This paper presents research on groundwater vulnerability to pollution in the municipal solid waste (MSW) landfill area. The study focuses on a large-capacity MSW landfill in central Poland, established in 1977 and closed in 1991. Following its closure, technical reclamation was carried out between 1994 and 2001, and biological reclamation was completed in 2005. Groundwater monitoring has been carried out regularly since reclamation. The DRASTIC and GOD methods were used to assess groundwater vulnerability. The results show different levels of vulnerability influenced by several hydrogeological conditions. The results of the groundwater vulnerability assessment were compared with monitoring data to assess their accuracy and relevance in identifying real contamination risks. The analyses of contaminant migration paths indicated the effectiveness of reclamation efforts. Chloride and ammonium concentrations in most piezometers were within acceptable ranges for good chemical status. Adopted an integrated approach of vulnerability assessment and monitoring data analysis, made it possible to identify critical areas at risk of contamination, assess reclamation effectiveness and provide recommendations for improved environmental protection. The results highlighted the usefulness of parametric methods as valuable tools to complement groundwater monitoring, particularly in landfill areas.