RMB Papers and Reports Since Last Update

Reports Since Last Update:

“Testing of Indoor Radon Reduction Tech-
niques in Central Ohio Houses: Phase 2
(Winter 1988-89),” Findlay, W.O., A.
Robertson, and A.G. Scott, submitted to EPA
by Acres Intemational Corp., EPA-600/8-
90-050, May 1990 (NTIS No. PB90-
222704).*

“Testing of Indoor Radon Reduction Tech-
niques in 19 Maryland Houses,” Gilroy, D.G.,
and W.M. Kaschak, submitted to EPA by
CDM Federal Programs Corp., EPA-600/8-
90-056, June 1990 (NTIS No. PB90-244393).
“Radon Mitigation Studies: Nashville Dem-
onstration,” Pyle, B.E., and A.D. Williamson,
submitted to EPA by Southern Research In-
stitute, EPA-600/8-90-061, July 1990 (NTIS
No. PB90-257791).

“Interim Radon-Resistant Construction
Guidelines for Use in Florida—1989,” Pugh,
T.D., submitted to EPA by Florida A&M
University, EPA-600/8-90-062, August 1990
(NTIS No. PB90-265349).

“Engineering Design Criteria for Sub-slab
Depressurization Systems in Low-perme-
ability Soils,” Fowler, C.S., et al., submitted
to EPA by Souther Research Institute, EPA-
600/8-90-063, August 1990 (NTIS No. PB90-
257767).

“Investigation of Radon Entry and Effective-
ness of Mitigation Measures in Seven Houses
in New Jersey,” Dudney, C.S., et al., submit-
ted to EPA by DOE/Oak Ridge National
Laboratory, EPA-600/7-90-016, August 1990
(NTIS No. DE89016676).

“Identification of Candidate Houses for the
North Florida Portion of the Florida Radon
Mitigation Project,” Roessler, G.S., et al.,
submitted to EPA by University of Florida,
EPA-600/8-90-070, September 1990 (NTIS
No. PB90-274077).

“Summary of EPA’s Radon Reduction Re-
search in Schools During 1989-90,” Leovic,
K.W., prepared in-house by EPA, EPA-600/
8-90-072, October 1990 (NTIS No. PB91-
102038).

“Testing of Indoor Radon Reduction Tech-
niques in Basement Houses Having Adjoin-
ing Wings,” Messing, M., submitted to EPA

by Infiltec, EPA-600/8-90-076, November
1990 (NTIS No. PB91-125831).

“Follow-Up Annual Alpha-Track Monitor-
ing in 40 Eastern Pennsylvania Houses with
Indoor Radon Reduction Systems (Decem-
ber 1988-December 1989),” Scott, A.G., and
A. Robertson, submitted to EPA by American
ATCON, EPA-600/8-90-081, November
1990 (NTIS No. PB91-127779).

Symposia Presentations:
“Building HV AC/Foundation Diagnostics for
Radon Mitigation in Schools: Part 2,” Leovic,
K.W., D. B. Harris, and A. B. Craig, pre-
sented at Indoor Air 1990, Toronto, Canada,
August 1990.

“Planning for Quality in Radon Mitigation,”
Ford, J. S., and B. Harris, presented at Indoor
Air 1990, Toronto, Canada, August 1990.

“Radon Diagnostics for Schools,” Leovic,
K.W., A. B. Craig, and D. B. Harris, pre-
sented at 83rd Annual AWMA Meeting,
Pittsburgh, PA, June 24-29, 1990.

* All reports with NTIS members are available
(prepaid) from the National Technical Informa-
tion Service, 5285 Port Royal Road, Spring-
field, VA 22161 (phone 703/487-4650).

Region 1

(CT, ME, MA, NH, RI, VT)
JFK Federal Building
Boston, MA 02203

(617) 565-4502

Region 2

(NJ, NY)

26 Federal Plaza

New York, NY 10278

(212) 264-4418

Region 3

(DE, DC, MD, PA, VA, WV)
841 Chestnut Building
Philadelphia, PA 19107
(215) 597-8320

Region 4

(AL, FL, GA, KY, MS, NC, SC, TN)
345 Courtland St. N.E.

Atlanta, GA 30365
(404) 347-3907

eoece ooe
Radon Hotline Number bd
1 (800) SOS-RADON :

eeeescccocscccccccce

5

EPA Regional Offices

Region 5 Region 8

(IL, IN, MI, MN, OH, WI) (CO, MT, ND, SD, UT, WY)

230 South Dearbom St. 999 18th Street

Chicago, IL 60604 Denver Place, Suite 500

From IN, MI, OH, MN, and WI Denver, CO 80202-2405

(600) 621-8431 (303) 293-1709

From IL Region 9

(800) 572-2515 (AZ, CA, HI, NV)

Region 6 Sun Francisco, CA.94105

(AR, LA, NM, OK, TX) ( 415) 744.1045

1445 Ross Avenue

Dallas, TX 75202 Region 10

(214) 655-7223, (AK, ID, OR, WA)

Region 7 1200 Sixth Avenue
Seattle, WA 98101

(IA, KS, MO, NE) (206) 42-7660

726 Minnesota Avenue

Kansas City, KS 66101 EPA Headquarters

(913) 551-7020 401 M Street $.W.
Washington, D.C. 20460
(202) 475-9605


tions and soil gas flows through slab test
holes, in determining the number and loca-
tion of active subslab depressurization (ASD)
suction holes. Findings suggest that pipes for
ASD systems should be located along the
perimeter of slabs and only at areas of rela-
tively high radon entry potentials. The model
also suggests that three or fewer properly
placed suction points will often reduce in-
door radon levels to below 2 pCi/L, even in
problem houses.

Radon Prevention in New
Construction

Building Radon Mitigation into Inacces-
sible Crawlspace New Residential Con-
struction; B. Harris and A.B. Craig,
Project Officers, and J. Haynes. Oral Pa-
per

Single, duplex, and quadruplex buildings
were constructed utilizing a below-grade
wood floor construction over an inaccessible
crawl space due to highly expansive soils.
Initial studies demonstrated the need for
complete sealing of the floor system until a
negative pressure could be maintained under
each corner of the floor (at least 2.5 Pa).
Early measurements indicated radon levels
of about 100 pCi/L in the unmitigated craw]
space. Tests in the first buildings completed
showed all units below 2.5 pCi/L except for
one unit where the depressurization fan had
been tumed off. This unit measured 16 pCi/L
and dropped to below 2.5 pCi/L when the
fan was activated.

The Effect of Subslab Aggregate Size on
Pressure Field Extension; A.B. Craig,
Project Officer, and K. Gadsby. Oral Pa-
per

The effects of particle size and particle size
distribution on sub-slab pressure field exten-
sion (PFE) were evaluated using laboratory
tests simulating conditions existing under
slabs. Findings indicate that PFE is propor-
tional to the average stone size (the smaller
the stone size, the less the PFE), the stone

size distribution (the narrower the stone size
distribution, the greater the void volume and
hence the PFE), and the shape of the stone
(the smoother the shape of the stone, the
lower the void volume and hence the PFE).

Preliminary Results Of HVAC System
Modifications To Control Indoor Radon
Concentrations; T.M. Dyess, Project Ofmi-
cer, and T.M. Brennan. Poster Paper
Preliminary testing in one energy-efficient
house indicates that residential forced-air
furnaces can be used to pressurize basements
and prevent radon entry. By adding a supply
air duct in the basement and modifying the
HVAC unit to nm continuously on low speed,
300 cfm of air was supplied to the basement
maintaining +4 Pa relative to outdoors. The
average radon levels dropped from 14.3 to
1.2 pCi/L. Further research will analyze the
economic impact of these modifications and
determine their viability as a low cost alter-
native to sub-slab depressurization in new
construction.

Radon in Schools

HVAC System Complications and Con-
trols for Radon Reduction in School
Buildings; K.W. Leovic, Project Officer.
Oral Paper

Tnitial data collected in four schools in Colo-
tado, Maryland, Virginia, and Washington
State confirm that, when outdoor air supply
is increased using HVAC systems (forced air
or unit ventilator), radon levels can be re-
duced. Depending on HVAC system design
and initial radon levels, this approach may or
may not be able to reduce levels to below 4
pCi/L. Table 1 illustrates reductions achieved
by pressurization of classrooms (using exist-
ing HVAC systems) in one Washington State
school.

Note that the classroom-to-hall doors had to
be kept closed for the unit ventilators to
teduce average levels to below 4 pCi/L, al-
though radon spikes (as high as 25 pCi/L)
still occurred.

Table 1. Average Radon Levels In Washington School During One Week

Test Operation

Normal Operation
Average Radon Time Door
Location Closed
pCIL = (max) (%)
Room 139-26 = (27) 7
Room14 $3 (29) 92
Roomi4l 48 (32) 8
Average 42 (29) 92

Average Radon Time Door —Subslab
Closed Radon

Sniff, August 90
PCL = (max) (‘%) pCuL
12 7) 76 40
32 (a) ” 500
21 5) Bs 700

22 (16) 78 533

Research over the next year will be focused
on determining optimal HVAC system op-
erations and limitations of pressurization.
Long-term research will include a compari-
son of HVAC modification and active subslab
depressurization in the same schools.
Design of Radon-Resistant and Easy-To-
Mitigate New School Buildings; A.B. Craig,
Project Officer, and K.W. Leovic. Oral
Paper

Recent experience in existing schools, new
house construction, and limited experience
in new school construction indicates that
radon resistant features can and should be
incorporated into new school buildings in
high risk areas. Radon-resistant features work
by reducing the potential for radon (soil gas)
entry and facilitating cost effective post-con-
struction mitigation. Pre-construction features
include: designing, installing, and operating
the HVAC system to pressurize the building
providing adequate makeup air for building
exhausts; laying down a minimum of 4 in. of
clean, coarse subslab aggregate; limiting
subslab barriers to air movement; and rough-
ing in subslab depressurization points.
Design and Application of Active Soil De-
pressurization Systems in School Build-
ings; K.W. Leovic, Project Officer. Poster
Paper

Recent research on active subslab depres-
surization (ASD) systems in two Kentucky
and two Maine schools indicates that: 1)
schools with low permeability material (i.e.,
sand) under the slab may require higher suc-
tion fans to adequately depressurize the
subslab area; 2) utility tunnel depressurization
may be an effective and relatively inexpen-
sive technique if the tunnels are not too leaky
and do not contain asbestos; 3) ASD systems
are typically preferred to passive systems in
existing schools to maximize radon reduc-
tions; and 4) subslab pressure field extension
(based on measurements conducted in one
school) is greater when suction is applied to
an interior point rather than from the building
exterior.

A Comparison of Radon Mitigation Op-
tions for Crawlspace Schoo! Buildings;
K.W. Leovic, Project Officer, B.E. Pyle.
Poster Paper

Research in one Tennessee school constructed
over a crawl space indicates that sub-mem-
brane depressurization is the most effective
technology for reducing radon levels in both
the classrooms and the crawl space. Crawl
space depressurization was effective in re-
ducing levels in the classrooms but increased
levels in the crawl space by a factor of two to
three. Both pressurization and natural venti-
lation of the crawl space were found to be
less effective technologies than sub-mem-
brane depressurization or crawl space de-
pressurization.


Response Form

AEERL welcomes your comments and suggestions regarding its programs and
reports. To forward your remarks or to be included on our mailing list for
future publications, please complete the following information and retum it to:
Kelly Leovic, MD-54, U.S. EPA, AEERL, Research Triangle Park, NC 27711.

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Penalty for Private Use $300

EPA/600/9-91/005



United States Ottice of Air and Energy Engineering
Environmental Protection Research and Research Laboratory
Agency Development Research Triangle Park, NC 27711

EPA/600/9-91/005_ March 1991

WEPA Radon Mitigation Research Update

Introduction

The Radon Mitigation Research Update is
the second in a series of research summaries
intended to provide recent information about

AEERL plans to publish future updates ap-
proximately two times a year. If you would
like more information about specific research

Project Highlights -..m.scsssssseseseseeseee 1 EPA's radon mitigation research activities activities or programs, you may contact the
« Indoor Radon by the Air and Energy Engineering Research appropriate RMB project officer at MD-54,
Research Program Laboratory (AEERL) and to compile a list- U.S. EPA, AEERL, Research Triangle Park,
ing of recent Radon Mitigation Branch NC 27711, or at the number listed below.
+ Florida Radon Program (RMB) research findings.
+ Measurements in Previously
Mitigated Houses RMB Contacts
+ Manual Updates Mike Osbome, Branch Chief Bruce Henschel
. (919) 541-4113 (919) 541-4112
New Technical Manual + EPA radon mitigation research and + Radon mitigation in existing houses
1991 International Symposium development program .
on Radon and Radon Reduction . . Kelly Leovic
Technology eesncsssserenenenereeensreerererernees 2 AB. “Chick” Craig (919) 341-7717 .
(919) 541-2824 « Radon mitigation in schools
+ AEERL Papers + Senior Physical Scientist - Radon Ron Mosley
Update of RMB Papers and Reports ....5 Tig Dyess (919) 541-7865
EPA Regional Off ces ........-sssecserereeeerseeeS — (919) 541-2802 + Radon data analysis
Response FOrM eveweeceeeesnnnennnennn6  * Radon resistant new construction John Ruppersberger

Bruce Harris
(919) 541-7807

+ Radon diagnostics and measurement tech-

(919) 541-2432
+ Radon barriers and block permeability

David Sanchez

nology (919) 541-2979
+ Mechanisms of radon entry and Florida
Radon Research Program
Project Highlights

Indoor Radon Research Program—Strategic
Plan

This expanded effort responds to EPA’s public health mission and the
1988 Indoor Radon Abatement Act's mandate to reduce radon-
related health risk by reducing indoor radon to near-ambient levels.

attached and unattached houses, 3) new houses (including pollution
prevention), 4) schools, and 5) technology transfer—into one com-
prehensive research effort.

An increased emphasis has been placed on innovative/supporting
research in an effort to accelerate improvements in technology, lower

the cost of technology, and facilitate the delivery of this technology to
a larger and broader audience.

‘The Indoor Radon Research Program has five areas of major empha-
sis:

1) developing new and improved radon reduction methods through
a better understanding of fundamentals,

2) de-emphasizing the demonstration of currently available radon
mitigation technology in existing and new houses,

3) increasing the emphasis on mitigation system durability assess-
ments and operating cost analyses,

4) continuing to identify, develop, and demonstrate radon mitiga-
tion options for schools and non-residential child care facilities,
and

5) supplying a greater variety of audience-specific technology
transfer products.

Utilizing this integrated approach, concepts developed in the Inno-
vative and Support Technology area will be demonstrated in existing
houses, new houses, and/or schools and other large buildings. Prod-
ucts resulting from each of these efforts will then be incorporated
into technical guidance documents.

. Printed on Recycled Paper

Cc


Florida Radon Research Program

RMB has coordinated and completed the delivery of recommenda-
tions and draft technical support documents to the Florida Depart-
ment of Community Affairs for Standards for Radon-resistant Con-
struction and Mitigation. The results of this effort will be published
in 18 reports covering recommendations for 1) improved floor
barriers, 2) subslab depressurization systems, 3) HVAC specifica-
tions, 4) fill material specifications, and 5) performance criteria. Data
gathered by the Florida Radon Research Program is available through
acentral Geographic Information System (GIS) data base maintained
by the Geoplan Center of the University of Florida.

Program and project planning for continuation of the EPA/Florida
interagency research agreement has also begun. These plans include
the initiation of a 2-year research effort to enhance the technical basis
for the five task areas listed above, and to begin work on the
development of a radon potential mapping basis for application of
construction and mitigation standards. Work in all task areas will be
undertaken in unoccupied research houses with development verified
in newly constructed houses. Problem assessment and building
characterization studies for large buildings will start in FY 91. (For
additional information on this program contact D. Sanchez, Project
Officer.)

Measurements In Previously Mitigated Houses

RMB is conducting measurements in previously mitigated (18 months
or longer) test houses in an effort to establish the long-term effective-
ness and durability of various mitigation systems.

Researchers have placed 6-month Alpha Track Detectors (ATDs) in
a number of basement and slab-on-grade houses, mitigated by EPA
or EPA contractors, to gather data on post-mitigation radon levels.

Plans are under way to initiate similar activities in a large number of
houses mitigated by private sector companies. The results of this
study will allow RMB researchers to identify radon mitigation
systems/strategies that are not effectively maintaining indoor radon
levels below 4 pCi/L. Study findings will also help identify mitiga-
tion systems/strategies which show the greatest potential for reduc-
ing indoor radon levels to near-ambient levels.

Follow-up research will focus on identifying equipment and installa-
tion problems as well as house and soil characteristics which may
have contributed to system failure. Research findings will be made
available through AEERL publications and in future issues of Radon
Mitigation Research Update. (For additional information contact B.
Harris, Project Officer.)

Update of Technical Manuals

AEERL is currently updating a number of EPA technical guidance
manuals to better assist in the dissemination of the most timely and
accurate radon reduction research information. These updated manu-
als are scheduled for release later this year and include Radon
Reduction for Detached Houses (Technical Manual), and Radon-
Resistant Construction Techniques for New Residential Construction
(Technical Guidance).

New Technical Manual

AEERL will also publish the first edition of EPA’s Radon-Resistant
New School Construction Manual. This new manual will be based
largely on RMB’s recent experience in existing schools and previous
experience with radon-resistant new house construction techniques.
It will provide the most up-to-date information available on the
design of radon-resistant/easy-to-mitigate new school buildings.

1991 International Symposium on Radon and Radon
Reduction Technology

Final plans are being made for the 1991 International Symposium on
Radon and Radon Reduction Technology “A New Decade of Progress”
to be held April 2-5 at the Adam's Mark Hotel in Philadelphia, PA.
EPA will co-sponsor the event with the Conference of Radiation
Control Program Directors (CRCPD). This is the third such confer-
ence to serve as a forum for the exchange of technical information.
The program includes 77 oral and 52 poster presentations in addition
to 13 invited papers.
Over 600 representatives from radon mitigation companies, local,
state, and federal governments, equipment manufacturers, academia,
and research and development firms are expected to attend. The
following agenda provides a summary of the conference's four
session days:
Tuesday, April 2

Session I: Government Programs and Policies Relating to Radon

Session II: Radon-Related Health Studies

Poster Session: All Posters Relating to Sessions I, II, and II

Wednesday, April 3

Session III: Measurement Methods

Session IV: Radon Reduction Methods

Session V: Radon Entry Dynamics

Session VI: Radon Surveys

Poster Session: All Posters Relating to Sessions IV, V, VI, and VI
Thursday, April 4

Session VII: State Programs and Policies Relating to Radon

Session VIII: Radon Prevention in New Construction

Session IX: Radon Occurrence in the Natural Environment

Poster Session: All Posters Relating to Sessions VIII, IX, and X
Friday, April 5

Session X: Radon in Schools and Large Buildings

If you would like more information about the symposium, please
contact Pat Heightchew, CRCPD, Inc., 205 Capital Avenue, Frank-
fort, KY 40601, (502) 227-4543. On-site registration will be avail-
able from 4 to 9 p.m. Monday, April 1, and from 7 a.m. to 5 p.m.
Tuesday through Thursday.


AEERL Papers

This section lists and briefly describes the 18
RMB oral papers and poster papers which
will be presented at the 1991 International
Symposium. RMB Project Officers and lead
authors are listed for each paper. For addi-
tional information on these research activi-
ties, please refer to the symposium pre-prints
(available with symposium registration) or
contact the appropriate RMB Project Officer
listed on page 1.

Measurement Methods

Predicting Long-term Indoor Radon Lev-
els from Short-term Measurements:
Evaluation of a Method Involving Tem-
perature Correction; R.B. Mosley, Project
Officer, and T.A. Reddy. Oral Paper

Daily averages of year-long continuous radon
measurements in three houses were used to
present a method for temperature-correcting
single short-term measurements of indoor
radon in order to predict long-term averages.
The thermal stack effect was demonstrated
to have the most important single influence
on radon concentrations. The method was
found to reduce the uncertainty in estimated
annual averages of radon concentrations sig-
nificantly in one house, moderately in the
second, and marginally in the third.
Correlation Between Short-term and
Long-term Indoor Radon Concentrations
in Florida Houses; D.C. Sanchez, Project
Officer, and S.E. McDonough. Poster Pa-
per

Eighty study homes, representative of typical
Florida housing construction, with indoor
radon concentrations in the 2-20 pCi/L range,
are being simultaneously monitored using
long-term and short-term monitors.

Data have been analyzed to isolate system-
atic seasonal variations and to derive confi-
dence limits for predicted long-term (annual)
averages from single or multiple short-term
measurements. Thresholds have been deter-
mined below which a single short-term mea-
surement can provide specific confidence
that the long-term average radon level does
not exceed 4 pCi/L. These results have been
incorporated into Florida’s draft building
standards.

Soil Gas Measurement Technologies; D.C.
Sanchez, Project Officer, and H.E. Rec-
tor. Poster Paper

This paper discusses soil-based radon and
radium measurement technologies capable
of providing useful information for evaluat-
ing land radon potentials. Findings indicate
that, while the use of soil gas measurements
to estimate radon potentials is still evolving,
both radium- and soil-gas-based measure-
ments can help identify land areas warrant-
ing special attention and consideration for
radon-resistant construction.

Radon Reduction Methods

Causes of Elevated Post-mitigation Radon
Concentrations in Basement Houses Hav-
ing Extremely High Pre-mitigation Val-
ues; D.B. Henschel, Project Officer, and
A.G. Scott. Oral Paper

Forty Pennsylvania basement houses with
1985-87 pre-mitigation radon levels in the
50 to 600 pCi/L range were reevaluated in
1989-90. The primary single cause of re-
sidual (post-mitigation) elevated radon lev-
els in houses using active soil depressuriza-
tion (ASD) was found to be reentrainment of
high-radon fan exhaust. In houses using block
wall depressurization systems, inadequate
sub-slab depressurization appeared to be the
major cause of problems. For other than
ASD systems, inherent limitations within the
systems are commonly the primary single
cause of residual levels. Airborne radon re-
sulting from radon in well water was an
important secondary contributor in some
houses.

Natural Basement Ventilation as a Radon
Mitigation Technique; R.B. Mosley,
Project Officer, and A. Cavallo, Oral Pa-
per

The effectiveness of natural ventilation in
reducing indoor radon levels was studied in
two basement houses. The study found that a
factor of two increase in the ventilation rate
(opening basement windows) corresponded
to as much as a factor of eight reduction in
radon concentration. The researchers found
a corresponding, but much smaller, decrease
in the pressure differentials (radon driving
forces) across the basement slabs.

Control Of Radon Releases in Indoor
Commercial Water Treatment; B. Harris,
Project Officer, and A.B. Craig. Poster
Paper

Municipal treatment facilities, industrial
process facilities, and other water treatment
facilities may be at risk for high indoor radon
levels, Water laden with relatively low levels
of radon (400 to 600 pCi/L), when used in
high volume commercial operations, may
release enough radon to result in indoor levels
in excess of 100 to 300 pCi/L in treatment
Tooms and adjoining offices.

Elevated radon levels identified in the Fish
and Wildlife Service's National Fish Hatch-
eries were controlled by vacuum-stripping
the incoming water and exhausting the radon
outdoors. Hooding and exhausting air from
immediately around discharge points also
proved to be successful in reducing indoor
levels.

Radon Mitigation Failure Modes; D.B.
Harris, Project Officer, and W.M. Yeager.
Poster Paper

Residential mitigation systems fail for a va-
riety of reasons and some failures may not be
immediately recognized by residents. This

3

study identified three primary failure catego-
ties (design flaws, component problems, and
occupant activities) and reviewed examples
of failure modes in each category. Results
indicate that some failures could be avoided
if mitigators would design systems to mini-
mize failures, install system monitors, and
instruct homeowners on continued system
maintenance.

Radon Entry Dynamics

Radon Entry into Dwellings Through
Concrete Floors; D.C. Sanchez, Project
Officer, and K.K. Nielson. Oral Paper

Porosities, radon diffusion coefficients, and
air permeability coefficients were measured
for typical Florida slab-on-grade housing ce-
ment mixes. Findings suggest that radon dif-
fusion through an intact slab may account
for indoor radon concentrations of 2 pCi/L if
greater than 3,000 pCi/L exists in the sur-
rounding soils. Radium concentrations of 5
pCi/g in the concrete similarly may account
for more than 1 pCi/L of indoor radon. Dif-
fusion measurements also exhibited a corre-
lation with the water/cement ratio of the
concretes,

Model Calculations of the Interaction of a
Soil Depressurization System with the
Radon Entry Process; R.B. Mosley, Project
Officer. Poster Paper

This study uses a simplified analytical model
of radon transport and entry into houses to
estimate the influence of a mitigation system
on the entry process. Modifications of the
diffusive flux and the entry rate into the
building by the action of the mitigation sys-
tem are estimated in order to determine the
total effect on emission of radon to the atmo-
sphere.

A Modeling Examination Of Parameters
Affecting Radon and Soll Gas Entry into
Florida-style Slab-on-grade Houses; D.C.
Sanchez, Project Officer, and R.G. Sextro.
Poster Paper

The influence of soil, backfill, and construc-
tion characteristics on radon and soil gas
entry is examined using a two-dimensional
finite difference model employing cylindri-
cal symmetry. At a constant building depres-
surization, steady state pressure, flow, and
radon concentration fields were predicted.
The model predicts that changes in backfill
permeability will have significant effects on
radon entry, while changes in block wall
permeability are somewhat offset by in-
creased flow and entry through other struc-
tural gaps.

Soil Gas and Radon Entry Potentials for
Slab-On-Grade Houses; D.B. Henschel,
Project Officer, and B.H. Turk. Poster
Paper

Asimple model is used to address the impor-
tance of subslab communications testing, in-
cluding measurements of radon concentra-