While some particularly caustic or contaminated brines can only be stored in deep wells or must go through multiple treatments, most of these liquids are safely stored in open and relatively simple brine ponds. Still, sizes, depths, volumes, and length of use will vary according to their specific mission.
Pond Profile
Brine ponds built for mineral harvesting focus on consistently high evaporation rates. Since only the layer of water exposed to the air can evaporate, this kind of pond will have a relatively shallow profile and large surface area. In contrast, storage ponds are intended to reduce evaporative loss, and are designed to be relatively deep, with a much smaller surface area to minimize opportunity for evaporation. The profile (surface area x average depth) will also determine your pond’s capacity. These factors may need to be adjusted when the evaporation rate is calculated, depending on the volume of brine you’ll be handling.
Evaporation Rate
While evaporation rates can vary over the course of a day, a week or a month, the average rate at which liquid is reduced can be estimated according to the pond design, local weather patterns, and the properties of a specific brine. This helps operators estimate the amount of time a batch of brine will require to remove the maximum volume of water. Evaporation rates drop as brine becomes more concentrated, so the rate of reduction is not linear.
To produce specific forecasts for your project, you’ll need to collect accurate information about the surface area, daily solar radiation, average wind speed, and chemical composition of the brine to be processed. Preliminary designs can be based on commonly used values, then adjusted once more precise data has been collected. Your state EPA is a good resource for accurate information on environmental data. You may also be able to consider designs for existing brine ponds in your area for comparison.
Wind
Aside from the profile, volume, and evaporation rates of your pond, other weather factors need to be considered in a brine pond design. Strong winds can generate waves that may send thousands of gallons of brine pouring out of the containment area. Failure to factor in the highest possible wind speeds in the area has led to numerous pond bank and berm collapses. This kind of failure can create major spills, expensive remediation processes, and even significant reputational damage for the companies and individuals involved. Evaporative ponds built with an excess capacity of 10 to 20 percent can manage most instances of wave disruption. Storage ponds benefit from the installation of a floating cover, which can eliminate dangerous wave action.
Precipitation
Precipitation can be a problem in any kind of brine pond. Simple precipitation directly entering an evaporation pond shouldn’t be a major problem. If rainfall is typically heavy in the area, the pond’s profile could be adjusted to increase surface area and increase evaporation rates. When considering the impact of direct precipitation, be sure to analyze the average amount of rainfall both over the year and in individual storm events over at least the most recent 25 years. Using this data when finalizing your design helps ensure your ponds will hold even during years with record-breaking storms. These periodic spikes in precipitation significantly increase the risk of flooding or containment breaches but aren’t discoverable in a simple annual rainfall figure.
If your pond will contain particularly hazardous brine (for example, if it requires double lining), you’ll probably need to establish secondary spill containment above ground as well. Typically, a fully lined system of secondary berms and dikes surrounding the pond is sufficient to ensure that even a record-breaking storm won’t trigger a disastrous breach. It’s important not to neglect these safety measures even if you don’t expect to ever use them. A single failure can cost millions and mark the end of a successful company, not to mention catastrophic effects on the local environment.
Liners
All brine ponds must be lined to prevent seepage into the underlying soil and groundwater contamination. This is a complex topic which will be addressed in detail in a later chapter.
