Construction and commisioning of general interceptor sewers on the right bank of the Ferrol Estuary

Until last April, the Ferrol estuary was going through a delicate environmental situation marked by the great degradation of its marine environment. This was mainly a consequence of urban wastewater discharged over decades from the right bank of the estuary, where the urban centres of Ferrol and Narón (population of 107,734). The construction and commissioning of the General Interceptor Sewers on the Right Bank of the Ferrol Estuary by Sociedad Mercantil Estatal Aguas de las Cuencas de España (ACUAES) represents a turning point for the inhabitants of one of Galicia’s main urban areas. The sewers are designed on the basis of environmental integration of new infrastructures with the receiving media and the result is a substantial improvement in water quality in both bathing areas and shellfish beds.

Introduction

Until April 2017, the Ferrol estuary, where the cities of Ferrol and Narón are located, was going through a delicate environmental situation marked by the great degradation of its marine environment. This was mainly due to the poor state and shortcomings of the sanitation infrastructures on the right bank of the estuary. The general sewer network and pumping stations built during the 1990s to collect the wastewater from the two cities were out of service owing to delays of a number of years in the construction of the Cabo Prioriño WWTP, which was completed in 2011.

FCC Aqualia central, Inodoro

Because of this situation, most of the wastewater generated by human and industrial activity in these two municipalities, with a total population of around 85,000, was discharged directly into the estuary at several points along its coastline, where the old rivers had turned into sewers that were mainly buried under urban growth. Allied to this was the lack of any type of structure to control and correctly manage runoff in rainy periods, runoff with a high pollutant load subsequent to flowing through the urban area.

These shortcomings and problems, added to the need to comply with increasing stringent quality legislation led to the Ferrol Treatment and Discharge project being declared an infrastructure of general interest in Act 22/1997. The project was later extended to become the Ferrol Sewage Network, Treatment and Discharge Infrastructure in Act 10/2001 of July 5th, legislation associated with the Spanish National River Basin Management Plan.

This declaration resulted in the Ministry of Agriculture and Fisheries, Food and Environment, through currently the Miño-Sil River Basin Management Authority commencing the project in collaboration with the Regional Government of Galicia. The project consisted of the design and construction of the new WWTP and the Cabo Prioriño subsea outfall, the terrestrial pipeline from A Malata to the plant, the A Malata pumping station and the pipeline running beneath this cove. These infrastructures would carry the wastewater from the two cities from the port of Ferrol to the new WWTP, located on the mouth of the estuary.

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However, although this work was completed in 2011, commissioning was limited due to the need to undertake an in-depth overhaul of the general sewers built in the 1990s.

These sewers were in a very poor state due to the fact that they had been out of service for a period of over twenty years, whilst awaiting the construction of the treatment infrastructure.

In 2010, the Ministry of Agriculture, currently the Ministry of Agriculture, Fisheries, Food and Environment. In collaboration with the GEAMA (Grupo de Ingeniería del Agua y del Medio Ambiente) research team from the Universidade da Coruña, drafted the first design of the new system. Based on this, the first plans were drawn up for the refurbishment of the general interceptors on the right bank of the Ferrol estuary, corresponding to the A Malata- Gándara and Gándara-Cadaval sections.

Shortly afterwards, the Ministry of the Environment and Marine and Rural Affairs entrusted ACUAES with undertaking the construction of the General Interceptor Sewers on the Right Bank of the Ferrol Estuary. The construction work was carried out in five large stages or projects:

1. A Malata – A Gándara section
2. A Gándara – Cadaval section
3. O Porto regulating station
4. River Inxerto section
5. Cadaval-Neda section

The contracts for the construction of each of these sections were awarded separately to: FCC CONSTRUCCIÓN, S.A., ACCIONA INFRAESTRUCTURAS, S.A., S.A. de Obras y servicios COPASA, GÉVORA CONSTRUCCIONES, S.A. and Sociedad General de Obras, S.A. (SOGEOSA). In addition, ACUAES awarded three contracts for the provision of technical assistance (supervision and control) to the works management of these construction projects to the PETTRATTU consortium, INECO and I+P Ingeniería y Prevención.

The construction of these five infrastructures, and the preliminary design projects of the O Porto regulating station, River Inxerto section and the Cadaval-Ned section (drafted by INGIOPSA), was carried out by ACUAES between 2012 and 2017. Total investment amounted to €54.3 million, and the work was co-funded by the Ministry of Agriculture, through ACUAES, the ERDF, the Government of Galicia and the Municipal Councils of Ferrol and Narón.

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Published in: FuturENVIRO #45 November 2017