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<br />Four samples of backfill were collected for laboratory permeability testing. The laboratory test <br />results, summarized on Table 2, range from 2.20x10"8 to 1.03x10-8 centimeters per second (cm/sec). <br />Bedrock Conditions <br />An area of highly cemented sandstone was encountered along the southern slurry wall alignment, <br />from approximately station 111+70 to 120+00. The bedrock was hard and brittle, and the fu114- <br />foot deep key could not always be achieved. Depth measurements were taken approximately every <br />3 feet instead of the standard 10 foot spacing. The key in this area ranged from 2.5 feet deep to 5 <br />feet deep. <br />In several areas lignite was found in the claystone bedrock. The key depth was extended when <br />necessary in these areas until there was one-foot of competent claystone beneath the layer of lignite. <br />These areas are shown on the as-built drawing (Plate 1). <br />CONCL iISIONS AND RECOMMENDATIONS <br />In general, construction of the Heit slurry wall was performed in conformance with the specified <br />quality control standards. Corrective field actions were quickly implemented when necessary due <br />to visual observations or results of quality control testing. When sand content and filtrate test <br />results did not meet specifications, fresh slurry was introduced into the trench. When results of <br />slump testing for the S-B backfill did not meet specifications, corrective 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- <br />L• <br />September 2007 <br />Heit Construction Report <br />