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� Work Plan Frontier Transportation Page 1 z� 1.0) INTRODUCTION 1 1-71 "� Blakely Environmental Investigations, Inc. (BEII) was contracted by Frontier Transportation, Inc. (909) 590-8200 to prepare a work plan to delineate the extent of dissolved 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 eight (8) monitoring wells. The additional work was requested by the San Joaquin County Public Health Services, Environmental V'' Health D WW (SJCP-HS-EHD), by Margaret Lagorio, REHS . The contact person for BEB is { Hiram Garcia, (760) 868-8572. 2.0) 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 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. .- 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 4 J analysis identified dissolved phase TPH-d in the diesel excavation pit at a maximum concentration of 12200 µg/L. In August of 1996, Twinning Laboratories, Inc advanced six vertical soil borings (B- 1 , B- 2, B-3 ,1MW- IRA, MW- IRB, and MW-2RA) and one angle boring (B-4) to depths between 4-0-. 5' S- and JA' below grade (bg) to assess subsurface conditions near the northeastern excavation. In Jnf 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 `1 I 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 �Ja MTBE (Methyl-tert Butyl Ether) as 1 ,300 gg/kg, 180. 7 µg/kg, and 110 µg/kg, respectively at 10 .5' bg. iJGroundwater 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 . In January of 1998, BEH advanced four (4) groundwater monitoring wells (MW-4 U