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Mr Jeff Wong <br /> November 6,2000 <br /> Page 3 of 3 <br /> �fl TPHg in groundwater ranged from 780 ppb in well MW4 to 200,000 ppb in well MW 1, benzene <br /> ranged from 2 3 ppb (MW4) to 7,200 ppb (MW1), and MTBE ranged from non-detect in well <br /> MW2 to 9,500 ppb in well MW4 <br /> Dissolved gasoline constituents have generally increased in all site wells since the last <br /> monitoring event m June 2000, although MTBE in well MW 1 decreased by approximately 29% <br /> All detectable gasoline constituents increased from June 2000 levels in each of wells MW2 <br /> through MW4 Most notably, MTBE in well MW4 increased from 300 ppb in June 2000 to <br /> 9,500 ppb in September 2000 Tune versus concentration plots of constituents of concern <br /> (TPHg, benzene, MTBE) for each site well are included in Attachment C <br /> CONCLUSIONS AND RECOMAMNDATIONS <br /> The lateral extent of dissolved groundwater contamination in the shallow aquifer beneath the site <br /> has not been defined, pending the results of additional subsurface investigations performed in <br /> October 2000 The apparent shift in groundwater flow from northeast to east-northeast has <br /> resulted in a marked increase in MTBE concentrations (by two orders of magnitude) in well <br /> MW4, located approximately 45 feet east-northeast of the former center of the USTs <br /> Additional subsurface investigations conducted in October 2000 consisted of the installation of <br /> four additional shallow groundwater monitoring wells and one deeper groundwater monitoring <br /> well A summary report is currently being prepared by Ground Zero and will be subrrutted <br /> under separate cover In addition, Ground Zero is preparing a work plan for destroying and <br /> replacing the water supply well that serves the facility The water supply well is located <br /> approximately 50 feet east-southeast of the former center of the USTs New and existing <br /> groundwater monitoring wells will be sampled on a quarterly basis to evaluate plume stability <br /> Please contact John Lane of Ground Zero at(209) 83 8-98 88 if you have any questions or require <br /> additional information <br /> Respectfully, p;E0 GAO <br /> Ground Zero Analysis, Inc CrQY <br /> JOHN P <br /> LAPSE <br /> No 6795 <br /> John P Lane ,,, <br /> CA Registered Geologist No 6795 O <br /> Attachments <br /> • cc Mr Ray Baglietto/Mr Frank Rauzi <br /> Mr Marty Hartzell, CA RWQCB <br /> G 1Data1GROUNDZEITULEBURG\Rcporba 3QM20006 doe <br />