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Open Letter to DEFRA: Mogden Sewer Works

April 27, 2015 3:55 PM

Hounslow Liberal Democrats
104 Boston Manor Road

Dan Rogerson MP
Department for Environment Food & Rural Affairs
Nobel House
17 Smith Square
25 April 2015

Dear Mr. Rogerson,

Open Letter re: Mogden Sewer works at Isleworth

In January of this year, you kindly met with representatives of Mogden Residents Action Group (MRAG) with respect to monitoring and intervention at national government level of the Mogden Sewer Works in Isleworth.

As a consequence, you directed the Environment Agency to conduct checks on the site to ensure that Thames Water were adhering to the restrictions placed on them for odour emissions. Some of the visits were to be unannounced and would focus on the flow of sewage that comes through the storm tanks, where the majority of the smell originates.

As Defra is no doubt now aware, storm tanks are being used so frequently at Mogden, that managers have deemed it necessary to divert sewage flow to the Thames on some 96 occasions following the increase of capacity at the site. This if far in excess of the estimates given by Richard Aylard (Thames Water External Affairs and Environment Director) that diversion to the river would be necessary only occasionally (approximately once a year) following site expansion.

The site is supposed to be capable of processing 1064 mg/l per day and once this is exceeded in any day, any extra flow can be diverted to the storm tanks. Only when all the storm tanks are full should flow be diverted directly to river.

Some years ago now, Liberal Democrat MP for Twickenham, Dr Vince Cable, secured a debate in parliament on how to regulate smell (unlike noise and lighting or air pollution there was no objective measure). DEFRA ministers (then Lord Whitty) visited the Mogden site to assess the seriousness of the problem. The upshot was that when the expansion of the works took place, subject to Hounslow planning permission, Thames Water installed new equipment to cover the main areas which generate odour.

S106 obligations dictate that any uncovered storm tank may not be used more than six times in a calendar year rolling 12 month period. However, it appears that all the storm tanks are in fact being used far more frequently.

Six of the eight tanks are uncovered and both Thames Water and Hounslow Council have attributed the majority of odour complaints to the use of the storm tanks. The lack of information on actual input flow on days when storm tanks are being used and / or input flow when sewage is diverted directly to River Thames led MRAG to petition the environment agency to bring about compliance with the DEFRA code of practice.

My understanding is that monitors have not as yet been placed near the open tanks, and as a consequence Hounslow Council cannot effectively monitor odour levels and issue the necessary Abatement Notices to effect compliance with the statutory provisions of EPA 1990.

While there are 13 odour monitors on site, designed to continuously record levels of H2S, several appear to be regularly out of order as documented in weekly site inspection reports.

The S106 agreement stipulates that odour monitor data for 6 of the 13 monitors should be uploaded weekly to Thames Water web page. For some reason this has been reduced to 5 monitors. The readings for 29 Dec 2014 to 11 January 2015 indicate that the south, west and east monitors were all out of order for this period. The two operating monitors (central and north) showed unacceptably high readings with the central monitor peaking well above the 0.015 trigger to 0.038ppm on 31 December, providing a very unwelcoming New Year atmosphere for local residents.

With the return of the warm weather this month, odour emissions yet again reaching intolerable levels across the surrounding residential areas.

I would at this time request that DEFRA seek a permanent solution to reducing odour emissions starting with the commissioning of a full odour elimination survey and installation of sufficient working odour monitors around the site's perimeter to monitor compliance with environmental obligations.

Yours sincerely.

Joe Bourke, Chairman
Email: Joe@hounslowlibdems.org.uk
cc: Brendon Walsh, London Borough of Hounslow, Regeneration, Economic Development and Environment Department.