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CGeolls,afTec(enirs Inc. Page S Soil Groundwater Investigation Report C&B Equipment Project No.: 336..2 December 22, 1997 4.0 CONCLUSIONS AND RECOMMENDATIONS Based on our interpretation of the data collected over the course of this subsurface investigation we have reached several conclusions. These conclusions are based on the -.J premise that the data we considered, although incomplete, are representative of actual site conditions. We acknowledge that there may be undiscovered conditions, which would upon ' their consideration, change our interpretation and thus our conclusions. ' Our recommendations are based on our knowledge of site conditions and the state and j limitations of subsurface investigative technology. I 4.1 Conclusions i Geological Technics Inc., taking into consideration the data obtained during previous site investigation work and the October 23, 1997 soil and groundwater investigations, makes the following conclusions. Subsurface Investijzation The following conclusions are made based on our professional interpretation of the field observations made during the completion of the soil borings, well installation, and soil and groundwater sample test data. 1. The groundwater plume appears to be migrating to some extent. This is evidenced by the recent non-detects of BTEX and TPH-G in MW-I and MW-2 and the positive results for BTEX and TPH-G in MW-3. 2. The plume is defined to the west, northwest,northeast and east by non-detects in both soil and groundwater from MW-4, 5, 6, and 7. MW-3 to the south southwest appears to be at the very edge of the plume. 3. The plume is not vertically defined as groundwater from MW-101, screened from 28.5 to i_-- 26 feet bgs, is testing positive for moderate levels of BTEX and TPH-G. However the soil sample taken from the same interval shows very low concentrations of BTEX and no - TPH-G. This supports the idea that the plume at this depth is primarily a dissolved groundwater plume and not sorbed to the soil. ` i 4. Groundwater gradient is N12°W at 0.00356 ft/ft. 4.2 Recommendations ` ' Geological Technics Inc. makes the following recommendations based on the conclusions outlined above. J =� Groundwater monitoring of the existing monitoring wells and domestic wells should be • continued on a quarterly basis to evaluate groundwater quality at the site and determine if `.i the initial groundwater monitoring results are reproducible. • Due to the thick clay, that appears to be at least 10 feet in MW-101, GTI does not recommend further vertical investigation at this site. The possibility of introducing # contamination into the possibly clean, deeper aquifer is considered too high of a risk. j