Pierre River Mine Project

AIR AENV SIRS 6 – 14
Section 11.1
Further analysis was completed for individual volatile organic compounds
(VOCs) by comparing the Existing Scenario predictions with monitored
concentrations. The VOC monitoring conducted in the region relies on noncontinuous
techniques that collect 24-hour samples on a set schedule; therefore,
only 24-hour and annual concentrations could be evaluated.
A review of the monitoring data showed that higher concentrations were
typically observed prior to 2008. This may be linked to higher annual average
solvent losses as operators worked to optimize their solvent recovery technology.
For example, the Shell Muskeg River Mine annual average solvent loss since
2003 has ranged from 3.7 to 10.6 bbl of solvent per 1,000 bbl of bitumen
produced (see the response to SIR 159a in the May 2009 Pierre River Mine,
Supplemental Information, Volume 1. While solvent loss information was not
available from other operators in the region, the annual average solvent losses
from these operations are expected to have been variable as well.
In 2008 and 2009, the monitored concentrations were generally lower and are
thought to correspond to the solvent loss rates used for the Existing Case. For
example, the Shell Muskeg River Mine annual average solvent loss was 4.0 bbl
of solvent per 1,000 bbl of bitumen produced in 2008 (see the response to SIR
159a in the May 2009 Pierre River Mine, Supplemental Information, Volume 1).
Since the Existing Case tailings pond emissions were based on solvent losses of 4
to 4.5 bbl of solvent per 1,000 bbl of bitumen produced, as stated previously, it is
likely that the VOC predictions are more representative of the 2008/2009 period.
When compared to the 2008/2009 monitoring data, the maximum 24-hour
predictions were generally within the same range when outlier concentrations
were excluded. The outlier concentrations were removed from the analysis since
they were likely due to upset events, which were not considered in the model.
Only two data points, which accounted for 2% of the data, were removed from
one station in the analysis.
The highest 24-hour benzene concentration monitored at Fort McKay in
2008/2009 was 1.8 µg/m³. Outliers were not identified in the Fort McKay data;
therefore, none of the monitoring data were excluded. The 24-hour predicted
maximum concentration at Fort McKay was 1.4 µg/m³. This difference of
0.4 µg/m³, while lower than the highest monitored concentration, is considered
within the accuracy of the model. The annual average Existing Scenario benzene
predictions were generally within 2 µg/m³ lower than 2008/2009 monitored
values at all the stations; however, this is considered within the accuracy of the
model.
While this analysis focused on VOCs, the same conclusions can be made for TRS
compounds which are also primarily emitted from tailings ponds.
11-2 Shell Canada Limited April 2010
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