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6.2 Collection and transfer (Topic b)

6.2.1 Situational overview

According to the European Environment Agency, there has been a dramatic increase in sewers connections in those EU counties where the connection rates were comparatively low. For example in Spain, it has nearly doubled over the past 15 years (EEA,1999). In Section 6.6.1 and Table 6.12, the programme for closing the gap and the financial implications are reviewed: in accordance with EU Directive 91/271, collection systems shall be provided at the latest by December 2000 for agglomerations with a population (pe) of more than 15000, and, at the latest by 31 December 2005 for those with a pe of between 2000 and 15000 (see Section 6.6.1).

More than half of the collection systems in Europe are combined. As much as 80% of the built up areas may be served by combined systems in some countries, and in practically no case, less than 50%. Table 6.6 exhibits the status of wastewater collection in EU Member States.

In its report of 1995, the European Waste Water Group also provides summary information on the length of collection systems in the countries studies. While there are many variations, the report indicates that the average length of public collection system in Western Europe typically falls within the following ranges (see Table 6.7):

The survey also produced information on the capital cost of providing new collection systems. The following are indicative ranges: as an average for a drainage area with a population of 10000; systems cost between 300 and 375 ECU per meter in established urban areas, and between 25 and 200 ECU per meter in open ground.

Directive 91/271 of the EU Council further stipulates that the design, construction and maintenance of collection systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs, notably regarding:

• Volume and characteristics of the urban wastewater.
• Prevention of leaks.
• Limitation of pollution of receiving waters due to stormwater overflows.

This implies that costs, the prevention of leaks and the control of pollution from stormwater overflows are given overall importance in the choice of technology, and that compatibility with existing systems or system components is important whenever extensions are planned.

Today, separate systems are generally preferred although they are usually more expensive than combined. The separation of existing combined systems is also very expensive and is often impossible to implement; also the benefit of the investment made for such separations has been shown uncertain in the case of some European cities. The problem is plaguing many of the Northern European countries where rainfall is higher than in the South.

The choice of technology and system design are governed by environmental and economic requirement. The integration and/or expansion of systems comprising both combined and separate components is intricate and involves consideration of:

• The associated operational and environmental implications.
• Rehabilitation of existing systems.
• Compliance with water quality requirements.

New collection systems or additions to existing ones are likely to be combined and they are considered the most economic and practical solution provided their design is responsive to the need to avoid gross water pollution at times of rain.

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