Pierre River Mine Project

WATER AENV SIRS 15 – 43
Section 12.1
1-5 of the Muskeg River Mine Expansion EIA. Considering that most of the
Pierre River Mine ETDA footprint will consist of areas of TT and of areas of
tailings sand that are overlain by MFT, which will effectively limit the seepage
rate to that of MFT, the overall hydraulic conductivity of 1 x 10 -8 m/s assigned to
the ETDA deposits is considered conservative, leading to higher assumed
seepage rates. Potential reduction of tailings sand hydraulic conductivity as a
result of bitumen or sludge deposits and entrapment (Hunter, 2001) were not
considered.
ETDA Fluid Level Elevation for GHB
The fluid level specified for the ETDA was constant and was based on the fluid
elevation that will be present following complete filling of the ETDA. In reality,
the fluid elevation will rise with time through the active lifetime of the ETDA.
Therefore, the vertical hydraulic gradient between the ETDA and the underlying
aquifer was also conservatively represented, as higher vertical gradients lead to
higher seepage rates.
Underlying Aquifer Hydraulic Conductivity
Reference
There is some uncertainty in the distribution and hydraulic conductivity of the
sediments which underlie the ETDA, as described in EIA, Volume 4B, Appendix
4-1, Section 1.2.4.5, page 98. Additional conservatism was built into the
simulation of ETDA seepage, as the entire aquifer underlying the ETDA was
represented by relatively high hydraulic conductivity sandy materials, with the
assigned hydraulic conductivity (5 x 10 -5 m/s) being at the upper end of the range
of hydraulic conductivity values measured in Quaternary deposits in Lease 9.
Hunter, G. P. 2001. Investigation of groundwater flow within an oil sand tailings
impoundment and environmental implications. M.Sc. Thesis, University
of Waterloo,
Request 17d Shell mentions that the expected time for groundwater extraction rates to
stabilize or reach steady state will be defined when a detailed groundwater
extraction system, with actual expected pumping well locations is designed and
produced. Describe the timeframe and the standard procedures for designing
and implementing a detailed groundwater extraction system.
Response 17d The detailed design of a seepage management system requires that the conceptual
models used to conservatively assess potential environmental impacts related to
ETDA seepage be refined and updated. This typically requires additional
geological and hydrogeological information specific to the proposed ETDA site
and surrounding area, and tailoring of plans to align with detailed design
purposes.
12-8 Shell Canada Limited April 2010
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