U.S. Department of the Interior WRIR 00-4276

U.S. Geological Survey December 2001

Use of Advanced Borehole Geophysical Techniques 

to Delineate Fractured-Rock Ground-Water Flow 

and Fractures Along Water-Tunnel Facilities in 

Northern Queens County, New York

Advanced borehole geophysical methods were 

used to assess the geohydrology of 

crystalline bedrock along the course of 

a new water tunnel for New York City. The 

logging methods include natural gamma, spontaneous 

potential, single-point resistance, mechanical and 

acoustic caliper, focused electromagnetic induction, 

electromagnetic resistivity, magnetic susceptibility, 

borehole-fluid temperature and conductance, differential 

temperature, heat-pulse flowmeter, acoustic televiewer, 

borehole deviation, optical televiewer, and borehole 

radar. Integrated interpretation of the geophysical logs 

from an 825-foot borehole (1) provided information 

on the extent, orientation, and structure (foliation and 

fractures) within the entire borehole, including intensely 

fractured intervals from which core recovery may be poor; 

(2) delineated transmissive fracture zones intersected by 

the borehole and provided estimates of their transmissivity 

and hydraulic head; and (3) enabled mapping of the 

location and orientation of structures at distances as much 

as 100 ft from the borehole. 

Analyses of the borehole-wall image and the 

geophysical logs from the borehole on Crescent Street, in 

northern Queens County, are presented here to illustrate 

the application of the methods. The borehole penetrates 

gneiss and other crystalline bedrock that has predominantly 

southeastward dipping foliation and nearly horizontal and 

southeastward-dipping fractures. The heat-pulse flowmeter 

logs obtained under pumping and nonpumping conditions, 

together with the other geophysical logs, indicate five 

transmissive fracture zones. More than 90 percent of the 

open-hole transmissivity is associated with a fracture zone 

272 feet BLS (below land surface). A transmissive zone 

at 787 feet BLS that consists of nearly parallel fractures 

lies within the projected tunnel path; here the hydraulic 

head is 12 to 15 feet lower than that of transmissive zones 

above the 315-foot depth. The 60-megahertz directional 

borehole radar logs indicate the location and orientation of 

two closely spaced radar reflectors that would intersect the 

projection of the borehole below its drilled depth. 

Subsequent excavation of the tunnel past the borehole 

allowed comparison of the log analysis with conditions 

observed in the tunnel. The tunnel was found to intersect 

gneiss with southeastward dipping foliation; many nearly 

horizontal fractures; and a southeastward dipping fracture 

zone whose location, character, and orientation was 

consistent with that of the mapped radar reflectors. The 

fracture zone produced inflow to the tunnel at a rate of 

50 to 100 gallons per minute. All conditions indicated by 

the logging methods were consistent with those observed 

within the tunnel.
2 

In 1970, the New York City Department of 

Environmental Protection (NYCDEP) began construction 

of a third tunnel to supply water to New York City in the 

event that one of the two existing tunnels should require 

repair. Test borings were drilled to identify the type of 

rock and its degree of fracturing at the proposed tunnel 

depths, but the cores were not oriented, and the coring 

process can cause new fractures and can alter the extent 

of existing fractures. Furthermore, neither the hydraulic 

characteristics of the fractures, nor the vertical deviation 

of the boreholes, were known.

In 1998, the U.S. Geological Survey (USGS), 

in cooperation with the NYCDEP, began a study 

to demonstrate the use of advanced borehole 

geophysical methods to provide a more 

comprehensive geologic and hydrologic assessment 

of the crystalline bedrock along the proposed tunnel 

routes. These techniques were used in the available 

boreholes to identify the bedrock lithology and major 

contacts; the location and orientation (true strike and 

dip) of fractures and foliation of the rock intersected 

by the borehole, and the hydraulic characteristics of 

transmissive fracture zones. This report describes the 

use of these methods in a borehole on Crescent Street 

in northern Queens County (fig. 1) and summarizes 

the geophysical interpretations.

Figure 1. Location of the Crescent Street borehole, in 

northern Queens County, N.Y.

INTRODUCTION

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• Natural-gamma (gamma) logs are a record of the total gamma radiation detected in a borehole (Keys, 1990) 

and are most commonly used for lithologic and stratigraphic correlation. Radioisotopes in bedrock minerals such 

as feldspar and mica are instrumental in correlating lithology. Clay minerals within fractures may be indicated by 

elevated gamma responses.

• Spontaneous-potential (SP) logs provide a record of the naturally occurring electrical potential difference along the 

borehole and can be used to identify changes in lithology, bed thickness, streaming potential due to water movement, 

and salinity of formation water under some geologic conditions (Keys, 1990).

• Single-point resistance (SPR) logs provide a measure of the electrical resistance of the rock or formation, 

and are used to obtain qualitative lithologic information with a depth resolution approximately equal to the 

borehole diameter.

• Caliper logs provide information on lithology and the location of major fractures. Mechanical calipers use springloaded arms to profile the surface of the borehole wall. Acoustic calipers calculate the distance to the borehole wall 

from the travel time of the acoustic signal emitted from an acoustic televiewer (ATV) to provide high-resolution, 

compass-oriented logs (Keys, 1990). 

• Focused electromagnetic induction (EM) logs provide a profile of formation electrical conductivity, from which 

ground water conductivity in situ can be inferred, with respect to depth. This technique uses an electromagnetic 

emitter coil to induce electrical eddy currents within a specified volume of the surrounding formation to generate a 

secondary electromagnetic field. The intensity of the secondary field received by the receiver coil is proportional to 

the formation’s conductivity (Keys, 1990; Serra, 1984; Keys and MacCary, 1971). 

• Magnetic-susceptibility (MAG) logs provide a record of the variations in magnetic minerals within the surrounding 

rock. Magnetite is the most common magnetic mineral, and local variations in its abundance may indicate lithologic 

contacts (McNeill and others, 1996). 

BOREHOLE-GEOPHYSICAL LOGGING METHODS AND APPLICATIONS

Borehole-geophysical logs collected in this investigation included natural gamma, spontaneous potential, 

single-point resistance, mechanical and acoustic caliper, focused electromagnetic induction, magnetic 

susceptibility, borehole-fluid temperature and conductance, differential temperature, heat-pulse flowmeter, 

acoustic televiewer, borehole deviation, optical televiewer, and borehole radar. These logs and their 

applications are described briefly below.
4 

• Temperature logs measure the temperature of the fluid column as a function of depth and, if a temperature contrast 

is present, can provide information on the movement of ground water through the borehole and the location of areas 

that produce or accept water (Keys, 1990). 

• Differential temperature logs depict the rate of change in temperature relative to depth, and help to indicate the 

location of areas of contrasting temperatures that are sometimes the result of inflow or outflow.

• Heat-pulse flowmeter logs measure vertical flow in boreholes using a thermal tracer, and can indicate which 

fractures are producing or accepting water in a borehole under pumping and nonpumping conditions (Keys, 1990). 

• Acoustic televiewer (ATV) uses a rotating transducer that transmits and receives high-frequency acoustic pulses to 

produce an image of the intensity of acoustic energy reflection and travel time. The ATV provides high-resolution 

information on the location and strike and dip of fractures within a borehole (Keys, 1990). The travel time of the 

acoustic signal is used to calculate distance to the borehole wall to provide an acoustic caliper log. 

• Borehole-deviation logs provide information on the borehole’s angle and direction of deviation from vertical. Most 

boreholes deviate from vertical; therefore, deviation logs must be obtained before three-dimensional information on 

fractures is interpreted (Keys, 1990). After processing, the resulting log indicates the true depth of the borehole, its 

distance from vertical, and the direction or azimuth of deviation.

• Optical televiewer (OTV) digitally records a high-resolution optical scan of the borehole wall that can be used to 

produce a “virtual” core. The virtual core is oriented to allow for visualization of major fractures as they were imaged 

within the borehole. Fractures, both opened and sealed, can be viewed in three-dimensional orientations. This system 

also allows measurement of true strike-and-dip orientation and fracture spacing. 

• Borehole radar, a 60-MHz directional radar unit (transmitter/receiver) that can be used in a single-hole reflectionmode to detect fracture zones and other structural features at distances to as much as 100 ft from the borehole 

in electrically resistive rocks. Directional radar logs can be used to calculate the orientation of features such as 

fractures or fracture zones. 

• Borehole fluid conductance logs of water in a borehole provide a record of the fluid’s electrical conductance 

to provide an indication of salinity, and may also be useful to indicate zones of inflow or outflow if fluid 

conductivity contrasts are present.
5

DELINEATION OF FRACTURES, AND DIRECTIONS OF GROUND-WATER FLOW

Fractures and foliation were delineated through the use of 

OTV, ATV, borehole radar, gamma, SP, SPR, and EM logs. 

Hydraulic characteristics of the bedrock were determined through 

the use of fluid-temperature, differential-temperature, fluid specificconductance, and heat-pulse flowmeter logs, in concert with waterlevel data.

GEOLOGIC CHARACTERISTICS OF BEDROCK

The Crescent Street borehole (fig. 1) was drilled to a depth of 

825 ft in February 1999 and cased with steel to a depth of 85 ft 

below land surface (BLS). The borehole has since been grouted. 

Land surface at the borehole was 25.56 ft above sea level. Depth 

to water at the borehole in February 1999 ranged from 17.36 to 

17.68 ft BLS. The borehole-deviation log indicated the borehole to 

have a true depth of 815.4 ft BLS. The borehole bottom appears to be 

only 2.7 ft (measured horizontally) off vertical at an azimuth N65oE. 

The regional foliation of rocks within the study area dips 

southeastward and contains several major faults (Baskerville, 1992). 

The Crescent Street borehole intersects bedrock of the Hartland 

Formation, of Middle Ordovician to Lower Cambrian age. Analysis 

of OTV and other logs, including core analysis by NYCDEP (C.A. 

Baskerville, Central Connecticut State University, written commun., 

1999) indicate that the bedrock consists of a sequence of gneiss and 

schist interlayered with amphibolite, granite, and mylonite.

The ATV, borehole radar, and OTV data indicate that the rock 

penetrated by the borehole is moderately fractured and contains 

several distinct zones of highly fractured rock (fig. 2). Five distinct 

fracture zones were delineated from the geophysical logs. The OTV 

data indicated a total of 232 fractures between 85 and 825 ft BLS. 

The ATV detected 84 of the 232 fractures delineated with the OTV. 

Plotting these data on an equal-area net as poles to planes (fig. 3) 

indicated two large fracture-population clusters—a major one and a 

minor one. The major cluster appears to be nearly horizontal, with a 

mean orientation of N42oE 16oNW (fig. 3); the minor cluster has a 

mean orientation of N39oE (plane strike) 59oSE (plane dip) (fig. 3). 

When fracture data were plotted with respect to depth of transmissive 

fractures, no clear pattern was detected.

Analysis of the 60-MHz directional radar data indicated two closely 

spaced strong radar reflectors that would intersect the borehole if 

it were drilled deeper (fig. 4). These are the strongest reflectors 

detected in this borehole and are interpreted as fractures that are 

infilled with either metallic minerals such as pyrite, or with water. 

Radar data indicate that these fractures extend more than 100 ft from 

the borehole and have orientations of N30oE 69oSE and N40oE 66oSE. 

This orientation indicates that these fractures, if water bearing, could 

pose a flooding hazard to equipment and personnel in the tunnel.

The OTV also detected the foliation of the 

metamorphic rocks penetrated by the borehole; 

208 measurements of foliation were made 

and their orientations plotted (fig. 3). Two 

clusters of data points can be seen; the major 

cluster (165 data points) has an orientation of 

N54oE 54oSE (fig. 3); the minor cluster has an 

orientation of N42oE 62oNW. Vertical variation 

in foliation and orientation is shown in tadpole 

plots (fig. 5). 

 The foliation and fracture data at depths of 

700 to 825 ft BLS were plotted on a stereo 

net (not shown). The foliation data (55 data 

points) produced a single cluster with a mean 

The 23-ft. diameter tunnel at the transmissive 

fracture zone. Note the roof instability and 

plastic sheeting used to divert ground-water 

seepage. 
6 

strike and dip of N45oE 60oSE. A total of 43 fracture-data 

points produced one major population cluster and several 

minor surrounding clusters. The majority of fractures 

have a mean strike and dip of N84oW 5oSW and are 

nearly horizontal.

The gamma log indicates some variation in clay 

and mica-mineral content of the rock penetrated by the 

borehole (fig. 5). Three distinct changes in the gamma 

logs were indicated—at depths of 169, from 471 to 485, 

and from 495 to 500 ft BLS, and corresponded with 

observations in the OTV log. An increase in gamma 

radiation at 169 ft BLS corresponds to clay minerals within 

a transmissive fracture. A decrease in gamma radiation 

in the zone from 471 to 485 ft corresponds to a thick 

sequence of amphibolite. Just below this zone, from 495 

to 500 ft, an increase in gamma radiation may correspond 

to clay minerals within a fracture at this depth. In general, 

the gamma log of this borehole is fairly uniform and shows 

only minor variations. The spontaneous potential (SP) log 

shows several peaks or increases in voltage (possibly from 

streaming potentials) that correspond to fractures at 91, 95, 

169, 272, and 384 ft, and from 495 to 500 ft BLS (fig. 5).

When compared with the OTV data, the SPR log 

(fig. 5) indicates detailed variations that correspond to 

changes in rock mineralogy and conductive material (clay 

or pyrite minerals) within fracture zones. The electrical 

resistance of the rock shows a greater variability above 

about 500 ft BLS than below this depth (fig. 5), and 

the magnetic-susceptibility log indicates a corresponding 

increase in magnetite above about 500 ft; in contrast, the area 

below this depth indicates almost no variation in magnetic 

susceptibility. The SPR log indicates decreases in resistance 

at 91, 95, 169, 272, 384, 500, and 787 ft BLS. These 

decreases correspond to significant clay or mineralized 

Figure 2. Acoustic caliper, acoustic televiewer, and optical televiewer images of fractures in the 

Crescent Street borehole, in northern Queens County, N.Y.

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fracture zones. Similar increases in electrical conductivity or 

decreases in resistivity are indicated in the EM-conductivity 

log (fig. 5). Conductivity increases gradually to a depth of 

272 ft BLS, below which it then gradually decreases with 

depth; this reversal suggests a change in rock composition. 

Tadpole plots of the fractures and foliation measured 

from the ATV and OTV logs indicate variations in the 

dip angle and dip azimuth of these fractures with depth. 

Foliation has dip angles from 30 to 80 ̊ toward the southeast. 

In general, foliation dip angles increase from 60 to 80 ̊ 

to the southeast at the tunnel depth. The tadpole plot of 

fractures indicate that the bedrock is moderately fractured 

with several zones that are highly fractured. The upper 

500 ft of bedrock has a significantly higher density of 

fractures than the rock below this depth. The dip azimuth and 

dip angle of fractures had no general pattern, with fracture 

dip angles ranging from sub-horizontal to nearly vertical. 

HYDRAULIC CHARACTERISTICS OF BEDROCK

Ground-water flow may cause erratic and abnormal 

temperature gradients near land surface; thus, 

temperature logs may indicate a decrease in temperature 

with depth—the inverse of the normal geothermal 

gradient (Keys, 1990; Williams and Conger, 1990). 

The fluid-temperature and differential-temperature logs 

of the borehole indicate several changes in water 

temperature under non-pumped (ambient) conditions 

(fig. 6). The fluid-temperature log indicates watertemperature changes at 91 to 95 ft, at 272 ft, at 

315 ft, and at 787 ft BLS. As discussed further on, these 

changes correspond to fractures that either accept water 

from, or yield water to the borehole. The fluid specific 

conductance log indicates changes at 91 to 95 ft, at 

169 ft, at 272 ft, and from 315 to 321 ft BLS under 

Figure 3. Equal-area net of A. fractures, and B. foliation from 85 to 825 ft below land surface from optical televiewer 

analysis of the Crescent Street borehole, in northern Queens County, N.Y.

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W E

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population

Major

population

Major

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Minor

cluster

Number of foliations: 208

Number of fractures: 232

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8 

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Figure 4. Directional 60-MHz radar image of the Crescent Street borehole, in 

northern Queens County, N.Y.

ambient conditions. Specific conductance ranged from 

about 700 μS/cm (microsiemens per centimeter) near 

the water surface at 90 ft BLS to about 580 μS/cm at 

the bottom of the hole (fig. 6). Sudden shifts in the 

water-temperature log or the specific-conductance log 

are indicative of ground water entering or leaving the 

borehole through fractures.

Ground-water temperatures were highest (62 ̊F) at the 

water surface and decreased with depth to about 53 ̊F 

at the 500-ft depth (fig. 6). Temperature decreased from 

about 58 ̊F to about 55 ̊F between 90 and 272 ft BLS, 

and a significant temperature change from 55 ̊F to 54 ̊F 

was recorded at 272 ft BLS. These temperature changes 

are probably due to ground-water inflow from several 

fracture zones. Below 500 ft, the water temperature 

increased gradually with depth, except at about 787 ft, 

where it abruptly increased from about 54 ̊F to about 

55 ̊F (fig. 6). The differential temperature log indicates 

a variation in fluid temperature with depth as rapid 

departures from a vertical line. 

Ground-water levels were measured during pumping 

and nonpumping conditions, and heat-pulse flowmeter 

logs were obtained to quantify hydraulically transmissive 

fractures at discrete depths within the borehole during 
9

pumping and nonpumping conditions (fig. 6). A 

submersible pump was used to lower the head in the 

borehole. The major hydraulically transmissive fracture 

zones were delineated, from several types of logs, at 

depths of 91 to 95 ft, 169 ft, 272 ft, 315 to 321 ft, and 

787 ft BLS.

Water levels, pumping rate, and the temperature and 

specific conductance of the pumped water were monitored 

during the heat-pulse flowmeter logging. The change in 

water levels over the duration of pumping was used to 

calculate the specific capacity of the open borehole. The 

water level decreased 3.57 ft over a 2.95-hour period of 

pumping at an average rate of 4.5 gal/min. The specific 

capacity for the entire borehole, based on these values, was 

1.26 (gal/min)/ft. The specific capacity data were analyzed 

with a program developed by Bradbury and Rothschild 

(1985) that estimated the range in transmissivity for the 

entire borehole to be 350 ft2/d to 420 ft2/d. 

The heat-pulse flowmeter log indicates that (1) all 

significant flow into the borehole is occurring above 

the 289-ft depth (fig. 6), and (2) fractures within the 

tunnel depth (764 to 787 ft BLS) are accepting water 

from the borehole at a rate of about 0.25 gal/min 

under ambient conditions. The heat-pulse flowmeter 

Figure 5. Suite of geophysical logs used to interpret geologic characteristics at the Crescent Street borehole, 

in northern Queens County, N.Y.

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data indicate a slight downward flow component under 

ambient conditions from below the casing to 787 ft BLS 

(fig. 6). Measurable changes in flow were noted in the 

transmissive zones at 272 ft and at 787 to 790 ft. The 

increase in downward flow from 255 to 279 ft indicates 

that one or more of the fractures at 272 ft are contributing 

water to the borehole. The decrease in downward flow 

from 88 to 98 ft and from 760 to 802 ft indicates that 

fractures at 91 and 95 ft and at 787 to 790 ft were 

accepting water under ambient conditions. Downward 

flow was noted below about 92 ft, with a small increase 

between 272 and 316 ft; all flow exited at about 787 ft 

(fig. 6). 

Under pumping conditions, the heat-pulse flowmeter 

detected upward flow from 68 to 265 ft BLS and at 

802 ft BLS (fig. 6). Downward flow was detected from 

315 to 760 ft. The reversal from upflow to downflow 

between 265 and 315 ft BLS suggests that water is 

entering the borehole from the fracture zone at 272 ft 

BLS. In contrast, the fracture zone at 787 to 790 ft BLS 

shows a reversal from downflow to upflow, indicating 

that the 787 to 790 ft BLS zone is taking water from the 

borehole (fig. 6). A nominal weak, upward flow response 

below 800 ft BLS is attributed to the buoyancy effect of 

a thermal tracer on the flowmeter response (Hess, 1986) 

and is interpreted as no measurable flow. 

The flowmeter logs were analyzed through the 

techniques of Paillet (1998; 2000), whereby differences 

between flow values at adjacent stations are attributed 

to measurement scatter and a possible net difference 

in borehole flow. Therefore, flow-log interpretation 

involves identification of the relative amounts of inflow 

Figure 6. Suite of geophysical logs used to interpret hydraulic characteristics of bedrock at the Crescent 

Street borehole, in northern Queens County, N.Y. 

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or outflow occurring at specific depth intervals. 

Inflow or outflow was interpreted at four different 

depth intervals, each of which coincides with 

a fracture, or sets of fractures. The effects 

of hydraulic-head differences between zones can 

be eliminated by subtracting the inflows under 

nonpumping conditions from the inflow under 

pumping conditions, where outflow is given as 

negative inflow, in accordance with the technique 

of Molz and others (1989). The result of the 

subtraction of inflows indicates that almost all of 

the transmissivity is associated with the fracture 

zone at 272 ft BLS. 

An alternative approach is to use a flow-modeling 

technique described by Paillet (2000), which involves 

inverting the two flow profiles and the measured 

drawdown under pumping conditions to give 

quantitative estimates of the transmissivity and relative 

hydraulic head of each transmissive zone. The results 

of this method indicate a 12- to 15-ft hydraulic-head 

difference between the fracture zones at 315 ft BLS 

and above, and the fracture zone at 787 ft BLS. 

The ambient flow is weak because the outlet fracture 

zone at 787 ft BLS has relatively low transmissivity. 

Pumping failed to reverse the ambient flow completely 

because the fracture zone at 272 ft is relatively 

transmissive, so that open-borehole drawdown is only 

a fraction of the hydraulic-head difference between the 

various fractures. 

GEOLOGIC AND HYDRAULIC CONDITIONS 

OBSERVED IN THE TUNNEL NEAR THE 

BOREHOLE

After the completion of the geophysical logging 

and log analysis, the tunnel-boring machine 

excavated past the Crescent Street borehole. 

The 23-ft diameter tunnel penetrated gneiss with 

southeastward dipping foliation and many nearly 

horizontal fractures. These fractures result in weak 

ceiling conditions in the tunnel—consistent with the 

prediction of a falling-rock hazard in that part of the 

tunnel identified from a plot of the mean orientations 

of the fractures and foliation delineated from the 

OTV log with respect to the tunnel. The tunnel 

also intersected a transmissive fracture zone whose 

location, character, and orientation were consistent 

with those of the mapped radar reflectors. The 

fracture zone, which contained some pyrite infillings, 

produced 50 to 100 gal/min of inflow to the tunnel. 

SUMMARY AND CONCLUSIONS

The Crescent Street borehole was drilled along the course of 

a new water tunnel through northern Queens County to provide 

cores and a site for the collection of geophysical logs. The 

geophysical logs provided data on the deviation of the borehole 

from vertical, the location and orientation (strike and dip) 

of fractures, the orientation of rock foliation, locations of 

contacts between rock units of differing types, and locations 

of water-producing fractures; they also provided information 

on the rocks’ magnetic susceptibility, electrical resistivity and 

resistance, spontaneous potential; the direction and quantity 

of ground-water flow, specific conductance and temperature 

of ground water, a profile of the borehole diameter, and the 

identification and orientation of significant fractures beyond the 

borehole.

The surrounding rocks are moderately fractured and contain 

several zones of extensive fracturing. The acoustic and optical 

televiewer data indicate a total of 232 fractures. Equal-area-net 

analysis of these fractures indicated the major cluster to have 

an orientation of N42 ̊E16 ̊NW and the minor cluster to have 

an orientation of N39 ̊E59 ̊SE.

Analysis of the 60-MHz directional radar indicates two 

closely spaced strong radar reflectors, which are probably 

fractures that extend beyond 100 ft from the borehole 

and would intersect the borehole if it were deeper. Radar 

analysis indicates these fractures to have an orientation of 

N30 ̊E69 ̊E and N40 ̊E66 ̊SE. This orientation indicates that 

these fractures, if water bearing, could pose a flooding hazard 

to equipment and personnel in the tunnel.

The foliation of rocks penetrated by the borehole was 

grouped into two large population clusters. The major cluster 

had a mean orientation of N54 ̊E54 ̊SW, and the minor cluster 

had a mean orientation of N42 ̊E62 ̊NW. Plotting the mean 

orientations of the fractures and foliation at the depth of the 

tunnel in three dimensions with respect to the tunnel indicates a 

potential for a falling-rock hazard in the tunnel. In addition, the 

large number of nearly horizontal fractures at this depth suggest 

a potential for rock weakness at the tunnel ceiling. 

The gamma, SP, SPR, EM, conductivity, resistivity, fluidtemperature, differential temperature, and specific conductance 

logs all detected some of the fracture zones. The magneticsusceptibility log indicated changes in magnetite content of the 

rock within the borehole.

Five transmissive fracture zones were delineated by 

correlating inflow zones interpreted from heat-pulse flowmeter 

logs with major fracture zones indicated by other geophysical 

logs. Modeling of the flow-log response indicates that more 

than 90 percent of the open-hole transmissivity is associated 

with the fracture zone at 272 ft BLS. These results indicate a 

12- to 15-ft hydraulic head difference at the time of logging 
Baskerville, C.A., 1992, Bedrock and engineering geologic 

maps of Bronx County and parts of New York and 

Queens Counties, New York: U.S. Geological Survey 

Miscellaneous Investigations Series, map I-2003, 2 

sheets, scale 1:24,000.

Bradbury, K.R., and Rothschild, E.R., 1985, A 

computerized technique for estimating the hydraulic 

conductivity of aquifers from specific-capacity data; 

Groundwater, v. 23, no. 2, p. 240-246. 

Hess, A.E., 1986, Identifying hydraulically conductive 

fractures with a slow-velocity borehole flowmeter: 

Canadian Geotechnical Journal, v. 23, no. 1, p. 69-78.

Keys, W.S., and MacCary, L.M., 1971, Application of 

borehole geophysics to water-resources investigations: 

U.S. Geological Survey Techniques of Water Resources 

Investigations, book 2, chap. E1, 126 p.

Keys, W.S., 1990, Borehole geophysics applied to 

water-resources investigations: U.S. Geological Survey 

Techniques of Water Resources Investigations, book 2, 

chap. E2, 150 p.

Molz, F.J., Morin, R.H., Hess, A.E., Melville, J.G., 

and Guven, Oktay, 1989, The impeller meter for 

measuring aquifer permeability variations—evaluation 

and comparison with other tests: Water Resources 

Research, v. 25, no. 7, p. 1677-1683. 

McNeill, J.D, Hunter, J.A., and Bosner, M., 1996, 

Application of a borehole induction magnetic 

susceptibility logger to shallow lithological mapping: 

Journal of Environmental and Engineering Geophysics, 

v. 0, no. 2, p. 77-90.

Paillet, F. L., 1998, Flow modeling and permeability 

estimation using borehole flow logs in heterogeneous 

fractured formations: Water Resources Research, v. 34, 

no. 5, p. 997-1010.

Paillet, F. L., 2000, A field technique for estimating aquifer 

parameters using flow log data: Ground Water, v. 38, 

no. 4, p. 510-521. 

Serra, Oberto, 1984, Fundamentals of well-log 

interpretation: New York, Elsevier, 423 p.

Williams, J.H., and Conger, R.W., 1990, Preliminary 

delineation of contaminated water-bearing fractures 

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(February 1999) between the fracture zones at 315 ft and 

higher and the fracture zone at 787 ft—the depth of the 

projected tunnel interval. 

The geophysical logging of the boreholes provided a 

unique opportunity for comparison of the cores with the 

geohydrologic conditions along the tunnel’s course. The 

geohydrologic conditions encountered during subsequent 

excavation of the tunnel near the borehole were consistent 

with those interpreted from the geophysical logs. 

This report and additional earth science information can be found on the World Wide Web at http://ny.usgs.gov

Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver, CO 80225

For additional information contact:

Subdistrict Chief

U.S. Geological Survey

2045 Route 112 

Coram, NY 11727

REFERENCES CITED

by Frederick Stumm, Anthony Chu, Andrew D. Lange, Frederick L. Paillet, John H. Williams, and John W. Lane, Jr.