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slurry pumped from the pond. This was performed until the slurry viscosity and/or unit <br />weight in the trench was within the allowable range. <br />Sand content of the slurry in the trench was measured with regards to percentage of sand <br />suspended in the slurry. Specifications required the sand content be less than or equal to <br />25 %. On one occasion the sand content value exceeded 25 %. On this occasion, Envirocon <br />removed existing slurry from the trench by bailing with the trackhoe bucket and <br />simultaneously pump freshly mixed slurry into the trench. This procedure was performed <br />until the sand content was within the acceptable range. <br />Filter cake formation of the slurry and filtration loss were analyzed using an ambient <br />temperature filter press assembly. Filter losses were within the acceptable range. <br />4.4 BackfillOuality <br />Slump cone and gradation results on the S -B backfill material were used to control the <br />backfill material properties. Test results for each of these parameters were within the <br />acceptable range. <br />Six samples of backfill were collected for laboratory permeability testing. The laboratory <br />test results, summarized on Table 2, ranged from 2.6 x 10 -8 to 5.8 x 10 -9 centimeters per <br />second (cm/sec). The specification for permeability was less than or equal to 1 x 10 -7 <br />centimeters per second, therefore, all permeability samples met specifications. <br />4.5 Slurry Wall Sloushinz and Sand Settlement <br />As a quality control measure, the depth of the trench was periodically measured and re- <br />measured (particularly between shifts) to check for indications of sand settlement or <br />possible trench wall sloughing. The measurement results indicated that trench depths were <br />maintained with minimal sand settlement on the bottom of the trench. As a precaution, the <br />trench bottom was cleaned with the trackhoe at the start of each shift or other prolonged <br />down time, to clear accumulated material from the trench. Severe slurry wall sloughing <br />and sand settlement were not observed. <br />4.6 Bedrock Conditions <br />Excavated soils and bedrock were observed during trenching to detect when bedrock was <br />encountered. This observation was supplemented by the excavator operator's opinion of <br />the change in excavation speed encountered at bedrock. Depth to unweathered bedrock <br />(top of key) and the depth of the trench bottom (bottom of key) were measured by <br />Envirocon using a weighted tape. The depth to unweathered bedrock and the total depth of <br />the trench were measured every 10 feet and are shown on the plan and profile sheets of the <br />as-built construction documents (Appendix A). <br />Bedrock encountered included moderately hard to hard, dry, claystone; hard, moist, <br />sandstone or interbedded claystone and sandstone conditions. The typical key depth into <br />- 5 - August 2013 <br />P:\235 W133- 23 5 1413 003\Docs\ Report s\ Wattenberg _Constmction_Report_2013.doc <br />