The removal of a natural mixture of As(III) (31 micrograms/L) and As(V) (57 micrograms/L) from a groundwater high in total dissolved solids (TDS), and also containing fluoride (2.0 mg/L), was studied in San Ysidro, NM using the University of Houston (UH)/U.S. Environmental Protection Agency (EPA) Mobile Drinking Water Treatment Research Facility. The objective of the study was to establish a cost-effective means of removing As(III), As(V), and fluoride from this and similar waters. Arsenic adsorption into fine-mesh activated alumina gave better-than-expected results. Approximately 9000 bed volumes (BV) could be treated at pH 6 before the arsenic maximum contaminant level (MCL) (0.05 mg/L) was reached. At the natural pH of 7.2, however, only 1900 BV could be treated before exceeding the MCL. Reverse Osmosis (RO) treatment resulted in >97% arsenic removal and >94% TDS removal. Electrodialysis (ED) removed 73% of the arsenic and was able to meet the arsenic MCL on the City Water containing 89 micrograms/L total arsenic; however, ED removed only 28% of the As(III) from a new well containing 100% As(III) at a level of 230 micrograms/L. Chloride-form anion exchange also performed better-than-expected (200 BV) but not well enough for it to be considered seriously for treatment. Point-of-use (POU) RO treatment was effected in removing >91% of the arsenic and >94% of the TDS at low (<15%) water recovery.

EPA 600/2-91/011".