A coal-fired power plant is a menace to its neighbors. It coats their homes with dust and ash. It emits nauseating gases. On some days, the pollution is so bad that the neighbors do not go outside, and do not open their windows. Visitors to the area are shocked at the conditions. They cannot fathom how the plant is allowed to operate in this manner, so obviously polluting the air that its neighbors breathe. The neighbors frequently complain to the regulatory authorities, but they are told that the plant is complying with regulatory standards, which—according to the regulatory authorities—is all that the plant is required to do.

Finally, a group of the neighbors contacts an environmental law attorney. The attorney explains to them that, regardless of whether the power plant is violating regulatory standards, it is violating their common law rights: it is committing a trespass against them if it is coating their properties with dust and ash, and it is causing a nuisance to them if its dust and ash and gas are substantially interfering with their use and enjoyment of their properties. Contrary to what the regulatory authorities have implied, the power plant is not doing all that it must to satisfy the law. It is violating the common law of trespass and nuisance.

Several of the neighbors retain the attorney, who files a class action in their names. All residents living within one mile of the plant—more than two thousand of them—become a part of the class. Joined together in one lawsuit, they have enormous leverage. The case ultimately settles. The power plant agrees to invest millions of dollars in advanced air pollution control systems, and to compensate the class members for their loss of use and enjoyment of their homes.