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b Mr Nuel Henderson Page 2 of 4 • The potentiometric surface was above the top of the screened intervals in all monitoring wells except MWI, MW2, MW3, MW13, and MW14 and all vapor wells except VW2, VW3, VW5 and VW6 Groundwater flow was in an east-northeasterly direction and the average gradient across the site was approximately 0 003 feet per foot A potentiometric surface map generated using the groundwater elevation data from all site monitoring wells is shown on Figure 2 Groundwater monitoring data are summarized in Table 1 Monitoring data sheets and well construction details are included in Attachment A On August 26, and August 27, 2002, a Ground Zero technician collected groundwater samples from monitoring wells MW 1 through MW5, MW7, MW8, MW9, MW12 and MW14 and vapor wells VWl 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 (FLAP #2359) under chain of custody protocol 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 GROUNDWATER ANALYTICAL RESULTS Groundwater Monitoring Wells TPHg and benzene were detected in all sampled wells except MW7, MW9 and MW12 Except for well MW8, which continues to exhibit a decreasing trend, the levels of TPHg and benzene detected in the remaining monitoring wells were within historical ranges TPHg and BTEX concentration data 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 in wells MW3 (24,000 parts per billion - ppb), MW4 (14,000 ppb), MW7 (280 ppb), and MW14 (140,000 ppb), which are located along the southern portion of the site (Figure 2) MTBE was also reported in well MW9, located on the north side of Market Street, and in downgradient well MW12 at concentrations of 8 2 ppb, and 110 ppb, respectively Concentrations of dissolved MTBE detected in wells MW7 and MW14 are the highest to date These wells are clearly affected by offsite MTBE releases • EDB was not detected in any monitoring wells sampled, however, 1,2-DCA was present in monitoring wells MW2 and MW12 at concentrations of 29 ppb and 19 ppb, respectively %NGZ%_FSSJYbol\D,Li1GROUNDZE\ROEK\Q[,Qt�2002\3gm2002 doc