Land fill site selection for municipal solid waste management using GSI method, Malayer, Iran.
Waste was an early problem of mankind, and a growing one that is of major concern to every nation of the world . In early pre-industrial times, waste generation was not an issue as populations were smaller. Municipal solid waste generation is among the most significant sources that threaten the global environmental health. Accordingly, it is essential that integrated systems of waste management be considered within the path towards achieving sustainable development. Such systems generally emphasize on functional elements of waste minimization (reduction), reuse, recycle and finally on placing the remained material in landfills . Landfill is an important component of any waste management system. Sustainable management of urban solid wastes may involve an integrated system of: (1) waste minimization in the production process; (2) reuse of products to extend their usefulness before entering the waste stream; (3) recovery of materials and energy from the waste; and (4) depositing the remaining material in landfills.
Landfill sitting is an extremely difficult task to accomplish because the site selection process depends on different factors and regulations . To ensure that an appropriate site is chosen, a systematic process should be developed and followed. Unsuccessful landfill sitting is typically the result of strong public opposition . The major goal of the landfill site selection process is to ensure that the disposal facility is located at the best location possible with little negative impact to the environment or to the population.
Geographic information system (GIS) is ideal for preliminary site selection studies, because it can manage large volumes of spatially distributed data from a variety of sources and efficiently store, retrieve, analyze and display information . Using GIS for site selection not only increases the objectivity and flexibility, but also ensures that a large amount of spatial data can be processed in a short time. Relatively easy presentations of GIS sitting results are also one of the advantages . The role of geographic information systems (GIS) in solid waste management is very large as many aspects of its planning and operations are highly depending on spatial data. GIS applications can help to determine the landfill location in accordance with the technical requirements, overlaying the thematic map to get an appropriate landfill. Sener et al.  from Akbari et al.  used GIS for multicriteria decision analysis (MCDA) to help the landfill site selection problem and developed a ranking of the potential landfill areas based on a variety of criteria. Kao et al.  from Azizi pointed out that a large amount of spatial data can be processed using GIS and thus, it potentially saves time that would normally be spent in selecting an appropriate site. The purpose of this research is to analyze and find suitable sites using geographic information system (GIS) for constructing landfill in Malayer region which is located in the west of the Iran.
2. The study area characteristics:
The study area (Malayer city) with an estimate population of 150,000 inhabitants and 1400 [km.sup.2] of area is the second largest city in Hamedan province, located at the 48[degrees]51' East longitude and 34[degrees]26' North latitude in west of Iran. Fig. 1 shows the considered location in proportion with Iran and Hamedan province. In the study area, the Jurasic metamorphic rocks have most extension. These rocks mostly consists schist, phyllite and slate. Other faces in this region are Cretaceous and Quaternary units consisting of grey limestones and recent sediments.
Economic growth in recent years has led to a remarkable increase in population and consequently in solid waste generation. Accordingly, appropriate site selection for regional solid waste land filling is a major need within the path towards sustainable development. The results show that average daily generation rate was 138 Tons and 0.88 Kg per person per day. The average percent of recyclable materials was about 11% of total daily generated wastes. The common disposal method for solid wastes in Malayer city is disposal in open dumps that can be source of worry to whoever cares about healthy living (Fig. 2). The samples of solid waste were taken in July, 2008. The physical composition of solid waste used for the study is depicted in Fig. 3. The dominant part of the degraded fraction is organic materials.
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Materials and Methods
The first step in the methodology consists of development of a digital GIS database in which spatial information is formed. Because of different scales upon which criteria are measured, it is necessary to standardize the effective factors before combination. In this study, 7 input map layers including geology, hydrology, geomorphology, slope, distance from the cities, main roads and faults were evaluated and prepared to be used in the analysis in GIS environment. All the data layers are derived and prepared from related maps by scanning, geocoding and digitizing the relevant information.
The information compiled from literature about the safe distances to a landfill site is used to determine the buffer zones for each layer. An extended collection of these safe distances from various case studies can be found at Sener (2004). After creation of the classes for each layer by using buffer zones, each layer is converted into individual raster maps. After the preparation of all input data layers, a methods named "simple additive weighting method" was selected among the decision rules to analyze the data for landfill site selection by using GIS.
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Results and Discussion
4.1. Criteria for selection:
To arrive at the selection criteria for choosing a site for landfill, relevant literature and decision makers' opinion were sought [3,7,14]. Several factors were considered in arriving at the suitable sites for landfill sitting. This is of great importance to consider the nature of what is to be sited. In this study, by taking into account the conditions of Malayer region, seven criteria were selected. Some of which are described below:
Areas that have not faults or have safe distance from the faults, are suitable for siting landfill. Faults increase permeability of rocks so that ground water may be polluted with leachate of landfill. This sub-criterion is divided into two components, major faults and minor faults. There is no main fault in studied area and minor faults are dominant.
From the geology point of view, materials have different suitability for being chosen as landfill sites. Materials with low permeability such as shale, marl, claystone and schist are suitable for this purpose (Class 3), while igneous and metamorphic rocks (Class 2) have lower suitability than those. Limestones, sandstones, dolomite and evaporatives, alluviums and terraces (Class 1) are the very unsuitable geological materials for landfilling. These formations are shown in geological map in the form of three distinguished classes (Fig.4). Regarding that, much of the region is composed of metamorphic and igneous rocks. Most parts of the study area are located in 2 and 3 classes.
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The higher the value of the slope reaches, the lower the suitability of the land for landfilling drops. As stated by Oweis et al.  and applied in this study, areas with slopes greater than 15[degrees] should be avoided for a landfill site. According to Lin , the appropriate slope for constructing a landfill is about 8-12%, because so steep a slope would make it difficult to construct and maintain. In spite, so flat a slope would affect the runoff drainage. High slopes can favour leachate drainage to flat areas and water bodies and cause contamination. Areas whose slope is greater than 20% are not suitable to allocate landfills . Based on the suggestions in the literature, slope map is classified into four groups. The final map used for analysis is shown in Fig. 5.
4. Surface waters:
This criterion has a direct effect on land suitability for being used as a landfill. In the other words, farther lands from streams and river banks will get more preferences for being selected. In some literature, researchers have suggested a distance up to 500 m away from a freshwater body of the water . Accordingly, four different zones were specified considering relative distance from rivers. Zoning process is schematically shown in Fig. 6.
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5. Settlements area:
Extensive studies on different aspects of resident's reaction in confrontation with landfilling show that public opposition decays exponentially while distance increases . Furthermore, future residential and industrial growth must also be considered in allocating the place of landfill. Based on current environmental regulations for the development of industrial and commercials projects, landfills cannot be located within residential area. After the digitization process, safe distances from the settlement areas are determined by literature review . By considering all suggestions based on the literature, minimum and safe distances for the study area was determined 1000 m for residential areas as illustrated in Fig. 7. These distances are used to create buffer zones around settlement areas and excluded from the study area.
6. Distance from main roads:
Landfill location must be close to roads network in order to facilitate transportation and consequently to reduce relative costs. According to Allen, the 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 the existing road networks to avoid the expensive cost of constructing connecting roads. Distance from main access roads should be between 0.2 km and 10 km of a major road. These suggested values having been considered, the buffer zone of 500 m was determined around main roads as shown in Fig. 8.
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4. 2. Analysis:
4.2.1. Simple Additive Weighting (SAW):
Simple additive weighting also known as weighted linear combination or scoring method is a simple and the most often used multiattribute decision technique [15,6,5]. This method is based on the weighted average. An evaluation score is calculated for each alternative by multiplying the scaled value given to the alternative of that attribute with the weights of relative importance directly assigned by decision maker followed by summing the products for all criteria. The simple additive weighting method evaluates each alternative, [A.sub.i], by the following formula:
S = ([summation] [W.sub.j] x [S.sub.ij]) (1)
Where [S.sub.ij] is the score of the ith alternative with respect to the jth attribute, [w.sub.j] is the normalized weight.
The first step of GIS-based SAW method is defining the set of evaluation criteria. The 7 map layers, each of which defines a criterion necessary to be considered in landfill site selection were prepared. The set of feasible alternatives which are the pixels of the map suitable for landfill sitting were obtained by exclusion of the areas restricted by rules and physical constraints. Because the scores of the criteria are given on different scales, they must be standardized to a common dimensionless unit. For this process, the score range procedure is selected and applied in which the standardized scores are calculated by dividing the difference between the maximum raw score and a given raw score by the score range. The layers, used buffer zones and rankings are summarized in Table 1. After the standardization of scores in each map layer, the criterion weights were defined as shown in the Table 2. The output maps produced by this method include the multiplication of data layers, weights and constraints as presented in Fig. 9.
The criterion weights are normalized to generate the overall score for each alternative. These weights are then converted into map forms. The score value of this resultant map is evaluated and the output values are divided into five classes (Table 3). The output map produced by the method of SAW is given in Fig. 10. As it can be seen from Fig. 9, the areas belonging to low and medium suitability are very minor while the areas with high and very high suitability are dominant.
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Landfill site selection is a complex procedure which involves evaluating numerous factors like regulations, environmental, socio-cultural, engineering and economic factors. Using GIS for locating landfill sites is an economical and practical way as it has capabilities of producing useful, high quality maps for landfill site selection in a short period of time. In this research, seven important criteria which have principal effect on determination of landfill locations are identified including geology, hydrology, geomorphology, slope, distance from the cities, main roads and faults. After determination of relative importance weight of each criterion and score value of sub-criteria in the GIS environment, final suitability map was prepared. In addition, the suitability index was applied to rank the proposed candidate sites and summarize the final selection. Based on the final suitability map, suitable areas for landfill construction are located in north and south parts of the study area. Based on this, the total land area of Malayer city can be classified into five groups namely regions with very low, medium, high and very high suitability for being as landfill sites.
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(1) Gholamreza Khanlari, (2) Yasin Abdilor, (2) Reza Babazadeh, (2) Yazdan Mohebi
(1) Department of Geology, Bu-Ali Sina University, Hamadan, Iran.
(2) Ph.D student, Bu-Ali Sina University, Hamadan, Iran
G.R. Khanlari, Dept of geology faculty of sciences, Bu-Ali Sina university, Mahdieh Ave. Hamedan-Iran. Postal cod: 65175-38695
E-mail: Khanlari_Reza@Yahoo. Com
Tele: 00989183130160 Fax: 0098 811 8253467
Table 1: The summary of the input layers used in analyzing. Parameter Ranking Buffer zone Score (Sij) Geomorphology A Desert, thicky clay flat 4 B Alluvial plains, pediment 3 C Hills, old flood plain 2 D Mountainous areas, rivers, 1 active flood plains Geology A Shale, marl, claystone, 3 schist, clay tuff, thick clay flat, loess B Igneous and metamorphic 2 rocks, massive tuff with low fractures C Sandstone, limestone, 1 dolomite, evaporatives, conglomerate alluvium fan, traces, recent alluvium Slope (percent) A 0-5 4 B 5-15 3 C 15-30 2 D >30 1 Distance from A >2000 4 Stream (m) B 1000-2000 3 C 500-1000 2 D 0-500 1 Distance A 0-500 3 from road B 500-1000 2 C >1000 1 Distance from A >3000 4 settlement B 2000-3000 3 C 1000-2000 2 D 0-1000 1 Distance A >1000 3 from fault B 100-1000 2 C 0-100 1 Table 2: The criterion weights defined for simple additive weighting (SAW) method. Data layer Weight Geomorphology 8 Geology 8 Slope 7 Stream 6 Distance from road 4 Distance from settlement 5 Distance from fault 2 Table 3: Final suitability classes for the resultant map. Class Rank Suitability A 0-20 Very low B 20-40 low C 40-60 medium D 60-80 high E 80-100 Very high Fig. 3: The physical characteristics of MSW being dumped at Malayer landfill site. Metal 12% Paper 16% Glass 9% Plastic 13% Organic 50% Note: Table made from pie chart.