amount of nh 4 in solution will maintain a large amount of nh 4 on the clay i e the clay prefers nh 4 to ca this is the reason that nh 4 is only very slowly released by flushing the clay with water containing only neutral dissolved salts in accordance with the present invention the contaminated space a 34 pore volume 34 of the formation is treated with a halogenated restoration fluid preferably comprising chlorinated water and or a hypochlorite solution e g naocl to decompose ammonium ions in the formation to components e g n 2 h 2 o which in turn offer no contamination threat to the formation the restoration fluid is injected into one of the wells previously used in the leach operation and fluids are produced from another until the ammonia concentration in the produced fluids reaches an acceptable level the produced fluids are made up with additional chlorine and or hypochlorite solution for recycle as fresh restoration fluid when the ammonia content of the produced fluids drops below an ecologically satisfactory level e g 3 parts per million indicating that substantially all of the ammonium ions have been removed or converted in the formation injection of the restoration fluid is stopped and the restoration of the formation is complete as stated above there are equilibria existing between nh 4 in the clay and nh 4 in the formation water see equation 2 and also between nh 3 and nh 4 in the formation water the latter being when chlorine cl 2 in the restoration fluids contacts the nh 3 in the formation water the following sequence of reactions occur equ1 the effect of cl 2 is to.