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Cleaning Alameda with Steam and Bugs
A team of environmental engineers from UC Berkeley just completed a multi-year study of contamination at the Alameda Naval Air Station, tackling three problem areas: an underground plume of solvents and waste oils that had leaked from a storage tank, an underground plume of aviation gas, and a lagoon that the Navy had used for landing seaplanes, berthing ships, and repairing aircraft. Their results demonstrate how science can help assess and address contaminant problems, using both nature and human ingenuity.
The first problem area, the seaplane lagoon, had trapped all kinds of wastes that the Navy had poured into its storm drain system -thinking they would flow out into a diluting bay - before the Clean Water Act prohibited such actions. When the multi-year study kicked off, the Navy knew the lagoon was contaminated, but wanted to know more about what was down in the mud and when it settled in. Rather than performing a traditional sediment analysis, which includes taking a chunk of sediment and homogenizing it, Berkeley researcher Jim Hunt created a "vertical profile" of the lagoon's bottom. First, a seismologist from Lawrence Berkeley National Laboratory sent sound waves down into the lagoon, revealing that four to six feet of material had been deposited since the lagoon was dredged down to the Merritt sand in the 1930s. The question for the Navy was whether that material was its responsibility or had been deposited by natural processes.
Hunt took sediment cores near an outfall in the lagoon, where he thought contamination might be high. Using radioisotopes found in the samples, he was able to determine more precisely when the sediments had been contaminated. He found Cesium 137, for example, introduced into the atmosphere in 1963 during nuclear weapons testing about 30 centimeters down. "The cesium spread around the globe, accumulated on particles that landed in the Bay, and got buried in the sediments," says Hunt. Hunt knew then that the contaminated sediments beneath the cesium-which "resembled the color and texture of black mayonnaise"-had to have been deposited prior to 1963.
At approximately 67 centimeters, the sediments held another clue, traces of radium. "During World War II, the Navy used luminescent paints (made from radium) on ship dials, railings, and other parts of ships," says Hunt. The radium-containing sediments had been contaminated about 50 years ago, but have remained quite immobile since then.
One of the proposed re-uses for the lagoon is as a marina. But small boats with anchors could bring up buried contaminants, so Hunt recommends that if a marina is decided upon, additional studies be performed to address the mobility of the sediments. Possible solutions, he says, are to remove the contaminated sediments or build barriers to isolate them from the water column. In any case, his results show the Navy is clearly responsible for the tainted deposits.
At the site of the second problem area, the aviation gas spill, Lisa Alvarez-Cohen found that microbes had been cleaning up contamination on their own, in effect by eating the hydrocarbons-at least where there was plenty of oxygen. The section of the site covered with grass had very little contamination left. But the portion that lay beneath asphalt was biodegrading much more slowly. "A very active microbial community is degrading the aviation gas to methane," says Alvarez-Cohen. But the methane is building up beneath the asphalt, creating a potential hazard and slowing the rate at which bioremediation takes place. Alvarez-Cohen recommended that the Navy remove the asphalt and plant the site with grass, which would allow the bugs to finish the job.
Steam, not bugs, was the tool used to deal with the third problem area, the underground plume of solvents and waste oils that had leaked from a storage tank years ago. After installing steam-injection wells around the perimeter of the spill and an extraction well in the center, project coordinator Kent Udell heated the soil to boiling point, vaporizing the underground pollutants. Pollutants included TCE and PCE (unlike the hydrocarbons in the aviation gas spill, these compounds would have taken years to degrade on their own, says Udell, and would have degraded to highly dangerous vinyl chloride). "After 70 days, we had recovered 600 gallons of oil and solvents and removed 99.9 percent of the chlorinated solvents," says Udell.
Before the steam-cleaning, Alvarez-Cohen had found 1,000 million microbes per gram of soil. Afterwards, that number dropped by a factor of 10, says Udell. But just four days later, the number of microbes was climbing back up again. The bugs will clean up any remnant pollution, he says. "They tend to deal better with contaminants at low concentrations. Now the site is conditioned to be a wonderful bioreactor."
Clearly, the Berkeley team has helped the Navy navigate its clean up morass. "I think we brought a lot of good will and competence into this process between the Navy, the regulators, and the public groups. We didn't take sides-we just focused on the science behind the problem."
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