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KLEINFELDER 2.3 BORROW OPERATION The excavation of borrow materials will be performed by the SJDPW or a qualified earthwork contractor. During excavation of materials soils with SC, CL, CH, ML and SM will be stockpiled for mixing and use in the barrier layer. Care will be exercised whenever clean sandy materials (SP) are encountered. It will likely be necessary to blend these with more cohesive or silty materials. 2.4 BARRIER LAYER SOIL DESIGN MIX A total of eight bulk samples were obtained from the two designated borrow areas; the existing Harney Lane site and the North County landfill. At the North County landfill site, two samples were taken around the existing stockpile located in the southern portion of the site. The soil samples collected at the stockpile were both very silty sand. A sample of clean fine sand was obtained directly from the current excavation at the North County site. At the existing Hamey Lane site, samples were collected at the base of the existing borrow area south of the present landfill. These samples varied from silty sand to sandy clayey silt. - While previous studies indicated that some of the untreated native materials would meet the minimum permeability requirements, it is evident that the majority of the materials currently at the two proposed borrow sites will consist of a more granular soil. lam. Based on our experience over the past five years, the most cost-effective large supplier of C� imported clay has been North American Refractories located in Ione. Permeability, gradation and Atterberg Limits tests were performed on samples composed of various percentages of this clay mixed with the eight bulk samples from the two borrow areas. Shown on Table 2-1 is a summary of these laboratory tests. As noted, the percent of Ione clay varied from 15 to 20 percent. During the preparation of test samples, it was intended that the minimum degree of compaction would vary from approximately 90 to 95 percent. The actual degree of compaction varied from 90 to 100 percent based on 3 laboratory L compaction curves. On past landfill and liner projects, the addition of 15 percent Ione clay has been sufficient to meet regulatory permeability requirements of 1 x 10-6 cm/sec. As L noted on Table 2-1, 20 percent Ione clay mixed with relatively clean sand, samples 3 did not meet project requirements. Except for sample 2, the addition of 15 percent Ione clay to SM & ML samples (1,4,6, & 7) met the minimum permeability requirements. However, , the "cushion", or difference between laboratory permeability and that required in the field L r 0 was not as high as desired. For this reason, we recommend that a minimum of 20 percent CR9-42 Page 7 of 28 Copyright 1991 Kleinfelder, Inc.