United States Solid Waste and EPA530-R-93-017

Environmental Protection Emergency Response November 1993

Agency (5305) www.epa.gov/osw

Solid Waste Disposal

Facility Criteria

Technical Manual
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.
i Revised April 13, 1998

TABLE OF CONTENTS

INTRODUCTION ......................................................... iv

CHAPTER 1. SUBPART 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 (cont.) 40 CFR §258.1 (c)-(e) .... 5

1.4 SMALL LANDFILL EXEMPTIONS 40 CFR §258.1 (f) ................... 7

1.5 APPLICABILITY 40 CFR §258.1 (g)-(j) ............................... 9

1.6 DEFINITIONS 40 CFR §258.2 ..................................... 10

1.7 CONSIDERATION OF OTHER FEDERAL LAWS 40 CFR §258.3 ......... 14

CHAPTER 2. SUBPART B ................................................. 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 IMPACT ZONES 40 CFR §258.14 .......................... . 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

CHAPTER 3. SUBPART C ................................................. 73

3.1 INTRODUCTION ............................................. . 76

3.2 PROCEDURES FOR EXCLUDING THE RECEIPT OF HAZARDOUS

WASTE 40 CFR §258.20 ....................................... . 77

3.3 COVER MATERIAL REQUIREMENTS 40 CFR §258.21 .............. . 84

3.4 DISEASE VECTOR CONTROL 40 CFR §258.22 .................... . 85

3.5 EXPLOSIVE GASES CONTROL 40 CFR §258.23 ................... . 87

3.6 AIR CRITERIA 40 CFR §258.24 ................................ . 101

3.7 ACCESS REQUIREMENT 40 CFR §258.25 ....................... . 103

3.8 RUN-ON/RUN-OFF CONTROL SYSTEMS 40 CFR §258.26 .......... . 104

3.9 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 ii

CHAPTER 4. SUBPART D ................................................ 117

4.1 INTRODUCTION ............................................ 121

4.2 PERFORMANCE-BASED DESIGN 40 CFR §258.40 ................ 122

4.3 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 §258.40(e) ......................... 191

4.6 FURTHER INFORMATION .................................... 193

CHAPTER 5. SUBPART E ................................................ 205

5.1 INTRODUCTION ............................................ 211

5.2 APPLICABILITY 40 CFR §258.50 (a) & (b) ....................... 211

5.3 COMPLIANCE SCHEDULE 40 CFR § 258.50 (c) ................... 214

5.4 ALTERNATIVE COMPLIANCE SCHEDULES 40 CFR 258.50 (d)(e) & (g)

.......................................................... 215

5.5 QUALIFICATIONS 40 CFR 258.50 (f) ........................... 217

5.6 GROUND-WATER MONITORING SYSTEMS 40 CFR §258.51 (a)(b)(d)

.......................................................... 219

5.7 GROUND-WATER MONITORING WELL DESIGN AND

CONSTRUCTION 40 CFR §258.51 (c) ........................... 241

5.8 GROUND-WATER SAMPLING AND ANALYSIS REQUIREMENTS 40

CFR §258.53 ................................................ 253

5.9 STATISTICAL ANALYSIS 40 CFR §258.53 (g)-(I) ................. 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(g) ....... 286

5.13 ASSESSMENT MONITORING PROGRAM 40 CFR §258.55(h)-(j) ..... 289

5.14 ASSESSMENT OF CORRECTIVE MEASURES 40 CFR §258.56 ...... 291

5.15 SELECTION OF REMEDY 40 CFR §258.57 (a)-(b) ................. 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 (b)-(d) .......................................... . 309

5.21 IMPLEMENTATION OF THE CORRECTIVE ACTION PROGRAM 40

CFR §258.58 (e)-(g) .......................................... . 311

5.22 FURTHER INFORMATION .................................... . 313
iii Revised April 13, 1998

CHAPTER 6. SUBPART F ................................................ 319

6.1 INTRODUCTION ............................................. 322

6.2 FINAL COVER DESIGN 40 CFR §258.60(a) ........................ 322

6.3 ALTERNATIVE FINAL COVER DESIGN 40 CFR §258.60(b) ......... 332

6.4 CLOSURE PLAN 40 CFR §258.60(c)-(d) ........................... 338

6.5 CLOSURE CRITERIA 40 CFR §258.60(e)-(j) ....................... 339

6.6 POST-CLOSURE CARE REQUIREMENTS 40 CFR §258.61 ........... 342

6.7 POST-CLOSURE PLAN 40 CFR §258.61(c)-(e) ..................... 345

6.8 FURTHER INFORMATION ..................................... 348

APPENDICES

CHAPTER 2

APPENDIX I FAA Order 5200.5A ............................................ 69

CHAPTER 3

APPENDIX I - SPECIAL WASTE ACCEPTANCE AGREEMENT ................. 115
 The Agency originally intended to extend to Indian Tribes the same opportunity to apply for permit program 1 

approval as is available to States, but a court decision blocked this approach. See the Tribal Process section

below for complete details.

 EPA finalized several revisions to 40 CFR Part 258 on October 1, 1993 (58 FR 51536) and issued a correction 2

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

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 membrane liner over 2 feet compacted soil with a

hydraulic conductivity of no more than 1x10-

 cm/sec. 7

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).

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 <www.epa.gov/osw>.

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. Whether in a State or 1

in Indian Country, landfill owners/operators must

comply with the revised MSWLF Criteria. 2

State Process

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
Introduction

v Revised April 13, 1998

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, groundwater 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
Introduction

 Backcountry Against Dumps v. EPA, 100 F.3d 147 (D.C. Cir. 1996). 3

 This manual uses the term “Indian Country” as defined in 40 CFR § 258.2. 4

 In the original 40 CFR Part 258 rulemaking, promulgated October 9, 1991, the Agency provided an 5

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

decision , however, the court ruled that EPA cannot approve tribal permitting programs. The

3

Agency has therefore developed a site-specific rulemaking process to meet its goal of quickly and

efficiently providing owners/operators in Indian Country the same flexibility that is available to

4

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)(1))

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)(1) 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
Introduction

vii Revised April 13, 1998

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;
Introduction

Revised April 13, 1998 viii

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. 
SUMMARY OF CHANGES TO THE EFFECTIVE DATES OF THE MSWLF CRITERIA

MSWLF Units MSWLF Units Accepting MSWLF Units That MSWLF Units

Accepting Greater 100 TPD or Less; Are Not Meet the Small Receiving Floodthan 100 TPD on the NPL; and Are Landfill Exemption in Related Waste

Located in a State That 40 CFR §258.1(f)

Has Submitted an

Application for Approval

by 10/9/93, or on Indian

Lands or Indian Country

General effective date. October 9, 1993 April 9, 1994 October 9, 1997; exempt Up to October 9, 1994 1,2,3

This is the effective date for location, requirements

operation, design, and closure/postclosure.

from the design as determined by State

Date by which to install final cover October 9, 1994 October 9, 1994 October 9, 1998 Within one year of date

if cease receipt of waste by the determined by State; no

general effective date. later than October 9, 2,3

1995

Effective date of ground-water Prior to receipt of waste October 9, 1993 for new Exempt from the October 9, 1993 for

monitoring and corrective action. for new units; October units; October 9, 1994 ground-water new units; October 9, 2,3

9, 1994 through October through October 9, 1996 for monitoring 1994 through October

9, 1996 for existing existing units and lateral requirements. 9, 1996 for existing 

units and lateral expansions units and lateral

expansions expansions

5

Effective date of financial April 9, 1997 April 9, 1997 October 9, 1997 April 9, 1997

assurance requirements.3,4

 If a MSWLF unit receives waste after this date, the unit must comply with all of Part 258. 1

 See the final rule and preamble published on October 1, 1993 (58 FR 51536) for a full discussion of all changes and related conditions. 2

 See the final rule and preamble published on October 6, 1995 (60 FR 52337) for a full discussion of all changes and related conditions. 3

 See the final rule and preamble published on April 7, 1995 (60 FR 17649) for a discussion of this delay. 4

 See the final rule and preamble published on September 25, 1990 (61 FR 50409) for a discussion of the ground-water monitoring exemption. 5
1

CHAPTER 1

SUBPART A

GENERAL
2

CHAPTER 1

SUBPART A

TABLE OF CONTENTS

1.1 INTRODUCTION .................................................... 3

1.2 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

1.3 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

1.4 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

1.5 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

1.6 DEFINITIONS 40 CFR §258.2 ......................................... 10

1.6.1 Statement of Regulation .......................................... 10

1.6.2 Applicability ................................................... 13

1.6.3 Technical Considerations ......................................... 13

1.7 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
3

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 CFR Part 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.
Subpart A

4

1.2 PURPOSE, SCOPE, AND 1.2.3 Technical Considerations

APPLICABILITY

40 CFR §258.1 (a)(b) Criteria that define a solid waste disposal

1.2.1 Statement of Regulation RCRA (Criteria for Classification of Solid

(a) The purpose of this part is to Definitions pertaining to the revised Criteria

establish minimum national criteria are included in the definition section of Part

under the Resource Conservation and 258. A MSWLF unit is defined as a discrete

Recovery Act (RCRA or the Act), as area of land or excavation that receives

amended, for all municipal solid waste household waste, and that is not considered

landfill (MSWLF) units and under the a land application unit, surface

Clean Water Act, as amended, for impoundment, injection well, or waste pile

municipal solid waste landfills that are as those terms are defined under §257.2. An

used to dispose of sewage sludge. These existing unit is a solid waste disposal unit

minimum national criteria ensure the that is receiving solid waste as of October 9,

protection of human health and the 1993. A lateral expansion is a horizontal

environment. expansion of the waste boundaries of an

(b) These Criteria apply to owners MSWLF unit that has not received waste

and operators of new MSWLF units, before October 9, 1993.

existing MSWLF units, and lateral

expansions, except as otherwise In addition to household waste, a MSWLF

specifically provided in this part; all unit may receive commercial waste, nonother solid waste disposal facilities and hazardous solid waste from industrial

practices that are not regulated under facilities including non-hazardous sludges,

Subtitle C of RCRA are subject to the and sewage sludge from wastewater

criteria contained in Part 257. treatment plants. The terms commercial

1.2.2 Applicability waste are defined in §258.2 (Definitions). 

Owners and operators of MSWLF units that The types of landfills regulated under Part

receive municipal solid waste or that receive 257 include those facilities that receive:

municipal waste combustion ash and are not

currently regulated under Subtitle C of ! Construction and demolition debris

RCRA must comply with the Criteria. only;

Furthermore, MSWLF units that receive and

co-dispose sewage sludge must comply with ! Tires only; and

Part 258 to be in compliance with Sections

309 and 405(e) of the Clean Water Act. ! Non-hazardous industrial waste only.

facility are contained within Part 257 of

Waste Disposal Facilities and Practices).

existing MSWLF unit. A new unit is a

solid waste, industrial waste and household
General

5

MSWLF units are not intended, nor receiving waste before October 9, 1993

allowed, to receive regulated quantities of are exempt from all the requirements of

hazardous wastes. Should a MSWLF Part 258, except the final cover

owner/operator discover that a shipment requirement specified in Section 258.60(a).

contains regulated quantities of hazardous The final cover must be installed within six

waste while still in the possession of the months of last receipt of wastes. Owners or

transporter, the owner/operator should operators of MSWLF units described in

refuse to accept the waste from the this paragraph that fail to complete cover

transporter. If regulated quantities of installation within this six month period

hazardous wastes are discovered after will be subject to all the requirements of

accepting the waste from the transporter, the Part 258, unless otherwise specified.

owner/operator must return the shipment or

manage the wastes in accordance with (e) All MSWLF units that receive

RCRA Subtitle C requirements. waste on or after October 9, 1993 must

Subtitle C of RCRA establishes procedures unless otherwise specified.

for making a hazardous waste

determination. These procedures are 1.3.2 Applicability

summarized in Chapter 3 and Appendix B of

this document. The applicability of Part 258, in its entirety or

1.3 PURPOSE, SCOPE, MSWLF unit relative to the date of

AND APPLICABILITY (cont.) publication, October 9, 1991, or the effective

40 CFR §258.1 (c)-(e) date of the rule, October 9, 1993 (see Figure

1.3.1 Statement of Regulation* exist:

*[NOTE: EPA finalized several revisions (1) The MSWLF unit received its last

to 40 CFR Part 258 on October 1, 1993 load of waste prior to October 9, 1991. These

(58 FR 51536) and issued a correction facilities are exempt from all requirements of

notice on October 14, 1993 (58 FR 53136). the Criteria. 

These revisions delay the effective date

for some categories of landfills. More (2) The last load of waste was

detail on the content of the revisions is received after October 9, 1991, but before

included in the introduction.] October 9, 1993. The owners and operators

(c) These Criteria do not apply to requirements of §258.60(a). If the final cover

municipal solid waste landfill units that do is not installed within six (6) months of the

not receive waste after October 9, 1991. last receipt of wastes, the owners and

(d) MSWLF units that receive waste requirements of Part 258.

after October 9, 1991 but stop

comply with all requirements of Part 258

with exemptions to specific requirements, is

based upon the operational status of the

1-1). Three possible operational scenarios

must comply only with the final cover

operators will be required to comply with all
Subpart A

6

Figure 1-1

Applicability Flow Chart
General

7

(3) The MSWLF unit continues to 1.4 SMALL LANDFILL

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 cm/sec, whichever is less. The system -5

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.

EXEMPTIONS

40 CFR §258.1 (f)

1.4.1 Statement of Regulation

(f)(1) 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)(1)(i) or (f)(1)(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)(1)(i) or (ii), the owner or

operator must notify the State
Subpart A

8

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.

Director of such contamination and, and corrective action requirements. The

thereafter, comply with Subparts D [and

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 groundwater 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 groundwater contamination, the landfill unit owner

or operator is eligible for the exemption

from the design, ground-water monitoring,

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 demonstrate 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:
General

9

Compliance with the 20 tons per day consideration of technical, economic, and

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 groundwater 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

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

10

to satisfy these Criteria violate sections criminal actions enforced under Section 309

309 and 405(e) of the Clean Water Act. of the Clean Water Act.

(j) The effective date of this part is

October 9, 1993, unless otherwise 1.6 DEFINITIONS

specified.* 40 CFR §258.2

*[NOTE: EPA finalized several revisions 1.6.1 Statement of Regulation

to 40 CFR Part 258 on October 1, 1993

(58 FR 51536) and issued a correction Unless otherwise noted, all terms

notice on October 14, 1993 (58 FR 53136). contained in this part are defined by their

These revisions delay the effective date plain meaning. This section contains

for some categories of landfills. More definitions for terms that appear

detail on the content of the revisions is throughout this Part; additional

included in the introduction.] definitions appear in the specific sections

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

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 nonmanufacturing activities, excluding

residential and industrial wastes. 
General

11

Director of an approved State means the products; inorganic chemicals; iron and

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 limited to, waste resulting from the following

manufacturing processes: Electric power

generation; fertilizer/agricultural

chemicals; food and related products/bysteel manufacturing; leather and leather

products; nonferrous metals manufacturing/foundries; organic chemicals;

plastics and resins manufacturing; pulp

and paper industry; rubber and miscellaneous 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.
Subpart A

12

Open burning means the combustion of Solid waste means any garbage, or refuse,

solid waste without: sludge from a wastewater treatment

(1) Control of combustion air to air pollution control facility and other

maintain adequate temperature for discarded material, including solid,

efficient combustion, liquid, semi-solid, or contained gaseous

(2) Containment of the commercial, mining, and agricultural

combustion reaction in an enclosed device operations, and from community

to provide sufficient residence time and activities, but does not include solid or

mixing for complete combustion, and dissolved materials in domestic sewage,

(3) Control of the emission of the irrigation return flows or industrial

combustion products. discharges that are point sources subject

Operator means the person(s) responsible source, special nuclear, or by-product

for the overall operation of a facility or material as defined by the Atomic Energy

part of a facility. Act of 1954, as amended (68 Stat. 923).

Owner means the person(s) who owns a State means any of the several States, the

facility or part of a facility. District of Columbia, the Commonwealth

Run-off means any rainwater, leachate, American Samoa, and the Commonor other liquid that drains over land from wealth of the Northern Mariana Islands.

any part of a facility.

Run-on means any rainwater, leachate, or administrative officer of the State agency

other liquid that drains over land onto responsible for implementing the State

any part of a facility. municipal solid waste permit program or

Saturated zone means that part of the

earth's crust in which all voids are filled Uppermost aquifer means the geologic

with water. formation nearest the natural ground

Sludge means any solid, semi-solid, or aquifers that are hydraulically

liquid waste generated from a municipal, interconnected with this aquifer within

commercial, or industrial wastewater the facility's property boundary.

treatment plant, water supply treatment

plant, or air pollution control facility Waste management unit boundary means

exclusive of the treated effluent from a a vertical surface located at the

wastewater treatment plant. hydraulically downgradient limit of the

plant, water supply treatment plant, or

material resulting from industrial,

or solid or dissolved materials in

to permit under 33 U.S.C. 1342, or

of Puerto Rico, the Virgin Islands, Guam,

State Director means the chief

other system of prior approval.

surface that is an aquifer, as well as lower

unit. This vertical surface extends down

into the uppermost aquifer.
General

13

1.6.2 Applicability must yield enough water for ground-water

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 258.

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 implementation 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

monitoring samples. An unconfined 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
Subpart A

14

land surface would be covered by waste 1.7 CONSIDERATION OF

after October 9, 1993. Expansions to the OTHER FEDERAL LAWS

existing unit have to be consistent with past 40 CFR §258.3

operating procedures or operating practices

to ensure good management. 1.7.1 Statement of Regulation

Spreading wastes over a large area to The owner or operator of a municipal

increase the size of an existing unit, prior to solid waste landfill unit must comply with

the effective date would not be consistent any other applicable Federal rules, laws,

with good management practices. If a new regulations, or other requirements.

land surface adjacent to an existing unit first

receives waste after October 9, 1993, that 1.7.2 Applicability

area is classified as a lateral expansion and

therefore, is subject to the new design Owners and operators of MSWLF units

standards. However, Part 258 regulations must comply with Federal regulations, laws,

provide the flexibility for approved States to rules or requirements that are in effect at the

determine what would constitute a lateral time of publication of Part 258 or that may

expansion. become effective at a later date.

Municipal solid waste landfill unit: 1.7.3 Technical Considerations

Municipal solid waste landfill units are units

that receive household waste, such as that Specific sections of Part 258 reference

from single and multiple residences, hotels major Federal regulations that also may be

and motels, bunkhouses, ranger stations, applicable to MSWLF units regulated under

crew quarters, campgrounds, picnic grounds Part 258. These regulations include the

and day-use recreation areas. Other Subtitle Clean Water Act (wetlands, sludge disD wastes, such as commercial solid waste, posal, point and non-point source disnonhazardous sludge, and industrial solid charges), the Clean Air Act, other parts of

waste, may be disposed of in a municipal RCRA (Subtitle C if the MSWLF unit

solid waste landfill. inadvertently receives regulated hazardous

New municipal solid waste landfill unit: Furthermore, additional Federal rules, laws,

A new MSWLF unit is any unit that has not or regulations may need to be considered.

received waste prior to October 9, 1993. The owner or operator of the MSWLF unit

Lateral expansions are considered new is responsible for deter-mining the

MSWLF units for the purpose of location conditions present at the facility that may

restrictions and design standards. New require consideration of other Federal Acts,

MSWLF units are subject to all rules, requirements, or regulations. Careful

requirements of Part 258. review of the Part 258 Criteria will help to

waste), and the Endangered Species Act.

identify most of the major Federal laws that

may be applicable to a particular MSWLF

unit.
15

CHAPTER 2

SUBPART B

LOCATION CRITERIA
16

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 IMPACT ZONES 40 CFR §258.14 ................................ 41

2.6.1 Statement of Regulation .......................................... 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
17

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

CFR §258.16 ....................................................... 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
18

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.
Location Criteria

19

Table 2-1

Location Criteria Standards

Restricted Applies to New Units Approved State"

Location Existing Units and Lateral OR 

Applies to "Director of an

Expansions Retain

Make

Demonstration to

Demonstration in

Operating Record

Existing

Units Must

Close if 

Demonstration Cannot

be Made

 Airport Yes Yes Operating Record Yes

 Floodplains Yes Yes Operating Record Yes

 Wetlands No Yes Director N/A

 Fault Areas No Yes Director N/A

 Seismic Impact No Yes Director N/A

 Zones

 Unstable Areas Yes Yes Operating Record Yes

2.2 AIRPORT SAFETY (b) Owners or operators proposing to

 40 CFR §258.10 site new MSWLF units and lateral

2.2.1 Statement of Regulation airport runway end used by turbojet

(a) Owners or operators of new affected airport and the Federal Aviation

MSWLF units, existing MSWLF units, and Administration (FAA). 

lateral expansions that are located within

10,000 feet (3,048 meters) of any airport (c) The owner or operator must place

runway end used by turbojet aircraft or the demonstration in paragraph (a) in the

within 5,000 feet (1,524 meters) of any operating record and notify the State

airport runway end used by only piston- Director that it has been placed in the

type aircraft must demonstrate that the operating record. 

units are designed and operated so that the

MSWLF unit does not pose a bird hazard (d) For purposes of this section:

to aircraft.

expansions within a five-mile radius of any

or piston-type aircraft must notify the
Subpart B

20

(1) Airport means public-use airport pose bird hazards to aircraft. The regulation

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 5200.5A

(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

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
Location Criteria

21

expansion. Topographic maps (USGS 15- • Shredding, milling, or baling the

minute series) or State, regional, or local waste-containing food sources; and

government agency maps providing similar or

better accuracy would allow direct scaling, or • Eliminating the acceptance of wastes

measurement, of the closest distance from the at the landfill unit that represent a

end of a runway to the nearest MSWLF unit. food source for birds (by alternative

The measurement can be made by drawing a waste management techniques such as

circle of appropriate radius (i.e., 5,000 ft., source separation and composting or

10,000 ft, or 5 miles, depending on the airport waste minimization).

type) from the centerline of each runway end.

The measurement only should be made Frequent covering of wastes that represent a

between the end of the runway and the nearest food source for the birds effectively reduces

MSWLF unit perimeter, not between any the availability of the food supply. Depending

other boundaries. on site conditions such as volume and types

To determine whether the runway is part of a of the working face, cover may need to be

public use airport and to determine whether applied several times a day to keep the

all applicable public airports have been inactive portion of the working face small

identified, the MSWLF unit owner/operator relative to the area accessible to birds. By

should contact the airport administration or maintaining a small working face, spreading

the regional FAA office. This rule does not and compaction equipment are concentrated

apply to private airfields. in a small area that further disrupts

The MSWLF unit design features and

operational practices can have a significant Milling or shredding municipal solid waste

effect on the likelihood of increased breaks up food waste into smaller particle

bird/aircraft collisions. Birds may be attracted sizes and distributes the particles throughout

to MSWLF units to satisfy a need for water, non-food wastes, thereby diluting food wastes

food, nesting, or roosting. Scavenger birds to a level that frequently makes the mixture

such as starlings, crows, blackbirds, and gulls no longer attractive as a food supply for birds.

are most commonly associated with active Similarly, baling municipal solid waste

landfill units. Where bird/aircraft collisions reduces the surface area of waste that may be

occur, these types of birds are often involved available to scavenging birds.

due to their flocking, feeding, roosting, and

flight behaviors. Waste management The use of varying bird control techniques

techniques to reduce the supply of food to may prevent the birds from adjusting to a

these birds include: single method. Methods such as visual

• Frequent covering of wastes that mixed success in an attempt to discourage

provide a source of food; birds from food scavenging. Visual

of wastes, waste delivery schedules, and size

scavenging by the birds. 

deterrents or sound have been used with

deterrents include realistic models (still or

animated) of the bird's natural predators
Subpart B

22

(e.g., humans, owls, hawks, falcons). Sounds approach to addressing this part of the airport

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

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
Location Criteria

23

Figure 2-1.

Bird Control Device
Subpart B

24

requested from the FAA. Topographic maps (3) Washout means the carrying away

(e.g., USGS 15-minute series) or other of solid waste by waters of the base flood.

similarly accurate maps showing the

relationship of the airport runway and the 2.3.2 Applicability

MSWLF unit should provide a suitable basis

for determining whether the FAA should be Owners/operators of new MSWLF units,

notified. existing MSWLF units, and lateral

2.3 FLOODPLAINS demonstrate that the units will not restrict

 40 CFR §258.11 the flow of a 100-year flood nor reduce the

2.3.1 Statement of Regulation in a wash-out of solid waste, must close the

(a) Owners or operators of new and temporary storage capacity of a

MSWLF units, existing MSWLF units, and floodplain. Higher flood levels and greater

lateral expansions located in 100-year flood damage both upstream and

floodplains must demonstrate that the unit downstream can be created and could cause

will not restrict the flow of the 100-year a potential hazard to human health and

flood, reduce the temporary water storage safety. The rule does not prohibit locating

capacity of the floodplain, or result in a MSWLF unit in a 100-year floodplain; for

washout of solid waste so as to pose a example, the owner or operator is allowed

hazard to human health and the to demonstrate that the unit will comply

environment. The owner or operator must with the flow restriction, temporary

place the demonstration in the operating storage, and washout provisions of the

record and notify the State Director that it regulation. If a demonstration can be made

has been placed in the operating record. that the landfill unit will not pose threats,

(b) For purposes of this section: operating record, and the State Director

(1) Floodplain means the lowland and made and placed in the record. If the

relatively flat areas adjoining inland and demonstration cannot be made for an

coastal waters, including flood-prone areas existing MSWLF unit, then the MSWLF

of offshore islands, that are inundated by unit must be closed in 5 years in accordance

the 100-year flood. with §258.60, and the owner or operator

(2) 100-year flood means a flood that accordance with §258.61 (see §258.16).

has a 1-percent or greater chance of The closure deadline may be extended for

recurring in any given year or a flood of a up to two years by the Director of an

magnitude equaled or exceeded once in 100 approved State if the owner or operator can

years on the average over a significantly demonstrate that no available alternative

long period. disposal capacity exists and there

expansions of existing units located in a

100-year river floodplain who cannot

water storage capacity, and will not result

unit(s). A MSWLF unit can affect the flow

the demonstration must be placed in the

must be notified that the demonstration was

must conduct post-closure activities in
Location Criteria

25

is no immediate threat to human health and Guidance on using FIRMs is provided in

the environment (see Section 2.8). "How to Read a Flood Insurance Rate Map"

2.3.3 Technical Considerations "The National Flood Insurance Program

Compliance with the floodplain criterion communities that may not be involved in the

begins with a determination of whether the National Flood Insurance Program but which

MSWLF unit is located in the 100-year have FIRMs or Floodway maps published.

floodplain. If the MSWLF unit is located in Maps and other FEMA publications may be

the 100-year floodplain, then the owner or obtained from the FEMA Distribution Center

operator must demonstrate that the unit will (see Section 2.9.2 for the address). Areas not

not pose a hazard to human health and the covered by the FIRMs or Floodway maps

environment due to: may be included in floodplain maps available

! Restricting the base flood flow; the U.S. Geological Survey, the U.S. Soil

! Reducing the temporary water storage; Management, the Tennessee Valley

and Authority, and State, Tribal, and local

! Resulting in the washout of solid waste.

Guidance for identifying floodplains and maps may have undergone modification for

demonstrating facility compliance is provided hydropower or flood control projects and,

below. therefore, the floodplain boundaries

Floodplain Identification representative. It may be necessary to

River floodplains are readily identifiable as air photographs to identify current river

the flat areas adjacent to the river's normal channel modifications and land use

channel. One hundred-year floodplains watersheds that could affect floodplain

represent the sedimentary deposits formed by designations. If floodplain maps are not

floods that have a one percent chance of available, and the facility is located within a

occurrence in any given year and that are floodplain, then a field study to delineate the

identified in the flood insurance rate maps 100-year floodplain may be required. A

(FIRMs) and flood boundary and floodway floodplain delineation program can be based

maps published by the Federal Emergency primarily on meteorological records and

Management Agency (FEMA) (see Figure physiographic information such as existing

2-2). Areas classified as "A" zones are and planned watershed land use,

subject to the floodplain location restriction. topography, soils and geologic mapping,

Areas classified as "B" or "C" zones are not and air photo interpretation of

subject to the restriction, although care should geomorphologic (land form) features. The

be taken to design facilities capable of United States Water Resource Council

withstanding some potential flooding. (1977) provides information for determining

published by FEMA. FEMA also publishes

Community Status Book" that lists

through the U.S. Army Corps of Engineers,

Conservation Service, the Bureau of Land

agencies.

Many of the river channels covered by these

represented may not be accurate or

compare the floodplain map series to recent
26

Figure 2-2

Example Section of Flood Plain Map
Location Criteria

27

the potential for floods in a given location by impinging river waters. Depending on the

stream gauge records. Estimation of the peak amount of inundation, the landfill unit may

discharge also allows an estimation of the act as a channel side slope or bank or it may

probability of exceeding the 100-year flood. be isolated as an island within the overbank

Engineering Considerations the river velocity would be part of a proper

If the MSWLF unit is within the 100-year

floodplain, it must be located so that the The assessment of flood water velocity

MSWLF unit does not significantly restrict requires that the channel cross section be

the base flood flow or significantly reduce known above, at, and below the landfill unit.

temporary storage capacity of the floodplain. Friction factors on the overbank are deterThe MSWLF unit must be designed to prevent mined from the surface conditions and vegethe washout of solid waste during the tation present. River hydrologic models may

expected flood event. The rule requires that be used to simulate flow levels and estimate

floodplain storage capacity, and flow velocities through these river cross sections.

restrictions that occur as the result of the

MSWLF unit, do not pose a hazard to human The Army Corps of Engineers (COE, 1982)

health and the environment. has developed several numerical models to

The demonstration that these considerations flow parameters, the effect of obstructions on

are met relies on estimates of the flow flow levels, the simulation of flood control

velocity and volume of floodplain storage in structures, and sediment transport. These

the vicinity of the MSWLF unit during the methods may or may not be appropriate for a

base flood. The assessment should consider site; however, the following models provide

the floodplain storage capacity and floodwater well-tested analytical approaches:

velocities that would likely exist in absence of

the MSWLF unit. The volume occupied by a HEC-1 Flood Hydrograph Package

MSWLF unit in a floodplain may (watershed model that simulates the

theoretically alter (reduce) the storage surface run-off response of a river basin

capacity and restrict flow. Raising the base to precipitation);

flood level by more than one foot can be an

indication that the MSWLF unit may reduce HEC-2 Water Surface Profiles (computes

and restrict storage capacity flow. water surface profiles due to

The location of the MSWLF unit relative to encroachment potential);

the velocity distribution of floodwaters will

greatly influence the susceptibility to HEC-5 Simulation of Flood Control and

washout. This type of assessment will Conservation Systems (simulates the

require a conservative estimate of the shear sequential operation of a reservoir

stress on the landfill components caused by channel system with a branched

the depth, velocity, and duration of network configuration; used to design

river channel. In both cases an estimate of

assessment. 

aid in the prediction of flood hydrographs,

obstructions; evaluates floodway
Subpart B

28

routing that will minimize downstream 2.4 WETLANDS

flooding); and 40 CFR §258.12

HEC-6 Scour and Deposition in Rivers 2.4.1 Statement of Regulation

and Reservoirs (calculates water surface

and sediment bed surface profiles). (a) New MSWLF units and lateral

The HEC-2 model is not appropriate for unless the owner or operator can make the

simulation of sediment-laden braided stream following demonstrations to the Director of

systems or other intermittent/dry stream an approved State:

systems that are subject to flash flood events.

Standard run-off and peak flood hydrograph (1) Where applicable under section 404

methods would be more appropriate for such of the Clean Water Act or applicable State

conditions to predict the effects of severe wetlands laws, the presumption that a

flooding. practicable alternative to the proposed

There are many possible cost-effective wetlands is clearly rebutted;

methods to protect the MSWLF unit from

flood damage including embankment designs (2) The construction and operation of

with rip-rap, geotextiles, or other materials. the MSWLF unit will not:

Guidelines for designing with these materials

may be found in Maynard (1978) and SCS (i) Cause or contribute to violations of

(1983). Embankment design will require an any applicable State water quality

estimate of river flow velocities, flow profiles standard,

(depth), and wave activity. Figure 2-3

provides a design example for dike (ii) Violate any applicable toxic

construction and protection of the landfill effluent standard or prohibition under

surface from flood water. It addresses height Section 307 of the Clean Water Act,

requirements to control the effects of wave

activity. The use of alternate erosion control (iii) Jeopardize the continued existence

methods such as gabions (cubic-shaped wire of endangered or threatened species or

structures filled with stone), paving bricks, result in the destruction or adverse

and mats may be considered. It should be modification of a critical habitat, protected

noted, however, that the dike design in Figure under the Endangered Species Act of 1973,

2-3 may further decrease the water storage and

and flow capacities.

expansions shall not be located in wetlands,

landfill is available which does not involve

(iv) Violate any requirement under the

Marine Protection, Research, and 

Sanctuaries Act of 1972 for the protection

of a marine sanctuary;
29

Figure 2-3. Example Floodplain Protection Dike Design 
Subpart B

30

(3) The MSWLF unit will not cause or unavoidable impacts to the maximum

contribute to significant degradation of extent practicable, and finally offsetting

wetlands. The owner or operator must remaining unavoidable wetland impacts

demonstrate the integrity of the MSWLF through all appropriate and practicable

unit and its ability to protect ecological compensatory mitigation actions (e.g.,

resources by addressing the following restoration of existing degraded wetlands

factors: or creation of man-made wetlands); and

(i) Erosion, stability, and migration (5) Sufficient information is available

potential of native wetland soils, muds and to make a reasonable determination with

deposits used to support the MSWLF unit; respect to these demonstrations.

(ii) Erosion, stability, and migration (b) For purposes of this section,

potential of dredged and fill materials used "wetlands" means those areas that are

to support the MSWLF unit; defined in 40 CFR §232.2(r).

(iii) The volume and chemical nature 2.4.2 Applicability

of the waste managed in the MSWLF unit;

(iv) Impacts on fish, wildlife, and wetlands are prohibited, except in approved

other aquatic resources and their habitat States. The wetland restrictions allow

from release of the solid waste; existing MSWLF units located in wetlands to

(v) The potential effects of with the other requirements of Part 258 can

catastrophic release of waste to the wetland be maintained.

and the resulting impacts on the 

environment; and In addition to the regulations listed in 40 CFR

(vi) Any additional factors, as may be applicable in siting a MSWLF unit in

necessary, to demonstrate that ecological a wetland. These include:

resources in the wetland are sufficiently

protected. ! Sections 401, 402, and 404 of the CWA;

(4) To the extent required under ! National Environmental Policy Act;

Section 404 of the Clean Water Act or ! Migratory Bird Conservation Act;

applicable State wetland laws, steps have ! Fish and Wildlife Coordination Act;

been taken to attempt to achieve no net ! Coastal Zone Management Act;

loss of wetlands (as defined by acreage ! Wild and Scenic Rivers Act; and the

and function) by first avoiding impacts to ! National Historic Preservation Act.

wetlands to the maximum extent

practicable as required by paragraph As authorized by the EPA, the use of

(a)(1) of this section, then minimizing wetlands for location of a MSWLF facility

New MSWLF units and lateral expansions in

continue operations as long as compliance

§258.12(a)(2), other Federal requirements

! Rivers and Harbors Act of 1989;

may require a permit from the U.S. Army
Location Criteria

31

Corps of Engineers (COE). The types of proposed in the Federal Register on August

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

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
Subpart B

32

acreage and a suitable type of upland may not • Cause or contribute to violation of

be present to allow construction of a new any requirement for the protection of

MSWLF unit or lateral expansion without a marine sanctuary; and

wetland impacts. Wetlands evaluations may

become an integral part of the siting, design, • Jeopardize the continued existence of

permitting, and environmental monitoring endangered or threatened species or

aspects of a landfill unit/facility (see Figure 2- critical habitats.

4).

Practicable Alternatives to significant degradation of wetlands.

EPA believes that locating new MSWLF units

or lateral expansions in wetlands should be • Ensure the integrity of the MSWLF

done only where there are no less damaging unit, including consideration of the

alternatives available. Due to the extent of erosion, stability, and migration of

wetlands that may be present in certain native wetland soils and dredged/fill

regions, the banning of new MSWLF units or materials;

lateral expansions in wetlands could cause

serious capacity problems. The flexibility of • Minimize impacts on fish, wildlife,

the rule allows owners or operators to and other aquatic resources and their

demonstrate that there are no practicable habitat from the release of solid

alternatives to locating or laterally expanding waste;

MSWLF units in wetlands.

As part of the evaluation of practicable release of wastes on the wetlands; and

alternatives, the owner/operator should

consider the compliance of the location with • Assure that ecological resources in the

other regulations and the potential impacts of wetlands are sufficiently protected,

the MSWLF unit on wetlands and related including consideration of the volume

resources. Locating or laterally expanding and chemical nature of waste

MSWLF units in wetlands requires managed in the MSWLF unit.

compliance with other environmental

regulations. The owner or operator must These factors were partially derived from

show that the operation or construction of the Section 404(b)(1) of the Clean Water Act.

landfill unit will not: These guidelines address the protection of the

• Violate any applicable State water

quality standards; After consideration of these factors, if no

• Cause or contribute to the violation of in wetlands is available, compensatory steps

any applicable toxic effluent standard must be taken to achieve no net loss of

or prohibition; wetlands as defined by acreage and

The MSWLF unit cannot cause or contribute

Therefore, the owner/operator must:

• Evaluate the effects of catastrophic

ecological resources of the wetland.

practicable alternative to locating the landfill
33

Figure 2-4

Wetlands Decision Tree for Owners/Operators

in Approved States
Subpart B

34

function. The owner/operator must try to a specific case. Typical criteria may include:

avoid and/or minimize impacts to the

wetlands to the greatest extent possible. • Distance from waste generation

Where avoidance and minimization still result sources;

in wetland impacts, mitigation to offset • Minimum landfill facility size

impacts is required. Mitigation plans must be requirements;

approved by the appropriate regulatory • Soil conditions;

agencies and must achieve an agreed-upon • Proximity to ground-water users;

measure of success. Examples of mitigation • Proximity of significant aquifers;

include restoration of degraded wetlands or • Exclusions from protected natural

creation of wetland acreage from existing areas;

uplands. • Degree of difficulty to remediate

Part 258 presumes that practicable alternatives • Setbacks from roadways and

are available to locating landfill units in residences.

wetlands because landfilling is not a waterdependent activity. In an approved State, the Wetland Evaluations

owner or operator can rebut the presumption

that a practicable alternative to the proposed The term "wetlands" includes swamps,

landfill unit or lateral expansion is available. marshes, bogs, and any areas that are

The term "practicable" pertains to the inundated or saturated by ground water or

economic and social feasibility of alternatives surface water at a frequency and duration to

(e.g., collection of waste at transfer stations support, and that under normal circumstances

and trucking to an existing landfill facility or do support, a prevalence of vegetation

other possible landfill sites). The feasibility adapted for life in saturated soil conditions.

evaluation may entail financial, economic, As defined under current guidelines, wetlands

administrative, and public acceptability are identified based on the presence of hydric

analyses as well as engineering soils, hydrophytic vegetation, and the wetland

considerations. Furthermore, the evaluations hydrology. These characteristics also affect

generally will require generation and the functional value of a wetland in terms of

assessment of land use, geologic, hydrologic, its role in: supporting fish and wildlife

geographic, demographic, zoning, traffic habitats; providing aesthetic, scenic, and

maps, and other related information. recreational value; accommodating flood

To rebut the presumption that an alternative relationships to surrounding natural areas

practicable site exists generally will require through nutrient retention and productivity

that a site search for an alternative location exportation (e.g., releasing nutrients to

be conducted. There are no standard downstream areas, providing transportable

methods for conducting site searches due to food sources).

the variability of the number and hierarchy

of screening criteria that may be applied in Often, a wetland assessment will need to be

features; and

storage; sustaining aquatic diversity; and its

conducted by a qualified and experienced
Location Criteria

35

multi-disciplinary team. The assessment of wetland that triggers State agency

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

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.
Subpart B

36

Other wetland and related assessment wetlands are formed in response to perched

methodologies include WET and HEP. WET water tables over geologic material of low

allows comparison of the values and functions hydraulic conductivity and, therefore,

of wetlands before and after construction of a significant drawdown impacts may not occur.

facility, thereby projecting the impact a

facility may have on a wetland. WET was It is possible that the landfill unit/facility will

developed by the Federal Highway not directly displace wetlands, but that

Administration and revised by the COE adverse effects may be caused by leachate or

(Adamus et al., 1987). HEP was developed run-off. Engineered containment systems for

by the Fish and Wildlife Service to determine both leachate and run-off should mitigate the

the quality and quantity of available habitat potential for discharge to wetlands.

for selected species. HEP and WET may be

used in conjunction with each other to provide Additional actions and considerations

an integrated assessment. relevant to mitigating impacts of fill

Impact Evaluation appropriate for MSWLF facilities are

If the new unit or lateral expansion is to be Adverse Effects) of 40 CFR §230

located in a wetland, the owner or operator (Guidelines for Specification of Disposal

must demonstrate that the unit will not cause Sites for Dredged or Fill Materials).

or contribute to significant degradation of the

wetland. Erosion potential and stability of Wetland Offset

wetland soils and any dredged or fill material

used to support the MSWLF unit should be All unavoidable impacts must be "offset" or

identified as part of the wetlands evaluation. compensated for to ensure that the facility has

Any adverse stability or erosion problems that not caused, to the extent practicable, any net

could affect the MSWLF or contaminant loss of wetland acreage. This compensatory

effects that could be caused by the MSWLF mitigation may take the form of upgrading

unit should be resolved. existing marginal or lower-quality wetlands

All practicable steps are to be taken to studies require review and development on a

minimize potential impacts of the MSWLF site-specific basis.

unit to wetlands. A number of measures

that can aid in minimization of impacts are To identify potential sites that may be

available. Appropriate measures are site- proposed for upgrade of existing wetlands

specific and should be incorporated into the or creation of new wetlands, a cursory

design and operation of the MSWLF unit. assessment of surrounding wetlands and

For example, placement of ground water uplands should be conducted. The

barriers may be required if soil and shallow assessment may include a study to define

ground-water conditions would cause the functional characteristics and interdewatering of the wetland due to the relationships of these potential wetland

existence of underdrain pipe systems at the mitigation areas. An upgrade of an existing

facility. In many instances, however, wetland may consist of transplanting

material in wetlands that may be

provided in Subpart H (Actions to Minimize

or creating new wetlands. Wetland offset
Location Criteria

37

appropriate vegetation and importing low- alternative setback distance of less than

permeability soil materials that would be 200 feet (60 meters) will prevent damage to

conducive to forming saturated soil the structural integrity of the MSWLF unit

conditions. Excavation to form open water and will be protective of human health and

bodies or gradual restoration of salt water the environment. 

marshes by culvert expansions to promote sea

water influx are other examples of (b) For the purposes of this section:

compensatory mitigation.

Individual States may have offset ratios to fractures in any material along which

determine how much acreage of a given strata on one side have been displaced with

functional value is required to replace the respect to that on the other side.

wetlands that were lost or impacted.

Preservation of lands, such as through (2) Displacement means the relative

perpetual conservation easements, may be movement of any two sides of a fault

considered as a viable offset option. State measured in any direction.

offset ratios may require that for wetlands of

an equivalent functional value, a larger (3) Holocene means the most recent

acreage be created than was displaced. epoch of the Quaternary period, extending

Due to the experimental nature of creating or the present.

enhancing wetlands, a monitoring program to

evaluate the progress of the effort should be 2.5.2 Applicability

considered and may be required as a wetland

permit condition. The purpose of the Except in approved States, the regulation bans

monitoring program is to verify that the all new MSWLF units or lateral expansions of

created/upgraded wetland is successfully existing units within 200 feet (60 meters) of

established and that the intended function of the outermost boundary of a fault that has

the wetland becomes self-sustaining over experienced displacement during the

time. Holocene Epoch (within the last 10,000 to

2.5 FAULT AREAS are located in fault areas.

 40 CFR §258.13

2.5.1 Statement of Regulation provided if the owner or operator can

(a) New MSWLF units and lateral State that a shorter distance will prevent

expansions shall not be located within 200 damage to the structural integrity of the

feet (60 meters) of a fault that has had MSWLF unit and will be protective of

displacement in Holocene time unless the human health and the environment. The

owner or operator demonstrates to the demonstration for a new MSWLF unit or

Director of an approved State that an lateral expansion requires review and

(1) Fault means a fracture or a zone of

from the end of the Pleistocene Epoch to

12,000 years). Existing MSWLF units are

neither required to close nor to retrofit if they

A variance to the 200-foot setback is

demonstrate to the Director of an approved
Subpart B

38

approval by the Director of an approved State. used. A series of maps known as the

If the demonstration is approved, it must be "Preliminary Young Fault Maps,

placed in the facility's operating record. The Miscellaneous Field Investigation (MF) 916"

option to have a setback of less than 200 feet was published by the USGS in 1978.

from a Holocene fault is not available in Information about these maps can be obtained

unapproved States. from the USGS by calling 1-800-USA2.5.3 Technical Considerations Center in Reston, Virginia, or by calling 303-

Locating a landfill in the vicinity of an area Sales Center in Denver, Colorado.

that has experienced faulting in recent time

has inherent dangers. Faulting occurs in areas For locations where a fault zone has been

where the geologic stresses exceed a geologic subject to movement since the USGS maps

material's ability to withstand those stresses. were published in 1978, a geologic

Such areas also tend to be subject to reconnaissance of the site and surrounding

earthquakes and ground failures (e.g., areas may be required to map fault traces and

landslides, soil liquefaction) associated with to determine the faults along which

seismic activity. A more detailed discussion movement has occurred in Holocene time.

of seismic activity is presented in Section 2.6. This reconnaissance also may be necessary to

Proximity to a fault can cause damage than 200 feet. Additional requirements may

through: need to be met before a new unit or lateral

• Movement along the fault which can

cause displacement of facility structures, A site fault characterization is necessary to

• Seismic activity associated with faulting a fault that has had movement during the

which can cause damage to facility Holocene epoch. An investigation would

structures through vibratory action (see include obtaining information on any

Figure 2-5), and lineaments (linear features) that suggest the

• Earth shaking which can cause ground of the site. The information could be based

failures such as slope failures. on:

Consequently, appropriate setbacks from fault • A review of available maps, logs,

areas are required to minimize the potential reports, scientific literature, or insurance

for damage. claim reports;

To determine if a proposed landfill unit is • An aerial reconnaissance of the area

located in a Holocene fault area, U.S. within a five-mile radius of the site,

Geological Survey (USGS) mapping can be including aerial photo analysis; or

MAPS, which reaches the USGS National

236-7477, which reaches the USGS Map

support a demonstration for a setback of less

expansion may be approved.

determine whether a site is within 200 feet of

presence of faults within a 3,000-foot radius
Location Criteria

39

Figure 2-5

Potential Seismic Effects

A schematic diagram of a landfill showing potential deformation of

the leachate collection and removal system by seismic stresses.

Source: US EPA, 1992
Subpart B

40

• A field reconnaissance that includes Based on this information as well as

walking portions of the area within 3,000 supporting maps and analyses, a qualified

feet of the unit. professional should prepare a report that

If the site fault characterization indicates that fault(s) and the associated 200-foot setback.

a fault or a set of faults is situated within

3,000 feet of the proposed unit, investigations If requesting an alternate setback, a

should be conducted to determine the demonstration must be made to show that no

presence or absence of any faults within 200 damage to the landfill's structural integrity

feet of the site that have experienced will result. Examples of engineering

movement during the Holocene period. Such considerations and modifications that may be

investigations can include: included in such demonstrations are as

• Subsurface exploration, including drilling

and trenching, to locate fault zones and • For zones with high probabilities of high

evidence of faulting. accelerations (horizontal) within the

• Trenching perpendicular to any faults or designs should be developed.

lineaments within 200 feet of the unit.

• Determination of the age of any slopes should be performed to guide

displacements, for example by examining selection of materials and gradients for

displacement of surficial deposits such as slopes.

glacial or older deposits (if Holocene

deposits are absent). • Where in-situ and laboratory tests

• Examination of seismic epicenter susceptible to liquefaction, ground

information to look for indications of improvement measures like grouting,

recent movement or activity along dewatering, heavy tamping, and

structures in a given area. excavation should be implemented.

• Review of high altitude, high resolution • Engineering options include:

aerial photographs with stereo-vision

coverage. The photographs are produced — Flexible pipes,

by the National Aerial Photographic

Program (NAPP) and the National High — Ground improvement measures

Altitude Program (NHAP). Information (grouting, dewatering, heavy

on these photos can be obtained from the tamping, and excavation), and/or

USGS EROS Data Center in Sioux Falls,

South Dakota at (605) 594-615 — Redundant precautionary

delineates the location of the Holocene

follows:

moderate range of 0.1g to 0.75g, seismic

• Seismic stability analysis of landfill

indicate that a potential landfill site is

measures (secondary containment

system).
Location Criteria

41

In addition, use of such measures needs to be acceleration will not be exceeded in 250

demonstrated to be protective of human health years, or the maximum expected horizontal

and the environment. The types of acceleration based on a site-specific seismic

engineering controls described above are risk assessment.

similar to those that would be employed in

areas that are likely to experience (3) Lithified earth material means all

earthquakes. rock, including all naturally occurring and

2.6 SEISMIC IMPACT ZONES that formed by crystallization of magma or

 40 CFR §258.14 by induration of loose sediments. This

2.6.1 Statement of Regulation such as fill, concrete, and asphalt, or

(a) New MSWLF units and lateral regolith lying at or near the earth surface.

expansions shall not be located in seismic

impact zones, unless the owner or operator 2.6.2 Applicability

demonstrates to the Director of an

approved State that all containment New MSWLF units and lateral expansions in

structures, including liners, leachate seismic impact zones are prohibited, except in

collection systems, and surface water approved States. A seismic impact zone is an

control systems, are designed to resist the area that has a ten percent or greater

maximum horizontal acceleration in probability that the maximum expected

lithified earth material for the site. The horizontal acceleration in lithified earth

owner or operator must place the material, expressed as a percentage of the

demonstration in the operating record and earth's gravitational pull (g), will exceed

notify the State Director that it has been 0.10g in 250 years.

placed in the operating record.

(b) For the purposes of this section: lateral expansions in a seismic impact zone

(1) Seismic impact zone means an area that the structural components of the unit

with a ten percent or greater probability (e.g., liners, leachate collection systems, final

that the maximum horizontal acceleration cover, and surface water control systems) are

in lithified earth material, expressed as a designed to resist the maximum horizontal

percentage of the earth's gravitational pull acceleration in lithified earth material at the

(g), will exceed 0.10g in 250 years. site. Existing units are not required to be

(2) Maximum horizontal acceleration or lateral expansions must notify the Director

in lithified earth material means the of an approved State and place the

maximum expected horizontal acceleration demonstration of compliance with the

depicted on a seismic hazard map, with a conditions of the restriction in the operating

90 percent or greater probability that the record.

naturally formed aggregates or masses of

minerals or small particles of older rock

term does not include man-made materials,

unconsolidated earth materials, soil, or

The regulation prohibits locating new units or

unless the owner or operator can demonstrate

retrofitted. Owners or operators of new units
Subpart B

42

2.6.3 Technical Considerations for the United States and Puerto Rico"

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

(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
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

44

systems as well as the leachate and gas precautionary measures should be designed

collection and removal systems. Tensional and built into the various landfill systems.

stresses within the liner system can result in

fracturing of the soil liner and/or tearing of For those units located in an area with an

the flexible membrane liner. Thus, when estimated maximum horizontal acceleration

selecting suitable sites from many potential greater than 0.1g, an evaluation of seismic

sites during the siting process, the effects should consider both foundation soil

owner/operator should try to avoid a site with: stability and waste stability under seismic

• Holocene fault zones, for the evaluation include the construction

• Sites with potential ground motion, and phase (maximum open excavation depth of

• Sites with liquefaction potential. new cell adjacent to an existing unit), closure

If one of the above types of sites is selected, waste and subsoil), and post-closure care

the owner/operator must consider the costs (after final consolidation of both waste and

associated with the development of the site. foundation soil). If the maximum horizontal

If, due to a lack of suitable alternatives, a site the design of the unit will not have to

is chosen that is located in a seismic impact incorporate an evaluation of seismic effects

zone, a demonstration must be made to the unless the facility will be situated in an area

Director of an approved State that the design with low strength foundation soils or soils

of the unit's structural components (e.g., with potential for liquefaction. The facility

liners, leachate collection, final covers, run-on should be assessed for the effects of seismic

and run-off systems) will resist the maximum activity even if the horizontal acceleration is

horizontal acceleration in lithified materials at expected to be less than 0.1g.

the site. As part of the demonstration,

owner/operators must: In determining the potential effects of seismic

• 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

loading. Conditions that may be considered

activities (prior to final consolidation of both

acceleration is less than or equal to 0.1g, then

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
Location Criteria

45

settlements of the ground surface (Winterkorn well-established analytical methods. Several

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

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 PCSlope 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
Subpart B

46

design to ensure that the integrity of the indicate that a natural or man-induced

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

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 maninduced 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
Location Criteria

47

natural or human-induced events or forces (e.g., heavy rain) or man-made events

that are capable of impairing or destroying the (e.g., explosions).

integrity of some or all of the structural

components. Structural components consist — Expansive soils usually are clayof liners, leachate collection systems, final rich soils that, because of their

cover systems, run-on and run-off control molecular structure, tend to swell

systems, and any other component necessary and shrink by taking up and

for protection of human health and the releasing water and thus are

environment. sensitive to a variable hydrologic

MSWLF units can be located in unstable smectite (montmorillonite group)

areas, but the owner or operator must and vermiculite clays; bentonite

demonstrate that the structural integrity of the is a smectite-rich clay. In

MSWLF unit will not be disrupted. The addition, soils rich in "white

demonstration must show that engineering alkali" (sodium sulfate),

measures have been incorporated into the anhydrite (calcium sulfate), or

design of the unit to ensure the integrity of the pyrite (iron sulfide) also may

structural components. Existing MSWLF exhibit swelling as water content

units that do not meet the demonstration must increases. Such soils tend to be

be closed within 5 years in accordance with found in the arid western states.

§258.60, and owners and operators must

undertake post-closure activities in — Soils that are subject to rapid

accordance with §258.61. The Director of an settlement (subsidence) include

approved State can grant a 2-year extension to loess, unconsolidated clays, and

the closure requirement under two conditions: wetland soils. Loess, which is

(1) no disposal alternative is available, and (2) found in the central states, is a

no immediate threat is posed to human health wind-deposited silt that is

and the environment. moisture-deficient and tends to

2.7.3 Technical Considerations Unconsolidated clays, which can

Again, for the purposes of this discussion, states, can undergo considerable

natural unstable areas include those areas that compaction when fluids such as

have poor soils for foundations, are water or oil are removed.

susceptible to mass movement, or have karst Similarly, wetland soils, which

features. by their nature are water-bearing,

• Areas with soils that make poor subsidence when water is

foundations have soils that are withdrawn.

expansive or settle suddenly. Such

areas may lose their ability to support a • Another type of unstable area is an

foundation when subjected to natural area that is subject to mass

regime. Such soils include:

compact upon wetting.

be found in the southwestern

also tend to be subject to

movement. Such areas can be situated
Subpart B

48

on steep or gradual slopes. They tend to have • A closed landfill as the foundation for a

rock or soil conditions that are conducive to new landfill ("piggy-backing") may be

downslope movement of soil, rock, and/or unstable unless the closed landfill has

debris (either alone or mixed with water) undergone complete settlement of the

under the influence of gravity. Examples of underlying wastes.

mass movements include avalanches,

landslides, debris slides and flows, and rock As part of their demonstration to site a

slides. landfill in an unstable area, owners/operators

• Karst terrains tend to be subject to to serve as a foundation as well as the ability

extreme incidents of differential of the site embankments and slopes to

settlement, namely complete ground maintain a stable condition. Once these

collapse. Karst is a term used to describe factors have been evaluated, a MSWLF

areas that are underlain by soluble design should be developed that will address

bedrock, such as limestone, where these types of concerns and prevent possible

solution of the rock by water creates associated damage to MSWLF structural

subterranean drainage systems that may components.

include areas of rock collapse. These

areas tend to be characterized by large In designing a new unit or lateral expansion

subterranean and surficial voids (e.g., or re-evaluating an existing MSWLF unit, a

caverns and sinkholes) and unpredictable stability assessment should be conducted in

surface and ground-water flow (e.g., order to avoid or prevent a destabilizing event

sinking streams and large springs). Other from impairing the structural integrity of the

rocks such as dolomite or gypsum also landfill component systems. A stability

may be subject to solution effects. assessment involves essentially three

Examples of human-induced unstable areas conditions, an analysis of slope stability, and

are described below: an examination of related design needs. An

• The presence of cut and/or fill slopes

during construction of the MSWLF unit • Assessing the stability of foundation

may cause slippage of existing soil or soils, adjacent embankments, and slopes;

rock.

• Excessive drawdown of ground water geological characteristics of the site to

increases the effective overburden on the establish soil strengths and other

foundation soils underneath the MSWLF engineering properties by performing

unit, which may cause excessive standard penetration tests, field vane

settlement or bearing capacity failure on shear tests, and laboratory tests; and

the foundation soils.

must assess the ability of the soils and/or rock

components: an evaluation of subsurface

evaluation of subsurface conditions requires:

• Investigating the geotechnical and
Location Criteria

49

• Testing the soil properties such as water Information on natural features can be

content, shear strength, plasticity, and obtained from:

grain size distribution.

A stability assessment should consider entitled "Engineering Aspects of

(USEPA, 1988): Karst," published in 1984;

• The adequacy of the subsurface • Regional or local soil maps;

exploration program;

• The liquefaction potential of the karst areas); and

embankment, slopes, and foundation

soils; • Site-specific investigations.

• The expected behavior of the To examine an area for possible sources of

embankment, slopes, and foundation soils human-induced ground instability, the site

when they are subjected to seismic and surrounding area should be examined

activity; for activities related to extensive

• The potential for seepage-induced subsurface units as well as construction or

failure; and other operations that may result in ground

• The potential for differential settlement.

In addition, a qualified professional must

assess, at a minimum, natural conditions (e.g., Failures occur when the driving forces

soil, geology, geomorphology) as well as imposed on the soils or engineered

human-made features or events (both structures exceed the resisting forces of the

subsurface and surface) that could cause material. The ratio of the resisting force to

differential settlement of ground. Natural the driving force is considered the factor of

conditions can be highly unpredictable and safety (FS). At an FS value less than 1.0,

destructive, especially if amplified by human- failure will occur by definition. There is a

induced changes to the environment. Specific high probability that, due to natural

examples of natural or human-induced variability and the degree of accuracy in

phenomena include: debris flows resulting measurements, interpreted soil conditions

from heavy rainfall in a small watershed; the will not be precisely representative of the

rapid formation of a sinkhole as a result of actual soil conditions. Therefore, failure

excessive local or regional ground water may not occur exactly at the calculated

withdrawal in a limestone region; earth value, so factors of safety greater than 1.0

displacement by faulting activity; and are required for the design. For plastic soils

rockfalls along a cliff face caused by such as clay, movement or deformation

vibrations resulting from the detonation of (creep) may occur at a higher factor of

explosives or sonic booms. safety prior to catastrophic failure.

• The USGS National Atlas map

• Aerial photographs (especially in

withdrawal of oil, gas, or water from

motion (e.g., blasting).

Types of Failures
Subpart B

50

Principal modes of failure in soil or rock settlement, which can be used to aid in

include: estimating differential settlement.

• Rotation (change of orientation) of an Allowable settlement is typically

earthen mass on a curved slip surface expressed as a function of total

approximated by a circular arc; settlement because differential settlement

• Translation (change of position) of an differential settlement is a more serious

earthen mass on a planar surface whose threat to the integrity of the structure

length is large compared to depth below than total settlement. Differential

ground; settlement also is discussed in Section

• Displacement of a wedge-shaped mass

along one or more planes of weakness; • Loss of bearing strength is a failure

• Earth and mud flows in loose clayey and have soils that tend to expand, rapidly

silty soils; and settle, or liquefy, thereby causing failure

• Debris flows in coarse-grained soils. MSWLF components. Another example

For the purposes of this discussion, three failures that have occurred at operating

types of failures can occur at a landfill unit: sites where excavations for landfill

settlement, loss of bearing strength, and expansions adjacent to the filled areas

sinkhole collapse. reduced the mass of the soil at the toe of

• If not properly engineered, a landfill in strength (resisting force) of the

an unstable area may undergo extreme foundation soil.

settlement, which can result in structural

failure. Differential settlement is a • Catastrophic collapse in the form of

particular mode of failure that generally sinkholes is a type of failure that occurs

occurs beneath a landfill in response to in karst regions. As water, especially

consolidation and dewatering of the acidic water, percolates through

foundation soils during and following limestone (calcium carbonate), the

waste loading. soluble carbonate material dissolves,

Settlement beneath a landfill unit, both overlying caverns can collapse suddenly,

total and differential, should be assessed resulting in sinkhole features that can be

and compared to the elongation strength 100 feet or more in depth and 300 feet or

and flexure properties of the liner and more in width.

leachate collection pipe system. Even

small amounts of settlement can Tables 2-2 and 2-3 provide examples of

seriously damage leachate collection analytical considerations for mode of failure

piping and sumps. The analysis will assessments in both natural and human-made

provide an estimate of maximum slopes.

is more difficult to predict. However,

6.3 of Chapter 6.

mode that tends to occur in areas that

or reducing performance of overlying

of loss of bearing strength involves

the slope, thereby reducing the overall

forming cavities and caverns. Land
Location Criteria

51

1. Slope in Coarse-Grained Soil with

Some Cohesion

 Low Groundwater High Groundwater

Failure of thin Failure at relatively

wedge, position shallow toe circles

influenced by

tension cracks

• 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 Ø' 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 High Groundwater

Stable slope angle Stable slope angle

= effective friction = 1⁄2 effective

angle 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 Ø' 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.

• 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 unconfined

compression test, unconsolidated undrained

triaxial test or vane shear.

Source: Soil Mechanics, NAVFAC Design Manual 7.01

Table 2-2. Analysis of Stability of Natural Slopes
Subpart B

52

4. Slope in Stratified Soil Profile

Location of failure depends on relative Failure surface is combination of active and

strength and orientation of layers.

• Location of failure plane is controlled by

relative strength and orientation of strata. 

passive wedges with central sliding block

chosen to conform to stratification.

• Analyze with effective stress using strengths C'

and Ø' for fine-grained strata and Ø' 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.

Source: Soil Mechanics, NAVFAC Design Manual 7.01

Table 2-2. Analysis of Stability of Natural Slopes (Continued)
Location Criteria

53

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 Ø' 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 unconfined 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 Ø from CU tests with effective

stress analysis, applying pore pressures of

3. Failure Following Cut in Stiff

Fissured Clay

Failure surface depends on pattern of

fissures or depth of softening.

• 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 Ø'

with total stress analysis. Analyze for longterm stability with C'r

 and Ø'm based on

residual strength measured in consolidated

drained tests.

Source: Soil Mechanics, NAVFAC Design Manual 7.01

Table 2-3. Analysis of Stability of Cut and Fill Slopes,

Conditions Varying With Time
Subpart B

54

Subsurface Exploration Programs Methods of Slope Stability Analysis

Foundation soil stability assessments for non- Slope stability analyses are performed for

catastrophic failure require field investigations both excavated side slopes and aboveground

to determine soil strengths and other soil embankments. The analyses are performed as

properties. In situ field vane shear tests appropriate to verify the structural integrity of

commonly are conducted in addition to a cut slope or dike. The design configuration

collection of piston samples for laboratory is evaluated for its stability under all potential

testing of undrained shear strengths (biaxial hydraulic and loading conditions, including

and triaxial). Field vanes taken at depth conditions that may exist during construction

provide a profile of soil strength. The of an expansion (e.g., excavation). Analyses

required field vane depth intervals vary, based typically performed are slope stability,

on soil strength and type, and the number of settlement, and liquefaction. Factor of safety

borings required depends on the variability of rationale and selection for different conditions

the soils, the site size, and landfill unit are described by Huang (1983) and Terzaghi

dimensions. Borings and field vane testing and Peck (1967). Table 2-4 lists

should consider the anticipated design to recommended minimum factor of safety

identify segments of the facility where critical values for slopes. Many States may provide

cross sections are likely to occur. Critical their own minimum factor of safety

sections are where factors of safety are requirements.

anticipated to be lowest.

Other tests that are conducted to characterize available for performing slope stability

a soil include determination of water content, analyses. Method selection should be based

Atterberg limits, grain size distribution, on the soil properties and the anticipated

consolidation, effective porosity, and mode of failure. Rationale for selecting a

saturated hydraulic conductivity. The site specific method should be provided.

hydrogeologic conditions should be assessed

to determine if soils are saturated or The majority of these methods may be

unsaturated. categorized as "limit equilibrium" methods

Catastrophic failures, such as sinkhole determined and compared. The basic

collapse in karst terrains or fault displacement assumption of the limit equilibrium

during an earthquake, are more difficult to approach is that the failure criterion is

predict. Subsurface karst structures may have satisfied along an assumed failure surface.

surface topographic expressions such as This surface may be a straight line, circular

circular depressions over subsiding solution arc, logarithmic spiral, or other irregular

caverns. Subsurface borings or geophysical plane. A free body diagram of the driving

techniques may provide reliable means of forces acting on the slope is constructed

identifying the occurrence, depth, and size of using assumed or known values of the

solution cavities that have the potential for forces. Next, the soil's shear resistance as it

catastrophic collapse. pertains to establishing equilibrium is

There are numerous methods currently

in which driving and resisting forces are

calculated. This calculated shear resistance
Location Criteria

55

Table 2-4

Recommended Minimum Values of Factor of Safety

for Slope Stability Analyses

Uncertainty of Strength Measurements

Consequences of Slope Failure Small1 Large2

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

The uncertainty of the strength measurements is smallest when the soil 1

conditions are uniform and high quality strength test data provide a consistent,

complete, and logical picture of the strength characteristics.

The uncertainty of the strength measurements is greatest when the soil 2

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.
Subpart B

56

then is compared to the estimated or available excavating a bench in the upper part of

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 twodimensional 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

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 
Location Criteria

57

Figure 2-7

Sample Output from PC STABL Model

Œ Subgrade: Internal friction angle = 32 degrees

œ Refuse: Internal friction angle of waste = 25 degrees

– Refuse: Internal friction angle of waste = 25 degrees
Scheme Applicable Methods Comments

1. Changing Geometry 1. Reduce slope height by 1. Area has to be accessible

excavation at top of slope to construction

2. Flatten the slope angle. needed for excavated soil.

3. Excavate a bench in incorporated in this

upper part of slope. method.

equipment. Disposal site

Drainage sometimes

2. Earth Berm Fill 1. Compacted earth or rock 1. Sufficient width and

berm placed at end thickness of berm

beyond the toe. Drainage required so failure will

may be provided behind not occur below or

the berm. through the berm.

3. Retaining Structures 1. Retaining wall: crib or 1. Usually expensive.

cantilever type. Cantilever walls might

2. Drilled, cast-in-place

vertical piles and/or slabs 2. Spacing should be such

founded well below that soil can arch between

bottom slide plane. piles. Grade beam can be

Generally 18 to 36 inches used to tie piles together. 

in diameter and 4- to 8- Very large diameter (6

foot spacing. Larger feet±) piles have been

diameter piles at closer used for deep slide.

spacing may be required

in some cases with

mitigate failures of cuts

in highly fissured clays.

have to be tied back.

Source: Soil Mechanics, NAVFAC Design Manual 7.01

Table 2-5

Methods of Stabilizing Excavation Slopes
Scheme Applicable Methods Comments

3. Drilled, cast-in-place 3. Space close enough so

vertical piles tied back soil will arch between

with battered piles or a piles. Piles can be tied

deadman. Piles founded together with grade beam.

well below slide plane. 

Generally, 12 to 30

inches in diameter and at

least 4- to 8-foot spacing.

4. Earth and rock anchors 4. Can be used for high

and rock bolts. slopes, and in very

5. Reinforced earth. 5. Usually expensive

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.

4. Other methods See TABLE 7, NAVFAC DM7.2, Chapter 1

Source: Soil Mechanics, NAVFAC Design Manual 7.01

Table 2-5 (continued)

Methods of Stabilizing Excavation Slopes
Subpart B

60

with steeply cut slopes where soil Monitoring

arching can be developed between the

piles. During construction activities, it may be

— The last retaining wall shown because of the additional stresses placed on

uses a cantilever setup along natural and engineered soil systems (e.g.,

with soil that has been slopes, foundations, dikes) as a result of

reinforced with geosynthetic excavation and filling activities. Postmaterial to provide a system that closure slope monitoring usually is not

is highly resistant to vertical and necessary.

lateral motion. This type of

system is best suited for use in Important monitoring parameters may

situations where vertically cut include settlement, lateral movement, and

slopes must have lateral pore water pressure. Monitoring for pore

movement strictly controlled. water pressure is usually accomplished with

Other potential procedures for stabilizing Lateral movements of structures may be

natural and human-made slopes include the detected on the surface by surveying

use of geotextiles and geogrids to provide horizontal and vertical movements.

additional strength, the installation of wick Subsurface movements may be detected by

and toe drains to relieve excess pore use of slope inclinometers. Settlement may

pressures, grouting, and vacuum and be monitored by surveying ground surface

wellpoint pumping to lower ground-water elevations (on several occasions over a

levels. In addition, surface drainage may be period of time) and comparing them with

controlled to decrease infiltration, thereby areas that are not likely to experience

reducing the potential for mud and debris changes in elevations (e.g., USGS survey

slides in some areas. Lowering the ground- monuments).

water table also may have stabilizing

effects. Walls or large-diameter piling can Engineering Considerations for Karst

be used to stabilize slides of relatively small Terrains

dimension or to retain steep toe slopes so

that failure will not extend back into a larger The principal concern with karst terrains is

mass (U.S. Navy, 1986). For more detailed progressive and/or catastrophic failure of

information regarding slope stabilization subsurface conditions due to the presence of

design, refer to Winterkorn and Fang sinkholes, solution cavities, and

(1975), U.S. Navy (1986), and Sowers subterranean caverns. The unpredictable

(1979). Richardson and Koerner (1987) and and catastrophic nature of subsidence in

Koerner (1986) provide design guidance for these areas makes them difficult to develop

geosynthetics in both landfill and general as landfill sites. Before situating a MSWLF

applications. in a karst region, the subject site should be

appropriate to monitor slope stability

piezometers screened in the sensitive strata.

characterized thoroughly.
Location Criteria

61

The first stage of demonstration is to heavily compacted to achieve the needed

characterize the subsurface. Subsurface stability. Similarly, in areas where the karst

drilling, sinkhole monitoring, and geophysical voids are relatively small and limited in

testing are direct means that can be used to extent, infilling of the void with slurry

characterize a site. Geophysical techniques cement grout or other material may be an

include tests using electromagnetic option.

conductivity, seismic refraction, groundpenetrating radar, gravity, and electrical In general, due to the unpredictable and

resistivity. Interpretation and applicability of catastrophic nature of ground failure in such

different geophysical techniques should be areas, engineering solutions that try to

reviewed by a qualified geophysicist. Often compensate for the weak geologic structures

more than one technique should be employed by constructing manmade ground supports

to confirm and correlate findings and tend to be complex and costly. For example,

anomalies. Subsurface drilling is reinforced raft (or mat) foundations could be

recommended highly for verifying the results used to compensate for lack of ground

of geophysical investigations. strength in some karst areas. Raft foundations

Additional information on karst conditions of a concrete footing that extends over a very

can come from remote sensing techniques, large area. Such foundations are used where

such as aerial photograph interpretation. soils have a low bearing capacity or where

Surface mapping of karst features can help to soil conditions are variable and erratic; these

provide an understanding of structural foundations are able to reduce and distribute

patterns and relationships in karst terrains. loads. However, it should be noted that, in

An understanding of local carbonate geology some instances, raft foundations may not

and stratigraphy can aid in the interpretation necessarily be able to prevent the extreme

of both remote sensing and geophysical type of collapse and settlement that can occur

techniques. in karst areas. In addition, the construction of

A demonstration that engineering measures on the size of the area.

have been incorporated into a unit located in

a karst terrain may include both initial

design and site modifications. A relatively 2.8 CLOSURE OF EXISTING

simple engineering modification that can be MUNICIPAL SOLID WASTE

used to mitigate karst terrain problems is LANDFILL UNITS

ground-water and surface water control and 40 CFR §258.16

conveyance. Such water control measures are

used to minimize the rate of dissolution within 2.8.1 Statement of Regulation

known near-surface limestone. This means

of controlling karst development may not be (a) Existing MSWLF units that

applicable to all karst situations. In areas cannot make the demonstration specified

where development of karst topography in §§258.10(a), pertaining to airports,

tends to be minor, loose soils overlying the 258.11(a), pertaining to floodplains, and

limestone may be excavated or 258.15(a), pertaining to unstable areas,

are a type of "floating foundation" that consist

raft foundations can be very costly, depending
Subpart B

62

must close by October 9, 1996, in 2.8.3 Technical Considerations

accordance with §258.60 of this part and

conduct post-closure activities in The engineering considerations that should be

accordance with §258.61 of this part. addressed for airport safety, 100-year

(b) The deadline for closure required are discussed in Sections 2.2, 2.3, and 2.7 of

by paragraph (a) of this section may be this chapter. Information and evaluations

extended up to two years if the owner or necessary for these demonstrations also are

operator demonstrates to the Director of an presented in these sections. If applicable

approved State that: demonstrations are not made by the owners or

(1) There is no available alternative according to the requirements of section

disposal capacity; §258.60 by October 9, 1996.

(2) There is no immediate threat to For MSWLF units located in approved States,

human health and the environment. this deadline may be extended if there is no

2.8.2 Applicability environment and no waste disposal alternative

These requirements are applicable to all disposal alternative should consider all waste

MSWLF units that receive waste after management facilities, including landfills,

October 9, 1993 and cannot meet the airport municipal waste combustors, and recycling

safety, floodplain, or unstable area facilities. The demonstration for the two-year

requirements. The owner or operator is extension should consider the impacts on

required to demonstrate that the facility: (1) human health and the environment as they

will not pose a bird hazard to aircraft under relate to airport safety, 100-year floodplains,

§258.10(a); (2) is designed to prevent washout or unstable areas.

of solid waste, will not restrict floodplain

storage capacity, or increase floodwater flow §§258.17-258.19 [Reserved].

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. 

floodplain encroachment, and unstable areas

operators, the landfill unit(s) must be closed

 

immediate threat to human health and the

is available. The demonstration of no
Location Criteria

63

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.
Subpart B

64

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 MF2120.

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.H., (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.
Location Criteria

65

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

1849 C St. N.W.

Washington, D.C. 20240

(202) 343-7220 (Locator)

(202) 343-5717 (Information)
Subpart B

66

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
Location Criteria

67

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
Subpart B

68

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.
69

APPENDIX I

FAA Order 5200.5A
70

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL AVIATION ADMINISTRATION

5200.5A

l/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.
71

(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.
72

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
CHAPTER 3

SUBPART C

OPERATING CRITERIA
74

CHAPTER 3

SUBPART C

TABLE OF CONTENTS

3.1 INTRODUCTION ........................................................... 76

3.2 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

3.3 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

3.4 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

3.5 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

3.6 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
75

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

3.8 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

3.9 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 ............................................. 111

3.12 FURTHER INFORMATION .................................................. 114

3.12.1 References ......................................................... 114

3.12.2 Addresses ......................................................... 114

APPENDIX I - SPECIAL WASTE ACCEPTANCE AGREEMENT ............ Following Page 114
76

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; ! Facility access;

! Cover material; ! Run-on/run-off control systems;

! Disease vector control; ! Surface water requirements;

! Explosive gases control; ! Liquid restrictions; and

! Air monitoring; ! 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.
Operating Criteria

77

3.2 PROCEDURES FOR EXCLUDING 3.2.2 Applicability

THE RECEIPT OF HAZARDOUS

WASTE 40 CFR §258.20 This regulation applies to all MSWLF units

3.2.1 Statement of Regulation 1993.

(a) Owners or operators of all MSWLF The owner or operator must develop a

units must implement a program at the program to detect and prevent disposal of

facility for detecting and preventing the regulated hazardous wastes or PCB wastes at

disposal of regulated hazardous wastes as the MSWLF facility. Hazardous wastes may

defined in Part 261 of this title and be gases, liquids, solids, or sludges that are

polychlorinated biphenyls (PCB) wastes as listed or exhibit the characteristics described

defined in Part 761 of this title. This in 40 CFR Part 261. Household hazardous

program must include, at a minimum: wastes are excluded from Subtitle C

(1) Random inspections of incoming conditionally exempt small quantity

loads unless the owner or operator takes generators (CESQGs) are not considered

other steps to ensure that incoming loads regulated hazardous wastes for purposes of

do not contain regulated hazardous wastes complying with §258.20; therefore, these

or PCB wastes; wastes may be accepted for disposal at a

(2) Records of any inspections;

(3) Training of facility personnel to program should be capable of detecting and

recognize regulated hazardous waste and preventing disposal of PCB wastes. PCB

PCB wastes; and wastes may be liquids or non-liquids (sludges

(4) Notification of State Director of 761.60. PCB wastes do not include small

authorized States under Subtitle C of capacitors found in fluorescent light ballast,

RCRA or the EPA Regional Administrator white goods (e.g., washers, dryers,

if in an unauthorized State if a regulated refrigerators) or other consumer electrical

hazardous waste or PCB waste is products (e.g., radio and television units).

discovered at the facility.

(b) For purposes of this section, intended to identify whether regulated

regulated hazardous waste means a solid hazardous waste or PCB waste was received

waste that is a hazardous waste, as defined at the MSWLF unit or facility prior to the

in 40 CFR 261.3, that is not excluded from effective date of the Criteria.

regulation as a hazardous waste under 40

CFR 261.4(b) or was not generated by a 3.2.3 Technical Considerations

conditionally exempt small quantity

generator as defined in §261.5 of this title. A solid waste is a regulated hazardous waste

that receive wastes on or after October 9,

regulation, and wastes generated by

MSWLF unit.

The MSWLF hazardous waste exclusion

or solids) and are defined at 40 CFR Section

The hazardous waste exclusion program is not

if it: (1) is listed in Subpart D of 40 CFR
Subpart C

78

Part 261 (termed a "listed" waste); (2) exhibits These sources are not regulated under 40 CFR

a characteristic of a hazardous waste as Part 761 and, therefore, are not part of the

defined in Subpart C of 40 CFR Part 261; or detection program required by §258.20.

(3) is a mixture of a listed hazardous waste Commercial or industrial sources of PCB

and a non-hazardous solid waste. wastes that should be addressed by the

Characteristics of hazardous wastes as defined program include:

in Subpart C of 40 CFR Part 261 include

ignitability, corrosivity, reactivity, and ! Mineral oil and dielectric fluids

toxicity. The toxicity characteristic leaching containing PCBs;

procedure (TCLP) is the test method used to

determine the mobility of organic and ! Contaminated soil, dredged material,

inorganic compounds present in liquid, solid, sewage sludge, rags, and other debris

and multiphase wastes. The TCLP is from a release of PCBs;

presented in Appendix II of Part 261.

The MSWLF Criteria exclude CESQG waste equipment containing dielectric fluids;

(as defined in 40 CFR §261.5) from the and

definition of "regulated hazardous wastes."

CESQG waste includes listed hazardous ! Hydraulic machines.

wastes or wastes that exhibit a characteristic

of a hazardous waste that are generated in The owner or operator is required to

quantities no greater than 100 kg/month, or implement a program to detect and exclude

for acute hazardous waste, 1 kg/month. regulated hazardous wastes and PCBs from

Under 40 CFR §261.5(f)(3)(iv) and (g)(3)(iv), disposal in the landfill unit(s). This program

conditionally exempt small quantity generator must include elements for: 

hazardous wastes may be disposed at facilities

permitted, licensed, or registered by a State to ! Random inspections of incoming loads or

manage municipal or industrial solid waste. other prevention methods;

Other solid wastes are excluded from ! Maintenance of inspection records;

regulation as a hazardous waste under 40

CFR §261.4(b) and may be accepted for ! Facility personnel training; and

disposal at a MSWLF unit. Refer to

§261.4(b) for a listing of these wastes. ! Notification to appropriate authorities if

PCBs are regulated under the Toxic detected.

Substances Control Act (TSCA), but PCBcontaining wastes are considered hazardous Each of these program elements is discussed

wastes in some States. PCBs typically are not separately on the following pages.

found in consumer wastes except for

fluorescent ballast and small capacitors in Inspections

white goods and electrical appliances. An inspection is typically a visual observation

! Transformers and other electrical

hazardous wastes or PCB wastes are

of the incoming waste loads by
Operating Criteria

79

an individual who is trained to identify Inspection priority also can be given to

regulated hazardous or PCB wastes that would haulers with unknown service areas, to loads

not be acceptable for disposal at the MSWLF brought to the facility in vehicles not typically

unit. An inspection is considered satisfactory used for disposal of municipal solid waste,

if the inspector knows the nature of all and to loads transported by previous would-be

materials received in the load and is able to offenders. For wastes of unidentifiable nature

discern whether the materials are potentially received from sources other than households

regulated hazardous wastes or PCB wastes. (e.g., industrial or commercial

Ideally, all loads should be screened; the transporter about the source/composition

however, it is generally not practical to of the materials.

inspect in detail all incoming loads. Random

inspections, therefore, can be used to provide Loads should be inspected prior to actual

a reasonable means to adequately control the disposal of the waste at the working face of

receipt of inappropriate wastes. Random the landfill unit to provide the facility owner

inspections are simply inspections made on or operator the opportunity to refuse or accept

less than every load. the wastes. Inspections can be conducted on

The frequency of random inspections may be transfer of the waste to the disposal facility.

based on the type and quantity of wastes Inspections also may occur at the tipping floor

received daily, and the accuracy and located near the facility scale house, inside the

confidence desired in conclusions drawn from site entrance, or near, or adjacent to, the

inspection observations. Because statistical working face of the landfill unit. An

parameters are not provided in the regulation, inspection flow chart to identify, accept, or

a reasoned, knowledge-based approach may refuse solid waste is provided as Figure 3-1.

be taken. A random inspection program may

take many forms such as inspecting every Inspections of materials may be accomplished

incoming load one day out of every month or by discharging the vehicle load in an area

inspecting one or more loads from designed to contain potentially hazardous

transporters of wastes of unidentifiable nature wastes that may arrive at the facility. The

each day. If these inspections indicate that waste should be carefully spread for

unauthorized wastes are being brought to the observation using a front end loader or other

MSWLF site, then the random inspection piece of equipment. Personnel should be

program should be modified to increase the trained to identify suspicious wastes. Some

frequency of inspections. indications of suspicious wastes are:

Inspection frequency also can vary depending • Hazardous placards or marking;

on the nature of the waste. For example,

wastes received predominantly from • Liquids;

commercial or industrial sources may require

more frequent inspections than wastes • Powders or dusts;

predominantly from households. 

establishments), the inspector should question

a tipping floor of a transfer station before
Figure 3-1

Hazardous Waste Inspection Decision Tree

Inspection Prior to Working Face

80
Operating Criteria

81

• Sludges; it is disposed of properly. Most facilities

• Bright or unusual colors;

• Drums or commercial size containers; or Characteristic Leaching Procedure (TCLP)

• Chemical odors. wastes including corrosivity, ignitability, and

The owner or operator should develop hazardous should be handled and stored as a

specific procedures to be followed when hazardous waste until a determination is

suspicious wastes are discovered. The made. 

procedure should include the following

points: If the wastes temporarily stored at the site are

• Segregate the wastes; operator is responsible for the management of

• Question the driver; from the facility, the waste must be: (1) stored

• Review the manifest (if applicable); requirements of a hazardous waste generator,

• Contact possible source; transporter, and (4) sent to a permitted

• Call the appropriate State or Federal facility for disposal. These requirements are

agencies; discussed further in this section.

• Use appropriate protective equipment; Alternative Methods for Detection and

• Contact laboratory support if required; and

• Notify a response agency if necessary. inspections as an acceptable means of

Containers with contents that are not easily wastes, preventing the disposal of these

identifiable, such as unmarked 55-gallon wastes may be accomplished through other

drums, should be opened only by properly methods. These methods may include

trained personnel. Because these drums could receiving only household wastes and

contain hazardous waste, they should be processed (shredded or baled) wastes that are

refused whenever possible. Upon verifying screened for the presence of the excluded

that the solid waste is acceptable, it may then wastes prior to processing. A pre-acceptance

be transferred to the working face for agreement between the owner or operator and

disposal. the waste hauler is another alternative method.

Some facilities may consider it reasonable to presented as Appendix I. The owner or

test unidentified waste, store it, and see that operator should 

would not consider this reasonable.

Testing typically would include The Toxicity

and other tests for characteristics of hazardous

reactivity. Wastes that are suspected of being

determined to be hazardous, the owner or

the waste. If the wastes are to be transported

at the MSWLF facility in accordance with

(2) manifested, (3) transported by a licensed

Treatment, Storage, or Disposal (TSD)

Prevention

While the regulations explicitly refer to

detecting regulated hazardous wastes and PCB

An example of a pre-acceptance agreement is
Subpart C

82

keep any such agreements concerning these Training also should address hazardous waste

alternatives in the operating record. handling procedures, safety precautions, and

Recordkeeping information is provided in training courses

A record should be kept of each inspection Safety and Health Act (OSHA) under 29 CFR

that is performed. These records should be §1910.120. Information covered in these

included and maintained in the facility courses includes regulatory requirements

operating record. Larger facilities that take under 40 CFR Parts 260 through 270, 29 CFR

large amounts of industrial and commercial Part 1910, and related guidance documents

wastes may use more detailed procedures than that discuss such topics as: general hazardous

smaller facilities that accept household waste management; identification of

wastes. Inspection records may include the hazardous wastes; transportation of hazardous

following information: wastes; standards for hazardous waste

! The date and time wastes were received for hazardous waste worker health and safety

inspection; training and monitoring requirements.

! Source of the wastes; Notification to Authorities and Proper

! 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.

recordkeeping requirements. This

designed to comply with the Occupational

treatment; storage and disposal facilities; and

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 
Operating Criteria

83

with all applicable Federal and State analogous State/Tribal requirements. The

regulations. owner or operator is required to:

Operators of MSWLF facilities should be ! Obtain an EPA identification number

prepared to handle hazardous wastes that are (EPA form 8700-12 may be used to

inadvertently received at the MSWLF facility. apply for an EPA identification number;

This may include having containers such as State or Regional personnel may be able

55-gallon drums available on-site and to provide a provisional identification

retaining a list of names and telephone number over the telephone);

numbers of the nearest haulers licensed to

transport hazardous waste. ! Package the waste in accordance with

Hazardous waste may be stored at the regulations under 49 CFR Parts 173, 178,

MSWLF facility for 90 days, provided that and 179 (The container must be labeled,

the following procedures required by 40 CFR marked, and display a placard in

§262.34, or applicable State requirements, are accordance with DOT regulations on

followed: hazardous wastes under 49 CFR Part

! 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 

Department of Transportation (DOT)

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
Subpart C

84

! Manifest the PCB waste for shipment to a 3.3.2 Applicability

permitted incinerator, chemical waste

landfill, or high efficiency boiler The regulation applies to all MSWLF units

(depending on the nature of the PCB receiving waste after October 9, 1993. The

waste) for disposal. regulation requires MSWLF unit owners and

3.3 COVER MATERIAL operating day. More frequent application of

REQUIREMENTS soil may be required if the soil cover does not

40 CFR §258.21 control:

3.3.1 Statement of Regulation ! Disease vectors (e.g., birds, flies and

(a) Except as provided in paragraph (b)

of this section, the owners or operators of ! Fires;

all MSWLF units must cover disposed solid

waste with six inches of earthen material at ! Odors;

the end of each operating day, or at more

frequent intervals if necessary, to control ! Blowing litter; and

disease vectors, fires, odors, blowing litter,

and scavenging. ! Scavenging.

(b) Alternative materials of an The Director of an approved State may allow

alternative thickness (other than at least six an owner or operator to use alternative cover

inches of earthen material) may be material of an alternative thickness or grant a

approved by the Director of an approved temporary waiver of this requirement. An

State if the owner or operator alternative material must not present a threat

demonstrates that the alternative material to human health and the environment, and

and thickness control disease vectors, fires, must continue to control disease vectors, fires,

odors, blowing litter, and scavenging odors, blowing litter, and scavenging. The

without presenting a threat to human only basis for a temporary waiver from the

health and the environment. requirement to cover at the end of each

(c) The Director of an approved State seasonal climatic conditions make compliance

may grant a temporary waiver from the impractical.

requirement of paragraph (a) and (b) of

this section if the owner or operator 3.3.3 Technical Considerations

demonstrates that there are extreme

seasonal climatic conditions that make Owners and operators of new MSWLF units,

meeting such requirements impractical. existing MSWLF units, and lateral expansions

operators to cover wastes with a 6-inch layer

of earthen material at the end of each

other insects, rodents);

operating day would be where extreme

are required to cover solid waste at the end of

each operating day with six inches of earthen

material. This cover 
Operating Criteria

85

material requirement is not related to the final 1) Side by side (six inches of earthen

cover required under §258.60. materials and alternative cover) test pads;

The placement of six inches of cover controls 2) Full-scale demonstration; and

disease vectors (birds, insects, or rodents that

represent the principal transmission pathway 3) Short-term full-scale tests.

of a human disease) by preventing egress

from the waste and by preventing access to Alternative daily cover materials may include

breeding environments or food sources. indigenous materials or commerciallyCovering also reduces exposure of available materials. Indigenous materials are

combustible materials to ignition sources and those materials that would be disposed as

may reduce the spread of fire if the disposed waste; therefore, using these materials is an

waste burns. Odors and blowing litter are efficient use of landfill space. Examples of

reduced by eliminating the direct contact of indigenous materials include (USEPA, 1992):

wind and disposed waste. Similarly,

scavenging is reduced by removing the waste • Ash from municipal waste

from observation. Should these unwanted combustors and utility companies;

effects of inadequate cover persist, the owner

or operator may increase the amount of soil • Compost-based material;

used or apply it more frequently. Any soil

type can meet the requirements of the • Foundry sand from the

regulation when placed in a six-inch layer. manufacturing process of discarding

Approved States may allow demon-strations

of alternative daily cover materials. The rule • Yard waste such as lawn clippings,

does not specify the time frame for the leaves, and tree branches;

demonstration; usually the State decides. A

period of six months should be ample time for • Sludge-based materials (i.e., sludge

the owner or operator to make the demonstra- treated with lime and mixed with ash

tion. There are no numerical require-ments or soil);

for the alternative cover; rather, the

alternative cover must control disease vectors, • Construction and demolition debris

fires, odors, blowing litter, and scavenging (which has been processed to form a

without presenting a threat to human health slurry);

and the environment.

Demonstrations can be conducted in a variety

of ways. Some suggested methods for • Discarded carpets; and

demonstrating alternative covers are:

used dies;

• Shredded automobile tires;

• Grit from municipal wastewater

treatment plants.
Subpart C

86

Commercially developed alternatives have ! Spreading and compacting the soil to

been on the market since the mid-1980s. achieve the required functions.

Some of the commercial alternative materials

require specially designed application Extremely cold conditions may prevent the

equipment, while others use equipment efficient excavation of soil from a borrow pit

generally available at most landfills. Some of or the spreading and compaction of the soil on

the types of commercially available daily the waste. Extremely wet conditions (e.g.,

cover materials include (USEPA, 1992): prolonged rainfall, flooding) may prevent

• Foam that usually is sprayed on the and may make it impractical to excavate or

working face at the end of the day; spread and compact. The duration of waivers

• Geosynthetic products such as a tarp or storms, or as long as several months for

fabric panel that is applied at the end of extreme seasonal climatic conditions.

the working day and removed at the

beginning of the following working

day; and 3.4 DISEASE VECTOR CONTROL

• Slurry products (e.g., fibers from

recycled newspaper and wood chip 3.4.1 Statement of Regulation

slurry, clay slurry).

Other criteria to consider when selecting an MSWLF units must prevent or control onalternative daily cover material include site populations of disease vectors using

availability and suitability of the material, techniques appropriate for the protection

equipment requirements, and cost. of human health and the environment.

The temporary climatic waiver of the cover (b) For purposes of this section,

requirement is available only to owners or disease vectors means any rodents, flies,

operators in approved States. The State mosquitoes, or other animals, including

Director may grant a waiver if the owner or insects, capable of transmitting disease to

operator demonstrates that meeting the humans.

requirements would be impractical due to

extreme seasonal climatic conditions. 3.4.2 Applicability

Activities that may be affected by extreme

seasonal climatic conditions include: The regulation applies to existing MSWLF

! Obtaining cover soil from a borrow pit; units. The owner or operator is required to

! Transporting cover soil to the working populations of rodents, flies, mosquitoes, or

face; or other animals, including other insects. The

transporting cover soil to the working face

may be as short as one day for unusual rain

40 CFR §258.22

(a) Owners or operators of all

units, lateral expansions, and new MSWLF

prevent or control on-site disease vector

techniques that may be used in fulfilling this

requirement must be appropriate for the
Operating Criteria

87

protection of human health and the Vectors may reach the landfill facility not

environment. only from areas adjacent to the landfill, but

3.4.3 Technical Considerations and breeding of disease vectors. Such modes

Disease vectors such as rodents, birds, flies, collection vehicles and transfer stations.

and mosquitoes typically are attracted by These transport modes and areas also should

putrescent waste and standing water, which be included in the disease vector control

act as a food source and breeding ground. program if disease vectors at the landfill

Putrescent waste is solid waste that contains facility become a problem. Keeping the

organic matter (such as food waste) capable of collection vehicles and transfer stations

being decomposed by micro-organisms. A covered; emptying and cleaning the collection

MSWLF facility typically accepts putrescent vehicles and transfer stations; using repellents,

wastes. insecticides, or rodenticides; and reproductive

Application of cover at the end of each disease vectors in these areas. 

operating day generally is sufficient to control

disease vectors; however, other vector control

alternatives may be required. These 3.5 EXPLOSIVE GASES CONTROL

alternatives could include: reducing the size 40 CFR §258.23

of the working face; other operational

modifications (e.g., increasing cover 3.5.1 Statement of Regulation

thickness, changing cover type, density,

placement frequency, and grading); repellents, (a) Owners or operators of all MSWLF

insecticides or rodenticides; composting or units must ensure that:

processing of organic wastes prior to disposal;

and predatory or reproductive control of (1) The concentration of methane gas

insect, bird, and animal populations. generated by the facility does not exceed 25

Additional methods to control birds are percent of the lower explosive limit for

discussed in Chapter 2 (Airport Safety). methane in facility structures (excluding

Mosquitoes, for example, are attracted by components); and

standing water found at MSWLFs, which can

provide a potential breeding ground after only (2) The concentration of methane gas

three days. Water generally collects in does not exceed the LEL for methane at the

surface depressions, open containers, exposed facility property boundary.

tires, ponds resulting from soil excavation,

leachate storage ponds, and siltation basins. (b) Owners or operators of all MSWLF

Landfill operations that minimize standing units must implement a routine methane

water and that use an insecticide spraying monitoring program to ensure that the

program ordinarily are effective in controlling standards of paragraph (a) of this section

mosquitoes. are met.

through other modes conducive to harborage

may include residential and commercial route

control are all measures available to reduce

gas control or recovery system
Subpart C

88

(1) The type and frequency of (4) The Director of an approved State

monitoring must be determined based on may establish alternative schedules for

the following factors: demonstrating compliance with paragraphs

(i) Soil conditions;

(ii) The hydrogeologic conditions explosive limit (LEL) means the lowest

surrounding the facility; percent by volume of a mixture of explosive

(iii) The hydraulic conditions 25 C and atmospheric pressure.

surrounding the facility; and

(iv) The location of facility

structures and property The regulation applies to existing MSWLF

boundaries. units, lateral expansions, and new MSWLF

(2) The minimum frequency of MSWLF structures can potentially result in

monitoring shall be quarterly. fire and explosions that can endanger

(c) If methane gas levels exceeding the occupants of nearby structures, or cause

limits specified in paragraph (a) of this damage to landfill containment structures.

section are detected, the owner or operator These hazards are preventable through

must: monitoring and through corrective action

(1) Immediately take all necessary steps limits in the facility structures (excluding gas

to ensure protection of human health and control or recovery system components), or at

notify the State Director; the facility property boundary. MSWLF

(2) Within seven days of detection, place with the following requirements:

in the operating record the methane gas

levels detected and a description of the ! Monitor at least quarterly;

steps taken to protect human health; and

(3) Within 60 days of detection, health in the event of methane gas levels

implement a remediation plan for the exceeding 25% of the lower explosive

methane gas releases, place a copy of the limit (LEL) in facility structures, such as

plan in the operating record, and notify the evacuating the building;

State Director that the plan has been

implemented. The plan shall describe the ! Notify the State Director if methane

nature and extent of the problem and the levels exceed 25% of the LEL in facility

proposed remedy. structures or exceed the LEL at the

(2) and (3).

(d) For purposes of this section, lower

gases in air that will propagate a flame at

o

3.5.2 Applicability

units. The accumulation of methane in

employees, users of the disposal site, and

should methane gas levels exceed specified

facility owners and operators must comply

! Take immediate steps to protect human

facility property boundary;
Operating Criteria

89

! Within 7 days of detection, place in the readily identified by its "rotten egg" smell at

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 (CH ),

4

carbon dioxide (CO ), and lesser amounts of 2

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 

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 
Subpart C

90

shallow portions of the landfill unit, which Stressed vegetation may indicate gas

may alter microbial activity, particularly migration. Landfill gas present in the soil

methane production and gas composition. atmosphere tends to make the soil anaerobic

Migration of landfill gas is caused by asphyxiating the roots of plants. Generally,

concentration gradients, pressure gradients, the higher the concentration of combustible

and density gradients. The direction in which gas and/or carbon dioxide and the lower the

landfill gas will migrate is controlled by the amount of oxygen, the greater the extent of

driving gradients and gas permeability of the damage to vegetation (Flowers, et. al, 1982).

porous material through which it is migrating.

Generally, landfill gas will migrate through Gas Monitoring

the path of least resistance. 

Coarse, porous soils such as sand and gravel unit/facility must implement a routine

will allow greater lateral migration or methane monitoring program to comply with

transport of gases than finer-grained soils. the lower explosive limit (LEL) requirements

Generally, resistance to landfill gas flow for methane. Methane is explosive when

increases as moisture content increases and, present in the range of 5 to 15 percent by

therefore, an effective barrier to gas flow can volume in air. When present in air at

be created under saturated conditions. Thus, concentrations greater than 15 percent, the

readily drained soil conditions, such as sands mixture will not explode. This 15 percent

and gravels above the water table, may threshold is the Upper Explosive Limit

provide a preferred flowpath, but unless finer- (UEL). The UEL is the maximum

grained soils are fully saturated, landfill gases concentration of a gas or vapor above which

also can migrate in a "semi-saturated" zone. the substance will not explode when exposed

Figure 3-2 illustrates the potential effects of to a source of ignition. The explosive hazard

surrounding geology on gas migration. range is between the LEL and the UEL. Note,

While geomembranes may not eliminate the UEL remain a significant concern; fire

landfill gas migration, landfill gas in a closed and asphyxiation can still occur at these

MSWLF unit will tend to migrate laterally if levels. In addition, even a minor dilution of

the final cover contains a geomembrane and if the methane by increased ventilation can bring

the side slopes of the landfill do not contain the mixture back into the explosive range.

an effective gas barrier. Lateral gas migration

is more common in older facilities that lack To demonstrate compliance, the

appropriate gas control systems. The degree owner/operator would sample air within

of lateral migration in older facilities also may facility structures where gas may accumulate

depend on the type of natural soils and in soil at the property boundary. Other

surrounding the facility. monitoring methods may include: (1)

by displacing the oxygen, thereby

The owner or operator of a MSWLF

however, that methane concentrations above

sampling gases from probes within the landfill

unit or from within the leachate collection

system; or (2) sampling gases
Figure 3-2

Potential Effects of

Surrounding Geology on Gas Migration

91
Subpart C

92

from monitoring probes installed in soil structures, and changes in landscaping or land

between the landfill unit and either the use practices. The rate of landfill gas

property boundary or structures where gas migration as a result of these anticipated

migration may pose a danger. A typical gas changes and the site-specific conditions

monitoring probe installation is depicted in provides the basis for establishing monitoring

Figure 3-3. frequency. Monitoring is to be conducted at

Although not required by the regulations,

collection of data such as water presence and The number and location of gas probes is also

level, gas probe pressure, ambient site-specific and highly dependent on

temperature, barometric pressure, and the subsurface conditions, land use, and location

occurrence of precipitation during sampling, and design of facility structures. Monitoring

provides useful information in assessing for gas migration should be within the more

monitoring results. For example, falling permeable strata. Multiple or nested probes

barometric pressure may cause increased are useful in defining the vertical

subsurface (gas) pressures and corresponding configuration of the migration pathway.

increased methane content as gas more readily Structures with basements or crawl spaces are

migrates from the landfill. Gas probe more susceptible to landfill gas infiltration.

pressure can be measured using a portable Elevated structures are typically not at risk.

gauge capable of measuring both vacuum and

pressure in the range of zero to five inches of Measurements are usually made in the field

water pressure (or other suitable ranges for with a portable methane meter, explosimeter,

pressure conditions); this pressure should be or organic vapor analyzer. Gas samples also

measured prior to methane measurement or may be collected in glass or metal containers

sample collection in the gas probe. A for laboratory analysis. Instruments with

representative sample of formation scales of measure in "percent of LEL" can be

(subsurface) gases can be collected directly calibrated and used to detect the presence of

from the probe. Purging typically is not methane. Instruments of the hot-wire

necessary due to the small volume of the Wheatstone bridge type (i.e., catalytic

probe. A water trap is recommended to combustion) directly measure combustibility

protect instrumentation that is connected of the gas mixture withdrawn from the probe.

directly to the gas probe. After measurements The thermal conductivity type meter is

are obtained, the gas probe should be capped susceptible to interference as the relative gas

to reduce the effects of venting or barometric composition and, therefore, the thermal

pressure variations on gas composition in the conductivity, changes. Field instruments

vicinity of the probe. should be calibrated prior to measurements

The frequency of monitoring should be monitoring activity. 

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 

least quarterly.

and should be rechecked after each day's
Operating Criteria

93

Figure 3-3

Typical Gas Monitoring Probe
Subpart C

94

Laboratory measurements with organic vapor soil within the area of concern. The

analyzers or gas chromatographs may be used investigation should consider possible causes

to confirm the identity and concentrations of of the increase in gas concentrations such as

gas. landfill operational procedures, gas control

In addition to measuring gas composition, closure activity. Based on the extent and

other indications of gas migration may be nature of the excessive methane migration, a

observed. These include odor (generally remedial action should be described, if the

described as either a "sweet" or a rotten egg exceedance is persistent, that can be

(H S) odor), vegetation damage, septic soil, implemented within the prescribed schedule. 2

and audible or visual venting of gases, The sixty-day schedule does not address the

especially in standing water. Exposure to protection of human health and the

some gases can cause headaches and nausea. environment. The owner or operator still

If methane concentrations are in excess of 25 protection of human health, including interim

percent of the LEL in facility structures or measures.

exceed the LEL at the property boundary, the

danger of explosion is imminent. Immediate Landfill Gas Control Systems

action must be taken to protect human health

from potentially explosive conditions. All Landfill gas may vent naturally or be

personnel should be evacuated from the area purposely vented to the atmosphere by

immediately. Venting the building upon exit vertical and/or lateral migration controls.

(e.g., leaving the door open) is desirable but Systems used to control or prevent gas

should not replace evacuation procedures. migration are categorized as either passive or

Owners and operators in unapproved States preferential flowpaths by means of natural

have 60 days after exceeding the methane pressure, concentration, and density gradients.

level to prepare and implement a remediation Passive systems are primarily effective in

plan. The remediation plan should describe controlling convective flow and have limited

the nature and extent of the methane problem success controlling diffusive flow. Active

as well as a proposed remedy. systems are effective in controlling both types

To comply with this 60-day schedule, an equipment to direct or control landfill gas by

investigation of subsurface conditions may be providing negative or positive pressure

needed in the vicinity of the monitoring probe gradients. Suitability of the systems is based

where the criterion was exceeded. The on the design and age of the landfill unit, and

objectives of this investigation should be to on the soil, hydrogeologic, and hydraulic

describe the frequency and lateral and vertical conditions of the facility and surrounding

extent of excessive methane migration (that environment. Because of these variables, both

which exceeds the criterion). Such an systems have had varying degrees of success.

investigation also may yield additional

characterization of unsaturated Passive systems may be used in conjunction

system failure or upset, climatic conditions, or

must take all steps necessary to ensure

active systems. Passive systems provide

of flow. Active systems use mechanical

with active systems. An example of this 
Operating Criteria

95

may be the use of a low-permeability passive 150 megagrams per year (167 tons per year)

system for the closed portion of a landfill unit or greater. Allowable control systems include

(for remedial purposes) and the installation of open and enclosed flares, and on-site or offan active system in the active portion of the site facilities that process the gas for

landfill unit (for future use). subsequent sale or use. EPA believes that,

Selection of construction materials for either systems may be more cost-effective than

type of gas control system should consider the passive systems in ensuring that the system

elevated temperature conditions within a effectively captures the gas that is generated

landfill unit as compared to the ambient air or within the landfill unit. The provisions for

soil conditions in which gas control system new landfill units are self-implementing and

components are constructed. Because will be effective upon promulgation of the

ambient conditions are typically cooler, water rule.

containing corrosive and possibly toxic waste

constituents may be expected to condense. In addition to the emissions standards for new

This condensate should be considered in municipal solid waste landfill units, the

selecting construction materials. Provisions regulations proposed on May 30, 1991

for managing this condensate should be establish guidelines for State programs for

incorporated to prevent accumulation and reducing NMOC emissions from certain

possible failure of the collection system. The existing municipal landfill units. These

condensate can be returned to the landfill unit provisions apply to landfill units for which

if the landfill is designed with a composite construction was commenced before May 30,

liner and leachate collection system per 1991, and that have accepted waste since

§258.40(a)(2). See Chapter 4 for information November 8, 1987 or that have remaining

regarding design. See Section 3.10 of this capacity. Essentially, the State must require

Chapter for information regarding liquids in the same kinds of collection and control

landfills. systems for landfill units that meet the size

Additional provisions (under the Clean Air for new landfill units. The requirements for

Act) were proposed on May 30, 1991 (56 FR existing facilities will be effective after the

24468), that would require the owners/ State revises its State Implementation Plan

operators of certain landfill facilities to install and receives approval from EPA.

gas collection and control systems to reduce

the emissions of nonmethane organic The rule is scheduled to be promulgated in

compounds (NMOCs). The proposed rule late 1993; the cutoff numbers for landfill size

amends 40 CFR Parts 51, 52, and 60. For and emission quantity may be revised in the

new municipal solid waste landfill units (those final rule. EPA expects that the new

for which construction was begun after May regulations will affect less than 9% of the

30, 1991), and for those units that have a municipal landfill facilities in the U.S.

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 

depending on landfill design, active collection

criteria and emissions levels outlined above
Subpart C

96

Passive Systems Some problems have been associated with

Passive gas control systems rely on natural may accumulate in vent pipes, preventing gas

pressure and convection mechanisms to vent from venting. Vent pipes 

landfill gas to the atmosphere. Passive at the surface are susceptible to clogging by

systems typically use "high-permeability" or vandalism. Biological clogging of the system

"low-permeability" techniques, either is also more common in passive systems.

singularly or in combination at a site. Highpermeability systems use conduits such as Active Systems

ditches, trenches, vent wells, or perforated

vent pipes surrounded by coarse soil to vent Active gas control systems use mechanical

landfill gas to the surface and the atmosphere. means to remove landfill gas and consist of

Low-permeability systems block lateral either positive pressure (air injection) or

migration through barriers such as synthetic negative pressure (extraction) systems.

membranes and high moisture-containing Positive pressure systems induce a pressure

fine-grained soils. greater than the pressure of the migrating gas

Passive systems may be incorporated into a the landfill unit in a controlled manner.

landfill design or may be used for remedial or Negative pressure systems extract gas from a

corrective purposes at both closed and active landfill by using a blower to pull gas out of

landfills. They may be installed within a the landfill. Negative pressure systems are

landfill unit along the perimeter, or between more commonly used because they are more

the landfill and the disposal facility property effective and offer more flexibility in

boundary. A detailed discussion of passive controlling gas migration. The gas may be

systems for remedial or corrective purposes recovered for energy conversion, treated, or

may be found in U.S. EPA (1985). combusted in a flare system. Typical

A passive system may be incorporated into Figure 3-5. Negative pressure systems may

the final cover system of a landfill closure be used as either perimeter gas control

design and may consist of perforated gas systems or interior gas collection/recovery

collection pipes, high permeability soils, or systems. For more information regarding

high transmissivity geosynthetics located just negative pressure gas control systems, refer to

below the low-permeability gas and hydraulic U.S. EPA (1985).

barrier or infiltration layer in the cover

system. These systems may be connected to An active gas extraction well is depicted in

vent pipes that vent gas through the cover Figure 3-6. Gas extraction wells may be

system or that are connected to header pipes installed within the landfill waste or, as

located along the perimeter of the landfill depicted in Figure 3-7A and Figure 3-7B,

unit. Figure 3-4 illustrates a passive system. perimeter extraction trenches could be used.

The landfill gas collection system also may be One possible configuration of an interior gas

connected with the leachate collection system collection/recovery system is illustrated in

to vent gases in the headspace of leachate

collection pipes.

passive systems. For example, snow and dirt

and drive the gas out of the soil and/or back to

components of a flare system are shown in
Operating Criteria

97

Figure 3-4 

Passive Gas Control System

(Venting to Atmosphere)
Subpart C

98

Figure 3-5. Example Schematic Diagram of a

Ground-based Landfill Gas Flare
Figure 3-6 Example of a Gas Extraction Well

99
Figure 3-7A. Perimeter Extraction Trench System

Figure 3-7B. Perimeter Extraction Trench System

100
Operating Criteria

101

Figure 3-8. The performance of active 3.6 AIR CRITERIA

systems is not as sensitive to freezing or 40 CFR §258.24

saturation of cover soils as that of passive

systems. Although active gas systems are 3.6.1 Statement of Regulation

more effective in withdrawing gas from the

landfill, capital, operation, and maintenance (a) Owners or operators of all

costs of such systems will be higher and these MSWLFs must ensure that the units do not

costs can be expected to continue throughout violate any applicable requirements

the post-closure period. At some future time, developed under a State Implementation

owners and operators may wish to convert Plan (SIP) approved or promulgated by the

active gas controls into passive systems when Administrator pursuant to section 110 of

gas production diminishes. The conversion the Clean Air Act, as amended.

option and its environmental effect (i.e., gas

release causing odors and health and safety (b) Open burning of solid waste, except

concerns) should be addressed in the original for the infrequent burning of agricultural

design. wastes, silvicultural wastes, land-clearing

There are many benefits to recovering landfill emergency clean-up operations, is

gas. Landfill gas recovery systems can reduce prohibited at all MSWLF units.

landfill gas odor and migration, can reduce

the danger of explosion and fire, and may be 3.6.2 Applicability

used as a source of revenue that may help to

reduce the cost of closure. Landfill gas can be The regulation applies to existing MSWLF

used with a minimal amount of treatment or units, lateral expansions to existing MSWLF

can be upgraded to pipeline standards units, and new MSWLF units. Routine open

(SWANA, 1992). An upgraded gas is one burning of municipal solid waste is

which has had the carbon dioxide and other prohibited. Infrequent burning of agricultural

noncombustible constituents removed. and silvicultural wastes, diseased trees, or

Raw landfill gas may be used for heating up operations is allowed when in compliance

small facilities and water, and may require with any applicable requirements developed

removal of only water and particulates for this under a State Implementation Plan (SIP) of

application. A slightly upgraded gas can be the Clean Air Act. Agricultural waste does

used for both water and space heating as well not include empty pesticide containers or

as lighting, electrical generation, waste pesticides.

cogeneration, and as a fuel for industrial

boilers-burners. Landfill gas also may be 3.6.3 Technical Considerations

processed to pipeline quality to be sold to

utility companies and may even be used to Air pollution control requirements are

fuel conventional vehicles. The amount of developed under a SIP, which is developed by

upgrading and use of landfill gas is dependent the State and approved by the EPA

on the landfill size. Administrator. The owner or operator of a 

debris, diseased trees, or debris from

debris from land clearing or emergency clean-
Figure 3-8

Example of an Interior Gas Collection/Recovery System

102
Operating Criteria

103

MSWLF unit should consult the State or local [Note: The Agency plans to issue regulations

agency responsible for air pollution control to under the Clean Air Act to control landfill gas

ascertain that the burning of wastes complies emissions from large MSWLF units in 1993.

with applicable requirements developed under These regulations are found at 40 CFR Parts

the SIP. The SIP may include variances, 51, 52, and 60.]

permits, or exemptions for burning

agricultural wastes, silvicultural wastes, landclearing debris, diseased trees, or debris from 3.7 ACCESS REQUIREMENT

emergency clean-up operations. Routine 40 CFR §258.25

burning of wastes is banned in all cases, and

the SIP may limit burning of waste such as 3.7.1 Statement of Regulation

agricultural wastes to certain hours of the day;

days of the year; designated burn areas; Owners or operators of all MSWLF units

specific types of incinerators; atmospheric must control public access and prevent

conditions; and distance from working face, unauthorized vehicular traffic and illegal

public thoroughfares, buildings, and dumping of wastes by using artificial

residences. barriers, natural barriers, or both, as

Requirements under the SIP also may include the environment.

notifying applicable State or local agencies

whose permits may: (1) restrict times when 3.7.2 Applicability

limited burning of waste may occur; (2)

specify periods when sufficient fire protection The regulation applies to existing MSWLF

is deemed to be available; or (3) limit burning units, lateral expansions, and new MSWLF

to certain areas. units. The owner or operator is required to

Open burning is defined under §258.2 as the except under controlled conditions during

combustion of solid waste: (1) without hours when wastes are being received.

control of combustion air to maintain

adequate temperature for efficient 3.7.3 Technical Considerations

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.

appropriate to protect human health and

prevent public access to the landfill facility,

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);
Subpart C

104

inadvertent or deliberate fires; and earth- 3.8.2 Applicability

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.

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 runoff/leachate 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
Operating Criteria

105

require treatment and generally can be The Soil Conservation Service (SCS) Method

combined with run-on waters. For landfills and/or the Rational Method are generally

with steep side slopes, a bench system may adequate for estimating storm flows for

provide the best solution for run-off control. designing run-on and/or run-off control

A bench creates a break in the slope where the systems. The SCS method estimates run-off

velocity of the stormwater run-off is expected volume from accumulated rainfall and then

to become erosive. The bench converts sheet applies the run-off volume to a simplified

flow run-off into channel flow. Benches triangular unit hydrograph for peak discharge

typically are spaced 30 to 50 feet apart up the estimation and total run-off hydrograph. A

slope. An alternative to benches is a system discussion of the development and use of this

of downchutes whereby stormwater is method is available from the U. S.

collected off the top of the landfill and Department of Agriculture, Soil Conservation

conveyed down the slope through a pipe or Service (1986).

channel. Caution should be taken not to

construct downchutes with heavy material The Rational Method approximates the

because of possible subsidence. Corrugated majority of surface water discharge supplied

metal pipes or plastic-lined channels are by the watershed upstream from the facility.

examples of lightweight materials that can be The Rational Method generally is used for

used for downchute construction. areas of less than 200 acres. A discussion of

Run-on and run-off must be managed in EPA (1988).

accordance with the requirements of the Clean

Water Act including, but not limited to, the Run-on/run-off control structures, both

National Pollutant Discharge Elimination temporary and permanent, may be

System (NPDES). [See Section 3.9 of this incorporated into the system design. Other

chapter for further information on compliance structures (not mentioned above) most

with the Clean Water Act.] frequently used for run-on/run-off control are

Run-on and run-off control systems must be and sedimentation basins. U.S. EPA (1985)

designed based on a 24-hour, 25-year storm. provides an in-depth discussion for each of

Information on the 24-hour, 25-year recurring these structures.

storm can be obtained from Technical Paper

40 "Rainfall Frequency Atlas of the United

States for Durations from 30 Minutes to 24 3.9 SURFACE WATER

Hours and Return Periods from 1 to 100 REQUIREMENTS

Years", prepared by the Weather Bureau 40 CFR §258.27

under the Department of Commerce.

Alternatively, local meteorological data can 3.9.1 Statement of Regulation

be analyzed to estimate the criterion storm.

To estimate run-on, the local watershed MSWLF units shall not:

should be identified and evaluated to

document the basis for run-on design flows. (a) Cause a discharge of pollutants into

the Rational Method may be found in U.S.

waterways, seepage ditches, seepage basins,

waters of the United States, including
Subpart C

106

wetlands, that violates any requirements of A MSWLF unit(s) that has a point source

the Clean Water Act, including, but not discharge must have a NPDES permit. Point

limited to, the National Pollutant Discharge source discharges for landfills include, but are

Elimination System (NPDES) not limited to: (1) the release of leachate

requirements, pursuant to section 402. from a leachate collection or on-site treatment

(b) Cause the discharge of a nonpoint (2) disposal of solid waste into waters of the

source of pollution to waters of the United United States; or (3) release of surface water

States, including wetlands, that violates (stormwater) run-off which is directed by a

any requirement of an area-wide or State- run-off control system into the waters of the

wide water quality management plan that United States. Leachate that is piped or

has been approved under section 208 or trucked off-site to a treatment facility is not

319 of the Clean Water Act, as amended. regarded as a point source discharge. 

3.9.2 Applicability The Clean Water Act (CWA) provides

The regulation applies to existing MSWLF waters of the United States, pollutants, and

units, lateral expansions, and new MSWLF discharge of pollutants. 

units. The owner or operator is required to

comply with the Clean Water Act for any Owners/operators also should be aware that

discharges to surface water or wetlands. there are regulations promulgated pursuant to

3.9.3 Technical Considerations from landfill facilities. These regulations

The owner or operator of a MSWLF facility applications to be submitted by certain

should determine if the facility is in landfills that accept or have accepted specific

conformance with applicable requirements of types of industrial waste. See 40 CFR Section

water quality plans developed under Sections 122.26(a)-(c), which originally appeared in

208 and 319 of the Clean Water Act, and the the Federal Register on November 16, 1990

National Pollutant Discharge Elimination (55 FR 47990).

System (NPDES) requirements under Section

402 of the Clean Water Act. The EPA and In addition, EPA codified several provisions

approved States have jurisdiction over pursuant to the Intermodal Surface

discharge of pollutants (other than dredge and Transportation Efficiency Act of 1991 into the

fill materials) in waters of the United States NPDES regulations. These regulations only

including wetlands. MSWLF units affect the deadlines for submitting permit

discharging pollutants or disposing of fill applications for stormwater discharges, and

material into waters of the United States they apply to both uncontrolled and controlled

require a Section 402 (NPDES) permit. sanitary landfills. "Uncontrolled sanitary

Discharge of dredge and fill material into landfills" are defined as landfills or open

waters of the United States is under the dumps that do not meet the requirements for

jurisdiction of the U.S. Army Corps of run-on or run-off controls that are found in

Engineers. the 

system into the waters of the United States;

clarifications of terms such as point source,

the CWA regarding stormwater discharges

require stormwater discharge permit
Operating Criteria

107

MSWLF Criteria, Section 258.25. this part. The owner or operator must

"Controlled sanitary landfills" are those that place the demonstration in the operating

do meet the run-on and run-off requirements. record and notify the State Director that it

The NPDES regulations specify that has been placed in the operating record. 

uncontrolled sanitary landfills owned or

operated by municipalities of less than (b) Containers holding liquid waste

100,000 (population) must submit a NPDES may not be placed in a MSWLF unit

permit application for their stormwater unless:

discharge or obtain coverage under a general

permit. For controlled sanitary landfills (1) The container is a small container

owned or operated by a municipality with a similar in size to that normally found in

population less than 100,000, there is no household waste;

requirement to submit a stormwater discharge

permit application (before October 1, 1992) (2) The container is designed to hold

unless a permit is required under Section liquids for use other than storage; or

402(p)(2)(A) or (E) of the Clean Water Act.

Other deadlines are set for municipalities with (3) The waste is household waste.

a population less than 250,000 that own or

operate a municipal landfill. For further (c) For purposes of this section:

information contact the Stormwater Hotline

(703) 821-4823. See the April 2, 1992 (1) Liquid waste means any waste

Federal Register (57 FR 11394), 40 CFR material that is determined to contain

122.26. "free liquids" as defined by Method 9095

3.10 LIQUIDS RESTRICTIONS Wastes, Physical/Chemical Methods" (EPA

40 CFR §258.28 Pub. No. SW-846).

3.10.1 Statement of Regulation (2) Gas condensate means the liquid

(a) Bulk or noncontainerized liquid process(es) at the MSWLF unit.

waste may not be placed in MSWLF units

unless: 3.10.2 Applicability

(1) The waste is household waste other The regulation applies to new MSWLF units,

than septic waste; or existing MSWLF units, and lateral expansions

(2) The waste is leachate or gas operator is prohibited from placing bulk or

condensate derived from the MSWLF unit non-containerized liquid waste, or

and the MSWLF unit, whether it is an containerized liquid waste into the MSWLF

existing or new unit, is designed with a unit. Liquids from households are exempt.

composite liner and leachate collection Tank trucks of wastes are not exempt.

system as described in §258.40 (a)(2) of 

(Paint Filter Liquids Test), as described in

"Test Methods for Evaluating Solid

generated as a result of gas recovery

of existing MSWLF units. The owner or
Subpart C

108

3.10.3 Technical Considerations special management requirements for sewage

The restriction of bulk or containerized

liquids is intended to control a source of Owners and operators of MSWLF units may

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

sludge that is codisposed with solid waste.]

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

30 cm.

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
Operating Criteria

109

Figure 3-9. Paint Filter Test Apparatus
Subpart C

110

have been a source of odor. In addition, a (6) Closure and post-closure care plans

discharge point may not allow for dissipation and any monitoring, testing, or analytical

of the leachate. (For additional information data as required by §§258.60 and 258.61 of

regarding the effectiveness of using leachate this Part; and

recirculation to enhance the rate of organic

degradation, see (Reinhart and Carson, (7) Any cost estimates and financial

1993).) assurance documentation required by

3.11 RECORDKEEPING (8) Any information demonstrating

REQUIREMENTS compliance with small community

40 CFR §258.29 exemption as required by §258.1(f)(2).

3.11.1 Statement of Regulation (b) The owner/operator must notify

(a) The owner or operator of a from paragraph (a) of this section have

MSWLF unit must record and retain near been placed or added to the operating

the facility in an operating record, or in an record, and all information contained in

alternative location approved by the the operating record must be furnished

Director of an approved state, the following upon request to the State Director or be

information as it becomes available: made available at all reasonable times for

(1) Any location restriction

demonstration required under Subpart B (c) The Director of an approved State

of this part; can set alternative schedules for

(2) Inspection records, training requirements as specified in paragraphs (a)

procedures, and notification procedures and (b), except for the notification

required in §258.20 of this Part; requirements in §258.10(b) and

(3) Gas monitoring results from

monitoring and any remediation plans 3.11.2 Applicability

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;

Subpart G of this Part.

the State Director when the documents

inspection by the State Director.

recordkeeping and notification

§258.55(g)(1)(iii).

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
Operating Criteria

111

procedures, notices, cost estimates, and • Date and time wastes were received during

financial assurance documentation. the inspection;

3.11.3 Technical Considerations • Names of the transporter and the driver;

The operating record should be maintained in • Source of the wastes;

a single location. The location may be at the

facility, at corporate headquarters, or at city • Vehicle identification numbers; and

hall, but should be near the facility. Records

should be maintained throughout the life of • All observations made by the inspector.

the facility, including the post-closure care

period. Upon placement of each required Training records should include procedures

document in the operating record, the State used to train personnel on hazardous waste

Director should be notified. The Director of and on PCB waste recognition. Notification

an approved State may establish alternative to EPA, State, and local agencies should be

requirements for recordkeeping, including documented.

using the State permit file for recordkeeping.

Recordkeeping at the landfill facility should remediation plans: If gas levels exceed 25

include the following: percent of the LEL for methane in any facility

(a) Location restriction demonstrations: the facility boundary, the owner or operator

Demonstrations are required for any location must place in the operating record, within

restrictions under Subpart B. The location seven days, the methane gas levels detected,

restrictions apply to: and a description of the steps taken to protect

• Airports; the owner or operator must place a copy of

• Floodplains; the operating record.

• Wetla (d) MSWLF unit design

• Fault areas; gas condensate in a MSWLF unit: If leachate

• Seismic impact zones; and MSWLF unit, documentation of a composite

• Unstable areas. of maintaining a maximum of 30 cm of

(b) Inspection records, training placed in the operating record.

procedures, and notification procedures:

Inspection records should include:

(c) Gas monitoring results and any

structures or exceed the LEL for methane at

human health. Within 60 days of detection,

the remediation plan used for gas releases in

documentation for placement of leachate or

and/or gas condensate are recirculated into the

liner and a leachate collection system capable

leachate head in the MSWLF unit must be
Subpart C

112

(e) Demonstration, certification, • A notice identifying the Part 258

monitoring, testing, or analytical finding Appendix II constituents that have

required by the ground-water criteria: exceededthe ground-water protection standard;

Documents to be placed in the operating

record include: • A certification by a qualified ground-

• Documentation of design, installation, the MSWLF unit caused the

development, and decommission of any contamination or an error in sampling,

monitoring wells, piezometers, and other analysis, statistical evaluation, or natural

measurement, sampling, and analytical ground-water variation caused a

devices; statistically significant increase (false

• Certification by a qualified ground-water constituents (if applicable);

scientist of the number, spacing, and

depths of the monitoring systems; • The remedies selected to remediate

• Documentation of sampling and analysis

programs and statistical procedures; • Certification of remediation completion.

• Notice of finding a statistically significant (f) Closure and post-closure plans and

increase over background for one or more any monitoring, testing, or analytical data

of the constituents listed in Appendix I of associated with these plans: The landfill

Part 258 (or alternative list in approved facility owner or operator is required to place

States) at any monitoring well at the waste a copy of the closure plan, post-closure plan,

management unit boundary (States with and a notice of intent to close the facility in

inadequate program) or the relevant point the operating record. Monitoring, testing, or

of compliance (approved States); analytical data associated with closure and

• Certification by a qualified ground-water ground-water and landfill gas monitoring

scientist that an error in sampling, analysis, must be placed in the operating record. A

statistical evaluation, or natural variation in copy of the notation on the deed to the

ground water caused an increase (false MSWLF facility property, as required

positive) of Appendix I constituents, or following closure, along with certification and

that a source other than the MSWLF unit verification that closure and post-closure

caused the contamination (if appropriate); activities have been completed in accordance

• A notice identifying any Appendix II (Part placed in the operating record.

258) constituents that have been detected

in ground water and their concentrations; (g) Estimates and financial assurance

water scientist that a source other than

positive) in Appendix II (Part 258)

ground-water contamination; and

post-closure information generated from

with their respective plans, also must be

documentation required: The following

documents must be placed in the operating

record:
Operating Criteria

113

• 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.
Subpart C

114

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. Gilman 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
115

APPENDIX I

Special Waste Acceptance Agreement
Appendix I. Example Special Waste Acceptance Agreement

116
CHAPTER 4

SUBPART D

DESIGN CRITERIA
118

CHAPTER 4

SUBPART D

TABLE OF CONTENTS

4.1 INTRODUCTION ........................................................ 121

4.2 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
119

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

CQA/CQC 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
120

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

4.5 PETITION PROCESS 40 CFR §258.40(e) ...................................... 191

4.5.1 Statement of Regulation ................................................ 191

4.5.2 Applicability ........................................................ 191

4.6 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
121

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 cm/sec, overlain by a flexible

-7

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 performancebased 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); 
Subpart D

122

! 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 the regulatory language for requirements

40 CFR §258.40(a)(1)

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

pertaining to composite liner and leachate

collection systems). 

(c) When approving a design that

complies with paragraph (a)(1) 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.)
Design Criteria

123

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

1,1,1-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)(1). 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 sitespecific data to adequately characterize the

existing ground-
Subpart D

124

water quality and the existing ground-water Assuming leachate is produced, the

flow regime (e.g., flow direction, horizontal demonstration should evaluate whether

and vertical gradients, hydraulic conductivity, constituents listed in Table 1 can be expected

stratigraphy, and aquifer thickness). to be present at concentrations greater than the

An assessment should be made of the effect must address the hydrogeologic characteristics

MSWLF facility construction will have on of the facility and the surrounding land to

site hydrogeology. The assessment should comply with §258.40(d). The following

focus on the reduced infiltration over the sections describe the various parts of a

landfill area and altered surface water run-off demonstration in greater detail.

patterns. Reduction of ground-water recharge

and changes in surface water patterns Leachate Characterization

resulting from landfill construction may affect

ground-water gradients in some cases and Leachate characterization should include an

may result in changes in lateral flow assessment and demonstration of the quantity

directions. One example of a hypothetical and composition of leachate anticipated at the

performance-based demonstration follows. proposed facility. Discussion of this

It is possible that a MSWLF unit located in an

arid climatic zone would not produce leachate Estimates of volumetric production rates of

from sources of water (e.g., precipitation) leachate are important in evaluating the fate

other than that existing within the waste at the and transport of the constituents listed in

time of disposal. In such an environment, an Table 1. Leachate production rates depend on

owner or operator may demonstrate that rainfall, run-on, run-off, evapotranspiration,

significant quantities of leachate would not be water table elevation relative to the bottom of

produced. The demonstration should be the landfill unit, in-place moisture content of

supported by evaluating historic precipitation waste, and the prevention of liquid disposal at

and evaporation data and the likelihood that the site. Run-on, run-off, and water table

the unit could be flooded as the result of factors can be managed traditionally through

heavy rains, surface run-off, or high water design and operational controls. The MSWLF

tables. It may be possible, through Criteria prohibit bulk or containerized liquid

operational controls, to avoid exposing waste disposal. Incident precipitation and

to precipitation or infiltration of water evapotranspiration can be evaluated using

through overlying materials. If significant models (e.g., HELP) or other methods of

leachate production would not be expected, estimating site-specific leachate production

the regulatory authority, when reviewing the (e.g., local historical meteorologic data). 

demonstration, should consider the

hydrogeologic characteristics of the facility If leachate composition data that are

and the surrounding area, in addition to the representative of the proposed facility are not

expected volume of leachate and climatic available, then leachate data with a similar

factors. expected composition should be presented.

MCLs. If such a demonstration is possible, it

assessment follows.

Landfill leachate composition is influenced

by:
Design Criteria

125

(1) The annual infiltration of precipitation In lieu of the existence or availability of such

and rate of leaching; information, conservative analytical

(2) The type and relative amounts of anticipated leakage rates.

materials in the waste stream; and

(3) The age and the biological maturity of through geomembranes differs in principle

the landfill unit, which may affect the from transport through soil liner materials.

types of organic and inorganic acids The dominant mode of leachate transport

generated, oxidation/reduction potential through liner components is flow through

(Eh), and pH conditions. holes and penetrations of the geomembrane,

An existing landfill unit in the same region, Transport through geomembranes where tears,

with similar waste stream characteristics, may punctures, imperfections, or seam failures are

provide information that will allow the owner not involved is dominated by molecular

or operator to anticipate leachate composition diffusion. Diffusion occurs in response to a

of the proposed landfill unit. A review of concentration gradient and is governed by

existing literature also may be required to Fick's first law. Diffusion rates through

assess anticipated leachate composition if geomembranes are very low in comparison to

actual data are unavailable (see U.S. EPA, hydraulic flow rates in soil liners, including

1987b). A wide range of leachate compacted clays. For synthetic liners, the

concentrations are reported in the literature most significant factor influencing liner

with higher concentrations of specific performance is penetration of the liner,

constituents typically reported for the initial including imperfect seams or pinholes caused

leachate from laboratory or field experimental by construction defects in the geomembrane

test fills or test cells. These "batch" one-day (U.S. EPA, 1989).

landfill tests do not account for the long-term

climatic and meteorological influences on a A relatively new product now being used in

full-scale landfill operation. Such high initial liner systems is the geosynthetic clay liner

concentrations are not typical of full-scale (GCL). GCLs consist of a layer of pure

operations (which are subject to the dilution bentonite clay backed by one or two

effects of incidental rainfall on unused geotextiles. GCLs exhibit properties of both

portions of the unit). soil liners and geomembranes, and have

Assessment of Leakage Through Liners component in composite liner designs. GCLs

An assessment of leakage (the volumetric through diffusion according to their low

release of leachate from the proposed hydraulic conductivities (i.e., 1 x 10 cm/sec

performance-based design) should be based reported by manufacturers). Applications for

on analytical approaches supported by GCLs are discussed further in the sections that

empirical data from other existing operational follow.

facilities of similar design, particularly those

that have leak detection monitoring systems Several researchers have studied the flow of

(see U.S. EPA, 1990b). fluids through imperfections in single

assumptions may be used to estimate

The transport of fluids and waste constituents

and Darcian flow through soil components.

successfully substituted for the soil

are believed to transport fluids primarily

-9
Subpart D

126

geomembrane and composite liner systems. degradation of contaminants. The degree of

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

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 nonreactive 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 
Design Criteria

127

components operating at the microscopic and alter its flow direction to conform to the

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 groundwater 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) 

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 nonuniform plume spreading. The changes in

aquifer properties that lead to this variability

in hydraulic conductivity may be threedimensional. 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 
Subpart D

128

used to describe porous flow (Darcy's Law) generally occurs at a relatively rapid rate

do not apply. compared to precipitation reactions.

Chemical Processes Controlling The dominant mechanism of organic sorption

Contaminant Transport in the Subsurface is the hydrophobic attraction between a

Chemical processes that are important in in some aquifers. The organic carbon content

controlling subsurface transport include of the porous medium, and the solubility of

precipitation/dissolution, chemical sorption, the contaminant, are important factors for this

redox reactions, hydrolysis, ion exchange, and type of sorption.

complexation. In general, these processes,

except for hydrolysis, are reversible. The There is a direct relationship between the

reversible processes tend to retard transport, quantity of a substance sorbed on a particle

but do not permanently remove a contaminant surface and the quantity of the substance

from the system. Sorption and precipitation suspended in solution. Predictions about the

are generally the dominant mechanisms sorption of contaminants often make use of

retarding contaminant transport in the sorption isotherms, which relate the amount of

saturated zone. contaminant in solution to the amount

Precipitation/dissolution reactions can control contaminants, these isotherms are usually

contaminant concentration levels. The assumed to be linear and the reaction is

solubility of a solid controls the equilibrium assumed to be instantaneous and reversible.

state of a chemical. When the soluble The linear equilibrium approach to sorption

concentration of a contaminant in leachate is may not be adequate for all situations.

higher than that of the equilibrium state,

precipitation occurs. When the soluble Oxidation and reduction (redox) reactions

concentration is lower than the equilibrium involve the transfer of electrons and occur

value, the contaminant exists in solution. The when the redox potential in leachate is

precipitation of a dissolved substance may be different from that of the soil or aquifer

initiated by changes in pressure, temperature, environment. Redox reactions are important

pH, concentration, or redox potential (Aller et processes for inorganic compounds and

al., 1987). Precipitation of contaminants in metallic elements. Together with pH, redox

the pore space of an aquifer can decrease reactions affect the solubility, complexing

aquifer porosity. Precipitation and dissolution capacity, and sorptive behavior of

reactions are especially important processes constituents, and thus control the presence and

for trace metal migration in soils. mobility of many substances in water.

Chemical adsorption/desorption is the most proportion of redox reactions that occur in

common mechanism affecting contaminant ground water. The redox state of an aquifer,

migration in soils. Solutes become attached and the identity and quantity of redox-active

to the solid phase by means of adsorption. reactants, are difficult to determine. 

Like precipitation/dissolution,

adsorption/desorption is a reversible process.

However, adsorption/desorption 

chemical and natural organic matter that exists

adsorbed to the solids. For organic

Microorganisms are responsible for a large
Design Criteria

129

Hydrolysis is the chemical breakdown of Therefore, these processes are usually

carbon bonds in organic substances by water grouped together as one mechanism.

and its ionic species H and OH . Hydrolysis + -

is dependent on pH and Eh and is most Biological Processes Controlling

significant at high temperatures, low pH, and Contaminant Transport in the Subsurface

low redox potential. For many biodegradable

contaminants, hydrolysis is slow compared to Biodegradation of contaminants may result

biodegradation. from the enzyme-catalyzed transformation of

Ion exchange originates primarily from Contaminants can be degraded to harmless

exchange sites on layered silicate clays and byproducts or to more mobile and/or toxic

organic matter that have a permanent negative products through one or more of several

charge. Cation exchange balances negative biological processes. Biodegradation of a

charges in order to maintain neutrality. The compound depends on environmental factors

capacity of soils to exchange cations is called such as redox potential, dissolved oxygen

the cation exchange capacity (CEC). CEC is concentration, pH, temperature, presence of

affected by the type and quantity of clay other compounds and nutrients, salinity, depth

mineral present, the amount of organic matter below land surface, competition among

present, and the pH of the soil. Major cations different types of organisms, and

in leachate (Ca, Mg, K, Na) usually dominate concentrations of compounds and organisms.

the CEC sites, resulting in little attenuation in The transformations that occur in a subsurface

soils of trace metals in the leachate. system are difficult to predict because of the

A smaller ion exchange effect for anions is reactions that may occur. Quantitative

associated with hydrous oxides. Soils predictions of the fate of biologically reactive

typically have more negatively charged clay substances are subject to a high degree of

particles than positively charged hydrous uncertainty, in part, because little information

oxides. Therefore, the transport of cations is is available on biodegradation rates in soil

attenuated more than the transport of anions. systems or ground water. First-order decay

Complexation involves reactions of metal ions

with inorganic anions or organic ligands. The The operation of Subtitle D facilities can

metal and the ligand bind together to form a introduce bacteria and viruses into the

new soluble species called a complex. subsurface. The fate and transport of bacteria

Complexation can either increase the and viruses in the subsurface is an important

concentration of a constituent in solution by consideration in the evaluation of the effects

forming soluble complex ions or decrease the of MSWLF units on human health and the

concentration by forming a soluble ion environment. A large number of biological,

complex with a solid. It is often difficult to chemical, and physical processes are known to

distinguish among sorption, solid-liquid influence virus and bacterial survival and

complexation, and ion exchange. transport in the subsurface. Unfortunately,

organic compounds by microbes.

complexity of the chemical and biological

constants are often used instead. 

knowledge of the processes and the available

data are insufficient to develop models that

can 
Subpart D

130

simulate a wide variety of site-specific evaluated by qualified investigators, should

conditions. adequately simulate the significant processes

Leachate Migration Models consistent with the complexity of the study

After reviewing the hydrogeologic of the study. 

characteristics of the site, the nature of liner

leakage, and the leachate characteristics, it First, an evaluation of the need for modeling

may be appropriate to use a mathematical should be made (Figure 4-1). When selecting

model to simulate the expected fate and a model to evaluate the potential for soil and

transport of the constituents listed in Table 1 ground-water contamination (Boutwell et al.,

to the relevant point of compliance. Solute 1986), three basic determinations must be

transport and ground-water modeling efforts made (Figure 4-2). Not all studies require the

should be conducted by a qualified ground- use of a mathematical model. This decision

water scientist (see Section 5.5). It is should be made at the beginning of the study,

necessary to consider several factors when since modeling may require a substantial

selecting and applying a model to a site. amount of resources and effort. Next, the

Travers and Sharp-Hansen (1991) provide a level of model complexity required for a

thorough review of these issues. The text specific study should be determined (Figure

provided below is a summary of their review. 4-3). Boutwell et al. (1986) classify models

Overview of the Modeling Process (complex/numerical) models. A flowchart for

A number of factors can influence leachate required is shown in Figure 4-3. Finally, the

migration from MSWLF units. These model capabilities necessary to represent a

include, but are not limited to, climatic particular system should be considered

effects, the hydrogeologic setting, and the (Figure 4-4). Several models may be equally

nature of the disposed waste. Each facility is suitable for a particular study. In some cases,

different, and no one generic model will be it may be necessary to link or couple two or

appropriate in all situations. To develop a more computer models to accurately represent

model for a site, the modeling needs and the the processes at the site. In the section that

objectives of the study should be determined follows, specific issues that should be

first. Next, it will be necessary to collect data considered when developing a scenario and

to characterize the hydrological, geological, selecting a model are described.

chemical, and biological conditions of the

system. These data are used to assist in the Models are a simplified representation of the

development of a conceptual model of the real system, and as such, cannot fully

system, including spatial and temporal reproduce or predict all site characteristics.

characteristics and boundary conditions. The Errors are introduced as a result of: 1)

conceptual model and data are then used to simplifying assumptions; 2) a lack of data; 3)

select a mathematical model that accurately uncertainty in existing data; 4) a poor

represents the conceptual model. The model understanding of the processes influencing the

selected should have been tested and fate and transport of contaminants; and

present in the actual system, and should be

area, amount of available data, and objectives

as Level I (simple/analytical) and Level II

determining the level of model complexity
131

Figure 4-1

Three Basic Decisions in Model Selection

(Boutwell et. al., 1986)
132

Figure 4-2

Flow Chart to Determine if Modeling is Required

(Boutwell et. al., 1986)
133

Figure 4-3

Flow Chart to Determine the Level of Modeling Required for

Soil and Groundwater Systems

(Boutwell et. al., 1986)
134

Figure 4-4

Flow Chart for Required Model Capabilities for Soil and Groundwater Systems

(Boutwell et. al., 1986)
Design Criteria

135

5) limitations of the model itself. Therefore, Model Selection

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. limited data available in most field situations

(1989) discuss options for selection and field

validation of mathematical models. 

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

may not justify the use of a detailed numerical

model; in some cases, results from simple

analytical models may be appropriate
Subpart D

136

(Huyakorn et al., 1986). Analytical models "screening level" model to define the range of

require simplifying assumptions about the possible values, and to use a numerical model

system. Therefore, complex interactions when there are sufficient data. 

involving several fate and transport processes

cannot be addressed in detail. Analytical A highly complex hydrogeologic system

models generally require a limited number of cannot be accurately represented with a

parameters that are often assumed to be simple analytical model. Heterogeneous or

constant in space and time (van der Heijde anisotropic aquifer properties, multiple

and Beljin, 1988). aquifers, and complicated boundary

Semi-analytical models approximate complex models. In addition, sophisticated numerical

analytical solutions using numerical models are available that can simulate

techniques (van der Heijde and Beljin, 1988). processes such as fracture flow. Because each

Semi-analytical methods allow for more site is unique, the modeler should determine

complex site conditions than those that can be which conditions and processes are important

simulated with a purely analytical solution. at a specific site, and then select a suitable

Semi-analytical solution methods can consider model. 

multiple sources or recharging and

discharging wells. However, they still require Spatial Characteristics of the System

simplifying assumptions about the

dimensionality and homogeneity of the Although actual landfill units and

system. hydrogeologic systems are three-dimensional,

Numerical models are able to evaluate more dimensions simulated in a mathematical

complex site conditions than either analytical model to one or two. Two- and threeor semi-analytical models. Numerical models dimensional models are generally more

provide the user with a large amount of complex and computationally expensive than

flexibility; irregular boundaries and spatial one-dimensional models, and therefore

and temporal variations in the system can be require more data. In some instances, a oneconsidered. Numerical models require dimensional model may adequately represent

significantly more data than analytical the system; the available data may not warrant

models, and are typically more the use of a multi-dimensional model.

computationally intensive. Use of a However, modeling a truly three-dimensional

numerical model requires an experienced system using a two-dimensional model may

modeler, and can involve a larger amount of produce results without adequate spatial

computer time than simulations using an detail. The choice of the number of

analytical or semi-analytical method. dimensions in the model should be made for

To select an appropriate model, the site and the availability of data.

complexity of the site hydrology and the

availability of data should be considered. If Steady-State Versus Transient Models

data are insufficient, a highly sophisticated

and complex model should not be used. In Models can simulate either steady-state or

some situations, it is beneficial to use an

analytical or semi-analytical model as a

conditions can be simulated using numerical

it is often desirable to reduce the number of

a specific site, based on the complexity of the

transient flow conditions. It may be 
Design Criteria

137

appropriate to assume that some ground-water One of the most significant boundary

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 groundwater 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 steadystate or temporally variable. The initial and

boundary conditions chosen to represent a site

can significantly affect the results of the

simulation. 

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 threedimensional 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 Heterogeneous

Aquifer/Soil Properties

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
Subpart D

138

isotropic aquifer properties, and to develop a Uncertainty in model predictions results from

"reasonable worst-case" scenario for the inability to characterize a site in terms of

contaminant migration in the subsurface. the boundary conditions or the key parameters

However, as Auerbach (1984) points out, the describing the significant flow and transport

assumption of homogeneous and isotropic processes (National Research Council, 1990).

aquifers often will not provide a "worst-case" The application of a mathematical model to a

scenario. For example, a continuous zone of site typically requires a large amount of data.

higher hydraulic conductivity in the direction Inexperienced modelers may attempt to apply

of ground-water flow can result in much a model with insufficient data and, as a result,

higher rates of contaminant movement than produce model results that are inconclusive. 

would be predicted in a completely

homogeneous aquifer. To develop a true To obtain accurate model results, it is

"worst-case" model, information on the essential to use data that are appropriate for

probable heterogeneity and anisotropy of the the particular site being modeled. Models that

site should be collected. include generic parameters, based on average

The number of aquifers in the hydrogeologic initial guidance and general information about

system also will affect the selection of a the behavior of a system, but it is

mathematical model. Some systems include inappropriate to apply generic parameters to a

only a single unconfined or confined aquifer, specific hydrogeologic system. An excellent

which is hydraulically isolated from the summary of the data required to model

surrounding layers. Some mathematical saturated and unsaturated flow, surface water

models, and in particular those with analytical flow, and solute transport is presented in

solutions, can simulate only single layers. In Mercer et al. (1983). This report provides

other cases, the upper aquifer may be definitions and possible ranges of values for

hydraulically connected to underlying source terms, dependent variables, boundary

aquifers. The MSWLF Criteria specify that conditions, and initial conditions.

MCLs not be exceeded at the relevant point of

compliance within the uppermost aquifer. Summary of Available Models

The uppermost aquifer includes not only the

aquifer that is nearest the ground surface, but Several detailed reviews of ground-water

also all lower aquifers that are hydraulically models are available in the literature. A

connected to the uppermost aquifer within the number of ground-water models, including

vicinity of the facility. saturated flow, solute transport, heat transport,

Availability of Data are summarized in van der Heijde et al.

Although computer models can be used to (1988) provides detailed descriptions of 64

make predictions about leachate generation ground-water flow and solute transport

and migration, these predictions are highly models that were selected for use in

dependent on the quantity and quality of the determining wellhead protection areas. A

available data. One of the most common review of ground-water flow and 

limitations to modeling is insufficient data.

values for similar sites, can be used to provide

fracture flow, and multiphase flow models,

(1988). A report by van der Heijde and Beljin
Design Criteria

139

transport models for the unsaturated zone is contaminant source terms and the releases of

presented in Oster (1982). A large number of contaminants to the subsurface. Flow and

ground-water flow and transport models are transport models simulate the transport of

summarized by Bond and Hwang (1988). contaminants released from the source to the

Finally, Travers and Sharp-Hansen (1991) unsaturated and saturated zones.

summarize models that may be applicable to Geochemical models are available that

problems of leachate generation and migration consider chemical processes that may be

from MSWLF units. (See References active in the subsurface such as adsorption,

supplied in Section 4.6.) precipitation, oxidation/reduction, aqueous

Table 4-1 (adapted from Travers and SharpHansen (1991)) provides information on Complex flow models have been developed to

select leachate generation models. Tables 4- simulate the effects of nearby pumping and

1a, b, and c list some of the available models discharging wells, fracture flow, conduit flow

that can be used to predict contaminant in karst terrane, and multiphase flow for fluids

transport. The factors used to select these that are less dense or more dense than water.

models include availability, documentation, However, the use of the more complex

uniqueness, and the size of the user models requires additional data based on a

community. These models are categorized by thorough investigation of the subsurface

the techniques used to solve flow and characteristics at a site as well as well-trained

transport equations. Table 4-1a lists users to apply the model correctly.

analytical and semi-analytical models, and

Tables 4-1b and 4-1c list numerical models Most of the ground-water flow and solute

that are solved by the finite-difference and the transport models are deterministic. However,

finite-element method, respectively. the use of stochastic models, which allow for

The types of models that are available for variability in systems, is increasing. A few of

application to the evaluation of MSWLF the models include a Monte Carlo capability

designs include leachate generation models for addressing the uncertainty inherent in the

and saturated and unsaturated zone flow and input parameters. 

transport models. The level of sophistication

of each of these types of models is based on The EPA Multimedia Exposure

the complexity of the processes being Assessment Model (MULTIMED)

modeled. The majority of the models

consider flow and transport based on EPA has developed a modeling package to

advection dispersion equations. More meet the needs of a large percentage of

complex models consider physical and MSWLF unit owners and operators who will

chemical transformation processes, fracture require fate and transport modeling as part of

flow, and multiphase fluid flow. the performance-based design demonstration.

Leachate generation models predict the Assessment Model (MULTIMED), is

quantity and characteristics of leachate that is intended for use at sites where certain

released from the bottom of a landfill. These simplifying assumptions can be made.

models are used to estimate MULTIMED can be used in

speciation, and kinetics. 

characterization of spatial and temporal

This model, the Multimedia Exposure
Table 4-1. Models for Application to Leachate Generation Problems (adapted from Travers and Sharp-Hansen, 1991)
Table 4-1a. Analytical and Semi-Analytical Models for Application to Leachate Migration Problems

(adapted from Travers and Sharp-Hansen, 1991)
Table 4-1a. Analytical and Semi-Analytical Models for Application to Leachate Migration Problems

(adapted from Travers and Sharp-Hansen, 1991) (continued)
Table 4-1b. Finite-Difference Models for Application to Leachate Migration Problems

(adapted from Travers and Sharp-Hansen, 1991)
Table 4-1b. Finite-Difference Models for Application to Leachate Migration Problems

(adapted from Travers and Sharp-Hansen, 1991) (continued)
Table 4-1c. Finite-Element Models for Application to Leachate Migration Problems

(adapted from Travers and Sharp-Hansen, 1991)
Table 4-1c. Finite-Element Models for Application to Leachate Migration Problems

(adapted from Travers and Sharp-Hansen, 1991) (continued)
Design Criteria

147

conjunction with a separate leachate source because the effects of lateral or vertical

model, such as HELP (Schroeder et al., 1984). dispersion may significantly affect the model

Output from HELP is then used in results. 

MULTIMED to demonstrate that either a

landfill design or the specific hydrogeologic Therefore, reducing the dimensions to one in

conditions present at a site will prevent this module would produce inaccurate results.

contaminant concentrations in ground water The saturated zone transport module also

from exceeding the concentrations listed in considers linear adsorption, first-order decay,

Table 1 of §258.40. (Refer to pp. 4-53 and 6- and dilution as a result of ground-water

8 for further discussion of HELP.) A recharge. In addition, MULTIMED has the

description of MULTIMED follows with capability to assess the impact of uncertainty

guidance for determining if its use is in the model inputs on the model output

appropriate for a given site. (contaminant concentration at a specified

[NOTE: Version 3.0 of the HELP model will technique.

be available during the fall of 1993. To

obtain a copy, call EPA's Office of Research The simplifying assumptions required to

and Development (ORD) in Cincinnati at obtain the analytical solutions limit the

(513) 569-7871.] complexity of the systems that can be

Overview of the Model not account for site-specific spatial variability

The MULTIMED model consists of modules land disposal facility, site-specific boundary

that estimate contaminant releases to air, soil, conditions, or multiple aquifers and pumping

ground water, or surface water. General wells. Nor can MULTIMED simulate

information about the model and its theory is processes, such as flow in fractures and

provided in Salhotra et al. (1990). chemical reactions between contaminants, that

Additionally, information about the may have a significant effect on the

application of MULTIMED to MSWLF units concentration of contaminants at a site. In

(developed by Sharp-Hansen et al. [1990]) is more complex systems, it may be beneficial to

summarized here. In MULTIMED, a steady- use MULTIMED as a "screening level" model

state, one-dimensional, semi-analytical to allow the user to obtain an understanding of

module simulates flow in the unsaturated the system. A more complex model could

zone. The output from this module, which is then be used if there are sufficient data.

water saturation as a function of depth, is used

as input to the unsaturated zone transport Application of MULTIMED to MSWLF

module. The latter simulates transient, one- Units

dimensional (vertical) transport in the

unsaturated zone and includes the effects of Procedures have been developed for the

dispersion, linear adsorption, and first-order application of MULTIMED to the design of

decay. Output from the unsaturated zone MSWLF units. They are explained in Sharpmodules is used as input to the semi-analytical Hansen et al. (1990) and are briefly

saturated zone transport module. The latter summarized here. The procedures are: 

considers three-dimensional flow 

point), using the Monte Carlo simulation

evaluated with MULTIMED. The model does

(e.g., aquifer heterogeneities), the shape of the
Subpart D

148

! Collect site-specific hydrogeologic data, 4-2. A "no" answer to any of the questions in

including amount of leachate generated Table 4-2 may indicate that MULTIMED is

(see Section 4.3.3); not the most appropriate model to use. As

! Identify the contaminant(s) to be and semi-analytical solution techniques to

simulated and the point of compliance; solve the mathematical equations describing

! 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 steadystate 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 

stated above, MULTIMED utilizes analytical

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 onedimensional, 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 "steadystate," 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.
Design Criteria

149

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
Subpart D

150

membrane liner (FML), and the lower Standard Composite Liner Systems

component must consist of at least a twofoot layer of compacted soil with a

hydraulic conductivity of no more than 1 x

10 cm/sec. FML components consisting of -7

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 HDPE, 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 cm/sec. -7

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.

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 Fick'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 
Design Criteria

151

difficult. The factor that most strongly Soil Liner

influences geomembrane performance is the

presence of imperfections such as improperly The following subsections discuss soil liner

bonded seams, punctures and pinholes. A construction practices including thickness

detailed discussion of leakage through requirements, lift placement, bonding of lifts,

geomembranes and composite liners can be test methods, prerequisite soil properties,

found in Giroud and Bonaparte (1989 (Part I quality control, and quality assurance

and Part II)). A geomembrane installed with activities.

excellent control over defects may yield the

equivalent of a one-centimeter-diameter hole Thickness

per acre of liner installed (Giroud and

Bonaparte, 1989 (Part I and Part II)). If the Two feet of soil is generally considered the

geomembrane were to be placed over sand, minimum thickness needed to obtain adequate

this size imperfection under one foot of compaction to meet the hydraulic conductivity

constant hydraulic head could be expected to requirement. This thickness is considered

account for as much as 3,300 gal/acre/day necessary to minimize the number of cracks

(31,000 liters/hectare/ day) of leakage. Based or imperfections through the entire liner

upon measurements of actual leakage through thickness that could allow leachate migration.

liners at facilities that have been built under Both lateral and vertical imperfections may

rigorous control, Bonaparte and Gross (1990) exist in a compacted soil. The two-foot

have estimated an actual leakage rate, under minimum thickness is believed to be sufficient

one foot of constant head, of 200 to inhibit hydraulic short-circuiting of the

liters/hectare/day or about 21 gallons/acre/day entire layer.

for landfill units.

The uniformity of the contact between the

geomembrane and the soil liner is extremely Soil liners should be constructed in a series of

important in controlling the effective flow compacted lifts. Determination of appropriate

area of leachate through the soil liner. Porous lift thickness is dependent on the soil

material, such as drainage sand, filter fabric, characteristics, compaction equipment,

or other geofabric, should not be placed firmness of the foundation materials, and the

between the geomembrane and the low anticipated compactive effort needed to

permeability soil liner. Porous materials will achieve the required soil hydraulic

create a layer of higher hydraulic conductivity. Soil liner lifts should be thin

conductivity, which will increase the amount enough to allow adequate compactive effort to

of leakage below an imperfection in the reach the lower portions of the lift. Thinner

geomembrane. Construction practices during lifts also provide greater assurance that

the installation of the soil and the sufficient compaction can be achieved to

geomembrane affect the uniformity of the provide good, homogeneous bonding between

geomembrane/soil interface, and strongly subsequent lifts. Adequate compaction of lift

influence the performance of the composite thickness between five and ten inches is

liner system. possible if appropriate equipment is used

Lift Thickness

(USEPA, 1988). Nine-inch loose lift

thicknesses that will yield a 6-
Subpart D

152

inch soil layer also have been recommended includes scarifying (roughening), and possibly

prior to compaction (USEPA, 1990a). wetting, the top inch or so of the last lift

Soil liners usually are designed to be of equipment before placing the next lift.

uniform thickness with smooth slopes over the

entire facility. Thicker areas may be Placement of Soil Liners on Slopes

considered wherever recessed areas for

leachate collection pipes or collection sumps The method used to place the soil liner on side

are located. Extra thickness and compactive slopes depends on the angle and length of the

efforts near edges of the side slopes may slope. Gradual inclines from the toe of the

enhance bonding between the side slopes and slope enable continuous placement of the lifts

the bottom liner. In smaller facilities, a soil up the slopes and provide better continuity

liner may be designed for installation over the between the bottom and sidewalls of the soil

entire area, but in larger or multi-cell liner. When steep slopes are encountered,

facilities, liners may be designed in segments. however, lifts may need to be placed and

If this is the case, the design should address compacted horizontally due to the difficulties

how the old and new liner segments will be of operating heavy compaction equipment on

bonded together (U.S. EPA, 1988). steeper slopes.

Bonding Between Lifts When sidewalls are compacted horizontally,

It is not possible to construct soil liners bottom of the soil liner to reduce the

without some microscopic and/or macroscopic probability of seepage planes (USEPA, 1988).

zones of higher and lower hydraulic A significant amount of additional soil liner

conductivity. Within individual lifts, these material will be required to construct the

preferential pathways for fluid migration are horizontal lifts since the width of the lifts has

truncated by the bonded zone between the to be wide enough to accommodate the

lifts. If good bonding between the lifts is not compaction equipment. After the soil liner is

achieved during construction, the vertical constructed on the side slopes using this

pathways may become connected by method, it can be trimmed back to the

horizontal pathways at the lift interface, required thickness. The trimmed surface of

thereby diminishing the performance of the the soil liner should be sealed by a smoothhydraulic barrier. drum roller. The trimmed excess materials

Two methods may be used to ensure proper specified moisture-density requirements.

bonding between lifts. Kneading or blending

a thinner, new lift with the previously Hydraulic Conductivity

compacted lift may be achieved by using a

footed roller with long feet that can fully Achieving the hydraulic conductivity standard

penetrate a loose lift of soil. If the protruding depends on the degree of compaction,

rods or feet of a sheepsfoot roller are compaction method, type of clay, soil

sufficient in length to penetrate the top lift and moisture content, and density of the soil

knead the previous lift, good bonding may be during liner construction. Hydraulic 

achieved. Another method 

placed with a disc harrow or other similar

it is important to tie in the edges with the

can be reused provided that they meet the
Design Criteria

153

conductivity is the key design parameter when characterize proposed liner soils should

evaluating the acceptability of the constructed include grain size distribution (ASTM Dsoil liner. The hydraulic conductivity of a soil 422), Atterberg limits (ASTM D-4318), and

depends, in part, on the viscosity and density compaction curves depicting moisture and

of the fluid flowing through it. While water density relationships using the standard or

and leachate can cause different test results, modified Proctor (ASTM D-698 or ASTM Dwater is an acceptable fluid for testing the 1557), whichever is appropriate for the

compacted soil liner and source materials. compaction equipment used and the degree of

The effective porosity of the soil is a function firmness of the foundation materials.

of size, shape, and area of the conduits

through which the liquid flows. The Liner soils usually have at least 30 percent

hydraulic conductivity of a partially saturated fines (fine silt- and clay-sized particles).

soil is less than the hydraulic conductivity of Some soils with less than 30 percent fines

the same soil when saturated. Because may be worked to obtain hydraulic

invading water only flows through water- conductivities below 1 x 10 cm/sec, but use

filled voids (and not air-filled voids), the of these soils requires greater control of

dryness of a soil tends to lower permeability. construction practices and conditions.

Hydraulic conductivity testing should be

conducted on samples that are fully saturated The soil plasticity index (PI), which is

to attempt to measure the highest possible determined from the Atterberg limits (defined

hydraulic conductivity. by the liquid limit minus the plastic limit),

EPA has published Method 9100 in However, soils with very high PI, (greater

publication SW-846 (Test Methods for than 30 percent), are cohesive and sticky and

Evaluating Solid Waste) to measure the become difficult to work with in the field.

hydraulic conductivity of soil samples. Other When high PI soils are too dry during

methods appear in the U.S. Army Corps of placement, they tend to form hard clumps

Engineers Engineering Manual 1110-2-1906 (clods) that are difficult to break down during

(COE, 1970) and the newly published compaction. Preferential flow paths may be

"Measurement of Hydraulic Conductivity of created around the clods allowing leachate to

Saturated Porous Materials Using a Flexible migrate at a relatively high rate.

Wall Permeameter" (ASTM D-5084). To

verify full saturation of the sample, this latter Soil particles or rock fragments also can

method may be performed with back pressure create preferential flow paths. For this

saturation and electronic pore pressure reason, soil particles or rock fragments should

measurement. be less than 3 inches in diameter so as not to

Soil Properties the soil liner (USEPA, 1989).

Soils typically possess a range of physical The maximum density of a soil will be

characteristics, including particle size, achieved at the optimum water content, but

gradation, and plasticity, that affect their this point generally does not correspond to the

ability to achieve a hydraulic conductivity of point at which minimum hydraulic 

1 x 10 cm/sec. Testing methods used to

-7

-7

should generally be greater than 10 percent.

affect the overall hydraulic performance of
Subpart D

154

conductivity is achieved. Wet soils, however, is difficult and may lead to inconsistent results

have low shear strength and high potential for with respect to complying with the hydraulic

desiccation cracking. Care should be taken conductivity criterion.

not to compromise other engineering

properties such as shear strengths of the soil The most common additive used to amend

liner by excessively wetting the soil liner. soils is sodium bentonite. The disadvantage

Depending on the specific soil characteristics, of using sodium bentonite includes its

compaction equipment and compactive effort, vulnerability to degradation as a result of

the hydraulic conductivity criterion may be contact with chemicals and waste leachates

achieved at moisture values of 1 to 7 percent (U.S. EPA, 1989).

above the optimum moisture content.

Although the soil may possess the required than sodium bentonite, also is used as a soil

properties for successful liner construction, amendment. Approximately twice as much

the soil liner may not meet the hydraulic calcium bentonite typically is needed to

conductivity criterion if the construction achieve a hydraulic conductivity comparable

practices used to install the liner are not to that of sodium bentonite.

appropriate and carefully controlled.

Construction quality control and quality Soil/bentonite mixtures generally require

assurance will be discussed in a later section. central plant mixing by means of a pugmill,

Amended Soils where water can be added during the process.

If locally available soils do not possess distribution must be controlled during mixing

properties to achieve the specified hydraulic and placement. Spreading of the

conductivity, soil additives can be used. Soil soil/bentonite mixture may be accomplished

additives, such as bentonite or other clay in the same manner as the spreading of natural

materials, can decrease the hydraulic soil liners, by using scrapers, graders,

conductivity of the native soil (USEPA, bulldozers, or a continuous asphalt paving

1988b). machine (U.S. EPA, 1988).

Bentonite may be obtained in a dry, powdered Materials other than bentonite, including lime,

form that is relatively easy to blend with on- cement, and other clay minerals such as

site soils. Bentonite is a clay mineral atapulgite, may be used as soil additives (U.S.

(sodium-montmorillonite) that expands when EPA, 1989). For more information

it comes into contact with water (hydration), concerning soil admixtures, the reader is

by absorbing the water within the mineral referred to the technical resource document on

matrix. This property allows relatively small the design and construction of clay liners

amounts of bentonite (5 to 10 percent) to be (U.S. EPA, 1988).

added to a noncohesive soil (sand) to make it

more cohesive (U.S. EPA, 1988b). Thorough Testing

mixing of additives to cohesive soils (clay) 

Calcium bentonite, although more permeable

cement mixer, or other mixing equipment

Water, bentonite content, and particle size

Prior to construction of a soil liner, the

relationship between water content, density,
Design Criteria

155

and hydraulic conductivity for a particular soil construction contractor during soil placement.

should be established in the laboratory. Figure 4-6 presents compaction data as a

Figure 4-5 shows the influence of molding function of dry unit weight and molding water

water content (moisture content of the soil at content for the construction of clay liners.

the time of compaction) on hydraulic The amount of soil testing required to

conductivity of the soil. The lower half of the determine these construction parameters is

diagram is a compaction curve and shows the dependent on the degree of natural variability

relationship between dry unit weight, or dry of the source material. 

density of the soil, and water content of the

soil. The optimum moisture content of the Quality assurance and quality control of soil

soil is related to a peak value of dry density liner materials involve both laboratory and

known as maximum dry density. Maximum field testing. Quality control tests are

dry density is achieved at the optimum performed to ascertain compaction

moisture content. requirements and the moisture content of

The lowest hydraulic conductivity of quality assurance provide an opportunity to

compacted clay soil is achieved when the soil check representative areas of the liner for

is compacted at a moisture content slightly conformance to compaction specifications,

higher than the optimum moisture content, including density and moisture content.

generally in the range of 1 to 7 percent (U.S. Quality assurance laboratory testing is usually

EPA, 1989). When compacting clay, water conducted on field samples for determination

content and compactive effort are the two of hydraulic conductivity of the in-place liner.

factors that should be controlled to meet the Laboratory testing allows full saturation of the

maximum hydraulic conductivity criterion. soil samples and simulates the effects of large

It is impractical to specify and construct a done conveniently in the field (U.S. EPA,

clay liner to a specific moisture content and a 1989).

specific compaction (e.g., 5 percent wet of

optimum and 95 percent modified Proctor Differences between laboratory and field

density). Moisture content can be difficult to conditions (e.g., uniformity of material,

control in the field during construction; control of water content, compactive effort,

therefore, it may be more appropriate to compaction equipment) may make it unlikely

specify a range of moisture contents and that minimum hydraulic conductivity values

corresponding soil densities (percent measured in the laboratory on remolded, precompaction) that are considered appropriate to construction borrow source samples are the

achieve the required hydraulic conductivity. same as the values achieved during actual

Benson and Daniel (U.S. EPA, 1990) propose liner construction. Laboratory testing on

water content and density criteria for the remolded soil specimens does not account for

construction of clay liners in which the operational problems that may result in

moisture-density criteria ranges are desiccation, cracking, poor bonding of lifts,

established based on hydraulic conductivity and inconsistent degree of compaction on

test results. This type of approach is sidewalls (U.S. EPA, 1988b). The

recommended because of the flexibility and relationship between field and laboratory

guidance it provides to the hydraulic conductivity testing has been

material delivered to the site. Field tests for

overburden stress on the soil, which cannot be

investigated by the U.S. Environmental
156

Figure 4-5

Hydraulic Conductivity and Dry Unit Weight as a

Function of Molding Water Content
Figure 4-6. Compaction Data for Silty Clay

157
Subpart D

158

Protection Agency using field case studies susceptible to the effects of temperature

(U.S. EPA, 1990c). variation; as the water temperature increases,

In situ, or field, hydraulic conductivity testing the system contracts. This situation could

operates on the assumption that by testing lead to erroneous measurements when the rate

larger masses of soil in the field, one can of flow is small.

obtain more realistic results. Four types of in

situ hydraulic conductivity tests generally are The sealed double-ring infiltrometer has

used: borehole tests, porous probes, proven to be the most successful method and

infiltrometer tests, and underdrain tests. A is the one currently used. The outer ring

borehole test is conducted by drilling a hole, forces infiltration from the inner ring to be

then filling the hole with water, and more or less one-dimensional. Covering the

measuring the rate at which water percolates inner ring with water insulates it substantially

into the borehole. In the borehole test, water from temperature variation.

also can percolate through the sidewalls of the

borehole. As a result, the measured hydraulic Underdrains, the fourth type of in situ test, are

conductivity is usually higher than that the most accurate in situ permeability testing

measured by other one-dimensional field device because they measure exactly what

testings. migrates from the bottom of the liner.

The second type of test involves driving or data for low permeability liners, because of

pushing a porous probe into the soil and the length of time required to accumulate

pouring water through the probe into the soil. measurable flow. Also, underdrains must be

With this method, however, the advantage of installed during construction, so fewer

testing directly in the field is somewhat offset underdrains are used than other kinds of

by the limitations of testing such a small testing devices.

volume of soil.

A third method of testing involves a device usually performed on the completed liner

called an infiltrometer. This device is because the tests may take several weeks to

embedded into the surface of the soil liner complete (during which time the liner may be

such that the rate of flow of a liquid into the damaged by desiccation or freezing

liner can be measured. The two types of temperatures) and because large penetrations

infiltrometers most widely used are open and must be made into the liner. If field

sealed. Open rings are less desirable because, conductivity tests are performed, they are

with a hydraulic conductivity of 10 cm/sec, usually conducted on a test pad. The test pad -7

it is difficult to detect a 0.002 inch per day should be constructed using the materials and

drop in water level of the pond from methods to be used for the actual soil liner.

evaporation and other losses. The width of a test pad is usually the width of

With sealed rings, very low rates of flow can length is one to two times the width.

be measured. However, single-ring Thickness is usually two to three feet. Test

infiltrometers allow lateral flow beneath the pads can be used as a means for verifying that

ring, which can complicate the interpretation the proposed

of test results. Single rings are also

the entire system expands. As it cools down,

However, under-drains are slow to generate

Field hydraulic conductivity tests are not

three to four construction vehicles, and the
Design Criteria

159

materials and construction procedures will ! Soil water content; and

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, inplace 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;

! 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 lbs 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 
Subpart D

160

the lift may be increased. Generally, fillers, plasticizers, processing aids,

compaction equipment should pass over the crosslinking chemicals, anti-degradants, and

soil liner five to twenty times to attain the biocides. The polymers used to manufacture

compaction needed to comply with the geomembranes include a wide range of

minimum hydraulic conductivity criterion plastics and rubbers differing in properties

(U.S. EPA, 1989). such as chemical resistance and basic

Efforts made to reduce clod size during 1988e). The polymeric materials may be

excavation and placement of the soil for the categorized as follows:

liner should improve the chances for

achieving low hydraulic conductivity in ! Thermoplastics such as polyvinyl

several ways. Keeping clods in the soil liner chloride (PVC);

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,

composition (U.S. EPA, 1983 and U.S. EPA,

! 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:
Design Criteria

161

! Differential settlement in foundation of the original material every thirty days. A

soils; software system entitled Flexible Liner

! Strain requirements at the anchor trench; in the hazardous waste permitting process,

and may aid in interpreting EPA Method 9090 test

! Strain requirements over long, steep side of both Method 9090 and FLEX is available

slopes. from EPA.

An extensive body of literature has been It is imperative that a geomembrane liner

developed by manufacturers and independent maintain its integrity during exposure to

researchers on the physical properties of short-term and long-term mechanical stresses.

liners. Geosynthetic design equations are Short-term mechanical stresses include

presented in several publications including equipment traffic during the installation of a

Kastman (1984), Koerner (1990), and U.S. liner system, as well as thermal expansion and

EPA (1988e). shrinkage of the geomembrane during the

The chemical resistance of a geomembrane to unit. Long-term mechanical stresses result

leachate has traditionally been considered a from the placement of waste on top of the

critical issue for Subtitle C (hazardous waste) liner system and from subsequent differential

facilities where highly concentrated solvents settlement of the subgrade (U.S. EPA, 1988a).

may be encountered. Chemical resistance

testing of geomembranes may not be required Long-term success of the liner requires

for MSWLF units containing only municipal adequate friction between the components of

solid waste; EPA's data base has shown that a liner system, particularly the soil subgrade

leachate from MSWLF units is not aggressive and the geomembrane, and between

to these types of materials. Testing for geosynthetic components, so that slippage or

chemical resistance may be warranted sloughing does not occur on the slopes of the

considering the waste type, volumes, unit. Specifically, the foundation slopes and

characteristics, and amounts of small quantity the subgrade materials must be considered in

generator waste or other industrial waste design equations to evaluate:

present in the waste stream. The following

guidance is provided in the event such testing • The ability of a geomembrane to

is of interest to the owner or operator. support its own weight on the side

EPA's Method 9090 in SW-846 is the

established test procedure used to evaluate • The ability of a geomembrane to

degradation of geomembranes when exposed withstand down-dragging during and

to hazardous waste leachate. In the after waste placement;

procedure, the geomembrane is immersed in

the site-specific chemical environment for at • The best anchorage configuration for the

least 120 days at two different temperatures. geomembrane;

Physical and mechanical properties of the

tested material are then compared to those 

Evaluation Expert (FLEX), designed to assist

data (U.S. EPA, 1989). A detailed discussion

construction and operation of the MSWLF

slopes;
Subpart D

162

• The stability of a soil cover on top of a Manufactured Sheet Specifications

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 (ASTM D-1505);

! Melt index (ASTM D-1238);

! Carbon black (ASTM D-1603); and

! Thermogravimetric analysis (TGA)

or differential scanning calorimetry

(DSC).

! Thickness (ASTM D-1593);

! Tensile properties (ASTM D-638);

! Tear resistance (ASTM D-1004);

! Carbon black content (ASTM D1603);

! Carbon black dispersion (ASTM D3015);

! Dimensional stability (ASTM D1204); and

! Stress crack resistance (ASTM D1693).

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
Design Criteria

163

geomembrane. Wrinkles on the in an EPA guidance document (USEPA,

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 

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 
Subpart D

164

(USEPA, 1992). In addition, scheduling soil tested non-destructively (U.S. EPA, 1988).

liner construction slightly ahead of the Destructive testing should be done at regular

geomembrane and drainage layer placement intervals along the seam (see page 4-66).

can reduce the exposure of the soil liner to the

elements. Consistent quality in fabricating field seams is

Deployment, or placement, of the that may affect seaming should be monitored

geomembrane panels or rolls should be and controlled during installation. An

described in the geomembrane layout plan. inspection should be conducted in accordance

Rolls of sheeting, such as HDPE, generally with a construction quality assurance plan to

can be deployed by placing a shaft through document the integrity of field seams. Factors

the core of the roll, which is supported and affecting the seaming process include (U.S.

deployed using a front-end loader or a winch. EPA, 1988):

Panels composed of extremely flexible liner

material such as PVC are usually folded on ! Ambient temperature at which the seams

pallets, requiring workers to manually unfold are made;

and place the geomembrane. Placement of

the geomembrane goes hand-in-hand with the ! Relative humidity;

seaming process; no more than the amount of

sheeting that can be seamed during a shift or ! Control of panel lift-up by wind;

work day should be deployed at any one time

(USEPA, 1988). Panels should be weighted ! The effect of clouds on the

with sand bags if wind uplift of the membrane geomembrane temperature;

or excessive movement from thermal

expansion is a potential problem. Proper ! Water content of the subsurface beneath

stormwater control measurements should be the geomembrane;

employed during construction to prevent

erosion of the soil liner underneath the ! The supporting surface on which the

geomembrane and the washing away of the seaming is bonded;

geomembrane.

Once deployment of a section of the

geomembrane is complete and each section ! Quality and consistency of the chemical

has been visually inspected for imperfections or welding material;

and tested to ensure that it is the specified

thickness, seaming of the geomembrane may ! Proper preparation of the liner surfaces

begin. Quality control/quality assurance to be joined;

monitoring of the seaming process should be

implemented to detect inferior seams. ! Moisture on the seam interface; and

Seaming can be conducted either in the

factory or in the field. Factory seams are ! Cleanliness of the seam interface (e.g.,

made in a controlled environment and are the amount of airborne dust and debris

generally of high quality, but the entire seam present).

length (100 percent) still should be 

critical to liner performance, and conditions

! The skill of the seaming crew;
Design Criteria

165

Depending on the type of geomembrane, design plans and specifications (USEPA,

several bonding systems are available for the 1988).

construction of both factory and field seams.

Bonding methods include solvents, heat seals, Geomembranes that are subject to damage

heat guns, dielectric seaming, extrusion from exposure to weather and work activities

welding, and hot wedge techniques. To should be covered with a layer of soil as soon

ensure the integrity of the seams, a as possible after quality assurance activities

geomembrane should be seamed using the associated with geomembrane testing are

bonding system recommended by the completed. Soil should be placed without

manufacturer (U.S. EPA, 1988). EPA has driving construction vehicles directly on the

developed a field seaming manual for all geomembrane. Light ground pressure

types of geomembranes (U.S. EPA, 1991a). bulldozers may be used to push material out

Thermal methods of seaming require not attempt to push a large pile of soil forward

cleanliness of the bonding surfaces, heat, in a continuous manner over the membrane.

pressure, and dwell time to produce high Such methods can cause localized wrinkles to

quality seams. The requirements for adhesive develop and overturn in the direction of

systems are the same as those for thermal movement. Overturned wrinkles create sharp

systems, except that the adhesive takes the creases and localized stresses in the

place of the heat. Sealing the geomembrane geomembrane that could lead to premature

to appurtenances and penetrating structures failure. Instead, the operator should

should be performed in accordance with continually place smaller amounts of soil or

detailed drawings included in the design plans drainage material working outward over the

and approved specifications. toe of the previously placed material.

An anchor trench along the perimeter of the place soil over the geomembrane that can later

cell generally is used to secure the be spread with a bulldozer or similar

geomembrane during construction (to prevent equipment. Although such methods may

sloughing or slipping down the interior side sound tedious and slow, in the long run they

slopes). Run out calculations (Koerner, 1990) will be faster and more cost-effective than

are available to determine the depth of burial placing too much material too fast and having

at a trench necessary to hold a specified length to remobilize the liner installer to repair

of membrane, or combination of membrane damaged sections of the geomembrane. The

and geofabric or geotextile. If forces larger QA activities conducted during construction

than the tensile strength of the membrane are also should include monitoring the

inadvertently developed, then the membrane contractor's activities on top of the liner to

could tear. For this reason, the geomembrane avoid damage to installed and accepted

should be allowed to slip or give in the trench geomembranes.

after construction to prevent such tearing.

However, during construction, the Leachate Collection Systems

geomembrane should be anchored according

to the detailed drawings provided in the Leachate refers to liquid that has passed

in front over the liner, but the operator must

Alternatively, large backhoes can be used to

through or emerged from solid waste and

contains dissolved, suspended, or immiscible
Subpart D

166

materials removed from the solid waste. At layer to collect leachate and carry it

MSWLF units, leachate is typically aqueous rapidly to a sump or collection header

with limited, if any, immiscible fluids or pipe;

dissolved solvents. The primary function of

the leachate collection system is to collect and ! A protective filter layer over the high

convey leachate out of the landfill unit and to permeability drainage material, if

control the depth of the leachate above the necessary, to prevent physical clogging

liner. The leachate collection system (LCS) of the material by fine-grained material;

should be designed to meet the regulatory and

performance standard of maintaining less than

30 cm (12 inches) depth of leachate, or ! Leachate collection sumps or header

"head," above the liner. The 30-cm head pipe system where leachate can be

allowance is a design standard and the Agency removed.

recognizes that this design standard may be

exceeded for relatively short periods of time The design, construction, and operation of the

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

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-
Design Criteria

167

percent grade as a post-settlement design friction angle between the geomembrane and

objective (U.S. EPA, 1991b). soil, and if possible, supported by laboratory

High-Permeability Drainage Layer

The high-permeability drainage layer is designation of GW or GP on the Unified Soils

placed directly over the liner or its protective Classification Chart can be expected to have

bedding layer at a slope of at least two percent a hydraulic conductivity of greater than 0.01

(the same slope necessary for the composite cm/sec, while sands identified as SW or SP

liner). Often the selection of a drainage can be expected to have a coefficient of

material is based on the on-site availability of permeability greater than 0.001 cm/sec. The

natural granular materials. In some regions of sand or gravel drains leachate that enters the

the country, hauling costs may be very high drainage layer to prevent 30 cm (12 in) or

for sand and gravel, or appropriate materials more accumulation on top of the liner during

may be unavailable; therefore, the designer the active life of the MSWLF unit LCS. The

may elect to use geosynthetic drainage nets design of a LCS frequently uses a drainage

(geonets) or synthetic drainage materials as an material with a hydraulic conductivity of 1 x

alternative. Frequently, geonets are 10 cm/sec or higher. Drainage materials

substituted for granular materials on steep with hydraulic conductivities in this order of

sidewalls because maintaining sand on the magnitude should be evaluated for biological

slope during construction and operation of the and particulate clogging (USEPA, 1988).

landfill unit is more difficult (U.S. EPA, Alternatively, if a geonet is used, the design is

1988). based on the transmissivity of the geonet.

Soil Drainage Layers If a filter layer (soil or geosynthetic) is

If the drainage layer of the leachate collection protect it from clogging, and the LCS is

system is constructed of granular soil designed and operated to avoid drastic

materials (e.g., sand and gravel), then it changes in the oxidation reduction potential of

should be demonstrated that this granular the leachate (thereby avoiding formation of

drainage layer has sufficient bearing strength precipitates within the LCS), then there is no

to support expected loads. This conceptual basis to anticipate that

demonstration will be similar to that required conductivity will decrease over time. Where

for the foundations and soil liner (U.S. EPA, conductivity is expected to decrease over

1988). time, the change in impingement rate also

If the landfill unit is designed on moderate-to- because the reduced impingement rate and

steep (15 percent) grades, the landfill design hydraulic conductivity may still comply with

should include calculations demonstrating that the 30 cm criterion.

the selected granular drainage materials will

be stable on the most critical slopes (e.g., Unless alternative provisions are made to

usually the steepest slope) in the design. The

calculations and assumptions should be

shown, especially the 

and/or field testing (USEPA, 1988).

Generally, gravel soil with a group

-2

constructed on top of a drainage layer to

should be evaluated over the same time period

control incident precipitation and resulting

surface run-off, the impingement rate during

the operating period of the MSWLF unit is
Subpart D

168

usually at least an order of magnitude greater Granular materials are generally placed using

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.

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 
Design Criteria

169

transmissivity of a geonet can be reduced critical specification is the ability to transmit

significantly by intrusion of the soil or a fluids under load. The specifications also

geotextile. A protective geotextile between should include a minimum transmissivity

the soil and geonet will help alleviate this under expected landfill operating (dynamic)

concern. If laboratory transmissivity tests are or completion (static) loads. The

performed, they should be done under specifications for thickness and types of

conditions, loads, and configurations that material should be identified on the drawings

closely replicate the actual field conditions. It or in the materials section of the

is important that the transmissivity value used specifications, and should be consistent with

in the leachate collection system design the design calculations (U.S. EPA, 1988).

calculations be selected based upon those

loaded conditions (U.S. EPA, 1988). It is also Geonets are often used on the sidewalls of

important to ensure that appropriate factors of landfills because of their ease of installation.

safety are used (Koerner, 1990). They should be placed with the top ends in a

The flow rate or transmissivity of geonets longitudinal length extending down the slope.

may be evaluated by ASTM D-4716. This The geonets need not be seamed to each other

flow rate may then be compared to design-by- on the slopes, only tied at the edges, butted, or

function equations presented in U.S. EPA overlapped. They should be placed in a loose

(1989). In the ASTM D-4716 flow test, the condition, not stretched or placed in a

proposed collector cross section should be configuration where they are bearing their

modeled as closely as possible to actual field own weight in tension. The construction

conditions (U.S. EPA, 1989). specifications should contain appropriate

Figure 4-7 shows the flow rate "signatures" of or the requirements of the geonet

a geonet between two geomembranes (upper manufacturer. All geonets need to be

curves) and the same geonet between a layer protected by a filter layer or geotextile to

of clay soil and a geomembrane (lower prevent clogging (U.S. EPA, 1988).

curves). The differences between the two sets

of curves represent intrusion of the The friction factors against sliding for

geotextile/clay into the apertures of the geotextiles, geonets, and geomembranes often

geonet. The curves are used to obtain a flow can be estimated using manufacturers data

rate for the particular geonet being designed because these materials do not exhibit the

(U.S. EPA, 1989). Equations to determine the range of characteristics as seen in soil

design flow rate or transmissivity are also materials. However, it is important that the

presented in U.S. EPA (1989), Giroud (1982), designer perform the actual tests using site

Carroll (1987), Koerner (1990), and FHWA materials and that the sliding stability

(1987). calculations accurately represent the actual

Generally, geonets perform well and result in specified material characteristics (U.S. EPA,

high factors of safety or performance design 1988).

ratios, unless creep (elongation under constant

stress) becomes a problem or adjacent

materials intrude into apertures (U.S. EPA,

1989). For geonets, the most 

secure anchor trench with the strongest

installation requirements as described above

design configuration, site conditions, and the
Figure 4-7. Flow Rate Curves for Geonets in Two Composite Liner Configurations

170
hmax

'

L c

2

[

tan2"

c

%1&

tan"

c

tan2"%c]

Design Criteria

171

Leachate Collection Pipes ! The required flow using known

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:

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):

 where c = q/k

 k = permeability

 q = inflow rate

 " = 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
Subpart D

172

Figure 4-8. Definition of Terms for Mound Model

Flow Rate Calculations
Design Criteria

173

storage, evapotranspiration, and lateral ! Diameter and wall thickness;

drainage. The program estimates run-off

drainage and leachate that are expected to ! Size and distribution of slots and

result from a wide variety of landfill perforations;

conditions, including open, partially open, and

closed landfill cells. The model also may be ! Type of coatings (if any) used in the

used to estimate the depth of leachate above pipe manufacturing; and

the bottom liner of the landfill unit. The

results may be used to compare designs or to ! Type of pipe bedding material and

aid in the design of leachate collection required compaction used to support the

systems (U.S. EPA, 1988). pipes.

Once the percolation and pipe spacing are The construction drawings and specifications

known, the design flow rate can be obtained should clearly indicate the type of bedding to

using the curve in Figure 4-9. The amount of be used under the pipes and the dimensions of

leachate percolation at the particular site is any trenches. The specifications should

located on the x-axis. indicate how the pipe lengths are joined. The

The required flow rate is the point at which placed with respect to the perforations. To

this value intersects with the pipe spacing maintain the lowest possible leachate head,

value determined from the Mound Model. there should be perforations near the pipe

Using this value of flow rate and the bottom invert, but not directly at the invert. The pipe

slope of the site, the required diameter for the invert itself should be solid to allow for

pipe can be determined (see Figure 4-10). efficient pipe flow at low volumes (U.S. EPA,

Finally, the graphs in Figures 4-11 and 4-12 1988).

show two ways to determine whether the

strength of the pipe is adequate for the landfill When drainage pipe systems are embedded in

design. In Figure 4-11, the vertical soil filter and drainage layers, no unplugged ends

pressure is located on the y-axis. The density should be allowed. The filter materials in

of the backfill material around the pipe is not contact with the pipes should be appropriately

governed by strength, so it will deform under sized to prevent migration of the material into

pressure rather than break. Ten percent is the the pipe. The filter media, drainage layer, and

absolute limiting deflection value for plastic pipe network should be compatible and should

pipe. Using Figure 4-11, the applied pressure represent an integrated design.

on the pipe is located and traced to the trench

geometry, and then the pipe deflection value Protection of Leachate Collection Pipes

is checked for its adequacy (U.S. EPA, 1989).

The LCS specifications should include (U.S. depends on the design used to protect pipes

EPA, 1988): from physical clogging (sedimentation) by the

! Type of piping material; material around the pipes is most effective if

drawings should show how the pipes are

The long-term performance of the LCS

granular drainage materials. Use of a graded

accompanied by proper sizing of pipe

perforations. The Army Corps of
Subpart D

174

Figure 4-9. Required Capacity of Leachate Collection Pipe
Figure 4-10. Leachate Collection Pipe Sizing Chart
Subpart D

176

Figure 4-11. Vertical Ring Deflection Versus Vertical Soil Pressure for 

18-inch Corrugated Polyethylene in High Pressure Soil Cell
Design Criteria

177

Figure 4-12. Example of the Effect of Trench Geometry

and Pipe Sizing on Ring Deflection
Subpart D

178

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, 1991a).

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 There are three parts to an analysis of a sand

units. There are no universally effective filter that is placed above drainage material.

methods of preventing such biological The first determines whether or not the filter

growth. Since organic materials will be allows adequate flow of liquids. The second

present in the landfill unit, there will be a evaluates whether the void spaces are small

potential for biological clogging. The system enough to prevent solids from being lost from

design should include features that allow for the upstream materials. The third estimates

pipe system cleanings. The components of the long-term clogging behavior of the filter

the cleaning system should include (U.S. (U.S. EPA, 1989).

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

The particle-size distribution of the drainage

system and the particle-size distribution of the

invading (or upstream) soils are required 
Design Criteria

179

in the design of granular soil (sand filter) specifications should indicate the extent of the

materials. The filter material should have its envelope. The construction quality control

large and small size particles intermediate program should document that the envelope

between the two extremes. Equations for was installed according to the plans and

adequate flow and retention are: specifications (U.S. EPA, 1988).

! Adequate Flow: A granular filter layer is generally placed

d85f > (3 to 5)d15d.s. using the same earthmoving equipment as the

! Adequate Retention: should be checked by optical survey or by

d < (3 to 5)d direct test pit measurement (U.S. EPA, 1988). 15f 85w.f.

Where f = required filter soil; This filter layer is the uppermost layer in the

 d.s. = drainage stone; and leachate collection system. A landfill design

 w.f. = water fines. option includes a buffer layer, 12 inches thick

There are no quantitative methods to assess drainage layer from damage due to traffic.

soil filter clogging, although empirical This final layer can be general fill, as long as

guidelines are found in geotechnical it is no finer than the soil used in the filter

engineering references. layer (U.S. EPA, 1988). However, if the

The specifications for granular filter layers leachate recirculation attempts.

that surround perforated pipes and that protect

the drainage layer from clogging are based on Geotextile Filter Layers

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 

granular drainage layer. The final thickness

(30 cm) or more, to protect the filter layer and

layer has a low permeability, it will affect

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
Subpart D

180

comparing the material (allowable) to the inside so that the glass beads used in the

permittivity to the design imposed test cannot escape around the edges of the

permittivity. Permittivity is measured by the geotextile filter. The particle-size distribution

ASTM D-4491 test method. The design of retained glass beads is compared to the

permittivity utilizes an adapted form of allowable value using any of a number of

Darcy's law. The resulting comparison yields existing formulas (U.S. EPA, 1989).

a design ratio, or factor of safety, that is the

focus of the design (U.S. EPA, 1989): The third consideration in geotextile design is

DR = øallow/øreqd problem that may be adopted by ASTM is

 called the Gradient Ratio Test. In this test,

where: the hydraulic gradient of 1 inch of soil plus

øallow = permittivity from ASTM the underlying geotextile is compared with the

 D-4491 hydraulic gradient of 2 inches of soil. The

 ø = (q/a) (1/h ) higher the gradient ratio, the more likely that reqd max

 q/a = inflow rate per unit area a clog will occur. The final ASTM gradient

 h max = 12 inches ratio test will include failure criteria. An

The second part of the geotextile filter design flow test that also is performed in a

is determining the opening size necessary for laboratory. The test models a soil-to-fabric

retaining the upstream soil or particulates in system at the anticipated hydraulic gradient.

the leachate. It is well established that the 95 The flow rate through the system is

percent opening size is related to particles to monitored. A long-term flow rate will

be retained in the following type of gradually decrease until it stops altogether

relationship: (U.S. EPA, 1989).

O95 < fct. (d50, CU, DR) The primary function of a geotextile is to

where: leachate pipes while allowing the passage of

O95 = 95% opening size of leachate. The most important specifications

 geotextile; are those for hydraulic conductivity and

d50 = 50% size of upstream particles; retention. The hydraulic conductivity of the

 CU = Uniformity of the upstream geotextile generally should be at least ten

 particle size; and times the soil it is retaining. An evaluation of

 DR = Relative density of the the retention ability for loose soils is based on

 upstream particles. the average particle size of the soil and the

The O size of a geotextile in the equation is The maximum apparent opening size, 95

the opening size at which 5 percent of a given sometimes called equivalent opening size, is

value should be less than the particle size determined by the size of the soil that will be

characteristics of the invading materials. In retained; a geotextile is then selected to meet

the test for the O95 size of the geotextile, a that specification. The material specifications

sieve with a very coarse mesh in the bottom is should contain a range of AOS values for the

used as a support. The geotextile is placed on geotextile, and 

top of the mesh and is bonded 

long-term clogging. A test method for this

alternative to this test method is a long-term

prevent the migration of fines into the

apparent opening size (AOS) of the geotextile.
Design Criteria

181

these AOS values should match those used in operational problems. Because they may run

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

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 
Subpart D

182

cover and then through the cover itself. If a sliding material to tear the geomembrane

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 

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 thirdparty 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
Design Criteria

183

officer's objectivity. Regulatory project plans and specifications,

representatives can then evaluate whether thereby allowing the contractor to

these mechanisms are sufficient to ensure an correct the construction process if the

acceptable CQA product. quality of the product is not meeting

Construction quality control (CQC) is an

on-going process of measuring and • Construction Quality Assurance

controlling the characteristics of the product (CQA) Testing by the Owner

in order to meet manufacturer's or project (Acceptance Inspection) performed by

specifications. CQC is a production tool the owner usually through the thirdthat is employed by the manufacturer of party testing firm, provides a measure

materials and by the contractor installing the of the final product quality and its

materials at the site. CQA, by contrast, is a conformance with project plans and

verification tool employed by the facility specifications. Due to the size and

owner or regulatory agency to ensure that costs of a typical MSWLF unit

the materials and installations meet project construction project, rejection of the

specifications. CQC is performed project at completion would be costly

independently of the CQA Plan. For to all parties. Acceptance Inspections

example, while a geomembrane liner as portions of the project become

installer will perform CQC testing of field complete allow deficiencies to be

seams, the CQA program will require found and corrected before they

independent CQA testing of those same become too large and costly.

seams by a third-party inspector.

The CQA/CQC plans are implemented performed by a regulatory agency to

through inspection activities that include ensure that the final product conforms

visual observations, field testing and with all applicable codes and

measurements, laboratory testing, and regulations. In some cases, the

evaluation of the test data. Inspection regulatory agency will use CQA

activities typically are concerned with four documentation and the as-built plans

separate functions: or "record drawings" to confirm

• Quality Control (QC) Inspection by

the Manufacturer provides an in- Soil Liner Quality Assurance/Quality

process measure of the product quality Control

and its conformance with the project

plans and specifications. Typically, Quality control testing performed on

the manufacturer will QC test results materials used in construction of the landfill

to certify that the product conforms to unit includes source testing and construction

project plans and specifications. testing. Source testing defines material

• Construction Quality Control (CQC) Source testing commonly includes moisture

Inspection by the Contractor provides content, soil density, Atterberg limits, grain

an in-process measure of construction size, and laboratory hydraulic conductivity.

quality and conformance with the Construction testing ensures that landfill

the specifications and plans.

• Regulatory Inspection often is

compliance with the regulations.

properties that govern material placement.
Subpart D

184

construction has been performed in Quality assurance testing for soil liners

accordance with the plans and technical includes the same testing requirements as

specifications. Construction testing specified above for control testing.

generally includes tests of soil moisture Generally, the tests are performed less

content, density, lift thickness, and frequently and are performed by an

hydraulic conductivity. individual or an entity independent of the

The method of determining compliance with quality assurance (CQA) officer are

the maximum hydraulic conductivity essential to document quality of

criterion should be specified in the QA/QC construction. The CQA officer's

plan. Some methods have included the use responsibilities and those of the CQA

of the criterion as a maximum value that officer's staff members may include:

never should be exceeded, while other

methods have used statistical techniques to ! Communicating with the contractor;

estimate the true mean. The sample

collection program should be designed to ! Interpreting and clarifying project

work with the method of compliance drawings and specifications with the

determination. Selection of sample designer, owner, and contractor;

collection points should be made on a

random basis. ! Recommending acceptance or

Thin wall sampling tubes generally are used work completed by the construction

to collect compacted clay samples for contractor;

laboratory hydraulic conductivity testing. It

is important to minimize disturbance of the ! Submitting blind samples (e.g.,

sample being collected. Tubes pushed into duplicates and blanks) for analysis by

the soil by a backhoe may yield disturbed the contractor's testing staff or one or

samples. A recommended procedure (when more independent laboratories, as

a backhoe is available during sample applicable;

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). 

contractor. Activities of the construction

rejection by the owner/operator of

! 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
Design Criteria

185

! Reporting to the owner/operator on between lifts or between placements in

monitoring results.

Soil Liner Pilot Construction (Test Fill)

A pilot construction or test fill is a smallscale 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 1x10 cm/sec

-7

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 costeffective 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

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
Subpart D

186

tests are performed on samples from the seam or reseaming the affected area (U.S.

installed seams. EPA, 1988). In situations where the seams

Quality assurance testing generally requires may have to be retrained.

that an independent laboratory perform peel

and shear tests of samples from installed Non-Destructive Testing

seams. The samples may be collected

randomly or in areas of suspect quality. Non-destructive test methods are conducted

HDPE seams are generally tested at in the field on an in-place geomembrane.

intervals equivalent to one sample per every These test methods determine the integrity

300 to 400 feet of installed seam for of the geomembrane field seams. Nonextrusion welds, and every 500 feet for destructive test methods include the probe

fusion-welded seams. Extrusion seams on test, air lance, vacuum box, ultrasonic

HDPE require grinding prior to welding, methods (pulse echo, shadow and

which can greatly diminish parent material impedance plane), electrical spark test,

strengths if excessive grinding occurs. pressurized dual seam, electrical resistivity,

Detailed discussion of polyethylene welding and hydrostatic tests. Detailed discussion of

protocol can be found in U.S. EPA (1991a). these test methods may be found in U.S.

For dual hot wedge seams in HDPE, both EPA (1991a). Seam sections that fail

the inner and outer seam may be subjected appropriate, non-destructive tests must be

to destructive shear tests at the independent carefully delineated, patched or reseamed,

laboratory. Destructive samples of installed and retested. Large patches or reseamed

seam welds are generally cut into several areas should be subjected to destructive test

pieces and distributed to: procedures for quality assurance purposes.

! The installer to perform construction the degree to which non-destructive and

quality control field testing; destructive test methods will be used in

! 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

continually fail testing, the seaming crews

The specifications should clearly describe

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;
Design Criteria

187

! Observation of seam overlap, seam they meet the construction plans and

preparation prior to seaming, and specifications. These include (U.S. EPA,

material underlying the liner; 1988):

! Observation of destructive testing ! Geonets;

conducted on scrap test welds prior to

seaming; ! Geotextiles;

! Observation of destructive seam ! Pipe size, materials, and perforations;

sampling, submission of the samples

to an independent testing laboratory, ! Granular material gradation and

and review of results for conformance prefabricated structures (sumps,

to specifications; manholes, etc.);

! Observation of all seams and panels ! Mechanical, electrical, and monitoring

for defects due to manufacturing equipment; and

and/or handling and placement;

! Observation of all pipe penetration

boots and welds in the liner; The leachate collection system foundation

! Preparation of reports indicating liner) should be inspected and surveyed

sampling conducted and sampling upon its completion to ensure that it has

results, locations of destructive proper grading and is free of debris and

samples, locations of patches, liquids (U.S. EPA, 1988).

locations of seams constructed, and

any problems encountered; and, During construction, the following

! Preparation of record drawings of the observed and documented (U.S. EPA,

liner installation, in some cases. 1988):

The last responsibility is frequently assigned ! Pipe bedding placement including

to the contractor, the owner's representative, quality, thickness, and areal coverage;

or the engineer.

Leachate Collection System including material quality and

Construction Quality Assurance thickness;

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 

! Concrete forms and reinforcement.

(geomembrane or low permeability soil

activities, as appropriate, should be

! Granular filter layer placement

! 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 
Subpart D

188

fabrics and geonets if applicable, and 4.4 RELEVANT POINT OF

weather conditions; COMPLIANCE

! Geonet placement including layout,

overlap, and protection from clogging 4.4.1 Statement of Regulation

by granular material carried by wind

or run-off during construction; (a) (See Statement of Regulation in

! Geotextile/geofabric placement the regulatory language for performanceincluding coverage and overlap; based design requirements.)

! Sumps and structure installation; and (b) (See Statement of Regulation in

! 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).

40 CFR §258.40(d)

Section 4.2.1 of this guidance document for

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 performancebased 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 hydrogeologi c

characteristics of the facility and

surrounding land;

(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;
Design Criteria

189

(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)(1). 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 wellspacing 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 groundwater flow rate, ground-water flow
Subpart D

190

direction, and the volume of ground-water unit, should be determined prior to

flow. Background ground-water quality establishing the relevant point of

data should be used to establish baseline compliance (see Section 5.6.3). The

concentrations of the monitoring performance standard for landfill design

constituents. This information will be requires that landfill units be designed so

required as input to determine if that the concentrations listed in Table 1 are

contaminants from the landfill unit have not exceeded at a relevant point of

been released and have migrated to the compliance. Issues for approved States to

relevant point of compliance. consider are whether the ground water is

Ground-Water Receptors be used as a drinking water source when

The goal of establishing the relevant point the ground water is not currently or

of compliance is to ensure early detection of reasonably expected to be used for drinking

contamination of the uppermost aquifer. water, the State may allow the relevant

The distance to the relevant point of point of compliance to be set near the 150-

compliance should allow sufficient time for meter limit.

corrective measures to be implemented prior

to the migration of contaminants to private Public Health, Welfare, Safety

or public water supply wells.

Existing users of ground water immediately potential overall effect on public health,

downgradient from the facility should be welfare, and safety of the proposed relevant

identified on a map. Users located at a point of compliance. Issues that should be

downgradient point where contaminants considered include:

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 

currently used or is reasonably expected to

setting a relevant point of compliance. If

Consideration should be given to the

! 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.
Design Criteria

191

Practicable Capability of the Owner or 4.5 PETITION PROCESS

Operator 40 CFR §258.40(e)

If the relevant point of compliance is placed 4.5.1 Statement of Regulation

farther from the waste management unit

boundary, the volume of water requiring (a) - (d) (See Statement of Regulation

treatment, should the ground water become in Sections 4.2.1, 4.3.1, and 4.4.1 of this

contaminated, will increase. One or more of guidance document for regulatory

the following conditions could affect the language.)

owner's or operator's practicable capability

(technical and financial) to remediate (e) If EPA does not promulgate a

contaminant releases: rule establishing the procedures and

! Area of impact, remedial costs, scope RCRA Section 4005(c)(1)(B) by October

of remedial investigation, and site 9, 1993, owners and operators in

characterization; unapproved States may utilize a design

! Increased response time due to higher §258.40(a)(1) if the following conditions

costs and increased technical scope of are met:

selected remedial method;

! A reduction of the removal efficiency meets the performance standard in

of treatment technologies; and §258.40(a)(1);

! Increased difficulty in ground-water (2) The State petitions EPA to

extraction or containment if these review its determination; and

technologies are chosen.

The Director may require some indication of determination or does not disapprove the

financial capability of the owner or operator determination within 30 days.

to maintain a longer and more costly

remedial program due to the longer [Note to Subpart D: 40 CFR Part 239 is

detection time frame associated with a reserved to establish the procedures and

relevant point of compliance located at a requirements for State compliance with

greater distance from the waste management RCRA Section 4005(c)(1)(B).]

unit boundary. Additional information on

remedial actions for ground water is 4.5.2 Applicability

provided in this document in Chapter 5.

requirements for State compliance with

meeting the performance standard in

(1) The State determines the design

(3) EPA approves the State

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)(1)) under

certain circumstances.
Subpart D

192

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.
Design Criteria

193

4.6 FURTHER INFORMATION

4.6.1 REFERENCES

(Specific to Performance-Based Design Assessment and Solute Transport Modeling)

Abriola, L.M., and G.F. Pinder, (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. Pinder, (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". BAS15, 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, Y.J.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. 
Subpart D

194

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.
Design Criteria

195

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 J.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 J.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. 
Subpart D

196

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(1):25-33.

Ostendorf, D.W., R.R. Noss, and D.O. Lederer, (1984). Landfill Leachate Migration through

Shallow Unconfined 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.
Design Criteria

197

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.
Subpart D

198

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. NTIS No. PB89-135859. 157 pp.

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. EPA660/9-78-016, U.S. EPA, Cincinnati, Ohio. 

van Genuchten, M.T., and W.J. 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.
Design Criteria

199

Weaver, J., 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"; EM1110-2-1906; Headquarters, Department of the

Army; Office of the Chief of Engineers; Washington, DC 20314.
Subpart D

200

FHWA, (1985). "FHWA Geotextile Engineering Manual." Contract No.l DTF H61-83-C00150.

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.
Design Criteria

201

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 PB81-166365 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.

NTIS PB-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.
Subpart D

202

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. NTIS PB-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
Design Criteria

203

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: MODFLOW , MODPATH , MOC , SUTRA , Quickflow, 386 386 386 386

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.
CHAPTER 5

SUBPART E

GROUND-WATER MONITORING

AND CORRECTIVE ACTION
206

CHAPTER 5

SUBPART E

TABLE OF CONTENTS

5.1 INTRODUCTION ................................................... 211

5.2 APPLICABILITY 40 CFR §258.50 (a) & (b) .............................. 211

5.2.1 Statement of Regulation .......................................... 211

5.2.2 Applicability .................................................. 212

5.2.3 Technical Considerations ......................................... 212

5.3 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

5.4 ALTERNATIVE COMPLIANCE SCHEDULES 40 CFR 258.50 (d)(e) & (g) ..... 215

5.4.1 Statement of Regulation .......................................... 215

5.4.2 Applicability .................................................. 216

5.4.3 Technical Considerations ......................................... 217

5.5 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

5.6 GROUND-WATER MONITORING SYSTEMS 40 CFR §258.51 (a)(b)(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
207

5.7 GROUND-WATER MONITORING WELL DESIGN AND CONSTRUCTION 40

CFR §258.51 (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

5.8 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
208

5.9 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(g) .............. 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)-(j) ............ 289

5.13.1 Statement of Regulation ......................................... 289

5.13.2 Applicability ................................................. 290

5.13.3 Technical Considerations ........................................ 290
209

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)-(b) ........................ 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
210

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 (b)-(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
211

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 groundwater 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 active life of the unit and the post-closure

40 CFR §258.50 (a) & (b) care period. This demonstration must be

5.2.1 Statement of Regulation scientist and approved by the Director of

(a) The requirements in this Part apply to upon: 

MSWLF units, except as provided in

paragraph (b) of this section. (1) Site-specific field collected

(b) Ground-water monitoring physical, chemical, and biological processes

requirements under §258.51 through affecting contaminant fate and transport,

§258.55 of this Part may be suspended by and 

the Director of an approved State for a

MSWLF unit if the owner or operator can (2) Contaminant fate and transport

demonstrate that there is no potential for predictions that maximize contaminant

migration of hazardous constituents from migration and consider impacts on human

that MSWLF unit to the uppermost health and environment.

aquifer (as defined in §258.2) during the

certified by a qualified ground-water

an approved State, and must be based

measurements, sampling, and analysis of
Subpart E

212

5.2.2 Applicability §258.51 through §258.55 if the owner or

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" demonstration must be based upon site-specific information 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 maximum anticipated concentrations of constituents 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 NoMigration 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 groundwater monitoring requirements at 

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, degree 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);
Ground-Water Monitoring and Corrective Action

213

! Climatic Conditions, including annual transport should be biased toward overprecipitation, leachate generation estimating transport and the anticipated

estimates, and effects on leachate concentrations. Assumptions and site

quality; specific data that are used in the fate and

! Leachate Characteristics, including transport principles and processes,

leachate composition, solubility, density, including adherence to mass-balance and

the presence of immiscible constituents, chemical equilibria limitations. Within

Eh, and pH; and these physicochemical limitations,

! Engineered Controls, including liners, objective of assessing the maximum

cover systems, and aquifer controls (e.g., potential impact on human health and the

lowering the water table). These should environment. The evaluation of sitebe evaluated under design and failure specific data and assumptions may include

conditions to estimate their long-term some of the following approaches:

residual performance.

Chemical Properties or Processes: parameters and conditions that will

! Attenuation of contaminants in the hydraulic conductivity, effective

subsurface, including adsorption/ porosity, horizontal and vertical

desorption reactions, ion exchange, gradients), rather than average values

organic content of soil, soil water pH,

and consideration of possible reactions ! Use of the lower range of known aquifer

causing chemical transformation or conditions and parameters that tend to

chelation. attenuate or retard contaminant transport

Biological Processes: cation exchange capacities, organic

! Microbiological Degradation, which may conditions), rather than average values

attenuate target compounds or cause

transformations of compounds, ! Consideration of the cumulative impacts

potentially forming more toxic chemical on water quality, including both existing

species. water quality data and cumulative health

The alternative design section of Chapter likely to migrate from the MSWLF unit

5.0 discusses these and other processes that and other potential or known sources.

affect contaminant fate and solute transport.

When owners or operators prepare a no- for evaluating contaminant or solute

migration demonstration, they must use transport is provided in Chapter 5. 

predictions that are based on maximum

contaminant migration both from the unit

and through the subsurface media.

Assumptions about variables affecting

transport predictions should conform with

assumptions should be biased toward the

! Use of the upper bound of known aquifer

maximize contaminant transport (e.g.,

(e.g., dispersivities, decay coefficients,

carbon contents, and recharge

risks posed by hazardous constituents

A discussion of mathematical approaches
Subpart E

214

5.3 COMPLIANCE SCHEDULE (4) New MSWLF units must be in

40 CFR § 258.50 (c) compliance with the ground-water

5.3.1 Statement of Regulation* §§258.51 - 258.55 before waste can be

*[NOTE: EPA finalized several revisions

to 40 CFR Part 258 on October 1, 1993 5.3.2 Applicability

(58 FR 51536), and these revisions delay

the effective date for some categories of The rule establishes a self-implementing

landfills. More detail on the content of schedule for owners or operators in States

the revisions is included in the with programs that are deemed inadequate

introduction.] or not yet approved. As indicated in the

(c) Owners and operators of MSWLF depends on the distance of the MSWLF unit

units must comply with the ground-water from drinking water sources. Approved

monitoring requirements of this part States may specify an alternative schedule

according to the following schedule unless under §258.50 (d), which is discussed in

an alternative schedule is specified under Section 5.4. 

paragraph (d):

(1) Existing MSWLF units and lateral than one mile from a drinking water intake

expansions less than one mile from a must be in compliance with the grounddrinking water intake (surface or water monitoring requirements by October

subsurface) must be in compliance with 9, 1994. If the units are greater than one

the ground-water monitoring mile but less than two miles from a drinking

requirements specified in §§258.51 - water intake, they must be in compliance by

258.55 by October 9, 1994; October 9, 1995. Those units located more

(2) Existing MSWLF units and lateral must be in compliance by October 9, 1996

expansions greater than one mile but less (see Table 5-1).

than two miles from a drinking water

intake (surface or subsurface) must be in New MSWLF units, defined as units that

compliance with the ground-water have not received waste prior to October 9,

monitoring requirements specified in 1993, must be in compliance with these

§§258.51 - 258.55 by October 9, 1995; requirements before receiving waste

(3) Existing MSWLF units and lateral supply intake. 

expansions greater than two miles from a

drinking water intake (surface or 5.3.3 Technical Considerations

subsurface) must be in compliance with

the ground-water monitoring For most facilities, these requirements will

requirements specified in §§258.51 - become applicable 3 to 5 years after the

258.55 by October 9, 1996; promulgation date of the rule. This period

monitoring requirements specified in

placed in the unit.

Statement of Regulation, this schedule

Existing units and lateral expansions less

than two miles from a drinking water intake

regardless of the proximity to a water
Ground-Water Monitoring and Corrective Action

215

Table 5-1. Compliance Schedule for Existing Units and Lateral Expansions

in States with Unapproved Programs

Distance From Water Supply Intake Time to Comply

From October 9, 1991

One mile or less 3 Years

More than one mile but less than two 4 Years

miles

More than two miles 5 Years

should provide sufficient time for the owner compliance by October 9, 1996. In

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 

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.
Subpart E

216

(e) Once established at a MSWLF 5.4.2 Applicability

unit, ground-water monitoring shall be

conducted throughout the active life and The Director of an approved State may

post-closure care period of that MSWLF establish an alternative schedule for

unit as specified in §258.61. requiring owners/operators of existing units

(f) (See Section 5.5 for technical ground-water monitoring requirements.

guidance on qualifications of a ground- The alternative schedule is to ensure that at

water scientist.) least fifty percent of all existing MSWLF

(g) The Director of an approved State by October 9, 1994 and that all units are in

may establish alternative schedules for compliance by October 9, 1996.

demonstrating compliance with

§258.51(d)(2), pertaining to notification In establishing the alternative schedule, the

of placement of certification in operating Director of an approved State may use siterecord; § 258.54(c)(1), pertaining to specific information to assess the relative

notification that statistically significant risks posed by different waste management

increase (SSI) notice is in operating units and will allow priorities to be

record; § 258.54(c)(2) and (3), pertaining developed at the State level. This siteto an assessment monitoring program; specific information (e.g., proximity to

§ 258.55(b), pertaining to sampling and receptors, proximity and withdrawal rate of

analyzing Appendix II constituents; ground-water users, waste quantity, type,

§258.55(d)(1), pertaining to placement of containment design and age) should enable

notice (Appendix II constituents detected) the Director to assess potential risk to the

in record and notification of notice in uppermost aquifer. The resource value of

record; § 258.55(d)(2), pertaining to the aquifer to be monitored (e.g., groundsampling for Appendix I and II; water quality and quantity, present and

§ 258.55(g), pertaining to notification future uses, and withdrawal rate of ground-

(and placement of notice in record) of SSI water users) also may be considered.

above ground-water protection standard;

§ 258.55(g)(1)(iv) and § 258.56(a), Once ground-water monitoring has been

pertaining to assessment of corrective initiated, it must continue throughout the

measures; § 258.57(a), pertaining to active life, closure, and post-closure care

selection of remedy and notification of periods. The post-closure period may last

placement in record; § 258.58(c)(4), up to 30 years or more after the MSWLF

pertaining to notification of placement in unit has received a final cover. 

record (alternative corrective action

measures); and § 258.58(f), pertaining to In addition to establishing alternative

notification of placement in record schedules for compliance with ground-

(certification of remedy completed). water monitoring requirements, the Director

and lateral expansions to comply with the

units within a given State are in compliance

of an approved State may establish

alternative schedules for certain
Ground-Water Monitoring and Corrective Action

217

sampling and analysis requirements of at existing MSWLF units, the Director of an

§§258.54 and 258.55, as well as corrective approved State may consider information

action requirements of §§258.56, 258.57, including the age and design of existing

and 258.58. See Table 5-2 for a summary facilities. Using this type of information, in

of notification requirements for which conjunction with a knowledge of the wastes

approved States may establish alternative disposed, the Director should be able to

schedules. qualitatively assess or rank facilities based

5.4.3 Technical Considerations resources.

The rule allows approved States flexibility

in establishing alternate ground-water 5.5 QUALIFICATIONS

monitoring compliance schedules. In 40 CFR 258.50 (f)

setting an alternative schedule, the State

will consider potential impacts to human 5.5.1 Statement of Regulation

health and the environment. Approved

States have the option to address MSWLF (f) For the purposes of this Subpart, a

units that have environmental problems qualified ground-water scientist is a

immediately. In establishing alternative scientist or engineer who has received a

schedules for installing ground-water baccalaureate or post-graduate degree in

monitoring systems

on their risk to local ground-water

Table 5-2. Summary of Notification Requirements

Section Description

§258.51(d)(2) 14 day notification period after well installation

certification by a qualified ground-water scientist (GWS) 

§258.54(c)(1) 14 day notification period after finding a statistical increase

over background for detection parameter(s)

§258.55(d)(1) 14 day notification period after detection of Appendix II

constituents

§258.57(a) 14 day notification period after selection of corrective

measures

§258.58(c)(4) 14 day notification period prior to implementing alternative

measures

§258.58(f) 14 day notification period after remedy has been completed

and certified by GWS
Subpart E

218

the natural sciences or engineering and 5.5.3 Technical Considerations

has sufficient training and experience in

ground-water hydrology and related A qualified ground-water scientist must

fields as may be demonstrated by State certify work performed pursuant to the

registration, professional certifications, following provisions of the ground-water

or completion of accredited university monitoring and corrective action

programs that enable that individual to requirements:

make sound professional judgements

regarding ground-water monitoring, ! No potential for migration

contaminant fate and transport, and demonstration (§258.50(b))

corrective action.

5.5.2 Applicability spacing, and depths of monitoring wells

The qualifications of a ground-water

scientist are defined to ensure that ! Determination that contamination was

professionals of appropriate capability and caused by another source or that a

judgement are consulted when required by statistically significant increase resulted

the Criteria. The ground-water scientist from an error in sampling, analysis, or

must possess the fundamental education and evaluation (§§258.54 (c)(3) and 258.55

experience necessary to evaluate ground- (g)(2))

water flow, ground-water monitoring

systems, and ground-water monitoring ! Determination that compliance with a

techniques and methods. A ground-water remedy requirement is not technically

scientist must understand and be able to practicable (§258.58(c)(1))

apply methods to solve solute transport

problems and evaluate ground-water ! Completion of remedy (§258.58(f)).

remedial technologies. His or her education

may include undergraduate or graduate The owner or operator must determine that

studies in hydrogeology, ground-water the professional qualifications of the

hydrology, engineering hydrology, water ground-water specialist are in accordance

resource engineering, geotechnical with the regulatory definition. In general, a

engineering, geology, ground-water certification is a signed document that

modeling/ground-water computer modeling, transmits some finding (e.g., that

and other aspects of the natural sciences. monitoring wells were installed according

The qualified ground-water scientist must to acceptable practices and standards at

have a college degree but need not have locations and depths appropriate for a given

professional certification, unless required at facility). The certification must be placed

the State or Tribal level. Some in the operating record of the facility, and

States/Tribes may have certification the State Director must be notified that the

programs for ground-water scientists; certification has been made. Specific

however, there are no recognized Federal details of these certifications will be

certification programs.

! Specifications concerning the number,

(§258.51(d))
Ground-Water Monitoring and Corrective Action

219

addressed in the order in which they appear representative than that provided by the

in this guidance document. upgradient wells; and

Many State environmental regulatory (2) Represent the quality of ground

agencies have ground-water scientists on water passing the relevant point of

staff. The owner or operator of a MSWLF compliance specified by the Director of

unit or facility is not necessarily required to an approved State under §258.40(d) or at

obtain certification from an independent the waste management unit boundary in

(e.g., consulting) ground-water scientist and unapproved States. The downgradient

may, if agreed to by the Director in an monitoring system must be installed at

approved State, obtain approval by the the relevant point of compliance specified

Director in lieu of certification by an by the Director of an approved State

outside individual. under §258.40(d) or at the waste

5.6 GROUND-WATER of ground-water contamination in the

MONITORING SYSTEMS uppermost aquifer. When physical

40 CFR §258.51 (a)(b)(d) obstacles preclude installation of ground5.6.1 Statement of Regulation point of compliance at existing units, the

(a) A ground-water monitoring system installed at the closest practicable

must be installed that consists of a distance hydraulically down-gradient

sufficient number of wells, installed at from the relevant point of compliance or

appropriate locations and depths, to yield specified by the Director of an approved

ground-water samples from the upper- State under §258.40 that ensures

most aquifer (as defined in §258.2) that: detection of ground-water contamination

(1) Represent the quality of background

ground water that has not been affected (b) The Director of an approved State

by leakage from a unit. A determination may approve a multi-unit ground-water

of background quality may include monitoring system instead of separate

sampling of wells that are not ground-water monitoring systems for

hydraulically upgradient of the waste each MSWLF unit when the facility has

management area where: several units, provided the multi-unit

(i) Hydrogeologic conditions do not the requirement of §258.51(a) and will be

allow the owner or operator to determine as protective of human health and the

what wells are hydraulically upgradient; environment as individual monitoring

or systems for each MSWLF unit, based on

 (ii) Sampling at other wells will provide

an indication of background ground- (1) Number, spacing, and orientation of

water quality that is as representative or the MSWLF units; 

more 

management unit boundary in

unapproved States that ensures detection

water monitoring wells at the relevant

down-gradient monitoring system may be

in the uppermost aquifer. 

ground-water monitoring system meets

the following factors: 
Subpart E

220

(2) Hydrogeologic setting; 5.6.2 Applicability

(3) Site history; The requirements for establishing a ground-

(4) Engineering design of the MSWLF §258.51 apply to all new units, existing

units; and units, and lateral expansions of existing

(5) Type of waste accepted at the in 40 CFR §258.50. A ground-water

MSWLF units. monitoring system consists of both

(c) (See Section 5.7 for technical point of compliance or waste management

guidance on monitoring well design and unit boundary (i.e., downgradient wells).

construction.) The ground-water monitoring network must

(d) The number, spacing, and depths of MSWLF unit. A sufficient number of

monitoring systems shall be: monitoring wells must be located

(1) Determined based upon site-specific intervals in the uppermost aquifer to ensure

technical information that must include contaminant detection. Generally,

thorough characterization of: upgradient wells are used to determine

(i) Aquifer thickness, ground-water

flow rate, ground-water flow direction The downgradient wells must be located at

including seasonal and temporal the relevant point of compliance specified

fluctuations in ground-water flow; and by the Director of an approved State, or at

(ii) Saturated and unsaturated States that are not in compliance with

geologic units and fill materials overlying regulations. If existing physical structures

the uppermost aquifer, materials obstruct well placement, the downgradient

comprising the uppermost aquifer, and monitoring system should be placed as close

materials comprising the confining unit to the relevant point of compliance as

defining the lower boundary of the possible. Wells located at the relevant point

uppermost aquifer; including, but not of compliance must be capable of detecting

limited to: thicknesses, stratigraphy, contaminant releases from the MSWLF unit

lithology, hydraulic conductivities, to the uppermost aquifer. As discussed

porosities and effective porosities. earlier in the section pertaining to the

(2) Certified by a qualified ground- compliance (Section 4.4), the point of

water scientist or approved by the compliance must be no greater than 150

Director of an approved State. Within 14 meters from the unit boundary.

days of this certification, the owner or

operator must notify the State Director The Director of an approved State may

that the certification has been placed in allow the use of a multi-unit ground-water

the operating record. monitoring system. MSWLF units in 

water monitoring system pursuant to

units according to the schedules identified

background wells and wells located at the

be capable of detecting a release from the

downgradient of the unit and be screened at

background ground-water quality.

the waste management unit boundary in

designation of a relevant point of
Ground-Water Monitoring and Corrective Action

221

States that are deemed not in compliance aquifer is defined in §258.2 as "the geologic

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 objective 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

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 GroundWater 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
Subpart E

222

primarily by the mineral composition of the ! The facility is located near production

geologic unit comprising the aquifer. As wells that influence the direction of

ground water moves from one geologic unit ground-water flow.

to another, its chemical composition may

change. To reduce the probability of ! Upgradient ground-water quality is

detecting naturally occurring differences in affected by a source of contamination

ground-water quality between background other than the MSWLF unit.

and downgradient locations, only groundwater samples collected from the same ! The proposed or existing landfill

geologic unit should be compared. overlies a ground-water divide or local

Ground-water quality in areas where the

geology is complex can be difficult to ! Geologic units present at downgradient

characterize. As a result, the rule allows the locations are absent at upgradient

owner or operator flexibility in determining locations.

where to locate wells that will be used to

establish background water quality. ! Karst terrain or fault zones modify flow.

If the facility is new, ground-water samples ! Nearby surface water influences groundcollected from both upgradient and water flow directions.

downgradient locations prior to waste

disposal can be used to establish background ! Waste management areas are located

water quality. The sampling should be close to a property boundary that is

conducted to account for both seasonal and upgradient of the facility.

spatial variability in ground-water quality.

Determining background ground-water

quality by sampling wells that are not A multi-unit ground-water monitoring

hydraulically upgradient may be necessary system does not have wells at individual

where hydrogeologic conditions do not MSWLF unit boundaries. Instead, an

allow the owner or operator to determine imaginary line is drawn around all of the

which wells are hydraulically upgradient. units at the facility. (See Figure 5-1 for a

Additionally, background ground-water comparison of single unit and multi-unit

quality may be determined by sampling systems.) This line constitutes the relevant

wells that provide ground-water samples as point of compliance. The option to

representative or more representative than establish a multi-unit monitoring system is

those provided by upgradient wells. These restricted to facilities located in approved

conditions include the following: States. A multi-unit system must be

! The facility is located above an aquifer State after consideration has been given to

in which ground-water flow directions the:

change seasonally.

source of recharge.

Multi-Unit Monitoring Systems 

approved by the Director of an approved

! Number, spacing, and orientation of the

MSWLF units
Figure 5-1. Comparison of Single Unit and Multi-Unit Monitoring System

223
Subpart E

224

! Hydrogeologic setting ! The geology at the owner's/operator's

! Site history structural setting)

! Engineering design of the MSWLF units ! The chemical properties of the

! Type of wastes accepted at the facility. layers relative to local ground-water

The purpose of a multi-unit system is to facility

reduce the number of monitoring wells that

can provide the same information. The ! Ground-water flow, including:

conceptual design of the multi-unit system

should consider the use and management of - The vertical and horizontal directions

the facility with respect to anticipated unit of ground-water flow in the uppermost

locations. In some cases, it may be possible aquifer

to justify a reduction in the number of wells

if the waste management units are aligned - The vertical and horizontal

along the same flow path in the ground- components of the hydraulic gradient

water system. in the uppermost and any hydraulically

The multi-unit monitoring system must

provide a level of protection to human - The hydraulic conductivities of the

health and the environment that is materials that comprise the upper-most

comparable to monitoring individual units. aquifer and its confining units/layers

The multi-unit system should allow

adequate time after detection of - The average linear horizontal velocity

contamination to develop and implement of ground-water flow in the uppermost

corrective measures before sensitive aquifer.

receptors are adversely affected.

Hydrogeological Characterization the hydrogeology of a site are discussed

Adequate monitoring-well placement addressed in more detail in "RCRA Grounddepends on collecting and evaluating Water Monitoring: Draft Technical

hydrogeological information that can be Guidance" (USEPA, 1992a).

used to form a conceptual model of the site.

The goal of a hydrogeological investigation Prior to initiating a field investigation, the

is to acquire site-specific data concerning: owner or operator should perform a

! The lateral and vertical extent of the investigation will involve reviewing all

uppermost aquifer available information about the site, which

! The lateral and vertical extent of the

upper and lower confining units/layers

facility (e.g, stratigraphy, lithology, and

uppermost aquifer and its confining

chemistry and wastes managed at the

connected aquifer

The elements of a program to characterize

briefly in the sections that follow and are

preliminary investigation. The preliminary

may consist of:
Ground-Water Monitoring and Corrective Action

225

! Information on the waste management Characterizing Site Geology

history of the site, including:

- A chronological history of the site, complete, the owner/operator will have

including descriptions of wastes information that he/she can use to develop a

managed on-site plan to characterize site hydrogeology

- A summary of documented releases

- Details on the structural integrity of include a subsurface boring program. A

the MSWLF unit and physical controls boring program is necessary to define site

on waste migration hydrogeology and the small-scale geology

! A literature review, including: usually requires more than one iteration.

- Reports of research performed in the refine the conceptual model of the site

area of the site derived from the preliminary investigation.

- Journal articles The subsurface boring program should be

- Studies and reports available from

local, regional, and State offices (e.g., ! The initial number of boreholes and their

geologic surveys, water boards, and spacing is based on the information

environmental agencies) obtained during the preliminary

- Studies available from Federal offices,

such as USGS or USEPA ! Additional boreholes should be installed

! Information from file searches, about the site.

including:

- Reports of previous investigations at borings at changes in lithology. For

the site boreholes that will be completed as

- Geological and environmental should be collected from the interval that

assessment data from State and Federal will be the screened interval. Boreholes

reports. that will not be completed as monitoring

The documentation itemized above is by no

means a complete listing of information Geophysical techniques, cone penetrometer

available for a preliminary investigation. surveys, mapping programs, and laboratory

Many other sources of hydrogeological analyses of borehole samples can be used to

information may be available for review plan and supplement the subsurface boring

during the preliminary investigation. program. Downhole geophysical techniques

After the preliminary investigation is

further.

Nearly all hydrogeological investigations

of the area beneath the site. The program

The objective of the initial boreholes is to

designed as follows:

investigation.

as needed to provide more information

! Samples should be collected from the

monitoring wells, at least one sample

wells must be properly decommissioned.
Subpart E

226

include electric, sonic, and nuclear logging. ! Seasonal/temporal, natural, and

Surface geophysical techniques include artificially induced (e.g., off-site

seismic reflection and refraction, as well as production well-pumping, agricultural

electromagnetic induction and resistivity. use) short-term and long-term

The data obtained from the subsurface and flow patterns

boring program should enable the owner or

operator to identify: ! The hydraulic conductivities of the

! Lithology, soil types, and stratigraphy vertical hydraulic conductivity of the

! Zones of potentially high hydraulic

conductivity Determining Ground-Water Flow

! The presence of confining formations or

layers Installing monitoring wells that will provide

! Unpredicted geologic features, such as downgradient water samples requires a

fault zones, cross-cutting structures, and thorough understanding of how ground

pinch-out zones water flows beneath a site. Developing such

! Continuity of petrographic features, such information regarding both ground-water

as sorting, grain size distribution, and flow direction(s) and hydraulic gradient.

cementation Ground-water flow direction can be thought

! The potentiometric surface or water follows as it passes through the subsurface.

table. Hydraulic gradient (i) is the change in static

Characterizing Ground-Water Flow direction. The static head is defined as the

Beneath the Site height above a standard datum of the surface

In addition to characterizing site geology, can be supported by the static pressure at a

the owner/operator should characterize the given point (i.e., the sum of the elevation

hydrology of the uppermost aquifer and its head and pressure head).

confining layer(s) at the site. The owner or

operator should install wells and/or To determine ground-water flow directions

piezometers to assist in characterizing site and hydraulic gradient, owners and

hydrology. The owner/operator should operators should develop and implement a

determine and assess: water level-monitoring program. This

! The direction(s) and rate(s) of ground- precise water level measurements in a

water flow (including both horizontal sufficient number of piezometers or wells at

and vertical components of flow) a sufficient frequency to gauge both

variations in ground-water elevations

stratigraphic units at the site, including

confining layer(s).

Direction and Hydraulic Gradient

representative background and

an understanding requires obtaining

of as the idealized path that ground-water

head per unit of distance in a given

of a column of water (or other liquid) that

program should be structured to provide

seasonal average flow directions and
Ground-Water Monitoring and Corrective Action

227

temporal fluctuations in ground-water flow the waste types managed at the facility) in

directions. Ground-water flow direction(s) the subsurface at the facility, both the

should be determined from water levels depth(s) to the immiscible layer(s) and the

measured in wells screened in the same thickness(es) of the immiscible layer(s) in

hydro-stratigraphic position. In the well should be recorded. 

heterogeneous geologic settings (i.e.,

settings in which the hydraulic For the purpose of measuring total head,

conductivities of the subsurface materials piezometers and wells should have as short

vary with location in the subsurface), long a screened interval as possible.

well screens can intercept stratigraphic Specifically, the screens in piezometers or

horizons with different (e.g., contrasting) wells that are used to measure head should

ground-water flow directions and different generally be less than 10 feet long. In

heads. In this situation, the resulting water circumstances including the following, well

levels will not provide the depth-discrete screens longer than 10 feet may be

head measurements required for accurate warranted: 

determination of the ground-water flow

direction. ! Natural water level fluctuations

In addition to evaluating the component of

ground-water flow in the horizontal ! The interval monitored is slightly

direction, a program should be undertaken greater than the appropriate screen

to assess the vertical component of ground- length (e.g., the interval monitored is

water flow. Vertical ground-water flow 12 feet thick).

information should be based, at least in part,

on field data from wells and piezometers, ! The aquifer monitored is homogeneous

such as multi-level wells, piezometer and extremely thick (e.g., greater than

clusters, or multi-level sampling devices, 300 feet); thus, a longer screen (e.g., a

where appropriate. The following sections 20-foot screen) represents a fairly

provide acceptable methods for assessing discrete interval.

the vertical and horizontal components of

flow at a site. The head measured in a well with a long

Ground-Water Level Measurements different heads over the entire length of the

To determine ground-water flow directions when interpreting water levels collected

and ground-water flow rates, accurate water from wells that have long screened intervals

level measurements (measured to the nearest (e.g., greater than 10 feet).

0.01 foot) should be obtained. Section 5.8

delineates procedures for obtaining water The water-level monitoring program should

level measurements. At facilities where it is be structured to provide precise water level

known or plausible that immiscible measurements in a sufficient number of

contaminants (i.e., non-aqueous phase piezometers or wells at a sufficient

liquids (NAPLs)) occur (or are determined frequency to gauge both seasonal average

to be potentially present after considering flow directions and temporal fluctuations in

necessitate a longer screen length.

screened interval is a function of all of the

screened interval. Care should be taken
Subpart E

228

ground-water flow directions. The USEPA (1989c) and Freeze and Cherry

owner/operator should determine and assess (1979). Methods for calculating hydraulic

seasonal/temporal, natural, and artificially gradient are provided by Heath (1982) and

induced (e.g., off-site production well- USEPA (1989c). 

pumping, agricultural use) short-term and

long-term variations in ground-water A potentiometric surface or water table map

elevations, ground-water flow patterns, and will give an approximate idea of general

ground-water quality. ground-water flow directions. However, to

Establishing Horizontal Flow Direction water flow direction(s) and hydraulic

and the Horizontal Component of gradient(s) should be established in both the

Hydraulic Gradient horizontal and vertical directions and over

After the water level data and measurement period at 3-month intervals).

procedures are reviewed to determine that

they are accurate, the data should be used Establishing Vertical Flow Direction and

to: the Vertical Component of Hydraulic

! Construct potentiometric surface maps

and water table maps based on the To make an adequate determination of the

distribution of total head. The data ground-water flow directions, the vertical

used to develop water table maps component of ground-water flow should be

should be from piezometers or wells evaluated directly. This generally requires

screened across the water table. The the installation of multiple piezometers or

data used to develop potentiometric wells in clusters or nests, or the installation

surface maps should be from of multi-level wells or sampling devices. A

piezometers or wells screened at piezometer or well nest is a closely spaced

approximately the same elevation in group of piezometers or wells screened at

the same hydrostratigraphic unit; different depths, whereas a multi-level well

! Determine the horizontal direction(s) nests and multi-level wells allow for the

of ground-water flow by drawing flow measurement of vertical variations in

lines on the potentiometric surface map hydraulic head. 

or water table map (i.e., construct a

flow net); When reviewing data obtained from

! Calculate value(s) for the horizontal in single boreholes, the construction details

and vertical components of hydraulic of the well should be carefully evaluated.

gradient. Not only is it extremely difficult to seal

Methods for constructing potentiometric within a single borehole, but sealant

surface and water table maps, constructing materials may migrate from the seal of one

flow nets, and determining the direction(s) piezometer/well to the screened interval of

of ground-water flow are provided by another piezometer/well. Therefore, the

locate monitoring wells properly, groundtime at regular intervals (e.g., over a 1-year

Gradient

is a single device. Both piezometer/well

multiple placement of piezometers or wells

several piezometers/wells at discrete depths
Ground-Water Monitoring and Corrective Action

229

design of a piezometer/well nest should be Further information can be obtained from

considered carefully. Placement of Freeze and Cherry (1979). 

piezometers/wells in closely spaced

boreholes, where piezometers/wells have Determining Hydraulic Conductivity

been screened at different, discrete depth

intervals, is likely to produce more accurate Hydraulic conductivity is a measure of a

information. The primary concerns with the material's ability to transmit water.

installation of piezometers/wells in closely Generally, poorly sorted silty or clayey

spaced, separate boreholes are: 1) the materials have low hydraulic conductivities,

disturbance of geologic and soil materials whereas well-sorted sands and gravels have

that occurs when one piezometer is installed high hydraulic conductivities. An aquifer

may be reflected in the data obtained from may be classified as either homogeneous or

another piezometer located nearby, and 2) heterogeneous and either isotropic or

the analysis of water levels measured in anisotropic according to the way its

piezometers that are closely spaced, but hydraulic conductivity varies in space. An

separated horizontally, may produce aquifer is homogeneous if the hydraulic

imprecise information regarding the vertical conductivity is independent of location

component of ground-water flow. The within the aquifer; it is heterogeneous if

limitations of installing multiple hydraulic conductivities are dependent on

piezometers either in single or separate location within the aquifer. If the hydraulic

boreholes may be overcome by the conductivity is independent of the direction

installation of single multi-level monitoring of measurement at a point in a geologic

wells or sampling devices in single formation, the formation is isotropic at that

boreholes. The advantages and point. If the hydraulic conductivity varies

disadvantages of these types of devices are with the direction of measurement at a

discussed by USEPA (1989f). point, the formation is anisotropic at that

The owner or operator should determine the

vertical direction(s) of ground-water flow Determining Hydraulic Conductivity

using the water levels measured in multi- Using Field Methods

level wells or piezometer/well nests to

construct flow nets. Flow nets should depict Sufficient aquifer testing (i.e., field

the piezometer/well depth and length of the methods) should be performed to provide

screened interval. It is important to portray representative estimates of hydraulic

the screened interval accurately on the flow conductivity. Acceptable field methods

net to ensure that the piezometer/well is include conducting aquifer tests with single

actually monitoring the desired wells, conducting aquifer tests with multiple

water-bearing unit. A flow net should be wells, and using flowmeters. This section

developed from information obtained from provides brief overviews of these methods,

piezometer/ well clusters or nests screened including two methods for obtaining

at different, discrete depths. Detailed vertically discrete measurements of

guidance for the construction and evaluation hydraulic conductivity. The identified

of flow nets in cross section (vertical flow references provide detailed descriptions of

nets) is provided by USEPA (1989c). the methods summarized in this section.

point. 
Subpart E

230

A commonly used test for determining to provide hydraulic conductivity data for

horizontal hydraulic conductivity with a that zone. Multiple-well tests for hydraulic

single well is the slug test. A slug test is conductivity characterize a greater

performed by suddenly adding, removing, proportion of the subsurface than singleor displacing a known volume of water from well tests and, thus, provide average values

a well and observing the time that it takes of hydraulic conductivity. Multiple-well

for the water level to recover to its original tests require measurement of parameters

level (Freeze and Cherry, 1979). Similar similar to those required for single-well

results can be achieved by pressurizing the tests (e.g., time, drawdown). When using

well casing, depressing the water level, and aquifer test data to determine aquifer

suddenly releasing the pressure to simulate parameters, it is important that the solution

the removal of water from the well. In most assumptions can be applied to site

cases, EPA recommends that water not be conditions. Aquifer test solutions are

introduced into wells during aquifer tests to available for a wide variety of

avoid altering ground-water chemistry. hydrogeologic settings, but are often applied

Single-well tests are limited in scope to the incorrectly by inexperienced persons.

area directly adjacent to the well screen. Incorrect assumptions regarding

The vertical extent of the well screen hydrogeology (e.g., aquifer boundaries,

generally defines the part of the geologic aquifer lithology, and aquifer thickness)

formation that is being tested. may translate into incorrect estimations of

A modified version of the slug test, known water scientist with experience in designing

as the multilevel slug test, is capable of and interpreting aquifer tests should be

providing depth-discrete measurements of consulted to ensure that aquifer test solution

hydraulic conductivity. The drawback of methods fit the hydrogeologic setting.

the multilevel slug test is that the test relies Kruseman and deRidder (1989) provide a

on the ability of the investigator to isolate a comprehensive discussion of aquifer tests.

portion of the aquifer using a packer.

Nevertheless, multilevel slug tests, when Multiple-well tests conducted with wells

performed properly, can produce reliable screened in different water-bearing zones

measurements of hydraulic conductivity. furnish information concerning hydraulic

Multiple-well tests involve withdrawing levels in these zones should be monitored

water from, or injecting water into, one during the aquifer test to determine the type

well, and obtaining water level of aquifer system (e.g., confined,

measurements over time in observation unconfined, semi-confined, or semiwells. Multiple-well tests are often unconfined) beneath the site, and their

performed as pumping tests in which water leakance (coefficient of leakage) and

is pumped from one well and drawdown is drainage factors (Kruseman and deRidder,

observed in nearby wells. A step-drawdown 1989). A multiple-well aquifer test should

test should precede most pumping tests to be considered at every site as a method to

determine an appropriate discharge rate. establish the vertical extent of the

Aquifer tests conducted with wells screened uppermost aquifer and to evaluate hydraulic

in the same water-bearing zone can be used connection between aquifers. 

hydraulic conductivity. A qualified groundcommunication among the zones. Water
Ground-Water Monitoring and Corrective Action

231

Certain aquifer tests are inappropriate for ! In designing aquifer tests and

use in karst terrains characterized by a interpreting aquifer test data,

well-developed conduit flow system, and owners/operators should account and

they also may be inappropriate in fractured correct for seasonal, temporal, and

bedrock. When a well located in a karst anthropogenic effects on the

conduit or a large fracture is pumped, the potentiometric surface or water table.

water level in the conduit is lowered. This This is usually done by installing

lowering produces a drawdown that is not piezometers outside the influence of

radial (as in a granular aquifer) but is the stressed aquifer. These

instead a trough-like depression parallel to piezometers should be continuously

the pumped conduit or fracture. Radial flow monitored during the aquifer test.

equations do not apply to drawdown data

collected during such a pump test. This ! Owners and operators should be aware

means that a conventional semi-log plot of that, in a very high hydraulic

drawdown versus time is inappropriate for conductivity aquifer, the screen size

the purpose of determining the aquifer's and/or filter pack used in the test well

transmissivity and storativity. Aquifer tests can affect an aquifer test. If a very

in karst aquifers can be useful, but valid small screen size is used, and the pack

determinations of hydraulic conductivity, is improperly graded, the test may

storativity, and transmissivity may be reflect the characteristics of the filter

impossible. However, an aquifer test can pack, rather than the aquifer.

provide information on the presence of

conduits, on storage characteristics, and on ! EPA recommends the use of a stepthe percentage of Darcian flow. McGlew drawdown test to provide a basis for

and Thomas (1984) provide a more detailed selecting discharge rates prior to

discussion of the appropriate use of aquifer conducting a full-scale pumping test.

tests in fractured bedrock and on the This will ensure that the pumping rate

suitable interpretation of test data. Dye chosen for the subsequent pumping

tracing also is used to determine the rate and test(s) can be sustained without

direction of ground-water flow in karst exceeding the available drawdown of

settings (Section 5.2.4). the pumped wells. In addition, this test

Several additional factors should be in the observation wells.

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.

will produce a measurable drawdown

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
Subpart E

232

a caliper log to measure the uniformity of hydraulic properties of the tested material).

the diameter of the well screen. The well is Special attention should be given to the

then pumped with a small pump operated at selection of the appropriate test method and

a constant flow rate. The flowmeter is test conditions and to quality control of

lowered into the well, and the discharge rate laboratory results. McWhorter and Sunada

is measured every few feet by raising the (1977), Freeze and Cherry (1979), and

flowmeter in the well. Hydraulic Sevee (1991) discuss determining hydraulic

conductivity values can be calculated from conductivity in the laboratory. Laboratory

the recorded data using the Cooper-Jacob tests may provide the best estimates of

(1946) formula for horizontal flow to a hydraulic conductivity for materials in the

well. Use of the impeller flowmeter is unsaturated zone, but they are likely to be

limited at sites where the presence of low less accurate than field methods for

permeability materials does not allow materials in the saturated zone (Cantor et

pumping of the wells at rates sufficient to al., 1987).

operate the flowmeter. The application of

flowmeters in the measure of hydraulic Determining Ground-Water Flow Rate 

conductivity is described by Molz et al.

(1990) and Molz et al. (1989). The calculation of the average ground-water

Determining Hydraulic Conductivity water flow), or seepage velocity, is

Using Laboratory Methods discussed in detail in USEPA (1989c), in

It may be beneficial to use laboratory and deRidder (1989). The average linear

measurements of hydraulic conductivity to velocity of ground-water flow (v ̄) is a

augment the results of field tests. However, function of hydraulic conductivity (K),

field methods provide the best estimates of hydraulic gradient (i), and effective porosity

hydraulic conductivity in most cases. (n ):

Because of the limited sample size,

laboratory tests can fail to account for v ̄ = - Ki 

secondary porosity features, such as n

fractures and joints, and hence, can greatly

underestimate overall aquifer hydraulic Methods for determining hydraulic gradient

conductivities. Laboratory tests may and hydraulic conductivity have been

provide valuable information about the presented previously. Effective porosity,

vertical component of hydraulic the percentage of the total volume of a given

conductivity of aquifer materials. However, mass of soil, unconsolidated material, or

laboratory test results always should be rock that consists of interconnected pores

confirmed by field measurements, which through which water can flow, should be

sample a much larger portion of the aquifer. estimated from laboratory tests or from

In addition, laboratory test results can be values cited in the literature. (Fetter (1980)

profoundly affected by the test method provides a good discussion of effective

selected and by the manner in which the porosity. Barari and Hedges (1985) provide

tests are carried out (e.g., the extent to default values for effective porosity.)

which sample collection and preparation USEPA (1989c) provides methods for 

have changed the in situ 

flow rate (average linear velocity of groundFreeze and Cherry (1979), and in Kruseman

e

e
Ground-Water Monitoring and Corrective Action

233

determining flow rates in heterogeneous preliminary investigation to verify the

and/or anisotropic systems and should be collected information.

consulted prior to calculating flow rates.

Interpreting and Presenting Data field data corroborate and are

The following sections offer guidance on porosity, hydraulic conductivity,

interpreting and presenting hydrogeologic lateral and vertical stratigraphic

data collected during the site relationships, and ground-water flow

characterization process. Graphical directions and rates.

representations of data, such as cross

sections and maps, are typically extremely After the hydrogeologic data are interpreted,

helpful both when evaluating data and when the findings should be reviewed to:

presenting data to interested individuals.

Interpreting Hydrogeologic Data

Once the site characterization data have additional data or reassessment of

been collected, the following tasks should existing data is required to fill in the

be undertaken to support and develop the gaps

interpretation of these data:

! Review borehole and well logs to likely to affect the ability to design a

identify major rock, unconsolidated RCRA monitoring system.

material, and soil types and establish

their horizontal and vertical extent and Generally, lithologic data should correlate

distribution. with hydraulic properties (e.g., clean, well-

! From borehole and well log (and high hydraulic conductivity). Additional

outcrop, where available) data, boreholes should be drilled and additional

construct representative cross-sections samples should be collected to describe the

for each MSWLF unit, one in the hydrogeology of the site if the investigator

direction of ground-water flow and one is unable to 1) correlate stratigraphic units

orthogonal to ground-water flow. between borings, 2) identify zones of

! Identify zones of suspected high the thickness and lateral extent of these

hydraulic conductivity, or structures zones, or 3) identify confining

likely to influence contaminant formations/layers and the thickness and

migration through the unsaturated and lateral extent of these formation layers.

saturated zones.

! Compare findings with other studies that will be used to monitor ground water in

and information collected during the hydrogeologic settings characterized by

! Determine whether laboratory and

sufficient to define petrology, effective

! Identify information gaps

! Determine whether the collection of

! Identify how information gaps are

sorted, unconsolidated sands should exhibit

potentially high hydraulic conductivity and

When establishing the locations of wells

ground-water flow in porous media, the

following should be documented:
Subpart E

234

! The ground-water flow rate should be Geologic and soil maps should be based on

based on accurate measurements of rock, unconsolidated material, and soil

hydraulic conductivity and hydraulic identifications gathered from borings and

gradient and accurate measurements or outcrops. The maps should use colors or

estimates of effective porosity symbols to represent each soil,

! The horizontal and vertical outcrops on the surface. The maps also

components of flow should be should show the locations of outcrops and

accurately depicted in flow nets and all borings placed during the site

based on valid data characterization. Geologic and soil maps

! Any seasonal or temporal variations in information describing how site geology fits

the water table or potentiometric into the local and regional geologic setting.

surface, and in vertical flow

components, should be determined. Structure contour maps and isopach maps

Once an understanding of horizontal and zone that comprises the uppermost aquifer

vertical ground-water flow has been and for each significant confining layer,

established, it is possible to estimate where especially the one underlying the uppermost

monitoring wells will most likely intercept aquifer. A structure contour map depicts

contaminant flow. the configuration (i.e., elevations) of the

Presenting Hydrogeologic Data particular geologic or soil formation, unit,

Subsequent to the generation and especially important in understanding dense

interpretation of site-specific geologic data, non-aqueous phase liquid (DNAPL)

the data should be presented in geologic movement because DNAPLs (e.g.,

cross-sections, topographic maps, geologic tetrachloroethylene) may migrate in the

maps, and soil maps. The Agency suggests direction of the dip of lower permeability

that owners/operators obtain or prepare and units. Separate structure contour maps

review topographic, geologic, and soil maps should be constructed for the upper and

of the facility, in addition to site maps of the lower surfaces (or contacts) of each zone of

facility and MSWLF units. In cases where interest. Isopach maps should depict

suitable maps are not available, or where the contours that indicate the thickness of each

information contained on available maps is zone. These maps are generated from

not complete or accurate, detailed mapping borings and geologic logs and from

of the site should be performed by qualified geophysical measurements. In conjunction

and experienced individuals. An aerial with cross-sections, isopach maps may be

photograph and a topographic map of the used to help determine monitoring well

site should be included as part of the locations, depths, and screen lengths during

presentation of hydrogeologic data. The the design of the detection monitoring

topographic map should be constructed system.

under the supervision of a qualified

surveyor and should provide contours at a

maximum of 2-foot intervals.

unconsolidated material, and rock type that

are important because they can provide

should be prepared for each water-bearing

upper or lower surface or boundary of a

or zone. Structure contour maps are
Ground-Water Monitoring and Corrective Action

235

A potentiometric surface map or water table a conceptual model. This model is the

map should be prepared for each water- integrated picture of the hydrogeologic

bearing zone that comprises the uppermost system and the waste management setting.

aquifer. Potentiometric surface and water The final conceptual model must be a sitetable maps should show both the direction specific description of the unsaturated zone,

and rate of ground-water flow and the the uppermost aquifer, and its confining

locations of all piezometers and wells on units. The model should contain all of the

which they are based. The water level information necessary to design a groundmeasurements for all piezometers and wells water monitoring system.

on which the potentiometric surface map or

water table map is based should be shown Monitoring Well Placement

on the potentiometric surface or water table

map. If seasonal or temporal variations in This section separately addresses the lateral

ground-water flow occur at the site, a placement and the vertical sampling

sufficient number of potentiometric surface intervals of point of compliance wells.

or water table maps should be prepared to However, these two aspects of well

show these variations. Potentiometric placement should be evaluated together in

surface and water table maps can be the design of the monitoring system. Sitecombined with structure contour maps for a specific hydrogeologic data obtained during

particular formation or unit. An adequate the site characterization should be used to

number of cross sections should be prepared determine the lateral placement of detection

to depict significant stratigraphic and monitoring wells and to select the length

structural trends and to reflect stratigraphic and vertical position of monitoring well

and structural features in relation to local intakes. Potential pathways for contaminant

and regional ground-water flow. migration are three-dimensional.

Hydrogeological Report monitoring network that intercepts these

The hydrogeological report should contain, three-dimensional approach.

at a minimum:

! A description of field activities Compliance Monitoring Wells

! Drilling and/or well construction logs Point of compliance monitoring wells

! Analytical data the edge of the MSWLF unit(s) and should

! A discussion and interpretation of the may act as contaminant transport pathways.

data The lateral placement of monitoring wells

! Recommendations to address data gaps. distribution of potential contaminant

The final output of the site characterization thicknesses of stratigraphic horizons that

phase of the hydrogeological investigation can serve as contaminant migration

is pathways.

Consequently, the design of a detection

potential pathways requires a

Lateral Placement of Point of

should be as close as physically possible to

be screened in all transmissive zones that

should be based on the number and spatial

migration pathways and on the depths and
Subpart E

236

Point of compliance monitoring wells In some settings, the ground-water flow

should be placed laterally along the direction may reverse seasonally (depending

downgradient edge of the MSWLF unit to on precipitation), change as a result of tidal

intercept potential pathways for influences or river and lake stage

contaminant migration. The local ground- fluctuations, or change temporally as a

water flow direction and gradient are the result of well-pumping or changing land use

major factors in determining the lateral patterns. In other settings, ground water

placement of point of compliance wells. In may flow away from the waste management

a homogeneous, isotropic hydrogeologic area in all directions. In such cases, EPA

setting, well placement can be based on recommends that monitoring wells be

general aquifer characteristics (e.g., installed on all sides (or in a circular

direction and rate of ground-water flow), pattern) around the waste management area

and potential contaminant fate and transport to allow for the detection of contamination.

characteristics (e.g., advection, dispersion). In these cases, certain wells may be

More commonly, however, geology is downgradient only part of the time, but such

variable and preferential pathways exist that a configuration should ensure that releases

control the migration of contaminants. from the unit will be detected.

These types of heterogeneous, anisotropic

geologic settings can have numerous, The lateral placement of monitoring wells

discrete zones within which contaminants also should be based on the physical/

may migrate. chemical characteristics of the contaminants

Potential migration pathways include zones in MSWLFs may limit the introduction of

of relatively high intrinsic (matrix) hazardous constituents into landfills, it is

hydraulic conductivities, fractured/faulted important to consider the physical/chemical

zones, and subsurface material that may characteristics of contaminants when

increase in hydraulic conductivity if the designing the well system. These

material is exposed to waste(s) managed at characteristics include solubility, Henry's

the site (e.g., a limestone layer that Law constant, partition coefficients, specific

underlies an acidic waste). In addition to gravity, contaminant reaction or degradation

natural hydrogeologic features, human- products, and the potential for contaminants

made features may influence the ground- to degrade confining layers. For example,

water flow direction and, thus, the lateral contaminants with low solubilities and high

placement of point of compliance wells. specific gravities that occur as DNAPLs

Such human-made features include ditches, may migrate in the subsurface in directions

areas where fill material has been placed, different from the direction of ground-water

buried piping, buildings, leachate collection flow. Therefore, in situations where the

systems, and adjacent disposal units. The release of DNAPLs is a concern, the lateral

lateral placement of monitoring wells placement of compliance point groundshould be based on the number and spatial water monitoring wells should not

distribution of potential contaminant necessarily only be along the downgradient

migration pathways and on the depths and edge of the MSWLF unit. Considering both

thicknesses of stratigraphic horizons that contaminant characteristics and

can serve as contaminant migration hydrogeologic properties is important when

pathways.

of concern. While the restriction of liquids
Ground-Water Monitoring and Corrective Action

237

determining the lateral placement of the boring program, and from samples

monitoring wells. collected while drilling the monitoring well.

Vertical Placement and Screen Lengths geophysical data, available regional/local

Proper selection of the vertical sampling provide the vertical distribution of hydraulic

interval is necessary to ensure that the conductivity. The vertical sampling interval

monitoring system is capable of detecting a is not necessarily synonymous with aquifer

release from the MSWLF unit. The vertical thickness. Monitoring wells are often

position and lengths of well intakes are screened at intervals that represent a portion

functions of (1) hydro-geologic factors that of the thickness of the aquifer. When

determine the distribution of, and monitoring an unconfined aquifer, the well

fluid/vapor phase transport within, potential screen typically should be positioned so that

pathways of contaminant migration to and a portion of the well screen is in the

within the uppermost aquifer, and (2) the saturated zone and a portion of the well

chemical and physical characteristics of screen is in the unsaturated zone (i.e., the

contaminants that control their transport and well screen straddles the water table).

distribution in the subsurface. Well intake While the restriction of liquids in MSWLFs

length also is determined by the need to may limit the introduction of hazardous

obtain vertically discrete ground-water constituents into landfills, it is important to

samples. Owners and operators should consider the physical/chemical

determine the probable location, size, and characteristics of contaminants when

geometry of potential contaminant plumes designing the well system.

when selecting well intake positions and

lengths. The vertical positions and lengths of

Site-specific hydrogeologic data obtained the same physical/chemical characteristics

during the site characterization should be of the contaminants of concern that

used to select the length and vertical influence the lateral placement of

position of monitoring well intakes. The monitoring wells. Considering both

vertical positions and lengths of monitoring contaminant characteristics and

well intakes should be based on the number hydrogeologic properties is important when

and spatial distribution of potential choosing the vertical position and length of

contaminant migration pathways and on the the well intake. Some contaminants may

depths and thicknesses of stratigraphic migrate within very narrow zones. Of

horizons that can serve as contaminant course, for well placement at a new site, it is

migration pathways. Figure 5-2 illustrates unlikely that the owner or operator will be

examples of complex stratigraphy that able to assess contaminant characteristics.

would require multiple vertical monitoring

intervals. Different transport processes control

The depth and thickness of a potential whether the contaminant dissolves or is

contaminant migration pathway can be immiscible in water. Immiscible

determined from soil, unconsolidated

material, and rock samples collected during

Direct physical data can be supplemented by

hydrogeological data, and other data that

monitoring well intakes should be based on

contaminant migration depending on
Subpart E

238

Figure 5-2

Upgradient and Downgradient

Designations for Idealized MSWLF
Ground-Water Monitoring and Corrective Action

239

contaminants may occur as light non ! "Down-the-dip" of lower hydraulic

aqueous phase liquids (LNAPLs), which are conductivity units that act as confining

lighter than water, and DNAPLs, which are layers, both upgradient and

denser than water. LNAPLs migrate in the downgradient of the waste

capillary zone just above the water table. management area. 

Wells installed to monitor LNAPLs should

be screened at the water table/capillary zone Because of the nature of DNAPL migration

interface, and the screened interval should (i.e., along structural, rather than hydraulic,

intercept the water table at its minimum and gradients), wells installed to monitor

maximum elevation. LNAPLs may become DNAPLs may need to be installed both

trapped in residual form in the vadose zone upgradient and downgradient of the waste

and become periodically remobilized and management area. It may be useful to

contribute further to aquifer contamination, construct a structure contour map of lower

either as free phase or dissolved phase permeability strata and identify lower

contaminants, as the water table fluctuates permeability lenses upgradient and

and precipitation infiltrates the subsurface. downgradient of the unit along which

 DNAPLs may migrate. The wells can then

The migration of free-phase DNAPLs may be located accordingly.

be influenced primarily by the geology,

rather than the hydrogeology, of the site. The lengths of well screens used in

That is, DNAPLs migrate downward ground-water monitoring wells can

through the saturated zone due to density significantly affect their ability to intercept

and then migrate by gravity along less releases of contaminants. The complexity

permeable geologic units (e.g., the slope of of the hydrogeology of a site is an important

confining units, the slope of clay lenses in consideration when selecting the lengths of

more permeable strata, bedrock troughs), well screens. Most hydrogeologic settings

even in aquifers with primarily horizontal are complex (heterogeneous and

ground-water flow. Consequently, if wastes anisotropic) to a certain degree. Highly

disposed at the site are anticipated to exist heterogeneous formations require shorter

in the subsurface as a DNAPL, the potential well screens to allow sampling of discrete

DNAPL should be monitored: portions of the formation that can serve as

! At the base of the aquifer (immediately screens that span more than a single

above the confining layer) saturated zone or a single contaminant

! In structural depressions (e.g., bedrock contamination of transmissive units, thereby

troughs) in lower hydraulic increasing the extent of contamination.

conductivity geologic units that act as Well intakes should be installed in a single

confining layers saturated zone. Well intakes (e.g., screens)

! Along lower hydraulic conductivity interconnect, or promote the interconnection

lenses and units within units of higher of, zones that are separated by a confining

hydraulic conductivity layer. 

contaminant migration pathways. Well

migration pathway may cause crossand filter pack materials should not
Subpart E

240

Even in hydrologically simple formations, would represent a fairly discrete interval in

or within a single potential pathway for a very thick formation. Formations with

contaminant migration, the use of shorter very low hydraulic conductivities also may

well screens may be necessary to detect require the use of longer well screens to

contaminants concentrated at particular allow sufficient amounts of formation water

depths. A contaminant may be concentrated to enter the well for sampling. The

at a particular depth because of its importance of accurately identifying such

physical/chemical properties and/or because conditions highlights the need for a

of hydrogeologic properties. In complete hydrogeologic site investigation

homogeneous formations, a long well screen prior to the design and placement of

can permit excessive amounts of detection wells.

uncontaminated formation water to dilute

the contaminated ground water entering the Multiple monitoring wells (well clusters or

well. At best, dilution can make multilevel sampling devices) should be

contaminant detection difficult; at worst, installed at a single location when (1) a

contaminant detection is impossible if the single well cannot adequately intercept and

concentrations of contaminants are diluted monitor the vertical extent of a potential

to levels below the detection limits for the pathway of contaminant migration, or (2)

prescribed analytical methods. The use of there is more than one potential pathway of

shorter well screens allows for contaminant contaminant migration in the subsurface at

detection by reducing excessive dilution. a single location, or (3) there is a thick

When placed at depths of predicted saturated zone and immiscible contaminants

preferential flow, shorter well screens are are present, or are determined to be

effective in monitoring the aquifer or the potentially present after considering waste

portion of the aquifer of concern. types managed at the facility. Conversely, at

Generally, screen lengths should not exceed contaminated by a single contaminant,

10 feet. However, certain hydrogeologic where there is a thin saturated zone, and

settings may warrant or necessitate the use where the site is hydrogeologically

of longer well screens for adequate homogeneous, the need for multiple wells at

detection monitoring. Unconfined aquifers each sampling location is reduced. The

with widely fluctuating water tables may number of wells that should be installed at

require longer screens to intercept the water each sampling location increases with site

table surface at both its maximum and complexity.

minimum elevations and to provide

monitoring for the presence of contaminants The following sources provided additional

that are less dense than water. Saturated information on monitoring well placement:

zones that are slightly greater in thickness USEPA (1992a), USEPA (1990), USEPA

than the appropriate screen length (e.g., 12 (1991), and USEPA (1986a).

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 

sites where ground water may be
Ground-Water Monitoring and Corrective Action

241

5.7 GROUND-WATER decommissioning of any monitoring well

MONITORING WELL DESIGN must be documented in the operating record

AND CONSTRUCTION of the facility and certified by a qualified

40 CFR §258.51 (c) ground-water scientist. Documentation is

5.7.1 Statement of Regulation devices, and water level measurement

(c) Monitoring wells must be cased in a

manner that maintains the integrity of The monitoring wells must be cased to

the monitoring well bore hole. This protect the integrity of the borehole. The

casing must be screened or perforated design and construction of the well directly

and packed with gravel or sand, where affects the quality and representativeness of

necessary, to enable collection of ground- the samples collected. The well casing must

water samples. The annular space (i.e., have a screened or perforated interval to

the space between the bore hole and well allow the entrance of water into the well

casing) above the sampling depth must be casing. The annular space between the well

sealed to prevent contamination of screen and the formation wall must be

samples and the ground water. packed with material to inhibit the

(1) The owner or operator must notify well. The well screen must have openings

the State Director that the design, sized according to the packing material

installation, development, and used. The annular space above the filter

decommission of any monitoring wells, pack must be sealed to provide a discrete

piezometers and other measurement, sampling interval. 

sampling, and analytical devices

documentation has been placed in the All monitoring wells, piezometers, and

operating record; and sampling and analytical devices must be

(2) The monitoring wells, piezometers, continued performance according to design

and other measurement, sampling, and specifications over the life of the monitoring

analytical devices must be operated and program. 

maintained so that they perform to design

specifications throughout the life of the 5.7.3 Technical Considerations

monitoring program.

§258.52 [Reserved]. monitoring wells will affect the consistency

5.7.2 Applicability design must be based on site-specific

The requirements for monitoring well (lithology and grain size distribution) will

design, installation, and maintenance are determine the selection of proper packing

applicable to all wells installed at existing and sealant materials, and the stratigraphy

units, lateral expansions of units, and new will determine the screen length for the

MSWLF units. The design, installation, and interval to be monitored. Installation 

required for wells, piezometers, sampling

instruments used in the monitoring program.

migration of formation material into the

maintained in a manner that ensures their

The design, installation, and maintenance of

and accuracy of samples collected. The

information. The formation material
Subpart E

242

practices should be specified and overseen ! Relative ease of well completion and

to ensure that the monitoring well is development, including the ability to

installed as designed and will perform as install the well in the given

intended. This section will discuss the hydrogeologic setting. 

factors that must be considered when

designing monitoring wells. Each well must In addition to these factors, USEPA (1989f)

be tailored to suit the hydrogeological includes matrices to assist in selecting an

setting, the contaminants to be monitored, appropriate drilling method. These matrices

and other site-specific factors. Figure 5-3 list the most commonly used drilling

depicts the components of a typical techniques for monitoring well installation,

monitoring well installation. taking into consideration hydrogeologic

The following sections provide a brief program. 

overview of monitoring well design and

construction. More comprehensive The following basic performance objectives

discussions are provided in USEPA (1989f) should guide the selection of drilling

and USEPA (1992a). procedures for installing monitoring wells:

Selection of Drilling Method ! Drilling should be performed in a

The method chosen for drilling a monitoring properties of the subsurface materials.

well depends largely on the following

factors (USEPA, 1989f): ! Contamination and/or cross-

! Versatility of the drilling method aquifer materials during drilling should

! Relative drilling cost

! Sample reliability (ground-water, soil, the collection of representative

unconsolidated material, or rock samples of rock, unconsolidated

samples) materials, and soil.

! Availability of drilling equipment ! The drilling method should allow the

! Accessibility of the drilling site appropriate location for the screened

! Relative time required for well

installation and development ! The drilling method should allow for

! Ability of the drilling technology to annular sealants. The borehole should

preserve natural conditions be at least 4 inches larger in diameter

! Ability to install a well of desired casing and screen to allow adequate

diameter and depth

settings and the objectives of the monitoring

manner that preserves the natural

contamination of ground water and

be avoided.

! The drilling method should allow for

owner/operator to determine when the

interval has been encountered.

proper placement of the filter pack and

than the nominal diameter of the well
Figure 5.3. Example of a Monitoring Well Design-Single Cased Well

243
Subpart E

244

space for placement of the filter pack Monitoring Well Design

and annular sealants.

! The drilling method should allow for

the collection of representative ground- Well Casing and Screen Materials

water samples. Drilling fluids

(including air) should be used only A casing and well screen are installed in a

when minimal impact to the ground-water monitoring well for several

surrounding formation and ground reasons: to provide access from the surface

water can be ensured. of the ground to some point in the

The following guidelines apply to the use of and to prevent hydraulic communication

drilling fluids, drilling fluid additives, and between zones within the subsurface. In

lubricants when drilling ground-water some cases, State or local regulations may

monitoring wells: specify the casing and material that the

! Drilling fluids, drilling fluid additives, comprehensive discussion of well casing

or lubricants that affect the analysis of and screen materials is provided in USEPA

hazardous constituents in ground-water (1989f) and in USEPA (1992a). The

samples should not be used. following discussion briefly summarizes

! The owner/operator should

demonstrate the inertness of drilling Monitoring well casing and screen materials

fluids, drilling fluid additives, and may be constructed of any of several types

lubricants by performing analytical of materials, but should meet the following

testing of drilling fluids, drilling fluid performance specifications: 

additives, and lubricants and/or by

providing information regarding the ! Monitoring well casing and screen

composition of drilling fluids, drilling materials should maintain their

fluid additives, or lubricants obtained structural integrity and durability in

from the manufacturer. the environment in which they are used

! The owner/operator should consider

the potential impact of drilling fluids, ! Monitoring well casings and screens

drilling fluid additives, and lubricants should be resistant to chemical and

on the physical and chemical microbiological corrosion and

characteristics of the subsurface and on degradation in contaminated and

ground-water quality. uncontaminated waters.

! The volume of drilling fluids, drilling ! Monitoring well casings and screens

fluid additives, and lubricants used should be able to withstand the

during the drilling of a monitoring well physical forces acting upon them

should be recorded. during and following their installation

Well Casing

subsurface, to prevent borehole collapse,

owner or operator should use. A

information contained in these references.

over their operating life.

and during their use -- including forces
Ground-Water Monitoring and Corrective Action

245

due to suspension in the borehole, background wells and downgradient

grouting, development, purging, wells and including:

pumping, and sampling and forces

exerted on them by the surrounding - Natural ground-water geochemistry

geologic materials.

! Monitoring well casing and screen contaminants

materials should not chemically alter

ground-water samples, especially with - Concentration of suspected or known

respect to the analytes of concern, as a contaminants

result of their sorbing, desorbing, or

leaching analytes. For example, if ! Design life of the monitoring well. 

chromium is an analyte of interest, the

well casing or screen should not Casing materials widely available for use in

increase or decrease the amount of ground-water monitoring wells can be

chromium in the ground water. Any divided into three categories:

material leaching from the casing or

screen should not be an analyte of 1) Fluoropolymer materials, including

interest or interfere in the analysis of polytetrafluoroethylene (PTFE),

an analyte of interest. tetrafluoroethylene (TFE), fluorinated

ethylene propylene (FEP),

In addition, monitoring well casing and perfluoroalkoxy (PFA), and

screen materials should be relatively easy to polyvinylidene fluoride (PVDF)

install into the borehole during construction

of the monitoring well. 2) Metallic materials, including carbon

The selection of the most suitable well steel, and stainless steel (304 and 316)

casing and screen materials should consider

site-specific factors, including: 3) Thermoplastic materials, including

! Depth to the water-bearing zone(s) to acrylonitrile butadiene styrene (ABS).

be monitored and the anticipated well

depth In addition to these three categories of

! Geologic environment (FRP) has been used for monitoring

! Geochemistry of soil, unconsolidated used in general application across the

material, and rock over the entire country, very little data are available on its

interval in which the well is to be cased characteristics and performance. All well

! Geochemistry of the ground water at strength-related characteristics and chemical

the site, as determined through an resistance/chemical interference

initial analysis of samples from both characteristics that influence their

- Nature of suspected or known

steel, low-carbon steel, galvanized

polyvinyl chloride (PVC) and

materials, fiberglass-reinforced plastic

applications. Because FRP has not yet been

construction materials possess

performance in site-specific hydrogeologic
Subpart E

246

and contaminant-related monitoring selecting monitoring well materials.

situations. Metallic casing materials are more subject

The casing must be made of a material materials are more susceptible to chemical

strong enough to last for the life of the well. degradation. The geochemistry of the

Tensile strength is needed primarily during formation water influences the degree to

well installation when the casing is lowered which these processes occur. If groundinto the hole. The joint strength will water chemistry affects the structural

determine the maximum length of a section integrity of the casing, then the samples

that can be suspended from the surface in an collected from the well are likely to be

air-filled borehole. affected.

Collapse strength is the capability of a Materials used for monitoring well casing

casing to resist collapse by any external must not exhibit a tendency to sorb or leach

loads to which it is subjected both during chemical constituents from, or into, water

and after installation. A casing is most sampled from the well. If a casing material

susceptible to collapse during installation sorbs constituents from ground water, those

before placement of the filter pack or constituents may either not be detected

annular seal materials around the casing. during monitoring or be detected at a lower

Once a casing is installed and supported, concentration. Chemical constituents also

collapse is seldom a concern. Several steps can be leached from the casing materials by

that can be taken to avoid casing collapse aggressive aqueous solutions. These

are: constituents may be detected in samples

1) Drilling a straight, clean borehole indicate contamination that is due to the

2) Uniformly distributing filter pack Casing materials must be selected with care

materials at a slow, even rate to avoid degradation of the well and to

3) Avoiding use of quick-setting (high

temperature) cements for thermoplastic In certain situations it may be advantageous

casings installation. to design a well using more than one

Compressive strength of the casing is a where stainless steel or fluoropolymer

measure of the greatest compressive stress materials are preferred in a specific

that a casing can bear without deformation. chemical environment, costs may be saved

Casing failure due to a compressive strength by using PVC in non-critical portions of the

limitation generally is not an important well. These savings may be considerable,

factor in a properly installed well. This type especially in deep wells where only the

of failure results from soil friction on lower portion of the well is in a critical

unsupported casing. chemical environment and where tens of

Chemical resistance/interference upper portion of the well. In a composite

characteristics must be evaluated before well design, dissimilar metallic 

to corrosion, while thermoplastic casing

collected from the well. The results may

casing rather than the formation water.

avoid erroneous results.

material for well components. For example,

feet of lower-cost PVC may be used in the
Ground-Water Monitoring and Corrective Action

247

components should not be used unless an threaded joints should be used on

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 factorythermoplastic 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 
Subpart E

248

that should be used to clean casing and because the owner/operator will need to

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 

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
Ground-Water Monitoring and Corrective Action

249

of the 50 percent retained size of the operators should remember that the entire

formation material (USEPA, 1990). length of the annular space filled with filter

Filter pack material should be installed in a monitored zone. Moreover, if the filter

manner that prevents bridging and particle- pack/sand extends from the screened zone

size segregation. Filter pack material into an overlying zone, a conduit for

installed below the water table should hydraulic connection is created between the

generally be tremied into the annular space. two zones. 

Allowing filter pack material to fall by

gravity (free fall) into the annular space is Annular Sealants

only appropriate when wells are relatively

shallow, when the filter pack has a uniform Proper sealing of the annular space between

grain size, and when the filter pack material the well casing and the borehole wall is

can be poured continuously into the well required to prevent contamination of

without stopping. samples and the ground water. Adequate

At least 2 inches of filter pack material within the well annulus. The materials used

should be installed between the well screen for annular sealants should be chemically

and the borehole wall. The filter pack inert with the highest anticipated

should extend at least 2 feet above the top of concentration of chemical constituents

the well screen. In deep wells, the filter expected in the ground water at the facility.

pack may not compress when initially In general, the permeability of the sealing

installed. Consequently, when the annular material should be one to two orders of

and surface seals are placed on the filter magnitude lower than the least permeable

pack, the filter pack compresses sufficiently part of the formation in contact with the

to allow grout into, or very close to, the well. The precise volume of annular

screen. Consequently, filter packs may need sealants required should be calculated and

to be installed as high as 5 feet above the recorded before placement, and the actual

screened interval in monitoring wells that volume used should be determined and

are deep (i.e., greater than 200 feet). The recorded during well construction. Any

precise volume of filter pack material significant discrepancy between the

required should be calculated and recorded calculated volume and the actual volume

before placement, and the actual volume should be explained.

used should be determined and recorded

during well construction. Any significant When the screened interval is within the

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 

pack material or sand is effectively the

sealing will prevent hydraulic connection

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),
Subpart E

250

or by dropping them directly down the When the annular sealant must be installed

annulus in shallow wells (less than in the unsaturated zone, neat cement or

approximately 30 feet deep). Dropping the shrinkage-compensated neat cement

bentonite pellets down the annulus presents mixtures should be used for the annular

a potential for bridging (from premature sealant. Bentonite is not recommended as

hydration of the bentonite), leading to gaps an annular sealant in the unsaturated zone

in the seal below the bridge. In shallow because the moisture available is

monitoring wells, a tamping device should insufficient to fully hydrate bentonite.

be used to prevent bridging from occurring.

A neat cement or shrinkage-compensated

neat cement grout seal should be installed Monitoring wells are commonly either

on top of the bentonite seal and extend above-ground completions or flush-tovertically up the annular space between the ground completions. The design of both

well casing and the borehole wall to within types must consider the prevention of

a few feet of land surface. Annular sealants infiltration of surface runoff into the well

in slurry form (e.g., cement grout, bentonite annulus and the possibility of accidental

slurry) should be placed by the tremie/pump damage or vandalism. Completing a

(from the bottom up) method. The bottom monitoring well involves installing the

of the placement pipe should be equipped following components:

with a side discharge deflector to prevent

the slurry from jetting a hole through the ! Surface seal

protective sand layer, filter pack, or

bentonite seal. The bentonite seal should be ! Protective casing

allowed to completely hydrate, set, or cure

in conformance with the manufacturer's ! Ventilation hole

specifications prior to installing the grout

seal in the annular space. The time required ! Drain hole

for the bentonite seal to completely hydrate,

set, or cure will differ with the materials ! Cap and lock

used and the specific conditions

encountered, but is generally a minimum of ! Guard posts when wells are completed

4 to 24 hours. Allowing the bentonite seal above grade.

to hydrate, set, or cure prevents the invasion

of the more viscous and more chemically A surface seal, installed on top of the grout

reactive grout seal into the screened area. seal, extends vertically up the well annulus

When using bentonite as an annular sealant, heave, the seal should extend at least 1 foot

the appropriate clay should be selected on below the frost line. The composition of the

the basis of the environment in which it is to surface seal should be neat cement or

be used, such as the ion-exchange potential concrete. In an above-ground completion,

of the sediments, sediment permeability, the surface seal should form at least a 2-foot

and compatibility with expected wide, 4-inch thick apron.

contaminants. Sodium bentonite is usually

acceptable. 

Surface Completion

to the land surface. To protect against frost
Ground-Water Monitoring and Corrective Action

251

A locking protective casing should be unavoidable, such as in active roadways, a

installed around the well casing to prevent protective structure, such as a utility vault

damage or unauthorized entry. The or meter box, should be installed around the

protective casing should be anchored below well casing. In addition, measures should

the frost line (where applicable) into the be taken to prevent the accumulation of

surface seal and extend at least 18 inches surface water in the protective structure and

above the surface of the ground. A 1/4-inch around the well intake. These measures

vent hole pipe is recommended to allow the should include outfitting the protective

escape of any potentially explosive gases structure with a steel lid or manhole cover

that may accumulate within the well. In that has a rubber seal or gasket and ensuring

addition, a drain hole should be installed in that the bond between the cement surface

the protective casing to prevent water from seal and the protective structure is

accumulating and, in freezing climates, watertight. 

freezing around the well casing. The space

between the protective casing and the well Well Surveying

casing may be filled with gravel to allow the

retrieval of tools and to prevent small The location of all wells should be surveyed

animal/insect entrance through the drain. A by a licensed professional surveyor (or

suitable cap should be placed on the well to equivalent) to determine their X-and-Y

prevent tampering or the entry of any coordinates as well as their distances from

foreign materials. A lock should be the units being monitored and their

installed on the cap to provide security. To distances from each other. A State Plane

prevent corrosion or jamming of the lock, a Coordinate System, Universal Transverse

protective cover should be used. Care Mercator System, or Latitude/Longitude

should be taken when using such lubricants should be used, as approved by the Regional

as graphite or petroleum-based sprays to Administrator. The survey should also note

lubricate the lock, as lubricants may the coordinates of any temporary

introduce a potential for sample benchmarks. A surveyed reference mark

contamination. should be placed on the top of the well

To guard against accidental damage to the well apron, for use as a measuring point

well from facility traffic, the owner/operator because the well casing is more stable than

should install concrete or steel bumper the protective casing or well apron (both the

guards around the edge of the concrete protective casing and the well apron are

apron. These should be located within 3 or more susceptible to frost heave and

4 feet of the well and should be painted spalling). The height of the reference

orange or fitted with reflectors to reduce the survey datum, permanently marked on top

possibility of vehicular damage. of the inner well casing, should be

The use of flush-to-ground surface mean sea level, which in turn is determined

completions should be avoided because this by reference to an established National

design increases the potential for surface Geodetic Vertical Datum. The reference

water infiltration into the well. In cases marked on top of inner well casings should

where flush-to-ground completions are be resurveyed at least once every 5 years,

casing, not on the protective casing or the

determined within ±0.01 foot in relation to
Subpart E

252

unless changes in ground-water flow When development is initiated, a wide range

patterns/direction, or damage caused by of grain sizes of the natural material is

freeze/thaw or desiccation processes, are drawn into the well, and the well typically

noted. In such cases, the Regional produces very turbid water. However, as

Administrator may require that well casings development continues and the natural

be resurveyed on a more frequent basis. materials are drawn into the filter pack, an

Well Development process. Inducing movement of ground

All monitoring wells should be developed to generally results in bridging of the particles.

create an effective filter pack around the A means of inducing flow reversal is

well screen, to rectify damage to the necessary to break down bridges and

formation caused by drilling, to remove fine produce a stable filter.

particles from the formation near the

borehole, and to assist in restoring the The commonly accepted methods for

natural water quality of the aquifer in the developing wells are described in USEPA

vicinity of the well. Development stresses (1989f) and Driscoll (1986) and include:

the formation around the screen, as well as

the filter pack, so that mobile fines, silts, ! Pumping and overpumping

and clays are pulled into the well and

removed. The process of developing a well ! Surging with a surge block

creates a graded filter pack around the well

screen. Development is also used to remove ! Bailing.

any foreign materials (drilling water, muds,

etc.) that may have been introduced into the USEPA (1989f) provides a detailed

well borehole during drilling and well overview of well development and should

installation and to aid in the equilibration be consulted when evaluating well

that will occur between the filter pack, well development methods.

casing, and the formation water. 

The development of a well is extremely Construction, and Development

important to ensuring the collection of

representative ground-water samples. If the Information on the design, construction, and

well has been properly completed, then development of each well should be

adequate development should remove fines compiled. Such information should include

that may enter the well either from the filter (1) a boring log that documents well drilling

pack or the formation. This improves the and associated formation sampling and (2)

yield, but more importantly it creates a a well construction log and well

monitoring well capable of producing construction diagram ("as built"). 

samples of acceptably low turbidity. Turbid

samples from an improperly constructed and

developed well may interfere with

subsequent analyses.

effective filter will form through a sorting

water into the well (i.e., in one direction)

Documentation of Well Design,
Ground-Water Monitoring and Corrective Action

253

Decommissioning Ground-Water In some States, similar regulations may

Monitoring Wells and Boreholes apply to the decommissioning of monitoring

Ground-water contamination resulting from involved regulatory agencies, as well as

improperly decommissioned wells and experienced geologists, geotechnical

boreholes is a serious concern. Any engineers, and drillers, should be consulted

borehole that will not be completed as a prior to decommissioning a well or borehole

monitoring well should be properly to ensure that decommissioning is

decommissioned. The USEPA (1975) and performed properly and to ensure

the American Water Works Association compliance with State law. If a well to be

(1985) provide the following reasons, decommissioned is contaminated, the safe

summarized by USEPA (1989f), as to why removal and proper disposal of the well

improperly constructed or unused wells materials should be ensured by the

should be properly decommissioned: owner/operator. Appropriate measures

! To eliminate physical hazards safety of individuals when decommissioning

! To prevent ground-water

contamination

! To conserve aquifer yield and AND ANALYSIS

hydrostatic head REQUIREMENTS

! To prevent intermixing of subsurface

water. 5.8.1 Statement of Regulation

Should an owner or operator have a (a) The ground-water monitoring

borehole or an improperly constructed or program must include consistent

unused well at his or her facility, the well or sampling and analysis procedures that

borehole should be decommissioned in are designed to ensure monitoring results

accordance with specific guidelines. that provide an accurate representation

USEPA (1989f) provides comprehensive of ground-water quality at the

guidance on performing well background and downgradient wells

decommissioning that can be applied to installed in compliance with §258.51(a) of

boreholes. In addition, any State/Tribal this Part. The owner or operator must

regulatory guidance should be consulted notify the State Director that the

prior to decommissioning monitoring wells, sampling and analysis program

piezometers, or boreholes. Lamb and documentation has been placed in the

Kinney (1989) also provide information on operating record and the program must

decommissioning ground-water monitoring include procedures and techniques for:

wells.

Many States require that specific procedures

be followed and certain paperwork be filed (2) Sample preservation and shipment;

when decommissioning water supply wells.

wells and boreholes. The EPA and other

should be taken to protect the health and

a well or borehole.

5.8 GROUND-WATER SAMPLING

40 CFR §258.53

(1) Sample collection;
Subpart E

254

(3) Analytical procedures; §258.55(a) of this Part. Background

(4) Chain of custody control; and at wells that are not located hydraulically

(5) Quality assurance and quality meets the requirements of §258.51(a)(1).

control.

(b) The ground-water monitoring establish ground-water quality data must

program must include sampling and be consistent with the appropriate

analytical methods that are appropriate statistical procedures determined

for ground-water sampling and that pursuant to paragraph (g) of this section.

accurately measure hazardous The sampling procedures shall be those

constituents and other monitoring specified under §258.54(b) for detection

parameters in ground-water samples. monitoring, §258.55(b) and (d) for

Ground-water samples shall not be field- assessment monitoring, and §258.56(b) of

filtered prior to laboratory analysis. corrective action.

(c) The sampling procedures and 5.8.2 Applicability

frequency must be protective of human

health and the environment. The requirements for sampling and analysis

(d) Ground-water elevations must be ground-water monitoring throughout the

measured in each well immediately prior active life, closure, and post-closure periods

to purging, each time ground water is of operation. Quality assurance and quality

sampled. The owner or operator must control measures for both field and

determine the rate and direction of laboratory activities must be implemented.

ground-water flow each time ground The methods and procedures constituting

water is sampled. Ground-water the program must be placed in the operating

elevations in wells which monitor the record of the facility.

same waste management area must be

measured within a period of time short For the sampling and analysis program to be

enough to avoid temporal variations in technically sound, the sampling procedures

ground-water flow which could preclude and analytical methods used should provide

accurate determination of ground-water adequate accuracy, precision, and detection

flow rate and direction. limits for the analyte determinations. Prior

(e) The owner or operator must elevations in the wells must be measured to

establish background ground-water allow determination of the direction of

quality in a hydraulically upgradient or ground-water flow and estimates of rate of

background well(s) for each of the flow. The time interval between

monitoring parameters or constituents measurements at different wells must be

required in the particular ground-water minimized so that temporal changes in

monitoring program that applies to the ground-water elevations do not cause an 

MSWLF unit, as determined under

§258.54(a), or 

ground-water quality may be established

upgradient from the MSWLF unit if it

(f) The number of samples collected to

apply to all facilities required to conduct

to sampling, the static ground-water
Ground-Water Monitoring and Corrective Action

255

incorrect determination of ground-water ! Chain of custody control

flow direction. 

Background ground-water quality must be

established at all upgradient or background The ground-water monitoring program must

wells. The background water quality may be documented in the operating record of

be determined from wells that are not the facility.

upgradient of the MSWLF unit, provided

that the wells yield representative ground- The objectives of the monitoring program

water samples. should clearly define the quality of the data

The sampling program must be designed in ground-water chemistry due to the operation

consideration of the anticipated statistical of the solid waste disposal facility. These

method applied by the owner or operator. data quality objectives should address:

The data objectives of the monitoring

program, in terms of the number of samples ! Accuracy and precision of methods used

collected and the frequency of collection, in the analysis of samples, including

should be appropriate for the statistical field measurements

method selected for data comparison. 

5.8.3 Technical Considerations procedures used to ensure the validity of

The purpose of a ground-water sampling record keeping, and data validation)

and analysis program is to establish a

protocol that can be followed throughout the ! Number of samples required to obtain a

monitoring period of the site (operating, certain degree of statistical confidence

closure, and post-closure). The protocol is

necessary so that data acquired can be ! Location and number of monitoring

compared over time and accurately wells required. 

represent ground-water quality. Sample

collection, preservation, shipment, storage, Sample Collection

and analyses should always be performed in

a consistent manner, even as monitoring Frequency

staff change during the monitoring period.

The owner's/operator's ground-water detection monitoring should be evaluated

monitoring program must include a for each site according to hydrogeologic

description of procedures for the following: conditions and landfill design. In States, the

! Sample collection semiannual. The background

! Sample preservation and shipment independent samples at each monitoring

! Analytical procedures (i.e., during the first 6 months of

! Quality assurance and quality control.

required to detect significant changes in

! Quality control and quality assurance

the results (e.g., use of blank samples,

The frequency of sample collection under

minimum sampling frequency should be

characterization should include four

location during the first semi-annual event
Subpart E

256

monitoring). (See the discussion under Measurements of the static water level and

Section 5.10.3 on collecting independent the depth to the well bottom can be made

samples to determine background.) More with a wetted steel tape. Electronic water

frequent sampling may be selected. For level measuring devices may also be used.

example, quarterly sampling may be Accepted standard operating procedures call

conducted to evaluate seasonal effects on for the static water level to be accurately

ground-water quality. measured to within 0.01 foot (USEPA,

The frequency of sample collection during be made at all monitoring wells and well

assessment monitoring activities will clusters in a time frame that avoids changes

depend on site-specific hydrogeologic that may occur as a result of barometric

conditions and contaminant properties. The pressure changes, significant infiltration

frequency of sampling is intended to obtain events, or aquifer pumping. To prevent

a data set that is statistically independent of possible cross contamination of wells, water

the previous set. Guidance to estimate this level measurement devices must be

minimum time to obtain independent decontaminated prior to use at each well. 

samples is provided in "Statistical Analysis

of Ground-water Monitoring Data at RCRA The ground-water monitoring program

Facilities - Interim Final Guidance" should include provisions for detecting

(USEPA, 1989). immiscible fluids (i.e., LNAPLs or

Water Level Measurements immiscible liquids that are less dense than

The ground-water monitoring program must surface. DNAPLs are relatively immiscible

include provisions for measuring static liquids that are more dense than the ground

water level elevations in each well prior to water and tend to migrate vertically

purging the well for sampling. downward in aquifers. The detection of an

Measurements of ground-water elevations immiscible layer may require specialized

are used for determining horizontal and equipment and should be performed before

vertical hydraulic gradients for estimation the well is evacuated for conventional

of flow rates and direction. sampling. The ground-water monitoring

Field measurements may include the LNAPLs will be detected. The program

following: also should include a contingency plan

! Depth to standing water from a surveyed analyzing these liquids. Guidance for

datum on the top of the well riser (static detecting the presence of immiscible layers

water level) can be found in USEPA (1992a).

! Total depth of well from the top of the Well Purging

riser (to verify condition of well)

! Thickness of immiscible layers, if

present.

1992a). Water level measurements should

DNAPLs). LNAPLs are relatively

water and that spread across the water table

program should specify how DNAPLs and

describing procedures for sampling and

Because the water standing in a well prior to

sampling may not represent in-situ

ground-water quality, stagnant water should
Ground-Water Monitoring and Corrective Action

257

be purged from the well and filter pack prior ensure that purging does not cause

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 

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 groundwater samples are collected. 

In certain situations, purging must be

performed with the pump placed at, or

immediately below, the air/water interface.
Subpart E

258

If a bailer must be used to sample the well, decontaminated prior to use. If the purged

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

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 (oxidationreduction) potential, dissolved oxygen,

temperature, and specific conductance. 

Field analyses should not be performed on

samples designated for laboratory analysis.

Any field monitoring equipment or fieldtest 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 groundwater 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
Ground-Water Monitoring and Corrective Action

259

application and limitations of various Bladder pumps are generally recognized as

sampling mechanisms. Sampling materials the best overall sampling device for both

and equipment should be selected to organic and inorganic constituents, although

preserve sample integrity. Sampling other types of pumps (e.g., low-rate

equipment should be constructed of inert submersible centrifugal pumps, helical rotor

material. Sample collection equipment electric submersible pumps) have been

should not alter analyte concentrations, found suitable in some applications.

cause loss of analytes via sorption, or cause Bailers, although inexpensive and simple to

gain of analytes via desorption, degradation, use, have been found to cause volatilization

or corrosion. Sampling equipment should of samples, mobilization of particulates in

be designed such that Viton®, Tygon®, wells and imprecise results (USEPA,

silicone, or neoprene components do not 1992a).

come into contact with the ground-water

sample. These materials have been The following recommendations apply to

demonstrated to cause sorptive losses of the use and operation of ground-water

contaminants (Barcelona et al., 1983; sampling equipment:

Barcelona et al., 1985b; Barcelona et al.,

1988b; Barcelona et al., 1990). Barcelona ! Check valves should be designed and

(1988b) suggests that sorption of volatile inspected to ensure that fouling

organic compounds on silicone, problems do not reduce delivery

polyethylene, and PVC tubing may result in capabilities or result in aeration of

gross errors when determining samples.

concentrations of trace organics in groundwater samples. Barcelona (1985b) ! Sampling equipment should never be

discourages the use of PVC sampling dropped into the well, as this will

equipment when sampling for organic cause degassing of the water upon

contaminants. Fluorocarbon resin (e.g., impact.

Teflon®) or stainless steel sampling devices

which can be easily disassembled for ! Contents of the sampling device should

thorough decontamination are widely used. be transferred to sample containers in

Dedicating sampling equipment to each a controlled manner that will minimize

monitoring well will help prevent cross- sample agitation and aeration.

contamination problems that could arise

from improper decontamination procedures. ! Decontaminated sampling equipment

Sampling equipment should cause minimal contact with the ground or other

sample agitation and should be selected to contaminated surfaces prior to

reduce/eliminate sample contact with the insertion into the well.

atmosphere during sample transfer.

Sampling equipment should not allow ! Ground-water samples should be

volatilization or aeration of samples to the

extent that analyte concentrations are

altered.

should not be allowed to come into

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
Subpart E

260

opportunity to exchange gases with the Once appropriate sampling equipment has

atmosphere and to interact with the been selected and operating procedures

well casing material (USEPA, 1991b). established, samples should be collected and

! The rate at which a well is sampled volatilization sensitivity of the parameter.

should not exceed the rate at which the The preferred collection order for some of

well was purged. Low sampling rates, the more common ground-water analytes is

approximately 0.1 L/min, are depicted on the flow chart shown in Figure

suggested. Low sampling rates will 5-4.

help to ensure that particulates,

immobile in the subsurface under The ground-water monitoring program

ambient conditions, are not entrained documentation should include explicit

in the sample and that volatile procedures for disassembly and

compounds are not stripped from the decontamination of sampling equipment

sample (Puls and Barcelona, 1989b; before each use. Improperly

Barcelona, et al., 1990; Puls et al., decontaminated equipment can affect

1991; Kearl et al., 1992; USEPA, samples in several ways. For example,

1991b). Pumps should be operated at residual contamination from the previous

rates less than 0.1 L/min when well may remain on equipment, or improper

collecting samples for volatile organics decontamination may not remove all of the

analysis. detergents or solvents used during

! Pump lines should be cleared at a rate regarding decontamination of the sampling

of 0.1 L/min or less before collecting equipment is available (USEPA 1992a). To

samples for volatiles analysis so that keep sample cross-contamination to a

the samples collected will not be from minimum, sampling should proceed from

the period of time when the pump was upgradient or background locations to

operating more rapidly. downgradient locations that would contain

! Pumps should be operated in a

continuous manner so that they do not Sample Preservation and Handling

produce samples that are aerated in the

return tube or upon discharge. The procedures for preserving and handling

! When sampling wells that contain the integrity of the samples as the collection

LNAPLs, a stilling tube should be device itself. Detailed procedures for

inserted in the well. Ground-water sample preservation must be provided in the

samples should be collected from the Quality Assurance Project Plan (QAPjP)

screened interval of the well below the that is included in the sampling and analysis

base of the tube. program description.

! Ground-water samples collected for

analysis for organic constituents or

parameters should not be filtered in the

field.

containerized in the order of the

decontamination. Specific guidance

higher concentrations of contaminants.

samples are nearly as important for ensuring
 

Figure 5-4

Generalized Flow Diagram of

Ground-Water Sampling Steps

261
Subpart E

262

Sample Containers maintains sample quality. Samples should

To avoid altering sample quality, the they are collected. These conditions should

samples should be transferred from the be maintained until the samples are received

sampling equipment directly into a prepared at the laboratory. Sample containers

container. Proper sample containers for generally are packed in picnic coolers or

each constituent or group of constituents are special containers for shipment. 

identified in SW-846 (USEPA, 1986b).

Samples should never be composited in a Polystyrene foam, vermiculite, and "bubble

common container in the field and then pack" are frequently used to pack sample

split. Sample containers should be cleaned containers to prevent breakage. Ice is

in a manner that is appropriate for the placed in sealed plastic bags and added to

constituents to be analyzed. Cleaning the cooler. All related paperwork is sealed

procedures are provided by USEPA in a plastic bag and taped to the inside top of

(1986b). Sample containers that have been the cooler. The cooler top is then taped

cleaned according to these procedures can shut. Custody seals should be placed across

be procured commercially. the hinges and latches on the outside of the

Most vendors will provide a certification of

cleanliness. Transportation arrangements should

Sample Preservation provide for effective sample pickup and

During ground-water sampling, every should be coordinated with the laboratory so

attempt should be made to minimize that appropriate sample receipt, storage,

changes in the chemistry of the samples. To analysis, and custody arrangements can be

assist in maintaining the natural chemistry provided. 

of the samples, it is necessary to preserve

the sample. The owner or operator should Most analyses must be performed within a

refer to SW-846 (USEPA, 1986b) for the specified period (holding time) from sample

specific preservation method and holding collection. Holding time refers to the period

times for each constituent to be analyzed. that begins when the sample is collected

Methods of sample preservation are from the well and ends with its extraction or

relatively limited and are intended to retard analysis. Data from samples not analyzed

chemical reactions, such as oxidation, within the recommended holding times

retard, biodegradation, and to reduce the should be considered suspect. Some

effects of sorption. Preservation methods holding times for Appendix I constituents

are generally limited to pH control, are as short as 7 days. To provide the

refrigeration, and protection from light. laboratory with operational flexibility in

Sample Storage and Shipment usually are shipped via overnight courier.

The storage and transport of ground-water influence sampling schedules. Coordination

samples must be performed in a manner that with laboratory staff during 

be cooled to 4EC as soon as possible after

cooler.

maintain proper storage conditions and

delivery to the laboratory. Sampling plans

meeting these holding times, samples

Laboratory capacity or operating hours may
Ground-Water Monitoring and Corrective Action

263

planning and sampling activities is ! Internal temperature of shipping

important in maintaining sample and container when samples were sealed into

analysis quality. the container for shipping

The documentation that accompanies ! Internal temperature of container when

samples during shipment to the laboratory opened at the laboratory

usually includes chain-of-custody (including

a listing of all sample containers), requested ! Any remarks regarding potential hazards

analyses, and full identification of the origin or other information the laboratory may

of samples (including contact names, phone need.

numbers, and addresses). Copies of all

documents shipped with the samples should An adequate chain-of-custody program

be retained by the sampler. allows for tracing the possession and

Chain-of-Custody Record time of collection through completion of

To document sample possession from the program should include:

time of collection, a chain-of-custody record

should be filled out to accompany every ! Sample labels to prevent

sample shipment. The record should misidentification of samples

contain the following types of information:

! Sample number integrity of the samples from the time

! Signature of collector in the laboratory

! Date and time of collection ! Field notes to record information about

! Media sampled (e.g., ground water) water monitoring program

! Sample type (e.g., grab) ! Chain-of-custody record to document

! Identification of sampling location/well

! Number of containers ! Laboratory storage and analysis records,

! Parameters requested for analysis and which record pertinent information

! Signatures of persons involved in the

chain of possession Sample Labels

! Inclusive dates of possession with time Each sample's identification should be

in 24-hour notation marked clearly in waterproof ink on the

handling of individual samples from the

laboratory analysis. A chain-of-custody

! Sample custody seals to preserve the

they are collected until they are opened

each sample collected during the groundsample possession from the time of

collection to analysis

which are maintained at the laboratory

about the sample.

sample container. To aid in labeling, the
Subpart E

264

information should be written on each ! Well depth

container prior to filling with a sample. The

labels should be sufficiently durable to ! Static water level depth and

remain legible even when wet and should measurement technique

contain the following information: 

! Sample identification number layers and the detection method

! Name and signature of the sampler ! Well yield (high or low) and well

! Date and time of collection

! Sample location

! Analyses requested.

Sample Custody Seal

Sample custody seals should be placed on layers

the shipping container and/or individual

sample bottle in a manner that will break the ! Sample withdrawal procedure and

seal if the container or sample is tampered equipment

with.

Field Logbook

To provide an account of all activities

involved in sample collection, all sampling ! Well sampling sequence

activities, measurements, and observations

should be noted in a field log. The ! Types of sample bottles used and

information should include visual sample identification numbers

appearance (e.g., color, turbidity, degassing,

surface film), odor (type, strength), and ! Preservatives used

field measurements and calibration results.

Ambient conditions (temperature, humidity, ! Parameters requested for analysis

wind, precipitation) and well purging and

sampling activities should also be recorded ! Field observations of sampling event

as an aid in evaluating sample analysis

results. ! Name of collector

The field logbook should document the ! Weather conditions, including air

following: temperature

! Well identification

! Presence and thickness of immiscible

recovery after purging (slow, fast)

! Well purging procedure and equipment

! Purge volume and pumping rate

! Time well purged

! Collection method for immiscible

! Date and time of sample collection

! Results of field analysis
Ground-Water Monitoring and Corrective Action

265

! Internal temperature of field and ground-water samples analyzed. The

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

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 μg/L range.

The ground-water monitoring plan must

specify the analytical method to be used.
Subpart E

266

Evaluation and documentation of analytical laboratory of choice is exercising an

performance requires that quality control appropriate QA/QC program. 

samples be collected and analyzed along

with the ground-water monitoring samples. The owner or operator should provide for

Chapter One of SW-846 (Quality the use of standards, laboratory blanks,

Assurance) describes the types of quality duplicates, and spiked samples for

control samples necessary, as well as the calibration and identification of potential

frequency at which they must be collected matrix interferences, especially for metal

and analyzed. In general, these quality determinants. Refer to Chapter One of

control samples may include trip blanks, SW-846 for guidance. The owner or

equipment rinsate samples, field duplicates, operator should use adequate statistical

method blanks, matrix spikes and procedures (e.g., QC charts) to monitor and

duplicates, and laboratory control samples. document performance and to implement an

Other mechanisms, including sample problems (e.g., instrument maintenance,

holding times, surrogate constituents, and operator training). Data from QC samples

standard additions, are also used to control (e.g., blanks, spiked samples) should be

and document data quality. The used as a measure of performance or as an

specification of and adherence to sample indicator of potential sources of crossholding times minimizes the sample contamination, but should not be used by

degradation that occurs over time. the laboratory to alter or correct analytical

Evaluating the recovery of surrogate data. All laboratory QC data should be

constituents spiked into organic samples submitted with the ground-water monitoring

allows the analyst and data user to monitor sample results. 

the efficiency of sample extraction and

analysis. The method of standard additions Field Quality Assurance/Quality Control

is used to eliminate the effects of matrix

interferences in inorganic analyses. To verify the precision of field sampling

Quality Assurance/Quality Control blanks, equipment blanks, and duplicates,

One of the fundamental responsibilities of sample also should be collected for

the owner or operator is to establish a laboratory QC samples.

continuing program to ensure the reliability

and validity of field and analytical All field QC samples should be prepared

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

effective program to resolve testing

procedures, field QC samples, such as trip

should be collected. Additional volumes of

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
Ground-Water Monitoring and Corrective Action

267

results, the owner/operator should resample Equipment rinsate samples are used to

the ground water. The owner/operator assess the efficacy of sampling equipment

should prepare the QC samples as decontamination procedures. The data

recommended in Chapter One of SW-846 validation process uses the results from all

and at the frequency recommended by of these QC samples to determine if the

Chapter One of SW-846 and should analyze reported analytical data accurately describe

them for all of the required monitoring the samples. All reported data must be

parameters. Other QA/QC practices, such evaluated -- a reported value of "non-detect"

as sampling equipment calibration, is a quantitative report just like a numerical

equipment decontamination procedures, and value and must be validated.

chain-of-custody procedures, are discussed

in other sections of this chapter and should The data validation process must also

be described in the owner/operator's QAPjP. consider the presence and quality of other

Validation (e.g., calibration frequency and descriptors,

The analytical data report provided by the criteria for data quality are described in the

laboratory will present all data measured by quality assurance project plan (QAPjP) or

the laboratory but will not adjust those data sampling and analysis plan (SAP). These

for field or laboratory quality control documents may reference criteria from some

indicators. This means that just because other source, (e.g., the USEPA Contract

data have been reported, they are not Laboratory Program). The performance

necessarily an accurate representation of the criteria must be correctly specified and must

quality of the ground water. For example, be used for data validation. It is a waste of

acetone and methylene chloride are often time and money to evaluate data against

used in laboratories as cleaning and standards other than those used to generate

extraction solvents and, consequently, are them. Several documents are available to

often laboratory contaminants, transmitted assist the reviewer in validation of data by

through the ambient air into samples. different criteria (i.e., Chapter One of Test

Method blanks are analyzed to evaluate the Methods for Evaluating Solid Waste,

extent of laboratory contamination. Physical/Chemical Methods, USEPA CLP

Constituents found as contaminants in the Functional Guidelines for Evaluating

method blanks are "flagged" in the sample Organics Analyses, USEPA CLP Functional

data. The sample data are not, however, Guidelines for Evaluating Pesticides/PCBs

adjusted for the contaminant concentration. Analyses, etc.).

Other kinds of samples are analyzed to In addition to specific data that describe

assess other data quality indicators. Trip data quality, the validator may consider

blanks are used to assess contamination by other information that may have an impact

volatile organic constituents during sample on the end-use of the data, such as

shipment and storage. Matrix spike/matrix background concentrations of the

spike duplicate sample pairs are used to constituent in the environment. In any

evaluate analytical bias and precision. event, the QAPjP or SAP also should

kinds of data used to ensure data quality

matrix specific detection limits). All of the

describe the validation procedures that will

be used. The result of 
Subpart E

268

this validation should be the classification ! Statistical methods to be used to evaluate

of data as acceptable or unacceptable for the ground-water monitoring data and

purposes of the project. In some cases, data demonstrate compliance with the

may be further qualified, based either on performance standard;

insufficient data or marginal performance

(i.e., qualitative uses only, estimated ! Approved demonstration that monitoring

concentration, etc.). requirements are suspended (if

Documentation

The ground-water monitoring program

required by §258.50 through §258.55 relies ! Piezometer and well construction logs

on documentation to demonstrate for the ground-water monitoring system.

compliance. The operating record of the

MSWLF should include a complete

description of the program as well as 5.9 STATISTICAL ANALYSIS

periodic implementation reports. 40 CFR §258.53 (g)-(i)

At a minimum, the following aspects of the 5.9.1 Statement of Regulation

ground-water monitoring program should be

described or included in the operating (g) The owner or operator must specify

record: in the operating record one of the

! The Sampling and Analysis plan that

details sample parameters, sampling

frequency, sample collection,

preservation, and analytical methods to

be used, shipping procedures, and chainof-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;

applicable);

! Boring logs;

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
Ground-Water Monitoring and Corrective Action

269

estimation and testing of the contrasts (2) If an individual well comparison

between each compliance well's median procedure is used to compare an

and the background median levels for individual compliance well constituent

each constituent. concentration with background

(3) A tolerance or prediction interval water protection standard, the test shall

procedure in which an interval for each be done at a Type I error level of no less

constituent is established from the than 0.01 for each testing period. If a

distribution of the background data, and multiple comparisons procedure is used,

the level of each constituent in each the Type I experiment wise error rate for

compliance well is compared to the upper each testing period shall be no less than

tolerance or prediction limit. 0.05; however, the Type I error of no less

(4) A control chart approach that gives must be maintained. This performance

control limits for each constituent. standard does not apply to tolerance

intervals, prediction intervals, or control

(5) Another statistical test method that charts.

meets the performance standards of

§258.53(h). The owner or operator must (3) If a control chart approach is used to

place a justification for this alternative in evaluate ground-water monitoring data,

the operating record and notify the State the specific type of control chart and its

Director of the use of this alternative test. associated parameter values shall be

The justification must demonstrate that protective of human health and the

the alternative method meets the environment. The parameters shall be

performance standards of §258.53(h). determined after considering the number

of samples in the background data base,

(h) Any statistical method chosen under the data distribution, and the range of the

§258.53(g) shall comply with the concentration values for each constituent

following performance standards, as of concern.

appropriate:

(1) The statistical method used to predictional interval is used to evaluate

evaluate ground-water monitoring data ground-water monitoring data, the levels

shall be appropriate for the distribution of confidence and, for tolerance intervals,

of chemical parameters or hazardous the percentage of the population that the

constituents. If the distribution of the interval must contain, shall be protective

chemical parameters or hazardous of human health and the environment.

constituents is shown by the owner or These parameters shall be determined

operator to be inappropriate for a normal after considering the number of samples

theory test, then the data should be in the background data base, the data

transformed or a distribution-free theory distribution, and the range of the

test should be used. If the distributions concentration values for each constituent

for the constituents differ, more than one of concern.

statistical method may be needed.

constituent concentrations or a groundthan 0.01 for individual well comparisons

(4) If a tolerance interval or a
Subpart E

270

(5) The statistical method shall account significant increase over background at

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 

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
Ground-Water Monitoring and Corrective Action

271

that are protective of human health and the useful for selecting other methods (Dixon

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 

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
Subpart E

272

shall be protective of human health and Multiple Well Comparisons

the environment

4) The level of confidence and percentage downgradient combined) are screened in the

of the population contained in an interval same stratigraphic unit, then the appropriate

shall be protective of human health and statistical comparison method is a multiple

the environment well comparison using the ANOVA

5) The method must account for data below procedure assumes that the data from each

the limit of detection (less than the PQL) well group come from the same type (e.g.,

in a manner that is protective of human Normal) of distribution with possibly

health and the environment different mean concentrations. The

6) The method must account for seasonal there are multiple background wells, one

and spatial variability and temporal should consider the possibility of trying to

correlation of the data, if necessary. pool these background data into one group.

These statistical analysis methods shall be for more accurate statistical comparisons,

used to determine whether a significant primarily because better information is

increase over background values has known about the background concentrations

occurred. Monitoring data must be as a whole. Downgradient wells should not

statistically analyzed after validated results be pooled, as stated in the regulations.

from each sampling and analysis event are Ground-water monitoring data tend to

received. follow a log normal distribution (USEPA,

The statistical performance standards prior to applying a parametric ANOVA

provide a means to limit the possibility of procedure. By conducting a log

making false conclusions from the transformation, ground-water monitoring

monitoring data. The specified error level data will generally be converted to a normal

of 0.01 for individual well comparisons for distribution. By applying a Shapiro-Wilk

probability of Type I error (indication of test, probability plots, or other normality

contamination when it is not present or false tests on the residuals (errors) from the

positive) essentially means that the analysis ANOVA procedure, the normality of the

is predicting with 99-percent confidence transformed data can be determined. In

that no significant increase in contaminant addition, data variance for each well in the

levels is evident when in fact no increase is comparison must be approximately

present. Non-detect results must be treated equivalent; this condition can be checked

in an appropriate manner or their influence using Levene's or Bartlett's test. These tests

on the statistical method may invalidate the are provided in USEPA (1992b) and

statistical conclusion. Non-detect results USEPA (1989).

are discussed in greater detail later in this

section. If the transformed data do not conform to

If more than two wells (background and

procedure. The parametric ANOVA

ANOVA tests for a difference in means. If

Such an increase in sample size often allows

1989), and usually need to be transformed

the normality assumption, a nonparametric

ANOVA procedure may be used. The
Ground-Water Monitoring and Corrective Action

273

nonparametric statistical procedures do not designed to contain a designated proportion

depend as much on the mathematical of the population (e.g., 95 percent of all

properties of a specified distribution. The possible sample measurements). Because

nonparametric equivalent to the parametric the interval is constructed from sample data,

ANOVA is the Kruskal-Wallis test, which it also is a random interval. And because of

analyzes variability of the average ranks of sampling fluctuations, a tolerance interval

the data instead of the measurements can contain the specified proportion of the

themselves. population only with a certain confidence

If the data display seasonality (regular,

periodic, and time-dependent increases or Tolerance intervals are very useful for

decreases in parameter values), a two-way ground-water data analysis because in many

ANOVA procedure should be used. If the situations one wants to ensure that at most a

seasonality can be corrected, a one-way small fraction of the compliance well

ANOVA procedure may still be appropriate. sample measurements exceed a specific

Methods to treat seasonality are described in concentration level (chosen to be protective

USEPA (1989). of human health and the environment).

ANOVA procedures attempt to determine Prediction intervals are constructed to

whether different wells have significantly contain the next sample value(s) from a

different average concentrations of population or distribution with a specified

constituents. If a difference is indicated, the probability. That is, after sampling a

ANOVA test is followed by a multiple background well for some time and

comparisons procedure to investigate which measuring the concentration of an analyte,

specific wells are different among those the data can be used to construct an interval

tested. The overall experiment-wise that will contain the next analyte sample or

significance level of the ANOVA must be samples (assuming the distribution has not

kept to a minimum of 0.05, while the changed). Therefore, a prediction interval

minimum significance level of each will contain a future value or values with

individual comparison must be set at 0.01. specified probability. Prediction intervals

USEPA (1992b) provides alternative can also be constructed to contain the

methods that can be used when the number average of several future observations.

of individual contrasts to be tested is very

high. In summary, a tolerance interval contains a

Tolerance and Prediction Intervals prediction interval contains one or more

Two types of statistical intervals are often statement or "confidence coefficient"

constructed from data: tolerance intervals associated with it. It should be noted that

and prediction intervals. A comprehensive these intervals assume that the sample data

discussion of these intervals is provided in used to construct the intervals are normally

USEPA 1992b. Though often confused, the distributed.

interpretations and uses of these intervals

are quite distinct. A tolerance interval is

level.

proportion of the population, and a

future observations. Each has a probability
Subpart E

274

Individual Well Comparisons monitoring data. Such data may be adjusted

When only two wells (e.g., a single degree of change over time. Guidance for

background and a single compliance point and limitations of intra-well comparison

well) are being compared, owners or techniques are provided in USEPA (1989)

operators should not perform the parametric and USEPA (1992b).

or nonparametric ANOVA. Instead, a

parametric t-test, such as Cochran's Treatment of Non-Detects

Approximation to the Behrens-Fisher

Students' t-test, or a nonparametric test The treatment of data below the detection

should be performed. When a single limit of the analytical method (non-detects)

compliance well group is being compared to used depends on the number or percentage

background data and a nonparametric test is of non-detects and the statistical method

needed, the Wilcoxin Rank-Sum test should employed. Guidance on how to treat nonbe performed. These tests are discussed in detects is provided in USEPA (1992b).

more detail in standard statistical references

and in USEPA (1992b). 5.10 DETECTION MONITORING

Intra-Well Comparisons 40 CFR §258.54

Intra-well comparisons, where data of one 5.10.1 Statement of Regulation

well are evaluated over time, are useful in

evaluating trends in individual wells and for (a) Detection monitoring is required at

identifying seasonal effects in the data. The MSWLF units at all ground-water

intra-well comparison methods do not monitoring wells defined under

compare background data to compliance §§258.51(a)(1) and (a)(2) of this part. At

data. Where some existing facilities may a minimum, a detection monitoring

not have valid background data, however, program must include the monitoring for

intra-well comparisons may represent the the constituents listed in Appendix I of

only valid comparison available. In the this part. 

absence of a true background well, several

monitoring events may be required to 1) The Director of an approved State

determine trends and seasonal fluctuations may delete any of the Appendix I

in ground-water quality. monitoring parameters for a MSWLF

Control charts may be used for intra-well removed constituents are not

comparisons but are only appropriate for reasonably expected to be in or

uncontaminated wells. If a well is derived from the waste contained in

intercepting a release, then it is already in the unit.

an "out-of-control" state, which violates the

principal assumption underlying control 2) The Director of an approved State

chart procedures. Time series analysis (i.e.,

plotting concentrations over time) is

extremely useful for identifying trends in

for seasonal effects to aid in assessing the

PROGRAM

unit if it can be shown that the

may establish an alternative list of

inorganic indicator parameters for a

MSWLF unit, in lieu of some or all of
Ground-Water Monitoring and Corrective Action

275

the heavy metals (constituents 1-15 in must be collected and analyzed during

Appendix I), if the alternative

parameters provide a reliable

indication of inorganic releases from

the MSWLF unit to the ground water.

I n 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 postclosure 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)

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 
Subpart E

276

background levels, and notify the State list has been established by the Director of

Director that this notice was placed in the an approved State.

operating record; and

(2) Must establish an assessment event, the owner or operator must collect at

monitoring program meeting the least four independent ground-water

requirements of §258.55 of this part samples from each well and analyze the

within 90 days, except as provided for in samples for all constituents in the Appendix

paragraph (3) below. I or alternative list. Each subsequent

(3) The owner/operator may minimum, the collection and analysis of one

demonstrate that a source other than a sample from all wells. The monitoring

MSWLF unit caused the contamination requirement continues throughout the active

or that the statistically significant life of the landfill and the post-closure care

increase resulted from error in sampling, period.

analysis, statistical evaluation, or natural

variation in ground-water quality. A If an owner or operator determines that a

report documenting this demonstration statistically significant increase over

must be certified by a qualified ground- background has occurred for one or more

water scientist or approved by the Appendix I constituents (or constituents on

Director of an approved State and be an alternative list), a notice must be placed

placed in the operating record. If a in the facility operating record (see Table 5-

successful demonstration is made and 2). The owner or operator must notify the

documented, the owner or operator may State Director within 14 days of the finding.

continue detection monitoring as Within 90 days, the owner or operator must

specified in this section. If after 90 days, establish an assessment monitoring program

a successful demonstration is not made, conforming to the requirements of §258.55.

the owner or operator must initiate an

assessment monitoring program as If evidence exists that a statistically

required in §258.55. significant increase is due to factors

5.10.2 Applicability may make a demonstration to this effect to

Except for the small landfill exemption and certified demonstration in the operating

the no migration demonstration, detection record. The potential reasons for an

monitoring is required at existing MSWLF apparent statistical increase may include:

units, lateral expansions of units, and new

MSWLF units. Monitoring must occur at ! A contaminant source other than the

least semiannually at both background wells landfill unit

and downgradient well locations. The

Director of an approved State may specify ! A natural variation in ground-water

an alternative sampling frequency. quality

Monitoring parameters must include all

Appendix I constituents unless an ! An analytical error

alternative 

During the first semiannual monitoring

semiannual event must include, at a

unrelated to the unit, the owner or operator

the Director of an approved State or place a
Ground-Water Monitoring and Corrective Action

277

! A statistical error Independent Sampling for Background

! A sampling error. The ground-water monitoring requirements

The demonstration that one of these reasons collected from each well to establish

is responsible for the statistically significant background during the first semiannual

increase over background must be certified monitoring event. This is because almost all

by a qualified ground-water scientist or statistical procedures are based on the

approved by the Director of an approved assumption that samples are independent of

State. If a successful demonstration is made each other. In other words, independent

and documented, the owner or operator may samples more accurately reflect the true

continue detection monitoring. range of natural variability in the ground

If a successful demonstration is not made independent samples are more accurate.

within 90 days, the owner or operator must Replicate samples, whether field replicates

initiate an assessment monitoring program. or lab splits, are not statistically

A flow chart for a detection monitoring independent measurements.

program in a State whose program has not

been approved by EPA is provided in Figure It may be necessary to gather the

5-5. independent samples over a range of time

5.10.3 Technical Considerations differences. If seasonal differences are not

If there is a statistically significant increase positives increases (monitoring results

over background during detection indicate a release, when a release has not

monitoring for one or more constituents occurred). The sampling interval chosen

listed in Appendix I of Part 258 (or an must ensure that sampling is being done on

alternative list of parameters in an approved different volumes of ground water. To

State), the owner or operator is required to determine the appropriate interval between

begin assessment monitoring. The sample collection events that will ensure

requirement to conduct assessment independence, the owner or operator can

monitoring will not change, even if the determine the site's effective porosity,

Director of an approved State allows the hydraulic conductivity, and hydraulic

monitoring of geochemical parameters in gradient and use this information to

lieu of some or all of the metals listed in calculate ground-water velocity (USEPA,

Appendix I. If an owner or operator 1989). Knowing the velocity of the ground

suspects that a statistically significant water should enable an owner/operator to

increase in a geochemical parameter is establish an interval that ensures the four

caused by natural variation in ground-water samples are being collected from four

quality or a source other than a MSWLF different volumes of water. For additional

unit, a demonstration to this effect must be information on establishing sampling

documented in a report to avoid proceeding interval, see Statistical Analysis of

to assessment monitoring. Groundwater Monitoring Data at RCRA

specify that four independent samples be

water, and statistical analyses based on

sufficient to account for seasonal

taken into account, the chance for false
Figure 5-5. Detection Monitoring Program

278
Ground-Water Monitoring and Corrective Action

279

Facilities - Interim Final Guidance, constituents from Appendix I may be

(USEPA, 1989). acceptable. Usually, a waste would have to

Alternative List/Removal of Parameters determination. The owner or operator may

An alternative list of Appendix I presence or absence of certain constituents

constituents may be allowed by the Director in the waste. The owner or operator also

of an approved State. The alternative list would have to demonstrate that constituents

may use geochemical parameters, such as proposed for deletion from Appendix I are

pH and specific conductance, in place of not degradation or reaction products of

some or all of the metals (Parameters 1 constituents potentially present in the waste.

through 15) in Appendix I. These

alternative parameters must provide a Alternative Frequency

reliable indication of inorganic releases

from the MSWLF unit to ground water. The In approved States, 40 CFR §258.54(b)

option of establishing an alternative list allows the Director to specify an alternative

applies only to Parameters 1 through 15 of frequency for ground-water monitoring.

Appendix I. The list of ground-water The alternative frequency is applicable

monitoring parameters must include all of during the active life, including the closure

the volatile organic compounds (Appendix and the post-closure periods. The

I, Parameters 16 through 62). alternative frequency can be no less than

A potential problem in substituting

geochemical parameters for metals on the The need to vary monitoring frequency must

alternative list is that many of the be evaluated on a site-specific basis. For

geochemical parameters are naturally example, for MSWLF units located in areas

occurring. However, these parameters have with low ground-water flow rates, it may be

been used to indicate releases from MSWLF acceptable to monitor ground water less

units. Using alternative geochemical frequently. The sampling frequency chosen

parameters is reasonable in cases where must be sufficient to protect human health

natural background levels are not high and the environment. Depending on the

enough to mask the detection of a release ground-water flow rate and the resource

from a MSWLF unit. The decision to use value of the aquifer, less frequent

alternative parameters also should consider monitoring may be allowable or more

natural spatial and temporal variability in frequent monitoring may be necessary. An

the geochemical parameters. approved State may specify an alternative

The types, quantities, and concentrations of analysis of Appendix I constituents based on

wastes managed at the MSWLF unit play an the following factors:

important role in determining whether

removal of parameters from Appendix I is 1) Lithology of the aquifer and the

appropriate. If an owner or operator has unsaturated zone

definite knowledge of the nature of wastes

accepted at the facility, then removal of

be homogeneous to allow for this kind of

submit a demonstration that documents the

annual.

frequency for repeated sampling and
Subpart E

280

2) Hydraulic conductivity of the aquifer 2) A comprehensive audit of sampling,

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 postclosure 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

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 
Ground-Water Monitoring and Corrective Action

281

conditions and findings of the 5.11 ASSESSMENT MONITORING

monitoring program. PROGRAM

The demonstration must be documented,

certified by a qualified ground-water 5.11.1 Statement of Regulation

scientist, and placed in the operating record

of the facility. (a) Assessment monitoring is required

Demonstrations of Other Sources of increase over background has been

Error detected for one or more of the

A successful demonstration that the alternate list approved in accordance

statistically significant change is the result with § 258.54(a)(2).

of an error in sampling, analysis, or data

evaluation may include the following: (b) Within 90 days of triggering an

! Clear indication of a transcription or annually thereafter, the owner or

calculation error operator must sample and analyze the

! Clear indication of a systematic error in identified in Appendix II of this part. A

analysis or data reduction minimum of one sample from each

! Resampling, analysis, and evaluation of analyzed during each sampling event.

results For any new constituent detected in the

! 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).

40 CFR §258.55(a)-(f)

whenever a statistically significant

constituents listed in Appendix I or in the

assessment monitoring program, and

ground water for all constituents

downgradient well must be collected and

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.
Subpart E

282

(c) The Director of an approved State I to this Part or in the alternative list

may specify an appropriate alternate approved in accordance with

frequency for repeated sampling and §258.54(a)(2), and for those constituents

analysis for the full set of Appendix II in Appendix II that are detected in

constituents required by §258.55(b) of response to paragraph (b) of this section,

this part, during the active life (including and record their concentrations in the

closure) and post-closure care of the unit facility operating record. At least one

considering the following factors: sample from each well (background and

(1) Lithology of the aquifer and analyzed during these sampling events.

unsaturated zone; The Director of an approved State may

(2) Hydraulic conductivity of the frequency during the active life

aquifer and unsaturated zone; (including closure) and the post closure

(3) Ground-water flow rates; this paragraph. The alternative

(4) Minimum distance between the alternate list approved in accordance

upgradient edge of the MSWLF unit and with §258.54(a)(2) during the active life

downgradient monitoring well screen (including closure) shall be no less than

(minimum distance of travel); annual. The alternative frequency shall

 (5) Resource value of the aquifer; and specified in paragraph (c) of this section;

(6) Nature (fate and transport) of any (3) Establish background concentrations

constituents detected in response to this for any constituents detected pursuant to

section. paragraphs (b) or (d)(2) of this section;

(d) After obtaining the results from the

initial or subsequent sampling events (4) Establish ground-water protection

required in paragraph (b) of this section, standards for all constituents detected

the owner or operator must: pursuant to paragraph (b) or (d)(2) of

(1) Within 14 days, place a notice in the protection standards shall be established

operating record identifying the in accordance with paragraphs (h) or (i)

Appendix II constituents that have been of this section.

detected and notify the State Director

that this notice has been placed in the (e) If the concentrations of all Appendix

operating record; II constituents are shown to be at or

(2) Within 90 days, and on at least a statistical procedures in §258.53(g), for 

semiannual basis thereafter, resample all two consecutive sampling events, the

wells specified by § 258.51(a), conduct owner or operator must notify the State

analyses for all constituents in Appendix

downgradient) must be collected and

specify an alternative monitoring

period for the constituents referred to in

frequency for Appendix I constituents or

be based on consideration of the factors

and 

this section. The ground-water

below background values, using the
Ground-Water Monitoring and Corrective Action

283

Director of this finding and may return to may specify an appropriate subset of wells

detection monitoring. to be included in the assessment monitoring

(f) If the concentrations of any also may specify an alternative frequency

Appendix II constituents are above for repeated sampling and analysis of

background values, but all concentrations Appendix II constituents. This frequency

are below the ground-water protection may be decreased or increased based upon

standard established under paragraphs consideration of the factors in

(h) or (i) of this section, using the §258.55(c)(1)-(6). These options for

statistical procedures in §258.53(g), the assessment monitoring programs are

owner or operator must continue available only with the approval of the

assessment monitoring in accordance Director of an approved State.

with this section.

5.11.2 Applicability the initial sampling for Appendix II

Assessment monitoring is required at all the owner or operator must place the results

existing units, lateral expansions, and new in the operating record and notify the State

facilities whenever any of the constituents Director that this notice has been placed in

listed in Appendix I are detected at a the operating record. 

concentration that is a statistically

significant increase over background values. Within 90 days of receiving these initial

Figure 5-6 presents a flow chart pertaining results, the owner or operator must resample

to applicability requirements. all wells for all Appendix I and detected

Within 90 days of beginning assessment list of constituents must be sampled at least

monitoring, the owner or operator must semiannually thereafter, and the list must be

resample all downgradient wells and updated annually to include any newly

analyze the samples for all Appendix II detected Appendix II constituents.

constituents. If any new constituents are

identified in this process, four independent Within the 90-day period, the owner or

samples must be collected from all operator must establish background values

upgradient and downgradient wells and and ground-water protection standards

analyzed for those new constituents to (GWPSs) for all Appendix II constituents

establish background concentrations. The detected. The requirements for determining

complete list of Appendix II constituents GWPSs are provided in §258.55(h). If the

must be monitored in each well annually for concentrations of all Appendix II

the duration of the assessment monitoring constituents are at or below the background

program. In an approved State, the Director values after two independent, consecutive

may reduce the number of Appendix II sampling events, the owner or operator may

constituents to be analyzed if it can be return to detection monitoring after

reasonably shown that those constituents are notification has been made to the State

not present in or derived from the wastes. Director. If, after these two

The Director of an approved State 

program. The Director of an approved State

Within 14 days of receiving the results of

constituents under assessment monitoring,

Appendix II constituents. This combined
Figure 5-6

ASSESSMENT MONITORING

284
Ground-Water Monitoring and Corrective Action

285

sampling events, any detected Appendix II the owner or operator must collect at least

constituent is statistically above background one sample from each downgradient well

but below the GWPSs, the assessment and analyze the samples for the Appendix II

monitoring program must be continued. parameters. If a downgradient well has

5.11.3 Technical Considerations constituent, four independent samples must

The purpose of assessment monitoring is to downgradient wells to establish background

evaluate the nature and extent of for the new constituent(s). The date, well

contamination. The assessment monitoring locations, parameters detected, and their

program is phased. The first phase assesses concentrations must be documented in the

the presence of additional assessment operating record of the facility, and the

monitoring constituents (Appendix II or a State Director must be notified within 14

revised list designated by an approved State) days of the initial detection of Appendix II

in all downgradient wells or in a subset of parameters. On a semiannual basis

ground-water monitoring wells specified by thereafter, both background and

the Director of an approved State. If downgradient wells must be sampled for all

concentrations of all Appendix II Appendix II constituents.

constituents are at or below background

values using the statistical procedures in Alternative List

§258.53(g) for two consecutive sampling

periods, then the owner or operator can In an approved State, the Director may

return to detection monitoring. delete Appendix II parameters that the

Following notification of a statistically not be anticipated at the facility. A

significant increase of any Appendix I demonstration would be based on a

constituent above background, the owner or characterization of the wastes contained in

operator has 90 days to develop and the unit and an assessment of the leachate

implement the assessment monitoring constituents. Additional information on the

program. Implementation of the program alternative list can be found in Section

involves sampling downgradient monitoring 5.10.3.

wells for ground water passing the relevant

point of compliance for the unit (i.e., the Alternative Frequency

waste management unit boundary or

alternative boundary specified by the The Director of an approved State may

Director of an approved State). specify an alternate sampling frequency for

Downgradient wells are identified in the entire Appendix II list for both the

§258.51(a)(2). Initiation of assessment active and post-closure periods of the

monitoring does not stop the detection facility. The decision to change the

monitoring program. Section 258.55(d)(2) monitoring frequency must consider: 

specifies that analyses must continue for all

Appendix I constituents on at least a 1) Lithology of the aquifer and unsaturated

semiannual basis. Within the 90-day period, zone;

detectable quantities of a new Appendix II

be collected from all background and

owner or operator can demonstrate would
Subpart E

286

2) Hydraulic conductivity of the aquifer 5.12 ASSESSMENT MONITORING

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 groundwater 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.

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
Ground-Water Monitoring and Corrective Action

287

(2) May demonstrate that a source installing and sampling an appropriate

other than a MSWLF unit caused the number of additional monitoring wells

contamination, or that the statistically

significant increase resulted from error in 2) Install at least one additional

sampling, analysis, statistical evaluation, downgradient well at the facility

or natural variation in ground-water property boundary in the direction of

quality. A report documenting this migration of the contaminant plume and

demonstration must be certified by a sample that well for all Appendix II

qualified ground-water scientist or compounds initially and thereafter, in

approved by the Director of an approved conformance with the assessment

State and placed in the operating record. monitoring program

If a successful demonstration is made the

owner or operator must continue 3) Notify all property owners whose land

monitoring in accordance with the overlies the suspected plume, if the

assessment monitoring program pursuant sampling of any property boundary

to §258.55, and may return to detection well(s) indicates that contaminants have

monitoring if the Appendix II migrated offsite

constituents are below background as

specified in §258.55(e). Until a successful 4) Initiate an assessment of corrective

demonstration is made, the owner or measures, as required by §258.56, within

operator must comply with §258.55(g) 90 days.

including initiating an assessment of

corrective measures. In assessment monitoring, the owner or

5.12.2 Applicability other than the MSWLF unit caused the

This requirement applies to facilities in significant increase was the result of an

assessment monitoring and is applicable error in sampling, analysis, statistical

during the active life, closure, and post- evaluation, or natural variation in groundclosure care periods. water quality. The demonstration must be

5.12.3 Technical Considerations scientist or approved by the Director of an

If an Appendix II constituent(s) exceeds a demonstration is made, the owner or

GWPS in any sampling event, the owner or operator must comply with §258.55(g) and

operator must notify the State Director initiate assessment of corrective measures.

within 14 days and place a notice of these If the demonstration is successful, the owner

findings in the operating record of the or operator must return to assessment

MSWLF facility. In addition, the owner or monitoring and may return to the detection

operator must: program provided that all Appendix II

1) Characterize the lateral and vertical two consecutive sampling periods.

extent of the release or plume by

operator may demonstrate that a source

contamination or that the statistically

certified by a qualified ground-water

approved State. Until a successful

constituents are at or below background for
Subpart E

288

Release Investigation semiannually or at an alternative frequency

If the GWPS is exceeded, a series of actions State. The initial sample must be analyzed

must be taken. These actions are described for all Appendix II constituents.

in the next several paragraphs. The owner

or operator must investigate the extent of Notification of Adjoining Residents and 

the release by installing additional Property Owners

monitoring wells and obtaining additional

ground-water samples. The investigation If ground-water monitoring indicates that

should identify plume geometry, both contamination has migrated offsite, the

laterally and vertically. Prior to such field owner or operator must notify property

activities, records of site operation and owners or residents whose land surface

maintenance activities should be reviewed overlies any part of the contaminant release.

to identify possible release locations within Although the requirement does not describe

the landfill and whether such releases are the contents of the notice, it is expected that

expected to be transient (e.g., one time the notice could include the following

release due to repaired liner) or long-term. items:

Due to the presence of dissolved ionic

constituents, such as iron, magnesium, ! Date of detected release

calcium, sodium, potassium, chloride,

sulfate, and carbonate, typically associated ! Chemical composition of release

with MSWLF unit leachates, geophysical

techniques, including resistivity and terrain ! Reference to the constituent(s), reported

conductivity, may be useful in defining the concentration(s), and the GWPS

plume. Characterizing the nature of the

release should include a description of the ! Representatives of the MSWLF facility

rate and direction of contaminant migration with whom to discuss the finding,

and the chemical and physical including their telephone numbers

characteristics of the contaminants.

Property Boundary Monitoring Well

At least one monitoring well must be protect human health and the

installed at the facility boundary in the environment.

direction of contaminant migration.

Additional wells may be required to Demonstrations of Other Sources of

delineate the plume. Monitoring wells at Error

the facility boundary should be screened to

monitor all stratigraphic units that could be The owner or operator may demonstrate that

preferential pathways for contaminant the source of contamination was not the

migration in the uppermost aquifer. In MSWLF unit. This demonstration is

some cases, this may require installation of discussed in Section 5.10.3.

nested wells or individual wells screened at

several discrete intervals. The well installed

at the facility boundary must be sampled

determined by the Director of an approved

! Plans and schedules for future activities

! Interim recommendations or remedies to
Ground-Water Monitoring and Corrective Action

289

Return to Detection Monitoring (3) For constituents for which the

A facility conducting assessment monitoring identified under subparagraph (1) above

may return to detection monitoring if the or health based levels identified under

concentrations of all Appendix II §258.55(i)(1), the background

constituents are at or below background concentration.

levels for two consecutive sampling periods

using the statistical procedures in (i) The Director of an approved State

§258.53(g). The requirement that may establish an alternative groundbackground concentrations must be water protection standard for

maintained for two consecutive sampling constituents for which MCLs have not

events will reduce the possibility that the been established. These ground-water

owner or operator will fail to detect protection standards shall be appropriate

contamination or an increase in a health based levels that satisfy the

concentration of a hazardous constituent following criteria:

when one actually exists. The Director of

an approved State can establish an (1) The level is derived in a manner

alternative time period (§258.54(b). consistent with Agency guidelines for

5.13 ASSESSMENT MONITORING 34006, 34014, 34028);

PROGRAM

40 CFR §258.55(h)-(j) (2) The level is based on scientifically

5.13.1 Statement of Regulation with the Toxic Substances Control Act

(h) The owner or operator must CFR Part 792) or equivalent;

establish a ground-water protection

standard for each Appendix II (3) For carcinogens, the level represents

constituent detected in the ground water. a concentration associated with an excess

The ground-water protection standard lifetime cancer risk level (due to

shall be: continuous lifetime exposure) with the 1

(1) For constituents for which a

maximum contaminant level (MCL) has (4) For systemic toxicants, the level

been promulgated under Section 1412 of represents a concentration to which the

the Safe Drinking Water Act (codified) human population (including sensitive

under 40 CFR Part 141, the MCL for that subgroups) could be exposed to on a daily

constituent; basis that is likely to be without

(2) For constituents for which MCLs during a lifetime. For purposes of this

have not been promulgated, the subpart, systemic toxicants include toxic

background concentration for the chemicals that cause effects other than

constituent established from wells in cancer or mutation.

accordance with §258.51(a)(1); or

background level is higher than the MCL

assessing the health risks of

environmental pollutants (51 FR 33992,

valid studies conducted in accordance

Good Laboratory Practice Standards (40

x 10 to 1 x 10 range; and -4 -6

appreciable risk of deleterious effects
Subpart E

290

(j) In establishing ground-water 5.13.3 Technical Considerations

protection standards under paragraph

(i), the Director of an approved State may For each Appendix II constituent detected,

consider the following: a GWPS must be established. The GWPS is

(1) Multiple contaminants in the ground Where the background concentration is

water; higher than the MCL, then the GWPS is

(2) Exposure threats to sensitive

environmental receptors; and Directors of approved States have the option

(3) Other site-specific exposure or constituents without MCLs. This alternative

potential exposure to ground water. GWPS must be an appropriate health-based

5.13.2 Applicability levels must:

The criteria for establishing GWPSs are ! Be consistent with EPA health risk

applicable to all facilities conducting assessment guidelines

assessment monitoring where any Appendix

II constituents have been detected. The ! Be based on scientifically valid studies

owner or operator must establish a GWPS

for each Appendix II constituent detected. ! Be within a risk range of 1x10 to 1x10

If the constituent has a promulgated

maximum contaminant level (MCL), then ! For systemic toxicants (causing effects

the GWPS is the MCL. If no MCL has been other than cancer or mutations), be a

published for a given Appendix II concentration to which the human

constituent, the background concentration of population could be exposed on a daily

the constituent becomes the GWPS. In basis without appreciable risk of

cases where the background concentration is deleterious effects during a lifetime.

higher than a promulgated MCL, the GWPS

is set at the background level. The health-based GWPS may be established

In approved States, the Director may constituent, exposure to sensitive

establish an alternative GWPS for environmental receptors, and other siteconstituents for which MCLs have not been specific exposure to ground water. Risk

established. Any alternative GWPS must be assessments to establish the GWPS must

health-based levels that satisfy the criteria in consider cumulative effects of multiple

§258.55(i). The Director may also consider pathways to receptors and cumulative

any of the criteria identified in §258.55(j). effects on exposure risk of multiple

In cases where the background contaminants. Guidance and procedures for

concentration is higher than the health- establishing a health-based risk assessment

based levels, the GWPS is set at the may be found in Guidance on Remedial

background level. Actions for 

to be set at either the MCL or background.

established at background.

of establishing an alternative GWPS for

level, based on specific criteria. These

-4 -6

for carcinogens

considering the presence of more than one
Ground-Water Monitoring and Corrective Action

291

Contaminated Groundwater at Superfund (3) The costs of remedy implementation;

Sites, (USEPA, 1988). and

5.14 ASSESSMENT OF as State or local permit requirements or

CORRECTIVE MEASURES other environmental or public health

40 CFR §258.56 requirements that may substantially

5.14.1 Statement of Regulation

(a) Within 90 days of finding that any of the results of the corrective measures

the constituents listed in Appendix II assessment, prior to the selection of

have been detected at a statistically remedy, in a public meeting with

significant level exceeding the ground- interested and affected parties.

water protection standards defined under

§258.55(h) and (i) of this part, the owner 5.14.2 Applicability

or operator must initiate an assessment of

corrective measures. Such an assessment An assessment of corrective measures must

must be completed within a reasonable be conducted whenever any Appendix II

period of time. constituents are detected at statistically

(b) The owner or operator must assessment of corrective measures must be

continue to monitor in accordance with initiated within 90 days of the finding.

the assessment monitoring program as During the initiation of an assessment of

specified in §258.55. corrective measures, assessment monitoring

(c) The assessment shall include an corrective measures must consider

analysis of the effectiveness of potential performance (including potential impacts),

corrective measures in meeting all of the time, and cost aspects of the remedies. If

requirements and objectives of the implementation requires additional State or

remedy as described under §258.57, local permits, such requirements should be

addressing at least the following: identified. Finally, the results of the

(1) The performance, reliability, ease of discussed in a public meeting with

implementation, and potential impacts of interested and affected parties.

appropriate potential remedies, including

safety impacts, cross-media impacts, and 5.14.3 Technical Considerations

control of exposure to any residual

contamination; An assessment of corrective measures is

(2) The time required to begin and depending on the design and age of the

complete the remedy; facility, the completeness of the facility's

(4) The institutional requirements such

affect implementation of the remedy(s).

(d) The owner or operator must discuss

significant levels exceeding the GWPS. The

must be continued. The assessment of

corrective measures assessment must be

site-specific and will vary significantly

historical records, the nature and

concentration of the contaminants found in
Subpart E

292

the ground water, the complexity of the site (e.g., unlined leachate storage ponds, failed

hydrogeology, and the facility's proximity cover system, leaky leachate transport pipes,

to sensitive receptors. Corrective measures past conditions of contaminated storm

are generally approached from two overflow), such information should be

directions: 1) identify and remediate the considered as part of the assessment of

source of contamination and 2) identify and corrective measures. 

remediate the known contamination.

Because each case will be site-specific, the Existing site geology and hydrogeology

owner or operator should be prepared to information, ground-water monitoring

document that, to the best of his or her results, and topographic and cultural

technical and financial abilities, a diligent information must be documented clearly and

effort has been made to complete the accurately. This information may include

assessment in the shortest time practicable. soil boring logs, test pit and monitoring well

The factors listed in §258.56(c)(1) must be data, and other information collected during

considered in assessing corrective measures. facility design or operation. The

These general factors are discussed below in information should be expressed in a

terms of source evaluation, plume manner that will aid interpretation of data.

delineation, ground-water assessment, and Such data may include isopach maps of the

corrective measures assessment. thickness of the upper aquifer and important

Source Evaluation contaminants, flow nets, cross-sections, and

As part of the assessment of corrective interpretation that may be useful in a source

measures, the owner or operator will need to evaluation is presented in RCRA Facility

identify the nature of the source of the Investigation Guidance: Volume I -

release. The first step in this identification Development of an RFI Work Plan and

is a review of all available site information General Considerations for RCRA Facility

regarding facility design, wastes received, Investigations, (USEPA 1989a), RCRA

and onsite management practices. For Facility Investigation Guidance: Volume IV

newer facilities, this may be a relatively - Case Study Examples, (USEPA 1989d),

simple task. However, at some older and Practical Guide For Assessing and

facilities, detailed records of the facility's Remediating Contaminated Sites (USEPA

history may not be as well documented, 1989e).

making source definition more difficult.

Design, climatological, and waste-type Plume Delineation

information should be used to evaluate the

duration of the release, potential seasonal To effectively assess corrective measures,

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

logs, geophysical data, water level elevation

strata, isoconcentration maps of

contour maps. Additional guidance on data

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
Ground-Water Monitoring and Corrective Action

293

least one additional well must be added at and effective porosity) should be developed

the property boundary in the direction of for modeling contaminant transport if

contaminant migration to allow timely sufficient data are not available. Anisotropy

notification to potentially affected parties if and heterogeneity of the aquifer must be

contamination migrates offsite. evaluated, as well as magnitude and

The following circumstances may require present and predicted plume configuration.

additional monitoring wells:

! Facilities that have not determined the ground-water contamination at MSWLF

horizontal and vertical extent of the units involve pump and treat or in-situ

contaminant plume biological technologies (bio-remediation).

! Locations where the subsurface is on the size of the plume, the pumping

heterogeneous or where ground-water characteristics of the aquifer, and the

flow patterns are difficult to establish chemical transport phenomena. Source

! Mounding associated with MSWLF measures to reduce the rate of contaminant

units. migration should be included in the costs of

Because the requirements for additional water modeling of the plume may be

monitoring are site-specific, the regulation initiated to establish the following:

does not specifically establish cases where

additional wells are necessary or establish ! The locations and pumping rates of

the number of additional wells that must be withdrawal and/or injection wells

installed.

During the plume delineation process, the concentrations at exposure points

owner or operator is not relieved from

continuing the assessment monitoring ! Locations of additional monitoring wells

program.

The rate of plume migration and the change may have on ground-water remediation

in contaminant concentrations with time

must be monitored to allow prediction of the ! The effects of advection and dispersion,

extent and timing of impact to sensitive retardation, adsorption, and other

receptors. The receptors may include users attenuation processes on the plume

of both ground-water and surface water dimensions and contaminant

bodies where contaminated ground water concentrations.

may be discharged. In some cases, transfer

of volatile compounds from ground water to Any modeling effort must consider that

the soil and to the air may provide an simulations of remedial response measures

additional migration pathway. Information and contaminant transport are based on

regarding the aquifer characteristics (e.g., many necessary simplifying assumptions, 

hydraulic conductivity, storage coefficients,

duration of source inputs, to help explain

Currently, most treatment options for

The cost and duration of treatment depends

control and ground-water flow control

any remedial activity undertaken. Ground-

! Predictions of contaminant

! The effect that source control options
Subpart E

294

which affect the accuracy of the model. ! Stratigraphy and hydraulic properties of

These assumptions include boundary the aquifer

conditions, the degree and spatial variability

of anisotropy, dispersivity, effective ! Treatment concentration goals and

porosity, stratigraphy, and the algorithms objectives.

used to solve contaminant transport

equations. Model selection should be The owner or operator should consider

appropriate for the amount of data available, whether immediate measures to limit further

and the technical uncertainty of the model plume migration (e.g., containment options)

results must be documented by a sensitivity or measures to minimize further

analysis on the input parameters. A introduction of contaminants to ground

sensitivity analysis is generally done after water are necessary.

model calibration by varying one input

parameter at a time over a realistic range The process by which a remedial action is

and then evaluating changes in model undertaken will generally include the

output. For additional information on following activities:

modeling, refer to the Further Information

Section of Chapter 5.0 and the RCRA ! Hydrogeologic investigation, which may

Facility Investigation Guidance: Volume II include additional well installations,

- Soil, Groundwater and Subsurface Gas detailed vertical and lateral sampling to

Releases (USEPA, 1989b). characterize the plume, and core

Ground-Water Assessment sorption of constituents on the geologic

To assess the potential effectiveness of

corrective measures for ground-water ! Risk assessment, to determine the impact

contamination, the following information is on sensitive receptors, which may

needed: include identification of the need to

! Plume definition (includes the types, GWPSs

concentration, and spatial distribution of

the contaminants) ! Literature and technical review of

! The amenability of the contaminants to further study or implementation

specific treatment and potential for

contaminants to interfere with ! Evaluation of costs of different treatment

treatability options

! Fate of the contaminants (whether ! Estimation of the time required for

chemical transformations have, are, or completion of remediation under the

may be occurring, and the degree to different treatment options

which the species are sorbed to the

geologic matrix)

sampling to determine the degree of

matrix

develop treatment goals other than

treatment technologies considered for
Ground-Water Monitoring and Corrective Action

295

! Bench-scale treatability studies ! The anticipated cost of the remediation,

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

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
Subpart E

296

different media (e.g., air stripping of of a qualified professional and will

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 

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
Ground-Water Monitoring and Corrective Action

297

wastewater treatment may include sending pilot field studies to determine the

the contaminated water to a local publicly feasibility and the reliability of full-scale

owned treatment works (POTW) or to a treatment. It must be demonstrated that the

facility designed to treat the contaminants of treatment techniques will not cause

concern. Treated ground water may be re- degradation of a target chemical to another

injected, sent to a local POTW, or compound that has unacceptable health risks

discharged to a local body of surface water, and that is subject to further degradation.

depending on local, State, and Federal Alternative in-situ methods may also be

requirements. Typical treatment practices designed to increase the effectiveness of

that may be implemented include desorption or removal of contaminants from

coagulation and precipitation of metals, the aquifer matrix. Such methodologies

chemical oxidation of a number of organic may include steam stripping, soil flushing,

compounds, air stripping to remove volatile vapor extraction, thermal desorption, and

organic compounds, and biological solvent washing, and extraction for removal

degradation of other organics. of strongly sorbed organic compounds.

The rate of contaminant removal from unsaturated zones where residual

ground water will depend on the rate of contaminants may be sorbed to the geologic

ground-water removal, the cation exchange matrix during periodic fluctuations of the

capacity of the soil, and partition water table. Details of in-situ methods may

coefficients of the constituents sorbed to the be found in several sources: USEPA (1988);

soil (USEPA, 1988). As the concentration USEPA (1985); and Eckenfelder (1989).

of contaminants in the ground water is

reduced, the rate at which constituents Plume Containment

become partitioned from the soil to the

aqueous phase may also be reduced. The The purpose of plume containment is to

amount of flushing of the aquifer material limit the spread of the contaminants.

required to remove the contaminants to an Methods to contain plume movement

acceptable level will generally determine include passive hydraulic barriers, such as

the time frame required for restoration. This grout curtains and slurry walls, and active

time frame is site-specific and may last gradient control systems involving pumping

indefinitely. wells and french drains. The types of

In-situ methods may be appropriate for containment include:

some sites, particularly where pump and

treat technologies create serious adverse ! Water naturally unsuited for human

effects or where it may be financially consumption 

prohibitive. In-situ methods may include

biological restoration requiring pH control, ! Contaminants present in low

addition of specific micro-organisms, and/or concentration with low mobility

addition of nutrients and substrate to

augment and encourage degradation by ! Low potential for exposure to

indigenous microbial populations. contaminants and low risk associated

Bioremediation requires laboratory with exposure

treatability studies and 

These methods also may be used in

aquifer characteristics that favor plume
Subpart E

298

! Low transmissivity and low future user ! Preventing additional leachate

demand. generation that may reach a liner failure

Often, it may be advantageous for the owner shelter during operations or capping

or operator to consider implementing landfill areas that contribute to leachate

ground-water controls to inhibit further migrating from identified failure areas).

contamination or the spread of

contamination. If ground-water pumping is In extreme cases, excavation of deposited

considered for capturing the leading edge of wastes for treatment and/or offsite disposal

the contaminant plume, the contaminated may be considered.

water must be managed in conformance

with all applicable Federal and State Public Participation

requirements. Under most conditions, it is

necessary to consult with the regulatory The owner or operator is required to hold a

agencies prior to initiating an interim public meeting to discuss the results of the

remedial action. corrective action assessment and to identify

Source Control contacting local public agencies, town

Source control measures should be posting a notice in prominent local

evaluated to limit the migration of the newspapers, and making radio

plume. The regulation does not limit the announcements are effective. The public

definition of source control to exclude any meeting should provide a detailed

specific type of remediation. Remedies discussion of how the owner or operator has

must control the source to reduce or addressed the factors at §258.56(c)(1)-(4).

eliminate further releases by identifying and

locating the cause of the release (e.g., torn

geomembrane, excessive head due to 5.15 SELECTION OF REMEDY

blocked leachate collection system, leaking 40 CFR §258.57 (a)-(b)

leachate collection well or pipe). Source

control measures may include the following: 5.15.1 Statement of Regulation

! Modifying the operational procedures (a) Based on the results of the corrective

(e.g., banning specific wastes or measure assessment conducted under

lowering the head over the leachate §258.56, the owner or operator must

collection system through more frequent select a remedy that, at a minimum,

leachate removal) meets the standards listed in paragraph

! Undertaking more extensive and notify the State Director, within 14 days

effective maintenance activities (e.g., of selecting a remedy, that a report

excavate waste to repair a liner failure or describing the selected remedy has been

a clogged leachate collection system) placed in the operating record and how it

(e.g., using a portable or temporary rain

proposed remedies. Notifications, such as

governments, and State/Tribal governments,

(b) below. The owner or operator must

meets the standards in paragraph (b) of

this section.
Ground-Water Monitoring and Corrective Action

299

(b) Remedies must: and comply with waste management

(1) Be protective of human health and

the environment; 5.15.3 Technical Considerations

(2) Attain the ground-water protection The final method selected for

standard as specified pursuant to implementation must satisfy the criteria in

§§258.55(h) or (i); §258.57(b)(1)-(4). The report documenting

(3) Control the source(s) of releases so as meet these four criteria should include such

to reduce or eliminate, to the maximum information as:

extent practicable, further releases of

Appendix II constituents into the ! Theoretical calculations

environment that may pose a threat to

human health or the environment; and ! Comparison to existing studies and

(4) Comply with standards for histories

management of wastes as specified in

§258.58(d). ! Bench-scale or pilot-scale treatability

5.15.2 Applicability

These provisions apply to facilities that

have been required to perform corrective The demonstration presented in the report

measures. The selection of a remedy is must document the alternative option

closely related to the assessment process and selection process.

cannot be accomplished unless a sufficiently

thorough evaluation of alternatives has been

completed. The process of documenting the 5.16 SELECTION OF REMEDY

rationale for selecting a remedy requires 40 CFR §258.57 (c)

that a report be placed in the facility

operating record that clearly defines the 5.16.1 Statement of Regulation

corrective action objectives and

demonstrates why the selected remedy is (c) In selecting a remedy that meets the

anticipated to meet those objectives. The standards of §258.57(b), the owner or

State Director must be notified within 14 operator shall consider the following

days of the placement of the report in the evaluation factors:

operating records of the facility. The study

must identify how the remedy will be (1) The long- and short-term

protective of human health and the effectiveness and protectiveness of the

environment, attain the GWPS (either potential remedy(s), along with the

background, MCLs, or, in approved States, degree of certainty that the remedy will

health-based standards, if applicable), attain prove successful based on consideration

source control objectives, of the following:

standards.

the capability of the selected method to

results of similar treatment case

test results

! Waste management practices.
Subpart E

300

(i) Magnitude of reduction of existing (ii) The extent to which treatment

risks; technologies may be used.

(ii) Magnitude of residual risks in (3) The ease or difficulty of

terms of likelihood of further releases due implementing a potential remedy(s) based

to waste remaining following on consideration of the following types of

implementation of a remedy; factors:

(iii) The type and degree of long-term (i) Degree of difficulty associated with

management required, including constructing the technology;

monitoring, operation, and maintenance;

(iv) Short-term risks that might be the technologies;

posed to the community, workers, or the

environment during implementation of (iii) Need to coordinate with and obtain

such a remedy, including potential necessary approvals and permits from

threats to human health and the other agencies;

environment associated with excavation,

transportation, and redisposal or (iv) Availability of necessary

containment; equipment and specialists; and

(v) Time until full protection is (v) Available capacity and location of

achieved; needed treatment, storage, and disposal

(vi) Potential for exposure of humans

and environmental receptors to (4) Practicable capability of the owner

remaining wastes, considering the or operator, including a consideration of

potential threat to human health and the the technical and economic capability.

environment associated with excavation,

transportation, redisposal, or (5) The degree to which community

containment; concerns are addressed by a potential

(vii) Long-term reliability of the

engineering and institutional controls; 5.16.2 Applicability

and

(viii) Potential need for replacement of selecting a remedy for corrective action.

the remedy. The rule presents the considerations and

(2) The effectiveness of the remedy in evaluate when selecting the appropriate

controlling the source to reduce further corrective measure.

releases based on consideration of the

following factors:

(i) The extent to which containment

practices will reduce further releases;

(ii) Expected operational reliability of

services.

remedy(s).

These provisions apply to facilities that are

factors that the owner or operator must
Ground-Water Monitoring and Corrective Action

301

5.16.3 Technical Considerations releases of contaminants to the environment,

The owner or operator must consider remedy to meet or exceed the GWPSs. The

specific topics to satisfy the performance owner or operator must make a reasonable

criteria under selection of the final effort to estimate and quantify risks, based

corrective measure. These topics must be on exposure pathways and estimates of

addressed in the report documenting the exposure levels and durations. These

selection of a particular corrective action. estimates include risks for both groundThe general topic areas that must be water and cross-media contamination. 

considered include the following:

! The anticipated long- and short-term implemented, including excavation,

effectiveness of the corrective action transportation, re-disposal, and

! The anticipated effectiveness of source respect to potential exposure and risk to

reduction efforts human health and the environment. The

! The ease or difficulty of implementing as an integral component of the overall

the corrective measure corrective action. Health considerations

! The technical and economic practicable and the general public and provide

capability of the owner or operator contingency plans should an unanticipated

! The degree to which the selected remedy consider both long- and short-term cases

will address concerns raised by the before, during, and after implementation of

community. corrective actions.

Effectiveness of Corrective Action The time to complete the remedial activity

In selecting the remedial action, the direct financial impacts on the project

anticipated long-term and short-term management needs and financial capability

effectiveness should be evaluated. Long- of the owner or operator to meet the

term effectiveness focuses on the risks remedial objectives. The long-term costs of

remaining after corrective measures have the remedial alternatives and the long-term

been taken. Short-term effectiveness financial condition of the owner or operator

addresses the risks during construction and should be reviewed carefully. The

implementation of the corrective measure. implementation schedule should indicate

Review of case studies where similar quality control measures to assess the

technologies have been applied provide the progress of the corrective measure. 

best measures to judge technical

uncertainty, especially when relatively new The operational reliability of the corrective

technologies are applied. The long-term, measures should be considered. In addition,

post-cleanup effectiveness may be judged the institutional controls and management

on the ability of the proposed remedy to practices developed to assess the reliability

mitigate further should be identified. 

as well as on the feasibility of the proposed

The source control measures that will be

containment, should be evaluated with

source control measures should be viewed

must address monitoring risks to workers

exposure occur. Potential exposure should

must be estimated, because it will have
Subpart E

302

Effectiveness of Source Reduction Technical considerations, including pH

Source control measures identified in or the ability to inject nutrients, may need to

previous sections should be discussed in be considered, depending on the proposed

terms of their expected effectiveness. If treatment method. Potential impacts, such

source control consists of the removal and as potential cross-media contamination,

re-disposal of wastes, the residual materials, need to be reviewed as part of the overall

such as contaminated soils above the water feasibility of the project.

table, should be quantified and their

potential to cause further contamination The schedule of remedial activities should

evaluated. Engineering controls intended to identify the start and end points of the

upgrade or repair deficient conditions in following periods:

landfill component systems, including cover

systems, should be quantified in terms of ! Permitting phase

anticipated effectiveness according to

current and future conditions. This ! Construction and startup period, during

assessment may indicate to what extent it is which initial implementation success

technically and financially practicable to will be evaluated, including time to

make use of existing technologies. The correct any unexpected problems

decision against using a certain technology

may be based on health considerations and ! Time when full-scale treatment will be

the potential for unacceptable exposure(s) to initiated and duration of treatment period

both workers and the public.

Implementation of Remedial Action source control measures, including the

The ease of implementing the proposed associated 

remedial action will affect the schedule and with interim management and disposal of

startup success of the remedial action. The waste materials or treatment residuals.

following key factors need to be assessed:

! The availability of technical expertise identified early in the process and those

! Construction of equipment or implementation occurs in the shortest

technology practicable period. 

! The ability to properly manage and Practical Capability

dispose of wastes generated by

treatment The owner or operator must be technically

! The likelihood of obtaining local chosen remedial alternative and ensuring

permits and public support for the project completion, including provisions for

proposed project. future changes to the remedial plan after

control, ground-water extraction feasibility,

! Implementation and completion of

timeframe for solving problems

Items that require long lead times should be

tasks should be initiated early to ensure that

and financially capable of implementing the

progress is reviewed. If either technical or

financial capability is inadequate for a
Ground-Water Monitoring and Corrective Action

303

particular alternative, then other alternatives (3) Availability of treatment or disposal

with similar levels of protectiveness should capacity for wastes managed during

be considered for implementation. implementation of the remedy;

Community Concerns (4) Desirability of utilizing technologies

The public meetings held during assessment which may offer significant advantages

of alternative measures are intended to elicit over already available technologies in

public comment and response. The owner terms of effectiveness, reliability, safety,

or operator must, by means of meeting or ability to achieve remedial objectives;

minutes and a record of written comments,

identify which public concerns have been (5) Potential risks to human health and

expressed and addressed by corrective the environment from exposure to

measure options. In reality, the final contamination prior to completion of the

remedy selected and implemented will be remedy; 

one that the State regulatory agency, the

public, and the owner or operator agree to. (6) Resource value of the aquifer

5.17 SELECTION OF REMEDY (i) Current and future uses;

40 CFR §258.57 (d)

5.17.1 Statement of Regulation users;

(d) The owner or operator shall specify (iii) Ground-water quantity and

as part of the selected remedy a quality;

schedule(s) for initiating and completing

remedial activities. Such a schedule must (iv) The potential damage to wildlife,

require the initiation of remedial crops, vegetation, and physical structures

activities within a reasonable period of caused by exposure to waste constituent;

time taking into consideration the factors

set forth in paragraphs (d) (1-8). The (v) The hydrogeologic characteristic of

owner or operator must consider the the facility and surrounding land;

following factors in determining the

schedule of remedial activities: (vi) Ground-water removal and

(1) Extent and nature of contamination;

(2) Practical capabilities of remedial alternative water supplies.

technologies in achieving compliance with

ground-water protection standards (7) Practicable capability of the owner

established under §§258.55(g) or (h) and or operator.

other objectives of the remedy;

that are not currently available, but

including:

(ii) Proximity and withdrawal rate of

treatment costs; and

(vii) The cost and availability of

(8) Other relevant factors.
Subpart E

304

5.17.2 Applicability affects the ultimate treatment rate. The size

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

of the treatment facility and the groundwater 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.
Ground-Water Monitoring and Corrective Action

305

In setting the implementation schedule, the 5.18 SELECTION OF REMEDY

owner or operator should assess the risk to 40 CFR §258.57 (e)-(f)

human health and the environment within

the timeframe of reaching treatment 5.18.1 Statement of Regulation

objectives. If the risk is unacceptable,

considering health-based assessments of (e) The Director of an approved State

exposure paths and exposure limits, the may determine that remediation of a

implementation time schedule must be release of an Appendix II constituent

accelerated or the selected remedy altered to from a MSWLF unit is not necessary if

provide an acceptable risk level in a timely the owner or operator demonstrates to

manner. the satisfaction of the Director of an

Establishment of the schedule also may

include consideration of the resource value (1) The ground water is additionally

of the aquifer, as it pertains to current and contaminated by substances that have

future use, proximity to users, quality and originated from a source other than a

quantity of ground water, agricultural value MSWLF unit and those substances are

and uses (irrigation water source or impact present in concentrations such that

on adjacent agricultural lands), and the cleanup of the release from the MSWLF

availability of alternative supplies of water unit would provide no significant

of similar quantity and quality. Based on reduction in risk to actual or potential

these factors, a relative assessment of the receptors; or 

aquifer's resource value to the local

community can be established. Impacts to (2) The constituent(s) is present in

the resource and the degree of financial or ground water that:

health-related distress by users should be

considered. The implementation timeframe (i) Is not currently or reasonably

should attempt to minimize the loss of value expected to be a potential source of

of the resource to users. The possibility that drinking water; and

alternative water supplies will have to be

developed as part of the remedial activities (ii) Is not hydraulically connected with

may need to be considered. waters to which the hazardous

Because owners or operators may not be migrate in a concentration(s) that would

knowledgeable in remediation activities, exceed the ground-water protection

reliance on the owner or operator to devise standards established under §258.55(h)

the schedule for remediation may be or (i); or

impracticable. In these instances, use of an

outside firm to coordinate remediation (3) Remediation of the release(s) is

scheduling may be necessary. Similarly, technically impracticable; or

development of a schedule for which the

owner or operator cannot finance, when (4) Remediation results in unacceptable

other options exist that do allow for owner cross-media impacts.

or operator financing, should be prevented.

approved State that:

constituents are migrating or are likely to
Subpart E

306

(f) A determination by the Director of from implementing some or all of the

an approved State pursuant to paragraph corrective measure requirements. The

(e) above shall not affect the authority of owner or operator must demonstrate that

the State to require the owner or operator cleanup of a release from its MSWLF unit

to undertake source control measures or would provide no significant reduction in

other measures that may be necessary to risk to receptors due to concentrations of

eliminate or minimize further releases to constituents from the other source. 

the ground water, to prevent exposure to

the ground water, or to remediate the A waiver from corrective measures also may

ground water to concentrations that are be granted if the contaminated ground water

technically practicable and significantly is not a current or reasonably expected

reduce threats to human health or the potential future drinking water source, and

environment. it is unlikely that the hazardous constituents

5.18.2 Applicability exceedance of GWPS. The owner or

The criteria under §258.57(e) and (f) apply uppermost aquifer is not hydraulically

in approved States only. Remediation of the connected with a lower aquifer. The owner

release of an Appendix II constituent may or operator may seek an exemption if it can

not be necessary if 1) a source other than the be demonstrated that attenuation,

MSWLF unit is partly responsible for the advection/dispersion or other natural

ground-water contamination, 2) the resource processes can remove the threat to

value of the aquifer is extremely limited, 3) interconnected aquifers. The owner or

remediation is not technically feasible, or 4) operator may seek the latter exemption if

remediation will result in unacceptable the contaminated zone is not a drinking

cross-media impacts. The Director may water resource. 

determine that while total remediation is not

required, source control measures or partial The Director of an approved State may

remediation of ground water to waive cleanup requirements if remediation

concentrations that are technically is not technically feasible. In addition, the

practicable and significantly reduce risks is Director may wave requirements if

required. remediation results in unacceptable cross5.18.3 Technical Considerations that remediation is not technically feasible

There are four situations where an approved to this demonstration. Technical

State may not require cleanup of hazardous impracticabilities may be related to the

constituents released to ground water from accessibility of the ground water to

a MSWLF unit. If sufficient evidence exists treatment, as well as the treatability of the

to document that the ground water is ground water using practicable treatment

contaminated by a source other than the technologies. If the owner or operator can

MSWLF unit, the Director of an approved demonstrate that unacceptable cross-media

State may grant a waiver impacts are uncontrollable under a given

would migrate to waters causing an

operator must demonstrate that the

media impacts. A successful demonstration

must document specific facts that attribute

remedial option 
Ground-Water Monitoring and Corrective Action

307

(e.g., movement in response to ground- (iii) Demonstrates compliance with

water pumping or release of volatile ground-water protection standard

organics to the atmosphere) and that the no pursuant to paragraph (e) of this section.

action option is a less risky alternative, then

the Director of an approved State may (2) Implement the corrective action

determine that remediation is not necessary. remedy selected under §258.57; and

A waiver of remedial obligation does not (3) Take any interim measures necessary

necessarily release the owner or operator to ensure the protection of human health

from the responsibility of conducting source and the environment. Interim measures

control measures or minimal ground-water should, to the greatest extent practicable,

remediation. The State may require that be consistent with the objectives of and

source control be implemented to the contribute to the performance of any

maximum extent practicable to minimize remedy that may be required pursuant to

future risk of releases of contaminants to §258.57. The following factors must be

ground water or that ground water be treated considered by an owner or operator in

to the extent technically feasible. determining whether interim measures

5.19 IMPLEMENTATION OF THE (i) Time required to develop and

CORRECTIVE ACTION implement a final remedy;

PROGRAM 

40 CFR §258.58 (a) (ii) Actual or potential exposure of

5.19.1 Statement of Regulation receptors to hazardous constituents;

(a) Based on the schedule established (iii) Actual or potential contamination

under §258.57(d) for initiation and of drinking water supplies or sensitive

completion of remedial activities the ecosystems;

owner/operator must:

(1) Establish and implement a corrective water that may occur if remedial action is

action ground-water monitoring program not initiated expeditiously;

that:

(i) At a minimum, meets the hazardous constituents to migrate or be

requirements of an assessment released;

monitoring program under §258.55;

(ii) Indicates the effectiveness of the potential for exposure to hazardous

corrective action remedy; and constituents as a result of an accident or

are necessary:

nearby populations or environmental

(iv) Further degradation of the ground

(v) Weather conditions that may cause

(vi) Risks of fire or explosion, or

failure of a container or handling system;

and
Subpart E

308

(vii) Other situations that may pose ground water degradation or the spread of

threats to human health and the the contaminant plume, replacement of the

environment. system with an alternative measure may be

5.19.2 Applicability condition of the aquifer must be monitored

These provisions apply to facilities that are may be necessary to install additional

required to initiate and complete corrective monitoring wells to more clearly evaluate

actions. remediation progress. Also, if it becomes

The owner or operator is required to achievable technically, in a realistic timecontinue to implement its ground water frame, the performance objectives of the

assessment monitoring program to evaluate corrective measure must be reviewed and

the effectiveness of remedial actions and to amended as necessary.

demonstrate that the remedial objectives

have been attained at the completion of Interim Measures

remedial activities.

Additionally, the owner or operator must health and the environment exist prior to or

take any interim actions to protect human during implementation of the corrective

health and the environment. The interim action, the owner or operator is required to

measures must serve to mitigate actual take interim measures to protect receptors.

threats and prevent potential threats from These interim measures are typically shortbeing realized while a long-term term solutions to address immediate

comprehensive response is being developed. concerns and do not necessarily address

5.19.3 Technical Considerations measures may include activities such as

Implementation of the corrective measures high-volume withdrawal of ground water or

encompass all activities necessary to initiate response to equipment failures that occur

and continue remediation. The owner or during remediation (e.g., leaking drums). If

operator must continue assessment contamination migrates offsite, interim

monitoring to anticipate whether interim measures may include providing an

measures are necessary, and to determine alternative water supply for human,

whether the corrective action is meeting livestock, or irrigation needs. Interim

stated objectives. measures also pertain to source control

Monitoring Activities of the overall corrective action. This may

During the implementation period, ground- source material or in-situ treatment of the

water monitoring must be conducted to contaminated source. Interim measures

demonstrate the effectiveness of the should be developed with consideration

corrective action remedy. If the remedial given to maintaining conformity with the

action is not effectively curtailing further objectives of the final corrective action. 

warranted. The improvement rate of the

and compared to the cleanup objectives. It

apparent that the GWPS will not be

If unacceptable potential risks to human

long-term remediation objectives. Interim

control of ground-water migration through

activities that may be implemented as part

include activities such as excavation of the
Ground-Water Monitoring and Corrective Action

309

5.20 IMPLEMENTATION OF THE equipment, units, devices, or structures

CORRECTIVE ACTION that are:

PROGRAM

40 CFR §258.58 (b)-(d) (i) Technically practicable; and

5.20.1 Statement of Regulation (ii) Consistent with the overall

(b) An owner or operator may

determine, based on information (4) Notify the State Director within 14

developed after implementation of the days that a report justifying the

remedy has begun or other information, alternative measures prior to

that compliance with requirements of implementing the alternative measures

§258.57(b) are not being achieved has been placed in the operating record.

through the remedy selected. In such

cases, the owner or operator must (d) All solid wastes that are managed

implement other methods or techniques pursuant to a remedy required under

that could practicably achieve compliance §258.57, or an interim measure required

with the requirements, unless the owner under §258.58(a)(3), shall be managed in

or operator makes the determination a manner:

under §258.58(c).

(c) If the owner or operator determines and the environment; and

that compliance with requirements under

§258.57(b) cannot be practically achieved (2) That complies with applicable RCRA

with any currently available methods, the requirements.

owner or operator must:

(1) Obtain certification of a qualified

ground-water specialist or approval by The requirements of the alternative

the Director of an approved State that measures are applicable when it becomes

compliance with requirements under apparent that the remedy selected will not

§258.57(b) cannot be practically achieved achieve the GWPSs or other significant

with any currently available methods; objectives of the remedial program (e.g.,

(2) Implement alternate measures to determining that the selected corrective

control exposure of humans or the action approach will not achieve desired

environment to residual contamination, results, the owner or operator must

as necessary to protect human health and implement alternate corrective measures to

the environment; and achieve the GWPSs. If it becomes evident

(3) Implement alternate measures for obtainable by existing practicable

control of the sources of contamination, technology, the owner or operator must

or for removal or decontamination of implement actions to control exposure of

objective of the remedy.

(1) That is protective of human health

5.20.2 Applicability

protection of sensitive receptors). In

that the cleanup goals are not technically

humans or the environment from residual
Subpart E

310

contamination and to control the sources of ! Inappropriately applied technology

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

! 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 reevaluation period, the owner or operator

may suspend treatment only if continuation

of remedial activities clearly increases the

threat to human health and the environment.
Ground-Water Monitoring and Corrective Action

311

5.21 IMPLEMENTATION OF THE (iii) Accuracy of monitoring or

CORRECTIVE ACTION modeling techniques, including any

PROGRAM seasonal, meteorological, or other

40 CFR §258.58 (e)-(g) environmental variabilities that may

5.21.1 Statement of Regulation

(e) Remedies selected pursuant to water.

§258.57 shall be considered complete

when: (3) All actions required to complete the

(1) The owner or operator complies with

the ground-water protection standards (f) Upon completion of the remedy, the

established under §§258.55(h) or (i) at all owner or operator must notify the State

points within the plume of contamination Director within 14 days that a

that lie beyond the ground-water certification that the remedy has been

monitoring well system established under completed in compliance with the

§258.51(a). requirements of §258.58(e) has been

(2) Compliance with the ground-water certification must be signed by the owner

protection standards established under or operator and by a qualified ground-

§§258.55(h) or (i) has been achieved by water specialist or approved by the

demonstrating that concentrations of Director of an approved State.

Appendix II constituents have not

exceeded the ground-water protection (g) When, upon completion of the

standard(s) for a period of three certification, the owner or operator

consecutive years using the statistical determines that the corrective action

procedures and performance standards in remedy has been completed in accordance

§258.53(g) and (h). The Director of an with the requirements under paragraph

approved State may specify an (e) of this section, the owner or operator

alternative length of time during which shall be released from the requirements

the owner or operator must demonstrate for financial assurance for corrective

that concentrations of Appendix II action under §258.73.

constituents have not exceeded the

ground-water protection standard(s) §258.59 [Reserved].

taking into consideration:

(i) Extent and concentration of the

release(s); These criteria apply to facilities conducting

(ii) Behavior characteristics of the complete when, after 3 consecutive years of

hazardous constituents in the ground monitoring (or an alternative length of time

water; as identified by the Director), the results

affect the accuracy; and

(iv) Characteristics of the ground

remedy have been satisfied.

placed in the operating record. The

5.21.2 Applicability

corrective action. Remedies are considered

show significant statistical evidence that
Subpart E

312

Appendix II constituent concentrations are State. Upon completion of the remedial

below the GWPSs. Upon completion of all action, in accordance with §258.58(e), the

remedial actions, the owner or operator owner or operator is released from the

must certify to such, at which point the financial assurance requirements pertaining

owner or operator is released from financial to corrective actions.

assurance requirements.

5.21.3 Technical Considerations require an alternate time period (other than

The regulatory period of compliance is 3 determining an alternate period the Director

consecutive years at all points within the must consider the following:

contaminant plume that lie beyond the

ground-water monitoring system unless the ! The extent and concentration of the

Director of an approved State specifies an release(s)

alternative length of time. Compliance is

achieved when the concentrations of ! The behavior characteristics (fate and

Appendix II constituents do not exceed the transport) of the hazardous constituents

GWPSs for a predetermined length of time. in the ground water (e.g., mobility,

Statistical procedures in §258.53 must be persistence, toxicity, etc.)

used to demonstrate compliance with the

GWPSs. ! Accuracy of monitoring or modeling

The preferred statistical method for meteorological or other environmental

comparison is to construct a 99 percent variabilities that may affect accuracy

confidence interval around the mean of the

last 3 years of data and compare the upper ! The characteristics of the ground water

limit of the confidence interval to the (e.g., flow rate, pH, etc.).

GWPS. An upper limit less than the GWPS

is considered significant evidence that the Consideration of these factors may result in

standard is no longer being exceeded. The an extension or shortening of the time

confidence interval must be based on the required to show compliance with

appropriate model describing the remediation objectives.

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

The Director of an approved State may

3 years) to demonstrate compliance. In

techniques, including any seasonal,
Ground-Water Monitoring and Corrective Action

313

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, 169 pp.

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.
Subpart E

314

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, 84 pp.

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, 4 Edition. th

Lamb, B. and T. Kinney (1989). "Decommissioning Wells - Techniques and Pitfalls."

Proceedings of the Third National Outdoor Action Conference on Aquifer Restoration, GroundWater 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 D.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.
Ground-Water Monitoring and Corrective Action

315

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, 12 pp.

Puls, R.W., and M.J. Barcelona. 1989a. "Filtration of Ground Water Samples for Metals

Analysis." Hazardous Waste and Hazardous Materials, v. 6, No. 4.

Puls, R.W., and M.J. 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.
Subpart E

316

USEPA, (1989). "Statistical Analysis of Groundwater Monitoring Data at RCRA FacilitiesInterim 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 GroundWater 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"; EPA/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-R93-001; 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.
Ground-Water Monitoring and Corrective Action

317

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.
Subpart E

318
CHAPTER 6

SUBPART F

CLOSURE AND POST-CLOSURE
320

CHAPTER 6

SUBPART F

TABLE OF CONTENTS

6.1 INTRODUCTION ...................................................... 322

6.2 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

6.3 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

6.4 CLOSURE PLAN 40 CFR §258.60(c)-(d) ................................ 338

6.4.1 Statement of Regulation ......................................... 338

6.4.2 Applicability ................................................... 338

6.4.3 Technical Considerations ........................................ 338

6.5 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

6.6 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
321

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
322

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 lowmaintenance 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 (1) Have permeability less than or

40 CFR §258.60(a) equal to the permeability of any bottom

6.2.1 Statement of Regulation or a permeability no greater than 1 x 10

(a) Owners or operators of all

MSWLF units must install a final cover (2) Minimize infiltration through

system that is designed to minimize the closed MSWLF unit by the use of an

infiltration and erosion. The final cover infiltration layer that contains a

system must be designed and constructed minimum of 18-inches of an earthen

to: material, and

liner system or natural subsoils present,

-5

cm/sec, whichever is less, and
Closure and Post-Closure

323

(3) Minimize erosion of the final In approved States, an alternate cover

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 cm/sec

-5 

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.

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
Subpart F

324

long-term performance with minimal Figure 6-3a. Figure 6-3b shows a final

maintenance. Surface water run-off should cover system for a MSWLF unit that has

be properly controlled to prevent excessive both a double FML and double leachate

erosion and soil loss. Establishment of a collection system.

healthy vegetative layer is key to protecting

the cover from erosion. However, The earthen material used for the infiltration

consideration also must be given to layer should be free of rocks, clods, debris,

selecting plant species that are not deeply cobbles, rubbish, and roots that may

rooted because they could damage the increase the hydraulic conductivity by

underlying infiltration layer. In addition, promoting preferential flow paths. To

the cover system should be geotechnically facilitate run-off while minimizing erosion,

stable to prevent failure, such as sliding, the surface of the compacted soil should

that may occur between the erosion and have a minimum slope of 3 percent and a

infiltration layers, within these layers, or maximum slope of 5 percent after allowance

within the waste. Figure 6-1 illustrates the for settlement. It is critical that side slopes,

minimum requirements for the final cover which are frequently greater than 5 percent,

system. be evaluated for erosion potential.

Infiltration Layer Membrane and clay layers should be placed

The infiltration layer must be at least 18 penetration to avoid freeze-thaw effects

inches thick and consist of earthen material (U.S. EPA, 1989b). Freeze-thaw effects

that has a hydraulic conductivity may include development of microfractures

(coefficient of permeability) less than or or realignment of interstitial fines, which

equal to the hydraulic conductivity of any can increase the hydraulic conductivity of

bottom liner system or natural subsoils. clays by more than an order of magnitude

MSWLF units with poor or non-existent (U.S. EPA, 1990). Infiltration layers may

bottom liners possessing hydraulic be subject to desiccation, depending on

conductivities greater than 1 x 10 cm/sec climate and soil water retention in the

-5

must have an infiltration layer that meets the erosion layer. Fracturing and volumetric

1 x 10 cm/sec minimum requirement. shrinking of the clay due to water loss may -5

Figure 6-2 presents an example of a final increase the hydraulic conductivity of the

cover with a hydraulic conductivity less infiltration layer. Figure 6-4 shows the

than or equal to the hydraulic conductivity regional average depth of frost penetration;

of the bottom liner system. however, these values should not be used to

For units that have a composite liner with a for a particular area of concern at a

FML, or naturally occurring soils with very particular site. Information regarding the

low permeability (e.g., 1 x 10 cm/sec), the maximum depth of frost penetration for a

-8

Agency anticipates that the infiltration layer particular area can be obtained from the Soil

in the final cover will include a synthetic Conservation Service, local utilities,

membrane as part of the final cover. A final construction companies, and local

cover system for a MSWLF unit with a universities.

FML combined with a soil liner and

leachate collection system is presented in

below the maximum depth of frost

find the maximum depth of frost penetration
Closure and Post-Closure

325

Figure 6-1

Example of Minimum Final Cover Requirements
Subpart F

326

Figure 6-2

Example of Final Cover With Hydraulic Conductivity(K) < K of Liner
Figure 6-3a

Example of Final Cover Design for a MSWLF Unit With a FML

and Leachate Collection System

Figure 6-3b

Example of Final Cover Design for a MSWLF Unit With a Double FML and

Leachate Collection System

327
Subpart F

328

Figure 6-4

Regional Depth of Frost Penetration in Inches
Closure and Post-Closure

329

The infiltration layer is designed and available but should be verified as

constructed in a manner similar to that used reasonable for the site modeled. Outputs

for soil liners (U.S. EPA, 1988), with the from the model include precipitation, runfollowing differences: off, percolation through the base of each

! Because the cover is generally not and lateral drainage from each profile. The

subject to large overburden loads, the model also calculates the maximum head on

issue of compressive stresses is less the barrier soil layer of each subprofile and

critical unless post-closure land use will the maximum and minimum soil moisture

entail construction of objects that exert content of the evaporative zone. Data from

large amounts of stress. the model are presented in a tabular report

! The soil cover is subject to loadings used and a summary of the simulation

from settlement of underlying results. Results are presented in several

materials. The extent of settlement tables of daily, monthly, and annual totals

anticipated should be evaluated and a for each year specified. A summary of the

closure and post-closure maintenance outputs also is produced, including average

plan should be designed to compensate monthly totals, average annual totals, and

for the effects of settlement. peak daily values for several simulation

! Direct shear tests performed on

construction materials should be The HELP model may be used to estimate

conducted at lower shear stresses than the hydraulic performance of the cover

those used for liner system designs. system designed for a MSWLF unit. Useful

The design of a final cover is site-specific includes surface run-off, duration and

and the relative performance of cover design quantity of water storage within the erosion

options may be compared and evaluated by layer, and net infiltration through the cover

the HELP (Hydrologic Evaluation of system to evaluate whether leachate will

Landfill Performance) model. The HELP accumulate within the landfill. For the

model was developed by the U.S. Army model to be used properly, the HELP Model

Corps of Engineers for the U.S. EPA and is User's Guide and documentation should be

widely used for evaluating expected consulted.

hydraulic performance of landfill

cover/liner systems (U.S. EPA, 1988). Geomembranes

The HELP program calculates daily, If a geomembrane is used as an infiltration

average, and peak estimates of water layer, the geomembrane should be at least

movement across, into, through, and out of 20 mils (0.5 mm) in thickness, although

landfills. The input parameters for the some geomembrane materials may need to

model include soil properties, precipitation be a greater thickness (e.g., a minimum

and other climatological data, vegetation thickness of 60 mils is recommended for

type, and landfill design information. HDPE because of the difficulties in making

Default climatologic and soil data are consistent field seams in thinner material).

cover layer subprofile, evapotranspiration,

format and include the input parameters

variables (U.S. EPA, 1988).

information provided by the HELP model
Subpart F

330

Increased thickness and tensile strengths X = RKLSCP

may be necessary to prevent failure under

stresses caused by construction and waste where X = Soil loss (tons/acre/year)

settlement during the post-closure care R = Rainfall erosion index

period. The strength, resistance to sliding, K = Soil erodibility index

hydraulic performance, and actual thickness L = Slope length factor

of geomembranes should be carefully S = Slope gradient factor

evaluated. The quality and performance of C = Crop management factor

some textured sheets may be difficult to P = Erosion control practice.

evaluate due to the variability of the

textured surface. Values for the Universal Soil Loss Equation

Erosion Layer Soil Conservation Service (SCS) technical

The thickness of the erosion layer is Rainfall Erosion Losses, Guidebook 537"

influenced by depth of frost penetration and (1978), available at local SCS offices

erosion potential. This layer is also used to located throughout the United States. State

support vegetation. The influence of frost or local SCS offices can provide factors to

penetration was discussed previously on be used in the soil loss equation that are

page 6-3. appropriate to a given area of the country.

Erosion can adversely affect the ratio due to the slope of the site as used in

performance of the final cover of a MSWLF the Universal Soil Loss Equation. Loss

unit by causing rills that require from wind erosion can be determined by the

maintenance and repair. As previously following equation (U.S. EPA, 1989a):

stated, a healthy vegetative layer can protect

the cover from erosion; conversely, severe X' = I'K'C'L'V'

erosion can affect the vegetative growth.

Extreme erosion may lead to the exposure of where X' = Annual wind erosion

the infiltration layer, initiate or contribute to I' = Field roughness factor

sliding failures, or expose the waste. K' = Soil erodibility index

Anticipated erosion due to surface water C' = Climate factor

run-off for given design criteria may be L' = Field length factor

approximated using the USDA Universal V' = Vegetative cover factor.

Soil Loss Equation (U.S. EPA, 1989a). By

evaluating erosion loss, the design may be A vegetative cover not only improves the

optimized to reduce maintenance through appearance of the site, but it also controls

selection of the best available soil materials erosion of the final cover; a vegetated cover

or by initially adding excess soil to increase may require only minimal maintenance.

the time required before maintenance is The vegetation component of the erosion

needed. Parameters in the equation include layer should have the following

the following:

parameters may be obtained from the U. S.

guidance document entitled "Predicting

Figure 6-5 can be used to find the soil loss
Closure and Post-Closure

331

Figure 6-5

Soil Erosion Due to Slope
Subpart F

332

specifications and characteristics (U.S. Selection of the soil for the vegetative cover

EPA, 1989b): (erosion layer) should include consideration

! Locally adapted perennial plants that species of the vegetation selected, mulching,

are resistant to drought and temperature and seeding time. Loamy soils with a

extremes; sufficient organic content generally are

! Roots that will not disrupt the low- sand in loamy soils provides an environment

permeability layer; conducive to seed germination and root

! The ability to thrive in low-nutrient soil

with minimum nutrient addition; The Director of an approved State can allow

! Sufficient plant density to minimize problems (e.g., the use of pavement or other

cover soil erosion; material) in areas that are not capable of

! The ability to survive and function with

little or no maintenance (i.e., selfsupportive); and 6.3 ALTERNATIVE FINAL COVER

! Sufficient variety of plant species to 40 CFR §258.60(b)

continue to achieve these characteristics

and specifications over time. 6.3.1 Statement of Regulation

The use of deep-rooted shrubs and trees is (b) The Director of an approved

generally inappropriate because the root State may approve an alternative final

systems may penetrate the infiltration layer cover design that includes:

and create preferential pathways of

percolation. Plant species with fibrous or (1) An infiltration layer that

branching root systems are suited for use at achieves an equivalent reduction in

landfills, and can include a large variety of infiltration as the infiltration layer

grasses, herbs (i.e., legumes), and shallow- specified in paragraphs (a)(1) and (a)(2)

rooted plants. The suitable species in a of this section, and 

region will vary, dependent on climate and

site-specific factors such as soil type and (2) An erosion layer that provides

slope gradient and aspect. The timing of equivalent protection from wind and

seeding (spring or fall in most climates) is water erosion as the erosion layer

critical to successful germination and specified in (a)(3) of this section.

establishment of the vegetative cover (U.S.

EPA, 1989b). Temporary winter covers 6.3.2 Applicability

may be grown from fast-growing seed stock

such as winter rye. The Director of an approved State may

of soil type, nutrient and pH levels, climate,

preferred. The balance of clay, silt, and

growth (USEPA, 1988).

alternate designs to address vegetative

sustaining plant growth.

DESIGN

approve alternative final cover systems that

can achieve equivalent performance as 
Closure and Post-Closure

333

the minimum design specified in The erosion layer may be made of asphalt or

§258.60(a). This provides an opportunity to concrete. These materials promote run-off

incorporate different technologies or with negligible erosion. However, asphalt

improvements into cover designs, and to and concrete deteriorate due to thermal

address site-specific conditions. expansion and due to deformation caused by

6.3.3 Technical Considerations over the landfill cover in areas where

An alternative material and/or an alternative rain, or temperature extremes commonly

thickness may be used for an infiltration cause deterioration of vegetative covers

layer as long as the infiltration layer (U.S. EPA, 1989b).

requirements specified in §258.60(a)(1) and

(a)(2) are met. Other Considerations

For example, an armored surface (e.g., one Additional Cover System Components

composed of cobble-rich soils or soils rich

in weathered rock fragments) could be used To reduce the generation of post-closure

as an alternative to the six-inch erosion leachate to the greatest extent possible,

layer. An armored surface, or hardened cap, owners and operators can install a

is generally used in arid regions or on steep composite cover made of a geomembrane

slopes where the establishment and and a soil component with low hydraulic

maintenance of vegetation may be hindered conductivity. The hydraulic properties of

by lack of soil or excessive run-off. these components are discussed in Chapter

The materials used for an armored surface

typically are (U.S. EPA, 1989b): Other components that may be used in the

! Capable of protecting the underlying a gas vent layer, and a biotic barrier layer.

infiltration layer during extreme These components are discussed in the

weather events of rainfall and/or wind; following sections and are shown in Figure

! Capable of accommodating settlement

of the underlying material without Drainage Layer

compromising the component;

! Designed with a surface slope that is soil or geosynthetic drainage material, may

approximately the same as the be constructed between the erosion layer

underlying soil (at least 2 percent and the underlying infiltration layer. The

slope); and drainage layer in a final cover system

! Capable of controlling the rate of soil infiltrated through the erosion layer after

erosion. surface run-off and evapotranspiration

subsidence. Crushed rock may be spread

weather conditions such as wind, heavy

4 (Subpart D).

final cover system include a drainage layer,

6-6.

A permeable drainage layer, constructed of

removes percolating water that has

losses. By removing water in contact with

the low-permeability layer, the potential for
Figure 6-6

Example of an Alternative Final Cover Design
Closure and Post-Closure

335

leachate generation is diminished. Caution evaluate the relative expected performance

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 cm/sec to 1 x 10 -2 -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

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 cm/sec to 1 x -2

10 cm/sec. Transmissivity can be

-3

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 coarsegrained 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
Subpart F

336

to an exterior collection point can be Biotic Layer

provided by means such as horizontal pipes

patterned laterally throughout the gas vent Deep plant roots or burrowing animals

layer, which channel gases to vertical risers (collectively called biointruders) may

or lateral headers. If vertical risers are used, disrupt the drainage and the low hydraulic

their number should be minimized (as they conductivity layers, thereby interfering with

are frequently vandalized) and located at the drainage capability of the layers. A 30-

high points in the cross-section (U.S. EPA, cm (12-inch) biotic barrier of cobbles

1989b). Condensates will form within the directly beneath the erosion layer may stop

gas collection pipes; therefore, the design the penetration of some deep-rooted plants

should address drainage of condensate to and the invasion of burrowing animals.

prevent blockage by its accumulation in low Most research on biotic barriers has been

points. done in, and is applicable to arid areas.

The most obvious potential problem with time-released herbicide into the matrix or on

gas collection systems is the possibility of the surface of the polymer also may be used

gas vent pipe penetrations through the cover to retard plant roots. The longevity of these

system. Settlement within the landfill may products requires evaluation if the cover

cause concentrated stresses at the system is to serve for longer than 30 to 50

penetrations, which could result in years (USEPA, 1991).

infiltration layer or pipe failure. If a

geomembrane is used in the infiltration Settlement and Subsidence

layer, pipe sleeves, adequate flexibility and

slack material should be provided at these Excessive settlement and subsidence, caused

connections when appropriate. by decomposition and consolidation of the

Alternatively, if an active gas control wastes, can impair the integrity of the final

system is planned, penetrations may be cover system. Specifically, settlement can

carried out through the sides of the cover contribute to: 

directly above the liner anchor trenches

where effects of settlement are less ! Ponding of surface water on the cap;

pronounced. The gas collection system also

may be connected to the leachate collection ! Disruption of gas collection pipe

system, both to vent gases that may form systems;

inside the leachate collection pipes and to

remove gas condensates that form within the ! Fracturing of low permeability

gas collection pipes. This method generally infiltration layers; and

is not preferred because if the leachate

collection pipe is full, gas will not be able to ! Failure of geomembranes.

move through the system. Landfill gas

systems are also discussed in Chapter 3 The degree and rate of waste settlement are

(Subpart C). difficult to estimate. Good records

Geosynthetic products that incorporate a

regarding the type, quantity, and location of

waste materials disposed will improve the

estimate. Settlement due to consolidation
Closure and Post-Closure

337

may be minimized by compacting the waste corrected during post-closure maintenance.

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 

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).
Subpart F

338

6.4 CLOSURE PLAN 1993, must prepare a closure plan and place

40 CFR §258.60(c)-(d) the plan in the operating record. The plan

6.4.1 Statement of Regulation that will be followed to close the unit at any

(c) The owner or operator must time it reaches its waste disposal capacity.

prepare a written closure plan that

describes the steps necessary to close all The closure plan must include at least the

MSWLF units at any point during their following information:

active life in accordance with the cover

design requirements in §258.60(a) or (b), ! A description of the final cover and the

as applicable. The closure plan, at a methods and procedures to be used to

minimum, must include the following install the cover;

information:

(1) A description of the final have to be covered (typically this is the

cover, designed in accordance with area that will exist when the final full

§258.60(a) and the methods and capacity is attained); and

procedures to be used to install the cover;

(2) An estimate of the largest area

of the MSWLF unit ever requiring a final The area requiring cover should be

cover as required under §258.60(a) at any estimated for the operating period from

time during the active life; initial receipt of waste through closure.

(3) An estimate of the maximum The closure plan must be prepared and

inventory of wastes ever on-site over the placed in the operating record before

active life of the landfill facility; and October 9, 1993 or by the initial receipt of

(4) A schedule for completing all operator must notify the State Director

activities necessary to satisfy the closure when the plan has been completed and

criteria in §258.60. placed in the operating record.

(d) The owner or operator must 6.4.3 Technical Considerations

notify the State Director that a closure

plan has been prepared and placed in the The closure plan is a critical document that

operating record no later than the describes the steps that an owner or operator

effective date of this part, or by the initial will take to ensure that all units will be

receipt of waste, whichever is later. closed in a manner that is protective of

6.4.2 Applicability plans provide the basis for cost estimates

An owner or operator of any MSWLF unit responsibility that must be demonstrated.

that receives wastes on or after October 9,

must describe specific steps and activities

time after it first receives waste through the

! An estimate of the largest area that will

! A schedule for completing closure.

waste, whichever is later. The owner or

human health and the environment. Closure

that in turn establish the amount of financial
Closure and Post-Closure

339

The closure plan must describe all areas of ! Preparing construction contract

the MSWLF unit that are subject to Part 258 documents and securing a contractor;

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;

! 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
Subpart F

340

§258.60(f), an owner or operator must notify the State Director that a

notify the State Director that a notice of certification, signed by an independent

the intent to close the unit has been registered professional engineer or

placed in the operating record. approved by Director of an approved

(f) The owner or operator must completed in accordance with the closure

begin closure activities of each MSWLF plan, has been placed in the operating

unit no later than 30 days after the date record.

on which the MSWLF unit receives the

known final receipt of wastes or, if the (i)(1) Following closure of all

MSWLF unit has remaining capacity and MSWLF units, the owner or operator

there is a reasonable likelihood that the must record a notation on the deed to the

MSWLF unit will receive additional landfill facility property, or some other

wastes, no later than one year after the instrument that is normally examined

most recent receipt of wastes. Extensions during title search, and notify the State

beyond the one-year deadline for Director that the notation has been

beginning closure may be granted by the recorded and a copy has been placed in

Director of an approved State if the the operating record. 

owner or operator demonstrates that the

MSWLF unit has the capacity to receive (2) The notation on the deed must

additional wastes and the owner or in perpetuity notify any potential

operator has taken and will continue to purchaser of the property that:

take all steps necessary to prevent threats

to human health and the environment (i) The land has been used as a

from the unclosed MSWLF unit. landfill facility; and

(g) The owner or operator of all (ii) Its use is restricted under

MSWLF units must complete closure §258.61(c)(3).

activities of each MSWLF unit in

accordance with the closure plan within (j) The owner or operator may

180 days following the beginning of request permission from the Director of

closure as specified in paragraph (f). an approved State to remove the notation

Extensions of the closure period may be from the deed if all wastes are removed

granted by the Director of an approved from the facility.

State if the owner or operator

demonstrates that closure will, of 6.5.2 Applicability

necessity, take longer than 180 days and

he has taken and will continue to take all These closure requirements are applicable to

steps to prevent threats to human health all MSWLF units that receive wastes on or

and the environment from the unclosed after October 9, 1993. The owner or

MSWLF unit. operator is required to:

(h) Following closure of each MSWLF ! Notify the State Director of the intent

unit, the owner or operator must to close;

State, verifying that closure has been
Closure and Post-Closure

341

! 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 groundwater 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
Subpart F

342

typically examined during a title search, that care must be conducted for 30 years,

the property was used as a MSWLF unit and except as provided under paragraph (b)

that its use is restricted under 40 CFR of this part, and consist of at least the

§258.61(c)(3). Section 258.61(c)(3) states: following:

"... Post-closure use of the property shall (1) Maintaining the integrity and

not disturb the integrity of the final cover, effectiveness of any final cover, including

liner(s), or any other components of the making repairs to the cover as necessary

containment systems or the function of the to correct the effects of settlement,

monitoring systems unless necessary to subsidence, erosion, or other events, and

comply with the requirements of Part preventing run-on and run-off from

258...and... The Director of an approved eroding or otherwise damaging the final

State may approve any other disturbance if cover;

the owner or operator demonstrates that

disturbance of the final cover, liner, or other (2) Maintaining and operating the

component of the containment system, leachate collection system in accordance

including any removal of waste, will not with the requirements in §258.40, if

increase the potential threat to human health applicable. The Director of an approved

or the environment." State may allow the owner or operator to

These restrictions are described further in operator demonstrates that leachate no

Section 6.7 (Post-Closure Plan) of this longer poses a threat to human health

document. and the environment;

The owner or operator may request (3) Monitoring the ground water

permission from the Director of an approved in accordance with the requirements of

State to remove the notation to a deed. The Subpart E and maintaining the groundrequest should document that all wastes water monitoring system, if applicable;

have been removed from the facility. Such and

documentation may include photographs,

ground-water and soil testing in the area (4) Maintaining and operating the

where wastes were deposited, and reports of gas monitoring system in accordance with

waste removal activity. the requirements of §258.23.

6.6 POST-CLOSURE CARE care period may be:

REQUIREMENTS

40 CFR §258.61 (1) Decreased by the Director of

6.6.1 Statement of Regulation operator demonstrates that the reduced

(a) Following closure of each MSWLF health and the environment and this

unit, the owner or operator must conduct demonstration is approved by the

post-closure care. Post-closure Director of an approved State; or

stop managing leachate if the owner or

(b) The length of the post-closure

an approved State if the owner or

period is sufficient to protect human
Closure and Post-Closure

343

(2) Increased by the Director of an does not pose a threat to human health and

approved State if the Director of an the environment.

approved State determines that the

lengthened period is necessary to protect 6.6.3 Technical Considerations

human health and the environment.

6.6.2 Applicability and maintenance may be necessary to keep

Post-closure care requirements apply to Maintenance may include inspection,

MSWLF units that stop receiving waste testing, and cleaning of leachate collection

after October 9, 1993. They also apply to and removal system pipes, repairs of final

units that stop receiving waste between cover, and repairs of gas and ground-water

October 9, 1991, and October 9, 1993, and monitoring networks.

fail to complete closure within six months

of the final receipt of waste. Inspections should be made on a routine

Post-closure care requirements are focused check that routine inspections are

on operating and maintaining the proper completed. Records of inspections detailing

functions of four systems that prevent or observations should be kept in a log book so

monitor releases from the MSWLF unit: that changes in any of the MSWLF units can

! Cover system; kept detailing changes in post-closure care

! Leachate collection system; will not affect post-closure care due to lack

! Ground-water monitoring system; and activities and frequency of inspections are

! Gas monitoring system. are monitored and maintained for as long as

Owners or operators must comply with these environment. 

requirements for a period of 30 years

following closure. In approved States, the Inspection of the final cover may be

post-closure care period may be shortened if performed on the ground and through aerial

the owner or operator demonstrates to the photography. Inspections should be

satisfaction of the Director that human conducted at appropriate intervals and the

health and the environment are protected. condition of the facility should be recorded

Conversely, the Director may determine that with notes, maps, and photographs. The

a period longer than 30 years is necessary. inspector should take notice of eroded

The requirement to operate and maintain the banks, patches of dead vegetation, animal

leachate collection system may be burrows, subsidence, and cracks along the

eliminated by the Director of an approved cover. The inspector also should note the

State if the owner or operator demonstrates condition of concrete structures (e.g.,

that leachate manholes), leachate collection and removal

When the final cover is installed, repairs

the cover in good working order.

basis. A schedule should be developed to

be monitored; in addition, records should be

personnel to ensure that changing personnel

of knowledge of routine activities. The

subject to State review to ensure that units

is necessary to protect human health and the
Subpart F

344

pipes, gas monitoring systems, and Erosion may lead to increased infiltration of

monitoring wells. surface water into the landfill. Areas

For larger facilities, annual aerial

photography may be a useful way to Certain types of vegetative cover (e.g., turfdocument the extent of vegetative stress and type grasses) may require mowing at least

settlement if either of these has been two times a year. Mowing can aid in

observed during routine inspections. It is suppression of weed and brush growth, and

important to coordinate the photography can increase the vigor of certain grass

with the site "walkover" to verify species. Alternatively, certain cover types

interpretations made from aerial (e.g., native prairie grasses) require less

photographs. Aerial photography should frequent mowing (once every three years)

not be used in place of a site walkover but in and may be suitable for certain climates and

conjunction with the site walkover. An facilities where a low-maintenance regime

EPA document (U.S. EPA 1987) provides is preferable. For certain cover types,

further information on using aerial fertilization schedules may be necessary to

photography for inspecting a landfill sustain desirable vegetative growth.

facility. (See the Reference section at the Fertilization schedules should be based on

end of this chapter.) the cover type present. Annual or biennial

Topographic surveys of the landfill unit(s) grasses, while legumes and native

may be used to determine whether vegetation may require little or no fertilizer

settlement has occurred. These should be once established. Insecticides may be used

repeated every few years until settlement to eliminate insect populations that are

behavior is established. If settlement plates detrimental to vegetation. Insecticides

are used, they should be permanent and should be carefully selected and applied

protected from vandalism and accidental with consideration for potential effects on

disturbance (U.S. EPA, 1987). Depressions surface water quality.

caused by settlement may lead to ponding

and should be filled with soil. Excessive Some leachate collection and removal

settlement may warrant reconstructing or systems have been designed to allow for

adding to portions of the infiltration layer. inspections in an effort to ensure that they

Damage caused by settlement such as are working properly. Leachate collection

tension cracks and tears in the synthetic and removal pipes may be flushed and

membrane should be repaired. pressure-cleaned on a regular schedule (e.g.,

Cover systems that have areas where the sediment and precipitation and to prevent

slope is greater than 5 percent may be biological fouling.

susceptible to erosion. Large and small rills

(crevices) may form along the cover where Similarly, gas collection systems should be

water has eroded the cover. This may lead inspected to ensure that they are working

to exposure of the synthetic geomembrane properly. Vents should be checked to

and, in severe cases, depending on the cover ensure they are not clogged by foreign

system installed, exposure of the waste. matter such as rocks. If not working

showing signs of erosion should be repaired.

fertilization may be necessary for certain

annually) to reduce the accumulation of
Closure and Post-Closure

345

properly, the gas collection systems should 6.7 POST-CLOSURE PLAN 

be flushed and pressure-cleaned. 40 CFR §258.61(c)-(e)

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.

6.7.1 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 postclosure 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 postclosure plan has been prepared and

placed in the operating record no later 
Subpart F

346

than the effective date of this part, ! The procedure for verifying that postOctober 9, 1993, or by the initial receipt closure care was provided in

of waste, whichever is later. accordance with the plan.

(e) Following completion of the In approved States only, the owner or

post-closure care period for each operator may request the Director to

MSWLF unit, the owner or operator approve a use that disturbs the final cover

must notify the State Director that a based on a demonstration that the use will

certification, signed by an independent not increase the potential threat to human

registered professional engineer or health and the environment.

approved by the Director of an approved

State, verifying that post-closure care has 6.7.3 Technical Considerations

been completed in accordance with the

post-closure plan, has been placed in the The State Director must be notified that a

operating record. post-closure plan, describing the

6.7.2 Applicability MSWLF unit, has been placed in the

Owners and operators of existing units, new should provide a schedule for routine

units, and lateral expansions of existing maintenance of the MSWLF unit systems.

MSWLF units that stop receiving waste These systems include the final cover

after October 9, 1993 are required to system, the leachate collection and removal

provide a post-closure plan. MSWLF units system, and the landfill gas and groundthat received the final waste shipment water monitoring systems.

between October 9, 1991 and October 9,

1993 but failed to complete installation of a The plan must include the name, address,

final cover system within six months of the and telephone number of the person or

final receipt of waste also are required to office to contact regarding the facility

provide a post-closure plan. throughout the post-closure period.

The post-closure plan describes the property during the post-closure period must

monitoring activities that will be conducted be provided in the plan. These uses may not

throughout the 30-year period. The plan disturb the integrity of the final cover

also establishes: system, the liner system, and any other

! The schedule or frequency at which monitoring systems unless necessary to

these activities are conducted; comply with the requirements of Part 258.

! Name, address, and telephone number of MSWLF components must be approved by

a person to contact about the facility; the Director of an approved State. An

! A description of a planned use that does include remedial action necessary to

not disturb the final cover; and minimize the threat to human health and the

maintenance activities required for each

operating record. The post-closure plan

Additionally, the planned uses of the

components of the containment or

Any other disturbances to any of the

example of an acceptable disturbance may

environment.
Closure and Post-Closure

347

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 postclosure 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.
Subpart F

348

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.
Closure and Post-Closure

349

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.