Impacts on Water During Well Drilling

The Marcellus Shale in New York lies 3000 to 5000 feet below the surface. In the area of New York underlain by the parts of the Marcellus shale likely to be exploited for natural gas, groundwater suitable for human use is at depths of less than 500 feet. Even though there is groundwater at deeper depths, this water is generally too high in salts or other solutes to be used for drinking, irrigation and most industrial processes. Therefore, most of the concern regarding the potential impact of the process of gas drilling on groundwater resources concerns drilling through the first several hundred feet in areas that contain utilized groundwater aquifers.

As drilling proceeds, the bore hole created is cased and sealed to surrounding rock with cement. Near the surface, the bore hole will be sealed with multiple casings. Between drilling and the sealing of the bore hole, groundwater may run out of the aquifer and into the bore hole. If the bore hole is not properly sealed, it is possible for water in aquifers near the surface to leak into lower aquifers, or water from deeper aquifers to move into surface aquifers. Hence, it is very important that the bore hole be well sealed. The New York State Department of Environmental Conservation (DEC) mandates casing and cementing (http://www.dec.ny.gov/energy/1536.html) of well bore holes. Since any water from higher layers that enter the gas play would likely have to be pumped out, it is also in the interest of the gas well owner that the bore hole be well sealed.

Another concern in the drilling process is that chemicals used in the drilling fluids or muds might enter an aquifer used for drinking water. The New York State Department of Environmental Conservation (DEC) requires drillers to use only air or freshwater when drilling through freshwater aquifers (http://www.dec.ny.gov/docs/materials_minerals_pdf/dgeisv1ch9.pdf).

In addition, wells must be a prescribed distance (known as a setback) from municipal water wells (1000 to 2000 feet), surface water bodies, streams and private wells (150 feet) (http://www.dec.ny.gov/docs/materials_minerals_pdf/dgeisv1ch8.pdf). Whether these setbacks are adequate to protect these surface resources should be addressed in the review that the DEC is currently undertaking. Some Marcellus shale gas wells could be located within the boundaries of the watershed in which New York City has reservoirs. Currently, some city officials are proposing that there be a mile buffer strip between the reservoirs and any drilling site (http://www.propublica.org/feature/natural-gas-drilling-watershed-806).