An injection-extraction well network in the Palo Alto Baylands along the San Francisco Bay, California, was designed to flush the shallow aquifer system of saline water and prevent further inland saline contamination. Clogging processes and solution migration in the vicinity of one injection well were studied. Cyclic evaporative concentration of bay water and infiltration have generated a concentrated ground-water brine. Montmorillonite and illite are the primary clay minerals present in the shallow aquifer system. X-ray diffraction analysis of these clays showed a marked increase in the d-spacing of the crystal lattice when native hypersaline pure water was replaced by injection water. Chloride:magnesium and chloride:potassium ratios in the aquifer system changed during injection, most likely due to ionic exchange reaction. Similar variations in chloride:boron, chloride:iron, and chloride:manganese ratios probably resulted from reduction-oxidation reactions. Ground-water quality appears to have been chiefly affected by the processes of dilution and dispersion. Extraction pump test data yielded a transmissivity value of 960 feet squared per day and a storage coefficient of 0.0005. Vertical permeability of the upper confining layer is 0.08 feet per day.
