“Because of the significant data gaps and uncertainties in the available data, it was not possible to fully characterize the severity of impacts, nor was it possible to calculate or estimate the national frequency of impacts on drinking water resources from activities in the hydraulic fracturing water cycle.” However, a nice addition to the final report was the “Synthesis” section. This sections written for state and local regulators identifies the factors that can be managed, changed, or used to help reduce current vulnerabilities of drinking water resources to activities in the hydraulic fracturing water cycle. Since the overall rate that fracking does impact our water resources is low, this section is excellent suggestions for reducing the risk even further through regulation and monitoring.
The final report examines all the potential vulnerabilities in the water lifecycle that could impact the 3,900 potential drinking water sources for the 8.6 million people living within one mile of a hydraulically fractured well. EPA’s assessment relies on existing scientific literature and data. Literature evaluated included articles published in science and engineering journals, federal and state government reports, non-governmental organization (NGO) reports, and industry publications. Data was gathered from databases maintained by federal and state government agencies, other publicly-available data and information, and data, including confidential and non-confidential business information, submitted by industry to the EPA.
EPA concluded that there are above and below ground ways that hydraulic fracturing can potentially impact drinking water resources. These mechanisms include water withdrawals in times of drought, or in areas with, limited water availability; spills of hydraulic fracturing fluids and produced water; fracking directly into underground drinking water resources; below ground migration of liquids and gases from inadequately cased or cemented wells; and inadequate treatment and discharge of wastewater.
EPA did not find evidence that there has been widespread impacts on drinking water resources; but did find specific instances where one or more failures in design, well completion and fluid storage led to contamination of drinking water wells. The number of identified cases, however, was small compared to the number of hydraulically fractured wells reported by EPA. This low level of documented contamination might be due to insufficient pre- and post-fracturing data on the quality of drinking water resources; the lack of long-term systematic studies of areas and lack of careful monitoring of groundwater resources and the presence of other sources of contamination precluding a definitive link between hydraulic fracturing activities and an impact when using fracking to redevelop and extend the life of existing oil and gas wells.
The assessment follows the water used for hydraulic fracturing from water acquisition, chemical mixing at the well pad site, well injection of fracking fluids, the collection of hydraulic fracturing wastewater (including flowback and produced water), and wastewater treatment and disposal. Though cumulatively, hydraulic fracturing used on average 44 billion gal of water a year in 2011 and 2012, this represented less than 1% of total annual water used in the United States. However, in areas of drought the need for a median of 1.5 million gallons to frack a well could impact water supplies.
The median amount of water used to frack a well is determined by well length, formation geology and the fracking fluid formulation. The overall amount of water used in fracking is a fraction of the daily water use in the United States.
EPA found that surface spills were by far the most common incident reported, though they are also the most easily observed. The reported volume of fracturing fluids or chemicals spilled ranged from 5 gallons to more than 19,000 gallons, with a median volume of 420 gallons per spill. Spill causes included equipment failure, human error, failure of container integrity, and other causes (e.g., weather and vandalism). The most common sited cause was equipment failure. The frequency of on-site spills from hydraulic fracturing could be estimated for only two states. If the estimates are representative, the number of spills nationally could range from approximately 100 to 3,700 spills annually, assuming 25,000 to 30,000 new wells are fractured per year.
EPA identified a list of 1,076 chemicals used in hydraulic fracturing fluids over multiple wells and years. These chemicals include acids, alcohols, aromatic hydrocarbons, bases, hydrocarbon mixtures, polysaccharides, and surfactants. According to the EPA’s analysis of disclosures, the number of unique chemicals per well ranged from 4 to 28, with a median of 14 unique chemicals per well. In addition, EPA reports an estimated 9,100 gallons of chemicals are mixed with the median 1.5 million gallons of water per well. Given that the number of chemicals per well ranges from 4 to 28, the estimated volume of chemicals injected per well may range from approximately 2,600 to 18,000 gallons.
EPA found that groundwater can be impacted by fracking fluids or methane gas if the casing or cement on a well are inadequately designed or constructed, or fail. A study done in the Williston Basin in North Dakota suggests that the risk of groundwater contamination from leaks inside the well decreases by a factor of approximately one thousand when the well casing extends below the bottom of the drinking water aquifer.
EPA suggests that fracking of older wells to restore production can contribute to casing degradation and failure, which can be accelerated by exposure to corrosive chemicals, such as hydrogen sulfide, carbonic acid, and brines. No data was provided on this risk. The study found that one of the best protections for groundwater is the physical separation between the gas production zone and groundwater resources. Many hydraulic fracturing operations target deep formations such as the Marcellus Shale or the Haynesville Shale, where the vertical distance between the base of drinking water resources and the top of the shale formation may be a mile or greater.
However, not all hydraulic fracturing is performed in zones that are deep below drinking water resources, but should be. The EPA’s survey of oil and gas production wells hydraulically fractured in 2009 and 2010 estimated that 20% of wells had less than 2,000 feet of vertical separation between the point of shallowest hydraulic fracturing and the base of the protected groundwater. There are also places in the subsurface where oil and gas resources and drinking water resources co-exist in the same formation. When hydraulic fracturing occurs within these formations the process injects of fracturing fluids into formations that may currently serve, or in the future could serve, as a source of drinking water for public or private use and should not be allowed.
Water, of variable quality, is a byproduct of oil and gas production. After hydraulic fracturing, the injection pressure is released and water flows back from the well. Initially this water is similar to the hydraulic fracturing fluid, but as time goes on the composition is affected by the characteristics of the formation and possible reactions between the formation and the fracturing fluid. EPA calls all this water produced water. The final area that EPA looked at was management of the produced water. Hydraulic fracturing generates large volumes of produced water that require management. In 2007, approximately one million active oil and gas wells in the United States generated 2.4 billion gallons a day of wastewater. It is unknown what portion of this total volume is produced by hydraulically fractured wells, but really, after the flowback period there is little difference.
As is pointed out in the report wastewater management and disposal could impact drinking water resources. Inadequate treatment of wastewater could result in discharge of contaminated water to rivers and streams. Though, in recent years a larger proportion of fracking produced water is reused. In addition, spills can occur during transportation of wastewater away from the well head or spills and leaks from wastewater storage pits. Also, migration of contaminants from inappropriate use of land application to dispose of of wastewater, and other inappropriate methods of wastewater treatment.
The take away is there is still the need for more research to be able to fully model and understand fracking. In addition there is a need for more extensive baseline studies prior to drilling and long term monitoring to even know if water (or human health) has been impacted by fracking. Predrilling data needs to include measurements of groundwater and surface-water quality and quantity. There have been virtually no comprehensive studies on the impact of fracking on human health while state regulators and laws in some instances allow fracking virtually in people’s backyards and without adequate vertical separation from groundwater supplies. Fracking needs to be well understood and the risks managed to make sure that is a boon to mankind and only is used in appropriate geology and low risk locations. Many of the sources of contamination identified by EPA could be prevented or reduced with more care, training and thought. Overall, hydraulic fracturing for oil and gas is a practice that continues to evolve and our methods and controls should continue to evolve with it.