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SOL-GAS RADON-222 ANOMALIES IN SOUTH CENTRAL ONTARIO, CANADA
Imshun Je
A thesis submitted in confomity &th the requirements for the degree of Master of Science, Graduate Depariment of Geology,
University of Toronto
O Copyright by Imshun Je, 1997
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NEAR-SURFACE RADON-222 ANOMALIES AS INDICATOR OF
SUBSUIPFACE STRUCTURES iN SOUTH CENTRAL ONTARIO, CANADA
Master of Science
1997
b Imshun Je
Graduaie Department of Geology
University of Toronto
ABSTRACT
Radon is a newly recoguized environmental hazard, however, few studies have been
conducted in Canada. Near-surface in-situ radon soi1 gas levels were measured at the eastern end
of the Greater Toronto Area (GTA) of south central Ontario, Canada. Transects cross mapped
surface lineaments (Stream valleys) that coincide witb a prominent Mid-Proterozoic shear m e
known as the Central Metasedimentary Beft Boundary Zone (CMBBZ) îhat crosses the GTA.
Overlying Paleomic and glacial strata are extensively fractureci.
Anomalous high radon le* (up to 1 O00 pCi/L) are identitïed at each location and range
fiom 2-6 tirnes above background levels. Resuits of repeat measurements support the continue.
presence of these anomalies occrimng at or adjacent to the same positions along each transect. It is
likely that subsurface stnictures such as hctures, provide pathways for radon transport to the
surface; work elsewhere has shown that hi& radon levels define hult boundaries. In light of these
findingç, hazardous or near-hazardous levels of radon may occur elsewhere across the GTA.
Mapping fractures and relateci structures may provide a usefil constraint on hazard identification.
1 wouid Iike to ttiank Nick Eyies for granting me this opportuniiy to further my studies, for
his tremendous support towards the publication of my work and his recogartion of my abilities. 1
also thank Drs. Akx Mohajer and Don Chipley for their enthusiastic support and interest as
reviewers and members of the graduate cornmittee.
Special thankç goes to James E. Tilsley of Aurora Environmental Consuking, not only for
the generous loan of his equipment that was vital to this entire project, but also for his d u s i a s m
and guidance.
1 am also indebted to Michel Doughty for his field assistance and technical expertise on
producing the figures. Assisîance was also provided by the staff of the Ontario Geological Society
library at Queen's Park and Dave Hanneson, President of Biomation in Ottawa. 1 am also grateful
to Mr. Edward Falkenberg and d e r area residents, for kindly permithg field work to be
conducted adjacent to theù property.
Research was supported by operating funds provided to N. Eyles by the National Sciences
and Engineering Research CounciI of Canada.
TABLE OF CONTENTS
ABSTRACT ............................................................................................................................. ii
... ACKNOWLEDGEMENTS ................................................................................................... rrr
LIST OF FIGURES .......................................................................................... vi LIST OF TABLES ....................................................................................................... vii
... LIST OF APPENDICES ....................................... , CHAPTER 1: FNTRODUCTION .......................................................................................... 1
I . I RATIONALE AND OBJECTIVES .......................................................................... 2
1.2 ORGANIZATION OF THESIS ............................................................................... 4
CHAPTER 2: RADON AS AN ENVIRONMENTAL HAZARD .......................................... 5
............................................................................................................. 2.1 SUMMARY 6
2.2 RECENT IDENTIFICATION OF RADON AS AN ENVIRONMENTAL HAZARD ................................................................................................................ 7
2.3 PRINCIPLES OF RADIOACTIVITY ...................................................................... 9 2.3.1 Properties of Radon ................................................................................ -13
2.4 GEOLOGIC CONTROLS ON RADON ................................................................ 15 2.4.1 Source Rocks .......................................................................................... 17
2.4.1.1 Uranium in igneous and metamorphic rocks .................................. 19 2.4.1.2 Uranium in sedimentary rocks ..................................................... -19
2.4.1.2.1 Black shales ................................................................ -20 2.4.1.2.2 Glacial deposits and soils ............................................ -23
2.5 TRANSPORT PROCESSES FROM SOURCE TO SURFACE ............................. 25 2.5.1 Alpha Recoil ................... .. ............................................................. -26 2.5.2 Dfis ion ................................................................................................ -28 2.5.3 Advection ................................................................................................ 29
2.6 RADON ENTRY INTO RESIDENCES ................................................................. 31
2.7 HEALTH RISKS FROM RADON EXPOSURE ................................................ 34 2.7.1 Radon in Dnnking Water ........................................................................ 37
2.8 RADON MEASURING TECHNIQUES ............................................................... -39
2.9 RADON RISK FROM UNREGULATED DUMPING OF RADIOACTIVE WASTES .................................................................................... 41
2.9.1 Example: Malvem, Scarborough, Ontario ............................................... -42 2.9.2 Example: Port Hope, Ontario ................................................................. -45 2.9.3 Example: Elliot Lake, Ontario ................................................................ -47
2.1.0 DISCUSSION ..................................................................................................... 48
CHAPTER 3: EUDON SOXL GAS SURVEYS IN SOUTH ................................................................................. CENTFWL ONTARIO -50
................................................................................................ 3.1 INTRODUCTION 51 ............................................................................. 3.1.1 Health Risks of Radon 56
3.2 PROPERTIES OF RADON GAS ........................................................................... 57 3 .2.1 Geologic ControIs on Radon ................................................................... -58
3.2.1.1 Source rocks ................................................................................ -59 ......................................................... 3.2.1.2 Role of fàdts and fractures -60
............................................................................... 3.2.2 Transport Processes -62 ................................................................................... 3.2.2.1 Advection -62
................................................................. 3.2.2.2 Camer gas mechanism 64
........................ 3.3 SUMMARY OF PREVIOUS WORK IN SOUTFEICT\I ONTARIO 68
................................................... 3.4 PHYSICAL SETTING OF THE STUDY M A 72 3 .4.1 Regional Geolog ................................................................................... -73 3 .4.2 Proterozoic .............................................................................................. 73
..................................................................................... 3 .4.3 Paleozoic Cover -74 ......................................................... 3.4.3.1 Buried bedrock topography -75
...................................... 3.4.4 PIeistocene .. ....................................................................................................... 3.5 FIELD WORK 77
................................................................................................. 3.5.1 Methods -78 3.5.1.1 Quiprnent ................................................................................. 78
............................................................. 3.5.1.2 Selection of transect sites 81 ........................................................................ 3 3.1.3 Sampling method -82
.................................................................................................... 3.5.2 Results 83 ........................................................................................ 3.5.2.1 Phase 1 88 ...................................................................................... 3 S.2.2 Phase II -90
............................................................... 3.5.2.3 Doubled radon detectors 94 ...................................................... 3.5.2.4 Radon emanation fiom clasts -96
3 .5.3 Interpretation .......................................................................................... 97
3.6 DISCUSSION ....................................................................................................... -98 3 .6.1 Conclusions .......................................................................................... 100
REFERENCES CITED ................................................................................................ 101
.................................................................................................................... APPENDIX A 1 7 APPENDIX B ...................................................................................................................... 119
.................................................................................................................... APPENDIX C 130
LIST OF FIGURES
Chapter 2:
Figure 2: 1 Figure 2:2 Figure 2:3
Figure 2: 4
Figure 2: 5
Figure 2: 6 Figure 2:7 Figure 2: 8
Figure 3: 1A
Figure 3 : 1B
Figure 3:2
Figure 3 : 3 Figre 3:4
Figure 3 : 5
Figure 3:6 Figure 3: 7 Figure 3 : 8 Figure 3:9
Sources of radiation and average annuai radiation doses in Canada Decay series for uranium, thorium and actinium Variation in radon concentration in ambient air, soil, groundwater and residences Radon activity in basements of single family dwellings in Onandaga County, New York State Top: Radon emanation process. Bottom: Decay of radium atom to produce radon and an alpha particle Radon entry into residences Contaminated sites in Maivem Area of Scarborough, Ontario Contaminated sites in residential area of McClure Crescent
Chapter 3:
Location map of study area within south centrai Ontario, highlighting Central Metasedimentary Belt Boundq Zone and associated geomorphic features Schematic west-east cross-section of t h s t faults within CMBBZ Structure Detailed map of study area with transect locations and finearnents mapped fiom satellite image interpretation North-south geologic cross-section through study area Schematic mode1 of radon transport through a fadt by carrier gas mechanism Example of radon soil gas measurements over faulted structures in southwestern Ontario Schematic diagram of detector package configuration Graphical presentation of Phase 1 radon soil survey results Graphical presentation of Phase 11 radon soil survey resdts Climatic data plotted against mean soil radon levels during Phase II
LIST OF TABLES
Chapter 2:
Table 2: 1 Units of radioactivity Table 2:2 Physical properties of radon Table 2:3 Typical concentrations of uranium, uranium-238 and thorium-232
in rocks and soils Table 2:4 Radon diffusion coefficients for various media
Chapter 3:
Table 3: 1 Summarized results of radon soil gas study by Tilsley et al. (1993) Table 3:2 Results of radon soil gas study in Markham-StoufïviUe area
by Tilsley et al. (1993) Table 3:3 Summarized results of Phase 1 and II radon soil gas surveys of
present study Table 3:4 Cornparison of estimated background, mean and anomalous radon
Levels Table 3:5 Cornparison of Phase Il results between summer and fall values Table 3:6 Results of doubled radon detectors per sarnple site
vii
LIST OF APPENDICES
Appendix A: Calibration equations for E - P E W system
Appendix B: Radon survey field data phase 1 & II)
Appendix C: Clast sample radon emanation results
CHAPTER 1:
INTRODUCTION
1.1 RATIONALE AND OBJECTIVES
In m e n t years, radon has become a recognized environmental hazard. Unlike the situation
in Canada, sigdicant efforts have been put forth by governent agencies in the United States to
mise public awareness of radon's potential to cause lung cancer. Radon, in particular the isotope
222 Rn, is a cornmon gas occurring virtualIy in every naturai envirom& on the earth. Produced by
the decay of uranium and thorium in rocks and soils, radon is an inert radioactive gas. Radioactive
daughter products of radon can attach to partidates and aerosols in the air. Inhalation of these
particles can lead to the develiopment of lung cancer. These effects are well documnted in
communities of uranium miners but have recently become a concem fôr the public at large. It bas
beai estimated that about 10% of al1 lung cancers in the U.S. rnay be due to radon exposure
(National Research Council, 1994).
The distribution and concentration of radon in the environment is primarily limite. by its
short haIf-lSe, therefore the transport processes that bring radon fiom source rocks to the s h c e
need to be well characterized. Upon initial release fiom its parent radionuclide into swounding
pore spaces, radon is then subject to molecular diffusion and advection for transport into s h c e
envimments. The principal natural geologic sources are uraniumrich gramtes, gneisses and black
shales. Such strata underlie many urban areas in mid-continent North Arnerica. Glacial deposits
and soils containhg clads derived fiom these strata can locally represent a sigdicant radon
source.
Elevated radon levels are also known to be associated with subsufice geologrcal
structures such as faults and fractures. These types of structures provide gas migration corridors
that aliow soi1 gases to travel through soils much faster than by diffision alone, even in saturated
environrnents, particularly where an abundant flow of a carrier gas occurs. Faults and fractures
can therefore be identifid as radon soil gas anomalies compared to background radon levels in
uudisturbed soils. Measurement of in-situ radon as a natural geochemical tracer has been
successfdly demonstrated to be an effective and retiabte method (Bertin and Bourg, 1994; Tilsley
et al., 1993; Tilsley and Nichoils, 1993; Hoehn et al., 1992; Bal1 et al., 1990; Ellins et al., 1990;
McCarthy and Reimer, 1986; Card et al., 1985; Ginprich, 1984; Morse et al., 1982).
Little is known regarding background radon levels and variabihy across southem Ontario.
Tiisley et al. (1993) report results of a regional radon soil gas sampling program in southem
Ontario, finding a distinct correIation of elevated radon levels in soils in areas over known fà&
and oil and gas deposits withiu underlying Paleozoic strata. It was suggested that uranium and
radium were being transported to surface environments by volatile hydrocarbons escaping upward
along fiuits. Surface release of hydrocarbon gases near Iaub in southem Ontario is also reported
by Noor et al. (1992). Regimd bedtock Eauits and fracture systems are known to have contr01Ied
the development of subsurface hydrocarbon reservoirs in southem Ontario (Sanfbrd et al., 1985;
Sherwood Loilar et al., 1994). These structures have guided the 'pre-glacial erosion' of a
chanueled topography on the bedrock surface (Eyles et al., 1993) suggesting that fiults and
hctures extend from depth to surlàce. Overlying Pleistocene deposits are also fractured (Wi11s et
al., 1992; Eyles, 1995). The same structures may localize the release of radon in urban
environments and control the spatial variation in soil radon gas.
The present study focuses on an area that overlies a major shear zone within the Mid-
Proterozoic basement in south central Ontario. The shear zone, known as the Central
Metasedimentary Belt Boundary Zone (CMBBZ; Fig. 3: 1 A), records the collision of two termes
during the Grenvilie Orogeny about 1.2 billion years ago (1.2 Ga). Recent evidence suggests that
the CMBBZ is characterized by low-level seisrnic activity (Mohajer et al., 1992). NNE-trendmg
linearnents (Fig. 3:2) parauel with the CMBBZ appear through Paleozoic and Quatemary
sedunents (cross-section in Fig. 3:IB) south ofthe Canadian Shield (Eyles, 1997; Rutîy, 1993;
Mohajer et al., 1992) suggesting recmt reactivation.
The main objective of this çhidy is to determine normal background levels and anomalies
within the soi1 gases across various parts of the CMBBZ over Paleozoic and Quaternary sediments
in south central Ontario (see map on Fig. 3:2). Mapping radon levels can provide usefil
tnformation on subsdàce structures in the study area and most importantly, provides a means of
i d e n m g areas where radon rnay be a hazard to health.
1.2 ORGANIZATION OF THESIS
This thesis is presented as a series of self-contained papers, which address the specific
research objectives outlined above. ï'bis format was deerned as the most eEective and concise way
of communicatxng the research results. The reader will note that the format does lead to minor
redundancy in the introductions and conclusions of each chapter. The original field data and other
radon measuremnts are attached in the appendices (Appendices A-C).
Chapter 2 has b m previously published as a paper and is presented here in its original
text format by the author. This chapter is included to provide the necessary background material
for the thesis, describing radon as an environmental hazard, its sources, distribution and nsks to the
general population including case studies of radidradon contamination in Ontario. Chapter 3 is
the core of the thesis, describing the field investigations of radon in the soils of south centra1
Orrtario over the Md-Proterozoic shear zone. This chapter provides a more detailed description of
the probable radon transport mechankm involved, as well as the geologic characteristics particdar
to the study area.
CHAPTER 2:
RADON AS AN ENVIRONMENTAL HAZARD
C W T E R 2: RADON AS AN ENMRBNMENTAL HMAIWID
2.1 SUMMARY
Radon is an inert, naturally-occuning radioactive gas produd by the decay of uranium
and thorium in rocks and soils. It has a half-life of 3.825 days and breaks dom into two polonium
daughters (*18po and '14po). These radioactive species are solids and becorne attachai to
particulates and aerosols in the air, which can then be inhaIed into the lungs and may lead to the
development of lung cancer. These effects are well docurnerrted in comunities of uranium miners
but have recently becorne a concem for the general public at large. It has been estirnated that
about 10% of all lung cancers in the U.S. rnay be due to radon exposure.
The diseriblrtion and concentration of radon in the environment is primarily limited by its
short half-Me, therefbre the transport processes that bring radon h m source rocks to the surface
need to be well characterized. Alpha-recoil is the initial mechanisrn that transports radon fiom the
source material into surroundhg pore spaces where it can &en be transported by molecular
difision and advection to ssurhce environrnents. The principal natural geologic sources are
uranium-nch granites, gneisses and black shales; such strata that underlie many urban areas in
midentinent North Arnerica. Locaiiy, glacial deposits and soifs containing clasts derived fiom
these strata, also represent a significant radon source.
The purpose of this paper is to review the origin of radon and what is currently understood
ofthe associated heaith risks to urban communities in mid-continent North America. This paper
will emphasize natural geologic controls on radon levels as identi&d by rnany studies, and will
conclude with a brief review of the problems associated with the historic unregulated dumping of
radioactive wastes of several sites in Ontario, Canada.
Radon is the single most important source of radioactivity that people are routinely
exposed to but, as a radiation hazard, has received comparatively very M e attention. Natural
background radiation levels are approximately 3 mSv/year (CNq 1991; Clarke and Southwood,
1989). A sievert (Sv) is a masure of the actual biological damage to be expected when the body is
inadiated. A dose from a single medical X-ray is equivalent to 10~' Sv. A dose of 0.1 to 7 Sv will
cause chronic radiation sichess; greater than 7 Sv is fatal. (Upton, 1982). For the average person,
natural background radiation constitutes over 70% of the total typical expoçure to radiation, which
includes x-rays, cosrnic rays and microwaves (Fig. 2: 1), of which two-thirds is fiom indoor radon.
The health risks associated with residential radon have only been recently recognized since 1984,
are still under much investigation and only tentative guidelines have been proposed for "acceptable"
levels of radon concentrations. It has long been r e c o g n 4 since the sixkenth century in fact, that
there is a much higher frequency of lung-related deaths among uranium miners îhan îhe rest ofthe
general population. M e r the discovery of radioactivtty in the early twentieth century, Margaret
W g proposed in 1921, that radium emanations might be the cause of the h g cancers (Cothem
and Smith, 1987). Since then, the association between radon and lurig cancer has been welI
established for miners, but it was not until 1984 that radon was recogwsd as a hazard affectkg
cornmunities at large.
On December 2,1984, a Philadelphia nuclear power plant worker named Stanley Watras
set off the radiationdetecting alarms as he made his way info work that moming (Brown et al.,
1992; Pearce, 1987). He continued to set off the alarms eveiy moming for a week until it was
finaiiy discovered that the source of the radioactivity was in his own home. It was found that the
FIGURE 2: 1
Sources of radiation and average annual radiation dose in Canada. (From Clarke and Southwood 1989; and Canadian Nuclear Association, 1991).
Source s Radon from earth materials (98% from indoor exposure)
Terrestrial gamma rays
lngested natural radionuclides
Medical exposures
Cosmic rays
Fallout (including Chernobyl)
Miscellaneous sources
Occupational exposure
Radioactive effiuent discharges
Total
Amount of radiation
(mSv) 1987
Waîras house was built on an excavated vein of uranium that forms part of a uraniferous
geological formation called the Reading Prong (trends in a northeast-southwest direction stretching
from Pennsylvania through to New York State). Breathing of the air in the Watras' house posed
the same risk of contracthg lung cancer as srnohg 135 packs of cigarettes a day (Pearce, 1987).
Although the arnount of radon radiation found in this instance represents the most extreme case
ever found, more than one-third of North Amerka has potmtially high geologic radon production
(Gundersen et al., 1992; Tilsley, 1992; see befow).
2.3 PRINCIfLES OF RADIOACTIVITY
A radioactive atom is the result of the naairal tendency for a nucleus to move fiom a
higher to lower energy state in which the protous and neutrons are more tightly bound (Cothem,
1990; Draganic, 1993; Wilkening, 1990). The nucleus achieves this lower energy state by the
emission of radiation of which there are three mes:
1. Alpha (a) emission - An a-partide is a positively charged helium nucleus. These are relatively
heavy particles that cm ody travel a féw mtimetres in the a u before combining with free
electrons to become neutral helium atomç. In the case of radon, this process occurs in following
fom:
?"&, = 218po + 4He2+
These particles can be easily stopped by a sheet of paper or by human skûi. However, they can be
very biologically damaging when c o n s m d or inhaled into the hurnan body.
2. Beta ($) emission - A f3-particle is simply a fi$ moving electron. By its expulsion from the
nucleus, an atom gains one more proton and becomes a different element.
n=J3-+p
B i s type of radiation can penetrate I cm of water and human flesh, but can be stopped by a thin
sheet of aluminurn several iniüintetres thick. In air, it can only travel less than a metre before it
combiues with positive ions and foms n e m l atomç.
3. Gamma (y) emission - A 7-ray is part of the electromaptic spectnrm, consistiug of hi&
energy photons. It is highIy penetrating, with a greater arnount of penetrabiiity than X-rays, but
can be stopped by a 1 m thck block of concrete or by appropriate thicknesses of other matenals.
Its emission creates no change in the element.
n = ySn
Inherent i n ç t a b i of the nucleus seems to occur among elements with 82 to 92 protons
(Pb to U) and mass numbers (neutrons plus protons) between 204 to 238 (Wilkening, 1990),
althougb there are radioactive elements with srnaUer numbers of protons, such as tritium ( 3 ~ ) aud
'"c .
As radioactive decay tends to pro& fiom lower to higher stabhty, the proton number
decreases. In nature there are three major decay series, two that begin with uranium (isotopes U8U
and ?J) and the third with thorium (=?h), al1 of which terminate with lead (Fig. 2:2).
The stability of radioactive elements is norrnaiiy measured by their half-life, which is the time
required for half of the nuclei in a sample of a particular nuclear species to decay. Cornmon units
of radioactivrty rneasurements are Iisted in Table 2: 1.
FIGURE 2:2
Decay series for uranium, thorium and actinium showing generation of radon isotopes @igbiighted). From Schmalz (1990).
Uranium Series
Thorium Series 220Rn 17
Actinum Senes
TABLE 2: 1
Units of radioactivty (Cathem and Smith, 1988).
1 Curie (Ci) 1 picocurie (pCi)
1 becquerel (Bq)
1 es 1 pc*
1 Working Level
1 gray (GY)
1 sievert (Sv)
3.7 x 10" radioactive decayslsecond 0.037 radioactive decayslsecond 1 radioactive decaylsecond (SI)
(wu 1 O0 pciL 1.3 xlo5 M ~ V 1 joulekg = 10,000 erglg = 100 rad 100 rem = 100 rad
2.3.1 Prsperties of Radon
Radon is a naturaliy occurring radioactive gas produced &in the Earth's cmst fiom the
decay of uranium and thorium. It is the 86th element of the Periodic Table and is one of the noble
gases along with helium, neon, argon, krypton, and xenon. Radon has no colour or smeli and is
almost chemically inert although it is known to form compounds such as fluorides and clathrates.
Clathrates form d e n radon atorns become incorporated into the crystal lattices of certain hydrogen
compounds. Radon bas a dens@ of 9.73 g/L, which makes it the heaviest gas under standard
conditions (Wilkening, 1990). It also has the highest melting point, boiling point, critical
temperature, and critical pressure of any other gas (see Table 2:2). It is soluble in cold water, and
its solubility decreases with increasing temperature.
The three most common isotopes of radon are 'lgRn, U o ~ n and "RU, ali of which are
radioactive. The isotope '"~n has a very short half-iife of only 3.96 seconds, formed through the
decay of =kJ. This form of uranium has a Iuw relative abundance of 0.7% of al1 naturally
occuning uranium (Cathem, 1990; Faure, 1986; Wiikening, 1990). With such a low abundance
and short haIf-life, 21%n is not considered environrnenblly significant.
Rn-220 also has a short half-Me (56 seconds), formed through the decay of =?h, which is
more abundant in nature than uranium. Thorium has a global average concentration of 11 ppm in
the cmst comparexi with that of uranium which is ody 2 to 3 ppm (WiIkening, 1990). The isotope
220 Rn (also referred to as "thoron") may conçtitute a significant hctian of natural radon gas
ernissions in sorne environments. Marteii (1985) and Schery et al. (1989) have identifiedtùoron's
signifiace to overall radioacîivrty in soil gaç.
The most important isotope of radon as an environmental hazard is 2 U ~ n , which has a
half-life of 3.82 days. It breaks down h o u & a succession of decay products into 'lOpb, which is
easily removed fiom the atmosphere by precipitation. During the decay process, two radioactive
TABLE 2:2
Physical properties of radon (%n). (Mer Cothem, 1988; Schmalz, 1990; and Willrening, 1990,
Density at O OC and 1 am Boiling Point Melting Point Critical Temperature Critical Pressure Diffusion coefficient in free air Viscosity at 1 atm and 20 OC Solubility in water at 1 atm partial pressure and 20 OC Solubility in various liquids at 1 atm and 18 O C :
Glycerine Ethyl alcohol Petroleurn (liquid paraffin) Toluene Carbon disulfide Olive oit
9.73 g/L -62 O C
-71 OC 104 OC 62 atm
0.1 cm2/s 229.0 micropoise
230 cm3/kg water
0.21 cm3/kg liquid 7.4 cm3/kg liquid 9.2 cm3/kg liquid 1 3.2 cm3kg liquid 23.1 cm3/kg liquid 29.0 cm3/kg liquid
Properties of Radon
- m
polonium daughters ( Z 1 8 ~ o and "$0) are produced. These become attached to particdates and
aerosols in the air, which can then be i&aIed into the lungs and cause damage to swrounding
tissues by the emission of alpha (a) particles. Although 2 2 2 ~ n is also a relatively short-lived
radioactive isotope, it can be transported by soil gas digusion, atmosphenc convection or
groundwater flow and bewme wideIy distribiited away from its source. This fom of radon is one
of the progeny of the 2 3 8 ~ decay series and its immediate parent is the radium isotope Of
tata1 uranium, =*u is by fir the most abundant nakurally occuning uranium isotope (99.3%).
Since radon is soluble in water, it may travel Iong distances fiom groundwater sources and
surface waters. It can enter households fiom welIs and be released into kitchens and bathroom
(Tilsley, 1992). It is however, more soluble in air than in water and will readily pass into the gas
phase when in contact with air, especially if water is agrtated mechanicaiiy, such as in a bathroom
shower.
Radioactivity is measured in picocuries @Ci). Ambient air has an average radon level of
about 0.2 pCi per litre of air; ambient soil has Ievels from 20 to more than 100,000 pCi/L. Radon
dissolved in groundwaters can be as high as 3,000,000 pCi/L (Otton, 1992; Fig. 2:3). Indoor air
has radon levels that averages about 2 p C f i and can be as high as 5000 pCi/L in uranium mines
but as high as 7000 pCin in homes (Ememoser et ai., 1993; see below).
2.4 GEOLOGIC CONTROLS ON RADON
The concentration of naturaliy occurring radon in soils is primarily controlled by two
fàctors:
1. Source rock.
2. Transport processes from source rocks into soil pore spaces.
FIGURE 2:3
Variation in radon concentration in ambient air, soil, groundwater and residences (after Otton, 1992).
Ground- water
Soi1 Air
lndoor Air Air
m -Ciround Suriaœ-
Outdoor
100
1,000
10,000
100,000
1,000,000
10,000,000
The short kalf-life of radon ultimately limits the importance of these fhctors. Even with a
low relative abundance of the source material, rapid transport processes such as the movernent of
groundwater, can cause indoor radon accumulations to exceed the proposeci action levels. This is
an important consideration where radon potential studies are canied out relying solely on
geological and gamrna-ray surveys. Several studies (e.g., de Jong et al., 1993; Hand and
Banikowski, 1988; Kodosky, 1994) have clearly shownthat such preIiminary surveys can grossly
underestimate a& soiJ gas concentrations of radon. Detaiied soil samphg surveys are required
to detennine the abundance of radon.
2.4.1 Source Rocks
The most important natural sources of radon are from uranium-rich rocks and soils. There
are two principal isotopes of uranium, 2 3 8 ~ and U 5 ~ with relative abundances of approximately
99.3% and 0.7% respectively (Dyck, 1978). A third isotope, "U is a decay product within the
238 U decay series, but it is only present in 0.0054% of occurrences (Faure, 1986). The half-life of
is about 4.5 x 10' years, which is nearly equal to the estirnatal age of the planet Earth.
Uranium concentrations display a very wide range depending on rock type (Table 2:3). In
general, sedimentary rocks that contain organic matenal are usually moderately enriched in metals,
including uranium (Bell, 1978; Dyck, 1978; Tilsley, 1992). Organic-rich black shales and rocks
c o n t a h g phosphate show the highest values, some approaching 1000 ppm. AdditionaUy,
glacialiy-eroded debris derived from uranium-rich source rocks has been transported long distances
and spread over large areas in tills and outwash depositç (Gundersen e t al., 1992; Tilsley, 1992).
Uranium usually occurs as oxides such as uraninite and camotite with phosphates and
monade sands being of importance in some cases. In general, is in equilibrium with u 8 ~ .
Thorium has a cru-1 abundance of 11 ppm and is found in m o n d e sands in India, Brazil, the
TABLE 2:3
Typical concentrations of uranium, umnium-238 and thorium-232 in rocks and soils (after Wiikening, 1 980).
Rock Type
Igneous: Basalt Granite
Sedimentary: Shale, sandstone Carbonate rocks Black shale
Continental upper crust (average)
Soils
. 0.01 0.1 1 1 O 100 1000 ppm
Uttrarnafrc igneous
Intenediate igneous Graniüc igneous
Felsic alkalic igneous
Sandstone Shale (green ,red, gray)
-Shale (black)
Limestone Bauxite
Phosphate rock
- -Coal
former Soviet Union and fiom areas in North Carolina and Virginia in the U.S. Monazite sands
contain approximately 10% thorium providing high extemal dose rates for local residents.
Table 2:3 gwes the normal ranges of 2 3 8 ~ and concentrations that can be expected in
nature. Thorium-232 ex& U-238 by a factor of 3 to 5 in many rock -es. &ough =2Th
exceeds U 8 ~ in the continental cmst by a factor of 3.8, the activlty of UZTh exceeds that of U 8 ~ by
about 20%. Since the *2Th decay series can only yield the ?Rn isotope, wIiich has a half-life of
only 55 seconds, uranium-23 8 is the primary radioactive source for indoor radon and is the focus
of the folfowing discussion.
2.4.1.1 Uranium in igneous and metamorphie rocks
Uranium, as well as thorium, has a tendency to be enrichecl in the more volatile phases in
moltm or partialiy melted r d as they ml. Rocks with low m e h g points, such as granrtes,
have a higher urariium content (10-40 ppm) than in higher temperature rocks, such as diodes and
basalt (0.5-5 ppm). Generally, the higher the silica content of igneous rocks, the higher the
uranium content. During metamorphism, rocks become more depleted in uranium as heating
proceeds and the uranium becomes remobilized and concentrated into the escaphg gases and
liquids; pegmattte veins become enriched in uranium and thorium by the same processes (Keppler
and Wyllie, 1990).
2.4.1.2 Uranium in sedimentary rocks
Under certain conditions, sedimentary rocks can also becme a sigmfïcant reservoir for the
adsorption of uranium. The presence of clay rninerals and organic matter enhances the adsorption
of uranium within sediments once uranium has been weathered fiom its host rock (Flexser et al.,
1993). Co-precipitauon with iron oxide and formation of secondary minerais in pore spaces or
fractures also commonly scavenge uranium and radium from solution. Thus, the surface of
sedimentary p i n s c m be reiatively enriched in radium. The work of de Jong et al. (1993);
Flexser et al. (1993); Keller et ai.. (1992); Loureiro et al. (1990) and McCallum (1992) confirm
this apparat relationship between grain size and radium content, with increasing content of clay
being associatd with higher radium content.
2.4.1.2.1 BIack shales
BIack, organic-rich &ales are associated with hgh uranium concentrailons and was &st
report4 for Lower Palaeozoic shales of the Baltic region in the 1890s (Beil, 1978). A &ale is
considered organic-rich if it has an organic carbon cuntent greater than 2% (Bell, 1978). The
uranium content of black shales is usually around 8 ppm (compared with average crustal
abundance of 2-3 ppm). Uranium is luiked wxth the organic fraction of the biack &ales; less than
7 ppm of U is SpicalIy adsorbed onto clastic particles (Bell, 1978; Otton, 1992). During
deposition, uranium is sorbed onto organic compounds and is directly precipitated as colloidal
uraninite, both at the sediment intedace and at shaliow depths within the sdiments under the
influence of hydrogm suEde (Harrel et al., 1991). Other metals also becorne preferentiaily
adsorbed in black shales due to the high organic content. In anoxic waters, the water typical of
deep marine basins in which black hales accumulate, reducing conditions dominate. Reduction
causes hexavaient uranium to be convertcd into a tekavalent fonn which is insoluble and is readily
adsorbed on organic matter and becornes incorporated into U-organic complexes (Gates and
Gundersen, 1989; Hand and Banikowski, 1988). Much of the organic material is composed of
terrestrial czilulose and Iignin and humic derivatives and are very effective scavengers of uranium
fkom seawater.
FIGURE 2:4
Radon actiwty @CiII,) in basements of single W I y dwellings in Onandaga County, New York State. Large nurnbers are mean values for geologic nits. Note restriction of high values to Marcellus black shale. From Hand and Banikowski (1988).
Radon (pCill) Siltstone, sandstone, shale 0 0 - 4 ml Marcellus (black) shale
4 -?O 10-20 ..,0.8,0,~ Carbonate rock (chieftly dolostone)
'20-100 mShale 400
A case study in Syracuse, New York (fIand and Banikowski, 1988) f o n d elevated Ievels of radon
associated vath Palaeozoic sedimentary strata (Fig. 2:4). The Marcellus (black) Shale of Silurian
age is enrichecl in uranium and is a source rock for uranium found in associated limestone and
dolostone strata and transported by hydrothennal groundwaters. This redistribution of uranium in
the shales has occurred over several tens of millions of years and gives rise to what has been
termed a "hot" beh of radon 12 km wide. The geological seaing of the Syracuse area is typical of
much of midecontinent North America where shales are an important wmponent of large
intracratonic basins such as the Appalachian, Michigan and Illinois basins (see Leighton et al.,
1990).
Harrell et al. (1991) investigated the potential radon hazards associated with Upper
Devonian shales in Ohio and found similar resuh to those reported by Hand and Banikowski
(1988). The average uranium concentrations found in the continental crustal materials are
typicaly around 2 to 3 ppm and this results in radon radioactimty levels on the order of 1 .O to 1.5
pCdL inside houses. The Devonian shale in Ohio has a high uranium concentration (10 to 40 ppm)
resuhmg in a mean radon concentration of 1165 pCikg within the shale. Measured radon levels in
homes d i n the study area correlateci very well wrth the radon levels in the rocks with indoor
values ranging between 2 to 20 pCiL wah a maximum of 94 pCi/L.
In southem Ontario, the northem part of the Greater Toronto Area is underlain by the
Middle Ordovician Collingwood Member of the Lindsay Formation which is a b i i o u s oil shale
(Churcher et al., 1991). Background uranium concentrations of 6 ppm are reported by Bell
(1 978). Bowever, this figure is based on few samples and is nut easily related to likely radon
levels in soils given the ability of transport processes to concentrate radon in near surface
sediments (e. g. Kodosky, 1 994). Of greater importance is the radon level h glacial sediments and
soils.
2.4.1.2.2 Glacial deposits and soils
Glacial deposits such as tills, outwash and glaciolacustrine sediments cover a very large
a r a of mid-continent Norîh Arnerica and contain granite and gneiss clasts derived from the
Canadian Shield. The role of glacial deposits in controlling radon levels is not well known. In
some instances the glacial overburden acts as a barrier to upward migration of radon, especially if
it is thick or of low-permeability. However, some locations with greater thicknesses of overburden
also display high levels of radon, suggesting that uranium-bearing clasts and boulders can rnake a
significant contribution to overall radon levels (HarreI et al., 1991).
A study of Saskatchewan soils by de Jong et al. (1993) demonstrated a clear correlation
bmeen radon gas levels and the clay content of soils. Soils derived fiom lacustrine sediments
showed 50% greater radon levels than tills. Radioactiwty levels mged from 3 to 8 Bqkg in tills,
with a mean of 6.0 Bqkg, and from 9 to 13 Bqkg in the lacustrine soils with a mean of 10.6
Bqkg. Levels of %, 2 3 s ~ and decreased as soil texture became coarser.
The importance of clay content in determining concentrations in soils is supported by
data from Ontario. McCallum (1992) detennined % a concentrations in sandy poorly developed
soils associated with coniferous forests in norihem Ontario and in soils typical of mixed forests in
southem Ontario, where weathering and eluviation results in distinct soil horizonation and higher
clay content. The mean ' * k a concentration of @rio soils ranges from 0.035 Bqlg to 0.053 Bqlg
with the highest concerrîrations in fine-textured soils of southem Ontario. This study was
completed to detennine natural background variation in 2 2 6 ~ a in soils in order to establish ALARA
(As Low As Reasonably Achievable) values for remedial action projects involving the clean-up of
sites contaminated by '%. Upper Limits of Normal ( 'LN) concentrations were also of interest,
again as a basis to establish the degree and extent of contamination of sites where low-level
radioactive waste is present. The ULN values reported by McCallum (1 992) for Ontario soils
range from 0.063 Bq/g to 0.1 13 Bq/g with an average of 0.083. Because of the considerable range
in ULN values, it is difficult to select any one value as a threshold for uniquely identiwg soils as
being "radioactive" at contaminated sites. This is because native soils having a higher ULN would
be required to be classified as contaminated. The study of McCallum identifies the need for further
study of background variation and particularly, the nature of *''ka profiles with depth in soils.
TilsIey ef al. (1993) report resuits of a regional soil radon gas sampling program in
southern Ontario and found a dstinct carrelation of elevated radon levels in soils with areas of
known oil and gas depositç wiîhin underlyilng Palaeozoic strata. It was suggested that the
transport of uranium and radium to surface environments was by volatile hydrwrbons escaping
upward dong faults. Surîàce release of gas n a r faults is also reported by Noor et al. (1992).
Regional bedcock fauits and fracture systems are known to have controlledthe development of
subsurface hydrocarban reservoirs in southern Ontario (Sanford et al., 1985; Sheiwood Lollar et
al., 1994) and guided the cutting ofa channelied topography on the bedrock s d c e (Eyles et al.,
1993) suggedng that faulfs and Eractures extend from depth to surlàce. Overlying Pleistocene
deposits are also fractured (Wills et al., 1992; Eyles, 1995). The same structures rnay localize the
release of radon in urban environrnents and control the spatial variation in soil radon gas. A survey
of 632 public schools in Metropolitan Toronto identifieci two schools with basement radon levels
equal to or above the praposed action level of 2pCifL; three schools had levels between 1 to 2
pC2L (Becker and Mondi, 1992). Controlling làctors were not investigated. Given that the largest
urban centre in Southern Ontario (the Greater Toronto Area) lies above a network of bÊdrock
channels and faults (Eyles, 1995), research aimed at identifjmg the relationship between
underlyintg geologic structures and surface radon emanation should be actively pursued. In this
regard, it can be noted that it has already become cornmon practice in California to predict
earthquake events by closely monitoring fluctuations in radon levels in groundwater wells close to
known faults Pipken, 1994). Bedrock topography rnapping rnay be a usefil tool in identifjing
prionty areas for soil radon gas surveys given the close relationship between such topography and
structure. In general, there are few data regarding the systernatic variation in radon across urban
cornmunities in Canada (see below) and such data are urgently required. The same conclusions
apply to other elements such as lead (see Beak and Raven Beck Environmental Ltd., 1994).
2.5 TRANSPORT PROCESSES FROM SOURCE TO SURFACE
Given the short haif-life of radon, radon levels in surface environments are controiied by
transport distances from source to surfàce. For exarnple, where it takes a period equivalent to six
half-lives (about 23 days) t o pass through near surface fractureci rock and soi], about 99% of the
gas will decay to non-mobile solids before reaching the surlàce (Harrell et al., 1991). Even in dry,
porous, hi&-pemeability materials, radon wiil be diminished 100-fold (only 1% will survive) after
a difision distance of only 6 m. The three main transport mechanisms that bring radon from its
source in soils or rocks to the surtace environments are:
1. Transport from the solid phase to either gas or liquid in pore
spaces by alpha recoil.
2. Transport of radon relative to the gas or liquid by rnolecular diffusion.
3. Transport o f radon within soil gas or water by advection.
2.5.1 Alpha Recoil
Alpha recoil is a microscopie-scale process that transfers radon fiom the solid grains of the
source rock into the pore spaces. D u h g alpha decay of radium to radon, the energy released
causes the alpha particle to be fired out from the nucleus, and the recoil affects the newly-formeci
radon progeny wfiich is fired in the opposite direction to that of the alpha particle (Fig. 2:5).
Energies involved in this process are 1000 to 10,000 times the typical chemical bond energies
(McheI, 1987). For radon, the typical remil range is about 20 to 70 nm and several diflerent
possible r m i l paîhs can be identifid In the case of a radium atom Iocated at a depth wrthin the
grain greater than the recoil range, the radon progeny remains embedded in the grain (A; Fig. 25).
Other atoms may escape fiom the original grain but become trapped in the adjacent grain (B; Fig.
25). Other atoms escape h the original grain and are fired into pore water which stops the
atom by absorbing any remaining recoil energy (C; Fig. 215). It is now fke to diffise through the
pores. Finally, atoms can also be fired into pore air where littie energy is absorbed. These rnay
travel across pore spaces and become embedded in adjacent grains 0; Fig. 2 5 ) .
The proportion of radon atoms that end their recoil path in a pore space relative to the tutal
number of rewils is termed the ernanation coefJicient and the emanated atoms are called the direct-
recoilfraction. The presence of water in pore spaces significantly hcreases the direct-recoil
fraction since water slows the recoiling atom travel better than air. Fleischer (1 988) found that
radon emanation is maximized by a thin film of water covering the solid grains. This has the effect
of nat only stopping atoms fiom travelling into adjacent grains but also leaches any radon atoms
that are shallowly embedded in the surfàce of adjacent grains (Rose et al., 1990).
The recoil range, R, (Fig.25) is a critical factor in determinhg how much radon escapes
fi-om the solid grain. In grains much larger than the recoil range, few recoil atoms wiIl be able to
FIGURE 2 5
Top: Radon ernanation process; see text for details. From Michel (1987). Battom: Decay of radium atom to produce radon and an alpha particle. Radon is fired into mineral grains or pore spaces (after Otton, 1992).
Mineral Grain
Mineral Grain
, 0.1 pm ,
escape by direct-remil. If the grain is 1 micron in diameter, about 5% of the atoms may recoil out
of the grain, whereas for millirnetre-size grains, onIy 0.005% leave the grain by direct recoil.
Generally, in coarsely crystalline rocks or coarse-texturd soils with a hornogeneous
distribution of radium, the emanation coefficient is less than 0.01. In fine-grained rocks and soils,
the normal range is between 0.15 to 0.35 (nichel, 1987). Radon emanation measured from
various geologic materials is much greater than that calculated assurning direct recoil only,
suggesting other processes of radon loss fiom mineral grains that as yet, are poorly underçtood
(Michel, 1987). Once a radon atom has been fired into a pore space it can then be transported by
diffusion and advection.
2.5.2 Diffusion
Diffusion is the migration of the gas relative b the host medium; radon obeys the standard
laws of difision, so the flux is proportional to the concentration gradient. Difision coefficients
for radon withiri various media are given in Table 2:4. The major fàctors goveming radon
diffusion in a rock or sediment involve properties such as grain size, distribution of radium within
the solid, porosriy, the amount of interstitial fluids and the presence of fractures and their degee of
intercomededness. The relative contribution of each factor varies with varying sediments and
rock types.
Difisive transport of radon in soils is lunited because of the short half-life of radon.
Migration by difision ranges fiom about 5 m in grave1 to about 2 cm in saturated mud or clay,
and distances greater than 1 m are probably unusual (Michel, 1987; Rose et al., 1990; Tilsley et
al., 1993). In unhctured crystalline rocks, the diffision coefficients for radon are extremely
small, and much of the radon will decay before moving any appreciable distance. The presence of
water in the pore spaces also tends to decrease radon migration, because difision in water is about
ttiree orders of magnitude smaller than in air.
2.5.3 Advection
Advection either by groundwater rnovement or pressure-driven air flow can transport
radon over significantly greater distances han by difision alone. Since radon is basically
chemically inert, its transport in groundwater systems is o f h controlled by the velocity of
groundwater flow itself. The limiting factor in the transport length of radon in groundwater is its
half-life. In 30 days, the radon content of groundwater will be l e s than 1% of its original activity
(Michel, 1987). The movement of groundwater is controlled by a number of hydrogological
parameters such as permeability, porosm and hydraulic head.
Transport of radon in air caused by pressure gradients is enhanced at times of low
atmospheric pressure, high winds, or siguificant temperature gradients between the soil air and the
atmosphere (Kokotti et al., 1992; Loureiro et al., 1990; Nazaroff et al., 1987). The pressure-
dnven flow of radon is directly dependent on the pemeability (k) of soils where the overall mean
grain size is larger than silt or fine sand, and where k>1 .O x 10-I2m2; below this value transport by
difision dominates (Loureiro et al., 1990).
In most cases, the transport distance of radon by diffusion and advective processes
combined is less than 3 m, and thus the source of radon is usualiy nearby within the soil or surficial
sediment, and nat in the deeper underlying bedrock (Michel, 1987). However, Harrell et al. (1 99 1)
in Ohio demonstrated that nearly al1 the radon measured in residential homes built above black
shales had been transported distances of well over 30 m.
TABLE 2:4
Radon dinision coefficients for various media (after Michel, 1987).
Medium Diffusion Coexcient Diffusion Length (cm2/s) ( rn )
Air 1 O-*
Water 1 os 2.4 Sand 3 x dom2 Argillite 8 x IO-' 1.5 Csncrete 2 x los Mineral Crystals -l0*- IO-^ 0.04 - 0.26
2.6 RADON ENTRY INTO IRESIDENCES
Diffusive and advective transport enables radon to enter residences via many possible
pathways and eniq points (Fig. 2:6). Due to its relative densq, there tends to be a
pronounced vertical gradient in radon concentration in arnbient air. A child breathing at a height of
0.5 m is exposed on the average to about 16% higher radon Ievels than an adult breathing at 1.5 m
(Michel, 1987). Kodosky (1994) found that basernents tend to have radon levels 2 to 3 times
higher than upper-level rooms. Ifence, the general emphasis on basernents in most radon stuàies.
The most important entry pathways are cracks and holes in the foundation, and uncapped
sumps. These were responsible for 23% of ]Rn seepage into the residences studied by Kodosky
(1 994) in southeast Michigan. Radon advected in groundwater accowited for 1 1% of the indoor
concentrations in homes that relied on private wells as their water source (see below). House
depressurization and escape of heated air is particularly significant as it allows radon to be drawn
into the houses through basement fractures. Negative pressure conditions in houses caused by
central heating in winter months enhances the release of radon fiom near-surface strata in contact
wrth basement walls. Nazaroff et al. (1 987) found that an indoor-outdoor pressure difference of
between 25-50 pascals (Pa) substantialIy increases the rate of transport of radon through soi1 air
and into houses; observed transport velocities e x 4 1 m per hour. The entry rate of radon by
pressure-dnven flow can exceed that due to diffusion by an order of magnitude (Nazaroff et al.,
1987). Reduced indoor air pressures tend to wcur in newer energy-efficient houses due to their
airtight structure, and it has been suggested that these types of houses are at greater risk than older,
better ventilated structures.
Kokotti et al. (1992) found that the radon entry rate exponentially increases with increases
in the outdoor-indoor pressure difference. The pressure difference provides the driving force
behind convective flow and the pressure difference tends to increase with increasing air-exchange
FIGURE 2:6
Radon entry into residences (after Otton, 1992).
rate. This is a case for concem as it has ben assumed in d e r studies that a higher ventilation
rate in houses will dzhte indoor radon concentrations (Hanulton, 1993; Kodosky, 1994). Kokotti
et al. (1992) conclude that a high ventilation rate does not guarantee lowered indoor radon levels.
In residences in Urnhausen, Austria, the summer median for basement areas is lower than
in the winter by a factor of about 10 (Ennemoser et al., 1993). About 40% of the basements
register radon levels above 10,000 I3q/m3 in winter but only 7% reach those levels in summer.
This clearly illustrates the importance of year-round monitoring for radon Ievels with particular
atîention to winter peak levels d e n central heating systems are operative.
Natural radon levels in homes cm approach those found in uranium mines. In uranium
mines with only natuml ventilation, typical radiation levels are in range between 75,000 to 190,000
~ ~ / m ~ (2,000 - 5,000 pCiL); (Wilkening, 1 990). Forced air ventilation of rnines in the late 1 940s
reduced these levels to about 2,000 ~ ~ / m ~ (50 pCi/L). In Umhausen, Austria, Ennemoser, et al.
(1993) identifid extrernely high indoor radon concentrations (up to 274,000 ~ ~ / r n ~ ) . The town is
built on alluvial fàn sediments having an extremely high penneabilxty; the ernanation factor is
enhanced by the presence of fractures in underlying granite gneiss becbock. These soi1
characteristics caupled with the slightly enriched uranium content of the granite gneiss are
responsible for the elevated radon levels. The medians measured were 3750 in winter and
361 ~ ~ / r n ~ in summer in the basements and 11 80 ~ ~ / r n ' and 210 on the ground floors,
respectively. Unusually high radon concentrations in Umhausen coincide with a statistically
signifiant increase in lung cancer morîality.
The difference between median concentrations measured in d e r and summer by
Ennemoser et ai. (1993) can not only be ascnbed to central heating effects fsee above) but also to
the great difference of soi1 permeability in summer and winter. In winter, the soi1 surface is fiozen
and radon becomes sucked into the houses by a low indoor air pressure. During summer rnost of
the soi1 emanates radon diredy into the abnosphere and lMe is able to penetrate into basements.
No association has been fomd between radon concentrations and building type; houses with earth
basement Boors showed the sarne radon levels as those with concrete basernent floors. It is likely
that the broad kdings established by Ennemoser et al. (1 993) can be applied to Canadian urban
seaings given similar climatic conditions and heating practices.
2.7 HEALTH RISKS FROM RADON EXPOSURE
Most data appertaining to health risks is derived f?om U.S. studies; to date very iitîle work
has been conducted in Canada. Nero et al. (1986) made quantitative measurements in randomly
selected buildings and homes throughout the United States. It was concluded that approxirnately
one million homes are expose- to radon levels that exceed the recomrnended action level of 2
Working Level Months (WLM) per year (se Table 2: 1). About 2% of the 60 million s ing le -My
residences in the U.S. are expected to have levels exceeding 8 pCi/L. It has been estimated that
between 7,000 to 30,000 lung cancer deaths are attributed to radon each year; which is equal to
approximattely 10% of aIl lung cancers in the U.S. (National Research Council, 1994). With
regard to radiation exposure in generai, prolonged exposure at low doses is associated with more
nsk than shorter exposure at higher doses. It has yet to be deterrnined whether this relationship
holds for the Iow radon levels found in residential areas. Exposures in childhood cany no greater
risk than exposures at older ages, and not surprisingly, smokers are at much greater nsk than non-
smokers (NRC, 1994).
As a noble gas, radon is chernically inert and does not form compounds. The major part of
mhaled radon is fherefore exhaled again. However, short-lived radioactive isotopes such as
polonium accumulate in the respiratory system. Between 20 and 50% of inhaled radon daughters
are retained in the respiratory tract, where alpha-emitting progeny expose the lung to radioactivity
(Ennemoser et al., 1993). Typically, most damage occurs to the surface walls of the bronchii
leadmg to the lungs because the mucous layer on the surface of the branchial tubes is not heavy
enough to absorb alpha particles. This usually results in damage to the underlying basal cells.
In the US., the National Research Council(1994) wams that it cannot state with any
degree of certainty the level of radiation below which there is no health risk. There have been
protests raised in the US. that the costs of remeàiating al1 homes that have radon levels above the
EPA guideline of 4 pCiL would amount to more than $50 billion (Horgan, 1994). The agency
argues that some 15% of lung cancer deaths caused by radon exposure could be avoided by
reducing radon levels greater than 4 pCi/L (estimatecl to occur in 5 million of the 60 million homes
in the US; Horgan, 1994). In addrtion, the Intemational Commission on Radiological Protection of
the United States has found that the risk of developing cancer fiom exposure to 1ow levels of
radiation fkom X-rays and gamma-rays is three to four times as hi& as previously thought
(Vaughan, 1990).
Proper rernediation in residential basements need not be costly or complicated. Houses
with earthen basement floors cm be outfi#ed with several sheets of hi& density polyethylene
plastic laid loosely on the fioor, a plastic pipe beneath the sheets to collect the radon gas and a
mechanical fan in the attic that exhausts the gas outside above the roofline. This technique
successfully reduceà indoor radon levels in houses on Mackinac Island, Michigan fiorn between
12.9 to 82.3 pCi/L to below 4 pCf i , and remained effective three years after its initiation
(Hamilton, 1993). In d e r types of basementç, entry points can be sealed by various readily
available, inexpensive methods and in areas of very high radon levels, ventilated fans can also be
installeci. Typical cos& range betwen $500 to $1500, depending on the size of the house (Tilsley,
1992). The remediation of homes with high radon levels does not pose a probIem. In absence of
any systernatic coverage in Canadian wrnmunities, the major problem is in determining which
areas are at nsk.
2.7.1 Radon in Drinking Water
Radon dissolved in drinking water is an important secondary source of radon imroduced
into residences particularly where water is derived fiom groundwater. Consumption of radon in
water is not as important as inhalation of radon that has escaped fiom the water source. Dissolved
radon can be released into indoor air ifwater is a-ed by the use of cornmon devices such as
showers and faucets. In general, water containhg a radon actiwty of 10,000 pCi/L d l release 1
pCi/L into indoor air (Otton, 1992). It is estimatecl that 137 people die every year in the U.S. fiom
exposure to radon in water, althougb drinking water only represents 1% of totai exposure fiom dl
sources of environmentaI radon (Swistock et al., 1993). Extreme cases have been reported in
Maine where radon from private wells drilled in gmnite bedrock contribute nearly 100% of indoor
air levels which were as high as 2000 p C i n (74 BqL) prior to remediation (Lowry et al., 1987).
The U.S. Environmental Protection Agency @PA) standard for radon in drinking water has been
set at 300 pCiL (1 1.1 BqL) (Valentine and Steams, 1994). However, even at this level there is
still a cancer nsk of 1 in 10,000 (Swiçtock et al., 1993).
Waterbome radon levels in rivers and lakes tend to be negligible (2.2 pCi per 100 kg;
NRCC, 1983), since exchange with the atmosphere is rapid enough to allow significant amounts of
radon to escape fiom the water phase. Thus, areas reliant on surface water supplies are at a
minimal risk. Large cities also generaily do not encounter any problerns with radon in drinkllig
water since processing in municipal treatment f'dcilities aerates the water sufficient to allow much
of the existing radon to be released into the air. Furthemore, the residence time in the supply
reservoirs is usually long enough that most of the rernaining radon will have decayd to
insignificant levels before ever entering residential outlets (Otton, 1992). However, in areas where
groundwater is used as the main source of water, dissolved radon cm pose a hazard. The closed
systems and short transit Gmes of smU. public water works and private domestic wells are not able
to remove radon from drinking water or allow it enou$ time to decay.
Levels of radon in groundwater will primady depend on the uranium and radium content
of the aquifers, which are in turn controlled by the factors described in previous sections.
Circulating groundwaters will dissolve uranium in the host rock and increase the mobilrty of
uranium (Beck and Brown, 1987). Redox conditions are less important in the mobilization and
transport of radium and even less so for radon. Radium ,will tend to adsorb ont0 clay rninerals,
organic matter and iron hydroxides and co-precipitation occurs in the presence of calcium,
strontium and bariurn sulfàtes (Humphreys, 1987). Concentrations of radon in groundwater will
reflect local radium sources because ofthe short half-life of radon and the generally slow
movement of groundwater.
Systematic surveying of radon in Canadian drinlung water has not been completed but
available data from pilot surveys suggest that relatively hi& levels of radon in Canadian drmking
water supplies are not uncornmon. Beck and Brown (1987) identified radon levels above the US.
EPA guideline in municipal and domestic wells of southem Ontario, with values up to 600 pCi/L
(1650 BqL). However, no provincial objective for radon in drinking water yet exists. The most
widely tested and available method for remediating drinking water containing high levels of radon
is by granular activateci carbon (GAC). This me of treatment system is able to achieve a steady
state removal geater than 99.95% over several years of use, even with radon levels of 37,000,000
~ ~ / m ~ in water supplies (Lowry et al., 1987). The disadvantage of this system is that over time the
GAC itself will give off radiation as the accumulated radon decays reaching levels as high as 3 to 5
times greater than background (Shapiro and Sorg, 1988). The simplest method is simply to
increase indoor ventilation in rooms of heavy water use (such as in bathrooms) since inhalation of
air-borne radon is more hazardous than ingesting it in dissolved form (Otton, 1992).
2.8 RADON MEASURING TECHNIQUES
There are several methods available for the detection and measurement of indoor levels of
radon. These inchde active and passive alpha track detectors, charcoal canisters, Electret Passive
Environmental Radon Monitors (EPERMs), Continuous Radon Monitoring (CRMs) and quick
sampling. There are certain advantages and disadvantages to each methud. Usually the limiting
hctor is the cost of the equipment and the lengîh of the study peiid. EPERMs and CRMs are the
most expensive (between $2500 to $10,000 US) and charcoal canisters the least at $1 O to $25 US
per unit (Anonymous, 1986).
The radiation fiom radon and radon daughters are recorded by alpha track detectors as tiny
pits in a small piece of plastic. The number of pits is counted using a microscope or an automated
counting system and gives an estimate of the concentration of radioactive atoms (Anonymous,
1986). The accuracy of the resuits is increased if multiple detectors are used in the same area.
Active detectors use a srnall pump to force air through a fiker that traps the radon daughters and
only require a test period of 7 days as opposed to a minimum of thirty days require. by the use of
passive detectors (Becker, 1991).
Charcoal canisters use activateù charcoal to trap radon over period of several days. Air
diffises through a screen on the canister and radon will adsorb onto the charcoal and begin to
decay. These devices do not generally provide an accurate average reading due to the day to day
fluctuations in radon levels and the short half-tife of radon. Using this method requires that the
canisters be quickly retumed for analysis before much of the collected radon decays.
EPERMs have a plastic chamber that contains an electrostatically charged disc, or
scintillation cell. The disc becomes discharged when it becornes exposed to radon in air. The
concentration of radon is recorded as the difference in surface voltage on the &SC rneasured before
and afier exposure. This device can be used for short tem (2 to 7 days) and long term (2 to 52
weeks) study periods (Becker, 1991). Similar devices, Continuous Radon Monitors (CRMs) use
an air pump and can be programme. to nui continuously to record hourly radon concentrations for
up to 24 hours (Anonymous, 1986).
Quick sampling, or "grab sampling", pumps air through a fiker or a measurement ce11 lined
with zinc sulfide phosphor for about five minutes. Using a filter, the total alpha activity is counted
and that nurnber is convertexi to disinteptions. With the zinc sulfide cell, a photomultiplier tube
counts the Iight puises (scintillations) produced by alpha decays in the sample that react to the
inner coating. The number of pulses is proportional to the radon concentration in the cell. This
method gives a rough estimate of radon level and its probable source within a house. It is used
only as a quick and general indication of the radon nsk involved. It cannot give accurate
measurements of average radon levels since these levels can show large fluctuations on a daily and
weekly basis depending on ambient air pressure gradients, weather, temperature, etc. (Gundersen
and Wanty, 1993).
Soi1 gas measurements can be made by either burying a passive monitor device, such as a
charma1 canister or by analyzing samples in an alpha-scintillometer. A new metbod was developed
by the US. Geological Survey involving the latter technique (Gates and Gundersen, 1992; Otton,
1992). A hollow carbon steel probe is driven 1 m into the soil and soil gas is drawn into the probe
through small holes at the bottom tip and into a 20 rnL syringe at the top. The sas samples are
analyzed at the end of the day through an alpha-scintillometer. An older method involves digging
holes up to 2 m deep, 10 cm in diameter and sarnples are directiy circulated through an alpha-
scintillometer under high vacuum pressure for 5 to 15 minutes. The newer method is preferred
since it involves minimal disturbance ofthe soil and is less tirne-consuming.
2.9 RADON RPSK FROM UNREGULATED DUMPING OF RADIOACTIVE
WASTES
The above discussion has fmused on naturally occurring radon but locally, some urban
areas are at risk fiom unregulated historic dumping of low-level radioactive wastes. Jn the 1940's
and 1950's, radioactive productç were in widespread industrial use without any understanding of
healîh xisks associated with the manufacture, use and disposal of these productç. Much radioactive
rnaterial was simply dumped in outlying rural areas and forgoth. In the meantime, urbanization
has encroached into these areas resuiting in unexpected discoveries of waçte sites in residential
areas. There is an estimated 1.2 million cubic metres of historie Low Level Waste (LLW) in
Canada which will remain hazardous over the next 500 years (Auditor General of Canada, 1995).
Most of this waste was produceci in Port Hope, Ontario; other sites are located in Scarborough,
Ontario (see below), in Surrey, British Columbia and in various areas in Alberta and the Northwest
Tenitories.
Much of historic LLW has b e n recovered and is now store. at temporary facilities, but
several sites, principally in the Port Hope area and at several abandoned uranium mines in northem
Ontario, have not been remediated. Unremediated sites at Port Hope are not thought to pose an
irnmediate risk to the public, but could become a hazard ifphysical containment is disrupted or if
proper waste management practices are not followed. Tailings at uranium mines that ceased
operations prior to 1976, in the Elliot Lake and Bancroft areas of n o d e m Ontario are not subject
to current regulations and have not b e n inspected or monitored since their abandonment (Auditor
General, 1995). It was not until 1976 that the Atomic Energy Coatrol Board (AECB) introduced a
licensing system to ensure that uranium mining companies comply with provincial health and
safety regulations. Since the impact on the environment remains unknown, the communities living
near these tailings sites rnay be exposed to hazardous levels of contamination, of which radon is of
primary concern. The AECB has begun discussions with known owners of the sites to include
them under current regdatory control.
2.9.1 Example: Malvern, Scarborough, Ontario
Abnormally high indoor radon gas concentrations were detected in 1983 in two residential
subdivisions in the southwest Malvem area of Scarborough, Ontario at McClure CrescentiBurrows
Hall Boulevard and McLevin Avenue (Eg. 2:7). Contamination results fiom the dumping of waçte
products of a srnall World War II radium incineration and processing plant wfiich produced
radium-luminous paint and nighttime markers. At that tirne, use of radium-226 (='ka) was
unregulated and wastes were d q e d on nearby fim (McCallum, 1992). Above background
levels of radon in residential basements are the product of insoluble radium salts such as RaS04
(Haque, 1982). The health hazard associatexi with radon gas present is still under investigation
and yet, only tentative guidelines have been proposed for "acceptable" levels of radon gas
concentrations in basements. A level of 2piCL has been set as a tentative guideline in Canada
(Haque, 1982). Typicai background levels of Ontario soiis are 0.1 Bq/g or 2-3 pCi/g (McCalium,
1992). The measured 98th percentile concentration for radium in Toronto area soiis is 0.073 Bq/g
(2 pCi/g).
At McLevin Avenue, remedial action has b e n taken to reduce radon concentrations
seeping through basement wâlls and approh te ly 2500 m3 soii has been excavated and sorted
(Acres International Limited, 2993). Radioactive markers were shipped to the Low-Level
Radioactive Waste Management Office warehouse at the Atomic Energy of Canada Limited
FIGURE 2:7
Contaminated sites in Malvern Area of Scaxborough, Ontario (afier Acres International, 1993).
CONTAMINATED S E S
TEMPORARY STORAGE FAClLmES m
FIGURE 2: 8
Contaminated sites in residential area of McClure Crescent (after Acres International, 1993).
/ ~ P m p e r t i e s Eligibk For Governrnenf Purchare Sheppard Ave.
1- Miiner Ave.
(AECL) Chalk River Laboratones for ternporary storage. Some of the rernaining "mildly-
contaminated" soil is temporarily stored in a single mound on the site that is surrounded by fencing.
The nearest residences are 250 rn away to the north. Radiation levels rapidly decrease to
background levels within about IO rn of the mound (Acres International Ltd., 1993). There still
remains subsurfàce contamination in 3867 m3 of soil in a band 60 m wide under the McLevin
Avenue road allowance, which narrows to 15 m wide under the pathway to the Malvem Town
Center. It is considerd to pose no health threat to pedeçtnans in the area and no residences are
nearby. Further excavation and cleanup of the site is still required,
By 1983,39 homes had been identifieci at McClure Crescent and Burrows Hall Boulevard
as having contaminated soil that required removal (Fig. 2:8). In 1989, 15 homes had been
identified with levels of interior radon and radon daughter levels exceBdrng the established criterion
of 2pCin. It has been estimated that 7200 m3 of contaminated soil requires excavation, but no soil
has yet been excavated. On average, radium-226 concentration levels in the contaminatecl soils had
a value of 1.4 Bqlg and a maximum value of up to 12 Bqlg (320 pCi/g). The exposure associated
with living inside a house on uncontaminated soil al1 year round with natural background levels is
qua1 t o about 20 X-rays. The Malvem exposure is thought to be double that, qua1 to about 40
X-rays (Acres International Ltd., 1993). A site investigation is currently undeway at the location
for a semi-permanent çtorage fàcility for additional excavateci and treated contaminated soils until a
permanent fdcility can be developed in perhaps 5 to 10 years. The proposed site is located
immediately souîh of Passmore Avenue between Tapscott Road and Neilson Road (Fig. 2:7).
2.9.2 Example: Port Hope, Ontario
Port Hope was a major centre for radium processhg from 1933 to 1952 which resulted in
severe contamination of the inner harbour area (Hart et al ., 1986). In 1983, the International Joint
Commission found that uranium concentrations in harbour waters exceeded the maximum
acceptable concentration for dnnking water (20 rng/L; IJC, 1983). Smeys carried out in 1981
and 1982 showed that radium actiwty levels in the harbour were near or below the detection limit
of 37 xdq/L (1 .O p C Z ) and a 1986 survey showed that sediments wiùiin the inner harbour had
radium levels around 1 S6 Bq/g (42.22 pCi/g; Hart et al., 1986).
Several investigations have identified deformities in the larvae of rnidge fies (chironomids)
in Port Hope Harbour. Hart et al. (1 986) identifie- b ioaccda t ion faceors (ratios of the amount
of a trace substance incorporated into body tissue to the amount in the organism's environment) for
radionuclides and heavy rnetals in 40 benthic invertebrate taxa (including chironomids). Radium-
226 had the second highest bioaccmulation factor (1.94) afkr (9.59). Warwick (1991)
studied deformities in chironomid larvae across several aquatic basins in western Canada, along the
St. Lawrence Seaway and including Port Hope Harbour. Port Hope Harbow has the highest
frequency of deformities (12.28%) of any of the other sites except Lac St. huis afong the St.
Lawrence Seaway, where the index chironomid species has completely disappeared due to the hi&
levels of contamination. Warwick et al. (1987) estimated the radiation dose to the chironomids in
the contaminated sediments of Port Hope Harbour at 1 mGy/day. This dose is significant enough
to suggest that radionuclides in the harbour are the cause of the observed deformities. However,
because of high concentrations of heavy metals that also occur in the harbour, it is difficult to
isolate the effects of the radionuclides alone. Apart fiom chironomids, similar radiation doses have
b e n found not to be significantly detrimental to other invertebrates or small mammals (Warwick et
al., 1987). There is a clear need to determine what levels of radionuclides pose a hazard to
different types of aquatic organisms before any one organism can be ernployed as a diable
bioindicator of the degree of radioactive contamination in a given environment.
2.9.3 Example: Elliot Lake, Ontario
Elliot Lake was until recently the pre-eminent uranium-producing region of Canada;
production has shifted to Saskatchewan. Large-scale minkg operations in this area have existecl
since 1954 @ubrovslcy et al ., 1 984) and resuked in the dumping of 120 million metric tonnes of
uranium tailings are over an a m of 600 ha p a v e et al., 1985; Wren et al., 1987). Uranium that
could not be extracted, was left as solid residues and discarded along the rest of the tailings to
eventually become a source of radionuclide contamination through decay into radium, polonium
and lead. Tailing waters have a pH between 6 to 9, but seepage and nuioff fiom abandoned
tailings have pH values of 2 to 3 (Silver et al., 1985); progressive acidification of the tailings
promotes the leaching of radionuclides into gromd and surface waters (Moffett and Tellier, 1978).
Acidification results fiom the chernical and biological oxidation of pynte d i n the waste matenal
(see Bezile et al., 1995); typical levels of radium in Elliot Lake tailings are about 336 pCi/g.
Predatory mammals (e.g. otter, raccoon, mink) that f d upon benthic aquatic organisrns
near tailing sites accumulate radium. Deteetable levels of radium-226 have been found in otter
wah values ranghg frMn 0.2 pCi/g to 12.6 pCi/g (Wren et al., 1987). A control otter fiom a
remote area did not show detectable levels of radium. The source of radium is likely fish and
clams. River and lake waters sampled near the uranium tailings contauid 1 18.1 mBqL (3.19
pCi/L) of dissolved radium compared to a control site near Sudbury, Ontario which had a value of
12.1 mBqL (0.33 pCi/L).
Clulow et al. (1992) foiand elevated radium levels in mffd grouse near tailings sites in the
Elliot Lake watershed. Mean values were found to be 28.5 mBq/g (0.77 pCiJg). The leaves of
aspen and fimgal material upon which they feed had mean radium levels of 52.7 rnBq/g (1 -42
pCi/g) and 215.4 mBq/g (5.82 pCi/g), which does not suggest strong bioaccurnulation of radium in
grouse. Overall, the consmption of grouse fiom Elliot Lake does not consbtute a health problem.
Above-normal levels of radium have been found on the surfhe of blueberries from tailings spill
sites, but it is highly unlikely that a person would consume a large enough quantrty to exceed the
recommended dose limit. Samples collected within 500 m of tailing piles had radium levels
between 20 to 290 mBq/g (0.54 to 7.83 pCi/g), while natural background levels were 2 to 6 Bqlg
(0.054 to 0.162 pCi/g). To exceed the dose Iunrt, a person would have to consume 47 kg of
bluebemes per year. Wind dispersal of dust is primarily responsible for transporting and
depositing radium onto the blueberries.
The Auditor General of Canada (1995) warns that radon gas is being released from
uranium tailings and may be a hazard to hose living close to the sites or ifthe tailings are used in
construction. Radioactive waste will conhue to pose a hazard for tens of thousands of years.
Impacts on the environment and public safety of tailings sites abandoned prior to 1976 are not
known, leaving the possibtlrty that people are exposed to unacceptable levels of radioactiwty and
chemical toxictty.
2.10 DISCUSSION
The occurrence of radon in urban environments appears to be a common but poorly
understood phenomenon. Work in the US. and Europe suggest radon can be a signficant hazard;
in the absence of data in Canadian settings there is no room for complacency. Wrth improvements
in understanding of the geologic controls on radon; its importance as a potential hazard is
increasingly apparent. Recent work clearly shows that natural background radiation from radium
in natural soils may in fsct be sufficiently high to warrant classification of natural materials as
radioactive. This stresses the need for an accelerated program of radon surveys in urban areas
combined with systernatic mapping of geologic structures such as f a u h and fractures. A detailed
inventory of historie, unregulated radioactive waste is aIso urgently required.
CHAPTER 3:
RADON SOIL GAS SURVEYS IN SOUTH CENTRAL ONTARIO
CHAPTER 3: RADON SOIL GGS SUI[PVEBIS IN SOUTH CENTRAL ONTARIO
3.1 INTRODUCTION
In recent years, radon has become a recognized environmental hazard. Unlike the situation in
Canada, signifiant efforts have been put forth by governent agencies in the United States to raise
public awareness of radon's potential to cause lung cancer. Radon, in particular the isotope 2 2 2 ~ ,
is a cornmon gas occurritfg virtually in every natural environment on the earth. Produced by the
decay of uranium and thorium in rocks and soils, radon is an inert radioactive gas. Radioactive
daughter produdç of radon can attach to particdates and aerosols in the air. Inhalation of these
particles cm lead to the development of lung cancer. These effects are well documentexi in
communlties of uranium miners but have recently becorne a concern for the public at large. It has
been eçtimatted that about 10% of al1 lung cancers in the US. may be due to radon exposure
(National Research Council, 1994).
The distribution and concentration of radon in the environment is primarily limited by its
short half-life, therefore the transport processes that bring radon from source rocks to the surface
need to be well characterized. Upon initial release fiom its parent radionuclide into surroundhg
pore spaces, radon is then subject to molecular difision and advection for transport into s d c e
environments. The principal natural geologic sources are uranium-rich granites, gneisses and black
shales. Such strata underlie many urban areas in rnid-coninent North Amerka. Glacial deposits
and soils containhg clasts derived fi-om these strata can locally represent a significant radon
source.
Elevated radon levels are also known to be associated with subsurface geological
structures such as f h h s and fractures. These types of structures provide gas migration comdors
that allow soi1 gases to travel through soils much faster than by diffusion alone, even in saturated
environments, particularly where an abundant flow of a carrier gas occurs ( s e Section 3.2.2).
Fadk and fractures can therefore be identified as radon soil gas anomalies compared to
backgound radon levels in undisturbed soils. Measurement of in-siru radon as a natural
geochemicd tracer has been successfully demonstrated to be an effective and reliable methoci
(Bertin and Bourg, 1994; Tilsley et al., 1993; Tilsley and Nicholls, 1993; Hoehn et al., 1992; Bal1
et al., 1990; Ellins et al., 1990; McCarthy and Reirner, 1986; Card et al., 1985; Gingrich, 1984;
Morse et al., 1982).
Little is known regarding background radon levels and variabil@ across southem Ontario.
Tilsley et al. (1993) report results of a regional radon soil gas sampling program in souîhem
Ontario, hd ing a distinct correlation of elevated radon levels in soils with areas over known fà&
and oil and gas depositç within underlymg Paleomic strata. It was suggested that uranium and
radium were being transported to surfàce environments by volatile hydrocarbons escaphg upward
along fauk. Surface release of hydrocarbon gases near faults in southern Ontario is also reported
by Noor et al. (1 992). Regonal bedrock Edults and fracture systems are hown to have controlled
the development of suhsurface hydrocarbon reservoirs in southern Ontario (Sanford et al., 1985;
Sherwood Lollar et al., 1994). These structures have guided the 'pre-glacial erosion' o f a
channeleci topography on the bedrock surface (Eyles et al., 1993) suggedng that Edults and
fractures extend from depth to surface. Overlying Pleistocene deposits are also fi-actured (Wills et
al., 1992; Eyles, 1995). The same structures may localize the release of radon in urban
environments and control the spatial variation in soil radon gas.
The present study focuses on an area that overlies a major shear zone within the Mid-
Proterozoic basement in soutb central Ontario. The shear zone, known as the Central
Metasaentary Belt Boundary Zone (CMBBZ; Fig. 3:1), records the collision of two terranes
during the GrenvilIe Orogeny about 1.2 billion years ago (1.2 Ga). Recent evidence suggests that
FIGURE 3 : 1
(A) Location map of study area d i r i south central Ontario, Canada (see inset). Trend of CMBBZ across eastern GTA and Lake Ontario showing associated geomorphic features. Note the distinct thinning of the Oak Ridges Moraine above the structure. Contours (m asl) show elevation of glacial cover and i d e d e northeastward tilt of basin in response to more rapid post-glacial uplifi in that direction (after Eyles, 1997).
@) Schematic west-east cross-section of thmst fauits within CMBBZ structure identified by seismic refraction data (after Milkereit et al., 1992). Reactivation of fiults and fracturing of overlying Paleozoic cover and Pleistocene sediment cover is suggested by many data (see Eyles, 1997).
FIGURE 3:2
Detailed map of study area (refer to Fig. 3: 1 for regional view) with approximate locations of transects of radon soi1 gas surveys indicated by circled crosshairs (see text for description of transects). Thin dashed lines mark the boundaries of underlying Paleozoic bedrock formations (after Cayley and Liberty, 1968). Thick dashed lines follows outline the Central Mebsedirnentary Belt Boundary Zone (CMBBZ; after Eyles, 2997). Series of dasheddoüed lines represent interpreted surface lineaments from satellite imagery (afier Rutty, 1993). Note alignment of lineaments along the Nonquon River, D u f i s Creek and the western edge of the CMBBZ. Strong alignrnents of surfàce linearnents are also apparent surrounding Lake Scugog. Transects were placed as close to mapped lineaments as possible. The enclosure labeled "Study 1 Ara" represents the Markham-Stoufille survey area conductecl by Tilsley et al., 1993, which is discussed later in the text (Section 3.3).
FIGURE 3:3
North-south geologic cross-section showing subsutiace geology of the south flank of the Oak Ridges Moraine and the western tributary of Duffins Creek (after Howard et al., 1997).
the CMBBZ is characterized by low-Ievel seismic activ@ (Mohajer et al., 1992). NNE-trending
lheaments (Fig. 3:2) parallel with the CMBBZ appear through f aleozoic and Quatemary
sediments (cross-section in Fig. 3:3) south of the Canadian Shield (Eyles, 1997; Rutty, 1993;
Mohajer et al., 1992) suggesting recent reactivation.
The main objective of this study is to detemine normal background levels and anomalies
within the soi1 gases across various parts of the CMBBZ over Paleozoic and Quaternary sediments
in south central Ontario (see transeet sites on Fig. 3:2). Mapping radon levels can provide useM
information on subsurfhce structures in the study are . and most importantly, provides a means of
identifjmg areas where radon may be a hazard to health.
3.1.1 Health Risks From Radon Exposure
Most data on heahh risks is denved fiom US. studies; to date very hie work has been
conducted in Canada. About 2% of the 60 million single-fimily residences in the US. are expected
to have indoor levels exceeding 8 pCi/L (Nero et al., 1986). The current action level for radon set
by the US. Environmental Protection Agency (EPA) is 4 pCi/L (see Chapter 2). It has been
estimated that between 7,000 to 30,000 lung cancer deaths are attributed to radon each year, which
is qua1 to approximately 10% of al1 lung cancers in the U. S. (National Research Council, 1994).
Yet relatively rninor efforts have been put forward by governments to ensure public safety. With
regard to radiation exposure in general, prolonged exposure at low doses is associated with more
risk than shorter exposure at higher doses. Whether this relationship holds for the low radon levels
found in residential areas remains in question.
The National Research Council (NRC; 1994) of the United States argues that some 15%
of lung cancer deaths caused by radon exposure could be avoided by reducing radon levels greater
than 4 pCi/L. This amount of radon is estimated to occur in 5 rniltion of the 60 million homes in
the U. S. (Horgan, 1994). Zn addition, the risk of developing cancer fiom exposure to low levels of
radiation fiom X-rays and gamma-rays is three to four times as hi& as previously thought
(Vaughan, 1990).
h Metropolitan Toronto, Canada, 632 public schools were surveyed for indoor radon
levels (Becker and Moridi, 1992). Two schools were identified with basement radon levels equal to
or above the proposed Canadian action level of 2pC&. Three schools had levels between 1 to 2
p C f i . Controlling factors, however, were not investigated and there are few data regarding the
systematic variation in radon across urban areas in south central Ontario.
3.2 PROPERTES OF RADON GAS
Radon is a naturaily occur~g radioactive gas produceci within the Earth's crust fiom the
decay of uranium and thorium. Radon has no colour or smeli and is almost chemically inert
although it iç known to form compoundç such as fluorides and clathrates (Clathrates foxm when
radon atom becorne incorporateci into the crystal lattices of certain hydrogen compounds). The
three most wmon isotopes of radon are 219~n, U%n and "RU, al1 of which are radioactive.
The isotopes 21%n and 220Rn have very short half-lives of only 3.96 seconds and 56
seconds, respectively. Radon-219 is fonned through the decay of 2 3 5 ~ . Rn-220 is formed through
the decay of Due to the very short half-lives of these isotopes, they are usually not
environmentally significant, wah the exception of which may occur in greater concentrations
in thorium-enriched rocks (Martell, 1985; Schery et al., 1989; Schery 1990).
The most important isotope of radon, both as an environmental hazard and as a naturai
tracer, is " ~ n that has a half-life of 3.82 days. This isotope of radon is part of the uranium-23 8
decay series and its irnmediate parent is the radium isotope %a. Of total uranium, U 8 ~ is by far
the most abundant naturally occurring uranium isotope (99.3% abundance; has an abundance
of 0.7%). Radon-222 breaks down through a succession of decay products into 2'%b, which is
easily removed from the atmosphere by precipIbtion. During the decay process, two radioactive
polonium daughters ( 2 ' 8 ~ o and 'l4po) are produced. They becorne attached to particdates and
aerosols in the air which c m then be inhaled into the lungs and cause damage to surrounding
tissues by the emission of alpha (a) particles. Although 222Rn is relatively short-lived, it cm be
transport& by soi1 gas diffision, atmosphenc advection or groundwater flow and become widely
distributed away fiom its source.
Arnbient air has an average radon ievel of about 0.2 pCi per litre of air. Ambient soi1 has
levels fkom 20 to more than 100,000 pCi/L. Radon is soluble in cold water and rnay travel long
distances fiom groundwater sources and surfice waters. It is, however, more soluble in air than in
water and will readily pass into the gas phase when Ui contact with air. Radon dissolved in
groundwater can be as high as 3,000,000 pCilL (Won, 19%). Indoor air has radon levels that
average about 2 pCi/L. Uranium mines can have levels as high as 5000 pCi/L. In unusual
geologic circumstances, residential homes can have as hi@ as 7000 pCVL of radon in indoor air
(Ennemoser et al., 1993).
3.2.1 Geologic Controls on Radon
The concentration of naturally occuning radon in soils is primarily controlled by two
factors: (1) the source rock and (2) transport processes frorn source rocks into soi1 pore spaces.
The short half-life of radon ultimately limits the importance of these factors. Even wrth a Iow
relative abundance of the source material, groundwater or gaseous transport through structurai
conduits can significantly increase near-sufice radon levels. This is an important consideration
where radon potential studies are camed out relying solely on geological and gamma-ray surveys .
Several studies (e.g., de Jong et al., 1993; Hand and Banikowski, 1988; Kodosky, 1994) have
clearly shown that such prelimhary sunieys can grossly underestimate actual soi1 gas
concentrations of radon. Detailed in-situ soi1 sampIing surveys are required to determine the actual
abundaxe of radon.
3.2.1.1 Source rocks
Uranium concentrations dispfay a very wide range depending on rock type. In igneous and
metamorphic rocks, uranium has a tendency to be enriched in the more volatile phases in rnolten or
partially melted rocks as they cool. Rocks with low melting points, such as granites, have a higher
uranium content (10-40 ppm) than in higher temperature rocks, such as diontes and basalt (0.5-5
ppm; Keppler and Wyllie, 1990). Generally, the higher the silica content of igneous rocks, the
higher the uranium content. During metamorphism, rocks become more depleted in uranium as
heating proceeds and the uranium becomes remobilized and concentrated into the escaping gases
and liquids; pegmatite veins become enriched in uranium and thorium by the same processes
(Keppler and Wyllie, 1990).
Under certain conditions, sedimentary rocks can also become a significant reservoir for the
adsorption of uranium. The presence ofciay miner& and organic rnatter enhances the adsorption
of uranium within sediments once uranium has been weathered from its host rock (Bell, 1978;
Dyck, 1978; Flexser et al., 1993). Co-precipitation with iron oxide and formation of secondas,
minerals in pore spaces or fractures also commonly scavenge uranium and radium fiom sdution.
T'us, the surface of sedimentary grains wi be relatively enriched in radium. Increasing clay
content is associated witb bigher radium content because of the greater surface area that clay
particles provide (de Jong et a1.,1993; Flexser er al., 1993; Keller et aL,1992; Loureiro et al.,
1990 and McCallum, 19%). Additionally, glaciallyeroded debris derived from uraniurn-rich
source rocks has been transported long distances and spread over large areas in tills and outwash
deposits (Gundersen et al., 1992; Tilsley, 1992).
The importance of clay content in determining z 6 ~ a concentrations in soils is supported by
data from Ontario. McCallurn (1992) determined 2 2 6 ~ a concentrations in sandy poorly developed
soils associated with coniferous forests in northern Ontario and in soils typical of mixed forests in
southem Ontario, where weathering and eluviation results in distinct soil horizonation and higher
clay content. The mean ' 'ka wncentration of Ontario soils ranges from 0.035 Bqfg to 0.053 Bq/g
with the highest concentrations in fine-textured soils of southem Onbrio.
Among sedirnentary rocks, organic-rich black shales and rocks containhg phosphate show
the highest uranium values, some approaching 1000 pprn. The uranium content of black shales is
usually around 8 ppm (compare- with the average crustal abundance of 2-3 ppm; Bell, 1978;
Won, 1992). In southern Ontario, the northern part of the Greater Toronto Area (GTA) is
underlain by Middle Ordovician black shales of the Collingwood Member of the Lindsay
Formation (Churcher et ai., 1992). Background uranium concefltrations of 6 ppm are reported by
Bell (1978). Uranium fiom the Collingwood Member may be the local source of radon gas within
the boundaries of the present study.
3.2.1.2 Role of faults and fractures
Many geochemical surveys show a close relationship of nea r - sdce gaseous anomalies
with underlying faults and fractures (see below). The formation of structural corridors or
intercomected microcracks within soils can sipificantly increase the migration distance of soil
gases. Such corridors can form along major unconfomities (Sherwood-LoIlar et al., 1994; Barker
and Pollock, 1984) or along fauks and fractures (Etiope and Lombardi, 1995; Jenden et al., 1993;
Gammage et al., 1992; Allan, 1989). Above-background Ievels of radon are predicted to occur
over these areas. Previous radon survey work has demonstrated that there is relatively little lateral
dispersion of radon as it travels toward the surface (Etiope and Lombardi, 1995; Tilsley et al.,
1993; Keller et al., 1992; Harrell et al., 1991; Schery and Siegel, 1986; Card et al., 1985;
Malmqvist and Kristiansson, 1985; Gingrich, 1984; Malrnqvist and Kristiansson, 1984; Morse et
al., 1982). This would allow near-surface radon detectors to identify the presence of a structural
migration pathway created by subsurface fiults or fractures where they penetrate into the near-
surface environment.
in crystalline rocks, groundwater velocities are significantly increased by the presence of
Çactures and can bring radon fiom depth to the surEdce (Folger et al., 1996; Andrews, 1991;
Krishnaswarni et al., 1982). However, this is not likely to occur Ui clays where water movement is
generally extremely slow, even if fractured, such that radon transport by groundwater is considerd
to be negligible in most cases (Gingrich, 1984). Diffusion alone can only transport radon over a
few meters on average. For greater distances, the principal mechanism for volatile migration is
mosi likely advective upflow via a camer gas induceci by pressure-driving forces such as those
created by fiult gases in seismically-active areas (Etiope and Lombardi, 1995; Virk and Singh,
1993; Bal1 et al., 1990).
Roberts (1991) suggests that the porosity and permeability of fault rocks change during
different increments of deformation due to gradua1 changes in the microtexture along the hult
plane. in this case, deformation likely occurs at a srnaII scale within fractures and result fiom
compaction and expansion of soils during pends of saturation or dessication. niffexentiai
movements along a fracture can seal some portions of the fiacture while opening up others. This
may reroute the migration of soi1 gases along different paths over t h e .
3.2.2 Transport Processes of Radon Gas
Given the short half-iife of radon, radon levels in surface environmenrs are controlled by
transport distances fiom source to surface. For example, where it takes a p e n d quivalent to six
half-lives (about 23 days) to pass through fiactured rock and soil, about 99% of the gas will decay
to non-mobiIe soiids before reaching the surface (Harrell et al., 1991). Even in dry, porous, high-
permeabhty matenals, radon will be diminished 100-fold (only 1% wiU survive) after a diffision
distance of only 6 m. The three main transport mechanisms that bring radon from its source in
soils or rocks to the surface environments are: (1) transport from the solid phase to either gas or
liquid in pore spaces by alpha recoil, (2) transport of radon relative to the gas or liquid by
molecular difision, and (3) transport of radon within soi1 gas or water by advection. Diffisive
transport of radon in soils is limitexi because of the short half-life of radon. Migration by diffusion
ranges trom about 5 m in grave1 to about 2 cm in saturateci mud or clay, and distances greater than
1 m are probably unusual (Tilsky et al., 1993; Rose et al., 1990; Michel, 1987). Advection is the
key mechanism in this study.
3.2.2.1 Advection
Advection either by groundwater rnovement or pressure-driven air flow can transport
radon over significantly greater distances than by diffision alone. Since radon is chemically inert,
the veIociS of groundwater flow itself ofhm controls its transport in groundwater systems. The
limiting factor in the transport length of radon in groundwater is its half-life. In 30 days, the radon
content of groundwater will be less than 1% of its original activity (Michel, 1987). The generally
slow movement of groundwater c m only transport radon 2 m before it decays to insignifiant
levels.
Transport of radon in air caused by pressure gradients is enhanced at times of low
atmospheric pressure, high winds, or significant temperatwe gradients between the soil air and the
atmosphere (Kokotti et al., 1992; Loureiro et al., 1990; Nazaroff et al., 1987). The pressure-
driven flow of radon is directly dependent on the permeabilQ (k) of soils where the overall mean
grain size is larger than sik or fine sand, and where k>1 .O x 1 ~ ' ~ m ' . Below this value, transport by
diffusion dominates Qureiro et al., 1990).
Atmospheric pressure changes can also cause a "pumpmg effect", bringing Rn fiom depths
to the surface (Chai er al., 1995; Schumann et al., 1992). A few percent change in barometric
pressure can result in changes of Rn flux by several tens percent (Gingrich, 1984). These
mechanisms however, would not provide the sufficient driving force for more clayey basins and
would require special fivourable conditions such as very permeable soil and extraordinary
geoîhennal and pressure gradients (Etiope and Lombardi, 1995).
In most cases, the transport distance of radon by diffusion and advective processes
combined is Iess than 3 m. Thus the source of radon is usually nearby within the soil or surficial
sediment, and not in the deeper underlying bedrock (Michel, 1987). However, Harrell et al. (1991)
in Ohio dernonstrated that nearly al1 the radon measured in residential homes buiit above black
shales had been transported distances well over 30 m.
An alternate mode1 of radon transport by carrier gases is presented below in Section
3.2.2.2. PubIished works on this subject matter is not extensive, but do provide an excellent
explanation of observed phenornena wiîh experimental and field data that strongly support the
theoql.
3.2.2.2 Carrier gas mechanism
Uranium is a common constituent in most geologic environments at an average cmçtal
abundance of 2-3 pprn (Wikening, 1990). Since U is such a ubiquitous element, Rn is naturally
found in detectable amounts everywhere in the atmosphere and in the soil gas. However, it
normally occurs only in trace amountç. In the near-surface environment, the radon concentration is
usually in the range of 10 to 1000 pCi/L. This is quivalent to 5 x 20-" to 5 x 10'15 parts of Rn per
part of soil gas on a weight basis (Etiope and Lombardi, 1995).
Since Rn nomlly exists oniy at these extremely low concentrations, it is always found
mixed with other soil gases, which are composed of mainly air of atmosphefic origin and water
vapour. The number of radon atoms is too smI1 to conçtihrte a macroscopic strearn of pure radon
gas; it is therefore more likely that radon atorns are being transported to the surface by a cimier
gas. Among the possible camer gases thought to be important in most environments are &, He,
CO, COZ, HzS, S02, CH, and H20 (Etiope and Lombardi, 1995; Gingrich, 1984; Malrnqvist and
Kristiansson, 1984; Sugisaki, 1987; Sugisaki et al., 1983). There are also several reports that
cIearly demonstrate a strong correlation between radon and volatile hydrocarbons over oil and gas
reservoirs (Morse and Zinke, 1995; Tilsley Nicholls, 1993; Card et al., 1985; Gingrich, 1984;
Morse and Alewine, 1983; Morse et al., 1982).
These soil gases are postulated to form ascending streams of microbubbles that can escape
to the surface through groundwater-filied fractures. The formation of these bubbles requires the
groundwater to be oversaturated with gases. In this way, once a gas bubble is formed it is able to
propagate upward through the groundwater due to its buoyancy. This condition of oversaturation
is a common occurrence in most groundwaters (Malmqvist and Kristiansson, 1984).
The creation of a gas bubble requires a nucleus, even in an oversaturated system. The a-
particle disintepration of U-senes radionuclides creates a large local energy transfer fiom a charged
particle to the oversaturated water. This energy transfer can trigger the formation of a stable gas
bubble. This effect is the fundamental principle behind the use of bubble chambers in high-energy
particle physics (fast-moving charged particles leave a track of tiny bubbles in a superheated
liquid; Serway, 1990). The creation of these bubbles can also be simulated in the laboratory by
submerging a uranium-nch rodc sample in ordhary carbonated minera1 water (Malmqvist and
Kristiansson, 1985). As the uranium undergoes adecay, tiny bubbles Stream upward from the
sample almost immediately, demonstrating how easily this phenomenon can occur in natural
groundwaters. Once the free gas bubble is created it is forced upwards by its buoyancy. The gas
can never again go into solution since the gromdwater at shallower Ievels is already saturatted with
gases. Etiope and Lombardi (1 995) have observed that favourable conditions for the bubbles to
ascend are in hcture zones, joint systems or fàults.
The ascending gas has the properties of sîrearning matter. Consequently, any impermeable
obstacle or any c a v i ~ can distort the flow pattern. Alternatively, structural corridors created by
bedding planes or fiachues cm channel the soi1 gas along a prefemd direction. Gas flow c m be
an order of magnitude higher than where channeling does not occur (Malmqvist and Kristiansson,
1984).
Microbubbles also have the abilrty to pick up matter @as as well as solid atoms) fiom
rocks. The bubbles can lift these upward by particdate flotation, as an aerosol inside the bubble
and bindmg of elements onto the surface of the bubble at the gas-water interface (Pattenden et al.,
198 1). Lifted matter may be released and concentrate where bubbles burst. Although it has been
experirnentally proved that radon appears on water surfaces after bubbling water with air, there are
FIGURE 3 :4
Schernatic model of radon transport through a fàult in low U-bearing rocks by a carrier gas mechanism. Continuous stream of CO~microbubbles lifts radionuclides by flotation or aerosol transport into the near-surface environment to produce a Rn-CO2 couplai anornaly. From Etiope and Lombardi l995.
Soil gas anornaly
Rn
CO2
diffusion or presçure-driven Row
groundwater lwel
water-filled fracture
.ascenjing tubties of carrier gas (CO2)
radionuulide lifting by flctation or aerosol traisport
no experimental data hown as yet on Ra and U transport by bubbles (Etiope and Lombardi,
1995).
Geogas flow probably does not transport Rn from localized or very deep sources. It may
be that microbubbles pick up Rn atoms emitted by the normal content of Ra of clayey rocks andior
directly pick up its parent radionuclides during upward migration through faults (Fig. 3:4; Etiope
and Lombardi, 1995). The geogas microbubbIes become increasingly ennched with radionuclides
drawing them fiom several geological horizons. Once the microbubbles reach the water table, they
burst and release the radionuclides. Radon then may migrate by diffusion andlor advection
towards the sufice. Since radium and uranium have long half-lives, high migration rates are not
required to produce soil-gas Rn anomalies. It is worth noting that such a process requires neirher
the occurrence of any specific or localized radon source nor large migration velocities essential for
admitting a radon orïgiri from very deep U-bearing rocks or fluids. This hypothesis, however, still
requires experimental validation (Etiope and Lombardi, 1995).
The follo~ving section describes radon soil gas surveys that havs been conducted to date in
southem Ontario. These surveys are of a reconnaissance nature and have not thoroughly exarnined
the regional or local geoiogcal controls on radon.
To date, the most signifiant work done regarduig radon soil gas masurement in southem
Ontario has been that of Tilsley et al. (1 993) and Tilsley and Nicholls (1 993). These will be
referred to as Study I and Study 2, respectively. Study 1 provided a testhg ground for the
reiiability of using radon soi1 gas measurements as a possible prospecting tool for hydrmrbon
resources in southem Ontario. Study 2 involved more intensive surveying in southwestern Ontario
over known oil and natural gas fields and fault zones. Their results confirmed the value of using
radon soil gas surveys as a means of delineating subsurfice structures in natural environments.
nie results of Study 1 are of particular importance in that they established background
radon levels in the Markham-StoufMle area, close to the present study area Ipartly outlineà in
Fig. 3:2). Resultç are sununanzed in Tables 3: 1 and 3:2. The average background radon level was
determinecl as 153 pCi/L, which is considered typical for glaciated terrains in southem Ontario.
Values that exceeded 300 pCi/L were considered to be related to movernent of hydrocarbon
volatiles fiom the black shdes of the underlying Collingwood Member of the Lindsay Formation
(refer to Section 3.4.3). It should be noted that this area overlies part of the Laurentian Channel,
which has the thickest overburden in southem Ontario approaching 150 m thick.
Results from Study 2 in southwestern Ontario confimed that typical background radon
levels over glacial sediments are between 100 to 200 pCUL (see Table 3:6). This study also showed
that radon levels measured over known faults were two to three times above background, wrth
values between 350 to 500 pCi/L. An exarnple of a typical transect readmgs above known faults is
illustrated in Fig. 3 5 . The highest radon levels were measured over boundaries of productive oil
FIGURE 3 : 5
Example of radon soil gas measurements over fiuited structures in oil and gas fields of southwestern Ontario, by Lake St. Clair, and acçompanying table of data. Anomalies ideritifid over hults are between 2 to 3 times above background radon levels (100-200 pCi/L). Note that apparent radium value is an indirect measurement based on radon generated from a soil sample within a confineci space of h m volume (fiom Tilsley and Nicholls, 1993).
Dover Gas Field 1 Mean Rn (pCÿ1) Rn Range (pCi ) 29.3 - 9 3 6 Standad Deviaibn U Concentration 3.63 mm Ra CmcenEratim 0.20 pcilg
TABLE 3: 1
Summanzed results of radon soi1 gas study in souîhern Ontario by Tilsley et al., 1993, referred to as Study I in text.
Windsor (380 km2)
Wallaceburg (680 km2)
Markham - Stouffville (290 km2)
Prince Edward Belleville
, (280 km2)
Study Area ( pc i i )
230.8 217.1
180.4 261.4 453.7
161.5
149.3
143.9
143.4
144.4 111.8
Clay Till over dolostone and lirnestone Clays/Clay Till on eskers over dolostone and limestone
Env't
Glaciolacustrine clay, siit, sand over black shale till Black shale till over Kettle Point Formation black shale Glaciolacustrine on black shale till within known oil and naturai gas pools
Rn Mean Range Environment Description
Sand and gravel veneer on Haiton Till over Collingwood Member black shale Haiton Till over Collingwood Mernber black shale Sand and gravel veneer on Haiton Till overlying Georgian Bay Formation limestone and dolostone Haiton Till overiying Georgian Bay Formation limestone and dolostone
Shallow till above fauit zones in lirnestone and dolostone Shallow till over unfauited limestone and dolostone
TABLE 3:2
Detailed resuits fiom Study 1 withm the Markham-Stouffville area (partly indicated on Fig. 2). These results represent the normal background radon levels typical of glaciated areas in southem Ontario. This area is adjacent to the present study area. Refer to Table 1 for description of Environments 1 to 4. From Tilsley et al., 1993.
Env't 1
2
3
4
1 Rn (1) Rn (2) Rn (3)l Total Mean 1 160.50 166.32 163.21 1 161.26
and gas fields widi values reaching over 1500 pC&. As noted in the previous section, outgassing
volatile hydrocarbons are an important carrier gas for radon. Volatile hydrocarbons are channeled
along faults to the suiface and are able to transport small quantrties of uranium and radium into the
soils of the region.
3.4 PEYSICAL SETITNG OF THE STUDY AREA
The study area (about 530 km2), shown in Figures 3: 1 and 3 2 , lies above a major geologic
structure in the underlying mid-Proterozoic basernent of south central Onbrio. This structure, the
Central Metasedimentary Belt Boundary Zone (CMBBZ) extends fiom Quebec south into Ohio
(Akron Magnetic Lineament). This structure passes below the eastem half of the Greater Toronto
Area (Fig. 3: 1). The geology of the structure has been documentecl by Milkereit er d. (1 992) and
is seisrnicaliy active (Mohajer et al., 1992). The structure is overlain by 200 m of Paleozoic strata
and up to 150 m of Pleistocene glacial strata and is expressed at surface by lineaments that form
depressions and elongate 'finger Iakes', which are depicted no& of Lake Scugog in Fig. 3: 1
(Rutiy, 1993; Eyles, 1997). Frenchmans Bay and DufIins Creek are closely associated with the
CMBBZ and a prominent lineament crosses a prominent glacial moraine (Oak Ridges Moraine;
Fig. 3: 1) that is no older than 13,000 y.b.p. LIneaments appear to lie above thmst Eaulîs that
compose the CMBBZ (Eyles et al., 1993; Eyles, 1997) suggesting geologically recent actiwty
along the CMBBZ.
A number of transects were chosen across the trend of the CMl3BZ and associated rnapped
linearnents in order to establish radon levels near the heaments. What foUows is a brïef overview
of the geology of the area prior to description of methodology and data collection.
3.4.1 RegionaI Geology
The regional geology of southem Ontario consists of three main units separated by major
unconformities:
Complexly stmctured Proterozoic basement rocks between 1300 and 1100 million years oId
(1300 Ma and 1100 Ma). These -ta extend to the base of the continental crust some 50 km
below the ground surface (Easton, 1992).
Southwestward-dipping lower Paleozoic sedimentary wver strata, up to 500 m thick, deposited
between 500 and 450 million years ago (Johnson et al., 19%).
Late Pleistocene glacial sediments yomger than 100 ka in age (Eyles and Williams, 1 992), but
as much as 200 m thick.
3.4.2 Proterozoic Basement
The basement in southem Ontario lies within an orogenic belt callecl the Grenville
Province, the result of a collisional event (Grenville Orogeny) that took place about one billion
years ago (Ga). During this event, the continental mass called the Central Metasedimentary Bek
(1100 Ma) was thmst over the Central Gneiss BeL (>1350 Ma) in a NW direction (Easton, 1992).
The shear zone that resulted from the d i s i o n of these two masses is calied the Metasedimentary
Belt Boundary Zone (CMBBZ) @aston, 1992; Fig. 3: 1 and 3:2). A cross-section. through the
CMEBZ is shown in Fig . 3 : 1 B.
The CMBBZ is at Ieast 200 km long and 8 to 10 km wide and trends along a NNE strike
fiom the Ottawa River near Pembroke across southern Oatario beneath the Paleozoic cover
(Hanmer and McEachem, 1992). The CMBBZ can be rnapped as an aerornagnetic linear anomaty
that extends from Ohio (the Akron magnetic lineament; Seeber and Ambruster, 1993) to western
Quebec.
In southeastem Ontario, the boundary zone has been calIed the Niagara-Pickering Linear
Zone (NPLZ) by Wallach and Mohajer (1990). Interpreted faults (Fig. 3: 1B) have a shallow dip
(15"-309 to the east below Lake Ontano and Lake Erie. Within the CMBBZ, brittle fàulting has
been observed in Precarnbrian rock, accompanied by vertical displacements of Upper Middle
Ordovician rocks, along major NNE-oriented lineaments (Wallach and Mohajer, 1990; Wallach,
1990). This suggests physical evidence of post-Upper Middle Ordovician reactivation of the
CMBBZ as has been identifid for areas of southwestern Ontario by Sanford et al. (1 985).
3.4.3 Paleozoic Cover
The Paieozoic sequence in south central Ontario has a regional dip away fiom the
Algonquin Arch of 5.5 to 8.5 m per kilometer fiom north to south. The Paleozoic sequence
thickens from 130 m at the northern end of the study area (Saintfield transect) to slightly over 200
m at the southern end, about 6 km north of Pickering @u&s Creek transects).
The gently dipping basement peneplain in southern Ontario is covered by a layer-cake
succession of Paleozoic sedunentary strata (lirnestones, dolostones, shales). The northern margin of
Paleozoic cover rocks m s approxirnately west-east some 50 km north of the GTA; to the north
lies the exposed Proterozoic basement (shield). The study area is underlain by shales of the upper
Ordovician Whitby (now calied Blue Mountain) and Lindsay formations (partly outlined in Fig.
3:2; Churcher ef al., 199 1; Lehmann et al., 1995; Tilsley et ni., 1993). The Blue Mountain
Formation, deposited d u ~ g the Upper Ordovician period, overlies the Middle Ordovician
Collingwood Member of the Lindsay Formation. The Collingwood Member consists of black,
biturninous oil shales (Churcher et al., 1991). As discussed in Section 2.2.1, black shales tend to
be enriched with uranium and the Collhgwood Member may be the local source of parent
radionuclides of radon in the study area. Background uranium concentrations of 6 ppm are
report4 by Bell (1 978), tiiough this may not represent the most accurate figure. These shales are
between 5 to 7.5 rn in thickness in the study areas, except at Shirley (SRY) where they are between
7.5 to 10 m thick (Churcher et al., 1991).
There is no sedimentary record of the period between the Silurian and the Pleistocene in
south central Ontario. Any sedimentary record fiom the long time interval between the Silurian
and the Pleistocene, if it was present, has been eroded. Late Jurassic igneous rocks occur as
intrusive dykes just beyond the eastern border of the GTA in Belleville. These record the opening
of the North Atlantic Ocean at about 175 Ma (Elarneîî et al., 1984) when southern Ontario was
subject to uplift, extension and erosion (Miller and Duddy, 1989). As much as 7 km of mata is
thought to have been eroded (Eyles et al., 1997).
3.4.3.1 Buried Bedrock Topography and Pre-Glacial Drainage
The upper surface of Paleozoic strata, now blanketed with Pleistocene glacial deposits,
forrns a distinct paleotopography. This surfice is in places deeply weathered (to depths of 10 m)
and is cut by nurnerous channels (e.g. Duffu-is Creek valley, Fig. 3:2). These channels identie a
former rnid-continent river system that either drained southwestward through the Erie Basin to the
Mississippi River, or more likely, east to the Atlantic (Eyles, 1997; Eyles et al., 1997). The age of
this system is unknown, but it has been rnodified, and in places overdeepened below the natural
grade of the channel, by glacial erosion. The orientation of bedrock channel segments, bedrock
joints and basement structures is, in many areas, virtualIy coincident, suggesting a structural pre-
design to the evolution of the channel systern (Eyles and Scheidegger, 1995). Subsuflace mapping
of the paleozoic peneplain surîace to the south also identifies northeast-trending faults passing
through the study area and below the GTA (Bailey Geological Services Ltd., 1984). These have
the same trend as faults wRhin the CMBBZ suggesting a genetic relationhip. Buried bedrock
valleys beIow the thick glacial cover have been eroded along these zones of fracturd rock.
3.4.4 Pleistocene Geology
The study area has been subject to several recent subsurfàce stratigraphic studies and there
is considerable information regarding the thickness and characteristics of Pleistocene strata
(Howard et al., 1997). The area comprises an extensive west-east trenrling belt of rnorainic
uplandç (Oak Ridges Moraine) where drift thichess approaches 150 m and the so-called 'South
Slope' (Chapman and Putnam, 1984) drainhg to Lake Ontario. A north-south stratigraphic cross-
sedion passing through the transects shown in Figure 3:3 and along the trend of the CMBBZ and
the buried Duffins Creek valley in Figure 3:2. The P le i s twe stratigraphy consiçts of extensive
aquitards (e.g., the sdty-sand Northem-Newrnarket Till) separated by aquifer units such as the
Thomcliffe Formation and were deposited during the last (Wisconsin) glaciation 1.e. over the last
80,000 years (Berger and Eyles, 1994). Sediments are exîensively fiactured resuhg in hi& rates
of vertical groundwater flow across aquitards (Gerber and Howard, 1997). Fracîures are
systematically related to regional neotectonic stress fields and it has been suggeçted that they have
propagated upwards ffom bedrock joints possibly as the result of repeated glacio-isostatic
uploading and unloadiug ofthe cmst (see Eyles and Scheidegger, 1995; Eyles et al., 1997). This
process continues at the present day and the area is slowly being uplifted at a rate of about 20 cm
per century (Eyles, 1997).
3.5 FIELD WORK:
Data were collected in two field seasons of 1995 and 1996, henceforth referred to as Phase
I and Phase II, respectively. Radon soi1 gas investigations during Phase I were conducted as
reconnaissance work to test the viabdity and reliabllrty of the radon detection method. Only single
readings were taken at each of the three transect locations of Phase 1. More transect locations were
added during Phase II and included repeat measurements in order to determine background radon
Ievels with greater confidence.
To test the reliabhty of the radon measurement equipment and sampling mediod, two
detectors were placed within one detedor package. Five paired detector packages were deployed in
Phase 1 and during Phase II, two pairs. Both detectors within a single pair should read the same
amount of radon emanating fiom each sample point. The resuhs of these measurements are
presented in Section 3.5.2.3.
Some smail-scale experiments were also condudeci to test the possibdity that uranium-
enriched clash could be producing some or aU of the obsenied radon anomalies. Usiog the same
deteaion method, radon ernanation of various clasts was measured within air-tight jars. Results
are presented in Section 3.5.2.4.
3.5.1 Methods
The methods and the equipment descnbed here follow the work of Tilsley et al. (1993) and
Tilsley and Nicholls (1 993).
3.5.1.1 Equipment
The E-PE- (Electret Passive Environmental Radon Monitor) system obtained from
Rad Elec hc . of Frederick, Maryland, USA. It was seleded as the most cost-efficient and sirnplest
m&od for the radon soil gas surveys and has passed a senes of tests conducted by the US.
Environmental Protection Agency (Kotrappa et al., 1990).
This system is based on a set of passive monitoring devices and a reader unit. The
monitoring device consists of an electret mounted inside a small(50 mt) ionization chamber made
of electrically conduding plastic, which minimizes the influence from natural gamma radiation.
An electret is a charged ~ e f l o n ~ disk that cames a static electric charge. Radon passively
diffuses into the ion chamber through a small filtered hole. The filter removes airborne radon
progeny and dust. Within the ion chamber radon spontaneously decays and creates ions that are
attracted by the surfàce charge on the electret. When ions strike the electret the &tic charge is
reduced. The vokage drop causeù by ions skiking the elecuet is proportional to the concentration
of radon in the ion chamber.
The reader unit is a calibrated surface voltage meter that measures the voltage on the
electret before and after radon exposure. The voitage drop can be converted to average radon
concentration during the p e n d of exposure by relatively simple calculation (see Appendix A).
The manufàcturer produces a variety of electret monitors for different applications. The
"long tenn" electrets were chosen for this work since relatively long exposure times are oecessary
for the evaluation of soil gas radon. This type of electret perrnits placement of a detector in an
FIGURE 3 :6
Schematic diagram of detector package conii@on for in-situ radon soil gas measurement.
Plastic sheet
environment with an average radon concentration of 200 pCdL for 85 to 90 days. Alternatively, it
can be placed in soils with 1000 pCi/L of radon for about 16 days before it discharges below a
usefül voltage. The Iower limit of detection (definecl as the radon concentration that c m be
measured with an error of 50%) is about 0.54 pC& at higher voltages (around 700V). At lower
voltages in the area of 200 V, the detection Ilmit iç 0.76 pCin (Kotrappa et al., 1990).
The E-PERM'M system was originally designed to monitor indoor radon levels and
therefore requires rninar modification for in-situ readings. The sweys of this study employed the
technique developed by Tilsley et al. (1993). The modifications involve the protection of the
detectors fiom wetness and dirt, since either can cause voltage discharge if they contact the electret
surface. The voltage readers must also be kept fie of dust, moisture and dirt.
Protection of the detectors was achieved by first placing each me in a ~ ~ v e k ~ envelope
which was folded around the detector and then pushed to the bottom of a 750 mL plastic container.
The envelope and detector were secured in the container by a smail plastic drinking cup wfiich, in
turn, was held in place by a glass fibre tape pulled across the mouth of the container. This
arrangement permits the "package" to be inverted when placed in an excavation in the soil (Fig.
3:6). This configuration, similar to the principle of a diving bell, keeps an air bubble in the
container to protect the detector fiom becoming wet if the sample location floods. The ~ ~ e k ~
envelope keeps the deteaor clean and relatively dry under most conditions. ~ ~ v e k ~ is waterproof
while capable of allowing water vapour (and radon gas) to pass through. A plastic sheet,
approximately 90 cm x 90 cm, was placed over the detector package in the excavated hole before
replacing the soil back on top. The ends of the plastic sheet were left extended out of the hole both
as a means of marking the hole and as a rneans of easily pulling out the soil plug to retrieve the
detector package.
A correction factor is necessary to account for background gamma radiation from cosmic
rays and fiorn isotopes such as within rocks and soils. An average background gamma dose
correction value of 10 pR/h was recommended by the manufacturer (1 @=~o'R, 1 roentgen
(~)=0 .87~10-~ gay (Gy)). In any case, the calculated correction for background gamma dose
usually only amounts to less than 5 pCi& flilsley et al., 1993). For areas with an average
background of 100 pCiL, this constitutes less than 5 % error.
3.5.1.2 Selection of transect sites
Transect sites were frrst determine- based on the satellite lineament interpretation maps
provided by Rutty (1993; Fig. 3:2). Field investigations of these areas identifid exact locations
for each transect based on access, topography, height above the water table and anthropogenic
factors. Since the lineaments on the satellite images refer to linear depressions on the surfice, at
ground level, these appear as valley systerns. Thus, transe& were placed at or near the bottom of
d e y s perpendicular to the interpreted linearnents in a generally east-west orientation along
roadside allowances, furthest away from the road as possible.
During the radon survey of 1995 field season, Saintfield (SF), D u f i s Creek @Cl) and
Claremont-Balsam (CH) were selected as initial trial locations. At that tirne, only 25 detectors in
total were available and five of them were doubled up to check the reliabil* of the readings. This
provided important information on how to improve the results for the subsequent 1996 survey.
For the1996 survey, five dBerent transect locations were selected. The Duffins Creek and
Claremont-Balsarn locations were used again although the actual transects were offset from their
original positions (hence named DC2 and CB2). The CB2 transect was discontinued because of
relatively high road traffic and pro* to private residential property. Greenwood-Kinsale (GK)
and Shirley (SRY) locations were relatively quiet, farmland areas. Another transect @C3) was
added adjacent to the DC2 transect, about 200 m further east to try to determine background radon
levels. One hundred detectors were available for this survey. About 20 detectors were deployed at
each transect location except at Shirley, where 40 detectors were used.
3.5.1.3 Sampling method
The procedures descnbed here follow those established by Tilsley et al. (1993). Each
detector package was p l a d in a 15-20 cm diarneter excavation made with a narrow peat spade.
Installation was at the botîom of the "B" soi1 horizon except in soils that had been altered by
construction or d e r disturbances. Placement depth ranged from 2540 cm. Most ofîhe sample
sites chosen for these studies were located on public lands, usuaUy within the lirnits of provincial
and municipal highway rightssf-way. Al1 sample sites were inspected to avoid placing detectors
where radon concentrations rnight be infiuenced by human actiwty (e.g. buried seMce lines, field
tile drainage and use of phosphate fertilizer).
It should be noted that when conducting soi1 gas surveys, that there may be pronounced
variabil@ in radon concentrations from one sample point to another, even within welldefined
geological envirouments. These variations may be attnbuted to geological factors, weather
changes, anthropogenic disturbances, et cetera. Therefore, the probabihy of repeating any assay
within +/- 10 % is generally low (Tilsley and Nicholls, 1993).
A sample spacing of 2 m to 10 m was chosen. Spacing greater than 10 m would lose detail
in radon variations such that the proposed migration comdor structures couid be missed entirely.
Each detector package was placed 20 to 30 cm below the surface. Twenty to thirty detectors were
used at each sample point, except in the first two preliminary assays. Since the number of
detectors available limits the study and most irnportantly by the amount of time available in which
to conduct the surveys, 20 detectors was considered to be the most reasonable number per transect.
At Shirley, however, 40 detectors were deployed wrth a wider spacing along each end of the
transect (up to 20 rn apart) in order to determine "normal" background levels of radon away fiom
the valley center.
The wide range of influences that can affect radon variability (ie. geology, weather, and
anthropogenic) further complicates soil sampling. Transient fluctuations due to changmg weather
conditions and other daily, monthly and seasonal &dors can dqress or accentuate short-term
concentrations. Nonetheless, it was determined that, except d u ~ g flooding of samp1i.g sites,
exposure times as short as 7 days were sufficient to define an anomaly (Tilsley and Nicholls,
1993). Radon measurements were taken at least 8 days after initial placement of detectors to
determine the electret discharge rate and the length of tirne the detector could be left in the ground
before reading and replacement would be neceçsaiy. Additional readings were taken after similar
lengths of t h e after deployment of detectors.
3.5.2 Results
This study has characterized radon in the soils of south central Ontario. These results
agree with those of previous workers but also extend earlier fjndings. The mean radon level of the
total survey is 22 1 pCi/L (Table 3:3). This is slightly higher than what is expected based on Study
1 and 2 in Section 3.3 (background levels fiom these studies ranged between 100 to 200 pCi/L).
This averaged value is also somewhat misleadhg since it does not reflect the wide range in data
that can be as low as 15 pCiL to as high as 1000 pCi/L, producing a standard deviation of 76%
(1 69 pCi/L). This mriability occurs over very short distances of only five to ten rnetres ( s e
graphs, Fig. 3:7 and 3:8). Part of this variability is due to differences in soil moisture at each
sarnple point and seasonal effects (see Table 3:5). As for the reg, there is no simple explanation
for such high contrasts in radon emanation under similar geological conditions.
TABLE 3 :3
Summarized results of Phase 1 and II of present study. Complete field data are in Appendix iii. Columns marked Rn(1) to Rn(4) represent repeat measurements made at separate intervals of time per iransect location.
Rn(1) Rn(2) Rn(3) Rn(4) Total 1
Cl Range (pCilL) Mean (pCiIL) SD (pCilL) SD (%)
:BI Range (pCiiL) Mean (pCill) SD (pCilL) SD (%)
Mean (pCilL) SD (pCiIL) SD (%)
Range (pCi/L) Mean (pCilL) SD (pCilL) SD (%)
Range (pCilL) Mean (pCilL) SD (pCi1L) SD (%)
Range (pCiIL) Mean (pCi/L) SD (pCilL) SD (%)
Range (pCi1L) Mean (pCiIL) SD (pCi1L) SD (%)
TABLE 3:4
Estimated background radon soi1 gas levels are listed here for each transect along with the mean of identified anomalies. The magnrtude ofthe anomalies is compared to the estimated background level. Anornaly magnitudes pater than 3 strongly suggest the presence of subsurface structures, while those between 2 to 3 indicate possible migration comdors for radon.
Phase Transed Total Estirnateci Anomaly Anomaly Location Mean Background Mean Magnitude
(pCilL) (pCi l l ) (pCilL) (from bkgd)
I SF 314 261 403 1.5 DCI 140 IO1 234 2.3 CBI 118 93 181 1.9
II OC2 161 85 31 8 3.7 DC3 257 21 6 373 1.7 CB2 490 443 683 1.5 GK 252 1 52 462 3.0 SRY 190 141 340 2.4
TOTAL 22 1 188 393 2.1
FIGURE 3:7
Graphical presentation of Phase I results of radon soi1 gas survey. Al1 transects are approximately perpaidicular to proposed linearnents, at the base of d e y s . Extreme anomaly at CB 1 with a radon value exceeding 500 p C f i may be an equipment error.
DC1 Transect
O 10 20 30 40 50 60 110 120 130 140 150 160
Distance (m)
SF Transed
O 10 20 30 40 50 60
Distance (m)
CB1 Transect
O 2 4 6 8 10 12 14 16 18 38 40 42 44 46 48 50 52 54 56
Distance (m)
FIGURE 3 : 8
Graphical presentation of Phase II results of radon soi1 gas survey. Note that DC2 and CB2 are nd positioned exactiy over DCl and CBl, but are adjacent to the original sites. Resuits of CB2 are combinai on the same graph as DC3, but are not meant for cornparison. See text for discussion of resulîs.
PHASE Il
DC2 Transect
Distance (ml - 0- -2nd Readin -3rd Reading - - X- - 4th Readina
DC3 I CB2 Transects
Distance (m) + OC3 1 st Reading 1 - Ci- -DC3 2nd Readin L=E%zJ
PHASE il
GK Transect
-1 Distance (m)
- - X- - 3rd Reading 4 4 t h Reading
SRY Transect
Distance (m) 1 +FirstReading 1 - - El- Second Reading
A quantitative, purely objective method of dihguishing anomalies fiom normal
background radon could not be achieved for this study. What would be required is a substantial
database of radon measurements taken across the whole of southern Ontario in non-fiachued areas
to determine with p a t e r precision, the natural variability of near-surface radon. As this study is
Iimited to a restricted area over fractured geologic units, a certain degre. of subjectivity was
necessary to evaluate the results. The principal method involved ploüing the radon measurements
in graphical format and distinguishing probable anomalies from background levels by visual
inspection, but with cautious conservatism. Resuits of previous radon work in southern Ontario
(Section 3.3) was used as a benchmark. Based on these considerations, the estimated "normal"
background level (i.e. in undisturbed soils) is 188 pCi/L for the entire study area (Table 3:3), wrth
a standard deviation of 60% (1 13 pCi/L). This is in closer agreement with eariier findmgs than the
total mean (221 pCi/L), although only by a relatively small rnargin.
Definite anomalies are evident, according to definitions set out by Etiope and Lombardi
(1995), Tilsley and Nicholls (1993) and Tilsley et al. (1993). The anomalies detxted from this
study are comparable to those that have been measured across known fauh (see Section 3.3).
Table 3:4 provides an indication of the magnitude of anomalies fiom each transect based on
average- results. However, anomalies are more clearly identified from the graphs in Figs. 3:7 and
3 3 . The following sections present the results of Phase 1 and II in detail.
3.5.2.1 Phase 1
The results from Phase 1 are plotted in graphical format in Fig. 3 :7 and summarized
numerically in Table 3:3. The graphs show radon activity levels along the y-axis in units of
picocunes per litre of soil air, as a function of distance in rnetres from west to east along each
trarisect. The mean soil radon level is 156 p C i L Except at the Saintfield location, ''normal"
background levels (i.e. of undisturbed soils) is easily identified in contrast to the appearance of
anomalies. At Saintfield (SF), where the mean radon level is 3 14 pCi/L, only seven detectors were
deployed, this is not sufficient to distinguish typical background levels from potential anomalies.
At Diiffins Creek @CI), background radon levels appear to be 60 pCi/L. At Claremont-Balsam
(CBI), background levels are around 100 pCi/L.
At Saintfield (SF), only one anomaly can be identifred. On Fig. 3:7, the anomaly at SF has
a value of 491 pCiL at sample point no. 6. This is a significantly higher value than typical
background levels of 100-200 p C f i for southern Ontario. However, because of the small sample
size, it is not clear from the results whether this area may have higher background levels between
200-3 00 pCi/L. At sampIe point no. 5, two detectors were plzced in the same hole and produced
very close resuks of 289 pCin and 293 pCin. The difference betweai them is only 4.9 pCilL,
which represents an error of d y 1.7%. Unfortunately, it was not feasible to continue radon
measurements at Saintfield during Phase II of the survey.
At DCl, two anomalies are identified at sample points no. 5 and 8 on Fig. 3:7. These have
values of 315 p C i n and 231 pCin, respectively. Radon values at sample points no. 1,6 and 7
appear to be intermediate between background levels and anomalies. Such intermediate values
complicate the determination of true background levels of radon. For simplicity and objeaiwty,
such intermediate values are included among those selected as tnie background.
At CBl, there appear to be two anomalies. However, the anornaly at sample point no. 6
may be in error since its value (552 pCi/L) is nearly six times above background and there are no
other anomalies along the transect of comparable or intermediate magnitude. Additionally,
detectors are spaced only 2 m apart at CBI. Possible reasons for measurernent error may involve
tiny mould particles or insect entering the detector chamber and touching the electret surface.
Physical contact would discharge the electret and produce a false reading. Alternatively, the error
may have been caused by flooding of the sample hole (explained further in Section 3.5 .Z.3 below).
The second anomaly at sample point no. 8 is less than half the size of the value of no. 6 (250
pCi/L), but is 611 nearly three times greater îhan background.
ïhese results of Phase 1, though relatively srnall in number, have provided sufFicient
evidence of anomalous behaviour of near-surface radon to allow Phase II to proceed.
3.5.2.2 Phase II
While most anomalies are between 2 to 3 times above background (see Table 3:4), there
are several instances where contrasts are as high as 4 to 6 times above background at bath the DC2
and the GK transects (see Fig. 3 9 ) . However, the first value of the third reading of DC2 (849
pCi/L) is likely an error. Across the survey, several anomaIies reached values fiom 500 pCin up
to 1000 p C i L By cornparison, in southwestern Ontario, radon anomalies were identified over
known oil and gas fields with values between 600 to 1500 pCiL with a contrast 3.4 times above
background (180 to 454 pC&; Tilsley and Nicholls, 1993).
A very important feature is the repeating pattern of anomalies along each transect. In
several places, anomalies appear to shift over a few mares in subsequent measurement intervals
(see graphs). This implies that radon levels may not be strictly related to the immediate
surroundings of each detector. This may be due to incremental changes in the stress regitne that
widens some portions of fractures while sealing others, as described earlier (Section 3.2.1.2;
Roberts, 1991). At such a small scale, however, this is more likely to be the result of thermal
expansion and compaction ofthe water content of soils.
There is also a significant contribution of seasonal effects to soi1 radon emanation. Based
on ihe total readings for aII siirvey locations combined, the mean is nearly twice as hi& in the
surnrner than in the fa11 (1.8 times higher; see Table 3 5 ) . This is attributed to the combined lower
TABLE 3 : 5
Cornpanson of Phase II results between summer and fall radon levels to i d e seasonal effects. (Note that resuits from sites A-H (see Appendix m) from GK transect are excluded from the calculations since s w e r values at these sites were not available for cornparison).
Location
DC2 DC3 CB2 GK* SRY
Fall Level (pCilL)
Total Mean (pCiIL)
88 280 NIA 170 126
Summer Level (pCilL)
Summerl Fall Ratio 1
NIA 2-551 NIA 1 . 3 / 1.77
FIGURE 3 :9
Mean radon levels of Phase LI radon soi1 gas survey are plotted against ciimatic data to illustrate seasonal effects on naturd radon levels. Mean radon levels include anomalous values. Note that no radon measurements were made m August. (climatic data fiom Environment Canada, 1996).
Climatic data for Phase II radon soi1 gas survey in ssuth central Ontario, Canada
July August Septern ber October
Months
. MeanRn
Manîh Reciplîation Temperature Mean Radon (mm) ("Cl (pCiL)
July 89.0 19.5 296 August 34.3 20.6 NIA Septnmber 149.6 17.4 241 October 58.1 10.3 150
mean temperatures and greater precipitation in the fall (see Fis. 3 :9). Lower surface temperatures
reduce the rnovernent of gas molecules in generai. Increased moisture levels in soils have also b e n
noted to depress overall radon levels by reçtricting gaseous flow through pore spaces (Tilsley et al.,
1993; see above). (Note: iUtbough îhere was a period of significant rainfàll in July, the higher
mean temperatures aIlowed for fàster rates of evaporation, which in turn pennitîed sufficient flow
of radon to the surface.)
The kuid of contrest identifieci in this study between background and anomalous values is
highly irregular for this a r a (Tilsley et al., 1993). It is not likely that the heterogeneity of the soi1
itself is responsible for the anomalies. The survey a ra is generally located over clayey andor
sandy diamicts (i.e. Northern Till and Sunnybraok Diamict, respectively) with a sandy aquifer in
between (Le. Thomcliffe Formation). Sandy materials usuaIly are l m in radon content, h i l e
clays on the d e r hanci, tend to have higher radon Ievels (de Jong er al., 1993; McCaliurn, 1990).
The majority of clasts within till or diarnict units are derived from limestones from the Paleozoic
bedrock. Although there is a significant number of grmitic clasts derived fiom the Canadian
Shield, informa1 experiments have only indicated very low radon emanations (up to 5 pCi/L
measured within sealed jars; Appendix C).
Differences in mean radon levels between transect locations are also apparent. DC3
displays unusually hi& levels compared to DC2 during the same pend of measurement (257
pCi1L compared to 88.2 pCilL). Thus, despite the close prownity to each other (<200 m), DC3
has three times more radon than DC2. Cl32 shows the highest average radon actiwty (490 pCin)
of al1 locations. Even the lowest values are al1 well above 300 pCi/L. Based on the experience of
previous workers (TiIsley and Nicholls, 1993; Tilsley et al., 1993), this could indicate a fracture
zone. Unfortunately, the proxmky to private residential property made it inconvenient to continue
further fieldwork there.
The GK transect displays high radon levels in unexpected areas along the transect. The
highest values are detected at the top of the valley instead of at the bottom. The transed at Shirley
(SRY) across a welldefined surface lineament, is the longest of al1 survey locations and the
intention there was to identi@ fluctuations in radon 1eveIs away from the valley center to identif)
natural background radon levels. However, readings display great variation along the entire length
of the transect (Fig. 3%). These results imply that lineaments defined by satellite images consist of
smaller-scale lineaments clustered together. These in tum represent a relatively wide zone
fiundreds of metres) of hctuxes andior microfractures in the subsurface.
The standard deviation of the total mean for all transe& is significantly higher (60%-92%)
than in previous work (53%-70%; Tilsley and Nicholls, 1993). The exceptions are DC3 and CB2,
where these areas display higher than average radon levels wiîh relatively less contrast between
anomalies and background. The mean background levels at Markham-Stouffville range between
160 pCilL (Tilsley et al., 1993). Local highs with values over 300 pCiL were related to fiults.
This is only a two-fold anomaly above rhe mean. In the Waflaceburg a ra , the mean can range
between 180 and 454 pC&, and anomalies reached 600 to 1500 pCiL over known oil and naturat
gas pools and fa& m e s . These hi& values are comparable to the range of the largest anomalies
seen in this study, which have values reaching between 600 to 1000 pCitL. This is a strong
indication that there may be a significant network of fractures in souîh central Ontario over the
CMBBZ structure.
3.5.2.3 Doubled radon detectors
Reliabiltty of the radon detection rnethod was tested by placing two detectors within one
detector package to compare radon measurements from the same sarnple point. Results ofthese
TABLE 3 : 6
Results of doubled radon detectors per sarnple site for Phase 1 and II, used to check for reliability of radon measurement technique. Detector A sits on top of Detector B within each detector package. Bracketed numbers under the 'Sample' column of Phase II rekr tc~ the repeat measurement period at the designateci transect (i.e. (3) = third repeat measurement). The percent error is calculated based on the difference ('Diff) in readings between Detector A and B, divided by the average of the two resuh. See text in Section 5.3.3 for explmation of resulîs.
Phase I I I
Sarnple DetA Det B Difi Avg Error (pCiL) (pCiiL) (pCi1L) (pCi1L) (%)
rneasurements are Iisted in Table 3:6 for both Phase 1 and Phase II. Great variabilq in results is
Vnmediately apparent during Phase 1 compared with those of Phase II.
Since Phase 1 was reconnaissance in nature, such variability is expected.
Therewere many instances of unexpected flooding of the sample points. Although the
Tyvekm envelopes are waterproof, the envelopes are not seaied around each detector.
Thus if flooding conditions persist for an extended period, water will eventually leak into
the detector housing. Physical contact with the electret surface wili cause it to discharge,
producing an incorrect measurement.
As cm be inferred fiom Fig. 3:6, doubled detectors must be placed one on top of the d e r
within each plastic container. If the excavated sample point becornes flooded, theoretically, air
within the container will form a bubble that will protect the entire contents frorn water penetration
as in a diving bell. However, if the container does not have sufficient weight fiom the overlying
soi1 plug to press it dom f i d y , the wntaher will rotate slightly within the hole and allow more
water inside the container. Remaining air will tend to be forced hto the top part of the container,
ailowing the bottom to become partly or completely saturateci. Thus the upper detector (Detector
A) will tend to be pratected w i t h the air bubble and the lower detector @etector B) is Iefi
susceptible to water saturation. Water that penetrates into Detector B will tend to discharge the
electret surfbce more than that of Detector A. Detector packages have occasionally been found
slightly overtumed within the hole, with the insides of the container noticeably wet.
3.5.2.4 Radon emanation from clasts
As part of an infornial survey, several rock samples of clasts of bath granitic and non-
granitic compositions were tes ta i for elevated radon emanation potential. Conditions were not
strictly controlled and accurate mineral analyses were not conducted. Arnbient radon Ievels in
indoor air have taken into account. Rock sample descriptions and results of their radon emanation
are in Appendix C.
The sarnples used in îhis experirnent have not demonstrated ernanation potentials that could
cause a radon anornaly of signifiant magnitude. The only possible exception is the black shale
sample, C2, which can emanate roughly 42 pC& per 1 kg mass. However, only one small sampIe
was anaIyzed and rnay not represent an accurate estimate of the radon emanation potential of black
shaIes of southem Ontario. No black shale rock fragments were encountered during the radon soi1
gas survey, and are nat typicaliy found as clasts within the tills of the survey areas as they are
fissile and break easily along cleavage planes. These resuks suggest that the source of the
anomalies, particularly those with values greater than 500 pCi/L, are not likely to result from cIasts
within the tilI units of the survey areas.
3.5.3 Interpretation
A hidden network of fractures in the subsufke may be a more Iikely scenario for
anomalous high radon values found in the study. A conceptual mode1 can be developed based on
radon transport theory described in previous sections (Sect. 3.2.2). The black shales of the
Collingwood Member are probably the principal source of uranium in s o d central Ontario soils.
Fractures developed through the Paleozoic units provide gas migration comdors that reach up into
overlying Pleistocene sediments. The rnicrobubble carrier gas mechanism proposed by Etiope and
Lombardi (1 995; see Fig.3:4), cames uranium, radium and radon fkorn the Collingvood into
overlying Blue Mountain shales through fractures andlor microhctures.
Radon can only travel at most 5 metres before decaying to însignificant leveIs, but over
t h e , enough uranium and radium build up on these fiachire walls to become a srnaller local
source. Continuous rnicrobubble transport brings up more U and Ra at higher levels toward the
surfàce through interconnecteci pores. In this way, radon soil gas anomalies appear in the near-
surface environment. Higher radon levels wiil tend to correlate with greater fracture or
microfracture development. Although this proposa1 will need furîher study, the previous work
done in southwestern Ontario gives this greater validity.
3.6 DISCUSSION
Radon is a common radioactive substance present in almost every natural environment and
can pose a serious hazard to human health. Potmûal high risk areas have been identified in the
United States, but M e information is known regarding potential radon hazard zones in Canada.
This should be of sorne concern, particularly in the densely populated region of southern Ontario.
Elevated radon soil gas levels have been identified fiom the present study. Anomalies
reach values of Z O00 pCiL (at GK transect) . This value is five times above the overall
background of 187 pCi/L for the study area. Accordhg to the Swedish Building Code of 1980
(Akerblom and Wilson, 1982), such anomalies lie at the upper limit of normal risk areas (270-1350
pCi/L). HXgh nsk areas are defined as having radon values greater than 1350 pCin and low risk
areas have radon levels less than 270 pCi/L. Since this study covers a relatively small sample
ara, there is the potential for even higher radon levels to occur in this region. Higher levels could
present a hazard to area residaits, pahcularly for those who rely on goundwater wells as their
primary source of drinking water.
Anomalous high radon 1eveIs appear to be related to fractures and structures within the
subsurface. A strong relationship between modem drainage patterns and bedrock structures in the
study area has b e n demonstrated by satellite image interpretation (Rutty, 1993) and bedrock joint
set orientation (EyIes et al., 1997; Eyles and Scheidegger, 1995; Eyles et al., 1993; Scheidegger,
1980). Further detailed mapping of fractures and related stnictures could ùierefore, provide a
usehl constraint on radon hazard mapping, çuch that potential hi& risk areas can be more easiIy
identified.
Previous radon soil sas studies in southwestern Ontario have s h o w that radon levels two
to three times above backgound levels define hu i t boundaries. Some of the radon Ievels of the
present study approach six timeç above background.
3.6.1 Conclusions
Backgoound levels of radoc w i t h -&e stvdy area of south central Bntario, Canada are
estirnated to have an overall mean of 187 pCi/L. This can Vary fiom as low as 15 pCdL to as
high as 440 pCi/L. The normal range of backgound radon fàlls between 100-200 pCi/L.
These levels, by themselves, would demonstrate that this region constitues a low-nsk zone for
natural radon hazards.
Anomalous radon levels have consistently appeared through repeat measurements of transects.
Clearly identified anomalies have values that are at least three tirnes above background.
Anomalies as hi& as six times above background have been identified with values approaching
1000 pCi/L. This magnitude of radon approaches the higher end of a normal risk a r a (270-
1350 pCi/L), accordhg to the 1980 Swedish Building Code (Akerblom and Wilson, 1982).
No such standards for natural radon in soi1 gas exist yet in Canada.
The contrast between identified radon anomalies compared to background, are consistent with
those found across known faultç. The anomalies detected in the study area may be related to
fractures or d e r similar Qpe of structures.
Mapping frcictures/subsu~fàce structures is a useh1 constraint on hazard identification for
radon. SurCace lineaments interpreteù fiom satellite imagery correlate well with the underlying
CMBBZ structure and buned bedrock channels.
Further radon soi1 gas surveying rnay reveaI areas at higher than normal nsk in other areas of
the heavily urbanized Greater Toronto Area in southern Ontario. Future work is needed to
determine potential risks to area residents.
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Characterization of overburden fractures and implications for DNAPL transport:
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Environmental Toxicology, v. 38, p 209-2 12.
APPENDIX A:
CALIBRATION EQUATIONS FOR E-PERMTM SYSTEM
Cdibration Equations for E - P E W System
The following are the proper calibration quations for calculating radon concentrations for the
combination of chamber and electret types used in this study. The calculations involve the
conversion of the voltage change of the electrets before and afkr exposure, into radon
concentration in units of pCi/L of air.
Al1 soi1 radon measurements were conducted with the red-IabeI, long-term electret with the L-
charnber configuration (referred to as 'LLT'). Radon measured fiorn rock sarnples in sealed jars,
were measured wiîh the blue-label, short-terrn electret with the L-chamber configuration (referred
to as 'SLT').
Step 1, Calculation of the calibration factor (CF)
Where I and F are the initial and hd voltages of the electret A and B are the calibmtion constants fkom Table (i) below.
Step 2. Calculation of radon concentration using the following equation:
RnC(pCi/L) = (1- F) - (C xM) CFxD
Where CF is the calibraiion factor calculated in Step 1 C is a constant from Table (i) in units of pCin per W M is the ambient gamma radiation level in piUh D is the e x p o m period in days.
Table (i). Calibration constants for E-PERMS.
Constant C E-PERM Configuration
LLT
SET
Constant A
0.02383 1 0.00001120
O. 1400 1 0.00005250
Constant B
0.120
0.087
APPENDIX B:
RADON SURVEY FIELD DATA (PHASE 1 & II)
E-PERM L-type, red-label, long-terni Ambient gamma radiation level (M) = 10uWh
Sarnple SFl SF2 SF3 SF4 S F5a SF5b SF6 S n
DUFFINS CREEK-ï
Sarnple # Electret DC1 LC1802 DC2 L B m CC3 LC 5358 DC4a LB4687 W b LC4908 DC5a LC5368 DCSb LC 4137 DCQ w 2542 DC6b LC8264 DC7a LC5366 DCib LC4236 M)8 LC5582 ûC9 LE3071 DClO LE4146 CC11 LC5618 CC12 LE5816 DC13 LC4293
Sarnple # Electret CBla CBI b CB2a CB2b CE3 CB4 CBSa Cssb CB6 CB7a CB7b cm C B9 CE10 CBlla CBl l b CB12 CB13 CB14 CB15 CB16 CB17 Cf318 Cf319 CE20
Hrs 15 17 17 17 16 16 18 16
Hrs 10 1 O 10 11 11 11 11 il 11 11 11 10 10 10 10 10 1 O
Min 30 15 25 40 1 O 10 55 40
Min 50 55 55
O O O O 5 5
1 O 10 40 35 35 30 25 20
Hrs. Mins.
D y Hrs Min 220 19 8 220 19 19 220 19 19 220 19 25 220 18 O 220 18 O 220 18 O 220 18 O
Day Hrs Min 228 11 30 228 11 35 228 11 40 228 11 45 228 11 45 228 11 55 228 11 55 228 12 O 228 12 O 228 12 25 228 12 25 228 12 20 228 12 18 228 12 75 228 12 73 228 12 10 228 12 5
Day Hrs. Mins. 2 1
V(î) Totaldays CF Rn (pCüL) 342 13.15 0.0280524 188.54 351 13.09 0.0283436 279.19 393 13.08 0.0287748 256.54 304 13.07 0.0280076 375.70 31 7 13.08 0.027974 288.58 298 13.08 0.0277568 293.49 286 12.96 0.0280356 491.38 297 13.06 0,0278564 342.51
Average 314.49- Lows 261.27 Highs 403.20
Total days CF Rn (SUL) 21 .O3 0.0277164 180.68 21.03 0.0283604 64.20 21.03 0.028142 103.55 21.03 0.0287636 155.84 21 .O3 0.0283156 154.97 21.04 0.0281756 21 1.36 21.04 0.0274812 358.57 21.04 0.0291892 111.16 21.04 0.0283716 131.15 21.05 0.0280412 117.38 21 .O5 0.0285172 90.41 21.07 0.0279516 209.35 21.07 0.0284108 52.25 21.07 0.0286124 48.56 21.07 0.0290436 49.45 21.07 0.028422 42.21 21.07 0.0287524 63.17
Average -7Z33E Lows 91 .IO15287 Highs 21 1.794667
V(f) Total days
Average I l / . 11 Lows 93.3396462 Highs 181.475126
N.B. V=voHs; CF=calibralion factor
Radon Suwey Field Data - PHASE II
E-PERM L-type. red-label, long-term Ambient gamma radiation level @l) = 10uRlh
DUFFINS CREEK-2
First Reading: 07/05/96 - 0711 8/96
Site # DC2 1 DC2 2 DC2 3 DC2 4 DC2 5 OC2 6 DC2 7 DC2 8 DC2 9 DC2 10 DC2 11 DC2 12 DC2 13 DC2 14 DC2 15 DC2 16 DC2 17 DC2 18 DC2 19
Electret LC 2867 t D 2788 LC 551 7 LC 4292 LC 4209 LC 8328 LB 371 4 LC 5610 LC 5520 LC 6927 LB 3986 LB 5985 LC 8276 LC 3632 LB 5?77 LC 6942 LC 5261 LC 571 3 LD 2584
Hrs 12 12 13 13 13 13 13 13 13 13 13 13 14 14 14 14 14 14 14
Second Reading: 07/18/96 - 08/01/96
Site # DC2 1 DC2 2 OC2 3 DC2 4 DC2 5 DC2 6 DC2 7 DC2 8 DC2 9 DC2 10 DC2 11 DC2 12 DC2 13 DC2 14 DC2 15 DC2 16 DC2 17 DC2 18 DC2 19
Electret LC 2867 LD 2788 LC 551 7 LC 4292 LC 4209 LC 8328 Li3 371 4 LC 561 O LC 5520 LC 6927 LB 3986 LB 5985 tC 8276 LC 3f32 LB 5777 LC 6942 LC 5261 LC 571 3 LD 2584
Hrs 11 11 11 11 11 11 11 11 11 11 11 11 11 I I 12 12 12 12 12
Min 34 50
O 5 9
12 15 25 35 40 45 55 1 O 15 17 25 34 39 44
Min 4 7
12 15 18 21 25 28 35 39 45 48 51 56
O 4 9
14 14
V(i) Day 445 200 400 200 413 2Oû 431 X#) 487 200 433 200 430 200 476 200 428 2M3 412 200 458 200 435 200 445 200 400 200 444 200 399 200 475 200 366 2ûû 425 200
V(i) Day 399 215 331 215 357 215 396 215 415 215
Hrs 11 11 11 11 11 11 11 11 11 11 11 11 11 11 12 12 12 12 12
Hrs 17 17 17 17 17
Min V(Q 4 399 7 331
12 357 15 396 18 415 21 387 25 214 28 456 35 396 39 372 45 223 48 335 51 378 56 253 O 389 4 366 9 260
14 266 14 308
Total CF Rn (pCiIL)
Min V(9 Total days CF Rn (pCi1L) 10 355 15.25 O.CE80524 101.6 11 286 1 5.25 0.0272852 106.9 12 202 15.25 Q.0269604 375.8 13 364 15.25 0.028086 73.5 14 230 15.25 0.027442 440.9
DUFFINS CREEK-2
Third Reading: 09/04/96 - 09/16/96
Site # Electret DC2 1 LC 5654 DC2 2 LC4139 DC2 3 LC 6970 DC2 4 LC 2867 DC2 5 LB4407 DC2 6 rnoved over DC2 7 rnoved over DC2 8 LC4273 DC2 9a LD2263 DC2 9b LC8320 DC2 10 LC 0625 DC2 II LC 5276 DC2 12 LC6913 DC2 13a LC 5651 DC2 13b LC4118 DC2 14 LD 2489 DC2 15 LB 4758 OC2 16 LD 2989 DC2 17 LC4314
Fourth Reading: 09/19/96 - 1011 1196
Site # OC2 1 OC2 2 DC2 3 OC2 4 OC2 5 OC2 6 OC2 7a DC2 7b OC2 8 OC2 9 DC2 10 OC2 I l a DC2 l l b OC2 12 OC2 13 OC2 14 OC2 15 DC2 16
Day Hrs 263 14 263 14 263 14 263 14 263 14 263 14 263 14 263 14 263 14 263 14 263 14 263 14 263 14 263 14
Min 25 27 29 31 32
41 37 37 43 48 8 50 50 52 54 56 57
Min 24 25 26 27 29 31 32 32 34 35 36 37 37 38
LB 4758 263 MISSING LD 2989 263 14 40 LC 4314 263 14 41 LB 2835 263 14 45
V(i) Day 363 260 315 260 424 260 355 260 315 260
220 260 408 260 181 260 372 260 249 260 343 260 427 260 414 260 247 260 395 260 388 260 309 260
V(i) Day 329 285 297 285 410 285 290 285 296 285 204 285 393 285 360 285 345 285 209 285 325 285 413 285 # 285 219 285
H rs 14 14 14 14 14
14 14 14 14 14 14 14 14 14 14 14 14
Hrs 13 13 13 13 13 13 13 13 13 13 13 13 13 13
Min V(f) Total days CF Rn (pCilL)
Min 36 37 39 41 45 45 47 47 48 49 51 52 52 53
V(f) Total days 265 21.97 260 21.97 372 21.97 249 21.97 270 21.97 1 73 21.97 359 21.97 324 21.97 3M 21.97 1 34 21.97 277 21.97 398 21.97 385 21.97 150 21 9 7
First Reading: 09/05/96 - 09/16/96
Site DC3 DC3 DC3 DC3 DC3 DC3 DC3 DC3 DC3 DC3
# Electret 1 LC5520 2 LC4209 3 LC5517 4 LC5610 5 LC6927 6 LC4292 7 LD2788 8 LC5729 9 LC3632
I O LC 6942
Day Hrs Min 249 15 15 249 15 24 249 15 32 249 15 40 249 15 47 249 16 6 249 16 12 249 16 20 249 16 30 249 16 40
Second Reading: 09/19/96 - 10/14/96
Site # DC3 1 DC3 2 DC3 3 DC3 4 DC3 5 DC3 6 DC3 7 DC3 8 DC3 9 DC3 10 DC3 11 DC3 12 DC3 13 DC3 14 DC3 15 DC3 16 DC3 17
Day Hrs 263 14 263 14 263 15 263 15 2ô3 15 263 15 263 15 263 15 263 15 263 15 268 14 268 14 268 14 268 14 268 14 268 15 268 15
Min 58 59
O 1 3 4 5 6 7
28 17 24 32 40 49 2
12
V(i) Day 363 260 230 260 M2 260 426 260 270 260 364 260 286 260 483 260 202 260 330 260
V(i) Day 282 288 313 288 359 288 334 288 336 288 2 9 288 294 288 334 288 290 288 214 288 531 288 349 288 352 288 520 288 254 288 375 288 366 288
Hrs Min 14 57 14 58 15 O 15 2 15 3 15 4 15 5 15 6 15 7 15 9
Hrs 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15
Min il 12 13 14 15 16 17 18 19 20 22 24 25 27 28 32 34
V(f) Total days 282 I a.99 137 10.98 1 36 10.98 334 10.97 1 57 10.97 250 10.96 173 10.95 334 10.95 48 10.94
21 4 10.94
V(f) Total days 1 98 25.01 in 25.01 31 O 25.01 269 25.01 275 25.01 1 25 25.01 160 25.01 21 6 25.01 1 46 25.01 48 24.99
4851 20.05 170 20.04 269 20.04 400 20.03 169 20.03 1 93 20.02 190 20.02
First Reading: 09105196 - 09/16/96
Site DC3 DC3 DC3 DC3 DC3 DC3 DC3 DC3 DC3 DC3
Hrs Min 15 15 15 24 15 32 15 40 15 47 16 6 16 12 16 îû 16 30 16 40
Second Reading: WlgI96 - 1 011 4/96
Site # DC3 I DC3 2 DC3 3 DC3 4 DC3 5 DC3 6 DC3 7 DC3 8 DC3 9 DC3 10 DC3 Il DC3 12 DC3 13 DC3 14 DC3 15 OC3 16 DC3 17
Electret LC 5520 LC 2855 LB 2922 LC 5610 LB 4877 LC 4292 LC 41 29 LC 5729 LC 1984 LC 6942 LD 281 4 LC 5337 L5 5777 LB 5224 LC 4321 LC 5354 LB 2702
Hrs 14 14 15 15 15 15 15 15 15 15 14 14 14 14 14 15 15
Min 58 59
O 1 3 4 5 6 7
28 17 24 32 40 49 2
12
Hrs 14 14 15 15 15 15 15 15 15 15
Hrs 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15
Min 57 58
O 2 3 4 5 6 7 9
V(f) Total days 282 10.99 1 37 10.98 1 36 10.98 334 10.97 1 57 10.97 250 10.96 173 10.95 334 10.95 40 10.94
21 4 10.94
Min V(f) Total days 11 198 25.01 12 177 25.01 13 310 25.01 14 269 25.01 15 275 25.01 16 125 25.01 17 160 25.01 18 216 25.01 19 146 25.01 2û 48 24.99 22 485 20.05 24 170 2û.04 25 269 20.04 27 4ûO îû.03 28 169 2û.03 32 193 20.M 34 190 20.02
GREENWOOD-KINSALE
First Reading: 07/12/96 - 07/31/96
Site GK1 GKl G K1 GK1 GU1 GK1 GKl GKl GK1 G K1 GKI G KI G K l G KI G KI G KI G KI G KI G K I GKl
Electret LC 3840 LB 8617 LC 4138 LB 8342 LB 3897 LAm LC 5477 LC 4247 LC 5690 LC 5606 LB 3981 LD 2445 LC 4321 LC 5354 LC 5255 LD 2665 LC 5337 LC 8363 LB 2702 LC 5698
Hrs 14 15 15 15 15 16 16 16 16 16 17 17 17 17 17 17 18 17 18 18
Min 54 7
23 25 52 1 O 15 30 42 55
O 13 20 25 35 55
O 50 15 25
V(i) Day 453 211 579 211 461 211 532 211 411 211 535 211 409 211 453 211 465 211 404 211 382 211 420 211 403 211 425 211 419 211 435 211 451 211 478 211 421 211 426 211
Hrs Min V(f) Total days CF Rn (pCill
Interim Reading: 07\29/96 - 08129196 Note: Only 5 detectors left behind because volt reader broke down.
Site # Electret Day Hrs Min GKl 1 LC384û 211 13 16 GK7 2 LB8617 211 13 30 GK1 3 LC4138 211 13 36 GKl 4 LB 8342 211 13 40 GK7 5 163897 211 14 2
Second Reading: 08/28/96 - 0911 0196
Site # Electret GK1 1 Li32472 GKl 2 LC6905 GKI 3 LC5401 GK1 4 LC5690 GK1 5 FC5698 GU1 6 LD2783 GU1 7 Li33800 GU1 8 LI32445 GKl 9LD2665 GKI I O LC 5255 GK1 11 18 4676 GKl 12 LC 4247 GKI 13LA3600 GKl 14 LD 2875 GKI 15 LCB363
Hrs 12 12 12 12 12 12 12 13 13 13 13 13 13 13 13
Min 19 21 23 47 48 53 56
O 3 5 6
14 16 18 20
V(i) Day Hrs Min V(fJ Total days CF Rn (pCill 370 242 12 11 216 30.95 0.0271116 182.1 498 242 12 12 397 30.95 0.028842 112.c 225 242 12 15 O 30.94 0.02509 288.C 311 242 12 30 76 30.95 0.M59972 290.5 363 242 12 45 302 30.95 0.027554 70.:
V(i) Day Hrs Min V(f) Total days CF Rn (pCiI1 324 254 19 7 309 12.28 0.0273748
GREENWOOD-KINSALE
Third Reading: 0911 1/96 - 09/19/96
Site # Electret GK1 H LC 4144 GKI G LC0682 GK1 F LC5696 GK1 E LC5359 GK1 O LC8276 GK1 C LD2584 GK1 B LD2335 GK1 A LC5477 GK1 1 LD 2472 GKI 2 LC6905 GKI 3 LC.5401 GK1 4 LC5690 GKI 5 LC5698 GK1 6 LD2ô65 GK1 7 LB3800 GK1 8 LC 5695 GK1 9 LDZS3 GKl 10 LB 3800 GK1 17 LB416 GKI 12 LC 4247 GKI 13 LA3600 GK1 14 LD2875 GKI 15 LC 83â3
Hrs Min 16 2 16 O 15 58 15 56 15 54 15 52 15 51 15 46 14 O 14 2 14 3 14 4 14 5 14 9 14 10 14 16 14 18 14 19 14 20 14 2s 14 23 14 25 14 26
Fourth Reading: 09/26/96 - 10/14/96
Sie # GKI H GK7 G GK1 F GKI E GK1 D GKI C GK1 B GK1 A GKI 1 GKI 2 GKI 3 GKI 4 GKI 5 GKI 6 GK1 7 GKI 8 GK1 9 GKI 10 GKI 11 GKI 12 GKI 13 GK1 14 GKI 15
Electret LC 41 44 LC 3633 LC 5636 LC 533 LC 4141 LC 5589 LD 2335 LC 5477 LD 2472 LC 6905 LC 5401 LC 3625 LC 56% LB 5582 L6 3800 LC 5695 LD 2783 Li3 3800 LB 4616 LC 4247 LA3600 LD 2875 LC 8363
Day Hrs Min 270 13 50 270 13 52 270 13 53 270 13 55 270 13 56 270 13 57 270 14 O 270 14 1 270 14 2 270 14 4 270 14 5 270 14 12 270 14 13 270 14 I O 270 14 11 270 14 12 270 14 13 270 14 15 270 14 16 270 14 19 270 14 20 270 14 21 270 14 22
V(i) Day 481 263 352 263 360 263 392 263 325 263 209 263 525 263 298 263 309 263 341 263 284 263 259 263 299 2E3 168 263 253 263 329 263 453 263 231 263 364 îô3 287 263 295 263 308 263 207 2a3
V(i) Day 369 288 362 288 209 288 299 288 315 288 391 288 428 288 190 288 278 288 322 28a 186 288 393 288 290 288 507 288 220 288 250 288 415 288 212 288 344 288 280 288 227 288 304 288 175 288
126
Hrs 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 16
Hrs 15 15 15 15 15 15 15 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16 16
Min V(f) Total days CF Rn (pCilL
Min V(f) Total days CF Rn (~Cili. 53 257 18.09 0.0273356
SHIRLEY
First Reading: 07/16/96 - 08/01/96
Site # SRY 1 SRY 2 SRY 3 SRY 4 SRY 5 SRY 6 SRY 7 SRY 8 SRY 9 SRY 10 SRY 11 SRY 12 SRY 13 SRY 14 SRY 15 SRY 16 SRY 17 SRY 18 SRY 19 SRY 20 SRY 21 SRY 22 SRY 23 SRY 24 SRY 25 SRY 26 SRY 27 SRY 28 SRY 29 SRY 30 SRY 31 SRY 32 SRY 33 SRY 34 SRY 35 SRY 36 SRY 37 SRY 38 SRY 39 SRY 40
Electret LC 5401 LC 2825 LC 5359 LB 3800 LC 6905 LC 4114 LC 5634 LB 3083 LB 8243 LD 2746 LC 8372 LB 7537 LC 5256 LB 4007 LC 2763 LC 361 6 LD 2547 LC 41 76 LC 5318 LC 5241 LD 2726 LC 41 49 LC 41 23 LC 4328 LB 4870 LC 2955 LC 5643 LC 5247 LC 5629 LB 9884 LC 6947 LC 5659 LC !5ex LD 2783 LB 2999 LC 3662 LB 4573 LD 2472 LB 5029 LC 5287
Day Hrs 198 16 198 16 198 16 198 16 198 16 198 16 198 16 198 15 198 15 198 75 198 15 198 15 198 15 198 14 198 14 198 14 198 14 198 14 198 14 798 14 798 14 7% 14 190 13 198 13 198 13 198 13 798 13 1% 13 198 12 198 15 198 17 196 17 198 17 198 17 198 17 1% 17 196 17 198 18 198 18
Min 45 40 35 30 25 20 2 O 55 45 35 15 10 O
50 45 35 30 25 15 1 O 5 O 30 25 20 15 10 5
55 50 15 23 30 35 43 50 55
O 1 0
V(i) Day 433 214 414 214 221 214 464 214 444 21 4 481 214 451 214 429 214 503 214 593 214 236 214 435 214 456 214 421 214 440 214 414 214 581 214 419 214 268 214 348 214 476 214 399 214 472 214 415 214 431 21 4 494 214 428 214 288 214 429 214 454 214 355 244 413 244 464 214 567 214 418 214 413 214 487 214 558 214 468 214 412 214
Hrs Min VM Total davs CF Rn (pCiII
waaon Survev Fïeld Uata - YHASJ1; ii
SHIRLEY
Second Reading: 08/31/96 - 09/16/96
Site # SRY 1 SRY 2 SRY 3 SRY 4 SRY 5 SRY 6 SRY 7 SRY 8 SRY 9 SRY 10 SRY 11 SRY 12 SRY 13 SRY 14 SRY 15 SRY 16 SRY 17 SRY 18 SRY 19 SRY 20 SRY 21 SRY 22 SRY 23 SRY 24 SRY 25 SRY 26 SRY 27 SRY 28 SRY 29 SRY 30 SRY 31 SRY 32 SRY 33 SRY 34 SRY 35 SRY 36 SRY 37 SRY 38 SRY 39
Electret
LC 4328 LD 2547 LC 5247 LD 2726 LB 4870 LB 3840 LC 5643 LB 98M LC 6943 LC 2955 LC 4149 LC 4252 LC 5629 LD 3717 LB 4663 LC 41 76 LB 3897 LB 8617 LC 5287 LC 5256 LB 5û29 LB 4573 LB 2999 LC 2825 LC 5626 LB 401 1 LC 3662 LB 9884 LB 7537 LC 2763 LB 3083 LB 4D07 LC 3622 LC 5634 LD 2745 LC 361 6 LC 4114
SRY 40 LB 8243
Day Hrs Min V(i) Day
329 255 517 255 225 255 412 255 237 255 216 255 285 255 382 255 496 255 320 255 319 255 443 255 373 255 513 255 368 255 335 255 302 255 397 255 230 255 297 255 297 255 431 255 198 255 296 255 296 255 424 255 349 255 251 255 303 255 262 255 351 255 286 255 474 255 388 255 435 255 239 255 383 255
Hrs Min V(f) Total days CF Rn (pCilL)
SHIRLEY
Third Reading: 09/16/96 - 1 011 1/96
Site # SRY 1 SRY 2 SRY 3 SRY 4 SRY 5 SRY 6 SRY 7 SRY 8 SRY 9 SRY 10 SRY 11 SRY 12 SRY 13 SRY 14 SRY 15 SRY 16 SRY 17 SRY 18 SRY 19 SRY 20 SRY 21 SRY 22 SRY 23 SRY 24 SRY 25 SRY 26 SRY 27 SRY 28 SRY 29 SRY 30 SRY 31 SRY 32 SRY 33 SRY 34 SRY 35 SRY 36 SRY 37 SRY 38 SRY 39 SRY 40
Electret LC 5629 LB 861 7 LB 3897 LD 3117 LC 41 76 LB 4663 LD 2726 LB 98û4 LC 4252 LC 4328 LC 2955 LC 4149 LC 5643 LD 2547 LB 4870 LB 3840 LC 6943 LC 5247 LC 8269 LB 4066 LC 5260 LC 5256 LB 5029 LB 4573 LC 4136 LC 2825 LC 5626 LB 401 1 LC 3662 LC 5241 LB 7537 LC 2763 LB 3083 LB 41 48 LC 3622 LC 5634 LD 2746 LD 2563 LC 4114 LB 8243
Hrs Min 12 28 72 32 12 32 12 35 72 37 13 39 12 41 12 43 12 48 12 51 12 53 12 54 12 55 12 n 12 59 13 O 13 2 13 4 13 14 13 15 13 17 13 20 13 21 13 22 13 24 13 25 13 27 13 34 13 36 13 37 13 39 13 40 13 42 13 44 13 45 13 47 13 48 13 50 13 51
Min 59 n 56 53 52 50 48 47 45 44 43 42 43 38 37 36 34 29 28 26 22 21 20 19 18 17 16 2 5 14 4 3 2 O
58 57 56 54 47 50
TotaI days 25.02 25.02 25.02 25.01 25.01 25.09 25.W 25.00 25.00 25.00 24.99 24.99 24.99 24.99 24.98 24.98 24.98 24.98 24.97 24.97 24.96 24.96 24.96 24.96 24.95 24.95 24.95 24.95 24.94 24.94 24.93 24.93 24.93 24.93 24.93 24.92 24.92 24.91 24.92
APPENDIX C:
CLAST SAMPLE RADON EMANATION RESULTS
Clast Sample Descriritions - (for radon emanation measurements)
l I I
Al 1 DioritcfGabbro 1 265 g 1 50% maiïc minerals (ppoxenes) 50% feldspan;
1 Sampie 1 Type Mass
1 borders small portion of pink granite. f.-mg.
Composition/Grain Size
A3
BI
B2
B3
B4
10 g ) 60% white m.g. plagiwlase, <40% feldspar, A2
quariz & rninor homblende.
Key: (grain size description) f. =fine m. =medium C. =cOarSe
g. = grain
Diorite
Granite
Fyroxenite
Carbonate
Syenite
Monzonite
Cl
C2
Measured Radon Emanation from Clasts
, BWl 1 GraniteISyenite
Sample
5 g
175 g
120 g
185 g
190 g
Sandstone
Shale
Mass
(g)
2 80 455 520 390 205 185 375 3 O 3 O
minor mafic mineds. M.g. quartz equiproportional to black homblende; <5% feldspar. Aphanitic dark green-black matri& f. to c.g. inclusions of pyrite crystais, minor quartz. Calcite, opaque gey with oxidized iron on surface; some chalcopyrite mineraiization. Dominant K-feldspar, minor plagioclase, minor quartz, 20% mafic minerals. 60% feldspar, 30% m. to c g quartz, 10% homblende.
25 g
205 g 1 Red sandstone, colour fIom iron minerais; f.g. to silt. ûrganic-rich black shate, very f.g.. fossiliferous withpreserved graptolites.
Rn Emanation
@ciW
50% K-feldspar (jaspar), 30% plagioclase, 20% ,
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