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3. DISCUSSION Available analytical data (GTI 1987 ) from the monitoring wells located near the tank field (MW1 , MW2, MW3 ) indicated the pre- sence of hydrocarbons in the groundwater, but their concentration quickly declined almost to the detection limits between March 1987 and February 1989 (the last time they were sampled) . Of the peripheral wells, only one, EA2, showed traces of benzene ( 0. 7 ug/L) , toluene ( 2. 5 ug/L), and xylenes ( 2 ug/L), in February 1988 . This well had dried- up by March 1989 and could not be sampled after that. No concentrations of petroleum hydrocarbons above the detection limits were found in the other wells before they were found to be dry in June 1989. Because hydrocarbons in the soil were found only in one borehole (MW1 ) , at a relatively low concentration of 8.8 mg/kg (Table 3 ) , there does not appear to be an active source of petroleum.:hydlro- carbons at the site. In addition, all of the soil excavated during the tank pull was spread on site and aerated for several months, and the excavated tank pit was left open during this time, permitting significant reduction of any hydrocarbons in unexcavated soil by evaporation. The rapid decreases in hydro- carbon concentrations in the groundwater and the low Concentra- tion detected in soil suggest that the fuel release at the site was small, and off-site development of the hydrocarbon plume in groundwater is not expected. A drop of groundwater of more than 10 feet left most of the dis- solved hydrocarbons adsorbed to soil in the vadose zone, further enhancing natural cleanup by evaporation nd biochemical degra- dation, and decreasing the risk of contamination of nearby well( s ) . Frequent shifts in groundwater flow direction consti- tute an additional factor limiting the movement of contaminants off the site (Figure 2 ) - _ c5 ! /97780/6-90/tx 4