FIELD EVALUATION OF VEGETATED HIGHWAY EMBANKMENTS FOR THE RETENTION OF PAH, METALS, AND PARTICULATES IN STORMWATER RUNOFF

The overall goal of this field study was to evaluate the potential effectiveness of vegetated highway embankments as a stormwater runoff best management practice (BMP) for retention of metals, polycyclic aromatic hydrocarbons (PAHs), and particulates. The study characterized roadway sediment particulate matter, annual pollutant mass loading, and long-term pollutant retention for three field sites in eastern Kansas. The field study indicated that pollutant retention was primarily a surficial phenomenon, limited to the 0 to 5 cm depth of highway embankments. Effectiveness of vegetated embankments for net particle retention was found to be greater than 70% for particles of 0.020 mm or greater. The 5.5 m long vegetated highway embankments evaluated in this study were effective stormwater runoff BMPs for zinc with 42 to 100% long-term pollutant mass retention. Moderate performance was observed for pyrene and chrysene with 20 to 100% mass retention. Vegetative embankments were less effective for copper and benzo(a)pyrene with 9 to 42% mass retention. The key benefits of utilizing highway embankments for runoff control include cost-effectiveness relative to other engineered systems and compatibility with roadway design and maintenance requirements. While specific pollutant mass retention was observed to be variable and dependent on metal or PAH properties in runoff, the overall result is a significant reduction in pollutant mass to the local watershed, particularly when embankments are greater than 10 to 15 m in length.