United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
Publication 9320.2-1 OFS
PB95-963320
EPA 540/F-95/033
May 1996
&EPA Clarifying the Definition of "Site1
Under the National Priorities List
Office of Emergency and Remedial Response
State, Tribal, and Site Identification Center (5204G)
Quick Reference Fact Sheet
The purpose of the National Priorities List (NPL) under the Superfund program is to identify sites where releases of
hazardous substances or pollutants and contaminants are priorities for further evaluation. Hence, the NPL is a list of
releases. Over the years, questions have arisen regarding how sites are defined for placement on the NPL. This fact sheet
is intended to answer some common questions on the definition of an NPL site. Subjects covered in this fact sheet include:
NPL site boundaries, the way sites are delineated, and the way site boundaries change over time.
DEFINITIONS
Although CERCLA does not define the term "site," it
does explain related terms such as. "facility" (CERCLA
§101(9)) and "release" (CERCLA. §101(22)). According
to CERCLA, there are two definitions of facility. The
first definition is in broad terms of operable portions of
properties (e.g.,. building, structure, installation,
equipment, lagoon,- landfill, etc.). The second defines a
facility as "... any site or area where a hazardous
substance has been deposited, stored, disposed of, or
placed, or otherwise come to be located ...." The second
CERCLA definition of facility is essentially synonymous
with the definition of "site" as defined in the Hazard
Ranking System (HRS), a screening tool that is EPA's
primary mechanism for placing sites on the NPL (55 FR
51587, December 14, 1990). However, the CERCLA
definition of facility is broader than the HRS definition
of site.
The National Oil and Hazardous Substances Pollution
Contingency Plan (NCP) (55 FR 8845, March 8, 1990)
specifies that the NPL is "... the list of priority releases
for long-term remedial evaluation and response." Thus,
the emphasis is on determining the extent of
contamination rather than on identifying strict
boundaries.
Based on these descriptions, a "site" is best defined as
that portion of a facility that -includes the location of a
release (or releases) of hazardous substances and
wherever hazardous substances have come to be located.
As such, the. extent of a site is not limited by property
boundaries, and does not include clean areas within a
facility's property boundaries. Furthermore, at the listing
stage only a limited amount of information has been
gathered in a preliminary assessment and site inspection.
These screening tools focus on identifying the possible
threat posed by a site, not on delineating the site
boundary. Therefore, the extent of contamination (site
extent) may not be precisely determined at the time a site
is listed on the NPL. In fact, the extent of the site may
change significantly as the cleanup process progresses.
HOW IS AN NPL SITE DELINEATED AT
LISTING?
CERCLA §105(a)(8)(A) requires EPA to list national
priorities among the known "releases or threatened
releases" of hazardous substances; therefore, the focus
is on the release, not on the precisely delineated site
boundaries. Usually, EPA identifies and lists releases
based on review of contamination at a facility, but this
does not necessarily mean that site boundaries are limited
to that facility's property. At listing, the. term "site"
corresponds with locations of any known releases (or
threatened releases) of hazardous substances or
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CERCLA eligible pollutants and contaminants associated
with the facility under evaluation. In addition, if another
area of contamination is discovered elsewhere on the
property or on nearby properties, EPA may decide to
evaluate that release for the NPL separately.
The main purpose of the NPL is to identify those sites
that may warrant further investigation to assess the
nature and extent of the public health and environmental
threats associated with the site relative to other candidate
sites (58 FR 27509, May 10, 1993). These sites may
also be subject to lengthy, extensive investigations to
determine the extent of a release later. Generally EPA
does not delineate the exact boundaries of a site at NPL
listing because the Agency's understanding of a
hazardous waste site broadens during subsequent steps in
the Superfund process as information becomes available.
EPA's first look at a potential hazardous waste site in the
site assessment process is a preliminary assessment
(PA), which is designed to verify site conditions and
screen for Superfund eligibility. EPA reviews technical
information on the site and on the location of
contamination. For example, if EPA receives reports of
a pile of hazardous wastes, the Agency will determine
whether there is any possibility for overland flow of
materials toward surface water or whether contaminants
could migrate to the ground water or become suspended
in the air. The "site" at this point is loosely defined as
the pile and any obvious contamination surrounding it.
During a site inspection (SI), which is a^ focused
screening study to identify releases, the EPA investigator
may collect samples of the pile, the soil, the air, surface
water/sediment, and/or the ground water. If another
source of contamination from the same facility is
discovered, it may be sampled as well. If the SI reveals
releases that pose a potential threat to human health or
the environment, EPA evaluates the site using the HRS
and, if the site scores sufficiently high, may propose it
to the NPL. EPA makes no definitive determination
about the extent of the site at the time of proposal to the
NPL nor at the tune the site is placed on the NPL.
HOW AND WHY DOES THE EXTENT OF THE
SITE CHANGE AFTER LISTING?
The extent and nature of a release becomes more refined
as information from the remedial investigation (RI) is
gathered. During the RI stage, EPA samples the site
more extensively. This investigation frequently results in .
finding or verifying additional contamination' that was
unknown or undocumented in the site inspection. After
the RI is completed, enough information is generally
available to determine areas to which contamination has
spread and, therefore, determine site boundaries.
For example, if during the site inspection contamination
is discovered in ground water as well as in a nearby
wetland, the ground water plume and contaminated
portions of the wetland are considered to be part of the
site. If, during remedial actions, contamination is found
to be either less or more extensive, site boundaries shift
again. This is especially true for ground water
contamination plumes, since their boundaries are in
constant motion.
NPL site boundaries will vary over tune. Throughout the
life of the project, information may develop that results
in finding more contamination than was previously
thought to be present. Conversely, as remedial action is
implemented, site boundaries may contract. This is
especially true when ground water plumes get smaller
during remediation and when portions of sites are
cleaned. According to recent EPA guidance (Procedures
for Partial Deletion at NPL Sites, Publication No.
9320.2-11, April 1996), portions of NPL sites can.be
deleted from the site when criteria for cleaning that
portion are met. r
WHAT DOES THE SITE NAME MEAN?
EPA uses the NPL primarily to identify those sites that
appear to present a significant threat to public health or
the environment and for which more study is needed, hi
naming the site, the Agency does not judge owner or
operator activities, nor does it require those persons to
undertake any action or assign liability. The name
merely helps the public to identify hazardous waste sites.
EPA's Regional Quality Control Guidance for NPL
Candidate Sites (December 1991) directs that the site
name should "clearly inform the public as to what
appears to be the primary source of the problems at the
site on the basis of the information available at the time.
In most cases this should be the principal operator." If
the site is commonly known by another name, that name
could be used. If it is unclear who is or was the
operator, or whether there are more than three
potentially responsible parties (PRPs), a geographic-
based site name can be assigned.
A site does not necessarily correspond to boundaries of
any specific property that may give the site its name.
Further, the name itself does not imply that the site is
within the property boundary of a certain plant or
installation or that all parts of the named property are
contaminated.
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IS THE OWNER OF TBE LAND ABOVE A
GROUND WATER PLUME RESPONSIBLE FOR
THE SITE?
In exercising its enforcement discretion, EPA will not
take actions against a residential property owner to
require the owner to undertake response actions or pay
response costs, unless the homeowner's activities lead to
a release or threat of release, of hazardous substances that
results in EPA taking a response action at the site (60 FR
34789, My 3, 1995). This policy is based on a May 24,
1995 memorandum entitled "Final Policy Toward
Owners of Property Containing Contaminated Aquifers."
This policy covers residential property owners whose
property is located above a ground water plume that is
proposed to or on the NPL, where the residential
property owner did not contribute to the contamination
of the site.
CERCLA LIABILITY
Identifying property that is part of an NPL site does not
establish CERCLA liability. CERCLA liability is
determined under CERCLA §107, which makes no
reference to NPL listing. Placing a site on the NPL does
not create CERCLA liability where it would not
otherwise exist. The fact that a parcel lies within the area
used to describe an NPL site does not impose liability on
the owner or subsequent purchaser; liability is based on
a release or threatened release of a hazardous substance
from a facility. The liability will exist regardless of
whether the site is listed on the NPL.
CASE STUDIES
The following actual case studies illustrate EPA's
approach to identifying sites.
The Byron Salvage Yard site was proposed to the NPL
as a site where all releases (or threatened releases) were
thought to have come from a single facility. Waste
containing cyanide and other plating waste was dumped
in and around the yard. After the record of decision
(ROD) was completed, the site boundaries changed to
include not only portions of Byron Salvage Yard, but
also portions of an adjacent property called "Dirk's
Farm" and contaminant plumes that extended north from
both properties to wells serving a nearby community.
The Hanford Facility sites are an example of one facility
containing four separate sites. The four sites were listed
on the NPL separately because the releases were from
separate sources and threatened different targets. EPA
evaluated the large number of potentially contaminated
areas (337) and determined that rather than listing ah* 337
areas separately, it was more appropriate to list them on
the NPL as four sites, each with similar production
processes and similar wastes. The four sites contained
over 90 percent of the potentially contaminated areas at
Hanford; the remaining 10 percent was handled under
other regulatory programs. This approach was
considered to be appropriate for the extremely large size
of the Hanford Facility (570 square miles) and the
CERCLA requirement that all criteria applicable to
inclusion on the NPL are also applicable to Federal
facilities, such as Hanford.
INTERAGENCY WORKGROUP
As a part of the Administrator's interest in clarifying the
NPL listing policy, EPA formed a workgroup with
representatives from the EPA Regions and the
Department of Defense. After' reviewing statutes,
regulations, guidance, and statements of policy on NPL
site listings, the interagency committee agreed that EPA
has consistently defined sites at listing, but that the
Agency needs to further clarify this definition. The focus
of the group, therefore, was to formulate and
disseminate a clear statement of what a listing on the
NPL includes.
The workgroup accomplished three goals:
• Clarifying language for proposed or final NPL
rules as published in 60 FR 50435, September 29,
1995;
* Amending currently proposed and final Superfund
docket listing packages to include a clear statement
that the sites are not based on property boundaries,
but rather the area of contamination; and
• Coordinating with the Regional EPA staff to ensure
HRS documentation records identify sites consistent
with this definition.
SUMMARY
Three key points govern the nature of an NPL site at the
time it is proposed for listing:
• An NPL site includes areas found to be
contaminated from releases of hazardous
substances. The boundaries of an NPL site are not
tied to the boundaries of the property on which a
facility is located. The release may be contained
within a single property's boundaries or may
extend across property boundaries onto other
properties. The boundaries can, and often do,
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change as further information on the extent and
degree of contamination is obtained.
Site names are chosen to aid the public in
identifying the geographic location of the
contamination.
Liability is not based on an NPL listing. The
liability associated with a Superfund site is based
on the release of hazardous substances and exists
whether a site is listed on the NPL or not.
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