Minatare Site

At the Minatare site, all wells used in the aquifer
test were developed in the alluvial aquifer of the North
Platte River. Depth to water in the pumping well at the
start of the aquifer test was 6.90 ft. Depth to bedrock
(Brule and Chadron Formations) near the Minatare site
is about 187 ft. The saturated thickness at this site is
about 180 ft. The pumping well at the Minatare site is
screened in the middle part of the aquifer (table 2,
fig. 8). The North Platte River, which is about 2 mi
south of the site, is the only substantial surface-water

Pumping well

vase) tes ana a

180 feet : E

(Bedrock Not to scale

feature in the area and is too far from the site to affect
the test results. Values of hydraulic conductivity
ranged from 5.8910! to 6.33x10° ft/d (table 2).
Values of specific yield ranged from 1.47x10TM to
2.50x107!. Results of the aquifer test indicate that the
hydraulic-conductivity values of the shallowest part of
the aquifer (indicated by well 18M-3, table 2) were
smaller than those of the deeper parts of the aquifer by
a factor of two. The composite analysis indicates a
hydraulic-conductivity value of 1.98x10? f/d anda
specific-yield value of 5.00x107? (table 2, fig. 9).

2IN 53W7 AAAA 9th Street)
Scotts Bluff County |
Minatare, Nebraska |
Municipal £
well house =
cy
&
Not to scale 1sM-4 fi]
EXPLANATION
2] Observation well ES Screened interval
@ Pumping well ZZ] Bedrock
— Land surface Conerete pad

~~ Water level

Figure 8. Diagrammatic cross section and plan view map showing the Minatare site.

AQUIFER-TEST RESULTS

15


Table 2. Results of aquifer tests in the North Platte Natural Resources District, western Nebraska, 1997-98

[All measurements in fect unless otherwise noted; f1/d, feet squared per day; fd, feet per day]

Screened Hydraulic Storativity Specific yield
Well site a nguiter _ deoth “trom peeve mmiseiity conductivity (Gimension- ‘dimension
pumping well °° able (7/0) (ftid) less) less)
Bayard 126 133 96-126
23M-1 133 25 3-126 7.37x10° 5.80x10! 5.22x10 —-2.46x10-!
23M-2 133 50 121-126 1.68x104 1.33x10? 3.55x103 ——-2.46x107!
oS 80 50 68-73 1.07x10* 8.50x10! 193x107 -2.54x1071
3231 .43x10° 1.10x10! 113x103 3.00x107

Gering 2
14M-1
14M-2
14M—4

47-12
40 52-72
39 6-21
3

1 1-71

519x104
401x104
5.11x10*

721x107
557x107
710x101

5.30x10>
2.40x104
213x107

2.33x10!
255x101
5.00x10

Lyman 99

6M-2

35-75
25 19-99
0-14

3.21x104
3.78x10°

3.24x107
3.82x10!

931x103
3.86x107>

1.00x107
Ltaxto!

Minatare 180
18M-1
18M-—2
18M-3
18M—4

105
81
100
30

58-98
28 160-180
19 82-92
23 2-28
8-188

1.14x10°
3.26x104
1.06x10*
4.09x104

633x107
1.81x10?
5.89x10!
2.27107

1.22x10°
2.2710
5.10x10>
631x107

250x107!
8.67x10
184x107!

147x107

Mitchell 108
10M-1
10M-2

115
md

48-108
7 28-108
3-23

5.43x10*
2.00x10*

5.03x10?
1.85x10!

448x107
1.78x10%

3.20x10!
170x107

Morrill 181
1H-1
1H-2
1H-3

136
195
1 ®

72-121

25 176-181
x 93-98
0-16

1.38x10*
2.62x10°
1.06x10°

7.10x10!
1.50x10!
5.89x 10?

101x107
4.23x10>
3.61x10"!

2.62x10!
3.00x107!
250x107!

Scottsbluff Airport 52
ISM-1
15M-2

32-52
36 41416
36 2-22
50 2-52

102x104
139x104
2.28x10*

1.96x10?
2.62107
4.38x10?

1.40x10°
1.46x104
8.17x10>

2.73x1071
141x107
160x107!

AQUIFER-TEST RESULTS 9


Morrill Site

At the Morrill site, all wells used in the aquifer
test were developed in the alluvial aquifer of the North
Platte River. Depth to water in the observation wells at
the start of the aquifer test was 14 ft. The pumping
well at the Morrill site is screened in the middle part of
the aquifer (table 2, fig. 12). The top of the Brule
Formation is about 195 ft below land surface. The
saturated thickness at this site is about 181 ft.

The predominant surface-water feature in the
area is Sheep Creek (fig. 1), which lies about 0.75 mi
west of the site. Sheep Creek is a perennial stream in
the reach that flows nearest Morrill and has an annual
mean daily discharge of about 80 ft/s and had a
discharge of 92 ft?/s during the test (Nebraska Depart-
ment of Water Resources, 1998). Data collected during
the test (fig. 13) did not show an appreciable deviation
from the predicted drawdown curve. Therefore, it was
assumed that Sheep Creek did not have an effect on
the test.

Results from this aquifer test indicate that the
hydraulic properties of this aquifer are variable with
respect to depth (table 2, fig. 13). The values of
hydraulic conductivity ranged from 1.50x10! to
5.89x10? ft/d (table 2). Values of specific yield for this
site ranged from 2.50x10"! to 3.00x10!. The

composite analysis indicates a hydraulic-conductivity
value of 9.90x10! ft/d and a specific-yield value of
3.00x107! (table 2, fig. 13).

The hydraulic-conductivity value determined for
the shallow well (1H-3) was an order of magnitude
greater than the value of the deeper well (1H-1).
However, the vertical distances between the screen of
the pumping well and the screens of the deeper well
(1H-1) and the shallow well (1H-3) are each about
60 ft. Therefore, the values of hydraulic conductivity
(table 2) for wells 1H-1 and 1H—3 may be more repre-
sentative of vertical hydraulic-conductivity values than
horizontal hydraulic-conductivity values. In the
shallow well (1H—3), water levels did not respond
immediately when the pumping well began pumping.
A delay of about 1 minute occurred, and total draw-
down in the shallow well (1H-3) during the discharge
part of the aquifer test was about | ft compared to
about 2.9 ft in the deep well (1H-1) and 5.7 ft in the
medium well (1 H-2). The reason for the delayed
response has not been determined. Lithologic logs
collected during the installation of these wells do not
indicate the presence of confining units. In the analysis
of the shallow well (1H-3), only early time data were
used to match the type curve.

Pumping well
23N 57W 16 ADAC
1H-1,2,3 a | Scotts Bluff County
Nn Be Morrill, Nebraska
nm a 2
= = £ t ® é
4
ees 6 0 = eee ee 2 Municipal | | 2
well house | / 3
25 foot
BL fe A
“Bs [ Not to scale
EXPLANATION
L| [EH] Observation well FE] Screened interval
iS @ Pumping well 7] Bedrock
— Land surface Gs Concrete pad
SZ~ Water level

Bodrosk Not to scale

Figure 12. Diagrammatic cross secton and plan view map showing the Morrill site.

AQUIFER-TEST RESULTS

19


CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain
Length
inch (in.) 25.4 centimeter
foot (ft) 0.3048 meter
mile (mi) 1.609 kilometer
Area
acre 4,047 square meter
square foot (ft”) 0.09290 square meter
Flow Rate
cubic foot per second (ft*/s) 0.02832 cubic meter per second
gallon per minute (gal/min) 0.06309 liter per second
foot per day (fv/d) 0.3048 meter per day
foot squared per day (ft?/d) 0.09290 meter squared per day

‘Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (° F) as follows:
oF = 1.8 (°C) +32
‘Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F -32)/1.8

Sea level: In this report “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929}—a geodetic datum derived from a geneval
adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.

Altitude, as used in this report, refers to distance above or below sea level.

Site Identification, as used in figures 2 through 14, and in tables | and 2.

This report uses two different methods of site identification. The first method, well site, uses the field identification number associated with the name of
the municipality (for the pumping well) or the NPNRD original field identification for the observation well—such as Bayard and 23M-I, respectively. The
second method. legal identification, is based on the land subdivisions in the Bureau of Land Management (BLM) survey of Nebraska. The number preceding
N (north) indicates the township or tier, the numeral preceding W (west) indicates the range, and the numbers preceding the terminal letters indicate the
section in which the well is located. The terminal letters designated A, B, C. and D denote the quarter section, the quarter-quarter section, the quarter-
quarter-quarter section, and the quarter-quarter-quarter-quarter section. The designation is given in a counterclockwise direction beginning with “A” in the
northeast comer of each subdivision, Each well also is assigned a terminal number “1” designating the order of inventory. and two or more wells are further
distinguished by adding a sequential digit to the well number, assigned by order of inventory.

iv CONTENTS


10 7 T 10 T T r T
eine
oe entire eet
5 5 ?
ra #
© ek _ Eh “a 4
= Pa =
z a
& 5
10" q 10" E q
: yo ous 3 sos
S : S | Parameters
a é Porometers d | Fort
Fa wrk ; T= 14giisquneteet | Fe wk | T=szep0euareteet |
= $ = 0177 = $ =z!
& §=028 s Sy = 0087
& 201 E | e200
S ; =
3 n n rT L i mn n n ul n
io? 107 10°10" St0” ag ——*T* rot 0? 10" 10 10° 10" 10°
ELAPSED TIME FROM BEGINNING OF ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES. TEST, IN MINUTES
10° T . 10! my T T i T
E E ee
= ok 4 2 10°F a 7q
= =
& a
é &
Soak of 4 <= oak 4
B 10 f ous ia) 10 2 1eM4
6 / 6
gS | Parameters Zz Paranetes
Gok j T= nppsuare fet | a ot T= toai0 ner tat |
erp ye err | ae
s | pias g | Rene
4 n n nl n 3g Li daul ul 1 ul nl
io* 10% 10 107 107 19 10" io? 107 10° 10" 10st ——«0
ELAPSED TIME FROM BEGINNING OF ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES. TEST, IN MINUTES
10' T T
G
i
= yoo b
Fea
=
a
3
5 10'F
a
a
q
107 —
pe
&
na
i Ps tatu i

10° a 1 1
1o* 10% 10% = 107 10% 10°10"

ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES PER SQUARE FOOT

Figure 9. Log-log plot of drawdown versus time for the Minatare site.

16 Hydrologic Characteristics of Selected Alluvial Aquifers in the North Piatte Natural Resources District, Western Nebraska


Ez a i z an
z
= a 2 wa
& io’ ? q g 10°F omeee ee 7"
B
3 J Fs ra
& / os & 7 ae
z : Sq
Swe | Forameters 7q 5 i'r /
& T = 10,200 squere feet g
= pee =
z sycoa =
=
= | =
2 m 1 . 1 . 2 rl 1 f nl n
0? 10? 10” 10” 10” 10” 108 Mio? to 10" 10" 10” 10° 10°
ELAPSED TIME FROM BEGINNING OF ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES. TEST, IN MINUTES.
10! m T 1 "y 10! T T T T
es jj 5 a
2 ——e d Lis ee oe
2 _— S ee
2 e, er oe
2 0 - f 4 S 10°F Yee q
a F on / ye
Ss } Btls Observation
2 B iy ‘aT
a © 15M3 o
5 / Z / ria
ge Pome YEE 1
E ete 2 me
& Sy= 016 =
Pr oe & $= 000371
st | 3 Bat
i
2 ni 1 1 1 f 2 1 1 f 1
wie? 107 10° 10' = 10, 10108 eo ti 10' iv 10° 10°
ELAPSED TIME FROM BEGINNING OF ELAPSED TIME FROM BEGINNING OF TEST,
TEST, IN MINUTES IN MINUTES PER SQUARE FOOT

Figure 15. Log-log plot of drawdown versus time for the Scottsbluff Airport site.

22 Hydrologic Characteristics of Selected Alluvial Aquifers in the North Platte Natural Resources District, Western Nebraska


G jr 4
ie fra a
z —4 z Le
2 of wl | 2 fue |

10 10
a a
= S
FI ° =
gw B
S 210M oa + 10M2
= w'F 4 = w'k "q
sar] Porameters ay Parameters
oe | T = 54,300 square feet ce T = 20,000 square feet
Bp pei day f per éay
& § = doe & or7e
= a 0005 = 03

io* 107 107 10° 10" 10? 10° 10° 10° 107 10" 10° 10' 107 10° 10%

ELAPSED TIME FROM BEGINNING OF ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES TEST, IN MINUTES

10" T T T
G
ira
2
B
ok
Ss 10
ag
3 /,
B
a . Gteaaton
@ vo mH
fa + Parameters
e ae
= § reg”

KzKr= 0.96
10% tut h ra vrrO OST mT
10 10 1° 107 = 10" 10°10"

ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES PER SQUARE FOOT

Figure 11. Log-log plot of drawdown versus time for the Mitchell site.

18 Hydrologic Characteristics of Selected Alluvial Aquifers in the North Platte Natural Resources District, Western Nebraska


Lyman Site

At the Lyman site, all wells used in the aquifer
test were developed in the alluvial aquifer of Horse
Creek. Depth to water in the pumping well at the start
of the aquifer test was 15.93 ft. The pumping well at
the Lyman site is screened in the bottom part of the
aquifer (table 2, fig. 6) near the top of the Brule
Formation, 115 ft below land surface. The saturated
thickness at this site is about 99 ft.

Pumping well
oor are ,
t i
y
25 eat
S|
=| ;-——
tee Ff —|
|
EI
E
Bedrock
Not to scale

Horse Creek, the predominant surface-water
feature in the area, is perennial and lies about 0.25 mi
south of the test site. Analysis of the aquifer-test data
(fig. 7) did not show an appreciable deviation from the
predicted drawdown curve; therefore, it was assumed
that influence from Horse Creek was negligible.

Values of hydraulic conductivity of the aquifer
at this site ranged from 3.82x10! to 3.24x10? fi/d
(table 2). Values of specific yield ranged from
100x107 to 1.14x107!. The composite analysis indi-
cates a hydraulic-conductivity value of 2.23x10? ft/d
and a specific-yield value of 5.00x10~ (table 2,
fig. 7).

23N 58W 34 BCCB

g Scotts Bluff County
3) Lyman, Nebraska
B) a2 Bl
g .
5] ,
:|
a]
|
|
Not to scale
EXPLANATION
LE] Observation well EJ Screened interval
{0} Pumping well CZ) Bedrock
—— _Landsurface [Concrete pad
Water level

Figure 6. Diagrammatic cross section and plan view map showing the Lyman site.

AQUIFER-TEST RESULTS


Table 1. Location of and construction information about pumping and observation
wells used in the aquifer tests, North Platte Natural Resources District, western Nebraska

[Shaded cells indicate pumping wells; NPR, North Platte River alluvium; HC, Horse Creek alluvium]

Well ‘Screened interval
Well site Legal identification diameter, below land Aquifer
in inches ‘surface, in feet

23M-1 25 10-133 NPR
23M-2 25 128-133 NPR
23M-3 25 75-80 NPR
23M-4 2.5 10-30 NPR

14M-1 2.5 61-81 NPR
14M-2 25 15-30 NPR
14M-4 25 10-80 NPR

oM-I 25 35-115 HC
oM2 25 10-30 HC
18M-1 25 168-188 NPR
18M-2 25 90-100 NPR
18M-3 25 10-30 NPR
18M-4 25 t-91 NPR
“1OM-1 25 35-115 NPR
10M-2 25 10-30 NPR

TH-1 25 190-195 NPR
1H-2 2.5 107-112 NPR
1H-3 25 10-30 NPR

15M-1 25 69-74 NPR
1SM-2 25 30-50 NPR
15M-3 2.5 30-80 NPR

DESIGN OF AQUIFER TESTS AND METHODS OF ANALYSIS

5


104°
T

North Platte
Natural Resources
District

NEBRASKA \

Index map

103°30'
T T
+ Morrill County

Scottsbluff

i

i
Scottsbluff i
Airport i

4145

Base from the U.S. Bureau of Census Tiger files, 1:100,000
Universal Transverse Mercator, Zone 13 Projection 0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

—— Surface water 9 —— Roads
—— Study area boundary AX Municipal well and observation well sites

~ County boundaries Municipal boundaries

Figure 1. Aquifer-test locations in the North Platte Natural Resources District, western Nebraska.

Hydrologic Characteristics of Selected Alluvial Aquifers in the North Platte Natural Resources District, Western Nebraska


Hydrologic Characteristics of Selected Alluvial
Aquifers in the North Platte Natural Resources

District, Western Nebraska

By G.V. Steele, J.C. Cannia, and K.G. Scripter

Abstract

Between 1997 and 1998 the U.S. Geolog-
ical Survey, in cooperation with the North Platte
Natural Resources District, conducted constant-
discharge aquifer tests at seven locations in
the western part of the North Platte Natural
Resources District—Bayard, Gering, Lyman,
Minatare, Mitchell, Morrill, and Scottsbluff
Airport. Hydraulic conductivity at the Bayard
site ranged from 1.10x10! to 1.33x10? feet per
day (ft/d), and values of specific yield ranged
from 2.46x10 to 3.00x107!. Hydraulic conduc-
tivity at the Gering site ranged from 7.10x10! to
8.40x10? ft/d, and values of specific yield ranged
from 5.00x10TM to 2.55x107!. Hydraulic conduc-
tivity at the Lyman site ranged from 3.82x10! to
3.24x 10? f/d, and values of specific yield ranged
from 1.00x10~ to 1.14107! Hydraulic conduc-
tivity at the Minatare site ranged from 5.89x10! to
6.33x10? f/d, and values of specific yield ranged
from 1.47x10~ to 2.50x107!. Hydraulic conduc-
tivity at the Mitchell site ranged from 1.85x10! to
5.03x10? ft/d, and values of specific yield for this
site ranged from 1.70x107! to 3.20x1071.
Hydraulic conductivity at the Morrill site ranged
from 1.50x10! to 5.89x107 ft/d. Values of specific
yield for this site ranged from 2.50x107! to
3.00x10-!. Hydraulic conductivity at the Scotts-
bluff Airport site ranged from 1.96x10? to
4.38x107 ft/d, and values of specific yield ranged
from 1.41x10~ to 2.73x107.

INTRODUCTION

Most public-supply wells in the North Platte
Natural Resources District (NPNRD) produce water
from alluvial aquifers. In order to assure adequate
supplies of water and to manage the water resource
effectively, water managers need information about the
hydraulic properties of the alluvial aquifers. Some of
the primary hydraulic properties of alluvial aquifers
include hydraulic conductivity, transmissivity, stora-
tivity, and specific yield, which are discussed later in
the report.

In 1997, the U.S. Geological Survey (USGS)
entered into a 2-year cooperative agreement with the
NPNRD to determine the hydraulic properties of seven
sites in alluvial aquifers in the NPNRD (fig. 1). This
study also helps resources managers gain an under-
standing of how the alluvial aquifers react to certain
stresses. The study will improve understanding of the
properties governing ground-water flow in the alluvial
aquifers in the NPNRD.

Purpose and Scope

The purpose of this report is to present the
results of seven aquifer tests conducted in the NPNRD
during 1997-98. These results are presented in the
form of data values and graphs. Results of the tests
will enable water managers to understand the vulnera-
bility of ground-water supplies to potential contamina-
tion.

Acknowledgments

The authors acknowledge the municipalities of
Bayard, Gering, Lyman, Minatare, Mitchell, Morrill,

Abstract

1


WATER-LEVEL DISPLACEMENT, IN FEET

WATER-LEVEL DISPLACEMENT, IN FEET

Figure 7. Log-log plot of drawdown versus time for the Lyman site.

10° T T r T 10° T T T
8
10'E 4 2 ok
E
a
peo | S
3 = 00
10'F q = 10°F
oot a
a fi
Parameters g q Parameters '
tok T = 32,100 square feet _] Foagth T = 3780 square feet |
ae E sia
2 Oobe = @ 006
102 ds ssl mt mn 1 10? rl fl f m L ,
107 10" 10° 10’ = 102, 4010 107 10’ 10° 10' = 10 10% 10
ELAPSED TIME FROM BEGINNING OF ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES TEST, IN MINUTES
10° nad A T mT
10'E |
wl a
Obsenat
Wells.
36M
a2
10" Parameters 4
T = 22,100 square feet
pet day
S$ = 0.00827
Sy = 005
Kz/Kr= 0.94
102 geal Ads aso ‘ L
10° 10° 10% 10° 107 107 10° 10°

ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES PER SQUARE FOOT

14 Hydrologic Characteristics of Selected Ailuviai Aquifers in the North Piatte Natural Resources District, Western Nebraska


Streamflow drainage in the NPNRD is predomi-
nantly northwest to southeast. The North Platte River
and its tributaries (fig. 1) dominate the surface-water
system in the NPNRD. Steele and Cannia (1997)
reported that part of the North Platte River generally
was a gaining stream. The tributaries of the North
Platte River in the NPNRD are a mix of ephemeral,
intermittent, and perennial streams.

DESIGN OF AQUIFER TESTS AND
METHODS OF ANALYSIS

Aquifer tests at seven sites were designed to
determine the hydraulic characteristics of the alluvial
aquifers in the western part of the NPNRD. The test
sites were located in or near the communities of
Bayard, Gering, Lyman, Minatare, Mitchell, Morrill,
and Scottsbluff (fig. 1). Public water-supply wells
were selected as the pumping wells for the aquifer
tests because detailed construction data were available
for each, and these wells were the only high-capacity
wells that were operational during the late fall and
early spring, when influences from irrigation activities
on the aquifers were minimal. At least two observation
wells were installed per site (table 1). These observa-
tion wells either were screened at different depths or
were fully screened. The observation wells were
located at distances of 25 to 131 ft from the pumping
well.

The aquifer tests were used to determine the
primary aquifer characteristics hydraulic conductivity,
transmissivity, and specific yield. Hydraulic conduc-
tivity is a measure of the capacity of a porous medium
to transmit water per unit time. Dimensions of
hydraulic conductivity are unit length per unit time
(L/t). Transmissivity is a product of the average
hydraulic conductivity and the thickness of the aquifer.
Dimensions of transmissivity are unit length squared
per unit time (L7/t). Specific yield is a dimensionless
measurement of the volume of water that would drain
under gravity alone per unit volume of aquifer. In addi-
tion, because confined aquifers are not dewatered,
specific yield is measured only in water-table aquifers.

In 1997 and 1998, seven 24- to 30-hour
constant-discharge aquifer tests were conducted. Each
aquifer test was designed and analyzed using standard
methods described by Dawson and Istok (1991),
Domenico and Schwartz (1990), Driscoll (1986),
Freeze and Cherry (1979), Kruseman and de Ridd-r
(1990), Lohman (1972), Moench (1993, 1994),
Neuman (1975), and Stallman (1965). Before eack
test, typically 1 week to 1 month, electronic water-
level monitoring instruments were installed in the
observation wells to measure pretest water levels.
Prior to the start of each test, data collected by the
instruments were downloaded, and the instruments
were synchronized, recalibrated, and set to start
measuring automatically at intervals of 6 seconds to
1 hour, with the more frequent measurements taken
near the beginning of the test when greater changes in
drawdown are expected to occur. Manual measure-
ments using electronic measuring tapes also were
taken to supplement and verify the data recorded by
the electronic water-level instrumentation.

Hydrographs of the data collected prior to the
aquifer tests indicate that natural variations in water
levels occurred in all monitoring wells. At five sites,
the pretest variations in the water levels were within
the tolerances set in the standard methods, and correc-
tions were not needed to adjust the aquifer-test draw-
down curve. At the Bayard site, pretest water-level
data were unavailable, so based on data from other
sites, it was assumed that pretest water levels did not
change enough to affect the test. At the Gering site,
pretest water-level data indicated that a ground-water-
level decline existed before the test. At this site,
corrections were made to the water levels collected
during the test to compensate for the effect of the
ground-water-level decline.

Water-table (unconfined) aquifers are different
from confined aquifers in that the top surface is a free
and moving boundary. The storativity of an uncor-
fined aquifer is dominated by the gravity drainage of
water from the media (specific yield) rather than the
elastic expansion of water and compressibility of the
aquifer media (storage coefficient). There also can be
additional head loss in an unconfined aquifer due to
vertical flow components near the falling water table.

4 — Hydrologic Characteristics of Selected Alluvial Aquifers in the North Platte Natural Resources District, Western Nebraska


10 T T T i 10 mT T T Sar

G ee a ir f£

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i fa i F4

g Fa

a wie o 4 B wb 4 q

3 & 10

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GB ° &

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& d Ee

aa faa

Ee 4 2 10%, 4

o 26
S s |
10% 10" 10" 40° 101010 io* 10° 10° 10" 10 010
ELAPSED TIME FROM BEGINNING OF ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES TEST, IN MINUTES.
10° 1 T T uy T 10! T

G G

i

z= 10° Zz WE

S S

= S *

& 10'E & 10'F

= a

B 22)

a 107 q °F |

& &

= 103 & 10% lo 7 EY

S = | [ Ric O82

wo* 10’ 10° 10" 1070810 1 10° =10° = 10% 10" 10°10
ELAPSED TIME FROM BEGINNING OF ELAPSED TIME FROM BEGINNING OF TEST,
TEST, IN MINUTES IN MINUTES PER SQUARE FOOT

Figure 13. Log-log plot of drawdown versus time for the Morrill site.

20 Hydrologic Characteristics of Selected Alluvial Aquifers in the North Platte Natural Resources District, Western Nebraska


ZUSGS

science for a changing world

Prepared in cooperation with the
NORTH PLATTE NATURAL RESOURCES DISTRICT

Hydrologic Characteristics of Selected
Alluvial Aquifers in the North Platte
Natural Resources District, Western
Nebraska

Water-Resources Investigations Report 01-4241

U.S. Department of the Interior
U.S. Geological Survey


= = fa sda(oB"] 19+ Sto) fy (2)
0 n=l

where

vagy = —LETEXPLE BY? = Fa)Heosh(7oZp) __sinh{Yo(—dp)1sinhl 7 (11 )]
(9° +0+0)% -(y* - 46)" / a} cosh( 7p) (1, -dp)sin(Yo)

and

oy = ELT expt BO" = 7,1} e08(%, 29) __ sin Y= dp —sinly,L=1p)]

(9° -d+ 07, -(9° +77)" 1a} cosy) (1, -—d,)sin(y,)

where Jy = Bessel function of first kind, zero order,
Tt. .
t, = —~ (dimensionless),
sr°

Zp = quotient of the distance above the bottom of the aquifer and the saturated thickness of the aquifer at the start
of the test,

dp = quotient of the distance between the top of the well screen in the pumping well and the initial position of the
water table and the saturated thickness of the aquifer at the start of the test,

1p = quotient of the distance between the bottom of the well screen in the pumping well and the initial position of
the water table and the saturated thickness of the aquifer at the start of the test,

Ss
O= —., and
S,

Yo and ¥,, = root of the following equations:

OY, sinh(Y,)—(y" — 7; )cosh(¥,)=0, ¥> <y?

oy, sin 7, ) + (y? — 2) cos(y,) = 0,(2n-D (4/2) <y, <na, n21

DESIGN OF AQUIFER TESTS AND METHODS OF Al!ALYSIS 7


Because all aquifer tests were completed in unconfined conditions and subject to delayed responses, the
water-level data collected during the aquifer test were analyzed using Neuman’s method (1975), which accounts
for delayed response with the well function W(U,, Ug, f) in equation 1. Neuman’s equation (1975) for water-level
drawdown in an unconfined aquifer is based on the equation:

Q
s= Fp VU Ua B) o)

where

s is drawdown in the observation well in units of length, and
W(Us,, Up, A) is the well function for the aquifer:

rs rs, ry) K,
Us=——_, Us= > B=\—~
4Tt 4Tt D) K,
= discharge in pumping well 9;
= aquifer transmissivity, which equals the product of K,, and D (LA);
P= radial distance of observation well from pumping well, feet squared (L”);
S= the volume of water instantaneously released from storage per unit surface area per
unit decline in head (elastic early-time storativity) (dimensionless);

time (t);

the volume of water released from storage per unit surface area per unit decline of the water table
(specific yield) (dimensionless);

K,= vertical hydraulic conductivity (L/t);

K,= hydraulic conductivity (L/t); and

D= _ saturated thickness of the aquifer at the start of the test (L).

It was assumed for the aquifer-test analyses that the aquifers were homogeneous, anisotropic, of infinite
areal extent, and that flow was radial to the well screen. It also was assumed that continuous and constant
discharge from the pumped wells occurred during the test; ground-water density and viscosity were constant; the
aquifer was unconfined and of uniform thickness with a horizontally flat bottom; negligible head losses through
the well screen occurred; and that ground-water flow was as described by Darcy's Law (Dawson and Istok, 1991).

Equation 1 assumes that all wells are fully penetrating. However, for this study none of the pumping wells
and few of the observation wells were fully penetrating. Kruseman and de Ridder (1990) report that partial pene-
tration causes the velocity of the flow lines in the vicinity of the pumping well to be greater than they otherwise
would be. Moreover, this leads to an extra loss of head, and converging flow lines are strongest nearest the screen
and decrease with increasing distance. Neuman (1975) altered the well-bore boundary condition to specify the
vertical position of the screen of the pumping well. This compensates for the vertically convergent flow lines in
the vicinity of a partially penctrating pumping well. Neuman’s solution for flow to a partially penetrating well,
which is the equation that was used for the analyses in this report, is:

6 Hydrologic Characteristics of Selected Alluvial Aquifers in the North Platte Natural Resources District, Western Nebraska


and Scotts Bluff that provided the land for well instal-
lation and the resources for the aquifer characteriza-
tions. Special appreciation is extended to the staff of
these municipalities who directly or indirectly assisted
with this project.

DESCRIPTION OF STUDY AREA

The study area consists of seven sites in the
North Platte River and Horse Creek Valleys in the
western part of the NPNRD (fig. 1). The NPNRD lies
in the panhandle of western Nebraska and is in the
High Plains section of the Great Plains Province
(Fenneman, 1946). The NPNRD is diverse in land-
forms including ridges, escarpments, bluffs, river
valleys, tablelands, and sand hills (Steele and Cannia,
1997). These diverse landforms relate to the geologic
units from which they are formed. The regional slope
of the study area is predominantly northwest to south-
east, which also characterizes the predominant direc-
tion of ground- and surface-water flow in this part of
the NPNRD.

Climate and Land Use

The climate of the NPNRD is semiarid with
relatively wide temperature ranges and low annual
precipitation (National Oceanic and Atmospheric
Administration, 1999). Most of this precipitation
occurs as rainfall from thunderstorms during the
months of May and June. Average monthly tempera-
tures for 1998 at the Scottsbluff Airport ranged from.
28.8°F in January, typically the coldest month, to
74.9°F in July, typically the hottest month. Tempera-
ture extremes for 1998 at the Scottsbluff Airport
ranged from —22°F (December 12, 1998) to 104°F
(July 18, 1998) (National Oceanic and Atmospheric
Administration, 1999). The annual precipitation for
1998 at the Scottsbluff Airport was 17.25 in. (National
Oceanic and Atmospheric Administration, 1999).

The NPNRD covers 3.2 million acres (Nebraska
Department of Natural Resources, 1999) that is pri-
marily irrigated and nonirrigated cropland, and range-
land. Land use around the aquifer-test sites is predom-
inantly residential/small community, rural, and
agricultural. In the agricultural areas, corn, hay, dry

edible beans, and sugar beets are the predorninant irri-
gated crops.

Hydrogeologic Settings

The hydrogeology of the NPNRD is diverse and
varies widely with location. Bedrock formations,
which serve as the base of the principal aquifer, are
massive, terrestrial, volcaniclastic to marine deposits.
The Gering, Brule, and Chadron Formations are
Tertiary in age and rest unconformably on the undif-
ferentiated marine deposits of Cretaceous age. The
Brule, as well as the Arikaree, and Ogallala Forma-
tions which also are Tertiary in age, typicall;’ make up
a majority of the upland areas flanking the river
valleys and can be significant sources of nor municipal
water supply.

The principal source of ground-water supply in
the NPNRD is the North Platte River alluvial aquifer
of Quaternary age. The alluvial aquifer is in valley-fill
deposits from rivers that incised the bedrocl- forma-
tions. The depth of the alluvial valley varies locally
with maximum thickness of about 210 ft (Verstraeten
and others, 1995) and from less than 1 mi tc over 5 mi
in width. This aquifer is composed of uncorsolidated
alluvial sands and gravels interlaced with clay lenses.
The clay lenses are not extensive enough to be
confining layers; thus, the North Platte River alluvial
aquifer is an unconfined, water-table aquifer. Aquifers
in tributaries of the North Platte River, such as Horse
Creek, are of similar composition to the No~th Platte
alluvial aquifer, but are thinner and narrower.

Ground water typically flows from th table-
lands to the north and south of the river valleys toward
the rivers, where it discharges into the rivers. Sources
of recharge to the alluvial aquifers can include local-
ized inflow from surface water, hydraulicall”
connected ground-water systems, and local precipita-
tion. Ground-water levels near the aquifer-test sites
typically range from 5 to 30 ft below the land surface.

Water levels in the alluvial aquifers vary greatly
with season and proximity to surface-water systems.
In areas where seepage from surface-water irrigation
systems does not occur, water levels typically are
highest in the spring and lowest in mid- to late
summer. In areas where seepage from surface-water
irrigation systems does occur, water levels eve typi-
cally highest in July through mid-September.

DESCRIPTION OF STUDY AREA

3


Mitchell Site

At the Mitchell site, all wells used in the aquifer
test were developed in the alluvial aquifer of the North
Platte River. Depth to water in the pumping well at the
start of the aquifer test was 6.96 ft. The pumping well
at the Mitchell site is screened in the bottom part of the
aquifer (table 2, fig. 10) near the top of the Brule
Formation, 115 ft below land surface. The saturated
thickness for this site is about 108 ft.

The predominant surface-water features in this
area are the Tri-State Canal and the North Platte River.
Water from the North Platte River is diverted into the
Tri-State Canal during irrigation season. When the
aquifer test (table 2, fig. 11) was conducted in late
October 1997, the canal had not been operational for

Pumping well

TOM-1 10M-2

a
=|

108 feet

25 feet

Bedrock
Not to scale

about 6 weeks. The North Platte River lies about

0.75 mi south of the site. However, data collected
during the aquifer test (fig. 11) did not show an appre-
ciable deviation from the predicted drawdown curve.

Values of hydraulic conductivity for this site
ranged from 1.85x10! to 5.03x 10? ft/d (table 2).
Values of specific yield at this site ranged from
1.70x107! to 3.20x107'. Results of the aquifer test
indicate that the hydraulic conductivity and the
storativity of the shallower part of the aquifer (indi-
cated by well 10M-2, table 2) were smaller than those
of the deeper parts of the aquifer. The composite anal-
ysis indicates a hydraulic-conductivity value of
4.63x10? ft/d and a specific-yield value of 3.20x107!
(table 2, fig. 11).

Not to seale 23N S6W 27 ABDC
} Scotts Bluff County
Mitchell, Nebraska
z fe) 10M-1,2
&|
2
S| pis ]
Municipal |
| well house
Est Street PE —
EXPLANATION
[EH] Observation well FES} Screened interval
@ Pumping well (77 Bedrock
—— Land surface ) Concrete pad
SZ_ Water level

Figure 10. Diagrammatic cross section and plan view map showing the Mitchell site.

AQUIFER-TEST RESULTS

17


SUMMARY AND CONCLUSIONS

Communities in the NPNRD use shallow
ground water in alluvial aquifers as a source of
drinking water. Between 1997 and 1998, the USGS,
in cooperation with the NPNRD, conducted constant-
discharge aquifer tests at seven sites to determine
hydraulic properties of alluvial aquifers in the western
part of the NPNRD. All aquifer tests were conducted
for a minimum of 24 hours, and data were analyzed
using Neuman’s (1975) solution for water-table
aquifers.

The hydraulic conductivity values ranged from
1.10x10! to 8.40x10? fi/d. Values of specific yield
ranged from 1.00x107? to 3.20x107!. In some areas,
responses to stresses on the system were instanta-
neous. In other areas, responses were delayed slightly.

At the Bayard site, the saturated thickness of the
aquifer was about 126 ft and the hydraulic conduc-
tivity of the aquifer was fairly consistent with depth.
The values of hydraulic conductivity ranged from
1.10x10! to 1.3310? ft/d. Values of specific yield
ranged from 2.46x107! to 3.00x107!.

At the Gering site, the saturated thickness was
about 72 ft. The North Platte River lies about 160 ft
north of the pumping well. Evaluation of drawdown
data collected during the test indicated that the prox-
imity of the North Platte River did not affect the test.
The hydraulic conductivity was smallest at the obser-
vation well (14M-4) farthest from the North Platte
River. Values of hydraulic conductivity ranged from
7.10x10! to 8.40x10 ft/d. Values of specific yield
ranged from 5.00x10~ to 2.55107!

At the Lyman site, the saturated thickness was
about 99 ft. Analysis of the aquifer-test data suggests
that induced recharge to the aquifer system from Horse
Creek was negligible during the test and the hydraulic-
conductivity value was larger in the shallow part of the
aquifer than in the deeper part of the aquifer. Values of
hydraulic conductivity ranged from 3.82x10! to
3.2410? f/d. Values for specific yield ranged from
1.00x10TM to 1.141071.

At the Minatare site, the saturated thickness was
about 180 ft. The hydraulic-conductivity values ranged
from 5.89x10! to 6.3310? ft/d and the specific-yield
values ranged from 1.47x10~ to 2.50x107!. Also, the
hydraulic-conductivity values of the shallower part of
the aquifer were smaller than those of the deeper parts.

At the Mitchell site, the saturated thickness was
about 108 ft. Values of hydraulic conductivity ranged

from 1.85x10! to 5.0310" ft/d. The values of specific
yield at this site ranged from 1.70x107! to 3.20x1071.
The hydraulic conductivity and the storativity values
of the shallower part of the aquifer were smaller than
those of the deeper parts of the aquifer.

At the Morrill site, the saturated thickress was
about 181 ft. Sheep Creek lies about 0.75 mi west of
the site, but analysis of the aquifer-test data indicated
that recharge to the aquifer from Sheep Creek was
negligible during the test. The hydraulic conductivity
ranged from 1.50x10! to 5.89x10? ft/d. Values of
specific yield ranged from 2.50x107! to 3.00x107!,

At the Scottsbluff Airport site, the saturated
thickness was about 52 ft. Aquifer-test results indicate
that the hydraulic-conductivity values were fairly
consistent with respect to depth. Here, values of
hydraulic conductivity ranged from 1.9610? to
4.38x10" ft/d. Values of specific yield range/ from
1.41x107 to 2.73x1071.

SELECTED REFERENCES

Darton, N.H., 1903, Preliminary report on the geology and
water resources of Nebraska west of the one hundred
and third meridian: U.S. Geological Survey Profes-
sional Paper 17, 69 p.

Dawson, D.J., and Istok, J.D., 1991, Aquifer testing—
Design and analysis of pumping and slug tests:
Chelsea, Mich., Lewis Publishers, 344 p.

Domenico, P.A., and Schwartz, F.W., 1990, Physical and
chemical hydrogeology: New York, Wiley end Sons,
824 p.

Driscoll, F.G., 1986, Groundwater and wells (2d ed.):

St. Paul, Minn., Johnson Division, 1089 p.

Fenneman, N.M., 1946, Physical divisions of the United
States: U.S. Geological Survey map, scale 1:7,000,000,
1 sheet.

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: Engle-
wood Cliffs, N.J., Prentice-Hall, Inc., 604 p.

Hantush, M.S., 1961, Drawdown around a partially pene-
trating well: Proceedings of the American Society of
Civil Engineers, Journal of Hydraulics Division, v. 87,
p. 83-98.

Kruseman, G.P., and de Ridder, N.A., 1990, Analysis and
evaluation of pumping test data (2d ed.): Wageningen,
The Netherlands, International Institute for Land
Reclamation and Improvement Publication 47, 377 p.

Lohman, S.W., 1972, Ground-water hydraulics: U.S.
Geological Survey Professional Paper 708, 70 p., 9 pl.

SUMMARY AND CONCLUSIONS

23


CONTENTS

Abstract..
Introduction.
Purpose and Scope
Acknowledgments
Description of Study Area ..
Climate and Land Use
Hydrogeologic Settings
Design of Aquifer Tests and Methods of Analysis
Aquifer-Test Results
Bayard Site.
Gering Site .
Lyman Site ..
Minatare Site.
Mitchell Sit
Morrill Site.....
Scottsbluff Airport Site
Summary and Conclusions ...
Selected References...

FIGURES

. Map showing aquifer-test locations in the North Platte Natural Resources District, western Nebraska
. Diagrammatic cross section and plan view map showing the Bayard site.
. Log-log plot of drawdown versus time for the Bayard site...
. Diagrammatic cross section and plan view map showing the Gering site .
. Log-log plot of drawdown versus time for the Gering site
. Diagrammatic cross section and plan view map showing the Lyman site ..
. Log-log plot of drawdown versus time for the Lyman site...
. Diagrammatic cross section and plan view map showing the Minatare site.
. Log-log plot of drawdown versus time for the Minatare site...
. Diagrammatic cross section and plan view map showing the Mitchell sit
. Log-log plot of drawdown versus time for the Mitchell site......
. Diagrammatic cross section and plan view map showing the Morrill site.
. Log-log plot of drawdown versus time for the Morrill site...
. Diagrammatic cross section and plan view map showing the Scottsbluff Airport site
. Log-lot plot of drawdown versus time for the Scottsbluff Airport site

PE Swern auAwHe

i:

AEG

TABLES

1. Location of and construction information about pumping and observation wells used in the
aquifer tests, North Platte Natural Resources District, western Nebraska.....
2. Results of aquifer tests in the North Platte Natural Resources District, western Nebraska, 1997-98 .

CONTENTS iii


WATER-LEVEL DISPLACEMENT, IN FEET
3
T

22M
Parameters
wk Ts 7aT0sqaretet
$ = 0.00522
Sy= 025
| B = 006
103 FY TT PT
10° 107 107 10° 10" 10? 190% 10°
ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES
10' " mr T
.
& >
s —
5 Wr as 4
=
S
s
a ook 4
2 10
Ss °73M3
>
Gg Parameters
& Sloe
= 8 = 006
10°C tad cul cel a cal Ll
wo’ 107 10% 10° 10' 107 40° 10°
ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES
10!

WATER-LEVEL DISPLACEMENT, IN FEET
3
T

10%

10°

Figure 3. Log-log plot of drawdown versus time for the Bayard site.

10 Hydrologic Characteristics of Selected Alluvial Aquifers in the North Platte Natural Resources District, Western Nebraska

ELAPSED TIME FROM BEGINNING OF TEST,
IN MINUTES PER SQUARE FOOT

WATER-LEVEL DISPLACEMENT, IN FEET

WATER-LEVEL DISPLACEMENT, IN FEET

10 - aaadid addi Ai
roo b w 4
10°F "q
+ 2BM-2
Porometers
wrk T= 1600 sauneteet |
'S = 0.00355
Sy=025
| B = 006
10% ul cht ul A ul ul I
10° 10% 107 10° 10’ 10? 10% 10
ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES.
10' mT T mT sy "
LS
10° F q
10° E / q
oT
| Parameters
ek | T= 1apsuaefeet |
| § =omn3
Sy = 030
B =02
1o* 10% 10% 10° 10' 10% 10° 10

ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES


WATER-LEVEL DISPLACEMENT, IN FEET

WATER-LEVEL DISPLACEMENT, IN FEET

10° —" q
oe
o/
} eave
10" / Parameters q
/ T= S150 quae et
j § = 0.0083
/ Sy=023
/ B =-04
|
102 L n nl u n
10% 10" = 10°40’ 1074910
ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES
10" m T T T
ek von |

af 14
10" E / Paremetors

T = 51,100 square feet
pei day

n nl n

2 ml fl

ioe i) 10 1o' 10" ~— 108

ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES

10°

WATER-LEVEL DISPLACEMENT, IN FEET

WATER-LEVEL DISPLACEMENT, IN FEET

T T T
10° L Pal 4
we
a
ft E + M2
10'E oe |
+/ T= 00 sue feet
/ S= ze
/ Sy = 0.26
/ B =008
|
192 n ! L n
10" 10° 10" 10° 10° = 10
ELAPSED TIME FROM BEGINNING OF
TEST, IN MINUTES.
10! T "T "T T T
10°F LE q
& :
4 ff ar
1 row of + M2
10" a / ey aM 4
[/ Parameters
WA T= 60 square fet
vA $a
| /[" Kakr= 095
10° 7L sa J ss {a sul 1
w® 1° 10% =10% = 10% 107 10° 40"
ELAPSED TIME FROM BEGINNING OF TEST,
IN MINUTES PER SQUARE FOOT

Figure 5. Log-iog piot of drawdown versus time for the Gering site.

12 Hydrologic Characteristics of Selected Alluvial Aquifers in the North Platte Natural Resources District, Western Nebraska


U.S. DEPARTMENT OF THE INTERIOR
GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY
Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does
not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchased
from:

District Chief U.S. Geological Survey

U.S. Geological Survey Information Services

406 Federal Building Box 25286

100 Centennial Mall North Federal Center

Lincoln, NE 68508 Denver, CO 80225


Scottsbluff Airport Site

At the Scottsbluff Airport site, all wells used in
the aquifer test were developed in the alluvial aquifer
of the North Platte River. Depth to water in the
pumping well at the start of the aquifer test was 27 ft.
The pumping well at the Scottsbluff Airport site is
screened in the bottom part of the aquifer (table 2,
fig. 14) near the top of the Brule Formation, 80 ft
below land surface. The saturated thickness of the
aquifer at this site is about 52 ft. The North Platte

ian

T i t T
fees ee
52 fect [|
=I 36 feet
4 50 fect CO

Bedrock
Not to scale

River, which is about 4 mi south of the site, is the only
substantial surface-water feature in the area and is too
far from the site to affect the test results.

Aquifer-test results indicate that the hydraulic-
conductivity values of the aquifer are fairly consistent
with respect to depth (table 2). Values of hydraulic
conductivity ranged from 1.96x 10? to 4.38x10? f/d.
Values of specific yield ranged from 141x107 to
2.73x10-!. The composite analysis indicates a
hydraulic conductivity value of 2.54x10? f/d and a
specific-yield value of 2.64x10 | (table 2, fig. 15).

22N S4W 21 CABA
Scotts Bluff County
Scottsbluff, Nebraska

1sm-3 [}

Figure 14. Diagrammatic cross section and plan view map showing the Scottsbluff Airport site.

Not to scale
EXPLANATION
[BH] Observation well — F2=} Screened interval
@ Pumping well (Z)_ Bedrock
—_ Land surface [Ds Conerete pad
Z_ Water level
AQUIFER-TEST RESULTS

2


Hydrologic Characteristics of Selected
Alluvial Aquifers in the North Platte
Natural Resources District,

Western Nebraska

By G.V. Steele, J.C. Cannia, and K.G. Scripter

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4241

Prepared in cooperation with the
NORTH PLATTE NATURAL RESOURCES DISTRICT

Lincoln, Nebraska
2002


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Basins, Colorado-Kansas-Nebraska-Wyoming—
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Moench, A.F., 1993, Computation of type curves for flow to
partially penetrating wells in water-table aquifers:
Ground Water, v. 31, no. 6, p. 966-971.

1994, Specific yield as determined by type-curve
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no. 6, p. 949-957.

National Oceanic and Atmospheric Administration, 1999,
Climatological data annual summary, Nebraska 1998:
National Oceanic and Atmospheric Administration,

v. 103, no. 13, 31 p.

Nebraska Department of Water Resources, 1998, 1998
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Department of Water Resources, 218 p.

Nebraska Department of Natural Resources, 1999,
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North Platte NRD: State of Nebraska, Nebraska
Natural Resources Commission (accessed September
13, 1999), URL: http://www.nre.state.ne.us/
databank/nrd/noplatte.html

Neuman, S.P., 1975, Analysis of pumping test data from
anisotropic unconfined aquifers considering delayed
gravity response: Water Resources Research, v. 11,
no. 2, p. 329-342.

Smith, F.A., and Souders, V.L., 1975, Groundwater geology
of Banner County, Nebraska: Lincoln, Nebr., Univer-
sity of Nebraska-Lincoln, Conservation and Survey
Division, Nebraska Water Survey Paper 3, 96 p.

Souders, V.L., 1986, Geological sections, groundwater
maps, and logs of test holes, Morrill County, Nebraska:
Lincoln, Nebr., University of Nebraska-Lincoln,
Conservation and Survey Division Open File Report,
90 p.

Stallman, R.W., 1965, Effects of water-table conditions on
water-level changes near pumping wells: Water
Resources Research, v. 1, no. 2, p. 295-312.

Steele, G.V., and Cannia, J.C., 1997, Reconnaissance of
surface-water quality in the North Platte Natural
Resources District, western Nebraska, 1993: U.S.
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Report 96-4316, 21 p.

Steele, G.V., Cannia, J.C., and Stanton, J.S., 1998, Geohy-
drology and water quality of the North Platte alluvial
aquifer, Garden County, western Nebraska, 1993-94,
U.S. Geological Survey Water-Resources Investiga-
tions Report 98-4033, 75 p.

Swinehart, J.B., Souders, V.L., DeGraw, H.M., and
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western Nebraska, in Proceedings of the Rocky Moun-
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Verstraeten, I.M.. Sibray, S.S., Cannia, J.C., and Tannet,
D.Q., 1995, Reconnaissance of ground-water quality in
the North Platte Natural Resources District, western
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Nebraska, 1995-99: U.S. Geological Survey Water-
Resources Investigations Report 01-4070, 56 p.

Wenzel, L.K., Cady, R.C., and Waite, H.A., 1946, Geology
and ground-water resources of Scotts Bluff County,
Nebraska: U.S. Geological Survey Water-Supply Paper
943, 150 p.

24 Hydrologic Characteristics of Selected Alluvial Aquifers in the North Platte Natural Resources District, Western Nebraska

4 U.S. GOVERNMENT PRINTING OFFICE: 2002 — 773-096 / 47095 Region No. 8


AQUIFER-TEST RESULTS

Hydraulic characteristics varied substantially in
the alluvial aquifers of the western part of the
NPNRD. Hydraulic conductivities determined from
analysis of the aquifer tests ranged from 1.10x10! to
8.40x 10 fi/d (table 2). Values of specific yield ranged
from 1.00x107* to 3.20x107!. The response of the
aquifer to the pumping stress was almost instantaneous
in most observation wells. However, response of some
water levels in some observation wells was delayed
slightly upon startup of the aquifer test.

Bayard Site

At the Bayard site, all wells used in the aquifer
test were developed in the alluvial aquifer of the North
Platte River. Depth to water in the pumping well at the
start of the aquifer test was 6.20 ft below land surface.

Pumping well

23M.2 23M-3 23M

oo

50 feet

Bedrock
Not to scale

The pumping well at the Bayard site is screened
through the bottom part of the aquifer (table 2, fig. 2)
just above the top of the underlying Brule Formation,
133 ft below land surface. The saturated thickness of
the aquifer at this site is about 126 ft.

Analysis of data collected during the aquifer
test indicates the hydraulic-conductivity value
of the aquifer is fairly consistent with depth.
Hydraulic-conductivity values ranged from 1.10x10!
to 1.33x10" ft/d (table 2). Values of specific yield
ranged from 2.46x107! to 3.00x107!. Pretest water-
level data were not available for this site. Water-level
changes at all sites (except Gering) were minimal.
Therefore, the pretest water-level change at this
site was assumed to be negligible. The composite
analysis indicates a hydraulic conductivity value of
6.70x10! fi/d and a specific yield of 3.00x10~!
(table 2, fig. 3).

21N 52W 35 BCAB
Morrill County
Bayard, Nebraska

3rd Street

Municipal ®

a house
oN

|
|
}

23M-2, 3.4 [a]
Not to scale
EXPLANATION
[LE] Observation well 5 _ Screened interval
@ __ Pumping well (Z] Bedrock
— Land surface [1 Concrete pad

Water level

Figure 2. Diagrammatic cross section and plan view map showing the Bayard site.

8 Hydrologic Characteristics of Selected Alluvial Aquifers in the North Platte Natural Resources District, Western Nebraskz


Gering Site

At the Gering site, all wells used in the aquifer
test were developed in the North Platte River alluvial
aquifer. Depth to water in the pumping well at the start
of the aquifer test was 9.18 ft below land surface. The
pumping well at the Gering site is screened in the
bottom part of the aquifer (table 2, fig. 4) near the top
of the Brule Formation, 81 ft below land surface. The
saturated thickness for this site is about 72 ft.

The North Platte River lies about 160 ft north of
the pumping well. Data collected during the test
(fig. 5) did not show an appreciable deviation from the
predicted drawdown curve; therefore, it was assumed
that the North Platte River did not have an effect on the

Pumping well

=

14-1 14M2

t t
Sonne v.
40 feet
131 feet
T2feet
Bedrock’
Peng Not to scale

test. Wells 14M-—1 and 14M-2 are about 160 ft south
of the North Platte River. Well 14M-—4 is about 285 ft
south of the North Platte River and about 131 ft south
of the pumping well.

The hydraulic-conductivity value for observa-
tion well 14M-—4 (table 2), which lies farthest
from the North Platte River, was smaller than the other
two observation wells (71 ft/d; table 2). Values of
hydraulic conductivity at this site ranged from
7.10x10! to 8.40x102 fi/d (table 2). Specific-yield
values ranged from 5.00x1 07 to 2.55x101. The
composite analysis indicates a hydraulic-conductivity
value of 8.40x10? ft/d and a specific-yield value of
8.40x10- (table 2, fig. 5).

22N 55W 26 DABD
Scotts Bluff County
Gering, Nebraska

\
14M-1 -40 feet from pumping well
14M-2 -39 feet from pumping well
14M-4 -131 feet from pumping well

Bum

Not to scale
EXPLANATION
[i] Observation well [=] Screened interval
© Pumping well (ZZ) Bedrock
— Land surface Concrete pad
= Water level

Figure 4. Diagrammatic cross section and plan view map showing the Gering site.

AQUIFER-TEST RESULTS W