The dataset contains borehole-GPR (ground penetrating radar) data from a shallow quaternary glacial aquifer at the test site "TestUM" in Wittstock/Dosse (Germany). At the test site a geological latent heat storage concept was tested while freezing and thawing a subsurface volume in a controlled manner. Therefore, 16 heat exchanger probes, 18 m deep each, are installed in a 1 m x 1 m-grid. 22 2-inch wells and eight multilevel wells are installed to provide direct access to the aquifer for groundwater sampling and borehole measurements. The borehole deviation of the 2-inch monitoring wells was measured using a deviation probe (DevProbe1, Geotomographie, Neuwied, Germany). Readings of tilt and direction were taken for every borehole, allowing calculation of the well path in the subsurface.
Reflection and crosshole borehole GPR measurements were performed before and during two freezing cycles. The data were collected from November 2022 to December 2023. The borehole GPR measurements were performed in the 2-inch monitoring wells. To record the data, we used a GSSI SIR 4000 (GSSI Geophysical Survey Systems, Inc., Nashua, USA) and one (reflection measurements) or two (crosshole measurements) Tubewave-100 antennas (Radarteam Sweden AB, Boden, Sweden). For reflection measurements, an antenna was used that served as both transmitter and receiver. It was lowered into a borehole, and measurements were taken every 0.25 meters starting at a maximum of 16.75 m up to 0.25 m depth. The crosshole measurements were realized as zero offset profiles with two antennas. One served as a transmitter and one as a receiver. They were placed in two boreholes and lowered simultaneously, with measurements taken every 0.25 m at the same depth starting at a maximum of 16.75 m up to 0.25 m depth.
The naming of the 2-inch wells was adjusted according to the groundwater flow direction from northeast to southwest. Wells located upstream of the freezing area start with the letter U, central wells with the letter C, and downstream wells with the letter D. For the reflection measurements, four boreholes were measured upstream (U03, U04, U05, U06), two in the center (C04, C05), and five downstream (D02, D04, D05, D06, D08). For crosshole, various measurements were chosen to characterize the subsurface before freezing, including combinations of upstream-downstream, upstream-center, center-center, and center-downstream. During the freezing phase, the crosshole measurements were conducted using combinations of upstream-upstream, upstream-downstream, center-center, and downstream-downstream.
The data set consists of eight crosshole seismic data sets obtained with a sparker source and two hydrophone string receivers in a near surface aquifer at the TestUM site in Wittstock/Dosse (Germany). The data has been collected before and after a methane gas injection experiment from April 2019 to May 2020. Therefore the data set comprises one baseline and seven monitoring measurements. Data collection was performed using a seismic sparker (borehole source SBS42, Geotomographie, Neuwied, Germany) as a source located in a 2” borehole operating at a depth between 8-13 m. The generator operated at frequency of 5 kHz. The hydrophone strings (Geotomographie, Neuwied, Germany) were placed each in a 2” borehole at a depth between 8-13 m covering a hydraulically low permeable layer between 9-11 m depth and part of the sandy aquifer down to 13 m depth. The data set is supplemented with additional information about the in situ hydraulic and electrical properties at three locations in the vicinity of the test site. These data were collected by using Hydraulic Profiling Tool (Geoprobe, Geoprobe Systems, Salina, KS, USA) obtaining the relative hydraulic conductivity. The in situ electrical properties where obtained depth-oriented with the Wenner-array with an EC probe (SC-500, Geoprobe Systems, Salina, KS, USA).