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Beacon Station No. 3641 October 26, 2005 Stockton,_California Quarterly Groundwater Monitoring/Remediation System Report Groundwater samples were collected from the wells MW-2 through MW-6, MW-9 through MW-13 and SW-l. The groundwater samples were submitted, under chain-of-custody documentation, to Kiff Analytical (Kiff), a California-certified analytical laboratory (ELAP No. 2236) located in Davis, California and were analyzed for total petroleum hydrocarbons as gasoline (TPHg), the volatile aromatic compounds benzene, toluene, ethylbenzene and total xylenes (BTEX), and the fuel oxygenate methyl-t-butyl ether (MTBE) by Environmental Protection Agency (EPA) Method 8260B. Groundwater samples collected from monitoring wells MW-9 through MW-13 were also analyzed for 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 underground storage tank area was westward and eastward, away from MW-13, under a variable gradient of approximately 0.001 to 0.002. Analytical data are summarized in Table 1. TPHg, benzene and MTBE concentration data were used to construct iso concentration maps (Figures 3, 4 and 5). The analytical report is contained in Attachment C. Vapor Extraction System Monitoring Construction for a vapor extraction system (VES) and an air sparging system was conducted in late 2004. The San Joaquin Valley Air Pollution Control District (APCD) issued a Authority to Construct permit in October 2004. Final equipment connections were made and final system preparations were conducted during first quarter 2005. Operation of the VES was initiated on March 4, 2005. Final inspection of the VES was conducted by the APCD on May 19, 2005. Horizon submitted the Authority to Construct Inspection Report on June 21, 2005. The APCD issued Permit to Operate N-5036-1-1 on August 18, 2005. The location of the remediation system compound is shown on Figure 6. The VES consists of a positive-displacement blower rated at 250 cubic feet per minute (cfin), a ThermTech Vac 25 thermal/catalytic oxidizer and other associated equipment as shown on Figure 7. The VES is set up to extract vapors from vapor extraction wells VW-I through VW-8. Soil vapor flow from each well is controlled by individual valves. The air sparging system consists of a'7.5 cfm air compressor and other associated equipment as shown on Figure 7. The air sparge system is set up to sparge air to sparge well SW-1. It is expected that air sparging will be initiated in fourth quarter 2005. This VES reporting period is June 23 to September 26, 2005. Blower electrical problems were remedied and the VES was re-started August 11, 2005. The VES operated for a total of approximately 27 days from August 11 to September 26, 2005. Influent and effluent vapor samples were collected on August 11 and September 14, 2005. Analytical reports are contained in Attachment C. Vapor extraction system data are summarized in Table 2. 641 gmrQ3o5.doc Project No. 1641.48 2 HORIZON ENVIRONMENTAL INC.