IIRC, the power plant at Centralia put in wet scrubbers to help reduce emissions. The plant at Boardman, on the other hand, has virtually no controls at all, because it was not in an urban area and the Oregon DEQ is more afraid of conservatives in the Oregon Legislature than they are of pollution. Now down-wind areas in other states are paying the price for that lack of foresight. Coal can be burned relatively cleanly if money is spent upfront on control equipment and clean coal-burning technology.