Central Valley aquifer contamination probed

TULARE
March 3, 2008 12:01am

The ground water near some of the more than 1,600 dairies in the Central Valley may be contaminated to the point of being undrinkable. But a team of scientists is trying to determine whether the dairies are the cause or other factors are at work.

A $1.56 million grant from the State Water Resources Control Board and the CALFED Bay-Delta Program is funding testing and studies of soil and water samples in Tulare and Kings counties.

"We believe there are many non-dairy sources of nitrate in groundwater," says UC Davis Cooperative Extension groundwater hydrologist Thomas Harter.

"Golf courses, water treatment plants, septic tanks and agricultural operations have all been implicated in groundwater contamination. If we find contamination, we want to know where it came from,” Mr. Harter says. “We are developing the technology to distinguish between, for example, nitrate derived from synthetic fertilizer and nitrate derived from humans or animals."

Last summer and fall, rigs drilled wells 140 feet, or about 14 stories, deep next to dairy waste lagoons, near the fields where manure is used as fertilizer, and adjacent to the corrals where cows spend the bulk of their time to extract soil cores.

The soil cores will help scientists understand the interaction of nitrogen's three forms with the different types of soil. Dairy manure water contains two forms: organic nitrogen and ammonium. When it is exposed to microbial action in soil, the organic nitrogen transforms to ammonium. Over time, the ammonium nitrogen converts to nitrate with the help of the oxygen in the top layer of soil.

Monitoring wells on dairies in Stanislaus and Merced counties, where the soil is sandy and the groundwater in some places is only 10 feet below the surface, are producing soil cores with higher levels of nitrate than found in cores taken in Tulare and Kings counties, the scientists say.

"We found high levels of nitrate in the top 10 to 20 feet of groundwater," Mr. Harter says of the samples from the northern end of the Valley.

Mr. Harter says he is confident that the data generated by this project will allow scientists to establish guidelines for monitoring and managing groundwater impact from dairies.

"It's a matter of getting the production management practices down to the right level," he says. "There are issues with the environment in running a dairy. I think we can use the data from this research to help determine how management practices must be modified so dairying can continue in a sustainable and economically viable manner."