134 REPORT OF INVESTIGATIONS No. 50
should be completely filled with cement or other fill. They should never be plugged at the top and covered over because their location may be forgotten and buildings constructed at the site with the possibility that ground subsidence at sometime in the future may cause appreciable damage and even loss of life.
PUMPING TESTS
The ability of an aquifer to transmit water is expressed by the coefficient of transmissibility (T), defined as the quantity of water, in gpd, that will move through a vertical section of the aquifer 1-foot wide and extending the full saturated height of the aquifer, under a unit hydrologic gradient at the prevailing temperature of the water (Theis, 1938, p. 892). The capacity of the aquifer to store water is expressed by the coefficient of storage (S), defined as the volume of water released from or taken into storage per unit surface area of the aquifer per unit change in head normal to that surface. The leakage coefficient (P/m) is a measure of the ability of the confining beds above and below the aquifer to transmit water to the main producing zone. It is defined as the quantity of water that moves through a unit area of the confining bed with a head difference across the bed of unity.
The above aquifer coefficients can be determined by analyzing the changes in water levels in observation wells at known distances from a well pumped at a constant rate.
Four pumping tests to determine the coefficients of the Floridan aquifer were made in Orange County (See fig. 2). Three of these tests were of wells in the upper zone of the aquifer and one was in the lower zone. In each case background data were collected before and after the tests to eliminate extraneous effects, such as natural fluctuation, from the drawdown curves.
The corrected drawdown data (s) were plotted versus time since pumping began (t), divided by the square of the distance from the pumped well to the observation well (r) (s versus t/r 2). The resulting curves were analyzed through use of a family of leaky aquifer type curves developed by Cooper (1963). This family of curves is based on the equation for nonsteady flow in an infinite leaky aquifer developed by Hantush and Jacobs (1955, p. 95-100) and described by Hantush (1956, p. 702-714). The equation assumes a permeable bed overlain by less permeable beds through which water, under constant head, can infiltrate to the aquifer. The equation also assumes that the aquifer is homogeneous and isotropic; that water flow is laminar, and that the wells are open