Evaluating transverse dispersivities obtained from large laboratory and field datasets

Transverse dispersivity 𝛼_𝑇[𝐿], both horizontal (𝛼_𝑇ℎ [L]) and vertical (𝛼_𝑇𝑣 [L]), is frequently cited as a major source of error in groundwater contamination modeling. These dispersivities depend on several subsurface factors (e.g., sediment structure, grainsize); however, their sub-centimeter scale makes accurate estimation for field data highly uncertain. Consequently, only limited highly reliable field transverse dispersivity data can be found in the literature, leading to their insufficient characterization and dependence on quantities’ affecting reactive transport in the groundwater.

This study evaluates over 150 laboratory transverse dispersivity data, obtained from the literature, considering various flow and transport factors (e.g., grainsize, flow-velocity). The evaluation considers the combined data as a global dataset, i.e., independent of a particular experimental setup. The analysis leads to a development of a new transverse dispersivity model: 𝐷_𝑇= 𝐷_𝑝+ 0.23𝐷_𝑎𝑞Pe^0.59, (similar to Olsson et al., 2007); 𝐷_𝑇, 𝐷_𝑝 and 𝐷_𝑎𝑞 [L²T⁻¹] denote the transverse dispersion coefficient, pore and aqueous diffusion coefficients, respectively and Pe [-] is the Peclet number.

Field based 𝛼_𝑇ℎ and 𝛼_𝑇𝑣 are obtained using field site data (over 60 sites, mostly BTEX sites) by inverting an Analytical Element Model (AEM) developed by Köhler et al (2026). The maximum plume length (𝐿_max) in the dataset was used as the controlling factor, while source geometry and different combination of reactants (O₂, NO₃, SO₄ etc.), among others, served as the experimental variables in quantifying 𝛼_𝑇. The obtained results for both 𝛼_𝑇ℎ and 𝛼_𝑇𝑣 range from 1mm to 60 mm and generally agree with literature results when the source thickness is much smaller (< 50%) than aquifer thickness and when combination of several reactants are considered. For all other scenarios, the obtained results significantly differ (up to order of magnitude) from the published values. In general, laboratory dispersivities are substantially smaller compared to field data. Furthermore, field 𝛼_𝑇ℎ is mostly less than 5 times compared to 𝛼_𝑇𝑣. The ongoing work involves analyzing obtained 𝛼_𝑇 results with different field properties (e.g., hydraulic  conductivity) and  applying the findings to contaminated sites.

References:

Köhler, A. V., J. R. Craig, P. K. Yadav, and R. Liedl. 2026. An Analytic Element Method solution for simulating multiple steady-state groundwater contamination scenarios. J. Contam. Hydrol. 276, January: 104733, https://doi.org/10.1016/j.jconhyd.2025.104733.

Olsson, A.H., Grathwohl, P. (2007): Transverse Dispersion of Non-reactive Tracers in Porous Media: A new Nonlinear Relationship to Predict Dispersion Coefficients. J. Contam. Hydrol., 92, 3-4, 149 – 161