A groundwater investigation performed before and after filling the reservoir to study the characteristics of groundwater quality at the rock fill dam two years form initial filling.
The results were as follows:
(1) Variation in groundwater quality before and after filling the reservoir became smaller than that of initial filling due to seepage from the reservoir into the rock for two years.
(2) Small variation in groundwater quality could be expressed clearly by the principal component analysis basd on the water quality.
(3) When the variation in groundwater quality is large, we can estimate the flow routes of seepage by electric conductivity of groundwater.
(4) In this area, investigating groundwater quality after 3 or 4 months froms the start of filling is effective for clarifing the variation in groundwater quality.