Diploma thesis in Physics submitted by Florian Freundt born in ...

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5.4. Borehole sealing 5 Results Figure 5.6: Continuous O2 and CO2 measurements at Site A, showing an increase of O2 and a decrease of CO2 starting at around 200 s of pumping, indicating an inflow of air more closely resembling atmospheric composition. This air inflow is not necessarily atmospheric though. Based on the associated 222 Rn and 220 Rn data it is more likely that an interconnection between the screens at 2 and 4 m exists. Since the 4 m soil air contained more O2 and less CO2 than the 2 m soil air at the time, the mixing only appears to be atmospherically influenced. Accuracy for both O2 and CO2 is 1 %, error bars have been omitted for better visibility. Figure 5.7: Continuous O2 and CO2 measurements at Site B, showing an increase of O2 and a decrease of CO2 starting at around 30 s of pumping, indicating an inflow of air more closely resembling atmospheric composition. Accuracies are 1 % for O2 and 0.5 % for CO2, error bars have been omitted for better visibility. 56
5 Results 5.5. Noble gases 5.4.2 Site B The 222 Rn data in Figure 5.5 clearly indicates an atmospheric leak leading to a dilution of the ground air with mostly 222 Rn-free atmospheric air on several, if not all, samplings. O2 and CO2 measurements shown in Figure 5.7 support the atmospheric leak scenario, showing an intrusion of differently composed air within 30 seconds of pumping at all depths except 5 m. A contrasting plot for Site A showing no atmospheric air inflow can be found in Figure C.6. Additionally, CO2 concentrations measured at 1 and 3 m at Site B are significantly lower than at 2 m at Site A while O2 concentrations are higher. While the resealing of the borehole at Site B initially seemed to have been successful 3 , the relatively dry period of September to October 2010 probably caused the deterioration of the sealing by inducing the formation of contraction cracks [Scheffer and Schachtschabel, 2010] in the drying clay soil. The recovery of the 222 Rn values during winter was likely caused by a partial and temporal resealing of the upper soil layer due to the increase in precipitation. This leads to the conclusion that most, if not all, samples taken at Site B do not contain soil air from the respective sampling depths, but rather a mixture of soil and atmospheric air and therefore cannot be used as a record to answer this thesis’ main objective. 5.5 Noble gases The accuracy achieved by the mass spectrometer was best for the isotopes measured with the faraday cup and significantly worse for those measured with the multiplier. The best relative accuracy was achieved for 20 Ne (see Table B.7). Based on these accuracy patterns, the five isotopes 4 He, 20 Ne, 22 Ne, 36 Ar and 40 Ar were chosen to be presented in detail as their average measurement error was below 1.5 %. The final accuracy of the presented data is influenced by the introduction of measured gas amount of each sample. The remaining three isotopes 3 He, 84 Kr and 132 Xe mirrored the general trends found in this study, but suffered from low accuracies and more pronounced scattering. Plots and data for all measured isotopes can be found in the Appendices B and C. 5.5.1 Effects of storage Immediate measurement of the sampled air in the mass spectrometer was usually not possible as the spectrometer was only available during certain time frames. Because the copper tubes contain air with high O2 concentrations and humidity, the possibility of chemical reactions occurring during storage affecting the noble gases was tested. This was done three times by measuring all three samples of a single depth, one only a few hours after collecting the samples. The remaining two backups were measured after storing them for different periods, the one for 3 Assuming the difference between absolute 222 Rn concentrations of Site A and Site B were caused by differing source strengths. Otherwise it might even be the case that only the 222 Rn concentrations measured in February 2011 at Site B represent a sealed borehole. 57
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Faculty of Physics and Astronomy He
Page 5: Measuring annual variation of soil
Page 8 and 9: CONTENTS CONTENTS 3.1 Setup of the
Page 11 and 12: Chapter 1 Introduction Understandin
Page 13: 1 Introduction Molins and Mayer [20
Page 16 and 17: 2.1. Noble gas temperatures 2 Theor
Page 24 and 25: 2.2. Physical processes and propert
Page 26 and 27: 2.2. Physical processes and propert
Page 28 and 29: 2.3. Soil atmosphere composition 2
Page 35 and 36: Chapter 3 Sampling sites and method
Page 37 and 38: 3 Sampling sites and methods 3.1. S
Page 43 and 44: Chapter 4 Measuring methods 4.1 Mas
Page 45 and 46: 4 Measuring methods 4.1. Mass spect
Page 47: 4 Measuring methods 4.2. On site me
Page 50 and 51: 5.2. Temperature profiles 5 Results
Page 52 and 53: 5.3. O2 and CO2 profiles 5 Results
Page 54 and 55: 5.4. Borehole sealing 5 Results 5.4
Page 58 and 59: 5.5. Noble gases 5 Results 8 days,
Page 60 and 61: 5.5. Noble gases 5 Results 5.5.3 So
Page 62 and 63: 5.5. Noble gases 5 Results 5.5.4 So
Page 64 and 65: 6 Discussion This rather extreme am
Page 66 and 67: )! )! *+,-./-01234*-56-20301.7*38*9
Page 68 and 69: 6 Discussion Table 6.1: Synthetic d
Page 71: Chapter 7 Summary The results of th
Page 74 and 75: 8 Outlook Considering the manifold
Page 76 and 77: A.1. Gas sample size A Calculations
Page 78 and 79: A.3. Fractionation-Values A Calcula
Page 80 and 81: Table B.3: Noble gas volume mixing
Page 82 and 83: Table B.5: Calculated values of rel
Page 84 and 85: Table B.8: Precipitation record of
Page 86 and 87: Table B.10: Complete dataset of nob
Page 89 and 90: Appendix C Additional plots and fig
Page 91 and 92: C Additional plots and figures Figu
Page 93 and 94: C Additional plots and figures �
Page 97 and 98: C Additional plots and figures O 2
Page 99 and 100: C Additional plots and figures 4 He
Page 101 and 102: C Additional plots and figures 20 N
Page 105 and 106: C Additional plots and figures 10 1
Page 107 and 108:
Appendix D Datasheets 107
Page 109 and 110:
D Datasheets LogTag TREX-8 Technica
Page 111 and 112:
Bibliography [Aeschbach-Hertig 1994
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BIBLIOGRAPHY BIBLIOGRAPHY [Friedric
Page 115 and 116:
BIBLIOGRAPHY BIBLIOGRAPHY [Riveros-
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Acknowledegment At the end of this
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Diploma thesis in Physics submitted by Florian Freundt born in ...

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