HA9 Ecological Risk Assessment: General Perspectives and Case Studies
8:00 AM - 12:00 PM, Thursday

() An integrated in situ approach to assess ecological risk from groundwater discharges to surface water at a mining site.

Greenberg, M1, 2, Rauscher, J3, Sciera, K3, Purcell, M3, Henry, R4, Forsythe, B4, Wagner, A5, 1 U.S. EPA Environmental Response Team, Edison, NJ, USA2 Wright State University, Dayton, OH, USA3 U.S. EPA Region VI, Dallas, TX, USA4 U.S. Fish and Wildlife Service5 Molycorp, Inc., Questa, NM, USA

ABSTRACT- Groundwater-surface water interactions were evaluated in the Red River, northern New Mexico, to assess potential impacts to aquatic receptors due to nearby mining activities. Six stream locations with groundwater discharge to surface water were selected for a 96-h investigation. The locations represented the mining and tailings areas, areas containing hydrothermal scars, and a historical upstream reference. Study elements included physicochemical characterization of metals in the media, daily measurements of vertical hydraulic gradients (VHGs), in situ exposures of Hyalella azteca and indigenous Drunella sp., and whole sediment laboratory toxicity tests using H. azteca and Chironomus tentans. Numerous metals exceeded screening benchmarks in groundwater sampled from 30 and 60 cm depth in the streambed, surface water, and sediments. All sites exhibited upwelling (i.e., groundwater discharge) during the study, with VHGs ranging from -0.4 to +1.2 cm/cm, and there was a progressive increase in the upwelling signal over 96-h. H. azteca mean percent survival during the in situ exposures ranged from 30 to 95% and 70 to 84%, for the surface water and sediment-water interface (i.e., at the discharge point) treatments, respectively. For the mayfly, Drunella sp., mean percent survival ranged from 72 to 98% across both in situ treatments. There were no significant differences for in situ survival between hydrothermal scar areas and mine or tailings locations. A critical discussion of the strengths and weaknesses of the individual components of the in situ study will be provided. Overall, there was no acute toxicity to H. azteca and Drunella sp. due to discharging groundwater. The groundwater and surface water metals chemistry are important for determining chronic exposure risks.

Key words: groundwater discharge, in situ study, groundwater-surface water interactions, risk assessment

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