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,t v <br /> A S S O C I A T E S I N C <br /> ,low�- — <br /> RESULTS <br /> Water levels have increased an average of 108 feet since the last monitoring event on December 18, <br /> 1998 (Table 1) A groundwater gradient map was created using the data collected on March 4, 1999 <br /> (Figure 2) Groundwater flows northeast, away from the slough, with a gradient of approximately 0 05 <br /> feet/foot or 264 feet per mile <br /> No petroleum hydrocarbon constituents were detected in the groundwater samples collected from <br /> wells MW 1 and MW4 TPHg and BTEX were not detected In any of the groundwater samples Wells <br /> MW5 and MW6 contained TPHd at concentrations of 120 parts per billion (ppb) and 140 ppb, <br /> respectively The samples from wells MW2, MW3, MW5, and MW6 contained MTBE at <br /> concentrations of 80 ppb, 12 ppb, 9,100 ppb, and 33 ppb, respectively Analytical results are <br /> summarized in Table 2 Laboratory reports with chain-of-custody documents are included in <br /> Attachment 2 <br /> RECONENIENDATIONS <br /> Due to the detectable concentrations of MTBE in the groundwater sample from wells MW 1, MW2, <br /> MW5, and MW6, ATC recommends continued monitoring and sampling of all site wells (MW 1 <br /> through MW6)for TPHg, TPHd, BTEX, and MTBE by EPA Methods 8015/8020 <br /> Nyou have any questions or comments regarding this project, please contact our office at (209) 579- <br /> 2221 <br /> Respectfully subrnitted, <br /> ATC Associates Inc <br /> Drew Van Allen <br /> Staff Scientist <br /> t.� 8 L'3:'t <br /> Jeanne Homsey IIt, <br /> CA Registered Civil Engineer No C47410 <br /> Attachments cl y civil. a\�' <br /> cc CRWQCB <br /> Jay Mills, Westrec Marinas <br /> w 1625141quartly\lgr-1999 doe 2 <br />