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Environmental <br /> Mr Harlin Knoll Resources <br /> 22 January 1999 Management <br /> Page 2 <br /> toluene, ethyl benzene, and xylenes (BTEX) compounds, and methyl <br /> tertiary butyl ether (MTBE) The results of these sampling events <br /> indicate that elevated concentrations of TPH-g and BTEX compounds are <br /> present in ground water immediately downgradient of the former UST <br /> locations However, the concentrations of TPH-g and BTEX compounds <br /> decrease rapidly in the downgradient direction from the former UST <br /> locations <br /> On 13 January 1993, representatives of ERM, Heinz, the County,and the <br /> Central Valley Regional Water Quality Control Boards (RWQCB) <br /> participated in a conference call to discuss the results of the investigation <br /> activities at the site The need for further investigation and/or remedial <br /> activities at the site was also discussed The RWQCB and County <br /> indicated that they had concerns regarding the definition of the depth of <br /> contamination in soil and ground water at each former UST location <br /> They also stated concerns regarding the concentrations of benzene in <br /> ground water immediately downgradient of each former UST location <br /> The County and RWQCB stated that the depth of TPH-g and BTEX <br /> compounds had not been adequately defined at UST-1 or UST-2 A soil <br /> sample collected at 11 feet below ground surface (bgs) at MW-4 (located <br /> immediately downgradient of UST-1) contained elevated TPH-g and <br /> BTEX concentrations This was the deepest sample collected in the area <br /> of UST-1 The County and RWQCB indicated that the vertical depth of <br /> soil and ground water impacts must be determined at this location to <br /> estimate the total mass of contamination remaining at the site The depth <br /> of impacts also must be deternuned to ensure that impacted ground <br /> water is not present at depths greater than the base of the monitoring <br /> wells installed around UST-1 A similar assessment of the depth of soil <br /> and ground water impacts is also required at UST-2 <br /> During the December 1998 sampling event, the concentrations of benzene <br /> in monitoring wells MW-4 and MW-6 were 120 and 90 mg/1, <br /> respectively The RWQCB indicated that these benzene concentrations in <br /> shallow ground water present an unacceptable health risk The County <br /> and RWQCB requested that Heinz evaluate potential remedial <br /> technologies for reducing the concentrations of benzene in ground water <br /> in the vicinity of the former tank locations <br />• The County and RWQCB indicated that the site closure could not be <br /> granted without fully delineating the vertical extent of impacts at each <br /> tank location or without reducing the concentration of benzene in <br /> ground water at each tank site <br />