Brine ponds tend to fall into one of the following general categories, each of which have unique design and maintenance needs.
Salt Harvesting
Underground salt deposits and seawater are mined all over the world and millions of tons of salt are still being produced using evaporative ponds. This salt is produced for purposes ranging from food-safe sea salt to industrial purposes like road deicing and manufacturing. Natural sea brine contains about 3.5 percent salt by weight, making it an efficient source of ready-to-use sodium chloride. Harvesting salt from seawater is a relatively straightforward process of slowly evaporating the water until only salt crystals are left behind. Lined brine ponds protect the surrounding soil and waterways from the damages of salinization.
It’s estimated that there are over 20,000 desalination plants currently operating worldwide, with many more to open in coming years. Desalination plants can use different techniques for extracting fresh water, but there will always be some amount of highly concentrated brine that remains. In many areas of the world, this highly caustic brine is simply released back into the ocean, where it can cause serious damage to marine ecosystems before it eventually has a chance to dissipate. Brine evaporation ponds are a significantly better treatment choice since the salt itself is a valuable resource and risks much less environmental damage.
Processing/Storing Natural Gas Produced Water
Natural gas may be extracted from the earth in its gaseous form, but it’s much easier to store as a liquid, where it takes up substantially less space. One of the most common places to store liquified natural gas (LNG) is in naturally occurring underground salt caverns, since the crystalized salt presents an impermeable barrier to liquids.
Not all salt caverns are large, and operators can significantly expand a cavern’s capacity by flushing it with high pressure water to dissolve the crystalline salt, which is then drawn out to be replaced by LNG. The briny water must be removed and can either be reused for future cavern expansions or processed for mineral harvesting. In either case, brine ponds are the safest and least expensive solution.
LNG is generally stored on a seasonal basis and withdrawn during winter when consumer demand is highest. Brine is injected into the storage caverns, which in turn pushes the LNG out for collection. In between uses, the brine is stored in securely lined ponds to prevent leaks, seepage and contamination of nearby aquifers. These ponds are usually double lined, with moisture monitoring equipment so that even tiny leaks through the primary membrane can be detected and repaired before the brine has a chance to even reach the secondary membrane.
Fracking
Fracking is the term commonly used today to refer to hydraulic fracturing, a method for extracting natural gas and oil from underground deposits that are too “tight” to access using traditional oil wells. In this process, high pressure liquid is injected underground to fracture nearby bedrock and open fissures through which oil and gas can flow. This liquid has several ingredients but is largely composed of concentrated brine. Millions of gallons of this water is returned from the well and is now called produced water. This produced water includes hazardous contaminants picked up from the underground deposits,
Oil and gas companies will usually re-use produced water to minimize the expense of creating new batches of fracking liquid with expensive fresh water and chemicals. After several uses, though, the brine becomes too concentrated and contaminated to be suitable.
Over the history of oil and gas mining, produced water has been handled in a variety of ways, but as environmental protections have been enforced, it is clear that brine ponds are the best alternative for storing hazardous brine for re-use.
Storage for Other Uses
If a brine pond isn’t used for processing wastewater in situations like those we’ve described, they’re generally intended for long-term storage. The brine may be intended for industrial reuse, seasonal spraying on roads for deicing and in some cases, even for irrigation.
Agricultural Use
In places where soil appears to be naturally saline and unsuited to agriculture, the cause may be traced to a shallow water table filled with brine. In some situations, that water can be pumped out and stored in a pond, allowing fresh water to flow in from nearby aquifers, and freeing up that land for agriculture. The stored brine can be purified for use as irrigation water, evaporated or even repurposed for fracking or LNG storage.
Disposal
Brine ponds are useful even for wastewater that’s ultimately unusable - where it has extremely high concentrations of salt, or the precipitates themselves aren’t valuable. Ultimately, it’s both safer and cheaper to dispose of this kind of waste in sludge or powder form, which is lighter and more compact.
Reject brine from inland desalination plants, especially in sunny arid regions, is a very good candidate for evaporation ponds. In coastal locations where suitable conditions exist for evaporative ponds, they are much preferable to ocean dumping, deep well injection, or other environmentally hazardous options.
