Tools Descriptions

Magnetometric Resistivity

• USGS 1987

Magnetometric resistivity measures the induced magnetic field created by a current passing between two electrodes. The investigation depth is controlled by electrode spacing.

Data Quality

• qualitative
• less sensitive to small conductivity variations near the measurement point
• less influenced by conductive overburden

Applicability/Advantages

• mapping preferential pathways in fractured or unconsolidated media
• more sensitive to conductive targets under moderately conductive overburden than other EM methods

Induction Resistivity (conductivity logging)

• Keys 1990
• Kobr, Mares, and Paillet 2005
• McNeill 1986
• McNeill, Bosner, and Snelgrove 1990

This tool performs inductive measurements of apparent conductivity. Given the appropriate contrasts, variations in lithology (especially relative clay or silt content) and water (relative porosity, relative total dissolved solids or conductivity/resistivity) can be recognized. With this tool, the formation without borehole and very-near borehole effects can be sensed.

Data Quality

• qualitative to quantitative depending on field conditions, prior knowledge/subsurface calibration, and experimental quality
• generally good detail and consistent except in low-conductivity environments

Applicability/Advantages

• focused beyond borehole, and thus relatively unaffected by diameter or borehole fluid conductivity
• fewer corrections needed for quantitative result
• can operate in polyvinyl chloride (PVC), not metal casing or screen

Resistivity

• COLOG 2012
• USEPA 2011b
• Keys 1997

This is a galvanic measurement of resistivity, with various configurations of current and potential electrodes. It averages over electrode spacing, typically 0.5m–2m.

Data Quality

• sensitivity to borehole diameter and fluid conductivity make results most often qualitative
• works best in highly resistive environments

Applicability/Advantages

• primarily characterizes lithology in terms of EC (i.e., water/clay content) and conductivity of pore water
• sensitive to borehole diameter, and thus can be used to detect large fractures; however, technique with typical electrode spacing (0.5m–2m) too unreliable for unsupported fracture detection

Ground Penetrating Radar Cross Well Tomography

• Annan 2005
• Chen, Hubbard, and Rubin 2001
• Dafflon et al. 2011
• Day-Lewis et al. 2003
• Ernst et al. 2007
• Irving et al. 2007

This type of imaging requires wells of appropriate diameter, casing/screen material (nonmetallic), spacing, and depth depending on the problem and aquifer dimensions and subsurface materials. The lateral penetration distance and resolution are functions of antenna frequency and EC and dielectric properties.

Data Quality

• qualitative to quantitative depending on field conditions, prior knowledge/subsurface calibration, experimental quality, and appropriate modeling

Applicability/Advantages

• can provide subsurface structure and proxy property information in an aquifer below conductive surface soil (i.e., where surface GPR may not be useful)

Optical Televiewer

• COLOG 2012
• USEPA 2004
• Keys 1997

This is an oriented visual image of the borehole wall. It aids in the evaluation of fracture orientation and aperture size in bedrock investigations. The image is originally in a downward direction, and undergoes restoration to correct for optical distortion.

Data Quality

• depends on water clarity

Applicability/Advantages

• identifies fractures and voids
• some lithologic information is interpretable from the data
• potentially finer resolution than acoustic televiewer
• works above the water table

Acoustic Televiewer

• COLOG 2012
• USEPA 2011b
• Keys 1997
• USEPA 2004

This tool obtains a highly detailed measurement of borehole diameter by timing the return reflection of an acoustic pulse off the borehole wall back to the probe. It provides a record of the location, character, and orientation of features in the casing or borehole wall that alter the reflectivity of the acoustic signal.

Data Quality

• varies depending on condition of borehole and careful data collection

Applicability/Advantages

• primarily measures fractures and their orientation
• measures borehole rugosity
• some lithologic information is interpretable
• provides borehole diameter
• provides borehole orientation
• can measure actual fracture dip
• independent of water clarity
• structural features like bedding, fractures, and solution openings

Natural Gamma Logging

• Keys 1990
• COLOG 2012
• Keys 1997
• USEPA 2004

This tool is most commonly used for identification of lithology and stratigraphic correlation. It is sensitive to the natural gamma radiation from minerals, detected at a sodium iodide crystal in the logging tool. Relatively higher counts in noncarbonate clastic sediments are commonly associated with fines (clay, silt), but also with K-feldspar, micas, and some mineral deposits (e.g., uranium, thorium, potash, phosphate). Sensitivity is related to crystal size and logging speed.

Data Quality

• qualitative to quantitative depending on field conditions, prior knowledge/subsurface calibration, and experimental quality

Applicability/Advantages

• can indicate lithology and changes in lithology
• can indicate relative abundance of silt or clay in sands
• can log in air or water and in metal or PVC cased or screened wells or uncased wells
• natural gamma logging can be combined with other sensors (e.g., fluid resistivity, temperature, caliper) in one tool
• relatively fast operation with fast turnaround on information
• information can help guide subsequent characterization work

Neutron (Porosity) Logging

• Keys 1990
• Hearst and Nelson 1985
• Barrash and Clemo 2002
• Keys 1997
• USEPA 2004

Neutron porosity probes with a large source and long spacing are used to measure saturated porosity and moisture content in a wide range of borehole diameters, above and below the water table.

The neutron source emits known flux at known energy. Collisions with hydrogen are highly moderated because of similar mass, so reduced count rates at a detector(s) in the tool indicate the presence of hydrogen (commonly water in shallow environmental applications) in the volume of influence. Water content in pores below the water table can be converted to porosity.

Well-known transforms can quantitatively convert count rates to porosity if calibration information is available from calibration wells, samples, or literature.

Data Quality

• qualitative to quantitative depending on field conditions, prior knowledge/subsurface calibration, and experimental quality

Applicability/Advantages

• can provide semiquantitative or quantitative information on porosity in wells
• can indicate relative abundance of silt or clay in sands and changes in lithology related to porosity or bound water content
• can log in metal or PVC cased or screened wells or uncased wells
• relatively fast operation with fast turnaround on information
• information can help guide subsequent characterization work

Nuclear Magnetic Resonance Logging

• Daughney, Bryar, and Knight 2000
• Grunewald and Knight 2011
• Maliva, Clayton, and Missimer 2009
• Walsh, Grunewald, and Turner 2010

The measured nuclear magnetic resonance (NMR) signal is generated directly by hydrogen nuclei in pore fluids, and it conveys detailed information about the physical and chemical pore environment in which the water resides. The NMR signal amplitude is linearly proportional to the volumetric water content; thus, NMR methods can be used to determine porosity in the saturated zone or moisture content in the unsaturated zone, without any site or lithology-specific calibration. Relaxation or decay behavior of the NMR signal is strongly sensitive to the pore size distribution—i.e., mobile water in large pores exhibits long decay time and water in small pores exhibits short decay time. Decay time behavior is commonly used to estimate a relative pore size distribution and, with porosity estimates based on the signal amplitude, form the basis for robust permeability estimation with the Kozeny-Carman relationship.

Data Quality

• emerging technique; quantitative analysis subject of ongoing research
• qualitative to quantitative depending on field conditions, prior knowledge/subsurface calibration, experimental quality, and appropriate modeling

Applicability/Advantages

• borehole tool now available for PVC screened wells
• provides quantitative profiles of porosity and permeability in aquifers, and of moisture content in the vadose zone
• physically based for unconsolidated sandy sediments
• may be able to identify DNAPL (in progress)

Video Log

• COLOG 2012

This is a typically digital video camera that records down the length of a borehole.

Data Quality

• varies and requires clear borehole fluid; resolution decreases in cloudy conditions

Applicability/Advantages

• primarily fracture and void detection
• water movement into borehole above water table and in some cases into and out of fractures
• rugosity and rock competence
• casing length and screen conditions
• basic interpretation is simple, but refined interpretation requires experience
• real-time inspection of borehole conditions

Caliper Log

• COLOG 2012
• Keys 1997

A caliper log is a mechanical measurement of borehole diameter based on the extension of three or four caliper arms. It is used to guide the interpretation of other downhole geophysical logs, because most types of logs are affected by changes in borehole diameter. It can provide information on lithology and secondary porosity.

Data Quality

• average borehole diameter based on three or four point measurements

Applicability/Advantages

• borehole diameter and rugosity
• fracture/void detection
• casing depth
• simple direct quantitative measurement of hole diameter
• uninfluenced by other activities in borehole or by water clarity

Temperature Profiling

• COLOG 2012
• Keys 1997

Temperature profiling involves the direct measurement of borehole fluid temperature. It provides information on the movement of water through a well, including the depths that produce or accept water.

Data Quality

• sensors measuring to within .001 degree Celsius (°C)
• older sensors with lower (0.1°C) resolution have limited applicability

Applicability/Advantages

• highlights critical flow zones under heterothermic conditions
• used to estimate infiltration
• heat can be used as an innocuous tracer between boreholes

• Passive Soil Gas Sampling
• ASTM 2011
• ASTM 1993
• Byrnes 2009

Passive soil gas (PSG) samplers can target a wide range of volatile organic compounds (VOCs) and semivolatile organic compounds (SVOCs) to identify source areas and vapor intrusion pathways, track groundwater contamination, and delineate the lateral extent of contaminants (e.g., Beacon BeSure PSG Samplers^TM and Gore-Sorber^®). PSG sorbent samplers consist of hydrophobic adsorbents housed in glass vials or membranes that are typically installed in shallow, small-diameter holes (e.g., 2.5 cm diameter and less than 1m deep) in uniform grid patterns or in transects. Compounds in soil gas diffuse through the soil pore spaces and are adsorbed by the sorbent samplers, which are exposed to soil gas for a few days to weeks to collect time-integrated measurements. Following exposure, samplers are analyzed at a fixed laboratory using accredited gas chromatography (GC) or GC/mass spectrometry (MS) methods that can achieve very low detection limits of individual compounds with documented accuracy. Passive soil gas surveys are performed to collect high-resolution data sets to identify source areas, track groundwater contamination, and delineate the lateral extent of contaminants.

Data Quality

• semiquantitative data – compound-specific quantitative measurements based on traceable standards but in units other than concentrations (e.g., nanograms or micrograms [μg]).

Applicability/Advantages

• enables collection of high-resolution data sets
• can provide indirect evidence of volatile NAPL present in the vadose zone, capillary fringe, and water table
• provides evidence of source areas and vapor intrusion pathways
• delineates groundwater contamination
• focuses and minimizes subsequent soil and groundwater sampling
• targets VOCs, as well as SVOCs
• detects contamination present at low concentrations
• effective in low-permeability soils and when soil is highly moist
• allows for rapid collection of samples
• requires only basic hand tools to install samplers
• minimal impact to sites
• not affected by the temporal variability of soil gas concentrations

Split Spoon Samplers

• ASTM 2013a
• ASTM 2013b
• ASTM 2013d
• ASTM 2013e
• ASTM 2013f
• ASTM 2013g

The split spoon is typically 24 inches (in) long and 2in outside diameter. The cutting shoe and drive head hold the split barrel of the sample tube together as it is pushed or driven into unconsolidated soils and sediments for sampling. It is often used through hollow-stem augers incrementally as the augers are advanced (e.g., one 2ft spoon sample for every 5ft of boring). It can be run continuously, and plastic liners can be used.

Spoons can be driven with a drop hammer to obtain standard penetration test (SPT) data if required for the investigation. Spoons may be hydraulically pushed or hammered with hydraulic hammers to collect samples if SPT data are not required. Split spoons can be used through DP installed casing to collect samples.

Split spoon samples are inspected and characterized in the field for geology using standard methods such as the Unified Soil Classification System (USCS) and qualitatively sampled with field instruments such photoionization detectors (PIDs) and field test kits (e.g., Hach).

Split spoon samples can be containerized and submitted to a laboratory for chemical and physical analysis (e.g., grain size).

Data Quality

• qualitative field inspection by visual, manual methods
• samples can be submitted for quantitative chemical analysis or other lab methods (e.g., sieve analysis)

Applicability/Advantages

• widely available
• generally used in unconsolidated formations for lithologic samples and SPT data
• spoon samples can be subsampled for chemical and physical analysis in the lab

Single-tube Solid Barrel Samplers

• ASTM 2013d
• ASTM 2013e
• ASTM 2013a
• ASTM 2013h
• Geoprobe 2011a
• Robbins et al. 1997
• Ohio EPA 2005

The single-tube solid barrel sampler is available in several lengths and diameters. Lengths are typically 3 ft–5 ft and sample diameters are approximately 1 in–4 in. Typical designs have a cutting shoe and drive head that hold a PVC sample liner inside the sample barrel. The sample is advanced incrementally into unconsolidated materials to recover samples. An outer casing is not used, so the sample tube is tripped in and out of the open borehole at increasing depths for continuous sampling. It is best used in cohesive formations.

These samplers are most often used with direct-push machines and methods, and can be used through hollow-stem augers.

Data Quality

• qualitative field inspection by visual manual methods most common
• samples can be submitted for quantitative chemical analysis or other lab methods (e.g., sieve analysis)
• best if used in cohesive soils and sediments

Applicability/Advantages

• widely available
• generally used in unconsolidated formations for lithologic samples and contaminant distribution assessment
• single-tube collected samples may be subsampled for chemical and physical analysis in lab
• rapid and cost-effective method under appropriate field conditions

Dual-Tube Samplers

• ASTM 2013a
• ASTM 2013d
• ASTM 2013e
• ASTM 2013h
• Geoprobe 2011b
• Geoprobe 2013b

These systems use an outer and inner casing or rods to advance the borehole and recover samples. The larger diameter outer casing is equipped with a cutting shoe and stays in place as the inner rod is retracted with the soil/sediment sample in a liner or sample tube. The outer casing controls the borehole wall, preventing formation collapse and increasing sample integrity as compared to single-single tube methods. Dual-tube techniques are used with DP methods, sonic methods, and hollow-stem auger methods in unconsolidated formations.

Data Quality

• qualitative field inspection by visual manual methods most common
• samples can be submitted for quantitative chemical analysis or other lab methods (e.g., sieve analysis)

Applicability/Advantages

• widely available
• generally used in unconsolidated formations for lithologic samples and contaminant distribution assessment; dual-tube collected samples may be subsampled for chemical analysis in lab
• outer casing controls borehole wall and eliminates potential for downhole collapse of formation materials
• rapid, cost-effective method under appropriate field conditions

Rock Coring

• ASTM 2013c

Rock coring is achieved through conventional or wire line tooling systems. Conventional systems require the entire rod string to be retrieved to access the core, while wireline systems allow core retrieval with a wire rope and winch. The purpose of both systems is to recover competent rock cores in a wide variety of diameters. Industry standard tooling system sizes are designated with the letters A, B, N, H, and P, the most common of which are N (1.8in core) and H (2.5in core). Most commonly, the sampling system consists of an outer barrel and inner barrel. Drill rods advance the outer barrel and cutting bit, while the inner barrel remains rotationally stationary and encompasses and grips the core for retrieval. Various carbide and diamond bits are manufactured to cut a wide range of rock types.

Rock coring requires high rotational speeds for good penetration rates. Most multipurpose geotechnical drill rigs perform well for shallow cores, while dedicated core rigs are used for deeper hole exploration work.

Data Quality

• high-quality samples can be retrieved with known orientation, allowing for accurate visualization with intact grain structure
• most accurate method for collecting competent rock samples for defining and assessing stratigraphy or rock type

Applicability/Advantages

• widely available
• used for investigation of contamination in fractured and competent rock formations
• used in consolidated formations to confirm bedrock in foundation investigations or for mineral exploration
• may be adapted to many different conditions ranging from dense sands and fractured formations to hard competent rock

Core Logging

• Kelleher 2003
• Lockman, George, and Hayes 1997
• Parker, Gillham, and Cherry 1994
• Parker, Chapman, and Cherry 2011, 2010
• Spence et al. 2005

Core is logged by a geologist for lithology and any small-scale heterogeneities. The information that can be gathered by this method includes the following:

• unconsolidated–color, grain size, sorting, roundness, plasticity, wetness, USCS class, laminations, and secondary material
• sandstone–color, grain size, sorting, roundness, wetness, secondary material, sedimentary structures, bedding, cementation index, and fractures
• carbonates–color, crystallinity, fossils (type and abundance), vugs and voids (size and abundance), sedimentary structures, bedding, cementation index, and fractures
• bedrock–lithology, lithologic changes, lithologic contacts, mineralogy, crystal size, texture, fractures, fracture orientation, fracture interconnectivity, and weathering

Data Quality

• quantitative

Applicability/Advantages

• widely available
• obtain the highest resolution of geologic units
• assists in understanding style of small-scale heterogeneities
• assists in understanding paleoenvironment conditions of subsurface and estimating vertical and lateral continuity of strata

Percent Recovery and/or Rock Quality Designation

• ASTM 2008b

Preliminary rock mass quality can be quickly estimated by measuring core recovery and calculating the rock quality designation. Core recovery is a percentage of the measured length of core in the core barrel divided by the length of the core run. Rock quality designation is a calculated percentage of the sum of recovered core pieces that are a minimum of 4in long (measured at core center) divided by the length of the core run.

Data Quality

• quantitative

Applicability/Advantages

• information essential to constructing complete borehole log
• low recovery commonly indicates high-permeability zones (i.e., sands and gravel, highly fractured rock)

Contaminant Analysis

• Camel 2000
• Dincutoiu, Gorecki, and Parker 2003, 2006
• Ganzler, Salgo, and Valko 1986
• Hewitt 1998
• Kennel 2008
• Kinniburgh and Miles 1983
• Lawrence et al. 1990
• Lopez-Avilla, Young, and Beckert 1994
• Richter et al. 1996
• Spence et al. 2005
• USEPA 1999

Contaminant analysis is best achieved by sampling the soil/rock core; however, the core can be screened using field instruments to minimize the number of samples analyzed in the laboratory.

Data Quality

• quantitative to qualitative depending on analytical method

Applicability/Advantages

• obtain vertical contaminant mass distributions
• identify soil/rock where contaminant resides

Geochemical Composition and Mineralogy

• Nicholson, Cherry, and Reardon 1983
• Nelson and Sommers 1982

This method involves testing for solid-phase organic carbon, reactive minerals (e.g., pyrite), carbonates, iron and manganese oxides, clay mineralogy, and leachable chloride.

Data Quality

• quantitative

Applicability/Advantages

• determine cation exchange capacity
• estimate sorption and other contaminant reactions
• understand contaminant retardation and degradation
• determine oxidant demand for remediation

Physical Properties

• ASTM 2008a, 2010, 1986, 2001
• Cooper and Jacob 1946
• Byers, Mills, and Stewart 1978
• Churcher and Dickhout 1987
• Tanikawa and Shimamoto 2009

The soil/rock core is sampled for physical and mineralogical analyses (e.g., permeability, porosity, fraction of organic carbon, mineralogy).

Data Quality

• quantitative

Applicability/Advantages

• obtain values for matrix K in rock core
• obtain values of other parameters needed for mass calculations and transport models

Hydraulic Profiling Tool

• Binder 2008
• Kober et al. 2009
• McCall 2010, 2011
• McCall et al. 2009
• McCall et al. 2014
• Geoprobe 2013c

The hydraulic profiling tool (HPT) is a direct-push probe with a screened injection port on the side of the tool where water is injected into unconsolidated formations as it is advanced—at 2 centimeters per second (cm/sec)—through virgin materials. A pressure sensor located in the probe assembly measures the pressure required to inject water into the formation at a flow rate of 200–300 milliliters (mL)/minute (min). A flow module at the surface contains a pump and flow meter that measures the injection flow rate. The HPT probe includes an electrical conductivity (EC) array that provides an EC log of the bulk formation. A notebook computer with Acquisition software provides real-time viewing of pressure, flow rate, and EC logs as the tool is advanced. Dissipation tests may be performed to evaluate hydrostatic pressure at multiple intervals and determine water levels. The HPT pressure log and EC log provide detailed information about lithology and hydrostratigraphy. Cross sections based on HPT pressure logs may be used to interpret hydrostratigraphy and define migration pathways and aquitards. The HPT flow rate and pressure data can be used to calculate a log of estimated hydraulic conductivity for the local formation. It takes about 1 hour to complete a 60ft (20m) log. Logs to depths of over 100ft (30m) have been obtained.

Data Quality

• high-resolution logs of HPT pressure and EC provide detailed information on lithology and hydrostratigraphy

Applicability/Advantages

• rapid, high-resolution (15 millimeter [mm]) hydrostratigraphic characterization tool capable of penetrating 300ft–600ft/day
• typically applied up to >100ft
• probe can be pushed and driven with a hydraulic hammer to penetrate difficult formations
• retraction grouting with 2.25in tools can be used to reduce risk of cross contamination
• compared to conventional CPT, Geoprobe® is less expensive, more maneuverable, and readily available
• greater depth penetration than push-only CPT tools
• small, maneuverable direct-push machines advance tools; can be used on slopes
• HPT probe includes EC array

Electrical Conductivity Logging

• Christy, Christy, and Wittig 1994
• USEPA 2000
• Beck, Clark, and Puls 2000
• McCall and Zimmerman 2000
• Schulmeister et al. 2003
• Schulmeister et al. 2004
• Wilson, Ross, and Acree 2005
• Sellwood et al. 2005
• McCall et al. 2006
• Harrington and Hendry 2006
• Binder 2008
• www.geoprobe.com

This robust DP probe can be pushed and advanced under a percussion hammer into unconsolidated formations to depths in excess of 100ft (30m) in amenable formations. The Wenner array probe has four evenly spaced electrodes where current is applied to the formation and the resultant voltage is measured. The probe can be advanced at rates as high as 5ft/min and EC data are acquired on a 15mm spacing for the log. A simple string pot tracks the depth of the probe and the rate of penetration. Uphole electronics process the analog signal and provide digital output to a notebook computer. The Acquisition software provides a live-time view of the EC log and speed/depth log as the probe is advanced.

The EC log provides an indication of lithology and permeability in fresh water formations. The EC of unconsolidated materials is primarily a function of clay content; high clay content yields higher EC readings, while sand and gravel formations yield lower EC readings. Some clays have low electrical conductance while electrically conductive fluids (e.g., salt water, sodium persulfate) can impart a very high conductance to low-EC materials.

Data Quality

• accurate soil stratigraphy at high resolution in fresh water formations

Applicability/Advantages

• rapid, high-resolution (15mm), stratigraphic characterization tool capable of penetrating 400ft–700ft/day
• typically applied to up to 100ft (30m) in unconsolidated formations; can go deeper in amenable materials
• an expendable dipole probe allows for retraction grouting to reduce risk of cross contamination; re-entry grouting with nonexpendable tools
• generally, greater depth penetration than push-only CPT methods
• small, maneuverable DP machines advance tools, can be used on slopes
• EC logs can be used to track/map ionic contaminants such as salt water or sodium permanganate

Cone Penetrometer

• ASTM D3441
• ASTM D6067-10
• Campanella and Robertson 1986
• Robertson et al. 1986
• Berzins 1993
• Lutenegger and DeGroot 1995
• Lunne et al. 1997
• McCall et al. 2006
• www.vertek.ara.com

Hydraulic rams, supported by the reaction weight of a 10- to 40-ton truck, are used to push a narrow-diameter (1.44in or 1.77in) rod with a conical point into the ground at a maximum steady rate of 2 cm/sec. An instrumented cone probe measures penetration tip resistance, sleeve (side) friction, and pore pressure. The tip resistance and friction values, which are measured using load cells, are then related to soil behavior type. Sandy soils have high tip resistance and low sleeve friction; clayey soils have low tip resistance and high sleeve friction. Pore pressure is measured using a pressure transducer connected to a ceramic screen mounted just above the cone tip. Pressure exerted on water by cone advancement dissipates more quickly in permeable media (e.g., sand) than in finer grained units. Hydraulic conductivity of tight media can be estimated in situ using the CPT pore pressure dissipation test. Penetration depth is measured using a linear displacement transducer. The soil behavior data are transmitted uphole via cabling, typically recorded each second (providing a spatial resolution of 2 cm), and compiled to generate logs, which are interpreted to delineate stratigraphy and estimate hydraulic conductivity.

Data Quality

• highly accurate soil stratigraphy at high resolution

Applicability/Advantages

• rapid, high-resolution (to 2 cm), stratigraphic characterization tool capable of penetrating 200ft–500ft/day
• typically applied to up to 300ft
• inclinometer measurements can be used to indicate if rods are bending (and push should be terminated)
• retraction grouting and grouting during advancement can be used to reduce risk of cross contamination
• greater depth penetration than percussion probing methods

Laser Induced Florescence

• ASTM D3441
• ASTM D6067-10
• Campanella and Robertson 1986
• Robertson et al. 1986
• Berzins 1993
• Lutenegger and DeGroot 1995
• Lunne et al. 1997
• USEPA 1997b
• McCall et al. 2006
• www.vertek.ara.com

Laser-induced fluorescence (LIF) tools employ a laser excitation light that pulses down fiber-optic cable within drill rods to a sapphire window, which is typically employed with a CPT tool on a DP (or similar) rig. The excitation light induces fluorescence of two-ring and higher polycyclic aromatic hydrocarbon (PAH) compounds and other fluorophores (e.g., naphthalene) located across the sapphire window. This fluorescent light is transmitted uphole through a second cable to a surface detection system. Fluorescence intensity and spectral waveforms are recorded continuously in real time and interpreted to infer NAPL presence and distribution. LIF systems that have been deployed on DP units include: SCAPS, ROSTÔ, UVOSTÔ, and TarGOSTÔ. UVOST and TarGOSTÔ probe are percussion tolerant and able to be advanced using DPT rigs (e.g., Geoprobe^®). Alternative types of downhole fluorescence probe include the fuel fluorescence detector, which uses a downhole mercury lamp for its ultraviolet (UV) light source, and the UV-induced florescence tool, which uses a UV lamp instead of a laser. Addition of fluorescing compounds to enhance DNAPL detection in situ is discussed under Dye-LIF™.

Data Quality

• semiquantitative, high-resolution NAPL detection

Applicability/Advantages

• used for continuous logging/detection of petroleum products (gasoline, diesel fuel, and jet fuel), coal tar, and creosote
• possible use for chlorinated solvent DNAPLs, commingled with fluorescing petroleum compounds or through addition of fluorescing compounds into DNAPL during probing (see Dye-LIF™)
• CPT/LIF provides concurrent delineation of stratigraphy and fluorescent contamination
• typical daily probing of 10 0m–16 0m
• with proper calibration, LIF waveforms allow product identification and rejection of noncontaminant fluorescence
• reduced investigation-derived waste and exposure to site contaminants

Membrane Interface Probe

• Christy 1996
• ESTCP 2002, 2011
• USEPA 2004
• Griffin and Watson 2002
• Bumberger et al. 2011
• ASTM D 7532
• Considine and A. Robbat 2008
• Geoprobe 2009
• Costanza & Davis 2000
• Kurup 2009, McAndrews, Heinze, and DiGuiseppi 2003
• Ravella et al. 2007
• Kober et al. 2009
• McCall et al. 2014
• Adamson et al. 2014

The membrane interface probe (MIP) is a volatile organic compound (VOC) screening tool that provides real-time data at the foot scale as it is advanced using DP methods. The MIP probe includes an EC array, and more recently has been combined with the HPT in the membrane interface probe hydraulic profiling tool (MiHpt) probe that provides both detector data for VOCs and HPT pressure data for permeability/lithology. The MIP tool uses heat to enhance the diffusion of VOCs through a membrane. The MIP membrane is made of semipermeable polymer impregnated into a stainless steel screen that is seated in a steel plate for heating to 100°C–120°C. The MIP membrane allows for the diffusion of VOCs, but resists the migration of water vapor or liquid phases. A clean, inert carrier gas (typically nitrogen) sweeps across the membrane and entrained VOCs are carried to the surface by the trunkline. The sample gas is directed to gas phase detectors at the surface. Detectors commonly used include a PID for aromatic hydrocarbons, a halogen specific detector (XSD) for halogenated compounds, and a flame ionization detector (FID) for aliphatic hydrocarbons. Detection limits vary, but are approximately as follows: 200 ppb for chlorinated compounds using an XSD; 500 ppb for individual benzene, toluene, ethylbenzene, and xylene (BTEX) compounds using a PID; and 1 ppm for BTEX and aliphatic hydrocarbons using a FID. The new low-level MIP system provides detection limits for many VOCs below 50 ppb. Results are reported as detector response in microvolts and reflect relative total VOC concentrations. The MIP also records and graphs sample depth, soil EC, and probe temperature.

Data Quality

• Qualitative to semiquantitative

Applicability/Advantages

• commonly available
• simultaneous log of VOCs and soil EC
• operates in vadose and saturated zones
• useful for delineating or focusing investigation to sources, NAPL, and elevated concentration zones
• rapid site screening, typically 200ft–400ft/day (60m–120m/day)
• using three detectors in tandem enables operator to identify different contaminant groups
• using combined MiHpt probe provides information about formation hydrostratigraphy and VOC distribution simultaneously
• new low-level MIP system provides detection limits below 50ppb for many VOC analytes

Hydrosparge

• Davis et al. 1998
• Davis et al. 1997
• Kram et al. 2001

Hydrosparge integrates a customized CPT probe with a small sampling port, a sparging device, and an above ground detector situated in a truck. The probe is advanced into the groundwater to a target depth and a liquid sample is allowed to enter the sample port. A direct sparging device bubbles helium carrier gas through the sample to purge VOCs. The stripped VOCs are carried to the surface for analysis using an ion trap mass spectrometer (ITMS) or GC spectrometer. The ITMS Hydrosparge system has demonstrated good correlation with United States Environmental Protection Agency (USEPA) Method 8260 for dissolved halogenated contaminant concentrations ranging from one to several thousand µg/L. Confirmation samples will be required when using a Hydrosparge probe for DNAPL source zone evaluation; however, a DNAPL source zone characterization approach incorporating the Hydrosparge probe techniques, when coupled with lithological sensors, will allow investigators to rapidly reach the t2 stage

Data Quality

• quantitative to semiquantitative

Applicability/Advantages

• indirect evidence based on VOC partitioning into carrier gas
• can be coupled with lithological sensors for correlation
• can use different types of detectors (FID, PID, ITMS)

CPT In Situ Video Camera (GeoVIS and ARA/Vertek)

• Lieberman et al. 2000
• Udell, Heron, and Heron 2000
• www.vertek.ara.com

The GeoVIS probe, developed by the Navy, is a real-time, in situ, microscopic soil video imaging system consisting of a miniature charge-coupled device video camera with magnification and focusing lens system integrated into a CPT platform. Soil in contact with the probe is illuminated with an array of white-light-emitting diodes and imaged through a sapphire window mounted on a probe. The video image from the camera is returned to the surface, displayed in real-time on a video monitor, and captured digitally with a frame grabber installed on the computer. The digital image can be incorporated into the SCAPS operation and data processing software to allow for depth-specific video clip recall. The standard GeoVIS optics system provides a viewing field of approximately 2 mm x 3 mm and a magnification factor of 100 when viewed on a standard 13in monitor. The system can be advanced at a rate of approximately 4 in/min. GeoVIS had been combined with a standard LIF probe to produce images of DNAPL globules known to yield fluorescence. For GeoVIS to be most effective, a recognizable color or textural contrast must exist between the DNAPL and the soil matrix. Another version of a CPT-deployed downhole video camera is sold by ARA/Vertek.

Data Quality

• quantitative to semiquantitative

Applicability/Advantages

• can provide direct evidence of NAPL presence and distribution based on video image processing
• provides continuous, high-resolution view of soil with depth
• can be used to identify geologic materials and delineate stratigraphy

Raman Spectroscopy

• USDOE 1999
• Rossabi et al. 2000
• Nielsen 2005
• Mosier-Boss, Newbery, and Lieberman 1997

Raman spectroscopy (Raman) is similar in concept and deployment to LIF spectroscopy, except that the laser used to raise the excitement state of the contaminant molecules. Raman uses a longer (785 nanometer) wavelength infrared laser and a different analytical method to identify the compounds of interest. Raman measures the light inelastically scattered from the incident light remediation. The energy shifts in the scattered light are correlated to the vibrational modes of the particular compound and constitute the Raman spectrum for the compound. As the material outside the sapphire window of the probe is exposed to laser light, the molecules in the compound present scatter light, vibrate in a distinctive way creating a vibrational fingerprint. The fingerprint is transmitted via fiber-optic cable to the analyzer where it is compared to a database of vibrational signals. The Raman system has been used to detect metals, organic compounds, oxidizers, and radionuclides in a complex mixture of waste, DNAPLS such as tetrachloroethylene and trichloroethylene, and a variety of other compounds

Data Quality

• quantitative to semiquantitative

Applicability/Advantages

• direct evidence based on Raman scatter
• fluorescence may be due to commingled materials (indirect evidence for DNAPL)
• sensitivity may be enhanced through surface coating (requires sample in contact with substrate for this configuration)

Co-Solvent Injection/Extraction

or Precision Injection/Extraction PIX Probe

• Looney, Jerome, and Davey 1998
• MSE Technology Applications 2000

The PIX method functions by solubilizing, mobilizing, and recovering NAPL in contact with a single well or specialized probe. The probe is advanced to a target depth, or the monitoring well is screened at a target depth and a known amount of water with a conservative tracer of fixed concentration is injected a few inches into the formation and is recovered by overextraction. Then, a known amount of alcohol is injected and overextracted. Differences in component concentrations, alcohol concentrations, and tracer concentrations are compared to determine the potential presence of DNAPL using a mass-balance approach. Lithologic sensors can be used to help identify candidate DNAPL zones based on potential migration pathways.

Data Quality

• qualitative

Applicability/Advantages

• potential direct evidence of presence of DNAPL
• can be coupled with lithologic sensors

Targost®

• Ferland et al. 1994

Visible wavelength LIF Tar-specific Green Optical Screening Tool (TarGOST®) is another LIF tool invented by Dakota Technologies for use on coal tar creosote, as well as bunker fuel or other multicomponent PAH-containing DNAPLs (“heavies”). TarGOST® uses visible wavelength fluorescence spectroscopy to yield monotonic response in the presence of heavies in soil. TarGOST® is a time-resolved front-face fluorometer that is fiber-optically connected to a sapphire window probe. The probe is advanced into the ground by a DP rig, and fluorescence measurements are made directly on the soil surface as the sapphire window passes by. TarGOST® can be combined with EC when using percussion DP or, when deployed on a CPT rig, geotechnical sensors that measure the mechanical properties of the soils. As the probe advances, very fast pulses of laser light are delivered by fiber-optic cable and reflected though the sapphire window by a mirror. The light is absorbed by the heavies and PAHs are driven to an electronically excited state. When the excited-state PAHs return to ground state, they emit visible and infrared fluorescence that is collected by the mirror and transmitted back up to the surface via the collection fiber-optic. Data are generated on ~1 in increments from the DP borings. The average daily production rate achieved (based on over 166 sites since 2004) is 330 ft/day. TarGOST® logging data can be used to develop high-resolution conceptual site models (CSMs) depicting the location of sites contaminated with heavy PAH DNAPLs. TarGOST® can be calibrated using DNAPL samples collected from the site.

Data Quality

• qualitative

Applicability/Advantages

• highest production heavy PAH NAPL logging technology available
• available throughout North America with 2–4 week lead times
• calibration results in accurate mapping of heavy PAH NAPL
• integration of data into GIS and other graphics systems is straightforward
• data-density reduction tools available from Dakota Technologies, Inc.

Grab Samplers; Hydrasleeve™ and Snap Sampler™

• ITRC 2006
• ITRC 2007
• HydraSleeve website http://www.hydrasleeve.com
• Snap Sampler website http://www.snapsampler.com

The HydraSleeve™ grab sampler consists of a reusable weight attached to the bottom of a long lay-flat disposable polyethylene sleeve with a self-sealing valve. Under water, the HydraSleeve™ can remain flat and sealed for indefinite time periods. It is opened for sample collection by pulling a suspension cord upward. The valve closes when the sampler is full. Samples are transferred to containers (e.g., 40 mL vials) at the surface. HydraSleeve™ samplers have been made to retrieve from 80 mL to >4,000 mL and for use in wells as small as 1 in diameter.

The Snap Sampler™ employs a cable to trigger release of a spring and close Teflon end caps on double-opening 40 mL VOA vials or polyethylene bottles (125 mL or 325 mL) in situ without headspace vapor. Once retrieved from the well, standard screw caps and preservatives can be added to the sample container. Up to six samplers can be attached in series to one trigger cable. Snap Samplers fit in 2 in or larger monitoring wells.

Data Quality

• quantitative - semiquantitative

Applicability/Advantages

• allow analysis for all common analytes (such as VOCs, SVOCs, and metals)

Accumulative Samplers

• ITRC 2006
• ITRC 2007

Accumulative samples are passive sampling devices that rely on diffusion and sorption to accumulate analytes into the sampler. Samples are a time-integrated representation of conditions at the sampling point over the deployment period. The accumulated mass and duration of deployment are used to calculate analyte concentrations in the sampled medium. Examples include:

• Semipermeable Membrane Devices (SPMDs)
• GORE™ Sorber Module
• Polar Organic Chemical Integrative Samplers (POCIS)
• Passive In Situ Concentration Extraction Sampler (PISCES)

All of these samplers involve the diffusion of chemicals, primarily VOCs and SVOCs, across a membrane from the environment into a medium that is then extracted and analyzed for contaminants of concern. SPDMs, POCIS, and PISCES are primarily designed for deployment in surface water and are used to measure bioaccumulation and toxicity, a variety of wastewater, and to identify sources of contamination. These tools are not directly relevant to DNPL site characterization.

Data Quality

• qualitative to semiquantitative

Applicability/Advantages

• simple to use and cost-effective
• can deploy in any setting
• wide range of VOCs and SVOCs
• sensitive to parts per trillion
• built-in duplicates
• disposable; no decontamination required

Membrane Diffusion Samplers

Polyethylene Diffusion Bag and Rigid Porous Polyethylene Samplers

• ITRC 2006
• ITRC 2007
• CAS lab website
• Eon Products website

Membrane diffusion samplers rely on groundwater flow through a screened or open well interval and equilibrium diffusion of dissolved chemicals through polyethylene film.

Polyethylene diffusion bag (PDB) samplers are a simple and inexpensive way to sample groundwater monitoring wells for a variety of VOCs. A typical PDB sampler consists of low-density polyethylene lay-flat tubing filled with distilled, deionized water and heat-sealed at both ends. The bags are suspended by a weighted line at the target horizon in monitoring wells and allowed to equilibrate with the surrounding water. Retrieved after the equilibration period (typically two weeks), the enclosed water is immediately transferred to appropriate sample containers for analysis. PDB samplers are typically 18 in–24 in long and 1.25 in–1.75 in diameter and provide 200 mL–300 mL of sample. One or more samplers are set at desired depths in screened or open well intervals and are left in place for at least two weeks. PDB samples, which are typically representative of adjacent well water quality during the last few days of deployment, are transferred to 40mL VOA vials for subsequent analysis.

Designed for sampling/analysis of a broader range of analytes than PDB samplers, rigid porous polyethylene (RPP) samplers are made of thin sheets of foam-like porous polyethylene with pore sizes of 6–20 microns. The pores allow a water-water interface facilitating equilibrium of water-soluble groundwater analytes with deionized water in the RPP sampler. RPP samplers can be used to sample all water-soluble analytes, including perchlorate, 1,4-dioxane, inorganic anions and cations, most metals, MEE parameters, methyl tertiary butyl ether (MTBE), hexavalent chromium, explosives, dissolved gases, and many SVOCs.

Data Quality

• qualitative to semiquantitative

Applicability/Advantages

(See above)

• used for analysis of VOCs and other parameters

FACT FLUTe

• FLUTe, Flexible Liner Underground Technologies, Ltd. L.C.
  6 Easy St., Santa Fe, NM 87506.
  505-455-1300
  www.flut.com

The FLUTe Activated Carbon Technique (FACT) is a method developed by FLUTe for mapping the distribution of contamination in the pore space and fractures of a borehole wall. The technique incorporates a 0.125 in x 1.5 in strip of activated carbon felt into the typical hydrophobic cover of the NAPL FLUTe system normally used for mapping the subsurface presence of a wide variety of NAPLs. The NAPL FLUTe cover is typically installed into a borehole on the outside of an everting FLUTe blank liner. The installation of a NAPL FLUTe cover with the added activated carbon strip allows one to draw, by diffusion, the dissolved contaminants from the formation into the activated carbon. Recovery of the liner by inversion prevents the carbon from contact with any other portion of the borehole wall. At the surface, the carbon is then sectioned for chemical analysis. With the combination of the NAPL cover and the FACT, one can map both the NAPL and the dissolved phase of many other contaminants.

(mouse over image to enlarge)

Data Quality

• qualitative

Applicability/Advantages

• direct evidence
• excellent screening tool
• fast, inexpensive, and direct method for identifying NAPL presence in soil or water boreholes
• capable of detecting clear, colorless NAPL at low saturations

Passive Flux Meter (emerging)

• Hatfield et al. 2004
• Annable et al. 2005
• www.enviroflux.com
• ITRC 2010

The EnviroFlux Passive Flux Meter™ (PFM) is designed to simultaneously measure contaminant and groundwater fluxes. It uses a sorptive permeable medium (a nylon mesh tube filled with sorbent/tracer mixture) that is placed in a borehole or monitoring well to passively intercept contaminated groundwater and release resident tracers. After a specified residence time (typically one to four weeks) in the flow field, the sorbent/tracer tube is retrieved for extraction and analysis. Detected contaminant masses are used to calculate time-averaged contaminant fluxes, and the residual tracer mass data are used to determine cumulative groundwater flux. By selecting appropriate sorbents, PFMs can be used for a wide variety of contaminants. For common organic contaminants, such as chlorinated solvents, activated carbon and a suite of different alcohols are used as the sorbent and tracers, respectively. Depth variations of groundwater and contaminant fluxes are measured by vertically segmenting sorbent/tracer mixture in a well or borehole. Fluxes across a transect perpendicular to flow are measured by placing PFMs in multiple wells.

Applicability/Advantages

• time-averaged measurements are increasingly less sensitive to short-term fluctuations in groundwater flow and contaminant concentrations
• only two site visits required
• can be used to measure vertical variations in horizontal fluxes
• passive technique requires no electrical power or pumping
• precise prior knowledge about local aquifer hydraulic conductivities not required

Hydropunch™

• Edge and Cordry 2007
• ITRC 2007

Hydropunch™ is a stainless steel and Teflon sampling tool that can collect discrete interval groundwater samples through a small-diameter drive pipe.

Data Quality

• quantitative to semiquantitative

Applicability/Advantages

• unconsolidated terrain, rapid, cost effective

Multilevel Sampling

• http://www.slb.com/services/
  additional/water/
  monitoring/multilevel_well_system/multilevel.aspx
• Black, Smith, and Patton 1986
• Patton and Smith 1988

Westbay Systems^a (Schlumberger)

First used in groundwater applications in 1978, it is a modular system using PVC or stainless steel casing with valves at the sampling point. Ports are most commonly isolated using packers that can be installed in 3 in–6.3 in (7.6 cm–16 cm) diameter boreholes. For holes ≥5 in (≥13 cm), it can be installed with backfilling option.^e

To date, the maximum installation depth achieved with the PVC version is 4,035 ft (1,235 m), and with the stainless steel version the maximum depth is 7,128 ft (2,173 m); however, deeper installations are feasible with the stainless steel version.^h

Data Quality

• quantitative

Applicability/Advantages

• least chemically reactive^c
• can be easily installed through temporary drill casing in weak rock or soils to prevent borehole collapse interfering with installation
• can monitor largest number of zones in deep boreholes
• can quality control (QC) individual packer seals from installation data and testing after MLS installation
• some design modifications can be made in the field
• can conduct hydraulic tests with the least restrictions when using the pumping port^f
• discrete sampling without repeated purging^g
• no fixed downhole (dedicated) instruments avoids irreplaceable instrument failure

Waterloo Systems^a (Solinst)

First used in groundwater applications in 1984, it is a permanent, modular system using PVC casing. Ports are isolated in 3 in–4.5 in (7.6 cm–11.4 cm) diameter boreholes using packers and in boreholes ≥5 in (≥13 cm) by backfilling option.^e

To date, the maximum installation depth achieved is 1,000 ft (305 m).^h

• http://www.solinst.com/Prod/Lines/
  MultilevelSystems.html
• Cherry and Johnson 1982
• Parker, Cherry, and Swanson 2006

Data Quality

• quantitative

Applicability/Advantages

• minimally reactive option available
• largest number of monitoring zones in shallow holes (<100 ft)
• Self-inflating permanent packers
• two options available: (1) dedicated pumps and transducers; and (2) peristaltic pump and water level tape
• wide selection of tubing materials available
• can be installed through casing using all drilling techniques
• more monitoring points can be used if only measuring head
• some design modifications can be made in the field

FLUTe Systems^b (FLUTe)

First used in groundwater applications in 1994, this system uses a continuous flexible urethane-coated nylon fabric tube (liner) to seal the borehole with spacers between the liner and the borehole wall to create monitoring zones. The entire system is pressed against the borehole wall with water or grout, and can be used in 3 in–20 in (7.6 cm–50 cm) diameter boreholes.

To date, the maximum installation depth achieved is 850 ft (260 m); however, deeper installations are feasible.^h

• http://www.flut.com/sys_1.html
• Cherry, Parker, and Keller 2007
• Keller 2009

Data Quality

• quantitative to semiquantitative

Applicability/Advantages

• most easily removable for repair/replacement or reuse of borehole^d
• smallest sampling reservoir volume
• seals entire borehole except for monitoring intervals; general overall seal is confirmed by water level measurement inside liner, except for zones with head larger than excess head in liner
• design is not restricted by individual component lengths
• simultaneous rapid high volume purging of all monitoring intervals
• more monitoring points can be used if only measuring head
• most easily installed in artesian holes
• most convenient for angled holes and holes in karst

NAPL FLUTe

• Keller 2012
• FLUTe, Flexible Liner Underground Technologies, Ltd. L.C.
  6 Easy St., Santa Fe, NM 87506.
  505-455-1300
  www.flut.com

The NAPL FLUTe is a hydrophobic cover installed over the standard impermeable liner that, following eversion, is in contact with the borehole wall. When NAPL comes in contact with the FLUTe, it penetrates the cover, resulting in a visually distinct stain that can be correlated to depth upon inversion and removal of the liner.

(mouse over image to enlarge)

Data Quality

• qualitative

Applicability/Advantages

• direct evidence
• complex method for identifying NAPL presence directly in contact with borehole
• capable of detecting clear, colorless NAPL at low saturations

Dye Techniques (e.g., Sudan IV dye, Red Oil DNAPL-Lens-Detect )

• Parker et al. 2003
• Cohen and Mercer 1993
• www.oilin-soil.com
• Cohen and Mercer 1993
• Pankow and Cherry 1996

Direct visual detection of NAPL in soil or water may be difficult where the NAPL is clear and colorless, present at low saturation, or distributed heterogeneously. Hydrophobic dye can assist visual detection of NAPL. The test involves adding a very small amount of a hydrophobic dye (e.g., 2 mg), such as Sudan IV, soil (e.g., ~20 cc), and a small volume of clean water (~15 mL) in a sealed plastic or glass jar (e.g., a 40 mL vial), which is then capped and shaken by hand. Sudan IV is a reddish-brown powder that dyes organic fluids red upon contact, but is practically insoluble in water at ambient temperatures. If NAPL is present in a sample (and contacts the dye), it will appear as red globules, a red meniscus, or a red film. Background and NAPL-contaminated samples should be examined to check for interference and site-specific response. A similar test can be made on water samples by adding dye. Test kits with enhancements are available commercially.

Data Quality

• qualitative

Applicability/Advantages

• direct evidence
• excellent screening tool
• fast, inexpensive, and direct method for identifying NAPL presence in soil or water samples
• capable of detecting clear, colorless NAPL at low saturations

Ultraviolet Fluorescence

• Kram et al. 2001
• Kram and Keller 2004a, 2004b
• www.ptslabs.com

Fluorescence refers to the spontaneous emission of visible light resulting from a concomitant movement of electrons from higher to lower energy states when excited by UV radiation. Samples and core can be inspected in a dark space under UV light (e.g., using a small portable UV light box) for fluorescence, which may indicate the presence of NAPL containing PAHs or other commingled fluorophores. Fluorescent response depends on UV excitation wavelength. Known background soil and NAPL-contaminated samples should be checked for interference and site-specific NAPL response.

Data Quality

• semiquantitative

Applicability/Advantages

• can illuminate NAPLs that fluoresce, including those that contain PAHs (coal tar, creosote, and petroleum products) and those mixed with fluorescent impurities (e.g., oil and grease removed by solvent during degreasing, humic compounds from natural organic matter)
• can provide detailed information on relationship between stratigraphy and fluorescent NAPL distribution
• can guide selection of subsamples for chemical or saturation analyses

Membrane Interface Probe

• Christy 1996
• ESTCP 2002, 2011
• Griffin and Watson 2002
• USEPA 2004
• ESTCP 2011
• SERDP 2002
• USACE 2002
• www.geoprobe.com

The MIP is a screening tool that provides real-time, near-continuous data on VOCs. The MIP tool uses heat to enhance the diffusion of VOCs through a membrane. The MIP membrane is made of semipermeable thin film polymer impregnated into a stainless steel screen that is seated in a steel plate for heating to 100°C–120°C. The MIP membrane allows for the diffusion of VOCs, but resists the migration of vapor or liquid phases. A clean, inert carrier gas (typically nitrogen) sweeps through tubing attached behind the membrane and carries VOCs that have diffused through the membrane to gas phase detectors at the surface. Gas phase detectors commonly used include a PID for aromatic hydrocarbons, an electron capture detector (EC or ECD) for halogenated compounds, and a FID for aliphatic hydrocarbons. Detection limits vary, but are around 200ppb for chlorinated compounds using an ECD, 1 ppm for BTEX compounds using a PID, and 1 ppm for BTEX and chlorinated compounds using a FID. Results are reported as detector response in microvolts and reflect relative total VOC concentrations. The MIP also records and graphs sample depth, soil conductivity, and temperature.

Data Quality

• qualitative to semiquantitative

Applicability/Advantages

• commonly available
• simultaneous log of VOCs and soil conductivity
• operates in vadose and saturated zones
• useful for delineating or focusing investigation to sources, NAPL, and elevated concentration zones
• rapid site screening (typically 50 m–100 m/day)

Background Fluorescence Analysis

• Otz 2005
• Otz et al. 2005

Background fluorescence analysis (BFA) can be successfully applied to identify and understand preferential groundwater flow pathways as well as to delineate extent of contaminated areas.

It relies on the principle that most mixtures of organic compounds emit at characteristic patterns of fluorescence when exposed to specific frequencies of EM radiations and BFA can fingerprint such fluorescence patterns. The fluorescence of a water sample has therefore a unique fluorescence fingerprint, which is based on the dissolved organic content of that water sample (resulting from naturally occurring and manmade organic substances).

When fluorescence fingerprints show similar patterns (similar slope and peaks in the scan), one averted BFA analyzer can conclude that the freight is also similar and a hydraulic connection is probable. In a homogenous isotropic aquifer, all fingerprints would be the same.

Increasing fluorescence intensities also correspond with increasing concentrations of a contaminant plume.

A useful supplement to the basic BFA is the introduction of artificial fluorescence drug- and cosmetic-grade dyes in a fluorescent dye-tracing test. Seven different fluorescent dyes may be implemented to quantitatively evaluate preferential groundwater flow paths.

Data Quality

• qualitative to semiquantitative

Applicability/Advantages

• analysis of water samples, minimum volume requirement of two 40 ml vials per location
• location of preferential groundwater flow paths
• identification of presence or absence of hydraulic connections between areas or monitoring wells
• potential separation of organic plumes resulting from releases at different locations and dates, identification of degradation products, and natural attenuation processes
• differentiation between impacted and non-impacted groundwater
• outline of degree of affected groundwater within a single plume
• nondetections are not an issue as many organic substances can be detected in lower parts per trillion

Colorimetric Screening

• http://www.aqrcolortec.com
• Triad Central 2011a

Color-Tec is a field-based analytical method that combines sample purging with colorimetric gas detector tubes to detect total chlorinated volatile organic halocarbon compounds in any ex situ liquid or solid sample at concentrations from ~3 µg/L or µg/kg. Samples are analyzed in 2 min or less by purging the volatile compounds from the sample directly through the colorimetric tube, which is designed to produce a distinct color change when exposed to chlorinated compounds. Estimated sample concentrations are obtained by comparing the tube readings to a conversion table, which was developed based on comparison of the method values to GC/MS analysis of split samples.

Data Quality

• semiquantitative

Applicability/Advantages

• on-site, real-time analysis
• low-cost analysis
• able to develop high-density data sets
• decision quality data

Direct Sampling Ion Trap Mass Spectrometer

• USEPA Method 8265
• Wise et al. 1997
• Wise and Guerin 1997
• www.triad-env.com
• Davis et al. 1998
• Costanza and Davis 2000
• Davis and Hayworth 2006

The direct sampling ion trap mass spectrometer (DSITMS) is a field portable instrument used for real-time, on-site analysis of VOCs. The DSITMS is the basis of USEPA SW-846 Method 8265. The method involves direct analysis of VOCs from field samples without chromatographic separation. The DSITMS has sample introduction capabilities for analysis of water, soil extracts (USEPA Method 5035), and vapor samples. The analysis times are 3 min/sample for water and soil samples and 6 min/sample for vapor samples. The short analysis time allows a single instrument and operator to analyze up to 80 samples/day for water and soil and 60 samples/day for vapor, plus full QC analyses.

Data Quality

• quantitative

Applicability/Advantages

• compound specific analysis in real-time
• limits of detections of single μg/L for water, 10–20 μg/kg for soil and <10 μg/m³ for vapor
• accurate and precise due to use of high-level QC
• due to the very short analysis time, extra QC beyond the minimum requirements are routine
• support rapid, on-site development of high-density data sets
• support real-time decisions for optimization of allocation of sampling resources

Fluorescence In Situ Hybridization

• Aman and Fuchs 2008
• Pernthaler and Amann 2002
• Wagner, Horn, and Daims 2003
• ITRC 2013

Fluorescence in situ hybridization (FISH) is a molecular biology method used to visualize and enumerate specific types of microorganisms or groups of microorganisms in an environmental sample. The method does not require isolation or cultivation of microorganisms and allows for examination of microorganisms in complex environmental samples with minimal disruption of the natural microbial community. Since its introduction in the late 1980s, FISH has been used in medical and developmental biology and environmental bacteriology. Today, FISH is considered to be a powerful tool for phylogenetic, ecological, diagnostic, and environmental microbiology studies.

FISH is a technique used to detect and locate a particular genetic sequence (DNA or RNA) on a chromosome by using a complimentary fluorescently-labeled genetic probe. This probe is designed to only bind to areas of the chromosome that have significant sequence similarity.

Data Quality

• qualitative

Applicability/Advantages

• for environmental applications, FISH typically used to identify microorganisms known to degrade a particular contaminant
• FISH results typically used with other lines of evidence in natural attenuation studies

Compound Specific Isotope Analysis

• ITRC 2011a
• USEPA 2008
• Kuder and Philip 2008
• Schmidt et al. 2004
• Kuder et al. 2005
• McHugh et al. 2011

Compound-specific isotope analysis (CSIA) is used to directly examine individual contaminants to learn both about their original isotopic composition and about any degradation the compound has undergone. CSIA establishes mass loss (biotic or abiotic degradation) as the mechanism for decreasing concentrations of contaminants.

A key feature of CSIA is that degradation processes produce distinct isotopic enrichments that are not caused by mass transfer processes such as dilution or adsorption.

CSI can be used to demonstrate degradation by measurement of an isotopic shift in the ratio of stable isotopes of elements such as carbon and hydrogen when multiple degradation processes are occurring. Fractionation results from degradation of lighter isotopes as compared to heavier isotopes due to thermodynamics and low bond energy within the former; therefore, an enrichment of the heavier isotopes occurs following degradation of the lighter isotopes of the parent compound (i.e., less negative δ13C values).

Data Quality

• quantitative to semiquantitative

Applicability/Advantages

• assessment of contaminant sources when multiple sources possible
• identification and quantification of degradation at lab- and field-scales vs. mass transfer
• estimating natural attenuation rates

Enzyme Activity Probes

• ITRC 2011a
• Clingenpeel et al. 2005
• Gu et al. 2011

Enzyme activity probes (EAPs) are chemicals used to detect and quantify specific activities of microorganisms in environmental samples (e.g., soil, water, or sediment). EAPs are transformed by the target enzyme into a readily detectable product that can be measured and predicted. Most microbial enzymes are not functional outside of a cell; therefore, EAP response provides direct evidence that microorganisms in the sample are active. There is also a strong positive correlation between the rate of transformation of an EAP and the number of microorganisms actively producing the enzyme, so the microorganisms’ abundance in the environment can be estimated. Some EAPs are designed to have a fluorescent product so that the cells with active enzymes will fluoresce when viewed on a fluorescence microscope. Other EAPs result in a readily detectable product that can be quantified by other means.

Data Quality

• quantitative to semiquantitative

Applicability/Advantages

• can be used to estimate the concentration of active microorganisms with the active enzyme of interest, e.g., responsible for biodegradation
• proven technology
• many EAPs available for both anaerobic and aerobic metabolic processes
• EAPs can be used to establish degradation rates
• total cells vs. active cells can be counted on same slide with two different fluorophores

DNA Microarrays

Environmental samples can contain thousands of different microorganisms and many different functional genes, some of which can serve as process-specific biomarkers. Phylogenetic microarrays evaluate community composition based on the presence/absence of microbial 16S rRNA genes present in a sample.

A microarray is a solid surface upon which microscopic spots of DNA probes are attached. These probes are designed to represent genes that, when expressed, indicate a microbial activity. A gene is expressed when it produces messenger RNA (mRNA) – the genetic sequence of the messenger RNA produced is copied as cDNA (complementary DNA) using fluorescently labeled nucleotides. This cDNA is then exposed to the microarray and sequences that are complementary hybridize to the gene probes and fluoresce. A single microarray can be used to compare expressed genes in different microorganisms by using different colors of fluorescent nucleotides.

Data Quality

• qualitative and semiquantitative

Applicability/Advantages

• test for many thousands of different microorganisms and many different functional genes, some of which can serve as process-specific biomarkers
• in addition to DNA microarrays, many other types (e.g., protein, cellular, tissue, antibody) are available
• detection and relative quantification of thousands of organisms or functional genes in a single analysis
• information about gene expression (i.e., activity) can be obtained

Microbial Fingerprinting

• ITRC 2011a
• Muyzer et al. 1993
• Hedrick et al. 2000
• Osborn, Moore, and Timmis 2001
• Bent, Pierson, and Forney 2007

Fingerprinting methods are used to provide an overall view of the microbial community, indications of microbial diversity, and insight into the types of metabolic processes occurring in the aquifer (e.g., notably the terminal electron-accepting processes such as sulfate reduction). Microbial fingerprinting methods differentiate microorganisms or groups of microorganisms based on unique characteristics of a universal component or section of a biomolecule (such as phospholipids, DNA, or RNA). Microbial fingerprinting methods provide an overall profile of the microbial community, indications of microbial diversity, and insights into the types of metabolic processes occurring. In some cases, they can be used to identify subsets of the microorganisms present.

Methods include: denaturing gradient gel electrophoresis (DGGE), terminal restriction length polymorphism (T-RFLP), and phospholipid fatty acid analysis (PLFA). PLFA analysis provides total microbial biomass and a general characterization of the microbial community. The relative abundance of several different microbial functional groups (e.g., sulfate-reducing bacteria) is measured based on the concentrations of membrane lipids. DGGE and T-RFLP are both genetic fingerprinting methods. DGGE provides a genetic fingerprint of the microbial community based on melting rates during electrophoresis. T-RFLP is similar to DGGE except that the separation is based on the sizes of the DNA/RNA fragments produced by digesting the DNA/RNA with restriction enzymes.

Data Quality

• qualitative to semiquantitative

Applicability/Advantages

• all three methods are commercially available
• does not require growth of measured microbial communities during testing; therefore robust compared to other EMDs
• identify predominant bacteria or group of organisms present in sample to family or even genus level
• requires little prior knowledge about which microorganisms are of interest
• evaluate whether the subsurface biogeochemistry at a site is conducive to known bioremediation pathways

Polymerase Chain Reaction

• ITRC 2011a
• Pavlov et al. 2006
• Saiki et al. 1988
• USEPA 2004
• Bartlett and Stirling 2003

Polymerase chain reaction (PCR) is a technique that can test for the presence of the specific microorganism, family of microorganisms, or expressed genes in environmental samples such as soil, water, or sediment. PCR is a category of laboratory methods that can be used to detect the presence of either (a) a specific microorganism or group of microorganisms that are known to be able to biodegrade a specific contaminant or group of contaminants or (b) DNA sequences (genes) that regulate the production of enzymes (proteins) that biodegrade or partially biodegrade these contaminants.

PCR capitalizes on the ability of DNA polymerase (the enzyme that copies a cell’s DNA before it divides in two) to synthesize new strands of DNA complementary to a template DNA strand. A DNA primer linked to a particular bacterium or microbial activity is amplified (30–40 times) to generate enough copies of the DNA so that it can be visualized to confirm the presence of that DNA and therefore that bacteria or metabolic capability in that environment.

Data Quality

• qualitative to semiquantitative

Applicability/Advantages

• mature technology (1960s)
• capable of detecting specific microorganisms or target genes within diverse microbial communities
• results are available within days
• can be performed on a variety of sample types (e.g., water, soil, sediment)

Quantitative Polymerase Chain Reaction

• ITRC 2011a
• Peirson and Butler 2007
• Davis et al. 2008
• Hendrickson et al. 2002
• Lee et al. 2008
• Baldwin et al. 2010
• DeBruyn, Chewning, and Sayler 2007
• Hristova et al. 2003
• Amos et al. 2007

Quantitative polymerase chain reaction (qPCR) and reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) are used to quantify the abundance and activity of specific microorganisms or expressed genes in pathways capable of biodegrading contaminants at a contaminated site. Quantitative PCR is a method for estimating the concentration of a particular genetic sequence in an environmental sample. The concentration of that genetic material is then related to the concentration of a particular microorganism or class of microorganisms.

Data Quality

• quantitative to semiquantitative

Applicability/Advantages

• commercially available
• quantify abundance of specific microorganisms capable of biodegrading identified contaminants
• identify whether or not specific genes are being expressed for contaminant biodegradation

Stable Isotopes

• Coplen, Herczeg, and Barnes 1999
• Harte 2013a

Deuterium, oxygen-18, and carbon-13 isotopes provide qualitative information on the origin of water that can be used to infer age in some cases.

Data Quality

• qualitative estimate of age and processes

Applicability/Advantages

• help identify environmental processes that affect water such as climate and vegetation

Radioactive Tracers

• Cook and Böhlke 1999
• McKinley 1994

Radioactive isotopes can be used to calculate the age of groundwater based on the rate of decay of a radioactive isotope and input concentration at the time of recharge into the groundwater system. Some common radioactive isotopes include hydrogen (tritium), helium, carbon-14, and chlorine-36.

Data Quality

• quantitative to semiquantitative

Applicability/Advantages

• independent assessment of fracture connectivity based on age of groundwater
• could be used to identify dual permeability or bimodal ages of multiple water origins
• assessing well integrity

Anthropogenic Chemical Tracers

• Cook and Böhlke 1999

Chemical tracers typically have distinct input concentrations at the time of recharge, from being in contact with the atmosphere, that can be used to estimate age. Some examples of chemical tracers include chlorofluorocarbons and sulfur hexafluoride.

Data Quality

• semiquantitative

Applicability/Advantages

• independent assessment of fracture connectivity based on age of groundwater
• identify dual permeability or bimodal ages of multiple water contributions