Data Quality

• Qualitative, based on interpretation.
• Topographic maps are updated every three years and are GIS based. They are digitized and easily print as a PDF.
  

Advantages

• A high-level view of site area for preliminary evaluation.
• Older maps can show pertinent features that may have been erased by development.

(Aerials 2017)

(Agriculture 2017)

Data Quality

• Qualitative, based on interpretation.
• With current technology, the quality of most recent aerial photography is relatively good, and has been digitally produced.
  

Advantages

• An overall view of the area of interest can be obtained prior to fieldwork, which can provide information regarding areas requiring further investigation such as ponding, lineaments, and other surface features.
• Can often be integrated into GIS.
• Can cover large areas relatively quickly.

• Quality of older photographs can sometimes be poor.
• High-altitude photographs sometimes limit resolution.
• Eye can be tricked by human created features (such as roads or walls).

(USGS 2017a)

(USGS 2017c)

(NASA 2017)

Data Quality

• Qualitative, based on interpretation.
  

Advantages

• An overall view of the area of interest can be obtained prior to fieldwork, which can provide information regarding areas requiring further investigation such as ponding, lineaments (see Regional Geologic Maps), and other surface features.
• Can often be integrated into GIS.
• Can cover large areas relatively quickly.
• Can view same area at different scales.
• Can view in normal light with true color image or false view color (infrared)

• Level of resolution detail can vary from weather satellites (low), NASA (moderate), and commercial satellites (high).
• Clouds can affect image, especially on large-scale images.
• Shadows on imagery can confuse interpretation of mountains or canyons, depending on satellite angle.

(USGS 2017d)

(USGS 2017e)

(USGS 2017b)

Data Quality

• Qualitative, based on interpretation.
  

Advantages

• Bedding planes, faults, orientation, and lithology are already mapped for interpretation.
• Maps occur at various scales and mapping qualities (such as reconnaissance or open-file reports).

• Geologic information on remote areas is not always ground-truthed.
• Scale of map may not provide sufficient detail.
• Some areas not mapped in detail.
• Limited by the degree to which mapping has been completed in an area and at what scale.

Data Quality

• Quantitative or qualitative. Varies depending on the source.
  

Advantages

• Can provide information on a specific area or site where no information is otherwise available.
• Upfront information prior to start of assessment or remediation work.

• Can be limited.
• Data may be questionable if not properly peer reviewed.
• The purpose of the research may not encompass the information needed for the site.

(Brown 1994)

Data Quality

• Qualitative, data varies depending on source. Similar limitations as aerial photographs.
  

Advantages

• Can give good baseline data before field investigation to pick out orientations and structure, and to evaluate potential well placement by intersection points.
• Can often be incorporated into GIS.

• Harder to discern lower angle imagery with respect to orientation of feature.
• Depending on quality and resolution, may require ground-truthing.

Data Quality

• Quantitative to qualitative
  

Advantages

• Outcrop surveys are valuable information used to design future investigations.
• Hands-on and reasonably inexpensive.

• Provides data point that must be used to extrapolate between outcrops.
• Data between outcrops can only be inferred.

Data Quality

• Qualitative to quantitative, based on available rock exposures, condition of the exposure, and three-dimensional exposure of the fracture plane.
  

Advantages

• Delineating fracture orientation from surface expression and outcrops offers direction to future subsurface investigation to determine aperture, connectivity, continuity, and roughness.

• Fracture orientation is based solely on surface expression and outcrops. Subsurface interpolation of the orientation should be confirmed using geophysical or intrusive subsurface techniques.

Data Quality

• Qualitative to quantitative, depending on data population and algorithm processing.
  

Advantages

• Images can be collected from distances ranging from meters to aerial to satellite-scale data.

• Visual representation of lineaments may be masked by overburden or vegetation.

Data Quality

• Qualitative to quantitative, depending on source.
  

Advantages

• Can give good baseline data before field investigation to pick out orientations and structure and evaluate potential well placement by intersection points.
• Another tool to evaluate fracture locations.

• May not be associated with fracturing.
• Data may be limited depending type of survey.
• Spring/wetland locations not always previously surveyed.

GPR generates a two-dimensional (2D) profile, but it can be run with multiple lines in a grid pattern to generate a pseudo-three-dimensional (3D) image. Penetration and resolution of features depend on antenna frequency and material conductivity and interferences, and are generally limited to a depth of 20 m or less. In some cases, GPR can identify internal structures between material-bounding reflectors (such as cross-bedding).

GPR can locate geologic material or property contacts associated with dielectric property contrasts (for example, proxy for porosity in some water-saturated clastic sediments) as well as subsurface infrastructure (such as pipes, tanks, and cavities). This method is often similar to the seismic reflection method to image bedrock troughs and offsets in bedrock surfaces. It is a rapid and relatively easy survey method, but limited by the presence of strong conductive layers that the method cannot penetrate. This method can be used in conjunction with other methods, particularly where the bedrock surface is at shallow to intermediate depths and is overlain by relatively resistive layers. In these cases, the method can be used to quickly assess whether linear features identified through lineament analyses are associated with increased depths with bedrock troughs or have another characteristic that might be related to fractures, such as a thickened weathered zone.

(Annan 2005b; Beres 1995; Clement 2006; Guerin 2005; Buursink 1991) (USEPA 2004)

Data Quality

• Varies with antennas and subsurface EC.
• Relatively sharp boundaries.
• Qualitative to quantitative, depending on field conditions, prior knowledge/subsurface calibration, experimental quality, and appropriate modeling.
  

Advantages

• Relatively fast to acquire, and processing methodology well established.
• Primarily used in materials with low EC (sand, gravel, or rock except shales)
• Can be run repeatedly in time-lapse mode to track changes in moisture (above water table) or electrical conductivity or dielectric properties (plume or spill bodies), including several experiments tracking presence and changes in DNAPL in sandy aquifers.

• Minimal penetration in electrically conductive (silts and clay-rich or conductive pore water) units.
• Interpretation of features and depths semiquantitative without independent reference (boring well or cone penetrometer).
• Possible interferences from radio frequency transmitters and large metal objects.

This type of imaging evaluates both compression (P) waves and shear (S) waves, and profiles multiple stratigraphic layers to large depths.

These data require more processing than other geophysical methods, but can provide highly detailed representations of the subsurface—particularly the soil/bedrock interface. The utility in fractured rock characterizations is to identify discontinuities that may be related to fracture zones, velocity contrasts that might be indicative of fractures, or bedrock troughs at the bedrock/overburden interface that may indicate zones of weakness. Shear wave and multicomponent seismic reflection data acquisition and processing can enhance data capture for interpreting fractures within geologic units.

(USEPA 2004) (ASTM 2005) (Wightman 2003)

Data Quality

• Varies depending on site conditions.
  

Advantages

• Identification of the bedrock surface and lithological layering, but not necessarily material type.
• Patterns can be diagnostic of depositional environment.
• Can be used in some cases to identify water table depth.
• Can be used with marine seismic survey to assess below-water bodies.
• Imaging at greater depths than refraction and surface waves.
• Potential high resolution of large voids, faults, and fractures at depth; S-wave surveys allow shallower surveys, but are still limited by near surface noise.

• Difficult to get reflections from shallow (<10m deep) boundaries.
• Resolution varies with input frequency and geometric and acoustic characteristics.
• Labor intensive, slow, relatively expensive.
• Difficult to implement in areas with extensive infrastructure.

Seismic refraction data can be used to map both vertical and horizontal changes in travel time and velocity. Delay time differences and changes in velocity can be used to infer the potential changes in velocity. One method of using refraction to identify fracture orientation is to complete seismic lines in incremental azimuths about a common center point. The seismic velocity for each point beneath each line is then plotted for each radial distance about that common point. High seismic velocities generally are aligned parallel to the primary alignment of fractures. Low seismic velocities are oriented perpendicular to the strike of the fractures. This approach assumes that the fractures or fracture zone is large and contiguous. Small fractures or disconnected fractures would not be imaged using this technique.

(ASTM 2000; USEPA 2004; Singhal B.B.S. 1999; Gupta 1999)

Data Quality

• Varies depending on site conditions.
• Low detail.
  

Advantages

• Identifies lithological layering, but not necessarily material type.
• Works on shallow layers.
• Identifies geologic boundaries (overburden layers, bedrock depth).
• In some cases, can identify water table.
• Identifies potential topographically influenced DNAPL flow pathways,

• Only identifies boundaries of progressively increasing velocity.
• Cannot detect thin layers.
• Limited to maximum of three to four layers.
• Maximum depth generally 40 m–50 m (requires long arrays).
• Cannot be implemented in areas with high levels of background vibrations (such as roads or active railways).

2D imaging is cross-sectional imaging of the ground-based reflection of a seismic pulse from the boundaries between layers of contrasting mechanical properties. S-wave velocity is a function of the elastic properties of the soil and rock and is directly related to the hardness and stiffness of subsurface materials. (Park 1999)

Data Quality

• Quantitative to Qualitative depending on spacing of detectors and depth
  

Advantages

• Determines the depth and thickness of subsurface stratigraphy.
• Can identify low-velocity (soft) zones beneath high-velocity (hard) zones.
• Evaluates shallow features that may serve as DNAPL transport and groundwater flow paths.
• Minimal effects from buried piping or utilities.
• Data to aid in monitoring well selection zones for vertical characterization.
• Identifies karst terrain, voids, waste pits, and surface bedrock features.

• Limited to depths ≤100 feet .
• Can be difficult to implement in some areas due to access restrictions.
• Difficult to use and interpret data in irregular terrain.
• Works best in areas with gradational contacts between lithologies.

Typical deliverables from a geophysical contractor consist of a report, figures, and interpretive resistivity cross-sections. A resistivity cross-section consists of a plot depicting the measured earth resistivity at various depths and locations along the cross section. These data are typically contoured and displayed using a gradational color-scheme ranging from low to high resistivity. The responses observed in and the utility of this method in fractured rock settings depend on several factors such as the rock type, degree of fracturing, nature of fracture infilling (if any), water within fractures, and mineralization.

Generally, this technique is most useful for identifying steeply dipping to near vertical, water-filled fractures. These features are interpreted from where areas of lower resistivity are separated by areas of higher resistivity areas. Typically, resistivity lines are laid out across a site and an attempt is made to correlate low conductivity areas across lines to infer fracture orientation. A variation of this technique, called the azimuthal square-array electrical resistivity, can determine the strike of a conductive feature in the subsurface. (Binley 2005; Telford 1990; ASTM 1999a)

Data Quality

• Varies with ground contact configuration (such as Wenner or dipole-dipole) and electrode spacing.
• Boundaries are gradational.
  

Advantages

• Works well to identify depth to rock and lithologic thicknesses.
• Can map lateral and vertical lithologic changes, indicates broad-scale lithologic variations.
• Useful in determining fracture orientations using azimuthal measurements water table depth.
• Maps electrically conductive pore water, including saltwater intrusion.
• Data quality varies with ground contact configuration (such as Wenner or dipole-dipole) and electrode spacing.

• Resolution decreases with depth, but effective to 60 m vertically.
• Deep applications require long straight line access; may not be suitable for small sites.
• Can be difficult to implement in some areas due to access restrictions.
• Influenced by nearby metallic infrastructure such as fences, piping, and electrical transmission lines.

(USEPA 2016b)

(McNeill 1991)

Data Quality

• Generally qualitative, a reconnaissance-level survey.
  

Advantages

• Variations in primary field orientation can be used to identify discontinuities (faults and large fractures).
• Can be used to map lateral variations in electrical resistivity down to approximately 25m–40m.
• Quick, inexpensive survey.

• Military transmitters are becoming obsolete.
• Relatively coarse survey.
• Orientation sensitive; multiple line directions may be necessary.
• Conductive structures affect local measurement of direction and strength of field.

Time-domain electromagnetic methods (TDEM) produce data that are interpreted similar to resistivity methods. In this case, the electrical conductivity of geologic and hydrogeologic phenomena are interpreted, but the decay of the current is measured over time. The setup generally consists of a large horizontal wire laid out in a square on the surface. The depth of penetration is related to the size of the square, with larger squares achieving deeper signal penetration into the subsurface. The transmitter is turned on and off while the decay of the secondary magnetic field is measured at a receiver.

In a low resistivity layer, the decay is slow, while in a highly resistive layer the decay is fast. Completing a profile over a conductor would show an increase in the delay as the array is passed over a conductor. Profiling is completed and interpretations of the delay times are used to evaluate changes conductivity that may be indicative of subsurface structures. This technique is most commonly used in mineralogical exploration, but can be adapted for groundwater and study of structures such as faults or near vertically oriented, fluid filled fractures.

Frequency domain electromagnetic methods (FDEM) methods (also known as EM or terrain conductivity) operate like TDEM, except that signals of known frequency are introduced using a transmitter coil while a receiver coil measures the secondary field response. Differences in the primary and secondary fields result from the effects of changes in conductance of subsurface materials in depth and along the survey line. Generally, the depth of penetration is related to the spacing of the transmitter and receiver coils. The farther apart the coils, the greater the depth of penetration.

Using this technique for fracture identification is like using the methods described above in that vertical to steeply dipping conductive features are apparent on profiles. Mapping profiles in plan-view can indicate likely fracture orientation. The thickness of the unconsolidated deposits above the bedrock surface affects the resolution of the results, with thin unconsolidated deposits resulting in a higher likelihood that a signal from a vertical to steeply-dipping, fluid-filled feature can be resolved. This technique alone does not confirm the presence of a fracture (McNeill 1994).

Data Quality

• Qualitative, primarily reconnaissance mapping.
  

Advantages

• Can be used to map lateral variations in EC from <1 m deep to >40 m deep.
• Identifies broad geologic variations or conductive plumes.
• Shallow, high-resolution systems can be used to map infrastructure.
• Quick, inexpensive survey technique.

• Resolution decreases with volume sampled (penetration).
• Can be subject to interference from surface infrastructure and power sources.
• Penetration can be varied by changing coil orientation and spacing, but vertical resolution of layers is poor.
• Generally qualitative rather than quantitative result.
• Vertical modeling of data is limited. Bulk measurement reduces void resolution potential to large, shallow voids; depth of investigation reduced by low-resistivity materials.

Data Quality

• Qualitative.
  

Advantages

• Interpreted data provides a profile of apparent resistivity versus depth. The interpreted profile can be used to identify water filled fractures.
• Surveys are relatively easy to conduct and once set up, data acquisition is rapid.

• Resistivity profiling is more qualitative than quantitative and requires high degree of subjective interpretation
• Survey layout can be labor intensive.

Data Quality

• Qualitative
  

Advantages

• Historically has been used with good success in measuring mineralogical changes particularly associate with massive sulfide deposits. Also, IP has been applied to mapping saltwater/freshwater changes and clays.

• Cannot be performed when ground is frozen or where there is pavement in place because good contact with the ground is required.
• Survey layout is labor intensive.
• Because profiles are qualitative rather than quantitative, analysis involves subjective interpretation.

A gravimeter is used along a survey line or grid. Many discrete measurements are made over the survey area and then are averaged to increase the signal-to-noise ratio. The data are postprocessed to remove effects of topography, earth tides, and drift. (ASTM 1999b)

Data Quality

• Qualitative
  

Advantages

• Identifies karst features (caves, voids, sinkholes).
• Can map top of rock or buried valleys/channels.
• Useful in situations where electrical or seismic techniques cannot be used due to interferences.
• Only requires a single operator.

• Technique is very sensitive to elevation changes and irregular topography. Requires a land survey with precise elevations.
• Detection of features depends on depth. A broad target at a shallow depth may produce a similar anomaly as a large void at a greater depth.

Data Quality

• Qualitative.
• Less sensitive to small conductivity variations near the measurement point.
• Less influenced by conductive overburden.
  

Advantages

• Mapping preferential pathways in fractured or unconsolidated media.
• More sensitive to conductive targets under moderately conductive overburden than other EM methods.

• Requires surface access for measurements.

Resistivity changes within the fluid-filled portion of the borehole are measured with this method. Changes or inflections in fluid resistivity may indicate the presence of a fracture contributing water to the borehole with either a higher or a different dissolved solids content than the fluid in the borehole. (Keys 1990; Kobr 2005; McNeill 1986, 1990)

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.
  

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.

• Can give poor response in low-conductivity/high-resistivity subsurface environments.
• Vertically averages over approximately 1m–2m.
• Metallic minerals (pyrite) or objects (such as centralizers) interfere with results.

Data Quality

• Sensitivity to borehole diameter and fluid conductivity make results most often qualitative.
• Works best in highly resistive environments.
  

Advantages

• Primarily characterizes lithology in terms of EC (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.

• Results depend on borehole diameter, grounding, and electrode configurations.
• Only works in open hole and below water table.
• Large historical database, but varying electrode configurations can make comparison problematic.

Borehole radar logging can be used in either reflection or cross-hole tomographic arrangements.

In the single-hole reflection mode (transmitter and receiver in the same borehole), fractures and cavities that may either be connected or may not intersect the borehole can be imaged, including some that do not intersect the borehole. In tomographic applications, the transmitter and receiver are placed in separate boreholes. As the position of each are changed, their positions are changed multiple times within each borehole, measurements of signal amplitude and travel time are made. Measurements of travel times and signal attenuation differences are combined in a tomogram, which is then used to interpret fractures, voids, and potentially lithologic differences based on the travel time and signal attenuation differences. (Annan 2005a; Chen J. S. 2001; Day-Lewis 2003; Dafflon, Irving, and Barrash 2011; Ernst 2007; Irving 2007)

Data Quality

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

Advantages

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

• Calibration of features more controlled where independent direct measurement information (contacts, material types, porosity, water chemistry) available for wells used in tomographic survey.

(USEPA 2016a)

Data Quality

• Quantitative to qualitative depending on data density
  

Advantages

• Most common cross-hole technique used. Useful in determining location of fractures, cavities, or solid rock between borings.

• Holes should be closely spaced (3-6 meters).

The optical televiewer may be used in either an air or water filled borehole and uses visible light to create a digital image the borehole wall. It has the advantage of operating in air, but the water must be clear to produce a useful image. The resulting optical image can be interpreted to identify planar features (such as fractures, joints, and bedding planes), voids, and solution features, which intersect the borehole. Using the appropriate software tools, the dip angle, dip azimuth, orientation and aperture of the planar features can be estimated. The data from the optical and acoustic televiewers complement one another. (USEPA 2004; Keys 1997; COLOG 2012)

Data Quality

• Depends on water clarity.
  

Advantages

• Identifies fractures and voids
• Some lithologic information can be interpreted from the data.
• Potentially finer resolution than acoustic televiewer.
• Works above the water table.

• Borehole diameter must be assumed.
• Difficult to interpret when water is cloudy.
• Clear water and clean borehole wall are necessary to determine lithologic and structural characteristics.
• Original view is oblique and distorted, requiring digital restoration; some features can be lost in processing.
• Dark lithologic features can be difficult to distinguish from fractures.

The acoustic televiewer can only be used in a fluid filled borehole and uses acoustic energy to image the borehole wall. It has the advantage of operating in water or mud filled boreholes. The resulting acoustic image can be interpreted to identify planar features (such as fractures, joints, and bedding planes), voids, and solution features, which intersect the borehole. Using the appropriate software tools, the dip angle, dip azimuth, orientation and aperture of the planar features can be estimated. The data from the acoustic and optical televiewers complement one another.(USEPA 2011; Keys 1997; USEPA 2004; COLOG 2012)

Data Quality

• Varies depending on condition of borehole and careful data collection.
  

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.

• only works below water table.
• requires experience to interpret well.
• must be well centralized.
• some thin bed exaggeration.
• Not likely to detect DNAPL directly or indirectly.

This technique can be useful in fractured sedimentary rock formations to differentiate sand units from shale units (or sands from clays in unconsolidated formations). This approach can aid significantly in correlating features between boreholes across a site. In fractured metamorphic and igneous terrane, this method can indicate clay-filled fractures and may help to differentiate between transmissive and nontransmissive features (Keys 1990)(Keys 1997; USEPA 2004; COLOG 2012).

Data Quality

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

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 (such as fluid resistivity, temperature, or caliper) in one tool.
• Relatively fast operation with fast turnaround on information.
• Information can help guide subsequent characterization work.

• Requires field confirmation.
• Not sensitive to DNAPLs.
• Can be influenced by well construction (for example, bentonite, feldspathic sand in filter pack, casing material, and borehole diameter)

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 (Keys 1990) (Barrash 2002; Keys 1997) (USEPA 2004).

Data Quality

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

Advantages

• Can provide semiquantitative or quantitative information on formation porosity in wells.
• Can indicate relative abundance of silt or clay in sands and/or 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 source tool requires licensed handling and commonly written consent for use in wells.
• Requires field confirmation for lithologic interpretation.
• Can be influenced by hydrogen sources in well construction (for example, bentonite seals).
• PVC casing and large water-filled diameter reduces signal strength, but generally this effect is not a major problem as a constant influence along a borehole.
• Cannot alone distinguish between hydrogen sources (bound water in clay, water, DNAPL).

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
  

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).

• Requires nonmetallic well screen, casing, or both.
• Quantitative permeability application without calibration or site-specific relationship is limited currently to unconsolidated sandy sediments.

Data Quality

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

Advantages

• Primarily fracture and void detection.
• Water movement into borehole above water table and in some cases into and out of fractures.
• Can be used to describe rugosity and rock competence.
• Casing length and screen conditions for wells.
• Basic interpretation is simple, but refined interpretation requires experience.
• Inexpensive and provides real-time inspection of borehole conditions.

• Analysis is mostly qualitative, although semiquantitative estimates of aperture and/or orientation are possible.

Data Quality

• Average borehole diameter based on three- or four-point measurements.
  

Advantages

• Identifies fractures and voids.
• Measures casing depth.
• Simple direct quantitative measurement of hole diameter and rugosity.
• Not influenced by other activities in borehole or by water clarity.

• Measures only at fixed points within borehole circumference and may not quantitatively represent all features
• Narrow, deep features are not accurately measured.
• Caliper arms can get caught, follow steeply dipping fractures, and overestimate the length of the interval with increased borehole diameter.

Data Quality

• Sensors measure to within .001 °C.
• Older sensors with lower (0.1 °C) resolution have limited applicability.
  

Advantages

• Highlights critical flow zones under heterothermic conditions.
• Used to estimate infiltration.
• Heat can be used as an innocuous tracer between boreholes.

• Borehole must be water-filled and preferably allowed to stabilize without other probes or testing prior to logging.
• Typically compromised when collected in open boreholes, but can be collected in lined boreholes.
• Requires thermal disequilibrium between water in fracture and rock (can be induced where not naturally present).

Data Quality

• Varies with rock competence and borehole quality.
  

Advantages

• Measures P-waves, S-waves, and Stoneley seismic waves.
• Quantitative and highly detailed measurement of material properties.
• Calculates bulk modulus.
• General rock competence and lithology.
• Detects tube waves indicative of some transmissive fractures.

• Wave forms can be difficult to interpret in irregular boreholes.
• Relies on algorithms to identify events in real time.
• Resolution can vary depending on signal frequency.

Data Quality

• Semiquantitative
  

Advantages

• Provides semiquantitative data on bedrock competency.
• Bit behavior (“bit drop”) may reveal presence of fractures or voids.

• Data is somewhat subjective and requires systematic monitoring during drilling operations.
• Results of bit behavior observations may be ambiguous and depths may not be definitive.

Data Quality

• Semiquantitative
  

Advantages

• Rates are semiquantitative. Observations can indicate presence of fractures that create loss of fluids or may be adding fluids to the borehole.
• Color changes may indicate presence of water bearing fractures.

• Difficult to discern exact rate of loss or return that is applicable to fracture transmittal.
• Inability to discern fracture zone from single productive fracture.
• Some ambiguity in discernment of depth of contributing or losing zone/fracture.

Data Quality

• Data is quantitative and is depth specific from measurement of depth during logging.
  

Advantages

• Provides information on lithologic changes, fluid temperature, and resistivity changes.
• Combining multiple tools may indicate where flow is entering/exiting borehole.

• Natural gamma logging dependes on contrast in lithologic characteristics (sandstones versus shales, for example). In the absence of changes in radiological characteristics, tool provides limited information.
• Temperature and fluid conductivity may indicate the presence of a water transmitting fracture, but will not be definitive as to depth, flow volume, or physical fracture characteristics.
• Additional information required to complete the interpretation of fracture characteristics.

Packers can also be used in an overburden well if the well construction allows meaningful data to be obtained. (Bliss 1984; Gale 1982; Lapcevic P.A. 1999; Maini 1971; NRC 1996; DM. 2006; Price 2009)(Reclamation 1977; Sara 1988)(Quinn 2012; Zeigler 1976)

Data Quality

• Quantitative to semiquantitative, depending on the presence of nonideal behavior.
  

Advantages

• Obtains depth-discrete T and S values.
• High precision values are obtained with lower flow rates.
• Conducting more than one type of test gives greater confidence in the T value.
• Can obtain fracture specific groundwater quality.

• Method is time consuming.
• Short circuiting to open hole can interfere with test results
• Non-Darcian flow causes T to be underestimated.
• Need to understand hydraulic characteristics of fracture (gaining/losing) to evaluate groundwater quality data.

The FLUTe Transmissivity Profile is a proprietary service offered by Flexible Liner Underground Technologies, LLC, and consists of a blank FLUTe liner deployed in an open borehole. The velocity at which the liner everts into the borehole is measured and decreases as the liner closes off transmissive features such as fractures, joints, and bedding planes. As the liner everts into the borehole the velocity is reduced. FLUTe uses the velocity data, borehole geometry, and head data to create a transmissivity and hydraulic conductivity profile of the borehole. The profiles are useful in identifying transmissive as well as nontransmissive features in the borehole.

The Flute Reverse Head Profile allows for interpretation of vertical gradients between features identified in the FLUTe Transmissivity Profile.

(Keller 2016)

Data Quality

• Quantitative to semiquantitative, depending on the presence of nonideal behavior.
• This tool provides continuous quantitative transmissivity measurements for the entire borehole. The transmissivity resolution limit is generally low (detects small variations in transmissivity), but will be adversely affected by large transmissive features.
  

Advantages

• Obtains T profile.
• The test is rapid.
• No water injected or withdrawn.
• Can be performed in conjunction with other FLUTe installments.

• Large downward gradients can interfere with test results.
• Borehole diameter changes can interfere with test results.
• Low-yielding wells can be time consuming to install liner.
• A highly transmissive feature decreases the resolution limit for the section of the borehole above this feature. This effect is a result of water preferentially escaping into the formation through the large feature as opposed to the smaller fractures with low transmissivity.
• The time required to complete the transmissivity profile is inversely proportional to the borehole transmissivity. The liner removal after completion of a profile, if necessary, requires approximately the same amount of time as the installation.

(Brainerd and Robbins 2004)

Data Quality

• Quantitative to semiquantitative, depending on the presence of nonideal behavior
  

Advantages

• Obtains values for Darcy flux.
• Semiquantitative to quantitative depending on the presence of non-ideal behavior.
• Inexpensive.

• Vertical gradients can affect data.
• Can be difficult to evenly distribute dye in deep wells with large volume of water.
• Need to account for density driven flow with some tracers (bromide).
• Some agencies require permits for these types of tests.

Data Quality

• Quantitative to semiquantitative.
  

Advantages

• Identifies inflow and outflow from hole.

• Low-flow zones cannot be identified.

More than 50 PITTs were used at contamination sites to derive quantitative estimates of saturation and volume of DNAPL in subsurface. In most cases, tests were performed to assess remediation performance. During a PITT, a suite of conservative and partitioning tracers injected via wells migrate with groundwater to the extraction wells. Partitioning tracer velocities are retarded to various degrees depending on their affinity to partition; thus, tracer travel times, in conjunction with laboratory measurements of NAPL-water partitioning coefficients, are analyzed to estimate saturation of NAPL in the interwell zone during the test.

Single-well, push-pull tests have been proposed to characterize near-well NAPL presence, and gas-phase PITTs have been applied to estimate NAPL volume in the vadose zone. (Hartog 2010; Cain 2000; Jin 1995)

(Jin 1997; Nelson 1999)

(Young et al. 1999; Mariner 1991; Rao 2000; Menardus 2002; Londergan 2001)

(ESTCP 2012); (Brooks 2002);

(Werner 2003; Imhoff 2003; Jalbert 2003; Moreno-Barbera 2006)

Data Quality

• Quantitative to semiquantitative.
  

Advantages

• Assesses contaminant distribution and remedial performance.
• Provides alternative means of estimating NAPL volume over relatively large areas, which typically relies on interpolation between point measurements.
• Extensive monitoring (such as multilevel samplers) and detailed data analysis can be used to evaluate architecture of subsurface DNAPL.

• Physical heterogeneities can cause significant tailing of tracer concentrating.
• Degradation of reactive and nonreactive tracers can cause overestimation or underestimation of NAPL saturations, respectively.
• Tracer partitioning to natural organic carbon can cause overestimation of NAPL.
• Nonequilibrium tracer partitioning can result in underestimation of NAPL.
• Pitts likely to underestimate NAPL present in pools.
• Tracers may bypass low-permeability zones and underestimate NAPL.
• Multiple confounding factors can lead to significant errors.
• Expensive, and may require recovery of tracers.

Data Quality

• Quantitative to semiquantitative depending on the presence of nonideal behavior.
  

Advantages

• Obtain values for T and specific storage.
• Identify dual permeability effects.
• Agreement between both tests increases confidence in the T values.
• Develop an understanding for anisotropy in the rock.

• Must measure flow rates and pressure responses accurately.
• Longest testing times.
• Withdrawal tests may require treatment of extracted water and special permits for discharge.

Single well tests may generally provide some information regarding specific capacity of an individual well and an estimate of potential transmissivity. Caution should be exercised regarding single well tests and estimates of aquifer transmissivity, particularly in tight formations where borehole storage may be a large influence on pumping behavior. Slug tests in fractured rock can provide estimates of transmissivity if multiple fractures or fracture zones are penetrated. Individual fractures zones may be tested via packer testing of those fractures using straddle-packers. Pneumatic slug testing provides the ability to test a borehole or selected interval without the addition or removal of water. (Barker 1983)(Butler 1997)

(Greene and Shapiro 2001; Levy 1993)(Shapiro A.M. 1998; Svenson E 2007; Zenner 2009; McElwee 1998; McElwee 2001; Murdoch 2006; R.G. 1993; Schwartz 1975; Schweisinger T 2009)

Data Quality

• Quantitative to semiquantitative, depending on the presence of non-ideal behavior
  

Advantages

• Obtains value for T.
• Test is rapid.
• No water is injected or withdrawn.

• Must measure pressure accurately.
• Must conduct more than one test to pseudo-validate Darcian flow conditions.
• Must conduct both rising and falling head tests to identify well development issues.

Data Quality

• Quantitative to semiquantitative, depending on the presence of nonideal behavior
  

Advantages

• Obtains value for T.
• Ensures results are free from errors due to non-Darcian flow.

• Must measure flow rates and pressure responses accurately.
• Withdrawal tests may require treatment of extracted water and special permits for discharge.

The HPFM is positioned above and then below each target (borehole features defined from optical/acoustic/fluid temperature/resistivity logs indicating the zone may be water bearing) and data are collected. The data consist of the direction, up or down, and rate of fluid flow (gallons per minute). These readings are collected under both ambient (static head) and pumping (stressed head) conditions. Features where water is either entering or existing the transmissive zones are indicated by changes in HPFM. The electromagnetic (EM) flow meter is better at measuring higher flow rates than the HPFM but is not widely available commercially. Spinner flow meters are also available but are not as sensitive as the HPFM (Keys 1990).

Data Quality

• Qualitative to Semiquantitative
• When used in conjunction with other tools, this technique can indicate which fractures are adding flow or removing flow from the borehole.
  

Advantages

• Indicates vertical flow and direction of vertical flow in a borehole.
• The tool can show how the fracture flow changes when stressed (pumped).

• Needs to be used in conjunction with other borehole techniques to definitively identify transmitting fractures.
• Data is logged by occupying vertical positions in the borehole based on other data that indicate presence of fractures. Requires good interpretation of a suite of other logging tools to properly position HPFM and get good data.
• Data will likely represent integrated response of borehole based on position and requires interpretation to differentiate various fracture flow rates.

Saline tracing of in-well flow is used to identify locations of transmissive fractures or fracture zones, locations of inflow and outflow fractures, direction and amount of vertical cross flows, and relative hydraulic heads between fractures by repeated logging of electrical conductivity following an injection of small-volume saline slug (Michalski 1990a).

Data Quality

• Qualitative
  

Advantages

• Inexpensive and more sensitive than heat-pulse flow meters in determining the direction and volume of vertical internal flows for low-flow boreholes.
• The flow measurements are continuous with depth, while flow meters readings are taken at discrete depths.

• When the EC value of water issuing from a fracture (inflow zone), and water in the borehole just upstream of the fracture are equal, the baseline EC log might be unaffected by the inflow; however, a trough or inflection on the saline tracer image would identify the inflow location. Density effects may need to be considered, but are inconsequential at a concentration of 10 g/L of NaCl.

Advantages

• Combining in-well heat tracer testing with DTS monitoring allows measurable flow from 10^-1to 10¹ m/min.
• Relatively new, and rapidly evolving technology. Lower flow rates may be achievable.

• Requires personnel with expertise in the deployment and operation of DTS equipment.
• Limited by the temperature resolution of the instrument.
• Some uncertainty remains with the impact of borehole diameter on heat flow in the borehole.

Typically, at least three deep, open-hole TTHs are installed, which are converted to monitoring wells upon completion of testing. Using an outside-in approach, two TTHs are sited along strike of bedding (or foliation) on either side of the suspected source and the third TTH is located down dip of bedding from the source area.

Characterization tools for the TTHs include: televiewer, caliper, electrical conductivity and temperature logs, in-hole flow tracing (or flow meter log), depth-discrete sampling of the cross flows, and packer testing. This approach enables the hydrogeologist not only to locate transmissive fractures within the TTH, but also to quantify transmissivity and hydraulic head for any such fractures, and to determine contaminant concentrations in inflow-producing fractures

(Michalski 1990b; Michalski 2010b; NJDEP 2012).

Data Quality

• Quantitative to qualitative
  

Advantages

• The TTH method has been successfully used multiple times in the fractured sedimentary rock of Newark Basin (Central NJ and southeastern Pennsylvania). It may also be applicable to other bedrock settings marked by preferential groundwater flow along a few transmissive fractures.

• Although vertical cross flows in bedrock wells may be harmful and should generally be avoided, they also offer an opportunity for rapid hydrogeologic exploration and characterization of bedrock sites, provided that two conditions for long open holes are satisfied:
  1) TTHs are installed and tested under controlled conditions so that any harm from cross-flows is assessed and harmful cross-flows are terminated (for example, by inflating a temporary packer).
  2) The TTHs remain open only for a limited testing time (a few days to weeks) and then are converted to a bedrock monitoring wells or are properly sealed.

Data Quality

• Quantitative to qualitative.
  

Advantages

• The HVSR method has many advantages including low cost, ease of use, one-man operation, single station, portability, noninvasive, quick, minimal data processing, specificity to a single interface (bedrock surface), and usefulness in culturally noisy areas. Additionally, it can be used as an independent depth calibration for modeling with other geophysical survey methods.

• Must have adequate acoustic impedance contrasts between overburden and underlying bedrock. The HVSR has no internal energy source and depends on naturally occurring seismic noise (wind, waves, flowing water, distant weather, and other) plus man-made noise (vehicles, industrial) as an energy source.

Data Quality

• This method provides high-resolution qualitative data of ambient fracture flow.
  

Advantages

• The logging instrument includes a tetrahedral temperature sensor array and tracks magnetic north. This combination allows for calculation of 3D vector flow within the borehole.
• After thermal equilibration, a borehole is profiled every few hours for approximately one day. Therefore, multiple boreholes can be profiled in sequence within the same day.

• Active line source profiling is a relatively time-consuming method, especially if limiting the work to only a few boreholes. The collected data set requires relatively complex analysis and interpretation compared to other down-hole geophysical methods. The results remain qualitative, thus do not allow for calculation of transmissivity.

Various methods exist for implementation of induced electrical conductivity logging. Fundamentally they work under the same principle, i.e. to create a uniform baseline conductivity and monitor the return to ambient conditions, which first occurs at flowing fractures. The induced baseline conductivity is created by replacing the borehole storage with de-ionized water, or by dissolving a salt.

Fluid Electrical Conductivity (FEC) logging, Hydrophysical Logging, and Saline Tracing are examples methods that profile in-well electrical conductivity.

(Pedler).

Data Quality

• Quantitative to qualitative
  

Advantages

• Allows for rapid collection of high resolution data.
• Non-destructive test, i.e. test can be reproduced.
• Uses harmless additives, e.g. de-ionized water or sodium chloride (table salt).

• Reduced resolution due to in-well mixing.
• Potentially subject to regulatory constraints due to injection of additives to groundwater.

Data Quality

• This method generates quantitative groundwater flow velocities. Results are based on a high number of particle measurements and presented as statistical averages.
  

Advantages

• Measurements can be collected in screened or open boreholes. The camera can detect particle sizes larger than 1 µm.

• Tests in screened boreholes may be biased by improperly constructed or fouled well screens. Open boreholes are preferred. The recommended turbidity of the water column is 200–500 NTU, which is representative of relatively cloudy water.
• Requires high-density interval measurements if the preferential flow zones within a borehole or well screen are established in advance.

The simplest of these karst tests involves timing of tracer transport from sink to spring locations. A tracer added to one well and an observation well is monitored to identify breakthrough. This test can be conducted under ambient flow conditions, or under the stress of pumping. (Horner 1951; Jacob 1946; Jacob 1963; Kazemi 1969; Lapcevic 1993; Novakowski 1994; Lapcevic P.A. 1999; Novakowski 2004b; Michalski 2010a; Novakowski 2004a; Wilson 1986).

Data Quality

• Semiquantitative to quantitative, depending on the presence of nonideal behavior and the tracer recovery.
  

Advantages

• Obtains Darcy flux and average groundwater velocity.
• Properly selected tracers are:
  • nontoxic to humans and the ecosystem
  • absent from the aquifer system or occur at a very low and constant level
  • soluble in water with the resultant density neutral relative to that of water
  • neutral in buoyancy and fine enough to prevent loss via filtration (particulate tracers)
  • resistant to adsorptive loss and/or to chemical, physical, or biological degradation
  • unambiguously detectable in very small concentrations – ideally via quantitative analysis
  • inexpensive and easy to obtain and administer

• Erroneous values can be obtained if wells have long screens due to vertical flow in hole.
• Difficult to obtain 100% mass recovery.
• Tracer tests are used to derive hydraulic and physical properties including groundwater flow direction, groundwater flow velocity, hydraulic conductivity of aquifer or zones of interest, aggregate fracture aperture, and aquifer porosity. More complex evaluations, where matrix diffusion is a factor, require use of at least two tracers with distinct free-water diffusion coefficients and may also require numerical modeling to yield unique solutions for aquifer properties. In these circumstances, test design and completion and model set-up and calibration must be performed by a qualified professional to yield results applicable to the problem description.

Dye tracing can provide valuable information about groundwater flow direction, preferential pathways, travel times, storage, or residence times, as well as provide insight into potential solute advection, dispersion, and dilution (depending on the test design and equipment used).

Tracer tests can be conducted using a wide range of injection and monitoring points ranging from naturally occurring springs to monitoring wells. Trace lengths can vary from tens of feet to tens of miles, depending on site conditions and project needs.

Qualitative dye tests collect samples using passive dye receptors (activated charcoal). Qualitative tests are used primarily for determination or confirmation of groundwater flow direction/pathway and delineation of drainage basins. Quantitative tests typically involve the use of automatic samplers to collect discrete groundwater samples for analysis. Quantitative tests are used primarily to determine groundwater travel times and higher level flow dynamics such as advection, dispersion, dilution, and residence time (USEPA 1998, 1989, 2002).

Data Quality

• Qualitative to quantitative.
  

Advantages

• Dye tracing can be conducted by two different methodologies: qualitative and quantitative.
• The equipment and costs to conduct dye traces are readily available and inexpensive.

• Proper test planning and execution is essential to prevent cross-contamination and false positives because many of these dyes can be detected at the part per thousand (ppt) level.
• Some understanding of the site geology, fracture orientation, and groundwater flow is needed to properly place dye receptors. In poorly understood or complex systems, it may be necessary to deploy many samplers to account for all probable flow scenarios to maximize the likelihood of dye recovery.

HT has been demonstrated in the field for unconsolidated sedimentary aquifers and similar HT testing in fractured rock is in progress. Aquifer storage properties also can be estimated (Brauchler 2011; Cardiff 2012, 2013; Illman 2009; Illman 2006; Illman 2008),

(Tiedeman 2016; Berg 2011).

Data Quality

• Semiquantitative to quantitative, depending on field conditions, prior knowledge of well and subsurface conditions, experimental quality, and appropriate modeling.
  

Advantages

• Provides estimates of K distribution in 3D for a heterogeneous investigated volume with a spatially continuous solution (rather than an interpolated solution from 1D measurement profiles in separate wells or discrete borings).
• K estimates at less than cubic meter scale can be generated with uncertainty quantification.
• Can be applied in unconsolidated sediments or fractured hard-rock environments given appropriate well configuration.

• Requires wells, DP bores, or both in appropriate configuration.
• Requires sufficient equipment and software for subdividing wells and monitoring numerous zones simultaneously.
• Tomographic inverse modeling is specialized and computing intensive, but is accessible and becoming progressively more accessible.
• Emerging technology with limited commercial availability

Pumping tests are routinely used in hydrogeological investigations to develop an understanding of aquifer responses and aquifer properties such as hydraulic conductivity and storage coefficient. In fractured rock studies, the responses are most often anisotropic in addition to being heterogeneous. This anisotropy may be reflected in an elliptical cone of depression in a uniform fracture field. In a nonuniform fracture field, the cone of depression is likely to be complex and evolve over time until a steady-state condition is reached. In fact, the transient response of the aquifer to the induced stress of a pumping test can be informative as to the connectivity of the fracture network. The timing and magnitude of observed responses from pumping provides valuable information relative on to both the individual fracture flow characteristics and the behavior of the bulk volume tested. Fracture conductivity, bulk conductivity, storage properties of secondary features and primary rock are often estimated from the analyses of these tests. In some cases, intervals can be isolated and testing conducted to evaluate the productivity and/or interconnectivity of individual fractures or fracture zones with the overall network.

Methods of analyses of data can consist of the following:

• plotting and contouring of resulting drawdown and elevation head at specific time intervals
• plotting of time series responses at individual wells including the pumping well
• analysis of time series data using curve matching techniques
• analysis of response data using modeling techniques, or
• geostatistical analyses of drawdowns/heads at specific time intervals

Pumping tests using multiple pumping/injection wells may also be performed to evaluate the superposition effects of pumping/injection or may be used in cases where discontinuous fracture networks limit the area of influence of individual wells. Multiple tests may also be used to evaluate the potential effectiveness of pump and treat remedial scenarios, such multiple capture wells or coupled pumping and injection scenarios

(McElwee 2001; Murdoch 2006; R.G. 1993; Schwartz 1975; Schweisinger T 2009; Shapiro A.M. 1998; Svenson E 2007; Zenner 2009; Bentall 1963; Boulton 1977; Bourdet 1989; Cooper and Jacob 1946; Gringarten 1972, 1984, 1987)

Data Quality

• Semiquantitative to quantitative depending on the presence of nonideal behavior in both the pumping and observation wells.
  

Advantages

• Obtains values for T and S.
• Identifies dual permeability effects
• identify boundaries (constant head, no flow).
• Identifies anisotropy if more than one observation well is used.
• Agreement between both tests increases confidence in the T values.

• Must measure flow rates and pressure responses accurately in both the pumping and observation wells.
• Longest testing times.
• Withdrawal tests may require treatment of extracted water and special permits for discharge.

(Atkinson 1994) (Elsworth 1986a)

(Doe 1980)(Haimson 1983; Mackie 1982; Price M 1977; Price M 1982; Quinn P.M. 2011; Barker 1983)(Greene and Shapiro 2001; Butler 1998; Levy 1993)(McElwee 1998; McElwee 2001).

Data Quality

• Semiquantitative to quantitative depending on the presence of nonideal behavior in both the pumping and observation wells.
  

Advantages

• Obtains values for T and S.
• Identifies anisotropy if more than one observation well is used.
• Agreement between both tests increases confidence in the T values.

• Must measure pressure responses accurately in both the pumping and observation wells.
• Initial displacement must be large enough to see response at observation well.
• Difficult to attain Darcian flow conditions with large displacements.

Vapors create a VOC and SVOC cloud footprint much larger than the adsorbed and dissolved phase footprint resulting in higher probability of detecting and delineating impacts in the subsurface and therefore the lowest probability of false nondetect. Soil gas surveys are a good screening tools for subsurface impacts of VOCs and SVOCs due to (1) the limitations of contaminant localization during soil and groundwater sampling and (2) the high probability of false nondetects resulting from heterogeneous distribution of adsorbed and dissolved phase compounds.

Passive soil gas (PSG) samplers can collect time integrated samples over days or weeks to target a wide range of VOCs and SVOCs to identify potential vapor intrusion pathways and delineate the lateral extent of contaminants (for example, Beacon BeSure PSG Samplers). PSG sorbent samplers consist of hydrophobic adsorbents housed in glass vials or membranes that are typically installed in shallow, small diameter holes (for example, 2.5 cm diameter and less than 1 m 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 GC or GC/MS methods that can achieve low detection limits of individual compounds with documented accuracy.

Fractured Bedrock Applications

Soil gas surveys may also be useful for tracking fracture connectivity. Specifically, if fractures in bedrock are exposed to vadose zone unconsolidated sediments, the fractures become conduits for VOCs and SVOCs preferentially migrating in the fractured media and can be detected near the surface by subsurface soil gas sampling methods. The quality of the results depends on the concentrations of target compounds, the vapor pressure of compounds, thickness and soil type of unsaturated overburden media, and depth to groundwater. Generally, closely spaced soil gas sampling transects combined with shallow groundwater conditions result in a high resolution and high confidence identification of preferential pathways and fracture connectivity in a fractured rock setting.

Field Deployment Guidance

Sample spacing with soil gas sampling depends on site- specific criteria and can generally be defined as high and low resolution. High resolution uses a tight sampling grid (such as 3–10 m spacing) that helps to define the edges of soil gas plumes related to source areas. Low resolution uses wider spacing intervals (such as 15–50 m spacing) that define soil gas plumes related to migrating dissolved phase VOCs and SVOCS in groundwater or LNAPL plumes (ASTM 2016; USEPA 2015)

Data Quality

• Quantitative and semiquantitative data: compound-specific quantitative measurements based on traceable standards, but in units other than concentrations (such as ng or µg).
  

Advantages

• Enables collection of high resolution data sets.
• Enables collection of time-integrated samples over days or weeks.
• Targets VOCs as well as SVOCs.
• Detects contamination present at low concentrations.
• Effective in low permeability soils and when high soil moisture present.
• Allows for rapid collection of samples.
• Requires only basic hand tools to install samplers.
• Minimal impact to sites.
• Active sampling involves short duration sampling snap-shot.
• Easy to use.
• Passive soil gas sampling devices (such as Beacon BeSure PSG samplers) are more sensitive soil gas sampling devices than currently available active soil gas sampling devices because they use strong adsorbents to adsorb hundreds of VOCs and SVOCs in a single sampler.
• Passive soil gas samplers are sensitive enough to detect 5 µg/L of dissolved phase VOCs in groundwater tens of meters beneath the surface (sampler placement at 30 cm beneath the surface). This method is significantly more dynamic and sensitive than active soil gas sampling methodology and beyond the range of abilities of active soil gas laboratory methods and sampling devices.

• Active soil gas sampling devices (typically Summa Canisters) are expensive and complicated to ship and transport. However, thermal desorption tube technology (USEPA Method TO-17) has recently been approved for use in many states.
• Active soil gas sampling requires complicated field procedures, including leak testing, multiple fittings, and tools.
• Active sampling has sample hold time restrictions
• Active sampling sensitivity varies by volume of gas being sampled and target compounds
• Typically includes or relies on installation of samplers in privately-owned structures requiring logistical (including tampering) and community relations-related drawbacks and delays.
• Passive Soil Gas Sampling offers both Semi-quantitative (SQ) and quantitative testing (Q) options.
• Two or more field deployments are needed.
• Not suited for targeting methane and other nonadsorbable compounds.

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 (ASTM 2013).

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.
  

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.

• Specialized tooling must be used for good sample recovery in unconsolidated formations.
• Water must typically be used to cool bit and flush cuttings out of hole.
• Slower penetration rates in dense or difficult formations result in higher cost per foot.

Data Quality

• Qualitative.
  

Advantages

• Useful for weakly consolidated to soft rocks such as marls, clayish sandstones or marly calcareous, or small diameter hole in weathered crystalline rock.

• Rock competency is inferred by drilling difficulty, lithology based on dust and ground up cuttings, depth approximate, requires communication with driller on drilling rates combined with observations of dust/drill cuttings at surface.
• Can only identify first water- bearing zone.

Data Quality

• Qualitative.
  

Advantages

• Good for highly competent crystalline rock.

• Requires extra air compressor to blow cuttings to surface, particularly with increasing depth; friction causes higher temperatures, which can evaporate water quickly and make low-producing water bearing zone difficult to identify.
• Can generally only identify first water bearing zone.

Data Quality

• Qualitative to semi-quantitative.
  

Advantages

• Good for identifying individual water-bearing fracture zones and multiple depths.

• Slow, requires special drill pipe.

Data Quality

• Qualitative.
  

Advantages

• Good for all consolidated/competent rock types.

• Difficult to determine depth to groundwater. Not recommended if depth to water is unknown or water-bearing zone is expected to be low producing.

• unconsolidated: color, grain size, sorting, roundness, plasticity, wetness, USCS class, laminations, and secondary material
• mudstone: color, moisture, secondary material, sedimentary structures, bedding, cementation index, and fractures
• sandstone: color, grain size, sorting, roundness, wetness/moisture, 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

The procedure for core logging is detailed in (ASTM 2014)

(Kelleher 2003; Parker 1994)

(Parker B.L 2011, 2010; Spence 2005; ASTM 2014)

Data Quality

• Quantitative.
  

Advantages

• Widely available.
• Obtains 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.

• Mechanical fractures (such as end of core runs, breaks to fit core into boxes) and natural fractures should be identified and labeled immediately upon retrieval to avoid misinterpretation.
• Difficult to complete logging during coring.
• Core should be revisited when more time can be allocated.

Data Quality

• Quantitative.
  

Advantages

• Obtains information essential to constructing complete borehole log.
• Low recovery commonly indicates high-permeability zones (such as sands and gravel or highly fractured rock).

• Measurements are taken during drilling/core retrieval and calculations are made afterwards.

In rock material sampling for evaluating metals and heavy metals contaminants, the technical record of the drilling crown is indispensable. The contamination elements are compared with the constituents of the alloy of the drilling crown. The stiffer the rock, the higher the contamination caused by the crown detrition. (Camel 2000; Dincutoiu 2003b, a; Dincutoiu, Gorecki, and Parker 2006; Ganzler, Salgo, and Valko 1986; Hewitt 1998; Kennel 2008; Kinniburgh and Miles 1983; Lawrence 1990; Lopez-Avilla 1994; Richter 1996; Spence 2005; USEPA 1999)

Data Quality

• Quantitative to qualitative, depending on analytical method.
  

Advantages

• Obtains vertical contaminant mass distributions.
• Identifies soil/rock where contaminant resides.
• Provides data to and understand potential for reverse matrix diffusion.

• Expensive.
• Most efficient to conduct transects perpendicular to groundwater flow.

Data Quality

• Quantitative.
  

Advantages

• Determines cation exchange capacity.
• Estimates sorption and other contaminant reactions.
• Explains contaminant retardation and/or degradation.
• Determines oxidant demand for remediation.
• XRF testing can be done directly on the core, immediately after the sampling.

• Take samples from core soon after drilling to avoid oxidation and other influences.
• In some cases, porosity, density, and surface area measurements are needed.

(ASTM 2008a, 2010a, 1986, 2001, 2010c)(Churcher 1987; Tanikawa 2009; ASTM 2008b; Cooper and Jacob 1946; Beyers 1978)

Data Quality

• Quantitative.
  

Advantages

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

• Difficult to obtain valid permeability measurement on unconsolidated core samples.

Data Quality

• Qualitative to semiquantitative.
  

Advantages

• Yields knowledge of indigenous microbe population to aid in studies of natural attenuation.

• Time consuming.

Data Quality

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

Advantages

• Rapid, high-resolution (15 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 2.25-inch 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.

• Data should be confirmed at targeted locations and depths with soil sampling.
• For penetration of unconsolidated materials only; no rock penetration.
• Penetration limitations in dense or cemented formations; usually will not penetrate cobble-rich materials.
• HPT pressure logs provide relative permeability data.

The EC log indicates 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 (for example, salt water or sodium persulfate) can impart a high conductance to low-EC materials. (Christy 1994; USEPA 2000; Beck 2000; McCall 2000; Schulmeister 2003; Schulmeister 2004; Wilson 2005; Sellwood 2005; McCall 2006b; Harrington 2006; Binder 2008),

Data Quality

• Accurate soil stratigraphy at high resolution in fresh water formations.
  

Advantages

• Rapid, high-resolution (15 mm), stratigraphic characterization tool capable of penetrating 400 ft–700 ft/day.
• Typically applied to up to 100 ft 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.

• EC is nonunique value; many materials display similar EC values, so targeted soil sampling needed to verify logs.
• Penetration limitations in dense or cemented formations; usually will not penetrate cobble-rich materials.
• Interference by electrically conductive fluids (such as salt water or potassium permanganate) can mask formation identity.

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 (such as 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 by cabling, typically recorded each second and compiled to generate logs, which are interpreted to delineate stratigraphy and estimate hydraulic conductivity.

(ASTM 2010c; Campanella 1988; Robertson. P.K. 1986; Berzins 1992; Lutenegger 1995; Lunne 1997; USEPA 1997; McCall 2005)

Data Quality

• Highly accurate soil stratigraphy at high resolution.
  

Advantages

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

• Data must be calibrated against conventionally logged boreholes.
• Penetration resistance limitations.
• Heavier trucks (which allow deeper penetration) more difficult to maneuver off road.
• Cannot be used on steep slopes.

Data Quality

• Semiquantitative, high-resolution NAPL detection.
  

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 100 m–160 m.
• With proper calibration, LIF waveforms allow product identification and rejection of noncontaminant fluorescence.
• Reduced investigation-derived waste and exposure to site contaminants.

• Primarily applicable to PAHs; limited use/experience at chlorinated solvent sites.
• Subject to interferences.
• NAPL must be adjacent to sapphire window.
• Penetration resistance limitations.
• Limited availability globally.
• Unconsolidated tool.

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.(Bumberger 2011; Considine 2008; ESTCP 2002, 2011; USEPA 2004) (Geoprobe 2009; Costanza 2000b) (Kurup 2009; McAndrews 2003; Ravella 2007; Kober 2009; Christy 1996)

Data Quality

• Qualitative to semiquantitative.
  

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 200 ft–400 ft/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 50 ppb for many VOC analytes.

• High detection limits for standard MIP, but well below the levels required for NAPL and high-level plume characterization.
• Qualitative analytical data; results reported as detector microvolt readout versus depth on log.
• No analyte specificity.
• Designed for VOCs (boiling points <250°F.
• Contaminant carryover likely in NAPL or high-concentration zones.
• Penetration limitations due to larger soil sizes, high-density or cemented soils.
• Shallow use (generally <100 ft).
• Unconsolidated tool only.
• Cannot readily distinguish between high-concentration soil levels and free-phase NAPL.
• Hole abandonment completed following removal of probe, thus hole collapse possible prior to grouting.

Data Quality

• Quantitative to semiquantitative.
  

Advantages

• Indirect evidence based on VOC partitioning into carrier gas.
• Can be coupled with lithological sensors for correlation.
• Can use different types of detectors (such as FID, PID, ITMS).

• User required to determine appropriate depths in the moment, which can be difficult in zones of ganglia.
• System purge not always rapid.
• Clogging can occur.
• Limited by lithology.

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 13 inch monitor. The system can be advanced at a rate of approximately 4 inches/min. GeoVIS has 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. (Lieberman 2000; Udell 2000)

Data Quality

• Quantitative to semiquantitative.
  

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.

• Unless NAPL is black or highly colored, it may be difficult to detect.
• Penetration resistance limitations.
• Slow rate of probe advancement (1ft every 3 min–5 min).
• Area viewed is small.
• Pressure or heat front may drive NAPL droplets away from window.
• Limited availability.

Data Quality

• Quantitative to semiquantitative.
  

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).

• Discontinuous stream of data.
• Fluorescence due to organic material can interfere.
• Detection threshold depends on probability of droplets appearing on sapphire window, amount of contaminant in soil/sediment, type of soil/sediment, soil moisture content, and heterogeneity.

Data Quality

• Qualitative.
  

Advantages

• Potential direct evidence of presence of DNAPL.
• Can be coupled with lithologic sensors.

• Difficult to ensure direct contact between cosolvent and DNAPL.
• Density differences between cosolvent and DNAPL could pose challenges.
• Best-guess approach for sampling location/depth.
• Requires relatively long sampling times (approximately two hours or more per sample).

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 is generated on approximately 1inch 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 CSMs depicting the location of sites contaminated with heavy PAH DNAPLs. TarGOST can be calibrated using DNAPL samples collected from the site (Ferland 2004).

Data Quality

• Qualitative.
  

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.

• Limited availability in Europe/Asia.
• Direct-push delivery prohibits use in consolidated materials.
• “Blind” to the dissolved phase (often considered an advantage).

Data Quality

• Qualitative.
  

Advantages

• High production rate of 200 ft–300 ft/day.
• Works either by direct LIF detection of DNAPL co-contaminants (such as PAHs) or dye labeling enhancement.
• Continuous data of about 0.5 inch vertical data density.
• Deliverable by both CPT and percussion.

• No availability in Europe/Asia.
• Direct-push delivery prohibits use in consolidated materials.
• “Blind” to the dissolved phase (sometimes considered an advantage).

The Snap Sampler employs a cable to trigger release of a spring-and-close Teflon end caps on double-opening VOA vials or polyethylene bottles 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 inch or larger monitoring wells (ITRC 2007).

Data Quality

• Quantitative to semiquantitative.
  

Advantages

• Allows analysis for all common analytes (such as VOCs, SVOCs, metals).

• Patented methods with sales/support available from a limited number of vendors.

• Semipermeable Membrane Devices (SPMDs)
• Amplified Geochemical Imaging (AGI) Sampler (formerly GORE Sorber Module)
• Polar Organic Chemical Integrative Samplers (POCIS)
• Passive In Situ Concentration Extraction Sampler (PISCES)

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 chemical 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. (ITRC 2007)

Data Quality

• Qualitative to semiquantitative.
  

Advantages

• Simple to use and cost effective.
• Can deploy in any setting.
• Detects wide range of VOCs and SVOCs.
• Sensitive to parts per trillion.
• Built-in duplicates.
• Disposable; no decontamination required.

• Gives total mass desorbed, calibration required to convert to concentrations.
• Single-source supplier and laboratory.
• No field parameters for inorganics.
• Cannot use where NAPL is present.

Polyethylene Diffusion Bag and Rigid Porous Polyethylene Samplers

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 inches–24 inches long and 1.25 inches–1.75 inches 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. (ITRC 2007)

Data Quality

• Qualitative to semiquantitative.
  

Advantages

• Used for analysis of VOCs and other parameters.

• PDB samplers generally not applicable for sampling SVOCs, ions, and MTBE.
• Patented methods with sales/support available from limited number of vendors.

Data Quality

• Qualitative.
  

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.

• False positive (obvious stain with no NAPL present) unlikely
• No stain means cover did not contact NAPL; does not indicate that NAPL is absent.
• Works to 2,000 ft.
• Must have open borehole without material casing.

Data Quality

• Quantitative.
  

Advantages

• Obtains depth-discrete groundwater concentrations.
• Minimizes purge volumes.
• Compares well with other sampling methods.

• When sampling an interval with multiple fractures, there may be a bias to pull water from largest fractures with highest head.
• Need to understand fracture hydraulics in open borehole (gaining/losing) to evaluate sample results.

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 (Hatfield 2004)

(ITRC 2010).

Data Quality

• Qualitative
  

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.

• Limited application of this recently developed method.
• Each PFM interrogates a small volume of formation, thus multiple PFMs must be deployed, and resultant data must be integrated to estimate mass flux across a plane.
• Competitive sorption or rate-limited sorption may affect ability of PFM to capture and retain contaminants.
• As with other methods, requires proper placement in groundwater flow field.
• Method assumes horizontal flow.

Data Quality

• Quantitative; discrete sampling.
  

Advantages

• Deployment easier than packer deployment in some cases.

• Pump rates must match rates of borehole flow; high yielding wells require high pumping rates.
• Current depth limitation of 400 ft.

Data Quality

• Quantitative to Semiquantitative
  

Advantages

• Semiquantitative data are used to establish groundwater stability. For groundwater remediation absolute measurements should be quantitative depending on rigor of calibration procedures

• Measurements can drift between calibrations, may need more calibration depending on desired data quality. Measurements are screening level unless higher data quality is required. Additional calibration, certification, or accreditation may be needed.

Data Quality

• Quantitative–semiquantitative
  

Advantages

• Relies on field measurements to determine if formation water is being drawn in, rather than stagnant well water. See Ground Water field measurements.

• Poorly producing formations may not supply water at a sufficient rate to prevent drawdown in the well. High producing formations (coarse grained) may be pumped at 1 L/min and still achieve low-flow.
• If nondedicated equipment is used, more time may be needed for equilibration before pumping to ensure stagnant well water is not being pumped. If dedicated equipment is used, the volume of stagnant in the pump and tubing must be purged before starting GW field measurement.

An MLS is used to obtain vertical profiles of hydraulic head, dissolved contaminants, or natural geochemistry in the saturated zone. The device can also be used in the unsaturated zone for soil gas profiling. An MLS can be equipped for single use (fluid sampling or head measurements) or dual use (both fluid sampling and head measurements).(Einarson 2006)

Monitoring wells are not definitive tools for detecting the presence of DNAPL; however, because concentrations measured with MLS relative to conventional monitoring wells are the least diluted and therefore most representative of actual concentrations in the formation, MLS-derived water chemistry is best for inferring the presence of DNAPL based on water concentrations relative to DNAPL solubility in water. Westbay Systems^a (Schlumberger) was first used in groundwater applications in 1978. This system is a modular, 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 inch–6.3 inch diameter boreholes. For holes ≥5inches, it can be installed with backfilling option.e

To date, the maximum installation depth achieved with the PVC version is 4,035 ft, and with the stainless steel version the maximum depth is 7,128 ft. Deeper installations are feasible with the stainless steel version.

Hydraulic tests can be conducted with all MLS; however, permeability can only be measured to a certain point, depending on the tubing size or other flow restrictions.

(Black 1986; Patton 1988)

• Quantitative.
  

Advantages

• Least chemically reactive.
• 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.
• Discrete sampling without repeated purging.
• No fixed downhole (dedicated) instruments avoids irreplaceable instrument failure.
• The Westbay system does not include any components that isolate water from the sampling point (e.g., tubing to the surface), and thus does not require purging to remove stagnant water from tubing before a relatively undisturbed sample is obtained.
• The Westbay system can be installed to the greatest depths using packers;

• Can only monitor head in one port at a time with single MOSDAX probe; however, string of MOSDAX probes can be used to monitor continuously in multiple ports at same time.
• When sampling using a measurement port, maximum amount of water obtained in a single trip is 1 L; if greater volume required, more downhole trips are needed
• Current version of pumping port not intended for repeated use; however, an improved version is under development.

First used in groundwater applications in 1984, it is a permanent, modular system using PVC casing. Ports are isolated in 3 inch–4.5 inch diameter boreholes using packers and in boreholes ≥5 inches by backfilling option. ⁽The backfilling option is not attractive for karstic rock with large zones that require too much sand or bentonite.) To date, the maximum installation depth achieved is 1,000 ft.

Westbay and Waterloo systems have three options: 1) using packers to isolate multiple screens in a cased well; 2) using packers to isolate borehole sections in an open hole in bedrock; and 3) using sand backfill in monitored sections with bentonite seals between sections in an open hole. When using packers, the Westbay system is removable, but may be difficult if the hole collapses on the system.

(Cherry 1982; Parker 2006)

Data Quality

• Quantitative
  

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.
• The Waterloo system can be installed to the greatest depths using packers;.

• Difficult to decommission due to stainless steel ports.
• Packer option restricts hole diameter to ≤5 inches.
• Cannot identify if self-inflating packers rupture, but chemical self-sealing effect minimizes leakage.

FLUTe systems have two options: (1) install in hole that has multi-screened casing; and (2) install in open borehole. Chemical reactivity refers to the system components being prone to sorption and/or diffusion of organic contaminants. Purging is more important for systems with greater reactivity to avoid adsorption/diffusion effects.

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 inch–20 inch diameter boreholes. To date, the maximum installation depth achieved is 850 ft; however, deeper installations are feasible.

(Cherry 2007; Keller 2009)

Data Quality

• Quantitative to semiquantitative.
  

Advantages

• Easily removable for repair/replacement or reuse of borehole.
• 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.
• Easily installed in artesian holes.
• Convenient for angled holes and holes in karst.
• The FLUTe system can be installed in holes with diameter >4in.

• Most chemically reactive; however, high-volume rapid purging system minimizes contact time for reactions to occur.
• Zone with significantly higher head than blended head may result in weak seal for this zone.
• Extremely low head at depth may cause liner rupture.

First used in groundwater applications in 1999, this system uses polyethylene tubing with three or seven chambers, and each chamber is converted into a depth-discrete monitoring tube in 4 inch–8 inch diameter boreholes using the backfilling option.^e Bentonite packers can be used for three-channel systems in boreholes of 2.5 inches–3.5 inches. To date, the maximum installation depth achieved is 300 ft.

Waterloo and CMT can be removed by overdrilling, or the CMT system can be decommissioned by grouting in place.

(Einarson 2002)

Data Quality

• Quantitative.
  

Advantages

• Lowest capital cost.
• Simple installation procedure does not require advanced training.
• Can be installed through casing using all drilling techniques.
• Most versatile system for design modifications in the field.
• Continuous tube; no joints minimizes potential leaking.
• Heads measured using narrower diameter water level tape, or option for dedicated pumps/transducers.
• Several methods for water sampling (such as double-valve pump, peristaltic pump, and inertial lift)
• Simple surface completion with minimally intrusive infrastructure.

• Moderately chemically reactive.
• Limited to a maximum of seven monitoring zones.
• Bentonite and sand cartridges only available for three-channel systems, but additional CMT packer options are being developed.

The FLUTe activated carbon technique (FACT) can be used in conjunction with the NAPL FLUTe to evaluate the vertical distribution of dissolved phase VOCs. The primary purpose of the NAPL/FACT is to aid in selection of well screen in the pore spaces or fractures in the borehole wall intervals.

The NAPL/FACT incorporates a 0.125 x 1.5-inch strip of activated carbon felt (FACT strip) into the typical hydrophobic cover of the NAPL FLUTe system attached to a carrier liner which when everted presses the NAPL FLUTe cover and the FACT strip against the borehole wall under hydrostatic pressure. The FACT strip absorbs dissolved phase VOCs from the borehole wall. Upon recovery from the borehole, the NAPL FLUTe cover is visually inspected in the field, while the FACT strip is sectioned and analyzed by standard laboratory analysis methods, with results are presented in mass per mass (grams VOC per grams carbon), thus provides qualitative screening results of VOC concentration vs depth. The NAPL cover can be used as a standalone option, while the FACT is always installed together with the NAPL cover. The NAPL cover consists of a hydrophobic fabric that reacts with free phase NAPL to create a visible stain on the fabric. The Felt Activated Carbon Test (FACT) consists of a carbon impregnated felt strip which absorbs dissolved phase NAPL. The NAPL cover is visually inspected in the field, while the FACT is sectioned and analyzed by standard laboratory analysis methods. FACT results are presented in mass per mass (grams VOC per grams carbon), thus provides qualitative screening results.(Keller 2012)

Data Quality

• Qualitative.
  

Advantages

• Direct evidence.
• Complex method for identifying NAPL presence directly in contact with borehole.
• False positive (obvious stain with no NAPL present) very unlikely.
• Capable of detecting clear, colorless NAPL at low saturations.

• FLUTe NAPL cover only reacts to direct contact with NAPL. For example, if NAPL is present as globules immediately behind the borehole wall, it would not be detected by the NAPL cover. However, it likely would be detected by the FACT.
• No stain indicates cover did not directly contact NAPL; does not mean NAPL is not present.
• Costs about $17/ft.
• Examination of the NAPL FLUTe, and separating the FACT from the liner, typically requires an extended area of unobstructed space to lay down the liner.
• It is theoretically possible to saturate the carbon strip with VOCs if the FACT remains exposed to the formation water for an extended time, eliminating the chance to compare relative concentrations within the saturated intervals.
• Separating the NAPL/FACT strip from the FLUTe carrier liner and sectioning the FACT can be challenging in freezing temperatures.
• NAPL cover only reacts to direct contact with NAPL. If NAPL is present, for example as globules immediately behind the borehole wall, it would not be detected by the NAPL cover. It would, however, most likely be detected by the FACT.

Data Quality

• Qualitative.
  

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.

• Best-guess approach for sampling location/depth.
• Volume of NAPL not easily quantifiable.
• Soil type and moisture condition may influence effectiveness and accuracy.
• Potential for false negatives; can only detects NAPL if present in actual subsample examined.
• Visual contrast can be difficult to see in dark soil.
• Precaution should be taken to avoid complete evaporation of highly volatile NAPL from sample.
• Many solvent dyes are irritants and possible mutagens; skin and eye contact should be prevented (refer to Safety Data Sheet for dye for proper handling procedures).

Data Quality

• Semiquantitative – qualitative.
  

Advantages

• Can illuminate NAPLs that fluoresce, including those that contain PAHs (coal tar, creosote, and petroleum products) and those mixed with fluorescent impurities (such as 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.

• Chlorinated solvents generally do not fluoresce when exposed to UV-visible light unless commingled with sufficient fluorescent impurities.
• Is not chemical-specific indiscriminate.
• Potential interference from nontarget fluorescent materials (such as shell fragments in coastal sediment).
• Significant potential for false positives and false negatives.

To measure the thickness of a NAPL product layer, the probe is lowered into the well until the signals activate. If there is an oil/product layer on top of the water (LNAPL), a specific signal is made by the instrument, indicating an air/product interface.

The depth is read off the permanently marked tape. The probe is then lowered further and the signal changes at the product/water interface. The thickness of the LNAPL product layer in the well is then determined by subtracting the first reading from the second.

The presence or absence of DNAPL is determined by continuing to lower the probe to the bottom of the well. If the signal changes, this indicates a nonconductive liquid. The depths should be measured the probe continued to be lowered until it touches bottom and the tape goes slack. To determine the thickness of the DNAPL layer in the well, the first reading from the bottom depth is subtracted.

Data Quality

• Qualitative.
  

Advantages

• Simple, accurate, cost-effective measurement of both LNAPL and DNAPL product thickness in monitoring wells.

• Product level and thickness of NAPL measured in monitoring wells not a reliable measurement of NAPL product presence, thickness, and location in formation.

Data Quality

• Qualitative to semiquantitative.
  

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).

• Useful for deployment in unconsolidated materials.
• High detection limits.
• Designed for VOCs (boiling points 121°C.
• Contaminant carryover likely.
• Nonphase description, only VOC monitored regardless of phase or where within formation.

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 industrial 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 very 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. (Otz 2005a, b)

Data Quality

• Qualitative to semiquantitative.
  

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 different (or similar) organic plumes resulting from releases at distinct locations and dates, identification of degradation products, and natural attenuation processes.
• Differentiation between impacted and nonimpacted groundwater.
• Outline of degree of affected groundwater within a single plume.
• Nondetects are not an issue because many organic substances can be detected in lower parts per trillion.

Data Quality

• Qualitative and semiquantitative.
• Total volatile organic halides.
  

Advantages

• On-site, real-time analysis.
• Low-cost analysis.
• Able to develop high-density data sets.
• Decision quality data.
• Low sample volume required (40 ml VOA; 30 g soil).

• Potential false positive from nontarget compounds.
• Not compound specific.
• Applicable to only halocarbon, providing total halocarbon estimates.
• Requires access to electrical outlet.

Data Quality

• Quantitative.
  

Advantages

• Compound specific analysis in real-time.
• Limits of detections of 5 μg/l for water, 10–20 μg/kg for soil and <10 μg/cubic meter for vapor.
• Accurate and precise due to use of high-level QC data is reproducible.
• Due to the short analysis time, extra QC beyond the minimum requirements are routine.
• Supports rapid, onsite development of high-density data sets.
• Supports real-time decisions for optimization of allocation of sampling resources.

• Compounds with identical mass spectra reported as group, for example, cis- and trans-1,2-DCE and 1,1-DCE.
• Cost of submittal of confirmation samples to off-site commercial laboratory for QA/QC.

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.

(Pernthaler 2002) (Wagner 2003; ITRC 2013)

Data Quality

• Qualitative.
  

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.

• Not a high throughput method
• When microbial population density is low (<106 cells/ml) or in stationary phase of growth sensitivity is reduced.
• Not widely commercially available.

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 (less negative δ13C values). (ITRC 2011; USEPA 2008; Kuder 2005)(Schmidt 2004; Kuder 2005)

Data Quality

• Quantitative to semiquantitative.
  

Advantages

• Assessment of contaminant sources when multiple sources possible.
• Identification and quantification of degradation at lab- and field-scales versus mass transfer.
• Estimating natural attenuation rates.

• In some cases, fractionation slight and difficult to validate/interpret without many samples.
• Limited number of labs that can analyze these samples; high cost per sample.
• Units of measure unfamiliar to many environmental professionals and stakeholders.

Data Quality

• Quantitative to semiquantitative.
  

Advantages

• Can be used to estimate the concentration of active microorganisms with the active enzyme of interest, such as one 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 versus active cells can be counted on same slide with two different fluorophores.

• Uncharacterized/unknown enzymes can also react with an EAP.
• Quantification is by microscopy, and therefore can be labor intensive with manual counting.
• Microbial enzymatic transformations not always detectable because products are either not identified or not detectable.
• Limited commercial availability.

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. (ITRC 2011; Øvreås 2002; Sei 2009)

Data Quality

• Qualitative and semiquantitative.
  

Advantages

• Tests 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 (such as protein, cellular, tissue, and antibody) are available.
• Detection and relative quantification of thousands of organisms or functional genes in a single analysis.
• Information about gene expression (activity) can be obtained.

• Limited commercial availability.
• Rapid advancements in both production techniques and reference database of microorganisms and functional genes.
• Quantification of results can be difficult.
• Interpretation of data typically requires significant expertise.

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 (such as 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. (ITRC 2011; Hedrick 2000)(Osborn 2001; Bent. S. J. 2007)

Data Quality

• Qualitative to semiquantitative.
  

Advantages

• All three methods are commercially available.
• Does not require growth of measured microbial communities during testing; therefore it is robust compared to other EMDs
• Identifies 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.
• Evaluates whether the subsurface biogeochemistry at a site is conducive to known bioremediation pathways.

• PLFA methods may not identify specific microorganisms.
• Number of microorganisms that can be identified depends on complexity of microbial community.
• Relevant microbial processes may not be detected in DGGE profile.
• Interpretation is somewhat subjective and less straightforward than for other EMDs.

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 or more) 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.(ITRC 2011)(Pavlov AR 2006; Saiki 1988; USEPA 2004)

Data Quality

• Qualitative to semiquantitative.
  

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 (such as water, soil, sediment).
• Can be used in conjunction with other EMDs.

• Results limited to known pathways and gene sequences.
• Some metals or humic acids may influence results.

Data Quality

• Quantitative to semiquantitative.
  

Advantages

• Commercially available.
• Quantifies abundance of specific microorganisms capable of biodegrading identified contaminants.
• Identifies whether specific genes are being expressed for contaminant biodegradation.

• qPCR analyses based on known biodegradation pathways and gene sequences.
• RT-qPCR must be used to distinguish between dead cells containing target gene and live cells.

Data Quality

• Qualitative to semiquantitative.
  

Advantages

• Commercially available.
• Proven technology.
• Does not require prior knowledge of microorganisms, genes, or enzymes involved in biodegradation processes.
• DNA-SIP can link functionality to phylogeny.
• Applicable to different environmental media (water, soil, sediment).

• Contaminants artificially enriched with high levels of stable isotopes such as ¹³C and ¹⁵N.
• Not appropriate for contaminants used as terminal electron acceptors, such as chlorinated ethenes or perchlorate.
• DNA/RNA SIP can identify organisms only if they have been identified in the past
• Extrapolating results of SIP studies to field conditions (lower than lab conditions) must be done carefully.

The most used are the water molecule stable isotopes deuterium (²H) and oxygen-18 (¹⁸O), to determine groundwater quality, origin, recharge mechanism, and rock-water interaction.

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.

Other stable environmental isotopes provide indications of groundwater age and serve as natural tracers for groundwater provenance, Stable isotopes of carbon, boron, nitrogen, and sulfur (i.e., ¹³C/¹²C, ¹¹B/¹⁰B, ¹⁵N/¹⁴N, and ³⁴S/³²S) can give valuable information about reactions involving these elements and also can serve as pollution tracers (Coplen 1999; Harte 2013a).

Data Quality

• Qualitative estimate of age and processes.
  

Advantages

• Helps to identify environmental processes that affect water such as climate and vegetation.
• Can be used as natural tracers.
• Can serve as pollution tracers.

• Isotopic compositions of water may be derived from nonunique processes and may require additional geochemical information.
• Some sampling, analysis and interpretation require specialized personnel.

Isotopes of the uranium series (234U, 238U, 226Ra, and 222Rn) are also useful tracers in isotope hydrogeology but are often not precise enough to establish the age of groundwater due to mineral-water interactions. Measurement of groundwater-surface water interactions and recharge processes is made possible with ²²²Rn (half-life = 4 days) (USEPA 1994; Cook 2000).

Data Quality

• Quantitative to semiquantitative.
  

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.
• Useful tracers in isotope hydrology.
• Groundwater residence time.
• Groundwater-surface water interactions and recharge processes.

• Tritium signal has decreased since reduction of atmospheric nuclear detonation and was absent prior to this time.
• Helium ratios provide higher resolution of age determination.

Data Quality

• Semiquantitative.
  

Advantages

• Independent assessment of fracture connectivity based on age of groundwater.
• Identifies dual permeability or bimodal ages of multiple water contributions.

• Interactions with DNAPL may affect estimates of groundwater age.
• Requires sampling for dissolved nitrogen and argon.

Data Quality

• Qualitative.
  

Advantages

• Identification of DNAPL saturations or pool geometry.

• Not commercially available.
• May require information on background uptake of uranium and thorium.

Data Quality

• Quantitative to qualitative.
• Quality assurance/quality control equivalent to fixed laboratory.
• Can use standard, published methods widely accepted by regulators.
  

Advantages

• Most applicable at sites where quantitative results are needed daily to guide field work.
• Most applicable where the throughput capabilities of the mobile laboratory are justified based on the number of samples being collected daily.

• Mobilization requires significant lead time especially if utility hookup is required.
• Permits may be required based on local zoning and state regulations.
• Operating the lab onsite is a fixed cost, so it is important to maintain the expected sample volume to maximize the efficiency of the onsite facility and personnel.
• Laboratory operations may generate hazardous waste which needs to be disposed of properly.

https://www.clu-in.org/characterization/technologies/gc.cfm

Data Quality

• Quantitative to qualitative.
  

Advantages

• A field portable GC is best utilized at sites where quantitative results are needed daily to guide field work.
• When proper analytical and calibration procedures are followed, quantitative results can be produced on a rapid turnaround basis. Split samples can be analyzed in the fixed laboratory to assess the accuracy and representativeness of the data.

• A portable GC is a sophisticated piece of hardware which must be operated by a trained and experienced chemist.
• While a portable GC can produce high quality, defensible data, the resulting deliverable package is not typically as comprehensive as that produced from a laboratory method.
• The detection limit of the portable GC may be higher than the laboratory method for the same compound.
• Even though the unit is portable it is usually best to set up the unit, and related supporting equipment and supplies, in a trailer, shipping container, and temporary office space and bring samples to the unit.

Data Quality

• Quantitative to qualitative.
  

Advantages

• GC separation coupled with MS detection is selective and sensitive, approaching laboratory quality.
• Portable systems can be carried by hand or as a backpack to the sample collection point and produce results in a few minutes.

• A portable GC/MS is a sophisticated piece of hardware which must be operated by a trained and experienced chemist.
• While a portable GC/MS can produce high quality, defensible data, the resulting deliverable package is not typically as comprehensive as that produced from a laboratory method.
• The detection limit of the field portable GC/MS may be higher than the laboratory method for the same compound.
• Even though the unit is portable it is usually best to set up the unit, and related supporting equipment and supplies, in a trailer, shipping container, or temporary office space and bring samples to the unit.