Pollution from fracking may harm the health of developing babies

From an Article by Ann Gibbons, Science Magazine, December 13, 2017

The extraordinary growth in fracking—the hydraulic fracturing of deeply buried shale rock to extract natural gas—has transformed the United States over the past 15 years, boosting energy stocks, cutting pollution from conventional coal-power plants, and creating new jobs. But this boom may have come at a cost. According to the first large-scale study of babies born before and after natural gas extraction began in Pennsylvania, those living near fracking sites had significantly lower birth weights—and worse health—than other babies.

Concerns about the health effects of fracking aren’t new. Absent solid evidence, some states, including Maryland and New York, have even banned the practice altogether. Now, a growing number of studies suggests that living near oil and gas developments is associated with a wide range of negative outcomes, from higher rates of asthma and migraines to more hospitalizations for cardiovascular disease, neurological disorders, and cancer. Earlier studies have also found associations with low–birth weight babies, but those were plagued by low sample sizes or a failure to show that health effects got worse closer to drilling sites, as expected if fracking were to blame.

Now, health economist Janet Currie at Princeton University and her colleagues have tried to overcome those problems by looking at birth certificates for all 1.1 million infants born in Pennsylvania between 2004 and 2013—a period that spanned the drilling of thousands of fracking wells in the state, which now has more than 10,000 of them. The birth certificates included addresses and vital statistics for each infant, such as birth weights, total months of gestation, birth defects, and other abnormal conditions. The researchers overlaid those data on maps showing when and where wells were drilled in Pennsylvania. They then drew concentric circles around each site: one at 1 kilometer, one at 2 kilometers, and one at 3 kilometers.

They found that infants born within 1 kilometer of a well were 25% more likely to have low birth weights (less than 2500 grams or 5.5 pounds) than infants more than 3 kilometers away, they report today in Science Advances. Babies born in the first circle also showed significantly lower scores on a standard index of infant health. Infants born in the outer circles—between 1 and 3 kilometers away—were smaller and less healthy than those who lived farther away, but they weren’t as badly off as babies born closest to the wells.

To rule out other factors that could lead to poor health outcomes, including race and socioeconomic status, the team removed babies born in urban areas like Pittsburgh and Philadelphia, which have comparatively high rates of lower birth weight babies. They also compared siblings born to the same mothers who lived near fracking sites before and after it started. Although this sample size was small—only 594 infants exposed to fracking had unexposed siblings—it showed that the exposed infants were smaller and less healthy.

The good news is that the effects don’t extend far beyond the fracking sites, Currie says. The study found no decrease in infant weight or health past 3 kilometers. But the team doesn’t know what aspect of fracking caused the low birth weights, which put babies at higher risk for infant mortality, asthma, attention deficit hyperactivity disorder, lower test scores, and lower lifetime earnings. Currie, who studies air pollution and health, says it’s likely air pollution from chemicals or the increased truck traffic and industrialization associated with fracking. Water pollution is an unlikely culprit because many people in the study got their water from municipal sources not close to fracking sites.

But Erica Clayton Wright, spokesperson for the Marcellus Shale Coalition in Pittsburgh, says the study doesn’t go far enough to address “crucial issues linked to low birth weights like smoking as well as alcohol and drug use. … Given these deep methodological flaws, it’s dangerously misleading and inflammatory to suggest that natural gas development has done anything but improve public health.”

Though there is no “smoking gun” that proves how fracking impairs infant health, economist Don Fullerton—who studies how public policies affect the environment at the University of Illinois in Urbana—calls the evidence “convincing” and says it adds to other studies that have also found evidence of preterm births and other negative health effects. That makes it even more important, he says, to regulate what chemicals are used in fracking or how close wells can be to residential areas.

Currie adds that infants, who are essentially the “canaries” near the fracking mines, probably aren’t the only victims. If they are experiencing negative effects, the elderly and other vulnerable people near wells are likely to also be at risk. “We really should move beyond the discussion of whether there is a health effect or not to figuring out how we can help people who live close to fracking.”

We can find ourselves in the mountains!

Science, Solitude And The Sacred On The Appalachian Trail

From an Article by Adam Frank, 13.7 Blog (NPR), August 15, 2017

This week, you can’t reach me by email, or text, or Tweet. This week, I’m not taking anyone’s calls, either.

That’s because I’m walking the Appalachian Trail — alone. And while I am, without doubt, scared of being eaten by a bear, I’ll be out there looking for that most precious of possibilities: solitude.

Solitude can be hard to find in the modern world. Cities are, of course, exactly about mixing it up with our fellow humans. That’s the source of their potent innovation. So, while you can find places in the city to be alone, it is much harder to find true solitude.

The difference between the two — being alone and being in solitude — is the secret many people find the wilderness teaches. Now, for a lot of folks, the idea of being alone can be discomforting — if not downright terrifying. That’s understandable because we are, by nature, social animals. Evolution tuned us to live in groups and be attentive to others.

But being in the wild without others doesn’t mean being alone; in fact, it can be quite the opposite.

I was raised in some of the denser regions of northern New Jersey. I loved every bit of growing up in that true melting pot of humanity. But I was lucky that my parents sent me to a YMCA day camp 40 minutes south of my industrialized home turf. That was my first experience of the wild (such as it was). I still have vivid memories of finding myself (relatively) alone in the forests around the camp. What I remember of those times is the profound sense of peace and calm that could make its appearance.

I’ve been searching for more of those kinds of experiences ever since. Mircea Eliade, the great scholar of human religion, knew about those experiences. For him they were the root of “sacredness.” That’s a word I’ve written about many times before in thinking about science and “spirituality.”

For me, sacredness is an experience that rises above any particular religion and speaks to those moments when we feel the essential, original and irreducible potency of life. It need not refer to anything anyone would call “supernatural” but, instead, is rooted in our very real and very natural experience of the world. In that way, it is also a root of the aspiration to do science. As Eliade wrote: “The sacred is equivalent to a power and in the last analysis to reality. The sacred is saturated with Being.”

For Elide, the experience of sacredness was the source of religiousness. But that experience came before any of our modern religions. In particular, it first appeared in what we now call “the wild.” In their early travels through the world, our ancestors would come to some glade or tree or cliff and have exactly the experience I had as a kid in the forests of my YMCA camp. Call it “awe” or “an overflowing”: Call it whatever you want, but the wild is its first home.

Going alone into the wild is also an ancient tradition. It makes up a common theme in the class of common myths Joseph Campbell called “The Hero’s Journey.” Taking a long journey anywhere alone can be scary. That’s also what makes it exciting.

But going into the wild alone takes us beyond just adventure. The reason, once again, is solitude. In the wild, in solitude, you’re never really alone.

In part, it’s all the life that’s there already. The pillars of individual trees stretch back into the woods and, after a while, you realize it’s the forest that’s really the organism. And then there are the bird calls in the air and frogs crossing the trail. After a few hours on an extended hike, you become just another of the forests’ inhabitants plodding along on your way. That experience of sacredness is enough for me.

But there is more.

When you come to a clearing where the sunlight makes it to the forest floor, or where a stream has cut a steep ravine into the mountainside, you can sometimes catch a hint of something. I don’t know what to call it. Words fail. But it feels something like a root, a core, an unvoiced song of the world’s own presence.

It’s powerful enough to get etched in your memory if you’re there with other hikers. But if you’re alone — if that moment is just between you and the world — then you are lucky indeed. That is when you can understand what Henry David Thoreau, one of the first great interpreters of American wilderness, meant when he said, “I never found the companion that was so companionable as solitude.”

I’ve been lucky to have been able to do lots of backpacking trips in my adult life. And in the last 10 years, I’ve become fond of solo hiking day trips. But putting the two together is a new thing for me. So I am both excited and a wee trepidatious about this trip (The bears. I have a thing about bears).

In the end, however, it’s all worth it (unless I get eaten by a bear). As a scientist, I’ve spent my whole life trying to get closer to the world and understand its ways more deeply. That means going to the source. But there is no greater source for science, for the inspiration to do science, than the wild. That is where the sense of sacredness — that I think lives at the root of science’s aspiration — lives.

So, as the great John Muir put it: “Keep close to Nature’s heart… and break clear away, once in a while, and climb a mountain or spend a week in the woods. Wash your spirit clean.”

Now, if only the bears have read Muir.

>>> Adam Frank is a co-founder of the 13.7 blog, an astrophysics professor at the University of Rochester, a book author and a self-described “evangelist of science.”

The scientific method is well established!

From an Essay by Prof. Adam Frank, 13.7 Blog, NPR, July 18, 2017

Just before joining other leaders at the G-20 summit, President Donald Trump gave a speech in Poland where he asked: “Does the West have the will to survive?”

Since then, a lot of ink (and electrons) has been spilled asking about the value, and values, of Western Civilization.

Far be it for me to pass judgment on entire civilizations — but as a whole I’m all in with the best parts of Western Civilization. That’s because one of the “best parts” of this thing that happened in the West was this other thing we call science.

What we call science had its roots in the achievements of the Hellenistic Greeks. It began with Thales of Miletus who first attempted to apply reason as a means of understanding the world. Later, Greek thinkers would expand on this reason-based method to map the stars, reveal the laws of geometry and establish the first classification schemes for life.

It’s important to note after the Greeks (and to some degree the Romans) the story of science’s progress moves away from what historian Ian Morris calls the “Western Core” of civilization. Beginning with the fall of Rome, “The West” goes fairly dark with respect to science for almost 1,000 years. Progress shifts in an easterly direction.

The Muslim empires take the lead in astronomy. Look at a star chart, where you’ll find a mess of Arab names like Algol, Deneb and Rigel. These cultures were also a force pushing mathematics forward. Look up the origins of the word “algebra.” Meanwhile, over in India, mathematicians were doing their own important work including figuring out how to deal with “0″ in calculations. And further to the east in China, the Tang and Song dynasties were piling up inventions and discoveries such as the compass, gunpowder, paper-making and printing.

So the story of science can never be seen as just the story of Western Civilization. But it was the West’s particular version of genius that gave us science’s all-important methodology and institutions.

It’s from these that science as we know it emerges with all its insight, reach and power.

From Galileo, Francis Bacon, Sir Issac Newton and others we got the mix of direct experimentation and mathematical description that is the hallmark of modern science. Together, these approaches would let us hear nature speak for itself. In the Age of Reason and the Enlightenment, these practices became codified into norms of behavior for science’s practitioners. Then, with the foundation of the Royal Society of London (1662), the Paris Académie Royale des Sciences (1666), and the Berlin Akademie der Wissenschaften (1700), a distinctly new kind of force was established in society.

As human institutions, each of these scientific academies had their deep imperfections. But, ultimately, each was dedicated to a way of knowing that would rise above prejudice, cronyism and the dictates of the powerful. Most importantly, this new way of knowing would be self-correcting. The Royal Society’s motto says it all: Nullis in Verba. Take no one’s word for it.

In other words, rely on evidence.

That scientific method for relying on evidence — on facts — was one of the supreme achievements of Western Civilization. The material wealth and power that stemmed from the codification of the scientific method is exactly why Western Civilization has been so successful over the last 500 years.

So given that history, you would think science would be worth defending. Given the success it has granted us, you would think those institutions of science would be cherished as a foundation on which Western Civilization rests.

Yes, that’s what you’d think. That’s what you would hope.

But just as the administration was asking about defending Western Civilization, it was being forced to defend its own decision to pull out of the Paris Climate Accord. At the root, this move was driven by the administration’s continued denial of climate science’s principle conclusion: that the Earth’s climate system is shifting due to human activity. It simply does not take climate science seriously.

But if climate science is hoax then what do we make of the fact that all of Western Civilization’s major scientific institutions affirm its overwhelming scientific evidence? The entire scientific community of the West (and everywhere else) is unanimous on climate change. How else could we have gotten something as difficult as the Paris Accords signed by practically every nation on Earth?

So what, then, does it mean to deny the conclusions of climate science or worse — call it a hoax?

To deny climate science is to deny the rest of science that it stands upon. And to deny all the rest of that science is to deny the network of institutions, practices and values that make science itself possible. And, finally, to deny those institutions and practices is to deny the values we all cherish about Western Civilization itself.

So, I agree with the administration: We should defend Western Civilization’s best achievements. Let us start with something obvious from which we all benefit. Let us defend science: the root of our prosperity, strength and well-being.

>>> Adam Frank is a co-founder of the 13.7 blog, an astrophysics professor at the University of Rochester, a book author and a self-described “evangelist of science.”

Bruce Alberts, Scientist

“Science is an amazing human invention—a huge community effort to discover truth…”

By Bruce Alberts, Science, 31 Mar 2017: Volume 355, Issue 6332, pp. 1353

Summary — The recent election cycle has made it abundantly clear to most scientists that a large fraction of adults in the United States are surprisingly susceptible to illogical arguments designed to fool them. Research suggests that a great many people assess evidence not as scientists are trained to do, but rather in an emotion-biased manner that is strongly influenced by the beliefs of their cultural cohort. The increasing dominance of social media reinforces this natural human tendency. The consequences are frightening for those who believe that, for humanity to prosper, both personal and community decisions must be based on the best science. This conclusion demands a major rethinking of the goals and methods of science education at all levels—from kindergarten through college.

Why science? Science is an amazing human invention—a huge community effort to discover truth through repeated cycles of testing and self-correction. As a result, we now have a deep understanding of how the natural world works. The same type of understandings that allow humans to precisely deliver the Curiosity Rover to Mars also enable us to ensure that vaccination is safe and to forecast the danger of continued carbon dioxide emissions.

But most of those who teach science, including myself, have failed to recognize the crucial importance of producing adults who understand the nature of the scientific enterprise well enough to defend its judgments. In a recent survey, for example, the statement that “climate scientists’ research findings are influenced by the best available scientific evidence most of the time” was supported by only 32% of U.S. adults (www.pewinternet.org/2016/10/04/the-politics-of-climate).

This result is shocking to scientists. But it becomes much less surprising once one admits that science courses are generally taught as the “revealed wisdom” of scientists, with little or no effort spent on conveying the nature of the scientific process. For example, there is a long-standing belief that every introductory college biology course must “cover” a staggering amount of knowledge. There is no time to focus on a much more important goal—insisting that every student understand exactly how scientific knowledge is generated. Science is not a belief system; it is, instead, a very special way of learning about the true nature of the observable world. And yet a large proportion of adults graduate from college without this realization, despite having been forced to memorize a great many scientific facts.

In previous commentaries on this page, I have argued that “less is more” in science education, and that learning how to think like a scientist—with an insistence on using evidence and logic for decision-making—should become the central goal of all science educators. I have also pointed out that, because introductory science courses taught at universities define what is meant by “science education,” college science faculty are the rate-limiting factor for dramatically improving science education at lower levels.

As an important aid for teaching college science, I call attention to an expanded and redesigned resource—Science in the Classroom, a growing collection of 80 research articles (www.scienceintheclassroom.org/).

As explained in a brief video (youtu.be/Y6LwiIniYmo), selected Science articles have been carefully annotated for teaching, thanks to the efforts of many volunteers. This free resource makes it readily possible for every college student to read an outstanding research paper as part of a course module focused on teaching the scientific process, and to thereby learn how science actually works.

Science Community

Please try it out, volunteer, and provide feedback at scienceeducation@aaas.org.

www.ClimateRealityProject.org

The divorce from reality while understandable, desperately needs correcting

Commentary by S. Tom Bond, Retired Chemistry Professor & Resident Farmer, Jane Lew, Lewis County, WV 

It is obvious to most well educated people that the world is approaching several kinds of crises at once.  I hardly need mentioning them – exponential population increase,  greater need for energy per person, improvement of war technology, increase in surveillance technology, approach to the carrying capacity of the earth (one half the earth’s primary production is now directed to human needs, such as food, shelter and clothing) and the most obvious one, climate change.

Many of my readers know the Norse colonized Greenland about 950 AD and were successful for about 500 years.  A climate change of about one-centigrade degree (worldwide average) during the Little Ice Age brought the colonies to extinction.  There are numerous examples of fertile lands becoming desert.  It is well known the great Sahara Desert was once fertile grassland that supported human life.  Climate change is not rare.

Society also knows how and why carbon dioxide absorbs energy from light. I took a course in transfer of energy between light and molecules in graduate school myself.  And if you understand the origin of coal, oil and gas, it follows that we humans are using in decades the carbon that went into earth over millions of years.  The atmosphere is large, but we billions of humans are adding to it enough to change its composition in the parts per million range. Assuming it has doubled since the Industrial Revolution for simplicity of calculation, that change is in the neighborhood of 0.02% of the atmosphere.  That change is basically irreversible over a period of a thousand years or more.  For humans to take it out would require more energy than was obtained by burning the hydrocarbons originally. Geoengineering to remove carbon dioxide is not practical.

Unfortunately, many people do not understand the nature of science, why it is so powerful.  It is a method of finding out truth about the physical world beyond the intuitive understandings or guesses of the practical person.  Such a person learns by experience how to manipulate objects and materials in the world to get a helpful result.  Science involves conjecture about the physical world which must be verifiable by experiment and repeatable by any careful experimenter, along with careful application of logic to build a consistent model explaining further observations to be expected, or the use of data from diverse sources to test the model.

Science is highly fraternal but also highly competitive – your experimental details, your observations and your logic are carefully examined by others working in your field and related fields.  Status is conferred by being correct and by new, original work.  It is not forgiving of errors.  Every trained person is free to find your errors.

Most of us live in a cultural world.  Our ideas are determined by people around us that we respect or are forced by circumstances to obey.  What is called truth, adherence to the physical world, is much more casual in the general culture.  Survival, fortunately (should I say obviously) does not require an exact map of reality.  The culture around us provides a map of reality which we can get along with but it is quite variable depending on where we were born, when, and our position in the society of that time and place.  Reality, then, is complex and diverse enough to allow survival with most of the maps one develops influenced by different places, religions, social classes, and all the rest if our differences.

But there is only one science.  In some cases it provides an eye on the future.

The worst case that develops in a culture is when a person becomes so powerful people are forced to take such a person’s will as a map of reality. Let’s call such a person a “potentate.”  That is a problem because people are forced to act on that person’s will for their actions.  Why?  The potentate is not confined by reason or review. Fantasy reigns.  Remember the ancient king who commanded the tide not to come in?  When it did, he had his soldiers to whip the sea!

So we come to the present.  Who are the powers beyond review today?  Obviously they are the people who control the corporations.  It was apparent to Rutherford B. Hays, 19th President of the U. S. (1877-81) when he said, “This is a government of the people, by the people and for the people no longer. It is a government of corporations, by corporations, and for corporations,” one hundred years ago, something far more obviously today.  They are majority stockowners and, increasingly, CEO’s.  They function entirely as profit makers, and have no social alignment whatsoever.  It is true some corporations exercise social responsibility, but it is not built in.  The results include the concentration of wealth in the hands of a few, and disavowal of those excluded, disregard for all but the most immediate and intense health effects and disregard for the environment.

The case history is obvious, with the oil and gas corporations leading the way.  They are powerful because they have a toll from almost all motion today – from people going to church and children going to school to big trucks, earthmovers, war machines, airplanes and oceangoing ships.  Everyone pays to move.

So there is great economic power concentrated in the hydrocarbon industry.  They buy the laws they want, and hire support from politicians.  They become “potentates” in the sense it was used above.  They support the kind of politician who brings a snowball into the Senate to disprove global warming.  If their science discovers an inconvenient truth (global warming) it then musters think tanks to deny that reality.  They support politicians like House Republican Rep. David McKinley of West Virginia, who says the military’s efforts (regarding global warming) amount to partisan gimmicks and distractions from fighting terrorism. “Why should Congress divert funds from the mission of our military and national security,” he wrote to colleagues in 2014, “to support a political ideology?”

The disconnect between the reality of global warming as demonstrated by science and counter-claims of the industry is caused for the reason a disconnect from reality always is: potentates don’t want to loose power, and with it status and influence.  Reality is an impediment to their goals and desires. 

As Henry Kissinger said, “control oil and you control nations.”  Including this one.

See also:  Climate Reality Project

AAAS Science, Issue June 27th

SCIENCE: Special Issue: Volume 344 no. 6191 pp. 1464-1467

From an Introduction by David Malakoff, SCIENCE, June 27, 2014

702—PERCENT INCREASE IN U.S. SHALE GAS PRODUCTION SINCE 2007

40—PERCENT SHALE GAS SHARE OF TOTAL U.S. PRODUCTION

47—PERCENT INCREASE IN U.S. ELECTRICITY GENERATED USING NATURAL GAS SINCE 2005

15,000,000—LITERS OF WATER AND CHEMICALS PUMPED INTO A TYPICAL FRACKING WELL

Nearly 70 years ago, a small group of engineers and geologists gathered at a dusty gas drilling site in southwestern Kansas to try an experiment. They pumped nearly 4000 liters of gelled gasoline and sand some 700 meters down a borehole into a thick bed of limestone, in hopes that the pressurized gunk would fracture the rock and release more natural gas. The “hydraulic fracturing” test failed. But success ultimately followed: Today, fracking, as it is known, is revolutionizing the energy industry, enabling firms to extract natural gas from a source once considered unpromising—vast deposits of shale, which is too dense for gas to flow freely (Science, 25 June 2010, p. 1624). By penetrating the shale with boreholes that bend horizontally, and then pumping in millions of liters of fluids and sand under high pressure, drillers can force open minute cracks that release valuable streams of gas.

Extensive shale gas deposits—or “plays” as they are known in the industry—are found around the world (see map). So far, however, the shale gas boom is largely confined to the United States, where over the past decade companies have drilled thousands of fracking wells into once obscure geological formations, including the Marcellus Shale in Pennsylvania, the Barnett in Texas, and the Haynesville in Louisiana. (In other shale plays, such as the Bakken in North Dakota, fracking is primarily used to produce oil.)

The resulting surge in natural gas is remaking U.S. energy markets—and causing economic ripple effects globally. Shale gas has made the United States the world’s leading natural gas producer and now accounts for about 40% of U.S. production, up from less than 2% in 2001. The share is projected to grow to 53% by 2040, and natural gas prices have tumbled as abundance grows (see graphs). That’s helped accelerate a shift away from coal to natural gas for generating electricity and prompted energy-intensive manufacturing firms to shift production from overseas factories to the United States, creating hundreds of thousands of jobs. The United States is also boosting natural gas exports to other nations—reversing its traditional role as an energy importer.

The shale gas shake-up has been accompanied by plenty of controversy—and new research—as the stories in this special section illustrate. Scientists are debating fracking’s impact on water quality (see p. 1468) and whether the shale gas boom will help or hurt efforts to curb climate change (see p. 1472). They are also exploring potential links to human-caused earthquakes (Science, 23 March 2012, p. 1436), air pollution, and habitat fragmentation.

Basic researchers are also sizing up this new resource. They are searching for life deep in shale deposits (p. 1470) and potentially transformative ways to convert the methane in natural gas into liquid fuels and other chemicals (p. 1474). Some are examining the origins of shale gas, trying to determine whether it is primarily the product of methane-producing microbes or thermal breakdown of organic matter (see p. 1500). And analysts continue to debate just how much shale gas is really out there—and how quickly the current boom could turn bust.

For the moment, any downturn seems distant. Canada, which already gets 15% of its natural gas from shale, is ramping up production. China, Europe, and Russia are eyeing their essentially untapped shale deposits. Public opposition to fracking is growing in some nations, however, and drilling technologies that have performed well in the United States may not work well overseas, where the shale can have very different properties. One thing is clear: The shale gas revolution is still in its infancy, with plenty of growing pains ahead.

Further reading

R. D. Vidic, S. L. Brantley, J. M. Vandenbossche, D. Yoxtheimer, J. D. Abad, Impact of shale gas development on regional water quality. Science 340, 1235009 (2013).

W. L. Ellsworth. Injection-induced earthquakes. Science 341, 1225942 (2013).

R. J. Conrado, R. Gonzalez, Envisioning the bioconversion of methane to liquid fuels. Science 343, 621–623 (2014).

A. R. Brandt et al., Methane leaks from North American natural gas systems. Science 343, 733–735 (2014).

B. G. Hashiguchi et al., Main-group compounds selectively oxidize mixtures of methane, ethane, and propane to alcohol esters. Science 343, 1232–1237 (2014).

X. Guo et al., Direct, nonoxidative conversion of methane to ethylene, aromatics, and hydrogen. Science 344, 616–619 (2014).

D. A. Stolper et al., Formation temperatures of thermogenic and biogenic methane. Science 344, 1500–1503 (2014).

1. Blowout When blowout prevention equipment is absent or fails, pressurized fluid and gas can explode out the wellhead, injuring people and spewing pollutants.

2. Gas leak Methane, the primary gas in natural gas, may be present in layers of rock above the target layer. Cracks in the cement that seal the well to the surrounding rock can provide a path for this methane to travel into the water table.

3. Air pollution Flare pipes that burn methane so it doesn’t build up, diesel truck exhaust and emissions from wastewater evaporation can dirty the air near a drill site. When methane is released without being burned, it acts as a potent greenhouse gas, trapping 20 times as much heat as carbon dioxide.

4. Wastewater overflow Fracking fluid, about 1 percent of which is made up of chemicals (sometimes including carcinogens), is increasingly recycled for use in other wells. But sometimes it is stored in open pits that emit noxious fumes and can overflow with rain.

5. Other leaks There are some worries that local geology in particular areas would allow fracking-produced fluid and methane to travel upward. But most evidence of exposure stems from surface problems such as spills or illicit dumping.

6. Home explosions If methane does get into the water table — because of cracked cement, local geology or the effects of old wells — it can build up in homes and lead to explosions.