Selection of the Appropriate Aggregation Function for Calculating Leachate Pollution Index

A technique to quantify the leachate pollution potential of landfills on a comparative scale using an index known as the Leachate Pollution Index (LPI) has been developed and reported elsewhere. The LPI is a quantitative tool by which the leachate pollution data of the landfill sites can be reported uniformly. It is an increasing scale index and has been formulated based on the Delphi technique. The formulation process involved selecting variables, deriving weights for the selected pollutant variables, formulating their subindices curves, and finally aggregating the pollutant variables to arrive at the LPI. The aggregation function is one of the most important steps in calculating any environmental index. If the aggregation function is ambiguous, the result will raise an unnecessary alarm, indicating a comparatively less polluted environmental situation as more contaminated. Similarly, if the aggregation function is eclipsed, a false sense of security may be created, indicating a highly polluted environmental situation as less polluted. In this paper, the concept of LPI is described in brief and the various possible aggregation functions are described and used to calculate LPI values for an actual landfill site to select the most appropriate aggregation function. Based on the results, it is concluded that the weighted linear sum aggregation function is the best possible aggregation function for calculating LPI. Sensitivity analysis of the six short-listed aggregation functions is performed to substantiate this conclusion.