Hydrochemistry of urban groundwater, Seoul, Korea: the impact of subway tunnels on groundwater quality.
Hydrogeologic and hydrochemical data for subway tunnel seepage waters in Seoul (Republic of Korea) were examined to understand the effect of underground tunnels on the degradation of urban groundwater. A very large quantity of groundwater (up to 63 million m3 year(-1)) is discharged into subway tunnels with a total length of 287 km, resulting in a significant drop of the local groundwater table and the abandonment of groundwater wells. For the tunnel seepage water samples (n = 72) collected from 43 subway stations, at least one parameter among pathogenic microbes (total coliform, heterotrophic bacteria), dissolved Mn and Fe, NH4+, NO3(-), turbidity, and color exceeded the Korean Drinking Water Standards. Locally, tunnel seepage water was enriched in dissolved Mn (avg. 0.70 mg L(-1), max. 5.58 mg L(-1)), in addition to dissolved Fe, NH4+, and pathogenic microbes, likely due to significant inflow of sewage water from broken or leaking sewer pipes. Geochemical modeling of redox reactions was conducted to simulate the characteristic hydrochemistry of subway tunnel seepage. The results show that variations in the reducing conditions occur in urban groundwater, dependent upon the amount of organic matter-rich municipal sewage contaminating the aquifer. The organic matter facilitates the reduction and dissolution of Mn- and Fe-bearing solids in aquifers and/or tunnel construction materials, resulting in the successive increase of dissolved Mn and Fe. The present study clearly demonstrates that locally significant deterioration of urban groundwater is caused by a series of interlinked hydrogeologic and hydrochemical changes induced by underground tunnels.
Chae
Gi-Tak
GT
Department of Earth and Environmental Sciences and the Environmental Geosphere Research Lab (EGRL), Korea University, Seoul 136-701, Republic of Korea.
Yun
Seong-Taek
ST
Choi
Byoung-Young
BY
Yu
Soon-Young
SY
Jo
Ho-Young
HY
Mayer
Bernhard
B
Kim
Yun-Jong
YJ
Lee
Jin-Yong
JY
D002021:Buffers; D002621:Chemistry / Q000379:methods; D004784:Environmental Monitoring / Q000379:methods*; D005844:Geology / Q000379:methods; D007501:Iron / Q000032:analysis; D007723:Korea; D008345:Manganese / Q000032:analysis; D010084:Oxidation-Reduction; D011890:Railroads; D014867:Water / Q000032:analysis; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000032:analysis*; D018508:Water Purification; D014881:Water Supply
D002021:Buffers; D014874:Water Pollutants, Chemical; D014867:Water; D008345:Manganese; D007501:Iron