Deep Resistivity Tomographic Imaging of The Qualibou Caldera, Saint Lucia

The Qualibou Caldera has been studied since the 1970’s for possible development of geothermal power generation. In 1974 dipole-dipole resistivity measurements were performed in the area. The apparent resistivity data was plotted as contours and a single line running through Sulphur Springs was interpreted by using forward models to generate a best fit model. The data is reanalyzed using a robust 2D inversion method. The result shows a resistive body beneath Sulphur Springs, the presence of which has been debated for nearly thirty years. The data from all 2D tomograms is interpolated into 3D, which generates images showing conductive features reminiscent of hydrothermal convection plumes

Complex conductivity of soils

The complex conductivity of soils remains poorly known despite the growing importance of this method in hydrogeophysics. In order to fill this gap of knowledge, we investigate the complex conductivity of 71 soils samples (including four peat samples) and one clean sand in the frequency range 0.1 Hz to 45 kHz. The soil samples are saturated with six different NaCl brines with conductivities (0.031, 0.53, 1.15, 5.7, 14.7, and 22 S m21, NaCl, 258C) in order to determine their intrinsic formation factor and surface conductivity. This data set is used to test the predictions of the dynamic Stern polarization model of porous media in terms of relationship between the quadrature conductivity and the surface conductivity. We also investigate the relationship between the normalized chargeability (the difference of in-phase conductivity between two frequencies) and the quadrature conductivity at the geometric mean frequency. This data set confirms the relationships between the surface conductivity, the quadrature conductivity, and the normalized chargeability. The normalized chargeability depends linearly on the cation exchange capacity and specific surface area while the chargeability shows no dependence on these parameters. These new data and the dynamic Stern layer polarization model are observed to be mutually consistent. Traditionally, in hydrogeophysics, surface conductivity is neglected in the analysis of resistivity data. The relationships we have developed can be used in field conditions to avoid neglecting surface conductivity in the interpretation of DC resistivity tomograms. We also investigate the effects of temperature and saturation and, here again, the dynamic Stern layer predictions and the experimental observations are mutually consistent

Induced Polarization with Electromagnetic Coupling: 3D Spectral Imaging Theory, EMSP Project No. 73836

This project was designed as a broad foundational study of spectral induced polarization (SIP) for characterization of contaminated sites. It encompassed laboratory studies of the effects of chemistry on induced polarization, development of 3D forward modeling and inversion codes, and investigations of inductive and capacitive coupling problems. In the laboratory part of the project a physico-chemical model developed in this project was used to invert laboratory IP spectra for the grain size and the effective grain size distribution of the sedimentary rocks as well as the formation factor, porosity, specific surface area, and the apparent fractal dimension. Furthermore, it was established that the IP response changed with the solution chemistry, the concentration of a given solution chemistry, valence of the constituent ions, and ionic radius. In the field part of the project, a 3D complex forward and inverse model was developed. It was used to process data acquired at two frequencies (1/16 Hz and 1/ 4Hz) in a cross-borehole configuration at the A-14 outfall area of the Savannah River Site (SRS) during March 2003 and June 2004. The chosen SRS site was contaminated with Tetrachloroethylene (TCE) and Trichloroethylene (PCE) that were disposed in this area for several decades till the 1980s. The imaginary conductivity produced from the inverted 2003 data correlated very well with the log10 (PCE) concentration derived from point sampling at 1 ft spacing in five ground-truth boreholes drilled after the data acquisition. The equivalent result for the 2004 data revealed that there were significant contaminant movements during the period March 2003 and June 2004, probably related to ground-truth activities and nearby remediation activities. Therefore SIP was successfully used to develop conceptual models of volume distributions of PCE/TCE contamination. In addition, the project developed non-polarizing electrodes that can be deployed in boreholes for years. A total of 28 of these electrodes were deployed at the SRS site in September of 2002. The project found that (1) currently available field instrumentation need to be faster by an order of magnitude for full SIP to be engaged for broadband characterization in the field, (2) some aspects of the capacitive coupling problem in borehole geometries can be solved by use of a high impedance receiver, (3) a careful investigation of ways to adequately compare inversion results to ground-truth data is warranted, (4) more laboratory studies should be directed to understand the influence of micro-organisms and long residence time of contaminants (aging) on spectral IP properties

An Unusual Case of Brugada Syndrome in an 82-Year Old Black Hypertensive Man

Rationale: Brugada syndrome (BrS) is a cardiac ion channel disease that is caused by an autosomal dominant genetic abnormality. It is frequently seen among young and middle-aged adults of Asian descent and rarely in blacks. Patient Concerns: We report an extremely rare case of an 82-year-old male known hypertensive with poor drug compliance, who suffered recurrent palpitations and pre-syncope. His electrocardiogram showed an unusual right bundle branch block with coved ST segment elevation in leads V1-V3. Diagnoses: The patient was eventually diagnosed with Brugada Syndrome with background hypertensive heart disease. He could not have genetic testing due to unavailability and cost. Interventions: The patient was treated with antihypertensives but could not afford a device implant. He was counseled to avoid risk factors such as fever, extreme physical and emotional exertions etc. Outcomes: At his last clinic visit two months post diagnosis he still had similar symptoms but no syncope nor sudden cardiac arrest. Lessons: To the best of our knowledge, this is possibly the first reported case of BrS in an elderly African with hypertensive heart disease.</jats:p