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the Yoast production well have been accounted for In the modeling scenarios and are of no <br />significance. <br />The Yoast production well pumpage will cause minor amounts (<.55 acre ft/yr) of <br />screamflow depletion (see Table 2, Attachment 16-2, Tab 16) Sn the Yampa, Fish, Middle, <br />and Trout Creek channels. The greatest amounts of atreamflow depletion will occur Sn Sage <br />and Grassy Creek with 4.9 and 5.8 acre ft/yr depletions, respectively. The surface water <br />depletion impacts are small in magnitude 1<6 acre ft/yr), of moderate extent (<10 mile <br />radius for drawdowns >1 food and long in duration 19 years of pumping and 20 years of <br />recovery). Since a portion of the surface water systems are over appropriated, a water <br />augmentation plan was developed by SCC and approved by the District Court. Any <br />minor Lmpacts to adjacent surface water users from the production well pumpage will be <br />mitigated according to the augmentation plan. The significance of the eu rface water <br />Impacts from production well pumpage Ss minimal as an approved augmentation plan is Sn <br />place to mitigate the depletions. <br />Impact of Replaced Spoil Material on Ground Water Flow and Recharge Capacity. Mining pits <br /> will remain open until all economic deposits of coal have been removed. The short-term <br /> impact to the ground water system will consist of a decline in the standing water level <br /> elevation due to the pumpage of ground water inflow [o [he pits. A potential long-term <br /> impact to the system will consist of the time period necessary for resaturatlon of spoil <br /> material and re-establishment of the natural hydraulic gradient. <br />Resatucation of spoil material is dependent upon Sts permeability and porosity that Ss <br />largely created during replacement of materl als Into the mined area. Spoil material <br />replaced using only a dragline or a sc ra pet yields hydraulic conductlvitiea of 35.3 ft/day <br />and 0.4 ft/day, respectively (Rahn, 1976). Since the spoil material is less dense after <br />it is mined than before it is mined, greater hydraulic conductivities result because of ~' <br />the changed spoil volume and increased spoil porosity. It Se estimated that hydraulic <br />conductivity and porosity increase by approximately 25 percent Sn the spoil upon <br />replacement, regardless of the equipment used to move the material (VanVOast and Hedges, <br />19751. <br />Since [he hydraulic conductivity of the replaced spoil will vary depending on the type of <br />i <br />14a Revised 11/01/95 <br />