The efficiency of landfill cover layers in gas retention is vital to mitigate environmental impacts, reduce biogas modeling uncertainties, and promote resource circularity and low-carbon transitions. This study applies the Geotechnical Performance Index (GPI) to evaluate the spatial relationship between geotechnical properties and greenhouse gas (GHG) emissions in a landfill in northeastern Brazil. The data was obtained through laboratory testing of the soil from the site, in situ testing at 21 points in the cover layer and physical-mechanical characterization of the soil. The GPI included parameters such as moisture (w), degree of compaction (C), dry density (gamma(d)), void ratio (e), porosity (n) and degree of saturation (S). Interpolate the data using QGIS (R), I'Moran to analyze the spatial correlation and Global Warming Potential (GWP) analyzes. The CH4 concentrations, of the 21 points analyzed, 95 % registered average values of less than 4 % v/v. The main CO2 hotspot had a flow of > 300 g.m(-2).d(-1), while for CH4 it was 39 g.m(-2).d(-1). The GPI was suitable for assessing the efficiency of the landfill cover layer, showing positive spatial correlations with CO2 (Moran's I = 0.105) and CH4 (Moran's I = 0.064) fluxes. Under conservative, moderate and optimistic carbon-pricing scenarios (CO2-eq), annual revenue estimates amounted to USD 63,285, USD 189,855 and USD 632,850, respectively, which highlights the economic leverage of methane-oriented interventions. The contributions demonstrate that landfill cover performance arises from coupled geotechnical, environmental, and biogeochemical interactions; targeted interventions can therefore elicit integrated responses and strengthen decision-making for landfill management and climate change mitigation.