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Creologcca[TechnicsInc Page 5 <br /> Groundwater Monitoring Report <br /> Project No 723 2 <br /> April 18, 2003 <br /> • Figure 7 illustrates the TPH-G concentrations contours in the shallow wells The high <br /> concentration in well MW-3 creates a localized node Additional site investigation will <br /> allow a snore accurate site conceptual model <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 It is noted that the groundwater elevation exceeded the level of the well screens <br /> 3 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 usually present in <br /> intermediate well MW-101 Generally, most of the wells show stable levels of <br /> contaminant concentrations over time <br /> 4 The groundwater contaminant plume is not defined laterally However, the decreasing <br /> ' concentration of contaminants in MW-201 suggests that this well may define the vertical <br /> edge of the plume in this location <br /> 5 Oxidation-Reduction Potential and Dissolved Oxygen measurements (Table 4) show <br /> that all eight wells are screened in areas of the groundwater plume that are affected by <br /> the biodegradation reactions occurring within the plume The highly negative ORP <br /> values indicate that the wells are within the halo of reaction depleted water caused by <br /> biodegradation of the contaminants This suggests that the contaminant plume is stable <br /> and that natural attenuation processes are near a stand still, which corroborates well with <br /> ' the laboratory data <br /> Recommendations <br /> 1 I In July 27, 2002, we submitted a work plan for additional site characterization, with <br /> subsequent addendums The San Joaquin County PHS/EHD has approved the <br /> installation of three multi-chamber wells and these will be installed pending receipt of <br /> encroachment pen-nits from the City of Stockton <br /> 2 Continue quarterly groundwater monitoring, with the next monitoring event scheduled <br /> ' in June 2003 <br /> 3 We recommend that inteinn remediation be considered before this plume migrates any <br /> further and the cost for cleanup continues to increase <br /> i <br />