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City of Stockton A68101.02C February 23, 1996 Page 8 dispenser location. Likewise, soil sample location SB-4 is proposed to delimit the extent of PPC migration on the southwest side of the former fuel dispenser location. Analytical results for the soil sample collected from the north wall of the former excavation detected the highest concentrations of TPH-G and benzene, toluene, ethylbenzene, and xylenes (BTEX). The purpose of sample location SB-5 is to delimit the northward extent of PPC migration. The purpose of soil sample location SB-6 is to investigate the possibility of gasoline constituents in the vicinity of the former gasoline UST. This location will also delimit the northwestward extent of PPC migration from the former diesel UST location. In the event field screening (as outlined in Section "4.1.3 Soil Sampling Technique") indicate the presence of PPCs in the subsurface soil at any of the sampling locations, more data will be need to delimit the migration of PPCs. Contingency soil sample locations would be used to further investigate PPC migration in the soil. These contingency soil sample locations would be "stepped out" away from the presumed source in logical increments in an attempt to develop additional data for PPC concentration attenuation and to delimit the extent of PPC migration in soil. . 4.1.2 Soil Sample Depths: Prior to collecting soil samples, the on-site monitoring wells will be sounded to determine the depth of groundwater beneath the site. Soil samples will not be collected from a depth which is greater than the groundwater depth. One sample will be collected at approximately 10 feet BSG at each sampling location. A second sample will be collected from approximately 1 foot above the measured groundwater depth at each sampling location. 4.1.3 Soil Sampling Technique: The soil samples will be collected from boreholes drilled to the sample depths using a 1.5-inch diameter, solid flight, portable power auger. Upon drilling to the sample depth, the power auger will be removed from the borehole for soil sample collection. Auger cuttings will be field screened using a photoionization detector (PID) consistent with our SOPS for evidence of PPCs and for the purpose of preparing lithologic logs. The auger flights will be decontaminated after completion of each borehole. Soil samples will be collected with a 1.5-inch diameter soil sampler equipped with a 6-inch long stainless-steel sample sleeve. The sampler will be driven into the undisturbed soil at the bottom of the borehole. After recovering the sampler, the sleeve will be labeled and preserved consistent with our SOPs for delivery to the chemical laboratory.The sampler will be decontaminated after collecting each sample. Soil samples will be submitted for laboratory testing consistent with the analytical methods outlined in Section " 4.3 Laboratoa Testing Pro am". The analytical results of soil i! samples collected are expected to provide data on PPC concentrations in subsurface soil. This data will be used to evaluate the lateral extent of PPC migration in soil.