From: Tom Gjelten, NPR
Published September 24, 2009 10:57 AM

Water Contamination Concerns Linger For Shale Gas

Advances in technology have helped boost the growth of shale drilling in the United States over the past few years. But as the practice of harvesting natural gas embedded in shale rock deep below the Earth's surface has expanded, it has raised concerns about the impact this type of drilling has on the environment — especially on groundwater.

At issue is the practice of "hydraulic fracturing," which in combination with horizontal drilling is an essential part of the shale gas production process. The shale rock in which the gas is trapped is so tight that it has to be broken in order for the gas to escape. A combination of sand and water laced with chemicals — including benzene — is pumped into the well bore at high pressure, shattering the rock and opening millions of tiny fissures, enabling the shale gas to seep into the pipeline.

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This fracturing technique has been in use since 1948, and industry sources say the procedure has been used in a million gas wells in the years since. But the practice has expanded in the past few years as energy companies began exploring shale formations.

The results have been so successful that energy analysts now see the development of shale gas reservoirs as a key step toward U.S. energy independence and a cleaner environment. When burned, natural gas produces about 25 percent less carbon dioxide than coal.

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