琵琶湖西岸比良山地東麓扇状地の自噴地下水の水質・ラドンおよび湧出量の時間変化

抄録

Time variations of chemical and ²²²Rn concentrations and discharge of groundwater from a flowing well were investigated from 1984 to 1989 to clarify principally the hydrogeological characteristics of a confined groundwater in an alluvial fan at the western shore of Lake Biwa. Chemical concentrations of the flowing well waters show no seasonal and secular variations. ²²²Rn concentrations of the flowing water are 20～30% higher than those of spring water around the well. ²²²Rn concentrations of both the waters generally show periodical change accompanied by a distinct short-term fluctuations after the heavy rainfall. The level of high ²²²Rn concentrations of each water shows nearly constant ; 1600～1700pCi/l for flowing well water and 1300～1400pCi/l for spring water, through the year. There is week correlation between ²²²Rn concentrations and discharge of flowing well water. Those high levels seem to be a steady state ²²²Rn concentrations in each aquifer when the infiltrating recharge is minimum.

Discharge of the flowing well shows an apparent seasonal change having with its high level from April to August and low from September to January. There is a high correlation between discharge and the former 20-days precipitations.

These results indicate that the groundwater in the fan is recharged by infiltration of the precipitation, and also a peculiar ²²²Rn concentrations in the shallow and deep groundwaters seem to be influenced strongly by the infiltrating recharge.