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Former 76 Station 4409 S E C O R July 28, 2005 y Page 2 i Fallowing removal of the former station canopy, canopy footings, and kiosk, additional over- excavation was completed in the dispenser area. Over-excavation was terminated when obviously impacted soil was removed, the structural integrity of the sidewalk was endangered, or groundwater was encountered. A total of approximately 1,707 tons of soil was transported offsite for disposal at the Forward Landfill in Manteca, California. On December 9 and 10, 1999, four groundwater monitoring wells (MW-1 through MW-4) were installed in the A monitoring zone to investigate the extent of petroleum hydrocarbons in soil and groundwater beneath the site (Attachment A). A vertical assessment by geoprobe was conducted in July 2000, and soil and groundwater impacts were encountered at depths of 60 feet bgs. 4 The San Joaquin County Environmental Health Department (SJCEHD) subsequently requested a work plan for further delineation of soil and groundwater impacts. Three on- site B monitoring zone groundwater monitoring wells (MW-5 through MW-7, Attachment A) were installed in November 2000. These wells identified B monitoring zone groundwater petroleum hydrocarbon impacts. In August and September 2001, three additional B monitoring zone groundwater monitoring wells (MW-8 through MW-10, Attachment A) were installed onsite to evaluate the extent of B monitoring zone groundwater impacts. In June and July 2003, four off-site B monitoring zone groundwater monitoring wells (MW-11 through MW-14, Attachment A) were installed to further delineate the lateral extent of dissolved petroleum hydrocarbon plume within the B monitoring zone. In November of 2004,' SECOR installed one on-site C monitoring zone groundwater } monitoring well, MWA 5. This well was incorporated.into the quarterly monitoring and sampling program immediately following its installation even though the remaining two wells } that were proposed under the work plan for the project were not completed during the fourth } quarter 2004. s In April 2005, SECOR field staff directed .Cascade Drilling Inc. of Rancho Cordova, California, during the installation of two C monitoring zone groundwater monitoring wells # (MW-16 and MWA 7) using the sonic drilling method. These wells were installed to further delineate the vertical and lateral extent of dissolved .petroleum hydrocarbon within the C monitoring zone. Following well development on April 20, 2005, MW-15, MW-16, and MW- 17 were sampled, and the results are reported below. MW-16 and MW-17 will be added to i the quarterly monitoring program starting with the third quarter 2005 sampling event. MONITORING AND SAMPLING Current and historical monitoring and analytical data are included in Tables 1 and 2, respectively. TRC's Data Transmittal, Groundwater Monitoring Field Notes and Laboratory Report dated May 5, 2005 is included in Attachment B. The report includes TRC's field and laboratory procedures, field data sheets, and certified laboratory analytical reports. The site has been monitored and sampled since the first quarter 2000. The field and laboratory procedures, field data sheets, and certified laboratory analytical reports for the sampling of the MW-15 through MWA 7 on April 20, 2005 is included in Attachment C. Currently, a total of 15 wells f E�