AWWA JAW37596

With a November 1995 deadline for proposing a new regulation for arsenic, the US Environmental Protection Agency (USEPA) has been moving to develop a clearer picture of arsenic occurrence and exposure throughout the United States. This article summarizes the studies that are the basis for USEPA's estimates of preliminary occurrence and exposure for arsenic, including several newer surveys that add information about low-level occurrences. The article does not attempt to evaluate the methodology or conclusions of these studies or to weigh the relative importance of one study over another. Better estimates of arsenic occurrence at levels as low as 0.5 ug/L have particular importance, because USEPA could consider a new arsenic limit below 0.05 mg/L. Preliminary occurrence estimates from USEPA show that arsenic occurs primarily in the source water of smaller (serving fewer than 10,000 people) groundwater systems in the western United States. Includes 9 references, tables, figures.