The Formation of Abandoned Mine Drainage

The Definition and Causation of Abandoned Mine DrainageLessons Prepared by Trout Unlimited

With Funds from Pennsylvania Department of Environmental Protection

Prior to 1977

• Prior to the Surface Mining Control and Reclamation Act (SMCRA) there were no federal regulations on mining

• This allowed mining companies to simply abandon a mine when they completed their mining

• Most mines prior to 1977 produced some degree of abandoned mine drainage (AMD)

Prior to 1977

• With approximately 5,500 miles of impacted waterways in the state of Pennsylvania AMD is the leading source of non-point source pollution

• The impacts of these mines which can be hundreds of years old are still seen and felt today

Abandoned Mines

• Any area that is impacted by these mines are called Abandoned Mine Lands (AML)

• Any water that is impacted by these mines is called Abandoned Mine Drainage (AMD)

AML in the Kettle Creek watershed. Provided by TU staff. AMD in the Clearfield Creek Watershed. Provided by Clearfield Creek Watershed Association.

Abandoned Mines Lands

• Deep Mines may look like caves, but they are dangerous!

• There can be a subsidence of the mine as well as water coming out of bore holes!

Borehole into an underground deep mine that is filled with polluted water. Provided by TU Staff. Inside an abandoned deep mine. Note the size of some of the rocks

and fallen down wooden supports. Provided by Rich Wykoff.

A sinkhole formed as the roof of an abandoned mine collapsed. Provided by PA Department of Environmental Protection http://www.dep.state.pa.us/dep/deputate/minres/districts/homepage/california/Underground/Mine%20Subsidence/mine_subsidence.htm

Abandoned Mines Lands

• Refuse piles (gob piles, culm banks, spoil piles, boney piles…) are left over coal and rock that was not able to be used

All photos provided by the Western PA Coalition for Abandoned Mine Reclamation http://amrclearinghouse.org/Sub/photogallery/

Abandoned Mines Lands

• Abandoned strip mines have no top soil left. Therefore nothing grows in these areas

• Historic strip mines also have dangerous pits and highwalls

A strip mine as seen from space. Generated using Google Earth.

Pits like these have been left by surface mining. Provided by Alder Run Engineering.

Highwalls like this one can be very high and steep. This highwall can be estimated to be 15-20 ft. high. Provided by TU Staff.

Abandoned Mine Drainage

• Metal-rich, generally acidic, water formed from a chemical reaction between water, oxygen and rocks containing sulfur-bearing minerals

• Forms when mineral deposits that contain sulfides are uncovered during mining

• Most common example is pyrite

Pyrite

• Commonly known as ‘Fools Gold’

• Chemical formula: FeS2

• AMD is formed when pyrite, an iron sulfide, reacts with air and water

• This forms sulfuric acid and ferric hydroxide

Iron Pyrite. Provided Richard Kruse http://richardkruse.com/Misc_Photos/Minerals/Mineral_Pyrite_RK.jpg

Abandoned Mine Drainage

Sulfuric AcidH2SO4

Ferric HydroxideFe(OH)3

PyriteFeS2

+ OxygenO2

+ WaterH2O

+

+ +

Abandoned Mine Drainage

Mine Pools

• Mines can be come filled with water called a mine pool if this water breaks out it can be dangerous

This mine pool (shown in purple) gives an idea of size, this pool actually has currents and flow. Provided by Office of Surface Mining http://www.arcc.osmre.gov/Divisions/TSD/Techservices/Hydrology/hydrology.shtm#MPFM

AMD Formation Reaction

Step One:

The pyrite oxidizes upon contact with air and water

Fe+2 + 1/4 O2 + H+ --> Fe+3 +1/2 H2O

AMD Formation Reaction

Step Two:

Iron oxidizes to ferric iron

FeS2 + 7/2 O2 + H2O --> 2SO4-2 + Fe+2 + 2H+

AMD Formation Reaction

Step Three:

Precipitation occurs with ferric iron to ferric hydroxide

Fe+3 + 3H2O --> Fe(OH)3 + 3H+

AMD Formation Reaction

Step four:

All combined to show a full formation of sulfuric acid

FeS2 + 15/4 O2 + 7/2 H2O --> 2H2SO4 + Fe(OH)3 4

AMD Characteristics

• Low pH- Typically 3-4, but can be lower– High Acidity– Low Alkalinity

• High metals- Iron, Aluminum and Manganese are the common metals in our area

• High Sulfates- Caused by land disturbance such as mining

• All of these lead to polluted and dead streams!

Water Chemistry

• pH- A measure of hydrogen ions in water– Determines Acid or Base

• Most healthy streams have a pH of 6-9

• Brook Trout can survive in pH 4.5-9.5

• AMD impaired waters can have a pH of 2-5pH scale with common solutions. Provided by Jackson Bottom

Wetland Preserve http://www.jacksonbottom.org/monitoring-restoration/water-quality-concepts/

Water Chemistry

• Alkalinity- This is a measure of the stream’s ability to buffer pH changes– Alkalinity is added by the rocks a stream flows over,

commonly limestone– The higher the alkalinity the more acid can be added

before pH is affected

Water Chemistry

50 ml of water

pH Before is 7.0

Add 10 ml of Acid

Alkalinity

pH After is 6.9

50 ml of water

pH Before is 7.0

Add 10 ml of Acid

Alkalinity

pH After is 6.0

Water Chemistry

• Streams in areas highly impacted by AMD have little naturally occurring alkalinity– This means small quantities of acid impact these waters

more than highly alkaline waters

• What alkalinity they do have is quickly removed by the highly acidic water

Water Chemistry

• Total Acidity- This is a measure of how many positive acidic ions are present– This is similar to pH, but it is a different measurement– This is mainly measuring the number of hydrogen ions,

however other ions can affect this number

Water Chemistry

H+

H+H+

H+

H+H+

Cl-

Cl-

Cl-Cl-

Cl-

Cl-

HCl

HClHCl

H+

H+

H+

Cl-Cl-

Cl-

pH 5 pH 7

Acidity 10 mg/l

Acidity 10 mg/l

Al3+Al3+

Al3+

Al3+

Acidity 15 mg/l

Water Chemistry

• Streams that have been impacted by AMD have high levels of acidity

• One of the major source of acidity beyond hydrogen ions is aluminum ions, which are common in AMD

Water Chemistry

• Iron- Some metals leach into water. Iron is a commonly found dissolved metal in our area– Iron becomes dissolved at very low pH’s

• AMD impaired streams have high levels of iron from the reaction with pyrite, and from the soils

• Dissolved iron is toxic in high levels, and the precipitated iron is deadly to creatures with gills

Iron precipitate on stream bottom. Provided by TU Staff

Water Chemistry

• Aluminum- Another commonly dissolved metal in our area– Aluminum is more dangerous at lower pH’s

• Aluminum is common due to the soil types in Pennsylvania

• The rule of thumb for aluminum is if the pH is less than 5.5 and the aluminum concentration is greater than 0.5 mg/l stream life will die!

Aluminum precipitate in the water. Provided by TU Staff

Water Chemistry

• Sulfates- Sulfates are naturally occurring but at high levels can be a sign of a problem

• Sulfates are released when the soil is disturbed such as mining

• Sulfates cause an unpleasant odor of rotten eggs

Water Chemistry

• These drainages have the most impact on the small 1st order streams they enter

• Most areas that have been mine have high concentrations of AMD impaired streams

• This does not allow enough clean water to enter the system and dilute the impacted water

• Brubaker is not the first or last source of pollution entering Clearfield Creek, it is one of the worst sources of pollution and stains the stream

Clearfield Creek

• In the headwaters of Clearfield Creek life thrives• Brubaker Run enters Clearfield Creek leaving it virtually lifeless

The upper sections of Clearfield Creek support life. Provided by Clearfield Creek Watershed Association.

After the confluence with Brubaker Run, Clearfield Creek is left stained and lifeless. Provided by Clearfield Creek Watershed Association.

Brubaker Run is highly polluted water that enters Clearfield Creek. Provided by Clearfield Creek Watershed Association.

Water Quality for Local Streams

PA DEP Standards

Clearfield Creek

Above BR

Brubaker Run

Clearfield Creek Below

BR

pH 6-9 7.3 3.1 6.5

Alk. >20 mg/l 21 mg/l 0 8.2 mg/l

Acid 0 mg/l 0 mg/l 550 mg/l 4.6 mg/l

Iron 1.5 mg/l 0.278 mg/l 180 mg/l 1.555 mg/l

Al 0.75 mg/l 0.335 mg/l 19 mg/l 1.305 mg/l

Sulf. 250 mg/l 67 mg/l High 104.4 mg/l

Water Quality Impacts

• The water quality impacts of these drainages are seen far downstream and inhibit some life for miles

• There are treatment options for these drainages

Anna S treatment system on Babb Creek. Generated using Google Earth.