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r Former Beacon Station No 419 June 20 2000 Stockton California Grounduater Monitonn R� ep rt Groundwater samples were collected from the ten groundwater monitoring wells MW-1 through MW-10 and air-sparge well AS-1 The screened interval for the wells are noted on Tables 1 and lA Vapor extraction wells VW-1 and VW-2 were dry Groundwater samples were submitted under chain-of-custody (COC) documentation to Kiff Analytical (Kif1), a California Department of Health Services-certified analytical laboratory (FLAP 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), the seven fuel oxygenates methyl-tertiary- butyl ether (MTBE), dasopropyl ether (DIPE), ethyl-tertiary-butyl ether (ETBE), tert-amyl methyl ether (TAME), tert-butanol (TBA), methanol and ethanol by Environmental Protection Agency (EPA) Method 8260B Laboratory results are summarized in Tables 1 and IA Copies of the laboratory data sheets and chain-of-custody reports are included as Attachment C Results Groundwater level data collected by Horizon was used to construct the Groundwater Contour Map (Figure 2) Depth-to-groundwater measurements were subtracted from the surveyed TQC elevations to calculate groundwater elevations The average measured groundwater elevation was approximately —20 0 feet mean sea level The average groundwater elevation represents an approximately 2 5-foot rise compared to that measured in February 2000 The calculated groundwater flow direction was generally eastward but locally ranged from northeast to south under gradients of approximately 0 002 to 0 0007 Concentrations of TPHg were reported in groundwater samples from monitoring wells MW- 2, MW-4, MW-7 MW-8, MW-9 and air-sparge well AS-1 Sample TPHg concentrations ranged from 53 to 790 micrograms per liter (parts per billion or ppb) in monitoring wells MW-2, MW-4, MW-7 MW-8 and MW-9, to 23,000 in air-sparge well AS-1 Benzene was reported in groundwater samples from monitoring well MW-9 and from air- sparge well A5-1 at concentrations of 9 6 and 2300 micrograms per liter (parts per billion or ppb), respectively Benzene concentrations reported for this quarter represent decreases compared to those reported for the first quarter 2000 monitonng round Benzene concentration data from this sampling event were used to construct a benzene isoconcentration map (Figure 3) Concentrations of the fuel oxygenates DIPE, ETBE, TAME, methanol and ethanol were not reported in any of the groundwater samples this quarter An MTBE concentration of 1 8 ppb (down from 2 0 ppb last quarter) was reported in the groundwater sample from monitoring 419qnuoaQ2 doc . 141943 2 HORIZON ENVIRONMENTAL INC.