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4 <br /> ti <br /> i ~ <br /> 3 . RESULTS AND CONCLUSIONS <br /> The results of the SVA are shown in Table 3-1 . Sampling points <br /> V1 , V2 , V3, V4 , V5 , and V8 were chosen to surround the former <br /> tank area. Of these, soil vapor constituents were detected only <br /> at point V2 , northeast of the tank area, and at point V5, south- <br /> west of the tank area. Point V2 showed the highest concentra- <br /> tions, with an instrument response of 11 , 600 VS (Volt-seconds ) in <br /> the region of compounds eluting prior to benzene. These points <br /> are generally representative of the more volatile limitation of <br /> gasoline (those compounds above benzene in Figure 1 -3 ) . Although <br /> the GC was not calibrated for these specific compounds a 1 VS <br /> response is approximately equal to 1 ppm. Points V7 , V9, and <br /> V10, were then chosen to define migration about point V2 . Of <br /> these, point V7 , located to the east of point V2 , exhibited a <br /> response of 160 VS in the region prior to benzene elution. <br /> Therefore, points V11 and V12 , east and northeast of point V7 , <br /> were chosen. No constituents were detected in the extracted <br /> vapor from points V11 and V12 . Vapor phase migration appears to <br /> be limited on the west, north and east sides of the tank. At <br /> sampling location point V5 , located southwest of the tank area, <br /> relatively small concentrations of compound vapors ( 14 VS in the <br /> prior-to-benzene region ) were detected. <br /> In order to delineate this unexpected migration, vapor samples <br /> extracted from points V6 and V13 , located to the south and west, <br /> respectively, of point V5 were analyzed and revealed no <br /> detectable constituents . Since higher concentrations of compound <br /> vapors were detected to the north and northeast of the tank, and <br /> points V1 and V4 , which are located very near the east and west <br /> sides of the tank area, revealed no compound vapors, the response <br /> obtained from vapor at point V5 may derive from an isolated <br /> spill. Another explanation for the ( relatively small ) response <br /> observed at point V5 may be the result of variable subsurface <br /> geology or the result of vapor phase transport. <br /> 7 <br />