Delineation of fractures, foliation, and groundwater-flow zones of the bedrock at the Harlem River Tunnel in northern New York County, New York

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Advanced borehole-geophysical methods were used to investigate the hydrogeology of the crystalline bedrock in 36 boreholes on the northernmost part of New York County, New York, for the construction of a utilities tunnel beneath the Harlem River. The borehole-logging techniques were used to delineate bedrock fractures, foliation, and groundwater-flow zones in test boreholes at the site. Fracture indexes of the deep boreholes ranged from 0.65 to 0.76 per foot. Most of the fracture populations had either northwest to southwest or east to southeast dip azimuths with moderate dip angles. The mean foliation dip azimuth ranged from 100º to 124º southeast with dip angles of 52º to 60º. Groundwater appears to flow through an interconnected network of fractures that are affected by tidal variations from the nearby Harlem River and tunnel construction dewatering operations. The transmissivities of the 3 boreholes tested (USGS-1, USGS-3, and USGS-4), calculated from specific capacity data, were 2, 48, and 30 feet squared per day (ft2/d), respectively. The highest transmissivities were observed in wells north and west of the secant ring. Three borehole-radar velocity tomograms were collected. In the USGS-1 and USGS-4 velocity tomogram there are two areas of low radar velocity. The first is at the top of the tomogram and runs from 105 ft below land surface (BLS) at USGS-4 and extends to 125 ft BLS at USGS-1, the second area is centered at a depth of 150 ft BLS at USGS-1 and 135 to 150 ft BLS at USGS-4. Field measurements of specific conductance of 14 boreholes under ambient conditions at the site indicate an increase in conductivity toward the southwest part of the site (nearest the Harlem River). Specific conductance ranged from 107 microsiemens per centimeter (μS/cm) (borehole 63C) to 11,000 μS/cm (borehole 79B). The secant boreholes had the highest specific conductance.

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Publication type Conference Paper
Publication Subtype Conference Paper
Title Delineation of fractures, foliation, and groundwater-flow zones of the bedrock at the Harlem River Tunnel in northern New York County, New York
Year Published 2013
Language English
Contributing office(s) New York Water Science Center
Description 12 p.
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title 20th Conference on the geology of Long Island and metropolitan New York
Conference Title 20th Conference on the Geology of Long Island and Metropolitan New York
Conference Location Stony Brook, New York, United States
Conference Date April 13, 2013
Country United States
State New York
Other Geospatial Harlem River Tunnel
Online Only (Y/N) N
Additional Online Files (Y/N) N
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