The document discusses various methodologies used for environmental impact assessments, including ad hoc methods, overlay maps, impact checklists, impact matrices, and cause-condition-effect networks. It provides detailed explanations and examples of each methodology. The network method uses an "impact tree" to relate primary, secondary, and tertiary effects by answering questions about impacts within project activities. Weighting schemes can incorporate probabilities and magnitudes of impacts.

1. Environmental Impact Assessment
Methodology
By
Dr. I.M. Mishra
Professor, Dept. of Chemical Engineering
Dean, Saharanpur Campus
Indian Institute of Technology, Roorkee

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

3. “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.

4. Illustrative Ad Hoc Approach to Environmental Impact Versus Environmental Area

5. “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.

6. 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.

7. “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”.

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

9. “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”.

10. Impact tree for a hypothetical bank stabilization project.

11. 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.

16. Typical Project Checklist by Impact Area
CONSTRUCTION POTENTIAL IMPACT PHASE OPERATING PHASE
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

17. Matrix Method
The 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.

18. Illustrative Example of Checklist Approach to Neighborhood Development
Project

19. 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

20. Ranking Example for Five Highway Project Alternatives and Seven Impact Areas

21. Rating Example for Five Highway Project Alternatives and Seven Impact Areas

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

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

24. mij = (+or-)
ij 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
åm w
ij ij
environmental factor from all actions =
j
åm w
ij ij
i
Total impact of the jth action on all environmental factors =
ååm w
ij ij
i j
Total Project impact =

25. 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.

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

27. 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.

28. The Potential impacts:
Impact Area Measures
Highway corridor alternatives
A B C D E
Number of dwelling units displaced
16 5 12 4 6
Number of units of farm land displaced
20 8 6 10 7

29. Candidate value Curves for Farmland impact

30. 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.

31. 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.

32. 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.

33. Illustrative Example of the Development of Impact Area Importance Weightings

34. 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.

35. 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.

36. 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

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

38. NETWORK METHOD
Network 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.

39. Network Method
Conceptual framework of impact networks.

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

41. (a) Illustrative impact tree
(b) corresponding branches

42. 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 let
pi = 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 X
and
I(X) = importance weighting of impact X,

43. (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
ΣM(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)

44. 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.

45. CONCLUSION
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