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Slurry Wall Design Report <br /> Loloff Pit <br /> 5/24/2016 <br /> Page 8 of 16 <br /> 5 BACKFILL MIX DESIGN <br /> 5.1 General <br /> Brierley Associates conducted a laboratory testing program to develop a mix design for the <br /> slurry wall backfill material. The backfill must meet several engineering criteria to provide <br /> adequate performance of the slurry wall. The proposed backfill is a soil-bentonite (SB) mixture. <br /> During the geotechnical investigation in January 2016, Brierley Associates collected bulk <br /> samples of the various components of the backfill mix. Samples of overburden, coarse alluvium, <br /> and bedrock were obtained from drill cuttings and from the test borings. The overburden layer at <br /> the project site is thin and its contribution as a supplemental fines source is negligible. Samples <br /> of clay borrow were collected from three potential borrow sites: an on-site stockpile, a stockpile <br /> comprised of imported fines located on the Derr property (Derr Import) and a stockpile <br /> comprised of site overburden located on the Davis Farms property (Davis Farm Fines). The <br /> groundwater sample was obtained from the pit. The source of the groundwater was collected at <br /> the end of the hose from one of the dewatering pumps, located in the southwestern corner of <br /> the gravel pit. <br /> The laboratory testing program consisted of performing laboratory analyses of the samples of <br /> the backfill components, creating mix designs based on the results of these analyses, and <br /> preparing and conducting permeability tests on the mix design. Brierley Associates conducted <br /> the backfill mix design for Martinez Associates who conducted the preparation and testing of the <br /> mix. Martinez Associates also determined engineering properties of sand and gravel, clay <br /> borrow and bedrock prior to the final mix design. Site groundwater was used in the mix design. <br /> Martinez Associates determined the engineering properties of the bentonite slurry during lab <br /> testing. <br /> 5.2 Backfill Components <br /> The following materials were the components of the prepared soil-bentonite mix designs: <br /> • Select backfill combination of clay borrow (Derr property) and coarse alluvium <br /> • Bentonite slurry made from dry bentonite powder <br /> The source and pertinent characteristics of these components are described in the following <br /> subsections. Index test results including fines content (passing the#200 sieve), gradation, and <br /> Atterberg Limits on the select backfill components are summarized on Table V. <br /> 5.2.1 Bentonite Slurry <br /> Bentonite slurry used in the backfill mixture was created with dry bentonite powder and with <br /> native groundwater collected from the site. Dry bentonite powder was provided by Wyo-Ben Inc. <br /> in Greybull Wyoming, which is the proposed bentonite to be used for the construction. A <br /> measured amount of dry powder bentonite was used to create slurry with a Marsh Funnel <br /> viscosity of 40 seconds. A summary of laboratory test results performed on the slurry is <br /> presented in Table V. <br /> BRIERLEY <br /> ASSOCIATES <br /> Creating Space Underground <br />