Summary Observations on Simple Matrices

The following observations are based upon numerous examples of matrices and over twenty years of experience in using such matrices:

1. In using a simple interaction matrix, one must carefully define the spatial boundaries associated with environmental factors, as well as each environmental factor; the temporal phases and specific actions associated with the proposed project; and the impact rating or summarization scales used in the matrix.

2. The most important concept in using an interaction matrix is to consider the matrix as a tool for purposes of analysis, with the key need being to clearly state the rationale used for the impact ratings assigned to a given temporal phase (or project action) and a given spatial boundary (or environmental factor).

3. The development of one or more interaction matrices can be a useful technique in discussing a proposed action and its potential environmental impacts. This development can be helpful in the early stages of a study to assist each team member in understanding the implications of the project and developing detailed plans for more extensive studies on particular factors.

4. The interpretation of information on resultant impact rating scales should be carefully considered, particularly when large differences in spatial boundaries, as well as temporal phases, for a proposed project may exist.

5. Interaction matrices are useful for delineating the impacts of the first and second or multiple phases of a two-phase or multiphase project; the cumulative impacts of a project when considered relative to other past, present, and reasonably foreseeable future actions in the area; and the potential positive effects of mitigation measures. Creative codes can be used in the matrix to delineate this information.

6. If interaction matrices are used to display comparisons between different alternatives, the same basic matrix must be used in terms of spatial boundaries and temporal phases for each alternative being analyzed. Completion of such matrices for each alternative can provide a basis for tradeoff analysis.

7. Impact quantification can provide a valuable basis for the assignment of impact ratings for different project actions and different environmental factors.

8. Color codes can be used to display or communicate information on anticipated impacts. Beneficial impacts could be displayed with green or shades of green; whereas, detrimental or adverse effects could be displayed with red or shades of red. Impact matrices can be used without incorporating number rating scales. For example, circles of varying size can be used to denote range of impacts.

9. One concern related to interaction matrices is that project actions or environmental factors are artificially separated when they should be considered together. Footnotes can be used in a matrix to identify groups of impacts which should be considered together. Footnote use allows the delineation of primary and secondary effects of projects.

10. The development of a preliminary interaction matrix does not mean that it must be included in a subsequent EIA report. The preliminary matrix can be used as an internal working document or tool in study planning and development.

11. Importance weighting for environmental factors and project actions can be used in a simple interaction matrix. If this approach is chosen, the rationale upon which differential importance weights are assigned must be carefully delineated.

12. One important advantage of a simple interaction matrix is that its use forces consideration of actions and impacts related to a proposed project within the context of other related actions and impacts. In other words, the matrix aids in preventing overriding attention being given to one action or environmental factor.


Topical Issue

Land Form

Will the project result in:

Unstable slopes or embankments?

Extensive disruption to or displacement of the soil?

Impact to land classified as prime or unique farmland?

Changes in ground contours, shorelines, stream channels, or river banks?

Destruction, covering, or modification of unique physical features?

Increased wind or water erosion of soils?

Foreclosure on future uses of site on a long-term basis?


Will the project result in:

Air pollutant emissions which will exceed federal or state standards or cause deterioration of ambient air quality (e.g., radon gas)?

Objectionable odors?

Alteration of air movements, humidity, or temperature?

Emissions of hazardous air pollutants regulated under the Clean Air Act?


Will the project result in:

Discharge to a public water system?

Changes in currents or water movements in marine or fresh water?

Changes in absorption rates, drainage patterns, or the rate and amount of surface water runoff?

Alterations to the course or flow of flood waters?

Impoundment, control, or modifications of any body of water equal to or greater than ten acres in surface area?

Discharges into surface waters or alteration of surface water quality including, but not limited to, temperature or turbidity?

Alteration of the direction or rate of flow of groundwaters?

Alterations in groundwater quality?

Contamination of public water supplies?

Violation of State Stream Quality Standards, if applicable?

Location in a riverine or coastal floodplain?

Exposure of people or property to water-related hazards such as flooding?

Location in a state's coastal zone and subject to consistency with the State Coastal Zone Management Plan?

Impact on or construction in a wetland or inland floodplain?

Solid Waste

Will the project:

Generate significant solid waste or litter?


Will the project:

Increase existing noise levels?

Expose people to excessive noise?

Plant Life

Will the project:

Change the diversity or productivity of species or number of any species of plants (including trees, shrubs, grass, crops, microflora, and aquatic plants)?

Yes Maybe No Comments

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Topical Issue

Reduce the numbers or affect the habitat of any state or federally designated unique, rare, or endangered species of plants? (Check state and federal lists of endangered species.)

Introduce new species of plant into the area or create a barrier to the normal replenishment of existing species?

Reduce acreage or create damage to any agricultural crop?

Animal Life

Will the project:

Reduce the habitat or numbers of any state or federally designated unique, rare, or endangered species of animals? (Check state and federal lists and the Migratory Bird Treaty Act.)

Introduce new species of animals into an area or create a barrier to the migration or movement of animals or fish?

Cause attraction, entrapment, or impingement of animal life?

Harm existing fish and wildlife habitats?

Cause emigration resulting in human-wildlife interaction problems?

Land Use

Will the project:

Substantially alter the present or planned use of an area?

Impact a component of the National Park system, the National Wildlife Refuge system, the National Wild and Scenic River system, the National Wilderness system, or National Forest land?

Natural Resources

Will the project:

Increase the use rate of any natural resource?

Substantially deplete any nonreusable natural resource?

Be located in an area designated as or being considered for wilderness, wild and scenic river, national park, or ecological preserve?


Will the project?

Use substantial amounts of fuel or energy?

Substantially increase the demand on existing sources of energy?

Transportation and Traffic Circulation

Will the project result in:

Movement of additional vehicles?

Effects on existing parking facilities or demands for new parking?

Substantial impact on existing transportation system(s)?

Alterations to present patterns of circulation or movement of people or goods?

Increased traffic hazards to motor vehicles, bicyclists, or pedestrians?

Construction of new roads?

Public Service

Will the project have an effect on, or result in, a need for new or altered governmental services in any of the following areas:

Fire protection?


Other governmental services?

Yes Maybe No Comments

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Topical Issue Yes


Will the project result in a need for new systems or alterations to the following utilities:

Power and natural gas?

Communications systems?


Sewer or septic tanks?

Storm sewers?


Will the project:

Alter the location or distribution of human population in the area?

Accident Risk

Does the project:

Involve the risk of explosion or release of potentially hazardous substances including oil, pesticides, chemicals, radiation, or other toxic substances in the event of an accident or "upset" condition?

Human Health

Will the project:

Create any health hazard or potential health hazard?

Expose people to potential health hazards?


Will the project:

Have any adverse effect on local or regional economic conditions, e.g., tourism, local income levels, land values, or employment?

Community Reaction

Is the project:

Potentially controversial?

In conflict with locally adopted environmental plans and goals?


Will the project:

Change any scenic vista or view open to the public?

Create an aesthetically offensive site open to the public view (e.g., out of place with character or design of surrounding area)?

Significantly change the visual scale or character of the vicinity?

Archaeological, Cultural, and Historical

Will the project:

Alter archaeological, cultural, or historical sites, structures, objects, or buildings, either in or eligible for inclusion in the National Register (e.g., be subject to the Historic Preservation Act of 1974)?

Hazardous Waste

Will the project:

Involve the generation, transport, storage or disposal of any regulated hazardous waste (e.g., asbestos, if demolition or building alterations is involved)?

Maybe No Comments

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