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18 November 1998 <br /> AGE-NC Project No 95-0143 <br /> Page 3 of 4 <br /> the same wells at concentrations as high as 55,000 ppb (toluene in the sample from MW-3) <br />' N-butyl 1 benzene was detected in MW-6 MW-7 and MW-9 at concentrations of 3 7 b 5 4 b and <br /> h' ppb, Pp <br /> t 29 ppb,respectively,below the State of California Action Level(AL) of 45 ppb l,2-Dichloroethane <br /> (1,2-DCA) was detected in MW-14 at a concentration of 6 1 ppb, above the State of California <br /> Maximum Contaminant Level (MCL) of 0 5 ppb BTE&X were detected by EPA Method 8260 at <br /> concentrations similar to EPA Method 602 Seven additional constituents that do not have <br /> established drinking water MCLs or action levels (ALs) were detected by EPA Method 8260 in <br /> samples collected during the May 1998 monitoring event(Table 4) <br /> iPetroleum hydrocarbons were not detected in the samples collected from MW-10,MW-14, MW-15, <br /> MW-16 and MW-17 Free product was not encountered in any of the wells on the site Analytical <br /> results of ground water samples are summarized on Tables 2 through 4 The laboratory report(MAI <br /> Laboratory I D Nos 93464 - 93472) and chain-of-custody forms are included in Appendix B <br /> 4.0. SUMMARY/CONCLUSIONS <br /> Based upon data collected from the site, AGE concludes <br /> 10 Ground water elevation decreased an average of 0 53 feet between May and August 1998 <br /> The inferred ground water flow direction remains towards the north to northeast at the site <br /> • Petroleum hydrocarbons were not detected in wells MW-10, MW-14, MW-15, MW-16 and <br />' MW-17, defining the lateral extent of impacted ground water toward the south, east and <br /> north <br /> • 1,2-DCA was again detected in the sample collected from MW-14 during the August 1998 <br /> monitoring event Other analytes previously detected in MW-14 were not present during the <br /> current monitoring event <br />' Free product was not encountered at the site during the August monitoring event However, <br /> ground water is above the screened interval in MW-3, which could prevent the detection of <br />' free product, if present Concentrations of detected hydrocarbons in MW-3 are indicative of <br /> free product <br />' • Monitoring wells MW-3 and MW-9 are the most intensely impacted wells despite also <br /> having the thickest saturated zone, nearly nine feet, above the well screens <br /> • Petroleum hydrocarbon concentrations remained generally stable at the site In general, <br />' hydrocarbon concentrations have followed a fluctuating,poorly defined trend since quarterly <br /> • monitoring began <br />' Advanced GcoEnvironmental,Inc <br />