Coal Ash Landfills –A Case Study

Roger ClarkeManager, Waste & Remediation

MPCA Aug. 25, 2008

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What is Coal Ash?

Unburned portion of fuelMostly comprised of minerals commonly found in soilHas trace elements such as arsenic, chromium, cadmium, lead & mercury

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How Coal Ash Is Generated?

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Types of Ash:

Fly AshBottom AshSlagScrubber Residues

Magnified view of Fly Ash Particles

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0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

Tons

Ash

Gen

erat

ed

NSP PSCO SPS

Xcel Energy Region

Tons DisposedTons Utilized

2007 Coal Ash Generation:

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What Factors Affecting Coal Ash Composition?

Fuel SourceCombustion Process

— Circulating Fluidized Bed — Pulverized Coal (example SHERCO)— Cyclone (example A.S. King)

Emission Control Devices— Sulfur Control — NOx Control— Particulate Control— Mercury Control

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Coal and Additives:Trace Metal Analysis

Rochelle Westmoreland Petcoke

Antimony mg/kg -1 1.029 4Arsenic mg/kg -1 1.263 -8Barium mg/kg 183 194.2 2.1Beryllium mg/kg -0.2 0.371 -0.2Boron mg/kg 24 77.3Bromine mg/kg -20Cadmium mg/kg -0.2 0.274 -0.4Chlorine mg/kg -50Chromium mg/kg 4 4.034 -0.8Cobalt mg/kg 2 2.579 -2Copper mg/kg 9 7.000 -2Fluorine mg/kg 68 -10Lead mg/kg 2 6.13 -2Lithium mg/kg 3 16.24Manganese mg/kg 9 78.89 1.1Mercury mg/kg 0.05 0.095 0.05Molybdenum mg/kg -2 3.395 8Nickel mg/kg 3 3.211 199Selenium mg/kg -1 1.158 -8Silver mg/kg -0.2 0.476 -0.4Strontium mg/kg 148 448.6 1Thallium mg/kg -1 -20Tin mg/kg -1 1.432 -8Vanadium mg/kg 9 10.053 1041Zinc mg/kg 6 5.211 2Zirconium mg/kg 8 15.778 -0.4

Current Blend

Coal Trace Element Summary:PPM – Dry Basis Cordero Rojo SoilArsenic (As) 1.4 1 to 50Barium (Ba) 373 100 to 3000Boron (B) 44 2 to 100Cadmium (Cd) 0.2 0.1 to 0.7Chromium (Cr) 6.1 1 to 100Copper (Cu) 14.5 2 to 100Lead (Pb) 3.1 2 to 200Mercury (Hg) 0.1 0.01 to 0.3Molybdenum (Mo) 2.1 0.2 to 5Nickel (Ni) 2.5 5 to 500Selenium (Se) 1.1 0.1 to 2Strontium (Sr) 254 50 to 1000Vanadium (Va) 21.7 20 to 500Zinc (Zn) 10.2 10 to 300

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Typical Chemical Composition of Fly Ash

Sulfur2.1% Moisture

0.1% Alkalines1.0%Magnesium Oxide

4.7%

Calcium Oxide28.3%

Iron Oxide6.3%

Aluminum Oxide19.9%

Unburned Carbon (LOI)0.4%

Silicon Dioxide37.3%

Major Constituents: Fly Ash

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Typical Chemical Composition of Cement

Sulfur0.00%

Moisture0.00%

Alkalines0.21%

Magnesium Oxide2.39%

Unburned Carbon (LOI)0.59%

Silicon Dioxide21.62%

Aluminum Oxide4.54%

Iron Oxide2.76%

Calcium Oxide67.89%

Major Constituents: Cement

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Typical Chemical Composition of Bottom Ash

Silicon Dioxide49.3%

Aluminum Oxide19.8%

Iron Oxide6.2%

Calcium Oxide18.8%

Magnesium Oxide4.2%

Potassium Oxide0.3%

Sodium Oxide1.4%

Major Constituents: Bottom Ash

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Relative Chemical Content:

Fly Ash Total Composition: (ppm, dry)

Black Dog 3&4 MN ChronicIndustrial SRVs

Arsenic (As) 13 25Barium (Ba) 5,260 12,500Boron (B) 582 23,000Cadmium (Cd) 2.7 250Chromium (Cr) 66 425 (as VI)Copper (Cu) 148 9,000Lead (Pb) 33 700Mercury (Hg) 0.10 2Molybdenum (Mo) 9.0 --Nickel (Ni) 30.2 3,000Selenium (Se) 10.4 1,250Sodium (Na) 10,483 --Sulfur (S) 30,136 --Zinc (Zn) 77 7,000

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What is Leachate?Leachate is defined as “liquid that has percolated through solid waste and has extracted, dissolved, or suspended materials from it”Leachate generation controlled by:

— Type of material and its porosity— Precipitation levels— Facility design— Operational controls such as size of working face

Leachate chemistry controlled by:— Characteristics of the waste material— Volume of contact water— Chemistry of the contact water

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Other2%

Potassium1%

Alkalinity1%

Calcium4%

Sodium36%Sulfate

56%

Leachate: Primary Constituents

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Leachate:Minor Constituents

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TCLP Test Results: 2008

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NSP Disposal Facility Design