The impact of water-filled boreholes on GPR data in a clayey-till environment

Jensen, Bolette Badsberg; Rosenberg, L. T.; Nielsen, Lars; Tuxen, Nina; Tsitonaki, Katerina; Hansen, Thomas Mejer; Looms, Majken C.

doi:10.1190/gpr2022-061.1

Cited by 1 publication

(2 citation statements)

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“…The boreholes were drilled as a part of the contaminated site investigation in 2019 and were equipped with plastic (PEH) casing tubes with an inner diameter of d = 0.051 m. The distance between B302 and B303 was 3.81 m. Since the casing tubes were screened at 13.0 m below ground, a specially designed packer system was installed in the boreholes to remove water from the casing tube before the GPR investigations. This was necessary, to prevent water from affecting the propagating EM wave, as investigated in Jensen et al (2022b).…”

Section: Methodsmentioning

confidence: 99%

“…The presence of water in the screened wells enforced the need for installing a packer system before conducting the GPR measurements. Dry boreholes are important for obtaining high-resolution tomograms in the saturated zone in clay till settings as the water downshifts the frequency content of the traveling EM wave and therefore reduces the possible resolution (Jensen et al 2022b). The boreholes were pumped dry using a packer system that was made especially for this field campaign using off-the-shelf products and deployment was a bit tedious and time consuming.…”

Section: Water In Wellsmentioning

confidence: 99%

See 1 more Smart Citation

High‐Resolution Geological Information from Crosshole Ground Penetrating Radar in Clayey Tills

Jensen¹,

Rosenberg²,

Tsitonaki³

et al. 2023

Groundwater Monitoring Rem

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Heterogeneous glacial deposits dominate large parts of the Northern Hemisphere. In these landscapes, high‐resolution characterization of the geology is crucial for understanding contaminant transport. Geological information is mostly obtained from multiple boreholes drilled during a site investigation, but such point‐based data alone do not always provide the required resolution to map small‐scale heterogeneity between boreholes. Crosshole ground penetrating radar (GPR) is suggested as a tool for adding credible geological information between boreholes at contaminated site investigations in industrial sites where infrastructure, such as electrical installations, can pose a challenge to other geophysical methods. GPR data are sensitive to the dielectric permittivity and the bulk electrical conductivity, which can be related to the distribution of water content and sand/clay occurrences. Here we present a detailed crosshole GPR dataset collected at an industrial contaminated site in a clay till setting. The data are processed using a novel inversion approach where information on changes in the velocity and attenuation of the radar signal are obtained independently. The GPR results are compared to borehole logs, grain size analyses, and relative permeability data from the site. The GPR data analysis provided valuable information on the understanding of the lateral geological variability. A silt layer with a thickness of a few decimeters, likely important for flow characterization, was confirmed and resolved by GPR data. Our findings suggest that crosshole GPR has the potential for contributing with high‐resolution geological information by filling the data gap between boreholes, thereby becoming a relevant tool in contaminated site investigations.

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Section: Methodsmentioning

confidence: 99%

Section: Water In Wellsmentioning

confidence: 99%