Assessment of landfill groundwater quality and regulating factors: a case study of northern Sichuan

Abstract

A total of 31 groundwater samples were obtained and analyzed in this research endeavor from a conventional rural landfill situated in the red-layer region of northern Sichuan. The Chemical characteristics, controlling factors and hydrogeochemical processes of the groundwater in the study area were elucidated through the application of multivariate statistical analysis and ionic ratio analysis. To predict the spreading range and concentration of the contaminants in the landfill, a groundwater flow model and a solute transport model were constructed using groundwater numerical simulation software. The Piper diagram revealed that the majority of the groundwater exhibited a chemical composition of HCO3-Na and SO4·Cl-Na, which is denoting neutral or weakly alkaline groundwater and belonged to the soft-fresh and hard-brackish water types, respectively. The concentrations of NH4-N in groundwater varied from 0.025 to 17.3 mg/L, with 51.61% of samples surpassing the limit of 0.5 mg/L established by the World Health Organization for drinking water. The groundwater chemistry in the studied area was primarily affected by cation exchange, human activities, and the weathering of carbonate rocks, according to the Gibbs plot, ionic ratio analysis, and SI calculations. According to the calculated weighted water quality index (EWQI), the majority of the groundwater quality indicators in the study area were classified as poor or very poor, with NH4-N concentration being the primary determinant. Numerical simulation results showed that the diffusion area of the NH4-N pollution plume in the horizontal plane along the direction of groundwater flow was 5618 m2, 10142 m2, and 11695 m2 for 1, 5, and 10 years of waste leachate leakage, respectively. In conclusion, the findings of this research offer a scientific basis for the remediation of groundwater attributable to the landfill situated in the red-layer region of northern Sichuan.