Cover. Sediment-core drilling site near Bayside, Mathews County, Virginia (borehole local number 60G 5-7). View is southward overlooking tidal wetland to Chesapeake Bay on the horizon. During summer 2001, continuous core was obtained of sediments filling the 35-million-year­ old Chesapeake Bay impact crater, overlying post-impact sediment, and underlying crystalline bedrock at an altitude of –2,322 feet. The continuous wire-line hydraulic rotary coring rig shown was operated by staff of the U.S. Geological Survey (USGS) Water Discipline Drilling Project in cooperation with the USGS Eastern Earth Surface Processes Team, the Virginia Department of Environmental Quality, and the Hampton Roads Planning District Commission. The Virginia Coastal Plain Hydrogeologic Framework By E. Randolph McFarland and T. Scott Bruce Prepared in cooperation with the Virginia Department of Environmental Quality Professional Paper 1731 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia: 2006 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: McFarland, E.R., and Bruce, T.S., 2006, The Virginia Coastal Plain Hydrogeologic Framework: U.S. Geological Survey Professional Paper 1731, 118 p., 25 pls. (available online at http://pubs.water.usgs.gov/pp1731/) Library of Congress Cataloging-in-Publication Data McFarland, E. Randolph. The Virginia coastal plain hydrogeologic framework / by E. Randolph McFarland and T. Scott Bruce. -- lst ed. p. cm. -- (Professional paper ; 1731) Includes bibliographical references and index. ISBN 1-4113-1065-9 (alk. paper) 1. Hydrogeology--Virginia. 2. Groundwater flow--Virginia. 3. Aquifers--Virginia I. Bruce, T. Scott, 1960- II. Title. GB1025.V8M34 2006 551.4909755--dc22 2006026537 iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................2 Purpose and Scope ..............................................................................................................................2 Description of Study Area ...................................................................................................................4 Geologic Setting ...........................................................................................................................4 Ground-Water Conditions ...........................................................................................................8 Methods of Investigation .....................................................................................................................8 Borehole Geophysical-Log Network ........................................................................................9 Borehole-Data Quality ..............................................................................................................10 Hydrogeologic Framework .........................................................................................................................14 Conceptual Development ..................................................................................................................14 Previous Investigations ............................................................................................................14 Pioneering Investigations by D.J. Cederstrom ............................................................14 Geologic Refinement ........................................................................................................14 Regional Aquifer-System Analysis .................................................................................15 Recent Hydrogeologic Advances ..................................................................................16 Chesapeake Bay Impact Crater and the James River Structural Zone ...................16 Stratigraphic and Structural Evolution ...................................................................................16 Formation of the Virginia Coastal Plain .........................................................................17 Cretaceous Period ............................................................................................................19 Tertiary Period ...................................................................................................................20 Late Paleocene and Early to Middle Eocene Epochs ........................................20 Late Eocene Epoch – Chesapeake Bay Impact Crater ......................................21 Oligocene, Miocene, and Pliocene Epochs ........................................................22 Quaternary Period ............................................................................................................23 Interpretive Analysis .................................................................................................................24 Hydrogeologic-Unit Classification .................................................................................25 Regional Correlation .........................................................................................................26 Limitations ..........................................................................................................................28 Hydrogeologic Units ...........................................................................................................................29 Potomac Aquifer ........................................................................................................................29 Geologic Relations ............................................................................................................31 Structural Configuration ..................................................................................................32 Recognition ........................................................................................................................33 Hydrologic Aspects ..........................................................................................................34 Potomac Confining Zone ..........................................................................................................35 Geologic Relations ............................................................................................................35 Structural Configuration ..................................................................................................37 Recognition ........................................................................................................................38 Hydrologic Aspects ..........................................................................................................38 Upper Cenomanian Confining Unit ..........................................................................................38 Geologic Relations ............................................................................................................40 Structural Configuration ..................................................................................................40 iv Recognition ........................................................................................................................41 Hydrologic Aspects ..........................................................................................................41 Virginia Beach Aquifer ..............................................................................................................42 Geologic Relations ............................................................................................................42 Structural Configuration ..................................................................................................42 Recognition ........................................................................................................................42 Hydrologic Aspects ..........................................................................................................44 Virginia Beach Confining Zone ................................................................................................44 Geologic Relations ............................................................................................................44 Structural Configuration ..................................................................................................46 Recognition ........................................................................................................................46 Hydrologic Aspects ..........................................................................................................47 Peedee Aquifer