Dense Nonaqueous Phase Liquids (DNAPLs)

The purpose of this section is to identify online documents that describe analytical methods and other techniques commonly used for detecting, measuring, and/or monitoring DNAPL chemicals. Innovative sample collection techniques are described, as well as methods, such as cone penetrometers and geophysical techniques, that are commonly used for other purposes but also can help to characterize DNAPL.

This first part of this section below identifies general documents on DNAPL characterization technologies. Documents on technologies specific to a chemical class can be found in the sections listed to the right.

General DNAPL Characterization Documents

These documents describe technologies and approaches that are applicable to most if not all classes of DNAPLs.

Assessment of the Natural Attenuation of NAPL Source Zones and Post-Treatment NAPL Source Zone Residuals
Johnson, P., R. Ekre, R. Krajmalnik-Brown, B. Rittman, P. Lundegard, and R. Hinchee.
ESTCP Project ER-200705, 416 pp, 2013

This project demonstrated a generalized data-driven paradigm for the assessment of source zone natural attenuation (SZNA) at CAHs cleanup sites. The method uses multiple lines of evidence and macroscopic mass balances, leading to confirmation of SZNA and quantification of the total mass loss rate resulting from degradation, dissolved-phase transport, and volatilization. Application of the method was demonstrated at three field sites, with multiple events per site spread out over 3 years. The mass loss rates were relatively consistent over time for each site, but varied from site to site, ranging between 1-10 kg/y at two sites and as high as ~600 kg/y at the third site.

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, which focuses primarily on organic contaminants, analyzes issues involving contaminant source zone characterization and remediation. It provides a contaminant source zone definition that is appropriate for DNAPL source zones.

Dense Non-Aqueous Phase Liquids (DNAPLs): Review of Emerging Characterization and Remediation Technologies
Interstate Technology & Regulatory Council (ITRC). DNAPLs-1, 81 pp, 2000

Three general types of emerging DNAPL characterization technologies are presented in this document: geophysical techniques (non-intrusive to minimally intrusive), direct push technologies employing one or a variety of DNAPL screening/sampling devices, and in situ, large-volume chromatography using chemical tracers.

DNAPL Characterization Methods and Approaches, Part 1: Performance Comparisons
M. Kram, A.A. Keller, J. Rossabi, and L.G. Everett.
Ground Water Monitoring and Remediation, Vol 21 No 1, p 67-76, 2001

This paper discusses approaches to DNAPLs characterization with descriptions of technologies current in 2001.

DNAPL Characterization Methods and Approaches, Part 2: Cost Comparisons
M. Kram, A.A. Keller, J. Rossabi, and L.G. Everett.
Ground Water Monitoring and Remediation, Vol 22 No 1, p 46-61, 2002

This paper compares the cost of several characterization methods.

DNAPL Site Evaluation
R. Cohen and J. Mercer.
EPA 600-R-93-022, 369 pp, 1993

An overview of DNAPL fate and transport theory is provided with discussions on characterization techniques. Although the characterization tools section is dated, the theoretical discussions are still pertinent.

Direct Push Chemical Sensors for DNAPL
S.H. Lieberman.
ESTCP Project ER-0109, 170 pp, 2007

Project ER-0109 evaluated two technologies: the halogen-specific detector (XSD) and the high resolution fluorescence (HRF) sensing system. The XSD can be operated downhole behind a membrane interface probe (MIP) that samples the soil formation for VOCs. Moving the detector downhole and measuring while the direct-push probe is continuously advanced can increase the spatial resolution of DNAPL detection by an order of magnitude (from feet to inches). Even higher spatial resolution (tenths of inches) can be obtained with a complementary HRF sensing system that can be applied whenever the DNAPL is fluorescent owing to dissolved petroleum products or humic substances. The ability of the characterization techniques to find DNAPL was verified via GeoVIS in situ video imaging. It should be noted that the XSD-MIP is a screening tool and is incapable of achieving analytical performance in real time on the inherently heterogeneous matrix of the subsurface. Although the logs are not analytically accurate in a quantitative sense, the reviewer stated that "the true value of tools such as the XSD-MIP are their ability to be used in a real-time sense to adaptively move about the site, follow gradients toward locations with higher signal levels both laterally and horizontally, and finally pinpoint the true hotspots and likely DNAPL source term areas."

Floater/Sinker Site Assessment Complicated by Asbestos
Merritt, C.A., Owens Corning, Granville, OH.
Proceedings of the Annual International Conference on Soils, Sediments, Water and Energy, Vol 15, Article 27, p 351-359, 2010

Most of the identified impacts to the soil and groundwater at this site are related primarily to the historic use of Dowtherm® (a heat transfer fluid—a mixture of 1,1-biphenyl and diphenyl ether, immiscible in water, specific gravity ~1.07), fuel oil, and various lubricants. The groundwater is affected by the Dowtherm® (sinker) and fuel oil (floater). Cone penetration testing and ultraviolet-induced fluorescence technologies were chosen to evaluate subsurface conditions involving hydrocarbons (both light and dense) as the principal site contaminants.

Geophysical Methods in DNAPL Investigations

Although geophysical techniques generally are not used to detect DNAPLs directly as they do not produce unique solutions, they can be useful in DNAPL site investigations.

Ground Water Issue: Assessment and Delineation of DNAPL Source Zones at Hazardous Waste Sites
B.H. Kueper and K.L. Davies.
EPA 600-R-09-119, 20 pp, 2009

This document provides a framework for assessing the presence of DNAPL and delineating the spatial extent of the DNAPL source zone, a priority at many sites due to the increasing use of in situ remediation technologies. The described strategy expands the applicability of the document to include both unconsolidated deposits and fractured bedrock, and encourage an iterative, flexible site investigation approach.

An Introduction to Characterizing Sites Contaminated with DNAPLs
Interstate Technology & Regulatory Council (ITRC), 73 pp, 2003

The purpose of this document is to discuss scientific approaches and strategies used to characterize sites that are known or suspected to be contaminated with DNAPLs. The document is written to introduce the fundamental concepts of site characterization strategies as they relate to DNAPLs. It is meant for a reader who is familiar with the principles of contaminant hydrogeology and conventional characterization approaches but may not be well versed in the issues surrounding the characterization of sites contaminated with DNAPLs.

Mass Flux Toolkit to Evaluate Groundwater Impacts, Attenuation, and Remediation Alternatives
Environmental Security Technology Certification Program (ESTCP), 135pp, 2006

To help site managers and site consultants estimate mass flux and understand the uncertainty in those estimates, ESTCP has funded the development of a computerized Mass Flux Toolkit, free software that gives site personnel the capability to compare different mass flux approaches, calculate mass flux from transect data, and apply mass flux to manage groundwater plumes. The toolkit spreadsheet and associated documentation are available in a zipped file on the ESTCP contractor's website.

Matrix Diffusion Toolkit User's Manual
Farhat, S.K., C.J. Newell, T.C. Sale, D.S. Dandy, J.J. Wahlberg, M.A. Seyedabbasi, J.M. McDade, and N.T. Mahler
ESTCP Project ER-201126, 160 pp, 2012

A new spreadsheet-based tool helps site managers and consultants determine if matrix diffusion processes in groundwater are likely to cause rebound of downgradient plume concentrations above remediation goals after plume remediation or isolation is complete. The user's manual details the tools provided to calculate and evaluate matrix diffusion effects, including a discussion of key parameters built into the toolkit and frequently asked questions related to matrix diffusion. The project summary presentation provides an overview. Additional information: Toolkit; Project Summary Presentation

Monitoring of In Situ Remediation Efforts

Most mobile treatment technologies (e.g., steam injection, chemical oxidation, biostimulation, surfactant/cosolvent flushing) change the electrical response of the subsurface in which they are implemented. It may be possible to track these changes with geophysical techniques to ensure all areas to be treated are included in the change in response. In addition, tracers can be used to measure retardation before and after treatment to estimate how much volume has been cleaned.

Optimal Search Strategy for the Definition of a DNAPL Source
G. Pinder, J. Ross, and Z. Dokou.
SERDP Project ER-1347, 154 pp, 2009

This report describes the search strategy developed for locating a DNAPL source area. The strategy uses a stochastic groundwater flow and transport model to calculate the concentration random field and its associated uncertainty. The algorithm has been tested successfully using various synthetic example problems of increasing complexity and also was used successfully for identifying a TCE DNAPL source at two field sites, Anniston Army Depot and Hunters Point Shipyard.

Sampling and On-Site Analytical Methods for Volatiles in Soil and Groundwater: Field Guidance Manual
A.D. Hewitt and K.F. Myers.
U.S. Army Corps of Engineers, Special Report 99-16, 20 pp, 1999

This report briefly addresses procedures, equipment, and logistics for the collection and timely (less than 48 hrs) on-site analysis of VOCs in discrete soil and groundwater samples. The collection, preservation, and preparation procedures presented are designed to acquire and maintain analyte concentrations that are representative of the location and medium from which the sample was removed.

Site Characterization Technologies for DNAPL Investigations
U.S. EPA, Office of Solid Waste and Emergency Response.
EPA 542-R-04-017, 165 pp, 2004

This report describes the following technologies for approaching DNAPL investigations: diffusion samplers, direct push technologies, in situ groundwater sampling devices, membrane interface probes, hydrophobic dye testing, hydrophobic flexible membranes, optical televiewer, tracer testing, soil gas profiling, geophysical techniques, and techniques that are still in development.

Third-Generation (3G) Site Characterization: Cryogenic Core Collection and High-Throughput Core Analysis, an Addendum to Basic Research Addressing Contaminants in Low Permeability Zones: A State of the Science Review
Sale, T., S. Kiaalhosseini, M. Olson, R. Johnson, and R. Rogers.
SERDP Project ER-1740, 131 pp, 2016

Core samples frozen in situ before recovery can preserve pore fluids, volatile compounds, dissolved gases, redox conditions, mineralogy, microbial ecology, and pore structure. The steps followed for collecting frozen cores are referred to in this text as cryogenic core collection. Processing core in the lab simplifies field work and improves the resources (e.g., anaerobic chambers) that can be used when preparing samples for analysis, while allowing "production line" processing and analysis of large quantities of samples (i.e., high-throughput core analysis). In this project, the combination of cryogenic core collection and high-throughput sampling yielded high quality samples suitable for a wide range of chemical, physical, and biological analyses of chlorinated solvents and other persistent contaminants in groundwater in unconsolidated sediments. The protocols for sample collection and processing are sufficiently robust that they can now be used routinely at field sites.

Analytical Methods

The analytical methods can be categorized as those deployed in the field and those used in the laboratory (bearing in mind that fixed-facility equipment may be deployed in the field by mobile laboratory). The analytical methods can be further subdivided into those that provide highly accurate and precise quantitative results and those that are used as screening tools.

Portable field instruments are useful for performing on-site analysis of many of the DNAPL chemicals. EPA's Environmental Technology Verification Program has tested many new technologies, including field analytical equipment applicable to many DNAPLs.

Fixed Laboratory Methods

Although these methods generally are associated with fixed laboratories, they can be performed in the field with portable instruments or in mobile laboratories.

USEPA Contract Laboratory Program Statement of Work for Organics Analysis: Multi-Media, Multi-Concentration
OLM04.2, 377 pp, May 1999

This method meets the Superfund requirements for laboratories performing medium-concentration organics analysis by GC/MS.

Method 8260B: Volatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS)

Method 8260B is a GC/MS method found in EPA's SW-846 manual. This method is used to determine volatile organic compounds in a variety of solid waste matrices and is applicable to nearly all types of samples, regardless of water content, including various air sampling trapping media, ground and surface water, aqueous sludges, caustic liquors, acid liquors, waste solvents, oily wastes, mousses, tars, fibrous wastes, polymeric emulsions, filter cakes, spent carbons, spent catalysts, soils, and sediments. See also Method 8260C (325KB/92pp/PDF). There are various techniques by which DNAPL compounds can be removed from the original matrices and introduced into the GC/MS system. The more common techniques are listed in the table in Section 1.1. Purge-and-trap, by Methods 5030 (aqueous samples) and 5035 (solid and waste oil samples), is the most commonly used technique for volatile organic analytes; however, other techniques are also appropriate and necessary for some analytes. These techniques include direct injection following dilution with hexadecane (Method 3585) for waste oil samples; automated static headspace by Method 5021 for solid samples; direct injection of an aqueous sample (concentration permitting) or injection of a sample concentrated by azeotropic distillation (Method 5031); and closed system vacuum distillation (Method 5032) for aqueous, solid, oil, and tissue samples. For air samples, Method 5041 provides a methodology for desorbing volatile organics from trapping media (Methods 0010, 0030, and 0031). In addition, direct analysis utilizing a sample loop is used for sub-sampling from polytetrafluoroethene (PTFE) bags (Method 0040). Method 5000 provides more general information on the selection of the appropriate introduction method. In addition to the DNAPL chemicals detected by 8260B, other volatile DNAPL chemicals may be analyzed by this method as tentatively identified compounds and may not appear as part of the laboratory report unless specifically requested.

Method 8270C: Semivolatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS)

Method 8270 is used to determine the concentration of semivolatile organic compounds in extracts prepared from many types of solid waste matrices, soils, air sampling media, and water samples. Direct injection of a sample may be used in limited applications. Method 8270 can be used to quantitate most neutral, acidic, and basic organic compounds that are soluble in methylene chloride and capable of being eluted, without derivatization, as sharp peaks from a GC fused-silica capillary column coated with a slightly polar silicone. Such compounds include polynuclear aromatic hydrocarbons, chlorinated hydrocarbons and pesticides, phthalate esters, organophosphate esters, nitrosamines, haloethers, aldehydes, ethers, ketones, anilines, pyridines, quinolines, aromatic nitro compounds, and phenols, including nitrophenols. See also Method 8270D (387KB/62pp/PDF). In addition to the DNAPL chemicals detected by 8270C , other volatile DNAPL chemicals may be analyzed by this method as tentatively identified compounds, but they may not appear as part of the laboratory report unless specifically requested.

Field Screening Methods

Direct Push Optical Screening Tool for High-Resolution, Real-Time Mapping of Chlorinated Solvent DNAPL Architecture
Einarson , M., A. Fure, R. St. Germain, S. Chapman, and B. Parker.
ESTCP Project ER-201121, 222 pp, 2016

A new direct-push optical screening tool for high-resolution 3D subsurface mapping of chlorinated solvent DNAPLs in unlithified sediments was field-tested at a formerly used defense facility in Massachusetts in fall 2013 (Geoprobe® delivery) and again in March 2014 (CPT delivery). The new tool, a laser induced fluorescence (LIF) technology—DyeLIF™—was developed and validated during this project and is now commercially available. Additional information: ESTCP Cost and Performance Report

Field Performance of the Radon-Deficit Technique to Detect and Delineate a Complex DNAPL Accumulation in a Multi-Layer Soil Profile
Barrio-Parra, F., M. Izquierdo-Diaz, J. Diaz-Curiel, and E. De Miguel.
Environmental Pollution 269:116200(2021)

The radon (²²²Rn)-deficit technique was evaluated at a site where a complex DNAPL mixture (primarily hexachlorocyclohexanes and chlorobenzenes) contaminated the backfill, silt, gravel, and marl soil profile layers. Soil gas samples were collected at 0.8 m and 1.7 m depths in seven field events, and 186 ²²²Rn measurements were collected with an ionization detector. A statistical assessment indicated that the location of the sampling point and ground-level atmosphere temperature affected the measurements; sampling depth and atmospheric pressure did not affect the measurements. To remove the bias introduced by varying field temperatures and interpret ²²²Rn measurements from different field events, ²²²Rn concentrations were rescaled by dividing each individual datum by the mean ²²²Rn concentration of its corresponding field event. The ²²²Rn-deficit technique was unable to describe the vertical variation of contamination with depth but can be effective when the distance between the sampling probe inlet and the contaminant accumulation of the soil profile is within the diffusion length of ²²²Rn.

Hydrophobic Flexible Membranes and Dyes

Two variants of hydrophobic flexible membranes have been employed in DNAPL characterization. The basic device is built around an inflatable tubular membrane. The membrane can be fitted with either discretely spaced hydrophobic sorbent packs, a dye-impregnated hydrophobic ribbon, or a cover that changes color in the presence of DNAPL chemicals. It is effective both in the vadose zone and beneath the water table.

Innovations in Site Characterization. Technology Evaluation: Real-Time VOC Analysis Using a Field Portable GC/MS
U.S. EPA, Office of Solid Waste and Emergency Response.
EPA 542-R-01-011, 38 pp, 2001

An evaluation of field-portable analytical technology is part of a series of case studies designed to provide cost and performance information for innovative tools that support less costly and more representative site characterization. Based on actual field projects, these case studies report on new technologies as well as innovative applications of familiar tools in the context of more efficient work strategies. The ultimate goal of this case study series is to aid practicing site professionals to enhance the cost-effectiveness and defensibility of decisions regarding the disposition of hazardous waste.

Membrane Interface Probe

The membrane interface probe is a downhole probe used in concert with a direct push-type rig. The heated membrane volatilizes chemicals, which are then swept to the surface for qualitative or quantitative analysis.

One-Off Geophysical Detection of Chlorinated DNAPL During Remediation of an Industrial Site: A Case Study
Fiorentino, E.A., S. Warden, M. Bano, P. Sailhac, and T. Perrier. AIMS Geosciences, 7(1):1-21(2021)

A geophysical survey was performed on an industrial site impacted by a chlorinated DNAPL to identify the location of contamination in the saturated zone. Sediments in the unsaturated zone were first excavated and treated. Geophysical measurements were then conducted at the bottom of the excavated pit. While electrical resistivity tomography yielded little information, ground-penetrating radar helped identify a possible source location.

Partitioning Tracers

The partitioning interwell tracer test (PITT) is an in situ technique for estimating the volume and percent saturation of DNAPLs in both the vadose and saturated zones.

Vertical Profiling of Groundwater Plume Concentrations

The distribution of DNAPL chemicals in the subsurface often leads to a plume with vertical and horizontal concentrations of varying strengths. The higher concentrations (generally those at or above one percent of a chemical's solubility constant) can be associated with residual source areas or pools. With direct push tools, it is possible to track these areas of higher contamination in the plume back to the source zone economically. These techniques are discussed in the following resources:

An Introduction to Characterizing Sites Contaminated with DNAPLs
Interstate Technology & Regulatory Council (ITRC), 73 pp, 2003

The purpose of this document is to discuss scientific approaches and strategies used to characterize sites that are known or suspected to be contaminated with DNAPLs. The document is written to introduce the fundamental concepts of site characterization strategies as they relate to DNAPLs. It is meant for a reader who is familiar with the principles of contaminant hydrogeology and conventional characterization approaches but may not be well versed in the issues surrounding the characterization of sites contaminated with DNAPLs.

Site Characterization Technologies for DNAPL Investigations
U.S. EPA, Office of Solid Waste and Emergency Response.
EPA 542-R-04-017, 165 pp, 2004

This report describes the following technologies for approaching DNAPL investigations: diffusion samplers, direct push technologies, in situ groundwater sampling devices, membrane interface probes, hydrophobic dye testing, hydrophobic flexible membranes, optical televiewer, tracer testing, soil gas profiling, geophysical techniques, and techniques that are still in development.

Remediation Measurement Tools

Measuring the progress of remediation is also a characterization function. Below are abstracts on different approaches to doing this.

Calculating Degradation Rates (Abstracts of Journal Articles)

Calculating Plume Growth Rates (Abstracts of Journal Articles)

Flux Resources

Geochemical Analysis for Evidence of Biodegradation (Abstracts of Journal Articles)

Isotope Analysis

Microcosm Delineation for Biodegradation (Abstracts of Journal Articles)

Modeling (Abstracts of Journal Articles)

Plume Architecture (Abstracts of Journal Articles)

Push-Pull (Abstracts of Journal Articles)

Tracers