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City of Stockton A68106.01A May 29, 1996 Page 4 The soil samples will be examined for the pure se of preparing lithologic logs. Soil descriptions will be logged on a field boring log consistent with the Unified Soil Classification System (USCS). The soil sample will e field screened for evidence of volatile organic chemicals (VOCs) and/or other contamina es. The field screening consist of; visual observation for straining or free fluids, unusual bdor, and head space analysis using a photoionization detector (PID). The procedure for performing head space analysis are described in the attached SOPs. The bottom six inches of the soil sample will be preserved for chemical analysis in the --i laboratory. The plastic liner will be cut, the open ends sealed with Teflon® tape and plastic caps, label attached, and placed in a cooler for transport to Twining's laboratory under chain-of-custody documentation. Soil samples will be collected at 4-foot intervals st rting at 6 feet BSG. Therefore the soil hsamples collected from soil probe SP-1 will represent soil conditions between 6 to 10, 12 to 16, and 18 to 22 feet BSG. Soil probe SP-4 will be advanced on an angle and soil samples collected at the same vertical depths as soil probe P-1. The sample intervals for SP-2 and SP.-3 will be the same as SP-1. Proposed soil same I Je intervals for soil probes SP-1 and SP-4 are shown on Drawing 3. Soil samples will be submitted for laboratory testing consistent with the analytical methods outlined in Section " 4.2 Laboratm Testing Program". The analytical results of soil samples collected are expected to provide data on PPC concentration attenuation in subsurface soil at vari us distances from the PPC source. This data will be used to evaluate the vertical and lateral extent of PPC migration in soil. The vertical extent of PPC migration beneath the former UST will be assessed by soil probe SP-1 located at the fill end of the former UST. pue to the proximity of the PPC source, soil samples collected from soil probe SPA are pected to provide data on the vertical extent of PPC migration beneath the former UST location. Twining's experience suggest �- that if field screening readings from the PID register VOCs at concentrations greater than 75 parts per million (ppm) there is a possibility that PPCs may be present in the soil sample at concentrations sufficient to be detected by lab ratory testing. Furthermore, based on standards of practice, two consecutive samples with no laboratory detectable constituents r of concern can demonstrate the vertical extent of PPC migration. Therefore, soil probe SP- 1 will be advanced until two consecutive samples are collected which do not indicate field evidence of PPCs. SPA will be advanced beyond the depth of first encountered groundwater which is estimated to be approximately 20 feet BSG to collect a groundwater sample as outlined in Section "4.1.2 Groundwater Investigation". Soil probes SP-2, SP-3, and SP-4 are intended to provide data on the lateral extent of PPC migration in soil around the former UST location. Soil probes SP-2, SP-3, and SP-4 will be advanced to the greatest depth at which PPCs were detected with field screening in soil probe SP-1 or to within three feet of the groundwater depth, whichever occurs first. Soil probe SP-4 will be advanced at an angle of approximately 30 degrees from vertical in a ''