U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2015–5054

In cooperation with the city of Palmdale, California

Feasibility and Potential Effects of the Proposed Amargosa 

Creek Recharge Project, Palmdale, California
Cover. Three-dimensional image created using U.S. Geological Survey National Elevation Dataset, U.S. Department of Agriculture 

National Agriculture Imagery Program (NAIP 2010) and ESRI ArcScene.
Feasibility and Potential Effects of the 

Proposed Amargosa Creek Recharge 

Project, Palmdale, California

By Allen H. Christensen, Adam J. Siade, Peter Martin, Victoria E. Langeheim, 

Rufus D. Catchings, and Matthew K. Burgess

In cooperation with the city of Palmdale, California

Scientific Investigations Report 2015–5054

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Christensen, A.H., Siade, A.J., Martin, Peter, Langeheim, V.E., Catchings, R.D., and Burgess, M.K., 2015, Feasibility 

and potential effects of the proposed Amargosa Creek recharge project, Palmdale, California: U.S. Geological Survey 

Scientific Investigations Report 2015–5054, 48 p., http://dx.doi.org/10.3133/SIR20155054.

2001051109

ISSN 2328-0328(online)
iii

Contents

Acknowledgments......................................................................................................................................viii

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

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

Purpose and Scope ..............................................................................................................................2

General Description of Study Area....................................................................................................2

Site Characterization.....................................................................................................................................2

Previous Geohydrologic Studies...............................................................................................2

Geohydrologic Setting ................................................................................................................5

Monitoring Well Construction.............................................................................................................6

Monitoring Site 1..........................................................................................................................6

Monitoring Site 2..........................................................................................................................6

Monitoring Site 3........................................................................................................................11

Water-Level Data Collected from Monitoring Wells............................................................12

Water-Quality Data Collected from Monitoring Wells.........................................................12

Water-Quality Data Collection........................................................................................12

Physical and Chemical Characteristics ........................................................................12

Source and Age of Groundwater...................................................................................19

Stable Isotopes ........................................................................................................19

Tritium .......................................................................................................................19

Carbon-14..................................................................................................................19

Surface Geophysical Surveys ..........................................................................................................23

Regional Gravity Survey ...........................................................................................................24

Gravity Survey and Reduction Data Sets......................................................................24

Geologic Maps ..................................................................................................................24

Water Wells .......................................................................................................................24

Gravity Field .......................................................................................................................24

Computation Method for Modeling Thickness of Valley-Fill Deposits.....................26

Gravity Results ..................................................................................................................27

Seismic Refraction and Reflection, and Direct- Current Resistivity Surveys..................27

Seismic Refraction and Reflection Survey...................................................................27

Seismic Data Acquisition and Processing ..........................................................30

Seismic Survey Results ..........................................................................................30

Resistivity Surveys............................................................................................................32

Resistivity Data Acquisition ...................................................................................32

Resistivity Data Processing ...................................................................................32

Resistivity Survey Results ......................................................................................33

Summary of Geophysical Surveys ..........................................................................................33

Geohydrologic Structure beneath the ACRP and Vicinity............................................................33

Groundwater-Flow Models ........................................................................................................................35

Local Model: Evaluation of Fault B ..................................................................................................36

Spatial Discretization ................................................................................................................36

Temporal Discretization............................................................................................................37
iv

Figures

1. Map showing study area and Leona Valley surface-water drainage basin 

(Amargosa Creek drainage basin), Antelope Valley, California............................................3

2. Map showing location of study area boundary, Antelope Valley, California......................4

3. Generalized geologic section showing relation of lacustrine deposits to aquifers in 

the Antelope Valley groundwater basin, Antelope Valley, California ..................................5

4. Map showing locations of monitoring sites 1, 2, and 3, near Palmdale, California...........7

5. Schematic showing geophysical logs and well construction for monitoring sites 

near Palmdale, California: site 1 (6N/12W-29B1).....................................................................9

6. Schematic showing geophysical logs and well construction for monitoring sites 

near Palmdale, California: site 2 (6N/12W-21G1)...................................................................10

7. Schematic showing geophysical logs and well construction for monitoring site 3 

(6N/12W-21G001-4), near Palmdale, California......................................................................11

8. Map showing hydraulic head at selected wells, Antelope Valley, California, 2009 ........13

9. Graph showing stable isotope data for samples collected from monitoring sites 1, 

2, and 3 and the vicinity of Palmdale, California, 2009–13....................................................22

10. Map showing location of geophysical surveys, Antelope Valley, California....................23

11. Map showing contoured isostatic residual gravity field, Antelope Valley, California ....26

12. Map showing the thickness of the valley-fill deposits calculated from gravity 

measurements in the Palmdale area, Antelope Valley, California .....................................28

Model Boundaries .....................................................................................................................37

Specified-Flux Boundaries..............................................................................................37

Specified-Head Boundaries............................................................................................37

Hydraulic Properties .................................................................................................................37

Model Calibration ......................................................................................................................38

Extended Model: Artificial-Recharge Scenarios...........................................................................38

Spatial Discretization ................................................................................................................38

Temporal Discretization............................................................................................................38

Model Boundaries .....................................................................................................................39

Specified-Flux Boundaries..............................................................................................39

Specified-Head Boundaries............................................................................................39

Simulated Faults................................................................................................................39

Hydraulic Properties .................................................................................................................39

Model Calibration ......................................................................................................................39

Model Results.............................................................................................................................39

Limitations and Appropriate Use of the Models............................................................................41

Summary and Conclusions.........................................................................................................................44

References Cited..........................................................................................................................................45

Contents—Continued
v

Tables

1. Well-site list and construction data for selected wells near Palmdale, Los Angeles 

County, California..........................................................................................................................8

2. Field measurements and water-quality data for water from selected monitoring 

wells near Palmdale, Los Angeles County, California, 2009–13..........................................14

3. Nutrient and organic carbon data for water from selected monitoring wells near 

Palmdale, Los Angeles County, California, 2009–13..............................................................16

4. Regulated volatile organic compounds data for water from selected monitoring 

wells near Palmdale, Los Angeles County, California, 2009–12..........................................17

5. Isotopic data for water from selected monitoring wells near Palmdale, Los Angeles 

County, California, 2009–13........................................................................................................20

6. Isotopic data for water from selected wells near Palmdale, California, 1997–2013 .......21

7. Thickness of alluvial deposits from drillers’ logs and gravity surveys for 14 wells 

near Palmdale, Los Angeles County, California.....................................................................25

8. Estimated density contrast with depth in the Palmdale area .............................................27

13. Map showing locations of seismic refraction and reflection surveys and direct 

current (DC) resistivity surveys along Amargosa Creek near Palmdale, California........29

14. Graphs showing seismic data collected along Amargosa Creek near Palmdale, 

California: A, seismic reflection, and B, average P-wave velocity images for the 

seismic line, and C, resistivity models for resistivity lines 1 and 2, 2009 ...........................31

15. Map showing line of section, model domain, model boundary location, type of 

boundary and location of Amargosa Creek Recharge Project, Antelope Valley, 

California ......................................................................................................................................34

16. Schematics showing generalized geologic cross section for the Palmdale and 

Lancaster area, Antelope Valley, California...........................................................................35

17. Schematic showing simplified geologic cross section used for model simulations 

beneath the Amargosa Creek Recharge Project and vicinity, Antelope Valley, 

California ......................................................................................................................................36

18. Map showing extended model domain, model boundary location, type of boundary 

and location of Amargosa Creek Recharge Project, Antelope Valley, California............40

19. Map showing scenario 1, change in head after 20-year artificial-recharge 

simulation, assuming that layer 1 hydraulic conductivity was equal to 10 feet per 

day and an artificial-recharge rate of 3,400 acre-feet per year, Antelope Valley, 

California ......................................................................................................................................42

20. Map showing scenario 2, change in head after 20-year artificial-recharge 

simulation, assuming that layer 1 hydraulic conductivity was equal to 100 feet per 

day and an artificial-recharge rate of 9,400 acre-feet per year, Antelope Valley, 

California ......................................................................................................................................43

Figures—Continued
vi

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

square mile (mi2) 259.0 hectare (ha)

Volume

gallon (gal) 3.785 liter (L) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

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

Flow rate

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

foot per second (ft/s) 0.3048 meter per second (m/s)

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

Density

pound per cubic foot (lb/ft3) 16.02 kilogram per cubic meter (kg/m3)

Radioactivity

picocurie per liter (pCi/L) 0.037 becquerel per liter (Bq/L) 

Specific capacity

gallon per minute per foot [(gal/min)/ft)] 0.2070 liter per second per meter [(L/s)/m]

Hydraulic conductivity

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

Supplemental Information

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

°F=(1.8×°C)+32

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

°C=(°F-32)/1.8

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

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

25 °C).

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

or micrograms per liter (μg/L).
vii

Datum

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

(NAVD 88).

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

Abbreviations

ACRP Amargosa Creek Recharge Project

BCM Basin Characteristic Model

bls below land surface

DC direct current

DOC dissolved organic carbon

Hz hertz

GPS Global Positioning System

MCL maximum contaminant level

NRP National Research Program

NWQL National Water Quality Laboratory

pmc percent modern carbon

PVC polyvinyl chloride

Qoa old alluvial valley deposits/Pleistocene

Qvoa very old alluvial valley deposits/Pleistocene

Qyf young alluvial fan deposits/Holocene to early Pleistocene

Qvol very fold lacustrine deposits/early Pleistocene to late Pleistocene

RTK Real Time Kinematic

SWP State Water Project

TU tritium units

UPW upstream weighted package

EPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC volatile organic compound

ybp years before present
viii

Acknowledgments

The authors acknowledge the cooperation and assistance of the city of Palmdale in providing 

funding for the study and logistical support in the field. The authors also thank local land owners 

for access to their property during collection of field data.

 The authors would also like to thank the reviewers of this report. Their reviews provided 

insightful comments and suggestions that greatly improved the quality of the report.
Abstract

Historically, the city of Palmdale and vicinity have relied 

on groundwater as the primary source of water, owing, in large 

part, to the scarcity of surface water in the region. Despite 

recent importing of surface water, groundwater withdrawal 

for municipal, industrial, and agricultural use has resulted 

in groundwater-level declines near the city of Palmdale in 

excess of 200 feet since the early 1900s. To meet the growing 

water demand in the area, the city of Palmdale has proposed 

the Amargosa Creek Recharge Project (ACRP), which has a 

footprint of about 150 acres along the Amargosa Creek 2 miles 

west of Palmdale, California. The objective of this study was 

to evaluate the long-term feasibility of recharging the Antelope 

Valley aquifer system by using infiltration of imported surface 

water from the California State Water Project in percolation 

basins at the ACRP.

Three monitoring sites were constructed, and geophysical 

surveys (gravity, seismic, and resistivity) were completed to 

define the thickness of valley-fill deposits, depth to water, 

and location of faults that could influence groundwater flow. 

Data collected at the monitoring sites, and results from the 

geophysical surveys, were used to identify three northwestsoutheast trending faults in the vicinity of the proposed 

recharge facility; these faults are probably related to the 

nearby San Andreas fault zone. Water levels collected from 

wells at the monitoring sites showed water-level altitude 

differences as much as 230 feet between the upgradient and 

downgradient sides of the faults, indicating that these faults 

are barriers to groundwater flow. Lithologic and geophysical 

logs indicated the presence of a coarse gravel and sand unit 

extending from land surface to about 150 feet below land 

surface that did not appear to be disrupted by faulting.

Water samples collected from the monitoring wells 

were analyzed for major ions, nutrients, trace elements, 

dissolved organic carbon, volatile organic compounds, stable 

isotopes of oxygen (oxygen-18) and hydrogen (hydrogen-2, 

or deuterium), and the radioactive isotopes of hydrogen 

(hydrogen-3, or tritium) and carbon (carbon-14, or 14C) to 

determine the water quality of the aquifer system and to help 

determine the source and age of the groundwater. Results of 

the water-quality analysis indicated that the source of natural 

recharge is Amargosa Creek near the ACRP, but that the creek 

does not provide modern-day recharge downstream of the 

ACRP.

Potential effects of artificial recharge at the ACRP were 

evaluated by using a local-scale model of groundwater flow. 

On the basis of geologic samples collected during drilling, the 

hydraulic conductivity of the sand and gravel unit in the upper 

150 feet was assumed to range from 10 to 100 feet per day. To 

address the goal of minimizing the potential for liquefaction 

during an earthquake from water-table rise associated with 

groundwater recharge at the ACRP, simulated water levels 

were constrained to remain at least 50 feet below land surface, 

except beneath the proposed artificial-recharge facility.

The hydraulic conductivities of faults were estimated 

on the basis of water-level data and an estimate of natural 

recharge along Amargosa Creek. With assumed horizontal 

hydraulic conductivities of 10 and 100 feet per day in the 

upper 150 feet, the simulated maximum artificial recharge 

rates to the regional flow system at the ACRP were 3,400 

and 9,400 acre-feet per year, respectively. These maximum 

recharge rates were limited primarily by the horizontal 

hydraulic conductivity in the upper 150 feet and by the 

liquefaction constraint. Future monitoring of water-level and 

soil-water content changes during the proposed project would 

allow improved estimation of aquifer hydraulic properties, the 

effect of the faults on groundwater movement, and the overall 

recharge capacity of the ACRP.

Introduction

Historically, the city of Palmdale and vicinity have relied 

on groundwater as the primary source of water, owing, in 

large part, to the scarcity of surface water in the region. Since 

1972, supplemental surface water has been imported from the 

California State Water Project (SWP) through the California 

Aqueduct to help meet the demand for water. Despite the 

importation of surface water, groundwater withdrawal for 

municipal, industrial, and agricultural use has resulted in 

groundwater-level declines in excess of 200 feet (ft) near the 

city of Palmdale since the early 1900s (Christensen, 1999). 

Feasibility and Potential Effects of the Proposed 

Amargosa Creek Recharge Project, Palmdale, California

By Allen H. Christensen, Adam J. Siade, Peter Martin, Victoria E. Langeheim, Rufus D. Catchings, and 

Matthew K. Burgess
2 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

To meet the growing demand for water in the area, the city of 

Palmdale has proposed the Amargosa Creek Recharge Project 

(ACRP). The ACRP plans to use the SWP water to artificially 

recharge the Antelope Valley groundwater system through 

percolation basins.

Purpose and Scope

In 2008, the U.S. Geological Survey (USGS) and the 

city of Palmdale entered into a cooperative agreement to 

investigate the feasibility and potential hydrologic effects of 

artificially recharging the groundwater system by infiltrating 

surface water from the SWP into percolation basins near 

Amargosa Creek. The purpose of this study was to evaluate 

the long-term feasibility of the proposed artificial recharge 

program by improving the understanding of the hydrogeology 

and geochemistry of the aquifer system underlying the 

study area and by simulating the potential hydrologic effects 

of artificial-recharge for a range of aquifer properties. 

Specifically, the study seeks to estimate a plausible range 

of artificial recharges rates by using a newly developed 

groundwater model and various aquifer property scenarios. 

Several methods were used to help characterize the thickness 

of valley-fill deposits, the basement geometry, and geologic 

features that could influence groundwater flow, including 

regional gravity surveys, seismic refraction and reflection 

surveys, resistivity surveys, and test borings completed with 

monitoring wells. Data collected as part of this study and 

previous studies were used to develop a local-scale numerical 

groundwater-flow model to simulate changes in water levels 

and flow resulting from artificial recharge. The calibrated 

model was used to evaluate the potential effects of two longterm recharge water-management scenarios.

General Description of Study Area

The ACRP is in the southwestern part of the Antelope 

Valley, approximately 4 miles (mi) west of Palmdale, in Los 

Angeles County, California (fig. 1). The proposed ACRP site 

comprises approximately 150 acres along Amargosa Creek 

near the San Gabriel Mountain front where the Creek exits 

Leona Valley (fig. 2). The Amargosa Creek drainage basin 

covers approximately 30 square miles (mi2) in the Leona 

Valley along the San Andreas fault zone in the eastern San 

Gabriel Mountains with land surface elevation varying from 

2,750 to 5,200 ft. Amargosa Creek provides drainage for the 

Leona Valley, then extends southeast from Leona Valley across 

the San Andreas fault zone on the west side of the city of 

Palmdale, before turning north near Lancaster and terminating 

at Rosamond Dry Lake (fig. 2).

Average annual precipitation at local weather stations 

(fig. 2) ranged from about 8 inches (in.) at Palmdale and at 

Vincent, south of Palmdale, to about 18 in. at Pine Canyon 

(Western Regional Climate Center, 2011a, 2011b, 2011c). 

Average annual discharge measurements along Amargosa 

Creek were not available, but estimates varied between 170 

(L.E. Flint, U.S. Geological Survey, written commun., 2011) 

and 800 acre-feet per year (acre-ft/yr; Los Angeles County 

Department of Public Works, 1991). Flows in Amargosa Creek 

are intermittent and usually only run during the winter rainy 

season or, infrequently, as a result of late summer monsoonal 

storms (Bloyd, 1967). Although the study focus was near 

the proposed ACRP, the study area was expanded to include 

western Palmdale, southern Lancaster, and the area west 

of Little Rock Wash to simulate the surrounding basement 

geometry better and to help reduce boundary effects in the 

groundwater-flow model simulations (fig. 2).

Site Characterization

The geohydrology of the study area was characterized 

by using previously published reports and maps; collecting 

and interpreting gravity, seismic, and resistivity surveys; and 

correlating geophysical and geologic logs from existing wells 

with those from the monitoring wells constructed as part of 

this study.

Previous Geohydrologic Studies

Several previous investigators have completed regional 

geohydrologic studies in the Antelope Valley area. Early 

surveys by Johnson (1911) and Thompson (1929) documented 

historic hydrologic conditions in the valley, describing the 

rapid development in the 1920s and the associated regional 

decline in the water table. Johnson (1911) also described 

the importance of recharge in the valley from the three main 

streams on the southwest side of the valley, Big Rock, Little 

Rock, and Amargosa Creeks. Dibblee (1960) mapped major 

faults in the valley, including the San Andreas fault zone, 

which forms the southern boundary of the Antelope Valley 

(fig. 1). Regional gravity surveying and areal mapping by 

Mabey (1960) indicated the presence of faults offsetting 

the basement complex and valley-fill deposits and of many 

northwest-trending faults that parallel the main strand of the 

San Andreas fault zone. Bloyd (1967) noted large differences 

in groundwater-level elevations along the southern boundary 

of the Antelope Valley near the San Andreas fault zone. Using 

water-level data, Bloyd (1967) also mapped faults in the valley 

that trend sub-parallel to the main strand of the San Andreas 

Fault. These faults form the southern boundary of the Antelope 

Valley groundwater basin (Bloyd, 1967) and the southern 

extent of the Lancaster groundwater subbasin (Durbin, 1978; 

Leighton and Phillips, 2003). A more detailed summary of the 

geologic setting of the Antelope Valley is provided in Leighton 

and Phillips (2003).
Site Characterization 3

sac11-0421_fig 01

California

Aqueduct

Bissell Hills

Rosamond Hills

 Wash

Rock

Amargosa

 Wash

Big

Rock

Little

Creek 

 Rogers 

Lake

(dry) 

Rosamond 

Lake

(dry) Little

Buttes

Antelope

Buttes

Alpine

Buttes

Lovejoy

Buttes

Creek

GARLOCK FAULT ZONE

WILLOW SPRINGS FAULT

SPRING

 FAULT

RANDSBURG -

MUROC FAULT

EL MIRAGE FAULT

ANTELOPE VALLEY FAULT ZONE

BLAKE RANCH 

 FAULT

 MOJAVE FAULT

NEENACH FAULT

Cottonwood

VINCENT

PALMDALE

PINE

CANYON

VINCENT

EXPLANATION

0

0

10

10

20

20 KILOMETERS

MILES

Geologic type Fault—Dashed where inferred

 (modified from Dibblee, 1963;

 Ward and others, 1993; 

 Nishikawa and others, 2001) 

SAN ANDREAS FAULT ZONE

Study area

Leona Valley

 surface-water

 drainage basin

Precipitation station

 and name

 

Palmdale

Lancaster

Littlerock

Quartz Hill

Rosamond

Mojave

Main 

Base

Boron

Fremont Valley

Tehachapi Mts

Buckhorn 

 Lake

(dry) 

Leona Valley

Amargosa Creek

recharge project

A A’ 

San Gabriel Mts

A

A’

City

Base modified from U.S. Geological Survey and other

Federal and State digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

Alluvial deposits

Bedrock

Playa surface

CALIFORNIA

Area of

 map

Pacific Ocean

Antelope Valley drainage basin

Antelope Valley groundwater basin

Groundwater subbasin

Line of geologic section, see figure 3

Figure 1. Study area and Leona Valley surface-water drainage basin (Amargosa Creek drainage basin), Antelope Valley, California.
4 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

sac11-0421_fig 02

VINCENT

PALMDALE

PINE CANYON

Leona Valley

118°20' 118°10' 118°00'

34°

40'

34°

30'

0 5 10 MILES

0 5 10 KILOMETERS

Amargosa

Little Rock

Wash

Creek

EXPLANATION

VINCENT

Precipitation station

 and name

Study area

Leona Valley

 surface-water

 drainage basin

California Aqueduct

Inferred fault (Bloyd, 1967) 

San Andreas fault zone 

Faults—

Palmdale

Lancaster

Rosamond

Dry Lake

Proposed recharge 

 facility

Base modified from U.S. Department of Agriculture National Agriculture

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

City

Figure 2. Location of study area boundary, Antelope Valley, California.
Site Characterization 5

Geohydrologic Setting

Antelope Valley was formed as a result of downfaulted 

basement and sedimentary fill between the Garlock and the 

San Andreas fault zones (fig. 1). The basement complex that 

underlies the sedimentary fill consists of pre-Tertiary igneous 

and Tertiary sedimentary rocks (Hewett, 1954; Dibblee, 1967). 

Locally, in the vicinity of the proposed recharge facility, the 

deepest material encountered during drilling of the monitoring 

wells showed the basement complex was composed of quartz 

monzonite. The unconsolidated deposits of Pliocene to 

Holocene age form the groundwater basin and are more than 

5,000 ft thick in places (Dutcher and Worts, 1963).

The unconsolidated units were described by Leighton 

and Phillips (2003) as lacustrine or alluvial and are 

divided hydrostratigraphically into the lower, middle, and 

upper aquifers (fig. 3). The confined lower and confined 

and unconfined middle aquifers consist of Pliocene and 

Pleistocene unconsolidated alluvial deposits that become 

increasingly compacted and indurated with depth and, thus, 

yield less water to wells with depth (Dutcher and Worts, 

1963). The lacustrine deposits, characterized as a thick 

sequence of blue to blue-green clays, form the confining 

layer between the middle and lower aquifers in the vicinity 

of Palmdale (Leighton and Phillips, 2003). The lacustrine 

deposits vary in age between early Pleistocene in the vicinity 

of Palmdale, where the lacustrine deposits are at depths in 

excess of 600 ft, to late-Pleistocene near Rodgers Lake, where 

the unit is exposed at the surface (fig. 3; Leighton and Phillips, 

2003). The unconfined upper aquifer consists of Pleistocene 

to Holocene unconsolidated alluvial deposits derived from 

local mountains. The upper aquifer readily yields water to 

wells and is the main production aquifer in the vicinity of 

Palmdale. For this study, the sedimentary units were grouped 

into five major units: (1) the lower aquifer, consisting of lower 

Tertiary deposits (Miocene-Pliocene); (2) lacustrine deposits 

(Pleistocene-Miocene), (3) the middle aquifer, consisting 

of relatively indurated old alluvial deposits (Pleistocene); 

(4) the upper aquifer, consisting of unconsolidated old alluvial 

deposits (Pleistocene); and (5) young alluvial-fan deposits 

(Holocene-Pleistocene).

−5,000

−4,000

−3,000

3,000

−2,000

2,000

−1,000

1,000

Upper aquifer Upper aquifer

Land surface

Lower aquifer

 Middle aquifer

FEET

A A'

NAVD

88

0

0

10

10

20

20 KILOMETERS

MILES

Interbedded

aquitards

Palmdale

Rogers Lake

Vertical scale greatly exaggerated

Little RockWash

Basement

complex

Lacustrine deposits

Study area of this report

Figure 3. Generalized geologic section showing relation of lacustrine deposits to aquifers in the Antelope Valley groundwater basin, 

Antelope Valley, California (modified from Londquist and others, 1993). Location of section shown in figure 1.
6 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

These units are laterally and vertically displaced by 

numerous faults in the valley, particularly along the San 

Andreas fault zone. Many of these faults form partial barriers 

to groundwater flow; for example, water-level differences 

across faults are approximately 300 ft near Palmdale 

(Christensen, 2005). The barrier effect of faults is probably 

caused by offsetting of units, compaction, and deformation 

of water-bearing deposits immediately next to the faults and 

by cementation from mineral deposition within the fault zone 

(Londquist and Martin, 1991).

Monitoring Well Construction

One multiple-well monitoring site and two single-well 

monitoring sites were completed as part of this study to enable 

detailed geohydrologic characterization, including depth to 

basement, lithology, groundwater hydraulic gradients, and 

groundwater quality near the ACRP. In mid-2009, the USGS 

Research Drilling Unit constructed two monitoring-well sites 

along Amargosa Creek using a mud-rotary rig. The first site 

(site 1) was constructed in the proposed recharge project 

boundary and the second (site 2) was 1.1 mi northeast of site 

1 along Amargosa Creek, downstream from the proposed 

recharge project (fig. 4, table 1). In March 2011, the city of 

Palmdale completed an additional monitoring well (site 3) 

near the northeastern extent of the ACRP boundary and 

approximately 0.33 mi northeast of site 1 (fig. 4).

Monitoring Site 1

Monitoring site 1 was constructed by using a large 

diameter borehole and 8 in. diameter casing to allow for highcapacity aquifer testing. The borehole for site 1 (6N/12W29B1) was drilled to a depth of 221 ft below land surface 

(bls) by using a 14.75 in. diameter tri-cone roller drill bit. 

After the borehole was drilled, a borehole geophysical survey 

was completed, and a single monitoring well was installed. 

The monitoring well was constructed by using threaded 

8 in. diameter, schedule 40 polyvinyl chloride (PVC) casing 

that was perforated from 80 to 220 ft bls. The annulus was 

filled with number 8 sand from the bottom of the borehole 

to 60 ft bls. A low-permeability bentonite grout was tremied 

in place from 60 ft bls to land surface to seal the borehole. A 

generalized well-construction diagram is presented in figure 5.

Geologic and geophysical data collected at site 1 during 

construction of the monitoring well were used to define 

the lithologic and water-bearing properties of the aquifer. 

Geophysical logs collected at the site included: caliper, natural 

gamma, conductivity, spontaneous potential, 16-in. and 

64-in. normal resistivity, lateral resistivity, electromagnetic 

induction, and sonic (fig. 5). A generalized description of 

the lithology is presented in figure 5. The materials from 

land surface to 150 ft bls are coarse-grained alluvium with 

minor fines; those from 150 to 220 ft bls are weathered and 

crystalline quartz-monzonite basement complex.

Depth to water at site 1 was about 103 ft bls after the 

well was fully developed. The land-surface datum at site 1 is 

about 2,745 ft; therefore, the water-table elevation measured 

at the site was about 2,642 ft. After development, the well 

was pumped at approximately 2.5 gallons per minute (gpm) 

for 10 hours, resulting in 4 ft of drawdown; therefore, the 

specific capacity of the well was about 0.6 gallons per minute 

per foot (gpm/ft) of drawdown. The pumping rate can change, 

however, if the depth to water at the site changes.

Monitoring Site 2

The borehole for site 2 (6N/12W-21G1-4) was drilled 

to a depth of 300 ft bls by using a 14.75 in. diameter tri-cone 

roller drill bit, from 300 to 500 ft bls by using a 12-in. bit, 

and from 500 to 640 ft bls by using a 9.75-in. bit. After the 

borehole was drilled, a geophysical survey was completed, 

and four monitoring wells constructed with threaded, 2 in. 

diameter, schedule 40 PVC casing were installed at four 

depths in the borehole: 620 (21G1), 460 (21G2), 350 (21G3), 

and 120 (21G4) ft bls (fig. 6). All of the monitoring wells 

were perforated in the bottom 20 ft. The annulus opposite the 

perforated interval of the monitoring wells was filled with 

number-3 sand, and a low-permeability bentonite grout was 

tremied into the annular space between the perforated intervals 

to effectively isolate the monitoring wells and was emplaced 

from the top of the sand pack around 21G4 to land surface to 

seal the borehole. A generalized well-construction diagram is 

shown in figure 6.

Geologic and geophysical data collected at site 2 during 

the construction of the monitoring site were used to define 

the lithologic and water-bearing properties of the aquifer. 

Geophysical logs collected at the site included caliper, natural 

gamma, spontaneous potential, 16-in. and 64-in. normal 

resistivity, electromagnetic induction, and sonic (fig. 6). 

A generalized description of the lithology is presented in 

figure 6. From land surface to about 150 ft bls, the materials 

consist of medium to coarse sand with gravel and minor 

interbedding of silts and minor clay; from 150 to 365 ft bls, 

the materials consist of fine, medium, and coarse sand with 

interbedded silty-sand with minor clay; from 365 to 550 ft 

bls, the materials are similar to the overlying materials, but 

contain more clays and are more indurated; and from 550 to 

630 ft bls, the materials consist of weathered quartz-monzonite 

basement complex. The resistivity and sonic logs indicated 

that the basement complex is fractured or weathered from 550 

to 630 ft bls.

Depth to water at site 2 (well 21G1) was about 470 ft bls 

after the well was fully developed. The land-surface datum 

at site 2 is about 2,695 ft; therefore, the water-table elevation 

measured at well 21G1 was about 2,225 ft or about 417 ft 

below that of site 1 (well 29B1). Because the depth to water 

was unknown and there is a possibility of existing or future 

perched water conditions, the shallower monitoring wells 

at site 2 [21G4 (120 ft bls, dry), 21G3 (350 ft bls, dry), 

21G2 (460 ft bls, dry)] were installed above clay layers and 
Site Characterization 7

sac11-0421_fig 04

118°11' 118°10' 118°09'

34°

36'

34°

35'

0 1 MILE

0 1 KILOMETER

Amargosa

Creek

EXPLANATION

Monitoring-well site

California Aqueduct

Inferred fault A (Bloyd, 1967) 

San Andreas fault zone 

Alquist-Priolo fault (from California

 Geological Survey, 2002) 

Faults—

Proposed recharge 

 facility

Site 1

Site 3

Site 2

0.05

0.05

Fault AFault A

Base modified from U.S. Department of Agriculture National Agriculture

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator

North American Datum of 1983

Figure 4. Locations of monitoring sites 1, 2, and 3, near Palmdale, California.
8 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project Table 1. Well-site list and construction data for selected wells near Palmdale, Los Angeles County, California. [State well number, see well-numbering diagram in text. Abbreviations: ft, feet; LSD, land surface datum; NAVD 88, North American Vertical Datum of 1988; USGS ID, U.S. Geological Survey identification number: the unique number for each site in USGS National Water Information System (NWIS) database; —, no data] State well number USGS ID Altitude of land surface (ft above NAVD88) Depth of well (ft below LSD) Depth to top of screen interval (ft below LSD) Depth to bottom of screen interval (ft below LSD) Link (USGS NWIS public web site) 006N011W06F001 343822118051901 2,493 820 400 800 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343822118051901 006N011W31A001 343419118044401 2,636 444

—

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343419118044401

006N012W07A001 343741118110301 2,600 432 276 432 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343741118110301006N012W09H003 343727118085202 2,613 910

—

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343727118085202

006N012W20R001 

(site 3)

343522118095701 2,730 390 350 390 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343522118095701

006N012W21E001 343550118094501 2,714

—

—

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343550118094501

006N012W21G001 

(site 2)

343546118091601 2,695 620 600 620 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343546118091601

006N012W29B001 

(site 1)

343515118101401 2,745 220 80 220 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343515118101401

007N011W14N001 344124118002101 2,430 600

—

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=344124118002101

007N011W16H003 344152118022701 2,406

—

—

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=344152118022701

007N011W27Q001 343939118013701 2,466 650 300 650 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343939118013701007N011W28Q001 343939118025201 2,453

—

—

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343939118025201

007N011W29G001 344005118034401 2,441

—

—

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=344005118034401

007N011W31M001 343909118053601 2,471 386

—

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343909118053601

007N012W19R001 344030118110001 2,389 400 100 400 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=344030118110001007N012W24A001 344120118055301 2,404 230.5 180 400 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=344120118055301007N012W26K003 343951118065902 2,461 674 310

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343951118065902

007N012W27F008 344005118082204 2,444 425 395 415 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=344005118082204007N012W27H008 344003118074804 2,448

— 347 367 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=344003118074804

007N012W27J005 343903118074801 2,452 700 350

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343903118074801

007N013W13N001 344122118125701 2,353 458.08

—

— http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=344122118125701

007N013W26J002 344000118130601 2,420 606 288 606 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=344000118130601007N013W34B001 343932118144001 2,436 475 250 475 http://nwis.waterdata.usgs.gov/usa/nwis/gwlevels/?site_no=343932118144001
Site Characterization 

9

sac11-0421_fig 05

0 10 20

Caliper,

in inches

0 75 150

Gamma,

in counts

per second

0 100 200

Conductivity,

in millimhos

per meter

0 41 82

Spontaneous

potential,

in millivolts

0 200 400

Resistivity

(64N blue, 

16N red),

in ohm-meters

0 100 200

Lateral,

in ohm-meters

0 250 500

Sonic (Delta T),

in microseconds

per foot

Sonic (N),

in microseconds

0 1,024

Sonic (F),

in microseconds

0 1,024

GROUT SAND

29B1

Well

construction

Lithology

Gravelly mediumto coarse sandMedium-coarse sandSlightly gravelly sand withvery coarse sandMedium-coarse sandinterbedded silty-clayVery coarse sand with gravelWeathered quartzmonzonitewith blue clayFractured and/or weathered crystallinequartzmonzonite

Site 1 [006N012W29B001 Land-surface datum 2,745 feet above North American Vertical Datum of 1988 (NAVD 88)] 

0

200400

Depth, in feet below land surface

Figure 5. Geophysical logs and well construction for monitoring sites near Palmdale, California: site 1 (6N/12W-29B1).
10 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

sac11-0421_fig 06

0 10 20

Caliper,

in inches

50 100 150

Gamma,

in counts

per second

0 100 200

Conductivity,

in millimhos

per meter

0 100 200

Spontaneous

potential,

in millivolts

0 200 400

Resistivity,

in ohm-meters

16N

64N

0 100 200

Lateral,

in ohm-meters

0 250 500

Sonic (Delta T),

in microseconds

per foot

Sonic (N),

in microseconds

0 1,024

Sonic (F),

in microseconds

0 1,024

Well

construction

GROUT

SAND

21G1

21G2

21G3

21G4

Lithology

Medium tocoarse sandGravelly mediumto coarse sandMedium to coarsesand with gravelSilty fine sand withclay and gravelFine tomediumsandMedium tocoarse sandFine to medium sandwith minor gravelClayey fine tomedium sand;minor coarse sandFine to medium sandwith sandy claySilty fine tocoarse sandFine to medium sandwith sandy clayFractured and/or weathered crystallinequartz monzonite

Site 2 (006N012W21G001-4 Land-surface datum 2,695 feet above North American Vertical Datum of 1988 (NAVD 88)] 

0

200400600800

Depth, in feet below land surface

Figure 6. Geophysical logs and well construction for monitoring sites near Palmdale, California: site 2 (6N/12W-21G1).
Site Characterization 11

0 10 20

Caliper,

in inches

50 100 150

Gamma,

in counts

per second

0 100 200

Spontaneous

potential,

in millivolts

0 200 400

Resistivity,

in ohm-meters

0 200 400

Lateral,

in ohm-meters

0 250 500

Sonic (Delta T),

in microseconds

per foot

GROUT

GROUT concrete seal

Well Lithology

construction

Cemented fine to

medium sand

with gravel

Cemented clay and silt

Fine sand 

Medium sand with gravel

Fine sand and silt with gravel

Fine to medium sand with

coarse sand, gravel and silt

Fine to medium sand

with silt

Coarse sand with

minor silt and gravel

Coarse sand with

gravel and boulders

Coarse sand with

gravel and boulders

Coarse gravel

Fractured and

crystalline quartz

monzonite 

Weathered quartz

monzonite with blue clay

0

200

400

600

800

Depth, in feet below land surface

Site 3 (6N/12W-20R1 Land-surface datum 2,730 feet above NAVD 88) 

16N

64N

Figure 7. Geophysical logs and well construction for monitoring site 3 (6N/12W-21G001-4), near Palmdale, California.

formation changes to monitor potential perching and future 

rises of the regional water table. At the time of drilling and 

well development, wells 21G4, 21G3, and 21G2 were noted as 

‘dry.’ Well 21G1 (620 ft bls) was installed in the fractured or 

weathered basement complex zone to provide data about the 

underlying basement complex. Since this well is completed in 

the uppermost part of the weathered and fractured basement 

complex, water-level data collected from this well could be 

representative of the hydraulic head in the deepest overlying 

alluvium.

Monitoring Site 3

The borehole for site 3 (6N/12W-20R1) was drilled to 

a depth of 512 ft bls by using a 10.875-in. diameter tri-cone 

roller drill bit. After the borehole was drilled, a geophysical 

survey was completed, and the single monitoring well was 

installed. The monitoring well was constructed with threaded, 

3-in. diameter, schedule 40 PVC casing, which was perforated 

from 350 to 390 ft bls (fig. 7). The annulus was sealed with 

low-permeability bentonite from the bottom of the hole to 

410 ft bls, with a mixture of number 8 and number 16 sand 

from 410 to 305 ft bls, and with a concrete seal to the surface 

(Rottman Drilling, written commun., 2011). A generalized 

well-construction diagram is presented in figure 7.

Geologic and geophysical data collected at site 3 during 

the construction of the monitoring well were used to define 

the lithology and water-bearing properties of the aquifer. 

Geophysical logs collected at the site included caliper, natural 

gamma, spontaneous potential, 16-in. and 64-in. normal 

resistivity, electromagnetic induction, and sonic (fig. 7). 

From land surface to about 390 ft bls, the materials consist 

of gravelly sand with occasional gravel and clay; from 390 to 

490 ft bls, the materials consist of cemented silty sand with 

occasional gravel; from 490 to 512 ft bls, the materials consist 

of weathered quartz -monzonite basement complex and of 

fractured and crystalline quartz -monzonite basement complex 

(fig. 7). The water level at site 3 was about 275 ft bls on 

April 11, 2011, after the well was developed. The land-surface 

datum at site 3 is about 2,730 ft; therefore, the water-table 

elevation measured at the site was about 2,455 ft.
12 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

Water-Level Data Collected from Monitoring 

Wells

In October 2011, the water-level elevation difference 

between site 1 (2,642 ft) and site 3 (2,454 ft) was about 188 ft; 

the water-level difference between sites 3 and 2 (2,224 ft) 

was 230 ft. These differences in water-table elevation 

among sites indicated the presence of potential groundwater 

barriers, such as faults, between sites 1 and 3 and between 

sites 3 and 2. The water-level elevation in well 21G1(site 2) 

was about 60 ft higher than the water-level elevation in the 

nearest downstream well measured in the Antelope Valley 

groundwater basin (2,166 ft ) east of inferred fault A (fig. 8).

Water-Quality Data Collected from Monitoring 

Wells

Groundwater samples collected from sites 1, 2, and 

3 were analyzed for major ions, nutrients, trace elements, 

dissolved organic carbon (DOC), volatile organic compounds 

(VOCs), stable isotopes of oxygen (oxygen-18 or 18O) and 

hydrogen (deuterium or 2H), and the radioactive isotopes of 

hydrogen (tritium or 3H) and carbon (carbon-14 or 14C) to 

determine the water quality of the aquifer system at these sites 

and help determine the source and age of the groundwater. 

VOC samples were collected to determine if the groundwater 

contained anthropogenic compounds that could come from 

paints, solvents, or as disinfectant by-products.

Water-Quality Data Collection

Groundwater samples were collected in accordance 

with the protocols established by the USGS National Field 

Manual (U.S. Geological Survey, variously dated). These 

protocols ensured that samples collected from each well were 

representative of the groundwater in the aquifer and were 

handled in a consistent way that minimized the potential 

for extrinsic contamination of samples. Prior to collecting 

samples, each well was pumped continuously to purge at 

least three casing-volumes of water from the well or until 

field parameters (water temperature, specific conductance, 

pH, and dissolved oxygen) were stable (Wilde, variously 

dated). Monitoring wells were sampled by using a pre-cleaned 

stainless-steel Bennett® submersible piston pump with a 

Teflon® discharge line. Groundwater and quality-control 

samples (equipment blank) collected for analysis were shipped 

within a few days of collection to the USGS National Water 

Quality Laboratory (NWQL) or other laboratories. Major 

ions, minor and trace elements, nutrients, organic carbon, 

and volatile organic compounds were analyzed by the USGS 

NWQL by various methods as described in Fishman and 

Friedman (1989), Fishman (1993), Garbarino and others 

(2006), Patton and Krysalla (2011), Patton and Truitt (1992, 

2000), Struzeski and others (1996), Brenton and Arnett 

(1993), and Connor and others (1998). Tritium activity was 

measured by the USGS National Research Program (NRP) 

Tritium-Light Isotope laboratory in Menlo Park, California, 

by electrolytic enrichment using glass cells with electrodes of 

nickel and stainless steel (Ostlund and Werner, 1962). Stable 

hydrogen and oxygen isotopes of water were analyzed by the 

NRP stable-isotope laboratory in Reston, Virginia (Révész 

and Coplen, 2008a, 2008b). Carbon-14 and stable isotopes of 

carbon in organic carbon were analyzed at the Woods Hole 

Oceanographic Institution by using methods of Karlen and 

others (1964) and Olsson (1970).

An equipment blank was collected to help determine 

if the equipment (Bennett® submersible piston pump with 

a Teflon® discharge line) was a source of contamination for 

constituents detected in groundwater samples, including 

anions and cations and selected trace elements. Analytical 

results of the blank sample showed that most constituents, 

when detected, were near or below the laboratory 

reporting levels for each constituent and much lower than 

concentrations in groundwater samples. The only exceptions 

were that the iron concentration in the equipment blank 

was 10.1 micrograms per liter (μg/L) and the aluminum 

concentration in the blank sample was 5.3 μg/L, both above 

the laboratory reporting level of 3.2 μg/L and 1.7 μg/L, 

respectively; however, these concentrations of iron and 

aluminum in the blank were 5–10 times lower than the 

concentrations measured in samples collected for this 

study (table 2). The uncertainty with respect to the actual 

concentration of these two constituents in groundwater 

samples caused by low-level detection in the blank did not 

have an important effect on the interpretation of the waterquality results.

Physical and Chemical Characteristics

In general, the water samples collected from sites 1, 2, 

and 3 indicated that the groundwater in the study area is good 

quality. Nitrate concentrations in water samples collected 

from sites 1, 2, and 3 averaged 3.7 milligrams per liter (mg/L), 

0.2 mg/L, and 1.65 mg/L as nitrogen, respectively (table 3). 

The U.S. Environmental Protection Agency (EPA) maximum 

contaminant level (MCL) for nitrate is 10 mg/L as nitrogen 

(U.S. Environmental Protection Agency, 2005). Fluoride 

concentrations in samples collected from sites 1, 2, and 3 were 

0.9 mg/L, 0.6 mg/L, and 0.3 mg/L, respectively (table 2). 

The EPA MCL for fluoride is 4 mg/L (U.S. Environmental 

Protection Agency, 2005). Arsenic concentrations in samples 

collected from sites 1, 2, and 3 were 1.1 micrograms per liter 

(μg/L), 6.4 μg/L, and 1.1 μg/L respectively (table 2). The EPA 

MCL for arsenic is 0.9 μg/L (U.S. Environmental Protection 

Agency, 2005).

The concentrations of dissolved organic carbon (DOC) 

in water samples from sites 1, 2, and 3 were 1.12, 0.48, 

and, 0.35 (estimated value) mg/L, respectively; however, 

because DOC was commonly detected in field blanks at 

higher concentrations than those detected, the measured 

concentrations should be regarded with caution (table 3). 

Concentrations of VOCs in samples from sites 1, 2, and 3 

were less than detection limits for each analyzed compound 

(table 4).
Site Characterization 13

sac11-0421_fig 08

T

8

N

T

7

N

T

6

N

T

5

N

T

4

N

R15W R14W R13W R12W R11W R10W

2,642 2,225 Site 1

2,455

Site 3

Site 2

12R3

118°20' 118°10' 118°00'

34°

40'

34°

30'

Amargosa

Creek

EXPLANATION

Leona Valley

Monitoring-well site

California Aqueduct

Inferred fault (Bloyd, 1967) 

San Andreas fault zone 

Faults—

Site with water-level data

 and value (2009)

Site with stable-isotope data

Site with stable-isotope data

 in Leona Valley

2,412

Leona Valley

 surface-water

 drainage basin 31A1

0 5 10 MILES

0 5 10 KILOMETERS

Proposed recharge 

 facility

16H3

14N1

13N1 24A1

19R1

26J2 27F8 26K3

27H8

34B1

31M1

7A1 6F1

9H3

31A1

29G1

28Q1

27Q1

2,168

2,166

2,207 2,180

2,149 2,150

2,184 2,114 2,122

2,148

2,146

2,153 2,227

2,135

2312 2,127

2,166

2,412

Fault AFault A

Base modified from U.S. Department of Agriculture National Agriculture

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

Figure 8. Hydraulic head at selected wells, Antelope Valley, California, 2009.
14 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project Table 2. Field measurements and water-quality data for water from selected monitoring wells near Palmdale, Los Angeles County, California, 2009–13. [Site locations are shown in figure 4. State well number, see well-numbering diagram in text. Data analyzed by U.S. Geological Survey (USGS) National Water Quality Laboratory in Arvada, Colorado (NWQL), except dissolved oxygen, specific conductance, and pH were analyzed in the field. The five-digit number in parentheses below the constittuent name is the USGS parameter code used to uniquely identify a specific constituent or property. Abbreviations: μg/L, microgram per liter; μS/cm, microsiemen per centimeter at 25 °C; E, estimated value; FET, fixed end-point titration; ft, feet; hhmm, hour:minute; INC, incremental titration; mg/L, milligram per liter; mm/dd/yyyy, month/day/year; NAVD 88, North American Vertical Datum of 1988; USGS ID, USGS identification; °C, degrees Celsius; —, no data; <, less than value shown] Date (mm/dd/yyyy) Time (hhmm) Dissolved oxygen, (mg/L) (00300) pH, water, field, standard units (00400) pH, water, laboratory, standard units (00403) Specific conductance, laboratory (μS/cm at 25 °C) (90095) Specific conductance, field (μS/cm at 25 °C) (00095) Temperature, water (°C) (00010) Altitude of land surface (feet above NAVD 88) Depth of well (ft) (72008) Depth to top of sample interval (ft) (72015) State well number 006N012W20R001S (site 3), USGS ID 343522118095701 03/24/2011 1200

— 8.5 8.0 1,050 1,000

— 2,730 390 350

08/08/2012 1530 8.9 7.5 7.7 1,080 1,010 24.8 2,730 390 350

11/26/2013 2100 11.0 7.4 7.7 1,080 1,060 15.3 2,730 390

—

State well number 006N012W21G001S (site 2), USGS ID 343546118091601

08/11/2009 1330

—

— 7.9 692 676

— 2,695 620

—

08/08/2012 1010 3.3 7.8 7.8 677 671 24.7 2,695 620 600

State well number 006N012W29B001S (site 1), USGS ID 343515118101401

08/11/2009 1500

—

— 7.7 1,350

—

— 2,745 220

—

08/07/2012 1400 6.9 7.6 7.8 1,340 1,270 20.4 2,745 220 80

11/26/2013 1540 6.0 7.6 7.7 1,310 1,290 18.1 2,745 220

—

Date 

(mm/dd/yyyy)

Time 

(hhmm)

Depth to bottom of 

sample interval 

(ft) 

(72016)

Calcium 

(mg/L as Ca) 

(00915)

Magnesium 

(mg/L as Mg) 

(00925)

Potassium 

(mg/L as K) 

(00935)

Sodium 

(mg/L as 

Na) 

(00930)

Alkalinity, water, 

filtered, FET field 

(mg/L as CaCO3) 

(39036)

Alkalinity, water, 

filtered, FET laboratory 

(mg/L as CaCO3) 

(29801)

Alkalinity, water, 

filtered, INC field 

(mg/L as CaCO3) 

(39086)

Bicarbonate, water, 

filtered, FET field 

(mg/L as HCO3) 

(29804)

State well number 006N012W20R001S (site 3), USGS ID 343522118095701—Continued

3/24/2011 1200 390 77.1 29.6 2.84 123 230 222 236 2798/8/2012 1530 390 90.2 33.0 2.72 103 250 257 248 29811/26/2013 2100

— 86.1 32.0 2.91 108

— 258 248

—

State well number 006N012W21G001S (site 2), USGS ID 343546118091601—Continued

8/11/2009 1330

— 23.1 2.77 4.12 113 170 173 168 202

8/8/2012 1010 620 25.6 3.74 4.79 112 180 192 179 218

State well number 006N012W29B001S (site 1), USGS ID 343515118101401—Continued

8/11/2009 1500

— 94.4 28.4 2.60 151 300 315 303 365

8/7/2012 1400 220 109 31.4 2.30 148 310 325 311 37411/26/2013 1540

— 101 29.8 2.66 152

— 310 302

—
Site Characterization 15

Table 2. Field measurements and water-quality data for water from selected monitoring wells near Palmdale, Los Angeles County, California, 2009–13.—Continued[Site locations are shown in figure 4. State well number, see well-numbering diagram in text. Data analyzed by U.S. Geological Survey (USGS) National Water Quality Laboratory in Arvada, Colorado (NWQL), except dissolved oxygen, specific conductance, and pH were analyzed in the field. The five-digit number in parentheses below the constittuent name is the USGS parameter code used to uniquely identify a specific constituent or property. Abbreviations: μg/L, microgram per liter; μS/cm, microsiemen per centimeter at 25 °C; E, estimated value; FET, fixed end-point titration; ft, feet; hhmm, hour:minute; INC, incremental titration; mg/L, milligram per liter; mm/dd/yyyy, month/day/year; NAVD 88, North American Vertical Datum of 1988; USGS ID, USGS identification; °C, degrees Celsius; —, no data; <, less than value shown]

Date 

(mm/dd/yyyy)

Time 

(hhmm)

Bicarbonate, water, 

filtered, INC field 

(mg/L as HCO3) 

(00453)

Bromide 

(mg/L as Br) 

(71870)

Carbonate, water, 

filtered, INC field 

(mg/L as CO3) 

(00452)

Chloride 

(mg/L as Cl) 

(00940)

Fluoride 

(mg/L as F) 

(00950)

Silica 

(mg/L as SiO2) 

(00955)

Sulfate 

(mg/L as SO4) 

(00945)

Aluminum 

(μg/L as Al) 

(01106)

Barium 

(μg/L as Ba) 

(01005)

State well number 006N012W20R001S (site 3), USGS ID 343522118095701—Continued

3/24/2011 1200 276 0.244 — 68.9 0.37 26.0 225 59.5 71.08/8/2012 1530 300 0.240 — 67.1 0.24 27.4 218 <4.4 20.511/26/2013 2100 301 0.246 0.5 70.1 0.28 25.0 227 2.5 20.4

State well number 006N012W21G001S (site 2), USGS ID 343546118091601—Continued

8/11/2009 1330 202 0.052 — 54.4 0.66 21.0 74.8 12.2 20.88/8/2012 1010 216 0.051 — 55.9 0.62 21.9 63.3 13.8 26.7

State well number 006N012W29B001S (site 1), USGS ID 343515118101401—Continued

8/11/2009 1500 368 0.302 — 89.8 0.90 23.6 241 12.0 25.98/7/2012 1400 377 0.318 — 108 0.85 24.5 227 <4.4 29.011/26/2013 1540 367 0.301 0.7 97.5 0.98 22.0 246 <2.2 27.2

Date 

(mm/dd/yyyy)

Time 

(hhmm)

Iron 

(μg/L as Fe) 

(01046)

Lithium 

(μg/L as Li) 

(01130)

Manganese 

(μg/L as Mn) 

(01056)

Strontium 

(μg/L as Sr) 

(01080)

Vanadium 

(μg/L as V) 

(01085)

Arsenic 

(μg/L as As) 

(01000)

Boron 

(μg/L as B) 

(01020)

Iodide 

(mg/L as I) 

(71865)

Uranium (natural) 

(μg/L as U) 

(22703)

State well number 006N012W20R001S (site 3), USGS ID 343522118095701—Continued

3/24/2011 1200 50.7 27.1 55.0 1,040 3.9 1.1 57 0.003 8.808/8/2012 1530 5.4 E19.0 0.38 1,260 — 0.83 55 <0.001 —11/26/2013 2100 <4.0 16.8 <0.20 1,270 4.7 0.83 56 0.002 8.24

State well number 006N012W21G001S (site 2), USGS ID 343546118091601—Continued

8/11/2009 1330 4.5 26.2 29.7 246 — 6.3 75 0.013 —8/8/2012 1010 7.5 E17.9 61.9 262 — 6.6 75 0.015 —

State well number 006N012W29B001S (site 1), USGS ID 343515118101401—Continued

8/11/2009 1500 24.5 13.7 12.7 825 — 1.4 130 0.002 —8/7/2012 1400 4.8 E9.66 0.84 892 — 0.96 120 0.002 —11/26/2013 1540 <4.0 9.01 4.67 933 5.1 0.83 115 0.003 12.2
16 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

Table 3. Nutrient and organic carbon data for water from selected monitoring wells near Palmdale, Los Angeles County, California, 

2009–13.

[State well number, see well-numbering diagram in text. Data analyzed by U.S. Geological Survey (USGS) National Water Quality Laboratory in Arvada, 

Colorado (NWQL). The five-digit number in parentheses below the constittuent name is the USGS parameter code used to uniquely identify a specific 

constituent or property. Abbreviations: E, estimated value; ft, feet; hhmm, hour:minute; mg/L, milligram per liter; mm/dd/yyyy, month/day/year; N, nitrogen; 

NAVD 88, North American Vertical Datum of 1988; P, Phosphorus; USGS ID, USGS identification; —, no data; <, less than value shown]

Date 

(mm/dd/yyyy)

Time 

(hhmm)

Altitude 

of 

land surface 

(ft above NAVD 88)

Depth 

of well 

(ft) 

(72008)

Depth to top of 

sample interval 

(ft) 

(72015)

Depth to bottom of 

sample interval 

(ft) 

(72016)

Ammonia plus 

organic nitrogen 

(mg/L as N) 

(00623)

State well number 006N012W20R001S (site 3), USGS ID 343522118095701

03/24/2011 1200 2,730 390 350 390 0.13

08/08/2012 1530 2,730 390 350 390 <0.07

11/26/2013 2100 2,730 390 — — <0.07

State well number 006N012W21G001S (site 2), USGS ID 343546118091601

08/11/2009 1330 2,695 620 — — <0.10

08/08/2012 1010 2,695 620 600 620 0.10

State well number 006N012W29B001S (site 1), USGS ID 343515118101401

08/11/2009 1500 2,745 220 — — E0.09

08/07/2012 1400 2,745 220 80 220 0.09

11/26/2013 1540 2,745 220 — — <0.07

Date 

(mm/dd/yyyy)

Time 

(hhmm)

Ammonia 

(mg/L as N) 

(00608)

Nitrate plus 

nitrite 

(mg/L as N) 

(00631)

Nitrite 

(mg/L as N) 

(00613)

Orthophosphate 

(mg/L as P) 

(00671)

Phosphorus 

(mg/L as P) 

(00666)

Total nitrogen 

(nitrate + nitrite + 

ammonia + organic-N) 

(mg/L) 

(62854)

Organic 

carbon 

(mg/L) 

(00681)

State well number 006N012W20R001S (site 3), USGS ID 343522118095701—Continued

03/24/2011 1200 0.029 1.39 0.019 0.012 <0.02 — —

08/08/2012 1530 <0.010 1.75 <0.001 0.021 <0.02 — 0.48

11/26/2013 2100 <0.010 1.81 <0.001 0.021 0.02 1.77 —

State well number 006N012W21G001S (site 2), USGS ID 343546118091601—Continued

08/11/2009 1330 <0.020 0.24 0.017 0.032 <0.04 — E0.35

08/08/2012 1010 0.012 0.203 0.005 0.049 0.05 — —

State well number 006N012W29B001S (site 1), USGS ID 343515118101401—Continued

08/11/2009 1500 <0.020 3.66 <0.002 0.108 0.11 — 1.12

08/07/2012 1400 <0.010 3.92 0.001 0.087 0.08 — —

11/26/2013 1540 <0.010 3.45 <0.001 0.078 0.07 3.48 —
Site Characterization 17

Table 4. Regulated volatile organic compounds data for water from selected monitoring wells near Palmdale, Los Angeles County, California, 2009–12.[Site locations are shown in figure 4. State well number, see well-numbering diagram in text. Data analyzed by U.S. Geological Survey (USGS) National Water Quality Laboratory in Arvada, Colorado (NWQL). The five-digit number in parentheses below the constittuent name is the USGS parameter code used to uniquely identify a specific constituent or property. Abbreviations: ft, feet; hhmm, hour:minute; mm/dd/yyyy, month/day/year; NAVD 88, North American Vertical Datum of 1988; USGS ID, USGS identification; VOC, volatile organic compound; μg/L, micrograms per liter; <, less than value shown]

Date 

(mm/dd/yyyy)

Time 

(hhmm)

Altitude of 

land surface 

(ft above 

NAVD 88)

Depth 

of well 

(ft) 

(72008)

Depth to top of 

sample interval 

(ft) 

(72015)

Depth to bottom of 

sample interval 

(ft) 

(72016)

1,2-Dichloroethane-d4, 

surrogate, water, unfiltered, 

percent recovery 

(99832)

1-Bromo-4-fluorobenzene, 

surrogate, VOC schedules, water, 

unfiltered, percent recovery 

(99834)

Toluene-d8, surrogate, 

water, unfiltered, 

percent recovery 

(99833)

State well number 006N012W20R001S (site 3), USGS ID 343522118095701

08/08/2012 1530 2,730 390 350 390 128 81.4 88.6

State well number 006N012W21G001S (site 2), USGS ID 343546118091601

08/11/2009 1330 2,695 620 600 620 137 76.1 88.9

State well number 006N012W29B001S (site 1), USGS ID 343515118101401

08/11/2009 1500 2,745 220 80 220 140 80.6 93.4

Date 

(mm/dd/yyyy)

Time 

(hhmm)

1,2-Dichloroethane, 

water, unfiltered, 

recoverable 

(μg/L) 

(32103)

1,2-Dichloropropane, 

water, unfiltered, 

recoverable 

(μg/L) 

(34541)

1,4-Dichlorobenzene, 

water, unfiltered, 

recoverable 

(μg/L) 

(34571)

1,1,1-Trichloroethane, 

water, unfiltered, 

recoverable 

(μg/L) 

(34506)

1,1,2-Trichloro-1,2,2-

trifluoroethane, water, 

unfiltered, recoverable 

(μg/L) 

(77652)

1,1-Dichloroethane, 

water, unfiltered, 

recoverable 

(μg/L) 

(34496)

State well number 006N012W20R001S (site 3), USGS ID 343522118095701—Continued

08/08/2012 1530 <0.2 <0.1 <0.1 <0.1 <0.1 <0.1

State well number 006N012W21G001S (site 2), USGS ID 343546118091601—Continued

08/11/2009 1330 <0.2 <0.1 <0.1 <0.1 <0.1 <0.1

State well number 006N012W29B001S (site 1), USGS ID 343515118101401—Continued

08/11/2009 1500 <0.2 <0.1 <0.1 <0.1 <0.1 <0.1

Date 

(mm/dd/yyyy)

Time 

(hhmm)

1,1-Dichloroethene, 

water, unfiltered, 

recoverable 

(μg/L) 

(34501)

1,2-Dichlorobenzene, 

water, unfiltered, 

recoverable 

(μg/L) 

(34536)

1,3-Dichlorobenzene, 

water, unfiltered, 

recoverable 

(μg/L) 

(34566)

Benzene, water, 

unfiltered, 

recoverable 

(μg/L) 

(34030)

Bromodichloromethane, 

water, unfiltered, 

recoverable 

(μg/L) 

(32101)

Chlorobenzene, 

water, unfiltered, 

recoverable 

(μg/L) 

(34301)

cis-1,2-Dichloroethene, 

water, unfiltered, 

recoverable 

(μg/L) 

(77093)

State well number 006N012W20R001S (site 3), USGS ID 343522118095701—Continued

08/08/2012 1530 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

State well number 006N012W21G001S (site 2), USGS ID 343546118091601—Continued

08/11/2009 1330 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

State well number 006N012W29B001S (site 1), USGS ID 343515118101401—Continued

08/11/2009 1500 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1
18 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project Table 4. Regulated volatile organic compounds data for water from selected monitoring wells near Palmdale, Los Angeles County, California, 2009–12.—Continued [Site locations are shown in figure 4. State well number, see well-numbering diagram in text. Data analyzed by U.S. Geological Survey (USGS) National Water Quality Laboratory in Arvada, Colorado (NWQL). The five-digit number in parentheses below the constittuent name is the USGS parameter code used to uniquely identify a specific constituent or property. Abbreviations: ft, feet; hhmm, hour:minute; mm/dd/yyyy, month/day/year; NAVD 88, North American Vertical Datum of 1988; USGS ID, USGS identification; VOC, volatile organic compound; μg/L, micrograms per liter; <, less than value shown] Date (mm/dd/yyyy) Time (hhmm) Dibromochloromethane, water, unfiltered, recoverable (μg/L) (32105) Dichlorodifluoromethane, water, unfiltered, recoverable (μg/L) (34668) Dichloromethane, water, unfiltered, recoverable (μg/L) (34423) Diethyl ether, water, unfiltered, recoverable (μg/L) (81576) Diisopropyl ether, water, unfiltered, recoverable (μg/L) (81577) Ethylbenzene, water, unfiltered, recoverable (μg/L) (34371) Methyl tert-butyl ether, water, unfiltered, recoverable (μg/L) (78032) State well number 006N012W20R001S (site 3), USGS ID 343522118095701—Continued 08/08/2012 1530 <0.2 <0.2 <0.2 <0.2 <0.2 <0.1 <0.2 State well number 006N012W21G001S (site 2), USGS ID 343546118091601—Continued 08/11/2009 1330 <0.2 <0.2 <0.2 <0.2 <0.2 <0.1 <0.2 State well number 006N012W29B001S (site 1), USGS ID 343515118101401—Continued 08/11/2009 1500 <0.2 <0.2 <0.2 <0.2 <0.2 <0.1 <0.2 Date (mm/dd/yyyy) Time (hhmm) Methyl tert-pentyl ether, water, unfiltered, recoverable (μg/L) (50005)

m-Xylene plus 

p-xylene, 

water, unfiltered, 

recoverable 

(μg/L) 

(85795)

o-Xylene, water, 

unfiltered, 

recoverable 

(μg/L) 

(77135)

Styrene, water, 

unfiltered, 

recoverable 

(μg/L) 

(77128)

tert-Butyl ethyl ether, 

water, unfiltered, 

recoverable 

(μg/L) 

(50004)

Tetrachloroethene, 

water, unfiltered, 

recoverable 

(μg/L) 

(34475)

Tetrachloromethane, 

water, unfiltered, 

recoverable 

(μg/L) 

(32102)

State well number 006N012W20R001S (site 3), USGS ID 343522118095701—Continued

08/08/2012 1530 <0.2 <0.2 <0.1 <0.1 <0.1 <0.1 <0.2

State well number 006N012W21G001S (site 2), USGS ID 343546118091601—Continued

08/11/2009 1330 <0.2 <0.2 <0.1 <0.1 <0.1 <0.1 <0.2

State well number 006N012W29B001S (site 1), USGS ID 343515118101401—Continued

08/11/2009 1500 <0.2 <0.2 <0.1 <0.1 <0.1 <0.1 <0.2

Date 

(mm/dd/yyyy)

Time 

(hhmm)

Toluene, water, 

unfiltered, 

recoverable 

(μg/L) 

(34010)

trans-1,2-Dichloroethene, 

water, unfiltered, 

recoverable 

(μg/L) 

(34546)

Tribromomethane, 

water, unfiltered, 

recoverable 

(μg/L) 

(32104)

Trichloroethene, 

water, unfiltered, 

recoverable 

(μg/L) 

(39108)

Trichlorofluoromethane, 

water, unfiltered, 

recoverable 

(μg/L) 

(34488)

Trichloromethane, 

water, unfiltered, 

recoverable 

(μg/L) 

(32106)

Vinyl chloride, 

water, unfiltered, 

recoverable 

(μg/L) 

(39175)

State well number 006N012W20R001S (site 3), USGS ID 343522118095701—Continued

08/08/2012 1530 <0.1 <0.1 <0.2 <0.1 <0.2 <0.1 <0.2

State well number 006N012W21G001S (site 2), USGS ID 343546118091601—Continued

08/11/2009 1330 <0.1 <0.1 <0.2 <0.1 <0.2 <0.1 <0.2

State well number 006N012W29B001S (site 1), USGS ID 343515118101401—Continued

08/11/2009 1500 <0.1 <0.1 <0.2 <0.1 <0.2 <0.1 <0.2
Site Characterization 19

Source and Age of Groundwater

Samples collected from sites 1, 2, and 3 were analyzed 

for the stable isotopes oxygen-18 and deuterium to help 

determine the source of water to wells and to evaluate the 

movement of water through the study area. Samples collected 

from sites 1, 2 and 3 were also analyzed for the radioactive 

isotopes of tritium and carbon-14 to determine the apparent 

age, or time since recharge, of groundwater.

Stable Isotopes

Oxygen-18 and deuterium are naturally occurring stable 

isotopes of oxygen and hydrogen, respectively. The isotopic 

ratios are expressed in delta notation (δ) as per mil (parts 

per thousand) differences relative to the standard known as 

Vienna Standard Mean Ocean Water (VSMOW) (Gonfiantini, 

1978). The oxygen (δ18O) and hydrogen (δD) isotopic ratios 

in precipitation throughout the world are linearly correlated 

because most of the world’s precipitation is derived from the 

evaporation of seawater. This linear relationship is known 

as the global meteoric water line (Craig, 1961). Differences 

in isotopic composition can be used to help determine 

general atmospheric conditions at the time of precipitation 

as well as the effects of evaporation before water entered 

the groundwater system. Information about the source and 

evaporative history of water can be used to evaluate the 

movement of groundwater. Because groundwater moves 

slowly, isotopic data collected near the end of long flow 

lines typically preserve a record of groundwater recharge 

and movement under predevelopment conditions. This is 

especially useful in areas where traditional hydrologic data 

(such as water levels) have been altered by pumping or by 

changes in recharge and discharge. Additional information 

regarding the use of stable isotopes in groundwater is available 

through the USGS at http://wwwrcamnl.wr.usgs.gov/isoig/

isopubs/itchch2.html.

Stable-isotope data were collected from sites 1, 2, and 3 

and other wells in the vicinity of the ACRP (fig. 8; tables 5, 6). 

The δ18O and δD measured in the samples collected at sites 1 

and 3 were notably heavier (less negative) than the δ18O and 

δD values in samples collected from the Palmdale area and 

site 2 (fig. 9; tables 5, 6). The δ18O and δD values of water 

sampled at sites 1 and 3 plotted near the sample collected 

at well 6N/14W-12R3, about 7.5 mi west of site 1 along the 

Amargosa Creek in Leona Valley (figs. 8 and 9). The similarity 

in isotopic values among these three samples and their 

proximity to Amargosa Creek indicated that the long-term 

average isotopic signature of natural modern-day recharge of 

Amargosa Creek was likely to be represented by these three 

samples. The sample collected at site 2 plotted near samples 

collected in the Antelope Valley groundwater basin in the 

vicinity of Palmdale, but was slightly lighter (more negative) 

with respect to δ18O and δD (fig. 9). This relationship indicated 

that water collected from site 2 has a similar source as the 

Palmdale samples, and that modern-day recharge from the 

Amargosa Creek is not a major source of the water sampled at 

site 2 or the Palmdale wells. Rather, the source of recharge at 

site 2 and Palmdale wells is likely to be precipitation that fell 

at higher elevations in the San Gabriel Mountains.

Tritium

Tritium is a naturally occurring radioactive isotope of 

hydrogen that has a half-life of 12.4 years (Clark and Fritz, 

1997). The concentration of tritium is measured in tritium 

units (TU); each TU equals 1 atom of tritium in 1,018 atoms 

of hydrogen. Approximately 800 kilograms of tritium was 

released to the atmosphere as a result of the atmospheric 

testing of nuclear weapons between 1952 and 1962 (Michel, 

1976). As a result, tritium concentrations in precipitation and 

groundwater recharge increased beyond naturally occurring 

concentrations during that time. Tritium concentrations are 

not affected by chemical reactions other than radioactive 

decay because tritium is part of the water molecule; therefore, 

tritium is an excellent tracer of the movement and relative age 

of water on timescales ranging from recent to about 60 years 

before present (post atomic bomb). The absence of tritium 

activity indicates water that infiltrated prior to 1952; high 

activity indicates water that infiltrated near the time of the 

bomb peak in the early 1960s; and low activity indicates either 

very recent recharge or a mixture of water with different ages. 

In this report, groundwater that had detectable tritium (greater 

than 0.8 TU) was interpreted to be water that contained at least 

some water that was younger than 1952 (post atomic bomb; 

Clark and Fritz, 1997).

Tritium concentrations in samples from sites 1, 2, and 

3 were 1.82, 0.15, and 0.22 TU, respectively (table 5). The 

tritium concentration in water sampled from site 1 was near 

the concentration in present-day precipitation, indicating at 

least some contribution from water before 1952 (Clark and 

Fritz, 1997). The presence of relatively young water at this site 

is expected given the proximity to the Amargosa Creek and 

the relatively shallow depth to water (about 100 ft). The near 

absence of tritium in the sample collected from site 2 indicated 

that the water was predominantly recharged prior to 1952. The 

low value of 0.15 TU from site 2 was consistent mixing of 

groundwaters recharged before and after 1952.

Carbon-14

Carbon-14 is a naturally occurring radioactive isotope 

of carbon that has a half-life of about 5,730 years (Mook, 

1980). Carbon-14 (14C) data are expressed as percent modern 

carbon (pmc) by comparing 14C activities of a sample to the 

specific activity of National Bureau of Standards oxalic acid: 

13.56 disintegrations per minute per gram of carbon in the 

year 1950 equals 100 pmc (Kalin, 2000). Carbon-14 also 

was produced, as was tritium, by the atmospheric testing of 

nuclear weapons (Mook, 1980). As a result, 14C activities 

can exceed 100 pmc in areas where groundwater contains 

tritium. Carbon-14 activities are used to determine the age 

of a groundwater sample on timescales ranging from recent 

to more than 20,000 years before present. Carbon-14 is not 
20 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project Table 5. Isotopic data for water from selected monitoring wells near Palmdale, Los Angeles County, California, 2009–13. [Site locations are shown in figure 4. State well number, see well-numbering diagram in text. Deuterium/protium and oxygen-18/16 analyzed at U.S. Geological Survey (USGS) National Research Program, Stable Isotope Laboratory, Reston,Virginia. The five-digit number in parentheses below the constittuent name is the USGS parameter code used to uniquely identify a specific constituent or property. Abbreviations: ft, feet; hhmm, hour:minute; mm/dd/yyyy, month/day/year; NAVD 88, North American Vertical Datum of 1988; TU, tritium units; USGS ID, USGS identification; —, no data] Date (mm/dd/ yyyy) Time (hhmm) Altitude of land surface (ft above NAVD 88) Depth of well (ft) (72008) Depth to top of sample interval (ft) (72015) Depth to bottom of sample interval (ft) (72016) Carbon-14 counting error, filtered, percent modern (49934) Carbon-14, filtered, percent modern (49933) Tritium, unfiltered (TU) (07000) delta Carbon-13, unfiltered, per mil (82081) Oxygen-18/ oxygen-16 unfiltered, per mil (82085) Deuterium/ protium unfiltered, per mil (82082) State well number 006N012W20R001S (site 3), USGS ID 343522118095701 03/24/2011 1200 2,730 390 350 390

—

—

—

— –8.50 –59.7

08/08/2012 1530 2,730 390 350 390 0.29 88.68 0.22 –10.25 –8.60 –60.3

11/26/2013 2100 2,730 390 350 390

—

—

—

— –8.58 –61.1

State well number 006N012W21G001S (site 2), USGS ID 343546118091601

08/11/2009 1330 2,695 620 600 620 0.06 4.71 0.15 –11.38 –10.64 –77.3

08/08/2012 1010 2,695 620 600 620

—

—

—

— –10.68 –78.1

State well number 006N012W29B001S (site 1), USGS ID 343515118101401

08/11/2009 1500 2,745 220 80 220 0.37 108.2 1.82 –12.21 –8.52 –60.9

08/07/2012 1400 2,745 220 80 220

—

— 1.70

— –8.54 –61.8

11/26/2013 1540 2,745 220 80 220

—

—

—

— –8.64 –61.9
Site Characterization 21

State well number Date 

(mm/dd/yyyy)

Time 

(hhmm)

Deuterium 

/protium 

unfiltered, 

per mil 

(82082)

Oxygen-18 

/oxygen-16 

unfiltered, 

per mil 

(82085)

005N011W03N003S 9/26/2002 1030 –71.6 –10.07

006N011W05G003S 2/12/2008 0910 –72.2 –9.72

006N011W06F001S 11/22/1997 0930 –73.6 –10.58

006N011W06G003S 11/21/1997 0930 –74.1 –10.48

006N011W06L001S 11/21/1997 1100 –72.6 –10.54

006N011W19C001S 10/21/2002 1510 –72.2 –10.48

006N011W19F002S 2/4/2008 0930 –72.4 –10.40

006N011W32P003S 9/26/2002 1050 –71.8 –10.13

006N011W34Q001S 9/26/2002 0940 –70.6 –10.00

006N012W07H001S 1/28/2008 1030 –71.3 –9.60

006N012W12M002S 3/19/2008 1000 –73.2 –10.46

006N012W13N001S 4/10/2008 1150 –70.8 –10.07

006N012W20R001S 3/24/2011 1200 –59.7 –8.50

006N012W20R001S 8/8/2012 1530 –60.3 –8.60

006N012W20R001S 11/26/2013 2100 –61.1 –8.58

006N012W21G001S 8/11/2009 1330 –77.3 –10.64

006N012W21G001S 8/8/2012 1010 –78.1 –10.68

006N012W29B001S 8/11/2009 1500 –60.9 –8.52

006N012W29B001S 8/7/2012 1400 –61.8 –8.54

006N012W29B001S 11/26/2013 1540 –61.9 –8.64

007N011W18R004S 8/12/2003 0830 –75.7 –10.70

007N011W18R004S 5/4/2006 0600 –72.8 –10.53

007N011W18R004S 5/4/2006 0930 –73.4 –10.53

007N011W18R004S 5/4/2006 1100 –72.7 –10.53

007N011W18R004S 5/4/2006 1145 –73.3 –10.50

007N011W18R004S 5/4/2006 1300 –73.5 –10.47

007N011W20G003S 8/12/2003 1030 –74.5 –10.57

007N011W20G003S 9/24/2003 1230 –73.7 –10.47

007N011W20G003S 9/24/2003 1400 –74.6 –10.71

Table 6. Isotopic data for water from selected wells near Palmdale, California, 1997–2013.

[State well number, see well-numbering diagram in text. The five-digit number in parentheses below the constittuent name is the U.S. Geological Survey 

(USGS) parameter code used to uniquely identify a specific constituent or property. Deuterium/protium and oxygen-18/16 analyzed by USGS National Research 

Program, Stable Isotope Laboratory, Reston, Virginia. Abbreviations: hhmm, hour:minute; mm/dd/yyyy, month/day/year]

State well number Date 

(mm/dd/yyyy)

Time 

(hhmm)

Deuterium 

/protium 

unfiltered, 

per mil 

(82082)

Oxygen-18 

/oxygen-16 

unfiltered, 

per mil 

(82085)

007N011W20G003S 9/24/2003 1500 –73.3 –10.50

007N011W20G003S 9/24/2003 1600 –74.6 –10.63

007N011W20G003S 9/24/2003 1630 –73.7 –10.61

007N011W20G003S 9/24/2003 1700 –74.8 –10.64

007N011W20G003S 5/25/2006 0915 –73.4 –10.56

007N011W20G003S 5/25/2006 1045 –72.6 –10.56

007N011W20G003S 5/25/2006 1130 –72.8 –10.58

007N011W20G003S 5/25/2006 1200 –72.8 –10.55

007N011W20G003S 5/25/2006 1240 –72.7 –10.59

007N012W15R003S 8/7/2003 1500 –75.7 –10.62

007N012W15R004S 8/7/2003 0830 –74.7 –10.58

007N012W21C002S 8/6/2003 1100 –75.7 –10.68

007N012W21C005S 8/5/2003 1500 –74.6 –10.56

007N012W22B002S 8/6/2003 0900 –73.6 –10.61

007N012W27F002S 5/19/2006 1110 –69.8 –9.80

007N012W27F002S 5/19/2006 1145 –70.2 –9.90

007N012W27F002S 5/19/2006 1245 –70.3 –9.80

007N012W27F002S 5/19/2006 1330 –70.2 –9.84

007N012W27F002S 5/19/2006 1400 –69.9 –9.90

007N012W27F002S 5/19/2006 1415 –70.3 –9.87

007N012W27F002S 8/5/2003 0900 –70.0 –9.71

007N012W27H003S 8/12/2003 1250 –74.7 –10.56

007N012W27J006S 8/7/2003 1245 –77.1 –10.62

007N012W27P002S 8/5/2003 1100 –73.6 –10.50

007N012W30B001S 8/6/2003 1245 –75.1 –10.64

007N012W34N005S 10/21/2002 0910 –67.7 –9.87

007N012W34N005S 8/5/2003 1300 –70.2 –9.90

007N012W34N005S 1/29/2008 1010 –70.3 –9.92

007N013W24M004S 8/6/2003 1445 –71.9 –10.04
22 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

–80 –11 –10.5 –10 –9.5 –9 –8.5 –8

–75

–70

–65

–60

–55

Delta oxygen–18, in per mil

Delta deuterium, in per mil

Global meteoric water line,

(Craig, 1961)

Palmdale area

6N/12W–29B1 (site 1) 

6N/12W–21G1 (site 2)

6N/14W-12R3 (Leona Valley)

6N/12W–20R1 (site 3)

EXPLANATION

sac11-0421_Figure 09

Figure 9. Stable isotope data for samples collected from monitoring sites 1, 2, and 3 and the vicinity of Palmdale, California, 2009–13.

part of the water molecule, and therefore, 14C activities can be 

affected by chemical reactions that remove or add carbon to 

solution. In addition, 14C activities are affected by the mixing 

of younger water that has high 14C activity with older water 

that has low 14C activity. Carbon-14 ages presented in this 

report do not account for changes in 14C activity resulting from 

chemical reactions or mixing and, therefore, are considered 

uncorrected ages. In general, uncorrected 14C ages are older 

than the actual age of the associated water. Izbicki and others 

(1995) estimated that uncorrected 14C ages were as much 

as 30 percent older than actual ages for groundwater in the 

regional aquifer in the neighboring Mojave River groundwater 

basin (not shown), about 40 mi east of the study area.

Carbon-14 values for samples collected at sites 1, 2 

(well 21G1), and 3 were 108.2 pmc, 4.7 pmc, and 88.7 pmc 

respectively (table 5). These 14C activities corresponded to 

uncorrected 14C groundwater age of less than 50 years for the 

sample collected at site 1, 25,300 years before present (ybp) 

at site 2, and 990 ybp for the sample collected at site 3. The 

14C activity at site 3, however, was within the range of values 

that could indicate mixing of modern water with 14C activity 

affected by modern atmospheric nuclear testing with premodern waters; consequently, the 14C values for site 3 do not 

definitively indicate a modern or pre-modern recharge age. 

Although each site was in close proximity to the Amargosa 

Creek, the combination of stable isotopic, tritium, and 14C 

results indicated that site 1 had modern-day recharge from 

Amargosa Creek, site 2 had pre-modern recharge not derived 

from Amargosa Creek, and site 3 had a mixture of modernand pre-modern recharge derived from Amargosa Creek.
Site Characterization 23

Surface Geophysical Surveys

In 2009, three surface geophysical surveys were 

completed to help define the thickness of the valley-fill 

deposits or depth to the basement complex in the regional 

study area; to identify possible features, such as faults, that 

might influence groundwater flow; and to estimate depth 

to groundwater (fig. 10). A regional gravity survey was 

completed, and the data collected were used to develop a 

valley-fill thickness model to estimate alluvial thickness and 

the associated basement-complex geometry. High-resolution, 

shallow-depth seismic refraction and reflection surveys 

were completed along the Amargosa Creek, near the ACRP, 

to delineate density contrasts associated with individual 

sedimentary units in the valley-fill deposits and between 

these deposits and the basement complex. Resistivity surveys 

were completed along the Amargosa Creek, near the ACRP, 

to delineate resistivity contrasts associated with coarser- and 

finer-grained sedimentary units in the valley-fill deposits and 

between unsaturated and saturated portions of the aquifer 

system.

T

7

N

T

6

N

T

5

N

R13W 118°12' 118°08' R12W 118°04' R11W 118°00'

34°

40'

34°

32'

34°

36'

0 5 MILES

0 5 KILOMETERS

Amargosa

Creek

EXPLANATION

Little Rock

Wash

1 2 3 4

1 2 3 4

Palmdale

Lancaster

Seismic

line

Resistivity line 1

Recharge

facility

Resistivity line 2

Monitoring-well site

California Aqueduct

Inferred fault (Bloyd, 1967) 

San Andreas fault zone 

Proposed recharge Faults—

 facility

Gravity sites from this study

Seismic line

Resistivity lines 1 and 2

Regional gravity sites

Control wells

Base modified from U.S. Department of Agriculture National Agriculture

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

Figure 10. Location of geophysical surveys, Antelope Valley, California.
24 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

Regional Gravity Survey

Aeromagnetic data collected by Roberts and Jachens 

(1999) were examined and used to characterize the nature of 

the basement rocks at the base of the valley-fill deposits. The 

valley-fill deposits consist of locally derived Quaternary and 

Tertiary sediments, which overlay pre-Tertiary metamorphic 

and crystalline rocks that form the basement complex. Roberts 

and others (1990) found a large density contrast, averaging 

40.6 pounds per cubic foot (lb/ft3) in the upper 650 ft, between 

the valley-fill deposits and the crystalline basement complex, 

indicating that gravity methods would be appropriate for 

determining the thickness of the valley-fill deposits.

A gravity survey was completed during this study to 

define the thickness of the valley-fill deposits, or depth to 

the basement complex, in the study area. The gravity survey 

included western Palmdale, southern Lancaster, and the 

foothills west of the San Andreas fault zone (fig. 10). Gravity 

data collected for this study were combined with regional 

gravity data collected by Roberts and others (1990). Gravity 

measurements made for this study were closely spaced along 

Amargosa Creek to help determine changes in the basement 

geometry below the recharge facility and to identify possible 

features, such as faults, that could influence groundwater flow. 

Geologic maps and lithologic data from water wells were used 

to constrain interpretation of the gravity data.

Gravity Survey and Reduction Data Sets

Gravity measurements were collected at 234 new 

locations for this study by using a LaCoste and Romberg 

Model D-79 with Aliod 100 gravity meter (fig. 10). The 

location and elevation of each gravity measurement was 

determined by using a Trimble Real Time Kinematic (RTK) 

Model 4400 Global Positioning System (GPS) base and 

mobile receivers. This system is capable of obtaining vertical 

and horizontal coordinates with a precision of plus-or-minus 

0.083 ft between receiver and base by using traditional RTK 

methods described by Morton and others (1993). The RTK 

survey was referenced to the North American Vertical Datum 

of 1988 (NAVD 88) by using local bench marks.

The gravity data were reduced by using the Geodetic 

Reference System of 1967 (International Union of Geodesy 

and Geophysics, 1971) and referenced to the International 

Gravity Standardization Net 1971 gravity datum (Morelli, 

1974). Gravity data were analyzed using standard gravity 

corrections, including (1) the earth tide correction, which 

corrects for tidal effects of the moon and sun; (2) instrument 

drift correction, which compensates for drift in the 

instrument’s spring; (3) the latitude correction, which 

incorporates the variation of the Earth’s gravity with latitude; 

(4) the free-air correction, which accounts for the variation in 

gravity with changes in elevation; (5) the Bouguer correction, 

which corrects for the attraction of material between the 

station and the vertical datum; (6) the curvature correction, 

which adjusts the Bouguer correction for the effect of the 

Earth’s curvature; (7) the terrain correction, which removes 

the effect of topography to a radial distance of about 104 mi 

(Telford and others, 1990). Isostatic and terrain correction 

beyond that distance were interpolated from a grid generated 

from Karki and others (1961).

Terrain corrections were computed to a radial distance 

of 104 mi and involved a three-part process: (1) HayfordBowie zones A and B with an outer radius of 223 ft were 

estimated in the field with the aid of tables and charts from 

Robbins and Oliver, 1970; (2) Hayford-Bowie zones C and 

D with an outer radius of 1,936 ft were computed by using a 

100-ft digital elevation model; and (3) terrain corrections from 

a distance of 1,936 ft to 104 mi were calculated by using a 

digital elevation model and an established procedure by Plouff 

(1977). Total terrain corrections for the stations collected for 

this study ranged from 0.62 to 6.23 milligal (mGal), averaging 

1.18 mGal; in comparison, corrected isostatic residual gravity 

values in the study area ranged from about −29 to +9 mGal.

Geologic Maps

Data from geologic maps were used primarily to 

delineate the valley-fill deposits from the basement complex 

outcrops. The geologic maps of Ritter Ridge 7.5-minute 

quadrangle (Hernandez, 2009) and Palmdale (Olson and 

Hernandez, 2013) 7.5-minute quadrangles were used for 

most of the study area, with additional information from the 

geologic maps of the Del Sur (Hernandez, 2010a), Lancaster 

West (Hernandez, 2010b), and San Andreas fault zone 

(Evans, 1978) 7.5-minute quadrangles.

Water Wells

Fourteen water wells with drillers’ logs were available 

for use as constraints for gravity interpretation (control wells 

on fig. 10 and table 7). These logs reported materials at the 

bottom of the drill hole consistent with the basement complex, 

including sandstone, shale, rock, or granite. Data from sonic 

logs and depths to the basement complex at monitoring 

wells completed as part of this study also were used as local 

basement-complex constraints.

Gravity Field

The gravity field of the study area (here expressed 

as the isostatic residual gravity field) primarily reflects 

the large density contrast between the basement complex 

and lower density valley-fill deposits (fig. 11). The most 

prominent features on the gravity maps are the high gravity 

values (greater than −5 mGal) that coincided with shallow 

alluvium and basement-complex exposures in the San Gabriel 

Mountains and Ritter Ridge, west of the San Andreas fault 

zone, and the low gravity values (less than −10 mGal) that 

coincided with thick basin-fill deposits east of the recharge 

facility in the Antelope Valley. There is a local gravity high, 

as indicated by the area of greater gravity values (shown in 

orange), underlying and to the northwest of the proposed 

ACRP, which was consistent with mapped exposures of 

quartz-monzonite basement and basement covered with 

shallow alluvium.
Site Characterization 25

Table 7. Thickness of alluvial deposits from drillers’ logs and gravity surveys for 14 wells near Palmdale, Los Angeles County, 

California.

[State well number, see well-numbering diagram in text. Abbreviations: DDD MM, degrees decimal minutes; ft, feet]

State 

well 

number

Latitude 

(DD MM)

Longitude 

(DDD MM)

Measured 

thickness of 

basin-fill deposits 

(ft)

Total 

hole 

depth 

(ft)

Estimated 

thickness of 

basin-fill deposits 

(ft)

Source

006N011W30 34° 34.804” –119° 54.897” 210 250 480 Department of Water Resources, 

written commun., 2008

006N012W07A001S 34° 37.683” –119° 48.895” 430 452 438 Department of Water Resources, 

written commun., 2008

006N012W07A002S 34° 37.833” –119° 48.878” 450 456 451 Department of Water Resources, 

written commun., 2008

006N012W08R001S 34° 37.066” –119° 50.012” 620 630 630 Department of Water Resources, 

written commun., 2008

006N012W17 34° 36.541” –119° 49.535” 810 820 822 Department of Water Resources, 

written commun., 2008

006N012W21A002S 34° 36.066” –119° 51.028” 704 704 692 Department of Water Resources, 

written commun., 2008

006N012W23M001S 34° 35.599” –119° 52.228” 615 651 605 Department of Water Resources, 

written commun., 2008

006N012W24C001S 34° 35.999” –119° 53.779” 1,106 1,275 1,280 Department of Water Resources, 

written commun., 2008

006N012W25 34° 34.781” –119° 53.831” 360 400 595 Department of Water Resources, 

written commun., 2008

006N012W26 34° 34.776” –119° 52.761” 140 300 566 Department of Water Resources, 

written commun., 2008

006N012W31H001S 34° 34.071” –119° 48.898” 60 262 122 Department of Water Resources, 

written commun., 2008

006N012W35 34° 33.921” –119° 52.773” 392 470 398 Department of Water Resources, 

written commun., 2008

006N013W12H001S 34° 37.516” –119° 47.828” 125 132 145 Department of Water Resources, 

written commun., 2008

006N013W12Q001S 34° 37.083” –119° 47.528” 94 97 83 Department of Water Resources, 

written commun., 2008
26 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

sac11-0421_fig 11

0

–5

–10

5

–15

–20

–25

–15

118°12’ 118°08’ 118°04’ 118°

34°

40’

34°

32’

34°

36’

0 5 MILES

0 5 KILOMETERS

Amargosa

Creek

EXPLANATION

–15

Monitoring-well site

California Aqueduct

Inferred fault (Bloyd, 1967) 

San Andreas fault zone 

Faults—

Proposed recharge

 facility

Gravity contour,

 in milligal

1 2 3 4

1 2 3 4

Palmdale

Lancaster

Ritter Ridge

San Gabriel Mts

Base modified from U.S. Department of Agriculture National Agriculture

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

Figure 11. Contoured isostatic residual gravity field, Antelope Valley, California.

Computation Method for Modeling Thickness of Valley-Fill 

Deposits

The thickness of the valley-fill deposits (or depth to the 

basement complex) in the study area was estimated by using 

the method of Jachens and Moring (1990), modified slightly 

to permit inclusion of constraints at points where the thickness 

was known from direct observations in drill holes. An initial 

estimate of the ‘valley-fill deposits gravity anomaly’ was made 

by fitting a smooth surface to the gravity values measured at 

stations where the basement-complex rocks crop out (initial 

estimate of the ‘basement gravity field’) and subtracting this 

from the isostatic residual gravity field. This represents only 

the initial estimate because the gravity values at points on 

the basement complex that lie close to the valley-fill deposits 

were affected by the lower-density valley-fill deposits and are, 

therefore, lower than they would be if the valley-fill deposits 

were not present. To compensate for this effect, the initial 
Site Characterization 27

estimate of the valley-fill deposits gravity anomaly was used 

to calculate an initial estimate of the thickness of the valleyfill deposits, and the gravity effect of these valley-fill deposits 

was calculated at all of the basement gravity stations. A second 

estimate of the basement gravity field was then made by fitting 

a smooth surface to the basement gravity values corrected 

by the valley-fill effect; this process was repeated to produce 

refined estimates of the thickness of the valley-fill deposits 

until further iterations did not result in notable changes to the 

modeled thickness of the valley-fill deposits.

The valley-fill deposits gravity anomaly was inverted to 

estimate the thickness of the valley-fill deposits by using an 

estimated density contrast that varied with depth (table 8). 

This density-depth relationship was used for a regional gravity 

inversion for the Basin and Range province that also included 

the Mojave Desert (Saltus and Jachens, 1995). The resulting 

density contrast of −40.6 lb/ft3 for the valley-fill deposits in 

the upper 660 ft was reasonable for Quaternary and Tertiary 

continental deposits overlying pre-Tertiary crystalline rocks. 

The density contrast was slightly less than that derived from 

the Banning Pass area approximately 100 miles southeast of 

the Palmdale (not shown in fig. 1) area along the southern 

margin of the San Bernardino Mountains, which was 

−34.3 lb/ft3 (Langenheim and others, 2005). This density 

contrast estimation was further verified by examining the 

basement gravity field for any indications of local anomalies at 

the sites where wells penetrated the basement.

Gravity Results

The gravity inversion resulted in a calculated thickness 

of the valley-fill deposits, or depth to basement complex, that 

ranged from 0 ft in the San Gabriel Mountains (shown as less 

than 250 ft on fig. 12) to about 4,700 ft in the northeastern 

part of the study area. The porosity and permeability of the 

valley-fill deposits decrease with depth because of compaction 

and cementation. Therefore, although the depth to basement 

complex is greatest in the northeastern part of the study area, 

the thickness of permeable water-bearing deposits likely is 

much less than the total calculated thickness of valley-fill 

deposits.

The calculated thickness of the valley-fill deposits where 

drill holes have penetrated the entire thickness of the valley-fill 

deposits agreed with the observed thickness within 25 ft, 

which was expected because the solution was constrained 

to honor these values. Basic uncertainties in the gravity data 

meant that the best resolution that could be expected, even in 

areas of good gravity coverage, was about 50 ft, and resolution 

was likely to be less in areas of poor gravity coverage or in 

areas far from either the basement outcrop or control wells. In 

addition, the calculations were done for grid cells that were 

1,000 ft by 1,000 ft; therefore, the results represent the average 

thickness of valley-fill deposits for each cell. Variations of the 

thickness of the valley-fill deposits over distances less than 

1,000 ft were not resolved. Gravity data reflect the average 

shape of the valley-fill deposits, and the averaging over thicker 

sections (deeper) from the gravity station. As a result, where 

the valley-fill deposits are the thickest are subject to averaging 

over greater volume of material; thus, contours appeared 

smoother in these areas than in those where the valley-fill 

deposits are thinner. Finally, the model assumed no lateral 

variations in density within the valley-fill deposits. This might 

not be valid if deposits coarsen toward the mountain front.

Analysis of the results from the valley-fill thickness 

model indicated an alluvial-filled trough in the basement 

trending northeast is to the north and northeast of the 

ACRP (fig. 12). The Amargosa Creek channel is generally 

sub-parallel and south of the trough and then trends north 

across the trough. The thickness of the valley-fill deposits 

in the trough increases to the northeast to greater than 

3,000 ft. Southeast of the ACRP and along the Amargosa 

Creek channel, the valley-fill deposits thin to less than 250 ft, 

forming a shallow plateau that extends southeast toward 

Palmdale.

Seismic Refraction and Reflection, and DirectCurrent Resistivity Surveys

As part of this study, the USGS Seismic Imaging Group 

collected shallow-depth combined seismic reflection and 

refraction data along the eastern part of ACRP and along 

Amargosa Creek to help delineate and visualize geologic 

structures. The approximately 7,400 ft long seismic line 

extended northeast along Amargosa Creek from a point 250 ft 

east of Highland Avenue and 600 ft north of Elizabeth Lake 

Road (fig. 13). In addition to the seismic data collected, directcurrent (DC) resistivity data were collected along two sections 

of the seismic profile (fig. 13).

Seismic Refraction and Reflection Survey

Seismic data were acquired in a manner that both allows 

refraction and reflection images to be produced. First-arrival 

refractions were inverted for velocity structure, to develop 

P-wave velocity images along the seismic line, by using a 

modified version of the tomographic inversion code of Hole 

(1992). The data were inverted by using a 16-ft by 16-ft 

grid along the profile to the depth of ray coverage. A firstarrival refraction on each seismogram from each seismic 

Table 8. Estimated density contrast with depth in the Palmdale 

area.

[ft, feet; lb/ft3, pound per cubic foot; >, less than]

Depth range

(ft)

Density contrast

(lb/ft3)

0–660 –40.6

660–2,000 –34.3

2,000–4,000 –21.8

>4,000 –15.6
28 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

sac11-0421_fig 12

Palmdale

1,000

250

2,000

3,000

4,000

118°12' 118°08' 118°04' 118°00'

34°

40'

34°

32'

34°

36'

0 5 MILES

0 5 KILOMETERS

Amargosa

Creek

EXPLANATION

1,000

Monitoring-well site Proposed recharge 

 facility

Generalized contact of

 alluvial deposits

 (Hernandes, 2009;

 Olson and Hernandez, 2013)

Modeled alluvial

 thickness, in feet

Lancaster

Ritter Ridge

1 2 3 4

1 2 3 4

California Aqueduct

Inferred fault A (Bloyd, 1967) 

San Andreas fault zone 

Alquist-Priolo fault (from California

 Geological Survey, 2002) 

Faults—

San Gabriel Mts

Base modified from U.S. Department of Agriculture National Agriculture

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

Figure 12. Thickness of the valley-fill deposits calculated from gravity measurements in the Palmdale area, Antelope Valley, California.
Site Characterization 29

sac11-0421_fig 13

Elizabeth Lake Rd

Brookdale Rd Kensington Way

Highland Ave

118°11' 118°10' 118°09'

34°

36'

34°

35'

Amargosa

Creek

EXPLANATION

Site 1

Site 3

Site 2

21E1

Seismic line

Resistivity line 1

Resistivity line 2

0

0 1,000 METERS

5,000 FEET

Monitoring-well site

Reference well

California Aqueduct

Proposed recharge 

 facility

21E2

Seismic line

Resistivity lines 1 and 2 Inferred fault A (Bloyd, 1967) 

San Andreas fault zone 

Alquist-Priolo fault (from California

 Geological Survey, 2002) 

Faults—

500

Base modified from U.S. Department of Agriculture National Agriculture 2,500

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

Figure 13. Locations of seismic refraction and reflection surveys and direct current (DC) resistivity surveys along Amargosa Creek 

near Palmdale, California.
30 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

source was inspected and measured, resulting in a total of 

20,295 seismograms. Because of the high level of cultural 

noise, however, it was not possible to determine first-arrival 

refractions on all the seismograms, particularly for those far 

from the shot source.

Seismic Data Acquisition and Processing

Data were recorded by using a linear array of three 

Geometrics StrataviewTM RX-60 seismographs, each with 60 

active channels. The recorded data were stored on the hard 

drive of the Strataview computers during field acquisition 

and later downloaded to 4-millimeter (mm) tape for storage 

in SEG-Y format (Norris and Faichney, 2001). Forty-hertz 

(Hz), single-element, Mark Products, L-40ATM geophones 

were spaced at approximately 33-ft intervals along the profile. 

Seismic sources (shots), at depths of about 1.5 ft, were 

laterally spaced approximately every 66 ft and co-located (3-ft 

lateral offset) with the geophones along the approximately 

7,400 ft profile. Each recording site and shot point was 

measured with a tape and flagged to obtain the proper 

spacing. The shots were generated by a BETSY SeisgunTM

using 8-gauge shotgun blanks. Shot timing was determined 

electronically at the seismic source when the hammer 

electrically closed contact with the SeisgunTM, sending an 

electrical signal to the seismograph. After the seismic data 

were acquired, the location and elevation of each recording 

and shot site were determined by using RTK-GPS methods 

described earlier in this report.

Reflection images were developed by using the seismic 

data and appropriate reflection processing schemes. The 

seismic processing procedures used for this study were 

similar to those outlined by Brouwer and Helbig (1998). 

Data processing steps included geometry installation, 

trace editing, timing corrections, elevation statics, muting, 

Automatic Gain Control, bandpass filtering, velocity analysis, 

Normal Move Out correction, stacking, depth conversion, 

and deconvolution. The reflection images were migrated 

using pre-stack depth migration to properly image complex 

structures such as dipping layers and abruptly terminated 

layers. Seismic-reflection images were developed from the 

seismic data by stacking shot gathers with approximately 

180 channels per shot and converting the time sections to 

depth sections by using the inverted tomographic velocity 

model (Hole, 1992; fig. 14A). Common Depth Point intervals 

along the line were 8 ft, resulting in a seismic trace every 

16 ft (U.S. Environmental Protection Agency, 2011). Several 

prominent reflectors were observed in the shot gathers within 

the first few hundred milliseconds, indicating that the seismic 

energy penetrated more than 1,000 ft in depth. The resolving 

ability of reflected seismic energy is about one-quarter of a 

wavelength (Dobrin and Savit, 1988). In theory, for the nearsurface strata with velocities of approximately 2,600 feet per 

second (ft/s), relatively small subsurface structures of 15–30 ft 

could be imaged with the reflection data.

The range of frequencies that could be used to measure 

first-arrival refractions was limited because of high attenuation 

in the sandy soils and high cultural noise levels; the data were 

filtered at relatively low frequencies (10, 20, 40, and 80 Hz) 

to maximize the propagation distance of the seismic data. 

The limited propagation distances of the seismic data allowed 

accurate P-wave seismic velocity images to be developed only 

for relatively shallow (approximately 250 ft) depths (fig. 14B).

Seismic Survey Results

The reflection image showed a change in reflective 

character of the strata overlying the depth of the basement 

complex (pink region in fig. 14A) interpreted from seismic 

data. The strata above this contact were characterized by 

multiple prominent reflectors, whereas the strata below the 

contact were characterized by relatively weak reflectors. 

This change in reflective character was interpreted to be the 

contact between valley-fill deposits, combined with weathered 

or fractured basement, and the unweathered or unfractured 

basement complex. The unweathered or unfractured basement 

complex is denser than the overlying material; therefore, 

much of the seismic energy reflected off of this boundary. The 

change in reflective character also coincided with increased 

resistivity in the 64-in. normal-borehole resistivity logs at 

the depth where bedrock was encountered at sites 1, 2, and 

3. The top of the weathered or fractured basement (sites 1 

and 2) and indurated valley-fill deposits (site 3), as noted 

from geophysical and lithologic logs, were plotted (in red) 

at well locations along the profile. The change in reflective 

character and change in apparent dip of reflectors at lateral 

distances from the southwest origin of the line of 900–1,600 

and 5,200–6,000 ft indicated the presence of faults. The 

seismic refraction image also showed changes in depth of the 

basement complex at lateral distances of 900–1,600 ft and 

about 5,200–6,000 ft along the profile, which further indicated 

the presence of faults.

The P-wave velocity image (fig. 14B) shows the average 

seismic velocities (averaged over a distance of 33 ft or more) 

measured from the surface to a maximum depth of about 

250 ft bls. The near-surface velocities ranged from about 

1,300 to about 2,300 ft/s in the upper 65 ft. From about 65 ft 

to about 250 ft bls, the velocities varied between about 2,600 

and 6,600 ft/s. In general, the seismic velocities greater 

than 4,265 ft/s (fig. 14B) represented more consolidated and 

saturated sediments. Velocities less than about 4,265 ft/s 

(fig. 14B) represented unconsolidated and unsaturated 

materials. Unconsolidated saturated sediments typically 

have P-wave velocities in excess of 4,920 ft/s, sedimentary 

rocks have velocities in excess of 7,218 ft/s, and unfractured 

granitic and metamorphic rocks have velocities in excess of 

13,000 ft/s in the shallow subsurface (Catchings and others, 

2009). P-wave velocities representative of unweathered or 

unfractured basement complex (in excess of 13,000 ft/s) were 

not measured in the limited-depth model; however, P-wave 

velocities in excess of 6,000 ft/s were measured at the base 

of the southwestern end of the seismic profile. These higher 

velocities probably reflected the presence of the weathered or 

fractured basement complex. The 4,921-ft/s velocity contour 
Site Characterization 31 Figure 14. Seismic data collected along Amargosa Creek near Palmdale, California: 

A, seismic reflection, and B, average P-wave velocity images for the seismic line, and 

C, 

resistivity models for resistivity lines 1 and 2, 2009. Location of the seismic line and of resistivity lines 1 and 2 are shown in figure 12.

sac11-0421_fig 14abc

20 60 100 140 180

Resistivity, in ohm-meters

250 350 450

Velocity,

in feet

per second

1,9682,2972,6242,9523,2813,6093,9374,2654,5934,9215,2495,5775,9056,2336,651

Borehole

resisitivity

Southwest Northeast

4,921 5,249

5,577

5,905

6,233

6,651

4,593

4,265 3,937 3,609

3,281

2,952 2,624 2,297 1,968

2,7502,7002,6002,500

Feet

2,7502,7002,6002,500

Feet

2,7502,7002,6002,500

Feet

RESISTIVITY LINE 1 RESISTIVITY LINE 2 SITE 1 SITE 3

SITE 1

SITE 1

SITE 3

SITE 2

?

Basement complex Water table Observed depth of lithologic

 contact in borehole

Indurated valley fill or weathered/ fractured basement

Distance, in feet

0 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500 500 1,000 1,500

Elevation, in feet above North American

Vertical Datum of 1988 (NAVD 88)

2,7002,6002,5002,4002,3002,2002,1002,000

?

? ?

? ?

Elevation, in feet

above NAVD 88

Elevation, in feet

above NAVD 88

7,000

ABC

Fault C Fault B
32 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

(fig. 14B) coincided with the measured depth of groundwater 

at site 1 (about 103 ft bls). The depth to the 4,921 ft/s contour 

(water table) increased from about 100 ft bls at site 1 to about 

250 ft bls at about 1,700 ft lateral distance from the west end 

of the line. Northeast of this point, the 4,921-ft/s velocity 

contour was below the depth imaged by the velocity model, 

indicating that the depth to groundwater was in excess of 

250 ft bls, which coincided with available water-level data 

shown in figures 14A and 7.

The P-wave velocity image showed increases in the depth 

of high-velocity basement between lateral distances of 900 to 

1,400 ft and at 5,250 to 6,000 ft along the profile, (fig. 14B). 

The low-velocity sediments are approximately 150 ft thick 

from lateral distances of 0 to about 1,000 ft, greater than 150 ft 

thick from lateral distances of about 1,000 to about 5,250 ft, 

and greater than 400 ft thick from about 5,250 ft to the end of 

the profile (fig. 14B). The changes in thickness of the lowvelocity sediments could be due to increased deposition of 

alluvium on the downthrown side of faults.

Resistivity Surveys

In addition to the seismic data, DC resistivity data were 

collected along two sections of the seismic profile (fig. 13). 

Resistivity data were collected along line 1, a 3,300-ft transect, 

and line 2, a 1,200-ft transect.

Resistivity Data Acquisition

The DC resistivity measurements were made by 

injecting a known current into the subsurface through two 

“transmitter” current electrodes and measuring the resulting 

voltage difference between two “receiver” electrodes. In 

two-dimensional resistivity surveys such as this one, an 

array of electrodes spaced at regular intervals is placed into 

the earth and many different combinations of transmitting 

and receiving electrode pairs are used to determine apparent 

resistivity of the earth beneath receiving electrode pairs. 

Information about lateral variability in the subsurface is 

gained as the measuring electrode pairs are shifted across the 

array, whereas information about greater depths is obtained 

by increasing the separation between electrodes. Details about 

the practical aspects of resistivity surveying techniques can be 

found in various texts (for example, Telford and others, 1990; 

Reynolds, 1997; and Binley and Kemna, 2005).

For this survey, a dipole-dipole array was used, which 

allows for rapid data acquisition and provides a good balance 

between lateral and depth resolution. With this geometry, the 

four electrodes used for each measurement are spread out 

across the line. The receiver electrodes are closely spaced and 

remote from the transmitter electrodes, which are also close 

together (Telford and others, 1990). For each pair of current 

electrodes, up to eight pairs of potential electrodes are used to 

gain depth information. For logistical purposes, 14 electrodes 

are attached to a single cable, then 4 individual electrode 

cables are strung together to make up the desired line length. 

Each cable interfaces with the resistivity meter through a 

switch box. An initial array of 56 electrodes was laid out for 

each line. Electrodes were set in the earth at 26.25-ft intervals. 

The length of each line in this survey exceeded the total length 

of the 4 electrode cables (1,470 ft), requiring a continuous 

profile, also known as a “roll-along” profile, to be collected 

by moving a group of 14 electrodes from the start of the line 

to the end. The depth of investigation is calculated on the 

basis of the electrode spacing during the inversion process. An 

apparent resistivity value, which refers to the homogeneous 

earth resistivity that produces the measured data, is calculated 

for each point from the injected current, measured voltage, 

and electrode geometry. Images of the data presented in this 

form are called pseudosections; they are a conventional way to 

show the data, but do not represent the true spatial distribution 

of resistivity values within the earth (Minsley and others, 

2009).

Resistivity data were collected by using an Advanced 

Geosciences Incorporated (AGI) SuperSting R8, 8-channel 

multi-electrode resistivity meter. This instrument can collect 

up to eight readings for each current injection. For this 

survey, transmitted currents were between 0.5 milliamp 

(mA) and 300 mA, with an average current of 50 mA and a 

standard deviation of 0.07 mA. The relatively low injectedcurrent levels are typically used in highly resistive desert 

environments (Minsley and others, 2009). Measurements 

were made over a period of 1.2 seconds, during which the 

polarity of the current electrodes was reversed in order to 

minimize electrode polarization effects and to improve contact 

resistance.

Resistivity Data Processing

Forward and inverse modeling are mathematical 

techniques that are used to generate a subsurface-resistivity 

model from measurements of the injected current, the voltage 

at the receiver electrodes, and the down-line locations of the 

four electrodes used for each measurement. Forward modeling 

refers to the process of predicting the data that would be 

measured from a given resistivity model and is based on 

the physics of electrical current flow in resistive media. The 

forward-modeling process is well-posed; that is, there is a 

unique set of predicted data for a given resistivity model. 

Inverse modeling refers to the derivation of a resistivity model 

from the measured data. The inverse-modeling process is nonunique, that is, there are many models that are consistent with 

the measured data. To overcome nonuniqueness, additional 

user-specified constraints are placed on the model, such as 

requiring it to be smooth, similar to a reference model, or both. 

These additional constraints often incorporate reasonable a 

priori geologic information and produce more stable inversion 

results. A detailed discussion of the resistivity inverse problem 

is widely available (for example, Oldenburg and Li, 1994; 

Zhang and others, 1995; Loke and Barker, 1996; and Binley 

and Kemna, 2005).

The data were inverted by using the Geotomo Software 

RES2DINV version 3.59.104 (Geotomo Software, 2009,

http://geotomosoft.com) that uses the “robust” inversion 

method, which performs well on noisy datasets because it 
Site Characterization 33

is based on the assumption that data errors are distributed 

exponentially. The inversion process seeks to find the 

subsurface distribution of resistivity values that (1) produce 

modeled data that match the measured data within an 

acceptable tolerance, (2) satisfy constraints that the model is 

both smooth and similar to a user-specified reference model 

and (3) is as simple as possible (Geotomo Software, 2009,

http://geotomosoft.com).

Inversions start from a homogeneous resistivity model 

(simplest possible) and then are iteratively updated to produce 

more complex heterogeneous models that reduce data 

misfit. The inversions were allowed to run for a maximum 

of 10 iterations, with stopping criteria of 6 percent or less 

root-mean-square (RMS) error between the measured and 

forward modeled data or an L2-norm (sum of squares) value 

of one or less for the error-weighted data misfit. If neither 

of the stopping criteria are met after reaching the end of the 

tenth iteration, noise in the data is reduced by eliminating 

measurements that have the poorest data fit. Multiple 

inversions were run with various reference models, data 

errors, and smoothing parameters in order to get a sense for 

the robustness, or stability, of the model results (Minsley and 

others, 2009).

Resistivity Survey Results

In general, resistivity values greater than 200 ohm-meters 

(ohm-m; fig. 14C) represented unsaturated sediments and 

bedrock, and resistivity values less than 200 ohm-m (fig. 14C) 

represented saturated sediments or unsaturated sediments 

with higher moisture content. The resistivity values less 

than approximately 40 ohm-m coincided with the measured 

depth of groundwater of 103 ft and 275 ft bls at sites 1 and 3, 

respectively (fig 14C). The high-resistivity values in the upper 

50 ft of Lines 1 and 2 were consistent with unsaturated sands 

and gravels described in lithologic logs and measured in the 

downhole geophysical logs for sites 1, 2, and 3. Resistivity 

values in two zones, between lateral distances of 700 ft 

and about 1,400 ft (Line 1) and between 5,400 and 5,600 ft 

(Line 2) along the profile, increased with depth across these 

zones, indicating vertical offset in the alluvium. Resistivity 

values indicative of saturated conditions (less than 40 ohmm) were also offset across the lateral zone between 700 ft and 

about 1,400 ft, indicating depth to water increases between 

site 1 and site 2. These offsets in alluvium and water level 

coincided with interpreted seismic faults and further supported 

the location of two fault zones along Amargosa Creek: fault C 

between sites 1 and 3 and fault B between sites 3 and 2 along 

the profile (fig. 14A).

Summary of Geophysical Surveys

The regional and local gravity data provided details of 

the subsurface topology in the study area, showing an alluvialfilled trough trending northeast from the ACRP, a buried 

basement ridge that trends north toward western Lancaster, 

and a buried plateau extending southeast of the ACRP toward 

Palmdale (fig. 12). Shallow-depth seismic refraction and 

reflection and resistivity surveys were completed along the 

Amargosa Creek to help delineate and visualize geologic 

structures that could affect groundwater flow. Consistent with 

observations from monitoring wells, the seismic velocity 

images indicated that the water table was in the upper 100 

ft of sediments west of fault C, at a depth of about 275 ft 

east of fault C, and at a depth of about 470 ft east of fault B. 

The seismic and resistivity data indicated that the basement 

complex is about 200 ft bls west of fault C. The seismic data 

indicated depth to basement ranges from approximately 500 

to 600 ft bls between Faults C and B and increases to greater 

than 600 ft east of fault B, which was similar to the gravitycalculated depth to basement complex. The seismic reflection 

images identified major disruptions in the basement interpreted 

as faults, which were not evident in the regional-gravity data 

because of the smoothing that resulted from averaging within 

cells that had 1,000-ft dimensions.

Geohydrologic Structure beneath the ACRP and 

Vicinity

A generalized geologic section was completed on the 

basis of the work of Leighton and Phillips (2003; fig. 3) and 

by using geophysical, drilling, and monitoring data collected 

as part of this study and using information from nearby wells 

(figs. 15 and 16).

For purposes of this study, the geologic units were 

generalized into pre-Tertiary igneous weathered and 

crystalline basement complex and Tertiary sedimentary units. 

Drill-cutting materials collected from the bottom of the holes 

during drilling of the monitoring sites consisted of pre-Tertiary 

weathered and crystalline quartz monzonite in the vicinity of 

the ACRP (figs. 5, 6, and 7).

Sedimentary deposits in the study area were grouped 

into five major sedimentary units: (1) continental sedimentary 

deposits (confined-lower aquifer), (2) very old lacustrine 

deposits (confining unit), (3) very old alluvial valley deposits 

(unconfined middle aquifer), (4) old alluvial valley deposits 

(unconfined-upper aquifer), and (5) young alluvial fan deposits 

(unsaturated; fig.16). These subdivisions reflect fundamental 

differences in porosity and permeability between the different 

deposits.

The geologic section also shows the location of three 

inferred faults: Faults A, B, and C (fig. 16). Fault A was 

inferred by Bloyd (1967) and is approximately 7,500 ft 

northwest of the ACRP. Fault B is a previously unmapped 

fault that is approximately 2,500 ft northwest of the ACRP. 

This fault location was based on water-level differences 

between sites 3 and 2 and geophysical data collected as part 

of this study. Fault C is also a previously unmapped fault that 

was located on the basis of water-level differences between 

site 1 and site 3 and geophysical data collected as part of this 

study. Fault C could be an extension of a previously mapped 

fault (California Geological Survey, 2002) approximately 1 mi 

southeast of site 1 (fig. 13).
34 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

sac11-0421_fig 15

A

A’

20R (Site 3)

21G (Site 2)

21A (34-5)

29B (Site 1)

15H (34-7)

AFP42 MW1

4-73

EXPLANATION

Fault A

Fault B

Fault C

0

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 METERS

5,000 10,000 15,000 20,000 25,000 FEET

21E1

Amargosa

Creek

118°12' 118°08' 118°04' 118°00'

34°

40'

34°

36'

R

O

W

COLUMN

Fault B

Fault C

A’

A

Well and identifier

California Aqueduct

Proposed recharge facility

Simulated mountain-front recharge

Simulated natural recharge

Area of

Simulated artificial recharge

Model domain

Active model cells

Inactive model cells

Section line

Inferred fault (Bloyd, 1967) 

Inferred fault (this study)

San Andreas fault zone 

San Gabriel Mts

Northern boundary

 

1

1

264

31

Base modified from U.S. Department of Agriculture National Agriculture

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

Figure 15. Line of section, model domain, model boundary location, type of boundary and location of Amargosa Creek Recharge 

Project, Antelope Valley, California.
Groundwater-Flow Models 35

sac11-0421_fig 16

1,000

1,500

2,000

2,500

3,000

Young alluvial

 fan deposits/

 Holocene to early

 Pleistocene

Old alluvial

 valley deposits/

 Pleistocene

 

Very old alluvial

 valley deposits/

 Pleistocene

Very old lacustrine

 deposits/Early Pleistocene

 to late Pleistocene

Tertiary continental

 sedimentary deposits/

 Pliocene to Miocene

pre-Tertiary basement

 complex

0 5,000 10,000 15,000 20,000

Distance along section, in feet

Elevation, in feet above sea level

25,000 30,000 35,000

A A’ (South) (North) 20R (Site 3) 20R (site 3) 21G (Site 2) 21A (34-5) 29B (Site 1)

Gravels and coarse sand

Inferred fault CInferred fault B 

Bloyd inferred fault A (1967)

Lacustrine deposits

Lower aquifer

Upper aquifer

Middle aquifer

? ?

?

15H (34-7)

AFP42 MW1

4-73

Bend insectionBend insection

Qoa

Qyf

Qvoa

Qvol

Tc

Qvoa

Qvoa

pTbc

Geologic units/Age Well

Qyf

Qoa

Qvoa

Qvol

Tc

pTbc

Water

table

Recharge facility

(1955)

(1978)

Perforated

interval

Resistivity log

EXPLANATION

Figure 16. Generalized geologic cross section for the Palmdale and Lancaster area, Antelope Valley, California.

Groundwater-Flow Models

Two numerical groundwater-flow models were developed 

to simulate the groundwater-flow system and the potential 

hydraulic effects of artificial recharge of imported water at 

the ACRP. The first, the local model, is a local-scale steadystate and transient model designed to determine if fault B 

is a barrier to groundwater flow and to estimate the fault 

conductance. The second model, the extended model, is a 

transient simulation designed for scenario-testing to estimate 

the maximum recharge flux that can be applied at the ACRP. 

Both models were developed on the same model grid and 

simulated aquifer properties. 

The models were developed by using the MODFLOWNWT formulation for MODFLOW-2005 (Niswonger and 

others, 2011). MODFLOW-NWT uses a finite-difference 

approach to simulate constant-density groundwater flow 

in three-dimensional heterogeneous porous medium 

(Harbaugh, 2005). The main difference between 

MODFLOW-2005 (Harbaugh, 2005) and MODFLOW-NWT 

is that the latter includes a Newton-type solver that allows 

a numerically stable simulation of drying and rewetting 

conditions (Niswonger and others, 2011).

The MODFLOW-NWT packages used in these models 

included Basic (BAS6), Discretization (DIS), Upstream 

Weighted Package (UPW), Recharge (RCH), Specified 
36 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

Time-Variant Head (CHD), and Well (WEL) Packages. The 

system solver in MODFLOW-NWT was used both for steadystate and transient simulations (Niswonger and others, 2011).

Local Model: Evaluation of Fault B

The local model was constructed to help determine if 

fault B is a barrier to groundwater flow and to estimate fault 

properties using both steady-state and transient simulations.

Spatial Discretization

The local model domain, designed for steady-state model 

calibration and transient simulation to determine properties of 

fault B, covers approximately 11.7 mi2 along Amargosa Creek 

(fig. 15). The southwestern boundary is sub-parallel to the San 

Andreas fault zone, about 0.1 mi southwest of site 1 (fig. 15). 

The northern boundary is parallel to the southwest boundary, 

about 200 ft southwest of site 2 and about 1.2 mi northeast 

of the southwest boundary. The other two boundaries are 

perpendicular to these boundaries and about 5 mi from where 

Amargosa Creek enters the southwestern model boundary. 

The region southwest of the inferred fault C was not simulated 

because of the limited unsaturated storage available for 

artificial recharge.

The active area of the local model (fig. 15) included 

alluvial valley deposits (Qoa and Qvoa, fig. 16). Because 

the younger alluvial fan deposits (Qyf, fig. 16) were above 

the water table in the solution, this unit was not included 

in the simulation. The local model consisted of one model 

layer because groundwater flow was assumed to be primarily 

horizontal through the old alluvial valley deposits (Qoa and 

Qvoa, layer 2 in fig. 17). The model domain was discretized 

into a 31-row by 264-column grid having 200-ft by-200 ft 

computational cells (fig. 15). Land-surface elevation for the 

top of the model was extracted from 10-meter (m) National 

Elevation Dataset (Gesch, 2007) data at model-cell centers. 

The resulting land-surface elevations in the model domain 

ranged from about 2,840 ft along the foothills west of 

Palmdale and along Amargosa Creek to about 2,700 ft along 

Amargosa Creek at the northern boundary (fig. 17, note that 

1,000

1,500

2,000

2,500

3,000

0 5,000 10,000 15,000 20,000

Distance along section, in feet

Elevation, in feet above sea level

25,000 30,000 35,000

A A’ (South) (North) Fault C Fault B Fault A

Layer 1

Layer 2

Not simulated

Layer 1

Layer 2

Not simulated

pre-Tertiary basement

 complex

Model units

Qoa

Qyf

Qvoa

Qvol

Tc

Geologic

units

from

figure 15

Approximate extent

of local model

EXPLANATION

Figure 17. Simplified geologic cross section used for model simulations beneath the Amargosa Creek Recharge Project and vicinity, 

Antelope Valley, California.

fi
Groundwater-Flow Models 37

the simplified geologic section shown on figure 16 is A-A’ 

shown on figure 15). The bottom elevation of the model 

domain was assumed to be the bedrock complex indicated 

by the valley-fill thickness model and by data collected from 

construction of the monitoring sites (figs. 16 and 17). The 

bottom elevation of the active model domain varied from 

about 2,200 ft along Amargosa Creek at the northeastern 

boundary to 2,700 ft along the southwestern boundary near the 

mountain front (fig. 17). The thickness of the model ranged 

from about 100 ft along the mountain-front of the western 

active boundary to about 550 ft along the Amargosa Creek at 

the northeastern boundary.

Temporal Discretization

Model simulation and calibration of the local model was 

done using combined steady-state and transient simulations 

to evaluate fault B. The steady-state simulation represented 

historical (pre-1924) pre-development conditions. The 

resulting steady-state hydraulic head distribution was used as 

an initial condition for a transient simulation that extended 

from 1924 to 2010 and used annual stress periods.

Model Boundaries

The local model contained two types of boundary 

conditions: specified flux and specified head. Specified-flux 

boundaries represent stream and mountain-front recharge, 

and no-flow boundaries are where zero-flux conditions exist 

(fig. 15). The specified-head boundary was based on observed 

water levels in wells in the Palmdale area.

Specified-Flux Boundaries

Natural mountain-front recharge was assumed to 

be constant during the steady-state and the transient 

simulations. Estimates of natural recharge associated with 

the Amargosa Creek drainage basin were estimated by 

using the results from a previous application of the Basin 

Characteristic Model (BCM, Flint and Flint, 2007) The BCM 

is a distributed-parameter water-balance model that uses 

topography, soils, geology, and vegetation, together with 

monthly time-series of precipitation and air-temperature data 

along with other information to generate regional runoff 

and recharge estimates by area or basin. Results from the 

BCM indicated that mountain-front recharge, represented 

by the average discharge from Leona Valley as underflow, is 

about 1,100 acre-ft/yr and that stream recharge, represented 

by the average discharge from Leona Valley through 

Amargosa Creek, is about 200 acre-ft/yr, resulting in about 

1,300 acre-ft/yr of recharge to the model area. Both for steadystate and transient simulations, delays associated with flow 

through the unsaturated zone were assumed to be negligible 

and were not simulated; natural mountain-front and stream 

recharge were simulated by directly applying recharge water 

to model cells. The mountain-front recharge was applied 

uniformly along the area shown in figure 15, and the stream 

recharge was applied uniformly along the Amargosa Creek 

channel near the mountain front by using the well package 

in the form of injection wells at the node centers (see fig. 15

inset).

Specified-Head Boundaries

The entire northern boundary was a specified-head 

boundary assigned values on the basis of water levels in wells 

in the Palmdale and Lancaster area. The pre-development 

(pre-1924) water level was approximately 2,400 ft and 

was assumed to be uniform in the study area east of 

fault B (Leighton and Phillips, 2003). For this simulation, 

the hydraulic gradient across fault A at pre-development 

was assumed to be negligible, such that the water level at 

the northern boundary of the model was 2,400 ft at an early 

time. Water-level measurements in 2009 and 2010 at site 

2 (just north of fault B) indicated that water levels were 

about 2,225 ft (figs. 8 and 15). Therefore, the specified-head 

boundary was defined so that head varied linearly from 

2,400 ft in 1924 to 2,225 ft in 2010. Although the change 

in water-levels might not have been linear during the entire 

period, this boundary condition represented a reasonable 

approximation of actual conditions and avoided sharp changes 

in boundary conditions that could have produced instabilities 

in the numerical simulations.

Hydraulic Properties

Aquifer properties assigned to each model cell, such as 

horizontal hydraulic conductivity, specific yield, and specific 

storage, affect the rate at which groundwater moves through 

an aquifer, the volume of water in storage, and the rate and 

areal extent of water-level rise caused by artificial recharge. 

Horizontal hydraulic conductivity, specific yield and specific 

storage were specified by using the UPW package (Niswonger 

and others, 2011). As stated earlier, fault B is a hydraulic 

barrier to groundwater flow, and the fault was simulated as a 

narrow region of low horizontal permeability between model 

cells. The horizontal hydraulic conductivity for the region 

north of fault B (fig. 15) was assumed to be 7 feet per day 

(ft/d); this value was based on the published value by Leighton 

and Phillips (2003) of 5 ft/d and on an aquifer test performed 

by RCS Consulting (written commun., 2011) indicating 

values ranged from about 5 to 7 ft/d. The horizontal hydraulic 

conductivity for the region south of fault B was assumed to 

be 10 ft/d on the basis of Leighton and Phillips (2003) and of 

data collected during the drilling of monitoring sites 1 and 3. 

The model was specified as unconfined; the hydraulic property 

quantifying storage, therefore, was the specific yield. The 

specific yield (Sy) is defined as the volume of water released 

from storage in an unconfined aquifer for each unit surface 

area of the aquifer for each unit decline in head (Lohman, 

1972). The specific yield of the entire model was set to 0.14 on 

basis of the work of Leighton and Phillips (2003).
38 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

During initial calibration, the local model was assumed 

to be horizontally homogeneous in order to determine if 

historic water-level data could be simulated without using 

horizontal-flow barriers, as if fault B did not exist. Simulations 

were completed by varying values of horizontal hydraulic 

conductivity in an attempt to match the historical water-level 

data. Results from these simulations showed that even with 

unrealistically low values of horizontal hydraulic conductivity 

for the entire layer 2 (below 1.5 ft/d), the model results did 

not match the historic data; therefore, fault B was included 

in the simulation by assigning a low value (0.05 ft/d) for the 

horizontal hydraulic conductivity along the corresponding row 

of model cells.

Model Calibration

Hydraulic conductivity and storage values of the porous 

medium were obtained from previous work and were based 

on inspection of geologic samples collected during drilling 

of the monitoring sites. Only the horizontal hydraulic 

conductivity of fault B was estimated. The water-level data 

from abandoned well 6N/12W-21E1 (21E1) and from site 

3 (fig. 15) were compared with corresponding simulated 

values. Water-level measurements collected at 21E1 showed a 

water-level elevation of 2,365 ft in late 1941, and subsequent 

measurements were dry. For calibration purposes, the dry 

measurements were assumed to be an indication of the water 

table dropping below the bottom of the well. The water-level 

elevation at site 3 was 2,455 ft in early 2011, which was 

considered representative of conditions in 2010. These two 

observations were used to calibrate the model by varying the 

horizontal hydraulic conductivity of model cells along fault 

B. The hydraulic conductivity of fault B was estimated to be 

about 0.05 ft/d.

Extended Model: Artificial-Recharge Scenarios

The purpose of the extended model was to estimate rates 

of recharge at the proposed recharge facility by using test 

scenarios and to determine how estimated rates of recharge 

affect the water table in the study area. To accomplish this, the 

domain of the model was extended to minimize the effects of 

boundary conditions on model results. The model domain was 

extended about 6.5 mi northeastward, such that the northwest 

corner of the extended model was north of the city of 

Lancaster (fig. 18). Artificial-recharge scenarios were designed 

to estimate the maximum 20-year recharge rates on the basis 

of a range of horizontal conductivity values determined 

from lithologic information obtained during drilling of the 

monitoring wells and from previously reported values. To 

address concerns for liquefaction, a liquefaction constraint 

based on the work of Martin and Lew (1999) was defined such 

that water levels cannot rise within 50 ft of land surface in the 

model domain, except beneath the proposed artificial-recharge 

facility.

Spatial Discretization

The extended model consisted of a 203-row by 

264-column grid with 200-ft by 200-ft cells. Two model layers 

were specified in order to simulate artificial-recharge scenarios 

in which the water table rises into the coarse-grained, more 

permeable gravels and coarse sand associated with young fan 

deposits (Qyf; figs. 16 and 17). 

Layer 1 comprises the fan deposits, with a thickness 

assumed to be about 150 ft in the model domain; therefore, 

the bottom elevation of model layer 1 was defined as land 

surface minus 150 ft. Land-surface elevation for the top of 

model layer 1 in the extended model was extracted from 10-m 

National Elevation Dataset 2009 data at model cell centers 

(Gesch, 2007). Land-surface elevations for the extended 

model range from about 2,840 ft along the foothills west of 

Palmdale and along Amargosa Creek to about 2,320 ft at the 

northwest corner of the model near Lancaster. The bottom 

elevation of layer 1 varies from 2,690 to 2,170 ft. 

Model layer 2 represents the lower part of the upper 

aquifer and the middle aquifer, consisting of older, less 

permeable material composed of old and very old alluvial 

deposits (Qoa and Qvoa); it extends from the bottom of layer 

1 to the bottom of the model domain (fig. 15 and 16). The 

bottom of the model domain was assumed to be either the 

bedrock complex or the extremely low-permeability blue clay 

of the lacustrine deposits (Qvol), whichever is shallowest 

(fig. 15 and 16). Because of the extremely low permeability 

of these units, they were not simulated (Leighton and Phillips, 

2003). The thickness of layer 2 ranges from about 10 to 150 ft 

along the mountain front to about 1,000 ft near the center of 

the model domain.

Temporal Discretization

Artificial-recharge scenarios were simulated by using a 

combined steady-state and transient simulation. The steadystate simulation represented conditions in 2011, prior to the 

application of SWP recharge water. This approach assumed 

that the system was in a state of equilibrium in 2011. This is 

not completely valid because the Antelope Valley groundwater 

basin was in a state of overdraft by 2003 (Leighton and 

Phillips, 2003). The effects of regional water-level declines 

on groundwater levels local to the ACRP have been gradual 

and have diminished during recent years; therefore, the local 

system near the ACRP was assumed to be in an approximate 

state of equilibrium. For the purposes of this study, the 

primary objective of which was to estimate the system 

response to artificial-recharge operations at the ACRP, the 

consequences of the steady-state assumption were minimal; 

relative changes in water levels were more important than 

their absolute magnitudes. Water levels change during the 

transient simulation only if artificial recharge is applied, which 

was consistent with the objective of this study. 
Groundwater-Flow Models 39

The hydraulic-head distribution of the steady-state 

simulation was used as the initial condition for the transient 

simulation. The transient simulation began in January 2012 

and ended in December 2031, totaling 520 biweekly stress 

periods.

Model Boundaries

The extended groundwater-flow model contains two 

types of boundary conditions: specified flux and specified 

head. Three specified-flux boundaries represent natural 

recharge, artificial recharge, and no-flow, or zero-flux (fig. 15). 

Specified-head boundaries were based on the 2011 water 

levels measured in wells along the northeastern boundary.

Specified-Flux Boundaries

Natural mountain-front recharge and natural stream 

recharge were the same as in the local model, about 

1,100 acre-ft/yr and 200 acre-ft/yr, respectively. For all 

simulations, delays associated with flow through the 

unsaturated zone were assumed to be negligible; mountainfront and artificial recharge were applied directly to the water 

table. Artificial recharge was applied to the upper most active 

layer and was assumed to be constant during the 20-year 

simulation. The artificial-recharge cells were located at the 

proposed recharge facility (fig. 15 inset). A model cell was 

considered an artificial-recharge cell if at least half of the cell 

was contained within the proposed recharge facility boundary. 

Recharge was applied uniformly over these cells.

Specified-Head Boundaries

The northeastern boundary for the extended model was a 

specified-head boundary condition (fig 18). The head specified 

at this boundary was constant at 2,150 ft, which was based 

on average water-level observations in 2009 at wells along 

the boundary (fig. 8). This temporally constant specified-head 

assumption did not consider the downward trend in 

water-levels in the regional basin that started the early 1900s 

(Leighton and Phillips, 2003). If this trend continues, it could 

increase the hydraulic gradient and associated groundwater 

flow across the faults, resulting in an increase in the maximum 

volume of potential artificial recharge at the ACRP site.

Simulated Faults

The extended model domain included fault A (figs. 14, 

15, and 16), described by Bloyd (1967). Similar to fault B, 

fault A was simulated by lowering the horizontal hydraulic 

conductivity of a row of model cells at the appropriate 

locations (fig. 17 and 18). The hydraulic conductivity of fault 

A required an additional calibration phase for the extended 

-domain steady-state model representing 2011 conditions. 

The hydraulic conductivity of fault B was the same as the 

calibrated values derived from the local model.

Hydraulic Properties

The same aquifer properties used in the steady-state local 

model were initially assigned to each model cell in the steadystate extended model. Both model layers were assumed to be 

convertible; that is, they can be either confined or unconfined 

depending on the elevation of the water table. Faults A and B 

were considered potential hydraulic barriers to groundwater 

flow; these faults were simulated as narrow regions of low 

conductivity. The horizontal hydraulic conductivity for layer 2 

in the portion of the model north of fault A was assumed to be 

homogeneous at 7 ft/d. The horizontal hydraulic conductivity 

of layer 2 in the region south of fault A remained 10 ft/d. The 

vertical hydraulic conductivity for all simulations was 1 ft/d.

The specific yield of layers 1 and 2 for the entire model 

remained 0.14, and the specific storage remained 10-6 ft-1. At 

the initial condition, layer 1 was completely dry, and therefore, 

layer 2 was completely unconfined. Model cells in layer 2 

only become confined in areas where the water level rises 

high enough to wet layer 1. Furthermore, layer 1 is always 

unconfined because of the liquefaction constraint of 50 ft 

below the top of the cell. Therefore, the specific storage of 

layer 1 is never used, and the specific storage of layer 2 is only 

used for a small portion of the model near the ACRP. As a 

result, the model is not sensitive to values of specific storage.

Model Calibration

The properties of model layer 1 cannot be calibrated 

because the entire model layer was dry at steady state. 

Therefore, the extended model contained only one additional 

parameter to be estimated—the hydraulic conductivity of fault 

A. The observation data consisted of the measured water level 

altitude at site 2 (about 2,225 ft in 2010) and the measured 

water level altitude at site 3 (about 2,455 ft in 2011). This 

calibration was performed manually using the steady-state 

(2011) simulation; the resulting hydraulic head distribution 

was used as the initial head distribution for transient-statemodel simulations of artificial-recharge potential at the ACRP 

site. The calibrated hydraulic conductivity of fault A was 

1.4 ft/d.

Model Results

The transient version of the extended model was 

used to determine how a range of possible horizontal 

conductivity values would affect the long-term volume of 

applied artificial recharge at the proposed recharge facility. 

The amount of water that can be recharged at the proposed 

artificial-recharge facility depends greatly on the horizontal 

hydraulic conductivity of layer 1, which represents the porous 

medium within 150 ft of the land surface. For this study, 

two layer-1 horizontal hydraulic conductivity values were 

tested: 10 (scenario 1) and 100 ft/d (scenario 2). The value 

of 10 ft/d was based on the work of Leighton and Phillips 

(2003) from deeper materials in (Qoa) layer 1. Previous 
40 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

sac11-0421_fig 18

Proposed recharge facility

Specified-head boundary

No-flow boundary

Model domain

for extended

model

EXPLANATION

Model domain

Active model cells

Inactive model cells

Palmdale

Lancaster

No-flow

boundary

No-flow boundary

R

O

W

COLUMN

Fault A

Fault B

Fault C

Base modified from U.S. Department of Agriculture National Agriculture

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

Amargosa Creek

118°12' 118°08' 118°04' 118°00'

34°

40'

34°

36'

0

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 METERS

5,000 10,000 15,000 20,000 25,000 FEET

California Aqueduct

Simulated fault A

Simulated fault B

Simulated fault C

San Gabriel Mts

1

203

1

264

Figure 18. Extended model domain, model boundary location, type of boundary and location of Amargosa Creek Recharge Project, 

Antelope Valley, California.
Groundwater-Flow Models 41

work of Leighton and Phillips did not simulate the young 

alluvial fan deposits because they were unsaturated because 

of dewatering early in the simulation period. The value of 

100 ft/d was based on the analysis of drill cuttings collected 

during drilling of the monitoring sites. As stated previously, 

the materials encountered in the upper 150 ft in the vicinity 

of the recharge facility were mainly clean sands and coarse 

gravels interbedded with silty sands; a horizontal conductivity 

value of 100 ft/d was consistent with these coarse-textured 

materials (Freeze and Cherry, 1979). In general, simulation 

results from scenario 1 indicated that the lower value of 

horizontal hydraulic conductivity in layer 1 slowed the lateral 

spread of recharge water, causing groundwater mounding near 

the ACRP. At a horizontal conductivity of 10 ft/d, simulated 

artificial-recharge rates exceeding 3,400 acre-ft/yr caused 

water levels surrounding the ACRP to rise within 50 ft of 

land surface (which was the selected liquefaction constraint). 

Artificial recharge at the ACRP must then be halted or reduced 

to prevent further water-level rise. In general, simulation 

results from scenario 2 indicated that the greater horizontal 

hydraulic conductivity (100 ft/d) in layer 1 would allow 

greater lateral spreading of artificial-recharge water, reducing 

the mounding effect. As a result, artificial recharge of up 

to 9,400 acre-ft/yr could be applied before the liquefaction 

constraint is reached in the scenario 2 simulation. 

Assuming hydraulic conductivities for model-layer 1 of 

10 and 100 ft/d, the maximum artificial-recharge rates were 

approximately 3,400 and 9,400 acre-ft/yr for the scenario 1 

and 2 20-year simulations, respectively. Figures 19 and 20

show the distribution of increases in hydraulic head at the 

end of the 20-year simulations for values of 10 and 100 ft/d 

for layer-1 hydraulic conductivity, respectively. As expected, 

greater recharge rates and hydraulic conductivities caused an 

increase in head further into the valley. The simulated-head 

increases for scenario 1 extended radially about 4 mi from 

the ACRP toward western Palmdale and southern Lancaster 

(fig. 19); for scenario 2, the head increase extended about 6 mi 

(fig. 20).

Using a hydraulic conductivity value of 10 ft/d resulted 

in the greatest rise in simulated hydraulic head beneath the 

recharge facility. The rise resulted from the low hydraulic 

conductivity preventing the water from spreading laterally 

from recharge facility to a greater degree during the 20-yr 

simulation period (fig. 19). Using a hydraulic conductivity 

value of 100 ft/d resulted in the greatest rise in simulated 

hydraulic head in the cells just north of fault B along 

Amargosa Creek (fig. 20). This rise resulted from increased 

recharge and lateral flow in layer 1, which mounded first at the 

south side of fault B. This mounding increased the hydraulic 

gradient across the fault, resulting in greater flow across the 

fault and in increased water levels on both sides of the fault. 

Additionally, at the end of scenario 2, the model cells in layer 

1 directly above fault B became active, or wet, indicating that 

flow could eventually go over the top of the fault through the 

more permeable materials of layer 1. The area affected by 

recharge down-gradient from the ACRP in scenario 2 was also 

approximately 50 percent larger than that in scenario 1. Based 

on a 20-year simulation period and hydraulic conductivities 

of 10 and 100 ft/d, the estimated maximum total artificialrecharge volume to the Antelope Valley groundwater basin 

using the ACRP was between 68,000 and 188,000 acre-ft 

(3,400–9,400 acre-ft/yr).

Limitations and Appropriate Use of the Models

The groundwater-flow models were developed to 

understand the groundwater-flow system better in the 

vicinity of the ACRP and to estimate potential recharge rates. 

Limitations of the modeling software, assumptions made 

during model development, and the focus and robustness of 

model calibration are factors that constrain the appropriate use 

of these models and point to potential improvements.

A numerical groundwater-flow model is a simplified 

representation of the actual groundwater-flow system. 

The models are based on simplifying assumptions and 

approximations, and, therefore, they do not exactly represent 

the inherent complexity of the geohydrologic framework. 

The results of model simulation are only an approximation 

or estimation of actual conditions and are only as accurate or 

realistic as the assumptions and data used in its development. 

Assumptions used to develop the models in this study 

included the following:

• Both models assumed that historical groundwater 

pumping did not cause aquifer deformation or 

compaction.

• Both models assumed active tectonism did not affect 

the groundwater-flow system during the model 

simulations.

• Both models assumed the older sedimentary deposits 

and crystalline basement rocks that underlie the study 

area did not contribute groundwater to the flow system.

• In the extended model, simulated water levels were not 

allowed to rise to within 50 ft of land surface to avoid 

potential liquefaction.

A steady-state model portrays a system that is in 

equilibrium. The work of Leighton and Phillips (2003) 

showed a general downward trend in the hydraulic head since 

the early 1900s. Long-term hydrographs were not available 

for some areas in the study area, including the southeastern 

part of the model area near Palmdale, where hydraulic heads 

could have changed over time. There were no long-term 

water-level records available for the local model area; water 

levels in the closest wells (within 5 mi) showed little change 

since the mid-1980s. Although many water-level hydrographs 

showed a general decline in the study area over time, the 

objective of the study was to determine the potential relative 

effects of artificial recharge at the ACRP. Errors related to the 

assumption of a steady-state condition could be important in 

places; however, this approach results in reasonable estimates 

of potential artificial-recharge rates. 
42 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

sac11-0421_fig19

118°20' 118°10' 118°00'

34°

40'

34°

30'

0 5 10 MILES

0 5 10 KILOMETERS

No change

0 to 10

>10 to 20

>20 to 30

>30 to 40

>40 to 50

>50 to 60

>60 to 70

>70 to 80

>80 to 90

>90 to 100

>100 to 110

>110 to 120

>120 to 130

>130 to 140

>140 to 150

>150 to 160

>160 to 170

>170 to 180

>180 to 190

>190 to 200

>200 to 210

>210 to 220

>220 to 230

>230 to 240

>240 to 250

Palmdale

Lancaster

Change in

water-level altitude

Fault C

Fault B

Fault A

Proposed recharge facility

EXPLANATION

Model domain

Active model cells

Inactive model cells

Base modified from U.S. Department of Agriculture National Agriculture

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

California Aqueduct

San Andreas fault zone

Simulated fault A

Inferred fault

Figure 19. Scenario 1, change in head after 20-year artificial-recharge simulation, assuming that layer 1 hydraulic conductivity was 

equal to 10 feet per day and an artificial-recharge rate of 3,400 acre-feet per year, Antelope Valley, California.
Groundwater-Flow Models 43

sac11-0421_fig 20

118°20' 118°10' 118°00'

34°

40'

34°

30'

Palmdale

Lancaster

Change in

water-level altitude

No change

0 to 10

>10 to 20

>20 to 30

>30 to 40

>40 to 50

>50 to 60

>60 to 70

>70 to 80

>80 to 90

>90 to 100

>100 to 110

>110 to 120

>120 to 130

>130 to 140

>140 to 150

>150 to 160

>160 to 170

>170 to 180

>180 to 190

>190 to 200

>200 to 210

>210 to 220

>220 to 230

>230 to 240

>240 to 250

>250 to 260

>260 to 270

>270 to 280

>280 to 290

>290 to 300

>300 to 310

>310 to 320

>320 to 330

Fault C

Fault B

Fault A

0 5 10 MILES

0 5 10 KILOMETERS

Proposed recharge facility

EXPLANATION

Model domain

Active model cells

Inactive model cells

Base modified from U.S. Department of Agriculture National Agriculture

Imagery Program (NAIP) and other Federal digital data, various scales

Universal Transverse Mercator, zone 11

North American Datum of 1983

Amargosa Creek

California Aqueduct

San Andreas fault zone

Simulated fault A

Inferred fault

Figure 20. Scenario 2, change in head after 20-year artificial-recharge simulation, assuming that layer 1 hydraulic conductivity was 

equal to 100 feet per day and an artificial-recharge rate of 9,400 acre-feet per year, Antelope Valley, California.
44 Feasibility and Potential Effects of the Proposed Amargosa Creek Recharge Project

Future improvements to the extended model could 

result from (1) completion of additional wells or borings to 

document the lateral extent of the coarse materials in the 

upper 150 ft; (2) additional wells completed to the water 

table between Faults A, B, and C to help determine gradients 

between or across faults; (3) unsaturated-zone monitoring sites 

near the proposed recharge facility to monitor or to document 

flow through, and storage in, the unsaturated zone; and (4) a 

pilot recharge test or documented natural recharge event 

coupled with monitoring to document the response to recharge 

in the vicinity of the proposed recharge facility. Results from 

all or some of these possible actions can be used to improve 

and recalibrate the extended model, which can, in turn, 

improve the quality of results from model simulations or from 

management decisions derived from model simulations.

Summary and Conclusions

Historically, the city of Palmdale and vicinity have relied 

on groundwater as the primary source of water, owing, in 

large part, to the scarcity of surface water in the region. Since 

1972, supplemental surface water has been imported from 

the State Water Project (SWP) to help meet the demand for 

water. Despite the importation of surface water, groundwater 

withdrawal for municipal, industrial, and agricultural use 

has resulted in ground-water-level declines near the city of 

Palmdale in excess of 200 feet (ft) since the early 1900s. To 

help meet the growing demand for water in the area, the city 

of Palmdale has proposed the Amargosa Creek Recharge 

Project (ACRP). Water delivered by the SWP through the 

California Aqueduct will be used to fill percolation basins at 

the site. The city of Palmdale is concerned about the effects 

of artificial recharge on groundwater levels near the recharge 

facility and, because of the proximity of the recharge facility 

to the San Andreas fault zone, the potential presence of 

faults that could act as groundwater barriers and impede the 

downgradient movement of recharge to the aquifer system 

underlying the Palmdale area.

Several methods were used to help describe the 

basement geometry and thickness of valley-fill deposits and to 

identify possible features, such as faults, that could influence 

groundwater flow. These methods included regional gravity 

surveys, seismic refraction and reflection surveys, resistivity 

surveys, test borings completed with monitoring wells, data 

collected from the monitoring wells, and the development 

of a numerical groundwater-flow model to simulate the 

groundwater-flow system and the potential effects of artificial 

recharge.

The regional gravity data provided details of the 

subsurface topology in the study area and showed an alluvialfilled trough trending northeast from the ACRP, a buried 

basement ridge that trends north toward Lancaster, and a 

buried plateau extending southeast of the ACRP toward 

Palmdale. Shallow-depth seismic refraction and reflection 

surveys and resistivity surveys along the Amargosa Creek 

identified major disruptions in the basement that were 

interpreted as faults, but were not evident in the regional 

gravity data. Differences in water levels across the faults 

indicated they are partial barriers to groundwater flow.

In general, water samples collected from sites 1, 2, and 

3 indicated that the groundwater near the ACRP is of good 

quality. Concentrations of common groundwater constituents 

of concern, including nitrate plus nitrite, fluoride, and arsenic, 

were below U.S. Environmental Protection Agency maximum 

contaminant levels in samples collected from sites 1, 2, and 3. 

Selected volatile organic compound concentrations were all 

below detection limits for samples collected from sites 1 and 

2. Stable-isotope data indicated that the source of water for 

wells at sites 1 and 3 was consistent with water found in Leona 

Valley, upstream in the Amargosa Creek watershed. This 

was consistent with carbon and tritium values that indicated 

water recharged since the 1950s at site 1, and a mixture of 

water recharged since the 1950s with older water at site 3. 

Stable isotope, 14C values, and trace detection of tritium in 

water collected at site 2, downstream of the ACRP along the 

Amargosa Creek and on the northeast side of fault B, indicated 

that groundwater at this site is similar to groundwater 

collected from the Antelope Valley groundwater basin and that 

modern-day recharge is not a major source for this well.

A local groundwater-flow model was used to estimate 

the hydraulic conductivity of fault B in the model domain. 

The extended groundwater-flow model was developed to 

simulate the groundwater-flow system and the potential 

effects of artificial recharge of imported water at the ACRP. 

The amount of water that can be recharged at the proposed 

artificial-recharge facility depended largely on the hydraulic 

conductivity of the coarse material closer to the land surface 

(upper 150 ft for the extended-model layer 1). The range 

for hydraulic conductivity of layer 1 was estimated to be 

between 10 and 100 feet per day (ft/d) on the basis of previous 

work and data collected as part of this study. A liquefaction 

constraint was set so that water levels cannot rise within 

50 ft of land surface in the model domain, except for the 

area directly beneath the proposed artificial-recharge facility. 

Assuming hydraulic-conductivity values of 10 (scenario 

1) and 100 ft/d (scenario 2), the calculated maximum 

artificial‐recharge rates were 3,400 and 9,400 acre-feet per

year (acre-ft/yr), respectively. Scenario 2 results showed 

elevated heads in an area 50 percent larger than the scenario 

1 results. Based on a 20-year simulation period and hydraulic 

conductivities of 10 and 100 ft/d, the estimated maximum total 

artificial-recharge volume to the Antelope Valley groundwater 

basin using the ACRP was between 68,000 and 188,000 acre-ft 

(3,400–9,400 acre-ft/yr).
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Allen H. Christensen, Siade, A.J., Martin, Peter, Langeheim, V.E., Catchings, R.D., and Burgess, M.K.—Feasibility and Potential Effects of the Proposed 

Amargosa Creek Recharge Project, Palmdale, California—Scientific Investigations Report 2015–5054

ISSN 2328-0328(online) 

http://dx.doi.org/10.3133/SIR20155054