Cleaning Up Our Drinking Water
August / September 2007
Volume 5 Number 4
Imagine drinking water that you wring out of the sponge you've just used to wash your car. This is what is happening around the world. Rain and snow pass through soil polluted with pesticides, poisonous metals and radionuclides into the underground lakes and streams that supply our drinking water.
Biologists, statisticians, hydrologists, geochemists, geologists and computer scientists at Pacific Northwest National Laboratory are working to clean up contaminated soils and groundwater. The teams begin by looking at the complexities of the whole environment, not just the soil or just the groundwater. PNNL researchers perform work for private industries under a unique use agreement between the Department of Energy and Battelle, which operates the laboratory for DOE. "We need to understand this natural system better to protect our groundwater and, by extension, our drinking water," said Wayne Martin, PNNL's applied geology and geochemistry group manager. This research leads to new remediation methods and technologies to tackle problems ranging from arsenic at old fertilizer plants to uranium at former nuclear sites. The results help regulators, policy makers and the public make critical decisions on complex environmental issues. These include:
FERTILIZER
In the mid-1800s, fertilizer manufacturers began obtaining the plant nutrient phosphate by processing apatite ore with sulfuric acid. One feedstock used for the onsite production of sulfuric acid was pyrite ore, which contained trace amounts of arsenic and lead. Waste fluids and solids from acid and fertilizer production were disposed of at the sites.
Today, researchers are helping petrochemical companies and others deal with the long-term legacy of contamination and costly cleanup problems at sites in South Carolina and Massachusetts. First, the teams locate contaminated areas. This can be a vexing problem as records may have been lost in the intervening century.
Next, they evaluate the site to determine the physical and geochemical processes controlling migration of the dangerous metals. Finally, they help design customized remediation methods to deal with the challenges of each site's soil. The researchers also assist with long-term monitoring.
PESTICIDES
It's good that pesticides are toxic to insects that can destroy food crops and carry malaria or other diseases. However, when these chemicals are disposed of improperly, the consequences can be devastating to humans and the environment. Just how devastating is what PNNL's geostatisticians helped determine.
Geostatistics combines geology and mathematical statistics to better understand the spatial distribution of one or more pollutants within a complex environment.
When high levels of pesticides were discovered on southern California's coastal shelf, PNNL scientist Chris Murray was asked to produce maps showing the thickness and contaminant concentrations of the polluted sediment. The client used the maps to estimate the mass of contaminants on the shelf and identify the sample locations that would provide the most valuable information at the lowest cost. The Environmental Protection Agency used the same maps to evaluate cleanup options.
EXPLOSIVES
Explosives are stored in depots around the country. Some of the containers at these depots have leaked chemicals into the soil. If the chemicals are near the surface, they can often be removed by digging up the explosive-laden soil and safely packaging it for disposal. But if they have leaked deep into the soil, they are far harder to treat and require a more sophisticated method.
That's the problem that scientists at PNNL are figuring out how to solve with some unique combinations of methods. The researchers are getting some exciting results for the explosives RDX and HMX.
Researchers begin by creating a reducing environment in the subsurface. Electrons easily add themselves to the explosives, breaking them into smaller chemicals. Next, microbes in the soil are fed glucose and trace nutrients. The microbes become more active and break apart the smaller chemicals into carbon dioxide and water.
"In laboratory tests, this combined method shows rates significantly faster than either treatment alone," said Jim Szecsody, the lead scientist on this work.
RADIONUCLIDES
About 2 million curies of radionuclides lie beneath the Hanford Site, a former plutonium production complex in southeastern Washington State. One concern is a persistent plume or smear of uranium that is moving underground toward the site's eastern border and the Columbia River. PNNL researchers have taken a holistic approach to understanding where the uranium will move and how it will react. They are studying not only the chemistry of the subsurface sediments and the effect is has on the uranium, but also how soil-inhabiting microbes may change the uranium. Microbes may change the number of electrons in a uranium atom. This slight change can render the uranium immobile and force it out of the groundwater.
"By looking at the microbes as one part of the subsurface environment, we're developing methods to monitor the effectiveness of treatments that halt the migration of uranium and protect the river," said PNNL scientist Terri Stewart, who is working with DOE on subsurface cleanup issues nationwide.
To reliably and cost-effectively test for uranium where the groundwater bubbles into the river, PNNL's scientists are looking at that ecosystem, which includes fungi, bacteria, algae and other small organisms living in the river. This team of ecologists, biologists and computer scientists is searching for biological signatures—€”a collection of genes, proteins and metabolites—€”that indicate the ecosystem has encountered uranium.
LOOKING AHEAD
The future of subsurface science may be up in the air, literally. Researchers are working to safely incorporate the greenhouse gas carbon dioxide into the subsurface. As part of a large consortium, the researchers are looking at the feasibility of pumping the gas deep underground. There, it would react and become harmless minerals within the soil.
Kristin Manke is an information specialist at the Pacific Northwest National Laboratory.
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