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� AMBRIA <br /> two separate plumes One plume is beneath the Shell site and the other plume is beneath the <br /> offsite property <br /> CONCLUSIONS <br /> The purpose of this investigation was to assess soil and groundwater conditions north of the <br /> subject site to provide delineation of the 1,2-DCA plume Groundwater analytical data collected <br /> from boring SB-27 achieved this purpose at the 110, 130 and 150 fbg depths where the 1,2-DCA <br /> concentration was below the reporting limit(0 50 ppb) The groundwater sample collected at 83 <br /> fbg from SB-27 contained 13 ppb 1,2-DCA, but this detection of 1,2-DCA may originate from <br /> the offsite property <br /> Soil and groundwater analytical data collected from the offsite property indicates that there is a <br /> separate source of petroleum hydrocarbons and possibly 1,2-DCA beneath the property Data <br /> that supports this conclusions are summarized below <br /> • Vadose zone soil contamination was found beneath the offsite property at depths ranging <br /> • from 20 5 to 50 5 fbg The concentration of TPHg detected beneath this property was as <br /> high as 19,000 ppb It is very unlikely the petroleum hydrocarbons detected beneath this <br /> property originate from the Shell site <br /> • Soil borings drilled between the Shell site and the offsite property show that there are <br /> lower petroleum hydrocarbons concentrations in the sidewalk area of each site These <br /> data suggest there is a clear separation between the elevated concentrations found on the <br /> Shell site and the elevated concentrations found on the offsite property <br /> • The predominant groundwater flow direction beneath the Shell site has been toward the <br /> southeast <br /> • Groundwater analytical data collected from the two sites and from borings located <br /> between the two sites shows that there are lower petroleum hydrocarbons concentrations <br /> in the sidewalk area of each site These data also suggest there is a clear separation <br /> between the elevated concentrations found on the Shell site and the elevated <br /> concentrations found on the offsite property <br /> • The offsite property was occupied by a former service station some time prior to 1960 <br /> This service station ceased operations some time prior to 1977 <br /> 0797 6 <br />