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�- Geokgical nchxics lnc. �"`� Page 2 Interim Remedial Action Plan Project No.622.2 March 28,2005 samples for petroleum hydrocarbon compounds. The results of the laboratory analyses did '-' not reveal shallow soil or groundwater contamination along the eastern or southern side of the property. L" In accordance with SJC/EHD directives, a continuously cored, single boring was installed on May 30, 2002. A discretely screened deep monitoring well, MW-104, was installed in the boring. This well has been sampled eleven times since its installation and it has contained MTBE on all occasions. After MW-104 was installed, SJC/EHD staffing had changed. In their November 18, 2002 `" letter correspondence, SJC/EHD rescinded previously submitted work plans and called for phased approach to continue the site investigation. The phased approached consisted of cone penetrometer testing (CPT), followed by monitoring well installation, and groundwater extraction well installation and aquifer testing. GTI submitted our January 17, 2003 work plan to meet the SJC/EHD directives and they approved the'CPT and groundwater extraction well portion of the work plan in their February 14, 2003 letter. Eight CPT borings, CPT-1 through CPT-8, and an extraction well, EW-1, were installed in December 2003. Groundwater samples obtained from the CPT boreholes reveal that the residual contamination is sourcing a submerged plume that has migrated east to the location of CPT- 7. A sand layer is present at a depth of 38 — 48 feet across the site and it appears to act as a preferential pathway for contaminant migration. GTI submitted our April 19, 2004 work plan for a dual phase extraction feasibility study and further soil and groundwater investigation. The work plan included provisions for: 1) the installation of a shallow soil vapor/groundwater extraction well, 2) performing a dual phase aquifer pumping test to determine if soil vapor extraction is feasible at the site and to determine aquifer pumping characteristics, and 3) the installation of two additional groundwater monitoring wells for further site definition. SJC/EHD approved the work plan in their May 21, 2004 facsimile correspondence. V The field activities proposed in our April 19, 2004 work plan were executed in October through December, 2004. The results of the well installations and the pilot test were documented in our February 22, 2005 "Dual Phase Pilot Test" report. The pilot test demonstrated that the site conditions are favorable for soil vapor extraction and groundwater extraction technologies. La GTI included the following recommendations in our report: 1. Perform interim remedial action by installing a high vacuum dual phase extraction L. unit to address the on site contamination. Dual phased extraction should be performed on well EW-2 with a separate dedicated groundwater pump on EW-1. The treatment system should include carbon filtration of extracted groundwater to be discharged to City of Manteca public treatment works. 2. A full scale Corrective Action Plan (CAP) should be deferred until after off site wells v MW-5 and MW-6 have been monitored for several quarters to determine contaminant