Introduction Disposal of wastes in landfills is the last step considered in a solid waste management plan. Landfilling is the final fate of all unwanted products which are considered insignificant from the producer's point of view. In other words, landfilling is a mandatory component in the structure of the waste management hierarchy. The current waste landfill of Mahabad, due to its proximity to rural areas as well as Maskan-e-Mehr apartments with impressive dwellers, an average distance of 620 meters from waterways, being located in a fault adjacency, and completing 70% of its capacity, cannot be considered as a good option for the future development, to handle wastes generated in Mahabad city in the next 20 years. In addition, the short distance from the current landfill to Mahabad Dam Lake, caused the accumulation of a significant number of large birds (mainly storks) to invade the current waste landfill and feed on food scraps. This unprecedented phenomenon has made animal wildlife extremely vulnerable. Therefore, finding a suitable place for burying solid waste in Mahabad is essential. The process of selecting a suitable place for burying municipal waste depends on various technical, economic, social, cultural, and environmental factors, and in most cases, urban communities face a lack of space to determine the appropriate location. Therefore, identifying regional constraints, assessing the extent of damage to affected communities, investigating possible damage to the environment, and anticipating practical actions to reduce the damage are part of the requirements of the process of locating, designing, implementing, and operating landfills. The tools available in the Geographic Information System (GIS) can be used to solve the problems and complexities of the process of determining the appropriate location for the construction of a waste landfill. In the location process using GIS, only technical factors are considered, however, a suitable place for waste landfill, in addition to technical criteria, must also satisfy social, cultural, economic, and environmental criteria. To study these factors and also to create compatibility and balance between the activities of a project and the surrounding environment, the proposed method can be used to assess the environmental impact. The matrix technique is one of the most popular methods used in most construction projects to assess environmental impacts. The Rapid Impact Assessment Matrix (RIAM) is one of the most widely used matrices developed by Pastakia and Jensen. This matrix has become an ideal process to provide a clear and fast assessment of the environmental impact of a construction project due to its ability to integrate all components and parameters of the environment. Another matrix that has been considered by many researchers to assess the environmental impact of landfills due to its simple operating system and multi-criteria assessment, is the Leopold matrix. One of the main advantages of this matrix is the summation of the negative and positive effects of a project in two stages of construction and operation. The main purpose of this paper is to provide a comprehensive model for site selection and assessing the environmental impact of waste landfills by GIS software and RIAM and Leopold matrix methods. Furthermore, by setting the same input parameters for the two mentioned matrices, an attempt has been made to examine the reasons for the similarities/differences of the obtained results in detail. Material and method In the first step, by overlaying the existing information layers (16 layers in the elimination phase and 13 layers in the phase of identifying susceptible areas) using GIS software, a suitable place for the construction of a landfill in Mahabad city has been determined. Then, by reviewing the technical literature, 21 parameters were selected to assess the environmental effects by two matrix methods, RIAM and Iranian Leopold. Finally, the results obtained from these two methods are presented and compared. It should be noted that in the Leopold method, unlike the RIAM matrix, which presents the project assessment in general, two phases of construction and operation are considered. Therefore, to analyze the causes of differences/similarities in the results of the two methods, The RIAM matrix, like the Leopold matrix, was examined in two phases of construction and operation. Also, the same input parameters were defined for the two mentioned matrices. Discussion and result After overlaying information layers in two elimination and identifying the susceptible area phases on the GIS space, as well as taking over the area for 20 years (35 hectares), a suitable place for burying waste of Mahabad city was obtained. The results of the RIAM matrix in the construction phase showed that the most negative effects of the selected site for construction of the landfill occurred in Physico-chemical, biological and socio-economic environments. Furthermore, the most positive effects occurred in the socio-economic environment. So that the most negative effect in the construction phase is related to the greenhouse gas production parameter, and the employment parameter has the most positive effect. The results of the Leopold matrix in the construction phase showed that the most negative effects belong to Physico-chemical and biological environments, and the most positive effects belong to the socio-economic environment. The parameters of adverse effects on traffic flow, noise pollution, dust production, greenhouse gas emission, and threat to animal habitats have the most negative effects, and employment has the most positive effects. The results of the RIAM matrix in the operation phase show the Physico-chemical, biological and socio-economic environments with the most negative effects and the cultural and socio-economic environments with the most positive effects. The parameters of greenhouse gas emission, soil pollution, dust production, unpleasant odors, increase in carriers, and population and migration have the largest share of negative effects and the parameters of health indicators and employment have the largest share of positive effects of this phase. The results of the Leopold matrix in the operation phase also show the Physico-chemical environment with the most negative effects and the biological environment with the most positive effects. The parameters of unpleasant odors, greenhouse gas emission, noise pollution, adverse effects on traffic flow, land use, and surrounding land acquisition costs have the most negative effects and the parameters of employment, soil erosion, and plant habitats have the most positive effects. The results obtained from both methods indicate that the design by making the necessary improvements, especially in the parameters that have received significant negative points in both methods (dust production, unpleasant odors, greenhouse gas emission, noise pollution, animal habitats) is applicable. Conclusion Most of the natural parameters considered in both methods have similar scores, but in some of the parameters, the results obtained from the two methods were different, (such as the parameters of plant habitats and soil erosion) or had significant differences (such as the parameters of plant habitats, soil erosion and health indicators in the operation phase). The reason for these differences and the inconsistency of the two methods can be explained by the fact that in the RIAM matrix the impact radius (importance of the effect), magnitude and intensity of the effect, stability, reversibility, and accumulation of the effect on the parameters are investigated but in Leopold matrix, only intensity and importance of the effect on the determined micro-activities on natural parameters is investigated. In other words, the Leopold matrix has a reasoned structure compared to the RIAM matrix due to the consideration of different micro-activities for each parameter, but the way the scores identified based on the parameters in the RIAM matrix are better than the Leopold matrix due to considering the stability, reversibility, and aggregation.