Pierre River Mine Project

WATER AENV SIRS 15 – 43
Question No. 18
Section 12.1
overburden deposits (see EIA, Volume 4A, Section 6.3.6.2, page 6-211).
Design considerations for the Pierre River Mine ETDA seepage interception
system include all seepage through the base of the ETDA into the overburden
deposits. This excludes seepage through the dike seepage faces, internal
seepage collection systems, and toe drains, as these components of seepage
are captured by different systems and do not enter the overburden deposits.
ii. EIA, Volume 4A, Section 6.3.6.2, page 6-229, evaluated a system of
recovery wells to capture seepage from the ETDA that entered the
overburden deposits. A technically viable measure that could be considered
is to increase the rate of pumping from the existing seepage interception
wells to capture the higher seepage rates. If necessary, the proposed or
existing pumps would be replaced with higher capacity pumps. Also, if
required, additional seepage interception wells, including horizontal wells,
could be installed to supplement the pumping efforts and effectively capture
the ETDA seepage.
Request Volume 2, SIR 279 a-b, Page 21-20.
Figures 279-1 to 279-4 provide visual inspection of the residual distribution in
the wells installed in different formations. The calibration results information
provided on page 29 to 36 of Appendix 4-1 provides validity of the calibration
based on the overall statistical results of residuals and visual observations.
Validation of the calibration results in different areas of the models, including
the wells in close proximity to the depressurization and dewatering areas in the
regional models (both steady state and transient model) and tailing areas and pit
lakes in JEMA and PRMA local models, is not provided. The concern is that
residuals in the monitoring wells range between +9.99 m and -9.39 m and
+28.5 m and -25.64 m in regional steady state and transient models, respectively,
which are high. The same applies for the local JEMA and PRMA models, where
the residuals range between +8.80 to – 27.50 m and +10.77 m and – 8.02 m.
18a The spread and range of residuals is very high and indicates that the correlation
is statistically weak. How has Shell compensated for this uncertainty in the final
model results?
Response 18a The range of residual values are not a good statistical measure of the quality of
the model calibration. The model-averaged residuals are generally preferred to
evaluate the overall quality of the model calibration. Average errors in the model
(residual and absolute residual means, standard deviation and the ratio of the
standard deviation to the range of values) were presented in EIA, Volume 4B,
Appendix 4-1, Figure 18 (regional model, steady-state calibration), Figure 20
(regional model, transient calibration), Figure 22 (Jackpine Mine Expansion local
12-10 Shell Canada Limited April 2010
CR029