TM 5-814-5
trenches that are placed parallel throughout the
ation should be given to making the penetrating
liner, at a spacing and slope determined by the
material the same as the liner material. To avoid a
designer. Collection laterals must be designed to
penetration, riser pipes with a sump pump at the
discharge to treatment and/or disposal facilities. In
bottom can be laid on the side slopes above the
addition, laterals should be spaced so that if one
liner. If a manhole is placed inside the liner a bed of
lateral is totally blocked, liquid can be removed
soil must be placed between the manhole and the
through an adjacent lateral.
liner. All manholes must be vented to release
(4) Maintenance.
landfill gases. (See figs 3-9 and 3-10.)
(a) One of the most important considerations
(b) It is extremely important to design a
is to design the system to facilitate inspection and
collection system to avoid clogging. For example,
maintenance. There should be access to all parts of
settling of solids can be avoided by properly
the system. This includes the placement of
selecting grain size distribution in the filter material
manholes and cleanouts so that maintenance
to exclude solids. As the permeability of the drainer
equipment can reach any length of pipe. The design
layer decreases the slope must increase. If a
should consider minimum pipe sizes, distance
sufficient quantity of permeable material is not
between access points, and maximum pipe bends
available, a synthetic geonet or drainage net can be
accessible by cleaning equipment. Pipes and
used. The drainage layer should be at least one foot
manhole penetrations through the liner must be
thick and be composed of fine gravel and course
minimized. When the liner is penetrated, consider-
sand with a minimum hydraulic conductivity of 1 x
3-7
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