This ratio becomes 1 for all metals in the Glatt. If the ratio
is smaller than 1, then the metal has been removed more
than boron; if the ratio is higher than 1, then the metal has
a source compared to the nonreactive boron. In Figure 2,
the ratio is shown for some metals on the direct flow path
from the river to GW1 and GW4. Cu, Zn, and Ni are higher
in GW1 than in the Glatt and decrease further on (see also
Table 1). Ca increases by a factor of nearly 2 from the river
to the deep groundwater. Due to our filtration technique, we