ANSWER: Improperly installed radon mitigation system vent.
This is a picture of the fan and exhaust vent for an active radon gas mitigation system. When a home is tested for radon and found to have a high level, this is the type of system usually installed to fix the problem and remove the radon gas.
The problem with this one is that it was not installed by a trained/certified/licensed company. This vent pipe is barely more than 3 feet above ground level. So the vented radon gas, which can be at a VERY high level, is easily re-entrained into the home through the lower openings such as windows, doors, and outlets.
This is easily fixed by having a qualified licensed radon mitigation contractor extend the vent pipe so it extends at least one foot above the roof line, allowing the radon gas coming out of that vent pipe to dissipate safely into the atmosphere. Luckily this is not a big expense...assuming the inside part of the installation is OK.