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L KEI-P86-084A-2 January 20, 1988 Page 2 DISCUSSION The analysis of groundwater samples from the seven wells indicated the presence of dissolved gasoline constituents in all wells except MW-1 and MW-2 , which continued to show non- detectable levels. Concentrations of the contaminants during October and November, 1987 have declined from the September readings. The wells which contained the highest concentrations of dissolved gasoline were wells MW-4 and MW-5 located adjacent to the tank complex. These wells contained 8,700 ppb and 2,500 ppb dissolved petroleum hydrocarbon concentrations respectively with BTX concentrations ranging from 6. 0 to 260 ppb. A comparison of the analytical results of November 20, 1987 sampling with those from September 21, 1987 reveals that T_PH and BTX concentrations have decreased. A significant decrease of the off-site wells (i.e. MW-6, MW-7 and MW-8) in the total dissolved petroleum hydrocarbon and BTX concentrations was also noted. This indicates an apparent natural degradation of the gasoline components across the site. Of greatest significance, however, was that BTX concentrations of all three off-site wells (MW-6 to MW-8) were below the drinking water standards during the November 1987 sampling. In summary, the analytical results showed the groundwater contamination is concentrated in the easterly portion of the site. In addition, the levels of dissolved gasoline constituents are low in the off-site wells suggesting that the plume is of limited extent. LIMITATIONS Soil deposits and rock formations may vary in thickness, lithology, saturation, strength and other properties across any site. In addition, environmental changes, either naturally- occurring or artificially-induced, may cause changes in groundwater levels and flow paths, thereby changing the extent and concentration of any contaminants. Our studies assume that the field and laboratory data are reasonably representative of the site as a whole, and assume that subsurface conditions are I reasonably conducive to interpolation and extrapolation. The results of this study are based on the data obtained from the field and laboratory investigations. We have analyzed this data using what we believe to be currently applicable engineering . techniques and principles in the Northern California region. We make no ,warranty, either expressed or implied, except that _our services"haver been performed in accordance with generally