DISCUSSIONS are taking place over plans to build another 6,000 homes at Truro.
The revelation emerged after it was also revealed the city's sewers can only take the waste of 500 more homes before they reach capacity, documents have revealed.
And a "race" may start between developers to take up the remaining space – which is effectively reserved when planning permission is granted.
The documents detailing the capacity of the city's sewers are contained in the Persimmon Homes' planning application for 320 houses on Tolgarrick Farm, on the corner of Green Lane and Arch Hill.
The paperwork explains that once the sewers are full extensive upgrades along the valley trunk sewer will be needed. This extends from the A390 near Threemilestone, south towards land to the rear of Truro College and then south east along the valley, roughly parallel to the stream.
South West Water (SWW) has said these works are already being discussed with developers, which have plans in the pipeline to build an additional 6,000 homes in the city – details of which have not yet been revealed.
One part of a utilities report submitted as part of the Persimmon planning application states: "The local sewage pipe network currently has spare capacity to accept foul flows from 500 residential units (or the equivalent)."
It continues: "South West Water noted that there are several other applications being prepared in the area and they noted that a planning consent would be necessary to 'reserve capacity' in the foul sewer network.
"It is possible that a 'race' could develop between competing developers.
"If and when upgrades are needed, these are likely to be quite extensive, extending along long lengths of the valley trunk sewer."
Mark Beighton, waste water supply demand manager at SWW, said a "number of options" were being considered to upgrade the sewerage. "We are still evaluating the options so it is not possible to give details of what needs to be done or when it will happen.
"However, it is clear that upgrading or replacement work will be required to the sewerage network and possibly pumping stations to accommodate the flows from the proposed developments."
An e-mail from SWW, which was included in a report covering foul drainage in the Persimmon planning application, confirms that developers will be given sewer space on a "first-come, first-served" basis.
A SWW statement said: "Without any strengthening of the sewerage network, around 500 more homes could be comfortably accommodated; however, we are in discussions with developers to provide additional capacity for up to 6,000 more properties when the Threemilestone development comes to fruition.
"We have already increased the capacity at Newham Sewage Treatment Works to cope with another 2,800 homes and work to upgrade the capacity further is in progress."