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Mr Nuel Henderson Page 4 of 5 On November 21, the VES was restarted The system operated for 251 hours between November 21 and December 3 The system is currently down pending repair of an electrical malfunction Vapor concentrations were monitored on four occasions with a flame ionization I ' detector (FID) Vapor samples were collected on November 25 and submitted to state-certified Air Toxics Laboratories for the analysis of TPHg, BTEX and MTBE by EPA Method TO-3 Field notes are included in Attachment C Analytical data are summarized in Table 4 Laboratory reports and chain of custody documentation are included in Attachment D Hydrocarbon Mass Removal ' During the period of operation the system operated for a total of 251 hours Based on the single set of lab data, it is estimated that the system removed approximately 461 pounds of hydrocarbons from the subsurface during this time at a rate of approximately 44 pounds per ' day The influent vapor concentrations measured with the FID during operation were higher than those measured in 2002 when the system was last operated Moreover, the vapor concentrations measured individually in wells VW2, VW5 and VW6 were similar This is attributed to the approximate 4-foot drop in water levels during the intervening period, which has exposed additional soil column to vapor extraction The vapor extraction system has now removed an estimated total of approximately 13,660 pounds of gasoline hydrocarbons from the site The recent period of intermittent operation accounts for approximately 3% of that total Operational periods and mass removal are summarized in Table 5 t RECOMMENDATIONS tGroundwater Monitoring and Sampling Reduce the sampling frequency for wells that are monitoring the plume of contamination originating from the onsite release Given the massive quantity of historical groundwater monitoring and chemical analysis data at this site, quarterly monitoring and sampling for this site is not warranted Transfer ownership or sampling responsibility for the wells that are affected by the offsite release(s) to the appropriate responsible parties Vapor Extraction System Operation Decreasing water levels have exposed previously saturated contaminated soils to vapor ' extraction We recommend repairing the electrical problem and restarting the vapor extraction system for an additional period of operation The mass removal rate and unit cost thereof will be evaluated to determine whether an extended period of additional vapor extraction is ' warranted \\G7A_FSIVOL_IOATAIGROUNDZEIROEK%QMR\2003\4gm2003 doc I