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Ge0 6 ica[Technics Inc. Page 3 Phase IIA ESA Report Bank of Stockton(Airport Way) Project No. 827.2 November 15, 1999 ■ Analyzed these samples for VOCs by method 524.2, DBCP by method 504.2, and nitrate by 300.0. 2.0 SUBSURFACE INVESTIGATION To determine if soil has been contaminated by release of petroleum hydrocarbons from the previous USTs on this Property, GTI drilled six boreholes using GeoProbe direct push methods to depths ranging from 10 to 20 feet bgs. 2.1 Borehole Drilling & Soil Sample Collection The boreholes were drilled with a GeoProbe rig owned and operated by V&W Drilling of Rio Vista, CA (C574 720904). The GeoProbe advances a coring tool with a pneumatic hammer to a selected depth. Upon reaching the sampling depth, the coring tool is opened and advanced further to fill the core barrel. The soil sample enters an acetate cylinder contained in the coring tool. Upon filling, the coring tool is pulled from the hole and the cylinder is removed. The cylinder is then cut and the selected interval is preserved for laboratory analysis. The remainder is used for geologic logging. All soil samples will be sealed with Teflon, capped with plastic end caps, labeled and placed in a cooler at 4° Celsius for transport to the laboratory following Chain of Custody protocol. The GeoProbe borings were to be advanced to 20 feet bgs in the area around the former USTs and to a depth of 10 feet in front of the truck maintenance shop area. Soil samples were collected at five-foot intervals for geologic logging and laboratory analyses. One soil sample from each borehole was submitted to the laboratory for analysis. Since only selected samples were submitted for laboratory analysis, a screening process was used to gather additional information through field observation. This information was used to assist in determining which samples were analyzed. Evidence of elevated contaminant concentrations as detected by field screening was used to determine if additional samples should be tested. The following characteristics were noted in the screening process: • sediment type, especially grain size and clay content • moisture content • visible evidence of contamination, i.e., color change due to reduction of iron or discoloration from hydrocarbons and other pollutants • readings above background on a organic vapor meter(OVM) The OVM is a portable photo ionization detector that uses a 10.0 eV lamp to detect compounds with ionization potential below 10.0 eV (hydrocarbon range). A boring log providing sediment description using the USCS and field observations will be maintained by a professional geologist working under the supervision of a registered geologist. The Site Map in Figure 2 shows the locations of the boreholes. The geology of the site is characterized by sandy soil to a depth of approximately 10 to 15 feet and clayey soil from there to 20 feet. Logs of the boreholes are given in Appendix B.