Dear Youcef Zemour ,

for example please have a look at:

Article Geochemical behaviour of Radium isotopes and Radon in a coas...

Article Natural radioactivity of 226Ra and 228Ra in thermal and mine...

Article Geothermal prospecting by ground radon measurements

https://www.nature.com/articles/s41598-017-12441-0

You may 'google' *) yourself by appropriate buzz-words. There is very lot of stuff...

good luck

*) e.g. : https://www.google.de/search?source=hp&ei=iLe6Xf6OLYbrrgSamJ_gCQ&q=+Radium+and+Radon+isotopes+applied+to+study+thermal+waters&oq=+Radium+and+Radon+isotopes+applied+to+study+thermal+waters&gs_l=psy-ab.3...4682.4682..6030...0.0..0.152.152.0j1......0....2j1..gws-wiz.3c7pkNem2Co&ved=0ahUKEwj-8oiYpcblAhWGtYsKHRrMB5wQ4dUDCAc&uact=5

In addition to solubility and leaching there is another way of introducing the radium isotopes to ground water that may be of specific interest to you. I have studied the Nubian Sandstone aquifer, which is found at depth under the Negev desert in Israel. This aquifer extends across North Africa, so it should apply to your region. It contains a paleowater that was replenished during recharge periods during the Pleistocene, The last significant recharge in the mountains of Sinai was approximately 120,000 ago (Godfrey-Smith et al, 2008, pp. 39-44). It is now essentially stagnant. This is a slightly brackish resource that is of a reducing nature. Thus, it contains very minor uranium activity ,which is soluble only under oxidizing conditions.Th-232, the parent nuclide of Ra-224 and Ra-228, is exceedingly insoluble.Yet, this water contains all four radium isotopes in amounts that would preclude its use for drinking purposes.That this water contains all four radium isotopes (whose half-lives range from less than 12 days for Ra-223 (from the U-235 decay- series) to slightly more than 1600 years for Ra-226 ( from the U-238 decay series) would be surprising; for, in the absence of a soluble parent nuclide to renew these short half-lived daughters , the radium should have decayed away long ago. An answer to this apparent conundrum, can be found in the analysis of the sediments ( Ph.D thesis of M. Goldberg, 1965) that make up the aquifer's host sediments. In the fine sand fraction (approximately 62 microns) is appreciable amounts of zircon. The mineral zircon , which is highly insoluble is known to contain both uranium and thorium in amounts up to several thousands ppm. The small radius of the zircon allows the radium nuclides from the uranium and thorium decay-series to be physically transferred by alpha-recoil, continuously, across the mineral grain boundary to the water, in the absence of leaching, to renew the radium that decays. That the recoil process is occurring can receive support by the high U-234/U-238 activity ratios in the sparse amounts of soluble uranium that is found in the water.

there are many studies related to radon measurement in thermal water, you can simply find the research articles on research gate too.