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Bank of Stockton - Cutter Lumber Site Page 6 Quarterly Groundwater Monitoring Report ' Project No 102 2 • 8 August 1999 ' 3.0 DISCUSSION ' 3.1 Discussion of Data ' Field and analytical data results are summarized in Tables 1 and 2 and illustrated in Figures 3 through 5 ' The map of groundwater gradient (Figure 3) suggests that the flow of groundwater is to the northeast The water table has fallen about two feet since the monitoring event in late March of this year and about 2 5 feet since the ' monitoring wells MW-6 through MW-11 were constructed in March of 1998 The direction and gradient of flow have remained generally consistent over this entire time The slight variation of depth to groundwater between MW-8A and ' MW-813 suggests the deeper well, which is completed opposite a permeable sand layer, may be responding more quickly to water recharge from an off-site trecharge area The analytic data suggest that contaminant levels are generally higher than in ' . recent monitoring events This may be a result of the recent high stand of ground water contacting and mobilizing hydrocarbons which previously were stranded in the vadose zone The presence of gasoline range hydrocarbons and BTEX compunds in the deeper groundwater as determined by well MW-8A have gradually fallen to non- detectable levels except for xylene which persists at a level slightly over the minimum detection limit This well is screened from 80 to 90 feet below grade The initial water sample from the well was collected on 13 March 1998 and it contained 136 ppb of Total Petroleum Hydrocarbons Insofar has TPH-G persisted for several quarters, although at lower levels, it was assumed that the groundwater at the 80 to 90 foot level had been impacted by the release from the nearby former UST release Over the past 5 monitoring events, however, the concentration of TPH have fallen steadily to the point where they are no longer ' detectable except for a trace of xylene This trend now suggests that the hydrocarbons found in samples from MW-8A was actually a result of cross- contamination from shallower impacted soil which was carried down during the ' drilling process If this interpretation is correct, it appears that it would be appropriate for the San Joaquin County PHS/EHD to modify their directive requiring additional characterization of deep groundwater at this site ' 2937 Veneman Ave ,#B240 Geo-Phase Environmental Inc Phone (209) 569-0293 , Modesto, CA 95356 Fax (209) 569-0293