Let’s step away from agriculture for a moment to have a look at energy. But really, if you’re doing your homework, you know that industrial agriculture does not solely rely on energy from the sun to power photosynthesis, rather it is heavily dependent on fossil fuels for machinery, fertilizer, biocides, seeds, etc.
For example, methane (the main constituent of natural gas) is used in the Haber-Bosch process for synthesizing nitrogen fertilizer, consuming about 3-5% of the world’s natural gas production . These days, you can’t get away with talking about natural gas production without talking about hydraulic fracturing (or “fracking”) and horizontal drilling (see illustration above). And since my roots are in western Pennsylvania, I’ve been following how fracking the Marcellus Shale has transformed the landscape and the economy in that area. Here I’ve summarized a publication from this past February in the journal Water Resources Research by Brian Lutz, Ph.D. and others. The major finding was (spoiler alert!) that fracking produces much less wastewater per unit energy than conventional natural gas drilling .
Wastewater treatment and storage is one of the leading environmental and human health concerns over fracking. There are three main pools of wastewater generated. First, “flowback” refers to frac fluids that have returned to the surface. Frac fluids are water mixed with various chemicals (including health and environmental toxins) to aid in the fracturing process. Second, “drilling fluid” is the water plus other additives to cool and lubricate the drill head. Finally, “brine” refers to the naturally occurring subsurface water that is brought to the surface as a byproduct of the drilling process. Typically this water is highly saline, hence the name, and can be even more toxic than the flowback, often containing high concentrations of metals, organic compounds and sometimes radioactive materials–all of which are naturally occurring and not contaminated as a result of the drilling process. Fracking wastewater is approximately 45% brine, 43% flowback, and 12% drilling fluid while conventional wastewater is approximately 87% brine, 8% plowback, and 5% drilling fluid.
What to do with this wastewater once it has reached the surface? Conventional natural gas drilling typically occurs in regions where the geology allows for the wastewater to be reinjected into deep geologic formations, essentially avoiding any need to treat the water or posing a threat to human or environmental well-being. However, the Marcellus Shale’s geology is such that reinjection is not possible. So dealing with wastewater from natural gas production is relatively new and legislation has evolved alongside the practice. Disposal of the wastewater has transitioned from municipal water treatment facilities (peaked in 2008 and is still the main mode of disposal for conventional well wastewater), to industrial water treatment (peaked in 2009 and 2010), to current efforts to reinject or recycle the wastewater. As lawmakers recognized that municipal facilities were not suited for dealing with such high total dissolved solids (TDS), industrial facilities were sought for processing the wastewater. However even industrial treatment facilities are incapable of removing the majority of ions that contribute to the high TDS wastewater. So the surface water neighboring the industrial treatment facility receives high TDS loads from the “treated” wastewater. Notably, most industrial wastewater treatment facilities in Pennsylvania are located in the Ohio River basin, so between 2009 and 2011 fracking well operators in eastern PA (Delaware or Susquehanna River basins) seeking industrial treatment facilities sent nearly 50% of their wastewater west to the Ohio River basin.
Guidelines constraining municipal and industrial treatment of the fracking wastewater increased demand for underground injection disposal since 2011. Due to the underlying geology of this region, there are only 7 commercial injection wells in Pennsylvania, 3 in West Virginia, and 184 in Ohio. In order to transport the wastewater to the injection wells, big rig trucks haul the wastewater sometimes hundreds of miles, mainly to Ohio. Since Ohio has recently experienced earthquakes believed to be associated with the wastewater injections, there is likely to be new regulations limiting injection disposal. Recycling wastewater makes some sense but has a limited capacity in that it depends on the installation of new wells to make use of the recycled wastewater.
This seems like a lot of trouble dealing with this wastewater, how is it economically feasible? According to Lutz and his co-auth0rs, “The average Marcellus well produced only approximately 35% of the amount of wastewater per unit gas recovered when compared to conventional wells.” In other words, conventional drilling produces about 13.4 liters of wastewater per million Btu gas energy while fracking produces only 4.8 liters of wastewater per million Btu gas energy. The authors continue, “However, Marcellus wells collectively generated approximately 570% more wastewater in 2011 than conventional wells.” This massive generation of wastewater is the result of dramatic increases in number of fracked wells and the lucrative amount of gas recovered from each well despite fracked wells’ greater efficiency in wastewater production over conventional wells.
While fracking appears to be wastewater intensive, this is a product of the size of the Marcellus Shale and not the method of drilling. Only ~1% of the Marcellus Shale has been explored, so the arms’ race between fracking technology and environmental regulation will continue to play out for years to come.
 pdf file of the original article: Lutz et al 2013 Water Resources Research. Generation, transport, and disposal of wastewater associated with Marcellus Shale gas development