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r Geological hchaics Inc. Page 2 Interim Soil Investigation Project No.750.2 f October 2,2003 the work plan on July 7, 2000. The work was performed during the week of October 16, 2000. On January 30, 2001, GTI prepared and submitted the Corrective Action Plan (Revised) Vadose Zone Remediation. The CAP discusses GTI's proposed methodology for mitigation of the documented petroleum hydrocarbon contamination at the site by vapor extraction. The CAP also discusses the confirmation testing outlined in this work plan. The CAP, as submitted, was approved by Ms Duncan in a letter dated April 02, 2001. v In February 2002 the soil vapor extraction system was initiated and has operated for approximately one year. Contaminant mass estimate calculations show that approximately 50% of the petroleum hydrocarbons contained in the subsurface at this site has been removed. The groundwater at this site is free of petroleum hydrocarbon contamination and possibly as much as 600 gallons of gasoline may remain in the vadose zone. On March 28, 2003, GTI submitted a work plan for additional site characterization. The work plan was approved, with reservation, by Lori Duncan in a letter dated April 8, 2003. The following report discusses the work performed on September 4 and 5, 2003 and the subsequent results from that work. 2.0 SOIL INVESTIGATION 2.1 Soil Boring Installation +..`, A well permit, SR#34865, for the installation of two soil borings was secured from San Joaquin County PHS-EHD and the local regulatory agency was notified 48 hours prior to commencing work. The subsurface was cleared of underground utilities by notifying Underground Service Alert. Late in the afternoon, on September 4, 2003, GTI and Gregg Drilling & Testing Inc. (Gregg) staff arrived at the site and cleared SB-1 and S13-2 by hand auger to a depth of 5 feet bgs. Gregg stored some equipment in the enclosure on site and left for the day. On September 5, 2003, GTI and Gregg staff arrived at the site. The hollow stem auger rig was set up on the location of S13-2 along the eastern edge of the property. The GTI Work Plan for Additional Site Characterization Soil Borings dated March 28, 2003, called for the borings to extend to the capillary fringe, expected to be approximately 50 feet bgs. Depth- to-water taken prior to drilling indicated that groundwater was approximately 64.8 feet bgs. Samples were collected at five-foot intervals, beginning at 5 feet bgs and a borehole log was kept by Eric L. Price of GTI. The first borehole was drilled to a depth of 50 feet bgs at which time Lori Duncan, SJC PHS-EHD, asked that we drill 5 more feet. After reaching a total depth of 55 feet bgs and collecting a sample at that depth the augers were left in the borehole and the rig set-up over the location of SB-1. The procedure was repeated for S13-1. After the completion of both borings Gregg mixed grout under the supervision of Ms. Duncan and filled both boreholes using tremie pipe. The boreholes were capped with cement. The boring logs (Appendix B) contain the details of lithology. u