Predictive modeling of petroleum retardation capacity in urban vadose soils: laser particle analysis for smart city groundwater resilience planning

With the construction of smart cities, the pollution and remediation of vadose zone soil have received increasing attention from people. As urban digital twins require millimeter-level environmental mapping accuracy, real-time monitoring of soil contaminant transport has become critical infrastructure for smart city resilience. In order to support precise governance of smart city environments, particularly in underground space utilization and pollution early-warning systems, an integrated methodology combining optical characterization and smart agriculture technologies enhanced with IoT sensor networks was applied in Zhangwu, which can reveal soil hydro-physical properties and retardation capacity of aquifer media. By means of laser particle size analysis, hyperspectral imaging (HSI), and laser-induced breakdown spectroscopy, soil hydro-physical properties experiments, soil particle size distribution and permeability are analyzed, taking hydrodynamic dispersion theory as a basis, one-dimensional solute transports of NaCl and petroleum in the semi-infinite, homogeneous media are simulated. The results show that, the soil types are mostly silt with weak permeability, hydraulic conductivity range from 0.621 to 1.247 m/d, dispersion coefficient range from 0.0205 to 0.0649 m² /d, and retard factor range from 2.90 to 4.12. Found by comparative analysis for different particle sizes, the particle size distribution more uniform, the larger the dispersion coefficient and hydraulic conductivity, and there is a positive correlation between blocking ability and specific surface area, the bigger the specific surface area, the larger the retard factors. Petroleum contaminants are obviously blocked by aquifer media in the study area, which confirm that the soil has the ability to intercept pollutants. This paper will provide important parameters and digital solutions for urban oil pollution remediation, sponge city underground space planning, and smart environmental protection platform construction.