The U.S. Geological Survey (USGS) has characterized fractures, foliation, and fractured-rock groundwater flow penetrated by test boreholes in crystalline bedrock underlying Manhattan Island, New York County, New York since 1998. New test boreholes will be drilled on Roosevelt Island in New York County for a Cornell University geothermal test project. Cornell University is partnering with the USGS in a cooperative program to use advanced borehole geophysical methods to characterize the fractured-rock groundwater flow system on the southern end of Roosevelt Island, and compare it to the flow system on nearby Manhattan Island. The USGS will assess the hydrogeology of the area and determine the strike and dip of the transmissive fractures within the drilled boreholes. The data collected in this investigation will help to both define the complex hydrogeology of the area and assist Cornell University and others in the design of geothermal systems.
Objectives
The principal objectives of this investigation are to: 1) delineate the three-dimensional distribution and orientation of fractures and foliation in each borehole, 2) determine the total borehole and fracture-zone transmissivity in each borehole, 3) determine the hydraulic interconnection between boreholes, 4) determine the tidal variation in total hydraulic head of each borehole, and 5) compare the fracture, foliation, and transmissivity of the area with the nearby boreholes in Manhattan for a regional assessment.
Relevance and Benefits
As the Nation’s leading, integrated earth sciences agency, the USGS applies existing and emerging technologies to develop new methods of assessing geologic and hydrologic conditions. The proposed scope of work will advance knowledge of the fractured-rock groundwater flow system in the region.
The USGS will be applying expertise gained over ten years of borehole geophysical research with the New York City Department of Environmental Protection water tunnel test boreholes in this area. In addition to furthering knowledge of the regional hydrogeology, the geophysical methods that will be used may reduce construction costs and optimize effectiveness of the geothermal system by helping to understand where complexities might exist that would otherwise be unknown, including high permeability zones and unstable fracture zones. The geophysical and hydrologic data from these test boreholes can be used by others to determine the geothermal energy potential for this area.
Approach
The USGS cooperative study with Cornell University will delineate the fractured-rock groundwater flow system in part of Roosevelt Island, NY, and compare it with that characterized by USGS analyzed boreholes in the region. A total of three 6-inch boreholes will be drilled to a depth of 500 feet below land surface. The three boreholes will be about 50 feet apart to facilitate crosshole flowmeter and tomographic analysis. Digital water-level recorders will be placed in each of the boreholes to measure tidal influences of the adjacent East River and crosshole pumping influences at half hour intervals. The USGS will geophysically log each borehole using acoustic and optical televiewers, mechanical caliper, gamma, single-point resistance, short-medium-long normal resistivity, fluid temperature, fluid resistivity, fluid specific conductance, fluid pH, fluid redox, fluid dissolved oxygen, heat-pulse and electromagnetic flowmeter. One of three boreholes will be logged using borehole radar in a reflection mode where large fractures up to 50 feet away from the borehole can be imaged. Radar tomography will be completed to image weathered and transmissive fractures zones between the test boreholes and a 2D tomographic image will be attempted.
Project
Location by County
New
York (Manhattan) County (FIPS 36061), NY
