Spring runoff water-chemistry data from the Standard Mine and Elk Creek, Gunnison County, Colorado, 2010
Water samples were collected approximately every two weeks during the spring of 2010 from the Level 1 portal of the Standard Mine and from two locations on Elk Creek. The objective of the sampling was to: (1) better define the expected range and timing of variations in pH and metal concentrations in Level 1 discharge and Elk Creek during spring runoff; and (2) further evaluate possible mechanisms controlling water quality during spring runoff. Samples were analyzed for major ions, selected trace elements, and stable isotopes of oxygen and hydrogen (oxygen-18 and deuterium). The Level 1 portal sample and one of the Elk Creek samples (EC-CELK1) were collected from the same locations as samples taken in the spring of 2007, allowing comparison between the two different years. Available meteorological and hydrologic data suggest that 2010 was an average water year and 2007 was below average. Field pH and dissolved metal concentrations in Level 1 discharge had the following ranges: pH, 2.90 to 6.23; zinc, 11.2 to 26.5 mg/L; cadmium, 0.084 to 0.158 mg/L; manganese, 3.23 to 10.2 mg/L; lead, 0.0794 to 1.71 mg/L; and copper, 0.0674 to 1.14 mg/L. These ranges were generally similar to those observed in 2007. Metal concentrations near the mouth of Elk Creek (EC-CELK1) were substantially lower than in 2007. Possible explanations include remedial efforts at the Standard Mine site implemented after 2007 and greater dilution due to higher Elk Creek flows in 2010. Temporal patterns in pH and metal concentrations in Level 1 discharge were similar to those observed in 2007, with pH, zinc, cadmium, and manganese concentrations generally decreasing, and lead and copper generally increasing during the snowmelt runoff period. Zinc and cadmium concentrations were inversely correlated with flow and thus apparently dilution-controlled. Lead and copper concentrations were inversely correlated with pH and thus apparently pH-controlled. Zinc, cadmium, and manganese concentrations near the mouth of Elk Creek did not display the pronounced increase observed during high flow in 2007, again perhaps due to remedial activities at the mine site or greater dilution in 2010. Zinc and cadmium loads near the mouth of Elk Creek were generally greater than those at the Level 1 portal for the six sample days in 2010. Whereas metal loads in September 2007 suggested that Level 1 portal discharge was the primary source of metals to the creek, metal loads computed for this study suggest that this may not have been the case in the spring of 2010. d18O values are well correlated with flow, becoming lighter (more negative) during snowmelt in both Level 1 discharge and Elk Creek. Seasonal variations in the chemistry of Level 1 discharge, along with portal flow tracking very closely with creek flow, are consistent with geochemical and environmental tracer data from 2007 that indicate short residence times (<1 year) for groundwater discharging from the Standard Mine.