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Quarterly groundwater monitoring and sampling of the 20 wells has been conducted since the 1St quarter 2001 to monitor the distribution of VOCs in groundwater. Time concentration plots of the groundwater monitoring results show that the concentrations of VOCs in groundwater have been variable in some of the monitoring wells following their installation in late 2000. Monitoring wells MW-06, MW-08, and MW-09 have shown changes of PCE concentrations greater than an order of magnitude since 2000. On the other hand, the data also indicate that VOC concentrations in monitoring well MW-02 have remained relatively consistent over time. Analytical sample data for City well CW#24 indicate VOC concentrations have decreased significantly with time and currently are either non-detect or at trace detection limits. 4.7 LNPA Groundwater Investigation Geomatrix conducted a Phase I Remedial Investigation (RI) of the northern portion of the City of Lodi that has been identified as the Lodi Northern Plume Area(LNPA) in Lodi, California (Figure 5). The purpose of the Phase I RI was to collect subsurface data to further evaluate the hydrogeologic conditions and the lateral and vertical extent of volatile organic compounds (VOCs) in groundwater underlying the LNPA. Work conducted during the Phase I RI addressed some of the recommendations for further characterization of VOC impacts in the LNPA as presented in Geomatrix's December 2003 Initial Site Investigation Report conducted for LNC (ISI Report) (Geomatrix, 2003). LNC was one of 8 parties participating in the LNPA RI. The scope of work proposed in the Geomatrix (2005) Work Plan was approved by the RWQCB on June 15, 2005. Previous investigations had identified concentrations of VOCs in groundwater at several locations within the LNPA boundaries. The majority of data collected previously had generally focused on the upper 90 feet of the subsurface. Previous groundwater data indicated that VOCs distributed within groundwater in the LNPA are present at greater depths from north to south and extend to a depth of at least 121 feet bgs in the central-eastern area of the LNPA (Henshaw and Associates, Inc., 2001). M ain\D:AEnvironmenta1\LN CV\10152007.wpd 22