It sets down the requirement for an effective, national seismic monitoring strategy and an advanced system linking national, regional, and urban monitoring networks. Ground water is obtained from wells and springs that are open to aquifers. Groundwater is replenished by precipitation that moves through the unsaturated zone of the land surface to the water table or by artificial replenishment. An aquifer may be only a few feet thick to hundreds of feet thick, and ground water can move within the rock pores or joints in an aquifer or it can move from one aquifer to another. Hydrologists use several techniques to locate ground water, including visual clues from the landscape and plants.
Hydrologists also estimate the visual clues from the landscape and plants.
Hydrologists also estimate the amount of ground water in an aquifer and conduct tests to determine if it is suitable for use. Ground water is less susceptible to bacterial pollution than surface water in lakes and streams because the soils and rocks through which groundwater flows screen out most of the bacteria. But water is a solvent, and it dissolves minerals from the rocks with which it comes into contact. Water typically is not considered desirable for drinking if the quantity of dissolved minerals in it exceeds 1,000 milligrams per liter. For the Nation as a whole, the chemical and biological character of ground water is acceptable for most uses.