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-5- In summary, liquids pumping recovered 2. 8 gpd of oil, and the water-to-oil ratio was 150: 1 . Pretreatment with a baffled tank reduced the oil and grease content of the produced groundwater to less than 100 ppm. Liquids pumping would be much less effective at other locations in the park where the oil is more viscous. Bioventing Test Bioventing is a new technology for mitigating oil contamination. The process promotes the natural biodegradation of the oil and it does not require excavation. Figure 5 shows how the process works . A vacuum pump is attached to a well . Air flows from the surface, through the ground, and into the well . Then the air is treated to remove any odors before it is released. We tested this process in Alden Park to see if we could obtain enough air flow and a large enough area of influence, or "reach" to be practical . During the first part of our test we did not obtain enough air flow. In order to get enough air flow through the dense clay soils, it was necessary to use a much higher vacuum. During bioventing the vacuum draws the water level up in the well . In fact, if the vacuum is too great the well will fill up with water which blocks the flow of air . This effect is similar to drinking with a straw. The problem can be solved by combining the liquids pumping and bioventing processes in a single well . We conducted a series of one-day tests at high vacuum. The results were very encouraging. We were able to pull a substan- tial flow of air through the clay soil . The concentration of CO2 in this air was about the same as our experience at other sites . Although the tests were not long enough to measure the steady- state oil degradation rate, we expect that the flow of air and CO2 is large enough to remove much more oil than liquids pumping alone. The groundwater pumping rate was about 0 . 5 gpd. This is consis- tent with the data from the Dames & Moore test . We measured the reach of the bioventing system with soil probes . Figure 6 shows the soil vacuum that we measured with a probe located 40 ft north of the well and at a depth of 7 ft . At first we did not measure a vacuum. Then we developed the soil probe by physically breaking up the soil near the probe tip. After this