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Remedial Action Plan RE: 425 W. Larch Street, Tracy, CA October 1 , 2008 W&A Project No. FTIM-08-001 Page 1 of 11 1 INTRODUCTION The site is located in Tracy, California at 425 Larch Road in the northwest quarter of section 16, Township 2 South, Range 5 East, Mount Diablo Baseline at Meridian (Figure 1 ) . The site consists of a trucking facility with one metal frame building (Figure 2). All parking and work areas are capped by cement and/or asphalt. The site is located in an industrial park. On July 21 , 1995, six underground fuel storage tanks (USTs) were removed from the site. Three of the USTs had been used to store diesel-fuel and had been located northeast of the terminal. Three of the USTs had been used to store gasoline and had been located southeast of the terminal. As part of the excavating and removal activities, soil samples were collected for laboratory analyses. The laboratory reported significant concentrations of gasoline (TPHg) and gasoline-related compounds in the samples collected from the excavation that held the USTs that stored gasoline. As well, groundwater samples were collected from the excavations and significant concentrations of diesel-fuel (TPHd) were reported by the laboratory in the samples. Based on the concentrations of TPHg and TPHd found during the removal of the USTs, a series of soil investigations, groundwater investigations, groundwater monitoring, and some remedial activities have occurred at the site since 1995 . During that time there has been a spread of significant concentrations of gasoline-related compounds spreading beneath site and now spreading off-site. A more detailed discussion of the investigations performed, the groundwater monitoring, and the remedial action performed is provided in Section 3 . Due to the increasing dimensions of the plume, the significant concentrations of gasoline-related compounds contained within it, and the flow of the compounds off site, the local oversight agency, the San Joaquin County, Environmental Health Department has requested that a remedial action plan (RAP) be prepared for this site. 2 SITE SETTING 2 . 1 Topographic The site is shown at an altitude of approximately 8 feet above mean sea-level (msl) on the Tracy, 7 . 5 -minute, topographic map issued by the USGS (Figure 1). The site is shown on relatively flat area approximately 5 . 5 miles northeast of the Diablo Range. The site is shown on an area that generally slopes gently downward to the northeast. There are several rivers that flow in the area. The rivers meander, but in general they flow west and north. The Old River is approximately 1/2-mile northeast of the site and flows westerly to the Clifton Court Forebay, which then drains north to several smaller bays into the San Pablo Bay and then to the San Francisco Bay. Approximately 5 . 5 miles east-northeast of the site is the San Joaquin River. The San Joaquin is the major drainage of the area and flows northerly and then northwesterly to the smaller bays that eventually drain to the San Francisco Bay. Other surface waters shown on the map near the site include sewage ponds and industrial waste ponds approximately 0,6 miles to the east and northeast. WINEFIELD E SAFU pONSULTANTS RM