Digesters, which cost millions of dollars and require economies of scale to make financial sense, have spread across the Central Valley in recent years. They process dairy manure to extract and refine methane for sale as a renewable transportation fuel.

Concerns about the growth of U.S. dairies, particularly in California, resurfaced in February with Food & Water Watch’s release of an analysis of data from the U.S. Department of Agriculture.

The group said the state’s average dairy herd size rose 72% between 2002 and 2022 to reach about 2,300 head. During the same period, it found, California lost about three-quarters of its family-scale dairies as the state tilted more toward what it called factory farming.

It said the problem with that trend is the amount of pollution and waste large dairies generate. According to Food & Water Watch, the 24,000 U.S. factory farms produce a combined 940 billion pounds of manure per year, or about twice as much sewage as the country’s human population.

While California does have large dairies, their average size ranks no higher than ninth among U.S. states, according to a report by Hoard’s Dairyman. Using federal data, the news source reported in January that New Mexico led the nation in average herd size in 2021, followed by Arizona and then Colorado.

In an email Monday, Co-Executive Director Phoebe Seaton at the Fresno-based Leadership Counsel for Justice and Accountability cited concerns that herd expansion and continued concentration of cows and waste will worsen air and water pollution.

Seaton blamed state policy for financial incentives she said make it more attractive for dairy owners to increase the size of their herds.

“Various subsidies designed to encourage the conversion of waste to gas seem — as evident in (Poso Creek Family Dairy #2’s) expansion — contribute to the concentration of pollution,” she wrote.