APPLICATION
OF REMOTE SENSING AND GEOPHYSICS TO THE DETECTION AND MONITORING
OF ACID MINE DRAINAGE
Mine Environment Neutral Drainage at CANMET-MMSL |
MEND Project
4.6.3
September 1994
Executive
Summary
The application
of remote sensing and geophysics to the detection and monitoring
of acid mind drainage is beyond the experimental stage and is being
applied in the management of waste from a number of producing and
abandoned mines. Experimental studies, mainly in North America and
Australia, have shown that non-invasive measurements by satellite,
airborne, ground and waterborne platforms can be used effectively
in recognising and mapping the movement of acid effluents in and
around mine workings. Some methods can only recognise changes in
the first meter or so of the ground surface; others are limited
to depths of one to five meters; others are capable of detecting
plumes at depths of several tens of meters or more. Some methods
are qualitative in nature while others can provide quantitative
answers within various degrees of accuracy and reliability. Studies,
mainly sponsored by government agencies, but supported in many cases
by industry, are attempting to establish the effectiveness of a
wide variety of methods and techniques, mainly by conducting test
surveys and examining available data in the vicinity of abandoned
mines. Possibly the most ambitious of these studies has just been
carried out in the Sudbury area, Ontario, under the MEND program
by INCO Exploration and Technical Services Limited, (King, 1994).
This study establishes useful parameters for applications of specific
techniques in a specific geological environment. Similar studies
are urgently needed to expand the range of methods and applications
and extend into other geological and topographic settings.
Important
progress has been made in the establishment of guidelines for the
cost-effective application of both remote sensing and geophysics
for AMD problems. To begin with, the non-geophysical remote sensing
techniques are most effective in establishing terrain and thematic
mapping parameters required for the proper monitoring of changes
in condition over time for both potential and active mine drainage
environments.
Mapping of
vegetation encroachment, die-off, stress and morbidity, as well
as percentage and distribution of ground cover and type, are effective
techniques in monitoring for the impacts of AMD seepage, and any
remediation of such conditions. While we can confidently recommend
LANDSAT and other satellite-borne remote sensing data for preliminary
studies, recent activity in airborne multi-spectral techniques would
indicate that this is a more effective process, by nature of its
improved resolution, both spatial and spectral.
The direct
detection and effective mapping of surface moisture from seepage,
ponding, and drainage patterns, uses the traditional techniques
of air photos for generation of three dimensional terrain or drainage
mapping, and satellite and airborne multi-spectral data for mapping
of ponds and detection of surface penetrating seepage. Detection
of sub-surface moisture uses thermal infrared techniques or the
indirect method of monitoring stress and vigor patterns in the vegetation
and ground cover. Other indicators may be found in mapping open
pit mines, diversion channel silting, dam failure and changing conditions
leading to imminent dam failure all of which can be detected using
combinations of air photo, multi-spectral and infrared monitoring.
While traditional
remote sensing methods, with the possible exception of near-infrared
measurements, are generally considered to be limited to the direct
detection of very shallow seepage conditions, the use of multi-spectral
techniques, both satellite and airborne, provides an ability to
detect changes in the vegetation or ground cover that are indicative
of sub surface AMD problems. These techniques are quite recent and
represent an area that deserves. and will likely see. more active
duty in the near future.
The use of
spectroradiometers is a relatively new field that is growing rapidly.
The collection of reference spectral signatures has become an important
component for site characterization for environmental remediation.
In addition, geologists are starting to use spectroradiometers for
mineral exploration in arid and semi-arid environments and for characterizing
mine tailings and waste rock. Image analysis software vendors are
beginning to market software that enable analysts to use collected
reference signatures or access existing spectral libraries that
can be used as an integral part of the analysis of airborne or satellite
data.
The real strengths
of these methodologies are to be found, not so much in the raw data,
but in the ability to analyze and integrate this data with other
data sources, homing in on the actual realities contained in a series
of inferential data sets. It is the image analysis and GIS (Geographic
Information System) systems that make this possible. AMD is an application
where this ability to integrate is crucial. As the necessary sources
of information are quite diverse, not only do the multiple remote
sensing data sets have to be properly analyzed and integrated, but
a wide range of geophysical data must also be incorporated into,
and analyzed through, this process.
Conventional
airborne geophysical survey data, primarily electromagnetic, but
also magnetic and gamma-ray spectrometry, can be used as baseline
information to establish the natural physical parameters of the
ground, and in the detection and ongoing monitoring of changes caused
by acid mine effluent. Depending upon the magnitude and composition
of the seepage, changes may be detected to tens or possibly hundreds
of meters below ground.
Borehole geophysical
techniques are being used widely in the waste management industry
to map contaminant plumes as well as the structure and stratigraphy
of disposal sites. These techniques are commonly followed by traditional
drilling and in-situ chemical and physical monitoring procedures.
The geophysical surveys act as inexpensive reconnaissance techniques
to recognise and establish limits for seepage problems, to direct
cost-effective drilling programs and to monitor changes taking place
outside the drilled areas.
Borehole geophysical
logging is widely used to determine physical parameters that are
affected by acid contamination and to identify zones of contamination
detected by surface measurements. Borehole-to-borehole and surface-to-borehole
measurements are being tested to provide three-dimensional images
of zones of anomalous electrical conductivity or acoustic impedance.
Borehole methods are outside the scope of the present study but
are referred to briefly in the text. References are included in
the General Bibliography.
All of these
geophysical techniques have, as a second objective, the determination
of stratigraphy, bedrock structure, waste-pile architecture etc.
that can assist in the design of a testing and remedial follow-up
program.
Ground geophysical
methods of greatest potential in AMD studies appear to be wideband
or multi-frequency EM, ground penetrating radar (GPR), Induced Polarization
(IP) and, oddly, Self Potential (SP). All three methods provide
direct information on contaminant plumes as well as indirect data
on the structure of the ground and potential leakage pathways. The
SP method is the only one that can sense the actual movement of
acid contaminant.
One message
that repeats Itself again and again in the available literature
is the importance of integrating methods in order to remove ambiguities
and improve identification of acid drainage. Very frequently an
anomalous condition might be caused by a change in lithology or
the presence of acidic groundwater. The use of a second method can
often eliminate one of these possibilities. Another important message
that applies to geophysical surveys is that neither raw nor processed
data, presented as profiles, contours or pseudo sections of measured
parameters is nearly as effective for understanding subsurface conditions
as inverted data. Data inversion, whether 2- or 3dimensional, attempts
to present a physical property distribution in the ground, which
should correspond to the properties encountered in a drill program.
Techniques for inverting most types of geophysical data are now
available but are only very recently finding their way into the
industrial marketplace. The authors believe that this is an area
where important advances will be made in the next few years.
This handbook
is the result of an m-depth literature search, an information survey
of more than 900 organizations, synthesis of catalogues from suppliers
of equipment and services, and numerous discussions between the
authors and scientists working in the remote sensing and geophysical
disciplines. None of these phases is, by itself, complete. For example,
the information survey failed to reach a number of organizations
active in the remote sensing and geophysical fields. However, our
analysis of the state of the art in terms of methods and applications,
again through a synthesis of information from the above sources.
is believed to be fairly accurate.
With respect
to specific techniques and instrumentation, it has not been possible
to include full details of all of the systems available for remote
sensing and geophysical surveys. Readers are encouraged to contact
the customer services departments of the firms listed in Chapters
5 and 12 and to consult professional directories for other suppliers
that have been omitted in this compendium.
Finally, it
should be recognised that while the technologies described in this
manual are, for the most part, relatively mature, their application
to environmental problems in general and AMD in particular, is quite
new. The authors have attempted to identify additional ways of applying
remote sensing and geophysical methods to AMD problems. Readers
are encouraged to conduct their own experiments, thereby adding
to the existing experience and information base.
Français
| Contact Us
| Help | Search
| Canada Site
Home | What's
New | CANMET-MMSL
| MMS Site
| NRCan Site
|