A coalition of conservation groups from around the Bay watershed is urging the U.S. Forest Service to stick to the prohibition on horizontal drilling for natural gas that it proposed in its draft management plan for the George Washington National Forest.

Their letter - along with a campaign that generated more than 50,000 comments from individuals - sought to bolster the proposed restrictions on drilling in the Marcellus Shale, which have drawn fire from members of Congress and the administration of Virginia Gov. Bob McDonnell.

The 1.1-million-acre forest, located in Virginia and West Virginia, is the largest single federal landholding in the Bay watershed.

The management plan proposed this spring would prohibit the drilling technique needed to access the gas in the deep Marcellus Shale formation underlying about half of the forest. No such prohibition was in the previous management plan.

Although there has been little interest to date in drilling in the Marcellus formation within the forest, the natural gas industry and its supporters in Congress worry that any drilling prohibition would set a precedent for other federal lands.

The draft plan led to a congressional hearing in July in which Rep. Doug Lamborn, R-CO, chairman of the House Energy and Mineral Resources Subcommittee, said the Forest Service "would essentially close the entire forest to a safe and efficient means of energy development."

Joe Holtrop, deputy chief of the Forest Service, insisted at the hearing that the plan did not set a national precedent, saying that forest management plans are "place based" documents for individual forests, and take into consideration local concerns. Horizontal drilling has been opposed by several counties and cities adjacent to the forest.

"I want to be clear," Holtrop said, "the U.S. Forest Service has no policy, nor do we have any plans to develop any policy to ban horizontal drilling and the associated hydraulic fracturing."

Extracting gas from the Marcellus Shale, a formation that stretches from southwestern Virginia to New York, has been controversial because accessing it requires drilling deep wells, then drilling horizontally.

Water and a wide variety of chemicals are pumped into the well under very high pressure to break up rocks, a process called hydraulic fracturing, or hydrofracking for short. The process creates large volumes of wastewater. This wastewater, bearing minerals, chemicals and sometimes radiation, has contaminated streams and caused other problems in some places where drilling has occurred.

Representatives of the oil and gas drilling industry testified at the hearing that the Obama administration was restricting access to a domestic energy source that burns cleaner than other fossil fuels. And, they insisted, hydraulic fracturing had caused relatively few problems relative to the number of wells drilled.

But environmental groups contend that the large amount of water which must be drawn from other sources to drill each well - as much as 4 million to 5 million gallons - and the threat of spills involving contaminated drilling wastes pose a threat to high-quality streams and drinking water supplies.

They also said drilling activities would affect wildlife habitat and interfere with recreational activities in the forest.

Choose Clean Water, a coalition of conservation groups in the Bay watershed, helped generate more than 50,000 individual comments in favor of the draft management plan before the comment period closed in mid-October.

In a letter signed by 75 organizations, the coalition stated that "due to the documented risks of horizontal drilling and high-volume hydraulic fracturing and the numerous public benefits that could be impacted through this type of gas drilling, our organizations feel strongly that the Forest Service would be well-justified in prohibiting horizontal drilling on future federal oil and gas leases" in the George Washington forest.

But they also expressed concern that about 93 percent of the forest, or almost 1 million acres, would remain open to leasing for vertical drilling, noting that 90 percent of all vertical wells also involve hydraulic fracturing, although they generally produce less wastewater than horizontal wells. Further, those wells would present the same risks for surface and ground water, as well as problems for wildlife habitat and recreation.

The letter stated that the plan did not sufficiently analyze those risks and said, at a minimum, that watersheds that supply local drinking water and other priority watersheds should not be available for leasing.

After reviewing comments, the Forest Service expects to finalize its management plan next March.