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Geological7-ahnicsInc. Page 5 Interim Soil Investigation Project No.750.2 October 2,2003 Conclusions SB-1 • SB-1 is located approximately 4 feet southwest of HP-1 and 6 feet north of MW-1. It is located about 12 feet south of the extraction well set, VEW-3 & 4. • Samples from 19.5, 44.5, and 54.5 feet bgs in SB-1 were submitted for analyses and were non-detect for all analyzed constituents. • This shows a remarkable change from the samples collected in 1999 from HP-1 and MW-I (refer to summary data table in Table 1: o The 20.5 foot sample collected from HP-1 (February 12, 1999) showed very high concentrations of BTEX, TPH-G and MtBE in the soil o The 46 foot sample collected from HP-1 showed elevated concentrations of BTEX, TPH-G and MtBE in the soil o The 56 foot sample collected from HP-1 showed detectable concentrations of toluene, xylenes, TPH-G and MtBE o The 25 foot sample collected from MW-1 (July 30, 1999) showed moderate levels of BTEX and TPH-G as well as a high concentration of MtBE o The 45 foot sample collected from MW-1 showed detectable BTEX concentrations and elevated levels of MtBE o The 55 foot sample collected from MW-1 showed trace levels of xylene and MtBE • It appears that the VES has removed the hydrocarbons in the subsurface soils in the area around SB-I SB-2 ~ • SB-2 is located nearly 10 feet south of HP-5 and about 20 feet south of extraction well set, VEW-1 & 2. • Samples collected above 20 feet bgs indicated the presence of petroleum hydrocarbon and fuel oxygenates. Samples submitted to the laboratory below 34 feet bgs were non- detect for all analyzed constituents. • The 14.5-foot sample from SB-2 had high levels of BTEX and TPH-G. These concentrations attenuated rapidly with depth. The 19.5-foot sample from SB-2 showed concentration 2 to 3 orders of magnitude less than the 14.5-foot sample. • One possible explanation for the concentrations detected in SB-2 is that the area is outside the radius of influence of the VES. There may be loss of influence to the uncapped surface of the site. • Groundwater has been non-detect for all analyzed constituents over the last five consecutive monitoring events with the following exception: o MW-1 showed trace levels of xylenes in September and December of 2002. Groundwater data is discussed in the Groundwater Monitoring Report 2rd Quarter 2003 dated July 22, 2003 Recommendations • Concentrate extraction efforts on VEW-1 and VEW-2 for 6 to 9 months. Also extract from VEW-3 &4 to further treat the area around these extraction wells. • After 6 to 9 months of operation, the vapor extraction should be discontinued. • Perform a spike test to determine degree of completion of vadose zone remediation. • If conditions remain stable, the site should be considered for closure. v v