CPS Energy’s Calaveras Power Station ranks 10th in the nation for the toxicity of the material it releases into waterways including nearby Calaveras Lake, according to a new study based on federal data. The report by comes as CPS Energy faces increasing pressure to close down J.K. Spruce, its coal-burning power plant at Calaveras. Spruce is the city-owned utility’s dirtiest power-generating facility and one of the region’s largest sources of air pollution.