Locations of Fracture Intervals Inferred From
Borehole Logs of Eight Wells at the
Holton Circle Super-fund Site,
Londonderry, New Hampshire
U.S. GEOLOGICAL SURVEY
Open-File Report 92-647
Prepared in cooperation with the
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASTE MANAGEMENT DIVISION, REGION I
-------
950R93005
LOCATIONS OF FRACTURE INTERVALS INFERRED FROM BOREHOLE
LOGS OF EIGHT WELLS AT THE HOLTON CHICLE SUPERFUND SITE,
LONDONDERRY, NEW HAMPSHIRE
By Bruce P. Hanson
U.S. GEOLOGICAL SURVEY
Open-File Report 92-647
Prepared in cooperation with the
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASTE MANAGEMENT DIVISION, REGION I
Marlborough, Massachusetts
1993
-------
U.S. DEPARTMENT OF THE INTERIOR
BRUCE BABBITT, Secretary
U.S. Geological Survey
Dallas L. Peck, Director
For additional information
write to:
U.S. Geological Survey
District Chief
Massachusetts - Rhode Island District
28 Lord Road, Suite 280
Marlborough, MA 01752
Copies of this report can
be purchased from:
U.S. Geological Survey
Books and Open-File Reports Section
Box 25425, Federal Center
Denver, CO 80225
-------
CONTENTS
Page
Abstract 1
Introduction 1
Borehole logs 1
Natural gamma 3
Spontaneous potential 3
Single-point resistance 3
Caliper 4
Temperature 4
Fluid resistivity 4
Inferred locations of fractures 4
Summary 22
References cited 22
ILLUSTRATIONS
Page
Figure 1. Map showing location of the Holton Circle Superfund site,
Londonderry, New Hampshire 2
2. Map showing locations of wells logged at the Holton Circle Superfund site .. 5
3-10. Graphs showing borehole geophysical logs for well:
3. MW1D 7
4. MW2D 8
5. MW3D 9
6. MW4D 10
7. MW5D li
8. MW6D 12
9. MW7D 13
10. MW8D 14
11-18. Diagrams showing depths of borehole-log anomalies that indicate fractures at well:
11. MW1D 15
12. MW2D 16
13. MW3D 17
14. MW4D 18
15. MW5D 19
16. MW6D 20
17. MW7D 21
18. MW8D 22
* • •
in
-------
TABLE
Table 1. Characteristics of wells drilled dining October and November 1990 at
the Holton Circle Superfund site, Londonderry, New Hampshire ...
Page
6
CONVERSION FACTORS AND VERTICAL DATUM
Multiply
foot per second (ft/s)
By
To obtain
inch (in.)
inch (in.)
foot (ft)
mile (mi)
Length
25.40
2.540
0.3048
1.609
millimeter
centimeter
meter
kilometer
meter per second
Velocity
0.3048
Temperature
Temperature in degrees Celsius (°C) can be converted to degrees Fahrenheit (°F)
as follows: °F = 9/5 (°C) +32.
Sea Level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD
of 1929)-a geodetic datum derived from a general adjustment of the first-order level nets of both the
United States and Canada, formerly called Sea Level Datum of 1929.
IV
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Locations of Fracture Intervals Inferred From
Borehole Logs of Eight Wells at the
Holton Circle Superfund Site,
Londonderry, New Hampshire
by Bruce P. Hansen
ABSTRACT
Ground water in fractured bedrock at the Holton
Circle Superfund site in Londonderry, New
Hampshire, contains volatile organic compounds
and chloride concentrations as high as
23,500 mg/L. Geophysical logs obtained from
eight bedrock observation wells that range in
depth from 65 to 382 feet were used to identify
depths of possible water-bearing fractures. Logs
included natural gamma, spontaneous potential,
single-point resistance, caliper, temperature, and
fluid resistivity. Ml but the natural-gamma log
had anomalies that indicate possible fractures.
Anomalies at the same depths on several logs from
a single well support identification of likely frac-
tures. Charts presented in the report show depths
of anomalies that may indicate fractures.
INTRODUCTION
Volatile organic compouno!s and high concen-
trations of dissolved constituents, principally so-
dium (Na) and chloride (Cl), are present in
ground water at the Holton Circle Superfund site
in Londonderry, N.H. (fig. 1). Water in the bed-
rock moves primarily through fractures in the
foliated schist. During October and November
1990, eight wells were drilled into bedrock by the
U.S. Environmental Protection Agency (USEPA)
to characterize the hydrology of the site. In coop-
eration with the USEPA, the U.S. Geological
Survey (USGS) logged these eight wells by means
of six borehole geophysical methods to identify
the locations of possible fractures and fracture
zones. Borehole logs were run on each of the
eight wells between November 16,1990, and Jan-
uary 23, 1991. The purpose of this report is to
describe the logging methods used, present the
logs obtained, and identify depths of possible
fractures in each well logged.
The author thanks James M. Di Lorenzo,
Waste Management Division, U.S. Environmen-
tal Protection Agency, Boston, Mass., who pro-
vided background information and logistical
assistance during the logging survey.
BOREHOLE LOGS
A borehole logger with single-conductor log-
ging cable was used for this survey. Continuous
-------
71'
1
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HAMPSHIRE
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MANCHESTER
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-------
graphic pen plots and digital data from each 0.1
ft interval were recorded.
Borehole logs obtained from each of the eight
wells included natural gamma, spontaneous po-
tential (SP), single-point-resistance, caliper, tem-
perature, and fluid resistivity. Logging methods
and methods of analysis are discussed briefly
below. Detailed descriptions of the theory, appli-
cation, and analysis of borehole geophysics for
ground-water investigations can be found in
Keys (1990).
Natural Gamma
Natural-gamma logs are a measure of the
gam ma radiation from naturally occurring radio-
active elements in subsurface formations. A
probe lowered through the borehole detects the
gamma radiation and transmits a signal through
the logging cable to the surface. In New England,
gamma radiation results largely from the potas-
sium-40 radioisotope; generally, the amount
(counts) of gamma radiation detected from a bed-
rock unit is directly related to the amount of
potassium feldspar in the rock. Minerals depos-
ited or precipitated in fractures sometimes have
different natural-gamma characteristics than
the adjacent bedrock and cause a deviation in the
log trace. An enlarged borehole diameter at in-
tersecting fractures also can cause minor deflec-
tion of the log trace by changing the amount of
gamma radiation detected.
Spontaneous Potential
The SP log is a record of the spontaneous
voltage measured between an electrode grounded
at the surface and a second electrode in the well.
When the electrode in the well is moved through
the rock-water system, small changes in voltage,
usually in the millivolt range, are recorded. Con-
tacts between lithologic units or fractures inter-
sected by the borehole commonly cause changes
in voltage. SP voltage is a function of the chem-
ical activities of fluids in the borehole and in
adjacent rock or fractures, borehole and (or) rock
temperature, and type and quantity of clay pres-
ent. Because SP voltage is largely related to
contrasts between the salinity of the fluid in the
borehole and fluid in the formation or fracture,
changes in either will cause an SP response. If
the borehole fluid is fresher than the formation
water, the SP response is negative opposite per-
meable beds or zones; this is called the standard
response. If the salinities are reversed, SP re-
sponse is positive opposite permeable beds or
zones. SP response is zero (straight line) when
the salinities of the borehole and formation or
fracture fluid are the same. An increase in bore-
hole diameter decreases the magnitude of the SP
recorded.
Single-Point Resistance
The single-point-resistance log measures the
resistance between an electrode grounded at the
surface and an electrode that is moved through
the well bore. The resistance measured is a func-
tion of the resistance of the formation, the forma-
tion water, and the borehole water. The volume
of investigation of the single-point-resistance
method is small-about 5 to 10 times the electrode
diameter. When a borehole in resistive rock is
filled with saline water, thin resistive units are
difficult to identify on the log because most of the
current flows in the borehole. Single-point-resis-
tance logs are sensitive to changes in borehole
diameter, partly because of the small volume of
investigation. [The volume of investigation is the
volume of borehole fluid and invaded and unin-
vaded formation surrounding the geophysical
logging probe that determines 90 percent of the
measurement obtained from the probe; the ra-
dius of this volume generally depends on both
probe configuration and properties of the forma-
tion and fluids (Keys, 1990)]. An increase in
borehole diameter will decrease the apparent
resistance. For this reason, the technique can be
used to locate fractures that cause borehole en-
largement.
-------
Caliper
Fluid Resistivity
Caliper logs provide a continuous record of
borehole diameter. Changes in borehole diame-
ter may be related to well construction, drilling
technique, lithology, structure, and fractures.
The caliper probe used for this study has three
interconnected arms that drive a linear potenti-
ometer. Changes in resistance, transmitted to
land surface as voltage changes, are proportional
to average hole diameter. Fractures are com-
monly detected by the three-arm caliper probe.
If the three arms enter the openings of a dipping
fracture at different depths, the separate re-
sponses indicate three individual fractures
rather than one. A three-arm caliper probe may
not function correctly in holes that deviate appre-
ciably from vertical because the weight of the tool
can force one arm to close, which closes the other
two arms.
Temperature
Temperature logs are a measure of the bore-
hole-fluid temperature. A small electrical cur-
rent is conducted through a thermistor in the
temperature probe to measure changes in resis-
tance that result from temperature changes. If
there is no flow of fluid in or adjacent to the
borehole, the temperature gradually increases
with depth, reflecting the geothermal gradient.
The geothermal gradient in New England is
about 0.76 degree Celsius per 100 feet of depth.
To identify possible water-bearing fractures, in-
vestigators examine temperature logs for evi-
dence of changing geothermal gradients caused
by the vertical flow of fluid in the borehole. Other
factors that can affect the temperature log and
its interpretation are the vertical flow of fluid in
the borehole caused by water removal before log-
ging, ground-water recharge, and seasonal fluc-
tuations in air temperature.
The resistance of water in a borehole is mea-
sured directly by fluid-resistivity logging. The
log is not affected by the resistance of the forma-
tion or by fluids within the formation adjacent to
the borehole. Variations in the fluid resistivity
log commonly indicate points of ground-water
inflow, such as those associated with fractures.
Because fluid resistivity is affected by tempera-
ture, interpretation of this log requires a temper-
ature log.
INFERRED LOCATIONS OF
FRACTURES
Locations of the eight wells logged (MW1D
through MW8D) are shown on figure 2. The wells
were drilled by the air-percussion method and
are approximately 6 in. in diameter. The wells
are uncased except for steel surface casing set
into bedrock through thin unconsolidated surfi-
cial deposits. Characteristics of the wells are
given in table 1.
Plots of the logs, constructed from digital
data recorded from each 0.1-ft interval, are
shown in figures 3 through 10. All depths shown
on the logs are from the top of the well casing.
Graphic pen plots of the log data were used
to identify possible fractures. Some details on
these graphic plots are not as obvious on the
digital logs shown in this report. The six logs for
each of the eight wells were examined for deflec-
tions in the log trace that may indicate fractures
or fracture zones. These deflections are referred
to as "anomalies" and are commonly observed at
the same depths on more than one log from a well.
The more logs that indicate an anomaly at the
same depth, the greater the probability that a
fracture zone is present. Some of the log anoma-
lies, however, may result from some other un-
known physical or lithologic conditions along the
borehole, and not all fractures can be detected
-------
71° 24'
71°23'
42° 521
42° 51
• BEDROCK WELL-Looged during
MW1D November 199010 January 1991.
number is U.S. Environmental
Protection Agency well number
B*M Km U.S. GMtogiul Survey
Nuhul NoTi. N.H.. 124.000
1968, ftnanmta 1M5.
1 MILE
J
1 KILOMETER
CONTOUR INTERVAL 10 FEET
DATUM IS SEA LEVEL
Figure 2.--Locations of wells logged at the Holton Circle Super-fund site.
with the logs. Anomalies on the temperature and
fluid resistivity logs usually indicate fluid move-
ment into or out of fractures.
The depths of anomalies that were noted on
logs for each well are shown on figures 11 through
18. The natural-gamma logs were not included
because they appear primarily to indicate varia-
tions in lithology; few of the anomalies observed
on these natural-gamma logs correspond to
anomalies on the other logs. Some peaks on the
natural-gamma logs (figs. 3-10) probably indicate
lithologic units or mineralized zones that have a
higher concentration of potassium-40.
-------
Table 1 .-Characteristics of wells drilled during October and November 1990 at Holton Circle Supertund site,
Londonderry, New Hampshire
[USEPA, U.S. Environmental Protection Agency; mm/doVyy, month, day, year. All wells are 6 inches in diameter]
Depth to
Well depth bedrock Top of casing Bottom of Water level Depth of
below land below land above land casing below Length of Elevation of below top of water level
USEPA well surface surface surface land surface casing top of casing casing measurement
number (feet) (feet) (feet) (feet) (feet) (feet) (feet) (mm/dd/yy)
MW1D
MW2D
MW3D
MW4D
MW5D
MW6D
MW7D
MW8D
185
185
185
185
185
185
382
65
26
17
16
21
31
6
5
17
1.70
1.50
1.75
1.85
1.45
1.25
.91
1.85
36
29
23
28
38
16
16
22
37.7
30.5
24.75
29.85
39.45
17.25
16.91
23.85
391.44
361.27
341.54
386.24
384.03
339.78
342.10
359.15
9.80
20.93
6.53
49.66
25.67
4.00
2.84
3.30
19.29
11/19/90
11/16/90
11/22/90
11/15/90
11/15/90
01/22/91
11/19/90
01/23/91
11/16/90
-------
HOLE DIAMETER,
IN INCHES
TEMPERATURE, IN
DEGREES CELSIUS
FLUID RESISTIVITY,
IN OHM-CENTIMETERS
NATURAL GAMMA, IN
COUNTS PER SECOND
SPONTANEOUS
POTENTIAL
IN MILLIVOLTS
12 500 550 600 650 700 750 0 100 200 300 400 500 -250
SINGLE-POINT
RESISTANCE, IN OHMS
250 0 50 100 150 200 250
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Figure 3.--Borehole geophysical logs for well MW1D.
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HOLE DIAMETER,
IN INCHES
TEMPERATURE, IN
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FLUID RESISTIVITY.
IN OHM-CENTIMETERS
NATURAL GAMMA, IN
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SPONTANEOUS
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IN MILLIVOLTS
SINGLE-POINT
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Figure 5.--Borehole geophysical logs for well MW3D.
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GEOPHYSICAL WELL LOGS
EXPLANATION
174 > POSSIBLE FRACTURE LOCATION-
Based on anomaly on indicated log.
Number is depth below top of
well casing
' POSSIBLE HIGH-ANGLE FRACTURE
? POORLY DEFINED ANOMALY--
Multiple queries if very poorly defined
Figure 11.— Depths of borehole-log anomalies that indicate fractures in well MW1D.
15
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GEOPHYSICAL WELL LOGS
EXPLANATION
iso> POSSIBLE FRACTURE LOCATION-
Based on anomaly on indicated log.
Number is depth below top of
well casing
* POSSIBLE HIGH-ANGLE FRACTURE
? POORLY DEFINED ANOMALY--
Multiple queries if very poorly defined
Figure 12.~ Depths of borehole-log anomalies that indicate fractures in well MW2D.
16
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144-147,
1 60-1 6-£
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182-1 85N
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GEOPHYSICAL WELL LOGS
EXPLANATION
182> POSSIBLE FRACTURE LOCATION-
Based on anomaly on indicated log.
Number is depth below top of
well casing
? POORLY DEFINED ANOMALY-
Multiple queries if very poorly defined
Figure 13.— Depths of borehole log anomalies that indicate fractures in well MW3D.
17
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86>
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178>
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178>
GEOPHYSICAL WELL LOGS
EXPLANATION
178> POSSIBLE FRACTURE LOCATION-
Based on anomaly on indicated log.
Number is depth below top of
well casing
? POORLY DEFINED ANOMALY--
Multiple queries il very poorly defined
Figure 14.- Depths of borehole log anomalies that indicate fractures in well MW4D.
18
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EXPUWATION
175> POSSIBLE FRACTURE LOCATION-
Based on anomaly on indicated log.
Number is depth below lop of
well casing
? POORLY DEFINED ANOMALY--
Multiple queries if very poorly defined
Figure 15.-- Depths of borehole log anomalies that indicate fractures in well MW5D.
19
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GEOPHYSICAL WELL LOGS
EXPLANATION
105> POSSIBLE FRACTURE LOCATION-
Based on anomaly on indicated log.
Number is depth below top of
well casing
? POORLY DEFINED ANOMALY--
Multiple queries if very poorly defined
Figure 16.-- Depths of borehole log anomalies that indicate fractures in well MW6D.
20
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19
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270> POSSIBLE FRACTURE LOCATION-
Based on anomaly on indicated log.
Number is depth below top o(
well casing
• POSSIBLE HIGH-ANGLE FRACTURE
? POORLY DEFINED ANOMALY- 36S ''
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111
41
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115
130
150>
172-177
216-218X
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330>
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GEOPHYSICAL WELL LOGS
Figure 17.- Depths of borehole log anomalies that indicate fractures in well MW7D.
21
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BOTTOM OF CASING
(22.0 feel)
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5
a.
GEOPHYSICAL WELL LOGS
EXPLANATION
54> POSSIBLE FRACTURE LOCATION-
Based on anomaly on indicated log.
Number is depth below top of
well casing
? POORLY DEFINED ANOMALY-
Multiple queries if very poorly defined
Figure 18.— Depths of borehole log anomalies that indicate fractures in well MW8D.
SUMMARY
Depths of anomalies are shown on charts for each
of the eight wells logged.
Eight wells that were drilled to characterize
the bedrock hydrology at the Holton Circle
Superfund site were logged to identify depths of
possible water-bearing fractures. Borehole geo-
physical logs included natural gamma, spontane-
ous potential, single-point resistance, cah'per,
temperature, and fluid resistivity. All but the
natural-gamma log were useful for identifying
anomalies indicative of possible fractures.
REFERENCE CITED
Keys, W.S., 1990, Borehole geophysics ap-
plied to ground-water investigations: U.S. Geolo-
gical Survey Techniques of Water Resources
Investigations, book 2, chap. E2,150 p.
22
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