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Beacon Station No 3641 August 4, 2003 Stockton, California Quarterly Groundwater Monitoring Report xylenes (BTEX), 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 contour map (Figure 2) The groundwater flow direction for this sampling event was west southwest under a gradient of approximately 0 015 Analytical data are summarized in Table 1 Benzene concentration data were used to construct a benzene isoconcentration map (Figure 3) Analytical reports and the chain-of- custody document are contained in Attachment C GeoTracker Electronic Data Deliverables ' The analytical electronic data deliverable (EDD) is uploaded by Kiff The groundwater well measurement file EDD for this quarterly monitoring event has been uploaded by Horizon The GEO_WELL file upload confirmation sheet is contained in Attachment D Recommendations A At the request of Ultramar, Horizon proposed in the fourth quarter 2002 monitoring report to modify the quarterly monitoring program The San Joaquin County Environmental Health Department (EHD) granted conditional approval of proposed monitoring program modifications in a letter dated March 7, 2003 The EHD requested submittal of a table that clearly shows the sampling frequency and analytical program for the site wells The groundwater monitoring program is presented in Table 2 Horizon performed an additional groundwater investigation in February 2003 The investigation report was submitted on July 10, 2003 and includes recommendations, as appropriate, for additional fieldwork to delineate the extent of petroleum hydrocarbons in soil and groundwater 641gmrQ2 03 doc Project No 1641 46 2 HORIZON ENVIRONMENTAL INC