Facilities are required to report the quantity of Toxics Release Inventory (TRI) chemicals they release to receiving streams or other water bodies.
The following graph shows the trend in the pounds of chemicals released to water bodies as reported to TRI.
From 2007 to 2017:
- Surface water discharges decreased by 20% (49 million pounds). Most of this decline is due to reduction in releases of nitrate compounds to water, which decreased by 21% (44 million pounds).
- Nitrate compounds are often formed as byproducts during wastewater treatment processes such as when nitric acid is neutralized, or when nitrification takes place to meet standards under EPA’s effluent guidelines. Nitrate compounds are released to water in quantities that are larger than any other TRI chemical released to water.
- Surface water discharges are often regulated by other programs and require permits such as the Clean Water Act National Pollutant Discharge Elimination System (NPDES) permits.
- Nitrate compounds alone accounted for 90% of the total quantity of all TRI chemicals discharged to surface waters.
The following graph shows the trend in the RSEI Scores for chemicals released to water bodies as reported to TRI.
- The biggest contributor to RSEI water scores is arsenic compounds.
- The high RSEI score for water discharges in 2008 includes a large one-time release of arsenic compounds due to a coal fly ash slurry spill, and a release of benzidine, which has a relatively high toxicity.
- For a complete, step-by-step description of how RSEI derives RSEI Scores from surface water discharges of TRI chemicals see “Section 5.4 Modeling Surface Water Releases” in Chapter 5 (“Exposure and Population Modeling”) of EPA’s Risk-Screening Environmental Indicators (RSEI) Methodology, RSEI Version 2.3.6.
- For information on how RSEI Scores are estimated, see Hazard and Potential Risk of TRI Chemicals.
This page was published in March 2019 and uses the 2017 TRI National Analysis dataset made public in TRI Explorer in October 2018.