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,o <br />-16- <br />Based on the information contained in t)~e application and the above observations, <br />the Division finds the application in compliance with this section. <br />ZX. Probable Hydrologic Consequent;es and Cumulative Im acts Assessment - <br />Rules 2.05.6(3) and 2.07.6(2) <br />The operator has provided a statement of probable hydrologic consequences for the <br />operation in a document included within the application entitled "Report of <br />Probable Hydrologic Consequences, Trinidad Basin Mining". In the Division's <br />Cumulative Impacts Assessment, all adjacent mines, anticipated mining and life-of- <br />mine plan for the operation are to be considered. In this situation, there are no <br />adjacent mines, or mines anticipated in the area, and Trinidad Basin Mining will <br />not be operating in this area after the completion of the 5-year permit plan. <br />Therefore, for the purpose of t)v s findings document, the probable hydrologic <br />consequences for the mine are also the cumulative impacts. <br />The primary impact associated with the operation will be increased sediment yields <br />caused by surface disturbance. The operator will mitigate this impact through <br />the use of a sediment control system. Since the receiving stream is naturally <br />high in suspended solids and the arx~unt of disturbed area is low in relation to <br />Del Agua Canyon drainage, this impact should not be significant. Past monitoring <br />data appears to support this. <br />Water quality characteristics of disturbed drainages have the potential to be degraded <br />from contact with spoils. However, except for a few isolated units, most of the <br />overburden is not of toxic character. The operator will mitigate this potential <br />impact by isolating potentially toxic strata and keeping it away from the surface <br />and ground water. The current surface water monitoring plan will help identify <br />any actual impacts. To date, the existing surface water monitoring data has not <br />identified any significant mining-related water quality impacts. <br />Another potential impact from the mine could be reduction of flows in Del Agua <br />Canyon drainage due to detention of water in ponds. The cumulative storage volume <br />of ponds at Trinidad Basin Mining is 168.21 acre-feet. This compares with a <br />predicted annual flow of 600 acre-feet of water for I~1 Agua Canyon watershed. <br />This potential impact is being mitigated by requiring all ponds to be dewatered <br />within 72 hours of the rainfall event. 7'he reduction in flows may also be somewhat <br />counterbalanced by the effect of an increase in runoff from the mine over that <br />which naturally occurs. This increase in runoff may be due to removal of vegetation <br />and topsoil, excessive compaction, and a reduction in infiltration at the mine. <br />At present, the state-of-the-art technology does not permit a more detailed or <br />quantified examination of this impact. <br />The only aquifer which appears to have the potential to be impacted by the mining <br />operations is the alluvial aquifer of Del Agua Canyon. Most of the mine facilities, <br />including the coal stockpile and several sediment ponds, are Located on the surface <br />of the aquifer. Leachate generated from the coal stockpile and the mine shop area <br />could conceivably percolate into the aquifer and degrade the water quality. In <br />addition, the springs and seeps that eminate from the coal outcrop will flow through <br />reclaimed spoils after mining is complete. If the resultant Ieachate were of <br />sufficient quantity to reach the aquifer, additional water quality degradation could <br />occur. Because of the small quantities of water involved, neither of these potential <br />impacts are considered significant enough to warrant changes in the proposed mining <br />and reclamation plan. However, hydrologic monitoring will be required to substantiate <br />this conclusion. <br />