Radon reduction in crawlspace foundations can be done by Green Radon & Remodeling using either sub-membrane depressurization or crawl space depressurization.

Sub-Membrane Depressurization

To help make other radon reduction techniques more effective and cost-efficient, the air pressure found on a crawl space floor may be lowered by placing a heavy plastic sheet on the ground, as a gas retarder membrane. Then the air pressure accumulated in the crawl space may be relieved and expelled safely outdoors by drawing it out from beneath the membrane with the use of a fan-powered vent

Crawl Space Depressurization

This method lowers air pressure in a crawl space relative to indoor air pressure by use of a fan-powered vent drawing air from within the crawl space.

With this system a 6 mil poly sheet is laid over the floor of the crawl space and sealed to the foundation walls and any penetrations.  A 3" pvc pipe is connected and routed to the radon fan either in the attic above or outside and vented above the roof.