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2.3 Red Wash Alluvial Monitoring Program <br />Portions of Red Wash experienced subsidence due to longwall mining at the Deserado <br />Mine. As required by CMLRD (now DRMS), BME initiated a detailed hydrology monitoring <br />program in Red Wash above the first longwall panel to be mined. The monitoring program <br />consisted of nine (9) holes drilled in the Red Wash alluvium across the predicted zone of <br />subsidence from longwall panel 1 (LW -1). Water levels in the holes were monitored before, <br />during, and after subsidence took place. The purpose of the monitoring program was to <br />determine if surface flow in Red Wash was lost to bedrock as the result of subsidence. <br />The monitoring data, analysis and conclusions were submitted to CMLRD in an Interim <br />Report, November 1987, and in the Third Annual Hydrology Report, January 1988. The <br />monitoring program determined that surface flow in Red Wash was not lost to bedrock as a <br />result of subsidence. The major conclusions of the study were: <br />• Recharge of the basal alluvium was from the upper sandstone facies (bedrock) <br />and not from infiltration of surface runoff. <br />• Subsidence cracks in Red Wash as the result of longwall mining were quickly <br />filled with clay and silt preventing loss of surface water flow to bedrock. <br />Longwall mining of panel 2 (LW -2) passed under Red Wash in September 1988. The <br />surface elevation subsided approximately 3.7 and 4.1 feet at RW -7 and RW -9 respectively. <br />Events in Red Wash over LW -2 were expected to occur in the same fashion as those seen <br />over LW -1. The subsidence trough was developed and any subsequent flow in Red Wash <br />was expected to form a pond. The pond would trap sediments carried in the flow(s) until <br />full, at which time flow in Red Wash would likely resume flowing in a relatively narrow active <br />channel. <br />The conclusions noted above were further confirmed during 1989. On July 29, 1989 a large <br />flow event occurred in Red Wash. The subsidence trough over LW -2 filled with water. The <br />trough over LW-1 also filled, but to a lesser depth as it had filled with sediment in the past. <br />Water level measurements were taken in the monitoring holes while standing water <br />surrounded them. Readings had been taken only 18 days before. Even though the holes <br />were surrounded by standing water (approximately 3 and 4 feet deep at RW -7 and RW -9 <br />respectively) the alluvial water depths had still decreased. <br />Although the purpose of the monitoring program was met, BME continued to monitor the <br />Red Wash alluvial holes until water year 1996 -1997. The latest monitoring results are <br />reported in Appendix F and hydrographs for each monitoring hole are presented in <br />Appendix G of the Thirteenth Annual Hydrology Report. <br />13 <br />