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Ms Mary Meays Page 3 January 14, 1993 trough situated along the southern portion of the site In the afternoon, water level measurements were elevated in the wells by up to 133 feet and the potentiometric surface formed a trough centered at MW-5 and oriented towards the southeast These result are consistent with those obtained during the previous recent quarters of monitoring The variability in flow direction and water elevation are probably due to the influence of tidally induced water level changes in the adjacent Stockton deep water channel Tidal data for the Stockton area are provided in Table 4 The difference in water elevations observed between the morning and afternoon coincide with the fact that the tide was higher when the afternoon measurements were obtained The laboratory findings (Table 2) indicate a continued slight decrease in the concentration of TPH-G and related petroleum compounds at MW-5 The measured TPH-G concentrations were historically the lowest level observed (1 8 mg/1) during quarterly monitoring activities BTEX concentrations were also lower than observed during any previous quarters of monitoring Thus, a decreasing trend in the concentrations of TPH-G and BTEX compounds has been established It is likely that the diminished concentrations are a result of natural microbial degradation of compounds � MW-4 showed no detectable quantities of TPH-G and BTEX During previous quarters, TPH-G and BTEX have been oberved at very low concentrations There have also been quarters in which these compounds were not observed Thus, it is probable that MW-4 is situated on the margin of the area affected by gasoline from the UST It is also likely that the diminished concentrations are a result of natural microbial degradation of compounds Wells MW-1, MW-2, and MW-3 showed no detectable quantities of TPH-G and petroleum compounds The absence of TPH-G and related compounds in these wells is consistent with the results from previous quarterly investigations Former Tank Site #2 Potentiometric surface contours are for Former Tank Site #2 are depicted in Figures 3 and 4 The contours shown for the measurements taken in both the morning and afternoon indicate a general southwest gradient In the afternoon, water level measurements were elevated in wells by up to Q 74 feet These result are consistent with those obtained during the previous recent quarters of monitoring As previously discussed, the variability in water elevation is probably due to the influence of tidally induced water level changes in the adjacent Stockton