Tracking U.S. Groundwater

During the past 50 years, groundwater depletion has spread from isolated pockets to large areas in many countries throughout the world. Groundwater occurs almost everywhere beneath the land surface. Its widespread occurrence is a major reason it is used as a source of water supply worldwide. Moreover, groundwater plays a crucial role in sustaining streamflow between precipitation events and especially during protracted dry periods. In addition to human uses, many plants and aquatic animals are dependent upon groundwater discharge to streams, lakes, and wetlands. The term "groundwater reserves" is used to emphasize the fact that groundwater, like other limited natural resources, can be depleted. This potential for depletion is a key concept, despite the fact that unlike nonrenewable resources such as mineral deposits, most groundwater resources are replenished. On the other hand, some "fossil" groundwaters in arid and semiarid areas have accumulated over tens of thousand of years (often under cooler, wetter climatic conditions) and are effectively nonrenewable except by artificial recharge of surface water or treated wastewater. Groundwater management decisions in the United States are made at a local level, which may be a state, municipality, or special district formed for groundwater management. Thus, monitoring of groundwater reserves should be designed to provide the information needed by these entities as a primary consideration. The issues to be addressed are varied and occur at many scales from preservation of a small spring fed by a nearby water source to the management of groundwater development throughout a large aquifer system or river basin.