2012-03-30_HYDROLOGY - M1979191 - Laserfiche WebLink

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Site Name T X W S East Rigden Pit 55,000 2,500 5,800 0.2 Three Bells Pit 45,000 1,900 4,800 0.2 Kyger Pit 45,000 1,800 5,200 0.2 Shields Mine 55,000 3,700 8,000 0.2 Mr. Jared Dains Lafarge Middle Poudre Combined SWSP March 29, 2012 Page 3 A stream depletion model using the Glover method was used to calculate the lagged depletions to the Cache La Poudre River. The alluvial aquifer model uses four aquifer input parameters for each site as follows: 1) X- distance from centroid of exposed ground water to river, 2) W- distance from the aquifer boundary through the well to the river channel, 3) T- transmissivity of the alluvial aquifer (in gallons per foot /day) between the well and the river, and 4) S- specific yield - 0.2 was used for all wells. The following parameters for each site listed in the table below were used in the model: The total lagged mining depletions for all four sites are 229.30 acre -feet. Including the credits that are dedicated to the Weitzel and Port of Entry Pits, the total projected depletions that are to be paid in 2012 are 405.34 acre -feet (see Table 1 — rev. 3/6/12). Dewatering The East Rigden, Kyger, and Three Bells Pits are assumed to have been continuously dewatered and to be in a steady state condition where dewatering accretions equal the lagged depletions. Lafarge estimates that the three pits are dewatered at a rate of 800 to 1,000 gpm for approximately 12 hours per day. Lafarge plans to maintain these operations throughout this SWSP approval period. Once dewatering ceases or is reduced in its flow, lagged depletions will immediately hit the river. At least three years prior to a modification in dewatering operations, the Applicant must provide a plan showing how lagged post - pumping depletions will be replaced in the proper time and amount. All volumes pumped for dewatering must be metered by a Totalizing Flow Meter and be reported on the accounting submitted monthly. Future SWSPs for these pits will not be approved until all volumes pumped for dewatering are properly metered. Replacements Replacement water for this combined plan will come from the following sources: accretion credits from recharge of 5 shares of the Box Elder Ditch and leases of augmentation water provided by the Lake Canal Reservoir Company ( "LCRC) and the Platter River Power Authority ( "PRPA "). Lafarge previously owned and dedicated to this plan 8.5 shares in the Box Elder Ditch. As a part of a stipulated agreement with Stoner & Company ( "Stoner ") regarding the sale of the Weitzel Pit, Lafarge conveyed 2 of its 8.5 shares to Stoner, and is leasing an additional 1.5 shares in 2012 with an option to renew the lease through 2016. The remaining 5 shares controlled by Lafarge will be used as a replacement source in this plan and will be diverted into a recharge pit (WDID 0302002) through an existing lateral from the ditch. The 5 shares are from the group of 5.5 shares that were historically associated with the Three Bells Farm. The recharge pit was constructed on the un -mined portion of the Three Bells Pit site and it was excavated to only the upper portion of the gravel deposit and will not expose additional ground water. The estimated recharge pit size is one acre. For the purposes of this plan, evaporation from open water was assumed for the entire surface area of the recharge pit for the number of days water was diverted into the recharge pit. Based on this approach, the proportion of days with water diverted into the recharge pit to the number of days per month was applied to the monthly gross evaporation rate, resulting in an evaporative consumptive use from the recharge pit of approximately 2.04 acre -feet. Box Elder Ditch is divided into 64 Box Elder Ditch Company ( "BEDC ") shares. Lafarge owns 5.5 shares of the 6.0 BEDC shares that were historically utilized for the irrigation of the Three Bells property