Unit 12 : Advanced Hydrogeology
Contaminant Hydrogeology
Contamination Problems
• So far we have concentrated on physical and
chemical processes of mixing dissolved
species in groundwater systems.
• Most of the discussion has largely avoid
issues of organic non-aqueous phase liquids
(NAPLs) and multiphase flow.
• In this section we will discuss practical
problems of groundwater systems where a
vapour phase and more than one liquid
phase may be present.
NAPLs
• In general, the complexity of
contamination problems increases when
NAPL’s are present.
• Instead of one, there are up to three
plumes to track:
– vapour phase plume
– immiscible liquid phase plume
– dissolved phase plume
DNAPLs and LNAPL’s
• NAPL’s are classified according to their
density relative to water:
– LNAPL’s (light non-aqueous phase liquids) are
lighter than water and tend to “float” at the watertable and give rise to associated vapour phase
and dissolved phase plumes.
– DNAPL’s (dense non-aqueous phase liquids) are
heavier than water and tend to “sink” to the bottom
of aquifers where they can also give rise to
dissolved phase plumes.
Complex Plumes
Flow
Clay Lenses
Mainly DNAPL Residual
Mainly LNAPL Vapour
Primary LNAPL
Secondary LNAPL
Primary DNAPL
Secondary DNAPL
Contamination Attributes
• Three important attributes distinguish sources
of groundwater contamination:
– degree of localization
• point or local
• non-point or diffuse
– loading history
• pulse
• continuous
– contaminant type
•
•
•
•
•
•
radionuclides
trace metals
nutrients
other inorganics
organics
biological
Degree of Localization of Source
• A point source is characterized by the
presence of an identifiable small-scale source
such as a leaking tank, a spill, a small pond
or a landfill.
• A diffuse source refers to a source
emanating from many poorly defined
locations. Pesticides, fertilizers, acid rain and
highway salt are typical non-point diffuse
sources.
Loading History
Time
Continuous Variable
Time
Concentration
Pulse
Concentration
Concentration
Concentration
• Loading history describes how the source
concentration varies as a function of time.
Continuous Constant
Time
Continuous Decaying
Time
Sources of Contamination
• A very long list of domestic, agricultural and industrial
activities have the potential to result in contamination.
• Category I: Designed Discharges
– Septic tanks, injection wells, land application of wastes, etc
• Category II: Designed Storage Facilities
– landfills, dumps, tailings piles, ponds, underground tanks, etc
• Category III: Designed Transportation Systems
– pipelines, transport routes, transfer stations, etc
• Category V: Other Planned Discharges
– pesticide/fertilizer application, deicing salts, mine drainage, etc
• Category V: Potential Conduits
– production wells, monitoring wells, construction excavations, etc
• Category VI: Naturally Occurring Sources
– natural leaching, saltwater intrusion, saline water upconing, etc
U.S. Office of Technology Assessment, 1984
Types of Contaminants
• The list of potential contaminants number in the tens
of thousands and organization of this list is a major
problem.
• Six major categories: (1) radionuclides (2) trace
metals (3) nutrients (4) other inorganics (5) organics
and (6) biological provide a framework for discussion.
• All the contaminants have the potential to produce
health problems. Too much of anything is a potential
health hazard but tolerable thresholds are finite.
• For some contaminants, particularly radionuclides,
the threshold level is such that anything above
natural background is of concern.
Radionuclides
• The nuclear fuel industry is the main source of
radioactive contaminants.
• Potential sources occur throughout the nuclear fuel
cycle.
• During mining when raw ore is processed 238U, 229Th,
226Ra, and 222Rn are potential contaminants.
• Fuel fabrication, fuel reprocessing and powergenerating facilities are other potential sources.
• Colorado, New Mexico, Utah, Wyoming,
Saskatchewan and Ontario are the U producing
regions of North America.
• The nuclear industry is very closely controlled and
monitored by federal, state and provincial authorities.
Trace Metals
• Trace metals are a natural component of all
groundwaters and represent the largest group of
elements in the periodic table.
• Additional sources include (1) mining effluents, (2)
industrial wastewaters, (3) urban runoff, (4) agricultural
wastes and fertilizers, and (5) fossil fuels.
• Some trace metals (B, Cu, Fe, Zn) are essential for
health but others have a tendency to accumulate in the
body (or bioaccumulate in organisms low in the food
chain) from sources at relatively low concentrations.
• The 13 trace metals that make the EPA list of 129
priority pollutants are: Ag, As, Be, Cd, Cr, Cu, Hg, Ni,
Pb, Sb, Se, Tl, Zn.
Nutrients
• Nutrients are ions and compounds containing
nitrogen and phosphorus.
• The dominant nitrogen species in groundwater in
NO3- and to a lesser extent NH4+.
• Phosphorus is less important as a contaminant
because of its low solubility and tendency to readily
sorb onto solids.
• Sources of N and P are largely agricultural including
the use of fertilizers and the cultivation of virgin soils
(when large quantities of N are released.)
• Sewage (N) and municipal wastewaters (P) are also
sources of nutrients.
Other Inorganic Species
• This group of “contaminants” includes the major ions
usually present in groundwater.
• Extremely high concentrations render water
unsuitable for human consumption, animal watering
and many industrial uses.
• Health related concerns are low for this group of
contaminants but high concentrations of Na+ can
disrupt blood chemistry and lower Na+ concentrations
may lead to hypertension.
• Fluoride a good example of a trace non-metal
contaminant. At low concentrations F- has the
beneficial effect of reducing tooth decay. At higher
concentrations (only x5 higher) F- can lead to serious
health problems including goitre and fluoridosis.
Organics
• Contamination of groundwater by organic compounds
is a consequence of the large number of petroleum
products and man-made organics in common use.
• The EPA list of 131 priority pollutants contains 116
organic compounds, 13 trace metals, asbestos and
cyanide. Over 90% are organics.
• The EPA divides the organics into four groups based
on the methods used for analysis but ultimately the
analytical tool is gas chromatography-mass
spectrometry (GC-MS):
–
–
–
–
base-neutral extractables (47)
acid extractables (12)
volatiles (32)
pesticides and PCBs (25)
Petroleum Products
• Organic compounds in crude oil and crude oil
products fall into three main groups:
– Alkanes (n-butane, n-hexane, cyclohexane, etc)
– Alkenes (ethene, propene, etc)
– Aromatics (BTEX group: benzene, toluene, ethylbenzene and
xylene; PAH group: anthracenes, naphthalenes, etc)
• Distillation separates crude oil into fractions:
– Gasolines (C4 to C12 alkanes, C4 to C7 alkenes, BTEX group)
– Middle Distillates (C10-C24 alkanes, some BTEX, some PAHs)
– Residual Products (C20-C78 alkanes, aromatics mainly PAHs)
Halogenated Compounds
• Aliphatics (chain molecules with H replaced
by F, Cl, Br) including PCE (CCl2CCl2), TCE
(C2HCl3) and CT (CCl4).
• Aromatics (benzene rings with substituted
halogens) including chlorobenzene (C6H5Cl)
and dichlorobenzene (C6H4Cl2)
• Both groups of halogenated compounds tend
to have densities greater than water and
usually fall in the DNAPL group.
PCBs
• Polychlorinated biphenyls (PCBs) .Due to their nonflammability, chemical stability, high boiling point and
electrical insulating properties, PCBs were used in
hundreds of industrial applications prior to 1977
(when N.American production was discontinued).
• They consist of joined, chlorine substituted benzene
rings.
• PCBs are relatively insoluble in water but are
extremely persistent in the environment breaking
down very slowly.
• PCBs are highly toxic and highly soluble in biological
lipids, and have been found to accumulate in animal
and human tissues.
Organics in Groundwater
Petroleum Derivatives
Fuels
benzene, xylene, hexane, octane
PAHs
benzopyrene, naphthalene
Alcohols
methanol, glycerol
Creosote
m-cresol, o-cresol
Ketones
acetone
Halogenated Compounds
Aliphatics
PCE, TCE, CT
Aromatics
chlorobenzene, dichlorobenzene
Polychlorinated Biphenyls
water soluble
2,4’-PCB, 4-4’-PCB
DNAPL
LNAPL
Biological Contaminants
• The important biological contaminants are:
– pathogenic bacteria (Fecal streptococci, Fecal
colliforms, Escherichia coli, Shigella dysenteriae,
Salmonella typhi, Vibrio cholerae)
– viruses (enteroviruses, hepatitis A virus, polio virus
and rotavirus )
– parasites (Giardia, Entamoeba, Cryptosporidium )
• The main sources are (1) land disposal of sewage
and septic tanks, (2) leachates from sanitary landfills
and (3) agricultural wastes.
• The contaminants are particulate rather than
dissolved, transport distances are limited and
problems tend to be related to localized sources.
Plume Morphology Basics
• Mass transport processes control:
– maximum plume extent
– geometric distribution of concentrations
• Advection is the dominant control on plume
shape.
• Hydrodynamic dispersion is usually a
secondary factor.
• Chemical, nuclear and biologic processes
generally attenuate spreading.
Controls on Advection
• Magnitude and direction of advective
transport is controlled by:
–
–
–
–
hydraulic conductivity field
potentiometric head distribution
distribution of sources and sinks
shape of the flow domain
• All these factors influence groundwater flow
velocity, which drives advective transport.
Hydraulic Conductivity Field
H
L
Hydraulic Conductivity
• Plume advects faster with increasing K.
• Plume migrates in highest K horizon
• Low K near surface delays plume.
development.
• Plumes tend not to invade low K units.
Dispersion
aL=0
aT=0
aL>0
aL>>aT
aL>0
aL>aT
aL>>0
aL>aT
Dispersion
• Increased dispersion gives broader
plume.
• Concentration pattern is spread and
high concentration zone is reduced with
increasing dispersivity.
• Increasing aT results in increased
vertical spreading.
• High aL and high aT gives most mixing.
Reaction Rate Half-Life
t1/2=30
t1/2=10
t1/2=
3
t1/2=
1
Reaction Rate Half-Life
• Reaction removes contaminant mass.
• As half life reduces, more material has
reacted and the plume shrinks.
• After about 5 half-lives the plume is
indistinguishable from background.
• Both biological degradation and
radioactive decay result in plume
shrinkage.
Sorption
Kd=0.01
Kd=0.1
Kd=1
Kd=10
Sorption
• Sorption is another attenuation process.
• As Kd increases the plume becomes
smaller as sorption retards and
attenuates the mass in solution.
• Sorption is a potent mechanism for
reducing the extent of contaminant
plumes.
Pulse Loading
t =50
Co=1
Dt=5
Co=1/2
Dt=10
Co=1/4
Dt=20
Co=1/8
Dt=40
Pulse Loading
• The same mass is added over an increasing
time period from 5 to 40 years.
• Peak concentrations are reduced by
spreading and the entire mass is advected
towards the discharge end of the flow system.
• For lower source concentrations over longer
periods the plume is closer to the source and
less compact.
QA/QC in Water Sampling
• Characterization of the distribution of
contaminants in the subsurface is an integral
part of any field study.
• The collection of these data is fraught with
difficulties and “bad data is worse than no
data at all.”
• Design of collection systems to ensure that
data is both reliable and representative is a
considerable challenge.
Screen Length
• When piezometers are designed to measure
hydraulic head, screen length is not a critical
concern.
• For chemical sampling, screen length can
lead to widely variable results.
1 mg/L
10 mg/L
1 mg/L
Point Sampling
• Point sampling implies a short screen section
and small diameter access tube to minimize
fluid volumes are avoid mixing and dilution.
• Narrow tubes are not ideal for head
measurements (where access for a tape is
required).
Chemical
Monitoring
Well
Piezometer
Sampling Points
• Sampling point locations need take account
of the complexity of the flow system.
• Plumes often have a restricted vertical extent
and may not resolve a plume.
• Multiport monitoring wells solve this problem
(at a price).
standpipe
piezometers
multilevel
sampler
QA/QC for Chemical Data
•
There are four potential problems that
can have a serious impact on
chemical data:
1) Contamination of samples with drilling
fluids.
2) Changes in water quality as a result of
well construction.
3) Sample deterioration prior to analysis.
4) Careless field and laboratory practices.
Sample Contamination
• Occasionally, samples become contaminated
with gas, oil, or water in combination with
foams, emulsions and muds used in the
drilling process.
• These contaminants are difficult to remove
once the well has been completed.
• Contamination can be avoided by using a
readily detected tracer in the drilling fluid and
developing the well until the tracer can no
longer be detected
Well Construction
• Cement and other soluble materials used in well
construction can influence groundwater chemistry.
• High pH (>9) is often characteristic of continuing
interaction between cement and the water being
sampled.
• Samples can also be contaminated with trace metals
from steel casing and adhesives from plastic casing
joints.
• Selection of threaded plastic casing avoids these
problems.
• Purging wells by removing at least 2 or 3 well
volumes before sampling is also recommended.
Sample Deterioration
• Temperature, pressure and gas content changes in
samples following collection can seriously impact
chemistry.
• Exposure to atmospheric oxygen can lead to rapid Eh
changes and metals precipitation from anoxic waters.
• Loss of CO2 can raise pH and decrease bicarbonate
concentrations (and perhaps precipitate CaCO3.
• These problems can be addressed by specialized
sampling equipment for high P-T environments, the
use of flow-through cells and various sample
treatments to minimize deterioration.
Field Sample Handling
• Field handling of samples requires
standardized bottle washing, filtering and use
of chemically pure preservatives.
• Sorption of organics onto containers or filters
and loss of volatiles during samples are
potential problem areas.
• Running “blanks” of ultra-pure distilled water
through the field sampling procedure allows
for rapid detection of problems.
Laboratory Sample Handling
• Ongoing QA/QC checks for analytical
laboratories are a necessity. Common
approaches include:
– Submitting “spiked” samples of known
composition for analysis.
– Submitting duplicate samples to different
laboratories.
– Submitting replicate samples of the same water.
Sampling Systems
•
Sampling systems capable of
providing point samples from the
saturated zone include:
1) Nests of standpipe piezometers
2) Multi-level (or multiport) samplers
installed in a single boreholes
3) Packers systems that can isolate various
levels in a single borehole.
Nested Standpipes
• Single wells are easier
to complete and seal:
–
–
–
–
–
Drill
Sand pack
Bentonite seal
Backfill
Surface cement seal
• Installation are durable
and reliable.
• Main disadvantage is
high cost of drilling.
Cement Seal
Fill
Bentonite Seal
Sand Pack
Slotted Screen
Multi-level Sampling
• Multi-level samplers involve placing
several sample points in a single hole:
– seals are required between sample points
– filter sand may or may not be required
– sand packs are difficult to install
– sand packs are often impossible to develop
– small internal volume
– reduced drilling costs
Multi-level Samplers
• A wide variety of multi-level samplers
are available:
– multiple standpipes in single hole
– bundled standpipes
– valved suction couplings
– retrievable downhole tools with packers
and suction ports
– gas-drive samplers
Multiple Standpipes
Bundled
Bentonite Seal
Sand pack
Screen
Suction Ports
PVC Pipe
Plastic Tube
Rubber Seal
Stainless
Steel
Screen
Installation involves multiple ports and does
not require sand pack or seals. Subject to
clogging. Works best in cohesive materials.
Westbay-Type Samplers
•
•
•
•
•
•
Downhole sampling tool.
Casing has sampling ports
Packers inflated to isolate particular port
Suction recovers small sample
Transducers measure pore-pressure
Effective but expensive system
Unsaturated Zone Samplers
• Most systems involve vacuum suction
through porous ceramic cup.
• Small sample chamber is filled.
• Sample moved to the surface by suction
or gas displacement.
• Problems include:
– reaction of pore fluids with ceramic
– loss of gases as a result of vacuum suction
Solids Samplers
• Another approach to fluids sampling is to take an
entire soil sample and extract the pore fluid.
• This method is often used for LNAPL and DNAPL
sampling.
• There are a variety of sampling devices:
• split spoons
• thin-walled tubes
• piston samplers
• Advantages include relating contamination directly to
lithology and minimal cross-contamination.
• Disadvantages include cost and difficulties with
resampling.
Soil-Gas Characterization
• Soil gas sampling has become the industry standard
for sampling organic volatiles in groundwater.
• A metal probe with a perforated tip is driven into the
ground.
• Small gas sample is extracted by pumping.
• Alternatively static collectors can be buried and
recovered for analysis.
• The collectors sorb volatiles onto activated charcoal.
• Samples are analyzed by GC.
• Gas sampling is a simple, rapid and cost-effective
screening tool.
Geophysical Methods
• Geophysical methods have been used for
plume delineation for decades.
– Surface Resistivity and EM conductivity methods
have met with most success.
– Ground Penetrating Radar (GPR) has become a
useful tool for shallow investigations.
– Magnetometry is very useful to locate buried
pipes, metal objects and containers.
– Shallow Seismic survey have met with limited
success in true groundwater applicationsand are
relatively high-cost.
ERT Measurements
• ERT (electrical resistance
tomography) is a DC
resistivity technique.
• Electric potentials
generated by a current
source are measured by
a receiver array.
• Measurements may be
made on the earth’s
surface or in boreholes.
ERT Data Processing
• Measured potentials are sensitive to the bulk
electrical properties, which are diagnostic of porosity,
connectivity of pore fluid, and pore fluid chemistry.
• The ERT image creation process involves solving
both forward and inverse problems on an FE mesh.
• Image resolution is a complicated function of many
factors, including reconstruction pixel size, data
signal-to-noise ratio, electrode and borehole
separation, the subsurface resistivity distribution, and
the degree to which the resistivity matches the twodimensional model used for the forward calculations.
• Resolution can be no better than one pixel; typical
pixel size is 1 to 3 meters and improves as borehole
spacing decreases.
ERT Images
%Change in Resistivity
Air Sparging Experiment, Florence, Oregon
ERT Section
EM Basics
• The electromagnetic (EM) geophysical method
determines electrical properties of earth materials by
inducing electromagnetic currents in the ground and
measuring the secondary magnetic field produced by
these currents.
• An alternating current is generated in a wire loop or
coil above the ground's surface. Both the primary
magnetic field (produced by the transmitter coil in the
instrument) and the secondary field (produced by
currents in the earth) induce a corresponding
alternating current in the receiver coil of the
instrument.
• The coils are kept at a fixed distance and orientation
relative to the ground to simplify data analysis.
EM Data Processing
• After compensating for the primary field, both the
magnitude and relative phase (in-phase and
quadrature-phase) of the secondary field are
measured.
• The quadrature-phase component is converted to a
value of apparent soil electrical conductivity (EC).
• This value represents an estimate of the local
average soil EC.
• The depth of measurement is dependent on the
instrument's coil spacing, orientation, and operating
frequency, and the actual subsurface EC variations.
EM Interpretation
• Averaging limits discrimination of thin, high
concentration brine intrusions from broader,
more diffuse plumes.
• Multiple profiles using differing coil spacing
can be performed to bracket approximate
depths of brine affected groundwater.
• Data quality may be degraded by cultural
interference as caused by utility lines, steel
fences or other large metallic objects.
EM Instrumentation
EM31 – 1 to 6 m
EM34 – up to 60 m
EM38 – 75 cm to 1.5 m
EM39 – downhole to 500 m
EM31
• The EM31 maps geological variations, groundwater
contaminants or any subsurface feature associated
with changes in the ground conductivity using an
electromagnetic inductive technique that makes the
measurements without electrodes or ground contact.
• With this inductive method, surveys can be carried
out under most geological conditions including those
of high surface resistivity such as sand, gravel and
asphalt.
• The effective depth of exploration is about six meters,
making it ideal for many geotechnical and
groundwater contaminant surveys.
EM31 Advantages
• Important advantages of the EM31 over conventional
resistivity methods include:
– the speed with which surveys can be conducted.
– the precision with which small changes in conductivity can
be measured.
– the continuous readout and data collection (logging) while
traversing a survey area.
• The in-phase component is especially useful for
detecting shallow ore bodies and buried metal
hazardous waste.
EM34
• The EM34-3 has been particularly successful
for mapping deeper groundwater contaminant
plumes and for groundwater exploration.
• Using the same patented inductive method as
the EM31, the EM34-3 uses 3 intercoil
spacings to give variable depths of
exploration down to 60 meters.
• With the 3 spacings and 2 dipole modes
vertical electrical soundings can be obtained.
EM38
• Designed to be particularly useful for agricultural
surveys measuring soil salinity, the EM38 can cover
large areas quickly without ground electrodes.
• Based on the same patented induction principle as
the EM31, the EM38 provides depths of exploration
of 1.5 meters and 0.75 meters in the vertical and
horizontal dipole modes respectively.
• The lightweight,one meter long, EM38 provides rapid
surveys with excellent lateral resolution.
• Measurement is normally made by placing this
instrument on the ground and recording the meter
reading.
EM39
• The EM39 provides measurement of the electrical
conductivity of the soil and rock surrounding a
borehole or monitoring well, using the inductive
electromagnetic technique.
• The unit employs coaxial coil geometry with an
intercoil spacing of 50 cm to provide a substantial
radius of exploration into the formation while
maintaining excellent vertical resolution.
• Measurement is unaffected by a conductive borehole
fluid or the presence of plastic casing. The instrument
operates to a depth of 500 metres.
EM Survey Results
Magnetometry
• Magnetomety detects changes in the earth’s
magnetic field created by buried ferromagnetic
objects.
• A magnetometer measures the intensity of the
earth’s magnetic field. The presence of ferrous
metals creates variations in the local strength of that
field, permitting their detection.
• A magnetometer’s response is proportional to the
mass of the ferrous target. Typically a single drum
can be detected at distances up to 6 meters, while
massive piles of drums can be detected at distances
up to 20 meters or more.
Magnetometers
• Modern magnetometers permit the acquisition of
continuous data as the magnetometer is moved
across the site.
• This continuous coverage is needed for high
resolution requirements and the mapping of
extensive areas.
• The effectiveness of a magnetometer can be reduced
or totally inhibited by noise or interference from timevariable changes in the earth’s field and spatial
variations caused by magnetic minerals in the soil, or
iron and steel debris, ferrous pipes, fences, buildings,
and vehicles.
Applications of Magnetometry
• Applications of magnetometry include:
– Location buried steel containers, such as 55–
gallon drums.
– Definition of boundaries of trenches filled with
ferrous containers.
– Location ferrous underground utilities, such as iron
pipes or tanks, and the permeable pathways often
associated with them.
– Selection of drilling locations that are clear of
buried drums, underground utilities, and other
obstructions.
Magnetometer Survey
GPR
• Ground penetrating radar (GPR) has been used for
over twenty years at chemical and nuclear waste
disposal sites as a non-invasive technique for site
characterization.
• Standard GPR surveys are conducted from the
surface of the ground providing geotechnical
information from the surface to depths of 2 to 15 m,
depending on GPR frequency of operation and soil
conductivity.
• Commercially available GPR systems operate over
the frequency range 50 MHz to 1000 MHz.
GPR Details
• Lower frequencies provide better penetration but
poor resolution, while the higher frequencies give
poor penetration but good resolution.
• There are many critical environmental monitoring
situations where surface GPR does not provide the
depth of penetration or necessary resolution.
• Borehole radar can place the sensor closer to the
region of interest, overcoming the high signal
attenuation in the near-surface soils.
GPR Images
GPR Borehole Tomography of Water Injection Well
Shallow Seismic
• Initiated by rapid technical developments over the
past two decades or so, multi-channel engineering
seismographs with wide dynamic range, powerful
computer facilities, and sophisticated seismic
software have become available to a broad
community of environmental and geotechnical users
at reasonable prices.
• Based on these instrumental improvements,
acquisition and processing techniques established for
deep seismic surveying in the hydrocarbon industry
have been successfully adapted and applied in
shallow seismic studies.
Difficulties with Shallow Surveys
• The most important difficulty to be overcome
in near-surface seismics is the inevitable
interference of strong source-generated noise
with reflections from the shallow subsurface.
• To extract shallow reflection signals from data
contaminated by source-generated noise,
careful choices of recording parameters (e.g.,
source type, source and receiver intervals,
minimum and maximum source-receiver
offsets) and processing strategies are even
more important than in deep seismic studies.
Resolution of Shallow Seismic Data
• Important considerations when designing
shallow seismic reflection investigations are
the spatial and temporal resolution.
• Mapping of small-scale features in the near
surface requires much higher resolution than
is demanded of conventional seismic surveys.
• Improvement of horizontal resolution may be
achieved by simply decreasing source and
receiver intervals.
• Higher vertical resolution requires broader
bandwidth signals. Sources must be capable of
generating a wide band of high frequencies
(>100 Hz), and receivers must be capable of
faithfully recording them.
Shallow Seismic Reflection Applications
• Shallow reflection methods have proved to be reliable
and valuable tools for non-destructive mapping of the
shallow subsurface associated with:
–
–
–
–
–
near-surface structural investigations
mapping the depth to bedrock
delineating shallow faults
locating subsurface cavities and tunnels
mapping suitable formations for potential construction and
waste disposal sites
– water table location and other groundwater studies
– mineral exploration and exploitation
– detecting fracture zones in crystalline rocks
3D Reflection Survey
3D Reflection Survey: P-wave seismic reflectors