Department of Energy and Environment (DOEE)
Apex, Low Impact Development Center, Michael Baker, Inc., Nspire Green, Peer Consultants
LimnoTech, along with several partners, developed a Consolidated Total Maximum Daily Load Implementation Plan (hereafter TMDL IP) to address all waste load allocations (WLAs) assigned to the District of Columbia (District) MS4 discharges. We also developed a Revised Monitoring Plan to ensure MS4 permit compliance, to evaluate MS4 program effectiveness, and to help inform management decisions.
The MS4 area within the District contains over 600 stormwater outfalls that drain approximately 20,000 acres. Like all major cities, the District has a MS4 permit with obligations to manage urban stormwater. The current permit requires a TMDL IP for all of the TMDL WLAs assigned to District MS4 discharges. Development was challenging as more than 380 WLAs are assigned to the MS4 for 23 different pollutants across 45 different water bodies. The landscape is further complicated by the presence of a substantial amount of federal property, persistent legacy pollutants, and the fact that upstream sources outside the District represent a major source of pollutants that affect water quality. A Revised Monitoring Plan was also needed to ensure data could be used to characterize pollutants in stormwater runoff and evaluate the overall effectiveness of the MS4 program.
LimnoTech worked with DOEE and the project partners to find effective and affordable ways to prioritize pollutant removal and protect water quality. In order to find the best solutions for developing a solid and science-based TMDL IP and Revised Monitoring Plan, our evaluation included:
- Careful review of the adequacy of supporting data used to list the impairments that brought about the TMDLs and WLAs.
- Linkage of pollutant removal to the 1.2 inch storm retention standard.
- Assessment of future development and redevelopment trends.
- Consideration of BMPs and source control methods capable of reducing multiple pollutants.
- Development of a city-wide, custom modeling tool to account for and track pollutants and pollutant reduction
As a result of our work, the TMDL IP and Revised Monitoring Plan were developed over a 30-month span. The TMDL IP relies on a comprehensive and custom modeling tool designed by LimnoTech that allows ease in forecasting, tracking and reporting progress on reductions of MS4 stormwater pollution. The work conducted by LimnoTech helped DOEE make decisions on where to focus their limited resources and provided them with a path forward to attain MS4 WLAs.
The Revised Monitoring Plan was developed to meet the following objectives: ensure compliance with MS4 monitoring requirements; evaluate MS4 program effectiveness; and provide support for any recommended changes in MS4 program activities. The revised plan represents a shift away from previous monitoring that was largely centered on the characterization of pollutants in stormwater runoff, but now focuses on a more holistic view and use of the monitoring program.
LimnoTech also supported DOEE’s formation of a stakeholder group composed of regulators, non-governmental organizations and environmental groups, other City agency staff, and internal DOEE staff to ensure that the TMDL IP and the Revised Monitoring Plan were developed in an open and transparent way. As a result, regulator support for the TMDL IP and Revised Monitoring Plan was strengthened.
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