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Mr. Nuel Henderson <br /> Page 2 of 4 <br /> • above the top of the screened intervals in monitoring wells MW4 through MW13B, MW15B, <br /> MW15C, MW16B and vapor wells VW1 and VW4. Vapor well VW5 was dry. <br /> During this event an upward vertical gradient component was present across the site. Wells <br /> screened deeper than 60 feet had higher potentiometric surface elevations than shallower wells in <br /> close proximity. Examples are well pairs MWI/MW6, MW3/MW7, MW15A/MW15B and <br /> MW16A/MW16B. A potentiometric surface map generated using the May 24, 2005 groundwater <br /> elevation data for most groundwater monitoring wells, regardless of screen depth, is shown on <br /> Figure 2. The gradient across the site according to this interpretation was approximately 0.001- <br /> 0.002 feet per foot in an easterly to northeasterly direction. Figure 3 is a gradient map utilizing <br /> data from the shallower wells only (screened above 60 feet). Gradient is approximately 0.002 ft/ft <br /> in a southeasterly direction. The gradient computed from the deeper wells only (screened below 60 <br /> feet) ranges from approximately 0.001 - 0.003 ft/ft. Flow direction in the deeper zone ranges <br /> from southeasterly to northeasterly (Figure 4). Groundwater monitoring data are summarized in <br /> Table 1. Monitoring data sheets and well construction details are included in Attachment A. <br /> On May 25, 2005, a Ground Zero technician collected groundwater samples from monitoring wells <br /> MWS, MW11, MW12, MW15A, MW15B and MW15C. <br /> A minimum of three well casing volumes was purged from each well prior to sampling. During <br /> the purging process, physical parameters (pH, electrical conductivity, and temperature) were <br /> monitored. Subsequent to parameter stabilization, and 100% recovery of initial depth to <br /> • groundwater measurements, groundwater samples were collected and placed in an iced cooler for <br /> transport to Argon Laboratories (FLAP#2359) under chain of custody protocol. <br /> Analysis consisted of gasoline oxygenates, EDB and 1,2-DCA by EPA Method 8260B, TPHg by <br /> EPA Method 8015B and BTEX by EPA Method 8021B. Purge water was transferred into labeled <br /> 55-gallon drums approved by the Department of Transportation (DOT). The waste is stored onsite <br /> within a secured area. Purge logs are included in Attachment A. <br /> GROUNDWATER ANALYTICAL RESULTS <br /> Groundwater Monitoring Wells <br /> TPHg and benzene was not detected in wells MW11, MW12, MW15A, MW15B and MW15C. <br /> TPHg and benzene was detected in well MW8 at concentrations of 230 parts per billion (ppb) and <br /> 15 ppb, respectively. Dissolved TPHg and BTEX levels were within historical ranges, and appear <br /> to be stable to decreasing. TPHg and BTEX concentration data are summarized in Table 2. <br /> Attachment B contains laboratory reports and chain of custody documentation. Attachment C <br /> contains graphs of contaminant concentrations over time. <br /> MTBE was not detected in well MW15C. MTBE was detected in wells MW8 (0.6 ppb), MW 11 <br /> (120 ppb), MW12 (97 ppb), MW15A (4.9 ppb), and MW15B (1,100 ppb). These wells are <br /> affected by MTBE releases originating at 101 S. Wilson Way and/or 130 S. Wilson Way. <br /> • <br /> G:\GROUNDZE\ROEKkQMR\2005\2qm2OO5.doc <br />