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Oield Sampling Plan for the Former UST Location at Stockton FMS #24 California Army National Guard bgs at locations adjacent to previous locations B30 through B32 to collect samples of the fill material (soil). The samples will be analyzed by EPA Methods SW8015G and D, SW8260, and SW6010 to determine if the fill material used to fill the pit contains contamination or is clean. FMS24SBOI will be drilled first to help determine the depth at which the UST excavation extended and, if fill is present and to what depth fill extends. FMS24SB02 will be drilled adjacent to the wash pad (northwest of former UST locations) to help determine if contamination from the wash pad is present, and if so, whether the contamination possibly commingled with the contamination beneath the former diesel and gasoline UST location. In addition, proposed location FMS24SB02 will help verify whether a solvent release occurred at the wash pad/holding tank location. FMS24SB03 through FMS24SB05 will be placed laterally around the previous boring locations (in a clockwise arrangement) and at least 50 feet from each one to determine the lateral extent of contamination in soil and groundwater beneath the former diesel and gasoline UST location. Each boring will be continuously cored to determine correct sample depths based on the depth of the bottom of the previous tank excavation. In addition, if evidence of soil contamination is present during drilling, soil samples will be collected at any depth interval where there is visual evidence (stained or discolored soil) of contamination, elevated photoionization detector (PID) readings, and/or if chemical or hydrocarbon odors are present. In addition, a PID will be used to screen cores as drilling occurs at all proposed locations. If elevated readings are present (indicating possible hot spot), shallow soil gas samples will be collected (at possible depths of 5, 10, and 15 feet bgs) using procedures consistent with the Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air (California Department of Toxic Substances Control, 2004). Following the completion of the investigation's initial borings, in which soil and/or groundwater contamination may or may not be defined after analyses are complete, a work plan addendum will be developed and additional sampling and monitoring well installation will be conducted to determine the extent of contamination that can be attributed to the former diesel and gasoline UST location and/or the wash pad/holding tank nearby. The intent of this field sampling plan is to describe the first phase of the site investigation at the former fuel tank location. After additional information from this investigation is gathered, the second phase of the former fuel tank location is scheduled to begin, in which the new information gathered will help increase the ability to place groundwater monitoring wells at optimal locations at the site. In addition to placing groundwater monitoring wells at the most advantageous locations at the former fuel tank locations, the first phase information will be used to help determine the quantity of wells, screen lengths and depths, estimated site gradient, and current existing concentrations and site conditions to be used during the second phase of the investigation. 7.0 REFERENCES Barclays Law Publishers, 2000. California Code of Regulations, Title 23. State Water Resources Control Board. Final. Volume 32. California Department of Toxic Substances Control, 2004. Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air. December. California Regional Water Quality Control Board, North Coast, San Francisco Bay, and Central Valley Regions, 1990. Tri -Regional Board Staff Recommendations for Preliminary Evaluation and Investigations of Underground Tank Sites. August. K:\Wprocess\00251\CA ARNG\Stockton FSP\FINAUStockton FSP.doc 23 August 2006