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Former Beacon Station No 12419 November 10,2000 Stockton,California Groundwater Groundwater Monitoring Report and air sparge wells AS-2 and AS-3, installed on 20 and 21 September 2000, were not sampled because the wells had not been developed at that time Analytical results of groundwater samples from the three wells shall be presented in an investigation report documenting their installation Sampling of the three wells shall also be included in future quarterly monitoring rounds Groundwater samples were submitted, under chain-of-custody (COC) documentation, to Kiff Analytical (Kiff), a California Department of Health Services-certified analytical laboratory (FLAP No 2236) Iocated 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 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), tert-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 —28 4 feet mean sea level The groundwater elevation represents an approximately 8-foot drop compared to that measured in May 2000 The calculated groundwater flow direction was generally westward but locally ranged from north to south under gradients of approximately 0 02 to 0 002 Concentrations of TPHg were reported in groundwater samples from monitoring wells MW-3, MW-5, MW-7 MW-8, MW-9 and air-sparge well AS-1 Sample TPHg concentrations ranged from 68 to 680 micrograms per liter (parts per billion or ppb) in monitoring wells MW-3, MW-5, MW-7 MW-8, MW-9 to 54,000 in air-sparge well AS-1 Benzene was reported in groundwater samples from monitoring wells MW-3 and MW-9 at concentrations of 9 2 and 1 1 ppb, respectively, and from air-sparge well AS-1 at a concentration 2600 ppb 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 419gmr00Q3 doc 141943 2 HORIZON ENVIRONMENTAL INC.