EJScreen Indicators Overview – Wastewater Discharge

What is the wastewater discharge indicator?

The “wastewater discharge indicator” measures how much relative risk there is of being exposed to pollutants from wastewater that flows into rivers or other bodies of water downstream. This relative risk is based on estimated concentrations of pollutants in downstream water bodies which EJScreen presents using percentile rank, ranging from 0 (lowest) to 100 (highest) with higher scores representing higher relative risks.

Why is wastewater discharge important?

• The NPDES permit program established by the Clean Water Act (CWA) addresses water pollution by regulating point sources that discharge pollutants to waters of the United States. There are approximately 6,700 major direct dischargers in the U.S. These facilities discharge around 50 billion pounds of pollutants each year directly into the nation’s streams and rivers (including conventional pollutants such as nitrogen and phosphorus).
• Water pollutants can have adverse human health or ecological effects depending on concentration in the water, exposure to the water, toxicity of the specific chemical, and other factors. People may be exposed to the discharged pollutants either directly or through indirect pathways. People swimming in the downstream waters or engaging in water-based recreation may be directly exposed through the skin, mouth, or by breathing in the volatile substances.
• If the released substances reach a downstream drinking water intake, consumers of the finished waters may consume whatever portion of the substances is not removed by the drinking water utility. Some portion of the discharged materials may enter the groundwater of neighboring areas and reach people through drinking water derived from wells that draw upon that aquifer.

How does EJScreen create the wastewater discharge indicator?

• The wastewater discharge indicator utilizes pollutant loadings from the Discharge Monitoring Report (DMR) Loading Tool along with the Risk-Screening Environmental Indicators (RSEI) model to estimate concentrations of pollutants in downstream water bodies and derive a toxicity-weighted concentration.
• The wastewater discharge indicator includes all National Pollutant Discharge Elimination System (NPDES) facilities with pollutant loadings greater than zero.
• To place higher emphasis on stream reaches with higher toxicity-weighted pollutant concentrations, the toxicity-weighted value for all stream reaches within 10 km of a census block centroid is divided by the distance in meters to the census block centroid to create a weighted proximity value indicating a block’s risk of exposure to pollutants in the stream reaches.
• For technical details on the calculations and source data, visit the EJScreen Technical Documentation.

Moving Forward – What You Can Do

• Stay informed on the latest relevant information and resources on the EPA Source Water Protection website.
• Help protect drinking water sources at the local level.
• Search for facilities in your community to assess their compliance with wastewater and other environmental regulations on the EPA’s Enforcement and Compliance History Online (ECHO) website.
• Search for facilities and wastewater dischargers in your community with the EPA’s Water Pollutant Loading Tool and TRI Toxics Tracker.
• Explore detailed information about the conditions of your local waters on the EPA How’s My Waterway Tool.