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Disinfection Byproducts from Treatment of Produced Waters
Questions and Answers

1. Why did USGS conduct this study?

The U.S. Geological Survey (USGS) provides information on the quality of our environment; identifies emerging environmental issues; and provides information to aid decisionmaking by regulators, policymakers, industry, and the public. The inadvertent formation of harmful disinfection byproducts (DBPs) during the treatment of drinking water and wastewater is an important environmental health concern. Information on the sources and factors that affect formation of DBPs can help reduce their formation and mitigate potential adverse impacts on environmental health. We initiated this specific study because fluids produced as a byproduct of oil and gas production can have elevated levels of bromide, which may affect the formation of brominated DBPs.

2. What did USGS do in this study?

The USGS sampled stream waters upstream and downstream of the outfall of Publicly Owned Wastewater Treatment Works (POTWs), POTWs that receive and treat waters produced by conventional and unconventional oil and gas development, and commercial treatment plants that treat similar produced waters. The samples were analyzed for a range of DBPs and selected precursors. The study was designed to determine if produced waters resulted in elevated levels of DBPs in the streams to which the treated wastewaters were discharged.

3. What did USGS find?

The results of this study indicate that significantly higher concentrations of brominated DBPs in effluents that are discharged from commercial or publicly owned wastewater treatment plants that treat produced waters than in the effluents from POTWs that do not treat produced waters. The evidence strongly indicates that naturally high bromide levels in the produced waters react with other chemicals when the water is disinfected and these reactions form high levels of the brominated DBPs. This is the first time it has been shown that these activities contribute DBPs to streams where the wastewaters are discharged.

4. What is the significance of these findings?

The knowledge that wastewaters with elevated levels of bromide, when treated, can produce the levels of disinfection byproducts observed in this study, enables evaluation of specific treatment and disinfection alternatives after consideration of the chemistry of the wastewater to be treated, thereby reducing the risk of formation of toxic disinfection byproducts.

5. What does this mean for fish and aquatic life?

This study did not assess the ecological impacts of the DBPs detected in the streams. The brominated disinfection byproducts observed in this study, however, are known to be toxic.

6. Were these toxic compounds found in the streams due to hydraulic fracturing?

It was not possible to discern the specific origins of the produced waters entering the wastewater treatment plants studied. The produced waters originate from both conventional oil and gas development and unconventional oil and gas development. Fluids produced in unconventional oil and gas development include those produced in the hydraulic fracturing process.

7. Did these toxic compounds exceed standards in federal or state water pollution laws?

There are drinking water standards for some DBPs in public drinking water systems. However, the water studied here was not drinking water and currently there are no aquatic life benchmarks or other standards for DBPs in environmental water.

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Hladik, M.L., Focazio, M.J. and Engle, M., 2014. Discharges of produced waters from oil and gas extraction via wastewater treatment plants are sources of disinfection by-products to receiving streams: Science of the Total Environment, v. 466-467, p. 1085-1093, doi:10.1016/j.scitotenv.2013.08.008.

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