- Adapted from materials by
the Conservation & Environmental Studies Center, Burlington
Back to Trash Goes to School
- GRADE LEVELS:
- SUBJECT AREAS:
All landfills produce some leachate. Whether the leachate contaminates
groundwater depends on how the landfill is built, as well as
on characteristics of the site.
To become aware that everything we do on and to the surface of
the earth affects our water.
- MATERIALS: Local
land use maps, soil maps, land use planning documents, solid
waste reports (see agencies listed below for sources of these
leachate, permeability, aquifer, water table
Groundwater, the source for wells and springs, supplies drinking
water to over half of the people in this country and over 90
percent of the residents in rural areas. Of the population served
by public water supplies, close to 40 percent rely on groundwater.
Geological formations which yield significant amounts of groundwater
are called aquifers. The top of the groundwater layer is called
the water table.
- Although traditionally groundwater
has been assumed to be free from contamination, numerous discoveries
in recent years of toxic chemicals in well water have proven
this assumption to be false. Groundwater contamination from
chemical dumpsites tends to attract the greatest public attention,
but a number of other sources including landfills, septic systems,
pesticides, and underground storage tanks also can be significant
- Water percolating through landfills
produces leachate, which may contain undesirable or toxic chemicals.
Modern sanitary landfills are constructed to prevent leachate
contamination of groundwater or surface waters. The bottom of
the landfill is lined with impermeable layers, and the leachate
is collected and treated before being released to the environment.
- Factors affecting the composition of
landfill leachate include:
- Landfill material. Is it biodegradable or non-biodegradable?
Is it soluble or insoluble? Organic or inorganic? Liquid or
solid? Toxic or nontoxic?
- Landfill conditions. The pH, temperature, degree of ongoing decomposition,
moisture content, climate, and landfill age.
- Characteristics of entering water. The pH, temperature, and amount.
- Soil characteristics under the landfill. Permeability, depth and thickness of geologic
strata, and mineral content.
- The risk of groundwater contamination
by any leachate that is not caught by collection systems is determined
by the following factors:
- Depth of the water table. If the water table is low (far below the ground
surface), water will become partially filtered as it percolates
downward through the soil. If the water table is high (close
to the ground surface), contaminants can enter the groundwater
directly, without filtration by soil.
- Concentration of contaminants. A high concentration of contaminants in leachate
will make groundwater pollution more likely.
- Permeability of the geologic strata. Highly permeable geologic strata allow water
to quickly percolate through, receiving little filtration along
the way. Strata consisting of relatively impermeable materials
such as silt and clay impede the downward percolation of water.
- Type of geologic strata. Some earth materials, such as clay, are more
effective at filtering out contaminants, not just because they
are impermeable but because chemicals can bind to their particle's
- The toxicity of the contaminants. Leachate is produced when water filters downward
through a landfill, picking up dissolved materials from the decomposing
wastes. Depending on characteristics of the landfill and the
wastes it contains, the leachate may be relatively harmless or
extremely toxic. Generally leachate has a high biochemical oxygen
demand (BOD) and high concentrations of organic carbon, nitrogen,
chloride, iron, manganese, and phenols. Many other chemicals
may be present, including pesticides, solvents, and heavy metals.
- The direction of groundwater flow. Groundwater moves slowly and continuously
through the open spaces in soil and rock. If a landfill contaminates
groundwater, a plume of contamination will occur. Wells in that
plume will be contaminated, but other wells, even those close
to the landfill, may be unaffected if they are not in the plume.
- Have the students write a report about
the sanitary landfill your community uses, including how the
leachate is collected and treated, and whether any groundwater
or surface water contamination problems have been found. This
could be a group project. There are many old town landfills,
so individuals or small groups could address different landfills.
- As part of the research for this project,
the students should contact some of the following organizations:
- - the local department of solid waste
- the New York State Dept. of Environmental Conservation
- the local planning board
- the local health department
- the local Environmental Management Council
- the regional office of the U.S. Geological Survey, for information
on aquifers and groundwater
- the Soil Conservation Service, for local soil data
- The students' research should address
questions such as the following:
- 1. Where are the local landfills?
(Plot them on a map.) How long will they continue to take waste?
- 2. Does the landfill have a leachate
collection system? If so, how is the leachate treated? What
other measures have been taken by the landfill operators to prevent
- 3. Have any water quality problems
(either groundwater or surface water) been identified in the
area surrounding the landfill?
- 4. Is there an aquifer near the landfill?
If so, is it used for any community water supplies? Where are
the nearest wells?
- 5. What is the depth of the water table
below the landfill? Are there any impermeable layers between
the landfill and underlying groundwater?
- 6. What water quality regulations apply
to the landfill operations? What types of water quality testing
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