Pierre River Mine Project

AIR AENV SIRS 6 – 14
Section 11.1
as low as 1 ppb (0.7 µg/m 3 ) by individuals who have been tested and found to
have a sense of smell that falls within the normal range of the general
population.
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1 Harvard University 2006. Comparison of Odor Thresholds and PEL’s/TLV’s of
Some Substances. http://research.dfci.harvard.edu/ehs/PPE/Respirators/
2 Iowa State University 2004. The Science of Smell Part 1: Odor Perception and
Physiological Response. PM 1963a, May 2004.
3 Lenntech Holding B.V. 2006. Odorous Substances (Osmogenes) and Odor
Thresholds. http://www.lenntech.com/table.htm
14a Justify use of the geometric mean when, as Shell indicates, much lower available
and scientifically valid thresholds could have been used.
Response 14a If the hydrogen sulphide (H2S) odour threshold were set to 0.7 µg/m 3 , the
predicted frequency of hours with concentrations above this revised odour
threshold would increase. However, the odour threshold used in the EIA is
appropriate for the following reasons:
• One of the five guiding principles for developing the Federal National
Ambient Air Quality Objectives (NAAQOs) states that the objectives should
recognize the variable sensitivities of subgroups of the Canadian population
and of particular ecosystems and organisms in the environment. Because of
the large range of these sensitivities, it might not be possible to protect every
sensitive individual and ecosystem from all effects (WGAQOG 1996). The
use of an H2S odour threshold of 0.7 µg/m³ would overestimate odour
impacts.
• The typical H2S odour threshold of 14.1 µg/m³ is similar to the 1-hour
Alberta Ambient Air Quality Objective (AAAQO), which is based on odour
perception and is meant to protect the general population. The AAAQO is
also one of the most stringent in Canada and the United States (AEP 1999;
AENV 2004).
• It is common practice in sensory evaluation to use geometric means as they
account for the wide range of responses over several orders of magnitude
(AIHA 1989). The odour standards and guidelines in Ontario are based on
the geometric mean of odour detection thresholds reported in literature
(Government of Ontario 2009, internet site).
• The odour thresholds taken from the available literature are valid. Additional
references of Harvard University (2006), Iowa State University (2004) and
Lenntech (2006) do not change the calculated geometric mean for H2S, nor
suggest that calculating an odour threshold using geometric mean is
inappropriate.
11-14 Shell Canada Limited April 2010
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