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i Mr Nuel Henderson • Page 7 of 9 I 1 ' QUARTERLY FIELDWORK Groundwater Monitoring and Sampling tDepth to groundwater was measured on February 19, 2003 in monitoring wells MW 1 through MW16B and in vapor wells VWl through VW6 Depth to groundwater was then subtracted from each respective wellhead elevation to determine groundwater elevation Water levels at the site rose an average of approximately 0 53 feet since November 13, 2002 ' Groundwater flowed in a northeasterly direction, and the average gradient across the site was approximately 0 002 feet per foot A potentiometric surface map generated using the groundwater elevation data from all site monitoring wells is shown on Figure 2 Water level data are summarized ' in Table 2 Monitoring data sheets and well construction details are included in Attachment D On February 20 and 21, 2003, a Ground Zero technician collected groundwater samples from monitoring wells MW1 through MW5, MW7 through MW9, MW12 through MW16B and from ' vapor wellsVW 1 and VW3 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 logs are included in Attachment D ' Analysis consisted of gasoline oxygenates, EDB and 1,2-DCA by EPA Method 8260, TPHg by EPA Y g Yg Method 8015 modified and BTEX by EPA Method 8020 Purge water was transferred into labeled ' 55-gallon drums approved by the Department of Transportation (DOT), which are stored onsite within a secured area ' Groundwater Analytical Results Groundwater Monitonng Wells ' Dissolved TPHg and BTEX concentrations in the monitoring wells were within histoncal ranges, and appear to be stable to decreasing In the new downgradient well series MW15A, Band C, TPHg was detected only in MW15B and BTEX were not detected in any of the wells TPHg and BTEX concentration data are summarized in Table 4 Attachment E contains laboratory reports and chain of custody documentation ' MTBE was detected in wells MW3 (41,000ppb), MW4 (5,300 ppb), MW7 (110 ppb), MW9 (5 1 ppb), MW 12 (78 ppb), MW 14 (110,000 ppb), MW 15A (59 ppb), MW 15B (86 ppb), MW 16A (2,900 ppb) and MW 16B (260 ppb) TBA was detected at a level of 66 ppb in the sample from well MW2 � �I ' \1GZA_FS\VOL_]\DATA\GROlTNM=OEKICLOSURE1Re;*M\Add_HSA Mud wells doc