Impact of Leachates from the Chupaca Landfill on Agricultural Soil Quality

Currently, at the municipal dump in the province of Chupaca, inadequate solid waste management results in leachate generation, constituting a significant environmental issue, thus constituting a significant environmental problem which negatively affects the diverse ecosystems and thereby damaging agricultural soils [1]. The generation of leachate is the main cause of this impact, since its components have high levels of contaminants which negatively alter the physical, chemical and, above all, biological properties of the soil [2]. This problem has become very relevant for this province, since one of its main sources of economic income and support for its population is agriculture. There are many studies which point out the harmful effects that improper management of leachate has on soils, where initially they can contribute positively by increasing nutrients in them, however, when these are not controlled they can introduce high concentrations exceeding optimal levels, thereby generating high degrees of toxicity, which negatively impacts the properties of the soil, resulting in the alteration of agricultural productivity and the general health of all surrounding ecosystems [3, 4]. Previous studies in Peru point out that existing correlations have been reported between the presence of leachate from landfills and high levels of heavy metals in agricultural soils, which emphasizes the urgency of having the need to be able to investigate this problem in provinces such as the Chupaca [5, 6].

In this context, this study integrates field and laboratory analyses with computational modeling to evaluate the transport of contaminants over a 20-year period using COMSOL Multiphysics. A quasi-experimental approach was applied, incorporating rigorous statistical methods, including t-tests to compare soil properties between contaminated and uncontaminated sites, as well as linear regression models to predict pH variations.

Although previous research has examined the effects of leachate on soil quality, significant knowledge gaps remain, especially in agricultural regions like Chupaca, Peru. This study addresses these gaps by integrating physicochemical and biological assessments with predictive modeling, providing a comprehensive understanding of contaminant migration and its long-term effects. The disappearance of earthworms, a key biological indicator of soil health, serves as direct evidence of soil degradation, underscoring the ecological impact of leachates. Thus, this research not only advances knowledge on leachate contamination in the Andean region but also provides crucial insights for developing mitigation strategies and soil conservation policies, ensuring agricultural sustainability and environmental protection.

The central research question guiding this study is: What is the impact of leachates from the Chupaca landfill on the physicochemical and biological properties of agricultural soils?

Accordingly, the general objective is to analyze and determine the extent to which leachate from the Chupaca landfill influences the physicochemical and biological properties of agricultural soils.

To address this, the following specific objectives are proposed: (a) Analyze the impact of leachates on soil physical properties, including bulk density, porosity, and water retention capacity; (b) Evaluate their influence on chemical properties, such as pH, electrical conductivity, and nutrient concentrations; (c) Examine their effects on biological properties, particularly microbial activity and the presence of macrofauna, such as earthworms; and (d) Model the transport dynamics of leachates within the soil profile using COMSOL Multiphysics, predicting their long-term behavior.

The hypothesis is that leachates from the Chupaca municipal landfill significantly alter the physical, chemical, and biological properties of adjacent agricultural soils. Specifically, these leachates are expected to cause soil acidification, nutrient imbalances, and a reduction in biological activity, as evidenced by the disappearance of earthworms. Such changes could jeopardize soil fertility and agricultural productivity, emphasizing the urgent need for effective mitigation strategies.

By integrating these analyses, this study enhances the understanding of leachate-induced contamination and contributes to the development of evidence-based mitigation strategies to preserve agricultural soil quality and long-term productivity.

The selection of the Chupaca municipal landfill as the study site is based on its environmental and socioeconomic impact in a region where agriculture is one of the main productive activities. This landfill lacks an adequate waste management system, which facilitates the infiltration of leachates into the surrounding agricultural soils, affecting their quality and productivity.

Moreover, previous studies in Peru have identified a correlation between landfill leachates and the presence of heavy metals in cultivated soils, yet there is a lack of specific research in this province. The site's location, its proximity to agricultural land, and the absence of proper control measures make this study essential for understanding the long-term effects of leachates on soil health and for proposing mitigation strategies based on scientific evidence.

Figures 1 and 2 indicate that the study area covered approximately 49 hectares and was carried out at the landfill located in the Chupaca district, Chupaca province, Junín department. This site is located at an altitude of 3,263 meters above sea level and is geographically located at the coordinates indicated in Table 1.

The materials used included 1 measuring tape, 2 medium transparent containers, 4 resealable plastic bags of 2 kg capacity for filling the samples, a small shovel for excavation, disposable gloves, a lab coat, safety glasses, 1 pen, 10 bond sheets for labeling the samples, 1 packing tape (for labeling the samples), 1 shopping bag for transporting the samples, and a double-layered plastic sheet or tarp of 2 meters to homogenize the extracted sample.

Soil sampling was conducted at depths ranging from 0 to 30 cm within a standardized area of 25 cm × 25 cm per sampling point. To ensure methodological rigor, two sampling points were randomly selected within the contaminated area, maintaining a 20-meter distance between them. The selection of sampling sites followed a quasi-experimental design, wherein contaminated and uncontaminated zones were identified based on their relative proximity to the landfill. Contaminated sites were situated in close proximity to the landfill, where visible evidence of leachate infiltration was observed. In contrast, uncontaminated sites were located 800 to 1000 meters away, serving as a reference for background soil conditions. Within each designated zone, the random selection of two sampling points was implemented to minimize selection bias and enhance the reliability of comparative analyses.

Uncontaminated agricultural land nearby (at a distance of 800 to 1000 m from the contaminated site) was sampled for soil at depths of 0 to 30 cm within an area of 25 cm × 25 cm. For each sampling point, a total of 2 sampling points were randomly selected (with a distance of 20 m between them).

Simultaneously with the soil sampling, earthworms (at a depth of 0 to 30 cm) must be collected at both the contaminated and uncontaminated sites. During the excavation, remove stones, plastic, and other objects that may be present in the extracted soil.

The samples from each extraction point must be placed on a tarp or double-layered plastic, thoroughly mixed, and 1 kg of sample should be taken and placed in a transparent resealable plastic bag.

Label the materials with the identification of each sampling point (points 1 and 2 correspond to the contaminated site, while points 3 and 4 correspond to the uncontaminated site), and georeferencing must be performed. Finally, a comparison of means test should be applied to analyze the earthworm count.

The materials used included 1 measuring tape, 2 medium transparent containers, 4 resealable plastic bags of 2 kg capacity for filling the samples, a small shovel for excavation, disposable gloves, a lab coat, safety glasses, 1 pen, 10 bond sheets for labeling the samples, 1 packing tape (for labeling the samples), 1 shopping bag for transporting the samples, and a double-layered plastic sheet or tarp of 2 meters to homogenize the extracted sample.

Based on the description of the study, the type of research that best fits is quasi-experimental research. This type of research involves the manipulation of an independent variable under controlled conditions but without the random assignment of participants or subjects to treatment groups [7]. In this case, the effects of leachates from the Chupaca dump site on agricultural soil properties are analyzed, which involves manipulating the presence or absence of these leachates in different sampling sites. However, there is no full control over all variables that might affect the results.

The level of research for this study can be defined as explanatory. This level of research focuses on understanding the causal relationships between variables, i.e., it seeks to explain why certain phenomena occur or how one variable affects another [8].

In this case, the study aims to explain how the presence of leachates from the Chupaca dump site affects the physical, chemical, and biological properties of agricultural soil. Authors have contributed to defining this level of research as one that goes beyond the mere description of phenomena, seeking to understand the relationships between variables and provide causal explanations [7, 9].

The electrometric procedure for measuring soil pH begins with sample preparation, where 20 grams of fine agricultural soil, air-dried, and sieved through a No.10 mesh (2 mm nominal size), are mixed with 50 ml of distilled water. The resulting suspension is stirred for 15 minutes and left to rest for another 10 minutes.

This step ensures proper homogenization and allows complete interaction between the soil and water. The potentiometer is then calibrated using buffer solutions with pH values of 4, 7, and 10. Figure 3 indicates that the electrode must be cleaned and dried after each measurement to avoid cross contamination. The electrodes are also dipped into the suspension without directly touching the soil, and the pH value is recorded.

The procedure for measuring soil conductivity starts with sample preparation, where 20 grams of fine agricultural soil, air-dried, and sieved through a No.10 mesh, are mixed with 50 ml of distilled water. The resulting suspension is stirred for 15 minutes and left to rest for another 10 minutes. This step ensures proper homogenization and allows complete interaction between the soil and water.

Conductivity is then measured, and the electrode must be cleaned and dried after each measurement to prevent cross-contamination. Finally, the electrodes are immersed in the suspension without directly touching the soil, and the conductivity value is recorded.

The modified Walkley-Black method for the determination of organic matter in soils is a well-established and widely used procedure due to its accuracy and reliability. The procedure involves weighing 1 g of the sample, which is then transferred to a 500 ml container. Subsequently, 10 ml of 1N potassium dichromate is added, and the mixture is stirred manually in a circular motion.

Then, 20 ml of sulfuric acid is added, followed by manual stirring (to ensure complete contact of the reagent with the soil). The mixture is left to rest for approximately 30 minutes and then diluted to 200 ml with distilled water. The sample is extracted into the reading cells, and the transmittance is measured at 660 nm.