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Ms Rebecca Setliff . Page 2 of 4 The potentiometric surface was above the top of the screened intervals in all wells except monitoring wells MW1, MW2, MW3, MW13 and MW14 and vapor wells VW2, VW3 VWS and VW6 Groundwater flowed in an easterly direction, with an average gradient of approximately 0 003 feet per foot A groundwater gradient map generated using the monitoring data from all site wells is shown on Figure 2 Groundwater monitoring data are summarized in Table 1 Monitoring logs are included in Attachment A On December 6, 2001 and December 7, 2001, a Ground Zero technician collected groundwater samples from monitoring wells MW3 through MW6, MW8, MW 10, MW I I and MW 14 and from vapor wells VW2, VW4, VW5, and VW6 A minimum of three well casing volumes was purged from each well prior to sampling During the purging process, physical parameters (pH, electrical conductivity, and temperature) were monitored Subsequent to parameter stabilization and a minimum of 80% recovery of initial depth to groundwater measurements, groundwater samples were collected and placed in an iced cooler for transport to Argon Laboratories (ELAP #2359) under chain of custody Purge water was contained in labeled 55-gallon drums approved by the Department of Transportation (DOT), which are stored onsite within a secured area Purge logs are included in Attachment A Analysis consisted of gasoline oxygenates, EDB and 1,2 DCA by EPA Method 8260, TPHg by EPA Method 8015 modified and BTEX by EPA Method 8020 AD GROUNDWATER ANALYTICAL RESULTS Groundwater Monitoring Wells TPHg was detected in all sampled wells except MW6, MW 10 and MW 11, while benzene was detected in all sampled wells except MW 10 and MW I 1 Concentrations of TPHg and BTEX were generally stable to decreasing relative to the concentrations present during the previous sampling event, however, in well MW3, TPHg and benzene levels increased approximately 6x (72,000 parts per billion (ppb) and 21,000 ppb, respectively) These are the highest concentrations reported in this well to date Overall, the extent of the plume of groundwater contamination associated with the onsite release is stable and concentrations are decreasing TPHg and BTEX concentrations are summarized in Table 2 Attachment B contains laboratory reports and chain of custody documentation Graphs depicting TPHg and benzene concentrations over time are included in Attachment C MTBE was the only gasoline oxygenate detected in the sampled wells MTBE was detected wells MW3 (17,000 ppb), MW4 (8,300 ppb), MWI 1 (3 1 ppb) and MW14 (34,000), which are located along the southern portion of the property, and in well MW10 (10 ppb), which is located offsite along the north side of Market Street MTBE in wells MW3 and MW 14 increased approximately one order of magnitude since the previous sampling event Concentrations of MTBE reported in wells MW3 and MW 14 are the highest to date MTBE was also detected 1n roeklgmr 4QM2001