Title: Introduction (1 of 3) Text: What is DNAPL? DNAPL - dense nonaqueous phase liquid. DNAPLs are chemicals with densities greater than that of water. They are hydrophobic and immiscible with water. DNAPLs persist in the subsurface in two major forms: free-phase DNAPL or residual DNAPL. Free-phase DNAPL exists when the saturation in soil is high enough to form pore-to-pore connections. It is mobile and will flow under positive pressure, unless it is contained within a stratigraphic trap. Residual DNAPL exists when the soil pores have been drained of mobile DNAPL, leaving behind a small amount of liquid trapped by capillary pressure. It is immobile and very difficult to detect. Visual Direction: Photo of a vial with LNAPL on the top, water in the middle, and DNAPL on the bottom.

Title: Introduction (2 of 3) Text: Common examples of DNAPL include: Chlorinated Solvents (i.e. TCE, PCE, DCE) Creosote/Coal Tar Polychlorinated Biphenyls (PCBs) Common uses of DNAPL include: Military equipment manufacturing and maintenance Vapor degreasing operations Dry cleaning Septic tank cleaning Visual Direction: No graphic.

Title: Introduction (3 of 3) Text: Environmental Challenges Related to DNAPL The cleanup of DNAPL-impacted sites is a major challenge. There are approximately 867 chlorinated solvent sites at Navy and Marine Corps installations. It is estimated that at least 5-10% of these sites have chlorinated solvent contamination that is present as DNAPL. DNAPL sources are difficult to locate and characterize. In many cases, only limited information exists about the potential source and the location of the release. Also, DNAPLs have complex migration patterns, and small amounts of residual DNAPL can produce large dissolved-phase plumes. These factors make DNAPL detection and removal from the subsurface challenging, as well as costly. Complete DNAPL removal may be impossible at most sites. It should be noted that, to date, no DNAPL site has been cleaned up to meet target maximum contaminant levels (MCLs) in groundwater. Visual Direction: Photo of a tanker truck at an industrial-looking site.

Title: Detection and Characterization Strategies (1 of 3) Text: The goal of DNAPL detection and characterization is to develop a realistic conceptual site model. A good understanding of the site stratigraphy is necessary in order to do this. Important questions to answer while characterizing your site include: Is DNAPL present? Where are DNAPL sources? How long has DNAPL been in the subsurface? What are the key characteristics of the DNAPL sources (i.e., quantity, phase, physical and chemical attributes)? The effects of capillary pressure and gravity should also be understood. Additionally, stratigraphic barriers and traps, migration pathways, and fine-grained diffusion sources should be identified. Visual Direction: Cross-sectional graphic of a conceptual site model where DNAPL is released and enters the groundwater. Graphic shows direction of flow, DNAPL pools, dissolved phase and residual DNAPL, and DNAPL distribution in bedrock with fractures.

Title: Detection and Characterization Strategies (2 of 3) Text: YOU MAY HAVE DNAPL AT YOUR SITE IF: DNAPL-related chemicals are detected (e.g., chlorinated solvents) Dissolved concentrations of these chemicals are >1% of the aqueous or effective solubility Concentrations of these chemicals in soil are >1% (e.g., >10,000 mg/kg) Organic vapor analyzer (OVA) readings exceed 100 to 1,000 parts per million Dissolved concentrations of these chemicals increase with depth (without other explanation) Dissolved concentrations of these chemicals increase upgradient from a source area There is evidence of tailing and rebound during remedial activities PVC wells at site are disintegrating Visual Direction: No graphic.

Title: Tools for DNAPL Characterization (3 of 3) Text: A variety of DNAPL characterization tools are available. These tools fall into two general categories: Noninvasive and Invasive. Noninvasive techniques are typically performed above ground surface or require minimal disruption of the vadose or saturated zones. Invasive techniques usually require advancement of boreholes into the subsurface and often create investigation-derived waste (IDW). When characterizing a DNAPL release in the environment, it is recommended that the investigation begin with noninvasive techniques coupled with minimally invasive methods. In general, source investigation methods should be selected to provide the desired remediation data, while minimizing the risk of uncontrolled contaminant mobilization. It is important to remember that each site is unique and that DNAPL detection and characterization is a challenging task even with a variety of tools available. Visual Direction: No graphic.

Title: Noninvasive Tools for DNAPL Characterization Text: The following information can be used to assist preliminary DNAPL site characterization: Site history information (i.e., chemical use, inventory, and disposal records) Historical aerial photographs Geologic fractures/outcrops Soil gas analysis Site infrastructure information (i.e. sewers) Employee/witness interviews Visual Direction: Cartoon graphic of a person looking at hazardous materials drums.

Title: Example Aerial Photograph Text: Aerial photographs can be used to compare historic site conditions to current conditions. Key information includes: source areas, land use, drainage, vegetative stress, surface contamination, and geology. Visual Direction: Aerial photographs of Love Canal in 1938 and 1951.

Title: Fracture Trace Analysis Text: Information pertaining to fractures in the subsurface is important for DNAPL characterization because it can be used to help delineate preferential pathways of contaminant migration. Visual Direction: Graphic showing 3-D cross-section with fracture trace at the surface and subsurface faults and fractures in bedrock. Also, an aerial photograph of fields crossed by a line of trees.

Title: Soil Gas Surveys Text: Soil gas surveys can be used to delineate volatile organic compounds (VOCs) evolving from NAPL in vadose zone source areas. Under certain conditions, this method can also be used to delineate shallow groundwater contamination. Active or passive soil gas sampling techniques can be used. More information on the interpretation of soil gas data is available in the references provided below. However, it should be noted that older releases may have a limited signal due to prior contaminant volatilization. Visual Direction: Two photos of people performing soil gas surveys. Log log plot of Freon 113 in Soil Gas vs. Freon 113 in Groundwater.

Title: Surface Geophysical Surveys Text: Surface geophysical surveys can be used to delineate subsurface stratigraphy, buried metal, and conductive fluids. This information can be very important for DNAPL characterization efforts. Additionally, there are several less-widely used high resolution techniques that can be used to delineate DNAPL traps and infer DNAPL presence. Common surface geophysical survey methods include: Ground-penetrating radar (GPR) Electromagnetic (EM) conductivity Electrical resistivity High-resolution seismic reflection These methods should be used with caution, because they are subject to numerous interferences and interpretation errors. DNAPL is generally a poor target for geophysical methods and direct detection of DNAPL is unlikely. Visual Direction: No graphic.

Title: Ground-Penetrating Radar (GPR) Text: Measures dielectric and conductivity properties by transmitting electromagnetic waves and recording their reflection. This technique is used to delineate stratigraphy, buried wastes, and utilities in cross section. Typically, penetration occurs between 6 to 30 feet below ground surface (bgs). Visual Direction: No graphic.

Title: Electromagnetic (EM) Conductivity Text: Measures bulk electrical conductance by recording changes in induced electromagnetic currents. This technique is used to infer the presence of conductive contaminants, buried wastes, and stratigraphy. The depth this method is capable of depends on transmitter-receiver spacing. Visual Direction: No graphic.

Title: Electrical Resistivity Text: Measures resistivity of the subsurface including effects of soil type (i.e. clay content), bedrock fractures, contaminants, and groundwater. This technique is used to delineate stratigraphy, infer depth to the water table, locate fractures and faults, identify karst features, etc. Visual Direction: No graphic.

Title: High-Resolution Seismic Reflection Text: This technique evaluates 3-D seismic reflection to detect DNAPL and delineate stratigraphy. However, this method has proven to be ineffective at directly detecting DNAPL, but potentially useful for imaging strata. Visual Direction: No graphic.

Title: Invasive Tools for DNAPL Characterization Text: The goal of invasive methods is to unambiguously identity DNAPLs in the subsurface. These methods minimize waste generation, eliminate the undesirable gravitational movement of DNAPLs, and provide cost savings. The following invasive methods can be used for direct DNAPL characterization: Test pits Soil examination Downhole analysis Groundwater profiling using direct push (DP) and multilevel wells Characterization of DNAPL samples Borehole geophysics Partitioning interwell tracer tests (PITTs) Visual Direction: Cartoon graphic of a backhoe excavating and filling a dump truck.

Title: Examples of Test Pits Text: Test pits can be used to define shallow soil stratigraphy, structure, and DNAPL distribution. The graphics are from the Love Canal Site in Niagara Falls, New York. Visual Direction: Four photos of test pits at Love Canal are shown: 1) silty sand and soft silty clay exposed, 2) pit with hard fractured clay, 3) DNAPL in fractured clay, and 4) pit filled with dark oily liquid.

Title: Probing and Drilling for DNAPL Characterization Text: Continuously cored samples acquired from borehole probing and drilling can help identify DNAPL presence and migration pathways. Probing Drilling Visual Direction: Pictures of probing and drilling including Percussion Probing (Geoprobe) rig, Cone Penetration drawing, Rotosonic Drilling photo, and a photo of rock cores obtained from drilling showing DNAPL.

Title: Probing Text: Soil coring using direct push technologies is less expensive than using other drilling techniques. Benefits of direct-push (DP) sampling include: rapid stratigraphic logging and contaminant detection using sensor systems, depth-discrete sampling of soil, soil gas, and water, no drill cuttings (minimal IDW), and reduced potential for contaminant drag-down. Visual Direction: No graphic.

Title: Drilling Text: Soil cores acquired from various drilling methods (i.e. rotasonic) can provide excellent quality, large diameter, relatively undisturbed core of soil and rock for characterization. This technique does present some concerns with contaminant drag-down and is more expensive than most DP methods. Visual Direction: No graphic.

Title: Methods for Examining Soil DNAPL Presence Text: The following methods can be used to help identify and locate the presence of DNAPL in the subsurface using soil samples that are brought to the surface: OVA Ultraviolet (UV) fluorescence Hydrophobic dye shake test Ribbon NAPL sampler (RNS) core strip test Chemical analysis of soil core samples Visual Direction: Three photos of RNS analysis with questionable, fairly certain, and definite DNAPL presence.

Title: Organic Vapor Analyzer (OVA) Text: This technique is quick, inexpensive, and can detect high concentrations of volatile organic compounds (VOCs) that are associated with the presence of NAPL. OVA analysis is useful to focus extended sampling efforts. OVA readings, however, can be sensitive to effective contaminant volatility, water content, sample temperature, and sample handling. Visual Direction: No graphic.

Title: Ultraviolet (UV) Fluorescence Text: Common chlorinated solvents generally "do not" fluoresce unless mixed with fluorescent impurities (i.e. oil and grease that was removed by a solvent during degreasing operations). Also, coal tar and creosote DNAPLs fluoresce. Advantages include: quick and inexpensive, many NAPLs fluoresce, it can provide detailed information on the relationship between stratigraphy and contaminant distribution, and data can be documented using a digital camera. Limitations include: it requires NAPLs that fluoresce, it is indiscriminant, interference from non-target fluorescent materials (i.e. shell fragments in coastal sediment), and there is significant potential for false positives and negatives. Visual Direction: No graphic.

Title: Hydrophobic Dye Shake Test Text: This method involves mixing a soil sample with water and a tiny amount of hydrophobic dye powder (i.e. Sudan IV). The NAPL will turn a separate color if it is present. With this method, there is potential for false positives and false negatives, and sometimes the visual contrast can be difficult to discern in dark soil. Visual Direction: No graphic.

Title: NAPL Sampler (RNS) Core Strip Test Text: This method can be used with a continuous core brought to the surface. The RNS is a hydrophobic dye-striped tubular fabric designed to contact soil cores. NAPL that contacts the RNS will react with its impregnated dye and produce a visible stain. Advantages include: simple, direct, and cost effective, RNS can provide detailed information on the relationship between stratigraphy and contaminant distribution, and RNS is amenable to rapid documentation via photography. Limitations include: some minor RNS discoloration can occur due to handling and contact with plastic core sleeves, some NAPLs only have a relatively faint reaction, color fading and/or non-detection can occur due to evaporation, wicking may exaggerate NAPL presence, and there is a potential for false positives and false negatives. Visual Direction: No graphic.

Title: Chemical Analysis of Soil Core Samples Text: With this method, the soil sample should be collected and preserved. Subsequently, the extract (preservative) should be analyzed and soil concentrations can be calculated. With additional data, these soil concentrations can be used to determine the DNAPL saturation in the soil phase. Visual Direction: No graphic.

Title: Methods for Determining DNAPL presence downhole Text: The following methods can be used to help identify and locate the presence of DNAPL in the subsurface using various tools that can be sent downhole: Membrane interface probe (MIP) Ribbon NAPL sampler (RNS) - (aka NAPL FLUTe) Downhole UV fluorescence probes Visual Direction: Graphic of a membrane interface probe with parts labeled.

Title: Membrane Interface Probe (MIP) Text: The MIP is a direct-push logging tool that records continuous relative VOC concentrations (and can be used in conjunction with an electrical conductivity sensor) with depth in soil. The MIP provides rapid, real-time, detailed characterization of stratigraphy and VOC contamination. Advantages include: wide availability, simultaneous logging of VOCs and soil conductivity, operates in the vadose and saturated zones, useful for delineating NAPL source zones, relatively inexpensive, and rapid site screening. Disadvantages include: high detection limits, qualitative analytical data, designed for volatile contaminants, contaminant carry over can be high, and ground penetration resistance limitations. Visual Direction: No graphic.

Title: Ribbon NAPL Sampler (RNS) - (aka NAPL FLUTe) Text: A flexible membrane with a color-reactive hydrophobic cover is installed downhole. NAPL wicks into the cover, leaches dye from its surface, and visibly stains the white backside of the reactive material. The liner/cover is inverted out of the hole to prevent cross contamination of the cover. The liner is then stripped from the cover to inspect the white side of the cover for stains. Advantages include: simple, direct, and cost effective method, provides a continuous record of NAPL distribution with depth in a borehole, and it can be deployed in a variety of borehole types. Limitations include: heterogeneity may limit the value of the information, some NAPLs only have a relatively faint reaction, wicking may exaggerate NAPL presence, there is a potential for false positives and false negatives, and there is a potential for cross contamination. Visual Direction: No graphic.

Title: Downhole UV Fluorescence Probes Text: Examples include SCAPS and Cone Penetrometer/ Laser Induced Fluorescence (LIF). Advantages include: real-time delineation of stratigraphy and fluorescent contamination, typical daily productivity of 300 to 400 ft at 10 to 15 locations, LIF waveforms offer product identification, verification, and rejection of non-contaminant fluorescence, reduced IDW, reduced exposure to site contaminants, and potential cost savings. Limitations include: primarily applicable to polycyclic aromatic hydrocarbons (PAHs), subject to interferences, NAPL has to be adjacent to sapphire window on apparatus, limited availability, and cost. Visual Direction: No graphic.

Title: Groundwater Profiling Text: Groundwater quality profiling using DP tools and multilevel wells can be used to locate a DNAPL source by collecting depth-discrete water samples in coarse sediments. Detailed groundwater concentration profiles developed using this method can be used to infer the location of upgradient DNAPL sources. Visual Direction: Figure showing groundwater profiling including the region of DNAPL use, concentration profile with solubility, and its transect.

Title: Characterization of NAPL Samples Text: If a DNAPL sample can be obtained, the following fluid and media related properties can be measured to better understand contaminant migration and potential remedial alternatives: Density Viscosity Interfacial Tension Wettability Saturation Capillary Pressure Relative Permeability Composition Partitioning Site specific contaminant properties should be profiled at the site because textbook values may not be representative of the impure subsurface DNAPL. These variations may be the result of off-spec materials or mixtures, chemical weathering, and chemical contact with water and solids in the subsurface. Visual Direction: Photo of a person pouring an NAPL sample into a beaker.

Title: Borehole Geophysics Text: Borehole geophysics can be conducted to help determine site stratigraphy. This information is important when determining potential DNAPL locations in the subsurface. Visual Direction: Figures of depth below surface vs. gamma, electromagnetic conductivity, and lithology and water quality are compared for two boreholes.

Title: Partitioning Interwell Tracer Test (PITT) Text: PITT estimates the residual DNAPL saturation by comparing the retardation of tracers which partition into the DNAPL phase (i.e., alcohols) to tracers that are not retarded (i.e., bromide). Some challenges to use of this technique include: The DNAPL location must be known. There must be sufficient hydraulic conductivity for the tracer test. The source zone must be small enough to allow adequate well spacing in order to conduct a tracer test in a reasonable time frame. The presence of natural organic carbon may interfere with test results. DNAPL volumes can be underestimated when its distribution is heterogeneous (i.e., pools). PITT is a very expensive characterization method. Regulators may require an underground injection permit and adequate recovery of tracers. Visual Direction: Plot of Relative Tracer Concentration vs. Time (PV) for conservative and retarded tracers.

Title: Summary Text: The goal of DNAPL detection and characterization is to develop a conceptual site model that focuses on stratigraphy, including migration pathways and traps. Source investigation methods that provide desired remediation data and simultaneously minimize the risk of contaminant mobilization should be selected. DNAPL detection and characterization strategies will vary depending on the remediation goal (i.e., containment vs. removal). IMPORTANT CONSIDERATIONS Many tools are available to perform DNAPL investigations Each site is unique and there is no practical cookbook approach Even with all the tools, DNAPL detection and characterization is difficult When performing a DNAPL investigation, use noninvasive and minimally invasive methods first Visual Direction: No graphic.

Title: Feedback Text: Visual Direction: Picture of a feedback form.

Title: References Text: The following sources provide useful information when considering DNAPL detection and characterization: Cohen, R.M., and J.W. Mercer. 1993. DNAPL Site Evaluation, CRC Press, 369 p. Griffin, T.W., and K.W. Watson, 2002.  "A Comparison of Field Techniques for Confirming Dense Nonaqueous Phase Liquids", GWMR 22(2):48-59. Kram, M.L., A.A. Keller, J. Rossabi, and L.G. Everett. 2001. DNAPL Characterization Methods and Approaches, Part 1: Performance Comparisons GWMR, Fall issue, 109-123. Kram, M.L., A.A. Keller, J. Rossabi, and L.G. Everett. 2002. DNAPL Characterization Methods and Approaches, Part 2: Cost Comparisons GWMR, Winter issue, 46-61. Pankow, J.F., and J.A. Cherry, eds. 1995. Dense Chlorinated Solvents and Other DNAPLs in Groundwater. Waterloo Press, 522 p. U.S. EPA. 2004. Site Characterization Technologies for DNAPL Investigations. EPA 642-R-04-017. September. Visual Direction: No graphic.

Title: Contact Information Text: For more information about DNAPL detection and characterization, please contact: NFESC POC (805) 982-1656 PRTH_NFESCT2@navy.mil Visual Direction: No graphic.