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CvvATc A S S O C I A T E S I N C CONCLUSIONS/RECOMMENDATIONS Petroleum hydrocarbons, in particular benzene, continue to exhibit concentrations exceeding applicable water quality objectives for groundwater at the subject site, A review of historical groundwater data (Table 1) indicate benzene in MW4 continues to fluctuate above concentrations observed as early as March 1992 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 12 times the MCL 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 included three phases The first phase included 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 included 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 was to 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 Sartini-Gardner, will apply for State funding pre-approval Pre-approval for the originally proposed work (as described in Smith Technology's Plan dated September 4, 1997, and addendum dated October 15, 1997) was approved by the Fund on November 10, 1997 With the removal of the deep monitoring well from the proposed work, modified well construction details and VET test methodologies, as well as additional tasks such as a groundwater receptor survey, ATC agreed to contact the Fund to discuss additional pre-approval requirements It is not anticipated the change of scope will exceed the amount previously pre-approved by the Fund on November 1997 w 1625821guaA1yl4gr-1998 doc 5