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i 22 February 2000 AGE-NC Project No 95-0128 Page 4 of 5 Laboratory results of water samples analyzed for petroleum hydrocarbons are summarized in Tables 2 and 3 The laboratory reports for the quarterly monitoring event (MAI Laboratory ID No 30147 to 30154) QA/QC reports and chain-of-custody form are included in Appendix B 4.0. SUMMARY AND CONCLUSIONS A summary of findings for the 31 January 2000 investigation includes the following points • All properly screened wells on site yield ground water samples that have been impacted by detectable concentrations of various BTEX compounds and petroleum hydrocarbons, although the MW7 sample contained only a low concentration of TPH-d • The three monitoring wells with deeper-screened intervals yielded samples with very low or non-detectable concentrations of various BTEX compounds and petroleum hydrocarbons The deeper-screened monitoring wells do yield samples with low concentrations of MTBE A few previous samples from monitoring wells MW2 and MW3 have also been impacted by low concentrations of TBA The data suggests that vertically downward migration of petroleum hydrocarbons is minor to insignificant, and also indicates that deeper hydrocarbon- impacted soil horizons are not significantly impacting the ground water with petroleum hydrocarbons This also suggests that the more significantly impacted ground water is confined to the upper twenty feet of the ground water column • The oxygenating fuel additive MTBE was detected In all of the ground water samples collected The concentrations of MTBE detected in the deeper-screened wells, MW1, MW2 and MW3 were 13 4g/l, 4 0µg/l and 10 4g/l, respectively Compared to the 53,ug/1 to 600 ugll MTBE detected in the properly screened, down-gradient wells in the core area and in the down-gradient area, the deeper concentrations are suggestive of minor vertical migration of MTBE • The MTBE concentration in the up-gradient wells, MW6 and MW7, was 6 1 ,ug/l, and 46 ug/l, respectively, slightly greater than the concentrations detected in samples from the deeper-screened wells • The decline of dissolved hydrocarbon concentrations in samples from MW6 and VW1, coupled with more than an order-of-magnitude increase in the samples from MW4 and MW5 compared to the March 1999 monitoring event are consistent with a shift of ground ' water flow direction from northwesterly in March 1999 to northeasterly in July 1999 through January 2000 Advanced GeoEnvironmental Inc I