Abandoned Mine Posts

by Andy McAllister, Watershed Coordinator

Do you have a stream that you think has improved due to a pollution abatement project? If you do, we need your help. The Pennsylvania Department of Environmental Protection’s Non-point Source Program has enlisted the aid of WPCAMR to help them find those improved streams.

The information you provide will assist PA DEP biologists in their efforts to target specific streams for a biological reassessment. If the stream or a segment of the stream has indeed improved, PA DEP could consider it for removal from the list of impaired waterways in the Commonwealth.

The list of impaired waters (formerly known as the 303(d) list) is now part of what is called the “Integrated List”. Impaired waters are those waterways that are not meeting their “designated use”, in other words, the biological community in those streams is adversely affected by AMD, sediment, or any number of other pollutants.

Designated uses are those uses specified in the state’s water quality standards for each water body or segment whether or not they are being attained. An example of a designated use in Pennsylvania is “CWF”, meaning a Cold Water Fishery, capable of sustaining a healthy cold water biological community (eg. a stream where trout can live and reproduce).

Removal of a stream or stream segment from the impaired waters list is a concrete way of showing that pollution reduction projects are having a positive impact on our streams.

If you think you have a stream or a segment of a stream that was impaired and is now not, we invite you to share what you know by filing out the information form at the WPCAMR “Improved PA Streams” page. By sharing your information, you can help direct state efforts to locate recovered streams.

by Bruce Golden, Regional Coordinator

Did you ever wonder why there’s such a wide range in the chemical make-up of coal mine drainage discharges? It’s because
there’s a great diversity in the mining environments in which mine drainage is formed. This multipart series of AMP will
explore, on an introductory level, the connection of mine drainage characteristics with the mining environments that created
it. It’s not meant to be rigorous, but to mainly get you thinking about the kinds of things that can happen underground that
are influential in the making of polluted water.

Part 5. Waste Coal Piles… Efficient AMD Factories

In the last three installments, I showed how the mineral pyrite is chemically reactive in the wet oxidizing environment we live in and depend on. Pyrite, as you’ll recall, is typically present in small percentages in coal and surrounding geologic strata. In its natural state, there is little opportunity for water and air to get to the pyrite, thus it’s protected from chemical reactions. Mining changes that big time.

Since the Abandoned Mine Drainage problems we currently deal with were created a long while ago, some dating back to the mid 1800s, it’s instructive to visit some of the mining processes of yesteryear to see if we can figure out how those processes have led to present day problems.

The first mining environment we’ll examine is waste coal piles. These man-made small black mountains go by a slew of colloquial names including gob piles, boney piles, slate dumps, slag heaps, and (as our friends in eastern PA’s anthracite region like to call them) culm banks. I once met a woman who called the pile close to her home Dmitri. I didn’t ask. Whatever we call them, they’re made up of the unwanted stuff discarded following the coal extraction process which most likely came from underground deep mines.

Thousands of waste piles accumulated over the course of mining in Pennsylvania. They are usually located in the vicinity of the old mine portals, as this was the most convenient and economical way of disposal. The piles are generally made up of a good bit of coal and a bunch of stuff that isn’t, including rocks called shale that are very commonly found adjacent to coal seams. (Note to my local newspaper: there’s no slate in waste coal. Please stop calling the piles slate dumps and the stuff in them slate. And while we’re at it, the orange stuff polluting streams isn’t sulfur. ) Why was so much coal discarded back in the old days? First, the separation techniques weren’t that great, and second, smaller pieces of coal had little economic value because the furnaces that burned coal required bigger chunks.

Anyway, throughout coal county it’s still fairly common to see these big, ugly, gray-black, steep-sided, highly eroded, loose-material, get-you-real-dirty, hard-to-walk-on piles with very little vegetation just sitting there as they have for decades. Their size varies greatly from one defunct mining operation to the next. Those associated with larger coal operations are really big and are measured in millions of tons. Sometimes, you’ll see pinkish-orangish streaks and patches in the piles. That’s the residue (sometimes called red dog) from the coal in the pile catching fire, sometimes spontaneously (that pesky oxidizing environment at work again) with a long slow burn that may have taken years to complete.

Because a waste coal pile’s origin is an accumulation of loose, relatively small material, it’s prone to shifts in the material. Think of mini landslides and being loose underfoot. Furthermore, because vegetation has trouble establishing and sustaining itself in this rather inhospitable growth medium, the piles are commonly devoid of most plant life. Without a good root system to stabilize the material, the material remains unstable over time. This is a perfect recipe for erosion. In fact, deep erosion gullies are a prominent feature of waste piles. This can result in siltation problems for adjacent streams. Those streams can also take on a decidedly orange color which, of course, is a very good indicator of AMD. Let’s see how that happens.

We’ll change gears and zero in on a small chunk of coal that might be found in a waste pile. For illustration’s sake, let’s assume it’s a perfect cube, say one inch on a side. That means that each face of our coal cube has an area of one square inch. Since cubes have 6 faces, our cube of coal has a surface area of 6 square inches. Now, the only pyrite contained in our coal cube having any opportunity to undergo that pyrite oxidation reaction we talked about several installments earlier is the pyrite located at the cube’s surface, on those 6 square inches. Water and oxygen can’t get to the pyrite located in the cube’s interior. The places on the cube’s surface where pyrite is exposed are the only places where oxygen, water, and pyrite can all team up and thus the only place that pyrite oxidation reaction can occur. Those 6 square inches of surface area on our cube puts an upper limit on the amount of pyrite that can oxidize on that piece of coal.

Okay, now let’s say we take our cube and carefully split it in two, making the split parallel to a cube face. We wind up with two rectangular solid chunks of coal. I think we can all agree that the original 6 square inches of surface area of the combined two pieces are still intact. In addition we have two new faces resulting from the split, each one having one square inch of surface area. So the two chunks of our carefully constructed mind experiment now have a combined surface area of 8 square inches. If we do a little ciphering, that comes out to a 1/3 increase in surface area with the opportunity of having exposed pyrite that can react. More exposed pyrite raises the limit of the amount of pollution that can be formed. Note: In the real world, we don’t see perfect cubes and often cracks, fissures, or fractures allow water to penetrate the interior regions of solid coal.

To generalize, when a solid is fractured or broken up into smaller pieces, the resulting surface area will increase. We’ve also seen that the pyrite reaction is dependent on having the pyrite exposed on a surface. Putting these facts together, it becomes clear that a waste coal pile, made up of lots and lots of relatively small broken-up chunks, is going to have an enormous amount of surface area with exposed pyrite which can be available to react when united with water and oxygen.

A waste coal pile is usually quite porous to water infiltration. This is particularly ominous when it comes to AMD formation. When it rains, water can easily find its way to a tremendous amount of exposed pyrite. On the pile’s outermost surface, the supply of atmospheric oxygen will be substantial. As water infiltrates into the pile’s interior regions atmospheric oxygen will become more scarce, yet water itself can transport oxygen in the form of dissolved oxygen. Even with available oxygen being the limiting factor, the initiating and most important reaction of AMD formation, the oxidation of pyrite, has tremendous opportunity to occur. Furthermore, pyrite not reacting during one rain will have the opportunity during the next, or the next, or the next after that. For piles that can interact with ground water, the situation is even worse: an almost continual source of water available as a reactant in pyrite oxidation (limited only by available oxygen).

The pyrite oxidation reaction occurs in copious amounts when it rains. The other AMD reactions described in previous installments, i.e. the ferrous to ferric oxidation and the hydrolysis of ferric ions, may also occur in or on the pile. The extent to which they occur will depend on the amount of available oxygen, the pH, and the presence of certain bacteria in the water. In addition, some complex chemical reactions (which are beyond the scope of this article) may result in the formation of highly reactive sulfate salts, easily visible as a light greenish-yellow solid. In essence, these solids are concentrated instant AMD, ready to dissolve during the next rain. No matter what, once the initiating pyrite oxidation reaction has occurred, the AMD express has left the station.

To sum things up, waste coal piles can be very prolific producers of AMD because of the tremendous amounts of exposed pyrite. Just add wind and rain with a dab of chemistry and you’ve got a pollution factory.

By: Bruce Golden, Regional Coordinator

Did you ever wonder why there’s such a wide range in the chemical make-up of coal mine drainage discharges? It’s because there’s a great diversity in the mining environments in which mine drainage is formed. This multipart series of AMP will explore, on an introductory level, the connection of mine drainage characteristics with the mining environments that created it. It’s not meant to rigorous, but to mainly get you thinking about the kinds of things that happen can underground that are influential in the making of polluted water.

Part 3.  The Chemical Action Continues.

In the last installment of AMD and Mining Environments, I talked in some detail about the first act of several in the formation of AMD.  To review, the chemical reaction that starts the whole AMD pollution ball rolling is the oxidation of pyrite in the presence of oxygen and water

which results in a complete chemical makeover with the chemical species of ferrous ions, sulfate ions, and hydrogen ions being dissolved in water.  This installment picks up from there.

I’d like to zero in on one detail of this reaction.  Notice that for every 4 molecules of pyrite consumed, there are 8 hydrogen ions produced.

In other words, 2 hydrogen ions are produced for every pyrite molecule that reacts.  This can result in high concentrations of dissolved hydrogen ions.  When a group of these hooligans of the chemical world get together, expect trouble.  They’re perfectly happy going around electron-less, flaunting their positive charges.  It’s what gets them in trouble.  You may have heard about them already.   They call themselves “Acidz”.  The more they crowd together, the nastier they get.  (For more detail on this subject, seehttp://amrclearinghouse.org/Sub/AMDbasics/Acids-Bases-ph.htm .)   Bottom line, the pyrite oxidation reaction can be a prolific acid producer.

Hydrogen ions are so prominent in aqueous chemistry that a special way of indicating their concentration is commonly used: the pH scale.  You were probably taught something like the following in high school science class.

• pH is a number from 0 to 14 indicating how acidic or basic water is.  A pH lower than 7 is acidic, above 7 is basic, and exactly 7 is neutral.  A unit change in pH represents a 10 fold change in concentration.  Lower numbers represent a higher concentration of hydrogen ions.  Examples: pH=5 is 10 times more concentrated in hydrogen ions than pH=6.  pH=5 has 1/100th  the concentration of hydrogen ions at pH=3.

I’m not much of a fan of this description. (This explanation coupled with the contrived invention of pH is actually number 7 on “Bruce’s All-Time Pet Peeve Countdown.”)   Yet since it’s so commonly taught this way, I’ll reluctantly perpetuate it… because it’s short.  My description would go on and on and on.  If you’re so inclined, check out http://amrclearinghouse.org/Sub/AMDbasics/Acids-Bases-ph.htm for my rambling explanation. The pH scale is to hydrogen ion concentration as the Richter scale is to the power of an earthquake… almost.  A decreasing pH implies increasing hydrogen ion concentration.  Mathematically speaking, both are logarithmic functions.

One of the most common classes of AMD has a pH in the vicinity of  3, which makes hydrogen ions in the neighborhood of 1,000 times more concentrated than pure water.  That’s moderately acidic which can really put the hurts to the critters living in streams.  It’s common to see streams impacted with this sort of water to be crystal clear, as well as clear of practically all life.

Well, let’s draw the curtain of the first and very crucial act of AMD formation, the oxidation of pyrite.

Act 2:   Next Stop…  Ferric Iron City

A product of the pyrite oxidation reaction is ferrous ions (Fe2+), a charged form of the element iron.  These ferrous ions are able to react with hydrogen ions (also produced by the pyrite oxidation reaction) and oxygen for the next important reaction on the road to AMD formation

One reaction product is water.  No big deal there since this reaction occurs in water.  The other reaction product is ferric ion (Fe3+), also a charged form of the element iron, having lost a (negative) electron in its transformation from the ferrous form.   There are several notable points of this reaction:

• This reaction requires oxygen (O2).  If oxygen is in short supply, as is a very common occurrence in some mining environments, it will limit the amount of ferrous ions that react, and thus the amount of ferric ion that is formed.  To put it another way, if the lack of oxygen limits this reaction in one place, a change of conditions where oxygen is more readily available will allow it to continue elsewhere.  Many mine discharges are like this.  This reaction has stalled until the mine water breaks out into the open where more oxygen is available.
• This, too, is an oxidation reaction.  Ferrous iron is oxidized to ferric iron.  In fact, let’s just call this the ferrous to ferric oxidation reaction.
• Optional stuff: The element iron has three preferred (nay, allowed) oxidation states: 0 (elemental), +2 (ferrous) and +3 (ferric).  An iron oxidation reaction results in an increase of its oxidation state, i.e. from 0 to 2, or from 2 to 3 as is the case here.  The terms ferrous and ferric apply only to iron. Each element has its own rules about what oxidation states are allowed.  Example: aluminum only has 0 and +3 oxidation states and doesn’t have a similar reaction to the ferrous to ferric oxidation reaction.  That has some significance later on. 
• This reaction consumes hydrogen ions on a one to one basis with the ferrous ions that react.  Look at the equation and see if you can figure out that one to one thing.  Because hydrogen ions are consumed, this tends to lower H+ concentration, with a corresponding increase in the pH.   We really aren’t that fond of the Acidz’ actions and anything that diminishes their numbers is something I’d call a good thing.

To sum up the ferrous to ferric oxidation reaction, ferrous ions are converted to ferric ions with a reduction in the numbers of hydrogen ions. That’s it.  I suppose I could have just said that in the beginning, but then we wouldn’t have been able to spend all this time together, would we?

You may have noticed I haven’t editorialized about ferric ion’s character.  That’s because ferric ions aren’t really into the wild ionic life of some other ions.  They’re more interested in getting into a permanent relationship and settling down, as we’ll see in the next installment of AMD and Mining Environments.

By Bruce Golden, Regional Coordinator

Did you ever wonder why there’s such a wide range in the chemical make-up of coal mine drainage discharges? It’s because there’s a great diversity in the mining environments in which mine drainage is formed. This multipart series of AMP will explore, on an introductory level, the connection of mine drainage characteristics with the mining environments that created it. It’s not meant to rigorous, but to mainly get you thinking about the kinds of things that happen can underground that are influential in the making of polluted water.

Part 2. Chemical Beginnings.

This installment of AMD and Mining Environments focuses on the chemistry of AMD formation. For those of you that aren’t fully comfortable with chemistry concepts, I’ve made an extra effort to provide enough detail and background to give you a decent picture. For this reason this installment won’t be as brief as we would generally like. For those of you already comfortable with chemistry stuff, take the day off.

Some background first. On the earth’s surface two of the most common and important chemical actors, oxygen and water, are generally abundant. Underground in coal seams, quite the opposite is generally true. In fact, the last time the vegetation that eventually became coal had likely experienced free oxygen was a quarter of a billion years ago. Because of the abundance of oxygen in our atmosphere and oxygen’s propensity for entering into chemical reactions with any number of substances, we’re said to live in an oxidizing environment. Our very existence depends on our oxidizing environment. The notable example of breathing or respiration wouldn’t be possible without oxygen. But oxygen can also enter into chemical reactions that are not so beneficial from our perspective, as we’ll see shortly.

In the last installment, we said that the weathering of the mineral pyrite leads to the formation of AMD. Here are some points that may be helpful in better understanding this menacing mineralogical misfit:

• Pyrite is comprised of atoms of iron (Fe) and sulfur (S) in the ratio of two sulfur atoms for every iron atom. It’s molecular formula is FeS2 .
• Pyrite exists in coal as a small percentage by weight. The actual percentage may vary considerably from coal seam to coal seam and can even vary significantly within a given coal seam. For instance, the coal near the top (roof coal) of the famous Pittsburgh seam is quite high in pyrite compared to the middle of the seam (the good stuff). The pyrite percentage can be up to a few percent by weight. Much of the sulfur content in coal is actually pyrite. (When burned, low sulfur coal produces less sulfur dioxide air pollution.)
• Pyrite is not the sole mineralogical culprit in coal; close cousins of pyrite more or less behave the same way. Yet pyrite generally takes the rap for the entire family.
• Pyrite in coal has remained unchanged for eons in its oxygen deprived underground sanctuary/prison. Only when something unearths it, for instance mining, and exposes it to its incorrigible chemical cohorts, oxygen and water, does pyrite awake from its extended nap ready to get on with the chemical party.
• And perhaps it’s really the over-reactive oxygen that we should view as the real trouble-maker. Oxygen has a rap sheet a mile long for being the ring leader in any number of oxidation reactions, a lot of them seen as destructive. Poor pyrite hadn’t bothered anything for practically forever. If pyrite had a lawyer, this would undoubtedly be part of the defense.
• Now suppose some coal mining has occurred enabling pyrite to get a visit from its reactive cohorts oxygen and water. Let’s take a look at the chemical mayhem that ensues as this motley trio hooks up.

Act 1: Pyrite has a Transformational Experience

For the first time since its formation eons ago, pieces of pyrite embedded in coal are free of complete burial and now have some exposure to a new, less confining environment. Surfaces of coal may now be in the open. Pyrite will still be immobile as it’s locked as a solid within coal, but pieces of it may now be exposed to the atmosphere. Assuming the air is fresh, oxygen molecules will certainly be paying regular visits to the pyrite. Even though in direct contact, pyrite and oxygen by themselves don’t interact chemically. That changes when water is added to the mix. Only then, when all three players are present at the same time does the first of several chemical reactions take place. Our actors, pyrite (a solid), oxygen (a gas), and water (a liquid), collectively known as reactants, are symbolized as

Each reactant substance will undergo a transformation resulting in products with totally new identities. Atoms of the reactant substances will rearrange into new product substances. The individual atoms of original reactant substances break up, then recombine with different partner atoms to form products unlike the original reactants. Talk about a makeover! This process of atomic rearrangement is a chemical reaction. With the exception of the electron configuration surrounding atoms, the various atoms themselves remain unchanged throughout the process. An iron atom remains an iron atom, an oxygen atom continues to be an oxygen atom, etc. From an atom’s standpoint, the only thing different following a chemical reaction is its electrons have a new hair-do. Well, not really, because atoms don’t actually have hair, it would be more of an electron-do, and… I’ll just shut up.

I am making the very important assumption that the amount of water available is far in excess of what is actually needed for the actual reaction to occur. In this sense, water will have a dual role both as a reactant and as the medium where the chemical transformation will physically take place. Having water as the medium for reactions to occur is so common that we lovingly refer to that what happens chemically in water as aqueous chemistry. The “aq” symbol you’ll see later simply means there’s plenty of water all around.

Let’s see what the makeover produces.

• The first is that the iron (Fe) atom’s bonds with the two sulfur (S) atoms in pyrite (FeS2) are broken.
• The iron atom then becomes dissolved in the excess water as a positively charged particle deficient in two electrons.It’s called a ferrous (Fe2+) ion.
• Each of the sulfur atoms teams up (bonds) with four oxygen atoms and a couple of electrons to form a negatively charged complex called sulfate ion (SO42-), which is also dissolved in water.
• The bonds between the atoms of water molecules that enter into the reaction are broken. The oxygen atom is used in the production of sulfate. The two hydrogen atoms become positively charged hydrogen ions (H+) dissolved in the excess water.
• The reaction products, all of which are dissolved in water, are symbolized as

By the way, all of the above reaction products are colorless and odorless when dissolved in water.

We can now put the reactants together with the products to symbolize the entire reaction as

The arrow symbolizes a chemical reaction proceeding from reactants to products. Shown this way, it’s kind of like a recipe, with the ingredients on the left and what you get on the right.

You may have noticed that something is missing… namely the amounts or proportions of both the individual reactants and products. Since a reaction is a rearrangement of atoms, there have to be equal numbers of oxygen atoms on both the reactant and product sides of the equation. This must also be true for iron, sulfur, and hydrogen atoms. In other words, the number and kinds of atoms must balance on both the reactant and product sides. They have to: they’re the same atoms, just rearranged. This clearly isn’t the case for the reaction symbolized above. For instance, there are 2 sulfurs on the left, and only one on the right. See if you can find other discrepancies. This is an unbalanced equation and only shows the substances involved and not their quantities.
Without going into the detail of how it’s done, I’ll now show a balanced form of the reaction in which the number preceding each substance indicates the proportion needed in balancing the reaction.

If you count up the numbers of each kind of atom of the left (reactant) side of a properly balanced equation, they now exactly equal the numbers of each kind of atom of the right (product) side. With a little practice, you can look at symbolism of this sort and spout off something like “Four molecules of solid pyrite react with 14 molecules of oxygen gas and 4 molecules of liquid water react to produce 4 dissolved ferrous ions, 8 dissolved sulfate ions, and 8 dissolved hydrogen ions”. Yes, it may sound impressive, but take my advice… do NOT use it as a pick-up line at a party… bad idea. Just be content the recipe is complete showing all the reactant and product substances with an accurate accounting of their relative amounts.

We’ll call this reaction the pyrite oxidation reaction, the one that gets the AMD pollution ball rolling. Repeated over and over and over, the amounts of ferrous, sulfate and hydrogen ions increase. Increases in hydrogen ion concentrations mean the water is getting more acidic. Sulfates aren’t generally considered to be a health concern, but at high concentrations can cause diarrhea with subsequent dehydration in extreme cases. And we’re concerned with what ferrous ions become as they are involved in subsequent chemical reactions.

Well, that about does it for our first chemical act where pyrite, awoken from a deep sleep, went from a glittery, kind of a classy looking mineral, to a totally changed life as water pollution at the urgings of two of the most common chemicals, oxygen and water.

Join us on the road to chemical ruin in our next installment of AMD and Mining Environments (Part 3).