2011-12-20_HYDROLOGY - M1978327 - Laserfiche WebLink

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Todd Williams Page 2 December 19, 2011 pit operator or property owner does not need to replace depletions that occur due to evaporation from ground water exposed prior to January 1, 1981 as a result of open mining of sand and gravel, regardless of whether mining continued after December 31, 1980. Therefore, the evaporative depletions are based on 3.8 'post -81' acres (40.0 total acres — 36.2 'pre-81' acres). The exemption from augmentation requirements for the pre -81 area is tied to the physical location identified on Map 3 and may not be re- allocated to other areas of ground water exposure within the gravel pit permit boundary. Net evaporative depletions were calculated using a gross annual evaporation of 38 inches from the exposed ground water surface, with a credit of 9.7 inches for effective precipitation. The net depletions of ground water due to evaporation from the 3.8 acres of the Kauffman #1 Pit post -81 area totals 8.95 acre -feet per year, as shown on the attached Table 1. The total annual consumptive use of water at the site is 14.32 acre -feet, which consists of 8.95 acre -feet of evaporation from the 3.8 acres of exposed pond area and 5.37 acre -feet for dust control (see attached Table 2). According to the SWSP request water will be pumped from the site for dust control purposes at the Kauffman No. 1 gravel pit and the Wagner- Kauffman No. 3 gravel pit. Based on information from the applicant, the area covered by M- 1978 -327 and that is the subject of this SWSP was largely wet mined when it was active, and has essentially been inactive for the last 20 years. Aerial photographs from 1999 show the site within the current boundary of M- 1978 -327 as having remained the same including the exposed ground water surface area. The applicant has therefore not included any post - pumping dewatering depletions on the basis that there are none associated with this permit. The monthly depletions to the Big Thompson River were lagged from the pit site using the AWAS program developed by the IDS Group at Colorado State University. The parameters used in the model were an estimated distance from the centroid of the exposed water surface area to the Big Thompson River (X) of 540 feet, an estimated distance from the river to the no flow aquifer boundary (W, measured perpendicular to the point of impact) of 4,000 feet, an aquifer transmissivity (T) of 50,000 gallons per day per foot, and a specific yield (S) of 0.2. The lagged stream depletions are estimated to total 13.6 acre -feet during the term of this approval, as shown on the attached Table 4. Replacements Replacement water for this pit will continue to be made available throughout the year from a lease of 65.0 acre -feet of fully consumable water from the City of Loveland ( "Loveland "). This lease also applies to losses at another gravel pit, Wagner /Kauffman Pit #3 (M- 1999 -069, WDID 0403008). A copy of the lease associated with the mining operation is attached to this letter. The duration of the lease is from January 1, 2010 through December 31, 2012. A 4 percent transit loss from Green Ridge Glade Reservoir to Kauffman Pit has been applied to the delivery of the replacement water. Under the terms of the lease, replacements can be made using a variety of water owned by Loveland including, but not limited to, Windy Gap reusable effluent, Loveland Storage Reservoir water as decreed in case no. 82CW202A, and Colorado Big Thompson Project ( "C -BT ") water. In the event that the City plans to use C -BT water as a replacement source, the City shall comply with the Interim Rule issued by the Northern Colorado Water Conservancy District ( "Northern District ") in May 2005, regarding the use of Colorado -Big Thompson ( "CBT ") Project water in substitute water supply plans. Prior to the use of C -BT Project water, the City is required to notify this office, the division engineer and the water commissioner of the amount of C- BT Project water dedicated to this plan and provide a copy of the Northern District's approval letter as required by paragraph I(g) of the Northern District's May, 2005 Interim Rule.