Flowback Water = More Than Fracking Fluid
There are already well publicized concerns by citizens groups and environmentalists about chemicals in fracking fluid, but many people don’t understand what flowback water is, and why it may be more dangerous than simple fracking fluid. Even the term “residual frac water” presumes that it’s essentially leftover or used fracking fluid, but the simple truth is that any fluid having traveled deep underground is going to carry toxins and contaminants that weren’t present beforehand.
Fracking Fluid
We already know that fracking fluid contains acids, petroleum distillates, salts, biocides, and many other chemicals added to optimize a well’s production. Once a well has been fracked, some of the fluid is drawn back out, although the recovered amounts may vary significantly from well to well. Typically, after a week or so, the flowback changes gradually from fracking fluid to produced water, which may continue to flow at varying rates for up to two years.
Produced water
Produced water is part of every mining operation, including oil and gas drilling and fracking. When a well is drilled and when resources are extracted from deep underground, the activity releases water naturally trapped in the same geologic formations. Since it emerges from so far underground the character of produced water is very different from the water you’ll find in underwater freshwater aquifers and wells for drinking water. In fact, the exact composition will vary significantly, based on the formation where it was trapped.
Aside from dirt and clay in varying amounts, produced water typically contains any number of other naturally occurring contaminants ranging from heavy metals, heavy concentrations of salts, and toxic hydrocarbons like benzene, to radioactive materials such as uranium and radon. While all of these “contaminants” naturally exist deep below ground, they are flushed out and brought to the surface as part of the extraction process. Since many of these substances carried to the surface are toxic, produced water is considered an industrial waste and must be carefully managed, although specific rules can vary by state.
Flowback Water
Flowback water is simply the combination of fracking fluid and produced water that is pumped out of a newly fracked well. Flowback water is sometimes filtered, mixed again with fracking chemicals, and used to frack more wells. When flowback water has been reused in this manner, it has picked up increasing amounts of contaminants, resulting in a wastewater that’s often too dirty to treat. Flowback water that cannot be made safe must be permanently disposed of so that it cannot re-enter the Earth’s hydrologic cycle.
Management
Water collected as it returns from the well is stored until it is either prepared for re-use or shipped off for treatment or disposal. It may be stored in large metal tanks, above the ground in pools equipped with special geosynthetic liners or in excavated pits with similar liners.
If the flowback water isn’t recycled to frac additional wells, it may be disposed of through deep well injection or treated at commercial or municipal wastewater treatment plants until it meets EPA standards for release into the environment.
Storage
When flowback water is stored awaiting re-use or when it’s shipped off for treatment or disposal, there are opportunities for accident or error that permits toxic wastewater to escape into the environment. Spilled, leaked, or dumped fracking wastewater has been found in nearby surface waters and in underground aquifers that supply drinking water to local residents. In some cases, it has simply soaked into the ground and passed down to the water table.
Closed-top steel tanks are a popular solution for storing and sequestering wastewater. Full size tanks can hold 21,000 gallons, and they may include extras such as insulation or heating coils, and alarm systems built in. They can be moved as needed, and some companies offer the choice of buying or renting. However, these can be expensive, especially considering how many gallons of wastewater may need to be stored on a site. Steel tanks, lined up side by side, require a significant amount of space, and there’s flexibility in storage volume. Over time, some metal tanks may be vulnerable to corrosion from the high concentration of salts in flowback water.
Rented, modular, above ground frac tanks can be quickly installed and configured to hold 1,000,000 or more gallons of wastewater. Modular components in these systems can be reconfigured or disassembled entirely as needs change. Specialized, highly durable geosynthetic liners with high chemical resistance are used to ensure primary and secondary containment and customized covers can be fabricated as well.
In-ground storage pits also used geosynthetic liners to prevent contact with the soil and potential movement into groundwater. Their main advantage is their one-time, relatively low cost installation. However, they’re vulnerable to extra risks like flooding or overflowing during heavy rains, and effective secondary containment can be difficult to achieve, so careful design, installation, and maintenance are critical.
Treatment or Disposal
The environmental risks of flowback water from fracking operations are significant, so there are a limited number of options available for handling it. Ideally, it would be possible to treat the wastewater, removing all salts, heavy metals, organics, and radioactive contaminants until it’s clean enough to discharge into the environment. However, this level of treatment would be both difficult and expensive. Both radioactive contaminants and heavy concentrations of salts are beyond the scope of what most treatment facilities are prepared to handle. In some cases, treatment facilities may simply rely on dilution of problematic chemicals once they’ve been discharged into surface waters.
Even if specialized facilities could be constructed to tackle the unique challenges of fracking wastewater, transporting millions of gallons over miles of highways would be extremely expensive and would present many potential points of failure that might result in a spill. Even then, the salts, heavy metals, and radioactive elements removed from wastewater would need to be safely disposed of.
Injection wells have been widely used to manage wastewater from fracking operations, but they have their own set of challenges. In an injection well, wastewater is injected thousands of feet below the surface into porous sedimentary rock formations, like sandstone. However, these formations aren’t necessarily found near some of the largest shale plays. Kansas and Oklahoma are two states where conditions are favorable but increasing use of injection wells in those states have been associated with increased seismic activity. In addition, not all wells are licensed to handle radioactive waste. In short, very much like most other mining activities, there are no ideal solutions for managing waste from fracking operations.
