The Dangers of Gas Drilling

“You don’t want a situation like we have with BP in the Gulf Coast. You don’t want an oil company saying ‘don’t worry.’ Instead, you want these effects tested carefully, in well established circumstances.”

—Dr. Daniel Botkin, PhD Ecologist and Professor Emeritus, University of California, Santa Barbara

Hydraulic Fracturing 101: The Process and The Risks

The gas industry is steadfast in its claims that hydraulic fracturing and associated drilling practices are safe and pose no threat to human and environmental health. But is it really true? Given the recent deluge of media coverage about gas industry threats, it appears current gas operations are demonstrating a lot of the same type of dangerous practices and cavalier industry culture that led to the BP oil disaster in the Gulf of Mexico. Much like offshore drilling, gas operations occur in a regulatory void, having outpaced federal and state oversight.

Traditional hydraulic fracturing is a process that has been employed by the gas industry since the 1940s, a favorite talking point among fracking defenders.[1] Pioneered by Halliburton, the process involves the injection of water, sand and chemicals into a well to release trapped gas deposits. Hydraulic fracturing has long been used to access conventional oil and gas deposits. However, recent technological developments in drilling have opened up previously inaccessible unconventional gas deposits across North America.

Gas extraction underwent a significant technological transformation in the 1990s, when operators began using a technique developed for oil extraction: horizontal drilling.[2] [3] With the combination of hydraulic fracturing and horizontal drilling into a new technique known as High Volume Slickwater Hydraulic Fracturing, the overall scope of gas extraction has transformed, calling for unprecedented amounts of water, chemical additives and drilling pressure. Hydraulic fracturing experts like Dr. Anthony Ingraffea consider current gas drilling “a relatively new combined technology.”[4] Although industry likes to characterize the process as successfully proven for over six decades “what they fail to say is that they’ve had fewer than 10 years of experience on a large scale using these unconventional methods to develop gas from shale,”[5] Ingraffea says.


Image: Checks and Balances

Unconventional gas, which does not flow easily, exists in small pockets trapped in tight or less permeable rock formations such as coalbed methane, tight sands or shale. The difficulties of accessing large amounts of unconventional gas by drilling lone vertical wells led to the expansion of production procedures. With the introduction of hydraulic fracturing and horizontal drilling, operators can now access a significantly larger area from one single well pad. Current drilling practices, requiring 50 to 100 times[6] the water needed in conventional gas wells and drilling pressures up to 13,500 psi, can access areas around 8,000 feet deep and up to 11,000 feet in horizontal directions.[7]

Chemical additives are used in the primary stages of drilling and in the fluids prepared for the fracking process. Drilling muds or slurries are a mixture of chemicals and fluids used to facilitate boring. Although fracturing fluids are more commonly known to contain chemicals linked to cancer, organ damage, nervous system disorders and birth defects,[8] drilling muds or slurries can contain a number of the same chemical constituents used in fracturing fluids.[9]

Once the drill bore has been prepared, a cement casing is poured around the exterior of the well to provide a barrier between the well and the surrounding underground formations. Traveling thousands of feet down, gas wells require numerous cement casings to isolate the various rock layers containing hydrocarbons, briny water and other contaminants.[10] The depth and width of cement casings will vary given the underlying geologic formation and whether the well will pass through an underground aquifer. Fracturing fluids, or ‘fracking fluids,’ a mixture of millions of gallons (at times as low as 2 million[11] and as high as 7.8 million[12]) of water, sand and chemicals, are injected into the well at extremely high pressure. The pressure blasts the rock apart allowing for the release of the trapped gas which can then flow up the wellbore.

The chemicals in fracking fluid can include friction reducers, surfactants, corrosion inhibitors, biocides, stabilizers and lubricants which perform a number of functions such as preventing buildup in the well bore and allowing for the smooth passage of the gas from the rock. The sand, called a proppant, is used to prop open the fissures which are created in the blast and allow for the free flow of gas.

The recovered gas, intermixed with the fracking fluid, flows to the surface of the well where it is retrieved for processing. An estimated 30% to 70% of the fracking fluid initially remains underground, although more of the contaminated fluid continues to surface for the life of the well, up to 20 or 30 years.[13] [14]

What is initially recovered is separated from the gas in heating tanks, or condensate tanks, which force the gas from the liquid under high temperatures.[15] The gas is then retrieved and transported, usually through a series of trucks and/or pipelines. The left over water, in the forms of produced, condensate and ‘flowback’ water, is a mixture of fracking chemicals and in some instances toxic substances from the underground rock such as naturally occurring radioactive matter (NORMs), total dissolved solids (TDS), liquid hydrocarbons including benzene, toluene, ethylbenzene, and xylene (BTEX), and heavy metals which can pose a problem if they find their way into waterways or drinking water. While all of the chemicals used throughout the hydraulic fracturing process are not known, it is well documented that some chemicals employed in fracturing and drilling, as well as unearthed substances in flowback water, are known to cause cancer, birth defects and nervous system disorders.[16] [17] [18]


The gas industry commonly claims that “no proven instances of water contamination have occurred due to hydraulic fracturing.” This misleading statement uses industry’s definition of hydraulic fracturing to refer “only to the process whereby hydrostatic pressure is used to force cracks in deep rock formations,” according to Dr. Ronald Bishop of State University of New York, College at Oneonta.

However, “even if you adopt industry’s definition of hydraulic fracturing (thus excluding incidents from drilling damage, failed well casings, spills, erosion and sedimentation, or tanker accidents), there is now evidence…that the isolated process of hydraulic fracturing has been responsible for water contamination.”[19]

The Worldwatch Institute reports that although hydraulic fracturing has become the focus of much controversy, “the most significant environmental risks associated with the development of shale gas are…gas migration and groundwater contamination due to faulty well construction, blowouts, and above-ground leaks and spills of waste water and chemicals used during drilling and hydraulic fracturing.”[20] Precisely how water contamination occurs due to gas drilling operations can at times be difficult to determine, although the growing number of documented cases[21] point to a variety of contamination sources.

Nearby waterways, domestic wells and underground sources of drinking water (USDW) such as underground aquifers have become contaminated across America due to poor industry practices and incomplete knowledge of underlying rock formations.[22]

An internal document from Pennsylvania’s Department of Environmental Protection outlines over 60 instances of water contamination and fugitive methane migration from gas drilling operations, many of which were due to unexpected pockets of underground pressure, the failure to contain well pressure, faulty production casing, or the accidental drilling into other abandoned or producing gas wells.[23]

The improper sealing of the drill bore with cement or faulty, unstable cement jobs are an easy and not uncommon way to contaminate water sources.[24] In this case, fracking fluids can escape the well bore and enter an aquifer which the well sometimes passes through directly.

At times operators are dangerously uncertain as to whether or not they are drilling directly through an underground aquifer.[25] In other instances, the pathways created from the fracking process can lead to the underground migration of chemicals, gasses and radioactive materials between rock layers.[26] How the underground rock will break, known as fracture propagation, during the drilling process is difficult to predict due to previously existing weaknesses and fracture networks in the rock. Natural fractures have the ability to divert the pathway of induced hydraulic fractures, leading to “complex behavior” of fractures in unconventional gas reservoirs.[27] Despite industry claims that the process is “highly engineered and controlled,”[28] in some instances the created fractures travel well beyond anticipated lengths.[29]

Once a well has become inactive it is up to the operator to ‘close’ the well according to state standards. This sometimes results in the filling of the drill bore with cement. The duty to regulate closed wells is left to state officials. Because of the intense pressure exerted during hydraulic fracturing, underlying rock formations become “thousands of times more permeable” allowing for the continued circulation of gas, briny water and contaminants long after the producing life of the well.[30] The EPA reported in 1992 that an estimated 1.2 million oil and gas wells were abandoned in the U.S. of which 200,000 were leaking.[31]

Using this information, Dr. Ronald Bishop calculatesa well failure rate of 16.7%, meaning approximately one in every six abandoned wells will leak into the surrounding area.[32]

A survey of past drilling practices across the states has led Dr. Bishop to conclude that “the probability that a project scope of as few as ten modern gas wells will impact local ground water within a century approaches 100% certainty.”[33] Better well-abandonment practices, although more expensive than current practices, are essential to reduce the slow seepage of gas to the ground surface.[34]

Drilling and Fracking Chemicals: Studies, Disclosure and Standards

Chemical additives are used throughout the gas drilling process. Fracturing fluids are known to contain numerous toxic substances although there is still incomplete knowledge regarding all chemicals that may be used in the drilling process. Hydraulic fracturing is also known to force heavy metals and radioactive substances from the underlying rock to the surface in the form of flowback water and drilling muds.

There are hundreds of possible chemicals available for and widely used in fracturing operations, most specifically as additives to drilling muds and fracking fluids. The specific mixture of chemicals in a given fracking fluid will change from well to well as the specifics of geography and other external factors will determine what is required. The chemical additives of fracking fluids are protected as an industry trade secret and as of yet no federal legislation requires their disclosure. The gas industry has complained about attempts to mandate disclosure of drilling chemicals, claiming this would violate their right to protect proprietary information.

Yet under the provisions of the Toxics Release Inventory, the EPA is able to protect trade secrets upon formal request.[35] According to this program, the EPA can both protect trade secrets and take measures to protect public health.[36]

Without proper knowledge of the chemicals used throughout the drilling process, medical and emergency personnel cannot adequately respond to accidents and spills. Investigations into water contamination have been hindered and delayed because researchers do not know what to test for.

Some gas companies have engaged in the ‘voluntary disclosure’ of some fracking fluid chemicals.

But this information offered on operator websites is not exhaustive and often does not contain the necessary information to reveal chemical toxicity, such as Chemical Abstracts Service (CAS) identification codes.[37] [38] [39] Environmental scientists say that without exhaustive information of fracturing fluids and how they are combined, it is impossible to fully assess their associated risks.[40] To date no federal oversight of chemical disclosure exists.

This federally endorsed silence stifles public participation in the important discussion surrounding the impacts of gas drilling.

Hannah Wiseman, assistant professor of law at the University of Tulsa, writes that statutes such as the Emergency Planning and Community Right-to-Know Act (EPCRA) and the Safe Drinking Water Act (SDWA), from which hydraulic fracturing is exempt, “envisioned that informed citizens would influence industrial activity through open public venues.” Without the removal of these trade secret protections, Wiseman continues, “communities experiencing the brunt of the energy boom may have inadequate tools to evaluate and address the potential impacts of this development.”[41]

The number of gas operators that have participated in ‘voluntary disclosure’ have also moved to discourage federal disclosure requirements, describing these oversight measures as costly and unnecessary. Companies such as Halliburton and industry-funded lobby groups such as Energy in Depth provide voluntary information that misleadingly compares fracturing fluids to household cleaning products and cosmetics —even ice cream ingredients.[42] Energy in Depth, an industry funded support group lists ‘petroleum distillates’ as a component of fracturing fluids, referencing the compound’s common use in “make up remover” and “candy.”[43]

The Environmental Working Group cautions against this tactic: what companies do not mention is that petroleum distillates include products which are known to cause cancer and in the U.S. the use of these products is “almost completely unregulated.”[44]

Halliburton and Energy in Depth also list guar gum as a fracturing fluid additive, citing its common use in cosmetics and ice cream. What is not mentioned is that the use of guar gum as a thickener is paired with “extremely toxic” cross-linkers and biocides as well as breaker additives to thin the mixture for a return from the well. Guar gum is often mixed with “hydrotreated light petroleum distillates” or deodorized kerosene.[45]

Other biocides that are commonly used include Glutaraldehyde, a respiratory toxin at a part-per-billion (ppb) level that, as a sensitizer, can induce allergies and has known mutagenic affects and 2,2-Dibromo-3-nitrilopropionamide (DBNPA), which is toxic to the respiratory system and skin, is a known sensitizer, and is corrosive to the eyes. Both of these biocides have dramatic effects on ecosystems and especially aquatic organisms when introduced to waterways at very low parts-per-billion concentrations. DBNPA can be lethal to some organisms at a parts-per-trillion level which is far below possible detection limits.[46]

A number of reports have been released on fracking chemicals and associated health risks, most notably by Dr. Theo Colborn of The Endocrine Disruption Exchange (TEDX). Generally, but not always, the chemicals used in fracking operations are reported in MSDS (Material Safety Data Sheets) which are required in most states for the safety of employees working with toxic substances. These sheets are intended to outline the potential health risks when handling these chemicals, however, as Dr. Colborn reports, in many instances the information presented is incomplete, unspecified or simply listed as ‘proprietary.’

By May 2010 Dr. Colborn had identified 944 chemicals associated with drilling and hydraulic fracturing. 407 of these 944 chemicals had less than 1% of the product composition available due to inadequate listed information.[47]

Another 2011 draft report authored by Dr. Ronald Bishop of State University of New York, College at Oneonta states that most of these chemicals have not been tested for “human or environmental toxicity.”[48] And although these chemicals can be diluted during the drilling process, some chemicals pose severe risk to human and environmental health “even at concentrations near or below their chemical detection limits.”[49] Industry groups maintain that hydraulic fracturing is largely performed using water and sand and that only a fraction, 0.5%, is made up of the chemical additives. Yet, given the enormous amounts of water required, this ‘fraction’ is not negligible: a conservative estimate arrives at 20 tons of chemicals per 1 million gallons of water.[50]

In a typical well this could amount to 34,000 gallons of chemicals by volume.[51] Recent investigations have revealed that companies also illegally performed hydraulic fracturing using diesel fuel. These companies did so in violation of an agreement with officials to ban the use of diesel in gas drilling altogether.[52]

The use of diesel for hydraulic fracturing is also regulated under the Safe Drinking Water Act.[53] Diesel fuel contains benzene, toluene, ethylbenzene and xylene, a collective of toxic compounds known as BTEX. Benzene is a known carcinogen while exposure to toluene, ethylbenzene and xylene can cause damage to the central nervous system, liver and kidneys. A report by the Environmental Working Group identifies other petroleum distillates, resembling diesel, used in hydraulic fracturing that were found to have 93 times more benzene than diesel but do not fall under any regulation.[54]

The gaps in regulation have allowed for the gross mismanagement of drilling waste, which as The New York Times has recently reported, has led to tremendous violations of public health standards[55]. States do not traditionally require an account of how drilling wastes will be handled when granting drilling permits,[56] leading to the widespread failure to adequately treat enormous amounts of highly toxic wastes.

Gas Drilling: Provoking A Water Crisis

The enormous water requirements for gas drilling, and the unavoidable pollution due to chemical additives and underground contaminants, pose a serious threat to water resources.

In a recent DeSmogBlog interview, Dr. Daniel B. Botkin of the University of California, Santa Barbara —an outspoken critic of unconventional gas and author of “Powering the Future: A Scientist’s Guide to Energy Independence”—suggested that issues of water contamination can be blamed on poor practice. [57]

“In New York and Pennsylvania most of the problems that have happened have been because of accidents. You don’t even have to start drilling and they’ve already handled materials on the ground in a sloppy way.”

Alongside concerns about water contamination, Dr. Botkin is also concerned with soil pollution where “the worst problem is with heavy metals and the drilling mud itself.” These byproducts of the drilling process have quickly outgrown the means of their disposal. Wastewater poses serious threats to waterways when not stored, transported or treated properly.

Existing laws designed to hold the gas industry accountable have come under tremendous scrutiny for failing to keep pace with the rapid development in unconventional gas extraction.[58] [59] Making matters worse, the oil and gas industry received numerous favors during the Bush administration in the form of regulatory rollbacks and exemptions, most notably the ‘Halliburton Loophole.’[60] [61]

“There is a lot of controversy over what deep drilling for natural gas will do. Beyond the potential for things already going on with human health, there is an unknown with what the effects of this kind of drilling are going to be. Another problem is water, “ Dr. Botkin says.

While much of the concern about the impacts of hydraulic fracturing centers on the contamination of drinking water, Dr. Botkin is also concerned about the industry’s extensive withdrawals of clean water from already stressed water supplies.

“We are already overusing our water supply and this technology is going to increase the tremendous stress on it.”

Average estimates of water usage at a single gas well using multi-stage hydraulic fracturing range from 2 million gallons and at times as high as 7.8 million gallons.[62]

One report from Schlumberger Water Services cites Encana figures at one million gallons per frack for wells that can be fracked up to 20 times.[63] Other sources confirm that in these multi-stage operations a single well can be hydraulically fractured up to 20 times.[64] Post extraction procedures, such as refining and transport, use an additional 400 million gallons of water each day, according to the Union of Concerned Scientists.[65] Dr. Botkin worries that if oversight does not keep up, decision-making will be left to a self-regulating industry. “You don’t want a situation like we have with BP in the Gulf Coast. You don’t want an oil company saying ‘don’t worry.’ Instead, you want these effects tested carefully, in well established circumstances.”

The industry wants to maintain that gas is an environmentally friendly, alternative energy source. Despite numerous reports and documented cases,[66] [67] companies[68] and industry groups such as Energy in Depth,[69] the Marcellus Shale Coalition,[70] the Independent Petroleum Association of America,[71] and the American Petroleum Institute,[72] are adamant that no instance of drinking water contamination has ever occurred due to hydraulic fracturing.

The removal of billions of gallons of clean water from watersheds across the nation —rivers, streams, lakes and underground aquifers that provide the water we all need for survival —is reason enough to pause to think about the wisdom of this practice. But tacking onto that the bill for rendering those millions of gallons of water contaminated and radioactive in the process - poses a real sustainability challenge.

Given the industry’s secrecy to date[73], lawmakers face an uphill struggle to comprehend the magnitude of the potential problems and consequences stemming from this uncontrolled boom in unconventional shale gas.


Image: Skytruth,

According to Dr. Anthony Ingraffea, a hydraulic fracturing expert from Cornell University, the enormous amount of water used in unconventional drilling - 50 to 100 times more water than used for conventional drilling - are, on the other side of drilling, destined to become enormous amounts of toxic drilling wastes. “In regard to the liquid waste stream, the fluids, the flowback fluids and so-called brines and produced waters, which the industry uses interchangeably to describe liquid waste…it is different from what is produced from an oil well or from a conventional well.

It cannot be taken to a public waste water treatment plant and then dumped into a river. It contains something more than salt. It contains heavy metals. It contains some amount of naturally occurring radioactive materials, which are signatures of shale gas. Public waste water treatment plants are not equipped to remove those materials from the waste stream.”[74]

Shale regions “exhibit fluctuations in radioactivity,” but some areas, like the Marcellus Shale spanning across New York, Pennsylvania and West Virginia, are “significantly radioactive.”[75] The naturally occurring radioactive substances in shale are affected by the chemicals used in the drilling process:

“surfactants and other additives used in drilling muds and hydraulic fracturing fluids can help to leach radioisotopes from their source rocks, leading to greater potential human exposure than would occur if these gas development additives weren’t used.”[76]

The returned fluid, once resurfaced, poses unique risks, according to Dr. Ingraffea: “I should also emphasize that once the fluid comes back…it contains not only the chemicals that were put in on the way down but the material that was picked up from the shale…In black shales, shales containing gas, the most dangerous of those are the heavy metals—strontium, barium, uranium, and radium—some of which are also naturally occurring radioactive materials.”[77]

Wastewater pollutants, which are often intermixed with drill cuttings, can contain some of the most significant toxins known to the drilling process.

Dr. Bishop discusses barium, lead, arsenic, chromium, benzene and radioactive materials as toxic at parts-per-billion concentrations. Radon, an intensely radioactive material, can be mobilized due to hydraulic fracturing. Radon is an extremely mobile gas which can cause nuclear decay to the lungs and is second only to tobacco smoke in causing lung cancer.[78] Another dangerous compound discovered in shale flowback fluids is 4-nitroquinoline-1-oxide (4-NQO), “one of the most potent carcinogens known, particularly for inducing cancer of the mouth.”[79] This toxin is not a chemical additive and does not occur naturally in shale and thus leads Dr. Bishop to question whether chemical interactions caused during the drilling process are responsible for its presence. He adds that no studies have been published on this question to date.[80]

Waste caused by unconventional gas extraction is a serious problem where storage and disposal sites are inadequate to handle such toxic materials. Industry has typically downplayed the risks associated with these wastes, often claiming that much of it remains safely underground.

According to Dr. Anthony Ingraffea, “The industry is fond of saying that most of what they pump down stays down. What they fail to talk about is the timeframe in which they’re counting. Typically, the returned fluid, after the fracturing process, is counted as returned fracturing fluid only during about the first week or two of flowback operations. However, all shale gas wells continue to produce fracturing fluid and brine containing heavy metals for the entire life of the well. One has to be very careful. One cannot say that on average, 50% of the fluid comes back.

One has to say under what timeframe one is making that measurement. Typically almost all of the fracturing fluid comes back during the life of the well.”[81]

There have been several reported incidents where wastewater storage failed to contain produced water from gas drilling operations and caused nearby water contamination.[82] [83] Some treatment facilities have taken in drilling wastewater, unable to properly treat it, while regulators have stood idly by.[84] Drilling wastes from certain areas are especially radioactive, threatening the communities near disposal sites.[85] [86] In Pennsylvania, toxic drilling wastewater taken into a sewage treatment plant killed the microbes needed to properly treat the sewage. As a result, improperly treated fecal matter was discharged into the Susquehanna River.[87]

There are also documented instances of wastewater facilities improperly treating produced water from hydraulic fracturing operations.[88] Concerns are growing over the fact that many of the gas producing states do not have the capacity to treat production wastewater.[89] Due to the failure of treatment facilities to cope with the degree of contaminants in drilling wastes, some have recommended that wastewater be treated as “industrial-strength hazardous materials” and kept separate from the treatment facilities that release treated water back into the water supply.[90] As the New York Times has recently reported, given its high levels of salt, radioisotopes and other contaminants, improper treatment of drilling wastes can have dire consequences for drinking water.[91] EPA documents reveal that federal regulators have failed to address this growing threat.[92]

Without placing restrictions on the rapidly growing gas industry, there is little to stem the flow of drilling wastes. Dr. Bishop recognizes the lax regulatory regime as central to this issue: “The sheer volume and peculiar noxious nature of these wastes pose significant challenges, even in the best of operating conditions.  Laws in host states tend to make information about additives confidential, so monitoring efforts are hindered —where they are attempted at all. The facilities in place to handle process wastes are NOT adequate, particularly in the northeastern United States where underground injection capacity is extremely limited.  This lack of facilities for process wastes may be the greatest obstacle currently faced by energy companies and state  regulators.”[93]

When not treated, wastewater is generally disposed of through underground injection. This procedure, however, cannot be performed in all states. There are concerns that disposal by means of underground injection will result in “creating yet another potential source of extremely toxic chemical contamination.”[94]

Some states require companies to demonstrate that the disposal injection will not escape target zones or contaminate fresh water aquifers.[95]

Some options remain for wastewater to be reused. But according to Dr. Anthony Ingraffea, “[wastewater] recycling in the U.S. is in its infancy. There are two types of recycling. One can hopefully reuse some of the return fluids in subsequent wells. Very few of the companies operating in New York, Pennsylvania, Arkansas, and Texas are doing that right now because it’s an enormous additional expense. Recycling also takes the form of transporting the waste fluids away from the well pad to specially designed new technologies that can remove most of the waste from the fluid.

What you’re left with is a smaller volume of more highly concentrated waste that can then be transported for safe disposal to underground injection wells, for example —which probably will not work…just like they won’t work in Pennsylvania and New York. But they do work in Arkansas and Texas.”[96]

Wastewater disposal through underground injection has recently been connected to a scourge of over 800 earthquakes in Guy, Arkansas.[97] Geologists from the American Geological Survey report that a “direct correlation” can be seen between the quakes and wastewater injection disposal sites.[98]

Regions which are “seismically active or intensively fissured pose greater risks for contamination than regions which are geologically stable.”[99] An upswing in earthquakes in areas experiencing gas drilling has recently become cause for additional concern. After drilling began in Cleburne, Texas, the town experienced more earthquakes in eight months than in the previous 30 years combined.[100] Towns sitting atop the Barnett Shale field in North-central Texas, areas of western New York, central Oklahoma and West Virginia have all experienced quakes suspected of being connected to gas drilling or wastewater injection.[101]

According to Ronald Martino, a geology professor at Marshall University, it has been known for a half-century that underground fluid injection can lead to induced seismic activity.[102] High-pressure fluid injection has the potential to activate faults, a concern for Jack Century of J.R. Century Petroleum Consultants Ltd., who cautions “when we start perturbing the system by changing fluid pressure, we have the potential for activating faults,” adding, “once local seismicity starts, it can’t be turned off.”[103] Most of the earthquakes experienced in these areas are relatively small, but pose a threat to cement casings, the only measure in place to protect drinking water from gas wells and underground disposal sites.[104]

[9] Bishop, Ronald E. “Chemical and Biological Risk Assessment for Natural Gas Extraction in New York.” January 21, 2011.

[15] Colborn, Theo. Et al. Natural Gas Operations from a Public Health Perspective.” International Journal of Human and Ecological Risk Assessment.

[19] DeSmogBlog Interview with Dr. Ronald Bishop. February 23, 2011.

[25] Mike Soraghan. “Drillers Say They Don’t Know if They’re Fracking in Drinking Water.” Greenwire. Monday July 19, 2010.; see also

[26] Worldwatch Institute. Assessing the Environmental Risks from Shale Gas Development.

[27] Jon Olson. Influence of Natural Fractures on Hydraulic Fracture Propagation.

[29] BC Oil and Gas Commission 2010 Safety Advisory on Fracture Stimulation.

[34] DeSmogBlog Interview with Dr. Maurice Dusseault. February 14, 2011.



[44] Environmental Working Group. Drilling Around the Law.

[45] Dr. Ronald Bishop in “Affirming Gasland.”

[50] Barbara Arrindell in “Affirming Gasland.”

[57] DeSmogBlog Interview with Dr. Daniel B. Botkin. July 21, 2010

[75] DeSmogBlog Interview with Dr. Ronald Bishop. February 23, 2011.

[76] DeSmogBlog Interview with Dr. Ronald Bishop. February 23, 2011.

[93] DeSmogBlog Interview with Dr. Ronald Bishop. February 23, 2011.

[99] DeSmogBlog Interview with Dr. Ronald Bishop. February 23, 2011.