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
on the conservative assumption of no grouting, it is estimated that groundwater inflow from these formations will be
0.38 L/s. However, during shaft sinking it is expected that these formations will be grouted, as required, to primarily
reduce groundwater inflow later during DGR operations (see below).
Once shaft sinking is complete and both shafts are fully lined with concrete, groundwater inflow through concrete liners
is estimated to be 0.45 L/s (GOLDER 2012). This estimate is based on the assumption that the majority of inflow
occurs from Salina A1 and Guelph Formations through a “leaky liner” and these two formations are ungrouted (see
responses to IR-LPSC-01-17 (OPG 2012a) and Undertaking TIS 11 (OPG 2012b)). However, since it is expected that
these formations will be grouted during shaft sinking, the groundwater inflow will be less than 0.45 L/s.
During lateral development at the repository level, the usage of process water for equipment, construction and dust
mitigation is assumed to be about 20 L/s (average). This estimate is very conservative to allow for a wide variety of
equipment selection and water demand criteria. The estimate has been derived using high water demand equipment
(e.g., high efficiency multi-boom drilling jumbos), high utilization estimates for operating hours per day, continuous
water suppression during operating hours and an allowance for continuous civil construction activities (e.g., floor
concrete). As well, this estimate does not take into consideration options for recirculation of process water.
The expected inflow rates during normal operations are described in the response to Undertaking TIS 11 (OPG 2012b).
During normal operations, the majority of groundwater inflow will be through both shaft concrete liners and as described
above is conservatively estimated to be 0.45 L/s. Due to the very low permeability of the Cobourg Formation Lower
Member, groundwater inflow at the repository level is expected to be negligible (0.006 L/s). This rate of groundwater
inflow would likely be less than the rate at which the water would evaporate and thus would not flow to the underground
dewatering system. A small allowance (0.06 L/s) has been made in the discharge water estimate to reflect potential
condensation in the ventilation shaft during summer conditions.
The underground dewatering system used for operations will be sized to handle both the aforementioned normal inflow
plus additional groundwater inflow that might occur during a postulated abnormal operations event. In the Preliminary
Safety Report (OPG 2011, Section 6.3.10.4) it was assumed that an abnormal ’in-rush scenario’ would lead to an
additional groundwater inflow of 15 L/s. Further assessment of potential additional inflow due to shaft liner impairments
has been completed (GOLDER 2011, enclosed). This assessment shows that a 1:2500 year seismic event, which is
consistent with the National Building Code of Canada (2010 edition) requirements, could lead to cracking of shaft liners
and an additional 0.1 L/s inflow. A further analysis was conducted for a beyond-design-basis 1:100,000 year seismic
event which resulted in a potential inflow of 3.4 L/s.
References:
GOLDER. 2011. Potential Inflows through Cracked Hydrostatic Concrete Shaft Liner. Golder Associates Ltd.
Technical Memorandum 1011170042-TM-G2100-0001-01 R01. (enclosed)
GOLDER. 2012. Underground Services (WP2-10) Underground Repository Dewatering – Preliminary Estimate of
Groundwater Inflow under Normal Operating Conditions. Golder Associates Ltd. Technical Memorandum No.
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