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Question DetailsAsked on 10/17/2016

a small amount of water runs into my leach tank from my septic system. I have shut off all sink and toilet valves.

I also shut off the main water shut off valve. Where can this water be coming from?

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2 Answers



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Answered 4 years ago by Member Services


I am a bit confused - do you mean the septic tank is getting backflow from the leach field, or your manifold box in the leach field is getting flow from the septic tank, or septic tank is getting flow from the sewer line coming from the house ? Terminology issue here I think - you say running into your leach tank (I presume you mean septic tank) from your septic system - do you mean from your leach field (part of the septic system) or from the sewer pipe leading from the house ?

1) Even if you shut off the main water shutoff valve, you would have to open the lowest elevation faucet (other than boiler or hot water tank drain) to see if it actually shut off all the way or not - older main shutoff valves commonly leak a fair trickle when full off. If you open lowest elevation drain/faucet/hose bib and let any water trickling through run into a pan or bucket or hose leading outside (anywhere but into sewer line), that would stop any water from leaking appliances or fixtures from going into the sewer line. IF that stops it, then water is not coming from your fresh water system EXCEPT if you have an exterior water line leak getting into the sewer line or tank.

2) If you mean water coming down the house sewer pipe into the septic tank, commonly that is a running toilet - try some food coloring in the tank and see if it leaks into the bowl. Course, if you have shut off and are trapping any water in 1) above, this flow would stop once you flush the toilet because it would not refill the tank/bowl.

3) If you have high groundwater, leaks around the inlet pipe where it enters the tank are common, as are outlet end leaks, especially in concrete tanks where the pipe is usually grouted in rather than using a bolted or welded fitting as with metal or plastic/fiberglass tanks. With real high groundwater it can sometimes leak in the access hatches or around a vent pipe too if not sealed tight.

4) If you have high groundwater or there has been a lot of rain or irrigation watering, the water table in the leach field can be higher than the outlet of the septic tank, causing backflow into the tank from the outlet pipe till it levels out or drains down the elevated water level in the leach field.

5) If your leach field is above the septic tank and you have a septic lift pump, its backflow valve could be failing to close all the way, letting leachate run back from the leach field into the tank when the lift pump is not running.

6) If you have a water pipe leak in the area, it can saturate the leach field or tank area and run back into the tank or the leach field - through outlet pipe or any other leak in the tank.

7) if coming down the sewer line from the house, could also possibly be from a sump pump (intermittent flow), or if continuous flow occasionally an infrequently used floor drain (like in laundry room or basement) may have a trickle feed of water piped to it to keep it from drying out - just a small tube coming off a small valve on a pipe nearby usually, running continuously.

8) rare, but a few (mostly very higher end) reefers have a flushing and drain feature to keep the water and ice fresh - flushes water through the system periodically, down a drain leading to the sewer line. Ditto to fancier automatic coffee makers and espresso units.

9) Intermittently, but continuous if the backflush cycle valve or timer has gotten stuck, is a water treatment/filtration/softener system, dumping the backflush/self-cleaning cycle water down the drain. Ditto to hot tub, pool, etc that does that sort of self-cleaning cycle.

10) trickle water feed with drain to automated house plant or greenhouse watering system or aquarium (typically only with much higher end systems) - or sometimes drains under aquariums or indoor/patio planters or such draining away overflow

11) leaking water feeds ending up in drain from sauna, hot tub, jacuzzi, indoor fountain or water feature overflow drain, etc.

12) trickle drainage (intermittent and usually very low flow amounts) can also be from dehumidifier or air conditioner drainage into sewer line

13) rarely, a french drain or basement under-drain will be legally or illegally plumbed directly to the sewer line (if at higher level than septic system) and drain to the tank.

Answered 4 years ago by LCD

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