Sump-Crock Draw Points...

(This method is only viable with sump crocks using internal drain-tile!)

Sump crock venting, which draws sub-slab gasses from the sump crock through the internal drain-tile end openings, is a very effective technique for radon mitigation. It entails pulling gasses from the sub-slab by making a sort of central vacuum system out of the drain-tile that ends at the sump crock, where there's always a good “pot” of air to draw from. The drain tile carries a great deal of air or pressurized ground gasses under the floor and back to the sump crock, even during heavy rains.
Since we want to keep the system piping as short as possible to minimize fan resistance and maximize the fan’s performance, sump crock venting should typically only be considered if the mitigation will be run vertically, out the rim joist or wall, to a fan outdoors or in the garage. If the desired exit point isn't above the crock, the venting… in most cases, should be done through the slab instead, still connecting into the drain-tile at the desired point around the outer basement walls (see Basement-Slab Draw Points).

Two scenarios which fall outside of these considerations are homes built with cement drain-tile, and homes built in areas of high ground-water. As cement drain-tile was often used to drain a wet spot or problematic area under the slab, it often wasn’t run around the entire circumference of the inner foundation. In these situations, a floor or slab draw-point can be a “toss-up” whether drain-tile will be at the chosen location or not. It’s often not imperative to use the drain-tile in a mitigation, but it does help with “communication” or air-flow from around the entire foundation. If a foundation plan is still available for the house, it should detail where the drain-tiles were run.

High-ground water under the slab can be a huge issue, as water can often segregate a sub-slab by creating pockets of air under the slab that can’t be reached by a single draw-point. In these cases, a sump-crock draw point should always be considered as it tends to pull latent water in the drain-tile back to the sump-crock, helping to keep water/air pockets under the slab open, and help dry out the sub-slab soils.

Using slab or floor draw-points under these conditions can cause the system to draw water away from the sump-crock, hold and even build water content under the slab, and in many situations, cause “slurping” noises at the draw point as the water is pulled to the draw point and the system gasps for air intake.