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The City of Prescott, Arizona is one of many Southwestern Community Water Systemsthat must comply with the new Arsenic MCL of 10 g/L by January 2006. This paper presentsthe technical challenges the City of Prescott faced during treatment process selection and designof their Arsenic treatment system. The City of Prescott operates the water production anddistribution system as an enterprise fund. The City of Prescott has 6 drinking water wells, whichhave Arsenic concentrations from 9-53 g/L and a combined capacity of 14.4 MGD. All of thewells are located in the Town of Chino Valley, a community 20-miles to the northeast ofPrescott. Water is also served to a portion of Chino Valley residents on its way to theCity's main pumping station (Chino Forebay) and the 20-mile pipeline serving the City ofPrescott. The individual wells are spread throughout the central portion of Chino Valley and areall less than 1.5 miles away from the Chino Forebay. The initial goal of the study was todetermine which Arsenic treatment technology out of four (e.g., adsorption, coagulation/filtration(C/F), coagulation/membrane filtration (C/MF) and ion exchange (IX)) would be mostappropriate for Prescott's specific water quality, and whether centralized treatment at the ChinoForebay or individual wellhead treatment would be more cost effective. Specific challengesincluded a lack of sewers for waste discharge; constrained space at several of the individual wellsites; a separate supply water piping system requirement to serve Chino Valley residents, aftertreatment, if centralized treatment is selected; all of the well capacity required in the summermonths to meet demand; and power is limited only to the Chino Forebay site.The Conceptual Design results led to a recommendation that design of a 14.4 MGD centralizedtreatment facility would be most cost effective. Two technologies were selected for furtherevaluation based on conceptual design cost assessments: adsorption and C/F. Bench testing wasconducted for adsorption and C/F to determine the lowest cost solution based on Prescott'sspecific water quality conditions. C/F jar tests were conducted to examine nineteen conditionswith varying ferric chloride coagulant doses and pH conditions. Rapid Small Scale Column Tests(RSSCTs) were conducted on three adsorption media (Bayoxide E33, GFH and As:Xnp) todetermine the approximate number of bed volumes that can be anticipated with this water andwhether any deviations in performance between media should be anticipated under full scaleconditions. Results from both tests were evaluated and C/F was selected as the most costeffective technology.The results of this study and design will help other water systems to understand the importance ofverifying treatment performance through bench testing when conducting Arsenic treatmenttechnology selection. While meeting the January 2006 compliance deadline is important, it isalso critical that water systems verify that the technology they are selecting is appropriate for thespecific water quality being treated before investing in costly treatment systems. Includes tables, figures.

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Edition: Vol. - No. Published: 11/01/2005 Number of Pages: 11File Size: 1 file , 1.1 MB