Base uses oil to clean solvents
An Army Corps of Engineers representative inspects a valve assembly for pumping vegetable oil into injection werlls across a solvent plume. Microbes eat the oil, which promotes the break-down of solvent contaminants into harmless compounds.(Courtesy photo/Glenn Anderson)
by Merrie Schilter-Lowe
60th Air Mobility Wing Environmental Public Affairs
8/23/2010 - TRAVIS AIR FORCE BASE, Calif -- It's edible, though probably not tasty. It's easy to handle, fairly inexpensive, will last for years and will not harm humans, animals or the environment.
The product is emulsified vegetable oil, or EVO, and it is one of several cutting-edge technologies the base's environmental restoration program team is using to clean up groundwater sites contaminated with trichloroethylene.
TCE is a chlorinated solvent that the Environmental Protection Agency banned as a possible carcinogen. Previously, it was used by both the military and commercial sectors to clean and degrease everything from clothing and electronic components to automobile parts and aircraft engines. As a result, more military installations are contaminated with TCE and similar solvents than with fuels and other petroleum-based products, according to a report from the Air Force Center for Engineering and the Environment.
"We have not used EVO in previous studies or interim remedial actions, so we need to demonstrate that it does the job under site-specific conditions," said Mark Smith, chief of the environmental restoration branch, 60th Civil Engineer Squadron.
Mr. Smith and his team measured TCE concentrations in the groundwater before starting EVO injections. They will continue to take quarterly samples to see if the levels are decreasing. "I expect to see positive results from the next round of sampling," Mr. Smith said.
The environmental restoration branch identified four areas on Travis as TCE "hot spots," meaning they have TCE levels at about 1,000 parts per billion in the groundwater. For drinking water, TCE levels can only be five parts per billion.
Travis does not use groundwater as part of the base's water supply; however most of the groundwater here flows toward Union Creek and potentially could migrate to the Suisun City Marsh, said Lonnie Duke, environmental scientist on the restoration team.
Since TCE is heavier than water, it moves through the subsurface until it forms a pool or dissolves into a plume. "Unlike a river, the plume flows very slowly," said Mr. Duke. "We want to break down the solvents in these plumes before they reach the creek or the marsh."
In June, an environmental contractor injected 25,000 pounds of EVO into the first site, located near building 888. CH2MHILL is now injecting another 37,000 pounds of the oil into a site near building 554. Two other sites are scheduled for injections by year's end.
"We're dealing with the most problematic sites in the most cost-effective manner," said Glenn Anderson, hydrologist on the team. He said sites with much higher TCE concentrations would require too much EVO to successfully clean up. At locations with much lower concentrations, "EVO would be overkill - like using a baseball bat to kill a fly," he said.
Travis has 23 contaminated groundwater sites. Most have at one time been cleaned with the "pump and treat" method that involved pumping groundwater from the soil or bedrock and treating to remove the contamination. But over time the contaminant concentration and water volumes decrease while the cost to operate the pumps increase, Mr. Anderson said. With EVO, the base not only saves on pump and treat equipment repair and maintenance, but also the cost of electricity to operate the pumps.
"Another reason we're using emulsified vegetable oil is because it works best with the type of soil at Travis," Mr. Anderson said. Travis has a mixture of clay and silt, he said. "EVO penetrates tight clays to get rid of contamination whereas the pump and treat method has difficulty in extracting contamination from clays."
A close cousin to extra virgin oil, EVO is a milky looking substance with the consistency of a certain glue kids use in school. The emulsion is injected under water pressure into the subsurface, creating an ideal environment for "in situ anaerobic biodegradation of chlorinated solvents and related contaminants."
In layman's terms, naturally-occurring bacteria eat the oil which reduces the oxygen levels in the groundwater, creating an environment for a second microorganism that breaks down the solvents.
EVO comes in drums or totes and is mixed with water in a batch tank. The mixture is then distributed through a valve assembly of pipes, water hoses and an ejection manifold. The pump is water powered.
The contactor can pump about 800 gallons of EVO into the subsurface per day. But since each site is different, the number of injection wells and the amount of EVO needed will vary, Mr. Anderson said.
Although EVO will last for years, is biodegradable, and poses no health or safety risks, there is one disadvantage. Since the terrain on base varies, there's no guarantee the microbes at a site will eat the oil fast enough to break down the solvent as rapidly as the restoration team hopes.
Such was the case in 2000 when Travis was involved in a pilot program to inject soybean oil in a contaminated soil site south of Hangar Avenue. Before samples could be collected for analysis, base officials decided to excavate the site for a major construction project. That site now houses an office building, the fuel truck maintenance facility and a parking area.
Still, that pilot program prompted AFCEE to test EVO under similar geochemical conditions at Altus AFB, Okla., which ultimately helped to sell EVO as a cleanup strategy. About 60 military and commercial agencies are currently using EVO in their remedial strategies.