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rf; Beacon Station No 3641 May 6, 2004 Stockton California uarterl Groundwater Monitoring Report . xylenes (BTEX), and the fuel oxygenates methyl tert-butyl ether (MTBE), diisopropyl ether (DIPE), ethyl-t-butyl ether (ETBE), tert-amyl methyl ether (TAME), tert-butanol (TBA), methanol, ethanol and 1,2-dichloroethane (DCA) 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 site area was southeastward under a gradient of approximately 0 005 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 (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 investigation 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 Ultramar is in the process of securing right-of-entry agreements with the off-site property owners to allow installation of additional off-site groundwater monitoring wells The Stockton Building Department has approved a permit to install the site interim remediation system The application for electrical and natural gas utility connections has been processed by Pacific Gas and Electric Company and Ultramar has finalized the contract to have the utilities installed Work will be initiated to install the remediation systems after Ultramar completes the contractor selection process 641gmrQ104 doc Project No 1641 47 2 HORIZON ENVIRONMENTAL INC.