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(V! ATC <br /> A S S O C I A T E S I N C <br /> `- • affected surface soils; <br /> • affected subsurface soils; <br /> • dissolved groundwater plume; <br /> • free-phase liquid plume; and <br /> • affected surface soils, sediments, or surface water. <br /> w <br /> Three of these five secondary sources are not present at the site, as described below. <br /> • Analytical results of soil samples and field observations indicated that surface soils at the site <br /> (less than 15 feet below bgs)were not impacted by the release. <br /> i.. • Evidence of free-phase liquid was not reportedly observed during the subsurface investigation <br /> performed at the site. Free-phase liquid is not considered a secondary source. <br /> • Sediments and surface water are not present on site, or in the vicinity of the site, and <br /> therefore, are not considered secondary sources. <br /> Subsurface soils, defined herein as soils at a depth greater than 15 feet bgs, are affected primarily <br /> at depths above 32 to 35 feet bgs. The results of soil sampling analysis associated with soil <br /> borings advanced at the site following the removal of the gasoline UST suggests that the presence <br /> of residual soil contamination can be considered a secondary source of contamination at the site. <br /> Based on results of groundwater samples collected from monitoring well MW 1 and from soil <br /> probe boring SP-1, a dissolved groundwater plume can also be considered a secondary source of <br /> contamination at the site. <br /> In conclusion, based upon site specific conditions, surface soils, free-phase liquids, and sediments <br /> and surface water are not secondary sources at the site. Subsurface soils and a dissolved <br /> groundwater plume are the only secondary sources that are present. <br /> Transport Mechanisms <br /> The second step in analyzing exposure pathways is to identify possible transport mechanisms. <br /> The potential transport mechanisms associated with subsurface soils and a dissolved groundwater <br /> plume are: <br /> • volatilization and atmospheric dispersion; <br /> • volatilization and enclosed space accumulation; and <br /> • leaching and groundwater transport. <br /> Volatilization and accumulation of residual BTEX constituents is a potential transport mechanism. <br /> In addition, volatilization from the groundwater and atmospheric dispersion is considered a <br /> transport mechanism. The third transport mechanism is leaching from the affected soil to <br /> w:162574.054repofU\closure-FS3.doc 6 <br /> v <br />