Acid Mine Acid Mine Drainage Drainage
Formation and TreatmentFormation and Treatment
IntroductionIntroduction
AMD is an environmental concern AMD is an environmental concern many states facemany states face
22ndnd largest polluter in PA streams largest polluter in PA streams PA has over 5000+ miles of streams PA has over 5000+ miles of streams
impactedimpacted 1910—AMD research began1910—AMD research began 1977—passage of Surface Mine 1977—passage of Surface Mine
Control and Reclamation Act Control and Reclamation Act (SMCRA)(SMCRA)
AMD FormationAMD Formation
AMD occurs due to the exposure of AMD occurs due to the exposure of overburden during miningoverburden during mining
Function of geology, hydrology and Function of geology, hydrology and mining technologymining technology
Neutralizing compounds are absent Neutralizing compounds are absent from soil and the water becomes from soil and the water becomes acidicacidic
Contaminated with high Contaminated with high concentrations of Fe, Mn, Al, and SOconcentrations of Fe, Mn, Al, and SO44
ChemistryChemistry
Pyrite + Oxygen + Water Pyrite + Oxygen + Water “Yellowboy” + Acid“Yellowboy” + Acid
4FeS4FeS22 + 15O + 15O22 + 14H + 14H22O O 4Fe(OH) 4Fe(OH)33 + + 8H8H22SOSO44
Effects of AMDEffects of AMD
Oxygen removalOxygen removal Depletes buffering capacityDepletes buffering capacity Decreases light penetrationDecreases light penetration Smothers bottom dwellersSmothers bottom dwellers Directly toxicDirectly toxic Economic: PA loses $67 million each Economic: PA loses $67 million each
yearyear
Treatment of AMDTreatment of AMD
1968—PA instituted strict effluent 1968—PA instituted strict effluent discharge limitsdischarge limits
Coal companies used chemical Coal companies used chemical treatment to meet standardstreatment to meet standards Calcium carbonate, sodium hydroxide, Calcium carbonate, sodium hydroxide,
anhydrous ammoniaanhydrous ammonia Raise pH and precipitate metalsRaise pH and precipitate metals
Active TreatmentActive Treatment
Mechanized procedure for addition of Mechanized procedure for addition of alkaline materialalkaline material
Needs constant monitoring and Needs constant monitoring and maintenancemaintenance
Can exceed $200,000 per year at one Can exceed $200,000 per year at one sitesite
Produces large volumes of sludgeProduces large volumes of sludge Potentially harmful chemicals are usedPotentially harmful chemicals are used
Caustic soda, soda ash, sodium hydroxideCaustic soda, soda ash, sodium hydroxide
Passive TreatmentPassive Treatment
Mid 1980sMid 1980s No input of manufactured chemicals No input of manufactured chemicals Lower operation costsLower operation costs Longer retention times and larger Longer retention times and larger
treatment areastreatment areas First passive system was natural First passive system was natural
Sphagnum wetlandSphagnum wetland
Constructed WetlandConstructed Wetland
Encourage oxidation processes to Encourage oxidation processes to precipitate metals and increase pHprecipitate metals and increase pH
AerobicAerobic Rely on oxidationRely on oxidation Shallow, vegetatedShallow, vegetated Surface flowSurface flow
AnaerobicAnaerobic No oxygenNo oxygen Organic layer with sulfate reducing Organic layer with sulfate reducing
bacteriabacteria
Anoxic Limestone DrainAnoxic Limestone Drain
Alkalinity produced by AMD reacting Alkalinity produced by AMD reacting with calcium carbonatewith calcium carbonate
Constructed as shallow channel Constructed as shallow channel sealed from atmospheresealed from atmosphere
Used of oxidation basin after for Used of oxidation basin after for metals to precipitatemetals to precipitate
Vertical Flow WetlandVertical Flow Wetland
Combine ALDs and anaerobic Combine ALDs and anaerobic wetlandswetlands
Constructed as ponds with grid like Constructed as ponds with grid like piping system, 3’ of limestone, 2’ of piping system, 3’ of limestone, 2’ of mushroom compost, and 2-3’ of mushroom compost, and 2-3’ of standing waterstanding water
Adds alkalinity through limestone Adds alkalinity through limestone dissolution and sulfate reductiondissolution and sulfate reduction
Open Limestone Open Limestone ChannelsChannels
Simplest passive treatment methodSimplest passive treatment method Construct drainage ditch and fill Construct drainage ditch and fill
with limestonewith limestone Or, add limestone directly to the Or, add limestone directly to the
streamstream High velocity and turbulence High velocity and turbulence
enhance performance, steep slopesenhance performance, steep slopes
Diversion WellsDiversion Wells
Well of limestoneWell of limestone Hydraulic force of the water causes Hydraulic force of the water causes
the limestone to mix and abrade the limestone to mix and abrade particles of limestoneparticles of limestone
Diverted back to the streamDiverted back to the stream
ProblemsProblems
Use depends on water chemistry and Use depends on water chemistry and flow ratesflow rates
Must calculate loadings!Must calculate loadings! High Fe may “coat” limestone, less High Fe may “coat” limestone, less
efficientefficient High Al will precipitate and plug High Al will precipitate and plug
pore spacepore space
Other SolutionsOther Solutions
ReminingRemining ReclamationReclamation Removal of “spoil” pilesRemoval of “spoil” piles Injection of alkaline material into Injection of alkaline material into
minesmines Sealing of deep mine portalsSealing of deep mine portals Fix at source instead of band-aid!Fix at source instead of band-aid!