U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 0

Stormflow Chemistry in the Santa Ana River below Prado 

Dam and at the Diversion Downstream from Imperial 

Highway, Southern California, 1995–98

Prepared in cooperation with the

ORANGE COUNTY WATER DISTRICT

0-4127

By John A. Izbicki, Gregory O. Mendez, and Carmen A. Burton

Sacramento, California

2000

5027-19
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

For additional information write to: Copies of this report can be purchased from:

U.S. Geological Survey

Information Services

Box 25286

Federal Center

Denver, CO 80225

The use of firm, trade, and brand names in this report is for identification purposes only and 

does not constitute endorsement by the U.S. Geological Survey.

District Chief

U.S. Geological Survey

Placer Hall, Suite 2012

6000 J Street

Sacramento, CA 95819-6129
Contents III

CONTENTS

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

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

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

Acknowledgments ......................................................................................................................................... 3

Description of the Santa Ana River Basin ............................................................................................................................. 3

Population, Land Use, and Water Use ......................................................................................................................... 3

Streamflow Characteristics .......................................................................................................................................... 5

Approach ............................................................................................................................................................................... 6

Sampled Stormflows.............................................................................................................................................................. 6

Timing and Distribution of Precipitation and Runoff.................................................................................................. 8

Regulation of Streamflow at Prado Dam ..................................................................................................................... 12

Stormflow Chemistry............................................................................................................................................................. 13

Changes in Nutrient Concentrations During Stormflow.............................................................................................. 13

Nitrate ................................................................................................................................................................ 14

Reduced Forms of Nitrogen............................................................................................................................... 15

Phosphate........................................................................................................................................................... 16

Changes in Concentration and Composition of Dissolved Organic Carbon During Stormflow ................................. 17

Dissolved Organic Carbon Concentrations........................................................................................................ 17

Dissolved Organic Carbon Composition ........................................................................................................... 18

Ultraviolet Absorbance ............................................................................................................................ 19

Nitrogen-to-Carbon Ratios ...................................................................................................................... 20

Comparison with Dissolved Organic Carbon Concentrations and UV Absorbance in Water from 

Other Sources ...................................................................................................................................... 21

Changes in Selected Organic Compound Concentrations During Stormflow............................................................. 21

Pesticides ........................................................................................................................................................... 22

Occurrence of Pesticides During Stormflow ........................................................................................... 22

Comparison with Reported-Use Data...................................................................................................... 24

Principal-Component Analysis ................................................................................................................ 28

Volatile Organic Compounds............................................................................................................................. 30

Changes in Selected Trace-Element Concentrations During Stormflow..................................................................... 32

Diversion of Stormflows and the Effects on the Quality of Recharge Water ........................................................................ 34

Summary................................................................................................................................................................................ 35

References Cited.................................................................................................................................................................... 36

Appendix A—Quality-Assurance Procedures ....................................................................................................................... 39

Appendix B—Sample Collection, Preservation, and Analytical Methods ............................................................................ 43

Appendix C—Data for Field Parameters, Major Ions, Nutrients, and Selected Trace Elements .......................................... 49

Appendix D—Data for Organic Carbon and Ultraviolet Absorption.................................................................................... 71

Appendix E—Data for Pesticides.......................................................................................................................................... 83

Appendix F—Data for Volatile Organic Compounds............................................................................................................ 93

FIGURES

1. Map showing Santa Ana River basin and location of stream gages, water-quality sites, and 

precipitation gages, southern California................................................................................................................... 2

2. Map showing land use in the Santa Ana River basin, southern California, 1990 .................................................... 4

3. Photographs showing the Santa Ana River below Prado Dam and at the diversion downstream from 

Imperial Highway, southern California .................................................................................................................... 7

4. Doppler radar images of precipitation in southern California, October 29–30, 1996.............................................. 8
IV Contents

5. Graphs showing sampled stormflows, precipitation, and stage at Prado Dam and streamflow in the 

Santa Ana River below Prado Dam during the 1995–96, 1996–97, and 1997–98 rainy seasons ............................ 9

6. Graphs showing precipitation and stormflow for selected sites in the Santa Ana River basin, 

southern California: October 30–November 1, 1996; January 25–30, 1997; and September 25–27, 1997 ............ 11

7. Box plots showing concentrations of dissolved nitrate, nitrite, ammonia, organic nitrogen, phosphate,

orthophosphate, and organic carbon and nitrogen-to-carbon ratios in base flow and in early season and 

late season stormflows in the Santa Ana River below Prado Dam and at the diversion downstream from 

Imperial Highway, southern California, 1995–98.................................................................................................... 14

8–10. Graphs showing:

8. Dissolved nitrate, ammonia, and organic nitrogen concentrations during stormflow in the Santa Ana 

River below Prado Dam and at the diversion downstream from Imperial Highway, southern 

California: October 30–November 1, 1996; January 25–30, 1997; and September 25–27, 1997.................... 15

9. Dissolved organic carbon concentrations and UV254 absorbance during selected stormflows in the 

Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California: October 30–November 1, 1996; January 25–30, 1997; and September 25–27, 1997 ..... 18

10. Dissolved organic carbon as a function of UV254, and UV285 as a function of UV254, in stormflow 

in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California, 1995–98 ........................................................................................................................... 20

11. Box plots showing concentrations of the 10 most commonly detected pesticides in base flow, stormflow 

dominated by runoff from urban areas downstream from Prado Dam, and all other stormflows in the 

Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, southern 

California, 1996–98 ................................................................................................................................................. 24

12–15. Graphs showing:

12. Diazinon, malathion, and chlorpyrifos concentrations during stormflow in the Santa Ana River below 

Prado Dam and at the diversion downstream from Imperial Highway, southern California: 

October 30–November 1, 1996; January 25–30, 1997; and September 25–27, 1997 ...................................... 25

13. Simazine, carbaryl, and diuron concentrations during stormflow in the Santa Ana River below Prado 

Dam and at the diversion downstream from Imperial Highway, southern California: October 30–

November 1, 1996; January 25–30, 1997; and September 25–27, 1997 .......................................................... 26

14. Pesticide use in Orange, Riverside, and San Bernardino Counties and frequency of detection in the 

Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California, 1996–98 ........................................................................................................................... 27

15. Common pesticide mixtures and frequency of detection in urban streams in the United States and in 

stormflow in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial 

Highway, southern California, 1996–98........................................................................................................... 28

16. Plot of principal-component scores calculated from pesticide concentrations in base flow and stormflow 

below Prado Dam and at the diversion downstream from Imperial Highway, southern California, 1996–98......... 29

17. Graphs showing MTBE and chloroform concentrations in the Santa Ana River below Prado Dam, at the 

diversion downstream from Imperial Highway, and in a storm drain tributary to the Santa Ana River near 

Imperial Highway, southern California.................................................................................................................... 30

18. Box plots showing dissolved iron, manganese, and zinc concentrations in base flow, and in early season 

and late season stormflows in the Santa Ana River below Prado Dam and at the diversion downstream from 

Imperial Highway, southern California, 1995–98.................................................................................................... 32

19. Graphs showing dissolved iron, manganese, and zinc concentrations during stormflow in the Santa Ana 

River below Prado Dam and at the diversion downstream from Imperial Highway, southern California: 

October 30–November 1, 1996; January 25–30, 1997; and September 25–27, 1997.............................................. 33

Appendix A:

Figure A1. Graph showing comparison of nitrate analyses from different U.S. Geological Survey laboratories ................ 42
Contents V

TABLES

1. Summary of stormflow sample collection in the Santa Ana River below Prado Dam and at the diversion 

downstream from Imperial Highway, southern California ..................................................................................... 10

2. Summary of detected pesticide data for the Santa Ana River below Prado Dam and at the diversion 

downstream from Imperial Highway, southern California, 1996–98 ..................................................................... 23

3. Eigenvectors composing the first and second principal components of pesticides in stormflow in the 

Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, southern 

California, 1996–98 ................................................................................................................................................ 29

4. Volatile organic carbon compounds detected in the Santa Ana River below Prado Dam and at the 

diversion downstream from Imperial Highway, southern California, and at other urban sites across 

the United States..................................................................................................................................................... 31

Appendix Tables:

A1. Replicate analyses by the USGS National Water Quality Laboratory (NWQL)............................................ 41

A2. Replicate analyses by the USGS San Diego Laboratory ............................................................................... 41

B1. Analytical methods and reporting limits ........................................................................................................ 44

B2. Pesticides determined by C-18 solid-phase extraction and gas chromatography/mass spectrometry............ 45

B3. Pesticides determined by Carbopak-B solid-phase extraction and high pressure liquid chromatography .... 45

B4. Volatile organic compounds and reporting limits........................................................................................... 46

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River 

below Prado Dam and at the diversion downstream from Imperial Highway, southern California............... 50

Appendix D. Data for organic carbon and ultraviolet absorption in the Santa Ana River below Prado Dam and 

at the diversion downstream from Imperial Highway, southern California ................................................... 72

Appendix E. Data for pesticides detected in the Santa Ana River below Prado Dam and at the diversion 

downstream from Imperial Highway, southern California............................................................................. 84

Appendix F. Data for volatile organic compounds detected in the Santa Ana River below Prado Dam, at the

diversion downstream from Imperial Highway, and in a storm drain tributary to the Santa Ana 

River near Imperial Highway, southern California ........................................................................................ 94

CONVERSION FACTORS, VERTICAL DATUM, WATER-CHEMISTRY UNITS, AND 

ABBREVIATIONS AND ACRONYMS

Conversion Factors

Temperature is given in degrees Celsius (°C), which can be converted to degrees Fahrenheit (°F) by

the following equation:

°F=1.8(°C)+32.

Multiply By To obtain

Length

inch (in.) 2.54 centimeter

inch (in.) 25.4 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

square mile (mi2

) 2.590 square kilometer

Volume

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

acre-foot (acre-ft) 0.001233 cubic hectometer

Flow Rate

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

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.

Chemistry Units

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

micrograms per liter (μg/L).

Abbreviations and Acronyms.

AFX, automated segmented flow

DOC, dissolved organic carbon

GS/MS, gas chromatography/mass spectrometry

HPLC, high performance liquid chromatography

kg, kilogram

MCL, Maximum Contaminant Level (U.S. Environmental Protection Agency)

MTBE, methyl tert-butyl ether (a volatile organic compound used as a gasoline additive)

nm, nanometer (one-billionth of a meter)

OCWD, Orange County Water District

PAH, polycyclic aromatic hydrocarbon

SARWQHS, Santa Ana River Water Quality and Health Study (Orange County Water District)

SMCL, Secondary Maximum Contaminant Level (U.S. Environmental Protection Agency)

SOC, suspended organic carbon

USEPA, U.S. Environmental Protection Agency

μS/cm, microsiemen per centimeter

USGS, U.S. Geological Survey

UV, ultraviolet

VOC, volatile organic compound
Introduction 1

Stormflow Chemistry in the Santa Ana River below Prado 

Dam and at the Diversion Downstream from Imperial 

Highway, Southern California, 1995–98

By John A. Izbicki, Gregory O. Mendez, and Carmen A. Burton

ABSTRACT

The Santa Ana River drains about 2,670 

square miles of the densely populated coastal area 

of southern California, near Los Angeles. Almost 

all the flow in the river, more than 200,000 acrefeet annually, is diverted into ponds where it 

infiltrates and recharges underlying aquifers. 

About 2 million people are dependent on these 

aquifers for water supply. Stormflow in the Santa 

Ana River is considered a source of “high-quality” 

water suitable for use as a source of ground-water 

recharge. To test this assumption, stormflow 

samples were collected at two locations—below 

Prado Dam and at the diversion point downstream 

from Imperial Highway—for 12 winter storms 

between 1995 and 1998. 

Nitrate concentrations decreased during 

stormflow from a median concentration of 7.8 

milligrams per liter in base flow to concentrations 

less than 1 milligram per liter in some large 

storms. Concentrations of chemically reduced 

forms of nitrogen (nitrite, ammonia, and organic 

nitrogen) increased during stormflow and are the 

predominant forms of nitrogen in large 

stormflows. Dissolved organic carbon (DOC) 

concentrations increased from a median 

concentration of 4.6 milligrams per liter in base 

flow to more than 20 milligrams per liter in some 

stormflows. Concentrations of DOC were 

especially high during the first storm of the rainy 

season, and large increases in DOC concentrations 

were measured even as a result of small early 

season storms that did not cause large increases in 

streamflow. DOC present during early season 

stormflow had less ultraviolet absorbance at 254 

nanometers (UV254 ) per unit of carbon than did 

DOC from late season stormflows. DOC in water 

held in storage behind Prado Dam had the highest 

UV254 absorbance per unit of carbon. Maximum 

pesticide concentrations in stormflow did not 

exceed U.S. Environmental Protection Agency 

Maximum Contaminant Levels. Most pesticide 

concentrations were less than 1 microgram per 

liter and less than the detection limits obtained 

using standard drinking water analyses. Increases 

in concentrations of pesticides such as diazinon, 

malathion, and chlorpyrifos in stormflow result 

from runoff from urban areas downstream from 

Prado Dam. In general, large late season 

stormflows have the most pesticide detections of 

all stormflows sampled. Concentrations of methyl 

tert-butyl ether (MTBE), a gasoline additive, 

during base flow were as high as 0.9 microgram 

per liter and concentrations decreased during 

stormflow. Like pesticides, the concentrations did 

not exceed the U.S. Environmental Protection 

Agency Maximum Contaminant Levels for 

MTBE. 

INTRODUCTION

The Santa Ana River drains about 2,670 square 

miles (mi2) of the densely populated coastal area of 

southern California near Los Angeles (fig. 1). Almost 

all flow in the Santa Ana River, more than 200,000 

acre-feet (acre-ft) of water annually, is diverted to 

ponds where it is allowed to infiltrate and recharge 

underlying aquifers (Orange County Water District, 
2 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Figure 1. Santa Ana River basin and location of stream gages, water-quality sites, and precipitation gages, southern California.
Description of the Santa Ana River Basin 3

1996a). Pumpage from these aquifers is the primary 

source of supply for about 2 million people in Orange 

County, California (Orange County Water District, 

1996a).

Base flow in the Santa Ana River is maintained 

almost entirely by discharges of treated municipal 

wastewater (Burton and others, 1998). At present 

(2000), the assumption guiding ground-water recharge 

operations is that stormflow in the Santa Ana River is 

“high-quality” water suitable to recharge aquifers 

pumped as a source of public supply. Large quantities 

of water recharged during stormflows in the winter are 

believed to improve the overall quality of water 

recharged from the Santa Ana River. However, 

stormflows include runoff from urban and agricultural 

areas and may contain high concentrations of inorganic 

and organic constituents that can degrade water quality. 

In the past, few data were available to address these 

concerns.

In 1995, the Orange County Water District 

(OCWD) began a series of studies to characterize the 

quality of the Santa Ana River water, the effects of 

recharge from the river on ground-water quality, and 

the potential health effects associated with using water 

from the Santa Ana River to recharge aquifers that are 

pumped for water supply. These studies are collectively 

known as the Santa Ana River Water Quality and 

Health Study (SARWQHS) (Orange County Water 

District, 1996b). This report is part of the SARWQHS 

and was funded by the Orange County Water District in 

cooperation with the U.S. Geological Survey (USGS). 

As part of the SARWQHS, historical changes in water 

chemistry in the Santa Ana River were evaluated by the 

USGS (Burton and others, 1998). Data from that report 

serve as a benchmark to evaluate changes in water 

chemistry that occur during stormflow.

Purpose and Scope

The purpose of this report is to evaluate changes 

in the concentrations of selected water-quality 

constituents in the Santa Ana River below Prado Dam 

and at the diversion downstream from Imperial 

Highway during stormflow. The first storm of the rainy 

season was of special interest because of potentially 

large changes in water chemistry if soluble material 

that accumulated in the basin during the dry season was 

washed into the Santa Ana River or its tributaries. The 

scope of the study included collection and analysis of 

water samples during 12 stormflows between 

December 1995 and February 1998 for dissolved 

nutrients, dissolved organic carbon, selected dissolved 

pesticides and volatile organic compounds, and 

selected dissolved trace elements. 

Acknowledgments

The authors thank Greg Peacock of the U.S. 

Army Corps of Engineers for precipitation and stage 

data for Prado Dam; and Alan Flowers, Chris 

McConaghy, and John Vandenburgh of the Orange 

County Water District for data on the surface flow and 

diversion of water by the Orange County Water District 

downstream from Imperial Highway. The authors 

thank the scientific review panel of the SARWQHS for 

sharing their expertise and for their input throughout 

this study.

DESCRIPTION OF THE SANTA ANA RIVER BASIN

The Santa Ana River hydrologic unit, which 

includes the Santa Ana River drainage basin and a few 

small streams near the coast that discharge into the 

ocean, is about 2,670 mi2

. The area includes parts of 

San Bernardino, Riverside, Los Angeles, and Orange 

Counties (fig. 1). The river flows to the west and 

discharges into the Pacific Ocean. The topography of 

the basin ranges from steep, rugged mountains, with 

peaks as high as 11,500 feet (ft) above sea level, to 

broad alluvial valleys and a coastal plain to the west. 

The climate is characterized by warm, dry summers 

and cool, moist winters. Average annual precipitation 

ranges from about 12 inches (in.) near the coast to 

about 18 in. in the inland valleys. In the higher 

mountains, cool summers and cold winters prevail. 

Average annual precipitation can exceed 40 in. in some 

of the higher mountains. Most precipitation occurs 

between November and March (U.S. Army Corps of 

Engineers, 1994), but in some years the rainy season 

may begin as early as September and (or) end as late as 

June. 

Population, Land Use, and Water Use

Since the 1940's, the population in the Santa Ana 

River basin has increased rapidly, and agricultural and 

undeveloped land uses have decreased while urban 

land uses have increased. In 1990, the population in the 
4 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Santa Ana River basin was more than 4.5 million 

(Santa Ana Regional Water Quality Control Board, 

1995), and land use ranged from dense urban 

development in the coastal plain and inland valleys to 

undeveloped wilderness in the high mountains (fig. 2). 

In 1990, land use in the study area was 32 percent 

urban, 11 percent agricultural, and 57 percent 

undeveloped. Agricultural land use was largely 

cropland and pastures but also included orchards and 

dairies.

In 1995, there were about 340 animalconfinement facilities and more than 340,000 animals 

(primarily dairy cows) within the Santa Ana River 

basin (Santa Ana Regional Water Quality Control 

Board, 1996). About 300 of these facilities and most of 

the animals (about 300,000) are in the area drained by 

Chino and Cucamonga Creeks to the north of Prado 

Dam (fig. 1).

Local water is extensively managed for public 

supply and additional water is imported from northern 

California and the Colorado River through aqueducts. 

Most of the water used for public supply is eventually 

discharged to the Santa Ana River, its larger tributaries, 

or adjacent shallow ground water as treated municipal 

wastewater. To meet water-quality objectives 

established for the basin by the Santa Ana Regional 

Water Quality Control Board (1995), almost all 

municipal wastewater discharged to the river is tertiary 

treated. Storm and sanitary sewers are separate in 

communities within the Santa Ana River basin, and 

combined sewer overflows to the river are not a 

problem (Burton and others, 1998). In addition to the 

tertiary treatment of municipal wastewater, about half 

of the base flow of the Santa Ana River is treated to 

remove nitrate by a series of artificial wetlands 

upstream from Prado Dam (O'Connor, 1995; Brian 

Figure 2. Land use in the Santa Ana River basin, southern California, 1990.
Description of the Santa Ana River Basin 5

Baharie, Orange County Water District, oral commun., 

1996). 

Almost all flow in the Santa Ana River, more 

than 200,000 acre-ft annually, is diverted by the Orange 

County Water District (1996a) for ground-water 

recharge downstream from Imperial Highway (fig. 1). 

Only water from the larger stormflows, which exceed 

the capacity of the diversion facility, is not diverted for 

ground-water recharge. 

Water rights to the Santa Ana River have been the 

subject of much litigation. The April 17, 1969, 

Stipulation for Judgement in Orange County Water 

District versus City of Chino, et. al. provides for a 

regional allocation of water supply among the major 

public water districts in the Santa Ana River basin; this 

decision covers both the quantity and the quality of 

streamflow in the Santa Ana River below Prado Dam 

(Santa Ana River Watermaster, 1996).

Streamflow Characteristics

For the purposes of this report, the Santa Ana 

River basin was divided into an upper basin and a lower 

basin (fig. 1). The upper basin is that part of the basin 

upstream from the Chino Hills and the Santa Ana 

Mountains. The upper basin drains the headwater areas 

in the mountains in the northern and eastern part of the 

basin and the inland alluvial valleys; the upper basin is 

about 2,470 mi2

, including 768 mi2 in the San Jacinto 

River/Lake Elsinore drainage. The San Jacinto River/

Lake Elsinore drainage does not normally contribute 

flow to the Santa Ana River, and in most years Lake 

Elsinore (a naturally occurring graben lake) is the 

terminus for flow in the San Jacinto River. However, 

flow from the San Jacinto River/Lake Elsinore drainage 

into Temescal Wash and the Santa Ana River occurred 

in 1917, 1980, and 1995 (California Department of 

Water Resources, 1982; O'Connor, 1995; Santa Ana 

River Watermaster, 1996). The lower basin is that part 

of the Santa Ana River basin downstream from the 

Chino Hills and the Santa Ana Mountains—an area of 

about 200 mi2

. The lower basin drains the western 

slopes of the Chino Hills and Santa Ana Mountains and 

the coastal plain.

Base flow in the Santa Ana River is maintained 

by discharges of treated municipal sewage. In 1995, 

base flow in the Santa Ana River below Prado Dam 

averaged 180 cubic feet per second (ft3

/s), almost 

equaling the combined discharge from upstream 

wastewater-treatment plants (Burton and others, 1998). 

Streamflow in the Santa Ana River also is 

supplemented by releases of imported water from 

northern California and from the Colorado River. 

Unlike wastewater discharges, these releases are 

intermittent and are intended to supplement local water 

supply.

High flows in the Santa Ana River occur during 

the rainy season as a result of precipitation and 

subsequent runoff. Most precipitation falls between 

November and March (U.S. Army Corps of Engineers, 

1994), but in some years the rainy season may begin as 

early as September and (or) end as late as June. The 

largest historical flow in the Santa Ana River occurred 

in January 1862 and was estimated to be about 

320,000 ft3

/s at Riverside Narrows, near MWD 

crossing (fig. 1) (U.S. Army Corps of Engineers, 1994).

Since 1940, streamflow between the upper and 

lower parts of the Santa Ana River basin has been 

regulated by Prado Dam. Regulation of streamflow has 

reduced peak flows during the winter by releasing 

stormwater gradually over a period of several days, 

weeks, or months (U.S. Army Corps of Engineers, 

1994). Since the construction of the dam, peak flows 

have been smaller in magnitude and have not exceeded 

7,500 f3

/s below Prado Dam or 10,600 ft3/s at Imperial 

Highway. In recent years, increased urbanization may 

have resulted in increased runoff and larger peak flows 

(U.S. Army Corps of Engineers, 1994): peak flows 

greater than 1,000 ft3

/s can occur at Imperial Highway 

as a result of runoff from urban areas downstream from 

Prado Dam, even when only small quantities of water 

are being released by the dam (Alan Flowers, Orange 

County Water District, oral commun., 1996).

Prado Dam is operated according to a complex 

set of procedures intended to minimize flood damage in 

the lower part of the Santa Ana River basin and to 

maximize availability of surface water for groundwater recharge by OCWD (U.S. Army Corps of 

Engineers, 1994). To help minimize flood damage, the 

channel of the Santa Ana River downstream from Prado 

Dam has been extensively modified to serve as an 

urban floodway. To minimize adverse effects on 

endangered species in wetland areas behind Prado 

Dam, water is not stored behind the dam during the dry 

season (U.S. Army Corps of Engineers, 1994).
6 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

APPROACH

Stormflows were sampled at two sites along the 

Santa Ana River, below Prado Dam and at the diversion 

downstream from Imperial Highway; the latter site is 

hereafter referred to as “Imperial Highway” (fig. 3). 

Imperial Highway is about 11 miles (mi) downstream 

from Prado Dam. Stormflow data from Imperial 

Highway reflects the quality of water diverted for 

recharge and is a combination of runoff from urban 

areas downstream from Prado Dam; runoff from areas 

upstream from Prado Dam; and, during the later part of 

the rainy season, runoff from previous storms that was 

stored behind Prado Dam. Data from both sites were 

combined to estimate water quality during base flow, 

and early season and late season stormflow. Data from 

the two sites were compared and contrasted to provided 

an estimate of the quantity and quality of runoff from 

urban areas between Prado Dam and Imperial 

Highway. One emphasis of the study was evaluation of 

possible “first flush” effects on water chemistry. 

Therefore, it was necessary that stormflow from the 

first storm of each rainy season be sampled.

Characterization of changes in water quality 

during stormflow required sample collection prior to 

the beginning of the stormflow and across the entire 

stormflow hydrograph, including the rising limb, peak 

flow, and recessional flow. Typical weather forecasts 

are not accurate enough to determine when to begin 

sample collection. Commercially available doppler 

radar was used to supplement weather forecasts and 

facilitate sample collection by providing advanced 

warning of storms (fig. 4). These data provided 4 to 6 

hours warning for storms from the northwest. They 

provided less warning and less accurate predictions of 

precipitation originating from the southwest or 

southeast. Doppler radar also provided real-time data 

on the current precipitation, and real-time data 

estimates of the expected amount and duration of 

precipitation from each storm. These data were used 

during storms to determine sample-collection 

frequency. The doppler radar record also was used with 

data from a tipping-bucket rain gage network operated 

by the U.S. Army Corps of Engineers to provide a 

record of the timing and distribution of precipitation 

during each storm. 

Detailed sample collection across the stormflow 

hydrograph is labor intensive and prohibitively 

expensive if done using conventional techniques, such 

as depth-integrated sampling. Automated samplers 

were used to collect many samples during a single 

stormflow and reduce costs. However, these samples 

collected are not depth-integrated and may not 

necessarily be representative of suspended sediment or 

sorbed constituents. Most samples were analyzed for a 

small number of constituents, such as nitrate or 

ultraviolet (UV) absorbance that are relatively 

inexpensive to analyze. Fewer samples were analyzed 

for other constituents, such as pesticides, that are more 

expensive to analyze. Automated samplers were not 

used for the collection of volatile organic carbon 

samples. Quality-assurance procedures are described 

in Appendix A. Sample collection, preservation, and 

analytical methods are described in Appendix B.

SAMPLED STORMFLOWS

Twelve stormflows were sampled between 

December 1995 and February 1998: two were sampled 

during the rainy season of 1995–96, and five were 

sampled during each of the two following rainy seasons 

(fig. 5). The sampled stormflows included the first 

stormflows of each rainy season. Precipitation at Prado 

Dam for sampled stormflows ranged from 0.03 to 

4.55 in. (table 1). The largest storm (December 5–9, 

1997) produced almost 10 in. of rain at some sites in the 

basin and caused flooding in parts of coastal Orange 

County.

The 1995–96 rainy season was drier than average 

and the 1996–97 rainy season was about average. The 

last storm of the 1996–97 rainy season occurred near 

the end of January, several months earlier than usual, 

and was followed by one of the driest periods on 

record—197 days with no precipitation in parts of the 

upper basin and 207 days with no precipitation in the 

lower basin. The 1997–98 rainy season was much 

wetter than average because of “El Niño,” a warming of 

the tropical Pacific Ocean that can result in extreme 

weather throughout the world and greater than average 

precipitation in southern California. As a result of El 

Niño, February 1998 was one of the wettest Februarys 

on record in southern California. 

Peak stormflows sampled as part of this study 

were as great as 5,830 ft3

/s below Prado Dam and 5,960 

ft3

/s at Imperial Highway (table 1). The largest 

stormflow occurred January 25–30, 1997, and included 

water that had been stored behind the dam. The 

inclusion of stored water occurred during many of the 

large, late season stormflows sampled as part of this 

study (fig. 5). 
Sampled Stormflows 7

Figure 3. Santa Ana River (A) below Prado Dam, and (B) at the diversion downstream from Imperial Highway, southern 

California.
8 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Comparison and contrast of precipitation and runoff during 3 

of the 12 storms, and resulting stormflows (fig. 6), were used to 

simplify the presentation of stormflow-chemistry data in this report. 

The three storms selected are representative of the types of storms 

that occur in the Santa Ana basin. Data from these three storms and 

stormflows will be used throughout this report to evaluate changes 

in stormflow water chemistry. 

The storm that produced the October 30–November 1, 1996, 

stormflow (fig. 6A) was the first storm of the 1996–97 rainy season. 

This storm was from the northwest and yielded 0.89 in. of rain at 

Prado Dam (table 1). This precipitation, although large in quantity 

and relatively intense for a first storm of the rainy season, is typical 

of early season winter storms in southern California in that 

precipitation began near the coast and moved inland (figs. 4 and 

6A).

The storm that produced the January 25–30, 1997, stormflow 

(fig. 6B) occurred later in the rainy season. This storm was from the 

northwest and yielded 1.7 in. of rain at Prado Dam. The quantity of 

precipitation was not exceptionally large; however, the stormflow 

was one of the largest sampled as part of this study because it 

included the release of water stored behind Prado Dam (table 1). 

Although this storm was from the northwest, analysis of regional 

satellite and doppler radar images show that this storm included 

precipitation from warm, moist air drawn into the basin from the 

southwest. These storms, which typically occur later in the rainy 

season, produced many of the larger magnitude, longer duration 

storms and stormflows sampled during this study. The “El Niño” 

storms that caused record precipitation during the 1997–98 rainy 

season were similar to this storm. The large stormflows during the 

1997–98 rainy season also included water released from behind 

Prado Dam.

The storm that produced the September 25–27, 1997, 

stormflow (fig. 6C) was the second storm of the 1997–98 rainy 

season, but the first to include runoff from the lower basin and the 

first significant stormflow of the 1997–98 rainy season. This storm 

was a hurricane that originated from the southeast and yielded 

0.75 in. of rain at Prado Dam (table 1). Although not usually 

destructive, precipitation from hurricanes is not unusual in the study 

area and two hurricanes occurred (September 14–16 and 25–27, 

1997) during the study. It was flooding from a hurricane in 1936 that 

prompted the construction of Prado Dam (U.S. Army Corps of 

Engineers, 1994).

Timing and Distribution of Precipitation and Runoff

The timing and distribution of precipitation and subsequent 

runoff during most storms causes some tributary streams, such as 

Cucamonga Creek, to produce more runoff, more quickly, than does 

the main stem of the Santa Ana River. Cucamonga Creek is in the 

Figure 4. Doppler radar images of precipitation 

in southern California, October 29–30, 1996.
Sampled Stormflows 9

Figure 5. Sampled stormflows, precipitation, and stage at Prado Dam and streamflow in the Santa Ana River below Prado Dam 

during the 1995–96, 1996–97, and 1997–98 rainy seasons.
10 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

northwestern part of the basin, which is closer to the 

coast than are other parts of the upper basin. As a result, 

during many storms it rains here first and runoff begins 

earlier here (fig. 6A). In addition, Cucamonga Creek is 

concrete-lined throughout much of its length and 

stormflow is flashy. Peak flows are larger and the water 

flows more rapidly to downstream sites in concretelined channels than in natural channels. This flashy 

response to rainfall in Cucamonga Creek produced 

runoff quicker than did the main stem of the Santa Ana 

River upstream from Prado Dam even when 

precipitation began in the southeastern part of the 

basin—as in the September 25–27, 1997, storm 

(fig. 6C). Although the data are not shown in figure 6, 

the timing and distribution of runoff in Chino Creek 

(fig. 1) is similar to the timing and distribution of runoff 

in Cucamonga Creek. As a result of their location, the 

timing and distribution of precipitation, flashy runoff, 

and infiltration of stormflow into the channel along the 

main stem of the Santa Ana River, Cucamonga and 

Chino Creeks have a larger effect on downstream 

stormflow than would be expected on the basis of their 

drainage areas—especially during the early part of the 

rainy season. 

Table 1. Summary of stormflow sample collection in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial 

Highway, southern California

[OCWD, Orange County Water District; USGS, U.S. Geological Survey; ft3/s, cubic feet per second]

1

Calculated from data reported by OCWD.

2

Accuracy of flow data is poor at high flows when diversion dam is deflated.

3

Base flow was augmented by releases of imported water to the Santa Ana River; only a small increase in streamflow, about 

20 ft3

/s, occurred during this storm.

Sample dates

Precipitation

at Prado Dam

(inches)

 Peak streamflow

Laboratory Classification Below

Prado Dam 

(ft3/s)

Diversion 

downstream 

from Imperial 

Highway 1

(ft3/s)

1995–96

(September-April precipitation 9.24 inches))

December 12–13 0.61 401 349 OCWD Early season storm

January 21–22 .38 470 467 OCWD Late season storm

1996–97

(September-April precipitation 13.95 inches)

October 30– November 1 0.89 799 799 USGS Early season storm

November 21–26 2.53 540 595 USGS Late season storm

December 9–17 2.42 561 970 USGS Late season storm

January 19–22 .26 500 565 USGS Late season storm

January 25–30 1.7 5,830 2

5,960 USGS Late season storm

1997–98

(September-April precipitation 32.49 inches)

September 14–16 0.03 3405 3406 USGS Early season storm

September 25–27 .75 655 717 USGS Early season storm

November 10–12 .58 379 413 USGS Early season storm

December 5–9 4.55 4,630 2

3,600 USGS Late season storm

February 3–5 2.25 3,060 22,080 USGS Late season storm
Sampled Stormflows 11

Figure 6. Precipitation and stormflow for selected sites in the Santa Ana River basin, southern California: (A) October 30–November 1, 1996; 

(B) January 25–30, 1997; and (C) September 25–27, 1997.
12 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

In contrast to the flashy conditions along 

Cucamonga and Chino Creeks, dry conditions at the 

beginning of the rainy season can reduce the amount of 

stormflow from upstream parts of the basin near San 

Bernardino. Although much of the main stem of the 

Santa Ana River is perennial, some infiltration capacity 

exists along the river channel prior to the first storm of 

the season. During the early part of the 1996–97 and 

1997–98 rainy seasons, infiltration of stormflow 

resulted in the reduction of peak flows between the 

Santa Ana River at E Street and MWD Crossing, and 

delayed the arrival of peak stormflows at downstream 

sites (figs. 6A,C). Later in the rainy season, less bank 

storage was available for stormflow, and infiltration 

along the channel of the Santa Ana River had less effect 

on peak flows and the timing of stormflows (fig. 6B). 

In most years, infiltration into dry stream 

channels and diversion for ground-water recharge 

reduce the contribution of runoff from mountain areas 

to near zero during the early part of the rainy season. 

However, runoff from mountain areas does contribute 

to stormflow at downstream sites later in the rainy 

season.

Regulation of Streamflow at Prado Dam

Regulation at Prado Dam has a direct effect on 

stormflow in the Santa Ana River below the dam and at 

Imperial Highway by reducing peak flows and by the 

storage and subsequent release of stormwater gradually 

over a period of several days, weeks, or months (U.S. 

Army Corps of Engineers, 1994; Burton and others, 

1998). 

When peak flows are reduced by regulation, 

stormflow at Imperial Highway may be composed 

primarily of runoff from urban areas downstream from 

Prado Dam. For example, on October 30, 1996, while 

regulation reduced streamflow below Prado Dam to 

about 80 ft3

/s, downstream runoff produced peak flows 

as high as 800 ft3/s in the Santa Ana River at Imperial 

Highway (fig. 6A). Regulation reduced streamflow 

below Prado Dam during the beginning of both the 

January 25–30, 1997, and September 25–27, 1997, 

storms in a similar manner but to a lesser extent 

(figs. 6B,C).

Under some conditions, stormflow below Prado 

Dam and at Imperial Highway may be dominated by 

water from previous storms that had been held in 

storage behind Prado Dam. The chemistry of stormflow 

stored behind the dam may be altered by mixing with 

subsequent baseflow, chemical and biochemical 

reactions, or dissolution of soluble material from soils 

and plants. Furthermore, stormflow entering the 

reservoir may either replace or mix with previously 

stored water. The storage dynamics, mixing, and Figure 6. Continued.
Stormflow Chemistry 13

chemical reactions that may occur in the flooded 

wetlands behind Prado Dam were not studied; 

however, all these factors influence the composition of 

stormflow below Prado Dam and at Imperial Highway 

when water is impounded and later released from the 

dam.

STORMFLOW CHEMISTRY

Under most conditions, stormflow water 

chemistry in the Santa Ana River, as in most streams, is 

dominated by inputs of nutrients, dissolved organic 

carbon (DOC), pesticides, and other organic 

compounds from sources outside the stream (Cole, 

1983). As a result, the concentrations of these 

constituents can change rapidly during stormflow as 

different parts of the basin contribute runoff to 

downstream sampling sites at different times. 

To facilitate interpretation, data from below 

Prado Dam and from Imperial Highway were grouped 

into base flow, early season stormflow, and late season 

stormflow. 

Base-flow samples were defined as samples 

collected prior to precipitation and runoff. At least one 

sample was collected prior to the beginning of 

precipitation and runoff for each storm. Base-flow data 

collected below Prado Dam and at Imperial Highway 

were consolidated for summary statistics presented in 

this report. However, samples composed primarily of 

water from previous stormflows that was stored behind 

Prado Dam and subsequently released were not 

included in statistics describing base flow. Similarly, 

samples from the September 14–16, 1997, stormflow 

that included a high percentage of imported water were 

not included in statistics describing base flow. 

Early season stormflows included the first 

stormflow of each rainy season. During the 1997–98 

rainy season, early season stormflows also included the 

second and third stormflows. This was done because 

the first stormflow of the 1997–98 rainy season 

(September 14–16) was small, with precipitation and 

subsequent runoff restricted to the upper basin. The 

second storm was the first storm that produced runoff 

across the entire Santa Ana River basin (September 24–

27) and was, in fact, the first stormflow of the season in 

the lower basin. Many water-quality changes common 

to the first stormflow of the season also were present in 

the third stormflow of the 1997–98 rainy season 

(November 10–12). Factors that may have contributed 

to this are (1) a large amount of material may have 

accumulated in the basin during the record dry period 

before the start of the 1997–98 rainy season and the 

first and second stormflows of the season may not have 

washed all the accumulated material from the basin, or 

(2) the relatively long time between the second and 

third stormflows (almost 2 months) may have allowed 

additional material to accumulate in the basin. 

Late season stormflows include all other 

stormflow. Many of these stormflows typically include 

water from previous stormflows that was released from 

storage behind Prado Dam. 

To determine if there are differences in water 

chemistry between base flow, early season stormflows, 

and late season stormflows, water-chemistry data were 

evaluated on the basis of the median test (Neter and 

Wasserman, 1974), with a confidence criterion of 

α=0.05.

Imperial Highway is only a short distance 

downstream from Prado Dam. During base flow, and 

during parts of some storms, water below Prado Dam 

flows downstream to Imperial Highway with little 

additional inflow. Hydrograph separation was used to 

determine the percentage of water that originated as 

runoff from urban areas downstream from Prado Dam 

and facilitate comparison between stormflow water 

chemistry at the two sites. Travel time between Prado 

Dam and Imperial Highway is about 4 hours (Alan 

Flowers, Orange County Water District, oral commun., 

1996) but may be less at high flows and greater at low 

flows. Three and one-half hours was used as the travel 

time for hydrograph separations presented in this 

report. Travel times may be greater for smaller 

stormflows. A more precise separation incorporating 

changes in travel time with changes in streamflow and 

dispersion within the stream channel was beyond the 

scope of this report. 

Changes in Nutrient Concentrations During 

Stormflow

Nutrients sampled as part of this study include 

nitrogen and phosphorus. Forms of nitrogen analyzed 

during stormflow were dissolved nitrate and more 

reduced forms of nitrogen such as dissolved nitrite, 

dissolved ammonia, and dissolved organic nitrogen. 

Forms of phosphorus analyzed include dissolved 

phosphate and dissolved orthophosphate.
14 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Nitrate

Median dissolved-nitrate concentration in base 

flow (sampled prior to the stormflows during 1995–98) 

in the Santa Ana River below Prado Dam and at 

Imperial Highway was 7.3 milligrams per liter (mg/L) 

as nitrogen (fig. 7). The maximum concentration of 

9.1 mg/L (Appendix C) as nitrogen is only slightly less 

than the U.S. Environmental Protection Agency 

(USEPA) Maximum Contaminant Level (MCL) for 

nitrate of 10 mg/L as nitrogen. High nitrate 

concentrations in base flow result from the discharge of 

treated municipal wastewater to the river. Nitrate 

concentrations in the Santa Ana River below Prado 

Dam increased at a rate of 0.15 mg/L as nitrogen per 

year over the last 25 years (Burton and others, 1998). 

Similar trends were observed in rivers and streams 

receiving large amounts of treated municipal 

wastewater throughout the United States, because the 

more reduced forms of nitrogen in wastewater are 

converted to nitrate by advanced wastewater-treatment 

technologies (Muller and Helsel, 1996).

In general, dissolved-nitrate concentrations 

decrease during stormflow (fig. 7). Median nitrate 

concentrations in early season and late season 

stormflows below Prado Dam and at Imperial Highway 

were 3.7 and 2.9 mg/L as nitrogen, respectively. These 

values are statistically different from concentrations in 

base flow at these sites. Decreases in nitrate 

concentrations during stormflow are consistent with 

dilution of nitrate from point sources, such as 

wastewater-treatment plants (Muller and others, 1995). 

The largest decreases in nitrate concentration were 

observed at Imperial Highway when stormflow was 

dominated by runoff from urban areas downstream 

from Prado Dam (fig. 8). Similar decreases also were 

observed below Prado Dam. 

Although dissolved-nitrate concentrations 

generally decrease during stormflow in the Santa Ana 

River, concentrations increased during the recessional 

flows of some early season storms below Prado Dam 

and at Imperial Highway (fig. 8C). These increases 

may be associated with the arrival of runoff from 

Cucamonga and Chino Creeks. In other areas, 

increases in nitrate concentrations during stormflow 

have been associated with nonpoint sources of nitrate 

such as fertilizer applications or animal confinement 

facilities (Muller and others, 1995).

The lowest dissolved-nitrate concentrations 

below Prado Dam and at Imperial Highway occurred 

during large, late season stormflows that replaced 

water held in storage behind Prado Dam. For example, 

during the January 25–30, 1997, stormflow (fig. 8B), 

nitrate concentrations initially decreased at Imperial 

Highway as a result of runoff from urban areas 

downstream from Prado Dam and then increased after 

Figure 7. Concentrations of dissolved nitrate, nitrite, 

ammonia, organic nitrogen, phosphate, orthophosphate, 

and organic carbon and nitrogen-to-carbon ratios in 

base flow and in early season and late season 

stormflows in the Santa Ana River below Prado Dam and 

at the diversion downstream from Imperial Highway, 

southern California, 1995–98. (mg/l, milligram per liter)
Stormflow Chemistry 15

water stored behind the dam was released. During this 

time, stage in the reservoir was held constant at 494 ft. 

This represents a total volume of 8,440 acre-ft. Given 

an outflow of 5,000 ft3

/s, about 20 hours would have 

been required to replace the volume of water stored 

behind the dam. After about 20 hours, approximately 

the length of time required for water in storage behind 

the dam to be replaced by stormflow from upstream 

areas, water released from Prado Dam was primarily 

stormflow from parts of the basin farther upstream and 

nitrate concentrations were less than 1 mg/L. Although 

simple piston flow of stormflow water through the 

reservoir behind Prado Dam may explain changes in 

nitrate concentrations observed during the January 

25–30, 1997, stormflow, water movement through the 

reservoir during stormflows is probably very complex, 

possibly having preferred flow paths and mixing with 

water stored in the reservoir.

Reduced Forms of Nitrogen

Nitrogen in nitrite, ammonia, and organic 

nitrogen is more reduced (has a lower oxidation state) 

than is nitrogen in nitrate. Nitrite, ammonia, and 

organic nitrogen can be oxidized to nitrate under 

aerobic conditions and thus contribute to nitrate 

contamination. For this reason, it is often important to 

consider total nitrogen concentration, the sum of 

nitrogen in all its different chemical forms, when 

assessing the suitability of water for use as a source of 

ground-water recharge in aquifers pumped for public 

supply. 

Figure 8. Dissolved nitrate, ammonia, and organic nitrogen concentrations during stormflow in the Santa Ana River below Prado Dam, and at 

the diversion downstream from Imperial Highway, southern California: (A) October30–November 1, 1996; (B) January 25–30, 1997; and (C)

September 25–27, 1997. (mg/L, milligram per liter)

Figure 8. Continued.
16 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Median concentrations of dissolved nitrite, 

dissolved ammonia, and dissolved organic nitrogen in 

base flow (sampled prior to stormflows) in the Santa 

Ana River below Prado Dam and at Imperial Highway 

were 0.06, 0.16, and 0.49 mg/L as nitrogen, 

respectively. Maximum concentrations were 0.79, 

0.56, and 1.1 mg/L as nitrogen, respectively (fig. 7). 

The USEPA MCL for nitrite is 1 mg/L as nitrogen. 

There are no MCL’s for the other reduced forms of 

nitrogen. However, ammonia is toxic to fish at 

concentrations as low as 0.4 mg/L (U.S. Environmental 

Protection Agency, 1976, 1986). The toxicity of 

ammonia is greater for the un-ionized form of 

ammonia; as a result, toxicity increases with pH.

Concentrations of nitrite, ammonia, and organic 

nitrogen in base flow are low, in part because of the 

advanced wastewater-treatment technologies used 

throughout the basin that convert reduced forms of 

nitrogen to nitrate prior to discharge. Possibly as a 

result of this treatment, ammonia concentrations in the 

Santa Ana River below Prado Dam have decreased at a 

rate of 0.04 mg/L as nitrogen per year over the last 25 

years (Burton and others, 1998). No statistically 

significant trends in nitrite or organic nitrogen 

concentrations were observed during that period 

(Burton and others, 1998). 

In general, reduced forms of nitrogen increase as 

a result of stormflow (fig. 7). Median concentrations of 

nitrite, ammonia, and organic nitrogen during early 

season stormflows were 0.06, 0.17, and 0.81 mg/L as 

nitrogen, and median concentrations during late season 

stormflows were 0.12, 0.35, and 0.69 mg/L as nitrogen, 

respectively. However, only the median organic 

nitrogen concentration in early season stormflows and 

median nitrite concentrations in late season stormflows 

were statistically different from the corresponding 

concentrations in base flow. 

The highest concentrations of ammonia and 

organic nitrogen occurred during late season 

stormflows (fig. 7). Increases also occurred during 

early season stormflows, especially during the 

recessional flows of early season stormflows (figs. 

8A,C), but those concentrations were lower than 

concentration in late season stormflows. Ammonia 

concentrations exceeded 2 mg/L in the Santa Ana River 

below Prado Dam during the January 25–30, 1997, 

stormflow (fig. 8B). Although other factors, such as 

dissolved-oxygen concentrations, are important, high 

ammonia concentrations could have contributed to fish 

kills observed during this study. Toxicity associated 

with increased ammonia may be partly offset by 

decreases in pH during stormflow (as measured during 

this study) that reduce un-ionized ammonia 

concentrations.

Because storm and sanitary sewers are separate 

in the Santa Ana River basin, combined sewer 

overflows are not a source of ammonia or organic 

nitrogen; however, water flushed from storm sewers 

could contain high concentrations of reduced nitrogen. 

Many late season stormflows contain water that 

was held in storage behind Prado Dam. It is possible 

that oxygen-poor conditions and biochemical reactions 

in the flooded wetlands behind the dam may result in 

the conversion of nitrate to more reduced forms of 

nitrogen. Contamination from nonpoint sources such as 

fertilizer applications or animal-confinement facilities 

(Muller and others, 1995) also may explain increases in 

reduced-nitrogen concentrations during the recessional 

flow. Increases in reduced nitrogen also could be 

associated with disturbance of the streambed materials 

of the Santa Ana River or tributaries by increased flow 

velocities.

Phosphate

Median dissolved phosphate and dissolved 

orthophosphate concentrations in base flow (sampled 

prior to stormflows during 1995–98) in the Santa Ana 

River below Prado Dam and at Imperial Highway were 

0.93 and 0.91 mg/L as P, respectively (fig. 7). These 

concentrations are high in comparison with 

concentrations in most large rivers in the United States 

but comparable to concentrations in smaller streams 

draining urban areas (Muller and others, 1995). 

Although phosphorous compounds have been largely 

removed from laundry detergent in recent years, there 

was no trend in phosphate concentrations in the Santa 

Ana River below Prado Dam (Burton and others, 

1998). However, orthophosphate concentrations 

increased at a rate of 0.03 mg/L as P per year over the 

last 25 years (Burton and others, 1998). This is contrary 

to the decreasing trend in phosphate and 

orthophosphate concentrations in the Nation’s rivers 

and streams observed by Muller and Helsel (1996). 

The median dissolved phosphate and dissolved 

orthophosphate concentrations in both early season and 

late season stormflows below Prado Dam and at 

Imperial Highway are statistically different from 

concentrations in base flow (fig. 7). Decreases in 
Stormflow Chemistry 17

phosphate and orthophosphate concentrations during 

stormflow are consistent with dilution. However, the 

highest phosphate and orthophosphate concentrations 

occurred during the largest late season stormflows, 

when phosphate absorbed on sediment can be 

mobilized during stormflows. This pattern is similar to 

changes in phosphate and orthophosphate 

concentrations observed during a nationwide study of 

stormflow in streams and rivers (Muller and others, 

1995).

Changes in Concentration and Composition of 

Dissolved Organic Carbon During Stormflow 

Because of health concerns it is desirable to 

minimize the amount of dissolved organic carbon 

(DOC) of wastewater origin in drinking water derived 

from ground water recharged from the Santa Ana River 

(Orange County Water District, 1996b). In addition, 

there is concern about the potential for trihalomethane 

formation when the water having high DOC 

concentrations is chlorinated. Trihalomethane 

formation is a function of both the concentration and 

composition of DOC (California Department of Water 

Resources, 1994; Orange County Water District, 

1996b).

Dissolved Organic Carbon Concentrations

The median DOC concentration in base flow 

(sampled prior to the beginning of stormflows during 

1995–98) in the Santa Ana River below Prado Dam and 

at Imperial Highway was 4.6 mg/L. Concentrations of 

3 to 5 mg/L are typical for surface water in arid regions 

(Thurman, 1985). However, because base flow in the 

Santa Ana River is primarily treated municipal 

wastewater, the DOC concentration is largely 

controlled by the concentration in the wastewater 

discharges. About half the base flow of the Santa Ana 

River is treated in artificial wetlands upstream from 

Prado Dam to remove nitrate. Gray and others (1996) 

showed that treatment within the wetlands increased 

the concentration and changed the composition of 

DOC in the Santa Ana River. 

During this study, DOC concentrations generally 

increased during stormflow (fig. 7). Median DOC 

concentrations during early season and late season 

stormflows were 8.8 and 6.8 mg/L, respectively. These 

values are significantly different from DOC 

concentrations in base flow. Maximum DOC 

concentrations in early season stormflows were as high 

as 23 mg/L. Data are given in Appendix D.

The highest DOC concentrations in stormflow 

were measured at Imperial Highway during the first 

storm of the 1996–97 rainy season (fig. 9A). At that 

time, most of the water at Imperial Highway was runoff 

from urban areas downstream from Prado Dam. 

Similar increases in DOC from urban areas 

downstream from Prado Dam also were observed 

during other early season stormflows. Increases in 

DOC concentrations from 3.6 to 8.1 mg/L measured 

during the first storm of the 1997–98 rainy season (not 

shown in figure 9) are noteworthy because the amount 

of precipitation was small (0.25 in. at Riverside and 

less than 0.03 in. at Prado Dam) and produced only a 

small increase in streamflow (table 1). For such large 

changes to occur during such a small storm, DOC in the 

basin must be highly mobile. Elevated DOC 

concentrations from urban areas downstream from 

Prado Dam were not present after the first stormflow of 

the 1996–97 rainy season, or after the first three storms 

of the 1997–98 rainy season. Apparently the source of 

this DOC was removed by the early season stormflows. 

However, elevated DOC concentrations occurred 

during late season stormflows when water stored 

behind Prado Dam was released. For example, DOC 

concentrations during the January 25–30, 1997, 

stormflow initially decreased as a result of runoff from 

areas downstream from Prado Dam and subsequently 

increased as water stored behind the dam was released 

(fig. 9B). 

Possible sources of readily soluble, highly 

mobile organic carbon include anthropogenic sources 

such as partly burned hydrocarbons washed from 

streets and parking lots, and natural sources such as soil 

or partly decayed plant material. Partly decayed soil 

and plant material that accumulated in storm drains 

during the dry season may be especially mobile. Some 

organic carbon also could be mobilized from the bed of 

the Santa Ana River if the streambed was disturbed by 

increased flow velocities. 

Increased DOC concentrations were measured in 

the Santa Ana River below Prado Dam during both the 

October 30–November 1, 1996 (fig. 9A), and the 

September 25–27, 1997, stormflows (fig. 9C). Sample 

collection at Imperial Highway continued over a longer 

period during the September 25–27 stormflow, and 

DOC from the upstream sample site was eventually 

observed at the downstream site. Increases in DOC 

observed during the later part of this stormflow 
18 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

coincided with increases in nitrate and reduced 

nitrogen species (fig. 8C). As previously discussed, this 

water may be associated with the arrival of runoff from 

Cucamonga and Chino Creeks.

Dissolved Organic Carbon Composition

Characterization of the composition of DOC 

during stormflow may help identify its origin and allow 

predictions about its fate in the environment and about 

its response to chlorination. Thorough characterization 

of DOC is a complex task requiring a hierarchical 

analytical approach that may determine, among other 

things, (1) operationally defined organic fractions, (2) 

functional-group characteristics, (3) molecular weight, 

and (4) ultimately, the concentration of specific organic 

compounds (Leenheer and Huffman, 1976; Barber, 

1992). This hierarchical analytical approach is time 

consuming, labor intensive, and expensive. Given the 

number of samples collected, the rapid changes in DOC 

concentrations, and the number of potentially different 

sources contributing runoff and DOC during 

stormflows, such a rigorous approach was not within 

the scope of this study. Instead, a simplified approach 

that measures differences in UV absorbance and 

changes in nitrogen-to-carbon ratios was used to 

characterize DOC contributed from different sources 

during stormflow. Therefore, interpretations about the 

origin, fate, and response of DOC are limited. Data 

presented in this report are best used to identify changes 

in DOC composition during different stormflows and to 

Figure 9. Dissolved organic carbon concentrations and UV254 absorbance during selected stormflows in the Santa Ana River below Prado 

Dam and at the diversion downstream from Imperial Highway, southern California: (A) October 30–November 1, 1996; (B) January 25–30, 

1997; and (C) September 25–27, 1997.

Figure 9. Continued.
Stormflow Chemistry 19

determine if these differences require further 

characterization.

Ultraviolet Absorbance

Absorbance of light at different wavelengths is 

related to the presence of specific functional groups 

within complex carbon molecules. When electrons in 

organic molecules are exposed to light they become 

“excited”; the less firmly bound the electrons, the 

easier they are to excite. Excitation causes changes at 

the atomic level such as the transition of electrons to 

higher energy levels, rotation or vibrational changes 

within bonds, or changes in the spin of atomic nuclei 

(Hart and Schuetz, 1972), and results in the absorbance 

of energy. These changes are complex and even a 

simple molecule such as methane (CH4) has several 

absorption bands. Despite the complexity of natural 

DOC, absorbance within the UV, visible, or infrared 

range can be useful in identifying similarities or 

differences between DOC from different sources. 

When this approach is used, DOC concentrations (or 

some other measure of organic material) are commonly 

compared with absorbance at selected wavelengths 

corresponding to the maximum absorbance for 

different functional groups (Black and Christman, 

1963; Mrkva, 1983; Thurman, 1985; Krazner and 

others, 1996). 

DOC absorbance within the UV range [220–

800 nanometers (nm)] is usually associated with 

unsaturated molecules such as those containing 

carbon-carbon double bonds, carbon-oxygen double 

bonds, or carbon-carbon double bonds in complex 

aromatic (benzene-like) ring structures (Gutsche and 

Pasto, 1975). Carbon-carbon double bonds within 

aromatic rings generally absorb near 254 nm and 

carbon-oxygen double bonds generally absorb near 

285 nm (Gutsche and Pasto, 1975). However, the exact 

wavelength absorbed increases with the length and 

complexity of the associated carbon chain and other 

structures. Ultraviolet absorbance spectra do not show 

pronounced peaks at wavelengths corresponding to 

specific functional groups but instead are smooth 

curves usually showing a maximum absorbance near 

254 nm. Maximum absorbance near 254 nm results 

because aromatic rings are the basic building blocks of 

many complex, naturally occurring organic 

compounds. These aromatic rings also are the basic 

building blocks of many anthropogenic compounds, 

such as lubricants, polycyclic aromatic hydrocarbons 

(PAH) produced by the partial combustion of fossil 

fuel, and many pesticides. Although UV absorbance 

spectra can be used to quantify the concentrations of 

individual compounds in simple mixtures, these data 

are not quantitative for solutions containing complex 

mixtures of natural and anthropogenic organic 

molecules. 

Ultraviolet absorbance data have been used in 

previous studies as a surrogate for DOC concentrations 

(California Department of Water Resources, 1994). In 

natural waters there commonly is large variability 

between DOC and UV absorbance and correlations 

may be poor. This variability results from differences in 

the composition of DOC and from interference with 

other compounds in water that also may absorb UV 

light (California Department of Water Resources, 

1994; Krazner and others, 1996).

In this study, comparison of DOC concentrations 

and UV absorbance at 254 nm (UV254) was used to 

determine qualitative differences in the composition of 

DOC in early season and late season stormflows. On 

the basis of an analysis of covariance (Neter and 

Wasserman, 1974), DOC in early season stormflows is 

different from DOC present in late season stormflows 

(fig. 10). The analysis of covariance has an R2 of 0.63, 

but it is highly significant with a p value of 0.001. The 

slopes of the lines shown in the upper part of figure 10 

have units of DOC in mg/L per absorbance at 254 nm; 

the inverse of these slopes is conceptually similar to 

specific UV absorbance (SUVA) discussed in many 

studies (Krazner and others, 1996). Because DOC in 

late season stormflows has a higher UV254 absorbance 

per unit of carbon, it may contain more carbon-carbon 

double bonds than DOC in early season stormflows. If 

this interpretation is correct, then DOC in late season 

stormflows may have a greater tendency (per unit of 

carbon) to form trihalomethanes as a result of 

chlorination (California Department of Water 

Resources, 1994; Krazner and others, 1996). 

Additional characterization of DOC would be required 

to verify differences in carbon composition and the 

potential for trihalomethane formation.

Nitrate and iron also absorb within the UV range, 

although the wavelengths of their maximum 

absorbance are different from 254 nm. When included 

in the analysis of covariance shown in figure 10, 

coefficients for nitrate and iron are small in magnitude 

but statistically significant. This result suggests that 

these constituents may interfere with UV254
20 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

measurements by increasing UV254 absorbance. After 

accounting for interference, the difference between 

early season and late season stormflow remained 

statistically significant and the R2

 of the analysis of 

covariance increased to 0.82. Interference from nitrate 

may be more important during base flow then during 

stormflow because, in general, dissolved nitrate 

concentrations decrease during stormflow (figs. 7 and 

8). In contrast, interference from iron may be important 

during stormflow because dissolved iron 

concentrations increase during stormflow (figs. 18 and 

19, later in this report). 

Carbon-oxygen double bonds in DOC have a 

maximum absorbance near 285 nm. Carbon-oxygen 

double bonds are a component of functional groups 

such as carboxylic acids and esters (Gutsche and Pasto, 

1975). Comparison of UV254 and UV285 was used to 

determine qualitative differences between DOC in 

early season and late season stormflows. On the basis of 

analysis of covariance (Neter and Wasserman, 1974) 

with a p value of 0.001, the relation between UV254 and 

UV285 in early season stormflows is different from the 

relation in late season stormflows (fig. 10). Dissolved 

nitrate and dissolved iron concentrations did not 

interfere with this relation. On the basis of these data, 

DOC from late season stormflows have more UV285

absorbance per unit of UV254 absorbance than DOC 

from early season stormflows, and DOC from late 

season stormflows may be compositionally more 

complex than DOC from early season stormflows. 

Additional characterization of DOC would be required 

to verify differences in carbon composition.

Differences in DOC composition suggested by 

UV absorbance data (fig. 10) are consistent with 

differences in the sources of DOC between early season 

and late season storms. DOC in early season storms is 

highly mobile and readily washed from the basin after 

the early season storms. This DOC may originate as 

partly decayed plant material that accumulated in storm 

drains and in stream channels. DOC from such a source 

would be expected to contain simpler organic 

compounds and have lower UV254 and UV285

absorbances than DOC that originated from the flooded 

wetlands behind Prado Dam during the late season 

storms. Increased UV254 absorbance during the 

recessionals of early season stormflows (fig. 10) could 

be explained by interference from increased dissolved 

nitrate concentrations present during these recessional 

flows.

Nitrogen-to-Carbon Ratios

Nitrogen-to-carbon ratios vary greatly in organic 

material and can change rapidly in response to 

chemical and biochemical processes. However, these 

data may be used to indicate the source of DOC in 

stormflow because, in this study, residence times in 

streams are short and water temperatures are cool. 

Short residence times and cool temperatures may 

Figure 10. Dissolved organic carbon as a function of UV254, and 

UV285 as a function of UV254, in stormflow in the Santa Ana 

River below Prado Dam and at the diversion downstream from 

Imperial Highway, southern California, 1995–98.
Stormflow Chemistry 21

minimize alteration of DOC in stormflow by chemical 

and biochemical processes.

During early season stormflows, nitrogen-tocarbon ratios are significantly lower than ratios in base 

flow (fig. 7). The lowest ratios are associated with high 

DOC concentrations that occur as a result of runoff 

from urban areas downstream from Prado Dam. Lower 

values of this ratio may reflect inputs of DOC from the 

decay of plant material that has accumulated in storm 

drains and the stream channel during the dry season, as 

discussed previously. This material typically has low 

nitrogen-to-carbon ratios (Thurman, 1985). The 

nitrogen-to-carbon ratio of late season stormflows is 

not significantly different from that of base flow. 

However, the range in nitrogen-to-carbon ratios in late 

season stormflows is greater than in base flow or early 

season stormflows (fig. 7). This may be because 

different sources of carbon are contributing to the 

DOC. During late season stormflows, samples with 

lower nitrogen-to-carbon ratios were associated with 

runoff from urban areas downstream from Prado Dam, 

whereas samples with higher nitrogen-to-carbon ratios 

were associated with water that had been in storage 

behind Prado Dam. In water stored behind Prado Dam, 

the DOC may have been altered by the dissolution of 

humic or fulvic acids present in the wetlands or by 

microbial activity, such as algal growth, and by the 

inclusion of cellular debris and exudates. These organic 

materials typically have high nitrogen-to-carbon ratios 

(Thurman, 1985; Paul and Clark, 1996).

Comparison with Dissolved Organic Carbon Concentrations 

and UV Absorbance in Water from Other Sources

Comparison of stormflow samples from the 

Santa Ana River with water from the California 

Aqueduct and agricultural drains within the San 

Joaquin Delta is useful because (1) water from these 

sources has been extensively characterized using UV 

absorbance and other techniques, (2) water from the 

California Aqueduct is used in addition to water from 

the Santa Ana River to recharge aquifers underlying 

Orange County, and (3) the San Joaquin Delta is the 

source of much of the DOC in water from the 

California Aqueduct (California Department of Water 

Resources, 1994). 

In general, DOC concentrations in stormflow in 

the Santa Ana River are higher than average 

concentrations in water from the California Aqueduct. 

DOC concentrations in aqueduct water range from 2 to 

6 mg/L (California Department of Water Resources, 

1994). At times, DOC concentration in stormflow from 

the Santa Ana River was within the range of water from 

some agricultural drains in the San Joaquin Delta, but 

maximum concentrations were not as high as the 

maximum concentration from agricultural drains. DOC 

concentrations in water from these drains can exceed 

100 mg/L (California Department of Water Resources, 

1994; Fujii and others, 1998). 

Trihalomethane formation potential is a function 

of the concentration and composition of DOC, as well 

as the pH, bromide concentration, and various other 

factors (California Department of Water Resources, 

1994; Krazner and others, 1996). The trihalomethane 

formation potential of DOC in water from many 

different sources sampled by Krazner and others 

(1996) ranged from 0.4 to 1 micromole per milligram 

of DOC. Typical trihalomethane formation potentials 

of water from the California Aqueduct (California 

Department of Water Resources, 1994) and agricultural 

drains in the San Joaquin Delta (Fujii and others, 1998) 

are near the high end of this range, about 0.8 micromole 

per milligram of DOC. On the basis of UV absorbance 

data (after correction for nitrate and iron interference), 

the composition of DOC in stormflow has relatively 

high absorbance per milligram of DOC; typical values 

are 0.04 and 0.06 absorbance units per milligram for 

early season and late season storms, respectively. These 

values are within the range of humic acids (Krazner 

and others, 1996) and similar to values measured in the 

California Aqueduct (California Department of Water 

Resources, 1994) and to water collected during the 

winter months from agricultural drains in the San 

Joaquin Valley (Fujii and others, 1998). On the basis of 

these data, DOC in stormflow also may have high 

trihalomethane formation potential. The 

trihalomethane formation potential of water recharged 

from the Santa Ana River is being studied as part of the 

SARWQHS by Orange County Water District (1996b). 

Some trihalomethanes were detected in stormflow 

water as part of this study (discussed later in this 

report).

Changes in Selected Organic Compound 

Concentrations During Stormflow 

Pesticides and volatile organic compounds in 

stormflow from the Santa Ana River were analyzed as 

part of this study. These compounds have urban, 
22 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

agricultural, and industrial uses within the basin, and 

many of these compounds are found in surface water 

and ground water across the United States (Barbash 

and Resek, 1996; U.S. Geological Survey, 1996, 1997). 

The volatile organic compounds analyzed as part of 

this study included compounds associated with urban 

runoff such as methyl tert-butyl ether (MTBE), a 

gasoline oxygenate, and chlorination byproducts such 

as chloroform. Other organic compounds such as 

polycyclic aromatic hydrocarbons (PAH’s) commonly 

associated with urban runoff were not analyzed as part 

of this study. 

Pesticides

Pesticides in low concentrations are widespread 

in surface waters across the United States and the 

concentrations follow strong seasonal patterns that 

result from streamflow conditions and the timing of 

pesticide applications (U.S. Geological Survey, 1997). 

The potential effects on human or aquatic systems are 

difficult to evaluate because of (1) incomplete 

information on the distribution of pesticides in the 

environment, (2) the effects of low-concentration 

mixtures of pesticides and their transformation 

products, and (3) the effects of long-term exposure to 

these compounds. In recent years, with the 

development of increasingly sensitive analytical 

methods, the distribution of pesticides in the 

environment has become easier to evaluate. 

This study addressed the distribution of 

pesticides in the Santa Ana River during 1996–98 

stormflows with an emphasis on the association of 

pesticides in runoff from different parts of the basin and 

the possibility that “first-flush” effects may result in 

increased pesticide concentrations during the early part 

of the rainy season. An evaluation of the distribution of 

pesticide concentrations in the Santa Ana River 

resulting from seasonal-application patterns is beyond 

the scope of this report.

Occurrence of Pesticides During Stormflow

During the first year of the study (1995–96), 49 

pesticides and selected organic compounds were 

analyzed by the Orange County Water District using 

USEPA drinking-water method 507, determination of 

nitrogen- and phosphorous-containing pesticides by 

gas-chromatography with a nitrogen phosphorus 

detector (U.S. Environmental Protection Agency, 

1995), and method 525, determination of organic 

compounds in drinking water (U.S. Environmental 

Protection Agency, 1995). Almost all concentrations 

were below the detection limits obtainable using these 

methods, and all measured concentrations were low for 

the analyzed compounds.

During the second (1996–97) and third (1997–

98) years of this study, 87 pesticides were analyzed 

using USGS solid-phase extraction methodology 

(Zaugg and others, 1995; Werner and others, 1996). 

These methods have detection limits several orders of 

magnitude lower than those of standard drinking-water 

methods (Appendix B). Using these methods, 25 

pesticides were detected below Prado Dam and at 

Imperial Highway during six storms (table 2). All 25 

compounds were detected at concentrations less than 

their respective MCL’s, and only carbaryl, simazine, 

and diuron exceeded 1 μg/L. Using these methods, 62 

pesticides included in the analyses were not detected. 

Results are given in Appendix E.

Concentrations of the 10 most commonly 

detected pesticides are shown as box plots in figure 11. 

The box plots show base flow, stormflow dominated by 

urban runoff originating downstream from Prado Dam, 

and all other stormflows determined on the basis of 

hydrograph seperation. This comparison is different 

from the comparison among base flow, early season, 

and late season stormflows presented elsewhere in this 

report and helps determine pesticides that are 

associated with runoff from urban areas downstream 

from Prado Dam for comparison with pesticides 

associated with runoff from areas upstream from the 

dam. 

On the basis of the median test (Neter and 

Wasserman, 1974), concentrations of 8 of the 10 most 

commonly detected compounds increased during 

stormflow (fig. 11). For many of these compounds, 

statistically significant increases in concentrations 

occurred regardless of the source of runoff. However, 

increases in concentrations of the insecticides diazinon, 

malathion, and chlorpyrifos were larger in runoff from 

urban areas downstream from Prado Dam. In contrast, 

increases in concentrations of the herbicides DCPA, 

simazine, and diuron were larger in runoff from areas 

upstream from Prado Dam. No statistically significant 

changes in metolachlor concentrations were observed 

during stormflow. Statistically significant decreases in 

atrazine concentrations were observed in runoff from 

urban areas downstream from Prado Dam. 

Concentrations of metolachlor and atrazine were low 
Stormflow Chemistry 23

Table 2. Summary of detected pesticide data for the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, so[Pesticides listed by frequency of detection. Number of analyses is 73. Active ingredient data from the California Department of Pesticide Regulation. μg/L, microgra

 —, no data or not reported]

1From Ware, 1982; Wagner and others, 1995; or Williamson and others, 1998.2From California Department of Water Resources, 1997.3Active ingredient applied and use figures for San Bernardino, Riverside, and Orange Counties. From California Department of Pesticide Reg

home and garden use.

4California Department of Health Services Action Level. From California Department of Water Resources, 1997.

Pesticide Trade

name1

Number of

detections

Minimum 

reporting

level

(μg/L)

Median 

concentration

(μg/L)

Maximum 

concentration

(μg/L)

Maximum 

contaminant

level2

(μg/L)

Active 

ingredient

applied in 

19953

(kg)

Insecticides and their metabolites

Diazinon Several 72 0.002 0.10 0.64 414. 30,000 Stru

Carbaryl Sevin 69 .008 .062 1.2 460. 17,400 CitrMalathion several 51 .005 .022 .22 4160. 40,200 AlfChlorpyfos Genpest 48 .004 .01 .10 — 74,200 StruLindane — 12 .004 <.004 .11 .2 60 LanPropoxur Baygon 3 .035 <.035 .11 — 411 StruDDE (metabolite of DDT) 1 .006 <.006 .004 — —

Herbicides and their metabolites

DCPA Dacthal 73 0.001 0.004 0.36 — 26,900 VegSimazine Aquazine 73 .005 .078 1.2 4.0 18,500 CitrPrometon Ptamitol 70 .018 .018 .054 — 5 LanAtrazine AAtrex 64 .001 .008 .057 3.0 57 LanMetolachlor Dual 54 .002 .007 .015 — 83,100 CitrDiuron Karmex 48 .02 .34 13 — 34,200 RigDeethyl atrazine (metabolite of atrazine) 15 .002 <.002 .013 — —Tebuthiuron Spike 13 .01 <.01 .025 — 912 Rig

Cyanazine Bladex 10 .004 <.004 .03 — 440 CotBromacil Hyvar X 10 .035 <.035 .50 — 9,880 CitrTriclopyr Garlon 10 .05 <.05 .93 — 4500 LanNorflurazon Evital 8 .02 <.02 .39 — 1760 LanTrifluralin Treflan 8 .002 <.002 .005 — 37,900 Alf

Napropamide Devrinol 7 .003 <.003 .085 — 260 LanBenfluralin Balan 5 .002 <.002 .007 — 2,150 Lan

Pendimethalin Prowl 4 .004 <.004 .018 — 8,860 Lan2,4-D several 3 .035 <.035 .41 70 2,140 LanPronamide Kerb 2 .004 <.004 .02 — — (pre
24 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

and near the minimum reporting level for these 

compounds.

The largest increases in the concentrations of the 

insecticides diazinon, malathion, and chlorpyrifos were 

during early season stormflows, and changes in 

concentration were rapid (figs. 12A, C). However, 

increases in diazinon concentrations also occurred later 

in the rainy season at Imperial Highway (fig. 12B). 

These data suggest that diazinon, unlike DOC, either is 

not readily washed from the basin during early season 

storms, or that diazinon may be applied throughout the 

rainy season and available to runoff during late season 

stormflows. In contrast, concentrations of the 

herbicides simazine, diuron, and carbaryl increased 

during stormflow that originated primarily from areas 

upstream from Prado Dam (fig. 13A). Concentrations 

of diuron and simazine decreased temporarily when 

streamflow was dominated by runoff from urban areas 

downstream from Prado Dam (fig. 13B), suggesting 

that there may be little use of these pesticides in that 

area during the rainy season. 

Comparison with Reported-Use Data

Pesticide detections and concentrations are 

compared with 1995 reported application data collected 

by the California Department of Pesticide Regulation 

(1995) in table 2. Reported application data include 

agricultural, commercial, industrial, institutional, and 

government pesticide use. They do not include home 

and garden use. Reported use in San Bernardino, 

Riverside, and Orange Counties was used to 

approximate use in the Santa Ana River basin. Because 

the combined area of these three counties is larger than 

the Santa Ana River basin, the amount of active 

ingredient applied (table 2) probably overestimates 

pesticide use in the basin. However, the data are 

assumed to correctly identify pesticides commonly 

used in the basin, the relative usage of different 

compounds, and the purpose for which these 

compounds are used.

In general, pesticides such as chlorpyrifos, 

malathion, diuron, diazinon, DCPA, simazine, and 

carbaryl that have high reported use have high 

frequencies of detection (fig. 14). Chlorpyrifos and 

diazinon are insecticides commonly used in urban areas 

for structural pest control (table 2), and malathion has 

been widely used in urban areas throughout southern 

California to control medfly infestations. In addition, 

these insecticides are common home and garden 

chemicals. In the study area, diuron and simazine are 

Figure 11. Concentrations of the 10 most commonly 

detected pesticides in base flow, stormflow dominated 

by runoff from urban areas downstream from Prado 

Dam, and all other stormflows in the Santa Ana River 

below Prado Dam and at the diversion downstream from 

Imperial Highway, southern California, 1996–98.
Stormflow Chemistry 25

used for citrus and for right-of-way maintenance 

(California Department of Pesticide Regulation, 1995). 

Diuron had the highest concentrations of any pesticide 

detected in this study. Panshin and others (1998) found 

that diuron used for right-of-way maintenance in the 

San Joaquin Valley was especially mobile. In the Santa 

Ana study area, carbaryl is used for citrus and animal 

husbandry (California Department of Pesticide 

Regulation, 1995) and may be associated with animalconfinement facilities in areas drained by Cucamonga 

and Chino Creeks. Carbaryl also is a common home 

and garden chemical used to kill snails.

In contrast, the herbicides prometon and atrazine 

have very low reported use but were present in 96 and 

88 percent of the samples, respectively. These 

herbicides may have a large amount of unreported use, 

although atrazine cannot be legally sold for home and 

garden use. Both prometon and atrazine are triazine 

herbicides. This group of herbicides has been shown to 

be highly mobile and to have a high frequency of 

detections in surface water in relation to application 

rates (Panshin and others, 1998). Another triazine 

herbicide that has a high rate of detection in relation to 

its reported application rates is cyanazine. 

Metolachlor has the highest reported use of any 

pesticide in the Santa Ana study area and was 

commonly detected, but only at low concentrations. 

The low concentrations may result from factors such as 

where the pesticide is used in the basin. For example, 

metolachlor is primarily used on citrus, and most of the 

remaining citrus is grown in the San Jacinto River 

basin, which rarely contributes flow to the Santa Ana 

Figure 12. Diazinon, malathion, and chlorpyrifos concentrations during stormflow in the Santa Ana River below Prado Dam and at the 

diversion downstream from Imperial Highway, southern California: (A) October 30–November 1, 1996; (B) January 25–30, 1997; and (C) 

September 25–27, 1997. (μg/L, microgram per liter)

Figure 12. Continued.
26 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

.01

Santa Ana River at diversion downstream from Imperial Highway

River. Other factors such as seasonal application of the 

pesticide, its tendency to degrade, or its tendency to 

sorb to soils and particulate material also may be 

important.

In contrast to the more commonly detected 

pesticides, trifluralin has high reported use but was 

detected infrequently. Trifluralin is more commonly 

detected in runoff from urban areas downstream from 

Prado Dam than from upstream areas. Although used 

primarily on alfalfa, trifluralin’s presence in stormflow 

derived from urban runoff may reflect use for landscape 

maintenance or unreported home and garden use.

Comparison of the frequency of detection for 

different pesticides in runoff derived from urban areas 

downstream from Prado Dam with runoff from urban 

and agricultural areas upstream from the dam shows 

differences in pesticide distribution in runoff from 

different parts of the basin (fig. 14). In general, 

insecticides are detected more frequently in runoff from 

urban areas downstream from Prado Dam (fig. 14). This 

result is consistent with reported-use data that suggests 

that some of these compounds, such as diazinon and 

chlorpyrifos, have high reported use for structural pest 

control (table 2). This also is consistent with the 

potentially large amount of unreported home and 

garden use of these chemicals. A number of herbicides, 

such as tebuthiuron, bromacil, triclopyr, and 

napropamide, also are detected more frequently in 

runoff from urban areas downstream from Prado Dam. 

These herbicides have a high reported use for landscape 

Figure 13. Simazine, carbaryl, and diuron, concentrations during stormflow in the Santa Ana River below Prado Dam and at the diversion 

downstream from Imperial Highway, southern California: (A) October 30–November 1, 1996; (B) January 25–30, 1997; and (C) September 25–27, 

1997. (μg/L, microgram per liter)

Figure 13. Continued.
Stormflow Chemistry 27

maintenance and also may have unreported home and 

garden use. Herbicides such as atrazine, metolachlor, 

lindane, cyanazine, and diuron may originate mainly 

from the upper basin (fig. 14).The herbicides are 

detected frequently at Imperial Highway, even when 

stormflow originated primarily as runoff from urban 

areas downstream from Prado Dam, because stormflow 

at Imperial Highway almost always contains some 

fraction of water that originated upstream from Prado 

Dam.

Recent studies (U.S. Geological Survey, 1999) 

show that pesticides usually occur in mixtures of 

several compounds rather than individually. A review 

of U.S. Geological Survey National Water-Quality 

Assessment (NAWQA) Program data shows that more 

than 50 percent of all stream samples contained five or 

Figure 14. Pesticide use in Orange, Riverside, and San Bernardino Counties and frequency of detection in the Santa Ana River below 

Prado Dam and at the diversion downstream from Imperial Highway, southern California, 1996–98.
28 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

more pesticides (U.S. Geological Survey, 1999). The 

most common pesticide mixtures in streams draining 

urban land in the United States are shown in figure 15. 

The frequency of occurrence of these mixtures in 

stormflows in the Santa Ana River also is shown in 

figure 15. These data show that common pesticide 

mixtures occur more frequently in stormflows in the 

Santa Ana River basin than in streams draining urban 

areas elsewhere in the United States. 

The pesticide mixtures that occur in the Santa 

Ana River stormflows are different from the most 

common pesticide mixtures that occur in streams 

draining urban land in the United States. For example, 

during this study, 100 percent of the stormflow samples 

collected at Imperial Highway when flow was 

dominated by runoff from urban areas downstream 

from Prado Dam contained the insecticides diazinon, 

carbaryl, malathion, and chlorpyrifos, and the 

herbicides DCPA, and simazine (fig. 14). However, it is 

unclear if the frequency of pesticide detections during 

stormflow in the Santa Ana River is typical of the 

frequency of pesticide detections in stormflows from 

other streams in the United States (compiled data are 

not available to compare stormflow samples from the 

Santa Ana River with stormflow samples from urban 

streams in the United States).

Principal-Component Analysis

The occurrence of pesticides in stormflow is 

difficult to evaluate in a systematic manner because of 

the large number of compounds detected at wide 

concentration ranges. In addition, pesticides have 

different physical and chemical properties, different 

uses, different application rates, and different modes of 

transport and degradation in the environment. An 

analysis of the distribution and occurrence of each 

pesticide is beyond the scope of this report. To simplify 

interpretation of the data, principal-component analysis 

was used as a tool to identify pesticides that behave 

similarly in stormflow and formed the basis for much of 

the previous discussion.

Principal-component analysis is a multivariate 

statistical technique that transforms a set of 

intercorrelated variables, in this case the concentrations 

of the pesticides, into a new coordinate system 

(Kshirsagar, 1972; Morrison, 1976; Gnanadesikan, 

1977). The transformed variables are known as 

principal components. Principal components are 

uncorrelated linear combinations of the original 

variables. They have a mean of zero and the same 

variance as the original data set. The values of the 

principal components are known as scores, and the 

scores are calculated on the basis of the contribution of 

each variable to the principal component (Preisendorfer 

and others, 1981). The magnitude and direction (plus or 

minus) of the contribution of each variable to the 

principal-component score is described by an 

eigenvector.

The eigenvectors composing the first and second 

principal components are listed in table 3. Of the 10 

most commonly detected pesticides, the first principal 

component contains large positive eigenvectors for the 

insecticides diazinon, chlorpyrifos, and malathion. The 

second principal component contains large positive 

eigenvectors for the herbicides diuron and simazine and 

the insecticide carbaryl. On the basis of the data 

presented earlier (fig. 12), concentrations of diazinon, 

chlorpyrifos, and malathion change in a similar manner 

in stormflow. Concentrations of diuron, simazine, and 

Figure 15. Common pesticide mixtures and frequency 

of detection in urban streams in the United States and 

in stormflow in the Santa Ana River below Prado Dam 

and at the diversion downstream from Imperial 

Highway, southern California, 1996–98.
Stormflow Chemistry 29

carbaryl also change in a similar manner during 

stormflow (fig. 13), but these changes are different 

from changes in the concentrations of diazinon, 

chlorpyrifos, and malathion. With the exception of 

carbaryl, these similarities and differences also are 

reflected in the results of the median tests and box plots 

shown in figure 11. This suggests that grouping of 

pesticides on the basis of principal-component analysis 

is a reasonable approach to evaluating pesticide 

distribution in stormflow.

Comparison of the first and second principalcomponent scores (fig. 16) shows that there are 

differences between the pesticide concentrations in 

early season stormflows and late season stormflows. At 

first glance, these data suggest a “first-flush” response 

with respect to insecticides. However, these differences 

actually result from negative second principalcomponent scores during early season stormflows. 

These negative scores are consistent with lower 

concentrations of diuron and simazine observed in 

early season stormflows in comparison with late season 

stormflows. This may occur because of increased use of 

these herbicides during the rainy season. The largest 

second principal-component scores were calculated for 

samples collected during the recessional flow of the 

February 3–5, 1998, stormflow (fig. 16). This was one 

of the largest storms sampled and was the first of a 

series of El Niño-driven storms during one of the 

wettest Februarys on record. The data in figure 16 also 

show that the first principal-components score increase 

with increasing magnitude of the stormflows. This 

Table 3. Eigenvectors composing the first and second principal 

components of pesticides in stormflow in the Santa Ana River below 

Prado Dam and at the diversion downstream from Imperial 

Highway, southern California, 1996–98

[Pesticides listed in order of frequency of detection]

Pesticide First principal 

component

Second principal 

component

Most commonly detected pesticides

Simazine 0.02 0.42

DCPA −.13 .13

Diazinon .41 −.15

Prometon .16 .16

Carbaryl .27 .35

Atrazine −.14 .08

Matolachlor −.21 .13

Malathion .35 −.18

Diuron .11 .46

Chlorpyrifos .36 −.20

Other pesticides detected

Deethyl atrazine −0.13 0.02

Tebuthiuron .12 −.22

Lindane −.06 −.03

Cyanazine −.11 −.03

Bromacil −.11 .07

Triclopyr .06 −.12

Norflurazon −.05 .06

Trifluralin .13 .08

Napropamide .18 −.18

Benfluralin .26 .04

Pendimethalin .20 .00

2,4-D .20 −.01

Propoxur −.11 −.04

Pronamide .20 .00

DDE .10 .30

Figure 16. Principal-component scores calculated from pesticide 

concentrations in base flow and stormflow below Prado Dam and at 

the diversion downstream from Imperial Highway, southern 

California, 1996–98.
30 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

result is consistent with higher concentrations of the 

insecticides diazinon, chlorpyrifos, and malathion 

during larger stormflows derived as runoff from urban 

areas downstream from Prado Dam. A similar trend 

was not apparent for the second-principal-component 

scores.

Volatile Organic Compounds 

Volatile organic compounds (VOC) occur in 

numerous commercial and industrial products 

including fuels, solvents, paints, adhesives, 

deodorants, and refrigerants (Smith and others, 1988). 

In addition, VOCs also occur in combustion-engine 

exhaust and can be produced as a byproduct of 

chlorinating water containing high concentrations of 

DOC (Hoekman, 1992; Lopes and Bender, 1998; 

Lopes and Dionne, 1998). Volatile organic compounds 

have been detected in surface water throughout the 

United States ( Lopes and Bender, 1998; Lopes and 

Dionne, 1998; Reiser and O’Brien, 1998) and have 

been identified as potential contaminants in 38 percent 

of the community water systems in the United States 

(U.S. Environmental Protection Agency, 1997). There 

is increased concern about these compounds in urban 

areas because infiltration of stormwater containing 

VOCs associated with combustion-engine exhaust has 

been shown to contaminate ground water (Pritt and 

others, 1996; Maine Geological Survey, 1998). The 

potential effects of low concentrations of VOCs in 

drinking water are difficult to evaluate because of 

inadequate information on the effects of lowconcentration mixtures, transformation products, and 

long-term exposure.

Volatile organic compounds were collected 

during the 1997–98 rainy season. Because these 

compounds have a high vapor pressure, they could not 

be collected with the automated samplers used in this 

study. Instead, grab samples for VOCs were collected 

during the September 14–16, 1997, November 10–12, 

1997, and February 3–5, 1998, stormflows. Because 

manual collection was required, the number of VOC 

samples collected during most stormflows was fewer 

than the number of samples collected for other 

constituents. The most complete data set was obtained 

for the February 3, 1998, stormflow: during this 

stormflow, samples also were collected from a storm 

drain that discharges to the Santa Ana River at Imperial 

Highway (fig. 17).

Of the 29 VOCs analyzed, 5 were detected at low 

concentrations in stormflow from the Santa Ana River 

below Prado Dam and at Imperial Highway (Appendix 

F). These compounds included three chlorinated 

compounds, chloroform, dichloromethane, and 

bromodichloro-methane, and two compounds 

associated with combustion-engine exhaust, toluene 

and methyl tert-butyl ether (MTBE).

Maximum concentrations of chloroform, 

dichloromethane, and bromodichloro-methane were as 

high as 3.4, 1.3, and 0.6 μg/L, respectively. As a group 

these compounds are known as trihalomethanes and 

they are formed by the chlorination of water that has 

high DOC concentrations, but they also may be present 

from other sources. The USEPA MCL for total 

trihalomethanes is 100 μg/L (California Department of 

Water Resources, 1997). Chloroform, 

dichloromethane, and bromodichloro-methane were 

detected in 69, 16, and 28 percent, respectively, of all 

samples from the Santa Ana River. This frequency of 

detection is higher than the frequency reported for 

Figure 17. MTBE and chloroform concentrations in the Santa 

Ana River below Prado Dam, at the diversion downstream 

from Imperial Highway, and in a storm drain tributary to the 

Santa Ana River near Imperial Highway, southern California. 

(μg/L, microgram per liter)
Stormflow Chemistry 31

stormwater from urban areas in the United States by 

Lopes and Bender (1998) (table 4). This result is not 

unexpected given the large quantity of treated 

municipal wastewater discharged to the Santa Ana 

River.

Maximum concentrations of toluene and MTBE 

in stormflow were as high as 3.9 μg/L and an estimated 

0.7 μg/L, respectively, and MTBE concentrations in the 

storm drain were as high as an estimated 0.9 μg/L. The 

USEPA MCL for toluene is 1,000 μg/L, and the 

California Department of Health Services Action Level 

for MTBE is 35 μg/L (California Department of Water 

Resources, 1997). Toluene and MTBE were detected in 

8 and 88 percent, respectively, of stormflow samples 

from the Santa Ana River. The frequency of detection 

for toluene is less than detection nationally in urban 

stormwater reported by Lopes and Bender (1998). The 

frequency of detection for MTBE is much higher than 

that reported by Lopes and Bender (1998), possibly 

because of the high use of MTBE in gasoline as an 

oxygenate during the winter months in California. 

Concentrations of MTBE are within the range 

expected for surface water in equilibrium with urban 

air (Lopes and Bender, 1998). In contrast, maximum 

toluene concentrations are much higher than expected 

for surface water in equilibrium with urban air, 

suggesting that spills or other sources also may 

contribute toluene to urban stormwater in the Santa 

Ana River basin. Because toluene was not frequently 

detected, it is probable that these sources are small and 

that toluene is readily washed from the basin.

Changes in chloroform and MTBE 

concentrations during the February 3–4, 1998, 

stormflow for the Santa Ana River below Prado Dam 

and at Imperial Highway, and for the storm drain 

tributary to the Santa Ana River, are shown in figure 17. 

In general, concentrations of chloroform decreased 

during stormflow, which is consistent with dilution by 

treated municipal wastewater that is the principal 

source of base flow in the Santa Ana River. Similar 

patterns have been observed for chloroform and other 

trihalomethanes in stormflow in other parts of the 

Table 4. Volatile organic carbon compounds detected in the Santa Ana River below Prado Dam and at the diversion downstream from 

Imperial Highway, southern California, and at other urban sites across the United States, 1997–98

[Percent detection in urban stormwater from Lopes and Bender (1998). IUPAC, International Union of Pure and Applied Chemistry; —, no data]

1

Statistics calculated on the basis of 24 analyses collected during three stormflows: September 14–16, 1997; November 10–12, 1997; and 

February 3–5, 1998. Data given in Appendix F.

Compound 

(IUPAC nomenclature) Common name

Percent detection in

United States urban

stormwater

1Percent detection 

in Santa Ana River 

stormflow

Chlorinated Compounds

Trichloromethane chloroform 13 69

Tetrachloroethene perchloroethylene (PCE) 8.0 0

Dichloromethane methylene chloride 5.9 16

Bromodichloro-methane — 5.8 28

Trichloroethene trichloroethylene (TCE) 4.7 0

cis-1,2-Dichloroethene — 4.6 0

1,1,1-Trichloroethane 1,1,-TCA 4.2 0

Dibromochloro-methane — 3.4 —

Gasoline-Related Compounds

Methylbenzene toluene 23 8

Dimethylbenzene xylene 18 0

1,2,4,-Trimethyl-benzene — 12 0

Napthalene — 7.4 —

Methyl tert-butyl ether MTBE 6.9 88

Ethylbenzene — 5.0 0

Benzene — 3.9 0
32 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

country (Lopes and Bender, 1998; Reiser and O’Brien, 

1998). 

Concentrations of MTBE initially decreased and 

later increased during stormflow. The decreases in 

MTBE concentrations were not expected and have not 

been reported in stormwater from urban areas in other 

parts of the country (Lopes and Bender, 1998; Reiser 

and O’Brien, 1998); in general, MTBE concentrations 

increase during stormflow. One possible explanation 

for the decrease is that water in the Santa Ana River 

initially was in equilibrium with MTBE concentrations 

in the urban air, but the large amount and intensity of 

the precipitation removed available MTBE from the 

atmosphere faster than it could be replaced. Later in the 

storm, MTBE concentrations increased when water 

stored behind Prado Dam, which was in equilibrium 

with MTBE in the atmosphere, was released. Toluene 

was not detected in the Santa Ana River, or the storm 

drain, during the February 3–4, 1998, stormflow. 

Changes in Selected Trace-Element 

Concentrations During Stormflow 

Trace elements sampled as part of this study 

were dissolved iron, manganese, and zinc. Iron and 

manganese are redox-active elements, and high 

concentrations of these dissolved metals are usually 

attributed to low dissolved oxygen conditions. Zinc is 

commonly used to protect other metals from corrosion. 

Motor vehicles, and especially motor oils, are believed 

to be a major source of zinc in the urban environment 

(Wigington and others, 1983). In this study zinc was 

evaluated for use as an indicator of contamination from 

highways. Zinc may be suitable for this purpose 

because it is commonly present in urban runoff (Harter, 

1983; Schroeder, 1995), has been frequently detected 

in the Santa Ana River below Prado Dam (Burton and 

others, 1998), and is more soluble than other trace 

elements associated with street, highway, and other 

urban sources of contamination (Harter, 1983).

The median dissolved iron and dissolved 

manganese concentrations in base flow were 9.5 and 23 

μg/L, respectively; maximum concentrations were 14 

and 40 μg/L (fig. 18). The USEPA Secondary 

Maximum Contaminant Levels (SMCL) for iron and 

manganese are 300 and 50 μg/L, respectively 

(California Department of Water Resources, 1997). 

During this study, dissolved iron and dissolved 

manganese concentrations in the Santa Ana River 

typically increased during stormflows. The median 

dissolved iron concentrations in both early season and 

late season stormflows below Prado Dam and at 

Imperial Highway are statistically different from 

concentrations in base flow. Median dissolved 

manganese concentrations in early season and late 

season stormflows were not statistically different from 

concentrations in base flow. However, about 35 percent 

of the concentrations in early season stormflows and 10 

percent of the concentrations in late season stormflows 

exceeded the USEPA SMCL for manganese. 

Figure 18. Dissolved iron, manganese, and zinc 

concentrations in base flow, and in early season 

and late season stormflows in the Santa Ana River 

below Prado Dam and at the diversion 

downstream from Imperial Highway, southern 

California, 1995–98. (μg/L, microgram per liter)
Stormflow Chemistry 33

High dissolved iron and dissolved manganese 

concentrations in early season stormflows are 

associated with runoff from urban areas downstream 

from Prado Dam and with the recession of early season 

stormflows; they also are associated with increases in 

the concentrations of reduced forms of nitrogen and 

high concentrations of DOC. In late season stormflows 

high iron and manganese concentrations are associated 

with release of water held in storage behind Prado 

Dam, such as during the January 25–30, 1997, 

stormflow (fig. 19), and can be attributed to low 

dissolved oxygen conditions that may develop in the 

flooded wetlands behind the dam. 

During the 1997–98 rainy season, zinc 

concentrations in the Santa Ana River below Prado 

Dam were as high as 680 μg/L (December 5, 1997). 

High concentrations were not observed during other 

years and may have been related to nearby bridge 

construction. Equipment blanks and field blanks done 

during the 1997–98 rainy season showed no evidence 

of trace element contamination. Excluding these high 

concentrations, zinc in base flow (three samples) 

ranged from 8 to 46 μg/L. The USEPA SMCL for zinc 

is 5,000 μg/L. Median zinc concentrations were not 

significantly different during early season and late 

season stormflow, and concentrations do not increase 

consistently with increases in runoff from urban areas 

below Prado Dam. On the basis of these results, zinc in 

filtered water may be a poor indicator of runoff from 

urban areas.

Figure 19. Dissolved iron, manganese, and zinc concentrations during stormflow in the Santa Ana River below Prado Dam and at the 

diversion downstream from Imperial Highway, southern California: (A) October 30–November 1, 1996, (B) January 25–30, 1997, and (C) 

September 25–27, 1997. (μg/L, microgram per liter)

Figure 19. Continued.
34 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

DIVERSION OF STORMFLOWS AND THE EFFECTS 

ON THE QUALITY OF RECHARGE WATER

Base flow in the Santa Ana River is maintained 

almost entirely by discharge of treated municipal 

wastewater. At present (2000), as mentioned previously 

in this report, the management assumption guiding 

ground-water recharge operations is that stormflow in 

the Santa Ana River is “high-quality” water that is 

suitable for diversion to aquifers that are pumped for 

public supply (Orange County Water District, 1996b). 

Large quantities of water recharged during stormflows 

are believed to improve the overall quality of water 

recharged from the Santa Ana River (Orange County 

Water District, 1996b). In the past, there have been few 

data to support or refute this assumption. Results of this 

study show that stormflows are not of uniform 

chemistry and that there are large differences in the 

concentrations of selected constituents within 

individual stormflows and between stormflows during 

different parts of the rainy season.

At present, stormflow-management practices for 

ground-water recharge operations result in a reduction 

in the overall concentration of nitrate in water 

recharged from the Santa Ana River. High nitrate 

concentrations in base flow result from the discharge of 

treated municipal wastewater to the river (Burton and 

others, 1998). This study shows that nitrate 

concentrations decrease because of dilution during 

stormflow and, although concentrations of reduced 

forms of nitrogen (such as organic nitrogen) increase 

during stormflow, these increases do not result in an 

increase in total nitrogen. 

Existing management strategies are less effective 

in minimizing DOC concentrations in water diverted 

for ground-water recharge. DOC concentrations 

increase during stormflows. DOC concentrations and 

ultraviolet absorbance data suggest that DOC may be a 

concern for trihalomethane formation when water is 

chlorinated for use as a drinking-water supply. 

Increases in DOC are greatest during early season 

stormflows, especially when stormflow is primarily 

runoff from urban areas downstream from Prado Dam. 

High DOC concentrations also are present during the 

recessional flow of some early season stormflows. This 

may be a special concern because streamflow data, and 

other chemical data, suggest that DOC may be 

associated with runoff from the Cucamonga and Chino 

Creek drainage basins. Large numbers of animalconfinement facilities are located in these basins. 

However, land use in these basins is mixed and includes 

large urban areas. Early season stormflows represent 

only a small part of the annual flow in the Santa Ana 

River, and it may be possible to time diversions to 

minimize the quantity of this water that is recharged. 

High DOC concentrations also are present during 

stormflows that occur later in the rainy 

season—especially if water has been held in the 

flooded wetlands behind Prado Dam for some time. 

Water is stored behind Prado Dam to reduce peak flows 

and allow for increased diversion of stormflow to 

recharge aquifers underlying Orange County. As a 

result, it may be difficult to manage stormflow to 

reduce DOC concentrations from late season 

stormflows. However, stormflow is not used directly as 

a source of public supply, and DOC may degrade after 

recharge. The potential for DOC to be degraded or 

removed within aquifers prior to withdrawal is being 

addressed as part of the SARWQH study.

All pesticide concentrations were below their 

respective USEPA MCLs, and most pesticide 

concentrations were less than the reporting limit 

obtainable using standard drinking-water analyses. 

Therefore, at this time, pesticide concentrations are not 

an important concern in stormflow diverted for 

recharging aquifers pumped for water supply. 

However, the long-term health effects of low levels of 

pesticides are poorly understood, and it may be 

necessary to reduce pesticide concentrations in water 

diverted for recharge in the future. On the basis of data 

collected as part of this study, stormflow contains 

higher concentrations of pesticides than does base flow. 

Management of stormflow to reduce pesticide 

concentrations would require (1) deciding which 

pesticides need to be controlled, (2) improving 

understanding of pesticide use within the basin, and (3) 

then developing stormwater-management plans to 

exclude runoff from different areas in the basin. For 

example, runoff from urban areas downstream from 

Prado Dam contains the highest concentrations of 

diazinon, malathion, and chlorpyrifos, and runoff from 

areas upstream from Prado Dam contains the highest 

concentrations of DCPA, simazine, and diuron. As a 

result, stormwater-management strategies intended to 

reduce diazinon concentrations may be different from 

management strategies intended to reduce diuron 

concentrations.
Summary 35

SUMMARY

The Santa Ana River, located in an extensively 

urbanized basin, drains about 2,670 square miles near 

Los Angeles, California. Almost all the flow in the 

river, more than 200,000 acre-feet annually, is diverted 

into ponds where it infiltrates and recharges underlying 

aquifers. About 2 million people are dependent on 

these aquifers for water supply. Stormflow in the Santa 

Ana River is believed to be a source of “high-quality” 

water suitable for use as a source of water supply. To 

test this assumption, stormflow samples were collected 

at two locations, below Prado Dam and at the diversion 

point downstream from Imperial Highway, for 12 

winter storms between 1995 and 1998.

The quality of stormflow diverted for groundwater recharge at Imperial Highway is a result of the 

magnitude, timing, and distribution of runoff in the 

basin. The influence of urban areas downstream from 

Prado Dam on water quality is increased when runoff 

from upstream areas is held behind the dam to control 

peak flows. Stormflow quality also is altered for short 

periods when water stored behind the dam is released. 

Water stored behind Prado Dam is a mixture of base 

flow and water from previous storms. In addition, 

chemical and biochemical reactions or dissolution of 

soluble material from soil and plants in flooded 

wetlands behind the dam may alter the chemistry of 

this water. Changes in water chemistry also may occur 

if the channel of the Santa Ana River or its tributaries is 

disturbed by increased flow velocities that occur during 

stormflow. This may occur in the natural channels and 

in concrete-lined channels and storm drains as they are 

flushed clean during stormflow. 

The median nitrate concentrations in base flow 

was 7.3 mg/L as nitrogen, and maximum base-flow 

concentrations were as high as 9.1 mg/L as nitrogen. 

These values are near the MCL for nitrate of 10 mg/L 

as nitrogen. In general, stormflow is low in nitrogen 

and lowers the average concentration of nitrate in water 

recharged from the Santa Ana River. Reduced forms of 

nitrogen are the predominant forms of nitrogen during 

stormflow. In some stormflows, ammonia 

concentrations can exceed 2 mg/L as nitrogen. 

Ammonia can be toxic to fish at concentrations as low 

as 0.4 mg/L as nitrogen.

It is desirable to minimize the DOC in water 

recharged from the Santa Ana River because of health 

concerns about carbon of wastewater origin and 

because of concerns about trihalomethane formation. 

In the Santa Ana River, DOC concentrations increased 

during stormflow and were as high as 23 mg/L. DOC 

concentrations may be especially high during the first 

storm of the rainy season when highly mobile organic 

carbon that accumulates in urban areas downstream 

from Prado Dam during the dry season washes into the 

river. On the basis of DOC concentrations and UV 

absorbance data, DOC in stormflow may have a 

trihalomethane formation potential similar to that of 

imported water from northern California. On the basis 

of UV absorbance data, the composition of DOC from 

early season stormflows is different from the 

composition of DOC in water that has been stored in 

the flooded wetlands behind Prado Dam. 

Twenty-five pesticides were detected out of 87 

compounds analyzed. All pesticide concentrations 

were below their respective USEPA MCLs, and most 

pesticide concentrations were less than the reporting 

limit obtainable using standard drinking-water 

analytical methods. Only carbaryl, simazine, and 

diuron had maximum concentrations greater than 

1 μg/L. Although pesticide concentrations in Santa Ana 

River stormflow are not an important concern at this 

time, the long-term health effects of low concentrations 

of pesticides are poorly understood. On the basis of 

data collected as part of this study, stormflow contains 

higher concentrations of most pesticides than does base 

flow. Diazinon, malathion, and chlorpyrifos 

concentrations are higher in runoff from urban areas 

downstream from Prado Dam, and simazine, diuron, 

and carbaryl concentrations are higher in runoff from 

the upper basin. Pesticide concentrations in stormflow 

are related to the magnitude of the storm.

Five volatile organic carbon compounds were 

detected out of 29 compounds analyzed. All 

compounds were below their respective USEPA 

MCLs. Three chlorinated compounds (chloroform, 

dichloromethane, and bromodichloro-methane) 

associated with the chlorination of water containing 

high concentrations of DOC were detected. MTBE, a 

gasoline oxygenate widely used in California, was 

detected in 88 percent of stormflow samples. This is a 

much higher frequency of detection than recently 

reported frequencies of detection in United States 

urban stormwater.

In general, dissolved iron and dissolved 

manganese concentrations increased during stormflow 

and manganese concentrations occasionally exceeded 

the SMCLs of 300 and 50 μg/L, respectively. High iron 
36 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

and manganese concentrations are probably related to 

low dissolved oxygen conditions that develop in the 

flooded wetlands when stormflow water is stored 

behind Prado Dam. Zinc concentrations were generally 

low and zinc was not a good indicator of urban runoff.

REFERENCES CITED

Barbash, J.E., and Resek, E.A., 1996, Pesticides in ground 

water—distribution, trends, and governing factors: 

Chelsea, Michigan, Ann Arbor Press, Inc., 588 p.

Barber, L.B., II, 1992, Hierarchical analytical approach to 

evaluating the transport and biogeochemical fate of 

organic compounds in sewage-contaminated groundwater, Cape Cod, Massachusetts, in Lesage, S., and 

Jackson, R.E., eds., Groundwater contamination and 

analysis at hazardous waste sites: New York, Marcel 

Dekker, Inc., p. 73–120.

Black, A.P., and Christman, F., 1963, Characteristics of colored surface waters: Journal of American Water Works 

Association, v. 55, p. 753–770.

Burton, C.A., Izbicki, J.A., and Paybins, K.S., 1998, Waterquality trends in the Santa Ana River at MWD Crossing 

and below Prado Dam, Riverside County, California: 

U.S. Geological Survey Water-Resources Investigations Report 97-4173, 36 p.

California Department of Pesticide Regulation, 1995, Pesticide use data for 1995 [digital data]: Sacramento, 

California Department of Pesticide Regulation.

California Department of Water Resources, 1982, Mineral 

increases from municipal use of water in the Santa Ana 

River basin: Southern District, Memorandum Report.

———1994, Five-year report of the municipal water quality 

investigations program: variously paged.

———1997, Compilation of federal and state drinking 

water standards and criteria, Quality Assurance Technical Document 3, 56 p.

Cole, G.A., 1983, Textbook of Limnology (3d ed.): Prospect 

Heights, Illinois, Waveland Press, Inc., 401 p. 

Fujii, Roger, Ranalli, A.J., Aiken, G.R., and Bergamaschi, 

B.A., 1998, Dissolved organic carbon concentrations 

and compositions, and trihalomethane formation potentials in waters from agricultural peat soils, Sacramento–

San Joaquin Delta, California: Implications for 

drinking-water quality: U.S. Geological Survey WaterResources Investigations Report 98-4147, 75 p.

Gnanadesikan, R., 1977, Methods for statistical data analysis 

of multivariate observations: New York, John Wiley and 

Sons.

Gray, K.A., McAuliffe, K.S., Bornick, Robert, and Simpson, 

Allen, 1996, Evaluation of organic quality in Prado 

wetlands and Santa Ana River by pyrolysis-GC-MS: 

Department of Civil Engineering, Northwestern 

University, 100 p.

Gutsche, C.D., and Pasto, D.J., 1975, Fundamentals of 

organic chemistry: Englewood Cliffs, New Jersey, 

Prentice-Hall Inc., 1240 p.

Hart, H., and Schuetz, R.D., 1972, Organic chemistry: A 

short course (4th ed.): Boston, Houghton Mifflin 

Company, 499 p.

Harter, R.D., 1983, Effects of soil pH on adsorption of lead, 

copper, zinc, and nickel: Soil Science Society of America Journal, v. 47, p. 47–51.

Hoekman, S.K., 1992, Speciated measurements and calculated reactivities of vehicle exhaust emissions from 

conventional and reformulated gasolines: Environmental Science and Technology, v. 26, p.1206–1216.

Krazner, S.W., Croue, J.P., Buffle, Jacques, Perdue, E.M., 

1996, Three approaches for characterizing NOM: Journal of American Water Works Association, v. 88, 

p. 66–79.

Kshirsagar, A.M., 1972, Multivariate analysis: New York, 

Marcel Dekker.

Leenheer, J.A., and Huffman, E.W.D., Jr., 1976, Classification of organic solutes in water by using macroreticular 

resins: Journal of Research of the U.S. Geological 

Survey, v. 4, no. 6, p. 737–751.

Lopes, T.J., and Bender, D.A., 1998, Nonpoint sources of 

volatile organic compounds in urban areas—Relative 

importance of land surfaces and air: Environmental Pollution, v.101, p. 221–230.

Lopes, T.J., and Dionne, S.G., 1998, A review of semivolatile 

and volatile organic compounds in highway runoff and 

urban stormwater: U.S. Geological Survey Open-File 

Report 98-409, 67 p.

Maine Geological Survey, 1998, Presence of MTBE and 

other gasoline compounds in Maine’s drinking water 

supplies—A preliminary report: Augusta, Maine, 

Department of Conservation, 15 p.

Morrison, D.F., 1976, Multivariate statistical methods (2nd 

ed.): New York, McGraw-Hill.

Mrkva, M., 1983, Evaluation of correlations between absorbance at 254 nm and COD of river waters: Water 

Resources Research, v. 17 p. 231–235.

Muller, D.K., Hamilton, P.A., Helsel, D.R., Hitt, K.J., and 

Ruddy, B.C., 1995, Nutrients in ground water and surface water of the United States—an analysis of data 

through 1992: U.S. Geological Survey WaterResources Investigations Report 95-4031, 74 p.
References Cited 37

Muller, D.K., and Helsel, D.R., 1996, Nutrients in the 

nation’s waters, too much of a good thing?: U.S. 

Geological Survey Circular 1136, 24 p.

Neter, John, and Wasserman, William, 1974, Applied linear 

statistical models: Homewood, Illinois, Richard D. 

Irwin, Inc., 842 p.

O’Connor, K.A., 1995, Watershed management planning: 

Bringing the pieces together: M.S. thesis, California 

State Polytechnic University, Pomona, 166 p.

Orange County Water District, 1996a, Recharge—building 

groundwater reserves, Fountain Valley, California: 2 p.

———1996b, Santa Ana River water quality and health 

study: Proceedings from the Scientific Advisory Panel 

Briefing and Investigators Workshop, June 3–5, 1996, 

Fountain Valley, California, 307 p.

Panshin, S.Y., Dubrovsky, N.M., Gronberg, J.M., and 

Domagalski, J.L., 1998, Occurrence and distribution of 

dissolved pesticides in the San Joaquin River basin, 

California: Water-Resources Investigations Report 

98-4032, 88 p.

Paul, E.A., and Clark, F.E., 1996, Soil microbiology and biochemistry (2d ed.): New York, Academic Press, 340 p.

Preisendorfer, R.W., Zwiers, F.W., and Barnett, T.P., 1981, 

Foundations of principal component selection rules: 

SIO Reference Series 81-4: LaJolla, California, Scripps 

Institute of Oceanography, 191 p.

Pritt, R., Clark, S., Parmer, K., and Field, R., 1996, Groundwater contamination from stormwater infiltration: 

Chelsea, Michigan, Ann Arbor Press.

Reiser, R.G., and O’Brien, A.K., 1998, Occurrence and seasonal variability of volatile organic compounds in seven 

New Jersey streams: U.S. Geological Survey WaterResources Investigations Report 98-4074, 11 p.

Santa Ana Regional Water Quality Control Board, 1995, 

Water Quality Control Plan: Santa Ana Region VIII, 

Riverside, California, variously paged.

———1996, Dairy annual report: Santa Ana Region VIII, 

Riverside, California, 6 p.

Santa Ana River Watermaster, 1996, Twenty-fifth annual 

report of the Santa Ana River Watermaster, for water 

year October 1, 1994–September 30, 1995: San 

Bernardino, California, 25 p.

Schroeder, R.A., 1995, Potential for chemical transport 

beneath a storm-runoff recharge (retention) basin for an 

industrial catchment in Fresno, California: U.S. 

Geological Survey Water-Resources Investigations 

Report, 93-4140, 38 p.

Smith, J.A., Witkowski, P.J., and Fusillo, T.V., 1988, Manmade organic compounds in surface waters of the 

United States—A review of current understanding: 

U.S. Geological Survey Circular 1007, 92 p.

Thurman, E.M., 1985, Organic geochemistry of natural 

waters: Boston, Nijhoff and Junk, 497 p.

U.S. Army Corps of Engineers, 1994, Water control manual, 

Prado Dam and Reservoir, Santa Ana River, California: 

83 p.

U.S. Environmental Protection Agency, 1976, Quality criteria for water: Washington, D.C., 256 p.

———1986, Quality criteria for water: Washington D.C.

———1995, Methods for determination of organic compounds in drinking water—Supplement III: EPA/600/

R-95-131, Washington, D.C.

———1997, Community water system survey, Volume 1: 

Overview: Office of Water EPA 816-R-97-009.

U.S. Geological Survey, 1996, Pesticides in ground water: 

U.S. Geological Survey Fact Sheet FS-244-95, 4 p.

———1997, Pesticides in surface waters: U.S. Geological 

Survey Fact Sheet FS-039-97.

———1999, The quality of our nation’s waters, nutrients 

and pesticides: U.S. Geological Survey Circular 1225, 

82 p.

Wagner, R.J., Ebert, J.C., and Roberts, L.M., 1995, Are agricultural pesticides in surface waters of the central 

Columbia Plateau?: U.S. Geological Survey Fact Sheet 

FS-241-95.

Ware, G.W., 1982, Pesticides: Theory and application: San 

Francisco, W.H. Freeman and Company, 308 p.

Werner, S.L., Burkhardt, M.R., and DeRusseau, S.N., 1996, 

Methods of analysis by the U.S. Geological Survey 

National Water Quality Laboratory—Determination of 

pesticides in water by Carbopak-B solid-phase extraction and high-preformance liquid chromatography: 

U.S. Geological Survey Open-File Report 96-216, 42 p.

Wigington, P.J., Jr., Randall, C.W., and Grizzard, T.J., 1983, 

Accumulation of selected trace metals in soils of urban 

runoff retention basins: Water-Resources Bulletin, 

v. 19, p. 709–718.

Williamson, A.K., Munn, M.D., Ryker, S.J., Wagner, R.J., 

Ebbert, J.C., and Vanderpool, A.M., 1998, Water quality 

in the central Columbia Plateau, Washington and Idaho, 

1992–95: U.S. Geological Survey Circular 1144, 35 p.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, 

K.M., 1995, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—Determination of pesticides in water by C-18 

solid-phase extraction and capillary-column gas chromatography/mass spectrometry with selected-ion monitoring: U.S. Geological Survey Open-File Report 

95-181, 49 p.
THIS PAGE INTENTIONALLY LEFT BLANK
Appendix A 39

APPENDIX A

Quality-Assurance Procedures
40 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

APPENDIX A—QUALITY-ASSURANCE 

PROCEDURES

Quality assurance is defined as the procedures 

used to control the unmeasurable components of the 

sample collection, handling, and analysis procedures. 

Quality-assurance elements include standard operating 

procedures, instrument maintenance logs, and 

personnel training records. Quality-assurance 

procedures for this study had two components: field 

quality assurance implemented by study personnel and 

the laboratories’ internal quality assurance. 

Field Quality-Assurance Procedures

Field quality-assurance procedures included the 

collection and processing of samples using the 

following standard operating procedures and data 

tracking from the field to the lab. Environmental 

samples were collected using an automatic sampler or 

by grab sampling (VOC’s). The intake line for the 

automatic samplers were made from Teflon tubing 

encased in a steel pipe. The line was replaced between 

storm seasons. The bottom 4 feet of the intake line was 

encased with stainless steel to minimize contamination 

from metals. The automatic sampler was programed to 

rinse the intake line twice before collecting each 

sample. Samples were processed and equipment was 

cleaned using methods adopted from USGS protocols 

developed for analysis of trace constituents at the partper-billion level as described by Shelton (1994). All 

samples, except pesticides, were filtered in the field. 

Protocols for filtration and extraction of pesticides are 

complex and require specialized equipment. Pesticide 

samples were shipped to the USGS National Water 

Quality Laboratory (NWQL) for filtration and 

extraction prior to analysis. 

Water-quality field forms were started and 

bottles were labeled on site. Samples were tracked by 

logging them into the USGS National Water 

Information System (NWIS), giving each sample a 

unique record number. Instrument-maintenance logs 

are kept for all equipment used to measure field 

parameters. All employees that collect and process 

water-quality samples are required to participate in a 

yearly National Field-Quality Assurance Program. 

Samples were reviewed for completeness and accuracy 

by the NWQL and by field personnel prior to release to 

public data bases.

Contamination and variability were assessed 

through field quality assurance. Contamination was 

assessed with field blanks and variability was assessed 

with replicate samples. Field blanks were done on the 

collection and processing equipment. Replicates were 

done on all schedules used to analyze environmental 

samples.

Blank samples are collected and analyzed to 

ensure that environmental samples have not been 

contaminated by any part of the collection, handling, or 

processing procedures. Many types of blank samples 

are possible; each is designed to isolate a different part 

of the overall data-collection process. Field blanks 

subjected to all aspects of sample collection, field 

processing, preservation, transportation, and laboratory 

handling to which an environmental sample is 

subjected were done during each storm season. If field 

blanks show no evidence of contamination there is no 

need to process other types of sample blanks. Blank 

solutions, free of the analyses of interest, were used to 

prepare field blanks. Three types of water were used for 

field blanks for this study: pesticide-free water, 

volatile-free water, and inorganic-free deionized water. 

Results from field blanks were less than their 

respected detection limit for all constituents analyzed 

as part of this study except dissolved-organic carbon 

(DOC). DOC concentrations less than 0.3 mg/L were 

present in two field blanks. These concentrations are 

more than an order of magnitude less than 

concentrations of environmental samples collected as 

part of this study. The results for all pesticides in field 

blanks were less than their detection limits and show no 

contamination. This is important because in a study on 

field blanks by Martin and others (1999), data provided 

by the National Water-Quality Assessment Program, 

showed contamination in surface water for cispermethrin, pronamide, p'-DDE, pebulate, propargite, 

ethalfluralin, and triallate. Although not present in any 

field blanks, pronamide and p,p'DDE were 

occasionally detected at low concentrations as part of 

this study. 

Replicates were used to determine the variability 

associated with sample collection, handling, and 

analytical measurement of environmental samples. 

Replicate samples are a set of environmental samples 

collected in a manner such that the samples are thought 

to be virtually identical in composition. There are 

several types of replicate samples possible, and each 

may yield slightly different results in a dynamic 
Appendix A 41

hydrologic setting, such as a flowing stream. The type 

of replicate sampling done for this project is a split 

sample. A split sample is a sample that is split into 

subsamples contemporaneous in time and space. The 

variability between replicate samples is represented as 

the percent difference, which is the absolute difference 

between replicates divided by the average of the sum of 

the replicates times 100. The replicates on 

environmental samples analyzed at the NWQL are 

summarized in table A1, and replicates on samples 

analyzed at the USGS San Diego Laboratory are 

summarized in table A2. The median percent 

difference between an environmental sample and its 

replicate provides information on the typical 

variability of the data. In general, percent differences 

were greater when constituents were present at low 

concentrations. 

Only one replicate was done on pesticide 

samples because it was not possible to collect an extra 

2 liters of water with the automatic sampler. The 

pesticide replicate was collected using equal-width 

increments at a flume 100 ft downstream. The median 

percent difference for the 12 pesticides detected was 

18.7 percent. However, like the other constituents, the 

variability associated with pesticides is small in 

relation to the changes in concentration during 

stormflow.

Laboratory Quality-Assurance Procedures

Laboratory quality-assurance procedures 

included the determination of surrogate compound 

recoveries in each sample, laboratory reagent-water 

blanks, laboratory reagent-water spikes, and an 

assessment of the instrument system. The NWQL in 

Denver, Colorado, analyzed most samples. The USGS 

San Diego Laboratory analyzed samples for nitrate, 

nitrite, chloride, and sulfate.

U.S. Geological Survey National Water Quality Laboratory

The NWQL, the primary analytical facility of 

the USGS, analyzes environmental samples from 

across the United States and from around the world. 

The NWQL has formal quality-assurance procedures 

to assess contamination, bias, and variability. Samples 

of water, sediment, aquatic biological materials, and air 

are analyzed at the laboratory using state-of-the-art 

instruments and methods. 

The NWQL uses a three-tiered approach to 

quality control divided into inorganic and organic 

analyses. The three-tiered approach is explained in 

more detail in a USGS Fact Sheet (Pirkey and Glodt, 

1998). 

The first tier is “Method Performance.” At this 

level, a chemist uses quality-control sample data to 

evaluate the analytical process for each batch of 

environmental samples. If prescribed acceptable 

criteria are not met, the analysis is discontinued until 

corrected. The second tier is the “Data Review and 

Table A1. Replicate analyses by the USGS National Water Quality 

Laboratory.

[Constituents in milligrams per liter—except iron, manganese, and zinc, 

which are in micrograms per liter. All constituents dissolved—except suspended organic carbon]

Number 

of

duplicates

Range

 Median 

percent 

difference

Trace elements

Iron 3 <10−110 17

Manganese 3 25−81 1.6

Zinc 3 17−400 10

Nutrients

Nitrite as nitrogen 6 .05−.11 3.7

Nitrate plus nitrite as nitrogen 6 3.4−7.4 2.8

Ammonia as nitrogen 6 .10−.95 1.6

Ammonia plus organic nitrogen 

as nitrogen

6 .60−2.3 5.3

Phosphorus 6 .5−.94 1.6

Orthophosphorus as phosphorus 6 .48−.97 1.6

Organic Carbon

Dissolved organic carbon 5 4.0−16 14

Suspended organic carbon 4 2.8−16 8.2

Table A2. Replicate analyses by the USGS San Diego Laboratory

[mg/L, milligrams per liter]

Number of

duplicates

Range

(mg/L)

Median 

percent 

differences

Major ions

Sulfate 12 0.05–3.6 2.4

Chloride 12 1.3–15 1.1

Nutrients

Nitrite 14 .02–.24 2.9

Nitrate 14 .92–.4.6 1.6
42 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Blind Sample Programs.” Chemists use data from these 

programs to monitor method performance throughout 

the laboratory and over long periods of time. The 

USGS laboratories and all laboratories working 

cooperatively with the USGS are required to 

participate in a Standard Reference Water Sample 

(SRWS) program. The blind-sample program began in 

1962, and since 1966 it has used filtered natural surface 

water as the base from which to prepare reference 

materials. The third tier is NWQL’s participation in 

“Performance-Evaluation Studies.” Local, State, or 

Federal agencies external to the NWQL manage these 

studies. Data from these studies are used to compare 

laboratories. These studies are explained in more detail 

in the USGS Fact Sheet (Glodt and Pirkey, 1998). 

Summary reports from many of these studies are 

available on the NWQL web site home page at <http:/

/wwwnwql.cr.usgs.gov/USGS/perf_eval.html> and on 

the Branch of Quality Systems web site home page at 

<http://btdqs.usgs.gov>.

U.S. Geological Survey San Diego Laboratory

The USGS laboratory at the San Diego Project 

Office analyzed samples for nitrate, nitrite, chloride, 

and sulfate. These analyses are done by ion 

chromatography (American Public Health Association, 

1992) and were intended to supplement analyses done 

by the NWQL. Twice a year, the San Diego laboratory 

is a participant in the NWQL blind-sample program. 

To calibrate the instrument, standard-reference 

samples (calibration standards) are used. Calibration 

samples used were purchased from a vendor and 

checked with samples from the SRWS program. 

Blanks were done on water used to clean equipment 

and check for contamination. Nitrate and nitrite were 

not present above their detection limits in blank water 

samples, 0.01 and 0.02 mg/L, respectively. 

As part of this study an interlaboratory 

comparison was done for more than 50 nitrate samples 

analyzed by the NWQL and the San Diego laboratory 

(fig. A1). Comparison of the data between the two 

laboratories is generally good with an R2

 of 0.74. On 

the basis of results of the t-test with a confidence 

criterion of α=0.05, the slope of the line shown on 

figure A1 is not significantly different from 1, 

indicating a lack of bias to higher or lower values from 

either laboratory. 

REFERENCES CITED IN APPENDIX A

American Public Health Association, 1992, Standard methods for the examination of water and wastewater (18th 

ed.): variously paged.

Glodt, S.R., and Pirkey, K.D., 1998, Participation in performance-evaluation studies by U.S. Geological Survey 

National Water Quality Laboratory: U.S. Geological 

Survey Fact Sheet FS-023-98, 6 p.

Martin, J.D., Gilliom, R.J., and Schertz, T.L., 1999, Summary and evaluation of pesticides in field blanks collected for the National Water-Quality Assessment 

Program, 1992–95: U.S. Geological Survey Open-File 

Report 98-412, 102 p.

Pirkey, K.D., and Glodt, S.R., 1998, Quality control at the 

U.S. Geological Survey National Water Quality Laboratory: U.S. Geological Survey Fact Sheet FS-026-98, 4 p.

Shelton, L.R., 1994, Field guide for collecting and processing stream-water samples for the National Water-Quality Assessment Program: U.S. Geological Survey OpenFile Report 94-455, 42 p.

Figure A1. Comparison of nitrate analyses from different U.S. 

Geological Survey laboratories.
Appendix B 43

APPENDIX B

Sample Collection, Preservation, and Analytical Methods
44 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Table B1. Analytical methods and reporting limits

[std, standard; ASF, automated segmented flow; USGS, U.S. Geological Survey; UV, ultraviolet; GC/MS, gas chromatography/mass spectrometry; HPLC, 

high performance liquid chromatography. μS/cm, microsiemens per centimeter at 25°C; mg/L, milligrams per liter; deg. C, degrees Celsius; nm, nanometers; 

μg/L, micrograms per liter]

Constituent Methodology Reporting 

limit Reference

Field parameters

pH pH electrode 0.1 std. units Fishman and Friedman, 1989

Specific conductance Wheatstone bridge 1.0 μS/cm Fishman and Friedman, 1989

Alkalinity Titrimetry with sulfuric acid 1.0 mg/L Fishman and Friedman, 1989

Major ions

Sulfate, dissolved Ion chromatography .31 mg/L Fishman and Friedman, 1989

Chloride, dissolved Ion chromatography .1 mg/L Fishman and Friedman, 1989

Dissolved solids Gravimetric, residue on evaporation at 180 deg. C 10 mg/L Fishman and Friedman, 1989

Nutrients

Nitrite, dissolved Colorimetry, ASF .01 mg/L Fishman, M.J., 1993

Nitrite + nitrate, dissolved Colorimetry, ASF, cadmium reduction-diazotization .05 mg/L Fishman, M.J., 1993

Ammonia, dissolved Colorimetry, ASF, salicylate-hypochlorite .02 mg/L Fishman, M.J., 1993

Ammonia + organic nitrogen, total Colorimetry, ASF, microkjeldahl digestion .10 mg/L C.J. Patton, USGS, written 

commun., 1999 

Ammonia + organic nitrogen, dissolved Colorimetry, ASF, microkjeldahl digestion .10 mg/L Patton and Truitt, 1992

Phosphorus, total Colorimetry, ASF, microkjeldahl digestion .05 mg/L Patton and Truitt, 1992

Phosphorus, dissolved Colorimetry, ASF, microkjeldahl digestion .05 mg/L Patton and Truit, 1992

Orthophosphate, dissolved Colorimetry, ASF .01 mg/L Fishman, M.J., 1993

Organic carbon

Dissolved organic carbon UV-promoted persulfate oxidation .100 mg/L Brenton and Arnett, 1993

Suspended organic carbon Wet-chemical oxidation .2 mg/L Burkhardt and others, 1997

UV absorbance at 254 nm UV-visible spectrophotometry .02 nm American Public Health

Association, 1992

Selected organic compounds

Pesticides - USGS Schedule 2001 C-18 solid-phase extraction, GC/MS see Table B2 Zaugg and others, 1995

Pesticides - USGS Schedule 2050 Carbopak-B solid-phase extraction, HPLC see Table B3 Werner and others, 1996

Volatile organic compounds GC/MS see Table B4 Connor and others, 1997

Trace elements

Iron, dissolved Inductively coupled plasma 10.0 μg/L Fishman, 1993

Manganese, dissolved Inductively coupled plasma 3.0 μg/L Fishman, 1993

Zinc, dissolved Inductively coupled plasma 20.0 μg/L Fishman, 1993

APPENDIX B—SAMPLE COLLECTION,

PRESERVATION, AND ANALYTICAL METHODS

Samples from the two storms obtained during the 

winter of 1995–96 were collected using depthintegrated samplers and equal-width-increment 

methodology (Wilde and others, 1999) following the 

protocols in Horowitz and others (1994). Bottles 

provided by Orange County Water District (OCWD) 

were filled and sent to OCWD for processing and 

analysis. 

Samples from 10 storms sampled during the 

winters of 1996–97 and 1997–98 were collected using 

automated samplers. Field parameters (pH, specific 

conductance, and alkalinity) were measured for each 

sample. Selected samples were processed in the field 

and sent to the U.S. Geological Survey’s National 

Water Quality Laboratory (NWQL) for analysis. 
Appendix B 45

Table B2. Pesticides determined by C-18 solid-phase extraction and gas chromatography/mass spectrometry

[Reporting limits in micrograms per liter]

Pesticide Reporting limit Pesticide Reporting limit

2,6-Diethylaniline 0.003 Metribuzin 0.004

Acetochlor .002 Molinate .004

Alachlor .002 Napropamide .003

Atrazine .001 Parathion .004

Azinphos-methyl .001 Parathion-methyl .006

Benfluralin .002 Pebulate .004

Butylate .002 Pendimethalin .004

Carbaryl .003 Phorate .002

Carbofuran .003 Prometon .018

Chlorpyrifos .004 Pronamide (Propyzamide) .003

Cyanazine .004 Propachlor .007

DCPA (Dacthal) .002 Propanil .004

Deethyl atrazine .002 Propargite .013

Diazinon .002 Simazine .005

Dieldrin .001 Tebuthiuron .010

Disulfoton .017 Terbacil .007

EPTC .002 Terbufos .013

Ethalfluralin .004 Thiobencarb .002

Ethoprophos .003 Triallate .001

Fonofos .003 Trifluralin .002

Lindane .004 alpha-HCH .002

Linuron .002 cis-Permethrin .005

Malathion .005 p,p'-DDE .006

Metolchlor .002

Table B3. Pesticides determined by Carbopak-B solid-phase extraction and high performance liquid chromatography

[Reporting limits in micrograms per liter]

Pesticide Reporting limit Pesticide Reporting limit

2,4,5-T 0.040 Dichlobenil 0.07 

2,4-D .11 Dichlorprop .032 

2,4-DB .10 Dinoseb .06 

2-(2,4,5-Trichlorophenoxy)propionic acid .06 Diuron .06 

3-Hydroxycarbofuran .11 Fenuron .07 

4,6-Dinitro-2-methylphenol .42 Fluometuron .06 

Acifluorfen .09 MCPA, ((4-chloro-2-methly)phenoxyaceyic acid) .17 

Aldicarb .21 MCPB, (4-(4-chloro-2-methlyphenoxy)butoanoic acid) .13 

Aldicarb sulfone .10 Methiocarb .026 

Aldicarb sulfoxide .021 Methomyl .017 

Bentazon .035 Neburon .07 

Bromacil .06 Norflurazon .042 

Bromoxynil .04 Oryzalin .31 

Chloramben .14 Oxamyl .018 

Chlorothalonil .48 Picloram .05 

Clopyralid .23 Propham .035 

Dacthal monoacid .039 Propoxur .08 

Dicamba .043 Triclopyr .25 
46 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Table B4. Volatile organic compounds and reporting limits

[Compound names in International Union of Pure and Applied Chemitry nomenclature, common names given in parentheses. Reporting limits in micrograms 

per liter]

Compound Reporting 

limit Compound Reporting limit

1,1,1,2,2,2-Hexachloroethane 0.19 2,2-Dichloropropane 0.05 

1,1,1,2-Tetrachloroethane .03 2,2'-Oxybis[propane] (Diisopropyl ether) .10 

1,1,1-Trichloroethane .032 2-Butanone 1.6 

1,1,2,3,4,4-Hexachloro-1,3-butadiene .14 2-Ethoxy-2-methylpropane (Ethyl tert-butyl ether, ETBE) .054 

1,1,2,2-Tetrachloroethane .09 2-Hexanone .7 

1,1,2-Trichloroethane .06 2-Methoxy-2-methyl butane (tert-Pentyl methyl ether) .11 

1,1,2-Trichloro-1,2,2-trifluoroethane .06 2-Methoxy-2-methylpropane (Methyl tert-butyl ether, MTBE) .17 

1,1,2-Trichloroethene (Trichloroethylene) .038 2-Methyl-2-propenenitrile (Methyl acrylonitrile) .6 

1,1-Dichloroethane .066 2-Propanone (Acetone) 7 

1,1-Dichloroethene (1,1-Dichloro-ethylene) .04 2-Propenenitrile (Acrylonitrile) 1.2 

1,1-Dichloropropene .026 3-Chloro-1-propene .20 

(1,1-Dimethylethyl)benzene (tert-Butylbenzene) .06 4-Methyl-2-pentanone .37 

1,1'-Oxybisethane (Diethyl ether) .17 Benzene .035 

1,2,3,4-Tetramethylbenzene .23 Bromobenzene .036 

1,2,3,5-Tetramethylbenzene .20 Bromochloromethane .044 

1,2,3-Trichlorobenzene .27 Bromodichloromethane .048 

1,2,3-Trichloropropane .16 Bromoethene (Vinyl bromide) .10 

1,2,3-Trimethylbenzene .12 Bromomethane .26 

1,2,4-Trichlorobenzene .19 n-Butylbenzene .19 

1,2,4-Trimethylbenzene .056 Chlorobenzene .028 

1,2-Dibromo-3-chloropropane .21 Chloroethane .12 

1,2-Dibromoethane .036 Chloroethene (Vinyl chloride) .11 

1,2-Dichlorobenzene .048 Chloromethane .5 

1,2-Dichloroethane .13 Dibromochloromethane .18 

cis-1,2-Dichloroethene .038 Dibromomethane .050 

trans-1,2-Dichloroethene .032 Dichlorodifluoromethane .27 

1,2-Dichloropropane .068 Dichloromethane (methylene chloride) .38 

1,2-Dimethylbenzene (o-Xylene) .038 Dithiocarbonic anhydride (Carbon disulfide) .07 

1,3,5-Trimethylbenzene .044 Ethenylbenzene (Styrene) .042 

1,3-Dichlorobenzene .054 Ethylbenzene .030 

1,3-Dichloropropane .12 Ethyl 2-methyl-2-propanoate (Ethyl methacrylate) .18 

cis-1,3-Dichloropropene .09 Iodomethane (Methyl iodide) .12 

trans-1,3-Dichloropropene .09 Methylbenzene (Toluene) .05 

1,3- and 1,4-dimethylbenzene (m- and p-Xylene) .06 Methyl 2-methyl-2-propenoate (Methyl methacrylate) .35 

1,4-Dichlorobenzene .050 Methyl-2-propenoate (Methyl acrylate) 1.4 

trans-1,4-Dichloro-2-butene .7 Naphthalene .25 

1,4-Epoxybutane (Tetrahydrofuran) 2.2 n-Propylbenzene .042 

1-Chloro-2-methylbenzene (o-Chlorotoluene, 2-Chlorotoluene) .042 Tetrachloroethene .10 

1-Chloro-4-methylbenzene (p-Chlorotoluene, 4-Chlorotoluene) .06 Tetrachloromethane .06 

1-Ethyl-2-methylbenzene (o-Ethyl toluene) .06 Tribromomethane (Bromoform) .06 

1-Isopropyl-4-methylbenzene .07 Trichlorofluoromethane .09 

(1-Methylethyl)benzene (Isopropylbenzene) .032 Trichloromethane (Chloroform) .052 

(1-Methylpropyl)benzene (sec-Butylbenzene) .032 
Appendix B 47

Samples for inorganic analysis were filtered in the field 

using a capsule filter having a pore size of 0.45-μm 

(Shelton, 1994). Nutrients were preserved by chilling 

at 4o

C and were analyzed within 7 days. Trace 

elements were preserved by acidification to pH < 2.0. 

Dissolved and suspended organic carbon samples were 

filtered with a stainless steel filtration unit that holds a 

silver filter with a 0.45 μm pore size (Shelton, 1994). 

Pesticide samples were shipped to the NWQL for 

filtering through a glass fiber filter and solid-phase 

extraction (Shelton, 1994; Werner and others, 1996; 

Zaugg and others, 1995). Grab samples for volatile 

organic compound samples were collected in septum 

bottles and preserved by acidifying with 1:1 

hydrochloric acid. Analytical methods and associated 

reporting limits are listed in tables B1–4.

Selected samples were analyzed in the San 

Diego Projects Office laboratory for anions (chloride, 

sulfate, nitrate) utilizing ion chromatography (U.S. 

Environmental Protection Agency, 1998). UV 

absorbance scans from 200 to 800 nm were done for 

selected samples. UV absorbance samples collected 

during the 1995–96 and 1996–97 rainy seasons were 

filtered through a 0.8-mm membrane filter and 

analyzed by Scripps Institute of Oceanography by 

ultraviolet-visible spectrophotometry (American 

Public Health Association, 1995). UV samples 

collected during the 1997–98 rainy season were filtered 

in the field through 0.45-μm pore size silver filters, in 

the same manner as dissolved organic carbon samples, 

and analyzed by Scripps Institute of Oceanography.

REFERENCES CITED IN APPENDIX B

American Public Health Association, 1992, Standard methods for the examination of water and wastewater (18th 

ed.): variously paged.

Brenton, R.W., and Arnett, T.L., 1993, Methods of analysis 

by the U.S. Geological Survey National Water Quality 

Laboratory—Determination of dissolved organic carbon by UV-promoted persulfate oxidation and infrared 

spectrometry: U.S. Geological Survey Open-File 

Report 92-480, 12 p.

Burkhardt, M.R., Kammer, J.A., Jha, V.K., O’Mara-Lopez, 

P.G., and Woodworth, M.T., 1997, Methods of analysis 

by the U.S. Geological Survey National Water Quality 

Laboratory—Determination of nonpurgeable suspended organic carbon by wet-chemical oxidation and 

infrared spectrometry: U.S. Geological Survey OpenFile Report 97-380, 12 p.

Connor, B.F., Rose, D.L., Noriega, M.C., Murtagh, L.K., and 

Abney, S.R., 1997, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—Determination of 86 volatile organic compounds 

in water by gas chromatography/mass spectrometry, 

including detections less than reporting limits: U.S. 

Geological Survey Open-File Report 97-829

Fishman, M.J., 1993, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—Determination of inorganic and organic constituents in water and fluvial sediments: U.S. Geological 

Survey Open-File Report 93-125, 217 p.

Fishman, M.J., and Friedman, L.C., 1989, Methods for 

determination of inorganic substances in water and fluvial sediments: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 5, Chapt. A1, 

545 p.

Horowitiz, A.J., Demas, C.R., Fitzgerald, K.K., Miller, T.L., 

and Rickert, D.A., 1994, U.S. Geological Survey protocol for the collection and processing of surface-water 

samples for the subsequent determination of inorganic 

constituents in filtered water: U.S. Geological Survey 

Open-File Report 94-539, 57 p.

Patton, C.J., and Truitt, E.P., 1992, Methods of analysis by 

the U.S. Geological Survey National Water Quality 

Laboratory—Determination of total phosphorus by a 

Kjedahl digestion method and an automated colorimetric finish that include dialysis: U.S. Geological Survey 

Open-File Report 92-146, 39 p.

Shelton, L.R., 1994, Field guide for collecting and processing stream-water samples for the National Water-Quality Assessment Program: U.S.Geological Survey OpenFile Report 94-455, 42 p.

U.S. Environmental Protection Agency, 1998, Method 

300.1: Determination of inorganic cations in drinking 

water by ion chromatography, revision 1.0: EPA 

600-R-98-118.

Werner, S.L., Burkhardt, M.R., and DeRusseau, S.N., 1996, 

Methods of analysis by the U.S. Geological Survey 

National Water Quality Laboratory—Determination of 

pesticides in water by Carbopak-B solid-phase extraction and high-performance liquid chromatography: 

U.S. Geological Survey Open-File Report 96-216, 42 p.

Wilde, F.D., Radtke, D.B., Gibs, Jacob, and Iwatsubo, R.T., 

1999, Collection of water samples, in National Field 

Manual for the Collection of Water-Quality Data: U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, book 9, chap. A4, variously paged.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, 

K.M., 1995, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of pesticides in water by C-18 solid-phase 

extraction and capillary-column gas chromatography/

mass spectrometry with selected-ion monitoring: U.S. 

Geological Survey Open-File Report 95-181, 60 p.
THIS PAGE INTENTIONALLY LEFT BLANK
Appendix C 49

 APPENDIX C

Data for Field Parameters, Major Ions, 

Nutrients, and Selected Trace Elements
50 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Station no. Date Time Streamflow (f3/s) Specific conductance (μS/cm) pH (standard units) Alkalinity (mg/L as CaCO3) Sulfate, dissolved (mg/L as SO4) Chloride, dissolved (mg/L as Cl) Dissolved solids (mg/L) Nitra

disso

(mg/L 

11074000 10/30/96 1045 90 966 8.1 200 110 100 598 811074000 10/30/96 1215 106 996 7.6 —————11074000 10/30/96 1415 89 898 7.8 174 100 99 556 911074000 10/30/96 1615 148 890 7.6 —————11074000 10/30/96 1815 153 842 7.4 172 96 86 526 811074000 10/30/96 1900 155 835 7.7 —————11074000 10/30/96 2100 155 721 7.5 162 97 87 520 811074000 10/30/96 2300 159 767 7.6 —————11074000 10/31/96 0100 159 714 7.3 141 83 76 452 711074000 11/21/96 0730 217 908 7.9 183 98 92 — 811074000 11/21/96 0830 226 918 8.0 — 110 93 — 811074000 11/21/96 0930 157 909 8.0 — 100 91 — 511074000 11/21/96 1030 110 804 8.0 167 97 80 — 711074000 11/21/96 1638 100 860 8.0 — 110 88 — 511074000 11/21/96 1838 102 764 8.0 — 110 74 — 311074000 11/21/96 2038 105 721 8.0 — 87 66 — 411074000 11/21/96 2238 111 690 7.8 — 67 61 — 411074000 11/22/96 0038 114 623 7.8 — 62 55 — 311074000 11/22/96 0238 113 610 7.8 — 73 57 — 311074000 11/22/96 0438 116 628 7.7 96 83 61 — 411074000 11/22/96 0715 118 623 7.4 91 89 66 — 311074000 11/24/96 0011 505 514 7.6 — 55 47 — 211074000 11/24/96 0341 506 510 7.6 — 54 48 — 211074000 11/24/96 0711 505 510 7.6 109 56 44 — 211074000 11/24/96 1041 505 507 7.5 — 55 45 — 211074000 11/24/96 1411 505 534 7.5 — 56 46 — 211074000 11/24/96 1741 504 557 7.6 — 57 47 — 211074000 11/24/96 2111 504 579 7.6 — 58 49 — 211074000 11/25/96 0041 505 559 7.6 — 57 47 — 211074000 11/25/96 0411 505 545 7.5 — 58 47 — 211074000 11/25/96 0741 504 544 7.6 — 59 48 — 211074000 11/25/96 1111 495 551 7.6 — 59 48 — 211074000 11/25/96 1441 500 585 7.6 — 62 52 — 211074000 12/9/96 1244 243 970 8.1 208 110 93 — 511074000 12/9/96 1444 243 990 8.1 — 100 89 — 6

11074000 12/9/96 1644 424 949 8.1

— 100 99

— 6

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the divers

Highway, southern California

[Alkalinity measured as filtered incremental titrations. 11074000, Santa Ana River below Prado Dam; 11075620, Santa Ana River at the diversion downstream from Im

ond; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligram per liter; μg/L, microgram per liter; <, less than; —, no data] 
Appendix C 51

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the diver

Highway, southern California—Continued

Station no. Date Time

Ammonia,

dissolved

(mg/L as N)

Ammonia +

organic 

nitrogen

(mg/L as N)

Ammonia + 

organic

nitrogen, 

dissolved

(mg/L as N)

Phosphorus,

total

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Orthophosphate,

dissolved

(mg/L as P)

Iron,

dissolved

(μg/L)

11074000 10/30/96 1045 0.16 2.4 0.8 0.72 0.89 0.92 10 11074000 10/30/96 1215 — — — — — — — 11074000 10/30/96 1415 .53 2.5 1.8 1.2 .94 .95 30 11074000 10/30/96 1615 — — — — — — — 11074000 10/30/96 1815 .35 2.4 1.6 1.1 .88 .87 50 11074000 10/30/96 1900 — — — — — — — 11074000 10/30/96 2100 .61 3.2 2.3 1.1 .82 .82 90 11074000 10/30/96 2300 — — — — — — — 11074000 10/31/96 0100 .26 3.0 2.0 1.1 .80 .77 80 11074000 11/21/96 0730 .11 — .6 — .99 .40 — 11074000 11/21/96 0830 — — — — — .70 — 11074000 11/21/96 0930 — — — — — < .60 — 11074000 11/21/96 1030 .31 — 1.8 — .82 .77 — 11074000 11/21/96 1638 — — — — — < .60 — 11074000 11/21/96 1838 — — — — — < .60 — 11074000 11/21/96 2038 — — — — — .40 — 11074000 11/21/96 2238 — — — — — .50 — 11074000 11/22/96 0038 — — — — — .60 — 11074000 11/22/96 0238 — — — — — .30 — 11074000 11/22/96 0438 .34 — 1.4 — .79 .71 — 11074000 11/22/96 0715 .31 — 1.8 — .78 .68 — 11074000 11/24/96 0011 — — — — — — — 11074000 11/24/96 0341 — — — — — < .60 — 11074000 11/24/96 0711 .35 — 1.4 — .59 .51 — 11074000 11/24/96 1041 — — — — — .30 — 11074000 11/24/96 1411 — — — — — .40 — 11074000 11/24/96 1741 — — — — — .50 — 11074000 11/24/96 2111 — — — — — — — 11074000 11/25/96 0041 — — — — — .50 — 11074000 11/25/96 0411 — — — — — .40 — 11074000 11/25/96 0741 — — — — — .60 — 11074000 11/25/96 1111 — — — — — .50 — 11074000 11/25/96 1441 — — — — — .50 — 11074000 12/9/96 1244 .53 — 1.0 — .92 .96 — 11074000 12/9/96 1444 — — — — — .60 — 11074000 12/9/96 1644 — — — — — < .30 — 
52 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the divers

Highway, southern California—Continued Station no. Date Time Streamflow (f3/s) Specific conductance (μS/cm) pH (standard units) Alkalinity (mg/L as CaCO3) Sulfate, dissolved (mg/L as SO4) Chloride, dissolved (mg/L as Cl) Dissolved solids (mg/L) Nitra

disso

(mg/L 

11074000 12/9/96 1844 57 868 8.0 179 89 93 — 711074000 12/9/96 2044 204 579 8.0 — 79 55 — 411074000 12/9/96 2244 217 650 8.0 — 76 65 — 411074000 12/10/96 0044 168 631 8.0 132 66 59 — 411074000 12/10/96 0244 172 538 8.0 — 73 48 — 311074000 12/10/96 0734 184 542 7.8 114 62 49 — 311074000 12/10/96 1134 368 473 7.8 — 49 41 — 211074000 12/10/96 1534 356 472 7.9 104 53 42 — 311074000 12/10/96 1934 370 459 8.0 — 51 41 — 211074000 12/10/96 2334 372 445 7.8 99 47 38 — 311074000 12/11/96 0334 379 458 7.8 — 50 40 — 311074000 12/11/96 0734 379 467 7.9 106 52 41 — 311074000 12/11/96 1134 268 511 7.9 — 55 44 — 311074000 12/17/96 0421 517 665 7.8 189 66 62 — 211074000 1/19/97 2304 461 578 7.9 — 55 54 — 211074000 1/20/97 0204 461 600 7.9 — 59 53 — 211074000 1/20/97 0504 461 610 7.9 — 57 52 — 311074000 1/20/97 0804 460 620 7.7 142 60 58 374 311074000 1/20/97 1119 394 640 7.7 — 59 54 — 311074000 1/20/97 1419 394 638 7.6 150 62 59 391 311074000 1/20/97 1719 394 656 7.6 — 61 55 — 311074000 1/20/97 2019 394 630 7.6 — 58 53 — 311074000 1/25/97 1157 520 708 7.9 145 67 67 416 411074000 1/25/97 1757 526 698 7.7 130 68 66 424 411074000 1/25/97 2357 2510 658 7.8 125 59 57 — 311074000 1/26/97 1430 5490 524 7.5 104 45 46 306 111074000 1/26/97 2030 4850 440 7.7 — 34 32 — 111074000 1/26/97 2359 5030 386 8.1 — 28 27 — 111074000 1/27/97 1300 4760 381 7.8 104 28 26 228 11074000 1/27/97 1900 1600 388 7.7 — 25 24 — 11074000 1/28/97 0100 1320 390 7.6 — 26 25 — 11074000 1/28/97 0700 1300 397 7.7 — 27 — — 111074000 1/28/97 0904 861 406 7.9 — 27 26 — 11074000 1/28/97 1504 394 416 7.9 — 30 28 — 111074000 1/28/97 2104 398 397 7.7 — 27 26 — 11074000 1/29/97 0304 397 411 7.7 — 29 28 — 111074000 1/29/97 0700 394 417 7.8 — 31 28 — 111074000 1/29/97 1300 610 420 8.0 — 31 28 — 1
Appendix C 53

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the diversHighway, southern California—Continued

Station no. Date Time

Ammonia,

dissolved

(mg/L as N)

Ammonia +

organic 

nitrogen

(mg/L as N)

Ammonia + 

organic

nitrogen, 

dissolved

(mg/L as N)

Phosphorus,

total

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Orthophosphate,

dissolved

(mg/L as P)

Iron,

dissolved

(μg/L)

11074000 12/9/96 1844 0.90 — 1.6 — 1.0 0.94 — 11074000 12/9/96 2044 — — — — — < .30 — 11074000 12/9/96 2244 — — — — — < .30 — 11074000 12/10/96 0044 .38 — 1.0 — .54 .50 — 11074000 12/10/96 0244 — — — — — .30 — 11074000 12/10/96 0734 .32 — .9 — .51 .49 — 11074000 12/10/96 1134 — — — — — < .30 — 11074000 12/10/96 1534 .26 — .7 — .45 .44 — 11074000 12/10/96 1934 — — — — — .40 — 11074000 12/10/96 2334 .35 — .8 — .47 .46 — 11074000 12/11/96 0334 — — — — — .90 — 11074000 12/11/96 0734 .37 — .8 — .51 .49 — 11074000 12/11/96 1134 — — — — — .30 — 11074000 12/17/96 0421 1.2 — 2.3 — 1.1 1.1 — 11074000 1/19/97 2304 — — — — — — — 11074000 1/20/97 0204 — — — — — — — 11074000 1/20/97 0504 — — — — — — — 11074000 1/20/97 0804 1.4 3.5 2.7 1.3 1.1 .99 70 11074000 1/20/97 1119 — — — — — — — 11074000 1/20/97 1419 1.4 3.3 2.6 1.3 1.1 1. 0 40 11074000 1/20/97 1719 — — — — — — — 11074000 1/20/97 2019 — — — — — — — 11074000 1/25/97 1157 1.8 3.3 3.2 1.3 1.4 1.1 60 11074000 1/25/97 1757 1.9 4.1 3.2 1.6 1.3 1.1 60 11074000 1/25/97 2357 — — — — — < .30 — 11074000 1/26/97 1430 2.2 4.8 3.5 2.0 1.4 1.2 160 11074000 1/26/97 2030 — — — — — 1. 0 — 11074000 1/26/97 2359 — — — — — .80 — 11074000 1/27/97 1300 1.7 5.2 2.8 2.2 1.2 1. 0 40 11074000 1/27/97 1900 — — — — — .80 — 11074000 1/28/97 0100 — — — — — 1.1 — 11074000 1/28/97 0700 — — — — — 1. 0 — 11074000 1/28/97 0904 — — — — — 1.3 — 11074000 1/28/97 1504 — — — — — 1.6 — 11074000 1/28/97 2104 — — — — — 1.3 — 11074000 1/29/97 0304 — — — — — .90 — 
54 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the divers

Highway, southern California—Continued Station no. Date Time Streamflow (f3/s) Specific conductance (μS/cm) pH (standard units) Alkalinity (mg/L as CaCO3) Sulfate, dissolved (mg/L as SO4) Chloride, dissolved (mg/L as Cl) Dissolved solids (mg/L) Nitra

disso

(mg/L 

11074000 1/29/97 1900 618 433 7.9 — 32 30 — 111074000 1/30/97 0100 625 460 8.0 — 32 31 — 111074000 1/30/97 0700 618 470 8.0 — 36 33 — 111074000 1/30/97 1300 457 474 7.9 — 36 33 — 111074000 9/14/97 2240 376 616 7.9 124 61 73 380 211074000 9/15/97 0240 362 584 7.9 125 61 76 385 311074000 9/15/97 0640 372 579 7.7 114 58 68 362 311074000 9/15/97 1040 372 623 7.7 — 62 74 399 411074000 9/15/97 1250 372 634 7.8 124 62 71 395 411074000 9/15/97 1415 376 654 7.7 — 72 77 — 211074000 9/15/97 1845 387 632 7.9 133 65 71 412 311074000 9/15/97 2315 390 635 8.0 — 65 74 — 111074000 9/16/97 0215 390 645 7.9 — 70 80 — 211074000 9/16/97 0515 398 655 8.0 — 69 77 — 211074000 9/16/97 0815 401 652 8.1 —————11074000 9/16/97 1115 352 674 8.1 — 69 77 — 211074000 9/24/97 1937 355 632 7.9 — 20 68 370 211074000 9/24/97 2107 355 621 8.0 — 16 68 — 211074000 9/24/97 2237 355 622 8.0 — 58 68 — 211074000 9/25/97 0007 355 620 8.2 — 56 67 — 211074000 9/25/97 0137 359 622 8.2 — 56 67 — 211074000 9/25/97 0307 359 623 8.1 — 55 67 — 211074000 9/25/97 0437 362 623 8.0 — 41 68 380 311074000 9/25/97 0607 362 626 8.0 — 56 69 — 311074000 9/25/97 0737 367 632 8.0 — 49 69 370 311074000 9/25/97 0907 369 634 7.9 — 58 70 — 311074000 9/25/97 1037 222 640 7.8 — 58 69 390 311074000 9/25/97 1207 209 620 7.9 — 55 66 — 311074000 9/25/97 1337 258 638 7.9 — 57 67 — 411074000 9/25/97 1507 275 664 7.7 — 62 69 440 511074000 9/25/97 1637 284 569 7.6 — 53 54 — 411074000 9/25/97 1807 290 538 7.6 — 53 50 — 411074000 9/25/97 1937 294 554 7.4 — 58 53 — 411074000 9/25/97 2107 300 572 7.4 — 61 54 — 411074000 9/25/97 2237 305 556 7.4 — 59 53 — 411074000 9/26/97 0007 312 574 7.4 — 62 53 — 411074000 9/26/97 0137 312 639 7.3 — 77 63 — 411074000 9/26/97 0307 313 691 7.3 — 92 67 — 311074000 9/26/97 0437 313 700 7.4 — 88 71 — 3
Appendix C 55

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the diversHighway, southern California—Continued

Station no. Date Time

Ammonia,

dissolved

(mg/L as N)

Ammonia +

organic 

nitrogen

(mg/L as N)

Ammonia + 

organic

nitrogen, 

dissolved

(mg/L as N)

Phosphorus,

total

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Orthophosphate,

dissolved

(mg/L as P)

Iron,

dissolved

(μg/L)

11074000 1/29/97 0700 — — — — — 1.6 — 11074000 1/29/97 1300 — — — — — .60 — 11074000 1/29/97 1900 — — — — — .70 — 11074000 1/30/97 0100 — — — — — .90 — 11074000 1/30/97 0700 — — — — — .70 — 11074000 1/30/97 1300 — — — — — 1.0 — 11074000 9/14/97 2240 0.07 5.2 0.4 3.6 0.44 .46 10 11074000 9/15/97 0240 .06 1.8 .4 1.4 .54 .53 30 11074000 9/15/97 0640 .15 1.5 .9 1.0 .63 .61 20 11074000 9/15/97 1040 .19 1.6 1.1 1.0 .70 .71 30 11074000 9/15/97 1250 .18 2.3 1.2 1.2 .68 .66 30 11074000 9/15/97 1415 — — — — — — — 11074000 9/15/97 1845 .19 1.4 1.2 .67 .58 .58 30 11074000 9/15/97 2315 — — — — — — — 11074000 9/16/97 0215 — — — — — — — 11074000 9/16/97 0515 — — — — — — — 11074000 9/16/97 0815 — — — — — — — 11074000 9/16/97 1115 — — — — — — — 11074000 9/24/97 1937 < .01 3.3 .5 2.5 .46 .45 20 11074000 9/24/97 2107 — — — — — — — 11074000 9/24/97 2237 — — — — — — — 11074000 9/25/97 0007 — — — — — — — 11074000 9/25/97 0137 — — — — — — — 11074000 9/25/97 0307 — — — — — — — 11074000 9/25/97 0437 .05 2.3 .4 1.0 .61 .59 20 11074000 9/25/97 0607 — — — — — — — 11074000 9/25/97 0737 .03 .9 .5 .99 .70 .68 30 11074000 9/25/97 0907 — — — — — — — 11074000 9/25/97 1037 .10 1.7 .6 1.0 .67 .61 40 11074000 9/25/97 1207 — — — — — — — 11074000 9/25/97 1337 — — — — — — — 11074000 9/25/97 1507 .47 3.1 2.1 1.2 .87 .79 110 11074000 9/25/97 1637 — — — — — — — 11074000 9/25/97 1807 — — — — — — — 11074000 9/25/97 1937 — — — — — — — 11074000 9/25/97 2107 — — — — — — — 11074000 9/25/97 2237 — — — — — — — 
56 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the divers

Highway, southern California—Continued Station no. Date Time Streamflow (f3/s) Specific conductance (μS/cm) pH (standard units) Alkalinity (mg/L as CaCO3) Sulfate, dissolved (mg/L as SO4) Chloride, dissolved (mg/L as Cl) Dissolved solids (mg/L) Nitra

disso

(mg/L 

11074000 9/26/97 0607 315 720 7.4 — 84 68 — 311074000 11/10/97 0900 215 872 7.9 130 100 94 — 711074000 11/10/97 1300 210 912 8.1 188 100 93 — 711074000 11/10/97 1700 285 661 7.9 125 70 67 — 611074000 11/10/97 2156 365 441 7.6 77 48 37 — 411074000 11/11/97 0256 376 578 7.5 101 82 48 — 411074000 11/11/97 0756 379 746 7.6 187 110 66 — 611074000 11/11/97 1459 376 786 7.8 153 100 75 — 611074000 11/11/97 1759 376 773 7.9 174 100 78 — 611074000 11/11/97 2059 376 779 8.0 176 99 78 — 511074000 11/11/97 2359 372 813 8.0 183 100 82 — 611074000 11/12/97 0259 372 821 8.0 182 99 84 — 611074000 11/12/97 0559 369 826 8.1 177 100 88 — 611074000 11/12/97 0859 365 840 8.0 185 100 88 — 611074000 12/5/97 1623 226 912 8.0 187 100 110 — 611074000 12/5/97 1923 228 923 8.0 — 100 110 — 711074000 12/5/97 2223 231 875 8.1 — 110 120 — 811074000 12/6/97 0123 231 952 8.1 — 100 110 — 711074000 12/6/97 0423 237 837 8.3 — 110 110 — 711074000 12/6/97 0723 286 908 8.1 185 110 110 — 711074000 12/6/97 1023 315 601 8.0 120 72 68 — 411074000 12/6/97 1305 340 478 7.7 — 72 53 — 311074000 12/6/97 1705 530 284 7.7 — 48 33 — 211074000 12/6/97 2105 545 277 7.7 — 43 28 — 211074000 12/7/97 0105 3060 288 7.7 — 37 28 — 211074000 12/7/97 0505 3160 283 7.6 62 38 29 — 111074000 12/7/97 0905 2530 310 7.6 — 39 31 — 211074000 12/7/97 1305 1560 388 7.6 — 41 33 — 211074000 12/7/97 1714 1540 342 7.8 71 41 34 — 211074000 12/7/97 2114 1540 358 7.7 — 43 36 — 211074000 12/8/97 0114 1540 358 7.7 — 44 38 — 211074000 12/8/97 0514 1540 366 7.6 76 45 38 — 211074000 12/8/97 0914 975 445 7.8 — 150 130 — 811074000 12/8/97 1314 964 432 7.6 — 54 49 — 311074000 12/8/97 1736 545 418 7.8 93 52 45 — 211074000 12/8/97 2136 542 417 7.8 — 55 48 — 311074000 12/9/97 0136 545 407 7.8 — 49 43 — 211074000 12/9/97 0536 547 422 7.7 91 48 47 — 2
Appendix C 57

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the diversHighway, southern California—Continued

Station no. Date Time

Ammonia,

dissolved

(mg/L as N)

Ammonia +

organic 

nitrogen

(mg/L as N)

Ammonia + 

organic

nitrogen, 

dissolved

(mg/L as N)

Phosphorus,

total

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Orthophosphate,

dissolved

(mg/L as P)

Iron,

dissolved

(μg/L)

11074000 9/26/97 0007 — — — — — — — 11074000 9/26/97 0137 — — — — — — — 11074000 9/26/97 0307 — — — — — — — 11074000 9/26/97 0437 — — — — — — — 11074000 9/26/97 0607 — — — — — — — 

11074000 11/10/97 0900 0.10 — 0.6 — 0.95 0.90 — 11074000 11/10/97 1300 .11 — .6 — .91 .94 — 11074000 11/10/97 1700 .86 — 2.1 — .68 .65 — 11074000 11/10/97 2156 .77 — 2.4 — .56 .52 — 11074000 11/11/97 0256 .81 — 2.0 — .56 .55 — 11074000 11/11/97 0756 .69 — 2.1 — .55 .53 — 11074000 11/11/97 1459 .35 — 1.2 — .66 .61 — 11074000 11/11/97 1759 — — — — — — — 11074000 11/11/97 2059 — — — — — — — 11074000 11/11/97 2359 — — — — — — — 11074000 11/12/97 0259 — — — — — — — 11074000 11/12/97 0559 — — — — — — — 11074000 11/12/97 0859 — — — — — — — 11074000 12/5/97 1623 .39 — 1.0 — .54 .50 < 3 11074000 12/5/97 1923 — — — — — — — 11074000 12/5/97 2223 — — — — — — — 11074000 12/6/97 0123 — — — — — — — 11074000 12/6/97 0423 — — — — — — — 11074000 12/6/97 0723 .47 — 1.0 — .79 .76 < 10 11074000 12/6/97 1023 .35 — .9 — .56 .53 20 11074000 12/6/97 1305 — — — — — — — 11074000 12/6/97 1705 — — — — — — — 11074000 12/6/97 2105 — — — — — — — 11074000 12/7/97 0105 — — — — — — — 11074000 12/7/97 0505 .17 — .8 — .35 .31 90 11074000 12/7/97 0905 .15 — .7 — .36 .31 60 11074000 12/7/97 1305 — — — — — — — 11074000 12/7/97 1714 .16 — .7 — .38 .33 60 11074000 12/7/97 2114 — — — — — — — 11074000 12/8/97 0114 — — — — — — — 11074000 12/8/97 0514 — — — — — — — 
58 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the divers

Highway, southern California—Continued Station no. Date Time Streamflow (f3/s) Specific conductance (μS/cm) pH (standard units) Alkalinity (mg/L as CaCO3) Sulfate, dissolved (mg/L as SO4) Chloride, dissolved (mg/L as Cl) Dissolved solids (mg/L) Nitra

disso

(mg/L 

11074000 12/9/97 0936 517 426 7.8 — 53 47 — 311074000 12/9/97 1336 507 447 7.9 105 55 49 — 311074000 12/9/97 1736 512 491 7.9 — 62 61 — 311074000 12/9/97 2136 510 509 7.9 — 64 60 — 311074000 2/3/98 0800 257 930 7.8 203 99 96 582 611074000 2/3/98 1130 272 937 7.9 197 97 93 570 611074000 2/3/98 1500 279 — — 188 100 95 564 611074000 2/3/98 1530 279———————11074000 2/3/98 1900 416 598 7.8 105 57 46 305 311074000 2/3/98 2300 2410 276 7.8 — 31 23 — 111074000 2/4/98 0300 2470 342 7.9 79 34 31 210 211074000 2/4/98 0700 831 320 7.9 — 34 26 — 211074000 2/4/98 1005 2570 — — 84 36 34 234 211074000 2/4/98 1405 1570 — — — 38 33 — 211074000 2/4/98 1805 1570 396 7.9 — 41 36 — 211074000 2/4/98 2205 535 399 7.8 — 39 37 — 211074000 2/5/98 0205 540 451 7.8 — 45 43 — 311074000 2/5/98 0605 535 492 7.8 — 50 48 — 311074000 2/5/98 1005 530 508 7.8 — 52 50 — 311074000 2/5/98 1405 535 505 7.8 — 52 49 — 311075620 10/30/96 0600 210 970 8.2 202 120 97 592 811075620 10/30/96 0650 225 961 8.1 178 120 100 568 811075620 10/30/96 0715 299 939 8.3 —————11075620 10/30/96 0745 712 712 8.0 130 100 70 458 511075620 10/30/96 0800 799 646 8.1 110 96 59 386 511075620 10/30/96 0845 731 617 8.0 96 97 58 380 411075620 10/30/96 1015 663 624 8.0 103 97 59 384 411075620 10/30/96 1200 559 554 8.0 93————11075620 10/30/96 1220 754 571 8.0 94 91 55 340 311075620 10/30/96 1415 466 607 7.9 99 100 58 370 411075620 10/30/96 1600 228 651 8.0 103 110 64 392 411075620 11/21/96 0600 258 961 7.8 — 110 86 — 611075620 11/21/96 0800 304 806 8.0 153 110 74 — 611075620 11/21/96 1000 348 824 8.0 151 110 72 — 611075620 11/21/96 1200 332 844 7.9 159 120 81 — 611075620 11/21/96 1300 412 508 7.5 118 62 43 — 311075620 11/21/96 1400 733 335 7.9 63 50 25 — 1
Appendix C 59

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the diversHighway, southern California—Continued

Station no. Date Time

Ammonia,

dissolved

(mg/L as N)

Ammonia +

organic 

nitrogen

(mg/L as N)

Ammonia + 

organic

nitrogen, 

dissolved

(mg/L as N)

Phosphorus,

total

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Orthophosphate,

dissolved

(mg/L as P)

Iron,

dissolved

(μg/L)

11074000 12/8/97 0914 — — — — — — — 11074000 12/8/97 1314 — — — — — — — 11074000 12/8/97 1736 — — — — — — — 11074000 12/8/97 2136 — — — — — — — 11074000 12/9/97 0136 — — — — — — — 11074000 12/9/97 0536 0.21 — 0.7 — 0.43 0.39 30 11074000 12/9/97 0936 — — — — — — — 11074000 12/9/97 1336 — — — — — — — 

11074000 12/9/97 1736 — — — — — — — 11074000 12/9/97 2136 — — — — — — — 11074000 2/3/98 0800 1.1 2.8 2.1 1.3 1.2 0.02 20 11074000 2/3/98 1130 .94 2.7 1.8 1.3 1.1 1.0 10 11074000 2/3/98 1500 .79 2.6 1.5 1.4 .95 .99 50 11074000 2/3/98 1530 — — — — — — — 11074000 2/3/98 1900 .22 2.0 .7 .92 .43 .46 20 11074000 2/3/98 2300 — — — — — — — 11074000 2/4/98 0300 .20 2.0 .6 1.0 .36 .37 20 11074000 2/4/98 0700 — — — — — — — 11074000 2/4/98 1005 .31 2.2 .9 1.2 .42 .38 60 11074000 2/4/98 1405 — — — — — — — 11074000 2/4/98 1805 — — — — — — — 11074000 2/4/98 2205 — — — — — — — 11074000 2/5/98 0205 — — — — — — — 11074000 2/5/98 0605 — — — — — — — 11074000 2/5/98 1005 — — — — — — — 11074000 2/5/98 1405 — — — — — — — 11075620 10/30/96 0600 .02 .6 .5 1.0 .93 .95 8 11075620 10/30/96 0650 .06 .6 .5 .97 .93 .93 7 11075620 10/30/96 0715 — — — — — — — 11075620 10/30/96 0745 .99 2.9 2.6 .88 .69 .66 130 11075620 10/30/96 0800 .95 2.8 2.3 .84 .60 .62 110 11075620 10/30/96 0845 .93 2.2 2.1 .64 .60 .56 80 11075620 10/30/96 1015 .82 — 1.8 — .59 .56 70 11075620 10/30/96 1200 — — — — — — — 11075620 10/30/96 1220 .63 2.0 1.5 .79 .61 .57 40 11075620 10/30/96 1415 .57 1.7 1.4 .75 .60 .57 30 11075620 10/30/96 1600 .53 1.6 1.4 .68 .62 .58 30 
60 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the divers

Highway, southern California—Continued Station no. Date Time Streamflow (f3/s) Specific conductance (μS/cm) pH (standard units) Alkalinity (mg/L as CaCO3) Sulfate, dissolved (mg/L as SO4) Chloride, dissolved (mg/L as Cl) Dissolved solids (mg/L) Nitra

disso

(mg/L 

11075620 11/21/96 2000 — 576 7.5 73 110 45 — 211075620 11/21/96 2300 — 396 7.8 56 77 29 — 111075620 11/22/96 0615 — 752 7.6 95 200 66 — 211075620 11/22/96 1112 198 945 7.9 — 200 80 — 311075620 11/22/96 1412 450 788 7.9 — 130 70 — 311075620 11/22/96 2012 361 400 7.9 — 74 29 — 111075620 11/22/96 2312 554 528 7.8 — 92 40 — 211075620 11/23/96 0212 558 551 — — 93 46 — 211075620 11/23/96 0512 559 550 7.8 — 77 45 — 211075620 11/23/96 0812 595 538 7.8 — 73 47 — 211075620 11/23/96 1112 576 533 7.8 — 71 46 — 211075620 11/23/96 1412 566 531 7.9 — 66 43 — 211075620 11/23/96 1712 559 540 7.9 — 70 47 — 211075620 11/23/96 2012 557 551 7.9 — 70 50 — 211075620 11/23/96 2312 554 562 7.9 — 70 51 — 211075620 11/24/96 0212 550 568 7.9 — 66 50 — 211075620 11/24/96 0512 551 563 7.9 — 67 51 — 111075620 11/24/96 0812 553 560 7.9 — 68 50 — 111075620 11/24/96 1112 554 554 7.9 111 65 48 — 211075620 11/24/96 1412 552 556 7.9 — 64 47 — 211075620 11/24/96 1712 546 552 7.9 — 67 49 — 211075620 11/24/96 2012 550 571 7.9 — 68 50 — 211075620 11/24/96 2312 546 594 7.9 — 68 52 — 211075620 11/25/96 0212 545 616 7.9 — 73 57 — 211075620 11/25/96 0512 548 607 7.9 — 72 55 — 211075620 11/25/96 0812 551 596 7.9 — 71 53 — 211075620 11/25/96 1112 550 593 7.9 — 70 52 — 211075620 11/25/96 1412 551 594 7.9 — 73 53 — 211075620 12/9/96 1252 280 1020 8.3 212 130 93 — 711075620 12/9/96 1430 416 901 8.3 184 110 77 — 611075620 12/9/96 1630 529 710 8.2 70 84 58 — 411075620 12/9/96 1830 978 417 8.1 74 65 33 — 211075620 12/9/96 2030 897 558 8.2 — 92 46 — 311075620 12/9/96 2230 666 664 8.2 121 110 58 — 311075620 12/10/96 0030 341 702 8.2 — 120 58 — 311075620 12/10/96 0230 339 830 8.2 147 120 74 — 411075620 12/10/96 0430 306 823 8.2 — 120 — — 411075620 12/10/96 0630 265 758 8.1 — 130 63 — 411075620 12/10/96 0830 262 814 8.2 — 130 70 — 3
Appendix C 61

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the diversHighway, southern California—Continued

Station no. Date Time

Ammonia,

dissolved

(mg/L as N)

Ammonia +

organic 

nitrogen

(mg/L as N)

Ammonia + 

organic

nitrogen, 

dissolved

(mg/L as N)

Phosphorus,

total

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Orthophosphate,

dissolved

(mg/L as P)

Iron,

dissolved

(μg/L)

11075620 11/21/96 0600 .29 — 1.4 — 0.81 0.73 — 11075620 11/21/96 0800 .51 — 1.5 — .70 .67 — 11075620 11/21/96 1000 .32 — 1.2 — .82 .65 — 11075620 11/21/96 1200 .25 — .9 — .74 .68 — 11075620 11/21/96 1300 .31 — 1.0 — .70 .45 — 11075620 11/21/96 1400 .29 — .8 — .34 .28 — 11075620 11/21/96 2000 .23 — .9 — .44 .36 — 11075620 11/21/96 2300 .24 — 1.0 — .38 .31 — 11075620 11/22/96 0615 .16 — .8 — .43 .36 — 11075620 11/22/96 1112 — — — — — .40 — 11075620 11/22/96 1412 — — — — — < .30 — 11075620 11/22/96 2012 — — — — — .40 — 11075620 11/22/96 2312 — — — — — — — 11075620 11/23/96 0212 — — — — — .10 — 11075620 11/23/96 0512 — — — — — — — 11075620 11/23/96 0812 — — — — — .40 — 11075620 11/23/96 1112 — — — — — < .30 — 11075620 11/23/96 1412 — — — — — < .30 — 11075620 11/23/96 1712 — — — — — < .30 — 11075620 11/23/96 2012 — — — — — < .30 — 11075620 11/23/96 2312 — — — — — < .30 — 11075620 11/24/96 0212 — — — — — < .30 — 11075620 11/24/96 0512 — — — — — < .30 — 11075620 11/24/96 0812 — — — — — < .30 — 11075620 11/24/96 1112 .25 — 1.3 — .58 .50 — 11075620 11/24/96 1412 — — — — — < .30 — 11075620 11/24/96 1712 — — — — — .40 — 11075620 11/24/96 2012 — — — — — .70 — 11075620 11/24/96 2312 — — — — — .40 — 11075620 11/25/96 0212 — — — — — < .30 — 11075620 11/25/96 0512 — — — — — < .30 — 11075620 11/25/96 0812 — — — — — < .30 — 11075620 11/25/96 1112 — — — — — < .30 — 11075620 11/25/96 1412 — — — — — .20 — 11075620 12/9/96 1252 .56 — 1.1 — .95 .92 — 11075620 12/9/96 1430 .58 — 1.2 — .80 .81 — 11075620 12/9/96 1630 .54 — 1.0 — .62 .61 — 11075620 12/9/96 1830 .45 — .8 — .40 .40 — 
62 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the divers

Highway, southern California—Continued Station no. Date Time Streamflow (f3/s) Specific conductance (μS/cm) pH (standard units) Alkalinity (mg/L as CaCO3) Sulfate, dissolved (mg/L as SO4) Chloride, dissolved (mg/L as Cl) Dissolved solids (mg/L) Nitra

disso

(mg/L 

11075620 1/19/97 2308 527 650 8.1 — 78 56 — 311075620 1/20/97 0208 528 647 8.1 — 77 58 — 311075620 1/20/97 0508 528 664 8.1 — 76 53 — 311075620 1/20/97 0808 531 643 8.1 128 76 56 403 311075620 1/20/97 1155 565 683 8.1 144 79 61 409 311075620 1/20/97 1455 542 665 8.1 143 85 61 414 311075620 1/20/97 1755 493 705 7.9 151 89 64 436 311075620 1/20/97 2055 460 702 8.0 — 88 59 — 311075620 1/25/97 1008 614 748 8.1 — 88 66 466 411075620 1/25/97 1308 612 700 8.0 137 90 68 458 411075620 1/25/97 1608 633 758 8.2 128 94 68 462 411075620 1/25/97 2114 700 478 7.9 73 67 38 282 211075620 1/25/97 2310 800 534 7.9 85 82 38 — 211075620 1/26/97 0130 1850 685 8.2 117 99 51 — 211075620 1/26/97 0400 3600 661 8.1 119 75 57 398 411075620 1/26/97 0930 5500 642 8.1 121 73 57 380 311075620 1/26/97 1630 5800 538 7.9 111 72 48 — 111075620 1/26/97 2130 5700 455 7.8 89 49 35 276 111075620 1/27/97 0030 5500 472 7.8 94 47 36 — 111075620 1/27/97 0330 5400 424 7.6 105 39 31 — 111075620 1/27/97 0630 5320 400 7.8 83 36 28 — 111075620 1/27/97 0930 5200 387 7.8 — 33 26 — 111075620 1/27/97 1230 5170 400 7.9 105 34 28 242 11075620 1/27/97 1530 5150 399 7.8 — 43 28 — 11075620 1/27/97 1830 5100 402 8.3 — 32 26 — 11075620 1/27/97 1930 2140 420 8.2 118 39 28 — 11075620 1/27/97 2130 1640 438 7.9 108 46 30 258 111075620 1/28/97 0330 400 458 7.7 — 46 31 — 11075620 1/28/97 0930 1300 462 7.8 111 50 33 282 111075620 1/28/97 1530 860 507 — — 61 34 — 111075620 1/29/97 0900 421 591 8.0 — 81 40 — 111075620 9/15/97 0010 385 660 8.0 142 76 76 421 311075620 9/15/97 0310 379 702 8.0 140 80 78 430 311075620 9/15/97 0610 383 670 8.0 135 76 75 412 211075620 9/15/97 0910 398 663 8.0 130 77 74 417 311075620 9/15/97 1115 388 632 8.2 132 75 73 414 311075620 9/15/97 1550 380 616 8.2 — 72 79 — 211075620 9/15/97 1850 377 631 8.1 — 66 79 — 3
Appendix C 63

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the diversHighway, southern California—Continued

Station no. Date Time

Ammonia,

dissolved

(mg/L as N)

Ammonia +

organic 

nitrogen

(mg/L as N)

Ammonia + 

organic

nitrogen, 

dissolved

(mg/L as N)

Phosphorus,

total

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Orthophosphate,

dissolved

(mg/L as P)

Iron,

dissolved

(μg/L)

11075620 12/9/96 2030 — — — — — <0 .30 — 11075620 12/9/96 2230 0.36 — 0.9 — .51 .50 — 11075620 12/10/96 0030 — — — — — .30 — 11075620 12/10/96 0230 .37 — 1.0 — .59 .59 — 11075620 12/10/96 0430 — — — — — < .30 — 11075620 12/10/96 0630 .29 — .7 — .48 .49 — 11075620 12/10/96 0830 — — — — — < .30 — 11075620 1/19/97 2308 — — — — — — — 11075620 1/20/97 0208 — — — — — — — 11075620 1/20/97 00508 — — — — — — — 11075620 1/20/97 0808 1.2 3.2 2.4 1.3 1.1 .98 30 11075620 1/20/97 1155 1.1 3.1 2.3 1.2 1.0 .94 30 11075620 1/20/97 1455 1.0 2.6 2.1 1.2 .99 .87 20 11075620 1/20/97 1755 .94 2.8 2.0 1.2 1.0 .90 20 11075620 1/20/97 2055 — — — — — — — 11075620 1/25/97 1008 1.4 2.8 2.8 1.2 1.2 1.1 40 11075620 1/25/97 1308 1.4 2.9 2.5 1.4 1.2 1.1 30 11075620 1/25/97 1608 1.4 2.9 2.6 1.3 1.2 1.0 20 11075620 1/25/97 2114 .71 2.0 1.4 1.0 .65 .57 20 11075620 1/25/97 2310 — — — — — .80 — 11075620 1/26/97 0130 — — — — — .90 — 11075620 1/26/97 0400 .97 1.8 2.0 .75 .76 .66 20 11075620 1/26/97 0930 1.5 4.4 2.4 2.2 .89 .82 20 11075620 1/26/97 1630 — — — — — .70 — 11075620 1/26/97 2130 1.6 3.8 2.7 1.5 .98 .70 40 11075620 1/27/97 0030 — — — — — 1.1 — 11075620 1/27/97 0330 — — — — — 1.6 — 11075620 1/27/97 0630 — — — — — 1.7 — 11075620 1/27/97 0930 — — — — — 1.0 — 11075620 1/27/97 1230 1.5 5.8 2.6 2.3 1.1 1.0 40 11075620 1/27/97 1530 — — — — — .90 — 11075620 1/27/97 1830 — — — — — 1.1 — 11075620 1/27/97 1930 — — — — — — — 11075620 1/27/97 2130 1.3 4.4 2.4 1.8 1.0 .98 30 11075620 1/28/97 0330 — — — — — .60 — 11075620 1/28/97 0930 1.3 3.5 2.4 1.4 1.1 1.0 30 
64 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the divers

Highway, southern California—Continued Station no. Date Time Streamflow (f3/s) Specific conductance (μS/cm) pH (standard units) Alkalinity (mg/L as CaCO3) Sulfate, dissolved (mg/L as SO4) Chloride, dissolved (mg/L as Cl) Dissolved solids (mg/L) Nitra

disso

(mg/L 

11075620 9/15/97 2350 390 662 8.0 130 75 74 428 411075620 9/16/97 0350 393 692 8.1 — 94 92 — 211075620 9/16/97 0650 398 692 8.3 — 83 82 — 111075620 9/16/97 0950 405 667 8.2 — 82 79 — 211075620 9/16/97 1250 406 692 8.3 — 83 79 — 211075620 9/24/97 2030 366 667 8.1 — 72 72 410 211075620 9/24/97 2200 366 632 8.0 — 80 74 — 311075620 9/24/97 2330 365 678 7.9 — 71 72 — 211075620 9/25/97 0100 368 672 8.0 — 71 71 — 311075620 9/25/97 0230 366 663 8.1 — 77 72 400 311075620 9/25/97 0400 363 677 8.0 — 76 70 — 211075620 9/25/97 0530 385 629 8.2 — 74 76 440 211075620 9/25/97 0700 394 599 7.9 — 75 65 — 211075620 9/25/97 0830 437 642 8.1 — 80 66 390 211075620 9/25/97 1000 414 642 8.0 — 77 67 — 311075620 9/25/97 1130 717 601 8.1 — 69 60 370 211075620 9/25/97 1300 715 487 7.8 — 62 39 — 211075620 9/25/97 1430 459 579 7.8 — 76 55 360 211075620 9/25/97 1600 396 642 7.7 — 77 64 — 311075620 9/25/97 1730 363 679 7.8 — 80 67 — 311075620 9/25/97 1900 329 654 7.8 — 84 67 380 311075620 9/25/97 2030 315 714 7.8 — 87 69 — 311075620 9/25/97 2230 — 693 7.8 — 84———11075620 9/25/97 2330 307 725 7.4 — 82 70 — 311075620 9/26/97 0100 300 660 7.7 — 83 67 440 411075620 9/26/97 0230 300 620 7.6 — 74 58 — 411075620 9/26/97 0400 304 625 7.5 — 74 56 — 311075620 9/26/97 0530 310 641 7.5 — 78 58 — 311075620 9/26/97 0700 304 636 7.5 — 76 57 — 311075620 9/26/97 0730 — 635 7.5 — 84 59 — 411075620 9/26/97 0900 338 674 7.6 — 70 64 — 411075620 9/26/97 1030 319 732 7.6 — 89 72 — 411075620 9/26/97 1200 322 730 7.7 — 100 72 470 411075620 9/26/97 1330 405 763 8.0 — 97 73 — 311075620 9/26/97 1500 597 748 7.6 — 87 73 — 311075620 9/26/97 1630 592 745 7.7 — 90 72 — 311075620 9/26/97 1800 584 736 7.7 — 88 72 — 311075620 9/26/97 1930 587 749 7.7 — 87 72 — 311075620 9/26/97 2100 575 761 7.8 — 83 70 — 3
Appendix C 65

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the diversHighway, southern California—Continued

Station no. Date Time

Ammonia,

dissolved

(mg/L as N)

Ammonia +

organic 

nitrogen

(mg/L as N)

Ammonia + 

organic

nitrogen, 

dissolved

(mg/L as N)

Phosphorus,

total

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Orthophosphate,

dissolved

(mg/L as P)

Iron,

dissolved

(μg/L)

11075620 1/28/97 1530 — — — — — 1.0 — 11075620 1/29/97 0900 — — — — — 3.1 — 11075620 9/15/97 0010 <0 .01 0.7 0.3 0.75 0.60 0.61 < 3 11075620 9/15/97 0310 .06 1.0 .6 .72 .57 .61 20 11075620 9/15/97 0610 < .01 .6 .4 .68 .59 .57 5 11075620 9/15/97 0910 .02 .8 .4 .65 .55 .55 10 11075620 9/15/97 1115 < .01 .6 .3 .66 .58 .57 7 11075620 9/15/97 1550 — — — — — — — 11075620 9/15/97 1850 — — — — — — — 11075620 9/15/97 2350 .14 1.5 1.2 .73 .60 .63 30 11075620 9/16/97 0350 — — — — — — — 11075620 9/16/97 0650 — — — — — — — 11075620 9/16/97 0950 — — — — — — — 11075620 9/16/97 1250 — — — — — — — 11075620 9/24/97 2030 .10 1.1 .6 .61 .49 .45 30 11075620 9/24/97 2200 — — — — — — — 11075620 9/24/97 2330 — — — — — — — 11075620 9/25/97 0100 — — — — — — — 11075620 9/25/97 0230 < .01 .7 .6 .65 .55 .52 20 11075620 9/25/97 0400 — — — — — — — 11075620 9/25/97 0530 .06 1.1 .5 .68 .52 .50 30 11075620 9/25/97 0700 — — — — — — — 11075620 9/25/97 0830 .18 .9 1.3 .85 .54 .48 40 11075620 9/25/97 1000 — — — — — — — 11075620 9/25/97 1130 .13 1.4 .8 .69 .54 .50 50 11075620 9/25/97 1300 — — — — — — — 11075620 9/25/97 1430 .15 1.3 .9 .7 .54 .49 50 11075620 9/25/97 1600 — — — — — — — 11075620 9/25/97 1730 — — — — — — — 11075620 9/25/97 1900 .07 1.1 .6 .74 .60 .56 40 11075620 9/25/97 2030 — — — — — — — 11075620 9/25/97 2230 — — — — — — — 11075620 9/25/97 2330 — — — — — — — 11075620 9/26/97 0100 .83 3.0 2.6 .96 .80 .73 100 11075620 9/26/97 0230 — — — — — — — 11075620 9/26/97 0400 — — — — — — — 
66 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the divers

Highway, southern California—Continued Station no. Date Time Streamflow (f3/s) Specific conductance (μS/cm) pH (standard units) Alkalinity (mg/L as CaCO3) Sulfate, dissolved (mg/L as SO4) Chloride, dissolved (mg/L as Cl) Dissolved solids (mg/L) Nitra

disso

(mg/L 

11075620 9/26/97 2230 577 768 7.9 — 85 73 — 311075620 9/27/97 0001 582 777 7.8 — 86———11075620 9/27/97 0130 580 815 7.8 — 100———11075620 9/27/97 0300 589 840 7.8 — 98———11075620 9/27/97 0430 570 849 7.8 — 99———11075620 9/27/97 0600 577 814 7.7 — 91 82 — 311075620 9/27/97 0730 570 773 7.8 — 87 78 — 311075620 11/10/97 1000 219 945 8.2 199 120 96 — 611075620 11/10/97 1230 395 886 8.2 175 120 85 — 611075620 11/10/97 1500 337 783 8.2 145 110 72 — 411075620 11/10/97 1951 256 824 7.9 173 120 83 — 511075620 11/10/97 2351 298 920 8.3 195 120 93 — 611075620 11/11/97 0351 341 453 7.8 85 53 39 — 411075620 11/11/97 1451 369 719 8.0 139 120 66 — 511075620 11/11/97 1721 364 819 8.1 160 120 75 — 611075620 11/11/97 1951 362 806 8.2 168 110 77 — 611075620 11/11/97 2221 366 818 8.3 165 110 79 — 611075620 11/12/97 0051 363 822 8.3 174 110 80 — 611075620 11/12/97 0321 366 821 8.4 156 110 81 — 511075620 11/12/97 0551 363 828 8.4 179 110 83 — 511075620 11/12/97 0821 368 860 8.2 182 110 85 — 511075620 12/5/97 1523 237 — — 198 140 120 — 711075620 12/5/97 1723 235 992 8.1 — 150 140 — 911075620 12/5/97 1923 241 — — — 140 120 — 711075620 12/5/97 2123 238 993 8.3 — 170 120 — 811075620 12/6/97 0123 288 936 8.2 202 140 120 — 611075620 12/6/97 0323 484 706 8.1 145 97 — — 411075620 12/6/97 0523 — 249 7.9 50 43 23 — 111075620 12/6/97 0723 — 298 8.0 27 — 28 — 111075620 12/6/97 0923 3050 360 8.1 50 84 35 — 111075620 12/6/97 1123 1820 531 7.8 — 140 50 — 211075620 12/6/97 1323 1230 642 7.8 80 160 76 — 211075620 12/6/97 2108 1500 449 7.9 55 110 42 — 111075620 12/7/97 0508 3460 416 8.0 59 88 37 — 111075620 12/7/97 1130 2520 346 7.8 71 47 36 — 111075620 12/8/97 1208 2320 441 8.0 — 61 48 — 311075620 12/8/97 1608 1750 512 8.0 — 67 52 — 211075620 12/8/97 2008 1800 495 8.1 — 77 57 — 3
Appendix C 67

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the diversHighway, southern California—Continued

Station no. Date Time

Ammonia,

dissolved

(mg/L as N)

Ammonia +

organic 

nitrogen

(mg/L as N)

Ammonia + 

organic

nitrogen, 

dissolved

(mg/L as N)

Phosphorus,

total

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Orthophosphate,

dissolved

(mg/L as P)

Iron,

dissolved

(μg/L)

11075620 9/26/97 0530 — — — — — — — 11075620 9/26/97 0700 — — — — — — — 11075620 9/26/97 0730 — — — — — — — 11075620 9/26/97 0900 — — — — — — — 11075620 9/26/97 1030 — — — — — — — 11075620 9/26/97 1200 0.46 2.9 2.3 1.0 0.82 0.73 120 11075620 9/26/97 1330 — — — — — — — 11075620 9/26/97 1500 — — — — — — — 11075620 9/26/97 1630 — — — — — — — 11075620 9/26/97 1800 — — — — — — — 11075620 9/26/97 1930 — — — — — — — 11075620 9/26/97 2100 — — — — — — — 11075620 9/26/97 2230 — — — — — — — 11075620 9/27/97 0001 — — — — — — — 11075620 9/27/97 0130 — — — — — — — 11075620 9/27/97 0300 — — — — — — — 11075620 9/27/97 0430 — — — — — — — 11075620 9/27/97 0600 — — — — — — — 11075620 9/27/97 0730 — — — — — — — 11075620 11/10/97 1000 .06 — .5 — .88 .82 — 11075620 11/10/97 1230 .41 — 1.2 — .78 .79 — 11075620 11/10/97 1500 .38 — 1.3 — .66 .66 — 11075620 11/10/97 1951 .15 — .7 — .81 .77 — 11075620 11/10/97 2351 .04 — .6 — .95 .90 — 11075620 11/11/97 0351 .65 — 1.6 — .55 .55 — 11075620 11/11/97 1451 .44 — 1.7 — .59 .57 — 11075620 11/11/97 1721 — — — — — — — 11075620 11/11/97 1951 — — — — — — — 11075620 11/11/97 2221 — — — — — — — 11075620 11/12/97 0051 — — — — — — — 11075620 11/12/97 0321 — — — — — — — 11075620 11/12/97 0551 — — — — — — — 11075620 11/12/97 0821 — — — — — — — 11075620 12/5/97 1523 .28 — 1.0 — .97 .94 10 11075620 12/5/97 1723 — — — — — — — 11075620 12/5/97 1923 — — — — — — — 11075620 12/5/97 2123 — — — — — — — 
68 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the divers

Highway, southern California—Continued Station no. Date Time Streamflow (f3/s) Specific conductance (μS/cm) pH (standard units) Alkalinity (mg/L as CaCO3) Sulfate, dissolved (mg/L as SO4) Chloride, dissolved (mg/L as Cl) Dissolved solids (mg/L) Nitra

disso

(mg/L 

11075620 12/9/97 0008 1600 487 8.0 — 73 52 — 211075620 12/9/97 0408 1570 497 8.0 106 74 54 — 311075620 12/9/97 0808 917 464 8.0 — 70 51 — 211075620 12/9/97 1208 684 480 8.1 — 71 52 — 311075620 12/9/97 1608 642 491 8.2 100 79 59 — 311075620 2/3/98 0603 275 964 7.8 — 110 92 592 611075620 2/3/98 0800 302 963 8.1 188 120 94 603 611075620 2/3/98 1000 700 486 7.9 104 64 45 302 311075620 2/3/98 1200 1580 486 7.9 104 44 21 175 111075620 2/3/98 1400 1140 410 7.9 72 65 29 243 211075620 2/3/98 1700 693 463 7.9 76 83 32 283 211075620 2/3/98 2000 445 — — 124 130 63 466 211075620 2/3/98 2300 900 739 8.0 — 140 65 — 311075620 2/4/98 0200 2050 376 7.8 66 50 30 238 111075620 2/4/98 0820 970 377 7.8 85 50 33 — 211075620 2/4/98 1218 2080 376 7.9 — 48 32 — 211075620 2/4/98 1556 1600 420 7.9 — 50 37 — 211075620 2/4/98 1956 1520 404 7.9 — 47 35 — 211075620 2/4/98 2356 580 468 7.9 — 60 42 — 211075620 2/5/98 0356 567 479 7.9 — 65 42 — 211075620 2/5/98 0756 580 537 8.0 — 70 55 — 311075620 2/5/98 1156 570 570 8.1 — 75 55 — 3
Appendix C 69

Appendix C. Data for field parameters, major ions, nutrients, and selected trace elements in the Santa Ana River below Prado Dam and at the diversHighway, southern California—Continued

Station no. Date Time

Ammonia,

dissolved

(mg/L as N)

Ammonia +

organic 

nitrogen

(mg/L as N)

Ammonia + 

organic

nitrogen, 

dissolved

(mg/L as N)

Phosphorus,

total

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Orthophosphate,

dissolved

(mg/L as P)

Iron,

dissolved

(μg/L)

11075620 12/6/97 0923 0.22 — 0.7 — 0.19 0.20 20 11075620 12/6/97 1123 — — — — — — — 11075620 12/6/97 1323 .21 — 1.1 — .27 .24 20 11075620 12/6/97 2108 .14 — .7 — .25 .22 20 11075620 12/7/97 0508 .08 — .6 — .33 .31 50 11075620 12/7/97 1130 .16 — .8 — .32 .30 70 11075620 12/8/97 1208 — — — — — — — 11075620 12/8/97 1608 .17 — .7 — .43 .40 30 11075620 12/8/97 2008 — — — — — — — 11075620 12/9/97 0008 — — — — — — — 11075620 12/9/97 0408 — — — — — — — 11075620 12/9/97 0808 — — — — — — — 11075620 12/9/97 1208 — — — — — — — 11075620 12/9/97 1608 — — — — — — — 11075620 2/3/98 0603 .69 2.2 1.6 1.4 1.2 1.2 20 11075620 2/3/98 0800 .68 2.1 1.6 1.3 1.3 1.4 20 11075620 2/3/98 1000 .43 1.2 1.0 .66 .59 .60 < 10 11075620 2/3/98 1200 .19 2.6 .6 1.3 .35 .36 20 11075620 2/3/98 1400 .20 6.6 .7 7.0 .38 .35 < 10 11075620 2/3/98 1700 .19 2.7 .8 1.8 .36 .38 < 10 11075620 2/3/98 2000 .18 5.8 .9 2.2 .50 .47 30 11075620 2/3/98 2300 — — — — — — — 11075620 2/4/98 0200 .10 3.1 .6 2.2 .36 .35 20 11075620 2/4/98 0820 — — — — — — — 11075620 2/4/98 1218 — — — — — — — 11075620 2/4/98 1556 — — — — — — — 11075620 2/4/98 1956 — — — — — — — 11075620 2/4/98 2356 — — — — — — — 11075620 2/5/98 0356 — — — — — — — 11075620 2/5/98 0756 — — — — — — — 11075620 2/5/98 1156 — — — — — — — 
THIS PAGE INTENTIONALLY LEFT BLANK
Appendix D 71

APPENDIX D

Data for Organic Carbon and Ultraviolet Absorption
72 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Appendix D. Data for organic carbon and ultraviolet absorption in the Santa Ana River below Prado Dam and at the diversion downstream 

from Imperial Highway, sourthern California

[Streamflow data for the entire flow of the river. USGS, U.S. Geological Survey; DOC, dissolved organic carbon; SOC, suspended organic carbon; UV254, 

ultraviolet absorbance at 254 nanometers; UV285, ultraviolet absorbance at 285 nanometers; mg/L, milligrams per liter; cm-1, per centimeter; >, greater than; 

—, no data. Streamflow data are for the entire flow of the River.] 

Staion name USGS station 

number Date Time DOC(mg/L)

SOC

(mg/L)

UV254

(cm-1)

UV 285

(cm-1)

Santa Ana River below Prado Dam 11074000 10/30/96 1045 5.6 3.8 0.101 0.073

11074000 10/30/96 1215 — — .158 .108

11074000 10/30/96 1415 15 1.3 .297 .195

11074000 10/30/96 1615 — — .356 .239

11074000 10/30/96 1815 18 1.3 .363 .245

11074000 10/30/96 1900 — — .365 .248

11074000 10/30/96 2100 18 3.4 .459 .369

11074000 10/30/96 2300 — — .453 .347

11074000 10/31/96 0100 18 1.9 .466 .379

11074000 11/21/96 0730 4.7 — .083 .058

11074000 11/21/96 0930 — — .090 .064

11074000 11/21/96 1030 7.6 — — —

11074000 11/21/96 1638 — — .154 .107

11074000 11/21/96 1838 — — .220 .153

11074000 11/21/96 2038 — — .251 .175

11074000 11/21/96 2238 — — .283 .198

11074000 11/22/96 0038 — — .307 .215

11074000 11/22/96 0238 — — .353 .251

11074000 11/22/96 0438 16 — .462 .349

11074000 11/22/96 0715 16 — .572 .435

11074000 11/24/96 0011 — — .402 .306

11074000 11/24/96 0341 — — .323 .234

11074000 11/24/96 0711 .2 — .397 .303

11074000 11/24/96 1041 — — .353 .258

11074000 11/24/96 1411 — — .334 .242

11074000 11/24/96 1741 — — .317 .230

11074000 11/24/96 2111 — — .340 .254

11074000 11/25/96 0041 — — .320 .234

11074000 11/25/96 0411 — — .332 .243

11074000 11/25/96 0741 — — .337 .247

11074000 11/25/96 1111 — — .319 .233

11074000 11/25/96 1441 — — .314 .229

11074000 12/9/96 1244 4.6 4.3 .106 .075

11074000 12/9/96 1444 — — .103 .072

11074000 12/9/96 1644 — — .104 .073

11074000 12/9/96 1844 6 5.1 .134 .093

11074000 12/9/96 2044 — — .158 .109

11074000 12/9/96 2244 — — .160 .114

11074000 12/10/96 0044 6 3 .182 .130

11074000 12/10/96 0244 — — .189 .133

11074000 12/10/96 0734 8.4 3.7 .209 .147
Appendix D 73

Appendix D. Data for organic carbon and ultraviolet absorption in the Santa Ana River below Prado Dam and at the diversion downstream 

from Imperial Highway, sourthern California—Continued

Staion name USGS station 

number Date Time DOC(mg/L)

SOC

(mg/L)

UV254

(cm-1)

UV 285

(cm-1)

Santa Ana River below Prado Dam 11074000 12/10/96 1134 — — 0.201 0.141

11074000 12/10/96 1534 6.7 4.5 .399 .319

11074000 12/10/96 1934 — — .229 .167

11074000 12/10/96 2334 6.4 2.8 .201 .142

11074000 12/11/96 0334 — — .207 .149

11074000 12/11/96 0734 7.2 2.4 .182 .128

11074000 12/11/96 1134 — — .222 .162

11074000 12/12/96 1221 — — .264 .198

11074000 12/13/96 2021 — — .285 .210

11074000 12/14/96 1221 — — .157 .112

11074000 12/15/96 0421 — — .226 .165

11074000 12/15/96 2021 — — .225 .163

11074000 12/16/96 1221 — — .260 .196

11074000 12/17/96 0421 8.3 3.5 .304 .226

11074000 1/19/97 2304 — — .271 .202

11074000 1/20/97 0204 — — .269 .201

11074000 1/20/97 0504 — — .269 .202

11074000 1/20/97 0804 8.4 2.3 .263 .196

11074000 1/20/97 1119 — — .247 .184

11074000 1/20/97 1419 7.9 3.3 .259 .193

11074000 1/20/97 1719 — — .263 .196

11074000 1/20/97 2019 — — .268 .200

11074000 1/25/97 1157 9.2 2.4 .257 .191

11074000 1/25/97 1757 — 3.5 .243 .179

11074000 1/25/97 2357 — — .199 .145

11074000 1/26/97 1430 9.2 6.6 .321 .242

11074000 1/26/97 2030 — — .337 .257

11074000 1/26/97 2359 — — .354 .272

11074000 1/27/97 1300 9.4 > 17 .420 .326

11074000 1/27/97 1900 — — .440 .344

11074000 1/28/97 0100 — — .458 .359

11074000 1/28/97 0700 — — .442 .340

11074000 1/28/97 0904 — — .442 .340

11074000 1/28/97 1504 — — .437 .338

11074000 1/28/97 2104 — — .489 .383

11074000 1/29/97 0304 — — .514 .392

11074000 1/29/97 0700 — — .368 .280

11074000 1/29/97 1300 — — .352 .266

11074000 1/29/97 1900 — — .393 .300

11074000 1/30/97 0100 — — .435 .340

11074000 1/30/97 0700 — — .456 .355

11074000 1/30/97 1300 — — .399 .307

11074000 9/14/97 2240 4.2 3.2 .100 .066
74 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Appendix D. Data for organic carbon and ultraviolet absorption in the Santa Ana River below Prado Dam and at the diversion downstream 

from Imperial Highway, sourthern California—Continued

Staion name USGS station 

number Date Time DOC(mg/L)

SOC

(mg/L)

UV254

(cm-1)

UV 285

(cm-1)

Santa Ana River below Prado Dam 11074000 9/15/97 0240 4.4 2.5 0.134 0.099

11074000 9/15/97 0640 8.8 2.4 .234 .144

11074000 9/15/97 1040 — — .343 .210

11074000 9/15/97 1250 12 2.1 .309 .185

11074000 9/15/97 1415 — — .541 .339

11074000 9/15/97 1845 8.9 2.9 .274 .164

11074000 9/15/97 2315 — — .239 .150

11074000 9/16/97 0215 — — .195 .125

11074000 9/16/97 0515 — — .222 .150

11074000 9/16/97 0815 — — .192 .126

11074000 9/16/97 1115 — — .169 .109

11074000 9/24/97 1937 3.4 > 8.4 .087 .058

11074000 9/24/97 2107 — — .073 .051

11074000 9/24/97 2237 — — .100 .069

11074000 9/25/97 0007 — — .095 .064

11074000 9/25/97 0137 — — .093 .063

11074000 9/25/97 0307 — — .098 .068

11074000 9/25/97 0437 3.9 3.3 .100 .069

11074000 9/25/97 0607 — — .088 .063

11074000 9/25/97 0737 4.5 4.1 .113 .078

11074000 9/25/97 1037 6 2.9 .158 .108

11074000 9/25/97 1207 — — .205 .138

11074000 9/25/97 1337 — — .328 .217

11074000 9/25/97 1507 16 2.7 .473 .307

11074000 9/25/97 1637 — — .697 .451

11074000 9/25/97 1807 — — .655 .433

11074000 9/25/97 1937 — — .643 .428

11074000 9/25/97 2107 — — .665 .445

11074000 9/25/97 2237 — — .687 .466

11074000 9/26/97 0007 — — .674 .462

11074000 9/26/97 0137 — — .706 .488

11074000 9/26/97 0307 — — .734 .509

11074000 9/26/97 0437 — — .641 .447

11074000 9/26/97 0607 — — .690 .480

11074000 11/10/97 0900 3.3 3.9 .076 .053

11074000 11/10/97 1300 4.1 2.8 .085 .059

11074000 11/10/97 1700 14 10 .334 .213

11074000 11/10/97 2156 14 6.7 .429 .287

11074000 11/11/97 0256 15 4.4 .425 .283

11074000 11/11/97 0756 15 3.3 .448 .295

11074000 11/11/97 1459 9.2 4.6 .291 .192

11074000 11/11/97 1759 — — .266 .177

11074000 11/11/97 2059 — — .244 .163

11074000 11/11/97 2359 — — .213 .144
Appendix D 75

Appendix D. Data for organic carbon and ultraviolet absorption in the Santa Ana River below Prado Dam and at the diversion downstream 

from Imperial Highway, sourthern California—Continued

Staion name USGS station 

number Date Time DOC(mg/L)

SOC

(mg/L)

UV254

(cm-1)

UV 285

(cm-1)

Santa Ana River below Prado Dam 11074000 11/12/97 0259 — — 0.189 0.127

11074000 11/12/97 0559 — — .168 .113

11074000 11/12/97 0859 — — .156 .106

11074000 12/5/97 1623 4.3 > 5.0 .076 .052

11074000 12/5/97 1923 — — .093 .064

11074000 12/5/97 2223 — — .095 .065

11074000 12/6/97 0123 — — .090 .062

11074000 12/6/97 0423 — — .094 .064

11074000 12/6/97 0723 4.4 2.6 .088 .062

11074000 12/6/97 1023 4.7 3.5 .121 .085

11074000 12/6/97 1305 — — .088 .062

11074000 12/6/97 1705 — — .230 .168

11074000 12/6/97 2105 — — .234 .173

11074000 12/7/97 0105 — — .231 .169

11074000 12/7/97 0505 6.1 7.9 .204 .151

11074000 12/7/97 0905 5.9 5.5 .188 .138

11074000 12/7/97 1305 — — .227 .166

11074000 12/7/97 1714 6.5 4.6 .200 .145

11074000 12/7/97 2114 — — .226 .165

11074000 12/8/97 0114 — — .226 .165

11074000 12/8/97 0514 — — .213 .154

11074000 12/8/97 0914 — — .210 .150

11074000 12/8/97 1314 — — .218 .158

11074000 12/8/97 1736 — — .216 .156

11074000 12/8/97 2136 — — .207 .147

11074000 12/9/97 0136 — — .212 .153

11074000 12/9/97 0536 5.8 2.1 .196 .140

11074000 12/9/97 0936 — — .200 .143

11074000 12/9/97 1336 — — .202 .144

11074000 12/9/97 1736 — — .209 .151

11074000 12/9/97 2136 — — .209 .151

11074000 2/3/98 0800 6.5 2.4 .164 .117

11074000 2/3/98 1130 6 2 .151 .106

11074000 2/3/98 1500 5.7 2.8 .146 .104

11074000 2/3/98 1900 5.8 4.4 .203 .146

11074000 2/3/98 2300 — — .169 .122

11074000 2/4/98 0300 5.2 6.6 .175 .125

11074000 2/4/98 0700 — — .242 .176

11074000 2/4/98 1005 5 6.4 .173 .123

11074000 2/4/98 1405 — — .155 .110

11074000 2/4/98 1805 — — .225 .163

11074000 2/4/98 2205 — — .194 .139

11074000 2/5/98 0205 — — .223 .162

11074000 2/5/98 0605 — — .161 .114
76 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Appendix D. Data for organic carbon and ultraviolet absorption in the Santa Ana River below Prado Dam and at the diversion downstream 

from Imperial Highway, sourthern California—Continued

Staion name USGS station 

number Date Time DOC(mg/L)

SOC

(mg/L)

UV254

(cm-1)

UV 285

(cm-1)

Santa Ana River below Prado Dam 11074000 2/5/98 1005 — — 0.180 0.132

11074000 2/5/98 1405 — — .189 .136

Santa Ana River at the diversion downstream from Imperial Highway11075620 10/30/96 0600 3.7 1.7 .074 .052

11075620 10/30/96 0650 3.6 — .087 .060

11075620 10/30/96 0715 — — .074 .052

11075620 10/30/96 0745 20 > 5.0 .451 .348

11075620 10/30/96 0800 16 2.9 .441 .322

11075620 10/30/96 0845 18 > 5.0 .427 .299

11075620 10/30/96 1015 16 > 5.0 .373 .251

11075620 10/30/96 1200 — — .313 .215

11075620 10/30/96 1220 13 2 — —

11075620 10/30/96 1415 14 > 5.0 .322 .221

11075620 10/30/96 1600 13 3.3 .318 .219

11075620 11/21/96 0600 8.3 — .223 .153

11075620 11/21/96 0800 10 — .295 .192

11075620 11/21/96 1000 6 — .197 .136

11075620 11/21/96 1200 7.6 — .180 .126

11075620 11/21/96 1300 6.8 — .207 .145

11075620 11/21/96 1400 8 — .187 .134

11075620 11/21/96 2000 11 — .228 .159

11075620 11/21/96 2300 10 — .209 .150

11075620 11/22/96 0615 9.6 — .230 .161

11075620 11/22/96 1112 — — .227 .157

11075620 11/22/96 1412 — — .329 .233

11075620 11/22/96 1712 — — .453 .339

11075620 11/22/96 2012 — — .277 .207

11075620 11/22/96 2312 — — .255 .182

11075620 11/23/96 0212 — — .288 .206

11075620 11/23/96 0512 — — .342 .249

11075620 11/23/96 0812 — — .349 .256

11075620 11/23/96 1112 — — .319 .231

11075620 11/23/96 1412 — — .341 .250

11075620 11/23/96 1712 — — .330 .239

11075620 11/23/96 2012 — — .314 .227

11075620 11/23/96 2312 — — .325 .237

11075620 11/24/96 0212 — — .321 .236

11075620 11/24/96 0512 — — .297 .214

11075620 11/24/96 0812 — — .339 .249

11075620 11/24/96 1112 11 — .326 .236

11075620 11/24/96 1412 — — .322 .232

11075620 11/24/96 1712 — — .333 .242

11075620 11/24/96 2012 — — .339 .247

11075620 11/24/96 2312 — — .303 .221

11075620 11/25/96 0212 — — .274 .197
Appendix D 77

Appendix D. Data for organic carbon and ultraviolet absorption in the Santa Ana River below Prado Dam and at the diversion downstream 

from Imperial Highway, sourthern California—Continued

Staion name USGS station 

number Date Time DOC(mg/L)

SOC

(mg/L)

UV254

(cm-1)

UV 285

(cm-1)

Santa Ana River at the diversion downstream from Imperial Highway11075620 11/25/96 0512 — — 0.307 0.225

11075620 11/25/96 0812 — — .309 .225

11075620 11/25/96 1112 — — .291 .211

11075620 11/25/96 1412 — — .317 .231

11075620 12/9/96 1252 4.4 .5 .108 .075

11075620 12/9/96 1430 4.8 .7 .144 .101

11075620 12/9/96 1630 5.6 — .146 .100

11075620 12/9/96 1830 5.2 1.8 .132 .097

11075620 12/9/96 2030 — — .134 .097

11075620 12/9/96 2230 5.2 4.9 .135 .092

11075620 12/10/96 0030 — — .269 .218

11075620 12/10/96 0230 5.4 2.3 .133 .093

11075620 12/10/96 0430 — — .156 .109

11075620 12/10/96 0630 5.6 2.6 .155 .108

11075620 12/10/96 0830 — — .151 .105

11075620 1/19/97 2308 — — .230 .170

11075620 1/20/97 0208 — — .283 .213

11075620 1/20/97 0508 — — .249 .186

11075620 1/20/97 0808 7.9 2.6 .262 .196

11075620 1/20/97 1155 7.1 3 .258 .192

11075620 1/20/97 1455 7.8 3.2 .242 .178

11075620 1/20/97 1755 7.4 2.8 .235 .175

11075620 1/20/97 2055 — — .237 .176

11075620 1/25/97 1008 8.8 2.5 .274 .205

11075620 1/25/97 1308 8.6 2.1 .258 .191

11075620 1/25/97 1608 8.8 2.3 .255 .187

11075620 1/25/97 2114 6.2 9.6 .553 .431

11075620 1/25/97 2310 — — .193 .142

11075620 1/26/97 0130 — — .274 .211

11075620 1/26/97 0400 6.8 17 .209 .153

11075620 1/26/97 0930 9 > 17 .214 .156

11075620 1/26/97 1630 — — .379 .292

11075620 1/26/97 2130 8.6 9.8 .283 .213

11075620 1/27/97 0030 — — .339 .258

11075620 1/27/97 0330 — — .341 .260

11075620 1/27/97 0630 — — .394 .306

11075620 1/27/97 0930 — — .389 .300

11075620 1/27/97 1230 9.8 15 .469 .367

11075620 1/27/97 1530 — — .493 .380

11075620 1/27/97 1830 — — .592 .420

11075620 1/27/97 1930 — — .431 .336

11075620 1/27/97 2130 10 > 17 .449 .349

11075620 1/28/97 0330 — — .438 .341

11075620 1/28/97 0930 9.6 9.7 .439 .341
78 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Appendix D. Data for organic carbon and ultraviolet absorption in the Santa Ana River below Prado Dam and at the diversion downstream 

from Imperial Highway, sourthern California—Continued

Staion name USGS station 

number Date Time DOC(mg/L)

SOC

(mg/L)

UV254

(cm-1)

UV 285

(cm-1)

Santa Ana River at the diversion downstream from Imperial Highway11075620 1/28/97 1530 — — 0.402 0.309

11075620 1/29/97 0900 — — .361 .274

11075620 9/15/97 0010 3.6 > 5 .096 .066

11075620 9/15/97 0310 8.1 2.3 .169 .105

11075620 9/15/97 0610 4.8 1.9 .179 .115

11075620 9/15/97 0910 5.4 1.6 .215 .144

11075620 9/15/97 1115 4.5 1.2 .130 .083

11075620 9/15/97 1550 — — .202 .126

11075620 9/15/97 1850 — — .301 .188

11075620 9/15/97 2350 13 1.1 .488 .305

11075620 9/16/97 0350 — — .326 .203

11075620 9/16/97 650 — — .240 .150

11075620 9/16/97 0950 — — .208 .132

11075620 9/16/97 1250 — — .184 .118

11075620 9/24/97 2030 5.7 1.4 .052 .035

11075620 9/24/97 2200 — — .128 .092

11075620 9/24/97 2330 — — .102 .071

11075620 9/25/97 0100 — — .112 .079

11075620 9/25/97 0230 3.7 1.7 .207 .132

11075620 9/25/97 0400 — — .285 .182

11075620 9/25/97 0530 5.7 1.2 .192 .122

11075620 9/25/97 0700 — — .223 .142

11075620 9/25/97 0830 8 1.4 .283 .183

11075620 9/25/97 1000 — — .348 .233

11075620 9/25/97 1130 6.5 2.2 .254 .171

11075620 9/25/97 1300 — — .274 .189

11075620 9/25/97 1430 6.6 2.1 .226 .156

11075620 9/25/97 1600 — — .149 .102

11075620 9/25/97 1730 — — .295 .215

11075620 9/25/97 1900 6.2 1.4 .229 .155

11075620 9/25/97 2030 — — .189 .129

11075620 9/25/97 2230 — — .273 .188

11075620 9/25/97 2330 — — .402 .274

11075620 9/26/97 0100 13 1.9 .568 .367

11075620 9/26/97 0230 — — .585 .381

11075620 9/26/97 0400 — — .608 .411

11075620 9/26/97 0530 — — .598 .398

11075620 9/26/97 0700 — — .498 .332

11075620 9/26/97 0730 — — .630 .433

11075620 9/26/97 0900 — — .645 .443

11075620 9/26/97 1030 — — .663 .456

11075620 9/26/97 1200 15 1.9 .630 .431

11075620 9/26/97 1330 — — .530 .362

11075620 9/26/97 1500 — — .611 .420
Appendix D 79

Appendix D. Data for organic carbon and ultraviolet absorption in the Santa Ana River below Prado Dam and at the diversion downstream 

from Imperial Highway, sourthern California—Continued

Staion name USGS station 

number Date Time DOC(mg/L)

SOC

(mg/L)

UV254

(cm-1)

UV 285

(cm-1)

Santa Ana River at the diversion downstream from Imperial Highway11075620 9/26/97 1630 — — 0.579 0.398

11075620 9/26/97 1800 — — .576 .398

11075620 9/26/97 1930 — — .518 .355

11075620 9/26/97 2100 — — .465 .319

11075620 9/26/97 2230 — — .436 .299

11075620 9/27/97 0001 — — .418 .286

11075620 9/27/97 0130 — — .411 .282

11075620 9/27/97 0300 — — .379 .266

11075620 9/27/97 0430 — — .331 .226

11075620 9/27/97 0600 — — .290 .199

11075620 9/27/97 0730 — — — —

11075620 11/10/97 1000 4 2.6 .108 .072

11075620 11/10/97 1230 8.5 3.4 .305 .195

11075620 11/10/97 1500 8.7 3.1 .301 .198

11075620 11/10/97 1951 5.2 3.4 .195 .133

11075620 11/10/97 2351 4 2.6 .112 .077

11075620 11/11/97 0351 7.4 4.1 .328 .217

11075620 11/11/97 1451 12 3.9 .408 .267

11075620 11/11/97 1721 — — .357 .236

11075620 11/11/97 1951 — — .299 .199

11075620 11/11/97 2221 — — .274 .183

11075620 11/12/97 0051 — — .256 .171

11075620 11/12/97 0321 — — .235 .157

11075620 11/12/97 0551 — — .222 .150

11075620 11/12/97 0821 — — .197 .133

11075620 12/5/97 1523 4.4 1.6 .100 .069

11075620 12/5/97 1723 — — .100 .069

11075620 12/5/97 1923 — — .100 .069

11075620 12/5/97 2123 — — .113 .076

11075620 12/6/97 0123 4.7 1.3 .110 .074

11075620 12/6/97 0323 4.6 3.1 .123 .083

11075620 12/6/97 0523 3.4 35 .104 .075

11075620 12/6/97 0723 3.5 27 .124 .089

11075620 12/6/97 0923 3.9 50 .137 .098

11075620 12/6/97 1123 — — .139 .097

11075620 12/6/97 1323 5.3 24 .282 .227

11075620 12/6/97 2108 5.7 50 .186 .144

11075620 12/7/97 0508 6.5 21 .174 .128

11075620 12/7/97 1130 6.7 10 .181 .133

11075620 12/8/97 1208 — — .210 .149

11075620 12/8/97 1608 6.2 3.9 .192 .136

11075620 12/8/97 2008 — — .208 .148

11075620 12/9/97 0008 — — .209 .150

11075620 12/9/97 0408 — — .206 .148
80 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Appendix D. Data for organic carbon and ultraviolet absorption in the Santa Ana River below Prado Dam and at the diversion downstream 

from Imperial Highway, sourthern California—Continued

Staion name USGS station 

number Date Time DOC(mg/L)

SOC

(mg/L)

UV254

(cm-1)

UV 285

(cm-1)

Santa Ana River at the diversion 

downstream from Imperial Highway

11075620 12/9/97 0808 — — 0.202 0.146

11075620 12/9/97 1208 — — .204 .145

11075620 12/9/97 1608 — — .199 .142

11075620 2/3/98 0603 7.2 1.2 .184 .132

11075620 2/3/98 0800 7.1 .3 .167 .120

11075620 2/3/98 1000 5.4 1.6 .150 .106

11075620 2/3/98 1200 4.2 9.3 .149 .108

11075620 2/3/98 1400 4.4 38 .143 .102

11075620 2/3/98 1700 5.4 14 .180 .131

11075620 2/3/98 2000 5.5 49 .177 .127

11075620 2/3/98 2300 — — .194 .139

11075620 2/4/98 0200 5.7 > 17 .198 .144

11075620 2/4/98 0820 — — .195 .142

11075620 2/4/98 1218 — — .203 .149

11075620 2/4/98 1556 — — .267 .197

11075620 2/4/98 1956 — — .267 .197

11075620 2/4/98 2356 — — .250 .183

11075620 2/5/98 0356 — — .247 .181

11075620 2/5/98 0756 — — .219 .159

11075620 2/5/98 1156 — — .243 .183
Appendix E 81

APPENDIX E

Data for Pesticides
82 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Appendix E. Data for pesticides detected in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California

[USGS, U.S. Geological Survey; μg/L, microgram per liter; <, less than; E, estimated (see note at end of table]; —, no data] 

Station name USGS station 

number Data Time 2,4-d (μg/L)

Atrazine

(μg/L)

Benfluralin

(μg/L)

Bromacil

(μg/L)

Carbarl

(μg/L)

Santa Ana River below Prado 

Dam

11074000 10/30/96 1045 <0.035 0.011 <0.002 <0.035 E0.009

11074000 10/30/96 1415 <.035 .012 <.002 <.035 E.024

11074000 10/30/96 1815 <.035 .011 <.002 <.035 E.049

11074000 10/30/96 2100 <.035 .012 <.002 <.035 E.111

11074000 10/31/96 0100 <.035 .012 <.002 <.035 E.693

11074000 1/20/97 0804 <.035 .007 <.002 <.035 E.034

11074000 1/20/97 1419 <.035 .007 <.002 <.035 E.032

11074000 1/25/97 1157 <.035 .057 <.002 <.035 E.030

11074000 1/25/97 1757 <.035 .054 <.002 <.035 E.041

11074000 1/26/97 1430 <.035 .040 <.002 <.035 E.052

11074000 1/27/97 1300 <.035 .014 <.002 <.035 E.040

11074000 9/14/97 2240 <.035 .007 <.002 <.035 E.022

11074000 9/15/97 0240 <.035 .007 <.002 <.035 E.062

11074000 9/15/97 0640 <.035 .007 <.002 <.035 E.119

11074000 9/15/97 1040 — .007 <.002 — E.111

11074000 9/15/97 1250 <.035 .008 <.002 <.035 E.107

11074000 9/15/97 1845 <.035 .007 <.002 <.035 E.138

11074000 9/24/97 1937 — .010 <.002 — E.012

11074000 9/24/97 2107 <.035 — — <.035 —

11074000 9/25/97 0437 — .008 <.002 — E.014

11074000 9/25/97 0607 <.035 — — <.035 —

11074000 9/25/97 0737 — .008 <.002 — E.015

11074000 9/25/97 0907 <.035 — — <.035 —

11074000 9/25/97 1037 — .009 <.002 — E.014

11074000 9/25/97 1207 <.035 — — <.035 —

11074000 9/25/97 1507 — .009 <.002 — E.063

11074000 9/25/97 1637 <.035 — — <.035 —

11074000 2/3/98 0800 <.15 .007 <.002 <.035 E.076

11074000 2/3/98 1130 <.15 .007 <.002 .370 E.054

11074000 2/3/98 1500 — .007 <.002 — E.048

11074000 2/3/98 1900 <.15 <.001 <.002 .340 E.449

11074000 2/4/98 0300 <.15 .009 <.002 .500 E1.12

11074000 2/4/98 1005 <.15 .010 <.002 .480 E1.04

Santa Ana River at the

diversion downstream from

Imperial Highway

11075620 10/30/96 0600 <.035 .010 <.002 <.035 <.010

11075620 10/30/96 0650 <.035 .011 <.002 <.035 <.009

11075620 10/30/96 0745 <.035 .009 <.002 <.035 E.109

11075620 10/30/96 0800 <.035 .007 <.002 <.035 E.167

11075620 10/30/96 0845 <.035 — — <.035 —

11075620 10/30/96 1015 <.035 .007 <.002 <.035 E.187

11075620 10/30/96 1220 <.035 .006 <.002 <.035 E.179

11075620 10/30/96 1415 <.035 <.008 <.002 <.035 E.167

11075620 10/30/96 1600 <.035 .007 <.002 — E.168

11075620 1/20/97 0808 <.035 .009 <.002 <.035 E.055

11075620 1/20/97 1155 <.035 .007 <.002 <.035 E.034

11075620 1/20/97 1455 <.035 .008 .005 <.035 E.048

11075620 1/20/97 1755 <.035 .007 <.002 <.035 E.027

11075620 1/25/97 1008 <.035 .055 <.002 <.035 E.025

11075620 1/25/97 1608 <.035 .054 <.002 <.035 E.038

11075620 1/25/97 2114 .200 .022 .005 <.035 E.098
Appendix E 83

Appendix E. Data for pesticides detected in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California—Continued

USGS station 

number Data Time Chlorpyrifos(μg/L)

Cyanazine

(μg/L)

DCPA

(μg/L)

p,p'-DDE

(μg/L)

Deethyl 

atrazine

(μg/L)

Diazinon

(μg/L)

Diuron

(μg/L)

11074000 10/30/96 1045 <0.004 <0.004 E0.003 <0.006 E0.011 0.018 <0. 02

11074000 10/30/96 1415 .020 <.004 .006 <.006 <.002 .050 .19

11074000 10/30/96 1815 .025 <.004 .007 <.006 <.002 .091 .49

11074000 10/30/96 2100 <.004 <.004 .006 <.006 <.002 .221 E5.9

11074000 10/31/96 0100 <.004 <.004 .008 <.006 <.002 .190 E3.9

11074000 1/20/97 0804 .010 .008 .220 <.006 E.0053 .095 1.20

11074000 1/20/97 1419 .007 .006 .218 <.006 E.0067 .099 1.10

11074000 1/25/97 1157 <.01 <.004 .098 <.006 <.002 .103 E2.9

11074000 1/25/97 1757 <.01 <.004 .091 <.006 <.002 .109 E2.9

11074000 1/26/97 1430 .021 <.004 .155 <.006 <.002 .139 E4.1

11074000 1/27/97 1300 <.004 <.004 .263 <.006 <.002 .083 E3.2

11074000 9/14/97 2240 <.007 .010 E.002 <.006 <.007 .009 <.02

11074000 9/15/97 0240 <.009 .009 E.002 <.006 <.006 .007 <.02

11074000 9/15/97 0640 .004 <.004 E.002 <.006 <.005 .019 <.02

11074000 9/15/97 1040 E.007 <.004 E.002 <.006 <.002 .018 —

11074000 9/15/97 1250 .010 <.004 E.003 <.006 <.002 .065 <.02

11074000 9/15/97 1845 <.004 <.004 E.003 <.006 <.002 .099 <.02

11074000 9/24/97 1937 <.004 <.004 E.003 <.006 <.002 .010 —

11074000 9/24/97 2107 — — — — — — E.07

11074000 9/25/97 0437 <.004 <.004 E.003 <.006 <.002 .009 —

11074000 9/25/97 0607 — — — — — — E.06

11074000 9/25/97 0737 <.004 <.004 E.002 <.006 <.002 .009 —

11074000 9/25/97 0907 — — — — — — <.02

11074000 9/25/97 1037 <.004 <.004 E.002 <.006 <.002 .013 —

11074000 9/25/97 1207 — — — — — — <.02

11074000 9/25/97 1507 <.004 <.040 E.003 <.006 <.002 .106 —

11074000 9/25/97 1637 — — — — — — <.02

11074000 2/3/98 0800 <.004 <.004 E.003 <.006 E.004 .059 E1.4

11074000 2/3/98 1130 .008 <.004 E.003 <.006 E.005 .056 E1.4

11074000 2/3/98 1500 .007 <.004 E.003 <.006 E.005 .055 —

11074000 2/3/98 1900 .013 <.004 .006 <.006 E.005 .161 E5.5

11074000 2/4/98 0300 .020 <.004 .011 E.004 <.002 .184 E13

11074000 2/4/98 1005 .010 <.004 .012 <.006 <.002 .173 E12

11075620 10/30/96 0600 <.004 <.004 E.002 <.006 E.008 .019 .08

11075620 10/30/96 0650 <.004 <.004 E.002 <.006 E.009 .017 .09

11075620 10/30/96 0745 .096 <.004 .009 <.006 <.002 .494 <. 02

11075620 10/30/96 0800 .087 <.004 .008 <.006 <.002 .559 .08

11075620 10/30/96 0845 —————— <. 02

11075620 10/30/96 1015 .099 <.004 .008 <.006 <.002 .642 <. 02

11075620 10/30/96 1220 .054 <.004 .006 <.006 <.002 .534 <. 02

11075620 10/30/96 1415 .094 <.004 .008 <.006 <.002 .468 <. 02

11075620 10/30/96 1600 .089 <.004 .008 <.006 <.002 .446 —

11075620 1/20/97 0808 .012 .013 .213 <.006 E.010 .117 1.20

11075620 1/20/97 1155 .008 .007 .192 <.006 E.006 .087 1.00

11075620 1/20/97 1455 .026 .009 .187 <.006 E.006 .165 1.00

11075620 1/20/97 1755 .010 .007 .188 <.006 E.006 .083 .71

11075620 1/25/97 1008 <.004 <.004 .104 <.006 E.005 .087 E2.9

11075620 1/25/97 1608 .016 <.004 .100 <.006 E.006 .154 E2.8

11075620 1/25/97 2114 .033 <.004 .039 <.006 <.002 .377 1.40
84 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Appendix E. Data for pesticides detected in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California—Continued

USGS station 

number Data Time Lindane(μg/L)

Malathion

(μg/L)

Metolachlor

(μg/L)

Napropamide

(μg/L)

Norflurazon

(μg/L)

Pendimethalin

(μg/L)

Prometon

(μg/L)

11074000 10/30/96 1045 0.011 <0.005 <0.002 <0.003 <0.024 <0.004 E0.012

11074000 10/30/96 1415 <.01 .013 <.002 <.003 <.024 <.004 E.029

11074000 10/30/96 1815 <.008 .034 <.002 <.003 <.024 <.004 E.043

11074000 10/30/96 2100 <.004 .064 <.002 <.003 <.024 <.004 E.048

11074000 10/31/96 0100 <.004 .060 <.002 <.003 <.024 <.004 E.051

11074000 1/20/97 0804 .007 .018 .007 <.003 <.024 <.004 .030

11074000 1/20/97 1419 .007 .018 .009 <.003 <.024 <.004 .021

11074000 1/25/97 1157 <.004 .023 .007 <.003 E.390 <.004 .018

11074000 1/25/97 1757 <.004 .028 .006 <.003 E.010 <.004 E.015

11074000 1/26/97 1430 <.004 .048 .009 <.003 E.240 <.004 .021

11074000 1/27/97 1300 <.004 .030 .008 <.003 <.024 <.004 E.016

11074000 9/14/97 2240 .007 <.005 .009 <.003 <.024 <.004 E.007

11074000 9/15/97 0240 .007 <.005 .009 <.003 <.024 <.004 E.007

11074000 9/15/97 0640 <.004 .011 .008 <.003 <.024 <.004 E.010

11074000 9/15/97 1040 <.004 <.005 .010 <.003 — <.004 .020

11074000 9/15/97 1250 <.004 .022 .008 <.003 <.024 <.004 .024

11074000 9/15/97 1845 <.004 .017 .015 <.003 <.024 <.004 .040

11074000 9/24/97 1937 <.01 <.005 .012 <.003 — <.004 E.009

11074000 9/24/97 2107 — — — — <.024 — —

11074000 9/25/97 0437 <.01 <.005 .012 <.003 — <.004 E.009

11074000 9/25/97 0607 — — — — <.024 — —

11074000 9/25/97 0737 <.01 <.005 .010 <.003 — <.004 E.007

11074000 9/25/97 0907 — — — — <.024 — —

11074000 9/25/97 1037 <.004 <.005 .012 <.003 — <.004 E.0081

11074000 9/25/97 1207 — — — — <.024 — —

11074000 9/25/97 1507 <.004 .036 .011 <.025 — <.004 .022

11074000 9/25/97 1637 — — — — <.024 — —

11074000 2/3/98 0800 .011 <.005 .005 <.003 <.024 <.004 E.014

11074000 2/3/98 1130 .010 <.005 .006 <.003 <.024 <.004 .019

11074000 2/3/98 1500 .010 <.005 .006 <.003 — <.004 .018

11074000 2/3/98 1900 <.004 .021 .005 <.003 <.024 <.004 .020

11074000 2/4/98 0300 <.004 .055 .011 <.003 <.024 <.004 .043

11074000 2/4/98 1005 <.004 .047 .011 <.003 <.024 <.004 .040

11075620 10/30/96 0600 .009 <.005 <.002 <.0030 <.024 <.004 E.012

11075620 10/30/96 0650 .009 <.005 <.002 <.003 <.024 <.004 E.012

11075620 10/30/96 0745 <.010 E.156 <.002 .023 <.024 <.004 .021

11075620 10/30/96 0800 <.008 E.176 <.002 .043 <.024 <.004 .022

11075620 10/30/96 0845 — — — — <.024 — —

11075620 10/30/96 1015 <.004 .220 <.002 .034 <.024 <.004 E.020

11075620 10/30/96 1220 <.004 .180 <.002 .017 <.024 <.004 E.021

11075620 10/30/96 1415 <.007 .136 <.002 .013 <.024 <.020 .039

11075620 10/30/96 1600 <.005 .139 <.002 <.008 — <.025 .043

11075620 1/20/97 0808 .013 .018 .011 <.003 <.024 <.004 .024

11075620 1/20/97 1155 <.004 .014 .005 <.003 <.024 <.004 .037

11075620 1/20/97 1455 <.004 .084 .007 <.003 <.024 <.004 .021

11075620 1/20/97 1755 <.004 .014 .005 <.003 <.024 <.004 E.005

11075620 1/25/97 1008 <.010 .018 <.002 <.003 E .35 E.008 .026

11075620 1/25/97 1608 <.008 .025 <.002 <.003 E .36 <.004 .029

11075620 1/25/97 2114 <.007 .023 <.002 <.003 E .29 <.004 <.018
Appendix E 85

Appendix E. Data for pesticides detected in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California—Continued

USGS station 

number Data Time Pronamide(μg/L)

Propoxur

(μg/L)

Simazine

(μg/L)

Tebuthiuron

(μg/L)

Triclopyr

(μg/L)

Trifluralin

μg/L)

11074000 10/30/96 1045 <0.003 <0.035 0.081 E0.012 <0.05 <0.002

11074000 10/30/96 1415 <.003 <.035 E.136 E.025 <.05 <.002

11074000 10/30/96 1815 <.003 <.035 E.151 E.025 <.05 <.002

11074000 10/30/96 2100 <.003 <.035 E.113 <.01 <.05 <.002

11074000 10/31/96 0100 <.003 <.035 E.209 <.01 <.05 <.002

11074000 1/20/97 0804 <.003 <.035 .527 <.01 <.05 .004

11074000 1/20/97 1419 <.003 <.035 .514 <.01 <.05 <.002

11074000 1/25/97 1157 <.003 <.035 .276 <.01 <.05 <.002

11074000 1/25/97 1757 <.003 <.035 .269 <.01 <.05 <.002

11074000 1/26/97 1430 <.003 <.035 .385 <.01 <.05 <.002

11074000 1/27/97 1300 <.003 <.035 .482 <.01 <.05 <.002

11074000 9/14/97 2240 <.003 <.035 .045 <.01 <.05 <.002

11074000 9/15/97 0240 <.003 <.035 .044 <.01 <.05 <.002

11074000 9/15/97 0640 <.003 <.035 .046 <.01 <.05 <.002

11074000 9/15/97 1040 <.003 — .039 <.01 — <.002

11074000 9/15/97 1250 <.003 <.035 .046 <.01 <.05 <.002

11074000 9/15/97 1845 <.003 <.035 .052 <.01 <.05 <.002

11074000 9/24/97 1937 <.003 — .042 <.01 — <.002

11074000 9/24/97 2107 — E.11 — — <.05 —

11074000 9/25/97 0437 <.003 — .037 <.01 — <.002

11074000 9/25/97 0607 — E.05 — — <.05 —

11074000 9/25/97 0737 <.003 — .036 <.01 — <.002

11074000 9/25/97 0907 — <.035 — — <.05 —

11074000 9/25/97 1037 <.003 — .038 <.01 — <.002

11074000 9/25/97 1207 — <.035 — — <.05 —

11074000 9/25/97 1507 <.003 — .038 <.01 — <.002

11074000 9/25/97 1637 — <.035 — — <.05 —

11074000 2/3/98 0800 <.003 <.035 .110 <.01 <.25 E.002

11074000 2/3/98 1130 <.003 <.035 .112 <.01 <.25 <.002

11074000 2/3/98 1500 <.003 — .114 <.01 — <.002

11074000 2/3/98 1900 <.003 <.035 .243 <.01 <.25 <.002

11074000 2/4/98 0300 <.003 <.035 1.090 <.01 <.25 <.002

11074000 2/4/98 1005 <.003 <.035 1.220 <.01 <.25 <.002

11075620 10/30/96 0600 <.003 <.035 .068 E.013 <.05 <.002

11075620 10/30/96 0650 <.003 <.035 .072 E.012 <.05 <.002

11075620 10/30/96 0745 <.040 <.035 E.096 E.018 .130 <.002

11075620 10/30/96 0800 <.035 <.035 E.072 E.020 .130 <.002

11075620 10/30/96 0845 — <.035 — — <.05 —

11075620 10/30/96 1015 <.003 <.035 E.039 .015 <.05 <.002

11075620 10/30/96 1220 <.003 <.035 E.032 .013 <.05 <.002

11075620 10/30/96 1415 <.003 <.035 E.041 E.022 .080 <.002

11075620 10/30/96 1600 <.003 — E.043 E.018 <.05 <.002

11075620 1/20/97 0808 <.003 <.035 .587 E.023 <.05 <.002

11075620 1/20/97 1155 <.003 <.035 .488 <.01 <.05 <.002

11075620 1/20/97 1455 <.003 <.035 .471 <.01 <.05 .005

11075620 1/20/97 1755 <.003 <.035 .459 <.01 <.05 .005

11075620 1/25/97 1008 <.003 <.035 .278 <.01 <.05 <.002

11075620 1/25/97 1608 <.003 <.035 .268 <.01 <.05 <.002

11075620 1/25/97 2114 0.009 <.035 .114 <.01 <.05 .004
86 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Appendix E. Data for pesticides detected in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California—Continued

Station name USGS station 

number Data Time 2,4-d (μg/L)

Atrazine

(μg/L)

Benfluralin

(μg/L)

Bromacil

(μg/L)

Carbarl

(μg/L)

Santa Ana River at the

diversion downstream from

Imperial Highway

11075620 1/26/97 0400 <0.035 0.045 <0.002 <0.035 E0.039

11075620 1/26/97 0930 <.035 .039 <.002 <.035 E.039

11075620 1/26/97 2130 <.035 .025 <.002 <.035 E.083

11075620 1/27/97 1230 <.035 .014 <.002 <.035 E.042

11075620 1/27/97 2130 <.035 .015 <.002 <.035 E.040

11075620 1/28/97 0930 <.035 .015 <.002 <.035 E.043

11075620 9/15/97 0010 <.035 .008 <.002 <.035 E.074

11075620 9/15/97 0310 <.035 .008 <.002 <.035 E.116

11075620 9/15/97 0610 <.035 .008 <.002 <.035 E.02

11075620 9/15/97 0910 <.035 .007 <.002 <.035 E.073

11075620 9/15/97 1115 <.035 .008 <.002 <.035 E.084

11075620 9/15/97 2350 <.035 <.001 <.002 <.035 E.173

11075620 9/24/97 2030 — .009 <.002 — E.013

11075620 9/24/97 2200 <.035 — — <.035 —

11075620 9/25/97 0230 — .009 <.002 — E.03

11075620 9/25/97 0400 <.035 — — <.035 —

11075620 9/25/97 0530 — .009 <.002 — E.032

11075620 9/25/97 0700 <.035 — — <.035 —

11075620 9/25/97 0830 — .009 <.002 — E.124

11075620 9/25/97 1000 <.035 — — <.035 —

11075620 9/25/97 1130 — .009 <.002 — E.102

11075620 9/25/97 1300 <.035 — — <.035 —

11075620 9/25/97 1430 — .008 <.002 — E.128

11075620 9/25/97 1600 <.035 — — <.035 —

11075620 9/25/97 1900 — .009 <.002 — E.09

11075620 9/25/97 2030 <.035 — — <.035 —

11075620 9/26/97 0100 — .009 <.002 — E.097

11075620 9/26/97 0230 <.035 — — <.035 —

11075620 9/26/97 1200 — .009 <.002 — E.177

11075620 9/26/97 1330 <.035 — — <.035 —

11075620 2/3/98 0603 <.15 <.001 <.002 <.035 E.054

11075620 2/3/98 0800 <.15 .006 <.002 <.035 <.003

11075620 2/3/98 1000 <.15 <.001 .007 .360 E.199

11075620 2/3/98 1200 .390 <.001 .006 .180 E.523

11075620 2/3/98 1400 <.30 <.001 <.002 .210 E.391

11075620 2/3/98 1700 .410 <.001 <.002 .190 E.410

11075620 2/3/98 2000 — <.001 <.002 — E.178

11075620 2/3/98 2300 <.15 — — .160 —

11075620 2/4/98 0200 <.15 <.001 E.002 .450 E1.2
Appendix E 87

Appendix E. Data for pesticides detected in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California—Continued

USGS station 

number Data Time Chlorpyrifos(μg/L)

Cyanazine

(μg/L)

DCPA

(μg/L)

p,p'-DDE

(μg/L)

Deethyl atrazine

(μg/L)

Diazinon

(μg/L)

Diuron

(μg/L)

11075620 1/26/97 0400 0.010 <.004 0.070 <0.006 E0.003 0.125 E3.9

11075620 1/26/97 0930 <.01 <.004 .052 <.006 <.002 .120 E3.0

11075620 1/26/97 2130 .023 <.004 .153 <.006 <.002 .176 E3.3

11075620 1/27/97 1230 <.0040 <.004 .358 <.006 <.002 .091 E3.7

11075620 1/27/97 2130 <.01 <.004 .159 <.006 <.002 .077 E2.7

11075620 1/28/97 0930 <.0040 <.004 .151 <.006 <.002 .081 E2.8

11075620 9/15/97 0010 <.004 <.004 E.002 <.006 E.005 .025 <.02

11075620 9/15/97 0310 .011 <.004 E.002 <.006 <.002 .132 <.02

11075620 9/15/97 0610 .005 <.004 E.002 <.006 <.002 .041 <.02

11075620 9/15/97 0910 .016 <.004 E.002 <.006 <.002 .087 <.02

11075620 9/15/97 1115 .008 <.004 E.002 <.006 <.002 .049 <.02

11075620 9/15/97 2350 <.004 <.004 E.004 <.006 <.002 .125 .050

11075620 9/24/97 2030 <.004 <.004 E.002 <.006 <.002 .010 —

11075620 9/24/97 2200 —————— <.02

11075620 9/25/97 0230 .012 <.004 E.003 <.006 <.002 .087 —

11075620 9/25/97 0400 —————— <.02

11075620 9/25/97 0530 .007 <.004 E.003 <.006 <.002 .061 —

11075620 9/25/97 0700 —————— <.02

11075620 9/25/97 0830 .017 <.004 .004 <.006 <.002 .418 —

11075620 9/25/97 1000 —————— <.02

11075620 9/25/97 1130 .014 <.004 .005 <.006 <.002 .344 —

11075620 9/25/97 1300 —————— E.12

11075620 9/25/97 1430 .022 <.004 .004 <.006 <.002 .512 —

11075620 9/25/97 1600 —————— <.02

11075620 9/25/97 1900 .011 <.004 E.003 <.006 <.002 .216 —

11075620 9/25/97 2030 —————— E.15

11075620 9/26/97 0100 .014 <.004 .004 <.006 <.002 .196 —

11075620 9/26/97 0230 —————— .190

11075620 9/26/97 1200 <.004 <.004 .006 <.006 <.002 .273 —

11075620 9/26/97 1330 —————— .680

11075620 2/3/98 0603 .005 <.004 E.003 <.006 <.002 .060 1.400

11075620 2/3/98 0800 E.002 <.004 E.003 <.006 <.002 .054 1.300

11075620 2/3/98 1000 .043 <.004 E.003 <.006 <.002 .431 1.000

11075620 2/3/98 1200 .042 <.004 E.003 <.006 <.002 .474 .580

11075620 2/3/98 1400 .031 <.004 E.003 <.006 <.002 .386 .630

11075620 2/3/98 1700 .029 <.004 E.003 <.006 <.002 .364 .510

11075620 2/3/98 2000 .020 <.004 E.003 <.006 <.002 .234 —

11075620 2/3/98 2300 —————— .850

11075620 2/4/98 0200 .017 <.004 .006 <.006 <.002 .242 E13
88 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98

Appendix E. Data for pesticides detected in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California—Continued

USGS station 

number Data Time Lindane(μg/L)

Malathion

(μg/L)

Metolachlor

(μg/L)

Napropamide

(μg/L)

Norflurazon

(μg/L)

Pendimethalin

(μg/L)

Prometon

(μg/L)

11075620 1/26/97 0400 <0.004 0.023 0.006 <0.003 E0.33 <0.004 E0.018

11075620 1/26/97 0930 <.004 .026 .006 <.003 E.27 <.004 E.014

11075620 1/26/97 2130 <.004 .038 .007 <.003 <.024 <.004 .023

11075620 1/27/97 1230 <.004 <.005 .010 <.003 <.024 <.004 <.018

11075620 1/27/97 2130 <.004 <.020 .008 <.003 <.024 <.004 <.018

11075620 1/28/97 0930 <.004 <.005 .008 <.003 <.024 <.004 E.013

11075620 9/15/97 0010 <.004 <.005 .011 <.003 <.024 <.004 E.009

11075620 9/15/97 0310 <.004 .029 .012 <.003 <.024 <.004 E.015

11075620 9/15/97 0610 <.004 <.005 .011 <.003 <.024 <.004 E.010

11075620 9/15/97 0910 <.004 .053 .010 <.003 <.024 <.004 E.008

11075620 9/15/97 1115 <.004 .009 .011 <.003 <.024 <.004 E.011

11075620 9/15/97 2350 <.004 .029 .010 <.003 <.024 <.004 .038

11075620 9/24/97 2030 <.004 <.005 .010 <.003 — <.004 E.010

11075620 9/24/97 2200 ———— <.024 — —

11075620 9/25/97 0230 <.004 .018 .011 <.003 — <.004 E.013

11075620 9/25/97 0400 ———— <.024 — —

11075620 9/25/97 0530 <.004 .020 .012 <.003 — <.004 E.010

11075620 9/25/97 0700 ———— <.024 — —

11075620 9/25/97 0830 <.004 .073 .011 <.003 — <.004 E.012

11075620 9/25/97 1000 ———— <.024 — —

11075620 9/25/97 1130 <.004 .079 .012 <.003 — <.004 E.013

11075620 9/25/97 1300 ———— <.024 — —

11075620 9/25/97 1430 <.004 .098 .010 <.003 — <.004 E.009

11075620 9/25/97 1600 ———— <.024 — —

11075620 9/25/97 1900 <.004 .052 .010 <.003 — <.004 E.011

11075620 9/25/97 2030 ———— <.024 — —

11075620 9/26/97 0100 <.004 .059 .012 <.003 — <.004 .045

11075620 9/26/97 0230 ———— <.024 — —

11075620 9/26/97 1200 <.004 .068 <.002 .085 — <.004 .054

11075620 9/26/97 1330 ———— <.024 — —

11075620 2/3/98 0603 .013 <.005 .004 <.003 <.024 <.004 .021

11075620 2/3/98 0800 .012 <.005 E.004 <.003 <.024 <.004 .020

11075620 2/3/98 1000 <.01 .075 E.004 <.003 <.024 .015 E.0145

11075620 2/3/98 1200 <.004 .051 E.003 <.003 <.024 .018 E.014

11075620 2/3/98 1400 <.004 .045 <.002 <.003 <.024 <.004 E.014

11075620 2/3/98 1700 <.004 .049 E.003 <.003 <.024 .011 E.013

11075620 2/3/98 2000 <.004 .018 <.002 <.003 — <.004 .020

11075620 2/3/98 2300 ———— <.024 — —

11075620 2/4/98 0200 <.004 .029 .005 <.003 <.024 <.004 .049
Appendix E 89

Appendix E. Data for pesticides detected in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, 

southern California—Continued

NOTE: When “E” is reported, the compound has passed all criteria used to identify its presence, and only the concentration is estimated 

(Connor and others, 1998).

USGS station 

number Data Time Pronamide(μg/L)

Propoxur

(μg/L)

Simazine

(μg/L)

Tebuthiuron

(μg/L)

Triclopyr

(μg/L)

Trifluralin

(μg/L)

11075620 1/26/97 0400 <0.003 <0.035 0.243 <0.01 <0.05 <0.002

11075620 1/26/97 0930 <.003 <.035 .195 <.01 <.05 <.002

11075620 1/26/97 2130 <.003 <.035 .315 <.01 <.05 <.002

11075620 1/27/97 1230 <.003 <.035 .580 <.01 <.05 <.002

11075620 1/27/97 2130 <.003 <.035 .381 <.01 <.05 <.002

11075620 1/28/97 0930 <.003 <.035 .384 <.01 <.05 <.002

11075620 9/15/97 0010 <.003 <.035 .046 <.01 <.05 <.002

11075620 9/15/97 0310 <.003 <.035 .052 <.01 <.05 <.002

11075620 9/15/97 0610 <.003 <.035 .047 <.01 <.05 <.002

11075620 9/15/97 0910 <.003 <.035 .041 <.01 <.05 <.002

11075620 9/15/97 1115 <.003 <.035 .045 <.01 <.05 <.002

11075620 9/15/97 2350 <.003 <.035 .048 <.01 <.05 <.002

11075620 9/24/97 2030 <.003 — .039 <.01 — <.002

11075620 9/24/97 2200 — <.035 — — <.05 —

11075620 9/25/97 0230 <.003 — .040 <.01 — <.002

11075620 9/25/97 0400 — <.035 — — <.05 —

11075620 9/25/97 0530 <.003 — .040 <.01 — <.002

11075620 9/25/97 0700 — <.035 — — .580 —

11075620 9/25/97 0830 <.003 — .038 <.01 — <.002

11075620 9/25/97 1000 — <.035 — — .230 —

11075620 9/25/97 1130 <.003 — .035 <.01 — <.002

11075620 9/25/97 1300 — <.035 — — .930 —

11075620 9/25/97 1430 <.003 — .031 <.01 — <.002

11075620 9/25/97 1600 — <.035 — — .440 —

11075620 9/25/97 1900 <.003 — .042 <.01 — <.002

11075620 9/25/97 2030 — <.035 — — E.25 —

11075620 9/26/97 0100 <.003 — .042 <.01 — <.002

11075620 9/26/97 0230 — <.035 — — .460 —

11075620 9/26/97 1200 <.003 — .078 <.01 — <.002

11075620 9/26/97 1330 — <.035 — — <.05 —

11075620 2/3/98 0603 <.003 <.035 .104 <.01 <.25 <.002

11075620 2/3/98 0800 <.003 <.035 .096 <.01 <.25 <.002

11075620 2/3/98 1000 .019 <.035 .048 <.01 .190 E.004

11075620 2/3/98 1200 <.003 <.035 .029 <.01 <.25 E.002

11075620 2/3/98 1400 <.003 <.035 .068 <.01 <.25 <.002

11075620 2/3/98 1700 <.003 <.035 .103 <.01 <.25 <.002

11075620 2/3/98 2000 <.003 — .144 <.01 — <.002

11075620 2/3/98 2300 — <.035 — — <.25 —

11075620 2/4/98 0200 <.003 <.035 .419 <.01 <.25 E.002

Appendix F 91

APPENDIX F

Data for Volatile Organic Compounds
92 Stormflow Chemistry in the Santa Ana River below Prado Dam and at the Diversion Downstream from Imperial Highway, Southern California, 1995–98 Appendix F. Data for volatile organic compounds detected in the Santa Ana River below Prado Dam, at the diversion downstream from Imperial Highw

the Santa Ana River near Imperial Highway, southern California [USGS, U.S. Geological Survey; μg/L, microgram per liter; E, estimated value; <, less than] Station name USGS station number Date Time 2-Methoxy-2- methylpropane (MTBE)

(μg/L)

Bromodichloromethane

(μg/L)

Dichloromethane

(Methylene chloride)

(μg/L)

M

Santa Ana River below Prado Dam 11074000 9/15/97 0640 0.3 0.4 < 0.4 

9/15/97 1040 .3 .4 < .4 9/15/97 1250 .4 .4 < .4 11/10/97 0900 .3 .4 < .2 11/10/97 1300 .3 .4 < .2 11/10/97 1700 < .8 .6 1.1 2/3/98 1530 .4 .5 < .2 2/4/98 1405 E .7 < .2 < .2 

Santa Ana River at the diversion downstream from Imperial Highway 11075620 9/15/97 0010 .2 < .2 < .2 

9/15/97 0610 .2 < .2 < .2 9/15/97 0910 .3 < .4 < .4 9/15/97 1115 .3 < .2 < .2 11/10/97 1000 .4 < .4 .9 11/10/97 1230 < .8 < .8 1.3 2/3/98 0603 .5 < .4 < .4 2/3/98 0800 .3 < .4 < .4 2/3/98 1000 .2 < .4 < .4 2/3/98 1200 .2 < .2 < .2 2/3/98 1400 .3 < .2 < .2 2/3/98 1700 .3 < .2 < .2 2/3/98 2000 .4 < .2 < .2 2/3/98 2300 E .6 < .2 < .2 2/4/98 0200 .6 < .4 < .4 2/4/98 1218 E .6 < .2 < .2 

Storm drain near Imperial Highway 335129117472101 2/3/98 0730 E .9 < .4 < .4 

2/3/98 0940 .4 < .2 < .2 2/3/98 1150 .3 < .4 < .4 2/3/98 1350 .4 < .4 < .4 2/3/98 1650 .3 < .4 < .4