CRC Street Sweep Eval 1999.pdf( 489.9 KB ) - Clearwater

COOPERATIVE RESEARCH CENTRE FOR CATCHMENT HYDROLOGY
runoff to be associated with particulates. While most
particulate matter found on street surfaces is in the
fractions of sand and gravel. Approximately 6% of
particles are in the silt and clay soil size and they
were found to contain over half the phosphorous and
some 25 percent of other pollutants, as indicated in
Table 6.1, adapted by Shaver (1996) from results of
Sartor et al. (1974).
Many other investigations have found the
concentrations of sediment-bound contaminants in
street dirt to be associated with the fine particle size
fraction. Pitt & Amy (1973), NCDNRCD (1993) and
Woodward-Clyde (1994) have all shown that higher
concentrations of pollutants such as heavy metals are
associated with the smallest particle size fractions of
urban dust and dirt. These data indicate that almost
half of the heavy metals (represented by copper, lead
and zinc) found on street sediments are associated
with particles of 60 to 200 µm in size and 75% are
associated with particles finer than 500 µm in size.
Dempsey et al. (1993) undertook an analysis of
particle size distributions for urban dust and dirt, and
partitioning of contaminants into a number of size
fractions to determine the concentrations of
contaminants in each particle size range. Results
show the highest recorded concentrations of Cu, Zn
and TP to be associated with sand particles between
74 and 250 µm in size.
Colwill et al. (1984) found 70% of oil and
approximately 85% of polycyclic aromatic
hydrocarbon (PAH) to be associated with solids in the
stormwater. That study demonstrated that over a
period of dry weather conditions, increasing
proportions of oil become solid associated where the
highest oil content was found in sediments of 200 to
400 µm in size.
Sansalone et al. (1997), Fergusson and Ryan (1984),
Baker (1980) and Wilber and Hunter (1979) all
reported that heavy metal concentrations increase
with decreasing particle size. Results presented by
Sansalone et al. (1997) from particle size distribution
and metal analysis indicate that zinc, copper and lead
concentrations increase with decreasing particle size
or, equivalently, increasing specific surface area. The
absorption of contaminants to particles is often
regarded as being directly related to the surface area
per unit mass available for ion absorption. Measured
specific surface area results presented by Sansalone et
al. (1997) indicated that the assumption of smooth
spherical particles to estimate available surface area
Table 6.1 Percentage of Street Pollutants in Various Particle Size Ranges
Particle Size Particle (Microns) Size (µm)
Pollutant 2000
Total Solids 5.9 9.7 27.8 24.6 7.6 24.4
Volitile Solids 25.6 17.9 16.1 12.0 17.4 11.0
COD 22.7 45.0 12.4 13.0 4.5 2.4
BOD 24.3 17.3 15.2 15.7 20.1 7.4
TKN 18.7 19.6 20.2 20.0 11.6 9.9
Phosphates 56.2 29.6 6.4 6.9 0.9 0.0
All Toxic Metals 27.8 - 23.5 14.9 17.5 16.3
(Source: Shaver; 1990; adapted from Sartor, Boyd, and Agardy, 1974)
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