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-13- l'I. Hydrologic Balance: (con't) After the pit is backfilled there is the potential for an effect on the water quality of the aquifers within the mined zone. Leaching of the backfilled spoil could contribute additional contaminants to these aquifers. The geochemical data indicate the presence of some parameters at substandard levels in the overburden which, upon weathering, could increase the already high levels of concentration in the ground water contained with the coal seams. Further contamination of this water will not be detrimental. It is very unlikely that contaminants leached through the pit would reach the underlying Twenty Mile sandstone because of the intervening sequence of siltstones, mudstones and minor sandstones which are greater than 150 feet in thickness. These intervening strata essentially isolate the Twenty Mile sandstone from the effects of the pit. 1•later quantity in the coal aquifers will be affected during the mining operation. Analysis by the applicant (see Section I of Appendix L, Volume V) indicates that the drawdown due to dewatering of the coals will be relatively insignificant. The actual dewatering of the aquifers will result in an elongated cone of depression extending down gradient which would be of limited extent. After reclamation it will be approximately 30 years before these aquifers begin to recharge (Appendix R, page 50, Volume VII). The estimated drawdown would occur within 20 days, based on applicant's '~orst case" analysis, after the pit is excavated. Because the mine has already progressed to the lowest coal and further mining will occur in a direction updip of the initial cut, the dewatering of the zone is nearly complete and no further dewatering by the pit should occur. Eighteen seeps and springs were identified in [he area of the mine. Most of these occur in strata below the mining zone and are isolated from the effects of the mine. A few of these springs originate in lenticular sandstones of limited extent which are above the mine zone but may be interrupted by the operation. None of these springs are expected to yield more than 1 gallon per minute and therefore do not contribute significant flow to the drainages they discharge into. One spring (SP-4) which discharges into Hayden Gulch, will be interrupted. The interruption of flow from this spring would only result in a depletion of about .04% of the flow in Hayden Gulch (measured at the confluence with the ldilliams Fork River). The applicant has estimated that SP-4, the lowest spring to be affected, will completely recharge approximately 30 years after reclamation of the site. Other springs which are affected will take longer because they are stratigraphically higher than SP-4 and because they discharge further from the recharge area (pit) than SP-4. As indicated earlier none of these springs contribute substantial amounts of flow to the receiving streams.