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5.0 CONCLUSIONS AND RECOMMENDATIONS The four new wells confirm that the area of impacted soil is limited The absence of detectable concentrations in any samples from these wells indicates that they are not near a source of Petroleum hydrocarbons This implies that the presence of hydrocarbons in the groundwater in these wells is due to hydrocarbon migration in the saturated zone from a more distant source The distance from the area of impacted soil near the dispenser island to VM-7 is only about 20 feet, so it is conceivable that groundwater contamination in this'well is due to migration from the dispenser, although the groundwater elevation data imply that a steep eastward gradient was present in the vicinity of this well in April Hydrocarbons would be unlikely to migrate westward to VM-7 under these conditions, so a change in the groundwater flow direction would be required to allow hydrocarbons to migrate westward to this well Future monitoring of water depths should help to resolve this question Petroleum hydrocarbon concentrations in VM-6 and VM-8 are much lower than in VM-1 and VM-2, but are still higher than anticipated and are difficult to understand in view of the present groundwater flow direction Prior to drilling, we assumed that VM-8 would not be impacted because of its distance (nearly 100 feet) northeast of the limit of contaminated soil Nevertheless, the TPH-g concentration in VM-8 might be reconcilable if the groundwater flow direction were northeastward from VM-2, but the data do not indicate that at this time Instead, it appears that the flow direction is mostly eastward on the south side of Main Street and southeastward on the north side of the street Thus, the concentrations in VM-6 and VM-8 are more compatible with a source nearer the northeastern corner of Main and Grant Street than they are with a source on the southeast corner As a result, the northern and eastern limits of groundwater contamination cannot be confidently identified with the data from the new wells Early in this investigation, various non-petroleum hydrocarbons (chlorinated solvents, etc ) were detected in water samples from VM-1 and VM-2, and we concluded that the source of these contaminants was not the Valley Motors property The source has never been identified, and it is possible that multiple contaminant sources are present in the vicinity Therefore, we recommend examining assessor parcel records, building permit files, and telephone directories to determine the history of ownership and property use of the parcels of land located on the north side of the Main Street- Grant Street intersection to determine whether other contaminant sources may have been present Petroleum hydrocarbon concentrations in VM-2 are clearly increasing This is apparently due to desorption of gasoline from the soil in the vicinity of the former dispenser island and eastward migration in groundwater, because concentrations have declined in VM-1 over the same time period This eastward migration has not led to a consistent rise in concentrations in VM-4, and we recommend taking interim steps to prevent that from occurring Currently, the depth to groundwater is greater than 35 feet, which means that the sandy aquifer beneath the site is entirely within the unsaturated zone This would therefore be an opportune time to utilize soil- vapor extraction technology to mitigate the impact to soil in the dispenser area Vapor extraction well VT-1 was installed in 2000 for this purpose, but the well has never been used We recommend plumbing VT-1 to a temporary vapor extraction blower and performing interim soil 6