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Cleanup of DNAPLs: A Widespread Challenge
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| A
Quick Look |
| Most commonly occurring DNAPLs
typically are industrial chlorinated solvents such as TCE, PCE, and
carbon tetrachloride (CCl4). Other prevalent DNAPLs include creosote,
pentachlorophenol (PCP), and PAH coal tars. |
| DNAPLs are present at 60
to 70 percent of the Superfund NPL sites. |
| Among the number of innovative
technologies that are demonstrating success and providing promising
results in reducing DNAPL contamination are in situ thermal treatment,
in situ chemical oxidation, and ISB. |
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It is estimated that billions of dollars will be spent by the private
and public sector to clean up sites contaminated with DNAPL. Denser than
water, DNAPLs tend to sink through the water table and form a product
pool on top of such impermeable soil layers as clay. DNAPLs also can sink
and migrate laterally through fractures in bedrock. Numerous variables
influence fate and transport of DNAPLs in the subsurface, and it can be
difficult to predict the path DNAPLs will take.
Because of these properties, DNAPLs act as a continuing source of contamination.
DNAPLs may cause serious, long-term contamination of groundwater and pose
a significant challenge to cleanup of the site, especially for established
technologies such as pump-and-treat. At sites with significant DNAPL contamination,
pump-and-treat systems may require several hundreds of years to clean
up the groundwater.
Sites likely contaminated with DNAPLs include dry cleaning facilities,
wood preservation sites, MGP sites, and solvent sites (industrial operations
using large quantities of solvents as well as solvent disposal and recovery
sites).
To accelerate the development and implementation of innovative technologies
for remediating DNAPLs in groundwater, the Interagency DNAPL consortium
(IDC) was formed. The consortium has developed a national action plan
that proposes collaborative efforts among federal agencies, private sector
entities, and responsible parties in research and development, technology
demonstrations, and full-scale technology deployment to reduce the perceived
risk associated with innovative technologies. The interagency agreement
supports the testing of new and existing technologies in side-by-side
demonstrations to compare cost and performance data that will be used
to expedite regulatory acceptance and use of innovative remedial technologies
at other sites.
EPA continues to support the evaluation and application of technologies
for the assessment and remediation of sites contaminated with DNAPLs.
In DNAPL Remediation: Selected Projects Approaching Regulatory Closure
STATUS UPDATE (EPA 542-R-04-016) (November 2004), EPA provides information
on the challenges of DNAPL characterization and remediation, and overview
of DNAPL remediation technologies, a description of DNAPL remediation
projects, and a summary of findings.
For more information see the following resources:
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Sunday, September 7, 2008
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