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Section 780.21(c) Continued. <br />I <br />of 8182 ac-ft within the backfill, the reclaimed mine area should <br />act as an efficient recharge area for recovery of the coal aquifer <br />from disturbance due to mining. Since the potential outflow rate <br />exceeds the estimated inflow rate, groundwater will not pool up <br />within the backfill to the extent of causing springs to develop at <br />the lowermost level of the backfilled mine pits. Thus, the hydrol- <br />ogic balance of ground water systems will be restored after mining <br />and reclamation is completed. <br />Solute Leaching <br />A potential impact of mining on ground water quality is an increase <br />in the level of dissolved solids as a result of the leaching of <br />disturbed overburden. The reasons for increased leaching are: 1) <br />greater quantities of water are able to move through spoil; and 2) <br />greater surface areas of spoil fragments and particles are exposed <br />• to water. <br />Iu an attempt to quantify the amount of solute leaching which will <br />take place as a result of proposed mining operations, and in order <br />to adequately address 30 CFR 780.21 (c), Kerr Coal worked with Dr. <br />Herbert Gardner in his work on a leaching study of overburden <br />material collected from the mine plan area. Dr. Gardner is with <br />the Science and Education Administration of the U.S. Department of <br />Agriculture at the Colorado State University campus in Ft. Collins, <br />Colorado. The purpose of the leaching study was to determine the <br />amount of water which would have to leach through the spoil until <br />the salt content of the leachate would attain the same level as in <br />the baseline groundwater. This value, represented by E.C., is 533 <br />umhos/cm. <br />For the leaching study, 19 overburden samples were collected from <br />seven drill holes. A list of these samples is given in Table 63, <br />List of Drill Holes Sampled for Leaching Study. The location and <br />780-117 <br />