Fracking on a slope: Deep shale drilling and its surface effects

As drilling for natural gas in deep shale rock continues to expand in Pennsylvania, researchers in Penn State's College of Agricultural Sciences have now identified some of the possible effects. In a study in the Sept.-Oct. issue of the Soil Science Society of America Journal, they report that 50 to 70 percent of shale-gas drill sites across Pennsylvania’s Appalachian Plateau are situated on slopes that could be prone to erosion and sedimentation problems.

Substantial erosion is far from inevitable, however, despite the findings, says Penn State assistant professor of pedology, Patrick Drohan, who led a 12-month study of the hydrologic implications of gas-well development and its effect on the plateau's landscapes and soils.

"Even though between 50 and 70 percent of the drill sites, or pads, are being constructed on soils and slopes at risk for excess water movement and erosion, that doesn't mean all sites are having problems," he says. "It just means that we have identified a large number of sites that have to be watched because there could be trouble if state Department of Environmental Protection best-management practices to limit erosion and sedimentation are not implemented quickly or effectively."

Thousands of feet below Pennsylvania and several other Appalachian states lies the Marcellus Shale, a deep rock formation with vast reserves of natural gas locked inside. To free the gas, drillers often must use the controversial technique known as hydraulic fracturing, or fracking, in which millions of gallons of pressurized water, sand, and chemicals are injected deep into the earth to fracture the shale.

Since 2004, more than 3,000 of these “deep shale” wells have been drilled in Pennsylvania, with about 10 percent of them situated on slopes at high-risk for surface erosion and sedimentation, according to the new research. Drohan worries about such areas every time there’s an intense rain event.

"Perhaps a statewide weather forecasting system for predicting the 24- to 72-hour risk of heavy rains—which could result in erosion and sedimentation—might help land managers and gas companies that are developing such areas to avoid problems," he says.

In the study, Drohan and Margaret Brittingham, professor of wildlife resources at Penn State, used Geographic Information Systems (GIS) tools to investigate the topographic and soil characteristics of existing and permitted shale gas well locations across Pennsylvania. These characteristics are important because they can affect infrastructure development and the success of reclamation efforts later on.

The pair also used aerial photography to analyze the extent of surface disturbance associated with gas pad development, as well as hydrologic modeling to assess potential erosion and sedimentation problems.

Most soils on the Allegheny Plateau, where shale-gas development is concentrated, are acidic, rocky, shallow, and of poor fertility, the study points out. Moreover, about a quarter of the sites are underlain by a "fragipan subsurface horizon" that restricts downward root growth and water movement.

"This presents unique challenges for gas developers and land managers because such soils can become even more problematic for plant growth and good drainage following disturbance," Drohan said. "Allegheny Plateau soils have been difficult to manage throughout Pennsylvania's history and have typically been less productive than many agricultural soils elsewhere in the state."

Another factor of concern to the researchers is that 21 percent of pads have been developed on potentially wet soils, where drainage problems around the site could result in the loss of amphibian habitat. This doesn’t necessarily mean that the state is losing wetlands, Drohan notes, because well drillers are required to look for and avoid wetlands before they develop pads.

"However, such places would be what soil scientists consider ‘hydrologically active’ locations,” he adds. “Development in such areas could disrupt local water movement around pad sites and other infrastructure and the recharge to nearby headwater streams, as well as present unique reclamation challenges down the road due to those sites' inherent wetness."

The researchers now are working with government agencies, such as the Pennsylvania Department of Conservation and Natural Resources, and with community groups to improve decisions about where well pads are placed to help minimize the disruption of landscapes and reduce potential erosion and sedimentation.

For example, one aspect of current research is evaluating the success of temporary and permanent restoration of infrastructure. So far, very few Marcellus drilling pads have been reclaimed, but many other types of infrastructure—such as pipelines and water impoundments—have been.


"During reclamation of shale-gas infrastructure, companies are using traditional amendments of fertilizer and lime to get the grass mixes to grow," he said. "We are concerned, however, about altering the inherently acidic and low-fertility soils of the Allegheny Plateau to such a degree that the growth of invasive plant species becomes potentially more favorable than native species."

Drohan and colleagues also have begun to focus their attention on ecological disruption caused by shale-gas infrastructure, such as pipelines, that often traverses steep slopes and poorly drained areas.

"[Our ability] to measure the effect of shale-gas development, its extensive landscape footprint and rate of growth would really benefit from better data on pipelines," he says. "For example, there is currently no statewide tracking of the various types of pipelines developed to support the natural-gas industry. Federal supply lines are mapped, and one or two counties have been tracking shale-gas pipelines.

"We now think that pad development is a lesser landscape disruption than the pipelines, and statewide pipeline tracking really would help land managers and researchers better understand their potential effect on ecosystems."

The abstract of this study, funded by the Heinz Endowment, can be viewed at

Based on a news release from Penn State University College of Agricultural Sciences.

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