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State Water Resources Control Board <br />Division of Water Quality <br />VAmA rroaran <br />Contaminant Transport groundwater or deep lake sediments (reducing <br />Characteristics, cont. environments). The solubility, mobility, and toxicity of As <br />in the environment are dependent upon its oxidation <br />state, and increase with increasing alkalinity and salinity. <br />Arsenic mobility in groundwater is dependent on the <br />physical and chemical properties of the aquifer, although <br />two types of processes generally control its movement: <br />adsorption/desorption reactions and <br />precipitation/dissolution reactions. During adsorption <br />reactions, dissolved arsenic adheres to the surface of <br />solid aquifer materials. Desorption removes the arsenic <br />from aquifer materials and releases it into the <br />surrounding groundwater. The mobility of arsenate is low <br />in acidic soils with high content of oxides and clays. <br />Arsenite is more mobile, toxic, and difficult to remove <br />from groundwater than arsenate. <br />REMEDIATION & TREATMENT TECHNOLOGIES <br />Arsenic remediation is typically expensive because large volumes of groundwater <br />must be treated. The main types of treatment processes used are: <br />• Precipitative processes using ferric and aluminum salts, including <br />coagulation/filtration, direct filtration, coagulation -assisted microfiltration, <br />enhanced coagulation, lime softening, and enhanced lime softening; <br />• Adsorption processes, specifically activated alumina; <br />• Ion exchange processes, specifically anion exchange; <br />• Membrane filtration, including reverse osmosis, and electrodialysis reversal; <br />and; <br />• Permeable reactive barriers (PR13): <br />Two promising arsenic removal processes are granular ferric hydroxide (GFH) <br />and zero -valent iron (ZVI) fillings. These methods involve chemical adsorption <br />of arsenic species to iron oxides. GFH and ZVI filters are easy to operate and <br />have been found suitable for individual wellhead or other small-scale treatment <br />systems. <br />Revised October 2017 <br />