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Creologkal rechnxs t" Page 6 ' Groundwater Monitoring Report Project No 770 2 • April 25,2005 ' to low water level in the well The plot in Figure 6 suggests that a previously direct relationship between groundwater elevation and contaminant concentrations has reversed ' since June 2002 Well MW-5 continues to contain the highest concentrations of detected contaminants (see ' Figure 8) It is not down gradient of the former UST location and the reason for this anomaly is not known, but could be related to geologic units that slope to the west MW-4 Well MW-4 lies adjacent to the former UST field Figure 7- MW-4 TPH-D vs Groundwater Elevation suggests that a predominantly inverse relationship exists between groundwater ' elevation and contaminant concentrations In this figure the sudden increase in diesel concentrations for August 2004 coincides with the same phenomenon observed in MW-5 The cause is unknown at this time, but the concentration of diesel has decreased since that ' event MW-105 TPH-D was not detected in MW-105 during this monitoring event Detection of TPH-D in the last two quarters of year 2004 indicated that the contamination has moved vertically downward in an oblique angle to the northwest from the source In Figure 9—MW-5 & MW- 105 TPH-D versus Groundwater Elevation, well MW-5 contaminant concentrations have previously exhibited a weak correlation with changes in the water table Since September 2001 the relationship has been reverse Well MW-105, screened below the water table, exhibits a typical on/off trend (alternating between detecting diesel at —100 Rg/1 to ND<50 µg/1), thus suggesting that the vertical extent of the diesel plume is near the depth interval of ' MW-105 Figure 10 illustrates the distribution of diesel in the deeper wells TPH-D was not detected in the deep wells so an iso-concentration diagram was not developed GTI makes the following recommendations ' 9 Maintain the quarterly monitoring schedule • In response to the comments from SJCEHD on the site conceptual model report, we C � recommend that an additional site characterization work plan (in progress) and interim ' remedial action plan be implemented ASAP s 1 6. 3.0 LIMITATIONS This report was prepared in accordance with the generally accepted standard of care and practice in effect at the time Services were rendered It should be recognized that definition and evaluation of environmental conditions is an inexact science and that the state or practice of environmental geology/hydrology is changing and evolving and that standards existing ats/cam