Resistivity Imaging Identifies Potential Contaminant Transport Pathway

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Resistivity Imaging maps potential subsurface transport pathway in south-central Oklahoma

Lithochimeia was retained to investigate complaints of strong hydrocarbon odors from a spring on in south-central Oklahoma.  

Initial sampling indicated the presence of hydrocarbons in waters flowing from the spring after larger rainfall events.   Pipelines transporting hydrocarbons traversed the property up-gradient from the spring that exhibited hydrocarbon odors.  Lithochimeia conducted a Resistivity Survey to examine the region between the pipelines and the spring for evidence of a pathway existed between the pipelines and the spring.  The Resistivity Survey involved obtaining data from forty north-south transects between the pipelines and the spring.

Electrical current was injected into the subsurface via the electrodes of the array and the resulting electrical activity at the surface was measured and interpreted to produce images representing the electrical properties of the subsurface.

The image resulting form the survey revealed potential subsurface transport pathways between the pipelines and the spring.  The karst geology of the area and diagonally oriented faults were visible as highly resistive cavernous porosity as well as clay and silt filled porosity in the subsurface. 

This 2-D rendering was mapped in 3-D to better visualize the subsurface geometry of the potential transport pathway.

Monitoring wells were installed to both confirm the results of the resistivity survey and to provide access to groundwater for sampling.

Groundwater sampling revealed hydrocarbon signatures similar to those found at the spring.

Widespread Salt Contamination Mapped on 15,000 Acre Ranch

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Lithochimeia was retained to investigate current and historic saltwater releases on a large ranch in northeast OK . 

Review of air photos showed numerous areas potentially impacted by salt contamination on the ranch.

Lithochimeia conducted frequency domain electromagnetic (EM) Terrain Conductivity Surveys using a Geonics EM-31-MK2 ground conductivity meter over areas potentially contaminated by saltwater in areas surrounding tank batteries, pumping units, flowline routes, and areas of visible surface damage.  EM Surveys use the principle of electromagnetic induction to measure the conductivity of the subsurface based on soil electrical properties and chemistry of pore fluids.  EM Surveys do not require ground contact and therefore allow rapid data acquisition.   Data can be processed and viewed in near real time.

In all, over 2 million square meters (540 acres) of surface area was surveyed using the EM-31-MK2 ground conductivity meter.  This was accomplished in in less than four weeks because of the ability to rapidly acquire data this geophysical method provides.

Results of the Terrain Conductivity Survey indicated probable widespread contamination of large portions of the ranch by high salinity produced water. The results of the Terrain Conductivity Survey were then confirmed by soil and water sampling and laboratory analysis.

Characterization of contamination this widespread through air-photo analysis, on-ground visual inspection and direct sampling alone would require collecting hundreds of samples and would be very expensive. When applicable, modern geophysical methods provide cost-effective and time-efficient solutions for projects requiring both large amounts of information while maintaining high data density.

Geophysical Investigation Uncovers Hidden Contamination

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Lithochimeia was retained to investigate high salinity liquids that had pooled on the surface of a private landowner’s property in Hughes County, Oklahoma.  Lithochimeia was tasked to characterize the extent of contamination and identify the potential source.

Client interviews revealed that a large diameter plastic pipe had been recently installed to transport frac water and flowback water. Over a portion of the property, this line was located adjacent to a steel line carrying natural gas.

A Terrain Conductivity Survey was planned and executed using Geonics EM-31-MK2 over the impacted area as well as the surrounding surface.  Electromagnetic (EM) Surveys use the principle of electromagnetic induction to measure the conductivity of the subsurface based on soil properties and chemistry of pore fluids.  EM Surveys do not require ground contact and therefore allow rapid data acquisition.   Data can be processed and viewed in near real time.

The data obtained was processed in the field, and the resulting contoured map of terrain conductivity showed that the EM Survey clearly imaged the location of the steel gas line and the area of elevated conductivity associated with the pooled saltwater.

the resulting contoured map of terrain conductivity also showed an detached and unexplained area of high conductivity to the west of the original focus of the survey.  As the result , the the survey area expanded to determine the extent and nature of the d unexplained area of high conductivity observed in the original survey.

The expanded EM-31 Survey produced a contoured terrain conductivity map that displayed a large plume of conductive material in the subsurface apparently emanating from the vicinity of the pipeline northwest of the original survey focus.  The data suggested a breach of the plastic line that had been undetected until the EM-31 Survey was conducted and processed. 

Relying exclusively on soil sampling and visual observation would not have been able to detect this subsurface plume of conductive fluids.  The high data density and efficiency of the EM-31 Terrain Conductivity Survey allowed for a larger area to be rapidly characterized.  Early detection of salt contamination will reduce injury to soil and ground water and reduce remedial costs for the responsible party.