WHAT IS A LANDFILL?
A secure landfill is a carefully engineered depression in the
ground (or built on top of the ground, resembling a football
stadium) into which wastes are put. The aim is to avoid any
hydraulic [water-related] connection between the wastes and the
surrounding environment, particularly groundwater. Basically, a
landfill is a bathtub in the ground; a double-lined landfill is
one bathtub inside another. Bathtubs leak two ways: out the
bottom or over the top.
WHAT IS THE COMPOSITION OF A LANDFILL?
There are four critical elements in a secure landfill: a bottom
liner, a leachate collection system, a cover, and the natural
hydrogeologic setting. The natural setting can be selected to
minimize the possibility of wastes escaping to groundwater
beneath a landfill. The three other elements must be engineered.
Each of these elements is critical to success.
THE NATURAL HYDROGEOLOGIC SETTING:
You want the geology to do two contradictory things for you. To
prevent the wastes from escaping, you want rocks as tight
(waterproof) as possible. Yet if leakage occurs, you want the
geology to be as simple as possible so you can easily predict
where the wastes will go. Then you can put down wells and
capture the escaped wastes by pumping. Fractured bedrock is
highly undesirable beneath a landfill because the wastes cannot
be located if they escape. Mines and quarries should be avoided
because they frequently contact the groundwater.
WHAT IS A BOTTOM LINER?
It may be one or more layers of clay or a synthetic flexible
membrane (or a combination of these). The liner effectively
creates a bathtub in the ground. If the bottom liner fails,
wastes will migrate directly into the environment. There are
three types of liners: clay, plastic, and composite.
WHAT IS WRONG WITH A CLAY LINER?
Natural clay is often fractured and cracked. A mechanism called
diffusion will move organic chemicals like benzene through a
three-foot thick clay landfill liner in approximately five
years. Some chemicals can degrade clay.
WHAT IS WRONG WITH A PLASTIC LINER?
The very best landfill liners today are made of a tough plastic
film called high density polyethylene (HDPE). A number of
household chemicals will degrade HDPE, permeating it (passing
though it), making it lose its strength, softening it, or making
it become brittle and crack. Not only will household chemicals,
such as moth balls, degrade HDPE, but much more benign things
can cause it to develop stress cracks, such as, margarine,
vinegar, ethyl alcohol (booze), shoe polish, peppermint oil, to
name a few.
WHAT IS WRONG WITH COMPOSITE LINERS?
A Composite liner is a single liner made of two parts, a plastic
liner and compacted soil (usually clay soil). Reports show that
all plastic liners (also called Flexible Membrane Liners, or
FMLs) will have some leaks. It is important to realize that all
materials used as liners are at least slightly permeable to
liquids or gases and a certain amount of permeation through
liners should be expected. Additional leakage results from
defects such as cracks, holes, and faulty seams. Studies show
that a 10-acre landfill will have a leak rate somewhere between
0.2 and 10 gallons per day.
WHAT IS A LEACHATE COLLECTION SYSTEM?
Leachate is water that gets badly contaminated by contacting
wastes. It seeps to the bottom of a landfill and is collected by
a system of pipes. The bottom of the landfill is sloped; pipes
laid along the bottom capture contaminated water and other fluid
(leachate) as they accumulate. The pumped leachate is treated at
a wastewater treatment plant (and the solids removed from the
leachate during this step are returned to the landfill, or are
sent to some other landfill). If leachate collection pipes clog
up and leachate remains in the landfill, fluids can build up in
the bathtub. The resulting liquid pressure becomes the main
force driving waste out the bottom of the landfill when the
bottom liner fails.
WHAT ARE SOME OF THE PROBLEMS WITH LEACHATE COLLECTION
SYSTEMS?
Leachate collection systems can clog up in less than a decade.
They fail in several known ways:
- they clog up from silt or mud;
- they can clog up because of growth of microorganisms in
the pipes;
- they can clog up because of a chemical reaction leading
to the precipitation of minerals in the pipes; or
- the pipes become weakened by chemical attack (acids,
solvents, oxidizing agents, or corrosion) and may then be
crushed by the tons of garbage piled on them.
WHAT IS A COVER?
A cover or cap is an umbrella over the landfill to keep water
out (to prevent leachate formation). It will generally consist
of several sloped layers: clay or membrane liner (to prevent
rain from intruding), overlain by a very permeable layer of
sandy or gravelly soil (to promote rain runoff), overlain by
topsoil in which vegetation can root (to stabilize the
underlying layers of the cover). If the cover (cap) is not
maintained, rain will enter the landfill resulting in buildup of
leachate to the point where the bathtub overflows its sides and
wastes enter the environment.
WHAT ARE THE PROBLEMS WITH COVERS?
Covers are vulnerable to attack from at least seven sources:
- Erosion by natural weathering (rain, hail, snow,
freeze-thaw cycles, and wind)
- Vegetation, such as shrubs and trees that continually
compete with grasses for available space, sending down roots
that will relentlessly seek to penetrate the cover;
- Burrowing or soil- dwelling mammals (woodchucks, mice,
moles, voles), reptiles (snakes, tortoises), insects (ants,
beetles), and worms will present constant threats to the
integrity of the cover;
- Sunlight (if any of these other natural agents should
succeed in uncovering a portion of the umbrella) will dry
out clay (permitting cracks to develop), or destroy membrane
liners through the action of ultraviolet radiation;
- Subsidence--an uneven cave-in of the cap caused by
settling of wastes or organic decay of wastes, or by loss of
liquids from landfilled drums--can result in cracks in clay
or tears in membrane liners, or result in ponding on the
surface, which can make a clay cap mushy or can subject the
cap to freeze-thaw pressures;
- Rubber tires, which "float" upward in a landfill; and
- Human activities of many kinds.
Prepared by:
Environmental Research Foundation
P.O. Box 5036
Annapolis, MD 21403-7036
phone (410) 263-1584
fax (410) 263-8944
Environmental Research Foundation's
Leaky Liners & Leachate
#90 Municipal Dump Leachate Is As Toxic As That From Hazardous
Waste Dumps
#119 Leachate Collection Systems: The Achilles' Heel Of
Landfills
#37 EPA Says All Landfills Leak, Even Those Using Best Available
Liners
#71 Decade-Old Study Revealed the Polluting Effects of Landfills
#116 Why All Landfills Leak
#117 The Best Landfill Liner: HDPE
#125 Clay Landfill Liners Leak In Ways That Surprise Landfill
Designers
#216 Some Hidden Hazards Of A Plastic World [Plastics Aren't
Biodegradable]
#217 Why Plastic Landfill Liners Always Fail
#316 New Evidence That All Landfills Leak
#109 Catch-22s of Landfill Design
#177 Unrecognized Cause of Landfill Failures
#226 Toxic Gases Emitted From Landfills
Hazardous Waste & Environmental Racism
#162 Fine Particles--Part 5: Incineration Worsens Landfill
Hazards
#164 The Landfiller's New Plan: Megafills
#180 Commercial Hazardous Waste Landfills
#182 Chemical Dumps Make Good Homes For Poor Families, EPA
indicates
#190 Incinerator Ash--Part 2: All Wastes Must Go Somewhere
Forever
#403 EDF Proposes Incinerator Ash Dumps
#224 Nation's Greatest Danger: Secrecy [Military Toxics]
#227 The Military Toxics Scandal Deepens
#239 The Poisoners Invade Indian Country
#272 Government Facts on Dumps Remain Sketchy
#278 Government Burial Of Asbestos On Sacred Navajo Land
#183 Coming Your Way: Radioactive Garbage
Superfund & Health
#176 Hooked on Danger: Expanding Solid Waste Landfills
#271 National Academy Superfund Dumps Make People Sick
#332 Why Exalt Wise Use? [industry can't stop polluting]
#370 Superfund Dumps & Health, Part 2
#371 Superfund Dumps & Health, Part 3
Landfill Politics
#231 EPA Proposes A Perfect Solution For New Municipal Solid
Waste Landfills
#238 The Regulatory-Industrial Complex
#241 Citizens Seek Reform Of The Nation's Hazardous Waste Law
#268 EPA's New Landfill Rules Protect Big Garbage Haulers
#288 New Tools For Citizens: 'Bad Boy' Laws
#292 Congress Creates A Monster: The ATSDR [superfund]
Strategies & Alternatives
#232 Public Ownership Of Dumps Is The Key
#260 Storing Superfund Waste In Concrete Buildings Seems to Make
Sense
#289 Good Solid Waste Alternatives [composting]
#307 New Garbage Strategies Are Now Possible
#352 Composting Municipal Solid Waste
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