Modeling the regional groundwater flow in Broome and Tioga counties, NY under high-olume water extraction scenarios driven by potential natural gas development of the Marcellus Shale
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The growth of unconventional shale gas development in the United States provides an important domestic energy solution while stimulating debate around the consequences of current extraction practices. Much of the controversy surrounds potential environmental impacts associated with high-volume hydraulic fracturing (HVHF), which combines the technologies of horizontal drilling and hydraulic fracturing. Natural gas development of the Marcellus Shale, for example, has met opposition in New York State (NYS) in response to increasing health and environmental concerns. While most of the media and research attention has focused on the protection of water quality, it is not well understood whether the large volume withdrawals of water required to fracture the target formations will have an effect on the water supply. This water quantity perspective is less often emphasized in regions of the country that are considered "water rich" – usually located in humid climates or near large surface water bodies. In the Southern Tier of NYS, where HVHF is projected to develop should the current moratorium be lifted, groundwater provides a significant portion of municipal drinking water. Broome and Tioga counties in NYS, the focus of the research described herein, overlie a glacial valley-fill aquifer system, which supplies more than half of the drinking water to nearby municipalities. It is, therefore, necessary for regulators to understand the implications of increased freshwater demands for both the water table and stream flow, which demonstrate high hydrologic connectivity. This research first tested whether high volume withdrawals of water would be sufficient enough to elicit a response from either groundwater or surface water. This research then quantified these effects under a range of development scenarios that incorporated variations in well pad density, water volume, and water source. The process of scenario testing was applied to a baseline groundwater flow model which was vital for recognizing the spatial distribution of both water source burden and hydrologic response. Results emphasize the spatial variability of effects, contingent on the water source and the total water volume required. Concentrated withdrawals, associated with municipal pumping scenarios, produce concentrated drawdown whereas distributed pumping produces more widespread water table effects. Drawdown from either groundwater pumping source increases with increasing development density and/or increasing water volume required for each pad. In both source scenarios, narrow valleys with limited access to induced recharge from streams are the most vulnerable. The water table is ultimately insensitive to stream withdrawals, exemplifying the distribution of water burden between groundwater and surface water. Stream flow reductions are apparent for all source scenarios. While the spatial distribution of stream flow response is nearly independent of water source, the magnitude of change is not. This finding underscores the necessity of incorporating transience into the model, as the implications of stream flow reduction will vary according to seasonal recharge deficits. Withdrawal rate variability is another critical addition to the model which should be considered for future work. The most significant contribution of this research is in quantifying potential changes to the water table and stream flow in a region that previously might not have focused on a water quantity perspective. Water budgets alone are not effective in quantifying spatial variability of system response. This research emphasizes that water permitting decisions should conservatively account for protecting a sustainable water supply for all the sectors of society that it supports. Furthermore, attention to water resource management in water rich regions should continually consider the effects of increased freshwater demand for the impacts of change may have both anthropogenic and environmental implications.