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1998 <br /> Based on these initial investigation results, the San Joaquin County Public Heath Services <br /> Environmental Health Division requested additional monitoring wells be installed to better <br /> define the horizontal extent of soil and groundwater contamination. After discussions with Ms. <br /> Lori Duncan of the San Joaquin County Public Heath Services Environmental Health Division, <br /> Clearwater submitted the Workplan for Site Investigation dated November 18, 1998 . An <br /> addendum to the workplan, dated December 10, 1998, was submitted in response to San Joaquin <br /> County Public Heath Services Environmental Health Division comments. The workplan and <br /> addendum were approved by the San Joaquin County Public Heath Services Environmental <br /> Health Division on December 15, 1998 . <br /> 1999 <br /> In January 1999, Clearwater supervised the installation of three additional groundwater- <br /> monitoring wells (MW-4 through MW-6) to delineate the extent of dissolved-phase <br /> contamination. Concurrently, Clearwater also performed a sensitive receptor survey. The results <br /> of the investigation indicated that the extent of sorbed-phase contamination was delineated and <br /> existed from approximately 10 to 25 feet bgs near the former USTs. Analysis of the <br /> groundwater samples indicated that the extent of dissolved-phase contamination remained <br /> undelineated downgradient from the former UST system . However, high contaminant <br /> concentrations in cross-gradient positioned wells suggested that off-site sources could be <br /> contributing to contamination detected beneath the site. Inquiries suggested and later confirmed <br /> the existence of a fuel transport line in the area of the site. The line was found to be filled with <br /> nitrogen gas. Based on this information, Clearwater recommended additional investigation along <br /> South Fresno Avenue to better understand the distribution of contamination and possible <br /> contribution from potential off-site sources. The results of this phase of investigation were <br /> presented in Clearwater's Well Installation and Groundwater Monitoring Report - First Quarter <br /> 1999. <br /> 2000 <br /> In March 2000, Clearwater supervised the completion of one hydropunch, six soil borings, the <br /> destruction of MW-5, and the installation of three additional monitoring wells (MW-5B, MW-7, <br /> and MW-8) in three of the soil borings . All three wells were placed in the downgradient <br /> direction of the plume to help determine the downgradient extent of contaminants. The <br /> hydropunch was performed in the former UST location to assess the vertical extent of <br /> groundwater contamination at 36 feet bgs. Three soil borings were taken to define the lateral <br /> extent of soil and groundwater contamination on the northeastern portion of the site and assess <br /> possible off-site sources. Three soil samples and one groundwater sample were analyzed from <br /> each boring. Soil concentrations of TPH-g and BTEX were detected only in boring MW-513 . <br /> The highest soil concentration of TPH-g ( 1 ,000 mg/kg) was detected at 25 feet bgs in MW-5B . <br /> This sample was also analyzed for TPH as Jet Fuel (TPH jf) and found to contain 55 mg/kg. <br /> TPH jf is unlikely to be present, but is an indicator of a hydrocarbon range on a chromatographic <br /> pattern, not a specific product. Detectable concentrations of BTEX were present in soil samples <br /> collected from boring MW-513 at 25 feet and 35 feet bgs. MTBE was not detected by EPA <br /> method 8260 in any of the soil samples analyzed . Groundwater concentrations of TPH-g and <br /> BTEX were detected in borings SB-9, MW-5B, MW-7 and MW-8. The highest groundwater <br /> I <br /> ZB 178 — Site Investigation History 2 Updated March 2010 <br /> Barnes Trucking Facility — 1817 South Fresno Avenue, Stockton, California <br />