FWDS inventory

Figure 1 shows the 58 municipalities of the state of Zacatecas, Mexico, and the 53 FWDS identified. Figure 2 shows the FWDS by region: northern, central, southern, and southeastern. One of the municipalities, El Salvador, does not have a FWDS. Therefore, the population of this city engages in practices that negatively impact the environment and human health, such as uncontrolled waste burning or disposing of garbage in clandestine dumps. However, these practices are widespread in the communities of Zacatecas and throughout the country (^{Aguilera-Flores et al. 2021}).

Fig. 1 Municipalities of the state of Zacatecas, Mexico, and final waste disposal sites (FWDS) by type. 

Fig. 2 Final waste disposal sites (FWDS) by type in Zacatecas: (a) northern region, (b) central region, (c) southern region, (d) southeastern region. 

The city of Zacatecas has an inter-municipal FWDS, which shares with the adjacent municipalities of Guadalupe and Morelos, as well as the municipalities of Vetagrande and Trancoso, adjacent to Guadalupe. The FWDS was named “JIORESA,” an abbreviation for Junta Intermunicipal para la Operación del Relleno Sanitario (Intermunicipal Board for the Landfill Operation). Regarding the site category based on NOM-083-SEMARNAT-2003 (^{SEMARNAT 2004}), two Type A FWDS (red color), three Type B FWDS (blue color), 17 Type C FWDS (yellow color), and 31 Type D FWDS (green color) were identified (Figs. 1 and 2).

Table III shows the municipality’s population obtained from ^{INEGI (2020)}, the amount of waste received daily provided by FWDS operators, the per capita generation of MSW calculated by equation 1, and the area occupied by waste disposal (available area) for the municipalities of Zacatecas.

It can be noted in table III that the amount of waste received daily ranges from 0.2 t/d (Susticacán municipality) to 154 t/d (Guadalupe, Morelos, Trancoso, Vetagrande, and Zacatecas municipalities), averaging 19.1 t/d of disposed waste in the 53 FWDS identified within the state of Zacatecas. Likewise, per capita generation of MSW ranges from 0.1127 kg/inhabitants/d (Villa García municipality) to 3.3816 kg/inhabitants/d (Atolinga municipality) with an average of 0.8124 kg/inhabitants/d). Susticacán is the municipality with the lowest FWDS area, and Jerez has the highest FWDS area (Table III).

A per capita generation of 0.944 kg/inhabitants/d was reported in 2017 for the western region of the country, including the states of Aguascalientes, Colima, Guanajuato, Jalisco, Michoacán, Nayarit, Querétaro, San Luis Potosí, and Zacatecas (^{SEMARNAT 2020}). The value reported by ^{SEMARNAT (2020)} was 1.16 times higher than the average value estimated in this study (0.8124 kg/inhabitants/d). Although there is a tendency for per capita generation to increase over time (^{SEMARNAT 2017}), the value obtained in this work is close to the true value, as Zacatecas is one of the five states that contributes the least to the gross domestic product (^{INEGI 2023c}). MSW generation is directly linked to a society’s purchasing power and economic growth (^{Vyas et al. 2022}). Additionally, it should be noted that the FWDS receives MSW only from the municipal seat and surrounding communities, resulting in 100% coverage of waste disposal only for these areas, as the entire municipal territory is not served (^{Aguilera-Flores et al. 2021}).

Assessment of FWDS location restrictions

The FWDS must comply with the location restrictions shown in table I. Table IV summarizes each FWDS’ compliance with location restrictions. Figures S1 to S53 in the supplementary material show the maps generated with the location restrictions for the 53 FWDS identified in the state of Zacatecas.

Based on the location restrictions stipulated in NOM-083-SEMARNAT-2003 (^{SEMARNAT 2004}), 13.2% of the FWDS are in appropriate zones based on the location restrictions stipulated by the Standard. El Plateado de Joaquín Amaro (Fig. S10), Loreto (Fig. S23), Luis Moya (Fig. S24), Nochistlán de Mejía (Fig. S32), Noria de Ángeles (Fig. S33), Río Grande (Fig. S37), and Tepetongo (Fig. S44) are the municipalities that accomplish these requirements (Table IV). Therefore, it is recommended that the other FWDS (86.8%) be closed in accordance with the Mexican Official Standard guidelines and that the new FWDS be opened to fulfill the location restrictions (SEMARNAT 2004). However, the opening or closing of the FWDS could involve high costs. ^{Araiza-Aguilar et al. (2018)} proposed a solution to the current problems of Mexico City by locating waste treatment and disposal infrastructure through a spatial analysis based on a multi-criteria evaluation technique and network analysis, with the support of GIS. Integrating methodologies supported by GIS could be valuable for decision-making and determining the appropriate location of FWDS in the cities. These tools also promote the optimization of economic resources by incorporating urban planning into waste management. Hence, standardizing the decision-making process for locating FWDS through automated spatial analysis by GIS is recommended, and mitigation actions must be implemented based on the unfulfilled restriction criteria of the current FWDS.

Sensitive places, such as educational institutions, offices, banks, bus and train stations, airports, hospitals, parks, water treatment plants, power stations, and cultural or religious sites, in an urban area, typically include locations where many people gather or where critical infrastructure is concentrated. These places must be considered for the suitable location of FWDS (^{Saha and Roy 2024}). Of the FWDS in Zacatecas, 98.1% are located at a distance of > 13 km from airfields and airports (Table IV). Only the FWDS in the municipality of Calera is 7 km from the civil aerodrome (Fig. S5), on the grounds that it is difficult for this facility to accomplish this restriction since the Zacatecas International Airport is located close to the municipality’s territory. Locating this FWDS far from Calera city would entail a high cost in transporting the waste. Furthermore, it is not feasible to move the airport. Therefore, the airport’s proximity to the Calera FWDS (Fig. S5) should be considered in the municipal waste management plan, as the restriction could not be achieved for this city.

According to table IV, 83% of the FWDS are located at a distance of > 500 m of localities with more than 2500 inhabitants. The FWDS of Apulco (Fig. S2), Huanusco (Fig. S16), Jiménez del Teul (Fig. S19), Melchor Ocampo (Fig. S26), Momax (Fig. S29), Moyahua de Estrada (Fig. S31), Sain Alto (Fig. S38), Sombrerete (Fig. S40), and Susticacán (Fig. S41) are at a distance < 500 m from localities. People living near FWDS could be at risk of health issues. The spread of water and airborne diseases (cholera, dengue, diarrhea, tetanus, and typhoid, among others), continual exposure to chemicals, inhalation of toxic fumes, direct contact with water contaminated by MSW, and dust from dumpsites affect the health of the nearby inhabitants. Likewise, FWDS is a favorable environment for the proliferation of disease-carrying organisms (cockroaches, flies, mosquitoes, rats, and others) (^{Zhao et al. 2015}, ^{Shammi et al. 2023}). Additionally, the value of properties and houses near FWDS decreases due to nuisances such as flies, noise, odors, and smoke, which are reasons why people do not want to live near FWDS (Shammi et al. 2023). It is essential to consider this situation so that the FWDS are not close to the localities.

Based on Table IV, 49% of the FWDS are located at a distance of > 500 m from surface water bodies. The FWDS of Apozol (Fig. S1), Apulco (Fig. S2), Benito Juárez (Fig. S4), Calera (Fig. S5), Cañitas de Felipe Pescador (Fig. S6), Concepción del Oro (Fig. S8), Cuauhtémoc (Fig. S9), Fresnillo (Fig. S11), Genaro Codina (Fig. S12), General Enrique Estrada (Fig. S13), Huanusco (Fig. S16), Jalpa (Fig. S17), Jerez (Fig. S18), Jiménez del Teul (Fig. S19), JIORESA (Fig. 20), Juchipila (Fig. 22), Mazapil (Fig. S25), Miguel Auza (Fig. 28), Momax (Fig. S29), Monte Escobedo (Fig. 30), Moyahua de Estrada (Fig. S31), Pánuco (Fig. 35), Pinos (Fig. 36), Sombrerete (Fig. S40), Susticacán (Fig. S41), Tabasco (Fig. S42), and Villanueva (Fig. S53) do not accomplish with this restriction. Surface water bodies near FWDS are highly susceptible to pollution by mixing with leachate rich in harmful organic and inorganic compounds (hydrocarbons, pesticides, heavy metals, halogenated compounds, and xenobiotics). Generally, this pollution occurs because the FWDS do not have liners or any impermeable barriers that prevent the migration of toxic leachate into ground and surface waters and aquifers (^{Naveen et al. 2017}, ^{Urooj et al. 2019}, ^{Koliyabandara et al. 2020}). Therefore, this condition represents a significant risk to human health and the environment. The construction and operation of liner systems to collect leachate and reduce pollution of both ground and surface water are recommended. ^{Saha and Roy (2024)} conducted a study to identify suitable FWDS in Cooch Behar municipality, West Bengal, utilizing GIS and multi-criteria decision analysis. They generated a land use and land cover map classified into five classes: agricultural land, fallow land, vegetation, built-up areas, and waterbodies, finding that areas designated for agricultural, residential, or commercial purposes are unsuitable due to potential conflicts with existing land uses and contamination risks to soil and water bodies. Therefore, in addition to the proximity of FWDS to water bodies, land use, and land cover should also be considered as a criterion in the spatial analysis of the site, which was a limitation in this study.

According to table IV, 67.9% of the FWDS is located at a distance of > 500 m of public supply wells. The FWDS of Apozol (Fig. S1), Atolinga (Fig. S3), Calera (Fig. S5), Chalchihuites (Fig. S7), Fresnillo (Fig. S11), Huanusco (Fig. S16), Jalpa (Fig. S17), Jerez (Fig. S18), Juan Aldama (Fig. S21), Mezquital del Oro (Fig. S27), Miguel Auza (Fig. S28), Ojocaliente (Fig. S34), Pánuco (Fig. S35), Pinos (Fig. S36), Sain Alto (Fig. S38), Sombrerete (Fig. S40), and Villa Hidalgo (Fig. S52) is at a distance < 500 m of public supply wells. Groundwater is susceptible to pollution by FWDS leachate, as mentioned. Studies of wells dug around FWDS have shown groundwater pollution associated with the leachate generated at these sites (^{Igboama et al. 2022}). Hence, it is necessary to ensure that water does not represent potential risks to public health. Studies must be conducted promptly in water supply wells near FWDS to correlate contamination issues with environmental and human health effects (^{Araiza-Aguilar et al. 2023}). Characterization and monitoring of water extracted from public supply wells near the FWDS must be carried out frequently, as stipulated in NOM-127-SSA1-2021 (^{SSA 2022}), which outlines permissible water quality limits for human use and consumption in Mexico.

Based on table IV, 96.2% of the FWDS are outside Natural Protected Areas. However, the Juchipila (Fig. S22) and Moyahua de Estrada FWDS (Fig. S31) are located inside the Natural Protected Area “Cerro de Piñones”, where Pinus maximartinezii (blue pine), an endemic species declared endangered in Mexico by NOM-059-SEMARNAT-2010 (SEMARNAT 2010), is found (^{CONABIO/CONANP 2024}). Furthermore, Moyahua de Estrada is inside the Natural Resources Protection Area named “Cuenca Alimentadora del Distrito Nacional de Riego 043 Estado de Nayarit” (^{CONABIO/CONANP 2024}). Although NOM-083-SEMARNAT-2003 (SEMARNAT 2004) indicates that FWDS can be in a Natural Protected Area when included in the management plan, this is not the case with the two above-mentioned FWDS. Therefore, FWDS must be included in the management plan for Natural Protected Areas to minimize ecological disruption and preserve biodiversity (^{Saha and Roy 2024}).

According to table IV, 100% of the FWDS are outside wet ecosystems, plains, and aquifer recharge areas (this restriction is the only one fulfilled by all the FWDS identified in Zacatecas), and 96.2% are outside geological faults and fractures (Table IV). However, the JIORESA (Fig. S20) and Teúl de González Ortega FWDS (Fig. S45) are inside. Steep slopes, geological faults and fractures, and landslide areas are related to the sites’ topography. Therefore, these characteristics are relevant since they influence the vertical extension of the waste body and its stability and determine the extent of excavation and leveling required (^{Araiza-Aguilar et al. 2018}). ^{Israde-Alcantara et al. (2005)} performed a geological characterization using GIS of the FWDS in Morelia, Michoacán, Mexico. They found that it lacks ideal impermeable subsurface strata, as it consists of highly fractured basaltic lava flows (with an east-west fault and fracture system trend) and sand-size cineritic material with high permeability and porosity. Many of the FWDS in Mexico are located on faulted or fractured zones or sandy substrata with high permeability. This situation is aggravated by seismic activity, which has not been included in the management plan despite being a factor in the failure of the FWDS (^{Israde-Alcantara et al. 2005}). Therefore, geological faults, fractures, and seismic activity in FWDS must be considered, as they affect the mechanical stability of MSW disposal, a recurring condition at several FWDS in Mexico.

The FWDS of Concepción del Oro (Fig. S8), El Plateado de Joaquín Amaro (Fig. S10), Fresnillo (Fig. S11), Jalpa (Fig. S17), JIORESA (Fig. S20), Loreto (Fig. S23), Luis Moya (Fig. S24), Mazapil (Fig. S25), Melchor Ocampo (Fig. S26), Mezquital del Oro (Fig. S27), Moyahua de Estrada (Fig. S31), Nochistlán de Mejía (Fig. S32), Noria de Ángeles (Fig. S33), Río Grande (Fig. S37), Sain Alto (Fig. S38), Tepetongo (Fig. S44), and Teúl de González Ortega (Fig. S45) are outside flood zones. Hence, the rest of the FWDS (69.8%) do not comply with the restriction, as they are located within flood zones (Table IV). This restriction is the least fulfilled and must be opportunely considered. During a flood event, FWDS becomes water-saturated, mobilizing pollutants since the presence of water enhances decomposition and transport processes. Likewise, water saturation of MSW may lead to mechanical stability issues, resulting in shear and sliding fractures (^{Pan et al. 2021}). ^{Araiza-Aguilar et al. (2018)} found that the FWDS in Chiapas, Mexico, are susceptible to flooding due to the region’s constant rainfall, which affects the stability of the works carried out in the FWDS. They proposed compensatory or mitigation measures, such as implementing natural barriers, constructing storm drains, and adapting roads. These actions must be addressed to the Zacatecas FWDS that have not met the restriction criteria.

Assessment of FWDS operating conditions

According to NOM-083-SEMARNAT-2003 (^{SEMARNAT 2004}), a controlled FWDS is defined as an inadequate site that complies with the specifications of a sanitary landfill (infrastructure and operating conditions) but does not comply with the waterproofing specifications, and an uncontrolled FWDS is a site that does not comply with the requirements established in this Mexican Official Standard. Therefore, the 53 FWDS identified in Zacatecas were classified as uncontrolled sites.

Although it was reported that Zacatecas had seven landfills, two controlled FWDS, and 48 uncontrolled FWDS in 2021 (^{SEMARNAT 2021}), 53 FWDS were identified in this study. JIORESA is the only FWDS designated as a sanitary landfill. However, leachates and biogas are not adequately controlled, so it was classified as an uncontrolled site. The other 52 FWDS correspond to open-air dumps. Therefore, their operating conditions also show opportunities for improvement.

The 53 FWDS show opportunities for improvement in the design of a waterproofing system, infrastructure for controlling biogas (extraction, capture, conduction, and control), infrastructure for controlling leachate (extraction and collection), design of a storm drain, inclusion of an emergency area, adequate MSW compaction and coverage, and control of waste that enters the site (hazardous waste must not be admitted).

It is imperative to implement a waterproofing system to prevent the infiltration of leachates into the subsoil and reaching groundwater. FWDS must have venting wells for biogas extraction, capture, and conduction since this contaminant is released into the atmosphere and poses risks of uncontrolled fires without this infrastructure. Likewise, FWDS must have a leachate collection system to avoid contamination risks of soil, surface water, and groundwater. This contamination problem may be exacerbated by the lack of infrastructure for diverting storm drains, as the volume of leachates increases when mixed with rainwater. Finally, there must be a control mechanism in the FWDS to monitor the type of waste received, ensure appropriate compaction, and maintain coverage (every 24 hours after deposit) to prevent MSW dispersion and the presence of harmful fauna (insects and rodents) that can cause illnesses to the nearby population. Therefore, municipal authorities and SAMA must take the relevant steps to regularize the location and operating conditions of the FWDS.

As discussed in the assessment of FWDS location restrictions, the conditions under which these facilities operate in Zacatecas, different states of Mexico (^{Israde-Alcantara et al. 2005}, ^{Araiza-Aguilar et al. 2018}, ^{Saldaña-Durán and Nájera-González 2019}, ^{Araiza-Aguilar et al. 2023}), and other countries (^{Ampofo et al. 2023}, ^{Bhowmick et al. 2024}, ^{Saha and Roy 2024}) are unfavorable. Therefore, waste management remains a high challenge for the global sustainability agenda of the United Nations in Mexico and other countries.