MAPS OF PROPERTIES OF QUATERNARY SEDIMENTS AND AQUIFERS IN THE GLACIATED CONTERMINOUS UNITED STATES

The glacial aquifer system, the collection of aquifers within Quaternary sediments in the glaciated conterminous United States, is a principal aquifer that supplies groundwater withdrawals accounting for about 25 percent of the Nation’s drinking water. A hydrogeologic framework is presented that divides the glaciated United States into seventeen hydrogeologic terranes using a geologically based approach. Each terrane contains Quaternary sediment that is generally derived from a common depositional history and characterized by similar texture and thickness. Characteristics of Quaternary sediments and aquifers within them are described using metrics computed from a lithologic database of more than 1.5 million well logs. Maps showing groundwater use in the glacial aquifer system are also included. The framework presents a nationwide picture of the glacial aquifer system, and provides generalizations concerning the nature of aquifers within it, for example, whether the aquifers are shallow or deep, and unconfined or confined. In this way insights can be gained from understanding the similarities and differences in distinct parts of the aquifer system, and how they relate to water use, quality and aquifer vulnerability.

Surficial mapping of Quaternary sediments is based on the USGS Quaternary Atlas Series and a surficial materials map. The lithologic database was compiled from State well records, with well logs standardized and using a consistent terminology. Total groundwater usage was compiled by county in the glaciated United States in 2010. Characteristics of Quaternary sediment and aquifer materials penetrated by the wells were computed from the lithologic logs. System-wide maps of selected metrics were interpolated using a kriging-based approach and the median values of each metric within a 1-km geospatial grid cell. Sediment and aquifer-material metrics are presented through box plots and bar charts grouped by hydrogeologic terrane.