Dense Nonaqueous Phase Liquids (DNAPLs)Chromium VI
Dense Nonaqueous Phase Liquids (DNAPLs)
1,4-Dioxane
Mercury
MTBE
Perchlorate
POPs
PCBs
TCE
Other Contaminants
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Treatment Technologies
The treatment section provides a comprehensive overview of treatment technologies currently being applied to the remediation of DNAPLs. The primary focus is on technologies capable of remediating DNAPLs in a source zone, with secondary importance given to contaminants dissolved in the aqueous phase.
Most of the technologies described in this section can be used to address source-zone DNAPL, except for permeable reactive barriers, which are applicable only to contaminants in the dissolved phase but appear here because they also serve to contain contaminant migration. Although individual technologies can be successful in removing significant mass from a DNAPL source, a sequential combination of technologies or the application of different technologies to various target treatment zones within the contaminated area may be more likely to meet remedial objectives. The planned combined use of several technologies is often referred to as a "treatment train" or "combined remedy" approach and can encompass both conventional and innovative techniques.
Selection of treatment options is constrained by regulations, cost, extent of contamination, presence of other contaminants, and a large number of other site-specific variables. Generally, a DNAPL site will have three major zones of contamination to consider: a source zone containing very high concentrations of potentially mobile DNAPL, a residual zone through which mobile DNAPL has already moved, and one or more plumes of dissolved contaminant emanating from the first two zones when groundwater is present. Recent research has also identified a fourth source of contamination, a residual zone through which the contaminated plume has moved, and where contaminant has diffused or sorbed onto the aquifer solids. These contaminated media can be a continuous source of contamination until addressed (Chapman and Parker 2005). Vapor intrusion concerns may also require that mitigation actions be put in place even if the source or groundwater do not require treatment.
The physical and chemical properties of DNAPLs, including their relatively low solubility, high specific gravity, and tendency to diffuse into fine-grained materials in an aquifer, can impact the effectiveness of conventional remedial technologies, such as groundwater pump and treat. The presence of DNAPLs also can make it more difficult to reach regulatory closure, which is a factor in the increasing use of source reduction technologies to remove or destroy DNAPLs in the subsurface. Once a DNAPL source is addressed, residual groundwater plumes may be more amenable to less aggressive remedial techniques, such as monitored natural attenuation.
Soil heterogeneity is also an important factor affecting DNAPL fate and transport. The site stratigraphy affects the distribution of the DNAPL in the subsurface, and the contaminant architecture then plays a critical role in the selection of the overall remedial approach. The success of any in situ technology depends both on its ability to perform in a particular subsurface environment and to alter DNAPL properties to the extent necessary for recovery or remediation. DNAPL fate and transport processes are discussed in the Chemistry and Behavior section.
The desired outcomes of source depletion include reduction of DNAPL mobility, if mobile DNAPL is present; reduction in environmental risk to receptors; reduced timeframe of groundwater remediation; and reduction of the rate of mass discharged from the DNAPL source zone. These results could then lead to enhanced efficiency of complementary technologies used for groundwater remediation, as well as reduction in life-cycle costs.
The following materials provide general overviews of technologies that have been used successfully to address DNAPL-contaminated sites.
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General Technology Overviews |
Abstracts of Journal/Conference Papers |
Specific Technologies
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Annual Report: DNAPL Source Zone Initiative
SERDP & ESTCP DNAPL Source Zone Initiative, 18 pp, 2004
This report discusses research needs and initiatives being taken on DNAPL source removal by the Department of Defense.
Assessing the Feasibility of DNAPL Source Zone Remediation: Review of Case Studies
Geosyntec Consultants
Naval Facilities Engineering Command, CR-04-002-ENV, 290 pp, 2004
This study provides an overview of technologies and qualitatively examines the experiences of deploying these technologies at over 100 sites.
Contaminants in the Subsurface: Source Zone Assessment and Remediation
National Research Council, Committee on Source Removal of Contaminants in the Subsurface.
National Academies Press, Washington, DC. ISBN: 030909447X, 383 pp, 2004
This report was researched and prepared at the request of the U.S. Army, which is why some attention is given chemical explosives, although chlorinated solvent DNAPLs are the primary focus. After discussing the definition of 'source zone' and the characterization thereof, the report reviews the suite of technologies available for source remediation and their ability to reach a variety of cleanup goals, from meeting regulatory standards for ground water to reducing costs. The report proposes elements of a protocol for accomplishing source remediation that should enable a project manager to decide whether and how to pursue source remediation at a particular site.
Dense Non-Aqueous Phase Liquids (DNAPLs): Review of Emerging Characterization and Remediation Technologies
Interstate Technology & Regulatory Council (ITRC). DNAPLs-1, 81 pp, 2000
Reviews three general types of emerging DNAPL characterization technologies: geophysical techniques, direct push probes, and tracer tests; and two categories of emerging DNAPL remediation technologies: thermal enhanced extraction and in situ chemical oxidation.
DNAPL Remediation: Selected Projects Approaching Regulatory Closure
EPA 542-R-04-016, 34 pp, 2004
This status update on the use of DNAPL source-reduction technologies provides information about eight recent projects where, following source reduction, the objective of regulatory closure has been reached or is near completion. These projects involved in situ implementation of thermal treatment, chemical oxidation, or bioremediation. The report discusses the challenges associated with DNAPL remediation and the relative effectiveness of in situ application of various technologies.
DNAPL Source Reduction: Facing the Challenge
Interstate Technology & Regulatory Council (ITRC).
DNAPLs-2, 42 pp, 2002
In situ technologies considered for their potential to eliminate or reduce DNAPL source zones include steam-enhanced extraction, dynamic underground stripping, electrical resistance heating, thermal conduction, chemical flushing, chemical oxidation, enhanced desorption, and bioremediation.
Enhanced Attenuation: Approaches to Increase the Natural Treatment Capacity of a System
Tom Early, et al.
WSRC-TR-2005-00198, 161 pp, 2006
This guide covers the following approaches to address chlorinated volatile organic contaminants: (1) hydraulic manipulation to reduce contaminant infiltration using low-permeability barriers, diffusion barriers, covers, encapsulation, and diversion of electron acceptors; (2) passive residual source reduction (e.g., bioventing); (3) increase in system attenuation capacity via biological processes, such as bioaugmentation, biostimulation, and wetlands development and other plant-based methods; (4) abiotic and biologically mediated abiotic attenuation methods; and (5) reactive barriers.
Guidance for Optimizing Remedy Evaluation, Selection, and Design, User's Guide
Battelle Memorial Institute
NAVFAC, UG-2060-ENV, 2004
This guidance presents approaches to optimize remediation efforts. It recommends a treatment train approach that considers source zone treatment as a starting point to get to a position where a passive treatment system can handle the cleanup.
In Situ Enhanced Source Removal
Carl Enfield (U.S. EPA), et al. EPA 600-C-99-002, 1999
Contact: Carl Enfield, enfield.carl@epa.gov
This report evaluates demonstrations of co-solvent solubilization, co-solvent mobilization, surfactant solubilization, surfactant mobilization, micro-emulsions, macromolecular complexation, steam injection, air sparging, and soil vapor extraction for both dense and light NAPLs.
Regulatory Overview DNAPL Source Reduction: Facing the Challenge
Interstate Technology and Regulatory Council, 39 pp, 2002
This document describes some aggressive in situ technologies that are being deployed to eliminate or substantially reduce DNAPL source zones with the expectation of achieving more rapid remediation and speedier site closure.
Strategies for Monitoring the Performance of DNAPL Source Zone Remedies
Interstate Technology and Regulatory Council (ITRC) Dense Nonaqueous-Phase Liquids Team. DNAPLs-5, 206 pp, Aug 2004
This document presents strategies for assessing remedial technology performance and ways in which the success or failure in treating a DNAPL source zone has been measured.
Synthesis Report on Five Dense, Nonaqueous-Phase Liquid (DNAPL) Remediation Projects
U.S. EPA, National Risk Management Research Laboratory, Cincinnati, OH.
EPA 600-R-07-066, 94 pp, 2007
Summarizes the performance and results of demonstration projects for the remediation of DNAPL contamination at five sites: (1) thermally enhanced remediation with resistive heating and with steam injection/extraction for TCE DNAPL at Launch Complex 34, Cape Canaveral, FL; (2) cosolvent flushing, surfactant flushing, cosolvent DNAPL mobilization, complex sugar flushing, and AS/SVE for PCE at Dover AFB, DE; (3) surfactant-enhanced aquifer remediation for chlorinated solvent contamination (primarily TCE) at Hill AFB, UT; (4) thermally enhanced remediation of fractured bedrock with steam injection for multiple contaminants, primarily PCE and TCE in the quarry site at Loring AFB, Limestone, ME; and (5) cosolvent flushing and enhanced bioremediation for PCE at Sages Drycleaners in Jacksonville, FL.
Technology Evaluation Report: Technologies for Dense Nonaqueous Phase Liquid Source Zone Remediation
John C. Fountain.
Ground-Water Remediation Technologies Analysis Center, TE-98-02, 70 pp, 1998
This report describes the following techniques for remediating DNAPLs: flushing, volatilization, thermal processes, electrokinetics, biodegradation, and emplaced permeable reactive treatment zones.
Abstracts of Journal/Conference Papers
AFCEE Source Zone Initiative - Back Diffusion of Contaminants in Source Zones and Plumes
Tom Sale et al., Hydrology Days, 2005.
This paper argues that removing the source zone may not result in a significant reduction in contaminant concentrations due to back diffusion from stagnant zones and fine-grained sediments.
Assessing the impacts of partial mass depletion in DNAPL source zones I. Analytical modeling of source strength functions and plume response
R.W. Falta, Suresh Rao, N. Basu. J Contam. Hydrol., Vol 78 No 4 p 259-80, August 2005.
This article discusses the development of analytical solutions for approximating the time-dependent contaminant discharge from DNAPL source zones undergoing dissolution.
Assessing impacts of partial mass depletion in DNAPL source zones: II. Coupling source strength functions to plume evolution
R.W. Falta, N Basu, and PS Rao. Contam. Hydrol., Vol 79 No 1-2 p 45-66, September 2005.
This article discusses the findings from modeling the effects on flux of partial mass depletion of a source zone.
DNAPL source depletion: linking architecture and flux response
A.D. Fure, J.W. Jawitz, and M.D. Annable. Contam. Hydrol., Vol 85 No 3-4, p 118-40, May 2006. Epub 2006 Mar 9
This article describes a laboratory experiment showing the relationship between source architecture and dissolution.
A review of NAPL source zone remediation efficiency and the mass flux approach
K. Soga, J.W. Page, T.H. Illangasekare. J Hazard Mater., Vol110 No1-3, p13-27, July 5, 2004.
This article reviews previous studies and examines the effectiveness of specific technologies on the actual reduction of NAPL from source zones.
Direct and Multiphase Recovery
Soil Vapor Extraction and Air Sparging
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Treatment_Technologies/
Last updated on Thursday, July 24, 2008