2012-12-12_HYDROLOGY - M2004013 - Laserfiche WebLink

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Michelle Cunico Johnson, Martin and Wood Page 2 December 12, 2012 In accordance with the letter dated April 30, 2010 (copy attached) from the Colorado Division of Reclamation, Mining, and Safety ( "DRMS "), all sand and gravel mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. The April 30, 2010 letter from DRMS requires that you provide information to DRMS to demonstrate you can replace long term injurious stream depletions that result from mining related exposure of ground water. In accordance with approach nos. 1 and 3, you have indicated that a bond has been obtained for $410,693 through the Division of Reclamation, Mining, and Safety ( "DRMS ") to assure that depletions from groundwater evaporation do not occur in the unforeseen event, or events, that would lead to the abandonment of the Pit. DEPLETIONS Under Scenario A for the two months when the cell is actively being mined, evaporation will occur from a total of 6.52 acres of water in the four settling and wash ponds and a dewatering trench. Total estimated annual aggregate production is 25,000 tons per year and the water lost with the mined product associated with 25,000 tons of aggregate is 0.74 acre -feet for both 2013 and 2014. The total annual water consumption for dust suppression is estimated at 0.56 acre -feet for both 2013 and 2014. Your attached Table 1A shows the site net evaporation calculations (25.23 acre -feet) and water consumed by site operations (1.30 acre - feet). Effective precipitation credit was applied to this plan. Under Scenario B, evaporation will occur from exposure of a total of 7.46 acres of water in four settling and wash ponds and in the mined cell for the ten months when it is not actively being mined. Your attached Table 1B shows the site net evaporation calculations (26.19 acre -feet) and water consumed by site operations (0 acre - feet). Effective precipitation credit was applied to this plan. You have provided a monthly breakdown of lagged depletions at this site for each of the aforementioned scenarios in your attached Table 2. The Glover stream depletion analytical model was used to determine the lagged effects of the evaporation and operational losses from the mine. The model was developed for depletions to the Arkansas River under the following assumptions: X =2,030 feet (the distance from the centroid of the exposed surface area to the river), 2) W =7,875 feet (the distance from the aquifer boundary through the exposed surface area to the river channel), 3) T= 100,000 gal/day/ft (transmissivity of the alluvial aquifer between the well and the river), and 4) S =0.2 (specific yield). Table 2 shows that under Scenario A, the lagged stream depletions during the period January 2013 — December 2013 are estimated to be 25.36 acre -feet and the lagged stream depletions during the period January 2014 — December 2014 are estimated to be 26.16 acre -feet. These estimates are based upon evaporative losses from the settling and washing ponds, mined cell, and dewatering trench, water removed in the mined product, and water used for dust suppression (see attached Table 1A). Depletions associated with refilling Pond 5 after the dewatering stops in July were accounted for in this request as shown in Table 2 under Scenario A. It was estimated that the mined cell (Pond 5) would return to its approximate current level (approximately 300 feet by 200 feet by 2 feet deep) within one month in August following mining. The volume of water refilled in the cell (2.75 acre -feet) was added to the total evaporation and operational losses in August 2013 and August 2014, and lagged to the stream. An instantaneous credit of 2.75 acre -feet from dewatering the cell prior to mining was removed from stream depletions in June 2013 and June 2014.