United States Solid Waste and EPA530-R-93-017
Environmental Protection Emergency Response November 1993
Agency (5305) www.epa.gov/osw
vvEPA Solid Waste Disposal
Facility Criteria
Technical Manual
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DISCLAIMER
The information in this document has been funded wholly or in part by the United States
Environmental Protection Agency under Contract Number 68-WO-0025. Mention of trade names
or commercial products does not constitute endorsement or recommendation for use.
NOTICE
The policies set out in this manual are not final Agency action, but are intended solely as guidance.
They are not intended, nor can they be relied upon, to create any rights enforceable by any party in
litigation with the United States. EPA officials may decide to follow the guidance provided in this
memorandum, or to act at variance with the guidance, based on an analysis of specific site
circumstances. The Agency also reserves the right to change this guidance at any time without
public notice.
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TABLE OF CONTENTS
INTRODUCTION iv
CHAPTER 1. SUSP ART A 1
1.1 INTRODUCTION 3
1.2 PURPOSE. SCOPE. AND APPLICABILITY 40 CFR $258.1 (a)(b} 4
1.3 PURPOSE. SCOPE. AND APPLICABILITY (conO 40 CFR $258.1 (cWe^) 5
1.4 SMALL LANDFILL EXEMPTIONS 40 CFR $258.1 (T) 7
1.5 APPLICABILITY 40 CFR $258.1 (g)-(i) 9
1.6 DEFINITIONS 40 CFR $258.2 10
1.7 CONSIDERATION OF OTHER FEDERAL LAWS 40 CFR $258.3 14
CHAPTER 2. SUSP ARTS 15
2.1 INTRODUCTION 18
2.2 AIRPORT SAFETY 40 CFR $258.10 19
2.3 FLOODPLAINS 40 CFR $258.11 24
2.4 WETLANDS 40 CFR $258.12 28
2.5 FAULT AREAS 40 CFR $258.13 37
2.6 SEISMIC IMP ACT ZONES 40 CFR $25 8.14 41
2.7 UNSTABLE AREAS 40 CFR $258.15 45
2.8 CLOSURE OF EXISTING MUNICIPAL SOLID WASTE LANDFILL UNITS
40 CFR $258.16 61
2.9 FURTHER INFORMATION 63
CHAPTERS. SUSP ART C 73
11 INTRODUCTION 76
12 PROCEDURES FOR EXCLUDING THE RECEIPT OF HAZARDOUS
WASTE 40 CFR $258.20 77
H COVER MATERIAL REQUIREMENTS 40 CFR $258.21 84
14 DISEASE VECTOR CONTROL 40 CFR $258.22 85
15 EXPLOSIVE GASES CONTROL 40 CFR $258.23 87
16 AIR CRITERIA 40 CFR $258.24 101
17 ACCESS REQUIREMENT 40 CFR $258.25 103
18 RUN-ON/RUN-OFF CONTROL SYSTEMS 40 CFR $258.26 104
19 SURFACE WATER REQUIREMENTS 40 CFR $258.27 105
3.10 LIQUIDS RESTRICTIONS 40 CFR $258.28 107
3.11 RECORDKEEPING REQUIREMENTS 40 CFR $258.29 110
3.12 FURTHER INFORMATION 114
Revised April 13, 1998
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CHAPTER 4. SUSP ARID 117
4J, INTRODUCTION 121
42 PERFORMANCE-BASED DESIGN 40 CFR $258.40 122
43 COMPOSITE LINER AND LEACHATE COLLECTION SYSTEM 40 CFR
$258.40 149
4,4 RELEVANT POINT OF COMPLIANCE 40 CFR §258.40(d) 188
4,5 PETITION PROCESS 40 CFR S258.40(e^ 191
16 FURTHER INFORMATION 193
CHAPTERS. SUBPARTE 205
5J, INTRODUCTION 211
12 APPLICABILITY 40 CFR $258.50 (a) & fb) 211
13 COMPLIANCE SCHEDULE 40 CFR § 258.50 (c) 214
14 ALTERNATIVE COMPLIANCE SCHEDULES 40 CFR 258.50 (d)(e) & (g)
215
15 QUALIFICATIONS 40 CFR 258.50 (f) 217
16 GROUND-WATER MONITORING SYSTEMS 40 CFR $258.51 (a)(b)(d)
219
17 GROUND-WATER MONITORING WELL DESIGN AND
CONSTRUCTION 40 CFR $258.51 (c) 241
18 GROUND-WATER SAMPLING AND ANALYSIS REQUIREMENTS 40
CFR $258.53 253
19 STATISTICAL ANALYSIS 40 CFR $258.53 (gV(D 268
5.10 DETECTION MONITORING PROGRAM 40 CFR $258.54 274
5.11 ASSESSMENT MONITORING PROGRAM 40 CFR §258.55(a)-(f) 281
5.12 ASSESSMENT MONITORING PROGRAM 40 CFR §258.55(e) 286
5.13 ASSESSMENT MONITORING PROGRAM 40 CFR §258.55(h)-(i) 289
5.14 ASSESSMENT OF CORRECTIVE MEASURES 40 CFR $258.56 291
5.15 SELECTION OF REMEDY 40 CFR $258.57 (a)-fb) 298
5.16 SELECTION OF REMEDY 40 CFR $258.57 (c) 299
5.17 SELECTION OF REMEDY 40 CFR $258.57 (d) 303
5.18 SELECTION OF REMEDY 40 CFR $258.57 (e)-(f) 305
5.19 IMPLEMENTATION OF THE CORRECTIVE ACTION PROGRAM 40
CFR $258.58 (a) 307
5.20 IMPLEMENTATION OF THE CORRECTIVE ACTION PROGRAM 40
CFR $258.58 fb)-(d) 309
5.21 IMPLEMENTATION OF THE CORRECTIVE ACTION PROGRAM 40
CFR $258.58 (e)-(g) 311
5.22 FURTHER INFORMATION 313
Revised April 13, 1998
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CHAPTER 6. SUBPARTF 319
6J, INTRODUCTION 322
£2 FINAL COVER DESIGN 40 CFR §258.60(a) 322
63 ALTERNATIVE FINAL COVER DESIGN 40 CFR §258.60fb) 332
6A CLOSURE PLAN 40 CFR §258.60(c)-(d) 338
£5 CLOSURE CRITERIA 40 CFR §258.60(e)-(i) 339
£6 POST-CLOSURE CARE REQUIREMENTS 40 CFR $258.61 342
6J_ POST-CLOSURE PLAN 40 CFR §258.61(c)-(e) 345
£8 FURTHER INFORMATION 348
APPENDICES
CHAPTER 2
APPENDIX I FAA Order 5200.5A 69
CHAPTER 3
APPENDIX I - SPECIAL WASTE ACCEPTANCE AGREEMENT 115
iii Revised April 13, 1998
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INTRODUCTION
This manual was originally published in November, 1993 as a companion to the Criteria for
Municipal Solid Waste Landfills (MSWLF Criteria) that were promulgated on October 9, 1991 as
40 CFR Part 258. Since that time the MSWLF Criteria have been modified several times due to
statutory revisions and court decisions that are discussed below. Most of the modifications delayed
the effective dates but all provisions are now effective. All changes to the rule are included in the
text of the manual. The technical content of the manual did not require revision and only
typographical errors were corrected.
The manual is now available in electronic format and can be accessed on the Environmental
Protection Agency's (EPA) web site .
Purpose of This Manual
This technical manual has been developed to
assist owners/operators of MSWLFs in achieving
compliance with the revised MSWLF Criteria. This
manual is not a regulatory document, and does not
provide mandatory technical guidance, but does
provide assistance for coming into compliance with
the technical aspects of the revised landfill Criteria.
Implementation of the Landfill Criteria
The EPA fully intends that States and Tribes
maintain the lead role in implementing and enforcing
the revised Criteria. States will achieve this through
approved State permit programs. Due to recent
decisions by the courts, Tribes will do so using a
case-by-case review process.1 Whether in a State or
in Indian Country, landfill owners/operators must
comply with the revised2 MSWLF Criteria.
State Process
Example of Technical and Performance
Standards in 40 CFR Part 258: Liners
Technical standard:
MSWLFs must be built with a composite
liner consisting of a 30 mil flexible mem-
brane liner over 2 feet compacted soil with a
hydraulic conductivity of no more than 1x10"
7 cm/sec.
Performance standard:
MSWLFs must be built in accordance with a
design approved by the Director of an
approved State or as specified in 40 CFR
§ 258.40(e) for unapproved States. The
design must ensure that the concentration
values listed in Table 1 of 40 CFR § 258.40
will not be exceeded in the uppermost aquifer
at the relevant point of compliance, as
specified by the Director of an approved
State under paragraph 40 CFR § 258.40(d).
The Agency's role in the regulation of MSWLFs is to establish national minimum standards
that the states are to incorporate into their MSWLF permitting programs. EPA evaluates state
1 The Agency originally intended to extend to Indian Tribes the same opportunity to apply for permit program
approval as is available to States, but a court decision blocked this approach. See the Tribal Process section
below for complete details.
2EPA finalized several revisions to 40 CFR Part 258 on October 1, 1993 (58 FR 51536) and issued a correction
notice on October 14, 1993 (58 FR 53136). Questions regarding the final rule and requests for copies of the
Federal Register notices should be made to the RCRA/Superfund Hotline at 800 424-9346.
Revised April 13, 1998
IV
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Introduction
MSWLF permitting programs under the procedures set out in 40 CFR Part 239, "Requirements for
State Permit Program Determination of Adequacy," proposed on January 26, 1996 (61 FR 2584),
to determine whether programs are adequate to ensure that MSWLF owners/operators comply with
the federal standards. As of early 1998, 40 States and Territories had received full approval and
another seven had received partial approval.
If their permitting programs have been approved by EPA, States can allow the use of flexible
performance standards established in 40 CFR Part 258 in addition to the self-implementing technical
standards for many of the Criteria. Approved States can provide owners/operators flexibility in
satisfying the location restrictions, operating criteria, and requirements for liner design, ground-
water monitoring, corrective action, closure and post-closure care, and financial assurance. This
flexibility allows for the consideration of site-specific conditions in designing and operating a
MSWLF at the lowest cost possible while ensuring protection of human health and the environment.
In unapproved states, owners/operators must follow the self-implementing technical standards.
EPA continues to work with States toward approval of their programs and recommends that
owners/operators stay informed of the approval status of the programs in their State. States may be
in various stages of the program approval process. The majority of states have received full
program approval and others have received "partial" program approval (i.e., only some portions of
the State program are approved while the remainder of the program is pending approval).
Regardless of a State's program approval status, landfill owners/operators must comply with the
Criteria. States can grant flexibility to owners/operators only in the areas of their program that have
been approved. For example, a state in which only the ground-water monitoring area of the
permitting program has been approved by EPA cannot grant owners/operators flexibility to use
alternative liner designs.
States are free to enact landfill regulations that are more stringent than the MSWLF Criteria.
Certain areas of flexibility provided by the Criteria (e.g., the small landfill exemption) may not be
reflected in a State program. In such instances, the owner/operator must comply with the more
stringent provisions (e.g., no exemption). These regulations would be enforced by the State
independently from the Criteria. NOTE: The program requirements for approved States may
differ from those described in this manual, which are based specifically on the Federal
Criteria. Therefore, owners/operators are urged to work closely with their approved State in
order to ensure that they are fully in compliance with all applicable requirements.
State regulatory personnel will find this document helpful when reviewing permit
applications for landfills. This manual presents technical information to be used in siting, designing,
operating, and closing landfills, but does not present a mandatory approach for demonstrating
compliance with the Criteria. This manual also outlines the types of information relevant to make
the demonstrations required by the Criteria, including demonstrations for restricted locations and
performance-based designs in approved States.
Tribal Process
From the beginning of EPA's development of the permitting program approval process, the
Agency planned to offer permitting program approval to tribes as well as to states. In a 1996 court
v Revised April 13, 1998
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Introduction
decision3, however, the court ruled that EPA cannot approve tribal permitting programs. The
Agency has therefore developed a site-specific rulemaking process to meet its goal of quickly and
efficiently providing owners/operators in Indian Country4 the same flexibility that is available to
landfill owners/operators in states with EPA-approved MSWLF permitting programs. The process
is described in Site-Specific Flexibility Requests for Municipal Solid Waste Landfills in Indian
Country—Draft Guidance (EPA530-R-97-016).
Under this process, an owner or operator can request to use certain alternative approaches
at a specific MSWLF site to meet the 40 CFR Part 258 performance standards. Unless the tribal
government is the owner/operator, the tribal government should review the request for consistency
with tribal law and policy and forward it to EPA with a recommendation. If EPA approves a
request, it will issue a site-specific rule allowing the use of the requested alternative approaches.
Owners/operators in Indian Country should therefore understand that when this manual refers to
areas of flexibility that can be granted by a "State Director," they would instead seek such flexibility
in the form of a site-specific rulemaking from EPA after tribal government review of their petition
for rulemaking. Although tribes will not issue permits as EPA-approved permitting entities under
the Criteria, they are free to enact separate tribal landfill regulations that are more stringent than the
Criteria. Tribal regulations are enforced by the tribe independently of the Criteria.
The site-specific process encourages active dialogue among tribes, MSWLF
owners/operators, EPA, and the public. The guidance is designed so that the Agency works in
partnership with tribes. Because EPA recognizes tribal sovereignty, EPA will respect tribal findings
concerning consistency of proposed approaches with tribal law and policy.
Revisions to Part 258
Some important changes have been made to Part 258 since its original promulgation. In
addition, other regulations that affect solid waste management have been implemented.
Ground-Water Monitoring Exemption for Small, Dry, and Remote Landfills (40 CFR
§258.1(f)(l))
The Land Disposal Program Flexibility Act (LDPFA) of 1996 reestablished an exemption
for ground-water monitoring for owners/operators of certain small MSWLFs. EPA revised 40 CFR
§ 258.1(f)(l) on September 25, 1996 (61 FR 50409) to codify the LDPFA ground-water monitoring
exemption. To qualify for an exemption, owners/operators must accept less than 20 tons per day of
MSW (based on an annual average), have no evidence of ground-water contamination, and be
located in either a dry or remote location. This exemption eases the burden on certain small
MSWLFs without compromising ground-water quality.5
3 Backcountry Against Dumps v. EPA, 100 F.3d 147 (D.C. Cir. 1996).
4 This manual uses the term "Indian Country" as defined in 40 CFR § 258.2.
5 In the original 40 CFR Part 258 rulemaking, promulgated October 9, 1991, the Agency provided an
exemption from ground-water monitoring for small MSWLF units located in dry or remote locations. In 1993, the
U.S. Court of Appeals for the District of Columbia set aside this ground-water monitoring exemption. Sierra Club
v. EPA, 992 F.2d 337 (D.C. Cir. 1993).
Revised April 13, 1998 vi
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Introduction
New Flexibility for Small Landfills (40 CFR §§ 258.21, 258.23, 258.60)
In addition to reestablishing the ground-water exemption for small, dry, and remote
MSWLFs, the LDPFA provided additional flexibility to approved states for any small landfill that
receives 20 tons or less of MSW per day. EPA revised 40 CFR Part 258 to allow approved states
to grant the use of alternative frequencies of daily cover, alternative frequencies of methane
monitoring, and alternative infiltration layers for final cover (62 FR 40707 (July 29, 1997)). The
LDPFA also authorized flexibility to establish alternative means for demonstrating financial
assurance, and this flexibility was granted in another action. The additional flexibility will allow
owners and operators of small MSWLFs the opportunity to reduce their costs of MSWLF operation
while still protecting human health and the environment.
Added Financial Assurance Options (40 CFR § 258.74)
A revision to 40 CFR Part 258, published November 27, 1996 (61 FR 60328), provided
additional options to the menu of financial assurance instruments that MSWLF owners/operators
can use to demonstrate that adequate funds will be readily available for the costs of closure,
post-closure care, and corrective action for known releases associated with their facilities. The
existing regulations specify several mechanisms that owners and operators may use to make that
demonstration, such as trust funds and surety bonds. The additional mechanisms are a financial test
for use by local government owners and operators, and a provision for local governments that wish
to guarantee the closure, post-closure, and corrective action costs for an owner or operator. These
financial assurance options allow local governments to use their financial strength to avoid incurring
the expenses associated with the use of third-party financial instruments. This action granted the
flexibility to all owners and operators (including owners and operators of small facilities) to
establish alternative means for demonstrating financial assurance as envisioned in the LDPFA.
Additionally, EPA promulgated a regulation allowing corporate financial tests and corporate
guarantees as financial assurance mechanisms that private owners and operators of MSWLFs may
use to demonstrate financial assurance (63 FR 17706 (April 10, 1998)). This test extends to private
owners and operators the regulatory flexibility already provided to municipal owners or operators
of MSWLFs. These regulations allow firms to demonstrate financial assurance by passing a financial
test. For firms that qualify for the financial test, this mechanism will be less costly than the use of
a third party financial instrument such as a trust fund or a surety bond.
How to Use This Manual
This document is subdivided into six chapters arranged to follow the order of the Criteria.
The first chapter addresses the general applicability of the Part 258 Criteria; the second covers
location restrictions; the third explains the operating requirements; the fourth discusses design
standards; the fifth covers ground-water monitoring and corrective action; and the sixth chapter
addresses closure and post-closure care. Each chapter contains an introduction to that section of the
Criteria. This document does not include a section on the financial responsibility requirements;
vii Revised April 13, 1998
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Introduction
questions regarding these requirements may be addressed to EPA's RCRA/Superfund Hotline at 800
424-9346.
Within each chapter, the Criteria have been subdivided into smaller segments. The
Statement of Regulation section provides a verbatim recital of the regulatory language. The second
section, entitled Applicability, provides a general explanation of the regulations and who must
comply with them. Finally, for each segment of the regulation, a Technical Considerations section
identifies key technical issues that may need to be addressed to ensure compliance with a particular
requirement. Each chapter ends with a section entitled Further Information, which provides
references, addresses, organizations, and other information that may be of use to the reader.
Limitations of This Manual
The ability of this document to provide current guidance is limited by the technical literature
that was available at the time of preparation. Technology and product development are advancing
rapidly, especially in the areas of geosynthetic materials and design concepts. As experience with
new waste management techniques expands in the engineering and science community, an increase
in published literature, research, and technical information will follow. The owners and operators
of MSWLFs are encouraged to keep abreast of innovation through technical journals, professional
organizations, and technical information developed by EPA. Many of the Criteria contained in Part
258 are performance-based. Future innovative technology may provide additional means for
owners/operators to meet performance standards that previously could not be met by a particular
facility due to site-specific conditions.
Deadlines and Effective Dates
The original effective date for the Criteria, October 9, 1993, was revised for several
categories of landfills, in response to concerns that a variety of circumstances was hampering some
communities' abilities to comply by that date. Therefore, the Agency provided additional time for
certain landfills to come into compliance, especially small units and those that accepted waste from
the 1993 Midwest floods. As the accompanying table indicates, the extended general effective dates
for all MSWLF categories have passed, and all units should now be in compliance.
Revised April 13, 1998 viii
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SUMMARY OF CHANGES TO THE EFFECTIVE DATES OF THE MSWLF CRITERIA
General effective date.1'2'3
This is the effective date for location,
operation, design, and closure/post-
closure.
Date by which to install final cover
if cease receipt of waste by the
general effective date.2 3
Effective date of ground-water
monitoring and corrective action.2 3
Effective date of financial
assurance requirements.3'4
MSWLF Units
Accepting Greater
than 100 TPD
October 9, 1993
October 9, 1994
Prior to receipt of waste
for new units; October
9, 1994 through October
9, 1996 for existing
units and lateral
expansions
April 9, 1997
MSWLF Units Accepting
100 TPD or Less; Are Not
on the NPL; and Are
Located in a State That
Has Submitted an
Application for Approval
by 10/9/93, or on Indian
Lands or Indian Country
April 9, 1994
October 9, 1994
October 9, 1993 for new
units; October 9, 1994
through October 9, 1996 for
existing units and lateral
expansions
April 9, 1997
MSWLF Units That
Meet the Small
Landfill Exemption in
40 CFR §258.1(f)
October 9, 1997; exempt
from the design
requirements
October 9, 1998
Exempt from the
ground-water
monitoring
requirements.5
October 9, 1997
MSWLF Units
Receiving Flood-
Related Waste
Up to October 9, 1994
as determined by State
Within one year of date
determined by State; no
later than October 9,
1995
October 9, 1993 for
new units; October 9,
1994 through October
9, 1996 for existing
units and lateral
expansions
April 9, 1997
1 If a MSWLF unit receives waste after this date, the unit must comply with all of Part 258.
2 See the final rule and preamble published on October 1, 1993 (58 FR 51536) for a full discussion of all changes and related conditions.
3 See the final rule and preamble published on October 6, 1995 (60 FR 52337) for a full discussion of all changes and related conditions.
4 See the final rule and preamble published on April 7, 1995 (60 FR 17649) for a discussion of this delay.
5 See the final rule and preamble published on September 25, 1990 (61 FR 50409) for a discussion of the ground-water monitoring exemption.
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CHAPTER 1
SUBPART A
GENERAL
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CHAPTER 1
SUBPART A
TABLE OF CONTENTS
U, INTRODUCTION 3
L2 PURPOSE. SCOPE. AND APPLICABILITY 40 CFR §258.1 (a)(b) 4
1.2.1 Statement of Regulation 4
1.2.2 Applicability 4
1.2.3 Technical Considerations 4
H PURPOSE. SCOPE. AND APPLICABILITY (cont.) 40 CFR §258.1 (c)-(e) 5
1.3.1 Statement of Regulation 5
1.3.2 Applicability 5
1.3.3 Technical Considerations 7
L4 SMALL LANDFILL EXEMPTIONS 40 CFR §258.1 (f) 7
1.4.1 Statement of Regulation 7
1.4.2 Applicability 8
1.4.3 Technical Considerations 8
L5 APPLICABILITY 40 CFR §258.1 (g)-(j) 9
1.5.1 Statement of Regulation 9
1.5.2 Applicability 10
1.5.3 Technical Considerations 10
L6 DEFINITIONS 40 CFR §258.2 10
1.6.1 Statement of Regulation 10
1.6.2 Applicability 13
1.6.3 Technical Considerations 13
L7 CONSIDERATION OF OTHER FEDERAL LAWS 40 CFR §258.3 14
1.7.1 Statement of Regulation 14
1.7.2 Applicability 14
1.7.3 Technical Considerations 14
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CHAPTER 1
SUBPART A
GENERAL
1.1 INTRODUCTION
Under the authority of both the Resource Conservation and Recovery Act (RCRA), as amended by
the Hazardous and Solid Waste Amendments (HSWA) of 1984, and Section 405 of the Clean Water
Act, the EPA issued "Solid Waste Disposal Facility Criteria" (40 CFRPart 258) on October 9, 1991.
These regulations revise the "Criteria for Classification of Solid Waste Disposal Facilities and
Practices," found in 40 CFR Part 257. Part 258 was established to provide minimum national
criteria for all solid waste landfills that are not regulated under Subtitle C of RCRA, and that:
• Receive municipal solid waste; or
• Co-dispose sewage sludge with municipal solid waste; or
• Accept nonhazardous municipal waste combustion ash.
Part 257 remains in effect for all other non-hazardous solid waste facilities and practices.
Subpart A of the regulations defines the purpose, scope, and applicability of Part 258 and provides
definitions necessary for proper interpretation of the requirements. In summary, the applicability
of the Criteria is dependent on the operational status of the MSWLF unit relative to the date of
publication of Part 258 and the effective date of the rule (October 9, 1993). An exemption from the
design requirements is provided for small MSWLF units if specific operating, environmental, and
location conditions are present. [The final rule as promulgated on October 9, 1991 exempted the
owner/operators of small landfill units from both Subparts D and E. On May 7, 1993 the U.S. Court
of Appeals for the District of Columbia Circuit issued an opinion that EPA did not have the
authority to exempt these small landfills from the ground-water monitoring requirements (Subpart
E), therefore, these small landfills can not be exempted from Subpart E. EPA is delaying the date
of compliance for these units until October 9, 1995 (58 FR 51536). In addition, the Agency is
investigating alternative ground-water monitoring procedures for these units.]
Owners or operators of MSWLF units that do not meet the Part 258 Criteria will be considered to
be engaging in the practice of "open dumping" in violation of Section 4005 of RCRA. Similarly,
owners and operators of MSWLF units that receive sewage sludge and do not comply with these
Criteria will also be in violation of applicable sections of the Clean Water Act.
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Subpart A
1.2 PURPOSE, SCOPE, AND
APPLICABILITY
40 CFR §258.1 (a)(b)
1.2.1 Statement of Regulation
(a) The purpose of this part is to
establish minimum national criteria
under the Resource Conservation and
Recovery Act (RCRA or the Act), as
amended, for all municipal solid waste
landfill (MSWLF) units and under the
Clean Water Act, as amended, for
municipal solid waste landfills that are
used to dispose of sewage sludge. These
minimum national criteria ensure the
protection of human health and the
environment.
(b) These Criteria apply to owners
and operators of new MSWLF units,
existing MSWLF units, and lateral
expansions, except as otherwise
specifically provided in this part; all
other solid waste disposal facilities and
practices that are not regulated under
Subtitle C of RCRA are subject to the
criteria contained in Part 257.
1.2.2 Applicability
Owners and operators of MSWLF units that
receive municipal solid waste or that receive
municipal waste combustion ash and are not
currently regulated under Subtitle C of
RCRA must comply with the Criteria.
Furthermore, MSWLF units that receive and
co-dispose sewage sludge must comply with
Part 258 to be in compliance with Sections
309 and 405(e) of the Clean Water Act.
1.2.3 Technical Considerations
Criteria that define a solid waste disposal
facility are contained within Part 257 of
RCRA (Criteria for Classification of Solid
Waste Disposal Facilities and Practices).
Definitions pertaining to the revised Criteria
are included in the definition section of Part
258. A MSWLF unit is defined as a discrete
area of land or excavation that receives
household waste, and that is not considered
a land application unit, surface
impoundment, injection well, or waste pile
as those terms are defined under §257.2. An
existing unit is a solid waste disposal unit
that is receiving solid waste as of October 9,
1993. A lateral expansion is a horizontal
expansion of the waste boundaries of an
existing MSWLF unit. A new unit is a
MSWLF unit that has not received waste
before October 9, 1993.
In addition to household waste, a MSWLF
unit may receive commercial waste, non-
hazardous solid waste from industrial
facilities including non-hazardous sludges,
and sewage sludge from wastewater
treatment plants. The terms commercial
solid waste, industrial waste and household
waste are defined in §258.2 (Definitions).
The types of landfills regulated under Part
257 include those facilities that receive:
• Construction and demolition debris
only;
• Tires only; and
• Non-hazardous industrial waste only.
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General
MSWLF units are not intended, nor
allowed, to receive regulated quantities of
hazardous wastes. Should a MSWLF
owner/operator discover that a shipment
contains regulated quantities of hazardous
waste while still in the possession of the
transporter, the owner/operator should
refuse to accept the waste from the
transporter. If regulated quantities of
hazardous wastes are discovered after
accepting the waste from the transporter, the
owner/operator must return the shipment or
manage the wastes in accordance with
RCRA Subtitle C requirements.
Subtitle C of RCRA establishes procedures
for making a hazardous waste
determination. These procedures are
summarized in Chapter 3 and Appendix B of
this document.
1.3 PURPOSE, SCOPE,
AND APPLICABILITY (cont.)
40 CFR §258.1 (c)-(e)
1.3.1 Statement of Regulation*
*[NOTE: EPA finalized several revisions
to 40 CFR Part 258 on October 1, 1993
(58 FR 51536) and issued a correction
notice on October 14,1993 (58 FR 53136).
These revisions delay the effective date
for some categories of landfills. More
detail on the content of the revisions is
included in the introduction.]
(c) These Criteria do not apply to
municipal solid waste landfill units that do
not receive waste after October 9,1991.
(d) MSWLF units that receive waste
after October 9, 1991 but stop
receiving waste before October 9, 1993
are exempt from all the requirements of
Part 258, except the final cover
requirement specified in Section 258.60(a).
The final cover must be installed within six
months of last receipt of wastes. Owners or
operators of MSWLF units described in
this paragraph that fail to complete cover
installation within this six month period
will be subject to all the requirements of
Part 258, unless otherwise specified.
(e) All MSWLF units that receive
waste on or after October 9, 1993 must
comply with all requirements of Part 258
unless otherwise specified.
1.3.2 Applicability
The applicability of Part 258, in its entirety or
with exemptions to specific requirements, is
based upon the operational status of the
MSWLF unit relative to the date of
publication, October 9, 1991, or the effective
date of the rule, October 9, 1993 (see Figure
1-1). Three possible operational scenarios
exist:
(1) The MSWLF unit received its 1 ast
load of waste prior to October 9, 1991. These
facilities are exempt from all requirements of
the Criteria.
(2) The last load of waste was
received after October 9, 1991, but before
October 9, 1993. The owners and operators
must comply only with the final cover
requirements of §258.60(a). If the final cover
is not installed within six (6) months of the
last receipt of wastes, the owners and
operators will be required to comply with all
requirements of Part 258.
-------
Subpart A
Date of
Publication
(Octob«ri, 1981)
C
o
S
YES
Effective Date -
(October9, 1993)
MSWLF Must
Comply with All
of Part 256
NO
Part 258 Does
Not Apply
Final Cover
Requirements of
§258.60(ai Apply
Did MSWLF
Recieve Cover
Within 6 Mos. of
Firta! Reeetp
of Waste
Figure 1-1
Applicability Flow Chart
-------
General
(3) The MSWLF unit continues to
receive waste after October 9, 1993. The
owners or operators must comply with all
requirements of Part 258, except where
specified otherwise.
1.3.3 Technical Considerations
MSWLF units that receive the last load of
waste between October 9, 1991 and October
9, 1993, must complete closure within six
months of the last receipt of waste. Closure
requirements are specified in Subpart F;
however, these MSWLF units will be
subject only to the closure requirements of
§258.60(a) unless they fail to complete
closure within the six-month period. The
alternative cover design is not an option for
MSWLF units in unapproved States.
The final cover system must be designed to
minimize infiltration and erosion. The final
cover must have a permeability that is less
than or equal to the permeability of the
bottom liner system or the natural subsoils
present, or a permeability no greater than 1
x 10"5 cm/sec, whichever is less. The system
must be composed of an erosion layer that
consists of at least six inches of an earthen
material capable of sustaining native plant
growth and an infiltration layer that is
composed of at least 18 inches of an earthen
material. However, if a MSWLF unit is
constructed with a synthetic membrane in
the liner system, it is anticipated that the
final cover also will require a synthetic
liner. Currently, it is not possible to
construct an earthen liner with a
permeability less than or equal to a synthetic
membrane. Detailed technical
considerations for the cover requirements
under §258.60(a) are provided in Chapter 6.
1.4 SMALL LANDFILL
EXEMPTIONS
40 CFR §258.1 (f)
1.4.1 Statement of Regulation
(f)(l) Owners or operators of new
MSWLF units, existing MSWLF units,
and lateral expansions that dispose of less
than twenty (20) tons of municipal solid
waste daily, based on an annual average,
are exempt from subparts D [and E]* of
this Part, so long as there is no evidence
of existing ground-water contamination
from the MSWLF unit and the MSWLF
unit serves:
(i) A community that experiences
an annual interruption of at least
three consecutive months of surface
transportation that prevents access to
a regional waste management
facility, or
(ii) A community that has no
practicable waste management
alternative and the landfill unit is located
in an area that annually receives less than
or equal to 25 inches of precipitation.
(2) Owners or operators of new
MSWLF units, existing MSWLF units,
and lateral expansions that meet the
criteria in (f)(l)(i) or (f)(l)(ii) must place
in the operating record information
demonstrating this.
(3) If the owner or operator of a
new MSWLF unit, existing MSWLF unit,
or lateral expansion has knowledge of
ground-water contamination resulting
from the unit that has asserted the
exemption in (f)(l)(i) or (ii), the owner or
operator must notify the State
-------
Subpart A
Director of such contamination and,
thereafter, comply with Subparts D [mttt
E]* of this Part.
* [Note: On May 7, 1993 the U.S. Court of
Appeals for the District of Columbia Circuit
issued an opinion that EPA did not have the
authority to exempt these small landfills
from the ground-water monitoring
requirements (Subpart E), therefore, these
small landfills can not be exempted from
Subpart E. EPA is delaying the date of
compliance for these units until October 9,
1995 (58 FR 51536; October 1, 1993).]
1.4.2 Applicability
The exemption from Subpart D (Design) is
applicable only to owners or operators of
landfill units that receive, on an annual
average, less than 20 tons of solid waste per
day. The exemption is allowed so long as
there is no evidence of existing ground-
water contamination from the MSWLF unit.
In addition, the MSWLF unit must serve a
community that meets one of the following
two conditions:
• For at least three consecutive months of
the year, the community's municipal
solid waste cannot be transported by
rail, truck, or ship to a regional waste
management facility; or
• There is no practicable alternative for
managing wastes, and the landfill unit
is located in an area that receives less
than 25 inches of annual precipitation.
If either of the above two conditions is met,
and there is no evidence of existing ground-
water contamination, the landfill unit owner
or operator is eligible for the exemption
from the design, ground-water monitoring,
and corrective action requirements. The
owner or operator must place information
documenting eligibility for the exemption in
the facility's operating record. Once an
owner or operator can no longer demon-
strate compliance with any of the conditions
of the exemption, the MSWLF facility must
be in compliance with Subpart D.
1.4.3 Technical Considerations
The weight criterion of 20 tons does not
have to be based on actual weight
measurements but may be based on weight
or volume estimates. If the daily waste
receipt records, which include load weights,
are not available for the facility, waste
volumes can be estimated by using
conversion factors of 1 ton = two to three
cubic yards per ton depending on the type of
compaction used at the MSWLF unit.
Waste weights may be determined by
counting the number of trucks and
estimating an average weight for each.
To determine the daily waste received, an
average may be used. If the facility is not
open on a daily basis, the average number
should reflect that fact. For example, if a
facility is open four days per week (208
days/year) and accepts 25 tons each day,
then the average daily amount of waste
received can be calculated as follows:
Average Daily Waste Calculation
4 days/week x 52 weeks/year = 208 days/year; and
25 tons/day x 208 days/year = 5200 tons/year; then
5200 tons/year •+• 365 days/year = 14.25 tons/day.
The facility would meet the criteria for receiving less than
20 tons per day.
-------
General
Compliance with the 20 tons per day
criterion should be based on all waste
received, including household waste and
agricultural or industrial wastes. As defined
in the regulations, household waste includes
any solid waste (including garbage, trash,
and sanitary waste in septic tanks) derived
from households (including single and
multiple residences, hotels and motels,
bunkhouses, ranger stations, crew quarters,
campgrounds, picnic grounds, and day-use
recreation areas).
The exemption from Subpart D requires that
there be "no evidence of existing ground-
water contamination" as a condition for
eligibility. Evidence of contamination may
include detected or known contamination of
nearby drinking water wells, or physical
evidence such as stressed vegetation that is
attributable to the landfill.
One of two other conditions must be present
for the exemption to apply. The first of
these conditions is an annual interruption in
transportation for at least three consecutive
months. For example, some rural villages in
Alaska may be restricted from transporting
wastes to a regional facility due to extreme
winter climatic conditions. These villages
would find it impossible to transport wastes
to a regional waste facility for at least three
months out of the year due to snow and ice
accumulation.
The second condition is composed of two
requirements: (1) the lack of a practicable
waste management alternative; and (2) a
location that receives little rainfall. The
exemption applies only to those areas that
meet both requirements.
The determination of a "practicable waste
management alternative" includes
consideration of technical, economic, and
social factors. For example, some small
rural communities, especially in the western
part of the United States, are located great
distances from alternative waste
management units (other MSWLF units,
composting facilities, municipal waste
combustors, transfer stations, etc.) making
regionalization of waste management
difficult.
Furthermore, many rural communities are
located in arid areas that receive 25 inches
or less of precipitation annually, which
reduces the likelihood of ground-water
contamination because of lessened leachate
generation and contaminant migration.
Rainfall information can be obtained from
the National Weather Service, the National
Oceanographic and Atmospheric
Administration (NOAA), and the United
States Geological Survey (USGS) Water
Atlases.
1.5 APPLICABILITY
40 CFR §258.1 (g)-(j)
1.5.1 Statement of Regulation
(g) Municipal solid waste landfill
units failing to satisfy these criteria are
considered open dumps for purposes of
State solid waste management planning
under RCRA.
(h) Municipal solid waste landfill
units failing to satisfy these criteria
constitute open dumps, which are
prohibited under Section 4005 of RCRA.
(i) Municipal solid waste landfill units
containing sewage sludge and failing
-------
Subpart A
to satisfy these Criteria violate sections
309 and 405(e) of the Clean Water Act.
(j) The effective date of this part is
October 9, 1993, unless otherwise
specified.*
*[NOTE: EPA finalized several revisions
to 40 CFR Part 258 on October 1, 1993
(58 FR 51536) and issued a correction
notice on October 14,1993 (58 FR 53136).
These revisions delay the effective date
for some categories of landfills. More
detail on the content of the revisions is
included in the introduction.]
1.5.2 Applicability
All MSWLF facilities that receive waste on
or after the effective date must comply with
all of Part 258 except where otherwise
noted. MSWLF facilities that fail to comply
with the Part 258 Criteria will be in
violation of Section 4005 of RCRA and with
Sections 309 and 405(e) of the Clean Water
Act if the facility receives sewage sludge.
1.5.3 Technical Considerations
Failure to comply with the Part 258 Criteria
will result in a MSWLF unit being
categorized as an open dump under Section
4005 of RCRA. The practice of operating
an open dump is prohibited.
If a MSWLF unit co-disposes sewage sludge
with municipal solid waste and fails to
comply with Part 258, it also will be in
violation of Section 405(e) of the Clean
Water Act (CWA), which requires that
sewage sludge be disposed of in accordance
with regulations established for such
disposal. If found to be in violation, owners
or operators may be liable for both civil and
criminal actions enforced under Section 309
of the Clean Water Act.
1.6 DEFINITIONS
40 CFR §258.2
1.6.1 Statement of Regulation
Unless otherwise noted, all terms
contained in this part are defined by their
plain meaning. This section contains
definitions for terms that appear
throughout this Part; additional
definitions appear in the specific sections
to which they apply.
Active life means the period of operation
beginning with the initial receipt of solid
waste and ending at completion of closure
activities in accordance with §258.60 of
this Part.
Active portion means that part of a
facility or unit that has received or is
receiving wastes and that has not been
closed in accordance with §258.60 of this
Part.
Aquifer means a geological formation,
group of formations, or portion of a
formation capable of yielding significant
quantities of ground water to wells or
springs.
Commercial solid waste means all types
of solid waste generated by stores, offices,
restaurants, warehouses, and other non-
manufacturing activities, excluding
residential and industrial wastes.
10
-------
General
Director of an approved State means the
chief administrative officer of the State
agency responsible for implementing the
State municipal solid waste permit
program or other system of prior
approval that is deemed to be adequate
by EPA under regulations published
pursuant to section 4005 of RCRA.
Existing MSWLF unit means any
municipal solid waste landfill unit that is
receiving solid waste as of the effective
date of this Part. Waste placement in
existing units must be consistent with
past operating practices or modified
practices to ensure good management.
Facility means all contiguous land and
structures, other appurtenances, and
improvements on the land used for the
disposal of solid waste.
Ground water means water below the
land surface in a zone of saturation.
Household waste means any solid waste
(including garbage, trash, and sanitary
waste in septic tanks) derived from
households (including single and multiple
residences, hotels and motels,
bunkhouses, ranger stations, crew
quarters, campgrounds, picnic grounds,
and day-use recreation areas).
Industrial solid waste means solid waste
generated by manufacturing or industrial
processes that is not a hazardous waste
regulated under Subtitle C of RCRA.
Such waste may include, but is not limit-
ed to, waste resulting from the following
manufacturing processes: Electric power
generation; fertilizer/agricultural
chemicals; food and related products/by-
products; inorganic chemicals; iron and
steel manufacturing; leather and leather
products; nonferrous metals manufac-
turing/foundries; organic chemicals;
plastics and resins manufacturing; pulp
and paper industry; rubber and miscel-
laneous plastic products; stone, glass,
clay, and concrete products; textile
manufacturing; transportation
equipment; and water treatment. This
term does not include mining waste or oil
and gas waste.
Lateral expansion means a horizontal
expansion of the waste boundaries of an
existing MSWLF unit.
Leachate means a liquid that has passed
through or emerged from solid waste and
contains soluble, suspended, or miscible
materials removed from such waste.
Municipal solid waste landfill unit means
a discrete area of land or an excavation
that receives household waste, and that is
not a land application unit, surface
impoundment, injection well, or waste
pile, as those terms are defined under
§257.2. A MSWLF unit also may receive
other types of RCRA Subtitle D wastes,
such as commercial solid waste,
nonhazardous sludge, conditionally
exempt small quantity generator waste,
and industrial solid waste. Such a landfill
may be publicly or privately owned. A
MSWLF unit may be a new MSWLF
unit, an existing MSWLF unit or a lateral
expansion.
New MSWLF unit means any municipal
solid waste landfill unit that has not
received waste prior to the effective date
of this Part.
11
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Subpart A
Open burning means the combustion of
solid waste without:
(1) Control of combustion air to
maintain adequate temperature for
efficient combustion,
(2) Containment of the
combustion reaction in an enclosed device
to provide sufficient residence time and
mixing for complete combustion, and
(3) Control of the emission of the
combustion products.
Operator means the person(s) responsible
for the overall operation of a facility or
part of a facility.
Owner means the person(s) who owns a
facility or part of a facility.
Run-off means any rainwater, leachate,
or other liquid that drains over land from
any part of a facility.
Run-on means any rainwater, leachate, or
other liquid that drains over land onto
any part of a facility.
Saturated zone means that part of the
earth's crust in which all voids are filled
with water.
Sludge means any solid, semi-solid, or
liquid waste generated from a municipal,
commercial, or industrial wastewater
treatment plant, water supply treatment
plant, or air pollution control facility
exclusive of the treated effluent from a
wastewater treatment plant.
Solid waste means any garbage, or refuse,
sludge from a wastewater treatment
plant, water supply treatment plant, or
air pollution control facility and other
discarded material, including solid,
liquid, semi-solid, or contained gaseous
material resulting from industrial,
commercial, mining, and agricultural
operations, and from community
activities, but does not include solid or
dissolved materials in domestic sewage,
or solid or dissolved materials in
irrigation return flows or industrial
discharges that are point sources subject
to permit under 33 U.S.C. 1342, or
source, special nuclear, or by-product
material as defined by the Atomic Energy
Act of 1954, as amended (68 Stat. 923).
State means any of the several States, the
District of Columbia, the Commonwealth
of Puerto Rico, the Virgin Islands, Guam,
American Samoa, and the Common-
wealth of the Northern Mariana Islands.
State Director means the chief
administrative officer of the State agency
responsible for implementing the State
municipal solid waste permit program or
other system of prior approval.
Uppermost aquifer means the geologic
formation nearest the natural ground
surface that is an aquifer, as well as lower
aquifers that are hydraulically
interconnected with this aquifer within
the facility's property boundary.
Waste management unit boundary means
a vertical surface located at the
hydraulically downgradient limit of the
unit. This vertical surface extends down
into the uppermost aquifer.
12
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General
1.6.2 Applicability
The definitions are applicable to all new,
existing, and lateral expansions of existing
MSWLF units regulated under 40 CFR
§258. Additional definitions are provided
within the body of the regulatory language
and will apply to those particular sections.
Definitions in Subpart A apply to all
Sections of Part 25 8.
1.6.3 Technical Considerations
Selected definitions will be discussed in the
following brief narratives.
Approved State: Section 4005(c) of RCRA
requires that each State adopt and
implement a State permit program. EPA is
required to determine whether the State has
developed an adequate program. States
have primary responsibility for implemen-
tation and enforcement of the Criteria. EPA
has the authority to enforce the Criteria in
States where EPA has deemed the permit
program to be inadequate. The Agency
intended to extend to Indian Tribes the same
opportunity to apply for permit program
approval as is available to States. A federal
court ruled, however, in Backcountry
Against Dumps v. EPA, 100 F.3d 147 (D.C.
Cir. 1996), that EPA cannot do so. The
Agency therefore developed a site-specific
rulemaking process to provide warranted
flexibility to owners and operators of
MSWLFs in Indian Country. Obtain the
draft guidance document Site-Specific
Flexibility Requests for Municipal Solid
Waste Landfills in Indian Country (EPA
530-R-97-016) for further information.
Aquifer: An aquifer is a formation or
group of formations capable of yielding a
significant amount of ground water to wells
or springs. To be an aquifer, a formation
must yield enough water for ground-water
monitoring samples. An unconfmed aquifer
is one where the water table is exposed to
the atmosphere through openings in the
overlying geologic formations. A confined
aquifer is isolated from the atmosphere at
the discharge point by impermeable
geological units. A confined aquifer has
relatively impermeable beds above and
below.
Existing unit: Any MSWLF unit that is
receiving household waste as of October 9,
1993 must continue to operate the facility in
a manner that is consistent with both past
operating practices and modified practices
that continue or improve good waste
management. Changes in operating
practices intended to circumvent the
purpose, intent, or applicability of any
portions of Part 258 will not be considered
in conformance with the Criteria. Facilities
spreading a thin layer of waste over unused
new areas will not be exempt from the
design requirements for new units. The
portion of a facility that is considered to be
an existing unit will include the waste
management area that has received waste
prior to the effective date of Part 258.
Existing units may expand vertically.
However, vertical placement of waste over
a closed unit would cause the unit to be
considered a new unit and would subject the
unit to the design requirements in Part 258.
Note: Not all units that have a valid State
permit are considered existing units. To be
an existing unit, the land surface must be
covered by waste by October 9, 1993.
Lateral expansion: Any horizontal
expansion of the waste boundary of a unit is
a lateral expansion. This means that new
13
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Subpart A
land surface would be covered by waste
after October 9, 1993. Expansions to the
existing unit have to be consistent with past
operating procedures or operating practices
to ensure good management.
Spreading wastes over a large area to
increase the size of an existing unit, prior to
the effective date would not be consistent
with good management practices. If a new
land surface adjacent to an existing unit first
receives waste after October 9, 1993, that
area is classified as a lateral expansion and
therefore, is subject to the new design
standards. However, Part 258 regulations
provide the flexibility for approved States to
determine what would constitute a lateral
expansion.
Municipal solid waste landfill unit:
Municipal solid waste landfill units are units
that receive household waste, such as that
from single and multiple residences, hotels
and motels, bunkhouses, ranger stations,
crew quarters, campgrounds, picnic grounds
and day-use recreation areas. Other Subtitle
D wastes, such as commercial solid waste,
nonhazardous sludge, and industrial solid
waste, may be disposed of in a municipal
solid waste landfill.
New municipal solid waste landfill unit:
A new MSWLF unit is any unit that has not
received waste prior to October 9, 1993.
Lateral expansions are considered new
MSWLF units for the purpose of location
restrictions and design standards. New
MSWLF units are subject to all
requirements of Part 258.
1.7 CONSIDERATION OF
OTHER FEDERAL LAWS
40 CFR §258.3
1.7.1 Statement of Regulation
The owner or operator of a municipal
solid waste landfill unit must comply with
any other applicable Federal rules, laws,
regulations, or other requirements.
1.7.2 Applicability
Owners and operators of MSWLF units
must comply with Federal regulations, laws,
rules or requirements that are in effect at the
time of publication of Part 258 or that may
become effective at a later date.
1.7.3 Technical Considerations
Specific sections of Part 258 reference
major Federal regulations that also may be
applicable to MSWLF units regulated under
Part 258. These regulations include the
Clean Water Act (wetlands, sludge dis-
posal, point and non-point source dis-
charges), the Clean Air Act, other parts of
RCRA (Subtitle C if the MSWLF unit
inadvertently receives regulated hazardous
waste), and the Endangered Species Act.
Furthermore, additional Federal rules, laws,
or regulations may need to be considered.
The owner or operator of the MSWLF unit
is responsible for deter-mining the
conditions present at the facility that may
require consideration of other Federal Acts,
rules, requirements, or regulations. Careful
review of the Part 258 Criteria will help to
identify most of the major Federal laws that
may be applicable to a particular MSWLF
unit.
14
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CHAPTER 2
SUSPART B
LOCATION CRITERIA
15
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CHAPTER 2
SUBPART B
TABLE OF CONTENTS
2.1 INTRODUCTION 18
2.2 AIRPORT SAFETY 40 CFR $258.10 19
2.2.1 Statement of Regulation 19
2.2.2 Applicability 20
2.2.3 Technical Considerations 20
2.3 FLOODPLAINS 40 CFR $258.11 24
2.3.1 Statement of Regulation 24
2.3.2 Applicability 24
2.3.3 Technical Considerations 25
Floodplain Identification 25
Engineering Considerations 27
2.4 WETLANDS 40 CFR $258.12 28
2.4.1 Statement of Regulation 28
2.4.2 Applicability 30
2.4.3 Technical Considerations 31
2.5 FAULT AREAS 40 CFR $258.13 37
2.5.1 Statement of Regulation 37
2.5.2 Applicability 37
2.5.3 Technical Considerations 38
2.6 SEISMIC IMP ACT ZONES 40 CFR $25 8.14 41
2.6.1 Statement of Regul ati on 41
2.6.2 Applicability 41
2.6.3 Technical Considerations 42
Background on Seismic Activity 42
Information Sources on Seismic Activity 42
Landfill Planning and Engineering in Areas of Seismic Activity 42
16
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2.7 UNSTABLE AREAS 40 CFR §258.15 45
2.7.1 Statement of Regulation 45
2.7.2 Applicability 46
2.7.3 Technical Considerations 47
Types of Failures 49
Subsurface Exploration Programs 54
Methods of Slope Stability Analysis 54
Design for Slope Stabilization 56
Monitoring 60
Engineering Considerations for Karst Terrain 60
2.8 CLOSURE OF EXISTING MUNICIPAL SOLID WASTE LANDFILL UNITS 40
CFRS258.16 61
2.8.1 Statement of Regulation 61
2.8.2 Applicability 62
2.8.3 Technical Considerations 62
2.9 FURTHER INFORMATION 63
2.9.1 References 63
2.9.2 Organizations 65
2.9.3 Models 68
APPENDIX I - FAA Order 5200.5A 69
17
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CHAPTER 2
SUBPART B
LOCATION RESTRICTIONS
2.1 INTRODUCTION
Part 258 includes location restrictions to address both the potential effects that a municipal solid
waste landfill (MSWLF) unit may have on the surrounding environment, and the effects that natural
and human-made conditions may have on the performance of the landfill unit. These criteria pertain
to new and existing MSWLF units and lateral expansions of existing MSWLF units. The location
criteria of Subpart B cover the following:
• Airport safety;
• Floodplains;
• Wetlands;
• Fault areas;
• Seismic impact zones; and
• Unstable areas.
Floodplain, fault area, seismic impact zone, and unstable area restrictions address conditions that
may have adverse effects on landfill performance that could lead to releases to the environment or
disruptions of natural functions (e.g., floodplain flow restrictions). Airport safety, floodplain, and
wetlands criteria are intended to restrict MSWLF units in areas where sensitive natural environments
and/or the public may be adversely affected.
Owners or operators must demonstrate that the location criteria have been met when Part 258 takes
effect. Components of such demonstrations are identified in this section. The owner or operator
of the landfill unit must also comply with all other applicable Federal and State regulations, such
as State wellhead protection programs, that are not specifically identified in the Criteria. Owners
or operators should note that many States are now developing Comprehensive State Ground Water
Protection Programs. These programs are designed to coordinate and implement ground-water
programs in the States; they may include additional requirements. Owners or operators should
check with State environmental agencies concerning Comprehensive State Ground Water Protection
Program requirements. Table 2-1 provides a quick reference to the location standards required by
the Criteria.
18
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Location Criteria
Table 2-1
Location Criteria Standards
Restricted
Location
Airport
Floodplains
Wetlands
Fault Areas
Seismic Impact
Zones
Unstable Areas
Applies to
Existing Units
Yes
Yes
No
No
No
Yes
Applies to
New Units
and Lateral
Expansions
Yes
Yes
Yes
Yes
Yes
Yes
Make
Demonstration to
"Director of an
Approved State"
OR
Retain
Demonstration in
Operating Record
Operating Record
Operating Record
Director
Director
Director
Operating Record
Existing
Units Must
Close if
Demonstra-
tion Cannot
be Made
Yes
Yes
N/A
N/A
N/A
Yes
2.2 AIRPORT SAFETY
40 CFR §258.10
2.2.1 Statement of Regulation
(a) Owners or operators of new
MSWLF units, existing MSWLF units, and
lateral expansions that are located within
10,000 feet (3,048 meters) of any airport
runway end used by turbojet aircraft or
within 5,000 feet (1,524 meters) of any
airport runway end used by only piston-
type aircraft must demonstrate that the
units are designed and operated so that the
MSWLF unit does not pose a bird hazard
to aircraft.
(b) Owners or operators proposing to
site new MSWLF units and lateral
expansions within a five-mile radius of any
airport runway end used by turbojet
or piston-type aircraft must notify the
affected airport and the Federal Aviation
Administration (FAA).
(c) The owner or operator must place
the demonstration in paragraph (a) in the
operating record and notify the State
Director that it has been placed in the
operating record.
(d) For purposes of this section:
19
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Subpart B
(1) Airport means public-use airport
open to the public without prior permission
and without restrictions within the physical
capacities of available facilities.
(2) Bird hazard means an increase in
the likelihood of bird/aircraft collisions
that may cause damage to the aircraft or
injury to its occupants.
2.2.2 Applicability
Owners and operators of new MSWLF units,
existing MSWLF units, and lateral expansions
of existing units that are located near an
airport, who cannot demonstrate that the
MSWLF unit does not pose a bird hazard,
must close their units.
This requirement applies to owners and
operators of MSWLF units located within
10,000 feet of any airport runway end used by
turbojet aircraft or within 5,000 feet of any
airport runway end used only by piston-type
aircraft. This applies to airports open to the
public without prior permission for use, and
where use of available facilities is not
restricted. If the above conditions are present,
the owner or operator must demonstrate that
the MSWLF unit does not pose a bird hazard
to aircraft and notify the State Director that
the demonstration has been placed in the
operating record. If the demonstration is not
made, existing units must be closed in
accordance with §258.16.
The regulation, based on Federal Aviation
Administration (FAA) Order 5200.5 A
(Appendix I), prohibits the disposal of solid
waste within the specified distances unless
the owner or operator is able to make the
required demonstration showing that the
landfill is designed and operated so as not to
pose bird hazards to aircraft. The regulation
defines a "danger zone" within which
particular care must be taken to ensure that no
bird hazard arises.
Owners or operators proposing to site new
units or lateral units within five miles of any
airport runway end must notify both the
affected airport and the FAA. This
requirement is based on the FAA's position
that MSWLF units located within a five mile
radius of any airport runway end, and which
attract or sustain hazardous bird movements
across aircraft flight paths and runways, will
be considered inconsistent with safe flight
operations. Notification by the MSWLF
owner/operator to the appropriate regional
FAA office will allow FAA review of the
proposal.
2.2.3 Technical Considerations
A demonstration that a MSWLF unit does not
pose a bird hazard to aircraft within specified
distances of an airport runway end should
address at least three elements of the
regulation:
• Is the airport facility within the regulated
distance?;
• Is the runway part of a public-use
airport?; and
• Does or will the existence of the landfill
increase the likelihood of bird/aircraft
collisions that may cause damage to the
aircraft or injury to its occupants?
The first element can be addressed using
existing maps showing the relationship of
existing runways at the airport to the
existing or proposed new unit or lateral
20
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Location Criteria
expansion. Topographic maps (USGS 15-
minute series) or State, regional, or local
government agency maps providing similar or
better accuracy would allow direct scaling, or
measurement, of the closest distance from the
end of a runway to the nearest MSWLF unit.
The measurement can be made by drawing a
circle of appropriate radius (i.e., 5,000 ft.,
10,000 ft, or 5 miles, depending on the airport
type) from the centerline of each runway end.
The measurement only should be made
between the end of the runway and the nearest
MSWLF unit perimeter, not between any
other boundaries.
To determine whether the runway is part of a
public use airport and to determine whether
all applicable public airports have been
identified, the MSWLF unit owner/operator
should contact the airport administration or
the regional FAA office. This rule does not
apply to private airfields.
The MSWLF unit design features and
operational practices can have a significant
effect on the likelihood of increased
bird/aircraft collisions. Birds may be attracted
to MSWLF units to satisfy a need for water,
food, nesting, or roosting. Scavenger birds
such as starlings, crows, blackbirds, and gulls
are most commonly associated with active
landfill units. Where bird/aircraft collisions
occur, these types of birds are often involved
due to their flocking, feeding, roosting, and
flight behaviors. Waste management
techniques to reduce the supply of food to
these birds include:
• Frequent covering of wastes that
provide a source of food;
• Shredding, milling, or baling the
waste-containing food sources; and
• Eliminating the acceptance of wastes
at the landfill unit that represent a
food source for birds (by alternative
waste management techniques such as
source separation and composting or
waste minimization).
Frequent covering of wastes that represent a
food source for the birds effectively reduces
the availability of the food supply. Depending
on site conditions such as volume and types
of wastes, waste delivery schedules, and size
of the working face, cover may need to be
applied several times a day to keep the
inactive portion of the working face small
relative to the area accessible to birds. By
maintaining a small working face, spreading
and compaction equipment are concentrated
in a small area that further disrupts
scavenging by the birds.
Milling or shredding municipal solid waste
breaks up food waste into smaller particle
sizes and distributes the particles throughout
non-food wastes, thereby diluting food wastes
to a level that frequently makes the mixture
no longer attractive as a food supply for birds.
Similarly, baling municipal solid waste
reduces the surface area of waste that may be
available to scavenging birds.
The use of varying bird control techniques
may prevent the birds from adjusting to a
single method. Methods such as visual
deterrents or sound have been used with
mixed success in an attempt to discourage
birds from food scavenging. Visual
deterrents include realistic models (still or
animated) of the bird's natural predators
21
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Subpart B
(e.g., humans, owls, hawks, falcons). Sounds
that have had limited success as deterrents
include cannons, distress calls of the
scavenger birds, and sounds of its natural
predators. Use of physical barriers such as
fine wires strung across or near the working
face have also been successfully used (see
Figure 2-1). Labor intensive efforts have
included falconry and firearms. Many of
these methods have limited long-term effects
on controlling bird populations at landfill
units/facilities, as the birds adapt to the
environment in which they find food.
Proper design and operation also can reduce
the attraction of birds to the landfill unit
through eliminating scavenger bird habitat.
For example, the use of the landfill unit as a
source of water can be controlled by
encouraging surface drainage and by
preventing the ponding of water.
Birds also may be attracted to a landfill unit as
a nesting area. Use of the landfill site as a
roosting or nesting area is usually limited to
ground-roosting birds (e.g., gulls). Operational
landfill units that do not operate continuously
often provide a unique roosting habitat due to
elevated ground temperatures (as a result of
waste decomposition within the landfill) and
freedom from disturbance. Nesting can be
minimized, however, by examining the nesting
patterns and requirements of undesirable birds
and designing controls accordingly. For
example, nesting by certain species can be
controlled through the mowing and
maintenance schedules at the landfill.
In addition to design features and
operational procedures to control bird
populations, the demonstration should
address the likelihood that the MSWLF unit
may increase bird/aircraft collisions. One
approach to addressing this part of the airport
safety criterion is to evaluate the attraction of
birds to the MSWLF unit and determine
whether this increased population would be
expected to result in a discernible increase in
bird/aircraft collisions. The evaluation of
bird attraction can be based on field
observations at existing facilities where
similar geographic location, design features,
and operational procedures are present.
All observations, measurements, data,
calculations and analyses, and evaluations
should be documented and included in the
demonstration. The demonstration must be
placed in the operating record and the State
Director must be notified that it has been
placed in the operating record (see Section
3.11 in Chapter 3).
If an owner or operator of an existing
MSWLF unit cannot successfully demonstrate
compliance with §258.10(a), then the unit
must be closed in accordance with §258.60
and post-closure activities must be conducted
in accordance with §258.61 (see §258.16).
Closure must occur by October 9, 1996. The
Director of an approved State can extend the
period up to 2 years if it is demonstrated that
no available alternative disposal capacity
exists and the unit poses no immediate threat
to human health and the environment (see
Section 2.8).
In accordance with FAA guidance, if an
owner or operator is proposing to locate a
new unit or lateral expansion of an existing
MSWLF unit within 5 miles of the end of a
public-use airport runway, the affected airport
and the regional FAA office must be notified
to provide an opportunity to review and
comment on the site. Identification of public
airports in a given area can be
22
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Location Criteria
Monofilament
Rope or Wire
" Guyed to
Movable Anchors
Source: SCS Engineers
Figure 2-1.
Bird Control Device
23
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Subpart B
requested from the FAA. Topographic maps
(e.g., USGS 15-minute series) or other
similarly accurate maps showing the
relationship of the airport runway and the
MSWLF unit should provide a suitable basis
for determining whether the FAA should be
notified.
2.3 FLOODPLAINS
40 CFR §258.11
2.3.1 Statement of Regulation
(a) Owners or operators of new
MSWLF units, existing MSWLF units, and
lateral expansions located in 100-year
floodplains must demonstrate that the unit
will not restrict the flow of the 100-year
flood, reduce the temporary water storage
capacity of the floodplain, or result in
washout of solid waste so as to pose a
hazard to human health and the
environment. The owner or operator must
place the demonstration in the operating
record and notify the State Director that it
has been placed in the operating record.
(b) For purposes of this section:
(1) Floodplain means the lowland and
relatively flat areas adjoining inland and
coastal waters, including flood-prone areas
of offshore islands, that are inundated by
the 100-year flood.
(2) 100-year flood means a flood that
has a 1-percent or greater chance of
recurring in any given year or a flood of a
magnitude equaled or exceeded once in 100
years on the average over a significantly
long period.
(3) Washout means the carrying away
of solid waste by waters of the base flood.
2.3.2 Applicability
Owners/operators of new MSWLF units,
existing MSWLF units, and lateral
expansions of existing units located in a
100-year river floodplain who cannot
demonstrate that the units will not restrict
the flow of a 100-year flood nor reduce the
water storage capacity, and will not result
in a wash-out of solid waste, must close the
unit(s). A MSWLF unit can affect the flow
and temporary storage capacity of a
floodplain. Higher flood levels and greater
flood damage both upstream and
downstream can be created and could cause
a potential hazard to human health and
safety. The rule does not prohibit locating
a MSWLF unit in a 100-year floodplain; for
example, the owner or operator is allowed
to demonstrate that the unit will comply
with the flow restriction, temporary
storage, and washout provisions of the
regulation. If a demonstration can be made
that the landfill unit will not pose threats,
the demonstration must be placed in the
operating record, and the State Director
must be notified that the demonstration was
made and placed in the record. If the
demonstration cannot be made for an
existing MSWLF unit, then the MSWLF
unit must be closed in 5 years in accordance
with §258.60, and the owner or operator
must conduct post-closure activities in
accordance with §258.61 (see §258.16).
The closure deadline may be extended for
up to two years by the Director of an
approved State if the owner or operator can
demonstrate that no available alternative
disposal capacity exists and there
24
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Location Criteria
is no immediate threat to human health and
the environment (see Section 2.8).
2.3.3 Technical Considerations
Compliance with the floodplain criterion
begins with a determination of whether the
MSWLF unit is located in the 100-year
floodplain. If the MSWLF unit is located in
the 100-year floodplain, then the owner or
operator must demonstrate that the unit will
not pose a hazard to human health and the
environment due to:
• Restricting the base flood flow;
• Reducing the temporary water storage;
and
• Resulting in the washout of solid waste.
Guidance for identifying floodplains and
demonstrating facility compliance is provided
below.
Floodplain Identification
River floodplains are readily identifiable as
the flat areas adjacent to the river's normal
channel. One hundred-year floodplains
represent the sedimentary deposits formed by
floods that have a one percent chance of
occurrence in any given year and that are
identified in the flood insurance rate maps
(FIRMs) and flood boundary and floodway
maps published by the Federal Emergency
Management Agency (FEMA) (see Figure
2-2). Areas classified as "A" zones are
subject to the floodplain location restriction.
Areas classified as "B" or "C" zones are not
subject to the restriction, although care should
be taken to design facilities capable of
withstanding some potential flooding.
Guidance on using FIRMs is provided in
"How to Read a Flood Insurance Rate Map"
published by FEMA. FEMA also publishes
"The National Flood Insurance Program
Community Status Book" that lists
communities that may not be involved in the
National Flood Insurance Program but which
have FIRMs or Floodway maps published.
Maps and other FEMA publications may be
obtained from the FEMA Distribution Center
(see Section 2.9.2 for the address). Areas not
covered by the FIRMs or Floodway maps
may be included in floodplain maps available
through the U.S. Army Corps of Engineers,
the U.S. Geological Survey, the U.S. Soil
Conservation Service, the Bureau of Land
Management, the Tennessee Valley
Authority, and State, Tribal, and local
agencies.
Many of the river channels covered by these
maps may have undergone modification for
hydropower or flood control projects and,
therefore, the floodplain boundaries
represented may not be accurate or
representative. It may be necessary to
compare the floodplain map series to recent
air photographs to identify current river
channel modifications and land use
watersheds that could affect floodplain
designations. If floodplain maps are not
available, and the facility is located within a
floodplain, then a field study to delineate the
100-year floodplain may be required. A
floodplain delineation program can be based
primarily on meteorological records and
physiographic information such as existing
and planned watershed land use,
topography, soils and geologic mapping,
and air photo interpretation of
geomorphologic (land form) features. The
United States Water Resource Council
(1977) provides information for determining
25
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Figure 2-2
Example Section of Flood Plain Map
26
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Location Criteria
the potential for floods in a given location by
stream gauge records. Estimation of the peak
discharge also allows an estimation of the
probability of exceeding the 100-year flood.
Engineering Considerations
If the MSWLF unit is within the 100-year
floodplain, it must be located so that the
MSWLF unit does not significantly restrict
the base flood flow or significantly reduce
temporary storage capacity of the floodplain.
The MSWLF unit must be designed to prevent
the washout of solid waste during the
expected flood event. The rule requires that
floodplain storage capacity, and flow
restrictions that occur as the result of the
MSWLF unit, do not pose a hazard to human
health and the environment.
The demonstration that these considerations
are met relies on estimates of the flow
velocity and volume of floodplain storage in
the vicinity of the MSWLF unit during the
base flood. The assessment should consider
the floodplain storage capacity and floodwater
velocities that would likely exist in absence of
the MSWLF unit. The volume occupied by a
MSWLF unit in a floodplain may
theoretically alter (reduce) the storage
capacity and restrict flow. Raising the base
flood level by more than one foot can be an
indication that the MSWLF unit may reduce
and restrict storage capacity flow.
The location of the MSWLF unit relative to
the velocity distribution of floodwaters will
greatly influence the susceptibility to
washout. This type of assessment will
require a conservative estimate of the shear
stress on the landfill components caused by
the depth, velocity, and duration of
impinging river waters. Depending on the
amount of inundation, the landfill unit may
act as a channel side slope or bank or it may
be isolated as an island within the overbank
river channel. In both cases an estimate of
the river velocity would be part of a proper
assessment.
The assessment of flood water velocity
requires that the channel cross section be
known above, at, and below the landfill unit.
Friction factors on the overbank are deter-
mined from the surface conditions and vege-
tation present. River hydrologic models may
be used to simulate flow levels and estimate
velocities through these river cross sections.
The Army Corps of Engineers (COE, 1982)
has developed several numerical models to
aid in the prediction of flood hydrographs,
flow parameters, the effect of obstructions on
flow levels, the simulation of flood control
structures, and sediment transport. These
methods may or may not be appropriate for a
site; however, the following models provide
well-tested analytical approaches:
HEC-1 Flood Hydrograph Package
(watershed model that simulates the
surface run-off response of a river basin
to precipitation);
HEC-2 Water Surface Profiles (computes
water surface profiles due to
obstructions; evaluates floodway
encroachment potential);
HEC-5 Simulation of Flood Control and
Conservation Systems (simulates the
sequential operation of a reservoir
channel system with a branched
network configuration; used to design
27
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Subpart B
routing that will minimize downstream
flooding); and
HEC-6 Scour and Deposition in Rivers
and Reservoirs (calculates water surface
and sediment bed surface profiles).
The HEC-2 model is not appropriate for
simulation of sediment-laden braided stream
systems or other intermittent/dry stream
systems that are subject to flash flood events.
Standard run-off and peak flood hydrograph
methods would be more appropriate for such
conditions to predict the effects of severe
flooding.
There are many possible cost-effective
methods to protect the MSWLF unit from
flood damage including embankment designs
with rip-rap, geotextiles, or other materials.
Guidelines for designing with these materials
may be found in Maynard (1978) and SCS
(1983). Embankment design will require an
estimate of river flow velocities, flow profiles
(depth), and wave activity. Figure 2-3
provides a design example for dike
construction and protection of the landfill
surface from flood water. It addresses height
requirements to control the effects of wave
activity. The use of alternate erosion control
methods such as gabions (cubic-shaped wire
structures filled with stone), paving bricks,
and mats may be considered. It should be
noted, however, that the dike design in Figure
2-3 may further decrease the water storage
and flow capacities.
2.4 WETLANDS
40 CFR §258.12
2.4.1 Statement of Regulation
(a) New MSWLF units and lateral
expansions shall not be located in wetlands,
unless the owner or operator can make the
following demonstrations to the Director of
an approved State:
(1) Where applicable under section 404
of the Clean Water Act or applicable State
wetlands laws, the presumption that a
practicable alternative to the proposed
landfill is available which does not involve
wetlands is clearly rebutted;
(2) The construction and operation of
the MSWLF unit will not:
(i) Cause or contribute to violations of
any applicable State water quality
standard,
(ii) Violate any applicable toxic
effluent standard or prohibition under
Section 307 of the Clean Water Act,
(iii) Jeopardize the continued existence
of endangered or threatened species or
result in the destruction or adverse
modification of a critical habitat, protected
under the Endangered Species Act of 1973,
and
(iv) Violate any requirement under the
Marine Protection, Research, and
Sanctuaries Act of 1972 for the protection
of a marine sanctuary;
28
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ASSUMPTIONS:
* FETCH = 2500 FT'
* WIND SPEED = 50 MPH
* AVE. WATER DEPTH ALONG FETCH = 5 FT
* OVERBANK WATER VELOCITY = 0,25 FT/S
DEFINITIONS
Zs = Wave Setup (tilting of water surface upward at downwind end)
Zw = Capillary Waves Height {developed by wind over water surface)
Zr = Wave Run-up (water run-up along dike from wave impact)
WIND
i
t
RIVER
LANDFILL
EQUATIONS
WIND
Free Board
2500 F x>t Fetch
Dike
Landfill
Flood Plain
Rood Plain
Section A
Total Wave Height (Zt = Zs + Zw + Zr)
\
.100 yr Flood Water
\ A
SECTION A
SOLUTIONS
where:
Zr = Wave run-up along dike
Zr/Zw = Relative run-up rafo from
chart below
A = Wavelength
tw = Wave period
Vw = wind speed (mph)
F = fetch (mites)
Zw= 0.034 V
where:
Zw = ave. height of heighest 1/3rd
of waves (ft)
F = fetch (miles)
140CW
where:
Zs = rise above stiff water [eve! (ft)
Vw = wind speed (mph)
F = fetch (miles)
d = water depth along fetch (ft)
w=-
KjH"
1000(0.0167
-since)'
where:
W = Rip - Rap stone weight (tos)
d - Rip - Rap stone diameter
K = Coefficient (30)
Y = Stone Density (Ib/cf)
H = height of design wave (ft)
o = bank slope (degrees)
From the data provided in the assumptions
at the beginning of the example:
Zs = 0.18 n., Zw = 1.55 ft., Zr = 2.40 ft '
Zt Design Height = 4.13 ft
Base 100 yr flood level = 5 ft
for Factor of Safety of 1.5
Dike Height = (1.5) (4.13 + 5) = 13.7 ft
For the Rip - Rap design given:
K = 30, y= 120, H = 1.55 ft., a = 185
For the protective stone on Dike
d = 0.5ft, W = 12lbs7stone
\~.^_1'*~ , "°: .TiTT -i------• -H
Wave run-up ratios vs. wave steepness and embankment slopes
Re'e^ence 'or Equations: U.S. Department of Interior, Bureau of Land Reclamation (1974)
Reference tor Wave Run-up Chart: L»nsiey and Franani (1972)
Figure 2-3. Example Floodplain Protection Dike Design
29
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Subpart B
(3) The MSWLF unit will not cause or
contribute to significant degradation of
wetlands. The owner or operator must
demonstrate the integrity of the MSWLF
unit and its ability to protect ecological
resources by addressing the following
factors:
(i) Erosion, stability, and migration
potential of native wetland soils, muds and
deposits used to support the MSWLF unit;
(ii) Erosion, stability, and migration
potential of dredged and fill materials used
to support the MSWLF unit;
(iii) The volume and chemical nature
of the waste managed in the MSWLF unit;
(iv) Impacts on fish, wildlife, and
other aquatic resources and their habitat
from release of the solid waste;
(v) The potential effects of
catastrophic release of waste to the wetland
and the resulting impacts on the
environment; and
(vi) Any additional factors, as
necessary, to demonstrate that ecological
resources in the wetland are sufficiently
protected.
(4) To the extent required under
Section 404 of the Clean Water Act or
applicable State wetland laws, steps have
been taken to attempt to achieve no net
loss of wetlands (as defined by acreage
and function) by first avoiding impacts to
wetlands to the maximum extent
practicable as required by paragraph
(a)(l) of this section, then minimizing
unavoidable impacts to the maximum
extent practicable, and finally offsetting
remaining unavoidable wetland impacts
through all appropriate and practicable
compensatory mitigation actions (e.g.,
restoration of existing degraded wetlands
or creation of man-made wetlands); and
(5) Sufficient information is available
to make a reasonable determination with
respect to these demonstrations.
(b) For purposes of this section,
"wetlands" means those areas that are
defined in 40 CFR §232.2(r).
2.4.2 Applicability
New MSWLF units and lateral expansions in
wetlands are prohibited, except in approved
States. The wetland restrictions allow
existing MSWLF units located in wetlands to
continue operations as long as compliance
with the other requirements of Part 258 can
be maintained.
In addition to the regulations listed in 40 CFR
§258.12(a)(2), other Federal requirements
may be applicable in siting a MSWLF unit in
a wetland. These include:
• Sections 401, 402, and 404 of the CWA;
• Rivers and Harbors Act of 1989;
• National Environmental Policy Act;
• Migratory Bird Conservation Act;
• Fish and Wildlife Coordination Act;
• Coastal Zone Management Act;
• Wild and Scenic Rivers Act; and the
• National Historic Preservation Act.
As authorized by the EPA, the use of
wetlands for location of a MSWLF facility
may require a permit from the U.S. Army
30
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Location Criteria
Corps of Engineers (COE). The types of
wetlands present (e.g., headwater, isolated, or
adjacent), the extent of the wetland impact,
and the type of impact proposed will
determine the applicable category of COE
permit (individual or general) and the permit
application procedures. The COE District
Engineer should be contacted prior to permit
application to determine the available
categories of permits for a particular site.
Wetland permitting or permit review and
comment can include additional agencies at
the federal, state, regional, and local level.
The requirements for wetland permits should
be reviewed by the owner/operator to ensure
compliance with all applicable regulations.
When proposing to locate a new facility or
lateral expansion in a wetland, owners or
operators must be able to demonstrate that
alternative sites are not available and that the
impact to wetlands is unavoidable.
If it is demonstrated that impacts to the
wetland are unavoidable, then all practicable
efforts must be made to minimize and, when
necessary, compensate for the impacts. The
impacts must be compensated for by restoring
degraded wetlands, enhancing or preserving
existing wetlands, or creating new wetlands.
It is an EPA objective that mitigation
activities result in the achievement of no net
loss of wetlands.
2.4.3 Technical Considerations
The term wetlands, referenced in §258.12(b),
is defined in §232.2(r). The EPA currently is
studying the issues involved in defining and
delineating wetlands. Proposed changes to
the "Federal Manual for Identifying and
Delineating Jurisdictional Wetlands," 1989,
are still being reviewed. [These changes were
proposed in the Federal Register on August
14, 1991 (56 FR 40446) and on December 19,
1991 (56 FR 65964).] Therefore, as of
January 1993, the method used for delineating
a wetland is based on a previously existing
document, "Army Corps of Engineers
Wetlands Delineation Manual," 1987. A
Memorandum of Understanding between
EPA and the Department of the Army, Corps
of Engineers, was amended on January 4,
1993, to state that both agencies would now
use the COE 1987 manual as guidance for
delineating wetlands. The methodology
applied by an owner/operator to define and
delineate wetlands should be in keeping with
the federal guidance in place at the time of the
delineation.
Because of the unique nature of wetlands, the
owner/operator is required to demonstrate that
the landfill unit will not cause or contribute to
significant degradation of wetlands. The
demonstration must be reviewed and
approved by the Director of an approved State
and placed in the facility operating record.
This provision effectively bans the siting of
new MSWLF units or lateral expansions in
wetlands in unapproved States.
There are several key issues that need to be
addressed if an owner or operator proposes to
locate a lateral expansion or a new MSWLF
unit in a wetland. These issues include: (1)
review of practicable alternatives, (2)
evaluation of wetland acreage and function, (3)
evaluation of impacts of MSWLF units on
wetlands, and (4) offsetting impacts. Although
EPA has an objective of no net loss of wetlands
in terms of acreage and function, it recognizes
that regions of the country exist where
proportionally large areas are dominated by
wetlands. In these regions, sufficient
31
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Subpart B
acreage and a suitable type of upland may not
be present to allow construction of a new
MSWLF unit or lateral expansion without
wetland impacts. Wetlands evaluations may
become an integral part of the siting, design,
permitting, and environmental monitoring
aspects of a landfill unit/facility (see Figure 2-
4).
Practicable Alternatives
EPA believes that locating new MSWLF units
or lateral expansions in wetlands should be
done only where there are no less damaging
alternatives available. Due to the extent of
wetlands that may be present in certain
regions, the banning of new MSWLF units or
lateral expansions in wetlands could cause
serious capacity problems. The flexibility of
the rule allows owners or operators to
demonstrate that there are no practicable
alternatives to locating or laterally expanding
MSWLF units in wetlands.
As part of the evaluation of practicable
alternatives, the owner/operator should
consider the compliance of the location with
other regulations and the potential impacts of
the MSWLF unit on wetlands and related
resources. Locating or laterally expanding
MSWLF units in wetlands requires
compliance with other environmental
regulations. The owner or operator must
show that the operation or construction of the
landfill unit will not:
• Violate any applicable State water
quality standards;
• Cause or contribute to the violation of
any applicable toxic effluent standard
or prohibition;
• Cause or contribute to violation of
any requirement for the protection of
a marine sanctuary; and
• Jeopardize the continued existence of
endangered or threatened species or
critical habitats.
The MSWLF unit cannot cause or contribute
to significant degradation of wetlands.
Therefore, the owner/operator must:
• Ensure the integrity of the MSWLF
unit, including consideration of the
erosion, stability, and migration of
native wetland soils and dredged/fill
materials;
• Minimize impacts on fish, wildlife,
and other aquatic resources and their
habitat from the release of solid
waste;
• Evaluate the effects of catastrophic
release of wastes on the wetlands; and
• Assure that ecological resources in the
wetlands are sufficiently protected,
including consideration of the volume
and chemical nature of waste
managed in the MSWLF unit.
These factors were partially derived from
Section 404(b)(l) of the Clean Water Act.
These guidelines address the protection of the
ecological resources of the wetland.
After consideration of these factors, if no
practicable alternative to locating the landfill
in wetlands is available, compensatory steps
must be taken to achieve no net loss of
wetlands as defined by acreage and
32
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Wetland Study
Not Required
Has a wet-
land Delineation
Study Been
Performed?
Is landfill
Site Adjacent to
of Impinging on
a Wetland''
Contact COE
Regarding a
Wetland
Delineation Study
A Wetland
Delineation Study
Should toe
Performed
Are
Practicable
Alternate
Disposal Optens
or Landfill Sites
Available'
Alternate
Disposal Study
Required
Cannot Build in
WeflarxJ
A/e Alternate
Disposal Options
or Landfill Sites
Available7
Identify Affected Acreage
and Functions ater
Minimizing Impact and
Arrange COE Site Visit
Contact State and COE to
Determine Wetland Offset
Ratios and Functional
Rank of Offset Options
File for Landfill
Permit /404 Permit
1. Impact Minimization Plan
2, Rebuttal of Alternatives
3. Wettartd Offset Plan
4. Offset Monitoring Plan
Figure 2-4
Wetlands Decision Tree for Owners/Operators
in Approved States
33
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Subpart B
function. The owner/operator must try to
avoid and/or minimize impacts to the
wetlands to the greatest extent possible.
Where avoidance and minimization still result
in wetland impacts, mitigation to offset
impacts is required. Mitigation plans must be
approved by the appropriate regulatory
agencies and must achieve an agreed-upon
measure of success. Examples of mitigation
include restoration of degraded wetlands or
creation of wetland acreage from existing
uplands.
Part 258 presumes that practicable alternatives
are available to locating landfill units in
wetlands because landfilling is not a water-
dependent activity. In an approved State, the
owner or operator can rebut the presumption
that a practicable alternative to the proposed
landfill unit or lateral expansion is available.
The term "practicable" pertains to the
economic and social feasibility of alternatives
(e.g., collection of waste at transfer stations
and trucking to an existing landfill facility or
other possible landfill sites). The feasibility
evaluation may entail financial, economic,
administrative, and public acceptability
analyses as well as engineering
considerations. Furthermore, the evaluations
generally will require generation and
assessment of land use, geologic, hydrologic,
geographic, demographic, zoning, traffic
maps, and other related information.
To rebut the presumption that an alternative
practicable site exists generally will require
that a site search for an alternative location
be conducted. There are no standard
methods for conducting site searches due to
the variability of the number and hierarchy
of screening criteria that may be applied in
a specific case. Typical criteria may include:
• Distance from waste generation
sources;
• Minimum landfill facility size
requirements;
• Soil conditions;
• Proximity to ground-water users;
• Proximity of significant aquifers;
• Exclusions from protected natural
areas;
• Degree of difficulty to remediate
features; and
• Setbacks from roadways and
residences.
Wetland Evaluations
The term "wetlands" includes swamps,
marshes, bogs, and any areas that are
inundated or saturated by ground water or
surface water at a frequency and duration to
support, and that under normal circumstances
do support, a prevalence of vegetation
adapted for life in saturated soil conditions.
As defined under current guidelines, wetlands
are identified based on the presence of hydric
soils, hydrophyte vegetation, and the wetland
hydrology. These characteristics also affect
the functional value of a wetland in terms of
its role in: supporting fish and wildlife
habitats; providing aesthetic, scenic, and
recreational value; accommodating flood
storage; sustaining aquatic diversity; and its
relationships to surrounding natural areas
through nutrient retention and productivity
exportation (e.g., releasing nutrients to
downstream areas, providing transportable
food sources).
Often, a wetland assessment will need to be
conducted by a qualified and experienced
34
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Location Criteria
multi-disciplinary team. The assessment
should identify: (1) the limits of the wetland
boundary based on hydrology, soil types and
plant types; (2) the type and relative
abundance of vegetation, including trees; and
(3) rare, endangered, or otherwise protected
species and their habitats (if any).
The current methods used to delineate
wetlands are presented in "COE Wetlands
Delineation Manual," 1987. In January 1993,
EPA and COE agreed to use the 1987 Manual
for purposes of delineation. The Federal
Manual for Identifying and Delineating
Jurisdictional Wetlands (COE, 1989) contains
an extensive reference list of available
wetland literature. For example, lists of
references for the identification of plant
species characteristic of wetlands throughout
the United States, hydric soils classifications,
and related wetland topics are presented.
USGS topographic maps, National Wetland
Inventory (NWI) maps, Soil Conservation
Service (SCS) soil maps, wetland inventory
maps, and aerial photographs prepared locally
also may provide useful information.
After completion of a wetland study, the
impact of the MSWLF unit on wetlands and
its relationship to adjacent wetlands can be
assessed more effectively. During the
permitting process, local, State, and federal
agencies with jurisdiction over wetlands will
need to be contacted to schedule a site visit.
It is usually advantageous to encourage this
collaboration as early as possible in the site
evaluation process, especially if the State
program office that is responsible for
wetland protection is different from the
solid waste management office.
Regulations will vary significantly from
State to State with regard to the size and type
of wetland that triggers State agency
involvement. In general, the COE will
require notification and/or consultation on
any proposed impact on any wetland
regardless of the actual degree of the impact.
Other agencies such as the Fish and Wildlife
Service and the SCS may need to be
contacted in some States.
Evaluation of ecological resource protection
may include assessment of the value of the
affected wetland. Various techniques are
available for this type of evaluation, and the
most appropriate technique for a specific site
should be selected in conjunction with
applicable regulatory agencies. Available
methods include analysis of functional value,
the Wetland Evaluation Technique (WET),
and the Habitat Evaluation Procedure (HEP).
The 1987 Manual does not address functional
value in the detail provided by the 1989
manual. The methodology for conducting a
functional value assessment should be
reviewed by the applicable regulatory
agencies. It is important to note that
functional value criteria may become a
standard part of wetland delineation following
revision of the federal guidance manual(s).
The owner or operator should remain current
with the accepted practices at the time of the
delineation/assessment.
The functional value of a given wetland is
dependent on its soil, plant, and hydrologic
characteristics, particularly the diversity,
prevalence, and extent of wetland plant
species. The relationship between the
wetland and surrounding areas (nutrient sinks
and sources) and the ability of the wetland to
support animal habitats, or rare or endangered
species, contributes to the evaluation of
functional value.
35
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Subpart B
Other wetland and related assessment
methodologies include WET and HEP. WET
allows comparison of the values and functions
of wetlands before and after construction of a
facility, thereby projecting the impact a
facility may have on a wetland. WET was
developed by the Federal Highway
Administration and revised by the COE
(Adamus et a/., 1987). HEP was developed
by the Fish and Wildlife Service to determine
the quality and quantity of available habitat
for selected species. HEP and WET may be
used in conjunction with each other to provide
an integrated assessment.
Impact Evaluation
If the new unit or lateral expansion is to be
located in a wetland, the owner or operator
must demonstrate that the unit will not cause
or contribute to significant degradation of the
wetland. Erosion potential and stability of
wetland soils and any dredged or fill material
used to support the MSWLF unit should be
identified as part of the wetlands evaluation.
Any adverse stability or erosion problems that
could affect the MSWLF or contaminant
effects that could be caused by the MSWLF
unit should be resolved.
All practicable steps are to be taken to
minimize potential impacts of the MSWLF
unit to wetlands. A number of measures
that can aid in minimization of impacts are
available. Appropriate measures are site-
specific and should be incorporated into the
design and operation of the MSWLF unit.
For example, placement of ground water
barriers may be required if soil and shallow
ground-water conditions would cause
dewatering of the wetland due to the
existence of underdrain pipe systems at the
facility. In many instances, however,
wetlands are formed in response to perched
water tables over geologic material of low
hydraulic conductivity and, therefore,
significant drawdown impacts may not occur.
It is possible that the landfill unit/facility will
not directly displace wetlands, but that
adverse effects may be caused by leachate or
run-off Engineered containment systems for
both leachate and run-off should mitigate the
potential for discharge to wetlands.
Additional actions and considerations
relevant to mitigating impacts of fill
material in wetlands that may be
appropriate for MSWLF facilities are
provided in Subpart H (Actions to Minimize
Adverse Effects) of 40 CFR §230
(Guidelines for Specification of Disposal
Sites for Dredged or Fill Materials).
Wetland Offset
All unavoidable impacts must be "offset" or
compensated for to ensure that the facility has
not caused, to the extent practicable, any net
loss of wetland acreage. This compensatory
mitigation may take the form of upgrading
existing marginal or lower-quality wetlands
or creating new wetlands. Wetland offset
studies require review and development on a
site-specific basis.
To identify potential sites that may be
proposed for upgrade of existing wetlands
or creation of new wetlands, a cursory
assessment of surrounding wetlands and
uplands should be conducted. The
assessment may include a study to define
the functional characteristics and inter-
relationships of these potential wetland
mitigation areas. An upgrade of an existing
wetland may consist of transplanting
36
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Location Criteria
appropriate vegetation and importing low-
permeability soil materials that would be
conducive to forming saturated soil
conditions. Excavation to form open water
bodies or gradual restoration of salt water
marshes by culvert expansions to promote sea
water influx are other examples of
compensatory mitigation.
Individual States may have offset ratios to
determine how much acreage of a given
functional value is required to replace the
wetlands that were lost or impacted.
Preservation of lands, such as through
perpetual conservation easements, may be
considered as a viable offset option. State
offset ratios may require that for wetlands of
an equivalent functional value, a larger
acreage be created than was displaced.
Due to the experimental nature of creating or
enhancing wetlands, a monitoring program to
evaluate the progress of the effort should be
considered and may be required as a wetland
permit condition. The purpose of the
monitoring program is to verify that the
created/upgraded wetland is successfully
established and that the intended function of
the wetland becomes self-sustaining over
time.
2.5 FAULT AREAS
40 CFR §258.13
2.5.1 Statement of Regulation
(a) New MSWLF units and lateral
expansions shall not be located within 200
feet (60 meters) of a fault that has had
displacement in Holocene time unless the
owner or operator demonstrates to the
Director of an approved State that an
alternative setback distance of less than
200 feet (60 meters) will prevent damage to
the structural integrity of the MSWLF unit
and will be protective of human health and
the environment.
(b) For the purposes of this section:
(1) Fault means a fracture or a zone of
fractures in any material along which
strata on one side have been displaced with
respect to that on the other side.
(2) Displacement means the relative
movement of any two sides of a fault
measured in any direction.
(3) Holocene means the most recent
epoch of the Quaternary period, extending
from the end of the Pleistocene Epoch to
the present.
2.5.2 Applicability
Except in approved States, the regulation bans
all new MSWLF units or lateral expansions of
existing units within 200 feet (60 meters) of
the outermost boundary of a fault that has
experienced displacement during the
Holocene Epoch (within the last 10,000 to
12,000 years). Existing MSWLF units are
neither required to close nor to retrofit if they
are located in fault areas.
A variance to the 200-foot setback is
provided if the owner or operator can
demonstrate to the Director of an approved
State that a shorter distance will prevent
damage to the structural integrity of the
MSWLF unit and will be protective of
human health and the environment. The
demonstration for a new MSWLF unit or
lateral expansion requires review and
37
-------
Subpart B
approval by the Director of an approved State.
If the demonstration is approved, it must be
placed in the facility's operating record. The
option to have a setback of less than 200 feet
from a Holocene fault is not available in
unapproved States.
2.5.3 Technical Considerations
Locating a landfill in the vicinity of an area
that has experienced faulting in recent time
has inherent dangers. Faulting occurs in areas
where the geologic stresses exceed a geologic
material's ability to withstand those stresses.
Such areas also tend to be subject to
earthquakes and ground failures (e.g.,
landslides, soil liquefaction) associated with
seismic activity. A more detailed discussion
of seismic activity is presented in Section 2.6.
Proximity to a fault can cause damage
through:
• Movement along the fault which can
cause displacement of facility structures,
Seismic activity associated with faulting
which can cause damage to facility
structures through vibratory action (see
Figure 2-5), and
Earth shaking which can cause ground
failures such as slope failures.
Consequently, appropriate setbacks from fault
areas are required to minimize the potential
for damage.
To determine if a proposed landfill unit is
located in a Holocene fault area, U.S.
Geological Survey (USGS) mapping can be
used. A series of maps known as the
"Preliminary Young Fault Maps,
Miscellaneous Field Investigation (MF) 916"
was published by the USGS in 1978.
Information about these maps can be obtained
from the USGS by calling 1-800-USA-
MAPS, which reaches the USGS National
Center in Reston, Virginia, or by calling 303-
236-7477, which reaches the USGS Map
Sales Center in Denver, Colorado.
For locations where a fault zone has been
subject to movement since the USGS maps
were published in 1978, a geologic
reconnaissance of the site and surrounding
areas may be required to map fault traces and
to determine the faults along which
movement has occurred in Holocene time.
This reconnaissance also may be necessary to
support a demonstration for a setback of less
than 200 feet. Additional requirements may
need to be met before a new unit or lateral
expansion may be approved.
A site fault characterization is necessary to
determine whether a site is within 200 feet of
a fault that has had movement during the
Holocene epoch. An investigation would
include obtaining information on any
lineaments (linear features) that suggest the
presence of faults within a 3,000-foot radius
of the site. The information could be based
on:
A review of available maps, logs,
reports, scientific literature, or insurance
claim reports;
An aerial reconnaissance of the area
within a five-mile radius of the site,
including aerial photo analysis; or
38
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Location Criteria
Figure 2-5
Potential Seismic Effects
Deformed Leachate
Collection Pipe
\
\Leachate
Collection Pipe
Clay Liner
A schematic diagram of a landfill showing potential deformation of
the leachate collection and removal system by seismic stresses.
Source: US EPA, 1992
39
-------
Subpart B
A field reconnaissance that includes
walking portions of the area within 3,000
feet of the unit.
If the site fault characterization indicates that
a fault or a set of faults is situated within
3,000 feet of the proposed unit, investigations
should be conducted to determine the
presence or absence of any faults within 200
feet of the site that have experienced
movement during the Holocene period. Such
investigations can include:
Subsurface exploration, including drilling
and trenching, to locate fault zones and
evidence of faulting.
Trenching perpendicular to any faults or
lineaments within 200 feet of the unit.
Determination of the age of any
displacements, for example by examining
displacement of surficial deposits such as
glacial or older deposits (if Holocene
deposits are absent).
• Examination of seismic epicenter
information to look for indications of
recent movement or activity along
structures in a given area.
Review of high altitude, high resolution
aerial photographs with stereo-vision
coverage. The photographs are produced
by the National Aerial Photographic
Program (NAPP) and the National High
Altitude Program (NHAP). Information
on these photos can be obtained from the
USGS EROS Data Center in Sioux Falls,
South Dakota at (605) 594-615
Based on this information as well as
supporting maps and analyses, a qualified
professional should prepare a report that
delineates the location of the Holocene
fault(s) and the associated 200-foot setback.
If requesting an alternate setback, a
demonstration must be made to show that no
damage to the landfill's structural integrity
will result. Examples of engineering
considerations and modifications that may be
included in such demonstrations are as
follows:
• For zones with high probabilities of high
accelerations (horizontal) within the
moderate range of 0. Ig to 0.75g, seismic
designs should be developed.
Seismic stability analysis of landfill
slopes should be performed to guide
selection of materials and gradients for
slopes.
Where in-situ and laboratory tests
indicate that a potential landfill site is
susceptible to liquefaction, ground
improvement measures like grouting,
dewatering, heavy tamping, and
excavation should be implemented.
• Engineering options include:
— Flexible pipes,
— Ground improvement measures
(grouting, dewatering, heavy
tamping, and excavation), and/or
— Redundant precautionary
measures (secondary containment
system).
40
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Location Criteria
In addition, use of such measures needs to be
demonstrated to be protective of human health
and the environment. The types of
engineering controls described above are
similar to those that would be employed in
areas that are likely to experience
earthquakes.
2.6 SEISMIC IMPACT ZONES
40 CFR §258.14
2.6.1 Statement of Regulation
(a) New MSWLF units and lateral
expansions shall not be located in seismic
impact zones, unless the owner or operator
demonstrates to the Director of an
approved State that all containment
structures, including liners, leachate
collection systems, and surface water
control systems, are designed to resist the
maximum horizontal acceleration in
lithified earth material for the site. The
owner or operator must place the
demonstration in the operating record and
notify the State Director that it has been
placed in the operating record.
(b) For the purposes of this section:
(1) Seismic impact zone means an area
with a ten percent or greater probability
that the maximum horizontal acceleration
in lithified earth material, expressed as a
percentage of the earth's gravitational pull
(g), will exceed O.lOg in 250 years.
in
(2) Maximum horizontal acceleration
lithified earth material means the
maximum expected horizontal acceleration
depicted on a seismic hazard map, with a
90 percent or greater probability that the
acceleration will not be exceeded in 250
years, or the maximum expected horizontal
acceleration based on a site-specific seismic
risk assessment.
(3) Lithified earth material means all
rock, including all naturally occurring and
naturally formed aggregates or masses of
minerals or small particles of older rock
that formed by crystallization of magma or
by induration of loose sediments. This
term does not include man-made materials,
such as fill, concrete, and asphalt, or
unconsolidated earth materials, soil, or
regolith lying at or near the earth surface.
2.6.2 Applicability
New MSWLF units and lateral expansions in
seismic impact zones are prohibited, except in
approved States. A seismic impact zone is an
area that has a ten percent or greater
probability that the maximum expected
horizontal acceleration in lithified earth
material, expressed as a percentage of the
earth's gravitational pull (g), will exceed
O.lOg in 250 years.
The regulation prohibits locating new units or
lateral expansions in a seismic impact zone
unless the owner or operator can demonstrate
that the structural components of the unit
(e.g., liners, leachate collection systems, final
cover, and surface water control systems) are
designed to resist the maximum horizontal
acceleration in lithified earth material at the
site. Existing units are not required to be
retrofitted. Owners or operators of new units
or lateral expansions must notify the Director
of an approved State and place the
demonstration of compliance with the
conditions of the restriction in the operating
record.
41
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Subpart B
2.6.3 Technical Considerations
Background on Seismic Activity
To understand seismic activity, it is helpful to
know its origin. A brief introduction to the
geologic underpinnings of seismic activity is
presented below.
The earth's crust is not a static system. It
consists of an assemblage of earthen masses
that are in slow motion. As new crust is
generated from within the earth, old edges of
crust collide with one another, thereby
causing stress. The weaker edge is forced to
move beneath the stronger edge back into the
earth.
The dynamic conditions of the earth's crust
can be manifested as shaking ground (seismic
activity), fracturing (faulting), and volcanic
eruptions. Seismic activity also can result in
types of ground failure. Landslides and mass
movements (e.g., slope failures) are common
on slopes; soil compaction or ground
subsidence tends to occur in unconsolidated
valley sediments; and liquefaction of soils
tends to happen in areas where sandy or silty
soils that are saturated and loosely compacted
become in effect, liquefied (like quicksand)
due to the motion. The latter types of
phenomena are addressed in Section 2.7,
Unstable Areas.
Information Sources on Seismic Activity
To determine the maximum horizontal
acceleration of the lithified earth material
for the site (see Figure 2-6), owners or
operators of MSWLF units should review
the seismic 250-year interval maps in U.S.
Geological Survey Miscellaneous Field
Study Map MF-2120, entitled "Probabilistic
Earthquake Acceleration and Velocity Maps
for the United States and Puerto Rico"
(Algermissen et al., 1991). To view the
original of the map that is shown in Figure 2-
6 (reduced in size), contact the USGS office
in your area. The original map (Horizontal
Acceleration - Base modified from U.S.G.S.
National Atlas, 1970, Miscellaneous Field
Studies, Map MF 2120) shows county lines
within each State. For areas not covered by
the aforementioned map, USGS State seismic
maps may be used to estimate the maximum
horizontal acceleration. The National
Earthquake Information Center, located at the
Colorado School of Mines in Golden,
Colorado, can provide seismic maps of all 50
states. The Center also maintains a database
of known earthquakes and fault zones.
Information on the location of earthquake
epicenters and intensities may be available
through State Geologic Surveys or the
Earthquake Information Center. For
information concerning potential
earthquakes in specific areas, the Geologic
Risk Assessment Branch of USGS may be
of assistance. Other organizations that
study the effects of earthquakes on
engineered structures include the National
Information Service for Earthquake
Engineering, the Building Seismic Safety
Council, the National Institute of Science
and Technology, and the American Institute
of Architects.
Landfill Planning and Engineering in
Areas of Seismic Activity
Studies indicate that during earthquakes,
superficial (shallow) slides and differential
displacement tend to be produced, rather
than massive slope failures (U.S. Navy
1983). Stresses created by superficial
failures can affect the liner and final cover
42
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Principal Islands at
Hawaii
9:111 n.wxe
Explanation
- Jlrti/unial inx
al a pcitunl nf gravity.
Altort Equal AIM Projsdion
H-.HI I '.W«M«">
Figure 2-6. Seismic Impact Zones
(Areas with a 10% or greater probability that the maximum horizontal acceleration will exceed .10g in 250 years)
-------
Subpart B
systems as well as the leachate and gas
collection and removal systems. Tensional
stresses within the liner system can result in
fracturing of the soil liner and/or tearing of
the flexible membrane liner. Thus, when
selecting suitable sites from many potential
sites during the siting process, the
owner/operator should try to avoid a site with:
Holocene fault zones,
Sites with potential ground motion, and
Sites with liquefaction potential.
If one of the above types of sites is selected,
the owner/operator must consider the costs
associated with the development of the site.
If, due to a lack of suitable alternatives, a site
is chosen that is located in a seismic impact
zone, a demonstration must be made to the
Director of an approved State that the design
of the unit's structural components (e.g.,
liners, leachate collection, final covers, run-on
and run-off systems) will resist the maximum
horizontal acceleration in lithified materials at
the site. As part of the demonstration,
owner/operators must:
Determine the expected peak ground
acceleration from a maximum strength
earthquake that could occur in the area,
• Determine the site-specific seismic
hazards such as soil settlement, and
Design the facility to withstand the
expected peak ground acceleration.
The design of the slopes, leachate collection
system, and other structural components
should have built-in conservative design
factors. Additionally, redundant
precautionary measures should be designed
and built into the various landfill systems.
For those units located in an area with an
estimated maximum horizontal acceleration
greater than O.lg, an evaluation of seismic
effects should consider both foundation soil
stability and waste stability under seismic
loading. Conditions that may be considered
for the evaluation include the construction
phase (maximum open excavation depth of
new cell adjacent to an existing unit), closure
activities (prior to final consolidation of both
waste and subsoil), and post-closure care
(after final consolidation of both waste and
foundation soil). If the maximum horizontal
acceleration is less than or equal to O.lg, then
the design of the unit will not have to
incorporate an evaluation of seismic effects
unless the facility will be situated in an area
with low strength foundation soils or soils
with potential for liquefaction. The facility
should be assessed for the effects of seismic
activity even if the horizontal acceleration is
expected to be less than 0. Ig.
In determining the potential effects of seismic
activity on a structure, an engineering
evaluation should examine soil behavior with
respect to earthquake intensity. When
evaluating soil characteristics, it is necessary
to know the soil strength as well as the
magnitude or intensity of the earthquake in
terms of peak acceleration. Other soil
characteristics, including degree of
compaction, sorting (organization of the soil
particles), and degree of saturation, may need
to be considered because of their potential
influence on site conditions. For example,
deposits of loose granular soils may be
compacted by the ground vibrations induced
by an earthquake. Such volume reductions
could result in large uniform or differential
44
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Location Criteria
settlements of the ground surface (Winterkorn
and Fang, 1975).
Well-compacted cohesionless embankments
or reasonably flat slopes in insensitive clay
are less likely to fail under moderate seismic
shocks (up to 0.15g and 0.20g acceleration).
Embankments made of insensitive cohesive
soils founded on cohesive soils or rock may
withstand even greater seismic shocks. For
earthen embankments in seismic regions,
designs with internal drainage and core
material most resistant to fracturing should be
considered. Slope materials vulnerable to
earthquake shocks are described below (U.S.
Navy, 1983):
• Very steep slopes of weak, fractured and
brittle rocks or unsaturated loess are
vulnerable to transient shocks caused by
tensional faulting;
• Loess and saturated sand may be
liquefied by seismic shocks causing the
sudden collapse of structures and flow
slides;
Similar effects are possible in sensitive
cohesive soils when natural moisture
exceeds the soil's liquid limit; and
• Dry cohesionless material on a slope at
an angle of repose will respond to
seismic shock by shallow sloughing and
slight flattening of the slope.
In general, loess, deltaic soils, floodplain
soils, and loose fills are highly susceptible to
liquefaction under saturated conditions
(USEPA, 1992).
Geotechnical stability investigations
frequently incorporate the use of computer
models to reduce the computational time of
well-established analytical methods. Several
computer software packages are available that
approximate the anticipated dynamic forces
of the design earthquake by resolving the
forces into a static analysis of loading on
design cross sections. A conservative
approach would incorporate both vertical and
horizontal forces caused by bedrock
acceleration if it can be shown that the types
of material of interest are susceptible to the
vertical force component. Typically, the
horizontal force caused by bedrock
acceleration is the major force to be
considered in the seismic stability analysis.
Examples of computer models include PC-
Slope by Geoslope Programming (1986), and
FLUSH by the University of California.
Design modifications to accommodate an
earthquake may include shallower waste
sideslopes, more conservative design of dikes
and run-off controls, and additional
contingencies for leachate collection should
primary systems be disrupted. Strengths of
the landfill components should be able to
withstand these additional forces with an
acceptable factor of safety. The use of
professionals experienced in seismic analysis
is strongly recommended for design of
facilities located in areas of high seismic risk.
2.7 UNSTABLE AREAS
40 CFR §258.15
2.7.1 Statement of Regulation
(a) Owners or operators of new
MSWLF units, existing MSWLF units,
and lateral expansions located in an
unstable area must demonstrate that
engineering measures have been
incorporated into the MSWLF unit's
45
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Subpart B
design to ensure that the integrity of the
structural components of the MSWLF unit
will not be disrupted. The owner or
operator must place the demonstration in
the operating record and notify the State
Director that it has been placed in the
operating record. The owner or operator
must consider the following factors, at a
minimum, when determining whether an
area is unstable:
(1) On-site or local soil conditions that
may result in significant differential
settling;
(2) On-site or local geologic or
geomorphologic features; and
(3) On-site or local human-made
features or events (both surface and
subsurface).
(b) For purposes of this section:
(1) Unstable area means a location that
is susceptible to natural or human-induced
events or forces capable of impairing the
integrity of some or all of the landfill
structural components responsible for
preventing releases from a landfill.
Unstable areas can include poor foundation
conditions, areas susceptible to mass
movements, and Karst terrains.
(2) Structural components means
liners, leachate collection systems, final
covers, run-on/run-off systems, and any
other component used in the construction
and operation of the MSWLF that is
necessary for protection of human health
and the environment.
(3) Poor foundation conditions means
those areas where features exist which
indicate that a natural or man-induced
event may result in inadequate foundation
support for the structural components of a
MSWLF unit.
(4)
Areas susceptible to mass
movement means those areas of influence
(i.e., areas characterized as having an
active or substantial possibility of mass
movement) where the movement of earth
material at, beneath, or adjacent to the
MSWLF unit, because of natural or man-
induced events, results in the downslope
transport of soil and rock material by
means of gravitational influence. Areas of
mass movement include, but are not
limited to, landslides, avalanches, debris
slides and flows, solifluction, block sliding,
and rock fall.
(5) Karst terrains means areas where
karst topography, with its characteristic
surface and subterranean features, is
developed as the result of dissolution of
limestone, dolomite, or other soluble rock.
Characteristic physiographic features
present in karst terrains include, but are
not limited to, sinkholes, sinking streams,
caves, large springs, and blind valleys.
2.7.2 Applicability
Owners/operators of new MSWLF units,
existing MSWLF units, and lateral
expansions of units that are located in
unstable areas must demonstrate the
structural integrity of the unit. Existing
units for which a successful demonstration
cannot be made must be closed. The
regulation applies to new units, existing
units, and lateral expansions that are located
on sites classified as unstable areas.
Unstable areas are areas susceptible to
46
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Location Criteria
natural or human-induced events or forces
that are capable of impairing or destroying the
integrity of some or all of the structural
components. Structural components consist
of liners, leachate collection systems, final
cover systems, run-on and run-off control
systems, and any other component necessary
for protection of human health and the
environment.
MSWLF units can be located in unstable
areas, but the owner or operator must
demonstrate that the structural integrity of the
MSWLF unit will not be disrupted. The
demonstration must show that engineering
measures have been incorporated into the
design of the unit to ensure the integrity of the
structural components. Existing MSWLF
units that do not meet the demonstration must
be closed within 5 years in accordance with
§258.60, and owners and operators must
undertake post-closure activities in
accordance with §258.61. The Director of an
approved State can grant a 2-year extension to
the closure requirement under two conditions:
(1) no disposal alternative is available, and (2)
no immediate threat is posed to human health
and the environment.
2.7.3 Technical Considerations
Again, for the purposes of this discussion,
natural unstable areas include those areas that
have poor soils for foundations, are
susceptible to mass movement, or have karst
features.
Areas with soils that make poor
foundations have soils that are
expansive or settle suddenly. Such
areas may lose their ability to support a
foundation when subjected to natural
(e.g., heavy rain) or man-made events
(e.g., explosions).
— Expansive soils usually are clay-
rich soils that, because of their
molecular structure, tend to swell
and shrink by taking up and
releasing water and thus are
sensitive to a variable hydrologic
regime. Such soils include:
smectite (montmorillonite group)
and vermiculite clays; bentonite
is a smectite-rich clay. In
addition, soils rich in "white
alkali" (sodium sulfate),
anhydrite (calcium sulfate), or
pyrite (iron sulfide) also may
exhibit swelling as water content
increases. Such soils tend to be
found in the arid western states.
— Soils that are subject to rapid
settlement (subsidence) include
loess, unconsolidated clays, and
wetland soils. Loess, which is
found in the central states, is a
wind-deposited silt that is
moisture-deficient and tends to
compact upon wetting.
Unconsolidated clays, which can
be found in the southwestern
states, can undergo considerable
compaction when fluids such as
water or oil are removed.
Similarly, wetland soils, which
by their nature are water-bearing,
also tend to be subject to
subsidence when water is
withdrawn.
Another type of unstable area is an
area that is subject to mass
movement. Such areas can be situated
47
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Subpart B
on steep or gradual slopes. They tend to have
rock or soil conditions that are conducive to
downslope movement of soil, rock, and/or
debris (either alone or mixed with water)
under the influence of gravity. Examples of
mass movements include avalanches,
landslides, debris slides and flows, and rock
slides.
Karst terrains tend to be subject to
extreme incidents of differential
settlement, namely complete ground
collapse. Karst is a term used to describe
areas that are underlain by soluble
bedrock, such as limestone, where
solution of the rock by water creates
subterranean drainage systems that may
include areas of rock collapse. These
areas tend to be characterized by large
subterranean and surficial voids (e.g.,
caverns and sinkholes) and unpredictable
surface and ground-water flow (e.g.,
sinking streams and large springs). Other
rocks such as dolomite or gypsum also
may be subject to solution effects.
Examples of human-induced unstable areas
are described below:
The presence of cut and/or fill slopes
during construction of the MSWLF unit
may cause slippage of existing soil or
rock.
Excessive drawdown of ground water
increases the effective overburden on the
foundation soils underneath the MSWLF
unit, which may cause excessive
settlement or bearing capacity failure on
the foundation soils.
A closed landfill as the foundation for a
new landfill ("piggy-backing") may be
unstable unless the closed landfill has
undergone complete settlement of the
underlying wastes.
As part of their demonstration to site a
landfill in an unstable area, owners/operators
must assess the ability of the soils and/or rock
to serve as a foundation as well as the ability
of the site embankments and slopes to
maintain a stable condition. Once these
factors have been evaluated, a MSWLF
design should be developed that will address
these types of concerns and prevent possible
associated damage to MSWLF structural
components.
In designing a new unit or lateral expansion
or re-evaluating an existing MSWLF unit, a
stability assessment should be conducted in
order to avoid or prevent a destabilizing event
from impairing the structural integrity of the
landfill component systems. A stability
assessment involves essentially three
components: an evaluation of subsurface
conditions, an analysis of slope stability, and
an examination of related design needs. An
evaluation of subsurface conditions requires:
Assessing the stability of foundation
soils, adjacent embankments, and slopes;
Investigating the geotechnical and
geological characteristics of the site to
establish soil strengths and other
engineering properties by performing
standard penetration tests, field vane
shear tests, and laboratory tests; and
48
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Location Criteria
Testing the soil properties such as water
content, shear strength, plasticity, and
grain size distribution.
A stability assessment should consider
(USEPA, 1988):
The adequacy of the subsurface
exploration program;
The liquefaction potential of the
embankment, slopes, and foundation
soils;
The expected behavior of the
embankment, slopes, and foundation soils
when they are subjected to seismic
activity;
The potential
failure; and
for seepage-induced
The potential for differential settlement.
In addition, a qualified professional must
assess, at a minimum, natural conditions (e.g.,
soil, geology, geomorphology) as well as
human-made features or events (both
subsurface and surface) that could cause
differential settlement of ground. Natural
conditions can be highly unpredictable and
destructive, especially if amplified by human-
induced changes to the environment. Specific
examples of natural or human-induced
phenomena include: debris flows resulting
from heavy rainfall in a small watershed; the
rapid formation of a sinkhole as a result of
excessive local or regional ground water
withdrawal in a limestone region; earth
displacement by faulting activity; and
rockfalls along a cliff face caused by
vibrations resulting from the detonation of
explosives or sonic booms.
Information on natural features can be
obtained from:
• The USGS National Atlas map
entitled "Engineering Aspects of
Karst," published in 1984;
• Regional or local soil maps;
• Aerial photographs (especially in
karst areas); and
• Site-specific investigations.
To examine an area for possible sources of
human-induced ground instability, the site
and surrounding area should be examined
for activities related to extensive
withdrawal of oil, gas, or water from
subsurface units as well as construction or
other operations that may result in ground
motion (e.g., blasting).
Types of Failures
Failures occur when the driving forces
imposed on the soils or engineered
structures exceed the resisting forces of the
material. The ratio of the resisting force to
the driving force is considered the factor of
safety (FS). At an FS value less than 1.0,
failure will occur by definition. There is a
high probability that, due to natural
variability and the degree of accuracy in
measurements, interpreted soil conditions
will not be precisely representative of the
actual soil conditions. Therefore, failure
may not occur exactly at the calculated
value, so factors of safety greater than 1.0
are required for the design. For plastic soils
such as clay, movement or deformation
(creep) may occur at a higher factor of
safety prior to catastrophic failure.
49
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Subpart B
Principal modes of failure in soil or rock
include:
Rotation (change of orientation) of an
earthen mass on a curved slip surface
approximated by a circular arc;
• Translation (change of position) of an
earthen mass on a planar surface whose
length is large compared to depth below
ground;
• Displacement of a wedge-shaped mass
along one or more planes of weakness;
• Earth and mud flows in loose clayey and
silty soils; and
Debris flows in coarse-grained soils.
For the purposes of this discussion, three
types of failures can occur at a landfill unit:
settlement, loss of bearing strength, and
sinkhole collapse.
• If not properly engineered, a landfill in
an unstable area may undergo extreme
settlement, which can result in structural
failure. Differential settlement is a
particular mode of failure that generally
occurs beneath a landfill in response to
consolidation and dewatering of the
foundation soils during and following
waste loading.
Settlement beneath a landfill unit, both
total and differential, should be assessed
and compared to the elongation strength
and flexure properties of the liner and
leachate collection pipe system. Even
small amounts of settlement can
seriously damage leachate collection
piping and sumps. The analysis will
provide an estimate of maximum
settlement, which can be used to aid in
estimating differential settlement.
Allowable settlement is typically
expressed as a function of total
settlement because differential settlement
is more difficult to predict. However,
differential settlement is a more serious
threat to the integrity of the structure
than total settlement. Differential
settlement also is discussed in Section
6.3 of Chapter 6.
Loss of bearing strength is a failure
mode that tends to occur in areas that
have soils that tend to expand, rapidly
settle, or liquefy, thereby causing failure
or reducing performance of overlying
MSWLF components. Another example
of loss of bearing strength involves
failures that have occurred at operating
sites where excavations for landfill
expansions adjacent to the filled areas
reduced the mass of the soil at the toe of
the slope, thereby reducing the overall
strength (resisting force) of the
foundation soil.
• Catastrophic collapse in the form of
sinkholes is a type of failure that occurs
in karst regions. As water, especially
acidic water, percolates through
limestone (calcium carbonate), the
soluble carbonate material dissolves,
forming cavities and caverns. Land
overlying caverns can collapse suddenly,
resulting in sinkhole features that can be
100 feet or more in depth and 300 feet or
more in width.
Tables 2-2 and 2-3 provide examples of
analytical considerations for mode of failure
assessments in both natural and human-made
slopes.
50
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Location Criteria
1. Slope in Coarse-Grained Soil with
Some Cohesion
Low Groundwater
Failure of thin
wedge, position
influenced by
tension cracks
High Groundwater
Failure at relatively
shallow toe circles
With low groundwater, failure occurs on
shallow, straight, or slightly curved surface.
Presence of a tension crack at the top of the
slope influences failure location. With high
groundwater, failure occurs on the relatively
shallow toe circle whose position is determined
primarily by ground elevation.
Analyze with effective stress using strengths C'
and 0' from CD tests. Pore pressure is
governed by seepage condition. Internal pore
pressures and external water pressures must be
included.
2. Slope in Coarse-Grained,
Soil Cohesion
Low Groundwater
Stable slope angle
= effective friction
angle
High Groundwater
Stable slope angle
= !/2 effective
friction angle
Stability depends primarily on groundwater
conditions. With low groundwater, failures
occur as surface sloughing until slope angle
flattens to friction angle. With high
groundwater, stable slope is approximately 1/2
friction angle.
Analyze with effective stress using strengths C'
and 0' from CD tests. Slight cohesion
appearing in test envelope is ignored. Special
consideration must be given to possible flow
slides in loose, saturated fine sands.
3. Slope in Normally Consolidated or
Slightly Preconsolidated Clay
Location of failure depends on variation of
shear strength with depth.
Strength constant
«,ith depth
Strength constant
with depth
Failure occurs on circular arcs whose position
is governed by theory. Position of
groundwater table does not influence stability
unless its fluctuation changes strength of the
clay or acts in tension cracks.
Analyze with total stresses, zoning cross
section for different values of shear strengths.
Determine shear strength from unconfmed
compression test, unconsolidated undrained
triaxial test or vane shear.
Suff or Hard Stratum
Source: Soil Mechanics, NAVFAC Design Manual 7.01
Table 2-2. Analysis of Stability of Natural Slopes
51
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Subpart B
4. Slope in Stratified Soil Profile
Location of failure depends on relative
strength and orientation of layers.
Strata oflow
strength
Location of failure plane is controlled by
relative strength and orientation of strata.
Failure surface is combination of active and
passive wedges with central sliding block
chosen to conform to stratification.
Analyze with effective stress using strengths C'
and 0' for fine-grained strata and 0' for
cohesionless material.
5. Depth Creep Movements in
Old Slide Mass
Bowl-shaped area of low slope (9 to 11%)
bounded at top by old scarp.
Strength of old slide mass decreases with
magnitude of movement that has occurred
previously. Most dangerous situation is in
stiff, over-consolidated clay which is softened,
fractured, or slickensided in the failure zone.
Failure surface of
low curvature which
is a portion of an
shear surface
Source: Soil Mechanics, NAVFAC Design Manual 7.01
Table 2-2. Analysis of Stability of Natural Slopes (Continued)
52
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Location Criteria
1. Failure of Fill on Soft Cohesive
Foundation with Sand Drains
Location of failure depends on geometry and
strength of cross section.
Usually, minimum stability occurs during
placing of fill. If rate of construction is
controlled, allow for gain in strength with
consolidation from drainage.
Analyze with effective stress using strengths C'
and 0' from CU tests with pore pressure
measurement. Apply estimated pore pressures
or piezometric pressures. Analyze with total
stress for rapid construction without
observation of pore pressures, use shear
strength from unconfmed compression or
unconsolidated undrained triaxial.
2. Failure of Stiff Compacted Fill on
Soft Cohesive Foundation
Failure surface may be rotation on circular arc or
translation with active and passive wedges.
Usually, minimum stability obtained at end of
construction. Failure may be in the form of rotation
or
translation, and both should be considered.
For rapid construction ignore consolidation
from drainage and utilize shear strengths
determined from U or UU tests or vane shear
in total stress analysis. If failure strain of fill
and foundation materials differ greatly, safety
factor should exceed one, ignoring shear
strength of fill. Analyze long-term stability
using C and 0 from CU tests with effective
stress analysis, applying pore pressures of
3. Failure Following Cut in Stiff
Fissured Clay
Original
ground line
Release of horizontal stresses by excavation
causes expansion of clay and opening of
fissures, resulting in loss of cohesive strength.
Analyze for short-term stability using C' and 0'
with total stress analysis. Analyze for long-
term stability with C'r and 0'm based on
residual strength measured in consolidated
drained tests.
Cut at toe
Failure surface depends on pattern of
fissures or depth of softening.
Source: Soil Mechanics, NAVFAC Design Manual 7.01
Table 2-3. Analysis of Stability of Cut and Fill Slopes,
Conditions Varying With Time
53
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Subpart B
Subsurface Exploration Programs
Foundation soil stability assessments for non-
catastrophic failure require field investigations
to determine soil strengths and other soil
properties. In situ field vane shear tests
commonly are conducted in addition to
collection of piston samples for laboratory
testing of undrained shear strengths (biaxial
and triaxial). Field vanes taken at depth
provide a profile of soil strength. The
required field vane depth intervals vary, based
on soil strength and type, and the number of
borings required depends on the variability of
the soils, the site size, and landfill unit
dimensions. Borings and field vane testing
should consider the anticipated design to
identify segments of the facility where critical
cross sections are likely to occur. Critical
sections are where factors of safety are
anticipated to be lowest.
Other tests that are conducted to characterize
a soil include determination of water content,
Atterberg limits, grain size distribution,
consolidation, effective porosity, and
saturated hydraulic conductivity. The site
hydrogeologic conditions should be assessed
to determine if soils are saturated or
unsaturated.
Catastrophic failures, such as sinkhole
collapse in karst terrains or fault displacement
during an earthquake, are more difficult to
predict. Subsurface karst structures may have
surface topographic expressions such as
circular depressions over subsiding solution
caverns. Subsurface borings or geophysical
techniques may provide reliable means of
identifying the occurrence, depth, and size of
solution cavities that have the potential for
catastrophic collapse.
Methods of Slope Stability Analysis
Slope stability analyses are performed for
both excavated side slopes and aboveground
embankments. The analyses are performed as
appropriate to verify the structural integrity of
a cut slope or dike. The design configuration
is evaluated for its stability under all potential
hydraulic and loading conditions, including
conditions that may exist during construction
of an expansion (e.g., excavation). Analyses
typically performed are slope stability,
settlement, and liquefaction. Factor of safety
rationale and selection for different conditions
are described by Huang (1983) and Terzaghi
and Peck (1967). Table 2-4 lists
recommended minimum factor of safety
values for slopes. Many States may provide
their own minimum factor of safety
requirements.
There are numerous methods currently
available for performing slope stability
analyses. Method selection should be based
on the soil properties and the anticipated
mode of failure. Rationale for selecting a
specific method should be provided.
The majority of these methods may be
categorized as "limit equilibrium" methods
in which driving and resisting forces are
determined and compared. The basic
assumption of the limit equilibrium
approach is that the failure criterion is
satisfied along an assumed failure surface.
This surface may be a straight line, circular
arc, logarithmic spiral, or other irregular
plane. A free body diagram of the driving
forces acting on the slope is constructed
using assumed or known values of the
forces. Next, the soil's shear resistance as it
pertains to establishing equilibrium is
calculated. This calculated shear resistance
54
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Location Criteria
Table 2-4
Recommended Minimum Values of Factor of Safety
for Slope Stability Analyses
Uncertainty of Strength Measurements
Consequences of Slope Failure Small, Large,
No imminent danger to human life or 1.25 1.5
major environmental impact if slope (1.2)* (1.3)
fails
Imminent danger to human life or 1.5 2.0 or greater
major environmental impact if slope (1.3) (1.7 or greater)
fails
1 The uncertainty of the strength measurements is smallest when the soil
conditions are uniform and high quality strength test data provide a consistent,
complete, and logical picture of the strength characteristics.
2 The uncertainty of the strength measurements is greatest when the soil
conditions are complex and when available strength data do not provide a
consistent, complete, and logical picture of the strength characteristics.
* Numbers without parentheses apply for static conditions and those within
parentheses apply to seismic conditions.
Source: EPA Guide to Technical Resources for the Design of Land Disposal
Facilities.
55
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Subpart B
then is compared to the estimated or available
shear strength of the soil to give an indication
of the factor of safety (Winterkorn and Fang,
1975).
Methods that consider only the whole free
body as a single unit include the Culmann
method and the friction circle method.
Another approach is to divide the free body
into vertical slices and to consider the
equilibrium of each slice. Several versions of
the slice method are available; the best known
are the Swedish Circle method and the Bishop
method. Discussions of these and other
methods may be found in Winterkorn and
Fang (1975), Lambe and Whitman (1969),
and U.S. Navy (1986).
A computer program that is widely used for
slope stability analysis is PC STABL, a two-
dimensional model that computes the
minimum critical factors of safety between
layer interfaces. This model uses the method
of vertical slices to analyze the slope and
calculate the factor of safety. PC STABL can
account for heterogeneous soil systems,
anisotropic soil strength properties, excess
pore water pressure due to shear, static ground
water and surface water, pseudostatic
earthquake loading, surcharge boundary
loading, and tieback loading. The program is
written in FORTRAN IV and can be run on a
PC. Figure 2-7 presents a typical output from
the model.
Design for Slope Stabilization
Methods for slope stabilization are presented
in Table 2-5 and are summarized below.
• The first illustration shows that stability
can be increased by changing the slope
geometry through reduction of the slope
height, flattening the slope angle, or
excavating a bench in the upper part of
the slope.
The second illustration shows how
compacted earth or rock fill can be
placed in the form of a berm at and
beyond the slope's toe to buttress the
slope. To prevent the development of
undesirable water pressure behind the
berm, a drainage system may be placed
behind the berm at the base of the slope.
The third illustration presents several
types of retaining structures. These
structures generally involve drilling
and/or excavation followed by
constructing cast-in-place concrete piles
and/or slabs.
— The T-shaped cantilever wall
design enables some of the
retained soil to contribute to the
stability of the structure and is
advisable for use on slopes that
have vertical cuts.
— Closely-spaced vertical piles
placed along the top of the slope
area provide reinforcement
against slope failure through a
soil arching effect that is created
between the piles. This type of
retaining system is advisable for
use on steeply cut slopes.
— Vertical piles also may be
designed with a tie back
component at an angle to the
vertical to develop a high
resistance to lateral forces. This
type of wall is recommended for
use in areas
56
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Location Criteria
Figure 2-7
Sample Output from PC STABL Model
CD Subgrade: Internal friction angle = 32 degrees
© Refuse: Internal friction angle of waste = 25 degrees
® Refuse: Internal friction angle of waste = 25 degrees
Sliding Block/Wedge
Failure Surface
Factor of Safety = 1.374
Circular Failure Surface,
Factor of Safety = 1.723
57
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Scheme
Applicable Methods
Comments
1. Changing Geometry
Excavation
1. Reduce slope height by
excavation at top of slope
2. Flatten the slope angle.
3. Excavate a bench in
upper part of slope.
Area has to be accessible
to construction
equipment. Disposal site
needed for excavated soil.
Drainage sometimes
incorporated in this
method.
2. Earth Berm Fill
Compacted earth or rock
berm placed at end
beyond the toe. Drainage
may be provided behind
the berm.
Sufficient width and
thickness of berm
required so failure will
not occur below or
through the berm.
3. Retaining Structures
Retaining
S true cure
Retaining wall: crib or
cantilever type.
Drilled, cast-in-place
vertical piles and/or slabs
founded well below
bottom slide plane.
Generally 18 to 36 inches
in diameter and 4- to 8-
foot spacing. Larger
diameter piles at closer
spacing may be required
in some cases with
mitigate failures of cuts
in highly fissured clays.
1. Usually expensive.
Cantilever walls might
have to be tied back.
2. Spacing should be such
that soil can arch between
piles. Grade beam can be
used to tie piles together.
Very large diameter (6
feett) piles have been
used for deep slide.
Source: Soil Mechanics, NAVFAC Design Manual 7.01
Table 2-5
Methods of Stabilizing Excavation Slopes
-------
Scheme
Applicable Methods
Comments
3.
Retainine Structure'
4.
Retainine Structure
Retaining
Structure
1
Drilled, cast-in-place
vertical piles tied back
with battered piles or a
deadman. Piles founded
well below slide plane.
Generally, 12 to 30
inches in diameter and at
least 4- to 8-foot spacing.
Earth and rock anchors
and rock bolts.
Reinforced earth.
3. Space close enough so
soil will arch between
piles. Piles can be tied
together with grade beam.
4. Can be used for high
slopes, and in very
restricted areas.
Conservative design
should be used, especially
for permanent support.
Use may be essential for
slopes in rocks where
joints dip toward
excavation, and such
joints daylight in the
slope.
5. Usually expensive
4. Other methods
See TABLE 7, NAVFAC DM-
7.2, Chapter 1
Source: Soil Mechanics, NAVFAC Design Manual 7.01
Table 2-5 (continued)
Methods of Stabilizing Excavation Slopes
-------
Subpart B
with steeply cut slopes where soil
arching can be developed between the
piles.
— The last retaining wall shown
uses a cantilever setup along
with soil that has been
reinforced with geosynthetic
material to provide a system that
is highly resistant to vertical and
lateral motion. This type of
system is best suited for use in
situations where vertically cut
slopes must have lateral
movement strictly controlled.
Other potential procedures for stabilizing
natural and human-made slopes include the
use of geotextiles and geogrids to provide
additional strength, the installation of wick
and toe drains to relieve excess pore
pressures, grouting, and vacuum and
wellpoint pumping to lower ground-water
levels. In addition, surface drainage may be
controlled to decrease infiltration, thereby
reducing the potential for mud and debris
slides in some areas. Lowering the ground-
water table also may have stabilizing
effects. Walls or large-diameter piling can
be used to stabilize slides of relatively small
dimension or to retain steep toe slopes so
that failure will not extend back into a larger
mass (U.S. Navy, 1986). For more detailed
information regarding slope stabilization
design, refer to Winterkorn and Fang
(1975), U.S. Navy (1986), and Sowers
(1979). Richardson and Koerner (1987) and
Koerner (1986) provide design guidance for
geosynthetics in both landfill and general
applications.
Monitoring
During construction activities, it may be
appropriate to monitor slope stability
because of the additional stresses placed on
natural and engineered soil systems (e.g.,
slopes, foundations, dikes) as a result of
excavation and filling activities. Post-
closure slope monitoring usually is not
necessary.
Important monitoring parameters may
include settlement, lateral movement, and
pore water pressure. Monitoring for pore
water pressure is usually accomplished with
piezometers screened in the sensitive strata.
Lateral movements of structures may be
detected on the surface by surveying
horizontal and vertical movements.
Subsurface movements may be detected by
use of slope inclinometers. Settlement may
be monitored by surveying ground surface
elevations (on several occasions over a
period of time) and comparing them with
areas that are not likely to experience
changes in elevations (e.g., USGS survey
monuments).
Engineering Considerations for Karst
Terrains
The principal concern with karst terrains is
progressive and/or catastrophic failure of
subsurface conditions due to the presence of
sinkholes, solution cavities, and
subterranean caverns. The unpredictable
and catastrophic nature of subsidence in
these areas makes them difficult to develop
as landfill sites. Before situating a MSWLF
in a karst region, the subject site should be
characterized thoroughly.
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Location Criteria
The first stage of demonstration is to
characterize the subsurface. Subsurface
drilling, sinkhole monitoring, and geophysical
testing are direct means that can be used to
characterize a site. Geophysical techniques
include tests using electromagnetic
conductivity, seismic refraction, ground-
penetrating radar, gravity, and electrical
resistivity. Interpretation and applicability of
different geophysical techniques should be
reviewed by a qualified geophysicist. Often
more than one technique should be employed
to confirm and correlate findings and
anomalies. Subsurface drilling is
recommended highly for verifying the results
of geophysical investigations.
Additional information on karst conditions
can come from remote sensing techniques,
such as aerial photograph interpretation.
Surface mapping of karst features can help to
provide an understanding of structural
patterns and relationships in karst terrains.
An understanding of local carbonate geology
and stratigraphy can aid in the interpretation
of both remote sensing and geophysical
techniques.
A demonstration that engineering measures
have been incorporated into a unit located in
a karst terrain may include both initial
design and site modifications. A relatively
simple engineering modification that can be
used to mitigate karst terrain problems is
ground-water and surface water control and
conveyance. Such water control measures are
used to minimize the rate of dissolution within
known near-surface limestone. This means
of controlling karst development may not be
applicable to all karst situations. In areas
where development of karst topography
tends to be minor, loose soils overlying the
limestone may be excavated or
heavily compacted to achieve the needed
stability. Similarly, in areas where the karst
voids are relatively small and limited in
extent, infilling of the void with slurry
cement grout or other material may be an
option.
In general, due to the unpredictable and
catastrophic nature of ground failure in such
areas, engineering solutions that try to
compensate for the weak geologic structures
by constructing manmade ground supports
tend to be complex and costly. For example,
reinforced raft (or mat) foundations could be
used to compensate for lack of ground
strength in some karst areas. Raft foundations
are a type of "floating foundation" that consist
of a concrete footing that extends over a very
large area. Such foundations are used where
soils have a low bearing capacity or where
soil conditions are variable and erratic; these
foundations are able to reduce and distribute
loads. However, it should be noted that, in
some instances, raft foundations may not
necessarily be able to prevent the extreme
type of collapse and settlement that can occur
in karst areas. In addition, the construction of
raft foundations can be very costly, depending
on the size of the area.
2.8 CLOSURE OF EXISTING
MUNICIPAL SOLID WASTE
LANDFILL UNITS
40 CFR §258.16
2.8.1 Statement of Regulation
(a) Existing MSWLF units that
cannot make the demonstration specified
in §§258.10(a), pertaining to airports,
258.11(a), pertaining to floodplains, and
258.15(a), pertaining to unstable areas,
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Subpart B
must close by October 9, 1996, in
accordance with §258.60 of this part and
conduct post-closure activities in
accordance with §258.61 of this part.
(b) The deadline for closure required
by paragraph (a) of this section may be
extended up to two years if the owner or
operator demonstrates to the Director of an
approved State that:
(1) There is no available alternative
disposal capacity;
(2) There is no immediate threat to
human health and the environment.
2.8.2 Applicability
These requirements are applicable to all
MSWLF units that receive waste after
October 9, 1993 and cannot meet the airport
safety, floodplain, or unstable area
requirements. The owner or operator is
required to demonstrate that the facility: (1)
will not pose a bird hazard to aircraft under
§258.10(a); (2) is designed to prevent washout
of solid waste, will not restrict floodplain
storage capacity, or increase floodwater flow
in a 100-year floodplain under §258.11 (a);
and 3) can withstand damage to landfill
structural component systems (e.g., liners,
leachate collection, and other engineered
structures) as a result of unstable conditions
under §258.15(a). If any of these
demonstrations cannot be made, the landfill
must close by October 9, 1996. In approved
States, the closure deadline may be extended
up to two additional years if it can be shown
that alternative disposal capacity is not
available and that the MSWLF unit does not
pose an immediate threat to human health and
the environment.
2.8.3 Technical Considerations
The engineering considerations that should be
addressed for airport safety, 100-year
floodplain encroachment, and unstable areas
are discussed in Sections 2.2, 2.3, and 2.7 of
this chapter. Information and evaluations
necessary for these demonstrations also are
presented in these sections. If applicable
demonstrations are not made by the owners or
operators, the landfill unit(s) must be closed
according to the requirements of section
§258.60 by October 9, 1996.
For MSWLF units located in approved States,
this deadline may be extended if there is no
immediate threat to human health and the
environment and no waste disposal alternative
is available. The demonstration of no
disposal alternative should consider all waste
management facilities, including landfills,
municipal waste combustors, and recycling
facilities. The demonstration for the two-year
extension should consider the impacts on
human health and the environment as they
relate to airport safety, 100-year floodplains,
or unstable areas.
§§258.17-258.19 [Reserved].
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Location Criteria
2.9 FURTHER INFORMATION
2.9.1 References
General
Linsley and Franzini, (1972). "Water Resources Engineering"; McGraw-Hill; pp. 179-184.
U.S. EPA, (1988). "Guide to Technical Resources for the Design of Land Disposal Facilities";
EPA/625/6-88/018; USEPA; Risk Reduction Engineering Laboratory and Center for
Environmental Research Information; Office of Research and Development; Cincinnati,
Ohio 45268.
USGS. Books and Open File Section, Branch Distribution, Box 25046, Federal Center, Denver,
CO 80225.
Floodplains
COE, (1982). HEC-1, HEC-2, HEC-5, HEC-6 Computer Programs; Hydrologic Engineering
Center (HEC); U.S. Army Corps of Engineers; Hydrologic Engineering Center; Davis
California.
Federal Emergency Management Agency, (1980). "How to Read a Flood Insurance Rate Map";
April 1980. Available from FEMA Regional Offices.
Maynard, S.T., (1978). "Practical Riprap Design"; Hydraulics Laboratory Miscellaneous Paper
H-78-7; U.S. Army Engineers Waterways Experiment Station; Vicksburg, Mississippi. SCS,
(1983).
"Maryland Standards and Specifications for Soil Erosion and Sediment Control"; U.S. Soil
Conservation Service; College Park, Maryland.
U.S. Water Resources Council, (1977). "Guidelines for Determining Flood Flow Frequency";
Bulletin #17A of the Hydrology Committee; revised June 1977.
Wetlands
COE, (1987). "Corps of Engineers Wetlands Delineation Manual," Technical Report (Y-87-1),
Waterways Experiment Station, Jan. 1987.
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Subpart B
COE, (1989). "Federal Manual for Identifying and Delineating Jurisdictional Wetlands,"
Federal Interagency Committee for Wetland Delineation; U.S. Army Corps of Engineers,
U.S. Environmental Protection Agency, U.S. Fish and Wildlife Service, and U.S.D.A.,
Soil Conservation Service; Washington, D.C., Cooperative Technical Publication. 1989.
Fault Areas, (1992). "Aspects of Landfill Design for Stability in Seismic Zones," Hilary I.
Inyang, Ph.D.
Seismic Impact Zones
Algermissen, S.T., et al., (1991). "Probabilistic Earthquake Acceleration and Velocity Maps
for the United States and Puerto Rico," USGS Miscellaneous Field Study Map MF-
2120.
Algermissen, S.T., et al., (1976). "Probabilistic Estimates of Maximum Acceleration and
Velocity in Rock in the Contiguous United States"; Open File Report 82-1033; U.S.
Geological Survey; Washington, D.C.
U.S. EPA, (1992). "Aspects of Landfill Design for Stability in Seismic Zones", Hilary I.
Inyang. Ph.D.
U.S. Navy, (1983). "Design Manual-Soil Dynamics, Deep Stabilization, and Special
Geotechnical Construction," NAVFAC DM-7.3; Department of the Navy; Washington,
D.C.; April, 1983.
Winterkorn, H.F. and Fang, H.Y., (1975). "Foundation Engineering Handbook." Van
Nostrand Reinhold. 1975.
Unstable Areas
Geoslope Programming Ltd., (1986). PC-SLOPE, Version 2.0 (May); Calgary, Alberta,
Canada.
Huang, U.K., (1983). "Stability Analysis of Earth Slopes"; Van Nostrand Reinhold Co.; New
York.
Koerner, R.M., (1986). "Designing with Geosynthetics"; Prentice-Hall Publishing Co.;
Englewood Cliffs, New Jersey.
Lambe, W.T. and R.V. Whitman, (1969). "Soil Mechanics"; John Wiley and Sons, Inc.; New
York.
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Location Criteria
Richardson, G.N. and R.M. Koerner, (1987). "Geosynthetic Design Guidance for Hazardous
Waste Landfill Cells and Surface Impoundments"; Hazardous Waste Engineering Research
Laboratory; USEPA, Office of Research and Development; Cincinnati, Ohio; Contract No.
68-07-3338.
Sowers, G.F., (1979). "Soil Mechanics and Foundations: Geotechnical Engineering," The
MacMillan Company, New York.
Terzaghi, K. and R.B. Peck, (1967). "Soil Mechanics in Engineering Practice", 2nd Edition; John
Wiley and Sons, Inc.; New York.
U.S. Navy, (1986). "Design Manual-Soil Mechanics, Foundations and Earth Structures,"
NAVFAC DM-7; Department of the Navy; Washington, D.C.; September 1986.
Winterhorn, H.F. and Fang, H.Y., (1975). "Foundation Engineering Handbook," Van Nostrand
Reinhold, 1975.
2.9.2 Organizations
American Institute of Architects
Washington, D.C.
(202) 626-7300
Aviation Safety Institute (ASI)
Box 304
Worthington, OH 43085
(614) 885-4242
American Society of Civil Engineers
345 East 47th St.
New York, NY 10017-2398
(212) 705-7496
Building Seismic Safety Council
201 L Street, Northwest Suite 400
Washington, D.C. 20005
(202) 289-7800
Bureau of Land Management
1849C St. N.W.
Washington, D.C. 20240
(202) 343-7220 (Locator)
(202) 343-5717 (Information)
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Subpart B
Federal Emergency Management Agency
Flood Map Distribution Center
6930 (A-F) San Thomas Road
Baltimore, Maryland 21227-6227
1-800-358-9616
Federal Emergency Management Agency
(800) 638-6620 Continental U.S. only, except Maryland
(800) 492-6605 Maryland only
(800) 638-6831 Continental U.S., Hawaii, Alaska, Puerto Rico, Guam, and the Virgin Islands
Note: The toll free numbers may be used to obtain any of the numerous FEMA publications such
as "The National Flood Insurance Program Community Status Book," which is published
bimonthly.
To obtain Flood Insurance Rate Maps and other flood maps, the FEMA Flood Map
Distribution Center should be contacted at 1-800-358-9616.
Federal Highway Administration
400 7th St. S.W.
Washington, D.C. 20590
(202) 366-4000 (Locator)
(202) 366-0660 (Information)
Hydrologic Engineering Center (HEC Models)
U.S. Army Corps of Engineers
609 Second St.
Davis, CA 95616
(916)756-1104
National Information Service for Earthquake Engineering (NISEE)
University of California, Berkeley
404A Davis Hall
Berkeley, CA 94720
(415)642-5113
(415) 643-5246 (FAX)
National Oceanic and Atmospheric Administration
Office of Legislative Affairs
1825 Connecticut Avenue Northwest
Room 627
Washington, DC 20235
(202) 208-5717
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Location Criteria
Tennessee Valley Authority
412 First Street Southeast, 3rd Floor
Washington, DC 20444
(202) 479-4412
U.S. Department of Agriculture
Soil Conservation Service
P.O. Box 2890
Washington, DC 20013-2890
(Physical Location: 14th and Independence Ave. N.W.)
(202)447-5157
U.S. Department of the Army
U.S. Army Corps of Engineers
Washington, DC 20314-1000
(202) 272-0660
U.S. Department of the Interior
Fish and Wildlife Service
1849 C Street Northwest
Washington, DC 20240
(202) 208-5634
U.S. Department of Transportation
Federal Aviation Administration
800 Independence Ave., S.W.
Washington, D.C. 20591
(202) 267-3085
U.S. Geological Survey
12201 Sunrise Valley Drive
Reston, Virginia 22092
(800) USA-MAPS
U.S. Geological Survey
Branch of Geologic Risk Assessment
Stop 966 Box 25046
Denver, Colorado 80225
(303) 236-1629
U.S. Geological Survey
EROS Data Center
Sioux Falls, South Dakota 57198
(605)594-6151
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Subpart B
U.S. Geological Survey
National Earthquake Information Center
Stop 967 Box 25046
Denver Federal Center
Denver, Colorado 80225
(303)236-1500
2.9.3 Models
Adamus, P.R., et al., (1987). "Wetland Evaluation Technique (WET); Volume II:
Methodology"; Operational Draft Technical Report Y-87; U.S. Army Engineer Waterways
Experiment Station; Vicksburg, MS.
COE, (1982). HEC-1, HEC-2, HEC-5, HEC-6 Computer Programs; Hydrologic Engineering
Center (HEC); U.S. Army Corps of Engineers; Hydrologic Engineering Center; Davis
California.
Geoslope Programming Ltd., (1986). PC-SLOPE, Version 2.0 (May); Calgary, Alberta, Canada.
Lysemer, John, et al., (1979). "FLUSH: A Computer Program for Approximate 3-D Analysis";
University of California at Berkeley; March 1979. (May be obtained through the National
Information Service for Earthquake Engineering at the address provided in subsection 2.9.2
of this document.)
Purdue University, Civil Engineering Dept, (1988). PC STABL, West Lafayette, IN 47907.
United States Fish and Wildlife Service, (1980). "Habitat Evaluation Procedures". ESM 102;
U.S. Fish and Wildlife Service; Division of Ecological Services; Washington, D.C.
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APPENDIX I
FAA Order 5200.5A
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U.S. DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION
5200.5A
1/31/90
SUBJ: WASTE DISPOSAL SITES ON OR NEAR AIRPORTS
1. PURPOSE. This order provides guidance concerning the establishment, elimination or monitoring of landfills, open dumps, waste disposal
sites or similarly titled facilities on or in the vicinity of airports.
2. DISTRIBUTION. This order is distributed to the division level in the Offices of Airport Planning and Programming Airport Safety and
Standards, Air Traffic Evaluations and Analysis Aviation Safety Oversight, Air Traffic Operations Service, and Flight Standards Service; to the
division level in the regional Airports, Air Traffic, and Flight Standards Divisions; to the director level at the Aeronautical Center and the FAA
Technical Center, and a limited distribution to all Airport District Offices, Flight Standards Field Offices, and Air Traffic Facilities.
3. CANCELLATION. Order 5200.5, FAA Guidance Concerning Sanitary Landfills On Or Near Airports, dated October 16, 1974, is canceled.
4. BACKGROUND. Landfills, garbage dumps, sewer or fish waste outfalls and other similarly licensed or titled facilities used for operations
to process, bury, store or otherwise dispose of waste, trash and refuse will attract rodents and birds. Where the dump is ignited and produces smoke,
an additional attractant is created. All of the above are undesirable and potential hazards to aviation since they erode the safety of the airport
environment. The FM neither approves nor disapproves locations of the facilities above. Such action is the responsibility of the Environmental
Protection Agency and/or the appropriate state and local agencies. The role of the FAA is to ensure that airport owners and operators meet their
contractual obligations to the United States government regarding compatible land uses in the vicinity of the airport. While the chance of an
unforeseeable, random bird strike in flight will always exist, it is nevertheless possible to define conditions within fairly narrow limits where the risk
is increased. Those high-risk conditions exist in the approach and departure patterns and landing areas on and in the vicinity of airports. The number
of bird strikes reported on aircraft is a matter of continuing concern to the FM and to airport management. Various observations support the conclusion
that waste disposal sites are artificial attractants to birds. Accordingly, disposal sites located in the vicinity of an airport are potentially incompatible
with safe flight operations. Those sites that are not compatible need to be eliminated. Airport owners need guidance in making those decisions and
the FM must be in a position to assist. Some airports are not under the jurisdiction of the community or local governing body having control of land
usage in the vicinity of the airport. In these areas, the airport owner should use its resources and exert its best efforts to close or control waste disposal
operations within the general vicinity of the airport.
5. EXPLANATION OF CHANGES. The following list outlines the major changes to Order 5200.5:
a. Recent developments and new techniques of waste disposal warranted updating and clarification of what constitutes a sanitary landfill.
This listing of new titles for waste disposal was outlined in paragraph 4.
b. Due to a reorganization which placed the Animal Damage Control Branch of the U. S. Department of Interior Fish and Wildlife Service
under the jurisdiction of the U.S. Department of Agriculture an address addition was necessary
c. A zone of notification was added to the criteria which should provide the appropriate FM Airports office an opportunity to comment
on the proposed disposal site during the selection process.
6. ACTION.
a. Waste disposal sites located or proposed to be located within the areas established for an airport by the guidelines set forth in paragraphs 7 a
b, and c of this order should not be allowed to operate. If a waste disposal site is incompatible with an airport in accordance with guidelines of
paragraph 7 and cannot be closed within a reasonable time, it should be operated in accordance with the criteria and instructions issued by Federal
agencies such as the Environmental Protection Agency and the Department of Health and Human Services, and other such regulatory bodies that may
have applicable requirements. The appropriate FM airports office should advise airport owners, operators and waste disposal proponents against
locating, permitting or concurring in the location of a landfill or similar facility on or in the vicinity of airports.
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(1) Additionally, any operator proposing a new or expanded waste disposal site within 5 miles of a runway end should notify the airport
and the appropriate FM Airports office so as to provide an opportunity to review and comment on the site in accordance with the guidance contained
in this order. FM field offices may wish to contact the appropriate State director of the United States Department of Agriculture to assist in this review.
Also, any Air Traffic control tower manager or Flight Standards District Office manager and their staffs that become aware of a proposal to develop
or expand a disposal site should notify the appropriate FM Airports office.
b. The operation of a disposal site located beyond the areas described in paragraph 7 must be properly supervised to ensure compatibility
with the airport.
c. If at any time the disposal site, by virtue of its location or operation, presents a potential hazard to aircraft operations the owner should
take action to correct the situation or terminate operation of the facility. If the owner of the airport also owns or controls the disposal facility and is
subject to Federal obligations to protect compatibility of land uses around the airport, failure to take corrective action could place the airport owner
in noncompliance with its commitments to the Federal government. The appropriate FM office should immediately evaluate the situation to determine
compliance with federal agreements and take such action as may be warranted under the guidelines as prescribed in Order 5190.6, Airports
Compliance Requirements, current edition.
(1) Airport owners should be encouraged to make periodic inspections of current operations of existing disposal sites near a federally
obligated airport where potential bird hazard problems have been reported.
d. This order is not intended to resolve all related problems but is specifically directed toward eliminating waste disposal sites, landfills
and similarly titled facilities in the proximity of airports, thus providing a safer environment for aircraft operations.
e. At airports certified under Federal Aviation Regulations, part 139, the airport certification manual/specifications should require disposal
site inspections at appropriate intervals for those operations meeting the criteria of paragraph 7 that cannot be closed. These inspections are necessary
to assure that bird populations are not increasing and that appropriate control procedures are being established and followed. The appropriate FAA
airport offices should develop working relationships with state aviation agencies and state agencies that have authority over waste disposal and
landfills to stay abreast of proposed developments and expansions and apprise them of the hazards to aviation that these present.
f. When proposing a disposal site, operators should make their plans available to the appropriate state regulatory agencies. Many states
have criteria concerning siting requirements specific to their jurisdictions.
g. Additional information on waste disposal, bird hazard and related problems may be obtained from the following agencies:
U.S. Department of Interior Fish and Wildlife Service
18th and C Streets, NW
Washington, DC 20240
U.S. Department of Agriculture
Animal Plant Health Inspection Service
P.O. Box 96464
Animal Damage Control Program
Room 1624 South Agriculture Building
Washington, DC 20090-6464
U.S. Environmental Protection Agency
401 M Street, SW
Washington, DC 20460
U.S. Department of Health and Human Services
200 Independence Avenue, SW
Washington, DC 20201
7. CRITERIA. Disposal sites will be considered as incompatible if located within areas established for the airport through the application
of the following criteria:
a. Waste disposal sites located within 10,000 feet of any runway end used or planned to be used by turbine powered aircraft
b. Waste disposal sites located within 5,000 feet of any runway end used only by piston powered aircraft.
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c. Any waste disposal site located within a 5-mile radius of a runway end that attracts or sustains hazardous bird movements from feeding,
water or roosting areas into, or across the runway and/or approach and departure patterns of aircraft.
Leonard E. Mudd
Director, Office of Airport Safety and Standards
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CHAPTER 3
SUSPART C
OPERATING CRITERIA
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CHAPTER 3
SUBPART C
TABLE OF CONTENTS
3.1 INTRODUCTION 76
32 PROCEDURES FOR EXCLUDING THE RECEIPT OF HAZARDOUS WASTE 40 CFR
§258.20 77
3.2.1 Statement of Regulation 77
3.2.2 Applicability 77
3.2.3 Technical Considerations 77
Inspections 78
Alternative Methods for Detection and Prevention 81
Recordkeeping 82
Training 82
Notification to Authorities and Proper Management of Wastes 82
33. COVER MATERIAL REQUIREMENTS 40 CFR §258.21 84
3.3.1 Statement of Regulation 84
3.3.2 Applicability 84
3.3.3 Technical Considerations 84
3A DISEASE VECTOR CONTROL 40 CFR §258.22 86
3.4.1 Statement of Regulation 86
3.4.2 Applicability 86
3.4.3 Technical Considerations 87
3J EXPLOSIVE GASES CONTROL 40 CFR §258.23 87
3.5.1 Statement of Regulation 87
3.5.2 Applicability 88
3.5.3 Technical Considerations 89
Gas Monitoring 90
Landfill Gas Control Systems 94
Passive Systems 96
Active Systems 96
3_A AIR CRITERIA 40 CFR §258.24 101
3.6.1 Statement of Regulation 101
3.6.2 Applicability 101
3.6.3 Technical Considerations 101
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3.7 ACCESS REQUIREMENT 40 CFR §258.25 103
3.7.1 Statement of Regulation 103
3.7.2 Applicability 103
3.7.3 Technical Considerations 103
M RUN-ON/RUN-OFF CONTROL SYSTEMS 40 CFR §258.26 104
3.8.1 Statement of Regulation 104
3.8.2 Applicability 104
3.8.3 Technical Considerations 104
3_J) SURFACE WATER REQUIREMENTS 40 CFR §258.27 105
3.9.1 Statement of Regulation 105
3.9.2 Applicability 106
3.9.3 Technical Considerations 106
3.10 LIQUIDS RESTRICTIONS 40 CFR §258.28 107
3.10.1 Statement of Regulation 107
3.10.2 Applicability 107
3.10.3 Technical Considerations 108
3.11 RECORDKEEPING REQUIREMENTS 40 CFR §258.29 110
3.11.1 Statement of Regulation 110
3.11.2 Applicability 110
3.11.3 Technical Considerations Ill
3.12 FURTHER INFORMATION 114
3.12.1 References 114
3.12.2 Addresses 114
APPENDIX I - SPECIAL WASTE ACCEPTANCE AGREEMENT Following Page 114
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CHAPTER 3
SUBPART C
OPERATING CRITERIA
3.1 INTRODUCTION
The Solid Waste Disposal Facility Criteria contain a series of operating requirements pertaining to
routine operation, management, and environmental monitoring at municipal solid waste landfill
units (MSWLF units). The operating requirements pertain to new MSWLF units, existing MSWLF
units, and lateral expansions of existing MSWLF units.
The operating requirements have been developed to ensure the safe daily operation and management
at MSWLF units. The operating requirements include:
The exclusion of hazardous waste;
Cover material;
Disease vector control;
Explosive gases control;
Air monitoring;
Facility access;
Run-on/run-off control systems;
Surface water requirements;
Liquid restrictions; and
Recordkeeping requirements.
Any owner or operator of a MSWLF unit must comply with the operating requirements by October
9, 1993.
In specific cases, the operating requirements require compliance with other Federal laws. For
example, surface water discharges from a MSWLF unit into the waters of the United States must
be in conformance with applicable sections of the Clean Water Act. In addition, burning of
municipal solid waste (MSW) is regulated under applicable sections of the Clean Air Act.
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Operating Criteria
3.2 PROCEDURES FOR EXCLUDING
THE RECEIPT OF HAZARDOUS
WASTE 40 CFR §258.20
3.2.1 Statement of Regulation
(a) Owners or operators of all MSWLF
units must implement a program at the
facility for detecting and preventing the
disposal of regulated hazardous wastes as
defined in Part 261 of this title and
polychlorinated biphenyls (PCB) wastes as
defined in Part 761 of this title. This
program must include, at a minimum:
(1) Random inspections of incoming
loads unless the owner or operator takes
other steps to ensure that incoming loads
do not contain regulated hazardous wastes
or PCB wastes;
(2) Records of any inspections;
(3) Training of facility personnel to
recognize regulated hazardous waste and
PCB wastes; and
(4) Notification of State Director of
authorized States under Subtitle C of
RCRA or the EPA Regional Administrator
if in an unauthorized State if a regulated
hazardous waste or PCB waste is
discovered at the facility.
(b) For purposes of this section,
regulated hazardous waste means a solid
waste that is a hazardous waste, as defined
in 40 CFR 261.3, that is not excluded from
regulation as a hazardous waste under 40
CFR 261.4(b) or was not generated by a
conditionally exempt small quantity
generator as defined in §261.5 of this title.
3.2.2 Applicability
This regulation applies to all MSWLF units
that receive wastes on or after October 9,
1993.
The owner or operator must develop a
program to detect and prevent disposal of
regulated hazardous wastes or PCB wastes at
the MSWLF facility. Hazardous wastes may
be gases, liquids, solids, or sludges that are
listed or exhibit the characteristics described
in 40 CFR Part 261. Household hazardous
wastes are excluded from Subtitle C
regulation, and wastes generated by
conditionally exempt small quantity
generators (CESQGs) are not considered
regulated hazardous wastes for purposes of
complying with §258.20; therefore, these
wastes may be accepted for disposal at a
MSWLF unit.
The MSWLF hazardous waste exclusion
program should be capable of detecting and
preventing disposal of PCB wastes. PCB
wastes may be liquids or non-liquids (sludges
or solids) and are defined at 40 CFR Section
761.60. PCB wastes do not include small
capacitors found in fluorescent light ballast,
white goods (e.g., washers, dryers,
refrigerators) or other consumer electrical
products (e.g., radio and television units).
The hazardous waste exclusion program is not
intended to identify whether regulated
hazardous waste or PCB waste was received
at the MSWLF unit or facility prior to the
effective date of the Criteria.
3.2.3 Technical Considerations
A solid waste is a regulated hazardous waste
if it: (1) is listed in Subpart D of 40 CFR
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Subpart C
Part 261 (termed a "listed" waste); (2) exhibits
a characteristic of a hazardous waste as
defined in Subpart C of 40 CFR Part 261; or
(3) is a mixture of a listed hazardous waste
and a non-hazardous solid waste.
Characteristics of hazardous wastes as defined
in Subpart C of 40 CFR Part 261 include
ignitability, corrosivity, reactivity, and
toxicity. The toxicity characteristic leaching
procedure (TCLP) is the test method used to
determine the mobility of organic and
inorganic compounds present in liquid, solid,
and multiphase wastes. The TCLP is
presented in Appendix II of Part 261.
The MSWLF Criteria exclude CESQG waste
(as defined in 40 CFR §261.5) from the
definition of "regulated hazardous wastes."
CESQG waste includes listed hazardous
wastes or wastes that exhibit a characteristic
of a hazardous waste that are generated in
quantities no greater than 100 kg/month, or
for acute hazardous waste, 1 kg/month.
Under 40 CFR §261.5(f)(3)(iv) and (g)(3)(iv),
conditionally exempt small quantity generator
hazardous wastes may be disposed at facilities
permitted, licensed, or registered by a State to
manage municipal or industrial solid waste.
Other solid wastes are excluded from
regulation as a hazardous waste under 40
CFR §261.4(b) and may be accepted for
disposal at a MSWLF unit. Refer to
§261.4(b) for a listing of these wastes.
PCBs are regulated under the Toxic
Substances Control Act (TSCA), but PCB-
containing wastes are considered hazardous
wastes in some States. PCBs typically are not
found in consumer wastes except for
fluorescent ballast and small capacitors in
white goods and electrical appliances.
These sources are not regulated under 40 CFR
Part 761 and, therefore, are not part of the
detection program required by §258.20.
Commercial or industrial sources of PCB
wastes that should be addressed by the
program include:
• Mineral oil and dielectric fluids
containing PCBs;
• Contaminated soil, dredged material,
sewage sludge, rags, and other debris
from a release of PCBs;
• Transformers and other electrical
equipment containing dielectric fluids;
and
• Hydraulic machines.
The owner or operator is required to
implement a program to detect and exclude
regulated hazardous wastes and PCBs from
disposal in the landfill unit(s). This program
must include elements for:
• Random inspections of incoming loads or
other prevention methods;
• Maintenance of inspection records;
• Facility personnel training; and
• Notification to appropriate authorities if
hazardous wastes or PCB wastes are
detected.
Each of these program elements is discussed
separately on the following pages.
Inspections
An inspection is typically a visual observation
of the incoming waste loads by
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an individual who is trained to identify
regulated hazardous or PCB wastes that would
not be acceptable for disposal at the MSWLF
unit. An inspection is considered satisfactory
if the inspector knows the nature of all
materials received in the load and is able to
discern whether the materials are potentially
regulated hazardous wastes or PCB wastes.
Ideally, all loads should be screened;
however, it is generally not practical to
inspect in detail all incoming loads. Random
inspections, therefore, can be used to provide
a reasonable means to adequately control the
receipt of inappropriate wastes. Random
inspections are simply inspections made on
less than every load.
The frequency of random inspections may be
based on the type and quantity of wastes
received daily, and the accuracy and
confidence desired in conclusions drawn from
inspection observations. Because statistical
parameters are not provided in the regulation,
a reasoned, knowledge-based approach may
be taken. A random inspection program may
take many forms such as inspecting every
incoming load one day out of every month or
inspecting one or more loads from
transporters of wastes of unidentifiable nature
each day. If these inspections indicate that
unauthorized wastes are being brought to the
MSWLF site, then the random inspection
program should be modified to increase the
frequency of inspections.
Inspection frequency also can vary depending
on the nature of the waste. For example,
wastes received predominantly from
commercial or industrial sources may require
more frequent inspections than wastes
predominantly from households.
Inspection priority also can be given to
haulers with unknown service areas, to loads
brought to the facility in vehicles not typically
used for disposal of municipal solid waste,
and to loads transported by previous would-be
offenders. For wastes of unidentifiable nature
received from sources other than households
(e.g., industrial or commercial
establishments), the inspector should question
the transporter about the source/composition
of the materials.
Loads should be inspected prior to actual
disposal of the waste at the working face of
the landfill unit to provide the facility owner
or operator the opportunity to refuse or accept
the wastes. Inspections can be conducted on
a tipping floor of a transfer station before
transfer of the waste to the disposal facility.
Inspections also may occur at the tipping floor
located near the facility scale house, inside the
site entrance, or near, or adjacent to, the
working face of the landfill unit. An
inspection flow chart to identify, accept, or
refuse solid waste is provided as Figure 3-1.
Inspections of materials may be accomplished
by discharging the vehicle load in an area
designed to contain potentially hazardous
wastes that may arrive at the facility. The
waste should be carefully spread for
observation using a front end loader or other
piece of equipment. Personnel should be
trained to identify suspicious wastes. Some
indications of suspicious wastes are:
• Hazardous placards or marking;
Liquids;
Powders or dusts;
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Waste Inspected by
Personnel Trained to
Recognize Hazardous
Wastes Prior to Delivery at
Working Face
Waste is Identified as
Non-Hazardous
Waste is Not Readily
Identifiable
Waste is Identified as a
Hazardous Waste
Deliver to
Working Face
Isolate Wastes by
Moving to Temporary
Storage Area
Record
Inspection
Refuse Waste
Have Wastes Tested
Including Unidentified
Containerized Wastes
Record
Inspection
Waste Determined to
be Non-Hazardous
Waste Determined to
be Hazardous
Return to Working
Face and Dispose
Record Inspection
Manifest and
Transport Wastes to
a Facility Permitted
to Handle the
Hazardous Waste
(E.G., A Facility with
a RCRA Permit or
Interim Status)
Record Inspection
and Notify State
Director
Figure 3-1
Hazardous Waste Inspection Decision Tree
Inspection Prior to Working Face
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• Sludges;
• Bright or unusual colors;
• Drums or commercial size containers; or
• Chemical odors.
The owner or operator should develop
specific procedures to be followed when
suspicious wastes are discovered. The
procedure should include the following
points:
• Segregate the wastes;
• Question the driver;
• Review the manifest (if applicable);
• Contact possible source;
• Call the appropriate State or Federal
agencies;
• Use appropriate protective equipment;
• Contact laboratory support if required; and
• Notify a response agency if necessary.
Containers with contents that are not easily
identifiable, such as unmarked 55-gallon
drums, should be opened only by properly
trained personnel. Because these drums could
contain hazardous waste, they should be
refused whenever possible. Upon verifying
that the solid waste is acceptable, it may then
be transferred to the working face for
disposal.
Some facilities may consider it reasonable to
test unidentified waste, store it, and see that
it is disposed of properly. Most facilities
would not consider this reasonable.
Testing typically would include The Toxicity
Characteristic Leaching Procedure (TCLP)
and other tests for characteristics of hazardous
wastes including corrosivity, ignitability, and
reactivity. Wastes that are suspected of being
hazardous should be handled and stored as a
hazardous waste until a determination is
made.
If the wastes temporarily stored at the site are
determined to be hazardous, the owner or
operator is responsible for the management of
the waste. If the wastes are to be transported
from the facility, the waste must be: (1) stored
at the MSWLF facility in accordance with
requirements of a hazardous waste generator,
(2) manifested, (3) transported by a licensed
transporter, and (4) sent to a permitted
Treatment, Storage, or Disposal (TSD)
facility for disposal. These requirements are
discussed further in this section.
Alternative Methods for Detection and
Prevention
While the regulations explicitly refer to
inspections as an acceptable means of
detecting regulated hazardous wastes and PCB
wastes, preventing the disposal of these
wastes may be accomplished through other
methods. These methods may include
receiving only household wastes and
processed (shredded or baled) wastes that are
screened for the presence of the excluded
wastes prior to processing. A pre-acceptance
agreement between the owner or operator and
the waste hauler is another alternative method.
An example of a pre-acceptance agreement is
presented as Appendix I. The owner or
operator should
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Subpart C
keep any such agreements concerning these
alternatives in the operating record.
Recordkeeping
A record should be kept of each inspection
that is performed. These records should be
included and maintained in the facility
operating record. Larger facilities that take
large amounts of industrial and commercial
wastes may use more detailed procedures than
smaller facilities that accept household
wastes. Inspection records may include the
following information:
• The date and time wastes were received for
inspection;
• Source of the wastes;
• Vehicle and driver identification; and
• All observations made by the inspector.
The Director of an approved State may
establish alternative recordkeeping locations
and requirements.
Training
Owners or operators must ensure that
personnel are trained to identify potential
regulated hazardous waste and PCB wastes.
These personnel could include supervisors,
designated inspectors, equipment operators,
and weigh station attendants who may
encounter hazardous wastes. Documentation
of training should be placed in the operating
record for the facility in accordance with
§258.29.
The training program should emphasize
methods to identify containers and labels
typical of hazardous waste and PCB waste.
Training also should address hazardous waste
handling procedures, safety precautions, and
recordkeeping requirements. This
information is provided in training courses
designed to comply with the Occupational
Safety and Health Act (OSHA) under 29 CFR
§1910.120. Information covered in these
courses includes regulatory requirements
under 40 CFR Parts 260 through 270, 29 CFR
Part 1910, and related guidance documents
that discuss such topics as: general hazardous
waste management; identification of
hazardous wastes; transportation of hazardous
wastes; standards for hazardous waste
treatment; storage and disposal facilities; and
hazardous waste worker health and safety
training and monitoring requirements.
Notification to Authorities and Proper
Management of Wastes
If regulated quantities of hazardous wastes or
PCB wastes are found at the landfill facility,
the owner or operator must notify the proper
authorities. Proper authorities are either the
Director of a State authorized to implement
the hazardous waste program under Subtitle C
of RCRA, or the EPA Regional
Administrator, in an unauthorized State.
If the owner or operator discovers regulated
quantities of hazardous waste or PCB waste
while it is still in the possession of the
transporter, the owner or operator can refuse
to accept the waste at the MSWLF facility,
and the waste will remain the responsibility of
the transporter. If the owner or operator is
unable to identify the transporter who brought
the hazardous waste, the owner or operator
must ensure that the waste is managed in
accordance
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with all applicable Federal and State
regulations.
Operators of MSWLF facilities should be
prepared to handle hazardous wastes that are
inadvertently received at the MSWLF facility.
This may include having containers such as
5 5-gallon drums available on-site and
retaining a list of names and telephone
numbers of the nearest haulers licensed to
transport hazardous waste.
Hazardous waste may be stored at the
MSWLF facility for 90 days, provided that
the following procedures required by 40 CFR
§262.34, or applicable State requirements, are
followed:
• The waste is placed in tanks or containers;
• The date of receipt of the waste is clearly
marked and visible on each container;
• The container or tank is marked clearly
with the words "Hazardous Waste";
• An employee is designated as the
emergency coordinator who is responsible
for coordinating all emergency response
measures; and
• The name and telephone number of the
emergency coordinator and the number of
the fire department is posted next to the
facility phone.
Extensions to store the waste beyond 90 days
may be approved pursuant to 40 CFR 262.34.
If the owner or operator transports the wastes
off-site, the owner or operator must comply
with 40 CFR Part 262 or the
analogous State/Tribal requirements.
owner or operator is required to:
The
• Obtain an EPA identification number
(EPA form 8700-12 may be used to
apply for an EPA identification number;
State or Regional personnel may be able
to provide a provisional identification
number over the telephone);
• Package the waste in accordance with
Department of Transportation (DOT)
regulations under 49 CFR Parts 173, 178,
and 179 (The container must be labeled,
marked, and display a placard in
accordance with DOT regulations on
hazardous wastes under 49 CFR Part
172); and
• Properly manifest the waste designating
a permitted facility to treat, store, or
dispose of the hazardous waste.
If the owner or operator decides to treat, store
(for more than 90 days), or dispose of the
hazardous waste on-site, he or she must
comply with the applicable State or Federal
requirements for hazardous waste treatment,
storage, and disposal facilities. This may
require a permit.
PCB wastes detected at a MSWLF facility
must be stored and disposed of according to
40 CFR Part 761. The owner or operator is
required to:
• Obtain an EPA PCB identification
number;
• Properly store the PCB waste;
• Mark containers or items with the words
"Caution: contains PCBs"; and
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Subpart C
Manifest the PCB waste for shipment to a
permitted incinerator, chemical waste
landfill, or high efficiency boiler
(depending on the nature of the PCB
waste) for disposal.
3.3 COVER MATERIAL
REQUIREMENTS
40 CFR §258.21
3.3.1 Statement of Regulation
(a) Except as provided in paragraph (b)
of this section, the owners or operators of
all MSWLF units must cover disposed solid
waste with six inches of earthen material at
the end of each operating day, or at more
frequent intervals if necessary, to control
disease vectors, fires, odors, blowing litter,
and scavenging.
(b) Alternative materials of an
alternative thickness (other than at least six
inches of earthen material) may be
approved by the Director of an approved
State if the owner or operator
demonstrates that the alternative material
and thickness control disease vectors, fires,
odors, blowing litter, and scavenging
without presenting a threat to human
health and the environment.
(c) The Director of an approved State
may grant a temporary waiver from the
requirement of paragraph (a) and (b) of
this section if the owner or operator
demonstrates that there are extreme
seasonal climatic conditions that make
meeting such requirements impractical.
3.3.2 Applicability
The regulation applies to all MSWLF units
receiving waste after October 9, 1993. The
regulation requires MSWLF unit owners and
operators to cover wastes with a 6-inch layer
of earthen material at the end of each
operating day. More frequent application of
soil may be required if the soil cover does not
control:
• Disease vectors (e.g., birds, flies and
other insects, rodents);
• Fires;
• Odors;
• Blowing litter; and
• Scavenging.
The Director of an approved State may allow
an owner or operator to use alternative cover
material of an alternative thickness or grant a
temporary waiver of this requirement. An
alternative material must not present a threat
to human health and the environment, and
must continue to control disease vectors, fires,
odors, blowing litter, and scavenging. The
only basis for a temporary waiver from the
requirement to cover at the end of each
operating day would be where extreme
seasonal climatic conditions make compliance
impractical.
3.3.3 Technical Considerations
Owners and operators of new MSWLF units,
existing MSWLF units, and lateral expansions
are required to cover solid waste at the end of
each operating day with six inches of earthen
material. This cover
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Operating Criteria
material requirement is not related to the final
cover required under §258.60.
The placement of six inches of cover controls
disease vectors (birds, insects, or rodents that
represent the principal transmission pathway
of a human disease) by preventing egress
from the waste and by preventing access to
breeding environments or food sources.
Covering also reduces exposure of
combustible materials to ignition sources and
may reduce the spread of fire if the disposed
waste burns. Odors and blowing litter are
reduced by eliminating the direct contact of
wind and disposed waste. Similarly,
scavenging is reduced by removing the waste
from observation. Should these unwanted
effects of inadequate cover persist, the owner
or operator may increase the amount of soil
used or apply it more frequently. Any soil
type can meet the requirements of the
regulation when placed in a six-inch layer.
Approved States may allow demon-strations
of alternative daily cover materials. The rule
does not specify the time frame for the
demonstration; usually the State decides. A
period of six months should be ample time for
the owner or operator to make the demonstra-
tion. There are no numerical require-ments
for the alternative cover; rather, the
alternative cover must control disease vectors,
fires, odors, blowing litter, and scavenging
without presenting a threat to human health
and the environment.
Demonstrations can be conducted in a variety
of ways. Some suggested methods for
demonstrating alternative covers are:
1) Side by side (six inches of earthen
materials and alternative cover) test pads;
2) Full-scale demonstration; and
3) Short-term full-scale tests.
Alternative daily cover materials may include
indigenous materials or commercially-
available materials. Indigenous materials are
those materials that would be disposed as
waste; therefore, using these materials is an
efficient use of landfill space. Examples of
indigenous materials include (USEPA, 1992):
• Ash from municipal waste
combustors and utility companies;
• Compost-based material;
• Foundry sand from the
manufacturing process of discarding
used dies;
• Yard waste such as lawn clippings,
leaves, and tree branches;
• Sludge-based materials (i.e., sludge
treated with lime and mixed with ash
or soil);
• Construction and demolition debris
(which has been processed to form a
slurry);
• Shredded automobile tires;
Discarded carpets; and
Grit from municipal wastewater
treatment plants.
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Subpart C
Commercially developed alternatives have
been on the market since the mid-1980s.
Some of the commercial alternative materials
require specially designed application
equipment, while others use equipment
generally available at most landfills. Some of
the types of commercially available daily
cover materials include (USEPA, 1992):
• Foam that usually is sprayed on the
working face at the end of the day;
• Geosynthetic products such as a tarp or
fabric panel that is applied at the end of
the working day and removed at the
beginning of the following working
day; and
• Slurry products (e.g., fibers from
recycled newspaper and wood chip
slurry, clay slurry).
Other criteria to consider when selecting an
alternative daily cover material include
availability and suitability of the material,
equipment requirements, and cost.
The temporary climatic waiver of the cover
requirement is available only to owners or
operators in approved States. The State
Director may grant a waiver if the owner or
operator demonstrates that meeting the
requirements would be impractical due to
extreme seasonal climatic conditions.
Activities that may be affected by extreme
seasonal climatic conditions include:
• Obtaining cover soil from a borrow pit;
• Transporting cover soil to the working
face; or
• Spreading and compacting the soil to
achieve the required functions.
Extremely cold conditions may prevent the
efficient excavation of soil from a borrow pit
or the spreading and compaction of the soil on
the waste. Extremely wet conditions (e.g.,
prolonged rainfall, flooding) may prevent
transporting cover soil to the working face
and may make it impractical to excavate or
spread and compact. The duration of waivers
may be as short as one day for unusual rain
storms, or as long as several months for
extreme seasonal climatic conditions.
3.4 DISEASE VECTOR CONTROL
40 CFR §258.22
3.4.1 Statement of Regulation
(a) Owners or operators of all
MSWLF units must prevent or control on-
site populations of disease vectors using
techniques appropriate for the protection
of human health and the environment.
(b) For purposes of this section,
disease vectors means any rodents, flies,
mosquitoes, or other animals, including
insects, capable of transmitting disease to
humans.
3.4.2 Applicability
The regulation applies to existing MSWLF
units, lateral expansions, and new MSWLF
units. The owner or operator is required to
prevent or control on-site disease vector
populations of rodents, flies, mosquitoes, or
other animals, including other insects. The
techniques that may be used in fulfilling this
requirement must be appropriate for the
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Operating Criteria
protection of human health and the
environment.
3.4.3 Technical Considerations
Disease vectors such as rodents, birds, flies,
and mosquitoes typically are attracted by
putrescent waste and standing water, which
act as a food source and breeding ground.
Putrescent waste is solid waste that contains
organic matter (such as food waste) capable of
being decomposed by micro-organisms. A
MSWLF facility typically accepts putrescent
wastes.
Application of cover at the end of each
operating day generally is sufficient to control
disease vectors; however, other vector control
alternatives may be required. These
alternatives could include: reducing the size
of the working face; other operational
modifications (e.g., increasing cover
thickness, changing cover type, density,
placement frequency, and grading); repellents,
insecticides or rodenticides; composting or
processing of organic wastes prior to disposal;
and predatory or reproductive control of
insect, bird, and animal populations.
Additional methods to control birds are
discussed in Chapter 2 (Airport Safety).
Mosquitoes, for example, are attracted by
standing water found at MSWLFs, which can
provide a potential breeding ground after only
three days. Water generally collects in
surface depressions, open containers, exposed
tires, ponds resulting from soil excavation,
leachate storage ponds, and siltation basins.
Landfill operations that minimize standing
water and that use an insecticide spraying
program ordinarily are effective in controlling
mosquitoes.
Vectors may reach the landfill facility not
only from areas adjacent to the landfill, but
through other modes conducive to harborage
and breeding of disease vectors. Such modes
may include residential and commercial route
collection vehicles and transfer stations.
These transport modes and areas also should
be included in the disease vector control
program if disease vectors at the landfill
facility become a problem. Keeping the
collection vehicles and transfer stations
covered; emptying and cleaning the collection
vehicles and transfer stations; using repellents,
insecticides, or rodenticides; and reproductive
control are all measures available to reduce
disease vectors in these areas.
3.5 EXPLOSIVE GASES CONTROL
40 CFR §258.23
3.5.1 Statement of Regulation
(a) Owners or operators of all MSWLF
units must ensure that:
(1) The concentration of methane gas
generated by the facility does not exceed 25
percent of the lower explosive limit for
methane in facility structures (excluding
gas control or recovery system
components); and
(2) The concentration of methane gas
does not exceed the LEL for methane at the
facility property boundary.
(b) Owners or operators of all MSWLF
units must implement a routine methane
monitoring program to ensure that the
standards of paragraph (a) of this section
are met.
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Subpart C
(1) The type and frequency of
monitoring must be determined based on
the following factors:
(i) Soil conditions;
(ii) The hydrogeologic conditions
surrounding the facility;
(iii) The hydraulic conditions
surrounding the facility; and
(iv) The location of facility
structures and property
boundaries.
(2) The minimum frequency of
monitoring shall be quarterly.
(c) If methane gas levels exceeding the
limits specified in paragraph (a) of this
section are detected, the owner or operator
must:
(1) Immediately take all necessary steps
to ensure protection of human health and
notify the State Director;
(2) Within seven days of detection, place
in the operating record the methane gas
levels detected and a description of the
steps taken to protect human health; and
(3) Within 60 days of detection,
implement a remediation plan for the
methane gas releases, place a copy of the
plan in the operating record, and notify the
State Director that the plan has been
implemented. The plan shall describe the
nature and extent of the problem and the
proposed remedy.
(4) The Director of an approved State
may establish alternative schedules for
demonstrating compliance with paragraphs
(2) and (3).
(d) For purposes of this section, lower
explosive limit (LEL) means the lowest
percent by volume of a mixture of explosive
gases in air that will propagate a flame at
25°C and atmospheric pressure.
3.5.2 Applicability
The regulation applies to existing MSWLF
units, lateral expansions, and new MSWLF
units. The accumulation of methane in
MSWLF structures can potentially result in
fire and explosions that can endanger
employees, users of the disposal site, and
occupants of nearby structures, or cause
damage to landfill containment structures.
These hazards are preventable through
monitoring and through corrective action
should methane gas levels exceed specified
limits in the facility structures (excluding gas
control or recovery system components), or at
the facility property boundary. MSWLF
facility owners and operators must comply
with the following requirements:
• Monitor at least quarterly;
• Take immediate steps to protect human
health in the event of methane gas levels
exceeding 25% of the lower explosive
limit (LEL) in facility structures, such as
evacuating the building;
• Notify the State Director if methane
levels exceed 25% of the LEL in facility
structures or exceed the LEL at the
facility property boundary;
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Operating Criteria
• Within 7 days of detection, place in the
operating record documentation that
methane gas concentrations exceeded the
criteria, along with a description of
immediate actions taken to protect human
health; and
• Within 60 days of detection, implement a
remediation plan for the methane gas
releases, notify the State Director, and
place a copy of the remediation plan in the
operating record.
The compliance schedule for monitoring and
responding to methane levels that exceed the
criteria of this regulation can be changed by
the Director of an approved State.
3.5.3 Technical Considerations
To implement an appropriate routine methane
monitoring program to demonstrate
compliance with allowable methane
concentrations, the characteristics of landfill
gas production and migration at a site should
be understood. Landfill gases are the result of
microbial decomposition of solid waste.
Gases produced include methane (CH4),
carbon dioxide (CO2), and lesser amounts of
other gases (e.g., hydrogen, volatile organic
compounds, and hydrogen sulfide). Methane
gas, the principal component of natural gas, is
generally the primary concern in evaluating
landfill gas generation because it is odorless
and highly combustible. Typically, hydrogen
gas is present at much lower concentra-tions.
Hydrogen forms as decomposition progresses
from the acid production phase to the
methanogenic phase. While hydrogen is
explosive and is occasionally detected in
landfill gas, it readily reacts to form methane
or hydrogen sulfide. Hydrogen sulfide is
toxic and is
readily identified by its "rotten egg" smell at
a threshold concentration near 5 ppb.
Landfill gas production rates vary spatially
within a landfill unit as a result of pockets of
elevated microbial activity but, due to partial
pressure gradients, differences in gas
composition are reduced as the gases
commingle within and outside the landfill
unit. Although methane gas is lighter than air
and carbon dioxide is heavier, these gases are
concurrently produced at the microbial level
and will not separate by their individual
density. The gases will remain mixed and
will migrate according to the density gradients
between the landfill gas and the surrounding
gases (i.e., a mixture of methane and carbon
dioxide in a landfill unit or in surrounding soil
will not separate by rising and sinking
respectively, but will migrate as a mass in
accordance with the density of the mixture
and other gradients such as temperature and
partial pressure).
When undergoing vigorous microbial
production, gas pressures on the order of 1 to
3 inches of water relative to atmospheric
pressure are common at landfill facilities, with
much higher pressures occasionally reported.
A barometric pressure change of 2 inches of
mercury is equivalent to 27.2 inches of water.
Relative gauge pressures at a particular
landfill unit or portion of a landfill unit, the
ability of site conditions to contain landfill
gas, barometric pressure variations, and the
microbial gas production rate control
pressure-induced landfill gas migration.
Negative gas pressures are commonly
observed and are believed to occur as a result
of the delayed response within a landfill unit
to the passage of a high pressure system
outside the landfill unit. Barometric highs
will tend to introduce atmospheric oxygen
into surface soils in
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Subpart C
shallow portions of the landfill unit, which
may alter microbial activity, particularly
methane production and gas composition.
Migration of landfill gas is caused by
concentration gradients, pressure gradients,
and density gradients. The direction in which
landfill gas will migrate is controlled by the
driving gradients and gas permeability of the
porous material through which it is migrating.
Generally, landfill gas will migrate through
the path of least resistance.
Coarse, porous soils such as sand and gravel
will allow greater lateral migration or
transport of gases than finer-grained soils.
Generally, resistance to landfill gas flow
increases as moisture content increases and,
therefore, an effective barrier to gas flow can
be created under saturated conditions. Thus,
readily drained soil conditions, such as sands
and gravels above the water table, may
provide a preferred flowpath, but unless finer-
grained soils are fully saturated, landfill gases
also can migrate in a "semi-saturated" zone.
Figure 3-2 illustrates the potential effects of
surrounding geology on gas migration.
While geomembranes may not eliminate
landfill gas migration, landfill gas in a closed
MSWLF unit will tend to migrate laterally if
the final cover contains a geomembrane and if
the side slopes of the landfill do not contain
an effective gas barrier. Lateral gas migration
is more common in older facilities that lack
appropriate gas control systems. The degree
of lateral migration in older facilities also may
depend on the type of natural soils
surrounding the facility.
Stressed vegetation may indicate gas
migration. Landfill gas present in the soil
atmosphere tends to make the soil anaerobic
by displacing the oxygen, thereby
asphyxiating the roots of plants. Generally,
the higher the concentration of combustible
gas and/or carbon dioxide and the lower the
amount of oxygen, the greater the extent of
damage to vegetation (Flowers, et. al, 1982).
Gas Monitoring
The owner or operator of a MSWLF
unit/facility must implement a routine
methane monitoring program to comply with
the lower explosive limit (LEL) requirements
for methane. Methane is explosive when
present in the range of 5 to 15 percent by
volume in air. When present in air at
concentrations greater than 15 percent, the
mixture will not explode. This 15 percent
threshold is the Upper Explosive Limit
(UEL). The UEL is the maximum
concentration of a gas or vapor above which
the substance will not explode when exposed
to a source of ignition. The explosive hazard
range is between the LEL and the UEL. Note,
however, that methane concentrations above
the UEL remain a significant concern; fire
and asphyxiation can still occur at these
levels. In addition, even a minor dilution of
the methane by increased ventilation can bring
the mixture back into the explosive range.
To demonstrate compliance, the
owner/operator would sample air within
facility structures where gas may accumulate
and in soil at the property boundary. Other
monitoring methods may include: (1)
sampling gases from probes within the landfill
unit or from within the leachate collection
system; or (2) sampling gases
90
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Clay or Synthetic Cap
(Low Permeability)
Clay Soil, Frozen or
Saturated Soil, or Pavement
(Low Permeability)
Sand and Gravel Soil
(High Permeability)
EXTENSIVE LATERAL MIGRATION
Clay or Synthetic Liner
~ (Low Permeability)
Daily Cover
(High Permeability)
Clay Soil
(Low PermeabMBy)
EXTENSIVE VERTICAL MIGRATION
Source: Emcon, 1981.
Figure 3-2
Potential Effects of
Surrounding Geology on Gas Migration
91
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Subpart C
from monitoring probes installed in soil
between the landfill unit and either the
property boundary or structures where gas
migration may pose a danger. A typical gas
monitoring probe installation is depicted in
Figure 3-3.
Although not required by the regulations,
collection of data such as water presence and
level, gas probe pressure, ambient
temperature, barometric pressure, and the
occurrence of precipitation during sampling,
provides useful information in assessing
monitoring results. For example, falling
barometric pressure may cause increased
subsurface (gas) pressures and corresponding
increased methane content as gas more readily
migrates from the landfill. Gas probe
pressure can be measured using a portable
gauge capable of measuring both vacuum and
pressure in the range of zero to five inches of
water pressure (or other suitable ranges for
pressure conditions); this pressure should be
measured prior to methane measurement or
sample collection in the gas probe. A
representative sample of formation
(subsurface) gases can be collected directly
from the probe. Purging typically is not
necessary due to the small volume of the
probe. A water trap is recommended to
protect instrumentation that is connected
directly to the gas probe. After measurements
are obtained, the gas probe should be capped
to reduce the effects of venting or barometric
pressure variations on gas composition in the
vicinity of the probe.
The frequency of monitoring should be
sufficient to detect landfill gas migration
based on subsurface conditions and changing
landfill conditions such as partial or complete
capping, landfill expansion, gas migration
control system operation or failure,
construction of new or replacement
structures, and changes in landscaping or land
use practices. The rate of landfill gas
migration as a result of these anticipated
changes and the site-specific conditions
provides the basis for establishing monitoring
frequency. Monitoring is to be conducted at
least quarterly.
The number and location of gas probes is also
site-specific and highly dependent on
subsurface conditions, land use, and location
and design of facility structures. Monitoring
for gas migration should be within the more
permeable strata. Multiple or nested probes
are useful in defining the vertical
configuration of the migration pathway.
Structures with basements or crawl spaces are
more susceptible to landfill gas infiltration.
Elevated structures are typically not at risk.
Measurements are usually made in the field
with a portable methane meter, explosimeter,
or organic vapor analyzer. Gas samples also
may be collected in glass or metal containers
for laboratory analysis. Instruments with
scales of measure in "percent of LEL" can be
calibrated and used to detect the presence of
methane. Instruments of the hot-wire
Wheatstone bridge type (i.e., catalytic
combustion) directly measure combustibility
of the gas mixture withdrawn from the probe.
The thermal conductivity type meter is
susceptible to interference as the relative gas
composition and, therefore, the thermal
conductivity, changes. Field instruments
should be calibrated prior to measurements
and should be rechecked after each day's
monitoring activity.
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Operating Criteria
Source: Warzyn Inc.
PVC caps with
petcocks
Protective casing
with lock
Bentonite soil seal
Bentonite seal
1 inch PVC pipe
1/2 inch PVC pipe
1 inch perforated
PVC pipe
Gravel backfill
Bentonite seal
Sand and gravel
Probe screen
Figure 3-3
Typical Gas Monitoring Probe
93
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Subpart C
Laboratory measurements with organic vapor
analyzers or gas chromatographs may be used
to confirm the identity and concentrations of
gas.
In addition to measuring gas composition,
other indications of gas migration may be
observed. These include odor (generally
described as either a "sweet" or a rotten egg
(H2S) odor), vegetation damage, septic soil,
and audible or visual venting of gases,
especially in standing water. Exposure to
some gases can cause headaches and nausea.
If methane concentrations are in excess of 25
percent of the LEL in facility structures or
exceed the LEL at the property boundary, the
danger of explosion is imminent. Immediate
action must be taken to protect human health
from potentially explosive conditions. All
personnel should be evacuated from the area
immediately. Venting the building upon exit
(e.g., leaving the door open) is desirable but
should not replace evacuation procedures.
Owners and operators in unapproved States
have 60 days after exceeding the methane
level to prepare and implement a remediation
plan. The remediation plan should describe
the nature and extent of the methane problem
as well as a proposed remedy.
To comply with this 60-day schedule, an
investigation of subsurface conditions may be
needed in the vicinity of the monitoring probe
where the criterion was exceeded. The
objectives of this investigation should be to
describe the frequency and lateral and vertical
extent of excessive methane migration (that
which exceeds the criterion). Such an
investigation also may yield additional
characterization of unsaturated
soil within the area of concern. The
investigation should consider possible causes
of the increase in gas concentrations such as
landfill operational procedures, gas control
system failure or upset, climatic conditions, or
closure activity. Based on the extent and
nature of the excessive methane migration, a
remedial action should be described, if the
exceedance is persistent, that can be
implemented within the prescribed schedule.
The sixty-day schedule does not address the
protection of human health and the
environment. The owner or operator still
must take all steps necessary to ensure
protection of human health, including interim
measures.
Landfill Gas Control Systems
Landfill gas may vent naturally or be
purposely vented to the atmosphere by
vertical and/or lateral migration controls.
Systems used to control or prevent gas
migration are categorized as either passive or
active systems. Passive systems provide
preferential flowpaths by means of natural
pressure, concentration, and density gradients.
Passive systems are primarily effective in
controlling convective flow and have limited
success controlling diffusive flow. Active
systems are effective in controlling both types
of flow. Active systems use mechanical
equipment to direct or control landfill gas by
providing negative or positive pressure
gradients. Suitability of the systems is based
on the design and age of the landfill unit, and
on the soil, hydrogeologic, and hydraulic
conditions of the facility and surrounding
environment. Because of these variables, both
systems have had varying degrees of success.
Passive systems may be used in conjunction
with active systems. An example of this
94
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Operating Criteria
may be the use of a low-permeability passive
system for the closed portion of a landfill unit
(for remedial purposes) and the installation of
an active system in the active portion of the
landfill unit (for future use).
Selection of construction materials for either
type of gas control system should consider the
elevated temperature conditions within a
landfill unit as compared to the ambient air or
soil conditions in which gas control system
components are constructed. Because
ambient conditions are typically cooler, water
containing corrosive and possibly toxic waste
constituents may be expected to condense.
This condensate should be considered in
selecting construction materials. Provisions
for managing this condensate should be
incorporated to prevent accumulation and
possible failure of the collection system. The
condensate can be returned to the landfill unit
if the landfill is designed with a composite
liner and leachate collection system per
§258.40(a)(2). See Chapter 4 for information
regarding design. See Section 3.10 of this
Chapter for information regarding liquids in
landfills.
Additional provisions (under the Clean Air
Act) were proposed on May 30, 1991 (56 FR
24468), that would require the owners/
operators of certain landfill facilities to install
gas collection and control systems to reduce
the emissions of nonmethane organic
compounds (NMOCs). The proposed rule
amends 40 CFR Parts 51, 52, and 60. For
new municipal solid waste landfill units (those
for which construction was begun after May
30, 1991), and for those units that have a
design capacity greater than 111,000 tons, a
gas collection and control system must be
installed if emissions evaluations indicate that
the NMOC emissions rate is
150 megagrams per year (167 tons per year)
or greater. Allowable control systems include
open and enclosed flares, and on-site or off-
site facilities that process the gas for
subsequent sale or use. EPA believes that,
depending on landfill design, active collection
systems may be more cost-effective than
passive systems in ensuring that the system
effectively captures the gas that is generated
within the landfill unit. The provisions for
new landfill units are self-implementing and
will be effective upon promulgation of the
rule.
In addition to the emissions standards for new
municipal solid waste landfill units, the
regulations proposed on May 30, 1991
establish guidelines for State programs for
reducing NMOC emissions from certain
existing municipal landfill units. These
provisions apply to landfill units for which
construction was commenced before May 30,
1991, and that have accepted waste since
November 8, 1987 or that have remaining
capacity. Essentially, the State must require
the same kinds of collection and control
systems for landfill units that meet the size
criteria and emissions levels outlined above
for new landfill units. The requirements for
existing facilities will be effective after the
State revises its State Implementation Plan
and receives approval from EPA.
The rule is scheduled to be promulgated in
late 1993; the cutoff numbers for landfill size
and emission quantity may be revised in the
final rule. EPA expects that the new
regulations will affect less than 9% of the
municipal landfill facilities in the U.S.
95
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Subpart C
Passive Systems
Passive gas control systems rely on natural
pressure and convection mechanisms to vent
landfill gas to the atmosphere. Passive
systems typically use "high-permeability" or
"low-permeability" techniques, either
singularly or in combination at a site. High-
permeability systems use conduits such as
ditches, trenches, vent wells, or perforated
vent pipes surrounded by coarse soil to vent
landfill gas to the surface and the atmosphere.
Low-permeability systems block lateral
migration through barriers such as synthetic
membranes and high moisture-containing
fine-grained soils.
Passive systems may be incorporated into a
landfill design or may be used for remedial or
corrective purposes at both closed and active
landfills. They may be installed within a
landfill unit along the perimeter, or between
the landfill and the disposal facility property
boundary. A detailed discussion of passive
systems for remedial or corrective purposes
may be found in U.S. EPA (1985).
A passive system may be incorporated into
the final cover system of a landfill closure
design and may consist of perforated gas
collection pipes, high permeability soils, or
high transmissivity geosynthetics located just
below the low-permeability gas and hydraulic
barrier or infiltration layer in the cover
system. These systems may be connected to
vent pipes that vent gas through the cover
system or that are connected to header pipes
located along the perimeter of the landfill
unit. Figure 3-4 illustrates a passive system.
The landfill gas collection system also may be
connected with the leachate collection system
to vent gases in the headspace of leachate
collection pipes.
Some problems have been associated with
passive systems. For example, snow and dirt
may accumulate in vent pipes, preventing gas
from venting. Vent pipes
at the surface are susceptible to clogging by
vandalism. Biological clogging of the system
is also more common in passive systems.
Active Systems
Active gas control systems use mechanical
means to remove landfill gas and consist of
either positive pressure (air injection) or
negative pressure (extraction) systems.
Positive pressure systems induce a pressure
greater than the pressure of the migrating gas
and drive the gas out of the soil and/or back to
the landfill unit in a controlled manner.
Negative pressure systems extract gas from a
landfill by using a blower to pull gas out of
the landfill. Negative pressure systems are
more commonly used because they are more
effective and offer more flexibility in
controlling gas migration. The gas may be
recovered for energy conversion, treated, or
combusted in a flare system. Typical
components of a flare system are shown in
Figure 3-5. Negative pressure systems may
be used as either perimeter gas control
systems or interior gas collection/recovery
systems. For more information regarding
negative pressure gas control systems, refer to
U.S. EPA (1985).
An active gas extraction well is depicted in
Figure 3-6. Gas extraction wells may be
installed within the landfill waste or, as
depicted in Figure 3-7A and Figure 3-7B,
perimeter extraction trenches could be used.
One possible configuration of an interior gas
collection/recovery system is illustrated in
96
-------
Operating Criteria
Gas Vent
Figure 3-4
Passive Gas Control System
(Venting to Atmosphere)
Top Layer
Low-Permeability Laye
Vent Layer
Waste
97
-------
Subpart C
77T—Waste Gas
Inlet Valve
Concrete Base
Gas From
Landfill
Source; E.G. Jordan Co., 1990.
Figure 3-5. Example Schematic Diagram of a
Ground-based Landfill Gas Flare
98
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48" Corr. Steel Pipe
w/ Hinged Lid
Backfill, Compact by
Hand in 6" Layers
Exist Ground Elev
Butterfly Valve
Monitoring Port
Header with 3"
Dia. Branch Saddle
Kanaflex PVC Hose
Source CH,H Hill. 1992
3'-0"
4" Dia Sch 80 PVC
Solid Pipe
Soil Backfill
*-
T
Varies
Bentonite/Soil Seal
4" Dia Sch 80 PVC
Slotted Pipe
Gravel Backfill
2'-C'
12"
Slotted Length
Varies
(2/3 Landfill
Depth)
4" Sch 80 PVC Cap-
Slotted Length
Varies
(1/2 Well Depth)
!
I
1 24" Dia
1— M
i Bore i
Figure 3-6 Example of a Gas Extraction Well
99
-------
- Geotextile
Existing Cover
Existing Cover
• Refuse
Washed Gravel
Oo
Sourca: Swana. 1991
Bottom of Trench Excavation
Figure 3-7A. Perimeter Extraction Trench System
Quick Connect
Coupling
Flexible Hose
Butterfly Valve
Source: Swana, 1991
Washed Gravel
Ground Surface
Clean Soil Backfill
HOPE Pipe
Figure 3-7B. Perimeter Extraction Trench System
100
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Operating Criteria
Figure 3-8. The performance of active
systems is not as sensitive to freezing or
saturation of cover soils as that of passive
systems. Although active gas systems are
more effective in withdrawing gas from the
landfill, capital, operation, and maintenance
costs of such systems will be higher and these
costs can be expected to continue throughout
the post-closure period. At some future time,
owners and operators may wish to convert
active gas controls into passive systems when
gas production diminishes. The conversion
option and its environmental effect (i.e., gas
release causing odors and health and safety
concerns) should be addressed in the original
design.
There are many benefits to recovering landfill
gas. Landfill gas recovery systems can reduce
landfill gas odor and migration, can reduce
the danger of explosion and fire, and may be
used as a source of revenue that may help to
reduce the cost of closure. Landfill gas can be
used with a minimal amount of treatment or
can be upgraded to pipeline standards
(SWANA, 1992). An upgraded gas is one
which has had the carbon dioxide and other
noncombustible constituents removed.
Raw landfill gas may be used for heating
small facilities and water, and may require
removal of only water and particulates for this
application. A slightly upgraded gas can be
used for both water and space heating as well
as lighting, electrical generation,
cogeneration, and as a fuel for industrial
boilers-burners. Landfill gas also may be
processed to pipeline quality to be sold to
utility companies and may even be used to
fuel conventional vehicles. The amount of
upgrading and use of landfill gas is dependent
on the landfill size.
3.6 AIR CRITERIA
40 CFR §258.24
3.6.1 Statement of Regulation
(a) Owners or operators of all
MSWLFs must ensure that the units do not
violate any applicable requirements
developed under a State Implementation
Plan (SIP) approved or promulgated by the
Administrator pursuant to section 110 of
the Clean Air Act, as amended.
(b) Open burning of solid waste, except
for the infrequent burning of agricultural
wastes, silvicultural wastes, land-clearing
debris, diseased trees, or debris from
emergency clean-up operations, is
prohibited at all MSWLF units.
3.6.2 Applicability
The regulation applies to existing MSWLF
units, lateral expansions to existing MSWLF
units, and new MSWLF units. Routine open
burning of municipal solid waste is
prohibited. Infrequent burning of agricultural
and silvicultural wastes, diseased trees, or
debris from land clearing or emergency clean-
up operations is allowed when in compliance
with any applicable requirements developed
under a State Implementation Plan (SIP) of
the Clean Air Act. Agricultural waste does
not include empty pesticide containers or
waste pesticides.
3.6.3 Technical Considerations
Air pollution control requirements are
developed under a SIP, which is developed by
the State and approved by the EPA
Administrator. The owner or operator of a
101
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Gas
Treatment/Processing
Facility
Source: Emcon, 1981
Figure 3-8
Example of an Interior Gas Collection/Recovery System
102
-------
Operating Criteria
MSWLF unit should consult the State or local
agency responsible for air pollution control to
ascertain that the burning of wastes complies
with applicable requirements developed under
the SIP. The SIP may include variances,
permits, or exemptions for burning
agricultural wastes, silvicultural wastes, land-
clearing debris, diseased trees, or debris from
emergency clean-up operations. Routine
burning of wastes is banned in all cases, and
the SIP may limit burning of waste such as
agricultural wastes to certain hours of the day;
days of the year; designated burn areas;
specific types of incinerators; atmospheric
conditions; and distance from working face,
public thoroughfares, buildings, and
residences.
Requirements under the SIP also may include
notifying applicable State or local agencies
whose permits may: (1) restrict times when
limited burning of waste may occur; (2)
specify periods when sufficient fire protection
is deemed to be available; or (3) limit burning
to certain areas.
Open burning is defined under §258.2 as the
combustion of solid waste: (1) without
control of combustion air to maintain
adequate temperature for efficient
combustion; (2) without containment of the
combustion reaction in an enclosed device to
provide sufficient residence time and mixing
for complete combustion; and (3) without the
control of the emission of the combustion
products. Trench or pit burners, and air
curtain destructors are considered open
burning units because the particulate
emissions are similar to particulate emissions
from open burning,
and these devices do not control the emission
of combustion products.
[Note: The Agency plans to issue regulations
under the Clean Air Act to control landfill gas
emissions from large MSWLF units in 1993.
These regulations are found at 40 CFR Parts
51, 52, and 60.]
3.7 ACCESS REQUIREMENT
40 CFR §258.25
3.7.1 Statement of Regulation
Owners or operators of all MSWLF units
must control public access and prevent
unauthorized vehicular traffic and illegal
dumping of wastes by using artificial
barriers, natural barriers, or both, as
appropriate to protect human health and
the environment.
3.7.2 Applicability
The regulation applies to existing MSWLF
units, lateral expansions, and new MSWLF
units. The owner or operator is required to
prevent public access to the landfill facility,
except under controlled conditions during
hours when wastes are being received.
3.7.3 Technical Considerations
Owners and operators are required to control
public access to prevent illegal dumping,
public exposures to hazards at MSWLF units,
and unauthorized vehicular traffic.
Frequently, unauthorized persons are
unfamiliar with the hazards associated with
landfill facilities, and consequences of
uncontrolled access may include injury and
even death. Potential hazards are related to
inability of equipment operators to see
unauthorized individuals during operation of
equipment and haul vehicles; direct exposure
to waste (e.g., sharp objects and pathogens);
103
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Subpart C
inadvertent or deliberate fires; and earth-
moving activities.
Acceptable measures used to limit access of
unauthorized persons to the disposal facility
include gates and fences, trees, hedges, berms,
ditches, and embankments. Chain link,
barbed wire added to chain link, and open
farm-type fencing are examples of fencing
that may be used. Access to facilities should
be controlled through gates that can be locked
when the site is unsupervised. Gates may be
the only additional measure needed at remote
facilities.
3.8 RUN-ON/RUN-OFF
CONTROL SYSTEMS
40 CFR §258.26
3.8.1 Statement of Regulation
(a) Owners or operators of all MSWLF
units must design, construct, and maintain:
(1) A run-on control system to prevent
flow onto the active portion of the landfill
during the peak discharge from a 25-year
storm;
(2) A run-off control system from the
active portion of the landfill to collect and
control at least the water volume resulting
from a 24-hour, 25-year storm.
(b) Run-off from the active portion of
the landfill unit must be handled in
accordance with §258.27(a) of this Part.
3.8.2 Applicability
The regulation applies to existing MSWLF
units, lateral expansions, and new MSWLF
units. The owner or operator is required to
prevent run-on onto the active portion of the
landfill units and to collect and control run-off
from the active portion for a 24-hour, 25-year
storm. Management of run-off must comply
with the point and non-point source discharge
requirements of the Clean Water Act.
3.8.3 Technical Considerations
If stormwater enters the landfill unit and
contacts waste (including water within daily
cover), the stormwater becomes leachate and
must be managed as leachate. The purpose of
a run-on control system is to collect and
redirect surface waters to minimize the
amount of surface water entering the landfill
unit. Run-on control can be accomplished by
constructing berms and swales above the
filling area that will collect and redirect the
water to stormwater control structures.
As stated above, stormwater that does enter
the landfill unit should be managed as
leachate. Run-off control systems are
designed to collect and control this run-off
from the active portion of the landfill,
including run-off from areas that have
received daily cover, which may have
contacted waste materials. Run-off control
can be accomplished through stormwater
conveyance structures that divert this run-
off/1 eachate to the leachate storage device.
After a landfill unit has been closed with a
final cover, stormwater run-off from this unit
can be managed as stormwater and not
leachate. Therefore, waters running off the
final cover system of closed areas may not
104
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Operating Criteria
require treatment and generally can be
combined with run-on waters. For landfills
with steep side slopes, a bench system may
provide the best solution for run-off control.
A bench creates a break in the slope where the
velocity of the stormwater run-off is expected
to become erosive. The bench converts sheet
flow run-off into channel flow. Benches
typically are spaced 30 to 50 feet apart up the
slope. An alternative to benches is a system
of downchutes whereby stormwater is
collected off the top of the landfill and
conveyed down the slope through a pipe or
channel. Caution should be taken not to
construct downchutes with heavy material
because of possible subsidence. Corrugated
metal pipes or plastic-lined channels are
examples of lightweight materials that can be
used for downchute construction.
Run-on and run-off must be managed in
accordance with the requirements of the Clean
Water Act including, but not limited to, the
National Pollutant Discharge Elimination
System (NPDES). [See Section 3.9 of this
chapter for further information on compliance
with the Clean Water Act.]
Run-on and run-off control systems must be
designed based on a 24-hour, 25-year storm.
Information on the 24-hour, 25-year recurring
storm can be obtained from Technical Paper
40 "Rainfall Frequency Atlas of the United
States for Durations from 30 Minutes to 24
Hours and Return Periods from 1 to 100
Years", prepared by the Weather Bureau
under the Department of Commerce.
Alternatively, local meteorological data can
be analyzed to estimate the criterion storm.
To estimate run-on, the local watershed
should be identified and evaluated to
document the basis for run-on design flows.
The Soil Conservation Service (SCS) Method
and/or the Rational Method are generally
adequate for estimating storm flows for
designing run-on and/or run-off control
systems. The SCS method estimates run-off
volume from accumulated rainfall and then
applies the run-off volume to a simplified
triangular unit hydrograph for peak discharge
estimation and total run-off hydrograph. A
discussion of the development and use of this
method is available from the U. S.
Department of Agriculture, Soil Conservation
Service (1986).
The Rational Method approximates the
majority of surface water discharge supplied
by the watershed upstream from the facility.
The Rational Method generally is used for
areas of less than 200 acres. A discussion of
the Rational Method may be found in U.S.
EPA (1988).
Run-on/run-off control structures, both
temporary and permanent, may be
incorporated into the system design. Other
structures (not mentioned above) most
frequently used for run-on/run-off control are
waterways, seepage ditches, seepage basins,
and sedimentation basins. U.S. EPA (1985)
provides an in-depth discussion for each of
these structures.
3.9 SURFACE WATER
REQUIREMENTS
40 CFR §258.27
3.9.1 Statement of Regulation
MSWLF units shall not:
(a) Cause a discharge of pollutants into
waters of the United States, including
105
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Subpart C
wetlands, that violates any requirements of
the Clean Water Act, including, but not
limited to, the National Pollutant Discharge
Elimination System (NPDES)
requirements, pursuant to section 402.
(b) Cause the discharge of a nonpoint
source of pollution to waters of the United
States, including wetlands, that violates
any requirement of an area-wide or State-
wide water quality management plan that
has been approved under section 208 or
319 of the Clean Water Act, as amended.
3.9.2 Applicability
The regulation applies to existing MSWLF
units, lateral expansions, and new MSWLF
units. The owner or operator is required to
comply with the Clean Water Act for any
discharges to surface water or wetlands.
3.9.3 Technical Considerations
The owner or operator of a MSWLF facility
should determine if the facility is in
conformance with applicable requirements of
water quality plans developed under Sections
208 and 319 of the Clean Water Act, and the
National Pollutant Discharge Elimination
System (NPDES) requirements under Section
402 of the Clean Water Act. The EPA and
approved States have jurisdiction over
discharge of pollutants (other than dredge and
fill materials) in waters of the United States
including wetlands. MSWLF units
discharging pollutants or disposing of fill
material into waters of the United States
require a Section 402 (NPDES) permit.
Discharge of dredge and fill material into
waters of the United States is under the
jurisdiction of the U.S. Army Corps of
Engineers.
A MSWLF unit(s) that has a point source
discharge must have a NPDES permit. Point
source discharges for landfills include, but are
not limited to: (1) the release of leachate
from a leachate collection or on-site treatment
system into the waters of the United States;
(2) disposal of solid waste into waters of the
United States; or (3) release of surface water
(stormwater) run-off which is directed by a
run-off control system into the waters of the
United States. Leachate that is piped or
trucked off-site to a treatment facility is not
regarded as a point source discharge.
The Clean Water Act (CWA) provides
clarifications of terms such as point source,
waters of the United States, pollutants, and
discharge of pollutants.
Owners/operators also should be aware that
there are regulations promulgated pursuant to
the CWA regarding stormwater discharges
from landfill facilities. These regulations
require stormwater discharge permit
applications to be submitted by certain
landfills that accept or have accepted specific
types of industrial waste. See 40 CFR Section
122.26(a)-(c), which originally appeared in
the Federal Register on November 16, 1990
(55 FR 47990).
In addition, EPA codified several provisions
pursuant to the Intermodal Surface
Transportation Efficiency Act of 1991 into the
NPDES regulations. These regulations only
affect the deadlines for submitting permit
applications for stormwater discharges, and
they apply to both uncontrolled and controlled
sanitary landfills. "Uncontrolled sanitary
landfills" are defined as landfills or open
dumps that do not meet the requirements for
run-on or run-off controls that are found in
the
106
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Operating Criteria
MSWLF Criteria, Section 258.25.
"Controlled sanitary landfills" are those that
do meet the run-on and run-off requirements.
The NPDES regulations specify that
uncontrolled sanitary landfills owned or
operated by municipalities of less than
100,000 (population) must submit a NPDES
permit application for their stormwater
discharge or obtain coverage under a general
permit. For controlled sanitary landfills
owned or operated by a municipality with a
population less than 100,000, there is no
requirement to submit a stormwater discharge
permit application (before October 1, 1992)
unless a permit is required under Section
402(p)(2)(A) or (E) of the Clean Water Act.
Other deadlines are set for municipalities with
a population less than 250,000 that own or
operate a municipal landfill. For further
information contact the Stormwater Hotline
(703) 821-4823. See the April 2, 1992
Federal Register (57 FR 11394), 40 CFR
122.26.
3.10 LIQUIDS RESTRICTIONS
40 CFR §258.28
3.10.1 Statement of Regulation
(a) Bulk or noncontainerized liquid
waste may not be placed in MSWLF units
unless:
(1) The waste is household waste other
than septic waste; or
(2) The waste is leachate or gas
condensate derived from the MSWLF unit
and the MSWLF unit, whether it is an
existing or new unit, is designed with a
composite liner and leachate collection
system as described in §258.40 (a)(2) of
this part. The owner or operator must
place the demonstration in the operating
record and notify the State Director that it
has been placed in the operating record.
(b) Containers holding liquid waste
may not be placed in a MSWLF unit
unless:
(1) The container is a small container
similar in size to that normally found in
household waste;
(2) The container is designed to hold
liquids for use other than storage; or
(3) The waste is household waste.
(c) For purposes of this section:
(1) Liquid waste means any waste
material that is determined to contain
"free liquids" as defined by Method 9095
(Paint Filter Liquids Test), as described in
"Test Methods for Evaluating Solid
Wastes, Physical/Chemical Methods" (EPA
Pub. No. SW-846).
(2) Gas condensate means the liquid
generated as a result of gas recovery
process(es) at the MSWLF unit.
3.10.2 Applicability
The regulation applies to new MSWLF units,
existing MSWLF units, and lateral expansions
of existing MSWLF units. The owner or
operator is prohibited from placing bulk or
non-containerized liquid waste, or
containerized liquid waste into the MSWLF
unit. Liquids from households are exempt.
Tank trucks of wastes are not exempt.
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Subpart C
3.10.3 Technical Considerations
The restriction of bulk or containerized
liquids is intended to control a source of
liquids that may become a source of leachate.
Liquid waste refers to any waste material that
is determined to contain free liquids as
defined by SW-846 (U.S. EPA, 1987) Method
9095 - Paint Filter Liquids Test. The paint
filter test is performed by placing a 100
milliliter sample of waste in a conical, 400
micron paint filter. The waste is considered a
liquid waste if any liquid from the waste
passes through the filter within five minutes.
The apparatus used for performing the paint
filter test is illustrated in Figure 3-9.
If the waste is considered a liquid waste,
absorbent materials may be added to render a
"solid" material (i.e., waste/absorbent mixture
that no longer fails the paint filter liquids
test). One common waste stream that may
contain a significant quantity of liquid is
sludge. Sludge is a mixture of water and
solids that has been concentrated from, and
produced during, water and wastewater
treatment. Sludges may be produced as a
result of providing municipal services (e.g.,
potable water supply, sewage treatment, storm
drain maintenance) or commercial or
industrial operations. Sewage sludge is a
mixture of organic and inorganic solids and
water, removed from wastewater containing
domestic sewage. Sludge disposal is
acceptable provided the sludge passes the
paint filter test.
[NOTE: Additional Federal regulations
restricting the use and disposal of sewage
sludge were published on February 19, 1993
in the Federal Register (58 FR 9248). These
regulations, however, do not establish
additional treatment standards or other
special management requirements for sewage
sludge that is codisposed with solid waste.]
Owners and operators of MSWLF units may
return leachate and gas condensate generated
from a gas recovery process to the MSWLF,
provided the MSWLF unit has been designed
and constructed with a composite liner and
leachate collection system in compliance with
40 CFR §258.40(a)(2). Approved States may
allow leachate and landfill gas condensate
recirculation in MSWLF units with alternative
designs.
Recirculating leachate or landfill gas
concentrate may require demonstrating that
the added volume of liquid will not increase
the depth of leachate on the liner to more than
30cm.
Returning gas condensate to the landfill unit
may represent a reasonable long-term solution
for relatively small volumes of condensate.
Gas condensate recirculation can be
accomplished by pumping the condensate
through pump stations at the gas recovery
system and into dedicated drain fields (buried
pipe) atop the landfill, or into other discharge
points (e.g., wells).
Because gas condensate may be odorous,
spray systems for recirculation are not used
unless combined with leachate recirculation
systems.
Leachate recirculation to a MSWLF unit has
been used as a measure for managing leachate
or as a means of controlling and managing
liquid and solid waste decomposition.
Leachate recirculation can be accomplished in
the same manner as recirculation of landfill
gas condensate. Because of the larger
volume, however, discharge points may not
be as effective as drainfields. In some cases,
discharge points
108
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Operating Criteria
Paint Filter
Ring Stand
Funnel
•Graduated Cylinder
Figure 3-9. Paint Filter Test Apparatus
109
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Subpart C
have been a source of odor. In addition, a
discharge point may not allow for dissipation
of the leachate. (For additional information
regarding the effectiveness of using leachate
recirculation to enhance the rate of organic
degradation, see (Reinhart and Carson,
1993).)
3.11 RECORDKEEPING
REQUIREMENTS
40 CFR §258.29
3.11.1 Statement of Regulation
(a) The owner or operator of a
MSWLF unit must record and retain near
the facility in an operating record, or in an
alternative location approved by the
Director of an approved state, the following
information as it becomes available:
(1) Any location restriction
demonstration required under Subpart B
of this part;
(2) Inspection records, training
procedures, and notification procedures
required in §258.20 of this Part;
(3) Gas monitoring results from
monitoring and any remediation plans
required by §258.23 of this Part;
(4) Any MSWLF unit design
documentation for placement of leachate or
gas condensate in a MSWLF unit as
required under §258.28 (a)(2) of this Part;
(5) Any demonstration, certification,
finding, monitoring, testing, or analytical
data required by Subpart E of this Part;
(6) Closure and post-closure care plans
and any monitoring, testing, or analytical
data as required by §§258.60 and 258.61 of
this Part; and
(7) Any cost estimates and financial
assurance documentation required by
Subpart G of this Part.
(8) Any information demonstrating
compliance with small community
exemption as required by §258.1(f)(2).
(b) The owner/operator must notify
the State Director when the documents
from paragraph (a) of this section have
been placed or added to the operating
record, and all information contained in
the operating record must be furnished
upon request to the State Director or be
made available at all reasonable times for
inspection by the State Director.
(c) The Director of an approved State
can set alternative schedules for
recordkeeping and notification
requirements as specified in paragraphs (a)
and (b), except for the notification
requirements in §258.10(b) and
§258.55(g)(l)(iii).
3.11.2 Applicability
The regulation applies to existing MSWLF
units, lateral expansions of existing MSWLF
units, and new MSWLF units. The
recordkeeping requirements are intended to be
self-implementing so that owners/ operators in
unapproved States can comply without State
or EPA involvement. The owner or operator
is required to maintain records of
demonstrations, inspections, monitoring
results, design documents, plans, operational
110
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Operating Criteria
procedures, notices, cost estimates, and
financial assurance documentation.
3.11.3 Technical Considerations
The operating record should be maintained in
a single location. The location may be at the
facility, at corporate headquarters, or at city
hall, but should be near the facility. Records
should be maintained throughout the life of
the facility, including the post-closure care
period. Upon placement of each required
document in the operating record, the State
Director should be notified. The Director of
an approved State may establish alternative
requirements for recordkeeping, including
using the State permit file for recordkeeping.
Recordkeeping at the landfill facility should
include the following:
(a) Location restriction demonstrations:
Demonstrations are required for any location
restrictions under Subpart B. The location
restrictions apply to:
• Airports;
• Floodplains;
• Wetla
• Fault areas;
• Seismic impact zones; and
• Unstable areas.
(b) Inspection records. training
procedures, and notification procedures:
Inspection records should include:
• Date and time wastes were received during
the inspection;
• Names of the transporter and the driver;
• Source of the wastes;
• Vehicle identification numbers; and
• All observations made by the inspector.
Training records should include procedures
used to train personnel on hazardous waste
and on PCB waste recognition. Notification
to EPA, State, and local agencies should be
documented.
(c) Gas monitoring results and any
remediation plans: If gas levels exceed 25
percent of the LEL for methane in any facility
structures or exceed the LEL for methane at
the facility boundary, the owner or operator
must place in the operating record, within
seven days, the methane gas levels detected,
and a description of the steps taken to protect
human health. Within 60 days of detection,
the owner or operator must place a copy of
the remediation plan used for gas releases in
the operating record.
(d) MSWLF unit design
documentation for placement of leachate or
gas condensate in a MSWLF unit: If leachate
and/or gas condensate are recirculated into the
MSWLF unit, documentation of a composite
liner and a leachate collection system capable
of maintaining a maximum of 30 cm of
leachate head in the MSWLF unit must be
placed in the operating record.
Ill
-------
Subpart C
(e) Demonstration. certification.
monitoring, testing, or analytical Finding
required by the ground-water criteria:
Documents to be placed in the operating
record include:
• Documentation of design, installation,
development, and decommission of any
monitoring wells, piezometers, and other
measurement, sampling, and analytical
devices;
• Certification by a qualified ground-water
scientist of the number, spacing, and
depths of the monitoring systems;
• Documentation of sampling and analysis
programs and statistical procedures;
• Notice of finding a statistically significant
increase over background for one or more
of the constituents listed in Appendix I of
Part 258 (or alternative list in approved
States) at any monitoring well at the waste
management unit boundary (States with
inadequate program) or the relevant point
of compliance (approved States);
• Certification by a qualified ground-water
scientist that an error in sampling, analysis,
statistical evaluation, or natural variation in
ground water caused an increase (false
positive) of Appendix I constituents, or
that a source other than the MSWLF unit
caused the contamination (if appropriate);
• A notice identifying any Appendix II (Part
258) constituents that have been detected
in ground water and their concentrations;
• A notice identifying the Part 258
Appendix II constituents that have
exceeded the ground-water protection standard;
• A certification by a qualified ground-
water scientist that a source other than
the MSWLF unit caused the
contamination or an error in sampling,
analysis, statistical evaluation, or natural
ground-water variation caused a
statistically significant increase (false
positive) in Appendix II (Part 258)
constituents (if applicable);
• The remedies selected to remediate
ground-water contamination; and
• Certification of remediation completion.
(f) Closure and post-closure plans and
any monitoring, testing, or analytical data
associated with these plans: The landfill
facility owner or operator is required to place
a copy of the closure plan, post-closure plan,
and a notice of intent to close the facility in
the operating record. Monitoring, testing, or
analytical data associated with closure and
post-closure information generated from
ground-water and landfill gas monitoring
must be placed in the operating record. A
copy of the notation on the deed to the
MSWLF facility property, as required
following closure, along with certification and
verification that closure and post-closure
activities have been completed in accordance
with their respective plans, also must be
placed in the operating record.
(g) Estimates and financial assurance
documentation required: The following
documents must be placed in the operating
record:
112
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Operating Criteria
• An estimate of the cost of hiring a third
party to close the largest area of all
MSWLF units that will require final cover;
• Justification for the reduction of the
closure cost estimate and the amount of
financial assurance (if appropriate);
• A cost estimate of hiring a third party to
conduct post-closure care;
• The justification for the reduction of the
post-closure cost estimate and financial
assurance (if appropriate);
• An estimate and financial assurance for the
cost of a third party to conduct corrective
action, if necessary; and
• A copy of the financial assurance
mechanisms.
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Subpart C
3.12 FURTHER INFORMATION
3.12.1 References
Flower, et al., (1982). "Vegetation Kills in Landfill Environs"; Franklin B. Flower, Ida A. Leone,
Edward F. Oilman and John J. Arthur; Cook College, Rutgers University; New Brunswick, New
Jersey 08903.
Reinhart, D.R., and D. Carson, (1993). "Experiences with Full-Scale Application of Landfill
Bioreactor Technology," Thirty-First Annual Solid Waste Exposition of the Solid Waste
Association of North America, August 2-5, 1993.
SWANA, (1992). "A Compilation of Landfill Gas Field Practices and Procedures"; Landfill Gas
Division of the Solid Waste Association of North America (SWANA); March 1992.
U.S. Department of Agriculture Soil Conservation Service, (1986). "Urban Hydrology for Small
Watersheds"; PB87-101580.
U.S. Department of Commerce, Weather Bureau, "Rainfall Frequency Atlas of the United States for
Durations from 30 Minutes to 24 Hours and Return Periods from 1 to 100 Years."
U.S. EPA, (1985). "Handbook - Remedial Action at Waste Disposal Sites"; EPA/625/6-85/006;
U.S. EPA, Office of Research and Development; Cincinnati, Ohio 45268.
U.S. EPA, (1986). "Test Methods for Evaluating Solid Wastes: Physical/Chemical Methods";
Third Edition as amended by Updates I and II. U.S. EPA SW-846; Office of Solid Waste and
Emergency Response; Washington, D.C.
U.S. EPA, (1988). "Guide to Technical Resources for the Design of Land Disposal Facilities";
EPA/625/6-88/018; U.S. EPA; Risk Reduction Engineering Laboratory and Center for
Environmental Research Information; Cincinnati, Ohio 45268.
U.S. EPA, (1992). "Alternative Daily Cover Materials for Municipal Solid Waste Landfills;"
U.S. EPA Region IX; San Francisco, California 94105.
3.12.2 Addresses
Solid Waste Association of North America (SWANA/GRCDA)
P.O.Box 7219
Silver Spring, MD 20910
(301)585-2898
114
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APPENDIX I
Special Waste Acceptance Agreement
115
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Code*
Generator Name:
Address:
Special Waste Acceptance Application
Originating Division:^
Disposal Facility
Location:
Telephone: ( )
Generator Contact:
General Material Description: _
Waste Quantities:,
Units: Cubic Ws.3 Tons 3
Frequency of Receipt: Daily a Weekly O Monthly 3 One Time 3
Other
Process Generating Waste:
Physical Properties: Physical State at 7(fF: Solida SemisolidU iiquida Density:,
Viscosity: low O Medium !3 High Q Flash Point:
Water Content: % by Weight Paint Filter Test: Passed 3 Failed1!
Reactive: No 3 YesO With
f/CY Color:
Odor. YesD No 3
Waste pH:
Chemical Properties: (Concentrations in mg/l)
(TCLP) Arsenic
Barium
Benzene
Cadmium
Carbon Tetrach/oride
Chlordane
Chlorobenzene
Chloroform
Chromium
o-Cresol
Other (iist):
Other Information: Delivery Method: Bulk 3
Regulatory Agency Appro\
Infectious: Yes 3 No J
m-Cresol
p-Cresol
Cresol
2,4-D
1,4 Dichlorobemene
1,2 Dich/oroethane
1, 1-Dichloroethylene
2,4-Dinitrotoluene
Endrirt
Heptach/or
Other
tal Received: VesQ AtoO
Hexachiorobenzene
Hexach/orobutadiene
Hexach/oroethane
Lead
Lindane
Mercurv
Methoxvchlor
Methyl Ethyl Ketone
Nitrobenzene
Pentachlorophenol
Permit Number:
Pyridine
Selenium
Silver
Tetrachloroethv/ene
Toxaohene
Trichloroethvlene
2. 4. S-Trich/oroohenol
2.4.6-Trichlorophenol
2.4.5-TP (Silvexl
Vinvl Chloride
Material Safety Data Sheet Provided: Yes 3
GENERA TOR CER TIFICA TION
To the best of my knowledge, the information
provided above is accurate anrj the material is
not classified as a hazardous waste in
accordance with current regulations-.
Authorised Representative
Signature
Name
Title
Date
|| FOR OFFICE USE ONLY ||
Conditions for Acceptance
1 Originating Division Manager
2 Disposal Facility Manager
3. District Manager
4 Regional Engineer
Date
Date
Date
Date
Recertification Frequency: HI Annual 3 Annual Q Semi Annual 3
"age Ic Owner'Cperator Second Page to Customer, Third Page to Laboratory
Appendix I. Example Special Waste Acceptance Agreement
116
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CHAPTER 4
SUBPART D
DESIGN CRITERIA
-------
CHAPTER 4
SUBPART D
TABLE OF CONTENTS
4J. INTRODUCTION 121
42. PERFORMANCE-BASED DESIGN
40 CFR §258.40 122
4.2.1 Statement of Regulation 122
4.2.2 Applicability 123
4.2.3 Technical Considerations 123
Demonstration Requirements 123
Leachate Characterization 124
Assessment of Leakage Through Liners 125
Leachate Migration in the Subsurface 126
Physical Processes Controlling Contaminant Transport in the Subsurface . . 126
Chemical Processes Controlling Contaminant Transport in the Subsurface
128
Biological Processes Controlling Contaminant Transport in the Subsurface
129
Leachate Migration Models 130
Overview of the Modeling Process 130
Model Selection 135
Analytical Versus Numerical Models 135
Spatial Characteristics of the System 136
Steady-State Versus Transient Models 136
Boundary and Initial Conditions 137
Homogeneous Versus Heterogeneous Aquifer/Soil Properties 137
Availability of Data 138
Summary of Available Models 138
The EPA Multimedia Exposure Assessment Model (MULTIMED) 139
Overview of the Model 147
Application of MULTIMED to MSWLF Units 147
118
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4.3 COMPOSITE LINER AND LEACHATE COLLECTION SYSTEM
40 CFR §258.40 149
4.3.1 Statement of Regulation 149
4.3.2 Applicability 150
4.3.3 Technical Considerations 150
Standard Composite Liner Systems 150
Soil Liner 151
Thickness 151
Lift Thickness 151
Bonding Between Lifts 152
Placement of Soil Liners on Slopes 152
Hydraulic Conductivity 152
Soil Properties 153
Amended Soils 154
Testing 154
Soil Liner Construction 159
Geomembranes 160
Material Types and Thicknesses 160
Chemical and Physical Stress Resistance 160
Installation 162
Leachate Collection Systems 165
Grading of Low-Permeability Base 166
High-Permeability Drainage Layer 167
Soil Drainage Layers 167
Geosynthetic Drainage Nets 168
Leachate Collection Pipes 171
Protection of Leachate Collection Pipes 173
Protection of the High-Permeability Drainage Layer 178
Soil Filter Layers 178
Geotextile Filter Layers 179
Leachate Removal System 181
Other Design Considerations 182
Construction Quality Assurance and Quality Control 182
COA/COC Objectives 182
Soil Liner Quality Assurance/Quality Control 183
Soil Liner Pilot Construction (Test Fill) 185
Geomembrane Quality Assurance/Quality Control Testing 185
Destructive Testing 185
Non-Destructive Testing 186
Geomembrane Construction Quality Assurance Activities 186
Leachate Collection System Construction Quality Assurance 187
119
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4.4 RELEVANT POINT OF COMPLIANCE 40 CFR §258.40(d) 188
4.4.1 Statement of Regulation 188
4.4.2 Applicability 189
4.4.3 Technical Considerations 189
Site Hydrogeology 189
Leachate Volume and Physical Characteristics 189
Quality. Quantity and Direction of Ground-Water Flow 189
Ground-Water Receptors 190
Alternative Drinking Water Supplies 190
Existing Ground-Water Quality 190
Public Health. Welfare. Safety 190
Practicable Capability of the Owner or Operator 191
4_J PETITION PROCESS 40 CFR §258.40(e^ 191
4.5.1 Statement of Regulation 191
4.5.2 Applicability 191
4A FURTHER INFORMATION 193
4.6.1 REFERENCES (Specific to Performance-Based Design Assessment and Solute
Transport Modeling) 193
4.6.2 REFERENCES (Specific to Design Criteria^ 199
4.6.3 Models 202
120
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CHAPTER 4
SUBPART D
DESIGN CRITERIA
4.1 INTRODUCTION
New MSWLF facilities and lateral expansions of existing units must comply with either a design
standard or a performance standard for landfill design. The Federal Criteria do not require existing
units to be retrofitted with liners. The design standard requires a composite liner composed of two
feet of soil with a hydraulic conductivity of no more than 1 x 10"7 cm/sec, overlain by a flexible
membrane liner (FML) and a leachate collection system. A performance-based design must
demonstrate the capability of maintaining contaminant concentrations below maximum contaminant
levels (MCLs) at the unit's relevant point of compliance. The performance standard has been
established to allow design innovation and consideration of site-specific conditions; approved States
may have adopted alternative design standards. Owners/operators are advised to work closely with
State permitting agencies to determine the applicable design standard. Owners/operators in
unapproved States may use the petition process (§258.40(c)) to allow for use of a performance-
based design. This process is discussed in Section 4.5.
The technical considerations discussed in this chapter are intended to identify the key design features
and system components for the composite liner and leachate collection system standards, and for
the performance standard. The technical considerations include 1) design concepts, 2) design
calculations, 3) physical properties, and 4) construction methods for the following:
1) Designs Based on the Performance Standard
• Leachate characterization and leakage assessment;
• Leachate migration in the subsurface;
• Leachate migration models; and
• Relevant point of compliance assessment.
2) Composite Liners and Leachate Collection Systems
• Soil liner component (soil properties lab testing, design, construction, and quality
assurance/quality control testing);
• Flexible membrane liners (FML properties, design installation, and quality
assurance/quality control testing);
• Leachate collection systems (strength and compatibility, grading and drainage, clogging
potential, and filtration);
121
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Subpart D
• Leachate removal systems (pumps, sumps, and standpipes); and
• Inspections (field observations and field and laboratory testing).
Designs based on the performance standard are described in Section 4.2. Requirements for
composite liners are discussed in Section 4.3. These sections address the minimum regulatory
requirements that should be considered during the design, construction, and operation of MSWLF
units to ensure that they perform in a manner protective of human health and the environment.
Additional features or procedures may be used to demonstrate conformance with the regulations or
to control leachate release and subsequent effects. For example, during construction of a new
MSWLF unit, or a lateral expansion of an existing MSWLF unit, quality control and quality
assurance procedures and documentation may be used to ensure that material properties and
construction methods meet the design specifications that are intended to achieve the expected level
of performance. Section 4.4 presents methods to assess ground-water quality at the relevant point
of compliance for performance-based designs. Section 4.5 describes the applicability of the petition
process for States wishing to petition to use the performance standard.
4.2 PERFORMANCE-BASED DESIGN
40 CFR §258.40(a)(l)
4.2.1 Statement of Regulation
(a) New MSWLF units and lateral
expansions shall be constructed:
(1) In accordance with a design
approved by the Director of an approved
State or as specified in §258.40(e) for
unapproved States. The design must ensure
that the concentration values listed in
Table 1 will not be exceeded in the
uppermost aquifer at the relevant point of
compliance as specified by the Director of
an approved State under paragraph (d) of
this section, or
(2) (See Statement of Regulation in
Section 4.3.1 of this guidance document for
the regulatory language for composite liner
requirements).
(b) (See Statement of Regulation in
Section 4.3.1 of this guidance document for
the regulatory language for requirements
pertaining to composite liner and leachate
collection systems).
(c) When approving a design that
complies with paragraph (a)(l) of this
section, the Director of an approved State
shall consider at least the following factors:
(1) The hydrogeologic characteristics
of the facility and surrounding land;
(2) The climatic factors of the area;
and
(3) The volume and physical and
chemical characteristics of the leachate.
(d) (See Statement of Regulation in
Section 4.4.1 of this guidance document for a
discussion of the determination of the relevant
point of compliance.)
122
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Design Criteria
TABLE 1
(40 CFR 258.40; 56 FR 51022;
October 9, 1991)
Chemical
MCL(mg/l)
Arsenic 0.05
Barium 1.0
Benzene 0.005
Cadmium 0.01
Carbon tetrachloride 0.005
Chromium (hexavalent) 0.05
2,4-Dichlorophenoxy
acetic acid 0.1
1,4-Dichlorobenzene 0.075
1,2-Dichloroethane 0.005
1,1-Dichloroethylene 0.007
Endrin 0.0002
Fluoride 4.0
Lindane 0.004
Lead 0.05
Mercury 0.002
Methoxychlor 0.1
Nitrate 10.0
Selenium 0.01
Silver 0.05
Toxaphene 0.005
l,l?l-Trichloroethane 0.2
Trichloroethylene 0.005
2,4,5-Trichlorophenoxy
acetic acid 0.01
Vinyl Chloride 0.002
4.2.2 Applicability
The Director of an approved State may
approve a performance-based design for new
MSWLF units and lateral expansions of
existing units (see Section 4.3.2), if it meets
the requirements specified in 40 CFR
258.40(a)(l). A performance-based design is
an alternative to the design standard
(composite liner with a leachate collection
system). The composite design is required in
unapproved States; however, if EPA does not
promulgate procedures for State approval by
October 9, 1993, the performance-based
design may be available through the petition
process (see Section 4.5).
4.2.3 Technical Considerations
Demonstration Requirements
For approval of landfill designs not
conforming to the uniform design standard of
a composite liner system and a leachate
collection system (40 CFR §258.40(a)(2)), the
owner or operator of the proposed MSWLF
unit must demonstrate to the Director of an
approved State that the design will not allow
the compounds listed in Table 1 of §258.40 to
exceed the MCLs in ground water at the
relevant point of compliance. The
demonstration should consider an assessment
of leachate quality and quantity, leachate
leakage to the subsurface, and subsurface
transport to the relevant point of compliance.
These factors are governed by site
hydrogeology, waste characteristics, and
climatic conditions.
The nature of the demonstration is essentially
an assessment of the potential for leachate
production and leakage from the landfill to
ground water, and the anticipated fate and
transport of constituents listed in Table 1 to
the proposed relevant point of compliance at
the facility. Inherent in this approach is the
need to evaluate whether contaminants in
ground water at the relevant point of
compliance will exceed the concentration
values listed in Table 1. If so, then the owner
or operator needs to obtain sufficient site-
specific data to adequately characterize the
existing ground-
123
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Subpart D
water quality and the existing ground-water
flow regime (e.g., flow direction, horizontal
and vertical gradients, hydraulic conductivity,
stratigraphy, and aquifer thickness).
An assessment should be made of the effect
MSWLF facility construction will have on
site hydrogeology. The assessment should
focus on the reduced infiltration over the
landfill area and altered surface water run-off
patterns. Reduction of ground-water recharge
and changes in surface water patterns
resulting from landfill construction may affect
ground-water gradients in some cases and
may result in changes in lateral flow
directions. One example of a hypothetical
performance-based demonstration follows.
It is possible that a MSWLF unit located in an
arid climatic zone would not produce leachate
from sources of water (e.g., precipitation)
other than that existing within the waste at the
time of disposal. In such an environment, an
owner or operator may demonstrate that
significant quantities of leachate would not be
produced. The demonstration should be
supported by evaluating historic precipitation
and evaporation data and the likelihood that
the unit could be flooded as the result of
heavy rains, surface run-off, or high water
tables. It may be possible, through
operational controls, to avoid exposing waste
to precipitation or infiltration of water
through overlying materials. If significant
leachate production would not be expected,
the regulatory authority, when reviewing the
demonstration, should consider the
hydrogeologic characteristics of the facility
and the surrounding area, in addition to the
expected volume of leachate and climatic
factors.
Assuming leachate is produced, the
demonstration should evaluate whether
constituents listed in Table 1 can be expected
to be present at concentrations greater than the
MCLs. If such a demonstration is possible, it
must address the hydrogeologic characteristics
of the facility and the surrounding land to
comply with §258.40(d). The following
sections describe the various parts of a
demonstration in greater detail.
Leachate Characterization
Leachate characterization should include an
assessment and demonstration of the quantity
and composition of leachate anticipated at the
proposed facility. Discussion of this
assessment follows.
Estimates of volumetric production rates of
leachate are important in evaluating the fate
and transport of the constituents listed in
Table 1. Leachate production rates depend on
rainfall, run-on, run-off, evapotranspiration,
water table elevation relative to the bottom of
the landfill unit, in-place moisture content of
waste, and the prevention of liquid disposal at
the site. Run-on, run-off, and water table
factors can be managed traditionally through
design and operational controls. The MSWLF
Criteria prohibit bulk or containerized liquid
disposal. Incident precipitation and
evapotranspiration can be evaluated using
models (e.g., HELP) or other methods of
estimating site-specific leachate production
(e.g., local historical meteorologic data).
If leachate composition data that are
representative of the proposed facility are not
available, then leachate data with a similar
expected composition should be presented.
Landfill leachate composition is influenced
by:
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Design Criteria
(1) The annual infiltration of precipitation
and rate of leaching;
(2) The type and relative amounts of
materials in the waste stream; and
(3) The age and the biological maturity of
the landfill unit, which may affect the
types of organic and inorganic acids
generated, oxidation/reduction potential
(Eh), and pH conditions.
An existing landfill unit in the same region,
with similar waste stream characteristics, may
provide information that will allow the owner
or operator to anticipate leachate composition
of the proposed landfill unit. A review of
existing literature also may be required to
assess anticipated leachate composition if
actual data are unavailable (see U.S. EPA,
1987b). A wide range of leachate
concentrations are reported in the literature
with higher concentrations of specific
constituents typically reported for the initial
leachate from laboratory or field experimental
test fills or test cells. These "batch" one-day
landfill tests do not account for the long-term
climatic and meteorological influences on a
full-scale landfill operation. Such high initial
concentrations are not typical of full-scale
operations (which are subject to the dilution
effects of incidental rainfall on unused
portions of the unit).
Assessment of Leakage Through Liners
An assessment of leakage (the volumetric
release of leachate from the proposed
performance-based design) should be based
on analytical approaches supported by
empirical data from other existing operational
facilities of similar design, particularly those
that have leak detection monitoring systems
(see U.S. EPA, 1990b).
In lieu of the existence or availability of such
information, conservative analytical
assumptions may be used to estimate
anticipated leakage rates.
The transport of fluids and waste constituents
through geomembranes differs in principle
from transport through soil liner materials.
The dominant mode of leachate transport
through liner components is flow through
holes and penetrations of the geomembrane,
and Darcian flow through soil components.
Transport through geomembranes where tears,
punctures, imperfections, or seam failures are
not involved is dominated by molecular
diffusion. Diffusion occurs in response to a
concentration gradient and is governed by
Pick's first law. Diffusion rates through
geomembranes are very low in comparison to
hydraulic flow rates in soil liners, including
compacted clays. For synthetic liners, the
most significant factor influencing liner
performance is penetration of the liner,
including imperfect seams or pinholes caused
by construction defects in the geomembrane
(U.S. EPA, 1989).
A relatively new product now being used in
liner systems is the geosynthetic clay liner
(GCL). GCLs consist of a layer of pure
bentonite clay backed by one or two
geotextiles. GCLs exhibit properties of both
soil liners and geomembranes, and have
successfully substituted for the soil
component in composite liner designs. GCLs
are believed to transport fluids primarily
through diffusion according to their low
hydraulic conductivities (i.e., 1 x 10"9 cm/sec
reported by manufacturers). Applications for
GCLs are discussed further in the sections that
follow.
Several researchers have studied the flow of
fluids through imperfections in single
125
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Subpart D
geomembrane and composite liner systems.
Further discussion of liner leakage rates can
be found in Section 4.3.3 below. For
empirical data and analytical methods the
reader is referred to Jayawickrama et al.
(1988), Kastman (1984), Haxo (1983), Haxo
et al. (1984), Radian (1987), Giroud and
Bonaparte (1989, Parts I and II), and Giroud
et al. (1989). Leakage assessments also may
be conducted with the use of the HELP model
(U.S. EPA, 1988). Version 3.0 of the model
is under revision and will include an updated
method to assess leakage that is based on
recent research and data compiled by Giroud
and Bonaparte.
Leachate Migration in the Subsurface
Leachate that escapes from a landfill unit may
migrate through the unsaturated zone and
eventually reach the uppermost aquifer. In
some instances, however, the water table may
be located above the base of the landfill unit,
so that only saturated flow and transport from
the landfill unit need to be considered. Once
leachate reaches the water table, contaminants
may be transported through the saturated zone
to a point of discharge (i.e., a pumping well,
a stream, a lake, etc.).
The migration of leachate in the subsurface
depends on factors such as the volume of the
liquid component of the waste, the chemical
and physical properties of the leachate
constituents, the loading rate, climate, and the
chemical and physical properties of the
subsurface (saturated and unsaturated zones).
A number of physical, chemical, and
biological processes also may influence
migration. Complex interactions between
these processes may result in specific
contaminants being transported through the
subsurface at different rates. Certain
processes result in the attenuation and
degradation of contaminants. The degree of
attenuation is dependent on the time that the
contaminant is in contact with the subsurface
material, the physical and chemical
characteristics of the subsurface material, the
distance that the contaminant has traveled,
and the volume and characteristics of the
leachate. Some of the key processes affecting
leachate migration are discussed briefly here.
The information is based on a summary in
Travers and Sharp-Hansen (1991), who in
turn relied largely on Aller et al. (1987),
Keely (1987), Keely (1989), Lu et al. (1985),
and U.S. EPA(1988a).
Physical Processes Controlling
Contaminant Transport in the Subsurface
Physical processes that control the transport of
contaminants in the subsurface include
advection, mixing and dilution as a result of
dispersion and diffusion, mechanical
filtration, physical sorption, multi-phase fluid
flow, and fracture flow. These processes, in
turn, are affected by hydrogeologic
characteristics, such as hydraulic conductivity
and porosity, and by chemical processes.
Advection is the process by which solute
contaminants are transported by the overall
motion of flowing ground water. A non-
reactive solute will be transported at the same
rate and in the same direction as ground water
flow (Freeze and Cherry, 1979). Advective
transport is chiefly a function of the
subsurface hydraulic conductivity distribution,
porosity, and hydraulic gradients.
Hydrodynamic dispersion is a non-steady,
irreversible mixing process by which a
contaminant plume spreads as it is transported
through the subsurface. Dispersion results
from the effects of two
126
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Design Criteria
components operating at the microscopic
level: mechanical dispersion and molecular
diffusion. Mechanical dispersion results from
variations in pore velocities within the soil or
aquifer and may be more significant than
molecular diffusion in environments where
the flow rates are moderate to high.
Molecular diffusion occurs as a result of
contaminant concentration gradients;
chemicals move from high concentrations to
low concentrations. At very slow ground-
water velocities, as occur in clays and silts,
diffusion can be an important transport
mechanism.
Mechanical filtration removes from ground
water contaminants that are larger than the
pore spaces of the soil. Thus, the effects of
mechanical filtration increase with decreasing
pore size within a medium. Filtration occurs
over a wide range of particle sizes. The
retention of larger particles may effectively
reduce the permeability of the soil or aquifer.
Physical sorption is a function of Van der
Waals forces, and the hydrodynamic and
electrokinetic properties of soil particles.
Sorption is the process by which contaminants
are removed from solution in ground water
and adhere or cling to a solid surface. The
distribution of a contaminant between the
solution and the solid phase is called
partitioning.
Multiphase fluid flow occurs because many
solvents and oils are highly insoluble in water
and may migrate in the subsurface as a
separate liquid phase. If the viscosity and
density of a fluid differ from that of water, the
fluid may flow at a different rate and direction
than the ground water. If the fluid is more
dense than water it may reach the bottom of
the aquifer (top of an aquitard)
and alter its flow direction to conform to the
shape and slope of the aquitard surface.
Hydraulic conductivity is a measure of the
ability of geologic media to transmit fluids
(USGS, 1987). It is a function of the size and
arrangement of water-transmitting openings
(pores and fractures) in the media and of the
characteristics of the fluids (density, viscosity,
etc.). Spatial variations in hydraulic
conductivity are referred to as heterogeneities.
A variation in hydraulic conductivity with the
direction of measurement is referred to as
anisotropy.
Variable hydraulic conductivity of the
geologic formation may cause ground-water
flow velocities to vary spatially. Variations in
the rate of advection may result in non-
uniform plume spreading. The changes in
aquifer properties that lead to this variability
in hydraulic conductivity may be three-
dimensional. If the geologic medium is
relatively homogeneous, it may be
appropriate, in some instances, to assume that
the aquifer properties also are homogeneous.
Secondary porosity in rock may be caused by
the dissolution of rock or by regional
fracturing; in soils, secondary porosity may be
caused by desiccation cracks or fissures.
Fractures or macropores respond quickly to
rainfall events and other fluid inputs and can
transmit water rapidly along unexpected
pathways. Secondary porosity can result in
localized high concentrations of contaminants
at significant distances from the facility. The
relative importance of secondary porosity to
hydraulic conductivity of the subsurface
depends on the ratio of fracture hydraulic
conductivity to intergranular hydraulic
conductivity (Kincaid et al., 1984a). For
scenarios in which fracture flow is dominant,
the relationships
127
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Subpart D
used to describe porous flow (Darcy's Law)
do not apply.
Chemical Processes Controlling
Contaminant Transport in the Subsurface
Chemical processes that are important in
controlling subsurface transport include
precipitation/dissolution, chemical sorption,
redox reactions, hydrolysis, ion exchange, and
complexation. In general, these processes,
except for hydrolysis, are reversible. The
reversible processes tend to retard transport,
but do not permanently remove a contaminant
from the system. Sorption and precipitation
are generally the dominant mechanisms
retarding contaminant transport in the
saturated zone.
Precipitation/dissolution reactions can control
contaminant concentration levels. The
solubility of a solid controls the equilibrium
state of a chemical. When the soluble
concentration of a contaminant in leachate is
higher than that of the equilibrium state,
precipitation occurs. When the soluble
concentration is lower than the equilibrium
value, the contaminant exists in solution. The
precipitation of a dissolved substance may be
initiated by changes in pressure, temperature,
pH, concentration, or redox potential (Aller et
al., 1987). Precipitation of contaminants in
the pore space of an aquifer can decrease
aquifer porosity. Precipitation and dissolution
reactions are especially important processes
for trace metal migration in soils.
Chemical adsorption/desorption is the most
common mechanism affecting contaminant
migration in soils. Solutes become attached
to the solid phase by means of adsorption.
Like precipitation/dissolution,
adsorption/desorption is a reversible process.
However, adsorption/desorption
generally occurs at a relatively rapid rate
compared to precipitation reactions.
The dominant mechanism of organic sorption
is the hydrophobic attraction between a
chemical and natural organic matter that exists
in some aquifers. The organic carbon content
of the porous medium, and the solubility of
the contaminant, are important factors for this
type of sorption.
There is a direct relationship between the
quantity of a substance sorbed on a particle
surface and the quantity of the substance
suspended in solution. Predictions about the
sorption of contaminants often make use of
sorption isotherms, which relate the amount of
contaminant in solution to the amount
adsorbed to the solids. For organic
contaminants, these isotherms are usually
assumed to be linear and the reaction is
assumed to be instantaneous and reversible.
The linear equilibrium approach to sorption
may not be adequate for all situations.
Oxidation and reduction (redox) reactions
involve the transfer of electrons and occur
when the redox potential in leachate is
different from that of the soil or aquifer
environment. Redox reactions are important
processes for inorganic compounds and
metallic elements. Together with pH, redox
reactions affect the solubility, complexing
capacity, and sorptive behavior of
constituents, and thus control the presence and
mobility of many substances in water.
Microorganisms are responsible for a large
proportion of redox reactions that occur in
ground water. The redox state of an aquifer,
and the identity and quantity of redox-active
reactants, are difficult to determine.
128
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Design Criteria
Hydrolysis is the chemical breakdown of
carbon bonds in organic substances by water
and its ionic species H+ and OH". Hydrolysis
is dependent on pH and Eh and is most
significant at high temperatures, low pH, and
low redox potential. For many biodegradable
contaminants, hydrolysis is slow compared to
biodegradation.
Ion exchange originates primarily from
exchange sites on layered silicate clays and
organic matter that have a permanent negative
charge. Cation exchange balances negative
charges in order to maintain neutrality. The
capacity of soils to exchange cations is called
the cation exchange capacity (CEC). CEC is
affected by the type and quantity of clay
mineral present, the amount of organic matter
present, and the pH of the soil. Major cations
in leachate (Ca, Mg, K, Na) usually dominate
the CEC sites, resulting in little attenuation in
soils of trace metals in the leachate.
A smaller ion exchange effect for anions is
associated with hydrous oxides. Soils
typically have more negatively charged clay
particles than positively charged hydrous
oxides. Therefore, the transport of cations is
attenuated more than the transport of anions.
Complexation involves reactions of metal ions
with inorganic anions or organic ligands. The
metal and the ligand bind together to form a
new soluble species called a complex.
Complexation can either increase the
concentration of a constituent in solution by
forming soluble complex ions or decrease the
concentration by forming a soluble ion
complex with a solid. It is often difficult to
distinguish among sorption, solid-liquid
Complexation, and ion exchange.
Therefore, these processes are usually
grouped together as one mechanism.
Biological Processes Controlling
Contaminant Transport in the Subsurface
Biodegradation of contaminants may result
from the enzyme-catalyzed transformation of
organic compounds by microbes.
Contaminants can be degraded to harmless
byproducts or to more mobile and/or toxic
products through one or more of several
biological processes. Biodegradation of a
compound depends on environmental factors
such as redox potential, dissolved oxygen
concentration, pH, temperature, presence of
other compounds and nutrients, salinity, depth
below land surface, competition among
different types of organisms, and
concentrations of compounds and organisms.
The transformations that occur in a subsurface
system are difficult to predict because of the
complexity of the chemical and biological
reactions that may occur. Quantitative
predictions of the fate of biologically reactive
substances are subject to a high degree of
uncertainty, in part, because little information
is available on biodegradation rates in soil
systems or ground water. First-order decay
constants are often used instead.
The operation of Subtitle D facilities can
introduce bacteria and viruses into the
subsurface. The fate and transport of bacteria
and viruses in the subsurface is an important
consideration in the evaluation of the effects
of MSWLF units on human health and the
environment. A large number of biological,
chemical, and physical processes are known to
influence virus and bacterial survival and
transport in the subsurface. Unfortunately,
knowledge of the processes and the available
data are insufficient to develop models that
can
129
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Subpart D
simulate a wide variety of site-specific
conditions.
Leachate Migration Models
After reviewing the hydrogeologic
characteristics of the site, the nature of liner
leakage, and the leachate characteristics, it
may be appropriate to use a mathematical
model to simulate the expected fate and
transport of the constituents listed in Table 1
to the relevant point of compliance. Solute
transport and ground-water modeling efforts
should be conducted by a qualified ground-
water scientist (see Section 5.5). It is
necessary to consider several factors when
selecting and applying a model to a site.
Travers and Sharp-Hansen (1991) provide a
thorough review of these issues. The text
provided below is a summary of their review.
Overview of the Modeling Process
A number of factors can influence leachate
migration from MSWLF units. These
include, but are not limited to, climatic
effects, the hydrogeologic setting, and the
nature of the disposed waste. Each facility is
different, and no one generic model will be
appropriate in all situations. To develop a
model for a site, the modeling needs and the
objectives of the study should be determined
first. Next, it will be necessary to collect data
to characterize the hydrological, geological,
chemical, and biological conditions of the
system. These data are used to assist in the
development of a conceptual model of the
system, including spatial and temporal
characteristics and boundary conditions. The
conceptual model and data are then used to
select a mathematical model that accurately
represents the conceptual model. The model
selected should have been tested and
evaluated by qualified investigators, should
adequately simulate the significant processes
present in the actual system, and should be
consistent with the complexity of the study
area, amount of available data, and objectives
of the study.
First, an evaluation of the need for modeling
should be made (Figure 4-1). When selecting
a model to evaluate the potential for soil and
ground-water contamination (Boutwell et al.,
1986), three basic determinations must be
made (Figure 4-2). Not all studies require the
use of a mathematical model. This decision
should be made at the beginning of the study,
since modeling may require a substantial
amount of resources and effort. Next, the
level of model complexity required for a
specific study should be determined (Figure
4-3). Boutwell et al. (1986) classify models
as Level I (simple/analytical) and Level II
(complex/numerical) models. A flowchart for
determining the level of model complexity
required is shown in Figure 4-3. Finally, the
model capabilities necessary to represent a
particular system should be considered
(Figure 4-4). Several models may be equally
suitable for a particular study. In some cases,
it may be necessary to link or couple two or
more computer models to accurately represent
the processes at the site. In the section that
follows, specific issues that should be
considered when developing a scenario and
selecting a model are described.
Models are a simplified representation of the
real system, and as such, cannot fully
reproduce or predict all site characteristics.
Errors are introduced as a result of: 1)
simplifying assumptions; 2) a lack of data; 3)
uncertainty in existing data; 4) a poor
understanding of the processes influencing the
fate and transport of contaminants; and
130
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Model Selection is
Not Required
Is Modeling
Necessary?
(See Figure
4.10)
What
Level of
Modeling is
Required?
(See Figure
4.10)
Complex/Numerical
Complex/Numerical
What are
the Required
Level II Model
Capabilities?
(See Figure
4-12)
What are
the Required
Level I Model
Capabilities?
(See Figure
4-12)
Figure 4-1
Three Basic Decisions in Model Selection
(Boutwell et. al., 1986)
131
-------
Develop Conceptual
Understanding of Site
Can
Assumptions
be Confirmed
with Existing
Data?
Will
Additional
Data Improve
Understanding?
Do
You Need
Quantitative
Estimates of
Future
Conditions?
Specify
Sampling
Requirements
Determine Level
of Modeling
Required
Figure 4-2
Flow Chart to Determine if Modeling is Required
(Boutwell et. al., 1986)
132
-------
Level of Modeling Required 1
r i
Level 1: Analytical Models 1 Level II: Numerical Models 1
j j
Identification of Remedial 1 Model Selection Criteria 1
Action-Specific Models I I
\
|
1 1 1 1
• r^- • r.. 1 Time I Resources/ I
Processes I Dimensionality I c 1 Data 1
*
Model Selection 1 Model Selection 1
Figure 4-3
Flow Chart to Determine the Level of Modeling Required for
Soil and Groundwater Systems
(Boutwell et. al., 1986)
133
-------
Are
OitJer of
Magnitude
Predictions
Acceptable
Reassess Goals
and Data Needs
is Ft
Reasonable
to Assume mat
Media Properties
are Uniform, and
Do Not Vary
is it
Reasonable
to Assume that
tr>e Ro* Fiatg
Uniform. Steady
and Regular''
IS it
Reasonabto
to Assume that
the 5» Geometry
is Regular
Are (ne
Selected
Remed4aj Actions
Reiatrveiy S«mpie in
ConAgurason'
Does
me PoUutant Have
ReBBvsty the Same
Density as
Water?
Do You Have Sufficient
Resources and Available
Data tor Numerical Models?
Use Level!: Anarylical Model
Use Level II: Numencal Model
Figure 4-4
Flow Chart for Required Model Capabilities for Soil and Groundwater Systems
(Boutwell et. al., 1986)
134
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Design Criteria
5) limitations of the model itself. Therefore,
model results should be interpreted as
estimates of ground-water flow and
contaminant transport. Bond and Hwang
(1988) recommend that models be used for
comparing various scenarios, since all
scenarios would be subject to the same
limitations and simplifications.
The quality of model results can depend to a
large extent on the experience and judgement
of the modeler, and on the quality of the data
used to develop model input. The process of
applying the model may highlight data
deficiencies that may require additional data
collection. The model results should be
calibrated to obtain the best fit to the observed
data. The accuracy of the results obtained
from modeling efforts should then be
validated. Model validation, which is the
comparison of model results with
experimental data or environmental data, is a
critical aspect of model application, and is
particularly important for site-specific
evaluations.
Several recent reports present detailed
discussions of the issues associated with
model selection, application, and validation.
Donigian and Rao (1990) address each of
these issues, and present several options for
developing a framework for model validation.
EPA's Exposure Assessment Group has
developed suggested recommendations and
guidance on model validation (Versar Inc.,
1987). A recent report by the National
Research Council (1990) discusses the issues
related to model application and validation,
and provides recommendations for the proper
use of ground-water models. Weaver et al.
(1989) discuss options for selection and field
validation of mathematical models.
Model Selection
Ground-water flow and solute transport
models range from simple, analytical
calculations to sophisticated computer
programs that use numerical solutions to solve
mathematical equations describing flow and
transport. A sophisticated model may not
yield an exact estimate of water quality at the
relevant point of compliance for a given set of
site conditions, but it may allow an estimate
of the effects of complex physical and
chemical processes. Depending on the
complexity of site conditions and the
appropriateness of the simplifying
assumptions, a fairly sophisticated numerical
model may provide useful estimates of water
quality at the relevant point of compliance.
The following considerations should be
addressed when selecting a model.
Analytical Versus Numerical Models
Mathematical models use either analytical,
semi-analytical, or numerical solutions for
ground-water flow and transport equations.
Each technique has advantages and
disadvantages. Analytical solutions are
computationally more efficient than numerical
simulations and are more conducive to
uncertainty analysis (i.e., Monte Carlo
techniques). Typically, input data for
analytical models are simple and do not
require detailed familiarity with the computer
model or extensive modeling experience.
Analytical solutions are typically used when
data necessary for characterization of the site
are sparse and simplifying assumptions are
appropriate (Javandel et al., 1984). The
limited data available in most field situations
may not justify the use of a detailed numerical
model; in some cases, results from simple
analytical models may be appropriate
135
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Subpart D
(Huyakorn et al., 1986). Analytical models
require simplifying assumptions about the
system. Therefore, complex interactions
involving several fate and transport processes
cannot be addressed in detail. Analytical
models generally require a limited number of
parameters that are often assumed to be
constant in space and time (van der Heijde
andBeljin, 1988).
Semi-analytical models approximate complex
analytical solutions using numerical
techniques (van der Heijde and Beljin, 1988).
Semi-analytical methods allow for more
complex site conditions than those that can be
simulated with a purely analytical solution.
Semi-analytical solution methods can consider
multiple sources or recharging and
discharging wells. However, they still require
simplifying assumptions about the
dimensionality and homogeneity of the
system.
Numerical models are able to evaluate more
complex site conditions than either analytical
or semi-analytical models. Numerical models
provide the user with a large amount of
flexibility; irregular boundaries and spatial
and temporal variations in the system can be
considered. Numerical models require
significantly more data than analytical
models, and are typically more
computationally intensive. Use of a
numerical model requires an experienced
modeler, and can involve a larger amount of
computer time than simulations using an
analytical or semi-analytical method.
To select an appropriate model, the
complexity of the site hydrology and the
availability of data should be considered. If
data are insufficient, a highly sophisticated
and complex model should not be used. In
some situations, it is beneficial to use an
analytical or semi-analytical model as a
"screening level" model to define the range of
possible values, and to use a numerical model
when there are sufficient data.
A highly complex hydrogeologic system
cannot be accurately represented with a
simple analytical model. Heterogeneous or
anisotropic aquifer properties, multiple
aquifers, and complicated boundary
conditions can be simulated using numerical
models. In addition, sophisticated numerical
models are available that can simulate
processes such as fracture flow. Because each
site is unique, the modeler should determine
which conditions and processes are important
at a specific site, and then select a suitable
model.
Spatial Characteristics of the System
Although actual landfill units and
hydrogeologic systems are three-dimensional,
it is often desirable to reduce the number of
dimensions simulated in a mathematical
model to one or two. Two- and three-
dimensional models are generally more
complex and computationally expensive than
one-dimensional models, and therefore
require more data. In some instances, a one-
dimensional model may adequately represent
the system; the available data may not warrant
the use of a multi-dimensional model.
However, modeling a truly three-dimensional
system using a two-dimensional model may
produce results without adequate spatial
detail. The choice of the number of
dimensions in the model should be made for
a specific site, based on the complexity of the
site and the availability of data.
Steady-State Versus Transient Models
Models can simulate either steady-state or
transient flow conditions. It may be
136
-------
Design Criteria
appropriate to assume that some ground-water
flow systems have reached approximate
"steady-state" conditions, which implies that
the system has reached equilibrium and no
significant changes are occurring over time.
The assumption of steady-state conditions
generally simplifies the mathematical
equations used to describe flow processes, and
reduces the amount of input data required.
However, assuming steady-state conditions in
a system that exhibits transient behavior may
produce inaccurate results. For example,
climatic variables, such as precipitation, vary
over time and may have strong seasonal
components. In such settings, the assumption
of constant recharge of the ground-water
system would be incorrect. Steady-state
models also may not be appropriate for
evaluating the transport of chemicals which
sorb or transform significantly (Mulkey et al.,
1989). The choice of simulating steady-state
or transient conditions should be based on the
degree of temporal variability in the system.
Boundary and Initial Conditions
The solution of differential equations
describing flow and transport processes
requires that initial and boundary conditions
be specified. The initial conditions describe
the conditions present in the system at the
beginning of the simulation. In many ground-
water flow and transport models, these
conditions are related to the initial hydraulic
conditions in the aquifer and the initial
concentration of contaminants. Boundary
conditions define the conditions present on the
borders of the system, which may be steady-
state or temporally variable. The initial and
boundary conditions chosen to represent a site
can significantly affect the results of the
simulation.
One of the most significant boundary
conditions in solute transport models is the
introduction of a contaminant to the system.
A source of ground-water contamination
should be described in terms of its spatial,
chemical, and physical characteristics, and its
temporal behavior. Spatially, a source may be
classified as a point source, line source, a
distributed source of limited areal or three-
dimensional extent, or as a non-point source
of unlimited extent (van der Hjeide et al.,
1988). Typically, temporal descriptions of the
source term boundary conditions for models
with analytical solutions are constant, constant
pulse, and/or exponential decay (Mulkey et
al., 1989). Numerical models typically handle
a much wider range of source boundary
conditions, allowing for a wide range of
contaminant loading scenarios.
Homogeneous Versus
Aquifer/Soil Properties
Heterogeneous
The extent of the spatial variability of the
properties of each aquifer will significantly
affect the selection of a mathematical model.
Many models assume uniform aquifer
properties, which simplifies the governing
equations and improves computational
efficiency. For example, a constant value of
hydraulic conductivity may be assumed at
every point in the aquifer. However, this
assumption may ignore the heterogeneity in
the hydrogeologic system. Bond and Hwang
(1988) present guidelines for determining
whether the assumption of uniform aquifer
properties is justified at a particular site.
They state that the error associated with using
an average value versus a spatial distribution
is site-specific and extremely difficult to
determine.
When site-specific data are limited, it is
common to assume homogeneous and
137
-------
Subpart D
isotropic aquifer properties, and to develop a
"reasonable worst-case" scenario for
contaminant migration in the subsurface.
However, as Auerbach (1984) points out, the
assumption of homogeneous and isotropic
aquifers often will not provide a "worst-case"
scenario. For example, a continuous zone of
higher hydraulic conductivity in the direction
of ground-water flow can result in much
higher rates of contaminant movement than
would be predicted in a completely
homogeneous aquifer. To develop a true
"worst-case" model, information on the
probable heterogeneity and anisotropy of the
site should be collected.
The number of aquifers in the hydrogeologic
system also will affect the selection of a
mathematical model. Some systems include
only a single unconfmed or confined aquifer,
which is hydraulically isolated from the
surrounding layers. Some mathematical
models, and in particular those with analytical
solutions, can simulate only single layers. In
other cases, the upper aquifer may be
hydraulically connected to underlying
aquifers. The MSWLF Criteria specify that
MCLs not be exceeded at the relevant point of
compliance within the uppermost aquifer.
The uppermost aquifer includes not only the
aquifer that is nearest the ground surface, but
also all lower aquifers that are hydraulically
connected to the uppermost aquifer within the
vicinity of the facility.
Availability of Data
Although computer models can be used to
make predictions about leachate generation
and migration, these predictions are highly
dependent on the quantity and quality of the
available data. One of the most common
limitations to modeling is insufficient data.
Uncertainty in model predictions results from
the inability to characterize a site in terms of
the boundary conditions or the key parameters
describing the significant flow and transport
processes (National Research Council, 1990).
The application of a mathematical model to a
site typically requires a large amount of data.
Inexperienced modelers may attempt to apply
a model with insufficient data and, as a result,
produce model results that are inconclusive.
To obtain accurate model results, it is
essential to use data that are appropriate for
the particular site being modeled. Models that
include generic parameters, based on average
values for similar sites, can be used to provide
initial guidance and general information about
the behavior of a system, but it is
inappropriate to apply generic parameters to a
specific hydrogeologic system. An excellent
summary of the data required to model
saturated and unsaturated flow, surface water
flow, and solute transport is presented in
Mercer et al. (1983). This report provides
definitions and possible ranges of values for
source terms, dependent variables, boundary
conditions, and initial conditions.
Summary of Available Models
Several detailed reviews of ground-water
models are available in the literature. A
number of ground-water models, including
saturated flow, solute transport, heat transport,
fracture flow, and multiphase flow models,
are summarized in van der Heijde et al.
(1988). A report by van der Heijde and Beljin
(1988) provides detailed descriptions of 64
ground-water flow and solute transport
models that were selected for use in
determining wellhead protection areas. A
review of ground-water flow and
138
-------
Design Criteria
transport models for the unsaturated zone is
presented in Oster (1982). A large number of
ground-water flow and transport models are
summarized by Bond and Hwang (1988).
Finally, Travers and Sharp-Hansen (1991)
summarize models that may be applicable to
problems of leachate generation and migration
from MSWLF units. (See References
supplied in Section 4.6.)
Table 4-1 (adapted from Travers and Sharp-
Hansen (1991)) provides information on
select leachate generation models. Tables 4-
la, b, and c list some of the available models
that can be used to predict contaminant
transport. The factors used to select these
models include availability, documentation,
uniqueness, and the size of the user
community. These models are categorized by
the techniques used to solve flow and
transport equations. Table 4-la lists
analytical and semi-analytical models, and
Tables 4-lb and 4-lc list numerical models
that are solved by the finite-difference and the
finite-element method, respectively.
The types of models that are available for
application to the evaluation of MSWLF
designs include leachate generation models
and saturated and unsaturated zone flow and
transport models. The level of sophistication
of each of these types of models is based on
the complexity of the processes being
modeled. The majority of the models
consider flow and transport based on
advection dispersion equations. More
complex models consider physical and
chemical transformation processes, fracture
flow, and multiphase fluid flow.
Leachate generation models predict the
quantity and characteristics of leachate that is
released from the bottom of a landfill. These
models are used to estimate
contaminant source terms and the releases of
contaminants to the subsurface. Flow and
transport models simulate the transport of
contaminants released from the source to the
unsaturated and saturated zones.
Geochemical models are available that
consider chemical processes that may be
active in the subsurface such as adsorption,
precipitation, oxidation/reduction, aqueous
speciation, and kinetics.
Complex flow models have been developed to
simulate the effects of nearby pumping and
discharging wells, fracture flow, conduit flow
in karst terrane, and multiphase flow for fluids
that are less dense or more dense than water.
However, the use of the more complex
models requires additional data based on a
thorough investigation of the subsurface
characteristics at a site as well as well-trained
users to apply the model correctly.
Most of the ground-water flow and solute
transport models are deterministic. However,
the use of stochastic models, which allow for
characterization of spatial and temporal
variability in systems, is increasing. A few of
the models include a Monte Carlo capability
for addressing the uncertainty inherent in the
input parameters.
The EPA Multimedia Exposure
Assessment Model (MULTIMED)
EPA has developed a modeling package to
meet the needs of a large percentage of
MSWLF unit owners and operators who will
require fate and transport modeling as part of
the performance-based design demonstration.
This model, the Multimedia Exposure
Assessment Model (MULTIMED), is
intended for use at sites where certain
simplifying assumptions can be made.
MULTIMED can be used in
139
-------
Table 4-1. Models for Application to Leachate Generation Problems (adapted from Travers and Sharp-Hansen, 1991)
Model
Reference
Bonazountas
and Wagner
(1984);
SESOIL
Carsel et al.
(1984) PRZM
EPRI (1981)
UNSAT1D
Knisel et al.
(1989)
GLEAMS
Schroeder et
al. (1984)
HELP
Model Flow Aquifer
Dimensions Conditions Conditions
1D/FD Ss.Unsat L,Hom,Iso
9
1D/FD Usat.Ss.Tr L.Hom.Iso
1D/FD Sat.Usat, Het.Hom.L
Ss.Tr Iso
1D/FD Usat.Tr.Ss Hom.Iso.L
quasi-2D FD Tr.Sat.Usat L.Homo,
Iso
Model
Processes
Ppt.Inf,
RO.ET,
Adv.Dif,
Ads.Vol,
Dec
Adv.Dis,
Dif.Dec,
Rxn.ET,
Vol.Inf
Ppt.Inf,
RO.ET
Inf.Dec.R
O.ET.Ads
ET.Ppt.In
f.Dra.RO
Chemical Additional Information
Species
single Seasonal Soil Compartment Model. Simulates transport of
water, sediment, and contaminants in soils. Includes affects of
capillary rise, biological transformation, hydrolysis, cation
exchange, complexation chemistry (metals by organic ligands).
Hydrology based on generalized annual water balance
dynamics model.
1 ,2, or 3 Pesticide Root £one M_odel. Also includes plant uptake,
leaching, runoff, management practices, and foliar washoff.
Hydrologic flow solved by water routing scheme, chemical
transport solved by finite difference scheme. Requires
meteorological data. Water balance model.
flow only Solves one-dimensional Richard's equation. Accounts for
capillary and gravitational effects. Requires landfill design
data.
single Groundwater Loading Effects of Agricultural Systems model.
Developed by modifying CREAMS (Knisel, 1980) to add
capability to estimate groundwater loadings. Simulates
erosion. Water balance computations.
flow only A quasi-two-dimensional, deterministic water budget for
landfills. Requires landfill design data. Model may be applied
to open, partially open, and closed landfills. Requires
meteorological data.
ID = One-dimensional Sat
2D = Two-dimensional Usat
3D = Three-dimensional Horn
H = Horizontal Het
V = Vertical Iso
Ss = Steady-State An
Tr = Transient C
Saturated Uc
Unsaturated Adv
Homogeneous Dis
Heterogeneous Dif
Isotropic Dec
Anisotropic Ads
Confined Aquifer Ret
Unconfined aquifer In
Advection ET
Decay Ppt
Diffusion RO
Decay Run
Adsorption W
Retardation L
Infiltration
Evapotranspiration
Precipitation
Runoff
Reaction
Discharge or pumping wells
Layers
-------
Table 4-la. Analytical and Semi-Analytical Models for Application to Leachate Migration Problems
(adapted from Travers and Sharp-Hansen, 1991)
Model Model Flow Aquifer Model Chemical
Reference Dimensions Conditions Conditions Processes Species
Additional Information
Bcljin (1983) ID(H), 2D(H) Ss, Sat
SOLUTE or 3D
C, Horn, Iso Adv, Dis, Ads, single
Dec
A package of 8 analytical models for solute transport
in groundwater. Also includes a program lor unit
conversion and error and function calculation.
Domcnicoand IDadvection Ss, Sal
Palciauakcs 2D dispcrsioh
(1982) VMS
C, Horn, Iso Adv, Dis
single
Model for Vertical and Horizontal Spreading.
Assumes infinite aquifer thickness. EPA considers
VHS to he a conservative model since retardation,
sorptions, precipitation, aquifer recharge not
considered. Source is continuous constant strip source.
Domenico and 3D (transport) Ss, Sat C, Horn, Iso Adv, Dis single
Rohbms
(1985)
Huyaknm el 3D Ss, Sal C, Uc, Horn, Adv, Dis, Ads, single
;U. (1987) Iso, An Dec
Conlaminanl transport from a finite or continuous
source in a continuous flow regimen. Assumes infinilc
thickness.
Model allows for estimation of maximum
concentration distribution along center line of a
leachate plume. Gaussian vertical strip source.
Javandcl ct 2D(H)
al. (1984)
RESSQ
Lindstrom 1D(H)
and Bocrams
(1989)
CXPHPH
Ss, Sat C, Horn, Iso Adv, Ads single
Ss, Sat C, Horn, Iso Adv, Dis, Dec, single
Ads, Rxn
Calculate transport by advcclion and adsorption in a
homogeneous, isotropic, uniform-thickness, confined
aquifer. Uses semi-analytical solution methods.
Analytical solutions of the general one-dimensional
transport equation for confined aquifers, will) several
differenl initial and boundary conditions.
Nelson and 2D(H)
Schur(1983)
PATHS
Ss, Tr, Sat C, Horn, Iso Adv, Ads single
Groundwater How equations solved analytically,
characteristic pathlines solved by Ruage-Kulls method.
Ostcndorf cl ID(H.V) Ss, Sat Uc, Horn, Iso Adv, Ads, Dec single
al. (1984)
Assumes transport of a simply reactive contaminant
through a landfill and initially pure, underlying,
shallow, aquifer with plane, sloping bottom.
Prakash ID, 2D or 3D Ss, Sat C, Horn, Iso Adv, Dis, Ads, single
(1984) I**
Source boundary condition: instantaneous or finite-lime
release of contaminants from a point, line, plane, or
parallel piped source.
-------
Table 4-la. Analytical and Semi-Analytical Models for Application to Leachate Migration Problems
(adapted from Travers and Sharp-Hansen, 1991) (continued)
Model
Reference
Model
Dimensions
Salhotrc el lD(vadosc
al. (1990) /one), 3D
MULTIMED (transport in
saturated /.one)
Flow
Conditions
Ss, Sal, Usai
Unge cl al.
(1986);
Summers cl
al. (1989)
MYGRT
(Version 1.0,
2.0)
I,2(H,V)
Ss, Sat
Aquifer
Conditions
tic, Horn, Iso,
I. (Usal)
Model
Processes
Chemical
Species
Adv, Dis, Ads, single
Dec, Vol
tic, Horn, Iso Adv, Dis, Rel, single
Dec
Additional Information
van 1D(H,V) Ss, Sal
Gcnuchtcn
and Alvcs
(1982)
Yen (1981) ID, 2D or 3D Tr, Sal
AT123D
C, Horn, Iso Adv, Dis, Dif, single
Ads
C, Uc, Horn, Adv, Dis, Dif, single
Iso, An Ads, Dec
Model simulates movement of contaminants in
saturated and unsaluraled groundwaler /.ones. In
surface water and emissions lo air. Includes Monte
Carlo capability. Unsalurated zone transport solution
is analytical, saturated zone is semi-analytical.
Gaussian or palch source boundary condition.
Simulates migration of organic and inorganic solulcs.
Constant pulse source boundary condition. Proprietary
code.
Three types of source boundary conditions are
considered: constant, exponential decay, and pulse step
function.
Analytical, semi-analytical, solution techniques based
on Green's function. Source boundary conditions
include: constant, instantaneous pulse, or finite-lime
release from a point, line, area, or volume source
ID = One-dimensional Sal
2D = Two-dimensional Usal
3D = Three-dimensional Horn
II = Horizontal Hel
V = Vertical Iso
Ss = Steady-state An
Tr = Transient C
Saturaled Uc
Unsaluratcd Adv
Homogeneous Dis
Heterogeneous Dif
Isolropic Dec
Anisotropic Ads
Confined aquifer Ret
Unconfincd aquifer Inf
Adveclion ET
Dispersion Ppl
Diffusion RO
Decay Rxn
Adsorption W
Retardation L
Infiltration
Evapoiranspiralion
Precipitation
Run-off
Reaction
Discharge or pumping wells
layers
-------
Table 4-lb. Finite-Difference Models for Application to Leachate Migration Problems
(adapted from Travers and Sharp-Hansen, 1991)
--••
Model Model
Reference Dimensions
Ahriclc and ID
Pinder (19X3)
»
Dillion ct al. 3D
(1981; 1986)
SWIFT/
SWIFT II
Erdogcnand ID
Hcufcld
(1983)
GeoTrans 3D
(1985); Faust
el al. (1989)
SWAN-
FLOW
Kipp(1987) 3D
NST3D
Konikow and 2D (H,V)
Bradshocfl
(1985)
USGS-NOC
Flow Aquifer
Conditions (Conditions
Ss, Tr, Sat, Uc, Iso, Horn
Usal
Ss, Tr, Sat C, Horn, Het,
Iso, An
Tr, Sal Horn, Iso
Ss, Tr, Sat, Uc, Horn, Hot,
Usat Iso, An
Tr, Sat C, Uc, Horn,
Hcl, Iso, An
Ss, Tr, Sat C, Uc, Horn,
Hel, Iso, An
Model Chemical
Processes Species
Dis. Dif multiphase
Adv, Dis, Dif, single
Dec, Rxn, W
Adv, Dis, Ads, single
Ppt
multiphase
Adv, Dis, Dif, single
Ads, Dec, W
Adv, Dis, Dif, single
Ads, Dec, ET,
W
Additional Information
Multiphase model for modeling aquifer contamination
by organic compounds. Simulates simultaneous
transport of contaminant in a nonaqucous phase,
aqueous phase and as a mobile fraction of gas phase.
Effects of capillarity, interphase mass transfer,
diffusion, and dispersion considered.
Coupled groundwaler flow, and heal or solute
transport. Includes fracture flow, ion exchange, salt
dissolution, in confined aquifer. SWIFT-II includes
dual porosity for fractured media.
Model describes the desorption process using
intraparliclc and external file diffusion resistances as
rate controlling mechanism (considers fluid velocity
and particle si/e). Predicts Icachale concentration
profiles at the boundary of the landfill. Simulates
precipitation with interrupted flow condilions.
Faust (1989) extends SWANFLOW to include a
solution technique which lakes advantage of parallel
computer processing.
Simulates coupled density dependent groundwater flow
and heal or mass transport in an anisotropic,
heterogeneous aquifer.
Groundwater flow solved by finite difference, solute
transport by the melliod of characteristics.
-------
Table 4-lb. Finite-Difference Models for Application to Leachate Migration Problems
(adapted from Travers and Sharp-Hansen, 1991) (continued)
Model
Reference
Harasiinhiin
cl al. (1986)
DYNAMIX
Prickctt cl al.
(19X1)
RANDOM
WALK or
TRANS
Ruachcl
(1985)
PORFLOW-
11 and III
Travis (1984)
TRACR3D
Walton
(1984) 35
Micro-
computer
Programs
Model
Dimensions
3D
ID or 2D(H)
2D(H,V) or
3D
3D
ID, 2D(H) or
3D (radial,
cyl)
Flow Aquifer
Conditions Conditions
Ss, Tr, Sal C, Uc, Horn,
Hcl, Iso, An
Ss, Tr, Sal C, Uc, Horn,
I lei, Iso, An,
L
Ss, Tr, Sal C, Uc, Horn,
Hct, Iso, An,
L.
Ss, Tr, Sat, C, Horn, Het,
Usat Iso, An
Ss, Tr, Sal C, Uc, Horn,
Hel, L
Model
Processes
Adv, Dis, Dif,
Dec
Adv, Dis, Ads,
Dec, ET, W
Adv, Dis, Dif,
Ads, Dec,
Rxn, W
Adv, Dis, Dif,
Ads, Dec
Adv, Dis, Rel
Chemical
Species
multiple
single
single
two-phase,
multiple
single
Additional Information
Model couples a chemical specification model
PHREEQE (Parkhursl cl al, 1980) with a modified
form of the transport code TRUMP (Edwards, 1969,
1972). Considers equilibrium reactions (see
gcochcinical codes).
Finite difference solution lo groundwatcr How,
random walk approach used lo simulate dispersion.
Simulates random movement. Aquifer properties vary
spatially and temporally.
Simulates density dependent How, heat and mass
transport. Aquifer and fluid properties may he
spatially and temporally variable. Integrated finite
difference solution. Includes phase change.
Simulates transient two-phase flow and multi-
component transport in deformablc, heterogeneous,
reactive, porous media.
A series of analytical and simple numerical programs
lo analyze flow and transport of solutes in aquifers
with simple geometry.
ID = One-dimensional Sat
2D = Two-dimensional Usat
3D = Three-dimensional Horn
H = Horizontal Hct
V = Vertical Iso
Ss = Steady-slate An
Tr = Transient C
Saturated
Unsaturaled
Homogeneous
Heterogeneous
Isotropic
Anisotropic
Confined aquifer
Uc = Unconfined aquifer Inf
Adv = Advection ET
Dis = Dispersion Ppt
Dif = Diffusion RO
Dec = Decay Rxn
Ads = Adsorption W
Ret = Retardation L
Infiltration
Evapotranspiration
Prccipilalion
Run-off
Reaction
Discharge or pumping wells
Layers
-------
Table 4-lc. Finite-Element Models for Application to Leachate Migration Problems
(adapted from Travers and Sharp-Hansen, 1991)
Model
Reference
Ccdcrbcrg el
al. (1985)
TRANQL
(19X9)
RUSTIC
Gupla el al.
(1982)
CFEST
Gureghian el
al. (1980)
Guvanssen
(1986)
NOT IF
Haji-Djalari
and Wells
(1982)
GEOFLOW
Huyakorn et
al. (1984)
SEFTRAN
Huyakorn el
al. (1986)
TRAFRAP
Osbomc and
Sykes(1986)
WST1F
Model
Dimensions
1 D, radial
vadose /.one);
2DH.V, radial
(saturated
/one)
2D(H,V) or
3D
2D
ID, 2D, or 3D
3D
ID or
2D(H,V)
2D(H,V)
2D
Flow
Conditions
Ss, Sat
Ss Tr Usat
Sal
Ss, Tr, Sal
Ss, Sal
Ss, Tr, Sal,
Usat
Ss, Tr, Sal
Ss, Tr, Sal
Ss, Tr, Sat
Tr, Sat, Usat
Aquifer
Conditions
C, Uc, Horn
C Uc Horn
Hct, Iso, An,
L
C, Uc, Horn,
Hel, Iso, An,
L
C, Uc, Iso, An
C, Uc, Horn,
Hel, Iso, An
C, Uc, Horn,
Hel, Iso, An,
L
C, Uc, Horn,
Hel, Iso, An,
L
C, Uc, Horn,
Hel, Iso, An
Uc, Horn, Hel,
Iso, An, L
Model
1'rocesses
Adv, Dis, Dif,
Ads, Dec
Adv, Dis, Ads,
Dif, Dec, ET,
W, Ppt, RO,
Ret
Adv, Dis, Dif,
Ads, Dec, W
Adv, Dis, Ads,
Dec
Adv, Dis, Dif,
Ads, Dec
Adv, Dis, Dif,
Dec, Rxn, Rel,
W
Adv, Dis, Dif,
Ads, Dec, W
Adv, Dis, Dif,
Ads, Dec,
Rxn, W
Chemical
Species
multiple
1, 2, or 3
single
single
single
single
single
single
two- phase
Additional Information
Multicomponenl transport model which links chemical
equilibrium code MICROQL (Weslfall, 1976) and
transport axle ISOQUAD (Pinder, unpublished
manuscripl, 1976). Includes a complexation in aqueous
phase.
Simulates fate and transport of chemicals through three
linked modules: root, values, and saturated /one.
Includes PRZN (Carsel et al., 1984). RUSTIC is in
Beta-lcsling phase. Includes Monte Carlo capability
PRZN solution by finite difference.
Solves coupled groundwater How, solute and heat
transport equations. Fluid may be heterogeneous.
Source boundary condition: Gaussian distributed
source. Transport only.
Groundwaler How and solute transport in fractured
porous media.
Simulation of arcal configuration only. Proprietary
axle.
Proprietary axle.
Simulates groundwater Row and solute transport in
fractured porous media. Includes precipitalion.
Model sirnulales Iransporl of immiscible organics in
groundwater. Assumes no mass transport belween
phases.
-------
Table 4-lc. Finite-Element Models for Application to Leachate Migration Problems
(adapted from Travers and Sharp-Hansen, 1991) (continued)
Model Model
Reference Dimensions
Thcis ct al. ID
(14X2)
FIESTA
van 1D(V)
Gcnuchlen
(1978)
SUMATRA-
I
Voss (19X4) 2D(H,V)
SUTRA
Ychand 2D(H,V)
Ward (1981)
FEMWATER
FEM WASTE
Ych (1990) 2D/3D
LEWASTE,
3DLEWASTE
Flow
Conditions
Sal
Tr, Sat, Usat
Ss, Tr, Sat,
Usat
Ss, Tr, Sat,
Usat
Ss, Tr, Sat,
Usat
Aquifer
Conditions
Horn, Iso
C, Uc, Horn,
Hcl, Iso, L
C, Uc, Horn,
Hct, Iso, An
Uc, Horn, Hct,
Iso, An
Uc, C, Horn,
Hct, Iso, An
Model
Processes
Adv, Dis, Ads,
Dec
Adv, Dis, Ads,
Dec, Ret
Adv, Dis, Oil,
Ads, Dec,
Rxn, W
Adv, Dis, Ads,
Dec, Ppt, W
Adv, Dis, Ads,
Dec, W
Chemical
Species Additional Information
multiple Combinations of a component transport model, FEAP,
and the chemical equilibrium speciation model
NINEQL (Wcstfall el al. 1976). Simulates up to 6
chemical components, including all solution and sorhcd
phase complexes.
single Simulates simultaneous How of water and solutes in a
one-dimensional, vertical soil profile.
single Fluid may be heterogeneous (density-dependent
groundwaler flow).
single FEMWATER simulates groundwaler flow.
FEMWASTE simulales waste Iransporl through
saturated unsaturaled porous media. Simulates
capillarity, infiltration, and recharge/discharge -sources
(e.g., lakes, reservoirs, and streams).
single Transport codes based on (lie Lagrangian-Eulcrian
approach, can be applied to Pcciel Numbers from 0 lo
infinity. LEWASTE is intended to simulate 2D local
How systems. 3DLEWASTE can simulate regional or
local flow systems. The LEWASTE series replaces the
FEMWASTE models.
ID = One-dimensional Sat =
2D = Two-dimensional Usat =
3D = Three-dimensional Horn =
II = Horizontal Hct =
V = Vertical Iso =
Ss = Steady-slate An =
Tr = Transient C • =
Saturated Uc
Unsaturaied Adv
Homogeneous Dis
Heterogeneous Dif
Isolropic Dec
Anisolropic Ads
Confined aquifer Re I
Unconfincd aquifer Inf
Adveclion ET
Dispersion Ppl
Diffusion RO
Decay Rxn
Adsorption W
Retardation L
Infiltration
Evapolranspiralion
Precipilation
Run-off
Reaction
Discharge or pumping wells
Layers
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Design Criteria
conjunction with a separate leachate source
model, such as HELP (Schroeder et al., 1984).
Output from HELP is then used in
MULTIMED to demonstrate that either a
landfill design or the specific hydrogeologic
conditions present at a site will prevent
contaminant concentrations in ground water
from exceeding the concentrations listed in
Table 1 of §258.40. (Refer to pp. 4-53 and 6-
8 for further discussion of HELP.) A
description of MULTIMED follows with
guidance for determining if its use is
appropriate for a given site.
[NOTE: Version 3.0 of the HELP model will
be available during the fall of 1993. To
obtain a copy, call EPA's Office of Research
and Development (ORD) in Cincinnati at
(513)569-7871.]
Overview of the Model
The MULTIMED model consists of modules
that estimate contaminant releases to air, soil,
ground water, or surface water. General
information about the model and its theory is
provided in Salhotra et al. (1990).
Additionally, information about the
application of MULTIMED to MSWLF units
(developed by Sharp-Hansen et al. [1990]) is
summarized here. In MULTIMED, a steady-
state, one-dimensional, semi-analytical
module simulates flow in the unsaturated
zone. The output from this module, which is
water saturation as a function of depth, is used
as input to the unsaturated zone transport
module. The latter simulates transient, one-
dimensional (vertical) transport in the
unsaturated zone and includes the effects of
dispersion, linear adsorption, and first-order
decay. Output from the unsaturated zone
modules is used as input to the semi-analytical
saturated zone transport module. The latter
considers three-dimensional flow
because the effects of lateral or vertical
dispersion may significantly affect the model
results.
Therefore, reducing the dimensions to one in
this module would produce inaccurate results.
The saturated zone transport module also
considers linear adsorption, first-order decay,
and dilution as a result of ground-water
recharge. In addition, MULTIMED has the
capability to assess the impact of uncertainty
in the model inputs on the model output
(contaminant concentration at a specified
point), using the Monte Carlo simulation
technique.
The simplifying assumptions required to
obtain the analytical solutions limit the
complexity of the systems that can be
evaluated with MULTIMED. The model does
not account for site-specific spatial variability
(e.g., aquifer heterogeneities), the shape of the
land disposal facility, site-specific boundary
conditions, or multiple aquifers and pumping
wells. Nor can MULTIMED simulate
processes, such as flow in fractures and
chemical reactions between contaminants, that
may have a significant effect on the
concentration of contaminants at a site. In
more complex systems, it may be beneficial to
use MULTIMED as a "screening level" model
to allow the user to obtain an understanding of
the system. A more complex model could
then be used if there are sufficient data.
Application of MULTIMED to MSWLF
Units
Procedures have been developed for the
application of MULTIMED to the design of
MSWLF units. They are explained in Sharp-
Hansen et al. (1990) and are briefly
summarized here. The procedures are:
147
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Subpart D
• Collect site-specific hydrogeologic data,
including amount of leachate generated
(see Section 4.3.3);
• Identify the contaminant(s) to be
simulated and the point of compliance;
• Propose a landfill design and determine
the corresponding infiltration rate; then
• Run MULTIMED and calculate the
dilution attenuation factor (DAF) (i.e.,
the factor by which the concentration is
expected to decrease between the
landfill unit and the point of
compliance); and
• Multiply the initial contaminant
concentration by the DAF and compare
the resulting concentration to the MCLs
to determine if the design will meet the
standard.
At this time, only contaminant transport in the
unsaturated and/or saturated zones can be
modeled, because the other options (i.e.,
surface water, air) have not yet been
thoroughly tested. In addition, only steady-
state transport simulations are allowed. No
decay of the contaminant source term is
permitted; the concentration of contaminants
entering the aquifer system is assumed to be
constant over time. The receptor (e.g., a
drinking water well) is located directly
downgradient of the facility and intercepts the
contaminant plume; also, the contaminant
concentration is calculated at the top of the
aquifer.
The user should bear in mind that
MULTIMED may not be an appropriate
model for some sites. Some of the issues that
should be considered before modeling efforts
proceed are summarized in Table
4-2. A "no" answer to any of the questions in
Table 4-2 may indicate that MULTIMED is
not the most appropriate model to use. As
stated above, MULTIMED utilizes analytical
and semi-analytical solution techniques to
solve the mathematical equations describing
flow and transport. As a result, the
representation of a system simulated by the
model is simple, and little or no spatial or
temporal variability is allowed for the
parameters in the system. Thus, a highly
complex hydrogeologic system cannot be
accurately represented with MULTIMED.
The spatial characteristics assumed in
MULTIMED should be considered when
applying MULTIMED to a site. The
assumption of vertical, one-dimensional
unsaturated flow may be valid for facilities
that receive uniform areal recharge.
However, this assumption may not be valid
for facilities where surface soils (covers or
daily backfill) or surface slopes result in an
increase of run-off in certain areas of the
facility, and ponding of precipitation in
others. In addition, the simulation of one-
dimensional, horizontal flow in the saturated
zone requires several simplifying
assumptions. The saturated zone is treated as
a single, horizontal aquifer with uniform
properties (e.g., hydraulic conductivity). The
effects of pumping or discharging wells on the
ground-water flow system cannot be
addressed with the MULTIMED model.
The MULTIMED model assumes steady-state
flow in all applications. Some ground-water
flow systems are in an approximate "steady-
state," in which the amount of water entering
the flow system equals the amount of water
leaving the system. However, assuming
steady-state conditions in a system that
exhibits transient behavior may produce
inaccurate results.
148
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Design Criteria
TABLE 4-2
ISSUES TO BE CONSIDERED
BEFORE APPLYING MULTIMED
(from Sharp-Hansen et al., 1990)
Objectives of the Study
• Is a "screening level" approach
appropriate?
• Is modeling a "worst-case scenario"
acceptable?
Significant Processes Affecting Contaminant
Transport
• Does MULTIMED simulate all the
significant processes occurring at the site?
• Is the contaminant soluble in water and of
the same density as water?
Accuracy and Availability of the Data
• Have sufficient data been collected to
obtain reliable results?
• What is the level of uncertainty associated
with the data?
• Would a Monte Carlo simulation be
useful? If so, are the cumulative
probability distributions for the parameters
with uncertain values known?
Complexity of the Hydrogeologic System
• Are the hydrogeologic properties of the
system uniform?
• Is the flow in the aquifer uniform and
steady?
• Is the site geometry regular?
• Does the source boundary condition
require a transient or steady-state solution?
MULTIMED may be run in either a
deterministic or a Monte Carlo mode. The
Monte Carlo method provides a means of
estimating the uncertainty in the results of a
model, if the uncertainty of the input variables
is known or can be estimated. However, it
may be difficult to determine the cumulative
probability distribution for a given parameter.
Assuming a parameter probability distribution
when the distribution is unknown does not
help reduce uncertainty. Furthermore, to
obtain a valid estimate of the uncertainty in
the output, the model must be run numerous
times (typically several hundred times), which
can be time-consuming. These issues should
be considered before utilizing the Monte
Carlo technique.
4.3 COMPOSITE LINER AND
LEACHATE COLLECTION
SYSTEM
40 CFR §258.40
4.3.1 Statement of Regulation
(a) New MSWLF units and lateral
expansions shall be constructed:
(1) See Statement of Regulation in
Section 4.2.1 of this guidance document for
performance-based design requirements.
(2) With a composite liner, as defined
in paragraph (b) of this section and a
leachate collection system that is designed
and constructed to maintain less than a 30-
cm depth of leachate over the liner,
(b) For purposes of this section,
composite liner means a system consisting
of two components; the upper component
must consist of a minimum 30-mil flexible
149
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Subpart D
membrane liner (FML), and the lower
component must consist of at least a two-
foot layer of compacted soil with a
hydraulic conductivity of no more than 1 x
10~7 cm/sec. FML components consisting of
high density polyethylene (HDPE) shall be
at least 60-mil thick. The FML component
must be installed in direct and uniform
contact with the compacted soil
component.
4.3.2 Applicability
New MSWLF units and expansions of
existing MSWLF units in States without
approved programs must be constructed with
a composite liner and a leachate collection
system (LCS) that is designed to maintain a
depth of leachate less than 30 cm (12 in.)
above the liner. A composite liner consists of
a flexible membrane liner (FML) installed on
top of, and in direct and uniform contact with,
two feet of compacted soil. The FML must be
at least 30-mil thick unless the FML is made
of FIDPE, which must be 60-mil thick. The
compacted soil liner must be at least two feet
thick and must have a hydraulic conductivity
of no more than 1 x 10"7 cm/sec.
Owners and operators of MSWLF units
located in approved States have the option of
proposing a performance-based design
provided that certain criteria can be met (see
Section 4.2.2).
4.3.3 Technical Considerations
This section provides information on the
components of composite liner systems
including soils, geomembranes, and leachate
collection systems.
Standard Composite Liner Systems
The composite liner system is an effective
hydraulic barrier because it combines the
complementary properties of two different
materials into one system: 1) compacted soil
with a low hydraulic conductivity; and
2) a FML (FMLs are also referred to as
geomembranes). Geomembranes may contain
defects including tears, improperly bonded
seams, and pinholes. In the absence of an
underlying low-permeability soil liner, flow
through a defect in a geomembrane is
essentially unrestrained. The presence of a
low-permeability soil liner beneath a defect in
the geomembrane reduces leakage by limiting
the flow rate through the defect.
Flow through the soil component of the liner
is controlled by the size of the defect in the
geomembrane, the available air space between
the two liners into which leachate can flow,
the hydraulic conductivity of the soil
component, and the hydraulic head. Fluid
flow through soil liners is calculated by
Darcy's Law, where discharge (Q) is
proportional to the head loss through the soil
(dh/dl) for a given cross-sectional flow area
(A) and hydraulic conductivity (K) where:
Q = KA(dh/dl)
Leakage through a geomembrane without
defects is controlled by Pick's first law, which
describes the process of liquid diffusion
through the membrane liner. The diffusion
process is similar to flow governed by Darcy's
law for soil liners except that diffusion is
driven by concentration gradients and not by
hydraulic head. Although diffusion rates in
geomembranes are several orders of
magnitude lower than comparable hydraulic
flow rates in low-permeability soil liners,
construction of a completely impermeable
geomembrane is
150
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Design Criteria
difficult. The factor that most strongly
influences geomembrane performance is the
presence of imperfections such as improperly
bonded seams, punctures and pinholes. A
detailed discussion of leakage through
geomembranes and composite liners can be
found in Giroud and Bonaparte (1989 (Part I
and Part II)). A geomembrane installed with
excellent control over defects may yield the
equivalent of a one-centimeter-diameter hole
per acre of liner installed (Giroud and
Bonaparte, 1989 (Part I and Part II)). If the
geomembrane were to be placed over sand,
this size imperfection under one foot of
constant hydraulic head could be expected to
account for as much as 3,300 gal/acre/day
(31,000 liters/hectare/ day) of leakage. Based
upon measurements of actual leakage through
liners at facilities that have been built under
rigorous control, Bonaparte and Gross (1990)
have estimated an actual leakage rate, under
one foot of constant head, of 200
liters/hectare/day or about 21 gallons/acre/day
for landfill units.
The uniformity of the contact between the
geomembrane and the soil liner is extremely
important in controlling the effective flow
area of leachate through the soil liner. Porous
material, such as drainage sand, filter fabric,
or other geofabric, should not be placed
between the geomembrane and the low
permeability soil liner. Porous materials will
create a layer of higher hydraulic
conductivity, which will increase the amount
of leakage below an imperfection in the
geomembrane. Construction practices during
the installation of the soil and the
geomembrane affect the uniformity of the
geomembrane/soil interface, and strongly
influence the performance of the composite
liner system.
Soil Liner
The following subsections discuss soil liner
construction practices including thickness
requirements, lift placement, bonding of lifts,
test methods, prerequisite soil properties,
quality control, and quality assurance
activities.
Thickness
Two feet of soil is generally considered the
minimum thickness needed to obtain adequate
compaction to meet the hydraulic conductivity
requirement. This thickness is considered
necessary to minimize the number of cracks
or imperfections through the entire liner
thickness that could allow leachate migration.
Both lateral and vertical imperfections may
exist in a compacted soil. The two-foot
minimum thickness is believed to be sufficient
to inhibit hydraulic short-circuiting of the
entire layer.
Lift Thickness
Soil liners should be constructed in a series of
compacted lifts. Determination of appropriate
lift thickness is dependent on the soil
characteristics, compaction equipment,
firmness of the foundation materials, and the
anticipated compactive effort needed to
achieve the required soil hydraulic
conductivity. Soil liner lifts should be thin
enough to allow adequate compactive effort to
reach the lower portions of the lift. Thinner
lifts also provide greater assurance that
sufficient compaction can be achieved to
provide good, homogeneous bonding between
subsequent lifts. Adequate compaction of lift
thickness between five and ten inches is
possible if appropriate equipment is used
(USEPA, 1988). Nine-inch loose lift
thicknesses that will yield a 6-
151
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Subpart D
inch soil layer also have been recommended
prior to compaction (USEPA, 1990a).
Soil liners usually are designed to be of
uniform thickness with smooth slopes over the
entire facility. Thicker areas may be
considered wherever recessed areas for
leachate collection pipes or collection sumps
are located. Extra thickness and compactive
efforts near edges of the side slopes may
enhance bonding between the side slopes and
the bottom liner. In smaller facilities, a soil
liner may be designed for installation over the
entire area, but in larger or multi-cell
facilities, liners may be designed in segments.
If this is the case, the design should address
how the old and new liner segments will be
bonded together (U.S. EPA, 1988).
Bonding Between Lifts
It is not possible to construct soil liners
without some microscopic and/or macroscopic
zones of higher and lower hydraulic
conductivity. Within individual lifts, these
preferential pathways for fluid migration are
truncated by the bonded zone between the
lifts. If good bonding between the lifts is not
achieved during construction, the vertical
pathways may become connected by
horizontal pathways at the lift interface,
thereby diminishing the performance of the
hydraulic barrier.
Two methods may be used to ensure proper
bonding between lifts. Kneading or blending
a thinner, new lift with the previously
compacted lift may be achieved by using a
footed roller with long feet that can fully
penetrate a loose lift of soil. If the protruding
rods or feet of a sheepsfoot roller are
sufficient in length to penetrate the top lift and
knead the previous lift, good bonding may be
achieved. Another method
includes scarifying (roughening), and possibly
wetting, the top inch or so of the last lift
placed with a disc harrow or other similar
equipment before placing the next lift.
Placement of Soil Liners on Slopes
The method used to place the soil liner on side
slopes depends on the angle and length of the
slope. Gradual inclines from the toe of the
slope enable continuous placement of the lifts
up the slopes and provide better continuity
between the bottom and sidewalls of the soil
liner. When steep slopes are encountered,
however, lifts may need to be placed and
compacted horizontally due to the difficulties
of operating heavy compaction equipment on
steeper slopes.
When sidewalls are compacted horizontally,
it is important to tie in the edges with the
bottom of the soil liner to reduce the
probability of seepage planes (USEPA, 1988).
A significant amount of additional soil liner
material will be required to construct the
horizontal lifts since the width of the lifts has
to be wide enough to accommodate the
compaction equipment. After the soil liner is
constructed on the side slopes using this
method, it can be trimmed back to the
required thickness. The trimmed surface of
the soil liner should be sealed by a smooth-
drum roller. The trimmed excess materials
can be reused provided that they meet the
specified moisture-density requirements.
Hydraulic Conductivity
Achieving the hydraulic conductivity standard
depends on the degree of compaction,
compaction method, type of clay, soil
moisture content, and density of the soil
during liner construction. Hydraulic
152
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Design Criteria
conductivity is the key design parameter when
evaluating the acceptability of the constructed
soil liner. The hydraulic conductivity of a soil
depends, in part, on the viscosity and density
of the fluid flowing through it. While water
and leachate can cause different test results,
water is an acceptable fluid for testing the
compacted soil liner and source materials.
The effective porosity of the soil is a function
of size, shape, and area of the conduits
through which the liquid flows. The
hydraulic conductivity of a partially saturated
soil is less than the hydraulic conductivity of
the same soil when saturated. Because
invading water only flows through water-
filled voids (and not air-filled voids), the
dryness of a soil tends to lower permeability.
Hydraulic conductivity testing should be
conducted on samples that are fully saturated
to attempt to measure the highest possible
hydraulic conductivity.
EPA has published Method 9100 in
publication SW-846 (Test Methods for
Evaluating Solid Wasted to measure the
hydraulic conductivity of soil samples. Other
methods appear in the U.S. Army Corps of
Engineers Engineering Manual 1110-2-1906
(COE, 1970) and the newly published
"Measurement of Hydraulic Conductivity of
Saturated Porous Materials Using a Flexible
Wall Permeameter" (ASTM D-5084). To
verify full saturation of the sample, this latter
method may be performed with back pressure
saturation and electronic pore pressure
measurement.
Soil Properties
Soils typically possess a range of physical
characteristics, including particle size,
gradation, and plasticity, that affect their
ability to achieve a hydraulic conductivity of
1 x 10"7 cm/sec. Testing methods used to
characterize proposed liner soils should
include grain size distribution (ASTM D-
422), Atterberg limits (ASTM D-4318), and
compaction curves depicting moisture and
density relationships using the standard or
modified Proctor (ASTM D-698 or ASTM D-
1557), whichever is appropriate for the
compaction equipment used and the degree of
firmness of the foundation materials.
Liner soils usually have at least 30 percent
fines (fine silt- and clay-sized particles).
Some soils with less than 30 percent fines
may be worked to obtain hydraulic
conductivities below 1 x 10"7 cm/sec, but use
of these soils requires greater control of
construction practices and conditions.
The soil plasticity index (PI), which is
determined from the Atterberg limits (defined
by the liquid limit minus the plastic limit),
should generally be greater than 10 percent.
However, soils with very high PI, (greater
than 30 percent), are cohesive and sticky and
become difficult to work with in the field.
When high PI soils are too dry during
placement, they tend to form hard clumps
(clods) that are difficult to break down during
compaction. Preferential flow paths may be
created around the clods allowing leachate to
migrate at a relatively high rate.
Soil particles or rock fragments also can
create preferential flow paths. For this
reason, soil particles or rock fragments should
be less than 3 inches in diameter so as not to
affect the overall hydraulic performance of
the soil liner (USEPA, 1989).
The maximum density of a soil will be
achieved at the optimum water content, but
this point generally does not correspond to the
point at which minimum hydraulic
153
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Subpart D
conductivity is achieved. Wet soils, however,
have low shear strength and high potential for
desiccation cracking. Care should be taken
not to compromise other engineering
properties such as shear strengths of the soil
liner by excessively wetting the soil liner.
Depending on the specific soil characteristics,
compaction equipment and compactive effort,
the hydraulic conductivity criterion may be
achieved at moisture values of 1 to 7 percent
above the optimum moisture content.
Although the soil may possess the required
properties for successful liner construction,
the soil liner may not meet the hydraulic
conductivity criterion if the construction
practices used to install the liner are not
appropriate and carefully controlled.
Construction quality control and quality
assurance will be discussed in a later section.
Amended Soils
If locally available soils do not possess
properties to achieve the specified hydraulic
conductivity, soil additives can be used. Soil
additives, such as bentonite or other clay
materials, can decrease the hydraulic
conductivity of the native soil (USEPA,
1988b).
Bentonite may be obtained in a dry, powdered
form that is relatively easy to blend with on-
site soils. Bentonite is a clay mineral
(sodium-montmorillonite) that expands when
it comes into contact with water (hydration),
by absorbing the water within the mineral
matrix. This property allows relatively small
amounts of bentonite (5 to 10 percent) to be
added to a noncohesive soil (sand) to make it
more cohesive (U.S. EPA, 1988b). Thorough
mixing of additives to cohesive soils (clay)
is difficult and may lead to inconsistent results
with respect to complying with the hydraulic
conductivity criterion.
The most common additive used to amend
soils is sodium bentonite. The disadvantage
of using sodium bentonite includes its
vulnerability to degradation as a result of
contact with chemicals and waste leachates
(U.S. EPA, 1989).
Calcium bentonite, although more permeable
than sodium bentonite, also is used as a soil
amendment. Approximately twice as much
calcium bentonite typically is needed to
achieve a hydraulic conductivity comparable
to that of sodium bentonite.
Soil/bentonite mixtures generally require
central plant mixing by means of a pugmill,
cement mixer, or other mixing equipment
where water can be added during the process.
Water, bentonite content, and particle size
distribution must be controlled during mixing
and placement. Spreading of the
soil/bentonite mixture may be accomplished
in the same manner as the spreading of natural
soil liners, by using scrapers, graders,
bulldozers, or a continuous asphalt paving
machine (U.S. EPA, 1988).
Materials other than bentonite, including lime,
cement, and other clay minerals such as
atapulgite, may be used as soil additives (U.S.
EPA, 1989). For more information
concerning soil admixtures, the reader is
referred to the technical resource document on
the design and construction of clay liners
(U.S. EPA, 1988).
Testing
Prior to construction of a soil liner, the
relationship between water content, density,
154
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Design Criteria
and hydraulic conductivity for a particular soil
should be established in the laboratory.
Figure 4-5 shows the influence of molding
water content (moisture content of the soil at
the time of compaction) on hydraulic
conductivity of the soil. The lower half of the
diagram is a compaction curve and shows the
relationship between dry unit weight, or dry
density of the soil, and water content of the
soil. The optimum moisture content of the
soil is related to a peak value of dry density
known as maximum dry density. Maximum
dry density is achieved at the optimum
moisture content.
The lowest hydraulic conductivity of
compacted clay soil is achieved when the soil
is compacted at a moisture content slightly
higher than the optimum moisture content,
generally in the range of 1 to 7 percent (U.S.
EPA, 1989). When compacting clay, water
content and compactive effort are the two
factors that should be controlled to meet the
maximum hydraulic conductivity criterion.
It is impractical to specify and construct a
clay liner to a specific moisture content and a
specific compaction (e.g., 5 percent wet of
optimum and 95 percent modified Proctor
density). Moisture content can be difficult to
control in the field during construction;
therefore, it may be more appropriate to
specify a range of moisture contents and
corresponding soil densities (percent
compaction) that are considered appropriate to
achieve the required hydraulic conductivity.
Benson and Daniel (U.S. EPA, 1990) propose
water content and density criteria for the
construction of clay liners in which the
moisture-density criteria ranges are
established based on hydraulic conductivity
test results. This type of approach is
recommended because of the flexibility and
guidance it provides to the
construction contractor during soil placement.
Figure 4-6 presents compaction data as a
function of dry unit weight and molding water
content for the construction of clay liners.
The amount of soil testing required to
determine these construction parameters is
dependent on the degree of natural variability
of the source material.
Quality assurance and quality control of soil
liner materials involve both laboratory and
field testing. Quality control tests are
performed to ascertain compaction
requirements and the moisture content of
material delivered to the site. Field tests for
quality assurance provide an opportunity to
check representative areas of the liner for
conformance to compaction specifications,
including density and moisture content.
Quality assurance laboratory testing is usually
conducted on field samples for determination
of hydraulic conductivity of the in-place liner.
Laboratory testing allows full saturation of the
soil samples and simulates the effects of large
overburden stress on the soil, which cannot be
done conveniently in the field (U.S. EPA,
1989).
Differences between laboratory and field
conditions (e.g., uniformity of material,
control of water content, compactive effort,
compaction equipment) may make it unlikely
that minimum hydraulic conductivity values
measured in the laboratory on remolded, pre-
construction borrow source samples are the
same as the values achieved during actual
liner construction. Laboratory testing on
remolded soil specimens does not account for
operational problems that may result in
desiccation, cracking, poor bonding of lifts,
and inconsistent degree of compaction on
sidewalls (U.S. EPA, 1988b). The
relationship between field and laboratory
hydraulic conductivity testing has been
investigated by the U.S. Environmental
155
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Hydraulic
Conductivity
Dry Unit
Weight
Molding Water Content
Source: U.S. EPA, 1989.
Note: The optimum moisture content occurs at the point at which maximum density is achieved.
The lowest hydraulic conductivity generally occurs at water contents higher than optimum.
Figure 4-5
Hydraulic Conductivity and Dry Unit Weight as a
Function of Molding Water Content
156
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£
*s
120
110
100
90
10
Acceptable
Zone
15 20
Molding Water Content (%)
An
D
OJ
Compactive Effort
25
Compaction Data for a Silty Clay (from Mitchell et al.. 1965).
Solid symbols represent specimens with a hydraulic
conductivity < 1 x 10'7 cm/s and open symbols represent
specimens with hydraulic conductivity > 1 x 10'7 cm/s.
Source: CERI 90-50 (USEPA, 1990)
Figure 4-6. Compaction Data for Silty Clay
157
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Subpart D
Protection Agency using field case studies
(U.S. EPA, 1990c).
In situ, or field, hydraulic conductivity testing
operates on the assumption that by testing
larger masses of soil in the field, one can
obtain more realistic results. Four types of in
situ hydraulic conductivity tests generally are
used: borehole tests, porous probes,
infiltrometer tests, and underdrain tests. A
borehole test is conducted by drilling a hole,
then filling the hole with water, and
measuring the rate at which water percolates
into the borehole. In the borehole test, water
also can percolate through the sidewalls of the
borehole. As a result, the measured hydraulic
conductivity is usually higher than that
measured by other one-dimensional field
testings.
The second type of test involves driving or
pushing a porous probe into the soil and
pouring water through the probe into the soil.
With this method, however, the advantage of
testing directly in the field is somewhat offset
by the limitations of testing such a small
volume of soil.
A third method of testing involves a device
called an infiltrometer. This device is
embedded into the surface of the soil liner
such that the rate of flow of a liquid into the
liner can be measured. The two types of
infiltrometers most widely used are open and
sealed. Open rings are less desirable because,
with a hydraulic conductivity of 10"7 cm/sec,
it is difficult to detect a 0.002 inch per day
drop in water level of the pond from
evaporation and other losses.
With sealed rings, very low rates of flow can
be measured. However, single-ring
infiltrometers allow lateral flow beneath the
ring, which can complicate the interpretation
of test results. Single rings are also
susceptible to the effects of temperature
variation; as the water temperature increases,
the entire system expands. As it cools down,
the system contracts. This situation could
lead to erroneous measurements when the rate
of flow is small.
The sealed double-ring infiltrometer has
proven to be the most successful method and
is the one currently used. The outer ring
forces infiltration from the inner ring to be
more or less one-dimensional. Covering the
inner ring with water insulates it substantially
from temperature variation.
Underdrains, the fourth type of in situ test, are
the most accurate in situ permeability testing
device because they measure exactly what
migrates from the bottom of the liner.
However, under-drains are slow to generate
data for low permeability liners, because of
the length of time required to accumulate
measurable flow. Also, underdrains must be
installed during construction, so fewer
underdrains are used than other kinds of
testing devices.
Field hydraulic conductivity tests are not
usually performed on the completed liner
because the tests may take several weeks to
complete (during which time the liner may be
damaged by desiccation or freezing
temperatures) and because large penetrations
must be made into the liner. If field
conductivity tests are performed, they are
usually conducted on a test pad. The test pad
should be constructed using the materials and
methods to be used for the actual soil liner.
The width of a test pad is usually the width of
three to four construction vehicles, and the
length is one to two times the width.
Thickness is usually two to three feet. Test
pads can be used as a means for verifying that
the proposed
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Design Criteria
materials and construction procedures will
meet performance objectives. If a test pad is
constructed, if tests verify that performance
objectives have been met, and if the actual
soil liner is constructed to standards that equal
or exceed those used in building the test pad
(as verified through quality assurance), then
the actual soil liner should meet or exceed
performance objectives.
Other than the four types of field hydraulic
conductivity tests described earlier, ASTM D
2937 "Standard Test Method for Density of
Soil in Place by the Drive-Cylinder Method"
may be used to obtain in-place hydraulic
conductivity of the soil liner. This test
method uses a U.S. Army Corps of Engineers
surface soil sampler to drive a thin-walled
cylinder (typically 3-inch by 3-inch) into a
completed lift of the soil liner to obtain
relatively undisturbed samples for laboratory
density and hydraulic conductivity testings.
This test can provide useful correlation to
other field and quality assurance testing
results (e.g, Atterberg limits, gradation, in-
place moisture and density of the soil liner) to
evaluate the in-place hydraulic conductivity of
the soil liner.
Soil Liner Construction
Standard compaction procedures are usually
employed when constructing soil liners. The
following factors influence the degree and
quality of compaction:
• Lift thickness;
• Full scale or segmented lift placement;
• Number of equipment passes;
• Scarification between lifts;
• Soil water content; and
• The type of equipment and compactive
effort.
The method used to compact the soil liner is
an important factor in achieving the required
minimum hydraulic conductivity. Higher
degrees of compactive effort increase soil
density and lower the soil hydraulic
conductivity for a given water content. The
results of laboratory compaction tests do not
necessarily correlate directly with the amount
of compaction that can be achieved during
construction.
Heavy compaction equipment (greater than
25,000 Ibs or 11,300 kg) is typically used
when building the soil liner to maximize
compactive effort (U.S. EPA, 1989). The
preferred field compaction equipment is a
sheepsfoot roller with long feet that fully
penetrates loose lifts of soil and provides
higher compaction while kneading the clay
particles together. The shape and depth of the
feet are important; narrow, rod-like feet with
a minimum length of about seven inches
provide the best results. A progressive change
from the rod-like feet to a broader foot may
be necessary in some soils after initial
compaction, to allow the roller to walk out of
the compacted soil. The sheepsfoot feet also
aid in breaking up dry clods (see Soil
Properties in this section). Mechanical road
reclaimers, which are typically used to strip
and re-pave asphalt, can be extremely
effective in reducing soil clod size prior to
compaction and in scarifying soil surfaces
between lifts. Other equipment that has been
used to compact soil includes discs and
rototillers.
To achieve adequate compaction, the lift
thickness (usually five to nine inches) may be
decreased or the number of passes over
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Subpart D
the lift may be increased. Generally,
compaction equipment should pass over the
soil liner five to twenty times to attain the
compaction needed to comply with the
minimum hydraulic conductivity criterion
(U.S. EPA, 1989).
Efforts made to reduce clod size during
excavation and placement of the soil for the
liner should improve the chances for
achieving low hydraulic conductivity in
several ways. Keeping clods in the soil liner
material small will facilitate a more uniform
water content. Macropores between clod
remnants can result in unacceptably high field
hydraulic conductivity.
Opinions differ on acceptable clod sizes in the
uncompacted soil. Some suggest a maximum
of one to three inches in diameter, or no larger
than one-half the lift thickness. The main
objective is to remold all clods in the
compaction process to keep hydraulic
conductivity values consistent throughout the
soil liner (U.S. EPA, 1988).
Geomembranes
Geomembranes are relatively thin sheets of
flexible thermoplastic or thermoset polymeric
materials that are manufactured and
prefabricated at a factory and transported to
the site. Because of their inherent
impermeability, use of geomembranes in
landfill unit construction has increased. The
design of the side slope, specifically the
friction between natural soils and
geosynthetics, is critical and requires careful
review.
Material Types and Thicknesses
Geomembranes are made of one or more
polymers along with a variety of other
ingredients such as carbon black, pigments,
fillers, plasticizers, processing aids,
crosslinking chemicals, anti-degradants, and
biocides. The polymers used to manufacture
geomembranes include a wide range of
plastics and rubbers differing in properties
such as chemical resistance and basic
composition (U.S. EPA, 1983 and U.S. EPA,
1988e). The polymeric materials may be
categorized as follows:
Thermoplastics such
chloride (PVC);
as polyvinyl
• Crystalline thermoplastics such as high
density polyethylene (HDPE), very low
density polyethylene (VLDPE), and
linear low density polyethylene
(LLDPE); and
• Thermoplastic elastomers such as
chlorinated polyethylene (CPE) and
chlorosulfonated polyethylene (CSPE).
The polymeric materials used most frequently
as geomembranes are HDPE, PVC, CSPE,
and CPE. The thicknesses of geomembranes
range from 20 to 120 mil (1 mil = 0.001 inch)
(U.S. EPA, 1983 and U.S. EPA, 1988e). The
recommended minimum thickness for all
geomembranes is 30 mil, with the exception
of HDPE, which must be at least 60 mil to
allow for proper seam welding. Some
geomembranes can be manufactured by a
calendering process with fabric reinforcement,
called scrim, to provide additional tensile
strength and dimensional stability.
Chemical and Physical Stress Resistance
The design of the landfill unit should consider
stresses imposed on the liner by the design
configuration. These stresses include the
following:
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Design Criteria
• Differential settlement in foundation
soils;
• Strain requirements at the anchor trench;
and
• Strain requirements over long, steep side
slopes.
An extensive body of literature has been
developed by manufacturers and independent
researchers on the physical properties of
liners. Geosynthetic design equations are
presented in several publications including
Kastman (1984), Koerner (1990), and U.S.
EPA(1988e).
The chemical resistance of a geomembrane to
leachate has traditionally been considered a
critical issue for Subtitle C (hazardous waste)
facilities where highly concentrated solvents
may be encountered. Chemical resistance
testing of geomembranes may not be required
for MSWLF units containing only municipal
solid waste; EPA's data base has shown that
leachate from MSWLF units is not aggressive
to these types of materials. Testing for
chemical resistance may be warranted
considering the waste type, volumes,
characteristics, and amounts of small quantity
generator waste or other industrial waste
present in the waste stream. The following
guidance is provided in the event such testing
is of interest to the owner or operator.
EPA's Method 9090 in SW-846 is the
established test procedure used to evaluate
degradation of geomembranes when exposed
to hazardous waste leachate. In the
procedure, the geomembrane is immersed in
the site-specific chemical environment for at
least 120 days at two different temperatures.
Physical and mechanical properties of the
tested material are then compared to those
of the original material every thirty days. A
software system entitled Flexible Liner
Evaluation Expert (FLEX), designed to assist
in the hazardous waste permitting process,
may aid in interpreting EPA Method 9090 test
data (U.S. EPA, 1989). A detailed discussion
of both Method 9090 and FLEX is available
from EPA.
It is imperative that a geomembrane liner
maintain its integrity during exposure to
short-term and long-term mechanical stresses.
Short-term mechanical stresses include
equipment traffic during the installation of a
liner system, as well as thermal expansion and
shrinkage of the geomembrane during the
construction and operation of the MSWLF
unit. Long-term mechanical stresses result
from the placement of waste on top of the
liner system and from subsequent differential
settlement of the subgrade (U.S. EPA, 1988a).
Long-term success of the liner requires
adequate friction between the components of
a liner system, particularly the soil subgrade
and the geomembrane, and between
geosynthetic components, so that slippage or
sloughing does not occur on the slopes of the
unit. Specifically, the foundation slopes and
the subgrade materials must be considered in
design equations to evaluate:
• The ability of a geomembrane to
support its own weight on the side
slopes;
The ability of a geomembrane to
withstand down-dragging during and
after waste placement;
• The best anchorage configuration for the
geomembrane;
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Subpart D
• The stability of a soil cover on top of a
geomembrane; and
• The stability of other geosynthetic
components such as geotextile or geonet
on top of a geomembrane.
These requirements may affect the choice of
geomembrane material, including polymer
type, fabric reinforcement, thickness, and
texture (e.g., smooth or textured for HDPE)
(U.S. EPA, 1988). PVC also can be obtained
in a roughened or file finish to increase the
friction angle.
Design specifications should indicate the type
of raw polymer and manufactured sheet to be
used as well as the requirements for the
delivery, storage, installation, and sampling of
the geomembrane. Material properties can be
obtained from the manufacturer-supplied
average physical property values, which are
published in the Geotechnical Fabrics Report's
Specifier's Guide and updated annually. The
minimum tensile properties of the
geomembrane must be sufficient to satisfy the
stresses anticipated during the service life of
the geomembrane. Specific raw polymer and
manufactured sheet specifications and test
procedures include (U.S. EPA, 1988e, and
Koerner, 1990):
Raw Polymer Specifications
• Density (ASTMD-1505);
• Melt index (ASTM D-1238);
• Carbon black (ASTM D-1603); and
• Thermogravimetric analysis (TGA)
or differential scanning calorimetry
(DSC).
Manufactured Sheet Specifications
• Thickness (ASTMD-1593);
• Tensile properties (ASTM D-638);
• Tear resistance (ASTM D-1004);
• Carbon black content (ASTM D-
1603);
• Carbon black dispersion (ASTM D-
3015);
• Dimensional stability (ASTM D-
1204); and
• Stress crack resistance (ASTM D-
1693).
Geomembranes may have different physical
characteristics, depending on the type of
polymer and the manufacturing process used,
that can affect the design of a liner system.
When reviewing manufacturers' literature, it
is important to remember that each
manufacturer may use more than one polymer
or resin type for each grade of geomembrane
and that the material specifications may be
generalized to represent several grades of
material.
Installation
Installation specifications should address
installation procedures specific to the
properties of the liner installed. The
coefficient of thermal expansion of the
geomembrane sheet can affect its installation
and its service performance. The
geomembrane should lie flat on the
underlying soil. However, shrinkage and
expansion of the sheeting, due to changes in
temperature during installation, may result in
excessive wrinkling or tension in the
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Design Criteria
geomembrane. Wrinkles on the
geomembrane surface will affect the
uniformity of the soil-geomembrane interface
and may result in leakage through
imperfections. Excessive tautness of the
geomembrane may affect its ability to resist
rupture from localized stresses on the seams
or at the toe of slopes where bridging over the
subgrade may occur during installation. In
addition to thermal expansion and contraction
of the geomembrane, residual stresses from
manufacturing remain in some geomembranes
and can cause non-uniform expansion and
contraction during construction. Some
flexibility is needed in the specifications for
geomembrane selection to allow for
anticipated dimensional changes resulting
from thermal expansion and contraction (U.S.
EPA, 1988).
Technical specifications for geomembranes
also should include: information for
protection of the material during shipping,
storage and handling; quality control
certifications provided by the manufacturer or
fabricator (if panels are constructed); and
quality control testing by the contractor,
installer, or a construction quality assurance
(CQA) agent. Installation procedures
addressed by the technical specifications
include a geomembrane layout plan,
deployment of the geomembrane at the
construction site, seam preparation, seaming
methods, seaming temperature constraints,
detailed procedures for repairing and
documenting construction defects, and sealing
of the geomembrane to appurtenances, both
adjoining and penetrating the liner. The
performance of inspection activities, including
both non-destructive and destructive quality
control field testing of the sheets and seams
during installation of the geomembrane,
should be addressed in the technical
specifications. Construction quality assurance
is addressed
in an EPA guidance document (USEPA,
1992).
The geomembrane sheeting is shipped in rolls
or panels from the supplier, manufacturer, or
fabricator to the construction site. Each roll
or panel may be labeled according to its
position on the geomembrane layout plan to
facilitate installation. Upon delivery, the
geomembrane sheeting should be inspected to
check for damage that may have occurred
during shipping. (U.S. EPA, 1992).
Proper storage of the rolls or panels prior to
installation is essential to the final
performance of the geomembrane. Some
geomembrane materials are sensitive to
ultraviolet exposure and should not be stored
in direct sunlight prior to installation. Others,
such as CSPE and CPE, are sensitive to
moisture and heat and can partially crosslink
or block (stick together) under improper
storage conditions. Adhesives or welding
materials, which are used to join
geomembrane panels, also should be stored
appropriately (U.S. EPA, 1992).
Visual inspection and acceptance of the soil
liner subgrade should be conducted prior to
installing the geomembrane. The surface of
the subgrade should meet design
specifications with regard to lack of
protruding objects, grades, and thickness.
Once these inspections are conducted and
complete, the geomembrane may be installed
on top of the soil liner. If necessary, other
means should be employed to protect the
subgrade from precipitation and erosion, and
to prevent desiccation, moisture loss, and
erosion from the soil liner prior to
geomembrane placement. Such methods may
include placing a plastic tarp on top of
completed portions of the soil liner
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Subpart D
(USEPA, 1992). In addition, scheduling soil
liner construction slightly ahead of the
geomembrane and drainage layer placement
can reduce the exposure of the soil liner to the
elements.
Deployment, or placement, of the
geomembrane panels or rolls should be
described in the geomembrane layout plan.
Rolls of sheeting, such as HDPE, generally
can be deployed by placing a shaft through
the core of the roll, which is supported and
deployed using a front-end loader or a winch.
Panels composed of extremely flexible liner
material such as PVC are usually folded on
pallets, requiring workers to manually unfold
and place the geomembrane. Placement of
the geomembrane goes hand-in-hand with the
seaming process; no more than the amount of
sheeting that can be seamed during a shift or
work day should be deployed at any one time
(USEPA, 1988). Panels should be weighted
with sand bags if wind uplift of the membrane
or excessive movement from thermal
expansion is a potential problem. Proper
stormwater control measurements should be
employed during construction to prevent
erosion of the soil liner underneath the
geomembrane and the washing away of the
geomembrane.
Once deployment of a section of the
geomembrane is complete and each section
has been visually inspected for imperfections
and tested to ensure that it is the specified
thickness, seaming of the geomembrane may
begin. Quality control/quality assurance
monitoring of the seaming process should be
implemented to detect inferior seams.
Seaming can be conducted either in the
factory or in the field. Factory seams are
made in a controlled environment and are
generally of high quality, but the entire seam
length (100 percent) still should be
tested non-destructively (U.S. EPA, 1988).
Destructive testing should be done at regular
intervals along the seam (see page 4-66).
Consistent quality in fabricating field seams is
critical to liner performance, and conditions
that may affect seaming should be monitored
and controlled during installation. An
inspection should be conducted in accordance
with a construction quality assurance plan to
document the integrity of field seams. Factors
affecting the seaming process include (U.S.
EPA, 1988):
• Ambient temperature at which the seams
are made;
• Relative humidity;
• Control of panel lift-up by wind;
• The effect of clouds on the
geomembrane temperature;
• Water content of the subsurface beneath
the geomembrane;
• The supporting surface on which the
seaming is bonded;
• The skill of the seaming crew;
• Quality and consistency of the chemical
or welding material;
• Proper preparation of the liner surfaces
to be joined;
• Moisture on the seam interface; and
• Cleanliness of the seam interface (e.g.,
the amount of airborne dust and debris
present).
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Design Criteria
Depending on the type of geomembrane,
several bonding systems are available for the
construction of both factory and field seams.
Bonding methods include solvents, heat seals,
heat guns, dielectric seaming, extrusion
welding, and hot wedge techniques. To
ensure the integrity of the seams, a
geomembrane should be seamed using the
bonding system recommended by the
manufacturer (U.S. EPA, 1988). EPA has
developed a field seaming manual for all
types of geomembranes (U.S. EPA, 199la).
Thermal methods of seaming require
cleanliness of the bonding surfaces, heat,
pressure, and dwell time to produce high
quality seams. The requirements for adhesive
systems are the same as those for thermal
systems, except that the adhesive takes the
place of the heat. Sealing the geomembrane
to appurtenances and penetrating structures
should be performed in accordance with
detailed drawings included in the design plans
and approved specifications.
An anchor trench along the perimeter of the
cell generally is used to secure the
geomembrane during construction (to prevent
sloughing or slipping down the interior side
slopes). Run out calculations (Koerner, 1990)
are available to determine the depth of burial
at a trench necessary to hold a specified length
of membrane, or combination of membrane
and geofabric or geotextile. If forces larger
than the tensile strength of the membrane are
inadvertently developed, then the membrane
could tear. For this reason, the geomembrane
should be allowed to slip or give in the trench
after construction to prevent such tearing.
However, during construction, the
geomembrane should be anchored according
to the detailed drawings provided in the
design plans and specifications (USEPA,
1988).
Geomembranes that are subject to damage
from exposure to weather and work activities
should be covered with a layer of soil as soon
as possible after quality assurance activities
associated with geomembrane testing are
completed. Soil should be placed without
driving construction vehicles directly on the
geomembrane. Light ground pressure
bulldozers may be used to push material out
in front over the liner, but the operator must
not attempt to push a large pile of soil forward
in a continuous manner over the membrane.
Such methods can cause localized wrinkles to
develop and overturn in the direction of
movement. Overturned wrinkles create sharp
creases and localized stresses in the
geomembrane that could lead to premature
failure. Instead, the operator should
continually place smaller amounts of soil or
drainage material working outward over the
toe of the previously placed material.
Alternatively, large backhoes can be used to
place soil over the geomembrane that can later
be spread with a bulldozer or similar
equipment. Although such methods may
sound tedious and slow, in the long run they
will be faster and more cost-effective than
placing too much material too fast and having
to remobilize the liner installer to repair
damaged sections of the geomembrane. The
QA activities conducted during construction
also should include monitoring the
contractor's activities on top of the liner to
avoid damage to installed and accepted
geomembranes.
Leachate Collection Systems
Leachate refers to liquid that has passed
through or emerged from solid waste and
contains dissolved, suspended, or immiscible
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Subpart D
materials removed from the solid waste. At
MSWLF units, leachate is typically aqueous
with limited, if any, immiscible fluids or
dissolved solvents. The primary function of
the leachate collection system is to collect and
convey leachate out of the landfill unit and to
control the depth of the leachate above the
liner. The leachate collection system (LCS)
should be designed to meet the regulatory
performance standard of maintaining less than
30 cm (12 inches) depth of leachate, or
"head," above the liner. The 30-cm head
allowance is a design standard and the Agency
recognizes that this design standard may be
exceeded for relatively short periods of time
during the active life of the unit. Flow of
leachate through imperfections in the liner
system increases with an increase in leachate
head above the liner. Maintaining a low
leachate level above the liner helps to improve
the performance of the composite liner.
Leachate is generally collected from the
landfill through sand drainage layers,
synthetic drainage nets, or granular drainage
layers with perforated plastic collection pipes,
and is then removed through sumps or gravity
drain carrier pipes. LCS's should consist of
the following components (U.S. EPA, 1988):
• A low-permeability base (in this case a
composite liner);
• A high-permeability drainage layer,
constructed of either natural granular
materials (sand and gravel) or synthetic
drainage material (e.g., geonet) placed
directly on the FML, or on a protective
bedding layer (e.g., geofabric) directly
overlying the liner;
• Perforated leachate collection pipes
within the high-permeability drainage
layer to collect leachate and carry it
rapidly to a sump or collection header
pipe;
• A protective filter layer over the high
permeability drainage material, if
necessary, to prevent physical clogging
of the material by fine-grained material;
and
• Leachate collection sumps or header
pipe system where leachate can be
removed.
The design, construction, and operation of the
LCS should maintain a maximum height of
leachate above the composite liner of 30 cm
(12 in). Design guidance for calculating the
maximum leachate depth over a liner for
granular drainage systems materials is
provided in the reference U.S. EPA (1989).
The leachate head in the layer is a function of
the liquid impingement rate, bottom slope,
pipe spacing, and drainage layer hydraulic
conductivity. The impingement rate is
estimated using a complex liquid routing
procedure. If the maximum leachate depth
exceeds 30 cm for the system, except for
short-term occurrences, the design should be
modified to improve its efficiency by
increasing grade, decreasing pipe spacing, or
increasing the hydraulic conductivity
(transmissivity) of the drainage layer (U.S.
EPA, 1988).
Grading of Low-Permeability Base
The typical bottom liner slope is a minimum
of two percent after allowances for settlement
at all points in each system. A slope is
necessary for effective gravity drainage
through the entire operating and post-closure
period. Settlement estimates of the
foundation soils should set this two-
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Design Criteria
percent grade as a post-settlement design
objective (U.S. EPA, 1991b).
High-Permeability Drainage Layer
The high-permeability drainage layer is
placed directly over the liner or its protective
bedding layer at a slope of at least two percent
(the same slope necessary for the composite
liner). Often the selection of a drainage
material is based on the on-site availability of
natural granular materials. In some regions of
the country, hauling costs may be very high
for sand and gravel, or appropriate materials
may be unavailable; therefore, the designer
may elect to use geosynthetic drainage nets
(geonets) or synthetic drainage materials as an
alternative. Frequently, geonets are
substituted for granular materials on steep
sidewalls because maintaining sand on the
slope during construction and operation of the
landfill unit is more difficult (U.S. EPA,
1988).
Soil Drainage Layers
If the drainage layer of the leachate collection
system is constructed of granular soil
materials (e.g., sand and gravel), then it
should be demonstrated that this granular
drainage layer has sufficient bearing strength
to support expected loads. This
demonstration will be similar to that required
for the foundations and soil liner (U.S. EPA,
1988).
If the landfill unit is designed on moderate-to-
steep (15 percent) grades, the landfill design
should include calculations demonstrating that
the selected granular drainage materials will
be stable on the most critical slopes (e.g.,
usually the steepest slope) in the design. The
calculations and assumptions should be
shown, especially the
friction angle between the geomembrane and
soil, and if possible, supported by laboratory
and/or field testing (USEPA, 1988).
Generally, gravel soil with a group
designation of GW or GP on the Unified Soils
Classification Chart can be expected to have
a hydraulic conductivity of greater than 0.01
cm/sec, while sands identified as SW or SP
can be expected to have a coefficient of
permeability greater than 0.001 cm/sec. The
sand or gravel drains leachate that enters the
drainage layer to prevent 30 cm (12 in) or
more accumulation on top of the liner during
the active life of the MSWLF unit LCS. The
design of a LCS frequently uses a drainage
material with a hydraulic conductivity of 1 x
10"2 cm/sec or higher. Drainage materials
with hydraulic conductivities in this order of
magnitude should be evaluated for biological
and particulate clogging (USEPA, 1988).
Alternatively, if a geonet is used, the design is
based on the transmissivity of the geonet.
If a filter layer (soil or geosynthetic) is
constructed on top of a drainage layer to
protect it from clogging, and the LCS is
designed and operated to avoid drastic
changes in the oxidation reduction potential of
the leachate (thereby avoiding formation of
precipitates within the LCS), then there is no
conceptual basis to anticipate that
conductivity will decrease over time. Where
conductivity is expected to decrease over
time, the change in impingement rate also
should be evaluated over the same time period
because the reduced impingement rate and
hydraulic conductivity may still comply with
the 30 cm criterion.
Unless alternative provisions are made to
control incident precipitation and resulting
surface run-off, the impingement rate during
the operating period of the MSWLF unit is
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Subpart D
usually at least an order of magnitude greater
than the impingement rate after final closure.
The critical design condition for meeting the
30 cm (12 in) criterion can therefore be
expected during the operating life. The
designer may evaluate the sensitivity of a
design to meet the 30 cm (12 in) criterion as
a result of changes in impingement rates,
hydraulic conductivity, pipe spacing, and
grades. Such sensitivity analysis may indicate
which element of the design should be
emphasized during construction quality
monitoring or whether the design can be
altered to comply with the 30 cm (12 in)
criterion in a more cost-effective manner.
The soil material used for the drainage layer
should be investigated at the borrow pit prior
to use at the landfill. Typical borrow pit
characterization testing would include
laboratory hydraulic conductivity and grain
size distribution. If grain size distribution
information from the borrow pit
characterization program can be correlated to
the hydraulic conductivity data, then the grain
size test, which can be conducted in a short
time in the field, may be a useful construction
quality control parameter. Compliance with
this parameter would then be indicative that
the hydraulic conductivity design criterion
was achieved in the constructed drainage
layer. This information could be incorporated
into construction documents after the borrow
pit has been characterized. If a correlation
cannot be made between hydraulic
conductivity and grain size distribution, then
construction documents may rely on direct
field or laboratory measurements to
demonstrate that the hydraulic conductivity
design criterion was met in the drainage layer.
Granular materials are generally placed using
conventional earthmoving equipment,
including trucks, scrapers, bulldozers, and
front-end loaders. Vehicles should not be
driven directly over the geosynthetic
membrane when it is being covered. (U.S.
EPA, 1988a).
Coarse granular drainage materials, unlike
low-permeability soils, can be placed dry and
do not need to be heavily compacted.
Compacting granular soils tends to grind the
soil particles together, which increases the
fine material and reduces hydraulic
conductivity. To minimize settlement
following material placement, the granular
material may be compacted with a vibratory
roller. The final thickness of the drainage
layer should be checked by optical survey
measurements or by direct test pit
measurements (U.S. EPA, 1988).
Geosynthetic Drainage Nets
Geosynthetic drainage nets (geonets) may be
substituted for the granular layers of the LCRs
on the bottom and sidewalls of the landfill
cells. Geonets require less space than
perforated pipe or gravel and also promote
rapid transmission of liquids. They do,
however, require geotextile filters above them
and can experience problems with creep and
intrusion. Long-term operating and
performance experience of geonets is limited
because the material and its application are
relatively new (U.S. EPA, 1989).
If a geonet is used in place of a granular
drainage layer, it must provide the same level
of performance (maintaining less than 30 cm
of leachate head above the liner). An
explanation of the calculation used to compute
the capacity of a geonet may be found in U.S.
EPA(1987a). The
168
-------
Design Criteria
transmissivity of a geonet can be reduced
significantly by intrusion of the soil or a
geotextile. A protective geotextile between
the soil and geonet will help alleviate this
concern. If laboratory transmissivity tests are
performed, they should be done under
conditions, loads, and configurations that
closely replicate the actual field conditions. It
is important that the transmissivity value used
in the leachate collection system design
calculations be selected based upon those
loaded conditions (U.S. EPA, 1988). It is also
important to ensure that appropriate factors of
safety are used (Koerner, 1990).
The flow rate or transmissivity of geonets
may be evaluated by ASTM D-4716. This
flow rate may then be compared to design-by-
function equations presented in U.S. EPA
(1989). In the ASTM D-4716 flow test, the
proposed collector cross section should be
modeled as closely as possible to actual field
conditions (U.S. EPA, 1989).
Figure 4-7 shows the flow rate "signatures" of
a geonet between two geomembranes (upper
curves) and the same geonet between a layer
of clay soil and a geomembrane (lower
curves). The differences between the two sets
of curves represent intrusion of the
geotextile/clay into the apertures of the
geonet. The curves are used to obtain a flow
rate for the particular geonet being designed
(U.S. EPA, 1989). Equations to determine the
design flow rate or transmissivity are also
presented in U.S. EPA (1989), Giroud (1982),
Carroll (1987), Koerner (1990), and FHWA
(1987).
Generally, geonets perform well and result in
high factors of safety or performance design
ratios, unless creep (elongation under constant
stress) becomes a problem or adjacent
materials intrude into apertures (U.S. EPA,
1989). For geonets, the most
critical specification is the ability to transmit
fluids under load. The specifications also
should include a minimum transmissivity
under expected landfill operating (dynamic)
or completion (static) loads. The
specifications for thickness and types of
material should be identified on the drawings
or in the materials section of the
specifications, and should be consistent with
the design calculations (U.S. EPA, 1988).
Geonets are often used on the sidewalls of
landfills because of their ease of installation.
They should be placed with the top ends in a
secure anchor trench with the strongest
longitudinal length extending down the slope.
The geonets need not be seamed to each other
on the slopes, only tied at the edges, butted, or
overlapped. They should be placed in a loose
condition, not stretched or placed in a
configuration where they are bearing their
own weight in tension. The construction
specifications should contain appropriate
installation requirements as described above
or the requirements of the geonet
manufacturer. All geonets need to be
protected by a filter layer or geotextile to
prevent clogging (U.S. EPA, 1988).
The friction factors against sliding for
geotextiles, geonets, and geomembranes often
can be estimated using manufacturers data
because these materials do not exhibit the
range of characteristics as seen in soil
materials. However, it is important that the
designer perform the actual tests using site
materials and that the sliding stability
calculations accurately represent the actual
design configuration, site conditions, and the
specified material characteristics (U.S. EPA,
1988).
169
-------
c
E
"co
•S
d>
75
en
o
c
E
OJ
75
CE
_o
LL
5,000 10,000 15,000
Normal Stress (1lbs./sq. R)
(a) FML - Geonet - FML Composite
20,000
20,000
5,000 10,000 15,000
Normal Stress (1lbs./sq. R)
(b) FML - Geonet - Geotextile - Clay Soil Composite
Source: U.S. EPA. 1989.
Figure 4-1. Flow Rate Curves for Geonets in Two Composite Liner Configurations
170
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Design Criteria
Leachate Collection Pipes
All components of the leachate collection
system must have sufficient strength to
support the weight of the overlying waste,
cover system, and post-closure loadings, as
well as the stresses from operating
equipment. The component that is most
vulnerable to compressive strength failure is
the drainage layer piping. Leachate
collection system piping can fail by
excessive deflection, which may lead to
buckling or collapse (USEPA, 1988). Pipe
strength calculations should include
resistance to wall crushing, pipe deflection,
and critical buckling pressure. Design
equations and information for most pipe
types can be obtained from the major pipe
manufacturers. For more information
regarding pipe structural strength, refer to
U.S. EPA (1988).
Perforated drainage pipes can provide good
long-term performance. These pipes have
been shown to transmit fluids rapidly and to
maintain good service lives. The depth of
the drainage layer around the pipe should be
deeper than the diameter of the pipe. The
pipes can be placed in trenches to provide
the extra depth. In addition, the trench
serves as a sump (low point) for leachate
collection. Pipes can be susceptible to
particulate and biological clogging similar
to the drainage layer material. Furthermore,
pipes also can be susceptible to deflection.
Proper maintenance and design of pipe
systems can mitigate these effects and
provide systems that function properly.
Acceptable pipe deflections should be
evaluated for the pipe material to be used
(USEPA, 1989).
The design of perforated collection pipes
should consider the following factors:
• The required flow using known
percolation impingement rates and pipe
spacing;
• Pipe size using required flow and
maximum slope; and
• The structural strength of the pipe.
The pipe spacing may be determined by the
Mound Model. In the Mound Model (see
Figure 4-8), the maximum height of fluid
between two parallel perforated drainage
pipes is equal to (U.S. EPA, 1989):
_ L\fc r tan2a _ tana
s 2 c c
where c = q/k
k = permeability
q = inflow rate
a = slope.
The two unknowns in the equation are:
L = distance between the pipes; and
c = amount of leachate.
Using a maximum allowable head, hmax, of 30
cm (12 in), the equation is usually solved for
"L" (U.S. EPA, 1989).
The amount of leachate, "c", can be estimated
in a variety of ways including the Water
Balance Method (U.S. EPA, 1989) and the
computer model Hydrologic Evaluation of
Landfill Performance (HELP). The HELP
Model is a quasi-two-dimensional hydrologic
model of water movement across, into,
through, and out of landfills. The model uses
climatologic, soil, and landfill design data and
incorporates a solution technique that
accounts for the effects of surface storage,
run-off, infiltration, percolation, soil-moisture
171
-------
Subpart D
Inflow
Source: L'.5. £W. /9S9
Figure 4-8. Definition of Terms for Mound Model
Flow Rate Calculations
172
-------
Design Criteria
storage, evapotranspiration, and lateral
drainage. The program estimates run-off
drainage and leachate that are expected to
result from a wide variety of landfill
conditions, including open, partially open, and
closed landfill cells. The model also may be
used to estimate the depth of leachate above
the bottom liner of the landfill unit. The
results may be used to compare designs or to
aid in the design of leachate collection
systems (U.S. EPA, 1988).
Once the percolation and pipe spacing are
known, the design flow rate can be obtained
using the curve in Figure 4-9. The amount of
leachate percolation at the particular site is
located on the x-axis.
The required flow rate is the point at which
this value intersects with the pipe spacing
value determined from the Mound Model.
Using this value of flow rate and the bottom
slope of the site, the required diameter for the
pipe can be determined (see Figure 4-10).
Finally, the graphs in Figures 4-11 and 4-12
show two ways to determine whether the
strength of the pipe is adequate for the landfill
design. In Figure 4-11, the vertical soil
pressure is located on the y-axis. The density
of the backfill material around the pipe is not
governed by strength, so it will deform under
pressure rather than break. Ten percent is the
absolute limiting deflection value for plastic
pipe. Using Figure 4-11, the applied pressure
on the pipe is located and traced to the trench
geometry, and then the pipe deflection value
is checked for its adequacy (U.S. EPA, 1989).
The LCS specifications should include (U.S.
EPA, 1988):
• Type of piping material;
• Diameter and wall thickness;
• Size and distribution of slots and
perforations;
• Type of coatings (if any) used in the
pipe manufacturing; and
• Type of pipe bedding material and
required compaction used to support the
pipes.
The construction drawings and specifications
should clearly indicate the type of bedding to
be used under the pipes and the dimensions of
any trenches. The specifications should
indicate how the pipe lengths are joined. The
drawings should show how the pipes are
placed with respect to the perforations. To
maintain the lowest possible leachate head,
there should be perforations near the pipe
invert, but not directly at the invert. The pipe
invert itself should be solid to allow for
efficient pipe flow at low volumes (U.S. EPA,
1988).
When drainage pipe systems are embedded in
filter and drainage layers, no unplugged ends
should be allowed. The filter materials in
contact with the pipes should be appropriately
sized to prevent migration of the material into
the pipe. The filter media, drainage layer, and
pipe network should be compatible and should
represent an integrated design.
Protection of Leachate Collection Pipes
The long-term performance of the LCS
depends on the design used to protect pipes
from physical clogging (sedimentation) by the
granular drainage materials. Use of a graded
material around the pipes is most effective if
accompanied by proper sizing of pipe
perforations. The Army Corps of
173
-------
Subpart D
Percolation, in Inches per Month
*Where b = width of area contributing to leachate collection pipe
Source: U.S. EPA. 1989
Figure 4-9. Required Capacity of Leachate Collection Pipe
174
-------
1000
o
o
600
300
200
1
0.9
0.8
0.7
0.6
0.5
0.4
\
A
V
\
\
\
\
\ \
\ \
\ V
V
\
\
\
\
\
•Sy"*-*^
U
c
A3
K
«-:
\---\
^s:
^
f^b
P
_c
&
ca
•s
VI
a
100
\^
'"k
"
*
0.2
50
0.1
V
\
V*
Pipe Flowing Full
Based on Manning's Equation n=0.010
0.1
0.2 0.3 0.4 0.5 0.6 0.8 1.0
2.0 3.0 4.0 5.0 6.0 8.0 10
10 20 30 40 60
Source: U.S. EPA, 1989
Slope of Pipe in Feet per Thousand Feet
Figure 4-10. Leachate Collection Pipe Sizing Chart
-------
Subpart D
n
95% Soil
Density
12.000
10.000
8.000
6.000
4.000
2.000
Initial Effect of Ring Stiffness i
i i
85% Soil
Density
90%
75% Soil
Density
75% Soil Density Plot of
Vertical Soil Strain £
0 5 10 15 20 25
Ring Deflection, AY/D (%) = 6 Except as Noted
Source: U.S. EPA. 1989
Figure 4-11. Vertical Ring Deflection Versus Vertical Soil Pressure for
18-inch Corrugated Polyethylene in High Pressure Soil Cell
176
-------
Design Criteria
a
•
B/D = 7.73
B/D = 7.5
B/D = 1.8
Vertical Soil Strain £
for Native Soil @
75% Density
25
30
Ring Deflection, AY/D (%)
Source: U.S. EPA, 1989
Figure 4-12. Example of the Effect of Trench Geometry
and Pipe Sizing on Ring Deflection
177
-------
Subpart D
Engineers (GCA Corporation, 1983) has
established design criteria using graded filters
to prevent physical clogging of leachate
drainage layers and piping by soil sediment
deposits. When installing graded filters,
caution should be taken to prevent segregation
of the material (USEPA, 199la).
Clogging of the pipes and drainage layers of
the leachate collection system can occur
through several other mechanisms, including
chemical and biological fouling (USEPA,
1988). The LCS should be designed with a
cleanout access capable of reaching all parts
of the collection system with standard pipe
cleaning equipment.
Chemical clogging can occur when dissolved
species in the leachate precipitate in the
piping. Clogging can be minimized by
periodically flushing pipes or by providing a
sufficiently steep slope in the system to allow
for high flow velocities for self-cleansing.
These velocities are dependent on the
diameter of the precipitate particles and on
their specific gravity. ASCE (1969) discusses
these relationships. Generally, flow velocities
should be in the range of one or two feet per
second to allow for self-cleansing of the
piping (U.S. EPA, 1988).
Biological clogging due to algae and bacterial
growth can be a serious problem in MSWLF
units. There are no universally effective
methods of preventing such biological
growth. Since organic materials will be
present in the landfill unit, there will be a
potential for biological clogging. The system
design should include features that allow for
pipe system cleanings. The components of
the cleaning system should include (U.S.
EPA, 1991b):
• A minimum of six-inch diameter pipes
to facilitate cleaning;
• Access located at major pipe
intersections or bends to allow for
inspections and cleaning; and
• Valves, ports, or other appurtenances to
introduce biocides and/or cleaning
solutions.
In its discussion of drainage layer protection,
the following section includes further
information concerning protection of pipes
using filter layers.
Protection of the High-Permeability
Drainage Layer
The openings in drainage materials, whether
holes in pipes, voids in gravel, or apertures in
geonets, must be protected against clogging
by accumulation of fine (silt-sized) materials.
An intermediate material that has smaller
openings than those of the drainage material
can be used as a filter between the waste and
drainage layer. Sand may be used as filter
material, but has the disadvantage of taking
up vertical space (USEPA, 1989). Geotextiles
do not use up air space and can be used as
filter materials.
Soil Filter Layers
There are three parts to an analysis of a sand
filter that is placed above drainage material.
The first determines whether or not the filter
allows adequate flow of liquids. The second
evaluates whether the void spaces are small
enough to prevent solids from being lost from
the upstream materials. The third estimates
the long-term clogging behavior of the filter
(U.S. EPA, 1989).
The particle-size distribution of the drainage
system and the particle-size distribution of the
invading (or upstream) soils are required
178
-------
Design Criteria
in the design of granular soil (sand filter)
materials. The filter material should have its
large and small size particles intermediate
between the two extremes. Equations for
adequate flow and retention are:
• Adequate Flow:
d85f> (3 to 5)d15ds
• Adequate Retention:
d15f< (3 to 5)d85wf
Where f = required filter soil;
d.s. = drainage stone; and
w.f = water fines.
There are no quantitative methods to assess
soil filter clogging, although empirical
guidelines are found in geotechnical
engineering references.
The specifications for granular filter layers
that surround perforated pipes and that protect
the drainage layer from clogging are based on
a well-defined particle size distribution. The
orientation and configuration of filter layers
relative to other LCS components should be
shown on all drawings and should be
described, with ranges of particle sizes, in the
materials section of the specifications (U.S.
EPA, 1988a).
Thickness is an important placement criterion
for granular filter material. Generally, the
granular filter materials will be placed around
perforated pipes by hand, forming an
"envelope." The dimensions of the envelope
should be clearly stated on the drawings or in
the specifications. This envelope can be
placed at the same time as the granular
drainage layer, but it is important that the
filter envelope protect all areas of the pipe
where the clogging potential exists. The plans
and
specifications should indicate the extent of the
envelope. The construction quality control
program should document that the envelope
was installed according to the plans and
specifications (U.S. EPA, 1988).
A granular filter layer is generally placed
using the same earthmoving equipment as the
granular drainage layer. The final thickness
should be checked by optical survey or by
direct test pit measurement (U.S. EPA, 1988).
This filter layer is the uppermost layer in the
leachate collection system. A landfill design
option includes a buffer layer, 12 inches thick
(30 cm) or more, to protect the filter layer and
drainage layer from damage due to traffic.
This final layer can be general fill, as long as
it is no finer than the soil used in the filter
layer (U.S. EPA, 1988). However, if the
layer has a low permeability, it will affect
leachate recirculation attempts.
Geotextile Filter Layers
Geotextile filter fabrics are often used. The
open spaces in the fabric allow liquid flow
while simultaneously preventing upstream
fine particles from fouling the drain.
Geotextiles save vertical space, are easy to
install, and have the added advantage of
remaining stationary under load. Geotextiles
also can be used as cushioning materials
above geomembranes (USEPA, 1989).
Because geotextile filters are susceptible to
biological clogging, their use in areas
inundated by leachate (e.g., sumps, around
leachate collection pipes, and trenches) should
be avoided.
Geotextile filter design parallels sand filter
design with some modifications (U.S. EPA,
1989). Adequate flow is assessed by
179
-------
Subpart D
comparing the material (allowable)
permittivity to the design imposed
permittivity. Permittivity is measured by the
ASTM D-4491 test method. The design
permittivity utilizes an adapted form of
Darcy's law. The resulting comparison yields
a design ratio, or factor of safety, that is the
focus of the design (U.S. EPA, 1989):
DR = 0allow/0reqd
where:
0aiiow = permittivity from ASTM
D-4491
0reqd= (q/a) (l/hmax)
q/a = inflow rate per unit area
h max = 12 inches
The second part of the geotextile filter design
is determining the opening size necessary for
retaining the upstream soil or particulates in
the leachate. It is well established that the 95
percent opening size is related to particles to
be retained in the following type of
relationship:
095 < fct. (d50, CU, DR)
where:
O95 = 95% opening size of
geotextile;
d50 = 50% size of upstream particles;
CU = Uniformity of the upstream
particle size; and
DR = Relative density of the
upstream particles.
The O95 size of a geotextile in the equation is
the opening size at which 5 percent of a given
value should be less than the particle size
characteristics of the invading materials. In
the test for the O95 size of the geotextile, a
sieve with a very coarse mesh in the bottom is
used as a support. The geotextile is placed on
top of the mesh and is bonded
to the inside so that the glass beads used in the
test cannot escape around the edges of the
geotextile filter. The particle-size distribution
of retained glass beads is compared to the
allowable value using any of a number of
existing formulas (U.S. EPA, 1989).
The third consideration in geotextile design is
long-term clogging. A test method for this
problem that may be adopted by ASTM is
called the Gradient Ratio Test. In this test,
the hydraulic gradient of 1 inch of soil plus
the underlying geotextile is compared with the
hydraulic gradient of 2 inches of soil. The
higher the gradient ratio, the more likely that
a clog will occur. The final ASTM gradient
ratio test will include failure criteria. An
alternative to this test method is a long-term
flow test that also is performed in a
laboratory. The test models a soil-to-fabric
system at the anticipated hydraulic gradient.
The flow rate through the system is
monitored. A long-term flow rate will
gradually decrease until it stops altogether
(U.S. EPA, 1989).
The primary function of a geotextile is to
prevent the migration of fines into the
leachate pipes while allowing the passage of
leachate. The most important specifications
are those for hydraulic conductivity and
retention. The hydraulic conductivity of the
geotextile generally should be at least ten
times the soil it is retaining. An evaluation of
the retention ability for loose soils is based on
the average particle size of the soil and the
apparent opening size (AOS) of the geotextile.
The maximum apparent opening size,
sometimes called equivalent opening size, is
determined by the size of the soil that will be
retained; a geotextile is then selected to meet
that specification. The material specifications
should contain a range of AOS values for the
geotextile, and
180
-------
Design Criteria
these AOS values should match those used in
the design calculations (U.S. EPA, 1988).
One of the advantages of geotextiles is their
light weight and ease of placement. The
geotextiles are brought to the site, unrolled,
and held down with sandbags until they are
covered with a protective layer. They are
usually overlapped, not seamed; however, on
slopes or in other configurations, they may be
sewn (U.S. EPA, 1988).
As with granular filter layers, it is important
that the design drawings be clear in their
designation of geotextile placement so that no
potential route of pipe or drainage layer
clogging is left unprotected. If geotextiles are
used on a slope, they should be secured in an
anchor trench similar to those for
geomembranes or geonets (U.S. EPA, 1988).
Leachate Removal System
Sumps, located in a recess at the low point(s)
within the leachate collection drainage layer,
provide one method for leachate removal
from the MSWLF unit. In the past, low
volume sumps have been constructed
successfully from reinforced concrete pipe on
a concrete footing, and supported above the
geomembrane on a steel plate to protect the
geomembrane from puncture. Recently,
however, prefabricated polyethylene
structures have become available. These
structures may be suitable for replacing the
concrete components of the sump and have
the advantage of being lighter in weight.
These sumps typically house a submersible
pump, which is positioned close to the sump
floor to pump the leachate and to maintain a
30 cm (12 in) maximum leachate depth.
Low-volume sumps, however, can present
operational problems. Because they may run
dry frequently, there is an increased
probability of the submersible pumps burning
out. For this reason, some landfill operators
prefer to have sumps placed at depths between
1.0 and 1.5 meters. While head levels of 30
cm or less are to be maintained on the liner,
higher levels are acceptable in sumps.
Alternatively, the sump may be designed with
level controls and with a backup pump to
control initiation and shut-off of the pumping
sequence and to have the capability of
alternating between the two pumps. The
second pump also may be used in conjunction
with the primary pump during periods of high
flow (e.g., following storm events) and as a
backup if the primary pump fails to function.
A visible alarm warning light to indicate
pump failure to the operator also may be
installed.
Pumps used to remove leachate from the
sumps should be sized to ensure removal of
leachate at the maximum rate of generation.
These pumps also should have a sufficient
operating head to lift the leachate to the
required height from the sump to the access
port. Portable vacuum pumps can be used if
the required lift height is within the limit of
the pump. They can be moved in sequence
from one leachate sump to another. The type
of pump specified and the leachate sump
access pipes should be compatible and should
consider performance needs under operating
and closure conditions (U.S. EPA, 1988).
Alternative methods of leachate removal
include internal standpipes and pipe
penetrations through the geomembrane, both
of which allow leachate removal by gravity
flow to either a leachate pond or exterior
pump station. If a leachate removal standpipe
is used, it should be extended through the
entire landfill from liner to
181
-------
Subpart D
cover and then through the cover itself. If a
gravity drainage pipe that requires
geomembrane penetration is used, a high
degree of care should be exercised in both the
design and construction of the penetration.
The penetration should be designed and
constructed in a manner that allows
nondestructive quality control testing of 100
percent of the seal between the pipe and the
geomembrane. If not properly constructed
and fabricated, geomembrane penetrations can
become a source of leakage through the
geomembrane.
Other Design Considerations
The stability of the individual leachate
collection system components placed on
geomembrane-covered slopes should be
considered. A method for calculating the
factor of safety (FS) against sliding for soils
placed on a sloped geomembrane surface is
provided in Koerner (1990). This method
considers the factors affecting the system,
including the slope length, the slope angle,
and the friction angle between the
geomembrane and its cover soil. Generally,
the slope angle is known and is specified on
the design drawings. A minimum FS is then
selected. From the slope angle and the FS, a
minimum allowable friction angle is
determined, and the various components of
the liner system are selected based on this
minimum friction angle. If the design
evaluation results in an unacceptably low FS,
then either the sidewall slope or the materials
should be changed to produce an adequate
design (U.S. EPA, 1988). For short slopes in
a landfill unit, the FS can be as low as 1.1 to
1.2 if the slope will be unsupported (i.e., no
waste will be filled against it) for only a short
time, and if any failures that do occur can be
repaired fairly easily. Longer slopes may
require higher factors of safety due to the
potential of
sliding material to tear the geomembrane
along the slope or near the toe of the slope.
Construction Quality Assurance and
Quality Control
The following section is excerpted from U.S.
EPA (1992). This section discusses quality
assurance and quality control (QA/QC)
objectives. For a more detailed discussion on
QA/QC and specific considerations, refer to
U.S. EPA (1992).
CQA/CQC Objectives
Construction quality assurance (CQA)
consists of a planned series of observations
and tests to ensure that the final product meets
project specifications. CQA plans,
specifications, observations, and tests are used
to provide quantitative criteria with which to
accept the final product.
On routine construction projects, CQA is
normally the concern of the owner and is
obtained using an independent third-party
testing firm. The independence of the third-
party inspection firm is important, particularly
when the owner is a corporation or other legal
entity that has under its corporate "umbrella"
the capacity to perform the CQA activities.
Although "in-house" CQA personnel may be
registered professional engineers, a perception
of misrepresentation may exist if CQA is not
performed by an independent third party.
The CQA officer should fully disclose any
activities or relationships with the owner
that may impact his impartiality or
objectivity. If such activities or
relationships exist, the CQA officer should
describe actions that have been or can be
taken to avoid, mitigate, or neutralize the
possibility they might affect the CQA
182
-------
Design Criteria
officer's objectivity. Regulatory
representatives can then evaluate whether
these mechanisms are sufficient to ensure an
acceptable CQA product.
Construction quality control (CQC) is an
on-going process of measuring and
controlling the characteristics of the product
in order to meet manufacturer's or project
specifications. CQC is a production tool
that is employed by the manufacturer of
materials and by the contractor installing the
materials at the site. CQA, by contrast, is a
verification tool employed by the facility
owner or regulatory agency to ensure that
the materials and installations meet project
specifications. CQC is performed
independently of the CQA Plan. For
example, while a geomembrane liner
installer will perform CQC testing of field
seams, the CQA program will require
independent CQA testing of those same
seams by a third-party inspector.
The CQA/CQC plans are implemented
through inspection activities that include
visual observations, field testing and
measurements, laboratory testing, and
evaluation of the test data. Inspection
activities typically are concerned with four
separate functions:
• Quality Control (QC) Inspection by
the Manufacturer provides an in-
process measure of the product quality
and its conformance with the project
plans and specifications. Typically,
the manufacturer will QC test results
to certify that the product conforms to
project plans and specifications.
Construction Quality Control (CQC)
Inspection by the Contractor provides
an in-process measure of construction
quality and conformance with the
project plans and specifications,
thereby allowing the contractor to
correct the construction process if the
quality of the product is not meeting
the specifications and plans.
Construction Quality Assurance
(CQA) Testing by the Owner
(Acceptance Inspection) performed by
the owner usually through the third-
party testing firm, provides a measure
of the final product quality and its
conformance with project plans and
specifications. Due to the size and
costs of a typical MSWLF unit
construction project, rejection of the
project at completion would be costly
to all parties. Acceptance Inspections
as portions of the project become
complete allow deficiencies to be
found and corrected before they
become too large and costly.
Regulatory Inspection often is
performed by a regulatory agency to
ensure that the final product conforms
with all applicable codes and
regulations. In some cases, the
regulatory agency will use CQA
documentation and the as-built plans
or "record drawings" to confirm
compliance with the regulations.
Soil Liner Quality Assurance/Quality
Control
Quality control testing performed on
materials used in construction of the landfill
unit includes source testing and construction
testing. Source testing defines material
properties that govern material placement.
Source testing commonly includes moisture
content, soil density, Atterberg limits, grain
size, and laboratory hydraulic conductivity.
Construction testing ensures that landfill
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construction has been performed in
accordance with the plans and technical
specifications. Construction testing
generally includes tests of soil moisture
content, density, lift thickness, and
hydraulic conductivity.
The method of determining compliance with
the maximum hydraulic conductivity
criterion should be specified in the QA/QC
plan. Some methods have included the use
of the criterion as a maximum value that
never should be exceeded, while other
methods have used statistical techniques to
estimate the true mean. The sample
collection program should be designed to
work with the method of compliance
determination. Selection of sample
collection points should be made on a
random basis.
Thin wall sampling tubes generally are used
to collect compacted clay samples for
laboratory hydraulic conductivity testing. It
is important to minimize disturbance of the
sample being collected. Tubes pushed into
the soil by a backhoe may yield disturbed
samples. A recommended procedure (when
a backhoe is available during sample
collection) is to use the backhoe bucket as a
stationary support and push the tube into the
clay with a jack positioned between the clay
and the tube. The sample hole should be
filled with bentonite or a bentonite clay
mixture, and compacted using short lifts of
material.
If geophysical methods are used for
moisture and density measurements, it is
recommended that alternative methods be
used less frequently to verify the accuracy
of the faster geophysical methods.
Additional information on testing
procedures can be found in U.S. EPA
(1988b) and U.S. EPA (1990a).
Quality assurance testing for soil liners
includes the same testing requirements as
specified above for control testing.
Generally, the tests are performed less
frequently and are performed by an
individual or an entity independent of the
contractor. Activities of the construction
quality assurance (CQA) officer are
essential to document quality of
construction. The CQA officer's
responsibilities and those of the CQA
officer's staff members may include:
• Communicating with the contractor;
• Interpreting and clarifying project
drawings and specifications with the
designer, owner, and contractor;
• Recommending acceptance or
rejection by the owner/operator of
work completed by the construction
contractor;
• Submitting blind samples (e.g.,
duplicates and blanks) for analysis by
the contractor's testing staff or one or
more independent laboratories, as
applicable;
• Notifying owner or operator of
construction quality problems not
resolved on-site in a timely manner;
• Observing the testing equipment,
personnel, and procedures used by the
construction contractor to check for
detrimentally significant changes over
time;
• Reviewing the construction
contractor's quality control recording,
maintenance, summary, and
interpretations of test data for
accuracy and appropriateness; and
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Design Criteria
• Reporting to the owner/operator on
monitoring results.
Soil Liner Pilot Construction (Test Fill)
A pilot construction or test fill is a small-
scale test pad that can be used to verify that
the soil, equipment, and construction
procedures can produce a liner that performs
according to the construction drawings and
specifications. An owner or operator may
want to consider the option of constructing
a test fill prior to the construction of the
liner. A test pad is useful not only in
teaching people how to build a soil liner, it
also can function as a construction quality
assurance tool. If the variables used to build
a test pad that achieves a IxlO"7 cm/sec
hydraulic conductivity are followed exactly,
then the completed full-size liner should
meet the regulatory requirements (U.S.
EPA, 1989). A test fill may be a cost-
effective method for the contractor to
evaluate the construction methods and
borrow source. Specific factors that can be
examined/tested during construction of a
test fill include (U.S. EPA, 1988b):
• Preparation and compaction of
foundation material to the required
bearing strength;
• Methods of controlling uniformity of
the soil material;
• Compactive effort (e.g., type of
equipment, number of passes) to
achieve required soil density and
hydraulic conductivity;
• Lift thickness and placement
procedures to achieve uniformity of
density throughout a lift and the
absence of apparent boundary effects
between lifts or between placements in
the same lift;
• Procedures for protecting against
desiccation cracking or other site- and
season-specific failure mechanisms for
the finished liner or intermediate lifts;
• Measuring the hydraulic conductivity
on the test fill in the field and
collecting samples of field-compacted
soil for laboratory testing;
• Test procedures for controlling the
quality of construction;
• Ability of different types of soil to
meet hydraulic conductivity
requirements in the field; and
• Skill and competence of the
construction team, including
equipment operators and quality
control specialists.
Geomembrane Quality Assurance/
Quality Control Testing
As with the construction of soil liners,
installation of geomembrane liners should
be in conformance with a quality
assurance/quality control plan. Tests
performed to evaluate the integrity of
geomembrane seams are generally
considered to be either "destructive" or
"non-destructive."
Destructive Testing
Quality control testing of geomembranes
generally includes peel and shear testing of
scrap test weld sections prior to
commencing seaming activities and at
periodic intervals throughout the day.
Additionally, destructive peel and shear
field
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Subpart D
tests are performed on samples from the
installed seams.
Quality assurance testing generally requires
that an independent laboratory perform peel
and shear tests of samples from installed
seams. The samples may be collected
randomly or in areas of suspect quality.
HDPE seams are generally tested at
intervals equivalent to one sample per every
300 to 400 feet of installed seam for
extrusion welds, and every 500 feet for
fusion-welded seams. Extrusion seams on
HDPE require grinding prior to welding,
which can greatly diminish parent material
strengths if excessive grinding occurs.
Detailed discussion of polyethylene welding
protocol can be found in U.S. EPA (1991a).
For dual hot wedge seams in HDPE, both
the inner and outer seam may be subjected
to destructive shear tests at the independent
laboratory. Destructive samples of installed
seam welds are generally cut into several
pieces and distributed to:
• The installer to perform construction
quality control field testing;
• The owner/operator to retain and
appropriately catalog or archive; and
• An independent laboratory for peel
and shear testing.
If the test results for a seam sample do not
pass the acceptance/rejection criteria, then
samples are cut from the same field seam on
both sides of the rejected sample location.
Samples are collected and tested until the
areal limits of the low quality seam are
defined. Corrective measures should be
undertaken to repair the length of seam that
has not passed the acceptance/rejection
criteria. In many cases, this involves
seaming a cap over the length of the rejected
seam or reseaming the affected area (U.S.
EPA, 1988). In situations where the seams
continually fail testing, the seaming crews
may have to be retrained.
Non-Destructive Testing
Non-destructive test methods are conducted
in the field on an in-place geomembrane.
These test methods determine the integrity
of the geomembrane field seams. Non-
destructive test methods include the probe
test, air lance, vacuum box, ultrasonic
methods (pulse echo, shadow and
impedance plane), electrical spark test,
pressurized dual seam, electrical resistivity,
and hydrostatic tests. Detailed discussion of
these test methods may be found in U.S.
EPA (199la). Seam sections that fail
appropriate, non-destructive tests must be
carefully delineated, patched or reseamed,
and retested. Large patches or reseamed
areas should be subjected to destructive test
procedures for quality assurance purposes.
The specifications should clearly describe
the degree to which non-destructive and
destructive test methods will be used in
evaluating failed portions of non-destructive
seam tests.
Geomembrane Construction Quality
Assurance Activities
The responsibilities of the construction
quality assurance (CQA) personnel for the
installation of the geomembrane are
generally the same as the responsibilities for
the construction of a soil liner with the
following additions:
• Observation of liner storage area and
liners in storage, and handling of the
liner as the panels are positioned in the
cell;
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Design Criteria
• Observation of seam overlap, seam
preparation prior to seaming, and
material underlying the liner;
• Observation of destructive testing
conducted on scrap test welds prior to
seaming;
• Observation of destructive seam
sampling, submission of the samples
to an independent testing laboratory,
and review of results for conformance
to specifications;
• Observation of all seams and panels
for defects due to manufacturing
and/or handling and placement;
• Observation of all pipe penetration
boots and welds in the liner;
• Preparation of reports indicating
sampling conducted and sampling
results, locations of destructive
samples, locations of patches,
locations of seams constructed, and
any problems encountered; and,
• Preparation of record drawings of the
liner installation, in some cases.
The last responsibility is frequently assigned
to the contractor, the owner's representative,
or the engineer.
Leachate Collection System
Construction Quality Assurance
The purpose of leachate collection system
CQA is to document that the system
construction is in accordance with the
design specifications. Prior to construction,
all materials should be inspected to confirm
that
they meet the construction plans and
specifications. These include (U.S. EPA,
1988):
• Geonets;
• Geotextiles;
• Pipe size, materials, and perforations;
• Granular material gradation and
prefabricated structures (sumps,
manholes, etc.);
• Mechanical, electrical, and monitoring
equipment; and
• Concrete forms and reinforcement.
The leachate collection system foundation
(geomembrane or low permeability soil
liner) should be inspected and surveyed
upon its completion to ensure that it has
proper grading and is free of debris and
liquids (U.S. EPA, 1988).
During construction, the following
activities, as appropriate, should be
observed and documented (U.S. EPA,
1988):
• Pipe bedding placement including
quality, thickness, and areal coverage;
• Granular filter layer placement
including material quality and
thickness;
• Pipe installation including location,
configuration, grades, joints, filter
layer placement, and final flushing;
• Granular drainage layer placement
including protection of underlying
liners, thickness, overlap with filter
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Subpart D
fabrics and geonets if applicable, and
weather conditions;
• Geonet placement including layout,
overlap, and protection from clogging
by granular material carried by wind
or run-off during construction;
• Geotextile/geofabric placement
including coverage and overlap;
• Sumps and structure installation; and
• Mechanical and electrical equipment
installation including testing.
In addition to field observations, actual field
and laboratory testing may be performed to
document that the materials meet the design
specifications. These activities should be
documented and should include the
following (U.S. EPA, 1988):
• Geonet and geotextile sampling and
testing;
• Granular drainage and filter layer
sampling and testing for grain size
distribution; and
• Testing of pipes for leaks,
obstructions, and alignments.
Upon completion of construction, each
component should be inspected to identify
any damage that may have occurred during
its installation, or during construction of
another component (e.g., pipe crushing
during placement of granular drainage
layer). Any damage that does occur should
be repaired, and these corrective measures
should be documented in the CQA records
(U.S. EPA, 1988).
4.4 RELEVANT POINT OF
COMPLIANCE
40 CFR §258.40(d)
4.4.1 Statement of Regulation
(a) (See Statement of Regulation in
Section 4.2.1 of this guidance document for
the regulatory language for performance-
based design requirements.)
(b) (See Statement of Regulation in
Section 4.3.1 of this guidance document for
the regulatory language for requirements
pertaining to composite liner and leachate
collection systems.)
(c) (See Statement of Regulation in
Section 4.2.1 of this guidance document for
the regulatory language for performance-
based design requirements.)
(d) The relevant point of compliance
specified by the Director of an approved
State shall be no more than 150 meters
from the waste management unit
boundary and shall be located on land
owned by the owner of the MSWLF unit.
In determining the relevant point of
compliance, the State Director shall
consider at least the following factors:
(1) The
characteristics of
surrounding land;
hydrogeologic
the facility and
(2) The volume and physical and
chemical characteristics of the leachate;
(3) The quantity, quality, and
direction of flow of ground water;
(4) The proximity and withdrawal
rate of the ground-water users;
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Design Criteria
(5) The availability of alternative
drinking water supplies;
(6) The existing quality of the
ground water, including other sources of
contamination and their cumulative
impacts on the ground water and whether
the ground water is currently used or
reasonably expected to be used for
drinking water;
(7) Public health, safety, and welfare
effects; and
(8) Practicable capability of the
owner or operator.
4.4.2 Applicability
In States with approved permit programs,
owners/operators may have the opportunity
to employ an alternative liner design, as per
§258.40(a)(l). In these situations, some
flexibility is allowed in terms of
establishing a relevant point of compliance.
The relevant point of compliance may be
located a maximum of 150 meters from the
waste management unit boundary; however,
the location must be on property owned by
the MSWLF unit owner or operator.
In unapproved States the relevant point of
compliance is set at the waste management
unit boundary. The waste management unit
boundary is defined as the vertical surface
located at the hydraulically downgradient
limit of the unit. This vertical surface
extends down into and through the entire
thickness of the uppermost aquifer.
4.4.3 Technical Considerations
At least eight factors should be considered
in establishing the relevant point of
compliance for any design under §258.40.
The factors provide information needed to
determine if the alternative boundary is
sufficiently protective of human health and
the environment and if the relevant point of
compliance is adequate to measure the
performance of the disposal unit.
Site Hydrogeology
The first factor to be considered when
determining the relevant point of
compliance is site hydrogeology. Site
hydrogeologic characteristics should be
used to identify additional information
required to set the relevant point of
compliance. The site data should be
sufficient to determine the lateral well-
spacing required to detect contaminant
releases to the uppermost aquifer.
Hydrogeologic information required to fully
characterize a site is presented in greater
detail in Section 5.6.3.
Leachate Volume and Physical
Characteristics
Data on leachate volume and quality are
needed to make a determination of the
"detectability" of leakage from the facility
at the relevant point of compliance. The net
concentration at any given point resulting
from the transport of contaminants from the
landfill is a function of contaminant type,
initial contaminant concentration, and
leakage rate. Assessment of leachate
volume is discussed in Sections 4.2 and 4.3.
The assessment of contaminant fate and
transport was discussed in Section 4.3.
Quality, Quantity and Direction of
Ground-Water Flow
The hydrogeologic data collected should
provide information to assess the ground-
water flow rate, ground-water flow
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Subpart D
direction, and the volume of ground-water
flow. Background ground-water quality
data should be used to establish baseline
concentrations of the monitoring
constituents. This information will be
required as input to determine if
contaminants from the landfill unit have
been released and have migrated to the
relevant point of compliance.
Ground-Water Receptors
The goal of establishing the relevant point
of compliance is to ensure early detection of
contamination of the uppermost aquifer.
The distance to the relevant point of
compliance should allow sufficient time for
corrective measures to be implemented prior
to the migration of contaminants to private
or public water supply wells.
Existing users of ground water immediately
downgradient from the facility should be
identified on a map. Users located at a
downgradient point where contaminants
might be expected to migrate during the
active life and post-closure care period of
the facility should be identified.
Alternative Drinking Water Supplies
Consideration should be given to the
availability of alternate drinking water
supplies in the event of a ground-water
contamination problem. If the uppermost
aquifer is the sole water supply source
available, all reasonable efforts should be
made to locate the relevant point of
compliance as close as possible to the actual
waste management unit boundary.
Existing Ground-Water Quality
The existing ground-water quality, both
upgradient and downgradient of the
MSWLF
unit, should be determined prior to
establishing the relevant point of
compliance (see Section 5.6.3). The
performance standard for landfill design
requires that landfill units be designed so
that the concentrations listed in Table 1 are
not exceeded at a relevant point of
compliance. Issues for approved States to
consider are whether the ground water is
currently used or is reasonably expected to
be used as a drinking water source when
setting a relevant point of compliance. If
the ground water is not currently or
reasonably expected to be used for drinking
water, the State may allow the relevant
point of compliance to be set near the 150-
meter limit.
Public Health, Welfare, Safety
Consideration should be given to the
potential overall effect on public health,
welfare, and safety of the proposed relevant
point of compliance. Issues that should be
considered include:
• Distance to the nearest ground-water
user or potentially affected surface
water;
• The response time (based on the
distance to the proposed relevant point
of compliance) required to identify
and remediate or otherwise contain
ground water that may become
impacted and potentially affect
downgradient water supplies; and
• The risk that detection monitoring data
may not be representative of a worst
case release of contaminants to ground
water.
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Design Criteria
Practicable Capability of the Owner or
Operator
If the relevant point of compliance is placed
farther from the waste management unit
boundary, the volume of water requiring
treatment, should the ground water become
contaminated, will increase. One or more of
the following conditions could affect the
owner's or operator's practicable capability
(technical and financial) to remediate
contaminant releases:
• Area of impact, remedial costs, scope
of remedial investigation, and site
characterization;
• Increased response time due to higher
costs and increased technical scope of
selected remedial method;
• A reduction of the removal efficiency
of treatment technologies; and
• Increased difficulty in ground-water
extraction or containment if these
technologies are chosen.
The Director may require some indication of
financial capability of the owner or operator
to maintain a longer and more costly
remedial program due to the longer
detection time frame associated with a
relevant point of compliance located at a
greater distance from the waste management
unit boundary. Additional information on
remedial actions for ground water is
provided in this document in Chapter 5.
4.5 PETITION PROCESS
40 CFR §258.40(e)
4.5.1 Statement of Regulation
(a) - (d) (See Statement of Regulation
in Sections 4.2.1, 4.3.1, and 4.4.1 of this
guidance document for regulatory
language.)
(e) If EPA does not promulgate a
rule establishing the procedures and
requirements for State compliance with
RCRA Section 4005(c)(l)(B) by October
9, 1993, owners and operators in
unapproved States may utilize a design
meeting the performance standard in
§258.40(a)(l) if the following conditions
are met:
(1) The State determines the design
meets the performance standard in
§258.40(a)(l);
(2) The State petitions EPA to
review its determination; and
(3) EPA approves the State
determination or does not disapprove the
determination within 30 days.
[Note to Subpart D: 40 CFR Part 239 is
reserved to establish the procedures and
requirements for State compliance with
RCRA Section 4005(c)(l)(B).]
4.5.2 Applicability
If EPA does not promulgate procedures and
requirements for state approval by October
9, 1993, owners and operators of MSWLF
units located in unapproved States may be
able to use an alternative design (in
compliance with §258.40(a)(l)) under
certain circumstances.
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Subpart D
Owners or operators of MSWLF units
should contact the municipal solid waste
regulatory department in their State to
determine if their State has been approved
by the U.S. EPA.
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Design Criteria
4.6 FURTHER INFORMATION
4.6.1 REFERENCES
(Specific to Performance-Based Design Assessment and Solute Transport Modeling)
Abriola, L.M., and G.F. Finder, (1985a). A Multiphase Approach to the Modeling of Porous
Media Contamination by Organic Compounds 1. Equation Development. Water Resources
Research 21(1):11-18.
Abriola, L.M., and G.F. Finder, (1985b). A Multiphase Approach to the Modeling of Porous
Media Contamination by Organic Compounds 2. Numerical Simulation. Water Resources
Research 21(1): 19-26.
Aller, L., T. Bennett, J.H. Lehr, R.J. Petty, and G. Hackett, (1987). DRASTIC: A Standardized
System for Evaluation Ground Water Pollution Potential Using Hydrogeologic Settings.
EPA-600/2-87-035, Kerr Environmental Research Lab, U.S. Environmental Protection
Agency, Ada, Oklahoma. 455 pp.
Auerbach, S.I., C. Andrews, D. Eyman, D.D. Huff, P.A. Palmer, and W.R. Uhte, (1984).
Report of the Panel on Land Disposal. In: Disposal of Industrial and Domestic Wastes:
Land and Sea Alternatives. National Research Council. National Academy Press.
Washington, DC. pp. 73-100.
Beljin, M.S., (1985). A Program Package of Analytical Models for Solute Transport in
Groundwater "SOLUTE". BASIS, International Groundwater Modeling Center, Holcomb
Research Institute, Butler University, Indianapolis, Indiana. 163 pp.
Bond, F., and S. Hwang, (1988). Selection Criteria for Mathematical Models Used in Exposure
Assessments: Groundwater Models. EPA/600/8-88/075, U.S. Environmental Protection
Agency, Washington, DC.
Boutwell, S.H., S.M. Brown, B.R. Roberts, and D.F. Atwood, (1986). Modeling Remedial
Actions at Uncontrolled Hazardous Waste Sites. EPA/540/2-85/001, U.S. Environmental
Protection Agency, Athens, Georgia.
Cederberg, G.A., R.L. Street, and J.O. Leckie, (1985). A Groundwater Mass Transport and
Equilibrium Chemistry Model for Multicomponent Systems. Water Resources Research,
21(8):1095-1104.
Dean, J.D., P.S. Huyakorn, A.S. Donigian, Jr., K.S. Voos, R.W. Schanz, YJ.Meeks, and R.F.
Carsel, (1989). Risk of Unsaturated/Saturated Transport and Transformation of Chemical
Concentrations (RUSTIC). EPA/600/3-89/048a, U.S. EPA, Athens, Georgia.
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Subpart D
de Marsily, G., (1986). Quantitative Hydrogeology: Groundwater Hydrology for Engineers.
Academic Press, San Diego, California. 440 pp.
Dillon, R.T., R.M. Cranwell, R.B. Lantz, S.B. Pahwa, and D.S. Ward, (1978). Risk
Methodology for Geologic Disposal of Radioactive Waste: The Sandia Waste Isolation
Flow and Transport (SWIFT) model. Sand 78-1267/NUREG-CR-0424, Sandia national
Laboratories, Albuquerque, New Mexico.
Domenico, P.A., and V.V. Palciauskas, (1982). Alternative Boundaries in Solid Waste
Management. Ground Water, 20(3):303-311.
Domenico, P.A., and G.A. Robbins, (1985). A New Method for Contaminant Plume Analysis.
Ground Water, 23(4):476-485.
Donigian, A.S., and P.S.C. Rao, (1990). Selection, Application, and Validation of
Environmental Models. In: Proceedings of the International Symposium on Water Quality
Modeling of Agricultural Non-Point Sources, Part 2. D.G. DeCoursey (ed.). ARS-81,
U.S. Department of Agriculture Agricultural Research Services, pp. 577-600.
Erdogen, H., and R.D. Heufeld, (1983). Modeling Leachates at Landfill Boundaries. Journal
of Environmental Engineering, 109(5): 1181-1194.
Faust, C.R., J.H. Guswa, and J.W. Mercer, (1989). Simulation of Three-Dimensional Flow of
Immiscible Fluids Within and Below the Unsaturated Zone. Water Resources Research,
25(12):2449-2464.
Freeze, R.A., and J.A. Cherry, (1979). Ground Water. Prentice-Hall, Englewood Cliffs, New
Jersey. 604 pp.
GeoTrans, Inc., (1985). SWANFLOW: Simultaneous Water, Air and Non-Aqueous Phase
Flow, Version 1.0-Code Documentation. Herndon, Virginia. 97 pp.
Grove, D.B., and K.G. Stollenwerk, (1987). Chemical Reactions Simulated by Groundwater
Quality Models. Water Resources Bulletin, 23(4):601-615.
Gupta, S.K., C.R. Cole, C.T. Kincaid, and F.E. Kaszeta, (1982). Description and Applications
of the FE3DGW and CFEST Three-dimensional Finite Element Models, Battelle Pacific
NW Laboratories, Richland, Washington.
Gupta, S.K., C.T. Kincaid, P. Meyer, C. Newbill, and C.R. Cole, (1982). CFEST:
Multidimensional Finite Element Code for the Analysis of Coupled Fluid, Energy and
Solute Transport. PNL-4260, Battelle Pacific NW Laboratories, Richland, Washington.
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Design Criteria
Gureghian, A.B., D.S. Ward, and R.W. Cleary, (1980). A Finite Element Model for the
Migration of Leachate from a Sanitary Landfill in Long Island, New York - Part I:
Theory. Water Resources Bulletin, 16(5):900-906.
Guvanasen, V., (1984). Development of A Finite Element Code and Its Application to
Geoscience Research. Proceedings 17th Information Meeting of the Nuclear Fuel Waste
Management Program, Atomic Energy of Canada, Ltd. Technical Record TR-199. pp.
554-566.
Haji-Djafari, S., (1983). User's Manual GEOFLOW Groundwater Flow and Mass Transport
Computer Program. D'Appolonia, Pittsburgh, Pennsylvania.
Huyakorn, P.S. et al., (1984). Testing and Validation of Models for Simulating Solute
Transport in Groundwater: Development, Evaluation and Comparison of Benchmark
Techniques. GWMI 84-13, International Groundwater Modeling Center, Holcomb
Research Institute, Indianapolis, Indiana.
Huyakorn, P.S., M.J. Ungs, L.A. Mulkey, and E.A. Sudicky, (1987). A Three-Dimensional
Analytical Method for Predicting Leachate Migration. Ground Water, 25(5):588-598.
Huyakorn, P.S., H.O. White, Jr., V.M. Guvanasen, and B.H. Lester, (1986). TRAFRAP: A
Two-dimensional Finite Element Code for Simulating Fluid Flow and Transport of
Radionuclides in Fractured Porous Media. FOS-33, International Groundwater Modeling
Center, Holcomb Research Institute, Butler University, Indianapolis, Indiana.
Javandel, I., C. Doughty, and C.F. Tsang, (1984). Groundwater Transport: Handbook of
Mathematical Models. Water Resources Monogram 10, American Geophysical Union,
Washington, DC 228 pp.
Keely, J.F., (1987). The Use of Models in Managing Ground-Water Protection Programs. U.S.
Environmental Protection Agency. EPA/600/8-87/003, Ada, Oklahoma. 72 pp.
Keely, J.F., (1989). Performance Evaluations of Pump-and-Treat Remediations. EPA/540/4-
89/005, U.S. Environmental Protection Agency, Ada, Oklahoma. 19 pp.
Kincaid, C.T., J.R. Morrey, and I.E. Rogers, (1984a). Geohydrochemical Models for Solute
Migration- Volume 1: Process Description and Computer Code Selection. EA-3417,
Electric Power Research Institute, Palo Alto, California.
Kincaid, C.T., J.R. Morrey, S.B. Yabusaki, A.R. Felmy, and I.E. Rogers, (1984b).
Geohydrochemical Models for Solute Migration- Volume 2: Preliminary Evaluation of
Selected Computer Codes. EA-3417, Electric Power Research Institute, Palo Alto,
California.
195
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Subpart D
Kipp, K.L., Jr., (1987). HST3D: A Computer Code for Simulation of Heat and Solute Transport
in Three-Dimensional Groundwater Flow Systems. WRI 86-4095, U.S. Geological
Survey, Lakewood, Colorado.
Konikow, L.F., and J.D. Bredehoeft, (1985). Method-of-Characteristics Model for Solute
Transport (1985 revision). U.S. Geological Survey.
Lindstrom, F.T., and L. Boersma, (1989). Analytical Solutions for Convective-Dispersive
Transport in Confined Aquifers with Different Initial and Boundary Conditions. Water
Resources Research, 25(2):241-256.
Lu, J.C.S., B. Eichenberger, and R.J. Stearns, (1985). Leachate Migration from Municipal
Landfills. Pollution Technology Review No. 19. Noyes Publications, Park Ridge, New
Jersey. 453 pp.
Mercer, J.W., S.D. Thomas, and B. Ross, (1983). Parameters and Variables Appearing in
Repository Siting Models. NUREG/CR-3066. Prepared for U.S. Nuclear Regulatory
Commission, Washington, DC. 244 pp.
Mulkey, L.A., A.S. Donigian, Jr., T.L. Allison, and C.S. Raju, (1989). Evaluation of Source
Term Initial Conditions for Modeling Leachate Migration from Landfills. U.S. EPA,
Athens, Georgia.
Narasimhan, T.N., A.F. White, and T. Tokunaga. 1986. Groundwater Contamination From an
Inactive Uranium Mill Tailings Pile 2. Application of a Dynamic Mixing Model. Water
Resources Research, 22(13): 1820-1834.
National Research Council, (1990). Ground Water Models: Scientific and Regulatory
Applications. National Academy Press, Washington, DC. 320 pp.
Nelson, R.W., and J.A. Schur, (1980). PATHS Groundwater Hydrologic Model. PNL-3162,
Battelle Pacific NW Laboratories, Richland, Washington.
Osborne, M., and J. Sykes, (1986). Numerical Modeling of Immiscible Organic Transport at
the Hyde Park Landfill. Water Resources Research, 22(l):25-33.
Ostendorf, D.W., R.R. Noss, and D.O. Lederer, (1984). Landfill Leachate Migration through
Shallow Unconfmed Aquifers, Water Resources Research, 20(2):291-296.
Oster, P. A. Review of Ground-Water Flow and Transport Models in the Unsaturated Zone,
(1982). NUREG/CR-2917, PNL-4427. Pacific Northwest Laboratory, Richland,
Washington.
Prakash, A., (1984). Groundwater Contamination Due to Transient Sources of Pollution. J. of
Hydraulic Engineering, 110(11): 1642-1658.
196
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Design Criteria
Prickett, T.A., T.G. Naymik, and C.G. Lonnquist, (1981). A Random-Walk Solute Transport
Model for Selected Groundwater Quality Evaluations. Bulletin 65, Illinois State Water
Survey, Champaign, Illinois.
Runchal, A.K., (1985). PORFLOW: A General Purpose Model for Fluid Flow, Heat Transfer
and Mass Transport in Anisotropic, Inhomogeneous, Equivalent Porous Media, Volume
I: Theory, Volume II: User's Manual. ACRI/TN-O11. Analytic and Computational
Research, Inc. West Los Angeles, California.
Runchal, A.K., (1985). Theory and Application of the PORFLOW Model for Analysis of
Coupled Flow, Heat and Radionuclide Transport in Porous Media. Proceedings,
international Symposium on Coupled Processes Affecting the Performance of a Nuclear
Waste Repository, Berkeley, California.
Salhotra, A.M., P. Mineart, S. Sharp-Hansen, and T. Allison, (1990). Multimedia Exposure
Assessment Model (MULTIMED) for Evaluating the Land Disposal of Wastes—Model
Theory. Prepared for U.S. Environmental Protection Agency, Environmental Research
Laboratory, Athens, Georgia.
Schroeder, A.C., A.C. Gibson, and M.D. Smolen, (1984). The Hydrologic Evaluation of
Landfill Performance (HELP) Model, Volumes I and II. EPA/530/SW-009 and
EPA/530/SW-010, U.S. Environmental Protection Agency, Cincinnati, Ohio.
Sharp-Hansen, S., C. Travers, P. Hummel, and T. Allison, (1990). A Subtitle D Landfill
Application Manual for the Multimedia Exposure Assessment Model (MULTIMED).
Prepared for the U.S. EPA, Environmental Research Laboratory, Athens, Georgia.
Summers, K.V., S.A. Gherini, M.M. Lang, M.J. Ungs, and K.J. Wilkinson, (1989). MYGRT
Code Version 2.0: An IBM Code for Simulating Migration of Organic and Inorganic
Chemicals in Groundwater. EN-6531. Electric Power Research Institute, Palo Alto,
California.
Temple, Barker and Sloane, Inc., (1988). Draft Regulatory Impact Analysis of Proposed
Revisions to Subtitle D Criteria for Municipal Solid Waste Landfills. Prepared for Office
of Solid Waste, U.S. Environmental Protection Agency.
Theis, T.L., D.J. Kirkner and A.A. Jennings, (1982). Multi-Solute Subsurface Transport
Modeling for Energy Solid Wastes. Technical Progress Report for the Period September
1, 1981-August 31, 1982, COO-10253-3, Prepared for Ecological Research Division,
Office of Health and Environmental Research, U.S. Department of Energy.
Travers, C.L., and S. Sharp-Hansen, (1991). Leachate Generation and Migration at Subtitle D
Facilities: A Summary and Review of Processes and Mathematical Models. Prepared for
U.S. EPA, Environmental Research Laboratory, Athens, Georgia.
197
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Subpart D
Travis, B., (1984). TRACR3D: A Model of Flow and Transport in Porous/Fractured Media.
LA-9667-MS. Los Alamos National Laboratory, Los Alamos, New Mexico.
Unge, M.J., K.V. Summers, and S.A. Gherini, (1986). MYGRT: An IBM Personal Computer
Code for Simulation Solute Migration in Groundwater, User's Manual. EA-4545-CCM.
Electric Power Research Institute, Palo Alto, California.
U.S. EPA, (1988). Superfund Exposure Assessment Manual. EPA/540/1-88/001, Washington,
DC. NTISNo. PB89-135859. 157pp.
U.S. EPA, (1993). Compilation of Ground-Water Models; PB93-209401; U.S. EPA; Office of
Solid Waste; Washington, D.C.
van der Heijde, P.K., Y. Bachmat, J. Bredehoeft, B. Andrews, D. Holtz, and S. Sebastian,
(1985). Groundwater Management: The Use of Numerical Models. American
Geophysical Union, Washington, D.C.
van der Heijde, P.K., and M.S. Beljin, (1988a). Model Assessment for Delineating Wellhead
Protection Areas. EPA-440/6-88-002, U.S. EPA, Washington, DC.
van der Heijde, P.K., El-Kadi, A.I., and S.A. Williams, (1988b). Groundwater Modeling: An
Overview and Status Report. EPA/600/2-89/028, U.S. EPA, Ada, Oklahoma.
van Genuchten, M.T., (1978). Simulation Models and Their Application to Landfill Disposal
Siting; A Review of Current Technology. In Land Disposal of Hazardous Wastes. EPA-
660/9-78-016, U.S. EPA, Cincinnati, Ohio.
van Genuchten, M.T., and WJ. Alves, (1982). Analytical Solutions of the One-Dimensional
Convective-Dispersive Solute Transport Equation. USDA, Technique Bulletin No. 1661.
U.S. Department of Agriculture, Washington, DC.
Versar, Inc., (1987). Current and Suggested Practices in the Validation of Exposure Assessment
Models, Draft Report. Prepared for U.S. EPA Office of Health and Environmental
Assessment, Exposure Assessment Group, Washington, DC. EPA Contract No. 69-02-
4254, Work Assignment No. 55.
Voss, C.I., (1984). SUTRA: A Finite Element Simulation Model for Saturated-Unsaturated
Fluid Density-Dependent Groundwater Flow with Energy Transport or Chemically
Reactive Single Species Solute Transport. Water Resources Investigations 84-4369, U.S.
Geological Survey.
Walton, W.C., (1984). 35 Basic Groundwater Model Programs for Desktop Microcomputers.
GWMI 84-06/4, International Groundwater Modeling Center, Holcomb Research Institute,
Butler University, Indianapolis, Indiana.
198
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Design Criteria
Weaver, I, C.G. Enfield, S. Yates, D. Kreamer, and D. White, (1989). Predicting Subsurface
Contaminant Transport and Transformation: Considerations for Model Selection and Field
Validation. U.S. EPA, Ada, Oklahoma.
Yeh, G.T., (1981). AT123D: Analytical, Transient, One-, Two-, Three-Dimensional
Simulation of Waste Transport in the Aquifer System. Publication No. 1439. Oak Ridge
National Laboratory, Oak Ridge, Tennessee.
Yeh, G.T., (1990). Users' Manual of a Three-Dimensional Hybrid Lagrangian-Eulerian Finite
Element Model of WASTE Transport through Saturated-Unsaturated Media. Pennsylvania
State University, University Park, PA.
Yeh, G.T., and D.S. Ward, (1981). FEMWASTE: A Finite-Element Model of Waste Transport
through Saturated-Unsaturated Porous Media. ORNL-5601. Oak Ridge National
Laboratory, Oak Ridge, Tennessee.
Yeh, G.T., and D.S. Ward, (1987). FEMWATER: A Finite-Element Model of Water Flow
through Saturated-Unsaturated Porous Media. ORNL-5567/R1. Oak Ridge National
Laboratory, Oak Ridge, Tennessee.
4.6.2 REFERENCES
(Specific to Design Criteria)
ASCE, (1969). "Design and Construction of Sanitary and Storm Sewers"; ASCE Manual on
Engineering Practice; No. 37.
Bear, Jacob and Arnold Veruijt, (1987). "Modeling Groundwater Flow and Pollution"; D.
Reidel Publishing Company; Dordracht, Holland.
Benson, Craig H. and David E. Daniel, (1990). "Influence of Clods on Hydraulic Conductivity
of Compacted Clay"; Journal of Geotechnical Engineering; Volume 116, No. 8; August,
1990.
Bonaparte, R. and Gross, B.A., (1990). "Field Behavior of Double-Liner Systems. In Waste
Containment Systems: Construction, Regulation, and Performance, Edited by R.
Bonaparte. Geotechnical Pub 1.26, ASCE.
Carroll, Jr., R.G., (1987). "Hydraulic Properties of Geotextiles." Geotextile Testing and the
Design Engineers, ASTEM 952, American Society for Testing and Materials, Philadelphia,
PA, pp 7-20.
COE, (1970). "Laboratory Soils Testing"; EMI 110-2-1906; Headquarters, Department of the
Army; Office of the Chief of Engineers; Washington, DC 20314.
199
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Subpart D
FHWA, (1985). "FHWA Geotextile Engineering Manual." Contract No.l DTP H61-83-C-
00150.
FHWA, (1990). "Geotextile Design & Construction Guidelines. Contract No. FHWA
DTFH61-86-C-00102.
GCA Corporation, (1983). "Draft Permit Writers' Guidance Manual for Hazardous Waste
Treatment, Storage, and Disposal Facility"; 1983.
Giroud, J.P., (1982). "Filter Criteria for Geotextiles," Proceeding 2nd International Conference
on Geotextiles, Las Vegas, Nevada.
Giroud, J.P. and R. Bonaparte, (1989). "Leakage Through Liners Constructed with
Geomembranes - Part I: Geomembrane Liners"; Geotextiles and Geomembranes 8(2);
0266-1144/89; pp. 27-67; Elsevier Science Publishers Ltd., England, Great Britain.
Giroud, J.P. and R. Bonaparte, (1989). "Leakage Through Liners Constructed with
Geomembranes - Part II: Composite Liners"; Geotextiles and Geomembranes 8(2); 0266-
1144/89; pp. 71-111; Elsevier Science Publishers Ltd., England, Great Britain.
Giroud, J.P., A. Khatami and K. Badu-Tweneboah, (1989). "Technical Note - Evaluation of the
Rate of Leakage Through Composite Liners"; Geotextiles and Geomembranes 8; 0266-
1144/89; pp. 337-340; Elsevier Science Publishers Ltd., England, Great Britain.
Haxo, H.E., Jr., (1983). "Analysis and Fingerprinting of Unexposed and Exposed Polymeric
Membrane Liners"; Proceedings of Ninth Annual Research Symposium: Land Disposal,
Incineration, and Treatment of Hazardous Waste; EPA/600/9-83/018; U.S. EPA;
Cincinnati, Ohio.
Haxo, H.E., Jr., J.A. Miedema and H.A. Nelson, (1984). "Permeability of Polymeric Membrane
Lining Materials"; Matrecon, Inc.; Oakland, California; International Conference on
Geomembranes; Denver, Colorado.
Industrial Fabrics Association International (1990). "1991 Specifiers Guide;" Geotechnical
Fabrics Report, Volume 8, No. 7, 1990.
Javendale, I., C. Doughty and C.F. Tsang, (1984). "Groundwater Transport; Handbook of
Mathematical Models"; American Geophysical Union; Washington, DC 20009.
Jayawickrama, P.W., K.W. Brown, J.C. Thomas and R.L. Lytton, (1988). "Leakage Rates
Through Flaws in Membrane Liners"; Journal of Environmental Engineering; Vol. 114,
No. 6; December, 1988.
200
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Design Criteria
Kastman, Kenneth A., (1984). "Hazardous Waste Landfill Geomembrane: Design, Installation
and Monitoring"; Woodward-Clyde Consultants, Chicago, Illinois; International
Conference on Geomembranes; Denver, Colorado.
Koerner, Robert M., (1990). "Designing with Geosynthetics"; 2nd Edition; Prentice Hall;
Englewood-Cliffs, New Jersey 07632.
Radian Corporation, (1987). "Technical Data Summary: Hydraulic Performance of Minimum
Technology Double Liner Systems"; Radian Corporation; Austin, Texas 78766 for U.S.
EPA; Contract No. 68-01-7310; Task 7-4.
U.S. EPA, (1982). "Landfill and Surface Impoundment Performance Evaluation"; SW-869;
Charles A. Moore; U.S. EPA. NTIS PB-81-166357.
U.S. EPA, (1983). "Lining of Waste Impoundment and Disposal Facilities"; SW-870; U.S.
EPA; Office of Solid Waste and Emergency Response; Washington, DC 20460. NTIS PB-
81-166365 Revised: PB-86-192796.
U.S. EPA, (1987a). "Background Document on Bottom Liner Performance in Double-Lined
Landfills and Surface Impoundments"; EPA/530/SW-87/013; U.S. EPA; Washington, DC.
NTISPB-87-182291.
U.S. EPA, (1987b) " Characterization of MWC Ashes and Leachates from MSW Landfills,
Monofills and Co-Disposal Sites: Volume VI of VII; Characterization of Leachates from
Municipal Solid Waste Disposal Sites and Co-Disposal Sites"; EPA/530/SW-87/028F,
Washington, D.C. NTIS PB-88-127998.
U.S. EPA, (1988). "Guide to Technical Resources for the Design of Land Disposal Facilities";
EPA/625/6-88/018; U.S. EPA; Risk Reduction Engineering Laboratory; Center for
Environmental Research Information; Cincinnati, Ohio 45268.
U.S. EPA, (1988a). Superfund Exposure Assessment Manual. EPA/540/1-88/001, Washington,
D.C., NTIS No. PB89-135.859, 157 pp.
U.S. EPA, (1988b). "Design, Construction and Evaluation of Clay Liners for Waste
Management Facilities; EPA/530/SW-86/007F; U.S. EPA; Office of Solid Waste and
Emergency Response; Washington, DC 20460. NTIS PB-86-184496.
U.S. EPA, (1988c). "Groundwater Modeling: An Overview and Status Report";
EPA/600/2-89/028; U.S. EPA; Environmental Research Laboratory; Ada, Oklahoma
74820. NTIS PB-89-224497.
201
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Subpart D
U.S. EPA, (1988d). "Multimedia Exposure Assessment Model for Evaluating the Land
Disposal of Hazardous Wastes, Volume I"; Woodward-Clyde Consultants, Oakland, CA
94607-4014 for U.S. EPA; Environmental Research Laboratory; Office of Research and
Development; Athens, Georgia 30613.
U.S. EPA, (1988e). "Lining of Waste Containment and Other Impoundment Facilities";
EPA/600/2-88/052; U.S. EPA; Risk Reduction Engineering Laboratories; Cincinnati, Ohio
45268. NTISPB-89-129670.
U.S. EPA, (1989). "Seminar Publication - Requirements for Hazardous Waste Landfill Design,
Construction and Closure"; EPA/625/4-89/022; U.S. EPA; Center for Environmental
Research Information; Office of Research and Development; Cincinnati, Ohio 45268.
U.S. EPA, (1990a). "Seminars - Design and Construction of RCRA/CERCLA Final Covers",
CERI 90-50; U.S. EPA; Office of Research and Development; Washington, DC 20460.
U.S. EPA, (1990b). "Draft - LDCRS Flow Data from Operating Units - Technical Support for
Proposed Liner/Leak Detection System Rule"; Geoservices, Inc. Consulting Engineers;
Norcross, Georgia 30093.
U.S. EPA, (1990c). "Relationship of Laboratory- and Field-Determined Hydraulic
Conductivity in Compacted Clay Layer"; EPA/600/2-90/025; U.S. EPA; Risk Reduction
Engineering Laboratory; Cincinnati, Ohio 45268. NTIS PB-90-257775.
U.S. EPA, (1991a). "Technical Guidance Document: Inspection Techniques for the Fabrication
of Geomembrane Field Seams"; EPA 530/SW-91/051, May 1991, Cincinnati, Ohio.
U.S. EPA, (1991b). "Landfill Leachate Clogging of Geotextiles (and Soil) Filters";
EPA/600/2-91/025, August 1991; Risk Reduction Engineering Laboratory; Cincinnati,
Ohio, 45268. NTIS PB-91-213660.
U.S. EPA, (1992). "Technical Guidance Document: Construction Quality Management for
Remedial Action and Remedial Design Waste Containment Systems"; EPA/540/R-92/073,
October 1992; Risk Reduction Engineering Laboratory, Cincinnati, Ohio 45268 and
Technology Innovation Office, Washington, D.C. 20460.
4.6.3 Models
List of Contacts for Obtaining Leachate Generation and Leachate Migration Models
Center for Exposure Assessment Modeling (CEAM), U.S. EPA, Office of Research and
Development, Environmental Research Laboratory, Athens, Georgia 30605-2720, Model
Distribution Coordinator (706) 546-3549, Electronic Bulletin Board System (706) 546-3402:
MULTIMED, PRZM, FEMWATER/FEMWASTE, LEWASTE/3DLEWASTE
202
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Design Criteria
Electric Power Research Institute, Palo Alto, California, (214) 655-8883: MYGRT,
FASTCHEM
Geo-Trans Inc., 46050 Manekin Plaza, Suite 100, Sterling, VA 20166, (703) 444-7000:
SWANFLOW, SWIFT, SWIFT II, SWIFT III, SWIFT/386.
Geraghty & Miller, Inc., Modeling Group, 10700 Parkridge Boulevard, Suite 600 Reston,
VA 22091: MODFLOW386, MODPATH386, MOC386, SUTRA386, Quickflow,
International Groundwater Modeling Center, Colorado School of Mines, Golden, Colorado
(303) 273-3103: SOLUTE, Walton35, SEFTRAN, TRAFRAP,
National Technical Information Services (NTIS), 5285 Port Royal Road, Springfield, VA
22161, (703) 487-4650: HELP
Dr. Zubair Saleem, U.S. EPA, 401 M Street SW, Washington, DC, 20460, (202) 260-4767:
EPACML, VHS
Scientific Software Group, P.O. Box 23041, Washington, DC 20026-3041 (703) 620-9214:
HST3D, MODFLOW, MOC, SUTRA, AQUA, SWIMEV.
203
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CHAPTER 5
SUBPART E
GROUND-WATER MONITORING
AND CORRECTIVE ACTION
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CHAPTER 5
SUBPART E
TABLE OF CONTENTS
5J, INTRODUCTION 211
12 APPLICABILITY 40 CFR $258.50 (a) & fb) 211
5.2.1 Statement of Regulation 211
5.2.2 Applicability 212
5.2.3 Technical Considerations 212
53. COMPLIANCE SCHEDULE 40 CFR $ 258.50 (c) 214
5.3.1 Statement of Regulation 214
5.3.2 Applicability 214
5.3.3 Technical Considerations 214
14 ALTERNATIVE COMPLIANCE SCHEDULES 40 CFR 258.50 (d)(e) & (a) 215
5.4.1 Statement of Regulation 215
5.4.2 Applicability 216
5.4.3 Technical Considerations 217
15 QUALIFICATIONS 40 CFR 258.50 (f) 217
5.5.1 Statement of Regulation 217
5.5.2 Applicability 218
5.5.3 Technical Considerations 218
16 GROUND-WATER MONITORING SYSTEMS 40 CFR $258.51 (a)fb)(d) 219
5.6.1 Statement of Regulation 219
5.6.2 Applicability 220
5.6.3 Technical Considerations 221
Uppermost Aquifer 221
Determination of Background Ground-Water Quality 221
Multi-Unit Monitoring Systems 222
Hydrogeological Characterization 224
Characterizing Site Geology 225
Monitoring Well Placement 235
206
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17 GROUND-WATER MONITORING WELL DESIGN AND CONSTRUCTION 40
CFRS258.51 (c) 241
5.7.1 Statement of Regulation 241
5.7.2 Applicability 241
5.7.3 Technical Considerations 241
Monitoring Well Design 244
Well Casing 244
Filter Pack Design 248
Surface Completion 250
18 GROUND-WATER SAMPLING AND ANALYSIS REQUIREMENTS
40 CFR $258.53 253
5.8.1 Statement of Regulation 253
5.8.2 Applicability 254
5.8.3 Technical Considerations 255
Sample Collection 255
Frequency 255
Water Level Measurements 256
Well Purging 256
Field Analyses 258
Sample Withdrawal and Collection 258
Sample Preservation and Handling 260
Sample Containers 262
Sample Preservation 262
Sample Storage and Shipment 262
Chain-of-Custody Record 263
Sample Labels 263
Sample Custody Seal 264
Field Logbook 264
Sample Analysis Request Sheet 265
Laboratory Records 265
Analytical Procedures 265
Quality Assurance/Quality Control 266
Field Quality Assurance/Quality Control 266
Validation 267
Documentation 268
207
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12 STATISTICAL ANALYSIS 40 CFR $258.53 (g)-(i) 268
5.9.1 Statement of Regulation 268
5.9.2 Applicability 270
5.9.3 Technical Considerations 271
Multiple Well Comparisons 272
Tolerance and Prediction Intervals 273
Individual Well Comparisons 274
Intra-Well Comparisons 274
Treatment of Non-Detects 274
5.10 DETECTION MONITORING PROGRAM 40 CFR $258.54 274
5.10.1 Statement of Regulation 274
5.10.2 Applicability 276
5.10.3 Technical Considerations 277
Independent Sampling for Background 277
Alternative List/Removal of Parameters 279
Alternative Frequency 279
Notification 280
Demonstrations of Other Reasons For Statistical Increase 280
Demonstrations of Other Sources of Error 281
5.11 ASSESSMENT MONITORING PROGRAM 40 CFR §258.55(a)-(f) 281
5.11.1 Statement of Regulation 281
5.11.2 Applicability 283
5.11.3 Technical Considerations 285
Alternative List 285
Alternative Frequency 285
5.12 ASSESSMENT MONITORING PROGRAM 40 CFR §258.55(e) 286
5.12.1 Statement of Regulation 286
5.12.2 Applicability 287
5.12.3 Technical Considerations 287
Release Investigation 288
Property Boundary Monitoring Well 288
Notification of Adjoining Residents and Property Owners 288
Demonstrations of Other Sources of Error 288
Return to Detection Monitoring 289
5.13 ASSESSMENT MONITORING PROGRAM 40 CFR §258.55(h)-(i) 289
5.13.1 Statement of Regulation 289
5.13.2 Applicability 290
5.13.3 Technical Considerations 290
208
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5.14 ASSESSMENT OF CORRECTIVE MEASURES 40 CFR $258.56 291
5.14.1 Statement of Regulation 291
5.14.2 Applicability 291
5.14.3 Technical Considerations 291
Source Evaluation 292
Plume Delineation 292
Ground-Water Assessment 294
Corrective Measures Assessment 295
Active Restoration 296
Plume Containment 297
Source Control 298
Public Participation 298
5.15 SELECTION OF REMEDY 40 CFR $258.57 (a)-fb) 298
5.15.1 Statement of Regulation 298
5.15.2 Applicability 299
5.15.3 Technical Considerations 299
5.16 SELECTION OF REMEDY 40 CFR $258.57 (c) 299
5.16.1 Statement of Regulation 299
5.16.2 Applicability 300
5.16.3 Technical Considerations 301
Effectiveness of Corrective Action 301
Effectiveness of Source Reduction 302
Implementation of Remedial Action 302
Practical Capability 302
Community Concerns 303
5.17 SELECTION OF REMEDY 40 CFR $258.57 (d) 303
5.17.1 Statement of Regulation 303
5.17.2 Applicability 304
5.17.3 Technical Considerations 304
5.18 SELECTION OF REMEDY 40 CFR $258.57 (e)-(f) 305
5.18.1 Statement of Regulation 305
5.18.2 Applicability 306
5.18.3 Technical Considerations 306
209
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5.19 IMPLEMENTATION OF THE CORRECTIVE ACTION PROGRAM
40 CFR $258.58 (a) 307
5.19.1 Statement of Regulation 307
5.19.2 Applicability 308
5.19.3 Technical Considerations 308
Monitoring Activities 308
Interim Measures 308
5.20 IMPLEMENTATION OF THE CORRECTIVE ACTION PROGRAM
40 CFR $258.58 fb)-(d) 309
5.20.1 Statement of Regulation 309
5.20.2 Applicability 309
5.20.3 Technical Considerations 310
5.21 IMPLEMENTATION OF THE CORRECTIVE ACTION PROGRAM
40 CFR $258.58 (e)-(g) 311
5.21.1 Statement of Regulation 311
5.21.2 Applicability 311
5.21.3 Technical Considerations 312
5.22 FURTHER INFORMATION 313
5.22.1 References 313
210
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CHAPTER 5
SUBPART E
GROUND-WATER MONITORING
AND CORRECTIVE ACTION
5.1 INTRODUCTION
The Criteria establish ground-water monitoring and corrective action requirements for all existing
and new MSWLF units and lateral expansions of existing units except where the Director of an
approved State suspends the requirements because there is no potential for migration of leachate
constituents from the unit to the uppermost aquifer. The Criteria include requirements for the
location, design, and installation of ground-water monitoring systems and set standards for ground-
water sampling and analysis. They also provide specific statistical methods and decision criteria for
identifying a significant change in ground-water quality. If a significant change in ground-water
quality occurs, the Criteria require an assessment of the nature and extent of contamination followed
by an evaluation and implementation of remedial measures.
Portions of this chapter are based on a draft technical document developed for EPA's hazardous
waste program. This document, "RCRA Ground-Water Monitoring: Draft Technical Guidance"
(EPA/530-R-93-001), is undergoing internal review, and may change. EPA chose to incorporate
the information from the draft document into this chapter because the draft contained the most
recent information available.
5.2 APPLICABILITY
40 CFR §258.50 (a) & (b)
5.2.1 Statement of Regulation
(a) The requirements in this Part apply to
MSWLF units, except as provided in
paragraph (b) of this section.
(b) Ground-water monitoring
requirements under §258.51 through
§258.55 of this Part may be suspended by
the Director of an approved State for a
MSWLF unit if the owner or operator can
demonstrate that there is no potential for
migration of hazardous constituents from
that MSWLF unit to the uppermost
aquifer (as defined in §258.2) during the
active life of the unit and the post-closure
care period. This demonstration must be
certified by a qualified ground-water
scientist and approved by the Director of
an approved State, and must be based
upon:
(1) Site-specific field collected
measurements, sampling, and analysis of
physical, chemical, and biological processes
affecting contaminant fate and transport,
and
(2) Contaminant fate and transport
predictions that maximize contaminant
migration and consider impacts on human
health and environment.
211
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Subpart E
5.2.2 Applicability
The ground-water monitoring requirements
apply to all existing MSWLF units, lateral
expansions of existing units, and new
MSWLF units that receive waste after
October 9, 1993. The requirements for
ground-water monitoring may be suspended if
the Director of an approved State finds that no
potential exists for migration of hazardous
constituents from the MSWLF unit to the
uppermost aquifer during the active life of the
unit, including closure or post-closure care
periods.
The "no potential for migration" demonstra-
tion must be based upon site-specific informa-
tion relevant to the fate and transport of any
hazardous constituents that may be expected
to be released from the unit. The predictions
of fate and transport must identify the max-
imum anticipated concentrations of constitu-
ents migrating to the uppermost aquifer so
that a protective assessment of the potential
effects to human health and the environment
can be made. A successful demonstration
could exempt the MSWLF unit from
requirements of §§258.51 through 258.55,
which include installation of ground-water
monitoring systems, and sampling and
analysis for both detection and assessment
monitoring constituents. Preparing No-
Migration Demonstrations for Municipal
Solid Waste Disposal Facilities-Screening
Tool is a guidance document describing a
process owners/ operators can use to prepare
a no-migration demonstration (NMD)
requesting suspension of the ground-water
monitoring requirements.
5.2.3 Technical Considerations
All MSWLF units that receive waste after the
effective date of Part 258 must comply with
the ground-water monitoring requirements.
The Director of an approved State may
exempt an owner/operator from the ground-
water monitoring requirements at
§258.51 through §258.55 if the owner or
operator demonstrates that there is no
potential for hazardous constituent migration
to the uppermost aquifer throughout the
operating, closure, and post-closure care
periods of the unit. Owners and operators of
MSWLFs not located in approved States will
not be eligible for this waiver and will be
required to comply with all ground-water
monitoring requirements. The "no-migration"
demonstration must be certified by a qualified
ground-water scientist and approved by the
Director of an approved State. It must be
based on site-specific field measurements and
sampling and analyses to determine the
physical, chemical, and biological processes
affecting the fate and transport of hazardous
constituents. The demonstration must be
supported by site-specific data and predictions
of the maximum contaminant migration.
Site-specific information must include, at a
minimum, the information necessary to
evaluate or interpret the effects of the
following properties or processes on
contaminant fate and transport:
Physical Properties or Processes:
• Aquifer Characteristics. including
hydraulic conductivity, hydraulic gradient,
effective porosity, aquifer thickness, de-
gree of saturation, stratigraphy, degree of
fracturing and secondary porosity of soils
and bedrock, aquifer heterogeneity,
ground-water discharge, and ground-water
recharge areas;
• Waste Characteristics, including quantity,
type, and origin (e.g., commercial,
industrial, or small quantity generators of
unregulated hazardous wastes);
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• Climatic Conditions, including annual
precipitation, leachate generation
estimates, and effects on leachate
quality;
• Leachate Characteristics, including
leachate composition, solubility, density,
the presence of immiscible constituents,
Eh, and pH; and
• Engineered Controls, including liners,
cover systems, and aquifer controls (e.g.,
lowering the water table). These should
be evaluated under design and failure
conditions to estimate their long-term
residual performance.
Chemical Properties or Processes:
• Attenuation of contaminants in the
subsurface, including adsorption/
desorption reactions, ion exchange,
organic content of soil, soil water pH,
and consideration of possible reactions
causing chemical transformation or
chelation.
Biological Processes:
• Microbiological Degradation, which may
attenuate target compounds or cause
transformations of compounds,
potentially forming more toxic chemical
species.
The alternative design section of Chapter
5.0 discusses these and other processes that
affect contaminant fate and solute transport.
When owners or operators prepare a no-
migration demonstration, they must use
predictions that are based on maximum
contaminant migration both from the unit
and through the subsurface media.
Assumptions about variables affecting
transport should be biased toward over-
estimating transport and the anticipated
concentrations. Assumptions and site
specific data that are used in the fate and
transport predictions should conform with
transport principles and processes,
including adherence to mass-balance and
chemical equilibria limitations. Within
these physicochemical limitations,
assumptions should be biased toward the
objective of assessing the maximum
potential impact on human health and the
environment. The evaluation of site-
specific data and assumptions may include
some of the following approaches:
• Use of the upper bound of known aquifer
parameters and conditions that will
maximize contaminant transport (e.g.,
hydraulic conductivity, effective
porosity, horizontal and vertical
gradients), rather than average values
• Use of the lower range of known aquifer
conditions and parameters that tend to
attenuate or retard contaminant transport
(e.g., dispersivities, decay coefficients,
cation exchange capacities, organic
carbon contents, and recharge
conditions), rather than average values
• Consideration of the cumulative impacts
on water quality, including both existing
water quality data and cumulative health
risks posed by hazardous constituents
likely to migrate from the MSWLF unit
and other potential or known sources.
A discussion of mathematical approaches
for evaluating contaminant or solute
transport is provided in Chapter 5.
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Subpart E
5.3 COMPLIANCE SCHEDULE
40 CFR § 258.50 (c)
5.3.1 Statement of Regulation*
*[NOTE: EPA finalized several revisions
to 40 CFR Part 258 on October 1, 1993
(58 FR 51536), and these revisions delay
the effective date for some categories of
landfills. More detail on the content of
the revisions is included in the
introduction.]
(c) Owners and operators of MSWLF
units must comply with the ground-water
monitoring requirements of this part
according to the following schedule unless
an alternative schedule is specified under
paragraph (d):
(1) Existing MSWLF units and lateral
expansions less than one mile from a
drinking water intake (surface or
subsurface) must be in compliance with
the ground-water monitoring
requirements specified in §§258.51 -
258.55 by October 9, 1994;
(2) Existing MSWLF units and lateral
expansions greater than one mile but less
than two miles from a drinking water
intake (surface or subsurface) must be in
compliance with the ground-water
monitoring requirements specified in
§§258.51 - 258.55 by October 9, 1995;
(3) Existing MSWLF units and lateral
expansions greater than two miles from a
drinking water intake (surface or
subsurface) must be in compliance with
the ground-water monitoring
requirements specified in §§258.51 -
258.55 by October 9, 1996;
(4) New MSWLF units must be in
compliance with the ground-water
monitoring requirements specified in
§§258.51 - 258.55 before waste can be
placed in the unit.
5.3.2 Applicability
The rule establishes a self-implementing
schedule for owners or operators in States
with programs that are deemed inadequate
or not yet approved. As indicated in the
Statement of Regulation, this schedule
depends on the distance of the MSWLF unit
from drinking water sources. Approved
States may specify an alternative schedule
under §258.50 (d), which is discussed in
Section 5.4.
Existing units and lateral expansions less
than one mile from a drinking water intake
must be in compliance with the ground-
water monitoring requirements by October
9, 1994. If the units are greater than one
mile but less than two miles from a drinking
water intake, they must be in compliance by
October 9, 1995. Those units located more
than two miles from a drinking water intake
must be in compliance by October 9, 1996
(see Table 5-1).
New MSWLF units, defined as units that
have not received waste prior to October 9,
1993, must be in compliance with these
requirements before receiving waste
regardless of the proximity to a water
supply intake.
5.3.3 Technical Considerations
For most facilities, these requirements will
become applicable 3 to 5 years after the
promulgation date of the rule. This period
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Table 5-1. Compliance Schedule for Existing Units and Lateral Expansions
in States with Unapproved Programs
Distance From Water Supply Intake
One mile or less
More than one mile but less than two
miles
More than two miles
Time to Comply
From October 9, 1991
3 Years
4 Years
5 Years
should provide sufficient time for the owner
or operator to conduct site investigation and
characterization studies to comply with the
requirements of 40 CFR §258.51 through
§258.55. For those facilities closest to
drinking water intakes, the period provides
2 to 3 years to assess seasonal variability in
ground-water quality. A drinking water
intake includes water supplied to a user
from either a surface water or ground-water
source.
5.4 ALTERNATIVE COMPLIANCE
SCHEDULES
40 CFR 258.50 (d)(e) & (g)
5.4.1 Statement of Regulation
(d) The Director of an approved State
may specify an alternative schedule for
the owners or operators of existing
MSWLF units and lateral expansions to
comply with the ground-water
monitoring requirements specified in
§§258.51 - 258.55. This schedule must
ensure that 50 percent of all existing
MSWLF units are in compliance by
October 9, 1994 and all existing MSWLF
units are in
compliance by October 9, 1996. In
setting the compliance schedule, the
Director of an approved State must
consider potential risks posed by the unit
to human health and the environment.
The following factors should be
considered in determining potential risk:
(1) Proximity of human and
environmental receptors;
(2) Design of the MSWLF unit;
(3) Age of the MSWLF unit;
(4) The size of the MSWLF unit;
(5) Types and quantities of wastes
disposed, including sewage sludge; and
(6) Resource value of the underlying
aquifer, including:
(i) Current and future uses;
(ii) Proximity and withdrawal rate of
users; and
(iii) Ground-water quality and
quantity.
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Subpart E
(e) Once established at a MSWLF
unit, ground-water monitoring shall be
conducted throughout the active life and
post-closure care period of that MSWLF
unit as specified in §258.61.
(f) (See Section 5.5 for technical
guidance on qualifications of a ground-
water scientist.)
(g) The Director of an approved State
may establish alternative schedules for
demonstrating compliance with
§258.51(d)(2), pertaining to notification
of placement of certification in operating
record; § 258.54(c)(l), pertaining to
notification that statistically significant
increase (SSI) notice is in operating
record; § 258.54(c)(2) and (3), pertaining
to an assessment monitoring program;
§ 258.55(b), pertaining to sampling and
analyzing Appendix II constituents;
§258.55(d)(l), pertaining to placement of
notice (Appendix II constituents detected)
in record and notification of notice in
record; § 258.55(d)(2), pertaining to
sampling for Appendix I and II;
§ 258.55(g), pertaining to notification
(and placement of notice in record) of SSI
above ground-water protection standard;
§ 258.55(g)(l)(iv) and § 258.56(a),
pertaining to assessment of corrective
measures; § 258.57(a), pertaining to
selection of remedy and notification of
placement in record; § 258.58(c)(4),
pertaining to notification of placement in
record (alternative corrective action
measures); and § 258.58(f), pertaining to
notification of placement in record
(certification of remedy completed).
5.4.2 Applicability
The Director of an approved State may
establish an alternative schedule for
requiring owners/operators of existing units
and lateral expansions to comply with the
ground-water monitoring requirements.
The alternative schedule is to ensure that at
least fifty percent of all existing MSWLF
units within a given State are in compliance
by October 9, 1994 and that all units are in
compliance by October 9, 1996.
In establishing the alternative schedule, the
Director of an approved State may use site-
specific information to assess the relative
risks posed by different waste management
units and will allow priorities to be
developed at the State level. This site-
specific information (e.g., proximity to
receptors, proximity and withdrawal rate of
ground-water users, waste quantity, type,
containment design and age) should enable
the Director to assess potential risk to the
uppermost aquifer. The resource value of
the aquifer to be monitored (e.g., ground-
water quality and quantity, present and
future uses, and withdrawal rate of ground-
water users) also may be considered.
Once ground-water monitoring has been
initiated, it must continue throughout the
active life, closure, and post-closure care
periods. The post-closure period may last
up to 30 years or more after the MSWLF
unit has received a final cover.
In addition to establishing alternative
schedules for compliance with ground-
water monitoring requirements, the Director
of an approved State may establish
alternative schedules for certain
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Ground-Water Monitoring and Corrective Action
sampling and analysis requirements of
§§258.54 and 258.55, as well as corrective
action requirements of §§258.56, 258.57,
and 258.58. See Table 5-2 for a summary
of notification requirements for which
approved States may establish alternative
schedules.
5.4.3 Technical Considerations
The rule allows approved States flexibility
in establishing alternate ground-water
monitoring compliance schedules. In
setting an alternative schedule, the State
will consider potential impacts to human
health and the environment. Approved
States have the option to address MSWLF
units that have environmental problems
immediately. In establishing alternative
schedules for installing ground-water
monitoring systems
at existing MSWLF units, the Director of an
approved State may consider information
including the age and design of existing
facilities. Using this type of information, in
conjunction with a knowledge of the wastes
disposed, the Director should be able to
qualitatively assess or rank facilities based
on their risk to local ground-water
resources.
5.5 QUALIFICATIONS
40 CFR 258.50 (f)
5.5.1 Statement of Regulation
(f) For the purposes of this Subpart, a
qualified ground-water scientist is a
scientist or engineer who has received a
baccalaureate or post-graduate degree in
Table 5-2. Summary of Notification Requirements
Section
§258.51(d)(2)
§258.54(c)(l)
§258.55(d)(l)
§258.57(a)
§258.58(c)(4)
§258.58(f)
Description
14 day notification period after well installation
certification by a qualified ground-water scientist (GWS)
14 day notification period after finding a statistical increase
over background for detection parameter(s)
14 day notification period after detection of Appendix II
constituents
14 day notification period after selection of corrective
measures
14 day notification period prior to implementing alternative
measures
14 day notification period after remedy has been completed
and certified by GWS
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Subpart E
the natural sciences or engineering and
has sufficient training and experience in
ground-water hydrology and related
fields as may be demonstrated by State
registration, professional certifications,
or completion of accredited university
programs that enable that individual to
make sound professional judgements
regarding ground-water monitoring,
contaminant fate and transport, and
corrective action.
5.5.2 Applicability
The qualifications of a ground-water
scientist are defined to ensure that
professionals of appropriate capability and
judgement are consulted when required by
the Criteria. The ground-water scientist
must possess the fundamental education and
experience necessary to evaluate ground-
water flow, ground-water monitoring
systems, and ground-water monitoring
techniques and methods. A ground-water
scientist must understand and be able to
apply methods to solve solute transport
problems and evaluate ground-water
remedial technologies. His or her education
may include undergraduate or graduate
studies in hydrogeology, ground-water
hydrology, engineering hydrology, water
resource engineering, geotechnical
engineering, geology, ground-water
modeling/ground-water computer modeling,
and other aspects of the natural sciences.
The qualified ground-water scientist must
have a college degree but need not have
professional certification, unless required at
the State or Tribal level. Some
States/Tribes may have certification
programs for ground-water scientists;
however, there are no recognized Federal
certification programs.
5.5.3 Technical Considerations
A qualified ground-water scientist must
certify work performed pursuant to the
following provisions of the ground-water
monitoring and corrective action
requirements:
No potential for
demonstration (§258.50(b))
migration
Specifications concerning the number,
spacing, and depths of monitoring wells
(§258.51(d))
Determination that contamination was
caused by another source or that a
statistically significant increase resulted
from an error in sampling, analysis, or
evaluation (§§258.54 (c)(3) and 258.55
• Determination that compliance with a
remedy requirement is not technically
practicable (§258. 58(c)(l))
• Completion of remedy (§25 8.5 8(f)).
The owner or operator must determine that
the professional qualifications of the
ground-water specialist are in accordance
with the regulatory definition. In general, a
certification is a signed document that
transmits some finding (e.g., that
monitoring wells were installed according
to acceptable practices and standards at
locations and depths appropriate for a given
facility). The certification must be placed
in the operating record of the facility, and
the State Director must be notified that the
certification has been made. Specific
details of these certifications will be
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Ground-Water Monitoring and Corrective Action
addressed in the order in which they appear
in this guidance document.
Many State environmental regulatory
agencies have ground-water scientists on
staff. The owner or operator of a MSWLF
unit or facility is not necessarily required to
obtain certification from an independent
(e.g., consulting) ground-water scientist and
may, if agreed to by the Director in an
approved State, obtain approval by the
Director in lieu of certification by an
outside individual.
5.6 GROUND-WATER
MONITORING SYSTEMS
40 CFR §258.51 (a)(b)(d)
5.6.1 Statement of Regulation
(a) A ground-water monitoring system
must be installed that consists of a
sufficient number of wells, installed at
appropriate locations and depths, to yield
ground-water samples from the upper-
most aquifer (as defined in §258.2) that:
(1) Represent the quality of background
ground water that has not been affected
by leakage from a unit. A determination
of background quality may include
sampling of wells that are not
hydraulically upgradient of the waste
management area where:
(i) Hydrogeologic conditions do not
allow the owner or operator to determine
what wells are hydraulically upgradient;
or
(ii) Sampling at other wells will provide
an indication of background ground-
water quality that is as representative or
more
representative than that provided by the
upgradient wells; and
(2) Represent the quality of ground
water passing the relevant point of
compliance specified by the Director of
an approved State under §258.40(d) or at
the waste management unit boundary in
unapproved States. The downgradient
monitoring system must be installed at
the relevant point of compliance specified
by the Director of an approved State
under §258.40(d) or at the waste
management unit boundary in
unapproved States that ensures detection
of ground-water contamination in the
uppermost aquifer. When physical
obstacles preclude installation of ground-
water monitoring wells at the relevant
point of compliance at existing units, the
down-gradient monitoring system may be
installed at the closest practicable
distance hydraulically down-gradient
from the relevant point of compliance or
specified by the Director of an approved
State under §258.40 that ensures
detection of ground-water contamination
in the uppermost aquifer.
(b) The Director of an approved State
may approve a multi-unit ground-water
monitoring system instead of separate
ground-water monitoring systems for
each MSWLF unit when the facility has
several units, provided the multi-unit
ground-water monitoring system meets
the requirement of §258.51(a) and will be
as protective of human health and the
environment as individual monitoring
systems for each MSWLF unit, based on
the following factors:
(1) Number, spacing, and orientation of
the MSWLF units;
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Subpart E
(2) Hydrogeologic setting;
(3) Site history;
(4) Engineering design of the MSWLF
units; and
(5) Type of waste accepted at the
MSWLF units.
(c) (See Section 5.7 for technical
guidance on monitoring well design and
construction.)
(d) The number, spacing, and depths of
monitoring systems shall be:
(1) Determined based upon site-specific
technical information that must include
thorough characterization of:
(i) Aquifer thickness, ground-water
flow rate, ground-water flow direction
including seasonal and temporal
fluctuations in ground-water flow; and
(ii) Saturated and unsaturated
geologic units and fill materials overlying
the uppermost aquifer, materials
comprising the uppermost aquifer, and
materials comprising the confining unit
defining the lower boundary of the
uppermost aquifer; including, but not
limited to: thicknesses, stratigraphy,
lithology, hydraulic conductivities,
porosities and effective porosities.
(2) Certified by a qualified ground-
water scientist or approved by the
Director of an approved State. Within 14
days of this certification, the owner or
operator must notify the State Director
that the certification has been placed in
the operating record.
5.6.2 Applicability
The requirements for establishing a ground-
water monitoring system pursuant to
§258.51 apply to all new units, existing
units, and lateral expansions of existing
units according to the schedules identified
in 40 CFR §258.50. A ground-water
monitoring system consists of both
background wells and wells located at the
point of compliance or waste management
unit boundary (i.e., downgradient wells).
The ground-water monitoring network must
be capable of detecting a release from the
MSWLF unit. A sufficient number of
monitoring wells must be located
downgradient of the unit and be screened at
intervals in the uppermost aquifer to ensure
contaminant detection. Generally,
upgradient wells are used to determine
background ground-water quality.
The downgradient wells must be located at
the relevant point of compliance specified
by the Director of an approved State, or at
the waste management unit boundary in
States that are not in compliance with
regulations. If existing physical structures
obstruct well placement, the downgradient
monitoring system should be placed as close
to the relevant point of compliance as
possible. Wells located at the relevant point
of compliance must be capable of detecting
contaminant releases from the MSWLF unit
to the uppermost aquifer. As discussed
earlier in the section pertaining to the
designation of a relevant point of
compliance (Section 4.4), the point of
compliance must be no greater than 150
meters from the unit boundary.
The Director of an approved State may
allow the use of a multi-unit ground-water
monitoring system. MSWLF units in
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Ground-Water Monitoring and Corrective Action
States that are deemed not in compliance
with the regulations must have a monitoring
system for each unit.
A qualified ground-water scientist must
certify that the number, spacing, and depths
of the monitoring wells are appropriate for
the MSWLF unit. This certification must be
placed in the operating records. The State
Director must be notified within 14 days
that the certification was placed in the
operating record.
5.6.3 Technical Considerations
The obj ective of a ground-water monitoring
system is to intercept ground water that has
been contaminated by leachate from the
MSWLF unit. Early contaminant detection
is important to allow sufficient time for
corrective measures to be developed and
implemented before sensitive receptors are
significantly affected. To accomplish this
objective, the monitoring wells should be
located to sample ground water from the
uppermost aquifer at the closest practicable
distance from the waste management unit
boundary. An alternative distance that is
protective of human health and the
environment may be granted by the Director
of an approved State. Since the monitoring
program is intended to operate through the
post-closure period, the location, design,
and installation of monitoring wells should
address both existing conditions and
anticipated facility development, as well as
expected changes in ground-water flow.
Uppermost Aquifer
Monitoring wells must be placed to provide
representative ground-water samples from
the uppermost aquifer. The uppermost
aquifer is defined in §258.2 as "the geologic
formation nearest to the natural ground
surface that is an aquifer, as well as lower
aquifers that are hydraulically
interconnected with this aquifer within the
facility property boundary." These lower
aquifers may be separated physically from
the uppermost aquifer by less permeable
strata (having a lower hydraulic
conductivity) that are often termed
aquitards. An aquitard is a less permeable
geologic unit or series of closely layered
units (e.g., silt, clay, or shale) that in itself
will not yield significant quantities of water
but will transmit water through its
thickness. Aquitards may include thicker
stratigraphic sequences of clays, shales, and
dense, unfractured crystalline rocks (Freeze
and Cherry, 1979).
To be considered part of the uppermost
aquifer, a lower zone of saturation must be
hydraulically connected to the uppermost
aquifer within the facility property
boundary. Generally, the degree of
communication between aquifers is
evaluated by ground-water pumping tests.
Methods have been devised for use in
analyzing aquifer test data. A summary is
presented in Handbook: Ground Water,
Vol. II (USEPA, 1991). The following
discussions under this section (5.6.3) should
assist the owner or operator in
characterizing the uppermost aquifer and
the hydrogeology of the site.
Determination of Background Ground-
Water Quality
The goal of monitoring-well placement is to
detect changes in the quality of ground
water resulting from a release from the
MSWLF unit. The natural chemical
composition of ground water is controlled
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Subpart E
primarily by the mineral composition of the
geologic unit comprising the aquifer. As
ground water moves from one geologic unit
to another, its chemical composition may
change. To reduce the probability of
detecting naturally occurring differences in
ground-water quality between background
and downgradient locations, only ground-
water samples collected from the same
geologic unit should be compared.
Ground-water quality in areas where the
geology is complex can be difficult to
characterize. As a result, the rule allows the
owner or operator flexibility in determining
where to locate wells that will be used to
establish background water quality.
If the facility is new, ground-water samples
collected from both upgradient and
downgradient locations prior to waste
disposal can be used to establish background
water quality. The sampling should be
conducted to account for both seasonal and
spatial variability in ground-water quality.
Determining background ground-water
quality by sampling wells that are not
hydraulically upgradient may be necessary
where hydrogeologic conditions do not
allow the owner or operator to determine
which wells are hydraulically upgradient.
Additionally, background ground-water
quality may be determined by sampling
wells that provide ground-water samples as
representative or more representative than
those provided by upgradient wells. These
conditions include the following:
• The facility is located above an aquifer
in which ground-water flow directions
change seasonally.
• The facility is located near production
wells that influence the direction of
ground-water flow.
• Upgradient ground-water quality is
affected by a source of contamination
other than the MSWLF unit.
• The proposed or existing landfill
overlies a ground-water divide or local
source of recharge.
• Geologic units present at downgradient
locations are absent at upgradient
locations.
• Karst terrain or fault zones modify flow.
• Nearby surface water influences ground-
water flow directions.
• Waste management areas are located
close to a property boundary that is
upgradient of the facility.
Multi-Unit Monitoring Systems
A multi-unit ground-water monitoring
system does not have wells at individual
MSWLF unit boundaries. Instead, an
imaginary line is drawn around all of the
units at the facility. (See Figure 5-1 for a
comparison of single unit and multi-unit
systems.) This line constitutes the relevant
point of compliance. The option to
establish a multi-unit monitoring system is
restricted to facilities located in approved
States. A multi-unit system must be
approved by the Director of an approved
State after consideration has been given to
the:
• Number, spacing, and orientation of the
MSWLF units
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Figure 5-1. Comparison of Single Unit and Multi-Unit Monitoring System
Single-Unit System
Ground-Water
Flow
Multi-Unit System
V G
V
Ground-Water
Flow
223
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Subpart E
• Hydrogeologic setting
• Site history
• Engineering design of the MSWLF units
• Type of wastes accepted at the facility.
The purpose of a multi-unit system is to
reduce the number of monitoring wells that
can provide the same information. The
conceptual design of the multi-unit system
should consider the use and management of
the facility with respect to anticipated unit
locations. In some cases, it may be possible
to justify a reduction in the number of wells
if the waste management units are aligned
along the same flow path in the ground-
water system.
The multi-unit monitoring system must
provide a level of protection to human
health and the environment that is
comparable to monitoring individual units.
The multi-unit system should allow
adequate time after detection of
contamination to develop and implement
corrective measures before sensitive
receptors are adversely affected.
Hydrogeological Characterization
Adequate monitoring-well placement
depends on collecting and evaluating
hydrogeological information that can be
used to form a conceptual model of the site.
The goal of a hydrogeological investigation
is to acquire site-specific data concerning:
• The lateral and vertical extent of the
uppermost aquifer
• The lateral and vertical extent of the
upper and lower confining units/layers
• The geology at the owner's/operator's
facility (e.g, stratigraphy, lithology, and
structural setting)
• The chemical properties of the
uppermost aquifer and its confining
layers relative to local ground-water
chemistry and wastes managed at the
facility
• Ground-water flow, including:
- The vertical and horizontal directions
of ground-water flow in the uppermost
aquifer
- The vertical and horizontal
components of the hydraulic gradient
in the uppermost and any hydraulically
connected aquifer
- The hydraulic conductivities of the
materials that comprise the upper-most
aquifer and its confining units/layers
- The average linear horizontal velocity
of ground-water flow in the uppermost
aquifer.
The elements of a program to characterize
the hydrogeology of a site are discussed
briefly in the sections that follow and are
addressed in more detail in "RCRA Ground-
Water Monitoring: Draft Technical
Guidance" (USEPA, 1992a).
Prior to initiating a field investigation, the
owner or operator should perform a
preliminary investigation. The preliminary
investigation will involve reviewing all
available information about the site, which
may consist of:
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Information on the waste management
history of the site, including:
- A chronological history of the site,
including descriptions of wastes
managed on-site
- A summary of documented releases
- Details on the structural integrity of
the MSWLF unit and physical controls
on waste migration
A literature review, including:
- Reports of research performed in the
area of the site
- Journal articles
- Studies and reports available from
local, regional, and State offices (e.g.,
geologic surveys, water boards, and
environmental agencies)
- Studies available from Federal offices,
such as USGS or USEPA
Information
including:
from file searches,
- Reports of previous investigations at
the site
- Geological and environmental
assessment data from State and Federal
reports.
The documentation itemized above is by no
means a complete listing of information
available for a preliminary investigation.
Many other sources of hydrogeological
information may be available for review
during the preliminary investigation.
Characterizing Site Geology
After the preliminary investigation is
complete, the owner/operator will have
information that he/she can use to develop a
plan to characterize site hydrogeology
further.
Nearly all hydrogeological investigations
include a subsurface boring program. A
boring program is necessary to define site
hydrogeology and the small-scale geology
of the area beneath the site. The program
usually requires more than one iteration.
The objective of the initial boreholes is to
refine the conceptual model of the site
derived from the preliminary investigation.
The subsurface boring program should be
designed as follows:
• The initial number of boreholes and their
spacing is based on the information
obtained during the preliminary
investigation.
• Additional boreholes should be installed
as needed to provide more information
about the site.
• Samples should be collected from the
borings at changes in lithology. For
boreholes that will be completed as
monitoring wells, at least one sample
should be collected from the interval that
will be the screened interval. Boreholes
that will not be completed as monitoring
wells must be properly decommissioned.
Geophysical techniques, cone penetrometer
surveys, mapping programs, and laboratory
analyses of borehole samples can be used to
plan and supplement the subsurface boring
program. Downhole geophysical techniques
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Subpart E
include electric, sonic, and nuclear logging.
Surface geophysical techniques include
seismic reflection and refraction, as well as
electromagnetic induction and resistivity.
The data obtained from the subsurface
boring program should enable the owner or
operator to identify:
• Lithology, soil types, and stratigraphy
• Zones of potentially high hydraulic
conductivity
• The presence of confining formations or
layers
• Unpredicted geologic features, such as
fault zones, cross-cutting structures, and
pinch-out zones
• Continuity of petrographic features, such
as sorting, grain size distribution, and
cementation
• The potentiometric surface or water
table.
Characterizing
Beneath the Site
Ground-Water Flow
In addition to characterizing site geology,
the owner/operator should characterize the
hydrology of the uppermost aquifer and its
confining layer(s) at the site. The owner or
operator should install wells and/or
piezometers to assist in characterizing site
hydrology. The owner/operator should
determine and assess:
• The direct!on(s) and rate(s) of ground-
water flow (including both horizontal
and vertical components of flow)
• Seasonal/temporal, natural, and
artificially induced (e.g., off-site
production well-pumping, agricultural
use) short-term and long-term
variations in ground-water elevations
and flow patterns
• The hydraulic conductivities of the
stratigraphic units at the site, including
vertical hydraulic conductivity of the
confining layer(s).
Determining Ground-Water Flow
Direction and Hydraulic Gradient
Installing monitoring wells that will provide
representative background and
downgradient water samples requires a
thorough understanding of how ground
water flows beneath a site. Developing such
an understanding requires obtaining
information regarding both ground-water
flow direction(s) and hydraulic gradient.
Ground-water flow direction can be thought
of as the idealized path that ground-water
follows as it passes through the subsurface.
Hydraulic gradient (i) is the change in static
head per unit of distance in a given
direction. The static head is defined as the
height above a standard datum of the surface
of a column of water (or other liquid) that
can be supported by the static pressure at a
given point (i.e., the sum of the elevation
head and pressure head).
To determine ground-water flow directions
and hydraulic gradient, owners and
operators should develop and implement a
water level-monitoring program. This
program should be structured to provide
precise water level measurements in a
sufficient number of piezometers or wells at
a sufficient frequency to gauge both
seasonal average flow directions and
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temporal fluctuations in ground-water flow
directions. Ground-water flow direction(s)
should be determined from water levels
measured in wells screened in the same
hydro-stratigraphic position. In
heterogeneous geologic settings (i.e.,
settings in which the hydraulic
conductivities of the subsurface materials
vary with location in the subsurface), long
well screens can intercept stratigraphic
horizons with different (e.g., contrasting)
ground-water flow directions and different
heads. In this situation, the resulting water
levels will not provide the depth-discrete
head measurements required for accurate
determination of the ground-water flow
direction.
In addition to evaluating the component of
ground-water flow in the horizontal
direction, a program should be undertaken
to assess the vertical component of ground-
water flow. Vertical ground-water flow
information should be based, at least in part,
on field data from wells and piezometers,
such as multi-level wells, piezometer
clusters, or multi-level sampling devices,
where appropriate. The following sections
provide acceptable methods for assessing
the vertical and horizontal components of
flow at a site.
Ground-Water Level Measurements
To determine ground-water flow directions
and ground-water flow rates, accurate water
level measurements (measured to the nearest
0.01 foot) should be obtained. Section 5.8
delineates procedures for obtaining water
level measurements. At facilities where it is
known or plausible that immiscible
contaminants (i.e., non-aqueous phase
liquids (NAPLs)) occur (or are determined
to be potentially present after considering
the waste types managed at the facility) in
the subsurface at the facility, both the
depth(s) to the immiscible layer(s) and the
thickness(es) of the immiscible layer(s) in
the well should be recorded.
For the purpose of measuring total head,
piezometers and wells should have as short
a screened interval as possible.
Specifically, the screens in piezometers or
wells that are used to measure head should
generally be less than 10 feet long. In
circumstances including the following, well
screens longer than 10 feet may be
warranted:
• Natural water level fluctuations
necessitate a longer screen length.
• The interval monitored is slightly
greater than the appropriate screen
length (e.g., the interval monitored is
12 feet thick).
• The aquifer monitored is homogeneous
and extremely thick (e.g., greater than
300 feet); thus, a longer screen (e.g., a
20-foot screen) represents a fairly
discrete interval.
The head measured in a well with a long
screened interval is a function of all of the
different heads over the entire length of the
screened interval. Care should be taken
when interpreting water levels collected
from wells that have long screened intervals
(e.g., greater than 10 feet).
The water-level monitoring program should
be structured to provide precise water level
measurements in a sufficient number of
piezometers or wells at a sufficient
frequency to gauge both seasonal average
flow directions and temporal fluctuations in
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Subpart E
ground-water flow directions. The
owner/operator should determine and assess
seasonal/temporal, natural, and artificially
induced (e.g., off-site production well-
pumping, agricultural use) short-term and
long-term variations in ground-water
elevations, ground-water flow patterns, and
ground-water quality.
Establishing Horizontal Flow Direction
and the Horizontal Component of
Hydraulic Gradient
After the water level data and measurement
procedures are reviewed to determine that
they are accurate, the data should be used
to:
• Construct potentiometric surface maps
and water table maps based on the
distribution of total head. The data
used to develop water table maps
should be from piezometers or wells
screened across the water table. The
data used to develop potentiometric
surface maps should be from
piezometers or wells screened at
approximately the same elevation in
the same hydrostratigraphic unit;
• Determine the horizontal direction(s)
of ground-water flow by drawing flow
lines on the potentiometric surface map
or water table map (i.e., construct a
flow net);
• Calculate value(s) for the horizontal
and vertical components of hydraulic
gradient.
Methods for constructing potentiometric
surface and water table maps, constructing
flow nets, and determining the direction(s)
of ground-water flow are provided by
USEPA (1989c) and Freeze and Cherry
(1979). Methods for calculating hydraulic
gradient are provided by Heath (1982) and
USEPA (1989c).
A potentiometric surface or water table map
will give an approximate idea of general
ground-water flow directions. However, to
locate monitoring wells properly, ground-
water flow direction(s) and hydraulic
gradient(s) should be established in both the
horizontal and vertical directions and over
time at regular intervals (e.g., over a 1-year
period at 3-month intervals).
Establishing Vertical Flow Direction and
the Vertical Component of Hydraulic
Gradient
To make an adequate determination of the
ground-water flow directions, the vertical
component of ground-water flow should be
evaluated directly. This generally requires
the installation of multiple piezometers or
wells in clusters or nests, or the installation
of multi-level wells or sampling devices. A
piezometer or well nest is a closely spaced
group of piezometers or wells screened at
different depths, whereas a multi-level well
is a single device. Both piezometer/well
nests and multi-level wells allow for the
measurement of vertical variations in
hydraulic head.
When reviewing data obtained from
multiple placement of piezometers or wells
in single boreholes, the construction details
of the well should be carefully evaluated.
Not only is it extremely difficult to seal
several piezometers/wells at discrete depths
within a single borehole, but sealant
materials may migrate from the seal of one
piezometer/well to the screened interval of
another piezometer/well. Therefore, the
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design of a piezometer/well nest should be
considered carefully. Placement of
piezometers/wells in closely spaced
boreholes, where piezometers/wells have
been screened at different, discrete depth
intervals, is likely to produce more accurate
information. The primary concerns with the
installation of piezometers/wells in closely
spaced, separate boreholes are: 1) the
disturbance of geologic and soil materials
that occurs when one piezometer is installed
may be reflected in the data obtained from
another piezometer located nearby, and 2)
the analysis of water levels measured in
piezometers that are closely spaced, but
separated horizontally, may produce
imprecise information regarding the vertical
component of ground-water flow. The
limitations of installing multiple
piezometers either in single or separate
boreholes may be overcome by the
installation of single multi-level monitoring
wells or sampling devices in single
boreholes. The advantages and
disadvantages of these types of devices are
discussed by USEPA (1989f).
The owner or operator should determine the
vertical direction(s) of ground-water flow
using the water levels measured in multi-
level wells or piezometer/well nests to
construct flow nets. Flow nets should depict
the piezometer/well depth and length of the
screened interval. It is important to portray
the screened interval accurately on the flow
net to ensure that the piezometer/well is
actually monitoring the desired
water-bearing unit. A flow net should be
developed from information obtained from
piezometer/ well clusters or nests screened
at different, discrete depths. Detailed
guidance for the construction and evaluation
of flow nets in cross section (vertical flow
nets) is provided by USEPA (1989c).
Further information can be obtained from
Freeze and Cherry (1979).
Determining Hydraulic Conductivity
Hydraulic conductivity is a measure of a
material's ability to transmit water.
Generally, poorly sorted silty or clayey
materials have low hydraulic conductivities,
whereas well-sorted sands and gravels have
high hydraulic conductivities. An aquifer
may be classified as either homogeneous or
heterogeneous and either isotropic or
anisotropic according to the way its
hydraulic conductivity varies in space. An
aquifer is homogeneous if the hydraulic
conductivity is independent of location
within the aquifer; it is heterogeneous if
hydraulic conductivities are dependent on
location within the aquifer. If the hydraulic
conductivity is independent of the direction
of measurement at a point in a geologic
formation, the formation is isotropic at that
point. If the hydraulic conductivity varies
with the direction of measurement at a
point, the formation is anisotropic at that
point.
Determining Hydraulic Conductivity
Using Field Methods
Sufficient aquifer testing (i.e., field
methods) should be performed to provide
representative estimates of hydraulic
conductivity. Acceptable field methods
include conducting aquifer tests with single
wells, conducting aquifer tests with multiple
wells, and using flowmeters. This section
provides brief overviews of these methods,
including two methods for obtaining
vertically discrete measurements of
hydraulic conductivity. The identified
references provide detailed descriptions of
the methods summarized in this section.
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Subpart E
A commonly used test for determining
horizontal hydraulic conductivity with a
single well is the slug test. A slug test is
performed by suddenly adding, removing,
or displacing a known volume of water from
a well and observing the time that it takes
for the water level to recover to its original
level (Freeze and Cherry, 1979). Similar
results can be achieved by pressurizing the
well casing, depressing the water level, and
suddenly releasing the pressure to simulate
the removal of water from the well. In most
cases, EPA recommends that water not be
introduced into wells during aquifer tests to
avoid altering ground-water chemistry.
Single-well tests are limited in scope to the
area directly adjacent to the well screen.
The vertical extent of the well screen
generally defines the part of the geologic
formation that is being tested.
A modified version of the slug test, known
as the multilevel slug test, is capable of
providing depth-discrete measurements of
hydraulic conductivity. The drawback of
the multilevel slug test is that the test relies
on the ability of the investigator to isolate a
portion of the aquifer using a packer.
Nevertheless, multilevel slug tests, when
performed properly, can produce reliable
measurements of hydraulic conductivity.
Multiple-well tests involve withdrawing
water from, or injecting water into, one
well, and obtaining water level
measurements over time in observation
wells. Multiple-well tests are often
performed as pumping tests in which water
is pumped from one well and drawdown is
observed in nearby wells. A step-drawdown
test should precede most pumping tests to
determine an appropriate discharge rate.
Aquifer tests conducted with wells screened
in the same water-bearing zone can be used
to provide hydraulic conductivity data for
that zone. Multiple-well tests for hydraulic
conductivity characterize a greater
proportion of the subsurface than single-
well tests and, thus, provide average values
of hydraulic conductivity. Multiple-well
tests require measurement of parameters
similar to those required for single-well
tests (e.g., time, drawdown). When using
aquifer test data to determine aquifer
parameters, it is important that the solution
assumptions can be applied to site
conditions. Aquifer test solutions are
available for a wide variety of
hydrogeologic settings, but are often applied
incorrectly by inexperienced persons.
Incorrect assumptions regarding
hydrogeology (e.g., aquifer boundaries,
aquifer lithology, and aquifer thickness)
may translate into incorrect estimations of
hydraulic conductivity. A qualified ground-
water scientist with experience in designing
and interpreting aquifer tests should be
consulted to ensure that aquifer test solution
methods fit the hydrogeologic setting.
Kruseman and deRidder (1989) provide a
comprehensive discussion of aquifer tests.
Multiple-well tests conducted with wells
screened in different water-bearing zones
furnish information concerning hydraulic
communication among the zones. Water
levels in these zones should be monitored
during the aquifer test to determine the type
of aquifer system (e.g., confined,
unconfmed, semi-confined, or semi-
unconfmed) beneath the site, and their
leakance (coefficient of leakage) and
drainage factors (Kruseman and deRidder,
1989). A multiple-well aquifer test should
be considered at every site as a method to
establish the vertical extent of the
uppermost aquifer and to evaluate hydraulic
connection between aquifers.
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Ground-Water Monitoring and Corrective Action
Certain aquifer tests are inappropriate for
use in karst terrains characterized by a
well-developed conduit flow system, and
they also may be inappropriate in fractured
bedrock. When a well located in a karst
conduit or a large fracture is pumped, the
water level in the conduit is lowered. This
lowering produces a drawdown that is not
radial (as in a granular aquifer) but is
instead a trough-like depression parallel to
the pumped conduit or fracture. Radial flow
equations do not apply to drawdown data
collected during such a pump test. This
means that a conventional semi-log plot of
drawdown versus time is inappropriate for
the purpose of determining the aquifer's
transmissivity and storativity. Aquifer tests
in karst aquifers can be useful, but valid
determinations of hydraulic conductivity,
storativity, and transmissivity may be
impossible. However, an aquifer test can
provide information on the presence of
conduits, on storage characteristics, and on
the percentage of Darcian flow. McGlew
and Thomas (1984) provide a more detailed
discussion of the appropriate use of aquifer
tests in fractured bedrock and on the
suitable interpretation of test data. Dye
tracing also is used to determine the rate and
direction of ground-water flow in karst
settings (Section 5.2.4).
Several additional factors should be
considered when planning an aquifer test:
• Owners and operators should provide
for the proper storage and disposal of
potentially contaminated ground water
pumped from the well system.
• Owners and operators should consider
the potential effects of pumping on
existing plumes of contaminated
ground water.
• In designing aquifer tests and
interpreting aquifer test data,
owners/operators should account and
correct for seasonal, temporal, and
anthropogenic effects on the
potentiometric surface or water table.
This is usually done by installing
piezometers outside the influence of
the stressed aquifer. These
piezometers should be continuously
monitored during the aquifer test.
• Owners and operators should be aware
that, in a very high hydraulic
conductivity aquifer, the screen size
and/or filter pack used in the test well
can affect an aquifer test. If a very
small screen size is used, and the pack
is improperly graded, the test may
reflect the characteristics of the filter
pack, rather than the aquifer.
• EPA recommends the use of a step-
drawdown test to provide a basis for
selecting discharge rates prior to
conducting a full-scale pumping test.
This will ensure that the pumping rate
chosen for the subsequent pumping
test(s) can be sustained without
exceeding the available drawdown of
the pumped wells. In addition, this test
will produce a measurable drawdown
in the observation wells.
Certain flowmeters recently have been
recognized for their ability to provide
accurate and vertically discrete
measurements of hydraulic conductivity.
One of these, the impeller flowmeter, is
available commercially. More sensitive
types of flowmeters (i.e., the heat-pulse
flowmeter and electromagnetic flowmeter)
should be available in the near future. Use
of the impeller flowmeter requires running
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Subpart E
a caliper log to measure the uniformity of
the diameter of the well screen. The well is
then pumped with a small pump operated at
a constant flow rate. The flowmeter is
lowered into the well, and the discharge rate
is measured every few feet by raising the
flowmeter in the well. Hydraulic
conductivity values can be calculated from
the recorded data using the Cooper-Jacob
(1946) formula for horizontal flow to a
well. Use of the impeller flowmeter is
limited at sites where the presence of low
permeability materials does not allow
pumping of the wells at rates sufficient to
operate the flowmeter. The application of
flowmeters in the measure of hydraulic
conductivity is described by Molz et al.
(1990) and Molz et al. (1989).
Determining Hydraulic Conductivity
Using Laboratory Methods
It may be beneficial to use laboratory
measurements of hydraulic conductivity to
augment the results of field tests. However,
field methods provide the best estimates of
hydraulic conductivity in most cases.
Because of the limited sample size,
laboratory tests can fail to account for
secondary porosity features, such as
fractures and joints, and hence, can greatly
underestimate overall aquifer hydraulic
conductivities. Laboratory tests may
provide valuable information about the
vertical component of hydraulic
conductivity of aquifer materials. However,
laboratory test results always should be
confirmed by field measurements, which
sample a much larger portion of the aquifer.
In addition, laboratory test results can be
profoundly affected by the test method
selected and by the manner in which the
tests are carried out (e.g., the extent to
which sample collection and preparation
have changed the in situ
hydraulic properties of the tested material).
Special attention should be given to the
selection of the appropriate test method and
test conditions and to quality control of
laboratory results. McWhorter and Sunada
(1977), Freeze and Cherry (1979), and
Sevee (1991) discuss determining hydraulic
conductivity in the laboratory. Laboratory
tests may provide the best estimates of
hydraulic conductivity for materials in the
unsaturated zone, but they are likely to be
less accurate than field methods for
materials in the saturated zone (Cantor et
al., 1987).
Determining Ground-Water Flow Rate
The calculation of the average ground-water
flow rate (average linear velocity of ground-
water flow), or seepage velocity, is
discussed in detail in USEPA (1989c), in
Freeze and Cherry (1979), and in Kruseman
and deRidder (1989). The average linear
velocity of ground-water flow (v) is a
function of hydraulic conductivity (K),
hydraulic gradient (i), and effective porosity
(ne):
v = - Ki
Methods for determining hydraulic gradient
and hydraulic conductivity have been
presented previously. Effective porosity,
the percentage of the total volume of a given
mass of soil, unconsolidated material, or
rock that consists of interconnected pores
through which water can flow, should be
estimated from laboratory tests or from
values cited in the literature. (Fetter (1980)
provides a good discussion of effective
porosity. Barari and Hedges (1985) provide
default values for effective porosity.)
USEPA (1989c) provides methods for
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determining flow rates in heterogeneous
and/or anisotropic systems and should be
consulted prior to calculating flow rates.
Interpreting and Presenting Data
The following sections offer guidance on
interpreting and presenting hydrogeologic
data collected during the site
characterization process. Graphical
representations of data, such as cross
sections and maps, are typically extremely
helpful both when evaluating data and when
presenting data to interested individuals.
Interpreting Hydrogeologic Data
Once the site characterization data have
been collected, the following tasks should
be undertaken to support and develop the
interpretation of these data:
• Review borehole and well logs to
identify major rock, unconsolidated
material, and soil types and establish
their horizontal and vertical extent and
distribution.
• From borehole and well log (and
outcrop, where available) data,
construct representative cross-sections
for each MSWLF unit, one in the
direction of ground-water flow and one
orthogonal to ground-water flow.
• Identify zones of suspected high
hydraulic conductivity, or structures
likely to influence contaminant
migration through the unsaturated and
saturated zones.
• Compare findings with other studies
and information collected during the
preliminary investigation to verify the
collected information.
• Determine whether laboratory and
field data corroborate and are
sufficient to define petrology, effective
porosity, hydraulic conductivity,
lateral and vertical stratigraphic
relationships, and ground-water flow
directions and rates.
After the hydrogeologic data are interpreted,
the findings should be reviewed to:
• Identify information gaps
• Determine whether the collection of
additional data or reassessment of
existing data is required to fill in the
gaps
• Identify how information gaps are
likely to affect the ability to design a
RCRA monitoring system.
Generally, lithologic data should correlate
with hydraulic properties (e.g., clean, well-
sorted, unconsolidated sands should exhibit
high hydraulic conductivity). Additional
boreholes should be drilled and additional
samples should be collected to describe the
hydrogeology of the site if the investigator
is unable to 1) correlate stratigraphic units
between borings, 2) identify zones of
potentially high hydraulic conductivity and
the thickness and lateral extent of these
zones, or 3) identify confining
formations/layers and the thickness and
lateral extent of these formation layers.
When establishing the locations of wells
that will be used to monitor ground water in
hydrogeologic settings characterized by
ground-water flow in porous media, the
following should be documented:
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• The ground-water flow rate should be
based on accurate measurements of
hydraulic conductivity and hydraulic
gradient and accurate measurements or
estimates of effective porosity
• The horizontal and vertical
components of flow should be
accurately depicted in flow nets and
based on valid data
• Any seasonal or temporal variations in
the water table or potentiometric
surface, and in vertical flow
components, should be determined.
Once an understanding of horizontal and
vertical ground-water flow has been
established, it is possible to estimate where
monitoring wells will most likely intercept
contaminant flow.
Presenting Hydrogeologic Data
Subsequent to the generation and
interpretation of site-specific geologic data,
the data should be presented in geologic
cross-sections, topographic maps, geologic
maps, and soil maps. The Agency suggests
that owners/operators obtain or prepare and
review topographic, geologic, and soil maps
of the facility, in addition to site maps of the
facility and MSWLF units. In cases where
suitable maps are not available, or where the
information contained on available maps is
not complete or accurate, detailed mapping
of the site should be performed by qualified
and experienced individuals. An aerial
photograph and a topographic map of the
site should be included as part of the
presentation of hydrogeologic data. The
topographic map should be constructed
under the supervision of a qualified
surveyor and should provide contours at a
maximum of 2-foot intervals.
Geologic and soil maps should be based on
rock, unconsolidated material, and soil
identifications gathered from borings and
outcrops. The maps should use colors or
symbols to represent each soil,
unconsolidated material, and rock type that
outcrops on the surface. The maps also
should show the locations of outcrops and
all borings placed during the site
characterization. Geologic and soil maps
are important because they can provide
information describing how site geology fits
into the local and regional geologic setting.
Structure contour maps and isopach maps
should be prepared for each water-bearing
zone that comprises the uppermost aquifer
and for each significant confining layer,
especially the one underlying the uppermost
aquifer. A structure contour map depicts
the configuration (i.e., elevations) of the
upper or lower surface or boundary of a
particular geologic or soil formation, unit,
or zone. Structure contour maps are
especially important in understanding dense
non-aqueous phase liquid (DNAPL)
movement because DNAPLs (e.g.,
tetrachloroethylene) may migrate in the
direction of the dip of lower permeability
units. Separate structure contour maps
should be constructed for the upper and
lower surfaces (or contacts) of each zone of
interest. Isopach maps should depict
contours that indicate the thickness of each
zone. These maps are generated from
borings and geologic logs and from
geophysical measurements. In conjunction
with cross-sections, isopach maps may be
used to help determine monitoring well
locations, depths, and screen lengths during
the design of the detection monitoring
system.
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A potent!ometric surface map or water table
map should be prepared for each water-
bearing zone that comprises the uppermost
aquifer. Potentiometric surface and water
table maps should show both the direction
and rate of ground-water flow and the
locations of all piezometers and wells on
which they are based. The water level
measurements for all piezometers and wells
on which the potentiometric surface map or
water table map is based should be shown
on the potentiometric surface or water table
map. If seasonal or temporal variations in
ground-water flow occur at the site, a
sufficient number of potentiometric surface
or water table maps should be prepared to
show these variations. Potentiometric
surface and water table maps can be
combined with structure contour maps for a
particular formation or unit. An adequate
number of cross sections should be prepared
to depict significant stratigraphic and
structural trends and to reflect stratigraphic
and structural features in relation to local
and regional ground-water flow.
Hydrogeological Report
The hydrogeological report should contain,
at a minimum:
• A description of field activities
• Drilling and/or well construction logs
• Analytical data
• A discussion and interpretation of the
data
• Recommendations to address data gaps.
The final output of the site characterization
phase of the hydrogeological investigation
is
a conceptual model. This model is the
integrated picture of the hydrogeologic
system and the waste management setting.
The final conceptual model must be a site-
specific description of the unsaturated zone,
the uppermost aquifer, and its confining
units. The model should contain all of the
information necessary to design a ground-
water monitoring system.
Monitoring Well Placement
This section separately addresses the lateral
placement and the vertical sampling
intervals of point of compliance wells.
However, these two aspects of well
placement should be evaluated together in
the design of the monitoring system. Site-
specific hydrogeologic data obtained during
the site characterization should be used to
determine the lateral placement of detection
monitoring wells and to select the length
and vertical position of monitoring well
intakes. Potential pathways for contaminant
migration are three-dimensional.
Consequently, the design of a detection
monitoring network that intercepts these
potential pathways requires a
three-dimensional approach.
Lateral Placement of Point of
Compliance Monitoring Wells
Point of compliance monitoring wells
should be as close as physically possible to
the edge of the MSWLF unit(s) and should
be screened in all transmissive zones that
may act as contaminant transport pathways.
The lateral placement of monitoring wells
should be based on the number and spatial
distribution of potential contaminant
migration pathways and on the depths and
thicknesses of stratigraphic horizons that
can serve as contaminant migration
pathways.
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Subpart E
Point of compliance monitoring wells
should be placed laterally along the
downgradient edge of the MSWLF unit to
intercept potential pathways for
contaminant migration. The local ground-
water flow direction and gradient are the
major factors in determining the lateral
placement of point of compliance wells. In
a homogeneous, isotropic hydrogeologic
setting, well placement can be based on
general aquifer characteristics (e.g.,
direction and rate of ground-water flow),
and potential contaminant fate and transport
characteristics (e.g., advection, dispersion).
More commonly, however, geology is
variable and preferential pathways exist that
control the migration of contaminants.
These types of heterogeneous, anisotropic
geologic settings can have numerous,
discrete zones within which contaminants
may migrate.
Potential migration pathways include zones
of relatively high intrinsic (matrix)
hydraulic conductivities, fractured/faulted
zones, and subsurface material that may
increase in hydraulic conductivity if the
material is exposed to waste(s) managed at
the site (e.g., a limestone layer that
underlies an acidic waste). In addition to
natural hydrogeologic features, human-
made features may influence the ground-
water flow direction and, thus, the lateral
placement of point of compliance wells.
Such human-made features include ditches,
areas where fill material has been placed,
buried piping, buildings, leachate collection
systems, and adjacent disposal units. The
lateral placement of monitoring wells
should be based on the number and spatial
distribution of potential contaminant
migration pathways and on the depths and
thicknesses of stratigraphic horizons that
can serve as contaminant migration
pathways.
In some settings, the ground-water flow
direction may reverse seasonally (depending
on precipitation), change as a result of tidal
influences or river and lake stage
fluctuations, or change temporally as a
result of well-pumping or changing land use
patterns. In other settings, ground water
may flow away from the waste management
area in all directions. In such cases, EPA
recommends that monitoring wells be
installed on all sides (or in a circular
pattern) around the waste management area
to allow for the detection of contamination.
In these cases, certain wells may be
downgradient only part of the time, but such
a configuration should ensure that releases
from the unit will be detected.
The lateral placement of monitoring wells
also should be based on the physical/
chemical characteristics of the contaminants
of concern. While the restriction of liquids
in MSWLFs may limit the introduction of
hazardous constituents into landfills, it is
important to consider the physical/chemical
characteristics of contaminants when
designing the well system. These
characteristics include solubility, Henry's
Law constant, partition coefficients, specific
gravity, contaminant reaction or degradation
products, and the potential for contaminants
to degrade confining layers. For example,
contaminants with low solubilities and high
specific gravities that occur as DNAPLs
may migrate in the subsurface in directions
different from the direction of ground-water
flow. Therefore, in situations where the
release of DNAPLs is a concern, the lateral
placement of compliance point ground-
water monitoring wells should not
necessarily only be along the downgradient
edge of the MSWLF unit. Considering both
contaminant characteristics and
hydrogeologic properties is important when
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Ground-Water Monitoring and Corrective Action
determining the lateral placement of
monitoring wells.
Vertical Placement and Screen Lengths
Proper selection of the vertical sampling
interval is necessary to ensure that the
monitoring system is capable of detecting a
release from the MSWLF unit. The vertical
position and lengths of well intakes are
functions of (1) hydro-geologic factors that
determine the distribution of, and
fluid/vapor phase transport within, potential
pathways of contaminant migration to and
within the uppermost aquifer, and (2) the
chemical and physical characteristics of
contaminants that control their transport and
distribution in the subsurface. Well intake
length also is determined by the need to
obtain vertically discrete ground-water
samples. Owners and operators should
determine the probable location, size, and
geometry of potential contaminant plumes
when selecting well intake positions and
lengths.
Site-specific hydrogeologic data obtained
during the site characterization should be
used to select the length and vertical
position of monitoring well intakes. The
vertical positions and lengths of monitoring
well intakes should be based on the number
and spatial distribution of potential
contaminant migration pathways and on the
depths and thicknesses of stratigraphic
horizons that can serve as contaminant
migration pathways. Figure 5-2 illustrates
examples of complex stratigraphy that
would require multiple vertical monitoring
intervals.
The depth and thickness of a potential
contaminant migration pathway can be
determined from soil, unconsolidated
material, and rock samples collected during
the boring program, and from samples
collected while drilling the monitoring well.
Direct physical data can be supplemented by
geophysical data, available regional/local
hydrogeological data, and other data that
provide the vertical distribution of hydraulic
conductivity. The vertical sampling interval
is not necessarily synonymous with aquifer
thickness. Monitoring wells are often
screened at intervals that represent a portion
of the thickness of the aquifer. When
monitoring an unconfined aquifer, the well
screen typically should be positioned so that
a portion of the well screen is in the
saturated zone and a portion of the well
screen is in the unsaturated zone (i.e., the
well screen straddles the water table).
While the restriction of liquids in MSWLFs
may limit the introduction of hazardous
constituents into landfills, it is important to
consider the physical/chemical
characteristics of contaminants when
designing the well system.
The vertical positions and lengths of
monitoring well intakes should be based on
the same physical/chemical characteristics
of the contaminants of concern that
influence the lateral placement of
monitoring wells. Considering both
contaminant characteristics and
hydrogeologic properties is important when
choosing the vertical position and length of
the well intake. Some contaminants may
migrate within very narrow zones. Of
course, for well placement at a new site, it is
unlikely that the owner or operator will be
able to assess contaminant characteristics.
Different transport processes control
contaminant migration depending on
whether the contaminant dissolves or is
immiscible in water. Immiscible
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Subpart E
Piezometric
Surface
Down Gradient Zone
Flow Path
69
65
Figure 5-2
Upgradient and Downgradient
Designations for Idealized MSWLF
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Ground-Water Monitoring and Corrective Action
contaminants may occur as light non
aqueous phase liquids (LNAPLs), which are
lighter than water, and DNAPLs, which are
denser than water. LNAPLs migrate in the
capillary zone just above the water table.
Wells installed to monitor LNAPLs should
be screened at the water table/capillary zone
interface, and the screened interval should
intercept the water table at its minimum and
maximum elevation. LNAPLs may become
trapped in residual form in the vadose zone
and become periodically remobilized and
contribute further to aquifer contamination,
either as free phase or dissolved phase
contaminants, as the water table fluctuates
and precipitation infiltrates the subsurface.
The migration of free-phase DNAPLs may
be influenced primarily by the geology,
rather than the hydrogeology, of the site.
That is, DNAPLs migrate downward
through the saturated zone due to density
and then migrate by gravity along less
permeable geologic units (e.g., the slope of
confining units, the slope of clay lenses in
more permeable strata, bedrock troughs),
even in aquifers with primarily horizontal
ground-water flow. Consequently, if wastes
disposed at the site are anticipated to exist
in the subsurface as a DNAPL, the potential
DNAPL should be monitored:
• At the base of the aquifer (immediately
above the confining layer)
• In structural depressions (e.g., bedrock
troughs) in lower hydraulic
conductivity geologic units that act as
confining layers
• Along lower hydraulic conductivity
lenses and units within units of higher
hydraulic conductivity
• "Down-the-dip" of lower hydraulic
conductivity units that act as confining
layers, both upgradient and
downgradient of the waste
management area.
Because of the nature of DNAPL migration
(i.e., along structural, rather than hydraulic,
gradients), wells installed to monitor
DNAPLs may need to be installed both
upgradient and downgradient of the waste
management area. It may be useful to
construct a structure contour map of lower
permeability strata and identify lower
permeability lenses upgradient and
downgradient of the unit along which
DNAPLs may migrate. The wells can then
be located accordingly.
The lengths of well screens used in
ground-water monitoring wells can
significantly affect their ability to intercept
releases of contaminants. The complexity
of the hydrogeology of a site is an important
consideration when selecting the lengths of
well screens. Most hydrogeologic settings
are complex (heterogeneous and
anisotropic) to a certain degree. Highly
heterogeneous formations require shorter
well screens to allow sampling of discrete
portions of the formation that can serve as
contaminant migration pathways. Well
screens that span more than a single
saturated zone or a single contaminant
migration pathway may cause cross-
contamination of transmissive units, thereby
increasing the extent of contamination.
Well intakes should be installed in a single
saturated zone. Well intakes (e.g., screens)
and filter pack materials should not
interconnect, or promote the interconnection
of, zones that are separated by a confining
layer.
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Subpart E
Even in hydrologically simple formations,
or within a single potential pathway for
contaminant migration, the use of shorter
well screens may be necessary to detect
contaminants concentrated at particular
depths. A contaminant may be concentrated
at a particular depth because of its
physical/chemical properties and/or because
of hydrogeologic properties. In
homogeneous formations, a long well screen
can permit excessive amounts of
uncontaminated formation water to dilute
the contaminated ground water entering the
well. At best, dilution can make
contaminant detection difficult; at worst,
contaminant detection is impossible if the
concentrations of contaminants are diluted
to levels below the detection limits for the
prescribed analytical methods. The use of
shorter well screens allows for contaminant
detection by reducing excessive dilution.
When placed at depths of predicted
preferential flow, shorter well screens are
effective in monitoring the aquifer or the
portion of the aquifer of concern.
Generally, screen lengths should not exceed
10 feet. However, certain hydrogeologic
settings may warrant or necessitate the use
of longer well screens for adequate
detection monitoring. Unconfmed aquifers
with widely fluctuating water tables may
require longer screens to intercept the water
table surface at both its maximum and
minimum elevations and to provide
monitoring for the presence of contaminants
that are less dense than water. Saturated
zones that are slightly greater in thickness
than the appropriate screen length (e.g., 12
feet thick) may warrant monitoring with
longer screen lengths. Extremely thick
homogeneous aquifers (e.g., greater than
300 feet) may be monitored with a longer
screen (e.g., a 20-foot screen) because a
slightly longer screen
would represent a fairly discrete interval in
a very thick formation. Formations with
very low hydraulic conductivities also may
require the use of longer well screens to
allow sufficient amounts of formation water
to enter the well for sampling. The
importance of accurately identifying such
conditions highlights the need for a
complete hydrogeologic site investigation
prior to the design and placement of
detection wells.
Multiple monitoring wells (well clusters or
multilevel sampling devices) should be
installed at a single location when (1) a
single well cannot adequately intercept and
monitor the vertical extent of a potential
pathway of contaminant migration, or (2)
there is more than one potential pathway of
contaminant migration in the subsurface at
a single location, or (3) there is a thick
saturated zone and immiscible contaminants
are present, or are determined to be
potentially present after considering waste
types managed at the facility. Conversely, at
sites where ground water may be
contaminated by a single contaminant,
where there is a thin saturated zone, and
where the site is hydrogeologically
homogeneous, the need for multiple wells at
each sampling location is reduced. The
number of wells that should be installed at
each sampling location increases with site
complexity.
The following sources provided additional
information on monitoring well placement:
USEPA (1992a), USEPA (1990), USEPA
(1991), and USEPA (1986a).
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5.7 GROUND-WATER
MONITORING WELL DESIGN
AND CONSTRUCTION
40 CFR §258.51 (c)
5.7.1 Statement of Regulation
(c) Monitoring wells must be cased in a
manner that maintains the integrity of
the monitoring well bore hole. This
casing must be screened or perforated
and packed with gravel or sand, where
necessary, to enable collection of ground-
water samples. The annular space (i.e.,
the space between the bore hole and well
casing) above the sampling depth must be
sealed to prevent contamination of
samples and the ground water.
(1) The owner or operator must notify
the State Director that the design,
installation, development, and
decommission of any monitoring wells,
piezometers and other measurement,
sampling, and analytical devices
documentation has been placed in the
operating record; and
(2) The monitoring wells, piezometers,
and other measurement, sampling, and
analytical devices must be operated and
maintained so that they perform to design
specifications throughout the life of the
monitoring program.
§258.52 [Reserved].
5.7.2 Applicability
The requirements for monitoring well
design, installation, and maintenance are
applicable to all wells installed at existing
units, lateral expansions of units, and new
MSWLF units. The design, installation, and
decommissioning of any monitoring well
must be documented in the operating record
of the facility and certified by a qualified
ground-water scientist. Documentation is
required for wells, piezometers, sampling
devices, and water level measurement
instruments used in the monitoring program.
The monitoring wells must be cased to
protect the integrity of the borehole. The
design and construction of the well directly
affects the quality and representativeness of
the samples collected. The well casing must
have a screened or perforated interval to
allow the entrance of water into the well
casing. The annular space between the well
screen and the formation wall must be
packed with material to inhibit the
migration of formation material into the
well. The well screen must have openings
sized according to the packing material
used. The annular space above the filter
pack must be sealed to provide a discrete
sampling interval.
All monitoring wells, piezometers, and
sampling and analytical devices must be
maintained in a manner that ensures their
continued performance according to design
specifications over the life of the monitoring
program.
5.7.3 Technical Considerations
The design, installation, and maintenance of
monitoring wells will affect the consistency
and accuracy of samples collected. The
design must be based on site-specific
information. The formation material
(lithology and grain size distribution) will
determine the selection of proper packing
and sealant materials, and the stratigraphy
will determine the screen length for the
interval to be monitored. Installation
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Subpart E
practices should be specified and overseen
to ensure that the monitoring well is
installed as designed and will perform as
intended. This section will discuss the
factors that must be considered when
designing monitoring wells. Each well must
be tailored to suit the hydrogeological
setting, the contaminants to be monitored,
and other site-specific factors. Figure 5-3
depicts the components of a typical
monitoring well installation.
The following sections provide a brief
overview of monitoring well design and
construction. More comprehensive
discussions are provided in USEPA (1989f)
andUSEPA(1992a).
Selection of Drilling Method
The method chosen for drilling a monitoring
well depends largely on the following
factors (USEPA, 1989f):
• Versatility of the drilling method
• Relative drilling cost
• Sample reliability (ground-water, soil,
unconsolidated material, or rock
samples)
• Availability of drilling equipment
• Accessibility of the drilling site
• Relative time required for well
installation and development
• Ability of the drilling technology to
preserve natural conditions
• Ability to install a well of desired
diameter and depth
• Relative ease of well completion and
development, including the ability to
install the well in the given
hydrogeologic setting.
In addition to these factors, USEPA (1989f)
includes matrices to assist in selecting an
appropriate drilling method. These matrices
list the most commonly used drilling
techniques for monitoring well installation,
taking into consideration hydrogeologic
settings and the objectives of the monitoring
program.
The following basic performance objectives
should guide the selection of drilling
procedures for installing monitoring wells:
• Drilling should be performed in a
manner that preserves the natural
properties of the subsurface materials.
• Contamination and/or cross-
contamination of ground water and
aquifer materials during drilling should
be avoided.
• The drilling method should allow for
the collection of representative
samples of rock, unconsolidated
materials, and soil.
• The drilling method should allow the
owner/operator to determine when the
appropriate location for the screened
interval has been encountered.
• The drilling method should allow for
proper placement of the filter pack and
annular sealants. The borehole should
be at least 4 inches larger in diameter
than the nominal diameter of the well
casing and screen to allow adequate
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Protective Cover
with Locking Cap
6 in (152mm)
Clearance for Sampler
Top of Riser 3 ft
(1.0m) Above Grade
2 ft (606mm) x 4" (101mm) Thic
Neat Concrete Pad
3 tt-5 ft (1.0-1.5m) Surface Seal of
Neat Cement Extended to at Least 1
ft below Frost Line
Minimum 2" (50mm) ID Riser with
Flush Threaded Connections
Well Identification Labeled Inside
and Outside the Cap
Vented Cap
Protective Casing
1/4" (6.3mm) Weep Hole at 6" Above Ground Level
3 ft-5 ft. (1.0 to'l.Sm) Protective Casing
Anchored Below Frost Line
Grout Length Varies
Borehole
Centralizer(s) As
Necessary
Plug
3 ft-5 ft (1.0m-1.5m) Bentonite Seal
1 ft-2 ft (303mm-€06mm) Filter Pack
Extended 2 ft (606mm) Above Slotted Well
Screen
Well Screen Length Varies
Sediment Sump (As Appropriate)
Figure 5.3. Example of a Monitoring Well Design-Single Cased Well
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Subpart E
space for placement of the filter pack
and annular sealants.
• The drilling method should allow for
the collection of representative ground-
water samples. Drilling fluids
(including air) should be used only
when minimal impact to the
surrounding formation and ground
water can be ensured.
The following guidelines apply to the use of
drilling fluids, drilling fluid additives, and
lubricants when drilling ground-water
monitoring wells:
• Drilling fluids, drilling fluid additives,
or lubricants that affect the analysis of
hazardous constituents in ground-water
samples should not be used.
• The owner/operator should
demonstrate the inertness of drilling
fluids, drilling fluid additives, and
lubricants by performing analytical
testing of drilling fluids, drilling fluid
additives, and lubricants and/or by
providing information regarding the
composition of drilling fluids, drilling
fluid additives, or lubricants obtained
from the manufacturer.
• The owner/operator should consider
the potential impact of drilling fluids,
drilling fluid additives, and lubricants
on the physical and chemical
characteristics of the subsurface and on
ground-water quality.
• The volume of drilling fluids, drilling
fluid additives, and lubricants used
during the drilling of a monitoring well
should be recorded.
Monitoring Well Design
Well Casing
Well Casing and Screen Materials
A casing and well screen are installed in a
ground-water monitoring well for several
reasons: to provide access from the surface
of the ground to some point in the
subsurface, to prevent borehole collapse,
and to prevent hydraulic communication
between zones within the subsurface. In
some cases, State or local regulations may
specify the casing and material that the
owner or operator should use. A
comprehensive discussion of well casing
and screen materials is provided in USEPA
(1989f) and in USEPA (1992a). The
following discussion briefly summarizes
information contained in these references.
Monitoring well casing and screen materials
may be constructed of any of several types
of materials, but should meet the following
performance specifications:
• Monitoring well casing and screen
materials should maintain their
structural integrity and durability in
the environment in which they are used
over their operating life.
• Monitoring well casings and screens
should be resistant to chemical and
microbiological corrosion and
degradation in contaminated and
uncontaminated waters.
• Monitoring well casings and screens
should be able to withstand the
physical forces acting upon them
during and following their installation
and during their use — including forces
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Ground-Water Monitoring and Corrective Action
due to suspension in the borehole,
grouting, development, purging,
pumping, and sampling and forces
exerted on them by the surrounding
geologic materials.
• Monitoring well casing and screen
materials should not chemically alter
ground-water samples, especially with
respect to the analytes of concern, as a
result of their sorbing, desorbing, or
leaching analytes. For example, if
chromium is an analyte of interest, the
well casing or screen should not
increase or decrease the amount of
chromium in the ground water. Any
material leaching from the casing or
screen should not be an analyte of
interest or interfere in the analysis of
an analyte of interest.
In addition, monitoring well casing and
screen materials should be relatively easy to
install into the borehole during construction
of the monitoring well.
The selection of the most suitable well
casing and screen materials should consider
site-specific factors, including:
• Depth to the water-bearing zone(s) to
be monitored and the anticipated well
depth
• Geologic environment
• Geochemistry of soil, unconsolidated
material, and rock over the entire
interval in which the well is to be cased
• Geochemistry of the ground water at
the site, as determined through an
initial analysis of samples from both
background wells and downgradient
wells and including:
- Natural ground-water geochemistry
- Nature of suspected or known
contaminants
- Concentration of suspected or known
contaminants
• Design life of the monitoring well.
Casing materials widely available for use in
ground-water monitoring wells can be
divided into three categories:
1) Fluoropolymer materials, including
polytetrafluoroethylene (PTFE),
tetrafluoroethylene (TFE), fluorinated
ethylene propylene (FEP),
perfluoroalkoxy (PFA), and
polyvinylidene fluoride (PVDF)
2) Metallic materials, including carbon
steel, low-carbon steel, galvanized
steel, and stainless steel (304 and 316)
3) Thermoplastic materials, including
polyvinyl chloride (PVC) and
acrylonitrile butadiene styrene (ABS).
In addition to these three categories of
materials, fiberglass-reinforced plastic
(FRP) has been used for monitoring
applications. Because FRP has not yet been
used in general application across the
country, very little data are available on its
characteristics and performance. All well
construction materials possess
strength-related characteristics and chemical
resistance/chemical interference
characteristics that influence their
performance in site-specific hydrogeologic
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Subpart E
and contaminant-related monitoring
situations.
The casing must be made of a material
strong enough to last for the life of the well.
Tensile strength is needed primarily during
well installation when the casing is lowered
into the hole. The joint strength will
determine the maximum length of a section
that can be suspended from the surface in an
air-filled borehole.
Collapse strength is the capability of a
casing to resist collapse by any external
loads to which it is subjected both during
and after installation. A casing is most
susceptible to collapse during installation
before placement of the filter pack or
annular seal materials around the casing.
Once a casing is installed and supported,
collapse is seldom a concern. Several steps
that can be taken to avoid casing collapse
are:
1) Drilling a straight, clean borehole
2) Uniformly distributing filter pack
materials at a slow, even rate
3) Avoiding use of quick-setting (high
temperature) cements for thermoplastic
casings installation.
Compressive strength of the casing is a
measure of the greatest compressive stress
that a casing can bear without deformation.
Casing failure due to a compressive strength
limitation generally is not an important
factor in a properly installed well. This type
of failure results from soil friction on
unsupported casing.
Chemical resistance/interference
characteristics must be evaluated before
selecting monitoring well materials.
Metallic casing materials are more subject
to corrosion, while thermoplastic casing
materials are more susceptible to chemical
degradation. The geochemistry of the
formation water influences the degree to
which these processes occur. If ground-
water chemistry affects the structural
integrity of the casing, then the samples
collected from the well are likely to be
affected.
Materials used for monitoring well casing
must not exhibit a tendency to sorb or leach
chemical constituents from, or into, water
sampled from the well. If a casing material
sorbs constituents from ground water, those
constituents may either not be detected
during monitoring or be detected at a lower
concentration. Chemical constituents also
can be leached from the casing materials by
aggressive aqueous solutions. These
constituents may be detected in samples
collected from the well. The results may
indicate contamination that is due to the
casing rather than the formation water.
Casing materials must be selected with care
to avoid degradation of the well and to
avoid erroneous results.
In certain situations it may be advantageous
to design a well using more than one
material for well components. For example,
where stainless steel or fluoropolymer
materials are preferred in a specific
chemical environment, costs may be saved
by using PVC in non-critical portions of the
well. These savings may be considerable,
especially in deep wells where only the
lower portion of the well is in a critical
chemical environment and where tens of
feet of lower-cost PVC may be used in the
upper portion of the well. In a composite
well design, dissimilar metallic
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Ground-Water Monitoring and Corrective Action
components should not be used unless an
electrically isolating design is incorporated
(i.e., a dielectric coupling) (USEPA, 1986).
Coupling Procedures for Joining Casing
Only a limited number of methods are
available for joining lengths of casing or
casing and screen together. The joining
method depends on the type of casing and
type of casing joint.
There are generally two options available
for joining metallic well casings: welding
via application of heat, or threaded joints.
Threaded joints provide inexpensive, fast,
and convenient connections and greatly
reduce potential problems with chemical
resistance or interference (due to corrosion)
and explosion potential. Wrapping the male
threads with fluoropolymer tape prior to
joining sections improves the watertightness
of the joint. One disadvantage to using
threaded joints is that the tensile strength of
the casing string is reduced to
approximately 70 percent of the casing
strength. This reduction in strength does
not usually pose a problem because strength
requirements for small diameter wells (such
as typical monitoring wells) are not as
critical and because metallic casing has a
high initial tensile strength.
Joints should create a uniform inner and
outer casing diameter in monitoring well
installations. Solvent cementing of
thermoplastic pipe should never be used in
the construction of ground-water monitoring
wells. The cements used in solvent welding,
which are organic chemicals, have been
shown to adversely affect the integrity of
ground-water samples for more than 2 years
after well installation; only factory-
threaded joints should be used on
thermoplastic well material.
Well Casing Diameter
Although the diameter of the casing for a
monitoring well depends on the purpose of
the well, the casing size is generally selected
to accommodate downhole equipment.
Additional casing diameter selection criteria
include the 1) drilling or well installation
method used, 2) anticipated depth of the
well and associated strength requirements,
3) anticipated method of well development,
4) volume of water required to be purged
prior to sampling, 5) rate of recovery of the
well after purging, and 6) anticipated
aquifer testing.
Casing Cleaning Requirements
Well casing and screen materials should be
cleaned prior to installation to remove any
coatings or manufacturing residues. Prior to
use, all casing and screen materials should
be washed with a mild, non-phosphate,
detergent/potable water solution and rinsed
with potable water. Hot pressurized water,
such as in steam cleaning, should be used to
remove organic solvents, oils, or lubricants
from casing and screens composed of
materials other than plastic. At sites where
volatile organic contaminants may be
monitored, the cleaning of well casing and
screen materials should include a final rinse
with deionized water or potable water that
has not been chlorinated. Once cleaned,
casings and screens should be stored in an
area that is free of potential contaminants.
Plastic sheeting can generally be used to
cover the ground in the decontamination
area to provide protection from
contamination. USEPA (1989f) describes
the procedures
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that should be used to clean casing and
screen materials.
Well Intake Design
The owner/operator should design and
construct the intakes of monitoring wells to
(1) accurately sample the aquifer zone that
the well is intended to sample, (2) minimize
the passage of formation materials
(turbidity) into the well, and (3) ensure
sufficient structural integrity to prevent the
collapse of the intake structure. The goal of
a properly completed monitoring well is to
provide low turbidity water that is
representative of ground-water quality in
the vicinity of the well. Close attention to
proper selection of packing materials and
well development procedures for wells
installed in fine-grained formations (e.g.,
clays and silty glacial tills) is important to
minimize sample turbidity from suspended
and colloidal solids. There may be
instances where wells completed in rock do
not require screens or filter packs; the State
regulatory agency should be consulted prior
to completion of unscreened wells.
The selection of screen length usually
depends on the objective of the well.
Piezometers and wells where only a discrete
flow path is monitored (such as thin gravel
interbedded with clays) are generally
completed using short screens (2 feet or
less). To avoid dilution, the well screens
should be kept to the minimum length
appropriate for intercepting a contaminant
plume, especially in a high-yielding aquifer.
The screen length should generally not
exceed 10 feet. If construction of a water
table well is the objective, either for
defining gradient or detecting floating
phases, then a longer screen is acceptable
because the owner/operator will need to
provide a margin of safety that will
guarantee that at least a portion of the
screen always contacts the water table
regardless of its seasonal fluctuations. The
owner or operator should not employ well
intake designs that cut across hydraulically
separated geologic units.
Well screen slot size should be selected to
retain from 90 percent to 100 percent of the
filter pack material (discussed below) in
artificially filter packed wells. Well screens
should be factory-slotted. Manual slotting
of screens in the field should not be
performed under any circumstances.
Filter Pack Design
The primary filter pack material should be a
chemically inert material and well rounded,
with a high coefficient of uniformity. The
best filter pack materials are made from
industrial grade glass (quartz) sand or beads.
The use of other materials, such as local,
naturally occurring clean sand, is
discouraged unless it can be shown that the
material is inert (e.g., low cation exchange
capacity), coarse-grained, permeable, and
uniform in grain size. The filter pack should
extend at least 2 feet above the screened
interval in the well.
Although design techniques for selecting
filter pack size vary, all use the filter pack
ratio to establish size differential between
formation materials and filter pack
materials. Generally, this ratio refers to
either the average (50 percent retained)
grain size of the formation material or to the
70 percent retained size of the formation
material. Barcelona et al. (1985b)
recommend using a uniform filter pack
grain size that is three to five times the size
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of the 50 percent retained size of the
formation material (USEPA, 1990).
Filter pack material should be installed in a
manner that prevents bridging and particle-
size segregation. Filter pack material
installed below the water table should
generally be tremied into the annular space.
Allowing filter pack material to fall by
gravity (free fall) into the annular space is
only appropriate when wells are relatively
shallow, when the filter pack has a uniform
grain size, and when the filter pack material
can be poured continuously into the well
without stopping.
At least 2 inches of filter pack material
should be installed between the well screen
and the borehole wall. The filter pack
should extend at least 2 feet above the top of
the well screen. In deep wells, the filter
pack may not compress when initially
installed. Consequently, when the annular
and surface seals are placed on the filter
pack, the filter pack compresses sufficiently
to allow grout into, or very close to, the
screen. Consequently, filter packs may need
to be installed as high as 5 feet above the
screened interval in monitoring wells that
are deep (i.e., greater than 200 feet). The
precise volume of filter pack material
required should be calculated and recorded
before placement, and the actual volume
used should be determined and recorded
during well construction. Any significant
discrepancy between the calculated volume
and the actual volume should be explained.
Prior to installing the annular seal, a 1- to
2-foot layer of chemically inert fine sand
may be placed over the filter pack to prevent
the intrusion of annular or surface sealants
into the filter pack. When designing
monitoring wells, owners and
operators should remember that the entire
length of the annular space filled with filter
pack material or sand is effectively the
monitored zone. Moreover, if the filter
pack/sand extends from the screened zone
into an overlying zone, a conduit for
hydraulic connection is created between the
two zones.
Annular Sealants
Proper sealing of the annular space between
the well casing and the borehole wall is
required to prevent contamination of
samples and the ground water. Adequate
sealing will prevent hydraulic connection
within the well annulus. The materials used
for annular sealants should be chemically
inert with the highest anticipated
concentration of chemical constituents
expected in the ground water at the facility.
In general, the permeability of the sealing
material should be one to two orders of
magnitude lower than the least permeable
part of the formation in contact with the
well. The precise volume of annular
sealants required should be calculated and
recorded before placement, and the actual
volume used should be determined and
recorded during well construction. Any
significant discrepancy between the
calculated volume and the actual volume
should be explained.
When the screened interval is within the
saturated zone, a minimum of 2 feet of
sealant material, such as raw (>10 percent
solids) bentonite, should be placed
immediately over the protective sand layer
overlying the filter pack. Granular
bentonite, bentonite pellets, and bentonite
chips may be placed around the casing by
means of a tremie pipe in deep wells
(greater than approximately 30 feet deep),
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Subpart E
or by dropping them directly down the
annulus in shallow wells (less than
approximately 30 feet deep). Dropping the
bentonite pellets down the annulus presents
a potential for bridging (from premature
hydration of the bentonite), leading to gaps
in the seal below the bridge. In shallow
monitoring wells, a tamping device should
be used to prevent bridging from occurring.
A neat cement or shrinkage-compensated
neat cement grout seal should be installed
on top of the bentonite seal and extend
vertically up the annular space between the
well casing and the borehole wall to within
a few feet of land surface. Annular sealants
in slurry form (e.g., cement grout, bentonite
slurry) should be placed by the tremie/pump
(from the bottom up) method. The bottom
of the placement pipe should be equipped
with a side discharge deflector to prevent
the slurry from jetting a hole through the
protective sand layer, filter pack, or
bentonite seal. The bentonite seal should be
allowed to completely hydrate, set, or cure
in conformance with the manufacturer's
specifications prior to installing the grout
seal in the annular space. The time required
for the bentonite seal to completely hydrate,
set, or cure will differ with the materials
used and the specific conditions
encountered, but is generally a minimum of
4 to 24 hours. Allowing the bentonite seal
to hydrate, set, or cure prevents the invasion
of the more viscous and more chemically
reactive grout seal into the screened area.
When using bentonite as an annular sealant,
the appropriate clay should be selected on
the basis of the environment in which it is to
be used, such as the ion-exchange potential
of the sediments, sediment permeability,
and compatibility with expected
contaminants. Sodium bentonite is usually
acceptable.
When the annular sealant must be installed
in the unsaturated zone, neat cement or
shrinkage-compensated neat cement
mixtures should be used for the annular
sealant. Bentonite is not recommended as
an annular sealant in the unsaturated zone
because the moisture available is
insufficient to fully hydrate bentonite.
Surface Completion
Monitoring wells are commonly either
above-ground completions or flush-to-
ground completions. The design of both
types must consider the prevention of
infiltration of surface runoff into the well
annulus and the possibility of accidental
damage or vandalism. Completing a
monitoring well involves installing the
following components:
• Surface seal
• Protective casing
• Ventilation hole
• Drain hole
• Cap and lock
• Guard posts when wells are completed
above grade.
A surface seal, installed on top of the grout
seal, extends vertically up the well annulus
to the land surface. To protect against frost
heave, the seal should extend at least 1 foot
below the frost line. The composition of the
surface seal should be neat cement or
concrete. In an above-ground completion,
the surface seal should form at least a 2-foot
wide, 4-inch thick apron.
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Ground-Water Monitoring and Corrective Action
A locking protective casing should be
installed around the well casing to prevent
damage or unauthorized entry. The
protective casing should be anchored below
the frost line (where applicable) into the
surface seal and extend at least 18 inches
above the surface of the ground. A 1/4-inch
vent hole pipe is recommended to allow the
escape of any potentially explosive gases
that may accumulate within the well. In
addition, a drain hole should be installed in
the protective casing to prevent water from
accumulating and, in freezing climates,
freezing around the well casing. The space
between the protective casing and the well
casing may be filled with gravel to allow the
retrieval of tools and to prevent small
animal/insect entrance through the drain. A
suitable cap should be placed on the well to
prevent tampering or the entry of any
foreign materials. A lock should be
installed on the cap to provide security. To
prevent corrosion or jamming of the lock, a
protective cover should be used. Care
should be taken when using such lubricants
as graphite or petroleum-based sprays to
lubricate the lock, as lubricants may
introduce a potential for sample
contamination.
To guard against accidental damage to the
well from facility traffic, the owner/operator
should install concrete or steel bumper
guards around the edge of the concrete
apron. These should be located within 3 or
4 feet of the well and should be painted
orange or fitted with reflectors to reduce the
possibility of vehicular damage.
The use of flush-to-ground surface
completions should be avoided because this
design increases the potential for surface
water infiltration into the well. In cases
where flush-to-ground completions are
unavoidable, such as in active roadways, a
protective structure, such as a utility vault
or meter box, should be installed around the
well casing. In addition, measures should
be taken to prevent the accumulation of
surface water in the protective structure and
around the well intake. These measures
should include outfitting the protective
structure with a steel lid or manhole cover
that has a rubber seal or gasket and ensuring
that the bond between the cement surface
seal and the protective structure is
watertight.
Well Surveying
The location of all wells should be surveyed
by a licensed professional surveyor (or
equivalent) to determine their X-and-Y
coordinates as well as their distances from
the units being monitored and their
distances from each other. A State Plane
Coordinate System, Universal Transverse
Mercator System, or Latitude/Longitude
should be used, as approved by the Regional
Administrator. The survey should also note
the coordinates of any temporary
benchmarks. A surveyed reference mark
should be placed on the top of the well
casing, not on the protective casing or the
well apron, for use as a measuring point
because the well casing is more stable than
the protective casing or well apron (both the
protective casing and the well apron are
more susceptible to frost heave and
spalling). The height of the reference
survey datum, permanently marked on top
of the inner well casing, should be
determined within ±0.01 foot in relation to
mean sea level, which in turn is determined
by reference to an established National
Geodetic Vertical Datum. The reference
marked on top of inner well casings should
be re surveyed at least once every 5 years,
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Subpart E
unless changes in ground-water flow
patterns/direction, or damage caused by
freeze/thaw or desiccation processes, are
noted. In such cases, the Regional
Administrator may require that well casings
be resurveyed on a more frequent basis.
Well Development
All monitoring wells should be developed to
create an effective filter pack around the
well screen, to rectify damage to the
formation caused by drilling, to remove fine
particles from the formation near the
borehole, and to assist in restoring the
natural water quality of the aquifer in the
vicinity of the well. Development stresses
the formation around the screen, as well as
the filter pack, so that mobile fines, silts,
and clays are pulled into the well and
removed. The process of developing a well
creates a graded filter pack around the well
screen. Development is also used to remove
any foreign materials (drilling water, muds,
etc.) that may have been introduced into the
well borehole during drilling and well
installation and to aid in the equilibration
that will occur between the filter pack, well
casing, and the formation water.
The development of a well is extremely
important to ensuring the collection of
representative ground-water samples. If the
well has been properly completed, then
adequate development should remove fines
that may enter the well either from the filter
pack or the formation. This improves the
yield, but more importantly it creates a
monitoring well capable of producing
samples of acceptably low turbidity. Turbid
samples from an improperly constructed and
developed well may interfere with
subsequent analyses.
When development is initiated, a wide range
of grain sizes of the natural material is
drawn into the well, and the well typically
produces very turbid water. However, as
development continues and the natural
materials are drawn into the filter pack, an
effective filter will form through a sorting
process. Inducing movement of ground
water into the well (i.e., in one direction)
generally results in bridging of the particles.
A means of inducing flow reversal is
necessary to break down bridges and
produce a stable filter.
The commonly accepted methods for
developing wells are described in USEPA
(1989f) and Driscoll (1986) and include:
• Pumping and overpumping
• Surging with a surge block
• Bailing.
USEPA (1989f) provides a detailed
overview of well development and should
be consulted when evaluating well
development methods.
Documentation of Well Design.
Construction, and Development
Information on the design, construction, and
development of each well should be
compiled. Such information should include
(1) a boring log that documents well drilling
and associated formation sampling and (2)
a well construction log and well
construction diagram ("as built").
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Decommissioning Ground-Water
Monitoring Wells and Boreholes
Ground-water contamination resulting from
improperly decommissioned wells and
boreholes is a serious concern. Any
borehole that will not be completed as a
monitoring well should be properly
decommissioned. The USEPA (1975) and
the American Water Works Association
(1985) provide the following reasons,
summarized by USEPA (1989f), as to why
improperly constructed or unused wells
should be properly decommissioned:
• To eliminate physical hazards
To prevent
contamination
ground-water
• To conserve aquifer yield and
hydrostatic head
• To prevent intermixing of subsurface
water.
Should an owner or operator have a
borehole or an improperly constructed or
unused well at his or her facility, the well or
borehole should be decommissioned in
accordance with specific guidelines.
USEPA (1989f) provides comprehensive
guidance on performing well
decommissioning that can be applied to
boreholes. In addition, any State/Tribal
regulatory guidance should be consulted
prior to decommissioning monitoring wells,
piezometers, or boreholes. Lamb and
Kinney (1989) also provide information on
decommissioning ground-water monitoring
wells.
Many States require that specific procedures
be followed and certain paperwork be filed
when decommissioning water supply wells.
In some States, similar regulations may
apply to the decommissioning of monitoring
wells and boreholes. The EPA and other
involved regulatory agencies, as well as
experienced geologists, geotechnical
engineers, and drillers, should be consulted
prior to decommissioning a well or borehole
to ensure that decommissioning is
performed properly and to ensure
compliance with State law. If a well to be
decommissioned is contaminated, the safe
removal and proper disposal of the well
materials should be ensured by the
owner/operator. Appropriate measures
should be taken to protect the health and
safety of individuals when decommissioning
a well or borehole.
5.8 GROUND-WATER SAMPLING
AND ANALYSIS
REQUIREMENTS
40 CFR §258.53
5.8.1 Statement of Regulation
(a) The ground-water monitoring
program must include consistent
sampling and analysis procedures that
are designed to ensure monitoring results
that provide an accurate representation
of ground-water quality at the
background and downgradient wells
installed in compliance with §258.51(a) of
this Part. The owner or operator must
notify the State Director that the
sampling and analysis program
documentation has been placed in the
operating record and the program must
include procedures and techniques for:
(1) Sample collection;
(2) Sample preservation and shipment;
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Subpart E
(3) Analytical procedures;
(4) Chain of custody control; and
(5) Quality assurance and quality
control.
(b) The ground-water monitoring
program must include sampling and
analytical methods that are appropriate
for ground-water sampling and that
accurately measure hazardous
constituents and other monitoring
parameters in ground-water samples.
Ground-water samples shall not be field-
filtered prior to laboratory analysis.
(c) The sampling procedures and
frequency must be protective of human
health and the environment.
(d) Ground-water elevations must be
measured in each well immediately prior
to purging, each time ground water is
sampled. The owner or operator must
determine the rate and direction of
ground-water flow each time ground
water is sampled. Ground-water
elevations in wells which monitor the
same waste management area must be
measured within a period of time short
enough to avoid temporal variations in
ground-water flow which could preclude
accurate determination of ground-water
flow rate and direction.
(e) The owner or operator must
establish background ground-water
quality in a hydraulically upgradient or
background well(s) for each of the
monitoring parameters or constituents
required in the particular ground-water
monitoring program that applies to the
MSWLF unit, as determined under
§258.54(a), or
§258.55(a) of this Part. Background
ground-water quality may be established
at wells that are not located hydraulically
upgradient from the MSWLF unit if it
meets the requirements of §258.51(a)(l).
(f) The number of samples collected to
establish ground-water quality data must
be consistent with the appropriate
statistical procedures determined
pursuant to paragraph (g) of this section.
The sampling procedures shall be those
specified under §258.54(b) for detection
monitoring, §258.55(b) and (d) for
assessment monitoring, and §258.56(b) of
corrective action.
5.8.2 Applicability
The requirements for sampling and analysis
apply to all facilities required to conduct
ground-water monitoring throughout the
active life, closure, and post-closure periods
of operation. Quality assurance and quality
control measures for both field and
laboratory activities must be implemented.
The methods and procedures constituting
the program must be placed in the operating
record of the facility.
For the sampling and analysis program to be
technically sound, the sampling procedures
and analytical methods used should provide
adequate accuracy, precision, and detection
limits for the analyte determinations. Prior
to sampling, the static ground-water
elevations in the wells must be measured to
allow determination of the direction of
ground-water flow and estimates of rate of
flow. The time interval between
measurements at different wells must be
minimized so that temporal changes in
ground-water elevations do not cause an
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Ground-Water Monitoring and Corrective Action
incorrect determination of ground-water
flow direction.
Background ground-water quality must be
established at all upgradient or background
wells. The background water quality may
be determined from wells that are not
upgradient of the MSWLF unit, provided
that the wells yield representative ground-
water samples.
The sampling program must be designed in
consideration of the anticipated statistical
method applied by the owner or operator.
The data objectives of the monitoring
program, in terms of the number of samples
collected and the frequency of collection,
should be appropriate for the statistical
method selected for data comparison.
5.8.3 Technical Considerations
The purpose of a ground-water sampling
and analysis program is to establish a
protocol that can be followed throughout the
monitoring period of the site (operating,
closure, and post-closure). The protocol is
necessary so that data acquired can be
compared over time and accurately
represent ground-water quality. Sample
collection, preservation, shipment, storage,
and analyses should always be performed in
a consistent manner, even as monitoring
staff change during the monitoring period.
The owner's/operator's ground-water
monitoring program must include a
description of procedures for the following:
• Sample collection
• Sample preservation and shipment
• Analytical procedures
• Chain of custody control
• Quality assurance and quality control.
The ground-water monitoring program must
be documented in the operating record of
the facility.
The objectives of the monitoring program
should clearly define the quality of the data
required to detect significant changes in
ground-water chemistry due to the operation
of the solid waste disposal facility. These
data quality objectives should address:
• Accuracy and precision of methods used
in the analysis of samples, including
field measurements
• Quality control and quality assurance
procedures used to ensure the validity of
the results (e.g., use of blank samples,
record keeping, and data validation)
• Number of samples required to obtain a
certain degree of statistical confidence
of monitoring
• Location and number
wells required.
Sample Collection
Frequency
The frequency of sample collection under
detection monitoring should be evaluated
for each site according to hydrogeologic
conditions and landfill design. In States, the
minimum sampling frequency should be
semiannual. The background
characterization should include four
independent samples at each monitoring
location during the first semi-annual event
(i.e., during the first 6 months of
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Subpart E
monitoring). (See the discussion under
Section 5.10.3 on collecting independent
samples to determine background.) More
frequent sampling may be selected. For
example, quarterly sampling may be
conducted to evaluate seasonal effects on
ground-water quality.
The frequency of sample collection during
assessment monitoring activities will
depend on site-specific hydrogeologic
conditions and contaminant properties. The
frequency of sampling is intended to obtain
a data set that is statistically independent of
the previous set. Guidance to estimate this
minimum time to obtain independent
samples is provided in "Statistical Analysis
of Ground-water Monitoring Data at RCRA
Facilities - Interim Final Guidance"
(USEPA, 1989).
Water Level Measurements
The ground-water monitoring program must
include provisions for measuring static
water level elevations in each well prior to
purging the well for sampling.
Measurements of ground-water elevations
are used for determining horizontal and
vertical hydraulic gradients for estimation
of flow rates and direction.
Field measurements may include the
following:
• Depth to standing water from a surveyed
datum on the top of the well riser (static
water level)
• Total depth of well from the top of the
riser (to verify condition of well)
• Thickness of immiscible layers, if
present.
Measurements of the static water level and
the depth to the well bottom can be made
with a wetted steel tape. Electronic water
level measuring devices may also be used.
Accepted standard operating procedures call
for the static water level to be accurately
measured to within 0.01 foot (USEPA,
1992a). Water level measurements should
be made at all monitoring wells and well
clusters in a time frame that avoids changes
that may occur as a result of barometric
pressure changes, significant infiltration
events, or aquifer pumping. To prevent
possible cross contamination of wells, water
level measurement devices must be
decontaminated prior to use at each well.
The ground-water monitoring program
should include provisions for detecting
immiscible fluids (i.e., LNAPLs or
DNAPLs). LNAPLs are relatively
immiscible liquids that are less dense than
water and that spread across the water table
surface. DNAPLs are relatively immiscible
liquids that are more dense than the ground
water and tend to migrate vertically
downward in aquifers. The detection of an
immiscible layer may require specialized
equipment and should be performed before
the well is evacuated for conventional
sampling. The ground-water monitoring
program should specify how DNAPLs and
LNAPLs will be detected. The program
also should include a contingency plan
describing procedures for sampling and
analyzing these liquids. Guidance for
detecting the presence of immiscible layers
can be found in USEPA (1992a).
Well Purging
Because the water standing in a well prior to
sampling may not represent in-situ
ground-water quality, stagnant water should
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Ground-Water Monitoring and Corrective Action
be purged from the well and filter pack prior
to sampling. The QAPjP should include
detailed, step-by-step procedures for
purging wells, including the parameters that
will be monitored during purging and the
equipment that will be used for well
purging.
Purging should be accomplished by
removing ground water from the well at low
flow rates using a pump. The use of bailers
to purge monitoring wells generally should
be avoided. Research has shown that the
"plunger" effect created by continually
raising and lowering the bailer into the well
can result in continual development or
overdevelopment of the well. Moreover, the
velocities at which ground water enters a
bailer can actually correspond to
unacceptably high purging rates (Puls and
Powell, 1992; Barcelona et al., 1990).
The rate at which ground water is removed
from the well during purging ideally should
be approximately 0.2 to 0.3 L/min or less
(Puls and Powell, 1992; Puls et al., 1991;
Puls and Barcelona, 1989a; Barcelona, et
al., 1990). Wells should be purged at rates
below those used to develop the well to
prevent further development of the well, to
prevent damage to the well, and to avoid
disturbing accumulated corrosion or
reaction products in the well (Kearl et al.,
1992; Puls et al., 1990; Puls and Barcelona,
1989a; Puls and Barcelona, 1989b;
Barcelona, 1985b). Wells also should be
purged at or below their recovery rate so
that migration of water in the formation
above the well screen does not occur. A low
purge rate also will reduce the possibility of
stripping VOCs from the water, and will
reduce the likelihood of mobilizing colloids
in the subsurface that are immobile under
natural flow conditions. The owner/operator
should
ensure that purging does not cause
formation water to cascade down the sides
of the well screen. At no time should a well
be purged to dryness if recharge causes the
formation water to cascade down the sides
of the screen, as this will cause an
accelerated loss of volatiles. This problem
should be anticipated; water should be
purged from the well at a rate that does not
cause recharge water to be excessively
agitated. Laboratory experiments have
shown that unless cascading is prevented, up
to 70 percent of the volatiles present could
be lost before sampling.
To eliminate the need to dispose of large
volumes of purge water, and to reduce the
amount of time required for purging, wells
may be purged with the pump intake just
above or just within the screened interval.
This procedure eliminates the need to purge
the column of stagnant water located above
the well screen (Barcelona et al., 1985b;
Robin and Gillham, 1987; Barcelona,
1985b; Kearl et al., 1992). Purging the well
at the top of the well screen should ensure
that fresh water from the aquifer moves
through the well screen and upward within
the screened interval. Pumping rates below
the recharge capability of the aquifer must
be maintained if purging is performed with
the pump placed at the top of the well
screen, below the stagnant water column
above the top of the well screen (Kearl et
al., 1992). The Agency suggests that a
packer be placed above the screened interval
to ensure that "stagnant" casing water is not
drawn into the pump. The packer should be
kept inflated in the well until after ground-
water samples are collected.
In certain situations, purging must be
performed with the pump placed at, or
immediately below, the air/water interface.
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Subpart E
If a bailer must be used to sample the well,
the well should be purged by placing the
pump intake immediately below the
air/water interface. This will ensure that all
of the water in the casing and filter pack is
purged, and it will minimize the possibility
of mixing and/or sampling stagnant water
when the bailer is lowered down into the
well and subsequently retrieved (Keeley and
Boateng, 1987). Similarly, purging should
be performed at the air/water interface if
sampling is not performed immediately after
the well is purged without removing the
pump. Pumping at the air/water interface
will prevent the mixing of stagnant and
fresh water when the pump used to purge
the well is removed and then lowered back
down into the well for the purpose of
sampling.
In cases where an LNAPL has been detected
in the monitoring well, special procedures
should be used to purge the well. These
procedures are described in USEPA
(1992a).
For most wells, the Agency recommends
that purging continue until measurements of
turbidity, redox potential, and dissolved
oxygen in in-line or downhole analyses of
ground water have stabilized within
approximately 10% over at least two
measurements (Puls and Powell, 1992; Puls
and Eychaner, 1990; Puls et al., 1990; Puls
and Barcelona, 1989a; Puls and Barcelona,
1989b; USEPA, 1991; Barcelona et al.,
1988b). If a well is purged to dryness or is
purged such that full recovery exceeds two
hours, the well should be sampled as soon as
a sufficient volume of ground water has
entered the well to enable the collection of
the necessary ground-water samples.
All purging equipment that has been or will
be in contact with ground water should be
decontaminated prior to use. If the purged
water or the decontamination water is
contaminated (e.g., based on analytical
results), the water should be stored in
appropriate containers until analytical
results are available, at which time proper
arrangements for disposal or treatment
should be made (i.e., contaminated purge
water may be a hazardous waste).
Field Analyses
Several constituents or parameters that
owners or operators may choose to include
in a ground-water monitoring program may
be physically or chemically unstable and
should be tested after well purging and
before the collection of samples for
laboratory analysis. Examples of unstable
parameters include pH, redox (oxidation-
reduction) potential, dissolved oxygen,
temperature, and specific conductance.
Field analyses should not be performed on
samples designated for laboratory analysis.
Any field monitoring equipment or field-
test kits should be calibrated at the
beginning of each use, according to the
manufacturers' specifications and consistent
with methods in SW-846 (USEPA, 1986b).
Sample Withdrawal and Collection
The equipment used to withdraw a ground-
water sample from a well must be selected
based on consideration of the parameters to
be analyzed in the sample. To ensure the
sample is representative of ground water in
the formation, it is important to keep
physical or chemical alterations of the
sample to a minimum. USEPA (1992a)
provides an overview of the issues involved
in selecting ground-water sampling
equipment, and a summary of the
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Ground-Water Monitoring and Corrective Action
application and limitations of various
sampling mechanisms. Sampling materials
and equipment should be selected to
preserve sample integrity. Sampling
equipment should be constructed of inert
material. Sample collection equipment
should not alter analyte concentrations,
cause loss of analytes via sorption, or cause
gain of analytes via desorption, degradation,
or corrosion. Sampling equipment should
be designed such that Viton®, Tygon®,
silicone, or neoprene components do not
come into contact with the ground-water
sample. These materials have been
demonstrated to cause sorptive losses of
contaminants (Barcelona et al., 1983;
Barcelona et al., 1985b; Barcelona et al.,
1988b; Barcelona et al., 1990). Barcelona
(1988b) suggests that sorption of volatile
organic compounds on silicone,
polyethylene, and PVC tubing may result in
gross errors when determining
concentrations of trace organics in ground-
water samples. Barcelona (1985b)
discourages the use of PVC sampling
equipment when sampling for organic
contaminants. Fluorocarbon resin (e.g.,
Teflon®) or stainless steel sampling devices
which can be easily disassembled for
thorough decontamination are widely used.
Dedicating sampling equipment to each
monitoring well will help prevent cross-
contamination problems that could arise
from improper decontamination procedures.
Sampling equipment should cause minimal
sample agitation and should be selected to
reduce/eliminate sample contact with the
atmosphere during sample transfer.
Sampling equipment should not allow
volatilization or aeration of samples to the
extent that analyte concentrations are
altered.
Bladder pumps are generally recognized as
the best overall sampling device for both
organic and inorganic constituents, although
other types of pumps (e.g., low-rate
submersible centrifugal pumps, helical rotor
electric submersible pumps) have been
found suitable in some applications.
Bailers, although inexpensive and simple to
use, have been found to cause volatilization
of samples, mobilization of particulates in
wells and imprecise results (USEPA,
1992a).
The following recommendations apply to
the use and operation of ground-water
sampling equipment:
• Check valves should be designed and
inspected to ensure that fouling
problems do not reduce delivery
capabilities or result in aeration of
samples.
• Sampling equipment should never be
dropped into the well, as this will
cause degassing of the water upon
impact.
• Contents of the sampling device should
be transferred to sample containers in
a controlled manner that will minimize
sample agitation and aeration.
• Decontaminated sampling equipment
should not be allowed to come into
contact with the ground or other
contaminated surfaces prior to
insertion into the well.
• Ground-water samples should be
collected as soon as possible after the
well is purged. Water that has
remained in the well casing for more
than about 2 hours has had the
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Subpart E
opportunity to exchange gases with the
atmosphere and to interact with the
well casing material (USEPA, 1991b).
The rate at which a well is sampled
should not exceed the rate at which the
well was purged. Low sampling rates,
approximately 0.1 L/min, are
suggested. Low sampling rates will
help to ensure that particulates,
immobile in the subsurface under
ambient conditions, are not entrained
in the sample and that volatile
compounds are not stripped from the
sample (Puls and Barcelona, 1989b;
Barcelona, et al., 1990; Puls et al.,
1991; Kearl et al., 1992; USEPA,
1991b). Pumps should be operated at
rates less than 0.1 L/min when
collecting samples for volatile organics
analysis.
Pump lines should be cleared at a rate
of 0.1 L/min or less before collecting
samples for volatiles analysis so that
the samples collected will not be from
the period of time when the pump was
operating more rapidly.
Pumps should be operated in a
continuous manner so that they do not
produce samples that are aerated in the
return tube or upon discharge.
When sampling wells that contain
LNAPLs, a stilling tube should be
inserted in the well. Ground-water
samples should be collected from the
screened interval of the well below the
base of the tube.
Ground-water samples collected for
analysis for organic constituents or
parameters should not be filtered in the
field.
Once appropriate sampling equipment has
been selected and operating procedures
established, samples should be collected and
containerized in the order of the
volatilization sensitivity of the parameter.
The preferred collection order for some of
the more common ground-water analytes is
depicted on the flow chart shown in Figure
5-4.
The ground-water monitoring program
documentation should include explicit
procedures for disassembly and
decontamination of sampling equipment
before each use. Improperly
decontaminated equipment can affect
samples in several ways. For example,
residual contamination from the previous
well may remain on equipment, or improper
decontamination may not remove all of the
detergents or solvents used during
decontamination. Specific guidance
regarding decontamination of the sampling
equipment is available (USEPA 1992a). To
keep sample cross-contamination to a
minimum, sampling should proceed from
upgradient or background locations to
downgradient locations that would contain
higher concentrations of contaminants.
Sample Preservation and Handling
The procedures for preserving and handling
samples are nearly as important for ensuring
the integrity of the samples as the collection
device itself. Detailed procedures for
sample preservation must be provided in the
Quality Assurance Project Plan (QAPjP)
that is included in the sampling and analysis
program description.
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STEP
PROCEDURE
ESSENTIAL ELEMENTS
Well Inspection
Well Purging
Hydrotogic Measurements
I
Removal or Isolation of Stagnant Water
Water Level Measurements
Representative Water
Access
Sample Collection'
Field
Determinations*
Determination of Well-Purging Parameters
(pH, Eh, -n, Q )*
Volatile Organics, TOX
Dissolved Gases, TOC
Large Volume
Samples for
Organic Compound
Determinations
Verification of
Representative Water
Sample Access
Sample Collection by
Appropriate Mechanism
Minimal Sample Handling
Head-Space
Free Samples
Head Space
Free Samples
Minimal Aeration or
Depressurization
Metal Samples
Cyanides
Adequate Rinsing against
Contamination
Preservation
Field Blanks
Standards
Assorted Sensitive
Inorganic Species
Nm"; Fe(lt)
Major Cations and
Anions
Storage Transport
(as needed for good
QA/QC)
Minimal Air Contact,
Preservation
Minimal Loss of Sample
Integrity Prior to Analysis
Denotes analytical determinations which should be made in the field.
'This is a suggested order tor sampling, not all parameters are required by Part 258.
Figure 5-4
Generalized Flow Diagram of
Ground-Water Sampling Steps
261
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Subpart E
Sample Containers
To avoid altering sample quality, the
samples should be transferred from the
sampling equipment directly into a prepared
container. Proper sample containers for
each constituent or group of constituents are
identified in SW-846 (USEPA, 1986b).
Samples should never be composited in a
common container in the field and then
split. Sample containers should be cleaned
in a manner that is appropriate for the
constituents to be analyzed. Cleaning
procedures are provided by USEPA
(1986b). Sample containers that have been
cleaned according to these procedures can
be procured commercially.
Most vendors will provide a certification of
cleanliness.
Sample Preservation
During ground-water sampling, every
attempt should be made to minimize
changes in the chemistry of the samples. To
assist in maintaining the natural chemistry
of the samples, it is necessary to preserve
the sample. The owner or operator should
refer to SW-846 (USEPA, 1986b) for the
specific preservation method and holding
times for each constituent to be analyzed.
Methods of sample preservation are
relatively limited and are intended to retard
chemical reactions, such as oxidation,
retard, biodegradation, and to reduce the
effects of sorption. Preservation methods
are generally limited to pH control,
refrigeration, and protection from light.
Sample Storage and Shipment
The storage and transport of ground-water
samples must be performed in a manner that
maintains sample quality. Samples should
be cooled to 4°C as soon as possible after
they are collected. These conditions should
be maintained until the samples are received
at the laboratory. Sample containers
generally are packed in picnic coolers or
special containers for shipment.
Polystyrene foam, vermiculite, and "bubble
pack" are frequently used to pack sample
containers to prevent breakage. Ice is
placed in sealed plastic bags and added to
the cooler. All related paperwork is sealed
in a plastic bag and taped to the inside top of
the cooler. The cooler top is then taped
shut. Custody seals should be placed across
the hinges and latches on the outside of the
cooler.
Transportation arrangements should
maintain proper storage conditions and
provide for effective sample pickup and
delivery to the laboratory. Sampling plans
should be coordinated with the laboratory so
that appropriate sample receipt, storage,
analysis, and custody arrangements can be
provided.
Most analyses must be performed within a
specified period (holding time) from sample
collection. Holding time refers to the period
that begins when the sample is collected
from the well and ends with its extraction or
analysis. Data from samples not analyzed
within the recommended holding times
should be considered suspect. Some
holding times for Appendix I constituents
are as short as 7 days. To provide the
laboratory with operational flexibility in
meeting these holding times, samples
usually are shipped via overnight courier.
Laboratory capacity or operating hours may
influence sampling schedules. Coordination
with laboratory staff during
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Ground-Water Monitoring and Corrective Action
planning and sampling activities is
important in maintaining sample and
analysis quality.
The documentation that accompanies
samples during shipment to the laboratory
usually includes chain-of-custody (including
a listing of all sample containers), requested
analyses, and full identification of the origin
of samples (including contact names, phone
numbers, and addresses). Copies of all
documents shipped with the samples should
be retained by the sampler.
Chain-of-Custody Record
To document sample possession from the
time of collection, a chain-of-custody record
should be filled out to accompany every
sample shipment. The record should
contain the following types of information:
• Sample number
• Signature of collector
• Date and time of collection
• Media sampled (e.g., ground water)
• Sample type (e.g., grab)
• Identification of sampling location/well
• Number of containers
• Parameters requested for analysis
• Signatures of persons involved in the
chain of possession
• Inclusive dates of possession with time
in 24-hour notation
• Internal temperature of shipping
container when samples were sealed into
the container for shipping
• Internal temperature of container when
opened at the laboratory
• Any remarks regarding potential hazards
or other information the laboratory may
need.
An adequate chain-of-custody program
allows for tracing the possession and
handling of individual samples from the
time of collection through completion of
laboratory analysis. A chain-of-custody
program should include:
Sample labels to
misidentification of samples
prevent
• Sample custody seals to preserve the
integrity of the samples from the time
they are collected until they are opened
in the laboratory
• Field notes to record information about
each sample collected during the ground-
water monitoring program
• Chain-of-custody record to document
sample possession from the time of
collection to analysis
• Laboratory storage and analysis records,
which are maintained at the laboratory
and which record pertinent information
about the sample.
Sample Labels
Each sample's identification should be
marked clearly in waterproof ink on the
sample container. To aid in labeling, the
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Subpart E
information should be written on each
container prior to filling with a sample. The
labels should be sufficiently durable to
remain legible even when wet and should
contain the following information:
• Sample identification number
• Name and signature of the sampler
• Date and time of collection
• Sample location
• Analyses requested.
Sample Custody Seal
Sample custody seals should be placed on
the shipping container and/or individual
sample bottle in a manner that will break the
seal if the container or sample is tampered
with.
Field Logbook
To provide an account of all activities
involved in sample collection, all sampling
activities, measurements, and observations
should be noted in a field log. The
information should include visual
appearance (e.g., color, turbidity, degassing,
surface film), odor (type, strength), and
field measurements and calibration results.
Ambient conditions (temperature, humidity,
wind, precipitation) and well purging and
sampling activities should also be recorded
as an aid in evaluating sample analysis
results.
The field logbook should document the
following:
• Well identification
Well depth
Static water level depth and
measurement technique
Presence and thickness of immiscible
layers and the detection method
Well yield (high or low) and well
recovery after purging (slow, fast)
Well purging procedure and equipment
Purge volume and pumping rate
Time well purged
Collection method for immiscible
layers
Sample withdrawal procedure and
equipment
Date and time of sample collection
Results of field analysis
Well sampling sequence
Types of sample bottles used and
sample identification numbers
Preservatives used
Parameters requested for analysis
Field observations of sampling event
Name of collector
Weather conditions, including air
temperature
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Ground-Water Monitoring and Corrective Action
• Internal temperature of field and
shipping containers.
Sample Analysis Request Sheet
A sample analysis request sheet should
accompany the sample(s) to the laboratory
and clearly identify which sample
containers have been designated for each
requested parameter and the preservation
methods used. The record should include
the following types of information:
• Name of person receiving the sample
• Laboratory sample number (if different
from field number)
• Date of sample receipt
• Analyses to be performed (including
desired analytical method)
• Information that may be useful to the
laboratory (e.g., type and quantity of
preservatives added, unusual conditions).
Laboratory Records
Once the sample has been received in the
laboratory, the sample custodian and/or
laboratory personnel should clearly
document the processing steps that are
applied to the sample. All sample
preparation (e.g., extraction) and
determinative steps should be identified in
the laboratory records. Deviations from
established methods or standard operating
procedures (SOPs), such as the use of
specific reagents (e.g., solvents, acids),
temperatures, reaction times, and instrument
settings, should be noted. The results of the
analyses of all quality control samples
should be identified for each batch of
ground-water samples analyzed. The
laboratory logbook should include the time,
date, and name of the person who performed
each processing step.
Analytical Procedures
The requirements of 40 CFR Part 258
include detection and assessment
monitoring activities. Under detection
monitoring, the constituents listed in 40
CFR Part 258, Appendix I are to be
analyzed for. This list includes volatile
organic compounds (VOCs) and selected
inorganic constituents. No specific
analytical methods are cited in the
regulations, but there is a requirement (40
CFR §258.53(h)(5)) that any practical
quantitation limit (PQL) used in subsequent
statistical analysis "be the lowest
concentration level that can be reliably
achieved within specified limits of precision
and accuracy during routine laboratory
operating conditions that are available to the
facility." Suggested test methods are listed
in Appendix II of Part 258 for informational
purposes only. Method 8240 (gas
chromatography with packed column; mass
spectrometry) and Method 8260 (gas
chromatography with capillary column;
mass spectrometry) are typical methods
used for all Appendix I VOCs. The
inorganic analyses can be performed using
inductively coupled plasma atomic emission
spectroscopy (ICP) Method 6010. These
methods, as well as other methods
appropriate to these analyses, are presented
in Tests Methods for Evaluating Solid
Waste, Physical/Chemical Methods,
SW-846 (USEPA, 1986), and are routinely
performed by numerous analytical testing
laboratories. These methods typically
provide PQLs in the 1 to 50 |ig/L range.
The ground-water monitoring plan must
specify the analytical method to be used.
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Subpart E
Evaluation and documentation of analytical
performance requires that quality control
samples be collected and analyzed along
with the ground-water monitoring samples.
Chapter One of SW-846 (Quality
Assurance) describes the types of quality
control samples necessary, as well as the
frequency at which they must be collected
and analyzed. In general, these quality
control samples may include trip blanks,
equipment rinsate samples, field duplicates,
method blanks, matrix spikes and
duplicates, and laboratory control samples.
Other mechanisms, including sample
holding times, surrogate constituents, and
standard additions, are also used to control
and document data quality. The
specification of and adherence to sample
holding times minimizes the sample
degradation that occurs over time.
Evaluating the recovery of surrogate
constituents spiked into organic samples
allows the analyst and data user to monitor
the efficiency of sample extraction and
analysis. The method of standard additions
is used to eliminate the effects of matrix
interferences in inorganic analyses.
Quality Assurance/Quality Control
One of the fundamental responsibilities of
the owner or operator is to establish a
continuing program to ensure the reliability
and validity of field and analytical
laboratory data gathered as part of the
overall ground-water monitoring program.
The owner or operator must explicitly
describe the QA/QC program that will be
used in the laboratory. Most owners or
operators will use commercial laboratories
to conduct analyses of ground-water
samples. In these cases, the owner or
operator is responsible for ensuring that the
laboratory of choice is exercising an
appropriate QA/QC program.
The owner or operator should provide for
the use of standards, laboratory blanks,
duplicates, and spiked samples for
calibration and identification of potential
matrix interferences, especially for metal
determinants. Refer to Chapter One of
SW-846 for guidance. The owner or
operator should use adequate statistical
procedures (e.g., QC charts) to monitor and
document performance and to implement an
effective program to resolve testing
problems (e.g., instrument maintenance,
operator training). Data from QC samples
(e.g., blanks, spiked samples) should be
used as a measure of performance or as an
indicator of potential sources of cross-
contamination, but should not be used by
the laboratory to alter or correct analytical
data. All laboratory QC data should be
submitted with the ground-water monitoring
sample results.
Field Quality Assurance/Quality Control
To verify the precision of field sampling
procedures, field QC samples, such as trip
blanks, equipment blanks, and duplicates,
should be collected. Additional volumes of
sample also should be collected for
laboratory QC samples.
All field QC samples should be prepared
exactly as regular investigation samples
with regard to sample volume, containers,
and preservation. The concentrations of any
contaminants found in blank samples should
not be used to correct the ground-water
data. The contaminant concentrations in
blanks should be documented, and if the
concentrations are more than an order of
magnitude greater than the field sample
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Ground-Water Monitoring and Corrective Action
results, the owner/operator should resample
the ground water. The owner/operator
should prepare the QC samples as
recommended in Chapter One of SW-846
and at the frequency recommended by
Chapter One of SW-846 and should analyze
them for all of the required monitoring
parameters. Other QA/QC practices, such
as sampling equipment calibration,
equipment decontamination procedures, and
chain-of-custody procedures, are discussed
in other sections of this chapter and should
be described in the owner/operator's QAPjP.
Validation
The analytical data report provided by the
laboratory will present all data measured by
the laboratory but will not adjust those data
for field or laboratory quality control
indicators. This means that just because
data have been reported, they are not
necessarily an accurate representation of the
quality of the ground water. For example,
acetone and methylene chloride are often
used in laboratories as cleaning and
extraction solvents and, consequently, are
often laboratory contaminants, transmitted
through the ambient air into samples.
Method blanks are analyzed to evaluate the
extent of laboratory contamination.
Constituents found as contaminants in the
method blanks are "flagged" in the sample
data. The sample data are not, however,
adjusted for the contaminant concentration.
Other kinds of samples are analyzed to
assess other data quality indicators. Trip
blanks are used to assess contamination by
volatile organic constituents during sample
shipment and storage. Matrix spike/matrix
spike duplicate sample pairs are used to
evaluate analytical bias and precision.
Equipment rinsate samples are used to
assess the efficacy of sampling equipment
decontamination procedures. The data
validation process uses the results from all
of these QC samples to determine if the
reported analytical data accurately describe
the samples. All reported data must be
evaluated — a reported value of "non-detect"
is a quantitative report just like a numerical
value and must be validated.
The data validation process must also
consider the presence and quality of other
kinds of data used to ensure data quality
(e.g., calibration frequency and descriptors,
matrix specific detection limits). All of the
criteria for data quality are described in the
quality assurance project plan (QAPjP) or
sampling and analysis plan (SAP). These
documents may reference criteria from some
other source, (e.g., the USEPA Contract
Laboratory Program). The performance
criteria must be correctly specified and must
be used for data validation. It is a waste of
time and money to evaluate data against
standards other than those used to generate
them. Several documents are available to
assist the reviewer in validation of data by
different criteria (i.e., Chapter One of Test
Methods for Evaluating Solid Waste,
Physical/Chemical Methods, USEPA CLP
Functional Guidelines for Evaluating
Organics Analyses, USEPA CLP Functional
Guidelines for Evaluating Pesticides/PCBs
Analyses, etc.).
In addition to specific data that describe
data quality, the validator may consider
other information that may have an impact
on the end-use of the data, such as
background concentrations of the
constituent in the environment. In any
event, the QAPjP or SAP also should
describe the validation procedures that will
be used. The result of
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Subpart E
this validation should be the classification
of data as acceptable or unacceptable for the
purposes of the project. In some cases, data
may be further qualified, based either on
insufficient data or marginal performance
(i.e., qualitative uses only, estimated
concentration, etc.).
Documentation
The ground-water monitoring program
required by §258.50 through §258.55 relies
on documentation to demonstrate
compliance. The operating record of the
MSWLF should include a complete
description of the program as well as
periodic implementation reports.
At a minimum, the following aspects of the
ground-water monitoring program should be
described or included in the operating
record:
• The Sampling and Analysis plan that
details sample parameters, sampling
frequency, sample collection,
preservation, and analytical methods to
be used, shipping procedures, and chain-
of-custody procedures;
• The Quality Assurance Project Plan
(QAPjP) and Data Quality Objectives
(DQOs);
• The locations of monitoring wells;
• The design, installation, development,
and decommission of monitoring wells,
piezometers, and other measurement,
sampling, and analytical devices;
• Site hydrogeology;
Statistical methods to be used to evaluate
ground-water monitoring data and
demonstrate compliance with the
performance standard;
Approved demonstration that monitoring
requirements are suspended (if
applicable);
Boring logs;
Piezometer and well construction logs
for the ground-water monitoring system.
5.9 STATISTICAL ANALYSIS
40 CFR §258.53 (g)-(i)
5.9.1 Statement of Regulation
(g) The owner or operator must specify
in the operating record one of the
following statistical methods to be used in
evaluating ground-water monitoring data
for each hazardous constituent. The
statistical test chosen shall be conducted
separately for each hazardous constituent
in each well.
(1) A parametric analysis of variance
(ANOVA) followed by multiple
comparisons procedures to identify
statistically significant evidence of
contamination. The method must include
estimation and testing of the contrasts
between each compliance well's mean and
the background mean levels for each
constituent.
(2) An analysis of variance (ANOVA)
based on ranks followed by multiple
comparisons procedures to identify
statistically significant evidence of
contamination. The method must include
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Ground-Water Monitoring and Corrective Action
estimation and testing of the contrasts
between each compliance well's median
and the background median levels for
each constituent.
(3) A tolerance or prediction interval
procedure in which an interval for each
constituent is established from the
distribution of the background data, and
the level of each constituent in each
compliance well is compared to the upper
tolerance or prediction limit.
(4) A control chart approach that gives
control limits for each constituent.
(5) Another statistical test method that
meets the performance standards of
§258.53(h). The owner or operator must
place a justification for this alternative in
the operating record and notify the State
Director of the use of this alternative test.
The justification must demonstrate that
the alternative method meets the
performance standards of §258.53(h).
(h) Any statistical method chosen under
§258.53(g) shall comply with the
following performance standards, as
appropriate:
(1) The statistical method used to
evaluate ground-water monitoring data
shall be appropriate for the distribution
of chemical parameters or hazardous
constituents. If the distribution of the
chemical parameters or hazardous
constituents is shown by the owner or
operator to be inappropriate for a normal
theory test, then the data should be
transformed or a distribution-free theory
test should be used. If the distributions
for the constituents differ, more than one
statistical method may be needed.
(2) If an individual well comparison
procedure is used to compare an
individual compliance well constituent
concentration with background
constituent concentrations or a ground-
water protection standard, the test shall
be done at a Type I error level of no less
than 0.01 for each testing period. If a
multiple comparisons procedure is used,
the Type I experiment wise error rate for
each testing period shall be no less than
0.05; however, the Type I error of no less
than 0.01 for individual well comparisons
must be maintained. This performance
standard does not apply to tolerance
intervals, prediction intervals, or control
charts.
(3) If a control chart approach is used to
evaluate ground-water monitoring data,
the specific type of control chart and its
associated parameter values shall be
protective of human health and the
environment. The parameters shall be
determined after considering the number
of samples in the background data base,
the data distribution, and the range of the
concentration values for each constituent
of concern.
(4) If a tolerance interval or a
predictional interval is used to evaluate
ground-water monitoring data, the levels
of confidence and, for tolerance intervals,
the percentage of the population that the
interval must contain, shall be protective
of human health and the environment.
These parameters shall be determined
after considering the number of samples
in the background data base, the data
distribution, and the range of the
concentration values for each constituent
of concern.
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Subpart E
(5) The statistical method shall account
for data below the limit of detection with
one or more statistical procedures that
are protective of human health and the
environment. Any practical quantitation
limit (PQL) that is used in the statistical
method shall be the lowest concentration
level that can be reliably achieved within
specified limits of precision and accuracy
during routine laboratory operating
conditions that are available to the
facility.
(6) If necessary, the statistical method
shall include procedures to control or
correct for seasonal and spatial
variability as well as temporal correlation
in the data.
(i) The owner or operator must
determine whether or not there is a
statistically significant increase over
background values for each parameter or
constituent required in the particular
ground-water monitoring program that
applies to the MSWLF unit, as
determined under §§258.54(a) or
258.55(a) of this part.
(1) In determining whether a
statistically significant increase has
occurred, the owner or operator must
compare the ground-water quality of
each parameter or constituent at each
monitoring well designated pursuant to
§258.51(a)(2) to the background value of
that constituent, according to the
statistical procedures and performance
standards specified under paragraphs (g)
and (h) of this section.
(2) Within a reasonable period of time
after completing sampling and analysis,
the owner or operator must determine
whether there has been a statistically
significant increase over background at
each monitoring well.
5.9.2 Applicability
The statistical analysis requirements are
applicable to all existing units, new units,
and lateral expansions of existing units for
which ground-water monitoring is required.
The use of statistical procedures to evaluate
monitoring data shall be used for the
duration of the monitoring program,
including the post-closure care period.
The owner or operator must indicate in the
operating record the statistical method that
will be used in the analysis of ground-water
monitoring results. The data objectives of
the monitoring, in terms of the number of
samples collected and the frequency of
collection, must be consistent with the
statistical method selected.
Several options for analysis of ground-water
data are provided in the criteria. Other
methods may be used if they can be shown
to meet the performance standards. The
approved methods include both parametric
and nonparametric procedures, which differ
primarily in constraints placed by the
statistical distribution of the data. Control
chart, tolerance interval, and prediction
interval approaches also may be applied.
The owner or operator must conduct the
statistical comparisons between upgradient
and downgradient wells after completion of
each sampling event and receipt of validated
data. The statistical procedure must
conform to the performance standard of a
Type I error level of no less than 0.01 for
inter-well comparisons. Control chart,
tolerance interval, and prediction interval
approaches must incorporate decision values
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Ground-Water Monitoring and Corrective Action
that are protective of human health and the
environment. Generally, this is meant to
include a significance level of a least 0.05.
Procedures to treat data below analytical
method detection levels and seasonality
effects must be part of the statistical
analysis.
5.9.3 Technical Considerations
The MSWLF rule requires facilities to
evaluate ground-water monitoring data
using a statistical method provided in
§258.53(g) that meets the performance
standard of §258.53(h). Section 258.53(g)
contains a provision allowing for the use of
an alternative statistical method as long as
the performance standards of §258.53(h) are
met.
The requirements of §258.53(g) specify that
one of five possible statistical methods be
used for evaluating ground-water
monitoring data. One method should be
specified for each constituent. Although
different methods may be selected for each
constituent at new facilities, use of a method
must be substantiated by demonstrating that
the distribution of data obtained on that
constituent is appropriate for that method
(§258.53(h)). Selection of a specific
method is described in Statistical Analysis
of Ground- Water Monitoring Data at RCRA
Facilities - Interim Final Guidance"
(USEPA, 1989) and in Statistical Analysis
of Ground- Water Monitoring Data at RCRA
Facilities - Addendum to Interim Final
Guidance (USEPA, 1992b). EPA also
offers software, entitled User
Documentation of the Ground-Water
Information Tracking System (GRITS) with
Statistical Analysis Capability, GRITSTAT
Version 4.2. In addition to the statistical
guidance provided by EPA, the following
references may be
useful for selecting other methods (Dixon
and Massey, 1969; Gibbons, 1976;
Aitchison and Brown, 1969; and Gilbert,
1987). The statistical methods that may be
used in evaluating ground-water monitoring
data include the following:
• Parametric analysis of variance
(ANOVA) with multiple comparisons
• Rank-based (nonparametric) ANOVA
with multiple comparisons
• Tolerance interval or prediction interval
• Control chart
• An alternative statistical method (e.g.,
CABF t-test or confidence intervals).
If an alternative method is used, then the
State Director must be notified, and a
justification for its use must be placed in the
operating record.
The statistical analysis methods chosen must
meet performance standards specified under
§258.53(h), which include the following:
1) The method must be appropriate for the
observed distribution of the data
2) Individual well comparisons to
background ground-water quality or a
ground-water protection standard shall
be done at a Type I error level of no less
than 0.01 or, if the multiple comparisons
procedure is used, the experiment-wise
error rate for each testing period shall be
no less than 0.05
3) If a control chart is used, the type of
chart and associated parameter values
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Subpart E
shall be protective of human health and
the environment
4) The level of confidence and percentage
of the population contained in an interval
shall be protective of human health and
the environment
5) The method must account for data below
the limit of detection (less than the PQL)
in a manner that is protective of human
health and the environment
6) The method must account for seasonal
and spatial variability and temporal
correlation of the data, if necessary.
These statistical analysis methods shall be
used to determine whether a significant
increase over background values has
occurred. Monitoring data must be
statistically analyzed after validated results
from each sampling and analysis event are
received.
The statistical performance standards
provide a means to limit the possibility of
making false conclusions from the
monitoring data. The specified error level
of 0.01 for individual well comparisons for
probability of Type I error (indication of
contamination when it is not present or false
positive) essentially means that the analysis
is predicting with 99-percent confidence
that no significant increase in contaminant
levels is evident when in fact no increase is
present. Non-detect results must be treated
in an appropriate manner or their influence
on the statistical method may invalidate the
statistical conclusion. Non-detect results
are discussed in greater detail later in this
section.
Multiple Well Comparisons
If more than two wells (background and
downgradient combined) are screened in the
same stratigraphic unit, then the appropriate
statistical comparison method is a multiple
well comparison using the ANOVA
procedure. The parametric ANOVA
procedure assumes that the data from each
well group come from the same type (e.g.,
Normal) of distribution with possibly
different mean concentrations. The
ANOVA tests for a difference in means. If
there are multiple background wells, one
should consider the possibility of trying to
pool these background data into one group.
Such an increase in sample size often allows
for more accurate statistical comparisons,
primarily because better information is
known about the background concentrations
as a whole. Downgradient wells should not
be pooled, as stated in the regulations.
Ground-water monitoring data tend to
follow a log normal distribution (USEPA,
1989), and usually need to be transformed
prior to applying a parametric ANOVA
procedure. By conducting a log
transformation, ground-water monitoring
data will generally be converted to a normal
distribution. By applying a Shapiro-Wilk
test, probability plots, or other normality
tests on the residuals (errors) from the
ANOVA procedure, the normality of the
transformed data can be determined. In
addition, data variance for each well in the
comparison must be approximately
equivalent; this condition can be checked
using Levene's or Bartlett's test. These tests
are provided in USEPA (1992b) and
USEPA (1989).
If the transformed data do not conform to
the normality assumption, a nonparametric
ANOVA procedure may be used. The
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nonparametric statistical procedures do not
depend as much on the mathematical
properties of a specified distribution. The
nonparametric equivalent to the parametric
ANOVA is the Kruskal-Wallis test, which
analyzes variability of the average ranks of
the data instead of the measurements
themselves.
If the data display seasonality (regular,
periodic, and time-dependent increases or
decreases in parameter values), a two-way
ANOVA procedure should be used. If the
seasonality can be corrected, a one-way
ANOVA procedure may still be appropriate.
Methods to treat seasonality are described in
USEPA(1989).
ANOVA procedures attempt to determine
whether different wells have significantly
different average concentrations of
constituents. If a difference is indicated, the
ANOVA test is followed by a multiple
comparisons procedure to investigate which
specific wells are different among those
tested. The overall experiment-wise
significance level of the ANOVA must be
kept to a minimum of 0.05, while the
minimum significance level of each
individual comparison must be set at 0.01.
USEPA (1992b) provides alternative
methods that can be used when the number
of individual contrasts to be tested is very
high.
Tolerance and Prediction Intervals
Two types of statistical intervals are often
constructed from data: tolerance intervals
and prediction intervals. A comprehensive
discussion of these intervals is provided in
USEPA 1992b. Though often confused, the
interpretations and uses of these intervals
are quite distinct. A tolerance interval is
designed to contain a designated proportion
of the population (e.g., 95 percent of all
possible sample measurements). Because
the interval is constructed from sample data,
it also is a random interval. And because of
sampling fluctuations, a tolerance interval
can contain the specified proportion of the
population only with a certain confidence
level.
Tolerance intervals are very useful for
ground-water data analysis because in many
situations one wants to ensure that at most a
small fraction of the compliance well
sample measurements exceed a specific
concentration level (chosen to be protective
of human health and the environment).
Prediction intervals are constructed to
contain the next sample value(s) from a
population or distribution with a specified
probability. That is, after sampling a
background well for some time and
measuring the concentration of an analyte,
the data can be used to construct an interval
that will contain the next analyte sample or
samples (assuming the distribution has not
changed). Therefore, a prediction interval
will contain a future value or values with
specified probability. Prediction intervals
can also be constructed to contain the
average of several future observations.
In summary, a tolerance interval contains a
proportion of the population, and a
prediction interval contains one or more
future observations. Each has a probability
statement or "confidence coefficient"
associated with it. It should be noted that
these intervals assume that the sample data
used to construct the intervals are normally
distributed.
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Subpart E
Individual Well Comparisons
When only two wells (e.g., a single
background and a single compliance point
well) are being compared, owners or
operators should not perform the parametric
or nonparametric ANOVA. Instead, a
parametric t-test, such as Cochran's
Approximation to the Behrens-Fisher
Students' t-test, or a nonparametric test
should be performed. When a single
compliance well group is being compared to
background data and a nonparametric test is
needed, the Wilcoxin Rank-Sum test should
be performed. These tests are discussed in
more detail in standard statistical references
andinUSEPA(1992b).
Intra-Well Comparisons
Intra-well comparisons, where data of one
well are evaluated over time, are useful in
evaluating trends in individual wells and for
identifying seasonal effects in the data. The
intra-well comparison methods do not
compare background data to compliance
data. Where some existing facilities may
not have valid background data, however,
intra-well comparisons may represent the
only valid comparison available. In the
absence of a true background well, several
monitoring events may be required to
determine trends and seasonal fluctuations
in ground-water quality.
Control charts may be used for intra-well
comparisons but are only appropriate for
uncontaminated wells. If a well is
intercepting a release, then it is already in
an "out-of-control" state, which violates the
principal assumption underlying control
chart procedures. Time series analysis (i.e.,
plotting concentrations over time) is
extremely useful for identifying trends in
monitoring data. Such data may be adjusted
for seasonal effects to aid in assessing the
degree of change over time. Guidance for
and limitations of intra-well comparison
techniques are provided in USEPA (1989)
andUSEPA(1992b).
Treatment of Non-Detects
The treatment of data below the detection
limit of the analytical method (non-detects)
used depends on the number or percentage
of non-detects and the statistical method
employed. Guidance on how to treat non-
detects is provided in USEPA (1992b).
5.10 DETECTION MONITORING
PROGRAM
40 CFR §258.54
5.10.1 Statement of Regulation
(a) Detection monitoring is required at
MSWLF units at all ground-water
monitoring wells defined under
§§258.51(a)(l) and (a)(2) of this part. At
a minimum, a detection monitoring
program must include the monitoring for
the constituents listed in Appendix I of
this part.
1) The Director of an approved State
may delete any of the Appendix I
monitoring parameters for a MSWLF
unit if it can be shown that the
removed constituents are not
reasonably expected to be in or
derived from the waste contained in
the unit.
2) The Director of an approved State
may establish an alternative list of
inorganic indicator parameters for a
MSWLF unit, in lieu of some or all of
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Ground-Water Monitoring and Corrective Action
the heavy metals (constituents 1-15 in
Appendix I), if the alternative
parameters provide a reliable
indication of inorganic releases from
the MSWLF unit to the ground water.
In determining alternative
parameters, the Director shall
consider the following factors:
(i) The types, quantities, and
concentrations of constituents in
wastes managed at the MSWLF unit;
(ii) The mobility, stability, and
persistence of waste constituents or
their reaction products in the
unsaturated zone beneath the
MSWLF unit;
(iii) The detectability of indicator
parameters, waste constituents, and
reaction products in the ground
water; and
(iv) The concentration or values and
coefficients of variation of
monitoring parameters or
constituents in the background
ground-water.
(b) The monitoring frequency for all
constituents listed in Appendix I, or the
alternative list approved in accordance
with paragraph (a)(2), shall be at least
semiannual during the active life of the
facility (including closure) and the post-
closure period. A minimum of four
independent samples from each well
(background and downgradient) must be
collected and analyzed for the Appendix
I constituents, or the alternative list
approved in accordance with paragraph
(a)(2), during the first semiannual
sampling event. At least one sample from
each well(background and downgradient)
must be collected and analyzed during
subsequent semiannual sampling events.
The Director of an approved State may
specify an appropriate alternative
frequency for repeated sampling and
analysis for Appendix I constituents, or
the alternative list approved in
accordance with paragraph (a)(2), during
the active life (including closure) and the
post-closure care period. The alternative
frequency during the active life
(including closure) shall be no less than
annual. The alternative frequency shall
be based on consideration of the following
factors:
1) Lithology of the aquifer and
unsaturated zone;
2) Hydraulic conductivity of the aquifer
and unsaturated zone;
3) Ground-water flow rates;
4) Minimum distance between
upgradient edge of the MSWLF unit
and downgradient monitoring well
screen (minimum distance of travel);
and
5) Resource value of the aquifer.
(c) If the owner or operator determines,
pursuant to §258.53(g) of this part, that
there is a statistically significant increase
over background for one or more of the
constituents listed in Appendix I or the
alternative list approved in accordance
with paragraph (a)(2), at any monitoring
well at the boundary specified under
§258.51(a)(2), the owner or operator:
(1) Must, within 14 days of this finding,
place a notice in the operating record
indicating which constituents have shown
statistically significant changes from
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Subpart E
background levels, and notify the State
Director that this notice was placed in the
operating record; and
(2) Must establish an assessment
monitoring program meeting the
requirements of §258.55 of this part
within 90 days, except as provided for in
paragraph (3) below.
(3) The owner/operator may
demonstrate that a source other than a
MSWLF unit caused the contamination
or that the statistically significant
increase resulted from error in sampling,
analysis, statistical evaluation, or natural
variation in ground-water quality. A
report documenting this demonstration
must be certified by a qualified ground-
water scientist or approved by the
Director of an approved State and be
placed in the operating record. If a
successful demonstration is made and
documented, the owner or operator may
continue detection monitoring as
specified in this section. If after 90 days,
a successful demonstration is not made,
the owner or operator must initiate an
assessment monitoring program as
required in §258.55.
5.10.2 Applicability
Except for the small landfill exemption and
the no migration demonstration, detection
monitoring is required at existing MSWLF
units, lateral expansions of units, and new
MSWLF units. Monitoring must occur at
least semiannually at both background wells
and downgradient well locations. The
Director of an approved State may specify
an alternative sampling frequency.
Monitoring parameters must include all
Appendix I constituents unless an
alternative
list has been established by the Director of
an approved State.
During the first semiannual monitoring
event, the owner or operator must collect at
least four independent ground-water
samples from each well and analyze the
samples for all constituents in the Appendix
I or alternative list. Each subsequent
semiannual event must include, at a
minimum, the collection and analysis of one
sample from all wells. The monitoring
requirement continues throughout the active
life of the landfill and the post-closure care
period.
If an owner or operator determines that a
statistically significant increase over
background has occurred for one or more
Appendix I constituents (or constituents on
an alternative list), a notice must be placed
in the facility operating record (see Table 5-
2). The owner or operator must notify the
State Director within 14 days of the finding.
Within 90 days, the owner or operator must
establish an assessment monitoring program
conforming to the requirements of §258.55.
If evidence exists that a statistically
significant increase is due to factors
unrelated to the unit, the owner or operator
may make a demonstration to this effect to
the Director of an approved State or place a
certified demonstration in the operating
record. The potential reasons for an
apparent statistical increase may include:
• A contaminant source other than the
landfill unit
• A natural variation in ground-water
quality
• An analytical error
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Ground-Water Monitoring and Corrective Action
• A statistical error
• A sampling error.
The demonstration that one of these reasons
is responsible for the statistically significant
increase over background must be certified
by a qualified ground-water scientist or
approved by the Director of an approved
State. If a successful demonstration is made
and documented, the owner or operator may
continue detection monitoring.
If a successful demonstration is not made
within 90 days, the owner or operator must
initiate an assessment monitoring program.
A flow chart for a detection monitoring
program in a State whose program has not
been approved by EPA is provided in Figure
5-5.
5.10.3 Technical Considerations
If there is a statistically significant increase
over background during detection
monitoring for one or more constituents
listed in Appendix I of Part 258 (or an
alternative list of parameters in an approved
State), the owner or operator is required to
begin assessment monitoring. The
requirement to conduct assessment
monitoring will not change, even if the
Director of an approved State allows the
monitoring of geochemical parameters in
lieu of some or all of the metals listed in
Appendix I. If an owner or operator
suspects that a statistically significant
increase in a geochemical parameter is
caused by natural variation in ground-water
quality or a source other than a MSWLF
unit, a demonstration to this effect must be
documented in a report to avoid proceeding
to assessment monitoring.
Independent Sampling for Background
The ground-water monitoring requirements
specify that four independent samples be
collected from each well to establish
background during the first semiannual
monitoring event. This is because almost all
statistical procedures are based on the
assumption that samples are independent of
each other. In other words, independent
samples more accurately reflect the true
range of natural variability in the ground
water, and statistical analyses based on
independent samples are more accurate.
Replicate samples, whether field replicates
or lab splits, are not statistically
independent measurements.
It may be necessary to gather the
independent samples over a range of time
sufficient to account for seasonal
differences. If seasonal differences are not
taken into account, the chance for false
positives increases (monitoring results
indicate a release, when a release has not
occurred). The sampling interval chosen
must ensure that sampling is being done on
different volumes of ground water. To
determine the appropriate interval between
sample collection events that will ensure
independence, the owner or operator can
determine the site's effective porosity,
hydraulic conductivity, and hydraulic
gradient and use this information to
calculate ground-water velocity (USEPA,
1989). Knowing the velocity of the ground
water should enable an owner/operator to
establish an interval that ensures the four
samples are being collected from four
different volumes of water. For additional
information on establishing sampling
interval, see Statistical Analysis of
Groundwater Monitoring Data at RCRA
Til
-------
Semiannual Monitoring for all Appendix I
• First semiannual monitoring-
Four independent samples from each well
(background and downgradient)
• Subsequent semiannual monitoring-
One sample from each well (background
and downgradient)
Subsequent significant
increase over background
for one or more Appendix
1 constituents?
Continue
semiannual
monitoring
YES
Within 14 days notify State director that
notice placed in record
Within 90 days establish assessment
monitoring program
May demonstrate other source responsible
or an error in sampling/analysis/statistics
Figure 5-5. Detection Monitoring Program
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Ground-Water Monitoring and Corrective Action
Facilities - Interim Final Guidance,
(USEPA, 1989).
Alternative List/Removal of Parameters
An alternative list of Appendix I
constituents may be allowed by the Director
of an approved State. The alternative list
may use geochemical parameters, such as
pH and specific conductance, in place of
some or all of the metals (Parameters 1
through 15) in Appendix I. These
alternative parameters must provide a
reliable indication of inorganic releases
from the MSWLF unit to ground water. The
option of establishing an alternative list
applies only to Parameters 1 through 15 of
Appendix I. The list of ground-water
monitoring parameters must include all of
the volatile organic compounds (Appendix
I, Parameters 16 through 62).
A potential problem in substituting
geochemical parameters for metals on the
alternative list is that many of the
geochemical parameters are naturally
occurring. However, these parameters have
been used to indicate releases from MSWLF
units. Using alternative geochemical
parameters is reasonable in cases where
natural background levels are not high
enough to mask the detection of a release
from a MSWLF unit. The decision to use
alternative parameters also should consider
natural spatial and temporal variability in
the geochemical parameters.
The types, quantities, and concentrations of
wastes managed at the MSWLF unit play an
important role in determining whether
removal of parameters from Appendix I is
appropriate. If an owner or operator has
definite knowledge of the nature of wastes
accepted at the facility, then removal of
constituents from Appendix I may be
acceptable. Usually, a waste would have to
be homogeneous to allow for this kind of
determination. The owner or operator may
submit a demonstration that documents the
presence or absence of certain constituents
in the waste. The owner or operator also
would have to demonstrate that constituents
proposed for deletion from Appendix I are
not degradation or reaction products of
constituents potentially present in the waste.
Alternative Frequency
In approved States, 40 CFR §258.54(b)
allows the Director to specify an alternative
frequency for ground-water monitoring.
The alternative frequency is applicable
during the active life, including the closure
and the post-closure periods. The
alternative frequency can be no less than
annual.
The need to vary monitoring frequency must
be evaluated on a site-specific basis. For
example, for MSWLF units located in areas
with low ground-water flow rates, it may be
acceptable to monitor ground water less
frequently. The sampling frequency chosen
must be sufficient to protect human health
and the environment. Depending on the
ground-water flow rate and the resource
value of the aquifer, less frequent
monitoring may be allowable or more
frequent monitoring may be necessary. An
approved State may specify an alternative
frequency for repeated sampling and
analysis of Appendix I constituents based on
the following factors:
1) Lithology of the aquifer and the
unsaturated zone
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Subpart E
2) Hydraulic conductivity of the aquifer
and the unsaturated zone
3) Ground-water flow rates
4) Minimum distance between the
upgradient edge of the MSWLF unit and
the downgradient well screen
5) The resource value of the aquifer.
Approved States also can set alternative
frequencies for monitoring during the post-
closure care period based on the same
factors.
Notification
The notification requirement under 40 CFR
§258.54(c) requires an owner or operator to
1) place a notice in the operating record that
indicates which constituents have shown
statistically significant increases and 2)
notify the State Director that the notice was
placed in the operating record. The
constituents can be from either Appendix I
or from an alternative list.
Demonstrations of Other Reasons
For Statistical Increase
An owner or operator is allowed 90 days to
demonstrate that the statistically significant
increase of a contaminant/constituent was
caused by statistical, sampling, or analytical
errors or by a source other than the landfill
unit. The demonstration allowed in
§258.54(c)(3) may include:
1) A demonstration that the increase
resulted from another contaminant
source
2) A comprehensive audit of sampling,
laboratory, and data evaluation
procedures
3) Resampling and analysis to verify the
presence and concentration of the
constituents for which the increase was
reported.
A demonstration that the increase in
constituent concentration is the result of a
source other than the MSWLF unit should
document that:
• An alternative source exists.
• Hydraulic connection exists between the
alternative source and the well with the
significant increase.
• Constituent(s) (or precursor constituents)
are present at the alternative source or
along the flow path from the alternative
source prior to possible release from the
MSWLF unit.
• The relative concentration and
distribution of constituents in the zone of
contamination are more strongly linked
to the alternative source than to the
MSWLF unit when the fate and transport
characteristics of the constituents are
considered.
• The concentration observed in ground
water could not have resulted from the
MSWLF unit given the waste
constituents and concentrations in the
MSWLF unit leachate and wastes, and
site hydrogeologic conditions.
• The data supporting conclusions
regarding the alternative source are
historically consistent with
hydrogeologic
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Ground-Water Monitoring and Corrective Action
conditions and findings of the
monitoring program.
The demonstration must be documented,
certified by a qualified ground-water
scientist, and placed in the operating record
of the facility.
Demonstrations of Other Sources of
Error
A successful demonstration that the
statistically significant change is the result
of an error in sampling, analysis, or data
evaluation may include the following:
• Clear indication of a transcription or
calculation error
• Clear indication of a systematic error in
analysis or data reduction
• Resampling, analysis, and evaluation of
results
• Corrective measures to prevent the
recurrence of the error and incorporation
of these measures into the ground-water
monitoring program.
If resampling is necessary, the sample(s)
taken must be independent of the previous
sample. More than one sample may be
required to substantiate the contention that
the original sample was not representative
of the ground-water quality in the affected
well(s).
5.11 ASSESSMENT MONITORING
PROGRAM
40 CFR §258.55(a)-(f)
5.11.1 Statement of Regulation
(a) Assessment monitoring is required
whenever a statistically significant
increase over background has been
detected for one or more of the
constituents listed in Appendix I or in the
alternate list approved in accordance
with § 258.54(a)(2).
(b) Within 90 days of triggering an
assessment monitoring program, and
annually thereafter, the owner or
operator must sample and analyze the
ground water for all constituents
identified in Appendix II of this part. A
minimum of one sample from each
downgradient well must be collected and
analyzed during each sampling event.
For any new constituent detected in the
downgradient wells as a result of the
complete Appendix II analysis, a
minimum of four independent samples
from each well (background and
downgradient) must be collected and
analyzed to establish background for the
new constituents. The Director of an
approved State may specify an
appropriate subset of wells to be sampled
and analyzed for Appendix II
constituents during assessment
monitoring. The Director of an approved
State may delete any of the Appendix II
monitoring parameters for a MSWLF
unit if it can be shown that the removed
constituents are not reasonably expected
to be contained in or derived from the
waste contained in the unit.
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Subpart E
(c) The Director of an approved State
may specify an appropriate alternate
frequency for repeated sampling and
analysis for the full set of Appendix II
constituents required by §258.55(b) of
this part, during the active life (including
closure) and post-closure care of the unit
considering the following factors:
(1) Lithology of the aquifer and
unsaturated zone;
(2) Hydraulic conductivity of the
aquifer and unsaturated zone;
(3) Ground-water flow rates;
(4) Minimum distance between
upgradient edge of the MSWLF unit and
downgradient monitoring well screen
(minimum distance of travel);
(5) Resource value of the aquifer; and
(6) Nature (fate and transport) of any
constituents detected in response to this
section.
(d) After obtaining the results from the
initial or subsequent sampling events
required in paragraph (b) of this section,
the owner or operator must:
(1) Within 14 days, place a notice in the
operating record identifying the
Appendix II constituents that have been
detected and notify the State Director
that this notice has been placed in the
operating record;
(2) Within 90 days, and on at least a
semiannual basis thereafter, resample all
wells specified by § 258.51(a), conduct
analyses for all constituents in Appendix
I to this Part or in the alternative list
approved in accordance with
§258.54(a)(2), and for those constituents
in Appendix II that are detected in
response to paragraph (b) of this section,
and record their concentrations in the
facility operating record. At least one
sample from each well (background and
downgradient) must be collected and
analyzed during these sampling events.
The Director of an approved State may
specify an alternative monitoring
frequency during the active life
(including closure) and the post closure
period for the constituents referred to in
this paragraph. The alternative
frequency for Appendix I constituents or
the alternate list approved in accordance
with §258.54(a)(2) during the active life
(including closure) shall be no less than
annual. The alternative frequency shall
be based on consideration of the factors
specified in paragraph (c) of this section;
(3) Establish background concentrations
for any constituents detected pursuant to
paragraphs (b) or (d)(2) of this section;
and
(4) Establish ground-water protection
standards for all constituents detected
pursuant to paragraph (b) or (d)(2) of
this section. The ground-water
protection standards shall be established
in accordance with paragraphs (h) or (i)
of this section.
(e) If the concentrations of all Appendix
II constituents are shown to be at or
below background values, using the
statistical procedures in §258.53(g), for
two consecutive sampling events, the
owner or operator must notify the State
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Director of this finding and may return to
detection monitoring.
(f) If the concentrations of any
Appendix II constituents are above
background values, but all concentrations
are below the ground-water protection
standard established under paragraphs
(h) or (i) of this section, using the
statistical procedures in §258.53(g), the
owner or operator must continue
assessment monitoring in accordance
with this section.
5.11.2 Applicability
Assessment monitoring is required at all
existing units, lateral expansions, and new
facilities whenever any of the constituents
listed in Appendix I are detected at a
concentration that is a statistically
significant increase over background values.
Figure 5-6 presents a flow chart pertaining
to applicability requirements.
Within 90 days of beginning assessment
monitoring, the owner or operator must
resample all downgradient wells and
analyze the samples for all Appendix II
constituents. If any new constituents are
identified in this process, four independent
samples must be collected from all
upgradient and downgradient wells and
analyzed for those new constituents to
establish background concentrations. The
complete list of Appendix II constituents
must be monitored in each well annually for
the duration of the assessment monitoring
program. In an approved State, the Director
may reduce the number of Appendix II
constituents to be analyzed if it can be
reasonably shown that those constituents are
not present in or derived from the wastes.
The Director of an approved State
may specify an appropriate subset of wells
to be included in the assessment monitoring
program. The Director of an approved State
also may specify an alternative frequency
for repeated sampling and analysis of
Appendix II constituents. This frequency
may be decreased or increased based upon
consideration of the factors in
§258.55(c)(l)-(6). These options for
assessment monitoring programs are
available only with the approval of the
Director of an approved State.
Within 14 days of receiving the results of
the initial sampling for Appendix II
constituents under assessment monitoring,
the owner or operator must place the results
in the operating record and notify the State
Director that this notice has been placed in
the operating record.
Within 90 days of receiving these initial
results, the owner or operator must resample
all wells for all Appendix I and detected
Appendix II constituents. This combined
list of constituents must be sampled at least
semiannually thereafter, and the list must be
updated annually to include any newly
detected Appendix II constituents.
Within the 90-day period, the owner or
operator must establish background values
and ground-water protection standards
(GWPSs) for all Appendix II constituents
detected. The requirements for determining
GWPSs are provided in §258.55(h). If the
concentrations of all Appendix II
constituents are at or below the background
values after two independent, consecutive
sampling events, the owner or operator may
return to detection monitoring after
notification has been made to the State
Director. If, after these two
283
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Figure 5-6
ASSESSMENT MONITORING
YES
Is There a
Statistically
Significant Increase
in Appendix I
Constituents?
YES
Continue/Return to
Detection Monitoring
iiiiiiiiiiiiiiiiiinnin iiimiiiiiiiiiiiimllin
[null
Assessment Monitoring (258.55)
• Sample for All Appendix II Constituents
• Set Ground-Water Protection Standard for Detected
Appendix II Constituents
• Resample for Detected Appendix II Constituents and All
Appendix I Constituents Semi-Annually
• Repeat Annual Monitoring for All Appendix II Constituents
• Characterize Nature and Extent of Release
Is There
a Statistically
Significant increase in
Appendix II Constituents
Over Ground-Water
Protection
Standard?
Are all
Appendix II
Constituents Below
Background?
Proceed to
Corrective Action
Continue Assessment
Monitoring
» IIIHIllllllllllHIIIIIIHIIlllllllllllllllllllllllL
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Ground-Water Monitoring and Corrective Action
sampling events, any detected Appendix II
constituent is statistically above background
but below the GWPSs, the assessment
monitoring program must be continued.
5.11.3 Technical Considerations
The purpose of assessment monitoring is to
evaluate the nature and extent of
contamination. The assessment monitoring
program is phased. The first phase assesses
the presence of additional assessment
monitoring constituents (Appendix II or a
revised list designated by an approved State)
in all downgradient wells or in a subset of
ground-water monitoring wells specified by
the Director of an approved State. If
concentrations of all Appendix II
constituents are at or below background
values using the statistical procedures in
§258.53(g) for two consecutive sampling
periods, then the owner or operator can
return to detection monitoring.
Following notification of a statistically
significant increase of any Appendix I
constituent above background, the owner or
operator has 90 days to develop and
implement the assessment monitoring
program. Implementation of the program
involves sampling downgradient monitoring
wells for ground water passing the relevant
point of compliance for the unit (i.e., the
waste management unit boundary or
alternative boundary specified by the
Director of an approved State).
Downgradient wells are identified in
§258.51(a)(2). Initiation of assessment
monitoring does not stop the detection
monitoring program. Section 258.55(d)(2)
specifies that analyses must continue for all
Appendix I constituents on at least a
semiannual basis. Within the 90-day period,
the owner or operator must collect at least
one sample from each downgradient well
and analyze the samples for the Appendix II
parameters. If a downgradient well has
detectable quantities of a new Appendix II
constituent, four independent samples must
be collected from all background and
downgradient wells to establish background
for the new constituent(s). The date, well
locations, parameters detected, and their
concentrations must be documented in the
operating record of the facility, and the
State Director must be notified within 14
days of the initial detection of Appendix II
parameters. On a semiannual basis
thereafter, both background and
downgradient wells must be sampled for all
Appendix II constituents.
Alternative List
In an approved State, the Director may
delete Appendix II parameters that the
owner or operator can demonstrate would
not be anticipated at the facility. A
demonstration would be based on a
characterization of the wastes contained in
the unit and an assessment of the leachate
constituents. Additional information on the
alternative list can be found in Section
5.10.3.
Alternative Frequency
The Director of an approved State may
specify an alternate sampling frequency for
the entire Appendix II list for both the
active and post-closure periods of the
facility. The decision to change the
monitoring frequency must consider:
1) Lithology of the aquifer and unsaturated
zone;
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Subpart E
2) Hydraulic conductivity of the aquifer
and unsaturated zone;
3) Ground-water flow rates;
4) Minimum distance of travel (between the
MSWLF unit edge to downgradient
monitoring wells); and
5) Nature (fate and transport) of the
detected constituents.
The Director of an approved State also may
allow an alternate frequency, other than
semiannual, for the monitoring of Appendix
I and detected Appendix II constituents.
The monitoring frequency must be
sufficient to allow detection of ground-
water contamination. If contamination is
detected early, the volume of ground water
contaminated will be smaller and the
required remedial response will be less
burdensome. Additional information on the
alternate frequency can be found in Section
5.10.3.
In an approved State, the Director may
specify a subset of wells that can be
monitored for Appendix II constituents to
confirm a release and track the plume of
contamination during assessment
monitoring. The owner or operator should
work closely with the State in developing a
monitoring plan that targets the specific
areas of concern, if possible. This may
represent a substantial cost savings,
especially at large facilities for which only
a very small percentage of wells showed
exceedances above background. The use of
a subset of wells likely will be feasible only
in cases where the direction and rate of flow
are relatively constant.
5.12 ASSESSMENT MONITORING
PROGRAM
40 CFR §258.55(g)
5.12.1 Statement of Regulation
(g) If one or more Appendix II
constituents are detected at statistically
significant levels above the ground-water
protection standard established under
paragraphs (h) or (i) of this section in any
sampling event, the owner or operator
must, within 14 days of this finding, place
a notice in the operating record
identifying the Appendix II constituents
that have exceeded the ground-water
protection standard and, notify the State
Director and all appropriate local
government officials that the notice has
been placed in the operating record. The
owner or operator also:
(1) (i) Must characterize the nature and
extent of the release by installing
additional monitoring wells as necessary;
(ii) Must install at least one additional
monitoring well at the facility boundary
in the direction of contaminant migration
and sample this well in accordance with
§258.55(d)(2);
(iii) Must notify all persons who own
the land or reside on the land that
directly overlies any part of the plume of
contamination if contaminants have
migrated off-site if indicated by sampling
of wells in accordance with §258.55(g)(i);
and
(iv) Must initiate an assessment of
corrective measures as required by
§255.56 of this part within 90 days; or
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Ground-Water Monitoring and Corrective Action
(2) May demonstrate that a source
other than a MSWLF unit caused the
contamination, or that the statistically
significant increase resulted from error in
sampling, analysis, statistical evaluation,
or natural variation in ground-water
quality. A report documenting this
demonstration must be certified by a
qualified ground-water scientist or
approved by the Director of an approved
State and placed in the operating record.
If a successful demonstration is made the
owner or operator must continue
monitoring in accordance with the
assessment monitoring program pursuant
to §258.55, and may return to detection
monitoring if the Appendix II
constituents are below background as
specified in §258.55(e). Until a successful
demonstration is made, the owner or
operator must comply with §258.55(g)
including initiating an assessment of
corrective measures.
5.12.2 Applicability
This requirement applies to facilities in
assessment monitoring and is applicable
during the active life, closure, and post-
closure care periods.
5.12.3 Technical Considerations
If an Appendix II constituent(s) exceeds a
GWPS in any sampling event, the owner or
operator must notify the State Director
within 14 days and place a notice of these
findings in the operating record of the
MSWLF facility. In addition, the owner or
operator must:
1) Characterize the lateral and vertical
extent of the release or plume by
installing and sampling an appropriate
number of additional monitoring wells
2) Install at least one additional
downgradient well at the facility
property boundary in the direction of
migration of the contaminant plume and
sample that well for all Appendix II
compounds initially and thereafter, in
conformance with the assessment
monitoring program
3) Notify all property owners whose land
overlies the suspected plume, if the
sampling of any property boundary
well(s) indicates that contaminants have
migrated offsite
4) Initiate an assessment of corrective
measures, as required by §258.56, within
90 days.
In assessment monitoring, the owner or
operator may demonstrate that a source
other than the MSWLF unit caused the
contamination or that the statistically
significant increase was the result of an
error in sampling, analysis, statistical
evaluation, or natural variation in ground-
water quality. The demonstration must be
certified by a qualified ground-water
scientist or approved by the Director of an
approved State. Until a successful
demonstration is made, the owner or
operator must comply with §258.55(g) and
initiate assessment of corrective measures.
If the demonstration is successful, the owner
or operator must return to assessment
monitoring and may return to the detection
program provided that all Appendix II
constituents are at or below background for
two consecutive sampling periods.
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Subpart E
Release Investigation
If the GWPS is exceeded, a series of actions
must be taken. These actions are described
in the next several paragraphs. The owner
or operator must investigate the extent of
the release by installing additional
monitoring wells and obtaining additional
ground-water samples. The investigation
should identify plume geometry, both
laterally and vertically. Prior to such field
activities, records of site operation and
maintenance activities should be reviewed
to identify possible release locations within
the landfill and whether such releases are
expected to be transient (e.g., one time
release due to repaired liner) or long-term.
Due to the presence of dissolved ionic
constituents, such as iron, magnesium,
calcium, sodium, potassium, chloride,
sulfate, and carbonate, typically associated
with MSWLF unit leachates, geophysical
techniques, including resistivity and terrain
conductivity, may be useful in defining the
plume. Characterizing the nature of the
release should include a description of the
rate and direction of contaminant migration
and the chemical and physical
characteristics of the contaminants.
Property Boundary Monitoring Well
At least one monitoring well must be
installed at the facility boundary in the
direction of contaminant migration.
Additional wells may be required to
delineate the plume. Monitoring wells at
the facility boundary should be screened to
monitor all stratigraphic units that could be
preferential pathways for contaminant
migration in the uppermost aquifer. In
some cases, this may require installation of
nested wells or individual wells screened at
several discrete intervals. The well installed
at the facility boundary must be sampled
semiannually or at an alternative frequency
determined by the Director of an approved
State. The initial sample must be analyzed
for all Appendix II constituents.
Notification of Adjoining Residents and
Property Owners
If ground-water monitoring indicates that
contamination has migrated offsite, the
owner or operator must notify property
owners or residents whose land surface
overlies any part of the contaminant release.
Although the requirement does not describe
the contents of the notice, it is expected that
the notice could include the following
items:
• Date of detected release
• Chemical composition of release
• Reference to the constituent(s), reported
concentration(s), and the GWPS
• Representatives of the MSWLF facility
with whom to discuss the finding,
including their telephone numbers
• Plans and schedules for future activities
• Interim recommendations or remedies to
protect human health and the
environment.
Demonstrations of Other Sources of
Error
The owner or operator may demonstrate that
the source of contamination was not the
MSWLF unit. This demonstration is
discussed in Section 5.10.3.
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Ground-Water Monitoring and Corrective Action
Return to Detection Monitoring
A facility conducting assessment monitoring
may return to detection monitoring if the
concentrations of all Appendix II
constituents are at or below background
levels for two consecutive sampling periods
using the statistical procedures in
§25 8.5 3 (g). The requirement that
background concentrations must be
maintained for two consecutive sampling
events will reduce the possibility that the
owner or operator will fail to detect
contamination or an increase in a
concentration of a hazardous constituent
when one actually exists. The Director of
an approved State can establish an
alternative time period (§258.54(b).
5.13 ASSESSMENT MONITORING
PROGRAM
40 CFR §258.55(h)-(j)
5.13.1 Statement of Regulation
(h) The owner or operator must
establish a ground-water protection
standard for each Appendix II
constituent detected in the ground water.
The ground-water protection standard
shall be:
(1) For constituents for which a
maximum contaminant level (MCL) has
been promulgated under Section 1412 of
the Safe Drinking Water Act (codified)
under 40 CFR Part 141, the MCL for that
constituent;
(2) For constituents for which MCLs
have not been promulgated, the
background concentration for the
constituent established from wells in
accordance with §258.51(a)(l); or
(3) For constituents for which the
background level is higher than the MCL
identified under subparagraph (1) above
or health based levels identified under
§258.55(i)(l), the background
concentration.
(i) The Director of an approved State
may establish an alternative ground-
water protection standard for
constituents for which MCLs have not
been established. These ground-water
protection standards shall be appropriate
health based levels that satisfy the
following criteria:
(1) The level is derived in a manner
consistent with Agency guidelines for
assessing the health risks of
environmental pollutants (51 FR 33992,
34006, 34014, 34028);
(2) The level is based on scientifically
valid studies conducted in accordance
with the Toxic Substances Control Act
Good Laboratory Practice Standards (40
CFR Part 792) or equivalent;
(3) For carcinogens, the level represents
a concentration associated with an excess
lifetime cancer risk level (due to
continuous lifetime exposure) with the 1
x 10"4 to 1 x 10"6 range; and
(4) For systemic toxicants, the level
represents a concentration to which the
human population (including sensitive
subgroups) could be exposed to on a daily
basis that is likely to be without
appreciable risk of deleterious effects
during a lifetime. For purposes of this
subpart, systemic toxicants include toxic
chemicals that cause effects other than
cancer or mutation.
289
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Subpart E
(j) In establishing ground-water
protection standards under paragraph
(i), the Director of an approved State may
consider the following:
(1) Multiple contaminants in the ground
water;
(2) Exposure threats to sensitive
environmental receptors; and
(3) Other site-specific exposure or
potential exposure to ground water.
5.13.2 Applicability
The criteria for establishing GWPSs are
applicable to all facilities conducting
assessment monitoring where any Appendix
II constituents have been detected. The
owner or operator must establish a GWPS
for each Appendix II constituent detected.
If the constituent has a promulgated
maximum contaminant level (MCL), then
the GWPS is the MCL. If no MCL has been
published for a given Appendix II
constituent, the background concentration of
the constituent becomes the GWPS. In
cases where the background concentration is
higher than a promulgated MCL, the GWPS
is set at the background level.
In approved States, the Director may
establish an alternative GWPS for
constituents for which MCLs have not been
established. Any alternative GWPS must be
health-based levels that satisfy the criteria in
§258.55(i). The Director may also consider
any of the criteria identified in §258.55(j).
In cases where the background
concentration is higher than the health-
based levels, the GWPS is set at the
background level.
5.13.3 Technical Considerations
For each Appendix II constituent detected,
a GWPS must be established. The GWPS is
to be set at either the MCL or background.
Where the background concentration is
higher than the MCL, then the GWPS is
established at background.
Directors of approved States have the option
of establishing an alternative GWPS for
constituents without MCLs. This alternative
GWPS must be an appropriate health-based
level, based on specific criteria. These
levels must:
• Be consistent with EPA health risk
assessment guidelines
• Be based on scientifically valid studies
• Be within a risk range of IxlO"4 to IxlO"6
for carcinogens
• For systemic toxicants (causing effects
other than cancer or mutations), be a
concentration to which the human
population could be exposed on a daily
basis without appreciable risk of
deleterious effects during a lifetime.
The health-based GWPS may be established
considering the presence of more than one
constituent, exposure to sensitive
environmental receptors, and other site-
specific exposure to ground water. Risk
assessments to establish the GWPS must
consider cumulative effects of multiple
pathways to receptors and cumulative
effects on exposure risk of multiple
contaminants. Guidance and procedures for
establishing a health-based risk assessment
may be found in Guidance on Remedial
Actions for
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Ground-Water Monitoring and Corrective Action
Contaminated Groundwater at Superfund
Sites, (USEPA, 1988).
5.14 ASSESSMENT OF
CORRECTIVE MEASURES
40 CFR §258.56
5.14.1 Statement of Regulation
(a) Within 90 days of finding that any of
the constituents listed in Appendix II
have been detected at a statistically
significant level exceeding the ground-
water protection standards defined under
§258.55(h) and (i) of this part, the owner
or operator must initiate an assessment of
corrective measures. Such an assessment
must be completed within a reasonable
period of time.
(b) The owner or operator must
continue to monitor in accordance with
the assessment monitoring program as
specified in §258.55.
(c) The assessment shall include an
analysis of the effectiveness of potential
corrective measures in meeting all of the
requirements and objectives of the
remedy as described under §258.57,
addressing at least the following:
(1) The performance, reliability, ease of
implementation, and potential impacts of
appropriate potential remedies, including
safety impacts, cross-media impacts, and
control of exposure to any residual
contamination;
(2) The time required to begin and
complete the remedy;
(3) The costs of remedy implementation;
and
(4) The institutional requirements such
as State or local permit requirements or
other environmental or public health
requirements that may substantially
affect implementation of the remedy(s).
(d) The owner or operator must discuss
the results of the corrective measures
assessment, prior to the selection of
remedy, in a public meeting with
interested and affected parties.
5.14.2 Applicability
An assessment of corrective measures must
be conducted whenever any Appendix II
constituents are detected at statistically
significant levels exceeding the GWPS. The
assessment of corrective measures must be
initiated within 90 days of the finding.
During the initiation of an assessment of
corrective measures, assessment monitoring
must be continued. The assessment of
corrective measures must consider
performance (including potential impacts),
time, and cost aspects of the remedies. If
implementation requires additional State or
local permits, such requirements should be
identified. Finally, the results of the
corrective measures assessment must be
discussed in a public meeting with
interested and affected parties.
5.14.3 Technical Considerations
An assessment of corrective measures is
site-specific and will vary significantly
depending on the design and age of the
facility, the completeness of the facility's
historical records, the nature and
concentration of the contaminants found in
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Subpart E
the ground water, the complexity of the site
hydrogeology, and the facility's proximity
to sensitive receptors. Corrective measures
are generally approached from two
directions: 1) identify and remediate the
source of contamination and 2) identify and
remediate the known contamination.
Because each case will be site-specific, the
owner or operator should be prepared to
document that, to the best of his or her
technical and financial abilities, a diligent
effort has been made to complete the
assessment in the shortest time practicable.
The factors listed in §258.56(c)(l) must be
considered in assessing corrective measures.
These general factors are discussed below in
terms of source evaluation, plume
delineation, ground-water assessment, and
corrective measures assessment.
Source Evaluation
As part of the assessment of corrective
measures, the owner or operator will need to
identify the nature of the source of the
release. The first step in this identification
is a review of all available site information
regarding facility design, wastes received,
and onsite management practices. For
newer facilities, this may be a relatively
simple task. However, at some older
facilities, detailed records of the facility's
history may not be as well documented,
making source definition more difficult.
Design, climatological, and waste-type
information should be used to evaluate the
duration of the release, potential seasonal
effects due to precipitation (increased
infiltration and leachate generation), and
possible constituent concentrations. If
source evaluation is able to identify a
repairable engineering condition that likely
contributed to the cause of contamination
(e.g., unlined leachate storage ponds, failed
cover system, leaky leachate transport pipes,
past conditions of contaminated storm
overflow), such information should be
considered as part of the assessment of
corrective measures.
Existing site geology and hydrogeology
information, ground-water monitoring
results, and topographic and cultural
information must be documented clearly and
accurately. This information may include
soil boring logs, test pit and monitoring well
logs, geophysical data, water level elevation
data, and other information collected during
facility design or operation. The
information should be expressed in a
manner that will aid interpretation of data.
Such data may include isopach maps of the
thickness of the upper aquifer and important
strata, isoconcentration maps of
contaminants, flow nets, cross-sections, and
contour maps. Additional guidance on data
interpretation that may be useful in a source
evaluation is presented in RCRA Facility
Investigation Guidance: Volume I -
Development of an RFI Work Plan and
General Considerations for RCRA Facility
Investigations, (USEPA 1989a), RCRA
Facility Investigation Guidance: Volume IV
- Case Study Examples, (USEPA 1989d),
and Practical Guide For Assessing and
Remediating Contaminated Sites (USEPA
1989e).
Plume Delineation
To effectively assess corrective measures,
the lateral and vertical extent of
contamination must be known. When it is
determined that a GWPS is exceeded during
the assessment monitoring program, it may
be necessary to install additional wells to
characterize the contaminant plume(s). At
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least one additional well must be added at
the property boundary in the direction of
contaminant migration to allow timely
notification to potentially affected parties if
contamination migrates offsite.
The following circumstances may require
additional monitoring wells:
• Facilities that have not determined the
horizontal and vertical extent of the
contaminant plume
• Locations where the subsurface is
heterogeneous or where ground-water
flow patterns are difficult to establish
• Mounding associated with MSWLF
units.
Because the requirements for additional
monitoring are site-specific, the regulation
does not specifically establish cases where
additional wells are necessary or establish
the number of additional wells that must be
installed.
During the plume delineation process, the
owner or operator is not relieved from
continuing the assessment monitoring
program.
The rate of plume migration and the change
in contaminant concentrations with time
must be monitored to allow prediction of the
extent and timing of impact to sensitive
receptors. The receptors may include users
of both ground-water and surface water
bodies where contaminated ground water
may be discharged. In some cases, transfer
of volatile compounds from ground water to
the soil and to the air may provide an
additional migration pathway. Information
regarding the aquifer characteristics (e.g.,
hydraulic conductivity, storage coefficients,
and effective porosity) should be developed
for modeling contaminant transport if
sufficient data are not available. Anisotropy
and heterogeneity of the aquifer must be
evaluated, as well as magnitude and
duration of source inputs, to help explain
present and predicted plume configuration.
Currently, most treatment options for
ground-water contamination at MSWLF
units involve pump and treat or in-situ
biological technologies (bio-remediation).
The cost and duration of treatment depends
on the size of the plume, the pumping
characteristics of the aquifer, and the
chemical transport phenomena. Source
control and ground-water flow control
measures to reduce the rate of contaminant
migration should be included in the costs of
any remedial activity undertaken. Ground-
water modeling of the plume may be
initiated to establish the following:
• The locations and pumping rates of
withdrawal and/or injection wells
• Predictions of contaminant
concentrations at exposure points
• Locations of additional monitoring wells
• The effect that source control options
may have on ground-water remediation
• The effects of advection and dispersion,
retardation, adsorption, and other
attenuation processes on the plume
dimensions and contaminant
concentrations.
Any modeling effort must consider that
simulations of remedial response measures
and contaminant transport are based on
many necessary simplifying assumptions,
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which affect the accuracy of the model.
These assumptions include boundary
conditions, the degree and spatial variability
of anisotropy, dispersivity, effective
porosity, stratigraphy, and the algorithms
used to solve contaminant transport
equations. Model selection should be
appropriate for the amount of data available,
and the technical uncertainty of the model
results must be documented by a sensitivity
analysis on the input parameters. A
sensitivity analysis is generally done after
model calibration by varying one input
parameter at a time over a realistic range
and then evaluating changes in model
output. For additional information on
modeling, refer to the Further Information
Section of Chapter 5.0 and the RCRA
Facility Investigation Guidance: Volume II
- Soil, Groundwater and Subsurface Gas
Releases (USEPA, 1989b).
Ground-Water Assessment
To assess the potential effectiveness of
corrective measures for ground-water
contamination, the following information is
needed:
• Plume definition (includes the types,
concentration, and spatial distribution of
the contaminants)
• The amenability of the contaminants to
specific treatment and potential for
contaminants to interfere with
treatability
• Fate of the contaminants (whether
chemical transformations have, are, or
may be occurring, and the degree to
which the species are sorbed to the
geologic matrix)
• Stratigraphy and hydraulic properties of
the aquifer
• Treatment concentration goals and
objectives.
The owner or operator should consider
whether immediate measures to limit further
plume migration (e.g., containment options)
or measures to minimize further
introduction of contaminants to ground
water are necessary.
The process by which a remedial action is
undertaken will generally include the
following activities:
• Hydrogeologic investigation, which may
include additional well installations,
detailed vertical and lateral sampling to
characterize the plume, and core
sampling to determine the degree of
sorption of constituents on the geologic
matrix
• Risk assessment, to determine the impact
on sensitive receptors, which may
include identification of the need to
develop treatment goals other than
GWPSs
• Literature and technical review of
treatment technologies considered for
further study or implementation
• Evaluation of costs of different treatment
options
• Estimation of the time required for
completion of remediation under the
different treatment options
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• Bench-scale treatability studies
conducted to assess potential
effectiveness of options
• Selection of technology(ies) and
proposal preparation for regulatory and
public review and comment
• Full-scale pilot study for verification of
treatability and optimization of the
selected technology
• Initiation of full-scale treatment
technology with adjustments, as
necessary
• Continuation of remedial action until
treatment goals are achieved.
Corrective Measures Assessment
To compare different treatment options,
substantial amounts of technical information
must be assembled and assessed. The
objective of this information-gathering task
is to identify the following items for each
treatment technology:
• The expected performance of individual
approaches
• The time frame when individual
approaches can realistically be
implemented
• The technical feasibility of the
remediation, including new and
innovative technologies, performance,
reliability and ease of implementation,
safety and cross media impacts
• The anticipated time frame when
remediation should be complete
• The anticipated cost of the remediation,
including capital expenditures, design,
ongoing engineering, and monitoring of
results
• Technical and financial capability of the
owner or operator to successfully
complete the remediation
• Disposal requirements for treatment
residuals
• Other regulatory or institutional
requirements, including State and local
permits, prohibitions, or environmental
restrictions that may affect the
implementation of the proposed remedial
activity.
The performance objectives of the
corrective measures should be considered in
terms of source reduction, cleanup goals,
and cleanup time frame. Source reduction
would include measures to reduce or stop
further releases and may include the repair
of existing facility components (liner
systems, leachate storage pond liners, piping
systems, cover systems), upgrading of
components (liners and cover systems), or
premature closure in extreme cases. The
technology proposed as a cleanup measure
should be the best available technology,
given the practicable capability of the owner
or operator.
The technologies identified should be
reliable, based on their previous
performance; however, new innovative
technologies are not discouraged if they can
be shown, with a reasonable degree of
confidence, to be reliable.
Because most treatment processes, including
biorestoration, potentially produce
byproducts or release contaminants to
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different media (e.g., air stripping of
volatile compounds), the impacts of such
potential releases must be evaluated.
Releases to air may constitute a worker
health and safety concern and must be
addressed as part of the alternatives
assessment process. Other cross media
impacts, including transfer of contaminants
from soils to ground water, surface water, or
air, should be assessed and addressed in the
assessment of corrective actions. Guidance
for addressing air and soil transport and
contamination is provided in USEPA
(1989b) and USEPA (1989c).
Analyses should be conducted on treatment
options to determine whether or not they are
protective of human health and the
environment. Environmental monitoring of
exposure routes (air and water) may
necessitate health monitoring for personnel
involved in treatment activities if
unacceptable levels of exposure are
possible. On a case-by-case basis,
implementation plans may require both
forms of monitoring.
The development and screening of
individual corrective measures requires an
understanding of the physio-chemical
relationships and interferences between the
constituents and the sequence of treatment
measures that must be implemented. Proper
sequencing of treatment methods to produce
a feasible remedial program must be
evaluated to avoid interference between the
presence of some constituents and the
effective removal of the targeted compound.
In addition, screening and design parameters
of potential treatment options should be
evaluated in the early stages of conceptual
development and planning to eliminate
technically unsuitable treatment methods.
In general, selection of an appropriate
treatment method will require the
experience
of a qualified professional and will
necessitate a literature review of the best
available treatment technologies.
Numerous case studies and published papers
from scientific and engineering technical
journals exist on treatability of specific
compounds and groups of related
compounds. Development of new
technologies and refinements of
technologies have been rapid. A
compendium of available literature that
includes treatment technologies for organic
and inorganic contaminants, technology
selection, and other sources of information
(e.g., literature search data bases pertinent
to ground-water extraction, treatment, and
responses) is included in Practical Guide
for Assessing and Remediating
Contaminated Sites (USEPA, 1989e).
The general approach to remediation
typically includes active restoration, plume
containment, and source control as
discussed below. The selection of a
particular approach or combination of
approaches must be based on the corrective
action objectives. These general approaches
are outlined in Table 5-3. It should be
emphasized that the objective of a treatment
program should be to restore ground water
to pre-existing conditions or to levels below
applicable ground-water protection
standards while simultaneously restricting
further releases of contaminants to ground
water. Once treatment objectives are met,
the chance of further contamination should
be mitigated to the extent practicable.
Active Restoration
Active restoration generally includes
ground-water extraction, followed by onsite
or offsite wastewater treatment. Offsite
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wastewater treatment may include sending
the contaminated water to a local publicly
owned treatment works (POTW) or to a
facility designed to treat the contaminants of
concern. Treated ground water may be re-
injected, sent to a local POTW, or
discharged to a local body of surface water,
depending on local, State, and Federal
requirements. Typical treatment practices
that may be implemented include
coagulation and precipitation of metals,
chemical oxidation of a number of organic
compounds, air stripping to remove volatile
organic compounds, and biological
degradation of other organics.
The rate of contaminant removal from
ground water will depend on the rate of
ground-water removal, the cation exchange
capacity of the soil, and partition
coefficients of the constituents sorbed to the
soil (USEPA, 1988). As the concentration
of contaminants in the ground water is
reduced, the rate at which constituents
become partitioned from the soil to the
aqueous phase may also be reduced. The
amount of flushing of the aquifer material
required to remove the contaminants to an
acceptable level will generally determine
the time frame required for restoration. This
time frame is site-specific and may last
indefinitely.
In-situ methods may be appropriate for
some sites, particularly where pump and
treat technologies create serious adverse
effects or where it may be financially
prohibitive. In-situ methods may include
biological restoration requiring pH control,
addition of specific micro-organisms, and/or
addition of nutrients and substrate to
augment and encourage degradation by
indigenous microbial populations.
Bioremediation requires laboratory
treatability studies and
pilot field studies to determine the
feasibility and the reliability of full-scale
treatment. It must be demonstrated that the
treatment techniques will not cause
degradation of a target chemical to another
compound that has unacceptable health risks
and that is subject to further degradation.
Alternative in-situ methods may also be
designed to increase the effectiveness of
desorption or removal of contaminants from
the aquifer matrix. Such methodologies
may include steam stripping, soil flushing,
vapor extraction, thermal desorption, and
solvent washing, and extraction for removal
of strongly sorbed organic compounds.
These methods also may be used in
unsaturated zones where residual
contaminants may be sorbed to the geologic
matrix during periodic fluctuations of the
water table. Details of in-situ methods may
be found in several sources: USEPA (1988);
USEPA (1985); and Eckenfelder (1989).
Plume Containment
The purpose of plume containment is to
limit the spread of the contaminants.
Methods to contain plume movement
include passive hydraulic barriers, such as
grout curtains and slurry walls, and active
gradient control systems involving pumping
wells and french drains. The types of
aquifer characteristics that favor plume
containment include:
• Water naturally unsuited for human
consumption
• Contaminants present in low
concentration with low mobility
• Low potential for exposure to
contaminants and low risk associated
with exposure
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• Low transmissivity and low future user
demand.
Often, it may be advantageous for the owner
or operator to consider implementing
ground-water controls to inhibit further
contamination or the spread of
contamination. If ground-water pumping is
considered for capturing the leading edge of
the contaminant plume, the contaminated
water must be managed in conformance
with all applicable Federal and State
requirements. Under most conditions, it is
necessary to consult with the regulatory
agencies prior to initiating an interim
remedial action.
Source Control
Source control measures should be
evaluated to limit the migration of the
plume. The regulation does not limit the
definition of source control to exclude any
specific type of remediation. Remedies
must control the source to reduce or
eliminate further releases by identifying and
locating the cause of the release (e.g., torn
geomembrane, excessive head due to
blocked leachate collection system, leaking
leachate collection well or pipe). Source
control measures may include the following:
• Modifying the operational procedures
(e.g., banning specific wastes or
lowering the head over the leachate
collection system through more frequent
leachate removal)
• Undertaking more extensive and
effective maintenance activities (e.g.,
excavate waste to repair a liner failure or
a clogged leachate collection system)
• Preventing additional leachate
generation that may reach a liner failure
(e.g., using a portable or temporary rain
shelter during operations or capping
landfill areas that contribute to leachate
migrating from identified failure areas).
In extreme cases, excavation of deposited
wastes for treatment and/or off site disposal
may be considered.
Public Participation
The owner or operator is required to hold a
public meeting to discuss the results of the
corrective action assessment and to identify
proposed remedies. Notifications, such as
contacting local public agencies, town
governments, and State/Tribal governments,
posting a notice in prominent local
newspapers, and making radio
announcements are effective. The public
meeting should provide a detailed
discussion of how the owner or operator has
addressed the factors at §258.56(c)(l)-(4).
5.15 SELECTION OF REMEDY
40 CFR §258.57 (a)-(b)
5.15.1 Statement of Regulation
(a) Based on the results of the corrective
measure assessment conducted under
§258.56, the owner or operator must
select a remedy that, at a minimum,
meets the standards listed in paragraph
(b) below. The owner or operator must
notify the State Director, within 14 days
of selecting a remedy, that a report
describing the selected remedy has been
placed in the operating record and how it
meets the standards in paragraph (b) of
this section.
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(b) Remedies must:
(1) Be protective of human health and
the environment;
(2) Attain the ground-water protection
standard as specified pursuant to
§§258.55(h) or (i);
(3) Control the source(s) of releases so as
to reduce or eliminate, to the maximum
extent practicable, further releases of
Appendix II constituents into the
environment that may pose a threat to
human health or the environment; and
(4) Comply with standards for
management of wastes as specified in
§258.58(d).
5.15.2 Applicability
These provisions apply to facilities that
have been required to perform corrective
measures. The selection of a remedy is
closely related to the assessment process and
cannot be accomplished unless a sufficiently
thorough evaluation of alternatives has been
completed. The process of documenting the
rationale for selecting a remedy requires
that a report be placed in the facility
operating record that clearly defines the
corrective action objectives and
demonstrates why the selected remedy is
anticipated to meet those objectives. The
State Director must be notified within 14
days of the placement of the report in the
operating records of the facility. The study
must identify how the remedy will be
protective of human health and the
environment, attain the GWPS (either
background, MCLs, or, in approved States,
health-based standards, if applicable), attain
source control objectives,
and comply with waste management
standards.
5.15.3 Technical Considerations
The final method selected for
implementation must satisfy the criteria in
§258.57(b)(l)-(4). The report documenting
the capability of the selected method to
meet these four criteria should include such
information as:
• Theoretical calculations
• Comparison to existing studies and
results of similar treatment case
histories
• Bench-scale or pilot-scale treatability
test results
• Waste management practices.
The demonstration presented in the report
must document the alternative option
selection process.
5.16 SELECTION OF REMEDY
40 CFR §258.57 (c)
5.16.1 Statement of Regulation
(c) In selecting a remedy that meets the
standards of §258.57(b), the owner or
operator shall consider the following
evaluation factors:
(1) The long- and short-term
effectiveness and protectiveness of the
potential remedy(s), along with the
degree of certainty that the remedy will
prove successful based on consideration
of the following:
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(i) Magnitude of reduction of existing
risks;
(ii) Magnitude of residual risks in
terms of likelihood of further releases due
to waste remaining following
implementation of a remedy;
(iii) The type and degree of long-term
management required, including
monitoring, operation, and maintenance;
(iv) Short-term risks that might be
posed to the community, workers, or the
environment during implementation of
such a remedy, including potential
threats to human health and the
environment associated with excavation,
transportation, and redisposal or
containment;
(v) Time
achieved;
until full protection is
(vi) Potential for exposure of humans
and environmental receptors to
remaining wastes, considering the
potential threat to human health and the
environment associated with excavation,
transportation, redisposal, or
containment;
(vii) Long-term reliability of the
engineering and institutional controls;
and
(viii) Potential need for replacement of
the remedy.
(2) The effectiveness of the remedy in
controlling the source to reduce further
releases based on consideration of the
following factors:
(i) The extent to which containment
practices will reduce further releases;
(ii) The extent to which treatment
technologies may be used.
(3) The ease or difficulty of
implementing a potential remedy(s) based
on consideration of the following types of
factors:
(i) Degree of difficulty associated with
constructing the technology;
(ii) Expected operational reliability of
the technologies;
(iii) Need to coordinate with and obtain
necessary approvals and permits from
other agencies;
(iv) Availability of necessary
equipment and specialists; and
(v) Available capacity and location of
needed treatment, storage, and disposal
services.
(4) Practicable capability of the owner
or operator, including a consideration of
the technical and economic capability.
(5) The degree to which community
concerns are addressed by a potential
remedy(s).
5.16.2 Applicability
These provisions apply to facilities that are
selecting a remedy for corrective action.
The rule presents the considerations and
factors that the owner or operator must
evaluate when selecting the appropriate
corrective measure.
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5.16.3 Technical Considerations
The owner or operator must consider
specific topics to satisfy the performance
criteria under selection of the final
corrective measure. These topics must be
addressed in the report documenting the
selection of a particular corrective action.
The general topic areas that must be
considered include the following:
• The anticipated long- and short-term
effectiveness of the corrective action
• The anticipated effectiveness of source
reduction efforts
• The ease or difficulty of implementing
the corrective measure
• The technical and economic practicable
capability of the owner or operator
• The degree to which the selected remedy
will address concerns raised by the
community.
Effectiveness of Corrective Action
In selecting the remedial action, the
anticipated long-term and short-term
effectiveness should be evaluated. Long-
term effectiveness focuses on the risks
remaining after corrective measures have
been taken. Short-term effectiveness
addresses the risks during construction and
implementation of the corrective measure.
Review of case studies where similar
technologies have been applied provide the
best measures to judge technical
uncertainty, especially when relatively new
technologies are applied. The long-term,
post-cleanup effectiveness may be judged
on the ability of the proposed remedy to
mitigate further
releases of contaminants to the environment,
as well as on the feasibility of the proposed
remedy to meet or exceed the GWPSs. The
owner or operator must make a reasonable
effort to estimate and quantify risks, based
on exposure pathways and estimates of
exposure levels and durations. These
estimates include risks for both ground-
water and cross-media contamination.
The source control measures that will be
implemented, including excavation,
transportation, re-disposal, and
containment, should be evaluated with
respect to potential exposure and risk to
human health and the environment. The
source control measures should be viewed
as an integral component of the overall
corrective action. Health considerations
must address monitoring risks to workers
and the general public and provide
contingency plans should an unanticipated
exposure occur. Potential exposure should
consider both long- and short-term cases
before, during, and after implementation of
corrective actions.
The time to complete the remedial activity
must be estimated, because it will have
direct financial impacts on the project
management needs and financial capability
of the owner or operator to meet the
remedial objectives. The long-term costs of
the remedial alternatives and the long-term
financial condition of the owner or operator
should be reviewed carefully. The
implementation schedule should indicate
quality control measures to assess the
progress of the corrective measure.
The operational reliability of the corrective
measures should be considered. In addition,
the institutional controls and management
practices developed to assess the reliability
should be identified.
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Effectiveness of Source Reduction
Source control measures identified in
previous sections should be discussed in
terms of their expected effectiveness. If
source control consists of the removal and
re-disposal of wastes, the residual materials,
such as contaminated soils above the water
table, should be quantified and their
potential to cause further contamination
evaluated. Engineering controls intended to
upgrade or repair deficient conditions in
landfill component systems, including cover
systems, should be quantified in terms of
anticipated effectiveness according to
current and future conditions. This
assessment may indicate to what extent it is
technically and financially practicable to
make use of existing technologies. The
decision against using a certain technology
may be based on health considerations and
the potential for unacceptable exposure(s) to
both workers and the public.
Implementation of Remedial Action
The ease of implementing the proposed
remedial action will affect the schedule and
startup success of the remedial action. The
following key factors need to be assessed:
• The availability of technical expertise
of equipment
Construction
technology
or
The ability to properly manage and
dispose of wastes generated by
treatment
The likelihood of obtaining local
permits and public support for the
proposed project.
Technical considerations, including pH
control, ground-water extraction feasibility,
or the ability to inject nutrients, may need to
be considered, depending on the proposed
treatment method. Potential impacts, such
as potential cross-media contamination,
need to be reviewed as part of the overall
feasibility of the project.
The schedule of remedial activities should
identify the start and end points of the
following periods:
• Permitting phase
• Construction and startup period, during
which initial implementation success
will be evaluated, including time to
correct any unexpected problems
• Time when full-scale treatment will be
initiated and duration of treatment period
• Implementation and completion of
source control measures, including the
timeframe for solving problems
associated
with interim management and disposal of
waste materials or treatment residuals.
Items that require long lead times should be
identified early in the process and those
tasks should be initiated early to ensure that
implementation occurs in the shortest
practicable period.
Practical Capability
The owner or operator must be technically
and financially capable of implementing the
chosen remedial alternative and ensuring
project completion, including provisions for
future changes to the remedial plan after
progress is reviewed. If either technical or
financial capability is inadequate for a
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particular alternative, then other alternatives
with similar levels of protectiveness should
be considered for implementation.
Community Concerns
The public meetings held during assessment
of alternative measures are intended to elicit
public comment and response. The owner
or operator must, by means of meeting
minutes and a record of written comments,
identify which public concerns have been
expressed and addressed by corrective
measure options. In reality, the final
remedy selected and implemented will be
one that the State regulatory agency, the
public, and the owner or operator agree to.
5.17 SELECTION OF REMEDY
40 CFR §258.57 (d)
5.17.1 Statement of Regulation
(d) The owner or operator shall specify
as part of the selected remedy a
schedule(s) for initiating and completing
remedial activities. Such a schedule must
require the initiation of remedial
activities within a reasonable period of
time taking into consideration the factors
set forth in paragraphs (d) (1-8). The
owner or operator must consider the
following factors in determining the
schedule of remedial activities:
(1) Extent and nature of contamination;
(2) Practical capabilities of remedial
technologies in achieving compliance with
ground-water protection standards
established under §§258.55(g) or (h) and
other objectives of the remedy;
(3) Availability of treatment or disposal
capacity for wastes managed during
implementation of the remedy;
(4) Desirability of utilizing technologies
that are not currently available, but
which may offer significant advantages
over already available technologies in
terms of effectiveness, reliability, safety,
or ability to achieve remedial objectives;
(5) Potential risks to human health and
the environment from exposure to
contamination prior to completion of the
remedy;
(6) Resource value of the aquifer
including:
(i) Current and future uses;
(ii) Proximity and withdrawal rate of
users;
(iii) Ground-water
quality;
quantity and
(iv) The potential damage to wildlife,
crops, vegetation, and physical structures
caused by exposure to waste constituent;
(v) The hydrogeologic characteristic of
the facility and surrounding land;
(vi) Ground-water
treatment costs; and
removal and
(vii) The cost and availability
alternative water supplies.
of
(7) Practicable capability of the owner
or operator.
(8) Other relevant factors.
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5.17.2 Applicability
The requirements of §258.57(d) apply to
owners or operators of all new units,
existing units, and laterally expanded units
at all facilities required to implement
corrective actions. The requirements must
be complied with prior to implementing
corrective measures. The owner or operator
must specify the schedule for remedial
activities based on the following
considerations:
• The size and nature of the contaminated
area at the time the corrective measure is
to be implemented
• The practicable capabilities of the
remedial technology selected
• Available treatment and disposal
capacity
• Potential use of alternative innovative
technologies not currently available
• Potential risks to human health and the
environment existing prior to completion
of the remedy
• Resource value of the aquifer
• The practicable capability of the
owner/operator
• Other relevant factors.
5.17.3 Technical Considerations
The time schedule for implementing and
completing the remedial activity is
influenced by many factors that should be
considered by the owner or operator. The
most critical factor is the nature and extent
of the contamination, which significantly
affects the ultimate treatment rate. The size
of the treatment facility and the ground-
water extraction and injection rates must be
balanced for system optimization, capital
resources, and remedial timeframe
objectives. The nature of the contamination
will influence the degree to which the
aquifer must be flushed to remove adsorbed
species. These factors, which in part define
the practicable capability of the alternative
(treatment efficiency, treatment rate, and
replenishment of contaminants by natural
processes), should be considered when
selecting the remedy.
In addition, the rate at which treatment may
occur may be restricted by the availability
or capacity to handle treatment residues and
the normal flow of wastes during
remediation. Alternative residue treatment
or disposal capacity must be identified as
part of the implementation plan schedule.
If contaminant migration is slow due to low
transport properties of the aquifer,
additional time may be available to evaluate
the value of emerging and promising
innovative technologies. The use of such
technologies is not excluded as part of the
requirement to implement a remedial action
as soon as practicable. Delaying
implementation to increase the availability
of new technologies must be evaluated in
terms of achievable cleanup levels, ultimate
cost, additional environmental impact, and
potential for increased risk to sensitive
receptors. If a new technology clearly is
superior to existing options in attaining
remediation objectives, it may be
appropriate to delay implementation. This
may require that existing risks be controlled
through interim measures.
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In setting the implementation schedule, the
owner or operator should assess the risk to
human health and the environment within
the timeframe of reaching treatment
objectives. If the risk is unacceptable,
considering health-based assessments of
exposure paths and exposure limits, the
implementation time schedule must be
accelerated or the selected remedy altered to
provide an acceptable risk level in a timely
manner.
Establishment of the schedule also may
include consideration of the resource value
of the aquifer, as it pertains to current and
future use, proximity to users, quality and
quantity of ground water, agricultural value
and uses (irrigation water source or impact
on adjacent agricultural lands), and the
availability of alternative supplies of water
of similar quantity and quality. Based on
these factors, a relative assessment of the
aquifer's resource value to the local
community can be established. Impacts to
the resource and the degree of financial or
health-related distress by users should be
considered. The implementation timeframe
should attempt to minimize the loss of value
of the resource to users. The possibility that
alternative water supplies will have to be
developed as part of the remedial activities
may need to be considered.
Because owners or operators may not be
knowledgeable in remediation activities,
reliance on the owner or operator to devise
the schedule for remediation may be
impracticable. In these instances, use of an
outside firm to coordinate remediation
scheduling may be necessary. Similarly,
development of a schedule for which the
owner or operator cannot finance, when
other options exist that do allow for owner
or operator financing, should be prevented.
5.18 SELECTION OF REMEDY
40 CFR §258.57 (e)-(f)
5.18.1 Statement of Regulation
(e) The Director of an approved State
may determine that remediation of a
release of an Appendix II constituent
from a MSWLF unit is not necessary if
the owner or operator demonstrates to
the satisfaction of the Director of an
approved State that:
(1) The ground water is additionally
contaminated by substances that have
originated from a source other than a
MSWLF unit and those substances are
present in concentrations such that
cleanup of the release from the MSWLF
unit would provide no significant
reduction in risk to actual or potential
receptors; or
(2) The constituent(s) is present in
ground water that:
(i) Is not currently or reasonably
expected to be a potential source of
drinking water; and
(ii) Is not hydraulically connected with
waters to which the hazardous
constituents are migrating or are likely to
migrate in a concentration(s) that would
exceed the ground-water protection
standards established under §258.55(h)
or (i); or
(3) Remediation of the release(s) is
technically impracticable; or
(4) Remediation results in unacceptable
cross-media impacts.
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(f) A determination by the Director of
an approved State pursuant to paragraph
(e) above shall not affect the authority of
the State to require the owner or operator
to undertake source control measures or
other measures that may be necessary to
eliminate or minimize further releases to
the ground water, to prevent exposure to
the ground water, or to remediate the
ground water to concentrations that are
technically practicable and significantly
reduce threats to human health or the
environment.
5.18.2 Applicability
The criteria under §258.57(e) and (f) apply
in approved States only. Remediation of the
release of an Appendix II constituent may
not be necessary if 1) a source other than the
MSWLF unit is partly responsible for the
ground-water contamination, 2) the resource
value of the aquifer is extremely limited, 3)
remediation is not technically feasible, or 4)
remediation will result in unacceptable
cross-media impacts. The Director may
determine that while total remediation is not
required, source control measures or partial
remediation of ground water to
concentrations that are technically
practicable and significantly reduce risks is
required.
5.18.3 Technical Considerations
There are four situations where an approved
State may not require cleanup of hazardous
constituents released to ground water from
a MSWLF unit. If sufficient evidence exists
to document that the ground water is
contaminated by a source other than the
MSWLF unit, the Director of an approved
State may grant a waiver
from implementing some or all of the
corrective measure requirements. The
owner or operator must demonstrate that
cleanup of a release from its MSWLF unit
would provide no significant reduction in
risk to receptors due to concentrations of
constituents from the other source.
A waiver from corrective measures also may
be granted if the contaminated ground water
is not a current or reasonably expected
potential future drinking water source, and
it is unlikely that the hazardous constituents
would migrate to waters causing an
exceedance of GWPS. The owner or
operator must demonstrate that the
uppermost aquifer is not hydraulically
connected with a lower aquifer. The owner
or operator may seek an exemption if it can
be demonstrated that attenuation,
advection/dispersion or other natural
processes can remove the threat to
interconnected aquifers. The owner or
operator may seek the latter exemption if
the contaminated zone is not a drinking
water resource.
The Director of an approved State may
waive cleanup requirements if remediation
is not technically feasible. In addition, the
Director may wave requirements if
remediation results in unacceptable cross-
media impacts. A successful demonstration
that remediation is not technically feasible
must document specific facts that attribute
to this demonstration. Technical
impracticabilities may be related to the
accessibility of the ground water to
treatment, as well as the treatability of the
ground water using practicable treatment
technologies. If the owner or operator can
demonstrate that unacceptable cross-media
impacts are uncontrollable under a given
remedial option
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(e.g., movement in response to ground-
water pumping or release of volatile
organics to the atmosphere) and that the no
action option is a less risky alternative, then
the Director of an approved State may
determine that remediation is not necessary.
A waiver of remedial obligation does not
necessarily release the owner or operator
from the responsibility of conducting source
control measures or minimal ground-water
remediation. The State may require that
source control be implemented to the
maximum extent practicable to minimize
future risk of releases of contaminants to
ground water or that ground water be treated
to the extent technically feasible.
5.19 IMPLEMENTATION OF THE
CORRECTIVE ACTION
PROGRAM
40 CFR §258.58 (a)
5.19.1 Statement of Regulation
(a) Based on the schedule established
under §258.57(d) for initiation and
completion of remedial activities the
owner/operator must:
(1) Establish and implement a corrective
action ground-water monitoring program
that:
(i) At a minimum, meets the
requirements of an assessment
monitoring program under §258.55;
(ii) Indicates the effectiveness of the
corrective action remedy; and
(iii) Demonstrates compliance with
ground-water protection standard
pursuant to paragraph (e) of this section.
(2) Implement the corrective action
remedy selected under §258.57; and
(3) Take any interim measures necessary
to ensure the protection of human health
and the environment. Interim measures
should, to the greatest extent practicable,
be consistent with the objectives of and
contribute to the performance of any
remedy that may be required pursuant to
§258.57. The following factors must be
considered by an owner or operator in
determining whether interim measures
are necessary:
(i) Time required to develop
implement a final remedy;
and
(ii) Actual or potential exposure of
nearby populations or environmental
receptors to hazardous constituents;
(iii) Actual or potential contamination
of drinking water supplies or sensitive
ecosystems;
(iv) Further degradation of the ground
water that may occur if remedial action is
not initiated expeditiously;
(v) Weather conditions that may cause
hazardous constituents to migrate or be
released;
(vi) Risks of fire or explosion, or
potential for exposure to hazardous
constituents as a result of an accident or
failure of a container or handling system;
and
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Subpart E
(vii) Other situations that may pose
threats to human health and the
environment.
5.19.2 Applicability
These provisions apply to facilities that are
required to initiate and complete corrective
actions.
The owner or operator is required to
continue to implement its ground water
assessment monitoring program to evaluate
the effectiveness of remedial actions and to
demonstrate that the remedial objectives
have been attained at the completion of
remedial activities.
Additionally, the owner or operator must
take any interim actions to protect human
health and the environment. The interim
measures must serve to mitigate actual
threats and prevent potential threats from
being realized while a long-term
comprehensive response is being developed.
5.19.3 Technical Considerations
Implementation of the corrective measures
encompass all activities necessary to initiate
and continue remediation. The owner or
operator must continue assessment
monitoring to anticipate whether interim
measures are necessary, and to determine
whether the corrective action is meeting
stated objectives.
Monitoring Activities
During the implementation period, ground-
water monitoring must be conducted to
demonstrate the effectiveness of the
corrective action remedy. If the remedial
action is not effectively curtailing further
ground water degradation or the spread of
the contaminant plume, replacement of the
system with an alternative measure may be
warranted. The improvement rate of the
condition of the aquifer must be monitored
and compared to the cleanup objectives. It
may be necessary to install additional
monitoring wells to more clearly evaluate
remediation progress. Also, if it becomes
apparent that the GWPS will not be
achievable technically, in a realistic time-
frame, the performance objectives of the
corrective measure must be reviewed and
amended as necessary.
Interim Measures
If unacceptable potential risks to human
health and the environment exist prior to or
during implementation of the corrective
action, the owner or operator is required to
take interim measures to protect receptors.
These interim measures are typically short-
term solutions to address immediate
concerns and do not necessarily address
long-term remediation objectives. Interim
measures may include activities such as
control of ground-water migration through
high-volume withdrawal of ground water or
response to equipment failures that occur
during remediation (e.g., leaking drums). If
contamination migrates offsite, interim
measures may include providing an
alternative water supply for human,
livestock, or irrigation needs. Interim
measures also pertain to source control
activities that may be implemented as part
of the overall corrective action. This may
include activities such as excavation of the
source material or in-situ treatment of the
contaminated source. Interim measures
should be developed with consideration
given to maintaining conformity with the
objectives of the final corrective action.
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5.20 IMPLEMENTATION OF THE
CORRECTIVE ACTION
PROGRAM
40 CFR §258.58 (b)-(d)
5.20.1 Statement of Regulation
(b) An owner or operator may
determine, based on information
developed after implementation of the
remedy has begun or other information,
that compliance with requirements of
§258.57(b) are not being achieved
through the remedy selected. In such
cases, the owner or operator must
implement other methods or techniques
that could practicably achieve compliance
with the requirements, unless the owner
or operator makes the determination
under §258.58(c).
(c) If the owner or operator determines
that compliance with requirements under
§258.57(b) cannot be practically achieved
with any currently available methods, the
owner or operator must:
(1) Obtain certification of a qualified
ground-water specialist or approval by
the Director of an approved State that
compliance with requirements under
§258.57(b) cannot be practically achieved
with any currently available methods;
(2) Implement alternate measures to
control exposure of humans or the
environment to residual contamination,
as necessary to protect human health and
the environment; and
(3) Implement alternate measures for
control of the sources of contamination,
or for removal or decontamination of
equipment, units, devices, or structures
that are:
(i) Technically practicable; and
(ii) Consistent with the overall
objective of the remedy.
(4) Notify the State Director within 14
days that a report justifying the
alternative measures prior to
implementing the alternative measures
has been placed in the operating record.
(d) All solid wastes that are managed
pursuant to a remedy required under
§258.57, or an interim measure required
under §258.58(a)(3), shall be managed in
a manner:
(1) That is protective of human health
and the environment; and
(2) That complies with applicable RCRA
requirements.
5.20.2 Applicability
The requirements of the alternative
measures are applicable when it becomes
apparent that the remedy selected will not
achieve the GWPSs or other significant
objectives of the remedial program (e.g.,
protection of sensitive receptors). In
determining that the selected corrective
action approach will not achieve desired
results, the owner or operator must
implement alternate corrective measures to
achieve the GWPSs. If it becomes evident
that the cleanup goals are not technically
obtainable by existing practicable
technology, the owner or operator must
implement actions to control exposure of
humans or the environment from residual
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Subpart E
contamination and to control the sources of
contamination. Prior to implementing
alternative measures, the owner or operator
must notify the Director of an approved
State within 14 days that a report justifying
the alternative measures has been placed in
the operating record.
All wastes that are managed by the MSWLF
unit during corrective action, including
interim and alternative measures, must be
managed according to applicable RCRA
requirements in a manner that is protective
of human health and the environment.
5.20.3 Technical Considerations
An owner or operator is required to continue
the assessment monitoring program during
the remedial action. Through monitoring,
the short and long term success of the
remedial action can be gauged against
expected progress. During the remedial
action, it may be necessary to install
additional ground-water monitoring wells or
pumping or injection wells to adjust to
conditions that vary from initial assessments
of the ground-water flow system. As
remediation progresses and data are
compiled, it may become evident that the
remediation activities will not protect
human health and the environment, meet
GWPSs, control sources of contamination,
or comply with waste management
standards. The reasons for unsatisfactory
results may include:
• Refractory compounds that are not
amenable to removal or destruction
(detoxification)
• The presence of compounds that
interfere with treatment methods
identified for target compounds
• Inappropriately applied technology
• Failure of source control measures to
achieve desired results
• Failure of ground-water control systems
to achieve adequate containment or
removal of contaminated ground water
• Residual concentrations above GWPSs
that cannot be effectively reduced further
because treatment efficiencies are too
low
• Transformation or degradation of target
compounds to different forms that are
not amenable to further treatment by
present or alternative technologies.
The owner or operator should compare
treatment assumptions with existing
conditions to determine if assumptions
adequately depict site conditions. If
implementation occurred as designed, the
owner or operator should attempt to modify
or upgrade existing remedial technology to
optimize performance and to improve
treatment effectiveness. If the existing
technology is found to be unable to meet
remediation objectives, alternative
approaches must be evaluated that could
meet these objectives while the present
remediation is continued. During this re-
evaluation period, the owner or operator
may suspend treatment only if continuation
of remedial activities clearly increases the
threat to human health and the environment.
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Ground-Water Monitoring and Corrective Action
5.21 IMPLEMENTATION OF THE
CORRECTIVE ACTION
PROGRAM
40 CFR §258.58 (e)-(g)
5.21.1 Statement of Regulation
(e) Remedies selected pursuant to
§258.57 shall be considered complete
when:
(1) The owner or operator complies with
the ground-water protection standards
established under §§258.55(h) or (i) at all
points within the plume of contamination
that lie beyond the ground-water
monitoring well system established under
§258.51(a).
(2) Compliance with the ground-water
protection standards established under
§§258.55(h) or (i) has been achieved by
demonstrating that concentrations of
Appendix II constituents have not
exceeded the ground-water protection
standard(s) for a period of three
consecutive years using the statistical
procedures and performance standards in
§258.53(g) and (h). The Director of an
approved State may specify an
alternative length of time during which
the owner or operator must demonstrate
that concentrations of Appendix II
constituents have not exceeded the
ground-water protection standard(s)
taking into consideration:
(i) Extent and concentration of the
release(s);
(ii) Behavior characteristics of the
hazardous constituents in the ground
water;
(iii) Accuracy of monitoring or
modeling techniques, including any
seasonal, meteorological, or other
environmental variabilities that may
affect the accuracy; and
(iv) Characteristics of the ground
water.
(3) All actions required to complete the
remedy have been satisfied.
(f) Upon completion of the remedy, the
owner or operator must notify the State
Director within 14 days that a
certification that the remedy has been
completed in compliance with the
requirements of §258.58(e) has been
placed in the operating record. The
certification must be signed by the owner
or operator and by a qualified ground-
water specialist or approved by the
Director of an approved State.
(g) When, upon completion of the
certification, the owner or operator
determines that the corrective action
remedy has been completed in accordance
with the requirements under paragraph
(e) of this section, the owner or operator
shall be released from the requirements
for financial assurance for corrective
action under §258.73.
§258.59 [Reserved].
5.21.2 Applicability
These criteria apply to facilities conducting
corrective action. Remedies are considered
complete when, after 3 consecutive years of
monitoring (or an alternative length of time
as identified by the Director), the results
show significant statistical evidence that
ill
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Subpart E
Appendix II constituent concentrations are
below the GWPSs. Upon completion of all
remedial actions, the owner or operator
must certify to such, at which point the
owner or operator is released from financial
assurance requirements.
5.21.3 Technical Considerations
The regulatory period of compliance is 3
consecutive years at all points within the
contaminant plume that lie beyond the
ground-water monitoring system unless the
Director of an approved State specifies an
alternative length of time. Compliance is
achieved when the concentrations of
Appendix II constituents do not exceed the
GWPSs for a predetermined length of time.
Statistical procedures in §258.53 must be
used to demonstrate compliance with the
GWPSs.
The preferred statistical
comparison is to construct a
method for
99 percent
confidence interval around the mean of the
last 3 years of data and compare the upper
limit of the confidence interval to the
GWPS. An upper limit less than the GWPS
is considered significant evidence that the
standard is no longer being exceeded. The
confidence interval must be based on the
appropriate model describing the
distribution of the data.
Upon completion of the remedy, including
meeting the GWPS at all points within the
contaminant plume, the owner or operator
must notify the State Director within
fourteen days that a certification that the
remedy has been completed has been placed
in the operating record. The certification
must be signed by the owner or operator and
a qualified ground-water scientist or
approved by the Director of an approved
State. Upon completion of the remedial
action, in accordance with §258.58(e), the
owner or operator is released from the
financial assurance requirements pertaining
to corrective actions.
The Director of an approved State may
require an alternate time period (other than
3 years) to demonstrate compliance. In
determining an alternate period the Director
must consider the following:
• The extent and concentration of the
release(s)
• The behavior characteristics (fate and
transport) of the hazardous constituents
in the ground water (e.g., mobility,
persistence, toxicity, etc.)
• Accuracy of monitoring or modeling
techniques, including any seasonal,
meteorological or other environmental
variabilities that may affect accuracy
• The characteristics of the ground water
(e.g., flow rate, pH, etc.).
Consideration of these factors may result in
an extension or shortening of the time
required to show compliance with
remediation objectives.
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5.22 FURTHER INFORMATION
5.22.1 References
Aitchison, J., and J.A.C. Brown (1969). "The Lognormal Distribution"; Cambridge University
Press; Cambridge.
American Water Works Association (1984). "Abandonment of Test Holes, Partially Completed
Wells and Completed Wells." Appendix I. American Water Works Association Standard for
Water Wells, American Water Works Association, Denver, CO, pp 45-47.
Barari, A., and L.S. Hedges (1985). "Movement of Water in Glacial Till." Proceedings of the
17th International Congress of International Association of Hydrogeologists.
Barcelona, M.J., J.A. Helfrich and E.E. Garske, (1985). "Sampling Tube Effects on
Groundwater Samples"; Analytical Chemistry 47(2): 460-464.
Barcelona, M.J., J.P. Gibb, J.A. Helfrich, and E.E. Garske, (1985b). "Practical Guide for
Ground-Water Sampling," USEPA, Cooperative Agreement #CR-809966-01, EPA/600/2-
85/104, 169pp.
Barcelona, M.J., et al. 1990. Contamination of Ground Water: Prevention. Assessment.
Restoration. Pollution Technology Review No. 184, Noyes Data Corporation, Park Ridge, NJ,
213 pp.
Cantor, L.W., R.C. Knox, and D.M. Fairchild (1987). Ground-Water Quality Protection. Lewis
Publishers, Inc., Chelsea, MI.
Cooper, H.H., Jr., and C.E. Jacob (1946). "A Generalized Graphical Method for Evaluating
Formation Constants and Summarizing Well-Field History." American Geophys. Union Trans.,
V. 27, No. 4.
Daniel, D.E., H.M. Liljestrand, G.P. Broderick, and J.J. Bounders, Jr. (1988). "Interaction of
Earthen Linear Materials with Industrial Waste Leachate in Hazardous Waste and Hazardous
Materials," Vol. 5, No. 2.
Dixon, W.J. and F.J. Massey, Jr. (1969). "Introduction to Statistical Analysis"; 3rd Edition;
McGraw-Hill Book Co.; New York, New York.
Driscoll, F.G., (1986). "Groundwater and Wells"; Johnson and Johnson; St. Paul, Minnesota.
Eckenfelder, W.W., Jr., (1989). Industrial Water Pollution Control. McGraw-Hill, Inc., Second
Edition.
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Subpart E
Fetter, C.W., Jr. (1980). Applied Hydrogeology. Charles E. Merrill Publishing Co., Columbus,
OH.
Freeze, R.A. and J.A. Cherry, (1979). Groundwater: Prentice-Hall, Inc.; Englewood Cliffs,
New Jersey.
Gibbons, J.D., (1976). "Nonparametric Methods for Quantitative Analysis"; Holt, Rinehart, and
Winston Publishing Co.; New York, New York.
Gilbert, R.O., (1987). Statistical Methods for Environmental Pollution Monitoring: Van
Nostrand Reinhold Co.; New York, New York.
Heath, R.C. (1982). Basic Ground-Water Hydrology. U.S. Geological Survey Water Supply
Paper 2220, 84pp.
Hsieh, P.A., and S.P. Neuman (1985). "Field Determination of the Three - Dimensional
Hydraulic Conductivity Teasor of Anisotropic Media." Water Resources Research, V. 21, No.
11.
Kearl, P.M., N.E. Korte, and T.A. Cronk. 1992. "Suggested Modifications to Ground Water
Sampling Procedures Based on Observations from the Colloidal Borescope." Ground-Water
Monitoring Review, Spring, pp. 155-160.
Kruseman, G.P., and N. A. de Ridder (1989). "Analysis and Evaluation of Pumping Test Data,"
International Institute for Land Reclamation and Improvement/ILRI, Bulletin II, 4th Edition.
Lamb, B. and T. Kinney (1989). "Decommissioning Wells - Techniques and Pitfalls."
Proceedings of the Third National Outdoor Action Conference on Aquifer Restoration, Ground-
Water Monitoring and Geophysical Methods, NWWA, May 22-25, 1989, pp 217-228.
McGlew, P.J. and J.E. Thomas (1984). "Determining Contaminant Migration Pathways in
Fractured Bedrock." Proceedings of the Fifth National Conference on Management of
Uncontrolled Hazardous Waste Sites.
McWhorter, D.B., and O.K. Sunada (1977). Ground-Water Hydrology and Hydraulics. Water
Resources Publications, Fort Collins, CO.
Miller, J.C. and J.N. Miller, (1986). Statistics for Analytical Chemistry: John Wiley and Sons;
New York, New York.
Molz, F.J., O. Guven and J.G. Melville (1990). "A New Approach and Methodologies for
Characterizing the Hydrogeologic Properties of Aquifers." EPA Project Summary. EPA
600/52-90/002.
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Ground-Water Monitoring and Corrective Action
Molz, F.J., R.H. Norin, A.E. Hess, J.G. Melville, and O. Guven (1989) "The Impeller Meter for
Measuring Aquifer Permeability Variations: Evaluation and Comparison with Other Tests."
Water Resources Research, V 25, No. 7, pp 1677-1683.
Puls, R.W. and R.M. Powell. 1992. "Acquisition of Representative Ground Water Quality
Samples for Metals." Ground-Water Monitoring Review, Summer, pp. 167-176.
Puls, R.W., R.M. Powell, D.A. Clark, and C.J. Paul. 1991. "Facilitated Transport of Inorganic
Contaminants in Ground Water: Part II." Colloidal Transport, EPA/600/M-91/040, 12pp.
Puls, R.W., and MJ. Barcelona. 1989a. "Filtration of Ground Water Samples for Metals
Analysis." Hazardous Waste and Hazardous Materials, v. 6, No. 4.
Puls, R.W., and MJ. Barcelona. 1989b. "Ground Water Sampling for Metals Analysis."
USEPA Superfund Ground Water Issue, EPA/504/4-89/001, 6 pp.
Sevee, J. (1991). "Methods and Procedures for Defining Aquifer Parameters," in D.M. Nielsen,
ed., Practical Handbook of Ground-Water Monitoring. Lewis Publishers, Chelsea, MI.
USEPA (1975). Manual of Water Well Construction Practices. USEPA Office of Water Supply,
Report No. EPA-570/9-75-001, 156 pp.
USEPA, (1985). "Handbook: Remedial Action at Waste Disposal Sites"; EPA/540/G-88/003;
U.S. EPA; Office of Emergency and Remedial Response; Washington, D.C.
USEPA, (1986a). "RCRA Groundwater Monitoring Technical Enforcement Guidance
Document"; Office of Solid Waste and Emergency Response - 9950.1.
USEPA, (1986b). "Test Methods for Evaluating Solid Waste - Physical/Chemical Methods";
EPA SW-846, 3rd edition; PB88-239-233; U.S. EPA; Office of Solid Waste and Emergency
Response; Washington, D.C.
USEPA, (1986c). "Superfund Public Health Evaluation Manual"; PB87-183-125; U.S. EPA;
Office of Emergency and Remedial Response; Washington, D.C. 20460.
USEPA, (1986d). "Superfund Risk Assessment Information Directory"; PB87-188-918; U.S.
EPA; Office of Emergency and Remedial Response; Washington, D.C. 20460.
USEPA, (1988). "Guidance on Remedial Actions for Contaminated Groundwater at Superfund
Sites"; PB89-184-618; U.S. EPA; Office of Emergency and Remedial Response; Washington,
D.C.20460.
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Subpart E
USEPA, (1989). "Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities-
Interim Final Guidance"; EPA/530-SW-89-026; U.S. EPA; Office of Solid Waste; Washington,
D.C.
USEPA, (1989a). "RCRA Facility Investigation (RFI) Guidance; Interim Final; Vol. I
Development of an RFI Work Plan and General Considerations for RCRA Facility
Investigations"; PB89-200-299; U.S. EPA; Office of Solid Waste; Washington, D.C.
USEPA, (1989b). "RCRA Facility Investigation (RFI) Guidance; Interim Final; Vol. II - Soil,
Ground Water and Subsurface Gas Releases"; PB89-200-299; U.S. EPA; Office of Solid Waste;
Washington, D.C.
USEPA, (1989c). "Criteria for Identifying Areas of Vulnerable Hydrogeology Under the
Resource Conservation and Recovery Act, Interim Final. Appendix B -Ground-Water Flow
Net/Flow Line Construction and Analysis."
USEPA, (1989d). "RCRA Facility Investigation (RFI) Guidance; Vol IV: Case Study
Examples;" PB89-200-299; U.S. EPA; Office of Solid Waste; Washington, D.C.
USEPA, (1989e). "Practical Guide for Assessing and Remediating Contaminated Sites - Draft";
U.S. EPA; Waste Management Division, Office of Solid Waste, 401 M Street, S.W.;
Washington, D.C. May 1989.
USEPA, (1989f). "Handbook of Suggested Practices for the Design and Installation of Ground-
Water Monitoring Wells"; PB90-159-807; U.S EPA; Office of Research and Development;
Washington, D.C.
USEPA, (1990). "Handbook: Groundwater Vol I;" EPA/625/6-90/016a; U.S. EPA; Office of
Research and Development; Cincinnati, Ohio.
USEPA, (1991). "Handbook: Groundwater Vol II"; EP A/625/6-90/016b; U.S. EPA; Office of
Research and Development; Cincinnati, Ohio.
USEPA, (1992a). "RCRA Ground-Water Monitoring: Draft Technical Guidance"; EPA/530-R-
93-001; U.S. EPA; Office of Solid Waste; Washington, D.C. PB93-139-350.
USEPA, (1992b). "Statistical Training Course for Ground-Water Monitoring Data Analysis",
EPA/530-R-93-003; U.S. EPA; Office of Solid Waste; Washington, D.C.
USEPA, (1992c). "User Documentation of the Ground-Water Information Tracking System
(GRITS) with Statistical Analysis Capability, GRITSTAT Version 4.2;" EPA/625/11-91/002;
USEPA Office of Research and Development, Center for Environmental Research, ORD
Publications.
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USGS, (1989). "Chapter C2, Computer Model of Two-Dimensional Solute Transport and
Dispersion in Groundwater"; L.F. Konikow and J.D. Bredehoeft; Book 7; U.S. Geological
Survey; U.S. Department of Interior.
Way, S.C., and C.R. McKee (1982). "In-Situ Determination of Three-Dimensional Aquifer
Permeabilities." Ground Water, V. 20, No. 5.
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CHAPTER 6
SUBPART F
CLOSURE AND POST-CLOSURE
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CHAPTER 6
SUBPART F
TABLE OF CONTENTS
6.1 INTRODUCTION 322
62. FINAL COVER DESIGN 40 CFR §258.60(a) 322
6.2.1 Statement of Regulation 322
6.2.2 Applicability 323
6.2.3 Technical Considerations 323
Infiltration Layer 324
Geomembranes 329
Erosion Layer 330
63. ALTERNATIVE FINAL COVER DESIGN 40 CFR §258.60(b) 332
6.3.1 Statement of Regulation 332
6.3.2 Applicability 332
6.3.3 Technical Considerations 333
Other Considerations 333
Drainage Layer 333
Gas Vent Layer 335
Biotic Layer 336
Settlement and Subsidence 336
Sliding Instability 337
6A CLOSURE PLAN 40 CFR §258.60(c)-(d) 338
6.4.1 Statement of Regul ati on 338
6.4.2 Applicability 338
6.4.3 Technical Considerations 338
6J. CLOSURE CRITERIA 40 CFR §258.60(e)-(j) 339
6.5.1 Statement of Regulation 339
6.5.2 Applicability 340
6.5.3 Technical Considerations 341
6J> POST-CLOSURE CARE REQUIREMENTS 40 CFR $258.61 342
6.6.1 Statement of Regulation 342
6.6.2 Applicability 343
6.6.3 Technical Considerations 343
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6.7 POST-CLOSURE PLAN 40 CFR §258.61(c)-(e) 345
6.7.1 Statement of Regulation 345
6.7.2 Applicability 346
6.7.3 Technical Considerations 346
6.8 FURTHER INFORMATION 348
6.8.1 References 348
6.8.2 Organizations 349
6.8.3 Models 349
6.8.4 Databases 349
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CHAPTER 6
SUBPART F
CLOSURE AND POST-CLOSURE
6.1 INTRODUCTION
The criteria for landfill closure focus on two central themes: (1) the need to establish low-
maintenance cover systems and (2) the need to design a final cover that minimizes the
infiltration of precipitation into the waste. Landfill closure technology, design, and maintenance
procedures continue to evolve as new geosynthetic materials become available, as performance
requirements become more specific, and as limited performance history becomes available for
the relatively small number of landfills that have been closed using current procedures and
materials. Critical technical issues that must be faced by the designer include the:
• Degree and rate of post-closure settlement and stresses imposed on soil liner components;
• Long-term durability and survivability of cover system;
• Long-term waste decomposition and management of landfill leachate and gases; and
• Environmental performance of the combined bottom liner and final cover system.
Full closure and post-closure care requirements apply to all MSWLF units that receive wastes
on or after October 9, 1993. For MSWLF units that stop receiving wastes prior to October 9,
1993, only the final cover requirements of §258.60(a) apply.
*[NOTE: EPA finalized several revisions to 40 CFR Part 258 on October 1, 1993 (58 FR
51536) and issued a correction notice on October 14, 1993 (58 FR 53136). Questions regarding
the final rule and requests for copies of the Federal Register notices should be made to the
RCRA/Superfund Hotline at (800) 424-9346. These revisions delay the effective date for some
categories of landfills. More detail on the content of the revisions is included in the
introduction.
6.2 FINAL COVER DESIGN
40 CFR §258.60(a)
6.2.1 Statement of Regulation
(a) Owners or operators of all
MSWLF units must install a final cover
system that is designed to minimize
infiltration and erosion. The final cover
system must be designed and constructed
to:
(1) Have permeability less than or
equal to the permeability of any bottom
liner system or natural subsoils present,
or a permeability no greater than 1 x 10 5
cm/sec, whichever is less, and
(2) Minimize infiltration through
the closed MSWLF unit by the use of an
infiltration layer that contains a
minimum of 18-inches of an earthen
material, and
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Closure and Post-Closure
(3) Minimize erosion of the final
cover by the use of an erosion layer that
contains a minimum 6-inches of earthen
material that is capable of sustaining
native plant growth.
6.2.2 Applicability
These final cover requirements apply to all
MSWLF units required to close in
accordance with Part 258, including
MSWLF units that received wastes after
October 9, 1991 but stopped receiving
wastes prior to October 9, 1993. Units
closing during this two-year period are
required to install a final cover.
The final cover system required to close a
MSWLF unit, whether the unit is an existing
unit, a new unit, or a lateral expansion of an
existing unit, must be composed of an
infiltration layer that is a minimum of 18
inches thick, overlain by an erosion layer
that is a minimum of 6 inches thick.
The final cover should minimize, over the
long term, liquid infiltration into the waste.
The final cover must have a hydraulic
conductivity less than or equal to any
bottom liner system or natural subsoils
present to prevent a "bathtub" effect. In no
case can the final cover have a hydraulic
conductivity greater than 1 x 10"5 cm/sec
regardless of the permeability of underlying
liners or natural subsoils. If a synthetic
membrane is in the bottom liner, there must
be a flexible membrane liner (FML) in the
final cover to achieve a permeability that is
less than or equal to the permeability of the
bottom liner. Currently, it is not possible to
construct an earthen liner with a
permeability less than or equal to a synthetic
membrane.
In approved States, an alternate cover
system may be approved by the Director
(see Section 6.3).
6.2.3 Technical Considerations
Design criteria for a final cover system
should be selected to:
• Minimize infiltration of precipitation
into the waste;
• Promote good surface drainage;
• Resist erosion;
• Control landfill gas migration and/or
enhance recovery;
• Separate waste from vectors (e.g.,
animals and insects);
• Improve aesthetics;
• Minimize long-term maintenance;
• Protect human health and the
environment; and
• Consider final use.
The first three points are directly related to
the regulatory requirements. The other
points typically are considered in designing
cover systems for landfills.
Reduction of infiltration in a well-designed
final cover system is achieved through good
surface drainage and run-off with minimal
erosion, transpiration of water by plants in
the vegetative cover and root zone, and
restriction of percolation through earthen
material. The cover system should be
designed to provide the desired level of
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Subpart F
long-term performance with minimal
maintenance. Surface water run-off should
be properly controlled to prevent excessive
erosion and soil loss. Establishment of a
healthy vegetative layer is key to protecting
the cover from erosion. However,
consideration also must be given to
selecting plant species that are not deeply
rooted because they could damage the
underlying infiltration layer. In addition,
the cover system should be geotechnically
stable to prevent failure, such as sliding,
that may occur between the erosion and
infiltration layers, within these layers, or
within the waste. Figure 6-1 illustrates the
minimum requirements for the final cover
system.
Infiltration Layer
The infiltration layer must be at least 18
inches thick and consist of earthen material
that has a hydraulic conductivity
(coefficient of permeability) less than or
equal to the hydraulic conductivity of any
bottom liner system or natural subsoils.
MSWLF units with poor or non-existent
bottom liners possessing hydraulic
conductivities greater than 1 x 10"5 cm/sec
must have an infiltration layer that meets the
1 x 10"5 cm/sec minimum requirement.
Figure 6-2 presents an example of a final
cover with a hydraulic conductivity less
than or equal to the hydraulic conductivity
of the bottom liner system.
For units that have a composite liner with a
FML, or naturally occurring soils with very
low permeability (e.g., 1 x 10"8 cm/sec), the
Agency anticipates that the infiltration layer
in the final cover will include a synthetic
membrane as part of the final cover. A final
cover system for a MSWLF unit with a
FML combined with a soil liner and
leachate collection system is presented in
Figure 6-3a. Figure 6-3b shows a final
cover system for a MSWLF unit that has
both a double FML and double leachate
collection system.
The earthen material used for the infiltration
layer should be free of rocks, clods, debris,
cobbles, rubbish, and roots that may
increase the hydraulic conductivity by
promoting preferential flow paths. To
facilitate run-off while minimizing erosion,
the surface of the compacted soil should
have a minimum slope of 3 percent and a
maximum slope of 5 percent after allowance
for settlement. It is critical that side slopes,
which are frequently greater than 5 percent,
be evaluated for erosion potential.
Membrane and clay layers should be placed
below the maximum depth of frost
penetration to avoid freeze-thaw effects
(U.S. EPA, 1989b). Freeze-thaw effects
may include development of microfractures
or realignment of interstitial fines, which
can increase the hydraulic conductivity of
clays by more than an order of magnitude
(U.S. EPA, 1990). Infiltration layers may
be subject to desiccation, depending on
climate and soil water retention in the
erosion layer. Fracturing and volumetric
shrinking of the clay due to water loss may
increase the hydraulic conductivity of the
infiltration layer. Figure 6-4 shows the
regional average depth of frost penetration;
however, these values should not be used to
find the maximum depth of frost penetration
for a particular area of concern at a
particular site. Information regarding the
maximum depth of frost penetration for a
particular area can be obtained from the Soil
Conservation Service, local utilities,
construction companies, and local
universities.
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Closure and Post-Closure
Erosion Layer:
Min. 6" Soil
• Infiltration Layer:
Min. 18" Compacted Soil (1 x
10-5 cm/sec)
Existing Subgrade
Figure 6-1
Example of Minimum Final Cover Requirements
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Subpart F
Erosion Layer: ^^^^^^^^^^^^^^^^ Infiltration Layer:
Min. 6" Soil ^ ' ^^F^^^^""""^^"^^^^^^^^ - Min-18" Compacted Soil (1 x 10-6
cm / sec)
=?/ . «=
2 Feet Compacted
Soil (1 x 10-6 cm/sec)
Figure 6-2
Example of Final Cover With Hydraulic Conductivity(K) < K of Liner
326
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Erosion Layer
To sustain vegetation
FML
Infiltration Layer: Min. 18"
compacted soil (1 x 10-5
cm/sec)
FML
Feet Compacted Soil
(1 x 10-7 cm/sec)
Figure 6-3a
Example of Final Cover Design for a MSWLF Unit With a FML
and Leachate Collection System
Erosion Layer:
To sustain vegetation
FML
2 Feet Compacted
Soil (1 x 10-7 cm/sec)
Infiltration Layer: Min. 18"
compacted soil (1 x
10-5cm/sec)
FML
12" Compacted
Soil (1 x 1.0-7 cm/sec)
Figure 6-3b
Example of Final Cover Design for a MSWLF Unit With a Double FML and
Leachate Collection System
327
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Subpart F
Source: USEPA (1989)
Figure 6-4
Regional Depth of Frost Penetration in Inches
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Closure and Post-Closure
The infiltration layer is designed and
constructed in a manner similar to that used
for soil liners (U.S. EPA, 1988), with the
following differences:
• Because the cover is generally not
subject to large overburden loads, the
issue of compressive stresses is less
critical unless post-closure land use will
entail construction of objects that exert
large amounts of stress.
• The soil cover is subject to loadings
from settlement of underlying
materials. The extent of settlement
anticipated should be evaluated and a
closure and post-closure maintenance
plan should be designed to compensate
for the effects of settlement.
• Direct shear tests performed on
construction materials should be
conducted at lower shear stresses than
those used for liner system designs.
The design of a final cover is site-specific
and the relative performance of cover design
options may be compared and evaluated by
the HELP (Hydrologic Evaluation of
Landfill Performance) model. The HELP
model was developed by the U.S. Army
Corps of Engineers for the U.S. EPA and is
widely used for evaluating expected
hydraulic performance of landfill
cover/liner systems (U.S. EPA, 1988).
The HELP program calculates daily,
average, and peak estimates of water
movement across, into, through, and out of
landfills. The input parameters for the
model include soil properties, precipitation
and other climatological data, vegetation
type, and landfill design information.
Default climatologic and soil data are
available but should be verified as
reasonable for the site modeled. Outputs
from the model include precipitation, run-
off, percolation through the base of each
cover layer subprofile, evapotranspiration,
and lateral drainage from each profile. The
model also calculates the maximum head on
the barrier soil layer of each subprofile and
the maximum and minimum soil moisture
content of the evaporative zone. Data from
the model are presented in a tabular report
format and include the input parameters
used and a summary of the simulation
results. Results are presented in several
tables of daily, monthly, and annual totals
for each year specified. A summary of the
outputs also is produced, including average
monthly totals, average annual totals, and
peak daily values for several simulation
variables (U.S. EPA, 1988).
The HELP model may be used to estimate
the hydraulic performance of the cover
system designed for a MSWLF unit. Useful
information provided by the HELP model
includes surface run-off, duration and
quantity of water storage within the erosion
layer, and net infiltration through the cover
system to evaluate whether leachate will
accumulate within the landfill. For the
model to be used properly, the HELP Model
User's Guide and documentation should be
consulted.
Geomembranes
If a geomembrane is used as an infiltration
layer, the geomembrane should be at least
20 mils (0.5 mm) in thickness, although
some geomembrane materials may need to
be a greater thickness (e.g., a minimum
thickness of 60 mils is recommended for
HOPE because of the difficulties in making
consistent field seams in thinner material).
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Subpart F
Increased thickness and tensile strengths
may be necessary to prevent failure under
stresses caused by construction and waste
settlement during the post-closure care
period. The strength, resistance to sliding,
hydraulic performance, and actual thickness
of geomembranes should be carefully
evaluated. The quality and performance of
some textured sheets may be difficult to
evaluate due to the variability of the
textured surface.
Erosion Layer
The thickness of the erosion layer is
influenced by depth of frost penetration and
erosion potential. This layer is also used to
support vegetation. The influence of frost
penetration was discussed previously on
page 6-3.
Erosion can adversely affect the
performance of the final cover of a MSWLF
unit by causing rills that require
maintenance and repair. As previously
stated, a healthy vegetative layer can protect
the cover from erosion; conversely, severe
erosion can affect the vegetative growth.
Extreme erosion may lead to the exposure of
the infiltration layer, initiate or contribute to
sliding failures, or expose the waste.
Anticipated erosion due to surface water
run-off for given design criteria may be
approximated using the USDA Universal
Soil Loss Equation (U.S. EPA, 1989a). By
evaluating erosion loss, the design may be
optimized to reduce maintenance through
selection of the best available soil materials
or by initially adding excess soil to increase
the time required before maintenance is
needed. Parameters in the equation include
the following:
X = RKLSCP
where X = Soil loss (tons/acre/year)
R = Rainfall erosion index
K = Soil erodibility index
L = Slope length factor
S = Slope gradient factor
C = Crop management factor
P = Erosion control practice.
Values for the Universal Soil Loss Equation
parameters may be obtained from the U. S.
Soil Conservation Service (SCS) technical
guidance document entitled "Predicting
Rainfall Erosion Losses, Guidebook 537"
(1978), available at local SCS offices
located throughout the United States. State
or local SCS offices can provide factors to
be used in the soil loss equation that are
appropriate to a given area of the country.
Figure 6-5 can be used to find the soil loss
ratio due to the slope of the site as used in
the Universal Soil Loss Equation. Loss
from wind erosion can be determined by the
following equation (U.S. EPA, 1989a):
X = I'K'C'L'V
where
X =
r =
K' =
c =
L' =
V' =
Annual wind erosion
Field roughness factor
Soil erodibility index
Climate factor
Field length factor
Vegetative cover factor.
A vegetative cover not only improves the
appearance of the site, but it also controls
erosion of the final cover; a vegetated cover
may require only minimal maintenance.
The vegetation component of the erosion
layer should have the following
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Closure and Post-Closure
0 100
200 300
400 500 600 700
800
Source L'SEPA. 1989
iOpe Length (Feet)
Figure 6-5
Soil Erosion Due to Slope
331
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Subpart F
specifications
EPA, 1989b):
and characteristics (U.S.
• Locally adapted perennial plants that
are resistant to drought and temperature
extremes;
• Roots that will not disrupt the low-
permeability layer;
• The ability to thrive in low-nutrient soil
with minimum nutrient addition;
• Sufficient plant density to minimize
cover soil erosion;
• The ability to survive and function with
little or no maintenance (i.e., self-
supportive); and
• Sufficient variety of plant species to
continue to achieve these characteristics
and specifications over time.
The use of deep-rooted shrubs and trees is
generally inappropriate because the root
systems may penetrate the infiltration layer
and create preferential pathways of
percolation. Plant species with fibrous or
branching root systems are suited for use at
landfills, and can include a large variety of
grasses, herbs (i.e., legumes), and shallow-
rooted plants. The suitable species in a
region will vary, dependent on climate and
site-specific factors such as soil type and
slope gradient and aspect. The timing of
seeding (spring or fall in most climates) is
critical to successful germination and
establishment of the vegetative cover (U.S.
EPA, 1989b). Temporary winter covers
may be grown from fast-growing seed stock
such as winter rye.
Selection of the soil for the vegetative cover
(erosion layer) should include consideration
of soil type, nutrient and pH levels, climate,
species of the vegetation selected, mulching,
and seeding time. Loamy soils with a
sufficient organic content generally are
preferred. The balance of clay, silt, and
sand in loamy soils provides an environment
conducive to seed germination and root
growth (USEPA, 1988).
The Director of an approved State can allow
alternate designs to address vegetative
problems (e.g., the use of pavement or other
material) in areas that are not capable of
sustaining plant growth.
6.3 ALTERNATIVE FINAL COVER
DESIGN
40 CFR §258.60(b)
6.3.1 Statement of Regulation
(b) The Director of an approved
State may approve an alternative final
cover design that includes:
(1) An infiltration layer that
achieves an equivalent reduction in
infiltration as the infiltration layer
specified in paragraphs (a)(l) and (a)(2)
of this section, and
(2) An erosion layer that provides
equivalent protection from wind and
water erosion as the erosion layer
specified in (a)(3) of this section.
6.3.2 Applicability
The Director of an approved State may
approve alternative final cover systems that
can achieve equivalent performance as
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Closure and Post-Closure
the minimum design specified in
§258.60(a). This provides an opportunity to
incorporate different technologies or
improvements into cover designs, and to
address site-specific conditions.
6.3.3 Technical Considerations
An alternative material and/or an alternative
thickness may be used for an infiltration
layer as long as the infiltration layer
requirements specified in §258.60(a)(l) and
(a)(2) are met.
For example, an armored surface (e.g., one
composed of cobble-rich soils or soils rich
in weathered rock fragments) could be used
as an alternative to the six-inch erosion
layer. An armored surface, or hardened cap,
is generally used in arid regions or on steep
slopes where the establishment and
maintenance of vegetation may be hindered
by lack of soil or excessive run-off
The materials used for an armored surface
typically are (U.S. EPA, 1989b):
• Capable of protecting the underlying
infiltration layer during extreme
weather events of rainfall and/or wind;
• Capable of accommodating settlement
of the underlying material without
compromising the component;
• Designed with a surface slope that is
approximately the same as the
underlying soil (at least 2 percent
slope); and
• Capable of controlling the rate of soil
erosion.
The erosion layer may be made of asphalt or
concrete. These materials promote run-off
with negligible erosion. However, asphalt
and concrete deteriorate due to thermal
expansion and due to deformation caused by
subsidence. Crushed rock may be spread
over the landfill cover in areas where
weather conditions such as wind, heavy
rain, or temperature extremes commonly
cause deterioration of vegetative covers
(U.S. EPA, 1989b).
Other Considerations
Additional Cover System Components
To reduce the generation of post-closure
leachate to the greatest extent possible,
owners and operators can install a
composite cover made of a geomembrane
and a soil component with low hydraulic
conductivity. The hydraulic properties of
these components are discussed in Chapter
4 (Subpart D).
Other components that may be used in the
final cover system include a drainage layer,
a gas vent layer, and a biotic barrier layer.
These components are discussed in the
following sections and are shown in Figure
6-6.
Drainage Layer
A permeable drainage layer, constructed of
soil or geosynthetic drainage material, may
be constructed between the erosion layer
and the underlying infiltration layer. The
drainage layer in a final cover system
removes percolating water that has
infiltrated through the erosion layer after
surface run-off and evapotranspiration
losses. By removing water in contact with
the low-permeability layer, the potential for
333
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20-mii FML—
or
60-mi I HDPE
60 cm
30cm
30cm
60cm
\ N N S \ -WS
/ f S /->-.••—
N. \ \ S X^^S
}
Vegetation/
Soil Top Layer
Filler Layer
Biotic Barrier Layer
Drainage Layer
- Low-Permeability
FML/Soil Layer
Gas Venting Layer
Waste
Figure 6-6
Example of an Alternative Final Cover Design
-------
Closure and Post-Closure
leachate generation is diminished. Caution
should be taken when using a drainage layer
because this layer may prematurely draw
moisture from the erosion layer that is
needed to sustain vegetation.
If a drainage layer is used, owners or
operators should consider methods to
minimize physical clogging of the drainage
layer by root systems or soil particles. A
filter layer, composed of either a low
nutrient soil or geosynthetic material, may
be placed between the drainage layer and
the cover soil to help minimize clogging.
If granular drainage layer material is used,
the filter layer should be at least 12 in. (30
cm) thick with a hydraulic conductivity in
the range of 1 x 10"2 cm/sec to 1 x 10"3
cm/sec. The layer should be sloped at least
3 percent at the bottom of the layer. Greater
thickness and/or slope may be necessary to
provide sufficient drainage flow as
determined by site-specific modeling (U.S.
EPA, 1989b). Granular drainage material
will vary from site to site depending on the
type of material that is locally available and
economical to use. Typically, the material
should be no coarser than 3/8 inch (0.95
cm), classified according to the Universal
Soil Classification System (USCS) as type
SP, smooth and rounded, and free of debris
that could damage an underlying
geomembrane (U.S. EPA, 1989b).
Crushed stone generally is not appropriate
because of the sharpness of the particles. If
the available drainage material is of poor
quality, it may be necessary to increase the
thickness and/or slope of the drainage layer
to maintain adequate drainage. The HELP
model can be used as an analytical tool to
evaluate the relative expected performance
of alternative final cover designs.
If geosynthetic materials are used as a
drainage layer, the fully saturated effective
transmissivity should be the equivalent of
12 inches of soil (30 cm) with a hydraulic
conductivity range of 1 x 10"2 cm/sec to 1 x
10"3 cm/sec. Transmissivity can be
calculated as the hydraulic conductivity
multiplied by the drainage layer thickness.
A filter layer (preferably a non-woven
needle punch fabric) should be placed above
the geosynthetic material to minimize
intrusion and clogging by roots or by soil
material from the top layer.
Gas Vent Layer
Landfill gas collection systems serve to
inhibit gas migration. The gas collection
systems typically are installed directly
beneath the infiltration layer. The function
of a gas vent layer is to collect combustible
gases (methane) and other potentially
harmful gases (hydrogen sulfide) generated
by micro-organisms during biological decay
of organic wastes, and to divert these gases
via a pipe system through the infiltration
layer. A more detailed discussion
concerning landfill gas, including the use of
active and passive collection systems, is
provided in Chapter 3 (Subpart C).
The gas vent layer is usually 12 in. (30 cm)
thick and should be located between the
infiltration layer and the waste layer.
Materials used in construction of the gas
vent layer should be medium to coarse-
grained porous materials such as those used
in the drainage layer. Geosynthetic
materials may be substituted for granular
materials in the vent layer if equivalent
performance can be demonstrated. Venting
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Subpart F
to an exterior collection point can be
provided by means such as horizontal pipes
patterned laterally throughout the gas vent
layer, which channel gases to vertical risers
or lateral headers. If vertical risers are used,
their number should be minimized (as they
are frequently vandalized) and located at
high points in the cross-section (U.S. EPA,
1989b). Condensates will form within the
gas collection pipes; therefore, the design
should address drainage of condensate to
prevent blockage by its accumulation in low
points.
The most obvious potential problem with
gas collection systems is the possibility of
gas vent pipe penetrations through the cover
system. Settlement within the landfill may
cause concentrated stresses at the
penetrations, which could result in
infiltration layer or pipe failure. If a
geomembrane is used in the infiltration
layer, pipe sleeves, adequate flexibility and
slack material should be provided at these
connections when appropriate.
Alternatively, if an active gas control
system is planned, penetrations may be
carried out through the sides of the cover
directly above the liner anchor trenches
where effects of settlement are less
pronounced. The gas collection system also
may be connected to the leachate collection
system, both to vent gases that may form
inside the leachate collection pipes and to
remove gas condensates that form within the
gas collection pipes. This method generally
is not preferred because if the leachate
collection pipe is full, gas will not be able to
move through the system. Landfill gas
systems are also discussed in Chapter 3
(Subpart C).
Biotic Layer
Deep plant roots or burrowing animals
(collectively called biointruders) may
disrupt the drainage and the low hydraulic
conductivity layers, thereby interfering with
the drainage capability of the layers. A 30-
cm (12-inch) biotic barrier of cobbles
directly beneath the erosion layer may stop
the penetration of some deep-rooted plants
and the invasion of burrowing animals.
Most research on biotic barriers has been
done in, and is applicable to arid areas.
Geosynthetic products that incorporate a
time-released herbicide into the matrix or on
the surface of the polymer also may be used
to retard plant roots. The longevity of these
products requires evaluation if the cover
system is to serve for longer than 30 to 50
years (USEPA, 1991).
Settlement and Subsidence
Excessive settlement and subsidence, caused
by decomposition and consolidation of the
wastes, can impair the integrity of the final
cover system. Specifically, settlement can
contribute to:
• Ponding of surface water on the cap;
• Disruption of gas collection pipe
systems;
• Fracturing of low permeability
infiltration layers; and
• Failure of geomembranes.
The degree and rate of waste settlement are
difficult to estimate. Good records
regarding the type, quantity, and location of
waste materials disposed will improve the
estimate. Settlement due to consolidation
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Closure and Post-Closure
may be minimized by compacting the waste
during daily operation of the landfill unit or
by landfilling baled waste. Organic wastes
will continue to degrade and deteriorate
after closure of the landfill unit.
Several models have been developed to
analyze the process of differential
settlement. Most models equate the layered
cover to a beam or column undergoing
deflection due to various loading conditions.
While these models are useful to designers
in understanding the qualitative relationship
between the various land disposal unit
characteristics and in identifying the
constraining factors, accurate quantitative
analytical methods have not been developed
(U.S. EPA, 1988).
If the amount of total settlement can be
estimated, either from an analytical
approach or from empirical relationships
from data collected during the operating life
of the facility, the designer should attempt
to estimate the potential strain imposed on
the cover system components. Due to the
uncertainties inherent in the settlement
analysis, a biaxial strain calculation should
be sufficient to estimate the stresses that
may be imposed on the cover system. The
amount of strain that a liner is capable of
enduring may be as low as several percent;
for geomembranes, it may be 5 to 12 percent
(U.S. EPA, 1990). Geomembrane testing
may be included as part of the design
process to estimate safety factors against
cover system failure.
The cover system may be designed with a
greater thickness and/or slope to compensate
for settlement after closure. However, even
if settlement and subsidence are considered
in the design of the final cover, ponding
may still occur after closure and can be
corrected during post-closure maintenance.
The cost estimate for post-closure
maintenance should include earthwork
required to regrade the final cover due to
total and differential settlements. Based on
the estimates of total and differential
settlements from the modeling methods
described earlier, it may be appropriate to
assume that a certain percentage of the total
area needs regrading and then incorporate
the costs into the overall post-closure
maintenance cost estimate.
Sliding Instability
The slope angle, slope length, and overlying
soil load limit the stability of component
interfaces (geomembrane with soil,
geotextile, and geotextile/soil). Soil water
pore pressures developed along interfaces
also can dramatically reduce stability. If the
design slope is steeper than the effective
friction angles between the material, sliding
instability generally will occur. Sudden
sliding has the potential to cause tears in
geomembranes, which require considerable
time and expense to repair. Unstable slopes
may require remedial measures to improve
stability as a means of offsetting potential
long-term maintenance costs.
The friction angles between various media
are best determined by laboratory direct
shear tests that represent the design loading
conditions. Methods to improve stability
include using designs with flatter slopes,
using textured material, constructing
benches in the cover system, or reinforcing
the cover soil above the membrane with
geogrid or geotextile to minimize the
driving force on the interface of concern.
Methods for applying these design features
can be found in (U.S. EPA 1989), (U.S.EPA
1991), and (Richardson and Koerner 1987).
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6.4 CLOSURE PLAN
40 CFR §258.60(c)-(d)
6.4.1 Statement of Regulation
(c) The owner or operator must
prepare a written closure plan that
describes the steps necessary to close all
MSWLF units at any point during their
active life in accordance with the cover
design requirements in §258.60(a) or (b),
as applicable. The closure plan, at a
minimum, must include the following
information:
(1) A description of the final
cover, designed in accordance with
§258.60(a) and the methods and
procedures to be used to install the cover;
(2) An estimate of the largest area
of the MSWLF unit ever requiring a final
cover as required under §258.60(a) at any
time during the active life;
(3) An estimate of the maximum
inventory of wastes ever on-site over the
active life of the landfill facility; and
(4) A schedule for completing all
activities necessary to satisfy the closure
criteria in §258.60.
(d) The owner or operator must
notify the State Director that a closure
plan has been prepared and placed in the
operating record no later than the
effective date of this part, or by the initial
receipt of waste, whichever is later.
6.4.2 Applicability
An owner or operator of any MSWLF unit
that receives wastes on or after October 9,
1993, must prepare a closure plan and place
the plan in the operating record. The plan
must describe specific steps and activities
that will be followed to close the unit at any
time after it first receives waste through the
time it reaches its waste disposal capacity.
The closure plan must include at least the
following information:
• A description of the final cover and the
methods and procedures to be used to
install the cover;
• An estimate of the largest area that will
have to be covered (typically this is the
area that will exist when the final full
capacity is attained); and
• A schedule for completing closure.
The area requiring cover should be
estimated for the operating period from
initial receipt of waste through closure.
The closure plan must be prepared and
placed in the operating record before
October 9, 1993 or by the initial receipt of
waste, whichever is later. The owner or
operator must notify the State Director
when the plan has been completed and
placed in the operating record.
6.4.3 Technical Considerations
The closure plan is a critical document that
describes the steps that an owner or operator
will take to ensure that all units will be
closed in a manner that is protective of
human health and the environment. Closure
plans provide the basis for cost estimates
that in turn establish the amount of financial
responsibility that must be demonstrated.
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The closure plan must describe all areas of
the MSWLF unit that are subject to Part 258
regulations and that are not closed in
accordance with §258.60. Portions of the
landfill unit that have not received a final
cover must be included in the estimate. The
area to be covered at any point during the
active life of the operating unit can be
determined by examining design and
planned operation procedures and by
comparing the procedures with construction
records, operation records, and field
observations. Units are operated frequently
in phases, with some phases conducted on
top of previously deposited waste. If the
owner or operator routinely closes landfill
cells as they are filled, the plan should
indicate the greatest number of cells open at
one time.
The estimate must account for the maximum
amount of waste on-site that may need to be
disposed in the MSWLF unit over the life of
the facility (this includes any waste on-site
yet to be disposed). The maximum volume
of waste ever on-site can be estimated from
the maximum capacity of each unit and any
operational procedures that may involve
transfer of wastes to off-site facilities.
Where insufficient design, construction, and
operational records are found, areas and
volumes may be estimated from topographic
maps and/or aerial photographs.
Steps that may be included in the closure
plan are as follows:
• Notifying State Director of intent to
initiate closure §258.60(e);
• Determining the area to receive final
cover;
• Developing the closure schedule;
• Preparing construction contract
documents and securing a contractor;
• Hiring an independent registered
professional engineer to observe
closure activities and provide
certification;
• Securing borrow material;
• Constructing the cover system;
• Obtaining signed certificate and placing
it in operating record;
• Notifying State Director that certificate
was placed in operating record; and
• Recording notation in deed to land or
other similar instrument.
The closure plan should include a
description of the final cover system and the
methods and procedures that will be used to
install the cover. The description of the
methods, procedures, and processes may
include design documents; construction
specifications for the final cover system,
including erosion control measures; quality
control testing procedures for the
construction materials; and quality
assurance procedures for construction. A
general discussion of the methods and
procedures for cover installation is
presented in Section 6.3.3.
6.5 CLOSURE CRITERIA
40 CFR §258.60(e)-(j)
6.5.1 Statement of Regulation
(e) Prior to beginning closure of
each MSWLF unit as specified in
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Subpart F
§258.60(f), an owner or operator must
notify the State Director that a notice of
the intent to close the unit has been
placed in the operating record.
(f) The owner or operator must
begin closure activities of each MSWLF
unit no later than 30 days after the date
on which the MSWLF unit receives the
known final receipt of wastes or, if the
MSWLF unit has remaining capacity and
there is a reasonable likelihood that the
MSWLF unit will receive additional
wastes, no later than one year after the
most recent receipt of wastes. Extensions
beyond the one-year deadline for
beginning closure may be granted by the
Director of an approved State if the
owner or operator demonstrates that the
MSWLF unit has the capacity to receive
additional wastes and the owner or
operator has taken and will continue to
take all steps necessary to prevent threats
to human health and the environment
from the unclosed MSWLF unit.
(g) The owner or operator of all
MSWLF units must complete closure
activities of each MSWLF unit in
accordance with the closure plan within
180 days following the beginning of
closure as specified in paragraph (f).
Extensions of the closure period may be
granted by the Director of an approved
State if the owner or operator
demonstrates that closure will, of
necessity, take longer than 180 days and
he has taken and will continue to take all
steps to prevent threats to human health
and the environment from the unclosed
MSWLF unit.
(h) Following closure of each MSWLF
unit, the owner or operator must
notify the State Director that a
certification, signed by an independent
registered professional engineer or
approved by Director of an approved
State, verifying that closure has been
completed in accordance with the closure
plan, has been placed in the operating
record.
(i)(l) Following closure of all
MSWLF units, the owner or operator
must record a notation on the deed to the
landfill facility property, or some other
instrument that is normally examined
during title search, and notify the State
Director that the notation has been
recorded and a copy has been placed in
the operating record.
(2) The notation on the deed must
in perpetuity notify any potential
purchaser of the property that:
(i) The land has been used as a
landfill facility; and
(ii) Its use is restricted under
§258.61(c)(3).
(j) The owner or operator may
request permission from the Director of
an approved State to remove the notation
from the deed if all wastes are removed
from the facility.
6.5.2 Applicability
These closure requirements are applicable to
all MSWLF units that receive wastes on or
after October 9, 1993. The owner or
operator is required to:
• Notify the State Director of the intent
to close;
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• Begin closure within 30 days of the last
receipt of waste (or 1 year if there is
remaining capacity and it is likely that it
will be used);
• Complete closure within 180 days
following the beginning of closure (in
approved States, the period of time to
begin or complete closure may be
extended by the Director);
• Obtain a certification, by an independent
registered professional engineer, that
closure was completed in accordance
with the closure plan;
• Place the certificate in the operating
record and notify the State Director; and
• Note on a deed (or some other
instrument) that the land was used as a
landfill and that its use is restricted.
Should all wastes be removed from the
unit in an approved State, the owner or
operator may request permission from
the Director to remove the note on the
deed.
6.5.3 Technical Considerations
Closure activities must begin within 30 days
of the last receipt of waste and must be
completed within 180 days. Some MSWLF
units, such as those in seasonal population
areas, may have remaining capacity but will
not receive the next load of waste for a
lengthy period of time. These MSWLF
units must receive waste within one year or
they must close. Extensions to both the
1-year and the 180-day requirements may be
available to owners or operators of MSWLF
units in approved States. An extension may
be granted if the owner or
operator can demonstrate that there is
remaining capacity or that additional time is
needed to complete closure. These
extensions could be granted to allow
leachate recirculation or to allow for
settlement. The owner or operator must
take, and continue to take, all steps
necessary to prevent threats to human health
and the environment from the unclosed
MSWLF unit. In general, this requirement
should be established for a unit in
compliance with the requirements of Part
258. The owner or operator may need to
demonstrate how access to the unclosed unit
will be controlled prior to closure or receipt
of waste and how the various environmental
control and monitoring systems (e.g.,
surface run-off, surface run-on, leachate
collection, gas control system, and ground-
water and gas monitoring) will be operated
and maintained while the unit remains
unclosed.
Following closure of each MSWLF unit, the
owner or operator must have a certification,
signed by an independent registered
professional engineer, verifying closure. In
approved States, the Director can approve
the certification. The certificate should
verify that closure was completed in
accordance with the closure plan. This
certification should be based on knowledge
of the closure plan, observations made
during closure, and documentation of
closure activities provided by the owner or
operator. The signed certification must be
placed in the operating record and the State
Director must be notified that the
certification was completed and placed in
the record.
After closure of all units at a MSWLF
facility, the owner or operator must record
a notation in the deed, or in records
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Subpart F
typically examined during a title search, that
the property was used as a MSWLF unit and
that its use is restricted under 40 CFR
§258.61(c)(3). Section 258.61(c)(3) states:
"... Post-closure use of the property shall
not disturb the integrity of the final cover,
liner(s), or any other components of the
containment systems or the function of the
monitoring systems unless necessary to
comply with the requirements of Part
258...and... The Director of an approved
State may approve any other disturbance if
the owner or operator demonstrates that
disturbance of the final cover, liner, or other
component of the containment system,
including any removal of waste, will not
increase the potential threat to human health
or the environment."
These restrictions are described further in
Section 6.7 (Post-Closure Plan) of this
document.
The owner or operator may request
permission from the Director of an approved
State to remove the notation to a deed. The
request should document that all wastes
have been removed from the facility. Such
documentation may include photographs,
ground-water and soil testing in the area
where wastes were deposited, and reports of
waste removal activity.
6.6 POST-CLOSURE CARE
REQUIREMENTS
40 CFR §258.61
6.6.1 Statement of Regulation
(a) Following closure of each MSWLF
unit, the owner or operator must conduct
post-closure care. Post-closure
care must be conducted for 30 years,
except as provided under paragraph (b)
of this part, and consist of at least the
following:
(1) Maintaining the integrity and
effectiveness of any final cover, including
making repairs to the cover as necessary
to correct the effects of settlement,
subsidence, erosion, or other events, and
preventing run-on and run-off from
eroding or otherwise damaging the final
cover;
(2) Maintaining and operating the
leachate collection system in accordance
with the requirements in §258.40, if
applicable. The Director of an approved
State may allow the owner or operator to
stop managing leachate if the owner or
operator demonstrates that leachate no
longer poses a threat to human health
and the environment;
(3) Monitoring the ground water
in accordance with the requirements of
Subpart E and maintaining the ground-
water monitoring system, if applicable;
and
(4) Maintaining and operating the
gas monitoring system in accordance with
the requirements of §258.23.
(b) The length of the post-closure
care period may be:
(1) Decreased by the Director of
an approved State if the owner or
operator demonstrates that the reduced
period is sufficient to protect human
health and the environment and this
demonstration is approved by the
Director of an approved State; or
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Closure and Post-Closure
(2) Increased by the Director of an
approved State if the Director of an
approved State determines that the
lengthened period is necessary to protect
human health and the environment.
6.6.2 Applicability
Post-closure care requirements apply to
MSWLF units that stop receiving waste
after October 9, 1993. They also apply to
units that stop receiving waste between
October 9, 1991, and October 9, 1993, and
fail to complete closure within six months
of the final receipt of waste.
Post-closure care requirements are focused
on operating and maintaining the proper
functions of four systems that prevent or
monitor releases from the MSWLF unit:
• Cover system;
• Leachate collection system;
• Ground-water monitoring system; and
• Gas monitoring system.
Owners or operators must comply with these
requirements for a period of 30 years
following closure. In approved States, the
post-closure care period may be shortened if
the owner or operator demonstrates to the
satisfaction of the Director that human
health and the environment are protected.
Conversely, the Director may determine that
a period longer than 30 years is necessary.
The requirement to operate and maintain the
leachate collection system may be
eliminated by the Director of an approved
State if the owner or operator demonstrates
that leachate
does not pose a threat to human health and
the environment.
6.6.3 Technical Considerations
When the final cover is installed, repairs
and maintenance may be necessary to keep
the cover in good working order.
Maintenance may include inspection,
testing, and cleaning of leachate collection
and removal system pipes, repairs of final
cover, and repairs of gas and ground-water
monitoring networks.
Inspections should be made on a routine
basis. A schedule should be developed to
check that routine inspections are
completed. Records of inspections detailing
observations should be kept in a log book so
that changes in any of the MSWLF units can
be monitored; in addition, records should be
kept detailing changes in post-closure care
personnel to ensure that changing personnel
will not affect post-closure care due to lack
of knowledge of routine activities. The
activities and frequency of inspections are
subject to State review to ensure that units
are monitored and maintained for as long as
is necessary to protect human health and the
environment.
Inspection of the final cover may be
performed on the ground and through aerial
photography. Inspections should be
conducted at appropriate intervals and the
condition of the facility should be recorded
with notes, maps, and photographs. The
inspector should take notice of eroded
banks, patches of dead vegetation, animal
burrows, subsidence, and cracks along the
cover. The inspector also should note the
condition of concrete structures (e.g.,
manholes), leachate collection and removal
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Subpart F
pipes, gas monitoring systems, and
monitoring wells.
For larger facilities, annual aerial
photography may be a useful way to
document the extent of vegetative stress and
settlement if either of these has been
observed during routine inspections. It is
important to coordinate the photography
with the site "walkover" to verify
interpretations made from aerial
photographs. Aerial photography should
not be used in place of a site walkover but in
conjunction with the site walkover. An
EPA document (U.S. EPA 1987) provides
further information on using aerial
photography for inspecting a landfill
facility. (See the Reference section at the
end of this chapter.)
Topographic surveys of the landfill unit(s)
may be used to determine whether
settlement has occurred. These should be
repeated every few years until settlement
behavior is established. If settlement plates
are used, they should be permanent and
protected from vandalism and accidental
disturbance (U.S. EPA, 1987). Depressions
caused by settlement may lead to ponding
and should be filled with soil. Excessive
settlement may warrant reconstructing or
adding to portions of the infiltration layer.
Damage caused by settlement such as
tension cracks and tears in the synthetic
membrane should be repaired.
Cover systems that have areas where the
slope is greater than 5 percent may be
susceptible to erosion. Large and small rills
(crevices) may form along the cover where
water has eroded the cover. This may lead
to exposure of the synthetic geomembrane
and, in severe cases, depending on the cover
system installed, exposure of the waste.
Erosion may lead to increased infiltration of
surface water into the landfill. Areas
showing signs of erosion should be repaired.
Certain types of vegetative cover (e.g., turf-
type grasses) may require mowing at least
two times a year. Mowing can aid in
suppression of weed and brush growth, and
can increase the vigor of certain grass
species. Alternatively, certain cover types
(e.g., native prairie grasses) require less
frequent mowing (once every three years)
and may be suitable for certain climates and
facilities where a low-maintenance regime
is preferable. For certain cover types,
fertilization schedules may be necessary to
sustain desirable vegetative growth.
Fertilization schedules should be based on
the cover type present. Annual or biennial
fertilization may be necessary for certain
grasses, while legumes and native
vegetation may require little or no fertilizer
once established. Insecticides may be used
to eliminate insect populations that are
detrimental to vegetation. Insecticides
should be carefully selected and applied
with consideration for potential effects on
surface water quality.
Some leachate collection and removal
systems have been designed to allow for
inspections in an effort to ensure that they
are working properly. Leachate collection
and removal pipes may be flushed and
pressure-cleaned on a regular schedule (e.g.,
annually) to reduce the accumulation of
sediment and precipitation and to prevent
biological fouling.
Similarly, gas collection systems should be
inspected to ensure that they are working
properly. Vents should be checked to
ensure they are not clogged by foreign
matter such as rocks. If not working
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Closure and Post-Closure
properly, the gas collection systems should
be flushed and pressure-cleaned.
At some landfill facilities, leachate
concentrations eventually may become low
enough so as not to pose a threat to human
health or the environment. In an approved
State, the Director may allow an owner or
operator to cease managing leachate if the
owner or operator can demonstrate that the
leachate no longer poses a threat to human
health and the environment. The
demonstration should address direct
exposures of leachate releases to ground
water, surface water, or seeps. Indirect
effects, such as accumulated leachate
adversely affecting the chemical, physical,
and structural containment systems that
prevent leachate release, also should be
addressed in the demonstration.
The threat posed by direct exposures to
leachate released to ground water, to surface
waters, or through seeps may be assessed
using health-based criteria. These criteria
and methods are available through the
Integrated Risk Information System (IRIS)
(a database maintained by U.S. EPA), the
RCRA Facility Investigation Guidance
(U.S. EPA, 1989c), the Risk Assessment
Guidance for Superfund (U.S. EPA, 1989d),
and certain U.S. EPA regulations, including
MCLs established under the Safe Drinking
Water Act and the ambient water quality
criteria under the Clean Water Act. These
criteria and assessment procedures are
described in Chapter 5 (Subpart E) of this
document. Concentrations at the points of
exposure, rather than concentrations in the
leachate in the collection system, may be
used when assessing threats.
6.7 POST-CLOSURE PLAN
40CFR§258.61(c)-(e)
6.7.1 Statement of Regulation
(c) The owner or operator of all
MSWLF units must prepare a written
post-closure plan that includes, at a
minimum, the following information:
(1) A description of the
monitoring and maintenance activities
required in §258.61(a) for each MSWLF
unit, and the frequency at which these
activities will be performed;
(2) Name, address, and telephone
number of the person or office to contact
about the facility during the post-closure
period; and
(3) A description of the planned
uses of the property during the post-
closure period. Post-closure use of the
property shall not disturb the integrity of
the final cover, liner(s), or any other
components of the containment system,
or the function of the monitoring systems
unless necessary to comply with the
requirements in Part 258. The Director
of an approved State may approve any
other disturbance if the owner or
operator demonstrates that disturbance
of the final cover, liner or other
component of the containment system,
including any removal of waste, will not
increase the potential threat to human
health or the environment.
(d) The owner or operator must
notify the State Director that a post-
closure plan has been prepared and
placed in the operating record no later
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Subpart F
than the effective date of this part,
October 9, 1993, or by the initial receipt
of waste, whichever is later.
(e) Following completion of the
post-closure care period for each
MSWLF unit, the owner or operator
must notify the State Director that a
certification, signed by an independent
registered professional engineer or
approved by the Director of an approved
State, verifying that post-closure care has
been completed in accordance with the
post-closure plan, has been placed in the
operating record.
6.7.2 Applicability
Owners and operators of existing units, new
units, and lateral expansions of existing
MSWLF units that stop receiving waste
after October 9, 1993 are required to
provide a post-closure plan. MSWLF units
that received the final waste shipment
between October 9, 1991 and October 9,
1993 but failed to complete installation of a
final cover system within six months of the
final receipt of waste also are required to
provide a post-closure plan.
The post-closure plan describes the
monitoring activities that will be conducted
throughout the 30-year period. The plan
also establishes:
• The schedule or frequency at which
these activities are conducted;
• Name, address, and telephone number of
a person to contact about the facility;
• A description of a planned use that does
not disturb the final cover; and
• The procedure for verifying that post-
closure care was provided in
accordance with the plan.
In approved States only, the owner or
operator may request the Director to
approve a use that disturbs the final cover
based on a demonstration that the use will
not increase the potential threat to human
health and the environment.
6.7.3 Technical Considerations
The State Director must be notified that a
post-closure plan, describing the
maintenance activities required for each
MSWLF unit, has been placed in the
operating record. The post-closure plan
should provide a schedule for routine
maintenance of the MSWLF unit systems.
These systems include the final cover
system, the leachate collection and removal
system, and the landfill gas and ground-
water monitoring systems.
The plan must include the name, address,
and telephone number of the person or
office to contact regarding the facility
throughout the post-closure period.
Additionally, the planned uses of the
property during the post-closure period must
be provided in the plan. These uses may not
disturb the integrity of the final cover
system, the liner system, and any other
components of the containment or
monitoring systems unless necessary to
comply with the requirements of Part 258.
Any other disturbances to any of the
MSWLF components must be approved by
the Director of an approved State. An
example of an acceptable disturbance may
include remedial action necessary to
minimize the threat to human health and the
environment.
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Closure and Post-Closure
Following completion of the post-closure
care period, the State Director must be
notified that an independent registered
professional engineer has verified and
certified that post-closure care has been
completed in accordance with the post-
closure plan and that this certification has
been placed in the operating record.
Alternatively, the Director of an approved
State may approve the certification.
Certification of post-closure care should be
submitted for each MSWLF unit.
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Subpart F
6.8 FURTHER INFORMATION
6.8.1 References
Giroud, J.P., Bonaparte, R., Beech, J.F., and Gross, B.A., "Design of Soil Layer -Geosynthetic
Systems Overlying Voids". Journal of Geotextiles and Geomembranes, Vol. 9, No. 1, 1990,
pp. 11-50.
Richardson, G.N. and R.M. Koerner, (1987). "Geosynthetic Design Guidance for Hazardous
Waste Landfill Cells and Surface Impoundments"; Hazardous Waste Engineering Research
Laboratory; USEPA, Office of Research and Development; Cincinnati, Ohio; Contract No.
68-07-3338.
U.S. EPA, (1987). "Design, Construction and Maintenance of Cover Systems for Hazardous
Waste: An Engineering Guidance Document"; PB87-19156; EPA/600/2-87/039; U.S.
Department of Commerce, National Technical Information Service; U.S. Army Engineering
Waterways Experiment Station; Vicksburg, Mississippi.
U.S. EPA, (1988). "Guide to Technical Resources for the Design of Land Disposal Facilities";
EPA/625/6-88/018; U.S. EPA; Risk Reduction Engineering Laboratory and Center for
Environmental Research Information; Office of Research and Development; Cincinnati,
Ohio 45268.
U.S. EPA, (1989a). "Seminar Publication - Requirements for Hazardous Waste Landfill
Design, Construction and Closure"; EPA/625/4-89/022; U.S. EPA; Center for
Environmental Research Information; Office of Research and Development; Cincinnati,
Ohio 45268.
U.S. EPA, (1989b). "Technical Guidance Document: Final Covers on Hazardous Waste
Landfills and Surface Impoundments"; EPA/530-SW-89-047; U.S. EPA; Office of Solid
Waste and Emergency Response; Washington, D.C. 20460.
U.S. EPA, (1989c). "Interim Final: RCRA Facility Investigation (RFI) Guidance"; EPA
530/SW-89-031; U.S. EPA; Waste Management Division; Office of Solid Waste; U.S.
Environmental Protection Agency; Volumes I-IV; May 1989.
U.S. EPA, (1989d). "Interim Final: Risk Assessment Guidance For Superfund; Human Health
Evaluation Manual Part A"; OS-230; U.S. EPA; Office of Solid Waste and Emergency
Response; July 1989.
U.S. EPA, (1991). "Seminar Publications - Design and Construction of RCRA/CERCLA Final
Covers"; EPA/625/4-91/025; U.S. EPA, Office of Research and Development; Washington,
D.C.20460.
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6.8.2 Organizations
U.S. Department of Agriculture
Soil Conservation Service (SCS)
P.O. Box 2890
Washington, D.C. 20013-2890
(Physical Location: 14th St. and Independence Ave. NW.)
(202)447-5157
Note: This is the address of the SCS headquarters. To obtain the SCS technical guidance
document concerning the Universal Soil Loss Equation (entitled "Predicting Rainfall
Erosion Loss, Guidebook 537," 1978), contact SCS regional offices located
throughout the United States.
6.8.3 Models
Schroeder, et al., (1988). "The Hydrologic Evaluation of Landfill Performance (HELP)
Model"; U.S.EPA; U.S. Army Engineer Waterways Experiment Station; Vicksburg, MS
39181-0631; October 1988.
Schroeder, P.R., A.C. Gibson, J.M. Morgan, T.M. Walski, (1984). "The Hydrologic Evaluation
of Landfill Performance (HELP) Model, Volume I - Users Guide for Version I (EPA/530-
SW-84-009), and Volume II - Documentation for Version I (EPA/530-SW-84-010); U.S.
Army Engineer Waterways Experiment Station, Vicksburg, MS, June 1984.
6.8.4 Databases
Integrated Risk Information System (IRIS), U.S. Environmental Protection Agency, Office of
Research and Development, Cincinnati, Ohio.
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