SURVEYING ARSENIC OCCURRENCE

Three surveys of arsenic occurrence in US drinking water supplies were synthesized to estimate how possible arsenic standards would affect c ompliance. Detectable levels of arsenic (0.5 mu g/L) were found in 73 percent of surface water sources and 58 percent of groundwater sources . For finished water, detectable arsenic occurred in 45 percent of sur face water systems and 53 percent of groundwater systems. The authors' compliance projections for arsenic standards ranging from 2 to 20 mu g/L agreed fairly well with initial estimates by the US Environmental Projection Agency. It was estimated that approximately 25 percent of a ll community water suppliers (11,550-11,890 systems) would violate an arsenic standard of 2 mu g/L. Between 6 and 17 percent of systems (2,7 75-7,870) were projected to violate an arsenic standard of 5 mu g/L, a nd 1-3 percent of systems (510-1,360) were estimated to violate an ars enic standard of 20 mu g/L.