Conducting Environmental Impact Assessment in Developing Countries (UNU, 1999, 375 pages)
 4. EIA methods
 4.3 Matrix
 4.3.3 Numeric and scaled matrices
 4.3.3.1 Simple numeric matrix 4.3.3.2 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.