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-6- probe development we measured a vacuum of 0 .1 in. of water (0. 1 in. H2O) . This is a very large soil vacuum--a vacuum of 0 .01 in. H2O would be considered significant . We verified that this vacuum was produced by the bioventing system, because it went away when we turned the bioventing system off . Table I shows the rest of the soil probe data. Three of the probes within 40 ft measured a soil vacuum. The rest of the probes did not show a vacuum, probably because the probe develop- ment technique does not work all the time. It is also possible that the airflow is not uniform through the soil . The reach of the bioventing system may improve with time as water drains out of the clay. Summary Liquids pumping alone recovered 2.8 gpd from a well where the oil was not very viscous . Other wells in the park would produce less than 0 . 3 gpd because the oil is more viscous in those wells. Bioventing removes more oil than liquids pumping. Furthermore, since bioventing is not affected by viscosity, it will be effec- tive throughout the park. At this point we have enough information to believe that biovent- ing is the most effective process for Alden Park. However, there are some gaps in the data needed to design the full-scale system. We need to further define the flow rate, reach, and the steady- state biodegradation rate. We need to confirm the rate of groundwater production and demonstrate that we can effectively treat it before discharging it to the sewer . We will fill in these data gaps during the first part of the mitigation as dis- cussed below. Mitigation Plan Objective The objective of the mitigation plan is to eliminate the nuisance of flowing oil to the residents of the Alden Park area. We have shown that seep collection vaults can be used to effectively mitigate oil seeps. We plan to remove flowing oil below the ground surface with bioventing. We are also developing a plan to monitor water quality.