Ontario Power Generation's Response to the Joint Review

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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 EIS-04-143 � Section 11.4.9, Effects of the Environment on the Project Information Request and Response GOLDER. 2011. Atmospheric Environment Technical Support Document. Golder Associates Ltd. report for the Nuclear Waste Management Organization NWMO DGR-TR-2011-02 R000. Toronto, Canada. (CEAA Registry Doc# 299) OPG. 2011. OPG’s Deep Geologic Repository for Low and Intermediate Level Waste - Preliminary Safety Report. Ontario Power Generation report 00216-SR-01320-00001 R000. Toronto, Canada. (CEAA Registry Doc# 300) Information Request: Provide an updated evaluation of the potential for climate change to affect precipitation, including extreme events. Provide an evaluation of how this may affect the design of the Project. Context: Potential increases in extreme precipitation from peer-reviewed climate modeling should be included in the report rather than only considering mean precipitation in the assessment. The implication of the potential changes to extreme values should be taken into consideration when adjusting engineering infrastructure requirements and calculating flood design standard values. At a minimum, this has implications for the design of the stormwater management system and for the design of the repository shaft collar elevations (i.e. OPG indicated it would design the repository shaft collars to be above the water levels arising from a Probable Maximum Precipitation/Probable Maximum Flood event). Climate modeling points to a greater increase in the frequency and intensity of extreme precipitation events than annual mean precipitation quantities under a changing climate (Kharin et al. Journal of Climate, Vol. 20, 2007 pp. 1419–1444; Kharin and Zwiers. Journal of Climate, Vol. 18, 2005 pp. 1156–1173). These studies found the annual mean precipitation rate over North America is projected to increase by less than 3% by the end of this century, however, the corresponding increase in the 20-year return values of annual extremes of 24-hour precipitation rates is projected to be 15% (A2 scenario). A more recent study focusing on Southern Ontario found that the return values of annual maximum 3-day accumulated rainfall totals in the study area are projected to increase by 25–60% for the period 2051–2100 (Cheng et al. Journal of Climate, Vol. 24, 2011 pp. 3667–3685). OPG Response: The environmental assessment for the DGR Project considers the potential for climate change to affect precipitation, including extreme events. This Information Request (IR) requests an updated evaluation of the potential for climate change to affect precipitation based on literature published since the submission of the Environmental Impact Statement (EIS, OPG 2011a) and the Preliminary Safety Report (PSR, OPG 2011b). Page 45 of 69
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 The response is provided in two parts: a) Precipitation intensity; and b) Probable Maximum Precipitation. Information Request and Response (a) Precipitation Intensity The DGR environmental assessment (GOLDER 2011, Appendix D, Section D2.3.4) considers changes in climate within the Great Lakes Basin, specifically changes in both mean precipitation and precipitation intensity. Forecasts from the Intergovernmental Panel on Climate Change (IPCC), and recent papers by Warren et al. (2004), Mortsch et al. (2003) and Kharin et al. (2007) were cited and the information presented. It was noted that Kharin et al. (2007) suggests the 20-year return period for total 24-hour rainfall could increase in intensity by 10% to 20% by the 2071 to 2100 forecast period. With respect to the Information Request for an updated evaluation, the literature was surveyed for recent literature on precipitation intensity relevant to southern Ontario, and one new paper was identified: Cheng et al. (2011) suggest an increase in frequency of future daily heavy rainfall events over the period 2081 to 2100 for four river basins in southern Ontario. Cheng et al. (2011) also predict increases in the return values of annual maximum 3-day accumulated rainfall. More specifically, for the 100-year return period storm (considered in the DGR stormwater management design), the 3-day accumulated rainfall totals are projected to increase from about 100 mm currently observed to 130-170 mm for the period 2051-2100. The 24-hour accumulated rainfall would be less than Cheng’s 3-day accumulated rainfall projection, but is not estimated in the paper. As outlined in OPG’s response to IR-EIS-04-130, the stormwater management pond is designed to: � provide a minimum retention time of 24 hours for runoff from 25 mm of rainfall in 6 hours; � ensure that the average annual total suspended solids concentration in effluent discharge does not exceed 40 mg/L; � attenuate post-development peak outflow rates for 24-hour rainfall events with return periods ranging from 2 to 100 years to pre-development values; and � safely convey the peak outflow rate from the 24-hour, 100-year rainfall event. The current design of the stormwater management pond considers a 24-hour rainfall event with a return period of 100 years (110 mm) based on data from Goderich, Ontario. As stated in the response to IR-EIS-04-130, it is expected that the rainfall amounts at Kincardine would be less than at Goderich. The design of the stormwater management pond has extra capacity if rainfall intensity is higher, in part because of conservative assumptions leading to the current design and the availability of 300 mm of planned freeboard on the sides of the pond. The capability of downstream Page 46 of 69
Page 2 and 3: Dr. Stella Swanson September 28, 20
Page 4 and 5: Attachment 1 to OPG letter, Albert
Page 74 and 75: Title: OPG’s Deep Geologic Reposi
Page 76 and 77: Table of Contents CLOSURE WALL CAPA
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Page 82 and 83: CLOSURE WALL CAPACITY The shear str
Page 84 and 85: (H-a) = 4.25 m Figure 5: Return air
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Serge Clement 1011170042-TM-G2100-0
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APPENDIX A Derivation of Conversion
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External radius of liner =
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ATTACHMENT 2 Attachment to OPG lett
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8. Letter from A. Sweetnam to S. Sw
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OPG’s L&ILW Deep Geologic Reposit
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Ontario Power Generation's Response to the Joint Review

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