Quick background first.
I chose to build a passive house using an insulated foundation system.
This means that all my soil pipes etc. leave the house through the floor.
This ultimately means that the pipes are much lower than standard 2 - 3 ft before they make their way to the septic tank.
The setup is that waste is gravity fed from the house to a septic tank. Planning was granted a long time ago so yes it's an actual septic tank.
The effluent leaves the tank again by gravity and feeds into a holding tank.
This tank contains a pump with a float switch.
When the float hits a certain level the pump kicks in and drives the effluent up to the percolation box.
I discovered over the last week that due to springs etc. caused by the weather etc. that both tank (holding and septic) are leaking ground water where the soil pipe enters the tanks. This has resulted in the pump running frequently and saturating the percolation area. We came within a couple of showers of backed up toilets!
So I got the track machine back on site to dig and we exposed the pipes. We also had a pump keeping the water level down so that we could attempt a reseal.
The photo below sums it up.
You can see the pipe linking the holding tank and septic tank fully submerged. I will say that at the time of this photo I was very pleased. Neither tank was leaking any water so I'd successfully sealed both. I used one of those new snag list emliminating sealants which allegedly even seal under water.
This evening I am deeply frustrated to see that after back filling the joints have failed again. The backfilling must have moved the pipe and broken the seal. They are much better than the were a week ago but I want them fully sealed.
Can anyone advise as to how this is normally done. I appreciate that my circumstances are not typical.
My current next move is to empty the tanks entirely and attempt to seal the tanks from inside i.e. no more digging and hence eliminate the risk of breaking the new seal.
Note: there is no option to draw the area around the tank to somewhere else. Due to all the above,we're simply too low in the ground and have no where to drain it to without using a pump.
All thoughts hugely appreciated or recommendations (by PM) on anyone that resolves such issues.
You sure that this is your problem? The tanks are sound, moreover, the connections of the PCC risers?
I assume you have the internals of the tank outlet (T's) constructed properly.. If so, given the nature of the pre cast tank, outlet heights and the fit around the 4" pipe should be VERY tight, therefore very little "spill", if any. Even expa-foam would suffice to seal pipes.
From the pic there appears to be no protection to the outlet pipe to sump. Granular fill to side/top of this before backfill would help.
Very hard to tell without actual visual inspection. Best thing to do is get someone on site who knows (AT/Eng) what they are talking about otherwise you will just be digging it out time again.
I'd be thinking of a bitumen sealant as it will adhere well and maintain a good degree of flexibility. We've used it to seal slurry tanks and never had any bother since.
As for the high water table round the tanks I think I'd be digging down well and backfilling with clean stone to soak away as much water as possible. The idea of a sump with solar pump comes to mind to keep it down but I've no idea as to how good these pumps are.
Since the water table in your site seems so high you might want to rethink the size of the percolation area. With a high water table percolation is badly affected. I've had this in the past and during extended wet weather it may just back up anyway, maybe now you have the digger in look at extending it.
The supervising Engineer was on site on friday morning and suggested sealing around the pipes with a sealant such as the one I used.
Water ingress around the pipe is definitely the problem. The holding tank has a pump which empties it. When it's empty the water could be seen streaming over\around the pipe entering it. It's very obvious.
The risers are above the water level on site so it's not that on this occasion. I've pretty much stood looking into the tanks for 2 days. The surface of the water in them can be seen being disturbed etc. so it's obvious where the water is coming from. We also lowered the level in the 2nd chamber of the septic tank below the outlet pipe in order to allow us to see if water was streaming in there too and it was.
The tank was installed following the details of the supplier. The fit around the pipes isn't very tight. I was there when it was put it. It took some effort to get the pipe in but it was far from perfect in my opinion.
I wasn't aware that expanding foam is water proof. With respect, is this a proven solution or theory? I'm dubious of the many miraculous uses of expanding foam.
Then entire tank including pipes was backfilled with clean 20mm chip. This is part of the problem. It's allowing the spring to bubble up too easily. The hole behind the tank in that pic is 3 foot deep. It fills from empty in about 4 hours. We emptied the water again before backfilling.
Eng. was on site as you recommended.
In the pic, we had dug the hole, emptied it and then I applied the sealant. It was left over night. The pic is from the next morning i.e. I believe this to be as bad as the water level will get.
When we installed the tank we were down about 9 ft with no sign of ground water. This may be a temporary condition given how bad the weather has been. It will also be an ongoing problem too though if the weather is a factor.
My main concern is the percolation area being overwhelmed i.e. ground water gets into holding tank, pump drives it into percolation area. This is what happened over the last 2 weeks on a couple of occasions. I'm going to try and determine this morning how long it takes for the tank to fill and pump to kick in.
My secondard concern is the electricity usage of pump kicking in alot more often than planned. I haven't looked at the specs for the pump though so can't determine the cost on that yet.
Thank you for your suggestions.
Will look into this.
The entire tank was back filled with stone. The stone allowed the water to enter easily. When we started digging were were around 4 foot from the edge of the tank and down 4 - 5 ft . No water at all. Then we broke through to the stone around the tank and it flowed through. We could see a couple of springs rising as we dug. Solar pump would be an interesting idea but may not be much use i.e. in wettest conditions we also get little sun.
Percolation area is already substantial. I didn't scrimp here. It was built to the letter of the law. I stood over them as it was done with regs in hand. The base of the stone in the percolation trenches is about level with the water level in the pic. So unless there's upward soakage, that may not be the biggest contributor to this.
If it was me, and I'm not an expert in this area, I would backfill (gravel and rock) the area between the two tanks with the pipe removed to about 1 foot below the level of the pipe inlets.
I would then construct a sealed shuttering box on top of this about 1 foot square so that the pipe will run through the box and connect both tanks.
Use a good quality sealing product to seal the box at its joints and either end.
Use a good quality sealing product to seal the pipes into both tanks (make sure the tank inlets are dry).
Once the sealant has had the correct amount of time to dry I'd either back fill the shuttering box with concrete or use a fine sand that you could remove if the sealant fails at a future date.
My logic on the concrete is the water won't seep into the openings around the tanks even if the sealant fails.
Best of luck with the problem.
I had the same problem , what we did was dug a big soak pit deside the tank filled it with large rubble broken blocks ect and took a pipe from the pit all the way to the land drainage ditch . No problem since . Note the hole was larger and deeper then the tank
Thanks, I'd been considering something along this line. Basically shuttering a 'u' shaped concrete section joining the 2 tanks with the pipe floating in that. Basically with stone\sand. Concrete is too permanent for me.
The problem for me is that the area is prone to springs so I could simply dig and uncover another one which would fill the soak pit rendering it useless.
We're simply too low in the ground. If we were at the typical height for a septic tank this issue simply wouldn't be occurring. I need to accept the water and try and keep it out of the system I reckon.
The amount of water getting in now may not be terribly significant. It's certainly alot less than a week ago.
I'm going to monitor the percolation area and sump tank on an on going basis.
If I need to take further action I'll consider options then.
Hope I misread that.
You dug a soakpit for effluent runoff and then drained it to a ditch?
Jebus. Who gave you that bright idea
If I took you up wrong, apologies in advance but if not, christ......
I came across a similar situation a few years ago where the treatment unit was basically put into a "hole" on the site. It was located in the only part of the site where the surrounding ground was falling towards the tank on all sides thus ensuring that there was a continuous flow of surface water running into the tank.
The pump was basically running 24/7 and while there was an option to dig around the tank and back fill with stone and pipe this to a lower part of the site where there was an open drain the ground levels were going to remain the same.
As the unit was placed about 5 metres from where it was supposed to go and as there was a good decent fall from the house we got the suppliers/installers back again and got them to remove the inlet pipe, lift the tank out of the ground completely, fill the hole with 1 metre deep of stone and then blinding and place the tank back on top of this.
Effectively the tank was raised by a metre which left the float above the highest level of surrounding water but the site levels allowed for this and that may not be applicable in the current situation.
Unfortunately the tank is already as high as possible while maintaining the recommended falls from the house. Even if we went for planning again there isn't anywhere else on the site that the tank could be placed while meeting the regs re distances from drains, boundaries, the house itself.
The issue is that the pipes leave the house about 800mm below finished floor level of the house due to the insulated raft.
Having discussed this with the engineer this morning, we're confident that sealing the tank in position is the only way to go. The how is up for debate. He's recommending bitumen or preferably concrete. My concern with concrete is that if that fails, there's no going back.
just had a quick look at the percolation test results for that site....
T = 10
and the test was done in april !
I've no idea what this means. Site was bought with OPP so I don't know if any shenanigans were involved because I didn't do the test.
Is there any possibility of draining the water away from around the septic tank. Can you post more photos of site. What size is the site. Is the site flat? Can you post site layout drawing - section drawing.
It may be that the T-Values are correct for percolation area - If this area is not giving trouble?
It could be that in digging the hole for the tank you disturbed a confining layer of clay over a aquifer? However there can be any number of reasons why something doesn't work. Can i get a look at the site assessment?