QUANTIFYING ARSENIC FLUXES TO A MINE-IMPACTED HEADWATER STREAM

We are investigating the biotic and hydraulic controls of arsenic fluxes in a headwater stream in southwestern Virginia which has been influenced by an abandoned arsenopyrite mine. By monitoring arsenic concentrations in springs, groundwater, hyporheic water, and stream water, we plan to characterize the spatial and temporal variations of arsenic fluxes by employing a mass-balance approach. The total dissolved arsenic of these water sources ranges from 0.002 to over 5 mg/L with the vast majority (>90%) occurring as arsenate (i.e., As(V)). Dilution gauging by solute injection paired with continuous discharge measurements collected from flumes stationed both upstream and downstream of the mine are being used to quantify the volume of groundwater the stream receives along the study reach. To date, our results suggest that fluxes of arsenic to the stream are controlled by groundwater discharge and by inputs from springs and are affected to a lesser extent by surface runoff over mine tailings. By comparing arsenic loads from upstream, springs, and groundwater we will address how the hyporheic zone (i.e., the zone of interaction between surface and ground water) influences the concentration and form of arsenic present in the stream.