Delineation of Faults, Fractures, Foliation, and
Ground-Water-Flow Zones in Fractured-Rock, on the Southern Part of Manhattan,
New York, Through Use of Advanced Borehole-Geophysical Techniques
by Frederick Stumm, Anthony Chu, and Jack Monti, Jr.
U.S. GEOLOGICAL SURVEY
Open-File Report 2004-1232
ABSTRACT
Advanced borehole-geophysical techniques were used to
assess the geohydrology of crystalline bedrock in 20
boreholes on the southern part of Manhattan Island, N.Y., in
preparation for construction of a third water tunnel for New
York City. The borehole-logging techniques included natural
gamma, single-point resistance, short-normal resistivity,
mechanical and acoustic caliper, magnetic susceptibility,
borehole-fluid temperature and resistivity, borehole-fluid
specific conductance, dissolved oxygen, pH, redox, heatpulse
flowmeter (at selected boreholes), borehole deviation,
acoustic and optical televiewer, and borehole radar (at
selected boreholes). Hydraulic head and specific-capacity
test data were collected from 29 boreholes. The boreholes
penetrated gneiss, schist, and other crystalline bedrock that
has an overall southwest to northwest-dipping foliation.
Most of the fractures penetrated are nearly horizontal or have
moderate- to high-angle northwest or eastward dip azimuths.
Foliation dip within the potential tunnel-construction zone
is northwestward and southeastward in the proposed North
Water-Tunnel, northwestward to southwestward in the
proposed Midtown Water-Tunnel, and northwestward to
westward dipping in the proposed South Water-Tunnel.
Fracture population dip azimuths are variable. Heat-pulse
flowmeter logs obtained under pumping and nonpumping
(ambient) conditions, together with other geophysical logs,
indicate transmissive fracture zones in each borehole. The
60-megahertz directional borehole-radar logs delineated the
location and orientation of several radar reflectors that did not
intersect the projection of the borehole.
Fracture indexes range from 0.12 to 0.93 fractures per
foot of borehole. Analysis of specific-capacity tests from
each borehole indicated that transmissivity ranges from 2 to
459 feet squared per day; the highest transmissivity is at the
Midtown Water-Tunnel borehole (E35ST-D).
Citation: Stumm, Frederick, Chu, Anthony, and Monti, Jack Jr., 2004,
Delineation of Faults, Fractures, Foliation, and
Ground-Water-Flow Zones in Fractured-Rock, on the Southern Part of Manhattan,
New York, Through Use of Advanced Borehole-Geophysical Techniques:
U.S. Geological Survey Open-File Report 2004-1232, 212 p.
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