The Stable Isotopes Approach as Tracers to Investigate the Origin of Groundwater In The Unconfined Aquifer of Denpasar, Bali

numerous purposes, so the use of groundwater must also pay
attention to the balance and preservation of the resource itself.
Knowing the origin of the groundwater and the recharge area on an
aquifer is essential to determine the conservation model. The purpose
of this research is to determine the Denpasar Meteoric Water Line
(DMWL), the recharge area, and the origin of groundwater in the
unconfined aquifer of Denpasar. The determination of the number
and location of samples, both rainwater samples, and groundwater
samples, using a purposive sampling approach. A total of 5 samples
of rainwater and 18 samples of groundwater were taken at several
locations in the Denpasar area. The stable isotopes of δ
18O and δ
2H
were carried out using laser spectrometry Picarro L2130-i. This
research shows the Denpasar LMWL is δD = 8.5839 x δ
18O + 19.876;
from the distribution of oxygen-18 isotope, the low 18O value is
dominated in the North and Northeast areas, so here this area can be
delineated as the potential recharge area; and based on the isotope
ratio, groundwater in the unconfined aquifer of Denpasar can be
divided into three geneses groups: (a) Groundwater Genesis-A and B
groups represent groundwater systems that come from direct rainfall
as well as local recharge with low (depleted) to moderate δ
18O and
δ
2H isotope ratios and groundwater groups Genesis-C, which has
high (enriched) δ
18O and δ
2H isotope ratios, is located below the
slope of the DMWL.