GIS as Decision Support Tool for Landfills Siting

GIS as Decision Support Tool for Landfills Siting

Data for land use/land cover was obtained from the Department of Agriculture and here 9 different classes of land use/land cover were identified: urban, horticulture, perennial and tree crops, cropland, grassland, forest and marshlands and swamps. The working group for Sandakan District decided that all land use/land cover should be compatible for building a landfill except for marshlands and swamps.

For the haul distance, the criteria identified that a 25km radius from the urban centre is the most appropriate distance for site location. Thus, a 25 metre radius was then identified in the map using the functionality in GIS ArcView software. There was not enough data to perform the spatial operation for the 9 th criteria, which concerns the slope of land and thus slope analysis was not conducted. This particular analysis acknowledges the limitation of this research due to the unavailability of data in digital format; however hard-copy maps were available from Department of Surveys and Mapping, Malaysia and have been used to manually cross check the data where necessary.

Results
The outlined methodology did produce the expected result and thus the GIS spatial operation using map layers as specified in the constraint criteria works very well using the GIS software in particular the ArcView 3.1 and 3.2. Table 1 presents the full result of this research while the Map in Figure 3 shows the result in graphical form.

As indicated in Table 1, the total area of Sandakan District is 218,200 hectares. The constraint mapping exercise manages to narrow down the search area by 57,273 hectares or about 26.98% of the total area which represented a 73.74% reduction. The search areas were located in 6 different locations as shown on the map in Figure 3.

Figure 3: Result indicating the location of Search Area A-F
Table 1: Result – The Potential Search Area

Potential Search Site was found to be scattered in 6 different areas. Therefore, it is necessary to rank the areas from 1 to 6, where area 1 indicates the most preferred search area and 6 which is the least preferred. In order to achieve that, GAM 1 rating was chosen as the most appropriate technique and the GAM scoring shows that Search Area A found to be the most preferred site followed by Search Area B.

Further work by the Sandakan Municipal Council would be to make use this information to finalize the location of Sandakan Dumping Site based on the GIS analysis provided under this research.

Discussion
The on-going discussions with Sandakan Municipal Council (SMC) concerning the determination of new landfills sites have something to do with management issues and budget allocation. On one hand the advocate proposed that the existing landfill should be maintained due to lack of funding to open a new one. The existing dumping site was large enough to cater for many years to come and the only requirement was that budget must be allocated for better maintenance and management. However, the question to be asked was whether the groundwater was unacceptably at risk from leachate from a landfill. This begs two further questions, firstly, was the groundwater beneath the landfill site part of a significant aquifer? Secondly, was the landfill likely to generate leachate in sufficient quantity that it might migrate to and contaminate the groundwater in the Sandakan area?

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