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• restarted Moreover, sparge well monitoring data for air flow and pressure Indicates that the sparge system is effectively reaching targeted areas However, the center of the plume needs to be more directly treated, therefore, ENSR proposed additional sparge points e Are the air flows unevenly distributed among the various wells in a multi- well system? Determine if this may be due to incorrect flow control valve settings, differences in depth to water in various wells, clogging of the wells, inconsistent well construction, or significantly different pressure drops in certain piping legs Yes, air flows are unevenly distributed among the sparge wells relative to the site ENSR intentionally restricts flow to the wells north of Robinhood Drive to inhibit migration of contaminants offsite It is most likely that there are different pressure drops in the different piping legs for the ISAS However, ENSR will conduct future site visits to detemnine if water or clogging is contributing to uneven air flows f Has there been unexpected contamination found outside the target zone or any Indication of an unknown sources (An investigation into another source may be warranted ) No The contaminants in groundwater are the results of commingled plumes between the former Unocal and former Montgomery Wards UST facilities The ISAS system was originally designed to address contaminants beneath the Wards site and was later modified by adding ISAS wells north of Robinhood Drive to address contaminants beneath the • Unocal site g Is there evidence that vapors are escaping to undesirable locations? These locations can include buildings or utility corridors. No evidence exists indicating that vapors are escaping to undesirable locations h is there evidence that water table fluctuations have affected the distribution of air, isolated contaminants, or introduced additional contaminants into the treatment zone? No evidence exists indicating that water table fluctuations have affected the distnbution of air or contaminants I Is increasing injection pressures required to achieve airflow? This may be due to biofouling, or siltation of the sparging wells, or rising water levels ENSR does not intend to increase injection pressures at the site ENSR has measured air flow rates in the ISAS wells ENSR intends to conduct future site visits to measure air pressure and flow to determine if the sparge wells are operating consistently 8 Alternatives for Possible Cost Savings a uas th^ �y�t.�.m rnwrhnri rte rrloaniln nhlArtwPC? (Determine if the ISAS operation is still necessary or have the concentrations decreased to that the operation can be terminated ) No The system has not reached cleanup objectives Concentrations of dissolved petroleum hydrocarbons in the vicinity of monitoring wells MW-3 and MW-11 indicate that the TPHg and benzene plumes have not reached cleanup objectives Concentrations of dissolved petroleum hydrocarbons in the vicinity of monitoring wells MW-14, MW-14A, MW-18, MW- 19S, MW-19D, MW-21S, MW-21D, MW-22S, MW-22D, MW-23S, MW-23D,