Push-pull tests for estimating effective porosity: expanded analytical solution and in situ application

The analytical solution describing the one-dimensional displacement of the center of mass of a tracer during an injection, drift, and extraction test (push-pull test) was expanded to account for displacement during the injection phase. The solution was expanded to improve the in situ estimation of e...

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Bibliographic Details
Published in:Hydrogeology journal 2018-03, Vol.26 (2), p.381-393
Main Authors: Paradis, Charles J., McKay, Larry D., Perfect, Edmund, Istok, Jonathan D., Hazen, Terry C.
Format: Article
Language:English
Subjects:
Aquatic Pollution
Aquifers
Data processing
Displacement
Earth and Environmental Science
Earth Sciences
Effective porosity
Effectiveness
Geology
Geophysics/Geodesy
Groundwater
Hydrogeology
Hydrology/Water Resources
Injection
Mathematical analysis
Mathematical models
Porosity
Spatial variability
Spatial variations
Test wells
Tests
Tracers
Unconfined aquifers
Waste Water Technology
Water Management
Water Pollution Control
Water Quality/Water Pollution
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Summary:The analytical solution describing the one-dimensional displacement of the center of mass of a tracer during an injection, drift, and extraction test (push-pull test) was expanded to account for displacement during the injection phase. The solution was expanded to improve the in situ estimation of effective porosity. The truncated equation assumed displacement during the injection phase was negligible, which may theoretically lead to an underestimation of the true value of effective porosity. To experimentally compare the expanded and truncated equations, single-well push-pull tests were conducted across six test wells located in a shallow, unconfined aquifer comprised of unconsolidated and heterogeneous silty and clayey fill materials. The push-pull tests were conducted by injection of bromide tracer, followed by a non-pumping period, and subsequent extraction of groundwater. The values of effective porosity from the expanded equation (0.6–5.0%) were substantially greater than from the truncated equation (0.1–1.3%). The expanded and truncated equations were compared to data from previous push-pull studies in the literature and demonstrated that displacement during the injection phase may or may not be negligible, depending on the aquifer properties and the push-pull test parameters. The results presented here also demonstrated the spatial variability of effective porosity within a relatively small study site can be substantial, and the error-propagated uncertainty of effective porosity can be mitigated to a reasonable level (
ISSN:1431-2174
1435-0157
DOI:10.1007/s10040-017-1672-3