Contaminated water in 2 states linked to faulty shale gas wells

Faulty well integrity, not hydraulic fracturing deep underground, is the primary cause of drinking water contamination from shale gas extraction in parts of Pennsylvania and Texas, according to a new study by researchers from five universities.

The scientists from Duke, Ohio State, Stanford, Dartmouth and the University of Rochester
published their peer-reviewed study Sept. 15 in the Proceedings of the National Academy of Sciences. Using noble gas and hydrocarbon tracers, they analyzed the gas content of more than 130 drinking water wells in the two states.

“We found eight clusters of wells — seven in Pennsylvania and one in Texas — with contamination, including increased levels of natural gas from the Marcellus shale in Pennsylvania and from shallower, intermediate layers in both states,” said Thomas H. Darrah, assistant professor of earth science at Ohio State, who led the study while he was a research scientist at Duke.

“Our data clearly show that the contamination in these clusters stems from well-integrity problems such as poor casing and cementing,” Darrah said.

“These results appear to rule out the possibility that methane has migrated up into drinking water aquifers because of horizontal drilling or hydraulic fracturing, as some people feared,” said Avner Vengosh, professor of geochemistry and water quality at Duke.

In four of the affected clusters, the team’s noble gas analysis shows that methane from drill sites escaped into drinking water wells from shallower depths through faulty or insufficient rings of cement surrounding a gas well’s shaft. In three clusters, the tests suggest the methane leaked through faulty well casings. In one cluster, it was linked to an underground well failure.

“People’s water has been harmed by drilling,” said Robert B. Jackson, professor of environmental and earth sciences at Stanford and Duke. “In Texas, we even saw two homes go from clean to contaminated after our sampling began.”

“The good news is that most of the issues we have identified can potentially be avoided by future improvements in well integrity,” Darrah stressed.

Using both noble gas and hydrocarbon tracers — a novel combination that enabled the researchers to identify and distinguish between the signatures of naturally occurring methane and stray gas contamination from shale gas drill sites — the team analyzed gas content in 113 drinking-water wells and one natural methane seep overlying the Marcellus shale in Pennsylvania, and in 20 wells overlying the Barnett shale in Texas. Sampling was conducted in 2012 and 2013. Sampling sites included wells where contamination had been debated previously; wells known to have naturally high level of methane and salts, which tend to co-occur in areas overlying shale gas deposits; and wells located both within and beyond a one-kilometer distance from drill sites.

Noble gases such as helium, neon or argon are useful for tracing fugitive methane because although they mix with natural gas and can be transported with it, they are inert and are not altered by microbial activity or oxidation. By measuring changes in ratios in these tag-along noble gases, researchers can determine the source of fugitive methane and the mechanism by which it was transported into drinking water aquifers — whether it migrated there as a free gas or was dissolved in water.

“This is the first study to provide a comprehensive analysis of noble gases and their isotopes in groundwater near shale gas wells,” said Darrah, who is continuing the analysis in his lab at Ohio State. “Using these tracers, combined with the isotopic and chemical fingerprints of hydrocarbons in the water and its salt content, we can pinpoint the sources and pathways of methane contamination, and determine if it is natural or not.”

Gas leaks from faulty wells linked to contamination in some groundwater

A study has pinpointed the likely source of most natural gas contamination in drinking-water wells associated with hydraulic fracturing, and it’s not the source many people may have feared.

What’s more, the problem may be fixable: improved construction standards for cement well linings and casings at hydraulic fracturing sites.

A team led by a researcher at The Ohio State University and composed of researchers at Duke, Stanford, Dartmouth, and the University of Rochester devised a new method of geochemical forensics to trace how methane migrates under the earth. The study identified eight clusters of contaminated drinking-water wells in Pennsylvania and Texas.

Most important among their findings, published this week in the Proceedings of the National Academy of Sciences, is that neither horizontal drilling nor hydraulic fracturing of shale deposits seems to have caused any of the natural gas contamination.

“There is no question that in many instances elevated levels of natural gas are naturally occurring, but in a subset of cases, there is also clear evidence that there were human causes for the contamination,” said study leader Thomas Darrah, assistant professor of earth sciences at Ohio State. “However our data suggests that where contamination occurs, it was caused by poor casing and cementing in the wells,” Darrah said.

In hydraulic fracturing, water is pumped underground to break up shale at a depth far below the water table, he explained. The long vertical pipes that carry the resulting gas upward are encircled in cement to keep the natural gas from leaking out along the well. The study suggests that natural gas that has leaked into aquifers is the result of failures in the cement used in the well.

“Many of the leaks probably occur when natural gas travels up the outside of the borehole, potentially even thousands of feet, and is released directly into drinking-water aquifers” said Robert Poreda, professor of geochemistry at the University of Rochester.

“These results appear to rule out the migration of methane up into drinking water aquifers from depth because of horizontal drilling or hydraulic fracturing, as some people feared,” said Avner Vengosh, professor of geochemistry and water quality at Duke.

“This is relatively good news because it means that most of the issues we have identified can potentially be avoided by future improvements in well integrity,” Darrah said.

“In some cases homeowner’s water has been harmed by drilling,” said Robert B. Jackson, professor of environmental and earth sciences at Stanford and Duke. “In Texas, we even saw two homes go from clean to contaminated after our sampling began.”

The method that the researchers used to track the source of methane contamination relies on the basic physics of the noble gases (which happen to leak out along with the methane). Noble gases such as helium and neon are so called because they don’t react much with other chemicals, although they mix with natural gas and can be transported with it.

That means that when they are released underground, they can flow long distances without getting waylaid by microbial activity or chemical reactions along the way. The only important variable is the atomic mass, which determines how the ratios of noble gases change as they tag along with migrating natural gas. These properties allow the researchers to determine the source of fugitive methane and the mechanism by which it was transported into drinking water aquifers.

The researchers were able to distinguish between the signatures of naturally occurring methane and stray gas contamination from shale gas drill sites overlying the Marcellus shale in Pennsylvania and the Barnett shale in Texas.

The researchers sampled water from the sites in 2012 and 2013. Sampling sites included wells where contamination had been debated previously; wells known to have naturally high level of methane and salts, which tend to co-occur in areas overlying shale gas deposits; and wells located both within and beyond a one-kilometer distance from drill sites.

As hydraulic fracturing starts to develop around the globe, including countries South Africa, Argentina, China, Poland, Scotland, and Ireland, Darrah and his colleagues are continuing their work in the United States and internationally. And, since the method that the researchers employed relies on the basic physics of the noble gases, it can be employed anywhere. Their hope is that their findings can help highlight the necessity to improve well integrity.

Breakthrough provides picture of underground water

Superman isn’t the only one who can see through solid surfaces. In a development that could revolutionize the management of precious groundwater around the world, Stanford researchers have pioneered the use of satellites to accurately measure levels of water stored hundreds of feet below ground. Their findings were published recently in Water Resources Research.

Groundwater provides 25 to 40 percent of all drinking water worldwide, and is the primary source of freshwater in many arid countries, according to the National Groundwater Association. About 60 percent of all withdrawn groundwater goes to crop irrigation. In the United States, the number is closer to 70 percent. In much of the world, however, underground reservoirs or aquifers are poorly managed and rapidly depleted due to a lack of water-level data. Developing useful groundwater models, availability predictions and water budgets is very challenging.

Study co-author Rosemary Knight, a professor of geophysics and senior fellow, by courtesy, at the Stanford Woods Institute for the Environment, compared groundwater use to a mismanaged bank account: “It’s like me saying I’m going to retire and live off my savings without knowing how much is in the account.”

Lead author Jessica Reeves, a postdoctoral scholar in geophysics, extended Knight’s analogy to the connection among farmers who depend on the same groundwater source. “Imagine your account was connected to someone else’s account, and they were withdrawing from it without your knowing.”

Until now, the only way a water manager could gather data about the state of water tables in a watershed was to drill monitoring wells. The process is time and resource intensive, especially for confined aquifers, which are deep reservoirs separated from the ground surface by multiple layers of impermeable clay. Even with monitoring wells, good data is not guaranteed. Much of the data available from monitoring wells across the American West is old and of varying quality and scientific usefulness. Compounding the problem, not all well data is openly shared.

To solve these challenges, Reeves, Knight, Stanford Woods Institute-affiliated geophysics and electrical engineering Professor Howard Zebker, Stanford civil and environmental engineering Professor Peter Kitanidis and Willem Schreüder of Principia Mathematica Inc. looked to the sky.

The basic concept: Satellites that use electromagnetic waves to monitor changes in the elevation of Earth’s surface to within a millimeter could be mined for clues about groundwater. The technology, Interferometric Synthetic Aperture Radar (InSAR), had previously been used primarily to collect data on volcanoes, earthquakes and landslides.

With funding from NASA, the researchers used InSAR to make measurements at 15 locations in Colorado’s San Luis Valley, an important agricultural region and flyway for migrating birds. Based on observed changes in Earth’s surface, the scientists compiled water-level measurements for confined aquifers at three of the sampling locations that matched the data from nearby monitoring wells.

“If we can get this working in between wells, we can measure groundwater levels across vast areas without using lots of on-the-ground monitors,” Reeves said.

The breakthrough holds the potential for giving resource managers in Colorado and elsewhere valuable data as they build models to assess scenarios such as the effect on groundwater from population increases and droughts.

Just as computers and smartphones inevitably get faster, satellite data will only improve. That means more and better data for monitoring and managing groundwater. Eventually, InSAR data could play a vital role in measuring seasonal changes in groundwater supply and help determine levels for sustainable water use.

In the meantime, Knight envisions a Stanford-based, user-friendly online database that consolidates InSAR findings and a range of other current remote sensing data for soil moisture, precipitation and other components of a water budget. “Very few, if any, groundwater managers are tapping into any of the data,” Knight said. With Zebker, postdoctoral fellow Jingyi Chen and colleagues at the University of South Carolina, Knight recently submitted a grant proposal for this concept to NASA.

Study finds tungsten in aquifer groundwater controlled by pH, oxygen

Two Kansas geologists are helping shed new light on how tungsten metal is leached from the sediment surrounding aquifers into the groundwater. The findings may have implications for human health.

Tungsten is a naturally occurring metal that is primarily used for incandescent light bulb filaments, drill bits and an alternative to lead in bullets. Though it is thought to be nonhazardous to the environment and nontoxic to humans, it can be poisonous if ingested in large amounts. In recent years, tungsten has been tentatively linked to cases of childhood leukemia in the Western U.S.

“Very little is known about the biogeochemistry of tungsten in the environment,” said Saugata Datta, professor of geology at Kansas State University. “We need to understand how this metal is leached from the soils into groundwater because humans can be exposed to tungsten through multiple pathways.”

Datta, along with Chad Hobson, master’s student in geology, Lavonia, Ga., and colleagues at Tulane University and the University of Texas, Arlington, found that the likelihood that tungsten will seep into an aquifer’s groundwater depends on the groundwater’s pH level, the amount of oxygen in the aquifer and the number of oxidized particles in the water and sediment. Analysis also showed that tungsten-IV is the most common form of tungsten in natural sediments.

These latest findings appear in the study “Controls on tungsten concentrations in groundwater flow systems: The role of adsorption, aquifer sediment Fe(III) oxide/oxyhydroxide content, and thiotungstate formation,” published in the journal Chemical Geology.

In addition to the publication, Datta and Hobson presented the findings at the International Conference on Biogeochemistry of Trace Elements.

For the study, researchers looked at Fallon, Nev.; Sierra Vista, Ariz.; and at the Cheyenne Bottoms Refuge near Hoisington, Kan. The sites were chosen based on previous studies analyzing plants and dust collected on trees in the locations. Additionally, these areas have natural tungsten mineral deposits, nearby military bases, and mining and smelting operations in the area, Datta said.

In 2002, the Centers for Disease Control investigated several clusters of acute lymphatic leukemia in both Nevada and Arizona. The investigation found that residents’ urine had tungsten levels above the 95th percentile.

“This was important for us to know because the goal is to clarify valuable information about tungsten’s geochemistry,” Datta said. “So, we needed sites that had tungsten — and enough tungsten to measure easily. The benefit of this study is that tungsten’s geochemistry has been overlooked and until recently, largely unknown. This work will help fill the gaps in the knowledge of tungsten, which is possibly carcinogenic, and help determine its future use.”

Datta and Hobson analyzed sediment samples lining the aquifers while researchers at Tulane University and the University of Texas, Arlington analyzed the groundwater samples. The National Synchrotron Light Source was used for spectroscopic analysis of the individual particles. This helped researchers understand the speciation of tungsten in natural sediments in the environment and helped them detect why tungsten forms organosulphur complexes that can be soluble in groundwater, Datta said. Analysis also showed that tungsten-VI is the most common form of tungsten in natural sediments.

Analysis of the sediment and groundwater showed that iron oxide and oxyhydroxide particles in both substances play a key role in regulating how much tungsten is in the groundwater. The fewer iron oxides or oxyhydroxide particles, the higher the amount of tungsten, Datta said.

Similarly, the team found that the number of tungsten-regulating iron oxide particles is controlled by the pH in the groundwater. A higher pH results in more tungsten entering the water.

“Tungsten is specifically bound to these iron oxides and oxyhydroxides,” Datta said. “One of the major factors controlling tungsten’s mobility and bioavailability is pH. Ranging values of pH can affect how tungsten behaves or transforms between different tungsten species, which have different properties and factors controlling mobility.”

When tungsten is in the water it is surrounded by oxygen atoms and forms an anion, Datta said. When in the presence of phosphates, this anion tends to bind with other transition metals, commonly iron, to form poloyoxometalates. In this form, tungsten can become more soluble in water.

Researchers also found that aquifers with less dissolved oxygen had greater traces of tungsten in the groundwater than aquifers with high dissolved oxygen levels.

The process of tungsten being leached from the surrounding sediment into the groundwater can be reduced if the ironoxides are in the water and the water has a neutral pH level, according to Datta.

The study is part of a three-year, $515,000 National Science Foundation-funded project between Kansas State University and Karen Johannesson at Tulane University that is titled “Collaborative Research: Chemical Hydrogeologic Investigations of Tungsten: Field, Laboratory, and Modeling Studies of an Emerging Environmental Contaminant.” It focuses on biogeochemistry of tungsten’s reaction to the environment and how it is transported from sediments into groundwaters once it becomes geochemically mobilized.

Technical reports examine hydraulic fracturing in Michigan

University of Michigan researchers today released seven technical reports that together form the most comprehensive Michigan-focused resource on hydraulic fracturing, the controversial natural gas and oil extraction process commonly known as fracking.

The studies, totaling nearly 200 pages, examine seven critical topics related to the use of hydraulic fracturing in Michigan, with an emphasis on high-volume methods: technology, geology and hydrogeology, environment and ecology, public health, policy and law, economics, and public perceptions.

While considerable natural gas reserves are believed to exist in the state and high-volume hydraulic fracturing has the potential to help access them, possible impacts to the environment and to public health must be addressed, the U-M researchers concluded.

Though modern high-volume hydraulic fracturing is not widely used in Michigan today, a main premise of the U-M study is that the technique could become more widespread due to a desire for job creation, economic growth, energy independence and cleaner fuels.

“There’s a lot of interest in high-volume hydraulic fracturing, but there really isn’t much activity at the moment in Michigan,” said John Callewaert, project director and director of integrated assessment at U-M’s Graham Sustainability Institute, which is overseeing the project. “That’s why now is a good time to do this assessment.”

These reports conclude the first phase of a two-year U-M project known formally as the Hydraulic Fracturing in Michigan Integrated Assessment. The seven documents-which should not be characterized or cited as final products of the integrated assessment-provide a solid informational foundation for the project’s next phase, an analysis of various hydraulic fracturing policy options. That analysis is expected to be completed in mid-2014 and will be shared with government officials, industry experts, other academics, advocacy groups and the general public.

“Nothing like this has been done before in Michigan,” Callewaert said. “Having this comprehensive, state-specific set of reports will be an invaluable resource that will help guide future decision-making on this issue-and hopefully will help Michigan avoid some of the pitfalls encountered in other states.”

Conclusions of the reports, which were written by faculty-led, student-staffed teams from various disciplines, include:

  • Technology. In view of the current low price of natural gas, the high cost of drilling deep shale formations and the absence of new oil discoveries, it is unlikely that there will be significant growth of the oil and gas industry in Michigan in the near-term future. However, considerable reserves of natural gas are believed to exist in deep shale formations such as the Utica-Collingwood, which underlies much of Michigan and eastern Lake Huron and extends into Ontario, Canada.

  • Geology/hydrogeology. A recent flurry of mineral rights acquisitions in the state associated with exploratory drilling suggests the potential for growth in natural gas production through high-volume hydraulic fracturing, though only a handful of such wells have been drilled to date. “Michigan is thus in a unique position to assess the future of high-volume hydraulic fracturing before the gas boom begins.”

  • Environment/ecology. Potential impacts of hydraulic fracturing on the environment are significant and include increased erosion and sedimentation, increased risk of aquatic contamination from chemical spills or equipment runoff, habitat fragmentation and resulting impacts on aquatic and terrestrial organisms, loss of stream riparian zones, and reduction of surface waters available to plants and animals due to the lowering of groundwater levels.

  • Public health. Possible hazards in the surrounding environment include impaired local and regional air quality, water pollution and degradation of ecosystems. Possible hazards in nearby communities include increased traffic and motor vehicle accidents, stress related to risk perception among residents, and boomtown-associated effects such as a strained health care system and road degradation.

  • Policy/law. The state is the primary source of law and policy governing hydraulic fracturing in Michigan. The operator of a high-volume hydraulically fractured well must disclose the hazardous constituents of chemical additives to the state Department of Environmental Quality for each additive within 60 days of well completion. Unlike most other states, DEQ does not require operators to report to, a nationwide chemical disclosure registry.

  • Economics. The gas extraction industry creates employment and income for Michigan, but the employment effects are modest compared with other industries and not large enough to “make or break” the state’s economy. In the future, the number of technical jobs in the industry will likely increase, while less-skilled laborer positions will decline.

  • Public perceptions. A slight majority of Michigan residents believe the benefits of fracking outweigh the risks, but significant concerns remain about the potential impacts to human health, the environment and groundwater quality. The public tends to view the word “fracking” as the entirety of the natural gas development process, from leasing and permitting, to drilling and well completion, to transporting and storing wastewater and chemicals. Industry and regulatory agencies hold a much narrower definition that is limited to the process of injecting hydraulic fracturing fluids into a well. These differences in perceived meaning can lead to miscommunications that ultimately increase mistrust among stakeholders.

In fracking, water, sand and chemicals (in a mix known as hydraulic fracturing fluid) are injected under high pressure deep underground to crack sedimentary rocks, such as shale, and free trapped natural gas or oil. Though the process has been used for more than half a century to improve well production, recent technical advances have helped unlock vast stores of previously inaccessible natural gas and oil, resulting in a boom in some parts of the United States.

Chief among the technical advances are directional drilling and high-volume hydraulic fracturing, which are often used together. In directional drilling, the well operator bores vertically down to the rock formation, then follows the formation horizontally.
High-volume fracking-the focus of recent attention and public concern-is defined by the state of Michigan as a well that uses more than 100,000 gallons of hydraulic fracturing fluid. For reference, an Olympic-size swimming pool holds about 660,000 gallons of water.

Since the late 1940s, an estimated 12,000 gas and oil wells have been drilled in Michigan using hydraulic fracturing, without any reported contamination issues. Most of those wells have been relatively shallow vertical wells that each used about 50,000 gallons of water.

But recently, a small number of deep, directionally drilled, high-volume hydraulically fractured wells have been completed in the northern part of the Lower Peninsula. Those wells sometimes use several million gallons of water, and one Michigan well required more than 20 million gallons.

Since 2010, when the Petoskey Pioneer Well spurred interest in high-volume hydraulically fractured wells in Michigan, 19 such wells are known to have been completed in the state, according to Sara Gosman, a lecturer at the U-M Law School and author of the technical report on policy/law.

In the public perceptions report, authors Kim Wolske and Andrew Hoffman of the U-M Erb Institute for Global Sustainable Enterprise note that chemical additives in high-volume hydraulic fracturing fluids “remain a primary point of contention for many stakeholders in Michigan.” Many nonprofits and concerned citizens stress the point that operators of high-volume wells are not required to report the composition of those fluids to the state until 60 days after the hydraulic fracturing event.

The often-repeated concern is that if a spill were to occur, responders would not be as well-prepared as they would have been if the fluid composition had been known beforehand, Wolske and Hoffman note.

Though groundwater contamination is often cited as a top concern, surface contamination from spills and improper disposal of waste fluids likely carries the greatest risk for harmful water-quality impacts, due to proximity to potable water resources, according to the geology/hydrogeology report written by Brian Ellis, assistant professor in the Department of Civil and Environmental Engineering.

When a well is fracked, the fluid is injected into rock formations to create cracks and to prop them open. Of the total volume of hydraulic fracturing fluids injected into a well, amounts varying from 10 percent to 70 percent may return to the surface as “flowback water” after the pressure is reduced and gas or oil begin to flow toward the wellhead.

In Michigan high-volume hydraulically fractured wells, the average amount of flowback water returning to the surface is about 37 percent of injected volumes, according to the Ellis report.

The flowback water is highly saline and can contain elevated levels of heavy metals and naturally occurring radioactive elements, in addition to methane and the original chemical additives in the fracturing fluids. In Michigan, common hydraulic fracturing fluid additives include ethylene glycol, hydrochloric acid, isopropyl alcohol, methanol and ammonium persulfate, according to the Ellis report.

“However, since in Michigan all flowback is disposed of by deep-well injection and it is not allowed to sit in open pits, the risk of this type of contamination will be lower than in other states without such disposal opportunities and regulations,” Ellis wrote.

On the topic of potential water contamination, the environment/ecology report notes that Michigan’s dense, interconnected aquatic ecosystems (streams, rivers, lakes, inland and coastal wetlands) and the groundwater aquifers to which they are linked are of particular concern. The connectivity between surface and groundwater bodies “can lead to impacts distant from, as well as close to, drilling sites,” according to the report by G. Allen Burton, professor in the School of Natural Resources and Environment and director of the U-M Water Center, and Knute Nadelhoffer, professor of ecology and evolutionary biology and director of the U-M Biological Station.

The potential migration of methane, the main component of natural gas, into groundwater reservoirs has also received a lot of attention lately.

But the probability of significant methane leakage associated with deep-shale drilling involving hydraulic fracturing in Michigan “is quite low provided that best practices are adhered to,” according to the U-M report on hydraulic fracturing technologies written by John Wilson, a consultant to the U-M Energy Institute, and Johannes Schwank, professor of chemical engineering.

The greatest challenge to understanding the potential public health risks of hydraulic fracturing in Michigan is the lack of state-specific data, according to Niladri Basu, author of the public health technical report and a former faculty member at the U-M School of Public Health. While thousands of hydraulically fractured wells have been drilled in Michigan, the potential public health risks related to these facilities have been poorly documented, Basu wrote.

For example, while operators of high-volume fracking wells are required to disclose the contents of their hydraulic fracturing fluids, operators of the 12,000 or so low-volume wells in the state are not. “There needs to be much greater understanding of what chemicals are being used in every well, with information related to volumes, amounts, disposal plans, etc., made available,” Basu wrote.

The U-M hydraulic fracturing study is expected to cost at least $600,000 and is being funded by U-M through its Graham Sustainability Institute, Energy Institute and Risk Science Center. State regulators, oil and gas industry representatives, staffers from environmental nonprofits, and peer reviewers provided input to the technical reports, and more than 100 public comments were considered.

In addition to the study authors mentioned above, the technical report authors include Roland Zullo, assistant research scientist, U-M Institute for Research on Labor, Employment and the Economy (economics report).

Contamination of La Selva geothermal system in Girona, Spain

The system works by refilling meteoric waters that penetrate the earth in high areas, move underground and reach an unknown thermal hot spot, where they heat up and acquire CO2, and probably metals as well. Afterwards the water leaches out (dissolve) the host rocks and flows out from the upwellings. -  SINC/A. Navarro et al.
The system works by refilling meteoric waters that penetrate the earth in high areas, move underground and reach an unknown thermal hot spot, where they heat up and acquire CO2, and probably metals as well. Afterwards the water leaches out (dissolve) the host rocks and flows out from the upwellings. – SINC/A. Navarro et al.

Monitoring the construction of wells, avoid over-exploiting cold groundwater close to hot groundwater, and controlling mineral water extraction. These are the recommendations from the Polytechnic University of Catalonia and the University of Barcelona, after analyzing the contamination of La Selva geothermal system, above all by arsenic pollution. In this region, which is known for its spa resorts and bottling plants, as well as in other Catalan coastal mountain ranges, uranium levels higher than what is recommended by the WHO have been detected.

The groundwater in La Selva (Girona, Spain) area show high levels of arsenic, antimony and other polluting elements. The area’s geothermal system, where hot and cold groundwater flow naturally, are the cause of this situation, according to a study that researchers from the Polytechnic University of Catalonia (UPC) and the University of Barcelona (UB) have published in the journal Geothermics.

“The system works by refilling meteoric waters that penetrate the earth in high areas, move underground and reach an unknown thermal hot spot, where they heat up and acquire CO2, and probably metals as well “Andrés Navarro, a lecturer at UPC and co-author of the project explained to SINC. “Afterwards the water leaches out (dissolve) the host rocks and flows out from the upwellings”.

In this process the waters naturally pick up pollutants. Consequently, the researchers have found high volumes of arsenic, silver, lead, antimony, zinc and other metals in the hydrothermal deposits, especially in the area of Caldes de Malavella (Girona), an area famous for its spa resorts and mineral water bottling companies.

The results show that groundwater in some areas has arsenic levels of up to 0.069 mg/l, when the legal limit in Spain and the rest of the European Union was 0.01 mg/l in water for human consumption.

“Fortunately, a few years ago a legislation for this was created, and since then bottled mineral has been controlled, although before then this did not occur” the researcher says. Furthermore, a plant to remove arsenic from public water supplies has been built in Caldes de Malavella.

In any case, the study recommends controlling the extraction of water for bottling plants, as well as over-exploiting cold groundwater close to hot water springs. This way the mixing of waters is avoided and so are the pollutants.

For the same reason it is not advisable to build wells close to geothermal upwellings, especially illegal ones for private supplies or irrigation. Studying geothermal liquid outlets in areas of diffused discharge, such as some humid areas, is also proposed.

The problem of uranium in waters

“Making a model for managing the whole aquifer to rationalize water extraction and consumption would be the solution” Navarro says. He also highlights the need to take action regarding the natural water pollutants: uranium.

The analysis in La Selva shows “relatively high” levels (37.7 microg/l) of this element, especially in samples from sources and wells not directly linked to thermal activity.

The mobility of uranium is linked to granite rocks and is frequently found in Catalan coastal mountain ranges, where researchers have carried out specific studies on the topic. The samples have been taken from wells and drilling at a depth of up to 100 metres.

The results published in the journal Tecnología del agua and they show “significant concentrations” of uranium in groundwater used for public supply and bottling. Specifically, in some parts of the Montseny-Guilleries mountain range, these levels are more than 140 microg/l.

There are no legal limits for uranium concentrations in water in the European Union, but the analysis carried out in Catalan coastal mountain ranges shows that these levels far exceed the recommendations of the World Health Organisation (WHO), or for example, the standard established by the Environmental Protection Agency (EPA) in the USA.

Both the EPA and the WHO establish a maximum uranium level of 30 microg/l. The European Food Safety Authority (EFSA) is considering establishing a guideline level for this element, but at the moment the legal loophole remains.

The toxicity of uranium is linked to the solubility of the compound: the more soluble it is, the more toxic it is. The experiments carried out on animals and people show the most affected organ is the kidney, and alterations in reproduction and development are seen when this element exists in high concentrations.