2012-02-29_HYDROLOGY - M2001107 - Laserfiche WebLink

Home Browse Search

Michelle L. Hatcher NCCI Pit #1 SWSP February 28, 2011 Page 2 Depletions Evaporation and Operations The exposed ground water surface area is 9.75 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 9.75 acres at the site totals 29.0 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 500,000 tons of aggregate will be mined in 2012. The aggregate is assumed to have a 4% moisture content and thus the water lost in mined product is projected to be 14.7 acre -feet per year. The anticipated total consumptive use for this plan is 49.9 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 2012 cause by past and projected mining activities at the NCCI # 1 Pit is 49.53 acre -feet as shown on Table 4. Dewatering The mining operation has continuously dewatered directly back to the South Platte River since mining operations commenced in 2003. Per an e-mail from the Applicant dated February 10, 2012, the operator estimates a continuous pumping rate of 4 million gallons per day, or approximately 2,778 gallons per minute. 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 2012, 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. If not already installed, a totalizing flow meter must be installed to accurately measure and record monthly dewatering amounts. This SWSP will not be renewed until such a meter is installed with monthly meter readings reported on submitted accounting. Replacements The source of replacement water is fully consumable water leased from Thornton. The leased water from Thornton will be released from the Metropolitan Wastewater Treatment Plant ( "Metro "). A 0.5% per mile transit Toss (14% overall loss for the 28 miles between Metro and the point of depletion) was accounted for in the SWSP. The quantity of replacement water needed for this plan in 2012 is 57.59 acre - feet. 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.