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GeoCoguafTechnics Inc. Page 5 <br /> Groundwater Monitoring Report <br /> Project No. 770.2 <br /> w January 10, 2002 <br /> �.r <br /> Elevation. The September 2001 event marked the first decrease in the TPH-D <br /> concentrations but they have increased again for the December 2001 event. The plot in <br /> Figure 4 suggested a direct relationship between groundwater elevation and contaminant <br /> �.. concentrations but this situation was reversed for this event. <br /> Well MW-4 lies adjacent to the former UST field. Figure 5- MW-4: TPH-D vs. <br /> �- Groundwater Elevation suggests an inverse relationship between groundwater elevation and <br /> contaminant concentrations in well MW-4. It is noted that the groundwater elevation <br /> exceeded the screened interval of well MW-4 and dilution may be taking place. <br /> Conversely, the water table lies within the screened interval of well MW-5 and this may <br /> represent a more accurate reflection of residual contamination leaching into groundwater. <br /> Well MW-5 continues to contain the highest concentrations of detected contaminants (see <br /> Figure 6) but it has not been down gradient of the former UST location for the six <br /> UP monitoring events completed by GTI to date. The reason for this anomaly is not known. <br /> A comparison of diesel concentrations in well pair MW-5/MW-105 versus groundwater <br /> y elevation reveals a pattern consistent with the difference between MW-4 & MW-5 noted <br /> above. In. Figure 7 — MW-5 & MW-105: TPH-D versus Groundwater Elevation, well MW- <br /> 5 contaminant concentrations correlate with changes in the water table. Well MW-105, <br /> .�� screened below the water table, exhibits an inverse relationship between contaminant <br /> concentrations and groundwater elevation. <br /> �- GTI makes the following recommendations: <br /> • Continue quarterly groundwater monitoring for determining direction and contaminant <br /> trends. <br /> W <br /> • Perform monthly groundwater level measurements for one year. <br /> • Install additional monitoring wells to evaluate possible differences in shallow versus <br /> '-' deep plume movement. GTI submitted an October 25, 2001 "Additional Site <br /> Characterization, Soil Boring & Monitoring Well Installation" work plan to the San <br /> Joaquin County PHS/EHD to complete the above recommendations. The SJC <br /> PHS/EHD replied to GTI's work plan by requiring two additional shallow monitoring <br /> wells in locations specified by SJC PHS/EHD. Our November 30, 2001 "Work Plan <br /> Addendum — Soil and Groundwater Investigation" included the two additional <br /> monitoring wells required by SJC PHS/EHD. A Cost Pre-Approval Application has <br /> been submitted to the USTCFP for authorization and we are awaiting a response. <br /> La <br />