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April 3, 2012 <br />RN4 <br />of the permit area, and perhaps across bedding planes from adjacent finer - grained <br />shales of the Burro Canyon and Morrison Formations. Approximately 90 to 100 feet of <br />interbedded shale, coal, and sandstone lenses separate the aquifer from the floor of the <br />proposed mining pit, and there is no evidence that the aquifer is under sufficient head <br />to cause leakage from the aquifer into the pit. <br />As the Burro Canyon has insufficient head to cause upward migration of water, no loss <br />of water is anticipated. Some infiltration of precipitation into the pit floor is likely, and <br />by way of fractures some of this water could reach the Burro Canyon aquifer. <br />However, infiltration would occur in such limited quantities that any water quality <br />impacts would be limited to the immediate permit area. <br />Sedimentary rocks of the Dakota Sandstone in the permit area, which will be exposed <br />in the pit walls, probably do not contain measurable amounts of water, as none has <br />been encountered in monitoring wells. Isolated lenses of perched water could be <br />encountered by the pit, however, they will not be sufficient to present either an <br />operational or an environmental problem. <br />Impacts to alluvial aquifers could occur in two ways, the diminution of recharge by <br />detention of water in sediment ponds, and contamination by discharges from spoil <br />springs. The relatively small maximum disturbed area of 257 acres will limit spoil <br />spring development and pond water retention. Therefore, associated impacts should be <br />minimal. <br />Detention of runoff in the ponds will be minor, as the disturbed areas make up very <br />small percentages of the watersheds in question. Therefore, alluvial impacts due to <br />retention of recharge water should be negligible. <br />The permit application states that spoil springs should not develop due to the low <br />precipitation in the area (approximately 12 inches per year). Assuming 2 inches of <br />infiltration per year (a conservative estimate based on 3 inches of infiltration reported <br />at the Seneca II Mine in Routt County, which receives more precipitation than the <br />Hamilton Mine area), approximately 43 acre -feet of water per year of recharge to the <br />spoil aquifer would occur. If the aquifer reaches a steady state which includes <br />discharge from springs at the topographically lowest points of the pit walls, this <br />amount of recharge would translate into an average spoil spring discharge of 26.6 <br />GPM (0.06 CFS) for all sources within the permit area. It is likely that spoil spring <br />development will be considerably less than this prediction, due to the limited amount of <br />contributing rainfall. The applicant projects there will be no spoil discharge. Any <br />spoil spring discharge would be of relatively poor quality, perhaps 2 to 3 times higher <br />in Total Dissolved Solids than background water quality, but would be easily diluted to <br />background quality prior to any use downstream. <br />When ground and surface monitoring resume, the applicant will conduct an annual <br />spoil spring survey that will presumably support these projections. Any springs with <br />discharge of at least 10 GPM will be identified and sampled for a full suite of <br />parameters, with a report to be submitted to the Division by June 15 of each year. <br />16 <br />