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Report:Groundwater-quality Monitoring—September 11,2001: 7500 West Eleventh Street, Tracy, C4. Page 7 As has been the case for samples recovered from well MW-6 during earlier groundwater- quality monitoring rounds, the sample recovered on September 11, 2001 from that well, located on the western side of the plume of affected groundwater, contained only a trace i_ of diesel-range hydrocarbons and a Iow concentration of MTBE. The concentrations of both analytes had fallen moderately from those measured in the sample recovered from MW-6 on May 30, 2001. The groundwater contours interpreted from the depth to groundwater measurements made on September 11, 2001, when compared to earlier measurements, indicate some veering E of the direction of groundwater flow toward the north. For this reason, the interpreted plan area of the plume of affected groundwater shown on Figure 2 has been adjusted slightly on its western side compared to the earlier interpretation. There were some changes in the detected analytes of concern in some wells around the fringes of the plume of affected groundwater. These changes, however, were not sufficient to justify modification of the previously established interpretation of the lateral and vertical extent of the principally affected zones of the subsurface as they are shown in section on Figures 3, 4and 5. 2.5 Disposal of Purge Water f When the results of the groundwater analyses were available, the monitoring well purge water held in 50-gallon drums on the 7500 West Eleventh Street property was segregated into two groups: drums holding purge water from wells in which water samples a recovered were affected by petroleum hydrocarbons and those containing clean water. The clean purge water was disposed by decanting it from the drum onto the surface of the 7500 West Eleventh Street property. The drums containing water affected by fuel hydrocarbons were left stored on that property. That water will be shipped to a permitted recycling facility for disposal when sufficient quantity has accumulated for that to be done economically following future rounds of groundwater sampling and analysis. 3.0 FUTURE ROUNDS OF GROUNDWATER SAMPLING AND ANALYSIS The SJCPHS has requested that additional rounds of groundwater sampling and analysis be conducted at the 7500 West Eleventh Street site until such time as that agency directs otherwise. The next round of groundwater sampling and analysis is scheduled for early December 2001. sic