Iron removal can be achieved ...

Iron removal can be achieved using aeration cascade, settlement lagoon or tank and then polish with reed bed/wetlands.  Any groundwater rich in iron might also contain manganese and aluminium plus sulphate.  It is therefore worth checking the alkalinity and acidity (as mg/l CaCO3) of the groundwater as low alkalinity (<300 mg/l) will often inhibit iron oxy-hydroxide floc formation.  The aeration cascade is used to elevate dissolved oxygen content, but it also helps liberate any entrained carbon dioxide which might depress the pH.  NB - Please note checking pH only gives a partial picture of the acid/alkali balance, alkalinity is the key parameter to buffer pH changes.