The best solution is to install a perforated pipe below the slab or the soil in the crawl space. Run this vent out your roof and install an exhaust fan to depressurize under your slab.
Is your house 100% basement or is there some crawl space area? If there is some crawlspace, it should be fairly simple to retrofit this system.
Adding an exhaust fan in your crawl space could help as well.
- Since you have an all foam insulated house (very tight construction) it is very important to have fresh air ventilation through an HRV or something similar.
- Although dilution is not the best solution for radon it can be extremely helpful for low quantities.
For more information:
Read "Why aren't more builders building homes with radon-resistant construction techniques? They fix radon and lower moisture!" a Q&A answered by Ray Pruban.