County constitute the most extensive aquifers in the county. Four areally distinct sand and gravel aquifers were mapped in the drift during the course of this study. The aquifer of greatest economic importance consists of sand and gravel deposits of glacial-outwash origin which coincide with the courses of the White River and Fall Creek. Ground water in this aquifer is generally unconfined. Three thin, areally discontinuous, sheetlike deposits of sand and gravel situated one above the other occur in the till-plain area of the county. These deposits coalesce in some areas, but generally are separated by beds of silt and clay of varying thickness which cause the ground water in the till-plain aquifers to be semiconfined.

The uppermost 100 feet (30 metres) or so of limestone and (or) dolomite underlying the glacial drift constitutes an aquifer of secondary importance in the county. This aquifer is separated from the unconsolidated aquifers either by silt and clay or by shale.

The present movement of ground water through these aquifers is generally toward the White River, Fall Creek, Eagle Creek or Buck Creek. Based on seepage data, water levels in the aquifers in April and May 1974, and subsequent electric-analog-model analysis, discharge of ground water by seepage into the streams in the glacial outwash averages about 42 cubic feet per day per foot (3.9 cubic metres per day per metre) of channel length.

A four-layer electric-analog model incorporating the geometry and hydraulic characteristics of the aquifers, the confining beds and the stream- aquifer connection was constructed to determine the feasibility and hydrologic results of proposed plans for future ground-water development.

Three large well fields were simulated in the model of the glacial-outwash aquifer, with pumping nodes situated so as to take advantage both of high transmissivity areas in the aquifer, and of recharge from the streams.

A series of model experiments were carried out to test the capacity of the aquifers to sustain increases in pumpage. In all of these, a new equilibrium was established within 6 years of simulated pumpage. In two of these experiments, water levels in the discharging wells were allowed to draw down to approximately half of the saturated thickness of the glacial-outwash aquifer. At this drawdown limit, the total discharge of wells in the system was found to be 59 million gallons per day (2.6 cubic second) assuming that the streams were fully connected to the upper third of the glacial-outwash aquifer. In two other experiments, discharging wells were allowed to drawdown an average of two-thirds of the saturated thickness of the glacial-outwash aquifer. At this limit, the total discharge was found to be 72 million gallons per day (3.2 cubic metres per second) using the conservative stream-aquifer connection, and 103 million gallons per day (4.5 cubic metres per second) assuming a full connection. Some dewatering of the aquifer was associated with the 72 million gallons per day (3.2 cubic metres per second) discharge. In all experiments, the amount that could be pumped from the confined aquifers without disturbing existing domestic wells was found to be small.