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' Geological rec/uucs Inc Page 5 Groundwater Monitoring Report Project No 723 2 November 13,2003 ' • 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 S 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 exhibit a decreasing trend in this well Figure 6 illustrates TPH-G and Benzene concentrations versus elevation in deep well MW-101, which hes near the core of the plume The TPH-G concentrations are approaching stability while the benzene concentrations have fallen to levels below the laboratory reporting limits The steep decline in the initial concentrations suggests that the contaminants detected in the well were initially a drilling artifact The continued presence of the TPH-G suggests 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-3 creates a localized node Additional site investigation will allow a more accurate site conceptual model 3.0 CONCLUSIONS & RECOMMENDATIONS Conclusions ' 1 Groundwater flow trends to the northeast to east The southerly flow direction recorded on December 4, 2000, appears to be anomalous 2 Huls levels of BTEX and TPH-G are present in the groundwater of all six water table Monitoring NAells Low concentrations of BTEX and TPH-G are present in intermediate well MW-101 Generally, most of the wells show stable levels of contaminant concentrations over time and the concentrations appear to mirror groundwater elevation chances- 3 The �n-ounduater contaminant plume is not defined laterally However, the lack of contaminants in MW-201 suggests that this well does define the vertical limit of the plume beneath the site 4 Oxidation-Reduction Potential and Dissolved Oxygen measurements (Table 4) show that all eight wells are screened in areas of the groundwater plume that are affected by ' the biodegradation reactions occurring within the plume The highly negative ORP and low DO values indicate that the wells are within the halo of reaction depleted water caused by biodegradation of the contaminants This suggests that the contaminant ' plume is stable and that natural attenuation processes are donnant, which corroborates well with the laboratory data