Vegetated Biofilter for Post Construction Storm Water Management for Linear Transportation Projects, Executive Summary Report

摘要

The goal of this project was to examine the slope portion of vegetated biofilters to evaluate capture and treatment of the water quality volume for highway storm runoff. This goal was accomplished through the following objectives: (1) Performing a review and synthesis of the literature; (2) Conducting a survey of state DOTs; (3) Developing a biofilter foreslope prototype and conduct testing to determine: Its ability to capture the water quality volume, Its performance in removing typical roadway runoff contaminants (Its performance efficiency computed as the percent change between influent and effluent quality), The impact of its slope, The accumulation of contaminants in the foreslope soil and vegetation, The suitability of foreslope designs to accommodate different concentrations of runoff and/or intensity of storms, Potential resuspension of particles.The vegetated biofilter is a low impact development technique that can be integrated into stormwater management of linear transportation systems and capitalize on the natural environment to mitigate stormwater. A 4 ft (1.2 m) wide by 14 ft (4.3 m) long prototype vegetated biofilter was constructed on a moveable frame. Artificial runoff was delivered to each of three grass beds for comprehensive tests at slopes and flow rates as follows: 8:1, medium; 4:1, medium; 2:1, medium; and 2:1, high. The medium and high flows represented storm runoff events typical in Ohio. First, baseline tests were performed to obtain concentrations of constituents native to the biofilter. Artificial runoff, formulated with metals, native soil, and motor oil, was applied to one bed at a high concentration for the first part of the event, followed by a medium concentration; a second bed received medium followed by low concentration runoff, and the third bed received low concentration followed by tap water. During the simulated storm events, samples were obtained from the inlet, surface runoff, and underdrain and analyzed for total and dissolved metals, TSS, and oil and grease. Prior to and at the end of testing, cores were extracted from the bed, separated into soil, roots and grass, and each component analyzed for metal content per mass of material. The two beds receiving the initial high and medium concentration flow performed well and removal of 7 total metals and TSS was above 75%. Removal of oil ranged from 30% to over 90%. The bed receiving low concentration runoff, which was near the baseline levels for constituents, had mixed performance of removals ranging from none to above 90%, illustrating the difficulty of any BMP to treat a relatively clean influent. Metals above background levels were found primarily in the first half (7 ft, 2.1 m) of each bed. Soil particles in the influent flow of the first test in each bed, tagged with La, were not resuspended in subsequent tests and were not measured at any significant concentration in the outlet surface flow.