Concrete in biological septic system 1

[Newnorthman]

A supplier is proposing a concrete tanked system for a biological green system for a septic system.
Would such a system be able to be located in an area with a high water table without causing environmental problems.
The intake will be piped directly to the tank and the tank is divided into concrete chambers with the final output chamber holding a UV disinfection unit to ensure a final teatyment of effluent before release. I wonder about the porosity of concrete tanks. WILL THERE BE SEEPAGE THROUGH WHICH COULD CAUSE PROBLEMS OR WILL ANY SEEPAGE BECAUSE ITS THROUGH CONCRETE EFFECTIVELY BE RENDERED HARMLESS? I would appreciate any members comments on this.

 

[Muggle]

Concrete has been used for many years. Will you get seepage - very little if any, and this is usually stopped by microbial growth on the inside of the tank. I really think this is a non-issue - as long as the concrete tank walls are 4-6" thick.

Having said that - if your worried - have the inside of the tank coated with a water-based asphalt - Henry's Brand 107 I believe or #106. We've used this for over 25-years on concrete biological filters and fresh water rearing systems (including hatching tanks) - with no ill effect - and the coating will last virtually forever. Just make sure it's water-based asphalt emulsion. Make sure the concrete is dry - apply one thin coat, and let dry, then a heavier coat and let dry - then your done. Cheap, easy, and non-toxic.

 

[Newnorthman]

Thanks Muggle, your information was very helpful. The answer you say is that the seepage will be very minimal. Can you comment on the possibility of transferring any microbes in that little amount of seepage? Considering that there is a high water table around the area. Do you think its a problem. The tank is already built.
In future we will coat the inside as you say.

 

[semo]

As muggle said, any seepage is probably a non-issue.

If your groundwater table is high, there will probably be little if any seepage (even with a small crack). The water will tend to only seek transfer because of a lower water level on either side of the concrete separation wall. If the interior and exterior water levels are equal, the wastewater will be contained in the tank.

If any microbes make it outside of the tank, they should not pose a problem. If outside microbes make it inside the tank, they also should not pose a problem unless something volatile or hazardous in nearby (probably unlikely).

I would coat the tank, particularly outside with an asphalt emulsion. The interior can have various coatings to keep any seepage to a minimum. A coating can also be used that will span any small cracks. A bituminous coating will not necessarily do this. It seals the pores of the concrete; but, as it ages and temperatures change it can get brittle.

I would be more concerned with seepage from a process chamber into the UV chamber as you will want to keep that equipment dry. You might even want that in a totally separate tank with a sump pump and proper ventilation for added protection.

The concrete will have a longer lifespan with less potential for problems than will steel structures.

 

[gibfrog]

Hi All;

If the water table is within two feet of the bottom of the discharge pipe from the septic tank, I would be concerned about denitrafication of the effluent.

If the water table reaches the invert of the outfall of the tank, then groundwater may flow into the tank.

I have three 50 year old septic tanks in a high ground water area (less than 12" below grade during the rainy season). All the tanks are still water tight except the joints at the lid are not water tight.

Microbes normally exit a septic tank system under normal operation. The also exit a waste water treatment plant, hence the need for chlorination (or some other anti microbal treatment) of the effluent.


Clifford H Laubstein
FL PE 58662

 

[koodi]

Someone that works with reinforced concrete on a regular basis should have designed the tanks. For instance, a loading which might occur is the possibility of the ground water table rising while the tank was empty.

Muggles comment above is as credible as my comments about biological septic systems (there is no 4 to 6" gaurantee). I see concrete 12" thick with severe cracking on a regular basis.

Seepage will not be a problem as long as no large cracks develop. This is contingent on the RC design and workmanship.

 

[SanEnr1]

I concur with the previous suggestions; coat the tank if you are concerned about seepage.

Regarding cracks, pay close attention to your bedding conditions during construction to minimize this possibility. Consider sufficient stone and geotextile fabric to prevent settlement.

If you expect the tank to be emptied (for maintenance, inspection, etc.), make sure you consider the buoyancy of the tank. Additional weight may be required to keep it from floating.