Abandoned Mine Posts

by Andy McAllister, Watershed Coordinator

Many different types of wildlife use abandoned mines, either for permanent or temporary habitat. From insects to owls, an abandoned mine opening can be a potential home for a multitude of residents.

One such animal is the much-maligned bat. Contrary to the frightening image of a blood-sucking Nosferatu portrayed in popular culture over the years, bats are vital both ecologically and economically to our nation. While very small (often weighing less than an ounce), bats can consume up to one-quarter of their body weight in insects each night and, depending on the number of individuals, a single colony of bats can consume up to a ton of insects each night.

Over half of the 43 species living in the U.S. are endangered or on the candidate list for endangered species. As their traditional habitats such as caves and tree hollows are being disturbed by human intrusion, bats are becoming more and more dependent on abandoned mine sites for suitable habitat. Many of the 43 species, including endangered species, have been observed using abandoned mines either as permanent roosts or temporary stops during migration. Abandoned mines provide microclimates similar to caves, suitable for rearing young, hibernation, and rest stops during migration in the spring and fall. Closure of mine openings without a biological survey can trap and destroy an entire colony of bats.

The most common bat in Pennsylvania is the Little Brown Bat (Myotis lucifugus). Little Brown Bats have adapted well to man’s activities, roosting in barns and attics. The Indiana Bat (Myotis sodalis) is the only federally endangered bat in Pennsylvania and while only on the fringe of this bat’s range, Pennsylvania is home to several over-wintering sites.

In 1998, the Office of Surface Mining signed a Memorandum of Understanding with Bat Conservation International (BCI), a non-profit organization formed to promote the conservation of bats and their habitat, to address the significance of protecting bat habitat while closing abandoned mines.

For more information on bats, visit the following websites:

Bat Conservation International

http://www.batcon.org/home/default.asp

The Bats of Pennsylvania

http://www.batmanagement.com/Batcentral/batspecs.html

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).

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 which are influential in the
making of polluted water.

Part 1: Introduction

The formation of polluted mine drainage is actually a natural process that has been greatly accelerated due to mining activities. The weathering of the common mineral pyrite, a.k.a. fool’s gold, (and its cousins) is the heart of the process. By weathering of pyrite, we mean that pyrite is exposed to the forces of air and water. A common place to see evidence of a non-coal related example is a road cut where rocks have been stained orange. That orange staining is likely to be a result of small amounts of pyrite being exposed to and reacting with water and oxygen.

Coal seams and surrounding strata commonly contain small percentages of pyrite which, being tucked away safely underground, has little chance of coming into contact with air and water. However, mining of coal exposes vastly greater quantities of pyrite to water and oxygen than would happen without the mining disturbance. If you examine a piece of freshly mined coal, you’re sometimes able to see fragments of pyrite in it, but not always because the pyrite particles may be too small. Even though you may not easily observe the pyrite directly, you can see evidence of its presence by what happens if the coal is left out in the weather. Eventually orange or yellow staining will become evident and the water that passes over it will have acquired some newly dissolved although undesirable constituents.

The water that becomes contaminated by this process goes by several names, which itself can cause some confusion. And since the topic comes up often enough, I’ll
try to make some sense of it here. Here’s at least a partial list of names:

• Acid Mine Drainage – perhaps the most common name. It’s accurate except in the case where local conditions have turned the water alkaline. Even if it’s alkaline, it may still be referred to as Acid Mine Drainage. Go figure.
• Alkaline Mine Drainage – see above.
• Coal Mine Drainage – accurate if the drainage occurs as a result of coal mining. However, other types of mining also can produce the same sort of stuff. And occasionally coal mine drainage isn’t even polluted. (Too bad there’s not more of that!)
• Abandoned Mine Drainage – accurate only if it’s coal mine drainage that originates from mining that occurred prior to the passage of the federal SMCRA legislation in 1977.
• Acid Rock Drainage - refers to drainage from “hard rock” mining, i.e. mining for minerals other than coal, but can also refer to non-mining related discharges (such as with the I99 Sky Top debacle).
• Contaminated Mine Drainage or Polluted Mine Drainage - about the most general terms covering all mining.
• Sulfur Water – a very colloquial term referring to Coal Mine Drainage. Many people believe the orange color in the water is sulfur. While sulfur is almost assuredly present in the form of colorless, odorless sulfate ions , the orange color is due to rust-like compounds of iron. Perhaps the rotten egg smell of hydrogen sulfide gas (H2S) that sometimes accompanies mine drainage (due to bacterial action with sulfate) may reinforce the idea it’s sulfur.
• I’m guessing there are others. Let me know.

So for the rest of this series, I’ll just refer to the polluted water simply as AMD. The “A”, in our case normally means “Abandoned”, just like the “A” in WPCAMR. In the next installment in this series we’ll delve into the chemistry involved in AMD formation. Following that, the underground conditions water may experience on its journey to becoming polluted will be explored.