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. The author presents, in the sequential two papers, the results of 2-D cross-sectional model studies under static/dynamic boundary conditions.
In this paper, the numerical results under static boundary conditions are presented. They can be summarized as follows.
(a) Under the same boundary conditions, two different processes, i. e., a washing-out process starting from saltwater saturated condition and a saltwater intrusion process starting from saltwater/freshwater separated condition, produce almost the same shape of FSTZ at steady state.
(b) The lower the regional permeability becomes, the longer the time required for attaining equilibrium of FSTZ becomes.
(c) Push-out of FSTZ to sea side by freshwater may occur when the rate of infiltration is high, and/or rock anisotropy is high, and/or the topographic high exists.
(d) Existence of a fault with relatively lower permeability than the peripheral rock may have greater effect on the position and shape of FSTZ, than that with higher permeability.
