A barrier between soil and living spaces is needed for effectiveness in creating a slight vacuum under the home. However: A substantial leakage area will exist undetectable to the eye regardless of meticulous sealing efforts.
Systems are still effective since soil air is pulled away from living spaces. Sealing of accessible, large openings to soil is typically a system component.

There is a minor energy penalty when air is pulled out of the home but major renovations to seal small cracks are not justified monetarily. Appropriate fan sizing aids this concern. For small sealed slabs, a very small fan can also be effective which maximizes all aspects of energy efficiency.

Sealing Items & Materials:
Sump cover: . . . . . . . . . . . . . . Customized from clear, non-breakable plastic.
Accessible floor-wall joint: Urethane caulking.
Tiny “hair line” cracks: . . . . .Typically not cost effective or meaningful.
Misc. cracks & openings: . . Caulk, expanding foam, mortar (as needed).
Drains that go to soil: . . . . . Air Traps. (a float prevents upward air flow.)
Open Earth: . . . . . . . . . . . . . . Poly sheeting over open earth and secured/sealed to walls.

DISCUSSION OF SEALING ALONE: .... “EPA does not recommend the use of sealing alone to reduce radon because, by itself, sealing has not been shown to lower radon levels significantly or consistently.”

Always unpredictable, sealing alone may sometimes reduce levels 10-50%. However, often little effect is seen (even if all gaps and openings are accessible to seal).

Responsible Sump Covers:

• Visual access to conditions in pit
• Removable port for arm access
• Anchored and sealed air tight
• Labeled
• Can hold the weight of an adult

These covers require a saw to gain access
when sump fails and flooding is immanent.

Other poor examples