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09 June 2003 AGF,-NC Project No. 95-0106 Page 3 of 4 : . . 4.0. SUMMARY AND CONCLUSIONS The following conclusions were drawn from the results of the site investigation: • The groundwater flow direction was generally northward on 20 March 2003, and gradients 'were calculated to range from 0.005 feet/feet toward-the north-northwest to 0.004 feet/feet toward the northeast. •' Dissolved petroleum hydrocarbons were detected in ground water samples from monitoring well MW-4;,located down-gradient-off site from the former UST excavation, and MW-1 located just north of the former UST area. • BTE&X compounds were detected in the water samples collected-from-MW-4 and MW-1: The concentrations of benzene in.the samples'exceeded the State of California maximum contaminant level (MCL) of 1 µg/1 for drinking water. • .Analytical data'from monitoring wells MW-2 and MW-7 limits the horizontal extent of -dissolved hydrocarbons south and east of the site, respectively. Analytical data from wells MW-3 and MW-6 limits the extent of dissolved hydrocarbons northeastward of the.site. Analytical data from monitoring well MW-5 limits the extent of dissolved hydrocarbons lie '. northwestward ofthe site.The extent of dissolved hydrocarbons to the west is not completely defined at this time. Continued detection of TPH-g and BTE&X in ground water samples collected from the off- site'well MW4 indicates that the:plume of impacted ground water has migrated off site towards'the north, however,-the general lack of detection of hydrocarbons in the•MW-7, MW-6, MW-5 and -MW-3.wells shows that the plume is not wide-spread and- has not migrated northeast of MW,-4 or northwest of the former UST excavation. • The extent of the plume around MW-4 is constrained-by data from MW-6 toward the north- northeast,, orth- " northeast MW75 toward''the soiithwest and MW-7 toward the east relative to MW74. The northwestern exterit.of the plume from MW-4 is not well defrned. 5.0. RECOMMENDATIONS ' - Based on this and previous site investigations, AGE recommends coritiriued quarterly monitoring . of the well network. The next,monitoring event should be scheduled for June 2003. An AGE-prepared Revised„Work Plan for Soil and Ground Water Investigation --Addendum, dated 04 January 2000,has been approved by the EHD by a letter dated 23 April 2001.The scope of work includes advancing several soil boringsto define the lateral;extent of hydrocarbon-impacted ground „Advanced GeoEnvironmental,Inc.