It has long been recognized that highway runoff contains pollutants that may be detrimental to receiving waters. A popular approach for improving the quality of highway runoff is wet detention ponds. Two wet detention ponds in Washington State were monitored from September 1997 to May 1999 for pollutants typically found in highway stormwater runoff. Monitoring activities included stormwater influent and effluent sampling, water column and sediment column sampling, and surveying. Constituents of concern specifically analyzed included total and soluble metals, nutrients, basic water quality parameters, total petroleum hydrocarbons, polycyclic aromatic hydrocarbons, chlorophyll a, and general toxicity.; Pollutants were characterized with respect to time, space, and phase to determine fate and transport within the ponds prior to discharge into receiving waters. Next, relationships between influent and effluent concentrations of those pollutants were analyzed to determine treatment efficiencies and potential control within detention ponds. Last, rate, volume, and distribution of sedimentation and associated metals were analyzed to determine impacts on pond flood control capacity and sediment quality. This information was applied to pond function and operation to develop improved methods for designing efficient wet detention ponds to treat highway stormwater runoff.
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