United States
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Response
Publication 9203.1-021
February 1993
Superf und Accelerated
Cleanup Bulletin
Presumptive Remedies for Municipal Landfill
Sites
Office of Emergency and Remedial Response
Office of Waste Programs Enforcement
Intermittent Bulletin
Volume 2 Number 1
The Presumptive Remedy Selection Initiative
Since Superfund's inception in 1980, the removal and remedial programs have found that certain categories of sites have
similar characteristics, such as the types of contaminants present, past industrial use, or the environmental media that are
affected. Based on a wealth of information acquired from evaluating and cleaning up these sites, Superfund is undertaking
an initiative to develop presumptive remedies that are appropriate for specific types of sites, contaminants, or both. This
initiative is part of a larger program, known as the Superfund Accelerated Cleanup Model (SACM), which is designed to
speed all aspects of the Superfund clean-up process.
The objective of the presumptive remedies initiative is to use clean-up techniques shown to be effective in the past at similar
sites in the future. The use of presumptive remedies will streamline removal actions, site studies, and clean-up actions, thereby
improving consistency, reducing costs, and increasing the speed with which hazardous waste sites are remediated.
Purpose
The Superfund Municipal Landfill Expert Team has com-
pleted four site visits under the Municipal Landfill Pilot
Project.1 The pilot project implements a 1991 streamlining
manual, "Conducting Remedial Investigations/Feasibil-
ity Studies for CERCLA Municipal Landfill Sites" (hereaf-
ter referred to as "the manual"). This bulletin presents key
findings from the pilots completed to date, particularly
with respect to the level of detail that was appropriate for
establishing risk, and therefore a basis for reme-
dial action, at two of the sites.
Background
i
The preamble to the National Con-
tingency Plan (NCP) identifies
municipal landfills as a type of site
where treatment of the waste may
be impracticable due to the size
and heterogeneity of the contents.
Because of this, containment will
often be the appropriate response
?ction for the source area of mu-
nicipal landfill sites. Such containment remedies are likely
to include a landfill cap; ground-water treatment or con-
trol; leachate collection and treatment; and landfill gas
collection and treatment, as appropriate.
Faster... C/eaner...Safer
The municipal landfill manual states that baseline risk
assessments at municipal landfill sites may be streamlined
or limited in order to initiate early remedial action on the
most obvious landfill problems (e.g., ground water/
leachate, landfill contents, and landfill gas). One method
for establishing risk using a streamlined approach is to
compare contaminant concentration levels (if available) to
standards that are potential chemical-specific applicable
or relevant and appropriate requirements (ARARs) for the
action. The manual states that where established standards
for one or more contaminants in a given medium
are dearly exceeded, remedial action is gen-
erally warranted.2 The manual further
r-k states that ultimately it is necessary to
^5j) demonstrate that the final remedy
^ addresses all pathways and con-
tarrunantsof concern, notjust those
that triggered the remedial action.
Pilot Project Findings
The experience of the expert team
supports the usefulness of a lim-
ited risk assessment to initiate early
action at two of the pilot sites. Specifically, for the source
area of these two sites (i.e., the discrete landfill area), a
qiiaptirafiyp risk assessment that considered all chemicals,
their potential additive effects, etc., was not necessary,
1 See "Superfund Accelerated Cleanup Bulletin. Presumptive Remedies for Municipal Landfill Sites," Publication 9203.1-021, Volume I, Number 1, April
1992.
2 See also OSWER Directive 9355.0-30, "Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions," April 22,1991, which states that
if MCLs or non-zero MCLGs are exceeded, (remedial) action generally is warranted.
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either to establish a basis for action or to establish clean-up
levels. For these two sites, the justification for early reme-
dial action was based on existing ground-water data.
Ground-water data are not available for the other two sites.
Sites with Ground-water Data
For the source areas of the two sites with existing ground-
water data, the basis for action was ground-water contami-
nation at levels exceeding non-zero MCLGs or MCLs;
therefore, a complete quantitative risk assessment was not
necessary to establish risk (and therefore a basis for action)
at these sites. Furthermore, a quantitative risk assessment
was not needed to evaluate whether the containment rem-
edy addressed all pathways and contaminants of concern
associated with the source. Rather, all potential migration
pathways were identified (using the conceptual site model)
and compared to those addressed by the containment
remedy as follows:
• direct contact threat and surface water run-off ad-
dressed by capping;
• exposure to contaminated ground water (including
any contaminated ground water moving off-site)
addressed by ground-water treatment/control (in-
cluding assessment of current exposure); and
* exposure to landfill gas addressed by gas collection
and treatment, as appropriate.
This comparison revealed that the containment remedy
addressed all pathways associated with the sources at
these sites.
Finally, a quantitative risk assessment was not required to
determine clean-up levels for the source areas, since the
type of cap will be determined by closure ARARs, and
ground-water clean-up levels may be based on MCLs, non-
zero MCLGs, or more-stringent, promulgated, state levels.
NOTE: In some cases, a risk assessment may be required to
determine the risk associated with contaminants in landfill
gas. Landfill gas collection will frequently be a necessary
component of the remedy to insure cap integrity. There
may be an additional need for treatment of the collected
gas based upon the contaminants present. In some cases,
state ARARs may identify clean-up levels for such con-
taminants, and in some cases health-based levels will be
appropriate. This issue will be addressed in further detail
in future guidance.
Sites with No Existing Ground-water Data
Ground-water data are not yet available for twodf the pilot
sites; for these sites, the following tiered approach was
recommended. Once ground-water data are obtained, a
clear basis for action may be established, and the remedy
selection may be streamlined as described for the two sites
with available ground-water data. If contaminants are not
identified above MCLs or non-zero MCLGs, however,
additional pathways, such as surface contamination and
landfill gas, will be characterized next, and a focused
quantitative risk assessment conducted to establish a basis
for remedial action.
Areas of Contaminant Migration
One of the expert team's key findings is that almost every
municipal landfill site has some unique characteristic that
may require additional study. Unique characteristics en-
countered during the pilot visits include leachate dis-
charge to a wetland atone site and significant surface water
run-off due to drainage problems at another. These path-
ways will require characterization and conventional risk
assessment to determine whether remedial action is war-
ranted beyond the source area, and if so, the type of action
that is appropriate.
Pilot Study Findings and Conclusions
The expert team's conclusions from the four pilots, then,
are that:
(1) a quantitative risk assessment was not warranted
for the source areas of the two pilot sites where
ground-water data were available and contami-
nants exceeded chemical-specific standards; justi-
fication for action was the exceedance of the stan-
dards;
Further, streamlining the risk assessment elimi-
nated the need for sampling and analysis of these
source areas to support the calculation of current
or future risk.
(2) a focused risk assessment generally will be neces-
sary for areas other than the landfill source itself
(such as areas where contaminants have migrated
from the source) to determine the need for addi-
tional remedial action beyond areas normally ad-
dressed by the cap; and
(3) a focused risk assessment generally will be neces-
sary to determine the need for remedial action at
sites where ground-water concentrations do not
exceed MCLs or non-zero MCLGs, unless other
conditions provide a clear justification (e.g. un-
stable slopes).
These conclusions are directly applicable to the four pilot
sites only; however, based on these findings, the municipal
landfill expert team is developing an Agency directive that
will provide additional guidance on conducting baseline
risk assessments at municipal landfill sites. For additional
information on the directive or the municipal landfill pilot
project, please call Andrea McLaughlin at 703-603-8793.
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