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City of Stockton A6810ZOIB July 14 1997 Page 4 Lchemicals (VOCs) and/or other contaminates. The field screening consisted of; visual observation for unusual strains or free fluids, unusual odor, and head space analysis using a photoionization detector (PID). The procedure for performing head space analysis is 1 described in the attached SOPs (Appendix A). j Selected six-inch sections of the soil samples were preserved for chemical analysis in the L laboratory based on the requirement of the investigation. 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. Soil probe location SP-1 was intended to investigate soil beneath the former UST location. A change in lithology encountered at approximately 12 feet BSG in soil probe SP-1 was presumed to represent the bottom of the former UST excavation. The soil at that depth was sand with silt and clay and gravel. The soil was very moist and had a distinct odor of diesel. Due to the amount of moisture encountered, it was inferred that a zone of"perched" water existed in the bottom of the former UST excavation. Soil samples collected at 13 and 16 feet BSG in soil probe SP-1 were selected for analysis. To prevent the downward migration of this perched water, soil probe SP-1 was abandoned after collecting the soil sample at 16 feet BSG. To reduce the chance of creating a conduit for the perched water to migrate downward a i second soil probe (SP-1A) was advanced through the former UST location using the following different sampling technique. A smaller diameter (approximately 1.5-inch outside diameter) 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 remained sealed by a j piston tip as it was being driven. When the sampler reached to within 24 inches of the desired sampling depth, an extension rod was lowered down through the inside of the probe } rods to the sampling tool. The extension rod was then used to disengage the stop-pin of the piston tip. The extension rod and stop-pin were then removed and the sampling tool was driven an additional 24 inches. The piston tip was displaced into the.body of the sampling tool by the soil as the bore sample was cut. The sampler was then recovered from the bore hole and the bore sample (soil sample) was extracted from the sampler. Soil samples were collected from SP-1A at 20 and 26 feet BSG were selected for analysis, and then the probe was extended into groundwater to a total depth of 48 feet BSG. Soil probe location SP-2 was intended to investigate soil adjacent to the east side of the former UST. Soil samples representing sub-surface soil conditions at 7, 10, 14, and 20 feet BSG were preserved for laboratory analysis from soil probe location SP-2. Soil probe location SP-3 was intended to investigate soil beneath the fire station building 1, adjacent to the north side of the former UST location. Soil probe SP-3 was advanced in a northerly direction on an angle of approximately 60 degrees from horizontal. Soil samples i i