EET 7 - Environmental Geophysics: Everything You Ever Wanted (Needed!) to Know but were Afraid to Ask!
|Instructor||Prof. Peter Styles (Keele University, UK)|
|Book||Available in EAGE Bookshop|
The people who need this course do not require a great understanding of the mathematical basis of geophysics but they do need to understand the physical principles and what techniques will do what and where they fail and why and what information can be gleaned from Geophysics and what are the limitations and boundaries of interpretation.
What is really important is how we combine techniques in a truly integrated way to solve subtle, complex and critical problems that one technique alone cannot satisfy.
In order to understand the physical, hydrological, and pollution situations which are present in the near subsurface, (often due to past industrial activity and presenting a need to regenerate safely) it is critical to be able to interrogate the shallow subsurface. In previous times this was done by trial pitting, drilling and excavation but the nature of the problems mean that these intrusive techniques, while essential for ground truthing, can liberate or compromise the very ground we are seeking to make safe. Therefore, legislators and developers are turning more and more to non-intrusive geophysical techniques to characterize the subsurface in order to make informed decisions as to where and how many intrusive confirmations (i.e., boreholes) are needed to obtain sufficient comfort to plan a strategy for remediation/containment or abandonment. Poor specification, poor advice, lack of knowledge about the appropriateness or otherwise of the tools available to address the task, adherence to methods which are defensible in litigation rather than right for the problem have all led to a position where there is a lack of trust between Engineers, who are usually in the position of client and Environmental Geophysicists, who are usually the contractor. It is not just the fault of the Purchaser; with the advent of much more automation in geophysical instrumentation there are practitioners who carry out surveys without a full understanding of what, where, why and in what order and also make promises which cannot be delivered because of the constraints imposed by the fundamental laws of physics. The scale of task (and financial risk) that Environmental Geophysics is being required to address is also growing exponentially; I sit on the Nuclear Decommissioning Agency Geosphere Characterization Panel and have become acutely aware that legislators such as the UK Environment Agency, Health and Safety Executive, Nuclear Installations Inspectorate impose strong controls on the number and position of exploratory boreholes in projects such as the site characterization and investigation for Radioactive Waste Geological Disposal Facilities and are relying on geophysics in all its forms to deliver the information on which siting, safety case , post closure safeguarding will be designed and delivered. Exactly the same will occur for Underground Gas Storage and Geological Sequestration of CO2 where monitoring of retention and stability are paramount. The days of claiming that 'only the drill will prove it' are fading as the drill will only be applied at a very late stage and NOT where the critical facility itself will be situated for fear of compromising the safety case. New sources of energy from Coal bed Methane and Underground Coal Gasification will also require remote monitoring of areas which CANNOT be investigated by intrusive techniques.
This course will address:
- The nature of Geophysics, the range of problems that can be addressed by it, what can be seen and what cannot and the limitations imposed by the laws of physics and 'environmental noise'.
- Problems such as Natural and Man-Made Cavities in Coal, Chalk, Limestone Karst, Salt and other Evaporites and their collapses, either potential or incipient. Their detection, characterization, geometries and state of stability and verification of the quality of their remediation. Brownfield site characterization and the scale of remediation necessary; LNAPL and DNAPL pollutants and leachates, buried infrastructure, archaeological features. Determination of engineering properties, topography, layering, strength and rippability of soil/bedrock. Monitoring gas storage and CO2 sequestration underground using microgravity and microseismic techniques
- How to detect sub-surface 'trouble ahead'! Techniques: When, Where and How They Should Be Used and When Not!
- Potential Field Techniques: Gravity and Magnetism, their similarities and differences, instrumentation, field methodologies for high resolution and accuracy, interpretation, target identification, definition and characterization. Time varying gravity, Magnetic gradiometry.
- Electrical Techniques Resistivity, field techniques, standard and Electrical Resistance Tomography, in the search for fluid targets, water, gas and pollution. Self Potential, Electroseismic and Electrokinetic signals and their significance in water investigations and fluid flow and leakage in dams and other structures. Induced and spontaneous polarization
- Electromagnetic techniques: Ground Penetrating Radar both for indentifying structure and determining physical properties , Electromagnetic techniques and Nuclear Magnetic Resonance techniques in Hydrogeophysics and Pollution as reconnaissance Tools. Controlled Source Magneto-Tellurics and other electromagnetic methods as more sophisticated techniques for specialist applications
- Seismic Techniques: Field data collection and a brief guide to reduction and interpretation. Shallow 2D and 3D seismic reflection and refraction for structure with noise-based microtremors and shear-wave techniques for engineering properties. Microseismic monitoring and acoustic emission in mines, slope stability and landslides, hydrofracturing and other applications
- Joint Inversion and Modelling: How do we improve the definition/resolution of already high-resolution techniques? Discussion of combined inversion of complementary techniques which utilize different geophysics fields.
Borehole Geophysics: In order to better resolve targets especially in areas where reconnaissance geophysics has indicated useful targets may exist, we need to emphasize the use of well chosen borehole techniques using both drilled borehole and push techniques. These include Borehole radar, Self-potential and electrical resistivity as well as, of course, cross-hole seismic tomography
Geoscientists, Environmentalists, Water, Civil and Geotechnical Engineers, Engineering, Mining and Hydro Geologists. In fact all those who have responsibilities for specifying and procuring geophysical services or appointing and directing geophysical staff but who do not feel that they understand the techniques, approaches, strengths and limitations of geophysics well enough to obtain optimal advice and understand the survey/interpretation information. The course will also be suitable for those who wish for an application/case-study-oriented introduction to Environmental Geophysics concentrating on the problems and their solutions with recourse to mathematical analysis only where really necessary.
Attendees should have experience/knowledge of the types and range of environmental/engineering problems that are encountered in the near-surface and a desire to learn how to best approach them. A working knowledge of elementary mathematics and physics will help but a willingness to engage with the material is more important.
About the instructor