… California is the top milk producer in the U.S., with more than 1.7 million cows generating over $8 billion worth of milk, according to the latest state tally, in 2024. But residents in Merced County say that windfall comes at a cost that’s difficult to quantify. Families say dairies are not required to strictly monitor the air nearby. Instead, air quality concerns are handled based on complaints to local agencies and self-monitoring practices. Documentation of negative impacts to water quality depends on when inspections occur and how dairies report waste discharges, so incremental impacts to drinking water remain opaque, residents complain. … Runoff from large-scale farms “can impair both surface and ground water beneficial uses” by producing “significant amounts of coliform, ammonia, nitrate and total dissolved solids contamination,” the Central Valley Regional Water Quality Control Board wrote in a 2019 water quality control plan.