Quantifying NSZD rates can be challenging

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Onshore petroleum spills pose unique environmental challenges requiring intensive risk assessment and management. Biodegradation, which is considered the most significant process in Natural Source Zone Depletion (NSZD), is carried out by naturally occurring soil microbes that readily consume and degrade petroleum. This process results in total contaminant mass reduction.

The Interstate Technology & Regulatory Council (ITRC) LNAPL Guidance Document and the recent American Petroleum Institute (API) NSZD Guidance Document include methods for estimating biodegradation (NSZD) rates. However, NSZD rates are not easily quantified. Most monitoring techniques estimate total mass reduction without eliminating non-contaminant signals or correcting for temporal variations in site conditions.

 

 

How E-Flux Fossil Fuel Traps quantify NSZD

Fossil Fuel Traps are passive samplers that measure naturally occurring biodegradation of Light Non-Aqueous Phase Liquids (LNAPL) such as petroleum by capturing the CO₂ emitted from the contaminated soil and groundwater using a sorbent.

A Fossil Fuel Trap installed in the field showing the transport of Modern CO₂, Fossil Fuel CO₂, and atmospheric CO₂ contributions.

A Fossil Fuel Trap installed in the field showing the transport of Modern CO₂, Fossil Fuel CO₂, and atmospheric CO₂ contributions.

Our traps include:

Time-integrated average flux measurements to account for diurnal and daily fluctuations.

The typical deployment time for Fossil Fuel Traps is 14 days (although can be modified within a range of 5-28 days without further modification of the traps). Measuring the total CO₂ flux over an extended period provides a time-averaged estimate of soil CO₂ flux that accounts for temporal variability in site conditions, including atmospheric pressure fluctuations and weather changes.

Patented dual-sorbent layer technology to avoid interference with the normal soil gas respiration regime and avoid atmospheric CO₂ interference.

Each Fossil Fuel Trap contains two layers of sorbent; the top layer captures ambient CO₂, which is used to eliminate ambient interference in the bottom layer, while the bottom layer absorbs soil-emitted CO₂. Since the Fossil Fuel Trap is open to the atmosphere and the CO₂ is captured by the sorbent and does not build up within the head space, the gas flow is not disturbed and the diffusion gradient is not altered.

¹⁴C analysis to differentiate fossil fuel-generated CO₂ from modern CO₂ interference.

Modern CO₂ contributions (i.e., from natural soil respiration processes) can be significant and need to be subtracted from the net CO₂ flux measurement before an accurate biodegradation rate can be estimated. To eliminate this modern carbon interference, every bottom layer of the sorbent is precisely analyzed for its radiocarbon (¹⁴C) content (ASTM D6866-18).

The Fossil Fuel Traps represent many years of testing and refinement, including many successful world-wide deployments.

 

What can the Fossil Fuel Traps do for you?

E-Flux’s patented CO₂ trap method provides all you need to map LNAPL sources, quantify NSZD rates, and monitor NSZD remediation efforts.

 

Map LNAPL sources

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Map LNAPL sources

A robust and accurate site map is the foundation for site management and remediation. However, most mapping techniques are intrusive and are not cost-effective. The few non-intrusive mapping techniques that currently exist are not specific to petroleum-based biodegradation, nor do they consider environmental variability over time. This makes their use questionable, a non-ideal situation when planning remediation. NSZD and soil gas transport play an important role when mapping oil spills at surface level, as the contaminants generate CO₂ as a byproduct of biodegradation.

The Fossil Fuel Traps provide a non-intrusive and time-integrated technique with ¹⁴C content analysis that delivers a clear indication of biodegradation of LNAPL on the surface which allows for source delineation. This makes the Fossil Fuel Traps a valuable, cost-effective decision-making tool for the placement of wells and a starting point for future remediation or NSZD monitoring efforts.

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A robust and accurate site map is the foundation for site management and remediation. Read more...

Map LNAPL sources

A robust and accurate site map is the foundation for site management and remediation. However, most mapping techniques are intrusive and are not cost-effective. The few non-intrusive mapping techniques that currently exist are not specific to petroleum-based biodegradation, nor do they consider environmental variability over time. This makes their use questionable, a non-ideal situation when planning remediation. NSZD and soil gas transport play an important role when mapping oil spills at surface level, as the contaminants generate CO₂ as a byproduct of biodegradation.

The Fossil Fuel Traps provide a non-intrusive and time-integrated technique with ¹⁴C content analysis that delivers a clear indication of biodegradation of LNAPL on the surface which allows for source delineation. This makes the Fossil Fuel Traps a valuable, cost-effective decision-making tool for the placement of wells and a starting point for future remediation or NSZD monitoring efforts.

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Quantify NSZD rates

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Quantify NSZD rates

Quantifying NSZD rates is valuable in determining the appropriate timing, scale, and aggressiveness of LNAPL remediation efforts. The Interstate Technology and Regulatory Council (ITRC) recommends including NSZD as part of a comprehensive remedial site plan.

  • Our ¹⁴C analysis differentiates modern CO₂ contributions from Fossil Fuel CO₂ to accurately quantify biodegradation rates.
  • Our patented time-integrated flux measurements account for daily ambient changes.
  • Our dual-sorbent layer technology avoids interferences with the normal soil gas respiration regime and atmospheric CO₂ interference.
“The use of ¹⁴C is arguably the best, most quantitative means for background correction, and it should be considered of utmost reliability.” API NSZD guidance document



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Quantifying NSZD rates is valuable in determining the appropriate timing and magnitude of LNAPL remediation efforts. Read more...

Quantify NSZD rates

Quantifying NSZD rates is valuable in determining the appropriate timing, scale, and aggressiveness of LNAPL remediation efforts. The Interstate Technology and Regulatory Council (ITRC) recommends including NSZD as part of a comprehensive remedial site plan.

  • Our ¹⁴C analysis differentiates modern CO₂ contributions from Fossil Fuel CO₂ to accurately quantify biodegradation rates.
  • Our patented time-integrated flux measurements account for daily ambient changes.
  • Our dual-sorbent layer technology avoids interferences with the normal soil gas respiration regime and atmospheric CO₂ interference.
“The use of ¹⁴C is arguably the best, most quantitative means for background correction, and it should be considered of utmost reliability.” API NSZD guidance document



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Monitor NSZD Remediation efforts

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Monitor NSZD Remediation efforts

NSZD has been shown to occur at most petroleum-contaminated sites. If NSZD is ignored, the total contaminant mass is considered constant throughout time unless remediation takes place. Following remediation, the total contaminant mass is estimated to be equal to the original contaminant mass minus the mass reduction by remediation. 

Monitoring NSZD rates throughout remediation efforts provide a baseline for evaluating active remedies.

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If NSZD is ignored, the total contaminant mass is considered constant throughout time unless remediation takes place. Read more...

Monitor NSZD Remediation efforts

NSZD has been shown to occur at most petroleum-contaminated sites. If NSZD is ignored, the total contaminant mass is considered constant throughout time unless remediation takes place. Following remediation, the total contaminant mass is estimated to be equal to the original contaminant mass minus the mass reduction by remediation. 

Monitoring NSZD rates throughout remediation efforts provide a baseline for evaluating active remedies.

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