Mining Impacts on Surface Water Using Isotopic and Geochemical Tracers
Downstream from the closed Big Springs Mine, elevated sulfate was detected in the headwaters of the North Fork of the Humboldt River, posing a potential risk to the endangered Lahontan cutthroat trout. Integral designed and implemented a study of stable and radioactive isotopes and major ion chemistry to identify solute sources, flow paths and residence times, and post-mining impacts on water quality. Results of oxygen-deuterium isotope data showed a strong evaporative signature downgradient of the pit lakes, indicating that outflow from the lakes to groundwater was occurring. Sulfur isotope data confirmed that most of the sulfate in downstream surface water and downgradient groundwater derived from a sulfide mineral weathering source (i.e., pyrite oxidation). These tools, combined with detailed evaluation of groundwater flow patterns, were used to develop groundwater and surface water balance estimates and predict future water surface elevations in the pit lakes.
This project reflects Integral staff experience gained under previous employment.
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