This study investigates the long-term effects of landfill leachate contamination on soil hydraulic conductivity and shear strength parameters over a 12-month period, addressing the current lack of comprehensive long-term experimental data in this field. Laboratory permeability tests and direct shear tests were performed on sandy clayey silt samples contaminated with leachate at concentrations ranging from 5% to 25%. Microstructural and mineralogical analyses were conducted using SEM and XRD to identify the mechanisms behind observed changes. The results identify a critical threshold at 15% contamination where soil behavior transitions from granular to cohesive characteristics, marked by significant changes in both hydraulic and mechanical properties. Hydraulic conductivity increases at low contamination levels but decreases significantly at higher levels, while friction angle shows an immediate reduction from 36.5 degrees to 31-31.5 degrees and cohesion exhibits a three-phase evolution pattern, reaching peak increases of 151.5% at 15% contamination. The hydraulic conductivity changes are controlled by contamination level rather than exposure time, maintaining stable values throughout the testing period, whereas shear strength parameters demonstrate more complex temporal evolution patterns. These findings provide essential parameters for landfill design and stability assessment, demonstrating how leachate concentration affects long-term soil behavior through mineral formation and structural modification.

Inadequate management of solid waste stands out as a primary cause of environmental contamination, leading to a decline in groundwater quality in the vicinity of landfill sites. Though landfills are required by federal regulation to have liners formed by plastic or clayey layers, these liners tend to have leaks, which can result in landfill leachate percolation into the soil and aquifers, contaminating nearby water sources and further damaging ecosystems. Currently, the elevated nitrate (NO3-) concentration in groundwater spurred by landfill leachates is becoming a growing global concern. Various regions across the world present groundwater NO3- concentrations exceeding the threshold limit (50 mg/L) of WHO for drinking purpose. In this scenario, it is requisite to consider and develop highly efficient and affordable solutions for the long-term management of groundwater resources. Therefore, a bibliographical review was conducted in this paper by searching literature in Web of Science, ScienceDirect, Google Scholar, SpringerLink, PubMed, and Scopus to analyze NO3- pollution in groundwater caused by landfill leachates and explore the impacts of landfills and NO3- pollution on the environment and human health. In addition, this review also presents an overview of the leachate treatment technologies to remove nitrogenous compounds, particularly NO3-. This review entails a worldwide appraisal of groundwater NO3- pollution to comprehend the human health risks and aid in optimizing groundwater quality. A resulting framework developed in this review provides an improved grasp of the link between inadequate landfill management and adverse environmental and health outcomes and urged all stakeholders to address the issue of solid waste to ensure environmental and human health. Overall, the results emphasize the need for immediate action and collaborative efforts to mitigate these impacts and ensure the long-term sustainability of waste management practices.