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r• ay it Mr Jeff Wong April 19, 2001 Page 3 of 4 (0 7 ppb) and xylenes (1 4 ppb) were detected at low levels Nitrates were detected at a concentration of 9 parts per million (ppm) in well MW9(B), and nitrates were not detected Groundwater analytical results are summarized in Table 2 Laboratory reports and chain-of-custody documentation are included in Attachment B SUNEWARY Groundwater levels in the shallow aquifer rose an average of 0 65 feet between October 2000 and February 2001 Groundwater flow was generally in an east-northeast direction, although an apparent groundwater depression was evident near well MW4 Elevated levels of dissolved gasoline constituents are present in wells MW I, MW2, MW3, MW4, and MW6 Time versus concentration plots of constituents of concern (TPHg, benzene, MTBE) in these wells are included in Attachment C No TPHg, benzene or MTBE was detected in the deeper aquifer well (MW9(B)), although toluene and xylenes were detected at very low levels CONCLUSIONS The lateral extent of groundwater contamination beneath the site has been essentially defined, with the exception of the northeastern extent of the dissolved contaminant plume Dissolved contamination in the upper water-bearing zone does not appear to extend to deeper zones based upon the absence of dissolved gasoline constituents, including MTBE, in well MW9(B) The very low detection of toluene (0 7 ppb) and xylenes(1 4 ppb) may be due to field or laboratory error The apparent groundwater depression near well MW4 may have resulted from operation of the facility well However, it could be an indicator that some vertical leakage of the shallow aquifer is occurring through the water supply well RECOMMENDATIONS Based upon the results of subsurface investigations conducted to date, Ground Zero makes the following recommendations • Install a new water supply well to replace the existing water supply well, which has apparently been impacted by petroleum hydrocarbons, • Destroy the existing water supply well in order to eliminate it as a potential vertical migration pathway to underlying aquifers, • Install additional groundwater monitoring wells to further define the lateral extent of dissolved MTBE contamination north and northeast of well MW6, t • Eliminate the requirement to analyze groundwater samples collected from well MW9(B) for G1Data1GROUWDZEITULEBURG\Rcport3lQW\IQM200t doc