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' Mr.Nuel Henderson <br /> Page 2 of 4 <br /> �iThe potentiometric surface was above the top of the screened intervals in monitoring wells <br /> MW4 through MW1313, MW1513, MW15C, MW16B and vapor wells VW1 and VW4. Vapor <br /> i ' well VW5 was dry. Groundwater flowed in an east-northeasterly direction. The gradient <br /> across the site was approximately 0.002 feet per foot. A potentiometric surface map generated <br /> using the groundwater elevation data from all site groundwater monitoring wells is shown on <br /> ' Figure 2. Groundwater monitoring data are summarized in Table 1. Monitoring data sheets <br /> and well construction details are included in Attachment A. <br /> ' On May 20, 2004 and May 21, 2004 a Ground Zero technician collected groundwater samples <br /> from monitoring wells MW3 through MW6, MWS, MW10, MW11, MW13B, MW14, <br /> ' MW 15A through MW 15C, MW 16A and MW 1613; and from vapor wells VW2, VW4 and <br /> VW6. <br /> A minimum of three well casing volumes was purged from each well, except VW2, prior to <br /> sampling. VW2 only contained enough water to collect a sample without purging. During the <br /> purging process, physical parameters (pH, electrical conductivity, and temperature) were <br /> monitored. Subsequent to parameter stabilization, and a minimum of 95% recovery of initial <br /> depth 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 /> t <br /> Analysis consisted of gasoline oxygenates, EDB and 1,2-DCA by EPA Method 826013TPHg <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 /> GROUNDWATER ANALYTICAL RESULTS <br /> 1 Groundwater Monitoring Wells <br /> TPHg and benzene were detected in all sampled wells except MW6, MW 10, MW 11 and <br /> MW 15A through MW 15C. Dissolved TPHg and BTEX levels in the remaining monitoring <br /> wells were within historical ranges, and appear to be stable to decreasing. TPHg and BTEX <br /> ' concentration data are summarized in Table 2. Attachment B contains laboratory reports and <br /> chain of custody documentation. Attachment C contains graphs of contamination <br /> concentrations over time. <br /> ' method detection limits MDLs in wells MWS MW6 MW8 <br /> MTBE was below laboratory ( ) , <br /> MW 10, MW 1313, MW 15C and MW 16B. MTBE was detected in wells MW3 (35,000 parts <br /> ' per billion - ppb), MW4 (5,900 ppb), MW11 (120 ppb), MW14 (26,000 ppb), and MW16A <br /> (760 ppb). These wells are located along the southern portion of the site (Figure 2). In <br /> downgradient wells MW 15A and MW 1513, MTBE was reported at concentrations of 4.6 ppb <br /> and 300 ppb, respectively. These wells are clearly affected by offsite releases. <br /> 1 <br /> ' 11GZA_FS%VOL_11DATAIGROUNDZEIROEKIQMR1200412gm2004.dce <br />