As the second largest city in the Czech Republic with over 400,000 inhabitants, around 30M m3 of wastewater is produced each year. Municipal wastewater is collected and conveyed via the 974km long public sewer network – incorporating six primary trunk sewers – and 15 pumping stations to a treatment plant at Modřice in the south.
The project was carried out in three specific components. The first involved reconstruction of the sewerage system in the old town area of Líšen to provide the area's 9200 residents with connection to the main sewerage system. It entailed building 21.5km of foul sewer using open-cut construction techniques.
The second component focused on completing the main and trunk sewers in principal areas to provide an additional 14,000 inhabitants with mains sewerage.
The third component involved drainage of the historic city centre by constructing secondary collectors – serving as utility ducts –within which pipes of between 400mm and 1000mm diameter were installed to replace the existing sewers. The ducts measure 3m by 4m internally with the depth to soffit ranging from 2m to 6m. They were constructed using tunnelling methods as the site is within the city's central shopping area, where the buildings are historic in character with deep cellars, often extending under the roadway up to the line of construction. The ducts also house various lengths of GRP water main.
Mott MacDonald‘s role – in joint venture with VRV – focused on transferring knowledge to the project implementation unit, supervising construction of the overall works and completing the duct network.