Identification and assessment of groundwater pollution from landfill leachate based on geophysical, spectroscopy, and hydrogeochemical methods.

As a precondition for groundwater remediation, pollution investigation of landfills requires enhanced accuracy and deeper understanding. Limited by the complexity of leachate and the inherent characteristics of each method, the application of a single method still has difficulty in comprehensively and accurately identifying groundwater pollution from landfills. To compensate for the limitations of a single method and enhance the accuracy, this study integrated survey, high-density resistivity exploration (HDR), and comprehensive analyses to develop a methodology. Using this methodology, the pollution area was identified to range from the landfill to Huang Jing River. The area from the landfill to 100 m downstream was identified as the core pollution area. The main inorganic chemical processes in polluted groundwater include the adsorption of K, the exchange of Ca and Mg in the aquifer by Na and K in the groundwater, and the supersaturation and precipitation of Ca and Mg. The transformation of organic pollutants included the dispersion and migration of refractory humic acids and the decomposition of degradable matter into humic substances, proteins, and tryptophan. Among the various methods, HDR performed excellently in rapidly identifying the polluted area. Cl and the contribution ratio (Y) of the leachate to the chemical composition of groundwater were the best indicators for defining the maximum pollution boundary.