It is a passive rough-in, common in newer construction. The pipe relies on natural stack effect alone and often does not reduce levels enough on its own. Test the house, and if it is above 4.0 pCi/L, adding a fan activates the system cheaply.
More detail
A passive system is a pipe run installed during construction from beneath the slab, up through the house, and out the roof, with no fan. It relies on the natural stack effect of warm air rising in the pipe to draw a small amount of soil gas out. Builders install them because the rough-in is inexpensive while the slab is open and the walls are framed, and because some jurisdictions require it in designated zones. What a passive system does not do is guarantee a result. Reduction from stack effect alone is modest and varies with weather and season. Plenty of homes with a correctly installed passive pipe still test above 4.0 pCi/L, which surprises owners who reasonably assumed the pipe was the solution. The good news is the expensive part is already done. Converting passive to active means installing an inline fan on the existing pipe run, adding a manometer, and confirming the discharge point meets standard. That is a fraction of the cost of a full retrofit, because nobody has to core the slab or find a pipe route through a finished house. So the sequence is simple: test the house rather than assume. If the result is under 2.0 pCi/L, the passive system is doing its job and no fan is needed. If it is above 4.0, activate it. If it lands between, the decision is yours, and the EPA suggests considering mitigation in that band. One detail worth checking on a new build: that the pipe actually terminates above the roofline and not into an attic, which does happen and is not a functioning system in either mode. Passive rough-ins are concentrated in the newer subdivisions across Franklin, Delaware, Licking, and Fairfield counties, installed either to code or from builder habit. If your house is in that group and has never been tested, the presence of the pipe tells you nothing about the current level in the house.