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1.0 INTRODUCTION., On behalf of the San Joaquin County Facilities Management Department (property'owner and responsible party), Ramage Environmental;Inc.,has prepared this Soil Vapor.Sampling and , Human Health Risk Assessment Report for submittal to the San Joaquin-County Environmental Health Division (EHD) and the Central Valley Regional Water Quality Control Board (RWQCB). 1.1 Site Description The Agricultural Commissioner's Office site is located-at 503 East 10t" Street in the city of Tracy (San Joaquin County), California (Figure 1). The property is an active county office building. The site is bordered to the north by Hamilton Alley, a city of Tracy right-of-way, and to the east 4 by a transmission repair shop on private property (Figure 2): The site is flat and mostly paved. Three, 1,000-gallon capacity, underground, storage tanks (UST) existed in the northeast part of ` the site. The northernmost and'southernmost USTs (Tanks 1 and 3) were used to'store weed �i oil (i.e., high-sulfur diesel fuel): The center UST was used to store unleaded gasoline. ' .1.2 Previous Work 1.2.1 UST System Removal { - A On October 28, 1988, the three 1,000-gallon capacity, USTs and associated product piping and dispenser island equipment were removed from the site by Tilford & Hall. During UST removal, the EHD inspector noted the presence of holes in both weed oil USTs and,"extensive contamination"within the limits of the excavation.° One soil sample p was collected from beneath each UST at a depth of 9 to 10 feet below round p g surface (bgs) and analyzed for Total Extractable Petroleum Hydrocarbons (TEPH), Total Volatile Petroleum Hydrocarbons (TVPH), benzene, toluene, ethylbenzene and xylenes (BTEX), ethylene dibromide and total lead by Canonie Environmental Services Corporation. Laboratory :results indicated that concentrations of petroleum hydrocarbons were detected in all three soil samples. Concentrations of petroleum hydrocarbons included 760 parts per million (ppm) TVPH beneath the center UST (Tank 2), 4,700 ppm TEPH from beneath the northern weed oil UST (Tank 1) and 4,800 ppm TEPH from beneath the southern weed oil UST (Tank 3). The soil sample analytical ical results are summarized in Table 1. F 4