regulations the tidal dam in the Miami Canal cannot be raised until the canal stage has receded to 2.2 feet above U. S. C. & G. S. mean sea level at Pennsucop about 7.2 miles northwest of the present well field.
Salt Water in the Miami Well Field.--Contamination of the Miami well field in 1939 was not brought about by movement of salt water at depth in the aquifer, but was occasioned by a salt incursion in the Miami Canal at a time when low flow in the cahal was insufficient to hold sea water at a relatively safe distance downstream from the well field$ A shallow cone of depression surrQunds the Miami well field and reaches the Mieni Canal much of the time. Water seeks to reach a level, so moves in laterally from the area surrounding the cone of depression, and the movement is always at right angles to the contours on the water table. Thus, when salty water occupied this reach of the Miami Canal, it came under the influence of the cone of depression around the well field and moved inward to the well field. It was inevitable that the water served the consumers became somewhat salty under the circumstances. Fortunately, the time that the salt water remained in the canal was not great so that the amount that reached the well field was not ruinous. Certain wells for a while, contained water of over 1,000 parts per million of chloride, but the large area of salty water in the well field reached a concentration of about 4OO parts per million. Thus, the damage was nominal (see plate 7).
Since then, Judicious pumping of the several supply wells, effective placement of barriers in the canals and timely rainfall has prevented a recurrence of the 1939 experience.
Further, pumping an average of about 28 million gallons per day
from the well field has removed much of this body of salty water from the