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For this reason, this portion of the slurry wall was built inside the final slurry wall alignment, and <br />ended up as an extra length which can be abandoned. Corners of the slurry wall alignment were <br />constructed to be radial curves or made by cross-cutting straight line segments. This was done to <br />ensure the slurry wall was keyed in three feet past the top of competent, unweathered bedrock along <br />the entire alignment. <br />Prior to construction of the slurry wall, berms were constructed along the inside of the slurry wall <br />alignment. These berms consisted of overburden soils from on-site, as well as dry fine-grained <br />bentonite delivered from offsite. The granular bentonite was added at a rate of approximately 0.5 <br />percent of dry weight of the backfill soils. <br />A slurry mixing/holding pond was constructed near the center of the site. A reservoir of hydrated <br />slurry was produced by combining and mixing bulk bentonite powder with water using a conical <br />static mixer. Groundwater was pumped from an on-site sump to the slurry pond and used for <br />making the slurry. The slurry in the holding pond was continuously circulated until thoroughly <br />hydrated. The finished slurry product was pumped through a four-inch high density polyethylene <br />tubing to the open trench section under construction. Pond re-circulation and slurry delivery was <br />accomplished using two eight-inch pumps. <br />The soil-bentonite (S-B) backfill was composed of four components: 1) soil excavated from the <br />trench, 2) high clay content soil material borrowed on-site, 3) slurry removed from the trench <br />heading during excavation and mixing operations, and 4) dry bentonite applied at an approximate <br />rate of 0.5 percent of the dry weight of the backfill soils. <br />QUALITY CONTROL TESTING <br />Resident engineering services were provided by D&A during the slurry wall construction. These <br />services included continuous on-site construction observation, sampling, field testing of soils for <br />various slurry trench parameters, and the assimilation of as-built information. A daily log of <br />construction progress was kept. A summary of the quality control test results is presented in <br />Appendix A. <br />A specified material quality control program was followed throughout the slurry wall construction. <br />Test types, frequency, and specified values are summarized on Table 1. In order to provide the <br />quickest possible testing result turn-around time, a testing laboratory was set up on-site. Testing <br />equipment included a mud balance, Marsh funnel, portable electric bench oven, electronic scale, <br />triple-beam balance, portable sieve shaker, various sieves, wet washing apparatus, ambient <br />temperature filter press, pH meter, sand content kit, and slump cone apparatus. <br />A rapid turn-around time of the test results allowed for near real-time adjustments to the various <br />slurry trench parameters throughout the project. Testing conformed to industry standards, including <br />the American Petroleum Institute - Specification 13A, the American Petroleum Institute <br />Recommended Practice - Specification 13-13-2, and ASTM C-143. Specific test results are shown <br />in Appendix A. <br />-3- January 2005 <br />Stagecoach Final Construction Report.doc