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[� p Mr Jeff Wong November 6,2000 Page 2 of 3 wells Analytical results were submitted to PHS/EHD under separate cover dated October 12, 2000 Groundwater Monitoring and Sampling An experienced Ground Zero technician monitored and sampled site morutoring wells MW 1 through MW4 on September 28, 2000 Groundwater elevations were calculated by measuring the depth to groundwater in each well and subtracting the measured depth from the respective well head elevation Groundwater elevations fell an average of 2 83 feet between June 13, 2000 and September 28, 2000 Groundwater flow was to the east-northeast with a hydraulic gradient of approximately 0 005 ft/ft Groundwater flow during previous monitoring events (October 1999 and June 2000) have been toward the northeast A potentiometric surface map generated using the September 28, 2000 monitoring data is presented on Figure 2 Groundwater monitoring data are summarized in Table 1 and field data sheets are included in Attachment A Prior to sampling, monitoring wells MW 1 through MW4 were purged of at least three well casing volumes During the purging process the physical parameters of temperature, pH and electrical conductivity were measured Samples were collected after the physical parameters stabilized and water levels recovered to at least 80% of their pre-purged levels Purged groundwater was contained in appropriately labeled DOT-approved 55-gallon drums, which are . currently stored on-site Purge logs are included in Attachment A Groundwater samples were delivered under chain of custody protocol to Argon Laboratories (ELAP #2359) for analysis of TPHg by EPA method 8015 modified, BTEX by EPA method 8020, and oxygenated gasoline additives and the lead scavengers 1,2-DCA and EDB by EPA method 8260B GROUNDWATER ANALYTICAL RESULTS Groundwater samples collected from monitoring well MW 1, located within the former UST excavation, contained elevated levels of gasoline constituents Dissolved TPHg in groundwater collected from MW 1 was detected at 200,000 parts per billion (ppb), benzene was detected at 7,200 ppb, and MTBE was detected at 3,900 ppb Well MW3 contained TPHg at 3,900 ppb, benzene at 250 ppb, and MTBE at 7,500 ppb Well MW4 contained TPHg at 780 ppb, benzene at 2 3 and MTBE at 9,500 ppb Upgradient well MW2 contained TPHg at 1,400 ppb and benzene at 15 ppb No MTBE was detected in well MW2 Groundwater analytical results are summarized in Table 2 Laboratory reports and chain-of- custody documentation are included in Attachment B SUMMARY Groundwater levels at the site fell an average of 2 83 feet between June and September, 2000 Elevated levels of dissolved gasoline constituents are present in wells MW1 through MW4 G 1Data1GROUNDZ81TMFBLJRG\Reporta\3QM2000h doc