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MUS01 �-W No/ �. Seventeen soil borings (H1 through H16 and H7A) were drilled in the vicinity of the former UST excavations, oil/water separator sumps, and storm sewer pipeline (ETIC, 2007a). Analytical data confirmed the presence of gasoline -range petroleum hydrocarbons in soil at depths ranging from approximately 15 to 54 feet BGS. "The highest concentrations were detected in the vicinity of the former gasoline UST excavation. TPH-g was not detected in shallow soil samples collected in the vicinity of the oil/water separator sumps (Hl, H2, and 144), the former 10,000 -gallon diesel UST excavation (H5), the former fuel pump island (H7), and the storm sewer pipeline (H4 and 116). Petroleum hydrocarbons detected in the diesel range use r/ did not exhibit a typical chromatographic pattern for diesel fuel, and may be attributable to 5,qQ10 gasoline present in the samples. Gs� g V"'X , 4 +" "110+w� 1" S44„004J -H vvf-r yt7�f• Grab groundwater samples were also collected during this investigation. TPH-g was detected in four of the nine samples. -A maximum TPH-g concentration of 82,000 µg/T- was detected in sample H9, collected beneath the center of the former gasoline UST excavation. Petroleum hydrocarbons were not detected in samples collected from H15, located downgradient of the ` former gasoline UST excavation, or H13, located cross -gradient of the former gasoline UST excavation. These groundwater data further define the lateral extent of contamination soyrflr 5zo� and east of the source area (the former gasoline UST excavation). V Groundwater Monitoring (1987 through 2007) 4 Groundwater monitoring has been performed at the site since 1987. April 2007 monitoring data indicate that the overall groundwater flow direction is generally to the east beneath the Site at a adient of approximately 0.002 foot per foot. TPH- BTEX, some fuel oxygenates, and 1,2 - DCA PP Y P g> Yg > DCA have been detected in groundwater samples collected during recent monitoring events. r. Graphs of chemical concentrations in groundwater versus time are included in Appendix B L 3.0 SITE CONCEPTUAL MODEL A site conceptual model has been developed based on field and analytical data obtained, to date, and is presented in the following subsections. The scope of work proposed in this work plan is intended to obtain data to fill data gaps in the site conceptual model. As additional data are obtained, the site conceptual model will be revised accordingly. 3.1 CHEMICALS -OF -CONCERN AND AFFECTED MEDIA Figure 3 illustrates the traces of two geologic cross-sections prepared from boring logs drilled at the Site. Figures 4 and 5 present the two cross-sections, illustrating the lithology, stratigraphy, �. and concentrations of TPH-g beneath the Site. Figures 6 and 7 illustrate TPH-g and benzene isoconcentration contours in groundwater, respectively. L SL ATR SCM. and RI WP 9 6n r -