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S E C 0 R <br /> I <br /> Mr Harlin Knoll <br /> March 27, 2006 <br /> Page 3 <br /> Detected constituents In groundwater are summarized below <br /> Number of Detections Minimum Maximum <br /> Constituents Above the MDL Concentration in irg/L Concentration in pglL <br /> Total Samples Collected=4 (well ID) (Well ID) <br /> TPHd 1 <50 560-(MW-4) <br /> TPHg i <50 2 500 (MW-4) <br /> Benzene 0 <0 5 <0 5 <br /> MtBE 2 <0 5 53(MW-3) <br /> Explanation <br /> MDL=Method detection limit <br /> ,ug/L= Micrograms per liter <br /> TPHd=Total petroleum hydrocarbons as diesel <br /> TPHg=Total petroleum hydrocarbons as gasoline <br /> MtBE=Methyl tert-butyl ether <br /> Notes <br /> a = Laboratory report indicates the observed sample pattern is not typical of#2 fuel/diesel It elutes in the DRO range <br /> . one earlier and one later than#2 fuels <br /> CONCLUSIONS <br /> Random, low concentrations of TPHg, TPHd, benzene, and MtBE have been reported In <br /> groundwater monitoring wells MW-1 and MW-2 Benzene and MtBE have never been <br /> detected in these wells at or above their primary maximum contaminant levels (MCL) of 1 <br /> erg/L and 13 yg/L, respectively TPHd detections may represent weathered gasoline, but <br /> additional chemical analyses would have to be performed to verify this <br /> Although TPHg, TPHd, benzene, and MtBE have been detected In wells MW-3 and MW-4 <br /> the concentrations of all these constituents rapidly decrease after May 2002 Benzene has <br /> not been detected In either of these wells since October 2002 The most recent detections <br /> of TPHd, TPHg, and MtBE occurred during the ,January 25, 2006 sampling event <br /> Detections of TPHg and TPHd occurred In monitoring well MW-4 at concentrations of 560 <br /> yg/L and 2,500 ,ug/L, respectively Detections of MtBE occurred In monitoring wells MW-3 <br /> and MW-4 at concentrations of 53 Ng/L and 6 erg/L, respectively The concentration of <br /> MtBE In MW-4 is below the MCL, but the concentration In MW-3 exceeds the MCL value <br /> RECOMMENDATIONS <br /> It appears that only low level concentrations of residual petroleum hydrocarbons remain in <br /> • the areas of the former UST pit and downgradient of the former UST excavation In 4 <br /> addition, benzene has not been detected in either of these wells since October 2002 MtBE <br /> i <br /> N IFtleslProjectslChevronlRetaill#9-82641Periodic Monitonng1200611Q2006_QMR doc <br />