Activists can work for years before Congress takes notice.

Just ask Theo Colborn, a scientist in Colorado who started studying the environmental impact of natural gas drilling in 2002. She has worked with dozens of grassroots groups to highlight the dangers of a natural gas extraction method.

Earlier this month, Colborn's message reached Capitol Hill. Lawmakers spent the better part of a hearing on ExxonMobil's proposed merger with XTO discussing hydraulic fracturing, or "fracking."

Companies use the technique, which requires pumping millions of gallons of chemical mixtures into the ground, to extract natural gas from shale rock. Environmental groups say the process contaminates drinking water.

XTO, a natural gas supplier, owns many of the nation's shale reserves, and ExxonMobil plans to mine those for natural gas. The oil executives testified that fracking would create jobs and provide Americans a domestic fossil-fuel alternative.

"It's tantamount that we find a way to continue that practice because it is such a valuable resource," XTO Founder Bob R. Simpson testified.

Simpson said the environmentalists' concerns were overblown, and that multiple layers of steel casing keep the chemicals from seeping into drinking water.

Colborn and her allies say they have the data to prove otherwise. They are pushing for regulations that would require the companies to disclose what chemicals are used in fracking.

To counter a lobby as strong as the oil and gas industry, Colborn reached out to local and national groups.

Together, the coalition of grassroots organizers and national lobbyists has been able to prompt action from local officials, members of Congress, and the Obama administration.

But the success was years in the making.