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19 January 1998 <br /> AGE-NC Project No 96-0229 <br /> Page 7 of 8 <br />' petroleum hydrocarbons are located near MW1 through MW3 and MW6 The dissolved <br /> plume is relatively undelineated to the east, southeast, north, west, northwest and northeast <br /> (Figure Nos 12 and 13 -Approximate Extent of Dissolved Total Petroleum Hydrocarbons <br />' and Approximate Extent of Dissolved Benzene, respectively) <br /> • During ground water monitoring activities, the lowest concentrations of dissolved oxygen <br /> were measured from MW3 and MW6 (dissolved petroleum hydrocarbon core-area), which <br /> Iis suggestive of aerobic biodegradation occurring in the core-area(Table 2) <br /> • Concentrations of benzene detected in MW 1 through MW6 were above the State of <br /> ICalifornia Maximum Contaminant Level (MCL) for drinking water of 1 0 ppb <br /> • Concentrations of toluene, ethylbenzene and xylenes detected from MW 1 through MW4 and <br /> MW6 exceeded the State of California MCLS of 150 ppb, 700 ppb and 1,750 ppb, <br /> respectively <br />' • Utilizing EPA methods 8260 and 8020, concentrations of MTBE were detected at higher <br /> concentrations than the State of California Action Limit of 35 ppb in ground water samples <br /> collected from MW1 through MW3 and MW6 <br /> • Field observations and laboratory data indicate that petroleum hydrocarbon-impacted soil <br /> was encountered from MW1 at depths between 35 and 60 feet bsg, from MW3 at depths <br /> between 35 and 55 feet bsg, from MW6 at depths between 30 and 35 feet bsg <br />' 5.0. RECOMMENDATIONS <br /> Based upon data collected during November 1997, AGE recommends <br />' 0 Preparation of a work plan addendum should be submitted for installation of additional <br /> P <br /> ground water monitoring wells east, southeast, north, northwest and northeast of the site in <br />' order to assess the full extent of off-site dissolved petroleum hydrocarbons <br /> • Continued quarterly ground water monitoring and sampling should be performed at the site <br /> in February 1998 <br /> • Arrangements should be made to dispose of stockpiled soil at the site by hauling off-site to <br />' a suitable hazardous waste facility (i e Forward Landfill) <br />' 6.0. LIMITATIONS <br /> Our professional services were performed using that degree of care and skill ordinarily exercised by <br /> 1 Advanced GcoEnironmental,Inc <br />