Abstract This document provides occurrence-related background information on 22 regulated drinking water contaminants in support of the Environmental Protection Agency’s (EPA’s) second Six-Year Review of National Primary Drinking Water Regulations (the “second Six-Year Review”). These 22 contaminants are referred to as “Category 1 contaminants” based on their: relatively high rates of occurrence at or near concentration thresholds of concern; new or ongoing health effects assessments; and potential new laboratory analytical capabilities. The 22 Category 1 contaminants are: benzene, carbofuran, carbon tetrachloride, chlordane, 1,2-dibromo3-chloropropane, 1,2-dichloroethane, dichloromethane, 2,4-dichlorophenoxyacetic acid, 1,2dichloropropane, endothall, heptachlor, heptachlor epoxide, hexachlorobenzene, hexachlorocyclopentadiene, oxamyl, tetrachloroethylene, toluene, toxaphene, 1,1,2trichloroethane, trichloroethylene, vinyl chloride, and xylenes (total).
This support document is divided into contaminant-specific chapters. The individual contaminant chapters include background information (regulatory history, general chemical information, and environmental fate and behavior), use and environmental release information, an overview of occurrence in ambient water, and national estimates of contaminant occurrence in public drinking water systems.
The national drinking water occurrence estimates presented here are based on the data contained in the National Compliance Monitoring Information Collection Request Dataset for the Second Six-Year Review (the “Six Year Review-ICR Dataset”), which includes data collected from 1998 to 2005. This is the largest and most comprehensive drinking water contaminant dataset ever compiled by EPA’s Drinking Water Program and includes 15 million records for 69 regulated contaminants submitted by 47 states/primacy agencies (45 states plus Region 8 and Region 9 tribes). Using this dataset, a variety of occurrence estimates were generated to characterize the national occurrence of regulated contaminants in public water systems (PWSs).
