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Ms Mary Meays Page 3 October 14, 1991 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 are at the lowest level observed (3 6 mg/1) during quarterly monitoring activities BTEX concentrations were measured in concentrations which are at least one third lower than those which were observed during the Second Quarter 1992 monitoring It is likely that the diminished concentrations are a result of natural microbial degradation of compounds MW-4 also showed very low concentrations quantities of gasoline and petroleum compounds These concentrations of gasoline and related constituents are within the lower portions of previously observed concentrations for this well No BTEX compounds were detected in MW-4, during the Third Quarter, benzene, toluene and xylenes were detected at very low levels 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 gasoline and petroleum compounds The absence of gasoline and related compounds in these wells is consistent with the results from previous quarterly investigations Former Tank Site #2 At Former Tank Site #2, groundwater level contours (Figure 3) indicate a groundwater gradient that is oriented towards the southwest This pattern is the same as the pattern observed during the Second Quarter 1992 monitoring However, it differs slightly from that which was observed during initial monitoring activities in April 1992, when groundwater flow directions were oriented towards the southeast The variability in flow direction is probably due to the influence of tidally induced water level changes in the adjacent Stockton deep water channel Tidal data for the Stockton area is provided in Table 4 The groundwater level at MW-2A was 0 27 feet higher than was previously measured In contrast, groundwater levels in the surrounding wells were at least 113 feet higher than previously measured This contrast provides further evidence that the groundwater in MW-2A is perched and unrelated to the other three wells The laboratory data (Table 3) indicate that MW-1A continues to have the highest measured concentrations of TPH-G and related petroleum compounds The concentration of TPH-G decreased slightly Furthermore, benzene, ethylbenzenes and xylenes concentrations decreased, while toluene concentrations slightly increased from the previous analysis The fact that