Tampon rainwater with aerial tank

[mathieus62]

Hello everybody

I allow myself to post my questions here, because I did not find a recent topic on this forum discussing my questioning recently.

I recently bought a house, supposed to be up to standard in terms of sanitation, but which is not really in reality ... I have the separation of used water / rainwater, but without being up to standard for the organization in charge of sanitation control in my neighborhood, which imposes the following standards:
- Buffering of rainwater up to 3000l minimum for my 90m² of roof
- Until the 3000l are collected, the water must be poured back into the public EP network at a flow rate of 2 liters per second maximum
- Then, we can pour rainwater back into the network in real time

Obviously, I do not have enough space for a buried tank: 4 meters in front of the house, 4 meters behind, and I don't want to dig too much
close to the foundations to avoid risks.
I am not a handyman very much, but I took to the game to find a way out of my problem. I finally proposed to this organization a system with two "aesthetic" overhead tanks (Roman column 2000 liters from Garantia for example), having the chance to have two gutters, one under each half of the roof. I was told it was possible.

Being sensitive to ecological and economic subjects, I see here the advisability of recovering rainwater at a lower cost at the same time as bringing it up to standard at this level:
- I take two tanks of 2000 liters. Each being connected to a gutter
- I keep the first 500 liters for personal use (car wash and garden watering for the moment)
- I make a gutter connection at 1/4 of the height of the tank, with a rigid PVC pipe correctly calibrated to have a flow of 1 liter per second on each tank (2 liters per second cumulated on the two tanks)
- I connect a collector at the top of the tank, with overflow function, which pours all the rainwater back into the tank until it is filled (despite the flow of 1 liter per second on the outlet at 1/4 height) , then let the water pass directly into the gutter

I have various questions regarding the technical implementation of this system, and I hope to find answers here.

- What are the prerequisites at ground level under the tank, apart from flat ground? Do you need a concrete base?
- Do you have "aesthetic" overhead tanks to recommend with a minimum capacity of 2000l? Or opinions on "Garantia Roman Column" tanks of this capacity?
- Are there gutter collectors that collect all the water flowing in the gutter to put it in the tank, with overflow management, and with tap (to cut in case of frost)? I think I have actually seen gutter collectors of this type, but I am really taking advice!
- Have some of you already made specific rigid PVC connections, whether for a "leakage flow" on the gutter, or to connect two tanks together? If so, how did you seal it all off every part? Rubber seal, specific product, ...?
- I think that the periods of frost in my department could be dangerous for an overhead PVC tank. So I looked on the net, but didn't find a lot of solutions. Most of the time this is either putting empty bottles and / or polystyrene in the tank, or emptying the tank and shutting off the collector during periods of freezing, which may not please the organism in charge. of control. Are there natural and non-toxic products that could be added to the tank to counter the effects of freezing? The "natural and non-toxic" side being first and foremost an ecological imperative for me, especially if I then run off part of this product in the network when the tank fills up.


A big thank you for reading this long message, and also thank you in advance for your answers!

[Ahmed]

Technically, your installation does not pose any particular problem and your choice of a device with a calibrated flow and an overflow in the upper part is wise.
Regarding the preparation of the soil on which the tank will rest, everything depends on the constitution of this tank; let's start from the principle that it is a plastic model: in this case a small thickness of fine sand will ensure it a good base (take care to eliminate any stones present near the surface).
The aesthetics can be improved at low cost with a covering of narrow planks and not necessarily contiguous (arranged vertically); it is also possible to use various climbing plants to hide the tanks.
The gel is not so worrying that the rectangular tanks can easily deform and elastically absorb the increase in volume; it is indeed possible to add submerged compressible elements; note: large volumes will have a hard time freezing completely in your ocean climate.
In terms of connections, you will not find anything ready-made, because you have to adapt to the particular case; this is easy with PVC pipes and fittings; everything sticks easily, but it is not essential to stick everything to allow easier cleaning interventions: simply nested, the connections are sufficiently tight, given that it is evacuation (therefore very low pressure ) and that possible seepage of clean water is not catastrophic outside the house.

[sicetaitsimple]

I do have the sewage / rainwater separation, but without meeting the standards for the organization in charge of sanitation control in my neighborhood, which imposes the following standards:
- Buffering of rainwater up to 3000l minimum for my 90m² of roof
- Until the 3000l are collected, the water must be poured back into the public EP network at a flow rate of 2 liters per second maximum
- Then, we can pour rainwater back into the network in real time

Hi,

I don't have much to add to Ahmed's answer, however I am really surprised (to say the least) by these regulations!

Because 2l / s of discharge authorized from the start of the rainy episode is 7,2m3 / h, i.e. for a 90m2 roof with 80mm / h precipitation!

An absolutely exceptional thing, in other words that in any case the 3m3 of "reserve" would be filled almost immediately.

What corner are you in?

[mathieus62]

Good evening to you,

Thank you very much Ahmed for the answers, it really helps me with the gel and the sand!
Regarding the rigid PVC junction between tank and gutter, I was thinking of a rubber gasket to hold indefinitely. The oozing annoys me a little because the front tank will be close to the house, so any impact on recent foundations if too much infiltration in the soil as and when?
The rear tank does not pose too many aesthetic problems for me, it is more that of the front for which I have very few alternatives, the subdivision regulations being very restrictive ...

Thank you very much "sicetaitsimple" also, this nickname is so suited to my current situation
I am in the Bethunois, and roughly I am in a city in which a river poses problem in strong rainy episodes. My subdivision is recent, and the rainwater from the network being discharged into this river, the organization in charge of sanitation requested the implementation of this buffering to avoid causing too rapid flooding of the river.
Indeed, 2l / s for 90m² of roof, I also find that enormous (and inconsistent). To my knowledge, all roofs have the same authorized flow of 2l / s, it is the quantity to be buffered which varies (3000 to 10000 liters of memory). In fact, they had to determine that X dwellings x 2 liters for every second could be absorbed by the river, and beyond that there is a risk of flooding. And from there, they must have been like "with or without the water from the subdivision, it will be flooded anyway".
This is where my knowledge of the situation is, as absurd as it is ...

Regarding the collector to put on the gutter, do you have any to recommend to ensure the "complete" collection of the water flowing into the gutter (as long as the "overflow" is not activated) please?

[Did67]

Because 2l / s of discharge authorized from the start of the rainy episode is 7,2m3 / h, i.e. for a 90m2 roof with 80mm / h precipitation!

An absolutely exceptional thing, in other words that in any case the 3m3 of "reserve" would be filled almost immediately.

What corner are you in?

I think the problem is different:

- the water drainage pipes had to be calibrated to ensure a certain flow

- there is a very curious thing, which one very often ignores (hydraulics is a strange science): in free load (if one does not pump!), an almost full pipe delivers much more than a full pipe; So a curious thing happens: it flows, it flows, the level rises and when it "hits the top", the flow becomes lower, and upstream, the system is put under pressure ... We see the vents of 'sewers that spit water; in the cellars, the water rises, etc ...

- it is therefore relevant to "buffer", up to a total flow on a network slightly lower than this capacity at which it saturates and puts itself under pressure ...

- in a stormy episode, it can be 5 or 10 minutes of very intense rain which triggers this ...

- and this can be solved very easily with the buffers - because indeed, as you say, the intensity of 2 l / s, if it can occur for 5 or 10 minutes, will last only very very exceptionally 1 h ! Because there, it will be anyway the "natural disaster"!

[sicetaitsimple]

This is where my knowledge of the situation is, as absurd as it is ...

That's saying something!

Because if we look at some sites, for example this one:
https://www.infoclimat.fr/climatologie/ ... 07015.html

we realize that the maximum rainfall in your area is not 80mm / hour as calculated above, but rather 50mm / day!

Even if these 50mm are concentrated over an hour, with a roof of 90m2, it remains below the 2l / s authorized.

In short you do nothing and you are good, you systematically respect the maximum authorized rejection value!

[mathieus62]

Thank you Did67 for this very pedagogical answer, in the form of a lesson in hydraulic behavior!

It helps to understand the constraints of the body in charge of sanitation. Even if as indicated in my previous message, I clearly put that on the fear of a flooded river, the problem actually seems larger than that!


Indeed sicetaitsimple, I had also seen statistics in the genre, and by smoothing I was far without setting up a tamponade. The rules being "it is necessary to put a tamponade of X thousands of liters" and "to deliver a maximum of 2l / s to the parcel", I had anyway the need to set up a tamponade. I also had quotes made for basement tanks, but near the foundations and in front of the garage (for lack of anything better), the quotes were quickly inflated, and the risks too high for my taste ... In short, with Did67's answer, I see another problem than that of the river flood, and it immediately becomes more consistent in terms of regulations!

[sicetaitsimple]

I think the problem is different:

I had not seen your answer, you may be right, I just wanted to say that these regulations are inconsistent. If the discharge rate had been set at 1l / s for example instead of 2, it would already have more meaning.

In any case I am willing to bet that if our friend installs his two tanks of 2000l with an overflow calibrated to 2l / s from 500l, never this one will be a day full!

[Ahmed]

Mathieu62, you write:

Regarding the rigid PVC junction between tank and gutter, I was thinking of a rubber gasket to hold indefinitely.

Another solution than simple interlocking is the use of screw fittings which guarantee both sealing and the possibility of disassembly. The range of fittings is extremely wide and allows multiple combinations. For this reason, you have to study your project on paper and carry it out in the simplest *.
A "tip": to respect the insertion angles of the different elements, make blank assemblies (for the delicate parts) and mark with a felt-tip pen or pencil the correspondence of each pair of elements, in order to glue the parts in the right position (you cannot "correct the shot" too much when gluing, because the setting is very fast and, as much as possible, it is necessary to fit straight).

* The connections are quite expensive and the hydraulics do not adapt well to tarabiscotés circuits.

[Gaston]

I do not have much to add to what has been said above apart from paying attention to the lifespan of the tanks exposed to the sun.

Also note that they are generally not made of PVC but of polyethylene, which slightly complicates bonding at the level of tank outlets.