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h Mr Ron Rowe Page 4 of 5 ' the MTBE plume and the increased concentrations of BTEX—rich gasoline suggests an offsite p g � contributing source It is suspected that the ARCO station at 130 S Wilson Way, the former Top ' Filling Station at 101 S Wilson Way, or both may the source of this encroaching contamination ' Hydrocarbon concentrations downgradient of the former onsite USTs remain within the low historic range in wells MW2 and MW8 Concentrations in wells MW5 and MW13 are stable ' VAPOR EXTRACTION SYSTEM ACTIVITIES ' VES Operation The soil vapor extraction system was shut down intentionally during the first quarter of 2000 tpending direction from PHS/EHD regarding further operation of the system Vapor Sample Analytical Results ' No samples were collected during the second quarter of 2000 RECOMMENDATIONS ' Develop Closure Criteria and Evaluate Current Conditions As proposed in our workplan (09117199), we recommend drilling soil borings to evaluate the ' effect vapor extraction has had on residual soil contamination and to further define the vertical limits of contamination We also recommend fate and transport modeling and a risk based ' corrective action evaluation Based on these evaluations, site specific criteria should be developed to determine at what point investigation and remediation should cease and the case be closed A workplan addendum is in the process of being finalized Pending completion of those ' tasks, we recommend the following VES Operation ' We recommend discontinuing vapor extraction System operation was suspended on January 3, 2000 Vapor Well Reconditioning The screened intervals in several of the vapor wells at the site are well suited for use as . monitoring wells at current water level conditions The screens are not submerged in vapor wells VW2, VW5 and VW6, the screen in VW3 is only slightly submerged However, due to the large ' r .k*mr12QM2000