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II _ Work Plan Frontier Transportation Page 1 1 .0) INTRODUCTION Blakely Environmental Investigations, Inc. (BEM was contracted by Frontier Transportation, Inc. ((909) 590-8200) to prepare a work plan to install one monitoring well to determine the lateral extent of dissolved petroleum hydrocarbons at the Frontier Transport facility, 425 Larch Road, Tracy, CA (See Figure 1 , Site Location Map). The San Joaquin County Public Health Services, Environmental Health Division (PHSIEHD), Vicki McCartney, EHS, requested the additional delineation on Septernbw ,-29A2. 2.0) SITE LOCATION AND HISTORY -1 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. The site consists of a trucking facility with one metal frame building and all parking and work areas capped by cement and/or asphalt. The site is located in an industrial park. 1Six (6) underground fuel storage tanks (USTs), three diesel tanks located northeast of the - I terminal and three gasoline tanks located southeast of the terminal, were removed from the site IV on July 21 , 1995 . Soil sample analysis identified total petroleum hydrocarbons as gasoline (TPH-g) and total petroleum hydrocarbons as diesel (TPH-d) in the gasoline tank excavation at maximum concentrations of 9,800 mg/kg and 120 mg/kg, respectively. Groundwater sample analysis identified dissolved phase TPH-d in the diesel excavation pit at a maximum concentration of 1 ,200 µg/L. In August of 1996, Twinning Laboratories, Inc (Twinning) advanced six vertical soil Jborings (13- 1 , B-2, B-3 , MW- IRA, MW- 1RB, and MW-2RA) and one angle boring (B-4) to depths between 10. 5 ' and 12 .5 ' below grade (bg) to assess subsurface conditions near the northeastern excavation. In addition, two hand augers (S- 1 and S-2) were advanced to 3 ' bg to assess subsurface conditions beneath the dispenser and product lines and three groundwater monitoring wells, MW- 1 through MW-3 , were drilled to approximately 25' bg to assess the subsurface water beneath the site. Initial subsurface water was encountered at 10 .5' bg. Boring B-4 located northwest of the former USTs identified maximum TPH-g, BTEX (Benzene, Toluene, Ethylbenzene, Xylene), and MTBE (Methyl-tert Butyl Ether) as 1 ,300 mg/kg, 180.7 mg/kg, and 110 mg/kg, respectively at 10.2' bg. However, no soil samples were collected below 11 ' bg to delineate the vertical extent of hydrocarbons. JGroundwater samples were collected from MW- 1 , MW-2, and MW-3 on August 30, 1996 and April 21 , 1997 by Twinning. Results are presented in Table 1 . hi January of 1998, BEII advanced four (4) groundwater monitoring wells (MW-4