A few weeks ago, fellow SINner Avante Garde published an article with claims that fracking is not that bad a thing. This was in response to me fussing at the Texas GOP leadership for telling US cities and counties that they could not ban fracking anymore.
I think we have good and strong evidence to put those myths to sleep once and for all, but may be I’m wrong and it would be nice if he could tell me why he thinks what he thinks.
Well, I disagree. I think that the evidence holds that fracking is bad. The article that he links to there is this one: Jackson, R. et al. The Environmental Costs and Benefits of Fracking. Annu. Rev. Environ. Resourc. 39, 327–362 (2014). That link is to the PDF.
To put it mildly, I think that this particular article is incorrect, at best. At worst, it’s a deliberate misrepresentation of the the facts and the references there-in. I do not think that the cited article supports the claim that fracking is not harmful. This is an exceptionally long, detailed, and researched post, so be warned.
Now, please understand, that this is not intended to be a condemnation of natural gas. While I loathe fossil fuels as only someone who grew up next to a refinery can, I understand that natural gas is better for the environment than coal. That is roughly equivalent to my preference HIV over ebola. Neither is good, but there is certainly one I would prefer catching over the other. I’ve talked a lot about renewables and my preferences should be quite obvious to any frequent reader.
Fracking, however, is not a fossil fuel. It is a method of obtaining said fossil fuels by what is called hydraulic fracturing. In the most basic sense, a hydraulic fluid with additives is pumped into wells at very high pressure. This cracks the rocks deep in the well, allowing fossil fuels (usually light oil and natural gas) to flow more freely.
This takes a tremendous amount of water and is the first discussion point in the paper.
Hydraulic fracturing and horizontal drilling require considerable water. A lateral from a single well might be drilled 1–3 km sideways (see above) and divided into 20 or so ∼100-m-long stages. Across many plays (37), including the Barnett, Marcellus, and Fayetteville Shales, hydraulic fracturing typically requires 8,000 to 80,000 m3 (2 to 20 million gallons) of water for a single well (Table 1). An additional 25% of water use is typically associated with drilling, extraction, and sand or proppant mining (20); in Table 1 we use a more conservative estimate of 1,900 m3 (500,000 gallons) per well for these processes to account for different practices, such as whether air drilling is used. (my emphasis)
In short, a well shaft is drilled. That shaft, which can be kilometers long, is pumped full of fluid (which is water mixed with stuff) at high pressure until the rock breaks. This article seems to accurately report the amount of water used for these operations with the knowledge that, especially for Texas, such reports are frequently not required and are industry reported. But then, inexplicably, the authors only assume one quarter of those values at the low end and less than 2% at the high end. Huh?
Let give an example. The Barnett Shale in Texas has over 14,000 wells drilled into it. According to the referenced article (20: Nicot, J.-P. P. & Scanlon, B. R. Water use for Shale-gas production in Texas, U.S.Environ. Sci. Technol. 46, 3580–6 (2012).) the Barnett Shale, from 2000 to 2011, had consumed some 38,300,000,000 gallons of water. Which is roughly what is shown in the Table 1 referenced in the quote.
Across Texas, for instance, the amount of water used for hydraulic fracturing yearly is ≤1% of total water use (20).
I have no idea why this comment is in this article, except to provide some kind of comment for a pro-fracking person to use in a discussion. It’s a meaningless point. IF we could transport trillions of gallons of water all over the state, then, perhaps it would be a valid statistic. However, as the recent weather events of Texas have shown, we can’t move that kind of water.
This is important, because shale oil fracturing operations are very localized in space. In spite of the huge number of wells and the vast distances a well can cover horizontally, it’s still a very local phenomenon. For example, that Barnett shale only covers some 48,000 square kilometers. The entire North Texas metro area (Dallas, Fort Worth, Denton) sits on top of this with one of the highest populations in the United States (4th in metro areas).
The Jackson et. al paper fails to mention some of the other stats listed by the Nicot paper they reference. Annual water use for the Barnett shale is about 9% of the water use for the city of Dallas (population 1.3 million).
Water use for shale gas is <1% of statewide water withdrawals; however, local impacts vary with water availability and competing demands. Projections of cumulative net water use during the next 50 years in all shale plays total ∼4350 Mm3 [ed. 1,100,000,000,000,000 gallons, that a million billion], peaking at 145 Mm3 in the mid-2020s and decreasing to 23 Mm3 in 2060. Current freshwater use may shift to brackish water to reduce competition with other users.
Now, we need to be clear about something here. Every single one of these estimates of water usage, is just that, an estimate. Texas has an unbelievable hodgepodge of environmental agencies, most with little or not enforcement powers, and a deep cultural history of promoting fossil fuel production over all other factors ( Rahm, D. Regulating hydraulic fracturing in shale gas plays: The case of Texas. Energy Policy 39, 2974–2981 (2011). ).
For example, it is up to the individual counties to monitor and/or permit water use for fracking purposes.
Interpretation of the law “depends on which lawyer you talk to,” said Slate Williams, general manager of the Crockett County Groundwater Conservation District in West Texas. His district does not require a permit for water wells used for fracking. It does ask drillers to report the amount of water they withdraw monthly.
“They don’t always do that, but it’s something we ask,” Williams said.
The confusion among groundwater districts stems from a provision in the Texas water codethat states that a groundwater district cannot require a permit if the well is drilled to supply water for a rig doing “drilling or exploration operations” for an oil or gas well. (source: Texas Tribune)
In other words, there are counties like Dimmit County, TX, where drillers can use as much water as they want, no reporting required and no questions asked.
This is by no means unusual.
States are primarily responsible for regulating fracking activities, as fracking is exempt from most federal laws targeted toward environmental protection, such as the Clean Water Act, National Environmental Policy Act, and the Safe Drinking Water Act. However, Michigan laws also largely exempt fracking from key water protection statutes, like Michigan’s codification of the Great Lakes Compact. In fact, Michigan’s codification of the Great Lakes Compact under the Natural Resources and Environmental Protection Act of 1994, Great Lakes Preservation section, exempts the oil and gas industry from complying with the requirements of large quantity water withdrawals, including obtaining a water withdrawal permit, stating a withdrawal undertaken as part of an oil and gas activity are exempt withdrawals unless they result in a diversion. Considering that fracking has been occurring in Michigan over the past few decades, and deep horizontal well drilling has been in abundance since 2010, Michigan’s laws and regulations are minimum at best. (Vermont Journal of Environmental Law, my emphasis)
OK, that’s a problem. We don’t actually know how much water fracking activities are using. The producers may not even know. Why would they monitor and keep records for something that they aren’t required to (and might be used in a court later)?
But what about recycling? Surely this water can be recycled and used again or treated and then returned to the environment. Well, many people say that water can be and is being recycled, but I find it exceedingly difficult to verify such claims.
As of mid-2014, the Dallas Morning News reports that
But estimates are that in places like the Eagle Ford and Permian Basin, 10 percent to 20 percent of the water being used now comes from recycling. And that number is expected to at least double over the next decade, said Marcus Gay, a water analyst at research firm IHS who has since left the company.
One former oil.gas consultant started a recycling business, seeing the trend. He said that, now, water might be 20%, but 2 years ago, it was zero. Further, it doesn’t make economic sense for most companies to recycle, not when they can inject the wastewater into deep wells (see a brief discussion on earthquakes below). If water is plentiful in the area, then there’s no economic sense in recycling the water. It’s only when water becomes scarce that it begins to make sense to recycle it. Once it becomes scarce for the drillers, then the non-fossil fuel users of that water are already hurting.
Parts of the Eagle Ford shale (south of San Antonio Texas) are reporting the aquifer has dropped 70 feet in a year. Sure, some is due to agriculture. But some is also due to fracking and oil/gas extraction. And that water, unless heavily treated cannot be reintroduced to the environment (see the discussion on toxic chemicals below). That water is now, for all intents and purposes, gone from our water cycle.
Fracking can be accomplished without water… although some technologies (to me) represent more a problem than using water. For example, propane fracking. Putting a lot of highly compressed, flammable material in a bore hole seems to be fraught with peril and letting the propane gas back out of the hole… But there are some other technologies. But so far, the watchword is “slowly” and in a very conservative industry, it will take lots of time (at billions of gallons of water per year). And there are fewer regulations on these technologies than for water-based fracking (which says a lot).
I’m not dismissing these out of hand. Of course, if water was the only issue (it’s not), then I would say go for it. But, at this point, why invest so much energy in a system that we don’t really need anymore and still isn’t going to fix global warming.
I will also admit that there are some benefits to natural gas. For example, natural gas power plants don’t use water. So, that’s more water available for other uses (like getting the natural gas). But then, solar and wind also don’t require water.
Going back to the Vermont Law statement. Read the first sentence again. Frackng activities are exempt from “most federal laws” for environmental protection.
The EPA says much the same thing.
While the SDWA [ed. Safe Drinking Water Act] specifically excludes hydraulic fracturing from UIC [ed. Underground Injection Control] regulation under SDWA § 1421 (d)(1), the use of diesel fuel during hydraulic fracturing is still regulated by the UIC program. Any service company that performs hydraulic fracturing using diesel fuel must receive prior authorization through the applicable UIC program.
It’s interesting that diesel fuel is specifically mentioned here. Since the industry has assured us that diesel fuel is not used in fracking and that the chemicals (many of which are “trade secrets” and have not been disclosed to anyone). But diesel fuel is definitely not to be used without a permit (key phrase there).
Between 2005 and 2009, 12 of the 14 companies used 32.2 million gallons of diesel fuel or fluids containing diesel fuel.[14] BJ Services used the most diesel fuel and fluids containing diesel, more than 11.5 million gallons, followed by Halliburton, which used 7.2 million gallons. Four other companies, RPC (4.3 million gallons), Sanjel (3.6 million gallons), Weatherford (2.1 million gallons), and Key Energy Services (1.6 million gallons), used more than one million gallons of diesel fuel and fluids containing diesel.
These 12 companies injected these diesel-containing fluids in 19 states. Diesel-containing fluids were used most frequently in Texas, which accounted for half of the total volume injected, 16 million gallons. The companies injected at least one million gallons of diesel-containing fluids in Oklahoma (3.3 million gallons), North Dakota (3.1 million gallons), Louisiana (2.9 million gallons), Wyoming (2.9 million gallons), and Colorado (1.3 million gallons).
Tables 1 and 2, which are attached to this letter, list the companies that reported using diesel-containing fluids and the states in which they injected them.
Diesel fuel was a significant component of the diesel-containing fluids these companies injected. The companies used 10.2 million gallons of straight diesel fuel and 21.8 million gallons of products containing at least 30% diesel fuel. (US House Committee on Energy and Commerce open letter to the EPA)
Let’s investigate some of the reports of what these fracking chemicals can do:
- Lesions, heavy metal intake, and acid stress in an endangered fish after fracking chemical spill.
- “The scientists presenting the work today at the 248th National Meeting & Exposition of the American Chemical Society (ACS) say that out of nearly 200 commonly used compounds, there’s very little known about the potential health risks of about one-third, and eight are toxic to mammals.”
- “Of the 24 U.S. states with active shale gas reservoirs, only five maintain public records of spills and accidents.”
- The authors reviewed chemical disclosure statements for 150 wells in three top gas-producing states and found that, on average, two out of three wells were fractured with at least one undisclosed chemical. ( Souther, S. et al. Biotic impacts of energy development from shale: research priorities and knowledge gaps. Frontiers in Ecology and the Environment 12, (2014).)
- Water samples, 89%, 41%, 12%, and 46% exhibited estrogenic, antiestrogenic, androgenic, and antiandrogenic activities, respectively. Testing of a subset of natural gas drilling chemicals revealed novel antiestrogenic, novel antiandrogenic, and limited estrogenic activities. ( Kassotis, C., Tillitt, D., Davis, J., Hormann, A. & Nagel, S. Estrogen and Androgen Receptor Activities of Hydraulic Fracturing Chemicals and Surface and Ground Water in a Drilling-Dense Region. Endocrinology 155, 897907 (2014).)
- A literature search of 632 chemicals (from 944 products) resulted in 353 chemicals identified by Chemical Abstract Service (CAS) numbers. More than 75% of the chemicals could affect the skin, eyes, and other sensory organs, and the respiratory and gastrointestinal systems. Approximately 40-50% could affec the brain/nervous system, immune and cardiovascular systems and the kidneys; 37% could affect the endocrine system; and 25% could cause cancer and mutations. ( Colborn, T., Kwiatkowski, C., Shuitz, K. & Bachran, M. Natural Gas Operations from a Public Health Perspective. Human and Ecological Risk Assessment 17, 1039–1056 (2011).)
Now, we should talk about ground water contamination. The Marcellus Shale has been studied and the suggestion is that deep well injection chemicals have found their way to the surface.
We present geochemical evidence from northeastern Pennsylvania showing that pathways, unrelated to recent drilling activities, exist in some locations between deep underlying formations and shallow drinking water aquifers. Integration of chemical data (Br, Cl, Na, Ba, Sr, and Li) and isotopic ratios (87Sr∕86Sr, 2H∕H, 18O∕16O, and 228Ra∕226Ra) from this and previous studies in 426 shallow groundwater samples and 83 northern Appalachian brine samples suggest that mixing rela-
tionships between shallow ground water and a deep formation brine causes groundwater salinization in some locations. The
strong geochemical fingerprint in the salinized (Cl > 20 mg∕L) groundwater sampled from the Alluvium, Catskill, and Lock Haven aquifers suggests possible migration of Marcellus brine through naturally occurring pathways. The occurrences of saline water do not correlate with the location of shale-gas wells and are consistent with reported data before rapid shale-gas development in the region; however, the presence of these fluids suggests conductive pathways and specific geostructural and/or hydrodynamic regimes in northeastern Pennsylvania that are at increased risk for contamination of shallow drinking water resources, particularly by fugitive gases, because of natural hydraulic connections to deeper formations. (Warner, N. et al. Geochemical evidence for possible natural migration of Marcellus Formation brine to shallow aquifers in Pennsylvania. Proceedings of the National Academy of Sciences 109, 11961–11966 (2012).)
And here
We analyzed 141 drinking water wells across the Appalachian Plateaus physiographic province of northeastern Pennsylvania, examining natural gas concentrations and isotopic signatures with proximity to shale gas wells. Methane was detected in 82% of drinking water samples, with average concentrations six times higher for homes <1 km from natural gas wells (P = 0.0006). Ethane was 23 times higher in homes <1 km from gas wells (P = 0.0013); propane was detected in 10 water wells, all within approximately 1 km distance (P = 0.01). Of three factors previously proposed to influence gas concentrations in shallow groundwater (distances to gas wells, valley bottoms, and the Appalachian Structural Front, a proxy for tectonic deformation), distance to gas wells was highly significant for methane concentrations (P = 0.007; multiple regression), whereas distances to valley bottoms and the Appalachian Structural Front were not significant (P = 0.27 and P = 0.11, respectively). Distance to gas wells was also the most significant factor for Pearson and Spearman correlation analyses (P < 0.01). For ethane concentrations, distance to gas wells was the only statistically significant factor (P < 0.005). Isotopic signatures (δ13C-CH4, δ13C-C2H6, and δ2H-CH4), hydrocarbon ratios (methane to ethane and propane), and the ratio of the noble gas 4He to CH4 in groundwater were characteristic of a thermally postmature Marcellus-like source in some cases. Overall, our data suggest that some homeowners living <1 km from gas wells have drinking water contaminated with stray gases. (Jackson, R. et al. Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction.Proceedings of the National Academy of Sciences (2013).)
Some disagree with this interpretation of the data.
Testing of 1701 water wells in northeastern Pennsylvania shows that methane is ubiquitous in groundwater, with higher concentrations observed in valleys vs. upland areas and in association with calcium-sodium-bicarbonate, sodium-bicarbonate, and sodium-chloride rich waters—indicating that, on a regional scale, methane concentrations are best correlated to topographic and hydrogeologic features, rather than shale-gas extraction. In addition, our assessment of isotopic and molecular analyses of hydrocarbon gases in the Dimock Township suggest that gases present in local water wells are most consistent with Middle and Upper Devonian gases sampled in the annular spaces of local gas wells, as opposed to Marcellus Production gas. Combined, these findings suggest that the methane concentrations in Susquehanna County water wells can be explained without the migration of Marcellus shale gas through fractures, an observation that has important implications for understanding the nature of risks associated with shale-gas extraction. (Molofsky, L., Connor, J., Wylie, A., Wagner, T. & Farhat, S. Evaluation of Methane Sources in Groundwater in Northeastern Pennsylvania. Groundwater51, 333–349 (2013).)
Even accounting for methane concentrations coming from non-shale gas rock, this report does nothing to dismiss the first reference showing that material can and does transport between formations. That is drilling water can get into water sources for homes and cities even though fracturing generally only occurs less than 1 kilometer from the drill bore. And while methane is an unhealthy contaminant, there are other studies that support the claim that water sent into bore holes can find its way to drinking water.
We evaluated samples from 100 private drinking water wells using analytical chemistry techniques. Analyses revealed that arsenic, selenium, strontium and total dissolved solids (TDS) exceeded the Environmental Protection Agency’s Drinking Water Maximum Contaminant Limit (MCL) in some samples from private water wells located within 3 km of active natural gas wells. Lower levels of arsenic, selenium, strontium, and barium were detected at reference sites outside the Barnett Shale region as well as sites within the Barnett Shale region located more than 3 km from active natural gas wells. Methanol and ethanol were also detected in 29% of samples. Samples exceeding MCL levels were randomly distributed within areas of active natural gas extraction, and the spatial patterns in our data suggest that elevated constituent levels could be due to a variety of
factors including mobilization of natural constituents, hydrogeochemical changes from lowering of the water table, or industrial accidents such as faulty gas well casings. ( Fontenot, B. et al. An Evaluation of Water Quality in Private Drinking Water Wells Near Natural Gas Extraction Sites in the Barnett Shale Formation. Environ. Sci. Technol. 47, 10032–10040 (2013).)
This is from the Barnett shale in Texas. And it isn’t talking about easily transported chemicals like methane and saltwater.
The EPA has found similar conditions in Wyoming (large PDF).
A lines of reasoning approach utilized at this site best supports an explanation that inorganic and organic constituents associated with hydraulic fracturing have contaminated ground water at and below the depth
used for domestic water supply.
This report found elevated levels of methane, diesel, benzene, and other hydrocarbons, even in shallow water wells. Further contaminants include potassium and chloride and between 14 and 18 times normal well water levels. Synthetic organic compounds found were Isopropanol, Diethylene glycol, tert-butyl alcohol and a variety of other glycols and alcohols. Also found were toluene, ethylbenzene, gasoline, napthalenes, naptha, etc, etc, etc.
All of these are either known or suspected compounds in fracking. I say suspected because we still have some unknown fracking chemicals due to trade secrets. I’ll quote the report here.
Material Safety Data Sheets do not indicate that fuel or tert-butyl hydroperoxide were used in the Pavillion gas field. However, Material Safety Data Sheets do not contain proprietary information and the chemical ingredients of many additives. The source of tert-butyl alcohol remains unresolved. However, tert-butyl alcohol is not expected to occur naturally in ground water.
The Jackson report mentions both of these cases, but labels them “controversial”.
Although part of the controversy concerns the lack of predrilling data at the site, one aspect is very different from typical practices. Hydraulic fracturing in this tight sandstone formation occurred as shallowly as 322 m, and local drinking-water wells were as deep as 244 m (91). A lack of vertical separation between fracturing and drinking water increases hydraulic connectivity and the likelihood of contamination.
This is very interesting. They label it as controversial because there is no data prior to the wells being developed. So, I’m really curious what the totally natural source for things like isopropanol or gasoline and diesel.
Further, they label them controversial, then admit that the vertical separation between the two is much smaller than the known distances that fracking can propagate.
I know that there is much, much more to this that I could go into detail on. I’ll briefly mention the evidence for earthquakes due to fracking AND deep injection of waste. But Avant Garde says that these are small earthquakes and therefore no big deal. That’s very much a head in the sand approach to this issue.
While it’s true that earthquakes directly due to fracking tend to be smaller (as far as we have seen), the injection induced earthquakes can reach destructive levels. The largest so far being a 5.8 magnitude earthquake in central Oklahoma that destroyed 14 houses and injured two people.
Between 1967 and 2000 there was an average of 27 earthquakes per year larger than magnitude 3. Between 2010 and 2012, the average was 100 earthquakes greater than 3. The states with the greatest increase in seismic activity include Arkansas, Colorado, Texas, Oklahoma, Ohio, New Mexico and Virginia.
Several examples since 2011 highlight the difficulty in determining whether earthquakes were induced by human activity. The Mw 4.0 earthquake on 31 December 2011 in Youngstown, Ohio, appears to have been induced by injection of wastewater in a deep Underground Injection Control (UIC) class II well (12). The Mw 4.7 27 February 2011 central Arkansas earthquake has also been linked to deep injection of wastewater (13). The Mw 4.4 11 September 2011 earthquake near Snyder, Texas, occurred in an oil field where injection for secondary recovery has been inducing earthquakes for years (14). The Mw 4.8 10 October 2011 earthquake near Fashing, Texas, occurred in a region where long-term production of gas has been linked to earthquake activity (15). For others, such as the Mw 5.7 6 November 2011 central Oklahoma earthquake (16) or the Mw 4.9
17 May 2012 east Texas earthquake (17), where active wastewater-injection wells are located near their respective epicenters, the question of natural versus induced remains an active topic of research. ( Ellsworth, W. Injection-Induced Earthquakes. Science 341, 1225942 (2013). )
These are from injection wells, not fracking wells. Injection wells are where the industry is disposing of untreatable (or too expensive to treat) wastewater from both fracking and non-fracking well processes. This water is pumped into deep wells either drilled for the purpose or into empty oil/gas wells. This pumped water can both increase pressure and lubricate movement along faults. There are many faults in the interior of tectonic plates, but they are rarely active (the New Madrid fault in Missouri being a notable exception).
For example, the Barnett Shale in Texas had zero earthquakes for the 25 year period prior to 1998. Since then, there have been 25 earthquakes greater than magnitude 3. That’s the date the production began in the field.
The Jackson report does discuss various induced earthquake types and then notes that, for deep injection, there are 5 steps to reduce their occurrence. So the question becomes, does the industry do these five steps? If so, then we’re still getting earthquakes, then that’s an issue. If the industry isn’t doing those five steps, then that’s a bigger issue.
In conclusion, I am not totally impressed by the reported suggested by Avant Garde as “good and strong” evidence. Honestly, it appears to me to be little more than an attempt to spin the direction of the discussion away from fracking and into areas that aren’t under discussion (like use of water by agriculture and dams also cause earthquakes).
In my opinion, we’re letting the fox totally guard the hen house. Every once in a while, we go out and ask the fox how many chickens we have and sometimes the fox tells us and sometimes he doesn’t. Honestly, I was surprised at the complete and utter level of control the oil/gas industry has. While some states have no trade secret laws (like California), other states (like North Carolina) have made it felony to reveal a trade secret. Even highly environmentally conscious states don’t ask questions about the oil/gas industry.
My research to date has done nothing to resolve my ill-will toward fracking and the oil/gas industry.
My conclusion is that fracking is bad. I will, of course, reserve the right to change my opinion when new evidence and a new regulatory framework comes into existence (probably by magic, because there’s no way our current government is going to do anything about it).
References Cited:
Colborn, T., Kwiatkowski, C., Shuitz, K. & Bachran, M. Natural Gas Operations from a Public Health Perspective. Human and Ecological Risk Assessment 17, 1039–1056 (2011).
Ellsworth, W. Injection-Induced Earthquakes. Science 341, 1225942 (2013).
Fontenot, B. et al. An Evaluation of Water Quality in Private Drinking Water Wells Near Natural Gas Extraction Sites in the Barnett Shale Formation. Environ. Sci. Technol. 47, 10032–10040 (2013).
Jackson, R. et al. Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction.Proceedings of the National Academy of Sciences (2013).
Jackson, R. et al. The Environmental Costs and Benefits of Fracking. Annu. Rev. Environ. Resourc. 39, 327–362 (2014)
Kassotis, C., Tillitt, D., Davis, J., Hormann, A. & Nagel, S. Estrogen and Androgen Receptor Activities of Hydraulic Fracturing Chemicals and Surface and Ground Water in a Drilling-Dense Region. Endocrinology 155, 897907 (2014).
Molofsky, L., Connor, J., Wylie, A., Wagner, T. & Farhat, S. Evaluation of Methane Sources in Groundwater in Northeastern Pennsylvania. Groundwater51, 333–349 (2013).
Nicot, J.-P. P. & Scanlon, B. R. Water use for Shale-gas production in Texas, U.S.Environ. Sci. Technol. 46, 3580–6 (2012).
Rahm, D. Regulating hydraulic fracturing in shale gas plays: The case of Texas. Energy Policy 39, 2974–2981 (2011).
Souther, S. et al. Biotic impacts of energy development from shale: research priorities and knowledge gaps. Frontiers in Ecology and the Environment 12, (2014).
Warner, N. et al. Geochemical evidence for possible natural migration of Marcellus Formation brine to shallow aquifers in Pennsylvania. Proceedings of the National Academy of Sciences 109, 11961–11966 (2012).
