Evaluating the environmental impacts to the groundwater and surface-water system of the Red River, northern New Mexico
Hagan, L.B., Crossey, L.J., Allen, B.D., and
Groffman, A.R., 1999, Evaluating the environmental impacts to the groundwater
and surface-water system of the Red River, northern New Mexico: EOS, v.
80, p. F316.
Evaluation of mining-related contamination of surface-water and groundwater in sulfide-mineralized areas may be complicated by contributions from natural sources of acidic, metal-laden water. The Red River stream system of northern New Mexico contains natural exposures of sulfide-enriched rocks (alteration scars) as well as extensive waste-rock dumps associated with mining activities, both of which generate acidic metal-laden water that infiltrates to the groundwater system and discharges into the Red River. The purpose of this investigation is to compare natural and anthropogenic sources of contamination to the Red River by collecting geochemical data from the shallow groundwater system in the vicinity of the stream and by modeling the hydrogeochemical evolution of these waters. Two primary localities have been established near the Red River. The Hansen Creek locality is located along a conceptual groundwater flow path below an extensive alteration scar, and represents hydrochemical conditions associated with natural alteration scars. The Capulin Canyon locality is located along a conceptual groundwater flow path below a mining-related waste-rock dump, and represents conditions associated with drainages altered by mining activities. Groundwater and surface water samples were collected 5 times between October, 1998, and July, 1999. Analytical data from water samples suggest that groundwater influenced by waste-rock dumps contains comparatively higher concentrations of dissolved species associated with oxidation of sulfides and generation of acidic waters. For example, shallow groundwater samples collected at the Capulin Canyon locality during baseflow conditions in the Red River yielded sulfate concentrations ranging from 1900-2200 mg/L. At the Hansen Creek locality sulfate concentrations ranged from 570-910 mg/L. Significantly higher concentrations from the Capulin Canyon locality suggest that the waste rock dumps are facilitating the generation of acidic water, probably due to increased surface area and enhanced exposure to atmospheric oxygen of the disturbed, sulfide-bearing materials. Alternative explanations include mineralogical variations in the country rock and sampling bias due to a limited number of monitoring wells. This study demonstrates that to assess the impact of mining on water quality in sulfide-mineralized regions, the natural background geochemistry of the groundwater system should be quantitatively established.
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