Digging into dirt -- Subsurface science at PNNL

Imagine drinking water that has dripped through the sponge you’ve just used to clean the breakfast dishes. This is happening around the world. Rain and snow pass through soil polluted with pesticides, poisonous metals and radionuclides into the underground streams that supply rivers, lakes and drinking water. “We need to understand this system better to protect our groundwater and, by extension, our drinking water,” said Pacific Northwest National Laboratory’s Applied Geology and Geochemistry Group Manager, Wayne Martin. PNNL builds synergistic teams of experts, including biologists, statisticians, hydrologists, geochemists, and computer scientists. These teams study the complexities of the whole environment, not just the soil or groundwater. The teams provide regulators with answers to make complex decisions and design innovative technologies to capture or convert pollutants.

Dealing with Arsenic and Lead at Old Fertilizer Plants In the mid 1800s, fertilizer manufacturers began obtaining the plant nutrient phosphate by processing apatite ore with sulfuric acid. Pyrite ore, with traces of arsenic and lead, was a feedstock used for the onsite production of sulfuric acid. Waste fluids and solids from acid and fertilizer production were disposed of at the sites. Over a century later, researchers at PNNL are helping ConocoPhillips and others deal with the long-term legacy of contamination and costly cleanup problems at sites in South Carolina and Massachusetts. The teams locate contaminated areas, evaluate the site to determine the physical and geochemical processes controlling migration of the dangerous metals, help design customized remediation methods, and assist with long-term monitoring.

Stopping Radionuclides at a Nuclear Weapons Site

Beneath the Hanford Site, a former plutonium production complex in southeastern Washington, lie about two million curies of radionuclides. One concern is a persistent plume or smear of uranium that is moving through the subsurface toward the Columbia River bordering the Site on the east. PNNL researchers have taken a holistic approach to understanding where the uranium will move and how it will react. By looking at the whole of the environment, not just the soil, researchers can develop methods that stop the migration of uranium and protect the river. To reliably and cost-effectively test for uranium in the hyporheic zone, where the groundwater bubbles into the river, PNNL researchers are looking at that ecosystem, including microbes and fungi that make up common rock slime, which grows at the river’s edge. By including ecologists, biologists and computer scientists, this team is searching for genes, proteins or metabolites that indicate the ecosystem has encountered uranium.

Mapping the Results of Pesticide Dumping

DDT and other pesticides are, by definition, toxic to insects that can destroy food crops and carry malaria or other diseases; however, when companies dispose of these chemicals 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 and can be used to understand the spatial distribution of one or more pollutants through a complex environment. When high levels of pesticides were discovered on southern California’s coastal shelf, PNNL Staff Scientist Chris Murray was asked to produce maps showing the thickness and contaminant concentrations of the polluted sediment. The Environmental Protection Agency used the maps to evaluate cleanup options.

Looking Ahead

The future of subsurface science may be up in the air, literally. Researchers at PNNL 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.