UC Toxics News: Spring 2001
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Groundwater
Experts Study Effects of Dairies, Pesticides and Fertilizers by Sylvia Wright Editor's Note: The research of Graham Fogg, Miguel Mariño, and Timothy Ginn is partially funded by the TSR&TP. |
Timothy Ginn focuses on how to predict contamination arrival at a water well when such detailed information isn’t available. He is building a model that integrates all the possible chemical, physical and microbiological phenomena that affect contaminant travel. His two main tools are streamtubes and memory. Streamtubes are the pathways through the gravel beds of an aquifer. Memory is a characteristic of some chemical reactions; the rate of the reaction is influenced by how long the agent has been at the reaction site. For example, when certain groundwater contaminants diffuse into a paleosol, they stick to the grains of the paleosol. The rate at which they come unstuck depends on how long they’ve been stuck. Ginn is collaborating with Tom Young, assistant professor of civil and environmental engineering, on models that take into account both these memory effects and transport in streamtubes.
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Timothy Ginn models contaminant travel using techniques
he has developed for situations when subsurface details are scanty. |
Ginn, an associate professor of civil and environmental engineering, came to UC Davis in 1997 from the Department of Energy’s Pacific Northwest National Laboratory. Pacific Northwest helps the Department of Energy clean up aquifers underlying nuclear-weapons production sites, which are some of the most contaminated sites in the world. One of these sites, the infamous Hanford atomic-weapons reservation adjacent to the Pacific Northwest lab, is the most contaminated subsurface site in the United States.
Long list of contaminants
Ginn can rattle off every category of groundwater contaminant
known to science—and it’s a long list. There are agrichemical agents
such as pesticides, fungicides and fertilizers; industrial agents such as
trichloroethylene, a solvent contaminating more than half the Superfund sites;
heavy metals such as cadmium, lead, nickel and arsenic from industrial processing,
weapons production and mining operations; radioactive wastes such as isotopes
of the elements uranium, cesium and strontium from nuclear-weapons research
and production; naturally occurring inorganic mineral salts; nutrients such
as nitrates and phosphates from fertilizers; and microbiological agents from
livestock wastes, such as bacteria, viruses and protozoans.
Ginn is pretty sure he won’t run out of work. "I
went into this field 20 years ago because I was interested in cleaning up
groundwater," he said. "Often in the sciences, the research questions
change. This hasn’t. It’s gotten worse and worse and worse. There’s
more groundwater to be cleaned up, the problems are continuing to grow, and
the supplies are continuing to diminish."
Mariño’s pesticide expertise
Another faculty member, Miguel Mariño, is known worldwide
among hydrologists for his expertise in groundwater contamination by agricultural
pesticides and nutrients. Mariño is a professor of hydrologic sciences,
civil and environmental engineering, and biological and agricultural engineering.
He and former student Mohamed Hantush developed a model that is widely used
by water regulators and managers to predict the expected effects of various
pesticides in both groundwater and surface water. The model is used to maintain
aquifers under corn and soybeans in Maryland, sugar cane in Australia and
golf courses in Spain. Mariño also uses models to address problems
of groundwater recharge and sustainability. As his colleagues have shown,
much of the water underground is "fossil water" that took a long
time to accumulate. Once pumped out, it isn’t easily put back.
In a recent project funded by the UC Water Resources Center,
Mariño and past students Keith Larson and Hakan Basagaoglu analyzed
historical irrigation practices to study land subsidence in the Los Baños–Kettleman
City area. He found the ground had already sunk as much as 28 feet during
1926–1972 and predicted future subsidence based on various growth scenarios.
"A lot of folks at the state and federal levels are
very interested in these questions. What areas can you pump the most from
and which should you stay away from?" Mariño said. "If present
practices could be sustained for 30 years for the Los Banos–Kettleman
City area, land subsidence would not be a serious problem. However, with the
continued growth of urban populations to the south and ecological concerns
about water exportation from the north, those practices may not be sustainable."
Teaching water users about all these findings is hydrologist Thomas Harter,
an associate UC Cooperative Extension specialist. Harter is the only groundwater
extension specialist in California and one of a few in the country. He spends
about half his time teaching people outside the university what is known about
groundwater and how they can put that knowledge to work to protect the resource
and save themselves money. His students include water managers, public planners,
policy makers, growers, ranchers and agricultural consultants.
Contributing to education
"Thomas’ contributions to public education are
huge, because when people try to manage groundwater or to legislate policy,
the outcomes are dominated by misconceptions," said UC Davis hydrogeologist
Graham Fogg, who often teaches in Harter’s workshops. "We’ll
never get past that until more people are educated on the fundamentals of
groundwater."
Said Harter, "My students are people in the real world
struggling to understand groundwater issues. I have seen the help I can give,
and it is great to see how it helps people make better decisions."
For the past five years, Harter has been based at UC’s
Kearney Agricultural Center, just south of Fresno. Last fall, in response
to rising requests for his expertise at the state capital, he moved his main
office to Davis. He will continue outreach in the Central Valley.
Harter also has a very active research program. One project
is a study of whether dairy operations have a significant impact on groundwater
quality. It’s an important question in California, where 1.4 million
cows produce most of the nation’s milk—and about 60 billion pounds
of liquid and solid manure annually.
Where does manure go?
Dairies typically deal with all that waste by spreading
it as fertilizer over the fields where they raise forage crops for the cows.
But it hasn’t been clear whether all the constituents of the manure,
some of which can make people sick, are taken up by the growing crops or else
filtered out in the soil. If not, they could be seeping into aquifers.
A key constituent of manure that Harter is tracking is nitrogen,
which turns to nitrate in groundwater. When consumed at high levels in drinking
water, nitrate can interfere with oxygen transport in babies and lead to "blue-baby
syndrome." To find out if high levels of nitrate are traveling from dairies
to drinking water, Harter has built a network of 79 wells on five cooperating
dairies in the San Joaquin Valley; it may be the most densely monitored dairy
system in the nation.
Harter is also working with Fogg and Ginn to make the group’s complex
models useful outside the research community, to Harter’s people in the
real world.
Said Fogg, "Today we are building models with millions
of bytes of information. One day we hope to have smarter mathematics that
will allow us to do the analyses more simply—perhaps even without a computer,
or with just a calculator."
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