Sustainable Development: The 6 Impact Assessment Stages

How can we ensure sustainable development? The answer is impact assessment, but what does it entail and how can it be done properly? Bram F. Noble, a professor at the University of Saskatchewan, wrote a comprehensive yet concise book about the concept: Introduction to Environmental Impact Assessment – A Guide to Principles and Practice. In the third edition, Noble writes, “Sustainability includes the desire to maintain, over an indefinite future, necessary and desired attributes of ecological and socio-economic environments that are necessary for system functioning and integrity.” Impact assessment is a process that is used to ensure that projects are developed in a sustainable manner. Noble outlines and details each part of the impact assessment process in his book phenomenally. This article contains a very condensed version of the impact assessment fundamentals in the form of six stages.

Screening is a process that is used to determine which projects have potentially significant impacts. There are several methods:

  • Case-based: Project characteristics are evaluated against a checklist of criteria or guidelines.
  • List-based: Project characteristics are listed according to impact assessment necessity from significant potential effects or regulatory requirements.
  • Threshold-based: Project characteristics are categorized and assigned a threshold according to impact type and magnitude.
  • Hybrid-based: Projects are evaluated using a combination of screening methods.

Screening describes the need and the purpose of projects, disclosing general information about the project, location, design, timetable, construction, operation, management, waste production, stakeholders, regulations, and authorization.

Scoping identifies Valued Environmental Components (VECs), referring to human and environmental aspects of vital importance. The condition of VECs can be assessed by defining parameters, evaluating the amount of stress that could be caused by the project versus an alternative project plan. A benchmark standard is then created as a point of reference, which is used to determine the spatial and temporal boundaries of the assessment. This refers to the establishment of a threshold:

  • Cautionary Threshold: A degree of monitoring efforts before adverse change may occur.
  • Target Threshold: A political or social margin of safety before mandatory management action.
  • Critical Threshold: A maximum capacity level for ecological or social effects before irreversible change.

In closed scoping, the process is conducted according to the law. In open scoping, the process is conducted through public consultation. Overall, scoping produces a baseline study, discovering and considering limits in any changes over time.

This stage derives predictions concerning the condition of VECs. In terms of environmental impacts, trends will be assessed according to biological, chemical, ecological, or physical changes. Regarding human impacts, trends will be assessed according to cultural, demographic, economic, institutional, medical, or social changes. An impact will then be classified according to its effects:

  • Direct Effects: Consequences that occur as a result of a project action.
  • Secondary Effects: Consequences that emerge from direct effects.
  • Incremental Effects: Consequences that cause marginal changes in the condition of an environment.
  • Additive Effects: Consequences that arise due to a combination of separate effects.
  • Synergistic Effects: Consequences that are greater than the interaction of separate effects summed together.
  • Antagonistic Effects: The offsetting or the cancellation of a consequence due to the interaction of adverse effects.
    • Functional Antagonism: The cancellation of physiological consequences due to the interaction of adverse impacts with opposite effects.
    • Chemical Antagonism: The reduction of a consequence due to the chemical reaction between separate impacts.
    • Dispositional Antagonism: The alteration of an impact in a diminishing manner through the influence of another impact.   
    • Receptor Antagonism: The blockage of an impact from the effect of a different impact.

These effects are then assessed according to their likelihood, addressing risks by analyzing and judging the significance of impacts upon VECs. Noble writes that the significance of an impact “is a function of the characteristics of the environmental effect or impact and the importance or value attached to the affected component”. Significance is determined through several approaches:

  • Technical: Judging the level of impact severity by using a standardized scale. Examples include fixed-point scoring, rating, or paired-comparisons.
  • Collaborative: Judging acceptable limits through public consultation.
  • Reasoned Argumentation: Considering information in a structured manner to build reasonable arguments that can be used to support matters deemed significant.
  • Composite: Judging impacts by using a combination of approaches.  

There are many methods to support such approaches, such as statistical significance testing, geographic information science (GIS) mapping, multi-criteria analysis testing, simulation modelling, and more.

It is important to identify and involve public participation in the decision-making process, considering those who may be positively or negatively affected by the project. Including the public allows project actors to properly define the problem, gain more information about expectations, educate people about plans, minimize conflict, reduce legal challenges, derive widely approved solutions, and facilitate overall project implementation. The International Association for Impact Assessment created a set of best practice principles for public participation:

  • Understand the context of affected communities
  • Provide information to communities early
  • Adapt the plan according to diverse interests
  • Ensure representation is inclusive and equitable
  • Educate the community about the plan for mutual understanding
  • Cooperate with the community
  • Improve the plan according to community feedback

Transparency must be valued in the impact assessment process, as it helps all stakeholders achieve their goals.

The management stage focuses on strategizing methods to deal with adverse impacts. Avoidance is the most desirable outcome, planning ways to prevent a negative impact from occurring at all. Planners will examine ways to minimize impacts if there are no alternative means to conduct a project. This is known as mitigation. If an impact cannot be avoided or mitigated, project managers will focus on restoring environmental quality, which is called remediation. If none of these outcomes can transpire, compensation is afforded to those affected by the damage. It is also important to consider how a project can create positive impacts, regarding how much its effects can enhance sustainability. There are several measures that can help support impact management efforts:

  • Environmental Management Systems: A system that helps identify and control impacts through setting targets and objectives, as well as tracking performance.
  • Environmental Protection Plans: A plan that describes general project information along with detailed action instructions.
  • Adaptive Management Strategies: A process that tests alternative methods to manage impacts, as well as monitors outcomes to gain knowledge about new courses of action.
  • Impact Benefit Agreements: An agreement ensuring that a community has the means to maximize potential positive benefits derived from the project.

Following-up is also important, as it allows managers to determine the accuracy and effectiveness of impact management measures and to identify the nature and cause of any change. Monitoring consists of observing and recording data in a repetitive manner, with a set of indicators that can be used to evaluate actual versus possible outcomes. There are many reasons for monitoring:

  • Compliance Monitoring: Seeing if a project adheres to agreement regulations or legislation.
  • Inspection Monitoring: Seeing if proper procedures were taken to prevent degradation.
  • Regulatory Monitoring: Seeing if conditions are being met for permit renewal.
  • Ambient Environmental Quality Monitoring: Seeing if there are differences in variables before versus after a project’s completion.
  • Management Monitoring: Seeing if there are any changes in environmental, economic, or social variables to derive future solutions.
  • Cumulative Effects Monitoring: Seeing if there is an impact from the total amount of effects caused by a project.
  • Project Evaluation Monitoring: Seeing if a project is performing according to its objectives in an efficient manner.
  • Experimental Monitoring: Seeing if environmental variables have changed according to any hypotheses.
  • Participatory Monitoring: Seeing if the local community has the capacity to handle any changes caused by the project.   

Conducting an impact assessment is an extensive and rewarding process that must be conducted according to specific laws and standards that differ in each location. Noble’s book thoroughly describes how impact assessments must be performed in Canada. It is a necessary read for Canadians pursuing an environmental or project management career, or for anyone wishing to gain insight about the complex nature of impact assessment.


Noble, Bram F. (2015). Introduction to Environmental Impact Assessment: A Guide to Principles and Practice, 3rd Edition. Canada: Oxford University Press.

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