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

3 Sampling sites and methods 3.1. Setup of the sampling sites
3.1.3 Development of the sites during the sampling period
Site A
The radon measurements at Site A suggest that atmospheric sealing of the borehole was maintained
during the entire sampling period from late August 2010 to May 2011. However, continuous
O2 and CO2 measurements in May 2011, exceeding 10 minutes, showed a change in
air composition after 200 seconds at 2 m depth. For a more detailed discussion of the borehole
sealing quality see Section 5.4.1.
The extensive and unusual dry period during spring 2011 (Table B.8 and Figure C.9) led to the
decision to artificially irrigate Site A in May 2011. Between May 9 th and May 13 th , the site was
irrigated four times. The amount of water was estimated to be similar to 30 mm of precipitation
per irrigation event. It was artificially created by irrigating an area with a radius of 3 m around
the borehole with tap water over one hour. A fifth irrigation of 30 minutes length was done on
May 18 th , leading to about 15 mm of artificial precipitation.
The water was sprayed to emulate a natural rain event as accurately as possible, the amount
of 30 mm/h is comparable with heavy rain [Baumgartner, 1996]. If evaporation during spraying
and horizontal spreading of the water within the soil into the surrounding dry soil is accounted
for, this value likely represents a generous upper limit estimate.
During the irrigation period O2 and CO2 measurements as well as noble gas samples were taken
at an increased rate (Sample IDs A17 to A23), documenting the effect of the increased abundance
of water within the soil. Site A represents the largest and most detailed set of samples taken
during this study.
Site B
Site B was sampled regularly throughout the sampling period with at least one sample per
month. However, the radon data suggests problems with the borehole sealing in November
2010 and from April 2011 onward, see Section 5.4.2 for a detailed discussion of sealing quality
of this particular site. While noble gas samples were taken during the entire sampling time,
measurement of most of the samples taken during the time of verified atmospheric contamination
had low priority due to limitations in measuring time on the mass spectrometer. Therefore most
of the noble gas samples taken in 2011 were not evaluated and remain in storage at the time
this thesis is finished.
Site C
The sampling Site C was abandoned after problems had arisen early on caused by heavy rainfalls
the day before the first sampling attempt (August 2010, sample ID C01). The precipitation
created a water saturated layer in the soil. While pumping from the depths 1 m and 3 m led to
normal airflow, pumping at a depth of 2 m caused highly liquid sludge to be transported up the
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