2008-11-03_REVISION - M1999098 - Laserfiche WebLink

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the event that open pond areas are left behind, Aggregate will have an application for a plan for augmentation filed in water court three years prior to completion of reclamation. At that time the appropriate amount of replacement water will be in place. Aggregate will also properly account for all post-pumping depletions associated with this site. The amendment properties in the north site lie outside the 100 year floodplain. A portion of the east site amendment property along the south boundary and adjacent to the existing permit boundary of Cell 2, lies within the 100 year floodplain. There are no structures proposed in the amendment properties within the 100 year floodplain. Flood Hazard Development Permit FHDP-359 was issued by Weld County on February 28, 2000 based upon information contained in a Flood Hazard Development Permit Applicatoin prepared by Tuttle Applegate, Inc. for the currently permitted property. Water Requirements The proposed annual consumptive use for the amendment sites during active mining is estimated to be 19.6 ac-ft and will result from evaporative losses and operational losses. Evaporative losses are dependent on the exposed water surface area, which may vary throughout the mining operation. The exposed surface area associated with the amendment sites is going to be the dewatering trenches which are estimated to be approximately 1 acre in size. To determine the evaporative loss, the product of net annual evaporation and total exposed groundwater surface area is taken. Net annual evaporation is the difference between gross annual evaporation and effective annual precipitation. The NOAA Technical Report NWS 33, Evaporation Atlas for the Contiguous 48 United States (U.S. Department of Commerce), was used to determine gross annual evaporation. For this location, gross annual evaporation was estimated at 43 inches. Monthly evaporation percentages, as suggested by the Office of the State Engineer, were used to calculate monthly evaporation. The average annual precipitation was determined to be 12 inches per year, based on the precipitation isohyetals from the Colorado Decision Support System (CDSS) website for this area. We obtained the data from Western Regional Climate Center for the Greeley UNC Weather station (#50950). This site had an average annual precipitation total of 14 inches. We took the monthly data from the Greeley UNC site and pro-rated each month to ensure a 12 inch annual total. We estimate that 2.88 acre-feet of evaporation will occur for each acre of exposure. The annual production from the Riverview Resource Amendment site is estimated at 500,000 tons. The moisture content of the material hauled off the site was assumed to be four percent by weight and results in an annual amount of 14.7 ac-ft of water retained in the product. Dust control is required for internal haul roads and stockpiles and was estimated to be 2 ac-feet from previous experience in mining operations similar to this one. River Resource Amendment to Permit M1999098 112C Page G2 of G37