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DuPont Biosystcu- <br /> i <br /> Page Two <br /> November 2, 1988 <br /> Job No. 1088-M-4 <br /> between soil particles. once equilibrium is established, the <br /> thickness of the liquid film on the soil remains constant. <br /> To reduce the film thickness, and thus the amount of trapped <br /> hydrocarbon liquid, the volatilized hydrocarbon concentration <br /> in the air space must be lowered. This can be achieved by <br /> circulating fresh air through the soil, i.e. , by soil vapor <br /> extraction. <br /> Remediation will consist of soil vapor extraction accomplished <br /> by applying a constant negative pressure, utilizing a low- <br /> vacuum blower, on existing wells located at approximately <br /> the .center of the subject site. Specific air flow rates, <br /> contaminant concentrations, moisture elimination system <br /> design, influence zones, and air inlet locations will be <br /> determined subsequent. to implementation of a pilot program <br /> designed to gather parameter information for a period of .30 <br /> days. The pilot program will consist of low-vacuum pumping <br /> of existing wells, as well as hydrocarbon-vapor concentration <br /> sampling at various locations within the contamination zone. <br /> During the pilot program, contaminated vapor extracted from <br /> wells will be pumped through a carbon canister, if necessary, <br /> to reduce contaminant levels to San . Joaquin County Air <br /> Pollution Control Agency acceptable levels. <br /> Upon completion of the pilot program, a complete vapor <br /> extraction system will be designed for the conditions specific <br /> to the subject site, if deemed appropriate. We expect that <br /> such a system will utilize a single, low-vacuum blower, <br /> working on one or more vapor extraction wells. Contaminated <br /> vapors will be processed to meet the requirements of the San <br /> Joaquin County Air Pollution Control District. The method of <br /> treatment will be based on the results of the pilot soil vapor <br /> extraction study. The system, designed for 24 hour a day <br /> service, will include provisions for monitoring the treated <br /> air. Air quality standards specified by the San Joaquin <br /> County Air Pollution Control Agency will be adhered to <br /> throughout the pilot program and the final vadose zone <br /> remediation operations. <br /> We are prepared to initiate the start of work, pending your <br /> approval. <br />