DEVELOPMENT AND EVALUATION OF BEST MANAGEMENT PRACTICES (BMPS) FOR HIGHWAY RUNOFF POLLUTION CONTROL

As non-point source pollution, storm water runoff is one of the main contributors to stream impairment in the United States. The United States Environmental Protection Agency (USEPA) requires Municipal Separate Storm Sewer Systems (MS4s) to obtain a permit under the National Pollution Discharge Elimination System (NPDES) to manage this pollution. Many municipalities and non-traditional MS4s such as the Nebraska Department of Roads are under federal regulations that require new developments or redevelopments of a certain size to capture (and treat) runoff from all new impervious surfaces (roofs, driveways, sidewalks, and so forth) onsite, instead of allowing it to run into the sewers or nearby waterways. To do this structural Best Management Practices (BMPs) are often used to treat the first half-inch of runoff which is commonly considered to contain the majority of pollutants from those sites. The objectives of this research were to: a) develop and test the feasibility of roadside BMPs that rely on bioretention, infiltration, and slow conveyance of storm water, b) test combinations of plants and soil media that will be sustainable in varied regions of Nebraska, and c) test the feasibility of using rubber chips as an alternative BMP medium. Four roadside field-scale BMPs were tested: 1) check dam filters, 2) bioretention, iii 3) infiltration trench, and 4) filter trench. Clogging was experienced by all BMPs except the bioretention; little hard data was collected due to a dry summer. Four bioretention test cells with different media types were monitored for plant establishment. It was found that a 50/50 mixture of compost and 47-B gravel had the best plant growth. Four types of rubber chip mediated soil mixtures were tested in lab bench-scale testing for physical properties related to plant growth and infiltration as well as storm water treatment effectiveness. It was found that a 50/50 mixture of rubber chips and sand had the best treatment, but lacked the best qualities for plant growth and may require addition of compost. Advisor: Tian C. Zhan