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','Okguat reclucicsW Page 5 <br /> Groundwater Momtonng Report <br /> Project No 723 2 <br /> January 19,2004 <br /> declined by an order of magnitude since the first monitoring event in December 2001, <br /> which supports the conclusion that the high concentrations were from a drilling artifact <br /> o Figure 4 illustrates TPH-G and Benzene concentrations versus elevation in well MW-3, <br /> which lies near the core of the plume There appears to be a direct relationship between <br /> the water table and the TPH-G concentrations Benzene concentrations have stabilized <br /> ' in the well <br /> ❑ Figure 5 illustrates TPH-G and Benzene concentrations versus elevation in well MW-4, <br /> which lies up gradient of the core of the plume The contaminant concentrations exhibit <br /> ' a decreasing trend in this well <br /> ❑ Figure 6 illustrates TPH-G and Benzene concentrations versus elevation in deep well <br /> MW-101, which lies near the core of the plume The TPH-G concentrations are <br /> approaching stability while the benzene concentrations have fallen to levels below the <br /> laboratory reporting limits The steep decline in the initial concentrations suggests that <br /> the contaminants detected in the well were initially a drilling artifact The continued <br /> presence of the TPH-G suggests that this well is within the plume <br /> ❑ Figure 7 illustrates the TPH-G concentrations contours in the shallow wells The high <br /> I concentration in well MW-3 creates a localized node Additional site investigation will <br /> allow a more accurate site conceptual model <br /> ❑ Oxidation-Reduction Potential (ORP) and Dissolved Oxygen (DO) measurements <br /> (Table 4) show that all eight wells are screened in areas of the groundwater plume that <br /> are affected by the biodegradation reactions occurring within the plume The highly <br /> negative ORP and low DO values indicate that the wells are within the halo of reaction <br /> depleted water caused by biodegradation of the contaminants <br /> ' 3.0 CONCLUSIONS & RECOMMENDATIONS <br /> Conclusions <br /> 1 Groundwater flow trends to the northeast to east The southerly flow direction recorded <br /> on December 4, 2000, appears to be anomalous <br /> ' 2 High levels of BTEX and TPH-G are present in the groundwater of all six water table <br /> monitoring wells Low concentrations of BTEX and TPH-G are present in intermediate <br /> well MW-101 Generally, most of the wells show stable levels of contaminant <br /> ' concentrations over time and the concentrations appear to mirror groundwater elevation <br /> changes <br /> 3 The groundwater contaminant plume is not defined laterally However, the lack of <br /> I contaminants in MW-201 suggests that this well does define the vertical limit of the <br /> plume beneath the site <br /> 4 The highly negative ORP and low DO values suggests that the contaminant plume is <br /> ' stable and that natural attenuation processes are dormant, which corroborates well with <br /> the laboratory data <br /> i <br />