Simulated changes in the sources of ground water for public-supply wells, ponds, streams, and coastal areas on western Cape Cod, Massachusetts

The U.S. Geological Survey, in cooperation with the Air Force Center for Environmental Excellence, developed a three-dimensional ground-water-flow model to simulate sources of water to public-supply wells, ponds, streams, and coastal areas for average and changing pumping and recharge conditions on western Cape Cod, Massachusetts. Understanding the changing sources of water that flows to these discharge areas under changing hydrologic conditions and stresses is needed to help water-resource managers protect the quality of the drinking water and the water resources of western Cape Cod.

The interconnection of hydrologic features through the ground-water-flow system on Cape Cod complicates the determination of the sources of water for changing pumping and recharge conditions. When pumping and recharge conditions change, the numerical model can help evaluate changes in the recharge areas to pumped wells, ponds, streams, and coastal areas.

The steady-state recharge area and time-of-travel zones to a pumping well represent the source of water and time of travel from the water table to the well once all of the water discharging to the well entered the aquifer after pumping began. Initially, the water that discharges to a pumped well over a specified period consists of a blend of waters that entered the aquifer over time. When pumping begins, a deep well may capture water that entered the aquifer many years earlier at a great distance from the well; therefore, determining the source of water discharging to a well for specified pumping times may be more important for protecting public-water supplies than determining only the steady-state recharge area and time-of-travel zones to the well.