Water is the foundation of life, and in a semi-arid climate where water is scarce, groundwater contamination is a critical problem. To tackle this issue, Oregon State researchers are partnering with the U.S. Army to produce groundbreaking applied research that will ensure clean water for a region that needs it and ultimately contribute to cleaner water throughout the nation and the world.
Starting in the early 1960s, the Umatilla Chemical Depot in Eastern Oregon housed a large supply of ammunition and explosives. Before the risks of dumping wastewater into the ground were fully understood, munitions were washed into a lagoon, which inadvertently created a plume of contaminated groundwater.
“This site is in an arid region where water is precious. So, having a large volume of unusable water is an issue,” said Jack Istok, a professor of water resources engineering at Oregon State.
After the Army identified the contamination, a pump-and-treat process was used to clean up the contaminated aquifer. The process involved extracting the groundwater and filtering it using activated carbon, then re-injecting the clean water through a series of large, horizontal pipes below the ground (called an infiltration gallery).
Unfortunately, the pump-and-treat process is quite slow, so after a few years of pumping and treating, the Army was looking for a more efficient approach. Mandy Michalsen (’07 Ph.D., Civil Engineering), a research engineer at the U.S. Army Engineer Research and Development Center Environmental Lab, partnered with Istok, her former doctoral advisor at Oregon State, to test a more efficient cleanup technology. The researchers used bioremediation, in which microorganisms break down contaminants.
To begin, Istok and Michalsen employed Istok’s single-well, push-pull method, which consists of injecting a prepared test solution into a well and extracting a combined sample of the test solution and groundwater. Within the aquifer, contaminants in the test solution are broken down by a combination of physical, chemical, and microbiological reactions. By measuring the concentrations of the solutes during the extraction phase, the mass of reactant consumed, and the product produced, the research team is able to calculate the reaction rates.
During their push-pull test, Istok and Michalsen amended the solution with fructose, which allowed the microbes to consume electron acceptors, such as oxygen and nitrate, until the environment became anaerobic.
“Under those anaerobic conditions, the contaminants degrade relatively quickly,” Michalsen said. Istok added: “Results of the small-scale, single-well push-pull tests showed that the fructose addition worked and allowed us to predict how fast it would happen. That gave everyone confidence that we could scale up the process.”
To decontaminate more of the area, Michalsen and a team from the U.S. Army Corps of Engineers (Seattle District) and the U.S. Army Engineer Research and Development Center introduced large quantities of fructose-amended groundwater throughout the aquifer by using the existing infiltration gallery that covered the original lagoon.
“It’s been remarkably successful,” Michalsen said. “The extent of the groundwater above the cleanup level is much smaller now. The plume map has changed significantly, and for the better.”
But that’s not where the story ends, she pointed out.
Although the new process removes contaminants, anaerobic bioremediation has drawbacks, including an unpleasant odor in treated groundwater. To improve their process, Istok and Michalsen teamed with a group of researchers to demonstrate how adding bacteria to the groundwater, a method known as bioaugmentation, could avoid some of the water quality impacts associated with anaerobic treatment.
“The special bacteria added can use the contaminants as a nitrogen source for growth under aerobic conditions, using 95 percent less fructose,” said Michalsen.
Now that Michalsen and her team have produced positive lab and field results using the bioaugmentation process and published their results, they are working on additional publications to share their lessons learned and support implementation at other sites.
“Top scientists and engineers worked with stakeholders, including state and federal regulators who offered valuable technical input, to solve problems and clean up a significant portion of the aquifer,” Michalsen said. “I feel really good about the work we did — it was carefully executed, well documented, and wildly productive.”
By JOHANNA CARSON