An analysis of hydrodispersive transfer in aquifers

Abstract

This work is concerned with the nonreactive transport of solute materials in groundwater, or hydro‐dispersive transfer. Several types of flow fields are considered: linear (or uniform) flow with one‐ and two‐dimensional dispersion and radial flow under diverging and converging conditions. The analysis includes the two main possibilities for introduction of solutes into an aquifer: continuous and instantaneous (or slug) injection. Different solutions from the literature plus some original solutions for dispersion in a linear flow field have been unified by transposing the solutions into dimensionless variables of concentration (CR), time (tR), and the Peclet number (P). This permits an analysis of the errors committed in some commonly used approximations for dispersion as a function of P. In the case of radial flow, a numerical method using finite differences has been developed that can be applied to either diverging or converging flow problems. Results in dimensionless form when compared to the only analytical approximations that could be found (for continuous injection in a diverging flow field) indicate that the approximate solutions are in error when P ≤ 10. The radial flow results are also compared to those for linear flow fields to demonstrate that in most cases either approach can be used as long as P > 3. A series of dimensionless type curves has been developed showing CR versus tR for practical ranges of P. A simple method of interpreting tracer tests is proposed using these type curves. One is able to directly determine dispersivity and kinematic porosity using curve matching techniques. Results from some recent field tests in France are analyzed using this approach. There is definite confirmation from these investigations that the apparent (macroscopic) dispersivity can vary depending on the distances used in the field.

Review of the use of Péclet numbers to determine the relative importance of advection and diffusion in low permeability environments

“…the distance from the contaminant source (m), D L is the longitudinal hydrodynamic dispersion coefficient (m 2 /s), V D is the Darcy velocity (m/s) and n e is the effective porosity for advection (Fetter 1999;Sauty 1980). This Péclet number occurs in the dimensionless form of the analytical solutions (Ogata and Banks 1961) of the advection-dispersion equation for aquifers.…”

Remediation of RDX- and HMX-contaminated groundwater using organic mulch permeable reactive barriers

“…where, (1) is valid for higher Peclet numbers (i.e., greater than 10) as it is an approximation of the step-response solution of the advection-dispersion equation for a conservative substance, where the contribution from the second term of the solution is assumed to be negligible (Sauty, 1980;Fetter, 1999). Under high Peclet number conditions, the effects of molecular diffusion become negligible compared to the advection and the longitudinal hydrodynamic dispersion coefficient, D L , can be effectively described using the following expression:…”

“…Hydrodynamic parameters can be determined by conducting a stepresponse tracer test using a tracer such as chloride, which is both non-reactive and non-sorbing. The change in concentration of the tracer in the column effluent with time can be described by the solution known as Sauty Approximation (Sauty, 1980):…”

An integrated model for assessing the risk of TCE groundwater contamination to human receptors and surface water ecosystems

“…It currently consists of a source release module, a contaminant transport module and a human health impact assessment module. Both mass release and contaminant transport in groundwater are quantified using transient models that are based on analytical approaches (Sauty, 1980;Huntley and Beckett, 2002;Eberhardt and Grathwohl, 2002;Peter et al, 2008). The existing contamination and its further development can be evaluated on the basis of contaminant mass fluxes, concentrations, and risk indices (carcinogenic/non-carcinogenic).…”