Radon is always heavy in the PA/MD area. Our old house in rural MD was so bad it had to have a fan installed to blow it out.
My current house in southern NH had radon air and water in excess of the recommendations. We split the cost of the remediation equipment with the sellers. It was about five grand for both. Our water level was extremely high. The house was built in 1972. The previous owners had lived there for 25 years. Radon is prevalent around here. It is very common in NH granite bedrock.
The air systems are installed in almost every new construction house. It is just a four inch PVC pipe that goes down under the concrete floor in the basement. It then has to go up to the roof line and away from Windows at its termination. You also want the pipe to be on the prevailing down wind side of the house. They install on inline fan that runs 24/7.
The water bubbler is a much more expensive piece of equipment. It runs about $3500.
Common in Minnesota, too.
Would it have anything to do with increased real estate sales? They were boom times. Radon testing is usually done when a house is sold.
The homes are built on Indian burial grounds..... beware!