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La SOIL QUALITY EVALUATION STOCKTON VEHICLE MAINTENANCE FACILITY 3131 ARCH ROAD STOCKTON, CALIFORNIA 1.0 INTRODUCTION 1.1 Purpose In this report, we present the results of the soil quality evaluation performed at the United States Postal Service's (USPS's) Stockton Vehicle Maintenance Facility (VMF) in Stockton, California. This work was performed for the USPS at the request of the San Joaquin County Public Health Services, Environmental Health Division (SJCEHD) to evaluate subsurface conditions in the area of the four former underground storage tanks (USTs), diesel fuel dispenser, and associated conveyance piping. �- 1.2 Site Background (URS Greiner Woodward Clyde, 1999; Ramcon, 1999) The two 12,000-gallon, steel USTs used to store gasoline and diesel fuel, respectively, L. and the associated fuel dispensers were removed from the site during May 1998. The fuel distribution pipelines were abandoned in-place by capping the pipes at the edge of the excavation, and filling the pipes with concrete. Reportedly, the removed USTs appeared in good condition with no apparent holes or leaks. An approximately 1-foot thick concrete slab was located beneath the USTs at a depth of approximately 13 feet. The contractor was unable to collect soil samples from beneath the concrete slab. Soil samples were collected from the gasoline and diesel UST excavation soil stockpiles, from beneath the former gasoline and diesel fuel dispensers, and from beneath the conveyance piping. During a subsurface investigation performed during July 1998, the concrete slab was cored and two soil samples were collected from native soil directly beneath the slab. Furthermore, during the same investigation, two soil samples were collected from native soil adjacent to the edge of the concrete slab. In general, no gasoline range petroleum hydrocarbons, BTEX compounds, or fuel oxygenates were detected in soil samples collected, with the exception of methyl tertiary butyl ether (MTBE). The MTBE was detected in one of the soil samples collected from beneath the conveyance piping at a concentration of 0.34 ppm. Diesel `' range petroleum hydrocarbons were also detected in the soil samples collected from: beneath the diesel fuel dispenser (817 ppm); beneath the gasoline dispenser (1.10 ppm); the diesel UST excavation soil stockpile (1.81 ppm); and one of the borings located adjacent to the concrete slab (2.47 ppm). The two 1,000-gallon, double-walled, fiberglass USTs used to store new oil and waste L. oil were removed from the site during July 1999. Soil samples were obtained from the base of each excavation immediately after removal of the USTs and from the stockpiled soil. Only low levels of oil-range petroleum hydrocarbons (up to 217 6.• ppm) were detected. La L OWT&TASSOCIATES Page 1 Environmental!GeotechnicaE/Engineering Services 864-76 Lr