Like a Cold War relic, the southeastern side of Moffett Field is showing its age with long swaths of empty asphalt lots, shuttered military housing and a former McDonald's that stopped serving burgers years ago.
But amid these drab buildings, there's an oasis of greenery -- a small forest of hundreds of poplar trees tucked between two baseball diamonds.
On a Friday morning, as he does on most days, John Freeman took a walk through the trees, inspecting the leaves for signs of disease or discoloration. It was a routine the 42-year-old had been doing for years, ever since he got permission from NASA Ames officials to plant the trees on an unused dirt lot.
Freeman is no groundskeeper, and his poplar trees are doing more than providing cheerful scenery. In fact, the trees are part of a long-running research program for finding new methods to clean up the chemical contaminants that linger in the area's groundwater. On any given day, his trees are sucking up about 40,000 gallons of toxic water through their roots and then breaking down the worst contaminants into benign byproducts.
Freeman, a plant physiologist, has become NASA's lead expert on phytoremediation -- using plant life to help clean up pollution. This research is showing promise for providing a cheaper, natural alternative to clean up trichloroethene (TCE), the carcinogenic contaminant found in groundwater flowing under Moffett Field, parts of Mountain View and about 1,000 Superfund sites across the United States.
"We have a number of collaborators and we hope to deploy this technology for everyone," Freeman said. "Trees have been used for this for decades, but now we're finding ways to up the efficiencies."
In August, Freeman and nine colleagues published their phytoremediation study based on the Moffett Field poplar trees in the science journal Environmental Science & Technology. Their research is the first phytoremediation field test of its kind, and experts are hailing it as a potential game-changer for the $2.5 billion market for cleaning up TCE contamination.
James Landmeyer, a U.S. Geological Survey research hydrologist who has closely studied phytoremediation, estimated that the technology highlighted in the study showed promise to cut the costs of groundwater remediation by 75 percent, given the right circumstances.
"The biggest benefit of having the trees pumping water from the ground is you're able to effectively remediate a much large volume of water and you're able to do it at a much faster pace," he said. "This is a cleanup method that's publicly appealing, effective and it's not resource intensive."
Even in antiquity, ancient Greek and Roman scholars noted that certain plants could proliferate in metal-loaded soils near mining excavations. For hundreds of years, human communities have unintentionally dabbled in phytoremediation by consolidating their waste in certain areas, often bogs and wetlands, forcing native plants to adapt to survive.
It wasn't until the last 40 years that researchers began deliberately working to identify and harness the microbes in plants that break down specific pollutants. In the lab, this idea has shown promise to break down a wide array of contaminants, including petroleum, explosives, metals and coal byproducts.
Freeman and his research firm, Intrinsyx, originally came to Moffett 17 years ago to support NASA space sciences. Starting around 2013, they received a two-year research grant for the phytoremediation study from the National Institute of Environmental Health Sciences. The project gained later funding from NASA, Intrinsyx, and a Colorado-based phytoremediation firm. To date, the research has cost more than $500,000.
For the experiment, the team decided the best spot to plant the trees would be a sliver of land where maps of the Middlefield-Ellis-Whisman Superfund site showed an underground channel of toxic water flowing north across Highway 101. This was a good location because the trees could serve as a firewall across the groundwater, going right between two wells that would serve for analysis, he said.
Poplars were the obvious plant to use, Freeman said. The trees are "water hogs," each capable of absorbing about 50 gallons a day. Poplars also are easy to uproot and move; they are adaptable and grow easily; and they have deep roots that can bore down into aquifers.
But most important, he said poplar trees are excellent candidates for bioaugmentation, or fortifying the trees with helpful bacteria to help break down specific compounds. Freeman's co-authors at the University of Washington had previously isolated a poplar microbe called Enterobacter PDN3. This bacteria strain was derived from poplars that had grown at a TCE-contaminated site in the Midwest, and it proved to have a ravenous hunger for consuming the chemical.
Prior to planting, Freeman and his team soaked poplar cuttings in a broth of PDN3 in order to inoculate them with the bacteria. Then, along the southeastern border of Moffett Field they planted about 800 poplars, about half of which had no bioaugmentation, to serve as a control group.
As months passed, the bioaugmented trees clearly had an advantage -- they grew taller, with wider trunks and healthier leaves. Meanwhile, the control group's trees apparently suffered from absorbing too much toxic material, showing stunted growth and withered leaves.
Perhaps most remarkable, the bioaugmented trees showed dramatic results in cleaning up the groundwater. Like a river, the groundwater plume flows in a specific direction, and the research team measured samples from a well upstream from the poplars and another one that is downstream. Trace TCE levels were detected upstream, but after the groundwater passed through the line of poplar trees that pollution was reduced to undetectable levels. In fact, the trees also apparently filtered out various other contaminants, including tetrachloroethylene and dichloroethene.
Sharon Doty, a microbiology professor at the University of Washington who co-authored the study, expressed enthusiasm that the new phytoremediation techniques could be quickly implemented at waste sites across the country.
"By partnering appropriate tree species with pollutant-degrading microbes, we were able to advance phytoremediation dramatically," she wrote in an email. "The overall method ... is so easy and so much cheaper than conventional engineering methods that it can be deployed on the many contaminated sites so far being ignored."
For many sites around Mountain View, the predominant system for purging these contaminants is a "pump and treat" method, which can cost up to $3 million per site, plus annual operating expenses. NASA Ames operates three such systems.
In the near future, Freeman said he would like to introduce his team's TCE-fighting trees to office campuses and neighborhoods in contaminated areas.
"We hope this can replace the pump-and-treat systems -- those systems are expensive and electric," Freeman said.
TCE was used as an industrial degreaser and solvent at hundreds of industrial and military sites across the country. In recent years, the chemical has been identified by the Environmental Protection Agency as a carcinogen through any route of exposure. In Mountain View, the biggest risk is via fumes that seep up from contaminated groundwater and build up to unsafe levels inside buildings.
NASA Ames Restoration Program Manager Kimberly Finch told the Voice that the agency will continue pursuing phytoremediation where it is feasible.