2018-08-22_REVISION - M1977493 (7)

Home Browse Search

Eagle Park Reservoir chemical Loading and Mixing Analysis For the purpose of developing a mass -balance mixing model, the upper portion of the reservoir with a volume of 1,077 acre-feet is used. This is the volume of the reservoir between the average elevation of approximately 10,711 feet and the elevation of the gravity outlet at 10,688 feet and also generally coincides with the water above the thermocline noted in the recent EPR Water Quality Evaluation Reports (LRE, 2014 & LRE, 2015). Water Quality Source Terms To establish water quality source terms for use in the mixing model, the proposed NPLs for monitoring well EV -MW -004 were used for groundwater inflow, as presented in Table 3. For the purpose of this analysis, all groundwater entering the reservoir was assumed to be of this same quality. With the exception of manganese, for which an ambient -based NPL value is proposed, the NPL values represents the most stringent table value standard for each constituent as presented in Tables 1, 2, and 3 in Water Quality Control Commission Regulation 41 (The Colorado Basic Standards for Groundwater). NPL values for cadmium, lead, and molybdenum are domestic water supply — human health standards (Table 1); iron, manganese, and sulfate are Domestic Water Supply — Drinking Water Standards (Table 2), based on secondary drinking water standards; and copper and zinc are Agricultural Standards (Table 3). Cadmium, copper, lead, and zinc are generally not present above the analytical detection limit in groundwater at monitoring well EVMW-1S, having been detected in only approximately 10% of the samples collected between October 2011 and November 2015. Table 3. NPL values for Groundwater Clualitv Source Terms In evaluating the representative water quality in the reservoir for this mixing analysis, recent analytical data collected from the EPR outlet from August 2013 to September 2014 (Table 4) were considered. The average plus two standard deviations (20) of water quality concentrations monitored at the EPR Outlet were selected to represent water quality within the reservoir. This representation of beginning water quality assumes, initial concentrations of manganese, molybdenum, and sulfate higher than any actual observed concentrations in the upper portion of the reservoir, and are more consistent with the somewhat higher concentrations of these constituents observed in recent samples collected from a depth of 100 feet within the reservoir (LRE, 2014 & 2015). Climax Molybdenum Company Page - 4 - Cadmium Copper Iron Lead Manganese Molybdenum Sulfate Zinc Groundwater Quality Dissolved Dissolved Dissolved Dissolved Dissolved Dissolved Dissolved Dissolved pH Source Term (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) S.U. NPLValues 0.005 0.20 0.3 0.05 0.319 0.210 250 2.0 7.5 In evaluating the representative water quality in the reservoir for this mixing analysis, recent analytical data collected from the EPR outlet from August 2013 to September 2014 (Table 4) were considered. The average plus two standard deviations (20) of water quality concentrations monitored at the EPR Outlet were selected to represent water quality within the reservoir. This representation of beginning water quality assumes, initial concentrations of manganese, molybdenum, and sulfate higher than any actual observed concentrations in the upper portion of the reservoir, and are more consistent with the somewhat higher concentrations of these constituents observed in recent samples collected from a depth of 100 feet within the reservoir (LRE, 2014 & 2015). Climax Molybdenum Company Page - 4 -