Consideration Of Cumulative Impacts In EPA Review of
NEPA Documents

U.S. Environmental Protection Agency, Office of Federal Activities (2252A)

EPA 315-R-99-002/May 1999


The combined, incremental effects of human activity, referred to as cumulative
impacts, pose a serious threat to the environment. While they may be
insignificant by themselves, cumulative impacts accumulate overtime, from one
or more sources, and can result in the degradation of important resources.
Because federal projects cause or are affected by cumulative impacts, this type
of impact must be assessed in documents prepared under the National
Environmental Policy Act (NEPA). The purpose of this guidance is to assist EPA
reviewers of NEPA documents in providing accurate, realistic, and consistent
comments on the assessment of cumulative impacts. The guidance focuses on
specific issues that are critical in EPA's review of NEPA documents under
Section 309 of the Clean Air Act. While there is no "cookbook" method of
assessing cumulative impacts, the guidance offers information on what issues to
look for in the analysis, what practical considerations should be kept in mind
when reviewing the analysis, and what should  be said in EPA comments
concerning the adequacy of the analysis.

The assessment of cumulative impacts in NEPA documents is required by
Council on Environmental Quality (CEQ) regulations (CEQ, 1987). Cumulative
impacts, however, are not often fully addressed in NEPA documents due to the
difficulty in understanding the  complexities of these impacts, a lack of available
information on their consequences,  and the desire to limit the scope of
environmental analysis. To  improve how cumulative impacts are assessed in
environmental impact analysis, CEQ developed a handbook entitled "Considering
Cumulative  Effects under the  National Environmental Policy Act" (CEQ 1997).
CEQ's handbook offers the most comprehensive and useful information to date
on practical methods for addressing cumulative effects in NEPA documents.
Consequently, the concepts presented in the handbook serve as the foundation
for this  guidance. Reviewers are urged to use this guidance and the CEQ
handbook simultaneously.

The guidance has four sections including this introduction. Section 2 What are
Cumulative Impacts briefly summarizes the definition and basic concepts used in
this guidance. Section 3 EPA's Review of Cumulative Impacts addresses several
fundamental questions concerning EPA's review of cumulative effects in a NEPA
analysis. Section 4 Major Review Areas discusses several of the key areas that
should be considered to adequately analyze cumulative impacts and offers
practical suggestions on how to prepare comments to address cumulative
impacts in NEPA documents. References are cited in a bibliography.


Cumulative impacts result when the effects of an action are added to or interact
with other effects in a particular place and within a particular time. It is the
combination of these effects, and any resulting environmental degradation, that
should be the focus of cumulative impact analysis. While impacts can be
differentiated by direct, indirect, and cumulative, the concept of cumulative
impacts takes into account all disturbances since cumulative impacts result in the
compounding of the effects of all actions over time. Thus the cumulative impacts
of an action can be viewed as the total effects on a resource, ecosystem, or
human community of that action and all other activities affecting that resource no
matter what entity (federal, non-federal, or private) is taking the actions .
Consistent with the CEQ regulations (CEQ, 1987), effects and  impacts are used
synonymously in the guidance.

CEQ's regulations (CEQ, 1987) explicitly state that cumulative  impacts must be
evaluated along with the direct  effects and indirect effects of each alternative. By
mandating the consideration of cumulative impacts, the regulations ensure that
the range of actions that is considered in NEPA documents includes not only the
project proposal but also all actions that could contribute to cumulative impacts.
Federal agencies prepare cumulative impact analysis using different terms and
approaches. To avoid arguing over semantic differences, EPA reviewers  should
avoid conflicts over terminology and pursue a common sense approach. The
concept of cumulative impacts as total impacts provided above is meant to
facilitate discussion in this document,  but it is not intended to replace other
usages that meet the intent of good cumulative effects analysis.


This section addresses fundamental questions concerning EPA's review of
cumulative impact analysis in NEPA documents.

Q. How should EPA review cumulative impacts analyses in NEPA documents?

A. The assessment of cumulative impacts is not substantially different from the
assessment of direct or indirect impacts. The same type of considerations are
made to determine the environmental consequences of the alternatives for direct,

indirect, or cumulative impacts. One possible difference is that cumulative impact
assessment entails a more extensive and broader review of possible effects.
Reviewers should recognize that while no "cookbook" approach to cumulative
impacts analysis exists, a general approach is described in the CEQ handbook.
As with the review of direct or indirect impacts, EPA review of cumulative impacts
analysis is most effective if done early in the process, especially in the scoping

Federal agencies have the responsibility of determining how and the extent to
which cumulative impacts are assessed in NEPA documents and documenting
that effort. In reviewing the analysis, the EPA reviewer should determine if the
information presented is commensurate with the impacts of the project, i.e., a
greater degree of detail is needed for more potentially serious  impacts. In
addition, in making  its rating  determinations, EPA will consider cumulative
impacts when determining the environmental impact of the action and the
adequacy of the analysis. EPA comments should identify significant cumulative
impacts that may affect resources of concern and suggest mitigation measures
that will avoid or minimize  adverse effects to the environment.  While this
guidance emphasizes the effects of projects on ecological resources, other
resources and areas that should be considered include socioeconomic
resources, human health, recreation, quality of life issues, and cultural and
historical resources.

Q. Should EPA reviewers expect that cumulative impact analysis be done in all
NEPA documents?

A. NEPA documents do not necessarily require cumulative impact assessments
in every case. However, EPA expects that the action agency consider whether
cumulative  impacts is a significant issue that should be addressed every time a
NEPA document is prepared. NEPA documents in this context includes both
environmental assessments  and environmental impact statements. As with most
NEPA assessments, the analysis should be commensurate with the project's
impacts and the resources affected.  In all phases of the cumulative impact
assessment, EPA should ensure that the level of analysis  and  scope are
commensurate with the potential impacts, resources affected, project scale, and
other factors. While projects  that have long-lasting and widespread effects in
environmentally sensitive areas should receive close scrutiny,  some projects may
not require  in-depth consideration of cumulative impacts. For example, small
scale projects that have minimal impacts that are of short-duration would not
likely contribute significantly  to cumulative impacts.

Q. Can cumulative  impacts be the basis for adverse ratings?

A. Cumulative impacts that result in significant  impacts can be the basis for
adverse ratings. EPA will consider cumulative impacts when determining the
rating for the environmental impacts of the proposed project. Ratings should be

based on the overall environmental impact of the proposed project or action,
which includes cumulative impacts. When the NEPA document does not contain
sufficient information, the determination of potential, total project impacts may be
based on other documents, information, or on-site surveys. In these situations,
the reviewer should identify the source of information that is the basis for EPA
comments including those related to cumulative impact analysis.

Q. Should EPA comments suggest mitigation measures to address cumulative

A. The EPA's manual on reviewing and commenting on federal actions under
NEPA and section 309 of the Clean Air Act (EPA, 1984) states that EPA's
comments should include mitigation measures " avoid or minimize damage to
the environment, or to protect, restore, and enhance the environment". It is
appropriate for EPA comments to include recommendations for mitigation that
address the cumulative impacts of the project. The comments should suggest a
range of mitigation that addresses differing sources of the cumulative impacts. At
a minimum, the mitigation should address the proposed project's contribution to
the cumulative impacts. In addition, it is appropriate to suggest mitigation to
address cumulative impacts that are caused by activities other than the proposed
project.  For example, mitigation could include forming partnerships among the
different governmental  agencies and private organizations to work on
environmental  restoration when those entities have contributed to cumulative
impacts over a long period of time.  It is important to note that EPA suggestions
for mitigation are not necessarily  constrained by whether the action agency has
jurisdiction to implement the measures but the  measures should be realistic and
technically feasible.

Q. Do EPA reviewers have to prove that cumulative impacts are occurring  if the
issue of cumulative impacts is raised by a proposed project?

A. Ultimately, the action agency is responsible for determining whether
cumulative impacts will occur. However, EPA reviewers should provide enough
information in their comments to show the likelihood that cumulative impacts will
occur. In order to make the case that the NEPA documents should include
cumulative impact analysis, EPA  comments need only to show the potential for
cumulative impacts to occur, not absolute proof that such impacts will take place.
EPA reviewers should use existing data to support an argument for considering
cumulative impacts in the document.


Several key areas of information should be considered by EPA reviewers in
determining whether the cumulative impacts assessment in a NEPA document is
adequate. These areas, as described below, expand on the approach presented
in the CEQ handbook. Each subsection presents background information on one

of five areas and offers guidance on what EPA reviewers should look for in the
assessment of cumulative impacts.

4.1 Resources and Ecosystem Components

EPA Review Approach

In reviewing cumulative impacts analysis, EPA reviewers should focus on the
specific resources and ecological components that can be affected by the
incremental effects of the proposed action and other actions in the same
geographic area. EPA reviewers should determine whether the NEPA analysis
has identified the resources and ecosystem components cumulatively impacted
by the proposed action and other actions. The reviewer can determine which
resources are cumulatively affected by considering:

(1) whether the resource is especially vulnerable to incremental effects;

(2) whether the proposed action is one of several similar actions in the same
geographic area;

(3) whether other activities in the area have similar effects on the resource;

(4) whether these effects have been historically significant for this resource; and

(5) whether other analyses in the area have identified a cumulative effects

Three documents that can provide useful information when considering important
resource  components include the 1993 EPA report, "Habitat Evaluation: Issues in
Environmental Analysis Review", the 1993 CEQ report, "Incorporating
Biodiversity Considerations Into Environmental Impact Analysis Under the
National Environmental Policy Act", and the 1994 EPA report "Evaluation of
Ecological Impacts from Highway Development".

Cumulative impacts can affect a broad array of resources and ecosystem
components. In addition to considering the biological resources that are the
staple of  NEPA analysis, examples of other resources that should be considered
include historic and archaeological sites, socioeconomic services and issues,
and community structure and character. While a broad consideration of
resources is necessary for the adequate assessment of cumulative impacts, the
analysis should be expanded for only those resources that are significantly
affected.  In similar fashion, ecosystem components should be considered when
they  are significantly affected by cumulative impacts. The measure of cumulative
effects is  any change to the function of these ecosystem components.


NEPA documents generally consider only a limited number of resources that may
be potentially affected by cumulative impacts. In addition, assessments of
impacts to biological resources generally have been limited to selected game
species, federally or state listed threatened and endangered species, and
wetlands habitats. These approaches are too limited and should be expanded to
consider other valuable resources which could be affected, while also
considering a broader array of potential effects.

As an example, federal assessment and mitigation for the loss of wetlands often
focus primarily on the acreage affected rather than the function of the wetland
within the broader ecosystem. In such a case, the impact to the wetland  might
not be deemed significant if the wetland had no immediate wildlife values or other
notable characteristics. However, by expanding the assessment to consider the
full array of wetland functions and their importance with a broader context,
cumulative impacts could be more fully assessed. For example, important
functions to focus on could include the wetlands'  role as a nursery for
recreationally and/or commercially valuable aquatic species; its ability to
minimize downstream  flooding; and its ability to improve water quality.

To ensure the inclusion of the resources that may be most susceptible,
cumulative impacts can be anticipated by considering where cumulative  effects
are likely to occur and what actions would most likely produce cumulative effects.
A framework for this consideration for forested areas is modified from Bedford
and Preston (1988). Certain types of forests  are more likely to be affected by
cumulative effects as described by the following examples:

1) forests downwind from major sources of air pollution that contain plant
organisms that are susceptible  to ozone and other airborne pollutants;

2) forested areas lower in a watershed because they are often closer to
development  and pollutants follow the movement of water;

3) forests that are susceptible to fragmentation because, with increasing
fragmentation, areas will have a large perimeter in relation to their area;  and

4) areas experiencing  development pressure.

Resources of concern may also be identified by considering actions that alter
ecological processes and therefore can be expected to produce cumulative
effects. Changing hydrologic patterns, for example, is likely to elicit cumulative
effects. Bedford and Preston (1988) offered the following alterations that would
likely initiate cumulative effects in wetlands or watersheds:

1) changes in sediment transport;

2) alteration of discharge and retention rates of water;

3) changes in velocity of water moving through the system;

4) disposal of organic pollutants where uptake is controlled by biological

5) disposal of chemicals that easily separate from  sediment and other materials
to which they are attached; and

6) filling of wetlands that results in increased pollutant loadings.

The NEPA document should identify which resources or ecosystem components
of concern might be affected by the proposed action or its alternatives within the
project area. Once these resources have been identified, consideration should be
given to the ecological requirements needed to sustain the resources. It is
important that the NEPA document consider these broader ecological
requirements when assessing how the project and other actions may
cumulatively affect the resources of concern. Often these ecological
requirements may extend beyond the boundaries of the project area,  but
reasonable limits should be made to the scope of the analysis.

NEPA Example: Several examples exist of agency NEPA documents that have
included a thorough consideration of resources. The Supplemental Information
Report for the Trail Creek Timber Sale, Wisdom Ranger District, Beaverhead
National Forest, MT was prepared by the Forest Service (Forest Service, 1991)
to consider two important resources (ecosystem components) that were not
included in the FEIS  for the project. The two resources were (1) the value of the
Trail Creek area as a biological corridor between adjacent wilderness and
roadless areas and (2) the biodiversity of the Trail Creek area and surrounding
lands as it might be affected by habitat fragmentation. The report considered
potential impacts in the context of the natural disturbance process, such as fire
and insects, that have continually altered the distribution and abundance of
mature forest and associated wildlife and plant species in the Trail Creek area
since the retreat of the Pleistocene glaciers about 10,000 years ago.

Ecosystem processes at the landscape level have traditionally been overlooked,
but are now considered among the resources most likely to be affected
cumulatively by multiple activities. The Forest Service and other agencies are
now applying an ecosystem approach to many NEPA analyses to better consider
these resources. Other examples include the Draft Supplemental EIS on
Management of Habitat for Late-Successional and Old-Growth Forest Related
Species (Forest Service and BLM, 1993) and the current Draft EISs for the
Interior Columbia Basin  Management Project (Forest Service and BLM,  1997).
The Federal Highway Administration (1996) is also beginning to apply an
analogous system approach to the impact assessment of human communities.

4.2 Geographic Boundaries and Time Period

EPA Review Approach

Geographic boundaries and time periods used in cumulative impact analysis
should be based on all resources of concern and all of the actions that may
contribute, along with the project effects, to cumulative impacts. Generally, the
scope of analysis will be broader than the scope of analysis used in assessing
direct or indirect effects. To avoid extending data and analytical requirements
beyond those relevant to decision making, a practical delineation of the spatial
and temporal scales is needed. The selection of geographic boundaries and time
period should be, whenever possible, based on the natural boundaries of
resources of concern and the period of time that the proposed action's impacts
will persist, even beyond the project life.  EPA reviewers should determine
whether the NEPA analysis has used geographic and time boundaries large
enough to include all potentially significant effects on the resources of concern.
The NEPA document should delineate appropriate geographic areas including
natural ecological boundaries, whenever possible, and should evaluate the time
period of the project's effects.


Spatial and temporal boundaries should not be overly restricted in cumulative
impact analysis. Agencies tend to limit the scope of their analyses to those areas
over which they have direct authority or to the boundary of the  relevant
management area or project area. This is often inadequate because it  may not
cover the extent of the effects to the area or resources of concern. The most
common temporal scope is the life of the project. This may not be appropriate if
the effects last longer than the project's useful life.

The EPA reviewer can determine an appropriate spatial scope of the cumulative
impact analysis by considering how  the resources are being affected. This
determination involves two basic steps:

(1) identifying a geographic area that includes resources potentially affected by
the proposed project and

(2) extending that area, when necessary, to include the same and other
resources affected by the combined impacts of the project and other actions.

In practice, the areas for several target species or components of the ecosystem
can often be captured by a single ecoregion or watershed. For example, an
impact assessment for a forest plan modification may have to be expanded
beyond its administrative forest management unit. Instead, the scope of the
assessment might consider the entire watershed for the area covering  portions of
wilderness areas, national or state parks, other federal lands, and private
holdings. Boundaries would  be based on the resources of concern and the
characteristics of the specific area to be assessed. Examples include stream

sections important for salmonid feeding or spawning that are within or
downstream of the administrative unit; maintenance of disturbance patterns to
ensure structural and functional integrity of regional forests; and biological
corridors and wildlife habitat that connect public and private lands. For practical
purposes, ecological boundaries may need to be combined with political
boundaries to adequately delineate the assessment area.

NEPA Example: The Final Supplemental EIS on Management of Habitat for Late-
Successional and Old-Growth Forest Related Species (Forest Service and BLM,
1994) is an important example of study boundaries combining administrative
units with natural regions. The planning area for the EIS included all lands
administered by the Forest Service and the Bureau of Land Management within
the range of the northern spotted owl.  This species range matched well with the
ecosystem consisting of late-successional and old-growth forest in the region.

EPA reviewers should recommend that the proper spatial scope of the analysis
include geographic areas that sustain the resources of concern. Importantly, the
geographical boundaries should  not be extended to the point that the analysis
becomes unwieldy and useless for decision-making. In  many cases, the analysis
should use an ecological region boundary that focuses  on the natural units that
constitute the resources of concern. Three examples of classifications of
ecological regions that may be useful for large geographic areas include
Omernik's EPA ecoregions (Omernik,  1989), Bailey's Forest Service ecoregions
(Bailey, 1978), and the USGS hydrologic units or watersheds. The Natural
Resources Conservation Service uses delineated areas termed Major Land
Resources Areas that are based on  soil types, climate,  geology, topography, and
hydrology. For non-ecological resources, other geographic areas, such as
historic districts (for cultural resources) or metropolitan  areas (for economics),
should be used.

NEPA Example: The Draft EIS on the Special Area Management Plan (SAMP)
for the Hackensack Meadowlands District, NJ (EPA and Army Corps of
Engineers,  1995) is another example of creating a study area that considers both
political boundaries and natural boundaries for both management utility and
resource relevance. The plan covers an area with 14 municipalities in two
counties that are experiencing continual pressure for development. Prepared by
the U. S. EPA, U. S. Army Corps of Engineers, and Hackensack Meadowlands
Development Commission,  the draft EIS assesses the cumulative impacts of
development scenarios within an area that includes 8,500 acres of wetlands that,
because of their position in the landscape, "perform a number of significant
ecological functions and support a diverse community of associated wildlife."

Determining the temporal scope  requires estimating the length of time the effects
of the proposed action will last. More specifically, this length of time extends as
long as the  effects may singly, or in combination with other anticipated effects, be
significant on the resources of concern. At the point where the contribution of

effects of the action, or combination of all actions, to the cumulative impact is not
significant the analysis should stop.  Because the important factor in determining
cumulative impact is the condition of the resource (i.e., to what extent it is
degraded), analysis should extend until the resource has recovered from the
impact of the proposed action.

For example, an impact assessment of ground water withdrawals to cool power
plant turbines should go beyond determining whether the capacity of the aquifer
is adequate to provide water for the  life of the power plant. The analysis should
also consider the long-term effects of lowering the aquifer level. Should municipal
drinking water and agricultural irrigation withdrawals increase in the future, the
cumulative effect of the power plant withdrawals may lower aquifer levels to the
point where, at predictable intervals  in the future, droughts will eliminate all
supply. The NEPA document may, therefore, have to consider time periods
beyond the life of the power plant.

NEPA Example: The Final Supplemental EIS on Management of Habitat for Late-
Successional and Old-Growth Forest Related Species (Forest Service and BLM,
1994) looked sufficiently forward in time to address the probability of restoring or
maintaining sustainable ecosystem conditions. The forest draft EIS determined
that previous alterations to the regional ecosystem prevented a return to pre-
settlement landscape condition  or recovery of aquatic resources within the next
100 years, but that the selected alternative would reverse a 50-year trend toward

There are no set or required formulas for determining the appropriate scope of
the cumulative impact analysis.  Both geographic boundaries and time periods
need to be defined  on a case-by-case basis. Determining the boundaries and
periods depends on the characteristics of the resources affected, the magnitude
and scale of the project's impacts, and the environmental setting. In practice, a
combination of natural and institutional boundaries may be required to
adequately consider both potential impacts and possible mitigation measures.
Ultimately, the scope of the analysis will depend on an understanding of how the
effects are occurring in the assessment area.

4.3 Past, Present,  and Reasonably Foreseeable Future Actions

EPA Review Approach

The adequacy of cumulative impact  analysis depends  on how well the analysis
considers impacts that are due to  past, present, and reasonably foreseeable
actions. EPA reviewers should determine whether the  cumulative analysis
adequately considered the following:

1) whether the environment has been degraded, and if so, to what extent:

2) whether ongoing activities in the area are causing impacts; and

3) the trends for activities and impacts in the area.

Considering the past, present, and reasonable foreseeable future actions
provides a needed context for assessing cumulative impacts. The inclusion of
other actions occurring in proximity to the proposed action is a necessary part of
evaluating cumulative effects. Agencies should identify activities occurring
outside of their jurisdiction that are affecting the same resources being affected
by their actions. Consultation with other agencies potentially affecting the
resources of concern is not usually done and a consideration of private activities
seldom occurs. In addition,  agencies may not always include other actions taken
by their agency. EPA reviewers should determine whether the NEPA document
considered all  past, present, and future actions that contribute to  significant
cumulative effects on the resources of concern. The analysis should include the
use of trends information and  interagency analyses on a regional basis to
determine the  combined effects of past, present, and future actions.  NEPA
documents should  only consider those past, present, and future actions that
incrementally contribute to the cumulative effects on resources affected by the
proposed  action. Actions affecting other resources,  or with cumulatively
insignificant effects on the target  resources, do not add to the value of the


To successfully assess cumulative impacts, NEPA documents should consider a
broad range of activities and patterns of environmental degradation that are
occurring  in  the vicinity of the project. The  following considerations (as modified
from Klein and Kingsley, 1994) can assist in identifying actions that may relate to
the project under review:

1) the proximity of the projects to each other either geographically or temporally;

2) the probability of actions affecting the same environmental system, especially
systems that are susceptible to development pressures;

3) the likelihood that the project will lead to a wide range of effects or lead to a
number of associated projects; and

4) whether the effects of other projects are similar to those of the project under

5) the likelihood that the project will occur - final approval is the best indicator
but long range planning of government agencies and private organizations and
trends information should also be used;

6) temporal aspects, such as the project being imminent;

As an example, the cumulative effect of transportation projects and other
development in an urban setting often results in alteration of topography, habitat
fragmentation, changes in water flows and water quality, increased sediment and
contaminant runoff, and direct mortality from road kills. To address these issues,
the actions included should start with the proposed project but also include other
present, past, and future actions. Other current development should include
related construction such as shopping malls within proximity of the new road
construction or upgrades undertaken on connecting roads within the area of
study. Past actions that should be considered include, for example, any housing
and commercial development, alteration of hydrologic flows to control flooding,
filling of wetlands, construction of other highways, and upstream development.
The analysis should also extend further back in time to include previous changes
to the area and region such as resource extraction or agricultural activities.
Future actions should include any planned communities or commercial areas,
induced growth and accompanying infrastructure, projected increase in
population and traffic, and road expansion.

The identification of the effects of past actions is critical to understanding the
environmental condition of the area. Knowing whether the resource is healthy,
declining, near collapse, or completely devastated is necessary for determining
the significance of any added impacts due to the proposed project. The NEPA
document should consider how past activities have historically affected and will
continue to detrimentally affect the resources of concern. How far back in time to
consider depends on how long the resources of concern have been affected.
Trends analysis, or how the resource condition has changed over time, is the
most useful tool for looking at the accumulated effect of past actions. For
example, if 50% of the wetland functions in a basin have been lost due to both
agriculture and urban development, any present or future impacts should be
taken into account in determining impacts to flood storage capacity and other
important wetland functions.

Other present actions that may be detrimentally affecting the resources of
concern need to be considered at the same time impacts of the proposed action
are considered. NEPA documents should consider information on all other
relevant activities in the study area including other actions of the proposing
agency, actions of other federal agencies,  actions of state and local
governments, and private actions. While EPA already monitors federal activities
on a regional basis, state and county resources should be used to monitor  local
and private activities.

The identification of future actions is also important. According to the response
for question 18 of the "Forty Most Asked Questions concerning CEQ's NEPA
Regulations" (CEQ, 1981), the NEPA document "must identify all the indirect
effects that are known, and make a good faith effort to explain the effects that are

not known but are 'reasonably foreseeable'." The critical question is "What future
actions are reasonably foreseeable?". Court decisions on this topic have
generally concluded that reasonably foreseeable future actions need to be
considered even if they are not specific proposals. The criterion for excluding
future actions is whether they are "speculative." The NEPA document should
include discussion of future actions to be taken by the action agency. The
analysis should also incorporate information based on the planning documents of
other federal agencies, and state and local governments. For example, projects
included in a 5-year budget cycle might be considered likely to occur while those
only  occurring in 10-25 year strategic planning would be less likely and perhaps
even speculative. For private actions, the analysis should use regional and local
planning documents. In the absence of these plans (and to refine expectations
where activities have diverged from the plans), the analysis should refer to
projected development trends. In all of these cases, the best information should
be used to develop scenarios that predict which future actions might reasonably
be expected as a result of the proposal.

NEPA Example: The Commencement Bay Natural Resource Damage
Assessment: Restoration Plan and Final Programmatic EIS (FWS and NOAA,
1997) addressed the problem of including the many and various past actions by
quantifying the previous loss of 98% of mudflat and marsh habitat through a
combination of historical records and photographic evidence. The Final EIS for
the Castle Mountain Project, San Bernardino County, CA (BLM 1990) considered
26 other existing and proposed activities that might cumulatively affect 12
resources of concern. The potential impact of activities in the categories of
utilities/services, commercial and residential, recreation, mining, and grazing
were evaluated based on their location and which resources they might affect.
The Draft EIS for the Disposal and Reuse of Naval Base, Philadelphia, PA
(Department of the Navy, 1995) addressed "connected, cumulative, and similar
existing and potential actions," including general growth trends in South
Philadelphia, other land use development initiatives, related actions by other DoD
services, realignment of the Naval Base, proposed leasing of shipyard facilities to
private shipbuilders, and significant, proposed off-base transportation

4.4 Describing the Condition of the Environment

EPA Review Approach

The NEPA analysis should establish the magnitude and significance of
cumulative impacts by comparing the environment in its naturally occurring state
with the expected impacts of the proposed action when combined with the
impacts of other actions.  Use of a "benchmark" or "baseline" for purposes of
comparing conditions is an essential part of any environmental analysis. "The
concept of a baseline against which to compare predictions of the effects of the
proposed action and reasonable alternatives is critical to the NEPA process."

(CEQ, 1997) To determine how the project will affect the resource's ability to
sustain itself, the NEPA document should include a description of the baseline
condition that considers " conditions have changed over time and how they
are likely to change in the future without the proposed action". (CEQ, 1997) If it is
not possible to establish the "naturally occurring" condition, a description of a
modified  but ecologically sustainable condition can be used in the analysis.  In
this context, ecologically sustainable means the system supports biological
processes,  maintains its level of biological productivity, functions with minimal
external management,  and repairs itself when stressed.

While a description of past environmental conditions is usually included in NEPA
documents, it is seldom used to fully assess how the system has changed from
previous  conditions. The comparison of the environmental condition and
expected environmental impacts can be incorporated into the environmental
consequences or affected environment sections of NEPA documents. EPA
reviewers should determine whether the NEPA analysis accurately depicts the
condition of the environment used to assess cumulative impacts. In addition,
reviewers should determine whether NEPA documents incorporate the
cumulative effects of all relevant past activities into the affected environment
section. For the evaluation of the environmental consequences to be useful, it is
important that the analysis also incorporate the degree that the existing
ecosystem will change over time under each alternative.


Often the current condition is  used as the benchmark for comparing the
environmental effects of the alternatives. However, the current condition typically
may not adequately represent how actions have impacted resources in the past
and present or how resources might respond to future impacts. Designating
existing environmental conditions as a benchmark may focus the environmental
impact assessment too narrowly, overlooking cumulative impacts of past and
present actions or limiting assessment to the proposed action and future actions
(McCold and Saulsbury 1996). For example, if the current environmental
condition were to serve as the condition for assessing the impacts of relicensing
a dam, the analysis would only identify the marginal environmental changes
between  the continued operation of the dam and the existing degraded state of
the environment. In this hypothetical case, the affected environment has been
seriously degraded for more than 50 years with accompanying declines in flows,
reductions in fish stocks, habitat loss, and disruption of hydrologic functions. If
the assessment took into account the full extent of continued impacts, the
significance of the continued operation would more accurately express the state
of the environment and thereby better predict the  consequences of relicensing
the dam.

For the purposes of section 309 reviews, different methods of depicting the
environmental condition are acceptable. The condition of the environment
should, however, address one or more of the following:

1) how the affected environment functions naturally and whether it has been
significantly degraded;

2) the specific characteristics of the affected environment and the extent of
change, if any, that has occurred in that environment; and

3) a description of the natural condition of the environment or, if that is not
available,  some modified, but ecologically sustainable, condition to serve as a

Two practical methods for depicting the environmental condition include use of
the no-action alternative and an environmental reference point.  Historically, the
no-action alternative (as reflecting  existing conditions) has usually been used as
a benchmark for comparing the proposed action and alternatives to existing
conditions. The no-action alternative can be an effective benchmark if it
incorporates the cumulative effects of past activities and accurately depicts the
condition of the environment.

Another approach for describing the environmental condition is  to use an
environmental reference point that would be incorporated into the environmental
consequences and affected environment sections of the document. The natural
condition of the ecosystem, or some modified but sustainable ecosystem
condition,  can be described as the environmental reference  point. In analyzing
environmental impacts, this environmental reference point would not necessarily
be an alternative. Instead, it would serve as a benchmark in assessing the
environmental impacts associated  with each of the alternatives. Specifically, the
analysis would evaluate the degree of degradation from the  environmental
reference  point (i.e., natural ecosystem condition) that has resulted from past
actions. Then the relative difference among alternatives would be determined for
not only changes compared to the  existing condition but also changes critical to
maintaining or restoring the desired, sustainable condition.

Determining what environmental condition to use in the assessment may not be
immediately clear. Choosing and describing a condition should  be based on the
specific characteristics of the area. In addition, the choice of condition can be
constrained by limited resources and information. For these reasons, the
environmental condition described by the environmental reference point or no-
action alternative should be constructed on a case-by-case basis  so that it
represents an ecosystem able to sustain itself in the larger context of activities in
the region. In this respect, there is  no predetermined point in time that
automatically should represent the environmental condition.  In addition, it may
not be practical to use a pristine condition in situations of intensive development.

For example, it may not be very useful to use a pre-development condition to
assess the extent of degradation in a heavily urbanized setting. It may be more
useful in this situation to consider the condition of several important resources of
concern (i.e., water quality, air quality, or quality of life) in comparison with
expected environmental consequences of the action. Since most ecosystems
can be delineated and have distinct characteristics, determination of the
environmental condition does not need to be a subjective process leading to
speculation about the condition of the environment before it was degraded.

Depending on whether the information is reasonably obtainable, the
environmental condition chosen may be a pristine environment, or at the very
least, a minimally functioning ecosystem that will not further degrade. The use of
the environmental condition to compare alternatives is not an academic exercise,
but one that  can most effectively modify alternatives and help decision making.
Examples of conditions might include before project, before "substantial"
development, or a reference ecosystem  that is comparable to the project area.
Selecting the best environmental condition for comparative purposes can be
based on the following:

1) consider what the environment would look like or how it would behave without
serious human alteration;

2) factor in the dynamic nature of the environment;

3) define the distinct characteristics and  attributes of the environment that best
represent that particular type of environment (focus on characteristics and
attributes that have to do with function); and

4) use available or reasonably obtainable information.

For example, in a hypothetical case of harbor dredging and disposal, the existing
condition of the aquatic ecosystem is highly modified from natural conditions.
Human settlement along major waterways spans hundreds of years  and
commercial development has become very intense in many areas. Following
practices used in some NEPA analyses, the degraded condition of the benthic
communities and shoreline vegetation would be considered the condition for
assessing the impacts of sediment dredging and disposal. By using this
environmental condition, the analysis would not recognize the full extent of the
degradation  and would possibly underestimate the actual impacts of the
proposed action. The environmental condition for this case could be  set at pre-
development (or at least at early development) or,  if historical data are not
available, use a reference point constructed from an understanding of how a
similar ecosystem would behave in a natural state. The affected environment
section should include a discussion of the extent of degradation that  the current
condition has experienced when  compared to the characteristics of an

undisturbed harbor environment. And finally, the extent of change and future
trends should be considered in each alternative.

NEPA Example: The Forest Service's Snowmass Ski Area Final Environmental
Impact Statement (Forest Service,  1994) and the Army Corps of Engineers Elk
Creek Lake Final Evironmental Impact Statement (Army Corps of Engineers,
1991) both define baseline conditions for comparison of alternatives. In
assessing the potential environmental impacts of the Snowmass Ski Area
expansion, the Forest Service established a "pre-development" reference point
from which all past, present, and reasonably foreseeable future environmental
impacts were examined.  Consequently, the EIS presented a comprehensive
discussion of the cumulative impacts upon various resources. The Elk Creek
Lake Final EIS also identified a "pre-development" reference point, defined by
the Corps as "base conditions", for sped fie resources along the Rogue River and
Elk Creek. The assessment then explored the alteration of resource conditions
with respect to other actions, including the proposed project.

Issue 4.5 Using Thresholds to Assess Resource Degradation

EPA Review Approach

Qualitative and quantitative thresholds can be used to indicate whether a
resource(s) of concern has been degraded and whether the combination of the
action's impacts with other impacts will result in a serious deterioration of
environmental functions.  In the context of EPA reviews, thresholds can be used
to determine if the cumulative impacts of an action will be significant and if the
resource will be degraded to unacceptable levels. EPA reviewers should
determine whether the analysis included specific thresholds required under law
or by agency regulations or otherwise used by the agency. In the absence of
specific thresholds, the analysis should include a description of whether or not
the resource is significantly affected and how that determination was made.


If adequate data and analytical procedures are  available, specific thresholds that
indicate degradation of the resources of concern should be included in the NEPA
analysis . The thresholds should  be practical, scientifically defensible, and fit the
scale of the analysis. Thresholds may be set as specific numerical standards
(e.g., dissolved oxygen content to assess water quality), qualitative standards
that consider biological components of an ecosystem (e.g., riparian condition and
presence of particular biophysical attributes),  and/or desired management goals
(e.g., open space or unaltered habitat).  Thresholds should  be represented by a
measurement that will report the  change in resource condition in meaningful
units. This change is then evaluated in terms of both the total threshold beyond
which the resource degrades to unacceptable levels and the incremental
contribution of the proposed action to reaching that threshold. The measurement

should be scientifically based. For example, thresholds for determining adverse
change in the functioning of a wetland could include the percentage of historic
wetland loss in the region, occurrence of species at risk, ambient water quality
data that exceed standards, and estuarine pollution susceptibility index.

Since cumulative impacts often occur at the landscape or regional level,
thresholds should be developed at similar scales whenever possible. Indicators
at a landscape level can be used to develop thresholds as well as assess the
condition of the environment. By using the following landscape indicators as
modified from O'Neil et al. (1997) and Jones et al. (1996), thresholds can be
crafted by determining the levels, percentages, or amount of each that indicate a
significant impact for a particular area. Examples of thresholds include:
     The total change in land cover is a simple indicator of biotic integrity;
      thresholds for areas with high alterations would generally be lower than
      areas that are not as degraded;  if open space or pristine areas are a
      management goal then the threshold would be a small percentage change
      in land cover.
     Patch size distribution and distances between patches are important
      indicators of species change and level of disturbance. Thresholds would
      be set to determine the characteristics of an area needed to support a
      given plant or animal species.

     Estimates of fragmentation and connectivity can reveal the magnitude of
      disturbance, ability of species to survive in an area, and ecological
      integrity. Thresholds would indicate a decrease in cover pattern, loss of
      connectivity, or amount of fragmentation that would significantly degrade
      an area.

     Indicators of water quality and watershed  integrity can be used to set
      thresholds. Specific concentrations and levels of nitrogen, phosphorous,
      turbidity, dissolved oxygen, and temperature can be used.
     Thresholds for a decline in water quality can take the form of size and
      amount of riparian buffer zones. Condition of riparian zones and changes
      in percent of buffer areas can indicate a decline in water quality due to soil
      erosion, sediment loading, and contaminant runoff.

In a hypothetical project to develop  a skiing resort to be constructed on federal
lands, thresholds would be developed for several resources of concern. The
impacts of road construction and use, ski runs, housing development, and water
use would have wide ranging effects on resources such as riparian condition,
water quality, wildlife habitat, and vegetation. Thresholds for cover and loss of
connectivity could be developed to determine the significance of impacts to
wildlife and vegetative cover. For example, thresholds could be developed from
known information on the amount of habitat necessary for successful ungulate

breeding. Numerical standards for dissolved oxygen and water temperature
could be used to determine significance of impacts to coldwater fisheries.
Narrative standards of stream condition would be used to determine thresholds
for successful fish spawning.

NEPA Example: NEPA analyses have examined actions where the cumulative
effects exceed a threshold which is tied to a national air quality or water quality
standard. In the Final EIS for Hydroelectric Development in the Upper Ohio River
Basin (FERC, 1988), the Federal Energy Regulatory Commission determined the
point at which dissolved oxygen fell below the standard by modeling the reduced
spillage and aeration caused by adding turbines to additional dams in
succession. Setting thresholds to represent the carrying capacity of an
ecosystem is more difficult. In the Draft EIS on Cumulative Impacts of
Recreational Boating on the Fox River and Chain O'Lakes Area in Lake and
McHenry Counties, IL, the U.S. Army Corps of Engineers assessed the impacts
of boat traffic on the carrying capacity of aquatic life by setting a  threshold of
water clarity needed for vegetation growth. At the same time, they set a social
carrying capacity threshold of the number of boats that made people feel
crowded. While the concept of translating exceedences of thresholds to
significant impacts on carrying capacities of both ecological and human
resources is being applied more extensively, analysts still often face situations
where there are limits to scientifically exact thresholds, and have to use other
methods to develop thresholds. For example, in the Draft Supplemental EIS on
Management of Habitat for Late-Successional and Old-Growth Forest Related
Species (Forest Service and BLM, 1993), it was necessary to rely on expert
opinion from panels to assess the  "probability of ensuring the viability of species."

Determining a threshold beyond which cumulative effects significantly degrade a
resource, ecosystem, or human community is sometimes very difficult because of
a lack of data. Without a definitive  threshold, the NEPA practitioner should
compare the cumulative effects of  multiple actions with appropriate national,
regional, state, or community goals to determine whether the total effect is
significant.  These desired conditions can best be defined by the cooperative
efforts of agency officials, project proponents, environmental analysts, non-
governmental organizations, and the public through the NEPA process. The
integrity of historical districts is an  example of a threshold that is  goal related.
These districts,  especially residential and commercial historic districts in urban
areas, are particularly vulnerable to clearance programs carried out by local
governments, usually with  use of federal funds. Though individual structures of
particular architectural distinction are often present, such districts are important
because they are a collection  of structures that relate to one another visually and
spatially; the primary importance of each building is the contribution that it makes
to a greater whole. Often in conjunction with code enforcement programs to
remove blighting influences and /or hazards to public safety, local governments
condemn and demolish properties. Viewed in isolation as an individual action,
such demolition of an individual structure does not significantly diminish the

historic and architectural character of the district and indeed may be beneficial to
the overall stability of the district. But the cumulative effect of a whole series of
such demolitions can significantly erode the district. Continued loss of historic
structures, often with resultant vacant lots and incompatible new construction,
can reach a point where the visual integrity of the district is lost. Once this
threshold is passed, subsequent demolitions become increasingly difficult to
resist and ultimately the qualities of the historic district are lost.


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