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"1 Former Beacon Station No. 12474 July 8,2004 <br /> Stockton California Quarterly Groundwater Monitoring Report <br /> 4 <br /> certified analytical laboratory (FLAP No. 2236) located in Davis, California. The samples <br /> were analyzed for total petroleum hydrocarbons as gasoline (TPHg), the volatile aromatic <br /> compounds benzene, toluene, ethylbenzene and total xylenes (BTEX), and the fuel <br /> oxygenate methyl-t-butyl ether (MTBE) by Environmental Protection Agency (EPA) <br /> Method 8260B. <br /> Groundwater Monitoring Results <br /> Depth-to-groundwater measurements were subtracted from the surveyed TOC elevations to <br /> calculate groundwater elevations. Groundwater elevation data, as summarized in Table 1, <br /> were used to construct the groundwater elevation contour map shown on Figure 2. The <br /> groundwater flow direction from the dispenser island area varied from southward to <br /> southeastward under an average gradient of approximately 0.002. <br /> Groundwater analytical results are summarized in Table 1. Benzene concentration data were <br /> used to construct an isoconcentration map as shown on Figure 3. Analytical reports are <br /> contained in Attachment C. Historical groundwater level and analytical data collected prior <br /> to 1998 are summarized in Tables I and 2 in Attachment D. <br /> GeoTracker Electronic Data Deliverables <br /> The analytical electronic data deliverable (EDD) is uploaded by Kiff. The groundwater well <br /> measurement file EDD (GEO_WELL) for this quarterly monitoring event was uploaded by <br /> Horizon. The GEO_WELL upload confirmation sheet for this quarter is contained in <br /> Attachment E. <br /> Recommendations <br /> In February 2004, Horizon drilled and installed additional groundwater monitoring wells <br /> (MW-13 though MW-17) for the purpose of evaluating the extent of impacted groundwater <br /> conditions. The draft report of the investigation is in preparation. Installation of an interim <br /> groundwater remediation system was initiated in September. Ultramar is in the process of <br /> securing electrical and natural gas utilities for operation of the remediation system. <br /> Report Distribution <br /> We recommend a copy of this report be forwarded to: <br /> Mr. Michael Infurna Jr., Senior R. E. H. S. . <br /> San Joaquin County Environmental Health Department <br /> 304 East Weber Avenue, Third Floor <br /> P. O. Box 388 <br /> Stockton, California 95201-0388 <br /> 474gmr Q264.doc <br /> Project No. 1474.47 2 HORIZON ENVIRONMENTAL INC. <br />