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Herman &Helen's Marina <br /> 15135 Eight Mile Road, Stockton - 2 - 29 March 2001 <br /> of 14 µg/1)have been identified directly downgradient of the former USTs in monitoring well MW-4, and low <br /> TPHg,BTEX, and high MtBE (maximum 190,000 µg/1), TBA, and TAME have been identified directly <br /> downgradient of the existing above ground tanks (AGTs) in monitoring wells MW-2, and-3. Historical <br /> groundwater monitoring data from Condor's QMR are included as Table 1. As shown on attached Figure 4, <br /> MtBE concentrations in MW-2 and-3 downgradient of the existing AGTs have fluctuated considerably since <br /> September 1997,whereas MtBE concentrations in MW-4 downgradient of the former USTs have decreased to <br /> low detections. <br /> Quarterly surface water sampling has been conducted since October 1998, and MtBE has been detected in the <br /> drainage ditch and the Island Drainage Channel. The maximum concentration of MtBE identified in surface <br /> water at the drainage ditch is 4,700 µg/1, and the maximum concentration of MtBE in the Island Drainage <br /> Channel near the pump house intake is 10 µg/1: Historical surface water monitoring data from Condor's QMR <br /> are included as Table 2. <br /> Due to the increasing MtBE concentrations in monitoring wells MW-2 and -3, I concur with the County's <br /> determination that the AGTs or conveyance piping are the probable source of MtBE contamination. Board <br /> staff from the UST Section and the Site Cleanup Section met on 12 March 2001 to discuss this site, and <br /> deternnned that the UST site should be closed and the site transferred to the Site Cleanup Section for <br /> regulatory oversight over the AGTs investigation. Attached to this memo is a No Further Action Required <br /> checklist for closure of this UST site. <br />