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3rd Quarter Report - Beacon Station #695 3 December 1992 both the shallow (4 to 20' below grade screened interval ) and deeper (41 to 71' below grade screened interval) regions. A secondary region of elevated concentrations was also evident on the east side of the tank field, near MW-1. Water remained present in MW-2 as had been the condition since November 1991 . Ambient dilution remained open on this date. In an effort to supply dilution air from the ground rather than the atmosphere, tank field extraction points VP-5 and MW-7 (both <1 ppm) were opened to the system. This allowed for a reduction in ambient dilution. Ambient dilution was reduced to the point where the exotherm across the catalyst was maximized, thus assuring maximum removal and destruction of the contaminants. The resulting adjustments increased the system vacuum to 5.9" Hg and increased the hydrocarbon extraction rate to over 400 lbs/day. Hydrocarbon emissions were below detectable limits indicating that the catalytic abatement system was performing with an exceptionally high . destruction efficiency in excess of 99.9%. 17 July 1992 Monitoring: The SUES operated continuously until 11 July at which time the system went down due to insufficient fuel . The propane company was contacted and reminded of the need to service the site more frequently. The propane tank was refilled and the unit restarted on 13 July and allowed to purge several days prior to monitoring. On 17 July, vapor concentrations again remained high at many extraction points. The region of 10,000+ ppm concentrations between the pump islands expanded slightly toward Cherokee Lane while the secondary area of concentrations east of the tank field increased to include 10,000+ ppm the area between MW-1 and MW-17. A verification air bag sample from MW-10 was analyzed in the lab according to modified EPA Method 8015. The results indicated a concentration of 9,066 ppm, thus confirming the high reading from the field instrument. Ambient dilution was further reduced, raising the vacuum slightly to 6.0" Hg. No valve positions were changed on this date with all but 3 extraction points remaining open. 28 July 1992 Monitoring. The system operated continuously since the previous monitoring. Vapor readings at several of the high concentration extraction points appeared to decline during this monitoring However, the same general pattern of r -3-