Documentation of a pilot workflow for reanalyzing the U.S. Geological Survey principal aquifers datasets and prototype principal aquifer version 2 dataset for three aquifer systems

A pilot workflow to refine the principal aquifers of the United States as defined in the Ground Water Atlas of the United States and create a new version of the principal aquifers (referred to as “version 2”) is documented in this report. The workflow incorporates decision points for creating finer scale spatial data for the principal aquifers and refining the original principal aquifer definitions if warranted. This workflow was applied to four principal aquifers in the upper Midwest region of the United States that were not previously refined as part of a U.S. Geological Survey regional groundwater availability study: the Cambrian-Ordovician aquifer system, the Jacobsville aquifer, the Silurian-Devonian aquifer, and the upper carbonate aquifer. The refinement resulted in the consolidation of two of these aquifers (the Silurian-Devonian and upper carbonate aquifers), an expansion of the Jacobsville aquifer into a larger newly defined Midcontinent Rift sandstone aquifers unit, and a slight refinement of the Cambrian-Ordovician aquifer system to exclude Precambrian units. The U.S. Geological Survey State Geologic Map Compilation geodatabase provided the base data used in the refined version 2 dataset, which are published in an accompanying U.S. Geological Survey data release as a prototype version 2 shapefile and include attributes describing the aquifer, data lineage, and source of the originally defined principal aquifer.