Core Concepts
This process naturally removes LNAPL via microbes, volatilization, and dissolution.
What is Natural Source Zone Depletion?
Elevated soil gas CO₂ signals this ongoing process.
What is hydrocarbon biodegradation?
NSZD rates are typically reported in gallons per acre per this period.
What is year?
NSZD is best when risk is controlled and these timelines are acceptable.
What are cleanup timelines?
LNAPL thickness is stable, CO₂ is high .... this indicates ongoing natural cleanup.
What is NSZD reducing mass?
The acronym for Light Non-Aqueous Phase Liquid.
What is LNAPL?
Low oxygen in soil gas usually indicates microbes are doing this.
What is consuming oxygen during NSZD?
This type of measurement directly estimates NSZD rates by monitoring CO₂ leaving the soil.
What is CO₂ efflux measurement?
Before relying solely on NSZD, you must confirm the plume is stable and this risk is absent.
What is immediate receptor risk?
Regulators ask for proof of NSZD .... the best response is to show multiple lines of this.
What is evidence (CO₂, temperature, soil gas, modeling)?
NSZD occurs through three main mechanisms: dissolution, bioremediation and this.
What is volatilization?
High subsurface methane suggests this type of biodegradation.
What is anaerobic biodegradation?
This method uses heat differences to estimate NSZD.
What is the temperature gradient method?
A major limitation of NSZD is that it proceeds at this pace.
What is relatively slow?
Relying solely on NSZD could take too long to achieve this.
What is cleanup completion?
Of the three NSZD mechanisms, this one usually dominates long-term mass loss.
What is biodegradation?
Measuring this temperature-related change helps estimate NSZD rates.
What is heat from microbial activity?
When NSZD rates rise, this happens to natural mass removal.
What is it becomes faster?
Combining active remediation with NSZD is smart because active methods do this.
What is remove bulk mass?
Stakeholders sometimes resist NSZD because it appears this way.
What is passive and slow?
The main products of aerobic NSZD are carbon dioxide and this.
What is water?
If oxygen is near zero and methane is high, this is happening underground.
What is anaerobic biodegradation?
After stopping active remediation, this indicator often spikes due to microbial rebound.
What is CO₂ flux?
If NSZD alone is too slow but risk is low, the best action is to do this.
What is supplement with active remediation?
NSZD is preferable to active methods when this type of risk is low.
What is environmental or receptor risk?