209 4 Airborne and Surface Geophysical Method Verification Prepared by* Ernest L. Majer Lawrence Berkeley National Laboratory, Berkeley, California 4.1 GEOPHYSICAL METHOD APPLICATION AND USE The complexity of using geophysical and remote sensing methods for hazardous waste containment transcends the already challenging problems associated with mineral exploration and groundwater and petroleum exploration and production. Hydrologists and petroleum reservoir engineers have studied the flow of water, oil, and gas in porous permeable rocks and unconsolidated sediments for many years. The oil industry has developed first-order methods of analysis that are remarkably successful in assessing the potential of an aquifer or reservoir to supply a given fluid or gas for some period of time. However, these analyses seem almost trivial compared to the task of finding, monitoring, and removing subsurface contaminants. In terms of monitoring barriers the task may or may not be as challenging as finding and characterizing subsurface contaminants. This is due to several different issues specific to barriers. If one is trying to see a change in the properties of a barrier it is not as challenging as seeing absolute changes. If one is trying to characterize or find a leak in the barrier this may be just as difficult as finding a contaminant. The issue is particularly challenging because of the following: * With contributions by Randolph J. Cumbest, Westinghouse Savannah River Company, Aiken, South Carolina; Bruce Davis, National Aeronautics and Space Administration, Stennis Space Center, Mis- sissippi; William E. Doll, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Leland Estep, Lockheed Martin, Midland, Texas; Susan S. Hubbard, Lawrence Berkeley National Laboratory, Berkeley, California; John D. Koutsandreas, Florida State University, Tallahassee, Florida; David P. Lesmes, Boston College, Chestnut Hill, Massachussetts; H. Frank Morrison, University of California, Berkeley, California; Lee D. Slater, University of Missouri at Kansas City, Kansas City, Missouri; Anderson L. Ward, Battelle Pacific Northwest Laboratory, Richland, Washington; Chester Weiss, Sandia National Laboratories, Albuquerque, New Mexico. 4040_C004.fm Page 209 Thursday, September 15, 2005 11:50 AM © 2006 by Taylor & Francis Group, LLC 210 Barrier Systems for Environmental Contaminant Containment & Treatment In traditional oil and gas subsurface applications, a 50% recovery rate is considered a great success. The great majority of geophysical and remote sensing methods were developed with this level of sensitivity. In remediation applications, this recovery rate is usually not sufficient. Although oil and gas applications are multi-phase, the variations in the prop- erties are not as large as in near-surface, partially saturated systems encountered in the vadose zone or even in saturated environments (i.e., groundwater contam- inants can be particles, chemicals that dissolve in water, or liquids or gases that are only partially soluble in water). Under certain conditions, some contaminants can move through unsaturated soils and rocks as vapor. Contaminants can also interact strongly with the minerals in the subsurface. Clays can absorb some contaminants while some may form chemical complexes with other groundwater chemicals. Immiscible dense liquids can settle vertically, while some may become nutrients for microbes that are present naturally or have been introduced. All of these interactions may or may not affect the geophysical signals. A variety of methods exist that could be classified as geophysical techniques; however, this chapter focuses on geophysical methods that are used to infer volumetric (average over a volume of material rather than at a point) rather than point properties, i.e., crosshole, surface, and surface to borehole methods rather than well-logging techniques which usually only measure a few centimeters to a meter away from the borehole. The methods are assumed to be applied from the surface and boreholes or by placing sensors and/or sources in or near the barriers, thus imaging the volume or planes between the surface and borehole, the volume from the surface to the borehole, or a volume from the surface to a reflector or other target in the subsurface. Last but not least, two main applications are assumed with respect to barriers: (1) the initial and subsequent characterization of the subsurface volume to be contained, and (2) the verification of the integrity and performance of the barriers. These issues are linked and must be addressed to validate overall system performance. 4.1.1 C HARACTERIZATION AND G EOPHYSICS A simple definition of characterization is mapping the distribution of contaminant sources and effluents as well as the physical, chemical, and biological properties of the subsurface materials that control their distribution, concentration, and movement. Some of the physical properties required are lithology, fault/fracture properties, porosity, permeability, grain size, and fluid type and saturation. Rock or soil types, mineralogy and distribution, and types of clay minerals are also needed to model chemical processes. Chemical state, temperature, fluid satura- tion, and other factors that affect the presence and amount of nutrients are also needed to determine microbe behavior. Characterization as defined here is the essential first step toward containment and/or remediation, but all too often the term is used only to describe the extent of the contamination itself, usually over 4040_C004.fm Page 210 Thursday, September 15, 2005 11:50 AM © 2006 by Taylor & Francis Group, LLC Airborne and Surface Geophysical Method Verification 211 a small area or volume that is relatively small compared to the entire groundwater system in which it resides. This concept of total system characterization is critical in containment applications because, as will be seen, the application of geophys- ical methods for containment depends on detecting changes from background or initial conditions. As a result, characterization efforts are currently often limited to determining the nature and extent of the toxic materials and not defining the whole regime in which they are traveling, interacting, and evolving. This limited definition can be useful in small-scale sites where the solution is excavation, but it is only half of the story at thousands of larger scale sites. The additional concept that the distribution of properties and processes should also be characterized is just now being incorporated into idealized or conceptual models of hypothetical sites in anticipation of when actual site data permit contaminant fate and transport simulation and eventual remediation. Only in the last five years have geophysical methods been used to measure the spatial distribution of the properties at actual sites to provide constraints for ground water models in a quantitative sense (Hubbard et al., 2001, 2003; Grote et al., 2003). If the subsurface were uniform or even uniformly layered, drilling on a loose grid of holes would probably suffice to characterize the site. Unfortunately, the subsurface is generally heterogeneous, and a program based on drill-hole samples and measurements would provide incomplete or, at worst, misleading information. Thus, volumetric information (information connecting the actual points of measurements) is needed. Geophysical methods are needed to: (1) provide the spatial distribution of certain physical properties that are essential for site characterization; (2) map the distribution of some contaminants; and, in some cases, (3) detect chemical changes associated with contaminant interaction with the subsurface and barriers. Indeed, a useful definition of applied geophysics is that it is the science of using physical measurements or experiments on the surface (or from boreholes drilled from the surface) to determine the physical properties and processes in the subsurface. Geophysics is ideally suited for extrapolating measurements obtained from a borehole to the large-scale volume away from the borehole (Peterson et al., 1985; Parra, 1991; Krohn, 1992; Sheets and Hendrickx, 1995; Majer et al., 1997). In this application, geophysical measurements obtained from the surface or between boreholes can be used to assess the continuity and homogeneity of the intervening material. Geophysics can also serve to map the subsurface in the absence of boreholes and can be used to detect the unexpected such as a change in lithology, fractures, or fast paths (Leary and Henyey, 1985, Davis and Annan, 1989, Hendrickx et al., 2002, Hubbard et al., 2002, 2003). Failure to be aware of such gross heterogeneity has a major impact on hydrologic flow models and contaminant transport (Majer et al., 1997). Finally, geophysical methods could be used to delineate contaminants if the waste was buried in containers because the waste containers produce a geophysical anomaly or the waste alters the properties of the medium (Doll et al., 2000). Table 4.1 shows the different reso- lution of the seismic and electrical methods and their expected use and application. 4040_C004.fm Page 211 Thursday, September 15, 2005 11:50 AM © 2006 by Taylor & Francis Group, LLC 212 Barrier Systems for Environmental Contaminant Containment & Treatment 4.1.2 P ERFORMANCE M ONITORING AND G EOPHYSICS An important need for geophysics is for monitoring the processes that are imple- mented to remove, contain, or treat contaminants. In the case of containments, the ability of geophysical methods to monitor the emplacement and performance of the barriers primarily depends on the geophysical contrasts of the barrier and subsurface. However, in some cases, even though the barrier does not look any different than the surrounding properties, geophysics could possibly monitor changes in the barrier properties relative to the native materials, monitor flow TABLE 4.1 Possible Surface Geophysical Methods for Verification of Subsurface Barriers Method Purpose Success Comments Expected Resolution a Surface Methods Seismic Host characterization, caps and walls Fair Use for structure and lithology of interior 0.5–5 m Electrical (electromagnetic, induced polarization, self potential, DC resistivity) Host characterization, caps and walls Good Fluid content and conductivity 1.0–10 m Radar Host characterization, caps and walls Good Water content and lithology 0.5–2.0 m Borehole Methods Radar zero off-set (ZOP) velocities Barrier detection Excellent Processed for differences 0.25 m Radar tomographic velocity Barrier detection Excellent Processed for differences 0.25 m Radar tomographic amplitudes Barrier detection Excellent Processed for differences 0.25 m Radar well-to-well reflection Barrier detection Poor Low signal-to- noise ratio Electrical resistance tomography Barrier detection Good 0.5 m Electrical resistance tomography Leak detection Excellent Differences during salt water flood 0.25 m Seismic ZOP and tomography Barrier detection Poor Injected air destroyed signal a Estimated only for successful borehole methods. 4040_C004.fm Page 212 Thursday, September 15, 2005 11:50 AM © 2006 by Taylor & Francis Group, LLC Airborne and Surface Geophysical Method Verification 213 paths within the contained zone, and/or detect processes occurring due to the presence of contaminants. Once a site has been characterized and modeled and a remediation process designed and implemented, it is necessary to assess the effectiveness of the remediation operation. Geophysical methods are ideally suited to this task, because it is often easier to monitor changes in some portion of the subsurface than it is to uniquely determine the subsurface properties themselves, i.e., time-lapse monitoring (Dailey and Ramirez, 2000). An example of time-lapse data is given in Figure 4.1. This is a plan view of a site where moisture monitoring is performed by observing the changes in signals from ground-penetrating radar (GPR) (Grote et al., 2003). As seen in the differences FIGURE 4.1 Comparison of volumetric water content estimates obtained from 900-MHz common off-set GPR ground wave data during two different times of the year over a natural field study site. These images reveal a persistence of near-surface water content spatial distribution at the site, which was interpreted to be controlled by near-surface soil texture. Vine number 60 900 MHz: Time 1 900 MHz: Time 2 WET DRY WET DRY 40 20 0 12 m 30 m 155 105 Row number Row number 55 Vine number 60 40 20 0 155 0.10 0.20 Volumetric water content 105 55 4040_C004.fm Page 213 Thursday, September 15, 2005 11:50 AM © 2006 by Taylor & Francis Group, LLC 214 Barrier Systems for Environmental Contaminant Containment & Treatment between the two plan views of the radar reflectivity, it is easy to determine where moisture changes occur. Some of the information provided by geophysical methods is indirect, but the parameters measured can be related to the rock/soil properties needed. For example, the distribution of electrical conductivity is not a parameter that is directly useful in hydrological modeling, but when conductivity is used to obtain information on porosity, saturation, pore fluid salinity, and clay content then it becomes a vital parameter needed for characterization. The relationship between the properties measured with geophysics and the hydrologic or mineralogic prop- erties is, in most cases, site-specific. To be effective, site characterization requires close integration of the geologic, hydrologic, chemical, and geophysical data. 4.1.3 G EOPHYSICAL M ETHODS FOR S ITE C HARACTERIZATION AND M ONITORING OF S UBSURFACE P ROCESSES The geophysical methods most directly applicable for characterizing and moni- toring hazardous waste sites can be divided into the following general categories: seismic; electrical and electromagnetic; natural field and magnetic (e.g., gravity, tilt); and remote sensing methods. These categories were chosen for the different properties that are fundamentally sensed. Well-logging applications are considered here as point measurements and are not included in the detailed discussions that follow. This is not to imply that well logging should not be included in a geophysical program. The opposite is true. Well logging is fundamental to all databases and should be the rule, not the exception. 4.1.3.1 Seismic Seismic methods are used to measure the distribution of elastic wave velocity (compressional and shear) and the attenuation of the different seismic waves in the ground. Seismic velocity depends on many factors, but the primary factors affecting seismic measurements are porosity, mechanical compressibility, shear strength, fracture content, density, fluid saturation, and clay content. Some of these parameters are directly related to important hydrologic properties and others are used to map the distribution of soil and rock types. The most common use of seismic methods is mapping interfaces between materials of different seismic velocities to provide high-resolution images of the locations of lithologic prop- erties and thus infer main flow channels and soil types. Cross-hole seismic tomography is now used for petroleum reservoir characterization and will be equally important in hazardous waste site characterization. 4.1.3.2 Electrical and Electromagnetic Electrical and electromagnetic methods are used to measure the distribution of electrical conductivity and the dielectric constant of the ground. Electrical con- ductivity of soils and rocks depends entirely on the conduction paths created by 4040_C004.fm Page 214 Thursday, September 15, 2005 11:50 AM © 2006 by Taylor & Francis Group, LLC Airborne and Surface Geophysical Method Verification 215 fluids in the pore spaces and is determined by porosity, saturation, pore fluid salinity, and clay content. In certain cases where the contaminants are ionic solutions, the electrical conductivity directly maps contaminant distribution (Endres et al., 2000). However, in most cases, the conductivity is used to extrap- olate hydrologic measurements obtained from boreholes. The presence of clays that is so important in fluid flow and chemical absorption models brings about a distinctive frequency-dependent conductivity — the induced polarization effect. This effect is of immense value in monitoring site remediation processes because many processes involve injecting materials that profoundly alter this effect (Slater and Binley, 2003). A separate electrical property of soils and rock is the streaming potential effect, which is but one aspect of a whole class of interactions called coupled flow phenomena. Basically, driving forces of temperature gradients, hydraulic pressure gradients, chemical potentials, and voltage gradients produce flows of heat, fluid, chemicals, and electric current (Slater and Binley, 2003). These flows are coupled in the ground in the sense that not only does a pressure gradient produce a fluid flow but it also produces an electrical current flow — the streaming potential. Similarly, temperature gradients drive currents to produce thermoelectric effects. Another cross-coupling term of immense potential in contaminant studies is electro-osmosis, which is a flow of fluid produced by a voltage gradient. This phenomenon has been used in geotechnical engineering applications to stabilize embankments and assist in pile driving. It could be used to alter subsurface flow patterns by directing a particular contaminant plume to an extraction or treatment region. Because electro-osmosis depends on fluid conductivity, rock permeability, and the configuration of the imposed voltage gradients, the site must be well characterized in fluid conductivity and permeability before the design of a prac- tical system can be implemented. 4.1.3.3 Natural Field and Magnetic Natural field methods consist of gravity, magnetic, and tilt methods. High accu- racy measurements of gravity over the surface of the Earth (i.e., microgravity surveys) yield a measure of the subsurface density distribution, which, in turn, depends on the distribution of porosity, water content, and rock type. Borehole gravity measurements yield direct average volume values of density. Similarly, high accuracy measurements of magnetic field can be used to infer the distribution of magnetic minerals, usually magnetite, which, in turn, is related to rock type and certain sedimentary depositional environments where heavy minerals settle out of fluid flows. Tilt measurements have recently been used to measure defor- mation associated with fluid withdrawal and injection. By monitoring the rate of tilt or deformation, the rate of fluid movement can be inferred and an average permeability for the formation can be determined. Tilt and strain methods are low resolution, but for near-surface application they can be of some use in barrier monitoring. If gross changes in the density or geometry of the barrier changes on the order of a few percent, then these methods may be applicable. The drawback 4040_C004.fm Page 215 Thursday, September 15, 2005 11:50 AM © 2006 by Taylor & Francis Group, LLC 216 Barrier Systems for Environmental Contaminant Containment & Treatment to achieving the necessary resolution is the installation of the gravity meters or tilt meters. Careful attention to stability and repeatability of the data must be maintained in addition to thermal stability and leveling. General directions of fluid movement, steam injections, or other density changes can also be monitored. In magnetic surveys, the distribution of the magnetization of the earth is measured from the surface, but these methods usually lack resolution for detailed subsurface studies. Borehole magnetometers are now being used to supplement more conventional well-logging tools to search for lithologic changes and chem- icals/minerals that cause magnetization to change. 4.1.3.4 Remote Sensing Remote sensing is defined as the noninvasive observation of natural phenomena. It involves collecting information about an object by detecting differences between the object and the surroundings without being in physical contact with the object of observation. The differences that can be detected between objects of interest and their background involve shifts in various fields as observation moves from the background to an object of interest. Electromagnetic, acoustic, potential, and radiological are typical fields sampled by remote sensors for object detection. These types of sensors mounted on spaced-based (satellite) or airborne platforms can be used to rapidly and noninvasively characterize and monitor features and events on the earth’s surface with broad coverage and high resolution. Space-based or airborne hyperspectral, thermal, radar, and/or radiation sensors can provide a cost-effective alternative to traditional approaches. The spatially synoptic look achieved by remote sensing methods can improve the accuracy of area interpolations generated by point-sampled data. Ideally, the characterization and monitoring of waste sites and their containment systems would include remote sensing data, ground-based geophysical measurements, and point-sampled data. These data streams could then be integrated in a geographic information system (GIS) database with ancillary data concerning the barrier construction, geology, watershed hydrology, and climatology of the site. 4.2 SPECIFIC METHODS Although each method has generally been described, there are subsets of each method for specific applications. For example, seismic methods can be catego- rized further into active and passive methods, and even further into surface and borehole methods or some combination. Specific methods that are most applicable to environmental remediation needs are described below. 4.2.1 S EISMIC M ETHODS Seismic methods can be divided into passive and active methods. Passive methods involve listening to seismic energy being created by stress changes or natural seismicity such as micro-earthquakes or acoustic emissions near the boreholes 4040_C004.fm Page 216 Thursday, September 15, 2005 11:50 AM © 2006 by Taylor & Francis Group, LLC Airborne and Surface Geophysical Method Verification 217 or underground openings. Acoustic emissions for purposes described here are of secondary use. When monitoring a barrier, however, the barrier may emit acoustic emissions if it is brittle and possibly failing. Monitoring would involve a simple process of emplacing sensors in or near the barrier and monitoring for discrete events above a certain threshold. Active methods involve introducing energy into the ground with either an impact or controlled swept frequency source and observing how the seismic waveforms change due to heterogeneity or anisotropy in the subsurface or barrier. Both the direct and reflected arrivals of seismic waves (i.e., travel time and amplitude) can be used for this process. More sophisticated uses can involve guided wave energy in the barrier either during emplacement or for monitoring. Seismic reflection methods are used extensively in the petro- leum industry for structural delineation and lithologic definition. New and sophis- ticated three-dimensional (3-D) surface and borehole methods have dramatically improved imaging capabilities for the petroleum industry, and can potentially be applied to remediation with proper instrumentation. The utility of seismic tech- niques also depends on the resolution obtainable in a given soil or rock type. For this reason, this discussion focuses on the seismic methods that have the highest resolution. Figure 4.2 shows the typical field configuration of a seismic surface and a cross-borehole configuration of a seismic survey. These configurations can be generalized to other techniques such as radar and electrical methods. Knowing the location of the source and receiver, the data can be inverted to derive the properties of the earth. A typical set-up of a surface geophysical survey (top image of Figure 4.2) consists of a source and receiver on the surface and documentation of the different arrivals from the source. This example is typical for a radar or seismic survey (Hubbard et al., 2003). The bottom figure shows a typical example of a cross- borehole survey with different sources and receivers at different points so that a tomographic and/or a reflection image between the boreholes is obtained. The goal of seismic surveys is to describe or map the velocity and attenuation of seismic waves through the volume of interest. In general, this process is referred to as imaging, although the extent to which a complete or 3-D image can be formed depends on the availability of a suitable distribution of source–receiver combinations and the frequency content of the seismic waves. When a cross section of seismic parameters can be determined, the process is also referred to as tomography. Surface methods depend on sources and receivers distributed on the surface. Combined with sources and/or receivers in boreholes or the barriers themselves, a true 3-D image can be formed. Figure 4.3 shows typical images from a surface radar survey and a cross-borehole tomographic survey. Shown are the source and receiver pairs and the ray path coverage, very similar to seismic geometry. Seismic imaging could play an important role in site characterization, per- formance confirmation, and monitoring tasks. It could be used to estimate and extrapolate the extent and shape of soil property distributions that are measured only at discrete points with borehole methods. It can also be effectively used to detect features not mapped in the exploratory or initial phase of remediation and 4040_C004.fm Page 217 Thursday, September 15, 2005 11:50 AM © 2006 by Taylor & Francis Group, LLC 218 Barrier Systems for Environmental Contaminant Containment & Treatment to monitor changes in properties in the site area from measurements obtained entirely outside the critical volume. The transmission and attenuation of seismic waves through the subsurface depends on the elastic parameters, which depend on, among other things, the state of stress and strain, porosity, clay content, grain size, and fluid saturation. As recent research shows, high frequency seismic wave propagation is sensitive to discontinuities (fractures or joints) in the media (Majer et al., 1997). Seismic tomography can, therefore, be used to detect changes in the soil column condition, locate major preexisting and new features, and measure overall changes in the widths of these features. The methods that can be used for these studies use sources on the surface and detectors either in a borehole [referred to as vertical seismic profiling (VSP)] or in cross-hole configurations with both sources and receivers in boreholes. VSP techniques are primarily used for eluci- dating subsurface structures and determining seismic velocities of the various rock and/or soil horizons. In addition to the more conventional uses of VSP, the FIGURE 4.2 A typical set-up of a surface geophysical survey (top) where one places a source and a receiver and records the different arrivals from the source, this example is for a radar or seismic survey (Hubbard et al., 2003). The bottom figure shows a typical example of a cross-borehole survey with different sources and receivers at different points so that one obtains a tomographic or reflection image between the boreholes. Locations of sources Locations of receivers 01234567 01234567 7 6 8 9 10 11 7 6 8 9 10 11 Air wave Critically refracted wave Ground wave Refracted wave ε 1 ε 2 ε 1 > ε 1 Reflected wave Air T X R X Example of tomographic data acquisition geometry 4040_C004.fm Page 218 Thursday, September 15, 2005 11:50 AM © 2006 by Taylor & Francis Group, LLC [...]... Airborne and Surface Geophysical Method Verification 9.0 7.9 6.9 5.9 4. 9 3.8 2.8 1.8 0.8 −0.3 −1.3 −2.3 −3.3 4. 4 −5 .4 −6 .4 −7 .4 −8.5 −9.5 mV 40 0750 40 0800 40 0850 40 0900 13 745 0 13 740 0 137350 137300 137250 137200 137150 137150 137200 137250 137300 137350 13 740 0 13 745 0 40 0750 40 0800 40 0850 40 0900 13 745 0 13 740 0 137350 137300 137250 137200 137150 137150 137200 137250 137300 137350 13 740 0 13 745 0 40 0750 40 0800 40 0850...5 4 3 2 1 0 5 4 3 2 1 0 34 34 36 36 38 38 38 2200 2100 2000 1900 1800 1700 1600 36 Velocity 40 40 40 5 4 3 2 1 0 5 4 3 2 1 0 7 6 5 4 3 2 1 0 40 0-2 07 (60 ft S of 40 7) 32 32 34 Silty-sandy zone 10 m 30 30 32 Days Silts 28 28 30 Aqulard 26 26 28 10 m Silt 24 24 26 MW155 (62 ft E of 40 6) Sands 22 22 24 Gravels 20 20 22 5m Yellow unconformity FIGURE 4. 3 A typical example of data... zero-valent iron and 1.2 m of sand Figure 4. 11a shows the cross-sectional geometry of the barrier and site geology Superimposed is the position of electrodes and the finite element mesh used to reconstruct the conductivity distribution between wells with electrical © 2006 by Taylor & Francis Group, LLC 40 40_C0 04. fm Page 244 Thursday, September 15, 2005 11:50 AM 244 Barrier Systems for Environmental Contaminant. .. 13 745 0 40 0750 40 0800 40 0850 40 0900 231 9 .49 8.97 8 .46 7.95 7 .44 6.92 6 .41 5.90 5.38 4. 87 4. 36 3.85 3.33 2.82 2.31 1.79 1.28 0.77 0.26 nT/m 40 0750 40 0800 40 0850 40 0900 FIGURE 4. 7 Comparison of (a) ORAGS-TEM measurements and (b) an analytic signal map derived from ORAGS-Arrowhead magnetic measurements for a bombing target in South Dakota TEM represent the first-time gate only, and data were acquired at... the lithology (left-hand side) The figure on the right shows typical results from a crosswell tomographic survey correlated with the lithology 219 © 2006 by Taylor & Francis Group, LLC 40 40_C0 04. fm Page 219 Thursday, September 15, 2005 11:50 AM C02-C03aa Airborne and Surface Geophysical Method Verification 40 7 -4 06 20 Sands Mappaturg scarp 40 8 -4 07 7 6 5 4 3 2 1 0 40 0-0 38 (49 ft N of 40 6) E W Surface reconnaissance... effectiveness, and performance of barriers, geophysics should be used in a total system performance mode to monitor the total fluid matrix system that includes not only the barrier but also the zone being contained © 2006 by Taylor & Francis Group, LLC 40 40_C0 04. fm Page 2 34 Thursday, September 15, 2005 11:50 AM 2 34 Barrier Systems for Environmental Contaminant Containment & Treatment 4. 2.6.1 Hyperspectral... construction and over the longterm design life Short- and long-term monitoring issues are thus treated separately in the subsections below © 2006 by Taylor & Francis Group, LLC 40 40_C0 04. fm Page 240 Thursday, September 15, 2005 11:50 AM Barrier Systems for Environmental Contaminant Containment & Treatment 800 Magnetic susceptibility (cgs × 106) Conductivity (mS/m) 240 100 Hz 1 kHz 600 40 0 200 0 0 0.25... porosity and sand-clay content Klimentos and McCann (1990) developed empirical relationships between P-wave attenuation, porosity, and permeability in sandstone Partially saturated materials pose a further complication Anderson and Hampton (1980a,b) performed considerable work in both theory and measurement to reach an understanding of seismic wave propagation in gas-bearing sediments Bedford and Stern... (49 ft N of 40 6) E W Surface reconnaissance line 1100 P4G3 40 40_C0 04. fm Page 220 Thursday, September 15, 2005 11:50 AM 220 Barrier Systems for Environmental Contaminant Containment & Treatment use of three-component VSPs for detecting and characterizing 3-D features has become routine in the oil industry In the last several years, the petroleum and gas industry have started to extend the traditional... the ORAGS-TEM (Transient Electrical Methods) system, as an electromagnetic complement to the ORAGS-Hammerhead system A photograph of the system is shown in Figure 4. 6, and data acquired © 2006 by Taylor & Francis Group, LLC 40 40_C0 04. fm Page 230 Thursday, September 15, 2005 11:50 AM 230 Barrier Systems for Environmental Contaminant Containment & Treatment N 100 0 100 200 Meters 300 23.7 22 .4 21.2 19.9 . 40 7) 5 4 3 2 1 0 20 22 24 26 28 30 32 34 36 38 40 5 4 3 2 1 40 7 -4 06 5 4 3 2 1 0 20 22 24 26 28 30 32 34 36 38 40 5 4 3 2 1 0 0 40 8 -4 07 5 6 7 4 3 2 1 0 20 22 24 26 28 30 MW155 (62 ft E of 40 6) 32 34. 212 Barrier Systems for Environmental Contaminant Containment & Treatment 4. 1.2 P ERFORMANCE M ONITORING AND G EOPHYSICS An important need for geophysics is for monitoring. (left-hand side). The figure on the right shows typical results from a crosswell tomographic survey correlated with the lithology. C02-C03aa 40 0-0 38 (49 ft N of 40 6) P4G3 40 0-2 07 (60 ft S of 40 7) 5 4 3 2 1 0 20