Pierre River Mine Project

HEALTH AENV SIRS 79 – 89
Methods
Section 14.1
• The greater the number of odourants in the mixture, the more difficult it was
to identify the individual constituents.
• The greater the number of components in the mixture, the greater the degree
of suppression of the individual constituents.
• Hydrogen sulphide was the least frequently suppressed odourant.
• The unpleasantness of the odourant mixture was typically greater than that of
the individual constituents, indicating that models for predicting complaint
levels in communities affected by odourous mixtures, but which are based on
single odourants, will usually underestimate the number of complaints.
This assessment evaluated almost 400 chemicals through the use of chemical
fractions and surrogates. As such, many of the odourants assessed might never be
detected. However, other odourants, such as hydrogen sulphide, are not typically
suppressed and make it very difficult to accurately predict the perceived intensity
of the odourous mixture.
It is possible that the individual odours could “cumulatively” register as a
nuisance. However, current information on odourous mixtures does not indicate
that hydrogen sulphide or any other odourants will be perceived at concentrations
lower than the odour based air quality objectives or reported odour thresholds as
a result of the odourant mixture.
Potential odours were assessed by comparing three-minute peak COPC air
concentrations with established odour thresholds. Three-minute peak
concentrations were derived from the highest predicted one-hour ground-level air
concentrations (i.e., including the eight highest one-hour predictions) using the
following equation:
C3-min = C1-hr x 3 minute multiplier
C3-min = C1-hr x (60 min/3 min) 0.2
Where:
C3-min = predicted three-minute peak concentration
C1-hr = predicted one-hour concentration
0.2 = exponent for the three-minute multiplier based on
neutral atmospheric conditions (OMOE 1996; Duffee et
al. 1991).
Three-minute peak concentrations were estimated for the COPCs given that
odours can appear instantaneously and are commonly observed over very short
periods. The potential for COPCs to contribute to nuisance odours was assessed
as follows:
April 2010 Shell Canada Limited 14-5
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