darlington Surveillance Area.

A derived survey criterion was calculated to represent radioactivity levels in specific media (such as water and air) that would result in a dose at or below 0.1 mSv/year, which is an order of magnitude lower than the regulatory public dose limit of 1 mSv. To supplement the core surveillance program associated with air (table 6.1) and drinking water (table 6.2), the ORSP also monitors precipitation, surface water, milk and vegetation.

In 2019, the ORSP concluded that the measured concentrations were well below the derived survey criteria that would result in a dose commitment of 0.1 mSv to the public from either inhalation or ingestion.

Table 6.1: 2020 Ontario Reactor Surveillance Program results for particulates in air (Be-7 and cesium-137) and tritium oxide
Sampling Location	No. of samples	Be-7 (μBq/m³)	Cs-137 (μBq/m³)	Tritium oxide (Bq/m³)
Port Darlington WPCP	8	3,349	˂80	0.50
Ajax WTP	11	4,133	˂80	N/A
Oshawa WTP	11	4,055	˂80	N/A
Courtice WCPC	12	4,344	˂80	N/A
Nash Road P.S.	11	4,275	˂80	N/A
Harmony Creek WPCP	11	3,966	˂80	N/A
Clarington Fire Station #4	11	3,635	˂80	N/A
Ken Hooper Fire Hall	11	4141	˂80	N/A

Guideline/Reference Levels:

Tritium: 340 Bq/m³
The concentrations of the γ-emitting nuclides (Be-7 and Cs-137) are below the minimum detectable concentration.

Table 6.2: Summary of 2020 Ontario Reactor Surveillance Program sampling of drinking water results
Sampling Location	No. of samples	Gamma emitters			Tritium (Bq/L)
Sampling Location	No. of samples	Co–60 (Bq/L)	Cs–134 (Bq/L)	Cs–137 (Bq/L)	Tritium (Bq/L)
Ajax WTP	52 (Tritium) 4 (Gamma emitter)	˂0.3	˂0.3	˂0.3	11.8
Bowmanville WTP	52 (Tritium) 4 (Gamma emitter)	˂0.3	˂0.3	˂0.3	11.1
Newcastle WTP	52 (Tritium) 4 (Gamma emitter)	˂0.3	˂0.3	˂0.3	11.0
Oshawa WTP	52 (Tritium) 4 (Gamma emitter)	˂0.3	˂0.3	˂0.3	12.5
Whitby WTP	52 (Tritium) 4 (Gamma emitter)	˂0.3	˂0.3	˂0.3	12.3

Guideline/Reference Levels:

Cs-137: 10 Bq/L
Cs-134: 7 Bq/L
Co-60: 2 Bq/L
Tritium oxide: 7,000 Bq/L

6.4 Health Canada’s Fixed Point Surveillance Program and Canadian Radiological Monitoring

The Canadian Radiological Monitoring Network (CRMN) ^{Footnote 184} routinely collects drinking water, precipitation, atmospheric water vapour, air particulate, and external gamma dose for radioactivity analysis at dozens of monitoring locations across the country. The closest CRMN monitoring location to the DN site is in Toronto. The results at the Toronto station for 2022 are consistent with data from previous years and are well below the public dose limit of 1 mSv per year.

The Fixed Point Surveillance (FPS) system ^{Footnote 184} functions as a real-time radiation detection system designed to monitor the public dose from radioactive materials in the air, including atmospheric releases associated with nuclear facilities and activities both nationally and internationally. Monitoring stations continuously measure gamma radioactivity levels from ground-deposited (ground-shine) and airborne contaminants.

Health Canada measures the radiation dose rate as Air KERMA (Kinetic Energy Released in Matter). These measurements are conducted every 15 minutes at 79 sites of its FPS network across the country. Air KERMA is also measured for 3 radioactive noble gases associated with nuclear fission which may escape into the atmosphere during the normal operation of nuclear facilities. These 3 noble gases are Argon-41, Xenon-133 and Xenon-135.

The Health Canada website reports the external absorbed dose from all gamma sources (natural and artificial) as well as the external gamma dose from the 3 monitored noble gases as nanoGray per month. The monthly data is provided on the Health Canada website and the results are below the public dose limit of 1mSv per year.

7.0 Engagement with Indigenous Nations and Communities

CNSC staff are committed to working directly with Indigenous Nations and communities and knowledge holders on integrating their knowledge, values, land use information, and perspectives in the CNSC’s EPR reports, where appropriate and when shared with the CNSC.

In response to feedback and comments raised previously by Hiawatha First Nation, Curve Lake First Nation and the Mississaugas of Scugog Island First Nation - the most actively engaged rights bearing Williams Treaties First Nations in relation to the Darlington site –– regarding the CNSC’s EPR reports, CNSC staff made efforts to engage these three First Nations with regards to this EPR Report prior to it being published. In December 2023, CNSC met individually with Hiawatha First Nation, Curve Lake First Nation and the Mississaugas of Scugog Island First Nation to discuss the EPR report. These meetings included a presentation by CNSC staff on the purpose of EPRs, the anticipated timeline as well as an open discussion on the First Nation’s key interests and opportunities to review the report and provide input. CNSC staff noted that this was in an effort to beginning addressing concerns raised with the EPR reports, including the need to consider and reflect their Aboriginal and treaty Rights, views, knowledge, and perspectives in the reports.

On September 4, 2024, CNSC staff shared the Darlington Nuclear Site EPR with Hiawatha First Nation, Curve Lake First Nation and the Mississaugas of Scugog Island First Nation to review and provide feedback on the report, acknowledging that the incorporation of the feedback received from the First Nations will be an ongoing process. CNSC staff noted that they will work to address and incorporate feedback in this version of the report and that if CNSC staff are unable to address all the feedback in this version of the report, CNSC staff are committed to working with the First Nations to address their feedback in future iterations of the report.

CNSC received feedback from Mississaugas of Scugog Island First Nation and Curve Lake First Nation. CNSC staff have incorporated some of the comments into the report and will continue to work to incorporate comments into future iterations of the report. CNSC staff are also working to provide responses directly to Curve Lake First Nation and Mississaugas of Scugog Island First Nation to some of the questions and comments received. CNSC staff also worked with Curve Lake First Nation and Mississaugas of Scugog Island First Nation to include the views expressed sections in the Darlington NGS Licence Renewal Commission Member Document (CMD 25-H2) to provide additional context and information regarding some of their broader concerns, views and perspectives.

CNSC staff are committed to working directly with Indigenous Nations and communities and knowledge holders on integrating their knowledge, Aboriginal and treaty Rights, values, land use information, and perspectives in the CNSC’s EPR reports, where appropriate and when shared with the CNSC.

7.1 Views expressed by Curve Lake First Nation on the EPR

The following views, perspectives and information about CLFN’s key issues were provided by CLFN as part of their October 11, 2024 submission of comments on the Darlington Site EPR Report.

On behalf of Curve Lake First Nation (CLFN), we would like to commend the Canadian Nuclear Safety Commission (CNSC) for ensuring that First Nations who hold Aboriginal and treaty Rights, are offered an opportunity to review the Environmental Protection Review Report (EPRR). CLFN was not able to exhaustively review and provide input to the EPRR in this instance but are supportive of the current attempt of inclusion in the review cycle. CLFN appreciates that CNSC staff will do their best to incorporate feedback in this iteration of the draft EPR report and if unable to address them in this iteration, that CNSC staff will collaborate with CLFN to address them in future iterations of this report. Reciprocally, CLFN will continue to make best efforts to review, understand, and share in future iterations of this report. Many small steps taken together will eventually lead to habits and systemic changes together.

CLFN has had the opportunity to contribute inputs on various hearings, public meetings and regulatory documents, thanks to the CNSC Participant Funding Program (PFP). We acknowledge the CNSC’s staff commitment to reviewing these comments with CLFN and compiling key issues to work on at a programmatic level with the CNSC. We recognize that our relationship with the CNSC staff is good and implementing systemic changes is a long and patient journey. We preface this in our subsequent comments, as we aim to highlight key issues, some of which may be beyond this single document. We look forward to working on these topics with the CNSC staff into 2025 and beyond.

Within the EPRR, CNSC states that:

“The purpose of this EPR is to report the outcome of CNSC staff’s assessment of the Ontario Power Generation Inc. (OPG)’s EP measures and CNSC staff’s health science and environmental compliance activities for the Darlington Nuclear Site (DN site) – operations at both the Darlington Nuclear Generating Station (DNGS) and the Darlington Waste Management Facility (DWMF). This review serves to assess whether OPG’s EP measures at the DN site meet regulatory requirements and adequately protects the environment and health and safety of persons.”

We wish to identify an opportunity to expand the scope and purpose of this review and utilize such processes to underscore the value and importance of Indigenous Rights, values and culture, and the role of the Crown, and by extension CNSC to understand and limit potential impacts on the Nation’s Aboriginal and Treaty Rights. An understanding of the ongoing impact to Aboriginal and Treaty Rights through such a review could help to inform ongoing discussions between the Nation and CNSC, about appropriate measures, mitigations and accommodations.

It is critical that the CNSC mandate, as a Crown Responsibility, be updated to respect the adaption of the United Nations Declaration on the Rights of Indigenous Peoples Act 2021, the subsequent the 2023-2028 Action Plan, and respect Free, Prior, and Informed Consent (FPIC) principles. This would include, but not limited to, the Duty to Consult and Accommodate and the Honour of the Crown inform the policies, processes and culture of the CNSC. This ensures that relevant First Nations are characterized as having Rights, rather than interests in policies and reports such as the EPRR.

Some consideration for implementations of the Act 2021:

Free, Prior, and Informed Consent (FPIC): Before granting licence to any projects, ensure the FPIC of the WTFNs’ is obtained, not just as a consultation but as a process to gain meaningful consent or at minimum, ensure proper accommodations will be met.

Indigenous Governance and Self-Determination: Respect the governance systems and decision- making processes of Anishinaabe peoples when planning and conducting environmental assessments.

Cultural and Environmental Preservation: Ensure that environmental and cultural heritage protection frameworks and policies respect the WTFNs’ connections and Rights to the land.

We note that the EPRR has been constructed through the lens of Western science and epistemology, which values certain characteristics and types of evidence. The language throughout this report implies a knowledge hegemony. We wish to note that there are other knowledge systems, values and lenses, including our own, which could be reflected. We appreciate that there is much work to be done in the area of working with Indigenous Knowledge Systems, and so as a first step, we would encourage the CNSC to acknowledge that its reports are developed using western-science approaches and values, and that there are other ways of knowing. We acknowledge the CNSC’s staff commitment in the area of Indigenous Knowledge Studies with the Wiliams Treaties First Nations (WTFN) communities and the related funding available for these studies. We hope upon completion of these studies that future documents, like this one, can be more holistic in its knowledge systems and representation.

The EPRR focused largely on releases of radiological material into the environment, however, we wish to highlight the importance of documenting, analyzing and understanding the overall impact of ongoing operations which results in impacts to Indigenous health and well-being. It is important to note that activities that impact the natural environment and human health, such as nuclear activities, have a disproportionate impact on Indigenous Peoples, their health and well-being. Well-being is not limited to physical radiological doses to a human receptor, but also those impacts to the emotional, spiritual and cultural aspects of well-being which are impacted by ongoing nuclear activities. We would encourage the CNSC to incorporate this reality into its analysis, especially when considering the impacts to vulnerable sectors, or understanding human-health impacts. As a first step in this direction, we are proud to say that the CNSC has taken samples of our traditional food manoomin (wild rice), as part of their Independent Environmental Monitoring Program, and we hope that this is a catalyst into a more inclusive look at the environmental impacts of nuclear operations in our Territory.

Throughout the EPRR, CNSC cites data as part of its analysis and understanding. We wish to note that this data ranges in terms of age, anywhere from a decade to a few years before the publication of this report. CLFN wishes to raise concern over the use of old data to make conclusions about the circumstances of the activities at Darlington. Additionally, while we appreciate that it was noted within the report that activities related to the Darlington New Nuclear Plant are not considered, it is our view that this represents a large gap in properly ground truthing the findings of this study. The activities at DNNP, Pickering Nuclear Generating Station, and the many other nuclear facilities within our Territory have a cumulative impact on the environment, which is not captured within this report.

We are encouraged by the understanding demonstrated by the CNSC of the relevance of the difference between Nations and communities and commend the CNSC for their efforts to continue to learn about these important nuances.

It is the submission of Curve Lake First Nation that there remain opportunities to clarify, center and prioritize Indigenous Peoples, their Rights, values and culture, Crown-Indigenous Relations and the Duty to Consult within the document.

7.2 Views expressed by the Mississaugas of Scugog Island First Nation on the EPR

The Mississaugas of Scugog Island First Nation (MSIFN) has expressed concerns that free, prior, and informed consent of MSIFN was not sought for the construction of the Darlington Used Fuel Dry Storage Facility, Darlington New Nuclear Project, and Refurbishment and Continued Operation. MSIFN requests the report indicate that OPG and the CNSC did not seek MSIFN’s informed consent on these activities.

MSIFN emphasized that the report does not provide evidence of collaboration with treaty rights holding First Nations, specifically regarding the selection of VECs. MSIFN requests that the CNSC provide evidence that the VECs used by the CNSC have been selected in collaboration with treaty rights holding First Nations.

MSIFN is concerned that processes used by CNSC and licensees, such as to characterize risk or establish control, have not been developed to protect MSIFN’s Treaty Rights. One example pointed to are the requirements set out in CSA N288.6-12, and REGDOC 2.9.1 which MSIFN views does not serve as the basis for the development of site-specific measures that would protect MSIFN’s Treaty Rights. MSIFN commented that there is a lack of consideration for methods that go beyond assessing single averages for radionuclides and hazardous chemicals or long-term analysis on aquatic organisms, particularly those harvested by WTFN members. MSIFN is of the view that the results presented in the EPR do not add to the body of evidence that MSIFN’s Aboriginal and Treaty Rights are protected in the vicinity of the DN site.

MSIFN has also raised questions on whether referenced studies were Indigenous-led or produced and requested that the EPR indicate as such.

7.3 CNSC response to views expressed by MSIFN and CLFN

CNSC staff greatly appreciate receiving feedback from MSIFN and CLFN on this EPR Report and take the concerns, views and perspective shared seriously. CNSC staff are currently working with CLFN, MSIFN and other Williams Treaties First Nations through:

Issues and concerns tracking and responses
Terms of Reference and long-term engagement work plans
Collaboration on monitoring activities including the IEMP
Support for the gathering of Indigenous Knowledge
Support for conducting cumulative effects studies
Support for community led monitoring initiatives
Collaborative oversight of OPG commitments and engagement activities with the Nations

CNSC staff look forward to continuing to work with MSIFN, CLFN and other WTFNs on enhancing the way our environmental monitoring, reporting and oversight reflects their knowledge, rights and interests as that information is shared with the CNSC by the First Nations.

8.0 Findings

This EPR report focused on items of current Indigenous, public and regulatory interest, including physical stressors, and airborne and waterborne releases from ongoing operations at the DN site. CNSC staff have found that the potential risks from physical stressors, as well as from nuclear and hazardous releases to the atmospheric, terrestrial, aquatic and human environments from the DN site, are low to negligible, and that people and the environment remain protected.

8.1 Canadian Nuclear Safety Commission staff’s follow-up

The following list summarizes CNSC staff’s recommendations regarding the EP measures implemented by OPG for the DN Site. CNSC staff will follow-up on these recommendations during the review of future submissions of EP documents. The following do not change CNSC staff’s findings and are included for transparency with Indigenous Nations and communities and the public. CNSC staff expect that OPG will:

complete air monitoring to reduce uncertainties with respect to NO_x concentrations in air;
complete an evaluation of soil concentrations to inform soil management for localized areas with soil contamination

8.2 Canadian Nuclear Safety Commission staff’s findings

CNSC staff’s findings from this EPR report may inform and support staff recommendations to the Commission in future licensing and regulatory decision making that pertains to the DN site. These findings are based on CNSC staff’s technical assessments associated with OPG’s DN site, such as the submitted ERA documentation and the conduct of compliance verification activities, including the review of annual and quarterly reports and onsite inspections. CNSC staff also reviewed the results from various relevant or comparable health studies, and other EMPs conducted by other levels of government, to substantiate CNSC staff’s findings. CNSC staff conducted IEMP sampling around the DN site in 2014, 2015, 2017, 2021 and 2023.

CNSC staff have found that the potential risks from climate change parameters, physical stressors, as well as from radiological and hazardous releases to the atmospheric, aquatic, terrestrial and human environments from the DN site, are low to negligible. The potential risks to the environment from these releases or stressors are similar to natural background, and the potential risks to humans health are indistinguishable from health outcomes in the general public. Therefore, CNSC staff have found that OPG has and will continue to implement and maintain effective EP measures to adequately protect the environment and the health and safety of persons. CNSC staff will continue to verify and ensure that, through ongoing licensing and compliance activities and reviews, the environment and the health and safety of persons around the DN site are protected.

9.0 Abbreviations

Units

Bq: becquerel
Bq/L: becquerels per litre
ha: hectares
hr: hours
kg: kilograms
km: kilometres
m: metres
MeV: Mega electron-volt
mGy: milligray
mGy/d: milligray per day
µGy/h: microgray per hour
mm: millimetre
m/s: metres per second
mSv: millisievert
µg: microgram
µSv: microsievert
ΔT: change in temperature

Acronyms

AAQC: ambient air quality criteria
AL: action level
ALARA: as low as reasonably achievable
ALW: active liquid waste
BAF: bioaccumulation factors
BTEX: benzene, toluene, ethylbenzene and xylenes
C-14: carbon-14
CANDU: CANada Deuterium Uranium
CCME: Canadian Council of Ministers of the Environment
CCW: condenser cooling water
CEAA 1992: Canadian Environmental Assessment Act, 1992
CEAA 2012: Canadian Environmental Assessment Act, 2012
CEPA 1999: Canadian Environmental Protection Act, 1999
CLFN: Curve Lake First Nation
CNSC: Canadian Nuclear Safety Commission
COG: CANDU Owners Group
COPC: contaminant of potential concern
Co-60: cobalt-60
COPD: chronic obstructive pulmonary disease
COSEWIC: Committee on the Status of Endangered Wildlife in Canada
CRMN: Canadian Radiological Monitoring Network
CSQG: Canadian Sediment Quality Guidelines
DFO: Fisheries and Oceans Canada
DN: Darlington
DN site: Darlington Site
DNGS: Darlington Nuclear Generating Station
DNNP: Darlington New Nuclear Project
DRHD: Durham Region Health Department
DRL: derived releases limit
DSC: dry storage container
DWMF: Darlington Waste Management Facility
DWSP: Drinking Water Surveillance Program
EA: environmental assessment
ECA: environmental compliance approval
ECCC: Environment and Climate Change Canada
EcoRA: ecological risk assessment
EMP: Environmental monitoring program
EMS: Environmental management system
EP: environmental protection
EPC: exposure point concentrations
EPG: emergency power generator
EPP: environmental protection program
EPR: environmental protection review
EPS: emergency power service
ERA: environmental risk assessment
ESA: Endangered Species Act
ESDM: Emission Summary and Dispersion Modelling
FAA: Fisheries Act authorization
FEQG: Federal Environmental Quality Guideline
FPS: fixed point surveillance
FUMP: follow-up monitoring program
GHG: greenhouse gas
GWMP: groundwater monitoring program
GWPP: groundwater protection program
HEPA: High Efficiency Particulate Air
HFN: Hiawatha First Nation
HHRA: human health risk assessment
HQ: hazard quotient
HT: elemental tritium
HTO: tritiated water
HWMB: heavy water management building
I-131: iodine-131
IAA: Impact Assessment Act of Canada
ICRP: International Commission on Radiological Protection
IEMP: Independent Environmental Monitoring Program
IIP: Integrated Implementation Plan
ILCR: incremental lifetime cancer risk
INWORKS: International Nuclear Worker Study
IWST: injection water storage tank
KERMA: Kinetic Energy Release in Matter
LCH: licence conditions handbook
LHIN: Local Health Integration Network
MECP: Ontario Ministry of the Environment, Conservation and Parks
MISA: Municipal Industrial Strategy for Abatement
MNRF: Ministry of Natural Resources and Forestry
MOU: memorandum of understanding
MSIFN: Mississaugas of Scugog Island First Nation
MWAT: maximum weekly average temperature
NO_x: nitrogen oxides
NPRI: National Pollutant Release Inventory
NSCA: Nuclear Safety and Control Act
OPG: Ontario Power Generation Inc
ORSP: Ontario Reactor Surveillance Program
PAH: polycyclic aromatic hydrocarbons
PCB: polychlorinated biphenyl
PDP: preliminary decommissioning plan
PHC: petroleum hydrocarbon
PHU: public health unit
PMF: probably maximum flood
PMP: probable maximum precipitation
PN: Pickering
POI: point of impingement
POR: points of reception
PSA: Probabilistic Safety Assessment
PSR: periodic safety review
PWQO: Provincial Water Quality Objective
RADICON: Radiation Exposure and Cancer Incidence Around Nuclear Power Plants
RLW: radioactive liquid waste
RWSB: Retube Waste Storage Building
SAP: sampling and analysis plan
SARA: Species at Risk Act
SARO: species at risk in Ontario
SENES: Specialist in Energy Nuclear Environmental Services
SO₂: sulphur dioxide
TKN: total Kjeldahl nitrogen
TOC: total organic carbon
TRC: total residual carbon
TRF: Tritium Removal Facility
TSS: total suspended solids
UCLM: upper confidence limit of the mean
UFDSF: used fuel dry storage facility
UNSCEAR: United Nations Scientific Committee on the Effects of Atomic Radiation
VC: valued component
VEC: valued ecosystem component
VOC: volatile organic compound
WTP: water treatment plant
WWMF: Western Waste Management Facility

10.0 References

Footnote 1

Government of Canada, "Nuclear Safety and Control Act (S.C. 1997, c.9)," amended January 1, 2017. [Online]. Available: https://laws-lois.justice.gc.ca/eng/acts/n-28.3/page-1.html#h-368751.

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Footnote 2

Canadian Nuclear Safety Commission, "Indigenous Knowledge Policy Framework," December 2021. [Online]. Available: https://nuclearsafety.gc.ca/eng/resources/aboriginal-consultation/indigenous-knowledge-policy.cfm.

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Footnote 3

Ontario Power Generation, "Application for Renewal of the Darlington Nuclear Generating Station Power Reactor Operating Licence 13.03/2025," May 2024. [Online]. Available: e-Doc 7293161.

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Footnote 4

Ontario Power Generation, "Preliminary Decommissioning Plan - Darlington Waste Management Facility," 2021.

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Footnote 5

Ontario Power Generation, "Darlington Nuclear Site Preliminary Decommissioning Plan," 2021.

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Footnote 6

Ontario Power Generation, "2019 Results of Environmental Monitoring Programs for Darlington and Pickering Nuclear," 2020. [Online]. Available: https://www.opg.com/reporting/regulatory-reporting/.

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Footnote 7

Ontario Power Generation, "2020 Results of Environmental Monitoring Programs for Darlington and Pickering Nuclear," 2021. [Online]. Available: https://www.opg.com/reporting/regulatory-reporting/.

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Footnote 8

Ontario Power Generation, "2021 Results of Environmental Monitoring Programs for Darlington and Pickering Nuclear," 2022. [Online]. Available: https://www.opg.com/reporting/regulatory-reporting/.

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Footnote 9

Ontario Power Generation, "2022 Results of Environmental Monitoring Programs for Darlington and Pickering Nuclear," 2023. [Online]. Available: Report No. N-REP-03443-10029.

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Footnote 10

Ontario Power Generation, "2023 Results of Environmental Monitoring Programs for Darlington and Pickering Nuclear," 2024. [Online]. Available: Report No. N-REP-03443-10031.

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Footnote 11

Ontario Power Generation, "2011 Results of Environmental Monitoring Programs," 2012.

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Footnote 12

Ontario Power Generation, "2012 Results of Environmental Monitoring Programs," 2013.

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Footnote 13

Ontario Power Generation, "2016 Results of Environmental Monitoring Programs," 2017.

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Footnote 14

Ontario Power Generation, "2017 Results of Environmental Monitoring Program," 2018.

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Footnote 15

Ontario Power Generation, "2018 Results of Environmental Monitoring Programs," 2019.

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Footnote 16

Ontario Power Generation, "2019 Results of Environmental Monitoring Programs," 2020.

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Footnote 17

Ontario Power Generation, "2016 Darlington Nuclear Groundwater Monitoring Program Results," 2017.

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Footnote 18

Ontario Power Generation, "2017 Darlington Nuclear Groundwater Moniotring Program Results," 2018.

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Footnote 19

Ontario Power Generation, "2018 Darlington Nuclear Groundwater Monitoring Program Results," 2019.

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Footnote 20

Ontario Power Generation, "2019 Darlington Nuclear Groundwater Monitoring Program Results," 2020.

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Footnote 21

Government of Canada, "Canadian Environmental Assessment Act," 1992. [Online]. Available: http://laws.justice.gc.ca/eng/acts/c-15.2/20100712/P1TT3xt3.html.

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Footnote 22

Government of Canada, "Canadian Environmental Assessment Act (Repealed, 2012, c. 19, s. 66)," 1992. [Online]. Available: https://laws-lois.justice.gc.ca/eng/acts/c-15.2/index.html.

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Footnote 23

Government of Canada, "Impact Assessment Act (c. 28, s. 1)," 2019. [Online]. Available: https://laws-lois.justice.gc.ca/eng/acts/I-2.75/.

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Footnote 24

Government of Canada, "Physical Activities Regulations (SOR/2019-285)," 2019. [Online]. Available: https://laws-lois.justice.gc.ca/eng/regulations/SOR-2019-285/FullText.html.

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Footnote 25

Canadian Nuclear Safety Commission, "Record of Decision in the Matter of OPG's Determination of Applicability of DNNP EA to OPG's Chosen Reactor Technology," April 2024. [Online]. Available: e-Doc 7250458.

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Footnote 26

Canadian Nuclear Safety Commission, "CNSC Staff Determination of Application of the CEAA to the Darlington Used Fuel Dry Storage Project," September 2001. [Online]. Available: e-Doc 970344.

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Footnote 27

Canadian Nuclear Safety Commission, "Screening Reort on the Environmental Assessment of the Proposed Darlington Used Fuel Dry Storage Project," May 2003. [Online]. Available: e-Doc: 1056148.

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Footnote 28

Canadian Nuclear Safety Commission, "Record of Proceedings, Incluing Reasons for Decision: Environmental Assessment Screening Report for the Proposed Darlington Used Fuel Dry Storage Project," November 2003. [Online]. Available: e-Doc 3008796.

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Footnote 29

Ontario Power Generation, "Darlington Used Fuel Dry Storage Project - Environmental Assessment Follow-Up Monitoring Report," February 2005. [Online]. Available: e-Doc 1306155.

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Footnote 30

Canadian Nuclear Safety Commission, "Closure of Environmental Assessment Follow-Up and Monitoring Program for the Darlington Waste Management Facility," March 2012. [Online]. Available: e-Doc 3895371.

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Footnote 31

Canadian Nuclear Safety Commission, "Darlington New Nuclear Project timeline," 2024. [Online]. Available: https://www.cnsc-ccsn.gc.ca/eng/resources/status-of-new-nuclear-projects/darlington/project-timeline/.

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Footnote 32

Canadian Nuclear Safety Commission, "Environmental Assessment Screening Report: The Refurbishment and Continued Operation of the Darlington Nuclear Generating Station," March 2013. [Online]. Available: e-Doc 3917932.

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Footnote 33

Canadian Nuclear Safety Commission, "Record of Proceedings, Including Reasons for Decision: Environmental Assessment Screening Regarding the Proposal to Refurbish and Continue to Operate the Darlington Nuclear Generating Station," December 2012. [Online]. Available: e-Doc 4044147.

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Footnote 34

Canadian Environmental Assessment Agency, "Final Decision on the Darlington New Nuclear Project," December 2012. [Online]. Available: e-Doc 4105509.

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Footnote 35

Ontario Power Generation, "Darlington New Nuclear Project Commitments Report, revision 9," January 2024.

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Footnote 36

Canadian Nuclear Safety Commission, "CMD: Determination for Ontario Power Generation Inc. Darlington New Nuclear Project (DNNP)," January 2024.

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Footnote 37

Ontario Power Generation, "DNGS Refurbishment and Continued Operation Follow-up Monitoring Plan," September 2013.

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Footnote 38

Canadian Nuclear Safety Commission, "DERPA Key Messages for Darlington Licence Renewal 2015 - Hearing Part 2," November 2015. [Online]. Available: e-Doc 4838154.

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Footnote 39

Ontario Power Generation, "Review of Future Refurbishment Planning at Darlington NGS Relative to Environmental," 2023.

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Footnote 40

Canadian Nuclear Safety Commission, "Environmental Assessment Information Report: Ontario Power Generation Darlington Nuclear Generating Station Licence Renewal," 2015.

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Footnote 41

Canadian Nuclear Safety Commission, "Record of Decision for the Application to Renew the Nuclear Power Reactor Operating Licence for the Pickering Nuclear Generating Station," 2019.

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Footnote 42

Canadian Nuclear Safety Commission, "Environmental Protection Review Report: Darlington Waste Management Facility," September 2023. [Online]. Available: https://www.cnsc-ccsn.gc.ca/eng/resources/publications/reports/dwmf22/.

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Footnote 43

Canadian Nuclear Safety Commission, "Record of Decision for the Application to Renew the Waste Facility Operating Licence for the Darlington Waste Management Facility.," April 2023. [Online]. Available: e-Doc 6968350.

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Footnote 44

Canadian Nuclear Safety Commission, "REGDOC-2.9.1, Environmental Protection: Environmental Principles, Assessments and Protection Measures," 2017. [Online]. Available: http://www.nuclearsafety.gc.ca/eng/pdfs/REGDOCS/REGDOC-2-9-1-Environmental-Principles-Assessments-and-Protection-Measures-eng.pdf.

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Footnote 45

CSA Group, "N288.0-22, Environmental management of nuclear facilities: Common requirements of the CSA N288 series of Standards," 2022. [Online]. Available: https://www.csagroup.org/store/product/CSA%20N288.0:22/.

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Footnote 46

CSA Group, "CSA N288.1-14, Guidelines for calculating derived release Limits for Radioactive Material in Airborne and Liquid Effluents for Normal Operation of Nuclear Facilities, Update No.1, 2014," 2014. [Online]. Available: https://www.csagroup.org/store/product/N288.1-14/.

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Footnote 47

CSA Group, "CSA N288.1-20, Guidelines for calculating derived release Limits for Radioactive Material in Airborne and Liquid Effluents for Normal Operation of Nuclear Facilities," 2020. [Online]. Available: https://www.csagroup.org/store/product/CSA%20N288.1:20/.

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Footnote 48

CSA Group, "CSA N288.4-19, Environmental monitoring programs at nuclear facilities and uranium mines and mills," 2019. [Online]. Available: https://www.csagroup.org/store/product/CSA%20N288.4:19/.

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Footnote 49

CSA Group, "CSA N288.5-22, Effluent and emissions monitoring programs at nuclear facilities," 2022. [Online]. Available: https://www.csagroup.org/store/product/CSA%20N288.5:22/.

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Footnote 50

CSA Group, "CSA N288.6-12, Environmental Risk Assessment at Class I nuclear Facilities and Uranium Mines and Mills," 2012. [Online]. Available: https://www.csagroup.org/store/product/N288.6-12/.

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Footnote 51

CSA Group, "CSA N288.6-22, Environmental risk assessments at nuclear facilities and uranium mines and mills," 2022. [Online]. Available: https://www.csagroup.org/store/product/CSA%20N288.6:22/.

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Footnote 52

CSA Group, "CSA N288.7-15, Groundwater Protection Programs at Class I Facilities and Uranium Mines and Mills," June 2015. [Online]. Available: https://www.csagroup.org/store/product/N288.7-15/.

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Footnote 53

CSA Group, "CSA N288.7-22, Groundwater Protection and monitoring programs for nuclear facilities and uranium mines and mills," 2022. [Online]. Available: https://www.csagroup.org/store/product/CSA%20N288.0%3A22/.

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Footnote 54

CSA Group, "CSA N288.8-17, Establishing and Implementing Action Levels to Control Releases to the Environment from Nuclear Facilities," 2017. [Online]. Available: https://www.csagroup.org/store/product/N288.8-17/.

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Footnote 55

Canadian Nuclear Safety Commission, "REGDOC-3.1.1, Reporting Requirements for nuclear power plant," 2018. [Online]. Available: https://nuclearsafety.gc.ca/eng/acts-and-regulations/regulatory-documents/published/html/regdoc3-1-1-v2/index.cfm.

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Footnote 56

Canadian Nuclear Safety Commission, "REGDOC-3.1.2, Reporting Requirements, Volume I: Non-Power Reactor Class I Facilities and Uranium Mines and Mills," January 2018. [Online]. Available: https://www.cnsc-ccsn.gc.ca/eng/acts-and-regulations/regulatory-documents/published/html/regdoc3-1-2-v1/.

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Footnote 57

Canadian Nuclear Safety Commission, "REGDOC-3.1.2, Reporting Requirements, Volume I: Non-Power Reactor Class I Facilities and Uranium Mines and Mills, Version 1.1," July 2022. [Online]. Available: https://laws-lois.justice.gc.ca/eng/regulations/SOR-2000-203/FullText.html.

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Footnote 58

Canadian Nuclear Safety Commission, "Licence Conditions Handbook - Darlington Nuclear Generating Station Nuclear Power Reactor Operating Licence," 2022.

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Footnote 59

Ontario Power Generation, "Regulatory Reporting," 2024. [Online]. Available: https://www.opg.com/reporting/regulatory-reporting/.

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Footnote 60

Canadian Nuclear Safety Commission, "Regulatory Oversight Reports - Canadian Nuclear Safety Commission," June 2023. [Online]. Available: https://www.cnsc-ccsn.gc.ca/eng/reactors/power-plants/regulatory-oversight-report-npp/.

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Footnote 61

Ontario Power Generation, "2020 Environmental Risk Assessment for the Darlington Nuclear Site," 2021.

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Footnote 62

Canadian Nuclear Safety Commission, "CNSC Staff Comments on OPG's 2020 Update to the Environmental Risk Assessment for the Darlington Site," 2021.

Return to first footnote 62 referrer

Footnote 63

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Government of Canada, "Federal Halocarbon Regulations, 2022 (SOR/2022-110)," 2022. [Online]. Available: https://laws-lois.justice.gc.ca/eng/regulations/SOR-2022-110/index.html.

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Province of Ontario, "O. Reg. 419/05: Air Pollution - Local Air Quality," 2023. [Online]. Available: https://www.ontario.ca/laws/regulation/050419.

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Specialist in Energy Nuclear Environmental Services, "Environmental impact Statement Darlington Nuclear Generating Station Refurbishment and Continued Operation Project Environmental Assessment," 2011.

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Ontario Power Generation, "Regulatory Reporting," 2022. [Online]. Available: https://www.opg.com/reporting/regulatory-reporting/.

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Government of Ontario, "Environmental Protection Act," February 2024. [Online]. Available: https://www.ontario.ca/laws/statute/90e19.

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Government of Ontario, "Ontario Water Resources Act," June 2021. [Online]. Available: https://www.ontario.ca/laws/statute/90o40.

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Footnote 77

Ontario Power Generation, "Amended Environmental Compliance Approval, Number 0585-D4KP24," May 28, 2024.

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Footnote 79

Ontario Power Generation, "Darlington Waste Management Facility - EA Follow-Up and Monitoring Program - Closure Report," 2011.

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Footnote 80

Ontario Power Generatoin, "Darlington Refurbishment Follow-Up Monitoring Program: Thermal Plume Monitoring 2017-2018," 2019.

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Ontario Power Generation, "Acoustic Assessment Report for New Nuclear Darlington Acoustic Conditions Update," 2020.

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Beacon Environmental, "Darlington Nuclear Generating Station Biodiversity Program Annual Report 2013," 2014.

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Beacon Environmental, "Darlington Nuclear Generating Station Biodiversity Program Annual Report 2014," 2015.

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Beacon Environmental, "Darlington Nuclear Generating Station Biodiversity Program Annual Report 2017," 2018.

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Beacon Environmental, "2019 Darlington Biodiversity Program Technical Memo," 2019.

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Ontario Power Generation and Kinectrics, "Entrainment Sampling at Darlington Nuclear Generating Station - 2004," 2005.

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Ontario Ministry of Natural Resources and Forestry, "Lake Ontario Fish Communities and Fisheries: 2018 Annual Report of the Lake Ontario Management Unit," 2018.

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P. Patrick, J. Parks, E. Mason, J. Powell, N. Garisto and A. Janes, "Effects of fixed and fluctuating temperatures on morality of Round Whitefish and Lake Whitefish eggs.," COG 2014, 2014.

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CANDU Owners Group, "Impacts of Temperature on Whitefish Egg Survival," 2017.

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Pandy, M., "The Round Whitefish Egg Mortality Data: Revision of the Logistic Model," University of Waterloo, 12 September 2016.

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Environment and Climate Change Canada, "Guidance document: environmental effects assessment of freshwater thermal discharge.," February 2019.

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Golder Associates Ltd., "Aquatic Environment Prediction of Temperature Effects on Fish Species from Operation of the NND Diffuser Based on Modelled Temperature Changes," 2010.

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Footnote 128

Ecometrix, "Groundwater Protection and Monitoring Programs for Pickering Nuclear – CSA 288.7 Implementation," 2022. [Online]. Available: e-doc 6850880.

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Footnote 129

Ecometrix, "2022 Environmental Risk Assessment Report for Pickering Nuclear," 2023.

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Footnote 130

Ecometrix, "Groundwater Protection and Monitoring Programs for Darlingon Nuclear - CSA 288.7 Implementation," 2022.

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Footnote 131

Ontario Power Generation, "2022 Darlington Nuclear Groundwater Monitoring Program Results," 2022.

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Footnote 132

CH2M Hill, "Safe Storage Groundwater Management Impact Assessment Pickering Nuclear Generating Station," 2016.

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Footnote 133

Health Canada, "Guidelines for Canadian Drinking Water Quality-Summary Tables," 2022.

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Footnote 134

Government of Ontario, "Ontario Regulation 169/03: Ontario Drinking Water Quality Standards," 2003. [Online]. Available: https://files.cvc.ca/cvc/uploads/2011/03/std01_079707.pdf

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Footnote 135

Government of Canada, "About cumulative effects," 2024.

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Footnote 136

Lemmen, E. Bush and D.S., "Canada's Changing Climate Report," 2019.

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Footnote 137

E. Bush, B. Bonsal, C.Derksen, G. Flato, J. Fyfe, N. Gillett, B.J.W. Greenan, T.S. James, M. Kirchmeier-Young, L. Mudryk, X. Zhang, "Canada's Changing Climate Report in Light of the Latest Global Science Assessment," 2022.

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Footnote 138

Environment and Climate Change Canada and the U.S. Environmental Protection Agency, "State of the Great Lakes 2022 Technical Report," 2022.

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Footnote 139

J.L. McDermid, S.K. Dickin, C.L. Winsborough, H. Switzman, S. Barr, J.A.Gleeson, G. Krantzberg, P.A. Gary, "State of Climate Change Science in the Great Lakes Basin: A Focus on Climatological Hydrologic and Ecological Effects," 2015.

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Footnote 140

P.J. Zuzek, "Lake Ontario Shoreline Management Plant," 2020.

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Footnote 141

F. Seglenieks and A. Temgoua, "Future water levels of the Great Lakes under 1.5°C to 3°C warmer climates," Journal of Great Lakes Research, vol. 48, pp. 865-875, 2022.

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Footnote 142

Ontario Ministry of Natural Resources and Forestry, "Lakes and Rivers Improvement Act Technical Guidelines - Criteria and Standards for Approval," 2004.

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Footnote 143

Ontario Power Generation, "Darlington Nuclear Generating Station, Hydrological Assessment," 2014.

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Footnote 144

Ontario Power Generation, "Darlington NGS Probabilistic Safety Assessment Report," 2021.

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Footnote 145

Environment and Climate Change Canada, "Draft technical guide related to the Assessment of Climate Change: Assessing Climate Change Resilience," March 15, 2022.

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Footnote 146

Canadian Nuclear Safety Commission, "Record of Proceedings, Including Reasons for Decision - Application to Renew the Nuclear Power Reactor Operating LIcence for the DNGS," 2015.

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Footnote 147

Canadian Nuclear Safety Commission, "Independent Environmental Monitoring Program (IEMP)," March 2023. [Online]. Available: https://nuclearsafety.gc.ca/eng/resources/maps-of-nuclear-facilities/iemp/index.cfm#.

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Footnote 148

Canadian Nuclear Safety Commission, "IEMP-2023 Site Specific Sampling Plan for Darlington site," 2023.

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Footnote 149

Canadian Nuclear Safety Commission, "Health Studies," 5 April 2024. [Online]. Available: http://www.nuclearsafety.gc.ca/eng/resources/health/index.cfm.

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Footnote 150

Durham Region, "Health Neighbourhoods in Durham Region," 2022. [Online]. Available: https://www.durham.ca/en/health-and-wellness/health-neighbourhoods.aspx.

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Footnote 151

Durham Region Health Department, "Health Neighbourhoods: Building on Health in Priority Neighbourhoods," 2015. [Online]. Available: https://www.durham.ca/en/health-and-wellness/resources/Documents/HealthInformationServices/HealthNeighbourhoods/buildingOnHealth.pdf.

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Footnote 152

Durham Region Health Department, "Mortality at a Glance," June 2017. [Online]. Available: https://www.durham.ca/en/health-and-wellness/resources/Documents/HealthInformationServices/HealthStatisticsReports/Mortality-at-a-Glance.pdf.

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Footnote 153

Durham Region Health Department, "Durham Region Cancer Data Tracker," November 2022. [Online]. Available: https://app.powerbi.com/view?r=eyJrIjoiZjMxNmZlNWEtMTNhYy00YjhjLTlhZTktZjcxZDk3NzAyNDg2IiwidCI6IjUyZDdjOWMyLWQ1NDktNDFiNi05YjFmLTlkYTE5OGRjM2YxNiJ9.

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Footnote 154

Canadian Cancer Society, "Cancer Statistics at a Glance," 2023. [Online]. Available: https://cancer.ca/en/research/cancer-statistics.

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Ontario Health (Cancer Care Ontario), "Ontario Cancer Statistics 2022," 2022. [Online]. Available: https://www.cancercareontario.ca/en/data-research/view-data/statistical-reports/ontario-cancer-statistics-2022.

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Ontario Health (Cancer Care Ontario), "Ontario cancer profiles," 2023. [Online]. Available: https://www.cancercareontario.ca/en/data-research/view-data/cancer-statistics/ontario-cancer-profiles.

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Footnote 157

Durham Region, "Public Health," 2024. [Online]. Available: https://www.durham.ca/en/regional-government/public-health.aspx.

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Footnote 158

Cancer Care Ontario, "Cancer in First Nations People in Ontario: Incidence, Mortality, Survival and Prevalence," 2017.

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Footnote 159

Chiefs of Ontario, Cancer Care Ontario and Institute for Clinical Evaluative Sciences, "Cancer in First Nations People in Ontario: Incidence, Mortality, Survival and Prevalence," Toronto, 2017.

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Footnote 160

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), "2020/2021 Report Volume III: "Sources, effects and risks of ionizing radiation," 2021. [Online]. Available: https://www.unscear.org/unscear/en/publications/index.html.

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International Commission on Radiological Protection, "The 2007 Recommendations of the International Commission on Radiological Protection," 2007. [Online]. Available: https://www.icrp.org/publication.asp?id=ICRP%20Publication%20103.

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Footnote 162

R. Lane, E. Dagher, J. Burtt, and P. A. Thompson, "Radiation Exposure and Cancer Incidence (1990 to 2008) around Nuclear Power Plants in Ontario, Canada," 13 August 2013. [Online]. Available: https://www.scirp.org/pdf/JEP_2013082813431470.pdf.

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Canadian Nuclear Safety Commission, "Verifying Canadian nuclear energy worker radiation risk: A reanalysis of cancer mortality in Canadian nuclear energy workers (1957-1994).," 2011. [Online]. Available: http://www.nuclearsafety.gc.ca/pubs_catalogue/uploads/INFO0811_e.pdf

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Footnote 164

L. B. Zablotska, R. S. D. Lane, and P. A. Thompson, "A Reanalysis of Cancer Mortality in Canadian Nuclear Workers (1956-1994) Based on Revised Exposure and Cohort Data," British Journal of Cancer , vol. 110, pp. 214-223," 2014. [Online].

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E.J. Grant, A. Brenner, H. Sugiyama, R. Sakata, A. Sadakane, M. Utada, E.K. Cahoon, C.M. Milder, M. Soda, H.M. Cullings, D.L. Preston, K. Mabuchi and K. Ozasa, "Solid Cancer Incidence among the Life Span Study of Atomic Bomb Survivors: 1958-2009," Radiation Research, pp. 187(5):513-537, 2017.

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Footnote 166

K. Ozasa, Y. Shimizu, A. Suyama, F. Kasagi, M. Soda, E. J. Grant, R. Sakata, H. Sugiyama, and K. Kodama, "Studies of Atomic Bomb Survivors, Report 14, 1950-2003: An Overview of Cancer and Noncancer Diseases," Radiation Research, pp. 177(3):229-243, 2012.

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Footnote 167

A.V. Brenner, D.L. Preston, R. Sakata, J. Cologne, H. Sugiyama, M. Utada, E.K. Cahoon, E. Grant, K. Mabuchi and K. Ozasa, "Comparison of All Solid Cancer Mortality and Incidence Dose-Response in the Life Span Study of Atomic Bomb Survivors, 1958-2009," Radiation Research, pp. 197(5):491-508, 2022.

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Footnote 168

LaMarre, R.L. Grasty and J.R., "The annual effective dose from natural sources of ionising radiation in Canada. Radiation Protection Dosimetry, vol 108(3), 215-226.," 2004. [Online].

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Footnote 169

United Nations Scientific Committee on the Effects of Atomic Radiation, "Sources and Effects of Ionizing Radiation," UNSCEAR 2008 Report to the General Assembly," 2008. [Online].

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Footnote 170

United Nations Scientific Committee on the Effects of Atomic Radiation, "Evaluation of Data on Thyroid Cancer in Regions Affected by the Chernobyl Accident, UNSCEAR White Paper," 2018. [Online]. Available: https://www.unscear.org/docs/publications/2017/Chernobyl_WP_2017.pdf.

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Footnote 171

United Nations Scientific Committee on the Effects of Atomic Radiation, "Effects of Ionizing Radiation," UNSCEAR Report to the General Assembly," 2006. [Online].

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Footnote 172

R. S. Lane, S. E. Frost, G. R. Howe, and L. B. Zablotska, "Mortality (1950-1999) and Cancer Incidence (1969-1999) in the Cohort of Eldorado Uranium Workers," Radiation Research, vol. 174, pp. 773-785," 2010. [Online].

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Footnote 173

Canadian Nuclear Safety Commission, "Update (January 2020- September 2020) Canadian Uranium Workers Study (CANUWS)," September 2020. [Online]. Available: e-doc 6360951.

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Footnote 174

K. Leuraud, D.B. Richardson, E. Cardis, R.D. Daniels, M. Gillies, J.A. O'Hagan, G.B. Hamra, R. Haylock, D. Laurier, M. Moissonnier, M.K. Schubauer-Berigan, I. Thierry-Chef, and A. Kesminiene, "Ionising Radiation and Risk of Death from Leukaemia and Lymphoma in Radiation-Monitored Workers: An International Cohort Study," The Lancet Haematology, vol. 2, no. 7, pp. 276-281," 2015. [Online].

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Footnote 175

D. Laurier, D.B. Richardson, E. Cardis, R.D. Daniels, M. Gillies, J. O’Hagan, G.B. Hamra, R. Haylock, K. Leuraud, M. Moissonnier, M.K. Schubauer-Berigan, I. Thierry-Chef, and A. Kesminiene, "The International Nuclear Workers Study: A Collaborative Epidemiological Study to Improve Knowledge about Health Effects of Protracted Low-Dose Exposure," Radiation Protection Dosimetry, vol. 173, no. 1-3, pp. 21-25," 2017. [Online].

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Footnote 176

D.B. Richardson, E. Cardis, R.D. Daniels, M. Gillies, J.A. O’Hagan, G.B. Hamra, R. Haylock, D. Laurier, K. Leraud, M. Moissonnier, M.K. Schubauer-Berigan, I. Thierry-Chef and A. Kesminiene, ""Risk of Cancer from Occupational Exposure to Ionising Radiation: Retrospective Cohort Study of Workers in France, the United Kingdom, and the United States," BMJ," 2015. [Online].

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Footnote 177

D.B. Richardson, E. Cardis, R.D. Daniels, M. Gillies, R. Haylock, K. Leuraud, D. Laurier, M. Moissonnier, M.K. Schubauer-Berigan, I. Thierry-Chef, and A. Kesminiene, "Site-specific Solid Cancer Mortality After Exposure to Ionizing Radiation A Cohort Study of Workers," Epidemiology, vol. 29, no. 1, pp. 31-40," 2019. [Online].

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Footnote 178

D.B. Richardson, K. Leuraud, D. Laurier, M. Gillies, R. Haylock, K. Kelly-Reif, S. Bertke, R.D. Daniels, I. Thierry-Chef, M. Moissonnier, A. Kesminiene, M.K. .Schubauer-Berigan, "Cancer mortality after low dose exposure to ionising radiation in workers in France, the United Kingdom, and the United States (INWORKS): cohort study," BMJ, p. 382, 2023.

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Footnote 179

Canadian Cancer Society, "Canadian Cancer Statistics 2023," Toronto, 2023.

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Footnote 180

Government of Canada, "National Pollutant Release Inventory," 2023. [Online]. Available: https://www.canada.ca/en/services/environment/pollution-waste-management/national-pollutant-release-inventory.html.

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Footnote 181

Government of Canada, "Radionuclide Release Datasets," March 2024. [Online]. Available: https://open.canada.ca/data/en/dataset/6ed50cd9-0d8c-471b-a5f6-26088298870e.

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Footnote 182

Ontario Ministry of Environment, Conservation and Parks, "Drinking Water Surveillance Program - Dataset - Ontario Data Catalogue," 2021. [Online]. Available: https://data.ontario.ca/dataset/drinking-water-surveillance-program.

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Footnote 183

Government of Ontario , "Ontario Ministry of Labour, Training and Skills Development Ontario Reactor Surveillance Program, Ontario Reactor Surveillance Program," 2022. [Online]. Available: https://www.ontario.ca/page/workplace-health-and-safety.

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Footnote 184

Health Canada, "Radiation Surveillance Program," [Online]. Available: https://www.canada.ca/en/health-canada/services/health-risks-safety/radiation/understanding/measurements.html.

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Footnote 185

Government of Canada, "Government of Canada's Response to the Joint Review Panel Report for the Proposed Darlington New Nuclear Power Plant Project in Clarington Ontario," May 2012. [Online]. Available: https://iaac-aeic.gc.ca/052/document-html-eng.cfm?did=55542.

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Footnote 186

Canadian Nuclear Safety Commission, "Mid-Term Report on Results of Compliance Activities and Performance of Ontario Power Generation's Darlington New Nuclear Project," November 2018. [Online]. Available: e-Doc 5721362.

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Footnote 187

A. e. al., 2006.

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Footnote 188

Ontario Power Generation, "Darlington New Nuclear Project Report for the Review of the Environmental Impact Statement for Small Modular Reactor BWRX-300," 2023.

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Footnote 189

Ontario Power Generation, "Darlington New Nuclear Project Phase 2 Climate Change Risk Treatment," March 5, 2024.

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11.0 Appendix A – Summary Pamphlet (placeholder)

Page details

Date modified:: 2025-02-13

Environmental Protection Review Report – Darlington Nuclear Generating Station

Executive summary

1.0 Introduction

1.1 Purpose

1.2 Facility overview

1.2.1 Site description

1.2.2 Facility operations

1.2.2.1 Darlington Nuclear Generating Station

1.2.2.2 Darlington Waste Management Facility

2.0 Regulatory oversight

2.1 Environmental protection reviews and assessments

2.1.1 Environmental assessments completed under Canadian Environmental Assessment Act

2.1.1.1 Construction of the Darlington Used Fuel Dry Storage Facility

2.1.1.2 Darlington New Nuclear Project

2.1.1.3 Refurbishment and Continued Operation of DNGS

2.1.2 Current environmental assessment follow-up monitoring program

2.1.2.1 Darlington New Nuclear Project

2.1.2.2 FUMP for the Refurbishment and Continued Operation of DNGS Footnote 37

2.1.3 Previous environmental protection review completed under the Nuclear Safety and Control Act

2.1.3.1 Darlington Nuclear Generating Station Licence Renewal

2.1.3.2 Darlington Waste Management Facility Licence Renewal

2.2 Planned end-state

2.3 Environmental regulatory framework and protection measures

2.3.1 Environmental protection measures

2.3.2 Environmental management system

2.3.3 Environmental risk assessment

2.3.4 Effluent and emissions control and monitoring

2.3.5 Environmental monitoring program

2.4 Requirements under other federal or provincial regulations

2.4.1 Greenhouse gas emissions

2.4.2 Ozone depleting substances

2.4.3 Sulphur dioxide emissions

2.4.4 Other environmental compliance approvals

2.4.5 Fisheries Act Authorization

2.5 Canadian Nuclear Safety Commission and federal partners consideration of climate change

Environmental assessment

Periodic safety reviews

Environmental risk assessment

CNSC and ECCC collaboration

3.0 Status of the environment

3.1 Releases to the environment

3.1.1 Licensed release limits

3.1.2 Airborne emissions

3.1.2.1 DN site radiological airborne releases

3.1.2.2 DWMF radiological airborne releases

3.1.2.3 DN site non-radiological releases

3.1.2.4 DWMF non-radiological releases

3.1.2.5 Findings

3.1.3 Waterborne effluent

3.1.3.1 Active Drainage System

3.1.3.2 Inactive Drainage System

3.1.3.3 Stormwater Management System

3.1.3.4 Findings

3.2 Environmental effects assessment

3.2.1 Atmospheric environment

3.2.1.1 Meteorological conditions

3.2.1.2 Ambient air quality

Radiological

Chemicals in air

Physical Stressors

3.2.1.3 Findings

3.2.2 Terrestrial environment

3.2.2.1 Radiological

3.2.2.2 Hazardous

3.2.2.3 Terrestrial habitat and species

Terrestrial species at risk

ERA predictions

Exposure to Radiological Nuclear Substances

Exposure to Hazardous substances

Exposure to physical stressors

Terrestrial environment monitoring

3.2.2.4 Findings

3.2.3 Aquatic environment

3.2.3.1 Surface water quality

Hazardous

Lake Ontario

Liquid effluent

Stormwater

Pond Water

Radiological

2.1.2.2 FUMP for the Refurbishment and Continued Operation of DNGS ^{Footnote 37}