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t Draft Environmental Impact Report Page IV.G-5 Forward Landfill Expansion The CL clay is found on flat-lying (0 to 2 percent slope), poorly drained area consisting of clay and clay/loam to a strongly cemented hardpan generally found at about 60 inches below ground surface (bgs). This type of soil is common along the north and south branches of Littlejohns Creek. Soil permeability is low and shrink-swell potential is high. Depth to groundwater in this area is generally 60 feet bgs or greater, except during peak rainfall times when the accumulation of infiltrating rainwater is briefly perched above the hardpan. t: Both soil types in the project area are substantially similar and typically put to the same use for field crops, according to the USDA Soil Conservation Land Use Capability Classification that delineates the general suitability of soils. ' More detailed studies of soil properties, depth, and volume have been completed at the site and site vicinity in order to verify its ability to meet stipulated "natural" liner characteristics and/or identify potential cover material for the landfill operations. Geotechnical tests performed by CH2M Hill in 1992 show the mainly clay soil to be dry and stiff with moisture contents typically below the plasticity limit, and an undrained moderate to high shear strength of approximately 2,000 to 5,000 pounds per square foot. Based on these data, it appears that the site soils are relatively strong and dense, with a low potential for soil erosion, instability, or settlement. �f Landfill operations require the use of soil that is generally excavated locally, often next to the cell that is being actively filled, if it meets the soil cover criteria. The daily waste deposited is covered by 6 to 12 inches of soil. The borrow pit would then often become the next disposal site once it is prepared with the appropriate liner and leachate collection system as stipulated by the CIWMB and RWQCB. Soil borrow material studies were completed at the existing borrow areas north and south of the current Austin Road Landfill disposal area. Results reported in the Final Draft Joint Technical Document(JTD) classify the soils as low plasticity clays, at an elevation of approximately 15 to 25 feet amsl in the borrow pit south of the current Austin Road Landfill disposal area. These 1 soils have permeabilities ranging from 1 x 10-7 to 1 x 10-8 when compacted to 90 percent relative compaction. The soil study at the smaller northern borrow area (CYA parcel) showed soils at 4 to 11 feet bgs composed of sandy clay with a soil permeability of 3 x 10-8 at 90 percent relative compaction. These soil properties make both borrow areas good sources of cover material. Approximately 2,405,400 cubic yards of soil borrow may be required over the project Jh' or lifetime. The majority of the soil would come from the borrow area north of the current y disposal area (CYA parcel), where no future landfill disposal is proposed or permitted. Soil excavated during each planned phase would be stockpiled in areas of future phases or on the former borrow area north of the formerAustin Road Landfill, as described in the JTD(2007). This stockpiled soil (estimated total excavation quantities are approximately 4.5 mcy), can be utilized for daily cover operations, if needed, or would be saved for final cover soil needs (approximately 564,974 cy). A total of about 6.7 mcy is projected to be needed for on-site cover f at the 6:1 refuse to soil ratio referenced in the JTD (2007),resulting in about 2.2 mcy of new soil needed for import or borrow material. The Forward Landfill currently accepts construction debris and contaminated soil in sufficient quantities to provide for daily cover operations. Any soil surplus or deficit will be stockpiled/borrowed from the existing CYA parcel borrow area. a