The ABCs of
Landfills
–Lori Stole, Recycling Advocates (Sept. 2002)
When we choose to no longer reuse or recycle a household item, it becomes
garbage. We put it in the garbage can, which we set it out for the garbage
truck to take away. All taken care of, right? Maybe for your purposes...
for now.
The hauler takes your garbage to the local municipal landfill. Here the items
in your garbage can start new phase in their lives.
If waste is simply buried in the ground, rain will percolate through, leaching
toxic materials out of the waste and eventually into the groundwater. Per
the Resource Conversation and Recovery Act (RCRA) and EPA requirements, landfills
are now designed in ways that are supposed to protect us, and our environment.
An effort is made to avoid any hydraulic (water-related) connection between
the wastes and the surrounding environment, particularly groundwater. This
includes a cover on the landfill to prevent rainwater from entering, a lining
on the bottom of the landfill to keep any potential leachate from leaving
the landfill, and a leachate collection system to prevent buildup over time.
In addition, the landfill must be sited such that the geology helps to minimize
contact with groundwater.
The landfill, cover usually consists of several sloped layers, one of clay
or membrane to keep rain out, overlain by a very permeable layer of sandy
or gravelly soil to promote runoff, overlain by topsoil with vegetation to
stabilize the cover. Long term maintenance of the cover is necessary to watch
for and correct the following problems: erosion by natural weathering, root
penetration, burrowing mammals, sunlight degradation of exposed clay or membrane
layers, subsidence caused by waste settling, rubber tires which float upward
and human activities.
The liquid that works its way through the landfill is called the leachate.
It becomes contaminated from chemicals in the waste, and eventually reaches
the sloped bottom of the landfill, where it is collected by a system of pipes.
The leachate is then pumped to a wastewater treatment plant, where the solids
are removed and sent to, yes, a landfill. Leachate, collection systems can
clog up in less than a decade, due to mud, and silt, growth of microorganisms
in the pipes, chemical reaction leading to mineral precipitation in the pipes
or chemical attack that weakens the pipes.
There are several types of bottom liners: clay, plastic and composite.
- Clay can fracture and crack. Organic chemicals can diffuse through clay,
and some chemicals can degrade clay.
- Today's best liners, flexible membrane liners (FMLs) are made from a high-density
polyethylene (HDPE) plastic film. Unfortunately, some - household chemicals
degrade HDPE, permeating, weakening,' softening or cracking it. Such common
substances as mothballs, margarine, vinegar, alcohol and shoe polish can
cause these problems. Also, liners always have some defects such as cracks,
holes and faulty seams.
Composite liners consist of a plastic liner plus compacted soil (usually
clay). The bottom line to bottom liners is that there is always some degree
of leakage, and the leakage rate increases over time. Detection of leakage
is difficult. Studies have shown that the leach ate from municipal landfills
has the same carcinogenic potency as that from industrial landfills.
Landfills, also generate greenhouse gases, the most abundant of which is
methane, formed by the
decomposition of organic material. Organics typically make up over half of
landfill waste.
Methane is 21 times more potent as a greenhouse gas than carbon dioxide.
Attempts sometimes are made to capture the methane for energy recovery, however,
their effectiveness is questionable. Much methane is released before the
recovery system is in place, and additional methane is produced decades later,
probably/after the recovery system is no longer in service. The better alternative
is to prevent gas formation by composting organics, bypassing the landfill
option altogether.
While municipal landfills have not been allowed to accept industrial waste
since the adoption of RCRA in 1976, they still have their share of nasty
chemicals. Toxic materials, from households, small quantity generators and
several other sources are exempted from regulation and enter such landfills
freely and regularly.
For example, color computer monitors (which we have been dealing with recently
as part of our electronics stewardship project), contain 4-8 pounds of lead
and are characterized as toxic by a standard leaching test. Therefore, businesses
are not allowed to dispose of monitors in a municipal landfill. But, the
household and small quantity generator exemption allows monitors from those
sources to enter the landfill, in the absence of other state or local restrictions.
So is our waste gone when we throw it away? No! Somebody else is supposed
to watch it for a while, as federal law requires a minimum landfill post
closure care period of 30 years. Who's watching it after that?
For more information on the inner workings of landfills, visit the following
Web sites:
http://grrn.org
http://www.ejnet.org/landfills/
http://www.gfredlee.com/plandfil2.htm
http://foe.org/ptp/manual.html#lch1intro
Recycling Advocates is based in Portland, Oregon, www.recyclingadvocates.org.