Cumulative Effects Assessment Practitioners' Guide

2.0 Assessment Fundamentals

2.1 Cumulative Effects Defined

Cumulative effects are changes to the environment that are caused by an action in combination with other past, present and future human actions. [Numerous definitions of CEAs exist in the literature. Many of these are quite complicated and refer to technical aspects of cumulative effect's interactions. The Working Group prefers a simple definition based on an important additional requirement of CEA as compared to EIA: the specific consideration of effects due to other projects. This definition is intended specifically for single-project assessments as opposed to regional planning (in which case there is not necessarily a single project that serves as the starting point and focus of the assessment), and borrows the broad definition of "environment" as used in the Canadian Environmental Assessment Act.] A CEA is an assessment of those effects (" Actions" Include Projects and Activities).

CEA is environmental assessment as it should always have been: an Environmental Impact Assessment (EIA) done well. In practice, the assessment of cumulative effects requires consideration of some concepts that are not always found in conventional approaches followed in EIAs. Specifically, CEAs are typically expected to:

  • assess effects over a larger (i.e., "regional") area that may cross jurisdictional boundaries; [Includes effects due to natural perturbations affecting environmental components and human actions.]
  • assess effects during a longer period of time into the past and future;
  • consider effects on Valued Ecosystem Components (VECs) due to interactions with other actions, and not just the effects of the single action under review;
  • include other past, existing and future (e.g., reasonably foreseeable) actions; and
  • evaluate significance in consideration of other than just local, direct effects.

Cumulative effects are not necessarily that much different from effects examined in an EIA; in fact, they may be the same. Many EIAs have focussed on a local scale in which only the "footprint" or area covered by each action's component is considered. Some EIAs also consider the combined effects of various components together (e.g., a pulp mill and its access road). A CEA further enlarges the scale of the assessment to a regional level. For the practitioner, the challenge is determining how large an area around the action should be assessed, how long in time, and how to practically assess the often complex interactions among the actions. In all other ways, CEA is fundamentally the same as EIA and, therefore, often relies on established EIA practice.

Definitions and Concepts

Conditions for Potential Cumulative Effects

Cumulative effects may occur if:

  • local effects on VECs occur as a result of the action under review; and
  • those VECs are affected by other actions.
Key Terms Defined
Any project or activity of human origin.
Assessment Framework:
A description of a process that organizes actions and ideas, usually in a step-by-step fashion. Frameworks help to guide practitioners in carrying out an assessment.
Any response by an environmental or social component to an action's impact [Under the Canadian Environmental Assessment Act , "environmental effect" means, in respect of a project, "(a) any change that the project may cause in the environment, including any effect of any such change on health and socio-economic conditions, on physical and cultural heritage, on the current use of lands and resources for traditional purposes by aboriginal persons, or on any structure, site or thing that is of historical, archaeological, paleontological or architectural significance and (b) any change to the project that may be caused by the environment, whether any such change occurs within or outside of Canada".].
Environmental Components:
Fundamental elements of the natural environment. Components usually include air, water (surface and groundwater), soils, terrain, vegetation, wildlife, aquatics and resource use.
Any area in which it is suspected or known that effects due to the action under review may interact with effects from other actions. This area typically extends beyond the local study area; however, as to how far will vary greatly depending on the nature of the cause-effect relationships involved.
A consultative process for identifying and possibly reducing the number of items (e.g., issues, VECs) to be examined until only the most important items remain for detailed assessment. Focussing ensures that assessment effort will not be expended in the examination of trivial effects.
A limit of tolerance of a VEC to an effect, that if exceeded, results in an adverse response by that VEC.
Valued Ecosystem Component (VEC):
Any part of the environment that is considered important by the proponent, public, scientists and government involved in the assessment process. Importance may be determined on the basis of cultural values or scientific concern.
"Actions" Include Projects and Activities

Human actions often cause a disturbance to the environment. These actions include projects and activities. Projects are typically some form of physical work that is planned, constructed and operated. Projects are usually identified by a specific name. Activities may be part of a project, or not associated with any particular project but arise over time due to ongoing human presence in an area. A mine development, a resource access road, or both together are examples of a project. Public traffic, hiking and hunting along that road are examples of activities.

For the purposes of a CEA, the effects on the environment of other projects and activities also have to be considered. For convenience, in this Guide, the term "Actions" is used when appropriate to represent both projects and activities. The term "project" is used only in reference to the project being proposed under assessment or under regulatory review.

In the Canadian Environmental Assessment Act, a project means "(a) in relation to a physical work, any proposed construction, operation, modification, decommissioning, abandonment, or other undertaking in relation to that physical work; or (b) any proposed physical activity not relating to a physical work that is prescribed or is within a class of physical activities that is prescribed pursuant to regulations made under paragraph 59(b) in the Act." The Act does not provide a definition for "activity"; however, it is commonly understood not to include a physical work. It is, therefore, considered in this Guide as any action that requires the presence, often temporary, of humans concentrated in a local area or dispersed over a large area.

Examples of Cumulative Effects
  • Air: combined SO2 emissions within a regional airshed from three operating natural-gas processing plants
  • Water: combined reductions in flow volumes within a particular river resulting from irrigation, municipal and industrial water withdrawals
  • Wildlife: combined black bear mortalities within a given wildlife management unit from hunter harvest, road kills and destruction of nuisance animals
  • Vegetation: clearing of land resulting in the removal of a patch of regionally rare plant species
  • Resource Use: continual removal of merchantable timber from a timber management area

Case Study
Cold Lake Oil Sands Project: Effects at a Regional Scale

Imperial Oil Resources proposed the expansion of an in-situ heavy oil facility in northern Alberta (IORL 1997a, è Appendix B). The following provides examples of some effects identified during early scoping exercises.

Environmental ComponentExamples of Potential Regional Effects
Air SystemsPlumes from stack emissions combining with the plumes from nearby burns
Surface WaterReductions of river water volumes due to use by the project, other energy projects and nearby communities
Aquatic ResourcesDecrease in productivity of spawning habitat due to combined sedimentation from the project and regional forestry operations and activities
Soils and TerrainContinued loss of soils
VegetationLess representation of certain plant species on a regional scale
WildlifeIncreased road access and changes to habitat resulting in further regional changes to numbers and distribution of certain wildlife species
Resource UseForestry activities, land use by the project, and increased road access changes the harvest potential for furbearer species

Case Study
Determining if there are Cumulative Effects: Joint Panel for the Express Pipeline Proposal

To assist in its deliberations on cumulative effects during the public hearings for a proposed pipeline in Alberta (NEB 1996), the Review Panel identified three requirements that must be met before they would consider as relevant any evidence related to cumulative effects:

  1. There must be an environmental effect of the project being assessed.
  2. That environmental effect must be demonstrated to operate cumulatively with the environmental effects from other projects or activities.
  3. It must be known that the other projects or activities have been, or will be, carried out are not hypothetical.

In the Panel's subsequent Decision Report (Priddle et al. 1996), the Panel noted that a further requirement was that the "cumulative environmental effect is likely to result".

2.2 An Overview of Basic Concepts

2.2.1 Effects Pathways

Cumulative effects occur as interactions between actions, between actions and the environment, and between components of the environment. These "pathways" between a cause (or source) and an effect are often the focus of an assessment of cumulative effects. The magnitude of the combined effects along a pathway can be equal to the sum of the individual effects (additive effect) or can be an increased effect (synergistic effect). [There are numerous other types of interactions defined in the literature by such terms as linear, multiplicative, compounding, structural surprise, space cycling, and space lags, etc. Although of interest in understanding the complexity of cumulative effects, determining which type is actually occurring (aside from additive effects) and measuring the interaction is often difficult in practice.]

Case Study
Saskatchewan Uranium Mines: Pathways of Radionuclides

A study of the effects of various proposed uranium mine developments in northern Saskatchewan (Appendix B) used pathways to define the various means by which radionuclides could disperse in the environment (Ecologistics 1992). Pathways were used to illustrate the linkages between a source (i.e., a mine), a dose on an environmental receptor (e.g., VECs such as moose, fish and benthic invertebrates), and the contribution of all pathways to a total dose on the environment. Generally, radionuclides could be dispersed in the atmosphere, groundwater or surface water. Dispersal may continue through vegetation and soils, forage crops, wildlife, aquatic plants and animals and sediment. An example of one pathway amongst these possible interactions is: Mine à Surface Water à Aquatic Plants à Total Dose.

2.2.2 How Cumulative Effects Occur

Cumulative effects can occur in various ways:

  • Physical-chemical transport: a physical or chemical constituent is transported away from the action under review where it then interacts with another action (e.g., air emissions, waste water effluent, sediment).
  • Nibbling loss: the gradual disturbance and loss of land and habitat (e.g., clearing of land for a new sub-division and roads into a forested area). [This can include alienation of wildlife habitat due to sensory disturbances.]
  • Spatial and temporal crowding: Cumulative effects can occur when too much is happening within too small an area and in too brief a period of time. A threshold may be exceeded and the environment may not be able to recover to pre-disturbance conditions. This can occur quickly or gradually over a long period of time before the effects become apparent. Spatial crowding results in an overlap of effects among actions (e.g., noise from a highway adjacent to an industrial site, confluence of stack emission plumes, close proximity of timber harvesting, wildlife habitat and recreational use in a park). Temporal crowding may occur if effects from different actions overlap or occur before the VEC has had time to recover.
  • Growth-inducing potential: Each new action can induce further actions to occur. The effects of these "spin-off" actions (e.g., increased vehicle access into a previously unroaded hinterland area) may add to the cumulative effects already occurring in the vicinity of the proposed action, creating a "feedback" effect. Such actions may be considered as "reasonably-foreseeable actions" (Section 3.2.4).
Can Project-Specific CEAs Adequately Address Regional "Nibbling" Effects?

Regional "nibbling" effects usually cannot be adequately dealt with on a project-by-project review basis. Although broad changes in a landscape can often be quantified (e.g., total cleared land, fragmentation of wildlife habitat), it is more difficult to determine a significance to this change that is only attributable to the specific action under review. To properly address this type of cumulative effect, regional plans are required that clearly establish regional thresholds of change against which the specific actions may be compared (Section 4.2). Project applications can at least be compared to restrictions or requirements under any applicable land use plans or policies (e.g., Alberta's Integrated Resource Plans).

Careful Use of Terms

Ideally, cumulative effects should be assessed relative to a goal in which the effects are managed on a regional basis. Terms such as ecological carrying capacity, ecosystem integrity, long-term population viability and sustainable development are often cited as goals to be accomplished by CEAs. What these terms represent are important and their successful implementation would substantially improve the value of an assessment. They often appear in CEAs because they relate to relatively large landscape-level changes in a regional study area, and their broad application appears amenable to the objectives of future regional-based planning efforts.

However, expectations of what should be accomplished in CEA often exceed what is reasonably possible given our knowledge of natural ecosystems, available information, level of effort required to obtain more information, and the limits of analytical techniques in predicting the effects of actions on the environment. These terms should not be used in a CEA unless they are carefully defined; otherwise, the uncertainty associated with their meaning will later bring into question the usefulness of the CEA during its interpretation by regulatory reviewers.

2.2.3 Improvements in the Evolving Practice of CEA

The growing body of CEA literature, the increasing number of assessments completed, and direction from reviewing agencies and Boards (or Panels) has raised expectations of what should be accomplished in CEAs. Each assessment creates a precedent for what can and should be done. The following identifies some aspects of CEA that require improvement:

  • Better identification of and focus on those project-specific effects with the greatest potential to act in a cumulative fashion with other actions.
  • Application of regional coordinated land use planning and practical measures of limits to growth.
  • Results that compare the incremental contribution of an action to regional thresholds for various VECs and indicate to what degree a threshold is approached or exceeded.
  • Conclusions relying on more quantitative analysis.
  • Broadening of the number of proven analytical approaches.
  • Finer breakdown of more specific interactions among various actions.
  • Ability to better examine synergistic effects, particularly the potential interactions between contaminant releases and direct physical effects and the influence these effects may have when combined with natural perturbations.
  • The influence of environmental cumulative effects on socio-economic systems, as well as the effects of cumulative socio-economic changes on the regional environment.
  • Selection of management options for dealing effectively with significant cumulative effects.
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