EVALUATION ON THE PERFORMANCE OF A PROPOSED SOIL BARRIER SYSTEM IN WASTE DISPOSAL SITE

摘要

Recently, migration of contaminants in the bottom liner of waste site has been caused much attention by most countries. North American and European countries have regulated strict bottom liner system in order to protect surroundings against contaminant migrating from the waste sites. However, compared with North American and European ones, Japanese bottom liner system has been questioned because of its higher hydraulic conductivity of the clay liner. In this study, a new soil barrier system consisting of Ariake clay liner underlain by a hydraulic control layer and sub-ground is proposed, expected to mitigate the pollution of contaminant to the base aquifer. The performance of this barrier system is evaluated by the numerical analysis using the program, POLLUTE V6.3. The contaminants adopted in this study include Chloride (Cl~-) and Cadmium (Cd~(2+)) because the former one is usually considered as conservative specie and the pollution of the latter one has been reported in Japan. The criteria of the evaluation are performed based on the peak concentration and corresponding arrival time of the contaminants at the top of the aquifer. As a comparison, A Japanese bottom liner, Subtitle A, is also evaluated. The numerical analysis results show that the proposed soil barrier system is enough to satisfy the fail-safe design requirement based on the peak concentrations of two types of contaminants at the top of the aquifer, whereas Subtitle A cannot satisfy the requirement. The factors controlling the migration of the contaminants in the soil barrier are discussed based on the parametric analysis. The results show that with the change in the adsorption ability, hydraulic conductivity, thickness of the Ariake clay liner and the Darcy velocity in the aquifer, the peak concentration and corresponding arrival time of the contaminants at the top of the aquifer intend to change.