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Water: National Contaminant Occurrence Database

A Review of Contaminant Occurrence in Public Water Systems

EPA 816-R-99-006
November 1999

This study represents the Environmental Protection Agency's (EPA's) most extensive analysis to date of the occurrence of contaminants in Public Water Systems (PWSs) regulated under the Safe Drinking Water Act (SDWA). EPA's Office of Ground Water and Drinking Water conducted this study to provide a better scientific basis for considering changes to the chemical monitoring requirements in the drinking water program.

Main Report (363KB, PDF)

Appendix A. Summary Tables of Contaminant Occurrence Data
Appendix B. USGS Studies Reviewed for Contaminant Occurrence Information
Appendix C. General Data Quality Issues
Appendix D. Summary Tables V.A.1 through V.A.8


State databases, comprised of SDWA compliance-monitoring data from PWSs, were the primary data sources for this analysis. Data from 12 states were analyzed in detail. Data from 8 States were used to develop a national cross-section of contaminant occurrence. The States were selected to represent the national range of hydrologic regimes and pollution potential. The data used represent more than 10.7 million analytical results from nearly 26,000 PWSs. More than 70% of the data are from 1993 or later; reflecting the beginning of the Phase II/V requirements.

Additional sources of national data were also used, such as: EPA's Unregulated Contaminant Monitoring Information System (URCIS), which includes data from 40 States and territories from the first round of unregulated contaminant monitoring; and U.S. Geological Survey studies of ambient monitoring, including results from the National Water Quality Assessment Program Exit EPA Disclaimer , covering parts of 42 States.

Related Links:
National Contaminant Occurence Database
Unregulated Contamintant Monitoring Rule
Drinking Water Contaminant Candidate List
Six Year Review of Drinking Water Standards

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