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sand suspended in the sluny. The desander was estimated to have been in operation for 95 percent of <br />the wall construction. <br />Backftll Ouality <br />Backfili quality was generally maintained within acceptable standards. At other locations where backfill <br />quality was out of specification, the on-site engineer notified the construction crew and the problem was <br />immediately resolved. Testing results are summarized in Appendix A. <br />Four samples of backfill were collected for laboratory permeability testing. The laboratory test results, <br />summarized on Table 2, were all in the range of 3 x 10"s to 6 x 10"y centimeters per second (cm/sec). <br />Bedrock Conditions <br />Hard, very fine-grained sandstone was encountered in the slurry wall key trench in numerous locations <br />on the easterntwo-thirds of the site. In several areas the sandstone Yvas hard enough that the specified <br />key trench depth, three feet deep into unweathered bedrock, could ndt be achieved. Hard sandstone <br />areas are summarized on Table 3 and shown on Figure 2. In these areas, there was generally a minimum <br />thickness of one to two feet of weathered claystone bedrock overlying the hard sandstone. The <br />cementation and hardness of the sandstone varied along the trench. Locally, within these areas the key <br />varied, ranging from the full three feet to zero feet into unweathered bedrock. The variation in key <br />depth is detailed in the daily construction records on file in our office. The mine highwall should be <br />visually inspected during mining operations for areas of seepage. The excavation records and Table 3 <br />will provide information for any remedial work that maybe necessary if excess seepage locally occurs <br />in.areas ofhard bedrock and shallow key. <br />CONCLUSIONS AND RECOMMENDATIONS <br />In general, construction of the Nissen Farm Resource Slurry Wall was performed in conformance with <br />the specified quality control standards. Full-time monitoring and testing of construction operations <br />allowed for quick action in remedying any problems. As a final quality control measure, periodic <br />inspections during mining are recommended to check for localized seep zones, especially in areas <br />outlined in the Bedrock Conditions section. If seepage is observed as mining progresses, remedial <br />activities may need to be implemented. <br />- 5 - November 2004 <br />F:W6J6 14TCOnnfunion RcportWiven Finil Covwaion Reportdoc <br />