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. Quarterly Groundwater Monitoring Report Frontier Transportation ' 0899-139 August 13, 1999 1.0) INTRODUCTION Blakely Environmental Investigations, Inc. (BEII) was contracted by Frontier Transportation, Inc. ((909)590-8200) to perform quarterly groundwater monitoring at the Frontier Transport facility,425 Larch Road, Tracy,CA (See Figure 1, Site Location Map). Quarterly groundwater sampling was requested by the San Joaquin County Public Health ' Services, Environmental Health Division(PHS/EHD), Carrol Oz, Senior REHS. 2.0) SITE LOCATION AND HISTORY The site is located in Trac California at 425 Larch Road in the northwest quarter of Y 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 analysis identified dissolved phase TPH-d in the diesel excavation pit at a maximum concentration of 1,200 µg/L. ' 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 ILaboratories, 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-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-tent 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, 1996 and April 21, 1997 by Twinning. Results are presented in Table 1. - - - In January of 1998, BEII advanced four(4) groundwater monitoring wells (MW4 through MW-7)to assess the extent of subsurface contamination beneath the site(See Figure 2, 1 i