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b Prepare air flow versus time graphs for each infection well to determine if past flow rates differ significantly from current conditions A quarterly O&M plan needs to be established so that this information can be collected on a regular basis ENSR currently has data from two events and has tabulated both events With data from future events, ENSR can determine if flow rates differ over time However, currently, there is insufficient data to make such a determination c Construct groundwater concentration versus time graphs for the contaminants of concern at each monitoring point Have individual monitoring points reached a consistent asymptote on the concentration versus time graph without significant rebound? Concentrations of total petroleum hydrocarbons as gasoline (TPHg) and benzene have been graphed over time for monitoring wells MW-2, MW-3, MW-4, MW-6, MW-8D, MW-919R, MW-11, MW-12, and MW-25D Wells MW-2, MW-4, MW-6, MW-8D, MW-919R, MW-12, and MW-25D have shown stable decreasing trends but concentrations are still elevated enough in MW-3 TPHg > 20,000 uglL, benzene > 4,000 ug/L and MW-11 TPHg > 11,000 ug/L, benzene > 4,000 ug/L) to justify the continued operation of the ISAS system at the site d Construct groundwater contaminant concentration iso-concentration maps of the site Do the contaminant concentrations indicate that the treatment is effective throughout the target zone? Quarterly groundwater monitoring data has been used to create isoconcentration maps These figures indicate that the TPHg and benzene plumes beneath the site have decreased significantly since remediation at the site began Quarterly isoconcentration maps show that the TPHg and benzene plumes in Unit B have increased in the vicinity of MW-11 6 Adequacy of Operations and Maintenance a Has the entire system been operating with enough consistency to achieve its objective in a reasonable time? (A good operational target should be 90% uptime or better) The ISAS has operated 1,480 hours since ENSR restarted the system on June 14, 2004, approximately 50 percent of available uptime The system has been operated on a week on 1 week off basis as approved by the RWQCB since June 14, 2004 which explains the 50% uptime b Are the monitoring points constructed to yield reliable results (e g , short screens, checked for plugging/response)? The ISAS wells are designed with screens that range in length from approximately 5 0 feet to 7 5 feet in length The screen lengths should be adequate for the purpose of air spargmg at this site c Verify that the air flows are balanced if multiple sparging wells are being used Pressure measurements collected from the the ISAS well-heads have shown to be fairly evenly distributed throughout the well field (ranging from 17 5 psi to --26 pounds per square inch (psi)) Air flows were not balanced due to the varying distances of the ISAS wells from the compressor and varying screen depths