United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/058 Sept. 1986
c/EPA Project Summary
Avoiding Failure of Leachate
Collection and Cap Drainage
Systems
Jeffrey Bass
Failure, caused by a variety of mecha-
nisms, is common to drainage systems
of all kinds. Leachate collection and cap
drainage systems, which remove ex-
cess liquid from hazardous waste land
disposal facilities, are no exception.
Failure of these systems, however, may
be a greater cause for concern than fail-
ure, for example, of agricultural
drainage systems. This is especially
true for leachate collection systems at
hazardous waste disposal facilities. Un-
detected failures may cause leachate to
build up on top of the liner. This can
lead to failure of the liner system and
contamination of groundwater.
Furthermore, failures which are de-
tected may be difficult to repair, and
replacement is no longer a simple last
resort since excavation of hazardous
wastes would be required. Information
is presented on those mechanisms
which may cause leachate collection'
and cap drainage systems failure.
Furthermore, information on design,
construction, inspection, and mainte-
nance for these systems is presented in
order to minimize the potential of fail-
ure. Techniques to repair a failed sys-
tem are also described.
This Project Summary was devel-
oped by EPA'» Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented In a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
The document summarized here was
written to provide general guidance to
design engineers, facility operators, and
state and Federal regulatory officials.
The document is not a comprehensive
design and operations manual for
leachate collection and cap drainage
systems. Rather, it summarizes current
knowledge and experience regarding
potential failure mechanisms and pre-
sents information on factors to consider
in design, construction, inspection,
maintenance and repair of such sys-
tems. Detailed design and operation
plans for leachate collection and cap
drainage systems at a specific facility
should be prepared by a qualified de-
sign engineer based on site-specific
conditions.
Emphasis is placed throughout the
document on avoiding failure of
leachate collection systems at haz-
ardous waste facilities. Most of the in-
formation presented for leachate collec-
tion systems can also be applied to cap
drainage systems, since the basic com-
ponents of the two systems are similar.
Failure of cap drainage systems, how-
ever, is less critical than failure of
leachate collection systems since the
cap drainage system is accessible and
therefore can be more readily main-
tained or repaired. Cap drainage sys-
tems are discussed separately in this
document only when the information
presented is significantly different from
the discussion of leachate collection
systems.
Failure Mechanisms
Leachate collection and cap drainage
systems can fail or clog through a vari-
ety of physical, chemical, biological,
and biochemical mechanisms. Some of
-------
the most common failure mechanisms
are those which lead to system clog-
ging. Clogging is defined as the physical
buildup of material in the collection
pipe, drainage layer, or filter layer to the
extent that leachate flow is significantly
restricted. Other failure mechanisms
which do not involve clogging include
differential settling and deterioration of
the collection pipe because of chemical
attack or corrosion. Failure may also oc-
cur because the design capacity is ex-
ceeded. In this case liquid is not ade-
quately removed from the system, even
though system components may not be
physically blocked.
As a first step in this project, confir-
mation testing was conducted to verify
that the failure mechanisms described
above are indeed possible for leachate
collection and cap drainage systems. A
three-step approach was utilized to con-
firm the failure mechanisms:
Step 1: Confirmation by experience;
Step 2: Confirmation by first princi-
ples;
Step 3: Confirmation by laboratory
investigation.
The results of the three-step confir-
mation testing process indicate that all
the failure mechanisms should be con-
sidered in the design, construction and
operation of leachate collection and cap
drainage systems.
Design
Leachate collection and cap drainage
systems must be designed to meet leg-
islated and regulatory performance
standards and design specifications.
For example, a leachate collection sys-
tem must be designed to ensure that the
leachate depth over the liner does not
exceed 30 cm (1 foot). In order to meet
this requirement, as well as other re-
quirements specified in the regulations,
the design must address the various
components of the leachate collection
or cap drainage system. These compo-
nents include the drainage layer, collec-
tion pipe network, filter layer, and asso-
ciated appurtenances (e.g., sumps,
pumps, manholes).
Drainage layers generally consist of
granular soils such as coarse sand
which provide sufficient hydraulic con-
ductivity for leachate flow and at the
same time protect the underlying syn-
thetic liner. The particle-size distribution
of the drainage layer must be selected
to allow liquid transport, prevent punc-
ture of the underlying synthetic liner,
and minimize migration of filter layer
materials into the drainage layer.
Increasingly, geotextiles are being pro-
posed and used as a substitute for gran-
ular material in portions or all of the
drainage layer. Geotextile materials in-
clude needlepunched, non-woven poly-
propylene or polyester fabric and
polyethylene grids. Combinations of
these materials may also be used, for
example, placing a grid between two
layers of geotextile fabric.
The collection pipe network of a
leachate collection system drains, col-
lects and transports leachate through
the drainage layer to a collection sump
where it is removed for treatment or dis-
posal. The pipes also serve as drains
within the drainage layer to minimize
mounding of leachate in the layer. In a
cap drainage system, pipes are used to
collect and transport water from the
drainage layer to surface drainage facil-
ities. Pipes used to collect and convey
leachate must be structurally able to
withstand the loading of the overlying
filter and drainage layers, wastes, cap
materials, and vehicular traffic that may
move over the disposal cell. These
pipes must be sized and spaced to re-
move liquid from the drainage layer
without causing any significant back-
up. In a leachate collection system, the
collection pipes must be designed to
carry the leachate without allowing
more than 30 cm (1 ft) of leachate
buildup within the drainage layer.
The filter layer is used above the
drainage layer in both leachate collec-
tion and cap drainage systems to trap
fines and prevent waste and other solid
materials from entering the drainage
layer while allowing the passage of liq-
uid. Information regarding physical
characteristics of the fines and the antic-
ipated loading rates is needed to formu-
late design criteria for constructing a fil-
ter that will continue to function
through the design life of the drainage
system. Typically, filter layers may ei-
ther be granular or a geotextile. Granu-
lar filters consist of a soil layer of combi-
nation of soild layers having a coarser
gradation in the direction of seepage.
Geotextiles may also be used as filters
and are either woven or non-woven.
Woven geotextiles are similar to
screens which have uniform sized open-
ings whereas the non-woven variety
consists of fibers placed in a random
orientation. Both types can be made
with high permeability relative to most
soils while having an opening or mesh
size sufficiently small to prevent soil
particle movement.
Appurtenances associated with
leachate collection systems include
sumps, pumps, manholes, discharge
lines, and liquid-level monitors. All of
these items are important factors in en-
suring the performance of leachate col-
lection and cap drainage systems and
should be designed in accordance with
established engineering practice and
where applicable, manufacturers' speci-
fications.
Construction
Construction of leachate collection
and cap drainage systems must be per-
formed in accordance with the design
specifications. If specific design proce-
dures are identified in the bid package,
then the construction contractor must
follow these procedures. Where perfor-
mance standards alone are specified,
then the construction contractor is al-
lowed flexibility in meeting that stand-
ard.
In order to ensure that the construc-
tion of the leachate collection or cap
drainage system is proceeding in ac-
cordance with the design, the haz-
ardous waste land disposal facility
owner may employ the design engi-
neer, or an independent party, to moni-
tor and report on the quality of con-
struction. Such activities do not
guarantee that the facility will not fail.
Rather, construction quality assurance
is a tool to ensure, with a reasonable
degree of certainty, that the completed
systems meet or exceed the specified
design.
Construction quality assurance (CQA)
serves to detect variations from design,
and to provide for suitable corrective
measures before wastes are accepted at
the facility. Without proper construction
quality assurance, problems with the
leachate collection or cap drainage sys-
tem that are caused by construction
may not be discovered until the system
fails during operation.
A Construction Quality Assurance
Plan is the written document describing
the specific approach to be followed in
attaining and maintaining consistently
high quality in the construction of a haz-
ardous waste disposal facility so that
the completed facility meets or exceeds
the specified design. While the overall
content of the CQA plan will depend on
the site-specific nature of the proposed
facility, specific elements that may be
included in the plan are:
• Responsibility and Authority—The
responsibility and authority of all or-
ganizations and key personnel in-
volved in permitting, designing, and
-------
constructing the hazardous waste
land disposal facility should be de-
scribed fully in the plan.
• CQA Personnel Qualifications—The
qualifications of the CQA officer and
supporting inspection personnel
should be presented in the plan to
demonstrate that they possess the
training and experience necessary to
fulfill their identified responsibilities.
• Inspection Activities—The observa-
tions and tests that will be used to
monitor the installation of the
leachate collection system should be
summarized in the plan.
• Sampling Requirements—The sam-
pling activities, sample size, sample
locations, frequency of testing, accep-
tance and rejection criteria, and plans
for implementing corrective mea-
sures as addressed in the project
specifications should be presented in
the plan.
• Documentation—Reporting require-
ments for sampling activities should
be described in detail in the plan. This
should include such items as daily
summary reports, inspection data
sheets, problem identification and
corrective measures reports, block
evaluation reports, design accep-
tance reports, and final documenta-
tion. Provisions for the final storage
of all records also should be pre-
sented in the plan.
Inspection
Leachate collection and cap drainage
systems must be inspected to ensure
that the constructed system continues
to operate according to design specifi-
cations. Undetected failure of drainage-
system components can lead to buildup
of excess liquid over the liner, liner fail-
ure, and/or contamination of ground-
water. Inspections serve to discover
failed components of the system as well
as to determine where failure mecha-
nisms are active. In addition, inspection
of the drainage system can be useful in
discovering problems with other com-
ponents of the disposal facility, espe-
cially the liner. Reduced outflow from
the drainage system, for example, may
indicate a variety of problems with the
drainage system or a leaky liner.
Federal regulations under the Re-
source Conservation and Recovery Act
require the leachate collection systems
to be inspected. While in operation, a
landfill, for example, "must be in-
spected weekly and after storms to de-
tect evidence of the presence of
leachate in the proper functioning of
leachate collection and removal sys-
tems, where present."
There are no similar Federal require-
ments for inspection of cap drainage
systems at closed facilities, although
the "integrity and effectiveness of the
final cover" must be maintained. This
implies the need for inspection to make
sure that the cap drainage system is
functioning as intended.
State regulatory agencies may make
requirements for inspecting leachate
collection or cap drainage systems in
addition to the Federal requirements.
Requirements vary from state to state,
and often from facility to facility within a
state. The Wisconsin Department of
Natural Resources (WIDNR), for exam-
ple, does not have a standard set of re-
quirements for the inspection of
leachate collection systems. Typical re-
quirements, based on WIDNR permit
approvals and conversations with
WIDNR staff include:
• cleaning the collection pipe after con-
struction and after the first lift of
waste is placed to verify continuity of
the lines (conducted with Department
representative present);
• field-checking collection pipe for
clogging at least annually;
• daily recording of leachate levels in
leachate collection tanks;
• quarterly recording of levels in
leachate-level wells installed at site
closure.
Inspections required at the Federal
and state levels are intended to provide
enough information to the regulatory
agencies to ensure that the leachate col-
lection or cap drainage system is per-
forming adequately. They also provide
the facility owner with performance
data. Guidance on how to conduct the
required inspections, however, is gen-
erally not given; it is left up to the facility
owner to specify in the permit applica-
tion how the requirements will be met.
Two types of inspection procedures
may be used. The first, Regular or Peri-
odic Inspections, includes visual inspec-
tion, monitoring leachate level over the
liner, indicators of system failure or
clogging, and direct inspection meth-
ods. The second section, Special In-
spections, includes cleaning to verify
the continuity of system construction
and after the first lift of waste is placed,
and methods to locate and diagnose
leachate collection system problems.
Maintenance
Maintenance of leachate collection
and cap drainage systems is needed to
ensure that liquid will be effectively re-
moved from over the liner throughout
the lifetime (and post-closure care pe-
riod) of the facility. There has been little
experience, however, with maintenance
of these systems. Typically, collection
pipes are maintained only when prob-
lems are noted; that is, maintenance
techniques are used as repair measures
rather than for system maintenance.
The notion that the need for preven-
tive maintenance is obviated by the abil-
ity to repair these systems seems short-
sighted for at least two reasons. First,
historical evidence indicates that drain-
age systems of all types require preven-
tive maintenance to operate at maxi-
mum efficiency and to prolong service
life. Second, some failure mechanisms
may be extremely difficult to stop once
the pipe is clogged. New iron deposits,
for example, may be easily removed by
preventive maintenance techniques
even though the effect of the deposit
may not yet be noticeable. However,
mature deposits which do affect
leachate flow may be extremely diffi-
cult, if not impossible, to remove by
standard maintenance or repair meth-
ods.
The basic objectives of a maintenance
program are:
• to keep the system operating near
maximum efficiency;
• to obtain the longest operating life of
the system; and
• to accomplish the above two objec-
tives at minimum cost.
Underground drainage systems, in
general, require minimal maintenance.
The amount of maintenance required
for a leachate collection or cap drainage
system will vary depending on design,
construction quality, operating proce-
dures, and leachate characteristics
(quantity and quality). Collection pipes,
for example, may need to be cleaned
several times a year if the leachate has
a high sediment load or if the system is
highly susceptible to other forms of
clogging. Alternatively, annual cleaning
may only be a safety measure at facili-
ties where clogging mechanisms are
not active. At all facilities, regular
maintenance of mechanical equipment
(e.g., pumps) is required. Further re-
search is needed to determine the cost-
effectiveness of preventive mainte-
nance in meeting the above objectives.
Mechanical and hydraulic methods
for cleaning collection pipes are dis-
cussed in this section. These techniques
were developed for maintenance of
-------
sewer pipes. Experience with these
techniques for leachate collection sys-
tem maintenance is limited. Two major
constraints on using these techniques
for leachate collection systems are
more limited access (e.g., risers used in-
stead of manholes, manholes sur-
rounded by waste) and the use of plastic
pipe.
Operator safety is also of great con-
cern for leachate collection system
maintenance because of the potentially
hazardous nature of the leachate.
Repair
Leachate collection and cap drainage
systems must be repaired when failure
mechanism systems malfunction or fail.
Failure occurs when the system be-
comes unable to remove leachate (ore
precipitation) and allows liquid to accu-
mulate over the liner. Maintenance pro-
cedures are used to address failure
mechanisms before actual failure of the
system occurs. Repair procedures are
used to correct the problem after it oc-
curs, thus allowing liquid to be removed
from over the liner.
Leachate collection and cap drainage
systems can fail as a result of problems
in the collection pipe, filter layer,
drainage layer and other system com-
ponents, including sumps and pumps.
Problems with components of the sys-
tem that are buried under the waste are
of particular concern since access to
these components is difficult. Evidence
of system failure includes:
• no flow out of the system when flow
is expected;
• high leachate levels in portions of the
facility; and
• leachate ponding or seepage at the
surface of the waste mass (or cap).
A variety of repair options are avail-
able to correct problems with failed
leachate collection or cap drainage sys-
tems. Maintenance techniques can be
used as repair methods primarily for
clogged collection pipe. Chemical meth-
ods may also be useful to remove (dis-
solve) material clogging a collection
pipe and may be applicable to address
clogging of the drainage or filter layer.
Finally, the failed portion of the system
can be replaced with a new system.
Selection of the appropriate repair
option depends on a number of factors.
Location of the problem influences the
choice considerably. Some repair op-
tions, for example, are-applicable only
to the collection pipe and would not be
of use for a clogged drainage layer. The
type and extent of the problem are also
important. Clogging of the drainage
layer around the collection pipe might
be addressed by chemical methods
while chemical methods would not be
applicable to extensive clogging of the
drainage or filter layer away from the
pipe. Also, the physical and chemical
characteristics of the clogging material
are important in determining the effec-
tiveness of a repair option. In general,
maintenance techniques and chemical
methods are applicable to problems in
and around the immediate area of the
collection pipe, and replacement tech-
niques are required for problems away
from the pipe area.
Landfill design and waste characteris-
tics must also be considered in selecting
the appropriate repair option. Mainte-
nance techniques, for example, may not
be the best option for a clogged collec-
tion pipe if access to the pipe was not
provided in the landfill design. Simi-
larly, excavation and replacement may
depend on the number of lifts of waste
which have been placed and how
"dangerous" those wastes are (e.g., ex-
plosive, reactive, volatile, unknown
composition).
In some cases, the effect of leachate
collection system failure can be elimi-
nated by significantly reducing leachate
generation. This would be accom-
plished, for example, by closing the site
with a final cover to control the water
balance at the site. Decreasing the
quantity of precipitation and ground-
water flow, and increasing runoff, sur-
face storage and evapotranspiration
can also be used to reduce the quantity
of water available for leachate genera-
tion at the site.
Jeffrey M. Bass is with Arthur D. Little, Inc., Cambridge, MA 02140.
Jonathan Q. Herrmann is the EPA Project Officer (see below).
The complete report, entitled "Avoiding Failure of Leachate Collection and Cap
Drainage Systems," (Order No. PB 86-208 733/AS; Cost: $16.95. subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
-------
._£
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES P
EPA
PERMIT No. G-3!
Official Business
Penalty for Private Use $300
EPA/600/S2-86/058
0000329 PS
U S ENVIR PROTECTION
* U.S. GOVERNMENT PRINTING OFFICE; 1986 — 846-017/47
------- |