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Geological TeclinuS inc Page 4 Groundwater Momtormg Report Project No 723 2 December 17,2002 The detection limits for the above analyses are listed in Table 2 of Appendix A while the Y pp ' lab analytical results are presented in Appendix B As required under AB2886, the laboratory data were submitted electronically to GeoTracker on October 2, 2002 - confirmation number 8962479174 2.0 FINDINGS AND DISCUSSION The results of the groundwater sample analysis show the following ' • The concentrations of BTEX and TPH-G continue to fluctuate in individual monitoring wells from one sampling event to the next • Intermediate well MW-101 continues to contain stable TPH-G concentrations, but benzene and toluene concentrations have fallen to non-detectable levels • Contaminant concentrations in deep well MW-201 are fluctuating from event to event Benzene and toluene concentrations have fallen to levels below the laboratory reporting limits Ethyl Benzene, Xylene and TPH-G were present at 0 4, 2 1 and 51 1 ug/l, 1 respectively MTBE was not present The contamination is probably a drilling artifact created by the use of mud rotary drilling It is noted that the contaminant concentrations in MW-201 have declined by an order of magnitude since the first monitoring event in December 2001, which supports the conclusion that the high concentrations were from a ' drilling artifact However, the continued presence of low concentration of the contaminants suggests that this inay be near the vertical extent of the plume • Figure 4 illustrates TPH-G and Benzene concentrations versus elevation in well MW-3, which lies near the core of the plume There appears to be a direct relationship between the water table and the TPH-G concentrations Benzene concentrations have stabilized in the well • Figure 5 illustrates TPH-G and Benzene concentrations versus elevation in well MW-4, which lies up gradient of the core of the plume The contaminant concentrations have ' stabilized in this well • Figure 6 illustrates TPH-G and Benzene concentrations versus elevation in deep well MW-101, which lies near the core of the plume The concentrations are approaching ' stability The steep decline in the initial concentrations suggests that the contaminants detected in the well were initially a drilling artifact Continued presences of the TPH-G compounds suggest that this well is within the plume ' • Figure 7 illustrates the TPH-G concentrations contours in the shallow wells The high concentration in well MW-2 creates a localized node Wells MW-3 & MW-5 exhibited a significant decrease in contaminant concentrations for this event The reason for this anomaly is not known, however the effect of this decrease is to displace the core of the plume to the north towards MW-2 Additional site investigation will allow a more accurate site conceptual model