Fugitive methane emissions from water resource recovery facilities (WRRFs) remain a key uncertainty in greenhouse gas (GHG) inventories for the wastewater sector. This study presents a multilevel monitoring framework to quantify fugitive methane emissions at a full-scale WRRF, supporting improved accuracy in emissions reporting and mitigation planning. The approach integrates complementary techniques across spatial and temporal scales, including fixed continuous sensors, mobile monitoring surveys, and facility-scale flux estimation. Measurements were conducted across critical process units such as anaerobic digestion, sludge handling, and biogas infrastructure. Data integration and advanced analysis enabled identification of emission hotspots, temporal variability, and previously unaccounted emission pathways. Results highlight that fugitive emissions can represent a significant fraction of total methane production, with variability driven by operational conditions and infrastructure performance. Comparison with conventional inventory methods revealed notable discrepancies, indicating potential underestimation of emissions using standard approaches. The study demonstrates the value of a multilevel, data-driven monitoring strategy for improving emission quantification and supporting targeted mitigation actions. These findings provide practical insights for utilities seeking to enhance sustainability performance, align with emerging regulatory expectations, and contribute to net-zero goals in the biosolids and wastewater sector.