EPA Document Regardig Airport Location Criteria
CHAPTER 2
SUBPART B
LOCATION CRITERIA
TABLE OF CONTENTS
2.1 INTRODUCTION
2.2 AIRPORT SAFETY 40 CFR Section Section 258.10
2.2.1 Statement of Regulation
2.2.2 Applicability
2.2.3 Technical Considerations
2.3 FLOODPLAINS 40 CFR Section 258.11
2.3.1 Statement of Regulation
2.3.2 Applicability
2.3.3 Technical Considerations
Floodplain Identification
Engineering Considerations
2.4 WETLANDS 40 CFR Section 258.12
2.4.1 Statement of Regulation
2.4.2 Applicability
2.4.3 Technical Considerations
2.5 FAULT AREAS 40 CFR Section 258.13
2.5.1 Statement of Regulation
2.5.2 Applicability
2.5.3 Technical Considerations
2.6 SEISMIC IMPACT ZONES 40 CFR Section 258.14
2.6.1 Statement of Regulation
2.6.2 Applicability
2.6.3 Technical Considerations
Background on Seismic Activity
Information Sources on Seismic Activity
Landfill Planning and Engineering in
Areas of Seismic Activity
2.7 UNSTABLE AREAS 40 CFR Section 258.15
2.7.1 Statement of Regulation
2.7.2 Applicability
2.7.3 Technical Considerations
Types of Failures
Subsurface Exploration Programs
Methods of Slope Stability Analysis
Design for Slope Stabilization
Monitoring
Engineering Considerations for Karst
Terrain
2.8 CLOSURE OF EXISTING MUNICIPAL SOLID WASTE LANDFILL
UNITS 40 CFR Section 258.16
2.8.1 Statement of Regulation
2.8.2 Applicability
2.8.3 Technical Considerations
2.9 FURTHER INFORMATION
2.9.1 References
2.9.2 Organizations
2.9.3 Models
APPENDIX I - FAA Order 5200.5A
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.
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TABLE 2-1
LOCATION CRITERIA STANDARDS
Make
Demonstra-
tion to
"Director
of an
Approved
State/ Existing
Tribe" OR Units Must
Retain Close if
Applies to Demonstra- Demonstra-
Applies to New Units tion in tion
Restricted Existing and Lateral Operating Cannot
Location Units Expansions Record be Made
Airport Yes Yes Operating Yes
Record
Floodplains Yes Yes Operating Yes
Record
Wetlands No Yes Director N/A
Fault Areas No Yes Director N/A
Seismic No Yes Director N/A
Impact Zones
Unstable Yes Yes Operating Yes
Areas Record
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2.2 AIRPORT SAFETY 40 CFR Section 258.10
2.2.1 Statement of Regulation
(a) Owners or operators of new MSWLF units, existing
MSWLF units, and lateral expansions that are located within
10,000 feet (3,048 meters) of any airport runway end used by
turbojet aircraft or within 5,000 feet (1,524 meters) of any
airport runway end used by only piston-type aircraft must
demonstrate that the units are designed and operated so that
the MSWLF unit does not pose a bird hazard to aircraft.
(b) Owners or operators proposing to site new MSWLF
units and lateral expansions within a five-mile radius of
any airport runway end used by turbojet or piston-type
aircraft must notify the affected airport and the Federal
Aviation Administration (FAA).
(c) The owner or operator must place the demonstration
in paragraph (a) in the operating record and notify the
State Director that it has been placed in the operating
record.
(d) For purposes of this section:
(1) Airport means public-use airport open to the public
without prior permission and without restrictions within the
physical capacities of available facilities.
(2) Bird hazard means an increase in the likelihood of
bird/aircraft collisions that may cause damage to the
aircraft or injury to its occupants.
2.2.2 Applicability
Owners and operators of new MSWLF units, existing MSWLF
units, and lateral expansions of existing units that are
located near an airport, who cannot demonstrate that the
MSWLF unit does not pose a bird hazard, must close their
units.
This requirement applies to owners and operators of
MSWLF units located within 10,000 feet of any airport runway
end used by turbojet aircraft or within 5,000 feet of any
airport runway end used only by piston-type aircraft. This
applies to airports open to the public without prior
permission for use, and where use of available facilities is
not restricted. If the above conditions are present, the
owner or operator must demonstrate that the MSWLF unit does
not pose a bird hazard to aircraft and notify the State
Director that the demonstration has been placed in the
operating record. If the demonstration is not made,
existing units must be closed in accordance with Section
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 pose bird hazards to aircraft. The
regulation defines a "danger zone" within which particular
care must be taken to ensure that no bird hazard arises.
Owners or operators proposing to site new units or
lateral units within five miles of any airport runway end
must notify both the affected airport and the FAA. This
requirement is based on the FAA's position that MSWLF units
located within a five mile radius of any airport runway end,
and which attract or sustain hazardous bird movements across
aircraft flight paths and runways, will be considered
inconsistent with safe flight operations. Notification by
the MSWLF owner/operator to the appropriate regional FAA
office will allow FAA review of the proposal.
2.2.3 Technical Considerations
A demonstration that a MSWLF unit does not pose a bird
hazard to aircraft within specified distances of an airport
runway end should address at least three elements of the
regulation:
* Is the airport facility within the regulated
distance?;
* Is the runway part of a public-use airport?; and
* Does or will the existence of the landfill
increase the likelihood of bird/aircraft
collisions that may cause damage to the aircraft
or injury to its occupants?
The first element can be addressed using existing maps
showing the relationship of existing runways at the airport
to the existing or proposed new unit or lateral expansion.
Topographic maps (USGS 15-minute series) or State, regional,
or local government agency maps providing similar or better
accuracy would allow direct scaling, or measurement, of the
closest distance from the end of a runway to the nearest
MSWLF unit. The measurement can be made by drawing a circle
of appropriate radius (i.e., 5,000 ft., 10,000 ft, or 5
miles, depending on the airport type) from the centerline of
each runway end. The measurement only should be made
between the end of the runway and the nearest MSWLF unit
perimeter, not between any other boundaries.
To determine whether the runway is part of a public use
airport and to determine whether all applicable public
airports have been identified, the MSWLF unit owner/operator
should contact the airport administration or the regional
FAA office. This rule does not apply to private airfields.
The MSWLF unit design features and operational
practices can have a significant effect on the likelihood of
increased bird/aircraft collisions. Birds may be attracted
to MSWLF units to satisfy a need for water, food, nesting,
or roosting. Scavenger birds such as starlings, crows,
blackbirds, and gulls are most commonly associated with
active landfill units. Where bird/aircraft collisions
occur, these types of birds are often involved due to their
flocking, feeding, roosting, and flight behaviors. Waste
management techniques to reduce the supply of food to these
birds include:
* Frequent covering of wastes that provide a source
of food;
* Shredding, milling, or baling the waste-containing
food sources; and
* Eliminating the acceptance of wastes at the
landfill unit that represent a food source for
birds (by alternative waste management techniques
such as source separation and composting or waste
minimization).
Frequent covering of wastes that represent a food
source for the birds effectively reduces the availability of
the food supply. Depending on site conditions such as volume
and types of wastes, waste delivery schedules, and size of
the working face, cover may need to be applied several times
a day to keep the inactive portion of the working face small
relative to the area accessible to birds. By maintaining a
small working face, spreading and compaction equipment are
concentrated in a small area that further disrupts
scavenging by the birds.
Milling or shredding municipal solid waste breaks up
food waste into smaller particle sizes and distributes the
particles throughout non-food wastes, thereby diluting food
wastes to a level that frequently makes the mixture no
longer attractive as a food supply for birds. Similarly,
baling municipal solid waste reduces the surface area of
waste that may be available to scavenging birds.
The use of varying bird control techniques may prevent
the birds from adjusting to a single method. Methods such
as visual deterrents or sound have been used with mixed
success in an attempt to discourage birds from food
scavenging. Visual deterrents include realistic models
(still or animated) of the bird's natural predators (e.g.,
humans, owls, hawks, falcons). Sounds that have had limited
success as deterrents include cannons, distress calls of the
scavenger birds, and sounds of its natural predators. Use
of physical barriers such as fine wires strung across or
near the working face have also been successfully used (see
Figure 2-1). Labor intensive efforts have included falconry
and firearms. Many of these methods have limited long-term
effects on controlling bird populations at landfill
units/facilities, as the birds adapt to the environment in
which they find food.
Proper design and operation also can reduce the
attraction of birds to the landfill unit through eliminating
scavenger bird habitat. For example, the use of the
landfill unit as a source of water can be controlled by
encouraging surface drainage and by preventing the ponding
of water.
Birds also may be attracted to a landfill unit as a
nesting area. Use of the landfill site as a roosting or
nesting area is usually limited to ground-roosting birds
(e.g., gulls). Operational landfill units that do not
operate continuously often provide a unique roosting habitat
due to elevated ground temperatures (as a result of waste
decomposition within the landfill) and freedom from
disturbance. Nesting can be minimized, however, by
examining the nesting patterns and requirements of
undesirable birds and designing controls accordingly. For
example, nesting by certain species can be controlled
through the mowing and maintenance schedules at the
landfill.
In addition to design features and operational
procedures to control bird populations, the demonstration
should address the likelihood that the MSWLF unit may
increase bird/aircraft collisions. One approach to
addressing this part of the airport safety criterion is to
evaluate the attraction of birds to the MSWLF unit and
determine whether this increased population would be
expected to result in a discernible increase in
bird/aircraft collisions. The evaluation of bird attraction
can be based on field observations at existing facilities
where similar geographic location, design features, and
operational procedures are present.
All observations, measurements, data, calculations and
analyses, and evaluations should be documented and included
in the demonstration. The demonstration must be placed in
the operating record and the State Director must be notified
that it has been placed in the operating record (see Section
3.11 in Chapter 3).
If an owner or operator of an existing MSWLF unit
cannot successfully demonstrate compliance with Section
258.10(a), then the unit must be closed in accordance with
Section 258.60 and post-closure activities must be conducted
in accordance with Section 258.61 (see Section 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
requested from the FAA. Topographic maps (e.g., USGS
15-minute series) or other similarly accurate maps showing
the relationship of the airport runway and the MSWLF unit
should provide a suitable basis for determining whether the
FAA should be notified.
************************************************************
Figure 2-1
Bird Control Device
[Graphic]
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2.3 FLOODPLAINS 40 CFR Section 258.11
2.3.1 Statement of Regulation
(a) Owners or operators of new MSWLF units, existing
MSWLF units, and lateral expansions located in 100-year
floodplains must demonstrate that the unit will not restrict
the flow of the 100-year flood, reduce the temporary water
storage capacity of the floodplain, or result in washout of
solid waste so as to pose a hazard to human health and the
environment. The owner or operator must place the
demonstration in the operating record and notify the State
Director that it has been placed in the operating record.
(b) For purposes of this section:
(1) Floodplain means the lowland and relatively flat
areas adjoining inland and coastal waters, including
flood-prone areas of offshore islands, that are inundated by
the 100-year flood.
(2) 100-year flood means a flood that has a 1-percent
or greater chance of recurring in any given year or a flood
of a magnitude equaled or exceeded once in 100 years on the
average over a significantly long period.
(3) Washout means the carrying away of solid waste by
waters of the base flood.
2.3.2 Applicability
Owners/operators of new MSWLF units, existing MSWLF
units, and lateral expansions of existing units located in a
100-year river floodplain who cannot demonstrate that the
units will not restrict the flow of a 100-year flood nor
reduce the water storage capacity, and will not result in a
wash-out of solid waste, must close the unit(s). A MSWLF
unit can affect the flow and temporary storage capacity of a
floodplain. Higher flood levels and greater flood damage
both upstream and downstream can be created and could cause
a potential hazard to human health and safety. The rule
does not prohibit locating a MSWLF unit in a 100-year
floodplain; for example, the owner or operator is allowed to
demonstrate that the unit will comply with the flow
restriction, temporary storage, and washout provisions of
the regulation. If a demonstration can be made that the
landfill unit will not pose threats, the demonstration must
be placed in the operating record, and the State Director
must be notified that the demonstration was made and placed
in the record. If the demonstration cannot be made for an
existing MSWLF unit, then the MSWLF unit must be closed in 5
years in accordance with Section 258.60, and the owner or
operator must conduct post-closure activities in accordance
with Section 258.61 (see Section 258.16). The closure
deadline may be extended for up to two years by the Director
of an approved State if the owner or operator can
demonstrate that no available alternative disposal capacity
exists and there is no immediate threat to human health and
the environment (see Section 2.8).
2.3.3 Technical Considerations
Compliance with the floodplain criterion begins with a
determination of whether the MSWLF unit is located in the
100-year floodplain. If the MSWLF unit is located in the
100-year floodplain, then the owner or operator must
demonstrate that the unit will not pose a hazard to human
health and the environment due to:
* Restricting the base flood flow;
* Reducing the temporary water storage; and
* Resulting in the washout of solid waste.
Guidance for identifying floodplains and demonstrating
facility compliance is provided below.
Floodplain Identification
River floodplains are readily identifiable as the flat
areas adjacent to the river's normal channel. One
hundred-year floodplains represent the sedimentary deposits
formed by floods that have a one percent chance of
occurrence in any given year and that are identified in the
flood insurance rate maps (FIRMs) and flood boundary and
floodway maps published by the Federal Emergency Management
Agency (FEMA) (see Figure 2-2). Areas classified as "A"
zones are subject to the floodplain location restriction.
Areas classified as "B" or "C" zones are not subject to the
restriction, although care should be taken to design
facilities capable of withstanding some potential flooding.
Guidance on using FIRMs is provided in "How to Read a
Flood Insurance Rate Map" published by FEMA. FEMA also
publishes "The National Flood Insurance Program Community
Status Book" that lists communities that may not be involved
in the National Flood Insurance Program but which have FIRMs
or Floodway maps published. Maps and other FEMA
publications may be obtained from the FEMA Distribution
Center (see Section 2.9.2 for the address). Areas not
covered by the FIRMs or Floodway maps may be included in
floodplain maps available through the U.S. Army Corps of
Engineers, the U.S. Geological Survey, the U.S. Soil
Conservation Service, the Bureau of Land Management, the
Tennessee Valley Authority, and State, Tribal, and local
agencies.
Many of the river channels covered by these maps may
have undergone modification for hydropower or flood control
projects and, therefore, the floodplain boundaries
represented may not be accurate or representative. It may
be necessary to compare the floodplain map series to recent
air photographs to identify current river channel
modifications and land use watersheds that could affect
floodplain designations. If floodplain maps are not
available, and the facility is located within a floodplain,
then a field study to delineate the 100-year floodplain may
be required. A floodplain delineation program can be based
primarily on meteorological records and physiographic
information such as existing and planned watershed land use,
topography, soils and geologic mapping, and air photo
interpretation of geomorphologic (land form) features. The
United States Water Resource Council (1977) provides
information for determining the potential for floods in a
given location by stream gauge records. Estimation of the
peak discharge also allows an estimation of the probability
of exceeding the 100-year flood.
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Figure 2-2
Example Section of Flood Plain Map
[Graphic]
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Engineering Considerations
If the MSWLF unit is within the 100-year floodplain, it
must be located so that the MSWLF unit does not
significantly restrict the base flood flow or significantly
reduce temporary storage capacity of the floodplain. The
MSWLF unit must be designed to prevent the washout of solid
waste during the expected flood event. The rule requires
that floodplain storage capacity, and flow restrictions that
occur as the result of the MSWLF unit, do not pose a hazard
to human health and the environment.
The demonstration that these considerations are met
relies on estimates of the flow velocity and volume of
floodplain storage in the vicinity of the MSWLF unit during
the base flood. The assessment should consider the
floodplain storage capacity and floodwater velocities that
would likely exist in absence of the MSWLF unit. The volume
occupied by a MSWLF unit in a floodplain may theoretically
alter (reduce) the storage capacity and restrict flow.
Raising the base flood level by more than one foot can be an
indication that the MSWLF unit may reduce and restrict
storage capacity flow.
The location of the MSWLF unit relative to the velocity
distribution of floodwaters will greatly influence the
susceptibility to washout. This type of assessment will
require a conservative estimate of the shear stress on the
landfill components caused by the depth, velocity, and
duration of impinging river waters. Depending on the amount
of inundation, the landfill unit may act as a channel side
slope or bank or it may be isolated as an island within the
overbank river channel. In both cases an estimate of the
river velocity would be part of a proper assessment.
The assessment of flood water velocity requires that
the channel cross section be known above, at, and below the
landfill unit. Friction factors on the overbank are deter-
mined from the surface conditions and vegetation present.
River hydrologic models may be used to simulate flow levels
and estimate velocities through these river cross sections.
The Army Corps of Engineers (COE, 1982) has developed
several numerical models to aid in the prediction of flood
hydrographs, flow parameters, the effect of obstructions on
flow levels, the simulation of flood control structures, and
sediment transport. These methods may or may not be
appropriate for a site; however, the following models
provide well-tested analytical approaches:
HEC-1 Flood Hydrograph Package (watershed model that
simulates the surface run-off response of a river
basin to precipitation);
HEC-2 Water Surface Profiles (computes water surface
profiles due to obstructions; evaluates floodway
encroachment potential);
HEC-5 Simulation of Flood Control and Conservation
Systems (simulates the sequential operation of a
reservoir channel system with a branched network
configuration; used to design routing that will
minimize downstream flooding); and
HEC-6 Scour and Deposition in Rivers and Reservoirs
(calculates water surface and sediment bed surface
profiles).
The HEC-2 model is not appropriate for simulation of
sediment-laden braided stream systems or other
intermittent/dry stream systems that are subject to flash
flood events. Standard run-off and peak flood hydrograph
methods would be more appropriate for such conditions to
predict the effects of severe flooding.
There are many possible cost-effective methods to
protect the MSWLF unit from flood damage including
embankment designs with rip-rap, geotextiles, or other
materials. Guidelines for designing with these materials
may be found in Maynard (1978) and SCS (1983). Embankment
design will require an estimate of river flow velocities,
flow profiles (depth), and wave activity. Figure 2-3
provides a design example for dike construction and
protection of the landfill surface from flood water. It
addresses height requirements to control the effects of wave
activity. The use of alternate erosion control methods such
as gabions (cubic-shaped wire structures filled with stone),
paving bricks, and mats may be considered. It should be
noted, however, that the dike design in Figure 2-3 may
further decrease the water storage and flow capacities.
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Figure 2-3
Example Floodplain Protection Dike Design
[Graphic]
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2.4 WETLANDS 40 CFR Section 258.12
2.4.1 Statement of Regulation
(a) New MSWLF units and lateral expansions shall not be
located in wetlands, unless the owner or operator can make
the following demonstrations to the Director of an approved
State:
(1) Where applicable under section 404 of the Clean
Water Act or applicable State wetlands laws, the presumption
that a practicable alternative to the proposed landfill is
available which does not involve wetlands is clearly
rebutted;
(2) The construction and operation of the MSWLF unit
will not:
(i) Cause or contribute to violations of any applicable
State water quality standard,
(ii) Violate any applicable toxic effluent standard or
prohibition under Section 307 of the Clean Water Act,
(iii) Jeopardize the continued existence of endangered
or threatened species or result in the destruction or
adverse modification of a critical habitat, protected under
the Endangered Species Act of 1973, and
(iv) Violate any requirement under the Marine
Protection, Research, and Sanctuaries Act of 1972 for the
protection of a marine sanctuary;
(3) The MSWLF unit will not cause or contribute to
significant degradation of wetlands. The owner or operator
must demonstrate the integrity of the MSWLF unit and its
ability to protect ecological resources by addressing the
following factors:
(i) Erosion, stability, and migration potential of
native wetland soils, muds and deposits used to support the
MSWLF unit;
(ii) Erosion, stability, and migration potential of
dredged and fill materials used to support the MSWLF unit;
(iii) The volume and chemical nature of the waste
managed in the MSWLF unit;
(iv) Impacts on fish, wildlife, and other aquatic
resources and their habitat from release of the solid waste;
(v) The potential effects of catastrophic release of
waste to the wetland and the resulting impacts on the
environment; and
(vi) Any additional factors, as necessary, to
demonstrate that ecological resources in the wetland are
sufficiently protected.
(4) To the extent required under Section 404 of the
Clean Water Act or applicable State wetland laws, steps have
been taken to attempt to achieve no net loss of wetlands (as
defined by acreage and function) by first avoiding impacts
to wetlands to the maximum extent practicable as required by
paragraph (a)(1) of this section, then minimizing
unavoidable impacts to the maximum extent practicable, and
finally offsetting remaining unavoidable wetland impacts
through all appropriate and practicable compensatory
mitigation actions (e.g., restoration of existing degraded
wetlands or creation of man-made wetlands); and
(5) Sufficient information is available to make a
reasonable determination with respect to these
demonstrations.
(b) For purposes of this section, "wetlands" means
those areas that are defined in 40 CFR Section 232.2(r).
2.4.2 Applicability
New MSWLF units and lateral expansions in wetlands are
prohibited, except in approved States. The wetland
restrictions allow existing MSWLF units located in wetlands
to continue operations as long as compliance with the other
requirements of Part 258 can be maintained.
In addition to the regulations listed in 40 CFR Section
258.12(a)(2), other Federal requirements may be applicable
in siting a MSWLF unit in a wetland. These include:
* Sections 401, 402, and 404 of the CWA;
* Rivers and Harbors Act of 1989;
* National Environmental Policy Act;
* Migratory Bird Conservation Act;
* Fish and Wildlife Coordination Act;
* Coastal Zone Management Act;
* Wild and Scenic Rivers Act; and the
* National Historic Preservation Act.
As authorized by the EPA, the use of wetlands for
location of a MSWLF facility may require a permit from the
U.S. Army Corps of Engineers (COE). The types of wetlands
present (e.g., headwater, isolated, or adjacent), the extent
of the wetland impact, and the type of impact proposed will
determine the applicable category of COE permit (individual
or general) and the permit application procedures. The COE
District Engineer should be contacted prior to permit
application to determine the available categories of permits
for a particular site. Wetland permitting or permit review
and comment can include additional agencies at the federal,
state, regional, and local level. The requirements for
wetland permits should be reviewed by the owner/operator to
ensure compliance with all applicable regulations.
When proposing to locate a new facility or lateral
expansion in a wetland, owners or operators must be able to
demonstrate that alternative sites are not available and
that the impact to wetlands is unavoidable.
If it is demonstrated that impacts to the wetland are
unavoidable, then all practicable efforts must be made to
minimize and, when necessary, compensate for the impacts.
The impacts must be compensated for by restoring degraded
wetlands, enhancing or preserving existing wetlands, or
creating new wetlands. It is an EPA objective that
mitigation activities result in the achievement of no net
loss of wetlands.
2.4.3 Technical Considerations
The term wetlands, referenced in Section 258.12(b), is
defined in Section 232.2(r). The EPA currently is studying
the issues involved in defining and delineating wetlands.
Proposed changes to the "Federal Manual for Identifying and
Delineating Jurisdictional Wetlands," 1989, are still being
reviewed. [These changes were proposed in the Federal
Register on August 14, 1991 (56 FR 40446) and on December
19, 1991 (56 FR 65964).] Therefore, as of January 1993, the
method used for delineating a wetland is based on a
previously existing document, "Army Corps of Engineers
Wetlands Delineation Manual," 1987. A Memorandum of
Understanding between EPA and the Department of the Army,
Corps of Engineers, was amended on January 4, 1993, to state
that both agencies would now use the COE 1987 manual as
guidance for delineating wetlands. The methodology applied
by an owner/operator to define and delineate wetlands should
be in keeping with the federal guidance in place at the time
of the delineation.
Because of the unique nature of wetlands, the
owner/operator is required to demonstrate that the landfill
unit will not cause or contribute to significant degradation
of wetlands. The demonstration must be reviewed and
approved by the Director of an approved State and placed in
the facility operating record. This provision effectively
bans the siting of new MSWLF units or lateral expansions in
wetlands in unapproved States.
There are several key issues that need to be addressed
if an owner or operator proposes to locate a lateral
expansion or a new MSWLF unit in a wetland. These issues
include: (1) review of practicable alternatives, (2)
evaluation of wetland acreage and function, (3) evaluation
of impacts of MSWLF units on wetlands, and (4) offsetting
impacts. Although EPA has an objective of no net loss of
wetlands in terms of acreage and function, it recognizes
that regions of the country exist where proportionally large
areas are dominated by wetlands. In these regions,
sufficient acreage and a suitable type of upland may not be
present to allow construction of a new MSWLF unit or lateral
expansion without wetland impacts. Wetlands evaluations may
become an integral part of the siting, design, permitting,
and environmental monitoring aspects of a landfill
unit/facility (see Figure 2-4).
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Figure 2-4
Wetlands Decision Tree for Owners/Operators
in Approved States
[Graphic]
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Practicable Alternatives
EPA believes that locating new MSWLF units or lateral
expansions in wetlands should be done only where there are
no less damaging alternatives available. Due to the extent
of wetlands that may be present in certain regions, the
banning of new MSWLF units or lateral expansions in wetlands
could cause serious capacity problems. The flexibility of
the rule allows owners or operators to demonstrate that
there are no practicable alternatives to locating or
laterally expanding MSWLF units in wetlands.
As part of the evaluation of practicable alternatives,
the owner/operator should consider the compliance of the
location with other regulations and the potential impacts of
the MSWLF unit on wetlands and related resources. Locating
or laterally expanding MSWLF units in wetlands requires
compliance with other environmental regulations. The owner
or operator must show that the operation or construction of
the landfill unit will not:
* Violate any applicable State water quality
standards;
* Cause or contribute to the violation of any
applicable toxic effluent standard or prohibition;
* Cause or contribute to violation of any
requirement for the protection of a marine
sanctuary; and
* Jeopardize the continued existence of endangered
or threatened species or critical habitats.
The MSWLF unit cannot cause or contribute to
significant degradation of wetlands. Therefore, the
owner/operator must:
* Ensure the integrity of the MSWLF unit, including
consideration of the erosion, stability, and
migration of native wetland soils and dredged/fill
materials;
* Minimize impacts on fish, wildlife, and other
aquatic resources and their habitat from the
release of solid waste;
* Evaluate the effects of catastrophic release of
wastes on the wetlands; and
* Assure that ecological resources in the wetlands
are sufficiently protected, including
consideration of the volume and chemical nature of
waste managed in the MSWLF unit.
These factors were partially derived from Section
404(b)(1) of the Clean Water Act. These guidelines address
the protection of the ecological resources of the wetland.
After consideration of these factors, if no practicable
alternative to locating the landfill in wetlands is
available, compensatory steps must be taken to achieve no
net loss of wetlands as defined by acreage and function.
The owner/operator must try to avoid and/or minimize impacts
to the wetlands to the greatest extent possible. Where
avoidance and minimization still result in wetland impacts,
mitigation to offset impacts is required. Mitigation plans
must be approved by the appropriate regulatory agencies and
must achieve an agreed-upon measure of success. Examples of
mitigation include restoration of degraded wetlands or
creation of wetland acreage from existing uplands.
Part 258 presumes that practicable alternatives are
available to locating landfill units in wetlands because
landfilling is not a water-dependent activity. In an
approved State, the owner or operator can rebut the
presumption that a practicable alternative to the proposed
landfill unit or lateral expansion is available. The term
"practicable" pertains to the economic and social
feasibility of alternatives (e.g., collection of waste at
transfer stations and trucking to an existing landfill
facility or other possible landfill sites). The feasibility
evaluation may entail financial, economic, administrative,
and public acceptability analyses as well as engineering
considerations. Furthermore, the evaluations generally will
require generation and assessment of land use, geologic,
hydrologic, geographic, demographic, zoning, traffic maps,
and other related information.
To rebut the presumption that an alternative
practicable site exists generally will require that a site
search for an alternative location be conducted. There are
no standard methods for conducting site searches due to the
variability of the number and hierarchy of screening
criteria that may be applied in a specific case. Typical
criteria may include:
* Distance from waste generation sources;
* Minimum landfill facility size requirements;
* Soil conditions;
* Proximity to ground-water users;
* Proximity of significant aquifers;
* Exclusions from protected natural areas;
* Degree of difficulty to remediate features; and
* Setbacks from roadways and residences.
Wetland Evaluations
The term "wetlands" includes swamps, marshes, bogs, and
any areas that are inundated or saturated by ground water or
surface water at a frequency and duration to support, and
that under normal circumstances do support, a prevalence of
vegetation adapted for life in saturated soil conditions.
As defined under current guidelines, wetlands are identified
based on the presence of hydric soils, hydrophytic
vegetation, and the wetland hydrology. These
characteristics also affect the functional value of a
wetland in terms of its role in: supporting fish and
wildlife habitats; providing aesthetic, scenic, and
recreational value; accommodating flood storage; sustaining
aquatic diversity; and its relationships to surrounding
natural areas through nutrient retention and productivity
exportation (e.g., releasing nutrients to downstream areas,
providing transportable food sources).
Often, a wetland assessment will need to be conducted
by a qualified and experienced multi-disciplinary team. The
assessment should identify: (1) the limits of the wetland
boundary based on hydrology, soil types and plant types; (2)
the type and relative abundance of vegetation, including
trees; and (3) rare, endangered, or otherwise protected
species and their habitats (if any).
The current methods used to delineate wetlands are
presented in "COE Wetlands Delineation Manual," 1987. In
January 1993, EPA and COE agreed to use the 1987 Manual for
purposes of delineation. The Federal Manual for Identifying
and Delineating Jurisdictional Wetlands (COE, 1989) contains
an extensive reference list of available wetland literature.
For example, lists of references for the identification of
plant species characteristic of wetlands throughout the
United States, hydric soils classifications, and related
wetland topics are presented. USGS topographic maps,
National Wetland Inventory (NWI) maps, Soil Conservation
Service (SCS) soil maps, wetland inventory maps, and aerial
photographs prepared locally also may provide useful
information.
After completion of a wetland study, the impact of the
MSWLF unit on wetlands and its relationship to adjacent
wetlands can be assessed more effectively. During the
permitting process, local, State, and federal agencies with
jurisdiction over wetlands will need to be contacted to
schedule a site visit. It is usually advantageous to
encourage this collaboration as early as possible in the
site evaluation process, especially if the State program
office that is responsible for wetland protection is
different from the solid waste management office.
Regulations will vary significantly from State to State with
regard to the size and type of wetland that triggers State
agency involvement. In general, the COE will require
notification and/or consultation on any proposed impact on
any wetland regardless of the actual degree of the impact.
Other agencies such as the Fish and Wildlife Service and the
SCS may need to be contacted in some States.
Evaluation of ecological resource protection may
include assessment of the value of the affected wetland.
Various techniques are available for this type of
evaluation, and the most appropriate technique for a
specific site should be selected in conjunction with
applicable regulatory agencies. Available methods include
analysis of functional value, the Wetland Evaluation
Technique (WET), and the Habitat Evaluation Procedure (HEP).
The 1987 Manual does not address functional value in
the detail provided by the 1989 manual. The methodology for
conducting a functional value assessment should be reviewed
by the applicable regulatory agencies. It is important to
note that functional value criteria may become a standard
part of wetland delineation following revision of the
federal guidance manual(s). The owner or operator should
remain current with the accepted practices at the time of
the delineation/assessment.
The functional value of a given wetland is dependent on
its soil, plant, and hydrologic characteristics,
particularly the diversity, prevalence, and extent of
wetland plant species. The relationship between the wetland
and surrounding areas (nutrient sinks and sources) and the
ability of the wetland to support animal habitats, or rare
or endangered species, contributes to the evaluation of
functional value.
Other wetland and related assessment methodologies
include WET and HEP. WET allows comparison of the values
and functions of wetlands before and after construction of a
facility, thereby projecting the impact a facility may have
on a wetland. WET was developed by the Federal Highway
Administration and revised by the COE (Adamus et al., 1987).
HEP was developed by the Fish and Wildlife Service to
determine the quality and quantity of available habitat for
selected species. HEP and WET may be used in conjunction
with each other to provide an integrated assessment.
Impact Evaluation
If the new unit or lateral expansion is to be located
in a wetland, the owner or operator must demonstrate that
the unit will not cause or contribute to significant
degradation of the wetland. Erosion potential and stability
of wetland soils and any dredged or fill material used to
support the MSWLF unit should be identified as part of the
wetlands evaluation. Any adverse stability or erosion
problems that could affect the MSWLF or contaminant effects
that could be caused by the MSWLF unit should be resolved.
All practicable steps are to be taken to minimize
potential impacts of the MSWLF unit to wetlands. A number
of measures that can aid in minimization of impacts are
available. Appropriate measures are site-specific and
should be incorporated into the design and operation of the
MSWLF unit. For example, placement of ground water barriers
may be required if soil and shallow ground-water conditions
would cause dewatering of the wetland due to the existence
of underdrain pipe systems at the facility. In many
instances, however, wetlands are formed in response to
perched water tables over geologic material of low hydraulic
conductivity and, therefore, significant drawdown impacts
may not occur.
It is possible that the landfill unit/facility will not
directly displace wetlands, but that adverse effects may be
caused by leachate or run-off. Engineered containment
systems for both leachate and run-off should mitigate the
potential for discharge to wetlands.
Additional actions and considerations relevant to
mitigating impacts of fill material in wetlands that may be
appropriate for MSWLF facilities are provided in Subpart H
(Actions to Minimize Adverse Effects) of 40 CFR Section 230
(Guidelines for Specification of Disposal Sites for Dredged
or Fill Materials).
Wetland Offset
All unavoidable impacts must be "offset" or compensated
for to ensure that the facility has not caused, to the
extent practicable, any net loss of wetland acreage. This
compensatory mitigation may take the form of upgrading
existing marginal or lower-quality wetlands or creating new
wetlands. Wetland offset studies require review and
development on a site-specific basis.
To identify potential sites that may be proposed for
upgrade of existing wetlands or creation of new wetlands, a
cursory assessment of surrounding wetlands and uplands
should be conducted. The assessment may include a study to
define the functional characteristics and
inter-relationships of these potential wetland mitigation
areas. An upgrade of an existing wetland may consist of
transplanting appropriate vegetation and importing
low-permeability soil materials that would be conducive to
forming saturated soil conditions. Excavation to form open
water bodies or gradual restoration of salt water marshes by
culvert expansions to promote sea water influx are other
examples of compensatory mitigation.
Individual States may have offset ratios to determine
how much acreage of a given functional value is required to
replace the wetlands that were lost or impacted.
Preservation of lands, such as through perpetual
conservation easements, may be considered as a viable offset
option. State offset ratios may require that for wetlands
of an equivalent functional value, a larger acreage be
created than was displaced.
Due to the experimental nature of creating or enhancing
wetlands, a monitoring program to evaluate the progress of
the effort should be considered and may be required as a
wetland permit condition. The purpose of the monitoring
program is to verify that the created/upgraded wetland is
successfully established and that the intended function of
the wetland becomes self-sustaining over time.
2.5 FAULT AREAS 40 CFR Section 258.13
2.5.1 Statement of Regulation
(a) New MSWLF units and lateral expansions shall not be
located within 200 feet (60 meters) of a fault that has had
displacement in Holocene time unless the owner or operator
demonstrates to the Director of an approved State that an
alternative setback distance of less than 200 feet (60
meters) will prevent damage to the structural integrity of
the MSWLF unit and will be protective of human health and
the environment.
(b) For the purposes of this section:
(1) Fault means a fracture or a zone of fractures in
any material along which strata on one side have been
displaced with respect to that on the other side.
(2) Displacement means the relative movement of any
two sides of a fault measured in any direction.
(3) Holocene means the most recent epoch of the
Quaternary period, extending from the end of the Pleistocene
Epoch to the present.
2.5.2 Applicability
Except in approved States, the regulation bans all new
MSWLF units or lateral expansions of existing units within
200 feet (60 meters) of the outermost boundary of a fault
that has experienced displacement during the Holocene Epoch
(within the last 10,000 to 12,000 years). Existing MSWLF
units are neither required to close nor to retrofit if they
are located in fault areas.
A variance to the 200-foot setback is provided if the
owner or operator can demonstrate to the Director of an
approved State that a shorter distance will prevent damage
to the structural integrity of the MSWLF unit and will be
protective of human health and the environment. The
demonstration for a new MSWLF unit or lateral expansion
requires review and approval by the Director of an approved
State. If the demonstration is approved, it must be placed
in the facility's operating record. The option to have a
setback of less than 200 feet from a Holocene fault is not
available in unapproved States.
2.5.3 Technical Considerations
Locating a landfill in the vicinity of an area that has
experienced faulting in recent time has inherent dangers.
Faulting occurs in areas where the geologic stresses exceed
a geologic material's ability to withstand those stresses.
Such areas also tend to be subject to earthquakes and ground
failures (e.g., landslides, soil liquefaction) associated
with seismic activity. A more detailed discussion of
seismic activity is presented in Section 2.6.
Proximity to a fault can cause damage through:
* Movement along the fault which can cause
displacement of facility structures,
* Seismic activity associated with faulting which
can cause damage to facility structures through
vibratory action (see Figure 2-5), and
* Earth shaking which can cause ground failures such
as slope failures.
************************************************************
Figure 2-5
Potential Seismic Effects
[Graphic]
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Consequently, appropriate setbacks from fault areas are
required to minimize the potential for damage.
To determine if a proposed landfill unit is located in
a Holocene fault area, U.S. Geological Survey (USGS) mapping
can be used. A series of maps known as the "Preliminary
Young Fault Maps, Miscellaneous Field Investigation (MF)
916" was published by the USGS in 1978. Information about
these maps can be obtained from the USGS by calling
1-800-USA-MAPS, which reaches the USGS National Center in
Reston, Virginia, or by calling 303-236-7477, which reaches
the USGS Map Sales Center in Denver, Colorado.
For locations where a fault zone has been subject to
movement since the USGS maps were published in 1978, a
geologic reconnaissance of the site and surrounding areas
may be required to map fault traces and to determine the
faults along which movement has occurred in Holocene time.
This reconnaissance also may be necessary to support a
demonstration for a setback of less than 200 feet.
Additional requirements may need to be met before a new unit
or lateral expansion may be approved.
A site fault characterization is necessary to determine
whether a site is within 200 feet of a fault that has had
movement during the Holocene epoch. An investigation would
include obtaining information on any lineaments (linear
features) that suggest the presence of faults within a
3,000-foot radius of the site. The information could be
based on:
* A review of available maps, logs, reports,
scientific literature, or insurance claim reports;
* An aerial reconnaissance of the area within a
five-mile radius of the site, including aerial
photo analysis; or
* A field reconnaissance that includes walking
portions of the area within 3,000 feet of the
unit.
If the site fault characterization indicates that a
fault or a set of faults is situated within 3,000 feet of
the proposed unit, investigations should be conducted to
determine the presence or absence of any faults within 200
feet of the site that have experienced movement during the
Holocene period. Such investigations can include:
* Subsurface exploration, including drilling and
trenching, to locate fault zones and evidence of
faulting.
* Trenching perpendicular to any faults or
lineaments within 200 feet of the unit.
* Determination of the age of any displacements, for
example by examining displacement of surficial
deposits such as glacial or older deposits (if
Holocene deposits are absent).
* Examination of seismic epicenter information to
look for indications of recent movement or
activity along structures in a given area.
* Review of high altitude, high resolution aerial
photographs with stereo-vision coverage. The
photographs are produced by the National Aerial
Photographic Program (NAPP) and the National High
Altitude Program (NHAP). Information on these
photos can be obtained from the USGS EROS Data
Center in Sioux Falls, South Dakota at (605)
594-6151.
Based on this information as well as supporting maps
and analyses, a qualified professional should prepare a
report that delineates the location of the Holocene fault(s)
and the associated 200-foot setback.
If requesting an alternate setback, a demonstration
must be made to show that no damage to the landfill's
structural integrity will result. Examples of engineering
considerations and modifications that may be included in
such demonstrations are as follows:
* For zones with high probabilities of high
accelerations (horizontal) within the moderate
range of 0.1g to 0.75g, seismic designs should be
developed.
* Seismic stability analysis of landfill slopes
should be performed to guide selection of
materials and gradients for slopes.
* Where in-situ and laboratory tests indicate that a
potential landfill site is susceptible to
liquefaction, ground improvement measures like
grouting, dewatering, heavy tamping, and
excavation should be implemented.
* Engineering options include:
-- Flexible pipes,
-- Ground improvement measures (grouting,
dewatering, heavy tamping, and excavation),
and/or
-- Redundant precautionary measures (secondary
containment system).
In addition, use of such measures needs to be
demonstrated to be protective of human health and the
environment. The types of engineering controls described
above are similar to those that would be employed in areas
that are likely to experience earthquakes.
2.6 SEISMIC IMPACT ZONES 40 CFR Section 258.14
2.6.1 Statement of Regulation
(a) New MSWLF units and lateral expansions shall not be
located in seismic impact zones, unless the owner or
operator demonstrates to the Director of an approved State
that all containment structures, including liners, leachate
collection systems, and surface water control systems, are
designed to resist the maximum horizontal acceleration in
lithified earth material for the site. The owner or
operator must place the demonstration in the operating
record and notify the State Director that it has been placed
in the operating record.
(b) For the purposes of this section:
(1) Seismic impact zone means an area with a ten
percent or greater probability that the maximum horizontal
acceleration in lithified earth material, expressed as a
percentage of the earth's gravitational pull (g), will
exceed 0.10g in 250 years.
(2) Maximum horizontal acceleration in lithified earth
material means the maximum expected horizontal acceleration
depicted on a seismic hazard map, with a 90 percent or
greater probability that the acceleration will not be
exceeded in 250 years, or the maximum expected horizontal
acceleration based on a site-specific seismic risk
assessment.
(3) Lithified earth material means all rock, including
all naturally occurring and naturally formed aggregates or
masses of minerals or small particles of older rock that
formed by crystallization of magma or by induration of loose
sediments. This term does not include man-made materials,
such as fill, concrete, and asphalt, or unconsolidated earth
materials, soil, or regolith lying at or near the earth
surface.
2.6.2 Applicability
New MSWLF units and lateral expansions in seismic
impact zones are prohibited, except in approved States. A
seismic impact zone is an area that has a ten percent or
greater probability that the maximum expected horizontal
acceleration in lithified earth material, expressed as a
percentage of the earth's gravitational pull (g), will
exceed 0.10g in 250 years.
The regulation prohibits locating new units or lateral
expansions in a seismic impact zone unless the owner or
operator can demonstrate that the structural components of
the unit (e.g., liners, leachate collection systems, final
cover, and surface water control systems) are designed to
resist the maximum horizontal acceleration in lithified
earth material at the site. Existing units are not required
to be retrofitted. Owners or operators of new units or
lateral expansions must notify the Director of an approved
State and place the demonstration of compliance with the
conditions of the restriction in the operating record.
2.6.3 Technical Considerations
Background on Seismic Activity
To understand seismic activity, it is helpful to know
its origin. A brief introduction to the geologic
underpinnings of seismic activity is presented below.
The earth's crust is not a static system. It consists
of an assemblage of earthen masses that are in slow motion.
As new crust is generated from within the earth, old edges
of crust collide with one another, thereby causing stress.
The weaker edge is forced to move beneath the stronger edge
back into the earth.
The dynamic conditions of the earth's crust can be
manifested as shaking ground (seismic activity), fracturing
(faulting), and volcanic eruptions. Seismic activity also
can result in types of ground failure. Landslides and mass
movements (e.g., slope failures) are common on slopes; soil
compaction or ground subsidence tends to occur in
unconsolidated valley sediments; and liquefaction of soils
tends to happen in areas where sandy or silty soils that are
saturated and loosely compacted become in effect, liquefied
(like quicksand) due to the motion. The latter types of
phenomena are addressed in Section 2.7, Unstable Areas.
Information Sources on Seismic Activity
To determine the maximum horizontal acceleration of the
lithified earth material for the site (see Figure 2-6),
owners or operators of MSWLF units should review the seismic
250-year interval maps in U.S. Geological Survey
Miscellaneous Field Study Map MF-2120, entitled
"Probabilistic Earthquake Acceleration and Velocity Maps for
the United States and Puerto Rico" (Algermissen et al.,
1991). To view the original of the map that is shown in
Figure 2-6 (reduced in size), contact the USGS office in
your area. The original map (Horizontal Acceleration - Base
modified from U.S.G.S. National Atlas, 1970, Miscellaneous
Field Studies, Map MF 2120) shows county lines within each
State. For areas not covered by the aforementioned map,
USGS State seismic maps may be used to estimate the maximum
horizontal acceleration. The National Earthquake
Information Center, located at the Colorado School of Mines
in Golden, Colorado, can provide seismic maps of all 50
states. The Center also maintains a database of known
earthquakes and fault zones.
************************************************************
Figure 2-6
Seismic Impact Zones
[Graphic]
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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 systems as well as the leachate
and gas collection and removal systems. Tensional stresses
within the liner system can result in fracturing of the soil
liner and/or tearing of the flexible membrane liner. Thus,
when selecting suitable sites from many potential sites
during the siting process, the owner/operator should try to
avoid a site with:
* Holocene fault zones,
* Sites with potential ground motion, and
* Sites with liquefaction potential.
If one of the above types of sites is selected, the
owner/operator must consider the costs associated with the
development of the site.
If, due to a lack of suitable alternatives, a site is
chosen that is located in a seismic impact zone, a
demonstration must be made to the Director of an approved
State that the design of the unit's structural components
(e.g., liners, leachate collection, final covers, run-on and
run-off systems) will resist the maximum horizontal
acceleration in lithified materials at the site. As part of
the demonstration, owner/operators must:
* Determine the expected peak ground acceleration
from a maximum strength earthquake that could
occur in the area,
* Determine the site-specific seismic hazards such
as soil settlement, and
* Design the facility to withstand the expected peak
ground acceleration.
The design of the slopes, leachate collection system,
and other structural components should have built-in
conservative design factors. Additionally, redundant
precautionary measures should be designed and built into the
various landfill systems.
For those units located in an area with an estimated
maximum horizontal acceleration greater than 0.1g, an
evaluation of seismic effects should consider both
foundation soil stability and waste stability under seismic
loading. Conditions that may be considered for the
evaluation include the construction phase (maximum open
excavation depth of new cell adjacent to an existing unit),
closure activities (prior to final consolidation of both
waste and subsoil), and post-closure care (after final
consolidation of both waste and foundation soil). If the
maximum horizontal acceleration is less than or equal to
0.1g, then the design of the unit will not have to
incorporate an evaluation of seismic effects unless the
facility will be situated in an area with low strength
foundation soils or soils with potential for liquefaction.
The facility should be assessed for the effects of seismic
activity even if the horizontal acceleration is expected to
be less than 0.1g.
In determining the potential effects of seismic
activity on a structure, an engineering evaluation should
examine soil behavior with respect to earthquake intensity.
When evaluating soil characteristics, it is necessary to
know the soil strength as well as the magnitude or intensity
of the earthquake in terms of peak acceleration. Other soil
characteristics, including degree of compaction, sorting
(organization of the soil particles), and degree of
saturation, may need to be considered because of their
potential influence on site conditions. For example,
deposits of loose granular soils may be compacted by the
ground vibrations induced by an earthquake. Such volume
reductions could result in large uniform or differential
settlements of the ground surface (Winterkorn and Fang,
1975).
Well-compacted cohesionless embankments or reasonably
flat slopes in insensitive clay are less likely to fail
under moderate seismic shocks (up to 0.15g and 0.20g
acceleration). Embankments made of insensitive cohesive
soils founded on cohesive soils or rock may withstand even
greater seismic shocks. For earthen embankments in seismic
regions, designs with internal drainage and core material
most resistant to fracturing should be considered. Slope
materials vulnerable to earthquake shocks are described
below (U.S. Navy, 1983):
* Very steep slopes of weak, fractured and brittle
rocks or unsaturated loess are vulnerable to
transient shocks caused by tensional faulting;
* Loess and saturated sand may be liquefied by
seismic shocks causing the sudden collapse of
structures and flow slides;
* Similar effects are possible in sensitive cohesive
soils when natural moisture exceeds the soil's
liquid limit; and
* Dry cohesionless material on a slope at an angle
of repose will respond to seismic shock by shallow
sloughing and slight flattening of the slope.
In general, loess, deltaic soils, floodplain soils, and
loose fills are highly susceptible to liquefaction under
saturated conditions (USEPA, 1992).
Geotechnical stability investigations frequently
incorporate the use of computer models to reduce the
computational time of well-established analytical methods.
Several computer software packages are available that
approximate the anticipated dynamic forces of the design
earthquake by resolving the forces into a static analysis of
loading on design cross sections. A conservative approach
would incorporate both vertical and horizontal forces caused
by bedrock acceleration if it can be shown that the types of
material of interest are susceptible to the vertical force
component. Typically, the horizontal force caused by
bedrock acceleration is the major force to be considered in
the seismic stability analysis. Examples of computer models
include PC-Slope by Geoslope Programming (1986), and FLUSH
by the University of California.
Design modifications to accommodate an earthquake may
include shallower waste sideslopes, more conservative design
of dikes and run-off controls, and additional contingencies
for leachate collection should primary systems be disrupted.
Strengths of the landfill components should be able to
withstand these additional forces with an acceptable factor
of safety. The use of professionals experienced in seismic
analysis is strongly recommended for design of facilities
located in areas of high seismic risk.
2.7 UNSTABLE AREAS 40 CFR Section 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 design to ensure that the
integrity of the structural components of the MSWLF unit
will not be disrupted. The owner or operator must place the
demonstration in the operating record and notify the State
Director that it has been placed in the operating record.
The owner or operator must consider the following factors,
at a minimum, when determining whether an area is unstable:
(1) On-site or local soil conditions that may result in
significant differential settling;
(2) On-site or local geologic or geomorphologic
features; and
(3) On-site or local human-made features or events
(both surface and subsurface).
(b) For purposes of this section:
(1) Unstable area means a location that is susceptible
to natural or human-induced events or forces capable of
impairing the integrity of some or all of the landfill
structural components responsible for preventing releases
from a landfill. Unstable areas can include poor foundation
conditions, areas susceptible to mass movements, and Karst
terrains.
(2) Structural components means liners, leachate
collection systems, final covers, run-on/run-off systems,
and any other component used in the construction and
operation of the MSWLF that is necessary for protection of
human health and the environment.
(3) Poor foundation conditions means those areas where
features exist which indicate that a natural or man-induced
event may result in inadequate foundation support for the
structural components of a MSWLF unit.
(4) Areas susceptible to mass movement means those
areas of influence (i.e., areas characterized as having an
active or substantial possibility of mass movement) where
the movement of earth material at, beneath, or adjacent to
the MSWLF unit, because of natural or man-induced events,
results in the downslope transport of soil and rock material
by means of gravitational influence. Areas of mass movement
include, but are not limited to, landslides, avalanches,
debris slides and flows, solifluction, block sliding, and
rock fall.
(5) Karst terrains means areas where karst topography,
with its characteristic surface and subterranean features,
is developed as the result of dissolution of limestone,
dolomite, or other soluble rock. Characteristic
physiographic features present in karst terrains include,
but are not limited to, sinkholes, sinking streams, caves,
large springs, and blind valleys.
2.7.2 Applicability
Owners/operators of new MSWLF units, existing MSWLF
units, and lateral expansions of units that are located in
unstable areas must demonstrate the structural integrity of
the unit. Existing units for which a successful
demonstration cannot be made must be closed. The regulation
applies to new units, existing units, and lateral expansions
that are located on sites classified as unstable areas.
Unstable areas are areas susceptible to natural or
human-induced events or forces that are capable of impairing
or destroying the integrity of some or all of the structural
components. Structural components consist of liners,
leachate collection systems, final cover systems, run-on and
run-off control systems, and any other component necessary
for protection of human health and the environment.
MSWLF units can be located in unstable areas, but the
owner or operator must demonstrate that the structural
integrity of the MSWLF unit will not be disrupted. The
demonstration must show that engineering measures have been
incorporated into the design of the unit to ensure the
integrity of the structural components. Existing MSWLF
units that do not meet the demonstration must be closed
within 5 years in accordance with Section 258.60, and owners
and operators must undertake post-closure activities in
accordance with Section 258.61. The Director of an approved
State can grant a 2-year extension to the closure
requirement under two conditions: (1) no disposal
alternative is available, and (2) no immediate threat is
posed to human health and the environment.
2.7.3 Technical Considerations
Again, for the purposes of this discussion, natural
unstable areas include those areas that have poor soils for
foundations, are susceptible to mass movement, or have karst
features.
* Areas with soils that make poor foundations have
soils that are expansive or settle suddenly. Such
areas may lose their ability to support a
foundation when subjected to natural (e.g., heavy
rain) or man-made events (e.g., explosions).
-- Expansive soils usually are clay-rich soils
that, because of their molecular structure,
tend to swell and shrink by taking up and
releasing water and thus are sensitive to a
variable hydrologic regime. Such soils
include: smectite (montmorillonite group)
and vermiculite clays; bentonite is a
smectite-rich clay. In addition, soils rich
in "white alkali" (sodium sulfate), anhydrite
(calcium sulfate), or pyrite (iron sulfide)
also may exhibit swelling as water content
increases. Such soils tend to be found in
the arid western states.
-- Soils that are subject to rapid settlement
(subsidence) include loess, unconsolidated
clays, and wetland soils. Loess, which is
found in the central states, is a
wind-deposited silt that is
moisture-deficient and tends to compact upon
wetting. Unconsolidated clays, which can be
found in the southwestern states, can undergo
considerable compaction when fluids such as
water or oil are removed. Similarly, wetland
soils, which by their nature are
water-bearing, also tend to be subject to
subsidence when water is withdrawn.
* Another type of unstable area is an area that is
subject to mass movement. Such areas can be
situated on steep or gradual slopes. They tend to
have rock or soil conditions that are conducive to
downslope movement of soil, rock, and/or debris
(either alone or mixed with water) under the
influence of gravity. Examples of mass movements
include avalanches, landslides, debris slides and
flows, and rock slides.
* Karst terrains tend to be subject to extreme
incidents of differential settlement, namely
complete ground collapse. Karst is a term used to
describe areas that are underlain by soluble
bedrock, such as limestone, where solution of the
rock by water creates subterranean drainage
systems that may include areas of rock collapse.
These areas tend to be characterized by large
subterranean and surficial voids (e.g., caverns
and sinkholes) and unpredictable surface and
ground-water flow (e.g., sinking streams and large
springs). Other rocks such as dolomite or gypsum
also may be subject to solution effects.
Examples of human-induced unstable areas are described
below:
* The presence of cut and/or fill slopes during
construction of the MSWLF unit may cause slippage
of existing soil or rock.
* Excessive drawdown of ground water increases the
effective overburden on the foundation soils
underneath the MSWLF unit, which may cause
excessive settlement or bearing capacity failure
on the foundation soils.
* A closed landfill as the foundation for a new
landfill ("piggy-backing") may be unstable unless
the closed landfill has undergone complete
settlement of the underlying wastes.
As part of their demonstration to site a landfill in an
unstable area, owners/operators must assess the ability of
the soils and/or rock to serve as a foundation as well as
the ability of the site embankments and slopes to maintain a
stable condition. Once these factors have been evaluated, a
MSWLF design should be developed that will address these
types of concerns and prevent possible associated damage to
MSWLF structural components.
In designing a new unit or lateral expansion or
re-evaluating an existing MSWLF unit, a stability assessment
should be conducted in order to avoid or prevent a
destabilizing event from impairing the structural integrity
of the landfill component systems. A stability assessment
involves essentially three components: an evaluation of
subsurface conditions, an analysis of slope stability, and
an examination of related design needs. An evaluation of
subsurface conditions requires:
* Assessing the stability of foundation soils,
adjacent embankments, and slopes;
* Investigating the geotechnical and geological
characteristics of the site to establish soil
strengths and other engineering properties by
performing standard penetration tests, field vane
shear tests, and laboratory tests; and
* Testing the soil properties such as water content,
shear strength, plasticity, and grain size
distribution.
A stability assessment should consider (USEPA, 1988):
* The adequacy of the subsurface exploration
program;
* The liquefaction potential of the embankment,
slopes, and foundation soils;
* The expected behavior of the embankment, slopes,
and foundation soils when they are subjected to
seismic activity;
* The potential for seepage-induced failure; and
* The potential for differential settlement.
In addition, a qualified professional must assess, at a
minimum, natural conditions (e.g., soil, geology,
geomorphology) as well as human-made features or events
(both subsurface and surface) that could cause differential
settlement of ground. Natural conditions can be highly
unpredictable and destructive, especially if amplified by
human-induced changes to the environment. Specific examples
of natural or human-induced phenomena include: debris flows
resulting from heavy rainfall in a small watershed; the
rapid formation of a sinkhole as a result of excessive local
or regional ground water withdrawal in a limestone region;
earth displacement by faulting activity; and rockfalls along
a cliff face caused by vibrations resulting from the
detonation of explosives or sonic booms.
Information on natural features can be obtained from:
* The USGS National Atlas map entitled "Engineering
Aspects of Karst," published in 1984;
* Regional or local soil maps;
* Aerial photographs (especially in karst areas);
and
* Site-specific investigations.
To examine an area for possible sources of
human-induced ground instability, the site and surrounding
area should be examined for activities related to extensive
withdrawal of oil, gas, or water from subsurface units as
well as construction or other operations that may result in
ground motion (e.g., blasting).
Types of Failures
Failures occur when the driving forces imposed on the
soils or engineered structures exceed the resisting forces
of the material. The ratio of the resisting force to the
driving force is considered the factor of safety (FS). At
an FS value less than 1.0, failure will occur by definition.
There is a high probability that, due to natural variability
and the degree of accuracy in measurements, interpreted soil
conditions will not be precisely representative of the
actual soil conditions. Therefore, failure may not occur
exactly at the calculated value, so factors of safety
greater than 1.0 are required for the design. For plastic
soils such as clay, movement or deformation (creep) may
occur at a higher factor of safety prior to catastrophic
failure.
Principal modes of failure in soil or rock include:
* Rotation (change of orientation) of an earthen
mass on a curved slip surface approximated by a
circular arc;
* Translation (change of position) of an earthen
mass on a planar surface whose length is large
compared to depth below ground;
* Displacement of a wedge-shaped mass along one or
more planes of weakness;
* Earth and mud flows in loose clayey and silty
soils; and
* Debris flows in coarse-grained soils.
For the purposes of this discussion, three types of
failures can occur at a landfill unit: settlement, loss of
bearing strength, and sinkhole collapse.
* If not properly engineered, a landfill in an
unstable area may undergo extreme settlement,
which can result in structural failure.
Differential settlement is a particular mode of
failure that generally occurs beneath a landfill
in response to consolidation and dewatering of the
foundation soils during and following waste
loading.
Settlement beneath a landfill unit, both total and
differential, should be assessed and compared to
the elongation strength and flexure properties of
the liner and leachate collection pipe system.
Even small amounts of settlement can seriously
damage leachate collection piping and sumps. The
analysis will provide an estimate of maximum
settlement, which can be used to aid in estimating
differential settlement.
Allowable settlement is typically expressed as a
function of total settlement because differential
settlement is more difficult to predict. However,
differential settlement is a more serious threat
to the integrity of the structure than total
settlement. Differential settlement also is
discussed in Section 6.3 of Chapter 6.
* Loss of bearing strength is a failure mode that
tends to occur in areas that have soils that tend
to expand, rapidly settle, or liquefy, thereby
causing failure or reducing performance of
overlying MSWLF components. Another example of
loss of bearing strength involves failures that
have occurred at operating sites where excavations
for landfill expansions adjacent to the filled
areas reduced the mass of the soil at the toe of
the slope, thereby reducing the overall strength
(resisting force) of the foundation soil.
* Catastrophic collapse in the form of sinkholes is
a type of failure that occurs in karst regions.
As water, especially acidic water, percolates
through limestone (calcium carbonate), the soluble
carbonate material dissolves, forming cavities and
caverns. Land overlying caverns can collapse
suddenly, resulting in sinkhole features that can
be 100 feet or more in depth and 300 feet or more
in width.
Tables 2-2 and 2-3 provide examples of analytical
considerations for mode of failure assessments in both
natural and human-made slopes.
************************************************************
TABLE 2-2.
ANALYSIS OF STABILITY OF NATURAL SLOPES
1. Slope in Course-Grained Soil with Some Cohesion
Low Groundwater
Failure of thin wedge, position influenced by tension cracks
[Graphic]
High Groundwater
Failure at relatively shallow toe circles
[Graphic]
* With low groundwater, failure occurs on shallow,
straight, or slightly curbed 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 stresses using strengths C prime
and Omega prime from CD tests. Pore pressure is
governed by seepage condition. Internal pore pressures
and external water pressures must be included.
2. Slope in Course-Grained, Cohesionless Soil
Low Groundwater
Stable slope angle = effective friction angle
[Graphic]
High Groundwater
Stable slope angle = one-half effective friction angle
[Graphic]
* 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
one-half friction angle.
* Analyze with effective stresses using strength Omega
prime. Slight cohesion appearing in test envelope is
ignored. Special consideration must be given to
possible slow slides in loose, saturated fine sands.
3. Slope in Normally Consolidated or Slightly
Preconsolidated Clay
Location of failure depends on variation of shear strength
with depth.
Strength constant with depth.
[Graphic]
* 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 tests,
unconsolidated undrained triaxial test or vane shear.
4. Slope in a Stratified Soil Profile
Location of failure depends on relative strength and
orientation of layers.
Strata of low strength
[Graphic]
* Location of failure plane is controlled by relative
strength and orientation of strata. Failure surface is
combination of active and passive wedges with central
sliding block chosen to conform to stratification.
* Analyze with effective stress using C prime and Omega
prime for fine-grained strata and Omega prime 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
Failure surface of low curvature which is a portion of an
old shear surface.
[Graphic]
* 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.
************************************************************
************************************************************
TABLE 2-3.
ANALYSIS OF STABILITY OF CUT AND FILL SLOPES, CONDITIONS
VARYING WITH TIME
1. Failure of Fill on Soft Cohesive Foundation with Sand Drains
Location of failure depends on geometry and strength of
cross section.
[Graphic]
* 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 C prime and Omega
prime from CU test 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.
[Graphic]
* 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 to fill. Analyze long-term stability
using C prime and Omega prime from CU tests with
effective stress analysis, applying pore pressures of
groundwater only.
3. Failure Following Cit in Stiff Fissured Clay
Failure surface depends on pattern of fissures or depth of
softening.
[Graphic]
* 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 prime and
Omega prime with total stress analysis. Analyze for
long-term stability with C prime_r and Omega prime_m
based on residual strength measured in consolidated
drained tests.
************************************************************
Subsurface Exploration Programs
Foundation soil stability assessments for
non-catastrophic failure require field investigations to
determine soil strengths and other soil properties. In situ
field vane shear tests commonly are conducted in addition to
collection of piston samples for laboratory testing of
undrained shear strengths (biaxial and triaxial). Field
vanes taken at depth provide a profile of soil strength.
The required field vane depth intervals vary, based on soil
strength and type, and the number of borings required
depends on the variability of the soils, the site size, and
landfill unit dimensions. Borings and field vane testing
should consider the anticipated design to identify segments
of the facility where critical cross sections are likely to
occur. Critical sections are where factors of safety are
anticipated to be lowest.
Other tests that are conducted to characterize a soil
include determination of water content, Atterberg limits,
grain size distribution, consolidation, effective porosity,
and saturated hydraulic conductivity. The site
hydrogeologic conditions should be assessed to determine if
soils are saturated or unsaturated.
Catastrophic failures, such as sinkhole collapse in
karst terrains or fault displacement during an earthquake,
are more difficult to predict. Subsurface karst structures
may have surface topographic expressions such as circular
depressions over subsiding solution caverns. Subsurface
borings or geophysical techniques may provide reliable means
of identifying the occurrence, depth, and size of solution
cavities that have the potential for catastrophic collapse.
Methods of Slope Stability Analysis
Slope stability analyses are performed for both
excavated side slopes and aboveground embankments. The
analyses are performed as appropriate to verify the
structural integrity of a cut slope or dike. The design
configuration is evaluated for its stability under all
potential hydraulic and loading conditions, including
conditions that may exist during construction of an
expansion (e.g., excavation). Analyses typically performed
are slope stability, settlement, and liquefaction. Factor
of safety rationale and selection for different conditions
are described by Huang (1983) and Terzaghi and Peck (1967).
Table 2-4 lists recommended minimum factor of safety values
for slopes. Many States may provide their own minimum
factor of safety requirements.
************************************************************
TABLE 2-4
RECOMMENDED MINIMUM VALUES OF FACTOR OF SAFETY FOR SLOPE
STABILITY ANALYSES
Uncertainty of Strength Measurements
Consequences of Slope Failure Small_1 Large_2
No imminent danger to human life 1.25 1.5
Or major environmental impact if (1.2)* (1.3)
Slope fails
Imminent danger to human life 1.5 2.0 or greater
or major environmental impact (1.3) (1.7 or greater)
1 The uncertainty of the strength measurements is
smallest when the soil conditions are uniform and high
quality strength test data provide a consistent,
complete, and logical picture of the strength
characteristics.
2 The uncertainty of the strength measurements is
greatest when the soil conditions are complex and when
available strength data do not provide a consistent,
complete, and logical picture of the strength
characteristics.
* Numbers without parentheses apply for static conditions
and those within parentheses apply to seismic
conditions.
Source: EPA Guide to Technical Resources for the Design of
Land Disposal Facilities.
************************************************************
There are numerous methods currently available for
performing slope stability analyses. Method selection
should be based on the soil properties and the anticipated
mode of failure. Rationale for selecting a specific method
should be provided.
The majority of these methods may be categorized as
"limit equilibrium" methods in which driving and resisting
forces are determined and compared. The basic assumption of
the limit equilibrium approach is that the failure criterion
is satisfied along an assumed failure surface. This surface
may be a straight line, circular arc, logarithmic spiral, or
other irregular plane. A free body diagram of the driving
forces acting on the slope is constructed using assumed or
known values of the forces. Next, the soil's shear
resistance as it pertains to establishing equilibrium is
calculated. This calculated shear resistance
then is compared to the estimated or available shear
strength of the soil to give an indication of the factor of
safety (Winterkorn and Fang, 1975).
Methods that consider only the whole free body as a
single unit include the Culmann method and the friction
circle method. Another approach is to divide the free body
into vertical slices and to consider the equilibrium of each
slice. Several versions of the slice method are available;
the best known are the Swedish Circle method and the Bishop
method. Discussions of these and other methods may be found
in Winterkorn and Fang (1975), Lambe and Whitman (1969), and
U.S. Navy (1986).
A computer program that is widely used for slope
stability analysis is PC STABL, a two-dimensional model that
computes the minimum critical factors of safety between
layer interfaces. This model uses the method of vertical
slices to analyze the slope and calculate the factor of
safety. PC STABL can account for heterogeneous soil
systems, anisotropic soil strength properties, excess pore
water pressure due to shear, static ground water and surface
water, pseudostatic earthquake loading, surcharge boundary
loading, and tieback loading. The program is written in
FORTRAN IV and can be run on a PC. Figure 2-7 presents a
typical output from the model.
************************************************************
Figure 2-7
Sample Output from PC STABLE Model
[Graphic]
************************************************************
Design for Slope Stabilization
Methods for slope stabilization are presented in Table
2-5 and are summarized below.
************************************************************
TABLE 2-5
METHODS OF STABILIZING EXCAVATION SLOPES
Scheme
1. Changing Geometry
Excavation
[Graphic]
Applicable Methods
1. Reduce slope height by excavation at top of slope.
2. Flatten the slope angle.
3. Excavate a bench in upper part of slope.
Comments
1. Areas has to be accessible to construction equipment.
Disposal site needed for excavated soil. Drainage
sometimes incorporated in this method.
Scheme
2. Earth Berm Fill
[Graphic]
Applicable Methods
1. Compacted earth or rock berm placed at and beyond the
toe. Drainage may be provided behind the berm.
Comments
1. Sufficient width and thickness of berm required so
failure will not occur below or through the berm.
Scheme
3. Retaining Structures
[Graphic]
Applicable Methods
1. Retaining wall: crib or cantilever type.
2. Drilled, cast-in-place vertical piles and/or slabs
founded well below bottom slide plane. Generally 18 to
36 inches in diameter and 4- to 8-foot spacing. Larger
diameter piles at closer spacing may be required in
some cases with mitigate failures of cuts in highly
fissured clays.
Comments
1. Usually expensive. Cantilever walls might have to be
tied back.
2. Spacing should be such that soil can arch between
piles. Grade beam can be used to tie piles together.
Very large diameter (6 feet plus or minus) piles have
been used for deep slides.
Scheme
Retaining Structure
[Graphic]
Applicable Methods
3. Drilled, cast-in-place vertical piles tied back with
battered piles or a deadman. Piles founded well below
side plane. Generally, 12 to 30 inches in diameter and
at 4- to 8-foot spacing.
Comments
3. Space close enough so soil will arch between piles.
Piles can be tied together with grade beam.
Scheme
Retaining Structure
[Graphic]
Applicable Methods
4. Earth and rock anchors and rock bolts.
Comments
4. Can be used for high slopes, and in very restricted
areas. Conservative design should be used, especially
for permanent support. Use may be essential for slopes
in rocks where joints dip toward excavation, and such
joints daylight in the slope.
Scheme
Retaining Structure
[Graphic]
Applicable Methods
5. Reinforced earth.
Comments
5. Usually expensive.
************************************************************
* The first illustration shows that stability can be
increased by changing the slope geometry through
reduction of the slope height, flattening the
slope angle, or excavating a bench in the upper
part of the slope.
* The second illustration shows how compacted earth
or rock fill can be placed in the form of a berm
at and beyond the slope's toe to buttress the
slope. To prevent the development of undesirable
water pressure behind the berm, a drainage system
may be placed behind the berm at the base of the
slope.
* The third illustration presents several types of
retaining structures. These structures generally
involve drilling and/or excavation followed by
constructing cast-in-place concrete piles and/or
slabs.
-- The T-shaped cantilever wall design enables
some of the retained soil to contribute to
the stability of the structure and is
advisable for use on slopes that have
vertical cuts.
-- Closely-spaced vertical piles placed along
the top of the slope area provide
reinforcement against slope failure through a
soil arching effect that is created between
the piles. This type of retaining system is
advisable for use on steeply cut slopes.
-- Vertical piles also may be designed with a
tie back component at an angle to the
vertical to develop a high resistance to
lateral forces. This type of wall is
recommended for use in areas with steeply cut
slopes where soil arching can be developed
between the piles.
-- The last retaining wall shown uses a
cantilever setup along with soil that has
been reinforced with geosynthetic material to
provide a system that is highly resistant to
vertical and lateral motion. This type of
system is best suited for use in situations
where vertically cut slopes must have lateral
movement strictly controlled.
Other potential procedures for stabilizing natural and
human-made slopes include the use of geotextiles and
geogrids to provide additional strength, the installation of
wick and toe drains to relieve excess pore pressures,
grouting, and vacuum and wellpoint pumping to lower
ground-water levels. In addition, surface drainage may be
controlled to decrease infiltration, thereby reducing the
potential for mud and debris slides in some areas. Lowering
the ground-water table also may have stabilizing effects.
Walls or large-diameter piling can be used to stabilize
slides of relatively small dimension or to retain steep toe
slopes so that failure will not extend back into a larger
mass (U.S. Navy, 1986). For more detailed information
regarding slope stabilization design, refer to Winterkorn
and Fang (1975), U.S. Navy (1986), and Sowers (1979).
Richardson and Koerner (1987) and Koerner (1986) provide
design guidance for geosynthetics in both landfill and
general applications.
Monitoring
During construction activities, it may be appropriate
to monitor slope stability because of the additional
stresses placed on natural and engineered soil systems
(e.g., slopes, foundations, dikes) as a result of excavation
and filling activities. Post-closure slope monitoring
usually is not necessary.
Important monitoring parameters may include settlement,
lateral movement, and pore water pressure. Monitoring for
pore water pressure is usually accomplished with piezometers
screened in the sensitive strata. Lateral movements of
structures may be detected on the surface by surveying
horizontal and vertical movements. Subsurface movements may
be detected by use of slope inclinometers. Settlement may
be monitored by surveying ground surface elevations (on
several occasions over a period of time) and comparing them
with areas that are not likely to experience changes in
elevations (e.g., USGS survey monuments).
Engineering Considerations for Karst Terrains
The principal concern with karst terrains is
progressive and/or catastrophic failure of subsurface
conditions due to the presence of sinkholes, solution
cavities, and subterranean caverns. The unpredictable and
catastrophic nature of subsidence in these areas makes them
difficult to develop as landfill sites. Before situating a
MSWLF in a karst region, the subject site should be
characterized thoroughly.
The first stage of demonstration is to characterize the
subsurface. Subsurface drilling, sinkhole monitoring, and
geophysical testing are direct means that can be used to
characterize a site. Geophysical techniques include tests
using electromagnetic conductivity, seismic refraction,
ground-penetrating radar, gravity, and electrical
resistivity. Interpretation and applicability of different
geophysical techniques should be reviewed by a qualified
geophysicist. Often more than one technique should be
employed to confirm and correlate findings and anomalies.
Subsurface drilling is recommended highly for verifying the
results of geophysical investigations.
Additional information on karst conditions can come
from remote sensing techniques, such as aerial photograph
interpretation. Surface mapping of karst features can help
to provide an understanding of structural patterns and
relationships in karst terrains. An understanding of local
carbonate geology and stratigraphy can aid in the
interpretation of both remote sensing and geophysical
techniques.
A demonstration that engineering measures have been
incorporated into a unit located in a karst terrain may
include both initial design and site modifications. A
relatively simple engineering modification that can be used
to mitigate karst terrain problems is ground-water and
surface water control and conveyance. Such water control
measures are used to minimize the rate of dissolution within
known near-surface limestone. This means of controlling
karst development may not be applicable to all karst
situations. In areas where development of karst topography
tends to be minor, loose soils overlying the limestone may
be excavated or heavily compacted to achieve the needed
stability. Similarly, in areas where the karst voids are
relatively small and limited in extent, infilling of the
void with slurry cement grout or other material may be an
option.
In general, due to the unpredictable and catastrophic
nature of ground failure in such areas, engineering
solutions that try to compensate for the weak geologic
structures by constructing manmade ground supports tend to
be complex and costly. For example, reinforced raft (or
mat) foundations could be used to compensate for lack of
ground strength in some karst areas. Raft foundations are a
type of "floating foundation" that consist of a concrete
footing that extends over a very large area. Such
foundations are used where soils have a low bearing capacity
or where soil conditions are variable and erratic; these
foundations are able to reduce and distribute loads.
However, it should be noted that, in some instances, raft
foundations may not necessarily be able to prevent the
extreme type of collapse and settlement that can occur in
karst areas. In addition, the construction of raft
foundations can be very costly, depending on the size of the
area.
2.8 CLOSURE OF EXISTING MUNICIPAL SOLID WASTE LANDFILL
UNITS 40 CFR Section 258.16
2.8.1 Statement of Regulation
(a) Existing MSWLF units that cannot make the
demonstration specified in Section 258.10(a), pertaining to
airports, 258.11(a), pertaining to floodplains, and
258.15(a), pertaining to unstable areas, must close by
October 9, 1996, in accordance with Section 258.60 of this
part and conduct post-closure activities in accordance with
Section 258.61 of this part.
(b) The deadline for closure required by paragraph (a)
of this section may be extended up to two years if the owner
or operator demonstrates to the Director of an approved
State that:
(1) There is no available alternative disposal
capacity;
(2) There is no immediate threat to human health and
the environment.
2.8.2 Applicability
These requirements are applicable to all MSWLF units
that receive waste after October 9, 1993 and cannot meet the
airport safety, floodplain, or unstable area requirements.
The owner or operator is required to demonstrate that the
facility: (1) will not pose a bird hazard to aircraft under
Section 258.10(a); (2) is designed to prevent washout of
solid waste, will not restrict floodplain storage capacity,
or increase floodwater flow in a 100-year floodplain under
Section 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 Section 258.15(a). If any of
these demonstrations cannot be made, the landfill must close
by October 9, 1996. In approved States, the closure
deadline may be extended up to two additional years if it
can be shown that alternative disposal capacity is not
available and that the MSWLF unit does not pose an immediate
threat to human health and the environment.
2.8.3 Technical Considerations
The engineering considerations that should be addressed
for airport safety, 100-year floodplain encroachment, and
unstable areas are discussed in Sections 2.2, 2.3, and 2.7
of this chapter. Information and evaluations necessary for
these demonstrations also are presented in these sections.
If applicable demonstrations are not made by the owners or
operators, the landfill unit(s) must be closed according to
the requirements of Section 258.60 by October 9, 1996.
For MSWLF units located in approved States, this
deadline may be extended if there is no immediate threat to
human health and the environment and no waste disposal
alternative is available. The demonstration of no disposal
alternative should consider all waste management facilities,
including landfills, municipal waste combustors, and
recycling facilities. The demonstration for the two-year
extension should consider the impacts on human health and
the environment as they relate to airport safety, 100-year
floodplains, or unstable areas.
Sections 258.17-258.19 [Reserved].
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.
COE, (1989). "Federal Manual for Identifying and
Delineating Jurisdictional Wetlands," Federal Interagency
Committee for Wetland Delineation; U.S. Army Corps of
Engineers, U.S. Environmental Protection Agency, U.S. Fish
and Wildlife Service, and U.S.D.A., Soil Conservation
Service; Washington, D.C., Cooperative Technical
Publication. 1989.
Fault Areas, (1992). "Aspects of Landfill Design for
Stability in Seismic Zones," Hilary I. Inyang, Ph.D.
Seismic Impact Zones
Algermissen, S.T., et al., (1991). "Probabilistic
Earthquake Acceleration and Velocity Maps for the United
States and Puerto Rico," USGS Miscellaneous Field Study Map
MF-2120.
Algermissen, S.T., et al., (1976). "Probabilistic
Estimates of Maximum Acceleration and Velocity in Rock in
the Contiguous United States"; Open File Report 82-1033;
U.S. Geological Survey; Washington, D.C.
U.S. EPA, (1992). "Aspects of Landfill Design for
Stability in Seismic Zones", Hilary I. Inyang. Ph.D.
U.S. Navy, (1983). "Design Manual-Soil Dynamics, Deep
Stabilization, and Special Geotechnical Construction,"
NAVFAC DM-7.3; Department of the Navy; Washington, D.C.;
April, 1983.
Winterkorn, H.F. and Fang, H.Y., (1975). "Foundation
Engineering Handbook." Van Nostrand Reinhold. 1975.
Unstable Areas
Geoslope Programming Ltd., (1986). PC-SLOPE, Version
2.0 (May); Calgary, Alberta, Canada.
Huang, U.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.
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)
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
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
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.
APPENDIX I
FAA Order 5200.5A
[Order]