Occurrence of Radon in Florida's Public Water Supplies

Executive Summary

Background

The U.S. Congress specified in the Safe Drinking Water Amendments of 1996 that the U.S. Environmental Protection Agency (EPA) shall propose a national primary drinking water regulation for radon by August 1999 and finalize the regulation by August 2000. A radon regulation may have a significant impact on public water systems (PWSs) in Florida. To estimate the impact, the Florida Department of Environmental Protection’s Drinking Water Section conducted a statewide study of radon occurrence in raw ground water used, and finished ground water produced, by PWSs. As of January 9, 2023, there is no standard for radon in drinking water.

Study Objective

The primary objective of the department’s radon occurrence study was to estimate the following:

• radon levels in raw ground water used by Florida’s PWSs; and
• the percentage of Florida’s PWSs that would exceed various possible maximum contaminant levels (MCLs) or alternative maximum contaminant levels (AMCLs) that could be established by the EPA in its national primary drinking water regulation for radon.

Study Approach

To accomplish the above objective, the department’s radon occurrence study was designed as follows:

• to include sampling for radon at a portion of Florida’s community water systems (CWSs) using ground water and at a portion of Florida’s non-transient non-community water systems (NTNCWSs) using ground water (at the time the study was designed, it was anticipated that the EPA’s drinking water regulation for radon would apply to CWSs using ground water and NTNCWSs using ground water);
• to include sampling for radon in raw ground water;
• to include sampling for radon in finished ground water if the water system treatment plant selected for sampling was using a treatment process other than just chemical addition;
• to limit sampling to one raw water sample set for each water system selected for sampling and, where applicable, one finished water sample set for each water system selected for sampling; and
• to accomplish sampling of raw ground water as near the source of water (i.e., the well) as possible and sampling of finished ground water downstream of all treatment processes.

From May 1999 to August 1999, 341 PWSs (213 CWSs and 128 NTNCWSs) were sampled for radon. Raw ground water samples were collected at all 341 of the sampled systems. Finished ground water samples were taken at 127 of the 341 sampled systems. However, for the remaining 214 systems, where the sampled water treatment plants were using just chemical addition treatment, it was assumed that the concentration of radon in finished water would be the same as the concentration of radon in raw ground water.

Conclusions

The EPA proposed a national primary drinking water regulation for radon after the department completed the sampling phase of its radon occurrence study. The proposed regulation would apply only to CWSs using ground water, would set an MCL for radon at 300 picocuries (pCi/L), and would set an AMCL for radon at 4,000 pCi/L.

Based upon the results of its radon occurrence study, the department formulated the following conclusions concerning Florida’s CWSs and a radon MCL or AMCL of 300 pCi/L or 4,000 pCi/L, respectively:

• The mean or average concentration of radon in raw ground water used by Florida’s CWSs is 664 + 141 pCi/L, and it is estimated that 57 + 6 percent of Florida’s CWSs using ground water have a radon concentration greater than 300 pCi/L in their raw ground water.
• An estimated 44 + 6 percent of Florida’s CWSs using ground water would exceed an MCL of 300 pCi/L for radon, but no more than two percent of these systems would exceed an AMCL of 4,000 pCi/L for radon.