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Dissolved Mineral Radioactivity In Drinking Water
GENERAL
New Hampshire's bedrock contains naturally occurring radioactivity.
A few examples with health importance include radon, radium 226,
radium 228 and uranium. Radon is a gas dissolved in water; most
other radionuclides are dissolved minerals in water.
OCCURRENCE
Radioactive minerals occur irregularly throughout New Hampshire in
the bedrock, similar to other minerals such as iron, arsenic and
quartz. Radionuclides dissolve easily in water. In some well water
the concentration of these minerals exceed the concentration
established in public drinking water standards. The standards for
the permissible amount of radioactivity in drinking water are called
maximum contaminant levels (MCLs).
Bedrock wells (also called artesian or drilled) can contain
elevated concentrations of any or all of these
radionuclides, even if nearby bedrock wells have low concentrations.
Wells that derive water from sand and gravel deposits, also known as
dug or point wells, generally have substantially lower
concentrations of both radon gas and dissolved mineral
radioactivity.
HEALTH EFFECTS
The U.S. Environmental Protection Agency (EPA) sets drinking water
standards and has determined that certain radioactive minerals as
specified above are a health concern. Exposure to radioactivity
increases one's risk of various cancers. Other sources of
radioactivity in the environment include x rays, radiation from the
sun, foods from plants that concentrate radioactivity as they grow,
fluorescent watch dials, and many other sources. At lower exposures,
the risk of cancer is reduced. The principal health concerns
associated with regulated radionuclides in water include: radon gas
increases the risk of lung cancer; uranium increases toxicity risk
to the kidneys; and radium increases one's risk of bone cancer.
EPA HEALTH STANDARDS
EPA finalized new health standards for radioactivity in drinking
water for public water systems in 2000. Additional revisions to
these MCLs may be proposed by 2005-2006. The following is a summary
of the current mineral radionuclide MCLs.
| Test Name |
Radiation
Type |
EPA
Standards |
Radon
Compliance Gross Alpha*
Uranium
{Radium 226
{Radium 228
Beta
|
Alpha
Alpha
Alpha
Alpha
Beta
Beta
|
Proposed 300/4,000 pCi/L (CFR
11/99)
15 pCi/L**
30 ug/L (approximately 20 pCi/L)***
}
} Total of 226 & 228 = 5 pCi/L
4 millirems per year
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* Compliance gross alpha equals the concentration of analytical
gross alpha (in pCi/L) minus the concentration of uranium (in pCi/L)
** pCi/L (picocuries per liter)
*** micrograms per liter (ug/L) can be converted to pCi/L by
multiplying the U (ug/L) by 0.67.
CFR = Code of Federal Regulations (proposed rule)
REMOVAL OF RADIOACTIVITY FROM DRINKING
WATER
Radionuclides can be effectively removed from drinking water. There
are different processes for different radionuclides. In general
these removal processes concentrate the radioactivity, thus creating
the need for proper disposal.
ADDRESSING RADIOACTIVITY IN DRINKING WATER
This fact sheet focuses on reducing dissolve mineral radioactivity
in drinking water. See fact sheet WD-WSEB-3-12 for information
concerning reducing radon gas.
New Well or Connection to a Public Water System
Wells that derive their water from the soil strata (i.e. sand and
gravel) generally do not have meaningful amounts of radionuclides.
Such wells are commonly called dug or point wells. See fact sheet
WD-WSEB-1-4 or WD-WSEB-1-5 respectively for more information on
these other types of wells. Another method of achieving a safe water
supply would be to extend the piping of a public water system if
nearby.
Wells that derive water from the bedrock may have high
concentration of radionuclides. The best way to determine if another
well into the bedrock would have a reasonable chance of better
quality is to do a neighborhood survey of all homes with bedrock
wells and evaluate their radionuclide data and well locations.
TREATMENT TO REMOVE RADIONUCLIDES
All radionuclides contaminants can be removed from well water. There
are different processes for different radionuclides. In general
these removal processes concentrate the radioactivity, thus creating
the need for proper handling and disposal of waste by-product and
possible shielding of the treatment devices where concentrations are
very high.
Size of Treatment Devices
Treatment devices come in two sizes. A whole house device
typically treats 200-300 gallons of water per day per home, enough
for a typical family of four persons; while a point-of-use
sized device typically treats two-five gallons per day, enough for
only drinking purposes.
Point-of-Use versus Whole House
In general, mineral radioactivity contaminants only need to be
removed from water that will be consumed or incorporated into food.
Thus a point-of-use (POU) device will typically be adequate. There
is no appreciable skin adsorption of radionuclides. To protect young
infants that might occasionally swallow bath water, DES recommends
whole house sized treatment where the radionuclide concentration is
above the level shown below:
|
Contaminant |
Concentration |
Compliance Gross alpha
Uranium
Radiums
Beta
|
250 pCi/L
500 ug/L
80 pCiL
Pending
|
Information Concerning Gross Alpha and Valance. There are
many elements that are radioactive and produce alpha emissions. The
analytical gross alpha test identifies all alpha radiation from all
radionuclides minerals. Precisely identifying each element producing
the alpha radiation is not needed. Rather it is sufficient to
determine which treatment process will provide an adequate amount of
reduction of the gross alpha concentration to meet the compliance
gross alpha MCL of 15 pCi/L.
Definition of Valance. An ion is the dissolved form of an
atom or molecule. Mineral contaminants can dissolve in water
producing either of two types of ions: those with a negative
electrical charge (i.e. valance) called anion, and those with a
positive valance (called cation). The ion exchange processes is
commonly used to remove radionuclides ions of either type.
Gross Alpha Identification. Contaminants producing gross
alpha radiation can dissolve into water producing both positive and
negative radioactive ions
POINT-OF-USE (POU) SIZED DEVICES
There are two sizes of point-of-use devices: under-the-sink
and screw-on. Screw-on devices are typically very small, and
are placed by the homeowner on the end of the kitchen faucet. They
have a brief service life. They remove the contaminant types
described on the label. Under-the-sink (POU) devices are
typically larger, installed by professionals, and have a
substantially longer operational life although still shorter than
whole house treatment equipment.
Screw-on devices have a first time lower purchase cost than
under-the-sink type systems. However, long-term operational costs
are generally higher for frequently replaced screw-on devices.
Point-of-use devices generally, being much smaller, typically have
lower operational cost than whole house treatment devices. This
document does not further evaluate screw-on devices.
POU Treatment Methods for Removing Radium, Uranium and some
Gross Alpha
The radiological concentrations at most homes can be very adequately
addressed by installing point-of-use sized equipment.
Reverse osmosis (RO) treatment addresses all uranium,
radium and gross alpha contaminants. In this treatment process,
water under pressure is placed against a special membrane. The RO
membrane allows water molecules to pass through, but retards the
passage of other contaminants, including radionuclides. The rejected
contaminants and the water that does not go through the membrane are
"wasted" from this device to prevent the overall buildup of the
contaminant(s) on the untreated side of the membrane. See fact sheet
WD-WSEB-2-11 for more information on RO. Typical installation cost
of RO is approximately $900-$1,100. The benefits of RO treatment are
that it will take out all dissolve mineral radionuclides, whether
positive or negative valance, and any other unrecognized
contaminants. In addition, there is no concern about the
contaminants accumulating within the treatment device.
Other POU Treatment Equipment Ion Exchange:
Radionuclides can also be removed by cartridge size cation and anion
exchange medias and certain adsorptive medias. Cation exchange (+)
will address all radium contaminants and that portion of the gross
alpha which has a positive valance. Anion exchange (-) addresses
uranium and the remaining factors contributing to gross alpha. These
radionuclides accumulate on the ion exchange cartridge until the
cartridge removal capability is equaled; thereafter all contaminant
could get through. Most modern devices have a water meter to alert
the user when the treatment capability is used up. First cost should
be lower than RO. Operating cost should be reviewed.
Adsorptive Media (possible associate with arsenic
treatment) are being packaged in cartridge forms and may reduce
uranium and some portion of gross alpha. The holding capacity and
their economies of these medias are being determined. See fact sheet
WD-WSEB-2-12. First cost of adsorptive media should be lower than
RO. Operating cost should be reviewed with your sales representative
before purchase.
Distillation is also another point-of-use treatment
process which will address all mineral radionuclide types in one
treatment process. Radon gas is not fully addressed by distillation.
WHOLE HOUSE TREATMENT
Whole house treatment will process 200-300 gpd. Whole house
treatment might be used for very high radionuclide concentrations or
where the user is highly concerned about the contaminant.
Introduction to Ion Exchange Treatment
General. At 200 + gallons per day, ion exchange (water
softening) is likely the most cost effectively treatment process for
whole house treatment of radionuclides. This method typically
removes the target contaminant by exchanging it for other
non-hazardous chemicals, typically salt (sodium or chloride) which
is added to the water. See fact sheet WD-WSEB-2-12 concerning the
specifics of ion exchange.
After purifying a substantial quantity of water, the ion exchange
media needs to be regenerated by immersion in the appropriate
regeneration solution. During regeneration the concentrated
radioactivity is forced out of the ion exchange media while part of
the regeneration solution, either the sodium (Na+ ) or chloride (Cl-
), is taken onto the resin media. The exchange rate is proportional
to the contaminant valance.
Treatment Methods for Radium 226 and Radium 228, and Some
Gross Alpha
Radium dissolved in water has a "plus two (++)" valance. Some
fraction of gross alpha also have a positive valance. Radium
treatment consists of passing the water through a bed of cation
exchange media, commonly known as a water softener. This media
attracts contaminants with a plus two (++) or greater electrical
charge, such as radium 226 and 228 and some gross alpha.
Regeneration of the media uses the sodium portion of salt.
Potassium chloride can be substituted for sodium chloride if it
is desired to reduce sodium addition to the drinking water.
Treatment for Uranium and the remainder of Gross Alpha
Anion exchange is the version of ion exchange used to remove uranium
and the remaining portion of gross alpha from drinking water. Above
pH = 6.0, uranium is typically an anion (ion with a negative
valance). Below pH 6.0, uranium may be either an anion or non-ionic.
Anion exchange will not treat non-ionic uranium. Above pH =
8.2, uranium may precipitate to form a solid which also will not be
treated by anion exchange. Thus, pH is an important treatment
efficiency parameter. Treatment consists of passing the water
through a bed of anion exchange media. This media attracts
contaminants with a two or greater negative valance. Chloride is the
chemical exchanged when contaminants are removed from the water.
Regeneration of the anion exchange media uses the chloride
portion of salt. Given the extremely heavy molecular weight of
uranium and its valance, the longevity of anion exchange resin would
likely be one to two months or more between regeneration cycles.
Uranium is very tightly held by the anion resin and thus a very high
concentration of brine is needed to regenerate the resin.
Environmentally, less frequent regeneration can compensate for the
high salt usage needed when regeneration is performed.
Anion exchange removes alkalinity from the water and thus could
make the water somewhat more corrosive for lead and copper in the
plumbing system. This can be partially mitigated by using soda ash
in the regeneration solution.
Multiple Radionuclide Contaminants
Where one radioactive contaminant is present, a single ion exchange
media can be used. When uranium and radium or other radionuclides
are present together, a "mixed bed" ion exchange media can be used.
These two media are sometimes combined into one tank or can be kept
separate.
Radionuclide Removal In The Presence of Iron and Manganese
Where iron or manganese are present, and where an oxidation filter
such as potassium permanganate greensand or birm is used, some
removal of mineral radioactivity can be expected. The amount of
removal varies. Thus, it is necessary to sample the treated water to
determine how well this treatment mode will work on any particular
water quality. Iron and manganese removal is described in the DES
fact sheets "Iron and Manganese in Drinking Water - A Technical
Summary" WD WSEB 3-7.
DISPOSAL OF THE WASTE
The spent regeneration solution and concentrated radionuclides are
typically discharged to the home's septic system or a separate dry
well. Proper disposal of the concentrated radioactivity is an
important aspect of any treatment process and should be discussed
with the staff of the N.H. Department of Health and Human Services
Bureau of Radiological Health at 271 4588
TESTING FOR MINERAL RADIOACTIVITY
From the laboratory perspective, multiple tests are necessary to
fully categorize the radioactivity level of a drinking water supply.
These tests include: Radon test
Radon test
Analytical gross alpha
Uranium
Radium 226, 228
Analytical beta test
For approximately 75 percent of the bedrock wells in New
Hampshire, the first two tests identified above will be sufficient
to determine a well's general level of radioactivity (when sampled
in accordance with EPA public water supply protocol). Testing for
beta radioactivity can be considered where other mineral
radionuclides are elevated. There is no dependable relationship
between the occurrence of these individual radioactivity forms. A
low radon test does not imply there will be a low uranium or radium
concentrations, nor does low uranium or radium concentrations imply
low radon levels.
The mineral radioactivity level of well water can vary
substantially based on rainfall, seasons and other factors. Thus, at
least two samples (taken a few months if possible) should be taken
before conclusions are reached regarding the average concentration
of any radionuclide.
The DES laboratory can test for the following types of
radioactivity in drinking water. Sample bottles can be obtained by
calling 271 3445/3446 or by writing to: DES Laboratory Services
Unit, PO Box 95, Concord, NH 03302-0095. The fee schedule for these
tests by the DES Laboratory, as of July 1, 2004, is shown below:
| Element |
Cost |
Volume
Required |
| Analytical gross alpha
|
$ 50
|
Pint*
|
Uranium
as measured by activity
as measured by weigh
Radon
|
$ 150
$ 10
$ 20
|
Two Qts*
Small Vial
|
| Radium 226
|
Not offered by
DES. See below.
|
| Radium 228
|
Not offered by
DES. See below.
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Please see document
www.des.state.nh.us/WSEB/pdf/RadLabs.pdf [pdf] for a list of
certified specialty radionuclide laboratories that process radium
and other radiological factors.
FOR MORE INFORMATION
For more information concerning the health effects of
mineral radioactivity call the State's Bureau of Radiological
Health at 271 4588. For health information concerning airborne
radon, telephone 271 4764 or 1 800 852 3345 ext. 4764. If
purchasing water treatment equipment, see the DES fact sheet WD WSEB
2-5 entitled, "Considerations When Purchasing Water Treatment
Equipment."
For additional water information, please call DES at 271 3139. We
would appreciate your suggestions concerning this fact sheet and
your experiences in treating for mineral radionuclides. Drinking
water fact sheets are available through the DES web site at:
www.des.state.nh.us/wseb
then select fact sheets. Please check the DES internet site
annually for changes to this document. 10/04 |
