Municipal Separate Storm Sewer System (MS4) Permittees in Virginia, including the Pentagon, are required to comply with state-mandated pollutant load reductions as outlined in their Virginia Pollutant Discharge Elimination System (VPDES) MS4 permits issued by the Virginia DEQ. Washington Headquarters Services (WHS) is the operator of the Pentagon’s MS4 Program and is responsible for compliance with the Virginia MS4 permit. The MS4 permit requires permittees to comply with the Chesapeake Bay TMDL by reducing pollutant loads for sediment, nitrogen and phosphorus in stormwater discharges.

The Pentagon has large amounts of impervious area and several infrastructure and security challenges relating to implementing stormwater management projects. This TMDL compliance study was performed to help WHS meet their reduction goals, specifically for projects to be implemented between 2023 and 2028. A variety of stormwater management BMPs were evaluated including traditional BMPs and green infrastructure techniques.

Site assessments were performed by AECOM to evaluate the proposed Study Areas and potential green infrastructure techniques. Based on the existing data, site assessments and discussions with the US Army Corps of Engineers (USACE) Baltimore District and WHS, multiple scenarios were selected for further evaluation and conceptual design development.

Preliminary concept designs and cost estimates were developed for each of the scenarios and pollutant reduction estimates were calculated based on these designs. A prioritization matrix was then developed with weighted parameters based on stakeholder importance in order to select the preferred scenario in each Study Area and to help prioritize implementation. The prioritization criteria for the matrix incorporated the TMDL compliance goals and feedback and from multiple stakeholders.

While the design details are classified as For Official Use Only, the evaluation process, prioritization and challenges will be discussed. Coordination with various stakeholders was also an important part of this effort, as feedback, maintenance concerns, parking impacts and site constraints were incorporated early in the design process.

This study showed that there are multiple scenarios and implementation strategies that the Pentagon could implement to achieve their 2028 TMDL pollutant reduction goals. AECOM, USACE and WHS are currently completing the final design-bid-build contract packages for the selected projects.