More than 50 Milton residents will have to find alternative ways to dispose of their stormwater because it is overflowing the town's sewerage system.
Tests by Clutha District Council staff revealed about 53 private properties have been illegally discharging stormwater into Milton's sewerage system via downpipes connected directly to the system.
Clutha District Council water services manager Hank Stocker said these would need to be permanently disconnected, meaning the property owner would have to make other arrangements for stormwater discharge.
The council would be writing to the affected property owners, and following up with a visit where necessary, to get the issue resolved.
Homeowners could discharge roof water into the stormwater system, or into a natural stream where applicable. Some connections had been in place for "decades" and some property owners had been unaware of the discharge, he said.
The council had approved a project aimed at improving the Milton sewerage system's ability to cope during times of heavy rain as it became overloaded during periods of heavy rain, an issue which was raised several years ago.
The cause of the problem is associated with large amounts of stormwater entering the sewerage network, either underground (known as infiltration) or above ground (known as inflow), resulting in two main problems for Milton.
The first issue was that sewage overflowed in parts of Milton township, and the second was that the Milton sewage treatment plant could not cope with the extra inflow, meaning the excess had to bypass the plant and be discharged directly into the Tokomairiro River.
The nearby Otago Correctional Facility at Milburn had not contributed to the problem, he said.
The Clutha District Council holds a resource consent from the Otago Regional Council to do this during wet weather periods, but the consent also requires the council to implement a programme to reduce the problem.
Mr Stocker said that recent major stormwater upgrades in the township, including the new floodbank and pumping station, had helped address the problem by reducing surface water and lowering the groundwater level during heavy rainfall events, but some sewage overflows still continued to occur.
Council assessments showed the main cause of stormwater entering the sewerage network was through surface inflow at various sumps, gully traps and building roof gutters.
