Introduction
Radon, a radioactive gas, is present in most well water. It doesn't
matter whether the wells are public or private and whether they
are shallow or deep. Levels of radon can vary dramatically from
one well to another, but almost all of Maine's groundwater contains
some radon. Officials estimate that Maine has more than 30,000
wells and that the wells have an average of 3,000 to 5,000 picocuries
(a measure of radioactivity) of radon per liter.
Although radon gas occurs naturally, it
can still make us sick. When you run water in your home, whether
in
the shower or at the kitchen sink, radon gas can escape into the
air and be inhaled. Taken into the lungs, it can cause lung cancer.
The U.S. Environmental Protection Agency (EPA) estimates that
5,000 to 20,000 cases of lung cancer occur each year as a result
of radon exposure. Theoretically, a person exposed to water containing
300 picocuries per liter* for an entire lifetime would run a 2
in 10,000 risk of getting lung cancer.
Radon in drinking water may cause cancer in the digestive tract.
However, the stomach, intestines and other digestive organs are
thought to be less vulnerable than the lungs. They regularly shed
cells that might be affected, and food absorbs a portion of the
radiation.
Radon also enters our homes from other sources. Radon from the
soil, for example, may be a significant share of our total exposure.
Preventing soil radon from entering the home is the subject of
another publication, Radon in Water and Air. To remove
waterbome radon, water treatment may be necessary for homes on
private wells and public water supplies which depend on groundwater.
There are two methods
of removing radon from well water:
aeration and
granulated activated carbon (GAC).
Although aeration is the more expensive of the two, it is preferred
for water containing more than 25,000 picocuries per liter. Both
aeration and GAC systems can remove more than 90% of the radon
in water.
The U.S. Environmental Protection Agency (EPA) suggests that public
water suppliers should remove radon from their water if radon
levels exceeds 300 picocuries per liter. Federal law prohibits
any amount of a Cancer causing substance from food and water.
However, EPA has no authority over private wells.
1. What is a GAC system
and how does it work?
A GAC system consists of a metal or fiberglass tank which contains
a bed of granular activated carbon
(GAC). The carbon bed consists of many tiny carbo particles which
hold onto impurities in the water.
This material can hold radon almost like a sponge holds water.
The type of carbon most effective for radon removal is not generally
available at hardware stores.
In your home's water system, the GAC unit is usually installed
in the main supply line after the pressure tank. Water moves through
the GAC unit every time showers are run, dishes are washed or
toilets are flushed.
While the GAC bed holds the radon, the radon atoms decay into
other elements, often referred to as daughters. The same decay
process would occur if the water were simply stored in a large
tank.
However, to achieve the same amount of radon removal for typical
home use, you would need a 4,000 gallon tank and about 30 days
of storage time.
2. What is an aeration
system and how does it work?
Located on the main water supply line in your house, an aeration
system consists of a metal or fiberglass tank in which water is
agitated. Two processes are used: air is blown through the water
or the water is sprayed to produce fine droplets. In either case,
radon bubbles out like fizz from a can of soda. It then escapes
or is blown through a vent which should be extended above the
roof. Locating the vent below the roof can allow radon rich air
to reenter the house. Under such circumstances, home occupants
may be exposed to high levels of radon.
3. Does radon accumulate
in the GAC unit?
Yes, but because it is also breaking down, radon does not build
up to dangerous levels. The amount of radon in the unit stabilizes
after about ten days. At that point, the amount of radon entering
the unit is equal to the
amount that is breaking down. The final element in this process
is lead.
4. Does radon leak
out of the GAC unit into the home?
No. It is held by the carbon. Even if the unit is detached from
the water lines, the radon remains in the carbon bed.
5. Is the GAC unit a
source of radiation to the home?
Yes. Radon decay products are a source of gamma ray radiation
which is similar to x-rays. The maximum radiation level occurs
near the top of the carbon bed where the water contacts the carbon.
Some radiation does pass through the tank walls into the immediate
vicinity. The tank can be shielded by any dense
material such as metal, brick, concrete, or a water bath.
6. Where should the
GAC unit be located in the home?
A GAC unit should not be located where people are likely to go.
7. Does radon accumulate
in the aeration system?
No. All the radon is blown out of the unit where it mixes with
the outside air and quickly reaches normal background levels.
8. Does radon leak
out of the aeration system into the house?
All properly installed aeration units have well sealed pipes and
vents. If the vent ends below the roof line, radon can enter the
house through doors and windows. It is essential that the vent
extend past the roof line.
9. Is the aeration
system a source of radiation to the house?
No. Since radon is not stored in the unit, there is very little
opportunity for radiation to be given off by the unit itself.
10. Where should
the aeration system be located?
Normally, a unit can be placed anywhere there is enough room.
It is often located in an out-of-the-way area of the basement
close (within two feet) to it on a regular basis. Appropriate
locations are basement comers or even an upstairs closet where
long periods of contact are unlikely.
The level of radiation from a GAC unit decreases rapidly with
distance. Field and laboratory measurements have shown that for
well water containing less than150,000 picocuries per liter (an
unusually high level), a distance of two to four feet is all that
is necessary to reduce radiation to near background levels.
Radiation levels on a floor immediately above a GAC unit are at
background levels in almost every case studied. Much radiation
is absorbed by the water over the top of the carbon bed, and additional
space between the unit and the ceiling further reduces radiation
levels.
Radiation from the GAC unit can be a concern if the well water
contains more than 25,000 picocuries per liter. It is recommended
that water over that level be treated with an aeration system.
11. What happens
to the radon?
Radon in the carbon bed decays into other radioactive elements.
This process occurs at a steady rate and is measured by the length
of time it takes for half of the material to decay. The half life
for radon is 3.8 days. near the pressure tank or water heater.
Some systems can take up to 18 square feet of floor space.
Noise from the fan may also be a concern.
After it mixes with outside air, radon becomes less concentrated.
Waterbome radon decays into other radioactive elements, just as
does radon from the soil. It takes about 3.8 days for half of
a given amount of radon to decay.
Most of Maine's wells contain between 1,000 and 1 0,000 picocuries
per liter of radon.
About 4% would meet the EPA's proposed standard of 300 picocuries
per liter. *
Source: Maine Division of Health Engineering
12. Does a GAC unit
continue to give off radiaion after it has been taken out of service?
Yes. Until all the radon has decayed int the final stage of the
radioactive process, the unit continues to give off radiation.
However, radon is the only element which is a gas. The final stage
in the process is lead, a solid. If you need to dispose of a GAC
unit, consult the environmental agency in your state. In Maine,
contact the Maine Department of Environmental Protection.
13. What size is
the most effective GAC unit?
GAC units are available in sizes ranging from half a cubic foot
to over 50 cubic feet. The higher the level, the higher the size
should be.
14. Does an aeration
unit give off radiation after it has been taken out of service?
No. Radon does not collect in the system.
15. What size is
the most effective aeration systemfor home use?
The size of the unit determines how much water it can treat in
a specified for residential application is one to three cubic
feet. If your water has a radon level below 25,000 picocuries
per liter, a well designed GAC unit will be adequate.
16. Are all GAC units
equally effective?
The effectiveness of GAC units ranges from 82.4% removal to 99.
1 %. The performance of any unit will vary depending on the conditions
under which it is operating. These conditions include:
Be sure to test the water (for example,
at the kitchen tap) to determine how well it is working.
17. Should I treat
water at the tap?
Treatment at the tap or shower is NOT recommended. Untreated points
in your plumbing system still pose a threat. These could include
taps for washing machines, bathtubs and bathroom sinks. The entire
household supply should be treated.
18. How long do GAC units
remain effective?
The life of GAC units is not precisely known. Research shows that
they can last many years before their efficiency is reduced. Units
have been in the field for more than ten years and show no loss
of function or efficiency. Aeration units for residential applications
are all about the same size.
19. Are all aeration
units equally effective?
The effectiveness of the system varies according to several factors:
Consult a radon mitigation expert to determine
the best system for your needs. Be sure to test the water coming
out of the unit (for example, at the kitchen tap) to determine
how effective it is.
20. Should I treat
water at the tap?
No. There is no known method to aerate water safely as it leaves
the tap or shower. Aeration at the tap would expose the home occupants
to radon. The entire household supply should be treated at the
point of entry.
21. How long do aeration
units remain effecve?
Removal efficiency does not decrease over time. However, mechanical
parts can wear out, and sediment and dissolved solids in the water
can interfere with operation.
22. Do GAC units
require much maintenance?
The major problem for GAC units is sediment and dissolved minerals
that accumulate in the carbon bed. These materials can reduce
the flow of water and cause a loss of water pressure. A sediment
filter can extend the life of a GAC unit.
If sediments and minerals interfere with the unit's operation,
it may need to be backwashed or the carbon
bed may need to be replaced. Ideally, a sediment filter ahead
of the GAC will make backwashing unnecessary. Backwashing decreases
the removal efficiency of the unit for a period of time. In a
backwashing operation, the direction of water flow is reversed.
Sediments and other particles that may have accumulated may be
flushed out of the unit. When it is first installed, a GAC unit
is typically backwashed to remove very fine carbon particles.
A radon removal unit should not be used as a filter. The unit
should last as long as a typical furnace.
23. Do aeration units
require much maintenance?
Most types of systems can become blocked by sediment or minerals
in the water. This problem can be overcome by installing a sediment
filter or a water softener ahead of the unit. Change the sediment
filter on a predetermined schedule or if you notice a significant
decrease in your water pressure (typical pressure is
40 to 60 pounds per square inch). Do not change the filter "just
because it looks dirty."
Some units may require more maintenance than others. Consult the
owner's manual for maintenance instructions. Backwashing is not
required for aeration units.
For radon removal purposes, automatic backwashing features should
be avoided. They add to the unit's cost, reduce the efficiency
of the GAC unit and temporarily increase radon levels in your
water.
A radon removal unit should not be used as a filter, and it should
not be back- washed routinely. A small sediment filter should
be installed ahead of the unit. Properly designed units which
have been installed in that fashion have operated for more than
two years without any backwashing.
Some units are designed with an automatic backwashing feature.
For example, many different GAC units are available for water
softening purposes and appropriately have automatic backwashing.
If carbon particles need to be changed, you should contact a consultant
or your installer. Disposal of used carbon from a residential
GAC is unregulated, but since the material is radioactive for
a period of time, it should be well sealed and stored in an out
of the way location until it is disposed.
24. Does the GAC
remove other radioactive particles?
Yes. The GAC can remove uranium and to a lesser extent, lead 210
and radium.
25. How much does
a GAC unit cost to buy and install?
The cost of a GAC unit typically ranges from $1,000 to $1,500
(1991 prices) for 1.5 cubic foot units. Installation costs vary.
Maintenance and operation costs are minimal Carbon particles may
need to be changed infrequently, depending o the other impurities
in the water.
Risks compared
For several reasons, radon is considered less of a health threat
in drinking water than it is in air. The digestive tract protects
itself by regularly shedding the cells which line the stomach
and other organs. In addition, much of the radon derived radiation
is absorbed by food. Finally, we are exposed to far
more air than water. An average adult drinks less than two liters
of water per day and inhales about 20,000 liters of air.
26. Does the aeration
unit remove other radioctive particles?
No. Treated water may still contain other radioactive particles
such as uranium and radium.
27. How much does
an aeration unit cost to buy and install?
Prices vary significantly. They range from $2,000 to $5,000 installed
(I 991 prices). The higher priced units tend to be more effective.
Any filters needed ahead of the system can add as much as $1,500
to this cost.
28. How do I test my
water for radon?
Homes with private wells should be tested for radon in water.
Test kits are available from several private laboratories as well
as the Maine Health and Environmental Testing Laboratory (formerly
the Maine Public Health Laboratory), 287-2727. In addition, the
Maine Department of Human Services recommends that
all homes be tested for airborne radon.
29. Where can I purchase
aeration and GAC systems?
They are available from water treatment and radon mitigation companies.
Consult your Yellow Pages for listings in your area.
For more information about removing radon from water or for a
list of air and water radon testing laboratories, contact:
Maine Department of Human Services
Division of Health Engineering
Statehouse Station #10
Augusta, ME 04333-0010
(800)232-0842
Copies of this publication are available
from:
Maine Department of Human Services, Division of Health Engineering
In Maine, (800)232-0842
County offices of the University of Maine
Cooperative Extension
Contact the Extension office in your county.
University of Maine Water Resources Program
11 Coburn Hall
University of Maine
Orono, ME 04469
(207) 581-1490
Written by Nicolas Houtman, University of Maine Water Resources Program, with assistance from Dr. Charles T. Hess, University of Maine Department of Physics and Eugene Moreau and Robert Stilwell, Division of Health Engineering, Maine Department of Human Services.
The activities on which this publication is based were financed in part by a grant from the United States Department of the Interior, U. S. Geological Survey, through the Maine Water Resources Program. The contents of this publication do not necessarily reflect the views and policies of the Department of the Interior, nor does mention of trade names or commercial products constitute their endorsement by the United States Government.
Published and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914, by the University of Maine Cooperative Extension, Judith 1. Bailey, Assistant Vice-President for the University of Maine Cooperative Extension, the University of Maine and the United States Department of Agriculture cooperating.
Publication of this document was paid in part by a grant from the U.S. Environmental Protection Agency to the Maine Department of Human Services.