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• impact to adjacent wells. Surface water systems, primarily Dry Creek and Sage Creek, will <br />show little impact from induced infiltration via drawdowns in the Trout Creek where the <br />unit outcrops in both stream beds. Since both surface water systems are over <br />appropriated, a water augmentation plan was developed by Peabody and approved by the <br />Colorado State Engineer's Office. Any minor impacts to adjacent water users from the <br />production well pump age will be mitigated according to the augmentation plan. <br />Impact of Replaced Spoil Material on Ground 14ater 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 to the pits. A potential long-term <br />impact to the system will consist of the time period necessary for resaturation of spoil <br />material and reestablishment of the natural hydraulic gradient. <br />Resatu ration of spoil material is dependent upon its permeability and porosity that is <br />largely created during replacement of materials into the mined area. Spoil material <br />replaced using only a dra gline or a scraper yields hydraulic conductivities 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 is estimated that hydraulic <br />conductivity and porosity increase 6y approximately 25 percent in the spoil upon <br />replacement, regardless of the equipment used to move the material (VanVoast and Hedges, <br />1975). <br />Since the hydraulic conductivity of the replaced spoil will vary depending on the type of <br />equipment used to move the mater~j al in place, several techniques will be used to replace <br />spoil material at Seneca II-W, Some spoil placement will be accomplished using cast <br />blasting. Some replacement wi 111 be conducted using scrapers and draglines. Final <br />contouring of the spoil surface will be conducted using dozers and scrapers. The overall <br />hydraulic conductivity of the (spoil should be higher than the conductivity of the <br />surrounding undisturbed material ~:ompri si ng the shallow aquifers, regardless of the method <br />of replacement. <br />The hydraulic character of the spoil will also be affected by the texture of the material <br />after it is replaced. Although +:he spoil will exhibit increased porosity, the degree of <br />particle sorting is decreased anti the material will have amore homogeneous texture. <br />15 <br />