A MASS-BALANCE APPROACH TO ASSESSING ARSENIC TRANSPORT THROUGH THE HYPORHEIC ZONE OF A MINE-INFLUENCED MOUNTAIN STREAM
By monitoring arsenic concentrations in groundwater, hyporheic water, and stream water, we are characterizing spatial and temporal variation in arsenic fluxes by employing a mass-balance approach. 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 groundwater inputs to the stream. Vertical hydraulic gradients along the stream bed indicate that that the stream is gaining throughout the study reach. Groundwater arsenic concentrations paired with groundwater discharge measurements will be used to determine the arsenic load (concentration*discharge) entering the hyporheic zone. The load leaving the study reach will be measured to determine if the hyporheic zone is retaining or releasing arsenic to the stream. Employing this mass-balance approach will allow us to determine the importance of this groundwater-surface water interface in the transport of trace elements.