Nice to see someone say it - there is No groundwater on Mars. Even if there was, it would quickly reach saturation with the ubiquitous MgSO4 - that is what groundwaters do - they try to reach equilibrium with their host rocks. At room temp 760 gm of Epsom salts dissolves per lite of water. The resulting solution has a density over 1.25 and a viscosity like oil. Anyone talking about groundwaters on Mars should make and observe such a solution. (Notice a salt-lake with such a hyperbrine can not float on a reservoir of lower density, less-saline water. Some published models would have Mr Archimedes spinning in his grave)
The ESA team described the theikiian period which ended some 3.5 billion - a period when sulfates were formed. Has this finding been ignored because a corollary of abundant MgSO4 is that there is no subsequent period of free water to dissolve away that MgSO4. The ESA team stated this describing the last era (the ‘‘siderikian’’) as dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing any major role. Maybe just an "inconvenient truth" but it puzzles me that simple chemistry points in one direction but there is a deluge of "research" pointing in the opposite.