This consultation was open from:
November 6, 2025
to December 21, 2025
Decision summary
A new Environmental Compliance Approval is granted to Aecon Kiewit Nuclear Partners for the collection, transmission, treatment and disposal of cooling water for a tunnel boring machine (TBM) and construction water at Darlington Nuclear Power Generation Station.
Location details
Site address
1 Holt Road South
(Immediately east of existing Darlington Nuclear Generating Station)
Bowmanville,
ON
Canada
Site location map
The location pin reflects the approximate area where environmental activity is taking place.
View this location on a map opens link in a new windowProponent(s)
Aecon Construction Group Inc and Kiewit Nuclear Canada Corp. carrying on business under the general partnership firm name Aecon
1 Holt Road South
Bowmanville,
ON
L1C 3Z8
Canada
Decision details
A new Environmental Compliance Approval is granted to granted to Aecon Kiewit Nuclear Partners for the collection, transmission, treatment and disposal of cooling water for a tunnel boring machine (TBM) and construction water management that includes a slurry treatment plant (STP) and water treatment plant (WTP) having a maximum discharge rate of 40 cubic metres/hour to the site ditch and ultimately to Lake Ontario, consisting of the following:
Slurry Treatment Plant (STP)
A separation plant with DN300 slurry inlet pipe, cyclone pumps, screen machines, screen underflow tanks, collecting and balancing tanks, together with interconnected piping, recirculating acceptable slurry back to the TBM and discharging slurry with unacceptable properties to the waste suspension tank and then to the centrifuge unit described below, and with dry solids transferred by conveyor and to be managed according to the Soil Management Plan:
- a centrifuge unit with a 650 millimetres bowl centrifuge, flocculant dosing station (3.3 cubic metres/hour capacity), centrate water collection tank (10 cubic metres capacity) and transfer pump (30 cubic metres/hour capacity);
- a storage tank system including a fresh suspension tank (150 cubic metres capacity), fresh water tank (250 cubic metres capacity) connected to the municipal supply, waste suspension tank (500 cubic metres capacity) discharging to the centrifuge unit, and centrate water tank (250 cubic metres capacity) with 152 millimetres outlet pipe, level sensors and controls;
- a jobsite wastewater collection basin that is lined with reinforced shotcrete with level sensors and controls having a capacity of 235 cubic metres
Water Treatment Plant (WTP)
A water treatment plant with a treatment capacity of 40 cubic metres/hour, treating effluent from the STP and discharging treated effluent to the site ditch and ultimately to Lake Ontario, consisting of the following:
- one feed pump having a maximum rated capacity of 40 cubic metres/hour;
- one incoming buffer tank having a capacity of 6.5 ubic metres equipped with level control, automatic pH, turbidity and temperature monitoring;
- one linear thickener with automatic flocculant dosing;
- three proposed sand filter pressure vessels (2 active, 1 for cleaning/backwash with automatic cleaning system monitoring/controls);
- three proposed granular activated carbon filters (2 active, 1 for cleaning/backwash with automatic cleaning system monitoring/controls);
- one transfer pump having a maximum rated capacity of 40 cubic metres/hour;
- one filter press to dewater the slurry
Effects of consultation
No comments were received.
Supporting materials
View materials in person
Some supporting materials may not be available online. If this is the case, you can request to view the materials in person.
Get in touch with the office listed below to find out if materials are available.
135 St Clair Ave West
1st Floor
Toronto,
ON
M4V 1P5
Canada
230 Westney Road South
Floor 5
Ajax,
ON
L1S 7J5
Canada
How to Appeal
This instrument decision can be appealed. You have 15 days from February 24, 2026 to begin the appeal process.
Carefully review the information below to learn more about the appeal process.
How to appealClick to Expand Accordion
Start the process to appeal
If you’re an Ontario resident, you can start the process to appeal this instrument decision.
First, you’ll need to seek leave (i.e. get permission) from the relevant appellate body to appeal the decision.
If the appellate body grants leave, the appeal itself will follow.
Seek leave to appeal
To seek leave to appeal, you need to do these three things:
- prepare your application
- provide notice to the minister
- mail your application to three parties
1. Prepare your application
You’ll need to prepare an application. You may wish to include the following things in your application:
- A document that includes:
- your name, phone number, fax number (if any), and/or email address
- the ERO number and ministry reference number (located on this page)
- a statement about whether you are a resident in Ontario
- your interest in the decision, and any facts you want taken into account in deciding whether you have an interest in the decision
- the parts of the instrument that you’re challenging
- whether the decision could result in significant harm to the environment
- the reason(s) why you believe that no reasonable person – having regard to the relevant law and to any government policies developed to guide decisions of that kind – could have made the decision
- the grounds (facts) you’ll be using to appeal
- the outcome you’d like to see
- A copy of the instrument (approval, permit, order) that you you are seeking leave to appeal. You’ll find this in the decision notice on the Environmental Registry
- Copies of all supporting documents, facts and evidence that you’ll be using to appeal
What is considered
The appeal body will consider the following two questions in deciding whether to grant you leave to appeal:
- is there is good reason to believe that no reasonable person, with respect to the relevant law and to any government policies developed to guide decisions of that kind, could have made the decision?
- could the decision you wish to appeal result in significant harm to the environment?
2. Provide your notice
You’ll need to provide notice to the Minister of the Environment, Conservation and Parks that you’re seeking leave to appeal.
In your notice, please include a brief description of the:
- decision that you wish to appeal
- grounds for granting leave to appeal
You can provide notice by email at minister.mecp@ontario.ca or by mail at:
College Park 5th Floor, 777 Bay St.
Toronto, ON
M7A 2J3
3. Mail your application
You’ll need to mail your application that you prepared in step #1 to each of these three parties:
- appellate body
- issuing authority (the ministry official who issued the instrument)
- proponent (the company or individual to whom the instrument was issued)
Aecon Construction Group Inc and Kiewit Nuclear Canada Corp. carrying on business under the general partnership firm name Aecon
1 Holt Road South
Bowmanville,
ON
L1C 3Z8
Canada
Registrar, Ontario Land Tribunal
655 Bay Street, Suite 1500
Toronto, Ontario
M5G 1E5
(416) 212-6349
(866) 448-2248
OLT.Registrar@ontario.ca
Include the following:
This is not legal advice. Please refer to the Environmental Bill of Rights for exact legal requirements. Consult a lawyer if you need help with the appeal process.
Connect with us
Contact
Client Services and Permissions Branch
135 St Clair Ave West
1st Floor
Toronto,
ON
M4V 1P5
Canada
Original proposal
Proposal details
This proposal is for a new Environmental Compliance Approval (ECA) for Aecon Kiewit Nuclear Partners to establish sewage works for the treatment and disposal of construction-related water for the operation of the tunnel boring machine (TBM) used for boring of the condenser cooling water (CCW) tunnels, at a maximum rate of 40 cubic meters per hour for Ontario Power Generation (OPG) Darlington New Nuclear Project (DNNP) in Clarington.
The DNNP will be constructed adjacent to the existing Darlington Nuclear Generating Station, which is approximately 5 kilometres from the nearest town. The tunnelling activities related to this water treatment plant are currently expected to run 24 hours a day, from Monday to Friday, with a potential for extension on Saturdays, for an estimated period of 12 months.
The proposed sewage works include a modular/self-contained water treatment plant (WTP) that discharges after treatment into the existing site stormwater management system, approved under ECA No. 3501-DCKHX5, or is recycled back to the TBM.
The ministry will impose effluent limits and/or monitoring requirements for effluent discharges from the facility.
Supporting materials
View materials in person
Some supporting materials may not be available online. If this is the case, you can request to view the materials in person.
Get in touch with the office listed below to find out if materials are available.
135 St Clair Ave West
1st Floor
Toronto,
ON
M4V 1P5
Canada
Comment
Commenting is now closed.
This consultation was open from November 6, 2025
to December 21, 2025
Connect with us
Contact
Client Services and Permissions Branch
135 St Clair Ave West
1st Floor
Toronto,
ON
M4V 1P5
Canada
Comments received
Through the registry
0By email
0By mail
0