Processes and conditions affecting elevated arsenic concentrations in groundwaters of Tulare Basin,California, USA

摘要

High concentrations of arsenic (As) in the shallow and deep groundwaters of theTulare Basin in California, USA, pose a hazardous risk to drinking water supplies.Both natural processes and anthropogenic activities affect As concentrations andmovement in groundwater in this region. Agricultural activities, particularly irriga-tion and drainage, enhance As mobilization; and high evapotranspiration ratesconcentrate As in surface and shallow groundwaters. The complexities of interac-tions among multi aquifers and water flow present challenges in identifyingthe source of As and its movement. Important biogeochemical processes affectingAs solubility and mobility include adsorption/desorption and redox reactions. Thelater processes, which transform inorganic arsenate [As(V)] to arsenite [A s(III)],remain poorly understood as to what extent they affect As concentration andits mobilization into groundwater. The presence of impermeable clay layers, e.g.,E-clay, and their roles in potentially retarding As movement into deeper aquifersare also not well understood because significant increase of vertical leakagewas predicted by computer modeling due to drilling of many irrigation wellspenetrating impermeable clay layers. Future research on the reactivity of As withsediments through biogeochemical processes under natural physical setting condi-tions, as well as reactive transport modeling are necessary to better our under-standing of As mobility and contamination in the groundwaters of the TulareBasin.