The RASA Program represents a systematic effort to study a number of the Nation's most important aquifer systems, which, in aggregate, underlie much of the country and which represent an important component of the Nation's total water supply. In general, the boundaries of these studies are identified by the hydrologic extent of each system and, accordingly, transcend the political subdivisions to which investigations have often arbitrarily been limited in the past. The broad objective for each study is to assemble geologic, hydrologic, and geochemical information, to analyze and develop an understanding of the system, and to develop predictive capabilities that will contribute to the effective management of the system. The use of computer simulation is an important element of the RASA studies to develop an understanding of the natural, undisturbed hydrologic system and the changes brought about in it by human activities and to provide a means of predicting the regional effects of future pumping or other stresses.The final interpretive results of the RASA Program are presented in a series of U.S. Geological Survey Professional Papers that describe the geology, hydrology, and geochemistry of each regional aquifer system. Each study within the RASA Program is assigned a single Professional Paper number beginning with Professional Paper 1400.

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Field tapes from a deep seismic survey for petroleum exploration were reprocessed in order to extract seismic information on shallow reflectors for use in ground-water exploration. Apotable aquifer in eastern Abu Dhabi occurs at depths less than 150 m. Field methods, acquisition parameters, and section processing were originally designed to enhance reflectors expected at depths up to 6,000 m. Seismic data collected from depths of about 110-330 mwere muted from the original sections, so that all seismic data concerning the aquifer were deleted from these sections. Reprocessing efforts concentrated on restoring information for the first second of seismic data.Aunique sequence of reprocessing parameters was established based on results from many experimental trials. Major enhancements to the resolution of shallow reflectors resulted from: (1) application of a 20-hertz, low-cut filter; (2) recomputation of static corrections to a datum nearer the land surface; (3) intensive velocity analyses; and (4) near-trace muting analyses. The number, resolution, and continuity of shallow reflectors were greatly enhanced on the reprocessed sections, as was the delineation of major faults and folds. The 33 reprocessed sections were instrumental in preparing a map of the major structural features Which affect the shallow aquifer system.Results from this study show that seIsmIC field tapes collected for deep petroleum exploration can also be reprocessed to explore for shallow ground water. 257

Introduction 1.1 Purpose and scope 2 1.2 Previous investigations 4 1.3 Methods of investigation 6 2.0 Hydrogeologic setting 2.1 Structural geology 10 2.2 Hydrogeologic relationships 14 2.3 Drift hydrogeology 16 2.4 Bedrock hydrogeology 18 2.5 Precipitation 22 3.0 Horizontal groundwater movement 3.1 Potentiometric surfaces 24 3.2 Undifferentiated drift aquifer 26 3.3 Upper Carbonate aquifer 30 3.4 St. Peter aquifer 34 3.5 Prairie du Chien-Jordan aquifer 38 3.6 Ironton-Galesville aquifer 42 3.7 Mount Simon-Hinckley aquifer 46 4.0 Vertical groundwater movement 50 References 54 Conversion factors 56 III GLOSSARY The geologic and hydrologic terms pertinent to this report are defined as follows: Alluvium sedimentary material deposited by modern rivers, including sediments laid down in river beds, flood plains, and in-stream lakes. Aquifer a formation, group of formations, or part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to wells or springs. Confining bed a body of material with low vertical permeability stratigraphically adjacent to one or more aquifers. Replaces the terms "aquiclude," "aquitard," and "aquifuge." Drift all deposits resulting from glacial activity. Equipotential line line connecting points of equal static head. (Head is a measure of the potential.) Evapotranspiration water withdrawn by evaporation from water surfaces and moist soil and by transpiration from plants. Ground water that part of subsurface water that is in the saturated zone. Groundwater divide a ridge in the potentiometric surface from which ground water represented by that surface moves away in both directions. Head, static the height above a standard datum of the surface of a column of water that can be supported by the static pressure at a given point. Hydraulic conductivity capacity of a rock to transmit water under pressure. It is the rate of flow of water at the prevailing kinematic viscosity passing through a unit section of area, measured at right angles to the direction of flow, under a unit hydraulic gradient. Ice contact stratified drift deposited in contact with melting glacier ice; includes eskers, kames, kame terraces, and features marked by numerous kettles, some being ice-block lakes. Karst a type of topography that is formed over limestone, dolomite, or gypsum by dissolution and that is characterized by closed depressions or sinkholes, caves, and underground drainage. Loess a sediment, commonly unstratified and unconsolidated, composed mainly of silt-size particles, ordinarily with accessory clay and sand, deposited primarily by the wind. Outwash sorted, stratified drift deposited beyond the ice front by melt-water streams. Paleozoic an era of geologic time that comprises the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian systems; commonly thought to have occurred from 225 to 570 million years ago. Potentiometric surface a surface that represents the static head of water in an aquifer; defined by the levels to which wat...