AWWA ACE94134

The United States Environmental Protection Agency (USEPA) is considering lowering the maximum contaminant level (MCL) for arsenic, which is currently 0.05 mg/L (50 ug/L) to 0.5-20 ug/L. The proposed National Primary Drinking Water Regulation for arsenic is expected in November 1995. In anticipation of this proposed new arsenic standard, the Metropolitan Water District of Southern California (Metropolitan) conducted a nationwide survey to help assess the impacts of a more stringent arsenic regulation on the water supply community and provide low-level arsenic occurrence information for regulatory input. The survey was aimed at utilities in the US with populations of at least 50,000, representing all 10 USEPA regions. The survey was conducted to establish both untreated- and treated-water arsenic levels in surface and groundwater. The survey results indicate that population exposure to arsenic levels of greater than 2 ug/L is extremely low on the East Coast, as compared to much higher exposures in the Midwest, Southwest, and West Coast areas. Arsenic levels increased west of the Mississippi River and became more prominent in states such as California, Utah, New Mexico, Nevada, and Arizona. Treated water arsenic levels averaged 1.3 ug/L (mean value--0.6 ug/L) and ranged from <0.5 to 38.6 ug/L, with higher levels in groundwater supplies. The survey results indicated that approximately 23 percent of the survey population is exposed to arsenic levels greater than 2 ug/L, and the vast majority of higher concentrations is in the western US.