Pebble will not fail in an earthquake, tailing pond detoxifytannin, thanks for your reply You state:
To be clear, it's not that all big mines pollute, it's that all mines, of any size, pollute.... All mines pollute, it's just the nature of the beast. What do you think tailings ponds contain? Not drinkable fluids I assure you. The sides of tailing ponds collapse ( no, they shouldn't...we're always assured it can't happen....but it does ), and/or the bottom of the pond is guaranteed to be impervious, either because they've lined it/or otherwise handled it, and, many years later, oops, guess liquid from tailing pond seeped ( somehow) into groundwater.......... It is possible to minimize the pollution, though costly, so costly it's still a hard sell for those in the biz of liquid pollution abatement.
Even though Pebble will follow all state and federal regulations, as you say, will these regulations be good enough to actually prevent tailings dam failures or leakage of the tailings pond toxic water into the groundwater?
People can argue it both ways, he said-she said arguments. Meaningless. What people really want to be given are the scientific groundings behind the arguments.
First, what are tailings ponds and tailings dams?
A mine's ore goes through a mill and is crushed. The crushed ore is put in vats that go along a conveyor belt. Water is added to the vats. Chemicals that are designed to latch on to the economic metals in the crushed ore are added to the water. Some attach to gold, others to the copper in the crushed ore, or the molybdenum, etc. Foaming agents are added and then air is blown through the crushed ore slurry at the bottom of the vats, which sends cascades of bubbles to the surface of the water covering the slurry. The foaming chemicals turn these into large strong-walled bubbles that don't pop and disappear when they reach the surface of the water. Instead, they form a thick layer of foam on top of the water. The chemicals attached to the various metals are bi-polar molecules. One side attaches to the metals, the other side of the molecule attaches to the walls of the bubbles. The bubbles carry the metals to the surface of the vats and the resulting foam is skimmed off into containers where the metals are further refined.
As the vats move along the conveyor belt, first the chemical agent that attaches to gold is added to the vats. The vats vibrate so that the slurry is agitated so that the chemical agent can interact with the gold in the slurry. Air is then blown through the slurry at the bottom of the vat, which carries the gold to the surface as a foam that is skimmed off for further refinement.
Next, as the vats move along the conveyor, the chemical to remove copper is added. After the copper is removed, the chemical to remove molybdenum is added, and so on. Finally, at the tail end of the conveyor, only uneconomical metals, and toxic metals, that were present in small amounts in the crushed ore from the deposit, such as cadmium, are all that remain in the slurry. The water covering the slurry is removed, to be recycled, and the leftover slurry at the tail end of the conveyor is dumped into a nearby large collecting pond. Since the slurry is from the tail end of the conveyor extraction process, the holding pond that the slurry is dumped into, by convention, is called the tailings pond. Also, by convention, the dam that holds in place the slurry of the tailing pond is called the tailings dam.
In addition to the economic metals, Pebble's ore contains large amounts of pyrite, iron sulfide (FeS), as well as some toxic metals, such as cadmium and mercury. Most of these metals are also present as sulfide compounds.
Because the ore was crushed when it went through the mill, they are present in the slurry in a crushed form, and that means that their sulfur is present as crushed sulfur.
Over time, the crushed sulfur in the tailings pond reacts with the water in the pond, plus the oxygen in the water, and the oxygen in the air at the pond's surface, to form sulfuric acid HSO. This dissolves the toxic metals in the slurry and they go into solution in the pond's water.
Normally, the small amounts of toxic metals in the slurry, would not be considered a danger if there was a dam failure that spilled the slurry into the countryside. The heavy sediment of the slurry would not travel far and the heavy metals would be sequestered in the stationary slurry.
However, because the toxic metals have been dissolving in the acidic water of the tailings pond, the dissolved toxic metals in the pond's water would be carried along with the massive flood of tailings pond water released by the breached tailings dam. That contaminated water would most likely enter nearby streams, which could carry their now contaminated water to surrounding rivers, and even to the Bristol Bay area, endangering its salmon population.
An additional danger is that the dissolved heavy metals are virulently more deadly in their soluble form. As an example, harmless insoluble Cr³, when it is dissolved by the sulfuric acid, is changed into the very deadly, soluble chromium, Cr.
The toxic water released by the tailings dam break could also seep down to the underground water table and be carried to distant areas.
You do not want Pebble's tailing dam to break. So the question is, will Pebble's tailings dam break?
Critics point to the recent Mount Polley tailings dam disaster of 2014, and say that that proves that even tailings dams built to today's standards can fail. Therefore, it is not a question of IF the Pebble mine's tailings dam can fail, but WHEN the Pebble tailings dam will fail.
Critics additionally say that because the engineering firm that designed the Mount Polley dam, Knight-Pisold, will also design the Pebble mine, it means that the Pebble tailings dam will also fail.
But these are not valid conclusions.
During the construction of the Mount Polley dam, the mining company that was building the dam ran short of rock fill in the area, the material used in the construction of the dam. In response to having less building material, the mine owners decided to build a thin dam. Knight-Pisold told the owners that it was dangerous to build such a thin dam wall, but the company overrode their objections and built a thin, weak dam to hold back the tons of tailings pond waste slurry.
The second problem was that the dam was built over a layer of glacial lacustrine soil (glacial silt), 25 feet under the site of the dam. The mining company was unaware of this layer of lacustrine soil because it had only done shallow drilling to check the structure of the ground under the proposed dam site.
When subjected to increasing pressure, lacustrine soil changes from a solid to a fluid. This is what happened when it was subjected to the increasing weight and pressure from the toxic waste and water that was accumulating behind the tailings dam. The loss of foundational support, plus the weak thin wall of the dam, caused it to fail.
Northern Dynasty chose Knight-Pisold to construct the Pebble mine because of their extensive knowledge and expertise in building giant mines. Northern Dynasty will not ignore their expert advice on how to build the Pebble mine.
Also, Northern Dynasty has tested the site of the planned mine and tailings dam to a depth of over 1,000 feet, and shown that they will be built on a solid foundation.
The Mount Polley dam failed because it was NOT built using modern engineering standards.
Still, can a mine be built that will not fail?
First, and foremost, there is the problem of earthquakes. Alaska is subject to multiple earthquakes every year, and some of them are very large.
There was the massive 1964, magnitude 9.2 earthquake, which occurred in the Prince William Sound region of Alaska, and which many environmentalists point to and say it would destroy the Pebble mine if it happened again. But, in fact, it did not affect the Pebble site.
The closest earthquake fault to the Pebble site is the Lake Clark Fault. But it is inactive. The U.S. Geological Survey concluded that there have been no earthquakes along the Lake Clark Fault in the last 1.8 million years.
Northern Dynasty's proposed mine would be able to withstand an earthquake stronger than any that have occurred in the area in the last 2,500 years as determined by the United States Geological Survey.
Some critics have said that, even though no earthquake faults have been found underlying the Pebble site, the area's earthquake faults could extend under the Pebble mine site, and that if a 7.8 magnitude earthquake occurred directly under the Pebble mine, it would cause a catastrophic failure of the mine.
The reason no earthquake faults have been found under the Pebble site is that, if any earthquake faults are there, they are too small to have been uncovered by the USGS mapping of the area.
The reason that this is significant, is because the magnitude of an earthquake is related to the size of the fault.
The Pebble mine has been designed to withstand a 6.5 magnitude earthquake occurring directly under it. A 6.5 magnitude earthquake is an extremely powerful earthquake and it would not be possible for a small fault to produce an earthquake even close to that magnitude. Any earthquake that could happen, would be much less than a 6.5 magnitude earthquake.
Still, authorities might say that the Pebble mine will have to be built to withstand a 7.8 magnitude earthquake. A 7.8 magnitude earthquake is the largest magnitude earthquake that has ever happened even remotely close to Pebble's site. To put that into terms that are easy to understand, the 1906 earthquake that destroyed San Francisco was a 7.8 magnitude earthquake.
Critics of Pebble say that that is not possible to build a mine that could withstand a 7.8 magnitude earthquake, but already there are mines that have been built to withstand earthquakes even stronger than a 7.8 magnitude earthquake. The mines in Chile, and their tailings dams, have all been built to withstand earthquakes stronger than 7.8 magnitudes.
Chile is a seismically active region, and in 1960 experienced a magnitude 9.5 earthquake, the highest magnitude earthquake ever recorded in the world by modern instruments, and no mines or their tailings dams failed. Because of Chile's seismic-risk status, its mines, some of which are the largest in the world, are built to withstand the massive earthquakes of the region. None have ever failed.
Even so, critics say that Pebble's tailing dams, which hold back discarded liquid mine waste, are so high that an earthquake would easily destroy them.
Neighboring Peru, which, like Chile, is earthquake-prone, has some of the world’s highest tailings dams for large-scale operating mines. Tailings facilities at the Cerro Verde and Antamina mines reach heights of 820 feet and 886 feet, respectively. Since 2018 there have been three earthquakes in Peru ranging from magnitude 7.0 to even 8.0, which is higher than 7.8, and none harmed any of Peru's mines or tailings dams.
The tailings facilities in Peru are designed and built to withstand intense, high-magnitude earthquakes. The heights of their tailings dams are much higher than any that are proposed for the Pebble Project.
Pebbles' original tailings dam was going to be 740 feet tall. The newer, smaller version, will be 600 feet tall. Both are significantly shorter than the Peru dams. And just like the Peru mines, they will be able to withstand intense, high-magnitude earthquakes. The CRITICS KNOW THIS and deliberately do not mention it.
How are mines built to withstand the destructive earth-shaking forces of an earthquake?
There are mathematical methods that take into account the cohesiveness of the soil, how it would act during an earthquake, and how stable a dam would be depending on the thickness and slope of the dam's walls.
The stability factor (SF) can be calculated depending on the shearing strength parameters of the soil and the dam.
SF = tgφ / tgβ where φ is the inside friction angle of the embankment and the material that composes it, corresponding to the shearing strength, and β is the gradient of the slope.
Also, equations, such as those that take into account the balance of the vertical forces (∑ i X ) and of the horizontal forces (∑ i E ), would also be used in determining the design of the tailings dam.
There are other equations that engineers can use, and put together, it would allow engineers to design a tailing dam that would withstand an earthquake equal to the strongest possible earthquake that can occur at the Pebble site. The equations would also enable them to design the mine itself to withstand such an earthquake.
Credit: Alberta government site
Engineers can calculate the required shape of a dam, but constructing it within parameters has been difficult, and if it isn't constructed to specification, it would be vulnerable to failure of the dam's wall.
The way that dams have been built is to take ground-based measurements, where you drive, or walk, to different areas of the dam as it is being built, and survey the thickness of the dam's wall, and the angle at which it is slanting, in order to make sure that it meets the engineer's specifications.
This has proven to be imprecise because the ground inside a mine's tailings dam will usually be too wet in many areas on which to drive a surveillance vehicle, and may even be too moist to walk on. There will only be scattered areas suitable for taking measurements, which will result in an incomplete, and imprecise, measurement of the overall dimensions of the dam wall that is being built.
Ground-based measurements have huge margins of error, so you don't know if the dam is being built within the engineer's specifications. This is also very time-consuming. You have to take measurements from the inside, and the outside, of that particular section of the dam, which results in only being able to do a few total measurements in a day's time.
Even though radar or laser measurements are now being used and are more precise, they can only be taken where the ground will support the laser or radar, and therefore the measurements will also only be able to be taken from scattered vantage points, which is imprecise. Plus even these measurements are time-consuming.
Drone surveying helps solves these problems. Drones can be automated, with flight planning apps taking care of the piloting and flying. Once it has finished surveying the dam, the data is uploaded into a processing platform, like Propeller, which views and measures the tailings dam in 3D. This would show areas of the dam where too much material has been deposited, causing a bulge; or not enough material, which would produce an indention in the mine wall. Both problems, a bulge in the dam's wall, or an indention, would cause stresses to form in those areas, and thus produce weak spots in those areas.
By highlighting these flaws early in the dam's construction, they can be corrected and prevented. Drone surveys are significantly faster and more complete than ground surveys, but there is still a significant amount of time spent surveying each section of the dam as it is being built and reviewing the drone's findings.
Now, an even more efficient and accurate tailings dam wall monitoring procedure is coming into use, which would be perfect for monitoring the construction of Pebble's giant tailings dam.
Photo-satellite surveying PhotoSat takes high-resolution stereo (3D) photographs accurate to within inches, of hundreds of square kilometers in minutes.
This gives a view of the entire dam site, which will be delivered in record time to the mine's engineers, and it will be in a format suitable for immediate use so that there will be no delays on any corrections to the angle or thickness of the dam's walls. Thus preventing the development of any weak spots in the dam, as well as speeding up the construction of the dam, and making sure that it is done to the engineer's specifications.
Thus ensuring that a safe dam is built.
This is a quantum leap in precision dam construction, and it will make sure that the tailings dam is built to the engineering specifications which took into consideration the strength and elasticity of the ground on which the dam is being built, the angle of the dam's wall so that there will be minimal stress/pressure against it from the slurry pressing against it, including during a maximum strength earthquake, and the thickness of the dam's wall. All of these calculations ensure that the tailings dam will not fail during a maximum strength earthquake.
Additionally, new building techniques are continuously being developed which makes tailing dams safer. In a recent experiment, geophones were embedded in a tailings pond wall and continuously monitored seismic source signals along with seismic interferometry to measure small changes in seismic velocity in the dam wall. Multi-channel analysis of the changes of seismic velocity in the dam wall was used to image the internal structure of the dam wall and show any pending dangerous changes that might be taking place because of stresses to the dam's wall. These can then be corrected before they become a problem.
NO mine, or tailings dam, have failed that were built using modern engineering standards, as well as today's modern engineering
techniques. There have been recent failings, such as the January 2019 Brumadinho tailings dam failure that didn't use PhotoSat in its construction. A follow-up investigation concluded that it would not have failed if it had been constructed using present-day standards.
Critics charge that even if a safe tailings dam can be built, that won't fail during an earthquake, the tailings pond, which is confined by the tailings dam, will, at some time during its use, leak acid-tinged, heavy metal toxic water into the water table below the site.
The groundwater, in its travels, would then contaminate the streams, rivers, and lakes in the surrounding area. Therefore, they state, the Pebble mine should never be built.
There is a method that has been developed that prevents leakage from the tailing pond into the water table below the site.
The Kittila mine located north of Finland, inside the Polar Circle, is located in an environment, and yearly temperature range, similar to the Pebble mine. The Finland Ministry of Environment mandated that its tailing pond have a water-tight liner.
For the floor of the tailing pond, the company used locally obtained glacial till. It was crushed and compacted into a 40-inch layer which ended up with a water permeability of less than 5x10E-8 m/s.
Over that, the company used sheets of bituminous geomembrane (BGM). These sheets of material are a composite, of which one component consists of the highest quality bitumen.
Bitumen is found worldwide but is best known as the tarry substance found in the La Brea Tar Pits in California. It is a sticky, black, highly viscous liquid.
This is combined with butadiene styrene, a type of rubber with good abrasion resistance and good aging stability, it doesn't break down with age. The combination makes an elastic material that is also self-sealing, the bitumen will flow and seal any punctures and penetrations.
These are combined with a sheet of glass fleece which is a dimensionally stable substance. Extremely high or low temperatures will not make it stretch or shrink. And even when physically stretched and stressed close to its point of rupture, it will return to its original size when the pressure is removed. It also has high strength with minimal weight. This makes the sheets of BGM light, but strong, and easier to maneuver and position so that they are correctly placed, and the glass fleece fabric prevents tearing of the composite sheet. It is also resistant to most acids.
Bituminous Geomembrane Liners stay flexible and do not stiffen, even at temperatures as low as -40°F. They lay flat, and in complete contact with the crushed glacial till floor of the tailing pond. Since they stay flexible, even at -40°F, they will mold themselves to any imperfections of the substrate over which they are being laid, even in deep sub-zero temperatures, and will form a tight seal with the substrate. They also have a high friction coefficient and can be laid over even steeply angled dam walls. This would ensure that there would be no leakage through the dam's wall.
The lowest temperature recorded at Pebble's site since 1947 is -31°F. Because temperatures at the Pebble site stay well above -40°F, even at the coldest times of the year, it would allow construction to be carried out year-round at the Pebble site.
Based on the resulting composite's physical durability and resistance to punctures and tearing, and to most chemicals, the U.S. Navy Nuclear Safety Agency certifies BGM for a 1,000-year life span.
BMG specifications call for it to be installed on a 2" compacted substrate, but in this case, it was 40". The Pebble area has an abundance of glacial till available, so it could also lay down a compacted substrate, which could also be 40" thick, which in itself would be considered a waterproof seal. The combination of BMG over the compacted substrate is called a dual seal.
Credit: Western Liner
Credit: Western Environmental Liners
This dual seal can be used for Pebble's tailings pond, as well as a lining for the containment sites that will hold the overburden of rock that covers the Pebble deposit, and that has to be removed in order to get to the ore deposit. This broken-up waste rock contains pyrite which can generate sulfuric acid when subjected to rainwater.
Bituminous Geomembrane Liners, used as a dual seal, will prevent any leakage into the groundwater table.
Critics say Pebble's tailing pond will have to be monitored indefinitely, and in the next hundred years, or even thousands of years, there is bound to be a leak, or spillage of the contents into the surrounding area, causing massive damage to the environment.
Therefore, no matter what, critics say that the Pebble mine is too dangerous to be built.
The flaw in that reasoning is that a way of decontaminating toxic tailings ponds has been developed and has been shown to be effective for tailings ponds.
Because the crushed sulfur in tailings ponds reacts with dissolved oxygen in the water, the sulfur forms sulfuric acid, HSO.
To put the tailings pond's sulfuric acid in perspective. Neutral is pH 7.0. Acids have a pH that is lower than 7.0. Stomach acid can be from pH 1.5 to 3.5. Battery acid is 0.8.
The average acidity of a tailing pond is a very acidic
1.5 to 3.5, and it can be as low as
0.5, which is even more acidic than battery acid.
Tailings pond runoff can be so acidic that In the abandoned Parys mine site,
people in the area would dissolve cars in it to dispose of them.
At present, conventional methods are not effective in decontaminating giant toxic tailing ponds. The amount of acid-neutralizing chemicals needed would be prohibitive, volume-wise, and cost-wise. Plus the large volume of crushed sulfur present in the slurry would continuously be forming additional sulfuric acid that would eventually overcome the acid-neutralizing chemicals that had been added to the slurry.
Solidification, a different method of decontaminating tailing ponds, is one of the more commonly used methods for small to medium-sized toxic waste slurries, which involves adding cement powder to the tailings pond's watery waste in order to turn the slurry into a solid block of concrete, but this has a basic flaw.
Although the toxic metals are physically bound in the cement matrix, they will eventually leach into the environment because cement is porous. Their leaching into the surrounding environment would only be reduced, not stopped.
Other methods, such as adding chemicals to precipitate the heavy metals, would not only take huge amounts of chemical reagents, they also tend to
produce secondary pollution.
Scientists have been studying the use of
bioremediation to clean up toxic tailing ponds. Bioremediation is the use of microbes to neutralize/detoxify, the toxic metals and acid of tailings ponds.
Such as using sulfate-reducing bacteria to neutralize the sulfuric acid (HSO) that is produced by the crushed sulfur in the tailing ponds. The sulfate-reducing bacteria neutralize the sulfuric acid by using the SO portion of the sulfuric acid for respiration and exhaling sulfide (S²).
Sulfate-reducing bacteria are anaerobic. Oxygen is toxic to them, so they live in low oxygen and oxygen-free environments, such as would be present in a tailings pond slurry. Their process of using sulfuric acid's SO is similar to the way we inhale oxygen (O) and exhale carbon dioxide (CO), except the bacteria, inhale (SO ) exhale sulfide (S²). The sulfide, S² reacts with several of the toxic heavy metals in the slurry's water, such as cadmium (Cd²), which then forms insoluble cadmium sulfide, CdS. Because the sulfide forms such a strong bond with the cadmium, the bipolar water molecules can't pull it apart into its separate ion components of Cd² and S², and therefore it comes out of solution.
This accomplishes two things at the same time, it neutralizes the tailing pond's sulfuric acid, by removing (destroying) the SO portion of the sulfuric acid, and the sulfide they exhale precipitates several toxic heavy metals out of solution, embedding them in the slurry's crushed ore, rendering them non-mobile.
Additionally,
sulfate-reducing bacteria use organic carbon sources for food, and, similarly to the way we excrete feces, they
excrete bicarbonate 2(HCO),
an acid-neutralizing compound into the acidic slurry. Tailing pond slurry would not normally contain organic matter, but it has been shown that by adding organic material into the slurry that is being discharged into the tailing pond, the bicarbonate that would then be produced by the microbes in the tailing pond,
would add additional neutralization of the tailing pond's acidic slurry.
Sulfate-reducing bacteria that are supplied with ethanol alcohol as a food source are able to
neutralize 99% of the SO4
from the sulfuric acid.
Most sulfate-reducing bacteria can not tolerate oxygen exposure, but there are three strains that can
tolerate a 6% oxygen environment which is about one-third of the oxygen concentration of air's 21% oxygen. There is also a sulfate-reducing
bacteria of the Desulfobacteriaeceae family that protects itself from oxygen by forming spheres of either zinc, selenium, or arsenic around itself
that blocks the oxygen and thus protects the bacteria. The form of selenium and arsenic that form the protective shell is nonsoluble, and therefore would remove these toxic metals from the tailings pond's water. The
concentration of the metal in the sphere is a million times higher than in the surrounding slurry. They would be very effective in removing these metals from the tailings pond's slurry.
Introducing oxygen tolerant microbes into Pebble's slurry will ensure that there will be microbes present, including the very effective Desulfobacteriaeceae bacteria, that will be neutralizing the sulfuric acid and toxic metals in the upper portion of the slurry.
There are other types of oxygen thriving micro-organisms that are very effective in detoxifying toxic metals and will be very useful in detoxifying the upper layer of the tailings pond.
Fungi sequester heavy metals in a polysaccharide gel on their cell walls, plus they use metal transport proteins in their cell walls to actively ingest heavy metal ions that surround them and sequester them in vacuole compartments in their cell walls. Fungi are able to sequester large amounts of heavy metals in this way. Fungi can tolerate a very broad range of pH conditions, from acidic environments of a very acidic pH of 1.0 to very alkaline environments of pH 11.0. They do this by decreasing their membrane permeability. Yeast can also tolerate a wide pH range.
Yeast, such as Saccharomyces cerevisiae, pump sulfide into the slurry and precipitate heavy metals as metal sulfides.
Algae protect themselves from acidic environments by increasing their cellular proton pump efficiency, and in doing so they maintain their cytoplasm's neutral pH.
Algae are known as pioneering organisms and can grow under the extreme acidic, and heavy metal contaminated conditions, of mine site tailings ponds. Algae multiply rapidly even in these extreme conditions and the algae, along with the fungi and yeast, would form a large mat over the surface of the tailings pond. The area under the mat would be anoxic and allow anaerobic sulfate-reducing bacteria, which neutralize sulfuric acid, to enter the upper layer of the tailing pond and neutralize the sulfuric acid of the upper layer. Anaerobic heavy metal neutralizing bacteria would also enter the upper layer of the tailing pond and help in removing heavy metals from the upper level of the tailings pond. The sulfuric acid and heavy metals of the pond's upper layer have to be made innoxious because it is the tailing pond's upper layer that will be used in reclaiming the site for regrowing indigenous plants.
Anaerobic Reductase-bacteria reduce the oxidation state of metal ions. They can neutralize toxic metal ions that are not precipitated by the sulfide (S²) ion. As an example, they change the very deadly and soluble chromium, Cr, which is not precipitated by (S²), to harmless insoluble Cr³. There are various bacteria that use different enzymes to change Cr to Cr³, such as bacteria that use quinone reductase, nitroreductase, or NADPH-dependent enzymes. These bacteria, in addition to neutralizing chromium, also neutralize other toxic metals that are not precipitated by the sulfide produced by the sulfate-reducing bacteria. Various reductase-bacteria work better on different toxic metal ions. So a mixture of reductase-bacteria would be more effective at removing the various toxic metals present in the slurry.
There are also species of anaerobic bacteria that use different methods of detoxifying various heavy metals, adding them to the toxic slurry increases the effectiveness and speed of the decontamination.
Some microbes
chelate the metals. Chelate is Greek for claw. The microbe binds the metal in two places and forms an irreversible bond. This protects the microbe from toxic metals, such as arsenic, because it is held so tightly by the bonds that it can not affect the microbe. When the chelated metal eventually re-enters the slurry after the microbe dies, it will still be bonded so tightly that it will be harmless and not a danger to the environment.
Other microbes produce
calcite and bind metals such as lead and cadmium inside it, which protects the microbe from toxic metals. When the microbes die and the calcite-coated lead and cadmium are released back into the slurry, the calcite coating isolates the metals from the slurry.
Also present in the Pebble deposit, and therefore the slurry, are poisonous antimony and arsenic. They are metalloids, not, chemically speaking, metals, but there are bacteria that react to them similarly to how they react to metals, in that they can neutralize them using methods similar to those used against toxic metals.
Arsenic (As) brings up an interesting point. Sulfide precipitates the soluble As, but not the soluble As³ which is also present in the slurry. It takes a combination of two bacteria to remove As³. Bactria that use the Calvin cycle to gain energy assimilate As³ and oxidize the As³ to As, which is then precipitated by the sulfide produced by the sulfate-reducing bacteria. This would be one of the reasons why it would be most effective to add multiple different types of detoxifying microbes to Pebble's slurry.
When microbes are first introduced into a contaminated site, they are
not very effective in removing the contaminants. But, over time, each of the differing areas in the tailing pond will become populated with microbes best suited to that area. As they multiply in numbers, they will remove greater and greater amounts of contaminates and the rate of remediation will increase.
In a test site, researchers added five different types of microbes, that used different means of neutralizing toxic metals. The efficiency of the microbial removal of toxic metals increased by a factor of 14.
Eventually, the rate of detoxifying the pond will increase even more than having the most efficient microbes present at the differing sites can account for. This is because microbes have plasmids.
A microbe's cytoplasm, in addition to having a large chromosome that directs the microbes' functions, has multiple tiny circles of DNA, called plasmids, floating in its cytoplasm, which work at protecting the microbe from outside dangers. These are how bacteria develop antibiotic resistance. It is also how microbes develop the ability to survive in the toxic environments of tailing ponds, by developing ways to protect themselves from the deadly heavy metals that are in the tailing ponds, and they can pass these traits on to other microbes.
When different groups of bacteria come in contact with each other, some of them transfer one or more of their plasmids to bacteria in the other group by extending a tube, called a pilus, to an adjacent bacteria, through which it transfers plasmids into the other bacteria. The new plasmid(s) may make the recipient bacteria more efficient in neutralizing its specific heavy metals, or may even give it the ability to neutralize additional types of heavy metals, thus increasing its ability to protect itself, while at the same time, making it more efficient in detoxifying the tailings pond because it will be detoxifying additional toxic metals.
With this enhanced ability to protect itself, by more efficiently neutralizing the heavy metals in its surroundings, it will have a better ability to survive and colonies of the bacteria will increase in the tailing pond slurry, which will increase the effectiveness of the decontamination of the site, not only because it will increase the number of bacteria detoxifying the site, but because these increased numbers of bacteria will at the same time be detoxifying additional different types of toxic metals.
Credit: Journal of Aquaculture Research & Development
Even different strains of bacteria can transmit beneficial traits to each other. For example, resistance to cadmium and cobalt was transferred to
completely different strains of bacteria: E. coli to A. eutrophus. Some microbes are more efficient than others in removing heavy metals, and as these genes are transferred to other microbes in the slurry, the cleanup of the tailing pond increases in efficiency.
There are other ways that will be increasing the efficiency of de-toxifying tailings ponds. Scientists are learning how to take genes from bacteria that use different methods of detoxifying heavy metals, and transcript them into other bacteria. The genetically altered bacteria have these new ways of detoxifying heavy metals added to their original way of detoxifying heavy metals, and this greatly enhances their ability to remove toxic metals from contaminated sites.
Genetic engineering of microbes has been shown to
increase by six-fold their ability to remove heavy metals.
Some microbes have had their ability to remove toxic metals increased by a factor of 25.
Bacteria from both
aerobic and anaerobic species have been found that can change toxic chromium
Cr to innocuous Cr³. The
aerobic bacteria, Pseudomonas ambigua, uses NADPH-dependent reductases to initiate this change, and it will be able to
remove chromium from the upper level of the tailing pond slurry. For anaerobic bacteria, Pantoea agglomerans uses Cr as an electron acceptor, while Shewanella oneidensis uses cytochrome to change the dangerous soluble chromium to insoluble chromium, which precipitates out of solution. Cytochromes are electron transport proteins.
Shewanella decolorationis LDS1 can
thrive in very high concentrations of chromiuim, which it proceeds to neutralize. It also thrives in a wide range of temperatures. It tolerates such extremes because it
has developed a phosphorthioate modification that protects its DNA from disruption from outside sources. With the multitude of
different species of bacteria that will be in the Pebble tailing pond
, this could be passed on to some of them via plasmids, or it could be bioengineered in suitable bacteria, both methods would significantly add to detoxifying the tailings pond.
Mobile bacteria with flagella will move throughout the slurry and whenever they come to an area that is best suitable for them, such as bacteria that use chromium for respiration, they will prosper and multiply in sections of the slurry that contain chromium. And as conditions change in different sections of the slurry, new bacteria, better adapted to thriving in those changed conditions, will colonize those areas. In that way, the various sections of the slurry will continuously be upgraded to have the best combination of microbes possible for each site.
Credit: Steps Health
The travel of flagella bacteria through the pond's slurry will constantly bring different bacteria in contact with each other. Some will pass their capabilities on to other bacteria by exchanging plasmids. Shewanella decolorationis LDS1 which has the ability to protect its DNA could pass this trait to other bacteria. Different combinations of traits will be passed between bacteria, and some bacteria will end up with a superior combination of traits.
Science has barely started to discover the microbes that can make heavy metals less toxic. Currently, less than 1% of the microbes that can detoxify heavy metals, and arsenic, are known to science. Over time, more will be discovered, and this will increase our ability to make tailings ponds safe.
While the mine is active and continuously adding toxic slurry to the tailings pond, bioremediation will be continuously detoxifying the slurry and keeping its toxicity from building to ever greater levels. The longer the mine is in operation, the more efficient the bioremediation will become, and the safer the tailings pond will become, even a tailings pond of a mine that is still in production.
After the mine is closed, and the more time the tailings pond's bacteria have in which to detoxify the site, the greater the number of species of bacteria with superior combinations of traits will develop. This will result in continuously increasing the efficiency of detoxifying the tailings pond, which will lead to the tailings pond becoming completely detoxified.
How long does it take to reclaim a site?
Prior to starting the construction of the mine and tailings dam site, the soil of the area is removed and stored so that it will be available to be replaced after the mine is discontinued.
At other mine sites, it has been discovered that when the stored soil was replaced after a mine was decommissioned, it did a poor job of supporting the regrowth of vegetation. This was because microbial activity which supports the transfer of nutrients was no longer present.
Stored soil is now supplied with natural carbon sources, such as wood residue and animal manure,
in order to maintain the microbial biota of the indigenous soil.
The areas to be reclaimed
must be covered with at least four feet of stored topsoil fortified with the best suitable material available, such as weathered rock because the newly placed topsoil which will be used for supplying the previous mine site with indigenous vegetation must not be compacted but kept loosely graded so that the plant's roots will be able to establish themselves.
The topsoil may become contaminated with some sulfuric acid and heavy metals from the mine site, but adding the fungi Pisolithus tinctorius provides protection. it protects plant roots from an environment as acidic as pH 3.0 and also protects against soil contaminated with heavy metals.
In one site where pine seedlings were being planted, only 5% survived, but after Pisolithus tinctorius was added to the soil, 95% survived.
In Alaska, there is only a five-month, or less, time frame before permafrost sets in and stops the reclamation process. There is also only a short growing season in Alaska. Alaska regulations state that the topsoil has to be distributed over the area and indigenous vegetation and seeding in place by August 15th. Otherwise, there is not enough time for root systems to establish themselves before freezing weather arrives.
Credit: Mining and Metallurgical Society of America
The same can take place with the Pebble mine. Alaska regulations stipulate that native vegetation be used in the reclamation project so that the reclaimed site will be open for the native fauna to return to the area.
It used to be that mines destroyed the environment. But, for over fifty years regulators, and then mining companies, have been striving to develop mining processes that would prevent these environmental disasters.
They have now reached that point. Even in areas with high earthquake occurrences, there have been no mine or tailings dam failures in recent decades when modern engineering protocols and regulations were followed.
This means that Pebble will not be a danger to the Bristol Bay area or the salmon.
Northern Dynasty has spent $150 million on environmental baseline data —one of the most extensive such databases ever submitted for a mining project in America. They will construct state-of-the-art crossings over all streams and rivers for the roads that they will be building. They will clean these streams of debris so that the salmon will have superior access to their spawning areas. Thus, not only will they not be harming the salmon, they will be helping and protecting the salmon.
Northern Dynasty has worked with the regulatory agencies to make sure that their mine plan will not harm any wildlife in the area. As an example, the gas pipeline that will supply their mine with natural gas will be built underground so as not to disturb the wildlife in the area.
The Pebble mine will be safe. Any agency that states that the mine will not be safe for the environment, or the wildlife in the area, including the salmon, should be required to show scientific proof to back up their claims.