Groundwater Fact SheetRadionuclides
Constituent of Concern

Summary

Gross Alpha, Gross Beta,
Radium, Radon, Uranium,
Tritium, Strontium-90, etc.

Radioactive forms of elements are called radionuclides.
Radioactive decay is when a radioisotope transforms intoanother radioisotope; this process emits radiation in some form.
Some radionuclides occur naturally in the environment, whileothers are man-made or produced as byproducts of nuclear
reactions. There are many radioactive elements present in theenvironment. Maximum Contaminant Levels (MCL) have been
established by the California State Water Resources Control
Board (SWRCB) for uranium, strontium, radium, gross alpha, grossbeta particle activity and tritium. The United States
Environmental Protection Agency (EPA) has established MCL
different from California for uranium, radon, strontium, tritium,and gross beta (adopted by California) particle activity. EPA’s
MCL for strontium and tritium are covered by gross beta activity.

Synonym
None

Chemical Formula
Gross Alpha
Gross Beta
RadiumRadon
Uranium
Tritium
Strontium..

proton-neutron
electron
Rd
Ra
U
3H
Sr-90
..

CAS Number
Gross Alpha
Gross Beta
Radium 226
Radium 228
Radon 222
Uranium 234
Uranium 235
Uranium 238
Tritium
Strontium..

12587-46-1
12587-47-2
13982-63-3
15262-20-1
14859-67-7
13966-29-5
15117-96-1
7440-61-1
10028-17-8
10098-97-2..

Storet Number
Gross Alpha
Gross Beta
Radium 226+228
Radon 222
Uranium
Tritium
Strontium
..

01501
03501
11503
82303
28012
82126
13501
..

Some levels of radiation exposure are due to natural
background sources (e.g., cosmic radiation, terrestrial, food,etc.). According to the U.S. Nuclear Regulatory Commission the
average natural background radiation dose in the United States
is approximately 310 mrem/year. Different radioactive
constituents will interact and damage biologic activity
differently. As a result, some constituents have greater or lower
MCL than others. The most common radionuclides in California’s
groundwater are uranium and gross alpha.
Uranium: Based on SWRCB data from 2007 to 2017, 276 standby
and active public supply water wells (4,423 wells tested, 3,643
detections) had at least one detection above the MCL of 20
pCi/L, with a maximum concentration of 1,000 pCi/L. MCL
exceedances were most common in San Bernardino (57 wells),
Fresno (37 wells), and Madera (30 wells) counties.
Gross alpha: Based on SWRCB data from 2007 to 2017, 561
standby and active public supply water wells (8,779 wells tested,
6,369 detections) had at least one detection of gross alpharadioactivity above the MCL of 15 pCi/L, with a maximum
concentration of 920 pCi/L. MCL exceedances were mostcommon in San Bernardino (95 wells), Kern (73), and Fresno (69)counties.

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REGULATORY WATER QUALITY LEVELS1RADIONUCLIDES
Constituent

Type

AgencyConcentration2

Gross AlphaMCL

EPA3 and SWRCB4

15 pCi/L

DLR5

SWRCB

3 pCi/LMCL (official)

EPA and SWRCB

4 mrem/year (dose)

MCL6 (trigger)

EPA

50 pCi/L

DLR

SWRCB

4 pCi/L

MCL

EPA

5 pCi/L

DLR

SWRCB

1 pCi/L

PHG7 (Ra-226)

SWRCB

0.05 pCi/L

PHG (Ra-228)

SWRCB

0.019 pCi/L

MCL8(advisory)

EPA

4,000 pCi/L

DLR

SWRCB

100 pCi/L

MCL

EPA

30 mg/L

MCL

SWRCB

20 pCi/L

DLR

SWRCB

1 pCi/L

MCL

SWRCB

20,000 pCi/L

DLR

SWRCB

1,000 pCi/L

MCL

SWRCB

8 pCi/L

DLR

SWRCB

2 pCi/L

PHG

SWRCB

0.35 pCi/L

Gross Beta

Radium (combined)

Radon

Uranium

Tritium

Strontium-90

1These levels generally relate to drinking water. Other water and air quality levels may exist.

For further information, see A
Compilation of Water Quality Goals, 17th Edition, (SWRCB, 2016).
2Concentrations are reported in milirems (mrem) per year and in picocuries per liter (pCi/L). A ‘rem’ is a unit of measuredescribing how a specific type of radiation damages biologic tissue. A milirem is one thousandth of a rem. A curie is astandard unit of radioactivity, where 1 curie is the radioactivity associated with 1 gram of radium. A picocurie is one
trillionth of a curie. There is no simple conversion between a curie and a rem.
3EPA – United State Environmental Protection Agency
4SWRCB - State Water Resources Control Board
5DLR = Detection Limit for Purposes of Reporting
6This MCL is no longer an official regulatory level, but is still in use as a trigger for EPA and
SWRCB-DDW. If the trigger level is exceeded additional testing is required to determine the source of beta radiation and if
the MCL has been exceeded.
7PHG = Public Health Goal
8MCL advisory level; there is no established requirement for radon monitoring. The levels listed here represent proposedlevels by the EPA for states that are taking action to reduce radon levels in indoor air by developing an enhanced indoor
air program. California currently has an EPA-approved indoor air program.

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RADIONUCLIDES DETECTIONS IN PUBLIC WATER WELL SOURCES9
Gross Alpha activities >15 pCi/L

561 of 8,779 wells tested, 6,369 detections

Gross Beta activities >50 pCi/Lzero of 646 wells tested

Radium-226 activities >5 pCi/L

12 of 2,138 wells tested

Radium-228 activities >5 pCi/L

7 of 5,379 wells tested

Radon activities >4,000 pCi/L

5 of 132 sources tested

Uranium activities >20 pCi/L

276 of 4,423 tested, 3,643 detections

Tritium activities > 20,000 pCi/Lzero of 164 sources tested

Strontium-90 activities > 8 pCi/Lzero of 143 sources tested

9Based on SWRCB data collected from 2007-2017.

ANALYTICAL INFORMATION
Constituent and Method

Detection Limit

Gross Alpha: EPA methods
900.0, 00-02 (drinking water),othersGross Beta: EPA methods 900.0(drinking water), others

1 pCi/L minimum
detectable levelRadium: EPA 903.0, 903.1, others

0.1 pCi/L and up, 1 pCi/L
minimum detectable level

Radon: ASTM D5072, SM-7500
series

1 pCi/L or lessGas extraction method (D5072) ismore accurate but more difficult andrequires specialized equipment.

Uranium: EPA 908.0, 908.1,
others

1 pCi/L to 0.03 pCi/L, 1
pCi/L minimum
detectable level

Roughly 15 methods are approvedby the EPA. Type of method selected
depends on need.

Tritium: EPA Method 906.0,
others300 pCi/L minimum
detectable level

There are eight total EPA approved
methods.

Strontium-89 and Strontium-90:
EPA Method 905.0, others

0.5 pCi/L minimum
detectable level

A total of nine methods areapproved by the EPA. Somemodifications may be required tomeasure for Sr-89.

0.5 pCi/L minimum
detectable level

Note

Detection limit may vary dependingon sample volume, solids
concentrations, counting system andtime.

10The analytical methods here are only a partial list. For a full list of EPA-approved analytical methods please see references

number 10 and 11 at the end of the fact sheet.

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Radionuclides Occurrence
Radionuclides are naturally occurring elements of the Earth and are present (usually at very low
levels) in every substance and material on the planet and may sometimes include several different
isotopic versions of the same element. Isotopes are atoms of an element with differing atomic
masses (specifically, different numbers of neutrons). Different isotopes will have different radioactive
decay properties. As a result, some isotopes may have established health regulatory levels, whileothers do not. An example is tritium, or 3H. Tritium is an isotope of hydrogen, with three neutrons. The
SWRCB-DDW established a regulatory level of 20,000 pCi/L for this isotope. However, the mostcommon isotope of hydrogen is 1H, with one neutron. This isotope of hydrogen is the most abundantelement (and isotope) in the universe, is not radioactive, and poses no health risk.
Exposure to naturally occurring radioisotopes is caused by “background radiation”. Somebackground radiation even comes from space. Most radiation detected in groundwater is the resultof interactions with natural geologic materials that contain trace levels of radioactive isotopes.
Radioactivity is a function of the abundance of radioisotopes and of the decay-rate of thatradioisotope.

Gross Alpha
Alpha particles (α-particles) are a type of radiation emitted by radionuclides. They consist of two
protons and two neutrons. Their travel range is only a few centimeters. Once alpha particles lose
energy, they pick up electrons and become helium. U-238, Ra-226 and Rd-222 are examples of alphaparticle emitters. Alpha emitters are used to treat cancer, as a static eliminator in paper mills andother industries, and in smoke detectors.

Gross Beta
Beta particles (β-particles) are a type of radiation emitted by some radionuclides. Beta particles areequivalent to electrons and can travel a few meters in air. After losing their energy, they are picked
up by positively charged ions. There are numerous sources of beta particles, including tritium,
strontium-90, cesium-137, and products of radium decay. Beta emitters have many uses, especially in
medical diagnosis, imaging, and treatment. They can also be used as tracers in agricultural studies(strontium-90), luminous aircraft and commercial exit signs (tritium), drug metabolism studies (tritium),dating organic matter (carbon14), and in a variety of industrial instrumentation.

RadiumRadium is a naturally occurring, silvery white metal formed by decay of uranium and thorium. Multiple
isotopes occur at very low levels in virtually all rocks, soil, water, plants and animals. Ra-226 is analpha emitter and has a half-life of about 1,600 years. Ra-228 is a beta emitter and has a half-life of
5.76 years. Radium decays to form isotopes of radioactive radon and stable lead. Before the risks ofradium exposure were understood, mixtures of light emitting radium salts and phosphors were widelyused in luminescent paints for clock dials and gauges.

Radon
Radon is a naturally occurring gas and is a product of uranium decay. Radon occurs in groundwaterand easily moves into the air. A radon concentration of 10,000 pCi/L in water results in aconcentration of 1 pCi/L in the air. Radon is naturally present wherever uranium and radium
concentrations in geologic materials are high and tends to be abundant in granitic terrains andcertain types of sedimentary deposits. Radon may accumulate in basements and enclosed areas
where gases are trapped, and air circulation is low.
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Uranium is a naturally occurring radioactive element in rocks, soil, water, plants, animals, andhumans. There are three main isotopes of uranium (U-234, U-235, and U-238). U-238 is a weakly
radioactive metal and contributes to low-level background radiation in the environment. U-238 hasa very long half-life of 4.47 billion years. Enriched U-235 is used as fuel in nuclear reactors and innuclear weapons. Depleted uranium, which is poor in U-235 but rich in U-238, is used by the military intank armor, bullets, and missiles for its strength and density. Uranium is common in specific types of
igneous, metamorphic, and sedimentary rocks.
Recent research indicates that increased concentrations of uranium in groundwater are caused bymobilization of uranium present in soil with irrigation waters containing bicarbonates. Also, nitrate canmobilize uranium through a series of bacterial and chemical reactions.

Tritium
Tritium (3H) is a naturally occurring isotope of hydrogen (H) that is widely found in all water, althoughusually at very low concentrations. Tritium is used commercially as an illuminating agent in exit signs
and other devices. Tritium is also used in metabolism and new drug studies. While most natural tritium
forms as a result of bombardment of the upper atmosphere by cosmic background radiation,
significant quantities of tritium are produced in nuclear reactors and in maintenance ofthermonuclear devices. Large quantities of Tritium were released into the atmosphere during
aboveground nuclear testing in the 1950s and early 1960s. The short half-life (12.32 yrs.) of Tritium isuseful in age-dating of young groundwater.

Strontium-90
Strontium-90 is a byproduct of thermonuclear fission between uranium and plutonium. There areseveral other naturally occurring isotopes of strontium as well. Large quantities of strontium-90 were
produced in the 1950s and 1960s by testing of nuclear devices. This strontium was rapidly distributedin the atmosphere throughout the world. The 1986 Chernobyl accident in Ukraine also released large
amounts of strontium90 into the atmosphere. Strontium-90 is used as a tracer in agricultural andmedical studies, and as a long-term power source for remote buoys, satellites, and other objects.

Remediation and Treatment Technologies
In general, mitigation of drinking water that exceeds a state or federal radionuclide standard iscomplicated since traditional water treatment processes and disposal methods cannot be routinely
implemented. Residuals and wastewater derived from the treatment process for these types ofcontaminants cannot be easily disposed of. Water systems with sources that exceed drinking water
standards for radionuclides may consider implementing the measures summarized below to comply
with drinking water quality regulatory requirements.

Mixing Solution: Interconnect with other non-impacted water systems in the area. This option often
may be the most cost-effective approach to resolving water quality problems for the long-term.
Depending on the water quality and yield of each source, water from different sources may be
blended to meet drinking water standards, or new sources may be developed.

Geologic solution: determine if certain water bearing zones can be isolated to improve water
quality and comply with radionuclide regulatory requirements.

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Gross Alpha
The presence of alpha particles in water usually indicates radium-226, U-235 and Rd-222 as thesource. As shown in the attached maps (Figs. 1, 2) distribution of uranium and gross alpha activities
above MCL levels is closely related. Water should be tested for a source of radioactivity and treatedappropriately.

Gross Beta
The presence of beta particles in water usually indicates radium-226 and tritium as the source. Water
should be tested for a source of radioactivity and treated appropriately.

Radium
The most inexpensive treatment method is synthetic zeolite ion exchange like home water softeners,
which removes roughly 90% of the radium. Other possible treatment methods include lime-soda ash
softening and reverse osmosis. Comparatively high start-up and operating costs may make these
options impractical for most affected systems. Technologies being tested include an adsorptive
media where water is passed through columns for treatment, and oxidationcoagulation flocculationfiltration method.

Radon
Granular activated carbon filters (GAC) use activated carbon to remove the radon. Aeration
devices, which bubble air through the water and carry radon gas out into the atmosphere throughan exhaust fan, are another alternative.

Uranium
Processes include reverse osmosis, anion exchange, special adsorbent media, distillation, or lime
softening.

Tritium
Mixing or geologic solutions are most effective.

Strontium-90
Reverse osmosis and activated charcoal is effective. Mixing and geologic solutions may also beappropriate.

Health Effect Information
Gross AlphaThe health effect of alpha particles depends upon how exposure takes place. External exposure is far
less of a concern than internal exposure because alpha particles lack the energy to penetrate theouter dead layer of skin. If alpha emitters have been inhaled, ingested, or absorbed into the bloodstream, living tissue may be exposed. Exposure of living tissue to alpha radiation is associated with anincreased risk of cancer, in particular lung cancer (inhalation). The greatest exposure to alpharadiation comes from the inhalation of radon and its decay products, several of which also emit
potent alpha radiation.

Gross Beta
Beta radiation can cause both acute and chronic health effects. Contact with a strong beta sourcefrom an abandoned industrial instrument may result in acute exposure. Chronic effect results fromlow-level exposure over a long period (approximately 5-30 years). The main chronic health effect6
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from radiation is cancer. When taken internally beta emitters can cause tissue damage, which
increases the risk of developing cancer. Some beta emitters, such as carbon-14, distribute widely
throughout the body. Others accumulate in specific organs; iodine-131 in the thyroid gland,strontium-90 in bone and teeth.

RadiumRadium is known to cause bone cancer when consumed in high doses. The National Academy of
Sciences (NAS) has concluded that a long-term exposure to elevated levels of radium in drinking
water poses a higher risk of bone cancer for those exposed. In the 1920s, radium paint was used tomake watch dials luminescent. The workers who painted the watch dials would touch the paintbrushtips to their tongues, and inadvertently swallowed high doses of radium. In the decades since, thisgroup of occupationally exposed workers (approximately 4,000) has developed an extremely highrate of death from bone cancer. This effect of radium has also been documented in laboratory
animals.

Radon
Breathing radon in indoor air can cause lung cancer. Radon inhalation is the second leading causeof lung cancer, behind smoking, and causes approximately 21,000 deaths a year in the U.S. Most
radon that enters indoor spaces comes from degassing of natural geologic deposits. Only about 1-2
percent of radon in the air comes from drinking water. Drinking water that contains radon alsopresents a risk of developing internal organ cancers, primarily stomach cancer. Based on a NAS
report, the EPA estimates than radon in drinking water causes about 168 cancer deaths per year:
89% from lung cancer caused by breathing radon released to indoor air from water and 11% fromstomach cancer caused by consuming water containing radon.

Uranium
Exposure to uranium can result in both chemical and radiological toxicity. Natural uranium consists
primarily of the U-238, which is very weakly radioactive, and it is not a hazardous radioactive
substance. However, uranium is a weak chemical poison that can seriously damage the kidneys athigh blood concentrations. This damage is dosage dependent and somewhat reversible. The
uranium ion (uranyl) can also deposit on bone surfaces and may be detected in the bone matrix forseveral years following exposure.

Tritium
Tritium is a beta-emitter, and like all beta emitters it contributes to an increased risk of cancer.
However, tritium rapidly exits the body and overall is one of the least-dangerous radionuclides. Tritium
is naturally found in very low levels in all water.

Strontium-90
Strontium is similar chemically to calcium, and tends to accumulate in bones, where calcium isnormally deposited. Increased exposure to strontium-90 has been linked to bone cancer, cancer
near bones, and leukemia.

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Key Resources
1. Argonne National Laboratory-Environmental Science Division (EVS)-Radiological andChemical Fact Sheets to support Health Risk Analyses for Contaminated Areas
https://remm.hhs.gov/ANL_ContaminantFactSheets_All_070418.pdf
2. California Safe Drinking Water Act & Related Laws and Regulations- Article 5. 2017.
Radioactivity from Title 22 California Code of Regulation.
https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/documents/lawbook/dwregulations-2017-04-10.pdf
3. Jurgens B., Fram M. S., Belitz K., Burow K. R., Landon M. K., 2010. Effects of Groundwater
Development on Uranium: Central Valley, California, USA. Groundwater, volume 48, Issue 6, p.
913-928. https://doi.org/10.1111/j.1745-6584.2009.00635.x
4. Maximum Contaminant Levels and Regulatory Dates for Drinking Water, EPA vs. California. July
2014.
https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/documents/ccr/MCL_
epa_vs_dwp.pdf
5. Maywood Superfund Site, Fact Sheets, http://www.fusrapmaywood.com/projmain.html
6. NAS (1988). Health Risks of Radon and Other Internally Deposited alpha-emitters. Report of theCommittee on Biological Effects of Ionizing Radiation (BEIR IV). National Academy of Sciences,
National Research Council, Washington, D.C. http://www.ncbi.nlm.nih.gov/pubmed/25032289
7. State Water Resources Control Board, A Compilation of Water Quality Goals 17th Edition,(SWRCB, 2016).
http://www.waterboards.ca.gov/water_issues/programs/water_quality_goals/docs/wq_goals_
text.pdf
8. United States Environmental Protection Agency, Drinking Water Contaminants-Radionuclides,
http://www.epa.gov/your-drinking-water/table-regulated-drinking-watercontaminants#Radionuclides
9. United States Environmental Protection Agency. 2000. Federal Register, 40 CFR Parts 9, 141 and
142-National Primary Drinking Water Regulations; Radionuclides; Final Rules-December 7, 2000
10. United States Environmental Protection Agency, Analytical Methods Approved for Drinking
Water Compliance Monitoring, http://www2.epa.gov/dwanalyticalmethods/approveddrinking-water-analytical-methods
11. United States Environmental Protection Agency, Compendium of EPA-Approved Analytical
Methods for Measuring Radionuclides in Drinking Water.1998.
https://www.orau.org/ptp/PTP%20Library/library/DOE/Misc/radmeth3.pdf
12. United States Environmental Protection Agency. 2007. Radiation Protection
http://www2.epa.gov/radiation/radionuclides
13. United States Environmental Protection Agency, What is Radon?
https://safewater.zendesk.com/hc/en-us/articles/212080177-What-is-radon14. Weber, K., Stange, M. Nitrate and Uranium in Drinking Water, University of Nebraska, Lincoln,
April, 2014.

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Figure 1. Active and standby public drinking water wells that had at least one detection of uranium
above the MCL, 2007-2017, 276 wells. Source: GAMA GIS.

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Figure 2. Active and standby public drinking water wells that had at least one detection of gross alphaactivity above the MCL, 2007-2017, 561 wells. Source: GAMA GIS.

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