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► � 1260 Graphics Drive <br /> V Modesto California <br /> 95351 <br /> 209 579 2221 <br /> Fax 209 579 2225 <br />• A S S O C I A T E S I N C <br /> RESULTS <br /> Water levels have increased an average of 2 05 feet since the last monitoring event in August 1997 <br /> (Table 1) A groundwater gradient map was created using the data collected on March 19, 1998 <br /> (Figure 2) Groundwater flows northeast, away from the slough, with a gradient of approximately <br /> 0 07 feet/foot or 396 feet per mile <br /> No petroleum hydrocarbon constituents were detected in the groundwater samples collected from <br /> wells MW1, MW3, and MW4R or from the domestic well Well MW5 contained benzene below <br /> the State Maximum Contaminant Level (MCL) and TPHg and TPHd at a concentrations of 70 <br /> parts per billion (ppb) and 110 ppb, respectively Well MW6 contained TPHd at 250 ppb The <br /> samples from wells MW2, MW5, and MW6 contained MTBE at concentrations of 63 ppb, 200 <br /> ppb, and 280 ppb, respectively No other oxygenate fuel additives were detected in any wells <br /> sampled Analytical results are summarized in Table 2 Laboratory reports with chain-of-custody <br /> documents are included in Attachment 2 <br /> RECOMMENDATIONS <br />• Due to the elevated concentrations of MTBE In the groundwater sample from wells MW2, MW5, <br /> and MW6, ATC recommends monitoring and sampling of all site wells (MWI through MW6) for <br /> TPHg, TPHd, BTEX,and MTBE during the second quarter of 1998 <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 /> �'Uv � ,� A&-- <br /> Drew Van Allen _y.�-� <br /> -y h <br /> Staff Scientist � �j �� ,a/"'l <br /> !E I` CCIO <br /> I\t <br /> LLJ <br /> LL' N3. 0l03A7"10 <br /> Jeanne Horase ; f ' <br /> CA Registered Civil Engineer No C47410 F-x� � � a <br /> Attachments 'r OF C <br />• cc CRWQCB <br /> Robert Taylor, Westrec Marinas <br /> w 1625141quartlyll qr-1998 doc 2 <br />