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