Water from coalbed natural gas production may contain sodium bicarbonate salts at concentrations that can harm or kill fish and other aquatic life, according to a new federal and state study released Thursday.
The aquatic species tested had difficulty surviving in waters in which sodium bicarbonate (NaHCO3) was found at levels ranging from 1,120 to greater than 8,000 milligrams (mg) of NaHCO3 per liter, said the study by the U.S. Geological Survey, Interior Department's Bureau of Land Management, Environmental Protection Agency and Montana Fish, Wildlife and Parks. It said results varied across species and depended upon the age of the organism.
Chronic toxicity -- damage due to repeated or long-term exposure of NaHCO3 -- was observed at concentrations that ranged from 450 to 800 mg, according to the study. It said the Tongue River has a natural baseline of approximately 280 mg of NaHCO3.
Salts such as NaHCO3 are found naturally in the water along the coalbed gas seams, but when excessive amounts of this water are discharged into freshwater streams and rivers, the results can adversely affect the ability of fish and aquatic organisms to survive, the study said.
The study focused on NaHCO3 concentrations from the Tongue and Powder Rivers, both of which are tributaries of the Yellowstone River in Montana and Wyoming. The study said that NaHCO3 was found to be a major constituent of coalbed gas-produced waters in the two rivers.
The study results may apply to other watersheds where NaHCO3 is a principle component of produced water, either from coalbed gas or from traditional or unconventional oil and gas development, the agencies said. Produced water is a by-product of coalbed 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 study noted.
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