TM 5-814-7
sophisticated instrumentation is available for detection
ments, such as those shown in chapter 5 of TM 5-820-2.
systems, direct collection in a porous medium, with
(2) Nondegradable synthetic filter cloths and
removal through slotted pipes, is a simple and reliable
geotextile fabrics have also been used to replace
method. Design details for such a system are similar to
granular materials in subdrain systems. However, the
those for leachate collection and removal systems.
long-term performance of such materials has not been
c.
Components of the leachate collection
firmly established; clogging and filter cake formation can
system.
reduce the perpendicular permeability of both geotextiles
Specific regulations concerning leachate
and filter cloths, and overburden pressures can
systems are summarized in table 6-4. EPA guidance
significantly decrease in-plane permeability of geotextile
documents recommend that the leachate collection
fabrics.
system consist of a drainage layer at least 1-foot-thick
d. Leachate collection pipe. Leachate collection
with a hydraulic conductivity > 1 x 10-3 cm/sec, and a
pipe networks should consist of slotted or perforated
minimum slope of 2 percent. When installed over a
drain pipe bedded and backfilled with drain rock. The
secondary clay liner with hydraulic conductivity of 1 x 10-
network should include collection pipes, installed around
7 cm/sec, such a system provides the four-order-of-
the base of the fill and across the base. Layouts must
magnitude difference in permeability known to
include base liner slopes >, 2 percent, pipe grades
significantly increase drainage efficiency.
>0.005, and pipe spacing determined for the unit. All
(1) A drainage layer of clean sand, classified by
pipes should be joined and, where appropriate, bonded.
USCS as SP or SW (with less than 5 percent passing the
(1) Collection pipes must be adequately sized
No. 100 sieve), and free of rock, fractured stone, debris,
and spaced to minimize the leachate head on the liner
and cobbles, will also satisfy the EPA requirement for a
system.
Layouts which incorporate 4-inch-diameter
minimum 6inch protective layer over synthetic liners. A
pipes on 50to 200-foot centers are considered adequate
sand layer or filter cloth should be provided over the
by the EPA.
drainage layer if drainage rock is used to prevent
(2) Procedures to evaluate and establish the
infiltration of fines from the waste and subsequent
spacing for collection drain pipes, based upon the
clogging of the drainage layer. Sands which act as filters
anticipated maximum infiltration rate and the hydraulic
must
meet
filter
graduation
require-
Table 6-4. Requirements for Leachate Collection and Removal Systems
Section of 40 CFR 264 Describing Requirements
K
L
M
N
Design Requirements
Surface Impoundments
Waste Pile
Land Treatment
Landfill
A leachate collection and removal system im-
mediately above the liner that is designed,
con- structed, maintained, and operated to
collect and remove leachate from the unit
The Regional Administrator will specify
design and operating conditions in the permit
to ensure that the leachate depth over the
liner does not exceed 30 cm (one foot) The
leachate collection and removal system must
be constructed of materials that are:
NA
264.251(aX2)
NA
264.301(aX2)
Chemically resistant to the waste
managed in the unit and the leachate
expected to be generated; and Of
sufficient strength and thickness to pre-
vent collapse under the pressures
exerted by overlying wastes, waste cover
materials, and by any equipment used at
the unit; and Designed and operated to
function without clogging through the
scheduled closure of the unit
NA
264.254(bX4)
NA
264.303(bX4)
While in operation, leachate collection
systems should be inspected weekly and
after storms for the presence of leachate and
proper functioning of the systems
After closure, continue to operate the
no longer detected Adapted from 40 CFR 264
NA
NA
NA
264.310(bX3)
6-12
Previous Page
