SEG Speaker Series

Spring 2014
 
Dr. B. Venkateswara Rao - May 13, 2014
Prof. of Water Resources & Director SCDE, Jawaharlal Nehru Technological University Hyderabad, India
TOPIC: Hydrogeological and Geophysical investigations for locating ground water potential zones in a typical hard rock terrain, India
 
Khondalitic suite of rocks (garnetiferrous sillimanite gneiss) occurs in Eastern Ghats of India along East Coast. They are sedimentary in origin and later metamorphosed to become hard rocks and are formed overlying the basement rocks of granite gneiss. Hydro geological and geophysical investigations have revealed that usually ground water occurs in these rocks under unconfined to semi confined conditions in the weathered and fractured layers respectively. Intense weathering of khondalite led to formation of kaolin resulting in decreased fractured rock thickness and consequently decreased well yields nearer to water courses. The kaolin cutoffs developed below the streams are evidently acting as barriers to lateral movement of ground water compelling it to accumulate between the streams where it's availability is plentiful particularly when the formation is intercalated with quartz veins. The kaolinised layer is sometimes acting as aquitard or semi confining stratum a top the main aquifer of fractured khondalite. 2D resistivity imaging proved to be better technique to identify the aolinised pockets and to reduce the well failures.  The highly weathered zone is identified with the resistivity values below 25 ohm m. The depth of highly weathered material at failed well is extended about 8-10 m more deeper than the successful wells at some places to as much as 20 m more deep at some other places. This extended deeper kaolinisation of the aquifer is responsible for failure of wells.  Layers having resistivities between 25 -65 Ohm.m are identified as aquifer layers which are composed of  moderately weathered and fractured khondalitic suit of rocks (Garneti ferrous sillimanite/biotite gneiss). Layers with resistivities greater than 65 Ohm.m are interpreted to have basement characteristics belonging to the granite gneiss.
 
 
Fall 2013
 
Perrine Fernandez - December 17, 2013
Norwegian University of Life Science, PhD student
TOPIC: Lab studies of contaminant degradation in unsaturated zone
 
Abstract:
Reliable tools for investigating redox conditions for a given geologic unit will be useful for both characterisation and remediation of soil contamination, and could be extended to other purposes such as the preservation of buried cultural heritage. The redox reactions associated with degradation change the chemical composition of the water phase and gas releases. These changes can potentially be mapped with geophysical and gas measurements at the soil surface. The redox potential combined with the local geological conditions determines the composition of available electron acceptors as well as microbial degradation pathways and how the soil system is affected in the long term.  For example, after oxygen and nitrate are depleted, manganese and iron should be reduced. However, in experiments conducted in the unsaturated zone at Gardermoen airport, Norway, it was found that for the degradation of the de-icing agent propylene glycol (PG), manganese and iron were preferred over nitrate as electron acceptor. Batch experiments were conducted to examine whether nitrate is a preferred electron acceptor over iron and manganese oxides as described in classical redox reaction theory. Gas releases during PG and glutamate degradation were measured in a sandy pristine soil with and without nitrate under anaerobic condition during two weeks of incubation. Sand box experiments are also conducting to determine if the influence of bacteria population over the oxidation of iron can be monitored by non-intrusively as a self-potential anomaly. 

Dr. Ernst Niederleithinger  - October 7, 2013
Senior Scientist and Deputy Division Leader at BAM
Visiting Scientist, Colorado School of Mines
TOPIC: New concepts from geophysics - new possibilities for NDT
 
Abstract:
The talk will give an overview on geophysical techniques used in non-destructive testing. Focus will be on ultrasonic methods applied on concrete. The application of ultrasonic techniques to concrete structures has improved significantly in the past decade. Many kinds of structural features can be mapped in detail, determination of compressional and shear wave velocities leads to insight on material quality and condition. However, a lot challenges still exist. Imaging techniques currently used fail to map vertical faces or backside of objects, subtle changes in materials are hard to detect. Two techniques recently introduced in geophysics might be able to advance the state of the art. Reverse Time Migration (RTM) has shown the capability to image complicated structures. Coda Wave Interferometry (CWI) is able to detect very small, distributed velocity changes in scattering materials. Both techniques will be explained by using synthetic and real data.

Dr. Trenton Franz - September 26, 2013
Assistant Professor of Hydrogeophysics
School of Natural Resources at the University of Nebraska-Lincoln
TOPIC: Quantifying the cosmic-ray neutron probe support volume in heterogeneous systems
 
Abstract:
Given the cosmic-ray neutron probe horizontal support at tens of hectares and tens of centimeters vertically; the probe has the potential to fill a critical measurement gap for validating and calibrating hyper-resolution land surface models. However, the estimate of probe support volume is complicated by two factors: 1) the probe sees all forms of hydrogen regardless of association and 2) the relationship between neutron counts and average hydrogen content is nonlinear resulting in non-uniqueness when averaging heterogeneous fields. In this work, I will first present a general framework accounting for all forms of hydrogen near the earth’s surface. Second, I will define the horizontal support and how it varies with changes in the mass and composition of the near surface atmosphere. Third, I will define the vertical support and how it changes with subsurface hydrogen content. Finally, I will present some hypothetical model scenarios of 1 and 2-dimensional soil moisture heterogeneity and its affect on average neutron count and thus area-average soil moisture. By quantifying the probe support volume and its dependence on system hydrogen content we can better constrain estimated area-average water flux and the parameters that control flux.