Dense Nonaqueous Phase Liquids (DNAPLs)
- Policy and Guidance
- Chemistry and Behavior
- Environmental Occurrence
- Detection and Site Characterization
- Treatment Technologies
- Conferences and Seminars
- Additional Resources
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.
Chapman, S. W., and B. L. Parker. 2005. Plume persistence due to aquitard back diffusion following dense nonaqueous phase liquid source removal or isolation. Water Resources Research 41(12):4224-4235.
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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
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.
Chlorinated Ethene Source Remediation: Lessons Learned
Stroo, H.F., A. Leeson, J.A. Marqusee, P.C. Johnson, C.H. Ward, M.C. Kavanaugh, T.C. Sale, C.J. Newell, K.D. Pennell, C.A. Lebron, and M. Unger.
Environmental Science & Technology 46(12):6438-6447(2012)
This review describes progress made over the past decade through ESTCP-sponsored research efforts to improve DNAPL characterization and remediation techniques. The article summarizes specific lessons learned related to recognizing limitations to treatment, improving DNAPL site characterization, and enhancing treatment. Experience has shown that different technologies are needed for different times and locations and that deliberately combining technologies can improve overall remedy performance.
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.
Decision Guide: A Guide for Selecting Remedies for Subsurface Releases of Chlorinated Solvents
Sale, T. and C. Newell.
ESTCP Project ER-200530, 145 pp, 2011
The document is intended to provide current knowledge in support of sound decisions. The section on "Understanding the Problem" describes the behavior of chlorinated solvents in subsurface environments. Other sections discuss formulating objectives, determining what can be attained, developing packages of remedial measures, and assessing limitations. This guide is not intended to foster or discourage efforts to clean up subsurface releases, but to help practitioners who are faced with difficult decisions and to lay the groundwork for developing realistic expectations regarding the outcome of such treatments. The authors assume that the reader has a general understanding of hydrogeology, the movement of chemicals in porous media, remediation technologies, and the overall remedy selection process.
Dense Nonaqueous Phase Liquid Cleanup: Accomplishments at Twelve NPL Sites
Serena Ryan, National Network of Environmental Management Studies Fellow, 84 pp, 2010
This document was prepared by a National Network of Environmental Management Studies grantee under a fellowship from the U.S. Environmental Protection Agency. This report was not subject to EPA peer review or technical review. EPA makes no warranties, expressed or implied, including without limitation, warranties for completeness, accuracy, usefulness of the information, merchantability, or fitness for a particular purpose. The objective of this report is to provide an overview of remedial accomplishments at 12 current or former NPL sites affected by DNAPL and/or associated dissolved, vapor, or sorbed phase contamination. This report summarizes relevant information about these sites, including site sizes, contaminants, technologies, concentration level reductions, and current remedial status. A discussion of DNAPL characteristics, fate, and transport, as well as a summary of DNAPL remediation technologies, is also included. Case studies of individual sites are also provided.
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 Dissolution in Bedrock Fractures and Fracture Networks
Schaefer, C., J. McCray, K. Christensen, P. Altman, P. Clement, and J. Torlapati.
SERDP Project ER-1554, 146 pp, 2011
This project focused on measuring and evaluating the architecture, dissolution rate, and impact on groundwater quality of residually trapped PCE DNAPL from discrete bedrock fractures and fracture networks constructed at the bench scale. This work showed that residual DNAPL in rock fractures is not well contacted by migrating water, resulting in reduced dissolution rates and persistence of DNAPL sources within the bedrock fractures. Bioaugmentation substantially enhanced the rate of DNAPL removal, despite dissolved PCE concentrations that were near solubility. ISCO was ineffective for treating DNAPL sources in bedrock fractures due to decreases in the effective DNAPL-water interfacial area, likely from oxidation reaction byproducts.
DNAPL Remediation: Selected Projects Where Regulatory Closure Goals Have Been Achieved
EPA 542-R-09-008, 52 pp, 2009
The purpose of this paper is to highlight sites where dense nonaqueous phase liquid (DNAPL) source reduction has been demonstrated as an aid in meeting regulatory cleanup goals. The presence of DNAPL in the subsurface can serve as a long-term source of dissolved contaminant plumes in groundwater, making it more difficult to reach regulatory closure. However, once the DNAPL source is addressed, residual groundwater plumes may be more amenable to treatment, including less aggressive techniques such as monitored natural attenuation (MNA) or bioremediation. This paper updates the document, DNAPL Remediation: Selected Projects Approaching Regulatory Closure, prepared in 2004 by providing more recent information on technologies and on five additional selected sites at which DNAPL source reduction technologies were applied.
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.
Development of a Protocol and a Screening Tool for the Selection of DNAPL Source Area Remediation
Lebron, C.A., D. Major, J. Konzuk, B.H. Kueper, and J. Gerhard.
ESTCP Project ER-200424, CR-NAVFAC ESC-EV-1201, 746 pp, 2012
The DNAPL Technology Evaluation Screening Tool (DNAPL TEST) enables the user to select and constrain their analysis to focus on particular site characteristics, performance goals, and remedial technologies. The technologies evaluated in DNAPL TEST include ISCO, thermal technologies, in situ flushing techniques, hydraulic displacement, enhanced in situ bioremediation, and chemical reduction with ZVI. The tool can be utilized to evaluate existing remedial systems and assist in determining whether there is a realistic expectation of meeting the remedial action objectives for a given site and technology, and then to provide an assessment of alternative technologies that might offer a higher likelihood of success. The tool is available for free download from the ESTCP website. ESTCP Cost and Performance Report
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.
Estimating Cleanup Times Associated with Combining Source-Area Remediation with Monitored Natural Attenuation
M. Widdowson, F. Chapelle, C. Casey, and M. Kram.
NFESC TR-2288-ENV, 192 pp, 2008
U.S. EPA guidance specifically requires a reasonable time frame for MNA to achieve site-specific cleanup objectives; thus, it is necessary to provide estimates of cleanup times whenever MNA is proposed as part of a cleanup strategy. The U.S. Navy, USGS, and Virginia Tech have developed Natural Attenuation Software (NAS) as a screening tool designed for estimating time of remediation for MNA with varying degrees of source area remediation. This report describes the software and the results of its use at 8 sites contaminated primarily with chlorinated ethenes.
Frequently Asked Questions Regarding Management of Chlorinated Solvents in Soils and Groundwater
T. Sale, C. Newell, H. Stroo, R. Hinchee, and P. Johnson.
Environmental Security Technology Certification Program (ESTCP), Project ER-0530, 38 pp, 2008
This brief document addresses 25 key questions, providing a concise overview of current knowledge regarding the management of subsurface chlorinated solvent releases. Source zone areas are defined and discussed, with summaries of the benefits and limitations of various source characterization and remediation technologies. The document addresses current technical and practical limitations, as well as the changes that have occurred over time at many chlorinated solvent sites. Although the document is meant neither to foster nor discourage source zone treatment, it takes a hard look at the costs and performance of the most commonly used source zone treatment technologies and compares source treatment to alternative containment approaches.
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.
Impacts of DNAPL Source Treatment: Experimental and Modeling Assessment of the Benefits of Partial DNAPL Source Removal
A.L. Wood, M.D. Annable, J.W. Jawitz, R.W. Falta, M.C. Brooks, C.G. Enfield, P.S.C. Rao, and M.N. Goltz.
EPA 600-R-09-096, SERDP Project ER-1295, 172 pp, Sep 2009
When it is not practical or economically feasible to achieve complete DNAPL mass depletion using aggressive remediation techniques, it must be determined if the aggregate benefits of partial DNAPL mass depletion are sufficient to reduce risks to an acceptable level and if the costs associated with this partial depletion are justified by the benefits received. This report summarizes field, lab, and modeling research conducted to address these issues, with the primary objective being the development of a scientifically defensible approach for assessing the long-term environmental impacts (benefits) of DNAPL removal from source zones.
PREMChlor: Probabilistic Remediation Evaluation Model for Chlorinated Solvents: User's Guide
Liang, H., R. Falta, C. Newell, S. Farhat, P.S.C. Rao, and N. Basu.
ESTCP Project ER-0704, 76 pp, Mar 2010
PREMChlor has been developed for simultaneously evaluating the effectiveness of source and plume remediation, considering the uncertainties in all major parameters. The technical foundation of PREMChlor is U.S. EPA's REMChlor model. PREMChlor is developed by linking the analytical model REMChlor to a Monte Carlo modeling package GoldSim via a FORTRAN dynamic link library application. Cost analysis of common technologies for DNAPL source removal and dissolved plume treatment are included. PREMChlor gives users a single platform where cost, source treatment, plume management, monitored natural attenuation, and risk assessment can all be evaluated together, and where uncertainty can be incorporated into the site decision-making process. A license-free file containing the user-friendly graphical user interface has been generated to make PREMChlor available for use by others: PREMChlorModelFiles.zip; Decision & Management Tools for DNAPL Sites: Optimization; ESTCP Cost and Performance Report (2011)
Proven Technologies and Remedies Guidance: Remediation of Chlorinated Volatile Organic Compounds in Vadose Zone Soil
Berscheid, M., K. Burger, N. Hutchison, H. Muniz-Ghazi, B. Renzi, P. Ruttan, and S. Sterling.
California Department of Toxic Substances Control, 154 pp, 2010
Presents an option for expediting and encouraging cleanup of sites with chlorinated VOCs in vadose zone soil by streamlining the cleanup process. This approach limits the number of evaluated technologies to excavation/disposal and SVE and provides resources to facilitate the design and implementation of both remedies. Considerations for operation and maintenance of SVE systems, including zone of capture assessment, operational assessment, and shutdown and cleanup confirmation are included.
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.
Remediation of Former Manufactured Gas Plants and Other Coal-Tar Sites
CRC Press, Boca Raton, FL. ISBN: 9780824791063, 1,398 pp, 2011
This massive compendium combines historic information about MGP processes and residues with modern data and technology in an exploration of the bases for selecting remedial alternatives to address sites contaminated with coal tar. Table of Contents
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.
The Use of Molecular and Genomic Techniques Applied to Microbial Diversity, Community Structure, and Activities at DNAPL and Metal-Contaminated Sites: Environmental Research Brief
Azadpour-Keeley, A., M.J. Barcelona, K. Duncan, and J.M. Suflita.
EPA 600-R-09-103, 19 pp, Sep 2009
Subsurface microbial communities will respond both to the presence of contaminants, which can be detected during characterization, and to the engineered manipulation of subsurface conditions, which can be monitored during remediation. This Brief provides a background on classic molecular and genomic sciences and discusses the results and interpretation of their application to field-scale subsurface remediation activities.
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.
Performance monitoring covers a wide range of activities during a site cleanup that are implemented to determine if the remedial technology is performing as designed and if remediation goals are being met. The following activities are examples of performance monitoring:
- Analysis of influent vapor contaminant concentrations during soil vapor extraction to determine if the concentrations are meeting design expectations and to monitor cleanup progress.
- Monitoring of soil temperatures across the cleanup zone during in situ thermal desorption to ensure all areas in the targeted subsurface reach the desired temperature.
- Geophysical monitoring of oxidant injection during in situ oxidation to estimate oxidant dispersal and potential preferential flow.
- Testing for geochemical parameters such as dissolved oxygen, oxidation reduction potential, total organic carbon, ferrous iron, manganese(IV), sulfate, and nitrate to determine if conditions continue to be favorable for anaerobic biodegradation.
- Tracer testing before and after in situ flushing to determine success in removing a DNAPL mass.
- Monitoring of dissolved oxygen, nitrate, and degradation products during in situ reduction to determine if degradation is taking place, where it is happening, and what mechanism is causing it.
The performance monitoring technology sections discuss potential performance monitoring activities for each of the selected technologies. The tables presented in these sections are meant to be comprehensive and generally are drawn from several sources. The parameters to be tested and how often to test depends upon the complexity of the site hydrogeology, the size of the plume and source areas, the number of chemicals present and their potential degradation products, and the amount of funding available for the whole project. For example, in a naturally occurring metals-rich subsurface, regulators could require inclusion of the metals in the analytical suite before approving a treatment that will cause a negative change in pH. This type of monitoring probably would not be required in a silica sand environment.
The performance and/or overall success of a DNAPL remediation effort can sometimes be estimated using a non-technology-specific characterization technique. See Remediation Measurement Tools.
Diagnostic Tools for Performance Evaluation of Innovative In-Situ Remediation Technologies at Chlorinated Solvent-Contaminated Sites. Final Report: Fort Lewis
Kavanaugh, M., R. Deeb, and E. Hawley.
ESTCP Project ER-200318, 134 pp, 2011
Innovative diagnostic tools were implemented during another ESTCP demonstration (Project ER-0218), and this report details performance assessment, cost, implementation issues, and advantages and limitations for each of the tools. Bioremediation studies in 2 hydraulically isolated treatment cells at the Fort Lewis EGDY NAPL Area 3 were monitored with the following innovative diagnostic tools: 3-D multi-level systems, passive flux meters, compounds-specific stable isotope analysis, and molecular tools (qPCR). Cell 1 was located on the fringe of the DNAPL source area and Cell 2 within the DNAPL (TCE) source area.
Diagnostic Tools for Performance Evaluation of Innovative In-Situ Remediation Technologies at Chlorinated Solvent-Contaminated Sites: Guidance Report
Kavanaugh, M. and R. Deeb.
ESTCP Project ER-200318, 231 pp, 2011
This report discusses a wide range of innovative diagnostic tools for characterization and remedial performance assessment at chlorinated solvent-contaminated sites, including tools for multi-level monitoring, rock matrix characterization, mass flux measurement, and compound-specific isotope analysis, as well as molecular biological tools.
Diagnostic Tools for Performance Evaluation of Innovative In-Situ Remediation Technologies at Chlorinated Solvent-Contaminated Sites. Final Report: Vandenberg Air Force Base
Kavanaugh, M., R. Deeb, and E. Hawley.
ESTCP Project ER-200318, 270 pp, 2011
Four different methods for measuring contaminant mass discharge were tested by applying them to an artificially created bromide tracer plume with known mass injection rate: 1) synoptic sampling of wells in transects, 2) steady-state pumping of wells in transects, 3) deployment of passive flux meters in wells in transects, and 4) recirculation flux measurement using pairs of wells in transects. Recommendations are given to optimize the use of these methods at other sites at full scale with general information on expected performance, advantages and disadvantages, and relative costs.
Diagnostic Tools for Performance Evaluation of Innovative In-Situ Remediation Technologies at Chlorinated Solvent-Contaminated Sites. Final Report: Watervliet Arsenal
Kavanaugh, M., R. Deeb, and E. Hawley.
ESTCP Project ER-200318, 275 pp, 2011
Innovative diagnostic tools used for site characterization to support remediation design and then to evaluate the performance of ISCO using permanganate (KMnO4 and NaMnO4) at the Arsenal for PCE, DCE, TCE, and VC. The innovative methods were compared with conventional diagnostic tools currently used for characterizing fractured rock sites and assessing ISCO performance. The following technologies were used: Westbay MP38 Multi-Level Sampling System; Solinst Continuous Multichannel Tubing (CMT®) Model 403 System; and Groundwater Flexible Liner Underground Technologies (FLUTe™) System. Also, performance of conventional nested wells was compared to the unique Zone Isolation Sampling Technology (ZIST™) System.
Improved Monitoring Methods for Performance Assessment During Remediation of DNAPL Source Zones
R. Siegrist, R. Oesterreich, L. Woods, and M. Crimi.
Strategic Environmental Research and Development Program (SERDP), Project ER-1490, 116 pp, 2010
Investigators evaluated (1) the effects that sampling methods can have on the accuracy of measurements made for chlorinated solvents in samples of porous media collected from intact cores, and (2) the effects that remediation agents can have on the ability to infer CVOC mass levels in the subsurface based on groundwater concentration data. The accuracy of VOC measurements was investigated using an experimental apparatus packed with sandy porous media and contaminated with known levels of VOCs (PCE, TCE, TCA) sampled using different methods under variable, but controlled, conditions. Five sampling methods were examined representing different degrees of porous media disaggregation and duration of atmospheric exposure that can occur during sample acquisition and preservation in the field. CVOCs were studied at dissolved, sorbed, and nonaqueous phases. Five porous media temperatures were examined ranging from 5 to 80 degrees C to represent ambient or thermal remediation conditions, and two water saturation levels were used to mimic vadose zone and groundwater zone conditions. Results show that sampling method attributes can impact the accuracy of VOC measurements in porous media by causing negative bias in VOC concentration data ranging from near 0 to 90% or more. In situ remediation technologies, such as thermal treatment, ISCO, and flushing, have the potential to alter subsurface properties, which can affect the behavior of CVOCs, including DNAPLs.
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