JOINT BASE SAN ANTONIO-LACKLAND, Texas -- From taming "tower plumes" to conquering contaminants, the Air Force Civil Engineer Center has a long history of leveraging technology to remediate and restore contaminated sites across the United States.
AFCEC, originally known as the Air Force Center for Environmental Excellence when founded in 1991, serves as the Air Force's center for environmental management and remediation expertise and is tasked with providing oversight on Air Force remediation activities.
"The primary focus of our restoration program is to protect human health and to return these contaminated natural resources to their original, uncontaminated state," said Ian Smith, chief of AFCEC's environmental restoration division.
Since 1991, the center has been involved in thousands of remediation efforts across numerous states.
One of its largest cleanup efforts has already spanned 18 years, and involves soil and groundwater cleanup at the Massachusetts Military Reserve, now known as Joint Base Cape Cod.
Both the Air Force and the Army are managing environmental cleanup programs at the base, and are heavily involved in remediating groundwater contamination, known as plumes, and their sources.
Remediating the plumes at Cape Cod presented many challenges. The contamination had spread beyond base boundaries, affecting Cape Cod's sole source aquifer and contaminating many private well systems. The plumes included the contaminants trichloroethene, or TCE, and perchloroethene, or PCE. Ethylene dibromide, or EDB, a highly toxic chemical often used in aviation gas prior to 1984, was also present.
Sixteen contamination plumes were identified by AFCEC's Installation Restoration Program as needing remediation at Cape Cod, and 80 locations have been evaluated as part of the agency's cleanup effort.
Today, 77 of these areas have been remediated and more than 50 billion gallons of groundwater have been cleaned. In addition, over the years the Air Force has replaced impacted drinking water supplies located off base and connected over 1,100 homes in the area of groundwater plumes to municipal water.
"The ultimate goal is to get it all cleaned up while ensuring that nobody is at risk from the groundwater contamination. We've made great progress in doing that over the years," said Douglas Karson, AFCEC community involvement lead at JBCC. "It's quite an exciting time for this program after many years of difficulty."
Two methods of groundwater remediation have proven particularly effective at the base: monitored natural attenuation and "pump and treat."
"Natural attenuation refers to a natural decrease of groundwater contaminants by natural physical, chemical and biological processes," said Dr. Kent Glover, remedial systems expert at AFCEC. "These processes act to reduce contaminants in soil and ground water without human intervention. The term monitored natural attenuation refers to the use of natural attenuation processes to help achieve overall site remediation."
Oftentimes, the decrease in petroleum contaminants is due to biological degradation resulting from microbes naturally present in the soil.
"Nature takes care of a lot of things on her own," said Rose Forbes, AFCEC restoration program manager at Cape Cod. "There are naturally occurring bacteria that degrade the contaminants over time. Microorganisms, such as bacteria, use petroleum products as an energy source like we use food."
The contamination at Cape Cod is also being remediated through engineered treatment systems, which generally has involved pumping the contaminated groundwater from the aquifer, using granular activated carbon to remove contamination, and then returning it to the aquifer or discharging it to a surface water body.
"At the highest point, we were treating close to 18 million gallons per day," Forbes said. "Now, we are treating 12 million gallons per day. The reason for the decrease is that 'pump and treat' does work - groundwater does get cleaned up."
While "pump and treat" systems remove contaminants from the groundwater directly, it is also important to address contamination in the soil above the water table, Glover said.
A treatment method known as soil vapor extraction, or SVE, has been used successfully at many installations to treat the soil above the water table. The technology works by applying a vacuum through a system of underground wells to pull contaminants to the surface as a vapor or gas. The vapor or gas is then treated at the surface, typically by use of granular activated carbon or thermal destruction. In some cases, SVE is used in conjunction with air sparging, which injects air below the groundwater table to increase air flow and improve the removal rate of the contaminant in groundwater.
At Cape Cod and other installations, complex groundwater models have been developed to track and predict movement of the plumes, while regular groundwater monitoring ensures that the contamination is being reduced as predicted and is not affecting drinking water supplies in the area, Forbes said.
In addition to the cleanup projects at Cape Cod, a large number of other AFCEC restoration projects have focused on groundwater remediation over the years.
At the former Reese Air Force Base near Lubbock, Texas, a three mile underground stretch of environmental contamination, once called the "Tower Plume," was reduced by more than 99 percent in less than 10 years.
The former base, closed under the Base Realignment and Closure Act in 1997, had numerous environmental concerns including petroleum products and chlorinated solvents in soil and groundwater, with one of the solvent plumes extending more than two miles off base and impacting more than two dozen residential water systems.
The Air Force issued its first performance-based remediation contract in 2004 to clean up the site, and partnered closely with the Lubbock Reese Redevelopment Authority, the U.S. Environmental Protection Agency and the Texas Commission on Environmental Quality to remediate the site as soon as possible.
Treatment included enhanced in-situ biodegradation, a form of natural attenuation in which bacteria are stimulated to consume contaminants through the addition of a non-toxic compound, such as molasses.
Like Cape Cod, a "pump and treat" technology was also used to decrease the size of the plume by extracting the water, cleaning it and returning it to the area for reuse.
From the original 800 acres of contaminated groundwater at Reese, less than one acre of contamination remains today. Three annual clean sample results are required by environmental regulators before the Air Force can officially complete remediation at the former base, which is scheduled for 2014.
Like Reese, at former McClellan Air Force Base, Calif., AFCEC has implemented an aggressive cleanup program aimed at removing contamination left from the cleaners and solvents used during daily operations at the base.
Treatment methods there also include SVE and "pump and treat" systems. A network of 100 extraction wells provides 1,500 gallons per minute of contaminated water to the treatment plant, which cleans and discharges the clean water to a local creek.
To date, more than 65,000 gallons of volatile organic compounds have been removed from the groundwater. While the majority of contaminants have been removed, it is anticipated that the pumping system will run for another 50 years at McClellan.
SVE treatment has also proven effective at the former base. To date, approximately 1.3 million pounds of contaminants have been removed from the soil there, preventing additional groundwater contamination.
Successful remediation at all installations is not only the result of applying innovative and effective technologies, but is also dependent on collaborative partnerships between the Air Force, contractors, regulators and the community, Smith said.
"By realizing that we all have the same end goals -- to protect human health and the environment -- and then working together diligently to select remedies that promote these goals, we can ultimately undo the damage that was done by these past activities and provide a safe environment for current and future generations," Smith said.