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(VATC � A S S O C I A T E S I N C Groundwater samples collected from wells MWI, MW2, MW3, MW-5, MWb and the nearby Supply Well contained no detectable concentrations of BTEX or TPHg These analytical results are generally consistent with historical levels Analytical results are summarized in Table I Laboratory reports and chain-of-custody documentation are presented in Attachment 2 CONCLUSIONS/RE COMMENDATIONS Benzene continues to exceed the 1 0 ppb California Primary Maximum Contaminant Level (MCL) A review of historical groundwater data (Table 1) indicates petroleum hydrocarbons continue to exhibit concentrations exceeding applicable water quality objectives for groundwater at the subject site and threatens the nearby Supply Well Natural Attenuation of the residual petroleum hydrocarbons at the project site should occur over time, however, shallow groundwater at the site and the documented soil contamination at the soil/water interface appear to reverse and threaten mass reduction of dissolved petroleum hydrocarbons in the vicinity of MW4, prolonging natural attenuation Due to benzene levels currently in well MW4 and with the well's close proximity to the municipal supply well, it remains questionable whether passive bioremediation would meet regulatory criteria for the protection of groundwater quality ATC recommends the Workplan dated October 30, 1997 and subsequent addendum dated December 15, 1997 (which was approved by PHS/EHD) be completed This work includes three phases The first phase includes well installation, obtaining permits and a property access agreement, installing three vapor wells, two monitoring wells, and an air sparge well, and collecting soil and groundwater samples The second phase includes preparing a workplan containing a summary of well installation activities and proposed pilot testing, and, conducting soil and groundwater pilot testing Upon obtaining results of the pilot tests, ATC will prepare a Corrective Action Plan (CAP), the third phase of work Topics discussed during the September 3, 1998 project meeting, including the indefinite postponement of a proposed deep monitoring well, the re-evaluation the construction of the proposed wells, a longer pilot test than originally proposed, and a groundwater receptor survey should be addressed in a modified workplan and submitted for PHS/EHD approval Following the submittal and subsequent PHS/EHD approval of a modified workplan, ATC, on behalf of Ms Donna Sartiri-Gardner, will apply for State funding pre-approval w 1625821quartlyl3gr-1999 doc 5