Coal Bed Methane Aquatic Influences
Coal bed methane is a form of natural gas extracted from coal beds. In recent decades it has become an important source of energy in United States, Canada, and other countries. The term refers to methane adsorbed into the solid matrix of the coal. It is called sweet gas because of its lack of hydrogen sulfide. The presence of this gas is well known from its occurrence in underground coal mining, where it presents a serious safety risk for miners. Water from coal-bed natural gas production may contain sodium bicarbonate at concentrations that can harm aquatic life, according to a new study by the U.S. Geological Survey and US EPA. An increase in the production of coal-bed natural gas has occurred throughout the nation. The results of this aquatic study may help resource managers achieve a balance between beneficial use of water resources (such as irrigation) and the protection of aquatic life throughout the nation and abroad. The study area included the Tongue and Powder Rivers in Montana and Wyoming, where several types of experiments and assessments were used for 13 aquatic species.
Coal bed methane is currently expanding in the Powder River Basin of northeast Wyoming and southeast Montana. Seven percent of the natural gas (methane) currently produced in the United States comes from such extraction. Methane from coal bed reservoirs can be recovered economically, but disposal of water is a potential environmental concern.
Sodium bicarbonate, which is also celled baking soda, is a commonly used chemical that people and animals are often exposed to in food and household products. So it is not considered highly toxic. However, it is a simple salt and enough salt to make fresh water salty water which can be harmful to freshwater fish.
The water extracted along with coal-bed natural gas is called produced water. Produced water is a by-product of the coal-bed natural gas extraction. Companies may dispose of produced water in several ways— discharging it directly into watersheds; treating and then discharging it; injecting it into deep wells; discharging it to drip irrigation systems; or capturing it in evaporation ponds. Produced water is not the same as water injected during hydraulic fracturing.
The aquatic species tested had difficulty surviving in waters in which sodium bicarbonate was found at levels from about 1,120 to greater than 8,000 milligrams (mg) of sodium bicarbonate per liter. Results varied across species and depended upon the age of the organism. Chronic toxicity was observed at concentrations that ranged from 450 to 800mg of sodium bicarbonate per liter. The specific concentration depended on the sensitivity of the four species of invertebrates and fish exposed. The Tongue River, for example, has a natural baseline of approximately 280mg of sodium bicarbonate per liter.
Deionization treatment practices employed in the Tongue and Powder River watersheds appear to reduce the concentrations of sodium bicarbonate and reduce the toxicity of untreated effluent water. Areas with concentrations likely to cause significant mortality in the Tongue and Powder River Basins appear to be limited to tributaries and parts of mixing zones with considerable additions of untreated discharge.
Conventional and unconventional (including hydraulic fracturing) oil and gas extraction practices often result in large volumes of produced water that contain elevated salts and dissolved solids from naturally occurring sources. The addition of sulfates and bicarbonates to surface waters may also result from the disturbances associated with mountain top removal mining. The current data can also be used to separate effects of saline discharges from those potentially posed by other constituents.
For further information see Sodium Bicarbonate.
Natural Gas image via Wikipedia.