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An evaluation of highway stormwater runoff quality in the G.V.R.D. Onwumere, George Chukwudi

Abstract

In the Greater Vancouver Regional District (G.V.R.D.), highway stormwater runoff from bridge decks along the Trans-Canada Highway (#1) in Burnaby and the New Westminster Highway (#91, east-west connector) in Richmond was assessed between 1995 and 1996. Discrete and composite samples of highway stormwater runoff, road dirt, surface soil sediment and grass clipping samples were collected manually from both sites. The stormwater runoff samples were analysed for total suspended solids (T.S.S.), chromium (Cr), nickel (Ni), cadmium (Cd), copper (Cu), iron (Fe), zinc (Zn), manganese (Mn), lead (Pb), calcium (Ca), oil/grease, pH and electrical conductivity (EC). The road dirt, soil sediment and grass clipping samples were analysed only for their metal content. All the parameters in highway stormwater runoff showed differences in seasonal concentration patterns except for Cu and Mn at both sites. However, these differences were not statistically significant at the 95% confidence level. Although concentrations of most pollutants were higher in the winter, LC50 daphnia bioassays were non-toxic. The non-winter Comp "A" runoff samples, on the other hand, had 70% and 57% survival rates after 24 and 48 hours respectively. Most contaminant concentrations exceeded the maximum allowable concentrations (MAC) set for drinking water or freshwater aquatic life protection. Between the two sites, the Burnaby site had higher rainfall amounts and runoff coefficients, thereby generating higher T.S.S., metal and oil/grease concentrations/loadings than the Richmond site. The Burnaby site grass drainage ditch was fairly efficient in its pollutant removal effectiveness which ranged from 48% for Cu to 77% for T.S.S. There were statistically significant differences in pollutant removal efficiencies for all the parameters except for Mn at the 95% confidence level. Pollutant concentrations forecasting, using single regression equations with individual environmental variable, yielded reasonably good predictions for T.S.S., Fe, and Mn at the Burnaby site; and T.S.S., and Ca at the Richmond site. Comparison between discrete sample and flow composite data indicated a significant difference only in the concentration of T.S.S. at the Burnaby site.

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