I am in the middle of building my ICF basement. My footer was poured on stone, and when it rains, water is getting into my hole, and runs under my footer, down my trench, and out the exit where the drain tile is. I obviously have an exterior drain tile installed, but until backfilling it doesn't collect any water (tile drains to daylight). I also ran a perforated pipe inside my footer to connect later to a passive radon vent stack. However, If this water can get under my footer, then air should also be able to get under my footer. This would prevent me from having any negative pressure, sucking the radon up and out, right? What are my options for fixing this problem? - use a high-end radon barrier below the slab, trying to be 100% air tight? - Forget the passive system pipe (laid inside the footers) and put one of those vent motors on my daylight drain, which a waterless trap? (I saw this on a passive-house blog, cat find the link again)

Not sure I followed, but a check valve on the drain pipe? Ie water can go out, but outside air can't come in.

Yes something like that, I hadn't heard of them before, but here is the link:
http://www.hepvo.com/

I also could put a P trap in the outlet pipe I guess, not sure if that could get clogged though.

Here is the original blog I read about this on! Found it:

http://www.jeromelisuzzo.com/?p=916

I don't see why letting outside air in is a bad thing for the system to work. I don't remember anything in the code against it. That saying "the solution to pollution is dilution"....you would just be diluting the radon. Is the entrance of the air close to where your radon stack connects? I would think to have as much space as possible is best. Do you have to install the pump or only if it fails. The only bad thing I see is letting lots of air in will cool your slab.

More flow also creates less pressure, perhaps not adequately depressurizing some areas underneath the slab. Same with a powered fan - too many air leaks and you need a larger fan, drawing more power.

Perhaps a 4" backwater valve? Verify that it closes when no water is present (ie, isn't float based).

Well, yes, I am worried that the passive radon system wont work with the footer drain letting air come in. That's my understanding of how those systems work at least.

Therefore if I have a radon problem, putting a powered vent on the stack still wont be the solution because of my footer drain again letting air in.

So, is the solution to have a powered vent running on the footer drain itself, and not using a radon stack at all?!?! I have no idea really.

Is there any super air tight product one could put under the slab to avoid radon completely?

I would put a taped/overlapped barrier under the slab regardless. IRT RADON, a barrier under the slab will help direct any gas that comes up mid slab outward toward where the vent piping is located instead of percolating up thru the slab.

As Jonr suggests, put a flapper valve on the daylight footing drain to limit air being drawn back in thru that drain...

Radon is definitely a concern of mine (granite mtn property). Radon is heavier than air and can penetrate concrete. A good vapor barrier beneath the slab (and foundation) prevents the radon from entering the habitat. If the foundation leaks water, I think the radon (if it cannot enter the abode will go through the footer and outside. Unfortunately, you cannot test for radon until the structure is built. If the structure is built, the cost of radon reduction is higher, unless, as you are doing, reduction is planned before construction is completed. Since your walls for the basement are in place, they represent your biggest radon risk (in my limited understanding).

It is logical that basement walls also present radon risk (like the slab). In new construction it might make sense to include wall depressurization. If post construction testing indicates that there isn't much radon, then the air flow can easily be reduced or disabled.

Even low levels of radon cause some number of deaths - there is no safe level that doesn't increase cancer rates. In a high radon area, I'd serious consider not having a basement. With the advent of FPSF foundations, I'm not sure they ever make sense.

Couple of thoughts on soil gas
New Canadian codes have a whole section on it and it is now mandatory to install an air barrier under the slab and to provide a rough in that can be used to depressurize the slab should the indoor AQ exceed Health Canada's spec's.
The air barrier spec's require a minimum of 6 mil poly. 9.25.3.6 CAN/CGSB-51.34-M.

The argument for uniform adaptation of this code requirement is that it is cheap to do at time of construction and expensive to do after construction.

Kind of makes sense except that as radon is a by product of granite degradation, it would not be need in many parts of the country.

If you put washed drainage rock under the slab, all you need to do is put in pipe so you can evacuate air from the center of the slab area should it become necessary. It does not have to be connected to anything. Its there if you need it.

If you are considering putting in a passive stack, it should be all in the heated area of the house if you live in cold climate. If to much of the pipe is exposed to cold, the falling cold air could pressurize the under slab and actually make things worse.

For OP
Instead of daylighting the drain pipe, consider dumping into a drainage stone filled drywell with about six inches of soil over it. This will limit reverse air flow and will also prevent rodents from entering the pipe.
If left to daylight, wind pressure could pressurize the underslab and force radon up into the house.

As the radon is heavier than air, it is unlikely to enter by way of vertical walls. Also basement walls should be sealed on the outside with some sort of waterproofing that will act as an air barrier. In areas of known high concentrations of radon, consider putting drain board (dimple material) against the concrete to provide an air gap. Also consider using Fast Form or similair liner under the footings.

FPSF foundation would not necessarily negate the radon risk as you still have concrete in contact with the ground.