solid waste landfills

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Solid Waste Landfills Robert B. Gilbert Assistant Professor of Civil Engineering The University of Texas at Austin

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Page 1: Solid Waste Landfills

Solid Waste Landfills

Robert B. Gilbert

Assistant Professor of Civil Engineering

The University of Texas at Austin

Page 2: Solid Waste Landfills

Background• More than 5,000 landfills in U.S.• More than 500 landfills in Texas• 75 % of Municipal Solid Waste (MSW) ends up in a

landfill (120 million tons/year)• Landfills are an economical solution

– $30/ton to landfill MSW (1992)– $52/ton for waste to energy of MSW (1992)

• Products of treatment (e.g., incinerator ash) must be landfilled

• Hence, landfills are not going away

Page 3: Solid Waste Landfills

Regulations

• Specify what can and cannot be put into a landfill

• Give design, construction and operation standards

• Give environmental monitoring requirements• Drive the industry

Investment ($) Profit ($)Permit

Page 4: Solid Waste Landfills

Regulations - History

• Environmental Activism in 1960’s • National Environmental Policy Act (1970)• Clean Air Act (1970)• Clean Water Act (1972)• Resource Conservation and Recovery Act (1976)– Clean Air and Water Acts pushed waste to land– RCRA intended to close the loop– Defined waste as hazardous and non-hazardous– Initial focus was on hazardous waste

Page 5: Solid Waste Landfills

Love Canal - Background

• William T. Love started a 7-mile long canal in 1890’s to harness power from Niagra Falls

• Development of alternating current (which could be transmitted farther than direct current) made canal obsolete: only two 1/4-mile sections were excavated

• AC power brought industry to area, particularly chemical companies

• Hooker Chemical and Plastic Corp. manufactured plastics, chemicals and pesticides (chlorinated organic chemicals)

Page 6: Solid Waste Landfills

Love Canal - Background

• 1930’s: Hooker began disposing waste in north section of canal

• 1947: other chemical companies, the city of Niagra Falls, and the U.S. government were using the canal as a landfill

• 1952: canal was closed and capped by Hooker

Page 7: Solid Waste Landfills

Love Canal - Plan View

N LoveCanal

1968 Expressway

Niagra River

Groundwater Flow

A A’

Page 8: Solid Waste Landfills

Love Canal - Cross Section

Canal

Silt

Clay

Water Table

Bedrock

0’

-10’

-40’

A A’

Page 9: Solid Waste Landfills

Love Canal - Problems

• 1953: City of Niagra Falls ignores Hooker’s warnings and buys canal for a new grade school

• 1955: 99th Street School completed on top of canal and homes built around perimeter

• 1958: Children burned in puddle in playground• 1959: Oily sludge oozing into basement of house• 1968: Expressway built and problems increase• 1974: Residential pool uplifted by yellow, blue

and orchid colored groundwater• 1975: Sink hole developed in playground

Page 10: Solid Waste Landfills

Love Canal - Response

• 1975: City began investigating problems– toxic substances in basement air– high levels of benzene, chloroform and trichloroethene in

groundwater– high rates of birth defects/miscarriages

• City slow to react (Hooker employed 3,000 workers locally)

• 1977: Local and regional news began reporting about problems

• 8/2/78: Headline of New York Times about Love Canal; lead story on national television news

Page 11: Solid Waste Landfills

Love Canal - Resolution

• 1978: 237 families relocated and school closed• 1980: 700 more houses evacuated• 1980’s: Hooker (now known as Occidental

Chemical) and residents settled out of court for $30 million

• 1980’s: New cap placed on canal • Today: People are moving back to the area

Page 12: Solid Waste Landfills

Love Canal - Questions

• Who was responsible?– Hooker– City of Niagra Falls– State or Federal Government– Other Landfill Users

• How many more Love Canals existed (ticking time bombs)?– Over 1,000 national sites identified

• How can we prevent future Love Canals?– Pits in clay and disposal practices were acceptable

under 1976 RCRA!!!

Page 13: Solid Waste Landfills

Love Canal - Significance

• 1980: Congress passed Comprehensive Environmental Response, Compensation and Liabilities Act (CERCLA)– require clean up of uncontrolled waste sites– create Superfund to temporarily support efforts

• RCRA given teeth– Hazardous and Solid Waste Amendments (1984)– Municipal Solid Waste Rules (1991)– Requirements for siting landfills– Requirements for engineered lining and cover systems

(prevent leakage and bath-tub effect)– Ban on liquids in hazardous waste landfills

Page 14: Solid Waste Landfills

What is Solid Waste?• Waste: Any material that is discarded, served its

intended purpose, or is a manufacturing or mining byproduct

• Solid Waste: Everything not covered by the Clean Air and Water Acts, including solids, liquids and gases (RCRA is a catch all)

Municipal Solid Waste (MSW) Industrial Waste (liquids)Combustion Residue (ash) Sewage Waste (sludge)Mining Waste Dredging WasteAgricultural Waste Radioactive WasteSpecial Waste

Page 15: Solid Waste Landfills

What is Hazardous Waste?

A waste is hazardous if…• It is not excluded by regulation– e.g., household waste, oil and gas drilling waste, etc.

• It exhibits one of the following:– Toxicity, Ignitability, Corrosivity, Reactivity or Leachability

• It is listed as a hazardous waste– e.g., K051: API separator sludge from petroleum refineries

• It is mixed with or derived from a hazardous waste

Page 16: Solid Waste Landfills

Properties of Waste• Hazardous Waste (RCRA Subtitle C)– 90 % liquid– 60 % organic, 40 % inorganic– Waste must be treated with Best Demonstrated Available

Technology (BDAT) before disposal– Product of treatment is typically a sand-like material

(liquids banned in landfills after 1983)

• Municipal Solid Waste (RCRA Subtitle D)

Page 17: Solid Waste Landfills

Siting Landfills

• Natural Threats– earthquakes, landslides, floods

• Environmental Impacts– wetlands, surface water, groundwater, air, endangered

species

• Social Issues– odors, noise, traffic, airports, aesthetics, industrial and

population growth, historical/archaeological sites

• Economic Issues– disposal costs, land development alternatives, tax base,

permitting costs, construction/operation costs

Page 18: Solid Waste Landfills

Engineered Containment

Waste

Leachate

Rainfall

Leakage

Groundwater

Gas

Cover System

Lining System

Page 19: Solid Waste Landfills

Containment Systems

Drainage Layer

Barrier Layer (Liner)

Infiltration

Leakage

Drainage and Collection

Leakage = Infiltration - Drainage

Page 20: Solid Waste Landfills

Barrier Layers• Natural Soil Liners

– typically clay– be wary of fissures

• Compacted Soil Liners– also known as compacted clay liners (CCLs)– 2 to 5 feet thick

• Geosynthetic Clay Liners– also known as GCLs– 0.5 inches of bentonite (a clay) between fabrics

• Geomembranes– also known as flexible membrane liners (FMLs)– typically polyethylene (PE) or polyvinyl chloride (PVC)– 40 to 80 mils (1 mil = 0.001 inches) thick

Page 21: Solid Waste Landfills

Drainage Layers

• Granular Soils– typically sands and gravels– 1 to 2 feet thick

• Geosynthetic (Man-made) Materials– geonets: polyethylene ribs– geotextiles: polypropylene and polyester fabrics– pipes: polyethylene and stainless steel

Page 22: Solid Waste Landfills

Example Configurations

GeomembraneCompacted Clay

Composite Liner

Primary Liner

Double Liner System

Primary Collection System

Secondary Liner

Secondary Collection System

Page 23: Solid Waste Landfills

Example Lining System

Gravel (2 feet)

Cushion GeotextileGeoemembraneGeosynthetic Clay LinerFilter GeotextileGeonetGeomembrane

CompactedClay (3 feet)

Waste

Leachate Collection

PrimaryLiner

LeakDetection

SecondaryLiner

Page 24: Solid Waste Landfills

Example Cover System

Cover Soil (2 feet)

Sand (1 foot)

Geomembrane

Vegetation

FrostProtection

Drainage

Barrier

Gas Collection

Geosynthetic Clay Liner

Sand (1 foot)

Waste

Page 25: Solid Waste Landfills

Estimating Leakage

Soil

Q = Rate of Outflow

hL

Water

Page 26: Solid Waste Landfills

Darcy’s Law

Hydraulic Gradient = h/L

OutflowRate, Q

(Volume of Flow per Time)

Sand

Clay

Page 27: Solid Waste Landfills

Darcy’s Law

Q is proportional to gradient, h/L

Q is proportional to area of flow, A

Q = K(h/L)A

where K is hydraulic conductivity (the slope of the Q versus h/L plot)

Page 28: Solid Waste Landfills

Hydraulic Conductivity

K (cm/s)

Gravel 1 to 100

Sand 10-3 to 1

Silt 10-6 to 10-3

Clay 10-9 to 10-6

Geomembrane 10-12 to 10-11

Page 29: Solid Waste Landfills

Example CalculationsProblem: Estimate leakage rate through liner

Clay LinerK = 1x10-7 cm/s 3 feet

1 footLeachate

Groundwater

Solution:

Q/A = K(h/L)

Q/A = (1x10-7 cm/s)(4’/3’) = 1.3x10-7 cm/s

Q/A = 1,120 liters per hectare per day (lphd)

Q/A = 120 gallons per acre per day (gpad)

Page 30: Solid Waste Landfills

Typical Leakage Rates

Leakage Rate(gpad)

Clay Liner 100

Intact Geomembrane 0.1

Typical Geomembrane 10,000

Composite Liner 1