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' Mr. Nuel Henderson <br /> Page 2 of 4 <br /> potentiometric surface was above the to of the screened intervals in <br /> • P monitoring wells MW4 <br /> through MW13B, MW15B, MW15C, MW16B and vapor wells VWI and VW4. Vapor well <br /> ' VW5 was dry. Groundwater flowed in a northeasterly direction. The gradient across the site <br /> was approximately 0.002-0.003 feet per foot. A potentiometric surface map generated using <br /> the November 16, 2004 groundwater elevation data from all site groundwater monitoring wells <br /> ' is shown on Figure 2. Groundwater monitoring data are summarized in Table 1. Monitoring <br /> data sheets and well construction details are included in Attachment A. <br /> On November 17 and 18, 2004 a Ground Zero technician collected groundwater samples from <br /> monitoring wells MW3 through MW6, MW8, MW10, MW11, MW13B, MW14, MW15A <br /> through MW15C, MW16A and MW16B; and from vapor wells VW4 and VW6. <br /> A minimum of three well casing volumes was purged from each well prior to sampling. <br /> tDuring the purging process, physical parameters (pH, electrical conductivity, and temperature) <br /> were monitored. Subsequent to parameter stabilization, and 98-100% recovery of initial depth <br /> to groundwater measurements, groundwater samples were collected and placed in an iced <br /> ' cooler for transport to Argon Laboratories (ELAP #2359) under chain of custody protocol. <br /> Analysis consisted of gasoline oxygenates, EDB and 1,2-DCA by EPA Method 8260B, TPHg <br /> by EPA Method 8015B and BTEX by EPA Method 8021B. Purge water was transferred into <br /> marked 55-gallon drums approved by the Department of Transportation (DOT). The waste is <br /> stored onsite within a secured area. Purge logs are included in Attachment A. <br /> I ' GROUNDWATER ANALYTICAL RESULTS <br /> Groundwater Monitoring Wells <br /> ' TPHg and benzene were detected in all sampled wells except MW6, MW8 (were only TPHg <br /> was detected), MW10, MW 11, MW15A, MW15B, and MW15C. Dissolved TPHg and BTEX <br /> ' levels in the remaining monitoring wells were within historical ranges, and appear to be stable <br /> to decreasing. TPHg and BTEX concentration data are summarized in Table 2. Attachment B <br /> contains laboratory reports and chain of custody documentation. Attachment C contains graphs <br /> ' of contaminant concentrations over time. <br /> MTBE was below laboratory method detection limits (MDLs) in wells MW5, MW6, MW8, <br /> ' MW10, MW13B, MW15A and MW15C. MTBE was detected in wells MW3 (42,000 parts <br /> per billion - ppb), MW4 (10,000 ppb), MW11 (520 ppb), MW14 (45,000 ppb), MW16A (960 <br /> ppb), and MW16B (14 ppb). These wells are located along the southern portion of the site and <br /> are affected by releases originating at 101 S. Wilson Way and/or 130 S. Wilson Way. In <br /> downgradient well MW15B, MTBE was reported at a concentration of 940 ppb. This well is <br /> ' also clearly affected by offsite releases. <br /> ' \\GZA_FSW0L tIDATA\GROUNDZE\ROEK\QMR0004\4gm2004.doe <br />