Although there are sizable areas where ground water is being withdrawn at rates that cause water levels to decline persistently, as in parts of the dry Southwest, this is not true throughout the country. For the Nation as a whole, there is neither a pronounced downward nor upward trend.
Water levels rise in wet periods and decline in dry periods.
A major responsibility of the U.S. Geological Survey is to assess the quantity and quality of the Nation's water supplies. The results of these investigations are indispensable tools for those involved in water-resources planning and management. Numerous inquiries concerning water resources and hydrology are directed to the Survey and to State water-resources and geological agencies. To locate ground water accurately and to determine the depth, quantity, and quality of the water, several techniques must be used, and a target area must be thoroughly tested and studied to identify hydrologic and geologic features important to the planning and management of the resource. The landscape may offer clues to the hydrologist about the occurrence of shallow ground water.