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-5- piping and into the vacuum pump. The system shuts down automat- ically if the discharge pressure from the vacuum pump gets too high. Finally, the air goes through a carbon adsorption bed where all nonmethane hydrocarbons are removed. This prevents objectionable odors. Hydrocarbon emissions will be measured to meet our agreement with the San Joaquin Air Pollution Control District . Spent carbon will be recycled to the supplier . The carbon bed may have to be changed occasionally during the course of the mitigation. The vacuum pump requires a flow of water which is used as a pump seal fluid. This water is recirculated through a closed system. None of this water is discharged to the sewer. Water is supplied to the vacuum pump by a small water recirculation pump. Water leaving the vacuum pump is stored in a water recirculation tank . Finally, the water is cooled by a chiller to remove heat gener- ated by the vacuum pump. The chiller is similar to a small refrigerator . Some of this water will evaporate into the air stream, so a water make-up is required from the City drinking water line. This water flow will be less than 1 gal ./hour. The process shuts down automatically if the water level in the recir- culation tank gets too high. A submerged pump will be used to control the level of the ground- water in the well . This pump has operated reliably at other sites . It uses compressed air which is supplied by a small com- pressor located inside the building. When the water level in the well rises a few inches above the top of the submerged pump, it begins to pump groundwater to the surface. This level control is an integral part of the pump. If the water level in the well gets higher than the design level , a separate system will auto- matically shut the process down. The groundwater containing some oil flows through underground piping to an oil/water separator in the block building. In the separator the oil floats to the top due to density differences. The treated water contains less than 100 ppm of oil and grease, and it flows into the sanitary sewer . The total flow of this stream will be about 1 or 2 gal ./minute. This is half as much as we discharged during the bioventing test last summer . The recovered oil will be transferred to a 55-gal . drum and removed by Chevron whenever necessary. The flow of oil will be about 0. 5 gal ./day. The existing soil probes will be used to monitor the reach of the vacuum in the soil surrounding the well . Figure 4 shows the design of the soil probes, and Figure 5 shows approximately where they are located. In our field tests last summer, we had mixed results with the soil probes--some worked well and others did not . We may have to modify some of the probes or install new ones. If this is necessary we will follow the same procedures as in our previous Work Plan ( 4 ) .