AWWA WQTC58826

Recent regulations have lowered the acceptable total arsenic level in drinking water to 10 Au/L. The arsenic levels in the two groundwater wells operated by the Walker River Paiute Tribe have been measured to range between 70 and 110 Au/L. A treatment technology is needed that can consistently reduce these levels to below regulatory limits. In addition to arsenic, significant levels of silica (54 mg/L) and an "elevated" pH (8.6) are present that must be addressed when selecting the appropriate treatment technology. The raw water quality can influence the effectiveness of the treatment options evaluated. The range of selected raw water quality parameters encountered during the study are presented in the paper. The ranges experienced were not considered unusual, as the Tribe generally draws alternately from two well sources for varying times. The arsenic was speciated on-site and subsequently determined to be all in the As⁺⁵ state. Seven technologies were evaluated through either bench- or pilot-scale testing for their ability to consistently remove arsenic. The technologies included coagulation/microfiltration (C/MF), coagulation with conventional direct filtration, coagulation with high-rate direct filtration, granular ferric hydroxide (GFH), iron doped activated alumina (AA FS-50), iron doped natural zeolite (Z-33), and ion exchange. The results of the study indicated that each technology was capable of removing arsenic from the Tribe's water. However, not every technology could consistently remove arsenic below the MCL or run for acceptable operation times. Includes tables, figures.