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Berlin Environmental Atlas

01.10 Sewage Farms

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Contamination of Sewage Farm Soils

Waste water nutrients and pollutants were retained in the soil during water passage. All such soils are contaminated with heavy metals (cf. Maps 01.03.1 and 01.03.2), some in considerable measure. This impairs the uses of these soils. Crops cultivated in this soil accumulate heavy metals (cf. Map 01.03.3). Determined loads are so high in some locations, that health risks resulting from direct contact with soils cannot be ruled out. This is relevant where former sewage farms are used for sensitive purposes, such as children's playgrounds. It can be assumed that pollutant loads of waste water increased during the operational span of sewage farms, because there was an increased use of household chemicals and detergents, and increased amounts of industrial waste water as well. Increasing loads of street waste water were also handled by the combined waste water collection system. Soil values of organic pollutants have not yet been studied. Relevant values of these pollutants can be expected because of the composition of sewage water.

There is considerable variation in the degree of pollution in these soils, depending upon the amounts of waste water treated. The duration of operation and sewage water amounts are decisive factors for pollution loads. Particularly high loads are to be expected at intensive filtration areas. Additional variations are caused by technical processes of operations. Terraces in the vicinity of sedimentation tanks are usually more heavily contaminated than areas somewhat more distant. Particularly high loads are to be assumed around sedimentation tanks and sludge drying areas which have no sealing.

Figure 2
Fig. 2: Schematic Illustration of Sewage Farm Divisions

After sewage farm operations were stopped, areas no longer used were usually leveled, filled, and plowed under. This resulted in a mixing of soils with different levels of contamination. Contaminated soil material was brought into deeper soil layers.

Not all contents of sewage water were retained in the soil passage. Considerable concentrations of nitrogen and phosphate compounds in sewage farm discharges polluted the receiving preclarification outlet trenches. Waters particularly affected in the urban area are Panke/Nordgraben, Tegeler Fließ, Wuhle, Unterhavel and Rudower Fließ. The closing of sewage farms has led to an improvement of water quality. Beyond the contamination of surface waters, a transfer of nitrogen compounds and organic pollutants into ground water has been detected. Heavy metals are largely retained in the surface soil.

Ending the intensive use of sewage farms has diverse effects on the eco-system: Nutrients accumulated during the operation of sewage farms are primarily bound in the soil's organic substances. The changed water economy and chemical condition of soils at abandoned sewage farms results in a decomposition of organic substances, and a reduction of binding capacity can be expected. Bound nutrients or pollutants can then be mobilized and washed out into the ground water, or the bordering preclarification outlet trenches.

Discontinuing sewage farm use has considerable consequences on the area water economy. A fall of ground water levels was registered at the southern sewage farms. This has direct consequences on vegetation and yield potentials of agricultural areas. The discontinuance of sewage farm treatment also results in a reduction of ground water for use in the Berlin metropolitan area. After discontinuance of the northern sewage farms, there were problems with water use in Panke and Tegeler Fließ. They had previously received some water from sewage farm outflows.

Various concepts to reduce negative consequences from closed sewage farms are being discussed and tested. Possible measures include:

  • maintaining binding strength of soils by introducing organic substances or lime to stabilize pH values
  • removal of pollutants by plants with high biomass production.
  • the renewed wetting or further flooding of sewage clarification plant outflows to achieve ground water accumulation (recharge) and the prevention of organic substance degradation.
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