2005-04-22_REVISION - M1977526 - Laserfiche WebLink

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G -Water Should a liner be constructed to isolate the WSF from groundwater, the liner will ensure minimal infiltration of groundwater. The ]finer will also mitigate potential groundwater impacts to shallow wells during dewatering of the WSF. After mining is completed at the Expansion Area North, the existing small lake will be backfilled, After reclamation of the Expansion Area North, groundwater will no longer be subject to evaporative loss. Water Requirements The estimated water requirements for the proposed mine expansion are summarized in Table G-2. Water losses and consumptive uses during mine operation include the following: • Evaporative loss of groundwater from exposed water surfaces, • Moisture loss from water entrained with mined materials, and • Water consumed for operation of the wash plant, dust suppression, irrigation (if needed) for interim revegetation. Total precipitation was reduced on a monthly basis by 30 percent to obtain effective precipitation as shown in Table G-1. Effective precipitation is used to calculate the net lake evaporation. Gross lake evaporation is offset by effective precipitation to estimate net lake evaporation. The total gross lake evaporation distribution per month for elevations below 6,500 feet mean sea level (Colorado State Engineer 2005) is shown in Table G-2. As recommended by the State Engineer's Office, the National Oceanic and Atmospheric Administration (NOAA) Technical Report NWS 33 (NOAA 1982) was used to determine fire gross evaporation for shallow lakes in the project area. The gross lake evaporation for fire proposed mining operation is estimated to be 3.75 feet per year. Net lake evaporation in feet is calculated by multiplying fire number of acres of total exposed surface area for the water bodies at the site by the maximum water depletions for lake evaporation. Maximum lake depletions aze fire primary water requirements for the mine. During mine operations, the maximum exposed lake surface area is estimated to be 59 acres. Prior to 1981, the existing exposed lake surface area was approximately 28 acres. The net additional exposed lake surface is approximately 31 acres. Assuming that effective precipitation is 70 percent of total precipitation, the total evaporation depletion from the net exposed lake surface is estimated at 89 acre-feet per year as shown in Table G-2. The proposed mining operation is anticipated to process approximately 250,000 tons of sand and gravel per yeas The estimated moisture loss of water entrained with the mined product is approximately 4 percent per by weight of sand and gravel extracted (Colorado State Engineer 2005). The moisture loss for the mined materials is estimated to be 7 acre-feet per year. Water will be consumed for operation of the wash plant and dust suppression. The existing Lake 1 at Worthing Pit will supply water for the wash plant, dust control, and other mine uses. Sources of water will include water from dewatering the pits and groundwater seepage. Water from the wash plant will be recycled to Lake ] . 1898-Frei 112 Hxhibits_(420.05).doc G-$