Storage,

 and Recovery of Freshwater in

Prepared in cooperation with the and

 the 

U.S. Geological Survey 

Report 03-4061 

 Analysis of Tests of Subsurface Injection,

 Lancaster, Antelope Valley, California 

 Los Angeles County Department of Public Works 

Antelope Valley-East Kern Water Agency 

Water-Resources Investigations 
Analysis of Tests of Subsurface Injection, 

Storage, and Recovery of Freshwater in 

Lancaster, Antelope Valley, California

By Steven P. Phillips, Carl S. Carlson, Loren F. Metzger, James F. Howle, Devin L. 

Galloway, Michelle Sneed, Marti E. Ikehara, Kenneth W. Hudnut, and Nancy E. King

Prepared in cooperation with the

LOS ANGELES COUNTY DEPARTMENT OF PUBLIC WORKS 

ANTELOPE VALLEY–EAST KERN WATER AGENCY

Sacramento, California

2003

Water-Resources Investigations Report 03-4061

U.S. GEOLOGICAL SURVEY 7212-55
For additional information write to:

District Chief

U.S. Geological Survey

Placer Hall—Suite 2012

6000 J Street

Sacramento, CA 95819-6129

http://ca.water.usgs.gov

CONTRIBUTING U.S. GEOLOGICAL SURVEY STAFF

Technical Support

Michael R. Carpenter, Hydrologist

Art Clark and Central Region drill crew

Allen H. Christensen, Hydrologist

Wesley R. Danskin, Research Hydrologist

John R. Freckleton, Hydrologist

A. Scott Lewis, Hydrologic Technician

Tracy Nishikawa, Research Hydrologist

Donald R. Pool, Hydrologist

Diane L. Rewis, Hydrologist

Eric G. Reichard, Research Hydrologist

Francis S. Riley, Hydrologist

Editorial, Graphical and Text Preparation Team

Susan G. Davis, Production Editor

Myrna DeBortoli, Technical Editor

Mary Gibson, Editorial Assistant

David Uyematsu, Scientific Illustrator

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director
Contents iii

CONTENTS

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

Introduction ......................................................................................................................................................... 2

Description of Study Area .......................................................................................................................... 4

Acknowledgments ...................................................................................................................................... 5

Geohydrologic Framework ................................................................................................................................. 6

Stratigraphy ................................................................................................................................................ 6

Conceptual Layering of Aquifer System .................................................................................................... 8

Ground-Water Movement .......................................................................................................................... 10

Land Subsidence ........................................................................................................................................ 11

Tests of Freshwater Injection .............................................................................................................................. 13

Preliminary Tests, 1994 ............................................................................................................................. 13

Pilot Tests, 1996–98 ................................................................................................................................... 18

Site Description ................................................................................................................................. 18

Test Procedure ................................................................................................................................... 18

Monitoring of Hydraulic Response ................................................................................................... 22

Historical Water Levels ........................................................................................................... 22

Water-Level Network and Conditions Prior to Injection Testing ............................................ 22

Water-Level Network Response to Injection Cycles ............................................................... 24

Water-Level Response Determined from Gravimetric Response ............................................ 31

Monitoring of Subsidence-Related Effects ....................................................................................... 33

Borehole Extensometers .......................................................................................................... 33

Continuous GPS ....................................................................................................................... 33

Spirit Leveling ......................................................................................................................... 37

Tiltmeters ................................................................................................................................. 37

Monitoring of Water Chemistry ........................................................................................................ 37

Analysis of Injection Test Results ....................................................................................................................... 46

Hydraulic Properties ................................................................................................................................... 46

Aquifer-System Deformation and Subsidence-Related Properties ............................................................ 46

Uplift of Land Surface During Injection ........................................................................................... 46

Estimation of Subsidence-Related Storage Properties at the Extensometer Site .............................. 48

Areal Distribution of Subsidence-Related Storage Properties .......................................................... 50

Chemical Response .................................................................................................................................... 54

Potential for Mineral Precipitation .................................................................................................... 54

Recovery of Injected Water .............................................................................................................. 54

Effects of Injection on Ground-Water Chemistry ............................................................................. 55

Development of a Numerical Model of Ground-Water Flow in the Lancaster Area .......................................... 56

Model Grid and Boundary Conditions ....................................................................................................... 57

Initial Conditions and Temporal Discretization ......................................................................................... 62

Hydraulic Properties of the Aquifer System .............................................................................................. 62

Recharge and Discharge ............................................................................................................................. 64

Natural Recharge ............................................................................................................................... 64

Other Forms of Recharge .................................................................................................................. 66

Ground-Water Extraction .................................................................................................................. 70

Model Calibration and Sensitivity ............................................................................................................. 71

Phase I Calibration ............................................................................................................................ 73

Phase II Calibration ........................................................................................................................... 75
iv Contents

Sensitivity Analysis ........................................................................................................................... 84

Appropriate Use and Improvement of the Ground-Water-Flow Model .................................................... 90

Limitations of Numerical Models ..................................................................................................... 90

Other Factors that Constrain Appropriate Use of the Model ............................................................ 90

Potential Improvements .................................................................................................................... 91

Development of a Simulation/Optimization Model ............................................................................................ 92

Model Objective ......................................................................................................................................... 93

Constraints on Water Supply and Demand ................................................................................................ 93

Imported Water-Supply Constraint ................................................................................................... 93

Ground-Water-Supply Constraints ................................................................................................... 94

Ground-Water Demand Constraint ................................................................................................... 97

Constraints on Hydraulic Head .................................................................................................................. 98

Model Components and Conversion to Uniform Grid ............................................................................... 100

Nonlinear Effects ....................................................................................................................................... 101

Preliminary Simulation/Optimization (LANOPT) Model Results ............................................................ 102

Comparison of Simulation/Optimization (LANOPT) Model Results for Scenarios ........................ 103

Sensitivity Analysis of Simulation/Optimization (LANOPT) Model ............................................... 113

Appropriate Use and Improvement of the Simulation/Optimization (LANOPT) Model .......................... 114

Assumptions Made during Model Development .............................................................................. 114

Limitations Associated with the Software ........................................................................................ 115

Potential Improvements .................................................................................................................... 117

Summary And Conclusions ................................................................................................................................. 118

References Cited ................................................................................................................................................. 119
Figures v

FIGURES

Figure 1. Map showing generalized surficial geology and location of study area and model area 

in Antelope Valley, California .......................................................................................................... 3

Figure 2. Graph showing population of Lancaster and Palmdale, Antelope Valley, California,

1970 to 1999 ...................................................................................................................................... 5

Figure 3. Conceptual geologic cross section showing generalized alluvial fan lithology above the 

lacustrine unit, Antelope Valley, California ..................................................................................... 7

Figure 4. Cross section showing delineation of aquifers and lacustrine unit, Antelope Valley, California .... 9

Figure 5. Graph showing velocity log, during extraction, for Los Angeles County Department of 

Public Works (LACDPW) well 4-32 (7N/12W-27P2), Antelope Valley, California ....................... 10

Figure 6. Map showing ground-water-level contours based on data from wells perforated in the 

upper or upper and middle aquifers, April 1996, Lancaster, Antelope Valley, California................ 11

Figure 7. Map showing land subsidence (1930–92) determined from leveling and Global Positioning 

System surveys (Ikehara and Phillips, 1994) and from interferometric synthetic aperture radar 

(InSAR) from October 1993 to December 1995, in Lancaster, Antelope Valley, California ........... 12

Figure 8. Map showing location of injection and extensometer sites, Lancaster, Antelope Valley, 

California .......................................................................................................................................... 17

Figure 9. Diagram and map of injection site showing location of piezometers 7N/12W-27P5–P8 and 

Los Angeles County Department of Public Works (LACDPW) production wells 

7N/12W-27P2–P3, Lancaster, Antelope Valley, California ............................................................. 19

Figure 10. Diagram and map of injection site showing location of piezometers 7N/12W-27F5–F8, 

extensometers 7N/12W-27F9–F10, and Los Angeles County Department of Public Works 

(LACDPW) production wells 7N/12W-27F2–F3, Lancaster, Antelope Valley, California ............. 20

Figure 11. Graph showing time line of activities associated with injection cycles 1–3 at Lancaster, 

Antelope Valley, California............................................................................................................... 21

Figure 12. Graphs showing injection and extraction flow rates for wells 7N/12W-27P2 and -27P3 in 

Lancaster, Antelope Valley, California, 1996–98 ............................................................................. 23

Figure 13. Hydrograph showing periodic measurements in the injection wells (7N/12W-27P and 27P3) in

Lancaster, Antelope Valley, California, March 1996 through June 1997 ........................................ 24

Figure 14. Hydrograph showing historical water levels in or near Lancaster and Palmdale, 

Antelope Valley, California, 1948–99 .............................................................................................. 25

Figure 15. Map showing locations of nested piezometers and current or former extraction wells used in 

the ground-water-level monitoring network, Lancaster, Antelope Valley, California ..................... 26

Figure 16. Map showing water levels and approximate water-level contours near injection site, before 

injection cycle 2, Lancaster, Antelope Valley, California, November 1996 .................................... 27

Figure 17. Hydrographs showing piezometers and wells closest to injection wells in Lancaster, 

Antelope Valley, California .............................................................................................................. 28

Figure 18. Hydrograph showing variability in water-level response to injection cycle 2, Lancaster, 

Antelope Valley, California .............................................................................................................. 31

Figure 19. Hydrographs showing water levels for the upper, middle, and deep aquifers at the injection 

and extensometer sites during injection cycle 3, Lancaster, Antelope Valley, California ............... 32

Figure 20. Map showing locations of gravity stations, Lancaster, Antelope Valley, California ....................... 34

Figure 21. South–north profile showing change in gravity from pre-injection survey (November 1996) 

to post-injection survey (April 1997) near Lancaster, Antelope Valley, California ......................... 35

Figure 22. Graphs showing aquifer-system deformation and water levels during injection cycles 1–3, 

Lancaster, Antelope Valley, California in (A) the upper aquifer and middle aquifer above the 

lacustrine unit and (B) the lacustrine unit and upper part of the lower aquifer, 1996–98 ................ 36
vi Figures

Figure 23. Graph showing Change in land-surface elevation at the injection site from continuous 

Global Positioning System (GPS) daily solutions for selected periods of injection cycles 1–3, 

Lancaster, Antelope Valley, California ............................................................................................ 38

Figure 24. Map showing locations of bench marks used to monitor changes in land-surface altitude, Lancaster, 

Antelope Valley, California .............................................................................................................. 39

Figure 25. Graph showing change in land-surface altitude of bench marks and gravity stations along the 

south–north survey line, 1995–98, Lancaster, Antelope Valley, California ..................................... 40

Figure 26. Map showing locations of tiltmeters used to monitor land-surface deformation near Lancaster, 

Antelope Valley, California............................................................................................................... 41

Figure 27. Graphs showing magnitude (note variable scale) and direction of tilt recorded during injection 

cycle 2 at tiltmeters 1N, 2N, and 3N, Lancaster, Antelope Valley, California ................................. 42

Figure 28. Piper diagram showing chemical contrast between native ground water and injected water, 

Lancaster, Antelope Valley, California ............................................................................................. 43

Figure 29. Graph showing chloride concentrations in injected and extracted water during injection cycles 1–3, 

Lancaster, Antelope Valley, California ........................................................................................... 45

Figure 30. Graph showing trihalomethane (THM) concentrations in injected and extracted water during 

injection cycles 1–3, Lancaster, Antelope Valley, California ........................................................... 45

Figure 31. Continuous plot from April 1996 to December 1998 of depth to water (stress) versus compaction 

(strain) for (A) the upper and middle aquifers and (B) lacustrine unit plus upper part of lower aquifer, 

Lancaster, Antelope Valley, California ............................................................................................ 49

Figure 32. Borehole geophysical logs, well-construction diagrams, and lithologic logs for nested piezometers 

7N/12W27-F5–F8 at the extensometer site, Lancaster, Antelope Valley, California ...................... 51

Figure 33. Map showing active region of the LAN model grid, Lancaster, Antelope Valley, California ......... 58

Figure 34. Generalized sections A–A ́ from south to north and B–B ́ from northwest to southeast through 

injection site showing delineation of model layers for the Lancaster area (LAN) and regional 

(AV) models, Antelope Valley, California........................................................................................ 59

Figure 35. Map showing lateral boundary conditions for layer 1 of the LAN model and 1996 water-level 

contours (modified from Carlson and others, 1998) used to define no-flow boundaries coincident 

with flowlines or ground-water divides, Lancaster, Antelope Valley, California ............................ 60

Figure 36. Maps showing contours of measured water levels for (A) spring 1983 (used as initial head 

values for both layers of the LAN model) and (B) April 1996 (modified from Carlson and 

others, 1998) in Lancaster, Antelope Valley, California .................................................................. 61

Figure 37. Graph showing estimated historical annual total and agricultural pumpage in the

Antelope Valley 

ground-water basin, California ......................................................................................................... 63

Figure 38. Map showing thickness of model layer 2, Lancaster, Antelope Valley, California ......................... 64

Figure 39. Maps showing distribution and values of hydraulic conductivity in the Lancaster-area (LAN) 

model, Antelope Valley, California. (A) initial values based on regional (AV) model (Leighton 

and Phillips, 2003), and (B) final calibrated values .......................................................................... 65

Figure 40. Map showing distribution and magnitude of recharge in the Lancaster-area (LAN) model, upper 

and middle aquifers only, Antelope Valley, California .................................................................... 67

Figure 41. Graphs showing data and estimates for (A) recharge, (B) pumpage, (C) seasonal distribution of 

pumpage, and (D) a comparison of recharge and pumpage, in the model area, upper and 

middle aquifers only, Lancaster, Antelope Valley, California ......................................................... 69

Figure 42. Map showing locations of production wells included in the Lancaster-area (LAN) model in 

Lancaster, Antelope Valley, California ............................................................................................ 70

Figure 43. Map showing location of wells and piezometers used in model calibration, Lancaster, 

Antelope Valley, California .............................................................................................................. 72
Figures vii

Figure 44. Diagram showing results of phase II calibration procedure for layer-1 hydraulic conductivity 

values (K1), of (A) 12, (B) 15, and (C) 18 ........................................................................................ 76

Figure 45. Diagram showing approximate predicted values of hydraulic conductivity (in foot per 

day) of layer 2 (K2) and effective vertical hydraulic conductivity (KV) compared to those 

determined from the phase II calibration procedure for layer-1 hydraulic conductivity (K1) of 

8 feet per day ..................................................................................................................................... 79

Figure 46. South-to-north profile with gravity-determined water-level changes compared to simulated 

injection mound geometries for a range of hydraulic conductivities, Lancaster, Antelope Valley, 

California .......................................................................................................................................... 80

Figure 47. Contour map based on measured water levels and those simulated using the calibrated LAN 

model, Lancaster, Antelope Valley, California ................................................................................ 81

Figure 48. Hydrographs of wells with long-term records during the calibration period, Lancaster, 

Antelope Valley, California .............................................................................................................. 82

Figure 49. Hydrographs of wells and piezometers with dense data during injections tests, Lancaster, 

Antelope Valley, California .............................................................................................................. 83

Figure 50. Plots showing sensitivity of calibrated hydraulic conductivities and simulated water levels 

near the injection site to changes in model variables, Lancaster, Antelope Valley, California ........ 86

Figure 51. Graphs showing historical deliveries of State Water Project water by the Antelope Valley–East 

Kern Water Agency (AVEK), Lancaster, Antelope Valley, California ........................................... 94

Figure 52. Map showing historical and recent land subsidence, and locations of Los Angeles County 

Department of Public Works (LACDPW) wells, Lancaster, Antelope Valley, California .............. 95

Figure 53. Graphs showing water delivered in Lancaster by the Los Angeles County Department of Public 

Works (LACDPW) and projected ground-water demand used in the simulation/optimization 

model, Lancaster, Antelope Valley, California ................................................................................ 99

Figure 54. Map showing location and dimensions of uniformly spaced model grid used in the 

simulation/optimization model, and simulated and measured water levels for April 1996, 

Lancaster, Antelope Valley, California ............................................................................................ 101

Figure 55. Hydrographs showing variable- versus uniform-grid results, Lancaster, Antelope Valley, 

California .......................................................................................................................................... 102

Figure 56. Graphs showing graphical results from simulation/optimization (LANOPT) model for four 

hypothetical management scenarios, Lancaster, Antelope Valley, California ................................. 104

Figure 57. Graphs showing optimal well capacity used for injection and extraction for three hypothetical 

management scenarios for Lancaster, Antelope Valley, California ................................................. 111

Figure 58. Graph showing optimal volumes of injection and extraction during the management period for

three hypothetical management scenarios, Lancaster, Antelope Valley, California ........................ 112

Figure 59. Graph showing water-table results from linear optimization and the ground-water-flow model 

using optimal injection and pumping rates for scenario 4 (all existing and proposed wells for 

injection during six months of the year), Lancaster, Antelope Valley, California ........................... 116
viii Tables

TABLES

Table 1. Construction and other data for wells used in the study, Antelope Valley, California ..................... 14

Table 2. Range and comparison of hydraulic conductivity values estimated during phase II of the 

model calibration for Lancaster, Antelope Valley, California .......................................................... 78

Table 3. Estimated maximum and long-term capacities of existing and proposed potential injection/extraction 

wells in Lancaster, Antelope Valley, California ............................................................................... 96

Table 4. Summary of simulation/optimization model objective and constraints, Lancaster, Antelope 

Valley, California .............................................................................................................................. 103

Table 5. Results from the simulation/optimization model for four hypothetical management scenarios for 

Lancaster, Antelope Valley, California, for management period 2000–2010 ................................... 108

Table 6. Effect of proposed wells on the objective value (2,083 feet without proposed wells), Lancaster, 

Antelope Valley, California .............................................................................................................. 113

Table 7. Effect of changes in optimization constraints on results from simulation/optimization (LANOPT) 

model of Lancaster, Antelope Valley, California, for management period, 2000–2010 .................. 114
Conversion Factors, Vertical Datum, and Abbreviations ix

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

CONVERSION FACTORS 

Temperature in degrees Celsius (oC) may be converted to degrees Fahrenheit (oF) as follows:

oF=1.8 oC+32.

Temperature in degrees Fahrenheit (oF) may be converted to degrees Celsius (oC) as follows:

oC=(oF-32)/1.8.

Changes in land-surface altitudes from differential-leveling surveys were measured in metric units and 

shown in this report as metric units so that comparisons can be made with Global Positioning System 

(GPS) data shown in this report. Coordinates determined by GPS surveying generally are reported in 

metric units. The industry standard for GPS usage is that field measurements are done in the metric 

system.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25oC).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or 

micrograms per liter (μg/L). 

VERTICAL DATUM

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD 

of 1929)—a geodetic datum derived from a general adjustment of the first-order level nets of both the 

United States and Canada, formerly called Sea Level Datum of 1929.

Multiply By To obtain

acre 0.4047 hectometer

acre-foot (acre-ft) 0.001233 cubic hectometer

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

centimeter (cm) 0.3937 inch

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

foot (ft) 0.3048 meter

foot per day (ft/d) 0.0348 meter per day

foot per second (ft/s) 0.0348 meter per second

foot per day (ft/yr) 0.0348 meter per year

foot per year (ft/yr) 0.3048 meter per year

gallon per minute (gal/min) 0.06309 liter per minute

inch (in.) 25.4 millimeter

inch per year (in./yr) 25.4 millimeter per year

mile (mi) 1.609 kilometer

square miles (mi2) 2.590 square kilometer
x Conversion Factors and Vertical Datum

Abbreviations

AFB Air Force Base

AVEK Antelope Valley–East Kern Water Agency

Br– bromide

CHBr3 bromoform

CHCl3 chloroform

Cl2 chlorine gas

DBP disinfection by-products

DOC dissolved organic carbon

GPS Global Positioning System

HOBr and OBr– hypobromous acid

HOC1 and OC1– hypochlorous acid

InSAR Interferometric Synthetic Aperture Radar

LACDPW Los Angeles County Department of Public Works

LAN ground-water-flow model of the Lancaster area (simulated)

LANOPT simulation/optimization model (modified version of the LAN model)

MODFLOW modular three-dimensional dinite-difference ground-water-flow model

SCAG Southern California Association of Governments

SCIGN Southern California Integrated GPS Network

SWP State Water Project

TDS total dissolved solids

THM trihalomethanes

USGS U.S. Geological Survey

cm centimeter

m meter

mm millimeter

mm/yr millimeter per year

μGal microgal
Well-Numbering System xi

WELL-NUMBERING SYSTEM

Wells are identified and numbered according to their location in the rectangular system for the subdivision of 

public lands. Identification consists of the township number, north or south; the range number, east or west; and the 

section number. Each section is divided into sixteen 40-acre tracts lettered consecutively (except I and O), 

beginning with "A" in the northeast corner of the section and progressing in a sinusoidal manner to "R" in the 

southeast corner. Within the 40-acre tract, wells are sequentially numbered in the order they are inventoried. The 

final letter refers to the base line and meridian. In California, there are three base lines and meridians; Humboldt 

(H), Mount Diablo (M), and San Bernardino (S). All wells in the study area are referenced to the San Bernardino 

base line and meridian (S). Well numbers consist of 15 characters and follow the format 007N012W34B001S. In 

this report, well numbers are abbreviated and written 7N/12W-34B1. Wells in the same township and range are 

referred to only by their section designation, 34B1. The following diagram shows how the number for well 

7N/1W-34B1 is derived.

R13W R12W R11W

Meridian

San Bernardino

T8N

T7N

T6N

RANGE

TOWNSHIP

R1W R1E

27

R12W

T7N

Well-numbering diagram

6 5 4 3 2 1

7

18 13

8 9 10 11 12

17 16 15 14

19 24

30 25

31 36

20 21 22 23

29 28 26

32 33 34 35

SECTION 34

D C A

EFGH

M L K J

N P Q R

B

7N/12W-34B1

R13W R12W R11W

Meridian

San Bernardino

T8N

T7N

T6N

RANGE

TOWNSHIP

R1W R1E

27

R12W

T7N

Well-numbering diagram

6 5 4 3 2 1

7

18 13

8 9 10 11 12

17 16 15 14

19 24

30 25

31 36

20 21 22 23

29 28 26

32 33 34 35

SECTION 34

D C A

EFGH

M L K J

N P Q R

B

7N/12W-34B1
Abstract 1

Analysis of Tests of Subsurface Injection, Storage, and 

Recovery of Freshwater in Lancaster, Antelope Valley, 

California

By Steven P. Phillips, Carl S. Carlson, Loren F. Metzger, James F. Howle, Devin L. Galloway, 

Michelle Sneed, Marti E. Ikehara, Kenneth W. Hudnut, and Nancy E. King

ABSTRACT

Ground-water levels in Lancaster, 

California, declined more than 200 feet during the 

20th century, resulting in reduced ground-water 

supplies and more than 6 feet of land subsidence. 

Facing continuing population growth, water 

managers are seeking solutions to these problems. 

Injection of imported, treated fresh water into the 

aquifer system when it is most available and least 

expensive, for later use during high-demand 

periods, is being evaluated as part of a 

management solution. The U.S. Geological 

Survey, in cooperation with the Los Angeles 

County Department of Public Works and the 

Antelope Valley–East Kern Water Agency, 

monitored a pilot injection program, analyzed the 

hydraulic and subsidence-related effects of 

injection, and developed a simulation/optimization 

model to help evaluate the effectiveness of using 

existing and proposed wells in an injection 

program for halting the decline of ground-water 

levels and avoiding future land subsidence while 

meeting increasing ground-water demand.

A variety of methods were used to measure 

aquifer-system response to injection. Water levels 

were measured continuously in nested (multidepth) piezometers and monitoring wells and 

periodically in other wells that were within several 

miles of the injection site. Microgravity surveys 

were done to estimate changes in the elevation of 

the water table in the absence of wells and to 

estimate specific yield. Aquifer-system 

deformation was measured directly and 

continuously using a dual borehole extensometer 

and indirectly using continuous Global Positioning 

System (GPS), first-order spirit leveling, and an 

array of tiltmeters. The injected water and 

extracted water were sampled periodically and 

analyzed for constituents, including chloride and 

trihalomethanes. Measured injection rates of about 

750 gallons per minute (gal/min) per well at the 

injection site during a 5-month period showed that 

injection at or above the average extraction rates at 

that site (about 800 gal/min) was hydraulically 

feasible.

Analyses of these data took many forms. 

Coupled measurements of gravity and water-level 

change were used to estimate the specific yield 

near the injection wells, which, in turn, was used 

to estimate areal water-table changes from 

distributed measurements of gravity change. 

Values of the skeletal components of aquifersystem storage, which are key subsidence-related 

characteristics of the system, were derived from 

continuous measurements of water levels and 

aquifer-system deformation. A numerical model of 

ground-water flow was developed for the area 

surrounding Lancaster and used to estimate 

horizontal and vertical hydraulic conductivities. A 

chemical mass balance was done to estimate the 

recovery of injected water.
2 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

The ground-water-flow model was used to 

project changes in ground-water levels for 10 

years into the future, assuming no injection, no 

change in pumping distribution, and forecasted 

increases in ground-water demand. Simulated 

ground-water levels decreased throughout the 

Lancaster area, suggesting that land subsidence 

would continue as would the depletion of groundwater supplies and an associated loss of well 

production capacity. A simulation/optimization 

model was developed to help identify optimal 

injection and extraction rates for 16 existing and 

13 proposed wells to avoid future land subsidence 

and to minimize loss of well production capacity 

while meeting increasing ground-water demands. 

Results of model simulations suggest that these 

objectives can be met with phased installation of 

the proposed wells during the 10-year period. 

Water quality was not considered in the 

optimization, but chemical-mass-balance results 

indicate that a sustained injection program likely 

would have residual effects on the chemistry of 

ground water.

INTRODUCTION

Ground water is an important component of the 

water supply in Antelope Valley, California (fig. 1), 

accounting for about 60 percent of the supply in years 

that have normal rainfall and as much as 90 percent in 

times of drought (Templin and others, 1995). 

Lancaster, which had a population of about 126,900 in 

1998, is the largest city in the valley followed closely 

by Palmdale (California Department of Finance, 1999, 

accessed June 1, 2000). Water delivered to Lancaster 

residents and businesses by the Los Angeles County 

Department of Public Works (LACDPW), Waterworks 

and Sewer Maintenance Division, represented about 26 

percent of total water use in Antelope Valley in 1995 

(Leighton and Phillips, 2003), of which about 

50 percent was ground water (Los Angeles County 

Department of Public Works, unpublished data, 1998). 

The remainder of Lancaster’s water supply is imported 

surface water from the State Water Project (SWP) 

treated to drinking-water standards by the Antelope 

Valley–East Kern Water Agency (AVEK). In recent 

years, the SWP generally was the primary source of 

water used in Lancaster (averaged 56 percent from 

1995 to 1999). Use of ground water and water from the 

SWP varied with seasonal demand (Los Angeles 

County Department of Public Works, unpublished data, 

1998).

Ground-water use in Antelope Valley in excess 

of recharge has caused ground-water levels to decline 

about 200 ft in the Lancaster area since the 1920s. 

Water levels presently are at or near historical lows 

(Carlson and others, 1998; Leighton and Phillips, 

2003). Negative consequences of this decline include 

the depletion of ground-water resources, possible 

degradation of ground-water quality, and land 

subsidence. The depletion of ground-water resources, 

which in this case primarily is reflected in the lowering 

of the water table, has resulted in the withdrawal of 

water from older, deeply buried sediment. These 

sediments are less permeable and store less water than 

those already drained; thus, wells that are screened 

only within these older materials generally are less 

productive. Ground water drawn from deeper parts of 

the aquifer system generally is poorer in quality than 

water from the shallower parts. Several of the deeper 

wells in the Lancaster area recently have been shut 

down for exceedences of the current (1999) 

Environmental Protection Agency Maximum 

Contaminant Level for arsenic of 50 μg/L (Mustafa 

Ariki, Los Angeles County Department of Public 

Works, oral commun., 1999).

Measured land subsidence from ground-water 

withdrawal exceeded 6 ft in Lancaster from 1930 to 

1992 (Ikehara and Phillips, 1994), and more recent 

evidence suggests that subsidence continues in this area 

(Galloway and others, 1998a). Negative consequences 

of land subsidence in Antelope Valley and similar areas 

include development of earth fissures; altered drainage 

gradients; increased flooding and erosion; failed well 

casings; structural damage to roads, buildings, 

pipelines, canals, homes, and other structures; and 

liability issues (Kennedy/Jenks Consultants, 1995; 

Prince and others, 1995; Galloway and others, 1999).
Introduction 3

Ground-water subbasin boundary and name

(Bloyd, 1967)

NEENACH

Boron

34°

30'

35°

00'

118° 30' 118° 00'

San Gabriel Mountains

Tehachapi Mountains

Rosamond

Lake (dry) Rogers

Lake (dry)

Redman

Mojave

Desert

Edwards Air Force Base Boundary

Los

Angeles

San

Francisco

0 5 10 15 20 25 Kilometers

0 5 10 15 20 25 Miles

117° 30'

area of

Figure 1

Main

Base

Bedrock

Alluvium

Antelope Valley drainage basin boundary

Antelope Valley ground-water basin boundary

(Carlson and others, 1998)

Playa surface

CALIFORNIA

A A' Cross section

GARLOCK FAULT

SAN ANDREAS FAULT ZONE

138

58

14

Rosamond

California Aque d uct

LOS ANGELES CO

KERN CO

SAN BERNARDINO CO

LOS ANGELES CO

Quartz

Hill

Lancaster

Palmdale

Littlerock

Model area

Study area

Amargosa Creek

B

B'

A'

A BUTTES

PEERLESS

PEARLAND

NEENACH

LANCASTER

FINGER BUTTES

OAK CREEK

WEST ANTELOPE

WILLOW

SPRINGS

GLOSTER

CHAFFE

NORTH MUROC

138

14

Air Force

Plant 42

Holly site

injection

site

Ground-water subbasin boundary and name

(Bloyd, 1967)

NEENACH

Boron

34°

30'

35°

00'

118° 30' 118° 00'

San Gabriel Mountains

Tehachapi Mountains

Rosamond

Lake (dry) Rogers

Lake (dry)

Redman

Mojave

Desert

Edwards Air Force Base Boundary

Los

Angeles

San

Francisco

0 5 10 15 20 25 Kilometers

0 5 10 15 20 25 Miles

117° 30'

area of

Figure 1

Main

Base

Bedrock

Alluvium

Antelope Valley drainage basin boundary

Antelope Valley ground-water basin boundary

(Carlson and others, 1998)

Playa surface

CALIFORNIA

A A' Cross section

GARLOCK FAULT

SAN ANDREAS FAULT ZONE

138

58

14

Rosamond

California Aque d uct

LOS ANGELES CO

KERN CO

SAN BERNARDINO CO

LOS ANGELES CO

Quartz

Hill

Lancaster

Palmdale

Littlerock

Model area

Study area

Amargosa Creek

B

B'

A'

A BUTTES

PEERLESS

PEARLAND

NEENACH

LANCASTER

FINGER BUTTES

OAK CREEK

WEST ANTELOPE

WILLOW

SPRINGS

GLOSTER

CHAFFE

NORTH MUROC

138

14

Air Force

Plant 42

Holly site

injection

site

Figure 1. Generalized surficial geology and location of study area and model area in Antelope Valley, California.

(Modified from Londquist and others, 1993).
4 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Facing future population growth and limited 

options for alternative water sources, water managers 

in Antelope Valley are seeking ways to make the best 

use of currently available resources. Injection of treated 

SWP water into the aquifer system during the winter 

(when it is most available) for later use in the summer 

(the peak demand period) is one potential element of a 

ground-water management plan. The U.S. Geological 

Survey (USGS), in cooperation with the LACDPW and 

AVEK, studied the feasibility of direct well injection 

through existing production wells and developed a 

simulation/optimization model to help evaluate the 

effectiveness of an injection program for halting the 

decline of ground-water levels and avoiding future land 

subsidence while meeting increasing ground-water 

demand.

The role of the USGS in this study was to collect 

and analyze hydraulic and aquifer-system deformation 

data, to develop a simulation/optimization model for 

use in designing and managing a larger scale injection 

program, and to determine the factors controlling the 

formation and fate of trihalomethanes (disinfection byproducts) in the aquifer system. This report describes 

the analysis of hydraulic and deformation data and the 

development of a simulation/optimization model. 

Companion reports describe the data and the methods 

used to collect the data analyzed in this report (Metzger 

and others, 2002); the use of microgravity surveys to 

determine water-level changes (Howle and others, 

2003); and the determination of the formation and fate 

of trihalomethanes (Fram and others, 2003; Fram and 

others, 2002).

This study was a cooperative effort between the 

USGS, LACDPW, and AVEK. The role of the 

LACDPW in this study was to conduct all engineering 

tasks required to convert existing production wells to 

injection/extraction wells; build the extensometer 

shelter; sample and analyze injected and extracted 

water during the injection tests; install tiltmeters and 

analyze resulting data; conduct repeat surveys for an 

extensive network of bench marks; and provide 

information for the simulation/optimization model. The 

role of AVEK in this study was to sample and analyze 

injected and extracted water during the tests, provide 

information for the simulation/optimization model, and 

provide the treated SWP water for the tests (more than 

1,300 acre-ft).

Description of Study Area

Antelope Valley is the wedge-shaped western 

extension of the Mojave Desert, nestled between the 

Tehachapi and the San Gabriel Mountains to the 

northwest and southwest, respectively (fig. 1), and 

separated from the Mojave River Basin to the east by 

low-lying hills. The valley is topographically closed, 

with the valley floor ranging in altitude from about 

3,500 ft adjacent to the foothills to about 2,270 ft at the 

playas. The climate in the valley is semiarid to arid, 

with less than 10 in./yr of rainfall (Rantz, 1969); the 

area has hot summers, cold winters, and high winds. 

Rainfall in Lancaster averaged 8 in./yr from 1974 to 

1998 (Western Regional Climate Center, accessed July 

10, 1999). The populations of Lancaster and Palmdale 

have grown rapidly during the past two decades, from a 

combined population of about 60,000 in 1980 to more 

than 250,000 in 1999 (fig. 2).

The Antelope Valley ground-water basin covers 

an area of about 940 mi2 and is subdivided into seven 

ground-water subbasins (fig. 1). Previous investigators 

have defined the ground-water basin and subbasins 

therein on the basis of geologic, water-level, and other 

evidence of faults that act as partial barriers to groundwater flow (Thayer, 1946; Bloyd, 1967; Durbin, 1978; 

Nishikawa and others, 2001; Leighton and Phillips, 

2003). 

The study area is in the south-central part of the 

Antelope Valley ground-water basin, within the 

Lancaster subbasin (fig. 1). Included in the study area 

are most of the cities of Lancaster and Quartz Hill, and 

the western part of Air Force Plant 42. The aquifer 

system in the study area is characterized as three 

distinct aquifers: upper, middle, and lower (Nishikawa 

and others, 2001; Leighton and Phillips, 2003).

Running from south to north through the study 

area is the ephemeral Amargosa Creek (fig. 1). 

Although flow in this creek is infrequent, flashy, and 

ungaged, it is thought to be the third largest drainage 

from the San Gabriel Mountains within the Antelope 

Valley drainage basin (Durbin, 1978).
Introduction 5

Acknowledgments

The authors gratefully acknowledge the 

contributions of the LACDPW and AVEK toward the 

successful completion of this study. Individuals who 

provided assistance and support for this study include 

Eleni Hailu, Mustafa Ariki, Ramy Gindi, Dean 

Efstathiou, Joe Aja, Dan Jones, Kenneth Rosander, and 

Eugene Betts of the Los Angeles County Department 

of Public Works, and Wallace Spinarski and Russell 

Fuller of the Antelope Valley–East Kern Water Agency.

Field office personnel of the Los Angeles County 

Department of Public Works, Waterworks and Sewer 

and Maintenance Division, Lancaster, constructed a 

building to house the dual extensometer and shelters 

for two sets of nested piezometers, and kept the 

injection cycles running despite the various mechanical 

challenges that arose throughout the study. 

Charles Peer, Gerald Campbell, and surveying 

crew of the Los Angeles County Department of Public 

Works Survey Division, assisted with the establishment 

and repeated surveying of the differential-leveling 

network. Robert Reeder and Darrel Bozarth of the Los 

Angeles County Department of Public Works, Survey 

Division, assisted in locating buried utilities and in 

organizing equipment, materials, and manpower for 

construction of the microgravity and differentialleveling networks.

Robert Larson of the Los Angeles County 

Department of Public Works, Materials Engineering 

Division, installed and operated the tiltmeter network.

Water-chemistry data and information on 

analytical methods were provided by Maureen Smith, 

Antelope Valley–East Kern Water Agency; Wilhelmina 

Solinap, Los Angeles County Department of 

Agricultural Commissioner and Weights and Measures, 

Environmental Toxicology Laboratory; and Ramy 

Gindi, Los Angeles County, Department of Public 

Works, Sewer and Maintenance Division. 

Permission to access privately owned wells to 

measure water levels was provided by American Auto 

Sales Incorporated, the U.S. Department of the Air 

Force and Lockheed-Martin, the El Dorado Mutual 

Water Company, the West Side Park Mutual Water 

Company, and the White Fence Farms Water Company.

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

1970 1975 1980

1983

1985 1990 1995 1999

Palmdale

Lancaster

Year

Population, in thousands

No data

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

1970 1975 1980

1983

1985 1990 1995 1999

Palmdale

Lancaster

Year

Population, in thousands

No data

Figure 2. Population of Lancaster and Palmdale, Antelope Valley, California,1970 to 1999.

(California Department of Finance, accessed 1999. Yearly data plotted as January 1.)
6 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Tracy Nishikawa, Eric Reichard, John 

Freckleton, and Wesley Danskin provided technical 

assistance and constructive reviews of the optimization 

aspects of the modeling effort.

Francis Riley of the U.S. Geological Survey 

helped design the dual extensometer, provided 

guidance during its construction, and helped assemble 

the above-ground instrumentation. Diane Rewis 

assisted in the drilling effort and in establishing an 

electronic water-level monitoring network.

Donald Pool, U.S. Geological Survey, shared 

expertise in designing and implementing the 

microgravity surveys. Michael Carpenter, U.S. 

Geological Survey, provided useful insight regarding 

the performance characteristics of the particular gravity 

meter used in this study. 

Kenneth Hudnut, U.S. Geological Survey, 

contributed the equipment and expertise for installing 

and operating a permanent continuous GPS station at 

the injection site, and processed the early data. Some of 

the GPS data was processed and provided by Jeffrey 

Behr, Southern California Earthquake Center. 

Additional GPS equipment was provided by Wayne 

Vallantine of the California Department of 

Transportation, Division 7. 

Scott Lewis, U.S. Geological Survey, used 

ground-water chemistry data from the first two 

injection tests to estimate the percentage of injected 

water recovered.

GEOHYDROLOGIC FRAMEWORK

The San Gabriel Mountains along the 

southwestern margin of Lancaster subbasin were 

uplifted tectonically along the San Andreas Fault Zone 

about 1 to 2 million years ago and became the primary 

source of the Quaternary-age deposits that make up the 

aquifer system (Dibblee, 1967; Ponti, 1985). The 

Tehachapi Mountains were uplifted simultaneously 

along the Garlock Fault and became a secondary source 

of sediment (Dibblee, 1967). Prior to the uplift of these 

mountains, surface drainage was toward the ocean, and 

erosional degradation (transport of materials from the 

area, resulting in lesser slopes) occurred until drainage 

gradients were relatively small. Significant 

late-Tertiary deposition may have occurred on this 

surface (Reed, 1933; Dutcher and Worts, 1963; 

Dibblee, 1967). Uplift of the San Gabriel Mountains 

and the smaller Tehachapi Mountains, and probable 

downwarping in-between, formed the structurally 

closed Antelope Valley and greatly altered directions 

and patterns of Quaternary deposition in this area.

The rest of this section focuses on the 

Quaternary stratigraphy that forms the primary aquifer, 

the importance of stratigraphy in conceptualization of 

the aquifer system, ground-water movement, and land 

subsidence. More detailed accounts of the regional 

geologic history of Antelope Valley can be found in 

Thayer (1946), Hewett (1954a,b), Dutcher and Worts 

(1963), Dibblee (1967, 1981), Ponti (1985), and 

Londquist and others (1993).

Stratigraphy

About 5,000 to 10,000 ft of deposits of lateTertiary and Quaternary deposits underlie the Lancaster 

area; these deposits are thickest in this part of the 

Lancaster subbasin (Mabey, 1960; Morin and others, 

1990). The Quaternary deposits were formed by 

ephemeral streams emanating from the surrounding 

hills and mountains, depositing eroded material in 

alluvial fans. Modern alluvial fans are present in 

Antelope Valley (Ponti, 1985). If perennial streams 

were present in the geologic past, any fine-grained 

fluvial deposits are buried and not present at the land 

surface.

The existence of sand dunes in some parts of 

Antelope Valley is evidence that wind plays a role in 

the modern depositional environment. Little is known, 

however, about the presence and distribution of the 

older subterranean eolian (wind-laid) deposits.

Given the evidence of modern alluvial deposition 

and the lack of evidence for fluvial or substantial eolian 

deposits, the primary Quaternary depositional 

environment probably was alluvial. Alluvial fans are 

fan-shaped mounds that slope away from the 

mountains, often coalescing with adjacent alluvial fans 

or interfingering with intersecting fans. Alluvial fans 

have three parts: the fanhead at the highest altitude, the 

midfan, and the distal fan at the lowest altitudes 

(Blissenbach, 1954; Reineck and Singh, 1980). The 

texture of the alluvium varies with position on the fan 

as the stream gradient changes (fig. 3). The fanhead is 

characterized as a high-energy environment in which 

large stream gradients favor the transport and 

deposition of coarse-grained materials (gravel, sand), 

whereas the distal fan is characterized as a low-energy 
Geohydrologic Framework 7

environment in which small gradients favor deposition 

of fine-grained materials (silt, clay). Unweathered 

(modern) alluvium ranges from about 4 percent silt and 

clay near the San Gabriel Mountains to 25 to 70 

percent silt and clay in the sandy to silty loam soils 

typical of the more distal areas (Ponti, 1985). Texture 

also varies with depth below land surface and radial 

position on the fans, as rates of tectonic uplift, climatic 

conditions, and stream locations changed with time. 

Changing climatic conditions seem to be responsible 

for about six episodes of rapid alluvial fan aggradation 

(growth) during the upper Quaternary (Ponti, 1985). 

These episodes are marked by relatively rapid 

deposition followed by soil development and varying 

degrees of erosion prior to the next episode of 

deposition. The resulting alluvial strata are texturally 

and geometrically complex.

Interwoven with alluvial strata are lacustrine 

deposits associated with deposition of fine-grained 

materials at the bottom of areally extensive lakes and 

(or) marshes (Dibblee, 1967). These deposits are 

chemically reduced, indicative of a low-oxygen 

environment, and are characteristically grey to bluishor greenish-grey. This is in contrast to the oxidized, 

brownish silty clays that comprise the modern playas 

(for example, Rogers and Rosamond Lakes). The 

primary lacustrine unit, referred to locally and by 

previous investigators (for example, Dutcher and 

Worts, 1963) as the “blue clay,” is present throughout 

most of the Lancaster subbasin; this unit is about 500 to 

750 ft below land surface in the Lancaster area (fig. 3).

The elevation of the lacustrine unit increases to 

the north (fig. 3); the unit crops out west of the 

southern end of Rogers Lake on Edwards Air Force 

Base (AFB) (Nishikawa and others, 2001; Leighton 

and Phillips, 2003). This configuration of the lacustrine 

unit suggests northward migration of the lake or marsh 

with time and accumulation of material eroded from 

the San Gabriel Mountains (Dutcher and Worts, 1963). 

Paleomagnetic analyses of core samples from southern 

Lancaster were used to provide information on the age 

of the lacustrine unit. Core samples from depths of 345 

and 450 ft below land surface show a magnetic reversal 

between these depths (Fram and others, 2002). The 

polarity was normal at a depth of 345 ft, but reversed at 

a depth of 450 ft, which was interpreted as the 

transition from the Brunhes to the Matuyama polarity 

chron. This transition occurred about 780,000 years 

ago; therefore, the lacustrine deposits, at a depth of 

more than 700 ft in the area, are older than that. In 

contrast, the lacustrine deposits on Edwards AFB 

interfinger with alluvial deposits less than 14,000 years 

old (Ponti, 1985).

land surface

Injection site

?

? ?

?

Palmdale

Lancaster

? ?

?

Northern boundary

of model area (fig. 1)

Southern boundary

of model area (fig. 1)

?

Distal fan

South North

Increasing fine-grained alluvial sediments

Possible gap between Lacustrine unit

and bedrock (San Gabriel Mts.)

Lacustrine unit

Fanhead

Midfan San Gabriel Mountains

land surface

Injection site

?

? ?

?

Palmdale

Lancaster

? ?

?

Northern boundary

of model area (fig. 1)

Southern boundary

of model area (fig. 1)

?

Distal fan

South North

Increasing fine-grained alluvial sediments

Possible gap between Lacustrine unit

and bedrock (San Gabriel Mts.)

Lacustrine unit

Fanhead

Midfan San Gabriel Mountains

Figure 3. Generalized alluvial fan lithology above the lacustrine unit, Antelope Valley, California.
8 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Lithologic and geophysical logs of boreholes 

show little evidence of coarse-grained materials within 

the lacustrine unit at Edwards AFB and in the 

Lancaster area; however, lithologic logs for the 

Palmdale area show extensive interfingering of finegrained lacustrine deposits and coarser grained alluvial 

deposits. The nature or presence of the lacustrine 

deposits at the contact between unconsolidated 

deposits and the foot of the San Gabriel Mountains is 

unknown; however, results of a ground-water-flow 

model of Antelope Valley suggest that this confining 

unit abuts the San Gabriel Mountains (Leighton and 

Phillips, 2003).

Many geophysical logs of boreholes in Antelope 

Valley suggest a disconformity between younger 

unconsolidated deposits and older, more compacted 

and indurated (hardened) deposits at an altitude of 

about 1,950 ft (Nishikawa and others, 2001; Leighton 

and Phillips, 2003).

Conceptual Layering of Aquifer System

The conceptual view of the aquifer system in 

Antelope Valley historically included two aquifers: an 

upper unconfined aquifer known locally as the 

“principal” aquifer and a “deep” aquifer overlain and 

confined by the thick, regionally extensive lacustrine 

unit where present (Durbin, 1978). The unconfined 

aquifer beyond the northern extent of the lacustrine unit 

(underlying part of Edwards AFB and northward) also 

was designated as the deep aquifer. Stratigraphic and 

other information collected for this study and other 

recent USGS studies in Antelope Valley (Nishikawa 

and others, 2001; Leighton and Phillips, 2003) has 

been used to change the historical conceptualization 

into three aquifers: upper, middle, and lower (fig. 4). In 

the study area, the lacustrine unit generally occupies 

the lower part of the middle aquifer, acting as a 

significant barrier to vertical flow between the middle 

and lower aquifers. Farther north, the lacustrine unit 

increases in elevation, forming a significant barrier to 

north–south ground-water flow within the middle and 

upper aquifers (fig. 4).

There are two key distinctions between the old 

and new conceptualizations of the aquifer system. The 

first is the recognition that the age of aquifer materials 

is a key factor controlling their hydraulic properties. 

Older materials have longer stress histories 

(compaction is more likely to have occurred) and are 

more likely to have undergone chemical cementation. 

Under the old conceptual model, surficial materials at 

Edwards AFB were considered part of the deep aquifer 

as were materials that started at a depth of about 900 ft 

below land surface in Lancaster. This configuration did 

not account for the differences in the age and depth of 

burial of the aquifer materials or the effects of these 

differences on hydraulic properties. 

The second distinction between these conceptual 

models is a recognition that aquifer properties above 

the lacustrine unit in the study area vary significantly 

with depth. Geophysical evidence of such variations in 

the Lancaster and Edwards AFB areas suggests a 

disconformity (an erosional surface that separates the 

younger strata from parallel, underlying older strata) 

between the younger, unconsolidated deposits and the 

older, more compacted and indurated (hardened) 

deposits at an altitude of about 1,950 ft (Nishikawa and 

others, 2001; Leighton and Phillips, 2003). Other 

evidence includes greater hydraulic responses at depth 

to extraction and injection and results from a velocity 

log of one of the wells (7N/12W-27P2) used in the pilot 

injection tests. The velocity log was generated in 1998 

during extraction using a dye-based method (Izbicki 

and others, 1999) and shows that most of the water 

produced from well 7N/12W-27P2 comes from the 

upper aquifer (fig. 5). The condition of the well screen 

and gravel pack may vary with depth, and thus, could 

have affected these results; however, the well screen 

(282–717 ft) was cleaned periodically during the 

project and inspected using a televiewer.

Aside from the physical evidence of variation in 

aquifer properties with depth, storage properties 

generally change with increasing depth from the water 

table in alluvial aquifers. At the water table, water 

drawn from the aquifer is obtained through drawdown 

of the water table and associated gravity drainage of the 

materials above the new water table. Water drawn at 

depth in an alluvial system cannot be immediately 

drawn from the water table because the vertical flow 

path is partly blocked by numerous overlapping bodies 

of fine-grained deposits. Instead, the immediate 

demand for water is met primarily through compaction 

of these deposits in response to decreased water 

pressure in pore spaces between grains of sediment. 

The storage values at depth, therefore, are much 

smaller than those at the water table.
Geohydrologic Framework 9

1,400

1,600

1,800

2,000

2,200

2,400

2,600

2,800

3,000

1,400

1,600

1,800

2,000

2,200

2,400

2,600

2,800

3,000

B B'

Northwest

South

Southeast

Bedrock

Bedrock

1,400

1,600

1,800

2,000

2,200

2,400

2,600

2,800

3,000

1,400

1,600

1,800

2,000

2,200

2,400

2,600

2,800

3,000

A A'

Land surface

1996 water table

Unsaturated zone

Upper aquifer

Middle aquifer

Land surface

1996 water table

Top of lacustrine unit

North

Unsaturated zone

Upper aquifer

Middle aquifer

Lower aquifer

Lacustrine unit

Boundary of bedrock uncertain

Vertical scale greatly exaggerated 20x.

Datum is sea level

Vertical scale greatly exaggerated 20x.

Datum is sea level

Top of lacustrine unit

Lower aquifer

Lacustrine unit

Boundary between aquifers

(Leighton and Phillips, 2003)

EXPLANATION

0

0

1

1 2 Kilometers

2 Miles

0 1

0 2 Kilometers 1

2 Miles

Injection site

Injection site

Altitude, in feet above sea level

Figure 4. Delineation of aquifers and lacustrine unit, Antelope Valley, California.

Cross-section locations shown in figure 1.
10 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Ground-Water Movement

Ground-water movement in the vicinity of the 

study area prior to significant development of ground 

water in the early 1900s was from the recharge zones 

where streams draining the San Gabriel and the 

Tehachapi Mountains enter the valley toward the playas 

in the northern part of the valley. Most of the discharge 

occurred as evapotranspiration within and surrounding 

these playas (Durbin, 1978; Leighton and Phillips, 

2003). Since the post-World War II agricultural boom, 

ground-water movement has been toward the 

production wells, which is evident in the contour map 

of 1996 water levels in the vicinity of Lancaster and 

Palmdale (fig. 6). Note that ground-water movement 

generally is toward the urban areas of Lancaster and 

Palmdale where ground-water extraction in this part of 

the valley is concentrated.

Vertical ground-water movement in most of the 

Antelope Valley, including the Lancaster area, is poorly 

understood. At two sites in southern Lancaster, the 

measured gradients across the lacustrine unit ranged 

from 0.02 to 0.06 (upward) in April 1996 (relatively 

static conditions) prior to injection activity and from 

0.03 (downward) to 0.06 (upward) in July 1996 

(pumping conditions). These measurements were made 

in proximity to the production wells; it is not known if 

these measurements are representative of undeveloped 

areas.

Pump intake

0 5 10 15 20 25 30

above 360

360–380

380–400

400–420

420–440

440–460

460–480

480–500

500–520

520–540

540–560

560–580

580–600

600–620

620–640

640–660

660–680

680–700

700–717

Depth interval, in feet below land surface

Percent of total flow

middle aquifer

upper aquifer

Figure 5. Velocity log, during extraction, for Los Angeles County Department of Public Works (LACDPW) well 4-32 (7N/12W-27P2), Antelope 

Valley, California.
Geohydrologic Framework 11

Land Subsidence

Global Positioning System (GPS) surveys and 

historical leveling data show that aquifer-system 

compaction from ground-water withdrawal caused 

more than 6 ft of land subsidence in Lancaster from 

about 1930 to 1992 and at least 1 ft of subsidence in an 

area of 290 mi2 in Antelope Valley (Ikehara and 

Phillips, 1994; Galloway and others, 1998b). Galloway 

and others (1998a) used Interferometric Synthetic 

Aperture Radar (InSAR) to measure land subsidence at 

a high spatial resolution from 1993 to 1995; results 

indicated continued subsidence in the Lancaster area 

(fig. 7). 

Negative consequences of land subsidence in 

Antelope Valley include altered drainage gradients; 

increased flooding and erosion; failed well casings; 

structural damage to roads and buildings; and 

development of earth fissures (Kennedy/Jenks 

Consultants, 1995; Prince and others, 1995; Dinehart 

and McPherson, 1998). Earth fissures on Edwards AFB 

have affected landings of space shuttles (Blodgett and 

Williams, 1992; Ward and Jachens, 1993). Fissures 

also have occurred in the eastern and northwestern 

parts of Lancaster (T.L. Holtzer and M.M. Clark, U.S. 

Geological Survey, unpublished data, 1981; Charles 

Swift, Geolabs–Weslake Village, written commun., 

1991).

T6N

T7N

T7N

R13W R13W R12W R12W R11W R11W R10W

8N

EXPLANATION

Study area

Water-level contours—Shows altitude

of water table, April 1996. Contour

interval 25 feet. Datum is sea level

Location of well with water-level data

Direction of ground-water movement

2,150 2,125

2,100

2,0752,050

2,150

2,175

2,225

2,250

2,225

2,200

2,175

2,250

2,225

2,200

2,200

Quartz Hill

Injection

site

Lancaster

Palmdale

12'30" 07'30" 118°02'30"

40'

34°35'00"

34°45'00"

118°17'30"

0

0 5 Kilometers

5 Miles

Cr eek

Amargosa

Figure 6. Ground-water-level contours based on data from wells perforated in the upper or upper and middle aquifers, April 1996, Lancaster, 

Antelope Valley, California.

(Modified from Carlson and others, 1998).
12 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

All parts of an aquifer system are subject to 

compaction with ground-water withdrawal; however, 

the fine-grained deposits, or aquitards, are far more 

susceptible to permanent compaction that results in 

land subsidence than are the coarse-grained deposits.

The principle of effective stress (Terzaghi, 1925) 

describes the relation between changes in hydraulic 

head (expressed as pore pressure, p) and associated 

changes in effective (intergranular) stress (σe):

(1)

where σT is the total stress caused by the overburden 

(weight of rock and water above the point of interest) 

and p is the pore pressure. With ground-water 

withdrawal, pore pressure decreases, effective stress 

increases proportionally, and the aquifer system 

deforms (compacts). For decreases in pore pressure to 

values higher than the previous lowest value (the 

preconsolidation head), deformation is elastic and the 

aquifer system recovers, or expands, when pore 

pressure again increases. If pore pressure decreases to 

below the preconsolidation head, effective stress 

exceeds the historical maximum, and compaction 

results in permanent deformation of the aquifer system.

σe σT = – p

Figure 7. Land subsidence (1930–92) determined from leveling and Global Positioning System surveys (Ikehara and Phillips, 1994) and from 

interferometric synthetic aperture radar (InSAR) from October 1993 to December 1995, in Lancaster, Antelope Valley, California.

Also shown are Los Angeles County Department of Public Works (LACDPW) extraction wells.
Tests of Freshwater Injection 13

Aquifer system deformation is expressed at the land 

surface as land subsidence during compaction and as 

uplift during expansion.

The above is a simplified explanation that does 

not always hold in practice because of the temporal 

aspect of compaction. When pore pressure decreases 

beyond its historical low, it takes time for pore 

pressures in the coarse-grained units and aquitards to 

equilibrate and for the associated compaction of the 

aquitards to take place. The time that this takes is a 

function of the vertical hydraulic conductivity and 

thickness of the aquitard; thin, permeable aquitards 

compact more quickly than thick, low-permeability 

aquitards. Thus, if pore pressure exceeds the 

preconsolidation stress for a relatively short period, the 

preconsolidation stress is not necessarily reset to the 

new low value; pore pressures only slightly below the 

original preconsolidation stress could trigger 

permanent compaction. Sneed and Galloway (2000) 

found that this residual compaction of thicker aquitards 

is a key element of subsidence at Edwards AFB; their 

report provides a more in-depth explanation of 

aquifer-system deformation.

Two conditions clearly need to be met for land 

subsidence to occur: hydraulic head must drop below 

the preconsolidation head, and compressible materials 

must be present. Where land subsidence has occurred 

and water levels have been measured, the 

preconsolidation head is relatively well understood. 

Where land subsidence has not occurred with waterlevel declines, either the preconsolidation head has not 

been exceeded or the materials are relatively 

incompressible. Fine-grained sediment such as silt and 

clay are the primary compressible materials in the 

Antelope Valley. The distribution of these materials and 

their compressibility is not well understood; however, 

the general distribution of fine-grained materials can be 

inferred from typical alluvial-fan stratigraphy (fig. 3). 

Accordingly, the aquifer system is likely to be coarser 

grained on the southern end of the study area nearest 

the San Gabriel Mountains and finer grained to the 

north.

The GPS and InSAR results for the study area 

(fig. 7) suggest that the potential for subsidence is high 

in central Lancaster where more than 6 ft had occurred 

between 1930 and 1992 and where the rates for 1993–

95 were among the highest in the valley. These rates 

were similar to the average historical rates. GPS and 

InSAR results also suggest that the potential for 

subsidence decreases dramatically to the south; about 

2 mi south of the area of maximum measured historical 

subsidence in Antelope Valley (central Lancaster) less 

than 1 ft of historical subsidence had occurred and the 

rates for 1993–95 were very low. Historical water-level 

declines in these areas are similar; thus, the sharp 

contrast in subsidence is likely tied to a difference in 

the total thickness and (or) the compressibility of finegrained materials and (or) a difference in the stress 

history (preconsolidation head). The total thickness of 

the fine-grained materials may not be the sole reason 

for the contrast; significant silty and clayey materials 

were encountered while drilling boreholes in the 

southern area.

TESTS OF FRESHWATER INJECTION

Five injection tests were done for this study: two 

preliminary tests in 1994 to determine the feasibility of 

using existing wells for injection, and three pilot tests 

from 1996 to 1998 to assess the general feasibility of a 

multi-well injection program and the potential 

hydraulic, subsidence-related, and chemical effects of 

such a program.

Wells and piezometers in the study area often 

have multiple designations. Table 1 describes these 

designations, and includes basic well-construction 

information where available. 

Preliminary Tests, 1994

The USGS, in cooperation with LACDPW and 

AVEK, tested the feasibility of injecting SWP water 

into the aquifer system at Lancaster through existing 

wells during spring 1994. Two wells in the Avenue K–8 

and Division Street well field (fig. 8) were tested: well 

7N/12W-27J5, an older abandoned production well 

screened in the upper and middle aquifers; and well 

7N/12W-27J6, a newer active production well screened 

in the upper, middle, and lower aquifers (table 1). A 

total of more than 118 acre-ft of SWP water, treated to 

drinking-water standards by AVEK, was injected into 

the aquifer system through these wells during separate 

tests. Ground-water levels were measured in nine 

nearby wells. Velocity logs were obtained for four of 

the wells to determine interaquifer wellbore flow 

between the middle and deep aquifers. GPS surveys 

were done to monitor land-surface deformation during 

the tests.
14 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

State well 

number 

USGS site 

identification 

number

Local well 

name

Landsurface 

altitude

(feet)

Use of well

Year of 

construction

Depth 

drilled 

(feet)

Casing Screened 

(perforated) 

interval 

(feet)

Aquifer 

zone 

perforated

Diameter 

(inches

Depth 

(feet)

6N/11W -1B1 343842117594001 3 2,500 Agricultural 1955 460 14 — 256-460 U

-3C1 343845118015201 MW19 2,485 Observation 1995 341 4 335 290-335 U

-3F_ — — — Agricultural — — — — 200-550 U

-3Q1 343754118013901 MW15 2,504 Observation 1995 330 4 330 285-330 U

-4H1 343820118022601 — 2,489 Agricultural 1936 722 20 722 170-650 U,M

-5G3 343826118035801 DW4-1 2,480 Industrial 1984 749 13 700 1420-700 U,M

-5G4 343826118035601 DW4-2 2,480 Industrial 1984 742 13 670 1410-670 U,M

-6F1 343822118051901 DW2-2 2,490 Industrial 1991 1,000 16 820 1400-800 U,M

-6H3 343821118043601 DW3-1 2,484 Industrial/domestic 1971 800 16 800 400-800 U,M

-6H4 343829118044101 DW3-3 2,479 Domestic/industrial 1986 810 16 800 500-800 U,M

-8M_ — 3 — Agricultural — — — — 200-451 U

-8R3 343700118034302 4 2,523 Agricultural 1946 709 16 708 252-708 U,M

-9D1 343752118031201 MW4 2,498 Observation 1988 334 4 334 289-334 U

-9H1 343717118023201 — 2,513 Agricultural 1948 500 8 500 200-500 U

-9P1 343700118031101 1 2,523 Agricultural 1946 652 — 652 537-652 U,M

-9Q1 343700118024001 — 2,526 Agricultural 1937 — 10 566 486-566 U

-11C1 343751118005801 MW18 2,513 Observation 1995 340 4 335 290-335 U

-15A1 343700118012801 MW16 2,537 Observation 1995 334 4 331 281-331 U

-16D_ — MW3 2,523 Observation — — — — 300-350 U

-16J1 343628118022701 — 2,547 Unused/observation 1964 630 14 630 322-630 U,M

-17_ — — — Agricultural — — — — 200-600 U,M

-17A_ — 5 — Agricultural — — — — 200-600 U,M

-17D1 343647118041601 DWX-2 2,531 Industrial 1988 600 11 600 200-600 U,M

-18A_ — — — Agricultural — — — — 500-800 U,M

-18H1 343644118044701 — 2,534 Domestic/industrial 1982 800 14 800 500-800 U,M

-19C_ — 8A 2,568 Public supply 1987 1,030 16 960 560-940 U,M,L

-19E5 343554118053401 2A 2,584 Public supply 1968 915 16 900 1450-900 U,M

-19E6 343545118052701 3A 2,586 Public supply 1960 868 16 848 396-848 U,M 

-19F1 343542118050701 4A 2,571 Public supply 1970 838 16 838 480-830 U,M 

-19F2 343554118050501 7A 2,563 Public supply 1985 1,020 16 920 570-900 U,M 

-19G1 343542118044801 24 2,569 Public supply 1985 950 16 920 570-900 U,M 

-19L_ — 23A 2,579 Public supply 1991 900 16 840 600-840 U,M 

-20A1 343559118033701 — 2,564 Agricultural 1960 — — 600 200-600 U,M

-20A_ — — — Agricultural — — — — 200-600 U,M

-20D1 343554118043001 MW2 2,558 Observation 1989 540 6 540 480-540 U

-20G2 343542118034101 10 2,568 Public supply 1956 694 16 694 310-694 U,M

6N/12W -5J_ — 3 2,565 Public supply — — — — 288-504 U

-9H3 343727118085202 — 2,610 Public supply 1992 1,015 16 910 500–900 U,M,L

-12M2 343717118063601 DW8-1 2,560 Industrial 1976 810 14 801 500–801 U,M

-12R1 343711118054001 DW7-1 2,538 Industrial 1951 — 16 800 380-800 U,M 

Table 1. Construction and other data for wells used in the study, Antelope Valley, California

[State well number, as reported or determined: _, underscored where part of well number is unknown. See well-numbering system on page xi. See figures 15, 

42, and 43 for location of wells. USGS, U.S. Geological Survey. USGS site identification number: The unique number for each site based on latitude and 

longitude of site, which is referenced to North American Datum of 1927 (NAD27); first six digits are latitude, next seven digits are longitude, and final two 

digits are a sequence number to uniquely identify each site; underscore indicates wells not canvassed and not in USGS digital database, information obtained 

from owner and (or) drillers’ logs. Altitude of land surface in feet above sea level. Depth of well, well casing, and screened (perforated) interval in feet below 

land surface. Screened (perforated) interval: estimated where italicized. Aquifer zones: U, upper; M, middle; L, lower; inferred where italicized. —, no data 

available; ~, about]
Tests of Freshwater Injection 15

6N/12W -13N1 343609118063801 15 2,591 Public supply 1960 880 16 800 420-800 U,M 

-15H_ — 34-6 2,620 Public supply 1988 1,074 16 1,050 500-1,050 U,M,L

-16A2 343655118090001 — 2,640 Public supply — (

2) — (2) 388-800 U,M

-23A1 343600118064901 6A 2,598 Public supply 1983 1,030 16 1,010 480-1,010 U,M,L

-24A3 343558118055001 14A 2,579 Public supply 1965 900 16 900 450-900 U,M 

-24C1 343600118061001 11A 2,585 Public supply 1963 1,275 16 1,275 504-900 U,M

7N/11W -8M1 344229118042901 1 2,372 Public supply 1962 605 14 600 310-600 U,M

-8M2 344229118043101 2 2,372 Public supply — — — — 290-600 U,M

-18R_ — 4-58 2,396 Public supply 1989 — 16 1,240 400-1,220 U,M,L

-18R_ — 4-59 2,397 Public supply 1989 1,260 16 1,240 400-1,220 U,M,L

-20G_ — 4-54 2,414 Public supply 1988 1,210 16 1,200 300-1,200 U,M,L

-20G_ — 4-55 2,416 Public supply 1989 1,208 16 1,200 360-1,200 U,M,L

-27Q1 343939118013701 — 2,463 Unused/observation — 650 14 650 300-650 U,M

-33A1 343926118024001 3 2,461 Agricultural — — — — 374-770 U,M

-33J2 343859118024002 2 2,471 Agricultural 1963 770 16 770 374-770 U,M

-33N1 343847118032001 — 2,473 Destroyed in 1996 — — 20 3351 — U

-33Q1 343846118025301 — 2,468 Agricultural — 700 16 700 318-700 U,M

7N/12W -9A_ — 4-50 2,321 Public supply 1989 754 16 510 280-500 U,M

-9B_ — 4-51 2,316 Public supply 1989 885 16 510 1250-490 U,M

-9E3 344239118094201 4-36 2,318 Public supply 1973 515 16 500 140-490 U,M

-11E_ — 4-52 2,340 Public supply 1988 1,175 16 1,000 240-980 U,M,L

-11M2 344240118074301 4-15 2,338 Public supply 1959 705 14 600 1180-525 U,M

-13F1 344151118061901 1 2,382 Agricultural 1948 552 12 552 175-552 U,M

-15R2 344123118075501 4-9 2,386 Industrial 1953 670 14 670 466–670 U,M

-15R3 344130118075701 4-17 2,375 Public supply 1958 1,227 14 1,227 1480–1,227 U,M,L

-15R4 344125118075801 4-26 2,384 Public supply 1965 700 14 693 235–693 U,M

-17C_ — 4-49 2,319 Public supply 1988 1,160 16 1,150 320-1,140 U,M,L

-17F_ — 4-48 2,324 Public supply 1988 1,135 16 1,110 320-1,100 U,M,L

-19R1 344030118110001 — 2,386 Unused/observation — 400 12 400 100-400 U

-21C2 344107118092401 4-12 2,357 Public supply 1955 639 14 639 300–639 U,M

-21C4 344109118092601 4-25 2,359 Public supply 1964 800 14 640 200–640 U,M

-21C5 344109118092201 4-38 2,358 Public supply 1974 750 16 733 210–720 U,M

-22B2 344120118081301 4-5 2,375 Public supply 1947 578 14 552 192–552 U,M

-22K1 344043118080301 — 2,407 Abandoned/

observation

— 400 8 — — U

-26K3 343951118065902 4-31 2,459 Abandoned 1969 770 16 687 310–674 U,M

-27F1 344004118082401 — 2,444 Abandoned — — — (

4) — U,M

-27F2 344005118081801 4-43 2,445 Public supply 1988 1,210 16 1,202 400–1,202 U,M,L

-27F3 344006118082601 4-44 2,440 Public supply 1988 1,220 16 1,202 400–1,202 U,M,L

-27F5 344005118082201 5K8-PZ1 2,441.6 Piezometer 1996 1,183 2 935 905–925 L

-27F6 344005118082202 5K8-PZ2 2,441.6 Piezometer 1996 1,183 2 735 705–725 M

-27F7 344005118082203 5K8-PZ3 2,441.6 Piezometer 1996 1,183 2 535 505–525 M

-27F8 344005118082204 5K8-PZ4 2,441.6 Piezometer 1996 1,183 2 425 395–415 U

-27F9 344005118082205 5K8-EX1 2,441.6 Extensometer 1996 735 7 725 — —

State well 

number 

USGS site 

identification 

number

Local well 

name

Landsurface 

altitude

(feet)

Use of well

Year of 

construction

Depth 

drilled 

(feet)

Casing Screened 

(perforated) 

interval 

(feet)

Aquifer 

zone 

perforated

Diameter 

(inches

Depth 

(feet)

Table 1. Construction and other data for wells used in the study, Antelope Valley, California—Continued
16 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

7N/12W -27F10 344005118082206 5K8-EX2 2,441.6 Extensometer 1996 1,205 7 1,190 — —

-27H1 344004118075901 — 2,449 Abandoned/

observation

1949 500 14 500 189–500 U

-27H3 344008118074701 4-33 2,443 Public supply 1971 730 16 710 260–700 U,M

-27H5 344003118074801 DK8-PZ1 2,449 Piezometer 1992 1,120 2 1,120 1,080–1,100 L

-27H7 344003118074803 DK8-PZ3 2,449 Piezometer 1992 1,120 2 724 684–704 M

-27J4 344002118074701 4-13 2,448 Public supply 1956 1,108 14 51,102 5362–1,102 U,M 

-27J5 343903118074801 4-8 2,449 Abandoned 1953 700 14 700 350–700 U,M

-27J6 344003118074901 4-42 2,449 Public supply 1987 1,174 16 1,150 400–1,140 U,M,L

-27P2 343943118081801 4-32 2,463 Public supply 1969 735 16 727 282–717 U,M

-27P3 343943118082101 4-34 2,462 Public supply 1972 740 16 720 280–710 U,M

-27P5 343943118081701 5L-PZ1 2,462.7 Piezometer 1998 918 2 910 890–910 L

-27P6 343943118081702 5L-PZ2 2,462.7 Piezometer 1998 918 2 560 540–560 M

-27P7 343943118081703 5L-PZ3 2,462.7 Piezometer 1998 918 2 460 440–460 U

-27P8 343943118081704 5L-PZ4 2,462.7 Piezometer 1998 918 2 390 330–370 U

-30B1 344028118112601 4-37 2,387 Public supply 1974 652 16 610 260–600 U,M

-30J_ — 8 — Public supply — — — — 260-610 U,M

-32A1 343936118100201 — 2,450 Public supply 1947 540 12 — 210-437 U

-33R3 343848118085203 — 2,519 Public supply 1993 824 16 780 440–760 U,M

-34B1 343931118081601 — 2,475 Abandoned 1953 425 8 — — U

-34N3 343848118083801 4-29 2,522 Public supply 1967 792 14 740 350–728 U,M

-34N4 343851118083801 4-30 2,517 Public supply 1968 800 16 770 350–760 U,M

-35G2 343912118071102 2 2,497 Public supply 1956 630 — 559 307-559 U 

7N/13W -14D1 344207118140801 3 2,351 Public supply 1941 500 14 480 321-480 U,M

-14D2 344207118140802 4 2,352 Public supply 1941 500 — 488 321-488 U,M

-23R1 344029118131301 — 2,384 Public supply 1950 437 12 437 199-437 U,M

-24M2 344044118125701 4-22 2,372 Public supply 1951 593 14 593 167-593 U,M

-24M3 344042118130001 4-27 2,375 Public supply 1965 602 14 575 150-575 U,M

-25M2 344003118120502 5 ~2,415 Public supply — 590 — 590 300-590 U,M

-26J2 344000118130601 — 2,417 Public supply 1957 606 14 606 288-606 U,M

-26J_ — — — Public supply — — — — 250-501 U,M

-34A_ — 2 — Public supply — — — — 250-475 U

State well 

number 

USGS site 

identification 

number

Local well 

name

Landsurface 

altitude

(feet)

Use of well

Year of 

construction

Depth 

drilled 

(feet)

Casing Screened 

(perforated) 

interval 

(feet)

Aquifer 

zone 

perforated

Diameter 

(inches

Depth 

(feet)

Table 1. Construction and other data for wells used in the study, Antelope Valley, California—Continued

1Not continuous.

2Depth, obtained from owner, is approximately 800 feet below land surface.

3Destroyed in 1996.

4 Depth at least 750 feet below land surface; sounded March 1996.

5Well casing filled with gravel to about 700 feet below land surface in early 1990s.
Tests of Freshwater Injection 17

Pump intake

0 5 10 15 20 25 30

above 360

360–380

380–400

400–420

420–440

440–460

460–480

480–500

500–520

520–540

540–560

560–580

580–600

600–620

620–640

640–660

660–680

680–700

700–717

Depth interval, in feet below land surface

Percent of total flow

middle aquifer

upper aquifer

0

0 3 Kilometers

3 Miles

34° 42'30"

118° 12'30" 118° 05'

34° 37'30"

lll l l l l l l l l l l l l l l l l l l lll l l lll l l l l l l l l l l l l l l l lll

llll l l l l l l l l l l l l l l l l l l l lllll l l l llll l l l l l lll l l lll l l l l l l l l l l l

EXPLANATION

Land-surface altitude—Contour interval 40 feet, dashed interval 20 feet.

Datum is sea level

T7N

T6N

T. 7 N.

T. 6 N.

R13 W R12 W R12 W R11 W

Air Force Plant 42

AVENUE I

AVENUE K

AVENUE L

AVENUE J

AVENUE M

AVENUE N

AVENUE O

40TH STREET WEST

30TH STREET WEST

20TH STREET WEST

10TH STREET WEST

10TH STREET EAST

20TH STREET EAST

UNION PACIFIC RAILROAD

LANCASTER BLVD

SIERRA HIGHWAY

2,600

2,640

2,640

2,600

2,480

2,520

2,520

2,560

2,560

2,400

2,400

2,400

2,440

2,440

2,320

2,360

2,360

2,560

Base modified from U.S. Geological Survey, Lancaster, 1:62,500, 1958;

Lancaster East, 1:24,000, 1958; Lancaster West, 1:24,000, 1958;

Palmdale, 1:24,000, 1958; Ritter Ridge, 1:24,000, 1958;

Amargosa Creek

Amargosa Creek (1999)

Amargosa Creek (1958)

AVENUE L

Amargosa Creek (1999)

5TH STREET WEST

27P3 27P2

5TH STREET WEST

27F3

AVENUE K-8 (bike path)

27F5-F8 (nested piezometer)

550 feet to CL

400 feet to CL

470 feet to CL

Overflow basin

Water

storage

tank

27F2

27F10

27F9

F6 F8

F5

F7

EXTENSOMETER SITE

INJECTION SITE

(injection wells)

180 feet

600 feet to CL

70 feet



GPS antenna

booster pump station

27P5-P8

(nested piezometer)

P6 P5

P7 P8

80' 50'

to CL

CL = centerline

CL = centerline

90' to CL

120' to CL

170' to CL

All distances are approximate

All distances are approximate

27F9-F10 (borehole extensometer)

K-8 & Division

well field

Figure 8. Location of injection and extensometer sites, Lancaster, Antelope Valley, California.

GPS, global positioning system.
18 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Key results of these preliminary tests indicated 

that

(1) unrestored abandoned wells may not be 

suitable for injection because of large head 

losses caused by encrusted well screens and 

gravel packs (for example, the water level in 

the injection well had to be near land surface to 

achieve reasonable injection rates);

(2) the lower aquifer accepted only 17 percent 

of the water injected into well 7N/12W-27J6, 

coupled with large increases in pressure, suggesting this aquifer has low transmissivity and 

very low storativity (generally a poor set of 

conditions for aquifer injection, storage, and 

recovery); and

(3) both injection tests appeared to cause temporary, measurable changes in land-surface 

elevation.

These findings influenced the selection of the 

site used in the pilot tests and the data-collection efforts 

for these tests. Wells at the new site were in the upper 

and middle aquifers, active, and far from structures that 

may be damaged by fluctuations in land-surface 

elevation.

Pilot Tests, 1996–98

 The USGS, in cooperation with LACDPW and 

AVEK, conducted three pilot injection tests from 1996 

to 1998 to assess the general feasibility of a multi-well 

injection program and to determine the potential 

hydraulic, subsidence-related, and chemical effects of 

such a program. The first test, which included about 

1 month of injection, was a warm-up for the subsequent 

long-term test, which involved 5 months of injection. 

Determination of the hydraulic feasibility and the 

effects of injection was the primary purpose of these 

two tests. Secondary goals included measurement of 

aquifer-system deformation and collection of waterchemistry data. The primary goal of the third pilot test 

was to determine the factors controlling the formation 

and fate of trihalomethanes.

Site Description

Selection of the site for the pilot injection tests 

was based on the results from the preliminary tests, the 

accessibility of AVEK (injection) water, and the 

relative dependence on the wells during periods of high 

water demand. The site selected, referred to herein as 

the injection site (fig. 8), has two relatively new 

production wells (7N/12W-27P2 and 27P3) screened 

only within the upper and middle aquifers and one 

nested piezometer (7N/12W-27P5–8) established in 

1998 for this study (fig. 9). The injection site is 

surrounded by undeveloped land, which minimized 

potential damage from land-surface deformation, and is 

near a source of AVEK water. There was enough 

redundancy in the system of wells, pipelines, and 

storage tanks to likely avoid unscheduled extraction at 

or near the site during the tests.

An extensometer site was established about 

0.5 mi north of the injection site (fig. 8) for measuring 

aquifer-system deformation during the pilot tests and 

for subsequent long-term subsidence monitoring. This 

site consists of a paired dual-borehole extensometer 

and one nested piezometer constructed in 1995 for this 

study. Near this site are two production wells 

(7N/12W-27F2 and 27F3) that are open to the upper, 

middle, and lower aquifers (fig. 10). 

Test Procedure

One or both of the production wells at the 

injection site were used during the three pilot injection 

tests. Each of these tests, referred to herein as cycles, 

involved several stages:

(1) pre-injection water-level recovery prior to 

the start of the test;

(2) injection;

(3) storage period; and

(4) extraction.

The first of these tests began in April 1996 and 

involved 28 days of injection. The second and the third 

tests were conducted in 1996–97 and 1998 and 

involved 5 and 1.5 months, respectively, of injection. 

Figure 11 shows a time line depicting the various 

stages and monitoring activities of these tests.
Tests of Freshwater Injection 19

EXPLANATION

Study area

Water-level contours—Shows altitude

of water table, April 1996. Contourinterval 25 feet. Datum is sea level

Location of well with water-level dataDirection of ground-water movement

150

2,125

2,1002,0752,

050

2,150

2,175

2,225

2,225

2,200

2,175

2,225

2,250

2,200

2,200

Quartz Hill

Injectionsite

Lancaster

Palmdale

0

0 5 Kilometers

5 Miles

r C kee

Ama gr osa

Approximate land surface

Static water level,about 329 feet

Well depth 390 feet

330 feet

280 feet

370 feet

440 feet

460 feet

540 feet560 feet

890 feet

910 feet

7N/12W-27P5

7N/12W-27P6

7N/12W-27P7

7N/12W-27P8

Piezometers

7N/12W-27P3

LACDPW 4-34

about 80 feet

about 260 feet

710 feet

Injection well Injection well

NOT TO SCALE

717 feet

7N/12W-27P2

LACDPW 4-32

282 feet

T. 7 N.T. 6 N.

2 5, 20 AVENUE L

5TH STREET WEST 27P3 27P2

INJECTION SITE

(injection wells)

180 feet

600 feet to CL

70 feet



GPS antenna

27P5–P8

(nested piezometer)

P5 P6

P8 P7

80'

50'

to CL

CL = centerline

All distances are approximate

about 513 feet

about 870 feet

about 913 feet

about 730 feet

Upperaquifer

Middleaquifer

Loweraquifer

Lacustrine

unit

Amargosa Creek

Figure 9. Location of piezometers 7N/12W-27P5–P8 and Los Angeles County Department of Public Works (LACDPW) production 

wells 7N/12W-27P2–P3, Lancaster, Antelope Valley, California.Diagram is not to scale, but does identify depths from land surface and distances between well. Map show relative locations. GPS, 

global positioning system.
20 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California about 490 feet about 740 feet about 900 feet Well depth 425 feet 395 feet 400 feet 400 feet 415 feet Well depth 535 feet 505 feet 525 feet 705 feet 725 feet 905 feet 925 feet Well depth 735 feet Well depth 935 feet about 892 feet

7N/12W-27F5

7N/12W-27F6

7N/12W-27F7

7N/12W-27F8

Upperaquifer

Middleaquifer

Loweraquifer

Lacustrine

unit

Piezometers

7N/12W-27F3

LACDPW 4-44

7N/12W-27F2

LACDPW 4-43

about 10 feet

about 230 feet

about 380 feet

1202 feet 1202 feet NOT TO SCALE

Extensometers

1,180 feet

700 feet

7N/12W-27F9

7N/12W-27F10

Extraction wells

Approximate land surface

AVENUE K

AVENUE J

AVENUE L

2,400

2,440

2,360

5TH STREET WEST

27F3

AVENUE K-8 (bike path)

27F5–F8 (nested piezometer)27F9–F10 (borehole extensometer)

550 feet to CL

400 feet to CL

470 feet to CL

Overflow basin

Water

storage

tank

27F2 27F10

27F9

F6 F8 F5

F7

EXTENSOMETER SITE

booster pump station

CL = centerline

90' to CL

120' to CL

170' to CL

All distances are approximate

Static water level,

about 304 feet

Figure 10. Location of piezometers 7N/12W-27F5–F8, extensometers 7N/12W-27F9–F10, and Los Angeles County Department of Public Works (LACDPW) production wells 7N/12W-27F2–F3, Lancaster, Antelope Valley, California.Diagram is not to scale, but does identify depths from land surface and distances between well. Map shows relative locations.
Tests of Freshwater Injection 21 S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S 1995 1996 1997 1998

CYCLE 1

Pre-injection (initial recovery period)

Injection (4/8/96–5/6/96)

Storage period

Extraction (5/21/96–10/21/96)

CYCLE 2

Pre-injection (water-level recovery)

Injection (11/12/96–4/17/97)

Storage period

Extraction (5/14/97–1/14/98)

CYCLE 3

Pre-injection (water-level recovery)

Injection (4/15/98–6/16/98)

Storage period

Extraction (6/30/98–beyond 9/30/98)

MONITORING ACTIVITIES

Vertical deformation monitoring

Water-level monitoring

Microgravity surveys

Continuous Global Positioning System surveying at:

the injection site

the Antelope Valley–East Kern Water Agency (control) site

Leveling surveys

Tilt monitoring

Geodetic monitoring

Flow-rate monitoring

Water-chemistry monitoring

Continuous/periodic measurements

Figure 11. Time line of activities associated with injection cycles 1–3 at Lancaster, Antelope Valley, California.
22 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Injection was accomplished by conveying AVEK 

water into the injection wells either through a 4-inch 

conductor pipe (with pump removed) or through the 

pump column with the electric turbine in place on the 

wellhead (unlocked so it could spin). A series of valves 

were used to reduce system pressure prior to release 

into the wells, and the wells were gravity-fed. Injection 

and extraction rates were measured continuously using 

an inline flow meter for each well and recorded on a 

data logger. Injection rates were held somewhat steady 

at about 750 gal/min per well, and extraction rates 

averaged about 850 gal/min per well during cycles 1 

and 2 and about 450 gal/min during cycle 3 (fig. 12). 

The highest measured water level in either injection 

well during injection was about 185 ft below land 

surface (fig. 13), which indicates that 750 gal/min was 

easily accommodated and may not represent the 

maximum attainable rate in these wells.

The pre-injection recovery period ranged from 1 

to 12 weeks; this stage of the pilot injection test 

allowed water levels and aquifer-system deformation to 

stabilize prior to injection and reach quasi-static 

conditions. This helped distinguish between the 

hydraulic response to the cessation of extraction and to 

the onset of injection. The storage period followed 

injection and ranged from 2 to 4 weeks. This period 

allowed water levels and aquifer-system deformation to 

stabilize, and provided time for specific chemical 

reactions (formation of trihalomethanes) to occur prior 

to extraction.

Data collected to document the hydraulic, 

subsidence-related, and chemical response to the 

injection cycles are described in the rest of this section 

of the report and analyses of these data are discussed in 

the following section. The timing of the injection 

cycles and the associated sampling is shown in 

figure 11.

Monitoring of Hydraulic Response

The hydraulic response of the aquifer system to 

stresses during the injection cycles was determined 

directly by measuring water levels in wells and 

piezometers and indirectly by measuring changes in 

gravity. Following is a discussion of historical water 

levels and a description of the water-level network used 

for this study, the response of water levels in this 

network during the injection cycles, and the use of 

microgravity surveys to estimate water-level changes in 

the absence of wells.

Historical Water Levels

Water levels in Antelope Valley are lower than 

they were prior to ground-water development in the 

valley in the early 1900s. Water levels in the study area 

were affected primarily by agricultural activity through 

the 1960s, but now are controlled largely by pumping 

for urban use (Templin and others, 1995; Leighton and 

Phillips, 2003). Water levels near Lancaster and 

Palmdale declined about 110 and 185 ft, respectively, 

since about 1965 (fig. 14). Longer term records show 

drawdowns exceeding 200 ft in the Lancaster area and 

300 ft in the vicinity of Palmdale since the early 1900s.

Water-Level Network and Conditions Prior to Injection 

Testing

The water-level network established for this 

study consists of 13 active or abandoned production 

wells, 2 nested piezometers installed by the USGS for a 

previous study, and 2 sets of 4 nested piezometers 

installed for this study (table 1; fig. 15) (Metzger and 

others, 2002). The areal distribution of the wells in this 

network is not ideal; more than 70 wells known to exist 

at one time within 2 mi of the injection wells were 

either destroyed, inaccessible, or could not be found. 

The screened intervals vary from 20 ft in most of the 

piezometers to 300 to 400 ft in most of the wells.

Water levels in all the network piezometers and 

wells were measured periodically using a calibrated 

electric sounder or a graduated steel tape. Continuous 

measurements were made at most of the piezometers 

and at one well. The measurements were collected with 

pressure transducers and recorded electronically. 

Metzger and others (2002) describe the methods and 

protocol used in collecting these data and present a 

complete tabular (except for continuous data) and 

graphical record of the measurements.
Tests of Freshwater Injection 23

0

200

400

600

800

1,000

1,200

AS N O D N O D J F MJ J AS J F MAMJ J A SO

1996 1997 1998

Year

A MJ J M A

Flow rate of injection or extraction, in gallons per minute

0

200

400

600

800

1,000

1,200

7N/12W-27P2

7N/12W-27P3

pause in injection

for cycle 3

pause in injection

for cycle 3

Injection cycle 1 Injection cycle 2 Injection cycle 3

Injection cycle 1 Injection cycle 2 Injection cycle 3

EXPLANATION

Injection Extraction

Figure 12. Injection and extraction flow rates for wells 7N/12W-27P2 and -27P3 in Lancaster, Antelope Valley, California, 1996–98.

Breaks in graphs indicate wells were not in use.
24 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

November 1996 water-level data for the study 

area are depicted in figure 16. All the wells in this 

figure are screened in the upper aquifer, but some are 

also screened in the other aquifers; therefore, the water 

levels shown on figure 16 may not represent the water 

table. These data were collected 3 weeks after 

extraction ceased in local LACDPW wells following a 

5- or 6-month period of relatively high extraction rates. 

The water-level contours on figure 16 are for 

November 1996, and therefore are not entirely 

representative of conditions prior to injection testing 

because the first cycle involved injection during April 

1996 and extraction from late May through 

mid-October. Because water levels were not available 

for the four wells south of well 7N/12W-34B1 prior to 

the April 1996 injection, the November 1996 data 

provide a more comprehensive view. These contours 

show ground-water movement toward the injection site 

in the Lancaster area and southeastward flow south of 

Lancaster toward Palmdale. Although there are no data 

between wells 7N/12W-34B1 (just south of the 

injection site) and 6N/12W-12M2 (at Air Force Plant 

42), the water-level contours indicate that a groundwater flow divide may exist between these wells. On 

the other hand, the April 1996 data prior to injection 

show water levels 4 to 9 ft higher in the northern area; 

later water-level measurements for well 6N/12W-12M2 

show little seasonal variation (2 ft maximum change 

from November 1996 through May 1998), suggesting 

that a very shallow southward gradient may exist 

during periods of low extraction rates (relatively high 

water levels) in Lancaster.

Water-Level Network Response to Injection Cycles

Measured water levels in the network 

piezometers and wells closest to the injection wells are 

shown on the hydrographs in figure 17 (locations 

shown in figure 15). An inspection of these 

hydrographs reveals that quantifying the difference 

between normal seasonal water-level recovery and that 

caused by injection is not possible using water-level 

data alone because subannual data were not available 

for the area near the injection site prior to the first 

injection cycle and because a full water-level recovery 

did not take place prior to subsequent injection cycles. 

However, continuous and periodic water-level data 

recorded during the injection cycles shows qualitatively 

that the hydraulic response to injection was significant 

(for example, wells 7N/12W-27F6, 34B1, and 27H7).

M A M J J A S O N D J F M A M J

1996 1997

150

350

200

250

300

7N/12W-27P2

Depth to water, in feet below land surface

7N/12W-27P3

2,313

2,263

2,213

2,163

2,113

Altitude of water level, in feet

EXPLANATION

Injection Extraction

Injection cycle 1 Injection cycle 2

Figure 13. Periodic measurements in the injection wells (7N/12W-27P and 27P3) in Lancaster, Antelope Valley, California, March 1996 

through June 1997.
Tests of Freshwater Injection 25

Continuous water levels just above the lacustrine 

unit measured at well 7N/12W-27F6 during the cycle-2 

injection at the extensometer site, about 2,270 ft north 

of the injection wells, are shown in figure 18. The rate 

of recovery clearly had slowed prior to the start of 

injection, but it quickly recovered at the onset of 

injection as indicated by a rapid increase in head of 

about 6 ft. Well 7N/12W-27H1, about 2,800 ft 

northeast of the injection wells, also responded rapidly 

to injection, though with less magnitude. Water levels 

in wells more than 1 mi away from the injection wells 

did not appear to be affected immediately, if at all, by 

injection; for example, well 7N/12W-26K3, which is 

1.2 mi to the east of the injection wells, did not 

respond perceptibly to injection. Water-level responses 

to the cessation of injection were similar for the three 

wells (fig. 18).

Continuous water-level data from the nested 

piezometers screened in the upper and middle aquifers 

show an increased response to injection and extraction 

with increased depth in the system (fig. 19A, B). 

Vertical hydraulic gradients above the lacustrine unit 

generally shift from upward during injection and 

recovery periods to downward during withdrawal. 

2,000

2,050

2,100

2,150

2,200

2,250

2,300

7N/12W-27H01

Inferred

6N/12W-24C01

1950195519601965197019751980198519901995

Altitude of water level, in feet

Year

Lancaster

Palmdale

Figure 14. Historical water levels in or near Lancaster and Palmdale, Antelope Valley, California, 1948–99.
26 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

0

0 3 Kilometers

3 Miles

34° 42'30"

118° 12'30" 118° 05'

34° 37'30"

l l l l l l l l l l l l l l l l l lll l l l l l l l l lll l l l l l lll l l l l l l l l l l l l l l l l l l l l l l l l l l l l lll l l l l llll l l l l l l l l l l l l l l l l l l l l l l l l

T7N

T6N

R13 W R12 W R12 W R11 W

Air Force

Plant 42

AVENUE I

AVENUE K

AVENUE L

AVENUE J

AVENUE M

AVENUE N

AVENUE O

40TH STREET WEST

30TH STREET WEST

20TH STREET WEST

10TH STREET WEST

10TH STREET EAST

20TH STREET EAST

UNION PACIFIC RAILROAD

LANCASTER BLVD

SIERRA HIGHWAY

2,600

2,640

2,640

2,600

2,480

2,520

2,560 2,520

2,560

2,400

2,400

2,400

2,440

2,440

2,320

2,360

2,360

Base modified from U.S. Geological Survey, Lancaster, 1:62,500, 1958; Lancaster East, 1:24,000, 1958; Lancaster West, 1:24,000, 1958; Palmdale, 1:24,000, 1958; Ritter Ridge, 1:24,000, 1958;

Amargosa Creek

Amargosa Creek (1958)

33R3

26K3

22K1

9H3 12M2

16A2

Land-surface altitude—Contour interval

40 feet. Dashed interval 20 feet. Datum

is sea level

Water-level monitoring sites

Water-level monitoring sites

2,440

Land-surface altitude—Contour interval

40 feet. Datum is sea level

2,400

27P5–P8

34B1

27F9

27P2

AVENUE L

Amargosa

Creek

(1999)

10TH STREET WEST

5TH STREET WEST

SIERRA HIGHWAY

0

0 53

0

0.5 Mile

0.5 Kilometer

27F3

27F1

27H1

27F9,F10

27P3

34B1

27P2

AVENUE K-8 (bike path) UNION PACIFIC RA

ILROAD

EXPLANATION

EXPLANATION

Current or former production well and

identifier

Extensometer and identifier

Injection well and identifier

2,440

2,460

2,480

Nested piezometer and identifer 27P5–P8

22K1 Current or former extraction well

and identifier

Nested piezometer

Area shown

in figure 16

27F5–F8

(injection wells)

27H5,H7

27J5

Figure 15. Locations of nested piezometers and current or former extraction wells used in the ground-water-level monitoring network, 

Lancaster, Antelope Valley, California.
Tests of Freshwater Injection 27

Air Force

Plant 42

AVENUE M

AVENUE N

SIERRA HIGHWAY

AVENUE K

27P3 AVENUE L

27P2

27J5

26K3

T7N

T6N

R 12 W R 12 W

2,125

2,150

2,160

2,170

2,140

2,130

2,164.9

9H3

2,173.2

16A2

2,126.7

12M2

2,125

2,123.6

34B1

2,125.2

2,126.0

2,132.1 2,132.6

27F1

27F8

2,130.4

2,134.6

2,134.8

2,144.6

22K1

27H1

Injection site

Extensometer

site

2,130

2,130 Altitude of water level, November 1996.

Contour interval variable, in feet.

Datum is sea level

Direction of ground-water flow

Well with location and measured

water-level altitude

0

0 1 Kilometer

1 Mile

7'30"

2,126.4

33R3

ground-water divide

Base modified from U.S. Geological Survey, Lancaster, 1:62,500, 1958;

Lancaster East, 1:24,000, 1958; Lancaster West, 1:24,000, 1958;

Palmdale, 1:24,000, 1958; Ritter Ridge, 1:24,000, 1958;

EXPLANATION

2,134.8

26K3

2,140

Figure 16. Water levels and approximate water-level contours near injection site, before injection cycle 2, Lancaster, Antelope Valley, 

California, November 1996.

All wells perforated in the upper aquifer; some also perforated in other aquifers (see table 1). Areal extent shown in figure 15.
28 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

2,171.6

2,161.6

2,151.6

2,141.6

2,131.6

2,121.6

2,111.6

2,101.6

2,091.6

Depth to water, in feet below land surface

Altitude of water level, in feet

350

340

330

320

310

300

290

280

270

1998

A MJ J A S N O D J F M MJ J AS N O D J F MA MJ J A S O

1996 1997

A

pause in injection

for cycle 3

27F7

27F8

27F5

7N/12W27F6

Depth of

screened

interval (ft)

905–925

705–725

505–525

395–415

Extensometer site

360

350

340

330

320

310

300

290

280

April May June July August September

1998

Injection cycle 3

Injection cycle 1 Injection cycle 2 Injection cycle 3

Power failure at

injection site

piezometers

2,182.7

2,172.7

2,162.7

2,152.7

2,142.7

2,132.7

2,122.7

2,112.7

2,102.7

Transducers temporarily

removed for water-chemistry

sampling

Pause of injection

at well 27P2

27P5

7N/12W27P6

27P8

Depth of

screened

interval (ft)

890–910

540–560

330–370

Injection site

EXPLANATION

Injection Extraction

Figure 17. Piezometers and wells closest to injection wells in Lancaster, Antelope Valley, California.

Unlabeled discontinuities in data are gaps in data collection. Aquifers associated with extensometer- and injection-site piezometers are 

shown in figures 9 and 10 (ft, foot).
Tests of Freshwater Injection 29

water-chemistry

sampling

at nearby wells

330

325

320

315

310

305

300

295

290

330

325

320

315

310

305

300

295

290

Year

Depth to water, in feet below land surface

7N/12W-27H5

7N/12W-27H7

water-chemistry

sampling

at nearby wells

2,119

2,124

2,129

2,134

2,139

2,144

2,149

2,154

2,159

2,119

2,124

2,129

2,134

2,139

2,144

2,149

2,154

2,159

Altitude of water level, in feet

water-chemistry sampling at nearby wells

power failure

330

325

320

315

310

305

300

295

290

2,119

2,124

2,129

2,134

2,139

2,144

2,149

2,154

2,159

1996 1997

AMJ J AS N O D J F M MJ A

7N/12W-27J5

Perforated interval:

1,080-1,100 feet

below land surface,

lower aquifer

Screened interval:

684-704 feet below

land surface, middle

aquifer

Screened interval:

350-700 feet below

land surface, upper

and middle aquifer

Injection cycle 1 Injection cycle 2

Injection

Extraction

Figure 17.—Continued.
30 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California 310 320 330 340 350 360 370

380390 2,085

2,1652,1552,1452,1352,1252,1152,1052,095

A ASO ND J FM MJ J A A S O ND MJ J J F MA A S O MJ J

1996 1997 1998

7N/12W-34B1

290300310320330340350360370

2,02,079

89

2,1592,1492,1392,1292,1192,1092,099

YEAR YEAR

Depth to water, in feet below land surface

Altitude of water level, in feet above sea level

7N/12W-27H1

Perforated interval:189-500 feet belowland surface. Upperaquifer

Perforated interval: unknown;depth drilled 425 feet belowland surface. Upper aquifer

270280290300310320330340350

2,1742,1642,1542,1442,1342,1242,1142,1042,094

7N/12W-27F1

270280290300310320330340350

2,1702,1602,1502,1402,1302,1202,1102,1002,090 A ASO ND J FM MJ J A A S O ND MJ J J F MA A S O MJ J

1996 1997 1998

7N/12W-27F3

Perforated interval: unknown;depth at least 750 feet belowland surface. Upper, middle, andpossiblylower aquifers

Perforated interval:400-1,202 feet belowland surface. Upper,middle, and loweraquifers

Injection cycle 1 Injection cycle 2 Injection cycle 3 Injection cycle 1 Injection cycle 2 Injection cycle 3

EXPLANATION

Injection Extraction

Figure 17.—Continued.
Tests of Freshwater Injection 31

Water levels for the upper, middle, and deep aquifers at 

the Water levels in the lower aquifer at the injection and 

extensometer sites responded similarly during the 

cycle-3 injection (fig. 19C and D, respectively). 

Responses to injection and during the storage period 

were highly subdued replicas of those in the middle 

aquifer. At the extensometer site, the head in the lower 

aquifer consistently exceeded that in the middle aquifer 

by 15 to 20 ft, maintaining an upward gradient. The 

greater head response in the middle aquifer at the 

injection site caused vertical gradients to reverse (to 

downward) during injection. The head responses 

during extraction were similar in magnitude to those in 

the middle aquifer, which is in sharp contrast to the 

subdued responses during injection and storage. This 

anomaly was caused by extraction, which started about 

July 9, 1998, from other nearby LACDPW wells to 

meet high water demand; it is clearly visible in the 

hydrographs for the extensometer site and for the lower 

aquifer at the injection site (fig.19B, C, D). 

Water-Level Response Determined from Gravimetric 

Response

Microgravity surveys conducted during cycle 2 

were used to estimate changes in water-table altitude 

during the injection tests (Howle and others, 2003). 

The surveys were done as an alternative to installing 

many additional monitoring wells for measuring 

ground-water levels. A rise or decline in the water table 

causes a net change in mass proportional to the volume 

of water that fills or drains pore spaces in the sediment.

7N/12W-27H1

7N/12W-26K3

27F6:

705–725 feet below land

surface, middle aquifer

27H1:

189–500 feet below land

surface, upper aquifer

26K3:

310–674 feet below land

surface, upper and middle

aquifer

Screened interval 7N/12W-27F6

7N/12W-27H1

360

280

300

320

340

ON D JFM AM

1996 1997

Depth to water, in feet below land surface

cycle 1

Injection

Injection cycle 2

EXPLANATION

Injection Extraction

Figure 18. Variability in water-level response to injection cycle 2, Lancaster, Antelope Valley, California.

Wells shown are not at the same location or altitude (see figure 15).
32 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

B

D

A

C

EXPLANATION

Injection Extraction

injection cycle 3

270280290300310320330340350360

7N/12W-27F5

2,171.62,161.62,151.62,141.62,131.62,121.62,111.62,101.62,091.62,081.6

270280290300310320330340350360

7N/12W-27P5

2,192.72,182.72,172.72,162.72,152.72,142.72,132.72,122.72,112.72,102.7

2,182.72,172.72,162.72,152.72,142.72,132.72,122.72,112.72,102.72,092.7

280290300310320330340350360370

75 9 2 7 14 12 19 21 28 26 23 30 16 21 28 14

April May June July

1998

75 9 2 7 14 12 19 21 28 26 23 30 16 21 28 14

April May June July

1998

75 9 2 7 14 12 19 21 28 26 23 30 16 21 28 14

April May June July

1998

75 9 2 7 14 12 19 21 28 26 23 30 16 21 28 14

April May June July

1998

Depth to water, in feet below land surface

7N/12W-27P67N/12W-27P8

Altitude of water level, in feet above sea level

Altitude of water level, in feet above sea level

pause in injection for cycle 3 pause in injection for cycle 3

pause in injection for cycle 3 pause in injection for cycle 3

Injection site

Injection cycle 3

Injection site

Extensometer site

Extensometer site

Upperaquifer

Loweraquifer

Loweraquifer

Middleaquifer

Upperaquifer

Middleaquifer

Injection cycle 3

Injection cycle 3Injection cycle 3

2,161.6

2,151.62,141.62,131.62,121.62,111.62,101.62,091.62,081.62,071.6

280290300310320330340350360370

7N/12W-27F6

7N/12W-27F8

Figure 19. Water levels for the upper, middle, and deep aquifers at the injection and extensometer sites during injection cycle 3, 

Lancaster, Antelope Valley, California.
Tests of Freshwater Injection 33

This mass change causes a small but measurable 

change in gravity. Precise measurements of gravity 

[determined from the microgravity surveys 

conducted at the gravity-station monitoring network 

(fig. 20)] were made before (November 1996 was the 

baseline) and during injection. The resulting gravity 

changes were used to estimate water-level changes at 

each gravity station based on a value of specific yield 

(0.13) determined from simultaneous water-level 

and microgravity measurements at well 7N/12W34B1 (Howle and others, 2003). This well is 

adjacent to gravity station G5S (fig. 20). A more 

detailed account of the theory for using microgravity 

surveys for determining water-level changes is given 

in Howle and others (2003). See Pool and Hatch 

(1991) and Pool and Eychaner (1995) for 

descriptions of similar applications.

The gravimetric response measured at the 

gravity stations along the central south–north survey 

line is shown in figure 21. The gravity response to 

injection was greatest near the injection wells and 

generally decreased with distance from the wells. 

The response along the west–east survey line was 

more complex; Howle and others (2003) provides a 

more detailed account.

Monitoring of Subsidence-Related Effects

Two forms of land-surface deformation were 

studied during the injection tests: land subsidence 

and temporary uplift of the land surface with the 

onset of injection. Although historical land 

subsidence was small at the injection site, it was 

substantial a short distance to the north (fig. 7); 

therefore, it was important to monitor the effects of 

injection activities on land subsidence. A temporary 

uplift of the land surface was measured using 

occasional static GPS measurements during the 

preliminary injection tests at the 

Avenue K–8 and Division Street well field in 1994. 

Maximum uplift and areal distribution of uplift were 

unknown; uplift measured during the preliminary 

injection tests, however, was about 4 to 6 cm. The 

error associated with the static GPS measurements is 

unknown.

Several methods were used to measure landsurface deformation during the injection cycles; they 

include borehole extensometry, continuous GPS, 

spirit leveling, and high-precision tiltmeters. These 

methods are described in detail by Metzger and 

others (2002). 

Borehole Extensometers

 A dual borehole extensometer was 

constructed about 0.5 mi north of the injection wells 

(fig. 8) to measure land-surface deformation during 

and beyond this study. A borehole extensometer is a 

device for establishing a reference point at the 

bottom of a borehole and measuring the vertical 

position of this reference point with respect to the 

land surface. As the intervening part of the aquifer 

system compacts, the reference point and land 

surface converge. At the extensometer constructed 

for this study, counter-weighted pipes rest on 

concrete plugs (the reference points) at the bottom of 

two boreholes of different depths [see Metzger and 

others (2002) for design details]. The movement of 

these pipes relative to land surface was measured to 

determine the compaction or expansion of the 

aquifer system. This set of pipe extensometers 

measures deformation continuously from about 15 ft 

below land surface (avoiding near-surface effects 

caused by temperature variation and shrink/swell of 

clays) to 700 and 1,180 ft. The 16- to 700-ft interval 

represents most of the upper and middle aquifers, 

and the difference between these measurements and 

those of the 16 to 1,180 ft interval represents the 

interval from 700 to 1,180 ft, which contains the 

entire lacustrine unit, other materials in the upper 

part of the lower aquifer, and the remainder of the 

middle aquifer. The extensometers are paired with 

four nested piezometers screened at various depths 

within this interval (fig. 10). This pairing provides 

simultaneous, continuous measurement of stress 

(water-level change) and strain (aquifer-system 

deformation) (fig. 22).

Continuous GPS

A permanent antenna mount for a continuous 

GPS site was established about 65 ft from injection 

well 7N/12W-27P2 (fig. 8). Continuous GPS was 

used to obtain continuous measurements of landsurface elevation near the injection wells to better 

understand the magnitude and transient nature of 

land-surface uplift with the onset of injection. The 

GPS data were collected at intervals of 30 to 

120 seconds using slightly different equipment and 

procedures for the different cycles, as described in 

Metzger and others (2002).
34 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California 10TH STREET WEST 5TH STREET WEST DIVISION STREET

4TH STREET EAST

AVENUE L

AVENUE K

AVENUE K-8 (bike path)

SIERRA HIG

HWAY

UNION PACIFIC RAILROAD

l l l lll l l l l l l l l l

l l l lllll l l l l l l l l

l l

lllll l l l l l l l l l l llll l l

Gravity station and identifier

Current or former extraction

well and identifier

Extensometer and identifier

EXPLANATION

0

0 0.5

0.5

1 Mile

1 Kilometer

G7S

G7S

G6S

GSW

G5W

G4W

GSE

BOAT

JOSH

GNE G4N

G6E

NW1

NW4

NW5

NW2

G5N

27F3

G8N

G6N

27F1

27F5–F8

27F9,F10

G7N

GR 27H1

34B1

27J5

27H5–H7

27J5

27F9

R12W

T7N

T6N

R12W

2,480

2,480

2,520

2,400

2,440

Land-surface altitude—Contour 2,440

interval 40 feet. Dashed interval

20 feet. Datum is sea level

2,520

G3W G2WG1WGZERO

G4S

G3S

G2S

G1S

G2E

(injection wells)

27P5–P8

27P5–P8

27P2

27P2

27P3

G3N

G2N

G1N

G1E G3E G4E G5E

G5E

AVENUE L

5TH STREET WEST

0

0 0.05

0.05

0.1 Mile

0.1 Kilometer

EXPLANATION

Amargosa Creek

G5S

Amargosa Creek

Gravity station and identifier

Nested piezometer and identifer

27P5–P8 Nested piezometer and identifer

Injection well and identifier

Base modified from U.S. Geological Survey, Lancaster, 1:62,500, 1958;

Lancaster East, 1:24,000, 1958; Lancaster West, 1:24,000, 1958;

Palmdale, 1:24,000, 1958; Ritter Ridge, 1:24,000, 1958;

Figure 20. Locations of gravity stations, Lancaster, Antelope Valley, California.
Tests of Freshwater Injection 35

Continuous GPS data collected during the first 

and third cycles were analyzed using GAMIT/GLOBK 

software (Herring, 1998; King and Bock, 1998), using 

methods described by Behr and others (1998). The data 

collected from the Lancaster injection site (LINJ) were 

used to calculate a position relative to three Southern 

California Integrated GPS Network (SCIGN) 

continuous-GPS stations—Chilao Flat (CHIL), 

Holcomb Ridge (HOLC), and Table Mountain (TABL). 

Data from the second cycle were collected from LINJ 

and from a temporary control site established at AVEK 

headquarters on Quartz Hill, a prominent bedrock 

outcrop, and analyzed using methods similar to those 

described in Ikehara and Phillips (1994).

Figure 21. Change in gravity from pre-injection survey (November 1996) to post-injection survey (April 1997) near Lancaster, Antelope 

Valley, California.

April 1997

January 1997

November 1996

(baseline)

= one standard deviation

SOUTH NORTH G5S G4S G3S G1S G1N G3N G5N

70

80

0

10

-10

20

30

40

50

60

Change in gravity, in microGals

Distance from GZERO, in feet

1,500 1,000 2,000 2,500 1,000 500 500 0 1,500

Injection wells

(one on each side of GZERO) Bend in section
36 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

EXPLANATION

Injection Extraction

2,171.6

2,161.6

2,151.6

2,141.6

2,131.6

2,121.6

2,111.6

2,101.6

2,091.6 AMJ J A S N O D J F M MJ J A S N A O D J F MAMJ J A S O

7N/12W-27F6

Ground-water levels in middle aquifer

A

B

0.040

0.035

0.030

0.025

0.020

0.015

0.010

0.005

0

-0.005

-0.010

Aquifer-system deformation from 700 to 1,180 feet

below land surface, in feet

Aquifer-system deformation from 16 to 700 feet

below land surface, in feet

0.040

0.035

0.030

0.025

0.020

0.015

0.010

0.005

0

-0.005

-0.010

Altitude of water level in exensometer-site

piezometer 7N/12W-27F5, in feet

Altitude of water level in exensometer-site

piezometer 7N/12W-27F6, in feet

Deformation above lacustrine unit

(shallow extensometer)

7N/12W-27F5

Ground-water levels in lower aquifer

1998

AMJ J A S N O D J F M MJ J A S N O D J F MAMJ J A S O

1996 1997

A

pause in injection

for cycle 3

Deformation from 40 feet above

top of lacustrine unit to 1,180

feet (difference of deep and

shallow extensometers)

2,171.6

2,161.6

2,151.6

2,141.6

2,131.6

2,121.6

2,111.6

2,101.6

2,091.6

Injection cycle 1 Injection cycle 2 Injection cycle 3

EXPLANATION

Injection Extraction

2,171.6

2,161.6

2,151.6

2,141.6

2,131.6

2,121.6

2,111.6

2,101.6

2,091.6 AMJ J A S N O D J F M MJ J A S N A O D J F MAMJ J A S O

7N/12W-27F6

Ground-water levels in middle aquifer

A

B

0.040

0.035

0.030

0.025

0.020

0.015

0.010

0.005

0

-0.005

-0.010

Aquifer-system deformation from 700 to 1,180 feet

below land surface

Aquifer-system deformation from 16 to 700 feet

below land surface

0.040

0.035

0.030

0.025

0.020

0.015

0.010

0.005

0

-0.005

-0.010

Altitude of water level in exensometer-site

piezometer 7N/12W-27F5, in feet

Altitude of water level in exensometer-site

piezometer 7N/12W-27F6, in feet

Deformation above lacustrine unit

(shallow extensometer)

7N/12W-27F5

Ground-water levels in lower aquifer

1998

AMJ J A S N O D J F M MJ J A S N O D J F MAMJ J A S O

1996 1997

A

pause in injection

for cycle 3

Deformation from 40 feet above

top of lacustrine unit to 1,180

feet (difference of deep and

shallow extensometers)

2,171.6

2,161.6

2,151.6

2,141.6

2,131.6

2,121.6

2,111.6

2,101.6

2,091.6

Injection cycle 1 Injection cycle 2 Injection cycle 3

Figure 22. Aquifer-system deformation and water levels during injection cycles 1–3, Lancaster, Antelope Valley, California in (A) the upper 

aquifer and middle aquifer above the lacustrine unit and (B) the lacustrine unit and upper part of the lower aquifer, 1996–98.

Breaks in graphs indicate wells were not in use.
Tests of Freshwater Injection 37

The continuous GPS data were processed to 

estimate absolute station positions in a global reference 

frame. Precise ephemerides (satellite orbits) generated 

by the International GPS Service (Beutler and Neilan, 

1997) and UT1/polar motion estimates provided by the 

U.S. Naval Observatory were used to provide optimal 

estimates of the satellite positions and orientation of 

the global reference frame. Daily and sub-daily 

positions were estimated from data recorded every 30 

to 120 seconds; the sub-daily solutions, however, did 

not provide additional relevant information and were 

associated with greater error. Daily solutions for all 

three cycles are shown in figure 23.

Spirit Leveling

Spirit-leveling surveys were done in the vicinity 

of the injection and extensometer sites to document the 

areal nature of land-surface deformation during 

injection. The monument array installed and used for 

the leveling surveys consists of more than 120 bench 

marks generally spaced 40 m (131 ft) apart (fig. 24). 

Static GPS was used to determine the altitude of bench 

mark ZERO. The horizontal locations of the remaining 

bench marks were determined by fast-static GPS using 

bench mark ZERO as a reference (Metzger and others, 

2002). All the surveys were done to first-order 

accuracy using laser leveling methods without 

temperature corrections (Federal Geodetic Control 

Subcommittee, 1984).

For the first injection cycle, it was assumed that 

the temporal pattern of uplift would be similar to that 

observed during the preliminary tests in 1994, which 

indicated that maximum uplift may occur after the first 

week of injection. Accordingly, leveling took place 

during the seventh and eighth day of injection. 

However, the initial continuous GPS results from the 

first cycle indicated that uplift may have occurred 

within 48 hours of the onset of injection, and therefore, 

leveling for the second cycle was done during the first 2 

days of injection. Leveling was not done for the third 

cycle except at the gravity monuments, which was done 

well into the test.

Leveling results in the form of change from the 

initial survey (September 25–28, 1995) are shown in 

figure 25 for selected periods for the bench marks 

along the south–north survey line; results of all the 

surveys are given in Metzger and others (2002). The 

primary assumption made from the results shown in 

figure 25 was that the southernmost bench mark, 

measured during successive surveys, was vertically 

stable between the surveys.

Using the assumption that the southernmost 

bench mark is vertically stable, results of the surveys 

for the first injection cycle indicate that uplift near the 

injection wells is less than 2.0 mm (0.006 ft) 7 and 21 

days from the start of injection. Longer term results, 

through cycle 2, show little or no uplift at the injection 

site and generally more variability toward the northern 

end of the survey line (fig. 25).

Tiltmeters

High-precision tiltmeters were used by Robert 

Larson, LACDPW Materials Engineering Division, to 

characterize the shape and estimate the extent of landsurface uplift during cycle 2 injection. Data were 

obtained from three tiltmeters installed north of 

injection well 7N/12W-27P3 at distances of 134, 305, 

and 1,323 ft from the well (fig. 26). The magnitude and 

direction of tilt for each tiltmeter during the first 2 

months of the cycle 2 injection are shown in figure 27.

Monitoring of Water Chemistry

Ground-water and injection-water chemistry was 

monitored to estimate the percentage of injected water 

recovered and the related residual effects of injection 

on ground-water chemistry. All water-chemistry data 

collected and analyzed prior to and during the first two 

injection tests are included in Metzger and others 

(2002). This discussion focuses on these two tests. 

Data collected for the third test, which involved a 

typical source of water, are included in Fram and others 

(2002) and analyzed by Fram and others (2003); the 

analytical methods are described in these reports.
38 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

-40

-32

-24

-16

-8

0

8

16

24

32

40

48

56

64

-8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24

Cycle 1 for April 7–13, 1996.

(Maximum uncertainty + 16 millimeters)

Daily solution with error bar showing one standard deviation:

Cycle 2 for November 6–December 4, 1996.

(Maximum uncertainty + 19 millimeters)

Cycle 3 for April 9–May 9, 1998.

(Maximum uncertainty + 9 millimeters)

Change in land-surface elevation, in millimeters

Days from start of injection

EXPLANATION

Figure 23. Change in land-surface elevation at the injection site from continuous Global Positioning System (GPS) daily solutions 

for selected periods of injection cycles 1–3, Lancaster, Antelope Valley, California.
Tests of Freshwater Injection 39

S35

27F9

EXPLANATION

Bench mark and identifier

Extensometer and identifier

Land-surface altitude—Contour

interval 40 feet. Dashed interval

20 feet. Datum is sea level

2,520

T7N

R12W

T6N

AVENUE K

AVENUE L

AVENUE M

20TH STREET WEST

10tTH STREET WEST

W23

N35

W21

W22

W20

S35

XT2

XT1

DE2

BM83

E19 E20

DL 3197

S35

27F9

EXPLANATION

Bench mark and identifier

Extensometer and identifier

Ama rgosa

Creek

lll l l l l l l l l l l l l l l l l l l l l lll l lll l l l l l llll l l l l l l l l l l l l l l llll

lll l l lll l l l l lll l l l

0

0

0.5

0.5 1 Kilometer

1Mile

2,480

2,520

2,400

2,440

Land-surface altitude—Contour

interval 40 feet. Dashed interval

20 feet. Datum is sea level

2,520

T7N

R12W R12W

T6N

E18

W6

W6

W5 W4 W3 W2 W1

S6

S7

S8

S4

S3

S2

S1

Bench mark and identifer

Injection well and identifer

Nested piezometer and identifer

AVENUE L

5TH STREET WEST

A

margosa Creek 0

0

0.1

0.1

0.2 Mile

0.2 Kilometer

EXPLANATION

E1 E2 E3 E4 E5 E6

N4

N3

N2

N1

NJ1E

NJ2E

NJ3E NJ3W NJ2W

NJ1W

ZERO

27P3

27P3

27P5-P8

27P5-P8

27P2

(injection wells)

S5

7N/12W-27F9–F10

Base modified from U.S. Geological Survey, Lancaster, 1:62,500, 1958;

Lancaster East, 1:24,000, 1958; Lancaster West, 1:24,000, 1958;

Palmdale, 1:24,000, 1958; Ritter Ridge, 1:24,000, 1958;

(dual extensometer)

Figure 24. Locations of bench marks used to monitor changes in land-surface altitude, Lancaster, Antelope Valley, California.
40 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Ground-water quality for pre-injection 

conditions was established by sampling the injection 

wells and other nearby production wells 1 year prior to 

the first pilot test and by analyzing field parameters, 

major ions, selected trace metals, and total 

trihalomethanes. Wells that penetrate the lower aquifer 

had a much higher salinity (total dissolved-solids 

concentrations of 314 to 630 mg/L) than those in the 

upper and middle aquifers (150–248 mg/L), and the pH 

ranged from 7.6 to 8.4. Major ion concentrations varied 

with depth and location (fig. 28). Sodium and 

potassium were the dominant cations in all wells, but 

the anions ranged from bicarbonate in the upper and 

middle aquifers to sulfate and chloride in wells that 

included the lower aquifer. Arsenic concentrations 

ranged from 4 to 51 μg/L; the larger concentrations 

were from the deep wells. Trihalomethanes were not 

detected.

-10

-8

-6

-4

-2

0

2

4

6

8

10

-5,000 -4,000 -3,000 -2,000 -1,000 0 1,000 2,000 3,000 4,000 5,000

Distance from bench mark ZERO, in feet

Bench marks and gravity stations measured

November 4, 1996 (prior to cycle-2 injection)

Bench marks and gravity stations measured

November 14, 1996 (third day of cycle-2 injection)

Bench marks and gravity stations measured

April 9, 1997 (near end of cycle-2 injection)

Bench marks and gravity stations measured

February 17, 1998 (34 days after cycle-2 extraction)

Change in land-surface altitude from initial

survey (September 25 to 28, 1995), in milliimeters

EXPLANATION

G7S

S29

S21

S16 S8 ZERO

N15

N23

N31

N35

Injection

site

Extensometer site

(500 feet to the west)

South North

Uplift

Subsidence

Change from initial survey, September 25 to 28, 1995

Figure 25. Change in land-surface altitude of bench marks and gravity stations along the south–north survey line, 1995–98, Lancaster, 

Antelope Valley, California.

See figure 20 for location of gravity station and figure 24 for location of bench marks.
Tests of Freshwater Injection 41

1N

27P2

27F3

27F9

EXPLANATION

Current or former extraction well and identifier

Extensometer and identifier

Injection well and identifier

Tiltmeter and identifier

Land-surface altitude—Contour interval 40 feet.

Dashed interval 20 feet. Datum is sea level

Water-level monitoring sites

2,480

Nested piezometer and identifer 27P5-P8

AVENUE L

5TH STREET WEST

7N/12W-27F1

7N/12W-27F3

7N/12W-27H1 AVENUE K-8 (bike path)

Tiltmeter 3N

Tiltmeter 1N

7N/12W-27P3

0 0.05

0 0.05

0.10 0.15 0.20 Mile

0.10 0.15 0.20 Kilometer

Amargosa

Creek

2,480

2,440

2,440

2,460

Tiltmeter 2N

(injection wells)

7N/12W-27P5–P8

7N/12W-27F9,F10

Extensometer

Site

Injection Site

T7N

T7N

R12W R12W

7N/12W-27F5-F8

7N/12W-27P2

Figure 26. Locations of tiltmeters used to monitor land-surface deformation near Lancaster, Antelope Valley, California. 
42 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Injection cycle 2

Injection cycle 2

Injection cycle 2

S

E

N

W

S

-10

-20

-30

0

-50

-40

DIRECTION (cumulative) MAGNITUDE (microradians)

S

E

N

W

S

-10

-20

-30

0

-40

DIRECTION (cumulative) MAGNITUDE (microradians)

S

E

N

W

S

-1

-2

-3

-4

-5

0

-7

-6

10 15 20 25 30 5 10 15 20 25 30 5 10 15

DIRECTION (cumulative) MAGNITUDE (microradians)

November December

1996 1997

January

Tiltmeter 1N

Tiltmeter 2N

Tiltmeter 3N

Figure 27. Magnitude (note variable scale) and direction of tilt recorded during injection cycle 2 at tiltmeters 1N, 2N, and 3N, Lancaster, 

Antelope Valley, California.

(From Robert Larson, Los Angeles County Department of Public Works, Materials Engineering Division, written commun., 1997)
Tests of Freshwater Injection 43

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Ground water—Upper and middle aquifers

Ground water—Upper, middle, and lower aquifers

Ground water—Injection wells 7N/12W-27P2–P3 (upper and middle aquifers)

Injection water—Cycle 2

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

EXPLANATION

SODIUM PLUS POTASSIUM

CHLORIDE

CALCIUM

CARBONATE PLUS BICARBONATE

MAGNESIUM

SULFATE

Figure 28. Chemical contrast between native ground water and injected water, Lancaster, Antelope Valley, California.
44 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

The injected water originated as surface water in 

reservoirs north of the Antelope Valley and was 

imported from the Sacramento–San Joaquin Delta via 

the California Aqueduct. All water was treated to meet 

the drinking-water standards by AVEK. Imported water 

is delivered to most Lancaster residents during the late 

autumn, winter, and early spring, and generally is 

blended with ground water during the rest of the year. 

The injection water type was indeterminate, with 

sodium and potassium the dominant cations and 

chloride the dominant anion (fig. 28). The total 

dissolved solids (TDS) ranged from 94 to 326 mg/L, 

and the pH ranged from 6.7 to 7.1.

There were some differences in the major-ion 

and trace-metal concentrations in the native ground 

water and the injected water. The concentrations of 

magnesium, potassium, sulfate, and chloride in injected 

water were greater than those in the native ground 

water, but the nitrate concentrations were lower. The 

only trace metal regularly detected in the injected water 

was zinc, which was not detected in the native ground 

water. Arsenic was not detected (<2 μg/L) in the 

injected water.

Water delivered by AVEK contains disinfection 

by-products (DBPs) not found in native ground water. 

Trihalomethanes (THMs) are DBPs formed from 

dissolved organic carbon (DOC) and bromide, both 

present in the imported SWP water, and chlorine gas 

(Cl2), used for disinfection. Cl2, which is added at the 

end of the treatment process, reacts with water to form 

HOCl and OCl– (hypochlorous acid). HOCl and OCl–

reacts with dissolved bromide (Br–) to form HOBr and 

OBr– (hypobromous acid). The hypochlorous and 

hypobromous acid species then react with DOC to 

form THMs and other DBPs (Fujii and others, 1998; 

Fram and others, 2003):

DOC + HOCl + OCl– + HOBr + OBr– —> 

THMs + other DBPs (2)

The THMs produced range from chloroform 

(CHCl3) to bromoform (CHBr3). The Maximum 

Contaminant Level for total THMs in drinking water 

was recently lowered by the U.S. Environmental 

Protection Agency from 100 to 80 μg/L (U.S. 

Environmental Protection Agency, accessed October 

2002).

The chemistry of the water injected into the 

aquifer system during the injection tests was variable 

owing to, in part, changes in water sources. The 

sources of the SWP water primarily were the 

Sacramento–San Joaquin Delta during the first two 

injections tests (there was a brief switch to San Luis 

Reservoir in March 1997) and from Lake Isabella 

during the third test. Figures 29 and 30 show measured 

concentrations of chloride and THMs, respectively, for 

all three injection cycles. Chloride concentrations in 

weekly samples of the injected water during cycles 1 

and 2 ranged from 4.7 to 94 mg/L, with a median of 53 

mg/L. THM concentrations in the injection water 

during the same period ranged from 21 to 62 μg/L, 

with a median of 37 μg/L. Chloride and THM 

concentrations were notably affected by the brief 

switch in water sources in March 1997. Median 

chloride and THM concentrations in injected water 

during cycle 3 were lower at 9 mg/L and 29 μg/L, 

respectively.

The initial concentrations of the THMs in 

extracted ground water following the injection and 

storage periods of the first two injection cycles were 

much higher than the maximum measured 

concentrations in the injected water ). The peak THM 

concentration in the water extracted from injection well 

7N/12W-27P2 during cycles 1 and 2 was 127 μg/L 

compared with the maximum measured concentration 

of 62 μg/L in the injected water. In contrast, the 

maximum chloride concentration in well 27P2, early in 

the extraction period of cycle 2, was 61 mg/L, which is 

close to the median concentration for the injected water 

during that cycle (56 mg/L) and consistent with the 

final chloride concentration measured during injection 

(57 mg/L; fig. 29). Chloride concentrations in ground 

water collected early in the extraction period of the first 

injection cycle exceed those measured during injection 

(fig. 29); however, given the extreme variability of the 

chloride concentrations in the injected water and only a 

weekly sampling rate, it is assumed that the extremes 

were not represented in the four samples taken during 

the cycle-1 injection period. The THM concentrations 

in the extracted water during the third injection cycle 

also increased during the storage period, but 

concentrations generally were lower (during injection) 

than those during the previous injection cycles 

(fig. 30). However, the chloride concentrations, unlike 

those during the previous cycles, generally were lower 

than those in the native ground water during injection 

but increased toward background concentrations during 

extraction (fig. 29).
Tests of Freshwater Injection 45

Total THM

AS N O D N O D J F MJ J A S J F MA MJ J A S O

1996 1998 1997

A MJ J M A 0

20

40

60

80

100

120

Concentration, in micrograms per liter

Injected water

27P2

27P3

27P6

27P7

27P8

EXPLANATION

Injection/extraction well

Piezometer

Pause in injection

for cycle 3

EXPLANATION

Injection Extraction

Figure 30. Trihalomethane (THM) concentrations in injected and extracted water during injection cycles 1–3, Lancaster, Antelope Valley, 

California.

Figure 29. Cloride concentrations in injected and extracted water during injection cycles 1–3, Lancaster, Antelope Valley, California.
46 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

ANALYSIS OF INJECTION TEST RESULTS

Aquifer-system properties of interest in this 

study include those affecting the hydraulic and 

subsidence-related responses to injection. A 

combination of analyses were used to estimate some of 

these properties, which were then tested and further 

refined through development of a simulation model. 

Water-chemistry data were analyzed to determine the 

chemical responses to injection.

Hydraulic Properties

Hydraulic properties of an aquifer system are 

physical characteristics that govern the capacity of the 

system to store and transmit water. For this study, these 

characteristics include storage coefficient, hydraulic 

conductivity, and transmissivity. Aquifer-test analyses 

can provide estimates of these properties. Such 

analyses were attempted to estimate hydraulic 

conductivity and transmissivity using water-level data 

from the injection-site piezometers during cycle 3; 

however, the unusual delayed water-level response in 

the shallow piezometer (7N/12W-27P8) during May 

1998 (fig. 19) and the lack of water-level 

measurements for the injection well (owing to technical 

difficulties) severely limited the viability of analytical 

approaches. Instead, these values were estimated 

through calibration of the model.

 The storage coefficient is the volume of water an 

aquifer releases from or takes into storage per unit 

surface area of the aquifer, per unit change in head. In 

the unconfined part of the system, removal of water 

from storage is manifested as a corresponding drop in 

the water table. This release of water from gravity 

drainage is described by the specific yield.

Specific yield was measured at one location in 

the study area where simultaneous measurements of 

water levels and gravity were available (Howle and 

others, 2003). Water levels were measured in well 

7N/12W-34B1 prior to (ho) and during injection (hi), 

and corresponding microgravity measurements (go and 

gi, respectively) were made at gravity monument G5S 

(fig. 20). The change in gravity was converted to a 

change in water mass (∆mw):

(3)

where gravity is in μGals and ∆mw is in feet of water 

(12.77 μGals is the mass equivalent of 1 ft of water). 

Specific yield (Sy) was then calculated as follows 

(Howle and others, 2003):

(4)

The resulting value of specific yield was about 0.13 at 

well 7N/12W-34B1, which is within the range of 

typical values (0.02–0.30) for unconfined aquifers 

(Fetter, 1994).

The storage coefficient decreases deeper in the 

aquifer system as cumulative fine-grained sedimentary 

layers, typical of alluvial deposits, effectively reduce 

the hydraulic connection to the water table. Thus, when 

water is removed from deeper parts of the system, the 

water is not provided by drainage of the water table but 

primarily by deformation of the aquifer-system matrix. 

This dependence on the elastic properties of the aquifer 

system associated with confined aquifers effectively 

lowers the storage coefficient, which is now governed 

by the elastic skeletal specific storage and aquifer 

thickness. The observed increase in hydraulic response 

to stress with depth (fig. 19A, B), despite strong 

evidence that less water is produced from deeper parts 

of the aquifer system (fig. 5), is indicative of confined 

conditions.

Aquifer-System Deformation and SubsidenceRelated Properties

The objectives of measuring aquifer-system 

deformation and associated deformation of the land 

surface included determining the spatial and temporal 

nature of land-surface uplift during injection and the 

subsidence-related properties of the aquifer system.

Uplift of Land Surface During Injection

An apparent uplift of the land surface of 4 to 

6 cm was measured using static GPS during 

preliminary injection tests at the Avenue K–8 and 

Division Street well field. Although some uplift was 

anticipated because of the elastic nature of the aquifersystem materials, 6 cm was more than expected. Spirit 

leveling, tiltmeters, and continuous GPS were used at 

the current injection site to better understand the spatial 

and temporal nature of this apparent uplift. ∆mw

gi go –

12.77 = ---------------

Sy

∆mw

hi ho – = ---------------
Analysis of Injection Test Results 47

Leveling results suggest that uplift occurred 

during injection but that this uplift probably was small 

[less than about 3 mm (0.01 ft)] during the first few 

weeks of injection at bench mark ZERO (fig. 25), 

which is about 30 ft northeast of injection well 

7N/12W-27P2 . Note, leveling was done only 

periodically and, thus, larger elevation changes 

between surveys may have been missed. The 

assumption of stability of the southernmost bench 

marks included in successive surveys may be a source 

of error, particularly for the shorter surveys. However, 

comparisons of the results of the leveling surveys that 

included bench mark GS7, almost 5,000 ft south of the 

injection wells (fig. 25), appear to be valid, as the 

measured elevation changes from the spur line to the 

deep extensometer agree with the extensometer 

measurements from each of the surveys (within 0.3 to 

0.6 mm [0.001–0.002 ft]). Only the survey lines that 

include bench mark GS7, which are consistent with 

respect to changes at the extensometer, are shown in 

figure 25.

Results from the tiltmeter array (fig. 27) show 

northward tilt during cycle 2 in all three tiltmeters, the 

most distant at about 1,320 ft from injection well 

7N/12W-27P3 (fig. 26). The meters closest to the 

injection well tilted the steepest away from the well, 

suggesting a concave-upward shape to the deformation. 

Rough estimates of uplift at well 7N/12W-27P3 can be 

calculated using the tilt data and making assumptions 

about the distribution of tilt between meters. Assuming 

the tilt between meters is best represented by that at the 

meter farthest from the injection well results in a 

minimum estimate of about 6 mm (0.02 ft) of uplift by 

January 16, 1997 (after just more than 2 months of 

injection during cycle 2). Assuming the tilt between 

meters is best represented by the average tilt at adjacent 

tiltmeters results in a higher estimate of about 11 mm 

(0.04 ft) of uplift during the same period. These 

estimates assume negligible uplift at the outermost 

meter and no increase in tilt over the 134 ft between the 

innermost meter and the injection well; uplift may have 

been greater than estimated if these assumptions are 

not correct.

Tilt increased at a fairly constant rate during the 

measured period suggesting a slow, steady rate of 

uplift. Uplift as of November 14, 1996 (the third day of 

the cycle-2 injection) was calculated, as described in 

the previous paragraph, for comparison with leveling 

results; however, early data were not available for 

tiltmeter 3N (farthest from the injection well; fig. 27). 

It was assumed that the ratio of uplift between 

tiltmeters 1N and 2N and between tiltmeters 2N and 

3N remained constant during injection; uplift from 

tiltmeters 2N and 3N was estimated from this ratio 

calculated as of January 16, 1997. The resulting highend estimate of uplift on November 14, 1996, at 

injection well 7N/12W-27P3 was about 0.6 mm, which 

agrees well with the leveling results at bench mark 

ZERO [uplift of about 0.5 mm (0.002 ft)] (fig. 25).

The continuous GPS results by themselves 

suggest that about 42 mm (±18 mm) (0.14 ft ± 0.06 ft) 

of uplift may have occurred at the injection site during 

the first 9 days of the cycle-2 injection, followed by a 

decrease to the average (of a noisy signal) of about 10 

mm (0.03 ft) above the pre-injection baseline (fig. 23). 

Leveling and tiltmeter results, however, do not support 

these GPS results. Leveling on November 14, 1996, 

indicates uplift of about 0.5 mm (0.002 ft) from the 

pre-injection baseline compared with about 16 mm 

(±11 mm) (0.05 ft ± 0.04 ft) indicated by GPS. The 

continuous tiltmeter record for the cycle-2 injection 

period suggests a slow, steady uplift; this contrasts 

sharply with the relatively extreme rise and fall 

suggested by the GPS data. GPS surveys can be 

influenced by several factors including changes in 

weather, stability of the control station(s), regional 

tectonic activity, and changes in the status of the GPS 

satellites. A weather front came through during the 

early part of the cycle-2 injection, and the antenna at 

the control station was found to have slipped downward 

3 cm (prior to the apparent maximum uplift), but it is 

not known if either of these factors or other factors 

significantly influenced the results.

 Combined results from the geodetic 

measurements described previously indicate there was 

uplift of the land surface during injection. This uplift 

was measured most accurately by the extensometers, 

followed by spirit leveling, which added a second 

dimension that proved to be very useful for 

interpretation. The tiltmeter data were used to 

determine the general shape and extent of deformation, 

but the continuous GPS data were too noisy to be of 

use for this study. None of these results differentiate 

between uplift caused by injection and that caused by 

normal water-level recovery from seasonal pumping. 

Examination of data from the shallow borehole 

extensometer and of associated water-level data shows 

that water levels and coupled aquifer-system 

deformation had not stabilized prior to the start of the 

cycle-2 injection (fig. 22A). Accordingly, uplift of the 

land surface during the cycle-2 injection likely was 

related to both injection and normal water-level 

recovery from seasonal pumping.
48 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Estimation of Subsidence-Related Storage Properties at the 

Extensometer Site

Simultaneous measurement of aquifer-system 

deformation and water-level changes at the dual 

borehole extensometer provided the information 

needed to determine the subsidence-related storage 

properties of the aquifer system at the extensometer 

site. The elastic properties were used in a model, which 

is described later in this report, and although the model 

does not simulate inelastic deformation, these 

properties were estimated for the benefit of future 

investigations. Note that the excellent agreement 

between the land-surface changes at the extensometer 

site measured by leveling surveys and the deformation 

measured by the deep extensometer suggests that there 

was little or no deformation below the deep 

extensometer (1,180 ft).

The aquifer-system properties that govern the 

response (compaction or expansion) of the system to 

applied stress are components of the aquifer-system 

storativity. Storativity of a confined aquifer, which 

describes conditions in deeper parts of the aquifer 

system in the study area, consists of three components: 

elastic skeletal storage coefficient, inelastic skeletal 

storage coefficient, and storage derived from the 

compressibility of water. The elastic skeletal storage 

coefficient represents the amount of water yielded from 

fully recoverable (elastic) deformation of the aquifersystem skeleton (sediment). When deformation 

exceeds the elastic range and results in permanent 

rearrangement of the aquifer-system skeleton, the 

amount of water yielded is greater than that within the 

elastic range, and is represented by the inelastic 

skeletal storage coefficient. The amount of water 

yielded from the compression or expansion of water is 

relatively small and, in most cases, can be ignored.

Continuous measurements of water-level change 

(stress) and aquifer-system deformation (strain) can be 

used to determine individual components of aquifersystem storativity. Elastic and inelastic storage 

coefficients were estimated using an established 

graphical method (Riley, 1969). This method is similar 

to the approach taken to determine the coefficients of 

compressibility from stress/strain relations derived 

from laboratory consolidation tests. Applied stress 

(hydraulic head) is plotted on the y-axis and vertical 

strain (displacement) on the x-axis. A change in water 

level (hydraulic head) represents a change in applied 

stress, which is equivalent to the change in effective 

stress on a confined aquifer system with a constant total 

stress (eq. 1). Riley (1969) showed that for aquifer 

systems where pressure equilibration can occur rapidly 

between aquifers and aquitards, the inverse slopes 

measured from the predominant linear trends in the 

stress/strain trajectories represent measures of the 

skeletal storage coefficients.

Stress/strain diagrams for the period April 1996 

through December 1998 were constructed for the 

aquifers above and below the lacustrine unit at the 

extensometer site. Aquifer-system deformation in the 

upper and middle aquifers was measured by the 700-ft 

(shallow) extensometer; deformation that occurred at 

the extensometer site in the depth interval 700 to 

1,180 ft below land surface was deduced by computing 

the difference between the daily deformation 

measurements from the shallow and deep (1,180 ft) 

extensometers. These deformation timeseries data were 

matched with water-level timeseries data from the 

appropriate piezometers (fig. 22) to produce 

stress/strain diagrams representative of these intervals 

of the aquifer system (fig. 31).

The closed loops evident in the stress/strain 

diagrams (fig. 31) are indicative of cyclical loading in 

the elastic, or recoverable, range of deformation. The 

linear trend evident from the recovery segments of the 

closed loops represents the elastic behavior of the 

skeletal component of the system. The inverse slope of 

this linear trend (chosen subjectively) represents the 

elastic skeletal storage coefficient, which is about

4.5 × 10-4 for the upper and middle aquifers and 

2.6 × 10-4 for the lower aquifer.

Inelastic compaction is evident both in the 

stress/strain diagrams (fig. 31) and in plots of water 

levels and deformation with time (fig. 22). Horizontal 

offsets of the large loops in the stress/strain diagrams 

indicate inelastic compaction on the order of the 

offsets, or about 0.008 ft in the upper and middle 

aquifers and 0.004 ft in the lower aquifer from 1996 to 

1997. Similar offsets (about 0.007 ft in the upper and 

middle aquifers and 0.003 ft in the lower aquifer) are 

shown in the compaction record on figure 22) despite 

the recovery of water levels close to those of the 

previous year.
Analysis of Injection Test Results 49

-0.005 0 0.005 0.010 0.015 0.020 0.025 0.030

290

300

310

320

330

340

350

Compaction, in feet

Depth to water, in feet below land surface Depth to water, in feet below land surface

D C

B

A

A'

A, A' Slope used to calculate

inelastic skeletal storage

coefficient

B–D Slopes used to calculate

elastic skeletal storage

coefficient

A—Upper and middle aquifers, 15–700 feet

-0.004 -0.002 0 0.002 0.004 0.006 0.008 0.010 0.012 0.014

270

280

290

300

310

320

330

340

A

B

C

A Slope used to calculate

inelastic skeletal storage

coefficient

B-C Slopes used to calculate

elastic skeletal storage

coefficient

B—Lacustrine unit and upper part of lower aquifer, 700–1,100 feet

Direction of increasing time

Direction of increasing time

April

1996

April 1996

December 1998

December 1998

Figure 31. Continuous plot from April 1996 to December 1998 of depth to water (stress) versus compaction (strain) for (A) the upper and 

middle aquifers and (B) lacustrine unit plus upper part of lower aquifer, Lancaster, Antelope Valley, California. 
50 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Measured inelastic compaction, though small, 

allows estimation of the inelastic skeletal storage 

coefficient. A linear trend between successive annual 

loops in the stress/strain plots represents inelastic 

behavior of the skeletal component of the aquifer 

system (Riley, 1969). The inverse slope of this linear 

trend represents the inelastic skeletal storage 

coefficient, which is about 7.0 × 10-3 for the upper and 

middle aquifers and 2.0 × 10-3 for the lower aquifer.

Because only 2.5 years of data were available, only two 

full loops could be plotted on in the stress/strain 

diagram; therefore, the slope drawn for this linear trend 

is somewhat subjective.

The estimated specific storages at different 

depths at the extensometer site were compared. The 

elastic specific storage was calculated using the entire 

thickness of the saturated materials within the 

extensometer range, which is about 385 ft for the 700-ft 

extensometer and 480 ft for the 1,180-ft extensometer 

(after the thickness of the 700-ft extensometer is 

subtracted). The inelastic specific storage was 

calculated using the combined thickness of the 

fine-grained materials in these intervals, which were 

estimated from the geophysical logs to be about 176 

and 280 ft for the shallow (20 ohm-meters resistivity or 

less) and deep (10 ohm-meters resistivity or less) 

intervals, respectively. The resistivity values were 

selected by comparing the lithologic and geophysical 

logs. From shallow to deep, the calculated elastic 

specific storages are about 1.2 × 10-6 and 5.4 × 10-7 per 

foot and the calculated inelastic specific storages are 

about 4.0 × 10-5 and 7.1 × 10-6 per foot. The decrease 

in elastic and inelastic storage values with depth is 

consistent with the consolidating effects of deeper 

burial and more advanced induration (cementation), 

which was noted during drilling and observed 

indirectly on the velocity log (fig. 5).

Areal Distribution of Subsidence-Related Storage Properties

An understanding of the areal distribution of 

subsidence-related storage properties can aid in 

managing land subsidence in Lancaster and 

surrounding areas. Information regarding the areal 

distribution of these properties can be gained by 

comparing calculated values for the Lancaster area 

with those from a study of the Holly site at Edwards 

AFB (Sneed and Galloway, 2000) and by examining 

the spirit leveling data. Storativity at the Holly 

extensometer site, which is about 20 mi northeast of 

Lancaster on Edwards AFB, was estimated by Sneed 

and Galloway (2000) using stress/strain analyses and 

detailed one-dimensional simulations of compaction. 

The Holly extensometer measures aquifer-system 

deformation to a depth of 840 ft, which is similar in 

thickness to the 700-ft interval measured by the 

shallow extensometer in Lancaster. A fundamental 

difference in the geology of the two sites is that the 

lacustrine unit is at depths greater than 700 ft below 

land surface at Lancaster but at depths of only 140 ft 

below land surface at Holly.

The elastic specific storage based on the 700-ft 

extensometer in Lancaster (1.2 × 10-6) is consistent 

with that determined at the 840-ft Holly extensometer 

(1.7 × 10-6) (Sneed and Galloway, 2000). Estimates of 

inelastic specific storage at the Holly site ranged from 

4.0 × 10-5 per foot for aquitards less than 18 ft thick to 

3.5 × 10-4 per foot for thicker aquitards. The lithologic 

and geophysical logs of the borehole for nested 

piezometers 7N/12W-27F5–8 at the extensometer site 

in Lancaster (fig. 32) suggest that the aquitards are 

relatively thin above the lacustrine unit. The associated 

inelastic specific storage is 4.0 × 10-5 per foot, which 

equals that calculated by Sneed and Galloway (2000) 

for relatively thin aquitards. This estimate of inelastic 

specific storage is small compared with that reported 

for other aquitards (Riley, 1998).

Although the estimates of elastic and inelastic 

storage for the relatively thin aquitards at the Holly and 

the Lancaster sites agree well, the estimates of inelastic 

storage for thick aquitards is 200 times smaller at the 

Lancaster site (7.1 × 10-6 per foot) than at Holly 

(3.5 × 10-4 per foot). Sneed and Galloway (2000) 

concluded that delayed drainage of the thick aquitards 

is responsible for most of the ongoing land subsidence 

at the Holly site. In contrast, the lacustrine unit at the 

Lancaster extensometer site appears to be less 

responsible for subsidence than the thinner aquitards. 

The extensometer data for Lancaster show that only 

about one third of the inelastic compaction measured at 

this site is occurring in the interval containing the 

lacustrine unit (fig. 22). 
Analysis of Injection Test Results 51

Spontaneous

potential, in

millivolts

16-inch normal

resistivity, in

ohm-meters

64-inch normal

resistivity, in

ohm-meters

Guard

resistivity, in

ohm-meters

Natural gamma,

in counts per

second

0 50 100 150 0 50 100 150 0 100 200 300 400 0

200

400

600

800

1,000

1,200

Depth, in feet below land surface

100

300

500

700

900

1,100

0 50 100 150 0 50 100 150

Static water level

Upper

aquifer

Middle

aquifer

Lower

aquifer

Lacustrine

Unit

Figure 32. Borehole geophysical logs, well-construction diagrams, and lithologic logs for nested piezometers 7N/12W27-F5–F8 at the 

extensometer site, Lancaster, Antelope Valley, California.

The color of the samples are described using numerical color designations from Munsell soil-color charts (Munsell Color, 1975).
52 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California 2,000 7,000 12,000

0

100

200

300

400

500

600

700

800

900

1,000

1,100

1,200 Depth, in feet below land surface

6 8 10 12 14

Moderately to poorly sorted, sand, silty, light yellowish brown (Munsell color

10YR 6/4) to moderate yellowish brown (10YR 5/4) clay, and some gravel to 0.6 in.

Poorly sorted, predominantly coarse-grained sand and gravel to 1.0 in.

Moderately to poorly sorted, silty, medium- to coarse-grained sand and

some gravel to 0.4 in. Minor clay, moderate yellowish brown (10YR 5/4).

Sandy clay, silt, and some fine-grained gravel. Clay color yellowish

brown (10YR 5/4). Streaks of reddish brown, reddish orange yellowish

orange, very pale orange, and olive gray beginning at about 310 feet.

Moderately to poorly sorted fine- to coarse-grained.

Silty, moderately to poorly sorted medium- to very coarse-grained sand

and gravel to 0.4 in. Some clay, moderate yellowish brown (10YR 5/4)

with streaks of reddish, very pale orange, and grayish clay.

Silty, sandy, moderate yellowish brown (10YR 5/4) clay with streaks of

very pale orange clay. Moderately sorted sand and minor, predominantly

fine-grained gravel.

Silty clay, moderate yellowish brown (10YR 5/4) to light yellowish brown

(10YR 6/4) with streaks of very pale orange, blackish red, and olive to grayish

black. Some fine- to coarse-grained sand and minor fine-grained gravel.

Sandy, moderate yellowish brown (10YR 5/4) clay with occasional streaks

clay, especially between 600 and 640 feet. Moderately to poorly sorted sand

and some predominantly fine-grained gravel.

Moderate yellowish brown (10YR 5/4) clay with streaks of very pale orange, greenish

to brownish black, and reddish brown clay. Minor silt, minor predominantly medium

medium-grained sand and minor fine-grained gravel.

Moderately sorted, predominantly coarse- to very coarse-grained sand and gravel

to 0.6 in. Minor silt. Minor clay above 1,110 feet. Clay colors greenish gray (5GY 4/1),

grayish green (10G 4/2) and dusky yellow (5Y 6/4).

Moderately well sorted, silty, fine- to coarse-grained sand and some gravel to 0.5 in.

Some clay, moderate yellowish brown (10YR 5/4) to grayish green (10GY 5/2).

Grayish green (10G 4/2) to greenish black (5G 2/1) sticky "blue" clay with occasional

streaks of grayish blue green and yellowish orange clay. Minor silt and sand with

slightly increased occurrence beginning at about 860 feet.

Silty, sandy, olive gray (5Y 5/2 and 5Y 6/2) clay with streaks of yellowish orange,

greenish, or brownish. Moderately to poorly sorted, medium-to coarse-grained sand.

Minor fine-grained gravel except from 950 to 960 feet where some gravel to 0.4 in.

Clayey, silty, medium- to very coarse-grained sand with some predoinantly finegrained gravel. Clay color light yellowish (10YR 5/6,10YR 6/4) with streaks of

grayish green and very pale orange.

Silty, sandy, light yellowish brown (10YR 6/4, 10YR 5/6) clay with streaks of very pale

pale orange, grayish green, olive gray, reddish brown, and grayish brown to grayish

black clay. Some fine-grained gravel. Sand moderately sorted, fine- to very coarse-grained

Bottom of borehole

0 ft

40 ft

110 ft

215 ft

430 ft

470 ft

560 ft

600 ft

670 ft

715 ft

740 ft

900 ft

1,015 ft

1,060 ft

1,183 ft

1,000 ft

Static water level Upper aquifer Middle aquifer Lower aquifer Lacustrine Unit

27F5

27F6

27F7

27F8

Description

Acoustic,

in feet per

second

Caliper,

in inches Lithology Well construction

Figure 32.—Continued.
Analysis of Injection Test Results 53

The contrast in the inelastic storage of the thick 

confining unit at Lancaster and at the Holly site may be 

related to differences in the depth of burial and the 

relative age of the thick aquitard. The top of the 

lacustrine unit is more than 700 ft below land surface at 

the Lancaster site but only 140 ft below land surface at 

Holly. The greater the depth of burial of the confining 

unit, the greater the total stress and corresponding 

stress on the aquifer matrix (effective stress, eq. 1) and 

the lower the potential for future strain (compaction).

The relative age of lacustrine deposits at the 

Lancaster and the Holly sites may be an important 

control on their compressibility because the older 

materials have longer stress histories and have been in 

contact with older, more saline water for a longer time 

(higher potential for cementation). The rising of the 

lacustrine unit toward the land surface from south to 

north has been interpreted as northward migration of an 

ancient lake or marsh associated with the uplift of the 

San Gabriel Mountains and associated development of 

alluvial fans (Dutcher and Worts, 1963). This 

interpretation suggests that the lacustrine deposits in 

the southern part of Antelope Valley may be 

significantly older than those in the northern part. 

Paleomagnetic data and alluvial sequence dating 

strongly support this interpretation and indicate that the 

lacustrine unit in Lancaster probably is at least 765,000 

years older than that at Edwards AFB (Fram and 

others, 2002; Ponti, 1985).

Borehole acoustic logs of the extensometer site 

in Lancaster (fig. 32) and of two sites near Holly 

suggest that more compaction and (or) cementation of 

the lacustrine unit has occurred at the Lancaster site 

than at the Holly site. Sound travels relatively slowly 

through unconsolidated materials and speed increases 

with higher consolidation whether by compaction or 

cementation. Acoustic logs of the two boreholes near 

the Holly site show low velocities (average of about 

4,650 ft/s) within the lacustrine unit (Londquist and 

others, 1993; Rewis, 1993) compared with that 

measured at the Lancaster site (about 5,260 ft/s). These 

relatively high velocities in the lacustrine unit at the 

Lancaster site are a clear indication of greater 

consolidation.

Leveling data from this study provide indirect 

evidence of the local variability of the skeletal storage 

properties. Figure 25 shows the results from a series of 

leveling surveys completed along the south–north 

survey line; the results are expressed as differences 

from the initial survey on September 25–28, 1995, and 

the survey on November 27, 1996. The initial survey 

was done near the end of a typical 6-month extraction 

period and therefore represents relatively low water 

levels and associated land-surface elevations. Note that 

although the November 4, 1996, survey followed about 

2 weeks of water-level recovery from the 1996 

extraction season, the elevation of almost all the bench 

marks were lower those than during the initial survey, 

and by significantly different amounts. This suggests 

that inelastic compaction may have occurred between 

these surveys and that stresses and (or) skeletal storage 

properties vary along this line.

Stresses along the survey line during this study 

were limited to extraction and injection at the injection 

site and to minor extraction at the extensometer site. 

No other significant production wells were active along 

the line or within about 1.4 mi north or south of the end 

points of the survey line. Although water-level 

measurements are not available near the end points of 

the survey line, it is reasonable to assume that changes 

in water levels at the end points were smaller than those 

at bench marks closer to the wells. Most of the landsurface change between the first two (and subsequent) 

surveys occurred at the northern end of the survey line, 

more than 4,000 ft from the injection site, suggesting 

that variability in skeletal storage properties was the 

controlling factor.

A fourth survey (April 9, 1997) was done after 

146 days of the cycle-2 injection. Results of a 

comparison of the initial survey (September 25–28, 

1995) with those from the April 9, 1997, survey show 

that land-surface elevations recovered along parts of 

the northern end of the survey line but had little change 

at the southern end (fig. 25). This suggests that the 

elastic skeletal specific storage is greater at the 

northern end. The final survey on February 17, 1998, 

was done about 1 month after the end of an unusually 

long period (8 months) of continuous extraction at the 

injection site. Despite 1 month of recovery, these 

elevations were significantly lower than previous 

measurements along most of the line. This suggests 

that inelastic compaction occurred during the extended 

extraction period.

The leveling data show a clear trend of generally 

increasing temporal and spatial variability in landsurface elevation from south to north (fig. 25); 

arguments based on these data have been made herein 

for a corresponding increase in the skeletal components 

of storage. Measurements of land subsidence from 

1993 to 1995, made using InSAR (fig. 7), show an 

increase in subsidence just north of the extensometer 

site, which supports this argument. 
54 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

A key component of aquifer-system deformation 

that has not been discussed is the preconsolidation head 

and its distribution within the aquitards. Johnson 

(1911) mapped the area of historically flowing wells in 

Antelope Valley that may be associated with high 

preconsolidation heads. Heads likely were high in the 

aquitards throughout this area, and today may have 

relatively high residual heads in their interior (Sneed 

and Galloway, 2000). The southern boundary of the 

area of historically flowing wells is roughly coincident 

with Avenue K, which is the northern extent of the 

survey line. Therefore, it is possible that long-term 

dewatering of aquitards, preferentially in the northern 

area, may be at least partly responsible for the observed 

increase in inelastic compaction in that area.

The overall trend of increasing variability in 

land-surface elevation from south to north is 

conspicuously broken at the injection site and possibly 

broken at the extensometer site (fig. 25). Long-term 

extraction from wells in these areas may have resulted 

in preferential aquifer-system compaction in the 

vicinity of these wells. Laboratory studies have shown 

that skeletal storage properties of aquifer-system 

materials decrease with increased applied stress 

(Poland, 1984). It is possible, therefore, that the areas 

nearest the extraction wells have relatively low skeletal 

storage values.

Chemical Response

The potential chemical responses to injection of 

imported water into native ground water were analyzed 

prior to injection to determine the likelihood of 

precipitation of minerals that could clog the screens of 

the injection wells. Water-chemistry data collected 

during cycles 1 and 2 were used to estimate the amount 

of injected water recovered during extraction and, in 

turn, the effects of injection on ground-water 

chemistry. The results from these analyses led to a 

more detailed investigation of the chemical response 

during cycle 3 (Fram and others, 2002; Fram and 

others, 2003), and are presented here as background for 

that work.

Potential for Mineral Precipitation

If mixing of native ground water and injection 

water were to cause precipitation, there could be 

temporary or permanent losses in well capacity from 

accumulation of mineral coatings on the well screen 

and within the gravel pack and aquifer system. A 

geochemical equilibria model, PHREEQE (Parkhurst 

and others, 1980), was used to evaluate the potential for 

mineral precipitation from the mixing of these waters. 

Ground-water samples that were collected from the 

injection wells prior to injection (Metzger and others, 

2002) and a random sample of AVEK (imported) water 

were used for this analysis. Results of the equilibria 

model indicate that the mixing of these waters would 

not cause precipitation (Scott Hamlin, U.S. Geological 

Survey, written commun., 1996); however, the full 

range of chemical conditions later observed in 

imported and extracted water during that study was not 

addressed.

Recovery of Injected Water

If a substantial volume of injected water cannot 

be recovered during the extraction period of a 

seasonally operated injection program, the injected 

water could have a residual effect on the chemistry of 

the ground water. Water-chemistry data collected 

during the cycle-2 injection, which involved about 5 

months of injection, were used to calculate a mass 

balance and associated residuals.

The mass-balance calculations of chloride in 

wells 7N/12W-27P2 and 27P3 were used to estimate 

the residual concentrations during the second cycle. 

Chloride generally is conservative in ground-water 

systems; the mean concentration of chloride in the 

injected water during this cycle exceeded that in 

ground water (figs. 28 and 29). It was assumed that 

chloride concentrations in the extracted water that 

exceeded the concentrations in ground water indicated 

the presence of injected water. 

The baseline chloride concentration in ground 

water in well 7N/12W-27P2 was assumed to be that at 

the end of cycle-1 extraction (about 8.7 mg/L in July 

1996) rather than that measured in April 1995, which 

was 1 year prior to the first injection test (about 14 

mg/L). The difference in these concentrations suggests 

that chloride concentrations in native ground water 

may be sensitive to pumping conditions: April 

represents the end of a long period of recovery, while 

July is well into the high-extraction period. Baseline 

concentrations in well 7N/12W-27P3 were 21 mg/L for 

the two periods.
Analysis of Injection Test Results 55

The mass of chloride injected was determined 

from weekly samples of AVEK water collected at the 

injection site and from continuous measurements of 

injection rates. The mean chloride concentration of 

injection water was calculated by dividing the total 

mass of chloride injected by the total volume of water 

injected. Similarly, the mean daily to weekly chloride 

concentrations of extracted water was determined from 

daily to weekly samples of extracted water (fig. 29) and 

from continuous measurements of extraction rates. 

Using the following equation, the mean injected 

chloride concentration and the daily to weekly 

estimates of extracted chloride concentrations were 

used to calculate the volume of injected water for each 

daily or weekly sampling period needed to raise the 

chloride concentration of ground water to that in the 

measured volume of extracted water: 

(5)

where

Results from the mass-balance calculations 

suggest that about 50 percent of the injected water was 

recovered during the cycle-2 extraction, split about 

evenly between the two wells (7N/12W-27P2 and 

27P3). The cycle-2 injection test involved 156 days of 

injection followed by 243 days of extraction; about 

156 percent of the total volume injected was extracted 

(injected and native ground water). The accuracy of 

this estimate may have been affected by the high 

variability of the chloride concentrations in the injected 

water and in the ground-water samples and is 

dependent on the assumption that chloride is 

conservative in this system.

The third injection cycle was designed, in part, to 

address the issues of recovery of injected water more 

quantitatively. A conservative tracer, sulfur 

hexafluoride, was added to the injection water. Results 

of the tracer experiment indicate that there was 

extensive mixing between the injected water and the 

native ground water. Analytical modeling of the mixing 

process indicate that this mixing was the primary cause 

of the incomplete recovery of injected water (Fram and 

others, 2003). 

Effects of Injection on Ground-Water Chemistry

Results of the mass-balance calculation, the 

tracer experiment, and analytical modeling indicate 

that seasonal operation of an injection program likely 

would have a residual effect on the chemistry of ground 

water for the same chemical and hydrologic conditions 

and for a similar ratio of injection to extraction volume. 

Results from an analytical mixing model, assuming 

complete mixing, are in agreement with this conclusion 

(Fram and others, 2003). Although both the imported 

water and the native ground water are of drinking-water 

quality and are delivered to customers in Lancaster, the 

imported water used during the first two injection 

cycles contained constituents, in addition to chloride 

and THMs, with concentrations greater than those in 

the native ground water. On the other hand, the 

imported water contained some constituents with lower 

concentrations than those in ground water including 

arsenic, which is a constituent of concern locally.

Determining the potential long-term effects of 

injection on ground-water chemistry was beyond the 

scope of this study; but results of a qualitative analysis 

of chemistry data collected for this study do provide 

some insight on those effects. There are many 

significant differences between the chemical 

composition of the native ground water and that of the 

injected water including differences in pH, several 

major ions, trace metals, and THMs. Early in the 

extraction period of cycle 2, the chemistry of the 

extracted water was similar to the median chemistry of 

the injected water, as might be expected. By the end of 

243 days of extraction, the chemistry of the extracted 

water was similar to that of the native ground water, 

with some exceptions: the extracted water had a lower 

pH (7.5) than the native ground water (8.3), possibly 

owing to geochemical reactions; and the THM 

concentration in the extracted water was 4.6 μg/L but 

was not detected in the native ground water 

Vinj is the volume of injected water 

in the extracted volume 

during the period;

[chloride]extr is the concentration of chloride 

in extracted water during the 

period;

[chloride]inj is the mean concentration of 

chloride during cycle-2 

injection; 

[chloride]o is the baseline concentration of 

chloride in ground water; and

Vextr is the total volume of water 

extracted during the period.

Vinj

[ ] chloride extr [ ] chloride o –

[ ] chloride inj [ ] chloride o – -------------------------------------------------------------------- Vextr = ×
56 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

(Metzger and others, 2002). These exceptions suggest 

that the injection water remained in the aquifer system, 

as is also indicated by the results of the mass-balance 

calculations. The similarities between the extracted 

water and the native ground water near the end of 

cycle 2 suggest that the rate of recovery of the 

remaining injected water was relatively slow by the end 

of the extraction period.

A large-scale injection effort using existing wells 

likely will involve equivalent periods of injection and 

extraction, which could affect the ability to recover 

injected water. Assuming that about 1 month is needed 

for maintenance, monitoring, and any physical 

modification required for switching between injection 

and extraction leaves about 5.5 months (166 days) each 

available for injection and extraction. The change in 

concentrations of many of the constituents is large for 

this period, particularly for THMs (fig. 30). For 

example, during the cycle-2 injection, total THMs 

concentrations decreased from 127 to 8.8 μg/L during 

the 166-day extraction period, but only to 4.6 μg/L 

during the remaining 77 days of the full 243 days of 

extraction. The rates of change for the other 

constituents were similarly reduced, suggesting that 

continued extraction beyond 166 days achieved only a 

minor recovery of the injected water.

THMs represent a change in ground-water 

chemistry because the native ground water had no 

detectable concentrations. For example, during cycle 2, 

the THM concentrations increased almost twofold in 

the extracted water compared with the concentrations 

in the injected water (fig. 30). A decrease in the 

measured concentrations of free chlorine, from 0.30 to 

0.80 mg/L (median 0.52 mg/L), in the injected water to 

below the detection limit in the extracted water 

suggests that the THMs continued to form in the 

aquifer system after injection. A comparison of the 

median concentrations of the THM species in injected 

water to those of extracted water early in the extraction 

period suggests preferential growth of the chlorinated 

species within the ground-water system: chloroform 

concentrations increased by 179 percent compared with 

bromoform, which increased only 38 percent. The 

controls on THM formation in the aquifer system after 

injection during cycle 3 are discussed in detail by Fram 

and others (2003). A key finding from their work is that 

THMs do not undergo biodegradation by aquifer 

bacteria under the aerobic conditions present at the 

injection site and that THMs do not adsorb the aquifer 

sediments from this site.

DEVELOPMENT OF A NUMERICAL MODEL 

OF GROUND-WATER FLOW IN THE 

LANCASTER AREA

A numerical model of three-dimensional groundwater flow in the Lancaster area (the area surrounding 

the injection site) from 1983 to 1998 was developed to 

aid in the analysis of the hydraulic data collected 

during the injection tests, and as part of a 

simulation/optimization model for use in planning and 

managing a potential larger scale injection program. A 

USGS finite-difference model code [MODFLOW 

(McDonald and Harbaugh, 1988), with the PCG2 

numerical solver (Hill, 1990)], was used to develop this 

model, which simulates transient three-dimensional 

ground-water flow in an 11- by 19-mi area surrounding 

the injection site (figs. 1 and 33). MODFLOW 

calculates directions and quantities of ground-water 

flow, and their associated effects on ground-water 

levels using input that describes the interaction 

between the modeled volume and its surroundings 

(boundary conditions); the state of the aquifer system 

at the start of the simulation (initial conditions); 

hydraulic properties of the aquifer system; and natural 

or artificial stresses affecting the aquifer system (for 

example, recharge from streams, or discharge from 

ground-water pumping). Simulated ground-water 

levels, streamflow, recharge rates, and (or) other 

indicators of the state of the aquifer system are 

compared with measured values to evaluate the 

accuracy of the simulation.

Although subsidence is a significant hydraulic 

process in the Lancaster area, it was not simulated in 

this model because additional subsidence was not 

considered an acceptable outcome of future groundwater management. Water levels were controlled in 

subsidence areas during management optimization 

simulations to avoid additional subsidence. The model, 

as discussed in this section of the report, was used to 

synthesize available hydraulic data and to estimate 

lesser known hydraulic properties that control the 

behavior of the aquifer system. Application of the 

model as a planning tool in the form of a 

simulation/optimization model is discussed in the 

section “Development of A Simulation/Optimization 

Model.”
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 57

Three models are discussed often in this report. 

One is a previously published model of ground-water 

flow and aquifer-system compaction (land subsidence) 

for the Antelope Valley ground-water basin (fig. 1), 

herein referred to as the AV model. This model was 

developed for another study and is documented in a 

report by Leighton and Phillips (2003). The groundwater-flow model of the Lancaster area, discussed in 

this section of the report, is referred to as the LAN 

model. A simulation/optimization model discussed 

later in this report, which incorporates a modified 

version of the LAN model, is referred to as the 

LANOPT model.

Sources of model input and measures of the state 

of the aquifer system include information gathered for 

this study, described earlier in this report, and by 

Howle and others (2003) and Metzger and others 

(2002); results from previous hydrologic studies, 

including Bloyd (1967), Londquist and others (1993), 

Templin and others (1995), Carlson and Phillips 

(1998), Carlson and others (1998); ground-water 

pumpage and well-construction data, as well as other 

data provided by the LACDPW; and results from 

previous regional-scale models of Antelope Valley 

(Durbin, 1978; Leighton and Phillips, 2003). 

Model Grid and Boundary Conditions

The model grid serves to divide the conceptual 

aquifer system into discrete three-dimensional blocks, 

or cells. Hydraulic properties and stresses are assigned 

to each cell. Hydraulic head and flow directions and 

rates are calculated for each cell on the basis of the 

input values and the simulated interactions with 

neighboring cells. Data collected during the injection 

tests were from wells that are densely spaced within a 

small area near the injection wells, where the hydraulic 

response to injection was greatest, and are more 

sparsely spaced with increasing distance from the 

injection site. Accordingly, the model grid (fig. 33) was 

constructed with relatively small cells at the injection 

site (about 100 ft on each side), increasing in cell size 

(by a factor of 1.1) with distance from the injection site, 

to a maximum dimension of about 1,980 ft. The 

resulting grid is 77 rows by 101 columns, some of 

which are inactive (rows 1 and 2 and 75 through 77, 

and columns 1 through 3 and 99 through 101).

The model domain was divided vertically into 

two layers at an altitude of 1,950 ft. Vertical 

discretization was required to adequately represent the 

contrast between younger, unconsolidated materials in 

the upper aquifer and the underlying older, more 

compacted and indurated (hardened) materials in the 

middle aquifer (fig. 34) (Leighton and Phillips, 2003). 

The lower aquifer and lacustrine unit were not included 

in the LAN model. The lacustrine unit, which was 

assumed to act as a significant barrier to both vertical 

and horizontal flow, formed the impermeable bottom 

and (or) sides of model cells, as appropriate. The 

specified thicknesses of model layers 1 and 2 were 

variable and dependent on the altitudes of the water 

table (variable in time and space), the lacustrine unit, 

and bedrock (fig. 34). The lateral extent of layer 2 is 

smaller than that of layer 1 because the aquifer system 

thins along the margins of the model area with rising 

bedrock to the south and the rising lacustrine unit to the 

north (figs. 33 and 34).

Boundary conditions are used to describe the 

hydraulic interaction across model boundaries. Ideally, 

model boundaries are placed far enough away from the 

area of interest to minimize their possible effects on the 

numerical solution on that area and reasonably 

represent true hydrologic conditions. For the LAN 

model, the lateral boundaries that parallel bedrock 

outcrops along the San Gabriel Mountains and Quartz 

Hill were assumed to be no-flow boundaries because 

the hydraulic interaction with bedrock probably is 

small (fig. 35). Interbasin subsurface ground-water 

flow into the model area from the upgradient Pearland 

and Buttes subbasins (fig. 1) was represented by a 

specified flux boundary in layer 1 (layer 2 not present) 

(fig. 35), and is based on the results from the AV model 

(Leighton and Phillips, 2003). Heads were specified in 

layer 1 along a stretch of the northern boundary to 

account for southward flow from a broad ground-water 

mound between Lancaster and Rosamond (Carlson and 

others, 1998). Measured water levels in wells within 

the ground-water mound decreased by 5 ft or less 

during the simulation period; accordingly, the specified 

heads were held constant with time. The remaining 

lateral boundaries, to the northwest and east, are 

represented as no-flow boundaries based on the 

flowlines and ground-water divides determined from 

contour maps of ground-water levels in 1983 and 1996 

(Carlson and others, 1998) (fig. 36A, B) and from 

results of the regional simulations (Leighton and 

Phillips, 2003). All lateral boundaries for layer 2 were 

no-flow. The upper boundary condition is the water 

table.
58 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

The lacustrine unit is not simulated in the LAN 

model, because vertical flow across the lacustrine unit 

was assumed to be negligible (a no-flow boundary). 

Although flow across the lacustrine unit likely does 

occur, and certainly occurs through production wells 

screened both above and below this unit and over much 

larger periods than simulated, such flow probably is 

small during the periods simulated. Information 

necessary for simulating the lower aquifer (particularly 

the transmissivity and lateral boundary conditions) and 

for assessing model performance in the lower aquifer is 

lacking. The AV model includes the lower aquifer, but 

the calibration of that aquifer was poorly constrained in 

the area of the LAN model (Leighton and Phillips, 

2003). The upper boundary of the LAN model is the 

water table, a free surface.

 The assumption of no flow across lateral 

boundaries defined by flowlines and ground-water 

divides was tested because of uncertainty in the waterlevel contour maps potential for variations in flow 

directions with depth, and possible movement of these 

features during the calibration period. Fluxes through 

these boundaries were simulated for the period 1983 to 

1995 using the AV model (Leighton and Phillips, 

2003). Results showed minor flow through most of the 

flowline boundaries, but relatively significant flow 

from the LAN model area toward the east, an 

agricultural area. This eastward flow ranged from about 

2,300 to 900 to acre-ft/yr, decreasing essentially 

linearly with time, and averaged 1,600 acre-ft/yr. The 

steady decrease in eastward flow is related to the 

eastward migration of the ground-water-flow divide 

along that boundary (fig. 36), which parses the 

recharge from the southeastern boundary into eastward 

and westward flow. Recharge along the eastern third of 

the southeastern boundary was reduced by these 

transient amounts from 1983 to 1995 (assuming linear 

decrease) to compensate for the portion that leaves the 

model area through the eastern boundary. Eastward 

flow from 1996 to 1998 was assumed to be 

900 acre-ft/yr.

T6N

T7N

T7N

T8N

R13W R13W R12W R12W R11W R11W

Model grid, layer 1

(red boundary)

Outline of layer 2

Shallow lacustrine unit

Shallow bedrock

Shallow bedrock

Quartz Hill

Injection

site

Lancaster

Palmdale

12'30" 07'30" 118°02'30"

40'

34°35'00"

34°45'00"

118°17'30"

0

0 5 Kilometers

5 Miles

Amarg osa

Cr eek

R10W

Figure 33. Active region of the LAN model grid, Lancaster, Antelope Valley, California.

Cells increase in size outward from about 100 feet square at injection site to maximum dimension of about 2,000 feet. Rows and columns are 

numbered sequentially from the northwest corner of the grid.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 59

1,400

1,600

1,800

2,000

2,200

2,400

2,600

2,800

3,000

1,400

1,600

1,800

2,000

2,200

2,400

2,600

2,800

3,000

B B'

Northwest

South

Southeast

Altitude, in feet above sea level

0

0

1

1 2 Kilometers

2 Miles

0 1

0 1 2 Kilometers

2 Miles

Injection site

Injection site

1,400

1,600

1,800

2,000

2,200

2,400

2,600

2,800

3,000

1,400

1,600

1,800

2,000

2,200

2,400

2,600

2,800

3,000

A A'

Land surface

1996 water table

Unsaturated zone

Upper aquifer

Middle aquifer

Land surface

1996 water table

Top of lacustrine unit

North

Unsaturated zone

Upper aquifer

Middle aquifer

Lower aquifer

Boundary uncertain

Layer 1, LAN model

Layer 2, LAN model

Vertical scale greatly exaggerated 20x

Vertical scale greatly exaggerated 20x

Top of lacustrine unit

Lower aquifer

Lacustrine unit

Lacustrine unit

Layer boundaries for Antelope Valley regional (AV) model (Leighton and Phillips, 2003)

EXPLANATION

Layer 1

Layer 2

Layer 1

Layer 2

Bedrock

Bedrock

Figure 34. Generalized sections A-A ́ from south to north and B-B ́ from northwest to southeast through injection site showing delineation 

of model layers for the Lancaster area (LAN) and regional (AV) models, Antelope Valley, California.

Cross-sections locations shown in figure 1. 
60 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Initial Conditions and Temporal Discretization

Ideally, transient models are developed by 

initially simulating the aquifer system during a period 

when it is in equilibrium (a steady-state model) and 

then incorporating the output as the initial condition for 

the transient simulation. It was not possible to use this 

methodology for this study because the system has not 

been in equilibrium since predevelopment and because 

the boundary conditions changed dramatically from 

predevelopment to the present. However, hydraulic 

parameters were available from the AV model 

(Leighton and Phillips, 2003) that was calibrated. The 

AV model included a steady-state model representing 

predevelopment conditions (prior to 1915) and 

transient conditions (1915–95). Parameters from the 

AV model were used initially in this model and 

adjusted as necessary to calibrate the LAN model. 

Although significant adjustments were made to 

individual parameters, the calibrated bulk properties 

were similar.

Spring 1983 measured water levels (fig. 36A) 

were used for the initial condition in the LAN model 

because the spring season generally represents 

recovered conditions prior to the summer pumping 

season. In addition, water-level data for 1983 are 

relatively plentiful and well distributed (Carlson and 

others, 1998), and 1983 represents a short-term quasisteady-state condition, falling between the end of an 

agricultural decline and the beginning of rapid urban 

expansion (figs. 2 and 37) (Templin and others, 1995; 

Leighton and Phillips, 2003). Although the measured 

water levels for 1983 do not indicate ideal steady-state 

conditions throughout the model area, the long-term 

hydrograph of well 7N/12W-27H1, which is within 

0.5 mi of the injection and extensometer sites, suggests 

that this is a reasonable approximation in the area of 

interest (fig. 14).

Quartz Hill

EXPLANATION

No-flow, coincident with flowline or

ground-water divide

No-flow, due to proximity of bedrock

Specified flux

April 1996 water-level contours,

contour interval 25 feet. Datum is

sea level

Specified head

2,150

Boundaries

no-flow

specified

flux

Specified head

2,125

2,1002,075

2,050

2,150

2,175

2,225

2,250

2,225

2,200

2,175

2,250

2,225

2,200

2,200

Injection

site

Lancaster

Palmdale

12'30" 07'30" 118°02'30"

40'

34°35'00"

34°45'00" 118°17'30"

0

0 5 Kilometers

5 Miles

Figure 35. Lateral boundary conditions for layer 1 of the LAN model and 1996 water-level contours (modified from Carlson and others, 1998) 

used to define no-flow boundaries coincident with flowlines or ground-water divides, Lancaster, Antelope Valley, California.

All lateral boundaries for layer 2 are no-flow.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 61

2,225

2,125

2,1002,075

2,050

2,150

2,175

2,225

2,250

2,225

2,200

2,175

2,200

2,250

2,200

EXPLANATION

LAN Model boundary, layer 1

April 1996 water-level contours,

contour interval 25 feet. Datum

is sea level

Well with water-level data

EXPLANATION

LAN Model boundary, layer 1

Spring 1983 water-level contours,

contour interval 25 feet. Datum

is sea level

Well with water-level data

6N

T8N

T7N

T7N

T6N

T6N

T8N

T7N

T7N

T6N

T6N

R13W R13W R12W R12W R11W R11W R10W

R13W R13W R12W R12W R11W R11W R10W

Quartz Hill

2,275 2,250

2,250

2,225

2,225

2,225

2,175

2,150

2,150

2,175

2,150

2,125 2,125

2,200

2,175

2,200

2,200

2,225

2,150

Lancaster

2,225

2,150

12'30" 07'30" 118°02'30"

40'

34°35'00"

34°45'00"

40'

34°35'00"

34°45'00"

118°17'30"

118°17'30" 12'30" 07'30" 118°02'30"

Injection

site

Quartz Hill

Lancaster

Palmdale

Injection

site

Palmdale

Amarg osa Cree k

Amarg osa Cr eek

Ground-water divide

Ground-water divide

Figure 36. Contours of measured water levels for (A) spring 1983 (used as initial head values for both layers of the LAN model) and (B) April 

1996 (modified from Carlson and others, 1998) in Lancaster, Antelope Valley, California.
62 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Spring 1983 water-level data were used to 

develop a contour map (fig. 36A), which, in turn, was 

used to assign initial head values for every cell in the 

model. Owing to a lack of distributed depth-specific 

data, it was assumed that heads in layers 1 and 2 were 

equal. Recent water-level data from the nested 

piezometers installed for this study (fig. 17) indicate 

this is a reasonable assumption for spring conditions 

prior to the injection tests.

The simulation period for the LAN model is May 

1983 through August 1998. This time period was 

divided into 185 monthly segments (30.4375 days 

each) called stress periods. Extraction and injection 

rates, as well as other stresses, are defined for each 

stress period. Given that most of the pumpage data was 

available as monthly totals and that the shortest 

injection cycle was 1 month in duration, this level of 

temporal discretization was considered appropriate. To 

ensure numerical accuracy of the solution, each stress 

period was divided into 15 time steps; the length of 

each time step was increased by a factor of 1.2 from 

that of the previous step.

Hydraulic Properties of the Aquifer System

The hydraulic properties of an aquifer system are 

the physical characteristics that govern the capacity of 

the system to store and transmit water. For this study, 

these characteristics are defined by the storage 

coefficient, hydraulic conductivity, and transmissivity. 

The storage coefficient is the amount of water taken 

into or released from the system per foot of water-level 

change. In the unconfined part of the system, removal 

of water from storage is manifested as a corresponding 

decline in the water table. This release of water from 

gravity drainage, termed the specific yield, was 

calculated for this study from coupled microgravity and 

water-level measurements (Howle and others, 2003) to 

be about 0.13 near the injection wells. As in the AV 

model (Leighton and Phillips, 2003), this was assumed 

constant across the model area in layer 1.

The storage coefficient decreases with increasing 

depth in an alluvial aquifer system because the 

cumulative fine-grained sedimentary layers, typical of 

alluvial deposits, effectively reduce the hydraulic 

connection to the water table. Thus, when water is 

removed from deeper parts of the system, this water is 

not from water-table drainage, but primarily from 

deformation of the aquifer-system matrix. This 

dependence on the elastic properties of the aquifer 

system dramatically lowers the storage coefficient, 

which is then governed by the specific storage and 

layer thickness. A specific storage of 1.2 × 10-6 per ft 

was used in the LAN model, which is the elastic 

skeletal specific storage determined from the 

stress/strain analysis at the extensometer site. The 

storage coefficient for layer 2 was the product of 

specific storage (assumed to be the same everywhere) 

and actual layer thickness (fig. 38). Values of storage 

coefficient ranged from 3.8 × 10-5 to 3.5 × 10-4. 

The inelastic component of storage was not 

simulated in the LAN model. A primary goal of 

ground-water management is to avoid subsidence; 

therefore, the inclusion of subsidence in the LAN 

model was not needed. The effects of ignoring inelastic 

compaction as a source of water in the LAN model 

vary with areal location. Measured inelastic 

compaction was small at the extensometer site (fig. 22), 

totaling about 0.01 ft in the upper and middle aquifers 

from 1996 to 1997. If this compaction is assumed to 

ultimately contribute water to the water table, the 

equivalent water-table increase from water derived 

from compaction would be about 0.08 ft/yr at a specific 

yield of 0.13. In central Lancaster, where the measured 

total subsidence rate was about 2 cm (0.066 ft) per year 

from 1993 to 1995 (fig. 7), the equivalent water-table 

increase would be about 0.34 ft/yr if it is assumed that 

about two thirds of the compaction occurred in the 

upper and middle aquifers (as at the extensometer site). 

Water from compaction could have a greater effect on 

water-level changes in the middle aquifer, but induced 

flow between the upper and middle aquifers would 

dampen large changes.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 63

The ability of aquifer-system materials to 

transmit water is defined by their horizontal and 

vertical hydraulic conductivities. Horizontal 

transmission of water is defined by the transmissivity, 

which is the product of horizontal hydraulic 

conductivity and saturated thickness of the aquifer. 

Initial horizontal hydraulic conductivity values (fig. 39) 

used in the LAN model were based on those used in the 

AV model (Leighton and Phillips, 2003), which, in 

turn, were, for the most part, based on specific-capacity 

data from Bloyd (1967) for wells throughout the 

region. The vertical hydraulic conductivities also 

initially were based on conductivity values used in the 

AV model, for which the ratio of horizontal to vertical 

hydraulic conductivity (vertical anisotropy) was 

assumed to be 100:1, but were adjusted during 

calibration.

Recharge and Discharge

Recharge and discharge refer to the 

replenishment and loss of water to and from the 

ground-water system. During the calibration period 

(1983–98) of the LAN model, recharge in the 

Lancaster area occurred by natural and artificial means 

and discharge occurred primarily by ground-water 

extraction. Simulated recharge was varied annually, 

depending on the contributions from local runoff, 

interbasin flow, agricultural return flow, and infiltration 

of treated wastewater and discharge was varied 

monthly according to measured and estimated 

ground-water pumpage.

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

1915 1925 1935 1945 1955 1965 1975 1985 1995

Year

Annual pumpage, in acre-feet

Total Pumpage

Agricultural Pumpage

Figure 37. Estimated historical annual total and agricultural pumpage in the Antelope Valley ground-water basin, California.

(From Leighton and Phillips, 2003).
64 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Natural Recharge

Natural recharge in Antelope Valley is believed 

to occur primarily through infiltration of runoff from 

the surrounding mountains, concentrated in stream 

channels along the mountain front (Thompson, 1929; 

Bloyd, 1967; Durbin, 1978). Aquifer materials 

generally are coarser at the heads of alluvial fans and 

are associated with relatively high infiltration rates. 

Aquifer materials are finer downgradient from the 

heads of the alluvial fans and less runoff infiltrates.

A primary source of natural recharge within the 

model area is Amargosa Creek, which lies in the 

central part of the southern boundary of the model 

(fig. 40). Flow in Amargosa Creek is ephemeral and 

flashy; however, there is a lack of information on the 

timing, duration, and volume of flow. Studies of 

recharge processes in the Mojave River Basin, the 

adjacent basin east of Antelope Valley, have shown that 

downward flow of infiltrated runoff through large 

thicknesses of alluvial materials can take from decades 

to centuries to reach the water table (Izbicki and others, 

1998; Izbicki, 1999). Downward movement of water is 

slowed by multiple laterally extensive, flat-lying, finegrained layers upon which perched water spreads 

laterally, effectively diffusing the recharge spatially and 

temporally. Thus, although there is extreme short-term 

and annual variability in runoff, this variability likely is 

damped by the time infiltrated runoff becomes recharge 

to the water table. Owing to the lack of flow 

measurements on Amargosa Creek and the results of 

Izbicki’s work, recharge from Amargosa Creek was 

assumed constant with time. Recharge initially was 

specified at 662 acre-ft/yr, as in the regional AV and 

Durbin (1978) models, and then adjusted to 

2,835 acre-ft/yr during calibration of the LAN model to

Figure 38. Thickness of model layer 2, Lancaster, Antelope Valley, California.

Thickness contours are in feet.

T6N

T6N

T7N

T7N

T8N

R13W R13W R12W R12W R11W R11W R10W

275

250

250

225

225

225

200

225

200

200

200

200

175

175

175

175

175

175

150

150

150

150

125

125

125

125

100

100 100

100

50

75

outline of layer 2

Quartz Hill

Injection

site

Lancaster

Palmdale

12'30" 07'30" 118°02'30"

40'

34°

35'

00"

34°

45'

00"

118°17'30"

0

0 5 Kilometers

5 Miles

Amargosa

Cre ek
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 65

24 ft/d

Palmdale

Lancaster-area model boundary, layer 1

Antelope Valley

regional model grid

A

Lancaster

5 ft/d

5 ft/d

10 ft/d

Injection

site

Lancaster-area model boundary, layer 1

Values from regional (AV) model

Calibrated values from Lancaster

area (LAN) model

Quartz Hill

0

0 5 Kilometers

5 Miles

40'

40'

34°35'00"

34°45'00"

12'30" 07'30" 118°02'30"

34°35'00"

34°45'00" 118°17'30"

7 ft/d

17 ft/d

14 ft/d

33 ft/d

Lancaster

Palmdale

Injection

site

Zone used in second phase

of calibration and sensitivity

analysis

Quartz Hill

B

10 ft/d

2 ft/d

Amargosa

Creek

Amargosa

Creek

EXPLANATION

Hydraulic conductivity of layer 1

Hydraulic conductivity of layer 2

Feet per day

17

1.7

1.7 ft/d

1.4 ft/d

ft/d

3.3 ft/d

0.7 ft/d

10 ft/d

10 ft/d

10 ft/d

10 ft/d

10 ft/d

10 ft/d

Lancaster-area model boundary, layer 2

Lancaster-area model boundary, layer 2

Figure 39. Distribution and values of hydraulic conductivity in the Lancaster-area (LAN) model, Antelope Valley, California. (A) initial values 

based on regional (AV) model (Leighton and Phillips, 2003), and (B) final calibrated values.
66 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

match the measured hydraulic gradient in wells on the 

Amargosa alluvial fan. These regional models also 

included recharge along the San Gabriel Mountains 

west of Amargosa Creek (fig. 40) to account for flow 

from many of the smaller intermittent streams in this 

area. Recharge from these smaller streams to the LAN 

model was specified as about 1,300 acre-ft/yr (same 

value specified in the regional models) and was not 

adjusted during calibration of the LAN model.

The southeastern specified-flux boundary 

represents the natural recharge upgradient of the model 

area that enters the model area as subsurface interbasin 

flow into the Lancaster subbasin from the Pearland and 

Buttes subbasins (fig. 40). Little Rock and Big Rock 

Creeks recharge the Pearland and Buttes subbasins; any 

recharge from these creeks that is not consumed or 

retained within these basins flows downgradient to the 

Lancaster subbasin; some of the flow enters the model 

area. This interbasin flow into the model area was 

estimated by the AV model as varying by less than 8 

percent from 1983 to 1995, at an average rate of about 

7,650 acre-ft/yr (Leighton and Phillips, 2003). This 

estimate was based on constant annual rates of recharge 

from Little Rock and Big Rock Creeks during this 

period and on variable rates of extraction in the area. 

Flows in these creeks, and associated recharge, were 

not constant during this period that includes both 

drought and relatively wet conditions. The estimated 

average annual recharge represents average conditions 

based on reasons similar to those described for constant 

recharge from Amargosa Creek.

 Simulations of the AV model suggested that net 

eastward flow was occurring through the eastern 

boundary of the LAN model area. This flow decreased 

from about 2,290 acre-ft in 1983 to 900 acre-ft in 1995, 

averaging 1,636 acre-ft/yr. The specified interbasin 

flow (recharge) through the eastern third of the 

southeastern boundary was reduced by these rates, 

linearly distributed on an annual basis, to compensate 

for the effect of the eastward migration of the groundwater flow divide that straddles the eastern boundary. 

Thus, net outward flow through the eastern boundary, 

in the form of discharge (or diverted recharge), was 

accounted for through a reduction in recharge from the 

adjacent southeastern boundary.

Other Forms of Recharge

In addition to artificial recharge by injection 

(only from the injection project within the LAN model 

area), other forms of recharge in the LAN model area 

include agricultural return flow (agricultural recharge), 

infiltration of secondary-treated wastewater ponded 

near the southeastern boundary (wastewater recharge), 

and southward flow through the northern boundary. 

The distribution and rates of agricultural and 

wastewater recharge are shown in figure. 40. 

Agricultural recharge was specified for current and 

former agricultural areas to account for irrigation water 

that percolates past crop roots through the unsaturated 

zone and reaches the water table, which was assumed 

to be 30 percent of total irrigation (Leighton and 

Phillips, 2003). Most of the irrigation water in these 

areas was ground water pumped from local wells, but 

the area along the western boundary (fig. 40) was 

irrigated using imported water provided by AVEK. 

Leighton and Phillips (2003) incorporated a delay of 

10 years between the onset of irrigation and the onset 

of agricultural recharge, and between the cessation of 

irrigation and the cessation of agricultural recharge, to 

improve the match between stimulated and measured 

water levels in agricultural areas in the AV model. 

Therefore, recharge was specified for some formerly 

irrigated lands and for several areas where farming 

continues. Irrigation returns were specified annually 

through 1995 using the same rates as those in the AV 

model and were assumed to remain at the 1995 rate 

from 1996 to 1998.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 67

Subsurface interbasin flow

(5,440 to 6,710 acre-ft/yr)

T8N

T7NT7NT6NT6N

R11W R10W R11W R12W R12W R13W R13W

671

acre-ft/yr 2,398

acre-ft/yr

0

8,0007,0006,0005,0004,0003,0002,0001,000

1984

1986

1988

1990

1992

1994

1996

1998

YEAR

RECHARGE, IN ACRE-FEET PER YEAR

0

800400

2,4002,0001,6001,200

WW

Ag

Ag

Ag=234 andAmargosa CK=437,

totaling 671 acre-ft/yr

Ag

Ag

Ag

Ag

Amargosa Creek

San Gabriel Mountains

EXPLANATION

Infiltration of irrigation water in

current or former agricultural area

Infiltration of treated wastewaterAssumed constant after 1995

Ag

WW

Recharge

RECHARGE, IN ACRE-FEET PER YEAR

RECHARGE, IN ACRE-FEET PER YEAR

RECHARGE, IN ACRE-FEET PER YEAR

RECHARGE, IN ACRE-FEET PER YEAR

RECHARGE, IN ACRE-FEET PER YEAR

RECHARGE, IN ACRE-FEET PER YEAR

YEAR

YEAR

YEAR

YEAR YEAR

YEAR

0

800400

2,4002,0001,6001,200

0

800400

2,4002,0001,6001,200

0

800400

2,4002,0001,6001,200

0

800400

2,4002,0001,6001,200

0

800400

2,4002,0001,6001,200

1984

1986

1988

1990

1992

1994

1996

1998

1984

1986

1988

1990

1992

1994

1996

1998

1984

1986

1988

1990

1992

1994

1996

1998

1984

1986

1988

1990

1992

1994

1996

1998

1984

1986

1988

1990

1992

1994

1996

1998

1984

1986

1988

1990

1992

1994

1996

1998

A

marg o as

k eer C Quartz Hill

Injection

Lancaster

site

Palmdale

12'30" 07'30" 118°02'30"

40'

34°35'00"

34°45'00"

118°17'30"

0

0 5 Kilometers

5 Miles

Small-intermittent streams

(1,295 acre-ft/yr)

Subsurface inflow

(average 5,130 acre-ft/yr)

Figure 40. Distribution and magnitude of recharge in the Lancaster-area (LAN) model, upper and middle aquifers only, Antelope Valley, 

California.
68 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Secondary-treated wastewater from the Palmdale 

Wastewater Reclamation Plant has been ponded on Los 

Angeles Department of Airports property since 1984 as 

a means for disposal. On the basis of field evidence, 

ongoing studies (Jose Saez, Los Angeles County 

Sanitation Districts, unpublished data, 1999), and 

mass-balance calculations from inflow volume and pan 

evaporation rates, these ponds are assumed to 

contribute recharge to the aquifer system. The massbalance calculations were based on inflow volumes 

from 1984 to 1998 (David Lambert, Los Angeles 

County Sanitation Districts, unpublished data, 1996, 

1998), a pan evaporation rate of 114in./yr (Bloyd, 

1967), and pond acreages. Prior to 1997, about 58 acres 

were ponded (David Lambert, Los Angeles County 

Sanitation Districts, written commun., 1996). In 1997, 

pond acreage increased to about 400 to 500 acres; 

however, the larger ponds were seldom fully wetted. 

Records of the wetted areas of the larger ponds are not 

available; therefore, it was assumed that, on average, 

about twice the area of the old pond was wetted from 

1997 to 1998. Calculated wastewater recharge 

increased from about 1,457 to 8,064 acre-ft from 1985 

to 1998 (fig. 40), which correlates well with population 

growth in Palmdale (about 23,150 to 117,100) for the 

same period (fig. 2). Because this source of water is 

continuous and essentially constant and the rate of 

infiltration per acre is much greater than that for 

agricultural recharge, it was assumed for both the AV 

and the LAN models that the delay between infiltration 

through the bottom of the pond and water-table 

recharge was less than 1 year.

The northern boundary of the LAN model area 

straddles a broad ground-water mound between 

Lancaster and Rosamond to the north (Carlson and 

others, 1998). Simulated southward flow from this 

mound in the LAN model, through the specified-head 

boundary, averages 5,130 acre-ft/yr (fig. 40). This 

mound is in an area that historically had not been 

developed, except for a few homesteads which had 

flowing wells (Johnson, 1911); this area has remained 

undeveloped. Because there are limited potential 

sources of recharge in the area, the ground-water 

mound probably is a remnant of past hydraulic 

conditions rather than a feature fed by recharge. Any 

simulated recharge from the northern boundary 

probably represents ground-water storage released 

during a slow northward retreat of the mound as 

widening cones of depression from the Lancaster area 

draw water southward. The specified-head boundary is 

a surrogate for this process, which cannot be simulated 

at this subregional scale.

A summary of estimated recharge from all 

sources considered is shown in figure 41A. Potential 

recharge that was assumed to be insignificant include 

upward flow from the lower aquifer, direct infiltration 

of precipitation, and urban sources. Although annual 

precipitation is small in the Lancaster area, even a 

small amount of rainfall reaching the water table over a 

large area would constitute a significant volume of 

recharge. However, given the very dry nature of desert 

soils, it commonly has been assumed that infiltrated 

precipitation is held in tension in near-surface soils and 

later evaporates rather than moves downward (Snyder, 

1955; Durbin, 1978).

Potential urban sources of recharge in the model 

area primarily include infiltration of irrigation water 

from urban landscaping and from pipe leakage. Grass 

lawns, for example, have irrigation requirements 

similar to alfalfa. The average home owner or 

municipal caretaker may irrigate a lawn more than the 

average farmer irrigates alfalfa, but because of thatch 

buildup in lawns, runoff to storm drains, and other 

factors, recharge from this source may be equal to or 

less than that from agriculture. Leakage from waterdelivery, storm-drain, and sewer pipes can be a 

substantial component of recharge in some areas 

(Phillips and others, 1993). Positive, but low

(0.05–0.11 mg/L), measurements of methylene-blueactive substances [an indicator of sewage source 

(Phillips and others, 1993)] from wells near the 

intersection of Avenue J and Sierra Highway (fig. 7) 

suggest that recharge from sewer-pipe leakage in this 

area may be small; concentrations in all other wells 

tested were below the detection limits (less than

0.05 mg/L) for this substance. A determination of 

recharge from these sources is beyond the scope of this 

work; however, it is important to recognize that these 

potential sources of recharge are not accounted for in 

the model. 
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 69

Percent of average annual pumpage

in acre-feet from 1983 to 1997

A Recharge

1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 0

5,000

50,000

45,000

40,00035,00030,00025,00020,00015,00010,000

Total pumpageLos Angeles County Department of Public WorksAgriculturePalmdale Water DistrictMutual water companiesOther

Acre-feet per year

Acre-feet per year

Acre-feet per year

Year

Year Year

Pumpage

B

9876543210

2019181716151413121110

Los Angeles County Department of Public Works

Palmdale Water District

Agriculture (est.)

C

Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec.

Monthly pumping

Month

Total recharge

1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 0

5,000

50,000

45,000

40,00035,00030,00025,00020,00015,00010,000

Total pumpage

D Recharge versus pumpage

0

5,000

30,000

25,000

20,00015,00010,000

1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Total rechargeWastewater returnInterbasin flowInflow from northAmargosa CreekAgricultural returnIntermittent stream

Figure 41. Data and estimates for (

A) recharge, (

B) pumpage, (

C) seasonal distribution of pumpage, and (

D) a comparison of 

recharge and pumpage, in the model area, upper and middle aquifers only, Lancaster, Antelope Valley, California.
70 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Ground-Water Extraction

Ground-water pumpage data were gathered and 

compiled from several sources (Templin and others, 

1995; Leighton and Phillips, 2003; and individual 

water purveyors). Figure 42 shows the location of the 

known production wells in the model area; construction 

information for these wells is given in table 1. Well 

depths are known for 70 of the 85 known production 

wells, and the screened intervals are known for 68 of 

the wells. Figure 41B shows annual ground-water 

pumpage for various groups of wells and total pumpage 

from 1983 to 1997. The sharp increase in pumpage 

during the late 1980s corresponds with increased 

agricultural use and rapid population growth in the area 

during that period (fig. 2). Pumpage plateaued during 

the early 1990s, which corresponds to water shortages 

and associated water conservation efforts during the 

1987–92 drought; pumpage increased after the drought.

Monthly meter readings were available for all the 

LACDPW and Palmdale Water District wells in the 

model area and account for most of the annual 

pumpage (fig. 41B). Because only annual pumpage 

data were available from all the other entities, the 

monthly distribution of pumpage for these wells was 

estimated. Because most of the urban suppliers in this 

group used little imported SWP water, it was assumed 

that the temporal distribution of ground-water pumpage 

for these suppliers would be similar to that of the 

Palmdale Water District, which had less seasonal 

variation in pumpage during most of the simulation 

period than that of LACDPW, which used SWP water 

extensively during the winter (fig. 41C).

T6N

T6N

T7N

T7N

T8N

R13W R13W R12W R12W R11W R11W R10W

Lancaster

Palmdale

Quartz Hill

Air Force Plant 42

HIGHWAY 14

LANCASTER BLVD

AVENUE I

AVENUE K

AVENUE L

20TH ST EAST

30TH ST EAST

10TH ST EAST

40TH ST EAST

50TH ST EAST

70TH ST EAST

10TH ST WEST

20TH ST WEST

30TH ST WEST

40TH ST WEST

50TH ST WEST

70TH ST WEST

60TH ST WEST

AVENUE G

AVENUE H

AVENUE J

AVENUE F

AVENUE M

AVENUE N AVENUE N

AVENUE O

Elizabeth Lake Rd.

SIERRA HIGHWAY

AVENUE P

AVENUE Q

PALMDALE BLVD

AVENUE R

80TH ST WEST

EXPLANATION

Lancaster-area (LAN)

model boundary

Production well and number

Urban supply

Agricultural supply

9C2

1B1

34A

26J

26J2

23R1

24M3

14D1

14D2

24M2

25M2

12M2

12R1

5J 6F1 6H4

6H3

5G4

5G3

18H1

18A

17D1

17A 17

20A1

20A

20G2 19G1

19F219F1

8K3 9P1

9H1

3F 1B1

4H1

33Q1

33J2

33A1

20G

20G

13F1

11M2

11E

9A

9B

9E3

17C

17F

30B1

21C4 21C5

22B2

15R4 15R3

15R2

21C2

30J

32A1 27P3

27P2

27J4

27H3

27J6

27F327F2

33R3

34N4

34N3

9H3

16A2 15H

23A1

13N1

24C1

24A3

19E5

19E619L

19C

35G2

18R

18R

8M2 8M1

9Q1

8M

Creek

0

0 5 Kilometers

5 Miles

12'30" 07'30" 118°02'30"

40'

34°35'00"

34°45'00"

118°17'30" 90TH ST WEST

Amarg osa

Figure 42. Locations of production wells included in the Lancaster-area (LAN) model in Lancaster, Antelope Valley, California.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 71

Agricultural pumpage is the least understood 

category of ground-water usage in the Antelope Valley 

(Templin and others, 1995; Leighton and Phillips, 

2003). Although estimates of agricultural water use 

were available from recordations provided to the State 

Water Resources Control Board, comparisons of these 

data with land-use information and crop production 

reports suggest that these data are incomplete (Templin 

and others, 1995; Leighton and Phillips, 2003). 

Leighton and Phillips (2003) estimated agricultural 

pumpage from land-use data, crop acreages, and 

estimated crop water demands and irrigation 

efficiencies. Annual agricultural pumpage values from 

the AV model for the area of the LAN model (fig. 41B) 

were divided evenly among the 17 known agricultural 

wells in the area (fig. 42). There may be additional 

agricultural wells in this area, but they likely would be 

near the known agricultural wells. Although this 

method results in an areawide average annual 

extraction value for each well, which ignores local 

variability, it produces a more reasonable total annual 

variability that agrees with known crop acreages. This 

method also concentrates the pumpage in areas with 

dense concentrations of agricultural wells, which 

seems appropriate assuming that the known 

distribution of wells reasonably represents the true 

distribution.

Data on the monthly distribution of agricultural 

pumpage were not available; therefore, the distribution 

was estimated using the monthly reference 

evapotranspiration for alfalfa (University of California 

Cooperative Extension, 1994) for March through 

October (fig. 41C). Alfalfa, which was the dominant 

crop in Antelope Valley, generally is not irrigated 

during the other months of the year. Although other 

crops were grown in the area of the LAN model, there 

is little information on the areal distribution by crop 

type; therefore, it was assumed that the monthly 

irrigation schedule for alfalfa (timing only, not volume) 

is representative of all crops grown in the area.

Monthly extraction rates for each well were 

assigned to the row and column in the model grid that 

coincides with the location of the well. Extraction rates 

for some model cells represent more than one well.

Pumpage from wells screened in the upper and 

middle aquifers was apportioned by the transmissivity 

of layers 1 and 2. The transmissivity of the upper 

aquifer (layer 1) changes in response to water-level 

changes because the aquifer is unconfined. These 

changes in transmissivity cause changes in the vertical 

distribution of flow into a well. Pumpage was 

redistributed vertically for 3 time intervals during the 

simulation (1983–1987, 1988–1992, and 1993–1996) 

to account for temporal changes in transmissivity.

For wells that are also screened in the lower 

aquifer, which was not simulated in the LAN model, 

the pumpage was reduced by the percentage of 

effective transmissivity attributed to the lower aquifer 

prior to distributing it to model layers. This effective 

transmissivity was calculated from the screened 

interval within the lower aquifer and the assumed 

hydraulic conductivity of this aquifer. The value of 

horizontal hydraulic conductivity used in the AV model 

for the lower aquifer was constant, 2.0 ft/d; however, 

that model was relatively insensitive to this value 

(Leighton and Phillips, 2003). This value was initially 

used for the entire area of the LAN model, but was 

increased to 7.0 ft/d for the northern part of the model 

area on the basis of relative well capacities and 

borehole flow data (described later in this report). The 

pumpage attributed to the lower aquifer in the 

calibrated LAN model was 13 percent of the total 

pumpage.

Ground-water recharge and pumpage in the 

model area during the calibration period are shown in 

figure 41D. A comparison of these data suggests a 

near-equilibrium condition from the beginning of the 

calibration period through about 1988, followed by 

depletion of ground-water storage through the end of 

the calibration period.

Model Calibration and Sensitivity

Model calibration involves adjusting the initial 

input values within reasonable ranges to obtain good 

agreement between simulated and measured (or 

estimated) values. Calibration of the LAN model was 

achieved in two phases: a trial-and-error process 

(phase I), followed by a more systematic parameter 

estimation process (phase II) that also served as a 

sensitivity analysis. The trial-and-error process is 

useful for learning about the aquifer system, and 

sometimes it is the only means available or practical for 

model calibration. Results from this process, however, 

can be non-unique and difficult to interpret. It was used 

for this study to determine the general sensitivity of the 

model results to changes in the conceptual model and 

reasonable ranges of input parameter values for the 

next phase of calibration. A more systematic approach
72 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

was used in phase II to address the uniqueness of the 

calibration results and to determine the sensitivity of 

model results to values not thoroughly considered 

during the trial-and-error calibration. In keeping with 

this approach, results from the trial-and-error process 

are discussed in general terms in the phase I section of 

the report. Presentations of model fit (hydrographs and 

water-level) are given in the phase II section.

The calibration criteria was various forms of 

hydraulic head. Hydraulic head was the only measured 

dependent value simulated, which is not ideal for 

model calibration. Preferably, calibration would 

include both head and flow, but no measurements of 

dependent flow were available. Simulated and 

measured water-table altitudes were compared using a 

contour map of the 1996 water table (fig. 36); 

hydrographs of 10 wells that, for the most part, show 

annual water-level changes throughout all or most of 

the calibration period; hydrographs of 5 piezometers 

and 3 wells that were measured frequently during the 

injection tests; and hydrographs of 20 wells with shortterm records. The locations of all the wells used in 

model calibration are shown in figure 43. Simulated 

hydraulic gradients from the upper aquifer (water table) 

to the middle aquifer were compared with the 

measured hydraulic gradients in nested piezometers.

Although it was considered important to 

simulate the measured heads and flow directions near 

the outer margins of the LAN model, the primary focus 

during calibration was the central part of the model. 

This area of the model includes the injection site for 

this pilot study and is the area where a larger scale 

injection program may be implemented.

Cree k

0

0 5 Kilometers

5 Miles

12'30" 07'30" 118°02'30"

40'

34°35'00"

34°45'00"

118°17'30"

HIGHWAY 14

LANCASTER BLVD

AVENUE I

AVENUE K

AVENUE L

20TH ST EAST

30TH ST EAST

10TH ST EAST

40TH ST EAST

50TH ST EAST

70TH ST EAST

10TH ST WEST

20TH ST WEST

30TH ST WEST

40TH ST WEST

50TH ST WEST

70TH ST WEST

60TH ST WEST

AVENUE H

AVENUE J

AVENUE M

AVENUE N AVENUE N

AVENUE O

SIERRA HIGHWAY

AVENUE P

AVENUE Q

PALMDALE BLVD

AVENUE R

80TH ST WEST

90TH ST WEST

Amargosa

27F6,8

27P6,8 27J5

T6N

T6N

T7N

T7N

T8N

R13W R13W R12W R12W R11W R11W R10W

Lancaster

Palmdale

Quartz Hill Injection

site

Air Force

Plant 42

27Q1

3C1

3Q1

9D1

16D

20D1

19G1

16J1

19F1

19E6

24C1

23A1

12M2

15A1

9H3

16A2

34B1

27H3

22K1

21C5

9B

9E3 11M2

19R1

30B1

24M3

26J2

27H1

27H7

26K3

11C1

33N1 34N4

EXPLANATION

Outline of model grid

Well with water-level data 9H3

26J2 Well with long-term hydrograph

shown in figure 48 34B1 Well or piezometer with short-term

hydrograph shown in figure 49

Figure 43. Location of wells and piezometers used in model calibration, Lancaster, Antelope Valley, California.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 73

Phase I Calibration

For the first phase of calibration, a trial-and-error 

approach was used to determine the general sensitivity 

of the model results to changes in the conceptual model 

and to determine reasonable ranges of the parameter 

values for the next phase of calibration. Values 

considered during the phase I calibration included the 

hydraulic conductivity of layer 1 (K1), transmissivity of 

layer 2 (T2), leakance (λ) between layers, specific yield 

(Sy), specific storage (Ss), the vertical distribution of 

ground-water pumpage, and recharge. All these 

hydraulic parameters, except leakance, are described in 

detail earlier in this report. The ability of aquifersystem materials to transmit water vertically is 

described by the leakance (λ):

(6)

where

Parameters values were adjusted by trial and 

error within reasonable ranges of measured values, 

when available, and of the calibrated values from the 

AV model (Leighton and Phillips, 2003). Measured 

values were available for Sy and Ss for individual sites. 

Sy was assumed to be 0.13 throughout the LAN model 

area; this value was based on the calculated value from 

simultaneous measurements of gravity and water-level 

change (Howle and others, 2003) and on the successful 

use of this value in the AV model (Leighton and 

Phillips, 2003). Although evidence presented earlier 

suggests variability in the elastic skeletal specific 

storage, which comprises the Ss of the LAN model, 

information needed for determining the areal 

distribution of this variability was not available. The 

AV model simulated subsidence measured at bench 

marks in the Lancaster area reasonably well. The 

calibrated value for compaction in the Lancaster area 

reasonably matched the measured value using a 

constant elastic skeletal specific storage of 1.7 × 10-6, 

which is essentially identical to that calculated from the 

stress/strain diagrams using data from the Lancaster 

extensometer site (1.2 × 10-6). Therefore, Ss was 

assumed to be 1.2 × 10-6 throughout the model area and 

the storage coefficient for each cell in layer 2 was 

calculated as the product of Ss and the thickness of the 

middle aquifer at the cell location. Values of Sy and Ss

were varied during the first phase of calibration but 

ultimately were returned to 0.13 and 1.2 × 10-6, 

respectively.

Measurements were not available for K1, T2, 

and λ, and therefore the calibrated values from the AV 

model were used as the initial values in the LAN 

model. The AV-model values of T2 and λ were not 

directly applicable to the LAN model, however, 

because these values were affected by the thickness of 

layer 2, which was different in the two models (fig. 34). 

Instead, the AV-model values for K2 and KV for the 

appropriate thicknesses were used in the LAN model.

The initial values for K1 (based on the calibrated 

value from the AV model) are shown in figure 39. 

Values of K1 were varied widely during calibration of 

the LAN model to determine the overall sensitivity, but 

generally were narrowed for the injection site to the 

range of values for nearby cells in the AV model 

(10–24 ft/d). Results from the AV model (fig. 39A) 

show that hydraulic conductivity decreases with 

increasing distance from the San Gabriel Mountains, 

the primary source of the aquifer materials, along the 

south–southwestern border of the LAN and AV 

models. However, a relatively low value of K1 was 

required during calibration of the AV model for the 

Palmdale area to match the measured water-level 

declines; a low value of K1 also was required during 

the first phase of calibration of the LAN model. It was 

assumed that because of the relatively large depth to 

the water table in the Palmdale area (fig. 36) and the 

corresponding increase in age and induration of the 

saturated materials, a relatively low hydraulic 

conductivity occurs in this area. A decrease in Sy

would have partly offset the decrease in K1; however, it 

was assumed that Sy is constant.

Another anomaly in the distributed K1 values in 

the AV model is the easternmost zone (fig. 39A) which 

had the highest hydraulic conductivity (24 ft/d), which 

includes an area relatively far from the San Gabriel 

Mountains. A high hydraulic conductivity was required 

for the southern part of this zone to transmit underflow 

from the southeast without generating simulated heads 

that were much higher than those measured in this area, 

where the water table is relatively shallow. The 

simulated heads in the northern part of this zone were 

relatively insensitive to hydraulic conductivity in both 

the AV and the LAN models; therefore, the actual K1

may be lower than that shown in figure 39 for the 

northern part of the easternmost zone.

KV is the effective vertical hydraulic 

conductivity between layers 1 and 2 (L/t), 

and

b is the thickness between the midpoints of 

layers 1 and 2 (L).

λ KV

b = -------
74 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

The hydraulic conductivity of layer 2 (K2) in the 

AV model was constant at 10.0 ft/d in the LAN model 

area, and transmissivity varied with the thickness of the 

model layer. The initial transmissivity of layer 2 of the 

LAN model was calculated using a value of 10 ft/d for 

K2 and the appropriate layer thickness for each model 

cell. The T2 was calibrated in the vicinity of the 

injection and extensometer sites on the basis of the 

measured water levels in the piezometers screened only 

within the middle aquifer. Results of the first phase of 

calibration showed that values of K2 considerably 

smaller than those of K1 were required to produce 

satisfactory results for these locations; this differs from 

results of the AV model, particularly if the ratio of 

K1:K2 is assumed to be consistent throughout the 

model area. Results of the phase I calibration suggested 

that the total transmissivity of layers 1 and 2 in the 

LAN model needed to be approximate to that in the AV 

model for most areas.

The leakance (λ) between the upper and middle 

aquifers in the AV model for the Lancaster area was 

based on a ratio of K1:KV of about 100:1. For the LAN 

model, the value of KV was also linked to K1; thus, 

their areal distribution was the same (fig. 39B). The 

ratio of K1:KV was varied during the phase I 

calibration. The measured vertical gradients were best 

simulated with ratios greater than 100:1, and KV was 

not linearly related to K1. These KV values were 

divided by the thickness between the midpoints of 

layers 1 and 2 to calculate λ for every cell.

The vertical distribution of ground-water 

pumpage was calculated for each well on the basis of 

the calculated effective transmissivity of each layer in 

the LAN model that each well is screened in and of the 

lower aquifer. The lower aquifer was not simulated in 

the LAN model, so these calculations were external to 

the model. The vertical distribution of pumpage was 

affected during calibration by changes in K1 and K2

and by the hydraulic conductivity assigned to the lower 

aquifer for the calculations. The hydraulic conductivity 

of the lower aquifer initially was assumed to be 2.0 ft/d 

throughout the LAN model area, as in the AV model. It 

was increased to 7.0 ft/d in the northern part of the 

LAN model area during the second phase of 

calibration.

Ground-water recharge was the only stress that 

was changed in magnitude during the phase I 

calibration. Recharge from Amargosa Creek was 

adjusted, and the effects of a previously ignored 

potential source of recharge was examined. The only 

known estimate of recharge from Amargosa Creek 

(about 662 acre-ft/yr) was by Durbin (1978); he based 

the estimate on the channel geometry method. This 

method is subject to large variation between estimates, 

particularly for desert environments where flashy 

runoff regularly alters and (or) leaves the channel. The 

calibrated value (2,835 acre-ft/yr) was based on the 

measured hydraulic gradient between wells 6N/12W16A2 and 9H3, which have similar depths and are 

similarly constructed (table 1); these wells are about 

1.5 and 2.2 mi north of the point where Amargosa 

Creek enters the model area, respectively (fig. 42). No 

other means was found to match this gradient and the 

water-table altitude without a substantial increase in 

recharge. Prior to increasing recharge, initial heads 

were checked and adjusted slightly where Amargosa 

Creek enters the model area. Amargosa Creek, which is 

ungaged, is the third largest drainage from the San 

Gabriel Mountains in Antelope Valley; for comparison, 

the estimated total recharge from the two larger 

drainages averages 16,200 acre-ft/yr (Leighton and 

Phillips, 2003).

The calibrated value for recharge from 

Amargosa Creek (2,835 acre-ft/yr) exceeds the 

previous estimate (662 acre-ft/yr) by Durbin by a factor 

of 4. It is possible that any simulated recharge that 

exceeds the estimated channel capacity of Amargosa 

Creek may occur as infiltration of precipitation falling 

on the coarse-grained fanhead where Amargosa Creek 

enters the valley and (or) by ground-water movement 

through coarse materials beneath the streambed.

It initially was assumed that no flow occurred 

between the middle or upper aquifer and the lower 

aquifer through the lacustrine unit. During calibration, 

this assumption was relaxed, and recharge was added to 

the middle aquifer as if upward flow were occurring. 

Water levels were sensitive to this potential source of 

recharge; however, the effects were not beneficial 

enough to warrant the uncertainty introduced from 

estimating the magnitude and distribution of upward 

and, at times, downward flow. The small measured 

vertical gradients suggest that flow across the 

lacustrine unit probably is a minor source of water. 

Data required for simulation of the lower aquifer in this 

area are lacking.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 75

Results of the phase I calibration suggested that a 

reasonable match between simulated and measured 

heads for most of the model area could be obtained 

using reasonable values for the calibration parameters 

and the existing conceptual model. However, an 

excellent match was not obtained at the extensometer 

and injection sites for any one set of parameters. Two 

specific difficulties in matching measured water levels 

were identified: a good match of both high (at peak 

injection) and low (during the August pumping season) 

water levels could not be made at the extensometer site 

nor could a good match be made for water levels in the 

middle aquifer at the extensometer and the injection 

sites with the same set of parameters. The phase I 

calibration was useful for determining the gross 

sensitivity of the model results to the input variables, 

and, in turn, for developing an approach for the next 

phase of calibration and the sensitivity analysis.

Phase II Calibration 

A systematic approach was developed for the 

second phase of calibration using what was learned 

during the phase I calibration. The primary assumption 

made in the transition was that the storage properties 

(Sy and Ss) are constant throughout the model area. 

This assumption was based on the results of the AV 

model, in which this parameter was constant 

throughout the area of the LAN model (Leighton and 

Phillips, 2003) and on the results of the phase I 

calibration. Results from the phase I calibration 

showed that the simulated long-term water-level 

changes are sensitive to the Sy where water-level 

changes are greatest and that a value of 0.13 provides a 

reasonable match to measured water-level changes. 

Although the value of elastic Ss estimated from the 

stress/strain analysis was consistent with that used 

throughout the AV model and with that determined at 

the Holly site at Edwards AFB (Sneed and Galloway, 

2000), there is abundant evidence that the elastic Ss

varies spatially. There is not enough information, 

however, to quantify the distribution of elastic Ss

throughout the model area. Simulated heads are 

relatively insensitive to reasonable changes in this 

value. The assumption that storage properties are 

uniform and known reduced the calibration variables to 

three parameters: K1, K2 (used to calculate T2), and KV

(used to calculate λ). Pumpage, recharge, and the 

model geometry were unchanged.

For a given value of K1, K2 and KV were varied 

systematically for specified ranges within a zone 

surrounding the injection site (fig. 39B). This zone was 

designed to be large enough to minimize effects of the 

“boundary conditions” outside the zone (areas with 

unchanging parameters), and small enough to avoid 

relatively drastic effects, such as dewatering of the 

upper aquifer, in some parts of the model with some 

combinations of these three parameters.

The upper and lower bounds of K2 considered 

initially in the phase II calibration were about 15 and 1 

ft/d, respectively; these values were based on results 

from the AV model (Leighton and Phillips, 2003) and 

from the phase I calibration of the LAN model. The 

bounds of KV were less constrained, so a larger range 

(0.001–1.0 ft/d) was explored. K1 was adjusted within 

the range of 12 to 18 ft/d.

The error associated with simulations using each 

combination of K1, K2, and KV was quantified by 

comparing 3 measured and simulated conditions: 

water-table rise during injection, and vertical gradients 

during injection and extraction. These errors were 

calculated for the injection and extensometer sites; 

however, only those for the injection site are presented 

because measured and simulated responses at the 

extensometer site to stresses at the injection site were 

insufficient (particularly at the water table) for use in 

this calibration procedure.

The errors associated with water-table rise and 

seasonal vertical gradients were plotted in 

2-dimensional space (K2 and KV) and contoured to 

form an error surface. This error surface reveals the 

shape and position of lines of zero error (fig. 44). Each 

point along these 3 lines of zero error represents a 

combination of parameters that results in zero error 

between measured and simulated values. The 

combination of parameters that best simulates the 3 

conditions (water-table rise during injection and 

vertical gradients during injection and extraction) is at 

the intersection of the 3 lines. The location of these 

intersections is sensitive to the value of K1 associated 

with each error surface (fig. 44).

The error in simulated water-table rise generally 

was sensitive to K1 and K2 and relatively insensitive to 

KV; the lines of zero error are subhorizontal in 

figure 44. The error in simulated vertical gradient was 

very sensitive to KV and mildly sensitive to K1 and K2; 

it is shown as vertically oriented contours in figure 44. 

These different sensitivities to the parameters help to 

constrain the location of the intersection of these 

zero-error lines.
76 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Effective vertical hydraulic conductivity, layer 1-2 (KV)

Log effective vertical hydraulic conductivity, layer 1-2 (log KV)

Log effective vertical hydraulic conductivity, layer 1-2 (log KV) Log effective vertical hydraulic conductivity, layer 1-2 (log KV

Log hydraulic conductivity, layer 2 (log K2) Log hydraulic conductivity, layer 2 (log K2)

Log hydraulic conductivity, layer 2 (log K2)

Hydraulic conductivity, layer 2 (K2) Hydraulic conductivity, layer 2 (K2)

1.2

1.0

0.8

0.6

0.4

0.2

0

15.85

10.00

6.31

3.98

2.51

1.58

1.00

-3.00 -2.50 -2.00 -1.50 -1.00 -0.50 0

0.001 0.0032 0.01 0.032 0.10 0.32 1.00

1.2

1.0

0.8

0.6

0.4

0.2

0

15.85

10.00

6.31

3.98

2.51

1.58

1.00

-3.00 -2.50 -2.00 -1.50 -1.00 -0.50 0

0.001 0.0032 0.01 0.032 0.10 0.32 1.00

1.2

1.0

0.8

0.6

0.4

0.2

0

15.85

10.00

6.31

3.98

2.51

1.58

1.00

-3.00 -2.50 -2.00 -1.50 -1.00 -0.50 0

0.001 0.0032 0.01 0.032 0.10 0.32 1.00

EXPLANATION

Vertical gradient during water-table peak

Vertical gradient during water-table low (extraction)

Water-table peak (during injection)

Parameter combinations simulated and for which

error was calculated

Solutions where layer 1 was desaturated

Approximate best-fit solutions for injection site













A

C

B



K1=12 ft/d

K1=18 ft/d

K1=15 ft/d

Lines of zero error between simulated and measured:

Figure 44. Results of phase II calibration procedure for layer-1 hydraulic conductivity values (K1), of (A) 12, (B) 15, and (C) 18 ft/d.

The curved lines in the diagram represent approximate parameter combinations that result in zero error between simulated and measured 

water-table rise during injection or between simulated and measured vertical gradients at the injection site during injection cycle 3. All values 

of hydraulic conductivity are in foot per day (ft/d).
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 77

There was a separation between the zero-error 

lines representing the vertical gradients at the injection 

and extensometer sites. Those for the extensometer site 

are not shown in figure 44, but were offset to the right 

(indicating a higher KV) and roughly parallel to those 

for the injection site. This separation is likely related to 

the inability to match the measured water levels in the 

middle aquifer at both sites with one set of parameters, 

as was noted during the phase I calibration. 

Simulations that matched the measured conditions at 

the injection site are associated with low hydraulic 

heads (about 20 ft lower than the measured value) in 

the middle aquifer at the extensometer site during the 

pumping season. Simulated conditions in the upper 

aquifer at the extensometer site reasonably matched the 

measured conditions year round. Calibration results 

indicate that an increase in the vertical hydraulic 

conductivity of at least one order of magnitude in the 

vicinity of the extensometer site over that for the 

injection site may correct this problem. There is no 

apparent justification, however, for increasing KV to 

the north, where fine-grained materials would be 

expected to increase, or for increasing it by such a large 

amount across a short distance (about 0.5 mi). This 

inability to match measured conditions in the middle 

aquifer at both sites is insensitive to the other 

parameters considered in the calibration procedure: K1

and K2.

A probable explanation for the inability to match 

simultaneously the water levels in the middle aquifer at 

both the extensometer and injection sites is that the 

effects of inelastic compaction were not simulated. 

Inelastic compaction measured by the shallow 

extensometer from 1996 to 1997 was about 0.007 ft, 

which yielded an equivalent amount of water. This 

amount is conservative because the shallow 

extensometer does not include the lower 40 ft of the 

middle aquifer (fig. 10), which contains fine-grained 

materials (fig. 32), and because compaction of the 

upper part of the lacustrine unit also would yield water 

to the middle aquifer. The deep extensometer includes 

both of these intervals. About 0.003 ft of additional 

compaction was recorded at this extensometer during 

the same period. The 20 ft of excess drawdown 

simulated for the same period multiplied by the 

specific-storage value used in the LAN model (1.2 ×

10-6/ft) and the thickness of the middle aquifer at the 

extensometer site (about 250 ft) yields 0.006 ft of 

water. The general agreement between the magnitude 

of inelastic compaction and the amount of water 

associated with excess simulated drawdown suggests 

that the simulation of too much drawdown in the 

middle aquifer at the extensometer site was probably 

caused by the use of a constant specific-storage value 

and the associated effect of omitting water contributed 

from inelastic compaction of the aquifer system.

Leveling data and simulated water levels for the 

only other local piezometer screened within the middle 

aquifer support the above argument. The leveling data 

suggest that little or no inelastic compaction occurred 

at the injection site and corroborate data from the 

extensometer; therefore, the assumption of constant 

storage appears to be valid for the injection site. The 

simulated water levels that match those measured at the 

injection site also match those at piezometer 

7N-12W-27H7, in the Avenue K–8 and Division Street 

well field about 0.5 mi east of the extensometer site. 

Like the injection site, Avenue K–8 and Division Street 

is distant (relative to the extensometer site) from areas 

where significant subsidence was measured from 1993 

to 1995 (fig. 7).

A comparison of the results of the phase I and 

phase II calibrations yielded quantitative information 

on qualitative relationships. A comparison of the 

parameter values at the approximate intersections of 

zero-error lines for the cycle-3 injection (shown as 

triangles on figure 44) reveals some predictability in 

the behavior of the model. Table 2 shows the parameter 

values at these intersections and key consistent 

relations between the parameters. Note that the sum of 

K1 and K2, which are proportional to transmissivity 

because the thicknesses of layers 1 and 2 are similar, is 

essentially constant at an average of about 19 ft/d. This 

makes intuitive sense, as these are the only 

significantly variable components of the overall 

transmissivity of the system—changes in this 

transmissivity would cause either an overestimation or 

an underestimation of head without changes in storage 

and (or) stresses to compensate. K2/KV is fairly 

constant and averages about 272 (table 2). These 

observations suggest that given a value of K1, K2, or 

KV, one can predict the other two values that will result 

in zero (or very low) error. This was tested by 

predicting the zero-error values of K2 and KV for a K1

of 8.0 ft/d and comparing the result with that for K1

values of 12, 15, and 18 ft/d.
78 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

The values of K2 and KV were predicted using 

the values of K1+K2 and K2/KV for a K1 of 12 ft/d 

(table 2), rather than using average values, because the 

line connecting the zero-error solutions (fig. 44) is not 

quite linear. Accordingly, the estimated values of K2

and KV were 10.5 and 0.042 ft/d, respectively. The 

predicted and the simulated values were almost 

identical (fig. 45).

An infinite set of parameter values, such as those 

shown in table 2, can produce simulated water levels 

that match those measured at the injection site, as long 

as the relations noted above hold. Given no additional 

information, any single solution within this set is 

clearly non-unique. Additional information, however, 

is available to help constrain the parameter values 

including information from the velocity log of injection 

well 7N/12W-27P2 (fig. 5) and from microgravity 

results. The velocity log shows that about 12 percent of 

the volume extracted from well 7N/12W-27P2 came 

from the middle aquifer (fig. 5). Assuming that the 

condition of the well screen and the error associated 

with the data-collection method was uniform with 

depth, this result can be used to estimate the relative 

hydraulic conductivities of the upper and middle 

aquifers at the injection site. Taking into account the 

relative saturated screened intervals during the velocity 

logging, it was assumed that K2 is about 10 percent of 

K1 in the vicinity of the injection site.

Howle and others (2003) compared water-table 

changes calculated from the measured changes in 

gravity and a specific yield (0.13) with those simulated 

using a simplified ground-water-flow model of the 

upper aquifer. Several values of hydraulic conductivity 

were used in the simulation, and the results were 

superimposed onto those from the gravity analysis 

(fig. 46). The hydraulic conductivity for the upper 

aquifer that best matches the results from the gravity 

analysis is about 18 ft/d.

Combining the results of these independent 

analyses, a K1 of about 18 ft/d and a K2 for layer 2 that 

is 10 percent of that for layer 1 are indicated. 

Accordingly, if K1 is 18 ft/d, the sum of K1 and K2

would be 19.8 ft/d, which slightly exceeds the ideal 

value of 19.1 (table 2). The estimated K2 value from 

the calibration procedure for a K1 of 18 ft/d is about 

1.06 (fig. 45), somewhat lower than 1.8 ft/d (10 percent 

of 18 ft/d). If K1 is reduced from 18 to 17 ft/d, the sum 

of K1 and K2 would be 18.7 ft/d, which is closer to the 

ideal value of 19.1 ft/d. The value of KV associated 

with a K1 of 17 ft/d, calculated from the average value 

of K2/KV (table 2), is 0.006 ft/d. The intersection of 

these calculated K2 (1.7 ft/d) and Kv (0.006 ft/d) values 

for a K1 of 17 ft/d plots very close to where the zeroerror solution of the calibration procedure would be for 

the same K1 value (fig. 45). Although there are 

potential errors inherent in both of the independent 

estimates used to narrow the infinite set of parameters, 

the close match of the values calculated using the 

relations shown in table 2 to those from the calibration 

results is compelling enough to put this forward as the 

preferred set of parameters (K1 of 17 ft/d, K2 of 

1.7 ft/d, and KV of 0.006 ft/d).

Table 2. Range and comparison of hydraulic conductivity values estimated during phase II of the model calibration for Lancaster, Antelope 

Valley, California

[All values are in feet per day]

Hydraulic conductivity 

of model layer 1

(K1)

Hydraulic conductivity 

of model layer 2

(K2)

Effective vertical hydraulic 

conductivity between model 

layers 1 and 2

(KV)

Hydraulic conductivity of 

model layers 1 and 2

(K1+K2)

Hydraulic conductivity of 

model layer 2/effective 

vertical hydraulic 

conductivity between 

model layers 1 and 2

(K2/KV)

12 6.51 0.026 18.5 250

15 3.92 .014 18.9 280

18 1.06 .0037 19.1 286
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 79

Figure 45. Approximate predicted values of hydraulic conductivity (in foot per day) of layer 2 (K2) and effective vertical hydraulic conductivity 

(KV) compared to those determined from the phase II calibration procedure for layer-1 hydraulic conductivity (K1) of 8 feet per day.
80 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Phase II calibration involved changing 

parameters only within the zone (figure 39B) 

surrounding the injection and extensometer. Results of 

periodic tests showed the zero-error solution for this 

zone was insensitive to the same changes outside this 

area. Using the preferred set of parameters, the same 

ratio of K1/K2 and K2/KV was used for the entire model 

area, while maintaining the same sum of K1 plus K2

generated during the phase I calibration (fig. 39B). This 

was done as an attempt to retain the relative differences 

in transmissivity inferred by the AV model and the 

phase I calibration of the LAN model while 

incorporating what was learned at the smaller scale.

Results from the calibrated LAN model are 

shown in figures 47–49. Contours of the simulated 

water levels for April 1996 compare well with the 

contours based on the measured water levels, 

particularly those in the Lancaster and Palmdale areas 

(fig. 47). The simulated values for the long-term waterlevel trends closely match the measured values 

throughout the model area (fig. 48). Short-term 

seasonal water levels measured during the injection 

tests also were simulated reasonably well (fig. 49).

A comparison of input values for the LAN model 

with those for the AV model for the same areas 

(Leighton and Phillips, 2003) shows that most of the 

values are similar, but that there also are some 

significant differences. Storage properties are 

essentially identical except for inelastic skeletal 

specific storage, which was simulated in the AV model 

but not in the LAN model. Pumpage and recharge from 

interbasin flow, small intermittent streams, and 

infiltration of treated wastewater and agricultural 

irrigation are essentially the same, though the 

distribution was slightly different in some cases. 

Recharge related to southward flow from the groundwater mound through the northern boundary of the 

LAN model was smaller than that simulated by the AV 

model. However, the northward retreat and degradation 

of the simulated mound in the AV model was much

Simulated water levels for a range of hydraulic conductivities (K, in feet per day)

Gravity inferred water level; shows value based on measured change in gravity

and two standard deviation error bars





Water-level measurement near completion of injection

Pre-injection water-level measurement and projected water-table surface

EXPLANATION

0 200 400 600 800 1,000 1,200 1,400

Distance, in meters

K=8

K=10

K=12 K=15

K=18

670

680

660

650

640

Elevation, in meters

Well 34B1 Well 27P2 Well 27F8

South North





Simulated water levels

Figure 46. South-to-north profile with gravity-determined water-level changes compared to simulated injection mound geometries for a 

range of hydraulic conductivities, Lancaster, Antelope Valley, California.

The simulations were done using a simplified one-layer model representing only the upper aquifer (from Howle and others, 2003).
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 81

more rapid than measured; thus, the ground-water 

mound in the AV model was much farther north and 

smaller in magnitude than it should have been by 1983. 

Similarly, specified recharge from Amargosa Creek 

was much greater in the LAN model than in the AV 

model, but heads in this area were simulated too low in 

the AV model.

There are significant differences in the calibrated 

hydraulic conductivities of the two models, but the total 

transmissivities are comparable. The hydraulic 

conductivity for the upper aquifer generally is greater 

in the LAN model than in the AV model and that for the 

middle aquifer is lower (fig. 39). In the vicinity of the 

injection site, K1 and K2 are 17 and 1.7 ft/d, 

respectively, in the LAN model; K1 ranges from 10 to 

24 ft/d and K2 is 10 ft/d in the AV model. K1 in the 

LAN model is within the range of values used in the 

vicinity of the injection site in the AV model, and the 

sum of K1 and K2 (proportional to the transmissivity, as 

thicknesses are similar) for the LAN model (18.7 ft/d) 

is near the low end of that for the AV model (20 ft/d). 

Vertical hydraulic conductivities near the injection site 

are 0.006 and about 0.10 ft/d in the LAN and AV 

models, respectively. The vertical hydraulic 

conductivity for the AV model was assumed, and was 

not adjusted from calibration of that model; however, 

the calibration was poorly constrained in the vertical 

dimension. 

T6N

T6N

T7N

T7N

R13W R13W R12W R12W R11W R11W R10W

T8N

2,225

2,125

2,100

2,100

2,075

2,0752,050

2,1502,175

2,175

2,150

2,125

2,200

2,150

2,225

2,200

2,175

2,225

2,250

2,250

2,225 2,225

2,200

2,175 2,175

2,200

2,200

2,225

2,225

2,250

2,200

EXPLANATION

Model boundary

April 1996 water-level contours.

Contour interval 25 feet. Datum

is sea level

Well

2,225

2,225

Measured

Simulated

Quartz Hill

Injection

site

Lancaster

Palmdale

12'30" 07'30" 118°02'30"

40'

34°35'00"

34°45'00"

118°17'30"

0

0 5 Kilometers

5 Miles

Amargosa

Cre ek

Figure 47. Contour map based on measured water levels and those simulated using the calibrated LAN model, Lancaster, Antelope Valley, 

California.
82 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California 1983 1985 1987 1989 1991 1993 1995 1997 1999 1983 1985 1987 1989

19911993199519971999

198319851987198919911993199519971999

198319851987198919911993199519971999

2,200

2,150

2,050

2,100

2,200

2,150

2,100

2,050

2,250

2,200

2,150

2,100

2,250

2,200

2,150

2,100

2,250

2,200

2,150

2,100

2,300

2,250

2,200

2,150

Monitoring wells screened in layer 1 and 2

Monitoring wells screened in layer 1

7N/12W-19R1

6N/11W-16J1

7N/11W-33N1

7N/12W-22K1

7N/12W-27H1

7N/13W-26J2

layer 2

layer 1

layer 2

layer 1

2,100

2,050

1,950

2,000

6N/11W-19E6

2,150

2,100

2,000

2,050

6N/12W-23A1

2,250

2,200

2,100

2,150

7N/11W-27Q1

2,220

2,170

2,070

2,120 7N/12W-9E3

Altitude of water level, in feet above sea level Altitude of water level, in feet above sea level

EXPLANATION

Measured data

Simulated layer 1

Simulated layer 2

Figure 48. Hydrographs of wells with long-term records during the calibration period, Lancaster, Antelope Valley, California.

Simulated results from phase II calibration of the Lancaster-area (LAN) model are shown only for the model layers included in the screened 

interval of the well. Well locations shown in figure 43.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 83

1998 1998

2,200

198319851987198919911993199519971999

198319851987198919911993199519971999

MAR. APR. MAY JUNE JULY AUG. MAR. APR. MAY JUNE JULY AUG.

2,150

2,100

2,050

2,200

2,150

2,100

2,050

2,200

2,150

2,100

2,050

2,200

2,225

2,175

2,075

2,125

2,150

2,100

2,050

Layer 1

Injection Wells

Layer 2

7N/12W-26K3 7N/12W-26K3

7N/12W-27F8 7N/12-W27F6

7N/12W-27J5 7N/12W-27H7

7N/12W-34B1

7N/12W-27P8 7N/12W-27P6

Altitude of water level, in feet above sea level in feet above sea level

Offsets and inaccuracies in timing of simulated events

are an artifact of one-month stress periods Offsets and inaccuracies in timing of simulated eventsare an artifact of one-month stress periods

EXPLANATION

Measured data

Simulated layer 1

Simulated layer 2

Figure 49. Hydrographs of wells and piezometers with dense data during injections tests, Lancaster, Antelope Valley, California.

Simulated results from phase II calibration are shown only for the model layers included in the screened interval of the well or piezometer. 

Well locations shown in figure 43.
84 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

The phase II calibration of the LAN model 

provided qualitative and quantitative improvements 

over the phase I calibration. The systematic parameter 

estimation procedure clarified the effects of not 

simulating aquifer-system compaction in subsiding 

areas; this procedure resulted in a more justifiable set 

of model parameters and, thus, in good model 

performance. The uniqueness of the parameter set was 

addressed, and the procedure developed aided in the 

remainder of the sensitivity analysis. Key findings are 

as follows:

• Simulation of inelastic storage, which was 

not simulated in the LAN model, likely 

would enable close simulation of measured 

head changes at both the injection and the 

extensometer sites; this was not feasible using 

justifiable changes of parameters in the 

current model.

• The sum of the estimated hydraulic 

conductivities of layers 1 and 2 of the LAN 

model, which are proportional to the 

transmissivities of those layers in the vicinity 

of the injection site, is about the same as the 

low end of the range for these in the AV 

model (20 ft/d).

• The hydraulic conductivity of layer 2 is about 

10 percent of that for layer 1 in the vicinity of 

the injection site.

• The ratio of the hydraulic conductivity of 

layer 2 to the equivalent vertical hydraulic 

conductivity between layers 1 and 2 is about 

270 in the vicinity of the injection site.

Sensitivity Analysis

A sensitivity analysis is a means for determining 

the sensitivity of model results to parameters in the 

model. The phase II calibration, for example, 

constituted a sensitivity analysis of the hydraulic 

conductivities specified in the model (K1, K2, and KV). 

Although other aspects of the ground-water system 

were represented in the model, not all were addressed 

or fully explored during calibration, including some of 

the boundary conditions, most system stresses 

(recharge and pumping), and storage values. The 

sensitivity of the model results to some of these aspects 

of the model was evaluated using plots of model error, 

like those in figure 44 (hereinafter referred to as 

sensitivity plots), generated using the same procedure 

developed for the phase II calibration, and hydrographs 

showing the effects of changes in the calibrated model. 

The sensitivity plots reflect relative head changes, 

whereas the hydrographs show error in absolute head; 

combined, they are effective tools for determining the 

effects of adjusting various model input. In addition, 

the sensitivity plots show quantitatively the effects of 

these adjustments on the preferred set of hydraulic 

conductivity parameters. For example, if reducing 

recharge in an area of the model causes substantial 

changes in head at the injection site, the zero-error lines 

on the sensitivity plots would shift, indicating a new set 

of parameters that would best fit the changed 

hydrologic regime.

Sensitivity is discussed in this report with respect 

to the central part of the model unless noted otherwise. 

Unreasonable changes in head in other areas generally 

are noted, but the focus of this analysis is on the area 

surrounding the injection site.

Hydrographs of the shallow and deep 

piezometers at the extensometer and injection sites and 

of well 7N/12W-27H1, which is within 0.5 mi of these 

sites and has the most complete long-term water-level 

record in the vicinity were used for the sensitivity 

analysis. The hydrographs were used to determine the 

effects of changes in the LAN model on simulated 

short- and long-term system behavior. Simulated 

hydrographs were interpolated from cell centers to 

measurement locations (Hanson and Leake, 1999). The 

sensitivity plots were based on the LAN model, 

modified as described on the plots.

For the no-flow boundary conditions, the lateral 

flowline boundaries were tested using the AV model, 

and the assumption of no flow through the lacustrine 

unit was tested during the calibration of the LAN 

model. Results from the AV model suggest that 

significant flow occurred through the eastern boundary 

of the LAN model during the calibration period and 

that this flow decreased significantly with time. This 

transient flow through the eastern boundary was 

accounted for in the LAN model by altering the 

specified flux (recharge) through the adjacent 

southeastern boundary. 
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 85

The northern specified-head boundary, which 

represents the water-table mound between Lancaster 

and Rosamond, provided 22 percent of the average 

annual recharge to the model area. The simulated water 

levels near the injection site were relatively insensitive 

to this source of water. Conversion to a no-flow 

boundary caused large water-level declines (not shown) 

in the northern area of the LAN model, as expected, but 

much smaller declines near the injection site (fig. 50A). 

The sensitivity of the estimated hydraulic 

conductivities near the injection site to the specifiedhead boundary was varied. Conversion to a no-flow 

boundary resulted in an increase in the estimated value 

of K2, by a factor of 1.2, but essentially no change in 

KV.

The southeastern specified-flux boundary, which 

represents subsurface interbasin flow from the Pearland 

and the Buttes subbasins, provided an average of 

26 percent of the annual recharge to the LAN model 

area. The volume of flow crossing this boundary 

simulated by the AV model was 7,650 acre-ft/yr 

(Leighton and Phillips, 2003); this volume was reduced 

in the LAN model by an average of 1,636 acre-ft/yr (21 

percent) to compensate for flow exiting the model area 

through the eastern boundary. To test the sensitivity of 

the LAN model results to these recharge estimates, the 

flux through the southeastern boundary was reduced 

and increased annually by an average of about 40 and 

85 percent, respectively. Although the simulated water 

levels near the southeastern boundary were sensitive to 

these changes (for example, increased 20 to 60 ft with 

increased recharge), the hydrographs fig. 50B) show 

that the simulated water levels near the injection site 

were essentially unaffected. The sensitivity plot shows 

very little change in the estimated hydraulic 

conductivities from those in the LAN model. Because 

the sources of recharge from treated wastewater and 

from agriculture generally are close to the southeastern 

boundary and because the average volumes of recharge 

from these sources are smaller than those from the 

southeastern specified-flux boundary, it was assumed 

that the sensitivity to these sources of recharge is 

similar to that for the southeastern flux.

The intermittent-stream recharge specified west 

of Quartz Hill is relatively small and remote from the 

Lancaster area; recharge from this source was not 

considered important with respect to model sensitivity. 

Amargosa Creek, however, is a significant source of 

recharge and is relatively close to Lancaster (fig. 40). 

The calibrated recharge from Amargosa Creek (2,835 

acre-ft/yr) was reduced and increased by about 50 and 

100 percent, respectively, which resulted in small, but 

noticeable changes in the model results (fig. 50C). The 

long-term hydrograph responded to these changes, but 

the difference in water levels simulated by the 

calibrated LAN model was less than about 6 ft during 

the 15-year period. The hydrographs of the piezometers 

show similar variability. The sensitivity plot also 

responded, indicating that minor adjustments in the 

parameter values would be required to match the 

measured water levels if large adjustments were made 

to simulated recharge from Amargosa Creek (fig. 50C). 

Note that such changes in recharge would alter the 

water-level altitude and hydraulic gradient in the 

vicinity of wells 6N/12W-16A2 and 9H3. As discussed 

in the phase I Calibration section, hydraulic conditions 

at these wells were very sensitive to recharge from 

Amargosa Creek.

The sensitivity of the model results to errors in 

ground-water pumpage was not tested. Urban groundwater pumpage was metered, and therefore any errors 

were assumed to be small. Agricultural pumpage, 

though not metered, was estimated from crop demand 

(Leighton and Phillips, 2003) and is remote from the 

area of interest. 

The storage properties of the aquifer system (Sy

and the elastic component of Ss) were varied during the 

phase I calibration of the model, but were assumed for 

the calibrated LAN model to be constant in the model 

area as had been assumed for the AV model (Leighton 

and Phillips, 2003). Results of the phase I calibration 

indicate that simulated hydraulic head throughout most 

of the model is insensitive to reasonable changes in the 

elastic component of Ss, but that simulated heads in the 

middle aquifer were very sensitive to Ss in areas where 

inelastic compaction occurred. Inelastic compaction 

was not accounted for in the LAN model, but is a 

source of water in the real system. Storage in the upper 

aquifer was large (0.13) relative to inelastic Ss (about 

4.0 × 10-5/ft); thus, the sensitivity of simulated 

hydraulic head to inelastic compaction in layer 1 would 

be very low. Elastic Ss in the middle aquifer 

(1.2 × 10-6/ft), however, was more than 30 times 

smaller than the inelastic Ss, which may have resulted 

in a significant overestimation of drawdown for areas 

where inelastic compaction occurred. The 

oversimulation of drawdown in layer 2 at the 

extensometer site may be accounted for by inelastic 

aquifer-system compaction. A quantitative sensitivity 

analysis of the effects of inelastic compaction on the 

total Ss is not straightforward because the Ss is headdependent (different above and below the preconsolidation head) and, therefore, an analysis was not 

done.
86 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

2,200

2,150

2,100

2,050

2,200

2,150

2,100

2,050

2,225

2,175

2,125

2,075

Layer 1

Layer 1

Layer 1 Layer 2

Layer 2

7N/12W-27H1

7N/12W-27F8

7N/12W-27P8

7N/12W-27F6

7N/12W-27P6

3/1/984/1/985/1/986/1/987/1/988/1/98

8/31/98

3/1/984/1/985/1/986/1/987/1/988/1/98

8/31/98

Injection-site piezometers

Extensometer-site piezometers

Abandoned well within 0.5 mile of

extensometer and injection sites

A1983

19851987198919911993199519971998

198319851987198919911993199519971998

198319851987198919911993199519971998

EXPLANATION

Specified-head boundary

Converted to no-flow boundary

Calibrated model

—Recharge from northern specified

head boundary eliminated

Altitude of water level, in feet above sea level

Vertical hydraulic conductivity, layer 1-2 (KV),

in feet per day

Log vertical hydraulic conductivity, layer 1-2

Log hydraulic conductivity, layer 2

Hydraulic conductivity, layer 2 (K2), in feet per day

0.80

0.60

0.40

0.20

0

-0.20

6.31

3.98

2.51

1.58

1.00

0.63

-3.00 -2.50 -2.00 -1.50 -1.00 -0.50

0.001 0.0032 0.01 0.032 0.10 0.32

Measured water levels

Vertical gradient during water-table peak

Vertical gradient during water-table low (extraction)

Water-table peak (during injection)

Lines of zero error between simulated and measured:

Figure 50. Sensitivity of calibrated hydraulic conductivities and simulated water levels near the injection site to changes in model variables, 

Lancaster, Antelope Valley, California.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 87

2,200

2,150

2,100

2,050

2,200

2,150

2,100

2,050

2,225

2,175

2,125

2,075

Layer 1

Layer 1

Layer 1 Layer 2

Layer 2

7N/12W-27H1

7N/12-W27F8

7N/12W-27P8

7N/12W-27F6

7N/12W-27P6

3/1/98 1983

19851987198919911993199519971998

198319851987198919911993199519971998

198319851987198919911993199519971998

4/1/985/1/986/1/987/1/988/1/98

8/31/98

3/1/984/1/985/1/986/1/987/1/988/1/98

8/31/98

Injection-site piezometers

Extensometer-site piezometers

Abandoned well within 0.5 mile of

extensometer and injection sites

EXPLANATION

Recharge from subsurface interbasin flow

along southeastern boundary

Reduced by 37.9–42.4 percent per year

Calibrated model

Increased by 75.9–93.6 percent per year

B —Varying recharge from subsurface

interbasin flow

Altitude of water level, in feet above sea level

Vertical hydraulic conductivity, layer 1-2 (KV),

in feet per day

Log vertical hydraulic conductivity, layer 1-2

Log hydraulic conductivity, layer 2

Hydraulic conductivity, layer 2 (K2), in feet per day

0.80

0.60

0.40

0.20

0

-0.20

6.31

3.98

2.51

1.58

1.00

0.63

-3.00 -2.50 -2.00 -1.50 -1.00 -0.50

0.001 0.0032 0.01 0.032 0.10 0.32

Measured water levels

All lines of zero error for vertical gradients are coincident

Vertical gradient during water-table peak

Vertical gradient during water-table low (extraction)

Water-table peak (during injection)

Lines of zero error between simulated and measured:

Figure 50.—Continued.
88 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

2,200

2,150

2,100

2,050

2,200

2,150

2,100

2,050

2,225

2,175

2,125

2,075

Layer 1

Layer 1

Layer 1 Layer 2

Layer 2

7N/12W-27H1

7N/12W-27F8

7N/12W-27P8

7N/12W-27F6

7N/12W-27P6

3/1/984/1/985/1/986/1/987/1/988/1/98

8/31/98

3/1/984/1/985/1/986/1/987/1/98

8/1/98

8/31/98

Injection-site piezometers

Extensometer-site piezometers

Abandoned well within 0.5 mile of

extensometer and injection sites

EXPLANATION

Recharge from Amargosa Creek: reduced by

50 percent and increased by 100 percent

Reduced by 50 percent per

Calibrated model

Increased by 100 percent

C —Varying recharge from Amargosa Creek

0.80

0.60

0.40

0.20

0

-0.20

6.31

3.98

2.51

1.58

1.00

0.63

-3.00 -2.50 -2.00 -1.50 -1.00 -0.50

0.001 0.0032 0.01 0.032 0.10 0.32

198319851987198919911993199519971998198319851987198919911993199519971998

198319851987198919911993199519971998

Altitude of water level, in feet above sea level

Log vertical hydraulic conductivity, layer 1-2

Log hydraulic conductivity, layer 2

Vertical hydraulic conductivity, layer 1-2 (KV),

in feet per day

Hydraulic conductivity, layer 2 (K2), in feet per day

Measured water levels

All lines of zero error for vertical gradients are coincident

Vertical gradient during water-table peak

Vertical gradient during water-table low (extraction)

Water-table peak (during injection)

Lines of zero error between simulated and measured:

Figure 50.—Continued.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 89

2,200

2,150

2,100

2,050

2,200

2,150

2,100

2,050

2,225

2,175

2,125

2,075

Layer 1

Layer 1

Layer 1 Layer 2

Layer 2

7N/12W-27H1

7N/12W-27F8

7N/12W-27P8

7N/12W-27F6

7N/12-W27P6

3/1/984/1/985/1/986/1/987/1/988/1/98

8/31/98

3/1/984/1/985/1/986/1/987/1/988/1/98

8/31/98

Injection-site piezometers

Extensometer-site piezometers

Abandoned well within 0.5 mile of

extensometer and injection sites

D

198319851987198919911993199519971998198319851987198919911993199519971998

198319851987198919911993199519971998

EXPLANATION

Specific yield change from 0.13:

Decreased to 0.09

Calibrated model (0.13)

Increased to 0.19

—Specific yield change from 0.13

0.80

0.60

0.40

0.20

0

-0.20

6.31

3.98

2.51

1.58

1.00

0.63

-3.00 -2.50 -2.00 -1.50 -1.00 -0.50

0.001 0.0032 0.01 0.032 0.10 0.32

Altitude of water level, in feet above sea level

Log vertical hydraulic conductivity, layer 1-2

Log hydraulic conductivity, layer 2

Vertical hydraulic conductivity, layer 1-2 (KV),

in feet per day

Hydraulic conductivity, layer 2 (K2), in feet per day

Measured water levels

Vertical gradient during water-table peak

Vertical gradient during water-table low (extraction)

Water-table peak (during injection)

Lines of zero error between simulated and measured:

Figure 50.—Continued.
90 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

The model results were sensitive to changes in 

Sy. The effects of changing Sy from 0.13 to 0.09 and 

0.19 are shown on the hydrographs and sensitivity plot, 

respectively (fig. 50D). The long-term hydrograph was 

not affected because long-term water-level changes 

were small; however, the amplitude of simulated water 

levels was sensitive to the Sy, particularly in layer 1. 

The sensitivity plot shows that the estimated hydraulic 

conductivities were relatively sensitive to Sy; for 

example, the reduction of Sy resulted in larger 

estimates of K2 and KV by factors of about 1.9 and 1.4, 

respectively. The value of Sy determined from coupled 

gravity and water-level measurements (0.13) provided 

reasonable results and was well-bracketed by the 

sensitivity analysis.

Model results and parameter estimates clearly 

are variably sensitive to changes in storage properties 

and various sources of recharge; however, there are 

consistent patterns in the responses to these changes. 

Decreases in recharge or Sy resulted in lower simulated 

water levels and greater seasonal water-level change. 

The sensitivity plots indicate that the calibrated K2 and 

KV values would have to be increased to compensate 

for these effects. Although the decreases in recharge or 

Sy would allow better simultaneous simulation of 

vertical gradients during peak and low water-level 

conditions, there are negative consequences with 

respect to long-term trends and (or) the magnitude of 

seasonal changes. This is also true for increases in 

recharge or Sy, but in the opposite sense. Model results 

and parameters estimates for the central part of the 

model were most sensitive to changes in local storage 

properties and local recharge and essentially were 

insensitive to changes in remote sources of recharge. 

Appropriate Use and Improvement of the GroundWater-Flow Model

The ground-water-flow model of the Lancaster 

area (the LAN model) was designed for estimating 

aquifer-system properties in the vicinity of the injection 

site and as the basis for a simulation/optimization 

model for planning and managing a larger scale 

injection program. Limitations of numerical models, 

assumptions made during model development, and 

results of model calibration and sensitivity analysis are 

factors that constrain the appropriate use of the model 

and highlight potential improvements.

Limitations of Numerical Models

Results from this model should be interpreted 

generally in time and space, and are best suited for 

comparative analysis rather than for prediction of 

absolute changes. A numerical model is a means for 

portraying and testing one’s conceptual view of a 

system. Because ground-water flow systems are 

inherently complex, simplifying assumptions are made 

during the development and application of such model 

codes (Wang and Anderson, 1982; McDonald and 

Harbaugh, 1988; Anderson and Woessner, 1992). 

Models solve for average conditions within each model 

cell for which the parameters are interpolated or 

extrapolated from measured values and (or) values 

estimated during calibration. In light of this, the intent 

in developing this ground-water flow model was not to 

reproduce the natural system exactly, but rather to 

portray its general characteristics.

The accuracy of model results for time and space 

is strongly related to the availability and accuracy of 

temporal and spatial input data and calibration criteria 

(for example, ground-water levels) for comparison with 

simulation results during model calibration. The central 

part of the LAN model area was the only part for which 

multi-depth time-series data were available for model 

calibration and had excellent records of ground-water 

extraction and injection. The south-central Lancaster 

area also is relatively isolated from known sources of 

recharge. A user should have relatively high confidence 

in model results for the central part of the model area, 

but less confidence in the results for other areas of the 

model.

Other Factors that Constrain Appropriate Use of the Model

The vertical distribution of pumpage between 

model layers was assumed to be the same for extraction 

and injection because accounting for temporal changes 

in the distribution would require prior knowledge of 

future head responses. If all aquifer materials adjacent 

to the well screen are saturated during extraction, this is 

a reasonable assumption; however, any change in the 

length of saturated well screen constitutes a change in 

the relative equivalent transmissivities. This limitation, 

which was previously discussed with respect to 

anomalous head responses, needs to be recognized 

because it may affect the ability of the model to 

accurately simulate head responses to both injection 

and extraction at some sites.
Development of a Numerical Model of Ground-Water Flow in the Lancaster Area 91

The areal distribution of aquifer-system storage 

was assumed constant for both confined and 

unconfined conditions. Geodetic data, however, 

showed spatial variability in both elastic and inelastic 

deformation, which is associated with variability in 

skeletal storage properties. Simulation of the confined 

middle aquifer may be affected significantly by this 

limitation, which would be manifested as excess 

drawdown, particularly within areas susceptible to 

subsidence. Simulation of the unconfined part of the 

system would not be affected significantly if aquifersystem compaction is accounted for because the 

specific yield is much greater than the inelastic skeletal 

storage, but it may be affected somewhat by changes in 

the simulated vertical gradient between layers. Model 

results for the upper aquifer are relatively sensitive to 

changes in the specific yield. Significant changes in 

specific yield in a given area of the model may require 

re-evaluation of hydraulic conductivities in that area.

The northern specified-head boundary provides 

significant recharge to the model area. This recharge 

was required to reasonably match measured water 

levels in the northernmost wells, which are very 

sensitive to this boundary condition. Because there are 

limited potential sources of recharge in that area of the 

valley, it was assumed that the source of this recharge 

probably is due to a change in storage owing to the 

slow growth of a cone of depression at Lancaster and to 

the associated northward retreat of the ground-water 

divide. Because this process cannot be simulated 

explicitly at the subregional scale, a user needs to 

consider the long-term effects of this boundary 

condition, to monitor water levels in that area, and to 

adjust the boundary condition accordingly.

It was assumed that no flow occurred between 

the middle and lower aquifers across the lacustrine 

unit. Where measured, vertical gradients were upward 

when the wells were inactive, which indicates that the 

lower aquifer is a source of water—particularly where 

wells screened in both aquifers can act as free-flowing 

conduits. Results of the phase I calibration indicate that 

the simulated heads are relatively sensitive to this 

source of water. Volumetrically, the lower aquifer likely 

is a relatively small component of total recharge 

because the vertical gradients are small and there is a 

strong contrast in water chemistry across the lacustrine 

unit; however, it may have local effects, particularly in 

the middle aquifer. 

Potential Improvements

Limitations of the current flow model can be 

addressed by technical improvements in model 

capabilities and by new and continued monitoring 

activities coupled with data analysis. Potential 

technical improvements include simulation of aquifersystem compaction, simulation of the lower aquifer, 

and better accounting for variability in the vertical 

distribution of stresses. Subsidence could be simulated 

in future models if water supplies become too limited 

to halt water-level declines. Use of the IBS1 package 

(Leake and Prudic, 1991) allows simultaneous 

simulation of ground-water flow and vertical aquifersystem compaction in MODFLOW. Key inputs to this 

package, including elastic and inelastic storage values, 

and information for estimating the areal distribution of 

these values are included in this report. Although 

current versions of the optimization tools used for this 

study cannot make direct use of IBS1 output, the head 

response in the middle aquifer within the subsidence 

area may be improved substantially.

Flow between the middle and lower aquifers 

across the lacustrine unit is poorly understood; 

however, it may have important local effects, as 

discussed previously. Simulation of the lower aquifer 

using the LAN model is presently not a viable option, 

but it may be in the future if new data allow reasonable 

definition of the boundary conditions in that aquifer.

For wells screened in both the upper and middle 

aquifers, as are most of the wells, the variability in the 

vertical distribution of extraction and injection 

generally is governed by changes in the water level in 

the well. If the water level in the well is within the 

screened interval, any change in the water level is a 

change in the effective transmissivity of that portion of 

the well within the upper aquifer. During extraction, the 

water level declines, as does the effective 

transmissivity of the upper aquifer; the opposite occurs 

during injection. The effective transmissivity of the 

middle aquifer is constant and, therefore, the vertical 

distribution of the extracted or injected water is subject 

to change. Ideally, the changing distribution would be 

accounted for within the flow model for each time step. 

This capability recently was developed for 

MODFLOW (Halford and Hanson, 2002).
92 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Monitoring activities can help address several of 

the uncertainties in the current model. Standard 

monitoring at each potential injection site would likely 

include continuous measurement of water levels in 

nested piezometers; continuous and (or) periodic 

measurement of land-surface deformation; continuous 

recording of injection and extraction rates; and periodic 

chemical analyses. A monitoring program also would 

include areas distant from the injection sites, but within 

their zone of influence. This information is essential for 

documenting the effects of an injection program, but 

also is needed for calibration of the flow model in these 

areas. 

Water-level and stress histories are vital for 

improved estimation of the hydraulic properties of the 

aquifer system in the vicinity of each injection site. 

Measurement of land-surface deformation in the 

subsidence-prone areas is equally vital for 

determination of storage properties required for 

simulation of land subsidence and the associated 

effects on water levels. These measurements would 

also serve to extend the calibration period, providing a 

more challenging history to match while further 

minimizing any long-term error associated with misspecification of initial conditions.

 The sensitivity analysis showed that the model 

results were most sensitive to changes in nearby 

sources of recharge (Amargosa Creek and the northern 

boundary condition) and the specific yield. Gaging 

Amargosa Creek, which is currently ungaged, would 

provide information necessary for improving estimates 

of recharge from that stream. A series of two or more 

gages and monitoring of inflows and diversions 

between the gages may be an effective way to measure 

recharge from this source. Monitoring the water table 

in the vicinity of the northern boundary would allow 

adjustment of the specified heads as needed to reflect 

long-term decreases in the southward hydraulic 

gradient.

Specific yield is relatively difficult to determine, 

but can be estimated using microgravity, simulation, or 

aquifer-test methods. Each of these techniques requires 

periodic to continuous measurement of water-table 

change. Coupled, precise measurements of water levels 

and gravity can be used to generate relatively accurate 

estimates of specific yield, particularly where the 

water-level change is large. Simulation of water-table 

changes during extraction and (or) injection can be 

used to estimate specific yield; however, simulation 

results depend on multiple variables. The likely 

outcome from simulation methods is a range of values 

of specific yield associated with ranges of other 

variables. The same holds for aquifer-test methods.

DEVELOPMENT OF A 

SIMULATION/OPTIMIZATION MODEL

A simulation/optimization model (LANOPT) 

was developed as an adaptable tool for use in planning 

and managing a larger scale injection program. The 

simulation model (LAN) was modified and 

incorporated into a linear-programming problem to 

determine optimal means for managing an injection 

program given an objective and a set of constraints. 

Thus, the LANOPT model considers simultaneously 

the physics of the aquifer system (built into the 

simulation model) and any physical or institutional 

considerations (in the form of constraints) in 

determining the optimal way to meet an objective.

The primary objective of the injection program 

for the Lancaster area is to halt the long-term decline of 

ground-water levels and associated land subsidence 

while meeting growing water demand. Overdraft of 

local ground-water resources has caused water-level 

declines, land subsidence, diminished well capacities, 

and increased dependence on deeper, lower quality 

ground water. A primary constraint of the program is 

that LACDPW must continue to meet water demand 

using existing and new wells and pipelines (as provided 

for in their 5-year development plan) and imported 

water of unknown reliability and for which cost and 

availability are affected seasonally. Additional 

constraints include maintaining minimum heads to 

avoid subsidence, staying 100 ft below land surface to 

avoid high water-table conditions, and using a set of 

specifications that constrain well performance and the 

vertical distribution of pumpage/injection.
Development of a Simulation/Optimization Model 93

Model Objective

The long-term decline of ground-water levels is 

the key issue to be addressed. The objective that was 

used to address this was to maximize the lowest value 

of head. This objective has associated head constraints, 

and the objective function has the form:

max(min h)

subject to

(7)

where

Given this objective function, the LANOPT 

model would seek to increase the head value at the 

location (within a set of specified locations) with the 

lowest head in each stress period by varying injection 

and extraction rates (the decision variables) in specified 

wells. The location with the lowest head value may 

change during a simulation; the optimization seeks 

equal heads at all specified locations, which is not 

always possible.

This solution, however, may not always result in 

a desirable outcome. If, for example, heads were 

relatively high in a subsidence-prone area, the optimal 

solution may result in significant drawdown in that area 

as heads in other areas recover to the same level; thus, 

land subsidence may be a negative consequence of this 

model objective. In this study, the measured heads, and 

presumably the preconsolidation heads, in the 

subsidence-prone areas are indeed higher than or equal 

to those in other areas; therefore, constraints on the 

minimum head in the subsidence area were added to 

the model to ensure that the optimal solution did not 

result in subsidence.

Another way to state the model objective, in this 

circumstance, is “to minimize the loss of well 

capacity.” The target of the optimization is always the 

area with the lowest water table, which is also the area 

where water-table altitudes and associated extraction 

capability of wells are decreasing.

Constraints on Water Supply and Demand

Several physical, institutional, and economic 

factors limit the acquisition of imported water and the 

supply of ground water. Some of these factors are 

included in the LANOPT model in the form of 

constraints. Future water demand, which drives the 

need for supplies, is also included as a constraint.

Imported Water-Supply Constraint

Availability and cost of imported water are 

controlled largely by climatic conditions and 

competing demands for water from the SWP. During 

seasonal low-demand periods (generally late autumn to 

early spring) in nondrought years, AVEK often 

purchases SWP water at reduced rates and sells the 

treated water at a discount which is ideal timing for the 

LACDPW with respect to artificial recharge because 

their demand also is low during that period (fig. 41C). 

Because of the low water demand, including that for 

ground water, existing production wells can be used for 

injection.

AVEK’s historical purchases from the SWP are 

far below their entitlement of 138,400 acre-ft/yr 

(fig. 51). The future capability of the SWP to deliver 

full entitlements, however, is unknown. Currently, the 

SWP does not have the facilities to deliver full 

entitlements, and the reliability of the SWP annual 

deliveries historically has been affected by drought 

conditions (see 1991 deliveries, fig. 51). Recent 

environmental legislation has designated more SWP 

water for protection of wildlife, and talks continue at 

the Federal, State, and local levels regarding future 

allocations of SWP water in California. 

Effects of future decisions on AVEK’s ability to 

obtain additional SWP water are difficult to predict. 

For planning purposes, AVEK estimates that their longterm average potential yield from the SWP will be 

91,400 acre-ft/yr (Russell Fuller, General Manager, 

Antelope Valley–East Kern Water Agency, oral 

commun., 2000). Assuming that the growth in 

deliveries from 1989 to 1999 will continue for another 

10 years, deliveries would reach about 97,000 acreft/yr by 2009, which slightly exceeds the projected 

yield. For the purpose of this study, however, it is 

assumed that AVEK will be able to deliver the 

additional water needed for injection during the 

10-year planning horizon. The primary reason for this 

assumption is that injection water would be purchased

h is the minimum head and

hit is the head in the cell containing well i (i = 1, 

number of wells) during stress period t

(t = 1, number of stress periods).

h hit – ≤ 0
94 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

from AVEK from late autumn through early spring 

when competition and prices for SWP water are lowest. 

Accordingly, injection was constrained to occur only 

during the late autumn/early spring period (stress 

periods 1, 5–7, 11–13, and so forth):

(8)

where

Ground-Water-Supply Constraints

The ground-water-supply constraints define 

physical limits on the way water is pumped from and 

injected into wells. These constraints were based on the 

extraction capacities and vertical distribution of 

pumpage from each well selected as a potential 

injection well. Figure 52 shows the 16 existing and 13 

proposed wells considered in the optimization, which 

are in the central, well-calibrated part of the LAN 

model. Only the LACDPW production wells that are, 

or will be, screened within the upper and middle 

aquifers (table 1) were considered for injection 

purposes because of the high arsenic concentrations 

and the low transmissivity and storativity in the lower 

aquifer. These conditions do not preclude the use of the 

lower aquifer for these purposes, but use of the lower 

aquifer for injection was not considered in this study.

All the selected injection/production wells are, or 

will be, connected to a network of pipelines that allow 

routing of AVEK water to the wells for injection and 

widespread distribution of pumped water to LACDWP 

customers. The locations of these wells were 

predetermined; well placement was not a goal in the 

optimization problem.

Qt

inj is the water injected during high-demand 

stress period t.

Qinj

t = 0

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Year

Deliveries, in acre-feet

Total

Agricultural

Municipal and industrial

Figure 51. Historical deliveries of State Water Project water by the Antelope Valley–East Kern Water Agency (AVEK), Lancaster, Antelope 

Valley, California.

(Russell Fuller, General Manager, Antelope Valley–East Kern Water Agency, written commun., 2000)
Development of a Simulation/Optimization Model 95

Because of the proximity of some of the 

injection/extraction wells to one another and the size of 

the model cells, some groups of nearby LACDWP 

injection/production wells are represented in the 

LANOPT model collectively. Each well, or group of 

nearby wells, was simulated as four wells; different 

wells were used for injection and extraction, and for the 

upper and middle aquifers. For the purposes of this 

report, these injection/production wells will be 

considered single wells, except where discussion 

requires they be considered separately.

The maximum extraction capacity of each well 

(expressed herein as a volumetric rate) (table 3) was 

determined from a combination of existing capacitytest data, maximum measured monthly pumpage in 

1997, and anecdotal information from LACDPW 

employees who maintain these wells. Because these 

wells may be used for long periods, their long-term 

capacities were assumed to be 80 percent of the 

maximum to allow for the effects of long-term 

drawdown and occasional maintenance.

AVENUE H

Air Force

Plant 42

LANCASTER BLVD

AVENUE I

20TH ST EAST

30TH ST EAST

10TH ST EAST

40tTH ST EAST

30TH ST WEST

40TH ST WEST

50TH ST WEST

AVENUE J

AVENUE M

AVENUE N

AVENUE O

SIERRA

HIGHWAY

AVENUE K

AVENUE L

24M2, 4-22

30B1, 4-37

21C5, 4-38

22B2, 4-5

15R2, 4-9

15R3, 4-17

11E, 4-52

15R4, 4-26

21C2,

4-12

17F, 4-48

17C,

4-49

9E3, 4-36

9B, 4-51

9A, 4-50

11M2, 4-15

34N3, 4-29

34N4, 4-30

27P3, 4-34 27P2, 4-32

27F3, 4-44

27F2, 4-43 27J4, 4-13

27J6, 4-42

27H3, 4-33

24M3, 4-27

21C4,

4-25

referred to as subsidence

area in text

LACDPW production well

Land subsidence from October 20, 1993

to December 12, 1995, in millimeters:

0–15

16–35

36–50

Historical land subsidence (1930–1992).

Contour interval 0.3 meters. Datum is

sea level

EXPLANATION

Existing unmanaged

Existing managed

Proposed

0

0 3 Kilometers

3 Miles

118°12'30" 118°07'30"

34°

40'

1.8

1.5

0.3

0.6

0.9

0.9

1.2

1.2

0.3

T7N

T6N

R13W R12W R12W R11W

Northern

Area

Avenue J and

Sierra Highway

Avenue M and

Avenue M and 5th St. East

7th St. West

Avenue K-8 and

Division

Avenue L and

5th St. West

Avenue K-8 and

5th St. West

Well 4-37

Figure 52. Historical and recent land subsidence, and locations of Los Angeles County Department of Public Works (LACDPW) wells, 

Lancaster, Antelope Valley, California.

Wells include existing and proposed wells with variable rates of injection and extraction in the simulation/optimization model (managed wells) 

and existing wells with fixed rates of extraction in the model (unmanaged wells).
96 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Table 3. Estimated maximum and long-term capacities of existing and proposed potential injection/extraction wells in Lancaster, Antelope 

Valley, California

[See figure 52 for location of wells. Long-term estimates, which were 80 and 72 percent of maximum for extraction and injection, respectively, were used in 

the simulation/optimization model. Well site designations are used to simplify presentation and discussion of model results. gal/min, gallon per minute; na, not 

applicable]

State well No.

(7N/12W-)

Local well 

name

Well site 

designation

Maximum 

capacity

(gal/min)

Long-term 

extraction 

capacity 

(gal/min)

Long-term 

injection capacity 

(gal/min)

9A 4-50 Northern Area 1,300 1,040 940

9B 4-51 Northern Area 1,090 870 780

9E3 4-36 Northern Area 880 700 630

15R2

15R4

4-9

4-26 Avenue J and Sierra Highway 1,770 1,420 1,270

22B2 4-5 Avenue J and Sierra Highway 1,040 830 750

27F2

27F3

4-43

4-44 Avenue K-8 and 5th West 11,750 11,400 na

27H3

27J4

4-33

4-13 Avenue K-8 and Division 1,090 870 780

27J6 4-42 Avenue K-8 and Division 2840 2670 na

27P2

27P3

4-32

4-34 Avenue L and 5th West 1,820 1,460 1,310

30B1 4-37 Well 4-37 1,040 830 750

34N3

34N4

4-29

4-30 Avenue M and 7th West 2,080 1,660 1,500

Two proposed wells near 4-13 and 4-33 Avenue K-8 and Division 1,450 1,160 1,040

Two proposed wells near 4-29 and 4-30 Avenue M and 7th West 2,080 1,660 1,500

Two proposed wells near 4-43 and 4-44 Avenue K-8 and 5th West 1,820 1,460 1,310

Four proposed wells (new site) Avenue M and 5th East 4,160 3,330 3,000

Two proposed wells near 4-9 and 4-26 Avenue J and Sierra Highway 2,080 1,660 1,500

One proposed well near 4-5 Avenue J and Sierra Highway 1,040 830 750

1Portion of capacity within upper and middle aquifers; total maximum extraction capacity is 3,680 gal/min. 2Portion of capacity within upper and middle aquifers; total maximum extraction capacity is 1,040 gal/min.
Development of a Simulation/Optimization Model 97

Results of the pilot injection test in wells 

7N/12W-27P2 and 27P3 showed that the injection 

capacity in these wells may equal, and probably 

exceed, the extraction capacity. However, this may not 

be the case for all the wells considered for injection in 

the LANOPT model, nor may it be representative of 

the long-term performance of the wells. In practice, 

maintenance generally is required more frequently 

during injection periods than during extraction periods, 

and injection rates are typically less than those for 

extraction (Pyne, 1995); therefore, the long-term 

injection capacities were reduced to 72 percent of the 

maximum extraction capacity (table 3).

For all the periods that injection was allowed, 

extraction also was allowed for the same wells, which 

was required at times to meet water demand. The total 

well capacity for each stress period is calculated as a 

weighted sum of the injection and extraction during 

that period in which the weights are related to the 

respective capacities. Thus, the constrained flow in a 

well can range from the long-term injection capacity 

(72 percent of the maximum extraction capacity) to the 

long-term extraction capacity (table 3). If both 

injection and extraction occur, the constraint will limit 

flow in the well to some value between these limits:

(9)

where

Just as the extraction capacity limits groundwater supply, the hydraulic properties of the aquifer 

system and screened intervals of wells control the 

relative amount of water that can be withdrawn from or 

injected into different depths within the aquifer system. 

The distribution of stress among the aquifers in the 

LANOPT model was constrained by the relative 

effective transmissivity within each aquifer:

(10)

where

This effective transmissivity was calculated for 

the flow model on the basis of hydraulic conductivity 

and length of screened interval in each aquifer and was 

assumed to be constant with time.

Ground-Water Demand Constraint

Future demand for ground water is difficult to 

predict because it is dependent on many variables. 

These variables include the future availability of SWP 

water and ground water, for which there are many 

competing interests; the financial costs of these and 

other sources of water; potential effects of future local 

ground-water-management legislation or adjudications; 

the potential effects of water-conservation efforts or 

development of new water sources; and potential 

growth in water demand. It was assumed for this study 

that growth in residential demand will be the dominant 

factor on ground-water demand within the model area 

and that this demand will be met by some combination 

of native ground water and injected water.

Several estimates of future population growth 

have been made for Lancaster, Palmdale, and other 

parts of Antelope Valley. In 1993, the Southern 

California Association of Governments (SCAG) 

projected a population growth of 56.5 percent for 

Lancaster for 1990 to 2000 (Templin and others, 1995). 

This agrees well with the growth of 57 percent 

calculated using data from the California Department 

of Finance (1999) for the same period, extrapolating to 

the year 2000 from the 1989 to 1999 trend (fig. 2). In 

1994, the Los Angeles County Department of Regional 

Planning estimated a population growth of about 68 

percent from 1990 to 2000 in District 4, the LACDPW 

district that serves Lancaster (Los Angeles County 

Department of Power and Water, written commun., 

1999). Owing to the close agreement between the 

SCAG estimates and data from the California 

Department of Finance (1999), their estimates for the 

2000–2010 population growth in Lancaster (essentially 

the same increase as 1990–2000) were used for the 

10-year projections. The equivalent population growth 

for this period was about 37 percent, or an annual rate 

of about 3.2 percent.

c is the ratio of extraction capacity to 

injection capacity,

is the injection (positive) in well i during 

stress period t,

is the extraction (negative) from well i

during stress period t, and

Ci is the extraction capacity of well i.

cQt

inji Qtexti – Ci ≤

Qt

inji

Qt

exti

Qi1 – cQi2 + = 0

is the flux in well i, model layer 1,

is the flux in well i, model layer 2, and

c is the ratio of effective transmissivity of 

layer 1 to effective transmissivity of 

layer 2.

Qi1

Qi2
98 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

The city of Palmdale experienced a much more 

rapid rate of growth from 1990 to 2000: 118 percent, 

calculated using data from the California Department 

of Finance (1999). SCAG and the California 

Department of Finance project a 2000–2010 population 

growth in Palmdale of over 50 percent. However, the 

LAN model indicated that at the constant (no growth) 

1995 rate of extraction, the simulated water table in 

Palmdale declined into the middle aquifer within this 

10-year period. It was assumed for this study that such 

a condition would not be reached because alternative 

sources of water would be used and (or) pumping 

would be redistributed to keep the water table within 

the upper aquifer thereby maintaining reasonable 

extraction capacities. Through trial and error, the 

pumpage for Palmdale was reduced in the model by an 

annual rate of 0.5 percent, which kept the water table 

within the upper aquifer. This reduction in pumping 

acted as a surrogate for combinations of future 

conservation, alternative water sources, and 

redistribution of pumping in the Palmdale area.

The population growth rate for areas outside the 

cities of Lancaster and Palmdale was assumed to be the 

same rate as that for Lancaster. The increase in urban 

water demand for this rate of population growth was 

applied to all non-agricultural wells in these areas 

except those at Air Force Plant 42 where no growth 

was assumed. Agricultural demand was assumed to be 

steady at the 1995 level. There is evidence of increased 

agricultural activity since 1995, but little information 

on the amount and distribution of increased groundwater extraction. The little information that was 

available suggests that most of the agricultural areas 

with increased activity as of 1998 are outside the LAN 

model area (Carlson and Phillips, 1998).

The initial ground-water demand in 2000 was 

assumed to be that during 1995, the year prior to 

injection testing; it appears to be representative of the 

overall ground-water use during recent nondrought 

periods (fig. 41B). The initial demand was increased 

linearly with time in accordance with the assumed 

growth rates. Figure 53 shows the estimated effect of 

population growth on ground-water demand in the 

Lancaster area during the 2000–2010 period relative to 

that in the recent past. Because 1995 through 2000 was 

assumed a no-growth period, the estimated water 

demands for the 10-year management period are 

considered conservative.

Ground-water demand (pumpage) was 

constrained in the optimization problem by specifying 

the total pumpage for all managed wells, incorporating 

the projected growth rate for Lancaster. The demand 

constraint has the form

(11)

where

Constraints on Hydraulic Head

The upper and lower bounds on hydraulic head 

were specified for all cells containing wells considered 

in the optimization (fig. 52). The upper bound was set 

at an elevation of 100 ft below land surface to avoid 

waterlogging, mobilization of near-surface 

contaminants, and susceptibility to liquefaction during 

an earthquake. For the 10-year management period, 

these upper bounds were required only in the 

northernmost wells where initial heads were within 

150 ft of the land surface. The upper head constraints 

have the form

(12)

where

The lower bounds were specified for wells in 

areas that are more susceptible to land subsidence; 

areas outside the subsidence area were unbounded. 

These constraints have the form

(13)

where

is the extraction (negative) from well i

during stress period t and

Dt is the total ground-water demand during 

stress period t.

hit is the head at the cell containing well i in 

stress period t, and

hmax is the maximum allowable head (land 

surface -100 ft) at the cell containing 

well i.

hit is the head at the cell containing well i in 

stress period t and

hmin is the minimum allowable head at the cell 

containing well i.

i

∑

t

∑ Qt

extri – Dt =

Qt

extri

hit hmax ≤

hit hmin ≥
Development of a Simulation/Optimization Model 99

Ideally, the lower bound is set at the 

preconsolidation head to ensure that no subsidence 

could occur; however, the magnitude and distribution 

of the preconsolidation head is complex and poorly 

understood. Comparisons of water-level and landsurface time-series data from Antelope Valley indicate 

that subsidence can continue for a decade or longer 

despite significant recovery in water levels (Galloway 

and others, 1998a), thus delayed drainage of aquitards 

may be a significant component of subsidence in this 

area, and the spatial and temporal distribution of the 

preconsolidation head is difficult to determine and to 

express in the context of an optimization constraint.

 Given the difficulty of determining 

preconsolidation head, the selection of lower bounds 

was somewhat subjective; selection, therefore, was 

partly based on the feasibility of obtaining an optimal 

solution. The range considered for the lower bound was 

between the initial (spring) conditions and the lowest 

water level recorded at or near the wells. The former 

would concede the amount of subsidence associated 

with delayed drainage from historical water-level 

changes, but not that caused by additional drawdown. 

The latter is what one would specify if compaction was 

essentially an instantaneous response to drawdown 

beyond the preconsolidation head, and delayed 

drainage did not occur. Because delayed drainage is 

known to occur in this aquifer system, it was 

considered important to be near the upper end of this 

range.

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

Acre-feet per year

Year

Total

1984

1986

1988

19901992199419961998200020022004200620082010

Imported

Ground water

Projected ground

water demand

Figure 53. Water delivered in Lancaster by the Los Angeles County Department of Public Works (LACDPW) and projected ground-water 

demand used in the simulation/optimization model, Lancaster, Antelope Valley, California.
100 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Initial runs of the LANOPT model indicated that 

the upper end of the range of lower bounds (the watertable peak in 1995) was not going to result in feasible 

solutions. Ground-water demand could not be met 

without pumping from wells within the subsidence area 

and violating the lower bounds, particularly early in the 

simulation before injection had much of an effect. 

Thus, these bounds were decreased until the model 

consistently reached a feasible solution for a variety of 

conditions. For all wells within about 0.25 mi of the 

area where subsidence was about 16 mm/yr or greater 

from 1993 to 1995 (fig. 52), the lower bounds were set 

10 ft lower than the starting head for the 10-year 

management period. An exception was made for the 

first pumping season; the lower bounds were decreased 

by an additional 10 ft to obtain a feasible solution. This 

set of lower bounds for the subsidence area represents a 

conservative assumption of the preconsolidation head 

that should limit additional land subsidence to that 

primarily caused by delayed drainage from the thick 

aquitards.

Model Components and Conversion to 

Uniform Grid

The LANOPT model was constructed using 

three software programs: MODMAN, version 3.0 

(Greenwald, 1993), LINDO (Schrage, 1991), and 

MODFLOW (McDonald and Harbaugh, 1988). 

MODMAN facilitates the formulation of an 

optimization problem and runs a MODFLOW-based 

ground-water-flow model multiple times to generate a 

response matrix. This response matrix contains the 

transient head response at specified locations in the 

model (in the form of a response coefficient) to a stress 

(extraction or injection) imposed by any single 

managed well. LINDO was then used to solve the 

linear optimization problem given the response matrix 

and specified constraints. Assuming the system reacts 

linearly and using the principle of superposition (Bear, 

1972; Ahlfeld and Mulligan, 2000), the response at the 

specified locations can be calculated by adding the 

responses caused by any combination of managed 

wells that are extracting/injecting at any rate. This 

general approach of using response coefficients is 

discussed in greater detail by Gorelick and others 

(1993).

MODFLOW is the software used to develop the 

ground-water-flow model (LAN) described earlier in 

this report. A significant change was made to this 

model for use in the LANOPT model: the variable 

model grid was converted to a uniform, fairly coarse 

grid. The primary reason for this conversion was that a 

uniform grid was required to avoid introducing bias 

into the optimization results owing to the different-size 

cells containing the managed wells. Simulated water 

levels in cones of depression, or impression, would be 

more exaggerated for wells in small cells than for those 

in large cells, so the constraints would not be equally 

applied. A secondary reason for this conversion was to 

reduce the execution time for the LANOPT model.

The new uniform grid was 37 rows by 60 

columns (fig. 54) with a 0.33-mi spacing. Rows 1 and 

35 through 37, and columns 1 through 3 and 59 and 60 

were inactive. This newly configured model was used 

to simulate the calibration period to determine the 

effects of re-discretization on model results. Figure 55

shows hydrographs of measured and simulated 

hydraulic heads for the variable and uniform grids, 

which have essentially identical long-term trends. 

Seasonal and injection-related fluctuations, though, are 

reduced with the uniform grid because the response to 

stresses that may be affecting water levels for a small 

area is distributed across a larger area. For this reason, 

and the fact that simulated heads do not perfectly 

match the measured water levels even in the variablegrid model, the initial (simulated) heads, rather than 

measured water levels, were used to specify the lower 

head constraints in the subsidence area.

The length of the stress period was increased to 

2 months (60.875 days) in the LANOPT model, double 

that used to calibrate the LAN model. This greatly 

reduced the execution time of the LANOPT model, and 

reflects more appropriately the role of this model as a 

management tool—as a general guide, not a blueprint 

for short-term well management.

The initial condition for the 2000–2010 

management period was generated by extending the 

LAN model from August 1998 through April 2000 

using measured pumpage values for months without 

pumpage in 1995 (prior to injection testing). The 

10-year management period ended in October 2010, 

the end of the final summer pumping season, for a total 

of 58 stress periods, each 2 months in length. All other 

input for the simulation component of the LANOPT 

model is identical to that in the LAN model.
Development of a Simulation/Optimization Model 101

The above approach emphasizes regional spatial 

and temporal changes in hydraulic head, not local, 

short-term changes. This approach is consistent with 

that of the uniform-grid model in matching long-term 

trends compared with short-term fluctuations. Some of 

the head constraints, however, are based on real world 

values, and may, in reality, be violated close to the 

wells. For example, the upper head limit of 100 ft 

below land surface may, in practice, be exceeded near 

injection wells. 

Nonlinear Effects

The LANOPT model uses a response matrix 

approach to solve a linear optimization problem. This 

approach assumes a linear response in hydraulic head 

to changes in extraction/injection rates; however, the 

upper aquifer is simulated as unconfined, which 

introduces a nonlinearity. In a confined aquifer, the 

saturated thickness and associated transmissivity are 

constant; changes in head are proportional to changes 

in stress. In an unconfined aquifer, the saturated 

thickness and associated transmissivity vary as the 

water table rises or declines in response to changes in 

stress; the head response, therefore, is a nonlinear 

function of extraction or injection.

The effect of this nonlinearity on the solution 

depends on the magnitude of the simulated head 

changes relative to the initial saturated thickness. If 

simulated head changes are small compared to the 

saturated thickness, the change in transmissivity and 

associated error from nonlinearity will be small; using 

relatively large model cells helps to reduce this source 

of error. The error was measured by comparing optimal 

heads at the managed wells (LINDO output generated 

from the response matrix) to those generated using the 

optimal extraction/injection rates in the LAN model. 

The results of this comparison are shown later in this 

report.

T6N

T6N

T7N

T7N

T8N

T13W T13W T12W T12W T11W T11W T10W

model grid,

layer 1

outline of layer 2

Quartz Hill

Injection

site

Lancaster

Palmdale

12'30" 07'30" 118°02'30"

40'

34°35'00"

34°45'00"

118°17'30"

0

0 5 Kilometers

5 Miles

Amargosa

Cre ek

2,225

2,125

2,1002,075

2,050

2,150

2,225

2,225

2,250

2,225

2,200

2,175

2,200

2,250

2,200

2,250

2,225

2,200

2,200

2,225

2,175

2,150

2,125

2,175

2,100

2,075

Study area

EXPLANATION

Water-level contours, April 1996.

Contour interval 25 feet. Datum

is sea level

Measured

2,225 Simulated

2,225

Figure 54. Location and dimensions of uniformly spaced model grid used in the simulation/optimization model, and simulated and 

measured water levels for April 1996, Lancaster, Antelope Valley, California. 
102 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Preliminary Simulation/Optimization (LANOPT) 

Model Results

The LANOPT model was used to compare 

results from maintaining present management practices 

(without injection) for a 10-year management period 

with those for three other injection-program scenarios. 

For reference, the current objective and constraints are 

summarized in table 4.

Scenario 1, which was not an optimization 

problem, represents maintenance of present 

management practices (without injection). Present 

practices were represented using the 1995 pumping 

distribution for existing wells assuming no growth in 

ground-water demand (fig. 53).

Scenario 2 represents extraction and injection 

using only the existing wells, assuming a feasible 

solution and allows injection for 6 months of the year, 

which is considered the maximum possible injection 

period. This scenario represents the best achievable 

result for the existing wells and the current constraints.

Scenarios 3 and 4 represent extraction and 

injection using existing and proposed wells. Scenario 3 

allows injection for 6 months; this scenario represents 

the best achievable result overall for the existing and 

proposed wells and the current constraints. Scenario 4 

restricted the injection period to 4 months of the year to 

allow for variability in SWP supply and other factors 

that may limit the length of an injection season. 

Layer 2

2,200

2,150

2,100

2,050

2,200

2,150

2,100

2,050

2,225

2,175

2,125

2,075

Layer 1

Layer 1 Layer 2

Layer 1

7N/12W-27H1

7N/12W-27F8 7N12W-27F6

7N/12W-27P8 7N/12W-27P6

EXPLANATION

Simulated water levels, uniform grid

Simulated water levels, variable grid

Measured water levels

3/1/984/1/985/1/986/1/987/1/988/1/98

8/31/98

198319851987198919911993199519971998

3/1/984/1/985/1/986/1/987/1/988/1/98

8/31/98

198319851987198919911993199519971998

198319851987198919911993199519971998

Altitude of water level

Figure 55. Variable- versus uniform-grid results, Lancaster, Antelope Valley, California.
Development of a Simulation/Optimization Model 103

Comparison of Simulation/Optimization (LANOPT) Model 

Results for Scenarios

Results of the four management scenarios are 

summarized in figure 56. Included in this figure are 

hydrographs showing the water-table responses to the 

scenarios and bar charts depicting the optimal 

injection/extraction rates during the 10-year 

management period. The optimal rates are expressed in 

the form of percentage well capacity used; the longterm capacities are shown in table 3. The bar charts 

were simplified by combining these rates for 6-month 

periods representing the high- and low-demand 

periods. The first stress period, however, represents 

only a 2-month period, March and April 2000, during 

which injection was allowed prior to the first highdemand period. Nearby wells are grouped by site 

designation for clarity (table 3). Optimal extraction 

rates for the three deep wells (7N/12W-27J6, 

7N/12W-27F2, and 7N/12W-27F3) for which injection 

was not allowed were combined and included with the 

rates for the Avenue K–8 and 5th Street West site 

where two of the three wells are located.

Numerical comparisons also are made, including 

comparisons of the objective value, average simulated 

water levels (directly related to average well capacity) 

at managed wells within and outside the subsidence 

areas (fig. 52) during the 10-yr management period, 

and total injection volumes (table 5). The average water 

levels were important because the minimum heads 

(optimal values) occurred near the beginning of the 

simulated scenarios that included the proposed wells; 

thus, the objective value was not always as sensitive as 

the average heads (outside the subsidence area).

When present practices were maintained 

(scenario 1) the average simulated water-table altitude 

at the existing wells during the 10-year management 

period was 2,131 ft in the subsidence area and 2,097 ft 

elsewhere. This reflects water-level declines of about 

15 to 65 ft at individual sites (fig. 56). Simulated 

drawdowns were greatest at Avenue J and Sierra 

Highway, Avenue K–8 and 5th Street West, and 

Avenue L and 5th Street West sites, followed by the 

Avenue K–8 and Division Street and Avenue M and 7th 

Street West sites, the northern area, well 4-37, and the 

Avenue M and 7th Street East site (no existing wells at 

this site). Optimization constraints did not apply for 

this scenario; however, the minimum heads specified 

for the other scenarios in the subsidence area were 

violated in every case and ranged from less than 15 ft at 

well 4-37 to about 100 ft at the Avenue J and Sierra 

Highway site (fig. 56). Although there is considerable 

uncertainty associated with the magnitude of these 

estimates, the trends strongly suggest that maintaining 

present practices would result in continued drawdowns 

and associated loss in well capacities, and increased 

land subsidence.

Table 4. Summary of simulation/optimization model objective and constraints, Lancaster, Antelope Valley, California

Description

Objective: Maximize lowest value of head Seeks the highest value possible for the lowest value of head.

Constraints: No injection during high-demand period Injection was not allowed from late spring through early fall, when State 

Water Project water is less available, more expensive, and competing 

demands are greater. Availability of well capacity is at a minimum during 

this period.

Well use cannot exceed capacity For each well and stress period, the sum of injection and extraction cannot 

exceed the total capacity of the well. The total capacity was adjusted for 

the difference between injection and extraction capacities.

Injected and extracted water is distributed by 

aquifer

For each well, injected and extracted water was partitioned to aquifers by the 

ratio of effective transmissivity within each aquifer (on the basis of 

hydraulic conductivity and length of perforated interval in that aquifer) to 

the total effective transmissivity.

Must meet ground-water demand The sum of extraction from all managed wells must equal ground-water 

demand. Demand was total extraction from these wells during 1995, and 

an annual growth rate was applied.

Upper head limits Limits were placed on the maximum head at all managed wells to avoid high 

water-table conditions.

Lower head limits Limits were placed on the minimum head at all managed wells within the 

subsidence area to avoid drawdown and associated land subsidence.
104 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Northern Area (7N/12W-9A,9B,9E3)

2,000

2,050

2,100

2,150

2,200

2,250

Avenue M and 7th St. West (7N/12W-34N3–N4,

and 2 proposed)

Scenario 2

Scenario 4

Scenario 3

Scenario 2

Scenario 4

Scenario 3

0

20

40

60

80

100

g py

0

20

40

60

80

100

0

20

40

60

80

100

4/1/008/1/002/1/018/1/012/1/028/1/022/1/038/1/032/1/048/1/042/1/058/1/052/1/068/1/062/1/078/1/072/1/088/1/082/1/098/1/09

Injection Extraction Total

EXPLANATION

4/1/008/1/002/1/018/1/012/1/028/1/022/1/038/1/032/1/048/1/042/1/058/1/052/1/068/1/062/1/078/1/072/1/088/1/082/1/098/1/09

Injection Extraction Total

EXPLANATION

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

Constrained minimum head

Constrained maximum head

Scenario 2 (existing wells, injection allowed 6 months per year)

Scenario 4 (existing and proposed wells, injection allowed 4 months

per year)

Scenario 3 (existing and proposed wells, injection allowed 6 months

per year)

Scenario 1 (maintain present practices)

[Constrained maximum head is above top of graph; minimum head

not constrained]

Simulated altitude of water table, in feet Simulated altitude of water table, in feet

EXPLANATION

Scenario 2 (existing wells, injection allowed 6 months per year)

Scenario 4 (existing and proposed wells, injection allowed 4 months

per year)

Scenario 3 (existing and proposed wells, injection allowed 6 months

per year)

Scenario 1 (maintain present practices)

EXPLANATION

2,000

2,050

2,100

2,150

2,200

2,250

Apr. 00

Aug. 00

Dec. 00

Apr. 01

Aug. 01

Dec. 01

Apr. 02

Aug. 02

Dec. 02

Apr. 03

Aug. 03

Dec. 03

Apr. 04

Aug. 04

Dec. 04

Apr. 05

Aug. 05

Dec. 05

Apr. 06

Aug. 06

Dec. 06

Apr. 07

Aug. 07

Dec. 07

Apr. 08

Aug. 08

Dec. 08

Apr. 09

Aug. 09

Dec. 09

Apr. 00

Aug. 00

Dec. 00

Apr. 01

Aug. 01

Dec. 01

Apr. 02

Aug. 02

Dec. 02

Apr. 03

Aug. 03

Dec. 03

Apr. 04

Aug. 04

Dec. 04

Apr. 05

Aug. 05

Dec. 05

Apr. 06

Aug. 06

Dec. 06

Apr. 07

Aug. 07

Dec. 07

Apr. 08

Aug. 08

Dec. 08

Apr. 09

Aug. 09

Dec. 09

Figure 56. Graphical results from simulation/optimization (LANOPT) model for four hypothetical management scenarios, Lancaster,

Antelope Valley, California.

Optimal well rates and associated water-table altitudes are shown for eight sites (table 4) representing all managed wells for the 10-year 

management period.
Development of a Simulation/Optimization Model 105

Scenario 2

Scenario 2

Scenario 4

Scenario 3

Scenario 4

Scenario 3

Percentage well capacity used Percentage well capacity used

4/1/008/1/002/1/018/1/012/1/028/1/022/1/038/1/032/1/048/1/042/1/058/1/052/1/068/1/062/1/078/1/072/1/088/1/082/1/098/1/09

Injection Extraction Total

EXPLANATION

4/1/008/1/002/1/018/1/012/1/028/1/022/1/038/1/032/1/048/1/042/1/058/1/052/1/068/1/062/1/078/1/072/1/088/1/082/1/098/1/09

Simulated altitude of water table, in feet Simulated altitude of water table, in feet

EXPLANATION

EXPLANATION

0

20

40

60

80

100

Avenue L and 5th St. West (7N/12W-27P2–P3)

0

20

40

60

80

100

0

20

40

60

80

100

Avenue K-8 and Division (7N/12W-27H3,27J4,

and 2 proposed)

Note -- does not include deep well 4-42

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

2,000

2,050

2,100

2,150

2,200

2,250

2,000

2,050

2,100

2,150

2,200

2,250

Apr. 00

Aug. 00

Dec. 00

Apr. 01

Aug. 01

Dec. 01

Apr. 02

Aug. 02

Dec. 02

Apr. 03

Aug. 03

Dec. 03

Apr. 04

Aug. 04

Dec. 04

Apr. 05

Aug. 05

Dec. 05

Apr. 06

Aug. 06

Dec. 06

Apr. 07

Aug. 07

Dec. 07

Apr. 08

Aug. 08

Dec. 08

Apr. 09

Aug. 09

Dec. 09

Apr. 00

Aug. 00

Dec. 00

Apr. 01

Aug. 01

Dec. 01

Apr. 02

Aug. 02

Dec. 02

Apr. 03

Aug. 03

Dec. 03

Apr. 04

Aug. 04

Dec. 04

Apr. 05

Aug. 05

Dec. 05

Apr. 06

Aug. 06

Dec. 06

Apr. 07

Aug. 07

Dec. 07

Apr. 08

Aug. 08

Dec. 08

Apr. 09

Aug. 09

Dec. 09

Scenario 4 (existing and proposed wells, injection allowed 4 months

per year)

Scenario 2 (existing wells, injection allowed 6 months per year)

Scenario 3 (existing and proposed wells, injection allowed 6 months

per year)

Scenario 1 (maintain present practices)

Scenario 4 (existing and proposed wells, injection allowed 4 months

per year)

[Constrained maximum head is above top of graph; minimum head

not constrained]

Scenario 2 (existing wells, injection allowed 6 months per year)

Scenario 3 (existing and proposed wells, injection allowed 6 months

per year)

Scenario 1 (maintain present practices)

Figure 56.—Continued.
106 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Well 4-37 (7N/12W-30B1)

Avenue J and Sierra Hwy. (7N/12W-22B2, 15R2,15R4)

Injection Extraction Total

EXPLANATION

Injection Extraction Total

EXPLANATION

Scenario 2

Scenario 4

Scenario 3

Scenario 2

Scenario 4

Scenario 3

0

20

40

60

80

100

0

20

40

60

80

Percentage well capacity used

100

0

20

40

60

80

100

4/1/008/1/00

2/1/018/1/01

2/1/028/1/022/1/038/1/032/1/048/1/042/1/058/1/052/1/068/1/062/1/078/1/072/1/088/1/082/1/09

8/1/09

4/1/008/1/00

2/1/018/1/01

2/1/028/1/022/1/038/1/032/1/048/1/042/1/058/1/052/1/068/1/062/1/078/1/072/1/088/1/082/1/09

8/1/09

2,000

2,050

2,100

2,150

2,200

2,250

Apr. 00

Aug. 00

Dec. 00

Apr. 01

Aug. 01

Dec. 01

Apr. 02

Aug. 02

Dec. 02

Apr. 03

Aug. 03

Dec. 03

Apr. 04

Aug. 04

Dec. 04

Apr. 05

Aug. 05

Dec. 05

Apr. 06

Aug. 06

Dec. 06

Apr. 07

Aug. 07

Dec. 07

Apr. 08

Aug. 08

Dec. 08

Apr. 09

Aug. 09

Dec. 09

Constrained minimum

[Constrained maximum head is above top of graph]

Simulated altitude of water table, in feet Simulated altitude of water table, in feet

EXPLANATION

0

20

40

60

80

100

Percentage well capacity used

Apr. 00

Aug. 00

Dec. 00

Apr. 01

Aug. 01

Dec. 01

Apr. 02

Aug. 02

Dec. 02

Apr. 03

Aug. 03

Dec. 03

Apr. 04

Aug. 04

Dec. 04

Apr. 05

Aug. 05

Dec. 05

Apr. 06

Aug. 06

Dec. 06

Apr. 07

Aug. 07

Dec. 07

Apr. 08

Aug. 08

Dec. 08

Apr. 09

Aug. 09

Dec. 09

Constrained minimum

EXPLANATION

0

20

40

60

80

100

0

20

40

60

80

100

2,000

2,050

2,100

2,150

2,200

2,250

Scenario 2 (existing wells, injection allowed 6 months per year)

Scenario 4 (existing and proposed wells, injection allowed 4 months

per year)

Scenario 4 (existing and proposed wells, injection allowed 4 months

per year)

Scenario 3 (existing and proposed wells, injection allowed 6 months

per year)

Scenario 1 (maintain present practices)

[Constrained maximum head is above top of graph]

Scenario 2 (existing wells, injection allowed 6 months per year)

Scenario 3 (existing and proposed wells, injection allowed 6 months

per year)

Scenario 1 (maintain present practices)

Figure 56.—Continued.
Development of a Simulation/Optimization Model 107

Scenario 2

Scenario 4

Scenario 4

Scenario 3

Scenario 3

Percentage well capacity used

4/1/008/1/002/1/018/1/012/1/028/1/022/1/038/1/032/1/048/1/042/1/058/1/052/1/068/1/062/1/078/1/072/1/088/1/082/1/098/1/09

4/1/008/1/002/1/018/1/012/1/028/1/022/1/038/1/032/1/048/1/042/1/058/1/052/1/068/1/062/1/078/1/072/1/088/1/082/1/098/1/09

Injection Extraction Total

EXPLANATION

Simulated altitude of water table, in feet

EXPLANATION

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

2,000

2,050

2,100

2,150

2,200

2,250

Apr. 00

Aug. 00

Dec. 00

Apr. 01

Aug. 01

Dec. 01

Apr. 02

Aug. 02

Dec. 02

Apr. 03

Aug. 03

Dec. 03

Apr. 04

Aug. 04

Dec. 04

Apr. 05

Aug. 05

Dec. 05

Apr. 06

Aug. 06

Dec. 06

Apr. 07

Aug. 07

Dec. 07

Apr. 08

Aug. 08

Dec. 08

Apr. 09

Aug. 09

Dec. 09

Avenue K-8 and 5th St. West (7N/12W-27F2–F3,

and 2 proposed)

Two proposed injection/extraction wells

Scenario 2 (existing wells, injection allowed 6 months per year)

Scenario 4 (existing and proposed wells, injection allowed 4 months

per year)

Scenario 3 (existing and proposed wells, injection allowed 6 months

per year)

Scenario 1 (maintain present practices)

[Constrained maximum head is above top of graph; minimum head

not constrained]

Figure 56.—Continued.
108 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

Well 4-37 (7N/12W-30B1)

Avenue J and Sierra Hwy (7N/12W 22B2 15R2 15R4)

Injection Extraction Total

EXPLANATION

Scenario 4

Scenario 3

Scenario 2

0

20

40

60

80

0

20

40

60

80

Percentage well capacity used

100

0

20

40

60

80

100

4/1/008/1/00

2/1/018/1/01

2/1/028/1/022/1/038/1/032/1/048/1/042/1/058/1/052/1/068/1/062/1/078/1/072/1/088/1/08

2/1/09

8/1/09

2,000

2,050

2,100

2,150

2,200

2,250

Apr. 00

Aug. 00

Dec. 00

Apr. 01

Aug. 01

Dec. 01

Apr. 02

Aug. 02

Dec. 02

Apr. 03

Aug. 03

Dec. 03

Apr. 04

Aug. 04

Dec. 04

Apr. 05

Aug. 05

Dec. 05

Apr. 06

Aug. 06

Dec. 06

Apr. 07

Aug. 07

Dec. 07

Apr. 08

Aug. 08

Dec. 08

Apr. 09

Aug. 09

Dec. 09

Constrained minimum

[Constrained maximum head is above top of graph]

Simulated altitude of water table, in feet

EXPLANATION

100

Scenario 2 (existing wells, injection allowed 6 months per year)

Scenario 4 (existing and proposed wells, injection allowed 4 months

per year)

Scenario 3 (existing and proposed wells, injection allowed 6 months

per year)

Scenario 1 (maintain present practices)

Figure 56.—Continued.

Scenario

Objective value, 

minimum head 

(feet)

Average simulated water level during 

management period at managed well locations Total injection 

management period

Within subsidence area (acre-feet)

(feet)

Outside of 

subsidence area 

(feet)

Scenario 1: Maintain present practices na 2,131.4 12,096.9 0

Scenario 2: Existing wells, 6 months injection 2,082.9 2,166.3 12,110.5 52,480

Scenario 3: Existing and proposed wells, 6 months 

injection

2,129.9 2,159.2 2,162.0 110,520

Scenario 4: Existing and proposedwells, 4 months 

injection

2,122.4 2,165.0 2,142.1 84,621

Table 5. Results from the simulation/optimization model for four hypothetical management scenarios for Lancaster, Antelope Valley, California

for management period 2000–2010

[na, not available]

1 Does not include Avenue M and 5th Street East, a proposed site having no existing wells.
Development of a Simulation/Optimization Model 109

The LANOPT model was used to test the 

feasibility of meeting the constraints while maintaining 

present practices (scenario 1), but allowing the 

pumping distribution to vary in time and space. No 

feasible solution was found, which was expected owing 

to the large drawdowns in the subsidence area. Feasible 

solutions were found, however, for the other three 

scenarios. 

The optimal solution for managing injection and 

extraction in the 16 existing wells (three of which are 

extraction-only wells) (scenario 2) required extensive 

injection in the subsidence area to maintain water 

levels above the constrained minimum (fig. 56). 

Injection into the wells in the subsidence area during 

the low-demand period (6 months) provided for 

continued use of these wells during the high-demand 

period. At least 50 percent of the extraction capacity of 

these wells was used for more than 86 percent of the 

high-demand periods during the 10-year simulation. 

Outside the subsidence area, extraction was dominant 

at the Avenue K–8 and 5th Street West, Avenue K–8 

and Division Street, and Avenue M and 7th Street West 

sites, where the spring water table (the seasonal 

maximum head) declined by about 10 to 28 ft. Injection 

exceeded extraction at Avenue L and 5th Street West, 

the site of the pilot injection tests, which resulted in an 

increase in water-table elevation of 12 ft. Overall, the 

annual amount of water injected decreased from about 

5,800 to 5,200 acre-ft during the management period, 

which represented 40 to 31 percent, respectively, of 

total well use. This decrease in injection with time is 

correlated to the constrained increase in ground-water 

demand.

The objective value (the minimum head) for 

managing the existing wells was 2,082.9 ft (table 5), 

which occurred in the final stress period at Avenue L 

and 5th Street West and Avenue M and 7th Street West. 

Heads at Avenue K–8 and 5th Street West and Avenue 

K–8 and Division Street were within 6 ft of the 

objective value indicating essentially equal heads at all 

the managed sites outside the subsidence area. The 

average simulated water-table altitude at the existing 

wells during the 10-year management period was 2,166 

ft in the subsidence area and 2,110 ft elsewhere 

(table 5). The average simulated water-table altitudes 

for scenario 2 improved about 35 and 14 ft, 

respectively, within and outside the areas of subsidence 

over maintaining present practices (scenario 1).

The addition of 13 proposed wells (scenario 3) 

constitutes a large increase in both injection and 

extraction capacity, which was reflected by the 47-ft 

increase in the objective value, to 2,130 ft and by a 

similar increase in average water levels outside the 

subsidence area (table 5). The average simulated water 

levels for all the managed locations outside the 

subsidence area were within 8 ft of the objective value, 

which remained above the minimum head constraints 

within the subsidence area. The injection volumes for 

scenario 3 about doubled those of scenario 2 and 

decreased during the 10-year management period from 

12,400 acre-ft/yr to 10,500 acre-ft/yr. The injection 

volumes for scenario 3 represented 58 to 48 percent of 

total well use. Extraction exceeded injection in the 

subsidence areas (while meeting subsidence 

constraints), but injection exceeded extraction 

elsewhere, resulting in substantial increases in watertable altitude (fig. 56). The spring water table outside 

the subsidence area rose 54 to 73 ft during the 

management period; the maximum increase was at the 

Avenue L and 5th Street West and Avenue M and 7th 

Street West sites. The deep wells, in which no injection 

was allowed, seldom were used, particularly during the 

latter two-thirds of the management period.
110 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

The 6-month period of injection allowed for 

scenario 3 was reduced to 4 months for scenario 4 to 

determine the effects of a substantial reduction in 

injection volume. Injection volumes may be reduced 

for a variety of reasons, including availability of SWP 

water, overestimation of injection capacities, 

underestimation of maintenance requirements during 

injection, and potential water-quality considerations. 

The objective value for scenario 4 decreased by 7.5 ft 

to 2,122.4 ft, but the average water level outside the 

subsidence area declined 20 ft, to 32 ft higher than that 

for scenario 2. The water table at all the managed 

locations during the last stress period of scenario 4 was 

equal to the objective value or the lower head 

constraint. Injection volumes decreased to about 8,700 

to 9,000 acre-ft/yr within and outside the subsidence 

area, respectively; the injected water represented 43 to 

50 percent of total well use, both decreasing with 

growth in demand. Extraction approximately equaled 

injection in the subsidence areas, and injection 

exceeded extraction elsewhere, except at the proposed 

site at Avenue M and 5th Street West. Unlike scenario 

3, extraction from the deep wells was extensive, 

exceeding 50 percent of capacity during more than half 

of the simulation. The spring water table outside the 

subsidence area rose by 23 to 55 ft during the 10-year 

management period, with the maximum increases at 

Avenue L and 5th Street West and Avenue M and 7th 

Street West, as in scenario 3 (fig. 56).

Another means for comparing the results of 

managements scenarios and for judging their relative 

feasibilities is evaluating the percentage of total well 

capacity used for injection and extraction. Figure 57

shows total well capacities and the combined totals for 

the management period. Note that for scenario 2 (only 

the existing wells used), growth in spring/summer 

demand resulted in extraction volumes that required an 

increase in well use from less than 65 percent at the 

beginning of the management period to 85 percent at 

the end. It may not be feasible to pump all the existing 

wells 85 percent of the time with the current 

infrastructure because additional storage and rigorous 

management of that storage may be required to allow 

for continued extraction during daily and (or) extended 

periods of low demand. The addition of the proposed 

wells (scenarios 3 and 4) reduces the maximum well 

use during high-demand periods to only 46 percent of 

long-term capacity to allow down time.

All wells operate at full capacity in all scenarios 

when injection is allowed, with the exception of the 

deep extraction-only wells (figs. 56, 57) and two other 

minor exceptions. This indicates that injection capacity 

is the binding constraint for this optimization problem. 

Thus, added capacity would improve the solution until 

another constraint becomes dominant.

Figure 58 shows the annual volumes of injected 

and extracted water for management scenarios 2, 3, and 

4, which represent a wide range of injection volumes 

and associated net stresses. The variability of the 

injection curve for scenario 4 is due primarily to the 

large annual variability in volumes extracted from the 

deep extraction-only wells, which was not the case for 

the other scenarios (fig. 56). When extraction 

decreased from these deep wells, the other wells 

switched from injection to extraction to compensate; 

the opposite occurred when extraction from the deep 

wells was increased. This sporadic extraction from the 

deep wells resulted in high variability in the totals for 

injection.

The accuracy of results from the LANOPT 

model depends on many factors, and one should not 

have too much confidence in the details—for example, 

the exact mix of injection and extraction at a specific 

site. The strength in this type of model is the ability to 

compare alternate scenarios knowing that one is 

comparing the optimal case for each scenario. The 

results for management scenarios 1–4 suggest that an 

injection program with existing wells would be a 

substantial improvement over no injection at all, 

although the water-table would continue to decline 

outside of the subsidence area. The high rates of well 

usage associated with this scenario may not be 

sustainable in practice. The results also indicate that 

installation and inclusion of all the proposed wells into 

the injection program would result in a significant 

water-table rise outside the subsidence area and 

average rates of well usage far below current values.
Development of a Simulation/Optimization Model 111

0

20

40

60

80

100

Injection

Extraction

Total

Scenario 4 (all existing and proposed wells, injection allowed

4 months per year)

Scenario 2 (all existing wells, injection allowed 6 months per year)

0

20

40

60

80

100

Scenario 3 (all existing and proposed wells, injection allowed

6 months per year)

0

20

40

60

80

100

4/1/00

8/1/00

2/1/01

8/1/01

2/1/02

8/1/02

2/1/03

8/1/03

2/1/04

8/1/04

2/1/05

8/1/05

2/1/06

8/1/06

2/1/07

8/1/07

2/1/08

8/1/08

2/1/09

8/1/09

4/1/00

8/1/00

2/1/01

8/1/01

2/1/02

8/1/02

2/1/03

8/1/03

2/1/04

8/1/04

2/1/05

8/1/05

2/1/06

8/1/06

2/1/07

8/1/07

2/1/08

8/1/08

2/1/09

8/1/09

4/1/00

8/1/00

2/1/01

8/1/01

2/1/02

8/1/02

2/1/03

8/1/03

2/1/04

8/1/04

2/1/05

8/1/05

2/1/06

8/1/06

2/1/07

8/1/07

2/1/08

8/1/08

2/1/09

8/1/09

Percentage well capacity used Percentage well capacity used Percentage well capacity used

EXPLANATION

Figure 57. Optimal well capacity used for injection and extraction for three hypothetical management scenarios for Lancaster, Antelope 

Valley, California.

Totals were adjusted to compensate for the difference in capacities for injection and extraction and are less than the sum of these 

components.
112 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

This dichotomy suggests that a more moderate, 

or phased-in approach to the addition of the proposed 

wells may accomplish the objective of avoiding 

additional land subsidence while maintaining, or even 

improving, extraction capacities outside the subsidence 

area. If a phased-in installation of the proposed wells is 

desired, the LANOPT model can be used to help decide 

the logical order of well installation. Although integer 

methods and other more complex techniques may be 

applied to answer this question more rigorously, a 

simple approach is to include groups of proposed wells 

into the problem and to compare the objective value to 

that without the proposed wells (scenario 2). The 

results of this approach are given in table 6.

The improvement in the objective value for 

individual proposed wells is generally correlated with 

the injection capacity (table 6). Assuming that the 

injection (and extraction) capacities are accurate in a 

relative sense, this analysis suggests that the Avenue M 

and 5th Street East site, where no wells presently exist, 

may be the most effective site for the proposed wells. 

Although there are twice as many proposed wells at 

this site than at most of the other sites, the 

improvement in the objective value exceeds that at the 

other sites by more than a factor of two. To ensure this 

result was not overly influenced by the large capacity at 

this site, a simulation was run using the wells at the 

Avenue M and 5th Street East site at half capacity. The 

resulting improvement in the objective value was 24 ft, 

4,000

6,000

8,000

10,000

12,000

14,000

Extraction, all scenarios

Scenario 2 (injection in existing wells, allowed 6 months per year)

Scenario 4 (injection in existing and proposed wells, allowed 4 months per year)

Scenario 3 (injection in existing and proposed wells, allowed 6 months per year)

Full year during management period

Annual injection or extraction, in acre-feet

EXPLANATION

5/1/00–4/30/01

5/1/01–4/30/02

5/1/02–4/30/03

5/1/03–4/30/04

5/1/04–4/30/05

5/1/05–4/30/06

5/1/06–4/30/07

5/1/07–4/30/08

5/1/08–4/30/09

Projected extraction, all scenarios

Figure 58. Optimal volumes of injection and extraction during the management period for three hypothetical management scenarios, 

Lancaster, Antelope Valley, California.
Development of a Simulation/Optimization Model 113

about twice that of any other site, and only 6 ft less than 

the objective value at the original capacity. This result 

strengthens the conclusion that the Avenue M and 5th 

Street East site may be the most effective site for the 

proposed wells, and it indicates that it may be more 

effective to install only two wells at that site in the 

early stages (four are proposed).

Sensitivity Analysis of Simulation/Optimization (LANOPT) 

Model

As with the LAN model, a sensitivity analysis 

was done for the LANOPT model to determine the 

sensitivity of model results to key variables. The 

following optimization constraints were considered in 

the sensitivity analysis: ground-water demand, 

injection capacity, minimum hydraulic heads, and the 

limit on summer injection. The estimated growth in 

ground-water demand was adjusted upward and 

downward by 50 percent (18 percent of the 2000 

population) because population forecasts and other 

assumptions (for example, no change in conservation 

practices) have a large potential for error. Injection 

capacities were changed from 72 to 64 and 80 percent 

of the estimated long-term capacity. Minimum heads in 

the subsidence area were increased and decreased by 

10 ft, except for the first four stress periods (through 

the end of the first summer). The limit on injection 

during the summer was raised from 0 to 3,000 acre-ft 

for a 6-month period, which represents about 25 

percent of the average injection during the winter 

period.

Management scenario 3, which included all the 

wells and 6 months of injection, was used for the 

sensitivity analysis and as a basis for comparison. The 

objective value for this scenario is relatively insensitive 

to fluctuations in most of the variables because the 

minimum head occurs during the first summer stress 

period; therefore, average changes in the heads at the 

managed wells within and outside the subsidence areas 

during the 10-year management period and changes in 

total injection were used as the primary indicators of 

sensitivity (table 7).

The optimal solution for scenario 3 required full 

usage of well capacity throughout the 10-year 

management period, except at the deep wells for which 

injection was not allowed and at two locations within 

the subsidence area (Avenue J and Sierra Highway and 

the northern area) where well usage dropped to 83 to 

97 percent on two occasions (fig. 56). If the constraints 

are tightened, the unused well capacity will decrease, 

which may not be feasible; and if the constraints are 

relaxed, the unused capacity will increase. 

Tightening the constraints results in lower water 

levels outside the subsidence area and generally causes 

increased use of wells in the subsidence area, which is 

a somewhat counterintuitive result. This occurs 

because the optimization procedure shifts as much 

extraction as possible to the subsidence area, allowing 

maximum injection outside the subsidence area (where 

the lowest heads are). Additional extraction in the 

subsidence area is achieved by increasing injection in 

that area during periods when injection is allowed. This 

shift in stresses with the tightening of constraints 

generally results in an increase in average water levels 

within the subsidence area and an accompanying 

increase in total injection. The opposite responses 

generally are observed when constraints are loosened 

(table 7). 

Proposed well site Number of proposed 

wells

Objective value 

(ft)

Improvement in 

objective value 

(ft)

Injection capacity 

(ft3

/d)

Avenue M and 5th Street East 4 2112.9 29.9 576,000

Avenue J and Sierra Highway 2 2094.9 11.9 288,000

Avenue K-8 and 5th Street West 2 2094.9 11.9 252,000

Avenue M and 7th Street West 2 2094.7 11.7 288,000

Avenue K-8 and Division Street 2 2093.8 10.8 205,200

Avenue J and Sierra Highway, near well 4-5 1 2090.2 7.2 144,000

Table 6. Effect of proposed wells on the objective value (2,083 feet without proposed wells), Lancaster, Antelope Valley, California

[ft, foot; ft3/d, cubic foot per second]
114 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

A limited amount of injection during the summer 

was slightly more effective than that during the winter; 

essentially the same average water levels were achieved 

using about 97 percent of the injection. However, 

increased cost and decreased reliability of SWP water 

during the summer were not taken into account in the 

LANOPT model.

Appropriate Use and Improvement of the 

Simulation/Optimization (LANOPT) Model

The LANOPT model described in this report was 

conceived as an adaptable tool for use in designing, and 

later managing, an injection program. It is best suited 

for comparative analysis of alternative scenarios. 

Potential sources of error and limitations associated 

with the optimization component of the LANOPT 

model are discussed here, but those associated with the 

simulation component also apply. Assumptions made 

during model development and limitations associated 

with the software should be kept in mind with respect 

to appropriate use and improvement of the model.

Assumptions Made during Model Development

Assumptions made during model development 

include those associated with well capacities, future 

availability of SWP water, future ground-water 

demand, water conveyance and storage, and the 

linearity of the optimization problem. The extraction 

capacity of existing wells was estimated for 1-month 

periods of full-time operation, but that for longer 

periods is unknown; it was arbitrarily assumed to be 80 

percent of the 1-month capacity. Injection capacity is 

known only for the wells at the injection site. Actual 

injection capacities may differ substantially, and may 

decline with time regardless of changes in water-table 

elevation. The estimated capacities for the proposed 

wells may have significant error, particularly the 

estimates for the new site (Avenue M and 5th Street 

East). Sensitivity analysis showed that the optimal 

solution is sensitive to small changes in injection 

capacities, which suggests a similar sensitivity to those 

for extraction.

An unlimited volume of SWP water was 

assumed to be available every year from November 

through April; in reality, this may not be the case. A 

combination of conservation efforts and alternative 

water supplies successfully averted large increases in 

ground-water use during the 1987–92 drought and the 

associated low availability of SWP water. SWP water 

would not have been water available for injection 

during some of those years and most likely will not be 

available in the future when drought conditions recur.

Change in optimization constraint

Change in average simulated water level during 

management period at managed well locations, 

compared to scenario (all wells with 6 months 

injection allowed)

Change in total 

injection, 

management 

period

(percent)

Within 

subsidence area 

(feet)

Outside of 

subsidence area 

(feet)

Increase growth in ground-water demand 50 percent 10.0 8.6 6.3

Reduce growth in ground-water demand 50 percent 0.3 1.4 11.1

Increase injection capacity from 72 to 80 percent of long-term 

extraction capacity

0.6 3.2 3.2

Reduce injection capacity from 72 to 80 percent of long-term 

extraction capacity

3.1 7.7 10.0

Increase minimum heads in subsidence area by 10 feet 11.7 9.1 4.3

Reduce minimum heads in subsidence area by 10 feet 8.5 3.5 12.3

Allow 3,000 acre-feet of injection during late spring through early fall 1.6 0.7 3.2

Table 7. Effect of changes in optimization constraints on results from simulation/optimization (LANOPT) model of Lancaster, Antelope Valley, 

California, for management period, 2000–2010
Development of a Simulation/Optimization Model 115

Ground-water demand was assumed to increase 

at the same rate as the projected growth in population. 

Population forecasts are associated with high potential 

error because unexpected changes in socioeconomic 

conditions can cause dramatic changes. Other factors 

that can affect ground-water demand include 

development of alternative water sources, increased 

conservation efforts, and contaminant issues. The 

sensitivity analysis of the LANOPT model showed that 

the model results were sensitive to large changes in 

ground-water demand.

Conveyance and storage facilities were assumed 

to be adequate for moving and storing water for all the 

management scenarios. All the managed wells are 

connected by a network of pipelines, which also 

connects a number of above-ground storage tanks and 

taps the AVEK pipeline. It is possible that additional 

storage and (or) connections would be required to 

implement a given scenario.

The presence of an unconfined aquifer in the 

flow model violates the assumption of linearity 

between stress and response; it should be noted that 

simulation/optimization results may be sensitive to this 

violation. Recall that the response matrix is built by 

applying stress at one managed well at a time and 

recording the transient head response at all the 

specified locations. The linear optimization procedure 

assumes these responses are additive for multiple 

wells; however, the change in transmissivity resulting 

from a change in water-table elevation is not taken into 

account.

Figure 59 shows linear (optimization results) and 

nonlinear (results from LAN model using optimal 

injection and extraction) water-table elevations during 

the management period (2000–2010) at two sites where 

hydraulic head changes, and associated errors, were 

greatest. The seasonal fluctuations of the water-table 

altitudes, based on the assumption of linearity, were 

greater than those simulated by the LAN model 

because the water table generally was higher than the 

initial condition; hence the transmissivity generally 

was greater. Although there clearly was some error 

associated with the assumption of linearity, that error 

was very small relative to the magnitude of seasonal 

head changes for the scenarios considered (fig. 59). If 

the errors associated with nonlinearity increase to 

unacceptable levels, an iterative linear approach may 

be affective in reducing these errors (Danskin and 

Gorelick, 1985; Greenwald, 1993; Nishikawa, 1998; 

Ahlfeld and Mulligan, 2000); otherwise, nonlinear 

methods may be required.

Limitations Associated with the Software

The optimization software used for this work has 

limitations, the effects of which should be understood 

by the user. The primary limitations include the 

inability of the software to account for various effects 

of changing water-table conditions, and no explicit 

means for addressing land subsidence. Changing 

water-table conditions not only introduce error between 

simulated and optimal hydraulic head response, but 

also introduce potentially large changes in constraints 

that are assumed to remain constant. Well capacity and 

the vertical distribution of extraction and injection 

between the upper and middle aquifers sometimes are, 

in reality, functions of water-table elevation. If heads 

decline below the top of the screened interval, well 

capacity decreases, as does the percentage of extracted 

water from the upper aquifer (the opposite occurs as 

heads rise within the screened interval). Neither the 

optimization software nor the LAN model account for 

these changes, which can result in significant error. 

This error is proportional to water-table change within 

screened intervals during the management period.

MODMAN (Greenwald, 1993) does provide for 

manual specification of well capacity and vertical 

distribution of stresses. Specification of these changes, 

however, would require prior knowledge of the optimal 

solution or the development of a complex iterative 

approach that would be time consuming and 

computationally expensive.

The version of MODMAN used for this 

investigation (Greenwald, 1993) does not 

accommodate use of the IBS1 package (Leake and 

Prudic, 1991), which enables simulation of aquifersystem compaction in MODFLOW. A newer version of 

MODMAN (Greenwald, 1998) does allow the use of 

the IBS1 package in the simulation model, but it does 

not allow use of compaction or subsidence within the 

objective or constraint set.
116 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

EXPLANATION

Avenue L and 5th St. West (7N/12W-27P2–P3))

2,000

2,050

2,100

2,150

2,200

2,250

Linear optimization Simulated water table

Simulated altitude of water table, in feet above sea level

Avenue M and 5th St. East (4 proposed wells)

2,000

2,050

2,100

2,150

2,200

2,250

Apr-00

Aug-00

Dec-00

Apr-01

Aug-01

Dec-01

Apr-02

Aug-02

Dec-02

Apr-03

Aug-03

Dec-03

Apr-04

Aug-04

Dec-04

Apr-05

Aug-05

Dec-05

Apr-06

Aug-06

Dec-06

Apr-07

Aug-07

Dec-07

Apr-08

Aug-08

Dec-08

Apr-09

Aug-09

Dec-09

initial water-table altitude

initial water-table altitude

Figure 59. Water-table results from linear optimization and the ground-water-flow model using optimal injection and pumping rates for 

scenario 4 (all existing and proposed wells for injection during six months of the year), Lancaster, Antelope Valley, California. 
Development of a Simulation/Optimization Model 117

Potential Improvements

The LANOPT model is useful for planning 

purposes, but its usefulness for management purposes 

is currently limited. This limitation is directly related to 

the assumptions and limitations discussed above, but it 

can be addressed by monitoring of injection sites, 

selecting appropriate optimization objectives, and 

improving the model, as needed. New information can 

be used to improve simulation results in areas that are 

currently poorly understood, and the objective and (or) 

constraints can be adjusted to better represent site 

conditions and future goals.

Monitoring the hydraulic and subsidence-related 

response to measured injection and extraction rates at 

each injection site would provide critical information 

needed to reduce model uncertainty. The water-level 

response would guide meaningful adjustment of the 

head constraints, which are highly subjective. If, for 

example, the water table rises too close to the land 

surface under optimal stresses, the upper head 

constraint should be adjusted downward and a new 

solution generated. Similarly, simultaneous monitoring 

of aquifer-system deformation and (or) land-surface 

elevation would allow determination of the 

preconsolidation head, on which the lower head 

constraint is based.

Improvement or adaptation of the LANOPT 

model may require changing the discretization of the 

model grid. Simulated water-level changes are sensitive 

to the size of model cells, particularly those cells in 

which stresses occur. Because simulated head changes 

represent the average change within a cell, large cells 

containing wells show a relatively muted response 

compared with smaller cells containing the same wells. 

Care must be taken to adjust head constraints 

appropriately.

Periodic evaluation of the availability of SWP 

water and any changes in ground-water demand is 

needed for development and maintenance of realistic 

constraints. No expanded monitoring is necessary, as 

these data are routinely gathered. The current 

constraints associated with these values are subject to 

significant short- and long-term error.

The conveyance, mixing, and storage of injected 

and extracted water was not accounted for in the 

LANOPT model. Difficulties may arise in 

implementing optimal strategies that do not take these 

aspects into account. In such cases, constraints could 

be added or modified to restrict capacities of individual 

or multiple wells sharing pipelines and (or) storage 

facilities.

The current optimization objective, to maximize 

the lowest value of head, is not the only approach to 

this problem, and may not be appropriate for future 

applications. Suppose, for example, that field 

measurements result in a minimum head for each well, 

below which capacity drops to unacceptable levels. 

One could then use these heads, or their equivalent, as 

minimum head constraints and the objective could be 

changed to maximize injection (if interested in using as 

much SWP water as possible) or to minimize injection 

(if costs are a concern). There is a wide range of 

objectives to choose from, and any change in focus or 

arrival of new information should result a re-evaluation 

of the objective.

The combination of measured stresses and waterlevel response is key to determining the magnitude and 

variability of well capacities. Long-term average 

injection and extraction capacities determined from 

field measurements would be an improvement from the 

current estimates. More importantly, perhaps, is the 

determination of the critical head below which 

extraction capacity will decrease rapidly. A 

combination of velocity logging within the well and 

simultaneous measurement of extraction and 

drawdown would provide an accurate means for 

determining this threshold. Once determined, the 

minimum head can be constrained at that well to avoid 

large losses in capacity.

If future management goals are changed to allow 

some subsidence to occur, the LANOPT model could 

be improved with respect to subsidence control and 

predicted head changes by simulating inelastic 

compaction. Future versions of optimization software 

likely will allow direct use of results from existing 

subsidence simulation tools. Note that because aquifersystem compaction and associated subsidence is not a 

linear function of head, nonlinearity would be 

introduced which may require an iterative linear or 

nonlinear approach.
118 Analysis of Tests of Subsurface Injection, Storage, and Recovery of Freshwater in Lancaster, Antelope Valley, California

SUMMARY AND CONCLUSIONS

This report documents the monitoring and 

analysis of the hydraulic, subsidence-related, and 

general chemical effects of a series of freshwater 

injection tests in Lancaster, California, and the 

development of the LAN and LANOPT models for use 

in planning and managing, respectively, a larger scale 

injection program. It is one of five U.S. Geological 

Survey reports describing this series of tests, which 

were designed to assess the feasibility of implementing 

an injection program as part of a management strategy 

to halt the depletion of ground-water resources and 

avoid future land subsidence.

Treated water from the State Water Project, 

which is potable, was gravity-fed at a rate of about 

750 gal/min into one or two existing wells in Lancaster 

for as much as 5 months, stored for 2 to 4 weeks, and 

extracted at about the same rate. The wells used for 

injection fully penetrate the upper unconfined aquifer 

and penetrate most of the middle confined aquifer 

above the lacustrine unit. A flow analysis (velocity log) 

for one of the injection wells showed that much of the 

flow between the well and the aquifer system took 

place in the upper aquifer.

Monitoring during the tests fell into three 

primary categories: hydraulic (water levels), 

subsidence-related (aquifer-system and land-surface 

deformation), and chemical. Hydraulic monitoring 

included electronic and periodic measurements in 

nested piezometers and wells and microgravity 

surveys. The direct measurements showed that the 

hydraulic response to injection was significant within 

about a 1-mi radius of the injection wells. Coupled 

water-level and gravity measurements were used to 

estimate the specific yield (0.13). This value was then 

used to estimate the shape of the injection mound using 

the distributed measurements of gravity change.

Aquifer-system deformation was measured 

directly using a dual borehole extensometer located 

about 0.5 mi north of the injection site, and indirectly 

using first-order leveling, continuous GPS (Global 

Positioning System), and high-precision tiltmeters. The 

extensometer showed expansion of the aquifer system 

during injection and compaction during extraction. A 

portion of this compaction (for example, about 0.01 ft 

at the extensometer site from 1996 to 1997) was 

inelastic (permanent). Leveling results showed the 

range of deformation increased to the north, which is 

consistent with measurements from previous studies of 

Antelope Valley made using static GPS and InSAR 

(interferometric synthetic aperture radar). Leveling and 

tiltmeter measurements indicated that about 6 to 

11 mm (about 0.02 to 0.04 ft) of uplift of the land 

surface at the injection site occurred during injection. 

Uplift may have exceeded this estimate, but it was not 

areally extensive, concentrated within several hundred 

feet of the well. Coupled measurements of water levels 

and aquifer-system deformation were used to estimate 

the elastic (1.2 × 10-6/ft) and inelastic (4.0 × 10-5/ft) 

skeletal specific storage values. 

Major ions, selected trace metals, and 

trihalomethanes samples were analyzed, and field 

parameters were measured periodically in injected and 

extracted water. Constituent concentrations in injected 

water, including those for chloride and 

trihalomethanes, generally exceeded those in native 

ground water. Trihalomethanes were not detected in 

native ground water, but concentrations increased 

substantially between injection and extraction. 

Chloride concentrations did not exhibit this behavior, 

suggesting that trihalomethanes formed within the 

aquifer system after injection. Mass balance 

calculations for the second injection cycle using 

chloride suggested that the water extracted, which was 

156 percent of the injected volume, contained 

51 percent of the injected water, indicating a significant 

residual effect on ground-water chemistry.

A three-dimensional numerical model of groundwater flow (LAN model) was developed to estimate the 

hydraulic properties of the aquifer system in the 

Lancaster area, which is a subset of the area covered by 

a regional model for Antelope Valley. Results of 

calibration of the model showed there is an infinite, but 

predictable, set of hydraulic conductivity values 

(horizontal hydraulic conductivity of the upper and 

middle aquifers and vertical hydraulic conductivity 

between the aquifers) that result in reasonable 

simulation of long-term and seasonal water levels. 

Combined with independent information (the velocity 

log and microgravity results), a unique combination of 

these values was chosen from this set (17, 1.7, and 

0.006 ft/d, respectively). The calibrated model closely 

simulated measured conditions in the vicinity of the 

injection wells, and reasonably simulated conditions 

elsewhere.
References Cited 119

A simulation/optimization model (the LANOPT 

model) was developed using a modified version of the 

LAN model and commercially available optimization 

tools. The LANOPT model was used to estimate the 

relative effectiveness of four hypothetical management 

scenarios for halting the decline of ground-water levels 

in the southern Lancaster area and avoiding future land 

subsidence in the northern Lancaster area while 

meeting increasing ground-water demand. The 

scenarios consisted of maintaining present practices 

with no injection (scenario 1); injection allowed in 16 

existing wells during a 6-month period (scenario 2); 

and injection allowed in the existing wells and the 13 

proposed wells during 6- or 4-month periods (scenarios 

3 and 4). Results of the LANOPT model indicate that a 

phased-in installation of the proposed wells will be 

required over a 10-year management period to maintain 

ground-water levels in the southern area of Lancaster 

while avoiding land subsidence in the northern area.

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