U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2014–5081

Prepared in cooperation with Fort Irwin National Training Center

Analysis of Potential Water-Supply Management Options, 

2010–60, and Documentation of Revisions to the Model of 

the Irwin Basin Aquifer System, Fort Irwin National Training 

Center, California
Cover. Aerial view of Fort Irwin Military Reservation, Fort Irwin, California. Photo taken by Bobak Ha’Eri, on July 27, 2009.
Analysis of Potential Water-Supply 

Management Options, 2010–60, and 

Documentation of Revisions to the Model of 

the Irwin Basin Aquifer System, Fort Irwin 

National Training Center, California

By Lois M. Voronin, Jill N. Densmore, and Peter Martin

Prepared in cooperation with Fort Irwin National Training Center

Scientific Investigations Report 2014–5081

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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Suggested citation:

Voronin, L.M., Densmore, J.N., and Martin, Peter, 2014, Analysis of potential water-supply management 

options, 2010–60, and documentation of revisions to the model of the Irwin Basin Aquifer System, Fort Irwin 

National Training Center, California: U.S. Geological Survey Scientific Investigations Report 2014–5081, 34 p., 

http://dx.doi.org/10.3133/sir20145081.

ISSN 2328-0328 (online) 
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................1

Location and Description of Study Area...........................................................................................2

Hydrogeologic Setting .........................................................................................................................2

Simulation of Groundwater Flow.................................................................................................................9

Model Design.........................................................................................................................................9

Model Calibration................................................................................................................................12

Groundwater Withdrawals................................................................................................................14

Groundwater Recharge .....................................................................................................................14

Simulated Effects of Future Withdrawals and Artificial Recharge .....................................................20

Description of Model Scenarios ......................................................................................................21

Scenario 1 ...................................................................................................................................21

Scenario 2 ...................................................................................................................................22

Scenario 3 ...................................................................................................................................24

Scenario 4 ...................................................................................................................................24

Results of Simulations........................................................................................................................24

Scenario 1 ...................................................................................................................................24

Scenario 2 ...................................................................................................................................31

Scenario 3 ...................................................................................................................................31

Scenario 4 ...................................................................................................................................31

Model Limitations................................................................................................................................31

Summary and Conclusions.........................................................................................................................32

References Cited..........................................................................................................................................33
iv

Figures

1. Map showing location of study area at Fort Irwin National 

Training Center, California...........................................................................................................3

2. Generalized map of the Irwin Basin, Fort Irwin National 

Training Center, California...........................................................................................................4

3. Figures showing generalized geology of the Irwin Basin, Fort Irwin 

National Training Center, California...........................................................................................5

4. Figure showing altitude of the basement complex and boundaries 

of groundwater model layers for the Irwin Basin, Fort Irwin National 

Training Center, California...........................................................................................................8

5. Cross-sectional view of model layers, hydraulic conductivities, and boundary

conditions of the Irwin Basin, Fort Irwin National Training Center, California.................10

6. Map showing simulated 1994 hydraulic heads, layer 1, Irwin Basin, Fort Irwin

National Training Center, California.........................................................................................13

7. Hydrographs of measured water levels and simulated hydraulic 

heads in 11 observation wells, Irwin Basin, Fort Irwin National 

Training Center, California.........................................................................................................15

8. Graph showing annual groundwater recharge and withdrawals 

from Bicycle, Irwin, and Langford Basins, Fort Irwin National Training Center, 

California, 1941–2010..................................................................................................................16

9. Hydrographs of measured water levels and simulated hydraulic heads in six

observation wells near the wastewater-treatment facility, Irwin Basin, Fort Irwin

National Training Center, California.........................................................................................20

10. Graph showing average 2001 to 2010 total monthly groundwater withdrawal

distribution for wells in the Bicycle, Irwin, and Langford Basins that were used to

provide water to Fort Irwin National Training Center, California........................................21

11. Map showing simulated difference in hydraulic head from October 2010 

conditions to October 2060 conditions, scenario 1, layer 1, Irwin Basin, 

Fort Irwin National Training Center, California.......................................................................23

12. Simulated difference in hydraulic head from October 2010 conditions to 

October 2060 conditions, scenario 2, layer 1, Irwin Basin, Fort Irwin 

National Training Center, California.........................................................................................25

13. Map showing simulated difference in hydraulic head from October 2010 

conditions to October 2060 conditions, scenario 3, layer 1, Irwin Basin, 

Fort Irwin National Training Center, California.......................................................................26

14. Map showing simulated difference in hydraulic head from October 2010 

conditions to October 2060 conditions, scenario 4, layer 1, Irwin Basin, 

Fort Irwin National Training Center, California.......................................................................27

15. Hydrographs of simulated hydraulic heads at 14 wells for four scenarios, 

Irwin Basin, Fort Irwin National Training Center, California................................................28
v

Tables

1. Simulated volumetric budget, for 1994 conditions (stress period 54), from the 

A) original, MODFLOW-88 model and B) 2010 model, Irwin Basin, Fort Irwin

National Training Center, California.........................................................................................14

2. Simulated annual 1941–2010 groundwater recharge and withdrawals, 

Irwin Basin, Fort Irwin National Training Center, California................................................17

3. Summary of 2001–10 groundwater withdrawals, and estimates of

evapotranspiration, evaporation, and recharge used in the 2010 model and

model scenarios, Irwin Basin, Fort Irwin National Training Center, California ................18

4. Summary of simulated monthly groundwater withdrawals from wells in the

Irwin Basin used in the four scenarios, Irwin Basin, Fort Irwin National Training

Center, California ........................................................................................................................22

5. Simulated hydraulic head at 14 wells for four model scenarios, Irwin Basin,

Fort Irwin National Training Center, California.......................................................................30

6. Summary of simulated groundwater discharge to drains, Irwin Basin, 

Fort Irwin National Training Center, California.......................................................................31
vi

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

acre-foot (acre-ft) 1,233 cubic meter (m3)

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3) 

Flow rate

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m3/yr)

acre-foot per year (acre-ft/yr) 0.001233 cubic hectometer per year (hm3/yr)

foot per day (ft/d) 0.3048 meter per day (m/d)

cubic foot per day (ft3/d) 0.02832 cubic meter per day (m3/d)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

acre-feet per month (acre-ft/mo) 0.000469 cubic meters per second (m3/s)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to North American Vertical Datum of 1988 

(NAVD 88).

Altitude, as used in this report, refers to distance above the vertical datum.
vii

Abbreviations

ASL above sea level

CIMIS California Irrigation Management Information System

GMG Geometric Multigrid Solver

MODFLOW-88 USGS Modular Three-Dimensional Finite-Difference Groundwater Flow-Model

NAVD 88 North American Vertical Datum of 1988

NTC Fort Irwin National Training Center

USGS U.S. Geological Survey
viii

Acknowledgments 

The authors thank the following personnel at Fort Irwin NTC: Justine Dishart, Muhammed Bari, 

and Chris Woodruff for providing groundwater withdrawal data.
Analysis of Potential Water-Supply Management Options, 

2010–60, and Documentation of Revisions to the Model 

of the Irwin Basin Aquifer System, Fort Irwin National 

Training Center, California

By Lois M. Voronin, Jill N. Densmore, and Peter Martin

Abstract 

 The Fort Irwin National Training Center is 

considering several alternatives to manage their limited 

water-supply sources in the Irwin Basin. An existing threedimensional, finite-difference groundwater-flow model—

the U.S. Geological Survey’s MODFLOW—of the aquifer 

system in the basin was updated and the initial input dataset 

was supplemented with groundwater withdrawal data for the 

period 2000–10. The updated model was then used to simulate 

four combinations, or scenarios, of groundwater withdrawal 

and recharge over the next 50 years (January 2011 through 

December 2060). The scenarios included combinations of continuing withdrawals from currently active production wells, 

supplementing any increases in demand with withdrawals 

from an inactive production well, reducing withdrawal 

amounts and rates, and reducing the discharge of treated 

wastewater to infiltration ponds that provide a recharge source 

to the underlying aquifer. Results of the simulations indicated 

that, depending on the scenario implemented, groundwater 

levels would rise (over the next 50 years) from 40 feet to as 

much as 65 feet in the northwestern part of the Irwin Basin, 

and from 5 feet to 10 feet in the southeastern part. 

Introduction

Fort Irwin National Training Center (Fort Irwin NTC) 

in the Mojave Desert of California has been used as a military training facility almost continuously since August 1940. 

The training center currently (2012) obtains its potable 

water supply by pumping from wells in the Irwin, Bicycle, 

and Langford Basins. Groundwater development began in 

the Irwin Basin in 1941. From 1941 to 1996, most of the 

groundwater pumpage was from the Irwin Basin which 

resulted in water-level declines of about 30 ft in the basin 

during this period. Pumping from the Bicycle and Langford 

Basins began in 1967 and 1992, respectively, and pumping 

from these basins has resulted in a decrease in the groundwater 

demand from the Irwin Basin. Since 1991, the combined 

pumping from the adjacent Bicycle and the Langford Basins 

has exceeded that in the Irwin Basin. Since the 1990’s, 

reduced pumping and artificial recharge of wastewater and 

irrigation in the Irwin Basin has caused water levels to stabilize or rise throughout the basin. Although water levels are 

currently rising in the Irwin Basin, treated wastewater that percolates through evaporate deposits underlying the wastewatertreatment facility and infiltration/holding ponds has resulted 

in high concentrations of dissolved solids in groundwater that 

is migrating toward the pumping-caused depression in water 

levels near the center of the basin (Densmore and Londquist, 

1997). Water-quality concerns have led to the abandonment or 

destruction of several production wells in the Irwin Basin. 

To effectively manage the water resources and plan for 

future water needs at the Fort Irwin NTC, it is important to 

have a complete understanding of the hydrogeologic and 

geochemical framework of the Irwin, Langford, and Bicycle 

Basins. To provide the information needed to develop that 

understanding, the U.S. Geological Survey (USGS), in cooperation with the Fort Irwin NTC, conducted a series of studies 

to evaluate the hydrogeologic system and conditions at the 

training center. This report describes the results of one of those 

studies. 

Purpose and Scope

This report describes the results of the simulation of 

groundwater flow in the aquifer system in the Irwin Basin 

at the Fort Irwin NTC, California, using an existing groundwater-flow model developed by Densmore (2003) that was 

updated to run with MODFLOW 2005, the most current version of the USGS three-dimensional, finite-difference groundwater model, and to use groundwater withdrawal data for the 

period 2000–10. The original model simulated the hydrologic 

conditions of the Irwin Basin for the period 1941–99. This 

report describes the hydrogeology of the Irwin Basin, the 
2 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

updates made to the existing model, and the results of the 

simulation of four scenarios of hypothetical combinations of 

groundwater recharge and withdrawal over the next 50 years. 

The updated groundwater-flow model is a useful tool to help 

estimate the long-term availability of groundwater from the 

basin by evaluating differences in groundwater-level altitudes (or water levels) among scenarios simulating different 

withdrawal and recharge rates. The updated model was used to 

evaluate the potential spatial effects on groundwater levels as a 

consequence of 1) continued withdrawals at the 2010 average 

rate of pumping, 2) supplementing water-supply needs with 

withdrawals from an inactive production well, 3) a reduction 

in groundwater recharge from treated wastewater.

Location and Description of Study Area

The Fort Irwin NTC is about 130 miles (mi) northeast 

of Los Angeles and 35 mi northeast of Barstow in southern 

California (fig. 1). The training center covers about 

970 mi2 (square miles) of the northern part of the Mojave 

Desert and encompasses several ground-water basins. Wells 

in the Irwin, Bicycle, and Langford Basins currently supply 

water to the base (fig. 1). 

The Irwin Basin has a fairly flat floor bordered to the east 

by Beacon Hill, to the north-northwest by Northwest Ridge, 

to the west by Southwest Ridge, and to the south by low-lying 

hills that separate the Irwin Basin from the Langford Basin 

(fig. 2). The surface-water drainage area of the basin is about 

30 mi2 and the floor of the basin is about 7 mi2. There are no 

perennial streams in the basin but several dry washes convey surface flow during, or immediately after, large storms. 

Surface-water flow out of the basin, when it occurs, is to 

the southeast into the Langford Basin, through an unnamed 

ephemeral wash near Garlic Spring (fig. 2).

The basin climate is typical of the Mojave Desert, 

with scant precipitation, hot summers, and cool winters. 

There are no official weather records for the Irwin Basin 

itself, but at Goldstone, about 15 mi northwest of the basin 

(fig. 1), 1973– 2006 average annual precipitation is about 

5.8 in. (inches), most of which falls during the winter, with a 

few isolated thunderstorms during the summer. At Barstow, 

35 mi southwest of the basin, 1997–2011 average annual precipitation is about 5.1 in. Between 1973 and 2011, the annual 

precipitation at Barstow ranged from about 2.0 in. in 1975 to 

about 13.2 in. in 2005. Between 1940 and 2013, temperatures 

at Barstow ranged from 3 °F to 116 °F and averaged about 

64 °F. The 1997–2011 average annual potential evaporation at 

Barstow is about 72 in., (National Oceanic and Atmospheric 

Administration, 1994; EarthInfo, Inc., 1995, 2000; David 

Inouye, California Department of Water Resources, written 

commun., 1996; California Irrigation Management Information System, 2013).

Hydrogeologic Setting

The Irwin Basin is filled with as much as 950 ft of 

unconsolidated deposits that consist of younger alluvium 

of Quaternary age and older alluvium of late Tertiary to 

Quaternary age (Densmore, 2003, fig. 3). The deposits are 

unconsolidated at land surface and become partly consolidated 

with depth. The unconsolidated deposits are the only waterbearing material in the basin from which appreciable amounts 

of groundwater can be obtained. These deposits are underlain 

by a basement complex of volcanic rocks of Tertiary age and 

igneous and metamorphic rocks of pre-Tertiary age, which 

convey insignificant amounts of groundwater except in areas 

where they are jointed, weathered or fractured.

The older alluvium (fig. 3, QTa and Tl) consists of sand, 

gravel, and clay derived predominantly from granitic material, 

except in the northern part of the basin, where volcanic material dominates. Where the older alluvium consists predominantly of sand and gravel, it yields moderate amounts of water 

to wells. In the southeastern part of the basin, however, the 

older alluvium consists almost entirely of low-permeability 

lacustrine deposits (fig. 3, B-B’, Tl) of silt and clay. These 

low-permeability deposits extend from well 14N/3E-33N1 

near the center of the basin to well 13N/3E-10E1-3 in the 

unnamed wash that leads to Garlic Spring, and are bounded by 

the Garlic Spring Fault on the northeast and an unnamed fault 

on the southwest. 

The younger alluvium (fig. 3, Qa) consists primarily 

of loose coarse sand and gravel with small amounts of clay. 

Some thin, discontinuous clay lenses overlie the lacustrine 

deposits within the older alluvium in the area beneath the former sprinkler-pivot field in the southeastern part of the basin 

(fig. 2) and may result in a perched water table in this area. 

Most of the younger alluvium lies above the water table; however, in areas where it is saturated, primarily in the center of 

the basin, it yields large quantities of water to wells (as much 

as 1,000 gal/min). Wellbore-flow tests of selected base supply 

wells indicate that most of the water pumped comes from the 

younger alluvium (Densmore and Londquist, 1997).

The aquifer system in the Irwin Basin consists of an 

upper aquifer and a lower aquifer. The upper aquifer is unconfined and is contained within the saturated part of the younger 

alluvium. This aquifer reaches a maximum thickness of 

about 200 ft in the west-central part of the basin (fig. 3). The 

lower aquifer is composed of older alluvium and is confined 

throughout most of the basin. This aquifer reaches a maximum thickness of about 600 ft in the central part of the basin 

(fig. 3). Although some water is contained in the underlying 

basement complex, the effective base of the groundwater 

system is at the top of basement complex. The altitude of the 

surface of the basement complex in the Irwin Basin is shown 

in figure 4.
Introduction 3

Figure 1. Location of study area at Fort Irwin National Training Center, California

IRWIN

BASIN

BICYCLE

BASIN

LANGFORD

BASIN

EXPLANATION

Drainage basin

Groundwater basin

 (approximate)

Boundary—

15

15

40

58

247

395

Los

Angeles

MAP

AREA

Mojave Desert

Base from U.S. Geological Survey digital elevation data, 1:250,000, 1987, and digital data, 1:100,000, 

1981–89; Universal Transverse Mercator Projection, Zone 11. Shaded relief base from 1:250,000-scale

Digital Elevation Model; simulated sun illumination from northwest at 30 degrees above horizon.

F.1

0 10 20

0 10 20

MILES

KILOMETERS

STUDY

AREA

BARSTOW

117°30’ 117° 116°30’

35°

35°30’

MOJAVE DESERT

Irwin Rd

FORT IRWIN

NATIONAL TRAINING

CENTER

CHINA LAKE

NAVAL WEAPONS

CENTER

CHINA LAKE

NAVAL

 WEAPONS

CENTER

GARLOCK

 FAULT

ZONE 

CUTTLEBACK LAKE

AIR FORCE

 RANGE

EDWARDS

AIR FORCE

BASE

MARINE CORPS

 LOGISTICS BASE

Goldstone

(See fig.2)
4 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

LANGFORD

BASIN

IRWIN

BASIN

BICYCLE

BASIN

Beacon

Hill

B

A'

A

A"

B' GARLIC SPRING FAULT

Geology by J.C. Yount, E.R. Schermer, T.J. Felger, D.M. Miller, and K.A. Stephens, 1994

Aquifer system boundary modified from Wilson F. So and Assoc., 1989

?

BICYCLE FAULT

1

32K1

33N1

6

5

8

9

7

3

4

1

2

10

11

12

12

3

10

5

4

7

8

9

2

Barstow Rd

Irwin Rd

N. Loop Rd

S. Loop Rd

Langford Lake Rd

5th St

4K2-4

4Q2-6

33R1

4C1-3

10E1-3

4B1-3

32B1-3

Former sprinkler

 -pivot field

Duck ponds

Golf course and

 percolation pond

Soccer field

Sanitary-landfill Baseball field

 facility

Old biological-

 evaporation ponds

Wastewater-treat- Army ball field

 ment facility pond Base housing

New base

 housing

New athletic

 fields

Potential sources of groundwater degradation—

34M2

31

35°17’

35°13’

116°43’ 116°39'

6

36

T 14 N

T 13 N

R 2 E R 3 E

0

0 1 2 MILES

1 2 KILOMETERS

EXPLANATION

SOUTHWEST

RIDGE

sac13-0507_Figure 02

6

1

Unconsolidated deposits—

Correlation and description of map units

QuaternaryTertiary

Consolidated rocks—

Well and number—

Installed by USGS

Production Fault—Dashed where approximately 

 located; queried where uncertain;

 dotted where concealed

Volcanic 

Igneous and metamorphic

Alluvium Playa

?

Line of geologic

 section—Sections

 shown on fig. 3

Boundary of aquifer

 system (approximate)

Test 9B1

A A"

NORTHWEST RIDGE

Garlic

Spring

{

{

{

Tertiary

pre-Tertiary

10D1

4D1-3

33N1

32N1-3

33E2-3

33A1

32P2-6

32K3-6 ?

33B1

32F1

32J1

32K1

33Q1

5G1

6P1

33F1

Drainage basin

 boundary

Figure 2. Generalized map of the Irwin Basin, Fort Irwin National Training Center, California.
Introduction 5

14N/3E-32P2-6

14N/3E-32K1

14N/3E-32K3-6 - 

14N/3E-32J1

14N/3E-33E2-3

14N/3E-33F1

14N/3E-33A1

14N/3E-32N1-3 (Projected)

13N/3E-6P1

SOUTHWEST NORTHEAST

Qa ? Qa

QTa

QTa

QTa

2,600

2,700

FEET

2,500

2,400

2,300

2,200

2,100

2,000

1,900

1,800

1,700

1,600

1,500

A A'

Soccer

 field Ball

field

Section B-B'

—(Projected)

?

?

5th Street

S.Loop Road

Barstow Road

Old

biologicalevaporation

ponds

GARLIC SPRING FAULT

14N/3E-33B1

—

Bend in section

(Projected)

Bend in section

Bend in section

Bend in section

Bend in section

?

?

?

?

?

?

sac13-0507_Figure 03a

A

?

QTa

Water table (Measured

 during 1994)

? Contact—Queried where uncertain

Fault—Queried where uncertain; arrows

 indicate direction of apparent movement 

Well and numberPerforated interval

Bottom of borehole

EXPLANATION

14N/3E-33E2-3

}

Qa

Consolidated rock

Younger alluvium

Older alluvium

Weathered and fractured

 consolidated rock 

Quaternary

QuaternaryTertiary

pre-Tertiary

(Perforated interval for wells

13N/3E-6P1 and 14N/3E-33B1

 is not known)

0 0.5

0 0.5 1 MILE

1 KILOMETER

Vertical scale greatly exaggerated

Horizontal scale 1.5X

Figure 3. Generalized geology of the Irwin Basin, Fort Irwin National Training Center, California (Densmore, 2003). [Section locations 

shown in fig. 2]
6 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

WEST EAST

2,500

FEET

2,400

2,700

2,800

2,600

2,300

2,200

2,100

2,000

1,900

1,800

A A''

?

?

?

Vertical scale greatly exaggerated

13N/3E-4C1-3 -Section B-B'

13N/3E-5G1

14N/3E-33Q1

14N/3E-33R1

13N/3E-4B1-3

14N/3E-34M2

13N/3E-6P1

?

Langford Lake Road

5th Street

S.Loop Road

GARLIC SPRING FAULT

13N/3E-4B1-3

Qa

QTa

Qa

QTa

Wastewatertreatment

facility

(projected)

?

?

Water table (Measured

 during 1994)

? Contact—Queried where uncertain

Fault—Queried where uncertain; arrows

 indicate direction of apparent movement 

Well and numberPerforated interval

Bottom of borehole

EXPLANATION

}

Qa

Consolidated rock

Younger alluvium

Older alluvium/lacustrine deposits

Weathered and fractured

 consolidated rock 

Quaternary {

{

{ pre-Tertiary

Bend in section

Bend in section

(projected)

Bend in section

Bend in section

Quaternary- QTa

Tertiary

 (Perforated interval for wells 

 13N/3E-6P1, 5G1, and 

 14N/3E-33R1 is not known)

Horizontal scale 1.5X

Tl

Tl

?

?

?

?

0 0.5

0 0.5 1 MILE

1 KILOMETER

sac13-0507_Figure 03b

B

Figure 3. —Continued
Introduction 7

?

? ?

?

14N/3E-33N1

14N/3E-32B1-3

14N/3E-32K3-6

14N/3E-32F1

13N/3E-4D1-3

13N/3E-4C1-3

13N/3E-4Q2-6

13N/3E-4K2-4

13N/3E-10D1

13N/3E-10E1-3 

NORTH SOUTH

2,600

2,700

2,900

2,800

FEET

2,500

2,400

2,300

2,200

2,100

2,000

1,900

1,800

Qa

Qa

Qa

QTa

QTa

B B'

Former

sprinkler-

 pivot field

Duck

ponds

13N/3E-10E1-3 

Section A-A"

Section A-A'

Lysimeter and

 number

Vertical scale greatly exaggerated

(Projected)

5th Street

5th Street

}

13N/3E-4Q2-6

(Projected)

Bend in section

Bend in section

Bend in section

Bend in section

Bend in section

?

Water table (Measured

 during 1994)

? Contact—Queried where 

 uncertain

Fault—Queried where 

 uncertain; arrows 

 indicate direction of 

 apparent movement 

Well and numberPerforated

 interval

Bottom of 

 borehole

EXPLANATION

Qa

Consolidated rock

Younger alluvium

Older alluvium/

 lacustrine deposits

Weathered and 

 fractured consol-

 idated rock 

Quaternary {

{

{ pre-Tertiary

 (Perforated 

 interval for well

13N/3E-10D1 is

 not known)

?

?

?

Quaternary- QTa

Tertiary

 Horizontal scale 1.5X

Tl

Tl

?

?

?

?

?

?

0 0.5

0 0.5 1 MILE

1 KILOMETER

sac13-0507_Figure 03c

C

Figure 3. —Continued
8 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

25 30 40 50 60

36

40

50

60

70

80

64

MODEL COLUMN

MODEL ROW

1,900

2,000

2,200

2,300

2,400

2,000

2,200

2,400

1,900

1,700

2,100

2,100

2,100

2,300

1,900

1,800

2,300

2,200

2,300

35°

15'

116°41' 116°39'

35°

17'

N

0

0 1 KILOMETER

1 MILE

Basement complex

Unconsolidated rocks 

Model layer 2

Bedrock Contour—Shows

 altitude of bedrock. Contour

 interval 100 feet. Datum is

 sea level

2,100

EXPLANATION

Model grid

Model layer 1

Boundaries–

Horizontal flow barrier

 (Model fault)

General head

Unnamed wash

sac13-0507_Figure 04-basement complex Figure 4. Altitude of the basement complex and boundaries of groundwater model layers for the Irwin Basin, Fort Irwin National 

Training Center, California (Densmore, 2003).
Simulation of Groundwater Flow 9

Numerous faults have been mapped in the bedrock 

hills surrounding the Irwin Basin (Yount and others, 1994) 

(figs. 2, 3); they include the Garlic Spring Fault, the Bicycle 

Lake Fault, and many unnamed faults. Most of these faults 

are buried beneath the unconsolidated deposits and thus their 

presence within the basin is largely unknown. Yount and 

others (1994) mapped the Garlic Spring Fault into the unconsolidated deposits, suggesting that the fault may cut through 

both the younger and the older alluvium in the southeastern 

part of the basin. Water-quality and water-level data, presented 

by Densmore and Londquist (1997), indicate that the Garlic 

Spring Fault and a parallel unnamed fault may be acting, 

in part, as a partial barrier to horizontal groundwater flow, 

primarily in the lower aquifer. The water-quality data indicate 

that vertical flow also is being impeded on the west side of the 

Garlic Spring Fault because of lithologic differences between 

the younger alluvium and the underlying lacustrine deposits of 

the older alluvium. Minor compaction and deformation of the 

water-bearing deposits immediately adjacent to the faults, fault 

gouge along the fault zone, and cementation of the fault zone 

by the deposition of minerals from groundwater are believed 

to create the barrier effect of the faults.

The areal extent of the aquifer system is defined by the 

intersection of the water table and the surrounding rocks 

of the basement complex. Under predevelopment conditions (pre-1941), the water table was about 2,300 feet above 

NAVD88. The boundary of the saturated aquifer system 

coincides with the 2,300-foot altitude contour of the basement 

complex shown in figure 4 (the approximate boundary of the 

aquifer system is shown in figure 2). All the alluvial deposits 

above this altitude were unsaturated under predevelopment 

conditions.

Simulation of Groundwater Flow

An existing groundwater-flow model of the aquifer 

system in the Irwin Basin (Densmore, 2003) was updated and 

used to simulate flow under four alternative withdrawal and 

recharge conditions, here called scenarios. Densmore (2003) 

developed a two-layer groundwater-flow model for the period 

1941–99 for the aquifer system in the Irwin Basin to assess the 

long-term availability and quality of groundwater, to evaluate groundwater conditions as a result of withdrawals, and to 

plan for future water needs at the base. Results of the model 

simulations of the scenarios were used to analyze the effects of 

the four alternative withdrawal and recharge conditions on the 

aquifer system.

Model Design

The existing groundwater-flow model was constructed 

using the USGS Modular Three-Dimensional FiniteDifference Groundwater- Flow Model (MODFLOW-88) 

developed by McDonald and Harbaugh (1988). For this study, 

the model input data was reformatted for a newer version of 

MODFLOW, MODFLOW-2005 (Harbaugh, 2005), and withdrawals were updated with 2000 to 2010 data. The updated 

model will be referred to in this report as the 2010 model.

The time intervals simulated in the original model were 

1-year stress periods from January 1941 to December 1999. 

For the 2010 model, the time intervals simulated were years 

from January 1941 to December 2007, and months from 

January 2008 to December 2010. 

The model grid developed for the original model was 

used for this study and is shown in figure 4. The origin of the 

model grid (the upper left corner of the grid; row 1, column 1) 

is at an easting of 2,373,237 ft and a northing of 669,380 ft in 

zone 5 of the California State Plane coordinate system. The 

grid consists of 80 rows and 64 columns with a cell size of 

500 ft on a side (fig. 4). 

The MODFLOW code consists of a main program and 

a series of independent subroutines called modules. The 

MODFLOW-2005 modules used in the 2010 model include 

Basic (BAS6); Block-Centered Flow (BCF6); GeneralHead Boundary (GHB); Drain (DRN); Discretization (DIS); 

Horizontal-Flow-Barrier (HFB6; Hsieh and Freckleton, 

1993); Multi-Node Well (MNW2, Konikow and others, 

2009); and Recharge (RCH) [BAS6, BCF6, GHB, DRN, 

and RCH, Harbaugh, 2005, MODFLOW-2005]. The original 

model (Densmore, 2003) used all of the above-mentioned 

modules except the MNW2, the WEL module (McDonald 

and Harbaugh, 1988) was used. For this study, the well input 

file was reformatted into the format for the MNW2 module. 

The 2010 model uses the Geometric Multigrid Solver (GMG, 

Wilson and Naff, 2004), whereas the original model used 

the Strongly Implicit Procedure Solver (SIP, McDonald and 

Harbaugh, 1988).

The model representation of the aquifer system, calibrated aquifer properties, and model boundaries simulated in 

the original model were not changed for this study. The model 

representation of the aquifer system is shown in figure 5.

Horizontal hydraulic conductivity of the aquifer system ranged 

from 3 to 25 ft/d (feet per day) for model layer 1 and 3 to 

22 ft/d for layer 2. Model boundaries are shown in figure 4.

The lateral boundaries of the model coincide with the lateral 

boundaries of the aquifer system. The top boundary of the 
10 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

sac13-0507_Figure 05a

Boundary of

aquifer system

Boundary of

aquifer system

14N/3E-32P2–6

14N/3E-32K1

14N/3E-32K3–6 

14N/3E-32J1

14N/3E-33E2–3

14N/3E-33F1

14N/3E-33A1

14N/3E-32N1–3

13N/3E-6P1

SOUTHWEST NORTHEAST

Qa ? Qa

QTa

QTa

2,600

2,700

FEET

2,500

2,400

2,300

2,200

2,100

2,000

1,900

1,800

1,700

1,600

1,500

A A'

Soccer

 field

Land

Surface Ball

field

Section B–B'

? ? 5th Street

S. Loop Rd

Barstow Rd

Old

biologicalevaporation

ponds

GARLIC SPRING FAULT

14N/3E-33B1

Bend in section

Bend in section

Bend in section

Bend in section

Bend in section

?

?

Hydraulic conductivity (K),

 in feet per day

Model

Layer 1 

Layer 2

K=15

K=3

K=20

K=15

K=25

K=22

K=20 K=15

K=15 K=3

K=7 K=3

K=15

LAYER 1 LAYER 2

QTa

?

QTa

Water table (Measured during 1994)

? Contact—Queried where uncertain

Fault—Queried where uncertain;

 arrows indicate direction of

 apparent movement 

Well and number—

Perforated interval

Bottom of borehole

Bottom of well

EXPLANATION

14N/3E-33E2–3

}

Qa

Basement complex

Younger alluvium—Upper aquifer

Older alluvium—Lower aquifer

Weathered and fractured

 basement complex

Quaternary

Quaternary–

Tertiary 

{

{

{ pre-Tertiary

(Perforated intervals for wells

13N/3E-6P1 and 14N/3E-33B1

 are not known)

Vertical scale greatly exaggerated

0

0 1 MILE Datum is sea level

1 KILOMETER

?

?

?

?

?

A

Figure 5. Cross-sectional view of model layers, hydraulic conductivities, and boundary conditions of the Irwin Basin, Fort Irwin 

National Training Center, California (Densmore, 2003). [Cross-section locations are shown in fig. 2]
Simulation of Groundwater Flow 11

?

?

?

13N/3E-4C1–3 -Section B–B'

13N/3E-5G1

14N/3E-33Q1

14N/3E-33R1

13N/3E-4B1–3

14N/3E-34M2

13N/3E-6P1

?

Langford Lake Road

5th Street

S.Loop Road

GARLIC SPRING  FAULT

Qa Qa

QTa QTa

Wastewatertreatment

facility

Land

surface

(projected)

?

Bend in section

Bend in section

Bend in section

Bend in section

?

?

?

? K=15

K=20

K=3

K=3

K=25

K=7 K=15

K=15

K=20

Hydraulic conductivity (K),

in feet per day

Model

Layer 1 

Layer 2

K=15

Water table (Measured during 1994)

13N/3E-4B1–3

Well and number—

Perforated interval

Bottom of borehole

Bottom of well

}

 (Perforated intervals for

 wells 13N/3E-6P1, and 

 5G1 are not known)

0

0 1 MILE Datum is sea level

1 KILOMETER

Vertical scale greatly exaggerated

?

? Contact—Queried where uncertain

Fault—Queried where uncertain; 

 arrows indicate direction of

 apparent movement 

EXPLANATION

Qa

Basement complex

Younger alluvium—Upper aquifer

Older alluvium—Lower aquifer

Lacustrine deposits

Weathered and fractured

 basement complex

Quaternary {

{

{ pre-Tertiary

Quaternary– QTa

Tertiary 

Horizontal scale approximately 1.4X

Tl

LAYER 1 LAYER 2

2,500

2,400

2,700

2,600

2,300

2,200

2,100

2,000

1,900

1,800

2,800

FEET

WEST EAST

A A"

Boundary of

aquifer system Boundary of

aquifer system

B

Tl

sac13-0507_Figure 05b

Figure 5. —Continued
12 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

?

? ? ?

?

14N/3E-33N1

14N/3E-32B1–3

14N/3E-32K3–6

14N/3E-32F1

13N/3E-4D1–3

13N/3E-4C1–3

13N/3E-4Q2–6

13N/3E-4K2–4

13N/3E-10D1

13N/3E-10E1–3 

Qa

Qa Qa

Qa

QTa

QTa

Former

sprinkler-

 pivot field

Duck

ponds

Section A–A"

Section

A–A'

(Projected)

5th Street

5th Street

(Projected)

Bend in section

Bend in section

Bend in section

Bend in section

Bend in section

LAYER 1 LAYER 2

?

?

?

NORTH SOUTH

2,600

2,700

2,900

2,800

FEET

2,500

2,400

2,300

2,200

2,100

2,000

1,900

1,800

B B'

?

K=20

K=20 K=25

K=22

K=15

K=25

?

K=3

?

LIX3

Hydraulic conductivity (K),

 in feet per day

Model

Layer 1 

Layer 2

K=15

Water table (Measured

 during 1994)

Boundary of

aquifer system

Boundary og

aquifer system

? Contact—Queried where uncertain

EXPLANATION

LIX3 

13N/3E-10E1–3 

Lysimeter and

 number

}

13N/3E-4Q2–6

Well and number—

Perforated

 interval

Bottom of borehole

Bottom of well

Destroyed well

 and number

Qa

Basement complex

Younger alluvium—Upper aquifer

Older alluvium—Lower aquifer

Lacustrine deposits

Weathered and fractured

 basement complex

Quaternary {

{

{ pre-Tertiary

 (Perforated interval for

Quaternary- QTa well LIX-3 is not known)

Tertiary Tl

0 1 KILOMETER

Vertical scale greatly exaggerated

Datum is sea level 0 1 MILE

?

Land

surface

C

Tl

sac13-0507_Figure 05c

Figure 5. —Continued

model, the water table, is simulated as a free-surface boundary (unconfined) to allow vertical movement in response to 

changes between inflow and outflow. No-flow boundaries 

are used around and below the modeled area to represent 

contact with the basement complex. The HFB6 package 

was used to simulate the 2 faults that impede the horizontal 

flow of groundwater. The GHB package was used to simulate underflow from layer 1 through the unnamed wash near 

Garlic Spring. The reader is referred to Densmore (2003) for a 

detailed description of the aquifer system framework, aquifer 

properties and model boundaries.

Model Calibration

The 2010 model was not re-calibrated, but the results of 

the simulations made with the original model and the 2010 

model were compared to ensure that the original level of calibration was maintained. Simulated 1994 hydraulic heads (or 

potentiometric surface) from the original model (Densmore, 

2003, fig. 19) were compared with those heads simulated in 

the 2010 model (fig. 6). The comparisons were only visual, 

however, because the original 1994 hydraulic heads generated 

by Densmore (2003) were not archived in GIS format. Model 

budgets calculated for each stress period by MODFLOW in 

the original and 2010 model were also compared. The original 

list file, lst.trand114, containing the model budgets, can be 

requested from the USGS California Water Science Center, 

San Diego, Calif.

The update of the original model was done in steps to 

allow for evaluation and analysis of simulation results and to 

maintain the original level of calibration. First, the original 

model input data was reformatted from MODFLOW-88 to 

MODFLOW-2005 format, and then the well input file was 

reformatted to the newer MNW2 format. The simulated 1994 

hydraulic heads, generated from the original model data that 

had been reformatted to run with MODFLOW-2005, are 

shown in red in figure 6 and compare well with the original 

1994 hydraulic heads generated by Densmore (2003). The 

MODFLOW-2005 model input data was then run with the 

original well data reformatted for the MNW2 module. The 

simulated 1994 hydraulic heads, generated from the 2010 

model with the MNW2 well data, are shown in purple in 

figure 6 and are slightly different in the area of the production 

wells 14N/3E-32F1, 14N/3E-32H1 and 14N/3E-32K1 (fig. 6) 

from the hydraulic heads simulated by using the original well 

data. Using the MNW2 module, the simulated 1994 hydraulic 

heads for layer 1 at production wells 14N/3E-32H1 and 
Simulation of Groundwater Flow 13

Figure 6. Simulated 1994 hydraulic heads, layer 1, Irwin Basin, Fort Irwin National Training Center, California.

LANGFORD

BASIN

IRWIN

BASIN

BICYCLE

BASIN

Beacon

Hill

GARLIC SPRING FAULT

Geology by J. C. Yount, E.R. Schermer, T.J. Felger, D.M. Miller, and K.A. Stephens, 1994

Aquifer system boundary modified from Wilson F. So and Assoc., 1989

?

BICYCLE FAULT

2,280

2,285

2,290

2,295

2,300

2,275

2,305

2,310

2,315

2,270

2,320

2,325

2,255

2,265

2,245

2,280

2,300

2,290

2,305

2,310

2,270

2,280

1

Barstow Rd

Irwin Rd

N. Loop Rd

S. Loop Rd

Langford Lake Rd

Infiltration pond

Athletic field

Road

31

35°17’

35°13’

116°43’ 116°39'

6

36 T 14 N

T 13 N

R 2 E R 3 E

0

0 1 2 MILES

1 2 KILOMETERS

EXPLANATION

SOUTHWEST

RIDGE

sac13-0507_Figure 06

Unconsolidated deposits—

Correlation and description of map units

QuaternaryTertiary

Consolidated rocks—

Well and number—

Fault—Dashed where approximately 

 located; queried where uncertain;

 dotted where concealed

Volcanic 

Igneous and metamorphic

Alluvium Playa

?

NORTHWEST RIDGE

Garlic

Spring

{

{

{

Tertiary

pre-Tertiary

?

32F1 32H1

32K1

Extent of model layer 1

Simulated 1994 hydraulic-head

 contour, using MODFLOW 2005

 with the well module. Contour

 interval is 5 feet. Datum is NAVD88 

Simulated 1994 hydraulic-head

 contour, using MODFLOW 2005 with

 the MNW2 module. Contour interval

 is 5 feet. Datum is NAVD88 32K1

Boundary of aquifer

 system (approximate)

Drainage basin boundary
14 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

14N/3E-32K1 are 2.61 and 3.51 ft higher, respectively, than 

the 1994 simulated hydraulic heads using the WEL module. 

In contrast, the 1994 hydraulic heads simulated by using the 

MNW2 module for layer 2 at production wells 14N/3E-32F1, 

14N/3E-32H1 and 14N/3E-32K1 are 1.28, 0.88 and 1.09 ft 

lower, respectively, than the 1994 simulated hydraulic heads 

using the WEL module. With the exception of the hydraulic heads within the closed 2,270-foot contour line (fig. 6), 

hydraulic heads from both models agree within 0.1 foot. 

This difference in hydraulic head may be attributed to how 

the withdrawals were distributed in the original model. The 

withdrawals from production wells were initially distributed as 

two-thirds from layer 1 and one-third from layer 2; this initial 

distribution was then varied between the two layers during 

calibration in the original model (Densmore, 2003). For the 

2010 model, the percentage of groundwater withdrawals from 

each model layer was calculated by the MNW2 module.

The volumetric model budgets, calculated by 

MODFLOW, for the original MODFLOW-88 model and the 

2010 model for 1994 conditions, which is stress period 54, are 

shown in table 1. Slight differences in the values for storage 

and head dependent boundary are probably a result of the 

difference in the distribution of withdrawals of the production 

wells calculated by the MNW2 module. Overall, the budget 

items compare well.

Hydrographs for 11 selected observation wells are 

shown in figure 7. Wells were selected on the basis of location and number of water-level measurements available, and 

only wells screened in a single layer were considered. The 

measured water levels and simulated hydraulic heads from 

the 2010 model are within 11 ft. Simulated hydraulic heads 

also matched the upward 1992–2010 trend in measured water 

levels. The upward trend is probably a result of recharge from 

the ponds near the wastewater-treatment facility and irrigation 

at the training center’s base housing.

Groundwater Withdrawals

The original model simulated hydrologic conditions from 

January 1941 to December 1999 with yearly stress periods. 

In the original model, groundwater withdrawals were averaged for the year. The 2010 model included 2000 to 2010 

withdrawal data. Monthly groundwater withdrawal records 

were available for January 2000 through December 2010. For 

the 2010 model, groundwater withdrawals were simulated 

for 1-year periods from January 1941 to December 2007 and 

for 1-month periods from January 2008 to December 2010. 

Annual groundwater withdrawals from Bicycle, Irwin, and 

Langford Basins are shown in figure 8.

Groundwater Recharge

There are two sources of recharge to the aquifer system in 

the Irwin Basin: natural recharge from precipitation and artificial recharge from wastewater-effluent infiltration at the ponds 

and irrigation-return flow (Densmore, 2003). Natural recharge 

in the basin is low because of low precipitation and high evaporation rates. The calibrated natural recharge simulated in the 

original model was about 50 acre-ft/yr. The natural recharge 

was simulated along the intermittent unnamed wash shown in 

figure 4. The natural recharge of 50 acre-ft/yr was used in the 

2010 model and simulated in the same model cells as those 

in the original model that represent the intermittent unnamed 

wash. Groundwater is imported to the Irwin Basin from 

Bicycle and Langford Basins. Some water is used for irrigation at the base housing; the water that is not consumed is 

treated at the wastewater-treatment facility and discharged to 

the infiltration ponds, referred to as the wastewater treatment 

facility pond, golf course pond and duck ponds. Estimated 

groundwater recharge has exceeded groundwater withdrawals 

Table 1. Simulated volumetric budget, for 1994 conditions (stress period 54), from the A) original, MODFLOW-88 model and B) 2010 

model, Irwin Basin, Fort Irwin National Training Center, California.

[Values in cubic feet per day. Abbreviation: —, none]

Budget component Original model 

(MODFLOW-88)

2010 model 

(MODFLOW-2005)

Percent difference between 

original and 2010 model

Inflow:

Storage 6,054.70 5,951.50 0.07

Recharge 152,271.55 152,271.61 –0.00

Total in 158,330.00 158,223.11 —

Outflows:

Storage 7,627.10 7,517.36 0.07

Groundwater withdrawals 140,691.00 140,691.00 0.00

Head dependent boundary 9,998.90 10,015.42 –0.01

Total out 158,320.00 158,223.78 —

Inflow–outflow 9.20 –0.67 —

Percent discrepancy 0.01 0.00 —
Simulation of Groundwater Flow 15

Figure 7. Hydrographs of measured water levels and simulated hydraulic heads in 11 observation wells, Irwin Basin, Fort Irwin 

National Training Center, California. [Well location shown in fig. 11]

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

EXPLANATION

Simulated value, 

 layer 1 

Measured value, well 

 screened in layer 1

Simulated value, 

 layer 2 

Measured value, well 

 screened in layer 2

Water-level altitude, in feet above NAVD 88

Figure 7a. Hydrographs of simulated and measured water levels in 11 observation wells,

 Fort Irwin National Training Center, California. (Well location shown in figure 11)

4D2 4D3

32B2 32B3

32K4 32K6

32P4 32P6

32F2 32F3

33E3

Year

Year
16 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

Figure 8. Annual groundwater recharge and withdrawals from Bicycle, Irwin, and Langford Basins, Fort Irwin National Training Center, 

California, 1941–2010.

0 

500 

1,000 

1,500 

2,000 

2,500 

3,000 

3,500 

1941 1943 1945 1947 1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 

Recharge and withdrawal, in acre-feet 

Year 

Figure 8. Annual groundwater recharge and withdrawals from Bicycle, Irwin, and

Langford Basins, Fort Irwin National Training Center, California, 1941-2010. 

Irwin Basin withdrawal 

Bicycle Basin withdrawal 

Langford Basin withdrawal 

Total estimated recharge in Irwin Basin 

EXPLANATION

in the Irwin Basin since 1967, except for the years 1984 and 

1986–91. From 1967, about 33,980 acre-ft was withdrawn 

from the groundwater-flow system within the Irwin Basin and 

an estimated 50,600 acre-ft recharged the basin, resulting in 

a net gain of 16,620 acre-ft of water to the groundwater-flow 

system (fig. 8 and table 2). Reduced pumping in the Irwin 

Basin, recharge from irrigation at the base housing, and artificial recharge from treated wastewater at the infiltration ponds 

has caused water levels to stabilize or rise throughout most of 

the Irwin Basin (fig. 7).

The recharge rate used in the original model at the 

recreational fields (soccer, baseball, and Army ball fields) and 

grass areas at the base housing (fig. 2) was used in the 2010 

model for January 2000 to December 2007. Additional base 

housing (fig. 2) was constructed in phases during May 2005, 

May 2008, and November 2008. Recharge was simulated 

in the 2010 model for these areas beginning in 2005. The 

original model simulated an average yearly recharge rate, in 

cubic feet per day, from January 1941 to December 1999. 

The recharge rate simulated in the original model was used in 

the 2010 model for the monthly stress periods from January 

2008 to December 2010. At the recreational fields and grass 

areas at the base housing, the recharge rate was decreased by 

half for the winter months, January, February, November and 

December. 

Estimates of daily evaporation and evapotranspiration 

from studies by the California Department of Water Resources 

(DWR) and the California Irrigation Management Information 

System (CIMIS) of DWR’s Office of Water Use Efficiency, 

respectively, were used in the calculation of water available 

for monthly recharge at the wastewater infiltration ponds 

(pond locations shown in fig. 2), where outflow from the 

wastewater-treatment facility is discharged in the Irwin Basin. 

Using an annual evaporation rate of 5.7 ft, the 2010 evaporation from the surface of wastewater infiltration ponds (area 

of ponds is 47 acres) was estimated to be about 270 acre-ft 

(table 3). Using an annual evapotranspiration rate of 6 ft, 

the 2010 evapotranspiration from the area (about 40 acres) 

around the wastewater infiltration ponds was estimated to 

be 240 acre-ft. There are no data available on the depth to 

groundwater within 500 ft of the ponds from wells screened 

within 20 ft of land surface. The well nearest to any of the 

infiltration ponds (pond locations shown in fig. 2) is observation well 13N/3E-10D1, screened 15 to 65 ft below land 

surface and located about 500 ft southeast of the southernmost 

duck pond. The water level in this well was 15 ft below land 

surface on October 21, 2010. A shallow depth to groundwater 

was assumed for the area around the ponds because of the 

vegetation growing there, and the water from the ponds would 

flow laterally, in addition to vertically, into the surrounding 

aquifer. A shallow depth to groundwater, less than 10 ft, was 
Simulation of Groundwater Flow 17

Year Withdrawal Recharge

1941 33 49

1942 130 71

1943 350 199

1944 480 273

1945 182 102

1946 57 50

1947 55 49

1948 55 49

1949 55 49

1950 55 50

1951 293 166

1952 336 193

1953 671 385

1954 668 382

1955 598 488

1956 602 71

1957 704 79

1958 686 70

1959 655 70

1960 746 99

1961 881 195

1962 1,119 344

1963 1,147 370

1964 1,202 408

1965 1,305 607

1966 1,509 790

1967 827 928

1968 764 864

1969 727 947

1970 549 742

1971 364 421

1972 399 785

1973 321 447

1974 200 352

1975 236 421

Year Withdrawal Recharge

1976 236 569

1977 64 224

1978 283 702

1979 502 883

1980 721 1,388

1981 660 702

1982 630 666

1983 720 901

1984 1,675 1,558

1985 1,133 1,548

1986 1,315 1,006

1987 1,927 1,257

1988 1,700 1,173

1989 1,696 1,073

1990 1,868 1,390

1991 1,331 1,022

1992 1,110 1,146

1993 997 1,196

1994 1,180 1,276

1995 1,270 1,645

1996 1,138 1,568

1997 580 1,343

1998 484 1,460

1999 781 1,460

2000 612 1,462

2001 331 1,640

2002 333 1,716

2003 168 1,781

2004 301 1,671

2005 370 1,701

2006 592 1,733

2007 755 1,690

2008 826 1,385

2009 765 1,376

2010 536 1,391

Table 2. Simulated annual 1941–2010 groundwater recharge and withdrawals, Irwin Basin, Fort Irwin National Training Center, 

California.

[Values in acre-feet per year.]
18 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California Table 3. Summary of 2001–10 groundwater withdrawals, and estimates of evapotranspiration, evaporation, and recharge used in the 2010 model and model scenarios, Irwin Basin, Fort Irwin National Training Center, California. [Numbers in parentheses are model cell numbers (row, column). Scenario 1 and 3 do not have a decrease in recharge in phases. Scenario 2, phase 1 uses Scenario 1 recharge values. Scenario 2, phase 4 has no recharge in the area of the ponds near the wastewater treatment facility. Values in acre-feet unless noted otherwise. Abbreviation: CA, California; NE, Northeast; ->, indicates range of cells in column; #, number] Month Groundwater withdrawals Treated wastewater Evaporation Evapotranspiration Total estimated evaporation and evapotrans- piration in Irwin Basin Simulated 2010 wastewater recharge Average 2001–10 from all basins1 2010 from all basins1 2010 to wastewater treatment facility2 Average from a water surface, feet per month3 Estimated from the surface of ponds in Irwin Basin4 San Bernardino, Barstow, CA NE - #134, feet per month5 Estimated evapotrans- piration from areas around ponds in Irwin Basin6 Duck ponds (64,55; 65,55; 66,55; 67,55; 68,55) Golf course pond (59,53; 60,53; 61,53; 62,53; 62,54; 63,53; 63,54) Wastewater- treatment facility pond (56,52->53; 57,51->53; 58,51->52; 59,51->52; 60,51->52) Total simulated recharge from ponds in Irwin Basin January 145 150 109 0.11 5 0.18 7 12 30 18 15 63 February 136 146 106 0.17 8 0.24 10 18 28 17 14 59 March 181 192 107 0.33 15 0.45 18 33 29 17 13 59 April 200 195 93 0.50 24 0.59 24 47 19 11 9 40 May 255 237 95 0.73 34 0.75 30 64 19 11 7 38 June 279 262 87 0.87 41 0.85 34 75 18 11 6 35 July 300 284 104 0.92 43 0.83 33 76 14 9 6 28 August 282 294 115 0.81 38 0.74 29 67 15 9 6 29 September 276 273 94 0.58 27 0.57 23 50 18 11 7 36 October 243 217 98 0.37 17 0.41 16 34 17 10 6 34 November 184 146 91 0.19 9 0.23 9 18 14 8 7 30 December 153 130 92 0.10 5 0.17 7 11 20 12 9 40 Total of column7 2,635 2,526 1,191 5.67 267 5.99 240 506 241 145 106 492
Simulation of Groundwater Flow 19

Table 3. Summary of 2001–10 groundwater withdrawals, and estimates of evapotranspiration, evaporation, and recharge used in the 2010 model and model scenarios, Irwin Basin, Fort Irwin National Training Center, California.—Continued [Numbers in parentheses are model cell numbers (row, column). Scenario 1 and 3 do not have a decrease in recharge in phases. Scenario 2, phase 1 uses Scenario 1 recharge values. Scenario 2, phase 4 has no recharge in the area of the ponds near the wastewater treatment facility. Values in acre-feet unless noted otherwise. Abbreviation: CA, California; NE, Northeast; ->, indicates range of cells in column; #, number]

Month

Scenario 1, 

January 2011 through December 2060

Scenario 2, 

phase 2, January 2012 through December 2013

Scenario 2, 

phase 3, January 2014 through December 2015

Estimated 

quantity 

of treated 

wastewater 

discharge 

to ponds in 

Irwin Basin8

Simulated wastewater recharge

Estimated 

quantity 

of treated 

wastewater 

discharge 

to ponds in 

Irwin Basin8

Simulated wastewater recharge

Estimated 

quantity 

of treated 

wastewater 

discharge 

to ponds in 

Irwin Basin8

Simulated wastewater recharge

Duck 

ponds 

(64,55; 

65,55; 66,55; 67,55; 

68,55)

Golf 

course 

pond 

(59,53; 

60,53; 61,53; 62,53; 62,54; 

63,53; 63,54)

Wastewatertreatment 

facility 

pond 

(56,52->53; 

57,51->53; 58,51->52; 59,51->52; 

60,51->52)

Total 

simulated 

recharge 

from 

ponds in 

Irwin 

Basin

Duck 

ponds 

(64,55; 

65,55; 66,55; 67,55; 

68,55)

Golf 

course

pond 

(59,53; 60,53; 

61,53; 62,53; 62,54; 63,53; 

63,54)

Wastewatertreatment 

facility 

pond 

(56,52->53; 

57,51->53; 58,51->52; 59,51->52; 

60,51->52)

Total 

simulated 

recharge 

from 

ponds in 

Irwin 

Basin

Duck 

ponds 

(64,55; 

65,55; 66,55; 67,55; 

68,55)

Golf 

course 

pond 

(59,53; 60,53; 

61,53; 62,53; 62,54; 63,53; 

63,54)

Wastewater 

treatment 

facility 

pond 

(56,52->53; 

57,51->53; 58,51->52; 59,51->52; 

60,51->52)

Total 

simulated 

recharge 

from 

ponds in 

Irwin 

Basin

January 103 30 18 15 63 101 30 18 15 63 98 30 18 15 63February 100 28 17 14 59 97 28 17 14 59 93 28 17 14 59March 93 29 17 13 59 86 29 17 13 59 79 29 17 13 59April 71 19 11 9 40 61 19 11 9 40 50 0 0 0 0May 66 9 6 4 19 51 0 0 0 0 36 0 0 0 0June 55 0 0 0 0 39 0 0 0 0 22 0 0 0 0July 70 0 0 0 0 53 0 0 0 0 37 0 0 0 0August 83 0 0 0 0 67 0 0 0 0 50 0 0 0 0September 65 0 0 0 0 51 0 0 0 0 36 0 0 0 0October 77 17 10 6 34 66 17 10 6 34 55 9 5 3 17November 77 14 8 7 30 70 14 8 7 30 64 14 8 7 30December 86 20 12 9 40 83 20 12 9 40 80 20 12 9 40Total of column7 946 166 100 78 344 823 157 94 75 325 701 129 77 62 269

1Groundwater withdrawals from Bicycle, Irwin, and Langford Basins.2Values from Fort Irwin National Training Center personnel.3Potential evaporation values from pans download from http://www.water.ca.gov.4Evaporation estimated from monthly pan evaporation multiplied by an estimated area of 47 acres for all ponds.5Potential evapotranspiration values download from January 1, 1997 through May 31, 2001; http://wwwcimis.water.ca.gov/cimis/frontMonthlyReport.do.6Evapotranspiration estimated from monthly evapotranspiration values and multiplied by an estimated area of 40 acres (area around all ponds with some vegetation).7Values may not add to totals due to rounding. 8Estimated values from Fort Irwin National Training Center personnel.
20 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

assumed for a radial distance of 250 ft from the edge of the 

wastewater infiltration ponds and evapotranspiration would 

occur over 40 acres around the ponds. Evapotranspiration 

would decrease the water available for groundwater recharge 

to the aquifer system. Simulated annual 1941 to 1999 recharge 

in the original model ranges from 49 to 1,644 acre-ft/yr 

(fig. 8). Simulated annual 2000 to 2010 recharge in the 

updated 2010 model ranges from 1,462 to 1,781 acre-ft/yr 

(fig. 8).

Periodic water-level measurements by USGS personnel 

at six observation wells (13N/3E-4B3, -4G1, 4K1,-4K4, 

-4Q4, and -10D1) near the wastewater-treatment facility were 

compared to simulated hydraulic heads to insure the calculated 

2008–10 monthly recharge rates did not have an adverse effect 

on model calibration. The observation wells are screened 

in model layer 1. The measured water levels and simulated 

hydraulic heads, which are within 1–20 ft, at the six observation wells (fig. 9). The larger differences between simulated 

and measured values may be due, in part, to inaccuracies in 

the distribution of pumpage to the individual wells during 

1999 and 2004 and an inaccurate estimation of the quantity 

and distribution of artificial recharge.

Simulated Effects of Future 

Withdrawals and Artificial Recharge

The updated 2010 model was used to assess the possible 

effect of four groundwater withdrawal and artificial recharge 

scenarios on the groundwater-flow system within the Irwin 

Basin. These four scenarios were developed in cooperation 

with Fort Irwin National Training Center personnel and used 

to simulate conditions from January 2011 to December 2060. 

All of the model scenarios use the simulated December 2010 

hydraulic heads as initial conditions. Monthly values for 

proposed withdrawals and estimated artificial recharge were 

simulated for January 2011 through December 2060. 

For the scenarios, the drain module was added to simulate groundwater discharge in areas where water levels rise 

above land surface because of groundwater recharge simulated 

in those areas. Groundwater levels rise above land surface 

in the southern area of the Irwin Basin where the land surface is topographically low, around 2,340 NAVD88, and are 

described in more detail in the Results of Simulations sections.

 Figure 9. Hydrographs of measured water levels and simulated hydraulic heads in six observation wells near the wastewatertreatment facility, Irwin Basin, Fort Irwin National Training Center, California. [Well locations shown in fig. 11]

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

1941 1950 1960 1970 1980 1990 2000 2010

2,240

2,260

2,280

2,300

2,320

2,340

Water-level altitude, in feet above NAVD 88

4B3 4G1

4K1 4K4

4Q2 10D1

EXPLANATION

Simulated value, layer 1 Measured value, well screened in layer 1

Year Year
Simulated Effects of Future Withdrawals and Artificial Recharge 21

Description of Model Scenarios

Artificial groundwater recharge simulated for each of 

the model scenarios was adjusted in the area of the ponds 

near the wastewater-treatment facility, based on estimates 

by Fort Irwin personnel of the quantity of wastewater that 

may be discharged to the ponds in the future. The quantity of 

treated wastewater discharged to the ponds is anticipated to be 

reduced as a result of plans to use the wastewater, rather than 

“newly pumped” groundwater, for irrigation. Groundwater 

withdrawals also were adjusted for each of the scenarios to 

represent the redistribution or reduction of estimated amounts 

that are anticipated by Fort Irwin personnel. Simulated 

groundwater withdrawals and artificial recharge for each scenario are described below. 

Scenario 1

Scenario 1 simulates the 2010 annual rate of withdrawals (536 acre-ft/yr) from production well 14N/3E-32H1 in the 

Irwin Basin (table 4) and remains constant from 2011 to 2060. 

The monthly distribution of withdrawals (fig. 10) was estimated as a percentage from the monthly withdrawals from all 

production wells in the Irwin, Bicycle, and Langford Basins 

for the 10-year period, 2001 through 2010 in order to reflect 

the monthly groundwater requirement needed by operations 

at the Fort Irwin NTC. The monthly groundwater withdrawals 

for the Irwin Basin were calculated by multiplying the 2010 

total groundwater withdrawals (536 acre-ft/yr) from production well 14N/3E-32H1 by the percentage for a particular 

month. The monthly withdrawals used in scenario 1 ranged 

from 27 to 61 acre-ft (table 4).

The estimated quantity of treated wastewater discharged 

to the infiltration ponds near the wastewater-treatment facility (pond locations shown in fig. 2) for 2011 through 2060 

was reduced from the 2010 values. The quantity of treated 

wastewater discharged to the ponds ranges from 55 to 

103 acre-ft/month (table 3) for scenario 1. Because less treated 

wastewater will be discharged to the ponds, less water will be 

available for recharge. If the quantity of treated wastewater 

discharged to the ponds exceeded the total of the evaporation 

and evapotranspiration rate and was greater than the 2010 

monthly recharge rate from the ponds , then the 2010 recharge 

rate from wastewater shown in table 3 was simulated for that 

month. If the quantity of treated wastewater discharged to the 

ponds was less than the total of the evaporation and evapotranspiration rate and there was wastewater left over from the 

previous month, then the simulated 2010 recharge rate from 

wastewater was decreased for that month. If the quantity of 

treated wastewater discharged to the ponds was less than 

the total of the evaporation and evapotranspiration rate and 

there was no wastewater left over from the previous month, 

then the simulated 2010 recharge rate is zero. The monthly 

recharge rate in the area of the ponds calculated from the 

quantity of treated wastewater in the ponds ranged from 0 to 

63 acre-ft/month (table 3).

Figure 10. Average 2001 to 2010 total monthly groundwater withdrawal distribution for wells in the Bicycle, Irwin, and Langford Basins 

that were used to provide water to Fort Irwin National Training Center, California.

0

2

4

6

8

10

12

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec 

Month 

Percentage of annual withdrawals 
22 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

Scenario 2

Scenario 2 simulates the 2010 groundwater withdrawals from production wells 14N/3E-32M1, -32H1 and 

13N/3E-5G2 (well locations shown in fig. 11). Currently 

(2010), production wells 14N/3E-32M1 and 13N/3E-5G2 are 

inactive. The simulated monthly groundwater withdrawals 

calculated for scenario 1 were redistributed among production wells 14N/3E-32H1 (33 percent) and -5G2 (67 percent) 

during 2010–16 (table 4); groundwater withdrawals from 

well 14N/3E-32M1 were zero until 2016 based on future 

seasonal water supply demand anticipated by Fort Irwin 

personnel. Beginning in March 2016 and continuing until 

December 2060, simulated withdrawals from production well 

14N/3E-32M1 for March, April, May, and June were 3, 10, 

12, and 6 acre-ft/month, respectively, and zero for all other 

months. The withdrawals from 14N/3E-32M1 are in addition 

to the withdrawals from production wells 14N/3E-32H1 and 

-5G2. 

For Scenario 2, the estimated quantity of treated 

wastewater discharged to the infiltration ponds was reduced 

in four phases from the quantity of treated wastewater in 2010 

(table 3). The quantity of treated wastewater discharged to 

the infiltration ponds for scenario 2, phase 1, (January 2011 

through December 2011) used the same values calculated for 

scenario 1 (January 2011 through December 2060) and ranged 

from 55 to 103 acre-ft/month. The simulated quantity of 

treated wastewater discharged to the infiltration ponds ranged 

from 39 to 101 acre-ft/month for phase 2, (January 2012 

through December 2013), 22 to 98 acre-ft/month for phase 3, 

(January 2014 through December 2015) and no discharge 

to the infiltration ponds for phase 4, (January 2016 through 

December 2060). 

The calculated monthly recharge rates in the area of 

the ponds for phase 2 and 3 of scenario 2 ranged from 0 to 

63 acre-ft/month (table 3). The calculated monthly recharge 

was zero in the model for phase 4 in the area of the ponds. The 

treated wastewater for phase 4 is assumed to be used for irrigation (currently (2010) supplied by groundwater) and cooling 

towers and any remaining wastewater will be discharged to 

a proposed 2-mile-long drainage ditch. The 1,400 acre-ft/yr 

of water used for irrigation (1,200 acre-ft/yr ) and cooling 

towers (200 acre-ft/yr), however, exceeds the quantity of water 

treated at the wastewater treatment facility, 1,190 acre-ft/yr. 

Hence, there will be no wastewater available to discharge to 

the proposed drainage ditch at the base.

Table 4. Summary of simulated monthly groundwater withdrawals from wells in the Irwin Basin used in the four scenarios, Irwin 

Basin, Fort Irwin National Training Center, California.

[Values in acre-feet. 14N/3E-32M1 (I-2A), 14N/3E-32H1(I-7), 13N/3E-5G2 (I-9), State well number and local well number in parentheses.]

Month

Scenario 1 Scenario 2

2

Scenario 3, 

30 percent 

reduced 

withdrawals

2

Scenario 4, 

30 percent reduced withdrawals

14N/3E-32H1 

(I-7) 

14N/3E-32H1 

(I-7) 

13N/3E-5G2 

(I-9)

1

14N/3E-32M1 

(I-2A)

14N/3E-32H1 

(I-7) 

14N/3E-32H1 

(I-7) 

13N/3E-5G2 

(I-9)

3

14N/3E-32M1 

(I-2A)

January 30 20 10 0 21 14 7 0

Febuary 27 18 9 0 19 13 6 0

March 37 25 12 3 26 17 9 3

April 41 27 13 10 29 19 9 10

May 52 35 17 12 36 24 12 12

June 57 38 19 6 40 27 13 6

July 61 41 20 0 43 29 14 0

August 57 38 19 0 40 27 13 0

September 56 38 19 0 39 26 13 0

October 50 33 16 0 35 23 11 0

November 37 25 12 0 26 18 9 0

December 31 21 10 0 22 15 7 0

Total 536 359 177 31 375 251 124 31

1

Simulated withdrawals begin in March 2016.

2

Simulated withdrawals are reduced 3 percent per year for 10 years, from January 2011 to December 20, then the 30 percent reduced withdrawals are 

simulated January 2021 through December 2060.

3

No reduction in simulated withdrawals.
Simulated Effects of Future Withdrawals and Artificial Recharge 23

Figure 11. Simulated difference in hydraulic head from October 2010 conditions to October 2060 conditions, scenario 1, layer 1, Irwin 

Basin, Fort Irwin National Training Center, California.

LANGFORD

BASIN

IRWIN

BASIN

BICYCLE

BASIN

Beacon

Hill

GARLIC SPRING FAULT

Geology by J.C. Yount, E.R. Schermer, T.J. Felger, D.M. Miller, and K.A. Stephens, 1994

Aquifer system boundary modified from Wilson F. So and Assoc., 1989

?

BICYCLE FAULT

? –55

–50

–45

–40

–35

–30

–60

–15

–10

–25

–20

–65

–25

4D2,3 4B3

4G1

5G2

4K1 4K4

4Q2

32F2,3 32H1 33E3

32M1 32K4,6

32P4,6

10D1

10Z1

32B3

1

Barstow Rd

Irwin Rd

N. Loop Rd

S. Loop Rd

Langford Lake Rd

31

35°17’

35°13’

116°43’ 116°39'

6

36 T 14 N

T 13 N

R 2 E R 3 E

0

0 1 2 MILES

1 2 KILOMETERS

EXPLANATION

SOUTHWEST

RIDGE

sac13-0507_Figure 11

Unconsolidated deposits—

Correlation and description of map units

QuaternaryTertiary

Consolidated rocks—

Fault—Dashed where approximately 

 located; queried where uncertain;

 dotted where concealed

Volcanic 

Igneous and metamorphic

Alluvium Playa

?

NORTHWEST RIDGE

Garlic

Spring

{

{

{

Tertiary

pre-Tertiary

Extent of model layer 1

Simulated difference in hydraulic head—

 October 2010 conditions minus 

 October 2060 conditions, in feet.

 All contour values are negative

 and indicates simulated hydraulic

 head has increased between

 2010 and 2060

–50

Road

Infiltration pond

Athletic field

5G2 Well and number—

Boundary of aquifer

 system (approximate)

Drainage basin

 boundary
24 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

Scenario 3

Scenario 3 simulates a 3 percent per year reduction in 

the 2010 withdrawal rate for 10 years, from January 2011 

through December 2020. The 30 percent reduction in withdrawal rate (from the initial 2010 rate) was then applied 

in the simulation from January 2021 until December 2060 

(table 4). The withdrawals are simulated from production well 

14N/3E-32H1 (I-7). The same quantity of treated wastewater 

discharged to the ponds near the wastewater-treatment facility 

for scenario 1 was used in scenario 3 (table 3). In addition, 

the same recharge rate simulated in the area of the ponds in 

scenario 1 was used in scenario 3.

Scenario 4

Scenario 4 simulates the same distribution of withdrawals 

among the production wells as scenario 2, but reduces 

the 2010 withdrawals 3 percent per year for 10 years 

(January 2011 through 2020) at wells 14N/3E-32H1 and 

13N/3E-5G2. As in scenario 3, the 30 percent reduction in 

withdrawal rates (from the initial 2010 rate) was then simulated from January 2021 until December 2060 (table 4). Withdrawals at well14N/3E-32M1 were not reduced. Similar to 

scenario 2, the estimated quantity of treated water discharged 

to the ponds near the wastewater treatment facility and the 

simulated recharge rate were varied in 4 phases beginning 

in January 2011, January 2012, January 2014, and January 

2016, and are shown in table 3. The same quantity of treated 

wastewater discharged to the ponds near the wastewater-treatment facility for scenario 2 was used in scenario 4. The same 

recharge rate simulated in the area of the ponds for scenario 2 

was used in scenario 4.

Results of Simulations

Results of the simulations of the four scenarios are 

presented as maps of the difference in hydraulic heads from 

October 2010 to October 2060 for model layer 1. (figs. 11–14). 

The head values for October are assumed to represent water 

levels after the high groundwater withdrawal rates during the 

summer. A negative value for the change in hydraulic head 

indicates the simulated hydraulic head has increased between 

2010 and 2060.

Hydrographs showing the simulated hydraulic 

heads for each of the four scenarios from 2011 to 2060 at 

14 well locations are presented in figure 15. Water levels 

in production wells 14N/3E-32M1 (I-2A), -32H1 (I-7) and 

13N/3E-5G2 (I-9) are representative of conditions in a cone 

of depression that may form in response to groundwater 

withdrawals. The aquifer response in the area of a cone of 

depression to changes in recharge will be most evident in 

the hydrographs of production wells. The water levels in 

observation wells 13N/3E-4D3, -4G1, -4K1, -4K4, -4Q2, 

-10D1, 14N/3E-32B3, -32F3, -32K6, -32P6, and -33E3 are 

representative of groundwater conditions in the Irwin Basin. 

The changes in simulated hydraulic heads at the 14 wells are 

summarized in table 5.

Scenario 1

 In scenario 1, the 2010 annual rate of withdrawals 

(536 acre-ft/yr) was held constant from 2011 to 2060, for a 

cumulative withdrawal of 26,800 acre-ft. Continuation of the 

2010 withdrawal rate and recharge from irrigation at the base 

housing, and a decrease in the recharge at the ponds, resulted 

in an increase in groundwater levels throughout Irwin Basin. 

These increases were as much as 55 ft in the area underlying 

the base housing in the northwestern part of the basin and 

10 ft in the southeastern area near the unnamed wash exiting 

the basin (fig. 11 and table 5). The rise in water levels in the 

northwestern part of the basin is a result of continued recharge 

from irrigation at the base housing. Even though there is a 

simulated decrease in recharge at the ponds, simulated groundwater levels continue to rise in the area of the ponds. Analysis 

of simulation results indicate groundwater levels rose to land 

surface around the golf course pond, duck ponds and well 

13N/3E-10D1. Simulated groundwater discharge to the drains, 

which was simulated around the golf course pond, duck ponds 

and the unnamed wash near well 13N/3E-10D1, ranges from 

1 to 205 acre-ft/year by 2060 (table 6). Beginning in March 

2044, simulated hydraulic heads rise to land surface at well 

13N/3E-10D1 (2,345 ft above sea level [NAVD 88] intermittently during the year (fig. 15). Prior to March 2044, simulated 

hydraulic heads remain below land surface. The altitude of 

land surface ranges from 2,344ft above sea level [NAVD 88] 

at well 13N/3E-10D1 to 2,310 ft above sea level [NAVD 88] 

at well 13N/3E-10Z1. Simulated groundwater levels remained 

below land surface north and west of the wastewater treatment 

plant.
Simulated Effects of Future Withdrawals and Artificial Recharge 25

Figure 12. Simulated difference in hydraulic head from October 2010 conditions to October 2060 conditions, scenario 2, layer 1, Irwin 

Basin, Fort Irwin National Training Center, California.

LANGFORD

BASIN

IRWIN

BASIN

BICYCLE

BASIN

Beacon

Hill

GARLIC SPRING FAULT

Geology by J.C. Yount, E.R. Schermer, T.J. Felger, D.M. Miller, and K.A. Stephens, 1994

Aquifer system boundary modified from Wilson F. So and Assoc., 1989

?

BICYCLE FAULT

?

4D2,3 4B3

5G2 4G1

4K1

4K4

4Q2

32F2,3 32H1 33E3

32M1

32K4,6

32P4,6

10D1

10Z1

32B3

1

Barstow Rd

Irwin Rd

N. Loop Rd

S. Loop Rd

Langford Lake Rd

31

35°17’

35°13’

116°43’ 116°39'

6

36 T 14 N

T 13 N

R 2 E R 3 E

0

0 1 2 MILES

1 2 KILOMETERS

EXPLANATION

SOUTHWEST

RIDGE

sac13–0507_Figure 12

Unconsolidated deposits—

Correlation and description of map units

Quaternary–

Tertiary

Consolidated rocks—

Fault—Dashed where approximately 

 located; queried where uncertain;

 dotted where concealed

Volcanic 

Igneous and metamorphic

Alluvium Playa

?

NORTHWEST RIDGE

Garlic

Spring

{

{

{

Tertiary

pre-Tertiary

Extent of model layer 1

Simulated difference in hydraulic head—

 October 2010 conditions minus 

 October 2060 conditions, in feet.

 All contour values are negative

 and indicates simulated hydraulic

 head has increased between

 2010 and 2060

Road

Infiltration pond

Athletic field

5G2 Well and number—

Boundary of aquifer

 system (approximate)

Drainage basin

 boundary

–30

–35 –25

–25

–15

–5

–40

–20

–10 0
26 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

LANGFORD

BASIN

IRWIN

BASIN

BICYCLE

BASIN

Beacon

Hill

GARLIC SPRING FAULT

Geology by J.C. Yount, E.R. Schermer, T.J. Felger, D.M. Miller, and K.A. Stephens, 1994

Aquifer system boundary modified from Wilson F. So and Assoc., 1989

?

BICYCLE FAULT

?

–65

–65

–60

–55

–50

–45

–40

–30

–30

–35

–70

–20

–15

–25

–10

–75

–25

4D2,3 4B3

5G2 4G1

4K1

4K4

4Q2

32F2,3 32H1 33E3

32M1

32K4,6

32P4,6

10D1

10Z1

32B3

1

Barstow Rd

Irwin Rd

N. Loop Rd

S. Loop Rd

Langford Lake Rd

31

35°17’

35°13’

116°43’ 116°39'

6

36 T 14 N

T 13 N

R 2 E R 3 E

0

0 1 2 MILES

1 2 KILOMETERS

EXPLANATION

SOUTHWEST

RIDGE

sac13-0507_Figure 13

Unconsolidated deposits—

Correlation and description of map units

QuaternaryTertiary

Consolidated rocks—

Fault—Dashed where approximately 

 located; queried where uncertain;

 dotted where concealed

Volcanic 

Igneous and metamorphic

Alluvium Playa

?

NORTHWEST RIDGE

Garlic

Spring

{

{

{

Tertiary

pre-Tertiary

Extent of model layer 1

Simulated difference in hydraulic head—

 October 2010 conditions minus 

 October 2060 conditions, in feet.

 All contour values are negative

 and indicates simulated hydraulic

 head has increased between

 2010 and 2060

–50

Road

Infiltration pond

Athletic field

5G2 Well and number—

Boundary of aquifer

 system (approximate)

Drainage basin

 boundary

Figure 13. Simulated difference in hydraulic head from October 2010 conditions to October 2060 conditions, scenario 3, layer 1, Irwin 

Basin, Fort Irwin National Training Center, California.
Simulated Effects of Future Withdrawals and Artificial Recharge 27

LANGFORD

BASIN

IRWIN

BASIN

BICYCLE

BASIN

Beacon

Hill

GARLIC SPRING FAULT

Geology by J.C. Yount, E.R. Schermer, T.J. Felger, D.M. Miller, and K.A. Stephens, 1994

Aquifer system boundary modified from Wilson F. So and Assoc., 1989

?

BICYCLE FAULT

?

–45

–40

–35

–30

–25

–20

–15

–50

–5

–10

–10

4D2,3 4B3

5G2 4G1

4K1

4K4

4Q2

32F2,3 32H1 33E3

32M1 32K4,6

32P4,6

10D1

10Z1

32B3

1

Barstow Rd

Irwin Rd

N. Loop Rd

S. Loop Rd

Langford Lake Rd

Road

31

35°17’

35°13’

116°43’ 116°39'

6

36 T 14 N

T 13 N

R 2 E R 3 E

0

0 1 2 MILES

1 2 KILOMETERS

EXPLANATION

SOUTHWEST

RIDGE

sac13-0507_Figure 14

Unconsolidated deposits—

Correlation and description of map units

QuaternaryTertiary

Consolidated rocks—

Fault—Dashed where approximately 

 located; queried where uncertain;

 dotted where concealed

Volcanic 

Igneous and metamorphic

Alluvium Playa

?

NORTHWEST RIDGE

Garlic

Spring

{

{

{

Tertiary

pre-Tertiary

Extent of model layer 1

Simulated difference in hydraulic head—

 October 2010 conditions minus 

 October 2060 conditions, in feet.

 All contour values are negative

 and indicates simulated hydraulic

 head has increased between

 2010 and 2060

Infiltration pond

Athletic field

5G2 Well and number—

–35

Boundary of aquifer

 system (approximate)

Drainage basin

 boundary

Figure 14. Simulated difference in hydraulic head from October 2010 conditions to October 2060 conditions, scenario 4, layer 1, Irwin 

Basin, Fort Irwin National Training Center, California.
28 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

Figure 15. Hydrographs of simulated hydraulic heads at 14 wells for four scenarios, Irwin Basin, Fort Irwin National Training Center, 

California.

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

Figure 15 Hydrographs of simulated and measured water levels at 14 wells for four scenarios, Irwin Basin,

Fort Irwin National Training Center, California. (Well location shown in figure 11) 

2010 2020 2030 2040 2050 2060 2010 2020 2030 2040 2050 2060

2010 2020 2030 2040 2050 2060 2010 2020 2030 2040 2050 2060

2010 2020 2030 2040 2050 2060 2010 2020 2030 2040 2050 2060

2010 2020 2030 2040 2050 2060 2010 2020 2030 2040 2050 2060

4D3 4G1

4K1 4K4

4Q2 5G2

10D1 32B3

EXPLANATION

Water-level altitude, in feet above NAVD 88

Year Year

Simulated water level 

Altitude of land surface Scenario 1

Scenario 2

Scenario 3

Scenario 4
Simulated Effects of Future Withdrawals and Artificial Recharge 29

Figure 15. —Continued

2010 2020 2030 2040 2050 2060 2010 2020 2030 2040 2050 2060

2010 2020 2030 2040 2050 2060 2010 2020 2030 2040 2050 2060

2010 2020 2030 2040 2050 2060 2010 2020 2030 2040 2050 2060

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

2,240

2,300

2,360

2,420

2,480

2,540

2,600

Figure 15-Cont. Hydrographs of simulated and measured water levels at 14 wells for four scenarios,

Irwin Basin, Fort Irwin National Training Center, California. (Well location shown in figure 11) 

32F3 32H1

32K6 32M1

32P6 33F3

EXPLANATION

Water-level altitude, in feet above NAVD 88

Year Year

Simulated water level 

Altitude of land surface Scenario 1

Scenario 2

Scenario 3

Scenario 4
30 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California Table 5. Simulated hydraulic head at 14 wells for four model scenarios, Irwin Basin, Fort Irwin National Training Center, California. [Location of wells shown in figure 12. NOTE: Negative values for the difference in hydraulic head (between October 2010 and October 2060) reflect an increase in head. Abbreviation: NAVD 88, vertical coordinate information is referenced to the North American Datum of 1988; —, not applicable] State well number Local well name Altitude of land surface (NAVD 88) (feet) Row Column October 2010 simulated hydraulic head (NAVD 88) (feet) Scenario 1, October 2060 simulated hydraulic head (NAVD 88) (feet) Scenario 1, difference between October 2010 and October 2060 simulated hydraulic head (feet) Scenario 2, October 2060 simulated hydraulic head (NAVD 88) (feet) Scenario 2, difference between October 2010 and October 2060 simulated hydraulic head (feet) Scenario 3, October 2060 simulated hydraulic head (NAVD 88) (feet) Scenario 3, difference between October 2010 and October 2060 simulated hydraulic head (feet) Scenario 4, October 2060 simulated hydraulic head (NAVD 88) (feet) Scenario 4, difference between October 2010 and October 2060 simulated hydraulic head (feet) 13N/3E-4D3 WC2-170 2,419.85 56 46 2,307.3 2,359.8 –52 2,335.4 –28 2,368.4 –61 2,349.5 –42 13N/3E-4G1 STP1 2,385.63 60 50 2,315.6 2,359.4 –44 2,334.1 –18 2,365.3 –50 2,347.4 –32 13N/3E-4K1 STP4 2,375.28 62 52 2,319.9 2,358.6 –39 2,333.2 –13 2,363.0 –43 2,346.2 –26 13N/3E-4K4 NIT2-135 2,385.00 63 50 2,318.1 2,358.8 –41 2,333.4 –15 2,363.6 –46 2,346.4 –28 13N/3E-4Q2 NIT1 2,385.00 65 50 2,319.1 2,358.2 –39 2,332.9 –14 2,362.6 –43 2,345.7 –27 13N/3E-5G2 I-9 2,460.00 60 41 2,308.3 2,361.8 –53 2,335.1 –27 2,370.5 –62 2,349.7 –41 13N/3E-10D1 STP6 2,344.85 68 57 2,321.4 2,346.0 –25 2,323.4 –2 2,346.4 –25 2,334.1 –13 14N/3E-32B3 NH1-300 2,530.00 45 39 2,304.6 2,360.6 –56 2,337.4 –33 2,370.6 –66 2,351.7 –47 14N/3E-32F3 BASEBALL-290 2,530.00 49 37 2,307.1 2,362.4 –55 2,339.0 –32 2,372.2 –65 2,353.3 –46 14N/3E-32H1 I-7 2,461.00 49 43 2,303.9 2,354.3 –50 2,332.4 –28 2,365.9 –62 2,348.2 –44 14N/3E-32K6 FI1-230 2,472.43 53 41 2,306.7 2,361.3 –55 2,337.3 –31 2,370.8 –64 2,351.7 –45 14N/3E-32M1 I-2A 2,550.00 52 35 2,309.3 2,364.3 –55 2,340.6 –31 2,373.9 –65 2,354.7 –45 14N/3E-32P6 SOCFLD-270 2,517.00 55 37 2,309.1 2,363.7 –55 2,339.6 –31 2,373.1 –64 2,353.7 –45 14N/3E-33E3 PICNIC-175 2,425.00 49 46 2,304.0 2,358.9 –55 2,335.1 –31 2,368.0 –64 2,349.3 –45 Minimum hydraulic head increase in the south eastern area of model

—

—

—

—

— 10

— less than 5

— 10

— 5

Maximum hydraulic head 

increase in area underlying the base housing

—

—

—

—

— 55

— 31

— 65

— 45
Simulated Effects of Future Withdrawals and Artificial Recharge 31

Table 6. Summary of simulated groundwater discharge to drains, 

Irwin Basin, Fort Irwin National Training Center, California.

[Values in acre-feet.]

Year Scenario 1 Scenario 3

2011–27 0 0

2028 0 1

2029 0 3

2030 0 5

2031 1 8

2032 2 11

2033 3 14

2034 6 19

2035 8 23

2036 10 26

2037 12 32

2038 15 39

2039 19 45

2040 22 51

2041 24 60

2042 28 78

2043 32 96

2044 37 115

2045 41 134

2046 46 153

2047 50 171

2048 56 189

2049 68 207

2050 82 225

2051 94 242

2052 107 259

2053 120 281

2054 133 304

2055 145 327

2056 157 350

2057 169 373

2058 181 394

2059 193 414

2060 205 432

Scenario 2

Scenario 2 simulates the monthly groundwater withdrawals that were calculated for scenario 1 distributed initially 

between two production wells and additional withdrawals later 

from a third production well. The total volume of simulated 

groundwater withdrawals was about 28,350 acre-ft in scenario 2. Discharge to the wastewater treatment plant used to 

calculate recharge is estimated to decrease from 2010 values, 

in 4 phases. The results from the scenario 2 simulation show 

the least rise in groundwater levels in the Irwin Basin of the 

four scenarios. Groundwater levels rise about 30 ft near the 

base housing to less than 5 ft in the unnamed wash exiting 

Irwin Basin near well 13N/3E-10Z1S (fig. 12 and table 5). 

Groundwater levels remain below land surface throughout 

Irwin Basin (fig. 15).

Scenario 3

Scenario 3 simulated a reduction of 3 percent per year in 

2010 withdrawals from 2011 to 2020 and then held withdrawals at a constant rate (30 percent less than in 2010) from 2021 

to 2060. The total volume of simulated groundwater withdrawals was reduced from about 26,800 acre-ft in scenario 1 to 

about 18,760 acre-ft in scenario 3. The reduced recharge rate 

simulated in scenario 1 was used in scenario 3. The simulated 

reduction in groundwater withdrawals and recharge rate at the 

wastewater treatment facility resulted in a rise in groundwater 

levels throughout the Irwin Basin. Groundwater levels rise 

65 ft in the area underlying the base housing in the northwestern part of the basin and by 10 ft in the unnamed wash 

near 13N/3E-10Z1 (fig. 13 and table 5). The results from this 

scenario show the greatest rise in groundwater levels in the 

Irwin Basin of the 4 scenarios. Analysis of simulation results 

indicate groundwater levels will rise to land surface around the 

golf course pond, duck ponds and well 13N/3E-10D1 (fig. 15). 

Groundwater discharge to the drains, simulated around the 

golf course pond, duck ponds and an unnamed wash near 

well 13N/3E-10D1, ranges from 1 acre-ft/year in 2028 to 

432 acre-ft/year by 2060 (table 6).

Scenario 4

Scenario 4 simulated a reduction of 3 percent per year 

in 2010 withdrawals from 2011 to 2020 distributed among 

2 wells, and then a constant rate of withdrawal from 2021 

to 2060. Beginning in 2016, an additional withdrawal of 

31 acre-ft/yr is simulated from an inactive production well 

14N/3E-32M1. The total volume of simulated groundwater 

withdrawals was about 20,300 acre-ft in scenario 4. The 

reduced recharge rate simulated in scenario 2 was used in 

scenario 4. Analysis of results from this simulation indicate 

groundwater levels rise by 45 ft near the base housing to less 

than 5 ft in the unnamed wash near 13N/3E-10Z1 (fig. 14). 

Groundwater levels remain below land surface in the Irwin 

Basin (fig. 15 and table 5). There is no simulated groundwater 

discharge to the drains.

Model Limitations

A numerical model is useful for testing and refining a 

conceptual model of a groundwater flow system, developing 

an understanding of the system, guiding data collection, and 

projecting aquifer responses to changes in aquifer stresses 

within specified limits. However, a model can only approximate the actual system and is based on simplified assumptions and estimated conditions. Thus, the results of model 

simulations are only as accurate as the input data and assumed 

boundary conditions used to constrain the simulations.
32 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

As designed and calibrated, the groundwater-flow model 

of the Irwin Basin is best used for analyzing basin-wide issues 

of water use and supply. The model is particularly useful for 

estimating changes in groundwater levels and flows in the 

Irwin Basin and flows in response to groundwater withdrawal 

and artificial recharge. Simulated water levels at locations 

adjacent to active production wells may not accurately reflect 

water levels at these locations because simulated water levels 

are averaged over each model cell and reflect general trends in 

water levels across a broad area. 

Because the model was used to test different quantities 

and distributions of artificial recharge, the artificial recharge 

estimates were as representative as possible considering 

the data limitations. The original model estimated artificial 

recharge from pumpage data because historical records on the 

quantities of water used for irrigation and discharged from the 

wastewater-treatment facility either were not available or may 

be inaccurate. For the model scenarios, artificial recharge at 

the wastewater-treatment facility ponds was estimated from 

2010 metered data of the quantity of wastewater processed 

at the wastewater-treatment facility. Estimating artificial 

recharge in the ponds from the quantity of water processed at 

the wastewater-treatment facility may be an improvement, but 

more accurate estimates of artificial recharge quantities and 

distribution could be used to update and verify the model as 

they become available. More accurate estimates of artificial 

recharge from irrigation could be derived if the quantity of 

water used for irrigation was metered.

Summary and Conclusions

Fort Irwin National Training Center presently (2012) 

obtains its potable water supply by pumping from wells in the 

Irwin, Bicycle, and Langford Basins. Groundwater development began in the Irwin Basin in 1941. Pumping from the 

Bicycle and Langford Basins began in 1967 and 1992, respectively; pumping from these basins has resulted in a decrease in 

the groundwater demand from the Irwin Basin. Groundwater 

from Bicycle and Langford basins is imported into the Irwin 

Basin. Some water is used for irrigation at the base housing; 

the water that is not consumed is treated at the wastewatertreatment facility and discharged to infiltration ponds. Estimated groundwater recharge has exceeded groundwater 

withdrawals in the Irwin Basin since 1967, except for the 

years 1984 and 1986–91. From 1967, about 33,980 acre-ft 

was withdrawn from the groundwater-flow system within 

the Irwin Basin and an estimated 50,600 acre-ft recharged 

the basin, resulting in a net gain of 16,620 acre-ft of water to 

the groundwater-flow system. Reduced pumping in the Irwin 

Basin, recharge from irrigation at the base housing, and artificial recharge from treated wastewater at the infiltration ponds 

has caused water levels to stabilize or rise throughout most of 

the Irwin Basin.

An existing groundwater-flow model of the aquifer 

system in the Irwin Basin (Densmore, 2003) was updated 

and used to simulate flow under four alternative withdrawal 

and recharge conditions, here called scenarios. The updated 

groundwater-flow model is a useful tool to help estimate 

the long-term availability of groundwater from the basin by 

evaluating differences in groundwater-level altitudes (or water 

levels) among scenarios simulating different withdrawal and 

recharge rates. The updated model was used to evaluate the 

potential spatial effects on groundwater levels as a consequence of 1) continued withdrawals at the 2010 average rate of 

pumping, 2) supplementing water-supply needs with withdrawals from an inactive production well, and, 3) a reduction 

in groundwater recharge from treated wastewater. The 

four scenarios simulate conditions from January 2011 to 

December 2060. Scenario 1 simulates the 2010 annual rate 

of withdrawals (536 acre-ft/yr) from a production well in the 

Irwin Basin and remains constant from 2011 to 2060. The estimated quantity of treated wastewater discharged to the infiltration ponds near the wastewater-treatment facility for 2011 

through 2060 was reduced from the 2010 values in scenario 

1. Scenario 2 simulates the 2010 annual rate of withdrawals 

(536 acre-ft/yr) from two production wells in the Irwin Basin 

until 2060 and additional withdrawals of 31 acre-ft/yr from 

an inactive well. Discharge to the wastewater treatment plant 

used to calculate recharge is estimated to decrease from 

2010 values, in 4 phases in scenario 2. Scenario 3 simulated 

a reduction of 3 percent per year in 2010 withdrawals from 

2011 to 2020 and then held withdrawals at a constant rate 

(30 percent less than in 2010) from 2021 to 2060. Scenario 

3 uses the same recharge rate simulated in scenario 1. Scenario 4 simulated a reduction of 3 percent per year in 2010 

withdrawals from 2011 to 2020 distributed among two wells, 

and then a constant rate of withdrawal from 2021 to 2060. 

Beginning in 2016, an additional withdrawal of 31 acre-ft/yr 

is simulated from an inactive production well. The reduced 

recharge rate simulated in scenario 2 was used in scenario 4. 

Analysis of the results from scenario 1 and 3 indicate 

groundwater levels rise throughout Irwin Basin. These 

increases were as much as 65 ft in the area underlying the 

base housing in the northwestern part of the basin and 10 ft 

in the southeastern area near the unnamed wash exiting the 

basin. The rise in water levels in the northwestern part of the 

basin is a result of continued recharge from irrigation at the 

base housing. Water levels rise to land surface around the golf 

course pond, duck ponds and in the southeastern area near the 

unnamed wash exiting the basin. Groundwater discharge to the 

drains, simulated around the golf course pond, duck ponds and 

the unnamed wash, ranges from 1 to 432 acre-ft/year by 2060. 

The results from the scenario 2 and 4 simulations show 

the least rise in groundwater levels in the Irwin Basin of the 

four scenarios. These increases were as much as 45 ft in the 

area underlying the base housing in the northwestern part of 

the basin and 5 ft in the southeastern area near the unnamed 

wash exiting the basin. Groundwater levels remain below land 

surface throughout the Irwin Basin in scenarios 2 and 4.
References Cited 33

References Cited

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A program in the Office of Water Use Efficiency, California, 

Department of Water Resources that manages a network 

of automated weather stations in California: Sacramento, 

Calif., Department of Water Resources, Office of Water Use 

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Densmore, J.N., 2003, Simulation of groundwater-flow in the 

Irwin Basin aquifer system, Fort Irwin National Training 

Center, California: U.S. Geological Survey Water-Resources 

Investigations Report 02–4264, 69 p. 

Densmore, J.N., and Londquist, C.J., 1997, Groundwater 

hydrology and water quality of Irwin Basin at Fort Irwin 

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EarthInfo, Inc., 1995, National Climatic Data Center summary 

of the day—West 1994: Boulder, Colo., EarthInfo, Inc., CDROM.

EarthInfo, Inc., 2000, EarthInfo CD2 reference manual—for 

all EarthInfo CD-ROM databases: Boulder, Colo., EarthInfo, Inc., CD-ROM.

Hsieh, P.A., and Freckleton, J.R., 1993, Documentation of a 

computer program to simulate horizontal-flow barriers using 

the U.S. Geological Survey modular three-dimensional 

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Harbaugh, A.W., 2005, MODFLOW-2005, the U.S. Geological Survey modular ground-water model—the GroundWater Flow Process: U.S. Geological Survey Techniques 

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Konikow, L.F., Hornberger, G.Z., Halford, K.J., and Hanson, 

R.T., 2009, Revised multi-node well (MNW2) package for 

MODFLOW ground-water flow model: U.S. Geological 

Survey Techniques and Methods 6-A30, 67 p.

McDonald, M.G., and Harbaugh, A.W., 1988, A modular 

three-dimensional finite difference groundwater flow model: 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 6, chap. Al, 586 p.

National Oceanic and Atmospheric Administration, 1994, 

Climatological data, annual summary, California, 1994: 

Asheville, N.C., National Oceanic and Atmospheric Administration, v. 98, no. 13.

Wilson F. So and Associates, Inc., 1989, U.S. Army National 

Training Center at Fort Irwin, California, Water Basin 

Development Plan, Final Report, June 1989: 85 p.

Wilson, J.D., and Naff, R.L., 2004, The U.S. Geological Survey modular ground-water model—GMG linear equation 

solver package documentation: U.S. Geological Survey 

Open-File Report 2004–1261, 47 p.

Yount, J.C., Schermer, E.R., Felger, T.J., Miller, D.M., and 

Stephens, K.A., 1994, Preliminary geologic map of Fort 

Irwin Basin, north-central Mojave Desert, California: U.S. 

Geological Survey Open-File Report 94–173, 27 p.
34 Analysis of Potential Water-Supply Management Options, 2010–60, Irwin Basin Aquifer System, California

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Voronin and Others—Analysis of Potential Water-Supply Management Options, 2010–60, and Documentation of Revisions to the Model of the 

Irwin Basin Aquifer System, Fort Irwin National Training Center, California—Scientific Investigations Report 2014–5081

ISSN 2328-0328

http://dx.doi.org/10.3133/SIR20145081