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' 29 December 2000 AGE-NC Project No 95-0128 ' Page 4 of 5 ' 4.0 SUMMARY AND CONCLUSIONS A summary of findings for the 24 October 18 2000 event indicated the following points ' 0 Monitoring wells on-site have been impacted by detectable concentrations of various BTEX compounds and petroleum hydrocarbons The wells on-site were also impacted with moderate levels of MTBE • The northwestern monitoring wells yielded samples with the highest concentrations of ' MTBE detected during the sampling event • The deeper-screened monitoring wells yield samples with lower concentrations of MTBE compared to the shallow-screened wells Ia MTBE detections in the former UST/dispenser area and in the down-gradient area suggest preferential horizontal migration of MTBE compared to vertical migration • The current ground water monitoring well system appears to be situated near the west and south margins of the MTBE-impacted ground water plume However, the northern edge of the network may be within the core of the dissolved MTBE, requiring additional well or soil lie borings to delineate the northern and eastern edges of the dissolved MTBE I50 RECOMMENDATIONS Based on the results of this and previous investigations, AGE recommends Y Continued qualteily monitoring of the ground water monitoring network • Initiation of ground water extraction activities detailed in the approved in the work plan titled Interim Gr nand Waley Remediation • Performance of a soil vapor extraction test in the shallow, fine grain soil to the current vadose zone to test feasibility for addressing impacted soil The previous vapor extraction pilot test was conducted at a time of low ground water level that left a significant sand mt-er.ral .n the vadose zone, the results are not likely to be applicable to currcnt s�tc conditions • Advanced GeoF nvironntental 1HL