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Y ORO Ms. Mary Meays September 29, 1995 (9347-3011) GWO began July 11, 1994, and following equipment adjustments, the hydrocarbon extraction rate of the VES slightly increased from 1.2 pounds per day to as high as 1.9 pounds per day on September 20, 1994. However, the slight increase in the hydrocarbon extraction rate is most likely attributed to a drop in the water levels during the corresponding time period. The hydrocarbon extraction rate of the VES has since continued to decrease to 0.7 pounds per day on July 3, 1995. Proposed Remediation of Residual Hydrocarbons Fugro proposes to shut down the VES and ground water extraction system but continue the GWO system to enhance the attenuation of the remaining dissolved- and adsorbed-phase petroleum hydrocarbons. The sand/silt/clay composition of the saturated zone appears suitable for the propagation of dissolved oxygen in ground water across the site. The GWO system will be connected to wells MW-3, MW-4, and RW-2. Ground water monitoring and sampling will continue to assess the progress of dissolved petroleum hydrocarbon attenuation and remediation and demonstrate the quality of ground water beneath the site. In addition, other natural processes, or passive remediation, will continue to reduce the volume and control the migration of petroleum hydrocarbons in the subsurface soil and ground water beneath the site. These processes include volatilization, adsorption, dispersion, and dilution. Conclusions Following are the conclusions of Fugro: 1. "Sources" of petroleum hydrocarbons in ground water and soil have been removed from the site by the operation of the VES and ground water recovery system. 2. The VES has removed all of the petroleum hydrocarbons that can be practically and economically remediated by vapor extraction. The petroleum hydrocarbon extraction rate of the vent system has dropped to approximately one-half of 1% of the original startup rate of extraction, with a corresponding drop in efficiency. 3. No sources of petroleum hydrocarbons have been present onsite since the former USTs were removed in 1981. 4. To date, approximately 528 gallons of petroleum hydrocarbons have been removed from the subsurface soil and ground water at the site. 5. The remediation systems have reached their limits of technical and cost effectiveness. Continued operation of the VES and ground water recovery system will not significantly improve the quality of the ground water at this site. 93473411.ARP 5 -