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Stormwater from roadways could have negative effects on the environment. Typical highway runoff pollutants include heavy metals, petroleum hydrocarbons, gasoline constituents, PAHs (polyaromatic hydrocarbons), oxygen demanding compounds measured as COD (chemical oxygen demand) and BOD (biochemical oxygen demand), and road salts.
The objectives of this research were: characterize the pollutants in roadway runoff and determine the effectiveness of the existing stormwater BMPs at the study site. To accomplish these objectives, eleven rainfall events were sampled from November 2008 through November 2010.
First flush and composite highway runoff samples were analyzed for heavy metals, anions, nutrients, particulates, BOD, COD, VOCs, and SVOCs. In addition to the concentrations, event loads were calculated using the hydrologic information from the study site. The results were compared to the Nebraska standards for water quality to establish which contaminants could have a negative impact in the environment. Additionally, an assessment of the effectiveness of the existing detention basin was completed, using the pollutant loads from the different outlet pipes.
Heavy metals, especially copper and zinc, total suspended solids (TSS), total dissolved solids (TDS), biological oxygen demand (BOD), and chemical oxygen demand (COD) were found to be the primary contaminants from the highway runoff. The current detention basin seems to be somewhat effective to reduce pollutant loads from small rainfall events. However, if pollutant reduction for all type of rainfall events is required, the basin should be modified into an extended detention basin which would provide better removal efficiency.