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25th Ave SWSP Page 2 of 7 July 8, 2014 whether mining continued after December 31, 1980. This office has previously recognized a total of 45.5 acres at the Greeley West Pit as having been exposed prior to January 1, 1981. Per our "General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pits" updated April 1, 2011, pre -81 areas are tied to the physical location at which the groundwater was exposed prior to January 1, 1981 with the exception for areas whose reallocation was approved by the State Engineer prior to January 1, 2011. In a letter dated August 11, 2011, the State Engineer's Office allowed 30 acres of the pre -81 area to be re- allocated and memorialized. Credit for 15.5 acres of pre -1981 area was not reallocated and may no longer be claimed. The applicant provided a map on July 28, 2011 showing the specific location of the 30 acres of pre -81 area. The credits for the pre -81 area are tied to the location identified on said map, consisting of Flatiron Pit 5, and may not be re- allocated to other areas of ground water exposure within the gravel pit boundary. Any pre -81 area that is backfilled will lose the pre -81 exemption should it be excavated in the future. Additionally, the backfilling of a pre -81 area does not create a credit to be used elsewhere. Depletions directly associated with mining at the pits, including the removal of mined product, dewatering, and post - mining refilling of the pits, will be replaced under this SWSP. During this plan period, operations will consist of mining of Flatiron Pits 3 and 4, and the reclamation and backfilling of Flatiron Pits 5 and C using the non - marketable materials removed during mining of Pits 3 and 4. The proposed replacement source for this SWSP will be water rights owned or controlled by the City of Greeley in the Cache la Poudre River basin. Operational Depletions The applicant has estimated that 445,649 tons of aggregate will be mined per year during this plan period. The material will be mined below the ground water table in a dewatered state and not washed; therefore the water retained in the mined product is considered to be 2.0% of the mined material by weight. This amounts to a ground water loss of approximately 6.56 acre -feet per year. It is estimated that a maximum of 1 acre -foot of water per year will be used for dust control purposes at the site, which is considered to be 100% consumptive. Based on the above, operation losses will total 7.56 acre -feet per year during each year of this plan period. The point of depletions is assumed to be on the Cache la Poudre River perpendicular to Flatiron Pits 3 and 4. The downstream calling right is the Ogilvy Ditch (WDID 0300937). The applicant tagged these depletions consistent with Exhibit 4 to the decree in case no. 1999CW231. Specifically, the IDS Alluvial Water Accounting System (AWAS) program was used to calculate the lagged depletions to the Cache la Poudre River. The following parameters were used in the model: • X, distance from the well (gravel pit) to the stream = 1,733 feet • W, width of the alluvial aquifer = 11,503 feet • T, transmissivity = 164,132 gallons per day per foot • S, specific yield = 0.20 Lagged operational depletions from both past and projected operations at the site are estimated to total 7.15 acre -feet during the first year of this plan period, and 7.37 acre -feet during the second year of this plan period.