The Cilix Method: A practical methodology for assessing cumulative impacts in environmental assessments

The Cilix Method: APractical Methodologyfor AssessingCumulative Impacts in EnvironmentalAssessments

Charles H. Eccleston

Performing a cumulative impact analysis that rigorously satisfies the regulatoryrequirements of the National Environmental Policy Act (NEPA) can be a chal-lenging and resource-intensive task, particularly when preparing environmen-tal assessments (EAs). A rigorous evaluation of cumulative impacts may requiresubstantially more effort than is necessary to assess the direct and indirect im-pacts of an action. This article describes a new approach, referred to as the CilixMethod, that can provide a practical, streamlined, and defensible technique forassessing cumulative impacts in an EA. © 2006 Wiley Periodicals, Inc.

The Council on Environmental Quality’s National EnvironmentalPolicy Act (NEPA) Implementing Regulations (Regulations) recognizethat even though direct and indirect impacts of an action may not besignificant in themselves, environmental quality might still be signifi-cantly degraded if such impacts are combined with those of other past,present, and reasonably foreseeable actions. This concept in codified inthe Regulations1:

“Cumulative impact” is the impact on the environment which re-sults from the incremental impact of the action when added to otherpast, present, and reasonably foreseeable future actions regardlessof what agency (Federal or non-Federal) or person undertakes suchother actions. Cumulative impacts can result from individuallyminor but collectively significant actions taking place over a periodof time.

Federal Facilities Environmental Journal/ Winter 2006 37© 2006 Wiley Periodicals, Inc. Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ffej.20072

Charles H. Eccleston, PhD is the author of the three leading textbooks on NEPA and envi-ronmental planning. He is listed in Who’s Who in America and Who’s Who in the World as aleading expert on environmental policy. His latest book, Megacrises: A Survivor’s Guide to theFuture deals with terrorism and other emerging global threats. He may be contacted [email protected].

38 Federal Facilities Environmental Journal/ Winter 2006DOI: 10.1002/ffej

The Cilix Method

The purpose of performing a Cumulative Impact Assessment (CIA)is to evaluate how an impact could affect environmental quality whenits effects are combined with those of other actions that compose whatcan be viewed as a cumulative impact baseline (past, present, and rea-sonably foreseeable future actions). The effects of a proposal are of in-creasing concern (and the threshold of significance is more likely to betriggered) if the proposal could substantially affect the cumulative im-pact baseline even though it may not result in any significant direct orindirect impact.

THE PROBLEMPerforming a cumulative impact analysis that rigorously satisfies

the definition and regulatory requirements set forth in 40 CFR 1508.7can be a daunting task. Moreover, experience indicates that CIAs arefrequently not performed in a rigorous manner sufficient to supportan informed assessment of potentially significant cumulative impacts.

STANDARD APPROACHUnder the standard approach, one needs to identify and assess a

potentially large array of past, present, and reasonably foreseeable fu-ture actions. Analysts then need to evaluate and add the impacts fromthe identified past, present, and reasonably foreseeable future actions(on a resource-by-resource basis) to produce a cumulative impactbaseline. The impact of the proposed action can then be added to thiscumulative impact baseline. If the cumulative baseline has alreadybreached the threshold of significance, then from a strict absolutestandpoint, any contribution beyond that point can be interpreted asbeing significant, and an Environmental Impact Statement (EIS)would need to be prepared.

The effort required to assess the direct and indirect impacts of aproposed action frequently involves a considerable amount of timeand resources; performing an analysis using a standard CIA approachthat adequately satisfies the regulatory definition and requirements setforth in 40 CFR 1508.7 may necessitate expending substantially moreeffort.

Consider the following example in which a standard CIA approachis used to evaluate the application of herbicides to control encroach-ment of nonnative invasive plants on a large tract of land such as a na-tional park or forest. Further assume that an environmental assess-ment (EA) is prepared to assess the effects of this proposal. Thepurpose of the EA is to determine if the proposal is eligible for a Find-ing of No Significant Impact (FONSI)—that is, a negative declarationstatement.

An adequate assessment of the cumulative impacts on a resourcesuch as soil or water quality might require identifying and evaluatingall persistent past, present, and reasonably foreseeable herbicides (andother relevant chemical) applications that have or might in the futureleach into soils or accumulate in streams and lakes (e.g., cumulative

Under the standardapproach, one needs toidentify and assess apotentially large array of past, present, andreasonably foreseeablefuture actions.

Federal Facilities Environmental Journal/ Winter 2006DOI: 10.1002/ffej

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impact baseline). The analyst would then need to add the proposedherbicide applications to this cumulative impact baseline. Such ananalysis might border on being impractical within the scope of a typi-cal EA.

A new approach developed by the author and referred to as theCilix Method2 provides a simpler and more practical approach fordemonstrating that a potentially significant impact is either significantor nonsignificant. The Cilix Method may even demonstrate nonsignif-icance in some situations where the cumulative baseline has alreadysustained a significant impact.

CILIX METHODWith respect to a CIA, the rationale behind the Cilix Method is

straightforward: simply perform an analysis that assesses the incre-mental impact of the proposed action. For actions that are eligible fora FONSI, the CIA need only demonstrate that the incremental impact isso small as to be negligible or unimportant and therefore is “nonsignificant”in terms of its contribution to the cumulative impact baseline. That is tosay that the environmental impact contribution from the proposalwhen added to the effects of other past, present, and reasonably fore-seeable actions is so small as to be of no practical consequence; sincethe proposal’s environmental impact contribution is negligible, itwould not affect, influence, or contribute to any significant change or in-crease in the cumulative impact to an environmental resource. As theCilix Method essentially amounts to a negative declaration statement, itis consistent with the purpose of most EAs.

ADVANTAGESBesides providing a more practical approach to the assessment of

cumulative impacts in EAs, the Cilix Method has a second importantadvantage. Even if the cumulative impact baseline of the applicable re-source is (or could be in the future) significantly affected, a FONSI canstill be issued (with respect to the CIA) as long as the incremental con-tribution from the proposed action relative to the baseline is so smallas to constitute no appreciable environmental change in the resource.This is because from an environmental quality standpoint, it wouldmake no practical difference whether the proposal is implemented ornot, since there would be no substantial change in the ultimate cumu-lative environmental impact.

JUSTIFICATIONAs long as the proposal’s contribution can be shown to be negligible,

there is no practical justification for performing a complicated assessment ofthe cumulative impact baseline (evaluation of all past, present, and rea-sonably foreseeable future impacts). The Cilix Method can thereforeprovide evidence that no further investigation is warranted. This istrue, even if the environmental resource has already been signifi-cantly affected.

. . . the rationale behindthe Cilix Method isstraightforward: simplyperform an analysis that assesses theincremental impact of the proposed action.


The Cilix Method

Conversely, a negative declaration of cumulative significance maynot be justified if the proposal’s effect is large enough to add a signif-icant contribution or to significantly change the cumulative impactbaseline (past, present, and reasonably foreseeable impacts). In thiscase, the action could be deemed to pose a significant impact requir-ing preparation of an EIS.

In essence, the difference between the standard approach and theCilix Method is that under the standard approach, significance as de-fined in 40 CFR 1508.7 is assessed from an absolute perspective (i.e., interms of whether the impact breaches a threshold level of signifi-cance); this can require a complicated assessment of the cumulativeimpact baseline to which the impact of the proposed action is added.In contrast, under the Cilix Method, significance is assessed from a rel-ative perspective (i.e., would the impact significantly contribute to orsignificantly change the cumulative impact baseline).

As we have seen, a rigorous CIA is often beyond the practicalscope of an EA. A close examination of CIAs in EAs reveals that suchanalyses are frequently inadequate or insufficient to rigorouslydemonstrate that the cumulative impact is nonsignificant pursuantto regulatory requirements set forth in 40 CFR 1508.7; the CilixMethod is therefore not only practical but justifiable, since it canoften provide a more rigorous demonstration that the impact is ei-ther significant or nonsignificant.

EXAMPLE USE OF THE CILIX METHODThe following abbreviated case example (based on an actual analy-

sis that used the Cilix Method to assess cumulative effects) demon-strates how the Cilix Method can be applied to evaluate cumulativeimpacts involving use of herbicides to control the spread of nonnativeinvasive plants in a national forest. The following cumulative impactdescriptions assume that a rigorous analysis of the direct and indirectimpacts have already been performed within the herbicide EA. TheCilix analysis of cumulative impacts is described for two different al-ternatives: (1) No-Action Alternative and (2) Proposed Action (herbi-cide application).

This example considers the abbreviated analysis of cumulative ef-fects on the following five different environmental resources: (1) airquality, (2) soils and water quality, (3) recreation, land use, and aesthet-ics resources, (4) biological resources, and (5) human health and safety.

AIR QUALITYThe following analysis demonstrates how the Cilix Method can be

used to assess cumulative impacts on air quality within an EA.

Alternative 1 (No-Action)As the No-Action Alternative would not directly result in any

measurable air emissions, this alternative would not contribute to anycumulative effect on air quality.

. . . the difference betweenthe standard approachand the Cilix Method isthat under the standardapproach, significance asdefined in 40 CFR 1508.7is assessed from anabsolute perspective. . .


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Alternative 2 (Herbicide Application)Herbicides are currently applied to surrounding areas including

private property and agricultural lands boarding the proposed projectarea. Relatively small concentrations of herbicides, applied as part ofthis alternative, could drift onto onsite or offsite nontargeted areas. Be-cause of the limited area to be treated and use of herbicide safety pro-cedures, the amount of herbicide drift is considered to be small to neg-ligible, and would therefore contribute to little or no incrementalincrease when combined with other present and reasonably foresee-able herbicide applications. Consequently, there would be no substan-tial increase in cumulative herbicide air concentrations in the sur-rounding area.

SOILS AND WATER QUALITYThe following analysis demonstrates how the Cilix Method could

be used to assess cumulative impacts on soils and water quality withinan EA.

Alternative 1 (No-Action)The No-Action Alternative would not directly affect soil or water

resources. Therefore, there would be no increase in cumulative effectsto these resources.

Alternative 2 (Herbicide Application)Areas that would be affected by herbicide treatment are relatively

small in size. Only herbicides registered for aquatic use would be usedover open water. Nearly all of the proposed herbicides rapidly de-grade in aquatic systems, and nearly all exhibit low toxicity to fish andaquatic invertebrates, and do not bioaccumulate.

Most of the herbicides are expected to decompose in the soil withinweeks or several months by natural processes. As the impacts fromthese activities are essentially small to negligible, they would have lit-tle or no incremental effect when combined with the impacts of otherpast, present, and reasonably foreseeable future activities.

Therefore, application of herbicides is not expected to result in anysubstantial increase in cumulative herbicide concentrations within po-tentially affected soil or water resources.

RECREATION, LAND USE, AND AESTHETICS RESOURCESThe following discussion describes how the Cilix Method could be

used in considering cumulative impacts on land use, recreation, andaesthetic resources within an EA.

Alternative 1 (No-Action)As no herbicides would be applied, the No-Action Alternative

would eliminate the need to temporally or spatially separate visitorsand recreationists from areas where herbicides would be applied.Since no control activities would be involved, this alternative would

. . . application ofherbicides is not expected to result in anysubstantial increase incumulative herbicideconcentrations withinpotentially affected soilor water resources.


The Cilix Method

not directly contribute to any cumulative effects on land use, recre-ation, and forest aesthetics.

However, when combined with impacts of other past, present, andreasonably foreseeable future actions, failure to effectively control thespread of nonnative invasive species could result in some long-termcumulative impact upon future aesthetics, land use, and recreationalactivities.

Alternative 2 (Herbicide Application)The proposed control activities would result in some limited short-

term adverse incremental effects on recreation, land use, and aesthet-ics; however, such adverse effects are deemed to be temporary and rel-atively minor.

Because impacts from these activities are essentially negligible,they would contribute little or no incremental adverse effects whencombined with impacts of other past, present, and reasonably foresee-able future activities. Therefore, they are not expected to contribute toany substantial cumulative loss of land use, recreation activities, oraesthetics in the foreseeable future. On balance, the control activitiescould result in some beneficial long-term cumulative effects in termsof protecting and preserving future land use, aesthetics, or recreationalactivities.

BIOLOGICAL RESOURCESThe following analysis demonstrates how the Cilix Method can be

used to assess cumulative impacts on biological resources within an EA.

Alternative 1 (No-Action)As the No-Action Alternative would not directly result in any

measurable adverse direct or indirect impacts on species or habitats,there would correspondingly be no measurable increase in cumulativeeffects to these resources as a result of this alternative. However, with-out use of control methods, the invasion of nonnative invasive plantspecies is expected to spread via infestation growth, wind, animals(birds, deer, and other wildlife), and vehicles. Such invasions mightendanger state or federal, threatened or endangered plant species, aswell as their natural habitats. When added to other past, present, andreasonably foreseeable future activities, failure to effectively controlthe spread of nonnative invasive plant species could result in a sub-stantial long-term adverse cumulative impact on natural species andhabitats, including threatened and endangered species.

Alternative 2 (Herbicide Application)Nearly all of the proposed herbicides rapidly degrade in aquatic

systems and nearly all exhibit low toxicity to fish and aquatic inverte-brates, and do not bioaccumulate. Herbicide impact on nontargetspecies is deemed to be relatively small; the proposed herbicide treat-ments would therefore contribute only a marginal adverse incremen-

Nearly all of the proposed herbicidesrapidly degrade inaquatic systems andnearly all exhibit lowtoxicity to fish andaquatic invertebrates, anddo not bioaccumulate.


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tal effect when combined with impacts of other past, present, and rea-sonably foreseeable future activities. Consequently, herbicides are notexpected to result in a substantial increase in adverse cumulative ef-fects to nontargeted species.

The proposed control methods could result in a substantial reduc-tion or eradication of nonnative invasive plant species within treatedareas. These control methods would complement efforts by adjacentlandowners and counties to control the noxious weeds and invasivespecies surrounding the proposed project area. When added to otherpast, present, and reasonably foreseeable future activities to controlnonnative invasive plant species, there could be a cumulative benefi-cial impact from controlling the spread of invasive species. The cumu-lative benefit would include protecting natural species, includingthreatened, endangered, and sensitive species and their habitats. Prop-erties adjacent to the proposed project area would benefit from re-duced weed populations.

HUMAN HEALTH AND SAFETYThe following analysis demonstrates how the Cilix Method can be

used to assess cumulative impacts on human health and safety withinan EA.

Alternative 1 (No-Action)Taking no action to control nonnative invasive plant infestations

would not directly result in an adverse cumulative impact to humanhealth. However, failure to control nonnative invasive species mightcontribute to a cumulative increase in drowning incidents amongswimmers.

Alternative 2 (Herbicide Application)Potential impacts to both workers and the public must be consid-

ered. Some herbicides are used by some members of the public such aslandowners adjacent to the boundaries of the proposed project, partic-ularly private home users. As a result of this alternative, smallamounts of herbicides might migrate offsite, contributing to a small in-crease in cumulative offsite concentrations.

Increasing numbers of the public are likely to recreate at future pic-nic areas, campgrounds, trails, and other areas within the proposedproject boundary. Because of the project-design criteria and the factthat members of the public may be temporarily restricted from areaswhere a treatment has recently occurred, they are expected to receivelittle or no cumulative exposure to herbicides.

Agency staff and herbicide applicators may be repeatedly exposedto cumulative herbicide doses. For instance, herbicide applicatorsmoving from site to site, repeatedly applying herbicides, could be at agreater risk for receiving cumulative herbicide exposures. Thus, theremay be some increased cumulative risk to workers who apply or workin the vicinity of applications on a regular basis, or who are exposed

. . . failure to controlnonnative invasivespecies might contributeto a cumulative increasein drowning incidentsamong swimmers.


The Cilix Method

to repeated herbicide exposures. However, project-design criteria andthe limited scope of the project should significantly reduce the riskthat this project would contribute to a substantial cumulative doseamong workers.

SUMMARYAs described earlier, performing a standard analysis that rigorously

satisfies the regulatory definition of 40 CFR 1508.7 can be a daunting,if not impractical task. The effort required to prepare a rigorous CIAmay require substantially more effort than would be expended in eval-uating the direct and indirect impacts.

The Cilix Method provides a simpler approach as it does not nec-essarily involve the direct assessment of the impacts from all past,present, and reasonably foreseeable future actions together and thenadding these impacts to those of the proposed action. Instead, the CilixMethod simply attempts to demonstrate that the incremental increasein the impact is so small as to be negligible or unimportant and there-fore insignificant in terms of its contribution to the cumulative base-line. If the proposal’s contribution can be shown to be negligible, thereis no practical justification for having to perform a complicated as-sessment of the cumulative impact baseline (evaluation of all past,present, and reasonably foreseeable future impacts). The Cilix Methodcan therefore provide evidence that no further investigation is war-ranted (i.e., a negative declaration statement).

As witnessed earlier, a close examination of CIAs reveals that theyare frequently inadequate or insufficient to rigorously demonstratethat the cumulative impact is nonsignificant; the Cilix Method is there-fore not only practical but justifiable, since it can often provide a morerigorous demonstration that the impact is either significant or non-significant. For this reason, the Cilix Method provides a practical,streamlined, and defensible technique for assessing cumulative im-pacts in an EA.�

NOTES1. 40 Code of Federal Regulations (CFR) 1508.7.

2. In Greek mythology, Cilix was the son of Agenor. His father sent him to investigateand determine what happened to Europa, his lost sister. Like Cilix, the methodologydescribed in this article is designed to investigate (search for) and determine if a cu-mulative impact is nonsignificant.

Documents

The Cilix Method: A practical methodology for assessing cumulative impacts in environmental assessments