Sewerage

No-one likes sewage bubbling up out of their garden, but that happens in Chilbolton.

What is being proposed?

The Flood Risk Assessment estimates that the development will generate a foul water discharge rate of 36,750 litres per day which equates to 0.426 litres per second. It will carried away by pumping it to connect with the existing sewerage in Eastman’s Field.

The foul water will gravitate towards a Type 3 Pumping Station in accordance with the [Design and Construction Guidance] which is located in the northeast corner of the site, then pumped via a rising main towards a foul water manhole located adjacent to Eastmans Field, then gravitating towards the exiting foul water manhole 3405.

From Eastman’s Field waste would flow to Branksome Avenue, and then to the Chilbolton wastewater treatment plant on West Down.

This means that it wouldn’t increase the flow of waste through the existing pumping station in Village Street near the Abbots Mitre. This pumping station has been at the centre of problems that have required tankers round the clock for months at times in the Village.

However, the analysis of foul water does not include any analysis of whether the existing sewerage can cope with the additional volume. It does say though that “A Section 106 agreement with Southern Water will be required before construction to connect into exiting public manhole 3405.” Section 106 of the Water Industry Act 1991 covers new connections to the sewerage system. Southern Water charges fees for any connections.

Comments:

Capacity uncertainty

The idea of having a pumping station to avoid sewage going down to the pump-house in the Village is a good one. However pumping up to connect to the existing system will put additional pressure on the pipe that goes along Branksome Avenue.

No analysis has been done within the application to ensure that there is sufficient capacity in the infrastructure that connects via the Branksome Avenue sewerage to the Chilbolton wastewater treatment plant to support a further 245 residents.

Inadequate foul water infrastructure

Tim McDonnell mentioned the smell due to overwhelmed surface drainage:

The current sewage infrastructure is not fit for purpose - there are foul smells on a regular basis due to an overwhelmed surface drainage and foul water system, the Chilbolton sewage works are too small and the existing infrastructure (not least pipework) is known to be in poor condition. Adding 75 houses and ‘drainage’ doesn’t get to the root the problem - the entire sewage and drainage system of the whole village needs to be upgraded.

Run-off from proposed footpath

The proposed new footpath will increase the flow of rainwater from the proposed site and the lower field, down the new path through Cart Lane and into Village Street.

During heavy rain, Cart Lane already turns into a stream, causing flooding in Village Street.

This ground water penetrates the sewerage system and requires round the clock tankering of foul water for months at a time.

The proposed footpath will make this significantly worse.