Dynamic evolution and response strategy of demand in buffer zone between scattered groundwater sources and hazardous waste landfill.

Groundwater contamination by landfill leachate is a major concern. Ignoring the long-term increase in leakage caused by the aging of engineered materials may lead to underestimation of the buffer distance (BFD) demand of landfills. In this study, a long-term BFD prediction model was developed by coupling an engineering material aging and defect evolution module with leachate leakage and migration transformation model, and was applicated and validated. The results showed that under landfill performance degradation, the required BFD was 2400 m, i.e., 6 times higher than under undegraded conditions. With the degradation of the performance, the BFD required to attenuate the heavy metal concentrations of groundwater increases more than the BFD required to attenuate organic pollutants. For example, the BFD required for zinc (Zn) was 5 times higher than that required for undegraded conditions, while for 2,4-dichlorophenol (2,4-D), the BFD was 1 times higher. Considering the uncertainties of the model parameters and structure, the BFD should be greater than 3000 m to ensure long-term safe water use under unfavorable conditions such as large leachate production and leakage, weak degradation and fast diffusion of pollutants. If the actual BFD does not meet the demand due to landfill performance degradation, the landfill owner can reduce the reliance on the BFD by reducing the waste leaching behavior. For example, the landfill in our case study would require a BFD of 2400 m, but by reducing the leaching concentration of zinc in the waste from 120 to 55 mg/L, this requirement could be reduced to 900 m.