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Hall-Irwin Corporation Hokestra Slurry Walls October 30, 2014 Page 3of8 ' 2 NORTH AND SOUTH SOIL-BENTONITE SLURRY WALLS ' 2.1 Working Platform Construction The construction of the working platform was necessary to produce a stable and flat working area for trench excavation and backfilling. Hall-Irwin constructed the working platform using a combination of Komatsu excavators and bulldozers. The total constructed working platform for both walls was approximately 10,266 ft. long and varied in width according to the amount of land available and depth of ' slurry wall. The working platform consisted of a combination of cuts and fills in order to create a level working platform as specified in the design report. 2.2 Slurry Wall Alignment Survey The slurry wall alignment was staked and surveyed by Morningstar Surveying LLC. (MS) before construction of the working platform and after construction of the slurry wall. Alignment stationing was ' established at 100-ft intervals. Hall-Irwin established construction stationing at 25 ft. intervals along the alignment using a tape measure. To generate the as-built alignment, Hall-Irwin placed lathe within the centerline of the slurry wall and noted the approximate construction stationing at the location. MS surveyed the lathe to create the as-built alignment shown in Appendix D. Appendix D also contains the northings and eastings of the centerline of the slurry wall. ' 2.3 Bentonite Slurry Mixing and Delivering The Contractor constructed a slurry pond using on-site material for the purpose of mixing and hydrating bentonite slurry. The slurry pond was located inside the south slurry wall. The bentonite was mixed with water in the constructed slurry pond using a shear mixer. The water for mixing was obtained from groundwater that seeped in the slurry pond excavation. The slurry was delivered from the slurry mixing pit to the open trench using a pump and a 4-inch HDPE surface pipeline. ' 2.4 Bentonite Slurry Quality Control Results 2.4.1 As-Mixed Slurry To ensure proper mixing and hydration of the powdered bentonite, the as-mixed bentonite slurry was tested approximately once per day. Brierley performed density and viscosity measurements according to API RP 1313-2. Results are presented in Table I. 2.4.2 In-Trench Slurry ' Slurry within the trench was tested on average twice daily, with samples taken near the bottom of the trench in the active excavation area once backfilling had commenced. Brierley performed density, ' viscosity and sand content measurements according to API RP 1313-2. Sand content was tested once a day. Results are presented in Table II. ' BRIERLEY ASSOCIATES ' Creating Space Underground