If you needed to find out how much pollution an industrial plant in your neighborhood was spewing, or what toxic chemicals were in a local river, where would you go? Until recently, you could discover the answer at one of the Environmental Protection Agency’s 29 libraries. But now the E.P.A. has obstructed the American public — as well as its own scientists and staff — by starting to dismantle its crown jewel, the national system of regional E.P.A. libraries.