Re-entrainment and dispersion of exhausts from indoor radon reduction systems: Analysis of tracer gas data

Tracer gas studies were conducted around four model houses in a wind tunnel, and around one house in the field, to quantify re-entrainment and dispersion of exhaust gases released from residential indoor radon reduction systems. Reentrainment tests in the field suggest that active soil depressurization systems exhausting at grade level can contribute indoor radon concentrations 3 to 9 times greater than systems exhausting at the eave. With a high exhaust concentration of 37,000 Bq/m(3), the indoor contribution from eave exhaust reentrainment may be only 20% to 70% of the national average ambient level in the U.S. (about 14 Bq/m(3)), while grade-level exhaust may contribute 1.8 times the ambient average. The grade-level contribution would drop to only 0.18 rimes ambient if the exhaust were 3, 700 Bq/m(3). Wind tunnel rests of exhaust dispersion outdoors suggest that grade-level exhaust can contribute mean concentrations beside houses averaging 7 times greater than exhaust at the eave, and 25 to 50 times greater than exhaust midway up the roof slope. With 37,000 Bq/m(3) in the exhaust, the highest mean concentrations beside the house could be less than or equal to the ambient background level with eave and mid-roof exhausts, and 2 to 7 times greater than ambient with grade exhausts.