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Ms Mary Meays Page 4 <br /> January 14, 1993 <br /> deep water channel Tidal data for the Stockton area are provided in Table 4 <br /> The difference in water elevations observed between the morning and <br /> afternoon coincide with the fact that the tide was higher when the afternoon <br /> measurements were obtained <br /> In the afternoon, the water level measured at MW-2A was 0 28 feet lower <br /> than was previously measured in the morning This observation is in <br /> contrast to all of the other wells in which the afternoon measurements were <br /> higher than those made in the morning It is probable that the drop in water <br /> elevation at MW-2A was a result of purging activities associated with <br /> sampling Tidal fluctuations do not appear to affect this well Instead, rain <br /> and purging activities cause the water level to rise and drop, respectively <br /> This contrast provides further evidence that the water in MW-2A is perched <br /> and unrelated to the other three wells Groundwater interconnection <br /> between MW-2A and the other three wells is therefore very unlikely <br /> The laboratory data (Table 3) indicate that MW-1A continues to have the <br /> highest measured concentrations of TPH-G and related petroleum <br /> compounds at Former Tank Site #2 The concentration of TPH-G and <br /> benzene decreased slightly The concentrations of toluene, ethylbenzenes and <br /> xylenes slightly increased from the previous analyses Further monitoring <br /> programs may provide an explanation for these elevated constituent <br /> iconcentrations at MW-1A TPH-D (non-diesel mixture) measured in <br /> groundwater at MW-1A was higher than was previously observed in this <br /> well <br /> MW-2A showed non-detectable levels of TPH-G, TPH-D (non-diesel mixture), <br /> and petroleum related compounds This represents a culmination of a trend <br /> of diminishing concentrations of these constituents observed during the <br /> previous quarters It is likely that the TPH-G, TPH-D and BTEX in this <br /> perched water have been removed during sampling and purging activities <br /> and natural degradation <br /> MW-3A and MW-4A showed no detectable quantities of gasoline, diesel and <br /> petroleum compounds The absence of these compounds in these wells is <br /> consistent with the results from the previous quarter However, in the April <br /> 1992 monitoring, MW-3A had very low levels of BTEX compounds Thus, it <br /> is probable that MW-3A is situated on the margin of the area affected by <br /> gasoline from the UST <br /> I <br />