When we turn on the faucet for a drink of water, most of us don’t think about geology. But the water filling our glasses in the Willamette Valley has direct links back to the last Ice Age and some of the most catastrophic floods on Earth.
“Geology really controls groundwater,” explained Roy Haggerty, a groundwater geologist at Oregon State University. The floods that filled the Willamette Valley left layers of bedrock and sediments that control the location, quality, and vulnerability of our groundwater today.
Haggerty, along with many scientists in OSU’s Agricultural Experiment Station and Extension, has been studying the groundwater in Oregon’s southern Willamette Valley for years. This populous region of the state is heavily dependent on groundwater pumped from wells for drinking and agriculture. Recently, the southern end of the valley has proved to be particularly vulnerable to groundwater contamination, especially by nitrate.
“Nitrate in groundwater may be like a canary in the coal mine,” said Haggerty. “If we have a problem with nitrate in the groundwater, we may have other contamination problems.” Nitrate can occur naturally or be present from manmade sources. In the environment, nitrate forms when proteins from plants, animals, and microorganisms break down. Very water soluble, nitrate is the form of nitrogen taken up by the roots of most plants. But this solubility also makes nitrate hard to manage.
To understand groundwater in the southern Willamette Valley, Haggerty invites us to travel in time to the end of the last Ice Age, when the continental ice sheet melted to form a huge lake in western Montana. Glacial Lake Missoula, held back by a huge dam of ice and debris, held more water than Lake Erie and Lake Ontario combined. Eventually, the ice dam gave way.
A wall of water more than a quarter of a mile high roared south and west, carrying with it icebergs, boulders, trees, and topsoil. In as little as 36 hours, debris-laden water spread out through the Idaho panhandle, rushing down the Columbia River to western Oregon. As floodwaters slowed, they left their mark. The scoured scablands of eastern Washington, the plunging waterfalls of the Columbia Gorge, and layers of cobble, sand, and clay in the Willamette Valley are all signatures of these cataclysmic Missoula floods. In essence, these floods swept up the topsoil from eastern Washington and carried it to the Willamette Valley. Thicker coarse layers of transported material cover the north valley. Thinner, finer layers are found in the south.
“Missoula flood deposits protect groundwater,” Haggerty said. “The sediments slow down the travel of chemicals in the aquifer. This leaves enough time for microbes and natural chemicals such as nitrate to degrade.” The relatively thin deposits in parts of Linn, Lane, and Benton counties are what make the southern Willamette Valley groundwater particularly vulnerable to contamination, he said. Nitrate has been showing up in well water in the southern regions of the Willamette Valley since the 1930s.
There are lots of sources of nitrates and its elemental nitrogen, according to John Bolte, chair of OSU’s Department of Biological and Ecological Engineering. “There’s residual nitrogen in soil from decomposing plants. There’s mineralized organic nitrogen and nitrogen moved in soil after irrigation. There’s nitrogen from fertilizer. When you study where nitrogen and nitrate travel, you have to consider precipitation and temperature as well as fertilizer and irrigation.
“We’ve learned that nitrate contamination not only comes from farming activities but from individuals, too,” continued Bolte. “Home composters, lawn owners, gardeners, and septic owners may contribute to the problem. It is really quite complicated to study and difficult to regulate and control.”
Nitrate pollution tends to enter the groundwater from many sources over large areas rather than from single sources. It can seep from the soil or surface water and percolate down into the saturated groundwater zone to contaminate wells.
Although research is far from conclusive, public health officials have been concerned about possible health risks to people who consume high levels of nitrate in drinking water. “The U.S. EPA’s standard for nitrate in drinking water is at 10 parts per million to protect infants and pregnant women,” explained Audrey Eldridge, a groundwater specialist with Oregon Department of Environmental Quality.
Concern about nitrate in groundwater surfaced in Lane County in the early 1990s, according to Ross Penhallegon, horticulturist in the Lane County office of the OSU Extension Service. “People were pointing fingers, especially at farmers. But there were no data. So I asked everyone, from environmental groups to farmers, ‘Do we have a nitrate problem? And if so, how do we know where this is coming from?’ No one was knowingly putting anything into the water. So I said ‘Let’s test your wells,’ and the local growers went along with me.”
Enlisting his local OSU Extension Master Gardener volunteers, Penhallegon organized a well-water testing program that invited rural landowners to bring in samples of their well water to be tested for nitrate. For seven years testing occurred in communities throughout Lane County. A few nitrate hotspots showed up. Penhallegon narrowed his investigation and eventually helped growers reduce the amount of nitrogen fertilizer they were applying to their fields by an average of 20 percent.
Today, the OSU Extension Well Water Program, funded by the federal Clean Water Act, regularly offers educational clinics to rural Oregon residents and has made contact with hundreds of citizens at county fairs, farmer’s markets, and Extension activities. “We want to help Oregonians learn to protect the groundwater that supplies their drinking water,” explained Gail Glick Andrews, coordinator of the program. To help raise awareness about groundwater and get people to understand risk, the OSU Extension Well Water program offers information on the web and in print, said Glick Andrews.
Part of the information the Extension program shares comes from long-term studies by groundwater hydrologist John Selker and his students and colleagues. Selker’s team has studied the effects of different agricultural practices on groundwater, examining the wide variety of crops grown in the southern Willamette Valley and analyzing 20,000 well water samples, looking for pesticides and nitrate.
“We found that with careful management of irrigation, growers could reduce the amount of nitrate leaching,” said Selker, a professor in OSU’s Department of Biological and Ecological Engineering. When crops are overwatered, the nitrate, which is water soluble, gets washed away with the excess water. So if you water too much, you need to add more nitrate to the surface soil.” One simple solution required only a crescent wrench and a few little nozzles to improve the efficiency of the sprinkers, Selker explained. “It was a simple fix with dramatic results that enhanced production, saved water, saved energy, and saved nitrogen,” he said.
“We have to be patient,” Selker said. “Water moves slowly underground. It may take 10 to 50 years in the south Willamette Valley for water quality to reflect our improved management practices. The groundwater we are seeing now reflects what was happening on the land as far back as the 1960s. The effects of what we are doing now won’t show up for years to come. So, essentially, what we do now will become our future.”