Constructed Wetlands for Nonpoint Source Pollution Control

About the report:

Wetland mitigation and stormwater management provisions in the 1987 Clean Water Act (CWA) significantly impact transportation agencies. CWA Section 404 stipulates that when highway construction results in the displacement of natural wetlands, the highway agency is required to create artificial wetlands to compensate for that loss. Section 402 directs the U.S. Environmental Protection Agency (EPA) to regulate stormwater runoff from certain areas under the National Pollutant Discharge Elimination System (NPDES). Highway stormwater runoff, runoff from road construction sites with five or more disturbed acres, and runoff from maintenance and storage facilities are subject to NPDES permit requirements. In addition to the EPA regulations, the Virginia Department of Transportation (VDOT) must also comply with the Chesapeake Bay Preservation Act, Virginia's Stormwater Management Regulations, and State Erosion and Sediment Control Regulations. A common requirement of all of these stormwater regulations is the use of best management practices (BMP), such as detention ponds and infiltration for the control of runoff quantity and quality. To date, VDOT has constructed over 220 wetlands and more than 350 stormwater detention basins. Wetland mitigation is a significant item in the VDOT road-building budget. Compliance with applicable stormwater regulations can add between ten and fifteen percent to the cost of an average construction project. A potentially cost-effective approach to satisfying wetland mitigation requirements and stormwater regulations is the use of mitigated wetlands as stormwater BMPs. It is believed that if a mitigated wetland site is properly engineered and maintained, it will perform adequately as a stormwater BMP without jeopardizing its desired wetland functions. It may also be possible to design a detention basin to include emergent wetland vegetation to enhance pollutant removal.

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