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Beacon Station No. 3641 March 30, 2005 <br /> Stockton, Catifornia Quarterly_Groundwater Monitoring Report <br /> gasoline (TPHg), the volatile aromatic compounds benzene, toluene, ethylbenzene and total 4`<_ <br /> xylenes (BTEX), and the fuel oxygenate methyl-t-butyl ether (MTBE) by Environmental <br /> Protection Agency(EPA) Method $26013. <br /> Results of Groundwater Monitoring <br /> Depth-to-groundwater measurements were subtracted from the surveyed TOC elevations to <br /> calculate groundwater elevations. Groundwater elevation data, summarized in Table 1, were <br /> used to construct a groundwater elevation contour map (Figure 2). Groundwater level data <br /> indicate flow in the immediate underground storage tank area was southeastward under an <br /> average gradient of approximately 0.004. <br /> Analytical data are summarized in Table 1. TPHg, benzene and MTBE concentration data <br /> were used to construct isoconcentration maps (Figures 3, 4 and 5). The analytical report is <br /> contained in Attachment C. <br /> GeoTracker Electronic Data Deliverables <br /> The analytical electronic data deliverable (EDD) is uploaded by Kif£ The groundwater we]] <br /> measurement file EDD (GEO WELL) for this quarterly monitoring event has been uploaded <br /> by Horizon. The GEO_WELL file upload confirmation sheet is contained in Attachment D. <br /> Recommendations <br /> Horizon recommends continued quarterly monitoring during the ongoing investigation and <br /> remediation phases of the project. <br /> As part of an additional subsurface investigation, Horizon installed off-site groundwater <br /> monitoring wells MW-9 and MW-10 and on-site monitoring wells MW-11, MW-12 and <br /> MW-13 during fourth quarter 2004. The report of the additional subsurface investigation is <br /> in preparation. <br /> Vapor extraction and air sparge systems have been installed at the site. An Authority to <br /> Construct permit was obtained from the San Joaquin Valley Air Pollution Control District <br /> (SJVAPCD) in October 2004. The vapor extraction system (VES) was test started during <br /> first quarter 2005. Inspection of the VES by the SJVAPCD and issuance of the Permit to <br /> Operate is expected during the second quarter 2005. Reporting on regular operation of the <br /> VES shall be initiated for the second quarter 2005 Quarterly Monitoring Report. <br /> E <br /> 641 gmrQ 105.doc <br /> Project No. 1641.48 2 HORIZON ENVIRONMENTAL INC. <br /> F <br />