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Characaterization of Highway Runoff in the Austin, Texas AreaBy Michael E. Barrett, M.S., Joseph F. Malina, JR., P.E., Randall J. Charbeneau, P.E., George H. Ward, Ph.D. ABSTRACT Water quality of highway runoff in the Austin, Texas area was determined by monitoring runoff at three locations on MoPac, which represented different daily traffic volumes, surrounding land uses, and highway drainage system types. The highest concentrations of all constituents were measured at the high traffic site. The concentrations at all sites were similar to median values for similar sites compiled in a nationwide study of highway runoff quality. Little adverse impact would be expected for all but the most sensitive receiving waters based on the quantity and quality of highway runoff generated during storms. The water quality of highway runoff is generally similar to that reported for urban runoff, and does not contain appreciably higher concentrations of toxic metals or oil and grease. The impacts of highway runoff alone, like many other nonpoint sources of pollution generally are not significant when considered singly, but may result in degradation of water quality when combined with other sources such as urban runoff. The effectiveness of grassy swales for treating highway runoff was evaluated by comparing the runoff at one of the sites, before and after passing across a swale. The grassy swale proved effective for reducing the concentrations of most constituents in runoff. The low runoff coefficient due to infiltration of runoff into the swale produced a large reduction (90%) in pollutant load discharged. This reduction of runoff volume effectively reduces the impact of constituents whose concentrations are not reduced by the swale. A first flush effect (i.e., higher pollutant concentrations at the beginning of an event) was very evident during selected events, but was generally limited to a small volume. When all monitored events were considered, the overall effect was small or negligible. In considering the potential effectiveness of storm water treatment systems, constant concentrations for individual storm events should be assumed.. The highlighted links that follow are connected to Adobe pdf files of the corresponding material. To view them you must have the Adobe Acrobat Reader 3.0. View the Whole Report...(180Kb) |
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