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i <br /> enviroso <br /> locations and soil analytical results are presented in Appendix A Well locations and <br />• ground water analytical results are presented in Appendix B <br /> In December 1991, one additional ground water monitoring well (MW-4) was installed <br /> Three soil samples from the boring for MW-4 were submitted for laboratory analyses <br /> TPH-G was detected in the sample collected from 29 fbg at a concentration of 1 1 ppm <br /> BTEX was not detected in any of the soil samples collected from Well MW-4 Soil <br /> analytical results are presented in Appendix A The boring log and well construction <br /> details are presented in Appendix C <br /> Petroleum hydrocarbons were removed from soil beneath the former UST pit over a two <br /> month period in 1991-1992 The soils beneath the former tanks were vented during an <br /> extended pilot vapor extraction test performed at the site from December 1991 to <br /> February 1992 Air monitoring data indicated petroleum hydrocarbons at concentrations <br /> of up to 6,500 parts-per-million-volume (ppmv) were removed from soil during the test <br /> Ground water samples collected from MW-4 following vapor extraction have contained <br /> very low concentrations of hydrocarbons when detected Air monitoring data collected <br /> during the vent test are presented in Appendix E <br /> Quarterly ground water monitoring began in July 1990 TPH-G and benzene have not <br /> been detected in Wells MWA, MW-2, or MW-3 since 1993 Benzene has been detected <br /> in ground water samples from Well MW-4 on only two occasions since 1993 and at <br /> concentrations barely above detection limits Most recently, petroleum hydrocarbons <br /> were not detected in any of the ground water monitoring wells <br /> Subsurface Characterization <br /> • Subsurface data suggest that near surface native materials consist of clayey silt and silt to <br /> depths ranging from approximately 15 to 18 feet This unit is underlain by sandy silt <br /> with minor clay lenses Deeper soils consist of clayey silt material underlain by a water <br /> bearing medium grained sandy silt at about 45 fbg Copies of soil cross-sections are <br /> presented in Appendix D <br /> Since 1990, depth to ground water has varied from a high of approximately 20 5 fbg to a <br /> low of approximately 32 fbg Ground water at the site flows predominantly easterly with <br /> an approximate gradient of 0 01 to 0 005 <br /> Soil Sampling Summary <br /> Soil samples collected by Aegis in October 1989 indicated that soils beyond the former <br /> UST pit were not impacted by petroleum hydrocarbons Soil samples collected in June <br /> 1990 from beneath the USTs upon removal indicated that soils directly beneath the <br /> former USTs had been impacted with petroleum hydrocarbons Soil samples collected <br /> during installation of the monitoring wells and vapor wells in July 1990 and in December <br /> 1991 confirmed that hydrocarbon impacted soils are delineated and limited to the vicinity <br /> of the former USTs <br /> Ground Water Monitoring and Sampling Summary <br /> Historically, depth to ground water has varied from a high of approximately 20 5 fbg to a <br /> low of approximately 32 fbg Ground water at the site flows predominantly easterly with <br /> an approximate gradient of 0 01 to 0 005 <br /> 96373 2 <br />