solid waste landfills
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Solid Waste Landfills
Robert B. Gilbert
Assistant Professor of Civil Engineering
The University of Texas at Austin
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)– $52/ton for waste to energy of MSW (1992)
• Products of treatment (e.g., incinerator ash) must be landfilled
• Hence, landfills are not going away
Regulations
• Specify what can and cannot be put into a landfill
• Give design, construction and operation standards
• Give environmental monitoring requirements• Drive the industry
Investment ($) Profit ($)Permit
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
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)
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
Love Canal - Plan View
N LoveCanal
1968 Expressway
Niagra River
Groundwater Flow
A A’
Love Canal - Cross Section
Canal
Silt
Clay
Water Table
Bedrock
0’
-10’
-40’
A A’
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
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
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
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!!!
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
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
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
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)
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
Engineered Containment
Waste
Leachate
Rainfall
Leakage
Groundwater
Gas
Cover System
Lining System
Containment Systems
Drainage Layer
Barrier Layer (Liner)
Infiltration
Leakage
Drainage and Collection
Leakage = Infiltration - Drainage
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
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
Example Configurations
GeomembraneCompacted Clay
Composite Liner
Primary Liner
Double Liner System
Primary Collection System
Secondary Liner
Secondary Collection System
Example Lining System
Gravel (2 feet)
Cushion GeotextileGeoemembraneGeosynthetic Clay LinerFilter GeotextileGeonetGeomembrane
CompactedClay (3 feet)
Waste
Leachate Collection
PrimaryLiner
LeakDetection
SecondaryLiner
Example Cover System
Cover Soil (2 feet)
Sand (1 foot)
Geomembrane
Vegetation
FrostProtection
Drainage
Barrier
Gas Collection
Geosynthetic Clay Liner
Sand (1 foot)
Waste
Estimating Leakage
Soil
Q = Rate of Outflow
hL
Water
Darcy’s Law
Hydraulic Gradient = h/L
OutflowRate, Q
(Volume of Flow per Time)
Sand
Clay
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)
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
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)
Typical Leakage Rates
Leakage Rate(gpad)
Clay Liner 100
Intact Geomembrane 0.1
Typical Geomembrane 10,000
Composite Liner 1