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X. Mr Nuel Henderson Page 2 of 4 During this event an upward vertical gradient component was present across most of the site Wells screened deeper than 60 feet had higher potentiometric surface elevations than shallower wells in close proximity Examples are well parrs MW11MW6, MW3IMW7, MW15AiMW15B, MW16AiMW16B, and ARCO well parr M`vV8IMW10 An exception was ARCO parr MW71MW9 where a downward gradient was in evidence An interpretive potentrometric surface map generated using the March 6, 2006 groundwater elevation data for the shallow groundwater monitoring wells is shown on Figure 2 A potentiometric surface map generated using groundwater elevation data for the deeper groundwater monitoring wells is shown on Figure 3 In both cases groundwater generally flowed towards the east Groundwater monitoring data are summarized in Table 1 Monitoring data sheets and well construction details are included in Attachment A Also included in Attachment A are tabulated results of depth to water measurements at the ARCO station On March 6 and 7, 2006, a Ground Zero technician collected groundwater samples from monitoring wells MW1, MW7, MW8, MW11, MW12, MW1313, MW15A, MW1513, MW15C, and VWI 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 98% 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 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 MW7, MW 11, MW 12, MW 15A, MW 15B and MW 15C TPHg was detected in well MWI. at a concentration of 200 parts per billion (ppb) No BTEX compounds were detected in MW1 TPHg and benzene were detected in well MW8 at concentrations of 3,500 ppb and 270 ppb, respectively TPHg and benzene were detected in well MW13B at concentrations of 130,000 ppb and 11,000 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 reports and chain of custody documentation G\GAOL fN1)ZF\R0CK\QNM\2006U gm2006 doe