The study of hydrology goes back at least as far as Noah and the Great Flood. But only recently have hydrologists studied water beneath the surface of the soil.
"It is because soil holds water that we have food to eat," said John Selker, a hydrologist in the Bioengineering Department at Oregon State University. "And it is because soil filters water and chemically changes contaminants that we have water to drink."
Selker tracks how fluids flow through soil. He looks below the surface, between the ground we walk on and the groundwater we drink, at a zone of unsaturated soil where most of our food is rooted and most of our drinking water is filtered.
"As Louis Pasteur said, ‘Luck favors the prepared mind.’ We follow interesting questions, and along the way, we are prepared for lucky encounters and discoveries," said Selker.
Various experiences have prepared Selker for a life of discovery. After graduating from Reed College in 1981, he worked as a carpenter, a photographer and directed development of the optical mouse that is still used with Sun workstations. A stint in Africa opened Selker to the problems of water and contamination.
"I was working in Somalia and Kenya in 1985, at the end of the deepest drought of that century," said Selker. "Water was the key to survival. I saw that designing water systems based on knowledge of how water flows would save lives. For the price of a cow, a family could have a reliable water supply on their farm that would sustain them between storms. I knew this was what I wanted to do. I was hooked."
Following graduate school at Cornell University in 1991, Selker joined the OSU faculty. His investigations, which extend from the green fields of the Willamette Valley to the radioactive soils at the Hanford Nuclear Reservation, began in the lab.
Examining soil microbes in laboratory chambers, Selker and his colleagues found that microbes engage in a kind of dance with soil moisture.
"As they develop, the microbes surround themselves with a soapy, slimy substance they use to access nutrients," explained Selker. "Like soap, this slippery stuff reduces the surface tension of the water, so water can’t get a grip on the soil. Water drains out of the soil and away from the microbes, leaving them surprisingly high and dry.
"So the microbes chase after the water. Microbes and moisture move together in reaction to each other, and by their movement they help form soil structure," said Selker.
Selker’s team now is working on a numerical model to explain this complex choreography.
"It will help us understand not just how, but also why, when and where soil gains the structure that makes it possible to grow plants and filter contaminants," said Selker.
This laboratory discovery prepared Selker’s mind for new questions, as he followed the movement of contamination through the soil at Hanford.
"We’ve known for years that storage tanks at Hanford are leaking into the soil," said Selker. "These huge tanks are filled with millions of gallons of very contaminated salt solutions used to refine plutonium. It’s boiling hot. So, you’ve got radiation, salt, heat and 50 years of time working on big steel tanks. The tanks cracked and the solution leaked."
"Hanford soil was deposited thousands of years ago during a series of Ice Age floods. It’s like a cake with hundreds of layers, and each layer has a gradient of fine to coarse soil. The layers carry the contaminated solution down through the coarse bands and then across the fine bands" said Selker.
"The solution is so salty that it pulls water vapor out of the soil, and the contaminated sediment oozes out between the layers like mayonnaise from a sandwich," said Selker. "We found that the contamination has traveled much farther laterally than anyone suspected."
"Ironically, the same layering structure was hoped to protect the nuclear waste repository at the Yucca Mountain site in Nevada," said Selker. However, studies by Selker’s graduate student Lorrie Flint showed that cracks in the mountain cut through these layers, allowing fluids to move rapidly down through the mountain and likely to the groundwater below.
Tracking contamination through soil led Selker to study how tiles collect water flowing from agricultural fields in the Willamette Valley. Not as toxic as radioactive sediments, irrigation water can carry fertilizer and pesticides to nearby streams and nitrites to groundwater and wells.
"We had expected to find problems with tiles, as effluent shunted into ditches and streams," said Selker. "But we were surprised to find just the opposite."
Selker’s research showed that contaminants that are carried in sediment along the surface of wet soil move down when they hit drained soil, where they are filtered. And tiles block contaminated water from reaching the groundwater and entering wells.
"We found that drain tiles are unexpectedly beneficial in controlling contaminant flow through soils," said Selker. "Drain tile effluent has as much as 1,000 times less pesticide load than surface water from the same fields."
From radioactive ooze to the humble drain tile, Selker’s mind is prepared to court the favor of luck and discovery.