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E11C�yt® \ James L Barton ' February 17, 2004 Page 2 ' Figure 4 On December 16, 2003, the groundwater flow direction for Unit B was generally southeast with an average hydraulic gradient of approximately 0 003 ' Copies of the groundwater sampling information sheets are Included in Attachment B A summary of groundwater elevations measured to date Is presented in Table 2 Well construction details are included in Attachment C ' Groundwater Sampling and Analytical Results ' Groundwater samples were collected from December 18, 2003 through December 29, 2003 Groundwater samples were submitted to California Laboratory Services (CLS) in Rancho Cordova, California for analyses of benzene, toluene, ethylbenzene and total xylenes (BTEX) by ' EPA Method 8021, total petroleum hydrocarbons (TPH) as gasoline by EPA Method 8015 Modified, and volatile organic compounds (VOCs) by EPA Method 8260B Tabular results of recent groundwater sampling analytical results are summarized In Table 1, Cumulative groundwater sampling analytical results are summarized in Table 3 Maps depicting dissolved ' concentrations of TPH as gasoline and benzene In groundwater are included as Figures 5 through 12 Copies of the groundwater sampling information sheets are included in Attachment B Laboratory analytical results with chain-of-custody documentation are included in Attachment D Site Conceptual Model Update In a letter dated February 8, 2002, the RWQCB requested completion of an updated Site Conceptual Model (SCM) for this site The Initial SCM was submitted to the RWQCB in an EAI report titled "Supplemental Investigation Report, Problem Assessment Report, and Work Plan, Cleanup and Abatement Order No 5-00-707, Montgomery Ward Auto Service Center and Fortner Unocal Site, 5400 and 5606 Pacific Avenue, Stockton, California," dated ' October 13, 2000 Site stratigraphy Is segregated into four hydro-stratigraphic units that generally correspond to screened intervals of site wells The shallowest wells are screened in the hydro-stratigraphic ' unit designated as Unit A and the deepest wells are screened across hydro-stratigraphic Unit D A cross-section location map and cross sections A-A' and B-B' are included in Attachment E Fourth Quarter 2003 analytical results are summarized on the respective cross-sections Remediation System Description ' The remediation system utilizes sod vapor extraction (SVE) and air sparge (AS) The SVE system is currently shut down When operational, the SVE system extracted soil vapors from 17 vapor extraction and monitoring wells A thermal oxidizer provided abatement of the hydrocarbons prior to atmospheric discharge The air sparge system consists of an air compressor that forces filtered air through piping routed to sparge points Installed in combination wells VEW-1 B, VEW-28, and VEW-3 through VEW-13, monitoring wells MW-19D, J 1Projects1069401293-50981Finall4th Qtr'03-QMR RSR doc ' 35 Years of Excellence in Environmental Services