Building history Tobl

Planning and construction of the ARA Tobl

Start of construction: 1991
End of construction: September 1995
Commissioning and functional checks: January 1996 to June 1996
In operation since: 3 July 1996


In search of a suitable location:

Ten locations were investigated from 1976 to 1990 by the team of the Castlunger engineering office (Bruneck), which was responsible for planning and site management. None of these sites were accepted by the population. Since the Middle Pustertal catchment area with its numerous tourists could no longer afford to pollute the River Rienz (which runs through the entire Pustertal), the idea was born to construct the Association Wastewater Treatment Plant Middle Pustertal as a cavern plant.


Advantages and disadvantages of the underground construction method


  • Saving of valuable cultural land, which is scarce in the narrow Alpine valleys;
  • Construction independent of weather conditions;
  • High acceptance by the population: What you don't see doesn't stink;
  • No odour emissions due to central ventilation;
  • No difficulties during winter operation (icing, snow, frost);
  • No complications due to wind influences (aerosol or mould sludge removal);
  • No algae formation in the canals and basins due to lack of sunlight;
  • Longer service life of structural and mechanical installations due to constant temperature conditions and lack of weather-related influences


  • Higher construction costs due to rock excavation and rock securing work;
  • Higher operating costs due to ventilation systems in the tunnels.

The Geological Situation

The caverns are located in the Brixner Quartzphyllitzone within a rocky outcrop on all sides on the orographically left side of the Pustertal valley. An extensive engineering geological and rock-mechanical investigation programme (drilling, seismic and geostructural surveys as well as directional tunnels) allowed an optimal alignment of the caverns and provided clear information for the planning and execution of the tunnelling work (interface structure, stratification/slate formation, fissures, classification of the rock quality, necessary safety and development measures, etc.).

Mountain classes:
With the exception of the stop area, all caverns were assumed to have a mountain class III (RMR = 60-41) and a mountain class IV (RMR = 40-21) according to Beniawsky. Structurally, class IV was predicted for the fault zones, while the rest was assumed to be class III.
In relation to the project, the complicated intersection and intersection areas were classified as Class IV.

costs of the plant

The total costs of the plant, including tunnel construction, sewage treatment plant, factory building and access road, amounted to € 64,557,112. If the belt drying plant and the thermal sewage sludge utilisation plant are added, the costs amount to € 72,357,112.

statement of costs
Caverns, access road and access tunnel Euro 25.306.388
master-builder works Euro 17.043.078
mechanical engineering Euro 11.878.509
Electrical systems, measurement and control technology Euro 7.746.853
drying plant Euro 2.582.284
Thermal sewage sludge utilisation plant Euro 4.300.000
Belt-drying plant Euro 3.500.000
Sum: Euro 72.357.112

Planning and supervision of construction

General project and supervision

INGENIEURBÜRO HOCH- UND TIEFBAU Dr. Ing. Peter Castlunger Bruneck

Project manager, process and control engineering

Dr. Ing. Konrad ENGL Bruneck

Preproject - Process Engineering and Consulence

Ingenieurbüro KUSTER & HAGER CH - Schweiz

Stollen aeration and venting

Thermostudio Walter Prighel Bruneck

Superstructure management

Dr. Ing. Alois STADLER Autonome Provinz Bozen
Fach. Ing. Georg SIMEONI Autonome Provinz Bozen
Manfred STEIN Autonome Provinz Bozen

Executing companies

Structural part

Fa. PANA AG Brixen
Fa. UNIONBAU GmbH Sand in Taufers
Fa. HOBAG AG Sand in Taufers
Fa. ZIMMERHOFER GmbH Sand in Taufers
Fa. MOSER & CO. Bruneck
Fa. WIESER Karl OHG Mühlen

Machinery equipment

Fa. Schmidhammer Bruneck
Fa. Hofer Group St. Christina

Electrotechnical equipment

Fa. LINEL Bozen
Fa. ELPO Bruneck