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Data Resources & Tools
EPA has developed a variety of tools and methodologies to evaluate effluent discharges. As part of the biennial planning process EPA primarily reviews wastewater discharge data from two EPA databases.
We used these databases in our biennial planning because of their nationwide coverage, relative accessibility, ability to link the source with the pollutant discharge, and the important types of toxic releases that they cover.
EPA also maintains a Toxic Weighting Factor Database containing aquatic life and human health toxicity data, as well as physical/chemical property data, for more than 1,900 pollutants compiled from over 100 references. The pollutants in this database are identified by a unique Chemical Abstracts Service (CAS) number. Toxic weighting factors (TWFs) calculated from these data account for differences in toxicity among the pollutants of concern and provide the means to compare mass loadings of different pollutants on the basis of their toxic potential. For example, a mass loading of a pollutant in pounds per year (lb/yr) may be multiplied by a pollutant-specific weighting factor to derive a "toxic-equivalent" loading (lb-equivalent/yr). EPA then ranks industries according to the amount of toxic pollutants in their wastewater. A detailed discussion of the Toxic Weighting Factor Database can be found in Toxic Weighting Factor Development in Support of CWA 304(m) Planning Process (PDF) (104 pages, 1.1MB, About PDF).