Great West Radon did an excellent job of installing a radon mitigation system in our house, sealing all major gaps in our 70s home with the appropriate material (e.g., concrete, poly, caulking) to create adequate negative pressure. Within 48 hours we went from >200 Bq/m3 to <20 Bq/m3! We finally feel safe in our basement again.
GWR was great to deal with from the quote to installation; they were exceptionally professional and tidy throughout. They also did a good job of placing it so that it didnt take up too much space, which is precious in our house!