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4 0 CONCLUSIONS, RECOMMENDATIONS AND PROJECT STATUS <br /> Results of the investigation confirmed and further defined the extent of diesel an I <br /> g d gasoline <br /> hydrocarbons in soil and groundwater beneath the site <br /> In soil, petroleum hydrocarbons are mostly concentrated as TPH-as-diesel TPH-as-gasoline is <br /> present in concentrations approximately one order of magnitude lower than those for TPH-as- <br /> diesel The highest concentrations are present in vadose (i e , unsaturated) soil near the former <br /> USTs Lateral to the area of the former USTs, relatively lower concentrations were observed <br /> ' within the capillary fringe and saturated sod intervals, probably carried away from the former UST <br /> source area by groundwater flow Since only two of the 12 soil samples collected during this <br /> investigation contained only TPH-as-diesel at a maximum concentration of 2 4 mg/kg, the extent <br /> of impacted soil appears to be mostly defined <br /> ' In groundwater, TPH-as-diesel and TPH-as-gasoline were observed in relatively equal <br /> concentration Given the relatively low concentrations of BTEX, the absence of any oxygenate <br /> compounds, and the time duration since the USTs were in service, the gasoline hydrocarbons in <br /> groundwater appear to be aged and/or weathered <br /> As shown on Figures 4, 5, and 6, the lateral extent of impacted groundwater at the groundwater <br /> table is mostly defined for TPH-as-diesel, undefined for TPH-as-gasoline, and fully defined for <br /> benzene Impacted groundwater appears to be concentrated beneath the former USTs and to the <br /> west and northwest (i e , downgradient) of the former USTs Based on the results of the <br /> groundwater-grab sample collected from B-6, the second groundwater-bearing interval beneath <br /> the former USTs appears to be impacted by relatively low concentrations of gasoline compounds <br /> As such, the vertical extent of impacted groundwater remains undefined <br /> ' Based on these conclusions, Ramage Environmental recommends that a work plan be prepared <br /> to expand the groundwater table monitoring network at the site In addition, one deeper <br /> ' monitoring well should be installed near the former USTs to evaluate the second groundwater- <br /> bearing interval The three existing monitoring wells will continue to be monitored and sampled on <br /> a quarterly basis The next monitoring event is scheduled for March 2003 <br /> 14 <br />