You need to seal the basement if there are cracks in the basement. I would like to recommend to install a radon fan in the basement if the reading is above 200. You can do it DIY or have somebody install one for you. You can search online to find video to watch to know how to do it yourself. I ordered the fan from amazon.ca. Or you can order fan and install kits from www.radondetect.ca. I bought install kits and monitors from that web site. Now the radon level drop below 20. If you need more info, I can share.