Radon is a naturally occurring radioactive gas. Radon comes from the radioactive decay of radium that is present in the earth's crust. It is ubiquitous and it is the leading cause of lung cancer among non-smokers. It is present, in varying amounts, everywhere. The levels inside your home change every day.
RADON LEVELS CHANGE EVERY DAY.
It is not the radon level that is the greatest concern, it is your EXPOSURE to it that is the problem. There is no "safe" level. There are diurnal variations (changes twice a day) as well as seasonal variations. During the winter months your home is buttoned up and with combustion appliances, like a running furnace, the negative pressure in the house acts to suck in radon from the surrounding soil. (Whether you have a basement or not) It also enters during the summer months.
A screening test, such as those used in real estate transactions DOES NOT tell you about the radon levels you may be exposed to. It merely indicates whether a long-term test is required.
Radon levels in NJ vary greatly. The NJDEP mapped each community in terms of risk level for finding elevated levels of radon based on prior test results. AH is a tier 2 community, meaning a moderate risk of finding elevated levels.
Typically, the radon levels on the 1st floor are about half what you'd find in the basement. The 2nd floor would have about half what is found on the 1st floor. This changes slightly with high efficiency homes. But overall. your EXPOSURE is the average radon level over a period of time. So if you work in the basement for 8 hours a day, a third of your exposure would be at the annual average level in the basement. A third of your life in your bedroom, and maybe a third of your time on the 1st floor.
The actionable remediation level is 4 picocuries of radon per liter of air (pCi/L). Meaning, if you are exposed to levels above 4 pCi/l on an ANNUAL basis, you should take steps to reduce the levels because it is reasonably cost effective to do so. Depending on the circumstances, there are a variety of remediation techniques, from covering up your sump pump or sealing drains with special fittings, to sub-slab depressurization systems or air-to-air heat exchanges.
The average cost for a remediation system is about $1200-$1500.
BUILDING RESISTANT STRUCTURES
In New Jersey, homes built in communities designated Tier 1 for higher risk are required to build radon resistant structures. It does not eliminate radon, but increases barriers to entry. Techniques like building a network of pipes beneath the slab during construction provides easier means of reducing levels if, after the building is complete, high levels are discovered.
One other point about structures. High efficiency buildings reduce air circulation. This can "trap" more radon in the buildings. Old drafty houses have a higher air change rate. Not to say you should not button up your home for energy savings, but your radon levels are impacted. To reduce radon concentrations in your building, you should reduce entryways for the gas. Seal cracks, sumps, cover the dirt in crawlspaces, or any opening to the soil around home from the basement or first floor. There are various means of entry in your home. In our part of the country, soil is the most common entry route. Other sources of indoor radon include outdoor ambient air, water from showers and flushing, and building materials.
Radon gas comes from the metal, radium. Radium is found throughout the Earth's crust in different concentrations and ends up in some building materials (or use to). It is also in the water. Look at your annual Water Report. It shows the radium content.
My research at the University of Maine showed that for every 10,000 picocuries per liter of radon in well water about one picocuries per liter of radon is contributed to the indoor air in a typical home in Maine. (Which has a higher percentage of people using well water).
The New Jersey DEP issued this guidance on radon.
For more information about radon, visit the New Jersey DEP Radon Section at: http://www.njradon.org/
(updated to include details on building structures)