Evidence of formation of entrapped saline bodies of water in a porous medium where fresh water displaces flowing sea water was observed in laboratory experiments, carried out on aquifer sands containing clay minerals. When sea water was flushed from these sands by fresh water, fluctuating changes of EC (electrical conductivity) appeared in the sample, and the hydraulic conductivity of the entire sample fluctuated before a lower value of hydraulic conductivity stabilized.

These results are explained by a sequence of mechanisms: (a) formation of small pockets of seawater surrounded bysemi-permeable membranes of deflocculated clay minerals; (b) bursting of the pockets by osmotic pressure and release of trapped sea water; and (c) deflocculation of clay minerals in the pockets formerly occupied by sea water.

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