Delineation of hydrocarbon contaminants with multi-frequency complex conductivity imaging

The characterization of contaminated sites is a serious issue that requires a number of techniques to be deployed in the field to reconstruct the geometry, hydraulic properties and state of contamination of the shallow subsurface, often at the hundreds of meter scale with metric resolution. Among the techniques that have been proposed to complement direct investigations (composed of drilling, sampling, and laboratory characterization) are geophysical methods, which can provide extensive spatial coverage both laterally and at depth with the required resolution. However, geophysical methods only measure physical properties that are indirectly related to contamination, and their correlation may be difficult to ascertain without direct ground truth. In this study, we present a successful example where the results of complex conductivity measurements conducted in an imaging framework are compared with direct evidence of subsoil contamination at a jet fuel impacted site. Thus, proving that a combination of direct and indirect investigations can be successfully used to image a site in its complex (potentially 3D) structure in order to build a reliable conceptual model of the site

Evaluation and Evolution of a Groundwater Contaminant Plume at the Former Shelby County Landfill, Memphis, Tennessee

The unlined former Shelby County Landfill in Memphis, Tennessee, lies in the flood plain of the Wolf River and is known to be the source of low-level contamination in the underlying alluvial (shallow) and Memphis aquifers. Prior to closure, discovery of a hydrogeologic window in the upper Claiborne confining unit overlying the Memphis aquifer 0.2 km north of the landfill led to several groundwater investigations by the U.S. Geological Survey to evaluate the threat posed to the Memphis aquifer, the regional source for municipal water supplies. As the landfill nears its 30th year of post-closure monitoring, this study examines the evolution of groundwater quality to determine if conditions have improved or degraded with time as well as determine the usefulness of surface resistivity and induced polarization (IP) to identify preferential pathways of migration in subsurface sediments of the Gulf Coastal Plain. A 2011 comprehensive groundwater sampling event re-established the extent of impacted groundwater which were compared to historical groundwater quality data and used to plan a subsequent resistivity survey in 2012. Leachate impacted groundwater had not diminished along the northern landfill boundary in the shallow aquifer and continues to enter the Memphis aquifer immediately north of the landfill further degrading water quality at depth. The current post-closure sampling regime at the former Shelby County Landfill is inadequate to properly address the water quality problems at the landfill and should be reassessed. Resistivity and IP demonstrated the ability to identify impacted versus non-impacted groundwater, as well as the water-table boundary, landfill waste cells, sewer lines, and clay-rich sediments. Future research should continue to focus on areas north of the landfill to determine the contact relationship between the shallow and Memphis aquifers and further downgradient in the Memphis aquifer to determine the true extent of contamination from the former Shelby County Landfill

Geophysical modeling for groundwater and soil contamination risk assessment

This PhD thesis is focused on the study of environmental problems linked to contaminant detection and transport in soil and groundwater. The research has two main objectives: development, testing and application of geophysical data inversion methods for identifying and characterizing possible anomaly sources of contamination and development and application of numerical models for simulating contaminant propagation in saturated and unsaturated conditions. Initially, three different approaches for self-potential (SP) data inversion, based on spectral, tomographical and global optimization methods, respectively, are proposed to characterize the SP anomalous sources and to study their time evolution. The developed approaches are first tested on synthetic SP data generated by simple polarized structures, (like sphere, vertical cylinder, horizontal cylinder and inclined sheet) and, then, applied to SP field data taken from literature. In particular, the comparison of the results with those coming from other numerical approaches strengthens their usefulness. As it concerns the modelling of groundwater flow and contaminant transport, two cellular automata (CA) models have been developed to simulate diffusion-dispersion processes in unsaturated and saturated conditions, respectively, and to delineate the most dangerous scenarios in terms of maximum distances travelled by the contaminant. The developed CA models have been applied to two study areas affected by a different phenomenon of contamination. The first area is located in the western basin of the Crete island (Greece), which is affected by organic contaminant due to olive oil mills wastes (OOMWs). The numerical simulations provided by the CA model predict contaminant infiltration in the saturated zone and such results are in very good agreement with the high phenol concentrations provided by geochemical analyses on soil samples collected in the survey area at different depths and times. The second case study refers to an area located in the western basin of Solofrana river valley (southern Italy), which is often affected by heavy flooding and contamination from agricultural and industrial activities in the surroundings. The application of a multidisciplinary approach, which integrates geophysical data with hydrogeological and geochemical studies, and the development of a CA model for contaminant propagation in saturated conditions, have permitted to identify a possible phenomenon of contamination and the delineation of the most dangerous scenarios in terms of infiltration rates are currently in progress

The application of resistivity and IP-measurements as investigation tools at contaminated sites : a case study from Kv. Renen 13, Varberg, SW Sweden

An old industry estate, Kv. Renen 13, is located in central Varberg, southwest Sweden, and is known from previous investigations as highly polluted. Pollution started in the late 19th century with textile manufacturing, and in the 1960´s changed into a precision mechanics industry using chlorinated solvents, primary trichloroethene (TCE) and 1,1,1-trichloroethane (TCA), as well as cyanide and metals. Wastewater was taken out through an es-cape valve to a sedimentation basin, which most likely leaked. With good subsurface conditions for dispersal, both in the sediments and in the highly fractured bedrock, a large area of the subsurface is polluted from contaminants due to the situation at Kv. Renen 13. This thesis investigates the subsurface conditions by using resistivity and induced polarization measurements, geo-physical methods based on different materials’ physical responses to an electrical current. Resistivity (Ωm) is a physical property of the ability to isolate against electrical current. Induced polarization (IP) measures the chargea-bility of a material, i.e. how electrical charges polarize and depolarize when subjected to an electrical current that is turned off after an interval of time. The aim with these geophysical surveys was to create a 3D model of the subsur-face ground conditions. The measurements were made at three occasions, to be able to investigate if it is possible to measure variation through time, and use the method for monitoring of in situ remediation. As a result of the survey, a fracture zone with a southwest-northeast direction crossing the industrial estate, could be identified. This fracture zone was not identified at the estate before and within the zone, there is a possibility of spreading the contamination. Variations in underground conditions through time in the subsurface were measurable using the geophysical methods, and the method shows good potential to be used for in situ monitoring of pollutant remediation. The work is part of the research project TRansparent Underground STructore, TRUST.Kv. Renen 13 i centrala Varberg är sedan tidigare känt som kraftigt förorenat. På fastigheten har det från slutet av 1800-talet fram till 2003 funnits verksamheter i form av textilindustri som avlösts av finmekanisk verkstadsindustri. Det är framförallt den sistnämnda verksamheten som har orsakat rådande situation med höga halter klorerade lösningsmedel, trikloreten (TCE) och 1,1,1-trikoletan (TCA), som i verksamheten använts som fettlösande medel. Dessutom har det använts en del metaller och cyanid. Processvatten har letts ut via ett internt avloppsystem till en sedimentationsbassäng i trädgården och indikationer finns på att bassängen har läckt. Stora delar av centrala Varberg är förorenat med klorerade lösningsmedel och metaller p.g.a. de tidigare verksamheterna på Kv. Renen 13. Detta till följd av att spridningsförutsättningarna är goda, både i de lösa avlagringar och i den sprickrika berggrunden. I det här examensarbetet har markförhållandena undersökts med geofysikiska mätningar i form av resistivitetsegen-skaper och inducerad polarisation. Resistivitet är en materialegenskap som mäter ett materials resistans mot en elektrisk ström. Inducerad polarisation (IP) undersöker markens uppladdningsförmåga. Geofysik kan vara svårt att använda i urbana miljöer då det finns mycket som stör och ger upphov till brus i mätdata. Målet med undersökning-en har varit att skapa en 3D- modell av markförhållandena. Mätningarna har gjorts vid flera tillfällen för att under-söka möjligheten att se förändringar med tiden och på sikt använda metoden för övervakning av in situ-saneringar. Som kalibrering för de geofysikska mätdata, har grundvattnet provtagits och analyserats. Resultatet av undersökningarna visar en trolig sydvästlig-nordostlig sprickzon som korsar fastigheten och ger goda spridningsförutsättningarna av föroreningen. Förändringar med tiden var mätbara i marken och metoden visar god potential för att användas för övervakning av förändringar. Arbetet ingår i forskningsprojektet TRansparent Underground STructore, TRUST

Detection of Cover Collapse Doline and Other Epikarst Features by Multiple Geophysical Techniques, Case Study of Tarimba Cave, Brazil

Reliable characterization of the karst system is essential for risk assessment where many associated hazards (e.g., cover-collapse dolines and groundwater pollution) can affect natural and built environments, threatening public safety. The use of multiple geophysical approaches may offer an improved way to investigate such cover-collapse sinkholes and aid in geohazard risk assessments. In this paper, covered karst, which has two types of shallow caves (vadose and fluvial) located in Tarimba (Goias, Brazil), was investigated using various geophysical methods to evaluate their efficiency in the delineation of the geometry of sediments filled sinkhole. The methods used for the investigation were Electrical Resistivity Tomography (ERT), Seismic Refraction Survey (SRS), Seismic Refraction Tomography (SRT) and the Very Low-Frequency Electromagnetic (VLF-EM) method. The study developed several (2D) sections of the measured physical properties, including P-wave velocity and electrical resistivity, as well as the induced current (because of local bodies). For the analysis and processing of the data obtained from these methods, the following approaches were adopted: ERT inversion using a least-square scheme, Karous-Hjelt filter for VLF-EM data and time-distance curves and Vp cross-sections for the SRS. The refraction data analysis showed three-layered stratigraphy topsoil, claystone and carbonate bedrock, respectively. The findings obtained from ERT (three-layered stratigraphy and sediment-filled doline), as well as VLF-EM (fractured or filled caves as a positive anomaly), were found to be consistent with the actual field conditions. However, the SRS and SRT methods did not show the collapsed material and reached the limited depth because of shorter profile lengths. The study provides a reasonable basis for the development of an integrated geophysical approach for site characterization of karst systems, particularly the perched tank and collapse doline.This research was funded by TCCE 01/2018—Vale/ICMbio, PROCESS Nº: 02667.000110/2017-10 “Susceptibilidade, Hidrologia e Geomorfologia Cárstica Aplicadas à Conservação do Patrimônio Espeleológico da Área de Proteção Ambiental das Nascentes do Rio Vermelho.” DOU N.99 SEÇÃO 3 de 24/05/2018

The detection of Forensic and Archaeological burials using geophysics and soil analysis

Graveyards and cemeteries around the world are increasingly being designated as full. There is growing requirements to identify burial space or to exhume and re-inter if necessary. Near-surface geophysical methods offer a potentially non-invasive target detection solution, with additional soil sampling analysis to provide ground truth information; however there has been lack of research to identify optimal detection methods. This study has collected multi-frequency (225 MHz – 900 MHz) ground penetrating radar, electrical resistivity, electromagnetic induction and magnetic susceptibility surface data over different burial scenarios (ancient, old and modern burials). Surveying ancient burial sites revealed they can be geophysically detectable even after 650+ years of burial, given optimum local soil type and depositional environment conditions. Surveying old and modern burials indicate that progressively older burials are more difficult to detect but complicated by local soil type. Different geophysical techniques were optimal in different sites, which therefore suggests a multi-technique approach should be utilised by survey practitioners. Graveyard geophysical targets included the grave soil above graves themselves, the grave contents, brick-lining (if present) and grave soil water that can be all detectable from background levels. Grave markers were also identified not to always be located where burials were positioned. Buried cadaver decomposition releases elements into the surrounding soil, which can significantly change the local site geochemistry. Resulting elevated element levels, associated with cadaver decomposition, can assist in identifying burial location(s), when compared to background levels and temporally vary. These included inorganic elements, pH and conductivity. Potassium, sulphate, sodium and phosphate were also identified as potential grave markers, which also showed strong correlation coefficients with grave soilwater conductivity values. Background elemental concentrations were consistently low and were controlled by rainfall

From microstructure to subsurface characterization. Spectral information from field scale time domain induced polarization.

A large variety of subsurface infrastructure projects of different types can gain valuable information from tomographic measurements of subsurface physical properties. With resistivity and time domain spectral induced polarization (IP), the distributions of the conductive and capacitive properties of the subsurface are obtained. Technical developments of time domain IP equipment and new inversion algorithms have led to the possibility of collecting large amounts of data and invert for spectral IP parameters. In this way, much more information about the subsurface can be extracted from a single measurement compared to what was possible previously. It is well-known that spectral IP effects arise through redistribution of ions at the pore scale, and that spectral IP parameters can be linked to microscale surface chemical and structural properties. However, much remains to be known about how to analyse and interpret spectral IP parameters from field scale time domain IP measurements. Therefore, the main objective of this licentiate thesis is to focus on these issues. In soils contaminated with free phase non-aqueous phase liquids (NAPLs), the contaminant phase affects the microgeometry inside the pore spaces of the soil. The results from paper I show that different configurations of the NAPL phase likely affect the spectral IP response of the soil in different ways. This is exemplified by measurements at a field site, where IP responses are absent in the NAPL source zone. In contrast, elevated IP responses are observed in the degradation zone, where the NAPL probably is configured as isolated droplets in the pore space. In order to investigate probable sources to observed varying IP responses in a Cretaceous limestone bedrock, the measured spectral IP parameters were compared with the investigations of the microstructure and composition of thin sections in paper II. Several characteristics that can affect the measurements were found, such as presence of certain minerals and varying texture of the limestone. However, more research is needed in order to understand the polarization mechanisms in limestones. Although most previous research has been carried out in sand- and claystones, there is a great potential to reveal textural and structural properties in any kind of bedrock by measurements of spectral IP parameters

The potential use of geophysical methods to identify cavities, sinkholes and pathways for water infiltration

The use of geophysical characterization of karst systems can provide an economical and non-invasive alternative for extracting information about cavities, sinkholes, pathways for water infiltration as well as the degree of karstification of underlying carbonate rocks. In the present study, three geophysical techniques, namely, Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Very Low Frequency Electromagnetic (VLFEM) methods were applied at three different locations in relation to fluvial karst, which is listed as an environmentally sensitive area in Rio Vermelho, Mambaí, Goiás, Brazil. In the data acquisition phase, the GPR, direct-current (DC) resistivity and VLFEM profiles were obtained at the three locations in the area. Data were analyzed using commonly adopted processing workflows. The GPR results showed a well-defined lithology of the site based on the amplitude of the signal and radar typologies. On the other hand, the inverted resistivity cross-sections showed a three-layered stratigraphy, pathways of water infiltration and the weathered structures in carbonate (Bambui group). The interpretation of VLFEM as contours of current density resulted from Fraser and Karous–Hjelt filters, indicated the presence of conductive structures (high apparent current density) that might be linked to the weathered carbonate and other conductive and resistive anomalies associated with the water-filled and dry cavities (cave), respectively. The results encourage the integrated application of geophysical techniques such as the reconnaissance for further detailed characterization of the karst areas.This research was funded by TCCE 01/2018—Vale/ICMbio, PROCESS Nº: 02667.000110/2017-10 “Susceptibilidade, Hidrologia e Geomorfologia Cárstica Aplicadas à Conservação do Patrimônio Espeleológico da Área de Proteção Ambiental das Nascentes do Rio Vermelho.” DOU N.99 SEÇÃO 3 de 24/05/2018