POWER July 2015 - 29

ENVIRONMENTAL ISSUES
1. Installing liner geosynthetics. Courtesy: Golder Associates Inc.
other configurations for leachate removal,
but this is the most common approach.
Having the landfill developed in cells
means that only a limited part of the total area
is exposed to precipitation at any one time.
This has the effect of reducing the amount
of potential leachate that must be treated/
disposed.
The size of the cell depends partly on the
rate of CCR generation and disposal. Generally,
the cells would be sized such that each
will have a three- to five-year lifespan. After
a cell is full, it is capped with a final closure
cap, often including an impervious geomembrane,
to minimize or prevent inflow of
stormwater that would contribute to ongoing
leachate generation (see opening photo).
It's possible to further reduce the volume
of leachate to be treated by dividing each cell
into sub-cells, during initial filling when the
entire cell " floor " is exposed to rainfall, instantaneously
becoming leachate as soon as
filling commences.
To see how this helps, visualize a newly
(LCRS, Figure 1) and limits the maximum
allowable head of leachate buildup atop of
the liner system to less than 30 centimeters
(12 inches). This head restriction requires the
regular and continuous removal of leachate
from the landfill liner system. The CCR
Rule, however, provides no further requirements
for the management of leachate after it
is removed from the landfill.
For CCR landfills, environmental regulators'
biggest concern about leachate from
CCR is heavy metals, including arsenic,
mercury, and cadmium. This means that utilities
will do well to look to methods that have
helped municipal landfill operators manage
leachate in a way that meets regulations and
reduces the quantity generated. Methods for
managing CCR landfills, developed in states
where these have long been required, can
also be helpful.
Next are some of the principles learned in
designing, building, and operating leachate
management systems for both MSW and
CCR landfills.
Less Leachate Produced = Less
Leachate to Manage
Leachate management and disposal can be
the single largest operational expense at a
landfill. One of the key principles of leachate
management is to keep the " problem " (and
July 2015 | POWER
cost) as small as possible. Producing less
leachate means lower costs, fewer liabilities,
and fewer things to go wrong.
One principle of good landfill management
that reduces leachate is to develop the
landfill in " cells " -subsections of the landfill,
each underlain by a regulatory-required
liner system, which often includes an impervious
barrier such as a high-density polyethylene
(HDPE) layer. Above that barrier
started cell, several acres in size, which has
only a thin layer of CCR over part of the cell
" floor. " Rain or snow falling on the cell would
come into contact with the CCR quickly and
produce a large volume of liquid that must
be considered leachate. The large volume of
liquid also carries the risk of overwhelming
the pump used to remove leachate for treatment.
This could also put the landfill owner
in breach of the CCR Rule's restriction on
maximum allowable head atop the liner.
By building berms within the cell to create
several subcells, the infilling with CCR can
be limited to only a subcell within the larger
cell. This means that any precipitation falling
on other subcells that do not yet contain
CCR can be considered stormwater rather
than leachate and can be sent to the facility's
Leachate management and disposal can
be the single largest operational expense
at a landfill.
layer is the LCRS, often a high-flow drainage
layer, which intercepts any infiltration
that percolates through the waste, or CCR in
this instance.
Each cell has an engineered low point, or
" sump, " into which leachate accumulates. A
pump, placed into the sump through a riser
pipe, removes the leachate for treatment or
disposal (Figures 2 to 4). Certainly, there are
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stormwater management system. This greatly
reduces the handling costs involved.
In addition, smaller subcells reach a greater
depth of CCR more quickly as they are
being filled, so that precipitation falling on
them has a chance to percolate more slowly
through the ash, and the pump is less likely to
be overwhelmed by a heavy storm.
There are several other operational consid29
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POWER July 2015

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