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More than a quarter million Californians rely on groundwater with nitrate levels in excess of state guidelines, according to a study released Tuesday by UC Davis researchers.

“First and foremost, this is a safe drinking water issue," says lead researcher Thomas Harter, groundwater hydrologist in the Department of Land, Air and Water Resources at Davis. "Nitrate will be an issue for decades to come, as past and present applications to the landscape take years to appear in drinking water wells.” Excess nitrate can reduce oxygen flow in infants, called Blue Baby Syndrome.

The State Water Quality Control Board contracted with UC Davis to conduct the study, as mandated by Senate Bill X1 2. Though Harter and co-author Jay Lund, professor of engineering and director of the UC Davis Center for Watershed Resources, say that nitrate in groundwater isn't a new problem, it's getting worse: They estimate annual leaching is up by 50 percent from last time a report went to the Legislature 25 years ago.

"Nitrate in drinking water today is a legacy contaminant, but years and decades from now the nitrate in drinking water will be from today’s discharges," the study says.

Though some of that nitrate originates with sources like leaky sewer lines, at least 90 percent comes from agriculture, according to the study. The problem, Harter says, is that plants don't take up as much nitrogen as is applied to the soil as fertilizer.

It's an issue that the Central Coast Regional Water Quality Control Board will take up Wednesday at a meeting in San Luis Obispo, where they're scheduled to vote on agricultural runoff rules known as the agricultural waiver.

Harter and Lund examined the Monterey County portion of the Salinas Valley and the Tulare Lake Basin in the Central Valley. In examining excess nitrogen applied to ag land, they found field crops, like those grown in the Salinas Valley, are the second worst offender after grain, and trailed by nuts, cotton, rice and tree fruit, which the researchers say don't require as dramatic reductions in fertilizer.

The study found the cost of cleaning up groundwater could run as much as $30 million annually for decades. It offers proposals to reduce nitrate contamination, including a cap-and-trade program for pollutants or levying an excise tax on runoff which could be used to create a cleanup fund.

Harter and Lund also recommend better monitoring, and themselves had to rely on modeling to fill gaps in the available data. "Information disclosure would have dischargers of nitrate or users of nitrogen make such information public," the report states. "Such disclosures should provide some motivation to reduce nitrate discharges."

Though the report doesn't specifically cover the ag waiver specifically, supporters of stricter runoff regulation view Harter and Lund's as a reason the board should approve the new rules.

“Growers need to buck up and face the reality that their pollution is harming the environment and jeopardizing the health of tens of thousands of residents," Steve Shimek, executive director of The Otter Project, said in a statement.

Shimek has long pushed for a stricter ag waiver and has pending civil complaints against the Monterey County Water Resources Agency for nitrate pollution and the Regional Water Board for extending the existing ag waiver for years. For him, this study should encourage the board to act tomorrow. "The Salinas Valley has the most innovative and resourceful growers in the world and it’s time for them to become better stewards,” he added.

Representatives of the Grower-Shipper Association and the Monterey County Farm Bureau could not immediately be reached for comment. But at Wednesday's hearing, ag interests will be joined by Congressman Sam Farr, D-Carmel, in urging the board to reject the staff-proposed rules and instead adopt an alternate proposal written by CSUMB Professor Marc Los Huertos. His report, commissioned by a coalition called Farmers for Water Quality, recommends continued monitoring on an aggregate basis, rather than singling out specific farms.

In some respects, Harter agrees with Los Huertos, especially when it comes to applying universal assumptions to nitrate runoff: "There is no one size fits all solution, whether that’s on the safe drinking water side or the farming side," Harter says.