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