Buffering distance between hazardous waste landfill and water supply wells in a shallow aquifer

Abstract

The vulnerability of engineering barrier and the toxicity of leachate increase the need to maintain a certain buffering distance between landfill and drinking water sources. In order to provide decision-making support and technical guidance for the determination, and management of buffering distance, this paper coupled the dose-response model, leakage estimation model, exponential decay source model, and the advection-dispersion model for contaminants transportation and transformation in vadose and aquifer groundwater, and constructed an integral risk-based framework to help to calculate the buffering distance in shallow aquifers against the leachate contamination. Based on the framework and method, a case study is carried out. The results indicate that Zn and Ni have experience a similar dilution and attention process, but due to its smaller RDAF (required dilution and attenuation factor, equal to the ratio of initial concentration to limit concentration) value, Ni needs only a vertical separation distance (VSD) of 4 m (a 4 m vadose zone with saturated conductivity of 1 × 10-5 cm/s) without additional requirement on horizontal buffering distance. While, Zn requires an additional buffering distance of 380 m in addition to the VSD to achieve to be diluted/attenuated to a risk-acceptable level. 2,4-D has larger RDAF than Zn, but due to its difference in degradation characteristics from Zn, it also needs a smaller buffering distance (135 m) than Zn; Further studies shown that the sensitivity of the dilution and attenuation of heavy metals to distance is relatively weak, especially when the distance is greater than 800 m; organic pollutants are more sensitive to distance, even more than 800 m; for the landfill site to dispose organic pollutants, the buffering distance of 400 m is a conservative choice, while for sites to dispose heavy metal wastes, 400 m may be a risky decision and needs further calculation and demonstration.