The volumetric activity of the radon isotope 222Rn in quarries mined for stone building materials within gabbro-dolerite intrusions of the Onega Palaeoproteozoic structure in the Kondopozhsky and Prionezhsky Districts of the Republic of Karelia was studied. Also, changes in the activity were explored along the highway running along the southwestern shore of Lake Onego, considering the known geological faults and uranium ore occurrences in quartzite sandstones of the Shoksha and Petrozavodsk suites. Volumetric activity measurements were conducted using the Alfarad+ ARP system outdoors and indoors by counting alpha decays in an ionization chamber during 20 min exposure. Experimental data were obtained using the techniques certified for such systems. Radon isotope measurements were taken in open spaces of active quarries before and after blasting. The results suggest there is a connection between the seismic impact on the rock massif and changes in 222Rn concentration in the air. We have also detected outlier concentrations of 222Rn, which can be associated with the known uranium content of rocks in the studied area.