Variabledensity groundwater flow and solute transport in fractured rock: Applicability of the Tang et al. [1981] analytical solution
Abstract
The effect of fluid density variations on mixed convective (advective and densitydriven) transport in fractured rock is examined. Assuming a representative natural hydraulic gradient in a vertical fracture, breakthrough curves for variabledensity systems are shown to be significantly different from those with constantdensity conditions for even very small solute source concentrations (as low as approximately 2.3 g L^{1} total dissolved solids, corresponding to 6.4% of seawater salinity). We compare analytical solutions with results of fully coupled numerical simulations of variabledensity groundwater flow and solute transport in fractured rock. Current analytical solutions for solute transport in fractured rock do not account for fluid density variations and therefore fail to predict variabledensity transport. Using a mixed convection ratio analysis, we determine the hydrogeologic conditions where variabledensity transport is important and hence when analytical solutions fail to predict variabledensity transport in fractured rock. We present a modified velocity term that includes a densitydriven flow component in a vertical fracture to account for fluid density variations. The modified velocity term is incorporated into the standard Tang et al. (1981) analytical solution. The original densityinvariant analytical solution is shown to be applicable near a solute source and at early time, while the velocitymodified densityvariant solution gives very good results for longterm and farfield behavior. These results suggest that analytical solutions may still be useful for analyzing variabledensity transport in fractured rock. This study has implications for the analysis of dense plume transport in fractured rock where reliable longterm predictions are important.
 Publication:

Water Resources Research
 Pub Date:
 February 2009
 DOI:
 10.1029/2008WR007278
 Bibcode:
 2009WRR....45.2425G
 Keywords:

 Hydrology: Modeling;
 Hydrology: Computational hydrology;
 Hydrology: Groundwater hydrology;
 Hydrology: Groundwater transport;
 density;
 fracture;
 model;
 analytical;
 numerical