Hydrogeology and Water Resources of Block Island, Rhode Island By ANNE I. VEEGER, University of Rhode Island, Kingston, Rhode Island and HERBERT E. JOHNSTON, U.S. Geological Survey, with a section on Geology By BYRON D. STONE, U.S. Geological Survey, and LESLIE A. SIRKIN, Adelphi University, Garden City, New York U.S. Geological Survey Water-Resources Investigations Report 94-4096 Prepared in cooperation with the TOWN OF NEW SHOREHAM, RHODE ISLAND Providence, Rhode Island 1996 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY GORDON P. EATON, Director For additional information write to: Copies of this report can be purchased from: Subdistrict Chief U.S. Geological Survey Massachusetts - Rhode Island District Earth Science Information Center U.S. Geological Survey Open-File Reports Section Water Resources Division Box 25286, MS 517 275 Promenade Street, Suite 150 Denver Federal Center Providence, Rl 02908 Denver, CO 80225 CONTENTS Abstract.............................................................................................................................................................................. 1 Introduction.......................................................^^ 2 Purpose and Scope.................................................................................................................................................. 2 Previous Investigations........................................................................................................................................... 3 Well, Spring, and Test-Hole Numbering System.................................................................................................... 3 Acknowledgments.................................................................................................................................................. 3 Study Area.............................................................................................................................................................^ 3 Climate.................................................................................................................................................................... 3 Topography and Drainage....................................................................................................................................... 6 Land Use and Population........................................................................................................................................ 7 Water Use.............................................................................................................................................. 8 Hydrogeology..................................................................................................................................................^ 8 Geology by Byron D. Stone and Leslie A. Sirkin.................................................................................................... 9 Overview of the Stratigraphy and Origin of the Moraine on Block Island................................................. 9 Regional Geologic Setting .......................................................................................................................... 10 Stratigraphy................................................................................................................................................. 11 Subsurface Materials ....................................................................................................................... 11 Bedrock............................................................................................................................... 11 Cretaceous Sediments......................................................................................................... 11 Surficial Materials............................................................................................................................ 14 Pleistocene (pre-Late Wisconsinan) Sediments.................................................................. 14 Pleistocene (Late Wisconsinan) Sediments, Lower Moraine Zone .................................... 14 Pleistocene (Late Wisconsinan) Sediments, Upper Moraine Zone..................................... 14 Age, Deposition, and Postglacial Modification of the Moraine.................................................................. 23 Surface-Water System............................................................................................................................................. 23 Ground-Water System............................................................................................................................................. 24 Hydraulic Characteristics............................................................................................................................ 25 Water Levels................................................................................................................................................ 27 Recharge and Discharge.............................................................................................................................. 32 Flow........................................................._ 33 Water Resources................................................................................................................................................................. 36 Water Quality.......................................................................................................................................................... 36 Precipitation................................................................................................................................................ 36 Surface Water.............................................................................................................................................. 37 Ground Water.............................................................................................................................................. 38 Physical Properties and Major Chemical Constituents.................................................................... 38 pH........................................................................................................................................ 39 Specific Conductance.......................................................................................................... 39 Sodium and Chloride........................................................................................................... 40 Nitrate.................................................................................................................................. 43 Iron and Manganese............................................................................................................ 43 Geologic Controls on Iron Distribution .............................................................................. 44 Trace Elements.................................................................................................................... 46 Organic Chemicals.............................................................................................................. 46 Temporal Trends.............................................................................................................................. 46 Potential Sources of Contamination ................................................................................................ 48 Saltwater Intrusion.............................................................................................................. 48 Septic Systems .................................................................................................................... 48 Underground Storage Tanks................................................................................................ 48 Landfill................................................................................................................................ 49 Contents III Water Resources Continued Water Availability................................................................................................................................................... 49 Surface Water.............................................................................................................................................. 49 Sands Pond....................................................................................................................................... 49 Fresh Pond....................................................................................................................................... 53 Ground Water.............................................................................................................................................. 54 Development of Future Public Water Supplies....................................................................................................... 60 Summary and Conclusions................................................................................................................................................. 60 References Cited ................................................................................................................................................................ 62 Glossary.............................................................................................................................................................................