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and the probability of future occurrence of such pollution. The evaluation concluded that all <br />reclamation has been completed in the bond release azea, and if water pollution is occurring, it does <br />not impair the postmining land use within the permit azea, and is not likely to cause material damage <br />outside the permit azea. The following sections of this findings document discuss erosional stability <br />and hydrologic impacts. <br />Erosional Stability <br />During the bond release inspection, rills and gullies were found at several locations on reclaimed <br />hillslopes in the bond release azea. These channels appazently formed during region-wide storms that <br />occurred 8 days before the inspection. These storms probably exceeded the intensity of a storm <br />having a 10-yeaz frequency on the mine site, as shown by area precipitation records. Rill and gully <br />erosion is a natural geomorphic feature in semi-arid southwestern Colorado, and the rill and gully <br />channels on the mine site comprise a hillslope drainage system that established itselfduring a greater <br />than 10-year storm. Further significant rill and gully formation is not expected because the existing <br />channels can adequately convey runoff down the slope. These channels should have long-term <br />stability because they are armored by rock in the bottom of the channels. To direct runoff into these <br />channels, away from open hillslopes, the operator shaped head-cut areas with hand tools in <br />December 2004. This work was conducted under Technical Revision TR-34. Rock riprap was <br />installed in the channels in May 2005, as approved in MR-53. The Division inspected the riprap <br />work on May 26, 2005, and found it met the design requirements of MR-53. The operator also <br />restored other permanent structures (a diversion ditch and drop structure} to original specifications as <br />required by 4.05.17. <br />Evaluation of Hvdroloeic Imuacts <br />Leachate Formation -Coal spoil leachate probably is forming in the backfilled pits of the reclaimed <br />Chimney Rock Mine. The leachate forms as slightly acidic meteoric water infiltrates from the <br />ground surface through spoil backfill. As the water percolates through the spoil, it dissolves and <br />oxidizes minerals in the spoil, resulting in a leachate high in dissolved solids. Sulfate would be a <br />main component of the leachate. The TDS concentration ofthe leachate can be expected to reach an <br />ultimate maximum in the range of 3000 to 4000 mg/1. This concentration may continue for several <br />hundred yeazs, as predicted for the Seneca II Mine in Routt County, Colorado (LTSGS Water- <br />Resources Investigations Report 92-4187). <br />Leachate Migration -Kaiser's backfilled mine pits may dischazge coal spoil leachate into the <br />Stollsteimer Creek alluvial aquifer where the pit was excavated in the alluvium. The following two <br />pathways are predicted for the dischazge: a) leachate may flow in the subsurface from the east side <br />of the backfilled Barren Ridge pit into the alluvium at the base of Barren Ridge in the center of <br />Section 30-T34N-R4W; and b) leachate may flow in the subsurface from the southwest corner ofthe <br />backfilled East pit into the alluvium in N 1/2 SEl /4 Section 30-T34N-R4W. The amount of leachate <br />dischazging into sandstones of the Fruitland Formation in the walls of the pits is probably small <br />because the preferred flowpath for leachate would be toward the much more permeable alluvium of <br />Stollsteimer Creek in the walls of the pits, rather than the low permeability sandstones in the walls of <br />11 <br />