TM 5-814-7
conductivity of the drainage layer material available, are
the EPA guidance document recommends use of a
presented in EPA SW-873, EPA SW-870 and EPA
granular layer above the drainage layer, if clean sand is
625/1-81-013.
used for the drainage layer, it will serve to preclude
e. Leak detection and leachate collection drains.
plugging and possibly eliminate the need for a filter cloth
or fabric.
As shown in figure 6-5, trench installations can be used
(3) The pipe used in leak detection and leachate
for leak detection drains in secondary clay liners.
collection systems must be of sufficient strength and
Projecting installations should be used for synthetic
thickness to withstand the pressures exerted by the
liners. Slopes for bedding should be no steeper than the
weight of the overlying waste, the cover materials, and
angle of repose of the drainage layers and all slope
any equipment to be used on the waste unit. Slotting will
breaks should be rounded. Collection drains over
reduce the effective strength of pipe and its ability to
synthetic liners should incorporate a 4-inch-minimum
carry loads and resist pipe deflection under loading. The
bedding of clean sand (SP) to satisfy requirements for
capacity of buried pipe to support vertical stresses may
liner protection. Drain rock used over synthetic liners
be limited by buckling and by the circumferential
should be rounded pea gravel. Geotextile fabrics might
compressive strength of the pipe.
Information on
be evaluated to serve as an alternative protective
deflection, buckling capacity and compressive strength
measure.
f. Leachate collection sump and riser. The
may be obtained from the pipe manufacturer.
(a) Even when correctly designed to withstand
current state-of-the-art in leachate collection system
waste loading, piping can fail from equipment loading
design uses sumps or basins at low points on the base
during construction or operation of the waste unit.
of the fill to which the leachate collection network
Moving loads result in impact loading one and one-half to
discharges. A riser pipe extending from the sump to the
two times greater than stationary loading. Therefore,
ground surface enables leachate removal. The lower
equipment should, if possible, not cross leachate
segment of the riser pipe in the drain rock of the sump is
collection drains installed in projecting installations or in
slotted, and can be connected to a slotted header pipe in
trenches with shallow cover. When equipment must be
the sump to allow a higher rate of flow to, and withdrawal
routed across a drain, impact loading should be
from, the riser pipe.
minimized by mounding material over the pipe to an
(1) The riser must be of a diameter that will
adequate depth to prevent pipe failures.
accommodate a pump suction line or submersible pump.
(b) Specific design procedures and examples
The riser pipe can be installed in a trench excavated in
used to determine loads resulting from the waste fill
the wall of the clay liner, or bedded in suitable soil on the
and/or construction equipment are provided in appendix
surface of the synthetic liner.
V.2 of SW-870.
(2) Leachate collection networks for landfills,
which must remain functional during the 30-year
6-5.
Surface water run-on and run-off control
postclosure period, should include pipe cleanouts
systems
extending from major collection drains to the ground
a. Regulatory requirements. Surface water run-
surface, to enable system inspection and/or cleaning.
on and run-off control systems are required for landfills,
g. Design considerations.
In designing a
waste piles and land treatment units and indirectly for
leachate collection system, one must consider resistance
surface impoundments. Regulatory requirements for
to chemical attack, prevention of clogging, and pipe
surface water control at land disposal facilities are
stability.
summarized in table 6-5. While federal regulations
(1) All components of leachate collection
require control systems for 24-hour, 25-year storms,
systems must be able to withstand the chemical attack
state regulations may require sized control for storms
which can result from waste or leachate. Plastic (PVC
with a return frequency up to 100 years. In such cases,
and polyethylene) and fiberglass piping are usually
the more stringent requirement should be considered in
selected for such systems; however, if solvents in the
sizing surface water run-on and run-off control facilities.
waste stream contain organics capable of attacking
The designer must also size collection and holding
collection pipes, sumps or risers, an alternative to the
facilities, and develop specific management procedures
use of plastic or fiberglass piping might be concrete or
to enable all run off from active disposal areas to be
cast iron. Any geotextile filter cloth or fabric used in the
retained for treatment prior to its evaporation or
leachate collection system shall be evaluated for its
discharge to natural drainage courses or back to an
ability to withstand attack from the hazardous waste and
approved hazardous waste facility.
the leachate generated from that waste.
b. Types of control systems. Run-on and run-
(2) The drainage layer, any geotextile filter cloth
off control systems at hazardous waste units utilize a
or fabric, drain rock, pipe slotting, and waste fines must
variety of structures for control of surface water,
be evaluated to determine the ability of the system to
including conveyance, barrier and control/retention
transmit leachate without clogging.
Although
systems.
6-14
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