By KEVIN BEGOSPITTSBURGH (AP) a¿¿ The U.S. Coast Guard wants to allow barges filled with fracking wastewater to ply the nation's rivers on their way toward disposal. Many environmentalists are horrified, but industry groups say barge transport has its advantages. Now, the wastewater is usually disposed of by truck or rail, which poses more risk for accidents than shipping by barge, according to a government report. And one barge can carry about the same amount of waste as 100 exhaust-spewing trucks. The disagreements go to the core of the fight over shale gas drilling. Environmentalists say the chemicals in fracking waste are a tragedy in the making, but the industry says far greater amounts of toxic chemicals are already being moved by barge, including waste from oil drilling. In 2010, U.S. barges carried 2,000 tons of radioactive waste, almost 1.6 million tons of sulfuric acid and 315 million tons of petroleum products, according to the U.S. Army Corps of Engineers. "We expect that shale gas wastewater can be transported just as safely," said Jennifer Carpenter, of American Waterways Operators, a trade group based in Washington, D.C. Environment America, a federation of 29 state-based groups, strongly disagrees. The group said in a statement that it gathered 29,000 comments opposed to the proposal from people around the country. Courtney Abrams, the clean water program director for the group, urged the Coast Guard to "reject this outrageous proposal." Extracting natural gas trapped in shale formations requires pumping hundreds of thousands of gallons of water, sand and chemicals into the ground to break apart rock and free the gas. Some of that water, along with large quantities of existing underground water, returns to the surface, and it can contain high levels of salt, drilling chemicals, heavy metals and naturally occurring low-level radiation. The Marcellus Shale formation, underlying large parts of Pennsylvania, West Virginia, Ohio and some neighboring states, is the nation's most productive natural gas field. Thousands of new wells have been drilled there since 2008, and hundreds of millions of gallons of wastewater needs to be disposed of each year.