Forensic Hydrogeography: Assessing Arsenic Contamination in Drinking Water, Livestock, and Agricultural Wells in Harney County, Eastern Oregon

Abstract:

This study investigates the relationship between elevated arsenic levels in groundwater and the regional geography within the Harney Basin in Eastern Oregon. There are multiple aquifers within this region used for public consumption, livestock production, and agriculture. Initial observations by the United States Geological Survey and independent residential water quality assessments have identified some wells containing arsenic concentrations an order of magnitude greater than the United States Environmental Protection Agency’s Maximum Contaminant Level of 10 parts per billion for drinking water. However, these data are inadequate to characterize the spatial extent of arsenic contamination throughout the basin; it remains unclear which aquifers are contaminated. The basin contains a geology comprised of tuffaceous sedimentary rocks and basalt formations with extensive faulting. Productive wells range in depth from 6 to 240 meters. The present study examines the spatial extent and seasonal variation of arsenic concentrations due to changing water levels stemming from agricultural pumping. These data will aid in the development of a regional model of arsenic contamination throughout the basin.