How Deep is the Critical Zone: A Scientific Question with Potential Impact For Decision-makers in Areas of Shale-Gas Development and Hydraulic Fracturing

Abstract:

Citizens living in areas of shale-gas development such as the Marcellus gas play in Pennsylvania and surrounding states are cognizant of the possibility that drilling and production of natural gas -- including hydraulic fracturing -- may have environmental impacts on their water. The Critical Zone is defined as the zone from vegetation canopy to the lower limits of groundwater. This definition is nebulous in terms of the lower limit, and yet, defining the bottom of the Critical Zone is important if citizens are to embrace shale-gas development. This is because, although no peer-reviewed study has been presented that documents a case where hydraulic fracturing or formation fluids have migrated upwards from fracturing depths to drinking water resources, a few cases of such leakage have been alleged. On the other hand, many cases of methane migration into aquifers have been documented to occur and some have been attributed to shale-gas development. The Critical Zone science community has a role to play in understanding such contamination problems, how they unfold, and how they should be ameliorated. For example, one big effort of the Critical Zone science community is to promote sharing of data describing the environment. This data effort has been extended to provide data for citizens to understand water quality by a team known as the Shale Network. As scientists learn to publish data online, these efforts must also be made accessible to non-scientists. As citizens access the data, the demand for data will grow and all branches of government will eventually respond by providing more accessible data that will help the public and policy-makers make decisions.