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For the second time in a year, a major environmental organization has published a report ripping the prospect of Utah and Colorado oil-shale development as an environmental and economic disaster.

The Natural Resources Defense Council released a 42-page report Thursday warning that a shale rush could deplete Colorado River Basin water, causing agricultural and municipal shortages affecting 30 million people and 15 percent of the nation's crops.

"Water is life in the arid West and already there is not enough to meet current demands," the authors wrote in "Between a Rock and a Dry Place: The Impact of Oil Shale Development and Climate Change on the Colorado River Basin Water Supply."

It comes nearly a year after Western Resource Advocates released a similarly sized report questioning shale's economics and environmental footprint. The two reports punctuate a period of renewed activity in oil-shale prospecting. An Estonian company that uses the rock has bought a Utah claim, and the U.S. Bureau of Land Management has begun a study that will determine how much public land to lease for such efforts.

The NRDC report notes a 2011 U.S. Bureau of Reclamation finding that the long-term Colorado basin water yield is 14.7 million acre-feet a year — a half million less than the Southwestern states that own it have used on average since 2000. It adds that government climate outlooks predict still less moisture for the region in coming decades and says any water used for oil-shale mining and processing would deplete the source and lead to struggles.

The outcome of those struggles hasn't been widely discussed, but it could harm rural Utahns most, NRDC senior scientist Monty Schmitt said Thursday.

"There are existing users for that water," he said, "and the losers are most likely going to be agriculture."

It's already clear, Schmitt added, that the region's continued urban development will require buying out farm water rights and shale development would add a new contributor.

Oil shale is a rock containing a waxy hydrocarbon that can be mined and heated to the point to giving up an oil-like liquid. America's richest known deposits are in eastern Utah and western Colorado, along with some in Wyoming.

The industry, which has yet to prove it can economically extract the energy, increasingly contends that it can do so with minimal water use.

Enefit American Oil, a U.S. subsidiary of the Estonian Eesti Energia, plans to bring Utah "the most efficient and environmentally advanced shale oil technology available today," company communications officer Elina Kink said in an email response to questions about the process. "It doesn't need additional power to operate, nor does it use water."

The company's planned Uintah County mine will "minimize water use," she added. Company officials have previously said they will need some water for dust suppression.

Using Government Accountability Office numbers for an estimated mid-range development of about 15 million barrels a day, NRDC says shale would require about 360,000 acre-feet of water, or about 1½ times what Denver uses.

Technological "trade secrets" notwithstanding, Schmitt said, those are the latest figures "deemed credible by the federal government."