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r r <br /> not contained sufficient water for sampling- since June-1990_ - _ -- <br /> The apparent groundwater flow direction is to the north/northeast. <br /> 3) During the most recent groundwater sampling event (July 23, <br /> 1993) , only monitor wells MW-9 to MW-13 contained sufficient water <br /> for sampling (see attached Groundwater Analytical Results - Table <br /> 2) . <br /> 4) The station was closed in 1988, with the product and waste oil <br /> tanks removed at that time. Two smaller product tanks (3000 and <br /> 4000 gallon capacity) were apparently removed at an earlier date, <br /> possibly during station remodeling activity in 1984 (see attached <br /> Site Map - Figure 3A) . <br /> i <br /> Comments <br /> 1) Benzene is the component considered for the analytical model due <br /> to the following characteristics of the compound: <br /> (a) it is considered a carcinogen, and as such, is a primary <br /> substance for site assessment and remediation activity. <br /> (b) dissolved benzene is the most mobile of the BTEX <br /> compounds. As a means of comparison, Table 1 (below) , provides a <br /> list of pure phase solubility values and the organic carbon <br /> partition coefficient (Koc) of the BTEX components. The water <br /> solubility is the amount of a pure chemical that can dissolve in <br /> water at a specific temperature and pressure. The Koc is inversely <br /> proportional to dissolved phase mobility, as the coefficient is a <br /> measure of the affinity of the compound to adsorb onto organic <br /> carbon within the sediment matrix.- <br /> Therefore, because benzene more readily .-dissolves in water and <br /> adheres less to soil, it is more mobile than the other BTEX <br /> compounds. <br /> Table 1 <br /> Water Solubility Koc <br /> (mg/1) --- m( 1La) <br /> Benzene 1791 97 <br /> Toluene 535 300 <br /> Ethylbenzene 152 1100 <br /> Xylenes 130 240 <br /> 2 <br />