Evaluation of permeable friction course (PFC), roadside filter strips, dry swales, and wetland swales for treatment of highway stormwater runoff

Summary: Stormwater runoff from roadways is a source of surface water pollution in North Carolina. The North Carolina Department of Transportation (NCDOT) is required to implement stormwater control measures (SCMs) in the linear environment. NCDOT has specific interest in evaluating pollutant loads from interstate highways and potential stormwater treatment measures. The research presented herein focuses on monitoring of highway runoff at four sites along Interstate 40 (I-40) in Johnston, Sampson, and Duplin counties. This entire stretch of I-40 had a permeable overlay [known as a permeable friction course (PFC)] applied in November, 1998. The overlay is porous, and allows water to pass through the surface of the pavement, reducing splash during rainfall and allowing for improved vehicle traction (Barrett et al. 2006). Drainage from the PFC was monitored at all four sites to determine highway pollutant concentrations and loads. Roadside filter strips are nearly ubiquitous on highways, as they are constructed to make grade and to hydraulically connect the roadway to the roadside swale. Two roadside filter strips (21.5 ft in width) were evaluated in this study. Finally, four linear roadside swales were monitored to determine their hydrologic and water quality benefits. Two of these swales were dry swales, meaning that they drained inter-event. The other two swales had wetland characteristics, including hydrophytic vegetation, hydric soils, and wetland hydrology.

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