Grassroots opposition is springing up against massive dairy operations in California, with environmentalists and community activists worried about the millions of pounds of manure produced by facilities with thousands and even tens of thousands of cows. The animal waste is collected in pits that can be larger than several football fields, and opponents say they pose serious threats to water and air quality. The San Francisco-based Center on Race, Poverty and the Environment has halted a number of dairy projects with lawsuits and is pressing local governments to more strictly regulate the operations.