9:15 AM - 9:30 AM
[HTT23-02] Study on groundwater flow system at Oshino Village in Yamanashi Prefecture – Report 1. Characteristics of water quality and stable isotopes of shallow and deep groundwater at Oshino Village.
Keywords:Oshino Village, Oshino Hakkai, groundwater flow, water quality, stable isotope, trace element
The filed observation in Oshino village were carried out at 18 to 19 in January, 2017. EC, pH, water temperature and depth of water table were measured and spring water and groundwater were sampled for 72 sites. Dissolved inorganic matters, trace elements and stable isotopes of oxygen and hydrogen were analyzed by using the analytical instruments (ICS-3000, Agilent 7500cx, L2130-i).
As a result of this observation, followings are revealed.
1) Dissolved inorganic matters and δ18O and δD of Oshino Hakkai springs (Okamaike, Choshiike, Nigoriike, wakuike, Kagamiike, Shobuike and sokonashiike) are mostly the same. However, the Deguchiike which is one of the Oshino Hakkai springs showsa little different water quality, it is considerate that the groundwater flow of Deguchiike is different from that of other springs of Oshino Hakkai.
2) The water quality of groundwater mostly show the Ca-HCO3 type, but there are some sites that contain the Na+ or Mg2+. The amount of dissolved inorganic matter of groundwater are lower at central part than the other area of Oshino Village. It is expected that the different groundwater flow system is existed.
3) There are some sites of shallow groundwater that show a little high nitrate concentration. It is thought that the high concentration of nitrate is due to fertilization to farmland.
4) The deep groundwater that well depth is about 100 m and some sites of shallow groundwater show the high pH (above 8.2), and also show the high concentration of vanadium and phosphorus and relatively low values of δ18O and δD. There's a high possibility that these sites’ groundwater is recharged at Mt. Fuji.
5) It is conceivable that δ18O and δD values are affected by the difference of recharge area. As a result of correlation chart which showed the EC versus δ18O, observation site was able to divide into three groups. The regression line of δ18O versus δD is δD=6.2δ18O-5.0 (r2=0.969).
6) The artesian well which is located at northwestern part of Oshino village shows Na-SO4 type. In this site, the water temperature is relatively high and δ18O and δD is relatively low. These water qualities of the artesian well differ from other sites.
7) From the contour map of water table, the groundwater flow at Oshino Village was divided into two. The groundwater flows from southeast to northwest in eastern part and from south to north in central and western part of Oshino Village.
In future, we are going to carry out the field observation at Spring and Summer in 2017, and to estimate the groundwater flow system and residence time.