A federal judge ruled for the second time in a month yesterday that a cement plant can’t be opened in a poor black and Latino neighborhood in Camden, N.J. In April, U.S. District Judge Stephen Orlofsky said the New Jersey Department of Environmental Protection had violated the federal Civil Rights Act in giving the plant the go-ahead. Five days later, the U.S. Supreme Court decided in an unrelated case, Alexander v. Sandoval, that a state cannot be sued for policies that discriminate unless it can be shown that the discrimination was intentional. Following that ruling, Orlofsky asked each side in the New Jersey case to submit briefs on how the Supreme Court decision affected their positions. Yesterday, he breathed new life into the residents’ arguments by invoking a federal law enacted after the Civil War as justification for the suit.