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Graphs showing relation between strontium-87/strontium-86 isotopic ratio and magnesium to calcium molar ratio and time series of strontium-87/strontium-86 isotopic ratio measured in groundwater samples collected from the San Antonio segment of the Edwards aquifer, south-central Texas, 2013-16..

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Cover: Left, Borehole geophysical suite collected at Tri-County transect well TC2, 2003-10. Right, Photograph of a U.S. Geological Survey borehole geophysical logging truck, April 2009. Background, Photograph of the Sun setting over the project site, San Antonio segment of the Edwards aquifer, south-central Texas, 2003.

The ground-water-level monitoring network in Iowa consists of 202 wells completed in the principal bedrock and surficial aquifers that supply ground water to numerous users throughout the State.The bedrock aquifers include the Cambrian-Ordovician aquifer system, the Silurian-Devonian aquifer, the Mississippian aquifer, localized Pennsylvanian aquifers, and the Dakota aquifer. The surficial aquifers can be divided into three types: (1) buried channel, (2) alluvial, and (3) glacial drift. Information about the location, date of construction, and depth of each well, and the year water-level measurements began are provided for wells completed in each aquifer.The objectives of the ground-water-level monitoring network in Iowa are to provide the data needed to: (1) determine the change in aquifer storage, (2) document the effects of climatic stress and human activities on discharge and recharge to the principal aquifers, (3) quantify the physical characteristics of ground-water flow including the transmissivity, hydraulic conductivity, and specific capacity of aquifers; and (4) provide historical baseline data for future research. The design of the ground-water-level monitoring network in Iowa that satisfies these objectives includes three types of data: (1) hydrologic data, (2) water-management data for use by State and local officials, and (3) baseline data.