C.S.Os (Combined Sewer Outflows)

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    There is every reason for us to be concerned that in the 2020s – well over a century since the UK developed effective wastewater-treatment processes – we still discharge raw sewage at a high frequency into The Teifi. How do we stop it? And are we prepared to make stopping it a priority?


    It appears that not all that stinks in a river is sewage! This is such useful information I have reproduced it here…

    In response to a fb post in ‘St Dogmaels Positive People Posts’ on 22-Dec-22 which was follows:

    “My most positive hope for the New Year is that sulphurous PONG that hangs over the village and Cardigan again today gets identified and dealt with before more harm is done. If you have any clues, message me, please.

    Piers Partridge replied …

    “In reply to St Dogmaels Local Producers’ Market, I’ve been looking in to this and, Yes, it’s a distinctly gassy smell, but probably not methane which is odourless. We’ve been getting this smell when there have been no sewage releases so it is also probably not sewage. Most likely it’s Hydrogen Sulphide, which has the classic rotten egg smell, and is coming from agricultural slurry, or waste. The gas is heavier than air so will travel downhill and settle on the river bed. People then think the river is the source of the smell, which confuses the issue. My reading suggests that there are certain modern bedding additives and food supplements given to cattle which change the chemical makeup of slurry and if not managed properly can create the release of Hydrogen Sulphide.

    It’s not harmful to human health if you can simply smell it, but being able to ‘taste’ it, as some people have reported suggests it is above safe levels. Please message me if you experience that or any other information you might have.”

    Many thanks to Piers for his research into this.


    More details from Piers….


    We were thrown off the scent, so to speak, because the terrible pong fitted with our impression of what bad sewage should smell like. And it seemed to be coming from the river. The smell of muck spread on a field is, in our minds, a very different , more animal smell. We were wrong. The smell is almost definitely coming from badly managed farm slurry.

    I’ve been looking into it and it is almost certainly Hydrogen Sulphide, H2S, the classic rotten eggs smell. It occurs at low levels in cattle manure but certain bedding materials and feed will increase the level. Someone asked about methane, but that is an odourless gas.

    Because Hydrogen Sulphide is heavier than air it will sink from the farms and into the valleys onto the rivers. The smell then seems to be coming from the river. This has caused some confusion and explains why Dwr Cymru were unable to find any of their assets malfunctioning.

    There are a number of issues that can cause elevated Hydrogen Sulphide levels in slurry.  Possibly the main one is poor mixing/stirring practise in the slurry tanks. You can read up on this at https://www.nidirect.gov.uk/news/stay-safe-when-mixing-slurry if you wish to know more.

    Also things like:

    1.     Gysum Bedding (often reclaimed from waste plasterboard). Highly absorbent and ‘drying agent’ in slurry management.

    hse.gov.uk :

    “There is clear evidence that the presence of gypsum in slurry will enhance the potential for generation of toxic H2S gas. The levels of the gas produced, even from the small, contained systems, would be toxic to anyone exposed to equivalent concentrations on a larger scale. Therefore, if gypsum residues enter slurry this could increase the risk of H2S gas accumulation in confined spaces in the close vicinity of slurry systems. It is important therefore that this is taken into account in managing risk.”

    1.     Distillers grain diet.

    Distillers grain diet:

    Cattle fed wet distiller’s grain had higher fecal and urinary sulfur excretions than control cattle not fed distiller’s grains (Spiehs and Varel, 2009). Although these authors did not measure hydrogen sulfide in their study, they conclude that it is likely that increased hydrogen sulfide would result from cattle being fed wet distiller’s grain.

    There may be other elements in the management of cattle which are causing these H2S releases, but without talking to the farmers, we won’t be able to find out. Insufficient

    Hydrogen Sulphide is an extremely toxic gas, and even at low levels can cause respiratory difficulties and skin reactions.

    “At low concentrations (less than 1 ppm), hydrogen sulfide is an irritant with the odor of rotten eggs. At higher concentrations, however, it deadens the sense of smell, often immediately, making detection difficult (Donham et al., 2006; Doss, Person and McLeod, 2002; Hooser et al., 2000). Abrupt exposure to amounts of greater than 500 ppm of hydrogen sulfide has killed humans; exposure to 200 ppm of hydrogen sulfide has killed swine. Extended exposure to lower amounts of hydrogen sulfide has also resulted in a range of symptoms from eye irrita- tion to respiratory illness to uncon- sciousness (Donham et al., 2006;”

    Anecdotal evidence on a recent Facebook thread about the smell, included villagers saying they could both smell and taste the Hydrogen Sulphide. This suggests the release is above safe levels.

    It would be interesting to get readings done ‘at source’. If it can be smelt throughout such a wide area, it’s possible that ‘at source’ there is a high concentration, which may well be hazardous to workers on that site.

    We might get quite low readings away from the source and be told that it is not hazardous to humans. The question then is whether a local community is willing to put with this degree of pollution in an area known for the good quality of its air.

    A bright and helpful person NRW rang me in response to my ‘incident log’ about the odour in St Dogmaels recently. She said they are aware of the situation but that anything odour based is a County Council issue and not one they are empowered to investigate. She pointed out that in order to the  the CC to act we need to get as many people as possible to log their complaint (with time and location). I will chase this up unless anyone else already has done so, or is planning to.

    As milk prices fall, the only way farmers can maintain income is to increase herds sizes and milk production so they are cramming more cattle into their winter sheds. Many cattle spend their entire lives in these sheds and are fed a cocktail of additives to maximise their yield and keep vets bills to a minimum. Managing the waste from these oversized herds with limited available agricultural land means that slurry tanks fill faster and need to be emptied more frequently. Quite a lot of farmers are pumping direct from the tanks onto the same available land. The good old days of grass fed, spillage fed cows producing a not unpleasant slurry smell are over, and instead we have shed farmed cattle producing a slurry that smells industrial.


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