Ms Geraldine Tallon:

Each of the plants under the design, build, operate and maintain approach is evaluated at the start on a whole-life cost, taking into account the full lifetime costs of the plant. We have figures for whole-life cost for the plants based on the design, build, operate and maintain approach compared with the typical costs of traditionally procured schemes. We also have operational costs for the individual schemes over the number of years in which they have been in operation. This is beginning to give us a sense of how robust the overall whole-life costing provided in advance is.

A whole variety of factors influence the operation of wastewater treatment plants and it can be difficult to anticipate in advance all of the associated costs and factors.