The Colorado River — the water source for 25 million Americans — is almost certainly on a collision course with a massive pile of uranium slag, according to a report released yesterday by the Department of Energy’s National Research Council. The 12 million tons of tailings, located near Moab, Utah, are left over from a uranium mill that provided material for nuclear weapons prior to being shut down in 1984. The council’s report said it was a “near certainty the river’s course will run across the Moab site at some time in the future.” Less certain is when; rivers tend to migrate, and the Colorado could reach the slag heap in a matter of years or a matter of millennia. The Clinton administration unveiled a plan to move the heap further from the river at an estimated cost of anywhere from $300 million to $1 billion, but the Bush administration put the plan on hold pending further study.