title: Geochemical Triggers of Arsenic Mobilization during Managed Aquifer Recharge.
abstract: Mobilization of arsenic and other trace metal contaminants during managed aquifer recharge (MAR) poses a challenge to maintaining local groundwater quality and to ensuring the viability of aquifer storage and recovery techniques. Arsenic release from sediments into solution has occurred during purified recycled water recharge of shallow aquifers within Orange County, CA. Accordingly, we examine the geochemical processes controlling As desorption and mobilization from shallow, aerated sediments underlying MAR infiltration basins. Further, we conducted a series of batch and column experiments to evaluate recharge water chemistries that minimize the propensity of As desorption from the aquifer sediments. Within the shallow Orange County Groundwater Basin sediments, the divalent cations Ca(2+) and Mg(2+) are critical for limiting arsenic desorption; they promote As (as arsenate) adsorption to the phyllosilicate clay minerals of the aquifer. While native groundwater contains adequate concentrations of dissolved Ca(2+) and Mg(2+), these cations are not present at sufficient concentrations during recharge of highly purified recycled water. Subsequently, the absence of dissolved Ca(2+) and Mg(2+) displaces As from the sediments into solution. Increasing the dosages of common water treatment amendments including quicklime (Ca(OH)2) and dolomitic lime (CaO·MgO) provides recharge water with higher concentrations of Ca(2+) and Mg(2+) ions and subsequently decreases the release of As during infiltration.
authors.affiliation: †Earth System Science Department, Stanford University, Stanford, California 94305, United States.
authors.forename: Sarah
authors.initials: S
authors.lastname: Fakhreddine
authors.affiliation: †Earth System Science Department, Stanford University, Stanford, California 94305, United States.
authors.forename: Jessica
authors.initials: J
authors.lastname: Dittmar
authors.affiliation: ‡Orange County Water District, 18700 Ward Street, Fountain Valley, California 92708, United States.
authors.forename: Don
authors.initials: D
authors.lastname: Phipps
authors.affiliation: ‡Orange County Water District, 18700 Ward Street, Fountain Valley, California 92708, United States.
authors.forename: Jason
authors.initials: J
authors.lastname: Dadakis
authors.affiliation: †Earth System Science Department, Stanford University, Stanford, California 94305, United States.
authors.forename: Scott
authors.initials: S
authors.lastname: Fendorf
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates; D001151:Arsenic / Q000032:analysis / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry; D002140:California; D000077215:Clay; D019015:Geologic Sediments / Q000737:chemistry; D060587:Groundwater / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry; D008903:Minerals; D059027:Recycling; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D018508:Water Purification / Q000379:methods; D014881:Water Supply
chemical_list: D000538:Aluminum Silicates; D008903:Minerals; D014874:Water Pollutants, Chemical; D008274:Magnesium; D001151:Arsenic; D002118:Calcium; D000077215:Clay