The ascent and development of Hydraulic fracturing or Fracking of deep sedimentary basins of which shales are the primary bulk media-within the United States and elsewhere- to extract Natural gas has generated legitimate concern surrounding the potential impacts fracking might impose on surrounding areas; whether near the surface or deep in the sub-surface. Hydraulic Fracturing involves the injection of fracking fluid at depths up to 1 km (Meyers 2012), under large pressures, into shallow or deep impermeable shale formations to force the formation of fractures within the shale.
These fractures create highly permeable channels within the low permeable shale, from which Natural gas can vertically flow to the surface. As Potential pathways of Natural gas are also potential pathways of fluids and contaminates, although transport time would take longer (Meyers 2012); there exists anxiety surrounding the potential of shorten transport times of contaminates to the near surface or into potable aquifers (Meyer 2012). Fracking fluid consists of water and additional additives, including Benzene at concentrations up to 560 ppm (Jehn 2011; as cited in Meyers 2012).
While additives only account for approximately 0.8% of the total liquid volume, the total mass of additives within the millions of liters of water injected isn’t insignificant (FracFocus 2012). When Fracking fluid is injected and thereafter extracted there is substantial loss of fluid within the media (Meyers 2012). As the fracking fluid flows throughout the shale, whether under pumping stress or not, it displaces and moves native fluids throughout fracture zones and bulk media.
The displacement of these fluids increases the variety and concentrations of contaminants within the bulk media. In the article, Potential Contaminant Pathways from Hydraulically Fractured Shale to Aquifers (Meyers 2012); the author cites substantial Geological evidence that remnants of fracking fluid and additional native contaminates will follow natural vertical pathways of flow to the near surface, without being under any pumping stress.
To help aid in determining potential travel times through potential pathways, Meyers uses Modflow-2000(Harbaugh et al. 2000) computations bounded by formation hydraulic parameters estimated by the author in Potential Contaminant Pathways from Hydraulically Fractured Shale to Aquifers (Meyers 2012).
With the addition of highly permeable fractures created for Natural gas extraction, there is additional concern that travel times to the near surface of said contaminates will be significantly shorten; along with the potential of other various forms of water pollution due to natural vertical flow. (Meyers 2012).
By using MODFLOW-2005, a single hypothetical scenario (#1) and its respective hydraulic parameters set forth by Meyers in the aforementioned paper, will allow for an attempt to re-create the author’s Modflow interpretive data. Based on critiques formulated in discussion papers by James E. Saiers and Erica Barth (2012), and again by Harvey A. Cohen, Toomas Parratt, and Charles B. Andrews (2013) additional adjustments to the hydrological estimations, model framework, and incorrect assumptions of physical conditions will be discussed.
In conclusion, why it is important to develop better modeling techniques (potable aquifer contamination) for the future applications.
The application of Modflow in solving complex questions regarding the fate of contaminate flow within aquifers begins with identifying what questions are being sought out; as not all hydrological problems can be reliably solved with Modflow. Additionally, providing real solutions to complex problems requires extensive hydrological information and analysis performed by those who have general hydrological expertise and experience.
Modflow is process based mathematical solver of the finite-difference groundwater flow equation (McDonald, M.G.; Harbaugh, A.W.1988), which creates a simplified re-creation of processes that are ongoing in the natural world in the form of a conceptual three-dimensional model (Anderson et. al 2015). A groundwater model will synthesize these processes to create a quantitative framework to process field information to better conceptualize these hydrological processes (Anderson et al. 2015).
Advective transport of contaminates within aquifers to the near surface can have substantial environmental impacts on potable aquifers ability to provide drinking water to those that are dependent. The various forms of water pollution that arise when Natural gas or other natural contaminates, such as brine, mix with potable aquifers are of growing concern due to the propagation of fracking operations throughout the United States. As of 2005 fracking operations have been established in seventeen states, with over 80,000 wells drilled or permitted (FracFocus 2012).
The utilization of Modflow to gain an improved conceptual 3D-model of potential pathways and fate of contaminates may help reduce further water pollution caused by Fracking operations by investigating the unknown sources and potential pathways of these contaminates. Groundwater models can be useful to help organize field data in a way that information can be tested conceptually by using Modflow to help identify exact sources and pathways of contamination.
Fracking fluid has been found in aquifers (DiGiulio et. al 2011; EPA 1987; as cited in Meyers 2012), but the exact source and pathway of fracking fluids in many cases remains unknown. The lack of data frequency regarding hydrological information inhibits the ability of professionals to make accurate assertions and predictions of exact pathways with which contaminates are reaching potable aquifers. The ability to accurately portray an aquifers physical property and the relationship between the aquifer and surrounding units can be hampered by misconceptions and incorrect assumptions regarding those properties.
