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i <br /> ' Mr. Ron Rowe <br /> Page 4 <br /> As of August 28 the system was again operating continuously, however the system again failed <br /> on September 14 due to an apparent malfunction in the chart recorder/system logic component <br /> ' r on a weeld basis The system monitoring data <br /> During the quarter, the VES was monitored y Y <br /> sheets are included in Attachment C. On August 19 and September 13 influent and effluent <br /> ' vapor samples were collected with a vacuum box/tedlar bag system and submitted to Sequoia <br /> Analytical for analysis The samples were analyzed for total purgeable petroleum hydrocarbons <br /> ' (TPPH) and BTEX <br /> Vapor Sample Analytical Results <br /> ' Laboratory reports are included in Attachment D and are summarized in Table 4 Based on the <br /> TPPH concentrations, the destruction efficiency of the thermal oxidizer during both sampling <br /> rounds was 99% or better <br /> Overall, analytical results of third quarter influent samples indicated vapor concentrations similar <br /> to those from second quarter 1998. Influent vapor concentrations measured in September were <br /> t lower than in August, reflecting the increased dilution necessary to prevent thermal overload of <br /> the blower motor <br /> System Evaluation <br /> The VES has been removing hydrocarbons from the subsurface since November 19, 1997 at <br /> combined flow rates ranging from 270 to 390 cubic feet per minute, including dilution air <br /> As of September 14, 1998, the system had been in operation for 3,965 hours Based on <br /> graphical interpolation between measured influent vapor concentrations, as of September 14 an <br /> ' estimated 9,500 pounds of hydrocarbon contamination had been removed from the soil Table <br /> 5 summarizes flow and vapor concentration averages as well as the total hydrocarbon mass <br /> removed from the soil <br /> ' REC MMENDATIONS <br /> Ground Zero recommends continuing quarterly sampling to monitor the extent of gasoline <br /> hydrocarbons in groundwater. Analysis for oxygenates should continue for wells MW1, MW3, <br /> MW4, MW 11, MW 12, and MW 13 for next two quarters The next sampling event is scheduled <br /> ' for November, 1998 Your office will be provided 48-hours notice of any field work <br /> roW9 mr13gm1998 doc <br /> I <br />