Check out our video of GGS Scotland colleagues conducting a flux box survey for one of our projects.
What are flux box surveys?
A flux box survey, sometimes called a closed chamber test, is a useful technique to establish the rate at which ground gases are migrating through the surface of a site.
A chamber of known volume and footprint - the flux box - is sealed to the site surface using a mix of damp sand and bentonite powder. This ensures the test area is isolated before we begin taking measurements.
We then use high-precision handheld instruments to measure methane (CH4) and carbon dioxide (CO2) concentrations at set intervals. We then record the results at each measurement interval, typically to parts per million (ppm) resolution. We carry out each test for between 15 - 60 minutes, depending on to site conditions.
We can then calculate the rate of flux into the chamber for each gas, using the concentration measurements along with the chamber volume and footprint.
What are they useful for?
Flux box surveying as a technique has been around for over twenty years. And it remains a simple and effective ground gas monitoring technique.
Unlike many other monitoring techniques, flux box surveys directly measure the rate of ground gas flux through the specific geology of a site. They target actual vertical ground gas migration which is the parameter which typically drives ground gas risk.
Flux box surveys are most commonly used in the landfill sector. However, they can also provide useful evidence when assessing ground gas risks in new and existing developments.
What benefits can they bring?
The benefits that flux box surveys can bring to your project include:
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adds additional spatial coverage and line of evidence for relatively little time and effort
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helps to understand the actual ground gas risk posed
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highly targeted to the specific ground gas parameter you are interested in measuring
So, in summary, this simple technique can quickly provide an additional line of evidence to your ground gas risk assessment, and help refine your conceptual site model.
Want to know more? Then feel free to get in touch.