Observations of Pressure Differentials and Air Flow Rates Associated with Indoor Radon from Two Passive Radon Mitigation Vents in an Extended Gravel-bed Foundation-type Large Building

Discrete and continuous measurement of indoor radon concentrations, air flow rates, and pressure differentials for passive and active operational configurations of a passive radon control system were performed at the Biotechnology Research and Development Facility of the University of Florida, in Alachua County, Florida. The system was installed during construction and incorporated an extended six-inch gravel bed underneath the entire foundation slab with upper and lower surfaces covered by reinforced polyethylene sheeting and vented by two vertical four-inch diameter metal vent pipes extended through the building roof. Pressure differentials were measured between the radon passive mitigation pipes and the outdoors and across mitigation pumps installed during the experiments. Air flow rates were continuously and simultaneously monitored at the radon vent pipes for different configurations of the building use. Measurements were performed using sensors that were integrated into an on-site data-logging system. Average indoor radon concentrations were reduced from above 4 pCiA to approximately 3.5 pCV1 with concentrations exceed 4 pCiI1 is some area, with only one system vent operating. The concentrations are further reduced by 36% with both vents operating. Concentrations are reduced by approximately 70% with a suction fan installed on one of the system vents while the other vent left capped. Evaluation of the measurement results for different testing configurations, and recommendation for aspects to be observed for designing similar passive radon mitigation systems are presented.