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"Ys <br /> of benzene (0. 69 ppm) , toluene (5. 2 ppm) , ethylbenzene <br /> (2 . 1 ppm) , and total xylene (13 ppm) were detected in <br /> SB-1 at 46 fbg. Concentrations of benzene, toluene, <br /> ethylbenzene, and total xylenes (BTEX) ranged from at <br /> or below the reported detection limit to less than <br /> 1. 5 ppm. <br /> 0 One source of adsorbed-phase hydrocarbons appears to be <br /> the former leaking product pipelines identified by NDE <br /> Technology, Inc. , December 2 , 1988 (Appendix H) . <br /> a Another potential source is the fill riser (west end) <br /> of the former gasoline tank. Analysis of soil samples <br /> collected from 14 fbg at the fill riser end of the tank <br /> indicated TPH-G concentrations of 2 , 000 ppm <br /> (Appendix G) . Soil impacted by adsorbed-phase <br /> hydrocarbons is probably from over spill of the fill <br /> riser, and therefore of limited extent. <br /> 0 Ground water has been impacted by dissolved-phase <br /> petroleum hydrocarbons. This may be caused by the <br /> adsorbed-phase hydrocarbons detected in the soil. <br /> 0 Based on available data, hydrogeologic conditions at <br /> the site, and results of field activities and <br /> laboratory analysis, the extent of dissolved-phase <br /> petroleum hydrocarbons in the ground water cannot be <br /> assessed. <br /> RECOMMENDATIONS <br /> Based on the findings and conclusions of this preliminary site <br /> investigation, Alton Geoscience recommends the following: <br /> ®� 1. Initiate a quarterly ground water monitoring and sampling <br /> program. p g <br /> 2 . Drill two additional offsite (downgradient) exploratory soil <br /> borings to be converted to ground water monitoring wells, <br /> and three additional ground water monitoring wells <br /> upgradient and crossgradient to assess the vertical and <br /> lateral extent of adsorbed- and dissolved-phase petroleum <br /> hydrocarbons beneath the site. <br /> 1603 �� � <br />