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R604 :UPDATE 10-JUNE, 1992 System Operation On March 31 , 1992 , the influent to the carbons was 4 . 02 pounds per day (lbs/day ) at a flow rate of 57 cubic feet per minute (cfm) and an effluent measurement from the last carbon of 0 . 32 lbs/day. This equates to a 92% absorption/destruction of the vapor stream hydrocarbons . The 57 cfm flow rate was not maintained, the blowers heat sensor shut the blower off for a 20 minute cool down. Once the blower came back on the pump bypass was used to decrease the flow rate to Ei 28 . 7 cfm, which decreases the pounds per day to 2 .02 on the ' E# influent and 0 .05 on the effluent, ie, 97% absoption/destruction E of the vapor stream hydrocarbons . On subsequent visits the flow rate ranged between 26 cfm to 32 cfm with the influent dropping from a high of 3.12 lbs/day on April 7 , 1992 to 1 .45 lbs/day on April 14 , 1992 . The effluent from the last carbon ranged from below detection limits to a high of 1 .07 r lbs/day. Presently, June 10 , 1992 , 6 . 34 pounds per day of hydrocarbons are being removed from the subsurface via vapor extraction. As can be seen when comparing the three per day effluent samples as shown on Table 3B (March 31 through April 24 , 1992 ) , a slight bleedthrough (channeling) is occurring from the last carbon, even during the first minutes of operation. This channeling occurs as specific molecules of the contaminant in the vapor stream absorb and "desorb" from the carbon surfaces and are not trapped in the micro or macro pores of the carbon. This absorption-desorption along with the low concentration of the influent stream ( 3 . 12 to 1 .56 lbs/day) , which allows the hydrocarbons to remain in equilibrium in the vapor stream, does not allow an effective absorption (greater than 90% ) to occur. CONCLUSIONS AND DISCUSSION Vapor extraction is successfully removing the degraded gasoline range petroleum hydrocarbons from the soil and the ground water at this site . The vapor recovery system, operated under Variances #91-19 and 91-20 was turned off awaiting the Permit to Construct, Permit # AP 91-106 . During this "off period" two periods of "re- equilibration" have occurred. Sample results from the vadose zone wells P1 , P3-Swarm and EX have indicated that these wells and the surrounding areas were being cleaned of the contaminant. Upon start-up for the Permit to Construct P1 , P3-Swarm and EX exhibited minor vapor recovery , 0 . 04 , 0 . 07 and 0. 01 lbs/day respectively. Since Update Status Report #9 , April 14 , 1992 , P1 has produced another 0 . 2 pounds , P3-Swarm another 12 . 62 pounds , and EX has produced another 0 . 89 pounds of hydrocarbons . Total production of hydrocarbons as of June 10 , 1992 : P1 = 2 . 17 pounds , P3-Swarm - 575 . 21 pounds , EX = 128 . 17 pounds , MWl - 2504 . 26 page 8