Responses of well-aquifer system to four earthquakes and implication for contaminant transport in Changan landfill, China

Evaluation of aquifer response to earthquakes is important to understanding the evolution of aquifer properties and contaminant transport. In Changan Landfill, a multi parameter monitoring system was installed to collect data every 12 h. Principal Component Analysis (PCA), energy density and wavelet analysis, and tidal analysis were used to reveal the response mechanisms to four earthquakes, sensitivity of various parameters to seismic stimuli, and permeability evolution, respectively. The results showed that the chemical characteristics of two aquifers were distinct. The shallow aquifer was polluted by leachate, and the deep aquifer was less polluted. Coseismic responses were dominated by the deep aquifer and the relative contribution of each aquifer remained stable. Coseismic chemical changes were domi-nated by the opening and closing of fractures, and the long-term evolution was controlled by seasonality. The deep aquifer had a higher sensitivity to seismic stimuli than the shallow aquifer. Tidal analysis showed that a general per-meability decrease during this monitoring period reduced contaminant transport, but some contaminants crossed the aquitard between the two aquifers after the Zizhong earthquake, due to an increase in vertical permeability.