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Area of Influence

Projects affect a specific area but this area can vary among resource types and by phase of development. The area of influence for a project is the combination of all of these.

Determining the area of influence (often called the region of influence [ROI] or affected environment) is the next step in performing an impact assessment. Determining the area of influence for a project can be complex and is rarely limited to the project footprint or some set distance from the project area.

The area of influence is often, if not always, variable and dependent on the impacting factor (both direct and indirect) and the affected resource. Some examples for different resources include:

  • Soils and Geology: The area of influence is usually localized and restricted to the project footprint, its immediate surroundings, and borrow areas (i.e., areas from which raw materials, such as gravel, are excavated).

  • Water Resources: The area of influence related to releases of pollutants to a water body will depend on the type of water body (e.g., stream, river, or lake), the volume and flow of that water body, the nature of the pollutant, and the chemical characteristics of the water body. For water releases, the area of influence can be limited to a single river or stream, but could extend many miles downstream. The area of influence related to use of water will depend upon the water source (e.g., surface water body, groundwater, captured wastewater), the volume of water required, and competing uses for the water.

  • Air Quality: The area of influence for air emissions will be influenced by prevailing winds, weather patterns, terrain, and the nature of the pollutant being considered. Sophisticated air dispersion models can predict spatial patterns of air dispersion and deposition for various chemicals and allow for close delineation of the area of influence.

  • Land Use and Socioeconomics: The area of influence will, in general, be localized and restricted to the project footprint and immediate surroundings, but land use in any area supplying workers to a project area can be affected. Area of influence will depend on regional socioeconomic conditions and can be quite different in rural as opposed to urban environments.

  • Ecological Resources: The area of influence will be the combination of areas of influence for geology and soils, water, and air. The area of influence can be complicated by the presence of migratory species that are not present year-round. Thus, areas that are a great distance away from the project can be influenced by the project.

The area of influence is also dependent on project phase and differs between direct, indirect, and cumulative impacts:

  • Site Characterization: The area of influence is usually limited to the immediate area of activities

  • Construction: The area of influence includes the project footprint and immediate surroundings, and the socioeconomic regions supplying workers.

  • Operations: The area of influence includes the project footprint and surroundings, areas affected by emissions and effluents, and the socioeconomic regions supplying workers.

  • Decommissioning: The area of influence includes the project footprint and immediate surroundings, and the socioeconomic regions supplying workers