CLU-IN.ORG | Contaminant Focus: DENSE NONAQUEOUS PHASE LIQUIDS (DNAPLS), Detection and Site Characterization

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.

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

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.

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 Detection and Characterization Tool
U.S. Navy, Naval Facilities Engineering Command, Environmental Restoration Technology Transfer, Multimedia Training Tools website, 24 pp, 2006

Approximately 867 chlorinated solvent sites have been identified at Navy and Marine Corps installations. An estimated 5 to 10% of these sites have chlorinated solvent contamination present as DNAPL. The goal of the DNAPL detection and characterization tool is to develop a conceptual site model that focuses on stratigraphy, including migration pathways and traps. It recommends source investigation methods that provide desired remediation data while simultaneously minimizing the risk of contaminant mobilization. This tutorial describes the invasive and non-invasive tools that are available to perform DNAPL investigations; however, each site is unique, and DNAPL detection and characterization strategies vary depending on the remediation goal (i.e., containment vs. removal)—no practical "cookbook" approach for characterization exists.

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

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.

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.

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.

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.

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.

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.

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.

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.

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

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

DNAPL Chemicals Detected by 8260B

Chemical	Chemical
Benzyl Chloride	cis-1,3-Dichloropropene
Bromochloromethane	trans-1,3-Dichloropropene
Bromodichloromethane	Hexachlorobutadiene
Bromoform	Iodomethane
Carbon disulfide	Methylene Chloride
Carbon tetrachloride	Naphthalene (coal tar/creosote component)
Chlorobenzene	Nitrobenzene
2-Chloroethyl vinyl ether	Pentachloroethane
Chloroform	1,1,1,2-Tetrachloroethane
1,2-Dibromo-3-chloropropane	1,1,2,2-Tetrachloroethane
1,2-Dibromoethane (ethylene dibromide)	Tetrachloroethene
1,2-Dichlorobenzene	1,2,4-Trichlorobenzene
1,3-Dichlorobenzene	1,1,1-Trichloroethane
1,1-Dichloroethane	1,1,2-Trichloroethane
1,2-Dichloroethane	Trichloroethene
1,1-Dichloroethene	Trichlorofluoromethane
trans-1,2-Dichloroethene	1,2,3-Trichloropropane
1,2-Dichloropropane

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.

DNAPL Chemicals Detected by 8270C

Chemical	Chemical
Aniline	4-Chlorophenyl phenyl ether
o-Anisidine	Di-n-butyl phthalate
Arochlor 1016	1,2-Dichlorobenzene
Arochlor 1221	1,3-Dichlorobenzene
Arochlor 1232	Dichlorovos
Arochlor 1242	Diethyl phthalate
Arochlor 1248	Dimethyl phthalate
Arochlor 1254	Hexachlorobutadiene
Arochlor 1260	Hexachlorocyclopentadiene
Bis(2-chloroethyl) ether	Malthion
Bis(2chloroisoproyl) ether	Naphthalene (coal tar creosote constituent)
Butyl benzyl phthalate	Nitrobenzene
2-Chlorophenol	Parathion

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.

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.

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.

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.

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:

DNAPL Detection and Characterization Tool
U.S. Navy, Naval Facilities Engineering Command, Environmental Restoration Technology Transfer, Multimedia Training Tools website, 24 pp, 2006

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

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Last updated on Thursday, July 24, 2008