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Soil_and Groundwater Investigation Based on the analytical results of the soil samples collected during the tank removal, a site assessment was initiated in August 1992 to determine the extent Of contamination at the above-referenced site Because previous onsite investigations have identified the presence of groundwater at depths of less than 12 feet, a groundwater investigation was also required Prior to the implementation of field activities, Canonie's workplan dated July 24, 1992 was submitted for your review Authorization to proceed with the proposed work was received from the Environmental Health Division on August 4, 1992 On August 27 , 1992, a soil vapor survey was performed to assist in determining the vertical and lateral extent of contamination at the subject site A pneumatic hammer was utilized to drive 9 soil vapor probes to depths of up to 15 feet in the vicinity of the former tanks Vacuum pumps and charcoal tubes were used to collect vapor samples from each probe at various depths Immediately after collection, each sample was submitted to an onsite mobile lab where it was extracted and injected into a gas chromatograph The results of the survey suggested that soil contamination was limited to the area of the north pump island and did not extend laterally to any great degree A copy of the soil vapor survey report is included as Appendix B of the site assessment report During the week of October 5, 1992 , a mobile drill rig was utilized to install four groundwater monitoring wells and three vadose zone vapor extraction wells in the vicinity of the former tanks During field activities, soils were found to consist of loose fine to medium sands to a depth of approximately 15 feet This strata was underlain by 1-foot to 4-foot thick layer of stiff silty clay which appeared to act as an aquitard (15 to 19 feet below ground surface) Just below the clay unit, saturated sands/silty sands were encountered, while moist silty clays were encountered at 30 feet Boring Logs are included as Appendix D in the attached report, and well locations are indicated on Figure 2 Wells Wl, W2 , and W4 were constructed as vadose zone extraction wells Each well was installed to a depth 15 feet and screened from a depth of 5 feet to the extent of the well with 4-inch diameter, 0 020-inch slotted well screen Wells W3, W5, W6, and W7 were installed as groundwater monitoring wells Because it was thought that the first clay unit represented a possible aquitard, these wells were constructed to insure that contamination to the groundwater dial not occur through the creation of a vertical conduit Accordingly, W5, W6, and W7 were completed as 30-foot monitoring wells, screened from a depth of 20 feet to the extent of the well with 2-inch diameter 0 020-inch slotted casing Due to its potential for use in a pumping system, W3 was constructed with 4-inch diameter casing and screened similarly to the 2-inch wells Well details are included as Appendix E in Canonie's report Two to three soil samples from each boring were transported to an analytical laboratory and analyzed for TPH, BTEX, and ethylene dibromide Gasoline and xylenes were indicated at 100 ppm and 2 ppm, respectively, in the sample collected from W2 at a depth of 5 feet, however, no contaminants were indicated at a depth of 15 feet Samples collected from W4 at a depths of 5 feet and 10 feet contained 26 ppm and 290 ppm gasoline, as well as ethylbenzene and xylenes However, soil samples collected from W3 (installed adjacent to W4) contained only 0 71 ppm gasoline and trace BTEX constituents at a depth of 14 feet, while no