Oil shale production's impact on water supplies is potentially large but difficult to quantify and pinpoint, according to an official with the General Accountability Office (GAO) who testified Wednesday before a House natural resources subcommittee.

Anu Mittal, director of GAO's natural resources and environment team, told the congressional panel that in the early stages of the potential development of the world's largest oil shale deposits in the Green River Formation in parts of Utah, Colorado and Wyoming it is impossible to quantify future impacts on water resources with any accuracy.

"There are a number of uncertainties associated with the impacts that a commercially viable oil shale industry could have on water availability and quality that should be an important focus for federal agencies and policymakers going forward," said Mittal, who relied heavily on an October 2010 GAO report that made recommendations to the Interior Department regarding oil shale development in the three western states.

She reminded the elected representatives that since 2006 the federal government has spent $22 million on oil shale development research with about $5 million of that going toward the "nexus" of oil shale and water. But the report from last October recommends more studies by Interior to develop "comprehensive baseline conditions" for groundwater and surface water quality in both the Piceance and Uintah Basins.

Mittal stressed that there still exists "a lack of comprehensive data" on the condition of surface water and groundwater and their interaction. This lack of data in turn limits any efforts that the states or federal government might develop to monitor and mitigate future impacts of oil shale development, she said.

Both Interior's Bureau of Land Management and the U.S. Geological Survey have been working on addressing modeling needs related to the unanswered water questions.

In summarizing the October 2010 report, Mittal noted that the water-oil shale conundrum is further exacerbated by the effects of nearly 10 years of drought in the West and the projections for a warming climate in the future.

"Some analysts project that large-scale oil shale development within Colorado could require more water than is currently supplied to more than one million residents in the Denver metropolitan area, and that water diverted to oil shale operations would restrict agricultural and urban development."

Since "only speculative assumptions" can be made at this point about the extent of the future oil shale development in the region, meaningful analyses of water impacts are still not possible, Mittal said in her 15 pages of written testimony.