A QUARTER of trunk main sewers in England and Wales are leaking badly or on the verge of collapse and could soon become a threat to drinking water supplies, sewerage experts told NCE this week.
According to John Reynolds of Portsmouth University's civil engineering department, the problem could be even more serious. He claimed that the remaining 75% of the sewerage network remains largely unmonitored or unmaintained.
A report into the problem prepared by Reynolds states that most smaller sewers are considered by water watchdog the Office of Water Services to be 'non-critical'. They are 'left to deteriorate and attended to in a reactive manner only, following collapse or flooding'.
Reynolds added that it was likely sewerage could already be seeping out of the sewers into groundwater supplies, posing a threat to water sources. Alternatively groundwater could be infiltrating the sewers, creating more volume for treatment. He warned that a serious pollution disaster was not far away.
An Environment Agency spokesman said: 'We have had problems with pollution from sewage and it is still happening as systems are not being maintained properly.'
However, Ofwat claimed that on the contrary the nation's major sewer network was in very good condition. Its figures suggest that of the 70,000km trunk network '94% of sewers are performing satisfactorily or better'.
Ofwat's figures are based only on the critical trunk sewers and on the regulator's serviceability assessment criteria - which requires only that sewers carry out the minimum customers' requirement of draining their premises.
But experts maintained that Ofwat's figures did not reveal the true condition of the network and urged that the problem be tackled without delay.
Paul Hayward, secretary of the Sewer Renovation Federation, added that the state of England and Wales' sewers was due to a lack of maintenance by water companies since privatisation in 1989.
He said: 'During the first years of privatisation, the water companies had a lot of money which they spent largely on themselves and their shareholders.'
He added that as Ofwat put pressure on water companies to reduce their prices, funds dried up and sewer maintenance fell in priority. Instead, he said, spending was directed towards reducing water supply leakage following the much-publicised droughts of 1996. New data published last week by Ofwat appears to back this theory as it says water supply leakage has reduced by 35% since 1994.
But the money has been misdirected, according to Hayward.
'The asset value of sewers is more than twice that of the water supply network. It's all driven by short term economics, not long term engineering.'