Pierre River Mine Project

WATER AENV SIRS 15 – 43
Question No. 19
Request Volume 2, SIR 297, Page 21-51.
Section 12.1
Shell describes details of previous experience with successfully mitigating pit
lake waters, those design and monitoring objectives that will be integrated into
pit management planning to achieve timely mitigation of pit waters, best case
time frames for pit water mitigation, and the state of current research that Shell
will use to prevent pit waters from potentially becoming methanogenic. Shell
states that modeling has been completed to confirm that the residence time will
be sufficient to biodegrade organic constituents to acceptable levels based upon
conservative degradation rates.
19a What were the maximum residence times used in the pit lakes modeling?
Response 19a Pit lake residence times are presented in EIA, Volume 4B, Appendix 4-2,
Table 21. The residence times for the Pierre North Pit Lake and the Pierre South
Pit Lake are one and 10 years, respectively. The residence time for the Pierre
South Pit Lake is presented in Table 21 as eight years in the upstream cell and
two years in the downstream cell, for a total residence time in the lake of 10
years.
Request 19b What are the conservative degradation rates used for each organic constituent of
concern, providing reference citations for similar climate environmental
settings?
Response 19b The conservative degradation rates used in the pit lake modelling are presented in
EIA, Volume 4B, Appendix 4-2, Table 42, and the respective source references
listed in the table are in EIA, Volume 4B, Appendix 4-2, Section 4. Decay rates
were corrected for temperature to account for slower decay in cold, northern
lakes.
The aerobic decay rates applied to lakes and wetlands for ammonia, sulphide,
acute toxicity and chronic toxicity are the slowest of the rates derived from
available field research studies conducted on process-affected waters from oil
sands operators.
The aerobic decay rate listed for total phenolics is based on the slowest rate of
degradation for phenol in studies listed in the CHEMFATE database (SRC 2007).
Field-based studies listed in CHEMFATE have associated decay rates that vary
from 28 y -1 at 21ºC for an estuarine river in Georgia (Lee and Ryan 1979) to
3,152 y -1 for in-situ waters spiked with phenol in the St. Lawrence River
downstream of oil refinery wastewater outfalls (Visser et al. 1977).
Tainting potential decay rates are based on decay of ethylbenzene. The aerobic
decay rate of 2.3 y -1 is derived from observed persistence of ethylbenzene in
shallow groundwaters monitored in the Netherlands (Zoetman et al. 1980), which
12-18 Shell Canada Limited April 2010
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