Homeowner Tips

Radon in Air and Water - An Overview for the Homeowner

WHAT IS RADON?

Radon is colorless, odorless and tasteless radioactive gas produced from the decay of naturally occurring radioactivity in soil and rocks worldwide. Radon gas can dissolve in groundwater and later be released into the air during such normal household activities as showering, dishwashing and doing laundry. When radon becomes trapped in an enclosed space (such as indoors) it can accumulate and pose an increased health risk.

RADON PATHWAYS INTO YOUR HOME

Radon can enter a home via at least three common pathways:

• Migration (up from the soil) into the basement through cracks and/or other openings in the foundation.

• Release of dissolved radon gas from the household water supply.

• Release from building materials such as a granite block foundation, some fireplace materials, floor or wall tiles, etc.

In New Hampshire and Massachusetts, the migration of radon up from the soil contributes the largest percent of radon found in the average home. Radon from groundwater type water supply source, particularly a bedrock (artesian, drilled) well, contributes the next largest percentage of radon in the home. The radon contributed from building materials is typically very small. DES recommends that these two predominant pathways should be evaluated and that initial action to reduce the radon exposure should target the pathway that contributes the largest percentage to the occupant's exposure.

HEALTH EFFECTS

The primary risk pathway from exposure to radon gas is through inhalation of the air in a home. Studies show that high levels of radon gas in the air increase the risk of developing lung cancer.

An additional health risk is associated with the ingestion of the radon that remains dissolved in the water. This risk is substantially lower than that associated with inhalation.

HOW MUCH RADON IS TOO MUCH?

Indoor Air Recommendation: The US EPA has set an advisory "action level" of 4 pCi/L for radon gas in indoor air. While not a mandated health standard, this level is a guideline for people to use in assessing the seriousness of their exposure to airborne radon.

Drinking Water Proposal: At present there is no federal or state standard (known as a maximum contaminant level (MCL) for radon in drinking water. Because radon is such an important issue to many persons in New Hampshire and Massachusetts, particularly those considering real estate purchase or sale, we offer the following discussion of EPA's development of a radon standard for public drinking water systems. Our goal is to provide you with up-to-date information so that you may make well informed decisions.

A federal drinking water MCL for radon of 300 pCi/L was proposed by EPA in July, 1991. This MCL would not have applied to private home water supplies, only to public water systems. It was expected that over 95 percent of bedrock (artesian/drilled) wells in New Hampshire and Massachusetts would have exceeded this 300 pCi/L concentration.

In response to the 1991 EPA proposal, the New Hampshire Department of Environmental Services (DES) and the New Hampshire Department of Public Health Services (DHHS) jointly proposed to EPA that a standard for radon gas in drinking water would be better set at 2,000 pCi/L. Massachusetts has recommended a standard of 10,000 pCi/L. The EPA received many other comments relative to the radon proposal including a directive, in 1993, from the US Congress to cease all work on its development.

For the next few years the US House, Senate and President attempted to develop a consensus on future water supply legislation which included development of a radon MCL from public water systems. In the late Spring of 1996 the House and Senate reached a compromise and on August 6, 1996 the President signed into law the reauthorization of the Safe Drinking Water Act.

Until such time as the federal standard for radon in water is finalized, the DES and DHHS suggest that homeowners investigate water treatment for the removal of radon if the concentration of radon in their drinking water exceeds an average of 2,000 pCi/L. (10,000 pCi/L in Massachusetts)

TRANSFER RATIO (Contribution of Radon in Water to Radon in Air)

As radon escapes from water it raises the radon level of the air within a building. The "transfer ratio" predicts the increased radon level of air. The transfer ratio in 10,000 pCi/L of radon in water can be expected to increase the overall annual average radon concentration of the air in a home by approximately 1pCi/L.

To illustrate this conversion assume the following example: if the radon in water concentration was 5,000 pCi/L, and the radon in the air measure was 3 pCi/L; then 0.5 pCi/L of the airborne radon would likely be attributable to the water and the remaining 2.5 pCi/L would be attributed to radon gas migration up from the soil through the home's foundation.

Additional information on Radon can be found at the U.S. EPA Website.