PB84-110550
Potential Clogging of
Landfill Drainage Systems
Little (Arthur D.), Inc., Cambridge, MA
Prepared for
Municipal Environmental Research Lab,
Cincinnati, OH
Oct 83
U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
MTTS
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EPA-600/2-83-109
October 1983
PD6U-11G550
POTENTIAL CLOGGING OF LANDFILL DRAINAGE SYSTEMS
by
Jeffrey M. Bass
John R. Ehrenfeld
James N. Valentine
Arthur D. Little, Inc.
Cambridge, Massachusetts 02140
Contract No. 68-01-5949
Project Officer
Robert Landreth
Solid and Hazardous Waste Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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TECHNICAL REPORT DATA
(Ptca e read Instruc:c ns on the reverze be/ore completing/
i REPORT NO. 2.
EPA—600/2—83—109
3 RECIPIENTS ACCESSION NO
PB8I. 11 0 5 50
4. TITLE AND SU8TITLE
POTENTIAL CLOGGING OF LANDFILL DRAINAGE SYSTEMS
S REPORT DATE
October 1983
6.PERFORMINGORGANIZATIONCO OS
REPORT NO.
7 AUTNOM(S)
Jeffery M. Bass, John R. Ehrenfeld, James N. Valentine
8. PERFORMING
PROGRAM ELEMENT NO.
9 PERFORMING ORGANIZATION NAME AND ADDRESS
A. 0. Little, Inc.
Acorn Park
Cambridge, Massachusetts 02140
10.
CBRD1A
11. CONYMACY/GRANT NO
68-01-5949
12. SPONSORING AGENCY NAME AND AOORESS
Municipal Environmental Research Laboratory——Gin., OH
ORD, U. S. Environmental Protection Agency
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final 10/82 — 12/82
14.SPONSORINGAGENCYCOOE
EPA/600/14
15. SUPPLEMENTARY NOTES
Robert E. Landreth, Project Officer, 513/684—7871
1 A8S CTpotential clogging of landfill drainage systems was investigated, with
particular emphasis on hazardous waste sites. The study accomplished five
basic tasks: (1) to provide general background on the subject of drain
clogging, (2) to examine the potential for clogging in leachate collection
systems, (3) to investigate some cemented materials found in a drain at a
landfill in Boone County, Kentucky, and to determine possible causes, (4) to
identify preventive or remedial techniques for drain clogging, and (5) to
identify avenues of research and development that might minimize the
likelihood or impact of clogging.
Study results indicate that clogging is likely to occur in a probabilistic
manner during the active and post-closure operational lifetime of a hazardous
waste landfill, but preventive and remedial techniques can be used to avoid or
mitigate clogging. Preventative methods (including increased safety factors
or redundancy in design, monitoring, periodic inspection, and maintenance) are
far superior to remedial techniques. Repair or replacement is expensive and
potentially dangerous in the hazardous environment at secure landfills.
Present regulations for hazardous waste landfills provide no guidance on
engineering, design, or operational practices to prevent clogging or remedy a
i ni 11 g KEY WORDS ANO DOCUMENT ANALYSIS
a. OESCRIP1 ORS
b.IOENTIFIERS/OPEN ENDED TERMS
C. COSATI F eid/Croup
18. DISTRI8’JTION STATEMENT 19. SECURITY CLASS (TIlLS Reporr
RELEASE TO PUBLIC UNCLASSIFIED
20. SECURITY CLASS (ThLSpCf I
UNCLASSIFIED
PA Fo ,m 2220—) (Ri’. 4—77) • CVI0U3 IDITION 1$ 0810LC1I
i
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D I SCLAIMER
The information in this document has been funded wholly or in part by the
United States Environmental ProtectIon Agency under Contract No. 68—01—5949
to Arthur D. Little, Inc. It has been subject to the Agency’s peer and
administrative review, and it has been approved for publication as an EPA
document. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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FOREWORD
The U.S. Environmental Protection Agency was created because of
increasing public and government concern about the nation’s environment and
its effect on the health and welfare of the American people. Noxious air,
foul water, and spoiled land are tragic testimonies to the deterioration of
our natural environment. The complexity of that environment and the
interplay of its components require a concentrated and integrated attack on
the problem.
Research and development is that necessary first step in problem
solution; it involves defining the problem, measuring its impact, and
searching for solutions. The Municipal Environmental Research Laboratory
develops new and improved technology and systems to prevent, treat, and
rianage wastewater and solid and hazardous waste pollutant discharges from
municipal and community sources, to preserve and treat public drinking water
supplies, and to minimize the adverse economic, social, health, and aesthetic
effects of pollution. This publication is one of the products of that
research and provides a most vital communications link between the researcher
and the user community.
This document examines the potential for clogging of leachate collection
systems at both sanitary and hazardous waste landfills, and discusses
appropriate preventive and remedial measures.
Francis T. Mayo
Director
Municipal Environmental Research
Labora tory
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ABSTRACT
The p tential clogging of landfill drainage systems was investigated,
with particular emphasis on hazardous waste sites. The study accomplished
five basic tasks: (1) to provide general background on the subject of drain
clogging, (2) to examine the potential for clogging in leachate collection
systems, (3) to investigate some cemented materials found in a drain at a
landfill in Boone County, Kentucky, and to determine possible causes, (4) to
identify preventive or remedial techniques for drain clogging, and (5) to
identify avenues of research and development that might minimize the
likelihood or impact of clogging.
Study results indicate that clogging is likely to occur in a
probabilistic manner during the active and post—closure operational lifetime
of a hazardous waste landfill, but preventive and remedial techniques can be
used to avoid or mitigate clogging. Preventive methods (including increased
safety factors or redundancy in design, monitoring, periodic inspection, and
maintenance) are far superior to remedial techniques. Repair or replacement
is expensive and potentially dangerous in the hazardous environment at secure
Landfills. Present regulations for hazardous waste landfills provide no
guidance on engineering, design, or operational practices to prevent clogging
or remedy a malfunctioning system.
This report was submitted in fulfillment of Contract No. 68—01—5949 by
Arthur D. Little, Inc. under the sponsorship of the U.S. Environmental
Protection Agency. The report covers the period 10/1/82 to 12/31/82, and
work was completed as of 12/31/82.
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CONTENTS
Section Page
FOREWORD iii
A BSTRACT iv
ACKNOWLEDGEMENT vi
1.0 INTRODUCTION 1
2.0 CONCLUSIONS 3
3.0 RECO 1MENDAIIONS 5
4.0 BACKGROUND 7
Introduction 7
EPA Permitting Standards 7
Design of Leachate Collection Systems 9
Leachate Characteristics 9
Relevant Experience 11
5.0 MECHANISMS FOR CLOGGING 14
Introduction 14
Physical Mechanisms 20
Chemical Mechanisms 21
Biochemical Mechanisms 22
Biological Mechanisms 23
Analysis of Deposits Found at Boone County 24
Landfill
6.0 POTENTIAL FOR CLOGGING AT HAZARDOUS WASTE LANDFILLS 32
Design Factors 32
Operational Factors 33
Waste/Leachate Factors 33
Condition and Event Factors 33
Relative Potential For Clogging 33
7.0 PREVENTION AND REMEDIES 36
Prevention 36
Remedies 40
REFERENCES 41
BIBLIOGRAPHY 42
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ACKNOWLEDGEMENTS
Arthur D. Little, Inc. (ADL) prepared this document for the EPA ’s Office
of Research and Development, Municipal Environmental Research Laboratory in
fulfillment of Contract No. 68—01—5949. Robert Landreth was the Project
Officer, and his contributions to the report are gratefully acknowledged.
Jeffrey Bass, John Ehrenfeld, and James Valentine were the principal
contributors for ADL. Raymond Cornish and Stephen Spellenburg assisted Mr.
Valentine in the analysis of the gravel sample from Boone County Test Cell
i1.
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SECTION 1
INTRODUCTION
Clogging caused by a variety of mechanisms is common to drainage systems
of all kinds——agricultural irrigation, sanitary landfills, septIc system
leach fields, etc. Concern is particularly great over the potential clogging
of leachate collection systems in hazardous waste landfills. Not only are
the consequences of failure much higher at a hazardous waste site, but
excavation and replacement are no longer simple last resorts.
In response to this concern, this report investigates the potential
clogging of landfill drainage systems with emphasis on hazardous waste sites
in particular. The study was designed to accomplish the following tasks:
o To provide general background on the subject or drain clogging,
o To examine the potential for clogging in hazardous waste leachate
collection systems,
o To investigate cementacious materials found in gravel around a drain
at a U.S. Environmental Protection Agency (EPA) demonstration
sanitary landfill in Boone County, Kentucky, and to determine
possible causal mechanisms,
o To identify and describe potentially useful preventive or remedial
techniques to avoid, minimize or eliminate drain clogging, and
o To identify fruitful avenues for research and development to
minimize the likelihood or impact of clogging.
The study was Initiated with a literature review, a survey of field
experience, arid a limited laboratory study of the materials recovered from
the Boone County landfill. The literature review was greatly expedited by
the availability of a recent draft report on drain clogging (EPA, 1982).
Conclusions of this investigation and recommendations for further study
are presented in Section 2 and Section 3, respectively.
The information base is summarized in Section 4. Analysis of the
information base was guided by a ccmposite of two related generic approaches
used in elucidating failures in complicated systems——fault tree analysis and
failure mode and effects analysis. These techniques, which have been
extensively used to estimate failure probabilities, were used only as an
organizing tool. The results of this analysis and brief summaries of the
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principal clogging mechanisms appear in Section 5. Results of the laboratory
studies are also presented in Section 5.
The general background on drainage system clogging is discussed in
relation to leachate collection systems in Section 6. The potential for
clogging is examined by comparing a number of conditions in hazardous waste
drain systems with those at other types of drains, and by examining
information collected from operators of both secure hazardous waste and
sanitary municipal waste landfills.
Techniques for preventing or remedying clogged drainage systems are
described and discussed briefly in Section 7. The discussion is designed to
provide a general background, not detailed information for design and
implementation purposes.
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SECTION 2
CONCLUSIONS
The following conclusions are based on the information and analyses
suarized in this report.
1. Based on past experience in agricultural drainage and landfill
leachate collection systems, and on the mechanistic analysis
present in this report, it is reasonable to expect clogging of
leachate collection systems to occur in a probabilistic manner
during the active and post—closure operational lifetime of
sanitary and hazardous waste landfills.
2. Mechanisms that affect other types of systems are expected to
contribute to clogging in leachate collection systems. This study
was limited to an examination of clogging in drainage system per
se——that Is, the pipe, drain layers and outlet system. The regu-
latory definition of “clogging” as used here could also involve
localized blockages within the waste mass that rests on the liner,
creating leachate head greater than the permissible limit. This
type of potential problem was not examined in depth.
3. Landfill operators exhibited a varying degree of concern over the
clogging potential of drainage systems. Most appeared to view the
potential problem as unimportant in both design and operational
considerations and felt that conventional practices should be
adequate to prevent or remedy clogging. Only one source noted
that the prevention and mitigation of clogging received careful
and special attention in their design and operational
considerations.
4. Established preventive and remedial techniques to avoid or miti-
gate clogging can generally be used at hazardous waste sites.
Acid flushing should be used with great care, particularly if
cyanides are known to be present.
5. Preventive methods (including increased safety factors or
redundancy in design, monitoring, periodic inspection and
maintenance) are far superior to remedial techniques. Repair or
replacement, often considered quite practical in other settings,
is expensive and potentially dangerous in the hazardous
environment at secure landfills.
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6. The present regulations regarding hazardous waste landfills do not
appear to treat clogging system design and head build up with the
same thoroughness and level of detail as liner design or loss of
integrity. The regulations give substantial discretion to
regional administrators with regard to the drainage system.
Neither the regulations nor ocher supporting documents provide
guidance on engineering, design or operational practices to
prevent clogging or remedy a malfunctioning system.
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SECTION 3
RECOMMENDATIONS
A number of recommendations for further research on leachate collection
systems can be made based on the results of this study. The recoendations
listed below are given with the understanding that it is important to
integrate technical solutions with practical experience and expectations.
Technical solutions arising from laboratory—based research and development
alone are not likely to be implemented if they are considered too expensive
or too complicated to apply under existing or future conditions. Conducting
technical research in conjunction with experience on operating leachate
collection systems can help avoid this problem.
1. Specific design and construction guidelines should be developed for
leachate collection systems similar, perhaps, to the EPA Technical
Resource Documents which provide guidance for the design and
construction of liner systems, for example. Such a guide could be
used by Regional Administrators in approving facilities or by the
Administrator in preparing regulation for leachate collection
systems. Aspects of any of the following recommendations could also
be included in this task.
2. Specific operational procedures should be developed for the
prevention of clogging. An effective program of treatment and
maintenance can control the factors necessary for clogging
mechanisms to occur and thereby avoid the clogging problems. This
task should include a cost analysis of alternative preventive
approaches.
3. Monitoring methods to detect clogging or conditions that promote it
should be developed to anticipate problems before they become too
serious. Conventional techniques can be applied from related fields
such as groundwater hydrology and new techniques can be developed to
indicate when significant clogging processes are occurring.
4. A quantitative analysis should be made of the probability of
occurrence of the various clogging mechanisms. Specific preventive
and remedial approaches can then be evaluated in the context of
hazardous waste landfills to determine their quantitative eftects on
clogging potential. This recommendation would involve both a paper
study and a field investigation under typical hazardous waste
landfill conditions.
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5. Methods for preventing and correcting clogs in drain envelopes or
filter layers should be developed. Currently, no satisfactory
remedial methods exist short of excavation and replacement.
6. Experimental data on the performance of leachate collection systems
(including detailed leachate flow and composition data) should be
gathered at both sanitary and hazardous waste landfills on a
continuing basis. Such a data base is vital in evaluating leachate
collection system performance and in developing design and
operational guides to ensure proper system functioning throughout
its required lifetime.
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SECTION 4
BACKGROUND
INTRODUCTION
In order to assess the potential for clogging of leachate collection
systems, information was obtained in a number of areas. These include:
o RCRA Regulations;
o design of leachate collection systems;
o leachate characteristics;
o mechanisms of drain clogging; and
o relevant experience.
Literature from related fields, such as agricultural drainage and
irrigation systems, provided most of the background because inforriation and
direct experience with leachate collection systems n general is sparse.
Although, as will be discussed below, there are many differences in
conditions between leachate drains and other kinds of drains, basic
mechanisms leading to clogging are similar in all systems. In particular, a
white paper prepared by GCA Corporation for EPA’s Hazardous Waste Management
Division of the Office of Solid Waste (EPA, 1982) was used as a starting
point for the research in this report. Many of its conclusions are
incorporated below. This section presents relevant background information
according to the topics listed above, except for the mechanisms of drain
clogging, which are presented in the next section.
EPA PERNITTING STA 1DARDS
Before promulgation of the new regulations for hazardous waste disposal
facilities on 15 July 1982, the Permitting Standards (40 CFR 264) did not
contain any specific standards for leachate collection systems. The most
specific requirement with respect to clogging was that liquid in the system
be kept free flowing to prevent backwater and excess pressure head in the
collection system (264.221(e), 222(c)). Leachate systems are only briefly
mentioned in a number of other sections.
The internal EPA draft of the new Part 264 regulations, reviewed by CCA
in preparation of the white paper, sought to “correct the inadequacies of
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currently existing regulations for leachate systems” which lacked specific
design and operating standards. This internal draft, however, only required
drain pipe “of sufficient strength... to resist collapse or clogging. . . ‘ and
“a graded granular or synthetic fabric filter above the drainage layer to
prevent clogging”. GCA felt that these requirements were inadequate to
“guarantee the proper functioning of a drainage system” (EPA, 1982).
Therefore, they recommended that the regulations incorporate performance
criteria, minimum design criteria, and inspection and maintenance
requirements.
As promulgated, the new EPA regulations require single and double—lined
waste piles and landfills (except for existing portions) to have (264.251
(a)(2), 264.301(a)(2)):
A leachate collection and removal system iediately above the liner
that is designed, constructed, maintained, and operated to collect
and remove leachate from the landfill. The Regional Administrator
will specify design and operation 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:
(i) Constructed of materials that are:
(A) Chemically resistant to the waste managed in the landfill
and the leachate expected to be generated; and
(B) Of sufficient strength and thickness to prevent collapse
under the pressures exerted by overlying wastes, waste
cover materials, and by any equipment used at the
landfill; and
(ii) Designed and operated to function without clogging through
the scheduled closure of the landfill.
The only other signifIcant mention of leachate collection systems is
under monitoring and inspection requirements for landfills and waste piles.
Part 264.303(b)(4) requires that “while a landfill is in operation it must be
inspected weekly and after storms to detect evidence of... the presence of
leachate in and proper functioning of leachate collection and removal
systems, where present”. The same requirement is made for waste piles.
There are no leachate collection or drainage system requirements for surface
impoundments.
To assume safe and legal operations at hazardous waste landfills and
wastepiles, therefore, leachate collection systems must maintain flow
capacity over the expected life and closure of the facility. In addition, it
is the responsibility of the Regional Administrator in permitting a facility
to specify design and operation conditions to ensure that these requirements
are met.
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DESIGN OF LEACHATE COLLECTION SYSTEMS
Although the specific configuration and specifications of every leachate
collection system are fitted to the facility, the basic design Includes the
following components:
o drain pipe
o drainage layer
o filter layer and
o collection sump
A typical drain cross—section is shown in Figure 1. Collection systems
should be designed to handle the maximum expected leachate flow as well as to
withstand expected physical loading. Important design parameters with
respect to clogging are discussed in more detail below.
It Is important to note that alternatives to these basic designs have
been developed specifically for hazardous waste disposal facilities. For
example, a layer of upright standard drums containing waste can be placed
immediately about the liner to serve as a drain layer for leachate. Bulk
waste may then be placed on top of the drum layer or additional layers of
drums may be added. The leachate would flow along the liner to a central
drainage sump (e.g., a 48 inch standpipe surrounded by gravel) where it would
be pumped out. Such alternate systems were not considered in detail in this
report. The clogging mechanisms in these and other designs, however, are
expected to be similar to those for conventIonal leachate collection system
configurations.
LEACHATE CHARACTERISTICS
Knowledge of the characteristics of leachate at sanitary and hazardous
waste landfills is important in understanding the potential for clogging at
these facilities. Many of the factors which contribute to clogging of
leachate collection systems depend on these characteristics. In addition,
comparing the important characteristics of sanitary and hazardous waste
leachate gives insight into the relative difference in clogging potential at
these facilities.
Information on leachate characteristics at sanitary landfills is
plentiful. In particular, “Evaluation of Leachate Treatment, Volume I:
Characterization of Leachate” (EPA, 1977) reports leachate characteristics
from 18 different sources. Steiner, et al, 1971 also gives leachate
concentration ranges, but for fewer pollutants. These two reports were used
to characterize leachate from sanitary landfills.
Information on leachate characteristics at co—disposal and hazardous
waste disposal facilities is reported in Ghassemi, et al, 1983. That report
concluded that, based on 30 different leachates from 11 landfills,
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riw iiw u
SCHEMATIC OF A TYPICAL LEACHATE COLLECTION SYSTEM
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inorganic constituents appearing in highest concentrations in the
leachate are iron, calcium, magnesium, cadmium, and arsenic, and
the organic constituents appearing in highest concentrations are
acetic acid, mechylene chloride, bucyric acid, 1,1—dichioroethane,
and trichioro—fluoromethane. The most frequently reported
inorganic constituents are iron, copper, nickel, cadmium,
chromium, zinc and manganese and the most frequently reported
organic constituents are mono— and di—chlorobenzene, and methylene
chloride. The constituent concentrations in the leachate from
hazardous waste landfills studied fall within the reported ranges
for municipal landfill leachate.
Statistical analysis of the data for sanitary leachate shows that the
standard deviations exceed the mean in all but 7 cases. This finding
indicates that concentrations of these parameters are highly variable. In
addition, it should be noted that hazardous leachate can potentially contain
a very high concentration of any chemical released in bulk form after being
placed in the landfill. Such chemicals may inhibit or increase the potential
for clogging.
RELEVANT EXPERIENCE
Most of the experience with drainage systems and drain clogging is in the
area of agricultural drainage. In its EPA white paper, GCA presented an
analysis of a study of 108 tile drains in Ohio. All of the drains over 40
years in age had required maintenance. A frequency analysis showed that an
average service life of 11.7 years is expected before repairs are required.
Most of the problems developed at drain junctions, and physical factors for
drain failure tended to predominate. GCA concluded that better design could
minimize drain failure, but that the analysis gave “a rather bleak outlook on
the service life of draining systems.” (EPA, 1982) Information from studies
of other drainage systems is used elsewhere in the report to highlight
specific failure mechanisms. Studies by other researchers support the
conclusion that the clogging of agricultural draInage systems can be a
serious problem.
Experience with leachate collection systems at hazardous and sanitary
landfills is more limited. While modern agricultural drains have been in use
for decades, leachate collection systems have generally been in use for less
than five years and are only currently becoming widely utilized.
A survey of over 20 landfill operators, including some interviewed by GCA
and some who operated more than one facility, discovered limited experience
with clogged leachate collection systems. Six incidents of drain clogging
were reported, including five at facilities which disposed of hazardous
wastes. These si c incidents are:
o biological clogging of a drain envelope at a co—disposal site due to
poor design;
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o clogging of a standpipe with solids at a hazardous waste disposal
facility due to design or construction errors (no filter layer was
installed);
o siltation of a drain pipe at a hazardous waste facility;
o leachate collection system rebuilt due to clogging at a hazardous
waste landfill;
o undefined drainage problems at a hazardous waste landfill; and
o cementation of a drain envelope at a test sanitary landfill.
The number, and nature, of clogging incidents reported, however, may not
be representative of the overall potential for system clogging. This is true
for a number of reasons. First of all, companies are not comfortable with
any type of leachate collection system failure and nay be reluctant to
volunteer information. Additionally, some personnel may not consider
clogging to be as important as other problems such as liner failure or
off—site contamination, so that all individuals in a company may not be aware
of or concerned about clogging incidents. This was observed in one case
where two individuals in the same company gave differing accounts of the
company’s experience with clogged collection systems. Second, many of the
leachate collection systems discussed had been operational for only a few
months or a few years. The oldest system was build in 1976. These systems,
therefore, are too new to experience clogging problems which, in other types
of systems, may be expected only after ten or twenty years of operation.
Finally, many operators assumed that as long as leachate was being collected
at a rate which seemed reasonable, the system was functioning properly. In
some cases, Leachate depths were not even monitored. As a result, some
operators would not know if clogging, as defined in the RCRA regulations, had
occurred and the incident would therefore go unreported.
Perhaps more significantly, conversations with landfill operators
manifested an attitude that drain clogging is considered to be a minor
problem. When asked whether or not they were concerned about potential
clogging of their leachate collection systems, most operators indicated they
expect no problems. This seemed to be due to an ignorance of potential
clogging problems or confidence in their ability to unclog the system when
necessary. In general, clogging problems were considered to be a minor
nuisance and not a major threat. Only one company, which operates a number
of hazardous waste landfills, considered clogging to be a major problem.
They are designing their collection systems to facilitate prevention and
correctIon of clogging problems. They are also one of the companies which
has experienced clogged collection systems.
Some of the results of interviews with landfill operators are given in
Table 1. . This table includes companies which operate more than one landfill
as well as individual facilities. Information is given on system design,
clogging e cperience and attitude, and other relevant facts. Coumients on the
30 cm head criterion in the present RCRA regulations are also included.
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TABLE 1
INTERVIEW RESULTS
Name/Type Waste
Age lnlorms .tion
Inlapsay A 110 I (tot ia LIOnS
Ila ardo .is ,
a few yearn
Cumllally I I i I .i I Icoi I at 101113
llnh:,r .lous P
a few years IIO ltlH
locally
possible
Company C ito I lanttal bus
lla a I dutia • 1.11 7—10.5
a few years 1.5’ average
head
System I)csIgn
—6” PVC 1.1110 • 6—8” grave I
—drums an,i gravel as .1 1 a i. ,agc
iaycr
—automat Ic siiiiui> l Il P
—6” l’VC pipe, 12” gravel
—cIeauioiit tot Listed
—use maiiluolea l.tateutl of
riSer?
—>1000 between ci enuliplit a
— ,lpo slotted oi. bottom o.uiy
—4” l’VC plpe, 12’ grout
0.52 slope
—grnvit y dm1 .. Li, tol Ie i_I 1.11,
tauik
—liner wi Lii I X slope to itaj ,,s
mai,liiilcs evel y 300’
—6” I’VL plpe ,2’ gravel. 1,2
slope
—ibral us to 4 • SIIm t
er li ,uti problem
design to 1 ’revel ,t
and remedy
clogging
crushing and sedi—
ment.itiu>n coil—
sidered main
I auses
no problems expet tail
wit ii now eyuttemfl ,
conceriieii about
scaling due to
iii gi l liii
take care Ii.
plaLing waste over
drain
“snake out” if
pr. ,l le n
.iont no problems
expCi tail
hOne i.e prol ic
expected
110110 I I I) proti lens
C X aleC t eu
COfltotCllt S
use “iustcrgradient” to. l ,i.ique(waat c
below potentbowoti Ic surface) 19
cm criteria “not.
determined by e ,uglneer”
need for batter ItItcu ilesigut
Jo LW cr4 ter Ion uue. I. ,a • i C le.i h ,ai
,l,’e not COIlS 1.1cr loi .11 iuuiiii ,il I uii
prob IOIIIS, ci (cc Live lic,uiI
rcqni res leacluite tot Ic, t ((Ill ii 1,1 C—
cipitation >25”/ye .r
ii . , knowledge 1,1 iii i.i ,iggluig
.neu_ loin I ama ox _ep t i I tisli I lug a iiul
I,lol u igica l
us, leathiale, I’ 5—1”/ye.ir
811511, t II t week I , •uui Li, I • ,g
we have is leaLhlat ,Ie ’
II PiPe loga. lC.ILl )lItc wi I i
.1 rid ii I lii ongli gi as,. I I .iyer’
mouji tur level S lit s, .tnp, sooii to
monitor heaLl ,.II e levels cm I Iner
llrcv busty acLelit ed hazardous
wastes
liner of (ompulLtLlI soil
C liigglt .g
Pxperlvi,u c
(:l .,ggl ,tg
Art I I. nile
11110 e r epo i Led uio roI’ I ems
expected
I - .
—48” perforatcd St ) hld [ lIllcS
surrounded by ‘57 hIolie
—drums with swabs u . n
drainage Luyer
—a,utOma tic sI.uu PUtoP
hiolog 11_a I
clogging of
drain envelope
at .o— ,IlspoaaI
sItc reason
poor design
i ioggbn 01
at anillilpe,
reuse.. ne—
gleeted to
i,istall filter
layer
siltation problem,
jt .L cleared
none
l .i . lIltY I iuui,ult ti).il
S ,iu ltary
( Ole mouLt,
1.11 lilLy 2
tlazardu ui ui
eight 150111115
E,, , ibity I
bin a rdous
Seven nuuitl,s
ho I lity 4 mctal 1111
C1 1l)(Sl)OHal, liii 7.5—B
1.5 yc. .t .
limited chemical —gravel .ir,ilu,s to IIUJU gatlou .
wastes Bump to trc.ICwcu lt (1 Ii tra—
Iii 6.5 tien to 1.1,1,1 lug p 1 1 1 1’ 1
Pacli Ity S o.g.inhs
Sanitary,
.1 few yeats
— “ perforated butte. spci In I
material, I) 52 slope, pea
1 1101 1(1 gravel
—6—8” pci imu_Li r di jliiu . I,,ii ed
drui 11111 In •,ew.)ge syst em
1101) 13 hut
prc.fdcmn
cxiuct tel
with pimps
I ,, prolu I clout
ex ,ei ted
-------
SECTION 5
MECHANISMS FOR CLOGGING
INTRODUCTION
Clogging mechanisms are occurrences or natural processes that inhibit the
flow of leachate to or through the leachate collection system. A leachate
collection system at a landfill is considered to be clogged if it cannot
maintain the leachate depth over the liner at less than the 30 cm limit
required in the RCRA Standards. The major types of clogging mechanisms in
leachate collection systems are physical, chemical, biochemical and
biological mechanisms.
Figure 2 presents a failure mode diagram for clogging of a leachate
collecc on system based on these mechanisms. A failure mode diagram on a
slightly different variation (a fault tree) represents the events and
conditions that could cause an unusual event, such as drain clogging, to
occur. This kind of analysis is often used where the causal events are
unpredictable or random and are generally of low probability. It can be
used, more generally, as a means to organize and display multiple causal
paths leading to a single event and, if sufficient data are available, to
estimate the probability of the event taking place. In this study, only the
first application (organizing) was used; no estimates of clogging
probabilities have been made. The diagram is set up so that the final event
(i.e., a clogged drain) is at the top with factors which contribute to that
event on subsequent levels. Each level moving down the page represents a
higher degree of detail.
The main branches relate to the two major parts of a leachate collection
system——the pipe and the envelope. The last factor in any branch of the
diagram is called an end factor and indicates that no further breakdown is
required. In addition, the letters beneath each end factor indicate the
factor type. Factor types are specified to differentiate between the various
categories of factors listed in the diagram’s key.
The fault tree indicates parallel or alternative failure (clogging)
mechanisms by connecting the pathways with an open circle (o) which
represents an “or” node or function. This kind of node means that the next
event or condition along the pathway toward clogging could occur when any one
or more of the indicated events or conditions occurrs. A condition is a set
of circumstances that is constant or persists for some time —— ambient
temperatures, pH, pipe size, etc. Conditions include design, operation,
waste/leachate and ambient condition factors. An event is an occurrence
14
-------
Figure 2. Faduru mode analysis of clogging mechanisms.
CA?ACI V
COLLAp
P P INSUFFICItNCV ENVEIOVE • UIC EMC
‘i 1 _________ _______
6LO AG E CAPVC TV
I—
L i i
I
c I
I
I I
Erii,n.
Mahainn
V v
S n
0.
AnJ
F K. Typ .
D.
C) -
C Atnb.M
WV - W..M&I , .Ic
-------
Figure 2. Failure mode analysii of clog jurig mechanisms (corn.).
DETERIORATION
Fo.c.
COLLAPSE
SuenWh
0
PLASTIC
Mt TAL
-------
Figure 2. Failure mode analysis of clogging mechanisms (cont.).
I
I I I I W•IE MICA I
I I
FOIIMA1IO*d ATTAC•MENF
I .11
I I
D “ w çj c I
__________ _________ I FIo _ IGIC.I I SA. _ UtII
N.. n I .
I .‘
WC I I C
1
I__
-------
Figure 2. Faulute mode analysis of clo(jgsng mechanisms (conE).
CHEMICAL
DEPOSITION
a
DU SOLVED
SAL IS
CaCO 3 INCFILJSTATION
ChANGE OF
COuIUBRRJM
CO 2 RELEASE
i
INCRUSTATION POTENIIAL
RATIO 1
________ LI
UsIa., S 1 .- •o, I
I P wi
_______ WI
[ bvaPolaIKJn I
CI
C . CO 3 is wo .,I oh I pouflon
-------
ATTACIIMEN r
VELOCITY
Figure 2. Failure mode analysis of clogging mechanisms (cont.).
BiOLOGICAl
0
GROWTH
I—
OXYGEN
-------
taking place unpredictably (e.g., an earthquake or a bulldozer being directed
over a drain pipe) or as a result of a combination of factors along the fault
tree.
Conditions or events that must occur together to cause advancement
towards clogging are linked by a solid circle (.) which represents an “and”
function. All of the events or conditions leading to an “and” node must
occur in order for advancement toward the top.
The conditional factor at the very top of the diagram indicates that even
though the system may have been inadequately designed or been deteriorated,
clogging will not occur unless the leachace flow (Q) exceeds the actual
system capacity (Q 9 ).
Countless formulations and endless levels of detail are possible with a
failure mode analysis. This particular diagram, however, is formulated to
given enough detail to present the important factors involved for each of the
clogging mechanisms. No attempt was made to make the diagram more detailed
beyond this point. Additionally, this diagram is constructed based on the
most common system design. Alternative designs would require different
diagrams, although the basic clogging mechanisms would be the same.
Each of the four types of failure mechanisms is described in the
following suosections. The last subsection in this chapter describes the
rasults of an investigation of a potential clogging condition discovered
during the disassembling of an EPA demonstration municipal waste sanitary
landfill in Boone County, Kentucky.
PHYSICAL MECHANISMS
Physical mechanisms appear to be the most common and are the most well
understood causes of drain failure. GCA concluded that “in general, physical
factors tend to predominate in many drainage systems although it is important
to recognize chat any combination of factors might occur”. (EPA, 1.982)
Physical failure of leachate collection systems can be due to:
o inadequate capacity;
o structural failure; or
o sedimentation or filtration.
Each of these is represented in the failure mode diagram.
Inadequate pipe carrying capacity can be caused by underestimation of the
maximum design flow, by problems in the outlet, by inadequate pipe spacing,
diameter or slope, or by insufficient slot area. These factors are closely
related and depend primarily on system design. Underestimation of maximum
design flow can be the result of a design error, an event which causes the
system to perform other than as expected (such as cover failure), or a
condition which was inadequately accounted for (such as groundwater flow).
20
-------
Outlet problems which cause inadequate capacity include design errors such as
undersized pump or outlet diameter, and events such as outlet blockage.
Outlet problems can also be due to operational procedures, as was the case
with Boone County Test Cell #1 during the first six months of operation. The
outlet of the upper drain was intentionally closed for periods of time
causing leachate to back up in order to create sufficient head to force flow
to the lower drain. Finally, inadequate pipe spacing, slope, or diameter can
cause inadequate capacity since they are the principal factors which
determine how much flow each pipe and the overall system can handle. They
are interrelated, as indicated by the “and” junction, and are parameters of
system design.
Inadequate flow capacity design in the envelope can also lead to clogging
(the right—most branch in Figure 2). Use of a gravel mixed wIth fine—grained
sand or too shallow a gravel layer could create sufficIently high flow
resistance at peak flows to cause backup and clogging as defined herein.
Structural failure or collapse can be caused by mechanical crushing or
displacement, and may be exacerbated by physical deterioration of the pipe
material. Mechanical causes are due to operational and event factor types.
Compaction of the waste and general loading during normal operations can
cause crushing or displacement of the collection pipe. Settling of the waste
and underlying soil, which is considered an event although it is influenced
by design and operation, can also cause displacement. Physical deterioration
can be caused by chemical attack due to pH extremes or oxidizing agents in
the waste. Plastic pipes may also be susceptible to organic solvents and
metal pipes to corrosion. These factors are primarily a function of the
characteristics of the waste and leachate.
Sedimentation of or trapping of solids in the collection system can be
caused by a number of design problems and events. Sedimentaticn in the pIpe
requires both a source of solids and a mechanism by which they can settle
out. In a leachate collection system the sedimentary material appears in the
leachate as suspended solids arising from the waste, daily cover, cap,
envelope, or filter materials. Envelope material can enter the pipe as a
result of incorrectly selected grain size distribution or pipe slot size
design. Suspended solids can also enter if piping occurs in the envelope due
to hydraulic failure or scouring.
Once solids have entered the pipe they can settle out if the flow is
insufficient to keep them entrained. Low flow can be caused by a pipe slope
which is too shallow and, also, by outlet problems. Quiescent regions can
form behind hydraulic perturbations such as objects, or clogs, which inhibit
flow around poorly designed or installed pipe joints and intersections.
CHEMICAL MECHANISMS
Chemical mechanisms for clogging involve the formation of insoluble
precipitates which deposit on the surfaces inside of drainpipes, in openings
(slots) and In the drain envelopes (gravel and geotexcile filters). The most
common form of chemical build—up Is calcium carbonate. Manganese carbonate
21
-------
(rhodochrosite) and other insoluble forms (sulfides and silicates) have been
found in clogged or partially incrusted drainage systems.
Chemical precipitates form under basic, neutral or slightly acidic (up to
pH of about 8) conditions. One reaction leading to calcium carbonate
incrustation is the formation of insoluble calcium carbonate (CaCO 3 ) from
calcium bicarbonate (Ca(HCO 3 ) 2 ) solutions when pressure reduction allows
carbon dioxide to escape (Baron, 1982). Another means is the depositing of
calcium carbonate on surfaces when residual leachate caught in pipes or the
drainage envelope evaporates during dry periods. This mechanism is similar
to that which creates stalagmites and stalactites in caverns.
It is possible to describe the likelihood of forming calcium precipitates
in terms of Incrustation Potential Ratio (IPR) (Baron, 1982) as:
IPR = (Total Alkalinity) (Hardness)
10.3 x io — pH)
where: Total alkalinity is expressed in ppm CaCO 3
Hardness is expressed as ppm CaCO 3
If the IPR is less than one, then no calcium carbonate precipitate can,
in theory, be produced. If the IPR is greater than one, precipitates can,
but not necessarily will, be formed.
Chemical reactions to form insoluble products are also part of the
biochemical mechanisms, described in the next subsection. The precipitaces
produced in the absence of biological activity are generally quite different
in form or structure from those accompanying biological activity, and may be
less effective in leading to clogging. The presence of slimes or other forms
of microbial biomass often enhance the adherent and clogging potential of the
chemical precipitates.
BIOCHEMICAL MECHANISMS
Inorganic precipitates can also be formed in conjunction with biological
systems in addition to the relatively simpler mechanisms discussed above.
The principal products resulting from biochemical mechanisms are iron
compounds, Fe(OHL or FeS (although manganese compounds may also be
involved), which eposit and build up on the pipe surfaces and in the
envelope material. The deposits generally contaIn organic material as well
in the form of adherent, sometimes filamentous slimes and organic complexes.
One of the most prevalent and also well understood biochemical mechanisms
is depicted in Figure ÷ In this mechanism, iron (or manganese) is initially
present as ferric (Fe ) compounds in soils or wastes, in the case of a
landfill, is reduced by anaerobic bacteria to the ferrous state. Ferrous
compounds may also arise from inorganic reaction in the soil directly from
materials deposited in a hazardous waste landfill.
22
-------
The biochemical process depends on the availability of iron as dissolved
(free) ions in the aqueous leachate which contacts soil, fill, and wastes
containing bacteria. The availability of the ions is influenced by their
tendency to become attached to soil particles (exchange), tied up in organic
complexes, or to be reoxidized by inorganic mechanisms to the ferric state.
Two physical chemical factors which influence availability are pH (low pH
enhances the free ion concentration) and redox potential (the electrochemical
potential that controls reduction or oxidation reactions) (Gotoh & Patrick,
1974).
Positive redox potentials lower the amounts of iron present as ferrous
ions. Complexing agents such as tannins, humic acid (products of natural
decay of vegetation) or certain classes of organic chemicals, such as
phenols, that may be placed in landfills may tie up the ferrous ions so that
they are not available for the next step in the process.
That next step is the oxidation of ferrous to ferric ions by bacterial
action to produce insoluble ferric hydroxide (Fe(OH) 3 ). The Fe(OH) 3
precipitates along with and is mixed into a biological slime made up of the
oxidizing bacterial colonies. This mixed type of precipitate (called ochre
in much of the literature) is particularly adherent and can very rapidly
block up interstices in a drain envelope, entrance slots, or even the inside
of a pipe. The biological oxidation occurs under aerobic conditions,
aithougn some strains of bacteria can function with very little oxygen
present.
This reaction scheme and the nature of the resultant products nay be
influenced by the presence of sulfate—reducing bacteria (Drew Chenical
Company, 1978). Sulfate—reducing bacteria form hvdrcgen sulfide
(contributing to the characteristic foul odor in anaerobic decay of organic
matter). The sulfide ion will react with ferrous ions to produce an
insoluble precipitate which, in conjunction with the organic biomass, can
fill the interstices of the envelope and pipe slots (Ford, 1974).
All of the biochemical mechanisms produce the same results, blocked
envelope, slots, or pipe, and, ultimately, a clogged drain system. The
Importance of understanding the specific operative mechanism at a particular
site lies in the selection of preventive or remedial measures to avoid or
mitigate clogging.
BIOLOGICAL MECHANISMS
Biological clogging is produced when organism growth fills the pipe or
interstices of the drain envelope and interferes with normal flow of leachate
(Ford, 1980). Figure 2 indicates that, for growth to occur, bacteria must be
present in a supportive environment. Many forms of bacteria that can utilize
hazardous organic chemicals for food are known (Kobayashi and Rittman, 1982),
and will, under the general range of conditions, grow at the temperature, pH
and oxygen content, found in landfills. Heavy metals, also often present at
hazardous waste landfills, may be toxic or inhibitory to the clog—forming
species.
23
-------
ANALYSIS OF DEPOSITS FOUND AT BOONE COUNTY, KENTUCKY, LANDFILL
When Test Cell 111 of the Boone County Field Site was dismantled in
September, 1980 after nine years of testing, a section of partially cemented
gravel was discovered in the drain envelope extending from 6.5 to 13.5 feet
from the collection sump (bulkhead). The discovery of the cemented section
was significant because the Test Cell, along with four others, was
constructed to provide a better understanding of the processes and related
environmental effects that occur in sanitary landfills (Wigh, undated). It
is therefore important to determine whether the causes of cementation are
unique to the condition at the small—scale test landfill, or whether they are
coton to sanitary and hazardous waste disposal landfills in general.
The gravel sample available for analysis consisted of a small amount of
loose, rounded pea—stone plus two or three large masses of similar stones
firmly held at contact points between the stones by a thin layer of red—brown
cement. The largest of these cemented aggregates was a flat, disc shaped
mass approximately 12 cm across and 5 cm in thickness. It appeared to be
graded or classified with large, individual stones of I to 2 cm diameter on
one side, and smaller stones of 0.5 to 1.0 cm on the other. A photograph of
the two larger masses of material is shown in Figure 3.
Two approaches were used in the initial analysis of the gravel sample.
The first involved a physical analysis of the cement material itself,
including scanning electron microscopy, optical microscopy, and X—ray
diffraction and fluorescence analysis. The second involved a more general
chemical analysis of the mass to determine the primary chemical constituents
in the cemented sample.
The results of these microscopic studies lead to the preliminary
conclusion that the cementing agent for the small stones is likely a
co—precipitated mixture of calcium carbonate and an insoluble iron hydroxide.
This combination, along with the silica, constitutes the principal components
of the cement. However, aside from a few isolated crystals, calcium
carbonate is not observed microscopically as a separate phase and is not
present i t t the X—ray diffraction pattern. Since the calcium is present in a
substantial quantity, we would expect to detect the crystalline form (either
calcite or aragonite) by this technique, if it were present as pure calcium
carbonate. This ambiguity suggests that the calcium and iron may well have
co—precipitated in an amporphous form and, as such, are not “see&’ by X—ray
diffraction.
Chemical Analysis
In a preliminary test it was determined that dilute hydrochloric acid
would not affect the gravel but would solubilize the material holding it
together. To determine the composition of the cemented gravel material, a
portion of the sample was treated with a known excess of acid and separated
into acid—soluble and insoluble fractions. The soluble fraction was
subjected to qualitative emission spectrographic analysis to identify the
principal metal species which were then quantified by emission spectrometrv.
The insolubles were separated into size fractions and weighed.
24
-------
FIGURE 3 — The two larger gravel sample masses.
NOT REPRODUCIBLE
25
-------
A known weight (100 grams) of the cemented gravel was treated with a
known amount of standardized hydrochloric acid and boiled for thirty minutes
to effect complete dissolution of the cement material and to drive off the
carbon dioxide formed. The insolubles were separated by decantation and
filtration, dried, sieve—sized and weighed.
A portion of the filtered solution was analyzed for residual acidity by
pH titration (to pH 5.0) using standardized sodium hydroxIde solution, to
measure the alkali content (acid consumption) of the dissolved material.
Physical Analysis
The microstructure of the cemented material as seen by the scanning
electron microscope (SEN) is shown in Figure 4. Accompanying the SEN
micrograph in Figure 4 is the spectrum of elements detected by the energy
dispersive X—ray analysis system (EDS) attached to the SEN. EDS analysis of
the cement material from various points on the sample indicated calcium and
iron as the principal elements present. (Elements lighter than sodium are
not detected). In addition, in the sample shown in Figure 4, a trace amount
of manganese was detected.
A larger amount of the red cement was isolated for analysis of the
crystalline content by X—ray fluorescence. X—ray diffraction indicated
silica (quartz) as the only crystalline material present.
X—ray fluorescence, which detects the presence of elements heavier than
aluminum in atomic number, indicated a relatively very strong signal for
phosphorous, zinc, sulfur and silica, and a very weak signal for manganese
and potassium.
Using optical microscopy under the petrographic (polarizing) microscope,
the reddish cement was observed to consist of three major constituents:
o silIca;
o a colorless, apparently crystalline phase with calcium carbonate
present; and
o an as yet unidentified phase consisting of an aggregated cluster of
small red particles comingled with colorless crystalline particles
of similar size range. The unidentified aggregates reacted
vigorously with dilute acid, evolving large volumes of gas ar’d
leaving opaque red particles without the comingled crystalline
phase.
The elemental composition of the major constituents in the cemented layer
was determined by atomic emission spectroscopy. An emission spectrum was
obtained using a Spectrospan III Direct Current Argon Plasma Optical Emission
Spectrophotometer for qualitative analysis. This revealed Ca, Fe, Mg, and P
as major constituents in solution, and Mn, Cr, Na, Ba, Si, Cu and Sr present
26
-------
NOT REPRODUCIBI.E
FIGURE 4 — Red cement niicrostructure with
trace of manganese in EDS spectra.
27
-------
at lower levels. The major constituents, along with sin, were quantified on
Spectrospan III Spectrometer using the method of standard additions for each
element analyzed. The results of these analyses are shown in Table 2.
Preliminary Findings on the Composition
The “cement” is principally a calcium—iron—magnesium product containing
significant proportions of carbonate (gas evolution) and phosphate. In
addition, a relatively large proportion of fine silica appears to be
dispersed in the cement.
The lack of significant X—ray diffraction patterns suggests that the
cement is an amorphous material rather than composed of discrete crystalline
phases. While little can be said yet about the clogging mechanism(s) at work
here, carbonate incrustation is likely to have contributed. The role of iron
is not clear——it may have been an active agent in precipitate formation, or
may only be present as discrete oxide (red, Fe 2 0 3 ?) particles which have
been carried along.
These findings leave several questions unanswered. Additional
investigation on chemical and physical characterization with emphasis on
elucidating the role of the fine silica particles and the distribution and
role of iron is needed to that end. Also, tests to determine the presence
and distribution of organic materials would provide some evidence as Co tne
possible role of biochemical mechanisms.
Location of the Clogging
Two questions, were important in the analysis of the cemar Eed pea gravel
in Test Cell f.kl.:
1. What is it? (addressed above)
2. Why did cementation occur only in a limited portion from 6.5 to 13
feet above the collection sump of the upper drain?
One explanation is that the condItions in the wastes above that sectfon
were different from those everywhere else in the landfill and caused the
deposits only in a limited regIon. There are insufficient data, however, to
evaluate this hypothesis. The discussion following suggests an alternative
mechanism.
From a perusal of operating logs, it was discovered that in the first
seven months of operation of Test Cell fr1, special procedures were used in
connection with the leachate draIn system. During the first three months
(from 6/11 to 8/27/71), the upper pipe was closed off in order to forte
leachace flow into the lower pipe. This procedure would cause leachate to
back up in the pipe until all additional flow was routed to the lower drain.
For the following four months (8/28 to 12/27/71) leachate was sampled and the
collection system drained on roughly a weekly basis. Again, triis operating
pattern caused leachate to back up in the pipe.
28
-------
TABLE 2
RESULTS OF CHEMICAL ANALYSES OF CE NTED MATERIAL*
Size Distribution in insolubles
Size Weight Found (g)
2.0 n 94.015 g
(#10 Sieve)
2.0 , 0.84 = 0.640 g
(through #10, on #20)
0.84 , 0.25 = 0.933 g
(through #20, on #60)
0.25 = 1.070 g
(through #60)
Elemental composition of dissolved material
Element Weight Found (g)
Ca 0.851 g
Fe 0.551 g
Mg 0.103 g
Mn 0.020 g
P 0.240 g
leight sample taken 100.488 g
leight insolubles remaining 96.958 g
pparent sample dissolved 3.530 g
29
-------
The distance that leachate would back up in the upper pipe and drain
envelope during each of these periods is approximated by:
x = k v
where:
x = the horizontal distance of leachate back up (and roughly equal
to the distance along the pipe due to the small slope of 1.875
percent);
k = a constant which is a function of pipe slope, wetted area and
radius, and the porosity of the gravel; and
v = the volume of leachate collected from the upper pipe.
Table 3 gives v and x from 8/28/71 to 1/17/72, as well as other leachate
characteristics. As can be seen, six of the first seven and the last four
values of x are at or above the location of the cemented gravel (6.5 to 13.5
feet). The five intervening values are from an insignificant quantity of
leachate. The three highest leachate quantities had an x value of about 32
feet, which is the length of the pipe.
This correlation suggests that the cementation may have occurred, or at
iea t begun, during this time of unique operation. Further investigation,
including a laboratory study, is necessary before more definitive conclusions
can be made. It should be possible to simulate the conditions in the Test
Cell and determine their effect on the gravel surrounding the upper pipe.
30
-------
TABLE 3
HORIZONTAL DISTANCE OF LEACUATE BACKUP
(Relative to Cemented Area @ 6.5 to 13.5 t)
Date
V (I) X (It)
pH
Fe*
Alk**
Hard**
Ca*
Hg*
8—28—71
125 above (
32)
6.3
42
927
1320
444
63
9—6
20 12
—
—
—
—
—
—
9—13
38 above (
17)
5.4
—
1630
2960
1010
132
9—20
22 13
5.4
190
1460
289
117
144
9—27
15 11
—
—
—
—
—
—
10—4
2 below
—
—
—
—
—
—
10—11
36 above (
16)
5.5
—
1730
4080
223
133
10—18
0 0
—
—
—
—
—
—
10—25
0 0
—
—
.
—
—
—
—
11—4
.4 below
—
—
—
—
—
—
11—11
1 below
—
—
—
—
—
—
11—18
1 below
—
—
—
—
—
—
12—6
1] 9
5.3
75
1130
1130
1170
152
12—13
]25 above (
32)
5.4
227
631
4310
1190
243
12—20
14 10
5.4
252
168
4120
1240
244
12—27
126 above (
32)
5.6
262
1980
1980
1500
275
1—3—72
127 —
—
—
—
—
—
—
1—10
202 —
—
—
—
—
—
—
1—il
276 —
—
—
—
—
—
—
Peak
Concentrations:
*mg/l
**rng/1 CaCO 3
7.07
5.10
high
low
616
(10/73)
8870
(3/73)
7500
(1/73)
2360
(10/73)
374
(11/72)
-------
SECTION 6
POTENTIAL FOR CLOGGING AT HAZARDOUS WASTE LANDFILLS
The potential for clogging of leachate collection systems at hazardous
waste landfills is of particular concern compared with sanitary landfills.
Not only are clogged systems more problematic in that excavation and
reolacemertc is no longer a simple last resort, but the consequences of
failure are much higher. This follows from technical factors, principally
questions of safety resulting from the hazardous nature of the wastes and
their leachates as well as institutional factors. The latter items include,
for example, the importance of public acceptance of secure hazardous waste
disposal sites. Problems with leachate collection systems could set off a
public reaction similar to the reaction to reported problems with landfill
liners. This is especially true since the collection system is an integral
part of the overall system, including the liner, for protecc ng groundwater
and the environment.
The literature clearly indicate that clogging is a serious problem in
agricultural drainage systems. Direct assessment of clogging potencial at
hazardous waste or sanitary landfills, however, is dIfficult since there is
little experience with modern leachate collection systems. It is therefore
useful to compare the clogging potential in leachate collection systems at
sanitary and hazardous waste landfills with agricultural drainage systems by
using the set of clogging mechanisms identified in the Failure Mode Diagram
(Figure 2) as a basis. The following discussion follows the major factor
type shown in Figure 2, above.
DESIGN FACTORS
Design factors are particularly important to physical mechanism such as
sedimentation or inadequate capacity. Design of agricultural drainage
systems is similar to that of leachate collection systems In many respects.
There are, however, more stringent requirements for leachate systems since
aspects of the design are specified by regulation and approval by the
appropriate agencies is required. In addition, large implicit costs of
non—compliance with regulations should enhance quality control during
construction of hazardous waste facilities. Design (and construction) error,
while possible with all three systems, are therefore more likely to occur
with agricultural drainage systems.
32
-------
OPERATIONAL FACTORS
Operational factors are involved primarily with structural failure
mechanisms. Compaction of waste and general equipment loading can cause oipe
crushing or displacement. Compaction of waste (e.g., with a 20—ton
compactor) occurs at both sanitary and hazardous landfills. General
equipment loading occurs at all three systems, but heavier equipment is
expected to be used at the landfill sites. Operational procedures which
cause clogging appear, therefore, more likely Co occur at hazardous waste and
sanitary landfills.
WASTE/LEACHATE FACTORS
Waste/leachate factors are the most important in pipe deterioration,
chemical, biochemical and biological clogging mechanisms. The composition of
agricultural drainage is generally very different than landfill leachate
except for a few parameters. Suspended solids, some common ions (e.g.,
Ca+++), nutrients, and bacteria are not necessarily very different. The most
important difference is that hazardous waste leachate contains various
chemical constituents not expected in the others, and may have a lower pH.
This means that mechanisms which require an environment which is riot toxic to
certain bacteria or favor a more basic pH range would be less likely to occur
in hazardous waste landfills. Alternatively, mechanisms which require a
Lower pH or certain chemical constituents would be less likely to occur in
sanitary landfills and agricultural drainage systems.
CONDITION AND EVENT FACTORS
Condition and event factors can be significant in all three types of
systems and will depend in a large part on local conditions. Certain
conditions, such as temperature, depend entirely on site—specific
characteristics. Others, such as water inputs and groundwater flow, depend
in part on design (e.g., cover, number of pipes) or operation (e.g.,
irrigation) or location. Clogging due to conditions and events is expected
to be the same, on the average, for all three system types.
RELATIVE POTENTIAL FOR CLOGGING
Combining the effects of the factors it is possible to estimate the
relative potential for clogging of leachate collection systems for each of
the mechanisms. This is presented in Table 4. A “*“ in the table indicates
that clogging is possible, while a or “—“ indicates that clogging is more
or less likely, respectively, relative to the “f”. A “—“ does not mean that
clogging is not possible, nor does a “f” mean that clogging will occur.
Table 4 gives the relative potential for clogging of agricultural drains and
leachate collection systems at sanitary and hazardous waste landfills based
on the major potential clogging mechanisms.
As can be seen in Table 4, crushing problems appear to be more likely to
occur at both hazardous waste and sanitary landfills, whereas chemical,
biochemical, and biological clogging appear less likely to occur in hazardous
waste systems. This difference is primarily due to the lower pH range and
33
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TAIH,E 4
RELAT EVE POTENT LAI.. FOR CLOCG [ NC OF LEACIIATE COLLECTiON SYSTEMS
AgriculLural Sanitary IIa ardous Waste Significant
Mechanism Drains Lan(IfIils Landfills Differences
Physical
Crushing * + + Compaction, greater
equipment loading
Sedimentation * — — Less careful design and
construction possible
Deterioration * * + Chemicals, solvents, low
p11 not expected
Chemical (CuCO 3 ) * * — Lower 1)11
Biochemical * * — Toxicity to indigenous
(Oclire, Fe) bacteria, lower p11
Biological * * Toxicity to indigenous
bacteria, lower pH
— less likely
+ more likely
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the potential toxicity of chemical constituents to indigenous bacteria. It
should be noted that various toxic chemicals can be nutrients to certain
bacterial strains, and hazardous leachate can have a high pH. Sedimentation
and pipe deterioration are also potential problems in hazardous waste
systems.
35
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SECTION 7
PREVENTION AND RENEDIES
Problems with clogging of drainage systems can be addressed by means of
preventive or remedial measures. Preventive measures are intended to
eliminate or render highly improbable one or more of the pathway links shown
earlier in Figure 2. Such measures would interrupt the sequence of causal
steps necessary for a particular clogging mechanism to occur and would
thereby avoid (prevent) the cloggIng problem. Prevention of drain clogging
can be accomplished in a number of areas, including:
o design and construction;
o operation and maintenance;
o waste disposal; and
o treatment.
Remedial measures are intended to eliminate the clogging problem once :he
majcr (ultimate) event ifl Figure 2 (i.e., a clogged drain) has occurred.
Remedial measures for clogged drain systems include:
o excavation and replacement;
o physical methods; and
o chemical methods.
In terms of these definitions, preventive measures would include undoing
or fixing conditions that exist before clogging as the final event (e.g.,
cleaning out partially clogged pipes). Examples of preventive and remedial
measures are presented in Tables 5 and 6, and are discussed briefly below.
PREVENTION
Design and Construction
Proper design and construction is the most basic preventive measure. A
study of agricultural drain systems found that more than 50% of draIn
failures were due to improper design and construction (in EPA, 1982). For
leachate collection systems, design mIstakes will need to be carefully
avoided. It Is also important that the system be constructed as designed.
36
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cxcii 1st ’ specIal
t are in desIgn
dliii ctiiutit lilt t I iiii
design for
prevent bit
tare iltiring
P t ,iiement
comp.itt lint
Opt.?I at 1 1)11 Itt
vii hilty ii i drain
rcgti l.ii wait ii orb hg
anti innpc’i I I tin
iii %yht(’m
I c tiiliig
lii I n Imi te
lilt t r I cit r’i
ii I ri 1 itt’.e li i iii ides,
Lox it i i
wiiiil.tiii low itli
,iviiid hiplvt’lil q,
set Iii hi hg •lgeiit a
I.li.i liii’s
iii lilt total
stil Iin.’tii al lint
boil intent ttbiiui
isaiultii I 525 C I C.lfll)ll L it , I • ii gi
pipe, c it.
lutist Iwlicirt:itlt for lii at lIlt
of waste
lilentily i.tt lots, t’.ii ly st.iges
iii t logging for p 1 eventat lvi
lentil iig
I ewoves pitt itil ml clogging lit
early si .igtm, time liiisliltig,
low preshlile lets
tirg.lii lea, N .ttiti I ’ ctisihliiiilhils
iii bet litnil i_al s
at lila, Ii.tnem heavy int l ii w tstt’s
tint t ilii,I eq to dcl ci liir.it bit
TABI.E ‘i
PREVENTIVE MEASURES FOR DRATN CLOCCINC
Ikiliolsms
Cii egitry Ptea’iiti e Al ii’i I i ii All tq I t ’iI I iiinint’iitm
I)omigii atid .lpe tll,inieler IIpc i,Itt_’, i NI liii it i_il .tii.ii It y la d I it.tte rt’iut’tIi.iI nit’.iiiiite’i,
oitatriit—I lo u 6’’ flow nriititi’ii.iiit 0 —
nIle Itt pr.i [ et live i_riialihiig itt in mi mI use hi 1 ) htieugtlu pipe
id I t 1 sub I i ny c
sealed joitit dis 1 il.it i-metal , ‘ dot ose altitteil sit pet for.tted lulls
t oust nu tboii q l ,e
corps gt •ilii sl.’e IllItu satir i.tl opt bus lot little graded, 2
illatribuution mo le laycts BeotextIle, 4’
LI tier Ia miii linisu sIt. lit It
suibtuet gel nail let wi ly I mcli It time ati.iet tuliji
D ci 1 14 1 1 1 5 Db
slope 2 luert’eot Ilelietlils a Iso on iiiiaiit It y of
flow
U )
-J
ati.it’i iili Ic i ,iiuil it loot,
I low late
till tleslgti
i litiiili ml, ui 0 , Itttslcal
ap.ic I ty, med Inientut Ittn
lilaitlienilt.ut, lutological
i ap.ii I ty , s Oil Iss’atat ion
at tit i I tint I
• lIteral ion ,tntl
1 1. -i li ii coma. e
W.talc IJl’Jjios.tl
Ii ei m m ci i i
,ilI it I
crittilihtig, dii-i 1 ii.t, iwt itt tilt in Ihi ,ul
I I
all
li.u. I t r Ia
ill
.ill
It Its lut’nili al, luiiiliugtc.tl
1.1 ii i litsii I c,i I , lii ii log I r.ti
lit ni Ii a I , Ii hut ltt’ni li_i I
Iilail.igis .ul
‘let ii lot .uI li si
b.ii let In
liii Let I u
i Instil. .11 . 1 1 1 ii I
lii’ I’9 It Iii . ’ . lii tili il, lilol .igit.iI hI d tItter -I ly Iii ciii li_it lo u t,v.hiuii
‘It lit iii tIl ki Il -i lii i Ii i Ii, ieinovts t’.ut ly
‘it igt’’i
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TABJ,E 6
REMEDiAL MEASIJRES FOR CLOCCED DRAINS
Category Measure RE fe iiv iiess Comments
Excavation and same complete remedy most expensive option; difficult
Replacement at hazardous waste sites
Physical —mechanical limited for [ nactive deposits, Rob—rooter, pigs, sewer balls,
Methods not effeci lye for slots, but snakes, buckets
good in combination with other
methods
—low pressure etective for ochre, FeS, 70 — 140 psi at nozzle
jets limited for mature deposits
—high pressure same as low pressure but can 440 — 1300 psI at nozzle
jets cause damage 10 drain envelope
and better for mature deposits
—flushing (sub— less than jets
irrigation
Chemical —SO. gas cffeciive for oclire, Mn in 2 rate of use = 1 lb/7.5 gal water
Methods cases, Ineffective In one dangerous to personnel and environ—
case tot ochre mont, cost Is 7 percent. of replace—
men t
—Sulfamic Acid effective [ or othre strength required depends on organic
matter and age of acute Na 2 CO 3 used
to neutralize treated drain
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There is already at least one case where errors in design and construction
have led to system clogging at a hazardous waste facility. In this case,
the builder neglected to install a filter layer around the collection sump
(although it is unclear whether this was actually a design or a construction
error.) In addition, it is important that the system be designed
specifically to prevent or minimize the potential for clogging. This
includes proper sizing of components (e.g., pump size, pipe diameter and
slope), material selection for strength and compatibility with wastes and
leachate, and special features included especially to prevent or remedy
clogging (e.g., cleanouts, graded or layered filter, submerged outlet).
Operation and Maintenance
Operation and maintenance is also of considerable importance in
preventing clogging. Operational considerations include taking special care
during placement and compaction of waste and during other operations when in
vicinity of the drain. Placement of the first lift of waste is of particular
concern since the filter layer is exposed and the cover over the drain is at
its shallowest point. Maintenance considerations include monitoring and
inspection of the collection system and regular preventive cleaning. Many of
the remedial techniques for unclogging drains are more effective when used as
preventive measures. Mature deposits of ochre, for example, can be
difficult, if not impossible, to remove, while young deposits are more easily
flushed out. This implies that careful system monitoring is also important
since the early stages of clogging are more readily dealt with than the later
stages when the ramifications of clogging may be more evident.
Control of waste Disposal
Control of waste disposal at the facility can also be used as a
preventIve measure. Minimizing nutrient—rich waste (e.g., containing
organics, nitrogen, phosphorus) and adding biocides or materials toxic to
bacteria (such as heavy metals) can decrease bacteria growth and control
biochemical and biological precipitation. Maintaining a low pH can also
rttnimize bacteria activity as well as reduce calcium carbonate precipitation.
Addition of solvents, oxidizing agents and caustic or corrosive chemicals
should also be minimized since they can contribute to the deterioration of
material used in the collection system. Maintaining a low pH may also
contribute to deterioration.
Direct Treatment
Finally, direct treatment of the collection system can be used to prevent
cloggIng. This involves the periodic application of biocides to kill
bacteria or acid to dissolve deposits in their early stages of development.
Treatment can be used in conjunction with pipe cleaning and other preventive
measures to inhibit clogging mechanisms in the pipe and remove accumulations
before clogging becomes a problem. Cleaning and treatment of the area
surrounding the pipe is more difficult so that other preventive measures will
need to be more heavily relied upon.
39
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REMEDIES
Excavation and Replacement
Excavation and replacement is the most difficult and expensive remedial
measure for clogged leachate collection systems. It involves actually
digging up the clogged pipe or envelope material and installing new drain
components. This is an expensive, but straightforward, procedure at sanitary
landfills, but at hazardous waste facilities becomes more problematic since
hazardous wastes may be exhumed. It should therefore be considered a last
resort alternative to be used when all other options are ineffective. For
example, for mature ochre deposits or a clogged envelope, excavation and
replacement may be the only effective alternative.
Physical Methods
Physical methods for unclogging pipes include mechanical devices and
hydraulic cleaning. Mechanical devices can be long, flexible tools, inserted
In the pipe such as snakes or roto—rooters, or objects, such as pigs
(bullet—shaped) and sewer balls, propelled through the pipe. These devices
all serve to dislodge the material in the pipe which is restricting leachate
flow. They may not, however, be effective for mature deposits or for
material in slots or drain openings. They are also useful in cor bination
with other techniques, for example in preparation for hydraulic flushing or
acid treatment. Hydraulic cleaning uses high or low pressure jets or simple
fl ishing to dislodge and remove deposited material. High pressure jets
(440—1300 psi at the nozzle) are the most powerful hydraulic method, but ‘nay
dnrnage the drain envelope. Low—pressure jets (70—140 psi at the nozzle) are
less powerful and are therefore safer for the drain envelope. Both types
have been effective in removing ochre, FeS, and sediment deposits ifl pipes.
No experience was noted for simple flushing. Presumably, the more pressure
behind the water the more stubborn a deposit which can be dislodged.
Chemical Methods
Chemical methods utilize acid to dissolve clogs ifl drain pipes. The
methods presented were developed to remove ochre and manganese deposits from
agricultural drains. Acids also may function as a biocide to kill bacteria.
The acid strength required to lower the pH to dissolve deposits and prevent
further accumulations depends on the nature of organic matter present and on
the age of the clogging material. Acid treatment Is inexpensive compared to
replacement (roughly 10%) but can also be dangerous to personnel. Fumigation
with SO 2 gas, which dissolves in the leachate, has had varied success in
reducing ochre and manganese deposits. Use of a dry, pelletized form of
sulfuric acid has been effectIve for ochre deposits. This form has the
advantage of being safer for personnel in handling than concentrated acId.
Sodium carbonate can be used to neutralIze acid—treated drainlines if
necessary. As wIth physical remedial methods, chemical methods apply
primarily to drain pipes and would be less effective for treating clogged
envelopes.
40
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REFERENCES
1. Baron, Donald M. A Well System can be Designed to MInimize the
Incrusting Tendency. The Johnson Driller’s Journal. First
Quarter, 1982. pp 8—11.
2. Drew Chemical Corporation. Principles of Industrial Water
Treatment. Second Edition, 1978, pp 91.
3. Environmental Protection Agency (EPA). “Evaluation of Leachate
Treatment, Volume I: Characterization of Leachate” MERL, ORD.
EPA Report No. 600 / 2 — 7 7—186a, Cincinnati, OH September, 1977.
4. EPA. “Clogging of Leachate Collection Systems Used In Hazardous
Waste Land Disposal Facilities” Draft Report by GCA to the
Hazardous Waste Man. D lv. of OSW, Washington, DC, June, 1982.
5. Ford, Harry W. Biochemical and Physical Factors Contributing to
Resistance in Drain Outflow in a Modified Spodosol. Soil and Crop
Science Society of Florida, 1974, 34:11—15.
6. Ford, Harry W., The Problem of Clogging in Low Volume Irrigation
Systems and Methods for Control. Paper presented at the Symposium
on Drip IrrigatIon in Horticulture with Foreign Experts
PartIcipating. Skierniewice, Poland. October 19809.
7. Gotoh, S., and W.H. Patrick, Jr. Transformations of Iron in a
Waterlogged Soil as Influenced by Redox Potential and pH. Soil
Soc. Am. Proc. 38:66—71, 1974.
8. Kobavaghi, Hester, and Bruce E. Rittmann. Microbial Removal of
Hazardous Organic Compounds. Env. Sd. Tech., 1982,
16(3) :170A—183A.
9. Shuckrow, A.J. et al. Management of Hazardous Waste Leachate.
Final Report to SHWRD, MERL, EPA Report, No. SW—871, Cincinnati,
OH, September, 1980, PB 81—166—354.
10. Steiner, R.C. et. al. Criteria for Sanitary Landfill
Development. Public Works, 103(3):77—79, 1971.
11. Wigh, R.J. Boone County Field Site. Final Report to U.S.
Environmental Protection Agency, Cincinnati, OH, undated.
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BIBLIOGRAPHY
Anonymous. Oregon Landfill Seeks to Control Leachate Under
Difficult Conditions. Solid Wastes Man. J./RRJ, September, 1979
pp 20—30, 92—96.
Anonymous. Drain System is Installed to Collect Leachate from
Love Canal ‘Bathtub’ Solid Wastes Man. J/RRJ, February, 1980 pp
20—21, 34—38.
Avnimelech, Y and Z. Nevo. Biological Clogging of Sands. Soil
Sd., 1964, 98:222—6. (?)
Barbic, Franc F., et al. Development of Iron and Manganese
Bacteria in Ranney Wells. Journal of American Water Works
Association. 1975, 67 (10) :565—572.
Benz, L.C. et al. Evaluation of Some Subsurface Drainage
Envelopes. Proceedings of the National Drainage Symposium,
Chicago, IL, 1976. pp. 31—33.
Daniel, T.C., and J. Bouma. Column Studies of Soil Clogging in a
Slowly Permeable Soil as a Function of Effluent Quality, J.
Environ. Quality, 1974 3:321—6.
DeVries, J. Soil Filtration of Wastewater Effluent and the
Mechanism of Pore Clogging, J. WPCF. 1972, 44:565—73.
Ford, Harry W., Characteristics of Slime and Ochre in Drainage
and Irrigation Systems. Transactions of the American Society of
Agricultural Engineers, 1979. Volume 22, No. 5, pp. 1093—6.
Ford, Harry W., The Complex Nature of Ochre. Z. F. Kulteutechnik
und Flurbereinigung. 1979, 20:226—232.
Ford, Harry W., Estimating the Potential for Ochre Clogging
Before Installing Drains. Transactions of the ASAE. Paper No.
8—2542. Submitted and approved for publication, December 1981, pp
1—11.
Ghassemi, Massod, et al. Compilation of Hazardous Waste Leachate
Data. U.S. Environmental Protection Agency, Office of Solid Waste,
Washington, DC 20460. (In preparation) 1983.
Grass, L.B., and A.J. Mackenzie, Restoring Subsurface Drain
Performance, J. Irrig and Drainage Soc., March 1972, 870106.
42
-------
Crass, L.B., et al. Manganese and Iron Solubility Changes as a
Factor in Tile Drain Clogging: I. Observations During Flooding
and Drying. Proceedings of the American Soil Science Society,
1973, 37:14—17.
Haasl, D.F. et al. Fault Tree Handbook, U.S. Nuclear Regulatory
Commission Dept. NUREC—0492, January, 1981.
Haxo, H.E., et al. Liner Materials Exposed to Municipal Solid
Waste Leachate. Draft Final Report to U.S. Environmental
Protection Agency, Matrecon, Inc. Contract 68—03—2134, November,
1981.
Kristiansen, R. Sand Filter Trenches for Purification of Septic
Tank Effluent: I The Clogging Mechanism and Soil Physical
Environn’ent. J. Environ. Quality, 1981, 10:53—64.
Mackenzie, A.J., Chemical Treatment of Mineral Deposits in Drain
Tile J. Soil and water Conserv., 1962, May—June, pp 124—5.
Magdoff, F.R., and J. Bouma, The Developmentment of Soil Clogging
in Sands Leached with Septic Tank Effluent. Proc. National Home
Sewage Disposal Syinp., 1974, pp 37—47.
Meiser, E.W., et al. Leachate Collection Using the Groundwater
Flow System: A Landfill Case History in Central Pennsylvania.
Municipal and Industrial Waste Research and Practice, 3rd Conf.,
U. Wisc. September 10—17, 1980, pp 214—227.
Nevo Z., and R. Mitchell, Factors Affecting Biological Clogging
of Sand Associated with Groundwater Recharge. Water Res. 1967,
1:231—6.
Patrick, W.H., Jr., and R.E. Henderson, Reduction and Oxidation
Cycles of Manganese and Iron in Flooded Soil and in Water
Solution Soil. Sci. Am. J., 1981, 45:855—9.
Rice, R.C., Soil Clogging During Infiltration of Secondary
Effluent. J. ‘JPCF, 1974, 46:708—16.
Samani, Z.A., and L.S. Williardson, Soil Hydraulic Stability in a
Subsurface Drainage System. Trans. ASAE 1981, 24:666—9.
Skinner P.N., Performance Difficulties of “Secure” Landfills for
Chemical Waste and Available Mitigation Measures in The Hazardous
W ” te Dilemma: Issues and Solutions . ASCE, New York, 1981.
43
-------
Wigh, R.J., and D.R. Brunner, Leachate Production from Landfilled
Municipal Waste——Boone County Field Site. Municipal Solid Waste:
Land Disposal. U.S. Environmental Protection Agency. Proc: 5th
Ann. Res. Symp., Report EPA 600 /9— 7 9—023a, August, 1979.
Winneberger, J.H., et al. A Study of the Biological Aspects of
Failure of Septic Tank Percolation Systems. 1st Progress Rept.
Sanitary Engineering Res. Lab. U. Cal., Richmond Field Sta.,
Richmond, Cal., December 3, 1958.
U.S. Department of Agriculture. Drainage of Agricultural Land.
Water Information Center, Inc. Port Washington, N.Y., 1973.
U.S. Army Corps of Engineers. Subsurface Drainage Investigation
1945—1946. Boston, Mass., September 1946.
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