Abstract
For giving basic understandings of the long-term safety of geologic isolation of high level radioactive wastes in a coastal deep subsurface region, behavior of the Freshwater-Saltwater Transition Zone (FSTZ), which might be a key factor in estimating and predicting the coastal groundwater flow field, is examined through numerical case studies.
Following the paper No. 1, the author here presents results of case studies of 2-D cross-sectional models under dynamic natural/artificial boundary conditions. The results can be summarized as follows.
(a) Multiple cycles of the sea level change through geologic time should cause the shape of FSTZ under coastal area to deviate from the GHYBEN-HERZBERG theoretical static shape. It is caused by the difference of the velocities of sea level transgression and regression, under the insufficiency of time for equilibrium. This suggests us that static modeling without sea level change might become inadequate for practical site analysis.
(b) The shaft and tunnels might have impacts on lowering the groundwater level and pulling the FSTZ toward the repository during the operation phase of several tens of years. Time for recovery of the FSTZ back to natural position needs much longer time, while groundwater level recovers in the order of period of the operation phase.
