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L�Claytoif Ms.Devra Lewis Page 4 RWQCB Clayton Project 70-03759.00 July 31, 2004 import clean soil for backfilling of the trench. The backfilled soil will be placed in lifts and compacted by vibratory or roller equipment to adequately compact the soil in each trench. No compaction testing is proposed. 3.4 SOII, BORINGS After the former pipeline alignment has been established in the field, Clayton will contract with a California-licensed drilling contractor to complete the subsurface investigation. Clayton will mark the proposed boring locations and the site boundaries with white paint and notify Underground Service Alert(USA) to clear an area approximately 100 feet wide along the former pipeline route at least 48 hours prior to commencement of any subsurface fieldwork, as required by law. Clayton will obtain necessary soil boring permits for the proposed drilling activities from the San Joaquin County Environmental Health Department(SJCEHD) for each land parcel. In addition,Clayton will provide the SJCEHD with a copy of the above- referenced written access agreements. The subsurface investigation is designed to complete a total of 336 soil borings at a spacing of 25 lineal feet. Soil samples will be collected to a total depth of approximately 6 feet below the ground surface(bgs). Additional soil borings to deeper depths(first encountered groundwater)will be completed in areas where evidence of petroleum hydrocarbon impact(staining,odors, etc.)in the shallow subsurface soils is discovered. Previous investigations to the northwest of the area indicate that the depth to groundwater is between 30 and 35 feet bgs. Due to hard drilling conditions with depth at the site, Clayton proposes utilizing a truck mounted Geoprobe rig to advance the shallow soil borings, and a truck mounted hollow stem auger drill rig to advance any deeper borings. �. Clayton assumes that the surface-soil conditions are adequate to support typical pickups and four-wheel drive vehicles during the sampling and surveying portions of the work. If special site conditions limit accessibility,then special equipment will have to be located to conduct the sampling. 3.4.1 Shallow Subsurface Investigation Clayton will contract a California-licensed(C-57) driller to operate truck-mounted GeoProbe direct push equipment and advance the proposed shallow boreholes every 25 feet. Soil cores will be obtained using a core barrel sampler, which are approximately 4 feet long and 2 inches in diameter. The core barrel sampler contains a plastic acetate liner that retains a relatively undisturbed soil core from which soil samples are collected.