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CV\/ATC <br /> A S S O C I A T E S I N C <br /> utilizing EPA Method 8015B, BTEX utilizing EPA Method 8021B, and oxygenate fuel additives <br /> including methyl tert-butyl ether(MTBE) utilizing EPA method 8260B <br /> ANALYTICAL RESULTS <br /> Petroleum hydrocarbons were detected in the groundwater samples collected from MWl and MW2 <br /> MTBE was detected in the groundwater sample collected from MW I at a concentration of 7 1 <br /> micrograms per liter (}ig/L) TPHg, benzene, toluene, and MTBE were detected in the groundwater <br /> sample collected from MW2 at concentrations of 190 µg/L, 1 2 µg/L, 2 5 µg/L, and 21 µg/L, <br /> respectively <br /> Groundwater samples collected from wells MW3, MW4, MW5, MW6, and MW7 did not contain <br /> concentrations of TPHg, TPHd, TPHk, BTEX constituents, or fuel oxygenates at or above the <br /> laboratory reporting limits Analytical results for groundwater samples are contained in Table 2 <br /> Laboratory data sheets and chain-of-custody documentation are contained in Attachment 2 <br /> CONCLUSIONS <br /> Concentrations of petroleum hydrocarbons in groundwater samples collected from MW 1 and MW2 <br /> are within the historical range as established by previous sampling events but have generally <br /> decreased over time (Figures 4 and 5) Concentrations of petroleum hydrocarbons remained below <br /> . laboratory reporting limits in samples collected from MW3, MW4, MW5, MW6, and MW7 TPHd <br /> and TPHk have not been detected in MWI through MW4 for the last six quarters and have never <br /> been detected in MWS through MW7 The lateral extent of the petroleum hydrocarbon plume in <br /> groundwater appears to be receding <br /> RECOMMENDATIONS <br /> Based on the recent historical groundwater quality data, we recommend the sampling frequency of <br /> MW3 through MW7 be changed to a semi-annual basis <br /> Please contact our office at(209) 579-2221 if you have any questions <br /> Respectfully submitted, <br /> ATC Associates Inc <br /> /vQ ^ <br /> Nathan Christman anne Homsey, P E <br /> Staff Geologist CA Registered Civil Engineer No 47410 <br /> cc Ms Lori Shields, Diesel Performance <br /> ve <br /> Mr Jim Barton, RWQCB ISANNE <br /> i <br /> IF - tat °k: <br /> Pj � yy 4 y <br /> w 16257714QR-2003 docs <br />