A series of geotechnical and geoenvironmental engineering tests were performed on samples obtained from Los Mangos Sanitary Landfill in Alajuela, Costa Rica. Geotechnical testing included natural water contents, grain size distribution, Atterberg Limits, Specific Gravity, And USCS soil classification. The Environmental engineering testing included Total Solids, Moisture Content, Fixed Solids, Volatile Solids, pH, Chemical Oxygen Demand, Biochemical Oxygen Demand, and Heavy Metals (Cd, Pb, Cu, and Fe). The samples were classified according to their age: one year old sample (soil and waste), a two-year sample (soil and waste), a 15-year old sample (soil and waste), and a 15-year old sample (only waste). After the laboratory testing was completed, 11 settlement prediction models were tried. Results obtained from the theoretical models were compared with actual settlement observed at the sanitary landfill and the best prediction model for the given conditions was the Sowers model [1].