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Frontier Transportation, Inc. r 425 Larch Road Site Assessment Work Plan May 6, 2005 ' Page 1 1 .0) INTRODUCTION Biophysics Environmental Assessments, Inc. (BEA) was contracted by Frontier Transportation, Inc. (909) 590-8200 to prepare a work plan to delineate the extent of dissolved I_I phase MTBE plume identified at 425 Larch Road, Tracy, California (See Figure 1 , Site Location Map). The proposed work will consist of the installation of three (3) monitoring wells. The ' additional work was requested by the San Joaquin County Public Health Services, Environmental -- Health Division (SJCPHS-EHD), by Victoria L. McCartney, Senior RENS . The contact person l for BEA is David Blakely, (310) 8334910. 20) SITE LOCATION AND HISTORY 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 if 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. r� Six (6) underground fuel storage tanks (USTs), three diesel tanks located northeast of the terminal and three gasoline tanks located southeast of the terminal, were removed from the site 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 advanced six vertical soil borings (B- 1 , 13,- .s, — 2, B-3 , MW- IRA, MW- 1RB , and MW-2RA) and one angle boring (134) to depths between 104' v+w and 1.2 ` below grade (bgs) to assess subsurface conditions near the northeastern excavation. In addition, two hand augers (S4 and S-2) were advanced to 3 ' bgs 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' bgs to assess the subsurface water beneath the site. I Initial subsurface water was encountered at 10. 5' bgs. 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 µgAg, 180. 7 gg/kg, and 110 µg/kg, respectively at 10 .5 ' bgs.