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