RBF_Cover (for eps) - National Water Research Institute

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contains the lowest concentration of wastewater indicators. For example, Figure 2 shows the
B concentration and the proportions of treated wastewater in surface water in September 2002. The
influence of the Nordgraben extends to transect Tegel Lake, while the field site Wannsee Lake is
under the influence of the Teltow Canal. The percentage of treated wastewater is higher during
the summer months, when the Ruhleben Treatment Plant discharges into the Teltow Canal.
Figure 2. (a) Percentage of treated wastewater in surface water (calculated with discharge only; evaporation,
storage changes, and precipitation neglected). (b) Boron concentration indicating the influence of
the Teltow Canal in the south and Nordgraben in the northeast for September 2002.
By combining the results of the discharge measurements with the concentrations of wastewater
indicators, proportions of treated wastewater can be calculated with a mixing formula for each
sampling point. In Figure 3, results are shown for Tegel Lake in front of the transect. In October
2001, a pumping device started operation, which pumps Havel River water into the PEA-Tegel, a
phophate elimination plant (see Figure 1), when the natural discharge of the Nordgraben is very
low in summer. This led to a strong decrease of treated wastewater in Lake Tegel near the transect
(from 33 to 46 percent [Fritz, 2002] to an average of 11.7 +/– 1.9 percent). For surface water near
transect Wannsee Lake, values of 20.1 percent in the summer (when Ruhleben discharges into the
Teltow Canal) and 8.5 percent in the winter were calculated.
Bank-Filtration System (Wannsee Lake)
At Wannsee Lake, two transects exist, running perpendicular to the shore of Wannsee Lake
between drinking-water Production Wells 3 (TS Wannsee 2) and 4 (TS Wannsee 1). The wells
of the local gallery (Beelitzhof) have several filter screens in different porous aquifers separated by
aquitards. A schematic overview is given in Figure 4. Also shown are the T and 4 He concentrations
originating from hydrogen bomb testing in the 1960s, as well as uranium and thorium decay
within the aquifer. In the two deeper aquifers, groundwater is considerably older than 50 years,
since T is already decayed and the 4 He values are high. In contrast, the shallow wells reflect the
present atmospheric concentrations of T, while 4 He could not be detected. The resulting age is less
than the detection limit of 3 months. The production well is a mixture of all aquifers.