Investigation of Groundwater Flow Using Δ18O and ΔD in a Sulfur Mine in Japan

Abstract

The A sulfur mine is located in the Iwate Prefecture of Japan. This mine has both surface and underground parts and was operated
from the late 1800s to the late 1900s. Since the early 1900s, acid mine drainage (AMD) has been reported in this mine, and the waste
water has been neutralized in a treatment plant since the mine was closed. Recently, reducing the AMD volume by decreasing water
inflow to the underground mine has been considered as a way to reduce the AMD treatment cost. The first step in such an approach
is to understand in detail the groundwater flow around the mine. However, part of the study area is covered by lava and comprises
crystalline rocks with complicated structures, making it difficult to understand the groundwater flow. Therefore, the present study
investigated the groundwater flow around this mine by focusing on water quality, such as pH and electrical conductivity (EC), stable
isotopes (i.e. δ18O and δD) and 3H in the surface and ground water. The spatial distributions of pH, Stiff diagrams, and δ18O and δD
values in the surface and ground water indicated that the groundwater flow system was divided into three basins in the study area,
as predicted from geomorphological information. Moreover, the spatial distribution of δ18O and δD in the surface and ground water
suggested that the groundwater recharged at the highest altitudes in the B mountain in the northwest of the mine might flow in the
underground mine. Furthermore, the 3H values in the waste water discharged from the underground part of mine implied that the
groundwater age was no more than approximately 60 years old.