Prince George's County

Sanitary Sewer Overflows (SSOs)

Sanitary sewer systems collect and convey domestic, commercial, and industrial wastewater, along with limited amounts of stormwater and infiltrated groundwater , to treatment facilities for processing. Sanitary sewers are distinct from combined sewer systems, which are designed to collect and transport large volumes of stormwater in addition to sewage and industrial wastewater. Under certain conditions, sanitary sewer systems may discharge untreated sewage. These discharges, known as sanitary sewer overflows (SSOs), can degrade water quality, pose risks to public health, and cause sewage backups in homes and businesses, resulting in property damage.

Common causes of SSOs include:

  • blockages within the collection system;
  • pipe failures or line breaks;
  • structural defects that allow stormwater or groundwater to infiltrate and overload the system;
  • power outages affecting pump stations;
  • inadequate or improper system design; and
  • vandalism.

The U.S. Environmental Protection Agency (EPA) estimates that between 23,000 and 75,000 SSOs occur annually in the United States, excluding sewage backups into buildings. Prince George's County (the County) monitors SSOs in and upstream of the county. Significant recent SSOs are reported on below. For a historical record of past SSOs in the area, see the "SSOs" tab at the bottom of the dashboard. 

Potomac Interceptor Sewage Spill

On January 19, 2026, a section of the Potomac Interceptor sewer line collapsed near the Clara Barton Parkway in Montgomery County, MD, releasing untreated sewage into the Potomac River. The Potomac Interceptor carries approximately 60 million gallons of wastewater daily to the Blue Plains Advanced Wastewater Treatment Plant in Southwest DC for treatment. Multiple government agencies are coordinating repairs and environmental monitoring. Together, they have developed a Potomac Interceptor Monitoring Data Dashboard dedicated to compiling E. coli testing from DC Water, DC Department of Energy & Environment (DOEE), Maryland Department of the Environment (MDE), Virginia Department of Environmental Quality (VADEQ), and the Potomac Riverkeeper Network with University of Maryland (UMD). The County is also conducting its own monitoring at National Harbor and Fort Washington Marina. Sampling locations and results from the County can be seen in the dashboard below. 

Bacteria 

Certain types of pathogenic bacteria, such as fecal coliform bacteria, act as pollutants when they enter surface waters through contaminated wastewater or runoff from agricultural, urban, or industrial sources. Bacterial pollution, which can lead to waterborne diseases, threatens human health and aquatic life. Fecal coliform bacteria are known to cause illness in humans when ingested through activities like swimming and wading or during consumption of shellfish. The County focuses on monitoring E. coli-a type of fecal coliform bacteria.

The Maryland Department of the Environment (MDE) classifies waterbodies in the state based on the waterbody’s existing conditions and the designated uses for the waterbody. The table below presents Maryland’s thresholds for bacteria impairment for two types of Class 1 waters (i.e., Water Contact Recreation, Fishing, and Protection of Nontidal Warmwater Aquatic Life, including fish [other than trout], agricultural and industrial water supply). For E. coli, MDE lists a waterbody as impaired if the steady-state geometric mean is greater than 126 MPN/100 mL in freshwater (MPN indicates the most likely number of bacteria present in a 100-milliliter portion of the sample). For the enterococci group of bacteria, MDE lists a waterbody as impaired if the steady-state geometric mean exceeds 35 MPN/100 mL for either freshwater or marine/estuarine waters.

Maryland bacteria water quality criteria for Class I waters (COMAR 26.08.02.03-3).

IndicatorSteady-State Geometric Mean Indicator Densitya      Statistical Threshold Valueb      Waterbody Type
E. coli126 MPN/100 mL410Freshwater
Enterococci      35 MPN/100 mL130Freshwater, Marine/Estuarine

Notes:

MPN=most probable number; mL=milliliters.

a The geometric mean of samples taken over a 90-day period shall not exceed the steady-state geometric mean values for the given indicator.

b 10% of samples taken over a 90-day period shall not exceed the statistical threshold value.

The County has three watersheds (i.e., Anacostia River, Piscataway Creek, and a portion of the Upper Patuxent River) that have total maximum daily loads (TMDLs) for exceedances in bacteria-related water quality standards. To move forward in meeting these goals, the County supports ongoing programs centered on bacterial source tracking and monitoring, as outlined in the County’s Bacteria TMDL Stormwater Wasteload Allocation (SW-WLA) Watershed Implementation Plan.

Dashboard Instructions 

Features

  • Use the filter bar, located at the top right of the screen, to refine data based on water quality constituent(s), subwatershed(s), and year(s) collected. Upon clicking the themed filter box, select one or more option from the drop-down menu. Data displayed in the map and tables will then update based on selection. Please note:
    • Filters from multiple themes can be selected at the same time. 
    • Due to the nature of the datasets, biological and stream monitoring data has been separated from the rest of the water quality constituents and is located in its own filter box (to the right of "Water Quality Constituent(s)).  
  • Use the vertical menu bar in the upper right of the map to customize the map.
    • To view the full menu and descriptions of the icons, click on the Expand icon (double arrows) at the bottom of the vertical menu (the last icon).
    • To view the list of symbols and their meanings, click on the Legend icon (bullet points). 
    • To change the preset view, click on the Bookmarks icon (bookmark). 
    • To view the different map layers, click on the Layers icon (stacked boxes). Hidden layers will have crossed-out eye icons, whereas visible layers will not have an icon present. 
    • To change the basemap, click on the Basemap icon (four small squares) and select from the options.
  • To move around the map, click and hold the cursor on the map, then drag it to see different areas. To zoom in, double click on area of interest on the map. There are also Zoom in (plus symbol)/Zoom out icons (minus symbol) located at the bottom right of the map.
  • To reset the entire dashboard to its preset layers and features, including the map, click the Reset icon (circular arrow) located in the lower right-hand corner of the dashboard. 

How to use

The map and tables (dashboard) show all available data for all water quality constituents. To select the constituents discussed above, click on the "abcd" filter and select the relevant one from the dropdown options. The dashboard should update automatically to show relevant monitoring stations (Station IDs). 

To explore the data using the map:

  1. Zoom in on a monitoring station and click on it.
  2. A pop up text box will appear showing a data summary for each constituent. 
  3. Use the left/right arrow icons at the top left of the pop up box to scroll through all records. Please note: Arrows are only present when the selected Station ID has data for more than one filtered constituent.
  4. To zoom in further on the station from the pop up box, click the magnifying glass icon in the top right corner (below the Station ID name). 
  5. Zooming in on the map will also filter the list of Station IDs in the table on the top right of the dashboard to show only those stations visible in the map extent.

To explore the data using the tables:

Select the "SSOs" tab at the bottom of lower table.