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EVALUATION AND PREDICTION OF POLLUTION CAUSED BY ACID WATER EXUDED FROM MUD SEDIMENT IN URBAN GROUND (2006)

The pollution of surface and/or ground water caused by the inflow of drainage water from mudstone excavation sites is a serious issue in Japan. It has been recognized that this issue results from the discharge of sulfate generated by the decomposition of pyrite contained in the mudstone. In general, marine mudstone includes the primary framboidal-type pyrite formed during sedimentation and diagenesis. The pyrite in mudstone discharges acid water into the environment by decomposition during the weathering process. The ground under the big Japanese cities of Tokyo and Osaka contains sand and/or mud sediments formed in the late Pliocene to Pleistocene. When the underground environment in these cities is altered by tunnels and other underground openings pollution by acid water originated from the mud sediments is possible. Therefore, the evaluation and prediction of the possibility of pollution by the acid water from mud sediment is an important theme of environmental geology when tunnels and other underground openings are constructed in these cities.
We examined the geochemical characteristics of the mud distributed underground in the periphery of the cities in Japan to establish an evaluation system for the exudation of acidic water from mud sediment. The ability of exudation of acidic water from the mud sediment can be evaluated by the mole ratio of sulfur content to calcium content in the sediment. We made another attempt to predict the spatial extent of pollution due to the exudation of the acid water and/or the heavy metals from mud sediment by numerical simulation which combines advection/diffusion and geochemical models.
Reference:
The 10th IAEG International Congress, Nottingham, United Kingdom, 6-10 September 2006, Paper number 265
Organization:
Railway Technical Research Institute, Japan
Japan
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