HOW BEDROCK AND FRACTURE ORIENTATION OF THE QUIMBY FORMATION ARE RELATED TO ARSENIC CONCENTRATIONS IN BEDROCK WELLS IN RANGELEY, ME

Some domestic wells around Dodge Pond, Rangeley, Maine, have arsenic levels well above the maximum contaminant level 0.01 mg/L; (US EPA, WHO). Although, extensive research on geochemical processes that release arsenic has been done, bedrock properties such as structural features and metamorphic history may have a role in arsenic mobility. The southern two thirds of Dodge Pond lies within the late Ordovician (?) Quimby Formation. The Quimby Formation is about3, 000 feet thick and consists of sulfidic metashale, metagraywacke, felsic metavolcanic rocks and thin beds of black calc-silicate rock. The northern third of Dodge Pond lies within a Devonian gabbro, which produced a narrow metamorphic aureole. Water and rock samples were collected at 11 sites located within shale and metagreywacke members of the Quimby Formation. All water samples contain high concentrations of arsenic ranging from 0.016 mg/L to 0.42mg/L, but samples from wells near the gabbro contact have lower concentrations. Analyses using thin section microscopy and SEM/EDS, and whole rock geochemistry are in progress. The metamorphic aureole is hypothesized as a mechanism for arsenic release. Bedrock and fracture orientation were measured at prominent outcrops. Joints that gently dip to the NW may be preferred avenues for arsenic mobility. Analysis of these datasets will determine whether there is a relationship between fabric orientations in the Quimby Formation and arsenic groundwater concentrations.