Padina settling basin

Padina settling basin is a storage facility for wastes from Solvay Sodi Jsc plant for production of soda ash, Devnya town, Bulgaria. The facility has been in operation since 1974.


Purpose: Settling basin

Location: Devnya town, Bulgaria

Client: Solvay Sodi Jsc

Services provided: Investigations and design of the various stages of design and construction


The total area of the facility is 175 ha. The enclosing dam of the settling basin is a rock-fill type, with a length along the crest of approximately 3 300 m. It was built-up and the basin was filled-up gradually, at stages. Following the construction of the Fifth stage dam (37 m total height and 38 million m3 volume of disposed sllime) in 2011, stability analyses were performed in order to identify the possibilities for further dam height increase. It was concluded that it is possible to be done at two stages: by consecutively building two new enclosing dams, each 5 m high. They will provide additional 17 million m3 volume for wastes disposal. The construction of the Sixth stage dam (up to elevation 52) was started in 2008 and will finish in 2016. At the end of 2015 the dam height was 42 m and disposed slime volume was 38 million m3. The rock fill of the Sixth stage dam is placed directly on the disposed slime, with an offset towards the lake (from the main dam) varying from 0 to 50 m, as it is laid on geomeshes in combination with geotextile and a layer of graded rock.

Padina 3

Sweco Energoproekt’s team has provided all necessary services related to the design and operation of this facility since its commissioning in 1974. Since 2001 the team of Sweco Energoproekt Jsc has provided the following services:

  • Operating manuals for the Fifth stage and the Sixth stage of dam height increase;

  • Stability analyses for identifying the possibilities for further increase of dam height;

  • Conceptual design for building the Sixth and the Seventh stages of dam height increase;

  • Detailed design and bidding documents for construction of reinforced embankment placed at the toe of the main dam;

  • Detailed design and bidding documents for construction of Sixth stage dam;

  • Detailed design of Control and Instrumentation System (C&I) of Sixth stage dam;

  • Basic design for construction of a new cell for disposal of wastes from Deven Thermal Power Plant on the territory of Padina settling basin;

  • Detailed design for partial technical re-cultivation of the offset between Fifth and Sixth stage dams;

  • Geological investigations and laboratory tests.

    Maintenance and enlargement of Padina settling basin is of key importance for the economic development of Northeast Bulgaria as it ensures the continuous production of the largest plant for soda ash in Bulgaria and Europe (Solvay Sodi Jsc) while complying with all up-to-date standards and requirements with regard to environmental protection.

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