CONSTRUCTION AND OPERATION
4-1. Construction Sequence.
c. Membrane liners are highly susceptible to
expansion and contraction during temperature
a. All trenches should be constructed as a series
changes, and must be laid in such a way as to avoid
of cells sized by the designer in the most cost
undue stress on the seams.
efficient manner. Cells should be divided by berms
d. Black liner material readily absorbs heat and
or other means, and storm water should be elimi-
can result in hazardous working conditions and bad
nated from the working portion of the landfill. The
seam construction. To avoid this, seaming should
purpose of this approach is to minimize--
not be done during hot periods when the
(1) The size of bottom and cap liners.
temperature exceeds 90 degrees F. Seaming is
(2) The quantity of excavation required.
generally done during morning hours after dew has
(3) The area of woodlands cleared. Efficient
evaporated. Also, in most locations it is best to
use of the landfill area should be maximized. The
schedule work in the spring or fall.
amount of initial excavation will be minimized
e. Liners should be held in place by anchor
because, while one cell is being filled with waste,
trenches, sand bags, or soil cover. Anchor trenches
the next cell in sequence is being partially exca-
are commonly used at the top of side slopes, but
vated. When the current working portion is com-
should not be compacted firmly. It is better for the
pleted, the liner system should be extended over the
liner to slip slightly than to cause stress. Methods of
newly excavated cells. Once the new cells become
anchoring a liner should be coordinated with the
the active cells, the cap system will be extended
over the completed cells.
f. If it is anticipated that a liner will be exca-
b. All of the first cell and approximately half of
vated and extended to cover a new cell at a later
the second cell will be excavated at the outset of
date, a minimum 5-foot edge of liner material
the project. (See fig 4-1). The leachate collection
should be protected to provide a clean, smooth
system and landfill liner will be installed in the
surface for future seaming. One method of doing
this is to sandwich the end between two pieces of
c. After the next cell is excavated and before the
liner before it is buried under a berm or anchor
active cell is full, the composite liner and leachate
collection systems will be extended over the new
g. Require the contractor to write the name of
cell. The anchors will be excavated and the liners
the seam installer along the side of the seam. This
connected to form a continuous liner system. If
will improve the quality of work.
berms are used, the berms will be left in place to
h. Seaming of wet membrane surfaces will not
separate leachate in each cell. Once the next cell
becomes the active cell, all completed cells will be
covered with the final cap and the gas venting
4-3. Construction Quality Assurance.
system will be installed. The cap liner and gas
a. All piping systems and compacted clay liner
venting system for each cell will connect to that of
the adjacent cells to form a continuous system. The
shall be inspected and tested in accordance with
driveway into the landfill will be moved as needed
applicable standards. The construction contractor
to accommodate construction.
shall be required to submit field installation direc-
tions for the flexible membrane liner as supplied by
4-2. Construction Practices.
the manufacturer, in addition to manufacturer
Important considerations in construction are:
quality control guidelines. The contractor shall
a. Construction equipment must never operate
follow the manufacturer's guidance during instal-
directly on or above a landfill liner and/or drainage
lation and inspection. All seams shall be visually
layer. All soil and layers on waste must be pushed
inspected by Government personnel in addition to
ahead of equipment as operations progress. Even
b. Nondestructive tests are available for various
foot traffic should be kept to a minimum on mem-
brane liners, and heavy boots should not be worn.
types of liner seams. One popular method of
b. A good access road must be maintained in the
constructing a seam is to solvent weld two parallel
trench with additional subbase installed between the
seams together leaving an air space between them.
This allows an air pressure test to be conducted