What is NAPL contamination?

What is NAPL contamination?

Non-aqueous phase liquids, or NAPLs, are organic liquid contaminants that do not dissolve in, or easily mix with, water (hydrophobic), like oil, gasoline and petroleum products. NAPLs tend to contaminate soil and groundwaters for very long period of time: they are persistent organic pollutants (POPs).


Mixed NAPL (Solvents) Wastes: Hazardous waste sites usually involve the co-disposal of various chemicals which collectively float or sink as a NAPL. For example, a mixed DNAPL composed primarily of bis, 2-chloro-ethyl ether (38%), DCA (2.5%), styrene, TCE, and an oil carrier was found at a Superfund site in Texas.

What are DNAPL and Lnapl?

Nonaqueous phase liquids are typically classified as either light nonaqueous phase liquids (LNAPLs) which have densities less than that of water, or dense nonaqueous phase liquids (DNAPLs) which have densities greater than that of water.

What is residual NAPL?

Residual NAPL is defined as immobile, nonwater entrapped NAPL that does not drain from the pore spaces and is conceptualized as being either continuous or discontinuous.

What does aqueous phase mean?

n. The water portion of a system consisting of two liquid phases, one that is primarily water and a second that is a liquid immiscible with water.

What does NAPL stand for?

NAPL stands for Non-Aqueous Phase Liquids. (Chlorinated compounds or petroleum hydrocarbon. products) LNAPL refers to Light Non-Aqueous Phase Liquids (those. that are lighter than water, generally petroleum.

How do you remediate TCE?

TCE usually is remediated through pump and treat, using either air stripping or granular activated carbon, but there are many innovative cleanup methods—physical, chemical, thermal, and biological—that have been applied successfully to remove TCE from soil and ground water or to convert it into nonhazardous compounds.

How do you remove TCE from soil?

Air stripping can be used to remove the majority of TCE, followed by adsorption which is used to polish the stripper effluent. This approach will lower construction costs of the air stripper and increase life expectancy of the adsorbent.

Is toluene a NAPL?

Examples of LNAPLs are benzene, toluene, xylene, and other hydrocarbons. …

Is diesel a LNAPL or DNAPL?

Common LNAPLs are gasoline and diesel fuel and typical DNAPLs are chlorinated hydrocarbons such as trichloroethylene (TCE), a common solvent.

What is free phase contamination?

Product Recovery – Deals with the “Free Phase”, recovery of the contaminant mass that has yet to partition into other phases in the various environmental media.

How is Dnapl treated?

Other technologies that have been used for treating DNAPL sources include ground water extraction (e.g., P or recirculation), excavation, and containment (e.g., engineered caps and slurry walls).

What are the four phases of NAPL in the unsaturated zone?

NAPLs in the unsaturated zone mainly occur in four phases: (1) immiscible free-phase (pure NAPL product), (2) residual phase (adsorbed on solid particles), (3) gaseous phase (VOCs in soil gas), and (4) aqueous phase (dissolved in water).

How are NAPL contaminants partitioned in the subsurface?

The processes causing partitioning of NAPL contaminants (in the subsurface) between the air-water-solid phases are mostly governed by volatilization, solubilization, and adsorption/desorption mechanisms.

How does evaporation affect gasoline-derived NAPL?

Gasoline-derived NAPL recovered from monitoring wells represents the free phase gasoline typically residing in soils at or near the water table. In general, these may appear less impacted by evaporation than surface and subsurface soil samples.

How do NAPLs move through the soil?

When NAPLs are spilled into the subsurface, they move downward in irregular paths, following a trail containing the largest available pores. If enough NAPL is spilled, it will accumulate at the top of the saturated zone (LNAPL) or on top of layers with small pores.