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<br />Revised 02/06/92 <br />IS. Assessment of Probable Cumulative impact <br />The purpose of this discussion is to provide an assessment of the <br />cumulative impacts of the proposed mine and any adjacent mines on <br />the hydrologic balance of the region. In this case there are no <br />other mines located near the Keenesburg mine that could effectively <br />impact the hydrologic balance above what is predicted for the <br />individual mine site. The original 1981 permit granted Coors Energy <br />Company the right to mine a 421 acre site with an additional 920 <br />acres anticipated over the next 20 years. <br />The purpose of this update is to provide the original assessment <br />made in 1981 with current information regarding current land use <br />practices at the Keenesburg mine site. As of December 1987, the <br />Keenesburg site no longer has been involved in the mining of coal <br />and has instead become a disposal facility for fly ash. All coal <br />stockpiles and coal mining activity ceased on December 1987. Fly <br />ash disposal began on October 1987 and was approved by the Division <br />on April 1, 1987 in Technical Revision #13. The revision was <br />approved with the addition of five stipulations that addressed both <br />the monitoring requirements and the placement of ash <br />specifications. Ash disposal practices have been both in Pit A and <br />Pit B. Pit C was never opened nor mined. <br />Since there are no surface drainages on the site, the effect of <br />mining and disposal of fly ash in the pits has no effect on the <br />surface hydrology. An occasional rain shower may saturate only a <br />small surface area of the spoil and ash. The primary effects of <br />the operation therefore, are to the ground water, in particular the <br />potentiometric surface. From the original assessment, the effects <br />of mining on the drawdown of the piezometric surface in the Laramie <br />Formation had been expected to increase from the current 1050 feet <br />to 2090 feet. Impacts from this slight increase in drawdown were <br />estimated to be minimal since there have been no users in the <br />vicinity of the site. Drawdown was estimated to be greater in the <br />western portion of the mine while minimal at Ennis Draw area to the <br />east. The question as to water quality moving through the spoils <br />and fly ash lifts in the pits has been addressed in the Annual <br />Hydrology Report (1981-present outlined in Stipulation 5) from <br />information gathered by two monitoring wells strategically placed <br />in the permit area. One well (SMW-2) has been placed southwest of <br />the ash disposal area in Pit A (Stipulation 23). This well has <br />monitored the effluent from the fly ash while the overburden <br />potentiometric surface has been altered. It is estimated that <br />mining activities may effect the potentiometric surface for as many <br />as 140 years. A second well (AMW-1) has been placed northeast of <br />the ash disposal area in the overburden aquifer. This well has <br />monitored the water quality leaving the ash disposal area for <br />migzation of fly ash effluent while the spoils and ash are <br />