Feasibility study on landfill site selection for Karaj city with sustainable development approach using GIS and the fuzzy AHP method

Determining the landfill site for municipal waste is an important issue in the urban planning process due to its great impact on the economy, ecology and environment of each region. In the process of site locating, it is tried to consider areas with the least risks to the environment and human health and conservation. During the recent three decades, the production of municipal solid wastes has increased considerably, beside that their specifications has been changed meaningfully due to the change in people’s life style, progress of industrialization and world economies. Still, one of the best methods of waste disposal is waste dumping or burying. Optimized selection of landfill sites may minimize any negative environmental or financial effect. Searching various places to locate landfills requires choosing an appropriate method. Therefore, applying mathematical methods and determining the influence of different criteria the selection of a suitable place can be very useful. This subject was examined here for the city of Karaj, which is one of the Iran’s megacities with a fast and uncontrolled population growth and increase in waste production.

In this research, the indicators and effective criteria in locating the landfill of Karaj city were identified, evaluated and prioritized with a sustainable development approach using GIS and Fuzzy Analytical Hierarchy Process (AHP). The research data were collected through literature review, internet searching, and technical survey. Using fuzzy logic and decision making techniques based on expert opinions, it was tried to limit the gap in the research field. The current research is descriptive-survey, and functional. To carry out the research, at first, the major influencing criteria were identified. The criteria were categorized into five major groups of geotechnical, environmental, municipal developing, socio economic, and hydrological items. Afterwards, an initial survey was utilized to control the items, and then, a pairwise comparison questionnaire was designed to collect the expert opinions. The research population was 30 experts, adopted from academia, industry, and environmental engineering sector, that 27 of them were selected randomly to answer the questions. It was adequate according to the Cochran’s formula. To ensure the data collected were acceptable, the validity and reliability of the questions were examined sufficiently. Due to its simplicity and accuracy, the triangular fuzzy number was adopted to assess the descriptive variables. In continue, and based on the GIS analysis method, extra specifications of the potential landfill sites proposed were further examined. It was accomplished through categorizing the information layers, then by weighting the potential landfill sites according to the total scores obtained. The information layers included: geotechnical effect, ground slope, land use, permeability, being subjected to flood, water quality, water level, distance from the city, and distance from power transmission lines. Based on the influence level of these layers upon the landfill sites, they were categorized into four classes of highly suitable, suitable, relatively suitable, and unsuitable. For overall ranking, the score of each landfill site in each information layer was calculated by multiplying each layer score by its weight. After completion of this computation phase, all available information layers obtained their own scores, demonstrating their suitability level to be a landfill site. Using the ArcView software, the simple additive weighting method was utilised for site locating.

The results showed that the urban development criteria with a weight of 0.270 was the most important criterion in locating municipal waste landfill, followed by the environmental criterion with a weight of 0.226. Accordingly, the socio-economic criterion with a weight of 0.152 was placed in the last rank. Moreover, in the geological group, the fault index weighted 0.261 and the climatic conditions index weighted 0.236. In the environmental group, the surface water distance index weighted 0.201, and the landfill odor index weighted 0.172. In addition, in the urban development group, the land use index with a weight of 0.283 and the access to equipment and facilities with a weight of 0.258 were the most influencing items. The Inconsistency Ratio of pairwise comparison matrix (I.R) for all matrices was less than 0.1, which confirmed the compatibility of the components.

In the complementary analysis, using the Fuzzy TOPSIS technique and the Geographic Information System (GIS) and utilizing the simple incremental weighting method (SAW), it was determined that Nazarabad site and Halqe Dare new-site are the most suitable options for constructing a new landfill site.