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The California Regional Water Quality Control Board, San Francisco Bay Region, has provided <br /> a guidance document: Guidance on Analytical Methods for Oxygenates and Additives at <br /> Gasoline UST Sites,May 15, 1998. The RWQCB states that"false positives are common in <br /> samples with high TPH concentrations". The guidance document states that EPA Method 8020 <br /> may be appropriate in areas with low concentrations of TPH,but recommends that detections of <br /> MTBE be confirmed by EPA Method 8260. <br /> Rpquest To Eliminate enat Tes in <br /> Oxygenate analysis (TBA, DIPS,ETBE,MTBE, and TAME)has been performed on <br /> groundwater samples from all wells at the Disco site for at least 4 quarters. None of the <br /> oxygenates have been confirmed, except for five isolated detections of tert-Butanol which were <br /> not substantiated by subsequent testing. There is no evidence that the gasoline released from the <br /> Disco tanks contained MTBE. Moreover, since the Disco tanks were in operation from the mid- <br /> 1960s to 1976 and MTBE was first added to gasoline in the mid-1980s, it is highly unlikely that <br /> the tanks contained gasoline-containing MTBE or other oxygenates. We understand the <br /> RWQCB requires four quarters of testing, and based on these results and facts, Del Monte <br /> requests permission to delete oxygenate analysis from the Disco site monitoring program. <br /> Request To Sample Monitoring Wells Bi-Aurally_ <br /> Del Monte has sampled the monitoring wells 11 quarters since the treatment system was shut <br /> down, and have observed only minor changes. Continuing to sample on a quarterly basis will <br /> not provide any additional useful information. As a result,Del Monte requests that monitoring <br /> well sampling be conducted only twice a year, during the first and third quarters. <br /> If you have any questions about this report, give me a call at 925-944-7276. <br /> Sincerely, <br /> •a <br /> Richard W. Fish <br /> Environmental Manager, Western Region <br /> cc: Margaret Lagorio - San Joaquin County PHS/EHD—W/O Attachment <br /> Jim Munch—UST Fund <br /> Elizabeth Dodge - CH2M HILL—W/O Attachment <br /> Steve Ronzone—DMF <br /> Susan Flieder—DMF <br /> Steve Balling—DMF—W/O Attachment <br /> Nancy Bice <br /> Vice President&Principal Geologist <br /> Geomatrix Consultants <br /> 100 Pine Street, 10th Floor <br /> San Francisco, CA 94111 <br />