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Pre-Design Investigation Workplan Former Manufactured Gas Plant—Lodi, California Excavation and sampling equipment that comes in contact with subsurface soils will be decontaminated following sample collection and completion of each trench to avoid cross- contamination between trench locations. Sampling equipment and any tools,measuring devices, or other equipment which will contact soil,groundwater or any media being assessed will be washed in a low-phosphate soap and water solution, and rinsed in clean water before each use. Decontamination water will be contained and placed in DOT-rated 55-gallon drums. The 55-gallon drums containing decontamination water will be temporarily stored on-site until characterization results are received, waste profiling is complete, and arrangements for off-site disposal can be made. All transportation and disposal activities will be conducted using appropriate manifests and documentation. 4.7 SOIL GAS PROBE INSTALLATION PROCEDURES Drilling activities will be conducted as described in Section 4.5 using a three-inch-diameter hand auger to drill the first five feet followed by drilling using a direct-push drill rig operated by a State of California licensed C-57 driller to reach the taregt soil gas boring total depth of 15 feet bgs. Continuous soil cores will be recovered and observed throughout the full depth of the borehole,and the soil lithology will be recorded on soil boring logs forms using the USCS system. 4.7.1 Dual-Depth Semi-Permanent Soil Gas Probe Construction Site data indicates groundwater occurs at approximately 60 feet bgs. In the event shallow groundwater is encountered during drilling, the deeper soil gas sampling depth (i.e., probe tip) will be adjusted a minimum of three feet above the depth of first encountered groundwater. Upon reaching the target deep soil gas sample depth (i.e., 15 feet bgs), the direct-push drill rods will be removed from the borehole. A typical temporary multi-depth soil gas well will be constructed in accordance with DTSC ASGI guidance (DTSC,2010) and,as illustrated in Figure 5. A six-inch long stainless steel probe tip connected to '/a-inch-diameter Teflon tubing will be lowered into the borehole to a target depth of approximately 14.75 feet bgs. An approximate one-foot thick filter pack consisting of#3 Monterey sand will be placed around the deep soil gas sample probe tip from approximately 14 to 15 feet bgs. A one-foot layer of dry granular bentonite followed by a hydrated bentonite seal will be placed above the filter pack to approximately 5.5 feet bgs. A second stainless steel probe connected to '/a-inch-diameter Teflon tubing will be lowered into the borehole to a depth of approximately 5.25 feet bgs. A one-foot thick filter pack consisting of#3 Monterey sand will be placed around the shallow soil gas sample probe tip from approximately 4.5 to 5.5 feet bgs. A one-foot layer of dry granular bentonite will be placed above the shallow sand pack. The borehole will then be sealed to the surface with hydrated bentonite. At the surface, a three-way tee-fitting check valve will be placed on the end of each probe tube to control the flow of soil gas from the subsurface. Following the completion of soil gas sampling, each soil gas probe will be abandoned by removing the '/a-inch Teflon tubing from the borehole. When the '/a-inch Teflon tubing is removed from the TERRA PACIFIC GROUP Page 14 April 4, 2012