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i <br />• <br />• <br />i <br />i <br />• <br />• <br />• <br />• <br />• <br />• <br />• <br />Desanding Operations <br />The desanding equipment consisted of a submersible pump, tank reservoir, and screened shaker <br />mounted to a reinforced steel sled with a diesel generator attached. The equipment used was <br />specifically manufachued for use in cleaning sand from the trench bottom and reducing the volume <br />of sand suspended in the slurry. The desander was estimated to have been in operation for 95 <br />percent of the slurry wall construction. <br />Backfill Quality <br />Backfill quality was maintained within acceptable standards. Testing results are summarized in <br />Appendix A. <br />Four samples of backfill were collected for laboratory permeability testing. The laboratory test <br />results, summarized on Table 2, were all in range of 3.31x10-$ to 1.25x10_s centimeters per second <br />(cm/sec). <br />Bedrock Conditions <br />In order to key into competent and unweathered bedrock, it was sometimes necessary to dig through <br />up to 12 feet of weathered bedrock (Figures 3a and 3b). Occasionally, loosely cemented sandstone <br />was encountered when digging into bedrock for construction of keyway. On these occasions, the <br />key was excavated five feet beneath the top of unweathered bedrock instead three feet. <br />CONCLUSIONS AND RECOMMENDATIONS <br />In general, construction of the Stagecoach slurry wall was performed in conformance with the <br />specified quality control standards. Corrective field actions were quickly implemented when <br />necessary due to visual observations or results of quality control testing. When sand content and <br />filtrate test results did not meet specifications, fresh slurry was introduced into the trench. When <br />results of slump testing for the S-B backfill did not meet specifications, con-ective actions included <br />addition/reduction of slurry added to the backfill material and adjustments to the mixing operations. <br />As a final quality control measure, periodic inspections during mining are recommended to check <br />for localized seep zones. If seepage is observed.during mining progresses, remedial actions may <br />need to be implemented. <br />_ 5 _ January 2005 <br />Smgemazh Final Cons~~uciron Rcpoadw <br />