Exploring the conservativeness of deuterated water as the artificial
tracer for hydrogeological tests
Abstract
Deuterated water has been applied in hydrogeological tracer tests in
recent years. However, there is a contradiction about the
conservativeness of artificial deuterium (D/2H). In this study, what
circumstances HDO behaved truly conservatively were investigated through
laboratory-scale experiments via comparing the widely used tracer
chloride (Cl-). And reasons for the non-conservativeness of HDO were
discussed comprehensively for the first time. In addition, the
advection-dispersion equation (ADE) and dual-domain mass transfer (DDMT)
equation were employed to describe the breakthrough curves (BTCs) of
tracers. HDO behaved conservatively when it transported in the porous
media with high permeability (approximately K > 1m/d), and
ADE could describe BTCs successfully. While hysteresis effect of HDO
expressed in the media with low permeability. And the lower the
permeability of the porous media, the stronger the hysteresis effect.
DDMT was more suitable for demonstrating BTCs in low permeability media.
Hydrogen bonds between HDO and H2O, the isotopic exchange effect, and
the dual-domain model of the media all could lead to the hysteresis
effect. The retardation factor (R = 1.712) was used to describe
transporting behaviors of HDO in clay firstly. And the threshold
hydraulic conductivity (Kcr) and the proportion of immobile regions of
HDO were greater than that of Cl-, while dispersion coefficients of HDO
were smaller. These could provide further considerations for using
deuterium in hydrogeological tracer tests.