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No petroleum hydrocarbons were detected in water samples from MW-8 or EW-1 during <br /> the June, September or December 1994 samplings This indicates a dramatic decrease in <br /> petroleum hydrocarbons since 1988. The process of vapor extraction in the vicinity of these <br /> wells, combined with natural degradation is most likely responsible for the sharp decrease " <br /> in petroleum hydrocarbons Concentrations of toluene and xylenes lust above reporting <br /> limits were detected in the sample from MW-9 during the June 1994 sampling However, <br /> hydrocarbons were not detected during the September or December 1994 samplings <br /> Concentrations of all contaminants detected during the June 1994 sampling were below the <br /> State of California Action Level (AL) and Maximum Contaminant Levels (MCLs) for <br /> drinking water. <br /> 5,2 Hydi ocarbon Impacted Soil <br /> The PHS/EHD stated in the October 5, 1994 letter that soil "contamination remaining is a <br /> threat to groundwater and further remediation is required " A narrow band of hydrocarbons <br /> was encountered fiom 30 to 40 feet in the cotiftinnatoiy borings drilled on June 14, 1994 <br /> (CB-1 and CB-2) TPH as gasoline was detected in borings CB-1 and CB-2 at concentrations <br /> up to 2,200 ppm However, no benzene was detected in any of the samples analyzed, and <br /> only low concentrations of toluene, ethylbenzene and xylenes were detected Therefore, the <br /> majority of the most mobile fractions of hydrocarbons has been remediated <br /> We iecoinmend the use of a modeling program to determine the potential for hydrocarbons <br /> to impact gioundwater Fuither soil remediation may be based on the results of this <br /> IV pioceduie <br /> G 0 LIMITATIONS <br /> Oui professional services Nt,eie peifoiined using that degiee of care and skill ordinarily <br /> exercised by enviioninental consultants practicing in this or similar localities The findings <br /> were based upon analytical results provided by air independent laboratory Evaluations of <br /> the geologic/hydiogeologic conditions at the site for the purpose of this investigation are <br /> made froth a limited number of available data points (i a monitoring wells) and subsurface <br /> conditions may vary away from these data points No other wairanty, expressed or implied, <br /> is made as to the professional re coin mend ations contained in this report <br /> APR 2 7 1995 <br /> ENVIRONMENTAL HEALTH <br /> Cob�wl Aud'l Srv,n., I„. PERMIT/SERVICES <br /> Ge—811-1 OR'IA2 9411 1 <br />