Evaluating Stormwater Compliance Through Best Management Practices and Water Quality Trading in Virginia

Stormwater has been recognized as a significant source of pollution and flooding which is aggravated by the increase in urbanization. During rainfall events, surface runoff washes nutrients and other pollutants into receiving waters. Impervious urban surfaces prevent infiltration and shorten the time required for runoff flows to peak, resulting in increased runoff volume and peak flows that lead to flooding. Best management practice facilities (BMPs) are commonly constructed to treat and control stormwater to meet regulatory requirements. Alternatively, water quality trading (WQT) may be allowed to achieve compliance. Under this option, regulated stormwater entities can purchase credits, representing reduced nutrient load resulting from mitigation achieved offsite by another party, to meet their stormwater regulatory requirements. However, our understanding of how compliance is achieved given the influence of Virginia’s active WQT program is not well understood.

This dissertation advances our understanding of 1) how stormwater compliance is achieved in practice, 2) the associated challenges of achieving compliance, and 3) identifies opportunities for reducing compliance costs using the Virginia Department of Transportation (VDOT) and the City of Roanoke as case studies. The first study uses BMP inspection and condition rating data from the VDOT to describe quantitatively how basin-type BMP conditions change over time, the condition issues that influence condition changes, and compares those condition issues with issues identified for basins experiencing rapid decline in condition. The second study compares site characteristics and stormwater quality and quantity compliance choices for development projects in Roanoke. This was achieved using a novel dataset collated from data harvested from land development project documentation stored in Roanoke’s permit tracking database. The third study develops GIS-based methods for calculating spatially explicit upper-bound estimates for WQT credits. The study applies the methodology on VDOT’s 6-year improvement projects and compares VDOT’s estimated credit needs with current credit supply levels in Virginia.

Key findings from this dissertation are (i) conditions of basin-type BMPs can fluctuate annually despite regular inspection and maintenance practices, as observed by nearly half of VDOT’s basin-type BMPs that had three consecutive years of inspections (ii) the occurrence of rapidly declining basin-type BMPs is due to few, specific issues that may or may not differ from the most frequently noted issues corresponding with conditions of basins with the same declined state and irrespective of differences in individual VDOT district management practices (iii) nutrient credits, influenced by comparative lower costs, are the preferred method for achieving stormwater compliance by land developers in Roanoke, Virginia; however, water quality issues may be of concern due to the ubiquitous practice of downstream trading observed (iv) current credit supplies across much of the Commonwealth of Virginia are likely adequate to support upper-bound estimates of credit need for VDOT’s 6-year improvement projects; however, the results of the applied methodology indicate the southwest region of Virginia does not currently have adequate credit supply to meet VDOT’s estimated credit needs. The findings of this dissertation serve to inform practitioners, regulatory program managers, and researchers of current challenges of meeting stormwater regulations using BMPs and provides considerations and methods for supporting environmental integrity and participation in WQT.