New unconventional gas extraction technology, involving horizontal drilling and explosive hydraulic fracturing of underground rock strata has been termed “fracking” a term which we employ here. The economic advantages of fracking have led to a rapid and on going growth in the extraction of natural gas globally. The method involves the explosive destruction of large volumes of underground gas and oil retaining rocks and the pumping down of large amounts of what is termed “produced water” which initially contains various chemical and sand additives . This produced water and backflow returns to the surface with a high load of dissolved and suspended solids including naturally occurring radioactive elements Uranium, Thorium, Radium and their decay products, collectively termed NORM (Naturally Occurring Radioactive Material) . The contaminated water has to be safely disposed of but this is often associated with violations of legal disposal constraints.
It has long been known that Radium dissolved in fracked pore water or adsorbed on clay particles and grain coatings can dissolve and return to the surface in produced water   a fact that has led to tightening of controls over radioactivity in the conventional oil industry. Radium and Total Dissolved Solids (TDS) in produced water are positively correlated  . Radium is released though variation in ionic strength (salinity) differentials (Sturchioet al. 2001). As an example, over the course of 20 days, Radium concentration in flowback from a Marcellus Shale gas well in Greene County Pennsylvania increased by almost a factor of four from 74 Bq/L to 240 Bq/L  . These high Radium activities are pointers to a more general radiological contamination of producedwater from the ingrowth of Radium progeny and other dissolved radionuclides  . These are radiologically significant activity levels; for example, the US Environmental Protection Agency (EPA) limit for Radium in drinking water is 0.185 Bq/L and for all NORM alpha is 0.555 Bq/L. These and other considerations have led to concerns about possible contamination of surface waters and local drinking water .
The health effects of exposure to low levels of NORM in drinking water even at the current legal limit have been the subject of a number of studies, which collectively raise the issue of the adequacy of this limit and current risk models underpinning it in protecting members of the public from the harmful effects of
internal exposures to Uranium, Radium and their progeny -. One of the earliest gas fracking developments where these concerns are relevant was the exploitation of the Marcellus Shale beds in Pennsylvania where shales and sandstones contain significant quantities of NORM