2014-03-10_HYDROLOGY - M2001107 - Laserfiche WebLink

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Michelle L. Hatcher NCCI Pit #1 SWSP March 7, 2014 Depletions Evaporation and Operations Page 2 of 5 The exposed ground water surface area is 8.48 acres. Net evaporative depletions were calculated using a gross annual evaporation of 45 inches from the exposed ground water surface, with a credit of 9.4 inches for effective precipitation. The net depletions of ground water due to evaporation from the 8.48 acres at the site totals 25.2 acre -feet per year, as shown on the attached Table 2. The Applicant projects a dust control water use of 10,000 gallons per day for 5 days per week and 40 weeks per year. In total this equates to a consumptive use of 6.2 acre -feet per year for dust control. The Applicant also estimates that 450,000 tons of aggregate will be mined in 2014. The aggregate is assumed to have a 4% moisture content and thus the water lost in mined product is projected to be 13.2 acre -feet per year. The anticipated total consumptive use for this plan is 44.6 acre -feet. See Table 3 for the monthly breakdown of these values. The IDS AWAS stream depletion model was used to determine the lagged depletions to the South Platte River caused by the NCCI # 1 Pit. The following parameters were used in the model: transmissivity (T), 150,000 gallons per day per foot; specific yield (SY), 0.2; distance from the South Platte River to the edge of the alluvium (W), 5,000 feet; and distance from the centroid of the exposed surface water areas to the South Platte River (X), 3,300 feet. The total lagged depletions during 2014 cause by past and projected mining activities at the NCCI # 1 Pit is 25.3 acre -feet as shown on Table 4 (excluding dewatering). Dewatering The mining operation has continuously dewatered directly back to the South Platte River since mining operations commenced in 2003. The Applicant estimates a continuous pumping rate of 4 to 10.5 million gallons per day for 2014. As long as the pit is continuously dewatered, the water returned to the stream system should be adequate to offset the depletions attributable to the dewatering operation. However, once the dewatering rate is reduced or ceases altogether, depletions will accrue to the river that will not be offset by the dewatering discharge. At least three years prior to completion of dewatering, a plan must be submitted that specifies how the post pumping dewatering depletions will be replaced in time place and amount. Should dewatering operations cease or be reduced during 2014, this SWSP will become invalid and an amendment showing how the lagged depletions will be replaced must be submitted to our office immediately. Dewatering operations must be metered to the satisfaction of the Division Engineer. Meters were installed on the dewatering pumps in May 2012. In order for the Applicant to claim net accretion credit for dewatering operations, the actual use as demonstrated by the dewatering meters, must be analyzed to show true pumping impacts. Replacements The source of replacement water is fully consumable water leased from Thornton. The quantity of replacement water needed for this plan in 2014 is 34.02 acre -feet. The leased water from Thornton will be released from the Metropolitan Wastewater Treatment Plant ( "Metro ", WDID 0200700). A 0.5% per mile transit loss (14% overall loss for the 28 miles between Metro and the point of depletion) was accounted for in the SWSP. Conveyance loss for delivery of augmentation water is subject to assessment and modification as determined by the water commissioner and /or division engineer. Thornton is the owner of the NCCI Pit #1 site and will continue to make replacement for depletions at the NCCI Pit #1 site. The lagged depletions include depletions resulting from past uses at the site, and the replacements are shown on attached Table 4.