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City of Stockton A68107.07A May 29, 1996 Page 3 k.. • Evaluate the field and analytical data and assess the lateral extent of PPC migration in soil; Assess the need for additional soil and/or groundwater characterization and/or identify remedial action alternatives; and L. • Prepare a technical report to document the investigative procedures, summarize the findings, and present conclusions and recommendations. 4.0 PROPOSED INVESTIGATIVE PROCEDURES This characterization will consist of a field investigation, a laboratory testing program, and preparation of a technical report. This work plan and the activities summarized below are intended to be consistent with the requirements of the SJCPHS. Standard operating procedures (SOPs), relevant to the field and laboratory activities, are described in Appendix A. Specific procedures and deviations to the SOPS which will be used in this work are summarized in the following sections. The SJCPHS will be notified 48 hours before commencing field work. 4.1 Field Investigation: The field investigation will consist of collecting subsurface soil and groundwater samples for chemical analyses. 4.1.1 Soil Sampling: Twining proposes to collect subsurface soil samples at selected locations around the former UST location to investigate soil conditions. It is proposed that soil samples be collected from the soil probe locations (SP-1 through SP-4) shown on Drawing 2. The final locations of the soil probes may be adjusted in the field due to underground utilities, other site improvements, and field screening data (as described below). Subsurface soil samples will be collected using a hydraulically-powered, soil probing machine that uses static force and percussion to advance small diameter sampling tools into subsurface soil for collecting soil cores. A sampling tool (bore sampler) is attached to the leading end of a probe rod and driven into the subsurface using the machine. The sampling tool remains sealed by a piston tip as it is being driven. When the sampler has reached to ,., within 24 inches of the desired sampling depth, an extension rod is lowered down through the inside diameter of the probe rods to the sampling tool. The extension rod is then used to disengage the stop-pin of the piston tip. The extension rod and stop-pin are then �. removed and the sampling tool is driven an additional 24 inches. The piston tip is displaced into the body of the sampling tool by the soil as the bore sample is cut. The sampler is the recovered from the bore hole and the bore sample (soil sample) is extracted from the sampler. The soil sample is contained within a sampler liner of clear plastic. The soil probe equipment will be decontaminated after completion of soil sample collection at each