What are average radon levels in Cumming, Georgia?

Average radon levels in the Cumming and Forsyth County area range from 4.0 to 6.5 pCi/L, which is above the EPA action level of 4 pCi/L. Forsyth County is classified as EPA Zone 1 (highest risk), and roughly 35-45% of tested homes exceed the action level. Some homes, particularly those with basements, test well above 10 pCi/L.

Why is Forsyth County one of the highest radon risk counties in Georgia?

Forsyth County sits on Piedmont granite bedrock with high uranium content. The granite is often close to the surface, especially in the northern and western parts of the county. This geology produces more radon gas than areas further south in Metro Atlanta. The combination of productive bedrock and permeable soil makes Forsyth County one of the highest radon risk counties in Georgia.

How much does radon testing cost in Cumming?

Professional radon testing in Cumming costs $125 to $250 for a 48-hour continuous radon monitor test. DIY charcoal test kits run $15 to $40 plus lab fees. For real estate transactions, professional CRM testing is the standard and provides hourly readings that charcoal kits cannot match.

Should I test for radon if I just built a new home in South Forsyth?

Absolutely. South Forsyth has seen explosive growth, but new homes are built on the same radon-producing granite as older homes. Even if your builder installed passive radon-resistant features, these do not guarantee low indoor radon levels. The EPA recommends testing every new home after construction, and homes in Forsyth County should be a particular priority given the Zone 1 designation.

Radon in Cumming, Georgia

1. Why Cumming Has High Radon Risk

Cumming and the greater Forsyth County area sit on some of the most radon-productive geology in Metro Atlanta. The county is classified as EPA Zone 1, the highest risk category, meaning the predicted average indoor radon level exceeds 4 pCi/L. This puts Forsyth County in a small group of Georgia counties with the most significant radon concern.

The source of the problem is the Piedmont granite bedrock that underlies the region. This ancient rock contains uranium that decays into radium and then into radon gas. In Forsyth County, the granite is often close to the surface, which means radon gas has a short path from its source to home foundations. The result is some of the highest average indoor radon readings in the Atlanta metro.

Forsyth County has experienced explosive population growth, jumping from roughly 100,000 residents in 2005 to over 260,000 today. Thousands of new homes have been built across the county, and every one of them sits on the same radon-producing geology. Whether your home is 2 years old or 20 years old, the only way to know your radon level is to get your home professionally tested.

2. Neighborhood Radon Risk Areas

The entire Forsyth County area carries elevated radon risk, but testing patterns show some variation across different parts of the Cumming area:

Downtown Cumming. The historic center of the city has older homes, many with crawl space foundations. These older structures tend to have more cracks, gaps, and openings that allow radon entry. Some homes near downtown test among the highest in the county due to the combination of older construction and shallow bedrock.

South Forsyth and Halcyon. The fastest-growing part of the county, with subdivisions, townhome communities, and mixed-use developments. Despite being mostly new construction, South Forsyth homes regularly test above the EPA action level. New homes are not immune to radon. The geology does not care when your home was built.

Coal Mountain. Located in the northern part of Forsyth County with more rural character. Homes here tend to sit on larger lots with varied terrain. The granite geology in this area is particularly productive, and many homes have basements or walk-out lower levels built into slopes. Testing data from Coal Mountain consistently shows elevated readings.

Check your specific risk level using our look up your zip code's radon risk.

For broader county-level data, see our Forsyth County radon guide.

3. Foundation Types and Radon Entry

The Cumming area has a wide range of foundation types, and each one interacts with radon differently:

Basements and walk-outs. Very common in Forsyth County due to the rolling terrain. Basements have the most soil contact and the highest radon accumulation potential. Walk-out basements with two or three below-grade walls are especially vulnerable. Radon enters through floor cracks, the wall-floor joint, sump pits, and utility penetrations.

Crawl spaces. Found in older Cumming homes and some newer construction. An unsealed crawl space allows radon to pool beneath the home and migrate into living areas through floor gaps and HVAC ductwork. Even encapsulated crawl spaces need proper sealing to prevent radon entry.

Slab-on-grade. Common in newer townhome communities and ranch-style homes. While slabs have less soil contact, the Forsyth County geology pushes enough radon through concrete cracks and plumbing penetrations to exceed safe levels in many homes. Slab homes in Cumming should not be assumed safe without testing.

Forsyth County's Zone 1 Status Is Not a Suggestion

The EPA's Zone 1 designation for Forsyth County reflects a serious radon risk. With average levels above the action threshold and 35-45% of homes testing high, every home in the Cumming area needs to be tested. Two homes on the same street can have completely different radon levels, so your neighbor's results mean nothing for your home.

4. Testing Your Cumming Home

Given Forsyth County's high-risk designation, testing should be a top priority. Here is how to approach it: Neighboring cities like Alpharetta, Canton, and Johns Creek show similar radon patterns due to shared geology.

Choose Your Test Type

A short-term test (48 hours minimum) works well for initial screening. Professional CRM testing ($125-250) is the standard for real estate transactions. DIY kits ($15-40 plus lab fees) are fine for general screening.

Place the Test Correctly

Test in the lowest livable area of your home. In Cumming, that is often the basement or lower level. Keep the device away from windows, drafts, and exterior walls. Maintain closed-house conditions during the test.

Understand Your Results

Below 2 pCi/L: Low risk, retest every 2 years. Between 2-4 pCi/L: Consider a long-term follow-up test. Above 4 pCi/L: The EPA recommends have a mitigation system installed. Above 8 pCi/L: Prioritize mitigation promptly.

Radon levels are typically 40-60% higher during winter months. A borderline summer result in a Forsyth County home almost certainly means elevated winter levels. Consider retesting in colder months for the most accurate picture.

5. Radon Mitigation Options

If your Cumming home tests above 4 pCi/L, mitigation is effective and usually completed in one day. The right system depends on your foundation:

Slab or Basement

$1,200-$2,500

Sub-slab depressurization: a suction point drilled through the foundation, connected to PVC pipe and a fan that exhausts radon above the roofline.

Crawl Space

$2,500-$5,000

Sub-membrane depressurization: a sealed vapor barrier over the soil with active suction pulling radon from beneath and venting it outside.

Both systems achieve 90-99% radon reduction. Many Forsyth County homes with levels of 8-15 pCi/L are brought down to below 2 pCi/L with a properly designed system. Use our check radon mitigation pricing for a more specific estimate.

For more information, read our first-time homebuyer radon checklist.

Cumming and Forsyth County Homeowners

Forsyth County has some of the highest radon potential in all of Georgia. With 35-45% of homes testing above the action level, the odds are not in your favor. A 48-hour test gives you a definitive answer, and if mitigation is needed, it is a one-day installation that permanently eliminates the risk.

Radon in Cumming, Georgia: What Homeowners Need to Know

1. Why Cumming Has High Radon Risk

2. Neighborhood Radon Risk Areas

3. Foundation Types and Radon Entry

Forsyth County's Zone 1 Status Is Not a Suggestion