Vibrocores from the samphire marshes south of the North Arm of the Port River are used to interpret the shallow subsurface stratigraphy. 2 marine sequences of Holocene and Late Pleistocene age, consist of saturated, unconsolidated and largely decalcified skeletal - quartz sands, separated by Bakara Calcrete, a thin but persistent calcrete horizon. They are porous and permeable, and are hydraulically connected with open waters of the estuarine channels. Saline ground waters are strongly acidic and reducing, possibly as a consequence of long term solid and liquid waste disposal. The marine strata are underlain by Hindmarsh Clay, a 70 metre thick sequence of stiff and largely impermeable alluvial silts and clays.