The Blue Plains Wastewater Treatment Plant in Washington D.C. is the largest advanced wastewater treatment plant in the world. The District of Columbia’s Water and Sewer Authority (WASA) operates the plant. LimnoTech’s expertise in sewer system and river modeling helped WASA make decisions about two complex programs: combined sewer overflow (CSO) control to improve local water quality, and nitrogen removal to help restore Chesapeake Bay.
To meet the Chesapeake Bay Program’s nutrient reduction goals, EPA Region 3 added strict nitrogen limits to the NPDES permit for the Blue Plains facility. WASA needed to determine how to integrate these new permit conditions into its wet weather management program for CSOs.
Working as an integral member of WASA’s program management contractor team, LimnoTech applied collection system and tunnel models to simulate different flow management scenarios and their effectiveness in complying with the modified permit. LimnoTech simulated extending the proposed Anacostia Tunnel an additional three miles to Blue Plains and adding an enhanced clarification facility. Four alternatives were modeled, including evaluations of real time controls and configurations that explored the possibility of de-rating (reducing the plant flow) so that nitrogen removal could be done more efficiently at the plant.
LimnoTech’s work allowed WASA to produce a supplement to its original CSO Long Term Control Plan that incorporated extension of the tunnel and reduction of the plant’s peak capacity from 740 to 555 mgd, with increased nitrogen removal. The new plan provided a higher level of water quality than the original plan and saved WASA over $500 million in capital costs.