This study investigated the predicted and abserved outflow of groundwater which occurredduring tunnel constructions. Among the 586 road construction projects from 1986 to 2006, 4route 25 tunnel construction areas and 26 waste water treatment facilities under constructionwere studied.Most of the tunnel outflow prediction in EIA (Environmental Impact Assessment) processhave been classified into the 17 types of units depending on the assessor’s options, which havenot conformed to the request of the residents and non government organizations.The investigation results showed that the outflow of underground water in tunnelconstruction areas averaged about 0.133m3/km · min with the maximum 0.386m3/km · min,and that the outflow mostly occurred in the early stage of tunnel excavation and diminishedgradually. The prediction of outflow of underground water in the EIA process showedexcessive results compared to observed outflow, the even 51.7 times.Consequently for more realistic prediction, current EIA method for prediction of outflow ofunderground water in tunnel construction areas has to adopt numerical methods coupled withhydraulics and geologic informations from unit methods of present time.