rock capable of accepting this fluid. In the US each such well is a closely regulated activity by the Environmental Protection Agency (EPA). If Europe followed this model, similar regulatory oversight would be required. But the geology of the area has to cooperate. On the US East Coast deep disposal is essentially not feasible in the prolific Marcellus and Utica prospects. The other disposal method is to treat and re-use for the same fracking purpose. This is the preferred option from an environmental standpoint in part because it minimizes handling and transport, which are subject to spills. The cost of the re-use option is less if the water does not have to be treated to fresh standards of 500 ppm salinity. In recognition of this, the service industry has been innovating to permit salty water to be used as the fracking fluid base. Today, 40,000 ppm salinity is completely tolerable. One could reasonably expect that number to go to 80,000 ppm shortly. Even higher salinity tolerance targets are also technically feasible. All this means that flowback water could re-used with minimal treatment in some cases. In other cases some fresh water could simply be added for dilution and some other steps may be needed, such as removal of bacteria. In the more difficult instances, desalination would be required, but targeting salinities of only 40,000 ppm today and even higher targets tomorrow. This limited desalination keeps the costs down. Because the water is being returned, minor impurities such as naturally occurring