 And that's where the methane is converted into biofuel to power vehicles. But environmental advocates worry methane digesters could lead to more cows and more pollution. Leslie Martinez is with the Leadership Council for Justice and Accountability. This is thousands of cows that are living next to people. A cow is producing waste and we are incentivizing this waste to be produced next to poor communities. The methane problem is especially acute in California, which leads the nation in dairy production.