Sewage Pollution: Hamwell Leaze and Dudbridge

One issue the Ruscombe Brook Action Group has discussed regularly is sewage pollution - at our meeting last week we considered Hamwell Leaze and Dudbridge Playing Field - I will do a blog on the meeting later today if I get chance - but wanted to say more on this topic as I've had several queries - and Julian Jones from Water 21 recently spoke to a sub-committee at Cainscross Parish Council.

Photo: ornamental reeds

Basically there is an overlap of issues relating to these two sites; particularly in respect of the periodic sewage pollution they suffer, as well as the likely solutions. The main cause of this contamination is insufficient sewer capacity at times of rainfall causing surcharges through sewer manholes.

Julian Jones has noted in the past that our local sewer has incapacity and poor integrity since well before the water industry privatisation (1989) and some may recall that for many years, until the construction of the Ebley by-pass, replacement sewer pipes intended to remedy this situation were stored on the old railway at Ebley. Unfortunately these were never installed.

Instead of increasing sewer capacity locally, a programme of closing off storm overflows (70 in number) was commenced in 1990 with the provision of small underground stormwater retention tanks (intended to store rainwater until sewer flows reduced after rainfall to enable the tanks to drain down). These tanks have proven to be inadequate (and apparently poorly maintained) - indeed in Puckshole there is one that has never worked - it is dry as a bone!!!

At the time this programme was commenced the Regional Manager of the National Rivers Authority described this procedure as “dangerous”. His view was that the closure of such a large numbers of overflows, on a sewer network of high head (height) differential and insufficient capacity, was likely to cause sudden surcharging of sewage from the sewer, exiting through manhole covers both onto and into both public and private property. Such events have now been occurring with increasing frequency, in line with the growing local population and new connections to the sewer network. Several such locations, at Dudbridge Bowling Club for example, exist within the parish.

As a response to the surcharging of manholes an ad hoc practice of bolting down manhole covers commenced. The Ruscombe Brook Action Group has expressed concerns to Severn Trent about this - some experts have told us this practice is 'irresponsible'. This passes the surcharge problem on to the next weak point on the network (usually in an unpredictable manner) either causing further surcharging and/or may cause fracturing of sewers leading to long term seepage of sewage into the ground and where watercourses are adjacent, into these also - as found in the Ruscombe Brook - indeed we have many photos of sewage.

As the sewer network in the area includes the main trunk sewer serving much of the Five Valleys, you are in effect - particularly at Dudbridge - suffering the effects of overloading from many points 'upstream', ultimately as far as Cranham.

The proposals for Hamwell Leaze include a small fenced reed bed construction (one of 25 or more proposed throughout the District) that would safely capture, control and treat such sewer surcharges.

One suggestion made by the sub-committee was that there should be a moratorium on new connections to the District sewer network. This seems an excellent idea but I don't think the Parish have taken it forward at this point - certainly they only have powers to recommend so could not stop a planning application. Another suggestion made by the Parish was apparently in those areas prone to sewer floods there should be fencing and signage to warn the public. I am not sure if this idea will go-ahead but again it seems very sensible.

Julian Jones has noted that any areas already prone to sewer floods, like the land at Dudbridge, would be ideal locations for reedbeds, and were the Parish Council the owners of such sites some financial income could in the longterm be derived from providing these important wastewater treatment services - at costs to consumers that are considerably less than the present poorly performing methods.