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