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5.0 CONCLUSIONS/RECOMMENDATIONS 5.1 Soil Contamination To date, approximately 750 cubic yards of contaminated soil associated with the former xylene tank have been excavated Soils were excavated vertically down to the water table Soils within the saturated zone were not removed Contaminated soils were removed laterally until field evidence (i e odor, discoloration, PID reading) suggested all affected soils had been excavated Verification soil sampling and analysis confirmed clean soils existed in side walls on the north, i northeast, and south walls of the excavation The excavation was limited on the west side by the warehouse and access ramp A verification sample collected from the west wall of the excavation contained xylene at 2 3 ppm, indicating that a small volume of slightly contaminated soil remains beneath the building foundation Soil analysis and field observations collected from Soil Barings MW 1 - MW6 confirm soil contamination is limited to the immediate vicinity of the former tank pit Although it is impractical to remove any remaining soil, the excavation area has been capped with asphalt, thereby mitigating the potential for contaminants leaching into the groundwater It is anticipated that the residual xylene and associated contaminants in the soil will break down through natural degradation processeover time Given the small volume of impacted soil and the fact that it is capped by a relatively impermeable asphalt layer, no additional mitigative measures are recommended with regard to existing soil conditions 5.2 Groundwater Contamination Laboratory results of groundwater samples collected on March 3, 1992 from site monitoring ' wells detected xylene at levels ranging from non-detectable to 500 ppb, well below the accepted MCL of 1750 ppb Benzene was not detected in any of the site wells, but ethylbenzene was present in MW3 at 1400 ppb, which exceeds the MCL of 680 ppb for this constituent Groundwater sampling has shown that the hydrocarbons associated with the former xylene tank have impacted groundwater beneath the site However, ethylbenzene is the only hydrocarbon constituent detected that exceeds the MCL for drinking water Laboratory analyses of LCR492 r]L 8