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Quarterly Groundwater Report Frontier Transportation ' 0501-131 May 17, 2001 Page 1 ' 1.0) INTRODUCTION Blakely Environmental Investigations, Inc. (BEII) was contracted by Frontier ' Transportation, Inc. to report the latest quarterly groundwater monitoring results at the Frontier Transport facility, 425 Larch Road, Tracy, California (See Figure 1, Site Location Map). The San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD), Carrol Oz, Senior REHS requested quarterly groundwater monitoring on September 8, 1999. 2.0) SITE LOCATION AND HISTORY The site is located in Trac California at 425 Larch Road in the northwest quarter of Tracy, 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 pg/L. ' In August of 1996, Twinning Laboratories, Inc. (Twinning) advanced six vertical soil borings (B-1, B-2, B-3, MW-IRA, MW-IRB, and MW-2RA) and one angle boring (B-4) to depths between I0.5' and 12.5' below grade (bg) to assess subsurface conditions near the northeastern excavation. In addition, two hand augers (S-I 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, and Xylene), and MTBE (Methyl-tert Butyl Ether) as 1,300 mg/kg, 1 180.7 mg/kg, and 110 mg/kg, respectively at 10.2' bg. Groundwater samples were collected from monitoring wells 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 (MW-4 through MW-7) to assess the extent of subsurface contamination beneath the site (See Figure 2, 1