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' Mr. Nuel Henderson Page 2 of 5 ' through MW13B, MW15B, MW15C, MW16B and or well vapor wells VW1 and VW4. Va • P P VW5 was dry. 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 MW1/MW6, MW3/MW7, MWI5AIMW15B and MW16A/MW16B. A potentiometric surface map generated using the August 17, 2005 ' groundwater elevation data for most groundwater monitoring wells, regardless of screen depth, is shown on Figure 2. The gradient across the site according to this interpretation was approximately 0.002-0.005 feet per foot in a northeasterly direction. Figure 3 is a gradient ' map utilizing data from the shallower wells only (screened above 60 feet). Gradient is approximately 0.002 ft/ft in a,easterly direction. The gradient computed from the deeper wells only (screened below 60 feet) ranges from approximately 0.002 - 0.004 ft/ft. Flow direction ' in the deeper zone is towards the northeast (Figure 4). Groundwater monitoring data are summarized in Table 1. Monitoring data sheets and well construction details are included in Attachment A. tOn August 18, 2005, a Ground Zero technician collectedsam roundwater les from g P ' monitoring wells MW1, MW8, MW11, MW12, MW13B, MW15A, MW15B, MW15C, and VW1. 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 100% 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 826013, 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 A. ' GROUNDWATER ANALYTICAL RESULTS Groundwater Monitoring Wells ' TPHg and benzene were not detected in wells MW 11, MW 12, MW 15A, MW15B and MW15C. TPHg was detected in well MW1 at a concentration of 180 parts per billion (ppb). No BTEX compounds were detected in MW 1. TPHg and benzene were detected in well MW8 at concentrations of 1,300 ppb and 67 ppb, respectively. TPHg and benzene were detected in ' well MW13B at concentrations of 140,000 ppb and 9,300 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 B contains laboratory G:\GkOUNVZE\RQ YC QMR12U0513gm2Oo1 .doe