Environmental Impact Assessment Methodology

Dr. I.M. MishraProfessor, Dept. of Chemical Engineering

Dean, Saharanpur Campus

Indian Institute of Technology, Roorkee

By

Methodologies:• adhoc methods.• map over lays.• impact checklists• impact matrices and• cause-condition-effect

networks.

“Adhoc Methods” provide minimal guidance for total impact assessment while suggesting the broad areas of possible impacts and the general nature of these possible impacts. For example, impacts on plant and animal life might be stated as minimal but adverse, whereas the impacts on the regional economy might be stated as significant and extremely beneficial. These statements are qualitative and could be based on subjective or intuitive assessments, or could be qualitative interpretations of quantitative results.

Illustrative Ad Hoc Approach to Environmental Impact Versus Environmental Area

“Overlay Methods” generally rely on a set of maps of a project area’s environmental characteristics (physical, social, ecological, aesthetic, etc.). These maps are overlaid to produce a composite characterization of the area’s environment. Impacts are then identified by noting the impacted environmental characteristics within the project area boundaries. This presents a graphical display of the types of impacts, the impacted areas, and their relative geographical location.

The “impact checklists” is a method of combining a list of potential impact areas that need to be considered in the environmental impact assessment process with an assessment of the individual impacts. This approach has been adopted by a number of public agencies since it insures that a prescribed list of areas is considered in the assessment process. Unfortunately, this type of method does not provide for the establishment of direct cause-effect links to the various project activities and, generally, does not include an overall interpretation of the collective environmental impacts.

“Matrix methods” basically incorporate a list of project activities or actions with a checklist of environmental conditions or characteristics that might be affected. Combining these lists as horizontal and vertical axes for a matrix allows the identification of cause-effect relationships between specific activities and impacts. The entries in the cell of the matrix can be either qualitative estimates or quantitative estimates of these cause-effect relationships. The later rate in many combined into a weighting scheme leading to a total “impact score”.

Illustrative Matrix Approach to Comparing Environmental Impact of Actions on Existing Characteristics and Conditions of the Environment

“Network methods” start with a list of project activities or actions and then generate cause-condition-effect networks (i.e., chains of events). This type of method is basically an attempt to recognize that a series of impacts may be triggered by a project action. Hence, this method provides a “roadmap” type of approach to the identification of second-and third-order effects. The idea is to start with a project activity and identify the types of impacts which would initially occur. The next step is to select each impact and identify the impacts which may be induced as a result. This process is repeated until all possible impacts have been identified. Sketching this in a network from result in what is commonly referred to as an “impact tree”.

Impact tree for a hypothetical bank stabilization project.

The checklist method is basically a variant of the ad hoc method for summarizing environmental impacts in the sense that it starts with a list of potential impact areas. The next step is to assess the character or nature of the impact. This is usually accomplished through the use of such descriptive terms as adverse or beneficial, short-term or long-term, no effect or significant effect. For example, next table provides an illustration of a typical checklist form which could be used to insure that all important aspects of an environment impact evaluation are considered. In the actual implementation of this form one would place a check mark as “X” opposite each item to indicate whether the proposed project will have an adverse effect, no effect, or a beneficial effect on the item in question.

Typical Project Checklist by Impact Area

CONSTRUCTION PHASE OPERATING PHASE POTENTIAL IMPACT

AREA Adverse effect

No effect

Beneficial effect

Adverse effect

No effect

Beneficial effect

A. LAND TRANSFORMATION AND CONSTRUCTION a. Compaction and settling

b. Erosion c. Ground cover d. Deposition (sedimentation, precipitation)

e. Stability (slides) f. Stress-strain (earthquake)

g. Floods h. Waste control i. Drilling and blasting j. Operational failure B. LAND USE a. Open space b. Recreational c. Agricultural d. Residential e. Commercial f. Industrial

Matrix MethodThe environmental impact of projects or actions generally encompass a broad range of impacts from air and noise pollution to effects on employment and neighborhood social structure. All of these impacts vary in magnitude as well as in their beneficial or adverse classification. As a result, a natural question arises as to what is the “collective” or “overall” environmental impact of the project or action taken. Is the project beneficial or is it adverse? To answer such a question requires a comparison of these impacts and, to some extent, a subjective evaluation of which impacts are more important than others.

Illustrative Example of Checklist Approach to Neighborhood Development Project

Sample Ranking of Highway Improvement Project Alternatives

Alternative Number of dwelling units destroyed

Rank

V 0 1

W 2 2

X 20 3

Y 24 4

Ranking Example for Five Highway Project Alternatives and Seven Impact Areas

Rating Example for Five Highway Project Alternatives and Seven Impact Areas

Incremental Ranking Example for Five Highway Project Alternatives and Seven Impact Areas

Rating Example Based on Incremental Rankings for Five Highway Project Alternatives and Seven Impact Areas

( )ijm or

ijw

ij ijj

m w

ij iji

m w

ij iji j

m w

magnitude of the jth action on the ith environmental factor

importance weighting of the jth action on the ith environmental factor,

Total impact on the ith

environmental factor from all actions =

Total impact of the jth action on all environmental factors =

Total Project impact =

The preceding measure of total project impact is in essence a quality-of-life indicator in the sense that mij represents the magnitude of impact of the jth action on the ith quality-of-life factor and wij represents the weighting of importance as viewed by members of society.

Illustrative Example of Weighted Impact on Actions on Existing Characteristics and Conditions of the Environment

Determination of Environmental Impact Importance.The matrix approach discussed in the previous section the

need for tables presenting comparisons of alternatives both require a statement of the impact on the particular environmental area, given a specific action. This calls for some kind of measurement in the most general sense. first, one must measure the impact itself, that is the magnitude, and then one must evaluate that level of impact in terms of its relative value to the appropriate constituency. In the first case, one is looking for data about changes in the environment and must rely on scientific knowledge. In the second case, one is looking for the relatives values of the society or segments of society concerned in the evaluation of a project.

The Potential impacts:

Impact Area Measures

Highway corridor alternatives

A B C D E

Number of dwelling units displaced16 5 12 4 6

Number of units of farm land displaced20 8 6 10 7

Candidate value Curves for Farmland impact

Steps for Determining Weightings of Importance

Step 1: Select a group of individuals for evaluation and explain to them in detail the weighting concept and the use of rankings and weightings.

Step 2: Prepare a table with columns corresponding to the range of values which can be assigned as a “score of importance” to each impact area- for example, if five values are possible, there would be five columns. The rows in the table would correspond to the impact areas being ranked as to importance.

Step 3: Give a copy of the table developed in Step 2 to each individual evaluator and repeat steps 4-9 until no further changes in the table entries are desired.

Step 4: Ask each individual to place an “X” or other signifying mark, in each column for each impact area. Thus, a value of importance is assigned to each impact area.

Step 5: Ask all individuals to compare the marked columns on a pair-wise basis to insure that the impact areas are ordered on the proper relative basis in their opinion. If not, they should reassign their scores so as to have the desired relative ordering of impact areas. (For example, on a scale from 1 to 10, if a value of 10 has been assigned to impact area A and it appears that A is twice as important as B, impact should be assigned a value of 5).

Step 6: Ask each individual to add the value (or importance score) selected for each of the impact areas to obtain a total.

Step 7: The individual should then divide the value selected for each impact area by the total obtained in Step 6 to determine the desired weighting for each area.

Step 8: Collect the tables from each individual evaluator and average the weightings determined for each impact area obtain a “group or composite average.”

Step 9: Present the averages obtained to the individual evaluators and ask them to compare the group weightings with those derived by each of them individually in Step 7.

Step 10: If any one or more individual desires to change the assignment of scores based on what the group decided, to Step 4 and repeat the entire process. If none desire to change their scores, stop the experiment, because the impact area relative weightings of importance will have been derived.

Illustrative Example of the Development of Impact Area Importance Weightings

Steps for Development of Value Functions

In estimating the value function for each impact measure, five steps have to be followed:

Step 1: Obtain scientific information when available on the relationship between the measure or parameter and the quality of the environment.

Step 2: Order the impact measure scale so that the lowest value of the parameter is zero and it increases in the positive direction-no negative values.

Step 3: Divide the quality scale (0-1) into equal intervals and express the relationship between this interval and the parameter. Continue this procedure until a curve is constructed.

Step 4: Average these values as expressed in curves over all persons in the experiment. (For parameters based solely on judgment, value functions should be determined by a representative population cross section)

Step 5: Replicate this experiment with the same group or another group of persons to increase the reliability of the functions.

Illustrative Example of Dissolved Oxygen Level Versus Environmental Quality

Level of dissolved oxygen (mg/L)

Relative environmental quality value at each level

0 0

1 0.05

2 0.10

3 0.15

4 0.25

5 0.50

6 0.75

7 1.0

8 1.0

9 1.0

10 1.0

Example of a value function for dissolved oxygen as a measure of Water quality.

NETWORK METHODNetwork approaches attempt to expand upon the matrix theme by introducing a cause-condition-effect network which allows identification of cumulative or indirect effects. The network is actually shown in the form of a tree, also called a relevance or impact tree, and is used to relate and record secondary, tertiary, and higher order effects. To develop a network of this type basically requires answering a series of questions relative to each of the project activities such as what are the primary impact areas, what are the secondary impacts within these areas, what tertiary impacts flow from these, etc. This is the approach which must be followed.

Network Method

Conceptual framework of impact networks.

Example of impact tree for new freeway const1l1ction in established downtown business district.

(a) Illustrative impact tree (b) corresponding branches

Consider the impact tree given above in which there are two basic project activities, say A and B. In a activity a has two primary impacts, three secondary impacts, and two tertiary impacts. Activity B has two primary impacts, four secondary impacts, and four tertiary impacts. There are ten branches of this tree given by the chains of events shown in part b.Now letpi = probability that the events on branch i occur

for i = 1,2,........, 10. Also for each impact X, define

M(X) = (+ or -) magnitude of impact Xand I(X) = importance weighting of impact X,

(Contd...........)

where both M(X) and I(X) have values ranging over some arbitrary scale (for example, from 1 to 10). Then we define the impact score for a given branch of the impact tree to be

∑M(X)I(X),

where the summation is over all impacts (events) X on the branch.For example, the impact score for branch 1 would be given by

M(A1)I(A1) + M(A1,1)I(A1,1) + M(A1,1,1)I(A1,1,1)

In a similar way one could compute the impact score of the other nine branches. Now since there is some uncertainty as to whether or not the identified primary, secondary, and tertiary impacts will actually occur, one might weight these branch impact scores by their probability of occurrence.

The checklist, matrix and network methods deal primarily with four basic aspects

Identification of impacts Measurement of impacts Interpretation of impacts Communication of results Further, all the

methods differ from one another in one or more

CONCLUSION