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i <br /> iMr Ron Rowe <br /> Page 2 of 5 <br /> elevations have not been determined for the vapor wells Water levels fell an average of 106 feet since <br /> last monitored on May 9, 2000 Groundwater flow direction was generally towards the northeast with <br /> a gradient averaging approximately 0 004 feet per foot A groundwater gradient map generated using <br /> the August 14, 2000 monitoring data is shown on Figure 2 Groundwater morutoring data are <br /> summarized in Table 1 Monitoring logs and well construction information are included in Attachment <br /> A <br /> On August 14, 2000 through August 17, 2000, Ground Zero collected groundwater samples from <br /> groundwater monitoring wells MWl through MW13, and vapor wells VW1 through VW6 Except for <br /> MW4, a muumum of three well casing volumes was purged from each well prior to sampling <br /> Physical parameters (pH, conductivity, and temperature) were monitored during purging and allowed <br /> to stabilize before sampling Samples were collected after groundwater recharged to 100% of the <br /> original depth to water level Purged water was contained in 55-gallon drums approved by the <br /> Department of Transportation (DOT) On August 15, 2000 approximately 700 gallons of purge water <br /> stored at the site was removed by American Valley (CAL 000827878) under non-hazardous manifest <br /> 20157203 Purgewater generated August 16 and 17, 2000 was placed in labeled DOT approved <br /> drums The drums are stored onsite in a locked enclosure Purge logs and purgewater disposal <br /> documentation is included in Attachment A <br /> . Samples collected for analysis were placed on ice, transported under chain of custody to Argon <br /> Laboratories (FLAP 92359), and analyzed for TPHg using EPA method 8015 modified and BTEX <br /> using EPA method 8020 Oxygenates, EDB, 1,2 DCA, methanol and ethanol were analyzed using <br /> EPA method 8260 Analytical results for TPHg, BTEX and MTBE are summarized in Table 2, <br /> oxygenate results are summarized in Table 3 Attachment B contains laboratory reports and chain of <br /> custody documentation <br /> Groundwater Analytical Results <br /> Groundwater Monitoring Wells <br /> The potentiometric surface was above the top of the screened intervals in all monitoring wells except <br /> MW13 No petroleum hydrocarbons were detected in wells MW2, MW7, and MW9 through MW12 <br /> The highest concentrations of TPHg and BTEX were detected in samples collected from wells MW3, <br /> MW4, MW5 and MW13 Most notably TPHg was at the highest concentration in well MW4 since <br /> sampling began (160,000 ppb) Hydrocarbon concentrations in well MW5 increased significantly <br /> since the previous event, but are still stable with respect to historic levels Contaminant concentrations <br /> in well MW13 continue to decrease, and in well MW2 no analytes were detected for the first time since <br /> sampling began <br /> Wells MW3 and MW4 located along the southern boundary of the subject property and are affected by <br /> offsite release(s) TPHg and BTEX concentrations are summarized in Table 2 <br /> • No EDB or gasoline oxygenate additives except MTBE were detected in any site wells MTBE was <br /> detected in wells MW3, MW4, and MW9 at concentrations of 1,200 parts per billion (ppb), 1,600 ppb <br /> and 15 ppb, respectively 1,2 DCA was detected in wells MW 10, MW 11 and MW 12 at <br /> roeklgnuI3QM2000 <br />