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The water quality in the alluvium may be impacted by recharge from the stream <br />during periods of extremely low flow. Salinity values within the stream will <br />be higher than normal and influenced more strongly by the mine. This may <br />result in a temporary increase in salinity of the alluvium. <br />Monitoring data collected at the Nucla site suggests that mining will not <br />deplete or degrade the underburden aquifers. Wells completed in the <br />underburden generally exhibit seasonal fluctuations which coincide with <br />recharge from the irrigation ditch. No measurable drawdowns attributable to <br />mining have been observed in underburden monitoring wells. <br />In summary, the hydrologic consequences to the ground water regime can he <br />classified as short and long term impacts. During mining, overburden and coal <br />aquifer flow through the 170 acres at Nuc1a and the 219.9 acres at Nucla East <br />will be interrupted, and will result in discharges of this water from <br />sedimentation ponds at the sites. The extent of drawdown from pumping of the <br />pit is predicted to be 2' at a distance of 0.7 mile from the Nucla East area. <br />Discharge of this water will have no impact on water quality during Deriods of <br />mean flow or greater and will increase total dissolved solids levels in the <br />San Miguel River less than 6~ during the 10-year, 7 day low flow event <br />(47-10)• Q7-10 is the low flow for seven consecutive days that is <br />expected to occur once every ten years. Thus, it rep resents a period where <br />mine-related flows could potentially have the maximum detrimental effects on <br />receiving waters. High salinities resulting from low-flow periods may result <br />in increases in salts found in the alluvium adjacent to Tuttle and Calamity <br />Draws. <br />Long-term impacts from mining at Nucla and Nucla East will consist of changes <br />in the characteristics of the aquifers within the mined area and in the point <br />of discharge of waters flowing through the coal and overburden aquifers. The <br />permeability (both horizontal and vertical) of the backfilled spoils will be <br />higher than that found in the bedrock and will result in a localized ground <br />water reservoir. This aquifer will discharge as saline springs and will <br />nominally affect water quality in adjacent surface waters when water levels <br />are low. <br />Based upon an analysis of the data collected at the site and a projection of <br />the probable hydrologic consequences of future mining, the cumulative <br />hydrologic impacts of mining to the prevailing hydrologic regime will be <br />insignificant. The Nucla permit area, with the Nucla Mine and Nucla East Mine <br />located within a mile-and-a-half of one another is the only permit area within <br />the ground water study area. The ground water of interest within the study <br />area is almost exclusively controlled by artificial recharge (irrigation). <br />Mining will interrupt this artificial system. However, due to the poor <br />quality and limited quantities of already existing ground water there is no <br />beneficial use of the overburden or coal aquifers, Mining does not appear to <br />affect the underburden aquifer. Therefore, the impacts to the around water <br />system will be insignificant. <br />Surface Water <br />The probable hydrologic consequences from coal mining to the surface water in <br />the Nucla permit area will be caused by three factors: a modification of the <br />local surface configuration, change in the runoff characteristics of the mine <br />sites, and alterations of water quality. <br />_21 _ <br />