Some states, such as Texas and Ohio, have many underground waste disposal wells. But Pennsylvania has only a few, meaning the leftovers have to be shipped elsewhere.The Coast Guard proposal says barge companies want to move waste from the Marcellus region "via inland waterways to storage or reprocessing centers and final disposal sites in Ohio, Texas, and Louisiana." That means large quantities of waste could be shipped on major rivers such as the Ohio; one of its main tributaries, the Monongahela; and the Mississippi. Critics say that if there were an accident, it could threaten the drinking water supply of millions of people. They also cite the uncertainty around what's in that toxic mix. The Coast Guard is proposing to address that by requiring chemical testing of each barge load before shipment; test results would also be kept on file for two years. A Marcellus wastewater spill wouldn't be any different from other threats, said Jerry Schulte, the emergency response manager for the Ohio River Valley Water Sanitation Commission, which has members in eight states. Occasional spills and other pollution are "a part of life" on industrialized waterways such as the Ohio, he said. "Things happen, whether it's naturally occurring, or spills," he said. Municipal water suppliers also monitor river water, and if there's a spill nearby, they shut intake valves until the problem has passed downriver. One of the largest river spills in the region's history took place in 1988, when an on-shore storage tank ruptured in Pittsburgh, spilling about a million gallons of fuel oil into the river. The sludge flowed down the Ohio River, forcing many water suppliers to shut intakes for a week. But according to a 2011 report by the U.S. Government Accountability Office, the fatality, injury and air pollution rates for barge transportation are far lower than truck or rail transport.