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City of Stockton A68101.02F July 24, 1997 Page 7 ' work plan was approved by the SJCPHS on December 3, 1996. An "Application for Well/Pump Permit" was submitted to the SJCPHS on August 7, 1996 and approved on October 25, 1996. Copies of the SJCPHS work plan approval and the approved permit application are attached in Appendix B. 4.2 Field Investigation: The field investigation consisted of collecting sub-surface soil and groundwater samples for chemical analysis. 4.2.1 Soil Sampling Technique and Locations: Subsurface soil samples were 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) was attached to the leading end of a probe rod and driven into the subsurface using the machine. The sampling tool collected a continuous soil sample as it was advanced. The sampler advanced approximately 48 inches and then was recovered from the bore hole. The bore sample (soil sample) was extracted from the sampler. The soil sample was contained within a sampler liner of clear plastic. Soil samples were collected to the depth of 16 feet BSG in each probe location. The soil samples were examined for the purpose of preparing lithologic logs. Soil descriptions were logged on a field boring log consistent with the Unified Soil Classification System (USCS). The soil samples were field screened for evidence of volatile organic chemicals (VOCs) and/or other contaminates. The field screening consisted of; visual observation for straining or free fluids, unusual odor, and head space analysis using a photoionization detector (PID). The procedure for performing head space analysis is described in the attached SOPs. ' A six-inch section of the soil sample was selected and preserved for chemical analysis in the laboratory. The plastic liner was cut at the appropriate interval, the open ends sealed with plastic caps, label attached, and the sample was placed in a cooler for transport to Twining's laboratory under chain-of-custody documentation. Previous work at this site has indicated that PPCs have impacted soil beneath 10 feet BSG. Soil samples from the intervals of 10 to 10.5 feet, and 15.5 to 16.0 feet BSG at each probe location were selected for laboratory testing. Soil samples were submitted for laboratory testing using the analytical methods outlined in Section " 4.3 Laboratory Testing Program". The soil probe equipment was decontaminated after sample completion of soil le collection P P at each probe location. The soil sampler was decontaminated after collection of each soil sample. After completion of sampling, the soil probe holes were backfilled with bentonite clay sealing material. The seal was placed into the open probe hole through a tremie pipe (casing) in a manner to preclude creating voids. I Drawing 4 shows the approximate soil probe locations (SB-1 through SB-7). Soil probe location SB-1 was investigated to observe the attenuation of TPH-D between the east wall