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sV <br /> 1 Sr IE C ® R <br /> Mr Mike Infurna <br /> July 15, 2003 <br /> Page 2 <br /> Quarterly Summary Report <br /> Second Quarter 2003 <br /> GaP Former Tosco (Unocal) Service Station #4409 <br /> rj 1502 N EI Dorado Street, Stockton, California <br /> City/County ID# Stockton <br /> County San Joaquin <br /> BACKGROUND <br /> The site Is located on northeast corner of EI Dorado Street and Harding Way in Stockton, California, <br /> and is a former operating Unocal service station On April 7, 1999, three 10,000-gallon capacity <br /> underground storage tanks (USTs), which contained gasoline and diesel fuel, were removed from <br /> the site Excavation dimensions were approximately 35 feet by 40 feet by 15 feet deep Initial <br /> remedial activities included source removal of obviously impacted soil to a depth of approximately 18 <br /> feet below ground surface (bgs) beneath the center of the western fuel tank Additional remedial <br /> activities included source removal of obviously impacted sod in the area beneath the former <br /> dispenser and product lines A concrete pad restricted the lateral extent of excavation During <br /> excavation of impacted soil, unidentified fiberglass piping was found Additional excavation and <br /> sampling was completed on April 8, 1999 to remove the unidentified piping Samples were collected <br /> from the bottom and sidewalls of the excavated area Following removal of the former station <br /> canopy, canopy footings and kiosk, additional over-excavation was completed in the dispenser area <br /> Over-excavation was terminated when obviously impacted soil was removed, the structural integrity <br /> of the sidewalk was endangered, or groundwater was encountered Residual hydrocarbons remain <br /> in the soil and groundwater A total of approximately 1,707 tons of sod was transported off-site for <br /> disposal at the Forward Landfill in Manteca, California <br /> Four groundwater monitoring wells (MW-1 through MW-4)were Installed in December 1999 Vertical <br /> assessment was conducted In July 2000, and sod and groundwater impacts were encountered at <br /> depths of 60 feet bgs. (GP-1 through GP-4) The SJCPHSIEHD verbally requested a workplan for <br /> further delineation of soil and groundwater Impacts Three on-site deep groundwater monitoring <br /> wells (MW-5 through MW-7) were installed In November 2000, which identified deep zone <br /> groundwater petroleum hydrocarbon impacts Results of this investigation Indicate that the lateral <br /> and vertical extent of petroleum hydrocarbon impacts have been defined across the site In August <br /> and September 2001, three additional deep zone groundwater monitoring wells (MW-8 through MW- <br /> 10)were installed to determine the extent of deep zone groundwater Impacts <br /> RECENT QUARTER ACTIVITIES (Second Quarter 2003) <br /> • Quarterly groundwater monitoring and sampling performed by GRI on April 28, 2003 <br /> • Prepared and submitted the quarterly summary report <br /> • Installed deep monitoring well (MW-11)on Yamada property at 135 East Harding Way <br /> • Received access agreement to AutoZone property, scheduled to Install off-site wells in the <br /> City of Stockton right-of-way July 8-July 10, 2003 <br /> 1 ICon000PhdUpslTosco Marketmg144091Qssrs=2003_QSR doc SECOR lntemational Incorporated <br />