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/ 40' <br /> City of Stockton A68101.02C <br /> February 23, 1996 Page 7 <br /> • Chemically analyze soil and groundwater samples in the laboratory for selected PPCs. <br /> • Evaluate the field and analytical data and assess the lateral extent of PPC migration <br /> in soil and groundwater. <br /> • Assess the need for additional soil and/or groundwater characterization and/or <br /> identify appropriate corrective action(s); and <br /> • Prepare a technical report to document the investigative procedures, summarize the <br /> findings, and present conclusions and recommendations. <br /> 4.0 PROPOSED INVESTIGATIVE PROCEDURES <br /> This characterization will consist of a field investigation, a laboratory testing program, and <br /> preparation of a technical report. This work plan and the activities summarized below are <br /> intended to be consistent with the requirements of the SJCPHS. Standard operating <br /> procedures (SOPs), relevant to the field and laboratory activities, are described in Appendix <br /> A. Specific procedures and deviations to the SOPS which will be used in this work are <br /> summarized in the following sections. <br /> 4.1 Field Investigation: The field investigation will consist of collecting subsurface soil <br /> samples for chemical analyses. <br /> 4.1.1 Soil Sample Locations: Twining proposes to collect subsurface soil samples at <br /> selected locations around the former UST and fuel dispenser locations to investigate soil <br /> conditions. Drawing 4 shows the proposed soil sample locations (SB-1 through SB-6). <br /> Analytical results from the soil sample collected on the south wall of the excavation on <br /> August 29, 1995 detected concentrations of toluene and xylenes which were just above the <br /> detection limits. It is therefore likely that concentrations of PPCs in soil attenuate to non- <br /> detectable concentrations a short distance south of the former excavation. Further <br /> investigation to the south does not appear to be warranted. <br /> Small concentrations (1 mg/kg) of TPH-D were also detected in a soil sample collected <br /> from the borehole drilled for monitoring well MW-1. SJCPHS has requested a soil sample <br /> be collected between the location of MW-1 and the east wall sample so the PPC attenuation <br /> pattern can be observed (telephone conversation between Mr.Steven Sasson of SJCPHS and <br /> Mr. K. D. Jones of Twining on February 12, 1996). Soil sample location SB-1 is proposed <br /> for this purpose. <br /> The purpose of sampling location SB-2 is to collect data to the west of the west wall sample <br /> . so the PPC attenuation pattern can be observed. The purpose of sampling location SB-3 <br /> is to delimit the westward extent of PPC migration and to investigate the possibility that <br /> PPCs may have migrated beneath the maintenance shop building from the former fuel <br />