Use of Water-Quality Indicators and

Environmental Tracers to Determine the

Fate and Transport of Recycled Water in

Los Angeles County, California

By Robert Anders and Roy A. Schroeder

Sacramento, California

2003

Water-Resources Investigations Report 03-4279

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

WATER REPLENISHMENT DISTRICT OF SOUTHERN CALIFORNIA 5005-12
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

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

not imply endorsement by the U.S. Government.

For additional information write to:

District Chief

U.S. Geological Survey

Placer Hall, Suite 2012

6000 J Street

Sacramento, CA 95819-6129

http://ca.water.usgs.gov
Contents iii

CONTENTS

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

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

Artificial Recharge Using Wastewater........................................................................................................ 2

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

Purpose and Scope ...................................................................................................................................... 3

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

Acknowledgments....................................................................................................................................... 4

Field and Analytical Methods .............................................................................................................................. 8

Production Wells Adjacent to Spreading Grounds ..................................................................................... 8

Downgradient Monitoring Wells ................................................................................................................ 11

Water-Quality Indicators and Environmental Tracers ......................................................................................... 16

Production-Well Results ............................................................................................................................. 16

Statistical Relations............................................................................................................................ 16

Nonparametric Test................................................................................................................... 16

Graphical Representation.......................................................................................................... 29

Two-Member Mixing Models for Selected Constituents .................................................................. 30

“Excess” Chloride and Boron ................................................................................................... 31

Boron Isotopes .......................................................................................................................... 33

Nitrogen Isotopes...................................................................................................................... 33

Organic Constituents................................................................................................................. 36

Tritium and Well-Water Ages............................................................................................................ 36

Multiple-Well Monitoring-Site Results ...................................................................................................... 41

Tritium/Helium-3 Age Determinations.............................................................................................. 51

Tracers of Recycled Water................................................................................................................. 54

Chloride and Boron................................................................................................................... 54

Nitrogen .................................................................................................................................... 58

Dissolved Gases ........................................................................................................................ 62

Chlorofluorocarbons ................................................................................................................. 68

Summary and Conclusions................................................................................................................................... 74

References Cited .................................................................................................................................................. 75

Appendixes........................................................................................................................................................... 79

A: Relation between percent recycled water and 22 selected wastewater constituents for each 

of the 23 production wells located in Los Angeles County, California ......................................... 80

B: Relation between percent recycled water in each of the 23 production wells located in Los 

Angeles County, California, for 22 selected constituents .............................................................. 92
iv Figures

FIGURES

Figure 1. Maps showing location of the study area in Los Angeles County, California, and a 

photograph of the Rio Hondo Coastal Basin Spreading Grounds in the Montebello 

Forebay, looking south toward the Pacific Ocean ............................................................................. 5

Figure 2. Graph showing source and amount of water recharged at the Rio Hondo and San Gabriel

Coastal Basin Spreading Grounds, Los Angeles County, California ................................................ 6

Figure 3. Graph showing percentages of water recharged at the Rio Hondo and San Gabriel

Coastal Basin Spreading Grounds, Los Angeles County, California ................................................ 7

Figure 4. Map showing location of 23 production wells near the spreading grounds, background 

production well upgradient from the Whittier Narrows, and the research site, 

Los Angeles County, California ........................................................................................................ 9

Figure 5. Graph showing depth and perforated interval of selected production wells in Los Angeles

County, California ............................................................................................................................. 10

Figure 6. Map showing location of multiple-well monitoring sites and line of hydrogeologic 

section A–A' along approximate ground-water flow path.................................................................. 12

Figure 7. Graph showing estimates of recycled-water percentages in selected production wells 

based on “excess” chloride and “excess” boron values, Los Angeles County, 

California ........................................................................................................................................... 32

Figure 8. Graph showing boron-isotope ratios and “excess” chloride values in selected production 

wells, Los Angeles County, California.............................................................................................. 34

Figure 9. Graph showing nitrogen-isotope ratios and nitrate concentrations in selected

production wells, Los Angeles County, California............................................................................ 35

Figure 10. Graph showing relation between “back-calculated” nitrogen concentration and

“excess” chloride values in selected production wells, Los Angeles County, California ................. 37

Figure 11. Graph showing estimates of recycled water in selected production wells based on 

ultraviolet absorbance and fluorescence, Los Angeles County, California ....................................... 38

Figure 12. Graph showing specific ultraviolet absorbance and fluorescence in selected production

wells, Los Angeles County, California.............................................................................................. 39

Figure 13. Graph showing extrapolated standard linear regression lines from selected productionwell data and concentration in recycled water for ultraviolet absorbance (UV), fluorescence,

and ethylenediaminatetraacetic acid (EDTA), Los Angeles County, California............................... 40

Figure 14. Graph showing relation between tritium concentration in wells and stratigraphicestimated traveltimes between spreading grounds and production wells, Los Angeles 

County, California ............................................................................................................................ 42

Figure 15. Diagram showing tritium concentration in 5 multiple-well monitoring sites and

tritium/helium-3 ages in 16 monitoring wells along ground-water flow path, 

Los Angeles County, California ........................................................................................................ 53

Figure 16. Graph showing relation between tritium/helium-3 ages and depth of the monitoring 

wells adjacent to the San Gabriel and Rio Hondo Coastal Basin Spreading Grounds, 

Los Angeles County, California ........................................................................................................ 55

Figure 17. Diagram showing chloride and boron concentrations in multiple-well monitoring 

sites along ground-water flow path, Los Angeles County, California............................................... 56

Figure 18. Graph showing estimates of recycled water in multiple-well monitoring sites based 

on “excess” chloride and “excess” boron values, Los Angeles County, California.......................... 57

Figure 19. Graph showing tritium/helium-3 age determinations and recycled-water percentages in

multiple-well monitoring sites based on “excess” chloride values, Los Angeles County, 

California ........................................................................................................................................... 59
Figures v

Figure 20. Graph showing relation between “back-calculated” nitrogen concentrations and estimates 

of recycled-water percentages in multiple-well monitoring sites based on “excess” chloride

values, Los Angeles County, California ............................................................................................ 60

Figure 21. Graph showing relation between net denitrification rate constants estimated from

“back-calculated” nitrogen concentrations and depth of the monitoring wells adjacent

to the San Gabriel and Rio Hondo Coastal Basin Spreading Grounds, Los Angeles 

County, California ............................................................................................................................. 61

Figure 22. Graph showing relation between net denitrification rate constants and tritium/helium-3 age 

determinations.................................................................................................................................... 63

Figure 23. Diagram showing amount of excess nitrogen required to lower high-calculated recharge

temperatures to 17 degrees Celsius in four monitoring wells, Los Angeles County, 

California ........................................................................................................................................... 65

Figure 24. Diagram showing methane and excess-air concentration in multiple-well monitoring 

sites along ground-water flow path, Los Angeles County, California............................................... 67

Figure 25. Diagram showing chlorofluorocarbons (CFCs) concentrations in multiple-well 

monitoring sites along ground-water flow path, Los Angeles County, California............................ 69

Figure 26. Graph showing comparison of modeled CFC-11 and CFC-12 recharge ages in 

multiple-well monitoring sites, Los Angeles County, California...................................................... 71

Figure 27. Graphs showing historical record of aqueous chlorofluorocarbon (CFC) concentrations

at 10 degrees Celsius, 15 degrees Celsius, and 20 degrees Celsius in equilibrium

with atmospheric levels ..................................................................................................................... 72

Figure 28. Graphs showing enrichment (depletion) in aqueous chlorofluorocarbon (CFC) concentrations

in selected multiple-well monitoring sites relative to theoretical atmosphere-water 

equilibrium, Los Angeles County, California.................................................................................... 73

Figure A.1. Graphs showing relations between percent recycled water and specific 

conductance (SC) and magnesium (Mg) for each of the 23 production wells 

located in Los Angeles County, California........................................................................................ 81

Figure A.2. Graphs showing relations between percent recycled water and sodium (Na) and

potassium (K) for each of the 23 production wells located in Los Angeles County, 

California ........................................................................................................................................... 82

Figure A.3. Graphs showing relations between percent recycled water and chloride (Cl) and 

deuterium (H-2)for each of the 23 production wells located in Los Angeles County, 

California ........................................................................................................................................... 83

Figure A.4. Graphs showing relations between percent recycled water and oxygen-18 (O-18) and 

boron-11 (B-11) for each of the 23 production wells located in Los Angeles County, 

California ........................................................................................................................................... 84

Figure A.5. Graphs showing relations between percent recycled water and nitrogen-15 (N-15) 

and “excess” chloride (exCl) for each of the 23 production wells located in 

Los Angeles County, California ........................................................................................................ 85

Figure A.6. Graphs showing relations between percent recycled water and “excess” boron (exB)

and “back-calculated” nitrogen (calN) for each of the 23 production wells located

in Los Angeles County, California .................................................................................................... 86

Figure A.7. Graphs showing relations between percent recycled water and dissolved organic 

carbon (DOC) and total dissolved carbon (TOC) for each of the 23 production 

wells located in Los Angeles County, California .............................................................................. 87

Figure A.8. Graphs showing relations between percent recycled water and ultraviolet absorbance

(UV) and specific ultraviolet adsorbance (SUVA) for each of the

23 production wells located in Los Angeles County, California....................................................... 88
vi Figures

Figure A.9. Graphs showing relations between percent recycled water and methylene blue 

activated substance (MBAS) and fluorescence (FLUO) for each of the 23 production

wells located in Los Angeles County, California .............................................................................. 89

Figure A.10. Graphs showing relations between percent recycled water and specific 

fluorescence (SFLU) and ethylenediaminetetraacetic acid (EDTA) for each of the

23 production wells located in Los Angeles County, California....................................................... 90

Figure A.11. Graphs showing relations between percent recycled water and alkylphenol 

polyethoxy carboxylate (APEC) and total organic halides (TOX) for each of the 

23 production wells located in Los Angeles County, California....................................................... 91

Figure B.1. Graphs showing relations between percent recycled water in wells 1 and 2 located 

in Los Angeles County, California, for 22 selected constituents.......................................................93

Figure B.2. Graphs showing relations between percent recycled water in wells 3 and 4 located 

in Los Angeles County, California, for 22 selected constituents.......................................................94

Figure B.3. Graphs showing relations between percent recycled water in wells 5 and 6 located 

in Los Angeles County, California, for 22 selected constituents....................................................... 95

Figure B.4. Graphs showing relations between percent recycled water in wells 7 and 8 located 

in Los Angeles County, California, for 22 selected constituents....................................................... 96

Figure B.5. Graphs showing relations between percent recycled water in wells 9 and 10 located 

in Los Angeles County, California, for 22 selected constituents....................................................... 97

Figure B.6. Graphs showing relations between percent recycled water in wells 11 and 12 located 

in Los Angeles County, California, for 22 selected constituents....................................................... 98

Figure B.7. Graphs showing relations between percent recycled water in wells 13 and 14 located

in Los Angeles County, California, for 22 selected constituents....................................................... 99

Figure B.8. Graphs showing relations between percent recycled water in wells 15 and 16 located 

in Los Angeles County, California, for 22 selected constituents.......................................................100

Figure B.9. Graphs showing relations between percent recycled water in wells 17 and 18 located

in Los Angeles County, California, for 22 selected constituents.......................................................101

Figure B.10. Graphs showing relations between percent recycled water in wells 19 and 20 located

in Los Angeles County, California, for 22 selected constituents.......................................................102

Figure B.11. Graphs showing relations between percent recycled water in wells 21 and 22 located

in Los Angeles County, California, for 22 selected constituents.......................................................103

Figure B.12. Graph showing relations between percent recycled water in well 23 located in 

Los Angeles County, California, for 22 selected constituents...........................................................104
Tables vii

TABLES

Table 1. Analyses performed on water samples collected in Los Angeles County, California, 1996–1999 ....... 14

Table 2. Well information, field measurements, and water-quality data for 23 production wells, a 

background well (B), and recycled water (E, effluent) in Los Angeles County, 

California, 1996 ................................................................................................................................. 17

Table 3. Spearman rank-order correlation matrix ................................................................................................ 25

Table 4. Water-quality data for multiple-well monitoring sites in Los Angeles County, 

California, 1998–1999 ....................................................................................................................... 43

Table 5. Water-quality data for the research site and recycled water in Los Angeles County, 

California, 1998–1999 ....................................................................................................................... 49

Table 6. Tritium/helium-3 data, recharge ages, “excess” chloride, “back-calculated” nitrogen, and net 

denitrification-rate constants for selected monitoring wells in Los Angeles County, 

California, 1998–1999 ....................................................................................................................... 52

Table 7. Dissolved-gases data, excess air concentrations, and calculated recharge temperatures for 

multiple-well monitoring sites in Los Angeles County, California, 1998–1999............................... 64

Table 8. Delta nitrogen-15 (δ15N) values of the ground-water dissolved nitrogen gas in multiplewell monitoring sites in Los Angeles County, California, 1998–1999 ............................................. 66

Table 9. Chlorofluorocarbon (CFC) data and calculated recharge dates for multiple-well monitoring 

sites along section A–A’ in Los Angeles County, California, 1998–1999......................................... 70
viii Conversion Factors and Vertical Datum

CONVERSION FACTORS, VERTICAL DATUM, WATER-QUALITY INFORMATION, 

AND ABBREVIATIONS

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

°F = (1.8 × °C) + 32

VERTICAL DATUM

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

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

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

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

WATER-QUALITY INFORMATION

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).

Multiply By To obtain

Length

inch (in.) 2.54 centimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

acre 4,047 square meter

acre 0.004047 square kilometer

Volume

gallon (gal) 3.785 liter

gallon (gal) 0.003785 cubic meter 

million gallons (Mgal) 3,785 cubic meter 

cubic inch (in3) 16.39 cubic centimeter 

cubic inch (in3) 0.01639 cubic decimeter 

cubic inch (in3) 0.01639 liter 

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

Flow rate

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

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

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

Mass

ounce, avoirdupois (oz) 28.35 gram 

pound, avoirdupois (lb) 0.4536 kilogram 
Conversion Factors and Vertical Datum ix

ABBREVIATIONS (constituents or properties) 

Ar argon 

ALK alkalinity 

APEC alkylphenol polyethoxy carboxylate

B boron

B-11 boron-11

11B/10B boron-11/boron-10 ratio

Bact total bacteria 

Br bromide

C carbon

Ca calcium

CaCO3 calcium carbonate 

calN “back-calculated” nitrogen (assumed to be nitrate)

CFCs chlorofluorocarbons 

CFC-11 trichlorofluoromethane 

CFC-12 dichlorodifluoromethane 

CFC-113 chlorotrifluoromethane 

CH4 methane 

Cl chloride

CO2 carbon dioxide

Coli total coliform

DIST horizontal distance to well

DO dissolved molecular oxygen

DOC dissolved organic carbon

DOM dissolved organic matter

EDTA ethylenediaminetetraacetic acid

exB calculated “excess” boron

exCl calculated “excess” chloride 

δ11B delta boron-11/boron-10 ratio

δD delta deuterium/protium ratio

δ15N delta nitrogen-15/nitrogen-14 ratio

δ15N-N2 delta nitrogen-15/nitrogen-14 ratio of dissolved nitrogen gas

δ15N-NO3 delta nitrogen-15/nitrogen-14 ratio of nitrate

δ18O delta oxygen-18/oxygen-16 ratio

F fluoride

Fe iron

FLUO excitation-emission fluorescence

H2O water

H2S hydrogen sulfide

H-2 deuterium

2H/1H deuterium/protium ratio

3H tritium

He helium

3He helium-3

4He helium-4

HPC heterotrophic plate count

K potassium

k net denitrification rate constant

KjlN ammonia plus organic nitrogen (Kjeldahl nitrogen)

MBAS methylene blue activate substances 

Mg magnesium

Mn manganese 

N nitrogen 
x Conversion Factors and Vertical Datum

N2 nitrogen gas

N-15 nitrogen-15

15N/14N nitrogen-15/nitrogen-14 ratio

Na sodium

Ne neon

NH3 ammonia

NH4 ammonium

NO2 nitrite 

NO3 nitrate 

NTA nitrilotriacetic acid

O2 oxygen gas

O-18 oxygen-18

18O/16O oxygen-18/oxygen-16 ratio

P phosphorus

PO4 phosphate

PATH three-dimensional distance to well 

Prot total protozoa

Salm Salmonella bacteria

SC specific conductance

SiO2 silica

Size average microbial size

SO4 sulfate 

SFLU specific fluorescence

SUVA specific ultraviolet absorbance

TDS total dissolved solids

Temp temperature 

THM trihalomethane

TIME stratigraphic-estimated travel time 

TOC total organic carbon

TOX total organic halides 

UV ultraviolet absorbance

Zbot depth to bottom of perforated interval

Zn zinc

Ztop depth to top of perforated interval

Other abbreviations 

α level of significance

atm atmospheres

AA atomic adsorption

β solubility isotope effect

cm3 cubic centimeters

cm3 STP/g cubic centimeters per gram of water at standard temperature and pressure 

cm3 STP/L cubic centimeters per liter at standard temperature and pressure 

day-1 per day oC degrees Celsius

DCP direct-current plasma

ε isotope-separation factor

IC ion chromatography

ICP inductively-coupled plasma 

GC gas chromatography

GC/MS gas chromatography/mass spectrometric detector

> greater than
Conversion Factors and Vertical Datum xi

< less than

L liter

M moles

M/L moles per liter

MCL maximum contaminant level

mm millimeter

MS mass spectrometry

μg/L micrograms per liter 

μS/cm microsiemens per centimeter

mg/L milligrams per liter

mL milliliter

μm micrometer

N-2 degrees of freedom minus two

nm nanometer 

NGVD National Geodetic Vertical Datum of 1929

#/mL number per milliter

pCi/L picocurries per liter 

pH log hydrogen-ion activity

pk/kg picograms per kilogram

pM/kg picomoles per kilogram

pptv parts per trillion by volume

PVC polyvinyl chloride

SAS Statistical Analysis System 

ρ Spearman rank correlation coefficient

% percent

o/oo per mil (parts per thousand)

r

2 coefficient of determination (correlation coefficient squared)

TU tritium units

Organizations 

DOHS (California) Department of Health Services

EPA (U.S.) Environmental Protection Agency

ITL (USGS) Isotope Tracers Laboratory

NRP (USGS) National Research Program Laboratory

NWIS (USGS) National Water Information System

NWQL (USGS) National Water Quality Laboratory

SIL (USGS) Stable Isotope Laboratory

USGS U. S. Geological Survey 

WRDSC Water Replenishment District of Southern California
xii Well-Numbering System

WELL-NUMBERING SYSTEM

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

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

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

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

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

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

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

base line and meridian (S) Well numbers consist of 15 characters and follow the format 002S011W018C004. In 

this report, well numbers are abbreviated and written 2S/11W-18C4. Wells in the same township and range are 

referred to only by their section designation, 18C4. The following diagram shows how the number for well 

2S/11W-18C4 is derived.

2S/11W-18C4

D C B A

E F G H

M L K J

N P Q R

6 5 4 3 2 1

7 8 9 10 11 12

18 17 16 15 14 13

19 20 21 22 23 24

30 29 28 26 25

31 32 33 34 35 36

27

R11W R10W

T3S

T2S

T1S

R12W

RANGE

TOWNSHIP

R14W R13W

T4S

T5S

Approximately

6 miles

Approximately

1 mile

Approximately

1/4 mile

R11W

Well-numbering diagram (Note: maps in this report use abbreviated well numbers such as "18C4")

SECTION 18

T2S
Abstract 1

Use of Water-Quality Indicators and Environmental 

Tracers to Determine the Fate and Transport of Recycled 

Water in Los Angeles County, California

By Robert Anders and Roy A. Schroeder

ABSTRACT

Tertiary-treated municipal wastewater 

(recycled water) has been used to replenish the 

Central Basin in Los Angeles County for over 40 

years. Therefore, this area provides an excellent 

location to investigate (1) the fate and transport of 

wastewater constituents as they travel from the 

point of recharge to points of withdrawal, and (2) 

the long-term effects that artificial recharge using 

recycled water has on the quality of the groundwater basin. The U.S. Geological Survey has been 

conducting such investigations in this area for 

about 10 years, beginning in 1992. For this 

investigation, a variety of inorganic, organic, and 

isotopic constituents were analyzed in samples 

from 23 production wells within 500 feet of the 

San Gabriel and Rio Hondo Coastal Basin 

Spreading Grounds, and tritium/helium-3, 

chlorofluorocarbons, dissolved gases, and nitrogen 

isotopes were analyzed in five multiple-well 

monitoring sites along a 10-mile flow path 

extending from just upgradient of the spreading 

grounds southward through the Central Basin.

Spearman rank-order correlation 

coefficients and level of significance calculated for 

about 40 water-quality indicators and several 

physical features show significant correlations 

between numerous inorganic and organic 

constituents that indicate the presence of recycled 

water. On the basis of a simple two-member 

mixing model, chloride, boron, ultraviolet 

absorbance at 254 nanometers, and excitationemission fluorescence yielded the most reasonable 

estimates of wastewater percentages in the 

production wells. Tritium/helium-3 age 

determinations indicated that samples of ground 

water tested range in age from less than 2 to more 

than 50 years. Chloride and boron concentrations, 

along with tritium/helium-3 age determinations, 

indicate more rapid recharge and (or) 

displacement of pre-existing ground water at the 

San Gabriel Coastal Basin Spreading Grounds 

than at the Rio Hondo Coastal Basin Spreading 

Grounds. Nitrogen-15 enrichment of the groundwater nitrate and dissolved nitrogen indicates that 

denitrification, an important process for the 

removal of nitrate at the shallower depths beneath 

the spreading grounds, continues to occur at 

distances of several miles from the spreading 

grounds and over a period of many years. Analysis 

of dissolved gases shows that areas that contain 

recycled water have no detectable methane, 

whereas methane is present in the native ground 

water older than 50 years. The absence of methane 

in the younger ground water suggests that artificial 

recharge using recycled water has the desirable 

effect of increasing slightly the redox potential of 

the ground-water basin. Finally, measured 

chlorofluorocarbon concentrations and 

tritium/helium-3 age determinations indicate that 

chlorofluorocarbon concentrations are markedly 

elevated above atmosphere-water equilibrium in 

ground water older than about 20 years but still 

young enough to contain recycled water. 
2 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

INTRODUCTION

Artificial Recharge Using Wastewater

Managers of planned ground-water recharge 

programs facing water shortages intentionally recharge 

ground water using treated municipal wastewater 

effluent (recycled water) to supplement the existing 

water supply. The practice of artificially recharging 

ground-water basins is accomplished by delivering 

water, including recycled water, into large holding 

ponds or spreading grounds, where the water infiltrates 

through the unsaturated zone to the water table and 

moves downgradient to drinking-water aquifers. In Los 

Angeles County, for example, the Los Angeles County 

Department of Public Works has been augmenting the 

potable ground-water supply in the Central GroundWater Basin (Central Basin) using recycled water 

supplied from the Water Replenishment District of 

Southern California (WRDSC) for over 40 years.

In the State of California, the California 

Department of Health Services (DOHS) regulates 

artificial recharge using recycled water under Title 22 

of the California Administrative Code (Barclay's 

California Code of Regulations, 1978; California 

Department of Health Services, 1978). In addition to 

ensuring compliance with the common drinking-water 

standards for all constituents, these regulations state 

that the proportion of recycled water in the total 

recharge to an area is limited to 50 percent annually 

and to 35 percent within three contiguous years. 

However, as the demand for drinking water in Los 

Angeles County continues to increase, water agencies 

are seeking to increase the percent of recycled water 

currently permitted for artificial recharge. Recently, the 

DOHS proposed new regulations for increasing the 

recycled water contribution for ground-water recharge 

projects in California. These new regulations limit the 

amount of nitrogen compounds to 3 mg/L total 

nitrogen in the recycled water used for ground-water 

recharge and sets an unregulated- and unknowncontaminant control level at 0.5 mg/L total organic 

carbon (R. Hultquist, DOHS, oral commun., 2002). 

Furthermore, these new regulations establish a new 

compliance point at the mound formed beneath the 

infiltration basin during recharge, eliminating any 

removal of nitrogen or organic carbon during 

subsurface transport as part of the consideration to 

meet the newly established contaminant levels. These 

new regulations being proposed are due partially to the 

lack of information on the fate and transport of 

wastewater constituents as they travel from the point of 

recharge to points of withdrawal or the long-term 

effects that artificial recharge with recycled water has 

on the quality of the ground water in the basin.

Previous Studies 

The earliest studies investigating water-quality 

changes related to sewage-contaminated ground water 

were conducted on Cape Cod at the Otis Air Base field 

site maintained by the U.S. Geological Survey (USGS), 

where the disposal of secondary-treated sewage onto 

rapid infiltration beds occurred between 1936 and 

1979. According to Garabedian and LeBlanc (1988), 

the plume of sewage-contaminated ground water was 

characterized by elevated concentrations of several 

constituents including dissolved solids, boron, 

chloride, sodium, phosphorous, ammonium, nitrate, 

detergents, and, in some locations, volatile organic 

compounds. Subsequent studies investigated major 

processes that affect the transport and attenuation of 

contaminants in the plume (LeBlanc, 1996) and used 

3H/3He age determinations to delineate the age 

structure within the plume (Shapiro and others, 1999). 

Vengosh and others (1994) utilized the boron 

isotopic signature of anthropogenic boron in 

wastewater to show that the source of sewage 

contamination in the Coastal Plain aquifer of Israel was 

the Dan Region Sewage Reclamation Project, located 

south of Tel Aviv, Israel. Furthermore, they monitored 

the chemical composition of recharge sewage effluent 

and associated contaminated ground water from the 

Dan Region Sewage Reclamation Project during 16 

years of recharge operation (Vengosh and Keren, 

1996). They observed that the recharge of a relatively 

high salinity effluent into a calcium bicarbonate ground 

water resulted in cation-exchange and adsorption 

reactions, although the effect of these reactions was 

limited to relatively short periods during the first stages 

of effluent arrival and to the exchangeable sodium 

percentage of clay minerals in the phreatic aquifer. 

However, they noted that once the exchangeable and 

absorbed sites became saturated, Na, K, and B were 

retained in the effluent and behaved conservatively 

similar to the chloride ion. Furthermore, they showed 

that degradation of organic matter takes place mainly in 

the unsaturated zone and only a small fraction of 

organic matter is removed during flow of contaminated 

ground water in the saturated zone.
Introduction 3

Fryar and others (2000) investigated the use of 

playas that focus recharge for wastewater retention. 

Specifically, they confirmed that microbially mediated 

reduction limits nitrate loading to the ground water 

during recharge of industrial wastewater, sewage, and 

feedlot runoff to the regionally important High Plains 

(Ogallala) aquifer in the Southern High Plains, Texas. 

The evidence for microbially mediated reduction of 

nitrate during ground-water recharge was provided by 

δ15N (delta nitrogen-15/nitrogen-14 ratio) values in 

ground water and soil gases, the presence of 

denitrifying and nitrate-respiring bacteria, and 

decreases in NO3/Cl and SO4/Cl ratios with depth in 

sediment cores. 

Anders and Schroeder (1997) and Schroeder and 

others (2003) conducted three recharge experiments at 

a constructed research site located adjacent to a large 

recharge facility in Los Angeles County to better 

understand the processes that contribute to the changes 

in the quality of the recycled water during artificial 

recharge occurring over intervals of several days and 

distances (vertical and horizontal) of about 25 ft. These 

recharge experiments showed that the reduction of 

aqueous nitrogen was slightly greater than one-third 

and the reduction of dissolved organic carbon (DOC) 

was about one-third, although actual removal rates of 

aqueous nitrogen varied under different environmental 

and operational conditions but DOC did not. 

A more comprehensive study of inorganic, 

isotopic, and organic analyses at 23 production wells 

within 500 ft of the San Gabriel and Rio Hondo Coastal 

Basin Spreading Grounds in the Montebello Forebay 

located in Los Angeles County was conducted to 

ascertain which constituents of wastewater origin could 

be identified and used as tracers to determine the 

presence and estimate the percent of recycled water 

(Barber and others, 1997; Schroeder and others 1997). 

No completely quantitative tracer was identified 

although chloride, boron, ultraviolet absorbance at 254 

nanometers, and excitation-emission fluorescence 

seemed to yield the most reasonable estimates.

Leenheer and others (2001) focused on the 

nature and chlorine reactivity of organic constituents in 

recycled water before, during, and after recharge at the 

Montebello Forebay in Los Angeles County. They 

found that dissolved organic matter (DOM) in the 

recycled water was altered, or selected fractions were 

preferentially degraded, into less polar constituents in 

the reducing ground-water environment. In fact, the 

only organic compounds that survive infiltration are 

sulfonic acid metabolites of anionic surfactants. 

Furthermore, they found that the bulk of the DOM in 

infiltrated recycled water is refractory DOM (fulvic 

acid) derived from wastewater treatment and naturally 

occurring in the water supply. Finally, they found that 

the mixing of recycled water with ground water does 

not appear to degrade the ground-water quality with 

respect to the production of chlorinated disinfection 

byproducts in drinking water.

Purpose and Scope

The purpose of the investigation was to: (1) 

identify water-quality indicators of wastewater origin; 

(2) determine the presence and percent of recycled 

water in production wells and multiple-well monitoring 

sites; and (3) evaluate the long-term effects that 

artificial recharge using recycled water has on the 

quality of the ground water in the basin. The scope of 

the investigation included: (1) analysis of a variety of 

inorganic, organic, and isotopic constituents in 23 

production wells located within 500 ft of the San 

Gabriel and Rio Hondo Coastal Basin Spreading 

Grounds in the Montebello Forebay in Los Angeles 

County; and (2) analysis of chlorofluorocarbons 

(CFCs), tritium/helium-3 (3H/3He), dissolved gases, 

and nitrogen isotopes in five multiple-well monitoring 

sites extending along a 10-mi flow path from just 

upgradient from the spreading grounds southward 

through the Central Basin. 
4 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Description of the Study Area

The study area transects about 25 mi in the 

eastern part of the Central Basin of Los Angeles 

County from the Whittier Narrows in the north to the 

West Coast Basin and lies between the San Gabriel 

River on the east and the Rio Hondo and Los Angeles 

River on the west (fig. 1). The water-bearing units 

contained in the Central Basin consist of 

unconsolidated to partly consolidated marine and 

nonmarine alluvial deposits of Holocene, Pleistocene, 

and Pliocene age (California Department of Water 

Resources, 1961). These water-bearing deposits 

compose a complex series of aquifers more than 

1,800 ft thick in parts of the study area and are 

subdivided into four aquifer systems: Recent, 

Lakewood, Upper San Pedro, and Lower San Pedro, 

with no active pumping from the underlying Pico 

stratigraphic unit (Land and others, 2002; Reichard and 

others, 2003). 

Artificial recharge occurs at the Montebello 

Forebay in the northern part of the Central Basin at two 

spreading grounds (constructed infiltration basins) that 

have a total area of recharge of almost 1,000 acres 

(fig.1). One of the spreading grounds is adjacent to the 

San Gabriel River and includes a short unlined part of 

the downstream river channel. The other is adjacent to 

the Rio Hondo. The recharged water moves down and 

laterally from the spreading grounds southward in the 

direction of regional ground-water flow (Reichard and 

others, 2003). Aquifer material in the area of the 

spreading grounds consists of alluvial deposits of 

nearly all sands and gravels, with some relatively finegrained materials of possibly limited lateral extent. 

Bookman-Edmonston Engineering, Inc., (1994) 

evaluated the potential traveltime of recycled water 

used for spreading in the Montebello Forebay to wells 

within 500 ft of the Rio Hondo and San Gabriel Coastal 

Basin Spreading Grounds using various flow paths. 

One flow path considered vertical flow at areas of 

mergence between aquifer units and horizontal flow 

within these aquifers. An alternative flow path 

combined a vertical flow path with a distance equal to 

the depth to the top perforation and a horizontal flow 

path with a distance equal to the distance of the well to 

the spreading grounds. This “minimum distance” flow 

path was considered for two geologic conditions: the 

clay layers are discontinuous, so vertical flow is 

through more permeable material; or the clay layers are 

continuous, so that vertical flow must go through the 

clay. On the basis of these various assumed flow paths, 

traveltime estimates in the area were found to range 

from 24 days to over 16 years.

Historically, most of the recharge in the area 

originated as precipitation in the mountains to the north 

and on the basin floor itself, infiltration from the Rio 

Hondo and San Gabriel River as they entered the basin 

at the Whittier Narrows from the inland San Gabriel 

Valley, and a small amount of underflow from the San 

Gabriel Valley. Artificial recharge using imported 

water from the Colorado River began in the early 1950s 

and continued until about 1975. Imported water from 

northern California was used for artificial recharge 

after the completion of the State Water Project in the 

late 1960s. The delivery of recycled water (tertiarytreated wastewater from treatment facilities located 

north of the Montebello Forebay and outside the 

Central Basin) began in 1962 (fig. 2). Tertiary 

treatment includes chlorination-dechlorination and 

dual-media (charcoal and sand) filtration. In general, 

the percentage of recycled water has steadily increased 

with time as the proportion of imported water has 

decreased, and since about 1991 recycled water has 

averaged about 30 percent of all the water used to 

replenish the underlying aquifers annually (fig. 3). 

Acknowledgments

The collection of data from the 23 production 

wells was made possible with the cooperation and 

support of several local water purveyors. Property 

access for the five multiple-well monitoring sites was 

granted by the Downey Unified School District, city of 

Lakewood, Pico Water District, city of Pico Rivera, and 

the Los Angeles County Department of Public Works. 

The Water Replenishment District of Southern 

California provided cooperative funding for this study. 
Introduction 5

Gabriel

Gabriel

River

San

Balboa

Cr

San

Rio Hondo

River

Los

Los

R

River

Angeles

Angeles R13W

R13W

R12W

R12W

R15W

R14W

R15W R14W

R11W

R11W

T

2

S

T

1

S

T

3

S

T

4

S

T

5

S

Long Beach

Sign

Hi

al

ll

Repetto Hills Merced

Hills

Elysian

Hills

Puente Hills

Dominguez

Hills

Palos Verdes Hills

San Valley Gabriel

San Fernando Valley

Santa Monica Mountains

Los Angeles

Huntington

Beach

Seal Beach

Orange County

Los Angeles

County

0 10 MILES

Geology redrawn from

Reichard and others, 2003

Base map from U.S. Geological

Survey digital maps 1:24,000

0 10 KILOMETERS

Central

Basin

West Coast Basin

Hollywood Basin

Santa Monica

Basin

Montebello

Forebay

Los Angeles

Forebay

Whittier

Narrows

Los

Angeles

Narrows Whittier Narrows

Flood Control Basin

118 30' 118 20' 118 10' 118 00'

34 40'

34 00'

34 10'

34 50'

Unconsolidated deposits

Consolidated rocks

Spreading ground

EXPLANATION

NewportInglewood

Uplift

View of

photograph

Rio Hondo

Coastal Basin

Spreading

Grounds

San Gabriel

Coastal Basin Spreading Grounds

Los Angeles

CALIFORNIA

San

Francisco

San Diego

Los Angeles

County

Study

area

North North

Rio Hondo

Coastal Basin

Spreading Grounds

Montebello

Forebay

Central Basin

Rio Hondo

Coastal Basin

Spreading Grounds

Figure 1. Location of the study area in Los Angeles County, California, and a photograph of the Rio Hondo Coastal Basin Spreading Grounds in the 

Montebello Forebay, looking south toward the Pacific Ocean.
6 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

WATER YEAR

WATER SPREAD, IN ACRE-FEET X 1000

1955 1960 1965 1970 1975 1980 1985 1990 1995

0

50

100

150

200

250

300

Other

Local

Recycled

Imported

Figure 2. Source and amount of water recharged at the Rio Hondo and San Gabriel Coastal Basin Spreading Grounds, Los Angeles County, California.
Introduction 7

WATER YEAR

WATER SPREAD, IN PERCENT

1955 1960 1965 1970 1975 1980 1985 1990 1995

0

20

60

80

40

100

Other

EXPLANATION

Local

Recycled

Imported

Percent recycled

water

Figure 3. Percentages of water recharged at the Rio Hondo and San Gabriel Coastal Basin Spreading Grounds, Los Angeles County, California.
8 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

FIELD AND ANALYTICAL METHODS

Production Wells Adjacent to Spreading Grounds

USGS personnel sampled 23 production wells 

within 500 ft of the San Gabriel and Rio Hondo Coastal 

Basin Spreading Grounds in the Montebello Forebay 

located in Los Angeles County, apparent background 

water-quality from a production well about 7 mi 

northeast of the spreading grounds in the San Gabriel 

Valley, and recycled water at the research site 

originating from a wastewater-treatment plant used to 

augment recharge by delivery to the spreading grounds 

(fig. 4). The 23 production wells and the background 

well range in depth from 250 to more than 900 ft, and 

some of the perforated intervals are as much as several 

hundred feet (fig. 5). All production wells and the 

background well were being pumped at the time of 

sampling at rates ranging from 500 to 3,000 gal/min. 

Samples were collected from taps located between the 

wellhead and any holding tanks and before any 

wellhead treatment, such as coagulation or 

chlorination. 

All water samples were collected using USGS 

field-sampling procedures (Sylvester and others, 1990). 

Field measurements of pH were made using an Orion 

250A meter with an Orion model 9106 pH combination 

electrode calibrated daily using pH 4, 7, and 10 

standards. Field specific-conductance measurements 

were made using a temperature compensated 

conductivity meter (Orion model 124) calibrated daily 

against standard reference solutions. Dissolved-oxygen 

measurements were performed by Winkler titration 

(Fishman and Friedman, 1989). Water and air 

temperatures were measured using a hand-held 

alcohol-filled thermometer. 

The water samples were analyzed for major and 

minor inorganic constituents, nutrients, several 

isotopes, and selected microbial populations. Water 

samples for analysis of common inorganic constituents 

and nutrients were pressure-filtered in the field through 

inline 0.45-μm polyether sulfone cartridge filters from 

Gelman Scientific. Aliquots for inorganic chemical 

analysis were dispensed into clear polyethylene bottles 

for storage after the bottle was rinsed three times. 

Bottles used for analysis of cations were acidified to 

approximately pH 2 by addition of nitric acid. Aliquots 

for nutrient analysis were distributed into 125-mL, prerinsed, opaque, polyethylene bottles and placed on ice 

to minimize microbial alteration. Inorganic chemical 

and nutrient analyses were done by the USGS National 

Water-Quality Laboratory in Arvada, Colorado, using 

methods described generally by Fishman (1993), 

Timme (1994), and Struzeski and others (1996). 

Samples for analysis of stable hydrogen and 

oxygen isotopes were collected into 60-mL glass 

bottles and sealed with a polyseal cap to minimize 

evaporative loss and exchange with the atmosphere. 

These samples were analyzed at the USGS Isotope 

Laboratory in Reston, Virginia, using methods 

described by Epstein and Mayeda (1953) and Coplen 

and others (1991). Stable hydrogen and oxygen 

isotopes concentrations are expressed in terms of per 

mil relative to Vienna standard mean Ocean Water 

(Gonfiantini, 1984), and the estimate of precision (twosigma) is 2 and 0.2 per mil (o/oo), respectively. Three 

liters of water for determination of nitrogen isotopes 

were collected at each production well to ensure 

availability of sufficient nitrogen for analyses. The 

samples were collected into three 1-L polyethylene 

bottles, sealed with a polyseal cap, and frozen until 

analyzed using methods described by Kendall and 

Grim (1990), Böhlke and Coplen (1995), and Böhlke 

and Denver (1995). Tritium (3H) samples were 

collected in 1-L polyethylene bottles, sealed with 

polyseal caps, and analyzed at the USGS Tritium 

Laboratory in Menlo Park, California, by liquidscintillation counting following electrolytic enrichment 

(Ostlund and Dorsey, 1977). The tritium content of 

water is reported in terms of tritium units (TU) with a 

two-sigma estimate of precision. Each TU is equal to 

one atom of 3H in 1018 atoms of hydrogen. Water 

samples intended for analysis of the stable isotope of 

boron-11 were collected in 250-mL polyethylene 

bottles and measured at the USGS Isotope Laboratory 

in Menlo Park, California, by negative-ion ratio mass 

spectrometry. The results are reported in per mil 

relative to the NBS-951 boric acid standard and are 

precise (two-sigma) to within 0.5 per mil (T. Bullen, 

USGS, oral commun., 1996). 
Field and Analytical Methods 9

23 24 19 21 20 23

28 27 26 29 28 27

33 34 35 36 31 32 34 35

4 3 4 2

9 7

8 11 10 9 10

16 15 14 18 16 15

22 21 23 24 19 20 21 22 23

28 27 26

25

30 29 28 27 26

22

26

3

11

14

21 22

25 30

33

2 1 6 5

12

17

13

T1S

T2S

R12W R11W

Gabriel

San

Hondo

Rio

River

60

60

Norwalk

Rosemead Blvd

Whittier Blvd

Washington Blvd

118 08' 118 06' 118 04' 118 02' 118 00'

34 00'

34 02'

34 58'

34 04'

0 2 MILES

0 2 KILOMETERS

Consolidated rocks

Unconsolidated deposits

EXPLANATION

Background production well

Production well

Research site

Spreading ground

Whittier Narrows

Flood Control Basin

Narrows

Whittier

Montebello

Forebay

Rio Hondo

Coastal Basin

Spreading

Grounds

San Gabriel

Coastal Basin

Spreading

Grounds

Puente Hills

Repetto Hills

605

5

10

Merced Hills

14B2

14B8

11R4

13D7

13L5

23B8

23B4

26D7

22J2

27A5

12E8

12E6, E7

12E5, M2

19F1

19M4

19M1

18Q1

18Q7

25G2 25G1

24R1

25Q5

26K3

26K3

Figure 4. Location of 23 production wells near the spreading grounds, background production well upgradient from the Whittier Narrows, and the 

research site, Los Angeles County, California.
10 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California WELL DEPTH, IN FEET BELOW LAND SURFACE

Well near spreading ground

Perforated interval

Perforated interval

Background well

0

200

400

600

800

1,000

1,200

1,400

WELL DESIGNATION

27A5 12M2 12E7 12E5 12E6 11R4 12E 22J2 8 23B4 23B8 26D7 13L5 14B 14B2 8 13D7 19M4 19F1 19M1 25G2 25G1 18Q1 18Q7 25Q5 26K3

1 34567 2 8 9 10 11 12 14 15 16 17 1 13 8 19 20 21 22 23 24

San Gabriel River

Coastal Basin

Spreading Grounds

Rio Hondo

Coastal Basin

Spreading Grounds

Figure 5. Depth and perforated interval of selected production wells in Los Angeles County, California.
Field and Analytical Methods 11

Formalin-preserved and raw water samples were 

collected in 2.5-L polyethylene bottles and analyzed 

for selected microbial populations at the USGS 

Subsurface Microbiology Laboratory in Boulder, 

Colorado. Formalin-preserved samples were analyzed 

for total bacterial and protozoan numbers by acridine 

orange direct counts using epifluorescence microscopy 

(Harvey and others, 1984), and sizing of both bacteria 

and protozoa were done by computer-coupled image 

analyses of the captured epifluorescent images (Harvey 

and others, 1996). Raw samples were analyzed for 

heterotrophic (utilize organic compounds as electron 

donors), total coliform, and Salmonella bacteria 

populations by standard methods (American Public 

Health Association, 1985; U.S. Environmental 

Protection Agency, 1996). It is emphasized that water 

samples were not analyzed until after the U.S. EPAsuggested maximum holding time for samples of 48 

hours. Therefore, these data should be used for 

comparative purposes only and not for regulatory 

purposes. 

Finally, organic constituents were analyzed by 

the hierarchical approach described by Barber and 

others (1997), Leenheer and others (2001), and 

Schroeder and others (2003). The hierarchical 

approach is designed to comprehensively characterize 

organic mater in recycled water. 

Downgradient Monitoring Wells

Major and minor inorganic constituents, 

nutrients, chlorofluorocarbons (CFCs), tritium/

helium-3 (3H/3He), dissolved gases, and nitrogen 

isotopes were evaluated from water and gas samples 

collected from five multiple-well monitoring sites 

aligned in the direction of ground-water flow from the 

San Gabriel and the Rio Hondo Coastal Basin 

Spreading Grounds (fig. 6). The five multiple-well 

monitoring sites contained 28 monitoring wells 

screened over short intervals (generally 20 ft) and 

constructed of small-diameter (generally 2 in.) PVC 

casing (Land and others, 2002). Other water samples 

were collected from galvanized-steel well points (2.5-ft 

screens) and 6-in. stainless steel implants (Geoprobe 

Systems, Salina, Kans.) installed at a small constructed 

research site located adjacent to the San Gabriel 

Coastal Basin Spreading Grounds (fig. 4).

Prior to the collection of water and gas samples, 

all multiple-well monitoring sites were purged by 

removing three casing volumes using a variable-speed 

submersible Redi-Flo2 sampling pump (Grundfos 

Pumps Corp., Clovis, Calif.). During the purging 

process, specific conductance, pH, and temperature 

were monitored using portable pH and conductivity 

meters and hand-held alcohol-filled thermometers until 

all measurements had stabilized. In a few cases, 

dissolved oxygen also was monitored. After the 

purging process was completed, the Redi-Flo2 pump 

was removed and replaced with a stainless steel 

submersible Model 1400 piston pump (Robert Bennett 

Co., Amarillo, Tex.). The sampling apparatus, which 

was developed by Busenberg and Plummer (1992) for 

the collection of CFCs and dissolved gases, was 

attached to the Bennett pump with 1⁄4-in refrigerationgrade copper tubing. The apparatus prevents contact of 

the water sample with the atmosphere. 
12 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Gabriel

Gabriel

River

San

Balboa

Cr

San

Rio Hondo

River

Los

Los

R

River

Angeles

Angeles

Newport- Inglewood

Uplift

Long Beach

Signal

Hill

Repetto Hills Merced Hills

Elysian

Hills

Puente Hills

Dominguez

Hills

Palos Verdes Hills

San

Valley

Gabriel

San Fernando Valley

Santa Monica Mountains

Los Angeles

Huntington

Beach

Seal Beach

Orange County

Los Angeles

County

0 10 MILES Geology redrawn from

Reichard and others, 2003

Base map from U.S. Geological

Survey digital maps 1:24,000

0 10 KILOMETERS

Central Basin

West Coast Basin

Hollywood Basin

Santa Monica

Basin

Montebello

Forebay

Los Angeles

Forebay

Whittier

Narrows

Rio Hondo Pico Rivera

San Gabriel

Lakewood

Downey

Los

Angeles

Narrows Whittier Narrows

Flood Control Basin

118 30' 118 20' 118 10' 118 00'

34 40'

34 00'

34 10'

34 50'

R13W

R13W

R12W

R12W

R15W

R14W

R15W R14W

R11W

R11W

T

2

S

T

1

S

T

3

S

T

4

S

T

5

S

Unconsolidated deposits

Consolidated rocks

Spreading ground

Line of hydrogeologic section

USGS multiple-well monitoring site

EXPLANATION

Research site

A

A A'

A'

5H5–10

9J1–6

26D9–14 18C4–7

25G3–8

Figure 6. Location of multiple-well monitoring sites and line of hydrogeologic section A–A' along approximate ground-water flow path.
Field and Analytical Methods 13

Prior to the collection of water samples for 

analysis of trichlorofluoromethane (CFC-11), 

dichlorodifluoromethane (CFC-12), and 

chlorotrifluoromethane (CFC-113), water samples 

were collected and filtered for analysis of common 

inorganic constituents, nutrients, and selected isotopes 

through a short length of tubing attached to the 

sampling apparatus following the same field-sampling 

procedures used for the production wells. In addition, 

samples were collected for analysis of several 

dissolved gases in 150-mL glass bottles and sealed with 

a rubber septum after making sure no bubbles were 

adhering to the sides of the bottle. The dissolved gas 

samples were analyzed at the USGS CFC Laboratory 

in Reston, Virginia, for nitrogen (N2), argon (Ar), 

methane (CH4), oxygen (O2) and carbon dioxide 

(CO2). After the collection of water and dissolved-gas 

samples was completed, the flow was switched to allow 

water to be routed through the sampling apparatus for 

collection of CFCs using procedures described by 

Busenberg and Plummer (1992). Water samples were 

collected in glass ampoules after flushing the ampoule 

using ultra-pure nitrogen gas; after collection, the 

ampoules were flame-sealed. Five replicate ampoules 

were collected from each sampling location and 

analyzed at the USGS CFC Laboratory in Reston, 

Virginia, using a purge and trap gas chromatography 

with an electron-capture detector (Busenberg and 

Plummer, 1992). CFC concentrations have an 

analytical uncertainty of approximately 3 percent for 

concentrations greater than 50 pg/kg and approach 50 

percent at the detection limit of 1 pg/kg (Szabo and 

others, 1996). After the collection of samples for CFCs 

and dissolved gases was completed, the copper tubing 

was disconnected from the sampling apparatus. Then 

approximately 40 mL of water for helium isotope 

analysis was collected by sealing off a portion of the 

end of the copper tubing with stainless steel pinch-off 

clamps while maintaining the water in the copper tube 

under pressure to avoid degassing of the sample. 

Helium isotopes were analyzed by Dr. Robert Poreda at 

the University of Rochester Department of Earth and 

Environmental Sciences in Rochester, New York. 

Water and gases were extracted from the copper tube 

using a vacuum extraction system. After purification 

and separation of He from Ne by means of a cryogenic 

cold trap filled with charcoal, the helium-3 (3He) 

concentration and the helium-3/helium-4 (3He/4He) 

ratio were measured using a dedicated He-isotope mass 

spectrometer (Poreda and others, 1988). Helium 

isotope concentrations are reported in TUs. The 

analytical uncertainty of the 4He data is about ±2 

percent; that of the 3He/4He ratios is about ±1 percent. 

Listed in table 1 are the constituents analyzed 

during this study, reporting limits and precision, 

laboratory where analyses were done, and the principal 

reference to methods. Quality-assurance procedures 

included: (1) laboratory analysis of samples in 

duplicate; (2) review of water-quality data to determine 

outliers; (3) the collection of samples from background 

sites; and (4) the comparison of water-quality data from 

multiple sampling rounds. 
14 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 1. Analyses performed on water samples collected in Los Angeles County, California, 1996–1999—Continued

Parameter

Where 

analysis was 

performed

Analytical

method

Reporting

limit

Approximate

precision Reference

SC Specific conductance at 

25°C

Field Electrometric 1 μS/cm 2% Wilde and Radtke (1998)

pH Log hydrogen ion 

concentration

Field Electrometric 0–14 0.05 do.

Temp Temperature, in degrees 

Celsius

Field Thermometer °C 0.5 — 

TDS Total dissolved solids NWQL mg/L Fishman (1993), Timme 

(1994)

Ca Calcium NWQL ICP .1 mg/L 4% do.

Mg Magnesium NWQL ICP .1 mg/L 4% do.

Na Sodium NWQL ICP .6 mg/L 10% do.

K Potassium NWQL AA .2 mg/L 6% do.

SiO2 Silica NWQL ICP .1 mg SiO2/L 7% do.

ALK Alkalinity to pH=4.5, as 

CaCO3

Field Titration 1 mg/L 2% Wilde and Radtke (1998)

SO4 Sulfate NWQL IC .3 mg/L 2% Fishman (1993), Timme 

(1994)

Cl Chloride NWQL IC .3 mg/L 3% do.

Br Bromide NWQL Colorimetric .01 mg/L 5% do.

NO3 Nitrate NWQL Colorimetric .05 mg N/L 4% do.

NO2 Nitrite NWQL Colorimetric .01 mg N/L 10% do.

NH3 Ammonia NWQL Colorimetric .01 mg N/L 3% do.

KjlN Ammonia + organic 

nitrogen

NWQL Colorimetric .2 mg N/L 6% Patton and Truit (1992)

PO4 Phosphate NWQL Colorimetric .01 mg P/L 10% do.

DO Dissolved molecular 

oxygen

Field Winkler titration .2 mg O2/L 0.2 Fishman and Friedman (1989)

Fe Iron NWQL ICP 3 μg/L 10% Fishman (1993), Timme 

(1994)

Mn Manganese NWQL ICP 1 μg/L 11% do.

Zn Zinc NWQL ICP 3 μg/L 4% do.

δD delta Deuterium/protium 

ratio

SIL MS per mil 2 Coplen and others (1991)

δ18O delta Oxygen-18/oxygen16 ratioSIL MS per mil 0.2 do.

δ11B delta Boron-11/boron-10 

ratio

ITL MS per mil 0.2 Vengosh and others (1994)

δ15N delta Nitrogen15/nitrogen-14 ratioSIL MS per mil 0.2 Kendall and Grim (1990)

exCl “Excess” chloride — calculated 3 mg/L 3% Schroeder and others (1997)

exB “Excess” boron — calculated 4 mg/L 3% do.

B Boron NWQL DCP 10 mg/L 3% Fishman (1993), Timme 

(1994)

Table 1. Analyses performed on water samples collected in Los Angeles County, California, 1996–1999

[USGS, U.S. Geological Survey; NWQL, USGS National Water Quality Laboratory; ITL, USGS Isotope Tracers Laboratory, Menlo Park, California; SIL, 

USGS Stable Isotope Laboratory, Reston, Virginia; NRP, USGS National Research Laboratories in Colorado; AA, atomic adsorption; CaCO3, calcium 

carbonate; DCP, direct-current plasma; ft, foot; GC, gas chromatography; GC/MS, gas chromatography/mass spectrometric detector; IC, ion chromatography; 

ICP, inductively-coupled plasma; MS, mass spectrometry; μg/L, microgram per liter; μS/cm, microseimens per centimeter; mg/L, milligram per liter; nm, 

nanometer; per mil, parts per thousand;%, percent; TU, tritium unit; UV, ultraviolet; oC, degrees Celsius; —, no data; do., ditto]
Field and Analytical Methods 15

calN “Back-calculated” nitrogen

(assumed to be nitrate)

— calculated .1 mg N/L 0.1 Schroeder and others (1997)

DOC Dissolved organic carbon NRP Wet oxidation .1 mg C/L 0.1 Barber and others (1997)

TOC Total organic carbon NRP Wet oxidation .1 mg C/L 0.1 do.

UV Ultraviolet absorbance at 

254 nm

NRP Spectrometry — 0.001 do.

SUVA UV absorbance/DOC — calculated — — do.

MBAS Methylene blue active 

substances

NRP Colorimetric 1 μg/L 1 do.

FLUO Excitation-emission 

fluorescence

NRP Spectrometry μg/L Tinopal 1 do.

SFLU Fluorescence/DOC — calculated — — do.

NTA Nitrilotriacetic acid NRP GC .1 μg/L 0.1 do.

EDTA Ethylenediaminetetraacetic 

acid

NRP GC 1 μg/L 1 do.

APEC Alkylphenol polyethoxy 

caboxylate

NRP GC 1 μg/L 1 do.

THM Total trihalomethanes NRP GC/MS 1 mg/L 6% do.

TOX Total organic halides NRP GC/MS 1 mg/L 50% do.

Ztop Depth to top of perforated 

interval

Field published ft 1 Bookman-Edmonston 

Engineering (1994)

Zbot Depth to bottom of 

perforated interval

Field published ft 1 do.

DIST Horizontal distance to well Field published ft 10 do.

PATH Length of flow path to well Field published ft 10 do.

TIME Time of ground-water flow 

to well

Field published days 1 do.

3H Tritium ITL Liquid 

scintillation

.1 TU 10% Ostlund and Dorsey (1977)

Table 1. Analyses performed on water samples collected in Los Angeles County, California, 1996–1999—Continued

Parameter

Where 

analysis was 

performed

Analytical

method

Reporting

limit

Approximate

precision Reference
16 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

WATER-QUALITY INDICATORS AND 

ENVIRONMENTAL TRACERS

In Los Angeles County, recycled water has been 

used to augment the potable ground-water supply in the 

Central Basin since 1962. Therefore, this area provides 

an excellent location to investigate the transport and 

fate of wastewater constituents as they travel from the 

point of recharge to points of withdrawal and the longterm effects that artificial recharge with recycled water 

has on the quality of the ground water in the basin. The 

USGS, in cooperation with the WRDSC, has been 

conducting such investigations in this area beginning in 

1992. The investigation included the analysis of a wide 

variety of inorganic, organic, and isotopic constituents 

in 23 production wells located within 500 ft of the San 

Gabriel and Rio Hondo Coastal Basin Spreading 

Grounds in the Montebello Forebay in Los Angeles 

County (fig. 4); and chlorofluorocarbons (CFCs), 

tritium/helium-3 (3H/3He), dissolved gases, and 

nitrogen isotopes in five multiple-well monitoring sites 

extending along a 10-mi flow path from just upgradient 

from the spreading grounds southward through the 

Central Basin (fig. 6). 

Production-Well Results

Well information, field measurements, and 

inorganic, organic, and microbiological data for 

samples collected in May 1996 from the 23 production 

wells located within 500 ft of the San Gabriel and Rio 

Hondo Coastal Basin Spreading Grounds, and an 

upgradient background well, as well as a recycledwater (effluent) sample, are given in table 2. The 

background production well is considered to represent 

water free of most anthropogenic effects because it is 

outside the Central Basin and the top of the perforated 

interval is over 1,000 ft below land surface. These data, 

previously reported in Schroeder and others (1997) and 

Barber and others (1997), include chloride, boron, 

nitrate, ultraviolet absorbance at 254 nanometers, and 

excitation-emission fluorescence, which are 

wastewater constituents used to determine presence of 

recycled water and wastewater percentages in 

production wells. 

Statistical Relations

Nonparametric Test

Spearman rank-order correlation coefficients, ρ, 

were calculated for 45 constituents in the 23 production 

wells using data in table 2 to determine which 

constituents in recycled water are present in the well 

water and ascertain the statistical strength of the 

recycled-water signal for each constituent. This 

statistical test is appropriate for a general evaluation 

such as this because of the large differences in range of 

values between constituents and non-normal 

distribution for most, if not all, of the constituents. A 

few of the constituents were then chosen for more 

detailed investigation using parametric tests to estimate 

percentages of the constituent derived from recycled 

water.

Spearman rank-order coefficients are linear 

correlations of the ranks of the variables. The method 

used for nonparametric or rank correlation is to replace 

the value of each variable by the value of its rank 

among all the other variables in the sample, and then 

the resulting list of numbers will be drawn from a 

perfectly known distribution function (Press and others, 

1992). Furthermore, the significance of a nonzero value 

of the rank-order correlation coefficient is distributed 

approximately as a Student's distribution with N-2 

degrees of freedom. The key point is that this 

approximation does not depend on the original 

distribution of each variable; it is always the same 

approximation. The Statistical Analysis System (SAS) 

(Statistical Analysis Software, 1982), a computer 

system for data analysis, was used to compute the 

Spearman rank-order coefficients for the 45 

constituents.
Water-Quality Indicators and Environmental Tracers 17

Table 2. Well information, field measurements, and water-quality data for 23 production wells, a background well (B), and recycled water (E, effluent) in Los 

Angeles County, California, 1996—Continued

Well 

No.

Station name

(Local identifier) Date Time

Depth 

of well 

(ft)

(72008)

Altitude

of land 

surface 

datum, ft 

above 

NGVD

(72000)

Flow rate, 

gal/min

(00059)

 Oxygen,

dissolved, 

mg/L

(00300)

pH, water,

whole,

field, 

standard 

units

(00400)

Specific 

conductance, 

field, 

μS/cm

(00095)

Water

temperature, oC

(00010)

1 2S/12W-27A5 05/22/96 1000 900 142 700 0.6 7.5 709 18.5

2 2S/12W-22J2 05/22/96 1200 624 — 850 .6 7.5 704 19.5

3 2S/12W-12M2 05/15/96 2030 600 211 800 .4 7.1 791 19.5

4 2S/12W-12E7 05/15/96 1200 250 200 1,200 .4 7.4 744 20.7

5 2S/12W-12E5 05/15/96 1900 350 200 1,250 .4 7.2 800 19.5

6 2S/12W-12E6 05/15/96 1730 285 200 1,130 .4 7.2 762 19.5

7 2S/12W-11R4 05/15/96 1430 380 170 1,100 1.2 7.3 772 19.5

8 2S/12W-12E8 05/15/96 1330 250 200 1,050 .4 7.4 787 19.5

9 2S/12W-23B4 05/21/96 0900 566 170 2,700 .4 7.1 796 19.5

10 2S/12W-23B8 05/21/96 0800 600 170 1,700 .4 7.1 763 19.0

11 2S/12W-26D7 05/21/96 1400 598 — 800 .4 7.2 612 19.0

12 2S/12W-13L5 05/17/96 0900 456 170 500 .4 7.1 698 19.0

13 2S/12W-14B2 05/20/96 1300 397 170 1,120 .4 6.9 748 19.0

14 2S/12W-14B8 05/20/96 0830 352 195 1,350 .4 6.9 702 19.5

15 2S/12W-13D7 05/20/96 1200 399 170 8,650 .4 7.0 706 19.5

16 2S/11W-19M4 05/14/96 1400 305 160 600 .5 7.2 919 21.0

17 2S/11W-19F1 05/14/96 1700 625 162 1,250 3.0 7.4 935 19.3

18 2S/11W-19M1 05/14/96 1530 698 160 1,000 2.2 7.3 896 19.5

19 2S/12W-25G2 05/21/96 1230 462 — 1,250 .4 7.4 901 19.5

20 2S/12W-25G1 05/21/96 1000 446 155 1,400 .4 7.2 900 19.5

21 2S/11W-18Q1 05/16/96 1230 462 165 2,200 .4 7.3 988 19.5

22 2S/11W-18Q7 05/16/96 1100 552 165 3,000 .4 7.2 1,040 19.5

23 2S/12W-25Q5 05/20/96 1500 494 135 1,050 3.0 7.5 776 18.5

B 1S/11W-26K3 05/17/96 1400 1,275 300 2,200 9.0 7.4 399 19.5

E Effluent 05/18/96 1000 — — 350 4.0 7.0 1,014 24.0

Table 2. Well information, field measurements, and water-quality data for 23 production wells, a background well (B), and recycled water (E, effluent) in Los 

Angeles County, California, 1996

[Number below the constituent or property is the data parameter code, which is a 5-digit number used in the U.S. Geological Survey computerized data system, 

National Water Information System (NWIS), to uniquely identify a specific constituent or property; μS/cm, microsiemens per centimeter at 25oC; oC, degrees 

Celsius; HPC, heterotrophic plate count; ft, feet below land surface; mg/L, milligrams per liter; μg/L, micrograms per liter; #/mL, number per milliliter; μm, 

micrometers; nm, namometers; gal/min, gallon per minute; per mil, parts per thousand; TU, tritium units; NGVD, National Geodetic Vertical Datum of 1929; 

<, actual value less than value shown; —, no data] 
18 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 2. Well information, field measurements, and water-quality data for 23 production wells, a background well (B), and recycled water (E, effluent) in Los 

Angeles County, California, 1996—Continued

Well 

No. Date Time

Calcium, 

dissolved,

mg/L as Ca

(00915)

Magnesium, 

dissolved,

mg/L as Mg

(00925)

Potassium, 

dissolved,

mg/L as K

(00935)

Sodium, 

dissolved,

mg/L as N

(00930)

Alkalinity, 

fixed 

endpoint, 

field, 

mg/L as 

CaCO3

(39036)

Bromide, 

dissolved,

mg/L as Br

(71870)

Chloride, 

dissolved,

mg/L as Cl

(00940)

Fluoride, 

dissolved,

mg/L as F

(00950)

Silica, 

dissolved,

mg/L as 

SiO2

(00955)

Sulfate, 

dissolved,

mg/L as 

SO4

(00945)

1 05/22/96 1000 83 15 3.4 33 162 0.14 52 0.3 21 120

2 05/22/96 1200 74 13 3.6 50 148 .12 57 .4 20 110

3 05/15/96 2030 76 15 4.3 66 178 .12 63 .3 23 120

4 05/15/96 1200 82 14 3.3 58 163 .18 58 .4 23 100

5 05/15/96 1900 84 14 4.2 63 194 .13 62 .3 22 120

6 05/15/96 1730 70 14 3.6 59 175 .14 61 .3 23 110

7 05/15/96 1430 84 13 3.8 58 71 .13 60 .3 23 130

8 05/15/96 1330 87 14 3.9 59 196 .13 58 .4 22 120

9 05/21/96 0900 64 14 3.8 73 143 .11 70 .3 22 130

10 05/21/96 0800 67 13 3.9 63 148 .12 65 .3 21 130

11 05/21/96 1400 50 12 3.8 52 129 .09 48 .4 18 93

12 05/17/96 0900 68 12 3.9 54 154 .10 55 .3 21 110

13 05/20/96 1300 56 16 4.9 69 137 .12 70 .4 16 120

14 05/20/96 0830 51 15 5.0 63 133 .10 60 .4 17 110

15 05/20/96 1200 61 13 4.2 63 144 .11 57 .4 21 110

16 05/14/96 1400 78 16 4.4 84 166 .13 91 .3 22 140

17 05/14/96 1700 110 20 4.2 56 211 .19 73 .3 23 150

18 05/14/96 1530 88 17 4.2 74 183 .15 91 .4 22 120

19 05/21/96 1230 77 17 4.1 77 184 .14 88 .4 21 120

20 05/21/96 1000 74 17 4.3 79 175 .13 87 .4 20 130

21 05/16/96 1230 92 19 4.8 82 191 .16 90 .4 19 180

22 05/16/96 1100 110 21 4.7 81 212 .20 83 .3 20 190

23 05/20/96 1500 95 18 3.4 38 192 .13 56 .3 22 120

B 05/17/96 1400 51 10 2.6 17 173 .02 9.2 .5 24 22

E 05/18/96 1000 55 16 12.0 120 149 .05 120 .7 23 110
Water-Quality Indicators and Environmental Tracers 19

Table 2. Well information, field measurements, and water-quality data for 23 production wells, a background well (B), and recycled water (E, effluent) in Los 

Angeles County, California, 1996—Continued

Well 

No. Date Time

Solids, 

sum of 

constituents, 

dissolved,

mg/L

(70300)

Ammonia

+ organic 

nitrogen, 

dissolved, 

mg/L as N

(00623)

Ammonia, 

dissolved,

mg/L as N

(00608)

Nitrate plus

nitrite,

dissolved,

mg/L as N

(00631)

Nitrite, 

dissolved,

mg/L as N

(00613)

Orthophosphate, 

dissolved,

mg/L as P

(00671)

Phosphorus, 

dissolved,

mg/L as P

(00666)

Boron, 

dissolved,

μg/L as B

(01020)

Iron, 

dissolved,

μg/L as Fe

(01046)

1 05/22/96 1000 466 <0.2 0.03 1.40 <0.01 .02 <0.01 123 89

2 05/22/96 1200 434 <.2 .02 2.40 <.01 .02 .02 177 3

3 05/15/96 2030 487 <.2 .08 1.70 <.01 .02 <.01 206 <3

4 05/15/96 1200 454 <.2 .03 1.10 <.01 .02 <.01 210 45

5 05/15/96 1900 483 <.2 .03 .84 .01 .02 <.01 211 12

6 05/15/96 1730 472 <.2 .02 3.00 <.01 .02 <.01 203 <3

7 05/15/96 1430 478 <.2 .09 .07 <.01 <.01 <.01 195 240

8 05/15/96 1330 490 <.2 .02 .78 <.01 .02 <.01 195 <3

9 05/21/96 0900 500 <.2 .03 2.88 .02 .04 .04 200 <3

10 05/21/96 0800 476 <.2 .02 2.00 <.01 .02 <.01 195 <3

11 05/21/96 1400 365 <.2 .02 1.90 <.01 .02 .02 165 <3

12 05/17/96 0900 434 <.2 .03 2.30 <.01 .01 <.01 184 11

13 05/20/96 1300 456 <.2 .02 3.70 <.01 .13 .12 170 33

14 05/20/96 0830 425 <.2 .02 3.00 <.01 .26 .26 194 5

15 05/20/96 1200 435 <.2 .02 2.90 <.01 .04 .03 186 <3

16 05/14/96 1400 558 <.2 .02 3.20 <.01 .02 .02 302 <3

17 05/14/96 1700 605 <.2 .02 4.20 <.01 .04 .02 194 <3

18 05/14/96 1530 550 <.2 .03 4.20 <.01 .04 .03 255 <3

19 05/21/96 1230 552 <.2 .02 4.40 <.01 .03 .02 287 <3

20 05/21/96 1000 553 <.2 .02 3.40 <.01 .03 .02 269 <3

21 05/16/96 1230 613 <.2 .03 .81 <.01 .03 .02 264 5

22 05/16/96 1100 656 <.2 .04 1.90 <.01 .02 <.01 261 <3

23 05/20/96 1500 502 <.2 .02 2.70 <.01 .02 .02 93 <3

B 05/17/96 1400 243 <.2 .03 .45 .02 .05 .05 43.8 <3

E 05/18/96 1000 589 4.5 3.6 3.80 2.6 1.80 1.9 399 43
20 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 2. Well information, field measurements, and water-quality data for 23 production wells, a background well (B), and recycled water (E, effluent) in Los 

Angeles County, California, 1996—Continued

Well

No. Date Time

Manganese,

dissolved,

μg/L as Mn

(01056)

Zinc, 

dissolved,

μg/L as Zn

(01090)

2

H/1H, H2O, 

per mil

(82082)

11B/10B, 

per mil

15N/14N, NO3, 

per mil

(82690)

18O/16O, H2O, 

per mil

(82085)

Tritium,

2-sigma, 

TU

(75985)

Tritium

TU

(07000)

1 05/22/96 1000 9 7 −65.3 14.2 18.02 −8.67 — 18.3

2 05/22/96 1200 <1 16 −62.5 8.0 19.96 −8.57 — 13.9

3 05/15/96 2030 <1 3 −59.5 6.2 19.50 −8.28 — 9.2

4 05/15/96 1200 3 78 −57.5 11.7 18.92 −8.21 — 11.7

5 05/15/96 1900 <1 94 −60.6 6.7 20.50 −8.40 — 10.8

6 05/15/96 1730 <1 5 −61.3 6.5 16.91 −8.38 — 10.3

7 05/15/96 1430 32 <3 −61.2 7.5 — −8.62 — 11.7

8 05/15/96 1330 <1 <3 −61.7 4.8 21.01 −8.55 — 10.6

9 05/21/96 0900 3 14 −61.9 5.5 23.63 −8.21 — 8.3

10 05/21/96 0800 16 <3 −63.5 8.2 21.57 −8.45 — 10.2

11 05/21/96 1400 <1 41 −58.2 6.2 22.03 −8.00 — 8.5

12 05/17/96 0900 6 <3 −59.2 6.5 17.06 −8.11 — 8.1

13 05/20/96 1300 10 3 −57.6 6.0 23.27 −7.79 — 8.6

14 05/20/96 0830 30 11 −56.4 6.0 25.30 −7.54 — 8.0

15 05/20/96 1200 4 8 −58.2 6.0 19.24 −7.91 — 8.2

16 05/14/96 1400 5 6 −63.2 4.0 31.36 −8.35 — 9.0

17 05/14/96 1700 1 <3 −61.9 11.2 17.28 −8.39 — 16.9

18 05/14/96 1530 3 5 −60.5 6.7 24.84 −8.26 — 12.5

19 05/21/96 1230 <1 <3 −60.6 6.7 24.00 −8.25 — 10.4

20 05/21/96 1000 3 <3 −61.4 6.5 25.79 −8.30 — 9.9

21 05/16/96 1230 22 12 −63 3.5 30.86 −8.35 0.8 10.2

22 05/16/96 1100 42 5 −60.7 7.7 22.70 −8.13 — 9.4

23 05/20/96 1500 <1 7 −65.4 9.2 12.49 −8.91 — 19.5

B 05/17/96 1400 <1 4 −56.5 10.5 1.64 −8.15 — .1

E 05/18/96 1000 17 160 −58.2 4.5 11.50 −8.23 1.0 7.5
Water-Quality Indicators and Environmental Tracers 21

Table 2. Well information, field measurements, and water-quality data for 23 production wells, a background well (B), and recycled water (E, effluent) in Los 

Angeles County, California, 1996—Continued

Well 

No. Date Time

“Excess” 

chloride, 

(mg/L)

“Excess” 

boron, 

(mg/L)

“Backcalculated” 

nitrogen, 

(mg/L)

Total 

bacteria 

(#/mL)

Total 

coliform 

(#/100mL)

Fecal

coliform plus 

Salmonella 

(#/100mL)

HPC 

bacteria 

(#/100mL)

Total

protozoa 

(#/mL)

1 05/22/96 1000 14.81 9.80 1.88 34,372 0 0 735 606

2 05/22/96 1200 26.37 27.45 3.53 83,618 1 0 — 0

3 05/15/96 2030 33.38 36.93 2.45 23,878 30 2 10,025 96

4 05/15/96 1200 9.28 38.24 1.54 133,002 185 60 53,155 0

5 05/15/96 1900 29.86 38.56 1.26 16,627 1 0 — 107

6 05/15/96 1730 26.08 35.95 3.84 51,861 1 0 20 37

7 05/15/96 1430 27.44 33.33 4,416 0 0 94,350 43

8 05/15/96 1330 25.02 33.33 1.20 4,240 1 2 5,950 0

9 05/21/96 0900 43.46 34.97 5.00 124,000 0 0 38,250 0

10 05/21/96 0800 35.72 33.33 3.16 118,607 8 10 400 121

11 05/21/96 1400 23.54 23.53 3.07 386 0 0 2,500 —

12 05/17/96 0900 28.81 29.74 2.96 135 4 3 — —

13 05/20/96 1300 41.56 25.16 6.32 62,005 70 14 26,885 0

14 05/20/96 0830 34.28 33.01 5.62 — 21 4 32,630 —

15 05/20/96 1200 28.76 30.39 4.12 6,200 0 0 3,275 39

16 05/14/96 1400 64.93 68.30 7.89 604 1 0 162,000 0

17 05/14/96 1700 28.21 33.01 5.46 66,430 0 0 11,000 0

18 05/14/96 1530 62.31 52.94 7.70 31,580 0 0 31,110 7

19 05/21/96 1230 59.91 63.40 7.77 2,700 5 5 — 0

20 05/21/96 1000 60.09 57.52 6.51 — — — 38,000 —

21 05/16/96 1230 59.50 55.88 1.95 97,000 0 0 41,296 400

22 05/16/96 1100 40.89 54.90 3.16 103,000 2 2 26,000 424

23 05/20/96 1500 3.03 −16.08 .29 1,000,005 0 0 15,300 0

B 05/17/96 1400 22.60 .00 2.82 482 2 1 — 0

E 05/18/96 1000 100.00 100.00 3.80 338,060 500 400 8,150 21,206
22 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 2. Well information, field measurements, and water-quality data for 23 production wells, a background well (B), and recycled water (E, effluent) in Los 

Angeles County, California, 1996—Continued

Well 

No. Date Time

Average 

microbial size 

(μm)

DOC

(mg/L)

TOC

(mg/L)

Ultraviolet 

absorbance 

at 254 nm

SUVA MBAS

(μg/L)

Fluorescence 

(μg/L, Tinopal 

equivalent)

SFLU

1 05/22/96 1000 0.49 0.5 0.4 0.004 0.008 5 29 61

2 05/22/96 1200 .48 .8 .7 .009 .011 8 40 53

3 05/15/96 2030 .545 1.0 1.0 .011 .011 6 60 58

4 05/15/96 1200 .883 1.1 1.2 .013 .012 7 57 54

5 05/15/96 1900 .408 1.2 1.3 .016 .013 7 68 58

6 05/15/96 1730 .5 .9 .9 .011 .012 6 52 56

7 05/15/96 1430 — .7 .7 .007 .010 4 43 66

8 05/15/96 1330 .46 1.1 1.1 .015 .014 8 66 59

9 05/21/96 0900 .631 1.1 .9 .015 .014 6 59 52

10 05/21/96 0800 .46 .9 .8 .009 .010 6 43 46

11 05/21/96 1400 — .8 .7 .01 .013 5 44 56

12 05/17/96 0900 .651 .9 .8 .009 .010 6 48 56

13 05/20/96 1300 — 1.4 1.4 .026 .019 8 90 63

14 05/20/96 0830 — 1.6 1.6 .029 .018 8 102 64

15 05/20/96 1200 .47 .9 1.0 .013 .014 6 53 58

16 05/14/96 1400 — 1.5 1.5 .023 .015 10 85 56

17 05/14/96 1700 .524 .7 .7 .008 .011 7 39 53

18 05/14/96 1530 .549 1.2 1.1 .017 .014 11 63 53

19 05/21/96 1230 .4 1.2 1.1 .015 .013 9 60 52

20 05/21/96 1000 — 1.4 1.3 .021 .015 8 73 54

21 05/16/96 1230 — 1.5 1.4 .02 .013 8 82 57

22 05/16/96 1100 — 1.4 1.4 .022 .016 11 84 58

23 05/20/96 1500 .784 .6 .5 .004 .007 7 27 49

B 05/17/96 1400 .39 .3 .3 .000 .000 4 0 2

E 05/18/96 1000 .785 8.0 8.0 .128 .016 30 408 51
Water-Quality Indicators and Environmental Tracers 23

Table 2. Well information, field measurements, and water-quality data for 23 production wells, a background well (B), and recycled water (E, effluent) in Los 

Angeles County, California, 1996—Continued

Well 

No. Date Time NTA (μg/L)

EDTA

(μg/L)

 APEC 

(μg/L)

THM 

(μg/L)

TOX 

(μg/L)

Ztop 

(ft)

DIST

(ft)

PATH

(ft)

TIME 

(days)

1 05/22/96 1000 0.0 1 <1 7 3 447 400 847 5,892

2 05/22/96 1200 .0 4 1 5 8 230 130 360 1,591

3 05/15/96 2030 .0 29 1 17 8 156 190 346 933

4 05/15/96 1200 .0 13 1 36 8 160 400 560 933

5 05/15/96 1900 .0 30 1 8 7 76 270 346 36

6 05/15/96 1730 .0 17 1 10 8 160 400 560 933

7 05/15/96 1430 .0 12 <1 10 6 240 320 560 696

8 05/15/96 1330 .0 18 1 13 8 122 340 462 57

9 05/21/96 0900 .0 10 1 5 10 288 110 398 5,132

10 05/21/96 0800 .0 7 1 7 7 281 130 411 5,132

11 05/21/96 1400 .0 4 1 7 4 234 60 294 2,066

12 05/17/96 0900 .0 13 <1 7 8 294 220 514 4,257

13 05/20/96 1300 .0 34 5 7 12 267 120 387 2,781

14 05/20/96 0830 .0 47 4 10 14 60 250 310 24

15 05/20/96 1200 .0 16 2 12 9 148 80 228 33

16 05/14/96 1400 .0 72 3 11 14 75 310 385 96

17 05/14/96 1700 .0 13 1 40 12 120 390 510 1,727

18 05/14/96 1530 .0 36 3 44 12 184 310 494 2,034

19 05/21/96 1230 .1 19 4 9 15 250 180 430 2,320

20 05/21/96 1000 .0 47 2 9 13 242 60 302 2,381

21 05/16/96 1230 .0 52 1 8 10 130 170 300 1,821

22 05/16/96 1100 .0 18 2 7 7 172 310 482 1,445

23 05/20/96 1500 .0 1 <1 4 4 314 50 364 4,915

B 05/17/96 1400 .0 0 1 12 0 1,000 — 100 —

E 05/18/96 1000 3.5 363 57 17 162 0 0 0 0
24 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Results of the nonparametric test are 

summarized in table 3. Correlation coefficients 

(multiplied by 100 to convert decimal values to whole 

numbers) are listed for each pair of constituents above 

the diagonal that divides the table. Level of 

significance (α) is designated below the diagonal by 

three stars (α < 0.001; strongly significant), two stars 

(α = 0.001 to 0.05; highly significant), and one star

(α = 0.05 to 0.10; moderately significant); and referred 

to as strong, moderate, and weak in subsequent 

discussions. The three levels of significance are related 

to the correlation coefficients by the following: 

α < 0.001, ρ>0.65; α = 0.001 to 0.05, ρ = 0.65 to 0.40; 

and α = 0.05 to 0.10, ρ = 0.40 to 0.35. The 45 

constituents are listed in order as groups that consist of 

inorganic species, trace elements, isotopes, 

“calculated” values, microbes, organic indicators, and 

physical features.

High numbers of significant correlations are 

readily apparent within certain groups; for example, 

several inorganic species and organic indicators. 

Correlations for more than half of the inorganic pairs 

and half of the organic pairs are strongly significant 

(α<0.001). The high number for inorganic species is at 

least partly an autocorrelation of all major ions with 

dissolved-solids concentration (TDS) and specific 

conductance (SC). As expected, correlations are 

weaker, but still significant, for inorganic species that 

are less conservative, such as calcium (Ca), magnesium 

(Mg), alkalinity (ALK), and sulfate (SO4).

The high number of significant correlations for 

organic pairs is explained by the fact that the organic 

compounds and broad organic indicators have a 

common source in the recycled water. In fact, only 

trihalomethanes (THMs) are uncharacteristic in that 

they exhibit few significant correlations (2 out of 10 

pairs) within the organic group. This could mean that 

there are THM sources other than chlorinated recycled 

water, or that THM biodegradation and (or) sorption 

differs greatly from that of the other constituents tested.

When the two groups are considered together, 

about half the inorganic-organic pairs exhibit 

statistically significant correlation; but the number is 

much higher for sodium and chloride. This reflects the 

addition of salt to wastewater during the treatment 

process (Nightingale and McCormick, 1985; Umari 

and others, 1995). In fact, the correlation coefficients 

between chloride and organic pairs are increased 

further when bromide is used to remove natural 

chloride and yield “excess” chloride (exCl), as 

discussed in the section “Two-Member Mixing Models 

for Selected Constituents.” Note that the absence of any 

significant correlations between bromide (Br) and 

organic constituents supports the method used to 

calculate “excess” chloride. Two other inorganic 

constituents, “excess” boron (exB) and “backcalculated” nitrogen (calN) assumed to be nitrate, also 

exhibit high numbers of significant correlations with 

organic pairs and, therefore, are also discussed in detail 

in the same section.

Three trace elements—iron (Fe), manganese 

(Mn), and zinc (Zn)—were analyzed in the production 

wells. Concentrations of these trace elements in 

recycled water (effluent) are 43, 17, and 160 μg/L, 

respectively (see table 2). Although zinc is abundant in 

wastewater, experiments at the constructed research 

site indicate that it is reduced by about two-thirds over 

a distance of less than 25 ft during recharge (Schroeder 

and others, 2003). Hence, it is not surprising that zinc 

in the production wells shows no significant 

correlations with any other constituents that are 

indicators of recycled water. Elevated iron and 

manganese concentrations are present in some of the 

wells, but they are unlikely to have their origin in 

recycled water. Rather they likely are both mobilized or 

removed from aquifer soils in response to local 

environmental conditions. Fe and Mn are moderately 

correlated (table 3), reflecting their similar behavior 

under reducing (soluble) and oxidizing (insoluble) 

conditions.
Water-Quality Indicators and Environmental Tracers 25

Table 3. Spearman rank-order correlation matrix—Continued.

SC TDS Ca Mg Na K ALK SO4 Cl Br NO3 DO

SC 98 68 76 68 43 72 84 84 67 15 13

TDS *** 71 79 61 35 73 85 77 67 16 21

Ca *** *** 61 5 −3 79 54 30 82 −23 52

Mg *** *** ** 48 47 66 61 65 67 37 25

Na *** ** — ** 74 23 55 87 21 29 −37

K ** — — ** *** 16 42 62 −2 29 −29

ALK *** *** *** *** — — 42 38 70 0 12

SO4 *** ***   **  ** ** 70 46 1 21

Cl *** *** — *** *** ** * *** 46 44 −2

Br *** *** *** *** — — *** ** ** −1 31

NO3 — — — * — — — — ** — 16

DO — — ** — * — — — — — —

Fe * ** — — — — * — — — ** —

Mn — — — — — * — * — — — —

Zn — — — — — — — * — — — —

δD * ** ** — — — — ** — — — **

δ18O — — ** — * ** — — — — — **

δ11B — — * — ** ** — — — — — **

δ15N * — — — *** ** — * *** — — —

exCl ** ** — * *** *** — ** *** — ** —

exB *** *** — * *** * ** ** *** ** — —

calN — — — —   — — **  — *** —

Bact — — — — — — — — — — — —

Coli — — — — — — — — — — — **

Salm — — — — — — — — — — — **

HPC * — — — ** — — — ** — — —

Prot — — — — — — — — — — ** —

Size — — — — — * — — — — — —

DOC ** — — * *** *** — — *** — — **

TOC * — — * *** *** — — ** — — **

UV * — — * *** *** — — ** — — **

SUVA — — — — *** *** — — ** — * **

MBAS — — —   **  * — ** — * —

FLUO * — — * *** *** — — ** — — **

SFLU — — — — — ** — — — — — —

EDTA ** — — ** *** *** — — *** — — —

APEC — — — * *** *** — — ** — ** —

THM — — — — — — — — — — — —

TOX — — — * ** ** — — *** — *** —

Ztop — — — — — ** — — — — — —

Zbot — — — — — — — — — — — **

Dist — — ** — — — — — — ** — —

Path — — * — — ** — — — ** — —

Time — — — — — — — — — — — —

3H — — *** — * ** ** — — ** — ***

Table 3. Spearman rank-order correlation matrix

[Explanation for abbreviations or constituents or properties found in “Conversion Factor” section of report; correlation coefficients (multiplied by 100 to 

convert decimal values to whole numbers) are listed for each pair of constituents above the diagonal that divides the table; level of significance is designated 

below the diagonal by three stars (α<0.001; strongly significant), two stars (α=0.001 to 0.05, highly significant), and one star (α=0.05 to 0.10; moderately 

significant, — (α >0.10)]
26 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 3. Spearman rank-order correlation matrix—Continued

Fe Mn Zn δD δ18O δ11B δ15N exCl exB calN Bact Coli

SC −37 4 −25 −38 −20 −8 42 58 74 23 18 −15

TDS −42 −5 −32 −48 −27 −4 35 51 65 19 22 −24

Ca −1 −2 −14 −44 −56 37 −12 −6 30 −31 26 −31

Mg −24 11 −16 −25 −5 6 31 41 41 24 37 −4

Na −32 29 −13 7 37 −54 80 90 82 54 −3 21

K −12 41 −18 28 48 −54 65 73 41 46 20 24

ALK −35 −31 −17 −32 −33 17 −11 8 43 −26 16 −4

SO4 −19 40 −37 −56 −30 −5 41 53 46 19 26 −23

Cl −32 20 −27 −13 11 −26 69 86 80 61 13 10

Br 0 5 −12 −29 −35 41 −2 4 48 −5 35 −10

NO3 −44 −12 −25 10 34 −5 22 47 11 88 −1 6

DO 5 −5 −8 −48 −58 48 −23 −20 −26 7 13 −54

Fe 40 23 21 −6 21 −13 −26 −25 −32 1 16

Mn * −14 5 25 −6 37 32 5 21 16 7

Zn — — 13 14 −6 2 −23 −12 −30 28 −17

δD — — — 80 −20 6 3 −1 17 −34 45

δ18O — — — *** −44 32 35 8 41 −20 36

δ11B — — — — ** −56 −46 −25 −24 41 0

δ15N — * — — — ** 83 60 56 −14 8

exCl — — — — — ** *** 68 72 −14 16

exB — — — — — — ** *** 36 −6 20

calN — — — — * — ** *** * −20 7

Bact — — — — — * — — — — 3

Coli — — — ** — — — — — — —

Salm — — — ** * — — — — — — ***

HPC — * — — — — ** * ** — — —

Prot — ** — — — — — — — — — —

Size — — — — — — ** — — — * —

DOC — — — — ** ** *** *** *** * — **

TOC — — — * ** ** *** ** *** — — **

UV — — — * ** ** *** *** ** ** — —

SUVA — — — * ** ** *** ** * ** — —

MBAS — — — — — — * ** * — — —

FLUO — — — * ** *** *** *** ** * — **

SFLU — — — * — * — — — — — —

EDTA — — — — * ** *** *** *** ** — —

APEC — — — * ** * *** *** ** *** — *

THM — — — — — — — — ** — — —

TOX — — — —   **  *** ** *** — —

Ztop — — — — — * — — * — — —

Zbot — — — — — * — — — — — —

Dist — — — — — — — — — — — —

Path — — — — — ** * — — — — —

Time — — — * — — — — — — — —

3H — — — ** *** *** * * — — — —
Water-Quality Indicators and Environmental Tracers 27

Table 3. Spearman rank-order correlation matrix—Continued

Salm HPC Prot Size DOC TOC UV SUVA MBAS FLUO SFLU EDTA

SC −17 39 8 −19 42 38 36 25 35 36 −7 49

TDS −20 35 4 −6 33 28 26 17 34 26 −12 40

Ca −27 18 16 10 −7 −3 −13 −23 23 −9 −10 6

Mg −1 29 −2 14 41 38 38 29 43 36 1 45

Na 17 47 10 −30 85 79 81 70 47 80 12 80

K 20 28 20 −36 77 76 77 70 48 80 45 83

ALK −7 −9 7 −14 15 17 9 −2 41 12 −16 26

SO4 −16 36 27 −20 26 21 20 13 16 22 5 28

Cl 6 48 −3 −20 67 60 62 49 47 59 −4 71

Br −8 17 16 5 9 14 4 −6 21 3 −10 18

NO3 4 −1 −47 4 22 15 28 36 38 15 −20 27

DO −53 14 −20 29 −49 −50 −47 −42 −5 −51 −18 −31

Fe 16 35 22 11 −5 1 −9 −21 −11 −2 35 −7

Mn 22 39 48 19 30 31 26 22 13 29 25 19

Zn −32 17 5 18 7 10 12 10 −20 5 −8 −11

δD 46 11 −10 14 30 38 37 41 11 39 37 29

δ18O 42 16 −12 22 51 51 57 64 29 54 26 37

δ11B 5 −27 11 17 −58 −54 −61 −62 −20 −65 −39 −59

δ15N 10 64 −1 −45 82 71 80 73 42 76 8 71

exCl 13 45 4 −28 75 64 70 60 54 67 −1 73

exB 8 52 12 −21 68 65 58 41 41 59 −10 70

calN 3 33 −31 −14 42 34 47 55 35 37 3 46

Bact 6 10 1 48 −4 −5 −7 −14 −9 −17 −32 −27

Coli 88 6 −11 −10 44 49 35 20 33 43 12 32

Salm 3 −11 −2 36 39 27 17 31 34 6 19

HPC — −32 82 55 51 47 34 40 47 −3 47

Prot — — −31 −2 −1 −7 −19 −30 2 28 2

Size — ** — −22 −23 −26 −26 2 −31 −19 −28

DOC * ** — — 97 97 82 62 97 20 89

TOC * ** — — *** 96 82 57 97 31 89

UV — ** — — *** *** 93 57 97 31 86

SUVA — — — — *** *** *** 45 87 41 71

MBAS — * — — **   **  55 −15 56

FLUO — ** — — *** *** *** *** ** 42 89

SFLU — — — — — — — * — * 31

EDTA — ** — — *** *** *** *** ** *** —

APEC — — — — *** *** *** *** ** *** — ***

THM — — — — — — — — — — — **

TOX —   — ** * ** ***   **  — ***

Ztop — — — —   **  ** — ** — **

Zbot — — — — * ** * * — ** * *

Dist — — — — — — — — — — — —

Path — — — — — — * * — — — —

Time — — — — — ** — — — —  

3H — — — — **  **   — **  — *
28 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 3. Spearman rank-order correlation matrix—Continued

APEC THM TOX Ztop Zbot Dist Path Time 3H

SC 26 24 34 −26 7 13 2 −2 23

TDS 17 18 29 −15 12 10 6 9 27

Ca −25 23 −16 −17 12 44 36 −7 70

Mg 37 15 39 −15 17 8 0 11 27

Na 70 22 63 −31 −17 −13 −30 −14 −41

K 69 24 59 −49 −10 −15 −46 −30 −51

ALK 0 24 5 −28 4 28 13 −8 45

SO4 7 −2 16 −5 20 5 6 17 13

Cl 61 31 66 −28 2 5 −5 −2 −5

Br 2 35 4 −17 3 59 49 −3 64

NO3 63 12 71 5 17 −22 −7 19 −14

DO −29 6 −14 12 42 20 32 13 69

Fe −29 −13 −24 10 −21 30 27 −4 14

Mn 13 −8 6 6 −2 11 14 5 −31

Zn −3 −23 −20 −22 −5 −13 −36 −20 −3

δD 41 35 23 −24 −33 0 −13 −39 −51

δ18O 60 11 45 −14 −16 −25 −30 −12 −80

δ11B −40 −11 −47 38 39 29 53 30 70

δ15N 70 8 61 −25 −8 −21 −42 −7 −37

exCl 68 11 71 −13 6 −22 −26 6 −40

exB 44 42 49 −40 −27 21 −3 −27 −7

calN 78 23 81 −10 6 −10 −7 0 −33

Bact −10 −28 −12 20 22 −9 7 32 35

Coli 37 9 23 −11 −36 10 5 −15 −31

Salm 32 6 21 9 −26 3 14 6 −30

HPC 24 13 49 −19 −34 −2 −5 20 −9

Prot −25 −10 −53 3 26 14 0 1 −7

Size −43 2 −2 34 7 6 31 26 9

DOC 75 20 66 −45 −40 −5 −34 −30 −48

TOC 75 30 61 −55 −52 4 −31 −44 −45

UV 83 20 65 −46 −40 −8 −37 −33 −51

SUVA 85 19 62 −42 −35 −14 −38 −34 −55

MBAS 50 6 55 −17 −11 2 −1 −4 −14

FLUO 74 24 59 −49 −46 −1 −34 −39 −52

SFLU 19 28 1 −40 −31 33 2 −52 −35

EDTA 70 48 71 −59 −40 8 −31 −44 −35

APEC 29 76 −37 −17 −15 −34 −26 −40

THM — 41 −65 −27 54 15 −60 8

TOX *** ** −36 −18 −7 −22 −17 −33

Ztop * *** * 42 −35 29 87 13

Zbot — — — ** −22 1 59 26

Dist — ** — — — 76 −35 38

Path — — — — — *** 21 45

Time — ** — *** ** — — 14

3H * — — — — * ** —
Water-Quality Indicators and Environmental Tracers 29

Only weak to moderate negative correlations 

exist in the production wells between several of the 

organic indicators and physical features such as depth 

to top (Ztop) and bottom (Zbot) of the perforated 

interval, stratigraphic-estimated traveltime (TIME), 

and tritium activity (3H). The stratigraphic-estimated 

traveltime is the less of the traveltime for the merged 

aquifer flow path and the “minimum distance” flow 

path provided by Bookman-Edmonston Engineering, 

(1994) (described in the section “Description of Study 

Area”). Furthermore, very few significant correlations 

exist between several of the organic indicators and 

either horizontal (DIST) or three-dimensional (PATH) 

distance between the spreading grounds and the 

production wells. Perhaps the most important 

observation is the lack of a significant correlation 

between stratigraphic-estimated traveltime and tritium 

activity (ρ = 0.14), presumably owing to the fact that 

the production wells draw water from various depths 

and ages owing to large perforated interval. 

Six microbial indicators were analyzed and an 

interpretation was made; however, some uncertainty 

exists in the data because samples were not analyzed 

within the 48-hour holding time that is customary for 

compliance testing. Furthermore, data from microbial 

analyses are inherently much more variable than are 

chemical data; therefore, several more samples 

collected over a longer period would be required for 

complete confidence. It is noted that the microbial data 

exhibit few significant correlations, even within the 

microbial group itself. Furthermore, the microbial data 

exhibit no significant correlations with factors such as 

traveltime, distance between the production wells and 

spreading grounds, or tritium activity, which would be 

needed to indicate transport from the spreading 

grounds. This lack of significant correlation suggests 

that the microbial activity identified in samples from 

the production wells was from local sources, and not 

due to transport with water from the spreading grounds. 

Weak and moderate positive correlations do exist 

between heterotrophic plate count (HPC) and several 

organic constituents. This suggests that perhaps the 

organic matter might serve as substrate stimulating 

additional activity, either in the production well or in 

the sample container after collection. 

Graphical Representation

Although nonparametric statistical tests are 

useful in indicating sources of wastewater constituents, 

they cannot be used to estimate percentages of recycled 

water in wells or to quantify trends. For that reason, 

percentages of recycled water were calculated using a 

simple two-member mixing model, which is an 

arithmetic parametric test. Using the two-member 

mixing model, a value of zero-percent recycled water is 

assigned to the lowest concentration (or highest value 

where appropriate) observed for each constituent in the 

23 production wells and 100 percent is assigned to the 

concentration measured in recycled water (effluent in 

table 2). The method provides a graphical display that 

permits visual comparison and contrast between 

constituents and wells; however, the non-normal 

distribution among the constituents indicates the 

analysis cannot provide a precise relation to sources. 

The relation between percent of recycled water and 22 

selected wastewater constituents for each of the 23 

production wells is shown in appendix A; the relation 

between percent of recycled water and 22 wastewater 

constituents among the 23 production wells is shown in 

appendix B. 

The most important observation from these data 

is that many of the constituents most closely identified 

by their significant correlations as indicators of 

recycled water co-vary fairly closely between wells. 

Several inorganic and organic indicators show that the 

percentage of recycled water is higher in the eight 

production wells (wells 16 through 23) adjacent to the 

San Gabriel Coastal Basin Spreading Grounds (data in 

lower rows of table 2 and displayed on right side of 

figure 5 and appendix B) than in the 15 production 

wells adjacent to the Rio Hondo Coastal Basin 

Spreading Grounds. The percentage of recycled water 

calculated using Cl and B concentrations is about 

60 percent in several of the wells near the San Gabriel 

Coastal Basin Spreading Grounds (using data in 

table 2). These percentages are substantially more than 

the 35 percent recycled water that is spread annually 

and suggests that this side of the recharge facilities may 

represent a greater proportion of recycled water, 

whereas the Rio Hondo Coastal Basin Spreading 

Grounds may represent a greater proportion of 

imported water and (or) stormwater.
30 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

The data displayed in the appendixes also show 

that percentages calculated from organic indicators are 

generally lower than for B and Cl, suggesting the 

partial removal of organic constituents. Given the 

finding that about one-third of organic carbon is 

removed from recycled water over distances of only 

several feet and traveltimes of only a few days on the 

basis of experiments at the constructed research site 

(Schroeder and others, 2003), it is very plausible that 

additional removal or organic constituents occurs as 

ground-water traveltime and distance increase to these 

nearby production wells. Furthermore, if there were no 

additional degradation of organic carbon, conservative 

tracers such as B and Cl indicate that DOC 

concentrations in production wells would be about 

double the observed concentrations, the highest of 

which is only 1.6 mg/L (from data in table 2).

Data on specific organic compounds (except for 

THMs) also suggest preferential removal. For example, 

ethylenediaminetetraacetic acid (EDTA) concentration 

is low (maximum is 4 μg/L) or nondetectable 

(<0.2 μg/L) in multiple-well monitoring sites in the 

Central Basin where ground water ranges in age from 

about 3 to 30 years (Leenheer and others, 2001) but 

equals or exceeds 4 μg/L in all but 2 of the 23 

production wells. The markedly higher concentrations 

in production wells in comparison with multiple-well 

monitoring sites suggests a mixture of very young 

ground water with substantial EDTA and older (but still 

younger than 50 years based on tritium values) ground 

water that contains little or no EDTA because it has 

been degraded or sorbed onto the aquifer soil.

If calculations based on THM data were 

presented graphically they would show recycled-water 

percentages exceeding 200 percent for wells 4, 17, and 

18 because the THM concentration in these three wells 

is more than double the THM concentration in recycled 

water, which is 17 μg/L. Total organic halide (TOX) 

concentration is nearly 10 times higher than THM 

concentration in recycled water (from effluent data in 

table 2); therefore, degradation of TOX is a potential 

source of THM after recharge. However, the 

stratigraphic-estimated traveltimes for wells 4, 17, and 

18 are 2.6, 4.7, and 5.6 years (Bookman-Edmonston 

Engineering, 1994), respectively, and there is nothing 

distinctive about their water quality or physical features 

that would suggest post-recharge formation of THMs 

in these or the other production wells. Regardless of the 

source, it should be noted that the THM concentration 

in these three wells is still less than half the regulatory 

MCL (maximum contaminant level) of 80 mg/L for 

drinking water.

Two-Member Mixing Models for Selected Constituents

An alternative approach to calculate recycledwater percentages in the production wells would be to 

use concentrations in the recycled water and the 

upgradient background well (26K3) in a two-member 

mixing model. In fact, low dissolved solids, high 

dissolved oxygen, and undetectable tritium are 

consistent with the absence of anthropogenic effects in 

the background well. However, ground water from the 

San Gabriel Valley represents only a minor source (as 

deep underflow) of either historical or current total 

recharge to the Montebello Forebay (Schroeder and 

others, 1997). Therefore, other methods were 

developed to represent ground water that is free of 

artificial recharge, although assigning a single 

background concentration and ignoring the 

contribution of ground water from the San Gabriel 

Valley may be an oversimplification. 
Water-Quality Indicators and Environmental Tracers 31

“Excess” Chloride and Boron

Two constituents added to water during the 

treatment process, Cl and B, were evaluated as tracers 

or recyled water in the subsurface. If unfractionated sea 

salt in atmospheric precipitation is the sole source of 

chloride (Cl) and bromide (Br), and both halides 

exhibit completely conservative physical and chemical 

behavior during subsurface transport, the Cl/Br mass 

ratio in ground water would be equal to 287, the ratio 

found in seawater (Schroeder and others, 1993). Cl is 

indeed enriched relative to Br in the production wells, 

and in the recycled water itself (Schroeder and others, 

1997). Deviation from a seawater-dilution line can be 

used to estimate recycled-water percentages, 

designated “excess” chloride, if it is assumed that the 

process of water reuse adds only Cl but no Br, using the 

following equation:

(1)

where

Similarly, boron (B) is added to the recycled 

water in large amounts during water reuse, primarily 

owing to its presence as a softener in detergents. It is 

used in a two-member mixing model to calculate 

recycled water percentages, designated “excess” boron, 

with the effluent concentration of 399 μg/L being one 

end member. The two-member mixing model assumes 

that the lowest concentration measured in any of the 23 

production wells (93 μg/L in well 23) represents 

conditions in which there is no contribution from 

recycled water. The percentage of recycled water can 

be estimated using the following equation:

(2)

where

Linear regression analysis was performed on the 

recycled-water percentages using the software program 

S-Plus (Mathsoft, Inc., Cambridge, Mass.) and the 

robust MM regression method. Regression models such 

as the robust MM regression method are useful for 

fitting linear relations when the random variation in the 

data is not Gaussian (normal) or when the data contain 

significant outliers. Furthermore, the results of the 

robust MM linear regression method returns a model 

that is almost identical in structure to a standard linear 

regression model allowing for the production of 

regression plots. On the basis of the results of the 

analysis, “excess” Cl and “excess” B are correlated 

with a coefficient of determination, r2, of 0.58 (fig. 7). 

The fact that “excess” chloride and “excess” boron are 

correlated supports the hypothesis that both 

constituents are at least semiquantitative indicators of 

the percentage of recycled water in the production 

wells, although the underlying assumptions are only 

approximately correct since the regression line neither 

passes through the origin nor has a slope of 1. 

Furthermore, the calculated percentages are higher than 

the average amount of about 30 percent that would be 

expected on the basis of quantity and sources of water 

delivered to the spreading grounds for recharge during 

the last 10 years. It is anticipated that these recycledwater percentages can be improved with more reliable 

information on background concentrations of ground 

water prior to recharge, spatial variations within the 

Montebello Forebay, and the contribution of ground 

water from the San Gabriel Valley. 

[Cl] = chloride concentration measured in 

production well [mg/L];

120 = chloride concentration measured in 

recycled water [mg/L];

287[Br] = chloride concentration in production 

well without recycled water [mg/L]; and 

x = calculated percentage of recycled water 

[%].

[ ] Cl = ( ) 120 – x 287[ ] Br

[B] = boron concentration measured in 

production well [μg/L];

399 = boron concentration measured in 

recycled water [μg/L];

[BNative] = boron concentration in production well 

without recycled water [μg/L]; and

x = calculated percentage of recycled water 

[%].

[ ] B x( ) 399 ( ) 1 – x BNative = + [ ]
32 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

PERCENT OF RECYCLED WATER, FROM "EXCESS" BORON

0 20 40 60 80 100

PERCENT OF RECYCLED WATER, FROM "EXCESS" CHLORIDE

0

20

40

60

80

100

Regression line

Production-well number

(r 2 = 0.58)

1

2

3

4

5

6 7

8

9

10

11

12

13

14

15

16

17

18

2120 19

22

23

1

Figure 7. Estimates of recycled-water percentages in selected production wells based on “excess” chloride and “excess” boron values, Los Angeles 

County, California.
Water-Quality Indicators and Environmental Tracers 33

Boron Isotopes

Isotopic analyses of B may provide another 

method for quantifying recycled-water percentages 

(Vengosh and others, 1994). A delta boron-11 (δ11B) 

value of +6 per mil (o/oo) for an effluent sample and 

values of about +13 o/oo measured in a few of the 

production wells indicate that boron is isotopically 

depleted in recycled water (Schroeder and others, 

1997). Furthermore, regression analysis indicates a 

negative correlation between “excess” Cl and δ11B 

(fig. 8) and supports the use of boron as an indicator of 

recycled water, although the correlation between δ11B 

and “excess” Cl (r2 = 0.14) is considerably weaker than 

the correlation between “excess” Cl and “excess” B. 

Nitrogen Isotopes

Nitrogen-isotopes measured during artificial 

recharge experiments at the San Gabriel Coastal Basin 

Spreading Grounds provided evidence that 

denitrification occurs beneath the reservoir site (Anders 

and Schroeder, 1997). The process of denitrification is 

accompanied by enrichment in nitrogen-15 in the 

remaining nitrate. Analyses of the effluent sample 

(table 2) yielded a delta nitrogen-15 (δ15N) value of 

+11.5 o/oo for nitrate and concentrations of 6.4 and 

4.5 mg/L as N for oxidized (NO3 + NO2) and reduced 

(NH4 + organic) species, respectively. A δ15N value of 

+25.4 o/oo for ammonia was reported in Schroeder and 

others (1997). Combining the isotope and 

concentration data yields an initial nitrogen isotope 

ratio of +17.2 o/oo for total N. This value represents a 

maximum that would occur if all forms of N were 

completely converted to NO3 and implies that any 

increment above this value for 

δ15N-NO3 in the ground water would indicate 

denitrification. Because nearly all of the 23 production 

wells have δ15N values that are higher than +17.2 o/oo, 

and all have values that markedly exceed the δ15N 

value for NO3 in recycled water, most of the NO3 in the 

production wells is concluded to be the result of 

partially denitrified recycled water (fig. 9). 

On the basis of the assumption of complete 

oxidation of N in recycled water followed by partial 

denitrification and negligible dilution with native 

waters, this enrichment of δ15N-NO3 can be expressed 

in terms of an isotope-separation (fractionation) factor, 

ε, by the Rayleigh fractionation equation:

(3)

where

Previous calculations using the Rayleigh 

fractionation equation and isotope-ratio and nitrateconcentration data from before and after recharge 

experiments at the research site yielded an isotopeseparation factor of about −22 o/oo (Anders and 

Schroeder, 1997) (fig. 9). Therefore, the amount of 

NO3 removal by denitrification during recharge and 

(or) subsequent ground-water transport to a production 

well can be estimated from measured isotope ratios by 

assuming that the isotope-separation factor of −22 o/oo

exists throughout the aquifer. Using the above 

assumptions yields N removals as high as 50 percent, 

with the highest N-removal percentage found in well 

19M4 (production well number 16) in which δ15N = 

+31.36 o/oo. Actual removal rates are likely to be 

slightly greater than calculated owing to lower δ15N 

values commonly found in stormwater used for 

recharge, which are composed of N of natural and 

fertilizer origins that typically have δ15N values much 

lower than those found in wastewater (Heaton, 1986, 

and Hübner, 1986). Furthermore, attempts were made 

to relate isotope ratios to plausible individual variables 

such as ground-water traveltimes or distance from the 

spreading grounds, depth of well, redox state as 

evidenced by oxygen and manganese concentrations, 

and even NO3 concentration itself. However, these 

attempts failed to yield any obvious relation owing to 

the complex interplay of all variables listed, in addition 

to timing and composition of recharge and mixing of 

water from different depths (Schroeder and others, 

1997). 

δ15Nf = final nitrogen isotope ratio measured in 

well at time of sampling [o/oo];

δ15Ni = initial (at time of recharge) nitrogen 

isotope ratio [o/oo];

[NO3]f = final nitrate concentration [mg/L]; and 

[NO3]i = initial (at time of recharge) nitrate 

concentration [mg/L]. 

δ

15Nf δ15Ni εLn

NO3 [ ]f

NO3 [ ]i

= + ----------------
34 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

0

5

10

15

20

1

2

3

4

5 6

7

8

9

10

11

12

15 14 13

16

17

19 18 20

21

22

23

B

2

0 20 40 60 80 100

DELTA BORON-11, IN PER MIL

Regression line

Production-well number

(r 2 = 0.14)

PERCENT OF RECYCLED WATER, FROM "EXCESS" CHLORIDE

Figure 8. Boron-isotope ratios and “excess” chloride values in selected production wells, Los Angeles County, California.
Water-Quality Indicators and Environmental Tracers 35

0

10

20

30

40

50

60

1

NITRATE CONCENTRATION, IN MILLIGRAMS PER LITER AS NITROGEN

0 2 4 6 8 10

DELTA NITROGEN-15, IN PER MIL

Production-well number

Recycled water (effluent)

Background well (26K3)

Effluent

Research site

1

2 3 4

5

6

8

9

10 11

12

13

14

15

16

17

1819

20

21

22

23

Ammonia Organic N

Nitrate Nitrite

Rayleigh fractionation

15N-Nitrogen

15N-Nitrate

Figure 9. Nitrogen-isotope ratios and nitrate concentrations in selected production wells, Los Angeles County, California.
36 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Furthermore, the Rayleigh fractionation equation 

previously used to calculate NO3 removal percentages 

by denitrification can be used to calculate NO3

concentrations in the production wells at the time of 

recharge. For these calculations, the Rayleigh 

fractionation equation was rearranged to compute 

[NO3]i as if there were no denitrification and is referred 

to as a “back-calculated” nitrogen (assumed to be 

nitrate) concentration (calN). The result yields a r2 of 

0.48 between the “back-calculated” nitrogen 

concentration and recycled-water percentage from 

“excess” Cl (fig. 10). Therefore, the “back-calculated” 

nitrogen concentration in the production-well water 

represents the concentration from recycled water just as 

for the conservative species such as Cl and B.

Organic Constituents

A number of organic constituents associated with 

recycled water have been identified in the production 

wells (Barber and others, 1997). Robust linear 

regression analysis indicates that ultraviolet absorbance 

at 254 nanometers (UV) and excitation 

(300–400 nm filter) — emission (410–500 nm filter) 

fluorescence are strongly correlated (r2 = 0.77). 

Furthermore, UV absorbance and fluorescence appear 

to be quantitative indicators of recycled water in 

production wells in much the same manner as Cl and B 

(fig. 11), although calculated percentages are less than 

those for “excess” Cl and “excess” B (fig. 7). Specific 

UV absorbance (SUVA) and specific fluorescence 

(SFLU) values are obtained by dividing by dissolved 

organic carbon (DOC) concentration. The fact that 

their “specific values” group together suggests a 

common origin (recycled water) and preservation (or 

nonspecific degradation) of the responsive component 

(perhaps surfactants and whitening agents in 

detergents) for most of the organic carbon that is 

present in the well water (fig. 12). 

Also, the fact that extrapolation of regression 

lines for UV absorbance and fluorescence using a 

standard linear regression method both pass near the 

data point for recycled water itself indicates little loss 

of both signals during recharge and subsequent travel 

to the production wells (fig. 13). This contrasts to the 

regression line for ethylenediaminetetraacetic acid 

(EDTA) using a standard linear regression method, 

whose extrapolated value falls more than 30 percent 

below its concentration in recycled water, suggesting 

that EDTA is not conservative.

Tritium and Well-Water Ages

Tritium (3H), a radioactive isotope of hydrogen, 

which has a half-life of 12.4 years, has been widely 

used to date ground water recharged less than about 50 

years before present (Unterweger and others, 1980). 

This dating technique takes advantage of the natural 

decay of 3H to 3He in the environment. The occurrence 

of 3H in the environment is due to atmospheric 

detonation of thermonuclear devices prior to 1963, and 

the subsequent gradual decline as a result of continuous 

removal from the atmosphere and by radioactive decay. 

The technique of 3H age dating of ground water 

includes the following principles: (1) ground water 

completely absent of tritium indicates recharge earlier 

than about 1950; (2) ground water containing the 

maximum 3H concentration indicates recharge water 

dating to about 1963 and; (3) ground water containing 

intermediate 3H concentrations indicates water 

recharged more recently than 1963 if recharge took 

place during the receding limb of the atmospheric 

source curve, or between 1950 and 1963 if recharge 

occurred on the rising limb. It should be noted that this 

simple interpretation of 3H concentrations in ground 

water is complicated when mixing of ground water of 

differing ages occurs, as could be the case in the 

Central Basin.
Water-Quality Indicators and Environmental Tracers 37

PERCENT OF RECYCLED WATER, FROM "EXCESS" CHLORIDE

0 20 40 60 80 100

Regression line

Production-well number

(r 2 = 0.48)

13

0

2

4

6

8

10

"BACK-CALCULATED" NITROGEN, IN MILLIGRAMS PER LITER

1

2

3

4

5

6

8

9

10 11 12

13

14

15

16

17

18 19

20

21

22

23

Figure 10. Relation between “back-calculated” nitrogen concentration and “excess” chloride values in selected production wells, Los Angeles County, 

California.
38 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Regression line

Production-well number

(r 2 = 0.77)

22

0

10

20

30

40

1

2

3

4

5

6

7

8

9

10 11

12

13

14

15

16

17

19 18

20

21

22

23

PERCENT OF RECYCLED WATER, FROM TOTAL FLUORESENCE

PERCENT OF RECYCLED WATER, FROM ULTRAVIOLET ABSORBANCE AT 254 NANOMETERS

0 10 20 30 40

Figure 11. Estimates of recycled water in selected production wells based on ultraviolet absorbance and fluorescence, Los Angeles County, California.
Water-Quality Indicators and Environmental Tracers 39

20

30

0 0.01 0.02 0.03

40

50

60

70

80

1

2

3

4

5

6

7

8

9

10

12 11

13

14

15

16

17 18

19

20

21

22

23

SPECIFIC FLUORESENCE

SPECIFIC ULTRAVIOLET ABSORBANCE AT 254 NANOMETERS

1 Production-well number

Figure 12. Specific ultraviolet absorbance and fluorescence (values divided by dissolved organic carbon concentration) in selected production wells, Los 

Angeles County, California.
40 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

DISSOLVED ORGANIC CARBON, IN MILLIGRAMS PER LITER

ULTRAVIOLET ABSORBANCE X 1000;

FLUORESCENCE and EDTA, IN MICROGRAMS PER LITER

01234567 8 0

50

100

150

200

250

300

350

400

450

UV absorbance

Fluorescence

EDTA

r2 = 0.60

r2 = 0.60

y = 46.59x 10.56

Fluorescence

EDTA

UV

y = 30.28x 8.78

y = 14.76x 1.08

r2 = 0.38

Productionwell dataRecycled

water

Regression

line

Figure 13. Extrapolated standard linear regression lines from selected production-well data (open symbols) and concentration in recycled water (solid 

symbols) for ultraviolet absorbance (UV), fluorescence, and ethylenediaminatetraacetic acid (EDTA), Los Angeles County, California.
Water-Quality Indicators and Environmental Tracers 41

Calculations from a large-scale 3H atmosphericdeposition model (Michel, 1989) yield an annual 

average of about 103 TU (corrected for decay to the 

time of sampling in 1996) for precipitation in the Los 

Angeles Basin at the time of the 1963 atmospheric 

nuclear-bomb maximum. Concentration then declined 

rapidly until about 1983, after which the decaycorrected annual average remains nearly constant at 3.7 

to 4.4 TU. Stratigraphic-estimated traveltimes 

(described in the section “Description of Study Area”) 

were calculated using an association between hydraulic 

properties and known stratigraphy along possible flow 

paths from the spreading grounds to the 23 production 

wells in the Montebello Forebay (BookmanEdmonston Engineering, Inc., 1994). The traveltimes 

are shown in table 2 and range from 24 days to more 

than 16 years. If these traveltimes are correct, 

calculations from a large-scale 3H atmosphericdeposition model predicts that the concentrations of 3H 

should be about the same in all 23 production wells. 

However, the measured 3H concentrations differ 

considerably among the production wells, ranging from 

about 8 to 19.5 TU (fig. 14; table 2). 

The high scatter of most values found in the 

production wells do not fit the simple decay prediction 

because a larger proportion of 3H-rich and older 

ground water (older than 15 years but still young 

enough to contain 3H) is drawn through a well screened 

over intervals intercepting ground-waters that have a 

wide range of ground-water ages. Furthermore, a single 

sample of recycled water was found to have a 3H 

concentration of 7.5 TU, indicating that a source of 

water supplied to the treatment plant itself has a 

composite age of slightly older ground water (table 2). 

Multiple-well monitoring-site data discussed in the 

section “Tritium/Helium-3 Age Determinations” 

confirms the composite age of well water from 

production wells.

Multiple-Well Monitoring-Site Results

Water and dissolved-gas samples were collected 

from five multiple-well monitoring sites, through 

galvanized-steel well points with stainless steel 

implants at a small constructed research site located 

adjacent to the San Gabriel Coastal Basin Spreading 

Grounds, and from stormwater from the San Gabriel 

Coastal Basin Spreading Grounds in April, May, and 

August 1998 and March 1999. The five multiple-well 

monitoring sites are aligned along the of ground-water 

flow path from the Montebello Forebay in the north, 

where the recycled water is applied to the San Gabriel 

and the Rio Hondo Coastal Basin Spreading Grounds, 

to the Central Basin in the south (fig. 6). The waterquality data for the five multiple-well monitoring sites 

are given in table 4, whereas the water-quality data for 

the research site itself and the recycled water are given 

in table 5. 

The southernmost multiple-well monitoring sites 

(4S/12W-5H5 through 4S/12W-5H9, excluding 5H10) 

located along the flow path served as a background 

insofar as absence of tritium confirmed that the ground 

water at this site is older than 1950s recharge and, 

therefore, still ahead of the advancing wastewater front 

(Land and others, 2002, Reichard and others, 2003). 

Results for chlorofluorocarbons (CFCs), 

tritium/helium-3 (3H/3He), chloride, boron, dissolved 

gases, and nitrogen isotopes were used to determine 

some of the long-term effects on the aquifer from 

augmenting recharge of imported water and local water 

with recycled water. 
42 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California TRITIUM CONCENTRATION, IN TRITIUM UNITS

1 10 100 1,000 10,000

0

5

10

15

20

25

30

1

2

3

4

5

6

7

8

9

10

11 12

13

14 15

16

17

18

19

20 21

22

23

TRAVELTIME, IN DAYS

1 Production-well number

Recycled water (effluent)

Figure 14. Relation between tritium concentration in wells and stratigraphic-estimated traveltimes between spreading grounds and production wells, Los 

Angeles County, California. [Traveltimes estimated by Bookman-Edmonston Engineering, Inc. (1994) from stratigraphic information.]
Water-Quality Indicators and Environmental Tracers 43

Table 4. Water-quality data for multiple-well monitoring sites in Los Angeles County, California, 1998–1999—Continued

State

well No.

Site

identification No. Date Time

Depth 

of well

(ft)

(72008)

Altitude of

land surface,

ft above NGVD

(72000)

Oxygen,

dissolved,

mg/L

(00300)

pH, water, 

whole, field,

standard units

(00400)

4S/12W-5H5 335112118090401 05/01/98 1400 1,009 48 0.5 8.8

4S/12W-5H6 335112118090402 04/29/98 1200 660 48 .3 8.0

03/24/99 1200 660 48 .1 7.9

4S12W-5H7 335112118090403 04/29/98 1800 470 48 .5 7.9

08/04/98 1500 470 48 .1 8.2

03/23/99 1700 470 48 .04 7.8

4S/12W-5H8 335112118090404 04/30/98 1700 300 48 .85 7.9

4S/12W-5H9 335112118090405 04/30/98 1500 160 48 .3 8.0

4S/12W-5H10 335112118090406 04/30/98 1100 90 48 .4 7.4

3S/12W-9J1 335517118081301 05/04/98 1500 1,190 98 .15 8.0

3S/12W-9J2 335517118081302 05/02/98 1500 960 98 3.3 7.8

3S/12W-9J3 335517118081303 05/02/98 1900 600 98 3.2 7.6

3S/12W-9J4 335517118081304 05/03/98 1130 390 98 .2 7.5

08/04/98 2000 390 98 .15 7.6

3S/12W-9J5 335517118081305 05/04/98 1100 270 98 .2 7.5

04/02/99 1300 270 98 .18 7.5

3S/12W-9J6 335517118081306 05/02/98 1100 110 98 .15 7.2

2S/12W-25G3 335818118051201 03/31/99 1600 1,200 150 2.5 7.3

2S/12W-25G4 335818118051202 03/30/99 1400 850 150 3.3 7.4

2S/12W-25G5 335818118051203 04/01/99 1700 580 150 3.52 7.3

2S/12W-25G6 335818118051204 03/30/99 1900 340 150 .14 7.3

2S/12W-25G7 335818118051205 04/01/99 1200 255 150 .18 7.2

2S/12W-25G8 335818118051206 03/31/99 1100 120 150 .14 7.1

2S/12W-26D9 335829118065201 05/08/98 1530 1,130 145 .2 8.1

2S/12W-26D10 335829118065202 05/07/98 1330 930 145 .15 7.7

2S/12W-26D11 335829118065203 05/09/98 1230 730 145 .75 7.5

03/25/99 1600 730 145 .44 7.6

2S/12W-26D12 335829118065204 05/07/98 1730 450 145 .15 7.5

08/05/98 1630 450 145 .6 7.4

2S/12W-26D13 335829118065205 05/08/98 1130 300 145 .1 7.4

03/26/99 1300 300 145 .14 7.3

2S/12W-26D14 335829118065206 05/08/98 1800 160 145 .1 7.2

08/05/98 1830 160 145 .2 7.2

03/29/99 1800 160 145 .14 7.2

2S/11W-18C4 340005118043301 05/06/98 1900 900 181 .05 8.1

08/06/98 1530 900 181 .1 7.9

2S/11W-18C5 340005118043302 05/06/98 1200 480 181 .15 7.6

2S/11W-18C6 340005118043303 05/06/98 1530 400 181 .05 7.1

2S/11W-18C7 340005118043304 05/05/98 1030 190 181 .15 7.3

Table 4. Water-quality data for multiple-well monitoring sites in Los Angeles County, California, 1998–1999

[Number below the compound is the data parameter code, which is a 5-digit number used in the U.S.Geological Survey computerized data system, National 

Water Information System (NWIS), to uniquely identify a specific constituent or property; μS/cm, microsiemens per centimeter at 25oC; oC, degrees Celsius; 

ft, feet; mg/L, milligrams per liter; μg/L, micrograms per liter; per mil, parts per thousand; TU, tritium units; NGVD, National Geodetic Vertical Datum of 

1929; <, actual value less than value shown; —, no data] 
44 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 4. Water-quality data for multiple-well monitoring sites in Los Angeles County, California, collected 1998 –1999—Continued

State

well No. Date Time

Specific

conductance,

μS/cm

(00095)

Air

temperature, oC

(00020)

Water 

temperature, oC

(00010)

Calcium,

dissolved,

mg/L as Ca

(00915)

Magnesium,

dissolved,

mg/L as Mg

(00925)

Potassium,

dissolved,

mg/L as K

(00935)

4S/12W-5H5 05/01/98 1400 271 24 23 10.5 0.4 0.6

4S/12W-5H6 04/29/98 1200 322 31 21 31.8 3.6 1.9

03/24/99 1200 320 20 23 31.6 3.8 2.1

4S12W-5H7 04/29/98 1800 349 31 21 37.8 4.5 2.1

08/04/98 1500 356 — 23 — — —

03/23/99 1700 356 16 22 37.9 4.7 2.3

4S/12W-5H8 04/30/98 1700 435 21 20 47.3 5.8 2.8

4S/12W-5H9 04/30/98 1500 398 23 20 47.3 8.2 2.2

4S/12W-5H10 04/30/98 1100 1,133 22 21 142.8 14.3 4.5

3S/12W-9J1 05/04/98 1500 347 22 20 39.1 5.3 3.0

3S/12W-9J2 05/02/98 1500 570 25 20 71.2 11.1 3.6

3S/12W-9J3 05/02/98 1900 793 21 19 100.5 18.9 3.3

3S/12W-9J4 05/03/98 1130 871 26 19 92.5 18.8 4.4

08/04/98 2000 866 — 20 — — —

3S/12W-9J5 05/04/98 1100 857 20 19 111.4 21.6 4.4

04/02/99 1300 837 15 19 112.8 21.3 4.0

3S/12W-9J6 05/02/98 1100 1,266 25 20 146.3 30.5 5.7

2S/12W-25G3 03/31/99 1600 766 12 20 70.5 20.8 6.4

2S/12W-25G4 03/30/99 1400 866 19 19 116.8 23.1 3.7

2S/12W-25G5 04/01/99 1700 810 11 19 101.2 19.9 4.0

2S/12W-25G6 03/30/99 1900 925 11 20 81.5 17.3 4.4

2S/12W-25G7 04/01/99 1200 860 15 20 71.5 16.7 4.4

2S/12W-25G8 03/31/99 1100 885 14 22 72.2 21.3 7.2

2S/12W-26D9 05/08/98 1530 453 21 19 35.3 7.2 3.7

2S/12W-26D10 05/07/98 1330 703 23 20 89.8 16.4 3.9

2S/12W-26D11 05/09/98 1230 722 20 19 77.7 14.3 4.0

03/25/99 1600 716 11 18 78.2 14.0 3.9

2S/12W-26D12 05/07/98 1730 750 20 19 70.3 13.4 4.0

08/05/98 1630 744 — 21 — — —

2S/12W-26D13 05/08/98 1130 586 21 20 49.7 10.1 3.6

03/26/99 1300 582 20 20 50.4 10.1 3.5

2S/12W-26D14 05/08/98 1800 566 19 19 45.9 12.6 4.1

08/05/98 1830 424 — 21 — — —

03/29/99 1800 448 17 21 33.5 9.2 3.4

2S/11W-18C4 05/06/98 1900 574 17 19 9.1 2.9 4.5

08/06/98 1530 566 — 22 — — —

2S/11W-18C5 05/06/98 1200 506 24 20 61.0 11.4 3.0

2S/11W-18C6 05/06/98 1530 1,041 22 20 120.7 24.6 4.6

2S/11W-18C7 05/05/98 1030 930 19 20 91.7 17.5 4.7
Water-Quality Indicators and Environmental Tracers 45

Table 4. Water-quality data for multiple-well monitoring sites in Los Angeles County, California, collected 1998–1999—Continued

State

well No. Date Time

Sodium,

dissolved,

mg/L as Na

(00930)

Alkalinity,

fixed endpoint, 

field,

dissolved,

mg/L as CaCO3

(39036)

Bromide,

dissolved,

mg/L as Br

(71870)

Chloride,

dissolved,

mg/L as Cl

(00940)

Fluoride,

dissolved,

mg/L as F

(00950)

Iodine,

dissolved,

mg/L as I

(71865)

4S/12W-5H5 05/01/98 1400 51.4 96 56 19.1 0.47 .048

4S/12W-5H6 04/29/98 1200 32.5 145 28 7.5 .29 .012

03/24/99 1200 31.4 138 29 6.4 .31 .009

4S12W-5H7 04/29/98 1800 31.7 158 32 9.3 .30 .016

08/04/98 1500 — 156 — — — —

03/23/99 1700 30.5 150 39 9.6 .35 .017

4S/12W-5H8 04/30/98 1700 35.2 182 93 19.5 .31 .029

4S/12W-5H9 04/30/98 1500 24.0 185 35 10.0 .48 .015

4S/12W-5H10 04/30/98 1100 51.5 215 1,444 210.5 .16 .089

3S/12W-9J1 05/04/98 1500 25.2 160 30 5.6 .36 <.001

3S/12W-9J2 05/02/98 1500 25.7 178 71 24.6 .34 <.001

3S/12W-9J3 05/02/98 1900 27.5 172 141 63.2 .38 .001

3S/12W-9J4 05/03/98 1130 55.8 201 157 72.6 .45 .013

08/04/98 2000 — 197 — — — —

3S/12W-9J5 05/04/98 1100 29.6 255 201 59.0 .37 .010

04/02/99 1300 29.7 223 207 58.2 .36 .011

3S/12W-9J6 05/02/98 1100 74.8 302 302 93.0 .34 .005

2S/12W-25G3 03/31/99 1600 52.1 158 124 58.9 .41 .007

2S/12W-25G4 03/30/99 1400 29.6 217 190 54.1 .31 .001

2S/12W-25G5 04/01/99 1700 34.2 185 160 58.6 .36 .002

2S/12W-25G6 03/30/99 1900 79.1 165 158 94.1 .46 .017

2S/12W-25G7 04/01/99 1200 73.5 153 156 88.1 .33 .022

2S/12W-25G8 03/31/99 1100 73.0 140 157 93.1 .47 .018

2S/12W-26D9 05/08/98 1530 46.6 152 85 18.7 .33 .029

2S/12W-26D10 05/07/98 1330 25.7 172 119 47.2 .29 .004

2S/12W-26D11 05/09/98 1230 45.2 158 124 57.1 .36 .004

03/25/99 1600 43.7 149 124 56.6 .34 .005

2S/12W-26D12 05/07/98 1730 59.6 148 102 64.3 .49 .018

08/05/98 1630 — 148 — — — —

2S/12W-26D13 05/08/98 1130 51.0 132 76 45.3 .41 .015

03/26/99 1300 48.3 121 99 51.7 .39 .014

2S/12W-26D14 05/08/98 1800 46.6 125 88 47.2 .29 .014

08/05/98 1830 — 98 — — — —

03/29/99 1800 40.6 97 72 33.7 .38 .010

2S/11W-18C4 05/06/98 1900 121.0 303 <10. 3.9 .28 .007

08/06/98 1530 — 294 — — — —

2S/11W-18C5 05/06/98 1200 20.9 172 75 18.0 .32 .003

2S/11W-18C6 05/06/98 1530 59.1 220 222 82.3 .22 .010

2S/11W-18C7 05/05/98 1030 74.7 208 185 70.0 .33 .011
46 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 4. Water-quality data for multiple-well monitoring sites in Los Angeles County, California, collected 1998–1999—Continued

State

well No. Date Time

Silica,

dissolved,

mg/L as SiO2

(00955)

Sulfate,

dissolved,

mg/L as SO4

(00945)

Solids,

sum of 

constituents,

dissolved

mg/L

(70300)

Ammonia +

organic 

nitrogen,

dissolved,

mg/L as N

(00623)

Ammonia,

dissolved,

mg/L as N

(00608)

Nitrate plus

nitrite,

dissolved,

mg/L as N

(00631)

4S/12W-5H5 05/01/98 1400 16.0 14.8 171 0.39 0.37 <.05

4S/12W-5H6 04/29/98 1200 22.2 14.8 207 .11 .13 <.05

03/24/99 1200 21.2 15.8 202 E.10 .09 <.05

4S12W-5H7 04/29/98 1800 24.8 14.4 224 .21 .22 <.05

08/04/98 1500 — — — .16 .20 <.05

03/23/99 1700 24.0 15.5 223 .20 .18 <.05

4S/12W-5H8 04/30/98 1700 21.9 15.0 235 .24 .30 <.05

4S/12W-5H9 04/30/98 1500 23.7 14.2 248 <.1 .11 <.05

4S/12W-5H10 04/30/98 1100 23.8 43.8 739 .47 .50 <.05

3S/12W-9J1 05/04/98 1500 19.9 15.8 217 <.1 .03 .05

3S/12W-9J2 05/02/98 1500 20.0 71.8 361 <.1 .03 1.82

3S/12W-9J3 05/02/98 1900 21.2 131.5 517 <.1 <.02 2.81

3S/12W-9J4 05/03/98 1130 20.8 131.1 553 <.1 .04 2.60

08/04/98 2000 — — — <.1 .05 2.55

3S/12W-9J5 05/04/98 1100 21.7 117.0 557 <.1 .03 <.05

04/02/99 1300 22.0 113.7 531 <.1 .02 <.05

3S/12W-9J6 05/02/98 1100 23.9 253.3 861 <.1 .05 <.05

2S/12W-25G3 03/31/99 1600 17.0 119.7 482 E.10 <.02 2.71

2S/12W-25G4 03/30/99 1400 22.0 130.4 559 <.1 <.02 2.82

2S/12W-25G5 04/01/99 1700 21.4 128.6 522 <.1 <.02 3.17

2S/12W-25G6 03/30/99 1900 20.6 135.1 582 E.09 <.02 3.23

2S/12W-25G7 04/01/99 1200 19.3 129.9 537 E.08 <.02 1.59

2S/12W-25G8 03/31/99 1100 17.3 139.2 559 .18 <.02 2.83

2S/12W-26D9 05/08/98 1530 24.1 50.0 288 .15 .15 <.05

2S/12W-26D10 05/07/98 1330 24.4 120.0 467 .15 .08 <.05

2S/12W-26D11 05/09/98 1230 21.3 113.6 464 <.1 .03 2.58

03/25/99 1600 21.3 114.8 456 <.1 <.02 2.52

2S/12W-26D12 05/07/98 1730 20.8 115.9 478 <.1 <.02 3.00

08/05/98 1630 — — — <.1 .05 2.99

2S/12W-26D13 05/08/98 1130 18.9 86.8 366 <.1 .04 1.19

03/26/99 1300 18.7 84.7 364 E.05 <.02 1.29

2S/12W-26D14 05/08/98 1800 15.5 77.2 348 <.1 .04 1.77

08/05/98 1830 — — — <.1 .05 1.18

03/29/99 1800 15.6 62.1 269 <.1 <.02 1.10

2S/11W-18C4 05/06/98 1900 27.9 3.7 368 2.19 <.02 <.05

08/06/98 1530 — — — 2.35 2.15 <.05

2S/11W-18C5 05/06/98 1200 21.7 63.0 324 .15 .12 <.05

2S/11W-18C6 05/06/98 1530 20.8 210.8 687 <.1 .03 <.05

2S/11W-18C7 05/05/98 1030 20.5 163.8 601 <.1 <.02 1.54
Water-Quality Indicators and Environmental Tracers 47

Table 4. Water-quality data for multiple-well monitoring sites in Los Angeles County, California, collected 1998 –1999—Continued

State

well No. Date Time

Nitrite,

dissolved,

mg/L as N

(00613)

Orthophosphate,

dissolved,

mg/L as P

(00671)

Phosphorus,

dissolved,

mg/L as P

(00666)

Boron,

dissolved,

μg/L as B

(01020)

Iron,

dissolved,

μg/L as Fe

(01046)

4S/12W-5H5 05/01/98 1400 <.01 0.07 0.04 62.6 <10.

4S/12W-5H6 04/29/98 1200 <.01 .08 .07 53.3 19

03/24/99 1200 <.01 .03 .02 48.7 E10.

4S12W-5H7 04/29/98 1800 <.01 .13 .11 62.0 20

08/04/98 1500 <.01 — — — —

03/23/99 1700 <.01 .03 .04 63.0 17

4S/12W-5H8 04/30/98 1700 <.01 1.45 1.34 75.6 56

4S/12W-5H9 04/30/98 1500 <.01 .07 .05 83.7 96

4S/12W-5H10 04/30/98 1100 <.01 .21 .18 91.1 145

3S/12W-9J1 05/04/98 1500 <.01 .03 .05 63.9 <10.

3S/12W-9J2 05/02/98 1500 <.01 .11 .11 68.8 <10.

3S/12W-9J3 05/02/98 1900 <.01 .09 .09 79.4 <10.

3S/12W-9J4 05/03/98 1130 <.01 .06 .06 195.4 <10.

08/04/98 2000 <.01 — — — —

3S/12W-9J5 05/04/98 1100 0.07 .03 .03 103.0 <10.

04/02/99 1300 <.01 .04 .04 105.4 <10.

3S/12W-9J6 05/02/98 1100 <.01 .35 .35 220.2 11

2S/12W-25G3 03/31/99 1600 <.01 .53 .62 161.5 <10.

2S/12W-25G4 03/30/99 1400 <.01 .04 .05 96.9 <10.

2S/12W-25G5 04/01/99 1700 <.01 .04 .04 123.9 <10.

2S/12W-25G6 03/30/99 1900 <.01 .07 .08 284.4 <10.

2S/12W-25G7 04/01/99 1200 <.01 .05 .04 233.0 <10.

2S/12W-25G8 03/31/99 1100 .17 .80 .90 262.7 <10.

2S/12W-26D9 05/08/98 1530 <.01 .01 <.01 74.4 11

2S/12W-26D10 05/07/98 1330 <.01 .02 .01 53.9 59

2S/12W-26D11 05/09/98 1230 <.01 .08 .07 148.2 <10.

03/25/99 1600 <.01 .04 .04 150.4 <10.

2S/12W-26D12 05/07/98 1730 <.01 .02 .03 203.4 <10.

08/05/98 1630 <.01 — — — —

2S/12W-26D13 05/08/98 1130 <.01 .02 <.01 148.9 <10.

03/26/99 1300 <.01 .04 .04 136.6 <10.

2S/12W-26D14 05/08/98 1800 <.01 .02 .02 152.0 <10.

08/05/98 1830 <.01 — — — —

03/29/99 1800 <.01 .02 .03 146.7 <10.

2S/11W-18C4 05/06/98 1900 <.01 1.92 1.85 609.0 33

08/06/98 1530 <.01 — — — —

2S/11W-18C5 05/06/98 1200 <.01 .05 .05 68.8 190

2S/11W-18C6 05/06/98 1530 <.01 <.01 .02 169.7 546

2S/11W-18C7 05/05/98 1030 .07 .02 .01 217.1 <10
48 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 4. Water-quality data for multiple-well monitoring sites in Los Angeles County, California, collected 1998 –1999—Continued

State

well No. Date Time

Manganese,

dissolved,

μg/L as Mn

(01056)

2H/1

H, H2O

per mil

(82082)

18O/16O, H2O

ratio per mil 

(82085)

Tritium,

2 sigma,

TU

(75985)

Tritium,

TU

(07000)

4S/12W-5H5 05/01/98 1400 7 −59.4 −8.96 0.6 <0.1

4S/12W-5H6 04/29/98 1200 37 −53.4 −8.10 .6 <.1

03/24/99 1200 22 −53.1 −8.18 .2 <.1

4S12W-5H7 04/29/98 1800 37 −50.2 −8.06 .6 <.1

08/04/98 1500 — — — — —

03/23/99 1700 27 −53.6 −8.05 .2 <.1

4S/12W-5H8 04/30/98 1700 131 −52.3 −7.89 .6 .1

4S/12W-5H9 04/30/98 1500 57 −53.5 −8.20 .6 <.1

4S/12W-5H10 04/30/98 1100 442 −51.6 −7.75 .6 2.4

3S/12W-9J1 05/04/98 1500 <4. −54.0 −8.30 .6 .1

3S/12W-9J2 05/02/98 1500 <4. −57.3 −8.63 .8 5.7

3S/12W-9J3 05/02/98 1900 <4. −68.0 −9.36 2.2 32.5

3S/12W-9J4 05/03/98 1130 6 −59.2 −8.39 1.4 18.0

08/04/98 2000 — — — — —

3S/12W-9J5 05/04/98 1100 190 −52.8 −8.00 .6 5.1

04/02/99 1300 176 −51.9 −7.83 .8 3.2

3S/12W-9J6 05/02/98 1100 88 −54.7 −7.79 1.2 16.4

2S/12W-25G3 03/31/99 1600 194 −53.6 −7.66 .6 8.4

2S/12W-25G4 03/30/99 1400 <3. −59.4 −8.32 1.4 16.9

2S/12W-25G5 04/01/99 1700 4 −63.3 −8.61 1.4 18.3

2S/12W-25G6 03/30/99 1900 37 −57.1 −8.08 1.0 8.5

2S/12W-25G7 04/01/99 1200 18 −54.8 −7.62 1.0 9.2

2S/12W-25G8 03/31/99 1100 1,161 −50.1 −7.06 1.0 8.4

2S/12W-26D9 05/08/98 1530 58 −55.2 −8.36 .6 .1

2S/12W-26D10 05/07/98 1330 136 −63.6 −8.95 1.4 18.4

2S/12W-26D11 05/09/98 1230 15 −64.3 −8.87 1.0 12.5

03/25/99 1600 5 −64.4 −8.79 1.0 10.0

2S/12W-26D12 05/07/98 1730 10 −58.2 −8.23 .8 8.0

08/05/98 1630 — — — — —

2S/12W-26D13 05/08/98 1130 8 −52.9 −7.60 .8 8.0

03/26/99 1300 45 −54.2 −7.56 .8 7.8

2S/12W-26D14 05/08/98 1800 32 −50.4 −7.31 .8 7.2

08/05/98 1830 — — — — —

03/29/99 1800 28 −48.9 −7.25 1.0 7.7

2S/11W-18C4 05/06/98 1900 36 −64.8 −9.61 .6 <.1

08/06/98 1530 — — — — —

2S/11W-18C5 05/06/98 1200 60 −57.6 −8.51 .6 3.6

2S/11W-18C6 05/06/98 1530 32 −60.3 −8.18 1.0 12.5

2S/11W-18C7 05/05/98 1030 5 −59.7 −8.30 1.0 12.7
Water-Quality Indicators and Environmental Tracers 49

Table 5. Water-quality data for the research-basin itself and recycled water in Los Angeles County, California, March 1998–May 1999—Continued

State

well No.

Site

identification No. Date Time

Depth 

of well,

ft

(72008)

Altitude of

land surface,

ft below 

NGVD

(72000)

Oxygen,

dissolved, 

mg/L

(00300)

pH, water, 

whole,

field,

standard 

units

(00400)

Specific

conductance,

field,

μS/cm

(00095)

Pond at Pico 335943118042246 05/05/98 1730 — — 9.4 8.4 673

Pond at Pico 335943118042246 04/02/99 1730 — — 5.0 7.1 1,033

Pond at Pico 335943118042246 06/30/99 1330 — — 8.2 7.2 1,008

Sewage effluent at Pico 335943118042247 05/05/98 1430 — — 4.2 7.1 1,006

Sewage effluent at Pico 335943118042247 06/30/99 1030 — — 3.4 7.1 962

State

well No. Date Time

Air

temperature, oC

(00020)

Water 

temperature, oC

(00010)

Calcium,

dissolved,

mg/L as Ca

(00925)

Magnesium,

dissolved,

mg/L as Mg

(00925)

Potassium,

dissolved,

mg/L as K

(00935)

Sodium,

dissolved,

mg/L as Na

(00930)

Pond at Pico 05/05/98 1730 19 21 55.0 16.9 5.3 50.8

Pond at Pico 04/02/99 1730 12 22 58.3 17.0 12.5 110.4

Pond at Pico 06/30/99 1330 33 27 — — — —

Sewage effluent at Pico 05/05/98 1430 19 24 52.6 15.4 11.4 100.1

Sewage effluent at Pico 06/30/99 1030 33 27 55.8 18.1 12.6 100.9

State

well No. Date Time

Alkalinity, 

fixed endpoint, 

field, 

mg/L as CaCO3

(39036)

Bromide,

dissolved,

mg/L as Br

(71870)

Chloride,

dissolved,

mg/L as Cl

(00940)

Fluoride,

dissolved,

mg/L as F

(00950)

Iodine,

dissolved

(mg/L)

(71865)

Silica,

dissolved,

mg/L as SiO2

(00955)

Pond at Pico 05/05/98 1730 139 50 53.2 0.4 14 14.9

Pond at Pico 04/02/99 1730 208 85 115.7 .7 17 19.0

Pond at Pico 06/30/99 1330 163 — — — — —

Sewage effluent at Pico 05/05/98 1430 137 81 114.5 .6 12 21.5

Sewage effluent at Pico 06/30/99 1030 162 79 114.8 .5 — 19.6

Table 5. Water-quality data for the research-basin itself and recycled water in Los Angeles County, California, 1998–1999

[Number below the compound is the data parameter code, which is a 5-digit number used in the U.S.Geological Survey computerized data system, National 

Water Information System (NWIS), to uniquely identify a specific constituent or property; μS/cm, microsiemens per centimeter at 25oC; oC, degrees Celsius; 

ft, feet; mg/L, milligrams per liter; μg/L, micrograms; per mil, parts per thousand; TU, tritium units; NGVD, National Geodetic Vertical Datum of 1929; <, 

actual value less than value shown; —, no data] 
50 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 5. Water-quality data for research-basin and recycled water in Los Angeles County, California, 1998–1999—Continued

State

well No. Date Time

Sulfate,

dissolved,

mg/L as SO4

(00945)

Solids, sum of 

constituents, 

dissolved,

mg/L

(70300)

Ammonia

plus organic 

nitrogen,

mg/L as N

(00623)

Ammonia, 

dissolved,

mg/L as N

(00608)

Nitrate plus 

nitrite. 

dissolved,

mg/L as N

(00631)

Pond at Pico 05/05/98 1730 87.5 408 1.93 1.38 2.21

Pond at Pico 04/02/99 1730 127.8 633 5.41 4.24 9.72

Pond at Pico 06/30/99 1330 — — 6.27 5.24 6.67

Sewage effluent at Pico 05/05/98 1430 97.3 565 6.02 7.47 5.07

Sewage effluent at Pico 06/30/99 1030 119.2 590 — — —

State

well No. Date Time

Nitrite, 

dissolved,

mg/L as N

(00613)

Orthophosphate,

dissolved

mg/L as P

(00671)

Phosphorus,

dissolved,

mg/L as P

(00666)

Boron,

dissolved,

μg/L as B

(01020)

Iron,

dissolved,

μg/L as Fe

(01046)

Pond at Pico 05/05/98 1730 0.42 0.11 0.12 153.2 <10

Pond at Pico 04/02/99 1730 2.98 2.32 3.06 423.7 34.4

Pond at Pico 06/30/99 1330 2.41 1.47 1.70 — —

Sewage effluent at Pico 05/05/98 1430 2.33 1.93 2.06 424.2 44.8

Sewage effluent at Pico 06/30/99 1030 — — — 415.4 54.9

State

well No. Date Time

Manganese,

dissolved,

μg/L as Mn

(01056)

2H/1H, H2O

(per mil)

(82082)

180/160, H2O

per mil

(82085)

Tritium,

2-sigma,

TU

(75985)

Tritium,

TU

(07000)

Pond at Pico 05/05/98 1730 5.8 −51.7 −7.71 0.8 7.4

Pond at Pico 04/02/99 1730 8.6 −64.8 −8.76 .8 8.2

Pond at Pico 06/30/99 1330 — — — — —

Sewage effluent at Pico 05/05/98 1430 11.7 −53.9 −7.84 .8 6.0

Sewage effluent at Pico 06/30/99 1030 24.7 −59.8 −8.46 — —
Water-Quality Indicators and Environmental Tracers 51

Tritium/Helium-3 Age Determinations

The interpretation of ages from tritium data 

alone is complicated because wells, as noted earlier, are 

screened over intervals that represent a wide range of 

ground-water ages. Depth-dependent variations in 3H 

concentrations are clearly apparent from data on the 

multiple-well monitoring sites given in table 4. 

Furthermore, a simple two-member mixing model 

cannot accurately represent this phenomenon, as is 

evident by the failure of the parametric calculations 

(discussed in section “Two Member Mixing Model, for 

Selected Constituents”) to yield more reasonable 

estimates of the wastewater percentages. Questions 

relating to whether the ground water at depth contains 

tritium solely from the falling limb (post-bomb peak, or 

after about 1965) of the tritium curve can further 

complicate the interpretation. Therefore, 

tritium/helium-3 (3H/3He) ages were determined to 

exclude artifacts of mixing of water with various ages 

in a well and to delineate vertical and lateral extent of 

recycled water in the Central Basin. 3H/3He age 

determinations depend on measurements of 3H and its 

daughter product 3He. Furthermore, 3H/3He ages 

represent the time since the water became isolated from 

the atmosphere and traveled to the sampling point and 

are independent of the tritium source function. 

Solomon and Cook (2000) define the 3H/3He age of a 

ground-water sample as: 

(4)

where

The 3Hetri concentration is used to separate the 

3He in ground water derived from 3H decay from other 

sources including: (1) 3He dissolved in the water owing 

to equilibration with the atmosphere during infiltration; 

(2) excess air (dissolution of small air bubbles); and (3) 

subsurface sources (such as degassing of the earth's 

mantle and lithium reactions). In most shallow groundwater systems, subsurface sources of 3He are minor 

and the following equation can be used to calculate 

3Hetri (Jenkins, 1987):

(5)

where

The factor 4.021 × 1014 is used to convert cm3

STP/g H2O into TU and β is the effect of the difference 

in solubility of the two isotopes of helium (0.983; 

Benson and Krause, 1980). Furthermore, the use of this 

age-dating technique assumes that the system is closed 

(does not allow 3He to escape) and is characterized by 

piston flow (no hydrodynamic dispersion) (Scanlon 

and others, 2002). Shown in table 6 are the 3Hetri and 

3He concentrations provided by the University of 

Rochester Department of Earth and Environmental 

Sciences and the USGS Tritium Laboratory, 

respectively, and the 3H/3He age determinations from 

equation 4 for ground-water samples collected from a 

selected group of multiple-well monitoring sites 

located along the northeast-southwest flow path 

(fig. 15). On the basis of the analytical uncertainties for 

the 3H and 3He measurements, the minimum age error 

is assumed to be about ±1 year. Previously collected 

tritium data were used to avoid analyzing water 

samples that have tritium concentrations less than 0.1 

TU (samples older than 50 years). One tritium-dead 

sample was analyzed from a monitoring well located in 

Lakewood (4S/12W-5H7) to confirm the (expected) 

absence of tritiogenic 3He.

t = 3H/3He age [years];

3Hetri = tritiogenic 3He concentration [TU];

3H = measured tritium concentration [TU]; 

and

λ = 3H decay constant (defined here as Ln2 

divided by the half-life of tritium) 

[year-1]. 

t λ–1Ln

He 3

tri

H

3 -------------

⎝ ⎠ ⎜ ⎟ ⎛ ⎞ = + 1

4Hetot = measured 4He concentration of the 

sample [cm3 STP/g H2O];

Rtot = measured 3He/4He ratio of the water 

sample [dimensionless];

Ratm

3He/4He ratio of atmospheric helium 

(1.384 x 10-6; Clarke and others, 1976) 

[dimensionless]; and

4Heeq = 4He concentration in air-equilibrated 

water [cm3 STP/g H2O].

He 3

tri 4.021 1014 = × ×

He 4

tot Rtot Ratm ( ) – He 4eqRatm [ ] + ( ) 1 – β
52 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 6. Tritium/helium-3 data, recharge ages, “excess” chloride, “back-calculated” nitrogen, and net denitrification-rate constants for selected monitoring 

wells in Los Angeles County, California, 1998–1999

[

3H, tritium; 3He, helium-3; 3Hetri, triogenic helium-3; k, net denitrification rate constant; exCL, calculated “excess” chloride; 15N/14N, nitrogen-15/nitrogen14 ratio; calN, “back-calculated” nitrogen (assumed to be nitrate); TU, tritium units; >, greater than; —, no data]

State

well No.

Site

identification

No.

Date Time

3Hetri

(in TU)

3H

(in TU)

3

H/3He

(age in 

years)

exCl

(percent)

15N/14N

(per mil)

calN

(mg/L)

k

(day-1)

4S12W-5H7 335112118090403 04/29/98 1800 −1.5 0.04 >50 — — — —

3S/12W-9J2 335517118081302 05/02/98 1500 32.7 5.7 34.1 4.27 — — —

3S/12W-9J3 335517118081303 05/02/98 1900 139.6 32.6 29.8 28.60 — — —

3S/12W-9J4 335517118081304 05/03/98 1130 58.4 18.0 25.9 36.73 — — —

3S/12W-9J5 335517118081305 05/04/98 1100 10.6 3.2 26.2 2.09 — — —

2S/12W-25G3 335818118051201 03/31/99 1600 20.3 8.4 22.0 27.64 19.3 3.87 4.42×10−5

2S/12W-25G4 335818118051202 03/30/99 1400 37.4 16.9 20.9 −0.59 14.8 3.27 1.97×10−5

2S/12W-25G5 335818118051203 04/01/99 1700 44.6 18.3 22.1 17.14 14.6 3.65 1.75×10−5

2S/12W-25G6 335818118051204 03/30/99 1900 8.1 8.5 12.0 65.34 28.2 6.90 1.74×10−4

2S/12W-25G7 335818118051205 04/01/99 1200 1.8 9.2 3.2 57.60 35.5 4.75 9.40×10−4

2S/12W-25G8 335818118051206 03/31/99 1100 .3 8.4 .6 64.13 35.7 8.49 5.27×10−3

2S/12W-26D10 335829118065202 05/07/98 1330 84.46 18.4 30.8 15.23 — — —

2S/12W-26D11 335829118065203 03/25/99 1600 20.8 10.0 20.1 25.44 16.9 3.21 3.34×10−5

2S/12W-26D12 335829118065204 05/07/98 1730 9.6 8.0 14.1 38.62 — — —

2S/12W-26D13 335829118065205 03/26/99 1300 1.4 7.8 3.0 23.93 28.0 2.73 6.96×10−4

2S/12W-26D14 335829118065206 03/29/99 1800 1.3 7.7 2.7 23.15 24.7 2.01 6.10×10−4
Water-Quality Indicators and Environmental Tracers 53

400

400

800

1,200

1,600

FEET

Sea

level

A A'

0

0 5 KILOMETERS

5 MILES

Central Basin Pressure Area Montebello Forebay

Spreading Grounds

?

?

Pico Rivera

Rio Hondo 2S/11W-18C4–7

2S/12W-26D9–14 Lakewood

4S/12W-5H5–10

Whittier

Long Beach, Narrows

CA

Los

Alamitos

Fault ?

Downey

3S/12W-9J1–6

San Gabriel*

2S/12W-25G3–8

Datum is sea level Vertical scale greatly exaggerated

<0.1 0.1

0.1

<0.1

3.6

12.7

12.5

16.4

<0.1/

>50.0

<0.1

0.1

2.4

<0.1

5.7/

34.1

18.4/

30.8

8.4/

22.0

16.9/

20.9

18.3/

22.1

8.5/

12.0

8.4/

0.6

9.2/

3.2

10.0/

20.1

8.0/

14.1

8.0/

3.0

7.2/

2.7

32.5/

29.8

5.1/

26.2 18.0/

25.9

5.7/

34.1

Geologic contact — Dashed

where approximately located;

queried where uncertain

Screened

interval

Well

casing

Local identifier

?

Lakewood

(Pleistocene)

(Pliocene)

Upper San Pedro

Lower San Pedro

Pico Unit

Tritium concentration — In tritium units

Tritium/helium age determination — In years.

Sampled 1998

* Well projected to section line

Rio Hondo

2S/12W-26D9–14 State well identification number

EXPLANATION

Recent Multiple-well monitoring site —

Figure 15. Tritium concentration in 5 multiple-well monitoring sites and tritium/helium-3 ages in 16 monitoring wells along ground-water flow path (see 

fig. 6 for locations), Los Angeles County, California.
54 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

The youngest 3H/3He age of 0.6 year was found 

in the water sample collected from a depth of 120 ft 

below land surface adjacent to the San Gabriel Coastal 

Basin Spreading Grounds (2S/12W-25G8). Other water 

samples collected from monitoring wells adjacent to 

the San Gabriel Coastal Basin Spreading Grounds at 

depths between 255 and 1,200 ft below land surface 

had 3H/3He ages ranging from 3.2 to 22.0 years. 

3H/3He ages for water samples collected from 

monitoring wells located adjacent to the Rio Hondo 

Coastal Basin Spreading Grounds at depths between 

160 and 930 ft below land surface ranged from 2.7 to 

30.8 years. The 3H/3He age for water samples collected 

from the monitoring wells located in the city of 

Downey at depths between 270 and 960 ft below land 

surface ranged from 25.9 to 34.1 years. These 3H/3He 

ages indicate that recycled water is present to a depth of 

more than 900 ft below land surface adjacent to both 

spreading grounds and to a distance of more than 4 mi 

downgradient from both spreading grounds. 

Linear regression analysis with the robust MM 

regression method (Mathsoft, Inc., Cambridge, Mass.) 

was preformed using the 3H/3He ages and the depth of 

the monitoring wells located adjacent to the San 

Gabriel Coastal Basin (2S/12W-25G4 through 25G8) 

and Rio Hondo Coastal Basin Spreading Grounds 

(2S/12W-26D10 through 26D14). The resulting 

correlation was higher adjacent to the Rio Hondo 

Coastal Basin Spreading Grounds (r2 = 0.89) then 

adjacent to the San Gabriel Coastal Basin Spreading 

Grounds (r2 = 0.56) (fig. 16). 

Although these correlations were calculated 

using a small number of data points and do not take 

into consideration asymmetric vertical flow that 

probably exists beneath the spreading grounds, they do 

provide some information about the recharge 

characteristics of the recycled water applied at the 

spreading grounds. The lower correlation for the 

monitoring wells adjacent to the San Gabriel Coastal 

Basin Spreading Grounds, along with similar 3H/3He 

ages of 22.1 and 20.9 years for water samples collected 

from 580 (2S/12W-25G5) and 850 (2S/12W-25G4) ft 

below land surface, respectively (fig. 15), probably is 

due to mixing and (or) complete displacement of 

recharged water with pre-existing ground water at these 

depths. The higher correlation for the monitoring wells 

at the Rio Hondo Coastal Basin Spreading Grounds 

owing to the linear increase in age with depth suggests 

less displacement of pre-existing ground water than at 

the San Gabriel Coastal Basin Spreading Grounds.

Tracers of Recycled Water

Chloride and Boron

Chemical results from the production wells 

suggested that Cl and B would be most useful in 

locating the extent of the recycled water along the flow 

path, and this expectation is confirmed by data from the 

multiple-well monitoring sites (fig. 17). Values of 

“excess” Cl and “excess” B were determined for the 

monitoring wells following the same procedure used 

for estimating recycled-water percentages in the 

production wells (table 6). One end-member used to 

calculate the “excess” boron value was the average 

boron concentration from the monitoring well in 

Lakewood previously identified as containing no 

contribution from recycled water (62.5 mg/L in well 

4S/12W-5H7). The “excess” Cl and “excess” B values 

of the monitoring wells show an r2 of 0.42 (fig. 18). 

Similarly, the “excess” Cl and “excess” B values of the 

production wells show an r2 of 0.58 (fig. 7). 

The percentage of recycled water in three of the 

five monitoring wells (2S/12W-25G6–8) adjacent to 

the San Gabriel River Coastal Basin Spreading 

Grounds is similar to the highest values found in the 

production wells along the east side of the San Gabriel 

Coastal Basin Spreading Grounds (figs. 7 and 18). The 

high percentage of recycled water at the San Gabriel 

Coastal Basin Spreading Grounds exceeds the 

35-percent limit DOHS sets on the allowable amount of 

recycled water that can be applied during any 3-year 

period, suggesting either greater use of this side for 

replenishment purposes during the dry months or 

higher natural levels of B and Cl on this side. 

Furthermore, those “excess” Cl and “excess” B values 

not showing a strong correlation either have a high 

concentration of bromide (4S/12W-5H10) or boron 

(3S/12W-9J6, 2S/11W-18C4, and 2S/11W-18C7) 

probably owing to surface anthropogenic effects such 

as oil-field brines and (or) local aquifer properties such 

as clay content or soil type. 
Water-Quality Indicators and Environmental Tracers 55

0

300

600

900

1,200

Rio Hondo (26D10–14)

(r 2 = 0.56)

Regression line

(r 2 = 0.89)

0 10 20 40 30

TRITIUM/HELIUM-3 AGE DETERMINATION, IN YEARS

DEPTH OF MONITORING WELL, IN FEET BELOW LAND SURFACE

San Gabriel (25G4–8)

Regression line

25G7

25G6

25G5

25G8

26D11

26D10

26D12

26D14

26D13

25G4

Figure 16. Relation between tritium/helium-3 ages and depth of the monitoring wells adjacent to the San Gabriel and Rio Hondo Coastal Basin Spreading 

Grounds, Los Angeles County, California.
56 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

400

400

800

1,200

1,600

FEET

Sea

level

A A'

0

0 5 KILOMETERS

5 MILES

Central Basin Pressure Area Montebello Forebay

Spreading Grounds

?

?

Pico Rivera

2S/11W-18C4–7

Lakewood

4S/12W-5H5-–10

Whittier

Narrows

Long Beach,

CA

Los

Alamitos

Fault ?

Downey

3S/12W-9J1–6

Datum is sea level Vertical scale greatly exaggerated

Rio Hondo

2S/12W-26D9–14 San Gabriel*

2S/12W-25G3–8

5.6/

63.9

19.1/

62.6 5.6/

63.9

24.6/

68.8

63.2/

79.4

59.0/

103.0 72.6/

195.4

93.0/

220.2

7.5/

53.3

9.3/

62.0

19.5/

75.6

210.5/

91.1 10.0/

83.7

18.7/

74.4 58.9/

161.5

3.9/

609.0

18.0/

68.8

82.3/

169.7

70.0/

217.1

54.1/

96.9

58.6/

123.9

94.1/

284.4

88.1/

233.0

93.1/

262.7

47.2/

53.9

47.2/

152.0

45.3/

148.9

57.1/

148.2

64.3/

203.4

EXPLANATION

Multiple-well monitoring site —

Geologic contact — Dashed

where approximately located;

queried where uncertain

Screened

interval

Well

casing

Local identifier

?

Lakewood

(Pleistocene)

(Pliocene)

Recent

Upper San Pedro

Lower San Pedro

Pico Unit

Chloride concentration — In milligrams

per liter

Boron concentration — In milligrams

per liter. Sampled 1998

* Well projected to section line

Rio Hondo

2S/12W-26D9–14 State well identification number

Figure 17. Chloride and boron concentrations in multiple-well monitoring sites along ground-water flow path (see fig. 6 for locations), Los Angeles 

County, California.
Water-Quality Indicators and Environmental Tracers 57

0

20

40

60

80

100

18C7

9J6

Rio Hondo

Regression Line

PERCENT OF RECYCLED WATER, FROM "EXCESS" CHLORIDE

5H10

[Br] = 1.4 mg/L

18C4 not shown

[B] = 217.1 g/L

[B] = 195 g/L

[B] = 609 g/L

Lakewood

Downey

San Gabriel

Pico Rivera

(r2 = 0.42)

0 20 40 60 80 100

PERCENT OF RECYCLED WATER, FROM "EXCESS" BORON

Figure 18. Estimates of recycled water in multiple-well monitoring sites based on “excess” chloride and “excess” boron values, Los Angeles County, 

California.
58 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

On the basis of 3H/3He age determinations, the 

highest recycled-water percentages calculated from 

“excess” Cl values are found in the three shallowest 

monitoring wells at the San Gabriel Coastal Basin 

Spreading Grounds (2S/12W-25G6 through 25G8)

(fig. 19). The high recycled-water percentages in the 

youngest ground water in monitoring wells adjacent to 

the San Gabriel Coastal Basin Spreading Grounds 

further suggest more rapid recharge and (or) greater 

displacement of pre-existing ground water during 

recharge then at the Rio Hondo Coastal Basin 

Spreading Grounds. 

Several monitoring wells, especially those not 

expected to contain recycled water on the basis of 

3H/3He age determinations, have negative “excess” Cl 

values owing to background chloride concentrations 

estimated from bromide concentrations that are greater 

then the actual measured concentrations (see eq. 1). 

These higher estimated background concentrations 

indicate a Cl/Br ratio less than 287, the ratio that is 

expected if the only source of Cl and Br is atmospheric 

precipitation. Therefore, more precise values for the 

background Cl and Br concentrations in ground water 

prior to the introduction of artificial recharge, as well 

as the identification of other sources of Cl and Br in the 

Central Basin, might make “excess” Cl a more 

quantitative indicator for the presence of recycled 

water. 

Nitrogen

Initial nitrogen concentrations in the monitoring 

wells during recharge were calculated using the 

Rayleigh fractionation equation, measured isotope 

ratios, and an isotope separation factor of −22 o/oo, as 

described in the section “Two Member Mixing Model 

for Selected Constituents” (table 6). However, the 

“back-calculated” nitrogen concentrations for the 

multiple-well monitoring sites (fig. 20) show a weaker 

correlation with “excess” Cl (r2 = 0.15), as do the 

values of the production wells (fig. 10). In fact, the 

rapid decrease in nitrate concentrations suggests 

denitrification is a possible removal process for nitrate 

in the shallower depths beneath the spreading grounds 

instead of dilution with native ground water. 

Therefore, the “back-calculated” nitrogen 

concentrations derived from the Rayleigh fractionation 

equation, along with 3H/3He age determinations for the 

monitoring wells, were used to estimate the net 

denitrification rates during recharge (table 6). The net 

denitrification rate constant, defined by a first-order 

rate expression (Laider, 1987), relates the consumption 

of nitrate to the overall ground water age by the 

following equation: 

(6)

where

The highest net denitrification rate constant of 

5.3 x 10-3 day-1 is obtained from the shallowest 

monitoring well adjacent to the San Gabriel Coastal 

Basin Spreading Grounds (2S/12W-25G8). The 

remaining net denitrification rate constants are 

distributed into two groups (fig. 21). The first group, 

which contains the monitoring wells between about 

150 and 350 ft below land surface adjacent to the San 

Gabriel (2S/12W-25G6 and -25G7) and the Rio Hondo 

(2S/12W-26D13 and -26G14) Coastal Basin Spreading 

Grounds, has denitrification rate constants that range 

between about 9.4 x 10-4 and 1.7 x 10-4 day-1. The 

other group contains the deeper monitoring wells along 

the spreading grounds that have net denitrification rate 

constants ranging from 4.4 x 10-5 to 1.7 x 10-5 day-1. 

[NO3]f = the measured nitrate concentration in the 

monitoring well [M/L];

[NO3]i = the “back-calculated” nitrogen (assumed 

to be nitrate) concentration [M/L];

t = the 3H/3He age determined for each 

monitoring well [days]; and

k = the net denitrification rate constant 

[days-1].

k 1

t

--Ln

NO3 [ ]

NO3 [ ]

---------------i

f =
Water-Quality Indicators and Environmental Tracers 59

0

20

40

60

80

100

Rio Hondo (26D11–14)

0 5 10 15 20 25 30 35

TRITIUM/HELIUM-3 AGE DETERMINATION, IN YEARS

PERCENT OF RECYCLED WATER, FROM "EXCESS" CHLORIDE

Downey (9J4,5)

San Gabriel (25G3,5–8)

25G7

25G6

25G5

26D12

25G8

26D11

26D14

26D13

25G3

9J4

9J5

Figure 19. Tritium/helium-3 age determinations and recycled-water percentages in multiple-well monitoring sites based on “excess” chloride values, Los 

Angeles County, California.
60 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Rio Hondo (26D11, 13, 14)

San Gabriel (25G3, 5-8)

0 20 40 60 80 100

0

2

4

6

8

10

25G7

25G6

25G5

25G8

26D11

26D14

26D13

25G3

"BACK-CALCULATED" NITROGEN, IN MILLIGRAMS PER LITER

PERCENT OF RECYCLED WATER, FROM "EXCESS" CHLORIDE

Regression Line

(r2 = 0.15)

Figure 20. Relation between “back-calculated” nitrogen concentrations and estimates of recycled-water percentages in multiple-well monitoring sites 

based on “excess” chloride values, Los Angeles County, California.
Water-Quality Indicators and Environmental Tracers 61

0

200

400

600

800

1,000

1,200

1,400

DEPTH OF MONITORING WELL, IN FEET BELOW LAND SURFACE

25G7

25G6

25G5

25G4

25G8

26D11

26D14

26D13

25G3

105 104 103 102

DENITRIFICATION RATE CONSTANT, DAY1

Rio Hondo (26D11, 13, 14)

San Gabriel (25G3–8)

Figure 21. Relation between net denitrification rate constants estimated from “back-calculated” nitrogen concentrations and depth of the monitoring wells 

adjacent to the San Gabriel and Rio Hondo Coastal Basin Spreading Grounds, Los Angeles County, California.
62 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

It should be noted that these rate constants take 

into consideration all the same assumptions used 

previously when the inverse of the Rayleigh 

fractionation equation was used to calculate NO3

concentrations in the production wells at the time of 

recharge and, therefore, are only estimates of 

denitrification rate constants. However, they do 

indicate that denitrification is an important process for 

the removal of nitrate at the shallower depths beneath 

the spreading grounds. Finally, the net denitrification 

rate constants approach a value of about 3 x 10-5 day-1, 

suggesting also that the process of denitrification 

continues to occur at distances of several miles from 

the spreading grounds and over a period of many 

miles(fig. 22), albeit at a very slow rate. 

Dissolved Gases

Further evidence for the long-term sustainability 

of denitrification is shown in the dissolved gases 

collected along the flow path. The dissolved-gases 

data, concentrations of excess air, and calculated 

recharge temperatures for the five multiple-well 

monitoring sites are given in table 7. Recharge 

temperatures were derived from N2/Ar data and 

assumes that the sample contains N2 and Ar from airwater equilibrium and dissolution of excess air, as well 

as N2 from denitrification. In this approach, a backsolving routine iterates on the recharge temperature 

until the amount of excess air calculated from N2 and 

Ar are the same. Although most calculated recharge 

temperatures ranged from15oC to 18oC, some were 

much higher. These unrealistically high recharge 

temperatures, along with their corresponding high 

excess air concentrations, were reduced by increasing 

the amount of N2 produced by denitrification. The 

amount of excess N2 required to lower the high 

calculated recharge temperatures to 17oC ranged from 

0.5 to more than 5 mg/L in several of the monitoring 

wells (fig. 23). Delta nitrogen-15 enrichment of the 

ground-water dissolved nitrogen gas (shown in table 8) 

was used to confirm the presence of denitrification, 

since denitrification produces N2 with a higher δ15N 

value than that of the residual nitrogen (Kendall and 

Aravena, 2000).

The dissolved-oxygen concentrations from the 

multiple-well monitoring site samples indicate that the 

drinking-water aquifers are mostly suboxic 

(O2 <1 mg/L) (table 7). The excess air concentrations 

owing to air trapped by rapid infiltration during 

recharge (in excess of equilibrium) and dissolved 

nitrogen gas produced from denitrification ranged from 

3.2 cm3 STP/L to 13.2 cm3 STP/L, with higher values 

associated with parts of the ground-water basin where 

recycled water is present (fig. 24). Furthermore, the 

highest excess-air concentrations found adjacent to the 

San Gabriel Coastal Basin Spreading Grounds are 

consistent with the highest recharge rates and 

denitrification rates found at the same location. These 

areas also have no detectable methane, whereas older 

water deeper or farther from the spreading basins 

contains methane between 0.3 μg/L and 19.3 μg/L. It is 

no longer possible to definitely determine what oxygen 

concentrations were prior to artificial recharge, but data 

from Lakewood, which predate recharge using 

imported Colorado River water, indicate either very 

little O2, or even slight H2S (Land and others, 2002) at 

some depths. Therefore, the absence of methane in 

parts of the aquifer where recycled water is present 

suggests that artificial recharge using recycled water 

has increased slightly the redox potential of the 

ground-water basin. One monitoring well, 

2S/11W-18C4, located upgradient from the spreading 

grounds has a methane concentration of 2.2 mg/L, 

indicating ground water that has not received any 

recycled water (fig. 24).

This observation is counterintuitive insofar as 

wastewater is generally thought to increase oxygen 

demand. For example, at the Cape Cod site discussed in 

section “Previous Studies,” reducing conditions exist 

within the wastewater plume (Garabedian and LeBlanc, 

1988). Possible reasons for the increase in the redox 

potential (more oxidizing conditions) observed in the 

Central Basin owing to the addition of recycled water 

include: (1) addition of massive amounts of excess air 

during recharge; (2) lower levels of biodegradable 

organic carbon in the wastewater organic matter than in 

the natural organic matter; and (3) inhibition of 

methanogenesis by higher sulfate in imported Colorado 

River water and recycled water than in natural recharge 

(note very low sulfate concentrations in older water at 

wells 4S/12W-5H5–10).
Water-Quality Indicators and Environmental Tracers 63

0 5 10 15 20 25 30 35

103

104

105

102

Rio Hondo (26D11, 13, 14)

25G7

25G6

25G5 25G4

25G8

26D11

26D14

26D13

NET DENITRIFICATION RATE CONSTANT, DAY1

TRITIUM/HELIUM-3 AGE DETERMINATION, IN YEARS

25G3

San Gabriel (25G3–8)

Figure 22. Relation between net denitrification rate constants and tritium/helium-3 age determinations.
64 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 7. Dissolved-gases data, excess air concentrations, and calculated recharge temperatures for multiple-well monitoring sites in Los Angeles County, 

California, 1998–1999

[cm3 STP/L, cubic centimeters per liter at standard temperature and pressure; oC, degrees Celsius; mg/L, milligrams per liter; *, indicates sample leaked]

State 

well No. Date Time Methane(mg/L)

Carbon 

dioxide

(mg/L)

Nitrogen

(mg/L)

Oxygen

(mg/L)

Argon

(mg/L)

Recharge

temperature

(

oC)

Excess

air

(cm3 STP/L)

4S/12W-5H5 05/01/98 1400 0.0003 0.320 19.982 0.085 0.6761 14.9 3.6

4S/12W-5H6 04/29/98 1200 .0085 1.967 19.878 .084 .6477 18.5 4.5

03/24/99 1200 .0031 1.695 19.513 .042 .6633 15.6 3.3

4S12W-5H7 04/29/98 1800 .0127 2.461 19.821* .067* .6484* 18.3* 4.4*

08/04/98 1500 .0193 2.114 19.794 .045 .6664 15.5 3.5

4S/12W-5H8 04/30/98 1700 .0095 5.979 19.871 .085 .6481 18.4 4.5

4S/12W-5H9 04/30/98 1500 .0026 4.922 21.154 .082 .6778 17.3 5.5

4S/12W-5H10 04/30/98 1100 .0089 18.706 24.663 .090 .7749 12.6 7.5

3S/12W-9J1 05/04/98 1500 .0000 3.978 18.698 .078 .6306 18.0 3.2

3S/12W-9J2 05/02/98 1500 .0000 7.953 25.811 .585 .7739 15.0 9.5

3S/12W-9J3 05/02/98 1900 .0000 9.908 27.464 .572 .8072 14.4 10.9

3S/12W-9J4 05/03/98 1130 .0000 14.934 25.832 .072 .7304 21.3 11.2

3S/12W-9J5 05/04/98 1100 .0000 15.825 23.655 .088 .7329 15.6 7.5

04/02/99 1300 .0000 15.573 23.221 .047 .7374 14.0 6.5

3S/12W-9J6 05/02/98 1100 .0009 38.148 29.717 .111 .8360 15.6 13.6

2S/12W-25G3 03/31/99 1600 .0000 17.210 24.448 .541 .7610 13.6 7.7

2S/12W-25G4 03/30/99 1400 .0000 16.281 25.723 1.936 .7774 14.3 9.1

2S/12W-25G5 04/01/99 1700 .0000 13.297 27.267 1.612 .8041 14.3 10.7

2S/12W-25G6 03/30/99 1900 .0012 15.179 26.025 .048 .7302 21.8 11.6

2S/12W-25G7 04/01/99 1200 .0005 13.264 25.894 .046 .6903 28.5 13.0

2S/12W-25G8 03/31/99 1100 .0000 22.614 24.363 .054 .7297 17.5 8.8

2S/12W-26D9 05/08/98 1530 .0085 2.869 23.822 .100 .7655 17.4 8.2

2S/12W-26D10 05/07/98 1330 .0012 7.344 27.846 .097 .7655 21.1 13.2

2S/12W-26D11 05/09/98 1230 .0000 8.579 27.339 .092 .7881 16.5 11.5

03/25/99 1600 .0000 8.380 27.230 .057 .7907 15.9 11.2

2S/12W-26D12 05/07/98 1730 .0000 10.581 27.642 .093 .7754 19.1 12.5

2S/12W-26D13 05/08/98 1130 .0000 11.097 24.558 .089 .6931 23.8 10.6

03/26/99 1300 .0001 9.803 25.085 .051 .7287 19.5 10.1

2S/12W-26D14 05/08/98 1800 .0000 19.781 25.606 .201 .7395 19.2 10.5

03/29/99 1800 .0000 12.238 25.425 .045 .6648 32.1 13.2

2S/11W-18C4 05/06/98 1900 2.1742 5.983 22.192 1.436 3.9639 14.0 5.5

2S/11W-18C5 05/06/98 1200 .0008 9.835 24.368* .089* .7201* 18.9* 9.2*

2S/11W-18C6 05/06/98 1530 .0000 40.842 23.843 .079 .6522 29.1 11.0

2S/11W-18C7 05/05/98 1030 .0000 21.453 22.421 .069 .6519 24.6 8.7

Pond at Pico 05/05/98 1730 .0003 9.703 14.126 .058 .5081 25.3 .5

Pond at Pico 04/02/99 1730 .0003 30.0576 14.782 .035 .5386 21.8 .3

Sewage effluent at Pico 05/05/98 1430 .0006 36.696 15.256 .056 .5254 25.6 1.7
Water-Quality Indicators and Environmental Tracers 65

0

2

4

6

0

5

10

15

30 24 18

EXCESS NITROGEN, IN MILLIGRAMS PER LITER

EXCESS AIR, I

N CUB

IC

CENTIMETERS PER LITER

AT

STANDARD TEMPERATURE

AND PRESSURE

RECHARGE TEMPERATURE, IN DEGREES CELSIUS

δ15N–N2, in per mil

26D13

26D14

25G6

25G7

1.79

1.32

1.13

2.90

Unadjusted Samples —

No Excess Nitrogen

Adjusted Samples —

Contains Excess Nitrogen

26D13

26D14

25G6

25G7

Figure 23. Amount of excess nitrogen required to lower high-calculated recharge temperatures to 17 degrees Celsius in four monitoring wells, Los Angeles 

County, California.
66 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 8. Delta nitrogen-15 (δ15N) values of the ground-water dissolved 

nitrogen gas in multiple-well monitoring sites in Los Angeles County, 

California, 1998–1999

[Per mil, parts per thousand; N2, nitrogen gas]

State

well

No.

Date Time δ15N−N2

(per mil)

4S12W-5H7 04/29/98 1800 0.8

3S/12W-9J4 05/03/98 1130 leaked

3S/12W-9J5 05/04/98 1100 1.7

2S/12W-25G3 03/31/99 1600 .8

2S/12W-25G4 03/30/99 1400 .7

2S/12W-25G5 04/01/99 1700 .6/0.8

2S/12W-25G6 03/30/99 1900 1.1/1.2

2S/12W-25G7 04/01/99 1200 2.7/3.1

2S/12W-25G8 03/31/99 1100 2.2

2S/12W-26D11 05/09/98 1230 .7

2S/12W-26D13 05/08/98 1130 1.6/2.0

2S/12W-26D14 05/08/98 1800 1.1/1.5
Water-Quality Indicators and Environmental Tracers 67

400

400

800

1,200

1,600

FEET

Sea

level

A A'

0

0 5 KILOMETERS

5 MILES

Central Basin Pressure Area Montebello Forebay

Spreading Grounds

?

?

Pico Rivera

2S/11W-18C4–7

Lakewood

4S/12W-5H5–10

Whittier

Narrows

Long Beach,

CA

Los

Alamitos

Fault ?

Downey

3S/12W-9J1–6

Datum is sea level Vertical scale greatly exaggerated

Rio Hondo

2S/12W-26D9–14 San Gabriel*

2S/12W-25G3–8

0.0/

3.2

0.3/

3.6

0.0/

3.2

0.0/

9.5

0.0/

10.9

0.0/

7.5 0.0/

11.2

0.9/

13.6

8.5/

4.5

12.7/

4.4

9.5/

4.5

8.9/

7.5 2.6/

5.5

Methane concentration — In micrograms per liter

Excess-air concentration — In cubic centimeters

per liter at standard temperature and pressure.

Sampled 1998

8.5/

0.0/ 8.2

7.7

2,174.0/

5.5

0.8/

9.2

0.0/

11.0

0.0/

8.7

0.0/

9.1

0.0/

10.7

1.2/

11.6

0.5/

13.0

0.0/

8.8

1.2/

13.2

0.0/

10.5

0.0/

10.6

0.0/

11.5

0.0/

12.5

EXPLANATION

Multiple-well monitoring site —

Geologic contact — Dashed

where approximately located;

queried where uncertain

Screened

interval

Well

casing

Local identifier

?

Lakewood

(Pleistocene)

(Pliocene)

Recent

Upper San Pedro

Lower San Pedro

Pico Unit

* Well projected to section line

Rio Hondo

2S/12W-26D9–14 State well identification number

Figure 24. Methane and excess-air concentration in multiple-well monitoring sites along ground-water flow path (see fig. 6 for locations), Los Angeles 

County, California.
68 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Chlorofluorocarbons

Other environmental tracers commonly used to 

date young ground water are chlorofluorocarbons 

(Busenberg and Plummer, 1992). Concentrations of 

chlorofluorocarbons (CFCs) in ground water indicate 

recharge after 1945, or mixing of older water with post1950 water. The distribution of CFCs in water samples 

collected from the five multiple-well monitoring sites 

is shown in figure 25. Given in table 9 are the CFC 

aqueous concentrations (average value of 3 ampoules) 

along with the calculated atmospheric partial pressure 

in equilibrium with the aqueous concentration and 

modeled CFC recharge dates based on a comparison to 

known atmospheric levels. Recycled water (effluent) 

and standing water from the San Gabriel River Coastal 

Basin Spreading Grounds indicate only slight 

enrichment of CFC aqueous concentrations. Very low 

concentrations at Lakewood (none are zero) indicate 

the possibility of some contamination during sampling. 

The deviation from a 1:1 ratio of CFC-11 and CFC-12-

modeled recharge ages indicates that there are 

processes altering the CFC-11 and CFC-12 

concentrations to different extents (fig. 26). According 

to previous studies, anaerobic microbial degradation of 

CFC-11 is more rapid than that of CFC-12 (Lovley and 

Woodward, 1992) and sorption of CFC-11 by soils is 

stronger than that for CFC-12 (Russell and Thompson, 

1983). Since modeled CFC-11 recharge ages are 

greater than modeled CFC-12 recharge ages for post1970 water, sorption and degradation appears to occur 

during the initial stage of recharge. The greater 

modeled CFC-12 recharge ages for pre-1970 water 

suggests greater amounts of CFC-11 were reaching the 

ground water in the past than in the present, an 

observation noted by Dawson and others (2003). 

Furthermore, all three CFCs are known to degrade in 

environments where methane is present (Dunkle and 

others, 1993), a condition possibly present in the 

Central Basin prior to the use of recycled water. 

Therefore, CFCs do not provide reliable ground-water 

ages in most water samples collected from the 

multiple-well monitoring sites along the flow path. 

However, they do provide a sensitive tracer for recycled 

water and a comparison of the present recharge 

operation with the early period of recharge using 

recycled water. 

The expected equilibrium chlorofluorocarbon 

concentrations were derived using the 3H/3He age 

determinations and CFC atmospheric concentrations 

provided by production records and release data of the 

Chemical Manufacturing Association (McCarthy and 

others, 1977). According to Plummer and Busenberg 

(2000), Henry's law gives the CFC solubility in water 

as: 

(7)

where

The partial pressure is defined as: 

(8)

where

A recharge altitude of 150 ft above sea level was 

used to estimate the total atmospheric pressure and the 

vapor pressure of water at the selected recharge 

temperature. The expected equilibrium CFC 

concentrations were calculated using Henry's law 

constants from tabulated CFC solubility data provided 

by the USGS CFC Laboratory and recharge 

temperatures of 10oC, 15oC, and 20oC (fig. 27).

Plots showing the ratio of the measured CFC 

concentration to the expected equilibrium 

concentration in ground water, using the 3H/3He age 

determinations, reveal markedly elevated CFC 

concentrations in older ground water, with the greatest 

CFC enrichment (>100) occurring in ground water 

older than about 20 years but still young enough to 

contain recycled water (fig. 28). One possible 

explanation is that recycled water prior to about 1980 

was much more contaminated with CFCs, and 

treatment was less efficient in the past.

Ci = CFC concentration of the ith CFC 

compound in water [pM/kg];

KH, i = Henry's law constant for the ith CFC 

compound [M atm-1]; and

pi = partial pressure of the ith compound in 

the atmosphere in equilibrium with the 

water [atm]. 

xi = dry air mole fraction of the ith CFC; 

P = total atmospheric pressure [atm]; and

pw = water vapor pressure [atm]. 

Ci KH i , pi = ×

pi xi P pw = ( ) –
Water-Quality Indicators and Environmental Tracers 69

400

400

800

1,200

1,600

FEET

Sea

level

A A'

0

0 5 KILOMETERS

5 MILES

Central Basin Pressure Area Montebello Forebay

Spreading Grounds

?

?

Pico Rivera

2S/11W-18C4–7

Lakewood

4S/12W-5H5–10

Whittier

Narrows

Long Beach,

CA

Los

Alamitos

Fault ?

Downey

3S/12W-9J1–6

Datum is sea level Vertical scale greatly exaggerated

CFC-11 concentration — In picograms per kilogram

CFC-12 concentration — In picograms per kilogram

CFC-113 concentration — In picograms per kilogram

18.1

3.7

0.0

25.3

33,009.6

0.0

166.0

3,949.9

35.3

5.3

353.6

0.0

339.9

263.7

215.3

143.3

189.1

14.7

221.4

302.4

69.4

4.9

3.4

0.0

2,882.9

765.7

1,239.8

311.0

255.6

66.2

5.3

6.3

0.0

5.7

1.5

0.0

1,312.9

2,712.5

386.6

22.8

83.3

1.6

20.5

6.3

0.0

39.5

2.7

0.2

55.4

6.4

1.9

26.0

7.9

1.7

38.7

80.2

6.3

60.8

76.3

1.7

87.8

373.8

142.2

1.2

768.3

16.5

2.9

58.2

0.0

3.4

0.4

0.0

83.2

240.0

10.3

483.5

3,646.8

302.4

2,256.2

735.5

6,322.3

2,269.4

1,991.9

3,598.2

Rio Hondo

2S/12W-26D9–14 San Gabriel*

2S/12W-25G3–8

EXPLANATION

Multiple-well monitoring site —

Geologic contact — Dashed

where approximately located;

queried where uncertain

Screened

interval

Well

casing

Local identifier

?

Lakewood

(Pleistocene)

(Pliocene)

Recent

Upper San Pedro

Lower San Pedro

Pico Unit

* Well projected to section line

Rio Hondo

2S/12W-26D9–14 State well identification number

5.7

1.5

0.0

Figure 25. Chlorofluorocarbons (CFCs) concentrations in multiple-well monitoring sites along ground-water flow path (see fig. 6 for locations), Los Angeles 

County, California.
70 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

Table 9. Chlorofluorocarbon (CFC) data and calculated recharge dates for multiple-well monitoring sites along section A–A’ in Los Angeles County, 

California, 1998–1999 (see fig. 6 for locations)

[Pg/kg, picograms per kilogram; pptv, parts per trillion by volume; Contam., contaminated; <, less than]

State

well No. Date Time

Concentration in solution Calculated atmospheric 

partial pressure Modeled CFC recharge dates

CFC-11

(pg/kg)

CFC-12

(pg/kg)

CFC-113

(pg/kg)

CFC-11

(pptv)

CFC-12

(pptv)

CFC-113

(pptv)

CFC-11

(years)

CFC-12

(years)

CFC-113

(years)

4S/12W-5H5 05/01/98 1400 26.0 7.9 1.7 11.8 15.3 1.8 1,960.2 1,953.7 1,964.3

4S/12W-5H6 04/29/98 1200 55.4 6.4 1.9 30.6 14.8 2.6 1,965.5 1,956.5 1,966.8

03/24/99 1200 21.6 1.6 .5 10.1 3.2 .6 1,959.5 1,946.3 1,958.5

4S12W-5H7 04/29/98 1800 39.5 2.7 .2 21.2 6.1 .3 1,963.5 1,950.5 1,957.5

08/04/98 1500 25.4 9.8 2.3 11.9 19.4 2.7 1,960.5 1,955.5 1,964.3

4S/12W-5H8 04/30/98 1700 20.5 6.3 .0 11.0 14.2 .0 1,960.2 1,953.7 <1,955

4S/12W-5H9 04/30/98 1500 18.1 3.7 .0 9.2 7.9 .0 1,959.0 1,950.2 <1,955

4S/12W-5H10 04/30/98 1100 22.8 83.3 1.6 9.2 144.5 1.5 1,959.0 1,970.8 1,963.0

3S/12W-9J1 05/04/98 1500 5.7 1.5 .0 3.0 3.3 .0 1,953.5 1,948.3 <1,955

3S/12W-9J2 05/02/98 1500 339.9 263.7 215.3 155.1 512.1 239.4 1,978.2 1,992.3 Contam.

3S/12W-9J3 05/02/98 1900 1,312.9 2,712.5 386.6 581.2 5,126.3 415.6 Contam. Contam. Contam.

3S/12W-9J4 05/03/98 1130 166.0 3,949.9 35.3 102.2 10,033.2 54.8 1,973.8 Contam. 1,986.7

3S/12W-9J5 05/04/98 1100 5.3 353.6 .0 2.5 705.4 .0 1,953.7 Contam. <1,955

04/02/99 1300 22.0 281.1 4.9 9.5 521.5 5.2 1,959.0 1,993.8 1,971.8

3S/12W-9J6 05/02/98 1100 25.3 33,009.6 .0 11.9 65,860.8 .0 1,960.7 Contam. <1,955

2S/12W-25G3 03/31/99 1600 483.5 3,646.8 302.4 205.8 6,654.9 311.3 1984.2 Contam. Contam.

2S/12W-25G4 03/30/99 1400 2,269.4 1,991.9 3,598.2 1,001.3 3,754.4 3,854.0 Contam. Contam. Contam.

2S/12W-25G5 04/01/99 1700 2,256.2 735.5 6,322.3 995.4 1,386.2 6,771.8 Contam. Contam. Contam.

2S/12W-25G6 03/30/99 1900 83.2 240.0 10.3 40.0 488.4 12.1 1,967.3 1,990.0 1,974.8

2S/12W-25G7 04/01/99 1200 38.7 80.2 6.2 18.6 163.1 7.3 1,962.8 1,972.0 1,971.3

2S/12W-25G8 03/31/99 1100 60.8 76.3 1.6 31.5 165.9 2.0 1,965.7 1,972.0 <1,955

2S/12W-26D9 05/08/98 1530 4.9 3.4 .0 2.5 7.4 .0 1,953.7 1,950.0 <1,955

2S/12W-26D10 05/07/98 1330 5.3 6.3 .0 3.2 15.9 .0 1,954.2 1,954.2 <1,955

2S/12W-26D11 05/09/98 1230 2,882.9 765.7 1,239.8 1,601.2 1,773.2 1,713.1 Contam. Contam. Contam.

03/25/99 1600 4,823.9 759.8 1,042.6 2,306.9 1,539.1 1,220.6 Contam. Contam. Contam.

2S/12W-26D12 05/07/98 1730 221.4 302.4 69.4 123.0 700.4 95.9 1,975.2 Contam. Modern

2S/12W-26D13 05/08/98 1130 311.0 255.6 66.2 215.9 722.9 117.4 1,985.0 Contam. Contam.

03/26/99 1300 303.8 217.2 61.8 172.7 513.6 87.6 1,980.3 1,992.3 1,994.0

2S/12W-26D14 05/08/98 1800 143.3 189.1 14.7 80.4 441.6 20.5 1,972.0 1,987.3 1,978.8

03/29/99 1800 238.1 222.2 8.2 114.4 452.0 9.7 1,974.7 1,987.8 1,973.2

2S/11W-18C4 05/06/98 1900 3.4 0.4 .0 1.9 .9 .0 1,952.8 1,945.5 <1,955

2S/11W-18C5 05/06/98 1200 2.9 58.2 .0 1.6 134.4 .0 1,952.5 1,970.2 <1,955

2S/11W-18C6 05/06/98 1530 1.2 768.3 16.5 .7 1,781.3 22.9 1,949.8 Contam. 1,979.5

2S/11W-18C7 05/05/98 1030 87.8 373.8 142.2 48.8 866.7 196.7 1,968.5 Contam. Contam.

Pond at Pico 05/05/98 1730 440.5 218.1 58.7 322.0 646.1 110.2 Contam. Contam. Contam.

Pond at Pico 04/02/99 1730 722.8 244.7 65.7 345.5 495.3 76.9 Contam. 1,991.0 1,990.2

Sewage effluent at 

Pico

05/05/98 1430 576.9 207.9 165.0 428.8 625.0 315.6 Contam. Contam. Contam.
Water-Quality Indicators and Environmental Tracers 71

1940 1950 1960 1970 1980 1990

1940

1950

1960

1970

1980

1990

2000

MODELED CFC-11 RECHARGE AGE, IN YEARS

MODELED CFC-12 RECHARGE AGE, IN YEARS

2000

Lakewood

Downey

San Gabriel

Rio Hondo

Pico Rivera

Figure 26. Comparison of modeled CFC-11 and CFC-12 recharge ages in multiple-well monitoring sites (see fig. 6 for locations), Los Angeles County, 

California.
72 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California EQUILIBRIUM CHLOROFLUOROCARBON CONCENTRATION, IN PICOGRAMS PER KILOGRAM WATER

CFC-11

CFC-12

CFC-113

Recharge temperature = 10°C

0

200

400

600

800

1,000

Recharge temperature = 15°C

CFC-11

CFC-12

CFC-113

0

200

400

600

800

TIME, IN YEARS

1940 1950 1960 1970 1980 1990 2000

CFC-11

CFC-12

CFC-113

Recharge temperature = 20°C

0

200

400

600

800

Figure 27. Historical record of aqueous chlorofluorocarbon (CFC) concentrations at 10 degrees Celsius, 15 degrees Celsius, and 20 degrees Celsius in 

equilibrium with atmospheric levels.
Water-Quality Indicators and Environmental Tracers 73

CFC-11

RATIO OF MEASURED TO EXPECTED EQUILIBRIUM CFC CONCENTRATIONS

9J2

9J3

9J4 25G3

25G4 25G5

26D11

9J5

26D10

25G6

25G7

25G8

26D12 26D13

26D14

0.01

0.1

1

10

100

CFC-12

9J2

9J3 9J4

25G3

25G4

25G5 26D11

9J5

26D10

25G6

25G7

25G8

26D12 26D13

26D14

0.01

0.1

1

10

100

1,000

CFC-113

1960 1970 1980 1990 2000

9J2 9J3

9J4

25G3

25G4

25G5

26D11

25G6

25G7

25G8

26D12

26D13

26D14

0.01

0.1

1

10

100

1,000

(9J5 and 26D10 not shown)

YEAR

Figure 28. Enrichment (depletion) in aqueous chlorofluorocarbon (CFC) concentrations in selected multiple-well monitoring sites relative to theoretical 

atmosphere-water equilibrium, Los Angeles County, California.
74 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

SUMMARY AND CONCLUSIONS

A variety of inorganic, organic, and isotopic 

constituents were analyzed in 23 production wells 

located within 500 ft of the San Gabriel and Rio Hondo 

Coastal Basin Spreading Grounds in the Montebello 

Forebay in Los Angeles County. The production wells 

range in depth from 250 to 900 ft, are screened over 

intervals ranging from 100 to 900 ft below land surface, 

and yielded 500 to 3,000 gal/min at the time of 

sampling. 

Spearman rank-order correlation coefficients and 

level of significance were calculated for about 40 

water-quality indicators and several physical features 

such as well depth and distance from spreading 

grounds to the production wells. The statistical testing 

indicated that significant correlations (α<0.001) 

existed between “excess” chloride and “excess” boron 

(defined as the amount above the natural background 

level), and “back-calculated” nitrogen concentrations 

(using nitrogen-isotope data to determine nitrogen 

concentrations at the time of recharge). However, these 

methods appeared to overstate recycled-water 

percentages. The estimates based on these naturally 

occurring constituents should improve if background 

concentrations can be obtained that better represent 

ground water that is free of artificial recharge. 

Furthermore, the failure of parametric calculations to 

yield precise estimates of the wastewater percentage 

show that the production wells draw water from various 

depths and ages (with variable extent of degradation) 

that are not accurately represented by a simple twomember mixing model. 

The organic indicators of UV absorbance and 

fluorescence yielded lower percentages than those 

derived from the conservative inorganic constituents, 

suggesting that some degradation of organic matter 

occurs in the aquifer. Furthermore, it appears that the 

presence of specific organic compounds, such as 

EDTA, in the production wells is actually due to 

dilution of fairly young water with water more than 

several years old, in which the compound is absent, 

rather than a simple indication of removal during 

subsurface transport. Finally, tritium data confirms that 

ground water of differing ages enters production wells 

that are often perforated over long intervals and open to 

multiple zones. 

Measurements of chlorofluorocarbons (CFCs), 

tritium/helium-3 (3H/3He), chloride, boron, dissolvedgas concentrations, and nitrogen isotopes were 

collected from five multiple-well monitoring sites 

extending along a 10-mi flow path from just upgradient 

from the San Gabriel and Rio Hondo Coastal Basin 

Spreading Grounds southward through the Central 

Basin. On the basis of tritium/helium-3 age 

determinations, ground-water samples ranged in age 

from less than 2 to more than 50 years. The age 

determinations based on tritium/helium-3 data 

eliminate the complications associated with tritium 

data alone. 

Chloride and boron concentrations generally are 

highest in the youngest ground water 3H/3He age 

determinations) and indicate the locations where the 

percentage of recycled water exceeds 60 percent. These 

high recycled-water percentages in the youngest 

ground water in monitoring wells adjacent to the San 

Gabriel Coastal Basin Spreading Grounds suggest 

more rapid recharge and (or) greater displacement of 

pre-existing ground water during recharge than at the 

Rio Hondo Coastal Basin Spreading Grounds. The 

3H/3He ages with depth also suggest a more rapid 

infiltration or displacement of pre-existing ground 

water at the San Gabriel Coastal Basin Spreading 

Grounds than at the Rio Hondo Coastal Basin 

Spreading Grounds. 

Denitrification, an important process for the 

removal of nitrate at the shallower depths beneath the 

spreading grounds, continues to occur even at times 

and distances from the spreading grounds of many 

years and over several miles. The presence of 

denitrification is confirmed by nitrogen-15 enrichment 

of the ground-water dissolved nitrogen. Analysis of 

dissolved gases shows that areas that contain recycled 

water have no detectable methane, whereas methane is 

present in the native ground water older than 50 years. 

These results suggest that artificial recharge using 

recycled water has the desirable effect of slightly 

increasing the redox potential of the ground water in 

the basin. Also, dissolved gases have higher 

concentrations of excess air in parts of the groundwater basin where recycled water is present. Some of 

the excess air probably originates as air trapped by 

rapid infiltration at the spreading grounds, but part has 

been identified as dissolved nitrogen resulting from 

denitrification. Finally, using tritium/helium-3 age 

determinations, in conjunction with measured CFC 

concentrations, it was found that CFC concentrations 

are markedly elevated above atmosphere-water 

equilibrium in ground water older than about 20 years 

but still young enough to contain recycled water.
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78 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

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Appendixes 79

APPENDIXES
80 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

APPENDIX A: RELATION BETWEEN PERCENT RECYCLED WATER AND 22 SELECTED 

WASTEWATER CONSTITUENTS FOR EACH OF THE 23 PRODUCTION WELLS LOCATED IN 

LOS ANGELES COUNTY, CALIFORNIA 

[SC, specific conductance; Mg, magnesium; Na, sodium; K, potassium; Cl, chloride; H-2, hydrogen-2/1; 

O-18, oxygen-18/16; B-11, boron-11/10; N-15, nitrogen-15/14; exCl, “excess” chloride; exB, “excess” boron; 

calN, “back-calculated” nitrogen; DOC, dissolved organic carbon; TOC, total organic carbon; UV, ultraviolet 

absorbance; SUVA, specific ultraviolet absorbance; MBAS, methylene blue activated substance; FLUO, 

fluorescence; SFLU, specific fluorescence; EDTA, ethylenediaminetetraactic acid; APEC, alkylphenol 

polyethoxy carboxylate; TOX, total organic halides]
Appendixes 81

PERCENT RECYCLED WATER

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

1234567 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

SC

Mg

0

50

100

150

200

250

0

20

40

60

80

100

120

Figure A.1. Relations between percent recycled water and specific conductance (SC) and magnesium (Mg) for each of the 23 production wells located in 

Los Angeles County, California
82 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California PERCENT RECYCLED WATER

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

1234567 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Na

K

0

20

40

60

80

100

120

0

5

10

15

20

25

30

Figure A.2. Relations between percent recycled water and sodium (Na) and potassium (K) for each of the 23 production wells located in Los Angeles 

County, California
Appendixes 83

PERCENT RECYCLED WATER

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

1234567 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Cl

H-2

0

20

40

60

80

100

120

0

20

40

60

80

100

120

140

Figure A.3. Relations between percent recycled water and chloride (Cl) and deuterium (H-2)for each of the 23 production wells located in Los Angeles 

County, California
84 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California PERCENT RECYCLED WATER

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

1234567 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

O-18

B-11

0

20

40

60

80

100

120

0

50

100

150

200

250

Figure A.4. Relations between percent recycled water and oxygen-18 (O-18) and boron-11 (B-11) for each of the 23 production wells located in Los Angeles 

County, California
Appendixes 85

PERCENT RECYCLED WATER

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

1234567 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

exCl

0

10

20

30

40

50

60

70

N-15

0

20

40

60

80

100

Figure A.5. Relations between percent recycled water and nitrogen-15 (N-15) and “excess” chloride (exCl) for each of the 23 production wells located in Los 

Angeles County, California
86 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California PERCENT RECYCLED WATER

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

1234567 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

caIN

0

50

100

150

200

250

exB

0

10

20

30

40

50

60

70

80

Figure A.6. Relations between percent recycled water and “excess” boron (exB) and “back-calculated” nitrogen (calN) (assumed to be nitrate) for each of 

the 23 production wells located in Los Angeles County, California
Appendixes 87

PERCENT RECYCLED WATER

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

1234567 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

TOC

0

5

10

15

20

DOC

0

5

10

15

20

Figure A.7. Relations between percent recycled water and dissolved organic carbon (DOC) and total dissolved carbon (TOC) for each of the 23 production 

wells located in Los Angeles County, California
88 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California PERCENT RECYCLED WATER

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

1234567 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

SUVA

0

20

40

60

80

100

120

140

UV

0

5

10

15

20

25

Figure A.8. Relations between percent recycled water and ultraviolet absorbance (UV) and specific ultraviolet adsorbance (SUVA) for each of the 23 

production wells located in Los Angeles County, California
Appendixes 89

PERCENT RECYCLED WATER

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

1234567 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

FLUO

0

5

10

15

20

25

MBAS

0

10

20

30

40

50

242

Figure A.9. Relations between percent recycled water and methylene blue activated substance (MBAS) and fluorescence (FLUO) for each of the 23 

production wells located in Los Angeles County, California
90 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California PERCENT RECYCLED WATER

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

1234567 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

EDTA

0

2

4

6

8

10

SFLU

0

50

100

150

200

250

300

350

Figure A.10. Relations between percent recycled water and specific fluorescence (SFLU) and ethylenediaminetetraacetic acid (EDTA) for each of the 23 

production wells located in Los Angeles County, California
Appendixes 91

TOX

0

2

4

6

8

10

1234567 8 9 10 11 12

WELL NUMBER

13 14 15 16 17 18 19 20 21 22 23

PERCENT RECYCLED WATER

APEC

0

2

4

6

8

10

Figure A.11. Relations between percent recycled water and alkylphenol polyethoxy carboxylate (APEC) and total organic halides (TOX) for each of the 23 

production wells located in Los Angeles County, California
92 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

APPENDIX B: RELATION BETWEEN PERCENT RECYCLED WATER IN EACH OF THE 23 

PRODUCTION WELLS LOCATED IN LOS ANGELES COUNTY, CALIFORNIA, FOR 22 

SELECTED CONSTITUENTS

[SC, specific conductance; Mg, magnesium; Na, sodium; K, potassium; Cl, chloride; H-2, hydrogen-2/1; O18, oxygen-18/16; B-11, boron-11/10; N-15, nitrogen-15/14; exCl, “excess” chloride; exB, “excess” boron; calN, 

“back-calculated” nitrogen; DOC, dissolved organic carbon; TOC, total organic carbon; UV, ultraviolet 

absorbance; SUVA, specific ultraviolet absorbance; MBAS, methylene blue activated substance; FLUO, 

fluorescence; SFLU, specific fluorescence; EDTA, ethylenediaminetetraactic acid; APEC, alkylphenol polyethoxy 

carboxylate; TOX, total organic halides]
Appendixes 93

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

0

20

40

60

80

Well 1

Well 2

0

20

40

60

80

100

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV MBAS SFLU APEC TOX

100

CONSTITUENT

217

Figure B.1. Relations between percent recycled water in wells 1 and 2 located in Los Angeles County, California, for 22 selected constituents.
94 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

0

20

40

60

80

Well 3

Well 4

0

20

40

60

80

100

120

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV MBAS SFLU APEC TOX

100

CONSTITUENT

Figure B.2. Relations between percent recycled water in wells 3 and 4 located in Los Angeles County, California, for 22 selected constituents.
Appendixes 95

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

0

20

40

60

80

100

CONSTITUENT

Well 5

Well 6

0

10

20

30

40

50

60

70

80

90

194

213

Figure B.3. Relations between percent recycled water in wells 5 and 6 located in Los Angeles County, California, for 22 selected constituents.
96 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

CONSTITUENT

Well 7

Well 8

0

10

20

30

40

50

60

70

80

0

10

20

30

40

50

60

70

80

90

100

250

274

Figure B.4. Relations between percent recycled water in wells 7 and 8 located in Los Angeles County, California, for 22 selected constituents.
Appendixes 97

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

CONSTITUENT

Well 9

Well 10

0

10

20

30

40

50

60

70

80

90

100

0

20

40

60

80

100

120

140

160

Figure B.5. Relations between percent recycled water in wells 9 and 10 located in Los Angeles County, California, for 22 selected constituents.
98 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

CONSTITUENT

Well 11

Well 12

0

20

40

60

80

100

120

140

160

180

0

50

100

150

200

250

300

Figure B.6. Relations between percent recycled water in wells 11 and 12 located in Los Angeles County, California, for 22 selected constituents.
Appendixes 99

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

CONSTITUENT

Well 13

Well 14

0

50

100

150

200

250

0

20

40

60

80

100

120

140

160

180

200

313

321

Figure B.7. Relations between percent recycled water in wells 13 and 14 located in Los Angeles County, California, for 22 selected constituents.
100 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

CONSTITUENT

Well 15

Well 16

0

50

100

150

200

250

50

100

150

0

231

Figure B.8. Relations between percent recycled water in wells 15 and 16 located in Los Angeles County, California, for 22 selected constituents.
Appendixes 101

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

CONSTITUENT

Well 17

Well 18

0

50

100

150

200

250

0

50

100

150

200

250

Figure B.9. Relations between percent recycled water in wells 17 and 18 located in Los Angeles County, California, for 22 selected constituents.
102 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

CONSTITUENT

Well 19

Well 20

0

50

100

150

200

250

0

20

40

60

80

100

120

140

160

180

200

Figure B.10. Relations between percent recycled water in wells 19 and 20 located in Los Angeles County, California, for 22 selected constituents.
Appendixes 103

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV

SUVA

MBAS

FLUO

SFLU

EDTA

APEC TOX

PERCENT RECYCLED WATER

CONSTITUENT

Well 21

Well 22

0

50

100

150

200

250

300

0

50

100

150

200

Figure B. 11. Relations between percent recycled water in wells 21 and 22 located in Los Angeles County, California, for 22 selected constituents.
104 Use of Water-Quality Indicators and Environmental Tracers to Determine the Fate and Transport of Recycled Water in Los Angeles County, California

SC Mg Na K Cl H-2 O-18 B-11 N-15 exCl exB calN DOC TOC UV MBAS SFLU APEC TOX

PERCENT RECYCLED WATER

CONSTITUENT

Well 23

0

20

40

60

80

100

120

140

160

Figure B.12. Relations between percent recycled water in well 23 located in Los Angeles County, California, for 22 selected constituents.