Protocol for the Derivation of Environmental and Human ... - CCME

Appendix E
C
K
L
V
is the climate factor.
is the surface roughness.
is the maximum unsheltered distance across a site along the direction of the prevailing wind.
is the vegetative cover factor.
2.3 Modelling
Both the above models are empirical, based on a number of regression equations between soil loss and
the various soil, climate, and management factors that affect it. Derivation of the input parameters is
difficult and in the case of the WEQ, calculation is also difficult because of complex mathematical
relationships between the input variables. However, computer models based upon these two equations
are available to calculate erosion losses from basic soil, climate, and management data. One of the most
commonly used is the Erosion/Productivity Impact Calculator (EPIC) (Williams et al., 1990). Although
EPIC is primarily used to evaluate the effect of agricultural practices on soil productivity, its ability to
estimate soil erosions rates (t/ha/y) from basic soil and climate data make it a valuable tool for evaluating
erosion under other land use scenarios.
3.0 Deposition
To estimate the impact of eroded soil on off-site areas, soil deposition on the area of concern must be
calculated. Although the above models are available for estimating soil loss by erosion, very little work
has been done on subsequent deposition. Process based models of erosion and subsequent deposition
are under development but will not be ready for application in the near future (Foster, 1991).
Deposition of the eroded material will depend on the landscape. In water erosion, most industrial sites
are designed to contain runoff within site boundaries and off-site erosion will be minimal. Soil eroded
from those sites without runoff controls will move with runoff until reaching the toe of the slope where it
will be deposited. The area covered by the deposited material will depend on local topography. Wind
eroded material will move until encountering a barrier acting as a windbreak or, in the case of fine
particles, until removed from suspension by rain.
One can assume that the eroded soil leaving a contaminated site will be deposited over an equivalent
area off-site. This soil will be deposited as a surface layer and will therefore be immediately available for
contact. The depth of this layer can be calculated from the quantity of soil deposited over a given area
and an assumed bulk density. Some mixing of the deposited material with native soil due to traffic,
runoff, or gardening will likely occur, diluting the contaminated soil. A reasonable surface microrelief is
2 cm and the mixing of deposited soil with uncontaminated native soil takes place within this zone. Soil
erosion and deposition are on-going processes. However gradual removal of the contaminated soil and
on-going mixing with uncontaminated soil through erosion occurring in other parts of the landscape
should result in contaminant concentrations reaching an equilibrium over time. In the absence of any
procedure for accounting for these mitigating processes, a period of five years was chosen as an
appropriate timeframe for contaminants to build up in the receiving soil.
4.0 Calculations
4.1 General
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