4. Water sampling
Water samples were collected in special bottles designed to
avoid contact between samples and the atmospheric air (Fig. 2).
The sampling bottle has a volume of about 3 dm3. Its lid has
one inlet, controlled by a gas tighten tap, which drives water
to the bottle bottom, and one outlet, also controlled by a gas
tighten tap, which drains the bottle when it is completely filled
with water. The lid has also a plug-in gas connection that allows
a striping gas to be bubbled in water through a porous glass
plug near the bottle bottom. When opened to the air, the plug-in
connection also drains the bottle when it is completely filled.
The water samples are collected at the well mouth after having
discarded a volume of at least 15 min of flow through the
sampling drain. At least three independent sample aliquots are
collected at each well in a sampling campaign.A sampling bottle,
with the internal volume clean and free of oil and fat, is
connected to the well drain through a plastic hose. Keeping the
inlet, the outlet and the plug-in connection open, water is allowed
into the sampling bottle. Water completely fills the bottle
and drains through the outlet and the plug-in connection,
removing all the air. After 5 min of continuous flushing, the
plug-in connection is closed and at least more 50 dm3 of water
is forced to flow through the sampling bottle volume.
Special care is taken to ensure that only minimal volume of
air bubbles, if any, remain in the plastic hose and in the sampling
bottle during the entire flushing period. After the flushing
period, the two taps are closed sealing a 3 dm3 water sample
with a radon activity that should be representative of the
groundwater at the sampling site. The sampling time is recorded
and the bottles are taken to the laboratory for radon activity
measurement.