Paleochannel aquifer potential at Montana State University : a test of hypotheses
by David Allen Donohue
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in
Earth Sciences
Montana State University
© Copyright by David Allen Donohue (1989)
Abstract:
Groundwater resources in the Gallatin Valley of southwestern Montana are controlled by several
factors. These include depositional controls on the Bozeman alluvial fan, tectonic activity in the
block-faulted valley and erosional activity due to base level changes within the basin during the
geologic past. The purpose of this study is to evaluate the presence of a postulated paleochannel within
the Bozeman alluvial fan interpreted from a seismic refraction survey by Brown and others (1983). To
test this hypothesis, a conceptual groundwater exploration model for the southeastern end of the
Gallatin Valley was developed. Field studies included drilling of a well within the trend of the
proposed paleochannel, an earth resistivity survey and shallow seismic refraction survey across the
paleochannel on the campus of Montana State University.
The Roskie well is drilled to a total depth of 56 m (184 ft). Aquifer analysis indicates that the well is
drilled into material that hydraulically compares with Tertiary material throughout the valley. The earth
resistivity survey included resistivity profiling at the 9 m (30 ft) and 30 m (100 ft) a-spacings in order
to intercept the postulated paleochannel at a relatively shallow and a relatively deep level.
Interpretation of the data suggests no deep paleochannel cut into fine-grained Tertiary material and
filled with a thick sequence of Quaternary gravels is present.
The seismic refraction survey utilized a 12-channel seismic recorder and did not repeat the results of
the study by Brown and others (1983). Seismic results indicate material with velocities greater than
2000 m/s (6500 ft/s) are located within 3 m (10 ft) of the surface throughout the study area. The
discrepancy between the results of the two studies appears to be due to the mis-interpretation of the
first arrival seismic wave with the single channel recorder used in the 1983 study.
The results of this study indicate that the study area is not underlain by Quaternary Bozeman alluvial
fan material. A Tertiary pediment surface underlies the area and material with seismic velocities
characteristic of Tertiary sediments is found to a depth greater that 56 m (184 ft). Future wells drilled
into this area cannot expect yields to be greater than 378 lpm (100 gpm) due to the hydraulic properties
of the Tertiary material. PALEOCHANNEL AQUIFER POTENTIAL AT
MONTANA STATE UNIVERSITY A TEST OF HYPOTHESES
by
David Allen Donohue
A thesis submitted in partial fulfillment
of the requirements for the degree
of
Master of Science
in
Earth Sciences
MONTANA STATE UNIVERSITY
Bozeman, Montana
June, 1989
ii
APPROVAL
of a thesis submitted by
David A. Donohue
This thesis has been read by each member of the thesis committee
and has been found to be satisfactory regarding content, English usage,
format, citations, bibliographic style, and consistency, and is ready
for submission to the College of Graduate Studies.
Date
Chairperson, Graduate Committee
Approved for the Major Department
Approved for the College of Graduate Studies
Date
Graduate Dean
iii
STATEMENT OF PERMISSION TO USE
In
presenting
this
thesis
in
partial
fulfillment
of
the
requirements for a master's degree at Montana State University, I agree
that
the
Library shall make it available to borrowers under rules
the Library.
Brief quotations from this thesis are allowable
special permission,
of
without
provided that accurate acknowledgment of source is
made.
Permission
for
extensive quotation from or reproduction of
thesis may be granted by my major professor,
Dean of Libraries when,
the
material
or in his absence, by the
in the opinion of either,
is for scholarly purposes.
this
the proposed use of
Any copying or use
of
the
material in this thesis for financial gain shall not be allowed without
my permission.
Signature_
Date_____ ^7/7 / 1?9
V
ACKNOWLEDGEMENTS
First and foremost,
I would like to thank
Dr.
Stephan G. Custer
for his suggestions and guidance throughout this project.
provided
Dr.
valuable encouragement when problems arose with
William W.
Locke and Dr.
Dr.
Custer
this
study.
Clifford Montagne provided constructive
criticism that was very helpful in the preparation of this thesis.
Dr.
Jim
the
Schmidt provided important suggestions for the development of
conceptual
Williams
model.
and
various
Carol
John
Bibler,
Jay Erickson,
David
Zim assisted in the collection of
times throughout the study.
Hazen,
field
Nick
data
at
Earl Maher proved invaluable
in
redesigning and repairing the seismic energy source.
The seismic
earth
resistivity equipment was loaned to me by the Montana Bureau
Mines
and
supported
Montana
well.
State
Special
patience
of
field
drafting.
Finally,
data
and added
was
a
test
wife,
Cindy,
who
daughters,
Adelle
and
Cindy also assisted in
the
and care for our
I worked on this project.
of
The Physical Plant at
thanks and love are extended to my
support,
while
University
University provided financial support to drill
collection
Donohue,
Graduate study at Montana State
in part by a teaching assistantship.
provided
Mariah,
Geology.
and
constructive
criticism
I would like to thank my parents,
to
my
Bill and Helen
who encouraged me to achieve my fullest potential and allowed
me the freedom to do it.
have been possible.
Without their support, this project would not
vi
TABLE OF CONTENTS
Page
LIST OF TABLES..........................
viii
LIST OF FIGURES.......... /...................................
ix
ABSTRACT.......................................................
xi
INTRODUCTION...................................
I
Problem..................
Purpose.........
Location..................
Geologic Setting................
Pre-Tertiary Rocks..........
Tertiary Sediments......
Late Tertiary-Early Quaternary....................
Quaternary Deposits...............................
Basin Tectonics.......
Laramide Regime...............................
Post-Laramide Regime..........
Bozeman Alluvial Fan...........................
Proximal Zone.........
Mid-fan Zone.............
Distal Zone.............
Paleochannel Hypotheses.... ..............
Paleochannel Model............ . ........................
I
2
3
6
8
9
12
13
14
14
15
19
20
21
22
23
25
METHODS OF STUDY..............................................
29
Air Photo and Geomorphology............................
Drilling and Well Development.....................
Resistivity..............
Seismic Refraction.........
29
30
31
33
vi i
TABLE OF CONTENTS— Continued
RESULTS AND DISCUSSION.......
Air Photo Interpretation...............................
Drilling and Well Development..............
Drill Data and Interpretation.....................
Water Level Measurements...............
Aquifer Analysis......
Pump tests.........
Slug tests...................................
Discussion. ....................... ................
Earth Resistivity Survey...............................
Previous Resistivity Work..................... . ...
Data and Discussion................................
Seismic Refraction Survey.........
Previous Seismic Investigations........
Data and Interpretation...........................
Discussion........................................
Page
35
35
35
36
38
38
38
42
44
46
48
49
56
56
57
61
CONCLUSIONS.............................
Alternative Model............................ . .. ......
Future Considerations....... ................ ..........
69
69
, 72
REFERENCES CITED...............................
74
APPENDICES..............
80
Appendix A —
Appendix B —
Appendix C -—
Roskie Well Aquifer Test Data............
Earth Resistivity Data....................
Seismic Refraction Data.......
81
85
93
viii
LIST OF TABLES
Table
1.
Page
Lithologic log of Roskie well, Roskie field study area,
Montana State University, Bozeman...................
37
2.
Water level measurements in the Roskie well.......
39
3.
Average seismic velocities for various compositions,
geologic ages, and burial depths......
59
Observed seismic velocities of material found in Roskie
study area and interpreted geologic age.............
60
Calculated depths to top of material with velocities
characteristic of Tertiary - age sediments in the
Roskie study area.......
61
6.
Roskie well pump test and recovery data, May 1985........
82
7.
Aquifer analysis using recovery method...................
83
8.
Slug test data, June 1985............... .............. .
84
9.
Resistivity profile data, 1985...........................
86
10.
Vertical electrical sounding data........................
91
11.
Seismic velocities, Roskie study area, 1985..............
94
4.
5.
ix
LIST OF FIGURES
Figure
1.
Page
General location of the Bozeman alluvial fan and the
Gallatin Valley, Montana.... ......
5
2.
Study site index map, Montana State University...........
6
3.
General tectonic map of the Gallatin Valley area.........
7
4.
Generalized Tertiary stratigraphic section for
southwestern Montana and the Gallatin Valley,
showing depositional and erosional cycles in
relationship to climate.....................
10
5.
Bouguer gravity map of the Bozeman area.... ..............
16
6.
Schematic structural cross-section across the southern
end of the Gallatin Valley near South Cottonwood
Creek.................
18
Schematic longitudinal cross-section of a general
alluvial fan facies model...........................
20
Schematic cross-section of the Gallatin Valley near
Belgrade.............
24
Block diagram of the conceptual exploration model for
the Bozeman alluvial fan, southwestern Montana.... .
26
Block diagram of hypothesis to be tested in Roskie
study area and vicinity.............................
28
11.
Wenner electrode array...........................
32
12.
Drawdown and recovery data, Roskiewell, May 25, 1985.....
40
13.
Coopei— Jacob semi-log plot of recovery data used to
estimate transmissivity for the Roskie well..... ...
42
Location of earth resistivity survey lines, Roskie
channel study area, Montana State University,
Bozeman....... .'....................................
50
7.
8.
9.
10.
14.
X
LIST OF FIGURES— Continued
Figure
15.
16.
17.
18.
19.
20.
21.
22.
Page
Map of apparent resistivity with a-spacing = 9 m
(30 ft)... ........................................
51
Map of apparent resistivity with a-spacing = 30 m
(100 ft).......
52
Comparison of vertical electrical sounding and drill
log, Roskie well............ ..................... .
55
Location map of refraction seismic survey lines, Roskie
channel study area, Montana State University,
Bozeman..................... ..... .................
58
Histogram of recorded seismic velocities, Roskie
study area, Montana StateUniversity, Bozeman...... ..
60
Comparison of seismic line 22 from 1982 survey and
seismic line 2R from 1985survey.............
62
Time - distance plots of seismic lines BR and 9R
across Roskie field and the hypothesized
paleochannel...........................
67
Block diagram of proposed alternative model for the
Roskie study area........... .......................
71
xi
ABSTRACT
Groundwater resources in the Gallatin Valley of southwestern
Montana are controlled by several factors.
These include depositional
controls on the Bozeman alluvial fan, tectonic activity in the blockfaulted valley and erosional activity due to base level changes within
the basin during the geologic past.
The purpose of this study is to
evaluate the presence of a postulated paleochannel within the Bozeman
alluvial fan interpreted from a seismic refraction survey by Brown and
others (1983).
To test this hypothesis, a conceptual groundwater
exploration model for the southeastern end of the Gallatin Valley was
developed.
Field studies included drilling of a well within the trend
of the proposed paleochannel, an earth resistivity survey and shallow
seismic refraction survey across the paleochannel on the campus of
Montana State University.
The Roskie- well is drilled to a total depth of 56 m (184 ft).
Aquifer analysis indicates that the well is drilled into material that
hydraulically compares with Tertiary material throughout the valley.
The earth resistivity survey included resistivity profiling at the 9 m
(30 ft) and 30 m (100 ft) a-spacings in order to intercept the
postulated paleochannel at a relatively shallow and a relatively deep
level.
Interpretation of the data suggests no deep paleochannel cut
into fine-grained Tertiary material and filled with a thick sequence of
Quaternary gravels is present.
The seismic refraction survey utilized a 12-channel seismic
recorder and did not repeat the results of the study by Brown and
others (1983).
Seismic results indicate material with velocities
greater than 2000 m/s (6500 ft/s) are located within 3 m (10 ft) of the
surface throughout the study area. The discrepancy between the results
of the two studies appears to be due to the mis-interpretation of the
first arrival seismic wave with the single channel recorder used in the
1983 study.
The results of this study indicate that the study area is not
underlain by Quaternary Bozeman alluvial fan material.
A Tertiary
pediment
surface underlies the area and material with
seismic
velocities characteristic of Tertiary sediments is found to a depth
greater that 56 m (184 ft). Future wells drilled into this area cannot
expect yields to be greater than 378 Ipm (TOO gpm) due to the hydraulic
properties of the Tertiary material.
I
INTRODUCTION
Problem
Alluvial fan deposits are the principal groundwater reservoir
many
areas
of the western U.S.
(Bull,
1972).
These
for
deposits
are
economically important to farmers, ranchers, and the general public who
depend
upon them as a source for water.
streams
control
groundwater
basins
the
much
of
The alluvial fans and
the groundwater recharge
basins (Bull,
1972;
Cehrs,
1979).
in
the
In the
system.
adjacent
block-fault
of southwestern Montana alluvial fans are an integral
groundwater
their
part
An important source of groundwater
in
of
the
Gallatin
Valley is the Bozeman alluvial fan located at the base of the
Gallatin
Range
alluvial
fan
(Hackett and others,
withdrawn
Understanding groundwater controls on the Bozeman alluvial fan as
well
as
have
sites
for
domestic
groundwater
and
the
use.
optimal
for both
within
irrigation
locating
is
1960). . Groundwater
withdrawal
can
considerable benefits for local groundwater users.
Previous
groundwater
scientific investigations regarding the availability
from the Bozeman alluvial fan began with Hazen (1942)
examined the Gallatin River basin on a reconnaissance basis.
(1953)
ran
several refraction seismic and resistivity surveys
resource
investigation
by
Hackett
and
others
who
Wantland
across
the alluvial fan and other parts of the Gallatin Valley to support
groundwater
of
the
(1960).
2
Wantland
in
was concerned with locating the depth to Precambrian
the valley and determining the extent of valley fill.
bedrock
Hackett
and
others (I960) explored recharge on the alluvial fan and recognized that
irrigation,
stream loss and rainfall were important.
Brustkern (1977)
modeled
the impact of land use change on groundwater resources of
the
Bozeman
area,
was
concerned
changes
in particular the Bozeman alluvial fan.
with
but
geophysical
how
the
aquifer would respond to
was limited by the availability
data.
Much
of
His model
various
land
use
geohydroIogical
and
more complete information regarding
inflow,
outflow, recharge, discharge and the details of the geology are needed.
Dunn
(1978)
chemistry
examined changes in groundwater
in
groundwater
levels
and.
groundwater
the Gallatin Valley to determine if any changes
in
the
had occurred since the study by Hackett and others (1960).
His findings indicate no significant changes in water availability
and
water chemistry have occurred.
Purpose
Groundwater
is
needed on the Montana State University campus
supply chlorine-free water for research purposes and to supplement
present
water
Precambrian
supply.
gneiss
The
primary
material
Brown
and
was
the
the
report
that
had been encountered in building foundations
near
the site where the wells were planned.
concern
to
Water wells drilled into
such
would be expensive and would potentially yield little
water.
others (1983) used refraction seismic techniques to
assess
the distribution of this neai— surface bedrock feature.
They found that
a 4500 m/s (15000 ft/s) velocity, suggestive of Precambrian bedrock, is
3
present under parts of the MSU campus,
but the seismic energy
sources
used could not detect this feature on all parts of the campus.
During
this study,
deep
channel
campus.
and
preliminary interpretations suggested that a 60 m (200 ft)
The
might
exist near Roskie Dormitory at the
west
end
channel interpretation was based on time-velocity
their relations to a topographic depression in the area.
of
plots
Such
a
channel or channels might serve as an important groundwater resource on
the
fan.
The difficulty with the interpretation was the sparse
and
potential
Additional
alternative
work is needed.
further test these ideas.
1.
interpretations of the
Do
The purpose
geophysical
data
data.
of this investigation is
to
Several questions need to be addressed.
additional hydrologic investigations confirm or deny
the
presence, size, extent and trend of the postulated channel?
2.
Do
additional
postulated channel,
geophysical
studies
confirm
and if the channel is confirmed,
or
deny
the
can it be better
delineated?
3.
Hackett
Can an understanding of the alluvial fan setting postulated by
and
groundwater
others
(1960)
be
refined
to
better
understand
potential on the west side of the MSU campus based on
the
the
hydrologic and geophysical data?
Location
The
morphology
Bozeman
by
alluvial
fan
was mapped on the
Hackett and others (1960).
They
basis
found
of
a
surface
Quaternary
alluvial fan with an apex at the mouth of Hyalite (Middle) Creek at the
north end of the Gallatin Range,
Montana.
The alluvial fan was mapped
4
with
km
an elongate shape and is approximately 18 km (11 mi) long and
(6 mi) wide at its widest section (Figure I).
10
The alluvial fan is
bounded on the east by Sourdough Creek, on the west by South Dry Creek,
on the south by the Gallatin Range,
of the East Gallatin River,
River.
The
on the northeast by the floodplain
and on the northwest by the West
Gallatin
city of Bozeman straddles the east-central portion of the
fan.
The
specific area on the Bozeman alluvial fan chosen to test
the
presence of the paleochannel interpreted by Brown and others (1983)
located
site
on the property of Montana State University (Figure
extends
Dormitory,
Lincoln
across
on
the
Avenue
Roskie
field,
the
east
Brown
buried
paleochannel
by
on the
and on the north by Garfield Street.
because
This
through
this
has
occurred
here
geophysical
lines
could
be run.
area.
previous
Only
to
a
this
This site is
University was interested in
minor
also
drilling
study
The
Roskie
south
by
area
was
of
the
and others (1983) had mapped the trend
development
State
on
west by Marsh Laboratory field,
chosen
Montana
bound
2).
is
amount
of
so
that
located
where
an
exploratory
irrigation well to test the model proposed by Brown and others (1983).
MONTANA
Figure
I:
General location of the Bozeman alluvial fan and the
Gallatin Valley, Montana (modified from Hackett, 1960).
6
IH 003'
I
Il
12
14 13
STUDY
S IT E x
College
*o>
MONTANA
Garfie ld
STATE
MARSH
U N IV E R S IT Y
LAB
R O S K IE
\
F IE L D
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F IE L D
:
Vi
Vv' W e l l
A r " " s ite
\
v L in c o l n . Rd
rI
M ann
Lab
0
1
I
O
Figure
400
I
1000
800
I
2000
m
ft
The
Study site index map , Montana State University.
intersection of South 19th and College is a section corner
with numbers indicating the sections in T 2 S, R 5 E.
2:
Geolooic Setting
The Bozeman alluvial fan is in a block-faulted basin characterized
by
basin and range style faulting in southwestern Montana
others,
1965;
alluvium
are
Reynolds,
generally
1979)
(Figure
3).
considered to fill
Large
these
(Davis
thicknesses
valleys.
of
the
the
Gallatin Valley is necessary in order to understand the structural
and
alluvial fan.
controls
history that led to
governing
the
the
hydrogeology
formation
A
of
depositional
geologic
of
Complex
faulting and extended periods of erosion complicate these deposits.
review
and
of
the
Bozeman
7
■
45 * 4 5 '
5 ml
5
Figure
3:
O
General tectonic map of the Gallatin Valley area.
Qbf =
Bozeman alluvial fan; Qu = Quaternary-age basin fill; QT =
older
Quaternary-Tertiary
sediments;
T
=
Tertiary
sediments; Tv = Tertiary volcanics; TKs = Tertiary
Cretaceous-age sediments; MP = Mesozoic-Paleozoic rocks;
PEb = Precambrian Belt Supergroup; PGa =
Precambrian
Archean rocks
(modified from Hackett and others,
1960;
Hughes, 1980; Lageson, 1989).
a
Pre-Tertiarv Rocks
Development
began
in
a
the geologic architecture of the Gallatin
early Precambrian time.
underlie
1963;
of
the
Archean
basement
valley and cropout along the valley
Zim and Lageson, 1984; Craiglow, 1986).
major
east-west
Dillon
Block
relative
to
consisting
the
conglomeratic
others,
sediments
1974).
northeastern
rocks
(Robinson,
During Proterozoic time
metamorphic
rocks
While this fault was active, the southern
of Archean metamorphic
northern
gneissic
margins
trending fault cut the Archean
(Harrison and others, 1974).
Valley
block;
The
uplift
rocks
shed
northward into the Belt Basin
was
uplifted
coarse-grained
(Harrison
and
Proterozoic Belt Supergroup strata are found along the
margin
of the Gallatin Valley.
Deposition of the
Belt
sediments was controlled by this major east-west trending normal
fault
called the Willow Creek (Central Park) Fault (Harrison, 1974).
Paleozoic
underlie
the
Deposition
and
basin'
Mesozoic sediments flank the Gallatin
(Robinson,
1961;
Davis
and
Valley
others,
and
1965).
of these sediments took place on a relatively stable craton
which developed after faulting ceased on the Willow Creek
trend.
The.
Paleozoic rocks are dominantly epicontinental marine muds and carbonate
deposits
with
sediments,
marine
a thickness of about 1500 m (5000
ft).
The
Mesozoic
approximately 1500 m (5000 ft) thick, consist dominantly of
shales and sandstones (Robinson,
1963).
Periods of erosional
activity are seen as unconformities within the stratigraphic section.
Late Cretaceous Elkhorn Mountain volcanic rocks are present
the
These
northern margin of the basin
(Robinson,
1961;
Chadwick,
along
1981).
late Cretaceous volcanic rocks underlie the source area for much
9
of
the early Paleocene stream-laid volcaniclastic sediments (Robinson,
1961).
Intrusive
Batholith
stocks,
most
probably offshoots
which lies to the west of the area,
of
the
underlie the
Boulder
northwest
and southwest portion of the basin.
Eocene-Paleocene
Gallatin
Basin
andesitic
to
conglomerates
in
volcanic
the
dacitic
rocks are found to the
Gallatin
flows,
(Chadwick,
Range.
flow
1981).
Composition
breccias,
These
south
mudflow
provided
of
the
ranges
from
breccias
and
additional
source
material for stream-laid Tertiary deposits in the Gallatin Valley.
Tertiary Sediments
Although
Oligocene,
the
rocks
stratigraphic
valley
of
is postulated to have been
this
age
are
not
recognized.
Sixmile
unconformity
units
produce
Two
units are recognized in the Gallatin Valley:
middle Eocene to early Miocene Renova Formation and
Miocene
formed
Creek
separates
Formation
(Hughes,
in
the
Tertiary
the
early
the middle to late
1980).
An
the two formations (Figure 4).
differing amounts of groundwater and are
erosional
Each of
these
important
to
identify when searching for water supplies.
Prior
from
to deposition of the Renova Formation,
most sediments
the uplifted mountains were transported eastward out of the basin
by through-flowing streams (Robinson, 1963; Glancy,
of
shed
1965).
Dissection
the landscape in early Eocene time left an erosional topography
on
which the Renova formation was deposited (Robinson, 1963; Hughes, 1980;
Thompson
and others,
1982).
The late Eocene saw a shift to a
drier
climate, development of internal drainage, and deposition of the Renova
Formation.
10
MYBP SedimentaryUnits
Pleistocene
Alluvium
Pliocene
5.2—
Sixmile
Creek
Miocene
Formation
24.6 -
•
Oligocene
Renovo
36.6—
Formation
Eocene
54.9-
Paleocene
Figure 4:
Generalized Tertiary stratigraphic section for southwestern
Montana and the Gallatin Valley, showing depositional and
erosional cycles and their relation to climate (modified
from Thompson and others, 1982).
11
The
The
Renova
lower
Formation is divided into a lower and an
part
consists dominantly of
floodplain sediments,
clastic
materials
low-gradient
from local sources are
part.
lacustrine
derived mostly from volcanic ash.
derived
scattered lenses.
fine-grained
upper
Some
present
coarse
as
minor
Deposition of Rehova sediments probably occurred in
streams (Hughes,
1980;
Fields and others,
1985).
The
upper part of the Renova Formation is dominated by large quantities
volcaniclastic
lenses
of
and
rocks and montmorillonitic mudstones.
coarse clastic
sediments,
arkose,
and
of
Minor scattered
conglomerate
are
present within this unit (Fields and others, 1985).
Deposition of both
members
internal
of
the Renova formation was controlled by
drainage
into what would become the Gallatin Valley basin.
Renova Formation deposition occurred until early Miocene time when
a
shift to a more humid climate occurred (Thompson and others,
1982).
Through-flowing drainage systems redeveloped and allowed removal of
unknown
erosional
1980).
quantity
of
Renova sediments from the
topography developed and produced an
basin.
A
unconformity
an
dissected
(Hughes,
This moister climate continued, until early middle Miocene time
when a more arid climate developed.
Deposition
of
the Sixmile Creek Formation
began
following
the
climatic change from moist to dry during the early middle Miocene time.
Basin filling resumed and gradually buried the erosional surface formed
during post-Renova time (Hughes, 1980; Thompson and others, 1982).
The
Sixmile Creek Formation is composed of a sequence of gravelly sediments
derived from developing fault-block mountains (Hughes, 1980; Fields and
others,
1985).
The
coarse clastic sediments were deposited as
fans,
12
mudflows,
debris
channel fills.
deposits.
were
ephemeral
stream
deposits and
some
large
Volcaniclastic sediments comprise the majority of
(Hughes,
1980;
Fields and others,
1985).
the
These sediments
deposited under high-gradient flow conditions such as those found
today
in the arid southwestern United States.
Sixmile
in
flows,
The
coarser
grained
Creek Formation rests upon Precambrian through Paleozoic rocks
other
parts of the Gallatin Valley where dissection has
cut
into
of the Sixmile. Creek Formation continued through
late
pre-Tertiary bedrock (Hughes, 1980).
Deposition
Miocene
time
occurred.
until
The
a climatic shift from a dry
basin
filling with Sixmile Creek
ended by middle or late Pliocene time.
the
to
wet
environment
Formation
sediments
This moist climate brought
development of through-flowing streams which cut into the
Creek Formation.
this
late
Sixmile
Some coarse-grained sediments were transported across
Tertiary surface.
These sediments are represented by
Quaternary-Tertiary older alluvium surface (Hackett and
Hughes, 1980).
on
others,
the
1960;
The time of deposition of these sediments is not clear.
Late Tertiary - Early Quaternary
Pediment
surfaces developed in the basins of southwestern Montana
during the extensive erosion of the Sixmile Creek Formation (Fields and
others,
1985).
paleodrainage
Up
to
direction
is
direction when not internal
1980).
uplift
But
during
late
Tertiary or early
thought
(Robinson,
to
have
1963;
Quaternary
been
in
Glancy,
1965;
late Tertiary-early Quaternary time,
to the south tilted most of the Gallatin Valley
formed the ancestral Missouri drainage (Robinson,
1961).
an
a
time
easterly
Hughes,
regional
northward
and
The Gallatin
1.3
River
cut
assumed
its
drainage
wet
the
through
the bedrock at the eastern end of the
present drainage direction to
and
This
new
northwest.
direction along with a climatic change to a relatively
warm,
climate most likely contributed to the progressive downcutting
streams
into
the
late
Tertiary
development of the pediment surfaces.
to
the
valley
the
Tertiary
Paleozoic
and
sediments,
Downcutting was not
sediments but excavated
Precambrian
leading
some
the
restricted
underlying
rock units as seen in the
to
of
Dry
Mesozoic,
Creek
and
Horseshoe Hills area (Hughes, 1980).
Quaternary Deposits
In the basins of southwestern Montana,
locally
Quaternary sediments
from
derived sources overly the Tertiary pediment surfaces and fill
dissected
portions
Glaciation
of
the
pediments
(Fields
and
others,
during the Pleistocene in the Gallatin Range to
contributed
sediments
southern end of the
superimposed
which
were
transported
the
northward
Gallatin basin (Weber, 1965).
1985).
south
into
the
These sediments are
over the Tertiary pediment surfaces as alluvial
fans
in
of
a
the valley (Hackett and others, 1960).
The
Quaternary
alluvial
fan
deposits
are
composed
heterogeneous mixture of coarse— and fine-grained sediments.
and
lenses
of
distributaries
deposits
Quaternary
relatively
that
clean sand and
by
the
built the alluvial fans are found throughout
the
(Hackett and others,
erosional channels,
1960).
gravel
deposited
Stringers
If this material
filled
pre-
as implied by Brown and others (1983),
the potential for large water-bearing zones exists.
14
Basin Tectonics
The basins of western Montana,
have
which include the Gallatin Valley,
a structural origin similar to that found in the Basin and
Province of the western U.S.
along
the
Willow
(Fields and others,
1985).
Creek Fault (Central Park Fault) and
during late Precambrian,
Range
Reactivation
other
faults
late Cretaceous and Cenozoic time contributed
to the present structure of the Gallatin Valley
(Robinson,
1963;
Zim
and Lageson, 1985).
Two
dominant and significant tectonic regimes are responsible for
the structural development of the Gallatin Valley: I) Laramide fold and
thrust faulting and block uplift, and 2) post-Laramide extension.
Laramide Regime
At
the
compressive
onset
of
forces
the
deformed
Laramide
and
Orogeny,
uplifted
Extensive erosion of the uplifts occurred.
oblique
these
slip
Garihan,
Valley,
forces.
of
motion
1983;
Zim
Phanerozoic
the
pre-basin
rocks.
Numerous northwest-trending
faults in southwestern Montana developed as a result
compressive
component
northeast-southwest
rocks,
These
faults
contain
and dip steeply to the
and Lageson,
as
1985).
a
northeast
of
left-lateral
(Schmidt
and
They cut both Archean
and
seen in the southwestern part of the
Gallatin
and probably extend beneath the basin sediments. Hughes (1980)
observed
several
small northward-trending
left-lateral
strike
slip
faults in the Dry Creek Valley at the north end of the Gallatin Valley.
These
faults cut most of the lower Paleozoic section in this area.
study of these faults by Lageson and Zim (1984) suggests that they
A
are
15
reactivated
Proterozoic
normal faults that were folded in the
earIy-
Eocene by uplift of the Archean core of the Bridger Range.
In
addition to these northwest-trending faults there is a
of northeast-trending thrust faults involving Archean,
Phanerozoic
rocks.
east
Proterozoic and
Major folds overturned to the east resulted
this thrusting episode.
to
system
resulting
from
Overall direction for the compression was west
in a shortening of the crust by
several
tens
of
kilometers (Schmidt and Garihan, 1983).
Several
high-angle reverse faults with a general east-west
trend
cut through the Bridger Range bordering the eastern margin of the basin
proper.
The
Precambrian
Pass
Fault
is interpreted to be an
extension
1955;
Craiglow, 1986).
Reactivation
during
Laramide
compression first caused strike-slip motion
fault,
followed
by later underthrusting of the Archean block
south
(Craiglow,
1985).
deposits
interpreted
the
Willow Creek Fault zone located in the central part of the
Gallatin Valley Basin (McMannis,
younger
of
at
from
This
Archean
block is
the southern end of the
gravity
to
concealed
Bridger
data as a narrow gravity
on
the
beneath
Range
high
this
and
(Davis
is
and
others, 1965) (Figure 5).
Post - Laramide Regime
The
development
(Reynolds,
second
tectonic
of
the
1979).
regime
Gallatin
The
responsible
Valley
intermontane
is
for
the
post-Laramide
basins
resulting
structural
extension
from
this
tensional stress became catchment basins for clastic material shed from
the
surrounding mountains.
contemporaneous
with
Basin structures suggest faulting
sedimentation (Fields and
others,
1985).
to
be
The
16
111*09'
EXPLANATION
—
-170
Gravity contour
Gravity contour
enclosing area
of low gravity
BOZEMAN
—
Figure 5:
present
45 * 40 '
Bouguer gravity map of the Bozeman area.
Contour interval
5 mi Iligals (modified from Davis and others, 1965)
stress
field
for the region responsible
for
this
faulting
appears to be east-west extension (Zoback and Zoback, 1980).
Structural development of the present Gallatin Basin area probably
began during Miocene time (Lageson,
responsible
basin
1989).
Extensional tectonics were
for early basin development and controls most of
geometry.
Range-front
faults became active during this
Early basin shapes were much broader and shallower than present
(Robinson,
along
late
offset
1963;
Fields and others,
1985).
of
time.
time.
basins
Normal faulting occurred
the eastern and southern margins of the Gallatin Valley
Tertiary
Cenozoic
Faulting has offset Tertiary sediments
overlying Quaternary alluvium has been documented
through
but
no
(Hackett
17
and others,
of
the
1960;
basin,
observation
and
Hughes, 1980).
where exposed,
dip into
the
mountain
front.
This
suggests a listric geometry for the basin margin structure
has important implications for any groundwater
for the Gallatin Valley.
of
Tertiary strata in the eastern part
exploration
model
Dips of Tertiary strata in the southern part
the valley are inferred to have a listric geometry as well but
not
well enough exposed to document.
gravity
data.
disturbed
affected
along
Along
This inference is supported
the Gallatin Range front,
are
by
Tertiary strata
are
but the Quaternary alluvial fan deposits are apparently
not
(Hackett and others,
1960). . This suggests latest
movement
the fault to be of late Miocene or early Pliocene time
(Tysdal,
1966).
Geophysical
southwest
trending
alluvial
fan.
separates
(Figure
data
This
supports the interpretation of
two
northeast-
normal faults at the southern end of
the
Bozeman
system of inferred Gallatin Range
Front
faults
the Gallatin Valley from the foothills of the Gallatin Range
6).
Gravity data along the southern margin of
the
Gallatin
Valley suggests a bedrock trough underlying Quaternary sediments (Davis
and others,
deep
trough
and
is
1965).
This trough is estimated to be approximately 2 km
3 km wide in the vicinity of South
Cottonwood
bounded on the southern and northern margins
step fault zones (Davis and others,
1965).
Creek.
by
The
concealed
The southern fault extends
approximately
from the mouth of the Gallatin Canyon eastward along the
range front.
The fault which bounds the north margin of the structural
trough
appears
to
have
more
displacement (Davis and others,
than
1965).
600
m
(2000
ft)
of
vertical
Gravity data suggests that the
18
bedrock
the
surface below the Tertiary-age sediments gradually rises
south
to the north where Precambrian crystalline rock
below the surface.
Hills,
Precambrian
location
lies
from
just
In some areas of the valley, such as the Camp Creek
crystalline rock crops out at
the
of near-surface Precambrian bedrock is a major
surface.
The
consideration
when
searching for groundwater in the valley since such gneiss
form
very poor aquifers (Hackett and others,
1960) and may
should
influence
the geomorphic history and geohydrologic conditions of the area.
N W
Figure
S E
6:
Schematic structural cross-section across the southern end
of the Gallatin Valley near South Cottonwood Creek.
Note
the relationship between the Gallatin Range Front Fault
and the structural trough of Davis and others (1960). See
Figure 3 for line of cross-section.
19
Bozeman Alluvial Fan
Groundwater
understanding
and
exploration in alluvial fan environments requires
of
processes controlling past and present
erosional periods (Cehrs,
associated
with
hydrologic
system
testable
1979).
(Butcher
and
the
Garrett,
1963;
depositional
controls
such fans in fault-block valleys also
structural-depositional
understand
Structural
commonly
influence
Fetter,
model is useful when
an
the
1980).
A
attempting
to
groundwater potential of a system such as the
Bozeman
alluvial fan.
Alluvial
fans can be generally thought of,
groundwater exploration,
from the standpoint of
as alternating vertical and lateral sequences
of aquifers and aquicludes (Cehrs,
1979).
These variations
primarily
result from controlling factors such as tectonic activity (Bull,
1984;
Heward,
1967;
Rust,
1982;
1979;
Nilsen,
Harvey,
Boothroyd and Ashley,
1975;
1982),
1984),
1972,
source rock lithologies (Hooke,
climatic variations (Bull,
1972;
Blissenbach, 1980; Westcott and Ethridge,
1980; Kochel and Johnson, 1984; Ritter and TenBrink, 1986) and drainage
basin size (Nilsen, 1982; Harvey, 1984).
These factors are complicated
by local geologic historical influences unique to a particular alluvial
fan.
An alluvial fan can be divided into three main zones:
(coarse-grained),
Figure
7
gradation
alluvial
2)
mid-fan,
diagrammaticalIy
that
fan
exists
and
shows
3) distal
(fine-grained)
these alluvial fan
between them.
I) proximal
The intersection
zones
areas.
and
point
is the point where the alluvial fan stream emerges
the
on
an
from
so
its
channel
Downstream
proximal
and spreads out across the
surface
(Hooke,
1967).
from this intersection point is where modern deposition
sediment occurs.
features,
fan
but
due
to
of
The Bozeman alluvial fan may display these
the lack of detailed
sedimentological
data,
separating out the three sections is not currently possible.
Mountain
Front
Proximal
Mid-fan
Distal
— in te rs e c tio n
ch a n n e l
p o in t
eV
o
\
— .
.V; -
Decreasing grain size
Figure
7:
Schematic longitudinal cross-section of a general
fan facies model (modified from Rust, 1979).
alluvial
Proximal Zone
The
proximal
zone
of an alluvial fan is
dominated
by
grained sediments usually transported only a relatively short
past the mouth of the canyon (Bull,
1972).
In other regions,
coarse­
distance
debris
flow ( or mudflow) deposits are also found in this area of the alluvial
fan.
Debris
flows
are caused by steep slopes,
lack of
vegetation,
short periods of abundant water supply and a source of debris with mudrich matrix (Johnson, 1970; Bull, 1977).
The sediments in the proximal zone of the Bozeman alluvial fan and
observed
in well logs consist of coarser-grained boulders and
cobbles
21
intermixed
1960).
with
finer grained gravels and sand (Hackett
Sediment sorting is poor in this zone.
A deep,
and
others,
broad, single
channel represented by present day Hyalite (Middle) Creek is present in
the
proximal zone of the Bozeman alluvial fan and is characteristic of
fans
in
general
(Bull,
1964,
1968).
Hyalite
(Middle)
Creek
is
presently incised at the head of the Bozeman alluvial fan.
Mid-fan Zone
The
boundary between the proximal and mid-fan zone on an alluvial
fan is difficult to ascertain unless sub-surface exposure is available,
so
only approximate limits can be made.
zone
will
vary
for
each individual
The extent of
alluvial
fan
the
proximal
(NiIsenj
1982).
Sediment size within the mid-fan zone is expected to consist of coarseto medium-grained sediments (cobbles,
than
those
downfan
gravel and sand),
found in the proximal zone since sediment
(McGowan,
1979).
Relatively
shallow,
finei— grained
size
decreases
discontinuous
distributary channels radiating outward from the main stream channel of
the proximal zone are often present in this zone (Nilsen, 1982).
These
shallow channels develop by avulsion as the channels fill and clog with
sediment.
Although the channels are usually braided,
straight
channels
sediment
type,
may also be present depending
sediment
supply
and climatic
upon
effects
anastomosing or
fan
gradient,
(Bull,
1968;
McGowan, 1979; Nilsen, 1982).
The boundary between the proximal and mid-fan zone of the
alluvial
fan is difficult to ascertain since very few cuts expose
material.
Lithologic
show
boundary but variations in driller's descriptive
this
Bozeman
the
logs from wells drilled in the alluvial fan may
logs
may
22
make identification of this boundary difficult.
of
outcrop,
the
shift
from poorly sorted
Because of this
coarser— grained
lack
deposits
f
characteristic of the proximal zone to the better sorted medium-grained
stream-laid deposits of the mid-fan zone has not been identified.
The upper part of the mid-fan zone of the Bozeman alluvial fan may
be
complicated
survey
the
the structural trough inferred
data (Davis and others,
Gallatin
confined
trough
by
Valley.
A
1965),
from
an
gravity
located at the southern end of
thick sequence
of
Cenozoic
within this trough and thins northward.
had
the
sediments
is
Whether or not this
effect on deposititinal controls of
the
alluvial
fan
material is uncertain.
Distal Zone
Finer— grained,
unconfined
distal
sand,
silt
and clay
low velocity stream flow processes often
transported
by
characterize
the
These deposits
may
with floodplain sediments near the farthest limits of
the
zone
interfinger
alluvial
sheet-like
of an alluvial fan (Nilsen,
fan.
1982).
Due to the lack of subsurface exposure,
the
between
the
Bozeman
alluvial
(1960),
the Bozeman alluvial fan distal zone would tend to be
boundary
mid-fan and distal zones has not been identified
fan.
Based
upon the work of
Hackett
on
and
the
others
similar
to that characterized by alluvial fans in general.
Paleochannel Hypotheses
An
problem
interesting feature of the Bozeman alluvial fan and
in
paleochannel
this
study is the postulated presence of
a
the
deep
inferred from seismic refraction data (Brown and
main
buried
others,
23
1983).
The
models
of
occurrence
alluvial
of such a channel does not fit most
fans.
The general model for
the
reported
mid-fan
area
usually includes, braided stream channels only of the magnitude of about
3
m
deep
structural
(10 ft) (Bull,
controls
in
1968).
the
But
local
Gallatin
Valley
geologic
basin
history
allow
for
and
the
feasibility of such a paleochannel.
A
similar
condition
southwestern Montana.
active
Madison
alluvial
the
in
the
upper
Madison
Valley
in
Ruby Creek flows westward from the tectonically
Range.
The
creek has cut a deep
channel
into
the
fan and the bedrock beneath the alluvial fan as it flows into
Madison
communication,
helps
exists
River
(B.
1989).
Locke,
Montana
State
University,
personal
The presence of this geomorphologicaI
feature
support the feasibility of such a condition to exist beneath the
Bozeman alluvial fan.
Several
hypotheses
can. be proposed to explain the
existence
of
such a paleochannel on the Bozeman alluvial fan:
I)
A thick sequence of Cenozoic sediments are downwarped and
northward beneath the Belgrade plain (Hackett and others, 1960) (Figure
8).
If the tectonic subsidence rate periodically exceeded the filling
rate
of the downwarped trough south of the Central Park Fault,
a
new
lowered
local baselevel might cause downcutting on the Tertiary strata
beneath
the present day Bozeman alluvial
fan.
would more likely be confined to the distal zone,
study
downcutting
the proximity of the
area to the toe of the fan could allow for some
the study area as well.
on
Although
downcutting
in
As filling rates increased, renewed deposition
the Tertiary sediments would occur.
Deposition of coarsei— grained
dip
24
S
N
Bozeman fan
Belgrade plain
-— -I^ C e n/■tr
a I Park (Wlllowx^
*___ I X r-__ i \ \ \ ^
Figure 8: Schematic cross-section of the Gallatin Valley near Belgrade.
Note the relationship between the Bozeman alluvial fan,
Belgrade plain (Gallatin Valley floodplain) and the Central
Park fault (modified from Hackett and others, 1960).
sediments
during the most recent development of the
Bozeman
fan could have been concentrated within this channel.
filled,
continued
deposition
alluvial
Once the channel
on the alluvial fan surface would
have
occurred.
2) The Precambrian bedrock ridge buried just below the surface
the
eastern
central part of the Bozeman alluvial fan could also
been a factor in development of a paleochannel.
have
caused
the
stream
could
fluctuated.
have
been
cause
flow in this section of
additional
downcutting as
the
valley
A straighten
the
local
within
such a channel
during
the
to
be
stream
baseIeveI
A concentration of coarse-grained lag gravels might
confined
have
The raised bedrock may
constricted as it flowed around this obstruction.
course
in
also
depositional
period.
3)
changed
A change in baselevel might result as the
drainage
direction
from east to west during the Iate-Tertiary to earIy-Quaternary
25
time.
the
As the Gallatin River cut through bedrock at the western end of
valley and drained into the Missouri River,
would
a downcutting
most likely have occurred on the Tertiary surface as
adjusted
to this new drainage direction.
dissection
Gallatin
of
the
Valley,
Tertiary
and
the
basin
Hughes (1980) has noted the
surfaces at the
northeast
end
it is reasonable to assume dissection
confined to that part of the valley.
period
of
the
was
not
The Tertiary paIeotopography cut
on Tertiary material then filled with Iate-Tertiary to earIy-Quaternary
age sediments as erosion of the uplifted Gallatin Range continued.
Paleochannel Model
With these hypotheses in mind,
the
a paleochannel could exist beneath
Bozeman alluvial fan and a thick sequence of Quaternary
could
be confined within it.
study
of
the
Quaternary,
The proposed conceptual model for
Bozeman alluvial fan consists of a
Tertiary,
sediments
thick
this
sequence
of
Paleozoic and Mesozoic sediments present in the
fault-bounded basin at the south end of the Gallatin Valley (Figure 9).
The.
sediments
thin
to
the
north
as
the
underlying
Precambrian
metamorphic rocks rise to just below the surface beneath Montana
State
University.
The
study
site is located within what is interpreted to
lower, mid-fan zone.
log
be
This interpretation is based solely on the
the
well
interpretations and geologic mapping of Hackett and others (1960).
Structural
Precambrian
University
complications
in this area are caused
by
a
near-surface
bedrock ridge located beneath the campus of Montana
and inferred by gravity data (Davis and others,
1965)
State
and
26
BOZEMAN
I ALLUVIAL
X
FAN
x /I / —
Figure
9:
Block diagram of the conceptual exploration model for the
Bozeman alluvial fan, southwestern Montana. MSU = Montana
State University; RP = postulated Roskie paleochannel; Qa
= older Quaternary alluvium; Qal = younger Quaternary
alluvium; I = Tertiary sediments; MP = Mesozoic-Paleozoic
rocks; PEa = Precambrian Archean rocks.
Inset Figure 10.
27
seismic
refraction
metamorphic
rocks
campus (C.
Bradley,
is
apparently
data
(Brown
and
others,
1983).
Weathered
were also observed in building site excavations
personal communication, 1989).
close to the surface,
on
Since the bedrock
a thin Quaternary
and
Tertiary
layer would be expected in this area overlying the Precambrian bedrock.
The
potential for groundwater withdrawal would be severely limited
the
area,
west
but thicker Cenozoic deposits are suspected further to
beneath
surface
Roskie field.
that
the
bedrock ridge slopes to the west beneath the Bozeman
fan (Davis and others, 1965).
of
Gravity data suggests
in
the
neai—
alluvial
This may allow for thicker accumulations
water-bearing units to be found west of this bedrock ridge,
in the
Roskie study site.
Brown
and
others (1983) proposed the location of a
field (Figure 10).
beneath
Roskie
channel
is proposed to be cut in Tertiary sediments and filled with
thick sequence of Quaternary gravels.
is
Based on
their
paleochannel
hypothesis,
the
a
A subtle topographic depression
postulated to represent a surface expression of this
paleochannel.
Examination of the subsurface by drilling, seismic refraction and earth
resistivity surveys are necessary to determine if the model is
and if the paleochannel does exist.
correct
28
Figure
10:
Block diagram of hypothesis to be tested in Roskie study
area and vicinity.
MSU = Montana State University; RP =
postulated Roskie paleochannel; RW = Roskie well site; ML
= Marsh Lab;
Qal = younger Quaternary alluvium; I =
Tertiary sediments; MP = Mesozoic-Paleozoic rocks; PEa =
Precambrian Archean rocks.
29
METHODS OF STUDY
Very
alluvial
an
little
fan.
subsurface
exposure is
available
the
Bozeman
Several geological exploration methods were utilized in
attempt
to
locate
paleochannel
at
the western end" of Montana State
These
on
the
methods . included
interpretation,
and
earth
present
air
photo
boundaries
of
the
University
interpretation,
resistivity
and
proposed
campus.
well
seismic
data
refraction
geophysical techniques.
Air Photo and Geomorpholoov
Air photos taken in the years 1937,
in
order
1965,
and 1971 were examined
to search for any surface expression that might suggest
subsurface geology in the study area.
reduce
the
which
would
The early photos were chosen to
effects of human disturbance on the alluvial
mask any surface expression of the
fan
subsurface
Brown and others (1983) had suggested that the postulated
also
examined to identify variations in the
could be confined to the trend of the paleochannel.
features.
Air photos
vegetation
which might suggest variations within the water table.
surface
paleochannel
could be traced as a topographic expression on the surface.
were
the
pattern
These patterns
30
Drilling and Well Development
The postulated paleochannel was further tested by drilling a water
well
near
Roskie
geophysical
Dormitory.
The
location was
selected
based
data and interpretations made by Brown and others
on
(1983).
A cable tool rig was used to drill a 0.15 m (0.5 ft) diameter well to a
total depth of 56.4 m (184 ft).
m (10 ft)
0.5
intervals or whenever the well was bailed.
average
drilled
size,
type
the
sampled
over
The
A
A standard size
I (2 cup) sample was sieved through a screen in order to
the percent gravel in the field.
the
Rock chip samples were collected at 3
This allowed for a crude estimate
and amount of cementation of
section.
A
drill
log
was
then
made.
well is fully cased from the surface to the screened section.
unable
to
control the screen
during
development.
The
driller
screen
floated up into the casing and its location could not be determined
the
of
the . sediments
plastic screen was originally installed in the well but the
was
estimate
well.
in
The plastic screen was removed and replaced with a 3 m (10
ft) long, # 15 slot, 0.038 cm (0.015 in) Johnson stainless steel screen
with a 1.52 m (5 ft) tail-pipe section.
by
The screen size was determined
sediment size analysis performed in the laboratory and verified
the screen manufacturer.
The well was deepened from 53 m (175 ft)
56
m (184 ft) when the steel screen was installed.
of
the
screen,
the
well was developed
attached to the bottom of the drill stem.
adapted
to
development
a
is
cable
tool rig (Todd,
using
a
by
to
Upon installation
flap-valve
bailer
This surge method is easily
1980).
The
to remove the finer grained material
purpose
of
surrounding
well
the
31
screened section and to concentrate coarser grained material outside of
the screen.
the
well
Ultimately specific capacity is increased,
is
eliminated and maximum economic well
sanding in of
life
is
obtained
(Todd, 1980).
A
gpm)
four hour pump test with a constant pumpage rate of 227 1/m (60
was
system.
208
used to determine the hydraulic parameters
controlling
the
Discharge was measured by recording the time needed to fill
I
(55 gal) drum.
Since no observation wells were available
a
the
recovery test method based on the Cooper-Jacob method described in Todd
(1980) was used to analyze the data.
Several
estimate
tests
the
slug tests were conducted on the Roskie well in order
the hydraulic conductivity of the aquifer system.
The
slug
were conducted at various times in order to test for changes
well hydraulics after development.
The Hvorslev method
to
of
in
data
analysis was used (HvorsleV, 1951).
Resistivity
A
resistivity
survey
was performed using a
current earth resistivity meter.
Bison
2350
direct
A Wenner array, as described in Zohdy
and others, (1974), was used to determine how resistivity values varied
in
map view for different depths.
distance
The
apart
Four electrodes are placed
in a straight line at the ground surface (Figure
resistivity of the earth material is a function of
subsurface material and the single-distance variable, a.
profile
map
equal
depth
probed,
A resistivity
of the subsurface was made using an a-spacing of 9 m
ft) and 30 m (100 ft).
11).
(30
The two a-spacings were chosen in order to give
32
\ Resistivity
r ,
Figure H s
Wenner electrode array.
A and B are current electrodes, M
and N are potential electrodes; a is electrode spacing.
AM = MN = NB = a.
I = current meter; V = voltage meter;
arrows indicate direction of current flow (modified from
Mooney, 1980).
a picture of the resistance of the subsurface material and to intersect
the
postulated paleochannel at a
deep depth.
exploration
and anisotropic stratigraphy.
depth
1974;
A first approximation of
is often taken to be 2/3 the a-spacing
Dobrin,
1976).
study
ft)
The
depth
and
An a-spacing of 30 m
appears to be the limit of reliable probing
area.
(Zohdy
For example, an a-spacing of 30 m (100
ft) probes a depth of approximately 20 m (67 ft).
(100
relatively
Probed depth is difficult to estimate in environments with
heterogeneous
others,
relatively shallow and a
depth
probed was a function of the limits
in
of
this
the
equipment due to the relatively small current source and the relatively
low
electrical
alluvial
conductivity
material.
of
the
heterogeneous
unconsolidated
Apparent resistivity values were recorded in
the
33
field and plotted on a base map.
A profile map was made for corrected
depths of approximately 6 m (20 ft) and HO m (67 ft).
In
addition to the Wenner profile,
several
vertical
electrical
soundings were completed in selected areas to determine how resistivity
varies with depth beneath one point.
Electrical sounding is performed
by expanding the electrode spread about a single central point (Mooney,
1980).
high
The
technique is useful for determining a layering sequence of
and low resistivity zones through a subsurface section,
gravels between clays.
such
as
A plot of the apparent resistivity was made on
log-log paper.
Seismic Refraction
A
area
shallow
seismic refraction survey was completed in
in order to further test the results of Brown and
regarding
and
the
the
others
depth to the boundaries low and high velocity
the shape of such contacts.
study
(1983)
material
The seismic survey was also used
to
verify the results of the seismic survey previously done in the area by
Brown
and others (1983).
seismic
recorder
was used in the survey.
length of 145 m (475 ft).
be
The
A Geometries 12-channel signal
lines
energy
source used was a 136 kg (300 lb) weight
a
dropped
1980).
from
a
A forward and reverse velocity-distance profile
was performed for each seismic line.
The energy source was offset 3 to
(10 to 15 ft) at a right angle to the geophone cable.
distance
had
This allowed for a depth of investigation to
approximately 50 m (160 ft) beneath the study area (Mooney,
height of 3 m (10 ft).
5m
The seismic
enhancement
This offset
"normally provides a direct arrival through the surface layer
34
and allows a determination of its velocity" (Redpath, 1973).
The slant
distances from shot point to geophone were computed for the first three
geophones.
First arrivals were interpreted from waveforms recorded on
the seismic screen.
All 12 channels were displayed at the same time,
allowing for accurate visible first-arrival picks to be made.
distance
assess
with
paper
plot
of the data was made in the field in order to
potential problems and data validity.
the time-distance plot,
copy
visually
If problems were
the line was re-done at
that
of the seismic waveform was then made in order to
the seismic data in the office.
A time-
found
time.
A
analyze
35
RESULTS AND DISCUSSION
Air Photo Interpretation
No
obvious vegetation patterns in the study area were
from the air photos examined from the years 1937,
recognized
1965, and 1971.
The
close proximity of this area to the city of Bozeman, along with farming
and
of
grazing activity in the area could have resulted in an
the vegetation pattern by human disturbance.
depression
suggesting
recognized
on
quadrangle.
near
both
Upon
surface
the
the
further
trend
air
of
photos
a
buried
and . the
alteration
A slight topographic
stream
Bozeman
channel
was
topographic
research it was found that this trend is
morphological
feature
that
construction fill in the Roskie study area.
has
been
altered
a
by
Further discussion of this
fill will be presented in the seismic refraction section.
Drilling and Well Development
A
well was drilled on the eastern edge of Roskie field in a
hypothesized
(200
by
area
Brown and others (1983) to contain greater than 60
ft) of coarse-grained alluvial material (see Figure 10).
well is expected to yield a large amount of water.
Such
Although the
m
a
best
location for the well based on seismic evidence is in the center of the
field,
the
paleochannel
well
was drilled on the eastern edge of the
because placement at the preferred location
hypothesized
would
prove
36
hazardous during recreational activities on the field.
the
drilling
analysis
allowed
of
paleochannel.
the
The
a
more
subsurface
first-hand
material
within
examination
the
hypothesized
and seismic refraction data.
other deep well was drilled in 1960 at the site of the
Laboratory
near
postulated
channel
available
grained
for
the western edge of the study area
constant
boundary.
this
sediment
and
well also allowed for a comparison of the drill log
and the electrical resistivity
One
detailed
The results of
well.
Only
and
outside
a very generalized well
The drill log reports
throughout the well.
Marsh
log
relatively
is
coarse­
The driller reported
flow of 1900 1/m (500 gpm) was produced for the
the
that
duration
a
of
the four hour pump test.
Drill Data and Interpretation
A
lithologic
log of the subsurface material encountered
in
the
well at Roskie field suggests a general fining downward sequence (Table
I).
Based on the estimated percent gravels in the sample, gravels are
more
abundant
frequency
with
grained sand,
are
near
depth.
the
The
surface
and
decrease
in
sediments at depth are
thickness
dominantly
silt and clay with minor amounts of gravel.
abundant in this lower zone.
Cemented sandstone
and
fine­
Clay lenses
fragments
were
identified in cuttings from the lowest 12 m (40 ft) of drilled section.
Prior
to drilling there was hope that Tertiary material might
be
differentiated from Quaternary material.
Both units were suspected of
having
history
a
similar
fluvial
depositional
overbank and alluvial fan deposits.
to
separating
- stream
channel,
Cementation may have been the key
the two formations but the cable tool
drilling
method
37
Table
I:
Lithologic log of Roskie well, Roskie field study area,
Montana State University, Bozeman. Data from 53.3 - 56.0 m
(175 - 184 ft) was supplied from driller.
No samples were
taken. Screened interval at 51.5 - 54.6 m (169 - 175 ft).
Depth
m (ft)
Thickness
m (ft)
Gravel
%
0-2.4 (0-E))
2.4-3.7 (E1-12)
2.4 (8)
1.2 (4)
3.7-8.2 (12-27)
8.2-8.9 (27-29)
4.6 (15)
0.6 (2)
8.9-10.4 (29-34)
10.4-11.9 (34-39)
1.5 (5)
1.5 (5)
11.9-12.5 (39-41)
12.5-14.0 (41-46)
0.6 (2)
1.5 (5)
25
30
14.2-20.1 (46-66)
6.1 (20)
2025
20.1-20.4 (66-67)
0.3 (I)
40
20.4-21.3 (67-70)
21.3-24.1 (70-79)
0.9 (3)
2.7 (9)
50
10
24.1-25.3 (79-83)
25.3-28.4 (83-93)
1.2 (4)
3.0 (10)
10
20
28.4-29.0 (93-95)
29.0-36,0 (95-118)
0.6 (2)
7.0 (23)
25 .
<10
36.0-40.8 (118-134)
4.9 (16)
<10
40.8-44.2 (134-145)
3.4 (11)
<15
44.2-53.3 (145-175)
9.1 (30)
110
53.3-54.8 (175-180)
54.8-56.0 (180-184)
1.5 (5)
1.2 (4)
40
30
4060
Lithology summary
clay and silt; no water
gravel (large cobbles)
uncemented
clay-bound gravels
clay and sand; water est.
at 37.9 1/m (10 gpm)
clay-bound gravels
gravel, water at 11.9 m
(39 ft), 7.5-11.4 1/m (2-3
gpm)
saturated sand
mixed clay-sand-gravel;
saturated
mixed cIay-sand-graveIs;
saturated; clay-bound
gravels; clayballs
quicksand; mixed clay-sandgravel; minor clayballs
clay-bound gravels
sandy clay; clay-bound
gravels
clay; minor gravels
clay-bound gravels; sand
and clay;
water between
26.2-28.4 m <86-93 ft)
quicksand; clay and sand
fine-grained sand and clay;
quicksand; clayballs
water saturated clay and
fine-grained sand
fine-grained sand and clay;
cemented sandstone
fine-grained sand and clay;
minor cemented fragments;
silica or clay cement
gravelly sand?
consolidated sand?
38
breaks
the
consolidated sediment into small
distinction
depth
of
samples
difficult.
about
higher
Some
particles,
making
this
evidence of cementation was noted at
41 m (134 ft) although it could have been
in the drill hole.
missed
But cementation cannot be
upon as a distinction between the two formations.
a
in
relied
The Tertiary unit in
parts of the valley.is very poorly consolidated and easily eroded.
Lithologic
differences
between
the
Tertiary
and
Quaternary
formations are not obvious in drilled materials because both units have
the
Gallatin
others
Range to the south as their source
area.
Hackett
(1960) used the increase in clay content noted in well logs
the boundary between Tertiary and Quaternary material.
Much clay
present throughout the total depth of the Roskie drill hole,
and
as
was
making it
difficult to determine if a boundary was present between the two units.
Water Level Measurements
Static
water level in the Roskie well was 3.87 m (12.7 ft)
ground level on January 6,
little.
1985 (Table 2).
below
This level has varied very
No seasonal fluctuations are evident in the Roskie well.
The
near constant water level in the well suggests the well is completed in
a
confined or semi-confined aquifer system.
supports
The geologic log further
this hypothesis since the numerous clay zones present in
the
well probably confine this system from water-bearing aquifers above and
below (see Table I).
Aquifer Analysis
Pump test.
(Figure
12).
The well was pumped for four hours at 227 1/m (60 gpm)
A fairly good estimate of the hydraulic characteristics
39
Table 2:
Water level measurements in the Roskie
ground level).
Date
12.7
11.8
11.7
11.0
10.6
10.7
11.4
11.3
11.5
11.1
10.8
10.8
pumpage
driller
level
A 380
1/m
rate was preferred to test the well properties
could not provide a pump for this purpose.
(100
but
The static
the
water
prior to pumping was 3.58 m (11.75 ft) below ground level (bgl).
During
the pump test,
sounder
and
cross
water levels were measured with an
checked
measurements compared well.
at
below
3.87
3.58
3.55
3.35
3.22
3.26
3.47
3.44
3.51
3.39
3.29
3.29
the subsurface materials at the screen was made.
gpm)
bgl =
Static Water Level (bgl)
ft
m
1/6/85
5/22/85
6/20/85
8/9/85
9/5/85
10/18/85
1/14/86
3/18/86
4/29/86
10/23/87
6/10/88
10/14/88
of
well.
with an electric
tape.
echo
Both
depth
types
of
After a rapid initial drop in water level
the start of the pump test,
the water level stabilized at 22.91
m
<75.15 ft) to 23.21 m (76.15 ft) bgl and remained at this level for the
last 2 hours of the pump test.
level
may
during
the
The 0.3 m (1.0 ft) fluctuation in water
have resulted from slight variations in
four
hour
pump test or from
minor
the
pumping
measurement
rate
errors.
Recovery levels were measured after the pump test was terminated.
The
recovery method described in Todd (1980) was used to
analyze
the pump test data and estimate transmissivity in the Roskie sediments.
- 20
o
owdown
— 40
e
—
60
— 80
Figure 12:
Drawdown and recovery data, Roskie well, May 25, 1985. (t is total elapsed time since
start of test, continuing without interruption through the recovery period; t ' is the
elapsed time since the pump is turned off).
■fr
O
41
The
advantages
and
aquifer thickness is not a factor in
Another
of this method is that no observation well was
advantage
uncontrolled
of
variations
this
method
of
calculating
aquifer
in the pumping rate are
needed
transmissivity.
analysis
not
is
that
important.
The
recovery data can be more useful than the actual drawdown data (Fetter,
1980).
. This recovery method is based on the principles of the Coopei—
Jacob
straight
(Theis)
line
equation.
method (Todd,
method which is rooted
in
the
non-equilibrium
Several underlying assumptions are inherent in the
1980).
The aquifer is assumed to be fully penetrated by
the screened section so that horizontal flow is everywhere equal within
the aquifer.
thickness
valid
then
flow
can be approximated from the drill log,
(Hantush,
turned
recovery
One
Since the aquifer thickness is relatively small and
off,
1961).
the
this assumption
is
If a well is pumped for a period of time and
the rate of recharge (Q) into the well
period is assumed to be equal to the original
during
pumpage
the
rate.
can assume that a hypothetical recharge well with the same rate of
was superimposed on the pumped well as soon as the pump
down (Todd, 1980).
is
shut
Based on this principle,
T = 2.30 Q
4Tf A s 1
where
T
= transmissivity,
Q = rate of recharge,
residual
drawdown
drawdown
(s') is a measurement of drawdown below the
water level,
data
used
per log cycle during recovery
As'
during the recovery period).
change
.
in
(Residual
original
static
Figure 13 is a plot of the
to determine transmissivity with the
Appendix A contains the pump test data.
period
=
Coopei— Jacob
method.
42
A,''5.2m (ITfI)
Illl
Time mllo, l/l'
Figure
13:
Coopei— Jacob semi-log plot of recovery data
estimate transmissivity for the Roskie well.
used
to
The calculated transmissivity values from the recovery method was
2
12
m /day
(930
gpd/ft >.
The
calculated
transmissivity
values
correspond well with the published values for the Tertiary sediments in
the valley.
Hackett and others (1960) report transmissivity values for
2
the finer-grained Tertiary sediments in the range from 3.7 m /day
gpd/ft)
to
75
2
m /day
(SOOOgpd/ft).
Coarser-grained
(300
Quaternary
sediments on the other hand, are reported to have transmissivity values
2
ranging
from
320 to 810 m /day (26000 to 65000 gpd/ft) and
averaging
2
about 600 m /day (48000 gpd/ft).
Slug tests.
well
to
Several slug tests were also conducted on the Roskie
independently
estimate
hydraulic
conductivity.
Hydraulic
43
conductivity
the
(K)
is a coefficient of proportionality which
rate at which water can move through a permeable
1980).
describes
medium
(Fetter,
The Hvorslev method of data analysis was chosen to estimate the
hydraulic
conductivity of the confined system from the slug test data.
This method was chosen because it is not restricted to conditions of
confined
aquifer
because
the
penetration
confining
The
or
well
fully penetrating
appears
to
be in
screen.
a
This
confined
is
important
system,
but
of the screen is not certain since the boundaries
aquifer
screen was installed.
Because of this oversight,
of the drill hole was not logged (see Table I).
full
of
could only be approximated by the drilling
driller failed to notify Montana State University when
a
the
method.
the
steel
the last 3 m (9 ft)'
This amounts to 1.5 m
(5 ft) of tail pipe section and 1.2 m (4 ft) of screened section.
screened section extends from 52 m to 55 m (169 to 179 ft).
The
This zone
contains an upper 1.8 m (6 ft) of fine-grained sand and clay, which was
logged,
and a lower 1.2 m (4 ft) of gravelly sand,
driller.
as reported by the
Since the screened section does not fully penetrate the upper
fine-grained zone nor the lower gravelly sand zone, the Hvorslev method
was
chosen
to
analyze the data and provide an independent
check
of
transmissivity as determined by the recovery method.
The equation used in determining K with the Hvorslev method is
K = r 2 In (L/R)
2 L T0
where
r=Casing radius,
L=Iength of intake,
T0 =time lag for one log cycle.
from
-5
10
a
R=radius of
The calculated hydraulic
intake,
and
conductivity
representative slug test for the Roskie well aquifer is 2.8 x
-5
m/s (9.15 x 10
ft/s).
This is equivalent to 2.1 m/day (52.5
44
2
gpd/ft ).
for
These
values correspond with the range of accepted
silty sands and fine sands (Fetter,
dominates
1980).
This
determined.
The
analysis
performed
when the
proper
type
screen
size
hydraulic
transmissivity,
conductivity
value calculated from
the
T = Kb
Hvorslev
where T
from the recovery method.
is not known for certain,
transmissivity
=
K = hydraulic conductivity, and b = aquifer thickness.
calculated transmissivity value can then be compared to the
calculated
was
Appendix A contains the ,slug test data.
method can be used to estimate transmissivity since
the
sediment
the lithology in the drill hole and is in agreement with the
sediment-size
The
values
values.
value
Since the true aquifer thickness
an upper and lower end was used to
estimate
Based on an estimate from the drill log data,
minimum aquifer thickness is 1.5 m (5 ft) and the maximum
thickness is 10.7 m (35 ft).
aquifer
Transmissivity values were calculated to
be
3.2 m /day (263 gpd/ft) for the minimum aquifer thickness and 22
.2
m /day (1838 gpd/ft) for the maximum aquifer thickness.
The average
2
transmissivity is 13 m /day (1050 gpd/ft) and compares very well with
2
the transmissivity value of 12 m /day (930 gpd/ft) calculated using the
recovery
data.
method,
The
considering the inadvertent problems with the
results
analysis
was
an
also
indicate that the Hvorslev
acceptable method to use to
method
interpret
drill
of
the
data
aquifer
conditions of the Roskie well.
Discussion
The
data
transmissivity
this
depth
from
the
Roskie well can only
and hydraulic conductivity.
be
used
to
estimate
A second well drilled
in the aquifer and utilized as an observation
well
to
would
45
allow for determination of the coefficient of storage.
test,
During the pump
the maximum amount of water capable of being withdrawn from
system
(60
gpm)
sustained over a 4 hour period only caused the water level in the
well
to
was
drop
not
reached.
A constant pump rate of 227 1/m
the
about 20 m (65 ft) below ground level.
This depth to
fluctuated only 0.3 m (I ft) during the last two hours.
water
Approximately
29 m (95 ft) of water still remained in the well during the duration of
the pump test.
This suggests that the aquifer could sustain a
pumpage rate before total drawdown is reached.
higher
A pump test designed to
determine the sustained yield is desirable to test the aquifer capacity
but
a larger pump is needed.
using
the
method
assumptions
were
conductivity,
The pumpage rate could be
described in Driscoll (1986).
used when estimating
additional
But
approximated
since
transmissivity
and
various
hydraulic
estimates will only compound the problem and
should not be considered until these uncertainties can be eliminated.
Tertiary
sufficient
1960).
strata
for
Enough
only
water
are
generally
thought
of
as
yielding
domestic or livestock use (Hackett
for
irrigation or other
and
large-scale
water
others,
use
are
generally not believed to be present due to the hydraulic properties of
the
sediment.
Whether
remains to be determined.
conductivity
for
the
drilling
or not this is the case for
the
Roskie
The calculated transmissivity and hydraulic
values of the Roskie well compare well with other
Tertiary
well
units elsewhere in the
Gallatin
Valley.
values
Further
and hydrologic analysis of Tertiary sediments throughout
Gallatin Valley may change this interpretation.
the
46
The
Roskie
well
does
postulated paleochannel.
present
not
appear
to
be
located
within
the
The nature o„f the fine-grained sand and clay
in the well suggests that either the well was drilled
outside
the channel margin while attempting to stay off of the playing field or
the
channel
does not exist.
No extensive section of
coarse-grained
sediments, the target of this study, was encountered in the drill hole.
Further
exploration
is
needed to
fully
evaluate
the
paleochannel
presence.
Earth Resistivity Survey
Electrical
test
the
resistivity
presence
exploration technique.
the
the
postulated
to
paleochannel
independently
using
another
Much fine-grained sediment was encountered
Roskie drill hole located at the east end of the study area.
presence
not
of
was used in this study
either
The
of this fine-grained sediment suggested that the channel
present or the well was located on the edge of
the
in
was
channel.
In
case it was assumed that materials of low electrical resistance
were present.
A
during
range
610
alluvium
resistivity values was expected
this survey.
resistivity
to
of
be
encountered
Sand and gravel saturated with fresh water
values ranging between approximately 15 ohm-m (50
ohm-m (2000 ohm-ft)
and
to
(Zohdy
and
others,
1974).
have
ohm-ft)
Unsaturated
sands have resistivity values ranging between 9
to
800
ohm-m (30 to 2600 ohm-ft), while clays range between I and 100 ohm-m (3
to
and
330 ohm-ft).
should
Moist clay contains both water and exchangeable ions
thus be a good electrical conductor.
The wide
range
in
published
values
suggests that exact determinations of
material thickness with apparent
in
a heterogeneous,
area.
Even
material
resistivity values would be difficult
anisotropic environment such as the Roskie
with such problems,
the distribution of high
of this study,
resistivity values were used to
study
resistivity
material might be approximated to test the channel hypothesis.
purpose
and
For the
estimate
potential
for
high
resistivity water-bearing sediments
and
determine
the
exact composition of the material associated
the
not
to
with
the
affect
the
observed resistivity.
The
presence
resistivity
1986).
values
The
unconfined
of
water in the pore space will
in
a groundwater environment
also
as
(Huntley,
seasonal variations associated with groundwater levels in
aquifers will affect resistivity values.
conductor
well
of
electric
current.
If the water
Water is a
table
is
high,
resistivity values may be low since the sediment has become
On the other hand,
increase
over
a
since
short
constant,
as the water table drops,
of time so that
water
this problem can be minimized.
the
saturated.
resistivity values might
the conductor has been removed.
period
good
If data is
levels
are
gathered
relatively
To avoid this problem,
the
earth resistivity survey was completed over a four week period when the
weather was consistently dry and hot.
High
also
amounts
of total dissolved solids (TDS) in the
decrease the apparent resistivity values.
assumed
to
sedimentary
Hackett
and
be
relatively
constant
in
the
water
Groundwater
study
area
will
TDS
was
since
the
units were similar and the range of TDS values reported by
others
(1960)
and
Dunn
(1977)
at
these
depths
was
48
relatively uniform,
approximately 229 parts per million. Water quality
was expected to be good since no reports of poor water from residential
houses near the study area have been made.
Given the above conditions,
the factor controlling resistivity values in the study area is probably
the grainsize of the subsurface material.
Previous Resistivity Work
Only
one published earth resistivity study has been done
Gallatin Valley previous to this study.
determine
valley
the
Wantland (1953) attempted
depth to gneissic bedrock at a number of points in
and to determine the thickness of potential saturated
material.
resistivity values can be made.
unconsolidated
or
areas
Gallatin
in
consisted
to
the
alluvial
the
of
Wantland (1953) found three
poorly consolidated valley fill
Valley.
The
surficial
units
material
permeable sands and gravels with an average
value of 259 ohm-m (850 ohm-ft).
Wantland
the
Based on the results from this study, a few generalizations
regarding
in
various
generally
resistivity
Two underlying units interpreted
by
to be Tertiary sediments had average resistivity values of 73
ohm-m (240 ohm-ft) and 23 ohm-m (75 ohm-ft),
also
in
respectively.
His study
concluded that relatively high resistivities could be related
greater thicknesses of sand and gravel.
to
Likewise the presence of more
clay and/or silt size material resulted in relatively lower resistivity
values.
These
present
study.
results are consistent with data obtained
during
The resistivity values determined by Wantland
for the Gallatin Valley were used as a reference in this study.
the
(1953)
Data and Discussion
Eighteen
vertical
horizontal
soundings
resistivity
a
much
generalized
contoured
resistivity
gravel
and
fourteen
underlying
environment.
each a-spacing.
during
The results of these investigations
clearer picture of the
depositional
for
lines
were completed as part of the Roskie study
the 1985 field season (Figure 14).
provide
profile
An
valley
isoresistivity
fill
and
map
was
At an a-spacirtg of 9 m (30 ft), higher
values correspond with more permeable sands
and
possible
lenses that might be suitable as an aquifer (Figure 15).
The
presence of such materials in close proximity to the surface could be a
problem
depth.
since groundwater contamination would be easier at
Water
level
a
shallow
fluctuations could also be large in such
shallow
units during the year.
Some of the anomalously high resistivity
with
values
with
man-made surface disturbances.
study
area
is
disturbance
areas
of
>183 ohm-m (600 ohm-ft) in this survey may be
has
the
communication,
of
averaging
lower
Roskie field in the
1988).
A
where
activity
causing
past
(C.
Roloff,
resistivities
to
MSU,
some
personal
The higher resistivity values would be a result
value
with
Since no surface expression
caution must be used before an
of
interpretation
Appendix B contains complete earth resistivity data.
test of deeper materials is desirable to assess
better
the
surface
Fill has been added
near surface fill having a high resistivity
condition exists,
can be made.
associated
This is due to the fact that
occurred in the past.
resistivity material at depth.
this
for
in a populated area
zones
aquifers.
at
Figure
16
is
a
contour
an a-spacing of 30 m (100 ft).
map
the
potential
of
There is a
apparent
general
11— I
S O B. I
8 RWF
7 RWF
3RW F
SRWF
2RWF
EXPLANATION
E le c tric o l sounding
RWF
R oskle well
4 RWF
6 RWF
400 ft
Figure
14:
Location
of
earth resistivity survey lines,
Roskie
channel
study
area,
Montana State University, Bozeman. Letters indent ify locations of survey lines. R =
Roskie field; RWF = Roskie west field; V = Marsh Lab (Vet Sciences) field.
Figure 15:
Map of apparent resistivity with a - spacing * 9 m (30 ft)
J
L.
J V
J \_____ ) L
^ r-"!
r
Tr
EXPLANATION
HO RIZO NTAL R E S IS T IV IT Y PRO FILE
Ul
ru
O-^OClng e 3 0 m ( I O O ft )
10
45
60
75 e hm -m
I e o r e s le tlv liy co n to u r. In o h m -m e te rs
Contour I n t e r v o l* 15 e h m -m
S u rvey p o in ts
50
IOO
S =
m
I
M o re h ____ T j
J
r
200
Figure 16:
Map of apparent resistivity with a-spacing = 30 m (100 ft)
Yi
SO
53
decrease in resistivity values at depth.
voltage
through
This results from the drop in
heterogeneous sediments as the distance
electrodes increases (Mooney,
for
the profile with
the
profile
1980).
separately
from
Each resistivity value must
considered in relationship to its respective profile.
a
the
Therefore the resistivity values
a = 9 m (30 ft) must be viewed
with a = 30 m (100 ft).
between
In other words,
180 ohm-m (600 ohm-ft) resistivity value at an a-spacing of 9 m
ft) may be obtained from similar sediment with
be
(30
a 90 ohm-m (300 ohm-ft)
value but at an a-spacing of 30 m (100 ft). In such a heterogeneous and
anisotropic environment as an alluvial fan deposit, the interbedded and
interfingering nature of the sediments complicate the data and
prevent
a simple layered model solution to be used.
Several
zones
of moderate resistivity sediments > 76
ohm-m
ohm-ft) are present at an approximate depth of HO m (70 ft).
center
of
Roskie
localized
field
both a-spacings contain
a
(250
Near the
relatively
resistivity zone when compared with surrounding
high
resistivity
values.
The overlying high resistance areas suggest the presence of a
possible
continuous
surface
not
sediments
material,
of
appears to have the most
higher resistive material
targets for groundwater,
resistivity
limited.
site
with
The
zones
O 180
coarse
zone.
ohm-m)
the
does
potential
development in a gravelly (higher resistance)
stringers
possible
the
from
Although the data
suggest a large deep buried stream channel filled in
groundwater
high
of higher resistivity
to at least a depth of 21 m (70 ft).
grained
small
zone
may
for
The
be
but the discontinuous nature of the
may pose a problem
since
storage
could
be
absence of any lateral and vertical continuity of these
54
zones
suggests
that no paleochanneI is present in
area.
Additional
resistivity
profiles
the
at various
Roskie
study
a-spacings
would
improve upon our understanding of the subsurface in this area.
hole in this area could determine the extent of the
porous
A drill
subsurface
material suitable for groundwater withdrawal.
Both
isoresistivity
maps seem to suggest a
pattern (see Figures 15 and 16).
interfingering,
high
and
contour
The pattern appears to demonstrate an
depositional
low resistivity values.
deposition
as
lense-shaped
distinctive
pattern of sediments
This pattern
is
with
consistent
with
of the sediments by laterally shifting braided streams such
would
be
expected on an alluvial fan surface
downstream
of
the
intersection point or other similar fluvial depositional environment.
The drill data from the Roskie well allowed a comparison between a
vertical
17).
electrical sounding and the subsurface
In
general,
decreased
the
sediment size interpreted from the
well
Resistivity values from the
sounding suggest this pattern as well.
sounding
curve
interpretation
log
in
resistivity
(Zohdy,
increase
in
sounding
curve
resistivity
Some scatter of points exist on
1965).
When correlated with a well
of
log,
the
appears
to
be
(coarsen— grained)
a result
material
of
The scatter
thin
layered
is
decrease . in
increase in conductivity) corresponds well with
fine-grained sediments with depth.
an
the
Although normal decrease in resistivity
this type of heterogenous environment,
(and
vertical
and would normally decrease the certainty
uncertainty is minimized.
expected
(Figure
from about 2.4 m (8 ft) below the surface to the total depth
of the well at 56.0 m (185 ft).
the
stratigraphy
zones
in
the
the
of
higher
between
lower
55
resistivity (finer-grained) material.
Well Depths and Electrode Spa
Apparent Resistivity (ohm-m)
Figure
17:
Comparison of vertical electrical sounding and drill log,
Roskie well. (Sounding located approximately 8 m (27 ft)
west of drill hole).
56
Seismic Refraction Survey
Since neither the drilling nor resistivity exploration
found
techniques
evidence to support the location of the postulated paleochannel,
additional seismic work was needed in the area.
to Redpath (1973),
additional
Dobrin (1976),
information
The reader is directed
Mooney (1984), and Haeni (1985) for
concerning refraction seismic
techniques
and
their problems.
Previous Seismic Investigations
Wantland
(1951)
conducted a
reconnaissance
refraction
survey
in the Gallatin Valley in conjunction with the U.S.
Survey
groundwater studies in the area.
long
Geological
His study involved 600-900 m
(2000-3000 ft) seismic lines in order to determine the
basement
seismic
rocks and the thickness of unconsolidated valley
lines
study area.
seismic
depth
fill.
from that study are within 3.2 km (2 mi) of the
to
Two
Roskie
One seismic line encountered upper (layer I) velocities of
1500 m/s (4900 ft/s).
The second seismic line found layer I velocities
to be 2200 m/s (7200 ft/s). No second layer velocities were encountered
in
either
of Wantlands1 seismic lines suggesting a depth to
layer
2
greater than 300 m (1000 ft) (WantIand, 1951).
Brown
across
and
most
included
of
others
(1983) completed a refraction
the Montana State
several
seismic
University
lines in
the
campus.
Roskie
study
seismic
survey
Their
area.
study
Their
hypothesis of a buried paleochannel was based on these lines along with
what
appeared to be a topographic expression of a subsurface
Interpretation
of
data
from
their
study
indicates
channel.
near-surface
57
Quaternary
alluvium
across
with
depth
paleochannel
a
most
of the study
greater than
60
area
m
and
(200
filling
ft).
a
Further
discussion of the interpretations made by Brown and others (1983), will
be presented after the results from this study.
Data and Interpretation
Sixteen
completed
Tertiary
forward
and
reverse
refraction
seismic
lines
were
during the summer of 1985 in order to determine the depth to
sediments
definitely
in the Roskie study area and to
attempt
to
more
test the existence and location of the hypothesized
buried
stream
channel (Figure 18).
A computer program modified from
(1977)
was then used to calculate depths and thicknesses of individual
layers
from
each seismic line.
Interpretation of seismic
based on expected velocities for material type,
of
burial
measured
in
on
sediments
Tertiary
ft/s)
literature (Table 3).
data
Tertiary
their
ranged
and
Brown
Precambrian units in the
measurements,
was
geologic age and depth
and
others
seismic velocities on visually identifiable outcrops
Quaternary,
Based
the
Mooney
from 300 m/s (1000 ft/s) to 1800
of
Gallatin
seismic velocities of
m/s
the
(1983)
the
Valley.
Quaternary
(6000
ft/s),
sediments ranged from 1800 m/s (6000 ft/s) to 4500 m/s (14000
and the Precambrian crystalline bedrock seismic velocities
were
>4580 m/s (15000 ft/s).
The
result
than
actual
seismic
velocities encountered in the field
of this study are presented in Figure 19.
Velocities of
400 m/s (1200 ft/s) are interpreted to correspond with
representative of modern alluvium (Table 4).
as
a
less
materials
These velocities are too
J
J L.
L
_j k____ ; L
'rV
Ir
ir
EXPLANATION
Seismic survey lines
9
1983 survey
SR ______ I
1985 survey
24
O
50
100
—
O
200
ft
,
400 m
V
Il R
fI
13 R
8 R
SR
23
2
3 R
2 R
22
I R
IO R
^
L in c o ln ^ ^ A v a ^
^
9 R
if
^
i r
Figure
IB:
Location of refraction seismic survey lines, Roskie channel study area, Montana
State University, Bozeman. Survey line numbers with letters identify 1985 survey
lines, numbers alone identify the survey lines of Brown and others (1983).
59
Table
3:
Average seismic velocities for various compositions,
geologic ages, and burial depths (Press, 1966; Mooney,
1984; Locke, 1987).
Velocity
m\s
ft\s
Comoosition
modern alluvium
soil
gravel, rubble or sand (dry)
sand (wet)
clay
water
crystalline metamorphic rocks
350-400
430-440
460-910
610-830
910-2740
1450-1700
3050-7010
1200-1300
1400-1450
1500-3000
2000-6000
3000-9000
4700-5500
10000-23000
Geolooic aqe
Quaternary
Tertiary (consolidated)
Precambrian Archean
30Q-2300
1500-4300
3800-7000
1000-7500
5000-14000
12500-23000
Burial Depth
(0-610 m; 0-2000 ft)
Pleistocene to Oligocene
Eocene
2000
2200
6500
7100
low
to
represent
Quaternary
gravel
material,
although
they
may
represent near-surface, unconsolidated slow velocity sediments or fill.
No
intermediate
velocities
characteristic
of
thick
sequences
of
Quaternary material were found as reported by Brown and others (1983).
A
range of values exist for the higher velocity material
located
beneath the upper modern alluvium layer. Seismic velocities of 2150 m/s
(7000 ft/s) to 2450 m/s (8000 ft/s) found in this study are interpreted
as
corresponding to dry Tertiary sediments.
2450
Velocities greater
m/s (8000 ft/s) are interpreted as corresponding to wet
sediments
and/or more consolidated or clay-rich deposits.
than
Tertiary
Appendix
C
contains the seismic survey data.
Thirty
two
depth-to-Tertiary measurements were calculated
from
60
Seismic Velocities
(ft/s x IO3 )
Seismic Velocities (m/s x IO2 )
Figure
19:
Table 4:
Histogram of recorded seismic velocities,
area, Montana State University, Bozeman.
study
Observed seismic velocities of material found in Roskie study
area and interpreted geologic age.
Velocity
m\s
Material
f t\s
500-1000
6500-8000
8500-11000
150-300
2000-2400
2600-3400
the seismic data.
area
Roskie
was
Modern alluvium; topsoil
Tertiary (dry)
Tertiary (wet)
The depth to Tertiary throughout most of the
found to be less than 3 m
(10 ft) (Table
5).
The
thickness of the overlying neai— surface layer is 2.0 m (6.4 ft).
study
average
61
Table
5:
Calculated depths to top of material with velocities
characteristic of Tertiary - age materials in the Roskie
study area. R = Roskie field, RW = Roskie west field, VS =
Vet Sciences.
East - west seismic spread
perpendicular to proposed channel
North - south seismic spread
parallel to proposed channel
Line
west
ft
m
east
ft
m
Line
north
m
ft
IR
2R
3R
SR
12RW
17RW
IBRW
14VS
15VS
19VS
2.7
2.3
1.4
1.3
2.5
3.8
1.1
1.7
1.4
3.0
2.5
2.4
1.4
1.7
1.3
3.1
1.3
1.3
1.4
2.2
SR
9R
IOR .
IlR
13R
16R
2.1
1.7
2.3
1.6
2.1
2.1
8.2
8.0
4.6
5.7
4.2
10.2
4.4
4.3
4.5
7.2
6.8
2.2
1.9
5.6
7.7
1.4
1.7
5.4
1.7
6.9
6.8 ■
7.1
6.2
4.7
5.5
5.5
6.8
CU
8.9
7.6
4.7
4.2
8.2
12.5
3.6
5.7
4.5
9.7
south
m
ft
Discussion
The seismic survey did not locate a deep channel filled with thick
Quaternary gravels as postulated by Brown and others (1983).
with
Materials
velocities expected to characterize Tertiary deposits were
within
4
m
velocities
thick
(12 ft) of the surface throughout
suggesting
sequence
of
the
study
area.
a thick gravel deposit or characteristic
Quaternary sediments were
found.
A
to
No
of
resurvey
seismic lines from the 1983 study also found no low velocities.
appears
found
be error in the interpretation of the data from
a
of
There
the
1983
survey.
Figure 20 shows a comparison of seismic velocities from two
surveyed
during
during the 1983 study and this study.
lines
Line 2R was completed
the 1985 study and is located adjacent and parallel to line
from the 1983 study.
22
The data from 1985 indicates that a thin layer of
62
L in e 2 2
Layer
VAI
VA 2
VA 3
1983
V e lo c it
m/s
240
1250
1150
VBI
VB2
VB 3
300
1500
1000
b s
800
4100
3800
1000
5000
3300
Time
( s-s-10
200 -
100 -
T
50
I
75
D ista n ce (m)
Line 2R
Layer
IC
1985
Veloclt
Tim e ( s-r I O )
m/s
100-
Figure 20:
VAI
VA 2
300
3020
1000
9900
VBI
VB2
230
2900
770
9500
Comparison of seismic line 22 from 1982 survey and seismic
line 2R from 1985 survey.
Dashed area indicates zone of
uncertain seismic data.
63
low velocity material directly overlies higher velocity sediments.
No
thick
of
sequences
Quaternary
study.
of
gravels
material
with
velocities
representative
are present along this or any other line
in
this
Examination of the two time-distance graphs from the same area
indicate
very
different geologic conditions if both sets of data
correct.
Upon examination of the graphs,
the following
are
discrepancies
arise:
1)
Line 22 contains an apparent jump in the curve while
Line
2R
lacks this jump.
2)
Seismic
velocities from layer V2 from the two surveys do
not
represent the same material.
The
dashed
area
located
near the center of
both
forward
reverse shots of the 1983 line (line 22) indicates a very low
area.
in
arid
velocity
During the 1985 study, it was found that gravel fill was spread
the
nearby
campus
buildings to cover a poorly drained area and to smooth over the
field.
This
area
of
Roskie field during construction
of
gravel fill would result in an extensive area with a low
velocity.
different
Layers
seismic
VA3 and VB3 from the 1983 study probably indicate a
seismic wave from layers VA2 and VB2 instead of a new
arrival from a third layer.
recorders (Lankston,
1986).
first
This problem is common with single channel
Such a recorder was used during the 1983
survey.
The
able
As
to
seen
seismic
construction fill may also explain the problem of
not
being
determine velocities for the full length of seismic line
2R.
by the dashed lines in the time-distance graph
2R,
energy
was
not
clearly received at the
of
geophones
line
after
a
64
certain
distance from the shot point.
recorder
a 12-channel
seismic
was used which visually displayed all 12 geophone records
the same time.
in
In 1985,
the
This allowed for accurate timing of the first arrivals
field
printout
of
at
and elimination of potential errors
the
seismic record was also
made.
in
The
the
data.
single
A
channel
seismic recorder used in the 1983 study used an oscilloscope screen for
each
geophone
record
compared
at
velocity
construction
so
data from all 12
the same time.
fill,
geophones
could
As the seismic wayes entered
not
the
the waves were refracted away
be
lower
from
the
surface.
Seismic lines traversing this area in both a north-south and
east-west
direction encountered this lower velocity zone.
appears
to be localized and not to extend to any great
resistivity
depth.
data located this zone within 6 m (20 ft) of the
but did not detect it on the deeper 30 m (100 ft) profile
1985
This
zone
Earth
surface,
line.
The
survey observed this phenomena but the 1983 data appears to
have
introduced a different seismic wave arrival time into its record.
The
study
second problem that exists concerns velocities found
area.
velocities
Data
ranging
from
1983
indicates
near— surface
in
the
Quaternary
from 1200 m/s (4000 ft/s) to 1500 m/s (5000
ft/s)
are present and extensive throughout the study area.
The results from
the
with
1985
study
indicate the presence
of
material
velocities
ranging
between
than 3 m
(10 ft) beneath the surface throughout the Roskie study
Such
1980 and 3350 m/s (6500 and 11000 ft/s) located
velocities are interpreted to represent Tertiary sediments.
velocities representative of modern alluvium were found directly
less
area.
Low
above
the Tertiary velocities. A third seismic experiment at line 2R and line
65
22 completed during the summer of 1987, independent of this study, also
showed
no
velocities
Quaternary material.
represent
Tertiary
suggestive
of
a
thick
gravel. sequence
or
Velocities of 2350 m/s (7700ft/s) interpreted to
sediments were found within 3 m (10
ft)
of
the
surface (Terry Nichols, Montana Tech, personal communication, 1987).
Why the discrepancy between the 1983 and 1985 data?
As alluded to
earlier, the problem may be due to difficulties associated with using a
single
channel
seismic recorder.
Lankston (1986,
p.45) notes
"single channel instruments with no hard copy capability are
for
that
notorious
allowing scatter to be introduced into the data because of reading
inconsistencies
on
the part of the seismograph operator".
work occurs in noisy or weak signal environments additional
in timing of the first arrivals will result.
seismograph
recorder
If
field
difficulty
In 1983 a single channel
was all that was available to Brown and
others.
There may well have been unrecognizable data problems.
The
Roskie study area can be considered a weak signal environment
due to the nature of the unconsolidated or semi-consolidated sediments.
Signal enhancement was necessary on all lines surveyed in order to pick
an accurate first arrival time for the distant geophones.
A
second
difference
between the 1983 and 1985 data may
moisture content in the area at the time of survey.
be
In wet areas,
may be difficult to generate clear compressive waves (Sverdrup,
the
it
1986).
This problem may create weak or unclear signals when trying to complete
a long line and using a single channel recorder.
Whether or not
soil
moisture is the reason for the discrepancies between the two studies is
hard to assess.
66
The single channel instrument may have introduced inadvertent data
errors
use
which were not recorded and are not reproducible.
of
a 12 channel recorder in 1983 would have
Perhaps the
produced
data
more
compatible with the results obtained from the 1985 study.
Additional seismic lines surveyed in the Roskie study area in 1985
produced data which consistently indicated a thin low velocity material
overlying
lines
Time-distance plots of
seismic
SR and 9R are shown in Figure 21 and are typical of the
results
obtained
higher velocity sediments.
from
other
seismic profiles in this
study.
Near
surface
velocities of 300 to 380 m/s (1000 to 1250 ft/s) are found along
two
lines.
These
higher
than normal Vl velocities may
be
these
due
to
compaction of near surface material in a heavily used area.
Velocities characteristic of Tertiary material were found on lines
SR
and 9R at a depth of 1.5 to 2.0 m (5 to 7 ft) beneath the
surface.
Velocities ranged from 2160 to 2410 m/s (7090 to 7920 ft/s).
seismic
were
profiles completed during this study.
Tertiary age
to 11000 ft/s) (see Figure 19).
lower
layer
is
present.
A range of velocities for
The higher end of the velocity
indicate zones of either water saturated materials,
content
saturated
in
or
areas
materials
differences
range
materials
found to have higher velocities in the range of 2740 to 3350
(9000
clay
On other
in
may
of
be
increased
compaction.
a result of a
perched
the amount of irrigated land.
moisture or decreased compaction.
this
range
may
zones of increased
Localized
water
The lower end
velocities may indicate increased gravel
m/s
content,
water
table
or
of
the
lack
of
67
Velocity
m/s
f t/s
300
1000
2400
7900
100-
380
2300
1300
7400
75
Distance (m)
Line
Layer
9R
Velocity
m/s
ft/s
340
I I OO
2400
7800
340
2200
IIOO
7100
” 50
75
Distance (m)
Figure
21:
Time - distance plots of seismic lines BR and 9R across
Roskie field and the hypothesized paleochannel, Montana
State University, Bozeman.
68
In
groundwater exploration using refraction seismic methods,
velocities
usually
indicate
areas
suitable for groundwater withdrawal.
of
(Zohdy
and others,
other sources,
drill logs,
made
permeable
zones
Water filling in pore
spaces
increase the velocity of the material by several hundreds of
porosity material.
from
and
But higher velocities must not be
ignored as potential groundwater zones.
will
porous
low
1974),
so higher velocities may not indicate
m/s
low
This demonstrates the need to consider information
such as geology,
earth resistivity
surveys,
or
before a conclusion about the groundwater potential can be
69
CONCLUSIONS
Alternative Model
The
results
hypothesis
reasons.
in
study
relatively
sand
and
site.
fine-grained
with
values
Gallatin Valley.
hypothesis
nor
sediments inter layered
paleochannel
for
transmissivity
from
the Tertiary aquifers
presence
is
present
of
properties
the
Roskie
elsewhere
of
well
in
the
channel
Small zones
interfingering
with
of
lower
relatively
high
within 3 m (10 ft) of the surface and no ,thick
These facts suggest that Brown and others (1983)
seismic
surveyed the area.
wave
forms and first-arrival
times
as
they
This misinterpretation may have resulted from
of construction fill found in Roskie field.
traced
the study area may have biased their interpretation towards
deep buried paleochannel.
the
The coincidence of
the location of the subtle linear depression at the surface and
through
for
coarse)— grained
that
Refraction seismic work found
velocities
misinterpreted
and
the
with
Aquifer tests indicate
material
gravel channel fills.
areas
the
the presence of a thick gravel zone.
sediments.
(Tertiary)
that
Earth resistivity data does not support the
resistive
resistive
indicate
Drill hole data demonstrated
conductivity
correlate
study
No thick sequences of Quaternary gravels were found
gravel lenses.
hydraulic
higher
this
proposed by Brown and others (1983) should be rejected
several
the
from
a
70
Based
on the results from this study,
an alternative
conceptual
model can be proposed for the Roskie study area (compare Figure 10
and
Figure
The Archean metamorphic rocks rise from the south to
the
beneath Montana State University.
the
22).
neai— surface
fault
at
southern
this
the
northern - margin of the
at
the
end of the Gallatin Valley may be the structural control
for
neat— surface bedrock feature.
fault-bounded
fault is suspected.
trough
The Archean metamorphic rock dips
steeply to the west beneath Roskie field.
nor
The extension of
A steep erosional surface or
The bedrock was not located by geophysical methods
encountered in the Roskie drill hole,
which suggests a
depth
to
bedrock greater than 50 m (160 ft) beneath Roskie field.
In
the
bedrock
revised model the Tertiary sediments overly
and are present within 3 m
Determining
the
whether the sediments are Tertiary or Quaternary units
to
ascertain directly.
Due to the
is
Whether the Renova
Sixmile Creek Formation is represented by these
difficult
Archean
(10 ft) of the surface (Figure 10).
complicated by the lack of paleontological control.
or
the
presence
sediments
of
is
coarser-
grained lenses and stringers observed in the drill hole and interpreted
from
the
the resistivity data,
Sixmile
layer
may
the depositional history characteristic of
Creek Formation best fits the
represent
a
Tertiary, pediment
model.
surface
The
similar
pediments on the flanks of the Gallatin Valley (Glancy,
1980).
1964;
to
the
Hughes,
The higher elevations of the pediment surfaces adjacent to the
Bozeman "alluvial fan" surface
and/or
neai— surface
tectonic
suggest a different geologic, erosional
history than the lower area where Hackett and
(1960) mapped the Bozeman "alluvial fan".
others
71
Figure 22:
The
Block diagram of proposed alternative model for the Roskie
study area.
MA = modern alluvium;
Qal = younger
Quaternary alluvium;
T = Tertiary sediments;
MP =
Mesozoic-Paleozoic rocks;
PGa = Precambrian Archean
rocks.
MSU = Montana State University; RW = Roskie well
site; ML = Marsh Lab.
Quaternary material within the study area consists of a
sheet of alluvium,
sediments.
area
to
topsoil and organic material overlying the Tertiary
The lack of an extensive and thick zone of gravels in this
has led to a rejection of the paleochannel hypothesis as well
a rejection of the previously accepted thoughts of an alluvial
depositional
thin
environment
held
by
Hackett
and
others
as
fan
(1960).
72
Groundwater
allocation
models
and land-use models
derived
for
the
Bozeman "alluvial fan" need to be revised in light of this new study.
Future Considerations
The
hole
extensive variability in the aquifer,
and
resistivity data,
depositional
environment.
demonstrates the changing nature
The
both horizontally
the
by
and
as the streams migrated back and forth across the surface.
permeability,
sediments
of
Aquifer characteristics are controlled
the addition of less permeable silts and clays,
vertically,
as seen from the drill
porosity and hydraulic conductivity of the
aquifer
is generally reduced with the addition of these clay
zones.
The amount of vertical water movement may be reduced and water movement
could be directed more horizontalIy (down slope).
in
Thus stratification
the sediments resulting from the controlling Tertiary
environment
depositional
appears responsible for the characteristics of the
Roskie
area aquifer.
The
surface
not
presence
of
throughout
Tertiary material within 3 m
(10
ft)
of
the study area suggests that a high yield well
a realistic target since the Tertiary has not been found to
major
water
producer
Valley (Hackett,
the
1960).
in
most of the eastern part
of
the
be
is
a
Gallatin
But the hydrologic studies on the Roskie well
suggests that at least 379 Ipm (100 gpm) may be a viable target for the
aquifer.
tested.
Whether
Lateral
constriction
This
this
yield can be sustained or not has yet
be
flow through the deep aquifer may be increased by the
of flow resulting from the Precambrian
situation,
to
along
bedrock
barrier.
with the increase in fine-grained material
at
73
depth
in
the Tertiary units,
horizontal
water
at
production.
33
m
Further
The
characteristics
aquifer
several
watei—
bearing
zones
area.
would
amount
of
Well
increase
tests
and
are
necessary
to
(500
determine
gpm)
the
well
yield.
aquifer
the effects high pumpage rates might have on
as well as surrounding shallow domestic wells near the
study area.
casing
well located at Marsh Laboratory was perforated in a
(107 ft) zone and has a substantial 1900 Ipm
pump
in
Proper well development could increase
potential from the Tertiary sediments in this
perforated
increase
flow at this site and an increase in the
water available for withdrawal<
the
may be responsible for an
the
Roskie
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80
APPENDICES
BI
APPENDIX A
ROSKIE WELL AQUIFER TEST DATA
)
82
Table
T ime
(min)
O
1.0
1.5
4.0
5.0
5.6
6.0
7.0
7.3
8.0
9.0
10.0
11.0
12.0
13.0
14.0
16.0
18.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
55.0
60.0
65.0
70.0
75.0
80.0
85.0
90.0
95.0
100.0
105.0
110.0
115.0
120.0
130.0
140.0
150.0
160.0
170.0
180.0
6:
Roskie well pump test and recovery
measurements from ground level.
Drawdown
(ft)
11.75
42.85
53.55
58.15
61.15
62.15
62.15
63.15
64.15
65.15
65.15
65.15
66.15
66.15
67.15
67.15
68.15
68.15
69.15
70.15
70.15
71.15
72.15
72.15
72.15
73.15
72.15
72.65
73.15
73.15
74.15
74.15
74.15
75.15
75.15
75.15
75.15
75.15
76.15
76.15
75.15
74.15
75.15
75.15
75.15
data,
May
1985.
Time
(min)
Al I
Drawdown
(ft)
190.0
200.0
210.0
220.0
230.0
240.0
75.15
75.15
76.15
76.15
76.15
76.15
Pump off
Time
(min)
0
0.25
0.50
0.75
1.0
1.2
1.3 .
2.0
2.5
3.0
4.0
4.5
5.0
17.0
22.0
26.5
30.0
35.0
42.0
55.0
60.0
70.0
80.0
100.0
120.0
240.0
360.0
460.0
795.0
960.0
1440.0
2820.0
4140.0
5520.0
6840.0
Recovery
(ft)
76.15
60.15
55.15
52.15
49.15
47.15
44.15
41.15
41.15
41.15
36.15
35.15
34.15
.27.15
26.15
22.15
23.15
21.10
20.65
19.15
19.05
18.35
17.85
17.55
17.25
14.75
13.95
13.45
12.70
12.50
12.20
11.95
11.85
11.85
11.75
83
Table
7:
Aquifer analysis using recovery method.
Discharge = 60
gallons per minute.
Static water level = 11.75 ft below
ground level.
(t 1= time since pump was shut off, t =
time since beginning of pump test, s'= residual drawdown).
t'
(min)
t
(min)
t/f
s'
(ft)
1.0
2.0
3.0
4.0
5.0
17.0
22.0
26.5
30.0
35.0
42.0
55.0
60.0
70.0
80.0
100.0
120.0
240.0
360.0
460.0
241
242
243
244
245
257
262
266
270
275
282
295
300
310
320
340
360
480
600
700
241
121
81
61
49
15.1
11.9
10.1
9.0
7.9
6.7
5.4
5.0
4.4
4.0
3.4
3.0
2.0
1.7
1.5
42.7
29.4
29.4
24.4
22.4
15.4
14.4
10.4
11.4
9.4
8.9
7.4
7.3
6.6
6.1
5.8
5.5
3.0
2.2
1.7
84
Table 8:
Slug test data, June 1985. All measurements from below top
of casing.
(t = time in seconds, h = recovery height at
later readings, H = initial static water level = 14,5 ft,
Ho = height at first reading).
t
(sec)
h
(ft)
5.0
13.0
35.0
44.0
55.0
73.0
84.0
93.0
104.0
125.0
134.0
144.0
173.0
197.0
208.0
243.0
273.0
306.0
317.0
357.0
399.0
509.0
582.0
761.0
932.0
10.5
11.9
12.5
12.6
12.9
13.3
13.5
13.5
. 13.6
13.7
13.8
13.9
14.0
14.1
14.2
14.2
14.3
14.3
14.4
14.4
14.4
14.4
14.4
14.5
14.5
H-h
(ft)
4.0
2.6
2.0
1.9
1.6
1.2
1.0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.1
0.1
0.1
0.0
0.0
H-h/H-Ho
0.65
0.50
0.48
0.40
0.30
0.25
0.25
0.23
0.20
0.18
0.15
0.13
0.10
0.08
0.08
0.05
0.05
0.03
0.03
0.03
0.03
0.03
0.00
0.00
85
APPENDIX B
EARTH RESISTIVITY DATA
86
Table 9s
Line
Resistivity profile data, 1985. All distances from east end
of line unless otherwise noted.
Resistivity = ohm-ft; a =
electrode profile spacing in feet.
Distance
a = 30
399
. 348
372
441
492
528
495
480
472
0
25
50
75
100
125
150
175
200
225
250
275
300
325
350
375
537
522
501
537
549
501
462
516
585
510
375
579
633
357
555
588
0
50
100
150
200
250
300
350
400
351
351
369
372
387
321
363
555
408
Line
Distance
a = 30
4R
0
25
50
75
100
125
150
175
200
225
250
275
300
325
350
375
66
429
510
495
474
522
507
474
510
258
321
480
441
375
543
612
0
25
50
75
100
125
150
175
200
225
250
275
300
325
350
375
537
360
546
510
447
582
522
462
531 .
429
420
399
273
300
255
351
137
148
130
127
147
130
a = 100
CU
0
50
100
150
200
250
300
350
400
a = 100
153
95
100
152
192
103
6R
120
131
132
106
93
96
116
132
116
148
116
128
172
141
87
Table 9:
Continued.
Line
Distance
a = 30
SR *
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
1050
1100
399
495
510
453
483
552
459
585
636
561
552
IRWF
0
50
65
100
115
150
. 165
200
215
250
265
300
350
492
450
699
699
705
672
606
588
486
603
645 .
543
498
a = 100
138
135
138
156
142
117
144
142
131
149
166
160
171
198
190
157
172
201
208
218
289
287
462
242
528
243
516
211
576
225
567
531
543
0
245
498
50
240
462
100
225
528
150
237
516
200
190
576
250
193
567
300
531
240
350
* = distances from south end of line.
2RWF
Line
Distance
a = 30
a = 100
3RWF
0
50
100
150
200
250
300
350
456
420
348
528
432
474
534
426
207
224
151
159
210
242
4RWF
0
50
100
150
200
250
300
350
400
450
500
550
600
393
516
504
453
462
495
459
459
450
441
465
420
390
165
187
160
156
158
160
193
191
189
209
242
5RWF
0
50
100
150
200
250
300
350
400
450
500
550
600
492
423
411
549
396
420
399
510
621
453
384
495
420
139
150
152
136
167
158
207
244
234
200
240
88
Table 9: Continued.
Line
Distance
6RWF
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
1050
1100
1150
7RWF*
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
a = 30
618
498
474
375
444
402
369
507
564
552
528
432
399
423
474
411
384
417
396
432
525
435
507
384
411
549
531
567
426
432
429
453
372
420
414
375
354
408
. 411
408
423
372
a = 100
Line
Distance
a = 30
185
180
175
171
173
180
182
161
148
137
128
140
146
134
141
139
138
150
160
185
183
173
8RWF
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
1450
441
438
429
381
504
495
462
408
477
522
510
477
462
170
214
244
223
256
296
267
220
238
249
255
225
210
161
180
263
* = distances from south end of line.
345
435
537
546
450
429
447
282
318
357
345
588
558
585
300
477
a = 100
190
159
179
180
145
127
131
135
132
159
151
108
120
178
162
131
156
210
174
173
220
214
152
167
161
169
89
Table 9: Continued.
Line
Distance
9RWF
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
1050
1100
1150
414
435
540
589
450
360
435
402
423
417
381
375
390
603
447
432
663
378
360
345
333
336
357
453
0
50
100
150
200
250
234
198
205
220
223
213
a = 30
a = 100
172
171
165
157
146
141
146
142
146
156
140
140
147
192
218
194
195
228
273
254
Line
Distance
a = 30
a =
V4
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
1050
1100
1150
372
339
399
448
429
450
402
309
318
339
396
345
405
372
339
339
354
342
396
423
405
453
492
435
196
189
164
156
188
192
184
217
162
162
173
167
171
168
173
170
180
184
197
202
90
Table 9: Continued.
Distance
a = 30
a =
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
1050
1100
1150
450
438
387
321
372
366
375
360
414
378
408
495
429
315
312
354
399
408
357
411
390
387
402
360
169
166
157
158
168
157
162
175
167
140
162
160
173
160
150
167
190
167
159
204
91
Table 10:
Vertical electrical sounding data, 1985. Resistivity = ohmft.
All electrode spreads are east-west unless otherwise
noted.
Distance from
center (ft)
IR
2R
3R
4R
SR
6R
5
10
20
40
60
80
100
120
580
714
710
309
276
197
145
120
399
650
678
337
230
179
HO
116
585
668
580
424
268
192
98
84
545
811
706
416
327
201
101
100
331
609
596
452
305
174
96
101
870
859
604
404
316
190
132
107
Distance from
center (ft)
IRWF
2RWF
3RWF
4RWF
5RWF
V3*
5
10
20 30
40
50
60
70
80
90
100
HO
120
130
140
165
291
418
450
448
442
419
368
343
316
276
234
194
160
276
440
519
480
441
401
377
328
285
249
219
187
179
286
418
363
373
353
301
272
248
224
214
187
158
445
605
462
502
459
400
372
331
288
255
191
482
597
590
486
348
352
323
297
278
261
247
233
220
192
157
117
209
312
336
358
350
350
319
313
286
261
160
* = electrode spread orientated north-south from center.
209
169
Table IOs Continued
Distance from
center (ft).
5
10
15
20
25
30
35
40
45
50
60
70
80
90
100
HO
120
130
Resistivity
(ohm-ft)*
388
599
762
628
595
528
406
372
329
295
249
207
134
131
121
108
109
83
* Sounding located 27 feet west of Roskie well.
orientated north-south.
Sounding
spread
is
93
APPENDIX C
SEISMIC REFRACTION DATA
94
Table 11:
Seismic velocities, Roskie study area, 1985.
Line
Layer
Forward
velocity
(ft/sec)
Reverse
velocity
(ft/sec)
Line
Layer
IR
Vl
VE
667
9090
1550
11111
19VS
Vl
VS
ER
Vl
VS
1000 .
9900
769
9500
SR
Vl
VS
555
8850
555
10638
SR
Vl
VS
667
7143
1000
8333
BR
Vl
VS
1000
7917
1S50
7364
9R
Vl
VS
1100
7308
1100
6985
ISR
Vl
VS
833
9500
1000
7787
IOR
Vl
VS
833
7308
500
896S
IlR
Vl
VS
6S5
8879
500
7540
16R
Vl
VS
68S
769S
714
7317
ISRW
Vl
VS
667
8879
667
6835
17RW
Vl
VS
1136
7965
1389
7377
18RW
Vl
VS
6S5
7308
556
74SS
14VS
Vl
VS
667
6376
833
7197
15VS
Vl
VS
8S0
6884
555
6785
Forward
velocity
(ft/sec)
Reverse
velocity
(ft/sec)
1818
7661
1000
7983
<
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