HydroGEOPHYSICS Inc.

Tucson, AZ, United States

HydroGEOPHYSICS Inc.

Tucson, AZ, United States
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Rucker D.F.,HydroGEOPHYSICS Inc. | Noonan G.E.,HydroGEOPHYSICS Inc. | Greenwood W.J.,Pacific Northwest National Laboratory
Engineering Geology | Year: 2011

Dredging and widening of the Panama Canal is currently being conducted to allow larger vessels to transit to and from the Americas, Asia, and Europe. Dredging efficiency relies heavily on knowledge of the types and volumes of sediments and rocks beneath the waterway to ensure the right equipment is used for their removal. To aid this process, a waterborne streaming electrical resistivity survey was conducted along the entire length of the canal to provide information on its geology. Within the confines of the canal, a total of 663 line-kilometers of electrical resistivity data were acquired using the dipole-dipole array. The support of the survey data for dredging activities was realized by calibrating and qualitatively correlating the resistivity data with information obtained from nearby logged boreholes and geological maps. The continuity of specific strata was determined in the resistivity sections by evaluating the continuity of similar ranges of resistivity values between boreholes. It was evident that differing geological units and successions can have similar ranges of resistivity values. For example, Quaternary sandy and gravelly alluvial fill from the former river channel of the Chagres River had similar resistivity ranges (generally from 40 to 250. Ω m) to those characteristic of late Miocene basalt dikes (from 100 to 400 Ω m), but for quite different reasons. Similarly, competent marine-based sedimentary rocks of the Caimito Formation were similar in resistivity values (ranging from 0.7 to 10 Ω m) to sandstone conglomerate of the Bohio Formation. Consequently, it would be difficult to use the resistivity data alone to extrapolate more complex geotechnical parameters, such as the hardness or strength of the substrate. A necessary component for such analyses requires detailed objective information regarding the specific context from which the geotechnical parameters were derived. If these data from cored boreholes and detailed geological surveys are taken into account, however, then waterborne streaming resistivity surveying can be a powerful tool. In this case, it provided inexpensive and highly resolved quantitative information on the potential volume of loose suctionable material along the Gamboa Sub-reach, which could enable large cost savings to be made on a major engineering project involving modification of one of the most important navigable waterways in the world. © 2010 Elsevier B.V.


Rucker D.F.,HydroGEOPHYSICS Inc.
Journal of Environmental and Engineering Geophysics | Year: 2011

First arrival travel times (FATTs) from critically refracted waves in crosswell radar applications have been known to cause incorrect estimates of electromagnetic wave velocities, if these waves are assumed to be a direct arrival. This is a particular problem when the FATTs are acquired from radar antennae placed near the ground surface. One way to accommodate critically refracted waves at the air-ground interface is to remove the upper 2 m of data and assume that the remaining FATTs within the profile travel directly from transmitter to receiver. An alternative method is to use simple ray-based inverse models that accommodate critically refracted waves to back calculate the near-surface electromagnetic wave velocity. In this work, we show the validity of these ray-based models in regions where critical refractions will occur, by first generating FATTs with a finite-difference time domain (FDTD) numerical model and assuming zero-offset profiling mode of acquisition. The ray-based inverse models were shown to reproduce the original electromagnetic wave velocity of the numerical model. A second test was also run using FDTD modeling, where an infiltrating wetting front moves past a set stationary antennae and the time series of FATTs were recorded for the duration of the infiltration experiment. The critically refracted waves occurring at the edge of the moving wetting front actually benefits the calculation of the hydraulic conductivity controlling the speed of the wetting front. Additionally, the sharper the wetting front, the more accurate the prediction for hydraulic conductivity. With the work presented here and elsewhere, obtaining reasonable estimates of electromagnetic wave velocity where critical refraction is known to occur should be easily applied and defended.


Rucker D.,HydroGEOPHYSICS Inc. | Rucker D.,ARCADISU.S. Inc.
Geophysics | Year: 2010

Cokriging has been applied to estimate the distribution of moisture within a rock pile of low-grade gold ore, or heap. Along with the primary data set of gravimetric moisture content obtained from drilling, electrical resistivity was used to supplement the estimation procedure by supplying a secondary data set. The effectiveness of the cokriging method was determined by comparing the results to kriging the moisture data alone and through least-squares regression (LSR) modeling of colocated resistivity and moisture. In general, the wells from which moisture data were derived were separated by distances far greater than the horizontal correlation scale. The kriging results showed that regions generally undersampled by drilling reverted to the mean of the moisture data. The LSR technique, which provides a simpletransformation of resistivity to moisture, converted the low resis-tivity to highmoisture, and vice versa. The sparse well locations created a high degree of uncertainty in the transformed data set. Extreme resistivity values produced nonphysical moisture values, either negative for the linear model or values greater than one for the power model. The cokriging application, which considers the correlation scale and secondary data, produced the best results, as indicated through the cross validation. The mean and variance of the cokriged moisture were closer to the measured moisture, and the bias in the residuals was the lowest. The application likely could be improved through optimal well placement, whereby the resistivity results guide the drilling program through gross target characterization, and the moisture estimation could be updated iteratively. © 2010 Society of Exploration Geophysicists.


Loke M.H.,Geotomo Software | Dahlin T.,Lund University | Rucker D.F.,HydroGEOPHYSICS Inc.
Near Surface Geophysics | Year: 2014

Three-dimensional resistivity surveys and their associated inversion models are required to accurately resolve structures exhibiting very complex geology. In the same light, 3D resistivity surveys collected at multiple times are required to resolve temporally varying conditions. In this work we present 3D data sets, both synthetic and real, collected at different times. The large spatiooral data sets are then inverted simultaneously using a least-squares methodology that incorporates roughness filters in both the space and time domains. The spatial roughness filter constrains the model resistivity to vary smoothly in the x-, y- and z-directions. A temporal roughness filter is also applied that minimizes changes in the resistivity between successive temporal inversion models and the L-curve method is used to determine the optimum weights for both spatial and temporal roughness filters. We show that the use of the temporal roughness filter can accurately resolve changes in the resistivity even in the presence of noise. The L1- and L2-norm constraints for the temporal roughness filter are first examined using a synthetic model. The synthetic data test shows that the L1-norm temporal constraint produces significantly more accurate results when the resistivity changes abruptly with time. The model obtained with the L1-norm temporal constraint is also less sensitive to random noise compared with independent inversions (i.e., without any temporal constraint) and the L2-norm temporal constraint. Anomalies that are common in models using independent inversions and the L2-norm and L1-norm temporal constraints are likely to be real. In contrast, anomalies present in a model using independent inversions but that are significantly reduced with the L2-norm and L1-norm constraints are likely artefacts. For field data sets, the method successfully recovered temporal changes in the subsurface resistivity from a landfill monitoring survey due to rainwater infiltration, as well as from an experiment to map the migration of sodium cyanide solution from an injection well using surface and borehole electrodes in an area with significant topography. © 2014 European Association of Geoscientists & Engineers.


Rucker D.F.,HydroGEOPHYSICS Inc. | Fink J.B.,HydroGEOPHYSICS Inc. | Loke M.H.,Geotomo Software
Journal of Applied Geophysics | Year: 2011

Highly industrialized areas pose challenges for surface electrical resistivity characterization due to metallic infrastructure. The infrastructure is typically more conductive than the desired targets and will mask the deeper subsurface information. The risk of this occurring may be minimized if steel-cased wells are used as long electrodes in the area near the target. We demonstrate a method of using long electrodes to electrically monitor a simulated leak from an underground storage tank with both synthetic examples and a field demonstration. Although the method of using long electrodes has been proposed by others, no time-lapse resistivity data have been collected, modeled, and analyzed within a nuclear waste tank farm environment. Therefore, the main objective of this work was to test whether the long electrode method using steel-cased wells can be employed to spatially and temporally track simulated leaks in a highly industrialized setting. A secondary objective was to apply a time-lapse regularization procedure in the inverse modeling code, similar to the 4D tomography approach by Kim et al. (2009), and to test the procedure's effect on the quality of the outcome regarding plume intensity and position.For the synthetic examples, a simple target of varying electrical properties was placed beneath different types of layers of low resistivity to simulate the effects of the infrastructure. Both surface and long electrodes were tested on the synthetic domain, and the test cases covered a variety of survey parameters including low and high electrode density, noise, array type, and the explicit location of the wells relative to the target. All data were processed in four dimensions, where the regularization procedure was applied in both the time and space domains. The synthetic test case showed that the long electrode resistivity method could detect relative changes in resistivity that was commensurate with the differing target properties. The surface electrodes, on the other hand, had a more difficult time matching the original target's footprint unless the electrodes were distributed at a greater density on the surface. The simulated tank leak in the field experiment was conducted by injecting a high conductivity fluid in a perforated well within the S tank farm at the Hanford Site, and the resistivity measurements were made before and after the leak test. The field results showed a lowered resistivity feature develops south of the injection site after cessation of the injections. The parameter used in the time-lapsed inversion had a strong influence on the differences in inverted resistivity between the pre- and post-injection datasets, but the interpretation of the target was consistent across all values of the parameter. The long electrode electrical resistivity monitoring (ERM) method may provide a tool for near real-time monitoring of leaking underground storage tanks given a sufficient density of wells. © 2011 Elsevier B.V.


Rucker D.F.,HydroGEOPHYSICS Inc.
Geophysical Journal International | Year: 2012

The resolution of the long electrode electrical resistivity tomography method is investigated through the comparison of arrays. The investigations included a synthetic model study and a pilot-scale field experiment, in which data from the 2-pole and 4-pole arrays were used to reconstruct known targets through inverse modelling. The results confirmed that the 2-pole array maps conductive targets with low lateral resolution and no vertical resolution. The 4-pole array performs extremely well or extremely poorly depending on the specific subset of data used in the inversion modelling. The worst performance was observed from using a randomized 4-pole subset. In this case, the reconstructed target was offset from the known location. The best performance came from evaluating the comprehensive data set comprising all possible 4-pole combinations and choosing favourable subsets that minimized outliers in transfer resistance, geometric factor, data error and apparent resistivity. These favourable 4-pole subsets were capable of resolving both conductive and resistive targets with higher fidelity than the 2-pole array. Unfortunately, it may not be possible to acquire the comprehensive 4-pole data set, especially for a large number of electrodes. A viable alternative is to acquire the comprehensive 2-pole data set and calculate any desired 4-pole subset using superposition. In this way, the geophysicist will also have full advantage of signal strength and shorter measurement cycle that accompanies the 2-pole array. © 2012 The Author Geophysical Journal International © 2012 RAS.


Rucker D.F.,HydroGEOPHYSICS Inc.
Advances in Water Resources | Year: 2011

Modeling unsaturated flow in porous media requires constitutive relations that describe the soil water retention and soil hydraulic conductivity as a function of either potential or water content. Often, the hydraulic parameters that describe these relations are directly measured on small soil cores, and many cores are needed to upscale to the entire heterogeneous flow field. An alternative to the forward upscaling method using small samples are inverse upscaling methods that incorporate soft data from geophysical measurements observed directly on the larger flow field. In this paper, we demonstrate that the hydraulic parameters can be obtained from cross borehole ground penetrating radar by measuring the first arrival travel time of electromagnetic waves (represented by raypaths) from stationary antennae during a constant flux infiltration experiment. The formulation and coupling of the hydrological and geophysical models rely on a constant velocity wetting front that causes critical refraction at the edge of the front as it passes by the antennae. During this critical refraction period, the slope of the first arrival data can be used to calculate (1) the wetting velocity and (2) the hydraulic conductivity of the wet (or saturated) soil. If the soil is undersaturated during infiltration, then an estimate of the saturated water content is needed before calculating the saturated hydraulic conductivity. The hydraulic conductivity value is then used in a nonlinear global optimization scheme to estimate the remaining two parameters of a Broadbridge and White soil. © 2010 Elsevier Ltd.


Rucker D.F.,HydroGEOPHYSICS Inc.
Hydrometallurgy | Year: 2015

A subsurface irrigation test, using a series of four rinse wells, was conducted on a copper oxide heap leach pad over a three week period. The pad has been significantly underperforming due to difficult drainage conditions imposed by a high degree of fine-grained material. The test was to determine whether it would be feasible to conduct the directed leaching method across the entire pad assuming that enough copper is liberated to pay for the upscaled well field installation. The rinse wells were connected directly to an existing raffinate line. Validation of the test included 1) hydraulic monitoring to ensure sufficient solution flow and coverage in the formation and 2) metallurgical monitoring of solution samples extracted from nearby monitoring wells to ensure copper liberation. The results showed that the mean flow rates to each rinse well exceeded expectations by a factor of at least 1.5 for an extended period of time, that radial solution coverage for optimal operating conditions was approximately 17 m, and copper grade was upwards of three times the anticipated grade. The test was then extended for an additional two months on a single well, where the copper grade remained approximately two times higher than that from surface irrigation. By the end of the testing, it was calculated that at least 191,000 kg of copper was liberated. The upscaled program is to include 170 additional wells spaced 31 m apart and the potential for 12 wells to be rinsed simultaneously, which would allow the program to be completed in less than three years. © 2015 Elsevier B.V. All rights reserved.


Trademark
HydroGEOPHYSICS Inc. | Date: 2016-11-07

Downloadable mobile applications for recording and correlating photographs, texts, data and geographic locations that allow sharing on social media. Software as a service (SAAS), namely, data management for recording and correlating photographs, texts, data and geographic locations, storing the information on designated servers and sharing on social media.


Trademark
HydroGEOPHYSICS Inc. | Date: 2016-11-07

Downloadable mobile applications for recording and correlating photographs, texts, data and geographic locations that allow sharing on social media. Software as a service (SAAS), namely, data management for recording and correlating photographs, texts, data and geographic locations, storing the information on designated servers and sharing on social media.

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