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• A S S O C I A T E S I N C <br /> RESULTS <br /> Water levels have decreased an average of 0 88 feet since the last monitoring event on March 19 <br /> 1997 (Table 1) A groundwater gradient map was created using the data collected on June 23, 1998 <br /> (Figure 2) Groundwater flows northeast, away from the slough, with a gradient of approximately <br /> 0 06 feet/foot or 324 feet per mile <br /> No petroleum hydrocarbon constituents were detected in the groundwater samples collected from <br /> well MW4R BTEX was not contained in any of the groundwater samples Wells MW5 and MW6 <br /> contained TPHd at concentrations of 280 parts per billion (ppb) and 210 ppb, respectively The <br /> samples from wells MWI, MW2, MW3, MW5, and MW6 contained MTBE at concentrations of <br /> 2 9 ppb, 3 9 ppb, 8 7 ppb, 7,700 ppb, and 100 ppb, respectively No other oxygenate fuel additives <br /> were detected in any wells sampled Analytical results are summarized in Table 2 Laboratory <br /> reports with chain-of-custody documents are included in Attachment 2 <br /> RECOMMENDATIONS <br /> Due to the detectable concentrations of MTBE in the groundwater sample from wells MW I, MW2, <br />• MW3, MW5, and MW6, ATC recommends continued monitoring and sampling of all site wells <br /> (MW 1 through MW6)for TPHg, TPHd, BTEX, and MTBE by EPA Methods 8015/8020 <br /> If you have any questions or comments regarding this project, please contact our office at (209) <br /> 579-2221 <br /> Respectfully submitted, <br /> ATC Associates Inc <br /> vC§,.,, 1 + <br /> Drew Van Allen <br /> Staff Scientist �����ESSion"? <br /> Je&Homsey °C No. CC. P M � <br /> CA Registered Civil Engineer No C47410 Exp. -1492 <br /> r� <br /> CML <br /> Attachments <br /> cc CRWQCB <br />. Jay Mills, Westrec Marinas <br /> w 1625141quart1yl2gr-1998 doe 2 <br />