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PUMP/NG COST ANALYSIS These pumping cost calculations are based on basic operating proce- dures common to the industry and from data supplied by two of the largest pump supply houses in Colorado. Awe understand the regulations, the Division would have to reclaim the pit using the low bid, perform the work the easiest way possible and at the lowest cost. The cheapest way to de-water the pit would be to place the largest pump possible in the lake and pump it down in the shortest period of time possible. To do this we have to make some valid assumptions based on the current conditions, industry standards and best management practices at that time. • An submersible electrical pump would be used and since there is a powerline to the site at this time. The powerline is an asset the landowners would want to keep if mining ceased. • The use of a 3,000 gallon per minute (GPM) pump is typical for this initial draw down. This is within in the existing NPDES permit limits we currently have. our typical discharges from this site during pump down activities is 1.5 to 2.6 million gallons per day (MGD). • Backfilling is a cut/fill operation, the important slopes are the 3h:ly slopes, so partially dewatering the pit is practical since it is common knowledge that gravel pushed into water tends to create 2~h:ly slopes or less. • An accurate estimate of the pumping costs come from actual data collected from the current electrical bills, pump rental information and operating costs at the site at this time. Our proposed dewatering costs are based on pumping the upper 14 feet of the East and the upper 10 feet of the existing west lake so the 3h:ly underwa- ter slopes could be created. By partially pumping the pit you decrease the project time and cost and still complete reclamation to the underwater slopes as required by the law. The 6:1 slopes references in the water volume calculations are for the north slope of the existing west lake because using that rate is closer to what now exists that using the same numbers of 3:1 slopes. This slope is shallower that 3:1 but until the lake is pumped down we can not get an accurate measurement To figure the water volume in the excavated area we calculated the volume of water on the slopes and added the cubic volume of water in the non slope area. The areas found on the slopes are shown on the typical cross-section sheet that is part of the analysis. We used a transmissibil- ity rate of 117,000 GPD which was provided by the Division during bonding calculation for another of our mining operations across the river. When these numbers are added together, you can come up with a number that represents the amount of water has to be pumped to complete the sloping. The 3h:ly slopes can then be created and the lower slopes will form naturally as the cut/fill process progresses. Review of the following sheets will explain the numbers we used to find the total cost and hourly cost used in the bond calculation. (Revised November 13 1997)