Washington State has begun a program to dispose of highway runoff in which a priority has been given to the use of infiltration type technologies (e.g., infiltration basins, dry wells, etc.). Heavy metals are the most prevalent priority pollutant in highway runoff. Though traditionally these heavy metals are thought to possess relatively large retardation factors within the subsurface, previous studies have indicated a possibility of their transport being facilitated through complexation with natural organic matter (NOM). If ignored this form of transport may pose serious errors in the prediction of metal(s) breakthrough times and mass loadings to underlying groundwaters. In addressing this issue, soil columns were tested under loading conditions similar to actual infiltration BMP's to assess the performance of these facilities in removing heavy metals (Cd, Cu, Pb, Zn) from infiltrating water. Experiments were performed investigating the effects of high and low concentrations of NOM on metals attenuation by field soils. Results show that high concentrations of NOM actually improved soil column performance. The data revealed that metals speciation and background metals present in the soil are important factors to consider, because they can affect expected metals removal rates of soils. The hydraulics of the system played a secondary role to the geochemistry. Results suggest that infiltration can be a viable alternative in disposing of runoff at low metals concentrations. Modifications to guidelines were discussed to improve the long-term performance of infiltration facilities.
Washington State Transportation Center (TRAC)
Best practices, Drainage, Geochemistry, Groundwater, Heavy metals, Infiltration, Management, Organic content, Pollution, Runoff.