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' Mr. Nuel Henderson Page 2 of 4 potentiometric surface was above the to of the screened intervals in • P monitoring wells MW4 through MW13B, MW15B, MW15C, MW16B and vapor wells VWI and VW4. Vapor well ' VW5 was dry. Groundwater flowed in a northeasterly direction. The gradient across the site was approximately 0.002-0.003 feet per foot. A potentiometric surface map generated using the November 16, 2004 groundwater elevation data from all site groundwater 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 November 17 and 18, 2004 a Ground Zero technician collected groundwater samples from monitoring wells MW3 through MW6, MW8, MW10, MW11, MW13B, MW14, MW15A through MW15C, MW16A and MW16B; and from vapor wells VW4 and VW6. A minimum of three well casing volumes was purged from each well prior to sampling. tDuring the purging process, physical parameters (pH, electrical conductivity, and temperature) were monitored. Subsequent to parameter stabilization, and 98-100% 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 protocol. Analysis consisted of gasoline oxygenates, EDB and 1,2-DCA by EPA Method 8260B, TPHg by EPA Method 8015B and BTEX by EPA Method 8021B. Purge water was transferred into marked 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 A. I ' GROUNDWATER ANALYTICAL RESULTS Groundwater Monitoring Wells ' TPHg and benzene were detected in all sampled wells except MW6, MW8 (were only TPHg was detected), MW10, MW 11, MW15A, MW15B, and MW15C. Dissolved TPHg and BTEX ' levels in the remaining monitoring wells were within historical ranges, and appear to be stable to decreasing. TPHg and BTEX concentration data are summarized in Table 2. Attachment B contains laboratory reports and chain of custody documentation. Attachment C contains graphs ' of contaminant concentrations over time. MTBE was below laboratory method detection limits (MDLs) in wells MW5, MW6, MW8, ' MW10, MW13B, MW15A and MW15C. MTBE was detected in wells MW3 (42,000 parts per billion - ppb), MW4 (10,000 ppb), MW11 (520 ppb), MW14 (45,000 ppb), MW16A (960 ppb), and MW16B (14 ppb). These wells are located along the southern portion of the site and are affected by releases originating at 101 S. Wilson Way and/or 130 S. Wilson Way. In downgradient well MW15B, MTBE was reported at a concentration of 940 ppb. This well is ' also clearly affected by offsite releases. ' \\GZA_FSW0L tIDATA\GROUNDZE\ROEK\QMR0004\4gm2004.doe