Project: Optimization of sewerage network of Valpantena
Location: Verona, Italy
Client: Acque Veronesi S.c.a.r.l.
Cost of total Works: 11.662.259 €
Services: Preliminary Design (Final Design, on going; Detailed Design, to be done)
Originally the district of Valpantena was provided with a primary pipeline of combined sewage network (16 km long), which serves the following towns: Dorighi, Bellori, Lugo, Stallavena, Grezzana, Marzana, Quinto and Poiano. All the secondary networks were of a mixed type, and only Marzana and Quinto were provided with separate foul sewage and stormwater sewerage systems. The sewage is conveyed to the wastewater treatment plant of Verona city.
This system is about 25 years old, and in some stretches is now in critical conditions due to:
- Inadequacy of the Diameter of the pipe, as a result of the increased flow as a consequence of the increment in P.E. (people equivalent) connected to the network
- Natural degradation of the pipe
- Opposite declination
- Presence of wastewater in the local stream (Progno Valpantena) at some spillways
- Stretch that operates under pressure
The objective of the project was to solve these critical issues. In a feasibility study four different scenarios were studied:
Option 1: strengthening and upgrading of the existing primary pipeline (Total length of intervention: 15 km);
Option 2: separation of the two networks, the main collector and the secondary pipelines. Upgrading of the existing network to be used as the new surface drainage sewer and realization of a new foul sewerage network. (Total length of intervention: 48 km)
Option 3: separation of the two networks, the main collector and the secondary pipelines. Upgrading of the existing network to be used as foul sewage network and realization of a new surface drainage sewerage network. (Total length of intervention: 43 km)
Option 4: separation of the two networks, as follows:
- Main Sewer: upgrading of the existing network to be used for the surface stormwater drainage system and realization of a new foul sewage network;
- Secondary Networks: upgrading of the existing network to serve the foul sewage and realization of a new surface drainage network (total length of intervention: 4 km).
In agreement with the Client, the first solution was chosen and the Preliminary Design was developed. The choice was made on the basis of the cost of works, the cost of maintenance including also the cost of energy for depuration, the timetable of the works, and considering also an analysis of the environmental impacts of the intervention during and after the construction phases.
In particular, the project involves the realization of about 15 km of a single network (both for foul sewage and stormwater runoff).
Further specific information
The main works included in the design (strengthening and upgrading of the existing primary pipeline) are the following:
- replacement of stretch of the main sewer with a sufficient diameter to guarantee the collective gravity of the waste
- replacement of the counterslope stretches
- adjustment of the spillways height along the main pipeline to guarantee the legally admissible overflow
- introduction of grids upstream of each spillway in accordance with the specific regional law
The new pipeline will have diameters ranging from 400 mm to 1200 mm in the final stretch close to Borgo Venezia, an area of Verona.
The excavation for the replacement of the pipes will be carried out, taking into account that the pipeline will be laid on a bed of sifted sand about 20 cm high and to ensure minimum overlap everywhere along the conduit of at least 1.50 m. The depth of the excavation will be approximately 2.5 m. The cross section width of excavation is tied to the depth of the trenches and the diameter of the pipeline.