Sewage leaking into groundwater may not seem attractive (NCE 9 May), but it does nevertheless comprise an important source of groundwater recharge in urban areas, which is considered routinely in catchment scale groundwater resource assessments.
The water resource consequences of reducing this recharge should be considered, before replacing the sewers.
In other cities, for example Cardiff, groundwater leaks into sewers (the Victorians designed them this way) and this leakage is an important part of the urban drainage system.
Replacing the sewers with water tight versions would have wider consequences. Go carefully!
John Heathcote, Entec UK, 160-162 Abbey Foregate, Shrewsbury SY2 6BZ