Closing an Open Dumpsite and Shifting - International ...

3. To intercept leachate movement below ground, an interceptor trench, cutoff wall, and
collection pipes may be constructed downgradient of the disposal site.
These measures do not ensure that ground or surface water contamination near the site will
not occur. They are only simple and inexpensive remedial measures that are intended to
reduce as much as practical, the potential contamination that may occur.
The collected leachate is usually treated using biological or chemical methods (or a
combination of both). Biological methods involve letting the wastewater pass through a series
of stabilization ponds or the use of vegetation to absorb or digest the pollutants, while
chemical methods involve the use of chemicals to treat leachate. The latter is less preferred
since it is more costly. However, it maybe implemented if the situation warrants because of
limited space for the treatment ponds, high organic characteristics of the influent, and if the
chemicals are available and affordable. Leachate treatment is discussed more thoroughly
under sanitary landfills in Subsection C.5 of Chapter IX, Part 2.
E. Gas Management Systems
Landfill gas, such as methane and carbon dioxide, will continue to be generated as long as
waste decomposition occurs. Methane is a highly combustible gas and may cause explosions
if it accumulates in an enclosed structure such as houses and buildings. Thus, depending on
the environmental sensitivity of the area, it may be necessary to collect the gas and vent it
freely, flare it, or recover it for energy use. Extracting gas from a waste fill has the additional
advantage of reducing the concentration of various chemicals in the leachate thereby
improving its quality. This is one way to lessen the impact of the leachate on area ground and
surface waters. Gas extraction, however, entails a significant capital investment, and for
many LGUs may not be an option.
Vent pipes may be made of perforated polyvinyl chloride (PVC), bamboo, or discarded oil
drums welded together at the edges. Figure 12 shows a closed disposal area with vent pipes
for gas management.
vent pipes
upgradient
groundwater
monitoring well
groundwater
flow
Figure 12. Vent Pipe and Monitoring Well Installation
18
downgradient
groundwater
monitoring well