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!