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staging area is 34.3 ac ft - 31.5 ac ft = 2.8 ac ft. This amount will be obtained from the clean <br />overburden portion of Phase 2 prior to any mining in any phase. This portion is the southwest <br />corner of the phase, which is approximately 1.4 acres x 2.5 ft depth = 3.5 ac ft, which is more than <br />the 2.8 ac ft needed to complete the coveting of the staging area. Once the staging area has been <br />covered and the fill has been compacted, mining of Phase 1 will commence. Trenches 1 and 2 will <br />not be installed unless monitoring anal sy es of wells shows contaminant plume movement to the <br />south of a concerning rate. This will not bepossible until at least a significant portion of Phase 1 is <br />mined and sufficient well data is collected. For this reason, the trenches shown on Ma~C-2 are <br />motional or potential, dependin¢ on the results of the analyses. CDPHE will 6e the sole <br />determinin a ency to decidesand when the trenches are to be installed. and will also determine <br />the exact nature of thge trenches. <br />Also prior to mining Phase 1, a 2.0 high berm of 2.SH:1V sideslopes will be constructed of existing <br />earth around the entire perimeter of the site. This will prevent any runoff from entering the site and <br />the berm will also be placed immediately outside (above) the 100 year floodplain to further prevent <br />that any flood waters could enter the pit. The existing berm on [he south edge of the permit area is <br />already more than 2.0 feet high. No additional work will be done to improve this berm. The 2.0 feet <br />high specification is meant to be a minimum specification for the berm around the permit area. This <br />berm will be left after reclamation to also prevent flood water from entering the lake. <br />Trench Details (if they are installed) <br />Since known petroleum hydrocarbon contamination exists on the top of the groundwater north of <br />the staging area, and since the mining of the designated areas requires pumping of the groundwater, <br />there is some risk that the free product from the area north of the permit area could be drawn down <br />to the mining pit as a result of pumping. Although levels are low and the risk may be low, 2 <br />trenches may be installed as shown on Map C-2 which will be kept at a water level elevation of <br />4452' or higher and dug to 5' below normal ground water level (4449 in order to provide positive <br />hydraulic gradient against the ground water to the north to keep any contamination from entering <br />the pit area. Therefore, the trenches will be dug to an elevation of 4444'. The sideslopes will be <br />Gilsonite Pit 1/04 9 <br />