2010-02-10_HYDROLOGY - M1978327 - Laserfiche WebLink

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Tom Hatton February 9, 2010 Depletions Page 2 Based on the information from your letter of November 12, 2009, the total exposed surfarce area at this site was 42.5 acres of which 36.2 acres of water surface was exposed prior to January 1, 1981. This results in 6.3 acres of exposed surface area that require replacement for evaporation losses. Net evaporative depletions were calculated using a gross annual evaporation of 38 inches from the exposed ground water surface; with a credit of 10.3 inches for effective precipitation. The net depletions of ground water due to evaporation from the 6.3 acres of the Kauffman #1 Pit exposed after December 31, 1980 totals 14.5 acre-feet per year, as shown on the attached Table 1. The total annual consumptive use of water at the site is 17.0 acre-feet, which consists of 14.5 acre-feet of evaporation from the 6.3 acres. of exposed pond area and 2.5 acre-feet for dust control (see attached Table 2). The mining operation has continuously dewatered directly back to the Big Thompson River since 1990. Due to the long period of continuous dewatering, you have assumed the dewatering at this site has reached a state of equilibrium with the Big Thompson River and there is no longer a net accretion to the river from the dewatering operation. 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 exposed water surface area to the Big Thompson River (X) of 250 feet, an estimated distance from the site 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 17.3 acre-feet during the term of this approval, as shown on the attached.Table 3. 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-99-069). 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. Additionally, please note that as a matter of law, the Division 1 Water Court determined in an Order dated November 25, 2009, in case no. 02CW392, that the 82CW202A decree did not grant Loveland any right to reuse or make successive use of the Barnes and Chubbuck Ditch inches. Accordingly, this plan does not approve the use of replacement water consisting of the Barnes and Chubbuck Ditch inches. For the purposes of this plan, the Applicant is required to provide