Radon in New Jersey's Ground Water

Radon is a cancer-causing, naturally-occurring radioactive gas resulting from the decay of uranium in rock, soil and water. Radon has a half-life, the time necessary for one-half of the concentration to decay, of approximately 4 days and decays to an isotope of lead, which is also carcinogenic. Radon is soluble in water and can be transported in a gas phase through the soil which causes numerous indoor air contamination problems. The presence of radon in indoor air and drinking water causes an estimated 14,000 deaths per year in the United States. As a result, a greater awareness of the presence of radon in our drinking-water supplies is needed and professionals in the ground-water field, such as hydrogeologists, pump installers and well drillers, should have an understanding of its sources and typical abatement methods.

Radon is commonly found to be an indoor air problem and the U. S. Environmental Protection Agency (USEPA) has promulgated an indoor air standard for radon of 4 picocuries per liter (pC/l). Radon is also found in drinking-water supplies and may pose a severe carcinogenic threat if present at high concentrations. A drinking-water standard has not yet been promulgated by the USEPA or the State of New Jersey; however, recent legislation by Congress is requiring that the USEPA enact a drinking-water standard. It is expected that the standard will be approximately 5,000 pC/l.

Sources of Radon

The presence of radon in indoor air or drinking water is derived from naturally occurring uranium in rocks and soil. Indoor radon problems and problems related to radon in drinking-water supplies are generally restricted to the Reading Prong area of northern New Jersey. The Reading Prong is a thin belt of igneous and metamorphic rocks, composed predominantly of granites and gneisses. Igneous rocks are initially derived from a melt, while metamorphic rocks were deformed under high levels of temperature and pressure.

Based on research completed by the New Jersey Geological Survey (NJGS) and the U. S. Geological Survey (USGS), it is known that hornblende granite, a formation which extends through much of northern New Jersey and parts of southeastern Pennsylvania, contains uranium-238 concentrations of up to 20 milligrams per kilogram (mg/kg) or "parts per million". Uranium-238 is a radioactive isotope which is used in the nuclear industry. Radon is a daughter product of, or decays from, uranium-238. Radon subsequently decays into lead-210 which has a half-life of 21.8 years. Other crystalline rocks, such as amphibolites or gneisses contain lesser concentrations of uranium-238.

Uranium-238 and other radioactive elements are known to concentrate in shear zones such as faults. According to studies completed in by the USGS in Warren County, New Jersey, uranium-238 concentrations are known to be the highest within pegmatites and mylonites present within hornblende granites. Pegmatites are zones of very-coarse-grained igneous rock that formed towards the later stages of the cooling of the melt. Mylonites are zones within the rock that have been subjected to deformation caused by faulting and have undergone volume loss, which leaves the rock enriched in uranium-238 and other radioactive elements.

In summary, high concentrations of radon in ground water may be found under the following conditions:

1. in localities within the Reading Prong Physiographic Province. As discussed above, the Reading prong is underlain by crystalline rocks such as granites and gneisses; within uranium-bearing formations such as the hornblende granite. The location of areas underlain by hornblende granite can be found on geological maps prepared by the USGS and the NJGS;
2. in the vicinity of shear zones such as faults. Uranium tends to accumulate in these zones because of the added temperature and pressure. The presence of faults can normally traced on geological maps, and
3. within pegmatite zones which are the coarse-grained portions of the igneous rock. Pegmatite zones are often not mapped and their presence would need to be determined by directly contacting the USGS or the NJGS.

It is noted that the geologic formations which are part of the Jutland Klippe, in the vicinity of Clinton, New Jersey, exhibit unusually high concentrations of radon. These formations consist of carbonate rocks, such as limestone, and the reason for the radon presence is not presently known. Therefore, elevated radon concentrations should be expected in ground water from potable wells installed in this vicinity.

Wells drilled under the above conditions have a much higher probability of encountering high levels of radon. Radon concentrations in excess of 500,000 pC/l, or 150 times the expected Federal standard, have been detected in ground-water samples collected from potable wells in New Jersey under the above conditions.

Monitoring and Treatment

It would be a prudent practice to sample all potable wells in northern New Jersey for a radon analysis. However, most communities only require a radon test for indoor air when applying for a Certificate of Occupancy (CO). We are not aware of any municipalities which require a radon analysis on well water. It is our recommendation that when any of the above conditions are met, the potential exists for the presence of radon in the drinking water and a radon analysis should be conducted.

If radon concentrations exceed the impending Federal standard, treatment of the water is an option. Because radon is a gas and, therefore, highly volatile, it can normally be treated with a simple stripping system. This point-of-entry treatment (POET) system would be installed within the residence and typically costs several hundred dollars. Removal rates are typically on the order of 95% to 99%.

Additional information on radon in drinking-water supplies and possible abatement methods can be obtained by contacting Hydrotechnology Consultants, Inc. at (609) 466-9628 or a radon analytical laboratory such as RAData, Inc. in Flanders, New Jersey at (908) 879-8977.