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i Former Beacon Station No. 12474 May 4,2004 Stockton California ()uarterly Groundwater Monitoring Re ort •r of-custody documentation to Kiff Analytical LLC (Kiff), a California Department of Health Services-certified analytical laboratory (ELAP No. 2236) located in Davis, California. The samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg), the volatile aromatic compounds benzene, toluene, ethylbenzene and total xylenes (BTEX), and the fuel oxygenates methyl-t-butyl ether (MTBE), diisopropyl ether (DIPE), ethyl-t-butyl ether (ETBE) and tert-amyl methyl ether (TAME), tert-butanol (TBA), methanol, ethanol, 1,2 dichloroethane and 1,2-dibromoethane by Environmental Protection Agency (EPA) Method 8260B. Groundwater Monitoring Results Depth-to-groundwater measurements were subtracted from the surveyed TOC elevations to calculate groundwater elevations. Groundwater elevation data, as summarized in Table 1, were used to construct the groundwater elevation contour map shown on Figure 2. The groundwater flow direction from the dispenser island area varied from northwestward to northeastward under an average gradient of less than 0.001. Groundwater analytical results are summarized in Table 1. Benzene concentration data were used to construct an iso concentration map as shown on Figure 3. Analytical reports are contained in Attachment C. Historical groundwater level and analytical data collected prior to 1998 are summarized in Tables 1 and 2 in Attachment D. GeoTracker Electronic Data Deliverables The analytical electronic data deliverable (EDD) is uploaded by Kiff. The groundwater well measurement file EDD (GEO_WELL) for this quarterly monitoring event was uploaded by Horizon. The GEO_WELL upload confirmation sheet for this quarter is contained in Attachment E. Recommendations Horizon has implemented the quarterly monitoring sampling and analytical modifications proposed in the fourth quarter 2002 quarterly monitoring report. In February 2004, Horizon drilled and installed additional groundwater monitoring wells (MW-13 though MW-17) for the purpose of evaluating the extent of impacted groundwater conditions. The draft report of the investigation is in preparation. Installation of an interim groundwater remediation system was initiated in September. Ultramar is in the process of securing electrical and natural gas utilities for operation of the remediation system. i • 474gmrQI04.doc Project No. 1474.47 2 HORIZON ENVIRONMENTAL INC.