Remediation Technologies Flashcards

Phytostabilization is distinguished from phytoextraction in that phytostabilization:

Answer: Immobilizes contaminants in the root zone, preventing uptake or leaching, without harvesting the plant

Phytostabilization uses tolerant plants to immobilize contaminants (particularly metals) through root-zone sorption and precipitation, reducing bioavailability without accumulating them in harvestable tissue.

The 'rebound effect' in groundwater remediation occurs when:

Answer: Contaminant concentrations rise again after active remediation is paused or terminated

Rebound occurs when residual contamination (sorbed to soil, trapped in low-permeability zones) slowly re-dissolves into groundwater after pumping or active treatment stops, causing concentration increases.

High-temperature thermal treatment of hazardous waste in a rotary kiln incinerator requires a minimum destruction and removal efficiency (DRE) of:

Answer: 99.99% (four nines) for principal organic hazardous constituents (POHCs)

RCRA regulations require hazardous waste incinerators to achieve at least 99.99% DRE for each POHC, meaning only 0.01% or less of the input POHC mass may exit the stack.

An aerobic bioventing system differs from soil vapor extraction (SVE) primarily in that bioventing:

Answer: Uses low air flow rates designed to deliver oxygen for in situ biodegradation rather than to volatilize contaminants

Bioventing uses low air flow rates to supply oxygen to indigenous microbes for in situ aerobic biodegradation of petroleum hydrocarbons, while SVE uses higher flows to physically extract VOCs to the surface.

When selecting between ex situ and in situ remediation approaches, a key advantage of in situ treatment is:

Answer: Avoidance of excavation and material handling, reducing worker exposure and site disturbance

In situ treatment treats contaminants where they are, eliminating excavation risks, dust generation, transport costs, and worker exposure associated with ex situ approaches.

Under CERCLA, the 'source control' element of a remedy focuses on:

Answer: Eliminating or reducing the release of contaminants from the primary source area

Source control measures address the primary contaminant source (e.g., soil hot spots, NAPLs, contaminated structures) to stop or significantly reduce ongoing releases that feed the dissolved-phase plume.

Activated carbon amendment injected into groundwater as a colloidal suspension functions primarily as:

Answer: A sorbent to immobilize hydrophobic organic contaminants and reduce their bioavailability

Colloidal activated carbon (e.g., PlumeStop) adsorbs dissolved hydrophobic organics (chlorinated solvents, PAHs) from groundwater, dramatically reducing aqueous-phase concentrations and bioavailability.