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Beacon Station No. 3641 January 17, 2005 Stockton, California Quarterly Groundwater Monitoring Report and the fuel oxygenate methyl-t-butyl ether (MTBE) by Environmental Protection Agency (EPA) Method 8260B. Results of Groundwater Monitoring Depth-to-groundwater measurements were subtracted from the surveyed TOC elevations to calculate groundwater elevations. Groundwater elevation data, summarized in Table 1, were used to construct a groundwater elevation contour map (Figure 2). Groundwater level data indicate flow in the immediate underground storage tank area was variable from eastward to southeastward under an average gradient of approximately 0.002. Analytical data are summarized in Table 1. TPHg, benzene and MTBE concentration data were used to construct isoconcentration maps (Figures 3, 4 and 5). The analytical report is contained in Attachment C. 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 has been uploaded by Horizon. The GEO_WELL file upload confirmation sheet is contained in Attachment D. Recommendations Horizon recommends continued quarterly monitoring during the ongoing investigatiou and remediation phases of the project. Horizon performed an additional groundwater investigation in February 2003. The investigation report was submitted on July 10, 2003 and included recommendations, as appropriate, for additional fieldwork to delineate the extent of petroleum hydrocarbons in soil and groundwater. In September 2004, Ultramar secured right-of-entry agreements with the off-site property owners to allow installation of additional off-site groundwater monitoring wells. Installation of the monitoring wells was conducted during the week of October 4, 2004. The report of the well installations is in preparation. Vapor extraction and sir sparge systems have been installed at the site. Permitting of the vapor extraction system (VES) with the San Joaquin Valley Air Pollution Control District was completed in October 2004. The VES is expected to be started during first quarter 2005. Distribution A copy of this report should be forwarded to: Mr. Michael Infurna Jr., Senior R. E. H. S. San Joaquin County Environmental Health Department 304 East Weber Avenue, Third Floor Stockton, California 95202-270$ 641gmrQ404.doc Project No. 1641.47 2 HORIZON ENVIRONMENTAL INC.