These courses are provided at no cost as a resource for radon professionals. 

Bob Promo a 

Resources for Radon Professionals

These resources provided to assist you in your business are provided to you at no charge. To access the resources, click on the course title "Resources for Radon Professionals" to the left. If you are not a registered student, when asked to log in, simply click on "log in as a guest"

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Free Category II Courses

These Category II courses are provided to you at no charge. They may apply towards Category II continuing education credits for NRPP.  Please note, in order to get credit you will need to be a registered CERTI student and log in to your account so that a certificate can be issued in your name.

EPA Publications


The US EPA is a great resource for information and publications. The publications indicated below are available for download by clicking on the "PDF Version" link next to the description.


For more publications and other EPA resources, go to



Home Buyer's and Seller's Guide to Radon

This booklet is intended for anyone who is buying or selling a home, real estate and relocation professionals, home inspectors and others. [EPA 402-K-06-093, November 2006]

PDF Version (PDF, 43 pp, 1MB)






A Citizen's Guide to Radon

The guide to protecting yourself and your family from radon.
This recently revised guidance offers strategies for testing your home for radon and discussions of what steps to take after you have tested, discussions of the risk of radon and radon myths. EPA 402-K-07-009, Revised May 2007]

PDF Version (PDF, 16 pp, 859KB)




Consumer's Guide to Radon Reduction

How to Reduce Radon Levels in Your Home...
You have tested your home for radon, but now what? This recently revised booklet is for people who have tested their home for radon and confirmed that they have elevated radon levels -- 4 picoCuries per liter (pCi/L) or higher. This booklet can help you: Select a qualified contractor to reduce the radon levels in your home, Determine an appropriate radon reduction method, and Maintain your radon reduction system. [EPA 402-K-06-094, December 2006]

PDF Version (PDF, 20 pp, 602KB)


A Radon Guide for Tenants

This guide, created by the Environmental Law Institute (ELI) with EPA's review, is for people who rent their apartments or houses. The guide explains what radon is, and how to find out if there is a radon problem in your home. The guide also talks about what you can do if there are high radon levels in your home. [EPA 402-K-98-004, 1996]

PDF Version (PDF, 10 pp, 50 KB)




Building Radon Out: A Step-by-Step Guide on How to Build Radon-Resistant Homes

This 81-page, fully illustrated guide contains all the info you need in one place to educate home builders about radon-resistant new construction (RRNC), including: Basic questions and detailed answers about radon and RRNC; Specific planning steps before installing a system; Detailed installation instructions with helpful illustrations; Tips and tricks when installing a system, Marketing know-how when dealing with homebuyers; and, Architectural drawings. [EPA 402-K-01-002, April 2001]

PDF Version (PDF, 84 pp, 5.52MB)



Radon Mitigation

All Homes Can be Fixed

Reliable techniques exist for reducing radon levels in homes. Experience with radon mitigation systems has developed to the point that virtually any home can be fixed, either by a trained radon contractor, or in some cases, by homeowners who accomplish the repairs themselves.

Radon Mitigation Key Elements

    • The system should be installed in accordance with the U.S. EPA's Radon Mitigation Standards if no local building codes exist. The EPA model standards provide helpful, specific guidance. For example:
    • The discharge shall be at least 10 feet above grade, 10 feet away from an opening which is two feet below the discharge, and above or at the eave of the roof.
    • If the exhaust pipe is routed outside the home, the discharge must still meet the above criteria
    • System fans should not be located inside the home or in a crawlspace. They can be in an attic, outdoors, or in a garage, provided there is no living space above the garage.
    • There should be an indicator located in a prominent place that will easily let the occupant know if the system is functioning properly.
    • Power to the fan should be supplied in accordance with local electric codes; including permits where required.
    • All portions of the system are to be labeled and a simple instruction manual, with warranties, provided to the homeowner.
    • All homes with mitigation systems should be retested no sooner than 24 hours nor later than 30 days after installation, to verify reduction. The home should also be retested every two years.




How do I treat radon?

Research by public and private agencies, combined with years of extensive hands-on mitigation experience and long-term follow-up studies on the durability of mitigation systems form a strong knowledge base of proven mitigation techniques. The techniques are straightforward and, for a typical single family residence, can be done in one day by a qualified contractor. Radon reduction requires more than just sealing cracks in a foundation. In fact, caulking and sealing of foundation openings, on its own, has proven NOT to be a reliable or durable technique. However, sealing is done in conjunction with other mitigation steps.

Active Soil Depressurization

ASDActive soil depressurization (ASD) has proven to be a very cost-effective and reliable technique for radon reduction. ASD systems collect the radon from beneath the building before it can enter. The systems can be simple or complex depending upon the design of the building. Operating costs of the system fans are modest, due to their low power consumption (typically less than 90 watts per fan).

The system draws the radon-laden soil gas from beneath the foundation and exhausts it outside of the building, far enough away from windows and other openings that it will not reenter. The system typically consists of a plastic pipe connected to the soil either through a hole in a slab floor, through a sump lid connection, or beneath a plastic sheet in a crawl space. Attached to the pipe is a quiet, continuously operating fan that discharges the radon outdoors.


The system's design depends on the construction of the home, rather than the indoor radon concentrations. For example, a home with more than one foundation can present challenges to collecting the soil gas from under all portions of the building. However, trained mitigation contractors can sometimes connect multiple systems together so that only one fan system is required.



Crawl Spaces

This kind of mitigation system also helps reduce moisture in the crawl space.

crawlA length of perforated pipe is laid on top of the soil running the length of the crawl space. The pipe will collect the radon from beneath the plastic sheeting when connected to a fan.

Perforated pipe used to collect soil gas laid on floor of crawl space

A high density, cross laminated polyethylene sheeting is then laid on the soil. This type of sheeting is very durable and resists tearing.

High density polyethylene lay on dirt with edges and seams sealed

The seams should be overlapped and sealed. The edges should also be sealed to the walls of the crawl space, to ensure system efficiency and to help keep the plastic stationary. The use of a durable plastic prolongs the life of the system and may allow storage in the crawl space.

After the plastic has been installed, a solid PVC pipe is connected to the perforated pipe beneath the plastic. The PVC pipe is then routed to the radon fan.

Slab on Grade Homes

sog pipeAt least one four to six inch hole is cored (drilled) through the slab. A small pit is hollowed out beneath the hole, and a PVC pipe is inserted. This pipe is routed to a fan that creates a vacuum beneath the slab. The number of suction points depends on the permeability of the soil beneath the slab and the number of footings within the building.

A single radon vent pipe is often all that is required in a residence. A general "rule of thumb" suggests the use of one vent pipe for roughly ever 2,000 square feet of floor space at ground level.

For a home that has a slab-on-grade or a basement, suction through a hole in the slab is applied. Radon-laden soil gas is drawn laterally through the rock and soil beneath the slab and then exhausted outside. The more permeable the soil, the better the system works.

If the soil is tightly compacted or if there are obstructions such as intermediate foundations under the slab, more than one suction point may be needed. If multiple suction points are needed, they can often be connected to a single depressurization fan.






Drainage Systems

drainageHomes that have sumps or French drains for control of rainwater can be effectively mitigated utilizing the sump to collect radon from the underlying soil. Two types of drainage systems can be readily adapted to collect radon from the soil below a house and exhaust it safely outside.

When the drainage system includes a sump, a lid with vent piping is placed on the sump pit. A radon fan connected to the vent pipe is used to draw radon from the soil and through the sump, to an outside exhaust point above the home's roof. When placing a lid on the sump pit, it is important to remember to allow for future removal of the lid, to allow servicing of the sump pump.


The second technique for using a drainage system works well when there is no sump but a foundation drain is in place that runs to daylight. A saddle can be used to tie into the drain and connect it to a pipe and fan. The pipe continues to a safe discharge point. Special check valves are used to seal the daylight end of the foundation drain. These check valves allow the fan to create a vacuum at the same time they allow water to drain. When using a drainage system to collect radon it is important to maintain the drainage characteristics of the drainage system.





Under Slab Ductwork

In some homes, return-air ductwork for the forced-air conditioning system is located beneath a slab floor. Although this can increase usable interior space and reduce the noise of recirculating air inside the home, the sub-floor ductwork, if unsealed, can add to radon problems. When the air conditioner fan is on, a fairly large vacuum created in the buried ductwork can draw radon-laden soil gas through the ducts and into the living space.

Even with this type of construction, there are effective ways to reduce radon. For example, if a house has a sump, a four-inch pipe connected to a sealed lid on the sump can route incoming soil gases to the radon fan. If the house has a perimeter foundation drain (French Drain), the vent pipe can be connected to the drain, taking care not to interfere with water drainage or sump pump function.

However, many homes have a slab floor; most of them without sumps or French Drain. For those houses, radon drawn inside through sub-floor ducts may require extra attention.

Radon laden soil can be drawn into a home through very small openings in the ductwork, especially when a forced air unit sits over a large opening in the slab.

Not all homes that have air return ducts under the slab floor will have radon concerns. The only way to know is to test. If a long-term test confirms elevated radon levels in a home that also has under-slab air returns, the following options should be considered.

  • Removal and replacement of ductwork

This is the last resort and very expensive. Although some contractors may recommend this solution first, it may be prudent to explore a few other options before replacing ductwork.









Pipe Material:     PVC or ABX
 Thickness:     Schedule 40
 Pipe Rating:     DWV (Cellular Core
 Size:     Four-inch



  • Follow manufacturer's recommendations when gluing pipe and fittings
  • Slope pipe back to suction point to avoid build up of condensation (1/8" per foot)
  • Support pipe every eight feet, vertically and every six inches horizontally
  • Place "Radon Deduction System" label on pipe on each level where visible
  • Two 45 degree fittings can be used to offset pipe
  • When penetrating fire walls with vent pipe, maintain fire wall rating with fire collars or appropriate fire caulk
  • Allow 30" of vertical space for installation of the fan in an attic
  • Downspout (3" x 4") is used outside for aesthetic reasons



  • Installed in attic, garage, or outside
  • Must not be installed inside of house
  • Quiet
  • 60 watts operating
  • 11 year expected life
  • Discharge should be high to avoid radon entering building
  • Minimum of 10 feet above grade
  • 10 feet from any openings 2 feet below discharge
  • Above eave
  • 1/4 inch bird screen

The suction piping is connected to a radon fan that must be located in an unoccupied attic, a garage, The suction piping is connected to a radon fan that must be located in an unoccupied attic, garage, or outside the home. These fans are quiet and use about 60 watts of electricity. Because radon is constantly generated in the soil beneath the home, the fans should operate continuously.

The fan discharge is routed through the roof or along an outside wall to a high point on the house. It must be pointed upward to force the collected radon up and away from the home. It is very important that the discharge not be near the ground. Otherwise, the radon might re-enter the structure and increase the level of radon in the home. Radon concentrations in excess of 2000 pCi/L have been measured in some discharge pipes.

Rain caps interfere with system efficiency and are not needed. However, screens should be placed on the discharge to keep birds and squirrels from entering the pipe.

System Indicators




As part of the installation of a depressurization system, an indicator must be installed which will tell the homeowner if something has changed the performance of the system. This is in addition to retesting the home for radon after the installation and repeating this test at least every two years.


Air Filtration Systems

Since it is the decay products of radon that actually present the risk from elevated radon levels, some homeowners have installed high efficiency air filters (HEPA) in their homes to not only reduce the the amount of decay products, but also to reduce other airborne particulates that can complicate allergies. The reduction of radon by air filtration systems is a relatively new approach that can be accomplished by three different methods, depending upon the type of heating or air conditioning system you presently have.


Heating or A/C System Approach
  •  Central forced air
Connect air filtration system to return duct in a manner that takes a portion of the air stream, filters it and re-injects it into the return duct.
  • No central forced air
  • Space in attic or crawl space can accomodate new ductwork
Install a stand-alone central HEPA filtration system that circulates air from the inteior of the home, filters it, and routes it back into the home.
  • No central forced air system
  • No space to route new ductwork
Install console unti HEPA filter systems for each frequently occupied room

Although it is typically more common that an active soil depressurization systems is installed, if you have allergies and your radon levels are relatively low, you may want to consider this approach. If you do, it is important to note the following:

  • HEPA systems that connect to your furnace and/or air conditioner, or units that function as whole house filtration systems, should be installed by a qualified mechanical contractor.
  • After installation, your home will need to be tested for radon decay products with a working level meter, to determine the effectiveness of the system.
  • Radon will not be reduced, but the more harmful radon decay products will be reduced.
  • The air filtration approach is appropriate for relatively low radon levels between 4 and 8 pCi/L.


How much does a mitigation system cost?

The cost of a radon mitigation system installed by a certified contractor can be $2,000 or more, although EPA often cites a national average of $1,200 to $1,500. The actual cost may depend on the contractor, the construction and foundation type of the home, location of the home site, and aesthetic factors. For instance, a vent-pipe system routed outside of the home may cost less to install than one routed through an interior closet and attic space. EPA suggests that you obtain bids from certified contractors and compare costs.

The cost of a mitigation system may vary according to the home's design, size, foundation, construction materials and the local climate.


Part of the mitigation cost can depend upon what is required to conceal the system and maintain the aesthetic value of the home. For example, a retrofit system routed outside the house can reduce radon quite well, but it may not be as visually pleasing as one routed through an interior closet.

Average US installation cost:      $1,200
Average operating cost:    $3/mo
Expected life span of fan:    11 years
Fan replacement cost:    $145 - $300
Periodic maintenance:    None








How do I find a qualified radon mitigation contractor?

To find qualified radon contractors, EPA recommends that you contact one or both of the two privately-run national certification programs listed below.

National Radon Proficiency Program (NRPP)
PO Box 2109; Fletcher, NC 28732
800-269-4174; 828-890-4117


National Radon Safety Board (NRSB)
PO Box 703; Athens, TX 75751
866-329-3474; 903-675-3748


In addition to asking about a radon contractor's training and credentials, homeowners should always:

  • Ask for references;
  • Require proof of certification, including agreement to follow protocols and codes of ethics;
  • Ask for proof of insurance including workers' compensation; and
  • Ask for a concise contract

Selecting a Contractor Checklist

Radon Resistant New Construction - RRNC

Some homebuilders add construction elements to new homes that help make the homes radon-resistant. Some go so far as to install a full system with fan, even though building codes in most areas do not specifically require radon-resistant construction features. In some states, some homebuilders include radon-resistant construction elements as a value-added feature, or when requested by homebuyers.

There are advantages to installing a system when building a house:

  • The piping can be easily concealed in a chase;
  • The vent pipe can exit the roof and appear as a normal roof penetration;
  • The sub-grade can be prepared to make it easy to collect radon; and
  • In many cases these systems work passively without need for fans.

RRNCThis figure illustrates the basic concept of a typical "soil depressurization" radon control system installed during the construction of a home. These systems draw radon and other soil gases from beneath the floor and upward through a pipe that exits above the roof. Soil air travels readily through the layer of gravel or sand that usually forms the base for a concrete slab.

Other options include a soil-gas collection system consisting of a loop of perforated plastic pipe buried inside the foundation footing, or a loop of gas-permeable matting laid on the sub-grade material directly under the slab and connected to a riser pipe.

The pipe riser should be routed through the interior of the building if possible, to allow the riser to be warmed, thus creating a natural stack effect. When this riser is combined with the gas-collecting system component installed below the slab, it can draw significant amounts of radon from beneath the home. The performance of this natural convection system is enhanced by sealing openings in the slab and walls so the air drawn up through the system comes from beneath the building rather than from within the building.

The efficiency of these passive systems is further enhanced when the riser pipe is routed through the warmest spaces in the home, such as the wall-cavity plumbing chase where the furnace and/or hot water flues are located. The radon vent should be dedicated only the radon reduction system and must not be connected to any combustion flues. Allowance is always made for adding a suction fan to the vent pipe, usually in the attic area, if needed later to increase system capabilities.

This passive-system approach is usually not chosen for retrofit mitigation of homes, because existing houses lack the specialized gas-collecting system component, such as perforated pipe, that is installed ony during new construction. Test the home to be sure it reduces the radon to levels you desire.

Ask your builder about radon resistant features; and if a system is installed.


Testing for Radon

Radon Measurement Key Points

  • There is no "totally safe" level of radon exposure
  • 4 picoCuries per liter is the "action level" recommended by the EPA
  • All radon problems can be fixed
  • Radon levels in homes can typically be reduced to between 2-4 picoCuries per liter
  • EPA's Testing Checklist


How to Test for Radon

There are reliable ways to measure indoor radon for short-term test periods that last only a few days, and for long-term test periods that may range from a few months to more than a year. Using recommended measurement devices, you can determine the radon potential of the home under "worst case conditions" (short-term test), or measure actual radon exposure under normal living conditions, (long-term test).

Homebuyers and sellers often prefer to have a radon test performed by a trained professional tester. In that case, EPA strongly recommends the use of a qualified radon measurement professional who has been trained in the proper placement of radon measurement devices and the interpretation of their results.

Short Term Tests – Potential Radon Exposure

Often, at the time of sale, it is desirable to know a building's potential for radon exposure, independent of how the building is currently used. Short-term tests are typically conducted over a two or three day period. Results of short-term tests represent the radon potential of the home, rather than the actual exposure encountered under normal living conditions, unless residents keep the home's windows and doors closed year-round. That's because EPA guidelines for short-term radon tests require "Closed-House Conditions," to promote maximum radon concentration during the brief test period.

The placement of the device within the home must follow the manufacturer's instructions and is dependent on whether or not the test is being conducted for a real estate transaction.

Short-term tests are usually 2 to 7 days long and are done under "closed-house" conditions that begin at least 12 hours before the test and remain in effect for the duration of the test.

Closed House Conditions

house a

Placing the test device in a closed room or leaving doors and windows open during the test is improper and can invalidate a test.

Short-term, "closed house" radon tests should not be conducted during rainy weather, especially when the rain is accompanied by persistent winds. Changes in barometric pressure and other forces can cause indoor radon levels to rise during a rain storm and skew the test results higher than found under otherwise normal conditions.

The following protocols should be followed to comply with the requirement for "closed-house" conditions:


  • Exterior windows and doors are kept shut, except for normal entrance and exit.
  • Fans and blowers which move air from the outside of the house to the inside, or exhaust inside air to the outside, are turned off, including swamp coolers
  • Whole house fans should be off
  • Air conditioners should be put on "recycle" or "max.-cool," but not on the "fresh air" setting
  • Combustion or makeup air to gas fired appliances are NOT to be closed
  • The house can be occupied during testing, provided the "closed house" conditions described above are maintained.
  • If testing during warm weather, keep the air-conditioning on and set the fan to recycle indoor air. Don't use the "fresh air" setting. Evaporative coolers, sometimes called "swamp coolers", should be turned off during the test, to avoid bringing outdoor air into the house

Radon Test Devices

test devices



There are several devices on the market. EPA recommends that you begin with a short-term test device placed in the home for a minimum of two days. The devices in most home test kits are actually small containers of activated charcoal. Look for kits approved by one of the national certification programs (NRPP or NRSB).

You can purchase a kit from hardware stores or other retail outlets, as well as through non-profit organizations such as the National Safety Council (800-767-7236). Most of the kits range in price from $10 to $20. The cost usually includes the test device, the price of postage to mail the detector back to the laboratory, and the written report you receive by return mail.

There are two types of short-term test devices:

  • Integrating Devices, which measure radon and provide an average reading over the time of the test; and
  • Continuous Radon Monitors, which measure radon and provide hourly readings as well as an overall average.

It is not appropriate to use "Grab Samples," which test for less than 48 hours, as this is more of a diagnostic device and will not provide a representative radon potential measurement for the home.

If a short-term radon test is conducted correctly for a minimum of two days, under closed-house conditions, one can reasonably say:

  • If the result is less than 4.0 pCi/L, the annual average of the home under normal lived-in conditions is also likely to be less than 4.0 pCi/L.
  • If the level is at or above 4.0 pCi/L, the house has the potential to average more than 4.0 pCi/L, and you should consider follow-up testing or taking action to reduce (mitigate) the radon in the home.

Test Device Location

The location of a radon test depends upon whether the test is being done for a real estate transaction or not. Since the purpose of the first, short-term test is to be able to identify homes that are clearly below 4.0 pCi/L, it is necessary to place the test device in a part of the home that would be expected to have the highest radon level.

test locationThe device should be placed in a room that is frequently occupied, but where high humidity in the air would not be expected. Examples of good locations would be bedrooms, dining rooms, and family rooms. Never place the device in a closet, crawl-space, storage area, kitchen, garage or bathroom.

In order to have confidence in the radon reading, the device should be placed in the lowest occupied space, for non-real estate transactions. A finished basement is normally chosen in those parts of the country that typically have basements.

In the case of a real estate transaction, the device should be placed in the lowest portion of the house that could be finished and occupied by future occupants.

If the radon measured is below 4.0 pCi/L, there is good reason to believe that the rest of the home is also below 4.0 pCi/L. Furthermore, if the closed-house test protocols are followed, there is good reason to believe that a low short-term test result (below 4.0 pCi/L) means that the average radon throughout the year will probably also be below 4.0 pCi/L, during normal use of the house.

Remember, short-term tests determine the radon potential of a home, independent of how future homeowners may operate or occupy the house.



Test Device Placement

test tableA proper location must be selected to obtain an accurate measurement of radon in air that represents the breathing space of the home. The test device should be at least 20 inches from the floor, 4 inches from another object, 12 inches from an exterior wall, and 3 feet from an outside window. The device can be placed near an interior wall, perhaps on a book shelf, but should be at least four inches from the wall or the back of the shelf, to allow good air circulation.

Devices that are designed to be hung by a string should be approximately 12 inches from the ceiling.

Test devices should also be located away from drafts and should not be placed in rooms with excess humidity.


  • 3 feet from windows or exterior doors
  • At least 20 inches above floor
  • 4 inches from other objects
  • Where it won't be disturbed
  • Away from drafts
  • Out of direct sunlight
  • Not on hot or warm surfaces

Long-Term Tests – Actual Radon Exposure

For the occupants of a home, actual radon exposure depends on how they use the home, where in the home the occupants spend their time, and how much freshair is brought into the living area. Since these factors may vary over time, the only reliable way of measuring the actual radon exposure is to conduct a long-term test for at least three months, under normal living conditions.

In the past, prospective homeowners have often been reluctant to purchase a home before performing a long-term test, for fear of not being able to correct a radon problem afterward. However, improved technology and the proven durability of radon mitigation systems have served to reduce much of that concern.

This does not mean that a short-term test is less valuable as part of a home inspection process; but rather, if the results of that test show a potential radon concern, a long-term test can more accurately show actual average radon levels. By conducting a long-term test after moving into a home, the homeowner can control test conditions and, if needed, make decisions on how a mitigation system will be installed.

The placement of the test device within the home must be in accordance with the manufacturer's instructions.

Test Results

test flowchart



If you perform the short-term test and the results are higher than 4.0 pCi/L, the EPA recommends you take further action. The next step should be to retest the home on a long term basis, ideally for a year, then decide if mitigation is necessary.

However, if the initial short-term test finds radon levels are significantly elevated, such as 10 pCi/L or more, you may want to repeat the short term test using a different test device to confirm the radon is still elevated. You can then average the two results and base your mitigation on the average.

The health risk from radon is cumulative, increasing over time if the radon level is elevated and not corrected. The health risks from radon occur over a long period of time and radon concentrations vary from season to season. An average radon level, measured over all four seasons, is a better indicator of actual health risk over time.

On the other hand, if your initial readings are significantly elevated, you should take action to quickly confirm these readings and then proceed to mitigate the home. Again, you may want to repeat the short-term test, using a different test device to confirm the radon is still elevated, then average the two results and base your mitigation on the average.

Testing for Radon Decay Products

Radon decay products can also be measured using a special monitor that reports in Working Levels (WL). This can be done as an initial measurement or, more typically, after initial measurements have identified a potential concern in commercial buildings or homes with relatively low initial radon readings. The EPA guidance for radon decay products (comparable to 4.0 pCi/L of radon) recommends people should avoid long-term exposures in excess of 0.02 WL of radon decay products.

Testing Water for Radon

Radon in the ground can dissolve into water that finds its way to a well. When well water that contains radon is brought directly into a building, the dissolved gas is released indoors as the water leaves the faucet, showerhead or other outlet.

The amount of radon brought into the building will depend upon the amount of water used and the amountof radon in the water. Given typical water usage rates and radon concentrations found in wells, this entry mechanism only accounts for about 1-2% of the radon that enters homes in the U.S.

Most indoor radon comes from the soil. Thus, most remediation efforts concentrate on reducing the entry of radon from soil rather than water. As a rule of thumb, it takes 10,000 pCi/L in the water to add 1pCi/L to the air in a home, after the radon dilutes and dissipates within the large volume of air indoors. This is above and beyond that which comes from the soil.

The US EPA has recommended maximum contaminant levels (MCL) ranging from a low of 300 pCi/L to as high as 4,000 pCi/L of water for community water supplies. The regulation, as proposed, would not impact private wells, and no firm implementation date has been set.