2012-12-07_HYDROLOGY - M1994005 - Laserfiche WebLink

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Mr. Peter Foster December 6, 2012 Colona Gravel Pit, Substitute Water Supply Plan Page 2 of 7 attached to this letter. For the purposes of this SWSP, this affidavit will be accepted for dedication to this plan; however, if the State Engineer determines that a different affidavit or dedication process is necessary to assure proper dedication of the shares, additional information may be required prior to future SWSP approvals. DEPLETIONS Depletions at the Colona Pit will occur as a result of evaporation from exposed ground water, dust suppression, water removed with the mined product, and water filling the gravel pit as a result of material removal. Anticipated net depletions for Year 1 of the proposed renewal period total 41.0 acre - feet, consisting of 17.37 acre -feet of evaporative losses from 6.8 acres of exposed ground water, 3.0 acre -feet used for dust suppression, and 20.7 acre -feet for ground water lost with the mined product and filling the pit resulting from mining of 60,000 tons of aggregate (10,000 tons per month for 6 months), as shown in the attached Table 2 -A. Anticipated net depletions fall to 30.7 acre -feet for Year 2 of the proposed renewal period; the values for depletions from evaporative losses and dust suppression are unchanged from Year 1, but depletions from ground water filling the pit due to mining of 30,000 tons of aggregate (5,000 tons per month for 6 months) will decline to 10.3 acre -feet, as shown in the attached Table 2 -B. No groundwater will be used for equipment washing, concrete production, reclamation, or any other purpose. Net evaporative depletions were calculated using a gross annual evaporation of 43.00 inches from the exposed water surface, with a credit of 9.63 inches for effective precipitation. Based on monthly average temperatures reported for the Montrose 2 and Ridgeway weather stations, ice cover was assumed for the months of December, January, and February; therefore no evaporative consumptive use was charged for those months. For the purposes of this SWSP, the Applicant shall replace the net evaporative depletions from the exposed ground water surface area that may occur during the assumed ice cover period (December through February) for any time that the pit is not completely covered by ice. The net depletion of ground water due to evaporation from the 6.8 acres of exposed ground water was calculated to be 17.37 acre -feet for each plan year, as shown on the attached Table 1. The Applicant has estimated that 5,400 gallons of water per day will be used for dust suppression, five (5) days per week for the period of March to November. This results in a total of 3.00 acre -feet of water used for dust suppression each year, as shown on the attached Tables 2 -A and 2 -B. An estimated 10,000 tons of aggregate will be removed monthly from the Colona Pit during the period of October through March of Year 1 and 5,000 tons of aggregate monthly during the period of October through March of Year 2. Based on a density of 1.8 tons of aggregate per cubic yard and 60,000 tons of aggregate removed in Year 1, 20.7 acre -feet of ground water will subsequently fill the pit; for 30,000 tons of aggregate removed in Year 2, 10.3 acre -feet of ground water will fill the pit. This amount includes the 4% of water removed with the mined material. A Glover stream depletion model was used to calculate lagged depletions to the Uncompahgre River, assuming steady state conditions. The following parameters were used in the model: transmissivity (T) = 50,000 gallons per day per foot; specific yield (SY) = 0.15; distance from the centroid of the pit to the river (X) = 2,000 feet; and distance from the aquifer boundary through the pit to the river (W) = 5,000 feet. Total annual lagged depletions were calculated to be 41.0 acre -feet in Year 1 and 30.7 acre -feet in Year 2, as shown in Tables 2 -A and 2 -B.