2013-09-26_HYDROLOGY - M2000156 - Laserfiche WebLink

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Bonser Pit SWSP Page 2 of 5 September 25, 2013 boundary. The Applicant's consultant provided to this office an aerial photograph dated 1978 that shows these three ponds in existence and in the same size and configuration as they exist today. Therefore evaporative depletions are not required for the three pre -81 ponds. The area to receive the pre -81 exemption is tied to the location shown on Figures 2 and 3 and may not be applied to other areas of ground water exposure within the gravel pit permit boundary. The exemption is limited to evaporation losses only and the Applicant remains responsible for replacing water from these pre -81 ponds when put to any other beneficial use. The total evaporative loss resulting from the 6.3 -acre borrow pit pond is 13.69 acre -feet per year. The applicant expects to pump an additional 10.02 acre -feet of water per year from the borrow pit pond for dust control purposes. Total unlagged depletions are therefore estimated to total 23.71 acre -feet per year, at the monthly rates shown in Table AI.2. A stream depletion model ( "IDS AWAS Model ") assuming an impervious alluvial aquifer boundary was used to determine the lagged depletions to the Big Thompson River for the Bonser Pit. The following parameters were used in the model: transmissivity (T) = 53,859 gallons per day per foot; the distance from the aquifer boundary through the well to the river channel (W) = 1,056 feet; the distance from the centroid of the exposed ground water to the river (X) = 413 feet; and specific yield (SY) = 0.2. This model was run to simulate a steady state condition and so the lagged depletions equal the unlagged depletions on an annual basis. The monthly breakdown of the lagged depletions is shown in the attached Table AI.2. Replacements The proposed source of replacement for the depletions described in this SWSP is fully consumable water leased from the City of Loveland. Coulson Excavating Company ( "Coulson ") entered into a twenty -five year lease with Loveland on January 13, 1998 for 100 acre -feet of fully consumable water, which is currently used for replacement purposes for six gravel pits, including the Bonser Pit. A supplemental lease for up to 19 acre -feet of augmentation water per year was obtained by Coulson on July 23, 2013 to ensure sufficient replacement water is available to all six gravel pits. A copy of each lease is attached to this letter. The leased replacement water shall be delivered at the City of Loveland Waste Water Treatment Plant ( "Loveland WWTP ") (WDID 0402300). Of the total of 119 acre -feet per year of leased replacement water, 24.10 acre -feet per year are dedicated exclusively to replacement of depletions at the Bonser Pit. A 1.65% transit loss has been applied to the projected depletions, based upon this site being located 3.3 miles downstream of the Loveland WWTP and a transit loss of 0.5% per mile. These transit loss amounts are subject to review and modification by the division engineer or water commissioner. If a different transit loss is determined by the division engineer or water commissioner the Applicant must modify their accounting and replacements, as necessary, to be consistent with the determined transit loss. The monthly depletions and replacement requirements are found on the attached Table AI.2. Under the terms of the lease, replacements can be made using a variety of water owned by Loveland including, but not limited to, Wind Gap reusable effluent, Loveland Storage Reservoir water as decreed in case no. 82CW202A, and Colorado Big Thompson ( "C -BT") Project water. In the event that Loveland plans to use C -BT water as a replacement source, Loveland shall comply with the Interim Rule issued by the Northern Colorado Water Conservancy District ( "Northern District ") in May 2005, regarding the use of C -BT Project Water in SWSPs. Prior to the use of C- BT water, Loveland is required to notify this office, the division engineer, and the water commissioner of the amount of CB -T 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.