Soil Flux: A Key Measurement to Understand Natural Attenuation of Petroleum Hydrocarbons in the Subsurface

The agronomic field has recognized for a long time that soils generate CO2, a “CO2 efflux”. In many soils, this CO2 flux is the result of natural soil respiration processes resulting from microbial and plant activity. This occurs in what is known as the “root zone”. In soils impacted from hydrocarbons (LNAPL), microbial degradation of the LNAPL also results in a net contribution of CO2 to the CO2 efflux. This latter process is known as natural attenuation (NA), and occurs where the LNAPL is, typically close to the groundwater level. Vadose zone conditions, such as temperature, water and LNAP saturation, determine the rate of LNAPL natural attenuation.

Together with carbon dating methodologies (i.e., 14C analysis), carbon trapping is a simple, cost-effective way to monitor natural attenuation. E-Flux CO2 traps easily enable allocating contributions from natural soil processes (modern carbon CO2 efflux) and from LNAPL natural attenuation (fossil fuel), The results unambiguously indicate what portion of the CO2 efflux is from LNAPL microbial degradation.

Industry Spotlight: Soil Flux and LNAPL Degradation

E-Flux technology has been used in about 20 sites impacted with petroleum hydrocarbon. Previous to field use, this technology was tested in the lab, to demonstrate quantitative recovery of the sorbent and the lack of interference of the trap hardware with gas transport in soils.

The traps often reveal that the rate of LNAPL degradation rates at petroleum contaminated sites are in the order of 1,000s to 10,000s of gallons per acre per year. Such rates measured with the traps are important and often rival the rates achieved by active remedies (i.e., hydraulic recovery).

As a result, E-Flux carbon traps are a valuable tool in determining the appropriate timing, scale and aggressiveness of LNAPL remediation.

E-Flux CO2 Traps are the Ideal Solution For:

  • Identification of zones where LNAPL Natural Attenuation is active
  • Long-term monitoring
  • Remote or limited access sites
  • Cost-controlled budgets
  • Minimizing environmental footprint of monitoring activities
  • Documenting natural source zone depletion (NSZD)