Investigation of dense plumes in porous media using CsNO3 solute and phenolphthalein tracer

We present results from the laboratory experiments performed to study the behaviour of dense plumes in porous media using Caesium Nitrate (CsNO₃) as the solute. Specifically, we consider the case of fixed volume release of a dense fluid into a saturated porous medium of lighter density. Our experiments consider the injection volume and concentration of CsNO₃ and the porous medium permeability as experimental variables. Our measurements show that the plume length and volume increase with time approximately as $t^{0.5}$. The mean concentration of the plume decreases with time as plume monotonically dilutes due to continuous mixing with the surrounding. From our measurements and with the help of dimensionless scaling, we present empirical models for the length, volume and mean concentration of the plume. Our results may be used to gain preliminary insights into the spatio-temporal evolution of plumes formed in the subsurface environment.