While a popular mantra among water-quality managers declares that “dilution is the solution to pollution,” it doesn’t always work that way.
Helen Dahlke, a UC Davis professor of integrated hydrologic sciences, said stormwater percolating into the ground will flush soil nitrates into groundwater basins, causing levels to jump.
Whether the concentrations drop again soon “depends on how much clean water comes along on the back end,” she said. Flooding will probably provide enough water to dilute nitrate-tainted runoff, while groundwater basins recharged by rainfall alone are likely to remain elevated, she said.
Michael Claiborne, an attorney with the Leadership Counsel for Justice and Accountability, which works with disadvantaged communities lacking clean water, is concerned that farms now or recently flooded have been swamped by filthy water that is now percolating into groundwater basins. These farms include Central Valley parcels intentionally flooded after Gov. Gavin Newsom issued an executive order on March 10 to encourage using stormwater to recharge depleted groundwater.
“There are a lot of dairies that are completely flooded, and that includes the lagoons where they store their manure,” he said.
Other groups, including the Community Water Center and Clean Water Action, have also raised concerns that the recent flooding of lands saturated with fertilizers and pesticide residues will contaminate groundwater.
We don t know whether a lot of recharge on these lands will make (nitrate contamination) worse or push it out.
Patrick Pulupa, Central Valley Regional Water Quality Control Board
Patrick Pulupa, an executive officer with the Central Valley Regional Water Quality Control Board, said it’s unknown how flooding will affect basins underlying large dairy farms.
“We don t know whether a lot of recharge on these lands will make (nitrate contamination) worse or push it out,” he said.
In some places, floodwaters have had clear and immediate impacts on groundwater.
In February, a levee protecting the small Tulare County town of Seville breached. Water swamped many properties and overtopped several drinking water wells.
Homeowner Linda Guttierez, who also serves on the town’s water service district, poured bleach into her well to kill any pathogens that might have entered the system.
Seville often doesn’t have enough water. Last summer and again in the early winter, farmers nearly depleted the community’s wells, she said. To get by, drinking water, paid for by the state, is delivered to residents. The community of about 600 people has also received a $1 million grant to drill a new, deeper well.
“Be careful what you ask for, because you just might get it, and you might get it all at once,” Guttierez said.
Water deliveries are a short-term fix
Thomas Harter, a UC Davis professor who co-authored the nitrate report for state officials, said the contamination will haunt at least another generation of Californians. That’s because the lag time between the application of fertilizer and its entry into groundwater basins can be many years, and decades more may pass before the nitrate reaches a well.
“Even if we were able to change how we manage agricultural fertilizer today, it would still take years or decades before wells actually see an improvement,” he said.
In southwest Sonoma County, a few miles west of Petaluma, the local groundwater is unsafe to drink — and the source of the issue is plainly visible. Beef and dairy cows range freely over the watersheds and creek bottoms that drain toward Bodega Bay.
Their manure festers in muddy watering holes, and for locals in and around the small town of Valley Ford, this means living on bottled water.
“Even if we were able to change how we manage agricultural fertilizer today, it would still take years or decades before wells actually see an improvement.”
Thomas Harter, UC Davis professor
Sampling of Valley Ford’s three main wells last June found nitrate at twice the federal drinking water standard of 10 milligrams per liter, and a few months earlier it was nearly triple, at 28. More recent sampling found it at almost 12, still enough to prompt a notice from the state warning residents that pregnant women and infants should not consume the water. Locals declined to discuss the issue with a CalMatters reporter.
State programs to bring safe drinking water to communities affected by nitrate are now serving at least 1,048 households in the San Joaquin Valley and about another 300 in the Central Coast region. These initiatives include the Central Valley Salinity Alternatives for Long-term Sustainability program, and the State Water Resources Control Board’s Cleanup and Abatement Account.
