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w - Work Plan Frontier Transportation May 31 , 2001 1 .0) INTRODUCTION J Blakely Environmental Investigations, Inc. (BEII) was contracted by Frontier Transportation, Inc. ((909) 590-8200) to prepare a work plan for an additional site investigation at the Frontier Transport facility, 425 Larch Road, Tracy, CA (See Figure 1 , Site Location Map). _I The additional site investigation was requested by the San Joaquin County Environmental Health Division, Public Health Services, by Margaret Lagorio. The contact person for BEII is Hiram (� Garcia, (760) 249-5498 . 'I 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 1 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 J 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 L - ) 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. _ 1 In August of 1996, six vertical soil borings (B- 1 , B-2, B-3 , MW- IRA, MW- IRB, and MW-2RA) and one angle boring (B-4) were advanced to depths between 10. 5' and 12.5 ' below grade (bg) to assess subsurface conditions near the northeastern excavation by Twinning -- Laboratories, Inc. 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- I 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, —� Eth lbenzene, Xylene), and MTBE (Meth 1-tert Butyl Ether) as 1 ,300 mg/kg, 180 . 7 mg/kg, and 110 mg/kg, respectively at 10.2' bg. Groundwater samples were collected from MW- 1 , MW-2, and MW-3 on August 30, I- 1996 and April 21 , 1997 by Twinning. Results are presented in Table 1 . In January of 1998, BEII advanced four (4) groundwater monitoring wells (MW-4 through MW-7) to assess the extent of subsurface contamination beneath the site (See Figure 2, Site Layout Map). Soil samples were collected every five feet. Laboratory analysis of soil ' ' 1