Septic tank on old property, what to do

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25 Dec 2012 18:45 by amogles Star rating in El Campello (holiday.... 164 posts Send private message

One property that our estate agent has showed us, and that we like a lot, has a septic tank on the property. The property itself is about 30 to 40 years old and although it has been renovated more recently than that, the renovation appears to have been more cosmetic than functional and so we are budgeting if we buy it to do some serious work soon (and will be trying to negotiate the corresponding reduction in the asking price). One of the things that worries us is that the property has a septic tank in the garden. This is rectangular, about 2 meters by 2 meters in area and made of brick and is quite old (judging by the looks of it) and also huge, occupying a prime piece of real estate precisely in the middle of the garden where we'd like to make a terrace. It also appears to be extemely filthy and smelly inside and I doubt it fulfills present day environmental requirements. Maybe it even leaks (some of the bricks appear to be crumbling). The surface is made of concrete and has a manhole in the middle and is actually about 30cm higher than the rest of the garden so it's a bit difficult to work around. The present owner of the house is quite old and disinterested and doesn't appear to understand much about it and isn't able to answer our questions satisfactorily.

So we have been thinking of getting rid of this feature and connecting to the local sewage system at the earliest opportunity. One problem is that the property is lower than the adjoining roadway so presumably we would have to pump sewerage uphill. But in the long run not having a septic tank would be worthe the investment, especially if it falls fould of some laws (I don't know). I haven't talked to the neighbours but guess there must be sewers locally as it is in an urbanisation and many of the neighbouring houses are modern and well kept.

Any input? Is connecting to the sewerage system as easy as I think? And what about demolishing or filling in the septic tank? Any ballpark figures on who much I should be budgeting? Or is this type of installation perfectly normal and should we live with it?

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25 Dec 2012 20:23 by eggcup Star rating. 567 posts Send private message

One option would be to get the old brick thing demolished, choose a better spot for a septic tank and get a 'maquina' in to dig a deeper hole and put in a new septic tank - they could fill in the old hole at the same time.  We bought a light-weight two-chamber septic tank recently for about 800 euros.  I've no idea about the logistics of the alternative idea you have of pumping sewage.  We have connected a house to the mains sewage system in the past, and it wasn't expensive, but we didn't have your problem of gravity.  All the best.


My account of moving to Spain."><img


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26 Dec 2012 09:03 by GuyT Star rating. 457 posts Send private message

I am no plumber, but have a lot of hands on, or hands in, experience of a septic tanks. I know more than I ever wanted to learn. No matter what size a builder tells you to install, double or treble it. If need be string a couple of tanks in series. The problem is that the average 3000 litre tank cannot cope with the amount of water a modern house uses, with people showering, dish washers, washing machines, etc. I suspect the ones one sees in builders yards were designed in an era where people bathed once a week and had no appliances. My wife and I use well over 600 litres a day for domestic use. (2 or 3 showers flattens 300 litres). So what happens is that the tank fills up to overflowing. This raises the waters above the compartment baffles and mixes up the sludges, liquids & crusts. This destroys the way septic tanks work. There is also no way that - using normal amount of perforated pipes - that you can dissipate 600 litres of liquid a day underground into your garden. Imagine emptying a bath into your septic tank - and how long it would take to seep away through pin holes.

Pumping sewage uphill sounds like an expensive challenge.


If one has the space and a little money, the best way forward is to have a separate pipe sytem for all your gray water (washing water, etc) . This way, nearly all the water you use can be used to irrigate or just allowed to run off your property. Only the toilet flushes then need to be processed - and a small septic tank can handle this.



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26 Dec 2012 13:36 by amogles Star rating in El Campello (holiday.... 164 posts Send private message

 Thank you all for your input. This has helped put my thinking into some sort of direction. I especially like the idea of separating grey and toilet water, as especially in Spain any extra water in the garden cannot be a bad thing.

How does one dissipate grey water? Surely it contains things like detergents that might do more harm than good? Can one just run a pipe into the garden and let it flow into the soil? Or are there devices you can buy to handle this?

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26 Dec 2012 14:26 by GuyT Star rating. 457 posts Send private message

 Plants seem to like detergent. The best way to dissipate the water would be to dig shallow sloping trenches and install drain tile. The more extensive your reticulation the more efficient it will be. But you are right, you kill two birds with the one stone. You have far less sewerage to manage, and lots of irrigation water.

Looking at eggcup's post, you must remember that the deeper you site your septic tank, then the even deeper you will have to site your run-off pipes. Once you get a few metres below surface level be prepared for impermeable rock strata and very compacted soil which isn't what you want unless you are prepared get in a Cat D10 and cross-rip. 

btw. The final "water" that comes out of a septic tank, is clear, doesn't smell at all, and  isnutrient rich. (urine is a high quality source of nitrogen/fertiliser. urinating near plants if both good for them and very eco-friendly, though my wife doesn't see my point of view). If you go to any vivero and ask them to sell you reeds, you can plant a couple of these near your soak away area - they grow like crazy and keep the area dry.

I've just googled  they show all sorts of septic tanks - 4800 litre/16 person ones, eg, but they neglect to explain what happens when 16 people have a shower in the morning, flush the loo, clean their teeth, etc...........the tank would be half full and that's before the daily clothes washing, dishwashing.........hold on, it's lunchtime and everyone's back from the swimming pool and wanting another would need - from my experience - over 100m of drainage, and even then I think your output would overtake it......and then everything would back up into your house. a gray water system would solve this problem. 

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