2016-12-31_REPORT - C1981035 - Laserfiche WebLink

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® RESOURCE HYDROGEOLOGIC V SERVICES trace metals, iron and manganese were detected in alluvial groundwater samples. The distributions (that is, the range of concentrations reported) of the concentrations of these two metals are shown in Figures 5 and 6. These may derive from the weathering of iron sulfide (pyrite) in the Mesaverde Group strata. When pyrite is oxidized by infiltrating, oxygenated water, it yields sulfate, iron and trace metals which are also present. The iron tends to drop out of solution as iron oxides, but the manganese may persist over longer distances. Manganese left behind on sandstone cliffs by evaporation forms the blue - black coating characteristic of many southwest bluffs. All other trace metals (aluminum, arsenic, cadmium, lead, mercury, molybdenum, selenium, uranium and zinc) were reported to be at concentrations below drinking water standards. Concentrations of total organic carbon, an indicator parameter of wastewater, disinfection or fertilizer impacts, were reported to be less than 4 mg/L in all alluvial groundwater samples. A program to sample and analyze the CDRMS-permitted waste rock refuse pile at the King I Mine facility is in progress with soil/rock samples currently being processed by a contract analytical lab per CDRMS Permit Minor Revision 41 (MR -41). The results of this program will include an assessment of the potential for the refuse pile to leach sulfate to the alluvium. This assessment will be completed in early 2017. Coal mine waste rock typically contains roof and floor rock (overburden and underburden) which commonly has several percent of pyrite or iron sulfide, which can generate sulfate in water that is in contact with these materials. Groundwater levels at the three compliance monitoring wells were measured and documented per CDRMS compliance requirements at the time of each sampling event. As discussed previously, all three monitoring wells are completed in the Hay Gulch Alluvium and are directly comparable. As such, a groundwater hydrograph has been prepared converting measured groundwater levels to groundwater elevations for the entire period of historical record, presented as Figure 7. The hydrograph shows fairly substantial seasonal variability at all three wells over time which is not only related to variability in precipitation but also subject to the variability in flood irrigation cycles of Hay Gulch irrigated pasture. Groundwater levels measured at the Wiltse well pre -2009 may have been impacted by pumping during periods of Hay Gulch Alluvium groundwater production for operation and then decommissioning of the King I Mine. This is shown as more pronounced variability on the order of 10 foot annual level range from 2002-2009. However, groundwater levels are demonstrated to lack any substantial trends up or down and can be considered overall stable for the period of record. Current King I and II Mine operations do not withdraw Hay Gulch Alluvium groundwater for purposes other than routine water quality monitoring, nor discharge any fluids to the Hay Gulch Alluvium, and therefore do not impact Hay Gulch Alluvium groundwater levels. Based on the groundwater elevations presented in Figure 7, the Hay Gulch Alluvium groundwater flow direction is as expected, downgradient in the direction of the Hay Gulch drainage. The geometric mean of calculated gradients for the period of record is 0.022 between the Wiltse well and Well #1 Upgradient and 0.015 between Well #1 Upgradient and Well #2 Downgradient. Each of these values is nearly equivalent to the ground surface gradient between the respective locations, as generally expected for an alluvial aquifer. GCC ENERGY, LLC 2016 ANNUAL HYDROLOGY REPORT 7