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f Ci of f Stockton A68107.07A May 29, 1996 Page 4 U probe location. The soil sampler will be decontaminated after collection of each soil sample. The soil samples will be examined for the purpose of preparing litholo is logs. Soil descriptions will be logged on a field boring log consistent with the Unified Soil ;t Classification System (USCS). The soil sample will be field screened for evidence of volatile L organic chemicals (VOCs) and/or other contaminates. The field screening consist 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 are 4: described in the attached SOPs. LThe bottom six inches of the soil sample will be preserved for chemical analysis in the 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 Lchain-of-custody documentation. Soil samples will be collected at 4-foot intervals starting at 12 feet BSG. Therefore the soil samples collected from soil probe SP-1 will represent soil conditions between 12 to 16, 18 to 22, and 24 to 28 feet BSG. 'Soil probe SP-4 will be advanced on an angle and soil samples collected at the same vertical depths as soil probe SP-1. The sample intervals for SP-2 and SP-3 will be the same as SP-1. Proposed soil sample 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 Laboratory Testing U Program". The analytical results of soil samples collected are expected to provide data on PPC concentration attenuation in subsurface soil at various distances from the PPC source. r LThis data will be used to evaluate the vertical and lateral extent of PPC migration in soil. r 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. Due to the proximity of the PPC source, U soil samples collected from soil probe SP-1 are expected to provide data on the vertical extent of PPC migration beneath the former UST location. Twining's experience suggests that if field screening readings from the PID register VOCs at concentrations greater than LI 75 parts per million (ppm) there is a possibility that PPCs may be present in the soil sample at concentration sufficient s s t to be detected by laboratory testing. Furthermore, based on f Li standards of practice, two consecutive samples with no laboratory detectable constituents of concern can demonstrate the vertical extent of PPC migration. Therefore, soil probe SP- I 1 will be advanced until two consecutive samples are collected which do not indicate field t evidence of PPCs. SP-1 will then be advanced to the depth of first encountered groundwater to collect a groundwater samples as outlined in Section "4.1.2 Groundwater " k Investigation". s 0 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 U k U ' 3