Experimental study of effectiveness of four radon mitigation solutions, based on underground depressurization, tested in prototype housing built in a high radon area in Spain

The present paper discusses the results of an empirical study of four approaches to reducing indoor radon concentrations based on depressurization techniques in underground sumps. The experiments were conducted in prototype housing built in an area of Spain where the average radon concentration at a depth of 1 m is 250 kBq m−3.Sump effectiveness was analysed in two locations: underneath the basement, which involved cutting openings into the foundation, ground storey and roof slabs, and outside the basement walls, which entailed digging a pit alongside the building exterior. The effectiveness of both sumps was likewise tested with passive and forced ventilation methods.The systems proved to be highly efficient, lowering radon levels by 91–99%, except in the solution involving passive ventilation and the outside sump, where radon levels were reduced by 53–55%. At wind speeds of over 8 m/s, however, passive ventilation across an outside sump lowered radon levels by 95% due to a Venturi effect induced drop in pressure.

► This experience can help to delimit effectiveness of this kind of depressurization solutions because all of them has been tested in the same radon exhalation rate conditions and in the same building. In this sense this paper constitute an original work and even more if we note that initial radon concentration were very high, in order of 40 kBq m−3 in the basement
► Radon reduction up to 300 Bq m−3 from 40 kBq m−3 (initial conditions inside the building)
► The systems proved to be highly efficient, reducing radon levels by 91–99%, with the exception of the outside sump-natural convection combination, where rates declined on the order of 53–55%
► The effectiveness of the sump located outside the basement walls rose by 40 percentage points (from 53 to 93%) when forced rather than passive extraction was used.
► The natural convection extraction systems proved to be 40% more effective at wind speeds of over 8 m/s.