SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

-4- Since the soils beneath. Alden Park are comprised of clays and silts, a single groundwater production well may produce limited amounts of water . Flow of oil into this well may be even more limited since the oil is more viscous (sticky) than water . The soil type and viscous nature of the oil make it difficult to pre- dict the recovery rate of oil from a groundwater pumping well. To assess this , we will perform a pumping test from an existing observation well . A detailed work plan will be submitted to the city of Tracy and agencies involved. Groundwater Treating Treatment equipment to remove oil from the produced groundwater has been designed, based on previous experience in Chevron. The water pumped during the test will be analyzed. Then bench-scale tests may be performed to confirm our designs . (To determine a preliminary basis for the designs , oil sampled from observation wells in Alden Park was agitated in water then analyzed. Oil and grease in this sample was 160 ppm, due to entrained droplets of oil. The water was then filtered and found to contain less than 10 ppm oil and grease. ) Soil Venting Soil venting can remove the liquid oil by stimulating micro- organisms that occur naturally in soil . The process is pictured in Figure 2 . A vacuum pump pulls air into subsurface soil through a series of vertical wells drilled into the soil . Bacteria use the oxygen in the air to aerobically biodegrade the oil to carbon dioxide and water . If nonvolatile oils are treated, the vent gas may be vented directly to the air without treatment . However, some treatment may be necessary to satisfy regulatory limits on hydrocarbon air emissions for more volatile oils. Chevron has experience operating soil venting systems in Oregon, Idaho, and Los Angeles . We ' ve evaluated stimulating biodegrada- tion with these systems and believe this can be .successful at Tracy. A similar system to the Tracy site is operating in Los Angeles where land was developed over fuel oil storage reser- voirs . A comparison of the site with Tracy is shown in Table I . Rough estimates of air flow and removals at Tracy are shown based on our experiences .