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} Former Beacon Station No 12419 January 19,2001 Stockton California Groundwater Groundwater Monitoring Report Groundwater samples were submitted, under chain-of-custody (COC) documentation, to Kiff . Analytical LLC (Kiff), a California Department of Health Services-certified analytical laboratory (ELAP No 2236) located in Davis, California The samples 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-tert-butyl ether (MTBE) by Environmental Protection Agency (EPA) Method 8260B Laboratory results are summarized in Table 1 Copies of the laboratory data sheets and chain-of-custody documents are included as Attachment C The quarterly monitoring analytical program has been modified with approval on 4 October 2000 from the San Joaquin County Environmental Health Division Groundwater monitoring samples shall be analyzed for TPHg, BTEX and MTBE on a continuing quarterly basis Groundwater samples collected for second quarter monitoring shall also be analyzed for the six other fuel oxygenates diisopropyl ether (DIPS), ethyl tert-butyl ether (ETBE), Cert-amyl methyl ether (TAME), tert-butanol (TBA), methanol and ethanol, and the lead scavenger compounds 1,2-dichloroethane and 1,2-dibromoethane Results Groundwater level data collected by Horizon was used to construct a groundwater contour map as shown on Figure 2 Depth-to-groundwater measurements were subtracted from the surveyed TOC elevations to calculate groundwater elevations The average measured groundwater elevation was approximately —27 0 feet mean sea level The groundwater elevation represents an approximately 1 4-foot drop compared to that measured in September 2000 Calculated groundwater flow direction was variable from west to north to southeast under gradient of approximately 0 003 Concentrations of TPHg were reported in groundwater samples from monitoring wells MW-3, MW-7, MW-9, MW-1 I and air-sparge wells AS-1 and AS-2 Sample TPHg concentrations ranged from 87 to 1400 micrograms per liter (parts per billion or ppb) in the monitoring wells and from 18,000 to 52,000 in the air-sparge wells Benzene was reported in groundwater samples from monitoring wells MW-3 and MW-9 at concentrations of 45 and 16 ppb, and 5,000 and 120 ppb in air-sparge wells AS-1 and AS-2, respectively Benzene concentration data from this sampling event were used to construct a benzene isoconcentration map as shown on Figure 3 No MTBE was reported in any groundwater sample Recommendations Horizon recommends continued quarterly monitoring be performed to evaluate trends in the groundwater gradient and concentrations of dissolved hydrocarbons over time Horizon also recommends completion of site feasibility testing on the recent installations followed by development and installation of remedial systems • 4l9gmr0004 doc 141943 2 HORIZON ENVIRONMENTAL INC.