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Geologeeal Tetlutus 14C Page 3 ' Additional Site Characterization Work Plan Project No 724 2 June 27,2002 Iborings were installed, one soil sample and five water samples were obtained The analyses of these groundwater samples indicated that the groundwater plume extended off site to the ' northeast in boring SP-1, to the north in boring SP-6, and to the northwest in borings SP- 5A A groundwater sample from up gradient location SP-4 did not contain detectable contaminants The lack of data from off site locations limits the accuracy of a site ' conceptual model to the data available from on site The historical soil and groundwater data are included in Appendix B The locations of the site borings are illustrated in Figure 3 This figure also indicates the lateral extent of the groundwater plume as confirmed by the groundwater data compiled to date In Figure 3, the model presented shows a groundwater plume sourced by contamination evident in eight on site wells The plume is depicted as extending to the north, northeast and east of the site in the predominant down gradient groundwater direction The historical groundwater gradients are included in Figure 4 Groundwater ' Gradient Rose Diagram The plume is shown as extending to the location of boring SP-1 This is the only data point available on which to base this conclusion The extent is then projected north, northeast, east and southeast to conform to the projected travel path as suggested by the dominant gradients included in Figure 4 The site geology is presented in two cross section diagrams Figures 5 & 6 (see Figure 2 for section locations) The site exhibits a primarily clayey geology with clayey sands, silts and gravel layers occurring less frequently Figures 5A & 6A are cross section diagrams with ' soil contaminant concentrations indicated next to the bonngs The groundwater TPH-G concentrations from the June 2002 quarterly monitoring event are also depicted next to the screened intervals of the wells In these diagrams, a soil plume is shown in the vicinity of the former dispenser island (near borings SB-101, MW-101 and MW-201) The groundwater plume is depicted as extending across the site as evidenced in the site wells The vertical extent is depicted from the historical water table depths to a depth of approximately 110 feet bgs This is regarded as the bottom of the groundwater plume because a soil sample from MW-201 at this depth was non-detect for all analytes Contamination has been detected in well MW-201 that is screened from 148 — 150 5 feet bgs GTI believes that this contamination may be an artifact from drilling of the well by mud rotary in October 2001 and not representative of actual groundwater conditions This conclusion is supported by the fact that the vertical profile of the soil column includes ' several clay units that would serve to inhibit the vertical migration of contamination In addition, the groundwater samples from MW-201 have displayed a reduction in concentrations for the three events in which the well was sampled The analytical data from well MW-201 is summarized in the following table