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Geological recknlcsInc. Page 3 Soil Vapor Extraction Pilot Test Work Plan Project No. 770.2 September 17,2003 2.2 Hydrogeology L.i Table 1 includes Summary of Groundwater Elevation and Gradients- Water Table Wells, Table 2 includes Summary of Groundwater Elevation and Gradients- Deep Wells and Table 6 contains the well construction details. , The water table well groundwater elevation on June 18, 2003 averaged —38.4'5"feet mean 1- sea level (MS�) or—63 feet below grade surface (bgs). The elevation of the water table has varied from 5 65 feet bgs during the course of the investigation. CThe historical groundwater gradients are illustrated in Figures 7 & 8: Groundwater Gradient Rose Diagrams for Water Table and.Deep Wells, respectively. The site's shallow aquifer displays highly variable shifts in groundwater direction. It is noted that groundwater direction has been predominantly to'the southeast since additional wells Were installed in May 2002. The deeper aquifer flow had been consistently to the east but on April 28 and May 23, 2003 the gradient reversed,180°from an easterly direction to a westerly direction. L The direction reversed again to the east for the June 2003 sounding event. A well receptor survey was completed in January 2001 and numerous agricultural, residential and conunercial wells were identified near the site. The variability in groundwater gradients and direction may be due to pumping influences from these wells. Vertical gradients are calculated for the MW-5/105 & MW-6/106 well pairs. Table 3 shows the calculated vertical gradients for the wells with both positive and negative vertical gradients recorded. Similar to the historical lateral directions, the direction of groundwater in the vertical plane also fluctuates at the site. The magnitude of vertical groundwater flow direction ranged from—0.02 to 0.0097 for the site investigation. As stated above, the site is probably under the influence of groundwater wells operating in the area that account for the variable vertical gradients. I 2.3 Contaminant Distribution `4 1 Tables 4 & 5 in Appendix A contain the site soil and groundwater data, respectively. Figures 4 and 6 illustrate the soil and groundwater contaminant distribution as j superimposed on the two cross-sections A - A' and B — 13% respectively. The groundwater Aie54 data from the June 18, 2003, monitoring event are presented in the diagrams adjacent to the respective well's screened interval. . In Figure 4, a column of soil contamination is present under the former UST L excavation/dispenser area. In the vicinity of MW-6/MW-106, no soil contamination was I detected and Win. Hunter & Associates stated no contamination was present in MW-3. This r suggests that the contamination migrated downward to impact the groundwater without less j L i