United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-90/016 Jan. 1991
&EPA Project Summary
Investigation of Radon Entry and
Effectiveness of Mitigation
Measures in Seven Houses in
New Jersey
C. S. Dudney, L M. Hubbard, and T. G. Matthews
Little previous work on radon
mitigation strategies has involved
detailed, continuous monitoring over
long periods of time in occupied
houses. With permission of the
owners, seven houses in New Jersey
were studied for 7 to 10 months.
The houses selected all had
basements that were partially or
completely below grade on all four
sides. Premitigation radon levels
were between 20 and 200 pCuL.* The
principal focus of the project was
understanding pressure-driven flows
of radon-laden gas into the
substructure of basement houses.
During the 7 to 10 months the
houses were studied, radon
concentrations, temperature,
pressure, and weather data were
continuously logged, and a variety of
experiments were performed to study
soil and building dynamics. This
report describes the results of these
measurements and how they relate to
pressure-driven flow of soil gas into
and through these residential
structures. The report also describes
design, implementation, and
refinement of radon mitigation
systems for these houses.
The principal findings of the study
are:
(1) Reversal of the pressure gradient
across the basement slab in
these houses resulted in a
dramatic, rapid decrease in
indoor radon levels.
(2) Diagnostic examinations of
possible radon reservoirs as well
* 1 pCi/L =37 Bq/m3.
as air flows and pressure
gradients resulting from applied
depressurization under the base-
ment slab were most important in
designing a successful subslab
depressurization system for
radon mitigation.
(3) Occupant behavior can
substantially perturb the forces
driving radon entry. The most
important factor in this regard is
the operation of the fan in the
central air handler.
(4) A time series analysis failed to
reveal consistent cross
correlation between radon in the
living area and such factors as
radon in the basement,
temperature differences, or
pressure differentials.
This Project Summary was
developed by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle Park, NC, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The discovery of residences with
indoor levels of radon far in excess of
those equivalent to federal limits for
occupational exposure to short-lived
progeny of radon have raised public
concern for a better understanding of
radon entry processes and how best to
reduce radon entry. Many
epidemiological studies have shown that
the incidence of fatal lung cancers among
miners in underground uranium mines
Printed on Recycled Paper
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increases according to cumulative
exposure to short-lived radon progeny.
Radon has been shown to enter
houses by several pathways or
mechanisms. The most important
pathway for detached, single-family
dwellings in most regions of the U.S. is
thought to be pressure-driven flow of soil
gas into the substructure.
Pressure-driven flow of radon may be
influenced by: (a) the rising of warm air
through the interior volume of the
structure, (b) the impact of wind on the
exterior shell of the building which results
in high pressure relative to indoor
pressure on one side and low pressure
on the other three sides, (c) falling
atmospheric pressure which may result in
a transient condition in which soil
pressures exceed pressures"above
ground or in the house, and (d) heavy
rainfall which may act as a
piston.compressing soil gas beneath the
surface layer in the soil.
Procedure
House screening and final selection
were completed by August 1986. A copy
of the questionnaire used in the house
sefectipn process is given in the report.
An instrument package was developed
by the Oak Ridge National Laboratory
(ORNL)/Princeton team and calibration of
the instrument packages was completed
by late October 1956.
Nearly continuous, premitigation
baseline monitoring was. conducted from
mid-October to mid-December 1986. The
premitigation diagnostic studies were
performed between mid-November and
the end of December 1986. These
studies included measurements to
characterize the -entry of radon into
structures and potential control
measures. Diagnostic measurements
were continued in selected houses
through the winter and spring of 1987 to
improve mitigation efficiency.
The selection and implementation of
mitigation measures in the study houses
were commonly divided into two major
phases: Phase I mitigation measures
~were"1nstalled -pTincipally"between~mid~
December 1986 and mid-January 1987,
and Phase II mitigation measures were
installed and refined over a period of time
from January through May 1987.
After installation and refinement of the
mitigation system, the performance of the
system was studied in several ways.
Subslab systems were operated in
pressurization, depressurization, and
passive modes. Tracer gases were used
to evaluate the energy penalties
associated with the installed slab
depressurization system.
C. S. Dudney, L. M. Hubbard and T. G. Matthews are with Oak Ridge National
Laboratory, Oak Ridge, TN 37831-6285
David C. Sanchez is the EPA Project Officer (see below).
The complete report, entitled "Investigation of Radon Entry and Effectiveness of
Mitigation Measures in Seven Houses in New Jersey," (Order No.
DE89016676; Cost: $39.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Spring field, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering^ Research Laboratory —-— -- —
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Results and Discussion
The concentration of radon and radon
progeny in indoor air depends on
generation and transport of radon from
radium-bearing materials to the indoor
environment and the characteristics of
indoor aerosols. The report discusses
gamma radiation surveys, geological
survey results, radon in well water, radon
progeny measurements, and time-
weighted-average radon measurements.
The rates at which air moves among
the various compartments of a house
strongly affects the spatial and temporal
distribution of radon. Data discussed in
the report include measurements of
building leakage using blower doors and
measurements of air exchange using
.^£tlyje_aj]^passiy_e_j^
systems.
Conclusions
Subslab ventilation is the most positive
and effective means for reducing indoor
radiation levels in detached, single-family
basement houses.
The effectiveness of subslab
ventilation is greatly increased by sealing
the basement slab to the wall.
The central air handling system
significantly affects radon entry into
structures.
United States
Environmental Protection
Agoncy
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
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EPA/60Q/S7-90/016
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