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The site is in an alluvial valley setting. The natural ground surface is flat or gently sloping to the west <br />and north in the general direction of the South Platte River. Geotechnical test holes were drilled along <br />the proposed slurry wall alignment prior to construction, which indicated bedrock is generally horizontal <br />with a deeper channel eroded into bedrock trending north-south across the central part of the site. <br />Observed drill cuttings and soil samples, soil types, and depth to bedrock measurements were used as <br />reference during construction. Test hole locations are shown on Figure 2 and summary logs are <br />presented on Figure 3. Depths to bedrock and total trench depths observed during construction are <br />illustrated on the as-built construction drawing (Figure 2). <br />The slurry wall as-built dimensions are as follows: an average total width of 3.5 feet, total trench depth <br />from 41 to 63 feet with an average value of approximately 47.5 feet, overall slurry wall length of 9,400 <br />I feet, and overall trench curtain area of approximately 446,500 square feet. The total area encompassed <br />by the slurry wall is approximately 114 acres. <br />r <br />i <br />f <br />a <br />t <br /> <br />CONSTRUCTIONSUMMARY <br />The typical slurry wall construction crew consisted of four to five men managed by one superintendent <br />who oversaw and coordinated construction activities. Motorized equipment used included a Komatsu <br />PC 1100 trackhoe excavator, which excavated the trench through a bentonite slurry; a smaller trackhoe <br />that provided initial soil-bentonite backfill mixing and constructed the slurry mixing pond; one John <br />Deere dozer that provided final soil-bentonite backfill mixing, trench backfilling, and slurry mixing <br />pond constmction; and two stand-alone pneumatic trailers for on-site storage of bulk bentonite. A slurry <br />pump/depending unit was positioned along the side of the active trench to clean the trench bottom and <br />reduce sands suspended in the slurry. <br />Constnuction was carried out starting in the northwest corner ofthe site at station 0+00 progressing <br />counter clockwise through the end of wall station 94+00 and continuing back to station 0+85. The <br />trench continued past the starting point providing 85 feet of overlap from station 0+00 to 0+85. Corners <br />of the slurry wall alignment were radial curves or made bycross-cutting straight line segments. <br />Prior to construction of the slurry wall, berms were constructed along the inside of the slurry wall <br />alignment. These backfill berms consisted of local select overburden soils placed in sufficient quantity <br />to supplement the trenched material, increasing the fine-grained soil component ofthe backfill. Fine- <br />grainedbentonite was added at a variable rate, depending on trench depth, creating a mix with at least <br />one percent bentonite based on the dry weight of the backfill. <br />Initial testing during construction start-up indicated the overburden soils on approximately the north <br />one-half of the site were very sandy. The overburden soils on the southern one-half of the site were <br />more clayey and were suitable for providing supplemental fines for the slurry wall backfill. The <br />organics were stripped from the clayey soils and scrapers were used to excavate the soils and stockpile <br />the supplemental fines in berms adjacent to the inside of the slurry wall alignment. Numerous quality <br />control,tests were performed on these supplemental materials as the soils were excavated and stockpiled. <br />- 2 - November 2004 <br />F:~llb16 IdTConnrvuion ReportVJrtsrn Final Construction Rcport.doc <br />