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  1. #1
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    Default Distance between borehole and septic tank

    Hi all
    There are probably differing municipal regulations, however what's a good practice minimum distance between a borehole and septic tank on a farm? Also does the depth of the borehole have anything to do with it?

    Google couldn't help much, I see anything from 10m to 30m in some countries, but can't find anything SA specific.
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    Default Re: Distance between borehole and septic tank

    My opinion: as far as possible. Bacteria can penetrate an aquifer. I've heard as far as 100m.
    Last edited by jelo; 2021/10/24 at 11:07 AM.
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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by jelo View Post
    My opinion: as far as possible. Bacteria can penetrate an aquifer. I've heard as far as 100m.
    The borehole and the aquifer are 2 different things, the aquifer could be 50-100m underground and over a very large area so I doubt any septic tank contamination will directly reach that far down?

    I'd thumbsuck and say somwhere in the range of 20-40m from the borehole should be fine, depending on what kind of underlying substrate there is, there are many variables to take into account.

    Also would probably be good to know how the local ground water drains into the aquifer and try place the septic tank in a location that will put it out of the way of any ground water flow.

  4. #4
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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by jelo View Post
    My opinion: as far as possible. Bacteria can penetrate an aquifer. I've heard as far as 100m.

    If I had a choice my head also says as far as possible.

    What I actually want to know here is whether there's a point where you steer clear of buying a place if you see that the borehole and septic tank is a certain distance apart. Or at least bargain on having to drill a new hole and then maybe only using the old hole for irrigation or something.

    This hole is maybe 40, 50m away from the septic tank if that far, it wasn't drilled too long ago and I don't think it's something the owners even considered when they drilled.

    I say that because it almost looks like they were lazy when drilling a new hole, as if they didn't want to drill a bit further from their house, they probably told the guy with the stokkies that he better find water within their yard.

    I don't know much about boreholes, but in my mind a bigger pump, more pipe, more cable will be worth the expense if you find good water some distance away over finding mediocre water on your doorstep.
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  6. #5
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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by bigboy529 View Post
    If I had a choice my head also says as far as possible.

    What I actually want to know here is whether there's a point where you steer clear of buying a place if you see that the borehole and septic tank is a certain distance apart. Or at least bargain on having to drill a new hole and then maybe only using the old hole for irrigation or something.

    This hole is maybe 40, 50m away from the septic tank if that far, it wasn't drilled too long ago and I don't think it's something the owners even considered when they drilled.

    I say that because it almost looks like they were lazy when drilling a new hole, as if they didn't want to drill a bit further from their house, they probably told the guy with the stokkies that he better find water within their yard.

    I don't know much about boreholes, but in my mind a bigger pump, more pipe, more cable will be worth the expense if you find good water some distance away over finding mediocre water on your doorstep.
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  8. #6
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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by Prof View Post
    Hulle dra jou goed weg as dit ver is....selfs naby....

    Ek het leeus oom, hulle gaan 'n ###### surprise kry as hulle eenige iets wil weg dra.

    Yes I know this is a factor, but it's in a big 5 game reserve which mitigates the risk quite a lot. They only have opportunistic petty crime, nothing serious from what I've heard from owners who has been living there for 20 plus years.
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    Default Re: Distance between borehole and septic tank

    Clarify Septic/Conservancy tank or a soak away. Septic or conservancy makes no difference where you put it. With a soak away on the other hand is a major problem. Regulations does say not within 300m of a water way or river. Underground water is fairly much an unknown.

    We have ground water at 2m from the surface in winter on the farm. Soak-aways are just not allowed here. If I had the slope, I could try proove that my soak away is in fact an evaporation field. But then it has to have a sealed bottom isolating it from the enviroment and any ground water supply. Thats kinda a mix of municipal rules and our own rules we have applied on our farm on the West Coast.
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  11. #8
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    Default Re: Distance between borehole and septic tank

    French drain is a soak-away. Have the borehole tested for potability. That's the only real test.
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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by jelo View Post
    French drain is a soak-away. Have the borehole tested for potability. That's the only real test.
    Do this anyway - check with the ;ab as regards the procedure and timing to sample and transport, particularly for e coli; I don't have that much experience but you will almost always pick up some. Luckily treatment is simple and cosy effective (chlorinator, uv light etc). Last test I did cost around R2 500 for more or less all the drinking water parameters which are as per the SA General Standard.

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    Default Re: Distance between borehole and septic tank

    Nobody without a crystal ball (or a Geotech armed with a multitude of borehole log sampling) will be able to give you a definitive answer. Even then soil sampling may vary and test results could change over time with seepage and bla bla.

    Rather assume that the water may have some contamination and get a simple treatment goodie as Mudgrubber suggests.

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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by mudgrubber View Post
    Do this anyway - check with the ;ab as regards the procedure and timing to sample and transport, particularly for e coli; I don't have that much experience but you will almost always pick up some. Luckily treatment is simple and cosy effective (chlorinator, uv light etc). Last test I did cost around R2 500 for more or less all the drinking water parameters which are as per the SA General Standard.
    Water test should be around R1k
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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by bigboy529 View Post
    Ek het leeus oom, hulle gaan 'n ###### surprise kry as hulle eenige iets wil weg dra.

    Yes I know this is a factor, but it's in a big 5 game reserve which mitigates the risk quite a lot. They only have opportunistic petty crime, nothing serious from what I've heard from owners who has been living there for 20 plus years.
    well this sounds awesome! Buying a place in a big 5 reserve? Very very cool.

    in terms of distances, it really depends on a lot of stuff. Geology for one.
    also, if itís up gradient of the septic tank youíll have a better chance as well.
    As has been mentioned, the only way might just be to do regular water testing.
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    Default Re: Distance between borehole and septic tank

    There cannot be a thumbsuck rule. It depends on the geohydrology of the area. Most important is the nature of the aquifer e.g. primary or secondary. Ideally you should not have a soakaway close to an aquifer.

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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by Kobus P Venter View Post
    There cannot be a thumbsuck rule. It depends on the geohydrology of the area. Most important is the nature of the aquifer e.g. primary or secondary. Ideally you should not have a soakaway close to an aquifer.
    Yep. The septic cannot be uphill from the borehole.
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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by jelo View Post
    Yep. The septic cannot be uphill from the borehole.
    Do you think gravity knows where the hill is below ground?
    Last edited by Facts; 2021/10/24 at 04:29 PM.

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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by Facts View Post
    Do you think gravity knows where the hill is below ground?
    in some cases.
    but more often than not groundwater flow direction is the same as topography. In SA at least.
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  22. #17
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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by Facts View Post
    Do you think gravity knows where the hill is below ground?
    Yes. In general, the water flows downhill in an aquifer.
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    Default Re: Distance between borehole and septic tank

    The septic tank is not the issue. The run off from the septic tank is key and must be away from the borehole. Also feed off to a well structured French drain - our farm one is 4metres x 2.5mts x 3 mts deep. Have a water spreader at the mouth of pipe where it enters. The best is drill holes 6mm along the length and close off end
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    Default Re: Distance between borehole and septic tank

    Quote Originally Posted by Facts View Post
    Do you think gravity knows where the hill is below ground?
    Yip. The water table mimics the surface.
    Also, when you extract water from the hole, recharge is mostly gravity feed. So a septic tank at a higher elevation will be able to feed towards the hole.
    Last edited by RoelfleRoux; 2021/10/24 at 05:17 PM.

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  26. #20
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    Default Re: Distance between borehole and septic tank

    Thanks all for the advice, my first step was going to be to get the hole tested and then also the water along with it to see what is what.
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