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Inc Mr. Kim Lawrence July 7, 1998 Page 2 2. DEPLETIONS Water depletions during mining of Sections 1 and 2 include: Evaporation from the dewatering trench initially around Section 1 and then Sections 1 and 2; Evaporation from a settling pond that will be used to settle sediments from the dewatering trench before the water is discharged back to Godding Hollow; Evaporation from the wash pond; Water lost through dust control, concrete hatching, and asphalt production; and Water lost through the material mined and hauled offsite. 2.1 Evaporation Evaporation losses are based on the NOAA Technical Report NWS 33, Evaooration Atlas for the Contieuous 48 United States. For this location, annual gross evaporation is approximately 41.5 inches. Monthly evaporation is calculated based on the percentage set forth by the guidelines from the Office of the State Engineer. Precipitation is from the Climatological Data published by NOAH at the Longmont 2ESE Station. The long term (1950 through 1996) average annual precipitation at the Longmont 2ESE Station is 13.37 inches. The net evaporation a[ the site is computed as the gross evaporation minus the effective precipitation, which is computed as 70 percent of the total precipitation. Hall-Irwin will mine the site in sections. A dewatering trench will be constructed prior to mining each section to control the groundwater. The dewatering trench will initially be constructed around Section 1. It will be extended to encompass each additional section prior to mining that section. For example, before Hall-Irwin is ready to begin mining Section 2, the existing dewatering trench around the perimeter of Section 1 would be expanded to include Section 2. Thus, when Section 6 is being mined, there will be a dewatering trench around the entire perimeter of the westerly pond. When Hall-Irwin completes mining around the westerly pond, the dewatering trench will be reclaimed. During mining of Section 1, groundwater will be exposed in the dewatering trench around Section 1 and at a settling pond. Water in the dewatering trench will gravity flow to the settling pond before it is discharged into Godding Hollow Gulch. The dewatering trench around Section 1 is approximately 2,050 feet in length and four feet wide, resulting in an exposed water surface area of 0.19 acres. The dewatering trench around Sections 1 and 2 is approximately 3,400 feet in length and four feet wide, resulting in an exposed water surface area of 0.31 acres. One settling pond will be constructed for the mining of each section. It will be removed at the completion of mining that section and a new settling pond will be built for the next section of mining. It is estimated that each settling pond will be about 0.11 acres. Evaporative losses from the Section 1 - dewatering trench and the settling pond. (0.19 acres + 0.11 acres = 0.30 acres) will total 0.81 acre- feet as shown on Table 1. Evaporative losses from the Section 2 dewatering trench and settling pond (0.31 acres + 0.11 acres = 0.42 acres) will total 1.11 acre-feet as shown on Table 2.