REPORT OF INVESTIGATIONS NO. 38 23
the ground-water divide is about 1,500 feet, assuming that the divide is midway between the two simulated streams. Based on these estimates, the water table is computed to rise to above 0.45 foot above sea level at a little less than 70 feet from the waterway. The toe of the salt-water wedge, therefore, is estimated to extend to about 70 feet from the edge of the waterway. If the toe of the salt-water wedge extends 70 feet from the edge of the waterway on both sides of the waterway, the width of the base of the salt-water wedge will be 300 feet (70 + 70 + 160 300), the sea-level width of the waterway being 160 feet.
COEFFICIENT OF LEAKAGE
Although the coefficient of leakage of the confining beds that separate the salt-water wedge, which will exist if the waterway is constructed, from the first artesian aquifer is not known, coefficients were determined at well 9S and at well 31. The coefficient as determined from the test at well 9S was 1.3 x 10-:1 gpd per ft". Well 98 is nearer than well 31 to the proposed waterway, and the coefficient determined at this well is probably more representative of the actual coefficient of the upper confining beds at the waterway than is the coefficient at well 31. It should be remembered, however, that the pumping tests were conducted in the well field and not along the route of the waterway where the leakage would occur.
In the estimates of the amount of salt-water leakage that follow, the coefficients of leakage as determined from the pumping tests are assumed to represent the coefficient of leakage of the confining beds between the salt-water wedge and the first artesian aquifer. This is equivalent to assuming that all the leakage into the first artesian aquifer is through the upper confining beds. Such a premise, of course, assumes that the upper confining beds are more permeable than they are.
HEAD DIFFERENTIAL ACROSS CONFINING BEDS
In order to determine the head differential that will exist across the confining beds when the waterway is constructed, the head at the base of the water-table aquifer and the pumping level of the first artesian aquifer beneath the waterway must be determined.