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March 27, 1995 <br /> Page 2 <br /> Rationale for the proposed groundwater monitoring program are as follows.' <br /> • Quarterly groundwater monitoring has been conducted at the site since <br /> February 1991. Sufficient data have been collected to develop trends in <br /> the groundwater quality and flaw direction. <br /> • Historically, the most significant concentrations of petroleum <br /> hydrocarbons have been detected in Monitoring Wells U-1, U-2, U-5, <br /> and U-6. Hydrocarbon concentrations within these wells have ranged <br /> from none detected to 6,100 parts per billion TPH-g. Typically, the <br /> maximum hydrocarbon concentrations in these wells have been detected <br /> during seasonal groundwater highs (January and February). <br /> • Monitoring wells proposed for annual sampling have not contained <br /> detectable concentrations of TpH-g or benzene for the past 6 <br /> consecutive quarterly sampling events. <br /> • The proposed monitoring and sampling frequency will be sufficient to <br /> define and monitor the hydrocarbon plume status during site remediation <br /> activities scheduled for 1995. <br /> PACIFIC recommends implementing this modified monitoring program in the second <br /> quarter 1995. If you have any questions regarding the contents of this letter, please call. <br /> Sincerely, <br /> Pacific Environmental Group <br /> s <br /> JOSEPH J. h;'!ZZ10 <br /> Y Fp <br /> Joseph Muzzio cr W <br /> Project Geologist ! ' <br /> CEG 1672 <br /> Attachment: Quarterly Data Report (prepared by MPDS Services, Inc.) <br /> cc: Ms. Mary Meays, San Joaquin County Public Heath Services, Environmental Health <br /> vision`f <br /> Ms. Elizabeth Thayer, Regional Water Quality Control Board- Central Valley <br /> Region <br /> 310011$/1995MRP <br />