National Arsenic Occurrence Survey

National Arsenic Occurrence Survey (NAOS) sampled raw water from approximately 270 public supply wells in all 50 states, and predicted arsenic concentrations in finished water based on known treatments implemented by the systems (Frey and Edwards, 1997). Frey and Edwards (1997) also provided national estimates based on reexamining the NIRS data and a dataset of finished water from 60 large systems (serving >10,000 people) sampled by the Metropolitan Water District of Southern California (Davis et al, 1994). In 1973 to 1997, the USGS analyzed for arsenic in 18,850 raw-water samples from wells in 49 states (all but Hawaii) and Puerto Rico this dataset included 2,262 samples from public supply wells (Focazio et al., 2000). Several older national surveys of arsenic have been described in documents prepared for the USEPA (ISSI Consulting Group et al., 2000). 

Water samples were taken from three deep wells in the blackfoot disease endemic area in Taiwan. An aliquot of each sample was Altered and speciated in the held to separate parAculate arsenic, arsenate [As(V)] and arsenite [As(III)] (7). Arsenic and co-occurring elements were measured with inductively coupled plasma mass specttometty (ICP-MS) or ICP emission specAoscopy (ICP-ES). These Taiwanese well samples were compared with results from the National Arsenic Occurrence Survey (NAOS), which obtained raw water samples from 428 water supplies in all 50 states of the United States (8,9). 

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