Radon in the Ground Water Drinking Supplies of North Carolina
Ted Campbell, NC Division of Water Quality,
Aquifer Protection Section
ted.campbell@ncmail.net
Contributors:
Dr. Felix Fong, NC Radiation Protection Division
U.S. Environmental Protection Agency
Staff of DWQ, Aquifer Protection Section
Staff of the NC Geological Survey
Duke University, Nicholas School of the Environment and
Earth Sciences
Radon-222
• a radioactive gas produced by the decay of uranium-238
Radon-222
• a radioactive gas produced by the decay of uranium-238
• a human carcinogen - 2nd leading cause of lung cancer
• found everywhere; very mobile; migrates from rock and soils into
atmosphere and indoor air
• readily dissolves in water….so it shows up in ground water supplies
• half life of 3.8 days….can’t travel “unsupported” for long distances
• not common in surface waters due to volatilization
Radon-222
• tends to occur at higher levels in private wells than in public supply wells
• degasses during showering can increase one’s overall exposure and health
risk over ambient levels alone
• Ongoing debate about “safe” levels in water. However, studies suggest
that risks from radon in water are larger than those caused by all other
radionuclides in the nation’s water supply.
• In most – though not all – cases, the main source of radon is from
underlying rock and soils.
Radon-222
• Radon in water can result in new pathways of exposure (upper floors,
for example).
• “10,000 to 1” rule of thumb; but does not account for daily acute doses
during showering, for example
Radon Standards
Indoor Air
• EPA “Action Level” = 4 pCi/L
Water
• EPA proposed standard for radon in water = 300 pCi/L
• EPA proposed alternate standard for radon in water = 4000 pCi/L (if a
supplier has a radon mitigation program)
In NC, monitoring radon in public water supply wells is voluntary.
Radon is not included in NC’s “new well” sampling list; private well
owners are “on their own”.
So what are the risks from radon-222 in water?
• Lung cancer (inhalation) and stomach cancer (ingestion)
• Follows “linear risk” model; any dose above zero carries risk; MCLG = zero
• At 4000 pCi/L: lifetime cancer risk (combined inhalation-ingestion) is
greater than lifetime cancer risk from:
arsenic, at MCL of 10 ug/L
combined radium-226 +radium-228, at MCL of 5 pCi/L
uranium, at MCL of 30 ug/L
most other regulated compounds, at their MCL
Some states have begun to establish their own standards/advisories.
Examples: Connecticut = 5,000 pCi/L
New Jersey = 300 pCi/L
New Hampshire = 2,000 pCi/L
Vermont = 5,000 pCi/L
Maine = 4,000 pCi/L
Massachusetts = 10,000 pCi/L
Wisconsin = 5,000 pCi/L
Standard does not exist for NC.
For perspective…
Across USA (Focazio and others, 2006)
Radon
75% of wells are above 300 pCi/L
Radon
9% of wells are above 4000 pCi/L
Nitrate
8% of wells are above 10 mg/L (MCL)
Arsenic
11% of wells are above 10 ug/L (MCL)
Predicted indoor radon across USA
Map was developed based on:
• geology and soil permeability
• gamma-ray fly-overs (U and Ra detected at land surface; NURE, 70s and 80s)
• indoor radon levels
• typical home construction (slab, basement, crawl space)
General Patterns of Radon Occurrence in the US
Rn exceeds 4000 pCi/L in about 9% of
private wells in the USA (Focazio and
others)
Background on Radon in NC
8 counties in NC, all in Western NC, are classified as EPA Zone 1 counties
(indoor radon levels are, on average, expected to exceed 4 pCi/L)
Indoor radon above 4 pCi/L
Indoor radon from 2 to 4 pCi/L
Indoor radon less than 2 pCi/L
Indoor Radon in NC
above 8 pCi/L
above 20 pCi/L
Meta-igneous rocks
EPA Zone 1 Counties
* Data from Airchek, Inc, 2006
Guilford, Forsyth, Wake
n = 16,384
max = 2146 pCi/L
median = 1.6 pCi/L
Background on Radon in NC
8 counties in NC, all in Western NC, are classified as EPA Zone 1 counties
(indoor radon levels are, on average, expected to exceed 4 pCi/L)
Uranium-rich rock exists across region
Uranium rich rock in NC
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Background on Radon in NC
8 counties in NC, all in Western NC, are classified as EPA Zone 1 counties
(indoor radon levels are, on average, expected to exceed 4 pCi/L)
Uranium-rich rock exists across region
About half of the population uses ground water as its principal drinking
water supply
Background on Radon in NC
8 counties in NC, all in Western NC, are classified as EPA Zone 1 counties
(indoor radon levels are, on average, expected to exceed 4 pCi/L)
Uranium-rich rock exists across region
About half of the population uses ground water as its principal drinking
water supply
Elevated radon and other radionuclides have been found in ground water
of the Piedmont and Mountains of NC since the 1970s
Existing data
Existing data
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- 2000 suppliers
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Mylonitized Rocks
of the Brevard
Fault Zone (ductile
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Henderson gneiss
near Brevard
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- 2.4% of suppliers exceededCEPA MCLs for gross alpha or combined radium
15 pCi/L
5 ug/L
From NURE database,
Geochemical Atlas of
NC (Reid, 1991)
Existing data
Radon in NC Ground Water
1974 - Environmental Science Lab
- 204 PWS wells across NC
- 60% contained radon above 2000 pCi/L
- Lowest radon levels are in Coastal Plain, and highest are in Mtns & Piedmont.
1975 - Aldridge, Sasser, and Conners
- 211 PWS wells across NC
- Median radon across NC ~ 1400 pCi/L
- Average radon across Western NC ~ 4100 pCi/L
Existing data
Radon in NC Ground Water
1987 - Loomis, Watson, & Crawford-Brown
- 96 suppliers
- Rock type effects radon levels.
bility
a
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v
High
btypes
u
s
n
i
with
granites
gneisses
mafics
sedimentary rocks of the Coastal Plain
- Well yield, depth, and casing length were not predictors of radon levels.
Existing data
Radon in NC Ground Water
1993 - University of North Carolina
- 277 private wells across mountains of NC
- 83% contained radon above 2000 pCi/L
1975 to Current 1) Many counties still have very limited radon-in-water
data. 2) Comprehensive studies underway in parts of Raleigh Belt and Blue
Ridge and Inner Piedmont Belts.
Radon in NC Ground Water
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Current Studies
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Counties with known
susceptibility to elevated
radon in ground water *
ta
la
lP
in
Slate Belt and Raleigh Belt
60 wells above
4,000 pCi/L
Metamorphosed
granitic rock
Guilford
Felsic and
mafic igneous
and metaigneous rock
Franklin
27 wells above
10,000 pCi/L
Orange
Wake
Median = 735 pCi/L
Max = 6,300 pCi/L
(70 private wells)
(Spruill and others, 1997)
Median = 586 pCi/L
Raleigh
gneiss
Granitic
plutons
Max = 4,229 pCi/L
(42 wells)
(Orange Co. staff, 1997)
Median = 2800 pCi/L
Max = 32,000 pCi/L
(305 private wells - Phase I & II)
Meta-igneous rock
(Cornell and others, 2005)
(Bolich and Stoddard, 2004)
Blue Ridge and Inner Piedmont Belts
• 2005 - sampled 103 private wells (Buncombe, Henderson, and Transylvania
Counties -- all EPA Zone 1 counties)
• 2006 - sampled 78 private wells (Buncombe, Henderson, Transylvania, Mitchell,
Madison, Watauga, Jackson)
• focused more heavily on areas underlain by meta-igneous rocks
• analyzed:
radionuclides
other parameters
well construction
radon
uranium, total
gross alpha activity
radium-226
radium-224
radium-223
indoor radon
DO
pH
spec cond
ORP
temperature
alkalinity
iron
manganese
well depth
casing depth
well yield
latitude
longitude
observed local geology
NCDWQ Study is Addressing 3 Questions
• Where do radionuclides occur and at what levels?
• What factors control radionuclide levels in our study area?
• What are the policy implications?
2005
Blue
Ridge
EPA Zone 1 Counties
Piedmont
Coastal
Plain
103 private
wells
Meta-igneous rock
Study Area
Buncombe
Meta-igneous rocks
Includes granites and granitic gneisses (Henderson,
Toxaway, Caesar’s Head)
Henderson
Meta-sedimentary rocks
Includes schists, metagraywackes, and
metavolcanics of the Ashe Metamorphic Suite
Transylvania
Meta-igneous rock
Sampled wells
Henderson gneiss
near Brevard
Henderson gneiss
near Rosman
Henderson gneiss
near Brevard
Mylonitized Rocks
of the Brevard
Fault Zone (ductile
shear; granitic origins)
Indoor radon
Source: data from Airchek,
Inc, obtained 2005
Above 8 pCi/L
Meta-igneous rock
Metasedimentary rock
Indoor radon
Source: data from Airchek,
Inc, obtained 2005
Above 20 pCi/L
Meta-igneous rock
Metasedimentary rock
Indoor radon
Source: data from Airchek,
Inc, obtained 2005
Above 50 pCi/L
Meta-igneous rock
Metasedimentary rock
Indoor radon
Source: data from Airchek,
Inc, obtained 2005
Above 100 pCi/L
Meta-igneous rock
Metasedimentary rock
Casing
saprolite
Regolith
Transition
zone
…igneous,
metasedimentary,
and metavolcanic
rocks
Fractured
rock
Open
hole
Scale = Regional
Wells are open hole in fractured rock (granite, gneiss, schist, metagraywackes,…)
typically about 100 to 600 ft deep
Depth to water ranges from a few feet to tens of feet below land surface
Ground water is slightly acidic, oxidizing, and minimally conductive
pH
median value (103 wells)
6.2
Spec Cond
uS/cm
65
Temp
C
14.8
DO
mg/L
7.4
ORP
mV
308
Summary of 2005 Data – 103 private wells
Counties sampled: Buncombe, Henderson, Transylvania
Radionuclide
No. of wells
Range
Median
RADON, pCi/L
URANIUM, ug/L
GROSS ALPHA, pCi/L
RADIUM-226, pCi/L
INDOOR RADON, pCi/L
103
103
103
103
67 homes
109 - 45600
BDL - 63
BDL - 56
BDL - 1.4
0.3 - 23
6060
<1
1
0.1
2.7
% above
% above proposed
proposed
MCL
alternate MCL
96%
2%
3%
0%
34%
64%
n/a
n/a
n/a
n/a
Results of 2005 data – 103 private wells
Radon above
proposed MCL
of 300 pCi/L
Buncombe
Uranium
above MCL of
30 ug/L
Gross alpha
above MCL of
15 pCi/L
Henderson
Transylvania
Meta-igneous rock
Metasedimentary rock
2005, 103 private wells
Radon above
300 pCi/L
Meta-igneous rock
Metasedimentary rock
2005, 103 private wells
Radon above
4,000 pCi/L
Meta-igneous rock
Metasedimentary rock
2005, 103 private wells
Radon above
10,000 pCi/L
(30X proposed MCL)
Meta-igneous rock
Metasedimentary rock
2005, 103 private wells
Radon above
20,000 pCi/L
(60X proposed MCL)
Meta-igneous rock
Metasedimentary rock
FACTORS THAT CONTROL OCCURRENCE
Geology
Wells in meta-igneous rock tended to have higher dissolved radon than
wells in meta-sedimentary rock…
9000
8000
7680
Median Radon, All Data
7000
6060 pCi/L
4000
3000
2000
1000
3820
3110
Brevard
Fault
5000
Metasedimentary
Dissolved
Radon,
pCi/L
Meta-igneous
6000
0
Meta-igneous
63 wells
Meta-sedimentary
39 wells
Brevard fault zone
5 wells
Detailed
Radon above
Formations
20,000 pCi/L
2005, 103 private wells
(60X proposed MCL)
Radon: 300 to 4000 pCi/L
Radon: above 4000 pCi/L
granite
gneiss
Ordivician, 438 M , interlayered
w/ biotite augens
granodiorite
Devonian, 390 M
Henderson
Gneiss
Cambrian, 500 M
Meta-igneous rock
Metasedimentary rock
Dissolved oxygen
• Most wells were oxic
• Oxic ground water was higher in radon-222 and uranium
• Oxic ground water was lower in radium-226
Ground water geochemistry
No. of samples Radon, pCi/L
oxidizing
reducing or moderately reducing
98
5
Ra-226, pCi/L
Uranium, ug/L
0.15
0.37
1.8
near zero
8018
1930
"Radon:Radium-226" ratio
Radon/Radium-226 ratio
250000
200000
Oxidizing vs
Reducing
Conditions
150000
100000
50000
0
oxidizing conditions
oxidizing
reducing conditions
reducing
Did radionuclides “co-occur”?
High indoor radon was not an obvious predictor of others radionuclides…
s
he
t
g
Hi 8 pCi/L
U = < 0.5
Rn = 5000 pCi/L
Ra = 0.4 pCi/L
12 pCi/L U = < 0.5
Rn = 9400 pCi/L
Ra = < 0.05
st
e
w
Lo 1 pCi/L
U = < 0.5
Rn = 30,000 pCi/L
Ra = 0.08 pCi/L
1 pCi/L
U = < 0.5
Rn = 13,800 pCi/L
Ra = 0.17 pCi/L
Did radionuclides “co-occur”?
High radon was not an obvious predictor of others radionuclides…
s
he
t
g
Hi Rn = 45,600 pCi/L
Rn = 37,300 pCi/L
U = < 0.5 ug/L Ra = 0.03 pCi/L
U = 1.4 ug/L
Ra = 0.03 pCi/L
U = 63 ug/L
Ra = 0.33 pCi/L
te
a
r
e
od
m
w/ Rn = 2750 pCi/L
o
L
Did radionuclides “co-occur”?
High uranium was not an obvious predictor of others radionuclides…
t
es
gh
Hi U = 63 ug/L
U = 16 ug/L
Rn = 2,800 pCi/L
Ra = 0.3 pCi/L
Rn = 5210 pCi/L
Ra = 1.4 pCi/L
Isotope disequilibrium
• Dissolved radon 3 to 5 orders of magnitude higher than 226Ra and
uranium
• Radium isotopes were used to determine source rock (U vs Th) and
radon transfer mechanisms
Radon levels were not correlated
with hydrologic setting, well depth,
casing depth, well yield, Fe, or Mn
2006 – 78 private wells
Counties sampled: Buncombe, Henderson, Transylvania, Mitchell,
Madison, Watauga, Jackson
Radionuclide
No. of wells
RADON, pCi/L
URANIUM
RADIUM-226
RADIUM-228
INDOOR RADON
78
75
75
75
55 homes
Range
Median
87 - 15742 pCi/L
BDL - 30 ug/L
BDL - 2.2 pCi/L
BDL - 1.1 pCi/L
Awaiting
BDL - 19.6 pCi/L
% above
proposed MCL
1897
96%
0.5
1%
0.3
0%
0.1
0%
results from lab
1.7
29%
% above
proposed
alternate MCL
31%
2006 – 78 wells
Watauga
Rn: greater than 4000 pCi/L
Rn: 300 to 4000 pCi/L
Rn: less than 300 pCi/L
Mitchell
Madison
Buncombe
Henderson
Jackson
Transylvania
Meta-igneous
Metasedimentary
HEALTH RISKS FOR RADON
Radon is a Class “A” Carcinogen.
Radon risk
Inhalation risk
25000
21,000
20000
17,400
Deaths
per year
15000
Smoking and radon do not
mix! (7 to 9 times greater
risk for smokers)
10000
8,000
3,900
5000
2,800
0
1
RADON
Source: EPA, 2003
Drunk
2
Driving
Falls3 in the
Home
Drowning
4
Home
5
Fires
Radon in Air
• National average for ambient (outdoor) radon is 0.4 pCi/L.
• National average indoor radon is 1.3 pCi/L.
• EPA “Action Guideline” is 4.0 pCi/L.
Radon in Water
Risks of radon in water are associated with off gassing to
indoor air
Radon in water (inhalation exposure) results in a few
hundred US deaths per year (studies ongoing)
Radon in water can result in new pathways of
exposure (upstairs living areas, for example)
Off gassing of shower water can result in increased overall radon
exposure…
Rn in water
=> Rn in air
HEALTH RISKS FOR RADON
Testing and Mitigation
• testing is easy; as low as $10 for indoor radon test and $25 for radon-inwater test
• radon can be removed from indoor air by sub-slab depressurization ($1000 to
$2000)
Sub-slab depressurization
• radon can be removed from a water supply by aeration ($2500 to $4000),
storage, or GAC filter (~$1000 to $1500, but disposal may be costly)
Aeration
• One should consider the levels of both indoor radon and radon in water when
determining an optimal mitigation system
Summary
• Elevated radon occurs in the ground water drinking supplies in several areas
of NC, particularly in the Blue Ridge, Inner Piedmont, and Raleigh Belts.
• Elevated radon is associated with meta-igneous rocks (granites and granitic
gneisses).
• Geochemistry controls radionuclide solubility and occurrence.
• Degassing from water during showers results in an acute (short term) daily
dose over that of ambient conditions.
Summary
• Main source of indoor radon is from underlying rock and soils.
• Risk of radon in water is much greater from inhalation than from ingestion.
• Risk from exposure to radon rich water is greater than the risk from exposure
to most other regulated compounds
Indoor Air Radon in NC
3 to 4 pCi/L
Meta-igneous rocks
* Data from Airchek, Inc, 2006
n = 16,384
max = 2146 pCi/L
median = 1.6 pCi/L
For more information:
Ted Campbell, NC Division of Water Quality,
Aquifer Protection Section
828-296-4683
ted.campbell@ncmail.net
Final report available: Radionuclides in Ground Water Drinking
Supplies in Western NC, 2005
http://h2o.enr.state.nc.us/admin/pubinfo/DWQPubInfoHotTopics.htm