Working to meet anticipated National Pollutant Discharge Elimination System (NPDES) permit requirements, the Frederick County Office of Sustainability & Environmental Resources identified the Peter Pan subwatershed as a site for potential stormwater retrofits. KCI conducted an assessment of 16 stormwater management facilities to evaluate retrofit opportunities and feasibility, estimate the pollutant removal and impervious treatment credits, and prioritize the sites.
The design approach was driven by the overall project goal to improve the amount of stormwater quality treatment that could be provided within the pond footprints. Our team assessed the current condition of the ponds, including the type of overall condition of the facility. Where it was easily accessible, the downstream channel was inspected to identify any channel erosion problems immediately downstream. The field work assessment was also designed to evaluate retrofit opportunities and feasibility by identifying site constraints that would prevent certain types of improvements from being implemented, or opportunities that would make others more likely to be successful.
We had to develop a way to estimate the pollutant load reductions for the proposed retrofits, even as the guidelines changed mid-stream, so we worked on-the-fly, which resulted in the client earning more credit under the new rules.
Bill Frost, PE, D.WREWatershed Planner
During the course of the project, the Maryland Department of the Environment changed how stormwater management facilities would receive pollutant removal credit for TMDL compliance and impervious treatment credit for the NPDES permit goal. The project team reviewed and accommodated the changes without the need for additional funding, much to the county’s appreciation.