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close this bookConducting Environmental Impact Assessment in Developing Countries (UNU, 1999, 375 pages)
close this folder4. EIA methods
close this folder4.3 Matrix
close this folder4.3.3 Numeric and scaled matrices
View the document4.3.3.1 Simple numeric matrix
View the document4.3.3.2 Scaled matrices

4.3.3.2 Scaled matrices

Weighted-scale matrices typically use a scale of 1 to 10 to score two impact attributes, significance and importance. One of the most popular scaled matrices is the "Leopold matrix'' named after Dr Luna Leopold of the US Geological Survey who developed it in the early 1970s. All development activities are listed across the top of the matrix and all environmental components that might be impacted are listed down the side. A Leopold matrix attempts to assign numerical ratings of magnitude and importance so that the completed matrices for alternative sites or technologies could each be added and compared. In the original Leopold matrix, scores from a 1-10 scale can be assigned to describe the importance and magnitude of individual impacts. Importance refers to the significance of an impact and the magnitude of its scale and extent. Leopold-type matrices are easy to use and are perhaps the most widely employed and successful of all EIA methods. Figure 4.2 shows a portion of a Leopold matrix, as used for the comparision of alternatives.

Another approach is the environmental impact matrix, with and without mitigation (from Biswas and Agarwal, 1992). This is a conventional technique for summarizing environmental impacts utilizing the matrix method. Initially, the predicted impacts are converted into an ordinal scale (ranking) of impact severity, as in the following example.

Severity

Impact score



No impact

0

Negligible

1

Minor (slight or short term)

2

Moderate

3

Major (irreversible or long term)

4

Severe (permanent)

5

A positive sign denotes a beneficial impact, while a negative sign denotes an adverse impact.


Figure 4.2 Site comparison matrix for a quarry

A significant value (weighting) is attached to each environmental component (independent of the predicted levels of impact) based upon some expert or consensual (Delphi) system. Individual impact scores can then be calculated as the product of impact severity and significance. These may be summed by row and/or column to gauge the net impact of the project on a particular environmental component or, conversely, the net effect of a single project activity on the environment as a whole.

In this way, project alternatives can be systematically compared, and possible mitigation measures can be explored. In addition, this method can draw attention to the most significant impacts in the matrix, as revealed by individual cell scores. This procedure can also be used to identify negative impacts on environmental components that surpass a critical threshold. Such instances will have to be addressed through mitigation or project alternatives (Tables 4.5 and 4.6)

Table 4.5 Environmental impact matrix without mitigation



Impacting actions


Environmental parameters

Importance value

Premining phase

Operational phase

Impact score



A

B

C

D

E

F

G

H

I

J

K


Air quality

100

-1

-1



-2


-2



-1


-700

Water resources

75


-1




-1



-1



-225

Water quality

100





-1

-2

-1


-1



-500

Noise and vibration

75

-1

-1

-1

+1

-2


-1



-1


-450

Land use

150

-3

-1


+1

-2


-1





-900

Forests and vegetation

150

-4



+1








-450

Wildlife

50

-2



+1

-1





-1


-150

Human settlements

75

-1

+1






+1




+75

Health

100




+1

-3






+1

-100

Infrastructures and support services

50









+2

+1

+2

+250

Employment

50

+1

+1



+2




+1



+250

Places of tourist or archaeological importance

20












0

Total

1000

-1350

-275

-75

+525

-1000

-275

-525

+75

-25

-175

+200

-2900

+ sign shows beneficial impact; - sign shows adverse impact.

A, land acquisition and transformation; B, civil works construction; C, erection of mechanical and mining equipment; D, green belt formation; E, mining operations including CHP; F, disposal of liquid effluent; G, disposal of solid wastes on land for reclamation; H, housing provision: I, provision of water, sewage, electricity, and other civic amenities; J, transportation; K, medical facilities.

Table 4.6 Environmental impact matrix without mitigation



Impacting actions



Environmental parameters

Importance value

Premining phase

Operational phase


Impact score



A

B

C

D

E

F

G

H

I

J

K

L


Air quality

100

-1

-1


+1

-1


-1



-1


+1

-300

Water resources

75


-1




-1



-1




-225

Water quality

100






-1

-1





+1

-100

Noise and vibration

75

-1

-1

-1

+1

-1


-1



-1



-375

Land use

150

-3

-1


+1

-1


+1





+2

-150

Forests and vegetation

150

-4



+1








+4

+150

Wildlife

50

-2



+1

-1





-1


+1

-100

Human settlements

75

-1

+1






+1





+75

Health

100




+1

-1






+1


+100

Infrastructures and support services

50









+2

+1

+2


+250

Employment

50

+1

+1



+2




+1




+250

Places of tourist or archaeological importance

25













0

Total

1000

-1350

-275

-75

+625

-375

-175

-125

+75

+75

-175

+200

+1150

-425

+ sign shows beneficial impact: - sign shows adverse impact.

A, land acquisition and transformation: B, civil works construction: C, erection of mechanical and mining equipment; D, green belt formation; E, mining operations including CHP; F, disposal of liquid effluent; G, disposal of solid wastes on land for reclamation; H, housing provision: I, provision of water, sewage, electricity, and other civic amenities; J, transportation: K, medical facilities: L, land reclamation.