The regional distribution, annual change and controlling 'factors of chloride concentration were investigated on deep groundwater of Musashino Plateau, west Saitama Prefecture. The published city water examination data were used as the basic data of this study, and especially chloride concentration was studied among water components.
The relations between the annual change of chloride concentration and the change of groundwater level were classified into four patterns, by which the investigated area was divided into four groups. Relatively, in the westward area, the chloride concentration was low and showed a small annual change. On the other hand, in the eastward area, it was high and had a tendency to increase even when the water level was recovering after the restriction of groundwater pumping.
It will be considered that the geological condition represented by gravel percentage has an influence on the regional distribution of chloride concentration. That is, the concentration is lower where there is a larger gravel percentage in the covering layer, but it is higher where there is a larger gravel percentage in the pumping layer.
Synthesizing the above results with a cell-model experiment and simulation results, we conclude that the annual change and regional feature of chloride concentration are indirectly influenced by the size of the recharge area and the volume of water leaked through the confining layer, and are directly caused by the downward seepage of polluted shallow groundwater and the squeezing out of pore water from the confining layer.