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~-='-= :l_=:. =: i S s i a A slurry mixing/holding pond was constructed near the central part of the site. A reservoir of hydrated slurry was produced by combining and mixing bulk bentonite powder with local groundwater using a conical static mixer. The groundwater was pumped from an excavation adjacent to the mixing pond. The slurry was continuously circulated until thoroughly hydrated. The finished slurry product was pumped through four-inch high density polyethylene tubing to the open trench section under construction. Pond re-circulation and slurry delivery was accomplished using an eight-inch pump. The soil-bentonite (S-B) backfill was composed of four components: 1) soil excavated from the trench, 2) supplemental soil material borrowed on-site and stockpiled next to the trench, 3) sluny removed from the trench heading during excavation and mixing operations, and 4) dry bentonite applied at an approximate rate of one percent of the dry weight of the backfill soils. OUALITYASSURAIVCE TESTING Resident engineering services were provided by Tetra Tech RMC during the slurry wall construction. These services included continuous on-site construction observation, sampling, field testing of soils for various slurry trench pazameters, and the assimilation of as-built information. A daily log of construction progress was kept. A summary of the quality control test results is presented in Appendix A. A specified material quality control program was followed throughout the slurry wall construction. Test types, frequency, and specified values are summarized on Table 1. In order to provide the quickest possible testing resultturn-around time, a testing laboratory was set up on-site. Testing equipment included a mud balance, Marsh funnel, portable electric bench oven, electronic scale, triple-beam balance, portable sieve shaker, various sieves, wet washing apparatus, ambient temperature filter press, pH meter, sand content kit, and slump cone apparatus. A rapid rum-around time of the test results allowed for near real time adjustments to the various slurry trench parameters throughout the project. Testing conformed to industry standards, including the American Petroleum Institute -Specification 13A, the American Petroleum Institute Recommended Practice -Specification 13-B-2, and ASTM C-143. Specific test results are shown in Appendix A. Slurry viscosity, as measured using a Marsh funnel apparatus, and unit weight values, as measured using a mud balance, were maintained within the acceptable range (V >40 seconds-Mazsh, S.G. = 1.03 gm/cc to 1.40 gm/cc) except as noted. The few cases of low viscosities were corrected at these locations so that the slurry viscosity in the trench was maintained above the minimum acceptable levels. Filter cake formation of the slurry and filtration loss were analyzed using an ambient temperature filter press assembly. Filter cake thickness and filtrate loss were generally within the acceptable range. The texture of the cake formation ranged from slightly sandy to very sandy. A sand content kit was used to measure the percent sand by volume suspended in the slurry. Sand content was found to range from five to 25 percent. In a few instances the sand content of the in-trench slurry sample was found to be above the desired value of 20 percent. In these cases, the problem was corrected by adding more slurry from the mixing pond at the point of trenching and a stoppage of backfilling. Trench depth measurements - 3 - November 2004 F:W6J6 IdTCorttruttion Rcpon\Nissrn Final Conswctbn Rcpon.doc