Geohydrology and Potential Water-Supply Development on Bumkin, Gallops, Georges, Grape, Lovell, and Peddocks Islands, Eastern Massachusetts By JOHN P. MASTERSON, BYRON D. STONE, and RICK R. RENDIGS U.S. Geological Survey Open-File Report 96-117 Prepared in cooperation with the MASSACHUSETTS DEPARTMENT OF ENVIRONMENTAL MANAGEMENT, OFFICE OF WATER RESOURCES and the DIVISION OF NATURAL RESOURCES Marlborough, Massachusetts 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: Chief, Massachusetts-Rhode Island District U.S. Geological Survey U.S. Geological Survey Earth Science Information Center Water Resources Division Open-File Reports Section 28 Lord Road, Suite 280 Box 25286, MS 517 Marlborough, MA 01752 Denver Federal Center Denver, CO 80225 CONTENTS Abstract................................................................................................................................................................................. 1 Introduction........................................................................................................................................................................... 3 Physiographic Setting of the Six Harbor Islands .................................................................................................................. 4 Bumkin Island............................................................................................................................................................. 4 Gallops Island.............................................................................................................................................................. 4 Georges Island.. .......................................................................................................................................................... 5 Grape Island................................................................................................................................................................ 5 Lovell Island................................................................................................................................................................ 5 Peddocks Island........................................................................_ 5 Geohydrology........................................................................................................................................................................ 6 Geologic Setting.......................................................................................................................................................... 6 Depositional History of Geologic Units...................................................................................................................... 10 Hydrologic System...................................................................................................................................................... 11 Hydraulic Properties.................................................................................................................................................... 12 Flow-Model Analysis.................................................................................................................................................. 13 Potential Water-Supply Development .................................................................................................................................. 15 Summary and Conclusions ................................................................................................................................................... 21 References Cited .......................................................................^ 21 FIGURES 1. Map showing location of the Boston Harbor Islands, eastern Massachusetts............................................................ 3 2. Map showing surficial geology of the Boston Harbor Islands, eastern Massachusetts.............................................. 7 3. Map showing topography of Governors Island, eastern Massachusetts..................................................................... 9 4. Hydrogeologic sections of Governors Island, eastern Massachusetts........................................................................ 10 5. Diagram showing generalized section of a drumlin island and simulated water table and flow paths..................... 14 6. Maps showing contact between till and beach deposits and zones of potential water-supply sources for each of the six Boston Harbor Islands, eastern Massachusetts............................................................................. 15 CONVERSION FACTORS AND VERTICAL DATUM CONVERSION FACTORS _______Multiply______________By_____________To obtain____ acre 4,047 square meter foot (ft) 0.3048 meter foot per day (ft/d) 0.3048 meter per day mile (mi) 1.609 kilometer square mile (mi2)_____________2.590______________square kilometer In this report the unit of hydraulic conductivity is foot per day (ft/d), the mathematically reduced form of cubic foot per day per square foot [ft3/d)/ft2]. VERTICAL DATUM Sea Level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929-a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929. Contents Geohydrology and Potential Water-Supply Development on Bumkin, Gallops, Georges, Grape, Lovell, and Peddocks Islands, Eastern Massachusetts By John P. Masterson, Byron D. Stone, and Rick R. Rendigs Abstract large boulders. The stratified deposit." primarily consist of sorted and layered sand and gravel An investigation of the geohydrology and that accumulated and formed the berches and of the potential for water-supply development on tombolos of the harbor islands. Thes*. deposits several of the Boston Harbor Islands, eastern overlie the till at altitudes generally less than 10 Massachusetts, was conducted to evaluate the feet above sea level. possibility of developing a permanent small- A cross-sectional, ground-water-flow capacity water supply to support recreational model was developed to estimate depth to the activities, such as camping, hiking, and swim­ water table for a hypothetical drumlin-island ming. The Boston Harbor Islands, including flow system, which was assumed to be represen­ Bumkin, Gallops, Georges, Grape, Lovell, and tative of the drumlin islands in Boston Harbor. Peddocks Islands are part of a larger group of Areas were identified in each island flow system glacially deposited drumlins, which are com­ with the greatest potential for small-capacity posed of thick, dense, homogeneous till in their water-supply development based on the model- core that are overlain by a thin layer of stratified- calculated depth to water and surficial geology beach deposits. The surficial materials overlie a of the islands. Model-calculated dep*h to water weathered zone of the metasedimentary Cam­ estimates were used because of the lack of avail­ bridge Argillite in the Boston Harbor area and able hydrologic data for the islands. Model were deposited by continental ice sheets that results indicate that the simulated depth to water covered New England twice during the late is less than 20 feet within 240 feet from the Pleistocene Epoch, and by near-shore processes shore of the hypothetical drumlin-island flow in the Holocene Epoch. The thickness of these system. This area on the topographic maps of the materials range from less than 1 to about 300 six Boston Harbor Islands roughly coincides feet where present. with the high transmissivity zones of stratified- The till was deposited by glacial ice and is beach deposits and weathered till on the lower characterized as an unsorted matrix of sand, silt, slopes of the drumlins where ground-water dis­ and clay with variable amounts of stones and charge and surface and subsurface runoff occurs. Abstract 1 INTRODUCTION The Massachusetts Department of Environmen­ tal Management (DEM) and the Metropolitan District The islands in Boston Harbor are in a lowland Commission (MDC) currently oversee the operation estuary in the western part of Massachusetts Bay, and maintenance of the State parks on several of the 31 which constitutes the major commercial waterway for Harbor Islands. These agencies are currently evaluat­ the metropolitan Boston area (fig. 1). The harbor is ing the possibility of developing a permanent small- about 50 mi2 in area and is dotted with 31 islands that capacity water supply to support recreational activities collectively cover about 1,200 acres of land. The such as camping, hiking, and swimming for each of the islands range in size from less than 1 acre to as large as islands, including Bumkin, Gallops, Gorges, Grape, 214 acres. Lovell, and Peddocks. 71*00' 70*55' 42*30' 70*W 42*20' 43*N - 0 INMITKAL tULtt I i S i 'i i ' 0 S KLOMCTCM Bas« from U.S. Geological Survey Boston, MaMachuMtts, 1956 (photorwlMd 1970) 1:250,000 seal* Figure 1. Location of the Boston Harbor Islands, eastern Massachusetts. (Modified from Rendigs and Olc'ale, 1990.) Introduction 3 The landforms that dominate these islands are the islands producing steep, bare slopes and cliffs on part of a larger group of glacially deposited, elongated the sides of the drumlins. Modern beach deposits have asymmetrical hills known as dmmlins. The drumlins of accumulated at the ends of