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This earthcache is now active. Come and learn a little about abandoned mine drainage.
Treatment of mine discharge depends on what contaminants are in the water and the geology of the coal seam. If the water is primarily acidic it is usually neutralized with limestone. If the contaminant is primarily iron the goal is to precipitate out (i.e. remove) iron out before it goes back into the stream. This is accomplished by either an active or passive treatment system. Active systems require the addition of chemicals to treat the water and remove the metals or contaminants. Passive systems use “natural” processes, like settling ponds, wetlands, or limestone beds that don’t require active chemical addition to improve water quality. Iron is a trace element necessary for most forms of life. Along with coal it is a vital component of this region’s industrial heritage. As a pollutant in water systems it’s devastating. The breakdown of pyrite or fool's gold (FeS2) by water (H2O) and oxygen (O2) in the mine creates two products, sulfuric acid (H2SO4) and ferric hydroxide (FeOH), the orange/rust looking material you see in mine drainage impacted streams. Iron hydroxide is a habitat killer. It covers the stream bottom decreasing the amount of stream insect habitat. It negatively impacts fish spawning areas and smothers insect and fish eggs. Without somewhere clean to spawn and with a reduction of its food web, fish have a hard time surviving. AMD (Abandoned Mine Drainage) is created when water comes in contact with reactive minerals that have been exposed through mining activities. The mineral responsible for the vast majority of AMD formation is pyrite, often called fool’s gold. A pyrite molecule is comprised of one atom of iron and two atoms of sulfur (FeS2, also known as iron sulfide). Pyrite reacts when it comes in contact with water and oxygen. While in actuality a series of chemical reactions occur to form contaminated water, the net result of these reactions can be summarized as follows: Pyrite + water + oxygen reacts to form sulfuric acid + yellow boy FeS2 + H2O + O2 g H2SO4 + Fe(OH)3 Sulfuric acid (H2SO4), a product of this reaction, is a strong acid capable of having devastating environmental consequences for plants and animals. Yellow boy (Fe(OH)3), also known as iron hydroxide, can form an orange or yellow sludge, coating the bottoms of streams, effectively smothering aquatic life. This is the orange material that can easily be seen in the Tanoma Wetlands. If this weren’t enough, the acidity generated by this reaction can further dissolve other minerals (such as clays), which can have high aluminum content, as well as other metals. The contaminated water may thus carry a variety of pollutants. These pollutants, in sufficiently high concentrations, can have a variety of negative effects on water quality and aquatic life. In some mine pools, like the pool where the Tanoma discharge originates, the mineral limestone may also be present in the geologic strata. As contaminated water comes in contact with limestone, a beneficial reaction sometimes occurs. The limestone, also known as calcium carbonate (CaCO3), acts to counteract, or neutralize, the acidity generated by the pyrite reaction. The AMD may actually become alkaline. While it may still carry a variety of other contaminants, such as iron hydroxide in the Tanoma Discharge’s case, the impacts are not as far reaching as if the acidity were present. At Tanoma, we have a passive treatment system to remove iron, which is the main problem with this discharge. We depend on dissolved oxygen and the right pH to help drop the iron out of the water. Slow passage of water through the passive system gives the iron time to drop out and the plants in the last few wetlands ponds help slow the water down and help take even more iron out of the water. Today YOU, citizen scientist, are going to be asked to perform two tests. Please read the signage along the trail to learn about the passive treatment system at this site. There is a red, plastic box located at the Tanoma site with all the materials you will need to do this activity. It is located on the back of the second shed (the shed beside the pavilion). First, please notice that in the container, there is: 1) A test kit for iron 2) pH strips in the bottle. 3) Paper and pen to record your data You will be asked to use the test kits twice, once at the inlet (N 40º 41.640’ – W079º 03.011’) (the area before the water turbine); and once at the discharge N 40º 41.783’ – W 079º 02.926’ of the wetlands (where the water discharges into Crooked Creek). Please record your findings on the paper forms included in the grey box. Testing for Iron: There are two test tubes with the kit, a color wheel, and a packet of reagent. 1. Fill the test tubes up to the lines with water from the system. Place them in the two holes in the color wheel. 2. Add the packet of reagent to the inner test tube, cap the tube, and shake thoroughly. 3. Match the colors with the wheel. 4. Record your findings to the nearest 0.2 mg/L. 5. Rinse both tubes with distilled water. pH Testing: Submerge a test strip into the water for 15 seconds and match the color on the bottle. Record your findings. Please replace the test materials and close the box. Remember to take your garbage with you! We hope you enjoyed your experience here at Tanoma and have learned something about Abandoned Mine Discharge treatment systems. Now that you have tested water before and after treatment, what changes did you observe in the iron concentration and in the pH. How do you explain the changes? What do your results mean? Iron If iron concentration decreased from the first (inlet) (N 40º 41.640’ – W079º 03.011’) to the last pond (discharge) (N 40º 41.783’ – W 079º 02.926’), the system is working properly! Our goal is to have iron concentration as low as possible at the discharge. We’ve recorded iron concentrations of <1 mg/L. If iron concentration increased from the first to the last pond, the system is malfunctioning. This could be because the water flow is too high. If there is too much water coming into the system, it does not have enough time to settle out and can scour the precipitated iron in the bottoms of the ponds and send the iron back into Crooked Creek. If the iron concentration stayed the same, then we need to increase the amount of oxygen into the ponds and/or increase the settling time. This is more common in winter months. (We are working to fix this!) pH If pH decreased, then the ponds are making the discharge more acidic. Remember, we want to increase the pH in order to drop out more iron. If pH increased, then the ponds are making the discharge more alkaline. This is what we want! If the pH stayed the same, then we are probably okay. The pH is normally around 6-7 throughout the system and is not a major concern with the Tanoma discharge. Has the pH remained within the acceptable range? Does the whole treatment system appear to be operating as intended.
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