Radon in the Ground Water Drinking Supplies of … in the Ground Water Drinking Supplies of North...

Radon in the Ground Water Drinking Supplies of North Carolina

Ted Campbell, NC Division of Water Quality, Aquifer Protection Section [email protected]

Contributors:

Staff of DWQ, Aquifer Protection Section

Dr. Felix Fong, NC Radiation Protection Division

U.S. Environmental Protection Agency

Duke University, Nicholas School of the Environment and Earth Sciences

Staff of the NC Geological Survey

• a radioactive gas produced by the decay of uranium-238

Radon-222

• a radioactive gas produced by the decay of uranium-238

• 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

Radon-222

• not common in surface waters due to volatilization

• a human carcinogen - 2nd leading cause of lung cancer

• half life of 3.8 days….can’t travel “unsupported” for long distances

Radon-222

• degasses during showering can increase one’s overall exposure and health risk over ambient levels alone

• tends to occur at higher levels in private wells than in public supply wells

• 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 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-222

Radon Standards

• 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”.

• EPA proposed standard for radon in water = 300 pCi/L

Water

• EPA “Action Level” = 4 pCi/L

Indoor Air

• Lung cancer (inhalation) and stomach cancer (ingestion)

So what are the risks from radon-222 in water?

• 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

Vermont = 5,000 pCi/L

Massachusetts = 10,000 pCi/L

New Hampshire = 2,000 pCi/L

Maine = 4,000 pCi/L

Wisconsin = 5,000 pCi/L

New Jersey = 300 pCi/L

Standard does not exist for NC.

For perspective…

Radon

Across USA

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)

(Focazio and others, 2006)

• 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)

Map was developed based on:

Predicted indoor radon across USA

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 NCabove 8 pCi/L

above 20 pCi/L

Meta-igneous rocks

* Data from Airchek, Inc, 2006n = 16,384max = 2146 pCi/Lmedian = 1.6 pCi/LGuilford, Forsyth, Wake

EPA Zone 1 Counties



Uranium-rich rock exists across region

Blue Ridge Belt

Inner Pied

mont Belt

Charlotte

Belt

Carolin

a Slate

Belt

Raleig

h Belt

Coastal

Plain

Major Geologic Belts in NC

Meta-igneous rocks

Uranium rich rock in NC

Granit

e, gn

eiss,

and s

chist

Granite

, gne

iss, a

nd sc

hist

Granite, g

neiss

, and sc

hist

NC minerals high in uranium include: monazite, allanite, and uraninite

Meta-igneous rocks tend to be higher in

uranium content


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

About half of the population uses ground water as its principal drinking water supply



Henderson gneiss near Brevard Mylonitized Rocks

of the Brevard Fault Zone (ductile shear; granitic origins)

From NURE database, Geochemical Atlas of NC (Reid, 1991)

Raleig

h Belt

Carolin

a Slate

Belt

Charlotte

Belt

Existing data

1983 - Menetrez & Watson; and Fong (2004)

- 2.4% of suppliers exceeded EPA MCLs for gross alpha or combined radium

- 2000 suppliers

15 pCi/L 5 ug/L

Existing data

- 211 PWS wells across NC

1975 -

- Median radon across NC ~ 1400 pCi/L

Aldridge, Sasser, and Conners

- Average radon across Western NC ~ 4100 pCi/L

1974 - Environmental Science Lab

- 60% contained radon above 2000 pCi/L

- Lowest radon levels are in Coastal Plain, and highest are in Mtns & Piedmont.

- 204 PWS wells across NC

Radon in NC Ground Water

Existing data

granitesgneisses

- 96 suppliers

1987 - Loomis, Watson, & Crawford-Brown

- Rock type effects radon levels.

- Well yield, depth, and casing length were not predictors of radon levels.

maficssedimentary rocks of the Coastal Plain

High variability

within subtypes


Existing data

1993 - University of North Carolina

- 83% contained radon above 2000 pCi/L

- 277 private wells across mountains of NC

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.


Blue Ridge Belt

Inner Pied

mont Belt

Charlotte

Belt

Carolin

a Slate

Belt

Raleig

h Belt

Coastal

Plain

Current Studies

Counties with known susceptibility to elevated radon in ground water *


Guilford

Orange

Wake

Meta-igneous rock

Franklin

Median = 735 pCi/L

Max = 6,300 pCi/L(70 private wells)

(Spruill and others, 1997)

Felsic and mafic igneous and meta-igneous rock

Median = 586 pCi/L

Max = 4,229 pCi/L(42 wells)

(Orange Co. staff, 1997)

Metamorphosed granitic rock

Granitic plutonsRaleigh

gneiss

Median = 2800 pCi/L

Max = 32,000 pCi/L(305 private wells - Phase I & II)

(Cornell and others, 2005)

(Bolich and Stoddard, 2004)

27 wells above 10,000 pCi/L

60 wells above 4,000 pCi/L

Slate Belt and Raleigh Belt

• 2005 - sampled 103 private wells (Buncombe, Henderson, and Transylvania Counties -- all EPA Zone 1 counties)

• focused more heavily on areas underlain by meta-igneous rocks

radionuclides other parameters well construction

radon DO well depthuranium, total pH casing depthgross alpha activity spec cond well yieldradium-226 ORP latituderadium-224 temperature longituderadium-223 alkalinity observed local geologyindoor radon iron

manganese

• analyzed:

• 2006 - sampled 78 private wells (Buncombe, Henderson, Transylvania, Mitchell, Madison, Watauga, Jackson)

Blue Ridge and Inner Piedmont Belts

• Where do radionuclides occur and at what levels?

• What factors control radionuclide levels in our study area?

NCDWQ Study is Addressing 3 Questions

• What are the policy implications?

EPA Zone 1 Counties

Meta-igneous rock

EPA Zone 1 CountiesBlue Ridge

Piedmont

Coastal Plain

Meta-igneous rock

Buncombe

Henderson

Transylvania

Study Area

Sampled wells

Meta-igneous rocks

Includes granites and granitic gneisses (Henderson, Toxaway, Caesar’s Head)

Meta-sedimentary rocks

Includes schists, metagraywackes, and metavolcanics of the Ashe Metamorphic Suite

103 private wells

2005

Henderson gneiss near Brevard

Henderson gneiss near Rosman

Henderson gneiss near Brevard Mylonitized Rocks

of the Brevard Fault Zone (ductile shear; granitic origins)

Above 8 pCi/L

Indoor radonSource: data from Airchek, Inc, obtained 2005

Meta-igneous rockMetasedimentary rock

Above 20 pCi/L



Above 50 pCi/L



Above 100 pCi/L



Open hole

CasingsaproliteRegolith

…igneous, metasedimentary, and metavolcanicrocks

Transition zone

Fractured rock

Open hole

Wells are open hole in fractured rock (granite, gneiss, schist, metagraywackes,…) typically about 100 to 600 ft deep

Ground water is slightly acidic, oxidizing, and minimally conductive

Depth to water ranges from a few feet to tens of feet below land surface

Scale = Regional

pH Spec Cond Temp DO ORPuS/cm C mg/L mV

median value (103 wells) 6.2 65 14.8 7.4 308

Summary of 2005 Data – 103 private wells

Counties sampled: Buncombe, Henderson, Transylvania

Radionuclide No. of wells Range Median% above proposed

MCL

% above proposed

alternate MCL

RADON, pCi/L 103 109 - 45600 6060 96% 64%URANIUM, ug/L 103 BDL - 63 <1 2% n/a

GROSS ALPHA, pCi/L 103 BDL - 56 1 3% n/aRADIUM-226, pCi/L 103 BDL - 1.4 0.1 0% n/a

INDOOR RADON, pCi/L 67 homes 0.3 - 23 2.7 34% n/a


Radon above proposed MCL of 300 pCi/L

Uranium above MCL of 30 ug/L

Gross alpha above MCL of 15 pCi/L

Results of 2005 data – 103 private wells

Buncombe

HendersonTransylvania

Radon above 300 pCi/L


2005, 103 private wells

Radon above 4,000 pCi/L





(30X proposed MCL)




(60X proposed MCL)


FACTORS THAT CONTROL OCCURRENCE

Wells in meta-igneous rock tended to have higher dissolved radon than wells in meta-sedimentary rock…

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

Meta-igneous Meta-sedimentary Brevard fault zone

Dissolved Radon, pCi/L

Median Radon, All Data

6060 pCi/L

63 wells 39 wells 5 wells

3110

7680

3820

Geology

Met

a-ig

n eou

s

Met

a-se

dim

ent a

ry

Br e

var d

Fa

ult



(60X proposed MCL)

Henderson Gneiss

granite gneiss

granodiorite

Radon: above 4000 pCi/L

Radon: 300 to 4000 pCi/L

Cambrian, 500 M

Devonian, 390 M

Ordivician, 438 M , interlayered w/ biotite augens

2005, 103 private wellsDetailed Formations

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 Ra-226, pCi/L Uranium, ug/L

oxidizing 98 8018 0.15 1.8reducing or moderately reducing 5 1930 0.37 near zero

"Radon:Radium-226" ratio

0

50000

100000

150000

200000

250000

oxidizing conditions reducing conditions

Radon/Radium-226 ratio

oxidizing reducing

Oxidizing vsReducing Conditions

High indoor radon was not an obvious predictor of others radionuclides…

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

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

Highest

Lowest

Did radionuclides “co-occur”?

Rn = 45,600 pCi/L U = < 0.5 ug/L Ra = 0.03 pCi/L

Rn = 37,300 pCi/L U = 1.4 ug/L Ra = 0.03 pCi/L

Rn = 2750 pCi/L U = 63 ug/L Ra = 0.33 pCi/L

High radon was not an obvious predictor of others radionuclides…

Highest

Low/moderate


U = 63 ug/L Rn = 2,800 pCi/L Ra = 0.3 pCi/L

U = 16 ug/L Rn = 5210 pCi/L Ra = 1.4 pCi/L

High uranium was not an obvious predictor of others radionuclides…

Highest


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

Awaiting results from lab

Radionuclide No. of wells Range Median% above

proposed MCL

% above proposed

alternate MCL

RADON, pCi/L 78 87 - 15742 pCi/L 1897 96% 31%URANIUM 75 BDL - 30 ug/L 0.5 1%

RADIUM-226 75 BDL - 2.2 pCi/L 0.3 0%RADIUM-228 75 BDL - 1.1 pCi/L 0.1 0%

INDOOR RADON 55 homes BDL - 19.6 pCi/L 1.7 29%

Rn: greater than 4000 pCi/L

Meta-igneousMetasedimentary

Rn: 300 to 4000 pCi/L

Rn: less than 300 pCi/L

2006 – 78 wells Watauga

Mitchell

Madison

Buncombe

Henderson

TransylvaniaJackson

HEALTH RISKS FOR RADON

Radon is a Class “A” Carcinogen.

0

5000

10000

15000

20000

25000

1 2 3 4 5RADON Drunk Driving

Falls in the Home

Drowning Home Fires

21,000

17,400

8,000

3,9002,800

Deaths per year

Source: EPA, 2003

Radon risk

Inhalation risk

Smoking and radon do not mix! (7 to 9 times greater risk for smokers)

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 can result in new pathways of exposure (upstairs living areas, for example)

Off gassing of shower water can result in increased overall radon exposure…

Risks of radon in water are associated with off gassing to indoor air

Radon in Water

Radon in water (inhalation exposure) results in a few hundred US deaths per year (studies ongoing)

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-in-water test

• radon can be removed from indoor air by sub-slab depressurization ($1000 to $2000)

Sub-slab depressurization

• One should consider the levels of both indoor radon and radon in water when determining an optimal mitigation system

• 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

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.

• 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

Summary

Meta-igneous rocks

Indoor Air Radon in NC

3 to 4 pCi/L

* Data from Airchek, Inc, 2006n = 16,384max = 2146 pCi/Lmedian = 1.6 pCi/L

Ted Campbell, NC Division of Water Quality, Aquifer Protection Section

For more information:

[email protected]

http://h2o.enr.state.nc.us/admin/pubinfo/DWQPubInfoHotTopics.htm

Final report available: Radionuclides in Ground Water Drinking Supplies in Western NC, 2005

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Radon in the Ground Water Drinking Supplies of … in the Ground Water Drinking Supplies of North...

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