Growing veg above old septic tank

[Leif]

At the bottom of my garden there is a disused septic tank (actually two concrete tanks from what I can see) and a drain field. The soil above is about 1 foot deep, and each tank is about 6 foot wide, and square, with a now open whole in the middle where the access cover was, and filled with mainly flints, and some soil. Over one I intend to grow a quince tree, and I think it will be able to establish roots over and around the tank, and into it via the access hole. I have dug the area over the drain field (where the outflow discharges) and I would like to grow fruit veg, specifically rhubarb, blackcurrants, perhaps jerusalem artichokes, beetroot etc. Could there be issues with diseases from the soil? The tanks have been out of use for ~20 years. The soil is curious. There is a lot of heavy clay and chalk bits near the surface. Below this there is some really lovely looking dark brown, almost black, soil, with a lot of small flints. It is very crumbly, and with no smell. I suspect it is enriched from the outflow. Could this have been clay that has broken down? Or was it originally different from clay?

Anyway, as I've said, my main concern is safety, and the possibility of diseases. I suspect faecal bacteria would be long gone, but what about viruses? Presumably anything picked above ground such as rhubarb is fine, but what about root veg?

Is anyone else in a similar situation?

By the way, the reason for cultivating this area is that it is at the bottom of the garden, away from the main sewer and a drain pipe from the road, hence I can grow things like a quince safely without worrying that roots will damage pipes. It also means it does not eat into the main lawn area, and is somewhat sheltered as there is a 2m fence nearby.

[darcyvuqua]

Sorry I have no idea I think this is a very interesting question though I can't wait to see the answers from the experts

Good luck pal

[Bigmallly]

Although I have not read the article, it may be relevant to your post.

Can Sewage Pathogens & Contaminants Appear in Fruits and Vegetables Grown Near Septic Drainfields?

[Leif]

Although I have not read the article, it may be relevant to your post.

Can Sewage Pathogens & Contaminants Appear in Fruits and Vegetables Grown Near Septic Drainfields?

Thank you. That confirms my suspicions that an active septic tank and drain field can contaminate fruit and veg grown on the overlying soil. The question then is how long do the pathogens survive in the soil after the septic tank has been put out of use?

I suppose one option is to send soil samples to a health laboratory for analysis.

[Leif]

To answer my own question, it looks like pathogens, both bacteria and viruses, as well as organisms such as parasitic worms and their eggs, cannot survive long, and usually 6 months will clear them all:

weblife.org: Humanure Handbook: Chapter 7: Persistence of Pathogens in Soil, Crops, Manure, and Sludge

So 20 years should be more than enough.

[snohare]

I would be surprised if sending off soil samples would be able to give you peace of mind.
The reason I say this is that although faecal coliform bacteria and most pathogens that live in sewage are likely to be long gone - they live in very specific circumstances in terms of pH and nutrients, once these change they are competing at a disadvantage against untold trillions of other bacteria, moulds and viruses - there are a few that may persist (I'm thinking of Mycobacterium avium paratuberculosis, which is not a proven pathogen but is in the running, and lives naturally in groundwater); and it would be a brave soil scientist indeed that would say to you, "Oh, you'll definitely be not catch anything". Legally and scientifically that would be well dodgy, because what percentage of the organisms would you have sampled ?
That said, unless you know of any specific outbreaks of disease, I really would think that the soil wouldn't be contaminated with any nasties, or at least nothing that you wouldn't potentially get in any other soil - like I say, the odds are tremendously against it after all this time. Me, I'd be looking at that lovely dark crumbly soil and thinking of all the wonderful things it will grow me...

[Potstubsdustbins]

I agree with Snohare but without the scientific expertise just common sense.

Is there any piece of land near human habitation that hasn't been pooped on etc in the last 200 years I doubt it very much. At one time human waste was used as fertilizer and in some parts of the world still is.

Nature has a way of taking care of the problem be thankful you have good fertile ground and get growing.

Colin

[Leif]

Thanks all.

Snohare: What you say makes a lot of sense, i.e. change the food supply, and hence the environment, and the micro-fauna/flora will change to suit, with the natural soil organisms taking over.

And as Colin says, what land has not been pooped on. There is probably more risk from the badger and fox poop that pops up on my lawn (so to speak) from time to time. Yes human poo - treated - is sometimes used on food crops but I think UK legislation bans its use on human feed crops, or applies some regulations to minimise the possibility of contamination with faecal bacteria etc.