According to reports from the US Energy Information Administration, natural gas production is at an all-time high. Unfortunately, this has led to enormous amounts of salty wastewater called brine or produced water. The fracking industry has improved its efficiency by increasing the size of horizontal wells, but this means more water is used to fracture the rock. On average, the process uses about 45 million liters of water per well, and much of that water is released from the ground with a much different chemistry. Dissolution of the underlying rock deposits salt into the water, and radioactive substances as well as chemicals added during the fracking process are also typically found.
An estimated 3,400 billion liters of produced water is extracted each year, and the EPA predicts that number will continue to increase along with an increase in natural gas production. The discharge of produced water to surface water and treatment plants is currently prohibited, however there is one exception: fracking companies may discharge produced water west of the 98th meridian if the water quality is acceptable for agriculture or wildlife and is specifically focused on programs for both. The problem is, no one really knows what “acceptable” actually means.
Disposing of produced water is usually done by injecting it into deep underground wells, but not all areas of the US consists of a geology that allows it, and serious concerns about seismic activity has the industry scrambling for new solutions. More and more, produced water is being reused, in particular when the water is less salty and suitable for crop irrigation or livestock. However, the EPA is considering giving the fracking industry more options to discharge and manage produced water. Still, major concerns exist about the lack of data on its chemical composition. Studies have shown that the most common elements found include sodium, magnesium, calcium, strontium, and barium, as well as metals manganese, iron, aluminum, arsenic, and selenium. Unfortunately, predicting how much of each is present is difficult because of the varying concentrations.
What we do know is that produced water is highly saline. Total dissolved solids (TDS) in produced water are mostly inorganic salts from the dissolution of fractured rocks. Also heavily prevalent are radionuclides 226Ra and 228Ram with the combined radium concentration correlating with the concentration of TDS. Over time, these concentrations decrease, but that can take many years. Membrane treatment, such as reverse osmosis, can be very effective in removing the salts and radioactive substances, but researchers and natural gas companies continue to seek fresh and creative ways to use produced water.
Potential beneficial uses can include fire protection, dust suppression, preservation of environmental and aesthetic values but each depends on federal and state jurisdiction, and the circumstances of each case. By far the most common application for reusing produced water is for injection into oil-producing formations to enhance oil production. About 45% of all produced water is reused for this purpose, but other applications continue to surface. Treated produced water from coalbed methane wells are used to restore overgrazed rangeland. Treated produced water in Colorado is being used for an aquifer storage and recovery project. Some states even allow municipalities to spread some of the more highly saline water on roads for winter ice control.
While new uses for produced water are generated on a consistent basis and could eventually prove to have strong economic value, complex water rights laws and regulations highlight liability and continue to vary nationwide.