(General session) Mineral processing / Environment / Recycling

[3101-09-04] Change of groundwater level and wastewater quality to rainfall events at mine waste dump

○Sereyroith Tum¹, Shinji Matsumoto¹, Miu Nishikata¹, Tetsuo Yasutaka¹ (1. Geological Survey of Japan/National Institute of Advanced Industrial Science and Technology)

Chairman:Takahiko Arima (Hokkaido University)

Keywords:Mine waste dump (MWD), Groundwater level (GL), Groundwater quality, Hysteresis pattern

For sustainable management of Acid Mine Drainage (AMD) from the mine waste dump (MWD), it is essential to understand the relationship between rainfall and wastewater discharge from MWD. The rainfall recharges into MWD change the groundwater level (GL) and accelerates the sulfide minerals dissolution, leading to a change in the groundwater quality. However, the relationship among rainfall, GL, and groundwater quality is complex. Therefore, we conducted a field investigation of the MWD and tried to evaluate the factors affecting water quality dynamics. This research aims (1) to understand the influences of rainfall on GL and wastewater quality in the MWD and (2) to characterize the hysteresis pattern of GL and groundwater quality of the MWD linkage to the rainfall events.
Three monitoring wells were installed in the MWD to investigate the GL and the groundwater quality, such as pH and electrical conductivity (EC). The hydrographs and hysteresis were analyzed using the time series plot of the hourly data of rainfall, GL, pH, and EC from the MWD. Ten rain events were investigated to determine the hysteresis patterns in the MWD. The GL and EC significantly increased during rainfall events, while the pH for each borehole decreased depending on rainfall intensity. These behaviors indicated that there was extra dissolution of sulfide minerals within the MWD. The hysteresis patterns of GL, pH and EC shown different loop line directions due to the influence of groundwater recharge sources. These phenomena are the potential indicators to interpret that the recharge sources that come from rainfall suggestively impact the discharge of MWD wastewater quality.