Radon gas is not the serious health(serious is actually too intense) issue. The secondary gases that occur when radon decays are the problems. Most agencies say any adverse health effects from exposure to radon take decades to occur---and the exposure has to be almost daily. Also, there have been no studies done to prove/pinpoint radon damage. The figures and info have been accumulated through statistics and empirical evidence. In other words, it is an educated guess.

First, has testing been done and a radon problem verified? Testing is rather involved, since the better tests require at least three samples and the areas being tested have to remain undisturbed for a day or so.Radon testing There are basically two types of radon mitigation systems, active and passive. Passive systems almost need to be installed during initial construction. Active systems have a fan which produces a pressure differential under the slab compared to above the slab. That draws the gas into the fan plumbing and it is exhausted outside the house. "In many cases, simple systems using underground pipes and an exhaust fan may be used to reduce radon. Such systems are called "sub-slab depressurization," and do not require major changes to your home. These systems remove radon gas from below the concrete floor and the foundation before it can enter the home." From this article Installing the mitigation system($600-$2,000) requires sealing all slab intrusion areas and cracks if a positive test indicates a radon problem.

Radon levels fluctuate. So the 1.5 reading you got was the level reading right that minute (which is still very good by the way). We have had a radon mitigation system in our basement since 2004. We bought a meter that not only measures the reading at that minute, but also did a 30 day average. We recently finished our basement and had the mitigation company come out again and performed their old readings since the meter we bought was several years old. Turns out their readings were the same as what our meter showed. But in order to have more peace of mind, we had a new meter installed that has an app where we can look at an hour by hour reading if we so choose. It also does monthly averages. I will say since our basement has been finished, out readings are consistently right around 1, where before finishing they were around 1.5 to 2. The level before our mitigation system was installed was I believe 6. Edit to add that it also depends on what part of the country you live in. Colorado, for instance, has very high radon levels and you will likely never test below 1 no matter how good your system is.

Thanks for the response. So I plan on running an active radon system from the existing roughed in pipe, up thru the roof, with the radon fan in the attic. Our levels were in the low 20s so i think an active (fan powered) system will be necessary. Mainly I was asking if it makes sense/is good practice to use the drain tile as a means of collecting the radon gas, as this appears to be the intended purpose (verified by the builder) with what I have for existing rough in. The drain tile appears to stay dry by the way. I was expecting to see the pipe go directly into the dirt. I was surprised to see a tee at the bottom of the pipe. I didn't know that the drain tile can/should serve dual purposes. Would it make sense to install the system and then preform a test before trying to seal control joints/basin cap, etc?