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Site Background Information: West Clay Properties Page 2 of 10 October 1999- Seven soil borings (B-10 through B-16)were advanced to collect and analyze soil samples; in addition, one soil sample collected from boring B-11 was analyzed for permeability, porosity, total organic content and specific gravity. Petroleum hydrocarbon-impacted soil was detected in soil samples collected from all soil borings except B-13;the highest concentrations were detected in soil samples collected from boring B-10, located adjacent to the former UST No. 3 excavation. July 2001 -An 8-hour step draw-down ground water extraction pilot test was conducted at the site. High concentrations of petroleum hydrocarbons were detected in extracted ground water samples. November 2004 - Based on the results of the July 2001 pilot test, a 24-hour constant rate ground water extraction feasibility test was performed at the site.Detected concentrations of target analytes in extracted ground water samples were significantly lower than those reported for the July 2001 pilot test. October 2005 - Ten ground water monitoring wells (MW-16 through MW-24 and EW-1) were installed between 10 and 19 October 2005. MW-16, MW-18, and MW-21 were screened in HU3, between 75 and 85 feet bsg. MW17, MW-19, MW-20, MW-22 through MW-24 were screened in HU4,between 95-105 feet bsg or between 135-140 feet bsg. EW-1 was screened in HU1, from 10 to 30 feet bsg. TPH-g and BTEX compounds were detected in the ground water samples from wells EW-1 and MW-21 at concentrations of 1,400 µg/1 and 1,600 gg/l, respectively, following their installation. EW-1 also contained MTBE, at a concentration of 120 µg/l. No other analytes of concern were detected in ground water samples from newly installed wells. June 2006- Two ground water monitoring wells (MW-25 and MW-26)were installed on 06 June 2006,and screened in HU 1,between 20 and 40 feet bsg.Four ozone sparge wells(OS-1 through OS- 4) were installed on 06 and 08 June 2006 at depths of 35 feet bsg. No analytes of concern were detected in the newly installed monitoring wells. Ground Water Monitoring- Based on analytical results of ground water samples collected during quarterly monitoring and site assessment activities, the lateral extent of impacted soil has been defined in HU2 to the east and west,and less well defined to the north and south. Vertical definition of the plume in the core of the contamination area has been achieved by MW-18,MW-19,and MW- 24. However, additional site assessments may be required to further delineate the plume laterally in all HUs. Cluster UST Area (North Area) December 1998 - Two 10,000-gallon USTs and one 6,000-gallon UST were removed from a common excavation at the site. Advanced GeoEnvironmental,Inc.