In a draft report on the potential impacts of fracking on drinking water, the U.S. Environmental Protection Agency (“EPA”) identifies vulnerabilities within the “fracturing water cycle,” but found no widespread, systemic problems.
EPA divided what they call the “fracturing water cycle” into five stages: 1) water acquisition, 2) chemical mixing, 3) well injection, 4) flowback and produced water and 5) wastewater treatment and waste disposal. Researchers provide an analysis of potential impacts at each stage.
Water Acquisition. EPA defined “water acquisition” as “the withdrawal of ground or surface water needed for hydraulic fracturing fluids,” and asked:
* How much water does fracking use?
* How much water is used per well?
* What types of water are used?
* How do withdrawals for fracking impact drinking water quantity?
* How do withdrawals for fracking impact drinking water quality?
While figures vary at the county and local levels, overall, hydraulic fracturing uses about 44 billion gallons of water annually—which is about 1% of the nationwide annual water use and consumption—from a mix of surface water, groundwater and reused hydraulic fracturing wastewater. The impact on both water quantity and water quality is the same as withdrawals for any use. Fracking does not directly impact drinking water quantity, but like with any other use, there is the potential for stress in the interaction of water use and water availability. Potential impacts to water quality include the possibility of drawing down of aquifers—which could mobilize contaminants or allow infiltration of contaminants from the land or adjacent formations—or lowering or altering streamflows—which could prevent a stream from effectively diluting contaminants.
Chemical Mixing. EPA defined “chemical mixing” as “the mixing of water, chemicals, and proppant on the well pad to create the hydraulic fracturing fluid,” and asked:
* How frequent and severe are spills of hydraulic fracturing fluid and what are the causes?
* What chemicals are used and in what quantities?
* What are the chemical, physical and toxicological properties of the additives used in hydraulic fracturing fluid?
* By what processes could spilled chemical additives contaminate drinking water?
There is no separation in state databases between spills of chemicals or hydraulic fracturing fluids and produced water, so EPA estimated that information based on state and industry data. Findings show that there were 151 spills of chemicals or hydraulic fracturing fluids in the period from January 2006 through April 2012, with the volume spilled ranging from 5 gallons to 19,000 gallons.
EPA found that there is a wide range of chemicals used. There is no chemical that is used universally, but there are several that are used widely. Injection volumes are estimated to range from 2,600 gallons to 18,000 gallons.
Key characteristics discussed were those that would cause the chemicals to impact a water source—mobility, solubility and volatility. Among the 20 most mobile chemicals, 18 are not commonly used. The other two are used in 11% and 14% of hydraulic fracturing wells. Solubility varies widely. Volatizing is rare, so a large proportion of the chemicals remain in water. In addition, chemicals can impact water supplies by flowing over land, contaminating soils or infiltrating groundwater sources.
Well Injection. EPA defined “well injection” as “the injection of hydraulic fracturing fluids into the well to fracture the geologic formation,” and asked:
* How effective are well construction practices at containing fluids—before, during and after fracking?
* What geological or artificial features would allow for subsurface migration of hydraulic fracturing fluids to drinking water supplies?
Wells are designed with a casing and cement to protect drinking water sources, though problems can arise due to inadequate design or construction or failure of the well structure. The data also show that there is little risk or migration to drinking water sources in deep formations, where there is a mile or more between the base of the drinking water source and the top of the shale. Shallower formations have some risk, and the greatest risk exists in the areas where drinking water source and oil or gas co-exist. In addition, liquid or gas can move to drinking water sources when fractures intersect with other wells. Older or inactive oil and gas, injection and drinking water wells are at a higher risk for this type of impact.
Flowback and Produced Water. “Flowback and produced water”—defined as “the return of injected fluid and water produced from the formation (collectively referred to as produced water in this report) to the surface, and subsequent transport for reuse, treatment, or disposal”—yielded questions similar to those examined in the “chemical mixing” stage:
* How frequent and severe are spills of flowback or produced water and what are the causes?
* What is the composition of flowback or produced water, and what effects the composition?
* What are the chemical, physical and toxicological properties of the constituents found in flowback and produced water?
* By what processes could spilled flowback or produced water contaminate drinking water?
The quality of produced water—which can contain high levels of major anions and cations, metals, organics, and naturally occurring radionuclides—ranges from fresh to highly saline. Generally, the type of formation affects the composition of the produced water, with produced water from shale formation having higher total dissolved solids (“TDS”) and ionic constituents and coalbed methane yielding lower TDS levels.
The constituents in produced water generally have low mobility in the environment and tend to stay in the soil near spill sites. Impacts to drinking water supplies are affected by the timing and volume spilled and the composition of the produced water. The greatest risks are posed by higher spill volumes, longer duration of releases and higher concentration of constituents.
Wastewater treatment and waste disposal. “Wastewater treatment and waste disposal” is defined as “the reuse, treatment and release, or disposal of wastewater generated at the well pad, including produced water.” In its analysis, EPA excludes the potential impacts of disposal by injection into underground injection control (“UIC”) wells and focuses on the impacts of using centralized waste treatment facilities (“CWT”) and publicly-owned treatment works (“POTW”). The questions evaluated include:
*What are the common treatment and disposal methods, and where are they practiced?
* “How effective are conventional POTWs and commercial treatment systems in removing organic and inorganic contaminants of concern in hydraulic fracturing wastewater?”
* What impacts could surface water disposal of treated hydraulic fracturing wastewater have on drinking water treatment facilities?
There are five primary wastewater treatment and waste disposal processes used in hydraulic fracturing: UIC wells, evaporation ponds, CWTs with reuse via discharge to surface water or delivery to POTWs, reuse with minimal or no treatment (i.e. reuse for subsequent hydraulic fracturing treatment), and land application or road spreading.
The draft report is currently in the public review process. EPA is accepting written comments through August 28, 2015. Teleconferences will be held September 30, October 1 and October 19, and a public face-to-face meeting is scheduled for October 28 -30.
EPA has referred to the report as a state-of-the-science assessment and expects that it will help federal, state, local, tribal, industry and public interests better understand the risks and address the vulnerabilities that hydraulic fracturing poses to drinking water supplies.
Written by Marta L. Weismann