Johns Hopkins researchers recently published a paper titled, “Predictors of Indoor Radon Concentrations in Pennsylvania, 1989-2013,” in Environmental Health Perspectives.  The study reported the results of a mathematical analysis of Pennsylvania Department of Environmental Protection (PADEP) data for radon in buildings, and, among other things, Marcellus Shale drilling and production data.  The study posited that “development of unconventional natural gas in the Marcellus shale in Pennsylvania has the potential to exacerbate several pathways for entry of radon into buildings,” including, 1) release of radon and radium in the drilling process to the ambient air (attributed to radon released from flow-back water and reserve pit soil), and 2) introduction of radon in natural gas used for cooking.

The study found a statistically significant association between a building’s proximity to unconventional natural gas wells drilled in the Marcellus Shale and first floor radon concentration measurements made during the summer.  According to the study, this finding suggests support for an outdoor ambient air pathway.  A common sense examination of the suggested pathways and ground-proofing with actual data, however, demonstrates the implausibility of a connection between natural gas drilling in the Marcellus Shale and first floor radon concentrations in buildings close to those wells.

Methodological Issues

A number of assumptions and other aspects of the study’s design and methods undermine the credibility of its theories and findings.  Instead of using measured distances between each building with radon concentration measurements and actual drilled and/or producing wells, the study derived “metrics” which included not only distance, but also factors such as duration of an indoor radon test, and the estimated amount of gas produced by the well per day.  A drilled well was assumed to contribute to a building’s radon values from the time that it was drilled until the end of the study period.

The study’s analysis of the relationship between radon in the first floor of buildings and proximity to Marcellus shale drilled wells is based on only a subset of actual radon measurements in the data set.  The model excluded data for the buildings whose first floor radon levels during the summer were most relevant – buildings that were determined to be < 800 m away from drilled and producing wells.  Instead, the “proximity” between buildings with elevated radon and wells drilled in the Marcellus Shale was somewhere between approximately 900 yards and 12 miles (between 800 m and 20 km).  The study also, in some cases, excluded measurements that were made in the same building over a period of time.  In the end, the findings regarding radon levels in the summer and Marcellus shale drilling was based on 1044 measurements.

The study’s analyses and findings either excluded or did not control for factors that more likely influence the first floor radon concentrations measured in the buildings during the summer.  The study included no information on the “degree of sealing of the building for energy efficiency, soil type near the building, wind speed and direction, and individual [socioeconomic status].”  In light of this, the authors admitted that “it is possible that the observed upward trend from 2004-2012 was simply the result of buildings being sealed more tightly during this time.”  It is quite reasonable for families experiencing increased income to invest in central air conditioning or energy-saving improvements.  In fact, improved financial circumstances in communities that have experienced an increase in natural gas drilling is an equally, if not more plausible explanation for an observed upward trend in first floor radon concentrations than the release of radon from wells located up to 12 miles away.

Environmental Measurements

In support of the theorized release of radon to ambient air pathways, the study references analysis of radium concentrations in produced water from wells in the Marcellus shale and in soil in reserve pits in Texas.  None of the studies cited report elevated ambient radon concentrations associated with the measured radium in produced water or soil.  Further, as part of a recent study (available at: of sources of naturally occurring radioactive material (NORM) in oil and gas production operations in the state, the PADEP measured radon concentrations in ambient air during flow-back of water at natural gas well sites.  Samples were collected at distances between 6 feet and 40 feet from the well head.  The radon measurement results were within the range of typical ambient background radon in outdoor air.  These results are inconsistent with finding any relationship between radon released to ambient air during drilling and radon concentrations during summer inside buildings up to 12 miles away.

The authors of the study acknowledged that the PADEP’s results disproved their second theorized pathway – use of Marcellus shale natural gas for cooking.  Based on the radon concentrations actually measured in natural gas samples taken from well heads, the PADEP determined that any incremental increase in radon in a home using Marcellus shale natural gas would be very small and not detectable by commercially available radon testing.  The PADEP’s calculation used the maximum radon concentration measured at the well head, and included a number of conservative assumptions, such as no radon decay during transit between the well head and a home, and that appliances using the natural gas were  not vented.


While the findings reported in “Predictors of Indoor Radon Concentrations in Pennsylvania, 1989-2013,” generated a great deal of publicity (, they are not an appropriate basis for assessing the potential radiation concerns associated with exploration and production of natural gas from the Marcellus shale and other unconventional formations.