Note from the Trevone representatives on the Liaison Group with South West Water
We have been meeting with South West Water (SWW) since 2012 in connection with the problem of overflows onto Rocky Beach from the Trevone Sewage Pumping Station (SPS). We hope this note will assist people in responding to the Public Consultation currently being carried out by the Environment Agency (EA) on South West Water’s application to shorten the overflow, and be allowed - as in the existing permit – to discharge in storm or emergency conditions.
We think that the following issues are those of the greatest importance:
1. They’ve repaired the pipe, so why shorten it?
South West Water has recently restored the whole length of the pipeline so that any discharge will be from the point given in its current consent. This is at the seaward edge of the rock shelf so that any discharge goes into the open sea with relatively good dispersal conditions. The proposed new discharge point is about 70 to 80 metres closer to the shore than this one (see map) in the vicinity of rock pools likely to be used by visitors to Rocky Beach. South West Water has advised that the proposed location would be exposed rather than submerged for "12% of the time at the low water spring tide level". A discharge at such times would have an open path along a rock gulley of about 25 metres length before reaching the somewhat enclosed water at the north end of the swimming channel.
Our view is that South West Water’s proposal should be refused, as
1) It would lead to a disbenefit to the environment, including people, as compared with the current situation, and
2) The change in location is neither necessary nor justified, given that the pipeline is now in operable condition over its full length.
2. The Trevone sewage pumping station needs to take larger volumes of sewage away when required, to reduce the risk of spills
The minimum pumping rate of 7 litres/second that is currently required by the Environment Agency’s consent is insufficient to cope with the incoming flow during and for many days after periods of rainfall, as demonstrated, for example, in the discharge episode that occurred in January this year, which went on for 11 consecutive days. The Trevone Sewage Pumping Station maintained a rate on average a little higher than 7 litres/second, but this did not prevent a very lengthy discharge from taking place. South West Water has claimed that competition with the pumped flow from Harlyn inhibits the Trevone Sewage Pumping Station capability; however, data sequences from its own monitoring records show that the Trevone Sewage Pumping Station is capable of maintaining rates of 10 litres/second even when Harlyn is sending 40 litres/second.
Our view is that a higher rate in the range 10 to 12 litres/second should be specified to reduce the risk of spills.
3. South West Water predicts there will be an illegal discharge of untreated sewage once a fortnight on average (during peak bathing season April to October)
South West has presented computer modelling results simulating the performance of the Trevone Sewage Pumping Station using historical rainfall data. The prediction is that for discharges greater than 50 cubic metres, on average, there will be no more than 3 during the Bathing Season, and about 14 over the remaining 7 months of the year, that is once a fortnight on average from October to April. These predictions deal only with the Trevone Sewage Pumping Station’s response to rainfall.
Our view is that that once a fortnight is too high a frequency (clearly very much higher than the now-abandoned once-in-5-years target announced at the 2012 public meeting), and also much higher than the frequency of weather conditions that could reasonably be described as a storm. The predicted values exclude discharges resulting from breakdowns at the Trevone Sewage Pumping Station, which we know have occurred previously and will add to the discharges from rainfall induced events.
Summary
We consider that the proposal should be refused. The currently-consented discharge point should be retained, since it provides a better level of protection to the environment and people than the proposed new location. Adoption of the new location would be a disbenefit. The minimum pumping rate during discharges, as specified in the permit, should be increased. South West Water has not justified the need for a new discharge point.
The above summarises our main concerns. We also have some issues of a technical nature regarding the assumptions made in the model (particularly that infiltration from rainfall should be taken into account throughout the year, not just from October to April, and that the pumping rate of 12 litres/second assumed in the May to September Bathing Season period is over-optimistic) and have identified to the Environment Agency and South West Water a number of areas where South West Water’s application is, in our view, inaccurate or incomplete.
Make Your voice heard…
The Environment Agency will be holding a consultation period, where the general public can comment on South West Water’s application to shorten the overflow pipe. Responses to the Environment Agency’s consultation should be sent by 4th June to:
psc-waterquality@environment-agency.gov.uk by email, or by post to
Permitting Support Centre WQ Team, Quadrant 2, 99 Parkway Business Park, Sheffield S9 4WF, quoting the Application Reference 300014/V001.
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