Regional Wastewater

In metropolitan Washington, there are over 37 different municipal wastewater treatment plants (WWTPs) serving the wastewater needs of the region with a combined treatment capacity of over 780 million gallons per day (mgd). Overall, approximately 90 percent of the region’s population are served by these WWTPs, with the remainder served by on-site/septic systems. Eighteen of those are considered locally as major WWTPs (i.e., at least 2 mgd in design capacity) that utilize highly advanced, state-of-the-art treatment processes and meet some of the most stringent treatment and permit requirements in the nation.  

Blue Plains is the largest wastewater treatment plant in the metropolitan Washington region, and the largest advanced treatment facility in the world. The plant, which is located in the District of Columbia and operated by DC Water, accounts for approximately 48 percent of the region’s current wastewater treatment capacity, serving millions of residents, businesses, and visitors in its multi-jurisdiction service area. Blue Plains is permitted to discharge an average of 370 million gallons a day (mgd) to the Potomac River.

COG supports its member governments and wastewater utilities by providing extensive monitoring and analysis on a wide range of issues that impact or may have implications for the COG Region’s WWTPs and their biosolids programs. This support includes providing briefings and presentations, as well as regular forums for the Water Resources Technical Committee (WRTC) to discuss technical issues and to develop policy recommendations for the Chesapeake Bay and Water Resources Policy Committee (CBPC).  Currently this support also includes very active engagement in EPA’s Chesapeake Bay Program restoration efforts – which have significant regional implications for the region’s water quality, wastewater, biosolids and stormwater programs. 

COG also provides specialized wastewater support to the parties of the Blue Plains 2012 Intermunicipal Agreement.

Wastewater Treatment Advances and Improved Water Quality

The fundamental purpose for wastewater treatment is to protect human health and to improve and restore water quality.  Originally those processes at WWTPs focused on reducing biodegradable pollutants and solids in the (liquid) wastewater before the treated effluent is discharged to the environment - through what is known as secondary and tertiary treatment processes.  However, starting in the early 1970s and continuing through today, the region’s major WWTPs have been continuously upgraded to ‘advanced’ levels of wastewater treatment – primarily to increase the degree to which their facilities remove nutrients (phosphorus and nitrogen) and other sources of pollution from their effluent. 

Originally, phosphorus was the major nutrient concern because of its role in stimulating harmful levels of algal bloom in the freshwater portion of the Potomac estuary. Together with a ban on phosphates in detergents in the mid-1980’s, additional phosphorus controls at the region’s WWTPs to meet strict permit requirements has reduced the amount previously discharged by about 96 percent. The result of all of those treatment process improvements directly led to the significant water quality improvements seen in the upper, tidal portions of the Potomac River.  Those phosphorus controls still achieve limit-of-technology treatment levels today.

Then beginning in the 1990’s, in response to additional permit requirements aimed at restoration of the Chesapeake Bay and its tributaries, like the Potomac River  - the region’s major WWTPs began to focus on reducing discharges of nitrogenThe first round of such reduction efforts, known as biological nutrient removal (BNR), reduced wastewater loadings by about 44 percent from previous levels. More recently, the plants have begun to install another round of nitrogen removal technologies, i.e., enhanced nutrient removal (ENR) or state-of-the-art (SOA); limit-of-technology processes which have already begun to result in significant reductions in nitrogen discharged to the Potomac River and the Bay.  Those nitrogen reductions by the WWTPs in the region are representative of the great success of the wastewater sector to meet their strict permit requirements and achieve its nutrient reduction goals under the 2010 Chesapeake Bay Total Maximum Daily Load or TMDL (a pollution diet for the Bay and region’s waterways) by the year 2025 goal.  In fact, reductions in wastewater nutrient loadings represent the greatest achievement in the over 30-year history of the Chesapeake Bay restoration effort.  To date, no other source of pollution has achieved anything close to the levels of nutrient reduction produced by WWTPs.  And although overall water quality in the Bay remains mixed, it is possible to document the impact of these reductions in wastewater pollutants on improved water quality in the Potomac River, particularly in the upper Potomac estuary into which almost all of the Washington region’s plants discharge their effluent.  In fact, monitoring efforts here have shown improvements in dissolved oxygen levels, a reduced incidence and severity of harmful algal blooms, and rebounding populations of several critical living resources, including submerged aquatic vegetation and American shad.