Frac pits may be designed with care and covered with liners warrantied to last decades, but they’re usually only used from six months to a few years at most. Hydraulic fracturing is a relatively quick process that produces a large initial flow and then tapering returns as the months pass. Eventually each well is abandoned and capped, unless there’s a desire to return to it later for higher pressure treatment. That means that every gallon that enters a frac pit needs to find a final resting place eventually. There are many options for dealing with produced water after it enters a frac pit, and some of them must be combined to get the desired results that meet all local environmental regulations. Other states may allow for the use of just one convenient disposal method to save both time and money. Regardless of the disposal method you eventually choose for your produced water from fracking, make sure you design your frac pits with it in mind.
Closed and Covered Pits
One of the lesser used, but intriguing options for storing waste from a fracking operation, is to use a deep pit. These frac pits are designed from the start with permanent storage and disposal in mind. While other types of temporary frac pits are relatively shallow and feature a large surface area, these pits take the opposite approach and have a deep design instead. This maximizes storage space for solid waste in particular. These pits and ponds tend to include equipment for dewatering the waste over time, even if it’s just accelerated evaporation, in order to leave mostly just solids behind. Once the pit reaches capacity, it must be capped and covered with up to 10 feet of solid concrete and dirt. This ensures that the pit won’t open back up and expose the waste to the surface again. These pits may sound ideal since you can pump in the produced water, treat it, and simply cap it over at the end without any further transport. However, they’re far more expensive to build than many site operators first guess. The depth necessary to offer appropriate storage for high volumes of solids necessitates extensive reinforcement of the sides and banks of the pit. They can still collapse and cause a release of solid waste as time passes. The cap used for covering and protecting the waste also has the potential to fall in as the base settles and creates a sinkhole effect. Covered pits will continue to need maintenance and repair as time goes by, so they may not be the best choice for a remote site that is hard to access once the temporary roads are gone. These pits are also limited in volume by the very cost of excavating deep into the ground without risking collapse.
Reuse and Recycling
For most hydraulic fracturing sites today, recycling as much produced water as possible has become a major goal. The benefits include:
- Reduced costs for trucking in water over long distances or installing expensive wells that are only used for a few months
- An on-site and steady supply of ready-to-use hydraulic fracturing fluid that already contains at least some of the chemicals necessary to achieve fracking goals
- Lesser chance of local groundwater contamination due to the reduced amount of water needing injection at the end of the cycle
- Less intensive treatment needed for fracturing reuse than for agricultural applications or open water discharge options.
Setting up the treatment pits and ponds necessary for reusing produced water will have its own costs. However, measure those initial installation costs against the long-term savings provided by recycling the wastewater. With savings provided by both reduced inputs and outputs from the system, it’s often a cost-effective measure when it’s priced out over the lifespan of the fracking project.
Intensive Treatment
Reusing produced water at the fracking site generally requires only a limited amount of treatment. While fracturing processes may initially begin with pure, fresh water, it’s mixed with a variety of chemicals and additives before it’s useful as a fracturing fluid. The flowback that comes out of an active well will contain much of these additives already, limiting the amount of treatment necessary before it’s useful again. More intensive water treatments are needed when you’d like to try a different discharge method or need to deal with what’s left after multiple cycles of reuse. These treatments can take months instead of weeks, and they can continue long after active work at the site has ceased. Make sure the frac pits will continue to be accessible for months and years after the shutdown of the rest of the equipment if you plan to continue long-term, intensive, treatment plans.
Discharge Over Land or Sea
Discharging the treated water over open land or nearby bodies of water can become the perfect solution for dealing with large volumes of flowback water. However, don’t underestimate the scale of water treatment needed to achieve local and state approval for this kind of release plan. The water must be as clean as physically possible, including from difficult to remove compounds like organic materials and heavy metals, before it can go into the soil or open waters. The EPA may be able to get involved in pits and ponds they usually can’t regulate if you start release waste into open waters of the United States. In general, it’s best to avoid this kind of costly release method unless it’s the only option for protecting other sensitive parts of the environment from long-term damage.
Deep Injection
For almost all hydraulic fracturing sites operating today, deep injection in an existing well or fractured formation is the ideal way to dispose of produced water. The water needs little to no treatment to be handled this way in most cases, allowing you to minimize extra equipment and chemical costs. Aside from desanding, to turn sludge into a thinner liquid, frac pits are primarily needed just to hold the water until it’s returned to the wells. This means that the liners on these ponds must stay leak-free since there’s no improvement to water quality happening while it’s being held. A leak or spill that occurs at the end of the holding period is likely to cause just as much damage as one early on. Make sure all frac pits that are built to hold waste that will eventually go to deep injection disposal, are properly lined to keep the waste right where you need it until it’s time.
Solid Waste Disposal
Almost all treatment and disposal methods for produced water will leave behind a sizeable amount of solid waste. This material is usually concentrated in some of the worst risk factors as well, including radioactive materials and abrasive particles. It can cause issues when allowed to remain suspended in slurries intended for well disposal, so it’s usually removed through desanding and dewatering procedures. Once it’s condensed and separated from as much liquid as possible, it’s generally disposed of in a solid waste landfill. Yet, not just any landfill can accept materials that are potentially as hazardous as these sands and particles. Check into the accessibility of hazardous solid waste dumps in the area around the fracking site before deciding on this route. It may be necessary to water down the slurry rather than trying to separate solids from liquids if there’s nowhere to dispose of separate solids. A thinned mixture can prevent clogging during injection while allowing most or all of the suspended solids to be disposed of that way.
Frac pits are often only needed for a year or less, so they must be built with access in mind for the final draining and dredging. The liner still can’t rip or tear as heavy equipment and pumps are brought in to clean up the pit. This would create contamination issues just as much as a leak that occurs earlier in the process. Make sure you choose a liner that can handle every stage of produced water storage, from the first shock of adding in a heavy slurry full of solids to the final steps of removing the last bits of waste. BTL Liners has the RPE products you need to keep all types of frac pits securely lined. Slipping, tearing, and hydrocarbon reactivity are no longer an issue with our liners on your side.
