A weight can be defined as a value assigned to an evaluation criterion which indicates its importance relative to other criteria under consideration .Assigning weights of importance to evaluation criteria accounts for 1) the changes in the range of variation for each evaluation criterion, and 2) the different degrees of importance being attached to these ranges of variation [14] . There are four different techniques when assigning the weights: Ranking, Rating, Pairwise Comparison and Trade of Analysis Method [14] . Calculating weight for the criteria using the method of pairwise comparison method, the weights of criteria have been computed using comparison matrix shown in figure 4 by using scale values of 1 - 9 as shown in table 4.

The comparison matrix indicating the relative importance of the criterion in the columns compared to the criterion in the rows. (For each comparison, it will decided which of the two criteria are the most important, and then a score is assigned to show how much more important it is). The resulting weights are given in table 5.

It is evident that many factors must be incorporated into landfill siting decisions. Geographic information systems (GIS) is ideal for this kind of preliminary studies due to its ability to manage large volumes of spatial data from a variety of sources. It efficiently stores, retrieves, analyzes and displays information according to user- defined specifications [4] .

1) Settlement Areas

Settlement areas were subdivided into two layers. First layer consists of residential areas, and the second layer was for industrial areas.

The reason for this division is the necessity of applying different buffer zones to residential and industrial areas. According to Allen et al. [23] , the location of a landfill should be at a distance of at least 5 km from residential areas should be and 500 m from isolated houses. The buffer distances for towns and villages within a population greater than 500 people were determined as 1000 m, and 500 m for all other identified centers of population and 250 m for private residences, businesses, social and community buildings by Cantwell [35] . Siddiqui et al. [4] suggested that no new landfill site should be located closer than 0.4 km (0.25 mi) from a collection of ten or more houses. On the other hand, the landfill site should be located within 10 km of an urban area due to economic considerations [36] . Accordingly; minimum distances for the study area were considered as 5 km for residential areas and 250 m for industrial areas. These distances were used to create buffer zones around settlement areas and it was excluded from the study area. After exclusion of absolutely unsuitable areas for a landfill site, the remained areas are classified according to their suitability. The layer of industrial areas are classified as suitable or unsuitable by assigning values 1 and 0 respectively (Table 6) and map shown in figure 5.

The layer concerning residential areas was divided into four classes. The classes and related ranks can be seen in Table 7. The residential areas layer was then prepared based on the ranking values shown in same table that is presented in figure 6.

2) Roads

Minimum distance from the network is imported in order to avoid visual impact and other nuisances. Roads plus 100 m around them applied as a buffer zone [37] .

As stated by Cantwell [35] , all roads including primary, secondary, regional and third class roads should be avoided and have a buffer of at least 30 m on both sides. According to Allen et al. (2000), distance greater than 1 km from main roads and highways should be avoided. On the other hand, the landfill site should not be placed too far away from existing road networks to avoid the expensive cost of constructing connecting roads [22] . Distance from main access roads should be smaller than 3 km according to Allen et al. [23] and between 0.2 km and 10 km of a major road according to World Bank [36] .

By considering these suggested values, the buffer zones and related ranks were determined for roads which are shown in table 8.

The values of table 8 were entered to the database and each value was assigned to its related class. Finally, the vector maps were converted to raster maps as shown in figure 7.

3) Railways

The necessary buffer zone distances and related rankings are directly used as shown in table 9 according to World Bank [36] .

The buffer zones were created (table 9). The layer of railways was classified as suitable or unsuitable by assigning values 1 and 0 respectively. Then, the vector map prepared was converted to a raster map as shown in figure 8.

Figure 4. comparison matrix. ^*Ur: Urban centers, Lu: Land use, Ai: Airports, Pi: Pipes, Pl: Power lines, Ra: Railways, Ro: Roads, Sl: slope, St: streams, Sw: Surface water, In: Industrial areas, Oi: Oil pipes, Lg: Liquid gas pipes, St: Soil types. ^*Source: [16] , λmax = 14.327, CI = 0.025, RI = 1.57 and CR = 0.016 < 0.1.

4) Airports

There are different values related to the safe distances from airports like 3000 m according to Chalkias and Stournaras [38] and 3.048 m according to Bagchi [39] . As stated by Allen et al. [23] , distance of 10 to 13 km from flight path should be considered as a buffer zone.

By considering these suggested values, the safe distance for an airport was considered as 3000 m. The layer of airport was classified as suitable or unsuitable for a landfill site by assigning values 1 and 0 respectively (Table 10). To finalize the map for analysis, the vector map was converted to raster map (Figure 9).

5) Surface water

The necessary buffer zone for swamp areas was considered 250 m [40] . The layer of wetlands was classified as suitable or unsuitable by assigning values 1 and 0, respectively (Table 11). The buffer zones were created and

the study area was divided into two classes in the GIS environment. Then, the vector map prepared is converted to a raster map shown in figure 10.

6) Pipelines

Pipelines in Babylon are for water and Waste Water Treatment Plants passing through the study area. The necessary buffer zone for pipeline was considered as 250 m on both sides [40] . The pipeline layer was classified as suitable or unsuitable for a landfill site by assigning values 1 and 0, respectively (Table 12). After the creation of buffer zones, the vector map prepared was converted to a raster map as shown in figure 11.

7) Power Lines

The necessary buffer zone distance according to Cantwell [35] , should have a buffer of 30 m on both sides. The buffer zones were created in the GIS environment. The layer of power lines was classified as suitable or unsuitable for a landfill site by assigning values 1 and 0 respectively (Table 13). Then, the vector map of Babylon electricity directorate was converted to a raster map shown in figure 12.

8) Soil Texture

According to Alsharify [41] , the texture of Babylon soil is almost silt clay loam. Table 14 shows adopted test results of texture of Babylon soil [41] .

Using the information in table 14 and table 15 plus figure 13, figure 14 was prepared which is a raster map to be used as an input map in the analysis.

9) Stream

The necessary buffer zone for stream was considered as 300 m on both sides [40] . The surface water layer was classified as suitable or unsuitable for a landfill site by assigning values 1 and 0, respectively (Table 16). After

the creation of buffer zones, the vector map prepared was converted to a raster map shown in figure 15.

10) Oil Pipes

The necessary buffer zone for oil pipes was considered 75 m on both sides. The surface water layer was classified as suitable or unsuitable for a landfill site by assigning values 1 and 0, respectively (Table 17). After the creation of buffer zones, the vector map prepared was converted to a raster map shown in figure 16.

11) Liquid Gas Pipes

The necessary buffer zone for liquid gas pipes was considered300 m on both sides. The surface water layer was classified as suitable or unsuitable for a landfill site by assigning values 1 and 0, respectively (Table 18). After the creation of buffer zones, the vector map prepared was converted to a raster map shown in figure 17.

12) Land Use

In the study area, there are different types of land uses (see table 19 and figure 18). The types of land use

were grouped and ranked according to their suitability for landfill site as unsuitable, moderate suitable and suitable by assigning values 0, 5 and 10 respectively. The land use vector map was then converted to a raster map (figure 19).

13) Digital Elevation Model

Digital Elevation Model (DEM), also referred as the Digital Terrain Analysis, is a digital representation of earth’s topography in a continuous way [43] . Slope map are usually generated from DEM.

The potential for slope failure was related to the degree or grade of the topography. Slope failure underneath or adjacent to landfills, will result in waste containment failure and release of debris into the surrounding area. Land with slopes greater than 15% should be considered unsuitable for waste disposal sites [39] . The slope layer was classified as suitable or unsuitable for a landfill site by assigning values 1 and 0, respectively (Table 20 and Figure 20).

14) Overlay Analysis

An output value of the resultant map which is the final suitability map was prepared using overlay analyses of ArcGIS Spatial Analyst. Land suitability of the study area was calculated by the Land Suitability Index LSI. Calculated LSI is varies between 0.436 and 4.161. The very high and very low suitable areas were determined. Pixels with 0.436 (colored red) are considered as very low suitable and were excluded from the alternative candidates’ sites to be examined as disposal areas. On the other hand pixels with values around 4.161 suggested sites that are likely to be more suitable and were colored blue (see figure 21).

1) District (Nahia) Center

Technically, the distance from the center of a collection route to the landfill should be less than 20 - 25 km [23] . Therefore, a distance about 20 km (to cover all zigzag roads) was adopted from centers of each districts (Nahia) to restrict suitable lands according to this criterion. The output map produced is shown in figure 22.

The suitable land intersected with specific layers of buffer zones around district centers selected as landfill sites. The output map produced is given in figure 23. This map shows the landfill site selected to cover all Al-Mahaweelqadaa municipal solid wastes disposal.

2) Landfill Area

To achieve right decision in landfill site selection, the area should be conformable or greater than the required area to municipal solid wastes assumption for disposal.

According to Tchobanoglous et al. [2] the principle methods used for landfilling dry areas may be classified as: 1) Area, 2) Trench, and 3) depression. The adopted method in this research was area method that is more suitable with Babylon environs lands of shallow ground water depth range from 3 to 4 m. Available areas of the selected landfill, and Nahias serve are shown in Table 21.

Once the amount of waste generated had been estimated, landfills should be designed in cells with sufficient capacity to receive the cumulative volume of waste generated. The optimal capacity of a landfill site should be not less than 5 years in order to ensure that the major investments required by the landfill are spread over large tonnage of waste.

The cumulative volume of wastes expected to be generated between 2013 and 2017 of the selected landfill is presented in table 22. The adopted density of the waste in the landfill is 450 kg/m³. It has not accounted for any reduction in the waste going to the landfill through recycling or composting at this stage.

Waste in the landfill should be covered daily by a cover in order to minimize health, safety and environmental impacts and nuisances. The volume of daily cover in the landfill varies between 10% and 15% of the waste volume [40] . Adopting a value of 10% of the waste volume, the required capacity of the landfill over the next five years can be estimated as shown in table 22.

Wastes are unloaded to landfill site and spread in long narrow strips on the surface of land in series of layers of 50 cm depth. Each layer is compacted at the filling progresses during the course of the day until the thickness of the compacted wastes reaches a high of 3 m. The cover material must be hauled in by earth moving equipment from adjacent land or from borrow bet areas. The width over which the wastes are compacted is 6 m [40] . Required area of the selected landfill is shown in table 22.

From table 21 and table 22, it can be recognized that the available area of selected landfill is quite more than the required areas estimated for 5 years. Therefore, the right decision is taken.

Table 23 shows the selected landfill with its location and coordinates in addition to the required and available area.

3) Official and Field visits review

The candidate site had been revealed. In order to check the suitable area derived from the analysis and the actual case requirement (Nahia center and landfill area), office and field checks were performed out to determine the accuracy and suitability of candidate sites.

The selected site was checked using satellite image for year 2006. Two directorates in Babylon Governorate (Physical Planning and Agriculture directorates) were consulted for the land ownership and other restrictions if exists. Accordingly, some adjustments were made on the areas chosen.

Antiquities directorate in Babylon Governorate didn’t have coordinates for all the religious and antique locations. Because of that, no layer for that criterion was prepared. This was solved by field visits to the selected site.

In view of the visits conducted with official departments concerned, no conflicts with activities of these departments were noticed about the site proposed.