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Mr. Harlin Knoll 1PR I I N San Joaquin County Environmental Health Division 27 June 2001 Awl Page 4 r L summarized in Table 1 . A description of the groundwater sampling procedures is included in Attachment 3. R k L Summary of Groundwater Monitoring Program Ir As directed by the SJCEHD, BFS has complied with the agency's request to install a L downgradient well (MW-4), collect two rounds of groundwater samples from well MW-4, and collect five rounds of groundwater samples from wells MW-1, MW-2, and MW-3. Since monitoring began in January 2000, TPHg decreased from 440 µg/l from previous L groundwater sampling results in MW-2 to 170 µg/I in April 2001 . MTBE changed from E 42 µg/I from the previous groundwater sampling results in MW-1 to 5.0 µg/1 in April 2001 . Newly installed groundwater monitoring well MW-4 contained non-detectable concentrations of hydrocarbon constituents in the soil samples analyzed. Groundwater from well MW-4 contained only a trace amount of MTBE (2.4 µg/I) in April 2001 and L below detection limits in June 2001 . Recent analytical data compared to previous investigation results show the concentration L of hydrocarbon constituents in the soils at the site are below regulatory goals or standards. -� In consideration of the length of time since these tanks were in operation, both the SJCEHD and the RWQCB agreed in a 7 March 2001 meeting that these USTs were not the source for the MTBE found in the groundwater. All groundwater monitoring wells were placed at locations agreed to by the agency to determine the extent of soil and L groundwater impacts. In EPA's Drinking Water Advisory. Consumer Acceptability Advice and Health Effects Analysis on MTBE (EPA-822-F-97-009 December 1997), regulators state regarding MTBE "that keeping concentrations in the range of 20 to 40 micrograms per liter (µg/I) of water or below will likely avert unpleasant taste and odor effects." Additionally, the State of California has proposed primary drinking water standards as a public health goal for MTBE of 13 µg/I. Although these values are proposed as goals and considered low by the industry, the concentrations of MTBE found in the shallow, unused groundwater at L the site are below these aggressive objectives. Rationale for Site Closure BFS is requesting site closure based on the following factors: L R ❑ Future and/or ongoing sources of gasoline and its constituents, specifically 9 MTBE, including USTs, related piping, and impacted soil in the vicinity of !..{ the USTs have been removed or properly closed in place at the site. �v L LSAB F5\sTOCKTON\LTR\LTR010.DOC 6/27/01