&EPA
United States
Environmental Protection
Agency
Office of
Solid Waste and " '
Emergency Response
DIRECTIVE NUMBER:
TITLEi"Waiver from Double Liner Requirements Pursuant to
Section 3015 (b)(l) and 40 CFR Section 265.301 (c)"
for CECOS International, Inc., Williamsburg, Ohio,
Landfill Cell NO. 9 <
APPROVAL DATE: 11/14/85,
EFFECTIVE DATE:
ORIGINATING OFFICE: osw
D FINAL
m DRAFT
STATUS: C - For regional review and comment
REFERENCE (other documents):
OS WER OS WER OS WER
/E DIRECTIVE DIRECTIVE D.
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a-n
vvEPA
Unueti Slates cri.'iror.menid. Pictection Agency
Washington. DC 20460
OSWER Directive Initiation Request
interim Directive Numoer
Originator Information
Name o( Contact Person
Kent Anderson
Mail Code
WH-565E
Telephone Number
382-4654
Lead Office
D OERR
Q OSW
D OUST
CD OWPE
LJ AA-OSWER
Approved for Review
Signature of Office Director
Qate
Title
"Waiver from Double Liner Requirements Pursuant to Section 3015(b)(1)
and 40 CFR Section 265.301(c)" for CECOS International, Inc.,
Williamsburg, Ohio, Landfill Cell No. 9.
Summary of Directive
/ CECOS International, Inc., in a letter to EPA of May 30, .1985,
formally requested a waiver, as provided for in Section 3004 (o) (2)
of the Solid Waste Disposal Act, as amended, from the double liner
requirements of Section 3004 (o) (1) .for their previously constructed
Cell No. 9. i .:
XI I «'
/"
The attached transmittal memorandum, Waiver, Fact Sheet, and
Evaluation Report resulted in a /finding that the CECOS Cell No. 9
design and operation can be considered to be as effective as
the interim statutory design of Section 3004 (o) (5) (B) and 40 CFR
Section 265. 301 (a) under the conditions stated in the Waiver.
Type of Directive /Manual. Policy Directive. Announcement, etc.)
Status
Waiver .
Draft
LJ Final
I
tLJ New
LJ Revision
Does this Directive Supersede Previous Directive(s)? | | Yes
If "Yes" to Either Question. What Directive (number, title)
No Does it Supplement Previous Directive^)?
yes
Review Plan
LJ AA-OSWER
D OERR
S OSW
D OUST
[HI OWPE
S Regions (V
D OECM
D OGC
OPPE
D
Other /Specify!
This Request Meets OSWER Directives System Format
Sigrature of Lead Office Directives Officer
Signature of OSWER Directives Officer
i Date
I Date
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DRAFT
.».u,M>ftKTniiM OSWER Directive
MEMORANDUM
SUBJECT: CECOS International, Inc., Williamsburg, Ohio, Landfill
Cell No. 9 Waiver from Double Liner Requirements
FROM: Marcia Williams, Director
Office of Solid-Waste (WH-562)
TO: Basil Constantelos , Director
Waste Management Division, Region V
CECOS International Inc., in a letter to John Skinner
dated May 30, 1985, requested a waiver from the minimum techno-
logical requirements of Section 3004(o)(l) of the Solid Waste
Disposal Act, as amended (SWDA), for Landfill Cell No. 9 at
CECOS' Aber Road Facility, Clermont County, Ohio.
The general authority to grant waivers for hazardous waste
disposal facilities, such as this request, has been delegated to
the Regional Administrator. Because this was the first request
for a waiver from the minimum technological requirements and
because we have not developed detailed guidance on evaluating
such waiver requests, our office, in conjunction with Ohio EPA
and the U.S. EPA Offices of Region V, the Office of Research and
Development - Cincinnati, the Office of General Counsel, the Office
of^Waste Programs Enforcement, and the Office of Enforcement and
Compliance Monitoring, has developed the attached draft Waiver
from Double Liner Requirements Pursuant to Section 3015(b)(l)
and 40 CFR §265.301(c) .
As we have discussed with your staff, we are turning the
draft waiver over to your office for completion of the waiver
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determination process. This will include the public notice and
public hearing requirements of 40 CFR Part 124 for the draft
waiver and the issuance (or denial) of the final waiver. Because
of the public interest in the general vicinity of the CECOS
facility, a public hearing would be advisable. In the interest
of concluding the Agency's action on this waiver request as
quickly as possible, I believe it is appropriate to announce the
time and place of the public hearing concurrent with the request
for public comments. I understand that CECOS is also interested
in a final determination in this case as soon as possible.
The package of materials that I am attaching for the purpose
_-~-
of assembling an administrative record regarding this waiver
request include:
- Draft Waiver from Double Liner Requirements Pursuant to
Section 3015(b)(l) and 40 CFR §265.301(c)
- Fact Sheet
- Correspondence between CECOS and EPA on Cell No. 9
- Memoranda documenting meetings between CECOS and EPA
- CECOS1 evaluation report entitled "Evaluation of Leachate
Collection and Liner System Performance, Facility No. 9
CECOS International, Clermont, Ohio", May, 1985.
- CECOS International, Clermont County, Ohio, Secured Chemical
Management Facility No. 9, AS BUILT drawings sheets 1 to 10,
January 31, 1985.
- US EPA's evaluation report entitled "Waiver Evaluation
for CECOS International Aber Road Facility Secure Chemical
Management Facility No. 9, Clermont County, Ohio",
October, 1985.
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- Draft Minimum Technology Guidance on Double Liner Systems
for Landfills and Surface Impoundments Design, Construction,
and Operation. December 19, 1984.
- Draft Guidance on Implementation of Minimum Technology
Requirements of HSWA of 1984. January 31, 1985.
- Draft Guidance on Implementation of the Minimum Technological
Requirements of HSWA of 1984, Respecting Liners and Leachate
Collection Systems, Reauthorization Statutory Interpretation
#5D, EPA/530-SW-85-012, May 24, 1985.
- Draft Minimum Technology Guidance on Double Liner Systems
for Landfills and Surface Impoundments Design, Construction,
and Operation, EPA/530-SW-85-014, May 24, 1985.
- Construction Quality Assurance for Hazardous Waste Land
Disposal Facilities, EPA/530-SW-85-021, October, 1985.
-'Federal Register, Vol. 50, No. 135, July 15, 1985.
- CECOS International "SCMF No. 9: Summary Geotechnical
Report", January 1985 (This report is not attached but
is already in the Regional Office).
- CECOS International "SCMF No. 9: Field and Laboratory
Quality Control Data of HOPE Liner Construction",
February 1985 (This report is not attached but is already
in the Regional Office).
- CECOS International "SCMF No. 9: Field Quality Control
Data of Compacted Soil Liner Construction," January 1985
(This report is not attached but is already in the Regional
Office).
Attachments
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DRAFT
Waiver from Double Liner Requirements
Pursuant to Section 3015(b)(l) and 40 CFR §265.301(c)
Section 3015(b)(l) of the Solid Waste Disposal Act (SWDA),
as amended, requires that new landfill units, that qualify to
operate under interim status, comply with the minimum technological
requirements of Section 3004(o), including the requirements of
Sections 3004(o)(l) (codified at 40 CFR §265.301(a)) and 3004(o)(2)
(codified at 40 CFR §265.301(c)), with respect to waste received
on or after May 8, 1985. Section 3004(o)(l) requires that the
owner or operator of a landfill install two or more liners and
leachate collection systems above and between such liners for
each new unit. These requirements apply to CECOS International,
Aber Road Facility Secure Chemical Management Facility Cell No.9,
Clermont County, Ohio.
Section 3004(o)(2) of the SWDA and 40 CFR §265.301(c) provide
that the above minimum technological requirements do not apply
where the Regional Administrator finds for such landfill that
alternative design and operating practices, together with location
characteristics, will prevent migration of hazardous constituents
to .ground water and surface water at least*, as effectively as
such liners and leachate collection systems. The Regional
Administrator for Region 5 here finds that Cell Number 9 qualifies
under the standards set out in Section 3004(o)(2) of the SWDA and
40 CFR §265.301(c) for a waiver from the minimum technological
requirements to the extent specified below, upon the specific
condition that CECOS incorporate the alternative design features
and observe the alternative operating practices described below.
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The design of CECOS' Cell Number 9 deviates from the
requirements of Section 3004(o)(l) of the SWDA and 40 CFR §265.301(a)
by the failure to have a secondary leachate collection system
that covers all areas of the landfill between the top and bottom
liners. This deficiency is compensated for, as documented by
the CECOS AS-BUILT drawing, sheet number 7, dated January 31,
1985, by the inclusion of a primary sidewall contingency leachate
./
collection system and a thicker compacted lower soil liner than
is provided for in the interim statutory design contained in
Section 3004(o)(5)(B) of the SWDA and 40 CFR §265.301(a).
/
/ To continue to qualify for this waiver, the alternative
design and operation of the primary leachate collection system
(including the contingency sidewall collection and removal system)
must include:
Design - The leachate collection system must have:
1) A primary leachate collection sump conveyance system
capable of automatic and continuous functioning.
2) A primary leachate collection system on the cell's
sidewall consisting of the following components (see
CECOS1 AS-BUILT drawing, January 31, 1985, sheet No. 7)
*.
above the top liner:
0 6-ounce protective geotextile
0 1-foot sidewall washed sand blanket with a
hydraulic conductivity of 1X10"^ cm/sec or
more
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0 Contingency leachate collection piping consisting
of 6-inch ABS schedule 80 pipe up the sidewall at 8
locations (at approximately 70-foot spacing). The
pipes extend 5 feet into the primary leachate
collection and removal system at the bottom of the
cell. This 5-foot section is perforated and
functions as a contingency leachate collection
system (see CECOS' AS-BUILT drawing, January 31,
1985, sheet No. 9).
0 16-ounce geotextile drainage media
0 Leachate collection pumps.
3) The ability to monitor leachate head levels within the
landfill at the sidewalls during the active life and the
post-closure care period.
4) Been designed as specified in EPA regulations and guidance
(e.g., 40 CFR §264.301 and "Permit Applicants Guidance
Manual for Hazardous Waste Land Treatment, Storage, and
Disposal Facilities," EPA/530-SW-84-004) so as to withstand
the stresses and disturbances from overlying wastes,
waste cover materials, and equipment operation.
5) Been designed as specified in EPA regulations and guidance
(e.g., 40 CFR §264.301 and "Permit Applicants Guidance
Manual for Hazardous Waste Land Treatment, Storage, and
Disposal Facilities," EPA/530-SW-84-004) so as to withstand
to function without clogging through the active life and
post-closure care period.
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Construction - Components must be properly installed to assure
that the specified performance of the leachate collection system
is achieved. Future construction of the sidewall primary leachate
collection system must be documented by a construction quality
assurance (CQA) program prior to operation of that portion of the
unit. The CQA program, as specified in EPA draft guidance
documents entitled "Draft Minimum Technology Guidance on
Double Liner Systems for Landfills and Surface Impoundments
Design, Construction, and Operation", EPA/530-SW-85-014, May 24,
1985 and "Construction Quality Assurance for Hazardous Waste
?'
Land Disposal Facilities", EPA/530-SW-85-021, October, 1985,
must be used to monitor and document the quality of materials
(e.g., liner, drainage, piping) used and the conditions and
manner of their placement. The program must be developed,
administered, and documented by a registered professional engineer.
The documentation must include a report containing a summary of
construction activities, observations, test data sheets, deviations,
and as-built drawings. The documentation for the CQA program
must be kept available for review.
Operation - The following operational procedures must be followed:
1) The primary leachate removal system must be operated
automatically and continuously during the active life
and post-closure care period whenever leachate is present
in the sumps (leachate standpipes) and must remove accumulated
leachate at the earliest practicable time to minimize (produce
very low or no) head of leachate on the top liner. The
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leachate depth above the top liner shall not exceed one
foot except temporarily (for a few days) after major
storms during the active life of the unit. ..
2) The contingency sidewall primary leachate removal system
must be operated daily during the active life and
post-closure care period whenever leachate is present in
the pipe and must remove accumulated leachate at the
earliest practicable time to minimize the leachate head
on the liner to a very low level. Even a very low leachate
depth shall not be present in the contingency leachate
collection pipes, except temporarily after major storms.
3) Inspect for proper operation of the primary leachate
(including contingency sidewall) collection and removal
system, and for the presence of leachate in the removal
sumps and the contingency leachate collection pipes
daily during the operating period and monthly during
closure and the post-closure care period. A record of
inspections and findings must be kept available for
review.
4) Repair of damaged primary leachate collection and contingency
sidewall system components as soon as practicable during the
operating period.
5) During the active life and post-closure care period,
notification of the Regional Administrator, in writing:
a) within 7 days of the presence of a removable
quantity of leachate, except temporarily
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(i.e., a few days) after major storms during the
active life, in the contingency sidewall leachate
collection and removal system;
b) within 7 days of the presence of a leachate
depth of one foot or more above the top liner;
c) within 15 days of known damage to the primary
leachate collection and contingency sidewall
system components; the notification should
outline procedures planned to repair the damage
and a projected schedule.
6) Collected leachate must be removed to a storage, treatment,
or disposal facility that is permitted under 40 CFR
Part 264 or operating under interim status pursuant to
40 CFR Part 265.
Any modifications to plans and specifications following
waiver approval must be approved in writing by the Regional
Administrator prior to construction and operation.
Date:
Regional Administrator
US .EPA, Region V
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FACT SHEET
for
Waiver from Double Liner
Requirements Pursuant
to Section 3015(b)(l) and
40 CFR i265.301(c) for CECOS International,
Aber Road Facility Secure Chemical
Management Facility No. 9
Clermont County, Ohio
A. Background: On May 30, 1985, CECOS International, Inc.,
requested a formal review of the design of their hazardous
waste, landfill Cell No. 9 at CECOS1 Aber Road Facility near
Williamsburg, Ohio, for compliance with Section 3015(b)(l)
of the Solid Waste Disposal Act (SWDA) as amended regarding
/
double liners and leachate collection and removal systems.
In EPA correspondence to CECOS on June 25, 1985, EPA stated
that this unit is a "new unit" (because no waste had been
placed in the unit as of November 8, 1984) and therefore is
required under Section 3015(b)(l) of the SWDA to comply with
the minimum technological requirements in Section 3004(o)(l)
or (2). But because Cell No. 9 does not meet the requirements
of Section 3004(o)(l) (as U.S. EPA Region V notified CECOS
on May 3, 1985), EPA regards the CECOS letter of May 30,
1985, as a formal request for a waiver under standards
set out in Section 3004(o)(2) of the SWDA. On July 15, 1985
EPA codified the SWDA Section 3004(o)(l) and (2) into 40 CFR
§265.301(a) and (c).
B. Legal basis for waiver including reference to statutes,
regulations, and supporting references:
The Hazardous and Solid Waste Amendments to the Solid
Waste Disposal Act were signed into law on November 8, 1984.
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These amendments, under Section 3004(o)(2), provide a provision
for a waiver from Section 3004(o)(1)(A)(i), which requires the
installation of two or more liners and a leachate collection
system above and between such liners for certain landfills seeking
permits. Section 3015(b)'(l) of the SWDA made the requirements
of Section 3004(o) applicable to certain interim status landfills,
including "new units" such as CECOS' Cell No. 9. On July 15,
./
1985, EPA codified the requirements of Sections 3004(o)(1)(A)(i),
(o)(2), and 3015(b)(l) of the SWDA in 40 CFR §§264.301(c) and
265.301(a) and (c). The waiver of Section 3004(o)(2) and 40 CFR
§265.301(c) is applicable to owners and operators of landfills
'that demonstrate that alternative design and operating practices,
together with location characteristics, will prevent the migration
of any hazardous constituents into the ground water or surface
water at least as effectively as the liners and leachate collection
systems, specified in Section 3004(o)(1)(A)(i) and 40 CFR §265.301(a).
Section 3004(o)(5)(B), 40 CFR §265.301(a), and 40 CFR §264.301(c)
provide an interim statutory design that can be used to satisfy
the liner and leachate collection system requirements of Section
3004(o)(l)(A)(i) and 40 CFR §265.301(a). EPA determined that
i,
the CECOS Cell No. 9 does not meet the design called for in
Section 3004(o)(l) because of the lack of a secondary leachate
collection and removal system in all areas between the liners,
and therefore CECOS would have to seek a waiver under
Section 3004(o)(2); i.e. 40 CFR §264.301(c).
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CECOS' Cell No. 9 was primarily constructed in advance of
EPA's draft Minimum Technology Guidance that specifies the use
of an extensive construction quality assurance (CQA} program to
ensure that the unit is constructed in conformance to the design.
While CECOS' CQA program did not completely conform to that
in EPA's draft guidance, it was considered at that time to
constitute very high CQA standards. Units constructed since
issuance of the May 24, 1985, draft guidance should undergo a much
more rigorous testing and construction quality assurance plan.
C. Reasons requested waiver appears justified:
CECOS conducted a comparative evaluation of the design of
Cell No. 9 vs a "preferred regulatory design" (from EPA's draft
liner guidance dated December 19, 1984) that differs somewhat
from the interim statutory design of Section 3004(o)(5)(B) of
SWDA and 40 CFR §2G5.301(a). The interim statutory design has a
lower liner that consists of three feet of low permeability
recompacted natural material while the "preferred regulatory
design" used by CECOS in their evaluation has a composite lower
liner consisting of a synthetic liner as the upper-most component
of the composite and a lower component consisting of two feet of
low permeability recompacted natural material. The CECOS comparative
evaluation is documented in a report entitled "Evaluation of
Leachate Collection and Liner System Performance, Facility No. 9,
CECOS International, Clermont County, Ohio". The report, prepared
by the consulting engineering firm of STS D'Appolonia Ltd. and
dated May 1985, concludes that the performance of the leachate
collection and liner systems of the Cell No. 9 design should
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exceed the capabilities of the preferred regulatory design in
mitigating leakage.
U.S. EPA conducted its own evaluation of the CECOS Cell
No. 9 landfill design and operation and compared its ability to
prevent migration of any hazardous constituents into the ground
water or surface water to that of the interim statutory design
of Section 3004(o)(5)(B) and 40 CFR §265.301(a). The EPA
./
evaluation compared the CECOS design to the interim statutory
design, rather than the "preferred regulatory design," since
this is the design that meets the requirements of the statute.
EPA's evaluation is fully documented in the report entitled
"Waiver Evaluation for CECOS International Aber Road Facility
Secure Chemical Management Facility No. 9, Clermont County,
Ohio," October 1985. The result of this study is that the
CECOS Cell No. 9 design and operation can be considered to be
as effective as the interim statutory design of Section 3004(o)(5)(B)
and 40 CFR §265.301(a) only under the conditions stated in the
"Waiver from Double Liner Requirements Pursuant to Section
3015(b)(l) and 40 CFR §265.301(c)" for CECOS Cell No. 9.
D. Description of procedures for reaching a final decision:
f- - .-
The draft Waiver will be made available for public comment,
including a public hearing in a location convenient to the public
living near the facility. The public comment" period will be for
45 days. Public notice of the draft Waiver and of the public
hearing will be given at least 30 days before the hearing.
Applicable methods outlined in the Code of Federal Regulations,
40 CFR §124.10, for making the notice public will be followed.
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The beginning and end dates of the public comment period
are November 1985 [DATE OF PUBLIC NOTICE] to
1985 [DATE 45 DAYS AFTER DATE OF PUBLIC NOTICE] . After the
close of the public comment period, the Regional Administrator
will issue a final Waiver decision.
E. The following person may be contacted for additional information
, regarding this request for waiver:
Bruce Sypniewski
U.'S. EPA, Region V
230 South Dearborn Street
Chicago, Illinois 60604
(312) 886-6189
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WAIVER EVALUATION FOR
CECOS INTERNATIONAL ABER ROAD FACILITY
SECURE CHEMICAL MANAGEMENT FACILITY NO. 9
CLEFMONT COUNTY, OHIO
OCTOBER 1985
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ACKNOWLEDGEMENT
The analysis for this report was conducted by Battelle Columbus
Laboratories for the U.S. Environmental Protection Agency
under Contract No. 68-03-3248.
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TABLE OF CONTENTS
Tables ill
Figures .. iv
1.0 Introduction 1
2.0 General Description of the Landfill Designs 2
2.1 Interim Statutory Design 2
2.2 CEOOS Cell No. 9 Design 2
3.0 Evaluation Approach 4
3.1 Performance Criteria 4
/'
3.2 Failure Scenarios 5
3.3 Hydraulic Modeling Methodology 6
3.4 Model Simulation 8
4.0 Model Results 9
5.0 Conclusions 17
6.0 Findings and Recommendations 17
References 19
ii
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TABLES
1. Hydraulic Conductivities of Materials .- 8
2. Summary of Model Input Data 10
3. Flow Distribution Within the Sidewall Region 11
4. Drainage Time Factor, Volume Exiting Sidewall Djring
Drainage Time, and Breakthrough Time 12
iii
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FIGURES
1. Schematic of Interim Statutory Design 3
2. Schematic of CECOS Cell No. 9 Design 3
3. Max imam Release Rate Comparison 13
4. Drainage Time Comparison 14
5. Breakthrough Time Comparison 15
iv
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WAIVER EVALUATION FOR
CECOS INTERNATIONAL ABER ROAD FACILITY
SECURE CHEMICAL MANAGEMENT FACILITY NO. 9
CLERMONT COUNTY, OHIO
OCTOBER 1985
1.0 INTRODUCTION
The Hazardous and Solid Waste Amendments (HSWA) of 1984, amends Section 3004
of RCRA by adding a new paragraph (o) imposing minimum technological requirements
on owners and operators of certain landfills and surface impoundments seeking
permits. HSWA also adds a new Section 3015 to RCRA imposing the minimum technological
requirements set out in Section 3004(o) on certain interim status landfills and
surface impoundments. Specifically, Section 3004(o)(1)(A) requires that affected
units must install two or more liners, a leachate collection system above (in the
case of a landfill) and between the liners, and ground water monitoring. Section
3004(o)(5)(B) allows the use of a particular type of liner design pending the
issuance of EPA regulations implementing the double liner requirements. Section
3004(o)(2) provides for an exemption from the Section 3004(o)(1)(A) standards for
liners and leachate collection systems if alternative design and operating practices,
together with location characteristics will prevent the migration of hazardous
constituents as effectively as systems under Section 3004(o)(1)(A).
The Section 3015 requirements are applicable to the CECOS International Aber
Road Facility, Secure Chemical Management Facility No. 9 (hereafter referred to as
CECOS Cell No. 9) in Clermont County, Ohio. The main issue with the CECOS Cell
No. 9 design is that a secondary leachate collection system does not cover all
areas of the landfill between the upper and lower liners. CECOS International
has requested a waiver for Cell No. 9 from EPA. The purpose of this report is to
document the hydraulic evaluation of CECOS Cell No. 9. This evaluation compares
the performance of CECOS Cell No. 9 with the interim statutory design contained in
Section 3004(o)(5)(B) per Section 3004(o)(2) (hereafter referred to as the interim
statutory design) which allows alternative designs under certain circumstances.
In enacting HSWA, Congress has mandated the use of two or more liners and a
leachate collection system above (in the case of a landfill) and between such
liners. The need for this system is based on the experience that some existing,
single lined landfills and surface impoundments have failed. The Congress intends
that, for general protection of human health and the environment, hazardous waste
facilities provide means to minimize the risk of waste migration out of the unit.
The statutory design for landfills in Section 3004(o)(l) provides for liners and
leachate collection systems covering all areas of the unit that are in contact
with the wastes (See Federal Register, Vol. 50 No. 135, July 15, 1985, p.28,709).
This means that the unit must have a leachate collection system above the top
liner, two or more liners, and a secondary leachate collection and removal system
between the liners on the landfill bottom and side walls.
The evaluation of the CECOS Cell No. 9 landfill design and operation was
performed to conpare its relative ability to prevent migration of any hazardous
constituents into the ground water or surface water at least as effectively as the
interim statutory design. In doing so, the evaluation focuses on conditions where
the lower liner and secondary leachate collection systems are required, i.e.,
various failures of the upper liner and primary leachate collection system.
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2.0 GENERAL DESCRIPTION OF THE LANDFILL DESIGNS
This evaluation conpares the CEOOS Cell No. 9 design to that of the interim
statutory design contained in Section 3004(o)(5)(B) which satisfies the require-
ments of Section 3004(o). The general features of the interim statutory design
and the CECOS Cell No. 9 design are provided in the following sections. Details
for the interim statutory design are based on the design presented in Section
3004(o)(5)(B) of HSWA. Details for CECOS Cell No. 9 design are based on the AS-BUILT
specifications (dated January 31, 1985) provided by CECOS International.
2.1 INTERIM STATUTORY DESIGN
The interim statutory design consists, at a minimum, of a primary leachate
collection and removal system. The top liner consists of a liner designed, operated,
and constructed to prevent the migration of any constituent into such liner during
the active life and post-closure care period (i.e., flexible membrane liner (FML)).
A secondary leachate collection system is between the two liners on the bottom and
sidewalls to detect, collect, and remove liquids entering the collection system.
The lower liner consists of a liner designed, operated, and constructed to prevent
the migration of any constituent through such liner during such period. HSWA
specifies that the bottom (lower) liner be deemed to satisfy this requirement if
it is constructed of at least a 3-foot thick layer of recompacted clay or other
natural material with a permeability of no more, than 1 x 10 cm/sec. Figure 1
is a schematic of the interim statutory design.
2.2 CECOS r-FTl. NO. 9 DESIGN
A schematic representation of the CECOS Cell No. 9 is shown in Figure 2. The
sidewall liner system consists of, from top to bottom, a protective soil layer, a
geotextile, 1-foot of sand (leachate collection layer), a geotextile, the FML, and
7.5-feet compacted soil liner (bottom or lower liner). The sidewall slope is 2:1
(horizontal to vertical). Eight 6-inch pipes, spaced approximately equally around
the facility, are located in the sand layer on the sidewalls and extend 5 ft.
into the primary leachate collection and removal layer at the bottom of the cell.
These pipes are perforated in the bottom layer and function as a contingency leachate
collection and removal system. This contingency leachate collection system is a
very important element of Cell No. 9 because it is designed to provide additional
and backup capability to remove liquids from the sidewall area.
The cell bottom liner system, from top to bottom, consists of a protective
soil layer, a geotextile, 1-foot of sand (primary leachate collection and removal
system), the FML, 4-feet of compacted clay, 1-foot of sand (secondary leachate
collection and removal system), and 2.5-feet of compacted clay (secondary liner).
The secondary leachate collection system is located below the 4-feet of compacted
clay except near the sidewall/bottom interface and under a center berm. An
additional leachate monitoring system is located below the 2.5-feet of clay layer
as a requirement under TSCA (not shown in Figure 2). For specific details of the
design see AS-BUILT Drawing.
Cell No. 9 is located within a zone of saturation. To help maintain slope
stability, a dewatering system is operated outside the unit until the cell becomes
sufficiently full to offset the hydrostatic pressure. Because of the presence of
1 AS-BUILT Drawing, sheet 7 of 10 by Soil and Material Engineers, Cincinnati, Ohio,
dated January 31, 1985.
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Figure 1. Schematic of Interim Statutory Design
Protective Soil or Cover
3 ft miniouB Lev Permeability
Kacoapacted Natural Material
Secondary Leachate
Collection and Removal
System
Primary Leachate
Collection and Removal
System
Native Soil Foundation
(Not to Scale)
Figure 2. Schematic of CECOS Cell No. 9 Design.
Ceotextile
7.S ft Recompacted
Soil Liner
tlngency Leach
Collection System
(at approx. 70 ft spaclng>
Native Foundation
Material
Secondary Leachate
Collection and Removal
System
(Not to Scale)
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ground water, the point of comparison for the CBCOS Cell No. 9 facility and
the interim statutory design is at the interface between the compacted soil
liner on the sidewalls (or the compacted clay liner on the bottom) and the
native material.
3.0 EVALUATION APPROACH
The evaluation approach was based on hydraulic modeling of the CECOS Cell
No. 9 design and the interim statutory design. Performance criteria and failure
scenarios were developed to characterize the ability of each design to prevent
or minimize migration of hazardous constituents into the ground water and surface
waters under conditions where the secondary leachate collection and liner systems
woulcj be needed. The performance criteria selected are (1) liner systems breakthrough
times, (2) maximum leakage release rates, and (3) a drainage time factor related
to the length of time a release could occur. The failure scenarios include various
situations where primary design components are assumed to fail and secondary systems
become necessary to minimize releases to the environment. The performance criteria,
failure scenarios, and hydraulic modeling methodology are described in more detail
in the next sections.
3.1 PERFORMANCE CRITERIA
The legislative history to the waiver provision indicates that alternative
designs should not only assure equivalent containment, but also provide for
equivalent leachate removal or other means of controlling the volume of hazardous
leachate. (Senate Report No. 284, 98th Congress, 1st Session, pp. 27-28, 1983.)
The performance criteria that were selected for this evaluation represent the
factors affecting migration: (1) when breakthrough will occur, (2) the maximum rate
of leakage, and (3) the duration of a release from the unit. The first two factors
consider the ability of the design to contain wastes within the unit while the
third criterion primarily evaluates the efficiency of the leachate collection and
removal system.
The three performance criteria were developed to establish a quantifiable
definition of "effectiveness" for each design. The CECOS Cell No. 9 design and
operation has to be at least as effective as the interim statutory design in terms
of these three performance criteria. The three performance criteria taken together
are conservative and will allow comparisons and ensure that the goals of the legis-
lation and regulations, primarily section 3004(o)(5)(B), are met.
Criteria I Breakthrough Time: This is a measure of the time required for
leachate or hazardous constituents to migrate through the bottom (lower) liner,
following a failure of the primary (top) liner system. In the case of CECOS Cell
No. 9, the facility is located within a zone of saturation and, therefore, any
migration beyond the secondary liner is a release to the ground water. A section
3004(o)(2) waiver would require that this breakthrough time for the alternative
design and operating condition be equivalent to or greater than the breakthrough
time for the interim statutory design.
Criteria II Maximum Leakage Release Rate: The maximum leakage release rate
is the maximum daily rate that liquids are released from the bottom (lower) liner
on the sidewall. This maximum rate is based on the "worst-case" condition where
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the facility has developed a very large hydraulic head above the liner systems.
This worst-case condition could occur if the primary leachate collection system
became severely clogged (or was not operated) and the final cover system failed to
prevent infiltration of water into the unit (i.e., the "bath tub" effect). A
section 3004(o)(2) waiver requires that the alternative design along with operating
practices has a maximum leakage release rate less than or equal to the interim
statutory design.
Criteria III Duration of a Release From the Unit: This is a measure
of the time required to empty from the unit the volume of leachate being modeled,
utilizing the secondary leachate collection systems. In this analysis the
volume of leachate was assumed to be one pore volume (i.e., the landfill waste
is saturated with leachate). While this analysis results in a measure of time,
it is also a measure of the effectiveness of the design to collect and ranove
leachate, which is dependent on the rejection efficiency of the liner. The
rejection efficiency is a measure of the liner's ability to prevent migration
into the liner. In this analysis, the primary leachate collection and removal
system was assumed to be nan-functioning. This criterion is a drainage time factor
calculated by dividing the volume of liquids stored in the unit by the removal
rate of the secondary leachate collection systems for the interim statutory design.
For the CECOS design, the volume of liquid is divided by the removal rate of
both the secondary leachate collection system on the bottom of the unit and the
contingency leachate collection and removal system on the sidewalls. Therefore,
the drainage time factor is an evaluation of the efficiency of the drainage
system to remove a given volume of liquid. The greater the efficiency of the
leachate collection system, the greater the quantity of liquids that will be
removed versus being absorbed into the liner. As a result, the drainage time
factor is the period of time that liquids are potentially available for release
into the liner. Even if an alternative design and operating practice has a
longer breakthrough time (Criteria I) and a smaller rate of release than the
interim statutory design (Criteria II), a larger total volume of hazardous constituents
could be released to the environment unless this third criterion is also considered.
If the alternative design along with operating practices has an equal or smaller
value for this third criterion when compared to the interim statutory design and
meets the other two performance criteria, it would provide an equivalent or
better level of environmental protection.
3.2 FAILURE SCENARIOS
Failure scenarios were developed to provide conditions where the secondary
systems would be needed. Since the main issue with CECOS Cell No. 9 is the
sidewall, the failure scenarios focused on conditions in which liquids, hydraulic
head driving forces, and leaks through the top FML are present at the sidewalls.
The first failure assumption is that the primary leachate collection system on
the bottom of the cell does not function. The second assumption is that infiltra-
tion into the waste cell results in the unit filling with liquids. These two
assumptions allow liquids (hydraulic head) to build up in the facility. The
third assumption is that the top liner, an FML, does not prevent migration.
Three permeation rates (represented as effective hydraulic conductivities) are
assumed for the FML on the sidewalls: 1 x 10~9 cm/sec, 1 x 10~7 cm/sec, and
1 x 10~4 cm/sec, which represent increasingly severe failures to the FML on
the sidewall. The hydraulic conductivity of the FML on the bottom of the unit
is assumed to have a very low hydraulic conductivity of 1 x 10"10 cm/sec.
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An operational assumption in the failure scenarios is that the secondary
leachate collection systems are functional and operated at design capacity
for both the CECOS and interim statutory designs. Corrective measures are triggered
by some circumstance, such as the presence of leachate in the secondary leachate
collection systems, detection of leachate in the monitoring wells, or observation
of high head levels within the waste cell. In the event that corrective measures
have not been triggered and the secondary leachate collection systems are not
operated, then the CEOOS Cell No. 9 design would have a slightly smaller release
rate due to the thicker liner on the sidewall (assuming that the interim statutory
design has the same as-built soil liner properties as the CECOS Cell No. 9 soil
liner). An operational assumption for the CECOS Cell No. 9 includes cases with
and without the operation of the contingency leachate collection system above
the top liner on the sidewall of the cell.
Worst-case assumptions were established for the hydraulic head for the
failure scenarios. The head was held at 50 feet above the bottom of the secondary
clay liner. A 50 foot head was selected since this is the approximate depth of
the landfill cell. While the head is held at 50 feet, this head would not be
transmitted through the secondary drainage layer because of the greater hydraulic
conductivity of the drainage layer as compared to that of the waste. Therefore,
in the case of the interim statutory design, the bottom liner is not subjected
to the full head. However, for the CECOS design, if the contingency side wall
collection system is not operated, the bottom liner on the sidewalls will be
subjected to the hydraulic head from the leachate in the landfill. The water
table was generally assumed to be 10 feet below the bottom of the secondary clay
liner except for one case where it was assumed to be 5 feet above the bottom of
the secondary clay liner.
These two cases (i.e., water table 10 feet below and 5 feet above the
bottom of the secondary clay liner) relate to CECOS Cell No. 9 (i.e., location
characteristics as required under Section 3004(o)(a)). During most of the active
life of the unit, the ground water is held below the unit by a dewatering system
operated outside the unit (i.e., the need to evaluate the design with the water
table 10 feet below the bottom of the secondary clay liner). After the unit
becomes sufficiently full to offset the hydrostatic pressure on the sidewalls,
the operation of the dewatering system will be stopped and the ground water will
be allowed to rise outside of the unit (i.e., the case where the water table
is 5 feet above the bottom of the secondary clay liner). The second case, where
the ground water is assumed to be above the bottom of the unit was used to
demonstrate that the most critical period is while the ground water is at or
below the unit.
3.3 HYDRAULIC MODELING METHODOLOGY
The performance of the CECOS Cell No. 9 and the interim statutory designs
can be effectively evaluated using two-dimensional (cross-section), saturated
ground-water flow, model analyses. Conceptually, each design is represented as
a saturated system, somewhat like a full bath tub with the same amount of water
flowing in as flowing out of the drain. The methodology and modeling approach
are discussed below.
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Engineered landfill facilities and failure scenarios are evaluated with CFEST
(Gupta et al., 1982), a saturated ground-water flow model. CFEST is one of nany
ground water models that could be used to conduct this study. It was selected
because it was documented and has been tested. The authors also have experience
with the application of CFEST. The failure scenarios can be conservatively evaluated
using steady-state saturated flow analysis because the maximum amount of liquid
will be forced through the system under saturated conditions. Under unsaturated
conditions, hydraulic conductivities of the lower liner (including the sidewalls)
could be an order-of-magnitude smaller, therefore, allowing less flow through the
system. The landfill designs modeled all contain a lower liner that extends up
the sidewall that is compacted with hydraulic conductivities of 1 x 10 on/sec
or 1 x 10 cm/sec. The materials overlying the lower liner are more permeable
with'the exception of the FML. The relatively "tight" lower soil liner, in contrast
to the "native material," that underlies it, down to the water table, provides an
over-drained condition; therefore, the soil liner is the rate-limiting material at
the base of the engineered facilities. The failure scenarios assume a consant
saturated level in the waste cell. All failure scenarios presume some degree of
leakage through the top FML and initial and steady-state saturated conditions.
The modeling analysis uses steady-state assumptions for material properties
and constant head conditions to determine how much flow will go to the operating
collection systems and how much flow will leak through the bottom soil liner. A
constant head condition (i.e., the landfill remains filled with leachate) is used
because there is an unlimited source of liquids to the overall system, so the
resulting release rates and leachate collection rates are essentially the worst-case
values. This methodology is conservative in that it will generally underestimate
the efficiency of each design because unsaturated flow analysis would have large
decreases in hydraulic conductivities of the various layers above the sidewall and
bottom soil liner. More detail flow analyses could be conducted, such as unsaturated
flow analysis or transient saturated flew analysis, however, those modeling approaches
are nuch more susceptible to unknown errors in the determination of basic parameters
(e.g., unsaturated moisture characteristic curves).
Breakthrough times are calculated with the Green-Ampt eqauation. The Green-Arrpt
(Green and Ampt, 1911) equation can be used to estimate the time for a wetting
front to advance in a soil column. In this study, the Green-Ampt equation was
used to provide relative time estiinates for water to pass through the bottom
soil liner on the sidewall.
This equation approximates the wetting front as a square wave to which
saturated Darcy flow analysis is applied. The equation captures the dynamics of
a wetting front and is a conservative method for estimating breakthrough times
(EPA, 1984). Heads above and below the soil liner on the sidewall (h^ and h-D)
for this equation are determined from the CFEST model runs.
The Green-Ampt equation can be written as:
t =
es - ei
K
Z - (ftp - he ) In
+ Z -
hp -
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8
where
t = time for the wetting front to advanoa through the liner;
es = saturated moisture content of the liner material (above
the wetting front);
e^ = initial moisture content of the liner material (below
the wetting front);
K = hydraulic conductivity of the liner material at some
average moisture content (i.e., between es and ej_);
' Z = liner thickness
hji = head at the top of the liner; and
hg = head at the base of the liner.
3.4 MODEL SIMULATION
The CFEST finite-element ground-water code was used to simulate CECOS Cell
No. 9 and the interim statutory design under various failure scenarios. A finite
element grid was set up to represent each layer within each design case. For
all cases, the head at the top of the landfill was held at 50 feet above the
bottom of the secondary liner which corresponds to a worst-case hydraulic head
condition. By doing so, liquids are always available at the top to replace
liquids that are removed by the leachate collection systems. The water table at
the bottom of the region was held at either 10 feet below the secondary liner or
5 feet above the secondary liner, depending on the failure scenarios. Liquids
flow from a higher to a lower head (i.e., from 50 feet to 5 feet or to -10 feet
relative to the bottom of the secondary liner). The hydraulic conductivity (K)
for all the materials siirulated are shown in Table 1.
Table 1. Hydraulic Conductivities of the Materials
Material K (on/sec)
Waste 1 x 10~5
*\
Sand (Leachate Collection Layers) 1 x 10~z
Compacted Soil* 1 x 10~6 and 1 x 10~7
FML (Sidewall)** 1 x 10~4, 1 x 10~7, and 1 x 10"9
FML (Bottom)** 1 x 10~10
Native Material 1 x 10~3
*CBCOS Cell No. 9 is evaluated with both K values
**EML's leaks are simulated using equivalent K values
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Two values of hydraulic conductivity for CECOS Cell No. 9 compacted soil
liner were used because of uncertainty in the as-built field hydraulic conductivity.
However, the soil utilized on the sidewalls is a silty till material that has
laboratory K values less than 1 x 10~7 cm/sec. In the construction of Cell No. 9,
CECOS used what was considered at the time to be good quality control to assure
that the unit was constructed as designed (i.e., hydraulic conductivity of less
than 1 x 10""' on/sec). A complete description of the model input'data in each
case is shown in Table 2.
Five failure scenarios were evaluated for the interim statutory design and
two versions of CECOS cell No. 9 design, version A with a soil liner K of 1 x 10~°
cm/sec and version B with a soil liner K of 1 x 10~7 cm/sec. A description of
each case is as follows:
Case 1 - Severe failure of the sidewall FML (K = 1 x 10"4 cm/sec).
Water table below the cell.
Case 2 - Moderate failure of the sidewall FML (K = 1 x 10" 7 cm/sec). Water
table below the cell.
Case 3 - Severe failure of the sidewall FML (K = 1 x 10"4 on/sec).
Water table above the cell bottom.
Case 4 - Severe failure of the sidewall FML (K = 1 x 10"4 cm/sec).
Water table below the cell. Contingency leachate collection
system operating in CECOS Cell No. 9.
Case 5 - Minor failure of the sidewall FML (K = 1 x 10~9 cm/sec). Water
table below the cell.
In all cases the primary leachate collection system on the bottom unit
is not operating, the secondary leachate collection systan is operating, and the
hydraulic head in the waste is held at 50 feet above the bottom of the cell.
The letter A designates CECOS Cell No. 9 with a sidewall soil liner K of 1 x 10~6
cm/sec, the letter B designates CECOS Cell No. 9 with a sidewall soil liner K of
1 x 10 on/sec, and the letter S designated the interim statutory design with a
sidewall soil liner K of 1 x 10~7 cm/sec.
Case 1, 2, and 5 demonstrate the effects of different leakage rates through
the top liner (FML). Case 1 versus Case 3 demonstrates the effect of different
assumptions of the location of the water table under the worst-case FML failure
condition. Case 1 versus Case 4 demonstrates the effect of operating the contingency
leachate collection systan in CECOS Cell No. 9 under the vorst case FML failure
condition. Case 1 and 4 represent the most severe cases.
4.0 MODEL RESULTS
The model results are presented in Tables 3 and 4. Graphical comparisons of
the three performance criteria for the failure scenarios are also presented in
Figures 3, 4, and 5. Table 3 shows the distribution of flow within the sidewall
region. Flow rates are expressed in units of ft /day/ft (rate of flow in cubic
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10
Table 2. Summary of Model Input Data
Design
Case
1A
IB
IS
2A
2B
2S
3A
3B
3S
4A
43
4S
5A
53
5S
Sidewall Compacted Water Table*
FML K Soil K Elevation
(cm/sec) (on/sec) (ft)
1 x 10"4 1 x lO"6 -10.0
1 x 10"7
ii M n
1 x 10~7 1 x ID"6
1 x 10~7
n M n
1 x 10~4 1 x 10~6 5.0
1 x 10~7
M M ii
1 x 10~4 1 x 10"6 -10.0
1 x 10~7
n n ii
1 x 10~9 1 x 10"6
1 x 10~7
II M II
Contingency Leachate
Collection System
Not Operated
N/A
Not Operated
ll ll
N/A
Not Operated
N/A .
Operated
'
N/A
Not Operated
'
N/A
Cases 1A-5A and IB-SB are CECOS Cell No. 9 simulations
Cases 1S-5S are Interim Statutory Design simulations
* Relative to the bottom of the secondary liner.
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11
Table 3. Flow Distribution Within the Sidewall Region
(all values are in units of ft3/d/ft)*
Design Maximum Release Rate Flow Rate Through Flow Rate Through
Case Through Sidewall Secondary Leachate Contingency Leachate
Collection System Collection System
1A 1.91 0.54 N/A
IB 0.23 0.07 N/A
IS " 0.07 4.98 N/A
2A 1.79 0.41 N/A
2B 0.23 0.07 N/A
2S 0.07 3.67 N/A
3A 1.33 0.53 N/A
3B 0.16 0.07 N/A
3S 0.06 2.76 N/A
4A 0.43 -0- . 9.73
4B 0.05 -0- 10.03
4S 0.07 4.98 N/A
5A 0.16 0.02 N/A
5B 0.10 0.01 N/A
5S 0.004 0.178 N/A
Rate of flow in cubic feet per day from a one-foot slice of the landfill
sidewall from top to bottom.
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12
Table 4.
Design
Case
Drainage Time Factor (Volume of Liquids in the Landfill
Divided by Leachate Collection Rate), Volume Exiting Sidewall
During Drainage Time, and Breaktlirough Tims
Drainage Time
(days)
Volume Exiting
Sidewall During
Drainage Time
(ft3/ft)
Breakthrough
Time
(days)
1A
IB
IS
2A
2B
2S
3A
3B
3S
4A
4B
4S
5A
5B
5S
876
7,045
390
974
7,158
525
1,151
9,231
700
211
213
390
12,596
19,391
10,808
1,672
1,637
27
1,744
1,640
37
1,535
1,509
42
91
10
27
1,950
1,894
43
19
157
253
20
170
312
25
204
372
98
947
253
81
234
899
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to
>>
p
E
pg
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Figure 5. Breakthrough Times (days)
P
p
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16
feet per day from a one-foot slice of the landfill sidewall frcn top to bottom) (
because the CFEST model analysis is based on a cross-section of each design.
Flows at or near the sidewall are either released through the sidewall (i.e.,
maximum release rate through sidewall) or collected by the secondary or contingency
leachate collection systems. These rates are maximum values because of the high
constant head conditions assumed in this analysis. Because CEOOS1 Cell No. 9
only has a secondary leachate collection system on the bottom of the cell (i.e.,
no sidewall secondary leachate collection systsn), very little flow from the
sidewall reaches the secondary leachate collection system.
The drainage times presented in Table 4 and Figure 4 are calculated by
dividing the total amount of liquids within each design by the flow rate through
the secondary and/or contingency leachate collection systems. The drainage time
factor relates directly to the length of time a release could occur given that
the secondary or contingency leachate collection systems were being operated to
remove all liquids from the landfill. Remember, however, that this analysis has
a constant head, while under normal field conditions, the head would be declining
eventually to zero if all liquid input into the cell were eliminated. Table 4
also contains the volume exiting the sidewall during the drainage time. These
values are determined by multiplying the maximum release rates by the drainage
time. These volumes are another measure of the effectiveness of each design.
The physical significance of these volumes is that while liquids are being removed
by the secondary or contingency leachate collection systems, releases through
the sidewall will occur; thus, more effective collection systems will reduce the
volume of liquids release to the environment.
Breakthrough times are presented in Table 4 and Figure 5. Breakthrough
times represent another measure of performance of each design but because of the
drastic head conditions and conservative breakthrough equation, these values have
little resemblance to breakthrough times that would occur under less severe conditions
(i.e., normal field conditions). The relative relationship between breakthrough
times for various designs and operating conditions should, however, be similar
with the smaller heads that are more likely to occur in an actual landfill.
The results generally indicate that the interim statutory design is not
significantly affected by various failure scenarios. Cases 1S-4S all have almost
identical maximum release rates through the sidewall. This result is due to the
secondary leachate collection system's ability to reduce the head on the sidewall
soil liner to a very small value. Case 5S has a much smaller release rate because
the moderate failure of the sidewall FML still significantly reduces the flow of
liquids into the secondary collection system. The drainage time factor, and
breakthrough times are also similar for each statutory case (except case 5S).
A comparison of A and B cases shows that different .assumed hydraulic
conductivity values for the sidewall in Cell No. 9 have a major effect on
performance of this design. Maximum release rates are about a factor of 8 higher
in Cases 1A-4A than Cases 1B-4B while drainage times and breakthrough times are
about a factor of 8 lower for Cases 1A-4A than Cases 1B-4B. Cases 5A and 5B are
not as different because flew rates are restricted by the top FML.
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17
Cases 1A, IB, and IS versus 3A, 3B, and 3S indicate the effects of water
table location. Because the location of the water table affects the net head
gradient on the sidewall, a lower water table gives more conservative results
(i.e., a worst case). CEODS Cell No. 9, after completion, will have water table
located above the cell bottom along the sidewall, so Cases 3A, 3B, and 3S are more
representative of this situation. However, a lower water table assumption, such
as during the construction of Cell No. 9, gives more conservative results. The
lower water table assumption was preferred in the modeling analysis because a
snail amount of liquid could enter the secondary leachate collection systems from
outside of the cell (i.e., ground water) in several cases. This ground water
could not be distinguished from liquids entering the collection system from within
the cell (i.e., leachates) by this modeling analysis.
K. comparison of Cases 1B-3B and 5B with Cases 1S-3S and 5S illustrate that
CECOS Cell No. 9 is not equivalent to the interim statutory design when the
contingency leadhate collection system is not operated. Maximum release rates
are about a factor of 3 higher in Cases IB-SB as compared to 1S-3S and a factor
of 25 higher in Cases 5B than interim statutory case 5S. Drainage times and
volumes exiting the sidewall during drainage times are drastically higher in the
gECOS Cases 1-3 and 5 versus the interim statutory design cases 1-3 and 5.
Cases 4A and 43 illustrate the effect of operating the contingency leachate
collection system. Case 4B demonstrates that the CECOS Cell No. 9 is more
effective, by all three criteria, than the interim statutory design when the
contingency leachate collection system is operated and the sidewall soil liner
hydraulic conductivity is at least 1 x 10 cm/sec. The maximum release rate
through the sidewall is 0.05 ft3/day/ft for Case 4B versus 0.07 ft3/day/ft for
Case 4S. The drainage time and volume exiting the sidewall during the drainage
time are smaller for Case 4B than Case 4S. The breakthrough time is larger for
Case 4B than Case 4S.
Since the CECOS Cell No. 9 design and operation (Case 4B) is batter than the
interim statutory design under catastrophic failure conditions for all three
performance criteria (i.e., breakthrough time, maximum release rate through
sidewall, and drainage time), the CECOS Cell No. 9 design and operation will be
more effective than the interim statutory design for the other failure conditions.
For example, under a moderate failure mode of the FML, the CECOS design would
exceed the performance of Case 5S if the contingency leachate collection system
is operated.
L i-
5.0 CONCLUSION
The result of Section 4 demonstrate that the CECOS Cell No. 9 design and
operation can be considered to be as effective as the interim statutory design
ONLY WITH THE OPERATION OF THE CONTINGENCY LEACHATE COLLECTION SYSTEM.
6.0 FINDINGS AND RECOMMENDATIONS
The modeling evaluation was based on properties of various materials as
reported by CECOS. They implemented a construction quality assurance program
to assure that the compacted soil liner was constructed as designed. EPA
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13
used the 1 x 10 an/sec hydraulic conductivity value for the sidewall comparison
based on the demonstration by CEQOS that they complied with regulations and
guidance available at the time of construction.
If CEOOS Cell No. 9 is given a waiver, it is strongly recommended, based
on this analysis, that leachate heads within the cell be keep to"an absolute
minimum at all times by operating the primary leachate collection system and the
contingency leachate collection system to keep leachate away from the sidewalls.
Future placement of the one-foot sand layer above the top liner on the sidewalls
should be inspected during placement in accordance with current EPA guidance.
During the post-closure care period the head levels should be monitored very
frequently on the sidewalls. The permit should have provisions for immediate
response to any head build-up in the cell.
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19
REFERENCES
Green, W.H. and G.A. Anpt. Studies in Soil Physics I: The Flow of Air
and Water Through Soils, Journal of Agricultural Science 4, 1911.
Gupta, S.K., C.T. Kincaid, P.R. Meyer, C.A. Newbill, and C.R. Cole. A
Multi-Dimensional Finite-Element Code for the Analysis of Coupled Fluid
Energy and Solute Transport (CFEST), PISL-426, Pacific Northwest.
Laboratories, Richland, WA, 1982.
U.S.EPA, Procedures for Modeling Flow Through Clay Liners to Determine
Required Liner Thickness, EPA/530-SW-34-002, OSW, Washington, D.C.
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