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" Mr. Nuel Henderson Page 2 of 4 During this event an upward vertical gradient component was present across the site. Wells screened deeper than 60 feet had higher potentiometric surface elevations than shallower wells in close proximity. Examples are well pairs 1V1Wl/MW6, MW3/MW7, MW15A/MW15B, MW16A/MW16B, and ARCO well pairs MW7/MW9 and MW8/MW10. A potentiometric surface map generated using the December 8, 2005 groundwater elevation data for most groundwater monitoring wells, regardless of screen depth, is shown on Figure 2. Figure 3 utilizes data from the shallower wells only (screened above 60 feet). The potentiometric surface computed from the deeper wells only (screened below 60 feet) is depicted on Figure 4. Groundwater gradient in each interpretation is toward the northeast at approximately 0.001 - 0.002 feet per foot. Groundwater monitoring data are summarized in Table 1. Monitoring data sheets and well construction details are included in Attachment B. On December 21 and 22, 2005, a Ground Zero technician collected groundwater samples from monitoring wells MW 1, MW7, MW8, MW 11, MW12, MW 13B, MW15A, MW 15B, MW15C, and VWL I 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 98% 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. Analysis consisted of gasoline oxygenates, EDB and 1,2-DCA by EPA Method 8260B, TPHg by EPA Method 8015M and BTEX by EPA Method 8021B. Purge water was transferred into labeled 55-gallon drums approved by the Department of Transportation (DOT). The waste is stored onsite within a secured area. Purge logs are included in Attachment B. GROUNDWATER ANALYTICAL RESULTS Groundwater Monitoring Wells TPHg and benzene were not detected in wells MW7, MW11, MW12, MW15A, MW15B and MW15C. TPHg was detected in well MW1 at a concentration of 200 parts per billion (ppb). No BTEX compounds were detected in MWL TPHg and benzene were detected in well MW8 at concentrations of 650 ppb and 31 ppb, respectively. TPHg and benzene were detected in well MW13B at concentrations of 60,000 ppb and 5,200 ppb, respectively. Dissolved TPHg and BTEX levels were within historical ranges, and appear to be stable to decreasing. TPHg and BTEX concentration data are summarized in Table 2. Attachment C contains laboratory reports and chain of custody documentation. MTBE was not detected in wells MW8, MW13B and MW15C. MTBE was detected in wells MW1 (6.4 ppb), MW7 (110 ppb), MW11 (260 ppb), MW12 (390 ppb), MW15A (7.5 ppb), G:\GROUN[)ZLIROEKIQMR1200514gm2005.doe