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' C,e6&g6cal7-edwCS rico. Page 10 Additional Site Characterization &4'n Quarter Groundwater Monitoring Project No. 1030.2 February 20,2004 The shallow geology of the site is characterized by clay and silt, primarily gray in color, with varied degrees of plasticity. A dirty sand layer was encountered through out the site at approximately 15-feet bgs. A clay layer dominates the site between 19 and 22 feet bgs. ' Each of the sites four water table wells terminated in "plastic" clay. The deep well (MW- 101) terminated in highly plastic "fat" clay. Groundwater was encountered between 11.5- 12.5 feet bgs. The capillary fringe extended approximately 4 feet above the water table. 3.3 Hydrology of Site 1 On October 15, 2003, the depth to groundwater was measured in the five existing monitoring wells (MW-1 through MW-4 and MW-101) prior to purging. Depths to groundwater in the monitoring wells averaged 11.24 feet below the top of casing. The new monitoring well was installed after the fourth quarter groundwater-monitoring event. The ' new well (MW-5) will be incorporated into the quarterly groundwater-monitoring routine beginning the first quarter of 2004. ' The average groundwater elevation for the October 2003 monitoring event was 65.37 feet above mean sea level (MSL). Site-specific groundwater bearing and slope were calculated using MW-1, MW-2 and MW-4 and found to be N40°E @ 0.0048 ft/ft. These results are consistent with historical groundwater calculations at the site. Groundwater elevation, bearing and slope were calculated from data gathered during the October 2003, monitoring event and the results are summarized in Table 7 of Appendix A. A groundwater gradient map is included as Figure 4. 1 4.0 CONCLUSIONS AND RECOMMENDATIONS This investigation was an effort to define the lateral extent of petroleum hydrocarbons and other fuel constituents in the soil to determine the boundaries of soil excavation as a remedial option. Groundwater was sampled in the locations of a potential NNW/SSE trending sand channel under the site. The following conclusions have been drawn from the data generated from this site investigation work: ' Soil Investigation • Shadow contamination was only detected near the locations of GP-1 and GP-3 ' o The upper 7.5 feet of soil beyond these points is relatively clean and can be used to back fill the excavation (if excavation is the remediation method used) The soil plume appears to be defined by the following points: ❑ to the north by SB-2: non-detect ❑ to the east by GP-7: non-detect ❑ to the south by GP-9: non-detect ❑ to the west by GP-10: non-detect ' - • -Shallow contamination between 6 and 11 feet bgs occupies anareaof approximately 2,100 square feet or approximately 375 cubic yards (Figure 5) Intermediate depth contamination is wider spread and appears to be upgradient from the site of the former UST. This is likely due to preferential pathways supplied by leach lines and tree roots. 1