GEOLOGIC CONTROLS ON ARSENIC DISTRIBUTION AND MOBILIZATION IN PENNSYLVANIA GROUNDWATER
Water samples have been collected from 53 groundwater wells in the Passaic formation and surrounding areas. Bedrock samples are being collected from local outcrops. Samples have been analyzed for As speciation (As III and As V) by coupling ion chromatography and hydride generation (HG) to ICP-MS. Samples will be analyzed for total As using HG-ICP-MS; Na, K, Ca, Mg, Fe, and Mn using ICP-MS; and SO4, Cl, F, NO3, NO2, and PO4 using IC. Redox potential, pH, and temperature were collected in the field.
Oxidizing conditions dominate the samples. Of 37 samples analyzed for As speciation, As V dominates 81% of samples under oxidizing conditions and As III dominates 8% of samples under low oxidizing or reducing conditions. Eleven percent of samples exhibit almost equal amounts of As III and As V under oxidizing conditions. There are ten results with elevated concentrations of As (>10 ppb). Nine samples were dominated by As V under oxidizing conditions. One sample was dominated by As III under low oxidizing conditions. The results show that both low and high concentrations of As tend to occur in oxidizing conditions. Preliminary plots on Eh-pH diagrams show As V species to dominate the sample set. Eh-pH relationships will be further analyzed to determine if the presence of other ions in solution are controlling factors.