Concentrations of Dissolved Solids and 

Nutrients in Water Sources and Selected 

Streams of the Santa Ana Basin,

California, October 1998–September 2001

By Robert Kent and Kenneth Belitz

Sacramento, California

2004

Water-Resources Investigations Report 03-4326

U.S. GEOLOGICAL SURVEY

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM 5033-19
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

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FOREWORD

The U.S. Geological Survey (USGS) is 

committed to serve the Nation with accurate and timely 

scientific information that helps enhance and protect 

the overall quality of life, and facilitates effective 

management of water, biological, energy, and mineral 

resources. (http://www.usgs.gov/). Information on the 

quality of the Nation’s water resources is of critical 

interest to the USGS because it is so integrally linked to 

the long-term availability of water that is clean and safe 

for drinking and recreation and that is suitable for 

industry, irrigation, and habitat for fish and wildlife. 

Escalating population growth and increasing demands 

for the multiple water uses make water availability, 

now measured in terms of quantity and quality, even 

more critical to the long-term sustainability of our 

communities and ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program to support 

national, regional, and local information needs and 

decisions related to water-quality management and 

policy. (http://water.usgs.gov/nawqa). Shaped by and 

coordinated with ongoing efforts of other Federal, 

State, and local agencies, the NAWQA Program is 

designed to answer: What is the condition of our 

Nation’s streams and ground water? How are the 

conditions changing over time? How do natural 

features and human activities affect the quality of 

streams and ground water, and where are those effects 

most pronounced? By combining information on water 

chemistry, physical characteristics, stream habitat, and 

aquatic life, the NAWQA Program aims to provide 

science-based insights for current and emerging water 

issues and priorities. NAWQA results can contribute to 

informed decisions that result in practical and effective 

water-resource management and strategies that protect 

and restore water quality.

Since 1991, the NAWQA Program has 

implemented interdisciplinary assessments in more 

than 50 of the Nation’s most important river basins and 

aquifers, referred to as Study Units. 

(http://water.usgs.gov/nawqa/nawqamap.html). 

Collectively, these Study Units account for more than 

60 percent of the overall water use and population 

served by public water supply, and are representative of 

the Nation’s major hydrologic landscapes, priority 

ecological resources, and agricultural, urban, and 

natural sources of contamination. 

Each assessment is guided by a nationally 

consistent study design and methods of sampling and 

analysis. The assessments thereby build local 

knowledge about water-quality issues and trends in a 

particular stream or aquifer while providing an 

understanding of how and why water quality varies 

regionally and nationally. The consistent, multi-scale 

approach helps to determine if certain types of waterquality issues are isolated or pervasive, and allows 

direct comparisons of how human activities and natural 

processes affect water quality and ecological health in 

the Nation’s diverse geographic and environmental 

settings. Comprehensive assessments on pesticides, 

nutrients, volatile organic compounds, trace metals, 

and aquatic ecology are developed at the national scale 

through comparative analysis of the Study-Unit 

findings. (http://water.usgs.gov/nawqa/natsyn.html). 

The USGS places high value on the 

communication and dissemination of credible, timely, 

and relevant science so that the most recent and 

available knowledge about water resources can be 

applied in management and policy decisions. We hope 

this NAWQA publication will provide you the needed 

insights and information to meet your needs, and 

thereby foster increased awareness and involvement in 

the protection and restoration of our Nation’s waters. 

The NAWQA Program recognizes that a national 

assessment by a single program cannot address all 

water-resource issues of interest. External coordination 

at all levels is critical for a fully integrated 

understanding of watersheds and for cost-effective 

management, regulation, and conservation of our 

Nation’s water resources. The Program, therefore, 

depends extensively on the advice, cooperation, and 

information from other Federal, State, interstate, 

Tribal, and local agencies, non-government 

organizations, industry, academia, and other 

stakeholder groups. The assistance and suggestions of 

all are greatly appreciated.

Robert M. Hirsch

Associate Director for Water

Contents v

CONTENTS

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

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

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

Description of Study Area........................................................................................................................... 3

Study Design ............................................................................................................................................... 5

Fixed Sites.......................................................................................................................................... 7

Mountain Sites ................................................................................................................................... 9

Synoptic Study Sites .......................................................................................................................... 9

Methods................................................................................................................................................................ 9

Sample Collection ....................................................................................................................................... 9

Sample Processing ...................................................................................................................................... 10

Laboratory Analyses ................................................................................................................................... 10

Data Analysis .............................................................................................................................................. 10

Quality Control..................................................................................................................................................... 16

Major-Ion Analyses.............................................................................................................................................. 18

Total Dissolved Solids ......................................................................................................................................... 21

Total Dissolved Solids and Concentrations of Some Individual Constituents Compared with 

Water-Quality Criteria.................................................................................................................... 21

Base-Flow Total Dissolved Solids Concentration by Water Source .......................................................... 24

Total Dissolved Solids in Stormflow .......................................................................................................... 24

Comparison of Calculated Mean-Daily, Discrete, and Flow-Weighted Average Stormflow 

Total Dissolved Solids Concentrations .......................................................................................... 34

Concentrations of Selected Nutrients................................................................................................................... 34

Total Nitrogen and Nitrogen Speciation ..................................................................................................... 34

Base-Flow Nitrate Concentrations by Water Source .................................................................................. 42

Nitrate in Stormflow ................................................................................................................................... 45

Ammonia..................................................................................................................................................... 48

Organic Nitrogen......................................................................................................................................... 51

Phosphorus .................................................................................................................................................. 51

Quality-Control Results........................................................................................................................................ 54

Summary .............................................................................................................................................................. 58

References Cited .................................................................................................................................................. 59
vi Figures

FIGURES

Figure 1. Map showing location of study area and sampling sites, Santa Ana Basin, California..................... 4

Figure 2. Diagram showing various sampling locations at the Mentone site, Santa Ana Basin, 

California ........................................................................................................................................... 8

Figure 3. Diagram showing elements of a boxplot as used in this report ......................................................... 12

Figure 4. Scatter plots showing regression and residual plots of total dissolved solids versus specific 

conductance at the six fixed sites, Santa Ana Basin, California........................................................ 13

Figure 5. Graphs showing one result of the hydrograph-separation technique to isolate concentrations

of total dissolved solids in stormflow, Santa Ana Basin, California ................................................. 17

Figure 6. Trilinear diagrams showing base-flow water composition at fixed and mountain 

sites, Santa Ana Basin, California ..................................................................................................... 19

Figure 7. Trilinear diagrams showing base-flow water composition at the various sampling

locations at the Mentone site, Santa Ana Basin, California............................................................... 20

Figure 8. Boxplots showing base-flow total dissolved solids concentrations at fixed sites, 

Santa Ana Basin, California............................................................................................................... 22

Figure 9. Boxplots showing base-flow total dissolved solids concentrations at mountain sites, 

Santa Ana Basin, California............................................................................................................... 23

Figure 10. Boxplots showing rainfall magnitude and duration for storms analyzed 

by hydrograph separation, Santa Ana Basin, California.................................................................... 27

Figure 11. Boxplots showing stormflow magnitude and duration for stormflow analyzed by hydrograph

separation, Santa Ana Basin, California ............................................................................................ 28

Figure 12. Boxplots showing total dissolved solids concentrations in stormflow at three urban sites, 

Santa Ana Basin, California............................................................................................................... 29

Figure 13. Graphs showing stormflow concentrations of total dissolved solids as a function of

rainfall magnitude at Warm Creek, Santa Ana Basin, California...................................................... 31

Figure 14. Graphs showing stormflow concentrations of total dissolved solids as a function of 

rainfall magnitude at MWD, Santa Ana Basin, California ................................................................ 32

Figure 15. Graphs showing stormflow concentrations of total dissolved solids as a function of

rainfall magnitude at Cucamonga Creek, Santa Ana Basin, California............................................. 33

Figures 16A–F. Time-series graphs showing mean daily discharge, mean daily total dissolved 

solids (TDS), and TDS in discrete base-flow and stormflow samples at the six fixed 

sites, Santa Ana Basin, California ..................................................................................................... 35

Figure 17. Pie charts showing mean nitrogen concentrations and speciation at fixed sites under 

base-flow and stormflow conditions, Santa Ana Basin, California................................................... 41

Figure 18. Boxplots showing nitrite+nitrate concentrations at fixed sites, Santa Ana Basin, 

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

Figure 19. Boxplots showing nitrite+nitrate concentrations at mountain sites, Santa Ana Basin, 

California ........................................................................................................................................... 44

Figure 20. Graphs showing time-series of nitrite plus nitrate concentrations in samples from sites 

where at least one stormflow sample was collected, Santa Ana Basin, California ........................... 46

Figure 21. Graph showing nitrite+nitrate concentrations in stormflow samples as a function of 

percentage of stormflow in the stream at the time of sample, Santa Ana Basin, California ............. 47

Figure 22. Graph showing concentrations of selected nutrients in 12 samples consisting of 

at least 75 percent stormflow, Santa Ana Basin, California .............................................................. 49

Figure 23. Graphs showing time-series of ammonia plus ammonium concentrations in samples 

from sites where at least one stormflow sample was collected, Santa Ana Basin, 

California ........................................................................................................................................... 50
Figures vii

Figure 24. Boxplot showing base-flow total phosphorus concentrations at mountain sites 

compared with reference conditions, Santa Ana Basin, California ................................................... 52

Figure 25. Boxplots showing base-flow total phosphorus and dissolved orthophosphate at sites

grouped by water source, Santa Ana Basin, California ..................................................................... 53
viii Tables

TABLES

Table 1. Stream sites from where samples were collected and analyzed for concentrations of dissolved 

solids and nutrients during this study, Santa Ana Basin, California, 

October 1998–September 2001 ......................................................................................................... 6

Table 2. Nitrite+nitrate (mg/L as N) and total dissolved solids (mg/L) concentrations in samples

consisting predominantly of urban runoff, Santa Ana Basin, California........................................... 25

Table 3. Nitrite+nitrate (mg/L as N) and total dissolved solids (mg/L) concentrations in samples 

consisting predominantly of rising ground water, Santa Ana Basin, California ............................... 25

Table 4. Summary of quality-control sample results when standard U.S. Geological Survey (USGS) 

protocols (USGS, variously dated) were used, Santa Ana Basin, California .................................... 55

Table 5. Summary of quality-control sample results when automatic samplers were used, 

Santa Ana Basin, California............................................................................................................... 56
Conversion Factors, Water-Quality Information, Vertical Datum, and Abbreviations ix

CONVERSION FACTORS, WATER-QUALITY INFORMATION, VERTICAL 

DATUM, AND ABBREVIATIONS

CONVERSION FACTORS 

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

oF=1.8 oC+32.

WATER-QUALITY INFORMATION

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

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

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.

ABBREVIATIONS AND ACRONYMS

Ca2+ calcium

Cl- chloride

CO3

2- carbonate

DOC dissolved organic carbon

DON dissolved organic nitrogen

EWI equal-width increment

F- fluoride

FWA flow-weighted average (stormflow)

HCO3

- bicarbonate

Multiply By To obtain

acre 4,047 square meters

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

cubic foot per second (ft3/s) 0.02832 cubic meter per second

foot (ft) 0.3048 meter

inch (in.) 2.54 centimeter

inch (in.) 25.4 millimeter

mile(mi) 1.609 kilometer

square mile (mi2) 2.590 square kilometer
x Conversion Factors, Water-Quality Information, Vertical Datum, and Abbreviations

HIP high-intensity phase (NAWQA data collection)

IBSP Inorganic Blind Sample Project (USGS)

IR interquartile range (in boxplots)

K+ potassium

LRL laboratory reporting level

MCL maximum contaminant level (USEPA)

Mg2+ magnesium

MWD Metropolitan Water District

μm micrometer

mi mile

mi2 square mile

Na+ sodium

NO2

- nitrite

NO3

- nitrate

NWQL National Water Quality Laboratory (USGS)

P phosphorus

PVC polyvinyl chloride

QC quality control

RIX rapid infiltration and extraction (treatment plant)

ROE residue on evaporation at 180°C

RPD relative percentage difference

SANA Santa Ana Basin Study Unit (NAWQA)

SO4

2- sulfate

TDS total dissolved solids

TN total nitrogen

TON total organic nitrogen

TP total phosphorus
Conversion Factors, Water-Quality Information, Vertical Datum, and Abbreviations xi

Organizations

NADP National Atmospheric Deposition Program

NAWQA National Water-Quality Assessment Program

OCWD Orange County Water District

RWQCB California Regional Water Quality Control Board

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey
Abstract 1

Concentrations of Dissolved Solids and Nutrients in 

Water Sources and Selected Streams of the Santa Ana 

Basin, California, October 1998–September 2001

By Robert Kent and Kenneth Belitz

ABSTRACT

 Concentrations of total dissolved solids 

(TDS) and nutrients in selected Santa Ana Basin 

streams were examined as a function of water 

source. The principal water sources are mountain 

runoff, wastewater, urban runoff, and stormflow. 

Rising ground water also enters basin streams in 

some reaches. Data were collected from October 

1998 to September 2001 from 6 fixed sites 

(including a mountain site), 6 additional mountain 

sites (including an alpine indicator site), and more 

than 20 synoptic sites. The fixed mountain site on 

the Santa Ana River near Mentone appears to be a 

good representative of reference conditions for 

water entering the basin.

 TDS can be related to water source. The 

median TDS concentration in base-flow samples 

from mountain sites was 200 mg/L (milligrams per 

liter). Base-flow TDS concentrations from sites on 

the valley floor typically ranged from 400 to 600 

mg/L; base flow to most of these sites is 

predominantly treated wastewater, with minor 

contributions of rising ground water and urban 

runoff. Sparse data suggest that TDS 

concentrations in urban runoff are about 300 

mg/L. TDS concentrations appear to increase on a 

downstream gradient along the main stem of the 

Santa Ana River, regardless of source inputs.

The major-ion compositions observed in 

samples from the different sites can be related to 

water source, as well as to in-stream processes in 

the basin. Water compositions from mountain sites 

are categorized into two groups: one group had a 

composition close to that of the alpine indicator 

site high in the watershed, and another group had 

ionic characteristics closer to those in tributaries 

on the valley floor. The water composition at 

Warm Creek, a tributary urban indicator site, was 

highly variable but approximately intermediate to 

the compositions of the upgradient mountain sites. 

Water compositions at the Prado Dam and 

Imperial Highway sites, located 11 miles apart on 

the Santa Ana River, were similar to one another 

and appeared to be a mixture of the waters of the 

upstream sites, Santa Ana River at MWD 

Crossing, Cucamonga Creek, and Warm Creek.

Rainfall usually dilutes stream TDS 

concentrations. The median TDS concentration in 

all storm-event discrete samples was 260 mg/L. 

The median flow-weighted average TDS 

concentration for stormflow, based on continuous 

measurement of specific conductance and 

hydrograph separation of the continuous discharge 

record, was 190 mg/L. However, stormflow TDS 

concentrations were variable, and depended on 

whether the storm was associated with a relatively 

small or large rainfall event. TDS concentrations 

in stormflow associated with relatively small 

events ranged from about 50 to 600 mg/L with a 

median of 220 mg/L, whereas concentrations in 

stormflow associated with relatively large events 

ranged from about 40 to 300 mg/L with a median 

of 100 mg/L. 
2 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

From the perspective of water managers, the 

nutrient species of highest concern in Santa Ana 

Basin streams is nitrate. Most mountain streams 

had median base-flow concentrations of nitrate 

below 0.3 mg/L as nitrogen. Nitrate concentrations 

in both urban runoff and stormflow were near 1 

mg/L, which is close to the level found in rainfall 

for the region. In fact, results from this study 

suggest that much of the nitrate load in urban 

storm runoff comes from rainwater. Nitrate 

concentrations in the Santa Ana River and its 

major tributaries are highest downstream from 

wastewater inputs, where median base-flow 

concentrations of nitrite+nitrate ranged from about 

5 to 7 mg/L. About 4 percent of samples collected 

from sites receiving treated wastewater had nitrate 

concentrations greater than 10 mg/L. Rising 

ground water also appears to have high nitrate 

concentrations (greater than 10 mg/L) in some 

reaches of the river. Concentrations of other 

nitrogen species were much lower than nitrate 

concentrations in base-flow samples. However, 

storm events increased concentrations and the 

proportion of organic nitrogen, ammonia, and 

nitrite relative to nitrate. 

Concentrations of total phosphorus at sites 

upstream from wastewater inputs were usually at 

or below 0.03 mg/L as phosphorus. Total 

phosphorus concentrations in base-flow samples 

from fixed sites below wastewater inputs were 

typically near 1 mg/L, indicating a departure from 

reference conditions and a potential for 

phosphorus-driven eutrophication. 

INTRODUCTION 

The Santa Ana River is the largest river in 

Southern California. In the Santa Ana Basin, which is 

home to over 4 million people, dissolved solids and 

nutrients (specifically inorganic nitrogen) have been 

identified as primary water-quality concerns 

(California Regional Water Quality Control Board, 

1995). Given these concerns, the U.S. Geological 

Survey (USGS) completed a study of water-quality 

conditions in the river and selected tributaries with 

respect to total dissolved solids (TDS) and selected 

nutrients. Data were collected from October 1998 to 

September 2001 in the first high-intensity phase (HIP) 

of data collection for the Santa Ana Basin Study Unit 

(SANA) of the U.S. Geological Survey National Water 

Quality Assessment Program (NAWQA). 

Human health issues related to nutrients in 

drinking-water sources stem chiefly from the nitrogen 

compounds of nitrite and nitrate. When infants 

consume water with relatively high nitrate 

concentrations, the nitrate may be converted to nitrite 

in the digestive tract. Once in the bloodstream, nitrite 

will combine with hemoglobin to form 

methemoglobin, which does not carry oxygen. 

Potentially fatal methemoglobinemia, or “blue-baby 

syndrome,” can then result from this internal 

suffocation, which actually causes infants to take on a 

peculiar lavender color (American Academy of 

Pediatrics, 1970; Johnson and Kross, 1990). Nitrite and 

nitrate also are suspected precursors of carcinogenic 

nitrosamines and nitrosamides (Neill, 1989), and there 

may be an increased risk for certain types of cancer in 

older women from even low-level nitrate exposure over 

many years (Weyer and others, 2001).

Regulatory criteria for the protection of aquatic 

life are generally not applied with respect to nitrate or 

nitrite because concentrations considered toxic to 

aquatic organisms rarely occur in nature (U.S. 

Environmental Protection Agency, 1986). However, 

Marco and others (1999) reported toxic responses by 

several amphibian larvae to nitrate and nitrite 

concentrations below limits recommended by the U.S. 

Environmental Protection Agency (USEPA) for 

drinking water and water inhabited by warm-water 

fishes. Three of the five species examined in that study 

[the red-legged frog (Rana aurora), the western toad 

(Bufo boreas), and the pacific tree frog (Hyla regilla)] 

are, or were, native to the Santa Ana River (Ed L. 

Ervin, Biological Resources Discipline, USGS, written 

commun., 2001). 

Inorganic nitrogen in the form of ammonia 

(NH3+NH4

+) also carries potentially hazardous effects 

for aquatic life (Pocernich and Litke, 1997; U.S. 

Environmental Protection Agency, 1999). Finally, 

inorganic nitrogen and phosphorus are essential plant 

nutrients, and their concentrations are often limiting to 

algal growth in streams. When these nutrients are in 

excess, accelerated eutrophication can result in 

nuisance algal growth and dissolved oxygen depletion. 
Introduction 3

Purpose and Scope 

The primary purpose of this report is to present 

an evaluation of dissolved solids and concentrations of 

selected nutrients in streams of the Santa Ana Basin as 

a function of water source. These sources include 

streamflow at reference sites in the foothills of two 

major mountain ranges (mountain sites), urban runoff 

(nonpoint source discharges unrelated to storm events), 

treated municipal wastewater, rising ground water, and 

stormflow. Constituent fluxes or loads are not 

presented in this report. The focus on water sources 

contrasts with the more common landscape-based 

approach to explain ambient surface-water-quality 

conditions. The hydrologic cycle of this semiarid, 

urban watershed differs from unaltered watersheds, and 

an understanding of the water quality related to each 

source may facilitate water-quality management 

decisions.

A secondary purpose of this report is to present a 

comparison of TDS and nutrient concentrations 

observed during the study to water-quality standards, 

goals, objectives, and reference conditions. Reference 

conditions refer to water quality that has been 

minimally affected by humans. High concentrations of 

dissolved solids and nutrients in surface water carry 

concerns for human as well as ecosystem health. 

Excessive concentrations of dissolved solids can 

collectively render water unfit for drinking (U.S. 

Environmental Protection Agency, 2002) and for 

supporting aquatic life. In addition, some individual 

dissolved constituents, such as chloride, sulfate, nitrate, 

and nitrite present their own water-quality concerns 

and have specific standards for maximum 

concentrations in drinking water or criteria for the 

protection of aquatic life (U.S. Environmental 

Protection Agency, 2002; 1999; 1988; 1986). Data used 

in this report are the product of more than 250 water 

samples collected from 37 stream sites during the study 

period of October 1998 to September 2001.

Description of Study Area

The Santa Ana NAWQA (SANA) study unit 

occupies about 2,700 mi2 in the Transverse (San 

Gabriel Mountains, San Bernardino Mountains) Range 

and the Peninsular (Santa Ana Mountains, San Jacinto 

Mountains) Range Provinces of southern California 

(fig. 1). The Santa Ana River is the largest stream 

system in southern California, beginning in the San 

Bernardino Mountains (which reach elevations 

exceeding 10,000 ft above sea level) and flowing more 

than 100 mi to the Pacific Ocean near Huntington 

Beach. The 2,700 mi2 watershed is home to over 

4 million people, and the population is expected to 

increase by more than 50 percent by the year 2020. 

Water demand is expected to increase by somewhat less 

than 50 percent during the same period (Santa Ana 

Watershed Project Authority, 1998)

The climate is mediterranean with hot, dry 

summers, and cooler, wetter winters. Average annual 

precipitation ranges from about 10 to 24 in. in the 

coastal plain and inland valleys, and from 24 to 48 in. 

in the San Gabriel and the San Bernardino Mountains. 

However, during the period described in this report the 

area was experiencing a drought, and rainfall was only 

about a third of normal. As a result of the drought the 

Santa Ana River upstream from wastewater inputs 

recorded its second lowest annual flow in recorded 

history in 2001 (City of Redlands, 2002).

Natural vegetation in the drainage area ranges 

from riparian habitat and coastal sage at lower 

elevations, to chaparral and mixed deciduous and 

conifer forests at higher elevations. Alpine tundra is 

also present at the mountain summits. Sycamore, 

cottonwood, willow, and other riparian plants are 

common throughout the river flood plain, as are many 

aquatic plants. The San Gabriel, the San Bernardino, 

and the San Jacinto Mountains lie within the Southern 

California Mountains Ecoregion; the remainder of the 

study unit lies within the Southern and Central 

California Plains and Hills Ecoregion (Burton, 2002).

The study area can be subdivided into three 

primary subunits: the Coastal Basin, the Inland Basin, 

and the San Jacinto Basin. Within these subunits, 

water-bearing deposits can be identified in the alluvialfilled valleys and coastal plain, and in the relatively 

impervious uplands. The uplands are generally steep 

and remain undeveloped. Urban and agricultural land 

uses occur primarily in the alluvial-filled valleys and 

coastal plain. However, local land use has little 

influence on surface-water quality in the basin under 

base-flow conditions, because base flow in the Santa 

Ana River is maintained almost entirely by effluent 

from municipal wastewater treatment plants (Burton 

and others, 1998).
4 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Prado

Wetlands

Lake

Matthews

Lake Perris

Chino

Irvine

Santa Ana

Huntington

Beach Santa Ana

San Jacinto

River

River

EXPLANATION

Basin boundary

Creek

San Timoteo

Riverside

Pacific

Ocean

0 10 20 MILES

0 10 20 KILOMETERS

Los Angeles

San Diego

San

Francisco

Santa Ana

Basin

California

Pacific

Ocean

118o00' 45' 30' 15' 117o00' 116o45'

33o

45'

34o

00'

34o

15' Big Bear Lake

Bear

Creek

Base from U.S. Geological Survey digital data, 1:24,000, 1999

Albers Equal-Area Conic Projection

Standard parallels 29o30' and 45o30',

central meridian -117o15"

Lake

Elsinore

Cucamonga Creek

2

4

5

6

1

2

3

Mentone

Cucamonga Creek

Warm Creek

MWD Crossing

Imperial Highway

Prado Dam

Day Creek

Cucamonga Creek

Near Upland

Devil Canyon Creek

East Twin Creek

Cajon Creek

South Fork

San Jacinto

Colton San Bernardino

MWD

Day

Creek

Fixed site

Mountain site

Synoptic site

Intermittently flooded 

 lakebed

Downstream terminus of

 numbered stream reach

(defined by the California

 Regional Water Quality

 Control Board)

Tesuesquito Creek

Hole Lake

Sunnyslope Channel Creek

COASTAL

BASIN

INLAND

BASIN

SAN JACINTO

BASIN

San Jacinto Mts

San Gabriel Mts

San Bernardino Mts

Chino Dairy Preserve

Hidden Valley

Wetlands

Mission Blvd. Bridge

Santa Ana Mts

Seven Oaks Dam

Prado Dam

Rapid-Infiltration

Extraction (RIX)

treatment plant

Rialto Wastewater

Treatment Plant

Figure 1. Location of study area and sampling sites, Santa Ana Basin, California.
Introduction 5

Ground water is the main source of water supply 

in the watershed, meeting about two-thirds of the total 

water demand [about 1.2 million acre-feet per year 

(acre-feet/yr)] (Santa Ana Watershed Project Authority, 

1998). Imported water from northern California and the 

Colorado River meet about one-quarter of the total 

consumptive demand. After delivery and domestic use, 

nearly all of the water is tertiary treated (Izbicki and 

others, 2000) in order to meet water-quality objectives 

established for the basin by the California Regional 

Water Quality Control Board (1995). This treated 

effluent is discharged to the Santa Ana River and 

several of its tributaries, and sites that receive 

wastewater constitute a major water-source group in 

this study. However, effluent quality at treatment-plant 

outfalls is variable, and its description is beyond the 

scope of this report. 

In some cases wastewater receives further 

treatment after leaving the plant to remove inorganic 

nitrogen. Effluent from treatment plants in Colton and 

San Bernardino is pumped to a regional facility using a 

treatment called Rapid Infiltration and Extraction 

(RIX). The facility consists of about 43 acres of 

infiltration basins where effluent filters through the 

soil. It is then pumped from the aquifer beneath the 

infiltration basins along with a small amount of native 

ground water, disinfected, and discharged to the river 

(Wildermuth Environmental, Inc., 1998). The Hidden 

Valley Wetlands in Riverside also remove nitrate from 

effluent before it reaches the river. The Orange County 

Water District diverts about half of the Santa Ana River 

base flow though a series of artificial wetlands for the 

same purpose above the Prado Dam (O'Connor, 1995). 

Other surface-water inputs besides treated 

wastewater include rising ground water in various parts 

of the basin and urban runoff (nonpoint source 

discharges not directly associated with storm events). 

Base flow in the Santa Ana River also is supplemented 

by intermittent releases of water imported from 

northern California and the Colorado River to increase 

streamflow available for ground-water recharge 

(Burton and others, 1998). The California Regional 

Water Quality Control Board (1995) refers to these 

releases as “non-tributary flow.”

A number of factors contribute to a 

disconnection between landscape and stream water 

quality in the Santa Ana Basin. Flow from the upper 

Santa Ana watershed is commonly diverted to 

detention basins located at the mountain front. Natural 

hydrologic processes also are short-circuited by the 

mostly concrete-lined urban storm-water conveyance 

network, which is designed to rapidly transfer water 

downstream. Base flow on the valley floor consists 

primarily of treated wastewater, which is discharged 

from several outfalls on the river and its tributaries. 

The California Regional Water Quality Control 

Board (1995) divides the Santa Ana River into six 

reaches, numbered in ascending order from the mouth 

to the headwaters (fig. 1). For internal consistency in 

this report, these reaches are described from upstream 

to downstream. Reach 6 extends from the headwaters 

in the San Bernardino Mountains to just above the 

Seven Oaks Dam near Mentone. Flow in Reach 6 is 

perennial and consists of rising ground water, 

stormflow runoff and, on occasion, snowmelt. Reach 5 

extends from the Seven Oaks Dam to the Bunker Hill 

Dike in San Bernardino (labeled “5” in fig. 1). Reach 5 

has intermittent flow. Reach 4 extends from the Bunker 

Hill Dike to the Mission Blvd. Bridge in Riverside 

(labeled “4” in fig. 1). Reach 3 is located between 

Mission Blvd. Bridge and the Prado Dam. In contrast 

to the intermittent flow in Reach 5, discharges of 

treated wastewater enter the river along Reaches 3 and 

4, resulting in perennial flow from near the top of 

Reach 4 to the recharge facilities at the bottom of 

Reach 2. Reach 2 extends from the Prado Dam to 17th 

Street in Santa Ana (labeled “2” in fig. 1). Reach 1 lies 

between 17th Street and the river mouth in Huntington 

Beach. This reach is usually dry because nearly all base 

flow of the Santa Ana River is captured by groundwater recharge facilities operated by the Orange 

County Water District near the downstream limit of 

Reach 2. 

Study Design

Data for this study were collected from October 

1998 to September 2001, corresponding to the high 

intensity phase (HIP) of the SANA study unit (Gilliom 

and others, 1995). In this report three general types of 

sites are identified: fixed sites, mountain sites, and 

synoptic sites (table 1).
6 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Table 1. Stream sites from where samples were collected and analyzed for concentrations of dissolved solids and nutrients during this study, Santa Ana 

Basin, California, October 1998–September 2001

[Water quality data used in this interpretive report is available at http://waterdata.usgs.gov/ca/nwis/qwdata; RIX, rapid-infiltration and extraction (treatment 

plant); USGS, U.S. Geological Survey; WQC, water quality control; MWD, Metropolitan Water District]

1Urban land-use gradient synoptic—19 sites (August 2000) (Burton and Brown, 2001)

2Dye tracer synoptic—15 sites (May 2001) (Mendez and Belitz, 2002)

Those sites listed here that do not appear on the figure 1 map of the study can be located on the map using their 15-digit station identification number 

and latitude/longitude coordinates bordering the map. The first six digits are latitude: digits 1–2, degrees; digits 3–4, minutes; digits 5–6, seconds. The next 

seven digits are longitude: digits 7–9, degrees; digits 10–11, minutes; digits 12–13, seconds. (The last two digits are sequence numbers without relevance for 

locating the site.)

USGS station ID No. USGS station name Site type(s)

11051500 Santa Ana River near Mentone Fixed, Mountain

11060400 Warm Creek near San Bernardino Fixed, Synoptic1

11066460 Santa Ana River at MWD Crossing Fixed, Synoptic1,2

11073495 Cucamonga Creek near Mira Loma Fixed, Synoptic1

11074000 Santa Ana River below Prado Dam Fixed, Synoptic1

11075610 Santa Ana River above spreading diversion below Imperial Highway near Anaheim Fixed

341014116494801 South Fork Santa Ana River near South Fork Campground near Angelus Oaks Mountain

11058500 East Twin Creek near Arrowhead Springs Mountain

11063680 Devil Canyon Creek near San Bernardino Mountain

11063510 Cajon Creek below Lone Pine Creek near Keenbrook Mountain, Synoptic1

11067000 Day Creek near Etiwanda Mountain

11073470 Cucamonga Creek near Upland Mountain, Synoptic1

340843117032501 Santa Ana River at Upper Powerhouse near Running Springs Synoptic1

340552117172701 Warm Creek above Orange Show Grounds near San Bernardino Synoptic1

340455117173801 Warm Creek above E Street near San Bernardino Synoptic1

335913117080701 San Timoteo Creek near Eastside Ranch near Yucaipa Synoptic1

335910117425801 Little Chino Creek above Pipeline Avenue near Los Serranos Synoptic1

335835117412701 Chino Creek above Central Avenue near Los Serranos Synoptic1

335655117395601 Chino Creek downstream of Pine Avenue at Prado Dam Synoptic1

335506117381201 Mill Creek near Splatters Duck Club in Prado Wetlands Synoptic1

340042117355901 Cucamonga Creek Main Channel at Chino Avenue near Ontario Synoptic1

340041117355901 Cucamonga Creek Wastewater Effluent at Chino Avenue near Ontario Synoptic1

340132117214401 Santa Ana River at Riverside Road near Riverside Synoptic1,2

335835117253401 Sunnyslope Channel near Rubidoux Nature Center at Santa Ana River Regional Park Synoptic1

335827117253801 Sunnyslope Channel at Santa Ana River Regional Park near Rubidoux Synoptic1,2

340217117211401 Santa Ana River downstream Confluence of RIX Outflow Synoptic2

335426117232701 Lake Evans Outflow at Riverside Synoptic2

11066440 Santa Ana River at Mission Boulevard at Riverside Synoptic2

335804117255201 Tesuesquito Creek near Mouth at Riverside Synoptic2

335806117260501 Santa Ana River above MWD Crossing Synoptic2

335748117275601 Riverside WQC Plant at Van Buren Boulevard near Riverside Synoptic2

335743117280501 Hole Lake Discharge above Santa Ana River near Pedley Synoptic2

335809117301001 Santa Ana River North of Hidden Valley Wetlands Synoptic2

335759117300201 West Hidden Valley Wetlands Lake near La Sierra Heights Synoptic2

335728117314101 Santa Ana River at Grulla Court at La Sierra Synoptic2

335645117332601 Santa Ana River at Hamner Road above Norco Synoptic2

335547117353601 Santa Ana River at Power Line Road near La Sierra Heights Synoptic2
Introduction 7

Fixed Sites 

In the NAWQA program, two types of fixed sites 

are recognized: indicator sites and integrator sites. 

Indicator sites are chosen to represent stream waterquality conditions resulting from specific land uses and 

important influences on water quality in the basin. In 

contrast, integrator sites are chosen to represent stream 

water-quality conditions affected by a combination of 

land uses, point sources, natural processes, and human 

influences. Fixed sites can be further divided into basic 

fixed sites and intensive fixed sites, the latter generally 

being sampled for more water-quality constituents and 

at greater frequency. The SANA fixed-site network 

consisted of six sampling locations (fig. 1). All of these 

were sampled at least monthly during the first two 

years of the high intensity phase (HIP), and nearly all 

storm sampling was conducted during this time. During 

the third year of the HIP, the fixed-site network was 

reduced to four sites.

The Mentone site is a fixed mountain site located 

on the Santa Ana River, just upstream from where the 

Santa Ana River exits the San Bernardino Mountains. 

Owing to upstream diversions of the Santa Ana River, 

discharge at Mentone is primarily from Bear Creek, a 

major tributary of the Santa Ana River. During the time 

period of this study, construction of the Seven Oaks 

Dam affected the flow of the Santa Ana River in the 

area of the Mentone site. Therefore, water-quality 

samples were obtained from several locations (fig. 2). 

The first six samples (October 1998 to March 1999) 

were collected at the USGS main gage (site 11051499 

in fig. 2). After March 1999 flow ceased at the main 

gage, and samples were collected at a supplemental 

gage (site 11051502), or at one of two non-permanent 

sites located between the supplemental gage and the 

dam outlet (fig. 2). The two gages and two nonpermanent sites are located at the upper boundary of 

Reach 5, and water-quality data for all four sites is 

published and archived under USGS site 11051500. In 

February 2000, a sample was collected about 3 mi 

upstream from the dam, which is in Reach 6. This site 

was subsequently established as a NAWQA site for 

monitoring water-quality status and trends (site 

11049400). Samples were collected monthly at the 

various Mentone sites from October 1998 to 

September 2001. 

The Warm Creek urban indicator site (site 

11060400) is concrete-lined; the drainage basin is 

small (12 mi2) and entirely urban. Ground-water 

sources of water include a hot spring routed through a 

park and seepage that enters the stream through cracks 

in the concrete bottom and through drainage holes 

perforated in the vertical concrete sides. Urban runoff 

also contributes a substantial part of the discharge to 

the channel. Streamflow from this site enters the Santa 

Ana River near the downstream terminus of Reach 5 as 

identified by the California Regional Water Quality 

Control Board (1995). The Warm Creek site was 

sampled monthly from October 1998 to June 1999, 

twice-monthly from July 1999 to March 2000, and then 

monthly again from April 2000 to September 2001. 

The site on the Santa Ana River at MWD 

Crossing (MWD, site 11066460) is an integrator on the 

Santa Ana River along Reach 3 downstream from the 

Rialto and RIX wastewater-treatment-plant outfalls 

(fig. 1). Although MWD is an integrator site, base flow 

is predominantly treated wastewater with minor 

contributions from rising ground water. Stormflow 

includes large contributions from tributaries that carry 

runoff from urban land use on the valley floor and from 

mountain runoff. Samples were collected monthly at 

this site from October 1998 to September 2000.

The Cucamonga Creek site (11073495) is 

located in the Chino Basin Dairy Preserve (fig. 1). 

However, discharge in Cucamonga Creek does not 

generally reflect land use in the adjacent area; the 

channel is concrete-lined and base flow consists 

primarily of treated wastewater with a small 

component of urban run-off. Under stormflow 

conditions, the discharge includes runoff from urban 

areas and undeveloped mountainous areas. Runoff 

from dairies also contributes to the discharge during 

intense rain events. Samples were collected here on the 

same schedule as at MWD. Cucamonga Creek 

becomes Mill Creek, as it enters the Prado Wetlands 

near the downstream terminus of Reach 3. 

The Prado site (11074000), located downstream 

from the Prado Dam, is an integrator in space and time 

for the Inland Basin. The site is located near the 

upstream terminus of Reach 2. Water quality at this site 

is affected by a number of factors including 

wastewater, wetland processes in the Prado Wetlands, 

urban runoff, dairy runoff, and impoundment of 

stormflows. Samples were collected monthly at the 

Prado site during the entire high-intensity phase of data 

collection from October 1998 to September 2001.
8 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Seven Oaks Dam

Spillway

330 feet

(100

meters)

1,800 feet

(400 meters)

Additional sampling site (11049400)

 located 3 miles (5 kilometers)

upstream from Seven Oaks Dam

980 feet

(300 meters)

USGS main gage

11051499

Supplemental gage

11051502

Additional sampling

locations between

gages and dam

(not established USGS stations)

(Not to scale, approximate distances)

Santa Ana River Stream flo

w

Figure 2. Various sampling locations at the Mentone site, Santa Ana Basin, California (USGS, U.S. Geological Survey).
Methods 9

The Imperial Highway integrator site 

(11075610) is located on the Santa Ana River about 

11 mi. downstream from the Prado Dam, and above 

diversion structures and ground-water recharge 

facilities maintained by the Orange County Water 

District (OCWD). This site is located in Reach 2. 

Under base-flow conditions, the discharge consists 

primarily of treated wastewater and minor amounts of 

urban runoff. Stormflows reaching this site have two 

sources: runoff from the Inland Basin that is released at 

Prado Dam, and runoff from urban areas located 

between the dam and the sampling site. The sampling 

schedule at Imperial Highway was the same as for 

Warm Creek until April 2001 when the last sample was 

collected for this study at Imperial Highway. 

The routine monthly samples collected from 

each fixed site were typically collected during baseflow conditions. An additional six to eight samples 

were collected at each site during stormflow 

conditions. These were collected during the first two 

years and resulted from thirteen different storm events. 

One exception to the sampling strategy described 

above is that no samples were collected in November 

2000.

Mountain Sites 

One of the fixed sites, Mentone, was a mountain 

site. Beginning in January 2000, six additional 

mountain sites were sampled quarterly (fig. 1). The 

purpose of the quarterly sampling at these sites was to 

help establish a reference for water quality before it is 

altered by the urban landscape. One of the quarterly 

sites was initially identified as an alpine indicator fixed 

site (South Fork, 341014116494801—fig. 1, table 1) to 

serve as a reference site. However, initial data indicated 

that the stream water at South Fork contained 

substantially lower concentrations of dissolved and 

suspended materials than did most mountain stream 

water entering the basin. Therefore, the site was 

considered unrepresentative of basin reference 

conditions, and sampling there was reduced to 

quarterly after the first year of the HIP. The other five 

sites are mountain tributaries that contribute discharge 

to the Inland Basin. The sites include two tributaries 

that exit the San Gabriel Mountains [Cucamonga Creek 

near Upland (11073470) and Day Creek(11067000)], 

two tributaries that exit the San Bernardino Mountains 

[East Twin Creek (11058500) and Devil Canyon Creek 

(11063680)], and one tributary that receives runoff 

from both mountain ranges [Cajon Creek (11063510)]. 

Cajon Creek may be affected by human factors because 

it is located in a transportation corridor between the 

two mountain ranges. 

Synoptic Study Sites

Two synoptic studies contributed to increased 

understanding of the role of spatial variability in 

controlling surface-water quality in the basin. One 

study was an urban land-use gradient study conducted 

in August 2000 (Burton and Brown, 2001). Nineteen 

sites were selected and characterized on the basis of 

water source and stream channel type; nutrients and 

dissolved solids were among the water-quality 

constituents sampled. The second study, a dye-tracer 

study, characterized the interaction between the Santa 

Ana River and the shallow ground-water system and 

quantified the percentage of wastewater and other 

sources of flow along an 18-mile reach (Mendez and 

Belitz, 2002). Dye-tracer measurements, along with 

additional data, were collected to characterize the water 

quality of the different water sources. These data, 

including nutrient samples, were collected over a 2-day 

period in May 2001 from nine sites on the main stem of 

the river and from six tributaries. 

METHODS

Sample Collection

Water samples were collected by equal-widthincrement [EWI] (USGS, variously dated), multiplevertical, grab, or point (automatic) sampling methods, 

as site conditions dictated. The preferred method was 

EWI, because a discharge-weighted water-quality 

sample is collected along the sampling cross-section. 

The multiple-vertical sampling method also strives to 

represent water quality in a cross-section by integrating 

several verticals across a stream; multiple-vertical 

samples are usually not depth-integrated because 

shallow stream depths prohibit the use of isokinetic 

sampling equipment (USGS, variously dated). Grab 

samples, the least preferred method, are collected near 

midstream when streams are too narrow for EWI or 

multiple-vertical methods. Most samples collected for 

this study were obtained using the EWI method. Storm 

samples were usually collected near the stream bank by 

grab or automatic sampler (which also represented a 

grab sample).
10 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Sample Processing

A cone splitter (USGS, variously dated) was 

used to divide the composited sample into subsamples, 

which theoretically contain equal concentrations of 

suspended and dissolved constituents (USGS, variously 

dated). Subsamples for whole-water nutrient analyses 

were collected directly from the cone splitter and 

preserved with 4.5 normal (N) sulfuric acid (U.S. 

Geological Survey Office of Water Quality, 1998). The 

subsamples analyzed for dissolved species were 

filtered through a capsule filter with an effective pore 

size of 0.45 micrometers (μm). All sample processing 

was carried out inside a clean mobile laboratory 

dedicated to this purpose. In addition, sample filtering 

was performed within a processing chamber, which 

consists of a clear plastic bag on a PVC frame to 

further avoid contamination from the atmosphere 

(Horowitz and others, 1994). Alkalinity and the 

concentrations of bicarbonate (HCO3

-

) and carbonate 

(CO3

2-) were measured on filtered samples by field 

titration (USGS variously dated). Cleaning procedures 

for all sample-collection and processing equipment 

followed USGS protocols (USGS variously dated). 

Laboratory Analyses

The USGS National Water Quality Laboratory 

(NWQL) analyzed the samples for dissolved and 

suspended species of nitrogen and phosphorus by 

colorimetric methods (Fishman, 1993; Patton and 

Truitt, 2000; Patton and Truitt, 1992; U.S. 

Environmental Protection Agency, 1993). These 

analyses quantified sample concentrations of dissolved 

nitrite, dissolved nitrite plus nitrate, dissolved total 

ammonia (ammonia plus ammonium), dissolved 

organic nitrogen plus ammonia, total organic nitrogen 

plus ammonia, dissolved orthophosphate, dissolved 

phosphorus, and total phosphorus. Analyses reported 

concentrations of nitrate and nitrite (nitrite+nitrate) as 

one analytical parameter. Nitrite was also reported as 

an isolated parameter. This allowed the determination 

that nitrite concentrations were a negligible proportion 

(typically less than 1 percent) of the nitrite+nitrate 

parameter in most samples. Therefore, the general term 

“nitrate” is used in the discussion of related waterquality issues. However, because health-related effects 

of exposure to high nitrate concentrations in water are a 

result of the metabolic conversion of nitrate to nitrite in 

an organism, concentration values are reported as the 

combined nitrite+nitrate parameter in order to present 

the entire concentration of concern. Total ammonia is 

reported by the NWQL as ammonia plus ammonium 

(NH3+NH4

+), although it exists in water primarily as 

the ammonium ion (Pocernich and Litke, 1997). 

Nutrient concentrations discussed in this report 

represent their concentrations expressed as either 

nitrogen or phosphorus. For example, a nitrate 

concentration expressed as 10 mg/L refers to a nitrate 

concentration of 10 mg/L as nitrogen.

Dissolved solids were measured both directly 

and indirectly. The NWQL provided direct analyses of 

dissolved solids by weighing the sample residue on 

evaporation at 180°C (Fishman and Friedman, 1989). 

In addition, the samples were analyzed for major ions 

(Na+, K+, Ca2+, Mg2+, Cl-

, SO4

2-, F-

) and silica by ion 

chromatography (Fishman, 1993; Fishman and 

Friedman, 1989). Summing these with the nitrate 

concentrations and 0.6 times the field alkalinity value 

provides an additional measure of total dissolved solids 

and a rough check on the comprehensiveness of 

analysis (Howard, 1933). Finally, the six fixed sites 

were continuously monitored for specific conductance, 

a parameter strongly correlated with dissolved solids. 

Sensors on the specific-conductance monitors were 

calibrated by study unit personnel during all routine 

site visits, and long-term measurement drifts were 

corrected by applying data corrections to the 

continuous record following USGS protocol (Wagner 

and others, 2000). It was therefore possible to use the 

continuous record of specific conductance to calculate 

the concentration of dissolved solids for the basic fixed 

sites continuously throughout the high-intensity phase 

of data collection.

Data Analysis

As stated earlier, the primary purpose of this 

report is to evaluate TDS and nutrient concentrations in 

Santa Ana Basin streams as a function of water source. 

These sources include mountain runoff, urban runoff, 

treated municipal wastewater, rising ground water, and 

stormflow. The TDS and nutrient concentrations are 

also compared with water-quality standards, goals, 

objectives, and reference conditions.
Methods 11

Trilinear diagrams (Piper, 1944) are used to 

characterize the ionic composition of samples collected 

during base flow at the different sites in order to 

evaluate similarities and differences between sites. 

Piper diagrams are trilinear plottings that show the 

chemical character of a water sample on the basis of its 

relative concentrations of major cations (Ca2+, Mg2+, 

and Na++K+) and anions (Cl-

+F-+NO2

-

+NO3

-

, SO4

2-, 

and HCO3

-

+CO3

2). Boxplots are used to summarize 

concentration data. A boxplot, as used in this report, 

consists of a rectangle (box) divided by a line at the 

median (50th percentile) of the sample data. The lower 

and upper boundaries of the box itself extend from the 

25th to the 75th percentiles, respectively, an interval 

referred to as the interquartile range (IR). Whiskers 

extend from the ends of the box as far as the last 

observed value within 1.5 times the IR. More extreme 

values appear as individual circles beyond the extent of 

the whiskers (fig. 3). Time-series graphs are used to 

show temporal variability for TDS and selected 

nutrients.

Data results are presented in the context of 

existing water-quality standards. These consist of 

primary or secondary standards in the form of 

maximum contaminant levels (MCLs) for drinking 

water (U.S. Environmental Protection Agency, 2002), 

water-quality objectives to protect designated 

beneficial water uses (California Regional Water 

Quality Control Board, 1995), and criteria to protect 

aquatic life or prevent stream eutrophication (U.S. 

Environmental Protection Agency, 1999, 1988, 1986). 

A primary drinking-water standard is legallyenforceable and applies to public water systems. A 

secondary drinking-water standard is a non-enforceable 

guideline regarding contaminants that may cause 

cosmetic effects (such as skin or tooth discoloration) or 

aesthetic effects (such as taste, odor, or color) in 

drinking water. Stream concentrations of total 

phosphorus also are compared with a reference 

condition determined using the 75th percentile (upper 

25th percentile) of total phosphorus concentrations in 

samples from SANA mountain-stream sites (U.S. 

Environmental Protection Agency, 2000). 

For some aspects of this study, specific 

conductance was used as a surrogate for TDS. For each 

fixed site a least-squares regression equation was 

calculated on the analytical values for TDS 

concentrations (mg/L) as a function of field-measured 

specific conductance (microsiemens per centimeter) for 

all samples collected. This relation then was used to 

estimate TDS concentrations at any time for each site 

using the continuous record of specific conductance. 

R-squared values for these linear regressions were at 

least 0.98 with better than 99 percent confidence for all 

sites except MWD, which had an r-squared value of 

0.86 (fig. 4). Plots of residuals versus specific 

conductance indicate constant variance across values of 

specific conductance, except for the Prado and Imperial 

Highway plots. These showed error variances 

increasing with specific conductance. The residual 

standard errors were between 9 and 20 mg/L for all 

sites except MWD, which had a residual standard error 

of 39 mg/L. The weaker correlation and higher error 

for predicting TDS concentrations from specific 

conductance at MWD probably resulted from having 

the continuous monitor for specific conductance placed 

on one bank at a location where field data have shown 

that dissolved solids are not well-mixed across the 

stream.

From the perspective of water managers, the 

nutrient species of greatest concern in the Santa Ana 

Basin is nitrate. Therefore, emphasis is placed on 

nitrate in this discussion of nutrients. Concentration 

values for this form of nitrogen are reported here as 

they were analyzed, nitrite+nitrate, although sample 

nitrite concentrations were usually negligible.

To generate figures and summary statistics, 

concentration values reported as less than the 

laboratory reporting level (LRL), were replaced with 

values one-half of that level. During the study, the LRL 

for some analytes varied. When this occurred, one-half 

the highest common LRL applied to a given analyte 

during the study period was used to replace all values 

for that analyte reported as less than the LRL. 
12 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Median

75th percentile

Number of samples

25th percentile

Extends as high as 1.5 times the interquartile range

above the 75th percentile

Extends as low as 1.5 times the interquartile range

below the 25th percentile

Data value less than 1.5 times

the interquartile range 

below the 25th percentile

Data value greater than 1.5 times 

the interquartile range above

the 75th percentile

Interquartile

range

n=xx

Figure 3. Elements of a boxplot as used in this report.
Methods 13

Mentone

-30

-20

-10

0

10

20

30

40

0 100 200 300 400 500 600

residual standard error = 9

Warm Creek

-60

-40

-20

0

20

40

60

0 200 400 600 800 1000 1200

residual standard error = 20

-100

-50

0

50

100

150

200

0 200 400 600 800 1,000 1,200

residual standard error = 39

TDS= 0.60(Left bank specific conductance) - 57

r

2

 = 0.86

0

100

200

300

400

500

600

700

0 200 400 600 800 1,000 1,200

Mentone

TDS = 0.64(specific conductance) + 4

r

2 = 0.99

TDS = 0.66(specific conductance) - 1

r

2 = 0.98

0

100

200

300

400

0 100 200 300 400 500 600

Warm Creek

MWD MWD

0

200

400

600

800

0 200 400 600 800 1,000 1,200

A B

C D

E F

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER AT 25o CELSIUS

Figure 4. Regression and residual plots of total dissolved solids versus specific conductance at the six fixed sites, Santa Ana Basin, California.
14 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Cucamonga

-50

-40

-30

-20

-10

0

10

20

30

0 100 200 300 400 500 600 700 800

residual standard error = 13

residual standard error = 12

residual standard error = 15

Prado

-30

-20

0

-10

10

20

30

0 200 400 600 800 1,000 1,200

Imperial

-50

-40

-30

-20

-10

0

10

20

30

0 200 400 600 800 1,000 1,200

Imperial

0

200

400

600

800

0 200 400 600 800 1,000 1,200

Prado

100

0

200

300

400

500

600

700

0 200 400 600 800 1,000 1,200

Cucamonga

0

100

200

300

400

500

0 100 200 300 400 500 600 700 800

TDS = 0.59(specific conductance) + 17

r

2

 = 0.99

TDS = 0.62(specific conductance) + 5

r

2

 = 0.98

TDS = 0.61(specific conductance) + 10

r

2

 = 0.98

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER AT 25o CELSIUS

G H

I J

K L

Figure 4.—Continued.
Methods 15

An important source of water in the Santa Ana 

Basin is stormflow, defined as stream discharge added 

to base flow during and temporarily after a rainfall 

event. It includes surface and subsurface runoff. The 

source of the water could be either precipitation from 

the storm or water that existed in the catchment prior to 

the storm. The stormflow end-member was evaluated 

by hydrograph separation at three sites: Warm Creek, 

MWD, and Cucamonga Creek. The hydrographseparation technique was not applied to the other three 

fixed sites; controlled water releases at Prado Dam 

complicated attempts to perform hydrograph 

separations at the Prado and Imperial Highway sites. 

The continuous record for discharge at the Mentone 

site is complicated because it is created from the record 

of a combination of gages. In addition, the continuous 

monitor for specific conductance at the Mentone site 

was moved from one gage to another, and its record 

was difficult to relate to the record of discharge. 

Separation of the hydrograph into base-flow and 

stormflow components was based primarily on the 

continuous record of discharge (Anderson and others, 

2001; Rockwell and others, 2000), and secondarily on 

the continuous record of specific conductance. For each 

measurable rainfall event, discharge and TDS 

(calculated from specific conductance) values were 

determined for base-flow conditions before and after 

the event. Base-flow discharge (Qb) during the storm 

was then estimated as a linear function of the discharge 

observed before and after the event:

(1)

where

Stormflow discharge (Qs) was estimated as the 

difference between the observed total discharge (Qt) 

and the estimated base-flow discharge:

(2)

With the base-flow and stormflow discharge 

components estimated, an average TDS concentration 

for the stormflow can be evaluated from the load of 

TDS contributed by the stormflow. The stormflow load 

(Ls) can be obtained by subtracting the base-flow load 

(Lb) from the total load (Lt). The total load of TDS is a 

function of the observed discharge (Qt) and the 

observed TDS concentration (Ct):

(3)

The dissolved-solids concentration is obtained 

from the continuous record of specific conductance 

converted to TDS concentration by the least-squares 

regression equation developed for each site. The baseflow load, (Lb), is a function of the base-flow discharge 

(Qb) and the base-flow concentration (Cb):

(4)

The base-flow concentration is assumed to vary 

linearly from its pre-storm value to its post-storm 

value:

(5)

where

t is time for which base-flow discharge is 

calculated (for ti < t < tf)

ti is initial time

tf is final time

Qb(i) is initial base-flow discharge at storm onset

Qb(f) is final base-flow discharge at storm onset

Qb Qb i( ) Qb f( ) Qb i( ) ( ) – t ti ( ) – tf ti = + [ ] ⁄ ( ) – ,

Cb(i) is initial base-flow TDS concentration at 

storm onset

Cb(f) is final base-flow TDS concentration at storm 

end

Qs Qt Qb, = –

Lt QtCt =

Lb QbCb =

Cb Cb i( ) Cb f( ) Cb i( ) ( ) – t ti ( ) – tf ti = + [ ] ⁄ ( ) – ,
16 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

With the total and base-flow loads calculated, the 

stormflow load (Ls) and the stormflow concentration of 

dissolved solids (Cs) can be calculated:

 and (6)

. (7)

Finally, the flow-weighted average stormflow 

TDS concentration (FWA) was calculated as:

(8)

The point at which discharge began to increase 

was chosen as ti, and tf was chosen as the time when 

discharge began to level off on the recession limb of the 

hydrograph. As an example, the analysis of stormflow 

arriving at Warm Creek on March 15, 1999 is 

illustrated in figure 5. Figure 5A shows an increase in 

discharge from 8.2 to 49 cubic feet per second within a 

time span of 15 minutes; ti was chosen at 12:15. The 

concentration of TDS in the stream (Ct) can be seen to 

decrease rapidly as a result of the relatively low TDS 

concentration in the stormflow, the dominant source of 

water during most of the event. After the initial rapid 

decrease, Ct levels off. Observed discharge (Qt) 

returned to about 110 percent of discharge prior to the 

event, and was leveling off at 17:30. Therefore, this 

time was chosen for tf. The flow-weighted average 

TDS concentration (fig. 5C) calculated for the event 

illustrated by this example is 220 mg/L.

In the analyses of some storms, the final baseflow discharge, Qb(f), was about equal to the initial 

value, Qb(i). In other cases it was about double the 

initial value. In general, the choice of tf could vary by 

one to three hours. However, the calculated flowweighted average TDS concentration was generally 

insensitive to changes of one to three hours in the 

selected value of tf; changes of one to three hours in tf

generally resulted in changes to the calculated TDS of 

0 to 5 percent. This lack of sensitivity to the selection 

of tf is because the volume of stormflow near the end of 

an event is very small compared to the volume of water 

during peak flows. 

The level-off point on the recession limb was 

chosen for tf because, after this, flows were just as 

likely to increase as they were to decrease at the sites 

where these analyses were performed. This is 

especially true for Cucamonga Creek where 

wastewater discharges are variable and cause frequent 

hydrograph spikes that are unrelated to stormflow.

Nutrient concentrations associated with 

stormflow were also evaluated with the aid of 

hydrograph separation. For each of the discrete 

stormflow samples collected at the three sites—Warm 

Creek, MWD, and Cucamonga Creek—the proportion 

of stormflow at the time of sample collection was 

estimated using the described hydrograph separation 

technique. Discrete samples collected at a time when 

stormflow was equal to or exceeded 75 percent of the 

total observed streamflow were assumed to be 

representative of stormflow. This proportion was 

chosen because it is intermediate of samples consisting 

entirely of stormflow and samples consisting of equal 

parts stormflow and base flow.

QUALITY CONTROL

Two kinds of quality-control (QC) samples, 

blanks and replicates, were collected at frequencies 

determined by NAWQA guidelines (Mueller and 

others, 1997). Blank samples are collected and 

processed using specially prepared analyte-free water 

to identify potential sources of contamination in the 

sampling process that could lead to a positive bias in 

the data. Replicates are two or more samples collected 

and processed so that the samples are as identical in 

composition as possible in order to provide a measure 

of data variability introduced during sample collection, 

processing, and analysis. 

Twenty-two equipment and field blank samples 

were collected for nutrients and constituents of TDS 

during the high-intensity phase (HIP) of data 

collection. Eight of these were collected through 

automatic samplers. Automatic samplers were used for 

routine samples only at the Prado site, and for storm 

samples at the Prado, Warm Creek, and Cucamonga 

Creek sites. Seventeen replicate samples were collected 

during this study; two of these were collected using 

automatic samplers.

Ls Lt Lb, = –

Cs Ls Qs = ⁄

FWA Ls Qs

ti

tf

⁄ ∑

ti

tf

= ∑
Quality Control 17

Storm event affecting 

Warm Creek 3/15/99

0

10

20

30

40

50

60

Observed discharge (Qt)

Observed total dissolved solids (Ct)

Discharge separation

0

10

20

30

40

50

60

Observed discharge (Qt)

Base-flow discharge (Qb)

Stormflow discharge (Qs)

Total dissolved solids 

concentration separation Observed total

 dissolved solids (Ct)

Base-flow total 

 dissolved solids (Cb)

Stormflow total 

 dissolved solids (Cs)

0

100

200

300

400

500

600

0

100

200

300

400

500

600

11:30 12:30 13:30 14:30 15:30 16:30 17:30

Total dissolved solids 

 of discrete sample

DISCHARGE, IN CUBIC FEET PER SECOND DISCHARGE, IN CUBIC FEET PER SECOND

TOTAL DISSOLVED SOLIDS,

IN MILLIGRAMS PER LITER

TOTAL DISSOLVED SOLIDS,

IN MILLIGRAMS PER LITER

A

B

C

TIME

ti tf

Figure 5. One result of the hydrograph-separation technique to isolate concentrations of total dissolved solids in stormflow, Santa Ana Basin, California.
18 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

In addition to quality-control measures 

performed by the study unit, the USGS operates an 

independent, external, quality-assurance project called 

the Inorganic Blind Sample Project (IBSP) to monitor 

and evaluate the quality of laboratory analytical results 

through the use of double-blind QC samples. Results 

from the project can be used to estimate the extent that 

laboratory errors contribute to overall errors in 

environmental data (Ludtke and Woodworth, 1997). 

Field measurements of water temperature, 

dissolved oxygen, pH, specific conductance and 

alkalinity were performed on-site at the time of each 

sample collection. All USGS field personnel who 

perform water-sample measurements of specific 

conductance, alkalinity, and pH are required to 

demonstrate their proficiency in making these 

measurements by participating in the USGS National 

Field Quality Assurance Program (Stanley and others, 

1998)

MAJOR-ION ANALYSES

Major-ion analyses for fixed and mountain sites 

are plotted on trilinear diagrams known as Piper plots 

(Piper, 1944) in figure 6. The plot shows that the 

variation of ionic composition at one particular site is 

generally smaller than between sites, indicating that 

water sources or instream processes are distinct and 

characteristic for each site. The ionic composition of 

the alpine indicator site—South Fork—was dominated 

by calcium bicarbonate, as were the sites fronting the 

San Gabriel Mountains: Cucamonga Creek near 

Upland and Day Creek. The mountain sites fronting the 

San Bernardino Mountains—Cajon Creek and Devil 

Canyon Creek—were dominated by calcium 

bicarbonate, with more chloride, sulfate, and 

magnesium than the other mountain sites. The other 

San Bernardino Mountains site, East Twin Creek, was 

dominated by a sodium/potassium sulfate composition. 

The ionic composition of the urban indicator 

site—Warm Creek—appears to be intermediate to the 

compositions of the upgradient mountain sites: Cajon 

Creek, Devil Canyon Creek, and East Twin Creek. 

Even though surface water from these sites does not 

currently flow to Warm Creek, these streams have 

historically recharged the ground-water system. 

Discharge at Warm Creek is partially provided by 

rising ground water and, therefore, part of the ionic 

composition of water in Warm Creek is representative 

of the rising ground water. High variability in ionic 

composition of base flow at Warm Creek may reflect 

varying proportions of rising ground water and urban 

runoff in the samples.

The ionic compositions of samples from the 

Santa Ana River sites below Prado Dam and near 

Imperial Highway are similar to each other. These sites 

are integrators of water from the upper basin, and their 

composition is consistent with a mixture of the fixed 

sites sampled upstream: Warm Creek, MWD, and 

Cucamonga Creek (fig. 6). Although there are 

additional sources of water to these integrator sites, 

such as Chino Creek, rising ground water and 

additional wastewater treatment plant outfalls, either 

the compositions of the additional water sources are 

similar to those of the fixed sites sampled upstream or 

the contributions of these additional sources are small. 

The ionic composition of samples collected from 

the sites located near Mentone was highly variable 

(fig. 7). The first six samples were collected at the main 

gage (site 11051499) (fig. 2), and are collectively 

referred to as “samples unaffected by dam 

construction.” TDS was low in these samples, and their 

composition on a trilinear plot was similar to that of the 

alpine indicator site (South Fork). After March 1999, 

construction of the Seven Oaks Dam stopped flow to 

this site and, as a result, samples were collected at three 

alternate sites. Water routed to these alternate sites 

passes through sand and rock that had been disturbed 

by dam construction. Water samples influenced by 

these disturbed materials were higher in dissolved 

solids and had a different ionic composition than the 

six samples collected at the initial site (fig. 7). 

Therefore, Mentone samples collected between April 

1999 and September 2001 are collectively referred to 

as “samples affected by dam construction.” The 

samples affected by dam construction often had a 

composition tending toward that of samples from the 

East Twin Creek site Northwest of Mentone (fig. 6).
Major-Ion Analyses 19

MWD

Mentone samples unaffected by

 dam construction

Day Creek

Warm Creek

Devil Canyon Creek

Cucamonga Creek

Cucamonga Creek - Upland

Cajon Creek

EXPLANATION

South Fork

Prado

Imperial Highway

East Twin Creek

 100 80 60 40 20 0

 20

 40

 60

80

 100 0

 0

 20

 40

 60

 80

 100

 0

 20 40 60 80

 100

 100

 80

 60

 40

 20

 0 100

 80

 60

 40

 20

 0

 20

 40

 60

 80

 100

 0

 20

 40

 60

 80

 100

 100

 80

 60

 40

 20

 0

 100

 80

 60

 40

 20

 0

0

PERCENT IN MILLIGRAMS PER LITER

Calcium (Ca2+)

CATIONS ANIONS

Magnesium (Mg2+)

Sodium (Na+) + Potassium (K+)

Chloride (Cl

-

), Flouride (F-), Nitrite(N02

-

) + Nitrate (N03

-

)

Carbonate (C03

2-) + Bicarbonate (HC03

-

)

Sulfate (S04

2-)

Sulfate (S04

) + Chloride (Cl

-)

Calcium (Ca2+) + Magnesium (Mg2+)

2-

Figure 6. Base-flow water composition at fixed and mountain sites, Santa Ana Basin, California.
20 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

 100 80 60 40 20 0

 20

 40

 60

80

 100 0

 20

 40

 60

 80

 100

 0

 20 40 60 80

 100

 100

 80

 60

 40

 20

 0 100

 80

 60

 40

 20

 0

 20

 40

 60

 80

 100

 0

 20

 40

 60

 80

 100

 100

 80

 60

 40

 20

 0

 100

 80

 60

 40

 20

 0

0

CATIONS ANIONS PERCENT IN MILLIGRAMS PER LITER

Sulfate (S04

) + Chloride (Cl

-)

2-

Calcium (Ca2+) + Magnesium (Mg2+)

Sodium (Na+) + Potassium (K+)

Carbonate (C03

2-) + Bicarbonate (HC03

-

)

Chloride (Cl

 -), Flouride (F-

), Nitrite(N02

-

) + Nitrate (N03

- Calcium (Ca ) 2+)

Sulfate (S04

2-

Magnesium (Mg

)

2+)

Mentone samples unaffected by dam construction

 (first six samples)

Mentone samples affected by dam construction

February 2000 sample collected above the dam

EXPLANATION

Figure 7. Base-flow water composition at the various sampling locations at the Mentone site, Santa Ana Basin, California.
Total Dissolved Solids 21

In February 2000, a sample was collected 

upstream and beyond the influence of the dam 

construction. This sample was low in TDS and its ionic 

composition resembled that of the first six samples 

collected at the main gage (fig. 7). Additional 

measurements of specific conductance and analyses for 

selected anions made from October 2001 to April 2003 

at this site above the dam are similar in value to those 

of the early Mentone samples. It appears that the initial 

six samples, along with the one collected above the 

dam, are most representative of water quality of 

mountain run-off at Mentone.

TOTAL DISSOLVED SOLIDS 

Total Dissolved Solids and Concentrations of 

Some Individual Constituents Compared with 

Water-Quality Criteria

The USEPA has established water-quality 

criteria consisting of secondary maximum contaminant 

levels (MCLs) for total dissolved solids in drinking 

water, as well as for some individual dissolved 

constituents such as chloride, sulfate, fluoride, and 

manganese. The secondary MCL for TDS (500 mg/L) 

was exceeded in most of the base-flow samples from 

the valley-floor sites (fig. 8). Base-flow TDS 

concentrations at these sites were usually lower than 

the water-quality objectives (550 to 700 mg/L) set by 

the California Regional Water Quality Control Board 

[RWQCB](1995). Although municipal and domestic 

supply is not a designated beneficial use for the Santa 

Ana River (California Regional Water Quality Control 

Board, 1995), most of the river flow is used for aquifer 

recharge just downstream from the Imperial Highway 

site. The replenished aquifers are pumped as the 

primary water supply for about 2 million people 

(Orange County Water District, 1996). TDS in samples 

from mountain sites was generally less than the 

secondary MCL and the water-quality objectives for 

these sites (200 to 475 mg/L). However, TDS in 

samples from two mountain sites—East Twin Creek 

and Cajon Creek—often exceeded both the secondary 

MCL and water-quality objective levels (fig. 9).

The secondary MCL for chloride (250 mg/L) 

was not exceeded in water samples collected for this 

study. The secondary MCL for sulfate (also 250 mg/L) 

was exceeded at one site, East Twin Creek, in three of 

the seven samples collected there. Fluoride 

concentrations in samples from the East Twin Creek 

also exceeded the secondary MCL (2 mg/L) in six of 

the seven samples, and exceeded the primary MCL

(4 mg/L) in four of these. The fluoride secondary MCL 

(2 mg/L) was also exceeded in 12 of the 50 samples 

(including storm samples) collected at Warm Creek. 

Prior to the construction of diversions that presently 

intercept flow from most mountain streams in the 

basin, East Twin Creek surface flows may have fed 

Warm Creek. The observation that East Twin Creek 

and Warm Creek streamflow presently share high 

fluoride concentrations provides additional evidence 

that basin ground water is a substantial source to Warm 

Creek. 

Manganese concentrations exceeded the 

secondary MCL (0.05 mg/L) in most (30 of 41) 

samples collected from the Santa Ana River below 

Prado Dam. Manganese is considered a trace element 

because it is generally found in water at concentrations 

less than 1.0 mg/L. Therefore, manganese rarely 

contributes significantly to TDS concentrations in 

streams, even when it occurs at high concentrations. 

Manganese concentrations were mostly below 

0.01 mg/L in samples collected for this study; however, 

it ranged from 0.02 to 0.35 mg/L in samples collected 

from the site below Prado Dam. The presence of 

manganese at concentrations exceeding the secondary 

MCL below the Prado Dam is probably a result of 

chemical reduction due to anaerobic conditions in the 

wetlands upstream from this site. Manganese is found 

in wetlands primarily in its reduced (manganous) form, 

which is more soluble than its oxidized (manganic) 

form (Mitsch and Gosselink, 1993). Three samples 

collected from the Santa Ana River below Imperial 

Highway also had manganese concentrations that 

exceeded the secondary MCL. This site is located

11 mi downstream from the site below Prado Dam. 

Samples were also collected from the Prado site on 

each of the days when the samples having unusually 

high manganese concentrations were collected from the 

Imperial Highway site. In each case, the sample 

collected from the Prado site had a higher manganese 

concentration than the sample collected from the 

Imperial Highway site. Therefore, it seems likely that 

the high manganese concentrations produced in the 

Prado Wetlands are occasionally carried downstream to 

the Imperial Highway site. Two samples collected from 

Cucamonga Creek, and one sample collected from 

Warm Creek also had manganese concentrations that 

slightly exceeded the secondary MCL. All three 

samples were collected under stormflow conditions.
22 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

0

200

400

600

800

1,000

1,200

TOTAL DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

CUCAMONGA

CREEK

MENTONE WARM MWD

CREEK

n=35

n=38 n=43

IMPERIAL

HIGHWAY

PRADO

Mountain

reference site

Valley-floor tributaries Valley-floor Santa Ana River sites 

n=34

n=24

n=24

California Regional Water Quality 

Control Board (1995) reach-specific

water-quality objective

Below drinking-water secondary 

maximum contaminant level 

(500 milligrams per liter)

EXPLANATION

Figure 8. Base-flow total dissolved solids concentrations at fixed sites, Santa Ana Basin, California.
Total Dissolved Solids 23

MENTONE

n=4

n=7

n=34

n=7

TOTAL DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

n=7

n=7

n=20

SOUTH

FORK

DAY

CREEK

CUCAMONGA

CREEK NEAR

UPLAND

DEVIL

CANYON

CREEK

CAJON

CREEK

EAST

TWIN

CREEK

California Regional 

Water Quality Control

Board (1995) reach-specific

water quality objective

Below drinking-water

secondary maximum 

contaminant level 

(500 milligrams per liter)

0

200

400

600

800

1,000

1,200

EXPLANATION

Figure 9. Base-flow total dissolved solids concentrations at mountain sites, Santa Ana Basin, California. 
24 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Base-Flow Total Dissolved Solids Concentration 

by Water Source

Of all the water sources sampled, mountain sites 

generally had the lowest TDS, with medians at most 

sites ranging from about 50 to about 300 mg/L (fig. 9). 

The Mentone site appears to be a good representative 

of reference conditions for water entering the basin, 

with a median TDS of 230 mg/L. That value is 

somewhat lower than the median at Devil Canyon 

Creek of 280 mg/L, but somewhat higher than the 

medians at the two sites in the San Gabriel Mountains: 

180 mg/L at Day Creek and 200 mg/L at Cucamonga 

Creek near Upland. The alpine indicator site, South 

Fork of the Santa Ana River, had TDS concentrations 

of about 50 mg/L, which seem too low to represent 

reference conditions for water entering the basin. Two 

mountain sites (East Twin Creek and Cajon Creek) had 

high TDS: East Twin Creek receives drainage from the 

San Bernardino Mountains and had a median TDS of 

560 mg/L; Cajon Creek receives drainage from both 

the San Bernardino Mountains and the San Gabriel 

Mountains and had a median TDS just over 500 mg/L. 

These concentrations are comparable to the highest 

levels found in samples collected from the valley floor. 

Streams on the valley floor had median TDS 

ranging from about 400 to 600 mg/L (fig. 8), and 

generally increasing downstream (with decreasing 

reach number) along the main stem of the river. Median 

concentrations at the two tributary fixed sites, Warm 

Creek (tributary to Reach 5 of the Santa Ana River) and 

Cucamonga Creek (tributary to Reach 3), were 

470 and 410 mg/L respectively. MWD, in Reach 3, had 

a median TDS of 560 mg/L. At the next integrator site, 

Prado Dam at the upstream terminus of Reach 2, the 

median TDS was 600 mg/L. About 11 mi downstream 

at the downstream terminus of Reach 2, the site below 

Imperial Highway had a median concentration of 

620 mg/L. 

The downstream increase in TDS appears to be 

independent of water source. Base-flow sources to 

Warm Creek are a mix of rising ground water and 

urban runoff, whereas base flow in Cucamonga Creek 

is usually about 90 percent treated wastewater with a 

small urban runoff component. Base flow at MWD in 

Reach 3 is about 70 percent wastewater (Mendez and 

Belitz, 2002), with rising ground water making up most 

of the balance. Base flow at Prado and Imperial 

Highway is predominantly wastewater. 

Total dissolved solids in urban runoff range from 

about 250 to 370 mg/L, on the basis of sparse data 

(table 2). This is somewhat lower than concentrations 

observed at sites receiving treated wastewater, and 

closely approximates TDS in water delivered for 

domestic use in the Santa Ana Basin (City of Redlands, 

2002; Metropolitan Water District of Southern 

California, 2002; Western Municipal Water District, 

2002; San Bernardino Valley Municipal Water District, 

2002). Some of the highest TDS in the basin may occur 

at sites on the valley floor that are dominated by rising 

ground water. However, this observation is based on 

just a few synoptic study samples collected from three 

valley-floor sites near MWD that are dominated by 

rising ground water. Total dissolved solids were 600 

mg/L in two samples collected from the Sunnyslope 

channel in August 2000 (table 3). Samples collected in 

May 2001 from two other sites dominated by rising 

ground water—Tesuesquito Creek and Hole Lake—

were not analyzed for dissolved solids. However, the 

specific conductance of samples from these sites was 

among the highest observed in this study, ranging from 

1,230 to 1,550 μS/cm and indicating that TDS 

concentrations were likely also high. 

Total Dissolved Solids in Stormflow

Stormflow is an important source of water to 

streams in the Santa Ana Basin, and it usually dilutes 

stream TDS. As a result, total dissolved solids in urban 

stormflow were generally low in comparison with 

urban runoff. During the period of this study, between 

six and eight samples were collected during storm 

events at each of the fixed sites. The median TDS in 

discrete samples collected under stormflow conditions 

was 260 mg/L. In addition to analyses of discrete 

stormflow samples, hydrograph separation was used to 

estimate TDS in the stormflow end-member at three 

sites: Warm Creek, MWD, and Cucamonga Creek. 

During the period of this study, 87 discrete storm 

events were identified in the study area from records of 

rainfall (U.S. Army Corps of Engineers, 2002) and 

stream discharge (Anderson and others, 2001; 

Rockwell and others, 2000). Each event affected one or 

more of the three evaluated sites. 
Total Dissolved Solids 25

Table 2. Nitrite+nitrate (mg/L as N) and total dissolved solids (mg/L) concentrations in samples consisting predominantly of urban runoff, Santa Ana Basin, 

California

[mg/L, milligrams per liter; <, less than indicated value; N, nitrogen; NO2

-

, nitrite; NO3

-

, nitrate; TDS, total dissolved solids; —, no data]

1Sample purpose refers to topical study for which sample was collected: (1) dissolved organic carbon characterization study, (2) Urban Land Use 

Gradient study (Burton and Brown, 2001), (3) Algal assimilation study (Kent and Burton, 2001), and (4) Low-Intensity-Phase of data collection for the Santa 

Ana Basin Study Unit of the National Water-Quality Assessment Program (samples collected subsequent to report study period). 2Total dissolved solids (TDS) calculated from specific conductance (r2=0.98)

Site Sample 

purpose1 Date Time NO2

-

+NO3

-

(mg/L)

TDS 

(mg/L)

Cucamonga Creek below Hwy. 60 1 03/10/99 15:30 0.02 —

Cucamonga Creek below Hwy. 60 1 04/15/99 16:30 .16 —

Cucamonga Creek below Hwy. 60 1 05/19/99 16:10 .34 —

Cucamonga Creek Main Channel 2 08/09/00 12:30 .61 330

Cucamonga Creek Main Channel 3 08/15/01 22:20 3.78 —

Cucamonga Creek Main Channel 3 08/16/01 13:45 .54 —

Warm Creek near San Bernardino 4 06/13/02 09:30 .10 369 

Warm Creek near San Bernardino 4 08/15/02 09:00 <.05 2316

Warm Creek near San Bernardino 4 10/16/02 11:00 .48 2315

Warm Creek near San Bernardino 4 12/02/02 09:00 .50 2333

Warm Creek near San Bernardino 4 01/16/03 09:00 .47 2353

Warm Creek near San Bernardino 4 03/13/03 09:00 .07 2334

Warm Creek near San Bernardino 4 06/12/03 09:00 .49 2352

Warm Creek near San Bernardino 4 08/14/03 09:00 .06 2265

Table 3. Nitrite+nitrate (mg/L as N) and total dissolved solids (mg/L) concentrations in samples consisting predominantly of rising ground water, Santa Ana 

Basin, California

[[mg/L, milligrams per liter; N, nitrogen; NO2

-

, nitrite; NO3

-

, nitrate; TDS, total dissolved solids]

1Sample purpose refers to topical study for which sample was collected: (2) Urban Land Use Gradient study (Burton and Brown, 2001),and (5) Dyetracer study (Mendez and Belitz, 2002).

Site Sample 

purpose1 Date Time NO2

-

+NO3

-

(mg/L)

TDS

(mg/L)

Sunnyslope Channel 2 08/17/00 11:00 10.4 604

Sunnyslope Channel 2 08/17/00 14:10 10.5 605

Sunnyslope Channel 5 05/22/01 05:00 11.0 —

Tequesquito Channel 5 05/22/01 04:50 14.0 —

Hole Lake 5 05/23/01 00:10 16.5 —
26 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Eighty of the identified events affected Warm 

Creek. Rainfall events affecting Warm Creek typically 

measured from 0.05 to 0.40 in. (fig. 10A) and typically 

lasted from 4 to 12 hours (fig. 10B). The peak 

discharges resulting from these events typically 

exceeded pre-storm base flow by a factor of from 8 to 

50 (fig. 11A), and receding discharges typically were 

leveling off (Qb(f)) within 5 to 13 hours after the arrival 

of stormflow to the site (fig. 11B).

During this study, fewer rainfall events affected 

MWD and Cucamonga Creek. One reason for this is 

that the period for which hydrograph separation was 

performed coincided with the period of sample 

collection for each site; samples were collected from 

MWD and Cucamonga Creek during only two years, 

compared to three years for Warm Creek. Also, MWD 

and Cucamonga Creek receive higher base-flow 

discharges than Warm Creek due to inputs of treated 

wastewater, and they have larger contributing drainage 

areas. These factors probably diminished streamflow 

response to small rainfall events at these sites. 

Twenty-three rainfall events affected MWD, 

typically measuring from 0.25 to 0.50 in. (fig. 10A) and 

lasting from 9 to 23 hours (fig. 10B). The peak 

stormflow discharges at MWD typically exceeded prestorm base flow by a factor of from 3 to 8 (fig. 11A), 

and receding discharges typically leveled off 11 to 18 

hours after the onset of stormflow (fig. 11B). 

Thirty-one rainfall events affected Cucamonga 

Creek, typically measuring from 0.14 to 0.35 in. (fig. 

10A) and lasting from 4 to 10 hours (fig. 10B). The 

peak stormflow discharges at Cucamonga Creek 

typically exceeded pre-storm base flow by a factor of 

from 9 to 24 (fig. 11A), and receding discharges 

typically leveled off 4 to 9 hours after the onset of 

stormflow (fig. 11B).

Storm events are usually of short duration in the 

Santa Ana Basin (fig. 10B). Stream channels are altered 

and base flow is sustained by other than natural 

processes, generally by treated wastewater or urban 

runoff. Stream response is rapid and also of short 

duration (fig. 11B) in these altered channels. The 

hydrograph separation technique typically delimited 

the periods of stormflow so that they were of duration 

similar to the rainfall events in order to limit analyses 

to periods during which stormflow was a major source 

of streamflow. 

 The median flow-weighted average TDS for 

stormflow, isolated by hydrograph separation at Warm 

Creek, MWD, and Cucamonga Creek, was 190 mg/L. 

This is less than the median of 210 mg/L for discrete 

samples collected under stormflow conditions at these 

three sites. However, the isolated stormflow TDS, 

which were calculated by hydrograph separation, were 

highly variable. Values were as high as 590 mg/L in 

stormflow reaching Warm Creek and as low as 

35 mg/L in stormflow reaching Cucamonga Creek

(fig. 12). Stormflow TDS concentrations are given as 

flow-weighted averages for each analyzed event.
Total Dissolved Solids 27

0.0

0.5

1.0

1.5

2.0

2.5

RAINFALL MAGNITUDE, IN INCHES

n=80

0

10

20

30

40

RAINFALL DURATION, IN HOURS

n=23

n=31

n= 80

n= 23

n= 31

A B

CUCAMONGA

CREEK

WARM MWD

CREEK

CUCAMONGA

CREEK

WARM MWD

CREEK

Figure 10. Rainfall magnitude (inches) and duration (hours) for storms analyzed by hydrograph separation, Santa Ana Basin, California.
28 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

100

101

102

2

4

6

8

2

4

6

8

2

4

6

0

10

20

30

40

STORMFLOW DURATION, IN HOURS

RATIO OF PEAK DISCHARGE TO PRE-STORM BASE FLOW

n=80

n=23

n=31

n=23 n=31

A B n=80

CUCAMONGA

CREEK

WARM MWD

CREEK

CUCAMONGA

CREEK

WARM MWD

CREEK

Figure 11. Stormflow magnitude (ratio of peak flow to pre-storm base flow) and duration (hours) for stormflow analyzed by hydrograph separation, Santa 

Ana Basin, California.
Total Dissolved Solids 29

0

200

400

600

800

n= 23 storms

MWD

n=30 storms

n=102 storms

TOTAL DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

CUCAMONGA CREEK WARM CREEK

California Regional 

Water Quality Control

Board (1995) reach-specific

water quality objective

Below drinking-water

secondary maximum 

contaminant level 

(500 milligrams per liter)

EXPLANATION

Figure 12. Total dissolved solids concentrations in stormflow (calculated by hydrograph separation) at three urban sites, Santa Ana Basin, California.
30 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

To help explain the variability observed over the 

entire population of storms analyzed by hydrograph 

separation, the results were divided into two groups: a 

low-rainfall group having a relatively high median, but 

variable TDS; and a high-rainfall group having a 

relatively low median and small variability in TDS 

(figs. 13, 14, and 15). The line dividing the two groups, 

or threshold-rainfall-magnitude, was chosen 

subjectively to minimize the concentration and 

variability of TDS in the high-magnitude rainfall group 

and, at the same time, include a substantial portion 

(greater than 20 percent) of the data in that group. 

Rainfall measurements were obtained from a U.S. 

Army Corps of Engineers (2002) website, which 

records rainfall to a precision of 0.01 inch. The values 

for the threshold-rainfall-magnitude were rounded to 

the nearest 0.05 inch.

The threshold rainfall magnitude was estimated 

at 0.45 in. for Warm Creek and MWD, and at 0.30 in. 

for Cucamonga Creek. The larger thresholds at Warm 

Creek and MWD may reflect the influence of groundwater inputs at these two sites. The dilution by rainfall 

at Warm Creek and MWD probably is offset by the 

input of high-TDS water stored in the catchment prior 

to the event as it is moved into the stream by increased 

potentiometric head in response to the rainfall. 

The median flow-weighted average TDS 

concentrations for storm events when rainfall was less 

than the rainfall thresholds were 250 mg/L at Warm 

Creek, 300 mg/L at MWD, and 130 mg/L at 

Cucamonga Creek. When the rainfall thresholds were 

exceeded, the median flow-weighted average TDS was 

140 mg/L at Warm Creek, 120 mg/L at MWD, and 

70 mg/L at Cucamonga Creek. These results suggest 

that a characteristic TDS for large events is 70 to 

140 mg/L, depending on location. These results also 

suggest that the characteristic TDS for small events is 

substantially higher. The relatively high TDS 

associated with low-magnitude events may provide 

significant annual stream TDS loads if small events 

collectively contribute significant proportions of the 

total yearly streamflow. This appears to be the case at 

Warm Creek, where even a small rainfall event can 

increase streamflow by one or two orders of magnitude 

(figs. 10A, 11A).

Storm samples collected near the beginning of a 

storm, as material is flushed from the landscape by 

stormwater runoff, would be expected to have higher 

TDS concentrations than those of samples collected 

later in the event. This was evident over the course of 

one event when two storm samples were collected from 

Cucamonga Creek. Prior to the storm, stream TDS was 

approximately 400 mg/L (based on the relation 

between TDS and continuously monitored specific 

conductance). The first sample was collected early in 

the event when, during a 15-minute time interval, 

discharge increased from 67 to 1,060 ft3/s. The TDS of 

this sample was 284 mg/L (analyzed residue-onevaporation). The second sample, collected 20 minutes 

later at peak discharge for the event (1,380 ft3/s), had a 

TDS of 64 mg/L. The second sample apparently 

contained a lower concentration of dissolved materials 

flushed from the landscape, probably as a result of 

dilution by stormflow.
Total Dissolved Solids 31

0 1.0 2.0

RAINFALL, IN INCHES

100

300

500

100

300

500

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

0.5 1.5 2.5

Flow-weighted average TDS in stormflow

Threshold rainfall-magnitude boundary between

relatively large (>0.45 inches) and 

relatively small rainfall events (<0.45 inches)

A

B

TDS concentrations in stormflow resulting 

from rainfall events less than (<) 0.45 inches

TDS concentrations in stormflow resulting 

from rainfall events greater than (>) 0.45 inches

n=63

n=17

Figure 13. Stormflow concentrations of total dissolved solids (analyzed by hydrograph separation) as a function of rainfall magnitude at Warm Creek, Santa 

Ana Basin, California.
32 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

0 1.0

RAINFALL, IN INCHES

100

200

300

400

100

200

300

400

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

0.5 1.5

Flow-weighted average TDS in stormflow

A

B

TDS concentrations in stormflow resulting 

from rainfall events less than (<) 0.45 inches

TDS concentrations in stormflow resulting 

from rainfall events greater than (>) 0.45 inches

n=15

n=8

Threshold rainfall-magnitude boundary between

relatively large (>0.45 inches) and 

relatively small rainfall events (<0.45 inches)

Figure 14. Stormflow concentrations of total dissolved solids (analyzed by hydrograph separation) as a function of rainfall magnitude at MWD, Santa Ana 

Basin, California. 
Total Dissolved Solids 33

0

RAINFALL, IN INCHES

100

200

300

100

200

0

0

300

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

0.2 0.4 0.6

A

B

TDS concentrations in stormflow resulting 

from rainfall events less than (<) 0.30 inches

TDS concentrations in stormflow resulting 

from rainfall events greater than (>) 0.30 inches

n=21

n=10

Flow-weighted average TDS in stormflow

Threshold rainfall-magnitude boundary between

relatively large (>0.30 inches) and 

relatively small rainfall events (<0.30 inches)

Figure 15. Stormflow concentrations of total dissolved solids (analyzed by hydrograph separation) as a function of rainfall magnitude at Cucamonga Creek, 

Santa Ana Basin, California. 
34 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Comparison of Calculated Mean-Daily, Discrete, 

and Flow-Weighted Average Stormflow Total 

Dissolved Solids Concentrations

Mean daily TDS, calculated from the continuous 

records of specific conductance, for the fixed sites 

during all or part of the period from October 1998 to 

September 2001 are shown in figures 16A–F. The 

concentrations obtained from laboratory analyses of 

discrete samples at base flow and stormflow are plotted 

with the concentrations calculated from the continuous 

record of specific conductance. Also plotted are the 

mean daily discharges for the period. For three of the 

sites, Warm Creek, MWD, and Cucamonga Creek, the 

flow-weighted stormflow TDS also are plotted (figures 

16B, C, D). Note that the plots are not all at the same 

scale.

For all six sites, the mean daily TDS, calculated 

from specific conductance, is in close agreement with 

the TDS of discrete samples collected during base-flow 

conditions. The continuous record of mean daily 

specific conductance for the Imperial Highway site was 

unavailable. Therefore, published records of daily 

minimum and maximum values of specific 

conductance were used in place of mean daily values in 

figure 16F.

In figures 16A–F, the mean daily TDS calculated 

from specific conductance is commonly higher than 

concentrations in discrete storm samples. Storms often 

lasted less than 1 day and, consequently, daily averages 

typically included a higher proportion of base-flow 

discharge than did discrete stormflow samples. Figures 

16B, C, D also show that the stormflow end-member, 

isolated by hydrograph separation at Warm Creek, 

MWD, and Cucamonga Creek had relatively low, flowweighted average TDS. 

CONCENTRATIONS OF SELECTED 

NUTRIENTS 

Total Nitrogen and Nitrogen Speciation

Mean total nitrogen concentrations in base-flow 

samples collected from fixed sites ranged from

0.3 mg/L for samples from Mentone to 7.9 mg/L for 

samples from Cucamonga Creek. Nitrogen at five of 

the six fixed sites was predominantly in the form of 

nitrate under base-flow conditions (fig. 17). More than 

seventy-five percent of the nitrogen in samples from 

the four fixed sites (MWD, Cucamonga Creek, Prado, 

and Imperial Highway that receive wastewater) was in 

the form of nitrate. Nitrogen in samples collected from 

Mentone was predominantly in the form of total 

organic nitrogen plus ammonia (TON+ammonia). 

Considering results from the other mountain sites 

sampled in the Santa Ana Basin, it appears that 

nitrogen speciation and concentrations of the different 

forms of nitrogen in samples from the Mentone site 

were representative of reference conditions for water 

entering the valley floor.

The concentration and proportion of 

TON+ammonia were usually higher in samples 

collected under stormflow conditions. This was most 

evident at Warm Creek, MWD, and Cucamonga Creek. 

Concentrations of all forms of nitrogen increased at 

Mentone and Warm Creek during stormflow, resulting 

in higher total nitrogen at these sites. At MWD, 

stormflow-related increases in concentrations of total 

organic nitrogen and ammonia were mostly offset by 

decreases in nitrate concentrations, resulting in little 

net change in total nitrogen concentrations. Nitrate 

concentrations also decreased at Cucamonga Creek 

during stormflow. However, total nitrogen at this site 

usually showed a net increase owing to stormflow and 

greater inputs of TON+ammonia. At the Prado and 

Imperial Highway sites, nitrogen concentrations and 

proportions of nitrogen species were similar under 

base-flow and stormflow conditions. This is likely due 

to flow regulation at Prado Dam. 
Concentrations of Selected Nutrients 35

Nov Jan Mar May Jul Sep

1999

Mean daily discharge

Mean daily TDS (calculated from specific conductance)

Discrete base-flow TDS (concentrations in samples collected)

Discrete stormflow TDS (concentrations in samples collected)

0

200

400

600

800

1,000

40

80

120

160

200

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

DISCHARGE, IN CUBIC FEET PER SECOND

Dec Feb Apr Jun Aug Oct

1998

A. Mentone

0

Figures 16A–F. Mean daily discharge, mean daily total dissolved solids (TDS), and TDS in discrete base-flow and stormflow samples at the six fixed sites, 

Santa Ana Basin, California. Graphs for B, C, and D also have flow-weighted average stormflow TDS obtained by hydrograph separation.
36 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

0

40

80

120

160

200

0

200

400

600

800

1,000

ON D A M

1998 1999 2000 2001

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

Mean daily discharge

Mean daily TDS (calculated from specific conductance)

Discrete base-flow TDS (concentrations in samples collected)

Discrete stormflow TDS (concentrations in samples collected)

Flow-weighted average TDS in stormflow

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

DISCHARGE, IN CUBIC FEET PER SECOND

B. Warm Creek

Figure 16.—Continued.
Concentrations of Selected Nutrients 37

0

200

400

600

800

1,000

0

200

400

600

800

1,000

Mean daily discharge

Mean daily TDS (calculated from specific conductance)

Discrete base-flow TDS (concentrations in samples collected)

Discrete stormflow TDS (concentrations in samples collected)

Flow-weighted average TDS in stormflow

O N D AM

1998 1999 2000

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

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

DISCHARGE, IN CUBIC FEET PER SECOND

C. MWD

Figure 16.—Continued.
38 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

D. Cucamonga Creek

0

200

400

600

800

1,000

0

200

400

600

800

1,000

O ND A M

1998 1999 2000

J F M J J A S O ND A J F M M J J A S

Mean daily discharge

Mean daily TDS (calculated from specific conductance)

Discrete base-flow TDS (concentrations in samples collected)

Discrete stormflow TDS (concentrations in samples collected)

Flow-weighted average TDS in stormflow

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

DISCHARGE, IN CUBIC FEET PER SECOND

Figure 16.—Continued.
Concentrations of Selected Nutrients 39

E. Prado

0

2,500

5,000

7,500

10,000

0

250

500

750

1,000

OND A M

1998 1999 2000 2001

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

Mean daily discharge

Mean daily TDS (calculated from specific conductance)

Discrete base-flow TDS (concentrations in samples collected)

Discrete stormflow TDS (concentrations in samples collected)

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

DISCHARGE, IN CUBIC FEET PER SECOND

Figure 16.—Continued.
40 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

F. Imperial Highway

OND A M

1998 1999 2000 2001

J F M J J A S OND A J F M M J J A S O ND A J F M M J J A

0

2,000

1,000

4,000

3,000

6,000

5,000

8,000

7,000

10,000

9,000

0

200

400

600

800

1,000

DISCHARGE, IN CUBIC FEET PER SECOND

Minimum daily TDS (calculated from specific conductance)

Maximum daily TDS (calculated from specific conductance)

Discrete stormflow TDS (concentrations in samples collected)

Discrete base-flow TDS (concentrations in samples collected)

Mean daily discharge

TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER TOTAL DISSOLVED SOLIDS (TDS), IN MILLIGRAMS PER LITER

Figure 16.—Continued.
Concentrations of Selected Nutrients 41

n=38 Number of samples (collected at base flow and stormflow respectively)

TN Total nitrogen 

Milligrams per liter

nitrite + nitrate, as nitrogen

Total organic nitrogen + ammonia, as nitrogen

 Base flow Stormflow

Mentone n=34

Mean TN=0.3 mg/L

n=6

Mean TN =0.6 mg/L

Warm Creek n=43

Mean TN=0.8 mg/L

n=7

Mean TN-6.1 mg/L

MWD

n=23

Mean TN=7.7 mg/L

n=6

Mean TN=8.0 mg/L

Cucamonga

Creek n=24

Mean TN=7.9 mg/L

n=8

Mean TN =14.9 mg/L

Prado

n=35

Mean TN =6.4 mg/L

n=6

Mean TN=7.6 mg/L

Imperial

Highway n=38

Mean TN=6.2 mg/L

n=6

Mean TN=6.0 mg/L

Area of circles is proportional to total nitrogen (TN) concentrations

EXAMPLE

mg/L

Figure 17. Mean nitrogen concentrations and speciation at fixed sites under base-flow and stormflow conditions, Santa Ana Basin, California.
42 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Base-Flow Nitrate Concentrations by Water 

Source

Nitrate concentrations are higher in Santa Ana 

Basin streams receiving treated wastewater than in 

most streams that have other sources of water. Median 

base-flow concentrations at the four fixed sites located 

downstream from wastewater-treatment-plant outfalls 

(MWD, Cucamonga Creek, Prado Dame, and Imperial 

Highway) ranged from 4.9 to 6.7 mg/L. Nitrite+nitrate 

concentrations exceeded the U.S. Environmental 

Protection Agency (2002) drinking water standard of 

10 mg/L in four samples collected at Cucamonga 

Creek and in one sample collected at MWD (fig. 18). 

Sites on stream reaches not receiving wastewater inputs 

had relatively low concentrations of nitrite+nitrate, 

with medians mostly below 1 mg/L (fig. 19).

Streams fed by mountain runoff in the Santa Ana 

Basin (the Mentone site and the other mountain sites) 

had median base-flow concentrations of nitrite+nitrate 

mostly below 0.3 mg/L (fig. 19). This agrees well with 

a national study by Clark and others (2000), which 

produced a mathematical model for predicting nitrate 

concentrations in undeveloped basins. Their model 

predicts that the flow-weighted mean nitrate 

concentration in undeveloped basin streams in the 

Santa Ana region should fall between 0.20 to 0.34 

mg/L (fig. 19). The mountain site on Cajon Creek had 

relatively high nitrite+nitrate concentrations with a 

median of 1.4 mg/L. This is more than twice the 

median concentrations found at other basin sites that 

receive mountain run-off, and exceeds the California 

Regional Water Quality Control Board (1995) objective 

of 1 mg/L for this site. The site is located in a pass 

between the San Bernardino and the San Gabriel 

Mountains and, therefore, its water source is not 

strictly mountain runoff. The pass also serves as a 

transportation corridor, possibly resulting in highway 

and railway runoff to the stream. 

Nitrite+nitrate concentrations in urban runoff in 

the Santa Ana Basin seem to be mostly below 1 mg/L 

(table 2). This estimate for urban runoff is based on 

fewer data than other water sources because none of the 

fixed sites had urban runoff as the sole source of water 

during the high-intensity phase (HIP) of data 

collection. Flow at the urban indicator site on Warm 

Creek usually consists of both urban runoff and rising 

ground water, and it had a mean nitrite+nitrate 

concentration of 0.4 mg/L (fig. 18). In eight samples 

collected subsequent to the HIP at this site, from June 

2002 to August 2003, the typical rising ground-water 

contribution was absent, leaving only the urban runoff 

component. The nitrite+nitrate concentrations for these 

samples all have been less than 1 mg/L (table 2) and are 

comparable to the concentrations observed at this site 

when it is receiving ground-water inputs. 

Results for those eight samples are presented in 

table 2, along with results for six samples collected 

from Cucamonga Creek upstream from the wastewater 

input where the flow is predominantly urban runoff. 

Nitrite+nitrate concentrations in all but one of these 

samples were less than 1 mg/L. The sample with a 

higher nitrite+nitrate concentration (3.8 mg/L) was 

collected at night from Cucamonga Creek. Conditions 

in this stream vary diurnally, with dissolved-oxygen 

concentrations ranging from 4 to more than 20 mg/L 

and pH ranging from 7.5 to more than 10 standard pH 

units in a single 24-hour period. Such extreme 

fluctuations can be attributed to high daytime primary 

productivity by attached algae. At night, the abundant 

algae may release nitrogen compounds, thus increasing 

the concentration of nitrite+nitrate. 

Some streams receiving rising ground water have 

high concentrations of nitrate. Samples collected from 

three ground-water-fed tributaries contributing to 

Reach 3 (fig. 1) had some of the highest nitrate 

concentrations observed in this study. The five samples 

collected from these tributaries had nitrite+nitrate 

concentrations ranging from about 10 to 16 mg/L 

(table 3). One of the tributaries—Sunnyslope 

Channel—emerges from a culvert below street level as 

a concrete-lined channel. From where it is first exposed 

to sunlight the channel is blanketed with algae, 

indicating eutrophy. Although these tributaries have 

high nitrate concentrations, their relative contribution 

to streamflow in the Santa Ana Basin is small by 

volume.
Concentrations of Selected Nutrients 43

CUCAMONGA

CREEK

MENTONE WARM MWD

CREEK

IMPERIAL

HIGHWAY

PRADO

Mountain site Valley floor tributaries

0

4

8

12

Drinking-water primary 

 maximum contaminant level

 U.S. Environmental Protection

 Agency, 2002 (USEPA 2002)

California Regional Water

 Quality Control Board (1995) reach-specific

 water-quality objective

NITRITE PLUS NITRATE, IN MILLIGRAMS PER LITER AS NITROGEN

n=24

n=35 n=38

n=24

n=34

n=43

EXPLANATION

Do not

receive

wastewater

 Receive

wastewater

Valley-floor Santa Ana River sites 

Figure 18. Nitrite+nitrate concentrations at fixed sites, Santa Ana Basin, California.
44 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

SOUTH MENTONE

FORK

DAY

CREEK

CUCAMONGA

CREEK NEAR

UPLAND

DEVIL

CANYON

CREEK

CAJON

CREEK

EAST

TWIN

CREEK

Mountain sites

0

1

2

3

4

5

6

n=20

n=7 n=7

n=7

n=7

n=4

California Regional Water

 Quality Control Board

 (1995) reach-specific

 water-quality objective

NITRITE PLUS NITRATE, IN MILLIGRAMS PER LITER AS NITROGEN

n=34

EXPLANATION

Range of 0.20 to 0.34 milligrams 

per liter predicted for streams in 

undeveloped basins in the study area.

Prediction uses a mathematical

model based on national data

(Clark and others, 2000)

Figure 19. Nitrite+nitrate concentrations at mountain sites, Santa Ana Basin, California.
Concentrations of Selected Nutrients 45

Nitrate in Stormflow

Nitrate concentrations are higher in stormflow 

samples than in base-flow samples from SANA sites 

not receiving wastewater inputs (fig. 20). The 

difference was small for the Mentone site. 

Concentrations in storm samples there ranged from 

0.11 to 0.77 mg/L, with a median of 0.17 mg/L; baseflow samples had nitrite+nitrate concentrations ranging 

from not detected (less than 0.05 mg/L) to 0.42 mg/L, 

with a median of 0.09 mg/L. The difference was greater 

for Warm Creek. Storm-sample concentrations at 

Warm Creek ranged from 0.27 to 3.8 mg/L, with a 

median of 0.98 mg/L; base-flow samples had 

nitrite+nitrate concentrations ranging from 0.07 to 

1.3 mg/L, with a median of 0.34 mg/L. 

One storm sample also was collected at each of 

the mountain sites on Cajon Creek and Devil Canyon 

Creek. Nitrite+nitrate concentrations in these storm 

samples were substantially higher than the 

concentrations observed in base flow at these sites. 

Concentrations in seven base-flow samples collected 

from Cajon Creek ranged from 1.0 to 1.7 mg/L, with a 

median of 1.4 mg/L. The storm sample collected from 

this site had a concentration of 4.3 mg/L. 

Nitrite+nitrate concentrations in four base-flow 

samples collected from Devil Canyon Creek ranged 

from 0.38 to 0.81 mg/L, with a median of 0.63 mg/L. 

The storm sample collected from this site had a 

concentration of 2.6 mg/L.

When nitrate concentrations increase as a result 

of stormflow in streams without point sources of 

nitrate, the increase is often attributed to nitrate running 

off the landscape from nonpoint sources (Schnoebelen 

and others, 1999; Mueller and others, 1995). In the 

Santa Ana Basin, rainwater has higher nitrate 

concentrations than does stream base flow at sites not 

receiving wastewater. The National Atmospheric 

Deposition Program (NADP) (2002) estimated nitrate 

concentrations in Santa Ana Basin precipitation at 

between 0.7 to 1.3 mg/L during the three years of this 

study. Base-flow nitrate concentrations at Santa Ana 

Basin sites not receiving wastewater inputs are usually 

lower than 1 mg/L. Therefore, part of the increase in 

nitrate concentrations at these sites during storm events 

may be contributed by rainfall itself. Other sources of 

nitrate to streams during storm events include nitrate 

washed in from land surfaces or nitrate that enters 

streams with ground water that existed in the catchment 

prior to the event (Kendall and McDonnell, 1998). 

In streams receiving wastewater, nitrate 

concentrations are lower in stormflow samples than in 

base-flow samples (fig. 20). The lower concentrations 

are a result of dilution of the relatively high nitrate 

concentrations of wastewater. Other researchers have 

observed similar decreases in nitrate concentrations as 

a result of storms and have also attributed them to 

dilution of point-source nitrate (Mueller and others, 

1995; Izbicki and others, 2000). 

The dilution of nitrate concentration by 

stormflow can be assessed by regressing nitrate 

concentration as a function of the percentage of 

stormflow in the stream discharge at the time of sample 

collection. Hydrograph separations, performed on data 

from three urban sites, allowed such a regression on 21 

storm samples. It appears that nitrite+nitrate 

concentrations are inversely correlated with percentage 

stormflow. However, there is wide variability in the 

stormflow nitrate concentrations (fig. 21). Possible 

sources of this variability include: first-flush effects in 

samples collected early in the rainy season, first-flush 

effects in samples collected early during individual 

storms, and variable inputs from the landscape (for 

example, releases from waste-stabilization ponds). 

Although the correlation coefficients are relatively low 

for the individual regressions, the slopes of the 

regression lines are similar. The linear correlation for 

all 21 storms represented in figure 21 was significant at 

the α = 0.05 level using Kendall's Tau, a nonparametric test of correlation (Helsel and Hirsch, 

1992). In addition, nitrate concentrations in samples 

with the highest percentage stormflow tend to approach 

concentrations estimated by National Atmospheric 

Deposition Program (2002) for rain. 
46 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Cajon Creek

0

2

4

6

8

10

12

14

16

Base-flow sample

Storm sample (percent stormflow undetermined)

Storm sample with >75% stormflow (by hydrograph separation)

Storm sample with <75% stormflow (by hydrograph separation)

Devil Canyon Creek

Mentone

0

2

4

6

8

10

12

14

16

Sites that do not ites that do not receive wastewate eive wastewater

Sites that ites that receive wastewate eive wastewater

Cucamonga Creek MWD

0

2

4

6

8

10

12

14

16

Prado

0

2

4

6

8

10

12

14

16

Oct

1998

Apr

1999

Nov

1999

May

2000

Dec

2000

Jun

2001

Imperial Highway

Oct

1998

Apr

1999

Nov

1999

May

2000

Dec

2000

Jun

2001

Warm Creek

Low sample concentration appears to 

 reflect temporary absence of input 

 from wastewater-treatment plant 

NITRITE PLUS NITRATE, IN MILLIGRAMS PER LITER AS NITROGEN

EXAMPLE

Figure 20. Time-series of nitrite plus nitrate concentrations in samples from sites where at least one stormflow sample was collected, Santa Ana Basin, 

California (>, greater than; <, less than).
Concentrations of Selected Nutrients 47

r

2

 = 0.21

r 2

 = 0.42

r 2

 = 0.59

r 2

 = 0.57

0

1

2

3

4

5

6

7

8

9

0 20 40 60 80 100

STORMFLOW, IN PERCENT 

MWD MWD regression line 

Warm Creek regression line 

Cucamonga Creek regression line 

Warm Creek 

Cucamonga Creek 

All data

NITRATE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS NITROGEN

Range of concentration

 in local rain

Concentrations in rain estimated by the 

 National Atmospheric Deposition Program (2002)

Nitrite plus

Nitrate

EXPLANATION

Figure 21. Nitrite+nitrate concentrations in stormflow samples as a function of percentage of stormflow in the stream (determined by hydrograph 

separation) at the time of sample, Santa Ana Basin, California.
48 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

The regressions for the three urban sites suggest 

that nitrite+nitrate concentrations are approximately 

1 to 2 mg/L as stormflow approaches 100 percent of 

stream discharge. Twelve storm samples were collected 

when hydrograph-separation results indicate that total 

stream discharge consisted of at least 75 percent 

stormflow (fig. 22). The median nitrite+nitrate 

concentration of the 12 storm samples was 1.3 mg/L. 

This suggests that stormflow nitrate comes mostly from 

rain and picks up little additional nitrate from the urban 

landscape. A study by Ebbert and Wagner (1987) also 

suggests that much of the nitrate load in urban storm 

runoff comes from rain.

Ammonia

In addition to nitrite and nitrate, inorganic 

nitrogen also exists in the form of ammonia (dissolved 

NH3 plus NH4

+). Concentrations of ammonia in baseflow samples for this study were usually well below 

1 mg/L, and contributed far less to total stream nitrogen 

than did nitrate. Mountain sites, including Mentone, 

usually had concentrations of ammonia below the LRL 

(0.02 or 0.04 mg/L) in base-flow samples. Sites on the 

valley floor frequently had relatively low, but detected, 

concentrations of ammonia in base-flow samples

(fig. 23). The generally low concentrations of ammonia 

in base flow at all sites showed little annual variability, 

except at the Prado site, where marked winter peaks 

occurred during all three years of the study. These 

peaks are dampened, but still visible in the time series 

for the site below Imperial Highway, 11 mi 

downstream from Prado.

At most fixed sites, ammonia concentrations 

were higher in storm samples than in base-flow 

samples (fig. 23). The National Atmospheric 

Deposition Program (NADP) (2002) estimates that 

ammonia in precipitation for this region ranged from 

0.17 to 0.35 mg/L during the period of this study. This 

is higher than base-flow median concentrations 

observed at any of the 12 fixed and mountain sites (less 

than 0.02 to 0.12 mg/L). However, the values estimated 

by the NADP are lower than the median storm-sample 

concentrations observed at three sites: 0.75 mg/L at 

Warm Creek, 1.18 mg/L at Cucamonga Creek, and 

0.57 mg/L at Prado. The 12 samples that were 

determined, by hydrograph separation, to consist of at 

least 75 percent stormflow provide the best estimate of 

stormflow concentrations of ammonia. The median 

concentration in those 12 samples was 0.9 mg/L 

(fig. 22). 

These storm-related ammonia concentrations of 

about 1 mg/L are above the concentrations found in 

local rain, according to NADP estimates. This suggests 

that, either the NADP estimates are low, or that 

stormflow ammonia enters valley-floor streams from 

the surrounding landscape. Alternatively, or in addition 

to this process, ammonia could be mobilized from 

streambed sediments to the water column by 

stormflow-induced turbulence. There were 11 storm 

samples that had ammonia concentrations greater than 

or equal to 1 mg/L. Six of these were collected at 

Cucamonga Creek. Relatively high stormflow 

concentrations of ammonia at this site, located in the 

Chino Basin Dairy Preserve, may indicate a landscape 

contribution as a result of rainfall. This contribution 

could occur as nonpoint runoff, or as point releases, 

either intentional or unintentional, from wastestabilization ponds. 

Ammonia concentrations also were elevated by 

storm events at Warm Creek. Storm-sample 

concentrations were between 0.2 and 1.6 mg/L at this 

site, where base-flow concentrations were typically 

near or below the laboratory reporting limit of 0.02 to 

0.04 mg/L (fig. 23). Three of the six storm samples 

collected at the Prado site also had relatively high 

concentrations (0.7 to 1.2 mg/L) that were between 

6 and 10 times the base-flow median concentration

(0.12 mg/L). However, stormflow did not appear to 

appreciably increase total ammonia concentrations at 

MWD, Imperial Highway, or the mountain sites. 
Concentrations of Selected Nutrients 49

0

1

2

3

4

5

Offset symbols indicate

2 separate but overlapping 

storm data 

Offset symbols indicate

2 separate but overlapping 

storm data 

median=1.3 millig median=1.3 milligrams per liter

AMMONIA PLUS AMMONIUM,

IN MILLIGRAMS PER LITER AS NITROGEN

NITRITE PLUS NITRATE, IN MILLIGRAMS

PER LITER AS NITROGEN

TOTAL PHOSPHORUS, IN MILLIGRAMS

PER LITER AS PHOSPHORUS

ORGANIC NITROGEN,

IN MILLIGRAMS PER LITER AS NITROGEN

0

1

2

3

4

5

WARM CREEK

n=6

MWD

n=1

CUCAMONGA CREEK

n=5

median=0.9 millig median=0.9 milligrams per liter

0

5

10

15

20

25

30

35

median=3.4 millig median=3.4 milligrams per liter

0

2

4

6

8

10

WARM CREEK

n=6

MWD

n=1

CUCAMONGA CREEK

n=5

median=1.0 millig median=1.0 milligrams per liter

Concentrations in rain estimated by the 

 National Atmospheric Deposition Program (2002)

 Analyte concentrations in Warm Creek samples

 Analyte concentrations in MWD samples

Analyte concentrations in Cucamonga Creek samples

EXPLANATION

Nitrite plus

Nitrate

Ammonia

Figure 22. Concentrations of selected nutrients in 12 samples consisting of at least 75 percent stormflow (determined by hydrograph separation), Santa 

Ana Basin, California.
50 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

0

0.2

0.4

0.6

0.8

1

0

0.4

0.8

1.2

1.6

2

0

1

2

3

4

0

0.4

0.8

1

1.4

1.8

2

Oct

1998

April

1999

Nov

1999

May

2000

Dec

2000

June

2001

Oct

1998

April

1999

Nov

1999

May

2000

Dec

2000

June

2001

Cajon Creek Devil Canyon Creek

Prado Imperial Highway

Mentone Warm Creek

Cucamonga Creek MWD

Storm sample with <75% stormflow

 (by hydrograph separation)

Base-flow sample

EXPLANATION

Storm sample (percent stormflow

 undetermined)

Storm sample with >75% stormflow

 (by hydrograph separation)

Sites that do not ites that do not receive wastewate eive wastewater

Sites that ites that receive wastewate eive wastewater

AMMONIA PLUS AMMONIUM, IN MILLIGRAMS PER LITER AS NITROGEN

Figure 23. Time-series of ammonia plus ammonium concentrations in samples from sites where at least one stormflow sample was collected, Santa Ana 

Basin, California (>, greater than; <, less than).
Concentrations of Selected Nutrients 51

Un-ionized ammonia NH3 is far more toxic to 

aquatic organisms than is the ammonium ion NH4

+. 

The U.S. Environmental Protection Agency (1999) has 

an ammonia criterion to protect freshwater aquatic life 

from acute and chronic effects of ammonia. Ammonia 

speciation and toxicity depend on pH and temperature. 

Therefore, the criteria take into consideration the 

concentration of total ammonia (NH3+NH4

+), sample 

pH and, in the case of the chronic effects criterion, the 

ambient water temperature. Neither the acute nor the 

chronic ammonia criteria were exceeded in surfacewater samples collected for this study. 

Organic Nitrogen

Concentrations of organic nitrogen, like 

ammonia, were usually low in comparison with nitrate 

in base flow, typically representing less than 20 percent 

of total stream nitrogen (suspended and dissolved). 

Mountain sites had base-flow concentrations of organic 

nitrogen as high as 0.8 mg/L, but the medians were less 

than 0.1 mg/L for all mountain sites. Base-flow organic 

nitrogen concentrations at Warm Creek ranged from 

less than 0.1 to 0.9 mg/L, with a median of 0.3 mg/L. 

Fixed sites downstream from wastewater inputs had 

base-flow concentrations ranging from 0.2 to 3.0 mg/L, 

with a collective median of 1.0 mg/L. 

Concentrations of organic nitrogen often 

increased in basin streams under stormflow conditions. 

Mountain sites (including Mentone) had storm-sample 

organic nitrogen concentrations ranging from less than 

0.1 to 1.8 mg/L, with a median of 0.3 mg/L. Warm 

Creek had storm-sample organic nitrogen 

concentrations ranging from 0.7 to 6.9 mg/L, with a 

median of 3.4 mg/L. Storm-sample organic nitrogen 

concentrations for fixed sites receiving wastewater 

inputs were variable, ranging from less than 0.1 to 

41 mg/L, with a median of 1.6 mg/L. The median 

concentration of organic nitrogen in the 12 samples that 

consisted of at least 75 percent stormflow was 

3.4 mg/L (fig 22). The highest observed concentration 

of organic nitrogen in any sample was 41 mg/L. This 

occurred in a storm sample from Cucamonga Creek 

that was shown to have only 41 percent storm flow. 

Such an extreme concentration of organic nitrogen at 

Cucamonga Creek in response to a storm event may be 

evidence of a dairy-landscape contribution to the 

stream.

Phosphorus 

No Federal or State drinking-water standard or 

maximum contaminant level exists for phosphorus, and 

phosphorus compounds that are typically found in 

streams (as opposed to elemental P) are not generally 

considered toxic to aquatic life. Using the 75th 

percentile of total phosphorus concentration data from 

SANA mountain sites, the reference condition is about 

0.02 mg/L total phosphorus (TP) (fig. 24). That value 

agrees closely with the level of 0.03 mg/L determined 

by the USEPA using reference conditions in streams 

for this ecoregion (U.S. Environmental Protection 

Agency, 2000). As an alternative, the USEPA (1986) 

has suggested a general goal that TP not exceed a 

concentration of 0.10 mg/L as P to control accelerated 

eutrophication in streams not discharging directly to 

lakes or impoundments. 

Base-flow TP concentrations in samples from 

sites receiving mountain runoff rarely exceeded even 

the U.S. Environmental Protection Agency (2000) 

reference criterion of 0.03 mg/L, let alone their general 

goal level (U.S. Environmental Protection Agency, 

1986) of 0.1 mg/L (fig. 25A). Base-flow TP 

concentrations at the urban indicator site on Warm 

Creek, which receives rising ground water and urban 

runoff, were typically at about 0.03 mg/L. This level 

indicates minimally impacted conditions using the 

statistical criterion based on reference conditions but is 

well within the general goal to control eutrophication. 

TP concentrations in samples from fixed sites with 

wastewater inputs typically have TP concentrations 

near 1 mg/L, indicating that phosphorus may be a 

factor in the eutrophication observed in many of the 

streams (fig. 25A). TP concentrations in stormflow 

were variable, but were typically higher than 

concentrations in base flow. The median concentration 

in the 12 samples that were determined to consist of at 

least 75 percent stormflow was 1.0 mg/L (fig. 22).
52 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

0

0.01

0.02

0.03

0.04

0.05

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

75th percentile

for mountain

sites in the 

Santa Ana Basin

Reference condition for ecoregion III,

subecoregion 6 (Southern and Central

California Chaparral and Oak Woodlands)

U.S. Environmental Protection Agency, 2000

n=66

Figure 24. Base-flow total phosphorus concentrations at mountain sites compared with reference conditions, Santa Ana Basin, California.
Concentrations of Selected Nutrients 53

0

1

2

3

MILLIGRAMS PER LITER AS PHOSPHORUS

MOUNTAIN SITES WARM CREEK FIXED SITES RECEIVING

WASTEWATER

TOTAL PHOSPHORUS

0

0.5

1.0

1.5

DISSOLVED ORTHOPHOSPHATE

A

B

USEPA (1986) general goal to prevent eutrophication = 0.05 milligram per liter

USEPA (1986) general goal to prevent eutrophication = 0.1 milligram per liter

n=86

n=86 n=43

n=43

 n=120

 n=120

Figure 25. Base-flow total phosphorus (A) and dissolved orthophosphate (B) at sites grouped by water source, Santa Ana Basin, California (USEPA, 

U.S. Environmental Protection Agency).
54 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Most phosphorus in base-flow samples collected 

for this study was in the form of dissolved 

orthophosphate, and this is the form of phosphorus 

most biologically available to aquatic organisms. 

The U.S. Environmental Protection Agency 

(1986) has set a general goal of less than 0.05 mg/L for 

phosphates in streams to control accelerated 

eutrophication. As with total phosphorus, sites not 

receiving wastewater usually had orthophosphate 

concentrations less than the goal. Dissolved 

orthophosphate was usually less than or equal to the 

LRL (0.01–0.02 mg/L) at mountain sites. Therefore, 

establishing a reference-condition criterion for 

dissolved orthophosphate based on the 75th percentile 

of environmental sample concentrations at Santa Ana 

Basin reference sites (U.S. Environmental Protection 

Agency, 2000), as was done for total phosphorus, 

would not be meaningful. Most base-flow dissolved 

orthophosphate concentrations at Warm Creek were 

also less than 0.02 mg/L, and no base-flow sample 

collected from Warm Creek had a concentration above 

0.05 mg/L. Fixed sites that received wastewater usually 

had concentrations above the U.S. Environmental 

Protection Agency (1986) goal of 0.05 mg/L, and the 

collective median for these sites was 0.76 mg/L 

(fig. 25B). 

QUALITY-CONTROL RESULTS

Quality-control results generally indicate high 

data integrity, although blank samples collected using 

automatic samplers were more prone to show carryover 

contamination than were blanks collected by 

equipment cleaned using USGS protocols. Therefore, 

QC sample results are summarized in two tables:

table 4 summarizes QC results for samples collected 

using standard USGS protocols (USGS, variously 

dated), and table 5 summarizes the results for samples 

collected by automatic samplers. 

Nutrient compounds usually were not detected in 

field and equipment blanks or, at most, were detected at 

only a few hundredths of a milligram per liter above the 

laboratory reporting level (LRL). There were two cases 

where detections of nutrient compounds 

(orthophosphate and nitrite) in blanks were of potential 

concern. In each of these cases, the compound was 

detected at a concentration that exceeded the lowest 

concentration detected in environmental samples, and 

the concentration was greater than the applicable LRL. 

In one case, dissolved orthophosphate was detected at a 

concentration of 0.024 in a blank collected using 

standard USGS protocols (USGS, variously dated). 

The concentration of dissolved orthophosphate in 

environmental samples collected from the mountain 

sites and from Warm Creek was commonly less than or 

equal to 0.01 mg/L (fig. 25B). Therefore, 

concentrations detected between 0.01 and 0.024 mg/L 

should be used with caution. 

In another blank, collected with an automatic 

sampler, nitrite was detected at a concentration of 

0.029. The LRL for nitrite varied from 0.006 to 0.01 

mg/L, and the lowest nitrite concentration detected in 

an environmental sample collected with an automatic 

sampler was 0.014 mg/L. However, nitrite 

concentrations isolated from the parameter 

nitrite+nitrate are not reported in this study because 

they were nearly always negligible in comparison with 

nitrate concentrations. Therefore, such a slight positive 

bias in sample nitrite levels would not affect the 

interpretation of data presented in this report. 

There were no detections of nitrite+nitrate in 

blank samples collected using standard USGS 

protocols. There was one detection of nitrite+nitrate in 

a blank collected by automatic sampler (0.054 mg/L). 

However, the lowest nitrite+nitrate concentration 

detected in any environmental sample collected by 

these samplers (0.27 mg/L) was five times greater than 

the concentration detected in the blank sample. 

Therefore, the potential positive bias introduced by 

carryover contamination of nitrite+nitrate appears to be 

negligible, even when automatic samplers were used. 
Quality-Control Results 55

Table 4. Summary of quality-control sample results when standard U.S. Geological Survey (USGS) protocols (USGS, variously dated) were used, Santa Ana 

Basin, California

[LRL, laboratory reporting limit; mg/L, milligrams per liter; >, greater than indicated value; <, less than indicated value; E, estimated value; oC, degrees Celsius; N, nitrogen; P, phosphorus; RPD, relative percentage difference; —, not detected]

Constituent (LRL, in mg/L)

 [USGS parameter code]

Number of 

equipment or 

field blank 

detections 

>LRL/analyses

Maximum 

concentration 

detected in 

blank 

samples

(mg/L)

Minimum 

concentration 

detected in 

surface-water 

samples

(mg/L)

 RPD

in 14 replicate samples

(percent)

Number of 

replicate samples 

with greater than 

10 percent RPD

Major ions Median Maximum

Calcium (0.01–0.02) [00915] 1/13 E0.03 6.5 0.49 3.9 0

Magnesium (0.004–0.014) [00925] 0/13 — .89 1.5 5.0 0

Potassium (0.1–0.24) [00935] 0/13 — .69 2.3 9.5 0

Sodium (0.06–0.09) [00930] 0/13 E.076 3.0 1.5 3.5 0

Chloride (0.1–0.29) [00940] 0/13 — .29 1.1 6.7 0

Fluoride (0.1) [00950] 0/13 — <.1 3.2 11 1

Silica (0.05–0.09) [00955] 0/13 E.047 3.9 1.1 6.2 0

Sulfate (0.1–0.31) [00945] 0/13 — 1.3 .19 1.3 0

Residue on evaporation at 180oC (10) 

[70300]

0/13 — 38 .52 2.1 0

Nutrients

Nitrogen species (as N)

mmonia (0.02–0.04) [00608] 1/14 .020 <.02 .73 14 1

 Ammonia + Dissolved Organic N (0.1) 

[00623]

0/14 E.079 <.10 3.5 >136 2

 Ammonia + Total Organic N (0.1) [00625] 1/14 .143 <.10 13 51 9

 Nitrite + Nitrate (0.05) [00631] 0/14 — <.050 1.5 8.2 0

 Nitrite (0.006–0.01) [00613] 0/14 — <.010 .00 67 2

Phosphorus species (as P) 

 Dissolved Phosphorus (0.004–0.05) 

[00666]

1/14 .0060 <.050 1.2 88 3

 Dissolved Orthophosphate (0.01–0.02) 

[00671]

2/14 .024 <.010 2.3 22 2

 Total Phosphorus (0.004–0.05) [00665] 0/14 — <.050 2.1 110 2
56 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

Table 5. Summary of quality-control sample results when automatic samplers were used, Santa Ana Basin, California

[LRL, laboratory reporting limit; mg/L, milligrams per liter; >, greater than indicated value; <, less than indicated value; oC, degrees Celsius; N, nitrogen; P, 

phosphorus; RPD, relative percentage difference; —, not detected]

1The RPD of 46 percent occurred for a replicate performed to compare the equal-width-increment (EWI) method with the automatic-sampling method. 

The large RPD may have been a result of the different sampling methods.

Constituent (LRL, in mg/L) 

[USGS parameter code]

Number of 

equipment or 

field blank 

detections 

>LRL/analyses

Maximum 

concentration 

detected 

inblank 

samples

(mg/L)

Minimum 

concentration 

detected in 

surface-water 

samples(

mg/L)

 RPD 

in 3 replicate samples

(percent)

Number of 

replicate 

samples with 

greater than 10 

percent RPD

Major ions Median Maximum

Calcium (0.01–0.02) [00915] 6/8 0.61 5.7 1.6 3.3 0

Magnesium (0.004–0.014) [00925] 2/8 .20 .58 1.4 2.8 0

Potassium (0.1–0.24) [00935] 0/8 — <.10 4.8 5.6 0

Sodium (0.06–0.09) [00930] 5/8 1.5 2.3 1.1 3.7 0

Chloride (0.1–0.29) [00940] 1/8 .61 2.0 .03 .90 0

Fluoride (0.1) [00950] 0/8 — .11 2.4 8.4 0

Silica (0.05–0.09) [00955] 2/8 .36 1.3 1.6 3.1 0

Sulfate (0.1–0.31) [00945] 1/8 1.3 2.2 .24 .54 0

Residue on evaporation at 180oC (10) 

[70300]

0/8 — 31 .57 3.4 0

Nutrients

Nitrogen species (as N)

 Ammonia (0.02–0.04) [00608] 1/8 .021 .027 .34 2.0 0

 Ammonia + Dissolved Organic N (0.1) 

[00623]

0/8 — .37 .74 461 1

 Ammonia + Total Organic N (0.1) [00625] 0/8 — .75 16 17 2

 Nitrite + Nitrate (0.05) [00631] 1/8 .054 .27 1.4 3.2 0

 Nitrite (0.006–0.01) [00613] 2/8 .029 .014 2.6 2.8 0

Phosphorus species (as P) 

 Dissolved Phosphorus (0.004–0.05) [00666] 0/8 — .076 .81 9.9 0

 Dissolved Orthophosphate (0.01–0.02) 

[00671]

2/8 .024 .057 1.3 1.5 0

 Total Phosphorus (0.004–0.05) [00665] 0/8 .020 .22 2.0 5.1 0
Quality-Control Results 57

Residue-on-evaporation at 180°C (ROE), the 

analytical measure of TDS, was never detected in 

blanks at the LRL of 10 mg/L. Concentrations of some 

major ions (constituents of TDS) were occasionally 

detected, up to a few tenths of a milligram per liter 

above their LRL in blanks collected with automatic 

samplers. However, no major ions were ever detected 

in blanks from either group (collected by standard 

USGS protocols or using automatic samplers) at 

concentrations exceeding the minimum concentration 

detected in environmental samples from the respective 

groups.

Replicate results were evaluated for each analyte 

of interest by calculating the relative percentage 

difference (RPD) between the analyte concentrations in 

environmental samples and the concentrations in their 

corresponding duplicate samples. The RPD is 

calculated for each sample pair using the following 

equation:

where

Seventeen replicates comparing analyzed 

concentrations of 17 nutrient and TDS constituents 

were performed for this study. Three of the seventeen 

replicates were performed using automatic samplers. 

Summarized in tables 4 and 5 are the RPDs calculated 

from the results of these replicates for each analyte. 

Seven nutrient analytes had an RPD of more than 

10 percent in at least one replicate. Most of the large 

RPDs were observed for the analyte consisting of total 

organic nitrogen plus ammonia (TON+ammonia). 

Eleven out of the seventeen replicates had RPDs 

greater than 10 percent for this analyte; the highest of 

these occurred in three replicates with relatively low 

sample concentrations (less than 0.1 mg/L) of 

TON+ammonia. These three replicates had RPDs of 

37, 50, and 51 percent. Replicates having more typical 

concentrations of TON+ammonia (0.1 to 2 mg/L) had 

lower RPDs ranging from 4 to 22 percent. However, 

even a replicate sample having extremely high 

concentrations of TON+ammonia (44 and 37 mg/L) 

had an RPD of 17 percent. High analytical variability 

for TON+ammonia could lead to substantial error in 

the calculation of total nitrogen in samples having high 

proportions of nitrogen in these forms. Such variability 

is of less consequence when most of the nitrogen in the 

sample is in the form of nitrate.

 Three RPDs for dissolved organic nitrogen + 

ammonia (DON+ammonia) were greater than 

10 percent in three replicates, but the high variability 

for two of these cases has possible explanations. In one 

of these the RPD was greater than 136 percent. For this 

replicate, DON+ammonia was not detected in the 

environmental sample at the LRL of 0.1 mg/L. The 

corresponding duplicate sample had a concentration of 

0.5 mg/L. Typically, DON+ammonia was not detected 

at the site where this replicate was collected (South 

Fork). Therefore, it seems likely that the duplicate 

sample was contaminated during processing, shipping, 

or analysis. In another replicate with a high RPD for 

DON+ammonia (46 percent), the environmental 

sample (0.71 mg/L) was collected by equal-widthincrement (EWI), and the duplicate sample (1.1 mg/L) 

was collected with an automatic sampler. The large 

variability in this case may have resulted from the 

different sampling methods. The third case of an RPD 

greater than 10 percent for DON+ammonia had an 

RPD of 14 percent, which represented a difference of 

less than 0.1 mg/L between the environmental sample 

(0.64 mg/L) and the corresponding duplicate 

(0.56 mg/L). This level of analytical variability in 

dissolved organic nitrogen + ammonia would not affect 

our ability to understand nitrogen dynamics in the 

study basin. 

For phosphorus species, RPDs were sometimes 

greater than 10 percent, but this usually only occurred 

at low sample concentrations (less than 0.1 mg/L). 

Only one replicate had an RPD greater than 10 percent 

for a phosphorus analyte at a concentration of potential 

environmental concern. In that case the environmental 

sample had a dissolved phosphorus concentration of 

0.98, and the corresponding duplicate sample had a 

concentration of 0.38—resulting in an RPD of 88 

percent. Considering the concentrations of other forms 

of phosphorus in both the environmental and duplicate 

samples, and the range of dissolved phosphorus 

observed in other base-flow samples collected from the 

site in question (Imperial Highway), it appears that the 

duplicate sample was compromised before analysis for 

this parameter. The result is considered an isolated 

case. Replicate analyses for ROE (the analytical 

measure of TDS) and major ions (constituents of TDS) 

generally did not show high variability. 

S1 is the concentration of the environmental 

sample; and

S2 is the concentration of the duplicate sample.

RPD 100 S1 S2 – S1 S2 = × ⁄ ( ) + ⁄ 2,
58 Concentrations of Dissolved Solids and Nutrients in Water Sources, Selected Streams of the Santa Ana Basin, California, October 1998–September 2001

The Inorganic Blind Sample Project (IBSP), a 

USGS quality-assurance program, reported laboratory 

variability and biases for some methods of nutrient 

analysis used by the USGS National Water Quality 

Laboratory for this study. Periodic quality-assurance 

summaries from their database reported analytical 

variability during at least some of the study period for 

dissolved phosphorus, ammonia, and nitrate. 

Additional information on the IBSP can be found at the 

following URL: 

http://bqs.usgs.gov/bsp/mainpage.html. 

SUMMARY

Total dissolved solids (TDS) and concentrations 

of nutrients in selected Santa Ana Basin streams were 

examined as a function of water source. The principal 

water sources are mountain runoff, wastewater, urban 

runoff, and stormflow. Six fixed surface-water sites 

were sampled at least monthly from October 1998 to 

September 2000 for species of nitrogen and 

phosphorus, residue on evaporation (the analytical 

measure of TDS), and individual major ions (the main 

constituents of TDS). At least six storm-event samples 

were collected from each fixed site during this period. 

Monthly sampling continued through April 2001 at one 

fixed site (Imperial Highway), and until September 

2001 at three of the fixed sites (Mentone, Warm Creek, 

and Prado), with the exception that no samples were 

collected in November 2000 at any site. One of the 

fixed sites (Mentone) was located at the base of the San 

Bernardino Mountains. Six additional mountain sites 

were sampled quarterly from January 2000 to July 

2001, including single storm-event samples collected at 

two of the sites. Water quality at the Mentone site 

appears to be representative of reference conditions for 

water entering the valley floor.

The major-ion compositions in samples from the 

different sites indicate distinct sources of water and instream processes in the basin. Base-flow samples from 

most mountain sites tended to have a calciumbicarbonate composition. However, the major-ion 

composition of East Twin Creek base-flow samples 

was dominated by sodium/potassium-sulfate, and the 

Mentone samples which were affected by the 

construction of Seven Oaks Dam also tended toward 

that composition. The water composition at Warm 

Creek was highly variable, but was approximately 

intermediate to the compositions of the mountain sites 

located upgradient of the site (Cajon Creek, Devil 

Canyon Creek, and East Twin Creek). Water 

compositions at the Prado Dam and Imperial Highway 

sites were similar and appeared to be a mixture of the 

waters at the MWD, Cucamonga Creek, and Warm 

Creek sites.

The median TDS in base-flow samples from 

mountain sites, including the fixed site near Mentone, 

was 200 mg/L. Base-flow TDS from valley-floor sites 

typically ranged from 400 to 600 mg/L regardless of 

water source. Sparse data indicate that TDS in urban 

runoff range from about 250 to 370 mg/L, which 

approximate levels reported for the basin domestic 

supply (City of Redlands, 2002; Metropolitan Water 

District of Southern California, 2002; Western 

Municipal Water District, 2002; San Bernardino Valley 

Municipal Water District, 2002). TDS increases 

downstream along the main stem of the Santa Ana 

River, regardless of source inputs.

Rainfall usually dilutes stream TDS. The median 

TDS of all samples collected during or shortly after 

storms was 260 mg/L. However, stormflow TDS was 

highly variable, especially during relatively small 

rainfall events. Hydrograph separations were 

performed to isolate stormflow from base flow for 87 

rainfall events at three fixed sites. The median flowweighted average TDS concentration for isolated 

stormflow during these events was 190 mg/L. However, 

stormflow TDS concentrations were lower and far less 

variable during relatively large events (greater than 

0.30 to 0.45 in. of rain), with values typically closer to 

100 mg/L. 
References Cited 59

Base-flow nutrient concentrations, like TDS, 

were usually lowest in samples from sites receiving 

mountain runoff. From the perspective of water 

managers, the nutrient species of greatest concern in 

the Santa Ana Basin is nitrate. Laboratory analyses for 

nitrate included a mostly negligible contribution of 

nitrite. However, because the nitrite compound carries 

the same concerns as nitrate, concentrations for the 

combined parameter (nitrite+nitrate) are presented in 

this report. Streams fed by mountain runoff had median 

base-flow concentrations of nitrite+nitrate mostly 

below 0.3 mg/L. Nitrite+nitrate concentrations in both 

urban runoff and stormflow were near 1 mg/L, which is 

close to the level found in rainfall for the region. 

Nitrite+nitrate concentrations in the Santa Ana River 

and its major tributaries are highest where stream flow 

is dominated by wastewater effluent. Nitrite+nitrate 

concentrations in samples collected from the four fixed 

sites located downstream from these inputs ranged 

from about 5 to 7 mg/L, mostly representing the 

wastewater discharges. In addition, rising ground water 

along this stretch of the river also had high 

nitrite+nitrate concentrations. Five samples were 

collected from sites dominated by rising ground water, 

and all five samples had nitrite+nitrate concentrations 

above 10 mg/L, the U.S. Environmental Protection 

Agency (2002) drinking-water standard.

Concentrations of other nitrogen compounds 

were much lower than nitrate in base-flow samples. 

Ammonia (dissolved NH3+NH4

+) was usually less 

than 0.04 mg/L in samples from mountain sites, and 

concentrations tended to be well below 1 mg/L in 

samples from the valley-floor sites. Using criteria 

established in 1999 by the USEPA, ammonia was not 

observed at levels considered toxic to aquatic life in 

samples collected for this study. Mountain sites 

typically had base-flow concentrations of organic 

nitrogen below 0.1 mg/L. Base-flow organic nitrogen 

concentrations at Warm Creek ranged from less than 

0.1 mg/L to 0.9 mg/L, with a median of 0.3 mg/L. 

Fixed sites downstream from wastewater inputs had 

base-flow concentrations ranging from 0.2 to 3.0 mg/L, 

with a median of 1.0 mg/L. Storm events increased 

concentrations and the proportions of organic nitrogen, 

ammonia, and nitrite relative to nitrate.

 Concentrations of total phosphorus (TP) were 

usually below 0.03 mg/L in samples from sites 

receiving mountain runoff. Base-flow TP 

concentrations at the urban indicator site on Warm 

Creek, which receives rising ground water and urban 

runoff, were typically at about 0.03 mg/L. These levels 

were well under the general goal set (in 1986) by the 

USEPA of less than 0.1 mg/L to control for 

eutrophication. TP concentrations in samples from 

fixed sites below wastewater inputs typically have TP 

concentrations near 1 mg/L, indicating a departure 

from reference conditions and a potential for 

phosphorus-driven eutrophication. The USEPA also set 

(in 1986) a general goal for total phosphates in streams 

of less than 0.05 mg/L to control for accelerated 

eutrophication. As with total phosphorus, sites not 

receiving wastewater usually had concentrations of 

dissolved orthophosphate under the goal, whereas sites 

that received wastewater usually had concentrations 

above the goal.

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