The shallower aquifer receives direct recharge from precipitation, and water moves along short flow paths in the aquifer to discharge at local streams. Some water percolates downward through the fine-grained confining unit to recharge the deeper, buried aquifer and moves along more lengthy flow paths before discharging to larger streams. Water in the upper parts of these aquifers discharges to local streams, lakes, or wetlands. Water in the deeper parts of the aquifers, however, flows beneath the local surface-water bodies and discharges to large rivers that are regional drains. Lenslike beds of clay and silt are interspersed with the permeable sand and gravel, and locally create confined conditions in the aquifers.
Large yields are common from wells completed in aquifers composed of glacial outwash.
Where these aquifers occupy channels in permeable bedrock, they generally receive much of their recharge from the bedrock, but locally discharge some water to it. Yields of wells completed in the glacial-deposit aquifers formed by continental glaciers are as much as 3,000 gallons per minute where the aquifers consist of thick sand and gravel. Locally, yields of 5,000 gallons per minute have been obtained from wells completed in glacial-deposit aquifers that are located near rivers and can obtain recharge from the rivers. Aquifers that were formed by mountain glaciers yield as much as 3,500 gallons per minute in Idaho and Montana, and wells completed in mountain-glacier deposits in the Puget Sound area yield as much as 10,000 gallons per minute.