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1 <br /> <br />' Lake Evaporation <br />' The mining operation will create an open water body with 78.6 <br />acres of surface area. This amount could be reduced by <br />backfilling some of the lake areas with overburden and water <br />material from the mining operation. The average annual <br />evaporation from a shallow lake is 35 inches based on NWS <br />Technical Report 33. A NOAA report, technical Paper 37 shows <br />Class A pan evaporation with a 0.7 pan coefficient to be 31.5 <br />' inches. A third source of pan evaporation data from NWS showed <br />Class A pan evaporation to be 30 inches. Using an average of the <br />three sources, the annual average evaporation is estimated to be <br />32 inches. A credit of 9.5 inches is given for effective <br />precipitation on the area. In addition, a credit for historic <br />consumptive use of plant life on the property before it was mined <br />is also given. In this case, the amount credited after <br />precipitation is removed is 14.5 inches per year based on the <br />crops (alfalfa and corn- that were grown on the farm. Assuming <br />full credit for crop usage, this would leave a deficit of 8 <br />' inches evaporation to be made up by the operator. Eight inches <br />per year would be equivalent to 52.4 acre-feet per year. <br />' A summary of the consumptive uses associated with the mining <br />operation are as follows <br />' Moisture losses 5.9 acre-feet <br />Wash Water 0.7 acre-feet <br />Dust Control 4.9 acre-feet <br />Lake Evaporation 52.4 acre feet <br />TOTAL ANNUAL WATER CONSUMPTION 63.9 acre-feet <br /> <br />1 <br /> <br />1 <br /> <br /> <br />1 <br />The method of dry Wining will cause a slight drop of the <br />groundwater table in the immediate vicinity of pit. This <br />typically reduces to less than 1 foot at a distance of <br />approximately 500 feet. The proposed mining operation is located <br />between St. Vrain Creek and Boulder Creek which both serve as a <br />hydrologic barrier. The wells and surface water rights located <br />in the area are not expected to be impacted by this mining <br />operation. <br />Although total consumptive use during the year is expected to be <br />63.9 acre-feet, the amount of water that must be replaced will be <br />less. Table G-1 shows typical monthly consumption based on sales <br />of nat•erial over a year. Some material is processed and moved <br />during winter months when there is no call in the river. The <br />operator will propose to replace only water that protects senior <br />water .right owners. These rights will typcially be calling the <br />river ~9uring the summer months from June through September. <br />G-3 <br />