United States
                   Environmental Protection
Solid Waste and
Emergency Response
Publication 9320.2-1 OFS
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.

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
     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.


     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

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.


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


 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


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.


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.


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.


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,

*    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.


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,

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
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.