2012-02-16_REVISION - M2002020 (9)

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groundwater on the 25 Avenue Site. No long -term impacts to the Cache la Poudre River or Greeley No. 3 Canal are anticipated. Dewatering associated with the proposed mining pit (SW Ponds) has the potential to impact alluvial groundwater wells near the pit. A well permit application search of the SEO database was used to locate wells near the proposed amendment area. The Water Resource Map (Exhibit C -4) illustrates existing recorded well permit applications within 600 feet of the proposed permit boundary and approximately 1/4 mile from the SW Ponds (proposed mining cell area). Although there may be other wells in the area, they are not recorded with the SEO. Water Requirements Evaporative losses during mining or reclamation activities are not expected to increase over existing conditions at the site. According to previous Greeley West Pit SWSP plans, the net annual depletion in the proposed amendment area is 86.9 acre -feet. This depletion is based on 29.7 acres of exposed groundwater and a net evaporative loss of approximately 2.9 feet per year. The 29.7 acres of groundwater surface area was determined from 75.2 combined surface acres from the NE Pond, SE Pond, and SW Ponds minus the pre -1981 exposed groundwater credit of 45.5 acres. During mining, the SW Ponds will be dewatered, reducing the exposed groundwater surface area by approximately 32.5 acres and annual evaporative losses by 95.1 acre -feet. Along with this decrease in annual evaporative losses, mining activities will add additional evaporative losses. Mining activities will include exposed groundwater from dewatering trenches and potential settling basins and operational water losses from dust control and water retained in product hauled off -site. The maximum exposed groundwater area for dewatering trenches and settling basins within the mining cell will amount to less than one acre, or an annual evaporative loss of less than 2.9 acre -feet. If the moisture content of the material transported off -site is assumed to be 4 percent by weight, and the annual mined product is estimated to be 200,000 tons per year, then the annual amount of water lost in product is approximately 5.9 acre -feet. It is also estimated that approximately one acre -foot of water will be needed for dust control during mining and reclamation activities. Therefore, the total annual loss from mining and reclamation operations is 9.8 acre -feet. A new SWSP for evaporation and operational losses will be obtained from the SEO. Sources of Replacement Water The replacement of consumptive uses will be accounted for in a new SWSP administered by the SEO. Previous Greeley West Pit SWSP plans list sources of replacement water as the Greeley Irrigation Canal No. 3 (WDID 030093) during irrigation season and fully consumable water provided by the City of Greeley (point of replacement is the Greeley Wastewater Treatment Plant) during non - irrigation season. Once mining is complete and the slurry wall is constructed, remaining evaporative losses at the site will be account for with a Greeley West Pit pre -1981 exposed groundwater credit of 45.5 acres (November 1, 2001, Office of the State Engineer to Greeley 25 Avenue Site DRMS 112 Permit Amendment Application Page 19