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�i <br /> S E C0 R <br /> • Mr Harlin Knoll <br /> January 23, 2006 C;al d3 � <br /> Page 2 <br /> IAV," s i t6AL1 H <br /> RERMIT/SEHVICES <br /> Number of Detections Minimum Maximum <br /> Constituents above the MDL of the 8 Concentration inyg1L(Well ID) Concentration in pglL(Weil ID) <br /> Total Samples <br /> TPHd 4 <50 280(MW-7) <br /> TPHg 2 <50 240(MW-7) <br /> Benzene 4 <0 5 19(MW-2) <br /> MtBE 3 <0 5 220(MW-2) <br /> Explanation <br /> MDL=Method detection limit <br /> uglL= Micrograms per liter <br /> Groundwater monitoring well MW-1 is located downgradient of the former waste oil and <br /> underground storage tank (UST) excavations The maximum detected concentration of <br /> MtBE In monitoring well MW-1 has been 29 micrograms per liter (pg/L) over the past two <br /> years Figure 1 graphically presents MtBE concentrations in MW-1 over the past 10 years <br /> and clearly indicates a consistently decreasing trend in MtBE with time <br /> • Monitoring wells MW-2, MW-3, and MW-5 are located to the southeast of MW-1 and <br /> downgradient of the former UST area and dispenser islands Although these wells have <br /> had consistent detections of TPHg, TPHd, benzene, and MtBE, Figures 2 through 5 <br /> Indicate a consistently decreasing trend in the concentrations of these constituents with <br /> time Monitoring well MW-5 reported concentrations of TPHg, benzene, and MtBE at or <br /> below the non-detect levels over the past nine consecutive sampling events In MW-5, <br /> concentrations of TPHd were reported slightly above the method detection limit (MDL) <br /> during the past two sampling events at 73 jig/L and 55 pg/L The laboratory analytical d <br /> report "indicates the observed sample pattern is not typical of 42 fuel/diesel The reported <br /> result Is due to Individual peak(s) eluting in the DRO range " <br /> Groundwater monitoring wells MW-6A and MW-613 are located downgradient and to the <br /> northwest of MW-1 and the former UST excavations Over the past three years, the <br /> maximum detected concentration of MtBE In well MW-6A has been 26/rg/L MtBE has not <br /> been detected In well MW-6A above Its primary Maximum Contaminant Level (MCL) of 13 <br /> erg/L in over a year MtBE has never been reported in well MW-613 at or above its MDL <br /> Only sporadic detections of TPHg, TPHd, and BTEX have been detected in wells MW-6A <br /> and MW-613 since sampling began In May 1995 Concentrations of these constituents have <br /> approached non-detect levels over several of the past quarterly events, except for benzene <br /> that has never been reported in these wells at or above Its primary MCL <br /> • <br /> N 1FileslPro1ectslChevronlRetatA#9-8632(Tracy)Panodic Mondonng1200514QMR0514Q2005 QMR 98632 doc <br />