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1 i Geokgual rechtua kc Page 3 Morita Additional Site Characterization Report Project No 724 2 April 19,2004 In their letter correspondence dated September 3, 2002, the SJCIEHD reviewed GTI's June � 27, 2002 work plan and made several recommendations SJC/EHD wanted changes to proposed well locations and screened intervals We responded by submitting a work plan addendum on October 3, 2002 that incorporated their comments and addressed the changes desired by SJC/EHD SJC/EHD approved the October 3, 2002 addendum in their October 23, 2002 letter The following sections summarize the field activities that were completed according to the approved June 27, 2002 GTI work plan and subsequent addendum 2.0 GROUNDWATER INVESTIGATION ' In order to investigate the lateral extent of the groundwater plume, GTI originally proposed installing four separate sets of monitoring wells Three sets MW-8, 108, & 208, MW 9, 109, & 209, and MW-10, 110, & 210, were to be placed to the northeast, east and southeast, respectively, of the site This placement was intended to define the down gradient extent of the plume The well sets were to be composed of shallow, intermediate and deep aquifer wells An additional set MW-11 & 111 was to be placed up gradient of MW-3 to define the ' up gradient extent of the plume In their September 3, 2003 letter, the SJC/EHD recommended changes to the proposed well installation based on their review and interpretation of on-site data In addition, they M reviewed data from two adjacent UST sites and incorporated this material into their site conceptual model for the Morita property They have concerns that contamination exists below the water table and a sandy zone at 70 - 80 feet bgs acts as a preferential pathway for lateral contaminant migration The SJC/EHD therefore denied approval of the shallow wells MW-8,-9,-10, and changed the proposed locations of the remaining well sets GTI responded by proposing that a single deep well, MW-202, be installed first This well would intercept the deeper 70 - 80 feet aquifer level of concern to the SJC/EHD and a grab groundwater sample would be taken immediately following well installation with expedited laboratory analysis If this well contained contamination then the number and locations of ' the remaining wells would change and the wells would be moved farther down gradient This approach was approved by SJCIEHD A site map indicating the proposed wells and their locations is included as Figure 3 On December 15, 2003, deep well MW-202 was installed and a grab groundwater sample obtained from the well (see Figure 3 for new well locations) The groundwater sample was processed with a 24 hour turn-around-time and the laboratory reported on December 16 that ' the well was impacted with gasoline petroleum hydrocarbons Therefore, the well installation activities were completed in accordance with GTI's October 3, 2002 work plan addendum On December 16 - 23, 2003, intermediate and deep well pairs MW-1081-208, MW-1091-209, and MW-110/-210 were installed approximately 60 feet northeast, 75 feet east and 40 feet southeast of, respectively, the eastern edge of the site Shallow and intermediate well set MW-111-111 was installed on the northwest edge of the parcel as ' originally proposed Well-set MW-110/-210 required a separate mobilization due to an inability to get the drill rig to the desired Iocation On December 19, 2003, the ground was saturated with the