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Interactive Map: Potomac Wastewater Mapper

March 6, 2023


Treated wastewater effluents are discharged into the Potomac River watershed at multiple points across the basin, which encompasses Washington, D.C. and parts of Virginia, West Virginia, Pennsylvania, and Maryland. Though treated and within regulated levels, effluent may still contain biologically active contaminants introduced through domestic and industrial activities. These contaminants often occur in trace amounts and are highly diluted; however, many synthetic organic compounds found in wastewater, such as pesticides and pharmaceuticals, are selected for their potency even in trace amounts, resulting in adverse effects following exposure even at low concentrations. Further, complex in-stream mixtures of wastewater contaminants have been shown to increase the risk posed to aquatic organisms. Streams may be especially vulnerable to these contaminants during low-flow conditions when in-stream dilution is reduced.


Runoff and wastewater contaminant form complex chemical mixtures in rivers, leading to negative effects of aquatic health.
Treated wastewater represents just one source of contaminant loading in rivers. Holistic integrated approaches are needed to assess the perceived versus actual risk posed to aquatic organisms and human health from exposure to complex chemical mixtures derived from wastewater and other sources.


About This Tool

Image: Potomac River
Stream flowing into the Potomac River in Whites Ferry, Virginia.

The Potomac Wastewater Mapper shares results from a wastewater modeling approach explained in additional detail by Faunce and others (2023; available under "Publications"). The underlying model used data compiled from a combination of public and literature-derived sources to calculate the following estimates for each stream reach in the Potomac River watershed: (1) accumulated wastewater as a percent of total streamflow (ACCWW%) for municipal-plus-industrial effluent discharges; (2) a risk index representing the predicted ecological risk posed by a complex chemical mixture of municipal effluent-derived contaminants. Model estimates at a stream reach represent the combined total upstream wastewater discharges as well as direct discharges into the segment. The model also accounts for dilution and instream decay of contaminants during transport.

The tool is intended to provide a screening-level assessment of wastewater and associated toxic contaminants in the watershed. It may be used to help identify streams that may require further attention by resource managers, either through targeted contaminant monitoring and sampling or wastewater treatment plant upgrades to improve contaminant removal. 

For additional information:

The data shared in this tool are available in the Faunce and others (2023) data release listed under the "Data" tab of this page. The modeling approach and interpretation of results is discussed in the Faunce and others (2023) manuscript listed under the "Publications" tab of this page.