Background Readings

Water Quality: Wastewater Disposal and Total Dissolved Solids (TDS)


This truck is carrying flowback water from the hydraulic
fracturing operation to a wastewater treatment site.
Photo Credit: Chief Oil and Gas.



During the fracturing process, a large volume of water is injected into the well under high pressure. Only about 10% of the water is returned to the surface after drilling is completed; the rest remains in the formation underground. Also known as flowback, this return water is classified as wastewater, because it contains trace amounts of additives from the fracturing process, as well as other solids, minerals, salts, and organic materials that dissolve from the bedrock. If flowback water accidentally spills into a stream or river, it may affect the water quality. The resulting increases in salinity (salt concentration in water, measured in parts per thousand) and total dissolved solids (the amount of dissolved matter in a water sample, including salt) can harm fish, mussels, and other aquatic life.

In recent years, while some of the flowback water was recycled, the majority of was disposed of in an “environmentally safe” manner, primarily through wastewater treatment or underground injection. Few treatment plants in Pennsylvania had the capacity to process such a large amount of wastewater and their ability to remove all of the total dissolved solids (TDS) from flowback water had not been proven. “In particular, salts and other dissolved solids in brines are not usually removed successfully by wastewater treatment, and reports of high salinity in some Appalachian rivers have been linked to the disposal of Marcellus Shale brines” (Soeder and Kappel, 2009).

In the spring of 2011, following reports of high levels of bromides and dissolved solids in public drinking waters, the Pennsylvania Department of Environmental Protection (PA DEP) asked the gas industry to stop discharging any flowback water to state waters or wastewater treatment facilities. Most of the flowback water in PA is now being recycled; one of the gas companies actively drilling in the region reported that their re-use rate increased from a mere 3% to 97% in 2011 (Jason de Wolfe, pers. comm.). Surrounding states have not followed PA’s lead on wastewater disposal regulations.

Is the concentration of total dissolved solids in flowback wastewater high enough to harm aquatic life? What effect might an increased concentration of total dissolved solids have on the water quality and biodiversity in the Susquehanna watershed? What about downstream in the Chesapeake Bay?

Background Reading: (Each reading opens a separate window.)

  1. PA Regulations Create Tech Puzzle for R&D, by Eric Lidji, for Greening of
  2. , May 25, 2010
  3. “Pennsylvania DEP calls on Natural Gas Drillers to Stop Giving Treatment Facilities Wastewater” PR Newswire, April 19, 2011.
  4. “Pa: Marcellus Wastewater Shouldn’t Go To Treatment Plants” by Don Hopey and Sean D. Hamill, Pittsburgh Post-Gazette, April 19, 2011.
  5. Marcellus Wastewater Issues in Pennsylvania- Current and Emerging Treatment and Disposal Technologies, Fact Sheet, Penn State Extension, April 2011.
  6. Tough New Standards to Protect PA Waterways from Drilling Wastewater Takes Major Step Forward, PR Newswire, May 17, 2010.
  7. “Impact on Bay Cleanup Not Known”, by David Thompson, Sun Gazette, April 14, 2010
  8. “Scientists Search for the Best Treatment”, by David Thompson, Sun Gazette, February 1, 2010
  9. Shaping Proposed Changes to Pennsylvania’s Total Dissolved Solids Standard, Pennsylvania State University.
  10. , 2010.
  11. A Fluid Situation from Energy In-Depth
  12. “Sudden Death of Ecosystem Ravages Long Creek”, Don Hopey, Pittsburgh Post-Gazette, Sept 20, 2009
  13. Pennsylvania DEP Investigates Elevated TDS in the Monongahela River, Water and Wastes Digest, October 27, 2008.
  14. PA DEP Secretary: New Wastewater Treatment Standards for TDS Now in Effect, Enforceable Water and Wastes Digest, August 30, 2010.


Discussion Questions:

  1. The figure to the right shows how changes in salinity affect the diversity of species in the aquatic environment. As salinity increases, the number of freshwater species decreases rapidly. What happens to the diversity of freshwater species when the salinity increases above 5 parts per thousand?

  2. If salty brine from the hydraulic fracturing process accidentally flows into a stream or river near a drilling site, what impact might this have on aquatic biodiversity in the stream? Consider aquatic species that are common and/or rare in the Susquehanna watershed, or native vs. invasive. Also consider the differences between species that are sessile (attached to the bottom) such as clams and mussels vs. species that can move freely upstream or downstream.

  3. What technologies can be used to help reduce the amount of total dissolved solids returned to the Susquehanna River basin from flowback water?