2017-04-04_HYDROLOGY - M1987049 - Laserfiche WebLink

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Jennifer Lindahl, P.E. Page 2 of 8 Bromley Lakes SWSP April 3, 2017 remaining surface area at the Plant Site. Backfilling and dewatering of the site is anticipated to end in March 2017. Depletions will result from: • evaporative losses of exposed ground water: (a) Bromley Lakes Cell 2, (b) Bromley Lakes Lot 2 • dewatering activity to facilitate mining – Bromley Lakes Lot 2 and Plant Site The proposed replacement sources are consumptive use credits from 5 Fulton Ditch (WDID 0200808) shares owned by the Applicant, fully consumable water in storage, and water leased from the City of Brighton. In accordance with the letter dated April 30, 2010 from the Colorado Division of Reclamation, Mining, and Safety (“DRMS”), all sand and gravel mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. The April 30, 2010 letter from DRMS required that you provide information to DRMS to demonstrate you can replace long term injurious stream depletions that 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, you have indicated that a bond has been obtained for $4,169,240 that can cover the cost of lining at the Bromley Lakes site to prevent the exposure of ground water. Depletions SWSP depletions are from evaporation of exposed ground water and dewatering. Tables 1A and 1B (attached) summarize projected depletions from January 2017 through March 2018. The exposed ground water will vary based upon hydrologic conditions and the amount of backfill. For the period of this SWSP, the area of exposed ground water is not expected to exceed 15.0 acres in Bromley Cell 2 and 2 acres in Bromley Lot 2/Plant Site. The applicant anticipates that all groundwater exposure will cease in March 2017. The gross evaporation rate at this location, based upon 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 4.8 acre-feet for Bromley Cell 2 and 0.6 acre-feet for Bromley Lot 2/Plant Site. Actual evaporation from exposed ground water will be accounted for based upon the actual exposed ground water areas. RMCC continues to dewater Bromley Lot 2. The dewatering pumping rate is expected to be less than or equal to 5.0 acre-feet per day and is expected to cease in M arch of 2017. The total consumptive use at this site for the period of this SWSP is 5.4 acre-feet. These depletions do not reach the river instantaneously and thus must be lagged back to the river. As described in the previous SWSP approvals the depletions are lagged to the South Platte River and the McCanne Ditch. With the 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 gallons per day per foot • 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: