Population growth and changes in socio-economic structures increase the per capita consumption leading to more waste production, which has a detrimental impact on the environment   . Municipal Solid Waste Management (MSWM) is considered one of the most crucial environmental challenges that developing countries face today   , as landfills are the common practices in most urban areas in developing countries because of their cost effectiveness  . Landfill site selection is also a critical issue in the urban planning process due to its enormous impacts on the economy  , ecology, health, and environment    .
Therefore, it is necessary to consider sanitary landfills which include an engineered facility for MSW, which is designed and operated to minimize public health and environmental impacts  . Sanitary landfills should be intended to protect humans and the environment from emitted gasses and fluids by using impervious liners, gas collection vents, and leachate collection pipes   . Many landfills are designed for a lifespan of 20 or 30 years and still require post closure monitoring for up to 30 years to ensure that their environmental effects are controlled   . Due to the negative impacts of landfilling on the environment and human health, selecting new proper landfill sites requires spatial process as well as identifying effective criteria   . The criteria associated with landfill sitting can be grouped into three main categories, namely, engineering and infrastructure, environmental and socio-cultural, and economical   . These criteria prohibit a landfill from being placed within a particular area. The selected criteria should be met by all acceptable landfill locations  .
Geographic Information Systems (GIS) is one of the most common tools used in selecting landfill sites. GIS can manage and analyze varied amounts of data associated with the process of setting up solid waste landfills, as well as its flexibility, numerical efficiency in calculations involving combinations and statistical exploration of spatial variables  . Previous studies also illustrate that the integration of GIS and multi-criteria analysis is a powerful method for the selection of landfill sites   . Moreover, GIS plays a significant role in providing a cost effective and efficient analysis of landfill site attributes; however, it can be limited to the lack of available data  .
In Kuwait, the amount of municipal solid waste has been rapidly increasing and its composition has been changing due to the growth in population, rise of urbanization, and change in lifestyles and food habits. 90% of the MSW is disposed in landfills and 10% is recycled    . Therefore, this paper presents an integrated approach for the selection of suitable locations for landfilling. The major objective is to develop a methodology for the selection of optimum landfill sites by integrating the ecological, social, and economical aspects using the Geographical Information System (GIS) and gap analysis technique. Specific objectives include: 1) developing a proper list of guidelines for the selection of landfill sites in Kuwait using the cap analysis approach, and 2) integrating environmental and socioeconomic criteria to select optimum locations for landfilling in Kuwait by utilizing GIS.
2. Methods and Materials
2.1. Study Area
The State of Kuwait is located in the northwestern corner of the Arabian Gulf. It encompasses an area of approximately 17,818 square kilometers extending between latitudes 28˚30'N and 30˚05'N, and longitudes 46˚33'E and 48˚30'E (Al Baz and Al Sarawi, 2000). Kuwait has a desert climate, hot and dry with occasional rain, mostly in the spring. Rainfall varies from 75 to 150 mm per year across the country. The summer seasons are relatively hot and are often accompanied by dust storms where the average daily temperatures in summer range from 42˚C to 46˚C. The prevailing wind is in the northwest direction, and humidity increases during late summer with thunderstorms. However, the weather gets colder in late November, dropping temperatures to as low as 3˚C at night; daytime temperature is in the upper 20˚C range (Ministry of Planning, 2007).
This study incorporates four stages for the selection of new MSW landfill sites in Kuwait (Figure 1). These stages include 1) the identification of sufficient criteria for site selection using gap analysis method, 2) determining unacceptable areas, 3) weighting the acceptable areas, and 4) studying the socioeconomic factors to evaluate the suitability of the selected areas in order to determine optimum locations for landfilling. The second and third stages were accomplished using spatial analysis and ModelBuilder in ArcGIS to produce suitability maps highlighting “suitable” geographic areas derived from weighted and combined map layers based on the established criteria in stage one.
2.2.1. Identification of Suitable Criteria for Landfill Site Selection
In this stage, Kuwait’s regulation for landfill site selection, which was established by the Kuwait Environment Public Authority (EPA) was compared to the World Bank, Australia EPA, and US EPA guidelines using Gap Analysis. This stage was conducted in order to evaluate the current criteria in Kuwait by filling out any gaps. The World Bank guidelines have been developed as international requirements, which are applicable to any region. Thus, Kuwait and other selected countries’ regulations are compared together based on the World Bank guidelines. Then, the gaps were analyzed to determine the ones that fit with the nature of Kuwait (Table 1).
Figure 1. Study methodology.
2.2.2. GIS Data Collection and Preparation
Data availability is one of the most important steps when using GIS. Based on the established criteria in stage one, 30 layers (Table 2) have been collected from different governmental institutions including the Kuwait Institute for Scientific Research (KISR), Public Authority of Agriculture and Fish Resources (PAAF), Kuwait University (KU), and Kuwait National Focal Point (KNFP), with a scale of 1:250,000. However, the lack of availability of some data leads to the omission
Table 1. Selected criteria for the selection of MSW landfill sites in Kuwait.
of their related cantons from the study, such as seismic zones, fault lines, archeological and historical areas, and vegetation types and communities. Furthermore, some of the available data have been collected in an analog format. They were first digitized into vector format by using on-screen digitizing and then introduced to the GIS system. All data were stored in the same coordinate system in order to display them together, and were all transferred to Universal Transverse Mercator (UTM) projection (WGS 1984, Zone 38N).
The digital elevation model (DEM) was built up by using 3D analysis tools. Contour lines and spot heights maps were used in building DEM map. The slope layer was derived from the DEM by using the surface function in the spatial analysis tools. However, depth to groundwater layer was created from the water level contour lines of Kuwait Group in the GIS software using the spatial analyses tools. Then, the differences between the groundwater levels and DEM were extracted using raster calculator in the spatial analyses tools to create the depth of groundwater layer.
2.2.3. Determining Unacceptable Areas
The present investigation was completed using ModelBuilder in GIS. This stage includes the logical combination of binary maps using constraint layers, which were used to distinguish between lands that are suitable for landfill siting and those lands that are restricted in order to determine the unacceptable areas for landfill site selection. Constraint layers were classified into six groups, where each group contains several layers (Table 3). These groups include groundwater, topographical aspects, soil, current and proposed land use areas, ecological aspects, and major infrastructure lines. Around 27 layers were applied in establishing the constraint maps following several geoprocessing in the GIS environment. Buffer distance was given to each constraint factor (Table 3). All
Table 2. Collected GIS layers.
developed layers were converted from vector format to raster format. The raster layers were reclassified into 0 and 1 in order to identify restricted and suitable areas for landfill site selection. This procedure created a constraint layer for each layer containing only two classes represented by 1 (for suitable land) and 0 (for
Table 3. Constraint criteria and buffer distance.
unsuitable land). Each group layers were merged to create a constraint layer for each group, and then the six constraint group layers were combined using the overlay function to create the final constraint map.
2.2.4. Weighting the Acceptable Areas
In practice, it is inappropriate to give equal importance to all criteria. Therefore, factor layers (Table 4) were applied at this stage to determine optimum sites for landfilling by classifying the remaining acceptable areas that were established in the second stage into classes of low and high suitability areas. All layers were weighted between 1 for highly suitable areas and increased to 9 for low suitable areas according to their level of significance. Six layers were involved in creating the factor maps, which include the soil characteristics, depth to groundwater, proximity to main roads network, urban, agriculture, and protected areas. These factors were selected as factor criteria due to their high sensitivity of selecting a landfill site close to these areas. The soil characteristics layer was weighted based on the soil penetration. However, each layer of urban areas, agriculture areas, protected areas, and main roads network have been given multi-buffer distance
Table 4. Factor criteria.
from 500 m (considered as a low suitability area) to 5000 m (considered as a high suitability area). Groundwater factor was weighted based on how deep the groundwater was from the surface, where the high depth areas were given low values as a high suitable area, while the low depth areas were given high values as low suitable areas. Factor layers were also converted into raster format, reclassified into different classes, and overlaid together using the weighted overlay function in the spatial analysis tools.
2.2.5. Final Suitability Map
This approach consisted of the identification of locations that may present favorable conditions to waste disposal. The various layers prepared for environmental aspects were intersected to screen out unsuitable lands. The final constraint layer and the final factor layer were merged together using raster calculator to produce the final suitability map. A custom scale of 1 to 4 was chosen for this overlay since only four classes are appropriate for the final suitability maps. These four classes’ areas comprise restricted, low suitability, moderate suitability, and high suitability. The high suitability locations were taken into consideration in the final stage.
2.2.6. Selecting the Optimum Locations
After the identification of suitable sites, the last stage is to evaluate these sites to locate the optimum locations by considering the socioeconomic aspects, namely waste transportation distance, proximity to roads network, and lifespan.
Waste transportation distance: It is estimated that a distance of more than 50 km from the waste generation center will take more than 40 minutes of driving. For this purpose, all areas located outside this range were eliminated.
Proximally to roads network: Landfill location must also be close to roads network in order to facilitate transportation and consequently reduce relative costs. However, the areas that are intersecting with roads network with a distance of 3 km were extracted.
Landfill lifespan: It is one of the critical criteria that must be considered due to the limited areas in Kuwait. Potential landfill area and volume must have the capacity to serve for at least 15 years. Therefore, the required volumes for MSW landfill sites and population projection were calculated using the following equation  :
In which VI is the required volume for the landfill per year, R is the specific solid waste projection rate (= 1.4 kg/capita/Day), W is volumetric weight of solid waste after compacted (800 kg/cubic meter), and D is number of day in one year (365 day/year).
3.1. Criteria Evaluation
The results showed that Kuwait regulations covered the lowest number of the World Bank guidelines compared with Australia and USA. The Australian guidelines covered about 70% of the World Bank guidelines, USA covered about 50%; however, Kuwait was the lowest, with 35%. Various gaps have been identified between Kuwait and other countries. However, these gaps may not be a weakness in the regulations of the countries due to regional, climatic, and topographic differences. Therefore, these gaps were reviewed in order to select the ones that are applicable to desert environments such as Kuwait, and eliminate the ones that are not applicable. We found that most of these criteria are applicable and were considered in our analysis. Eighteen criteria were modified and added to the Kuwait regulations. We then generated a new list of criteria for the selection of municipal solid waste landfill sites in Kuwait, which was applied in this study to select suitable locations for landfilling in Kuwait. We also selected the needed information in order to assess each creation in the list. The new list of guidelines and needed data are summarized in the form of a table (Table 5). The results showed that the major weaknesses were concentrated in four components including lifespan, land use, site access and transportation, and socioeconomic factors.
3.2. Optimum Locations for Landfill Sites
The final factor layer (Figure 2(a)) and the final constraint layer (Figure 2(b)) were merged using raster calculator to produce the final suitability layer (Figure 2(c)). The final suitable locations were classified into four classes including high suitability, moderate suitability, low suitability, and restricted based on the number of criteria covered by each class. The results showed that only 24.3 km2 of the entire country are highly suitable for landfilling. However, 1548 km2 are considered moderate suitability, 347 km2 are considered low suitable, and 14,367 km2 are restricted areas for landfilling. This illustrates that only few areas are highly suitable for landfill sites where all the selected criteria were met.
The suitability areas were then evaluated using socioeconomic criteria including waste transportation distance, proximity to roads network, and lifespan, to determine the optimum locations for landfilling. The lifespan was estimated for the highly suitable locations. As a result, the landfill volume depends on the
Table 5. List of guidelines for the selection of suitable locations for landfilling in Kuwait.
Figure 2. Suitable locations for Landfill sites in Kuwait: (a) Final factor layer, (b) Final constraint layer, and (c) Final suitability layer.
operation year. Moreover, starting early requires less volume instead of starting late due to the increase in waste generation and population every year. For such reasons, assumptions for the year 2018 were calculated. So, if the operation year starts at 2018, then the required volume for the landfill site will be 44,000,000 m3. Based on the required volume for landfill, it is assumed that the depth of the landfill is 10 m based on the average depth of the current landfill sites. Therefore, a total area of 4.5 square kilometers or greater is required to serve the waste generation at least 15 years (in case of starting the operation in 2015). Therefore, areas less than 4.5 square kilometers were eliminated. The results showed that only one location was greater than 4.5 km2; however, the remaining areas were less than 1 km2 to end up with only one optimum location with a total area of 12 km2 (Figure 3(a)) which can serve for at least 15 years (Table 6).
Since only one location was considered as an optimum location for landfilling, we relaxed the criteria to provide other alternative areas to support decision makers in Kuwait with alternative solutions. Alternative areas were extracted from the moderate suitability areas in the final suitability layer, which were also considered suitable areas. The same economic aspects criteria (including the waste transportation, distance to roads and landfill lifespan) were also applied to these areas. As a result, several alternative areas were located as suitable areas for landfill sites in Kuwait with a total area of 1328 km2 (Figure 3(b)). However, these locations could be considered suitable areas, but not optimum areas since they did not meet all the selected criteria. Therefore, they will require special implementation process to prevent any environmental disturbance.
4. Discussion and Conclusions
Our results show that developing a list of suitable criteria is a critical stage in the selection of suitable locations for landfilling. It is also necessary to integrate both environmental and socioeconomic aspects as the results show that the socioeconomic aspects including waste transportation distance, proximity to roads network, and lifespan play an important role in evaluating the suitable locations for landfilling.
We also find that the use of GIS model in the selection of suitable landfill sites incorporating the evaluation of multiple criteria has many advantages. Firstly, GIS is a powerful tool that enables organized and systematic analysis of spatial data. For instance, large amounts of data including thirty layers covering several different criteria are integrated and analyzed together, which is difficult to process without using the GIS spatial analysis. Secondly, the results of the analysis can also be presented in the form of functional output maps. Finally, the model and its operational procedures can be visually simplified and represented as a schematic diagram (flow chart). Therefore, GIS technology proves to be an effective tool that can be used in the landfill site selection. This system has the capability to handle a huge amount of spatial data and evaluate changes in scenarios as well as to save huge amounts of time.
The results of this work also show that only one location is conceded as an optimum site for landfilling. This indicates that there is an urgent need to implement the integrated waste management system   by considering other options such as reuse and recycling. Alternative locations are also identified as another solution for landfill locations due to the limited optimum locations, and to provide decision makers with other alternatives. However, these alternative areas will most likely have environmental risks. Therefore, selecting landfill sites in these areas requires special designs that include liners, pipe network for
Figure 3. (a) Optimum Locations for landfilling after conducting the socioeconomic criteria, and (b) alternative locations for landfilling after relaxing the selected criteria to support decision makers.
Table 6. Total area for future potential landfill locations in Kuwait.
gas and lechate collection, as well as groundwater monitoring. In addition, wind direction is another issue that must be considered in selecting landfill sites in the north and medial central areas of Kuwait, since the predominant wind direction in Kuwait is north-west  , which may move the pollutant gases to urban areas. Furthermore, the moderate suitability sites located in southern areas are close to Al Wafra agriculture areas, which may also be affected if landfills are selected in close proximity.
It is also necessary to take into consideration the future increase in the volume of household waste due to the rapid population growth and the changes in life style. According to Kuwait-EPA  , there is a relatively large increase in household waste generation, estimated at about 1.4 kg per person per day, generating about 1.5 million tons annually. More than 90% of the municipal solid wastes in Kuwait are disposed in landfill sites. Most of the current landfill sites are selected randomly and are close to urban areas. Currently, most of the existing landfills are under the rehabilitation program in order to reduce their potential negative impacts on the environment and human health   . In view of the anticipated increase in population growth and the volumes of municipal solid wastes and limited waste management system in the country, landfilling will continue to be the main alternative in managing the produced volumes of wastes. Therefore, it is of a paramount importance to identify and locate the best suitable sites for MSW landfills to minimize their negative impacts on human health and the environment, as well as to develop a long-term strategic program (for the next ten to fifteen years) to conduct alternative environmental friendly options instead of landfilling.
This work presents an integrated methodology for selecting MSW sites by conducting and integrating environmental and socioeconomic criteria using GIS. We also believe that the developed methods in this work can be applicable to the selection of landfill sites at any location. However, in the next stage, we believe that it is important to conduct ground trothing field visit to evaluate these locations in the field, especially the alternative locations as several locations are identified and ranked from the highest to the lowest suitability. It is also important to update the criteria for landfill site selection in Kuwait as several gaps are identified. Therefore, we recommend using the selected criteria in this project to update the Kuwait EPA criteria.
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