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Severn Trent

Inland Severn Trent Water has no coastline to clean, so the priority is safeguarding precious water resources.

Full treatment

Landlocked Severn Trent Water has relatively little catch-up work to do on its wastewater treatment compared with companies with long lengths of coastline.

All the large centres of population in the Severn Trent area are situated at the headwaters of what become significant water courses further downstream. The consequence is that water flowing in the upper reaches of the Midlands rivers consists largely of effluent, which has always put a premium on high treatment standards. Secondary treatment or more has been the norm.

The problem of dealing with sludge from the treatment plants was confronted soon after privatisation with two incinerators built in AMP 1. Much of the remaining sludge goes to controlled use in agriculture but there is concern as to what might happen if politics made that impossible at some time in the future.

Director of engineering John Upton estimates that planning clearance for a new incinerator in the Midlands might take five to 10 years.

Despite the historically high standards, substantial investment is now going into upgrading sewage works to meet the Urban Waste Water Treatment Directive.

The biggest single project is at Minworth which serves Birmingham. And at Finham £40M is being spent on Coventry's treatment works to reduce nutrient discharges to the Sowe and Avon.

Main contractor at Coventry, Carillion, has a complex sequence of construction in and around the existing plant which has to continue in operation throughout.

The extensive borders with other water suppliers create a big unknown for Severn Trent - the risk of creating 'stranded assets'. Upton gives the hypothetical example of a water treatment works built to deliver 100M litres/d.

'If someone supplies 10M litres/d from across the border we will have a plant running at only 90% capacity for years.'

Monitoring resources

Severn Trent's relatively tight balance between supply and demand has driven the company's work on measuring where water goes to in the distribution system. Leakage control has improved and from being one of the worst offenders Severn Trent now claims the best record in the country.

'Leakage has reduced from a percentage in the high 20s to between 15% and 16%,' says director of engineering Ian Elliott.

In 1995 some 665M litres/d was lost and last year the figure was 344M litres/d.

The economic leakage target is 330M litres/d, says water resources planning manager Will Bradford.

He emphasises that below this level cutting leakage becomes very expensive and would cost far more than developing new resources.

Measuring how much water is used was a speciality of the company before privatisation. In 1986 meters were installed as non-charging monitors in 1,500 representative households.

Bradford says that the meters show demand to average 138litres/d/person. He is sceptical about other companies whose leakage estimates are based on a higher assumption for per capita use.

Severn Trent spent more than £0.5M installing meters on the distribution system to monitor the flow into 2,300 distinct areas and give a reading every six hours.

'It gives better detection and speeds up repair,' says Bradford. 'Leakage control is owned right at the top of the organisation as something that had to be done.'

Main assets

Water main renewal and relining have been top of Severn Trent's asset management programme.

Over the past decade, and with work mainly concentrated in the last five years, the company has rehabilitated 10,000km of mains - about a third of its total infrastructure says head of quality and environmental services Dr Bob Breach. Some 60% of this work has been achieved by No Dig methods which have minimised disruption.

Mains which do not require total replacement have been cleaned and relined with mortar and epoxy systems, while those beyond rescue have been replaced by high density polyethylene pipe drawn in behind bursting tools.

One of the characteristics of the area's water is its mix of hard and soft sources. This can give discoloration and taste problems as well as varying rates of corrosion in mains.

Collapsing sewers do not seem to have been a problem with the company's inherited assets.

But poor hydraulic performance is, and this is very visible where there are storm overflows. Hence Severn Trent has a substantial combined sewer overflow renewal programme in most areas, except for Derby which has already been re-sewered.

Research and development work on managing underground assets has involved widespread use of computerised records and geographical information systems.

Head of technology and development John Upton foresees that relatively soon it will be possible to take a computerised recording out to site and obtain a three-dimensional view of all services beneath the ground.

Robust, cheap technology is the future envisaged by director of engineering Ian Elliott.

He contrasts the grand scale of the industry in the 19th century, exemplified by relics such as Nottingham's grand pumping station, with today's low maintenance process equipment, housed simply in a metal shed.

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