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A survey of national groundwater supplies conducted from June1998 to June 1999 found that arsenic (As) concentrationsexceeding 0.010 mg/L are widespread in the United States. InJanuary 2001, the US Environmental Protection Agency published afinal rule to lower the As maximum contaminant level from 0.05 to0.010 mg/L. To meet this new standard, many utilities may need toupgrade current facilities or investigate new treatment options. Theyalso need an accurate appraisal of the ability of existing treatmenttechnologies to consistently reduce As to low levels.The authors conducted a year-long study to evaluate theperformance of five full-scale facilities for removing As from rawwater. The two coagulation-filtration plants evaluated consistentlyachieved low levels of As. However, when one facilitychanged its coagulant from alum to polyaluminum chloride, averageremoval efficiency plunged from 84 to 43%, a reduction thatmight be attributable to difference in pH. Of the two iron-removalfacilities, one consistently reduced As concentrations; addition ofa coagulant, however, should help improve the other plant's Asremoval. The lime-softening plant was unable to consistentlyreduce As to low levels, but raising the operating pH throughincreased lime dosage may improve removal efficiencies.Conventional treatment technologies are capable of removingAs from water supplies to levels

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Edition: Vol. 94 - No. 9 Published: 09/01/2002 Number of Pages: 14 File Size: 1 file , 1.1 MB