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CLOSURE REQUEST 5-31-94 • limits, <2 .2 MPN, for fecal coliform. VAPOR EXTRACTION Vapor Recovery Summary: The vapor extraction system was shut down on November 21, 1991 on completion of operation under Initial Variance #91-19 and 90 day Variance #91-20 A calculated 13 , 116 pounds of gasoline range hydrocarbons were removed from the soil and ground water beneath this site by that time . The vadose zone vapor recovery wells (PI, P3-Swarm and EX) contributed little to the total recovered hydrocarbons during this time period P1 = 1 . 3 pounds, P3--Swarm = 561 .4 pounds and EX = 127 pounds . The system was restarted under the Authority to Construct Permit (AP 91-106) on March 31, 1992 . On July 21, 22 , and 23, 1992 , four new vadose zone vapor recovery wells were installed and manifolded to the recovery system. As of July 22, 1992 the existing vapor extraction system (MW5, P1, P3-Swarm and EX) had produced 13902 . 8 and the newly installed well VSB3 produced 3 . 6 pounds of gasoline range hydrocarbons Since that time only the newly installed wells (VSB3 , VSB5, VSB9 and VSB11) and MW5 have been used for vapor extraction Prior to turning the system off on December 30, 1993, the new wells and MW5 had removed 4285 pounds of gasoline range hydrocarbons, for a total recovery of 18191 pounds, see Table 3 and Charts of vapor recovery (Figures 5A . 5F) The VES was turned off on December 30, 1993 for evaluation of site closure . Confirmation soil sample borings were performed on February 2, 1994 Field screening of the samples obtained from these borings indicated that some petroleum range hydrocarbons still existed in the soil beneath the site. Subsequently these borings were converted into vapor recovery wells VSB13, VSB14 and VSB15 . The VES was not turned on again until after completion of quarterly ground water sampling on February 16, 1994 At that time MW5, VSB13 , VSB14 and VSB15 were connected to the VES manifold and the system was restarted Samples of the VES obtained on April 26, 1994 indicated that only 0 . 83 pounds of hydrocarbons were being removed by the VES per day. From February 16 thru May 19 , 1994 an estimated 60 pounds of gasoline range have been removed, making a total of 18, 255 pounds of gasoline range hydrocarbons removed by vapor extraction Calculations of petroleum hydrocarbons remaining in the soil at the time of the confirmation drilling on February 2 , 1994 is 531 pounds of benzene free, degraded gasoline range hydrocarbons . This estimate of petroleum hydrocarbons remaining in the soil, was calculated from the VLEACH model, see Appendix B. This is a 85k reduction (531 lbs/3436 lbs) since the drilling and sampling that occurred on July 20-22, 1992 . Vapor analysis indicate that page32