Dense MASW shear-wave imaging of weak-zone networks and preferential leachate pathways beneath rumah landfill site,...

Landfills in arid regions may contribute to potential soil and groundwater concerns, as episodic rainfall, heterogeneous cover materials, and fractured carbonate bedrock may create preferential infiltration pathways. In central Saudi Arabia, landfill sites commonly overlie carbonate formations where weathering, fracturing, and dissolution can produce strong lateral variations in near-surface stiffness and hydraulic susceptibility. This study presents a dense MASW-based stiffness model to screen for shallow weak zones and fractured/weathered carbonate intervals beneath Rumah landfill site in central Saudi Arabia. We acquired 26 MASW profiles using a 24-channel split-spread array with 1 m receiver spacing and a 10 kg weight-drop source, and processed the data to image the near surface to an effective depth of approximately 30 m. The resulting 2D shear-wave velocity sections define three Vs-based geoseismic units: (1) a surficial cover/near-surface low-stiffness unit with Vs of approximately 0.35-0.76 km/s and thickness of about 2-8 m; (2) an intermediate fractured/weathered carbonate interval with Vs of approximately 0.76-1.50 km/s and typical thickness of about 5-15 m; and (3) a deeper competent carbonate/limestone domain with Vs > 1.50 km/s, locally approaching approximately 2.3 km/s. Localized low-Vs weak zones (< 0.76 km/s) are repeatedly detected, mainly within the upper 2-12 m and commonly 2-6 m thick. These anomalies are interpreted as zones of reduced shear stiffness that may reflect disturbed ground, elevated moisture, increased porosity, weathering, fracturing, or combinations of these factors. The results, therefore, provide a defensible MASW-based pathway-susceptibility screening framework and identify priority targets for confirmatory drilling, hydrochemical sampling, and fluid-sensitive geophysical methods such as ERT/IP. The findings should be interpreted as evidence of susceptibility and subsurface heterogeneity, not as direct proof of active leachate migration.