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Proposed Radon in Drinking Water Rule
United States
Environmental Protection Agency |
Office of Water
(4607) |
EPA 815-F-99-006
October 1999 |
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The U.S. Environmental Protection Agency (EPA) is proposing new regulations to protect
people from exposure to radon. The proposed regulations will provide States flexibility in how
to limit the public's exposure to radon by focusing their efforts on the greatest public health risks
from radon - those in indoor air - while also reducing the highest risks from radon in drinking
water. The framework for this proposal is set out in the Safe Drinking Water Act as amended in
1996, which provides for a multimedia approach to address the public health risks from radon in
drinking water and radon in indoor air from soil. The Safe Drinking Water Act directs the EPA
to propose and finalize a maximum contaminant level (MCL) for radon in drinking water, but
also to make available an alternative approach: a higher alternative maximum contaminant level
(AMCL) accompanied by a multimedia mitigation (MMM) program to address radon risks in
indoor air. This framework reflects the unique characteristics of radon: in most cases, radon
released to indoor air from soil under homes and buildings is the main source of exposure and
radon released from tap water is a much smaller source of radon in indoor air. It is more cost-effective to reduce risk from radon exposure from indoor air, than from drinking water. EPA
strongly encourages States to take full advantage of the flexibility and risk reduction
opportunities in the MMM program.
What are the Public Health Concerns?
Radon is a naturally-occurring radioactive gas that emits ionizing radiation. National and
international scientific organizations have concluded that radon causes lung cancer in humans.
Most of the radon in indoor air comes from the breakdown of uranium in soil beneath homes.
Breathing radon from the indoor air in homes is the primary public health risk from radon,
contributing to about 20,000 lung cancer deaths each year in the United States, according to a
1999 landmark report by the National Academy of Sciences (NAS) on radon in indoor air. The
U.S. Surgeon General has warned that radon in indoor air is the second leading cause of lung
cancer. EPA and the U.S. Surgeon General recommend testing all homes and apartments
located below the third floor for radon in indoor air. If you smoke and your home has high
indoor radon levels, your risk of lung cancer is especially high.
Radon from tap water is a smaller source of radon in indoor air. Only about 1-2 percent of
radon in indoor air comes from drinking water. However breathing radon released to air from
household water uses increases the risk of lung cancer over the course of your lifetime.
Ingestion of drinking water containing radon also presents a risk of internal organ cancers,
primarily stomach cancer. This risk is smaller than the risk of developing lung cancer from
radon released to air from tap water. Based on a second 1999 NAS report on radon in drinking
water, EPA estimates that radon in drinking water causes about 168 cancer deaths per year, 89
percent from lung cancer caused by breathing in radon released from water, and 11 percent
from stomach cancer caused by drinking radon-containing water.
Who Must Comply with the Proposed Rule?
The proposed radon in drinking water rule applies to all community water systems (CWSs) that
use ground water or mixed ground and surface water (e.g., systems serving homes,
apartments, and trailer parks). The proposed rule would not apply to CWSs that use solely
surface water, nor to non-transient non-community public water supplies and transient public
water supplies (e.g., systems serving schools, office buildings, campgrounds, restaurants, and
highway reststops).
What does the Rule Propose to Require?
The rule proposes a maximum contaminant level goal (MCLG), a maximum contaminant level
(MCL), an alternative maximum contaminant level (AMCL), and requirements for multimedia
mitigation (MMM) program plans to address radon in indoor air. The proposal also includes
monitoring, reporting, public notification and consumer confidence report requirements,
proposed best available technologies and analytical methods.
Maximum Contaminant Level Goal (MCLG), Maximum Contaminant Level (MCL), and
Alternative Maximum Contaminant Level (AMCL)
The proposed MCLG for radon in drinking water is zero. This is a non-enforceable goal.
The proposed regulation provides two options for the maximum level of radon that is allowable
in community water supplies. The proposed MCL is 300 picoCuries per liter (pCi/L) and the
proposed AMCL is 4,000 pCi/L. The drinking water standard that would apply for a system
depends on whether or not the State or CWS develops a MMM program. The regulatory
expectation of CWSs serving 10,000 persons or less is that they meet the 4,000 pCi/L AMCL
and be associated with an approved MMM program plan - either developed by the State or by
the CWS.
The enforceable MCL or AMCL would apply under the following circumstances:
Small CWSs: Proposed regulatory expectation for systems that serve 10,000 or fewer people
Does State develop MMM
program? |
Does CWS develop local MMM program? |
CWS Complies with: |
yes |
not needed |
AMCL: 4000 pCi/L* |
>no |
yes** |
AMCL: 4000 pCi/L |
* Small systems may elect to comply with the MCL of 300 pCi/L
** Small systems may elect to comply with the MCL of 300 pCi/L, instead of developing a local MMM program. |
Large CWSs: Proposed compliance options for systems that serve more than 10,000 people
Does State develop MMM
program? |
Does CWS develop local MMM
program? |
CWS Complies with: |
yes |
not needed |
AMCL: 4000 pCi/L* |
no |
yes |
AMCL: 4000 pCi/L |
no |
no |
MCL: 300 pCi/L |
* Large systems may elect to comply with the MCL of 300 pCi/L |
Monitoring Requirements
CWSs must monitor for radon in drinking water according to the requirements described in the
table below and report their results to the State. If the State determines that the radon level in a
CWS is below 300 pCi/L, the system only needs to continue meeting monitoring requirements
and is not covered by the requirements regarding MMM programs.
Type |
Frequency |
Condition |
Initial |
Four consecutive quarters
of monitoring for one year. |
At each entry point to the distribution system which is
representative of each well after treatment and/or storage |
Routine |
One sample per year |
If running average from four consecutive quarterly samples
is less than MCL/AMCL, and at the discretion of State. |
Reduced |
One sample every three
years |
If average from four consecutive quarterly samples is less
than &#frac12; the MCL/AMCL, no samples exceed the
MCL/AMCL, and State determines the system is "reliably and consistently below MCL/AMCL." |
Increased |
Four consecutive quarters of monitoring |
If the MCL/AMCL for radon is exceeded in a single sample, when monitoring annually. Can return to one sample per year if meet routine monitoring conditions, listed above. |
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