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CvvATC <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 MW1 and MW2 <br /> TPHg, benzene, total xylenes, and MTBE were detected in the groundwater sample collected from <br /> MWl at concentrations of 210 micrograms per liter (ug/L), 1 2 µg/L, 1 3 µg/L, 8 4 pg/L, <br /> respectively TPHg, benzene, ethyl benzene, and MTBE were detected in the groundwater sample <br /> collected from MW2 at concentrations of 200 4g/L, 1 8 �tg/L, 0 7 µg/L, and 13pg/L., 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 I 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, MW 5, MW6, and MW7 TPHd <br /> and TPHk have not been detected in MW 1 through MW4 for the last five quarters and have never <br /> been detected in MW5 through MW7 The lateral extent of the petroleum hydrocarbon plume in <br /> groundwater appears to be receding <br /> RECOMMENDATIONS <br /> In a letter dated July 8, 2003, the San Joaquin County Environmental Health Department (SJCEHD) <br /> reiterated its directive requiring submittal of a corrective action plan The SJCEHD also requested <br /> submittal of a site conceptual model ATC will submit the requested documents In the interim, based <br /> on recent historical groundwater quality data, we recommend the sampling frequency of MW3 <br /> through MW7 be changed to an annual basis <br /> Please contact our office at(209) 579-2221 if you have any questions <br /> Respectfully submitted, <br /> ATC Associates Inc <br /> Todd Hafner Jeanne l-lomsey, P E <br /> Project Geologist CA Registered Civil E <br /> JEANINE �` <br /> cc Ms Lori Shields, Diesel Performance liq . <br /> Mr Jim Barton, RWQCB e�; r <br /> r <br /> w lwordpro162577r3QR-2003 doc 3 <br />