NGWA Darcy Lecture Series presented by Kamini Singha

A Tale of Two Porosities: Exploring Why Contaminant Transport Doesn’t Always Behave the Way It Should

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  • August 18
    Fri 3:00PM –  4:00PM
    1. $0.00 incl. GST


A Tale of Two Porosities: Exploring Why Contaminant Transport Doesn’t Always Behave the Way It Should

Presented by Kamini Singha, Ph.D. 
Transport through preferential flowpaths is important in a broad range of scientific disciplines. In hydrology, the ability to quantify subsurface transport is an issue of paramount importance due to problems associated with groundwater contamination. Observational challenges and complexity of hydrogeological systems lead to severe prediction challenges with standard measurement techniques. One important example of a prediction challenge is “anomalous” solute-transport behavior, defined by characteristics such as concentration rebound, long breakthrough tailing, and poor pump-and-treat efficiency.

These phenomena have been observed at research and aquifer-remediation sites in diverse geologic settings, and are not predicted by classical theory. Numerous conceptual models have been developed to explain anomalous transport, such as the presence of two distinct populations of pores — one where solutes are highly mobile and another where they are not — but verification and inference of controlling parameters in these models in situ remains problematic, and often estimated based on data fitting alone. Recent tests using simple electric geophysical methods directly measure the process of mobile-immobile mass transfer and allow estimation of parameters controlling anomalous transport.

This lecture presents a rock-physics framework, an experimental methodology, and analytical expressions that can be used to determine parameters controlling anomalous solute transport behavior from colocated hydrologic and electrical geophysical measurements in a series of settings, including groundwater and surface water/groundwater systems. The long-term goals of this work are to contribute toward improving the predictive capabilities of numerical models and enhancing the fidelity of long-term groundwater monitoring frameworks.


The Critical Role of Trees in Critical Zone Science: An Exploration of Water Fluxes in the Earth’s Permeable Skin​

Earth’s “critical zone” — the zone of the planet from treetops to base of groundwater — is critical because it is a sensitive region, open to impacts from human activities, while providing water necessary for human consumption and food production. Quantifying water movement in the subsurface is critical to predicting how water-driven critical zone processes respond to changes in climate and human perturbation of the natural system. While shallow soils and aboveground parts of the critical zone can be easy to instrument and explore, the deeper parts of the critical zone — through the soils and into rock — are harder to access, leaving many open questions about the role of water in this environment.

This presentation opens the black box in the subsurface and sheds light on a few key subsurface processes that control water movement and availability: linkages between changes in evapotranspiration and subsurface water stores, water movement in three dimensions over large areas, and potential control of slope aspect on subsurface permeability. Geophysical tools are central to the quantitative study of these problems in the deeper subsurface where we don’t have easy access for observation. In particular, this lecture explores the role of trees in the critical zone, and their connection to soil moisture, groundwater and streams through innovative imaging​.

The 2017 Darcy Lecture in Groundwater Sciences is made possible by grants from:

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