Introduction
Author(s) | Tracer(s) | Injection | Methodology | Measuring method |
---|---|---|---|---|
Drost et al. 1968 | Radioisotopes (NH482Br, 198Au, Na131I) | Point | Apparatus with two packers, mixing spiral, and injection syringe | Collimated scintillation-counter |
Grisak et al. 1977 | NaF | Point | Borehole dilution apparatus with two packers and mixing pump, tracer injection with peristaltic pump | Ion-selective electrode |
Hall 1993 | LiBr | Uniform | Hosepipe lowered into the borehole, filled with tracer solution, and then pulled out | 12 ion-selective electrodes in different depths |
Riemann et al. 2002 | NaCl | Point | Circulating tracer with a pump in 2 m section, withdrawal 5 h after injection | Electrical conductivity sensor |
Lamontagne et al. 2002 | KCl, KBr | Point | Recirculation of the water in a sealed 0.5 m section with a peristaltic pump, injection with an in-line tracer reservoir | In-line electrical conductivity cell |
Williams et al. 2006 | NaCl | Uniform | Hosepipe lowered into the borehole, filled with salt solution and then removed | Electrical conductivity sensor |
Bernstein et al. 2007 | 2,6-Difluorobenzoic acid | Point | Injection with peristaltic pump, mixing in injection well, forced gradient by pumping in a well 3 m away | Not specified by author |
West and Odling 2007 | NaCl | Uniform | Hosepipe lowered into the borehole, filled with salt solution and then removed, conducted near a pumped well | Electrical conductivity meter |
Pitrak et al. 2007 | Brilliant Blue FCF, NaCl | Uniform, Point | Plastic hose with syringes for point injection | Photometric sensor |
Brouyère et al. 2008 | Iodide, Lithium, Bromide, Uranine, Sulforhodamine B | Uniform | Circulation in the well with immersed pump, tracer injection with peristaltic pump | Samples taken before reinjection |
Gouze et al. 2008 | Low salinity water, Uranine | Point | Withdrawal (push-pull) tests in a segment between two packers | Electrical conductivity sensor, optical sensor |
Shafer et al. 2010 | NaCl | Uniform | NaCl-solution injected with funnel and circulated with pump for 30 min (extraction near the bottom, reinjection on top) | EC profiles with electrical conductivity sensor |
Maurice et al. 2011 | NaCl | Uniform, Point | Hosepipe lowered into the borehole, filled with salt solution and then removed; point injection container filled with salt and opened by a weight dropped down the line | Electrical conductivity sensor |
Leaf et al. 2012 | Heated water | Point | Water is extracted in the cased part of the well, heated and reinjected in one or more depths | Fiber optic distributed temperature sensing |
Banks et al. 2014 | Heated water, NaCl | Uniform | Heated water: Electrical heating cables increase the temperature throughout the saturated zone NaCl: Starting at the bottom, tracer solution is pumped into the well through a hosepipe which is pulled upwards at a constant rate | Fiber optic distributed temperature sensing, multi parameter probe |
Libby and Robbins 2014 | Rhodamine WT | Uniform | Tracer pumped through hosepipe, starting at the bottom, then the pipe is pulled out, extraction at the top to maintain the static well head, afterwards mixing tool with propeller blades, combined with slug test | Optical probe attached to multiparameter probe |
Jamin et al. 2015 | Uranine | Point | Circulation between double packer system, injection with an in-line tracer reservoir | Field fluorimeter |
Read et al. 2015 | Heated Water | Point | Discrete volume of water heated with point heater, combined with different extraction rates near the top | Fiber optic distributed temperature sensing |
Poulsen et al. 2019b | NaCl | Point | Continuous point injection near one end of the well combined with extraction at the other end | Multi parameter probe |
Yang et al. 2019 | KCl, Rhodamin WT | Point | Isolation of a section with two packers, injection and recirculation between the packers with pumps | Electrical conductivity sensor, field fluorimeter |
Materials and methods
Study site
GMW-No. | Water level below surface (saturated length) [m] | Date | Injection method | Injection Depth [m] | Number of EC profiles | Duration [h] | Half-time [h] | Max. (mean) apparent filtration velocity) [m/h] | Vertical flow |
---|---|---|---|---|---|---|---|---|---|
7733 | 26.11 (13.89) | 05.09.16 | PIB | – | 9 | 22.5 | 0.78 | 0.21 (0.09) | No |
26.49 (13.51) | 07.04.17 | PIB | – | 16 | 23.0 | 0.63 | 0.24 (0.10) | No | |
26.21 (13.79) | 14.08.18 | PIB | – | 27 | 22.1 | 0.83 | 0.23 (0.09) | No | |
26.58 (13.42) | 08.07.19 | PIB | – | 19 | 22.9 | 0.70 | 0.23 (0.10) | No | |
26.59 (13.41) | 09.07.19 | PIB | – | 18 | 12.1 | 0.65 | 0.24 (0.10) | No | |
7721 | 22.9 (51.1) | 06.09.16 | PIB | – | 7 | 22.4 | 2.73 | n.d. | Yes |
25.4 (48.6) | 12.04.17 | PIB | – | 13 | 22.4 | 0.48 | n.d. | Yes | |
25.8 (48.2) | 17.10.18 | PIB | – | 20 | 21.1 | 1.12 | n.d. | Yes | |
26.01 (47.99) | 10.07.19 | PIB | – | 15 | 23.6 | 1.32 | n.d. | Yes | |
26.01 (47.99) | 11.07.19 | PIB | – | 12 | 9.1 | 1.50 | n.d. | Yes | |
7313 | 59.40 (14.35) | 07.09.16 | PIB | – | 10 | 1,039.1 | 8 | 0.05 (0.01) | No |
65.27 (8.48) | 12.07.17 | PIB | – | 27 | 820.5 | 111 | 0.04 (−) | No | |
7939 | 8.40 (20.60) | 14.08.18 | PIB | – | 16 | 379 | 44 | 0.01 (−) | No |
5303 | 7.68 (8.32) | 21.08.19 | PIB | – | 16 | 3.6 | 0.17 | n.d. | Yes |
7.78 (8.22) | 29.08.18 | HP | – | 11 | 1.4 | 0.23 | n.d. | Yes | |
5304 | 6.58 (6.42) | 31.07.17 | PIB | – | 15 | 4.2 | 0.48 | n.d. | Yes |
6.68 (6.32) | 16.08.17 | HP | – | 14 | 7.1 | 0.35 | n.d. | Yes | |
6.95 (6.05) | 15.08.18 | PIB | – | 24 | 6.1 | 1.40 | n.d. | Yes | |
5312 | 7.24 (8.51) | 19.07.17 | HP | – | 12 | 2.4 | 0.43 | n.d. | Yes |
7.24 (8.51) | 20.07.17 | PIB | – | 12 | 3.2 | 0.92 | n.d. | Yes | |
7.40 (8.35) | 02.08.18 | PIB | – | 18 | 2.9 | 0.55 | n.d. | Yes | |
7.53 (8.22) | 24.08.18 | PIB | – | 16 | 2.9 | 0.65 | n.d. | Yes |
Injection methods
Hosepipe method
Permeable injection bag method
Filtration velocity
Results and discussion
Permeable injection bag SBDTs
Reproducibility
Comparison of injection methods
Performance criterion | Hosepipe method | Permeable injection bag method |
---|---|---|
Required personnel | 0 | ++ |
Preparation time | + | ++ |
Duration of Injection | ++ | + |
Flexibility (depth range) | – | ++ |
Deep GMWs or boreholes | – | ++ |
Handling | + | ++ |
Homogeneous injection | ++ | + |
Costs | + | ++ |
Conclusions
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The first SBDT in a GMW or borehole should be a uniform injection, since it delivers results for the entire saturated length and leads to a basic understanding of in- or outflow. The injection method should be chosen depending on the depth and the accessibility.
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Results show that increasing the natural background conductivity by a factor of 3–5, or 1,000–2,000 μS/cm, which in this case corresponds to a maximum of 2–3 g/L NaCl in the water column, is sufficiently high to identify flowing features. Also, similar to Lamontagne et al. (2002), no density effects were observed within these limits. In general, tracer use should be minimized to avoid impacts on natural flow conditions and density affecting the interpretation.
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Normalized graphs compensate unequal injections and can be used to separate effects caused by flowing features from methodical influences. Normalizing concentration profiles helps to compare multiple SBDTs conducted in the same GMW or borehole; however, it is not suitable for dominant vertical flow.
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In the absence of vertical flow, both injection methods can be used to calculate horizontal flow within wells or boreholes. For the determination of filtration velocities, both linear regression and CXTFIT provide good results; cross-validation of individual values can be used for verification. Since the determination of the correction factor α, used to convert apparent filtration velocities to filtration velocities, is often not possible due to unknown permeabilities, the apparent filtration velocity can be used to compare different GMWs.
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Despite being conducted in boreholes equipped with slotted casing, all SBDTs could identify the major flowing features in the tested wells.
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SBDTs in the karst aquifer showed the expected wide range of results, with test durations between several hours and multiple weeks. Also, the heterogeneity within each well, e.g. outflow horizons next to inactive segments, could be shown nicely, making SBDTs especially interesting in karst aquifers. In contrast, GMWs in the alluvial aquifer show a more homogeneous behavior and no abrupt changes within the profiles.