PBS’ follow up to Erin Brockovich left key details out

OSHA

Recently, PBS NewsHour ran a two-part investigative story that must have seemed to have all the elements of a compelling piece. There was a relatively unknown but apparently widespread carcinogen and a great hook—it was tied to the story of contaminated water behind the film Erin Brockovich (and the book A Civil Action). Issues relating to public health threats demand careful and thorough reporting. Unfortunately, those qualities were at times absent from the PBS story.

The story focused on hexavalent chromium (Cr⁶⁺) in drinking water. Most chromium is trivalent, which isn’t very soluble in water. When oxidized to hexavalent chromium, however, it becomes mobile. Unlike the trivalent variety, hexavalent chromium is carcinogenic. It's much worse if inhaled, but there’s evidence that it is dangerous when ingested as well. As the NewsHour story noted, recent sampling has shown that hexavalent chromium is present in drinking water across the country. Does that mean we have a public health crisis on our hands, caused by shockingly widespread contamination? Let’s slow down and get some context.

Meet the metal

Hexavalent chromium occurs naturally. That’s a rather important fact never mentioned in the NewsHour story, which describes the water as “tainted” by industrial chemicals. Chromium, like many elements, is present in Earth’s crust. Some types of rock have more than others, but it’s actually a little bit more common than copper or zinc—the average concentration in the upper crust is something like 90 parts per million. Oxidize some of that chromium to the hexavalent state, and it can be mobilized into groundwater. If hexavalent chromium is showing up in wells nearly everywhere we look, it might be because it’s naturally present rather than a ubiquitous, human-introduced contaminant.

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Can humans cause an earthquake?

St. James Church in Lorca, Spain after an earthquake on May 11, 2011.

Wikimedia Commons

One of the things people often wonder about earthquakes is whether human activity can play a role in their occurrence. Sometimes that comes from a desire to assign blame, but often it’s related to a bigger question: could we actively trigger small earthquakes to prevent the big, damaging ones from occurring? While that lofty piece of geoengineering may not be feasible (or even possible), it is true that humans can sometimes trigger earthquakes.

Earthquakes are fundamentally controlled by two factors. The first is the movement of rock, such as tectonic plates. This constant, gradual movement is the source of conflict in an active fault zone—one region of rock is being forced past another. If the two blocks simply slid smoothly by each other along the fault surface, this would be a pretty peaceful process. But this is where the second factor comes along—the friction between the blocks. The stress builds up until it’s great enough to overcome that friction, at which point seismic energy is released violently as the blocks catch up on decades' (or centuries') worth of motion in just a few seconds.

For the most part, the accumulating stress that creates this situation is much too large for human activities to make a difference. We can, however, affect the friction that locks up the fault. Hydraulic fracturing, where fluids are pumped into the ground at extremely high pressures to crack rocks that release natural gas and oil, has been shown to do just that in certain situations. Increasing the fluid pressure inside the fault partially de-stabilizes the friction-lock, lowering the stress threshold necessary to trigger an earthquake just enough for one to occur.

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EPA fracking investigation in Wyoming revisited after objections

EPA workers in protective gear obtain samples for studying groundwater contamination in Pavillion, Wyoming.

US EPA

In December of last year, Ars reported on a major EPA study in Pavillion, Wyoming that concluded hydraulic fracking operations there had contaminated the groundwater aquifer. While there wasn’t a clear link to contamination detected in some shallow private water wells, EPA believed that the deeper contamination was very likely related to fracking. This determination came primarily from two deep monitoring wells that EPA had installed for the investigation.

Encana, the gas exploration company that owned the natural gas wells, disagreed vehemently. They asserted that EPA had drilled monitoring wells into a zone where gas was naturally present. As for the other compounds EPA detected in the wells, which were known to be components of fluids used during fracking, Encana said these were likely introduced into the aquifer during the drilling of the monitoring wells. EPA had foreseen this objection, and went to great lengths to avoid contaminating the monitoring wells, but Encana was not satisfied.

In the end, the EPA, the United States Geological Survey (USGS), the Wyoming Geological Survey, the Wyoming Department of Environmental Quality, the Wyoming Oil and Gas Conservation Commission, and the Wyoming Water Development Office met to discuss these objections. They decided that the EPA and USGS would carefully re-sample the deep monitoring wells to verify the results EPA had gotten previously.

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Fracked Pennsylvania shale could be naturally leaky

A fracking rig targets the Marcellus Shale.

Wikimedia Commons

Hydraulic fracturing—fracking—for natural gas has revolutionized the energy industry in many places, including the United States. The pushback over contamination concerns has been a prevailing storyline in the public eye. This possibility has been viewed as unlikely, though, as the shale gas layers being fracked are typically several thousand feet deeper than any aquifers used for drinking water. Fractures would have to propagate tremendous distances, through a number of confining layers, to create a pathway for contamination.

The physics required to make something like that happen just aren’t there. In nature, however, it’s usually true that to consider something to be impossible is to be disappointed. And so the nagging question remained: what if there are already some pathways present through those confining layers?

In 2011, researchers from Duke University published results (open access) showing a correlation between methane concentrations in private water wells and proximity to local natural gas production wells in parts of Pennsylvania and New York. While that suggested the water well contamination could be related to recent fracking, it was not at all a sure thing. The work was controversial, too—triggering a string of comments and replies in the journal that published it.

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Groundwater responsible for nearly half of sea level rise?

urbanworkbench

No, you don’t need to check the prescription on your eyeglasses (or medications)—we really are talking groundwater depletion and sea level rise again. Just a few weeks ago, we covered a recent study on the topic published by researchers from Taiwan and the Netherlands and compared it to one from last year that was done by Leonard Konikow of the United States Geological Survey. There’s a good reason that we’re back at it again. But first, for those who didn’t take notes—what are we talking about?

In many places, the water table is dropping as groundwater is depleted. When groundwater is pumped up for use, whether for drinking water or irrigation, some portion of it fails to infiltrate back down into the ground. (In drier regions, that portion approaches nil). Instead, the water evaporates into the atmosphere or ends up in surface streams. In either case, most of it eventually makes its way to the ocean. In many places, the amount of precipitation that infiltrates into the ground is too small to make up for that loss. And as the volume of groundwater decreases, sea level must rise in turn. It’s an awfully big planet we’re on, though. Most of its surface is ocean, so you might not expect this to add up to much.

That’s where these studies become so interesting. They estimated that, currently, the volume of groundwater being depleted is equivalent to about 13 to 20 percent of the ocean volume change. This isn't the whole story, however. The construction of dams on rivers creates large reservoirs (or lakes) behind them, increasing the storage of water on land. As long as you keep building new dams, you continually counteract some portion of sea level rise.

Damned if you don’t (dam): groundwater use outpacing dam building

Three Gorges Dam on the Yangtze River in China

Photo by Pedro Vásquez Colmenares

Last year, we had covered a study on the non-trivial contribution of groundwater depletion to sea level rise. It concluded that humans have pumped enough water from underground sources to account for up to 13 percent of the rise in ocean levels that occurred between 2000 and 2008.

A caveat, from a related paper, was that this might be offset by an increased retention of surface water in large reservoirs behind new dams. That would make the net effect of these human activities a wash. In fact, the 2007 IPCC report left out groundwater depletion when projecting sea level rise because of the uncertainty of existing estimates and the presumed balance with reservoir impoundment.

A new estimate, published recently in Geophysical Research Letters, takes a closer look at dam building and projects current trends into the future. While groundwater depletion continues, dam construction is on the decline. The result should be an increasing contribution to sea level rise.

Feature: How the EPA linked "fracking" to contaminated well water

Hydraulic fracturing (more commonly referred to as “fracking”) involves the injection of fluid at high pressure into a well, opening or widening fractures in the rock below that free up the flow of natural gas. Domestic natural gas production has been booming as a result, but opponents claim the technique contaminates drinking water, causing serious health effects.

Rigorous studies on fracking have been sparse, and the impassioned debate has raged on. A new investigation by the US Environmental Protection Agency (EPA) at a site in Wyoming is one of the first to look thoroughly at the potential link between fracking operations and groundwater contamination. The agency's report was released yesterday—and it provides a clear link between fracking and water supply problems.