Impact Assessment of Natural Gas Production in the NYC Water Supply Watershed

Shale formations with gas producing potential are distributed throughout much of the United States. The process required to extract gas from low permeability shale formations, termed hydraulic fracturing or "Tracking," entails injecting large volumes of water, sand, and chemicals at high pressures into the formation, resulting in fractures that increase permeability, allowing the gas to be collected and delivered to the surface. Additionally, wells are generally drilled horizontally underground to increase the area of production for a single well. Whereas variations of the technology have been in use for many years, it has only been in the last decade that the technology has improved to allow economic production from unconventional shale formations on a widespread basis (Airhart, 2007). The technology has been most widely used in the Barnett Shale formation in Texas, which has seen over 13,000 wells developed since 2000 (EIA, 2009; TXRRC, 2009). Portions of the Marcellus Formation, which extends over 95,000 square miles and underlies portions of New York, Pennsylvania, Ohio, and West Virginia, have begun to experience substantial gas leasing and development activity in recent years. The Catskill and Delaware watersheds that provide 90 percent of New York City's unfiltered drinking water supply are underlain by relatively thick sections of the Marcellus that are expected to have high gas production potential (NYCDEP, 2009b). Over 65 percent (∼1,000 square miles) of the NYC watershed could potentially be exploited for natural gas development. Natural gas development activities have the potential to impact the quality and quantity of NYC's water supply through land disturbance, chemical spills, disruption of groundwater flow pathways, water consumption, and waste generation. In recognition of these potential impacts, the New York City Department of Environmental Protection (NYCDEP) has undertaken the project, Impact Assessment of Natural Gas Production in the NYC Water Supply Watershed. The overall goal of the project is to identify potential threats to the continued reliability and high quality of New York City's water supply from future natural gas development activities in or near the NYC watershed. This paper summarizes major findings from this project.