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Mr. Steve Osborne -2 - 20 June 2011 <br /> KMEP Stockton Terminal <br /> laboratory detection limits in wells SP/M-3, SP/M-4, SP/M-5, SP/M-6, SP/M-7, <br /> and SP/M-8 since at least 2006. Board staff concur with KMEP's proposal to <br /> include Mann-Kendall statistical tests for trend analysis, estimates of attenuation <br /> rates, and an estimate of time to achieve WQOs for benzene for SP/M-1, <br /> SP/M-9, and SP/M-10 in future monitoring reports. <br /> 3. The Comment Letter clarified that methyl tert butyl ether (MTBE) can contribute <br /> to the TPHg concentrations. According to KMEP's laboratory, MTBE (C5) elutes <br /> within the TPHg range (C4 to C13) in the gas chromatograph analysis. KMEP <br /> states that when MTBE is present at high concentrations relative to the TPHg <br /> concentrations (50 percent or more) the MTBE peak will represent a significant <br /> area that becomes integrated into the TPHg quantitation. Central Valley Water <br /> Board staff concur that MTBE can contribute to the TPHg concentrations; <br /> however recent data indicate that MTBE concentrations have decreased. Board <br /> staff concur with KMEP's proposal to include Mann-Kendall statistical tests for <br /> trend analysis, estimates of attenuation rates, and an estimate of time to achieve <br /> WQOs for TPHg in future monitoring reports. <br /> 4. KMEP has divided the Site wells into the following three groups 1) manifold wells <br /> (SP/M-1 and SP/M-9), 2) commingled wells (SP/M-3, SP/M-4, SP/M-6, and <br /> SP/M-10) and 3) distal or deeper zone wells (SP/M-5, SP/M-7, and SP/M-8). <br /> The Comment Letter provides further clarification on the rationale for the <br /> conclusion that wells SP/M-3, SP/M-4, SP/M-6, and SP/M-10 are commingled <br /> with adjacent off-site sources. <br /> KMEP states wells SP/M-3 and SP/M-6 may be commingled because of their <br /> proximity downgradient of the Tesoro facility. Tesoro monitoring well TS/MW-1A <br /> is upgradient of wells SP/M-3 and SP/M-6 and contains TPHg and TPH as diesel <br /> (TPHd) above WQOs. SP/M-3 contains TPHg and TPHd at concentrations of <br /> similar magnitude to TS/MW-1A. SP/M-6 is between SP/M-3 and the manifold <br /> area and has only contained MTBE above laboratory detection limits since 2006. <br /> It is unclear how KMEP can conclude that well TS/MW-1A is responsible for the <br /> MTBE, TPHg, and TPHd in well SP/M-3, but only causes an increase of MTBE in <br /> SP/M-6. Central Valley Water Board staff are not convinced the SP/M-6 is <br /> commingled with the petroleum hydrocarbons from TS/MW-1 A. <br /> Central Valley Water Board staff concur with KMEP's proposal to include further <br /> clarification for considering wells SP/M-3 and SP/M-6 commingled in future <br /> monitoring reports. In addition, the Comment Letter does not clarify the rationale <br /> for concluding that SP/M-4 is commingled with off-site sources. Board staff do <br /> not see evidence that SP/M-4 is commingled with the Tesoro Site wells and <br /> KMEP needs to include this evaluation in upcoming monitoring reports. <br /> 5. The Comment Letter includes the rationale for concluding that well SP/M-10 is <br /> commingled with sources at the adjacent NuStar facility. In 2008, NuStar drilled <br /> soil borings NS-6 and NS-13 upgradient of SP/M-10 and collected grab <br /> groundwater samples within the C and D zones, respectively. SP/M-10 is an A <br /> zone well. Although NuStar did not collect groundwater samples within the A <br /> zone, KMEP reviewed the boring logs for NS-6 and NS-13 and noted that <br />