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Ceobgua(7echnus14C Page 5 <br /> l <br /> Soil Gas Survey Report <br /> ie Project No 701 2 <br /> July 23,2002 <br /> ' 2.0 CONCLUSIONS AND RECOMMENDATIONS <br /> ' The following conclusions have been drawn regarding the soil gas survey data <br /> Conclusions <br /> ' 1 Gasoline impacted soils are present on the eastern portion of the survey area The <br /> presence of gasoline range hydrocarbons in groundwater has been confirmed in this area <br /> from previous GeoProbe groundwater sampling activities and from MW-7 Based on <br /> ' the prevalence of gasoline range hydrocarbons in this location, there are several sources <br /> possible, including <br /> ' ■ ASTs — the former ASTs are in an up-gradient direction from a portion of the <br /> gasoline plume So it is conceivable that in the past, one or more ASTs may have <br /> contained gasoline However, it is not probable during the use by Ted Peters A <br /> ' preliminary review of their records shows that the tanks were only used for diesel <br /> storage and sale and that they were removed in 1999 <br /> ■ USTs - a detached plume from the former gasoline USTs located at the front of the <br /> ' parcel is a possible source The "smear" of BTEX extending southward supports <br /> this conclusion, but it is acknowledged that the absence of contamination in well <br /> MW-8 does not credit this mobile plume theory A rose diagram of historical <br /> Mgroundwater gradients is included in Figure 3 The range of directions evident <br /> makes it possible that a plume could have migrated in a north and westerly direction <br /> ' from the former gasoline USTs <br /> ■ Sump — the sump is also a possible source of the gasoline The use of this device is <br /> not known, but it is also up-gradient of a portion of the gasoline plume and is <br /> ' suspect Plume displacement would have to account for the remote location of the <br /> plume from the sump, similar to what would have occurred for the AST or UST <br /> possible source <br /> ' ■ Surface Spillage — it is possible that the gasoline plume or a portion of it is sourced <br /> from an undocumented surface release in the area of the current plume <br /> 2 Diesel contamination is present along the eastern edge of the study area This is <br /> ' presumed to be a result of releases from the former diesel ASTs <br /> 3 Figures 4 and 5 illustrate the location of the GeoProbe sample locations and contaminant <br /> concentrations in soil and groundwater respectively The results of the soil gas survey <br /> ' correlate with the contamination previously detected in the vicinity of well MW-7 and <br /> northeast of this location This suggests that the source of the contamination is from on <br /> site sources rather than off site <br /> 1 <br /> 1 <br />