Abstract
Arsenic with concentration over the environmental standard was detected in groundwater samples at an industrial property located in the south-eastern part of Matsumoto Basin. Groundwater qualities within and on the periphery of the site were investigated and high content of arsenic was found in groundwater from a deep well. Upon investigation using a bore-hole camera it is turned out that groundwater in confined aquifers contaminated by arsenic was discharging to the overlying unconfined aquifer via a channel of the well pipe with multi-screens and holes opened by corrosion. Three-dimensional, transient, saturated-unsaturated flow analysis using a finite element method was performed and the results were compared satisfactory with observed groundwater tables. The numerical results also demonstrated the pattern of groundwater flow from the confined aquifer to the unconfined aquifer via the well casing. Correlation and Eh-pH diagrams based on the data from the groundwater quality investigation showed that there is a high positive correlation between As and Fe and that the lower Eh, the higher As becomes regardless of pH.
