Development and Testing of a Partial Exfiltration Trench for In Situ Treatment of Highway Drainage

Urban roadway drainage often contains high concentrations of anthropogenic metal elements, solids, and organic compounds. Metal elements and solids accumulate on the pavement surface between precipitation events and are transported to surficial soils, receiving waters, and ground-water by pavement drainage. A report is provided on the design and performance of a bench-scale and prototype in situ control strategy, called a partial exfiltration trench (PET). The PET serves as a modification to the current practice of pavement underdrainage, providing a water quality function, in addition to water quantity control. The water quality modification functions by immobilizing infiltrated metal elements within the PET. The PET utilizes sand modified with an oxide coating (OCS). Bench-scale PET simulations were utilized to evaluate PET feasibility and breakthrough capacity. Results indicate OCS capacity for zinc, cadmium, lead, and copper was significantly improved as the pH increased from 6.5 to 8.0. Based on characteristic metal loadings from urban Cincinnati pavement drainage, bench-scale PET performance indicates that the design life of a PET may exceed 15 years in a humid climate. Performance of a prototype PET installed along an urban Cincinnati highway indicates metal element mass removal efficiency is generally greater than 80 percent after nearly 1 year of pavement drainage loadings.