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i 1 I ' Ms Margaret Lagono Page 2 of 5 The potentiometric surface was above the top of the screened intervals in all wells except monitoring wells MW1, MW2, MW3, MW13 and MW14 and vapor wells VW2, VW3, VW5 and VW6 A table of well construction details is included in Attachment A Groundwater flowed in an east-northeasterly direction, with an average gradient of approximately 0 002 — 0 003 feet per foot A groundwater gradient map generated using the monitoring data from all site wells is shown on Figure 2 Groundwater monitoring data are summarized in Table 1 Monitoring data sheets are included in Attachment A ' On May 22, and May 23, 2002, a Ground Zero technician collected groundwater samples from monitoring wells MW3 through MW6, MW8, MW10, NMI 1, and MW14 and from vapor wells VWl and VW2, ' and VW4 through VW6 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 a minimum of 80%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 Purge water was contained in labeled 55-gallon drums approved by the Department of Transportation (DOT), which are stored onsite ' within a secured area Purge logs are included in Attachment A Analysis consisted of gasohne oxygenates, EDB and 1,2-DCA by EPA Method 8260, TPHg by EPA ' Method 8015 modified and BTEX by EPA Method 8020 i ' GROUNDWATER ANALYTICAL RESULTS Groundwater Monitoring Wells ' TPHg was detected in all sampled wells except MW6, MWI0 and MWl l and benzene was detected in all sampled wells except MW10 and MWl l Concentrations of TPHg and BTEX were within historical ' ranges TPHg and BTEX concentration date are summarized in Table 2 Attachment B contains laboratory reports and chain of custody documentation Graphs depicting TPHg and benzene concentrations over time are included in Attachment C MTBE was the only gasoline oxygenate detected in the sampled wells MTBE was detected in wells MW3 (34,000 parts per billion - ppb), MW4 (15,000 ppb), MWII (7 1 ppb), and MW14 (81,000 ppb), ' which are located along the southern portion of the property, and in well MW 10 (3 9 ppb) which is located offsite along the north side of Market Street The concentrations of MTBE in wells MW3, MW4 and MW14 are the highest to date These wells are clearly affected by offsite releases and the increasing concentrations in wells MW7 MW 11 and MW 12 attest to the mobility of the plume 1 EDB was not detected in any monitoring wells sampled, however, 1,2-DCA was present in monitoring ' wells MW10 and MW11 at concentrations of 16 ppb and 2 6 ppb, respectively Analytical results for gasoline oxygenates, EDB and 1,2-DCA are summarized in Table 3 Attachment B contains laboratory reports and chain of custody documentation II 1 roeklgw\1 gm2002