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FJ Mr. Mike Infurna April 26, 2004 Page 2 February 26, 2004, the groundwater flow direction for Unit B was generally to the southeast, with l the hydraulic gradient ranging from approximately 0.002 ft/ft to 0.004 ft/ft. Copies of the groundwater sampling information sheets are included as Attachment B. Tabular results of recent depth to water (DTW) measurements are summarized in Table 1. Well construction details are included as Attachment C. Groundwater Sampling and Analytical Results Groundwater samples were collected on February 26, 2004. Groundwater samples were �l 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 as gasoline (TPHg). by EPA Method 8015 Modified, and volatile organic compounds (VOCs) by EPA Method 8260B. Tabular results of recent groundwater 1 J sampling analytical results are summarized in Table 1. A summary of groundwater elevations measured to date is presented in Table 2. Cumulative groundwater sampling analytical results are summarized in Table 3. Maps depicting dissolved concentrations of TPHg and benzene in groundwater are included as Figures 5 through Figure 12. 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 FJ 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 F] Former 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. First quarter 2004 analytical results are summarized on the respective cross-sections. ` Remediation System Description to The remediation system utilizes soil vapor extraction (SVE) and air sparge (AS). The SVE system is currently shut down. When operational, the SVE system extracted soil vapors from 13-vapor extraction and combination wells, and four 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 10 air sparge points, and air sparge well AS-26. Well construction details are included in Attachment C. The system layout is shown in Figure 13. r/ J:1Projects10694015098-2931FinallReportslist Qtr'04-QMR RSR.doc r 35 Years of Excellence in Environmental Services F.