9:15 AM - 9:30 AM
[HTT18-02] Study on groundwater flow system at Oshino Village in Yamanashi Prefecture – Report 3. Characteristics of groundwater flow at Oshino Village by using observations of 2017.
Keywords:Oshino Village, groundwater, water quality, stable isotopes, groundwater flow
The filed observation in Oshino village were carried out at 18 to 19 in January and 8 to 10 in August, 2017. EC, pH, water temperature and depth of water table were measured and spring water and groundwater were sampled for 75 sites of January and 96 sites of August. In this study, “shallow groundwater” is defined as several meters to some dozen meters depth, and “deep groundwater” is defined as about 100 m depth.
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). And for estimating of the residence time, CFCs, SF6 and 3H of some spring water and deep groundwater samples were analyzed. As a result of this observation, followings are revealed.
1) The water quality of spring water (including Oshino Hakkai springs) and shallow groundwater show mainly Ca-HCO3 type. On the other hand, water quality of deep groundwater shows (Na+Ca)-HCO3 type and Na-HCO3 type. The nitrate (NO3-) concentration of some sites for shallow groundwater is high especially in August, so it is considered that the water quality of shallow groundwater is influenced by the fertilizer. The water quality of deep groundwater is almost constant.
2) The vanadium concentration of some deep groundwater is over 100 μg/L. The vanadium concentration of the water which is recharged at Mt. Fuji is relatively high, so we can use this result for estimating the recharge area.
3) Stable isotopes (δ18O or δD) of monthly precipitation which have been taken at 11 sites and elevation have strong negative correlation. The altitude effect is -0.19‰/ 100 m of δ18O and -1.6‰/100 m of δD.
4) 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.
5) From the contour map of water table, the shallow and deep groundwater flow at Oshino village was divided into two. The groundwater flows from south to north in western part and from east to west in central and eastern part of Oshino Village.
6) As a result of CFCs, SF6 and 3H analysis, it is estimated that the residence time of spring water (including Oshino Hakkai springs) is about 20 years and that of deep groundwater is about 30-40 years.
We will continue the field observation of Oshino village at 2018, and estimate the groundwater flow system and residence time.