Pierre River Mine Project

PIERRE RIVER MINE
SUPPLEMENTAL INFORMATION
PART 3: AENV SIRS – ROUND 2
Question No. 15
Request Volume 2, SIR 265, Page 21-3.
WATER
AENV SIRS 15 – 43
Section 12.1
Shell describes the polishing ponds water treatment, pond residence time and
other items.
15a Since the ponds are designed to contain and convey flows for all hydrologic
conditions up to the 100 year flood without uncontrolled spillage, provide the
emergency response plans for potential spillage in the unlikely event of flows
exceeding 100 year flood flows.
Response 15a Polishing ponds are primarily required for mitigating elevated levels of total
suspended solids (TSS) in runoff during high flow events. During a flood event
exceeding the 100-year flood event, the outlet of the polishing pond would likely
erode, becoming wider and deeper. Flows through the compromised pond would
discharge along the outlet channel into the receiving streams. Levels of TSS
discharging from the pond would be high, but would be similar to those in
receiving streams. As a result, receiving stream TSS levels would not
substantially increase with the addition of polishing pond discharge beyond the
range of natural variability.
Given that the TSS levels of the discharge would be similar to the receiving
streams and that the flow path would remain intact, a detailed emergency
response plan (ERP) for this unlikely failure scenario has not been developed.
Request 15b Since the pond residence time is about eight hours and the TSS monitoring
frequency is three times per week, what measures are proposed to be in place to
confirm that uncontrolled releases are not occurring between sampling events?
How will potential releases during these times be addressed, with specific
reference to each potential parameter of concern?
Response 15b As noted in the response to SIR 265 in the May 2009 Pierre River Mine,
Supplemental Information, Volume 2, Shell will monitor at the frequency
specified in the EPEA approval, and may increase the monitoring frequency as
appropriate when monitoring results indicate a potential non-compliance. In
Shell’s experience, the frequency and quantity of monitoring prescribed by
April 2010 Shell Canada Limited 12-1
CR029