Impacts on Groundwater During Well Drilling
In parts of New York likely to be exploited for shale gas, the Marcellus formation lies 3000 to 5000 feet below the surface, and groundwater suitable for human use generally lies at depths of less than 500 feet. Even though groundwater exists at deeper depths – perhaps down to 1000 feet, it is generally too high in salts or other solutes to be used for drinking, irrigation and most industrial processes. Therefore, shale gas-associated drilling within the first several hundred feet of the surface is a key area of concern and regulatory attention.
Creation of a well, whether it is for gas, water, or oil, can disrupt natural groundwater flow and/or quality. Alteration of the natural pressure gradient during drilling operations can cause groundwater to flow in an abnormal direction, potentially interrupting water production in nearby water wells. Introduction of air and oxygen as the drilled well is exposed to the atmosphere can cause changes in groundwater chemistry that may lead to increased turbidity (cloudiness) or taste and odor issues.
Additionally, the development of a shale gas well entails other groundwater risks. As drilling proceeds, the bore hole created is cased with steel pipe which is then sealed into place with cement, as shown in the figure above that was taken from the EPA Plan to Study the Potential Impacts of Hydraulic Fracturing on Drinking Water Resources. Closest to the surface, multiple layers of steel pipe and cement can be used. If done properly, this separates and protects the surrounding rock, soil, and groundwater from the drilling fluids and natural gas that flows inside and around the pipe. This cement seal should extend from the surface through and beyond the several hundred to 1000 feet of groundwater. If the bore hole is not properly sealed, it is possible for natural gases and groundwater from deeper layers to travel up the space outside of the casing and mix with potable groundwater near the surface. This is often a difficult concept to understand, since the risk involved may not have anything to do with gas found in the Marcellus shale itself, and since these risks may arise before or in the absence of hydraulic fracturing operations. More information and illustrations that help to visualize the process in general can be found at:
Regulations and Risks
A variety of regulations, primarily at the state level, exist with respect to protection of groundwater resources and the potential impacts of drilling. For example, The New York State Department of Environmental Conservation (DEC) mandates casing and cementing of well bore holes, and also prescribes a number of practices that must be carried out during the casing process (http://www.dec.ny.gov/energy/1757.html). In addition, drillers are required to use only air or freshwater when drilling through freshwater aquifers (http://www.dec.ny.gov/docs/materials_minerals_pdf/dgeisv1ch9.pdf). Besides regulations pertaining to the casing and cementing, DEC proposed regulations stipulate that wells or well pads be a certain distance (known as a setback) from public water wells (2000 feet) and private wells (500 feet). Proposed regulations also prohibit shale gas development from occurring in a zone containing a primary aquifer, or where the target shale formation is not greater than 2000 feet below the surface and 1000 feet below the base of potable water (rdSGEIS Chapter 3).
Despite state regulations in NY and elsewhere, risks to groundwater do persist. It is difficult if not impossible to eliminate risk entirely, and chances of accidents remain due to operator error, unforeseen geological conditions, or other unpredicted events. The NY DEC has released a fact sheet, as well as a list of "non-routine incidents" (accidents) that identifies issues of concern noted during development of shale gas in Pennsylvania. Risk to groundwater as a result of insufficient casing and cementing is among those concerns. The US EPA also notes the potential risks associated with poor casing and cementing in its draft report on the possible relationship between groundwater quality and natural gas development in the Pavillion, Wyoming area. WRI has suggested that such risks, and the potential impacts that could result from casing and cementing failure, should prompt both state and federal regulators to review, update, and possibly strengthen their rules and policies pertaining to well drilling. At the same time, more research is needed to develop better well sealing practices that protect adjacent groundwater and are less likely to deteriorate or fail over time. All in all, well casing and cementing is likely to continue to be an important topic for all stakeholders for as long as drilling-based resource extraction continues.
Updated 4/19/12 bgr
Runoff From Wellpads
Drilling Impacts on Groundwater
Spills and Leaks at the Surface
Wastewater management trends in PA (link)
Lessons for NY from EPA Pavilion Study (link)
Regional, collective impacts on water resources (link)
Testing Drinking Water (link)
On-going study of drinking water in New York by Cornell University Soil & Water Lab (link)
Understanding Isotopes (link)
Framework for Assessing Water Resource Impacts (link)
Marcellus thickness, depth (link)
Marcellus extent in NY (link)
Marcellus in Susquehanna Basin (link)
Marcellus in Delaware Basin (link)
NY and Chesapeake Bay (link)
References for understanding shale gas impacts (link)