2016-02-01_HYDROLOGY - M1977439 - Laserfiche WebLink

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Upper Poudre Combined SWSP Page 4 of January 28, 2016 You have estimated that a total of 29.00 acre-feet of water will be pumped from the Curry Pit at the Home Office Site for dust control purposes, but may periodically come from the North Taft Hill Expansion Site during this plan period. Water pumped for dust control purposes is considered to be 100% consumed. All pumping for dust control purposes must be metered. You have estimated that 848,000 tons of aggregate will be mined at the North Taft Hill Expansion Site during this plan period. Of this amount, 350,700 tons is anticipated to be crushed and 497,300 tons is anticipated to be washed. You have estimated that an additional 59,000 tons of aggregate will be mined at the Home Office Pit Site in December 2016, of which 29,500 tons is anticipated to be crushed and 29,500 tons is anticipated to be washed. The material is mined below the ground water table, but in a dewatered state, therefore the water retained in the crushed product is considered to be 2.0% of the mined material by weight, and the water retained in the washed product is considered to be 4.0% of the mined material by weight. The Alluvial Water Accounting System (AWAS), which uses the Glover method, was used to determine the lagged depletions to the Cache la Poudre River from past and projected evaporation and operational losses at each site. The following parameters were used in the model with the alluvial aquifer boundary condition: the distance (X) from the centroid of the exposed ground water surface to the river; the width (W) of the aquifer on the side of the river where the pit is located; the transmissivity (T); and the specific yield (S). The Glover parameters used for each site are shown in Table C below. Table C - Glover Parameters Site Name X (ft) W (ft) T (gpd/ft) S Home Office Pit (Curry Pit) 1,000 6,500 160,000 0.2 Home Office Pit (area to be mined) 1,675 4,675 160,000 0.2 Overland Ponds Pit 2,000 3,000 160,000 0.2 North Taft Hill Expansion Site Pit 1,600 2,900 160,000 0.2 The estimated consumptive use and lagged stream depletions due to past and projected evaporation and operational losses at the subject sites will total 88.51 acre-feet for this plan period as shown on the attached Table 5. Lagged depletions due to past evaporation and operations at the two Treiber Lakes and three Lamb Lakes are replaced under the Partners Combined SWSP. Dewatering The Home Office Pit will be dewatered prior to mining and continued throughout the remainder of this SWSP. The North Taft Hill Expansion Site will be continuously dewatered throughout this plan period. For the purposes of this SWSP, you have assumed the site to be in a steady state condition where dewatering accretions equal the lagged depletions. All dewatering from the North Taft Hill Expansion Site and Home Office pit site will be pumped to the unlined pre-81 ponds just south of each site. The ponds have the ability to overflow directly to the Cache la Poudre River. A totalizing flow meter has been installed on the pump and monthly meter readings are reported on the submitted accounting for this plan. All water spilled from the ponds is also metered. As long as the dewatering operations are constant the North Taft Hill Expansion Site and Home Office Pit site may continue to operate assuming steady state conditions. Once dewatering ceases or is reduced in its flow, lagged depletions will impact the river. At least three years prior to a modification in dewatering operations, the Applicant must provide a plan showing how lagged post-pumping depletions will be replaced in the proper time and amount. The post pumping analysis shall use the meter data from the dewatering totalizing flow meter. All cells of the Overland Ponds Site were fully lined, therefore dewatering at the site has ceased.