Evaluation of VOC fluxes at the soil-air interface using different flux chambers and a quasi-analytical approach

Abstract

Dense nonaqueous-phase liquids (DNAPLs) spilled on the soil migrate vertically depending upon gravity and capillary forces through the unsaturated zone of the porous aquifer, forming a vapour plume. These volatile organic compounds (VOCs) can be transferred by advection-diffusion to the groundwater or to the atmosphere. Evaluating DNAPL vapour fluxes at the soil-air interface is one of the key challenges in the remediation of contaminated sites. This work discusses the results of a large-scale vapour plume experiment with a well-defined trichloroethylene (TCE) spill, including a sequential raising and lowering of the water table, where the TCE vapour fluxes at the soil surface were experimentally quantified in two ways: (i) directly, with measurements at the soil-air interface using different flux chambers at various operational modes under both transient and steady-state conditions of the vapour plume, and (ii) indirectly, using a quasi-analytical approach based on soil gas measurements. It was shown that upward displacement of the water-air front during the controlled raising of the water table (approximately 10 cm h −1 ) increased the TCE vapour flux measured at the soil surface by factors of 4 to 10. Under steady-state transport conditions, TCE vapour fluxes measured using five types of flux chambers and three operational modes were similar. The effects of the flux chamber geometry, the accumulation of TCE vapours in the chamber headspace or the air recirculation at a low flow rate on the measured TCE vapour fluxes were low. At steady-state transport conditions, TCE vapour fluxes measured with the flux chambers and estimated using the quasianalytical approach were of the same order of magnitude. However, under transient conditions of the vapour plume, the TCE vapour flux predicted by the quasi-analytical approach greatly underestimated or overestimated the real TCE vapour flux at the soil-air interface.

Soil carbon dioxide fluxes to atmosphere: The role of rainfall to control CO2 transport

“…Uncertainties in the experimental CO2 mass fluxes measured with this flux chamber were calculated according to the method used by Cotel et al (2015). Thus, uncertainties in the flux measurements were determined using a total derivative expansion for correlated variables of FCO2:…”

“…The gas flux is then calculated by relating the concentration increase during a given time to the chamber volume and the concerned soil surface area. Due to the low cost of this non-intrusive method which is easy to set up, it has been widely used (Cotel et al, 2015;Elío et al, 2016;Jassal et al, 2005;Matthias et al, 1980;Norman et al, 1997;Reinhart et al, 1992;Rochette and Hutchinson, 2005;Viveiros et al, 2008). Indeed, this technique allows to carry out in situ measurements quickly and on a large number of points compared to other techniques (Schroder et al, 2016).…”

New Estimation of the NOx Snow‐Source on the Antarctic Plateau

“…Flux chambers are the most widely used equipment to quantify gaseous emissions from solid or liquid surface sources (Besnard & Pokryszka, 2005;Cotel et al, 2015;Pokryszka & Tauziède, 1999;Verginelli et al, 2018), and they are widely used nowadays to assess emissions of pollutants into the atmosphere from the surface (Scheutz et al, 2008;Sihota et al, 2010;Tillman et al, 2003). A dynamic FC method developed to measure production rates from hazardous waste sites employs an inert gas that is continuously introduced at a controlled rate while an equivalent amount of gas is allowed to leave the chamber (Eklund, 1992) air at the outlet of the chamber analyzed, similar to Cotter et al (2003) laboratory FC experiment.…”

Numerical model for static chamber measurement of multi-component landfill gas emissions and its application

“…However, estimation models for landfill gases transport in the static chamber are limited to either empirical or single component models (Livingston et al 2005 ; Senevirathna et al 2007 ; Sahoo and Mayya, 2010 ; Parkin et al, 2012 ). For example, the traditional advection–diffusion (AD) model was widely used for investigating gas emission into the chamber headspace (Webb and Pruess 2003 ; Sahoo and Mayya, 2010 ; Cotel et al, 2015 ). Webb and Pruess ( 2003 ) pointed out that AD model may accurately describe emission of gases from a limited sample set on a single landfill site although it may over predict fluxes of traced gas for a lower gas permeability ( k g < 10 –13 m 2 ).…”