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CLEARWATER <br />' G R O U P I N C <br /> • Environmental Services <br /> 4 0 CONCLUSIONS AND RECOMMENDATIONS <br /> 41 Conclusions <br /> Extent of Hydrocarbons in Soil <br /> Previous subsurface investigation, which included the advancement of six soil borings in September <br /> 1997, has delineated the vertical extent of sorbed-phase hydrocarbons as being restricted to <br /> approximately 10 to 25 feet bgs depth interval <br /> Results from tlus phase of investigation provided delineation of the extent of the sorbed-phase <br /> hydrocarbon plume, although low concentrations of sorbed hydrocarbons were detected in the saturated <br /> zone at depths of 19 to 20-foot bgs in MW-5 and MW-b, respectively, to the southeast and east of the <br />' former USTs However, the lateral and vertical extent of Sorbed-phase contaminants appears to be <br /> adeg �y delineated at this time <br /> Z <br /> 10 Extent of Dissolved Hydrocarbons <br /> Analytical results from groundwater samples collected from the three new monitoring wells indicate <br />' the presence of significant concentrations of TPHg and BTEX in the well located directly downgradient <br /> (MW-5) and in the well located cross-gradient to the east (MW-5) relative to the former USTs <br />' Reported concentrations in MW-5 some 70 feet downgradient from the plume source are significantly <br /> higher than those detected in MW-1, immediately downgradient from the source Concentrations in <br /> cross-gradient well MW-6 are similar to those in MW-1 The upgradient extent of the plume is <br /> essentially defined at MW-2 <br /> 1 Results of analyses of groundwater samples collected during this investigation indicate that the <br /> hydrocarbon plume associated with the subject release extends downgradient from the source, beyond <br /> 1 the investigated area The presence of high concentrations of dissolved hydrocarbons jcross-gradient <br /> from the former USTs suggests the presence of possible additional off-site sources Preliminary <br /> 1 inquiries regarding the nature of possible additional sources indicates that fuel transport pipelines may <br /> be present in the immediate vicinity of the site Additionally, onsite personnel observed significant <br /> 1 hydrocarbon vapor release during subsurface road construction activities on South Fresno Avenue 1 l,.rc� of -� <br /> 1 <br /> 1i <br /> 1 C-178 WELL lNs7 RPT 6 May 7, 1999 <br />