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Geological7eelti a litc Page 8 Groundwater Monitoring Report Project No 723 2 June 15,2404 ' The results of the groundwater sample analysis show the following ❑ Review of the historic groundwater elevations show that groundwater levels experience ' seasonal fluctuations from the mid 1990s to spring 2000 but have been decreasing steadily with each seasonal cycle since spring 2000 ❑ The concentrations of BTEX and TPH-G continue to fluctuate in individual monitoring ' wells from one sampling event to the next However, there is a general trend of concentrations tracking the groundwater elevations ' a Interinediate well MW-101 did not contain petroleum hydrocarbon contaminants above the laboratory reporting limits for the first time in the investigation The previous contamination is probably a drilling artifact It is noted that the contaminant ' concentrations in MW-101 have continuously declined since the well's installation in contrast to the shallow wells that do not show a similar contaminant decline ❑ Deep well MW-201 did not contain contaminant concentrations above the laboratory ' reporting limit for the second time since its installation The previously noted contamination is probably a drilling artifact created by the use of mud rotary drilling The contaminant concentration decline since the first monitoring event in December ' 2001 supports the conclusion that the initial high concentrations were from a drilling artifact ❑ Figure 10 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 I 1 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 12 illustrates TPH-G and Benzene concentrations versus elevation in deep well MW-101, which lies near the core of the plume The TPH-G and 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 ' ❑ Oxidation-Reduction Potential (ORP) and Dissolved Oxygen (DO) measurements (Table 4) show that all seventeen wells are screened in areas of the groundwater plume that are affected by the biodegradation reactions occurring within the plume The highly ' negative ORP values indicate that the wells are within the halo of reaction depleted water caused by biodegradation of the contaminants The low DO values in fourteen of the wells also reflect this condition But the higher DO values in shallow wells MW-7 ' and MW-8 (6 9 and 6 3 ppm, respectively) indicate aerobic conditions The lower DO value in up gradient well MW-9 (3 4 ppm) appears to be anomalous 1