Ontario Power Generation's Response to the Joint Review

Attachment 1 to OPG letter, Albert Sweetnam to Dr. Stella Swanson, “Deep Geologic Repository Project for Low and Intermediate Level Waste – Submission of
Responses to the Final Sub-set of Package #4 Information Requests”, CD#: 00216-CORR-00531-00143.
IR# EIS Guidelines
Section
Information Request and Response
5. Stormwater Management Pond – Discharges
Runoff will be allowed to continuously discharge from the SWMP in response to storm runoff and underground
dewatering inputs. The objective of providing retention is to provide sufficient time for sediment in water inflows to the
pond to settle out.
The retention time in the SWMP will be achieved by:
� satisfying or exceeding criteria provided in MOE (2003) for the volume, depth, length and length-width ratio of a
wet pond facility; and
� designing the outlet structure to control the rate of discharge from the pond, thereby slowing the rate at which
water moves through the pond.
A minimum retention time of 24 hours will be achieved by designing the pond and its outlet structure such that the time
difference between the centroids of the inflow and outflow hydrographs (plots of the flow rate versus time) is greater
than or equal to 24 hours.
The provision of a permanent pool will also increase the effectiveness of the SWMP in controlling suspended solids
concentrations in effluent discharges. During storm events, the influent loading will be diluted in the permanent pool.
After storm events, suspended solids remaining in the permanent pool will have the inter-event times to settle out in the
pond. Inter-event times are additional to the retention times provided for in pond design.
6. Water Quality Criteria
Final water quality criteria for the effluent from the SWMP will be developed as part of the Ontario Environmental
Compliance Approval (ECA). The limits will be established taking into consideration the Provincial Water Quality
Objectives, the acute toxicity thresholds for sensitive species that are present in the receiving environment, and the
existing water quality in the receiving water at MacPherson Bay. The regulatory process will not allow the release of
effluent from the SWMP that is acutely toxic to aquatic receptors.
The surface water quality assessment and associated geochemical testing performed for the environmental
assessment indicated several water quality parameters of potential concern in SWMP discharge. These include:
� total dissolved solids (TDS);
� chloride;
� total suspended solids (TSS);
� nitrogen compounds from blasting residues;
� pH, temperature, conductivity; and
� various metals (aluminum, boron, cobalt, thallium, vanadium).
The DGR Follow-up Monitoring Program (NWMO 2011, Tables 3a and 6) presents a set of targets for these
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