2015-04-22_HYDROLOGY - M1987049 - Laserfiche WebLink

Home Browse Search

Julia Keedy Bromley Lakes SWSP April 8, 2015 Page 3 evaporation atlases in NOAA Technical Report NWS 33 is 44.5 inches per year. Using the effective precipitation of 10 inches per year the projected net evaporative loss is 84 acre -feet for Bromley Cell 2 and 2.9 acre -feet for Bromley Lot 2. Actual evaporation from exposed ground water will be accounted for based upon the actual exposed ground water areas. Some mining will occur above the ground water surface and some will occur below the ground water surface. For gravel mining within the Kenneth Mitchell Lake 1 slurry wall or above the static ground water table in Bromley Cell 2 a 2% water loss by weight has been charged. For Bromley Lot 2 projected mining is assumed to be below the ground water surface and has been charged 4% water loss by weight. For the period of this SWSP, RMCC projects 1,500,000 tons of gravel production at this site (1,420,000 tons at Bromley Cell 2 and 80,000 tons for Bromley Lot 2). The gravel production depletions are projected to a maximum water loss of 20.9 acre -feet Bromley Cell 2 and 2.4 acre -feet for Bromley Lot 2. RMCC continues to dewater Bromley Lot 2. The dewatering pumping rate is expected to be less than or equal to 1.2 acre -feet per day until the end of January when the Applicant plans to stop dewater Bromley Lot 2 and transition to mining Kenneth Mitchell Lake 1 land bridge. Since RMCC is backfilling Bromley Lot 2 with material as they mined it, there is not expected to have any exposed ground water or a "first fill" when the dewatering is stopped at the end of January. However you indicated the RMCC may continue to dewater Bromley Lot 2 throughout 2015, depending upon their operational needs. The total consumptive use at this site for the period of this SWSP is 132.4 acre -feet. These depletions do not hit the river instantaneously and thus must be lagged back to the river. As described in the previous SWSP approval the depletions are lagged to the South Platte River and the McCanne Ditch. With the recent approval of the liner for Bromley Cell 3 /Lot 1, the Applicant has separated the lagging analysis for the Bromley Lot 2, which are located east of the McCanne Ditch, with the lined gravel pit expected to block most of the depletions from impacting the South Platte River. Therefore, for the Bromley Lot 2, the Applicant performed a lagging analysis to the McCanne Ditch, which flows year round and discharges to the South Platte River. The Glover parameters applied for the Bromley Lot 2 are as follows: • specific yield = 0.2 • transmissivity = 100,000 gpd /ft • distance from centroid of mining area to McCanne Ditch = 600 feet • distance from McCanne Ditch to alluvial boundary = 3,500 feet The depletions from'Bromley Cell 2 occur west of the McCanne Ditch and are lagged to the South Platte River using the following Glover parameters: • specific yield = 0.2; • distance from the stream to the alluvial boundary= 5,300 feet • transmissivity = 100,000 gallons per day per foot; • distance from the centroid of the exposed ground water to the stream = 1,016 feet. The distance to the alluvial boundary is based on the Applicant's analysis of geologic cross sections showing that the alluvium is pinched at approximately the railroad east of the site.