United States
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Response
Directive: 9355.3-11FS
September 1990
unicipal Landfill Sites
Office of Emergency and Remedial Response
Hazardous Site Control Division
Quick Reference Fact Sheet
Approximately 20 percent of the sites on the National Priorities List (NPL) are municipal landfills which typically share similar
characteristics. Because of this similarity the Superfund Program anticipates that their remediation will involve similar waste management
approaches. As stated in the National Contingency Plan, EPA expects that containment technologies will generally be appropriate for waste
that poses a relatively low long-term threat or where treatment is impracticable (Sec. 300.430(a)(l)(iii)(B), 55 FR 8846 (March 8,1990)).
In addition, EPA expects treatment to be considered for identifiable areas of highly toxic and/or mobile material that constitute the principal
threat(s) posed by the site (Sec. 300.430(a)(l)(iii)(A)). The similarity in landfill characteristics and the NCP expectations make itpossible
to streamline the RI/FS for municipal landfills with respect to site characterization, risk assessment, and the development of remedial action
alternatives. This fact sheet outlines available streamlining techniques for each of these three phases of an RI/FS. Additional information,
including tools to assist in scoping activities, will be included in the document Conducting Remedial Investigations/Feasibility Studies for
CERCLA Municipal Landfill Sites (November 1990, Directive No. 9355.3-11). This document will be available from the Center for
Environmental Research Information (FTS 684-7562 or 513-569-7562).
Landfill Site
Characteristics
For the purpose of this fact sheet,
CERCLA municipal landfills are those
facilities where a combination of princi-
pally municipal and to a lesser extent haz-
ardous wastes have been co-disposed.
Because of the volume and heterogeneity of
waste within these landfills, treatment of the
entire contents is often impracticable. Po-
tential threats to human health and the envi-
ronment resulting from municipal landfills
may include: (1) leachate generation and
groundwater contamination; (2) soil con-
tamination; (3) landfill contents; (4) landfill
gases; and (5) contamination of surface
waters, sediments, and adjacent wetlands.
A conceptual model of the potential path-
ways of exposure to hazardous substances
that may exist at municipal landfill sites is
presented in Figure 1. Affected media and
their pathways of exposure that are unique
to landfills are the subject of this fact sheet;
other media are discussed in the forthcom-
ing guidance.
Streamlining Site
Characterization
The characterization of a municipal
landfill site can be expedited by focusing
field activities on the information needed to
(1) sufficiently assess risks posed by the
site, and (2) evaluate practicable remedial
actions. Additionally, site characterization
may be streamlined by conducting a limited
field investigation during scoping of the RI/
FS to assist in identifying necessary
fieldwork. Examples of limited field inves-
tigation activities may include evaluating
usefulness of an existing monitoring well
network or verifying that the landfill was
constructed as designed.
Leachate/Groundwater
Contamination
Characterization of a site's geology and
hydrogeology are necessary to adequately
assess the design of extraction and treat-
ment systems for leachate and groundwater
as well as capping options. Groundwater
contamination at municipal landfill sites
may vary in composition from that at other
types of sites in that it often contains high
levels of organic matter and metals. Data
gathered during the hydrogeologic investi-
gation, however, are similar to those gath-
ered at other types of NPL sites.
Leachate generation is of specific con-
cern when characterizing municipal landfill
sites. The main factors contributing to
leachate quantity include precipitation as
well as recharge from groundwater and
surface water. Information to be gathered
during characterization of leachate gener-
ally may be limited to:
• Surface water drainage patterns
• Climatological characteristics (e.g., pre-
cipitation and evapotranspiration)
1
• Leachate characteristics (e.g., TCL or-
ganics, TAL metals, BOD, COD, pH,
TDS, TSS, phosphorus, nitrogen, and oil
and grease)
• Identification of Class I and II aquifers
and their associated water levels, flow
rates, and chemistry
In many landfills, leachate is perched
within the landfill contents, above the water
table. The placement of a limited number of
leachate wells in the landfill is an efficient
means of gathering information regarding
the depth, thickness, and types of waste, the
moisture content and degree of decomposi-
tion of the waste, leachate head levels, the
composition of the leachate, and the eleva-
tion of the underlying natural soil layer.
Additionally, leachate wells provide good
locations for landfill gas sampling. It should
be noted that, without the proper precau-
tions, placing wells into the landfill con-
tents may create health and safety risks.
Additionally, installation of wells through
the landfill base may create conduits through
which leachate can migrate to lower geo-
logic strata. The installation of wells into
landfill contents may also make it difficult
to ensure the reliability of the sampling
locations.
Landfill Contents/Hot Spots
Characterization of a municipal landfill's
contents generally is not necessary because
containment, which is often the most prac-
ticable technology, does not require such
information. Certain data, however, are
-------
Figure 1
Potential Exposure Pathways for Municipal Landfills
CONTAMINANT
SOURCE
CONTAMINANT
RELEASE/TRANSPORT
SECONDARY
RECEPTOR
Terrestrial
Wildlife
People Who
Consume Wildlife
necessary to evaluate containment alterna-
tives. These include:
• Contour maps
• Fill thickness, lateral extent, and age
• Estimate of landfill settlement rate
• Estimate of raleof landfill gasproduction
and landfill gas composition
• Soil characteristics, including permeabil-
ity, grain size, Atterbcrg limits, and ero-
sion rates
• Climaticconditions.includingfrostdepth,
and the appropriate storm event creating
the potential for significant erosion
• Geologic and hydrogeologic characteris-
tics, particularly the permeability of the
layer underlying the landfill; the depth to
groundwater; thickness of waste below
the water table; and groundwater flow
through the waste, if applicable
• Physical characteristics cf any existing
cap including thickness, area, slope sta-
bility, evidence of freeze-thaw protec-
tion, and soil characteristics as well as its
ability to reduce surface gas emissions
and odors, prevent oxygen intrusion into
the refuse, prevent surface water infiltra-
tion, provide erosion control, and im-
prove site aesthetics
• Potential future uses of the site (e.g.,
residential or recreational use)
More extensive characterization activi-
ties and development of remedial alterna-
tives (such as thermal treatment or stabiliza-
tion) may be appropriate for hot spots. Hot
spots consist of highly toxic and/or highly
mobile material and present a potential prin-
cipal threat to human health or the environ-
ment (see NCP Sec. 300.430 (a)(l)(iii)(C)).
Excavation or treatment of hot spots is
generally practicable where the waste type
or mixture of wastes is in a discrete, acces-
sible location of a landfill. A hot spot should
be large enough that its remediation will
significantly reduce the threat posed by the
overall site, but small enough that it is
reasonable to consider removal and/or treat-
ment. It may generally be appropriate to
excavate and/or treat the contents of a landfill
where a low to moderate volume of toxic/
mobile waste (e.g., 100,000 cy or less) poses
a principal threat to human health and the
environment.
Hot spots should be characterized if docu-
mentation and/or physical evidence exists
to indicate their presence and approximate
location. Hot spots may be delineated using
geophysical techniques or soil gas surveys
and typically are confirmed by excavating
test pits or drilling soil borings. When chnm
acterizing hot spots, soil samples should^
collected to determine hot spot waste char-
acteristics, including TAL metals, TCL
organics, RCRA waste characteristics (e.g.,
-------
TCLP), total Btu content, and bulk weight
of the material. Treatability or pilot testing
Biay be required to evaluate treatment alter-
natives.
Landfill Gas
Several gases typically are generated by
decomposition of organic materials in a
landfill. The composition, quantity, and
generation rates of the gases depend on such
factors as refuse quantity and composition,
refuse placement characteristics, age of the
disposal unit, landfill depth, refuse mois-
ture content, and amount of oxygen present.
The principal gases generated by volume
are carbon dioxide, methane, trace thiols,
and occasionally, hydrogen sulfide. Vola-
tile organic compounds are also present in
landfill gases, particularly at co-disposal
facilities. Data generated during the site
characterization of landfill gases should
include:
• Contour drawings and rate of settlement
• Geologic and hydrogeologic characteris-
tics, including permeability, moisture
content, geologic strata, pH, depth to
bedrock, and depth to groundwater
• Presence of offsite, subsurface migration
• Surface emissions
• Ambient air monitoring
• Landfill gas characteristics, including
composition, moisture content, quantity,
temperature, and methane content
Figure 2
Technologies Frequently Implemented for
Remedial Action at CERCLA Municipal Landfills
REMEDIAL ACTION
OBJECTIVE
REMEDIAL TECHNOLOGY
Cap
Disposal
Thermal Treatment
Physical Treatment
Vertical Barrier
PROCESS OPTION
Soil Cover
Single Barrier
Double Barrier
Leachate Collection
Groundwater Collection
Consolidation
Incineration
Solidification/Fixation
Slurry Wall
Vertical Extraction Wells
Subsurface Drains
Treat
Contaminated
Groundwater
& Leachate a
Chemical Treatment
Biological Treatment
Physical Treatment
Offsite Treatment
Passive Systems
Active Systems
Thermal Treatment
Metals Precipitation
Aerobic
Anaerobic
Adsorption
Air Stripping
POTW
RCRATSD
Pipe Vents
Trench Wells
Extraction Wells
Flaring
• Other treatment technologies may be appropriate
Streamlining
The Baseline Risk
Assessment
The purpose of the baseline risk assess-
ment is to determine whether a site poses
risks to human health and the environment
that are significant enough to warrant reme-
dial action. Because options for remedial
action at municipal landfill sites are limited,
it may be possible to streamline or limit the
scope of the baseline risk assessment by:
1. Using the conceptual site model and RI-
generated data, to perform a qualitative
risk assessment that identifies contami-
nants of concern in the affected media,
their concentrations, and their hazard-
ous properties which may pose a risk
through the routes of exposure.
2. Identifying all pathways that are an
obvious threat to human health or the
environment (see Figure 1) by compar-
ing Rl-derived contaminant concentra-
tion levels to standards that are potential
chemical-specific ARARs for the ac-
tion. These may include: (1) Non-zero
MCLGs and MCLs for groundwater
and leachate and (2) State air quality
standards for landfill gases.
When potential ARARs do not exist for
a specific contaminant, risk-based
chemical concentrations should be used.
3. Where established standards for one or
more contaminants in a given medium
are clearly exceeded, the basis for tak-
ing remedial action is warranted (i.e.,
quantitative assessments that consider
all chemicals, their potential additive
effects, or additivity of multiple expo-
sure pathways are not necessary to initi-
ate remedial action).
4. In cases where clear exceedance of stan-
dards does not occur, a more thorough
risk assessment will be necessary prior
to initiating remedial action.
This streamlined approach may facili-
tate early action on the most obvious landfill
problems—groundwater and leachate,
landfill gas, and the landfill contents—while
analysis continues on other problems such
as affected wetlands and stream sediments.
However, the effect of early action on obvi-
ous problems should be factored into any
ongoing risk assessment. For example, if
leachate seepage that had been contaminat-
ing surface water and wetlands is stopped as
a result of an early action, then the risk
assessment developed subsequently for the
-------
stream sediments and wetlands should as-
sume no further loading. Any early actions
also need to be designed for flexibility so
that they will be consistent with subsequent
actions. For example, it may be necessary to
adjust a groundwater pump-and-treat early
action designed to attain MCLs so that even
lower levels, determined to be necessary
under a subsequent risk assessment, are
achieved in the interest of protecting envi-
ronmental receptors in the wetlands into
which the groundwater discharges.
Ultimately, it will be necessary to dem-
onstrate that the final remedy, once imple-
mented, will in fact address all pathways and
contaminants of concern (including envi-
ronmental risks), not just those that trig-
gered the remedial action. The approach
outlined above facilitates rapid implementa-
tion of protective, remedial measures for the
major problems at a municipal landfill site.
Streamlining
The Development
Of Alternatives
Figure 2 identifies remedial technologies
and process options for achieving various
Figure 3
Landfill Cover Selection Guide
LANDFILL CHARACTERISnCS
Minimal Hazardous Substances In
Landfill and Minimal Contamination
of Groundwater
Significant Percentage of Hazardous*
Substances In Fill Are Below the
Water Table, And Lowering the
.Water Table Is not Practicable J
/Leaching of Hazardous Substances
I to Groundwater Is Expected to
I Contribute to Unacceptable Human
I Health or Environmental Risks, and
I Reliability of Single Barrier Is
I Considered Adequate c
REMEDIAL OBJECTIVES
:Prevent Direct Contact;^
Minimize Erosion a I
C
COVERTYPE
Native Soil Cover
Prevent Direct Contacts
Minimize Erosion;
Minimize Infiltration )
C
Single Barrier Cap b 1
Significant Contaminant Mass
In Fill, and Risks of Hazardous
Substances Leaching to
Groundwater Are Great
Prevent Direct Contact; |
Minimize Erosion; |
Prevent Infiltration J
C
Double Barrier Cap
High Degree of Reliability Needed
In Method of Minimizing Leaching
of Hazardous Substances to
Groundwater
Primary objective )• to prevent direct contact, although the soil cover can be designed to reduce
intltlratlon.
Single barrier cap< may Include additional layers that provide protection to that barrier.
Examples Include iltuatlon* where Infiltration Is not the primary concern and may Include sites
containing • small volume of contaminant mass, regions with low annual precipitation, or sites
where groundwater Is not being used as a source of drinking water.
remedial action objectives pertaining to mu-
nicipal landfill sites. The following points
should be considered in order to streamline
the development of remedial action altern^
lives:
• The most practicable remedial alternative
for landfills is generally containment.
Figure 3 is a simplified decision tree for
identifying the appropriate type of cap.
• Treatment of soils and wastes may be
practicable for hot spots. Consolidation
of hot spot materials under a landfill cap
is a potential alternative in cases when
treatment is not practicable or necessary.
• Extraction and treatmentof contaminated
groundwaterandleachatemay be required
to control offsite migration of wastes.
Collection and treatment may be neces-
sary for an indefinite amount of time
because of continued contaminant load-
ings from the landfill.
• Constructing an active landfill gas collec-
tion and treatment system should be con-
sidered in the following situation: (1)
when existing or planned structures may
be adversely affected through either ex-
plosion or inhalation hazards, (2) when
final use of the site includes allowirj
public access, or (3) when the land
produces excessive odors. Most landfills
will require at least a passive gas collec-
tion (i.e., venting) system to prevent
buildup of pressure below the cap and to
prevent damage to the vegetative cover.
Onsite remedial actions at municipal
landfill sites must comply with all ARARs
of other environmental statutes, unless a
waiver can be justified. The most signifi-
cant ARARs for municipal landfills include:
• RCRA closure requirements (Subtitle D
requirements will be applicable unless
Subtitle C is determined to be applicable
orrelevantand appropriate; see CERCLA
Compliance with Other Laws Manual,
August 1988, for information on how to
make these determinations.)
• More stringent state closure requirements
• Federal or state requirements pertaining
to landfill gas emissions
wind
ndfH
NOTICE: The policies and procedures set out in this document are intended solely for the guidance of response personnel. They are not intended,
nor can they be relied upon, to create any rights, substantive or procedural, enforceable by any party in litigation with the United States. EPA of-
ficials may decide to follow this guidance, or to act at variance with these policies and procedures based on an analysis of specific site circum-
stances, and to change them at any time without public notice.
------- |