RESULTS OF GEOPHYSICAL SURVEYS OF
GLACIAL DEPOSITS NEAR A FORMER WASTE
DISPOSAL SITE, NASHUA, NEW HAMPSHIRE
U.S. GEOLOGICAL SURVEY
Open-File Report 95-142
Prepared in cooperation with
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGION I
-------
950R95003
RESULTS OF GEOPHYSICAL SURVEYS OF
GLACIAL DEPOSITS NEAR A FORMER WASTE-
DISPOSAL SITE, NASHUA, NEW HAMPSHIRE
By Joseph D. Ayotte and Tracy H. Dorgan
U.S. GEOLOGICAL SURVEY
Open-File Report 95-142
Prepared in cooperation with the
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGION I
Bow, New Hampshire
1995
-------
U.S. DEPARTMENT OF THE INTERIOR
BRUCE BABBITT, Secretary
U.S. GEOLOGICAL SURVEY
Gordon P. Eaton, Director
For additional information write to:
Chief, New Hampshire-Vermont District
U.S. Geological Survey
525 Clinton Street
Bow, NH 03304
Copies of this report can be purchased from:
U.S. Geological Survey
Earth Science Information Center
Open-File Reports Section
Box25286, MS 517
Denver Federal Center
Denver, CO 80225
I Results of Geophysical Surveys of Glacial Deposits Near a Former Waste-Disposal Site, Nashua, New Hampshire
-------
CONTENTS
Abstract 1
Introduction 1
Purpose and scope 2
Previous investigations 2
Acknowledgments 2
Geohydrologic setting 2
Stratified drift 2
Till 4
Bedrock 4
Geophysical methods 4
Ground-penetrating radar 4
Seismic-refraction profiling 6
Results of geophysical surveys 6
Ground-penetrating radar 6
Seismic refraction 12
Summary and conclusions 12
Selected references 16
ILLUSTRATIONS
Figure 1. Map showing locations of ground-penetrating radar profiles, test borings, and observation wells,
Nashua, New Hampshire 3
2. Map showing locations of seismic-refraction profiles, test borings, and
observation wells,Nashua, New Hampshire 7
3-6. Unprocessed ground-penetrating radar profiles, Nashua, New Hampshire:
3. A-A' 9
4. B-B' 10
5. C-C' 11
6. D-D' 13
7-8. Geohydrologic sections interpreted from seismic-refraction data for profiles:
7. a-a', b-b', and c-c' 14
8. d-d'ande-e' 15
TABLES
1. Lithologic logs of selected wells and borings, Nashua, New Hampshire 5
Contents III
-------
CONVERSION FACTORS
Multiply
inch (in)
foot (ft)
mile (mi)
foot per nanosecond (ft/ns)
square mile (mi )
gallon per minute (gal/min)
By
25.4
0.3048
1.609
0 .3048
2.59
0.06308
To Obtain
millimeter
meter
kilometer
meters per nanosecond
square kilometer
liter per second
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.inch
In this report, 1 nanosecond (ns) is equal to 10 seconds.
iv Results of Geophysical Surveys of Glacial Deposits Near a Former Waste-Disposal Site, Nashua, New Hampshire
-------
RESULTS OF GEOPHYSICAL SURVEYS OF GLACIAL
DEPOSITS NEAR A FORMER WASTE-DISPOSAL SITE,
NASHUA, NEW HAMPSHIRE
By Joseph D. Ayotte and Tracy H. Dorgan
Abstract
Geophysical investigations were done near a
former waste-disposal site in Nashua, New Hamp-
shire, to determine the thickness and infer hydrau-
lic characteristics of the glacial sediments that
underlie the area. Data will be used to help define
the ground-water-flow system near the Gilson
Road Comprehensive Environmental Response,
Compensation, and Liability Act site.
Approximately 5 miles of ground-penetrating
radar (GPR) data were collected in the study area
by use of dual 80-megahertz antennas. Three dis-
tinct radar-reflection signatures were evident from
the data and are interpreted to represent (1)
fine-grained glacial lake sediments, (2) coarse sand
and gravel and (or) glacial till, and (3) bedrock.
The GPR signal penetrated as much as 70 feet of
sediment in coarse-grained areas, but penetration
depth was generally less than 40 feet in extensive
areas of fine-grained lacustrine deposits. Geologic
features were evident in many of the profiles.
Fine-grained lacustrine deposits were the most
common of the three types of deposits identified.
Other features include deltas deposited in glacial
Lake Nashua and lobate fans of sediment deposited
subaqueously at the distal end of deltaic sediments.
Cross-bedded sands were commonly identifiable in
the deltaic sediments.
Seismic-refraction data also were collected at
five of the GPR data sites. In most cases, depths to
the water table and to the till and (or) bedrock sur-
face indicated by the seismic-refraction data com-
pared favorably with depths calculated from the
GPR data.
Test holes were drilled at three locations to
confirm depths to radar reflectors and to determine
the types of geologic material represented by the
various reflector types. Observation wells were
installed at three of the sites so that periodic water-
level measurements could be made.
INTRODUCTION
During the 1960's and 1970's, various waste
products, including hazardous materials, were disposed
of at a site on Gilson Road in Nashua, N.H. (fig. 1). The
State of New Hampshire received a U.S. Environmental
Protection Agency grant in 1981 to remediate the site;
since then, many ground-water investigations have been
done. Most of these investigations have concentrated
on the areas in the immediate vicinity of the disposal
site. In 1981, water from domestic wells downgradient
from the Gilson Road site was found to be contaminated
with volatile organic compounds and other hazardous
chemicals (Weston, 1989). The site is currently (1994)
undergoing remediation under the authority of the
Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA) of 1980.
Much of the population within the study area is served
by a privately owned community water system;
therefore, geohydrologic data from drilled wells outside
of the hazardous-waste site are sparse. Efforts are
presently focusing on the ground-water-flow system
outside the immediate area of contamination. As part of
these efforts, a study was done by the U.S. Geological
Introduction 1
-------
Survey, in cooperation with the U.S. Environmental
Protection Agency, to provide hydrogeologic
information for ongoing and future remediation
activities at this site. In addition, efforts to construct a
ground-water-flow model of the site have resulted in a
need to examine the geohydrology of the stratified-drift
deposits at and near the site.
Purpose and Scope
This report presents the results of geophysical
investigations over glacial stratified drift near the
Gilson Road waste-disposal facility and in the vicinity
of Lyle Reed Brook near its confluence with the Nashua
River. Included in the report are geophysical profiles
that provide information about the various lithologies
and, in some locations, depths to bedrock. Test-boring
data also are presented in the report and were used to
confirm the results of the geophysical surveys. The
investigation was limited to the 1 -mi area bounded by
Gilson Road, Countryside Drive, the Nashua River, and
Jensens River Pines trailer park (fig. 1).
Previous Investigations
The surficial geology of the Pepperell Quadrangle,
in which the study area is located, was mapped at a scale
of 1:24,000 by Koteff and Volckmann (1973). That map
report describes the various levels of glacial Lake
Nashua and associated deposits. Toppin (1987)
describes the hydrogeology of the area as part of a
regional study to map the stratified-drift aquifers and
determine their hydraulic properties. In conjunction
with the site-remediation activities, numerous
hydrogeologic studies have been done since 1980 by
private consultants, and several studies have been done
by State and Federal agencies; a review of these can be
found in Weston (1989). Previous studies, however,
have focused primarily on the areas within or near the
main area of contamination.
Acknowledgments
We thank the many private landowners who
allowed us access to their land during this investigation.
In addition, we thank the private consulting firms who
supplied additional data used for this study, and officials
of the city of Nashua for their cooperation.
GEOHYDROLOGIC SETTING
Ground water flows through three geohydrologic
units in the study area. These geohydrologic units are
(1) stratified drift, the uppermost aquifer unit, which
stores and transmits the largest quantities of water; (2)
till, a discontinuous layer between the stratified drift and
the bedrock surface that transmits only minor amounts
of water; and (3) bedrock, which transmits variable
amounts of water primarily through fractures.
Stratified Drift
The waste-disposal site and surrounding area.are
underlain by a stratified-drift aquifer composed of
glaciofluvial sands and gravels and glaciolacustrine fine
sands and silt that were deposited in and near glacial
Lake Nashua (Koteff and Volckmann, 1973). This
glacial lake formed between the till and (or) bedrock
uplands to the south and the retreating ice margin to the
northeast. Because preglacial drainage was to the
northeast, retreating ice uncovered successively lower
outlets or spillways through which the glacial lake
drained. Glacial Lake Nashua lowered in six successive
stages (Koteff and Volckmann, 1973), and the deposits
in the study area consist of sands and gravels associated
with stages 4 and 5.
Coarse-grained deposits associated with stage 4 of
glacial Lake Nashua are present along Trout Brook
Drive and near Gilson Road to the south. These deposits
are partly covered by fine-grained glacial-lake-bottom
deposits. Stage 4 deposits are graded to a spillway at
an elevation of approximately 215 ft above sea level
(Koteff and Volckmann, 1973). Along Trout Brook
Drive, an esker that is noticeable on the surficial
geologic map of the Pepperell Quadrangle has since
been removed by excavation. Well NAW-220,
constructed for Pennichuck Water Works in 1969 and
located near the eastern edge of the coarse-grained
deposit, was screened in coarse-grained deposits
48 to 68 ft below land surface. The superimposition of
glacial-lake-bottom sediments over the coarse material
indicates that the esker is partly buried by fine-grained
deposits from a later glacial lake stage (stage 5). Well
NAW-220 was tested at more than 1,100 gal/min.
2 Results of Geophysical Surveys of Glacial Deposits Near a Former Waste-Disposal Site, Nashua, New Hampshire
-------
7f32'
71'31'30
42°43'30'
42°43'
') WASTE-
,-/ DISPOSAL
BASE FROM U.S. ARMY CORPS OF ENGINEERS, SEPTEMBER 1993
500
i
1,000 FEET
j
WATER BODY
GROUND-PENETRATING RADAR
EXPLANATION
TEST WELLS AND BORINGS
100 200 300 METERS
71°
WELL OR
BORING
O
NAW-220
USGS WELL
OR BORING
.NAW-242
D D'
h_ J Part of profiles reproduced
"" \ in figures 3 - 6
.RFW-1B
PENETRATED
UNCONSOLIDATED
DEPOSITS ONLY
REACHED REFUSAL
OR BEDROCK
PENETRATED
BEDROCK
0 25 50 75 100 MILES
I .III. I
I ^\ ' I ^ r
0 50 100 150 KILOMETERS
Figure 1. Locations of ground-penetrating radar profiles, test borings, and observation wells,
Nashua, New Hampshire.
Geohydrologic Setting 3
-------
Deposits associated with stage 5 are limited to a
small area near Jensens River Pines trailer park. These
deposits are graded to the next stage of Glacial Lake
Nashua, which was approximately 10 ft lower than
stage 4, and they include sands and gravels.
Fine-grained lake-bottom deposits are present
throughout most of the study area and, in places, overlie
or are in contact with coarse-grained deposits. Koteff
and Volckmann (1973) identify glacial-lake-bottom
sediments at land surface near Gilson Road. Logs from
test holes drilled for previous studies indicate that
fine-grained lake-bottom deposits are extensive and
underlie much of the stream-terrace deposits along the
Nashua River near its confluence with Lyle Reed Brook
(table 1). Very fine to medium sands are 20 to 30 ft
below land surface at well NAW-240. Till underlies
these sands.
Stream-terrace deposits are present mainly from
the Nashua River east to Trout Brook Drive. Recent
alluvium is present primarily along the Nashua River
and is not areally extensive in the study area.
Till
Till is an unsorted mixture of clay, silt, sand, and
rock fragments with variable composition and degree of
compactness. Two distinct tills have been recognized in
this region and are thought to represent two separate ice
advances over the region (Koteff, 1976; Koteff and
Volckmann, 1973). The lower till is fairly compact and
oxidized, whereas the upper till is generally sandy and
unoxidized. Till is rarely exposed in the study area but
discontinuously underlies the stratified deposits.
Lithologic samples from test drilling done for this study
(wells NAW-240, NAW-241, and NAA-219) included
only a sandy till.
Bedrock
The bedrock underlying most of the study area is
composed of schists and phyllites of the Merrimack
Group and is similar to the rocks of the Berwick
Formation (Lyons and others, 1986). Previous studies,
summarized by Weston (1989), have indicated that the
bedrock surface in the study area is highly fractured.
This fracturing indicates that the secondary
permeability of the bedrock is significant and that a
measurable amount of ground water may flow between
the upper part of the bedrock and the overlying till and
(or) stratified drift.
GEOPHYSICAL METHODS
Ground-penetrating radar (GPR) and seismic
refraction were used to investigate the geohydrology of
the glacial deposits in the study area. Both methods
provide a nearly continuous profile of the subsurface.
For this study, seismic-refraction data were collected to
provide continuous profiles of the water-table surface
and the till and (or) bedrock surface. GPR provides
greater resolution and detail relative to the stratigraphy
and physical properties of the subsurface deposits than
seismic refraction. For this study, depths to reflectors
and types of lithologies were verified by comparing
depths to reflectors with depths to lithologic units
inferred from well and test-boring logs.
Ground-Penetrating Radar
GPR surveys were done according to methods
described by Beres and Haeni (1991) at the survey
locations shown in figure 1. The GPR-survey system
transmits radio-frequency electromagnetic pulses into
the ground and receives energy reflected back from
subsurface reflectors. Reflectors can be any subsurface
contact between geologic materials with different
physical and electrical properties, such as the interface
between lithologic units or layers within a unit. The
surveys were conducted with dual 80 MHz (megahertz)
center-frequency transmitting and receiving antennas
that were towed at approximately 75 ft behind a vehicle.
The profiles can be examined visually to provide
indications of lithologic properties. Analysis of GPR
profiles are improved by the use of additional
geophysical data and (or) lithologic logs acquired
during test drilling.
Beres and Haeni (1991) provide an interpretation
guide for various types of reflection configurations for
unconsolidated deposits. Parallel reflectors indicate the
presence of laminated fine-grained sediments, such as
glacial-lake-bottom sediments. Complex, subparallel,
and chaotic reflectors may indicate coarse-grained
sediments and may give evidence as to the depositional
environment. Inverted V-shaped reflectors probably
4 Results of Geophysical Surveys of Glacial Deposits Near a Former Waste-Disposal Site, Nashua, New Hampshire
-------
Table 1. Lithologic logs for selected wells and borings, Nashua, New Hampshire
[--, no data]
Well or boring
identifier
NAA-219
NAW-220
NAW-240
NAW-242
M4
M5
M6
Al
RFW-1B
RPW-2B
Depth to
top
(feet)
0
7
16
0
30
48
50
0
10
21
31
40
0
12
15
24
0
8
9
39
49
86.5
91.5
0
16
49
76
90.5
0
9
46
0
17
29
44
0
5
10.5
0
17
34
65
Depth to
bottom
(feet)
7
16
30
48
50
10
21
31
40
12
15
24
--
8
9
39
49
86.5
91.5
--
16
49
76
90.5
-
9
46
--
17
29
44
--
5
10.5
-
17
34
65
--
Lithology
Sand, fine to very fine; few pebbles
Till; sandy and silty; few pebbles and cored cobbles
Firm refusal; probably bedrock
Sand, fine, brown
Sand, fine to medium
Sand, coarse and medium gravel
Gravel, coarse, end at 67.5 feet
Sand, very fine to fine, tan; coarser with depth
Sand, medium to coarse, tan; moderately to well sorted
Sand, fine with some coarser layers
Till; loosely compacted, mostly coarse sand
Firm refusal; probably bedrock
Very fine sand and silt
Sandy till
Sand, very fine and silt
Till; loosely compacted; refusal at 33.5 feet
Fill
Black organic material; sand and silt
Sand, fine to medium
Sand, fine
Sand, fine and silt
Till
Bedrock; cored to 101.5 feet
Fill
Sand, fine
Sand, fine; variable density
Sand, fine, dense; some gravel near bottom of unit
Till; refusal at 103.5 feet
Sand and gravel, medium to coarse
Sand, fine; trace silt
Till; refusal at 49.5 feet
Sand, fine to medium; some gravel
Sand, fine to medium
Sand, medium
Till; end of hole at 52 feet
Sand, coarse; trace fine gravel
Sand and gravel, fine to coarse
Dark gray binary granite and quartz monzonite
Sand, fine, dark tan, some silt
Sand, fine to coarse; some gravel, little silt
Sand, fine to coarse; little silt; some gravel;
Till, end of hole at 68 feet
Geophysical Methods 5
-------
indicate the presence of cobbles and boulders in till.
Near-surface inverted V-shaped reflectors may indicate
buried pipelines, culverts, or conduits.
Transmission velocities of the radar signal were
used to interpret depth to a reflector. The velocity of
electro-magnetic waves in saturated unconsolidated
sediments is approximately 0.2 ft/ns and, in unsaturated
unconsolidated sediments, is approximately 0.4 ft/ns
(Beres and Haeni, 1991). Interpretation of a GPR
profile, which includes unsaturated and saturated
sediment, thus requires the use of two depth scales. For
any radar frequency, the primary factor limiting depth
of penetration is the electrical conductivity of the
subsurface materials (Beres and Haeni, 1991); however,
high frequencies are attenuated faster than low
frequencies. Electrically conductive materials, such as
clay minerals, limit radar-signal penetration. Dry,
unconsolidated coarse-grained sediments enhance
signal penetration.
Lithologic information obtained from test drilling
is used to help interpret or confirm interpretations of
GPR profiles. Electromagnetic reflectors could be
present, for example, at a water-table surface, at a
coarse to fine-grained interface, or at a bedrock surface,
and all could be represented as a dark, continuous band
on the GPR profile; however, a thin electrically
conductive layer, such as a clay lens, also could be
represented by a dark band. An extensive capillary
fringe in fine-grained sediments may prevent the water
table from showing as a continuous reflector; therefore,
independently derived depths to the water table are
needed to determine the correct depths to reflectors on
the profile.
Seismic-Refraction Profiling
Seismic-refraction profiling was used to determine
depths to the water table and depths to the bedrock
surface. Locations of these profiles are shown in
figure 2. The seismic-refraction method is based on a
layered-earth model, whereby the velocity of sound
varies with the lithologic characteristics of the material
present and increases with depth. As sound waves
travel across the boundary between layers having
different velocity-propagation characteristics, some of
the energy is refracted. When the angle of incidence is
equal to the critical angle for the first layer, the sound
energy is transmitted along the upper surface of the
second layer at the speed of sound in the second layer.
As the refracted sound wave travels, it continuously
generates new sound waves that travel upward and are
received by the geophones at the surface. The methods
used in this survey are described by Haeni (1988). Each
seismic profile was approximately 500 ft long. A
two-component explosive was used as a sound source,
and each explosive charge was buried 2 to 4 ft below
land surface. The seismic data were collected by use of
a 12-channel, signal-enhancing seismograph, and
interpreted by use of a time-delay, ray-tracing computer
program developed by Scott and others (1972).
Lithologic data from nearby wells and test holes were
used to verify the interpretations (table 1; fig. 2).
RESULTS OF GEOPHYSICAL SURVEYS
The results of the geophysical surveys presented in
this section include selected GPR and
seismic-refraction profiles. All original data from the
surveys are filed at the U.S. Geological Survey, Water
Resources Division, New Hampshire-Vermont District,
in Bow, N.H.
Ground-Penetrating Radar
Ground-penetrating radar surveys were done along
approximately 5 mi of survey lines within the study
area. The areas where GPR data were collected and the
locations of selected profiles are shown in figure 1.
These surveys helped delineate glaciolacustrine
sediments in several places. In many places along the
survey lines, the data were used to delineate subsurface
lithologies. Places where data collection were
successful were limited primarily but not entirely to
unpaved surfaces and to areas where geologic materials
were coarse grained or where bedrock was less than
30 to 40 ft below land surface.
In areas where GPR data-collection efforts yielded
usable data, three distinct reflector signatures are
evident. The first reflector signature consists of thin,
continuous, and mostly horizontal line patterns that
represent fine-grained glaciolacustrine sediments. This
reflector is common in most of the areas surveyed, but
it is generally absent in profiles made over
coarse-grained deltaic sediments.
The second reflector signature is chaotic and
hummocky in places and is indicative of coarse-grained
sediment. This reflector can represent coarse sand and
6 Results of Geophysical Surveys of Glacial Deposits Near a Former Waste-Disposal Site, Nashua, New Hampshire
-------
71°32'
71'31'30
42"43'30"
42'43'
BASE FROM U.S. ARMY CORPS OF ENGINEERS, SEPTEMBER 1993
EXPLANATION
500
i
1,000 FEET
100 200 300 METERS
71"
WATER BODY
SEISMIC-REFRACTION
PROFILE
TEST WELLS AND BORINGS
O
WELL OR
BORING
NAW-220
USGS WELL
OR BORING
.NAW-242
.RFW-1B
PENETRATED
UNCONSOLIDATED
DEPOSITS ONLY
REACHED REFUSAL
OR BEDROCK
PENETRATED
BEDROCK
75 100 MILES
I j
50 100 150 KILOMETERS
Figure 2. Locations of seismic-refraction profiles, test borings, and observation wells, Nashua, New Hampshire.
Results of Geophysical Surveys 7
-------
gravel or sandy till. Where the reflection is from till, the
radar record commonly contains numerous small
diffraction patterns that appear as inverted V's
throughout the reflector zone. The inverted V's may
represent large cobbles or boulders in a till. Reflections
from till in this area tend to attenuate the radar signal,
probably, in part, as a result of electrically conductive
clay minerals in the till.
The third reflector signature is a strong, two- to
three-band reflector that is generally found beneath the
other two types. This reflector is representative of the
bedrock surface but, in some places, may represent a
dense or electrically conductive till surface.
A reliable water-table reflector was not found on
most of the profiles and, therefore, is not discussed. The
lack of a well-defined water-table reflector may result
from capillarity and (or) a discontinuous perched water
table above the fine-grained sediments near the surface.
In places, where a water-table reflector is evident, it is
delineated on the profile with a dotted line.
The locations of four selected profiles are shown
on figure 1. The selected profiles illustrate the three
types of reflectors commonly found in the study area.
These profiles and associated reflectors are described
below. Test-boring data were used where available to
aid in interpreting the data; some uncertainty, however,
is always inherent in visual interpretations of raw GPR
data.
Profile A-A' (fig. 3) is in the western part of the
study area, near the Nashua River (fig. 1). The water
table is not well defined on the record, probably because
of the presence of a discontinuous perched water table
that was detected during the drilling of test well
NAW-242. Additionally, the water table is not as sharp
in fine-grained stratified drift (where the capillary fringe
may be several feet thick) as it is in coarse-grained
stratified drift (where the capillary fringe may be only a
few inches thick). Fine-grained lacustrine sediments
dominate the uppermost part of the record. The surficial
material in this area is mapped as stream terraces in
former glaciolacustrine deposits (Koteff and
Volckmann, 1973); the terraces are generally less than
10 ft thick. The thin, parallel, mostly flat-lying
reflectors in the upper part of the profile near 50 to
150 ns (10- to 20-ft-depth) represent these fine-grained
glaciolacustrine sands. The chaotic, sometimes
hummocky reflectors near 150 to 200 ns (20- to
30-ft-depth on the record) represent sandy till. The log
from observation well NAW-242 (table 1) shows 24 ft
of very fine sand and silt underlain by till to a depth of
33 ft. A thin (2- to 3-ft-thick) till layer approximately
12 ft below land surface and underlain by fine sand was
found during drilling; however, this feature is not
resolvable on the GPR record. The thick, dark
continuous band beneath the till is interpreted to be
bedrock. Drilling of observation well NAW-242 was
terminated, because of firm refusal, probably on
bedrock, at depth of 33.5 ft.
Profile B-B' (fig. 4) is in the center of the study
area (fig. 1). Most of the GPR record shows the
presence of thin, flat-lying reflectors indicative of
fine-grained glacial-lake-bottom sediment. The logs
made at observation well M6 (table 1), on the western
end of the line, show the presence of 46 ft of fine to
medium sand overlying till. The log made at test well
NAW-220 (table 1), shown on the profile but
approximately 100 ft to the south, shows the presence of
48 ft of fine to medium sand overlying approximately
20 ft of coarse gravel. This GPR section shows loss of
record at approximately 350 to 450 ns; (35- to
45-ft-depth). This loss of record may represent the
contact between the fine sands and the coarse gravel and
(or) till below. This coarse-grained unit may be part of
a buried esker, which is shown on the surficial geologic
map of the Pepperell quadrangle (Koteff and
Volckmann, 1973) several hundred feet to the west, and
which has been largely removed by excavation. On the
eastern part of the profile, more than 50 ft of fine to
medium sand (glaciolacustrine sediment) is identifiable.
The logs from observation wells M4 (table 1), 200 ft to
the south, and M5 (table 1), 200 ft to the north, indicate
that the bedrock surface is more than 90 ft below the
land surface in this area.
Profile C-C' (fig. 5) is in the southern part of the
study area, north of Lyle Reed Brook and south of the
former waste-disposal facility (fig. 1). The
predominantly coarsegrained sediment is the buried
part of a kame delta mapped by Koteff and Volckmann
(1973). The top of the strongly reflected, chaotic, and
hummocky signature represents coarse sand and gravel
associated with the delta. Truncated, dipping reflectors
may indicate cross bedding. The distinct, lacustrine
continuous reflector that represents fine-grained
sediment. The second reflector signature is a chaotic,
locally hummocky reflector indicative of
8 Results of Geophysical Surveys of Glacial Deposits Near a Former Waste-Disposal Site, Nashua, New Hampshire
-------
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l^^f'-^g
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ftMst^r':^.'^" ^jiair- ''ia^S
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.Ti'^'Mraxii,;. ft";>ii. *v> i :-., .?" ,'''fe:-'ift,:- .jfr..""" i
100
I
200 FEET
i
20
APPROXIMATE VERTICAL
EXAGGERATION X 4
40
60 METERS
-o
-10
-20
-30
-40
Q
I
piu
^ |0
LU
LU
LJJ
-20 ^
-40
cc
g
co
LU
g
f
APPROXIMATE HORIZONTAL DISTANCE
o
EXPLANATION
LJTHOLOGY INDICATED AT WELL NAW-242
I: -I Rne to very fine sand and silt
Approximate location of geologic contact-Dashed
where inferred
Approximate location of water table
Figure 3. Unprocessed ground-penetrating-radar profile A-A', Nashua, New Hampshire
-------
a
I
«
°
CD
8
o
9
Q
i
APPROXIMATE VERTICAL EXAGGERATION X 3
60 METERS
APPROXIMATE HORIZONTAL DISTANCE
EXPLANATION
LITHOLOGY INDICATED AT WELL NAW-220
I/- J--I Rne to very fine sand and silt
Coarse sand and gravel
Approximate location of water table
CO
i-O
-50
LJJ
^
Q
LLJ
co
o
tr
I
LL.
O
co
co
O
f
-75
Figure 4. Unprocessed ground-penetrating-radar profile B-B', Nashua, New Hampshire.
-------
grained
glaciolacustrine
deposits
Cross section
of kame-delta deposits
o
%
CC|-
n
r°
MO |5
-20 OLU
-30
U40 O
0 20 40 60 METERS
APPROXIMATE HORIZONTAL DISTANCE
APPROXIMATE VERTICAL
EXAGGERATION X 3
-0 LU
LL
-20
-40
C/3
Q
QC
LL
o
g
X
o
TJ
EXPLANATION
Approximate location of geologic contact-
Dashed where inferred
Approximate location of water table
o
Q
in
c
O
Figure 5. Unprocessed ground-penetrating-radar profile C-C', Nashua, New Hampshire.
-------
concave-upward structures visible in the profile may
depict lobes of the delta as it built southward into the
stage 4 level of glacial Lake Nashua. The low parts of
these lobes are covered by flat-lying, continuous
reflectors that appear to indicate the presence of
fine-grained glaciolacustrine sediment (Ayotte, 1994).
Profile D-D' (fig. 6) is in the south-east corner of
the study area (fig 1). The dominant features on this
profile are the thin, continuous, relatively flat-lying
reflectors indicative of fine-grained glaciolacustrine
stratified drift. These beds extend to depths greater than
30 ft. Immediately below these reflectors, on the left
side of the profile, are chaotic reflectors that may
indicate the presence of coarse-grained material, such as
till and (or) coarse sand and gravel. Loss of record
below this point precluded interpretation of this unit; a
test hole would be necessary to confirm the material
types and depths. The strong, dark reflector on the left
side of the profile, below the lost record (30- to
60-ft-depth interval), is interpreted to be the bedrock
surface.
On the right side of the record, between 0 and
150 ns (0- to 20-ft-depth), the reflectors become
subparallel and somewhat hummocky, in contrast to the
fairly parallel and flat reflectors below and to the left
(southeast). This pattern indicates that the sediment
here is coarser than the sediments below and to the
southeast. High-angle diffractions originating near the
top of the profile on the right are from point reflectors,
such as utility conduits crossing the road where the
radar traverse was made. Low-angle diffractions in the
lower parts of the profile probably represent radar
reflections from trees or buildings near the survey lines.
Seismic Refraction
Five seismic-refraction surveys were done
throughout the area to help interpret the GPR data. The
locations of the five surveys and resulting profiles are
shown in figure 2. Geohydrologic sections interpreted
from seismic-refraction data are shown in figures 7-8
and are described below.
Profile a-a' (fig. 7) is shown on figure 2. Perched
ground water was found above lenses of fine-grained
sediment during test drilling at test well NAW-242
(table 1). The depth to refusal was approximately 16 ft
at NAA-219 and approximately 33 ft at NAW-24 (table
1). The depths predicted by seismic-refraction methods
were similar to those determined from test drilling;
however, depths determined from seismic-refraction
data at the northeastern end of profile a-a' were slightly
less than the depths determined from test drilling. GPR
profile A-A' shows a similar bedrock profile and similar
depths at the northeastern end of the line and illustrates
the complex lithology at the site.
Profile b-b' (fig. 7) is approximately 1,000 ft to the
north of profile a-a' and on the northern side of Lyle
Reed Brook (fig. 2). The depth to bedrock is
approximately 40 ft along most of the profile but
decreases to less than 30 ft below land surface near the
southwestern end. The log of test well NAW-240
(fig. 2, table 1) shows refusal at 40 ft below land
surface.
Profile c-c' (fig. 7) is located in the center of the
study area (fig. 2). The bedrock surface is 43 to 57 ft
deep. The log of test well M-6 (table 1) approximately
100 ft from the northern end of the line shows refusal at
49.5 ft below land surface.
Profile d-d' (fig. 8), in the southern part of the
study area near Lyle Reed Brook (fig. 2), approximately
100 ft southeast of the waste-disposal site, shows that
the thickness of unconsolidated sediments is
approximately 60 ft over most of the profile. The water
table is approximately 3 to 4 ft below land surface on the
western end, near Lyle Reed Brook, and 10 ft below
land surface on the east. These data are consistent with
the data on the log of test well RFW-2B (table 1).
Profile e-e' (fig. 8) is about 1,000 ft southeast of the
waste-disposal site (fig. 2). This profile shows that the
bedrock surface is approximately 80 ft deep near the
western end of the line and less than 60 ft deep at the
eastern end. The water table is 10 to 20 ft deep.
SUMMARY AND CONCLUSIONS
Ground-penetrating radar and seismic-refraction
surveys were completed near a former waste-disposal
site in Nashua, New Hampshire. GPR profiles indicated
lithologies in the glacial sediments and detected the
bedrock surface in several profiles. The GPR profiles
could not be used to delineate the water-table surface in
many places because of the absence of a well-defined
water-table reflector. In areas that yielded usable data,
three distinct reflector signatures are evident. The first
reflector signature is a thin, mostly horizontal and
12 Results of Geophysical Surveys of Glacial Deposits Near a Former Waste-Disposal Site, Nashua, New Hampshire
-------
D
c
o
Q.
O
I
100
i
20 40
APPROXIMATE HORIZONTAL DISTANCE
200 FEET
-H
60 METERS
APPROXIMATE VERTICAL
EXAGGERATION X 4
EXPLANATION
Approximate location of geologic contact-
Dashed where infeired
Approximate location of water table
Figure 6. Unprocessed ground-penetrating-radar profile D-D', Nashua, New Hampshire.
rO
grained deposits? ^
LU
:D I-
u-z
OLU
i-O
o
f
LU
-20 I
LU
CO
Q
CC
[An co
-40
CO
CO
LU
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f
-------
FEET
Dobbens Storage Building
METERS
170-,
NAA-219
NAW-242
Unconsolidated sediment
75
METERS
FEET
VERTICAL EXAGGERATION X 1.3
DATUM IS SEA LEVEL
Dobbens field along Nashua River
b'
Unconsolidated sediment
FEET
190n
170
25 50 75
VERTICAL EXAGGERATION X 1.0
Trout Brook Road
Unconsolidated sediment
25
50
VERTICAL EXAGGERATION X 1.2
DATUM IS SEA LEVEL
55
45
25
15
METERS
-40
-30
-20
-10
-0
METERS
r55
45
-35
-25
-15
Figure 7. Geohydrologic sections interpreted from seismic-refraction data for profile a-a', b-b', c-c'.
14 Results of Geophysical Surveys of Glacial Deposits Near a Former Waste-Disposal Site, Nashua, New Hampshire
-------
FEET
Gilson Road near Lyle Reed Brook
d'
METERS
Unconsolidated sediment
50-i
50
75
VERTICAL EXAGGERATION X 1.1
DATUM IS SEA LEVEL
r65
-55
-45
-35
-25
-15
FEET
Gilson Road near Saturn Lane
METERS
200-]
180-
160-
140-
120-
100-
80-
60-
40-
20-
SEALEVEL-
Land surface
Water table *" Unconsolidated sediment
25 50 75
VERTICAL EXAGGERATION X 1.1
,-60
-50
-40
-30
-20
-10
-0
Figure 8. Geohydrologic sections interpreted from seismic-refraction data for profile d-d' and e-e'.
Summary and Conclusions 15
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coarse-grained sediment. The third reflector signature is
a strong, two- to three-band reflector that generally
underlies the other two types and represents the till and
(or) bedrock surface.
The GPR profiles successfully identified
glaciolacustrine sediments consisting of fine sand to
clay that underlie much of the study area. This
fine-grained unit generally prevented penetration of the
radar signal to depths of more than 50 ft.
Coarse-grained features identified in GPR records
include outwash and deltaic deposits such as kame
deltas. Till and coarse sand and gravel deposits were
identified beneath fine-grained glaciolacustrine deposits
in several of the profiles. Continuous bedrock
reflectors were detected only to depths of 50 ft.
Five seismic-refraction profiles were completed in
the area; they identified depths to the water table and to
the bedrock surface. These depths were used to
corroborate depths to reflectors shown by the GPR
surveys; in most cases, depths of reflectors determined
by GPR and seismic-refraction surveys were similar.
Test drilling was completed at three sites to identify
material types identified by the GPR and to corroborate
depths to reflectors determined from the GPR and
seismic-refraction surveys.
SELECTED REFERENCES
Ayotte, J.D.,1994, Use of ground-penetrating radar to deter-
mine the depositional environment of glacial deposits in
southern New Hampshire in Bell, R.S., and Lepper,
CM., eds., Symposium of the application of geophysics
to engineering and environmental problems, Boston,
Mass., March 27-31, 1994: v. 2, p. 629-643.
Beres, Milan, Jr., and Haeni, P.P., 1991, Application of
ground-penetrating-radar methods in hydrogeologic
studies: Ground Water, v. 29, no. 3, p. 375-386.
Geophysical Survey Systems, Inc., 1974, Continuous subsur-
face profiling by impulse radar: Hudson, N.H., Geo-
physical Survey Systems, Inc., 20 p.
Haeni, P.P.,1988, Application of seismic-refraction tech-
niques to hydrologic studies: U.S. Geological Survey
Techniques of Water-Resources Investigations, book 2,
chap. D2, 86 p.
Haeni, P.P., 1992, Use of ground-penetrating radar and con-
tinuous seismic-reflection profiling on surface-water
bodies in environmental and engineering studies in Bell,
R.S., ed., Symposium on the application of geophysics
to engineering and environmental problems, Oak Brook,
Illinois, April 26-29, 1992, Proceedings: Golden, Colo.,
Society of Engineering and Mineral Exploration Geo-
physicists, p. 145-162.
Hansen, B.P., 1986, Exploration for areas suitable for
ground-water development, Central Connecticut Valley
Lowlands, Massachusetts: U.S. Geological Survey
Water-Resources Investigations Report 84-4106, p. 25.
Johnson, D.G., 1992, Use of ground-penetrating radar for
water-table mapping, Brewster and Harwich, Massachu-
setts: U.S. Geological Survey Water-Resources Investi-
gations Report 90-4086, 27 p.
Koteff, Carl, 1970, Surficial geologic map of the Milford
Quadrangle, Hillsborough County, New Hampshire:
U.S. Geological Survey Geologic Quadrangle Map
GQ-881, scale 1:62,500.
Koteff, Carl, 1976, Surficial geologic map of the Nashua
North Quadrangle, Hillsborough and Rockingham
Counties, New Hampshire: U.S. Geological Survey
Geologic Quadrangle Map GQ-1290, scale 1:24,000.
Koteff, Carl and Volckmann, R.P., 1973, Surficial geologic
map of the Pepperell Quadrangle, Middlesex County,
Massachusetts, and Hillsborough County, New Hamp-
shire: U.S. Geological Survey Geologic Quadrangle
MapGQ-1118, scale 1:24,000.
Lieblich, D. A., Haeni, P. P., and Lane, J. W., Jr., 1992, Inte-
grated use of surface geophysical methods to indicate
subsurface fractures at Milford, New Hampshire: U.S.
Geological Survey Water-Resources Investigations
Report 92-4506, 38 p.
Lyons, J.B., Bothner, W.A., Moench, R.H., and Thompson,
J.B., Jr., eds., 1986, Interim geologic map of New
Hampshire: Concord, New Hampshire Department of
Resources and Economic Development, Open File
Report 86-1, scale 1:250,000.
Scott, J.H., Tibbetts, B.L., and Burdick, R.G., 1972, Com-
puter analysis of seismic-refraction data: U.S. Bureau of
Mines Report of Investigations RI 7595, 95 p.
Toppin, K.W., 1987, Hydrogeology of stratified-drift aquifers
and water quality in the Nashua Regional Planning
Commission Area, south-central New Hampshire: U.S.
Geological Survey Water-Resources Investigations
Report 86-4358, 45 p.
Weston, Roy P., Inc., 1989, Remedial program evaluation,
Gilson Road site, Nashua, New Hampshire: Concord,
N.H.,v. 1, 135 p.
16 Results of Geophysical Surveys of Glacial Deposits Near a Former Waste-Disposal Site, Nashua, New Hampshire
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