2017-06-28_HYDROLOGY - M1983176 - Laserfiche WebLink

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Speer Mining Resources Substitute Water Supply Plan Page 2 of 5 June 28, 2017 result from mining related exposure of ground water. The DRMS letter identified four approaches to satisfy this requirement. In accordance with approach nos. 1 and 3, a bond has been obtained for $678,169 that can cover the cost of lining or backfilling the Speer Mining Resources Pit to prevent the exposure of ground water. Depletions The depletions at the site consist of evaporation from exposed groundwater and water used for dust suppression. Lagged depletions resulting from the cessation of dewatering, and lagged depletions resulting from the ‘first fill’ accrued to the river by the end of 2014. The total exposed groundwater surface area at this site as of January 2017 was 12.11 acres. As of April 2017 the site has been backfilled so that 9.44 acres of groundwater are exposed. For the purposes of this SWSP, it is assumed that the pit will be backfilled at a steady rate of 0.89 acres per month so that by September 2017 the exposed groundwater at the site will be 5.0 acres. Net evaporative depletions were calculated using a gross annual evaporation of 44.5 inches from the exposed water surface, with a credit of 9.93 inches for effective precipitation. The net depletion of ground water due to evaporation from the ground water exposed at the site was calculated to be 20 acre-feet for 2017, and 14.12 acre-feet in 2018 as shown on the attached Table AI.1. Computation of evaporation under this SWSP was reduced during the ice covered period. You have assumed the ice covered period will occur during the months of December and January based on average monthly temperatures less than 32°F taken from the Brighton 1 NE (ID 950, record 1973- 2010) NOAA weather station. However, for the purpose of this SWSP, the Applicant shall replace the net evaporation depletions from the exposed ground water surface area that may occur during the assumed ice covered period (the months of December and January) for any time that the pit is not completely covered by ice. The Applicant has estimated that a small amount (0.33 acre-feet) of water used for dust control on roadways will remain in service for the inert fill operation. There will be no material mined at the site during this plan period and no other operations that would consume groundwater. The Alluvial Water Accounting System (“AWAS”) model was used with the alluvial aquifer boundary condition option to lag depletions to the South Platte River. The following parameters were used in the model: transmissivity (T) = 96,043.2 gallons per day per foot, distance (X) from the centroid of the surface of the exposed ground water to the river = 578 feet, distance (W) from the aquifer boundary through the exposed ground water to the river channel = 6,800 feet, and specific yield (SY) = 0.2. The location of the stream depletion is assumed to be perpendicular to the river. The lagged depletions due to evaporation and dust control during the SWSP period are shown in Table AI.3 and are estimated to total 22.51 acre-feet for 2017 and 16.03 acre-feet for 2018. Replacements Out-of-priority depletions associated with the mining operation at this site will be replaced using fully consumable municipal return flows leased from the City of Aurora (“Aurora”). A copy of the lease with Aurora was provided to this office with this SWSP request and is attached to this letter. Under the lease, water will be delivered to the outfall of the Robert W. Hite Treatment Facility (aka Metro Sewer, WDID 0200700) located on the South Platte River. Aurora may alternatively deliver water at other points along a reach of the South Platte River beginning at or below the Hite Treatment Facility extending downstream to where the South Platte crosses the Adams/Weld County line at 168th Avenue (aka Baseline Road). The Applicant must notify the water commissioner