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R604 : UPDATE 12 9-18--1992 INTRODUCTION • This report includes the results of the September, 1992 ground water quarterly sampling, along with the events that have occurred at this site since the 11th Update Status Report, that covered events up through July 29, 1992. t Confirmation soil sample borings to verify the removal of aged gasoline range hydrocarbons from the soil in the vadose zone beneath the tank field and pump island areas occurred on July 20 , 21 , and 22 , 1992 . The soil sample results indicated that the area near P1 (northeaster pump island) has been remediated (SB4 ) and P1 f was then destroyed. The area of P3-Swarm has minor gasoline range hydrocarbons remaining ; SB5-20 100 ppm TPH, 0 . 14 ppm toluene and 2 . 1 ppm xylenes , SB5-25 32 ppm TPH, 0 .085 ppm xylenes and SB5-30 90 ppm TPH and 0 . 51 xylenes . This boring was converted in a vapor extraction well (VSBS ) . The area southeast of the former tank field also contained degraded gasoline contaminated soils and those borings were also converted into vapor extraction wells ( SB3 - VSB3 , SB9 - VSB9 , SB11 - VSB11 ) . The following are the conclusions and recommendations from Update Status Report #11 : UPDATE #11 I CONCLUSIONS AND DISCUSSION E Vapor extraction has successfully removed the lighter fractions (lighter than ethyl benzene) of the gasoline range petroleum hydrocarbons from the soil beneath this site and has removed all of the gasoline range hydrocarbons from the ground water associated with this site . The vapor recovery system, operating under the Permit to Construct, Permit # AP 91-106 has removed 13 ,924 . 5 pounds of gasoline range hydrocarbons , see Table 3 . Vapor extraction has greatly reduced the dissolved contaminant found in the ground water . The March 5, 1992 sampling occurred 80 days after the vapor recovery system was shut down and showed that since vapor recovery has been used at this site, MW1 has been reduced from 2 mg/L TPH to <0 . 05 mg/L TPH. MWS , likewise has been reduced from 31 mg/L TPH to 0 .08 mg/L TPH. The BTEX's have also been removed from the ground water beneath the site to below the detection limits . Vapor extraction was resumed on March 31 , 1992 and has operated 1507 hours prior to sampling on June 2 , 1992 . The sample analysis for the June 2 , 1992 sampling is below detection limits for all constituents analyzed for (TPH-g, BTEX) , see Table 2A. Ground water gradients , corrected for vacuum influence, have shown potentiometric lows at MW1 and MW5 , which are being used for vapor recovery. Once the vapor recovery is shut off, normal flow directions again take place to the east-southeast ; with the exception of the March 5 , 1992 gradient, which flowed to the north northwest and may represent a recharge and/or a decline in water • usage of the municipal wells to the east of the site. f page 1