Characterization of low traffic volume highway storm water runoff

摘要

A study was performed to determine the extent of contamination in storm water runoff from low traffic volume highways. In-field automated sampling and data collection of storm water runoff from a 30,000 average daily traffic highway in Fairfield County, Ohio, was completed for 65 rainfall events from October 1996 to November 1997. The runoff area consisted of two inner lanes of a four-lane highway, composed of 1166 square meters of asphalt, which drained to 290 square meters of vegetated median (a total drainage of 1456 square meters). The runoff was collected in a median drain that flowed by conduit to the highway drainage ditch. In situ data collection included rainfall volume and frequency, conduit flow rate, and temperature, conductivity, pH, and dissolved oxygen in the runoff. In addition, up to 24 individual aliquots of runoff were sampled during each rainfall-runoff event and analyzed for metals, total suspended solids, and chemical oxygen demand. During 29 rainfall events, flow proportioned composite samples of sheet flow from the highway embankment adjacent to the conduit were collected and analyzed. Analysis of results indicated that the storm water runoff contained significant concentrations of metals, suspended solids and chemical oxygen demand. Particularly, concentrations of copper, iron, lead and zinc in the runoff violated Ohio Water Quality Standards. Violations were lessened by the high hardness content of the runoff. Partitioning analysis of runoff conveyed from the highway median indicated metals were predominantly (> 60 percent) dissolved. As expected, first flush storm water concentrations were the greatest. No correlation of contaminant concentrations, based on event mean concentrations, to number of antecedent dry days was noted. Analysis of one snowfall event indicated that suspended solids, chemical oxygen demand, and metal concentrations declined exponentially with distance from the edge of the pavement. Contaminants in the runoff that had passed through a grassy median had significantly lower concentrations than runoff coming directly from the pavement over the highway embankment. Contaminated runoff from high volume traffic corridors has been of sufficient concern to warrant mitigation. Based on the concentrations of suspended solids, chemical oxygen demand, and metals contained in the runoff, this study indicated that consideration should be given to mitigating first flush storm water runoff from low traffic volume highways in situations where receiving water quality would be compromised.