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�1 M1 ciulkogicaITechnics Inc. Page 5 Groundwater Monitoring Report Project No. 723.2 j f March 10, 2003 stability. 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. a 3.0 CONCLUSIONS & RECOMMENDATIONS 3 a Conclusions I. Groundwater flow trends to the northeast to east. The southerly flow direction recorded on December 4, 2000, appears to be anomalous. 2. It is noted that the groundwater elevation exceeded the level of the well screens. 3. High levels of BTEX and TPH-G are present in the groundwater of all six water table 4 monitoring wells. Low concentrations of BTEX and TPH-G are usually present in both 1 �I of the deeper wells. Generally, most of the wells show stable levels of contaminant concentrations over time. l r 4. The groundwater contaminant plume is not defined vertically or laterally. However, the decreasing concentration of contaminants in MW-201 suggests that this well may define the vertical edge of the plume in this location. 5. 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 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 near a stand still, which corroborates well with the laboratory data. p Recommendations i ' 1. In July 27, 2002, we submitted a work plan for additional site characterization, with subsequent addendums. The San Joaquin County HS/EHD has approved the installation of three multi-chamber wells and these will be installed pending USTCFP cost pre-approval. 2. Continue quarterly groundwater monitoring, with the next monitoring event scheduled a in March 2003. 3. We recommend that interim remediation be considered before this plume migrates any further and the cost for cleanup continues to increase.