The Function and Effectiveness of Engineered Ditch Filter

Roadside ditches have the potential to transport a variety of pollutants from within and outside of the road right of way. As flows concentrate in roadside ditches, there is an increased likelihood that pollutants will reach a surface water resource. Surface water degradation from concentrated ditch flow has been well documented. Road maintenance and construction best management practices installed focus primarily on erosion control on the shoulder, inslope, ditch bottom and backslope. Effective erosion control in these areas is essential but there is generally little attention paid to post-construction pollutant treatment within these swales. Increasingly, sediment control and stormwater quantity and quality best management practices (BMPs) are being required to control pollutants of concern in sensitive areas. In narrow linear rights of way along roadsides, engineered filter systems provide a unique opportunity for stormwater treatment. Compost/mulch and sand underdrain filters could be built in the field by DOT personnel given the right site conditions and design but function and effectiveness have not been documented in Maine. The project will consist of field sampling of flow rates and flow-weighted composite samples of inflow and outflow of a constructed ditch filter system(s). Samples will be taken for a number of storm events and composite samples will be analyzed for pollutants of concern. Attempts will be made to capture samples during a variety of precipitation intensities and antecedent soil moisture conditions.