E.P.A. Considers Risks of Gas Extraction," Tom Zeller Jr., New York Times, July 23, 2010.
A public meeting concerning hydraulic fracturing (extracting natural gas "with a cocktail of water, sand and chemicals") at Canonsburg PA was well-attended. People came with horror stories which industry representatives tried to refute.
More regulation, the industry warned, would kill jobs and stifle production of gas.
"Pennsylvania is at the center of the battle over hydraulic fracturing, or fracking, which promises to open up huge swaths of land for natural gas extraction, but whose environmental risks are still uncertain." --------------
"...the potentially enormous natural gas play of the Marcellus Shale has many residents lining up to lease their land to the prospectors."

Fracking mixtures are water, sand, and small amounts of "chemical thickeners, lubricants and other compounds."
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From experience, I can say that no harmful radioactive compounds are included; occasionally some tracers are used to work out migration paths.

I do have worries about the use of the method in many parts of the Marcellus Shale.
The Marcellus is at relatively shallow depths in many areas, and fracking may allow mixing of released gas into aquifers which supply water to wells.
The fracking essentially disrupts parts of the formation. The Marcellus Shale has low porosity and acts as a seal, keeping fluids in formations below it from migrating upwards. Disruption of this seal could allow stored water in aquifers below it to escape, thus reducing the water available for agriculture, home use and limiting the future of usable water in areas under exploration.
Hydraulic fracturing has a long history of use. My experience is limited to its use in oil production, where it was used to open up sands not quite porous enough to release the oil. This was done at depths greater than beds used as aquifers. There were occasional cases where, if there were several porous layers that were drilled through, salt water, e.g., in a lower layer could contaminate potable water in an upper layer.

Examine the geology of the area of your interest; if there are danger points do not allow leasing and work to convince neighbors of the dangers to their water supplies. Talk with University geologists near you to get information.