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Radon Mitigation Abstracts
Abstract
This technical guidance document has been prepared to serve as a comprehensive aid in the detailed selection, design, installation, and operation of indoor radon reduction measures for existing houses based upon active soil depressurization techniques. It is intended for use by radon mitigation contractors, building contractors, concerned homeowners, State and local officials, and other interested persons.
This document represents a third edition of EPA's technical guidance for indoor radon reduction techniques. This document addresses primarily radon reduction techniques based upon active soil depressurization technology, which is one of the most widely utilized approaches for reducing radon in existing houses. The document also addresses active soil pressurization and passive soil depressurization techniques, because these less widely utilized techniques bear a number of similarities to active depressurization systems.
This edition incorporates additional and updated information on active soil depressurization techniques, reflecting new results and perspectives that have been obtained in this developing field since the second edition of EPA's technical guidance (EPA-625/5-87/019) was published in January 1988. Thus, this document should be viewed as replacing Section 5 ("Soil Ventilation") of the second edition.
This document does not provide guidance regarding indoor radon reduction techniques other than active soil depressurization (and active soil pressurization and passive soil depressurization). Persons interested in other techniques — including house ventilation, entry route sealing, house pressure adjustments, air cleaners, and well water treatment — are referred to the second edition of the technical guidance document.
Homeowners and occupants who are interested in a brief overview of the alternative radon reduction techniques available, and of the steps to follow in getting a radon reduction system installed in their home, are referred to the booklet entitled "Consumer's Guide to Radon Reduction," EPA-402-K92-003.
Abstract
A computational sensitivity analysis was conducted to identify the conditions under which residential active soil depressurization (ASD) systems for indoor radon reduction might most likely exacerbate or create back-drafting of natural-draft combustion appliances. Parameters varied included: house size; normalized leakage area; exhaust rate of exhaust appliances other than the ASD system; and the amount of house air exhausted by the ASD system.
Even with a reasonably conservative set of assumptions, it is predicted that ASD systems should not exacerbate or create back-drafting in most of the U.S. housing stock. Only at normalized leakage areas lower than 3 to 4 cm2 (@ 4 Pa) per m2of floor area should ASD contribute to back-drafting, even in small houses at high ASD exhaust rates (compared to a mean of over 10 cm2/m2 determined from data on over 12,000 U.S. houses). But on the other hand, even with a more forgiving set of assumptions, it is predicted that ASD systems could contribute to back-drafting in some fraction of the housing stock — houses tighter than about 1 to 2 cm2/m2 — even in large houses at minimal ASD exhaust rates. It is not possible to use parameters such as house size or ASD system flow rate to reliably estimate the risk that an ASD system might contribute to back-drafting in a given house. Spillage/back-draft testing would be needed for essentially all installations.
Abstract
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.
Re-entrainment 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/m3, the indoor contribution from eave exhaust re-entrainment may be only 20 to 70% of the national average ambient level in the U. S. (about 14 Bq/m3), while grade-level exhaust may contribute 1.8 times the ambient average. The grade-level contribution would drop to only 0.18 times ambient if the exhaust were 3,700 Bq/m3.
Wind tunnel tests 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/m3 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.