U.S. Department of the Interior

U.S. Geological Survey

Open File Report 2010–1234

November 2010 Printed on recycled paper

Figure 1. Smoke from the Harris 

Fire drifting over Sweetwater 

Reservoir, San Diego County, 

California.

Photograph taken by Michael S. Majewski, 

U.S. Geological Survey, October 2007.

By Gregory O. Mendez

Water-Quality Data from Storm Runoff after the 2007 Fires,

San Diego County, California

Abstract

The U.S. Geological Survey collected water-quality samples during 

the first two storms after the Witch and 

Harris Fires (October 2007) in southern 

California. The sampling locations represent an urban area (two residential sites 

in Rancho Bernardo that were affected 

by the Witch Fire; a drainage ditch and 

a storm drain) and a rural area (Cottonwood Creek, which was downstream of 

a mobile home park destroyed by the 

Harris Fire). 

Fires produce ash and solid residues that contain soluble chemicals that 

can contaminant runoff. The contaminants, whether sorbed to soil and ash 

or dissolved, can seriously affect the 

quality of water supplies and sensitive 

ecosystems.

Stormflow water samples were analyzed for field parameters, optical properties, and for a variety of constituents, 

including nutrients, dissolved organic 

carbon (DOC), suspended sediment,

and metals. 

pH values for storm runoff from the 

urban areas (7.6 to 8.5) were less than pH 

values for ash and burned soil from previous studies (12.5 to 13). pH values for 

storm runoff from the rural area (about 

7.7) also were less than pH values for ash 

and burned soil collected from the rural 

area (8.6 to 11.8), but were similar to 

pH values for wildland burned soil from 

previous studies. Turbidity values were 

much lower for the urban area than for 

the rural area.

Nitrate concentrations in stormflow 

samples from all sites were less than a 

quarter of the U.S. Environmental Protection Agency’s (2006) maximum allowable contaminant level of 10 milligrams 

per liter (mg/L) (as nitrogen). Phosphorus 

concentrations were half as much in 

filtered samples and two orders of magnitude smaller in unfiltered samples at 

the urban sites than at the rural site. DOC 

concentrations in stormflow samples 

were one order of magnitude lower at the 

urban sites than at the rural site. Ultraviolet (UV) absorbance at 254 nanometers 

(UV254 ) in samples ranged from 

0.145 to 0.782 per centimeter 

(cm-1). UV-absorbance data at 

the urban sites indicate that the 

composition of DOC remained 

similar during both storms even 

though the DOC concentration 

changed.

Total suspended-sediment 

concentrations ranged from 7 to 

349 mg/L at the urban area, and 

were 64,800 and 36,800 mg/L at 

the rural area. Trace metals analyzed in unfiltered water samples 

had lower concentrations in 

the urban area than in the rural area. No 

concentrations of arsenic or mercury 

measured in the samples were above 

aquatic-life criteria. In the urban area, 

most concentrations of aluminum, iron, 

and lead exceeded aquatic-life criteria. 

In the rural area, aluminum, cadmium, 

iron, lead, and zinc exceeded aquatic-life 

criteria. Concentrations of aluminum and 

iron were two orders of magnitude larger 

in the rural area than in the urban area.

Introduction

More than 20 fires burned throughout southern California in October 

2007. The two largest fires in San Diego 

County were the Witch and Harris 

Fires. Smoke from the Harris Fire was 

extensive, nearly covering Sweetwater 

Reservoir (fig. 1). The Witch Fire (fig. 2) 

burned about 200,000 acres of urban 

and rural landscape and damaged or 

destroyed 1,125 homes (Federal Emergency Management Agency, 2009). The 

Harris Fire (fig. 2) burned about 90,000 

acres and destroyed more than 200 homes 
SAN DIEGO

POWAY

CHULA VISTA

CARLSBAD

OCEANSIDE VISTA

ESCONDIDO

SANTEE

SAN MARCOS

ENCINITAS

EL CAJON

CORONADO

LINDBERGH

FIELD

AIRPORT

LA MESA

NATIONAL CITY

IMPERIAL BEACH

LEMON GROVE

SOLANA BEACH

DEL MAR

SAN LUIS REY

SAN DIE G O

ROSARITO

Highways

Urban sites

Rural site

Lakes

Watersheds

National forests 

SAN JUAN

Ammo/Horno Fire Rice Fire

Riverside

Co

SANTA MARGARITA

CLARK

San Diego

Co

Orange

Co

ANZA-BORREGO

Poomacha Fire

M E X I C O

Witch Fire

Harris Fire

SAN DIEGUITO CARLSBAD

PENASQUITOS

SWEETWATER

TIJUANA

OTAY

OTAY

PUEBLO SAN DIEGO

SAN DIEGO BAY

78

94

94

163

125

67

78

56

52

54

8 8

15

15

5

5

805

805

Rancho

Bernardo

0 2.5 5 10

Miles

Source : San Diego County ECO GIS Force Group,

San Diego State University,

http://sdfires.pbwiki.com 

Areas burned in both

 years 2003 and 2007

Water-quality sampling

 locations

Approx. 2007 wildfire

 perimeters

Approx. 2003 wildfire

 perimeters

EXPLANATION

Area of

 map CALIFORNIA

Pacific Ocean

Lake

Hodges

Barrett

Reservoir

Water-Quality Data

U.S. Department of the Interior 2

U.S. Geological Survey

November 2010

Figure 2. Study area and water-quality sampling locations for stormflow samples collected in 

Cottonwood Creek and storm drains in Rancho Bernardo, California.

(Public Broadcasting Service, 2009). By 

the second day of the 2007 fires, approximately 500,000 people had received 

mandatory evacuation orders (San Diego 

Association of Governments, 2009). 

These large fires significantly affect 

urban and rural areas, but water-quality 

data following such fires are limited. 

Urban fires, more than forest fires, can 

result in increased availability of chemicals and contaminants, mainly in the 

form of ash and debris. When rains come, 

contaminants can be mobilized by the 

rainfall runoff and associated wind. Contaminants, whether sorbed to soil and ash 

or dissolved in the runoff water, have the 

potential to seriously affect the quality of 

water supplies and sensitive habitat areas 

or ecosystems. 

After the fires and before the rains, 

the U.S. Geological Survey (USGS) collected ash and soil samples in many areas 

of San Diego County for analysis of metals and other constituents (Plumlee and 

others, 2007). The pH of leachate from 

these ash samples was compared to the 

pH in water samples from the post-fire 

rainfall runoff.

Purpose and Scope

The purpose of this report is to 

present water-quality data collected from 

runoff in two areas burned in the 2007 

Witch and Harris Fires. This runoff may 

contain contamination that can end up 

in the waterways and reservoirs. Waterquality samples were collected during the 

first runoff events following the fires. The 

sampling locations were selected to identify water-quality differences between 

urban and rural settings and to evaluate 

runoff that may end up in local drinkingwater reservoirs. 

Approach

Discrete water-quality samples were 

collected during the first two storms that 

followed the 2007 San Diego fires. Initial 

samples were collected shortly after 

runoff began, followed by periodic sampling during the recession of the storm. 

Samples were collected during the first 

storm after the fires (November 30, 2007) 

in the urban and rural areas. Samples 

were collected during the second storm 

after the fires (December 7, 2007) only in 

the urban area (Rancho Bernardo, at two 

residential sites; fig. 2). The collection of 

samples from each site included samples 

used for measurement of field parameters 

and for analysis of nutrients, organic 

carbon, UV absorbance, suspended sediment, and trace metals. Partial samples 

were collected for full-spectrum UV 

absorbance scans.

Site Selection for Sampling

The Witch Fire burned part of the 

upper San Diego River watershed and 

a large part of the San Dieguito River 

watershed (fig. 2). Two urban residential sites were sampled (table 1) in the 

San Dieguito River watershed. Flow 

from these urban sites drains into Lake 

Hodges, a drinking-water reservoir. These 

sites, situated across the street from one 

another in Rancho Bernardo (fig. 2), were 

sampled to determine whether there are 

differences between runoff into a storm 

drain from a heavily-burned residential 

hillside and runoff into a drainage ditch 

from the rest of the neighborhood that 

was not completely burned. In the burned 

hillside area, only masonry structures 

and charred vehicles remained at many 

of the home sites (fig. 3). Erosion-control 

devices were installed within days of the 

fires to reduce the amount of sediment 

and burned debris transported by runoff. 

The Harris Fire burned a large part 

of the Otay and Tijuana River watersheds 

(fig. 2). A rural site, on Cottonwood 

Creek at Barrett Junction below Barrett Reservoir, was sampled (fig. 2); 

this site is about 1 mile downstream of 

a mobile home park (fig. 4) that burned 

and is located near the head waters of the 

Tijuana River. Hydro-mulch, a slurry of 

grass seed and mulch that promotes quick 

germination and inhibits soil erosion, was 

placed at this location within days after 

the fire.

Storms Sampled

Precipitation in San Diego County 

can be highly variable during most 

storms, with rain distributed unevenly 

across the county. The first post-fire 

storm (November 30, 2007) came from 

the northwest, and rainfall was not 

widely distributed across the county. 
32.8

33.5

33.0

34.9

34.5

34.0

0000 0200 0400 0600 0800 1000 1200 1400 1600 1800 2000 2200 0000

TIME, IN HOURS

STAGE, IN POUNDS PER SQUARE INCH

Ditch Complete sample

Partial sample

Complete sample

Partial sample

Storm drain

December 7, 2007

OFR 2010-1234

U.S. Department of the Interior 3

U.S. Geological Survey

November 2010

November 30, 2007

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

TIME, IN HOURS

RAINFALL, IN INCHES

0000 0200 0400 0600 0800 1000 1200 1400 1600 1800 2000 2200

December 7, 2007

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

RAINFALL, IN INCHES

0000 0200 0400 0600 0800 1000 1200 1400 1600 1800 2000 2200

Figure 6. Response to flow for storm on December 7, 2007, Rancho Bernardo, California.

Figure 5. Hourly precipitation in Rancho 

Bernardo for storm events on November 30, 

and December 7, 2007. Data provided by Western 

Solutions, Inc.

Figure 3. Home 

destroyed by the 

Witch Fire in Rancho 

Bernardo, California. 

Photographs taken by 

Gregory O. Mendez, 

U.S. Geological Survey, 

November 2007.

Figure 4. Mobile home 

park in Cottonwood 

Creek that was 

burned by the Harris 

Fire near Barrett 

Junction, California.

4:20 p.m. (1620 hours) and 9:45 p.m. 

(2145 hours). 

During the second storm (December 

7, 2007), water-quality samples were collected only at the two urban Rancho Bernardo sites—no samples were collected 

at the rural site. The 24-hour-composite 

rainfall in Rancho Bernardo was about 

0.5 inches and fell in a few hours (fig. 5). 

The runoff response to the second storm 

was recorded in both the ditch and the 

outflow from the storm drain (fig. 6). 

Water-quality samples were collected 

every 2 hours from the ditch and collected every hour from the storm drain, 

from about 5:00 a.m. (0500 hours) until 

7:00 p.m. (1900 hours).

Analytical Methods 

Measurements of water temperature, pH, and specific conductance were 

taken by using a multi-parameter water 

sonde. Dissolved-oxygen measurements 

were taken by using a VVR photometer. 

Procedures for collecting and processing water samples to determine chemical 

content were based on established protocols (Shelton, 1994). Storm water-quality 

samples were collected using either an 

equal-width increment (EWI) method 

or a grab-sample method, depending on 

flow conditions. Samples obtained using 

the grab-sample method were collected 

by submerging a churn splitter or a 

1-liter (L) glass jar into the center of the 

channel to collect a sample, then processing the sample into the appropriate 

The 24-hour-composite rainfall was 

0.0 inches at Otay Reservoir, 0.9 inch 

at Lindbergh Field airport, 2.0 inches 

near Rancho Bernardo, 2.6 inches in the 

foothills to the east, and 2.7 inches in 

Oceanside to the north (fig. 2). It started 

raining in the urban area of Rancho 

Bernardo around 6:00 a.m. (0600 hours) 

and rained intermittently throughout the 

day. Water-quality samples were collected from noon (1200 hours) to 7:00 

p.m. (1900 hours). Rain began to fall at 

the Cottonwood Creek site about 4:00 

p.m. (1600 hours) and lasted a few hours. 

Water-quality samples were collected at 
Station name Station number

Date 

(yyyymmdd)

Sample 

time 

Location 

type

Altitude 

of land 

surface 

(feet )

Absorbance, 

UV254

nm, ( per 

centimeter)

Alkalinity, 

fi eld 

(milligrams 

per liter as 

CaCO3)

Dissolved 

oxygen 

(milligrams 

per liter)

Nitrate 

plus nitrite 

(milligrams 

per liter 

as N)

Organic 

carbon, 

fi ltered 

(milligrams 

per liter)

Organic 

carbon, 

unfi ltered 

(milligrams 

per liter)

pH, fi eld 

(standard 

units)

Phosphorus, 

fi ltered 

(milligrams 

per liter)

Drainage ditch on 

West Bernardo 

Drive at Rancho 

Bernardo

330226117044001 20071130 1140 Urban 360 0.339 26.0 10.5 0.783 12 22.0 8.0 0.335

20071130 1430 0.262 23.2 na 0.637 11 17.0 8.2 0.328

20071130 1900 0.625 69.7 10.0 na 18 25.4 8.2 na

20071207 0900 0.210 31.1 10.8 0.555 9.4 19.1 8.2 0.226

Storm drain on 

West Bernardo 

Drive at Rancho 

Bernardo

330225117044101 20071130 1900 Urban 370 0.782 198 10.1 2.08 22 30.5 7.6 0.335

20071207 0600 0.145 24.7 11.1 0.494 7.0 28.3 8.5 0.221

20071207 0910 0.170 36.2 11.6 0.765 9.6 12.8 8.1 0.293

20071207 1200 0.536 165 11.5 2.73 15 21.1 8.0 0.345

Cottonwood Creek 

at Highway 94 

bridge at Barrett 

Junction

323631116420201 20071130 1825 Rural 860 0.703 166 na 1.46 180 198 7.8 0.722

20071130 2145 0.497 225 na 2.45 280 2,870 7.7 0.741

Table 1. Field parameters and selected 

constituents in stormflow samples collected 

at Rancho Bernardo and Barrett Junction, 

California. [UV absorbance, turbidity, alkalinity, 

and residue on evaporation (ROE) was analyzed 

at the U.S. Geological Survey (USGS) National 

Water Quality Laboratory in Denver, Colorado. 

Sediment samples were analyzed at the USGS 

sediment laboratory in Marina, California. NTRU, 

nephelometric turbidity ratio unit; nm, nanometer; 

CaCO3, calcium carbonate; na, not analyzed; E, 

estimated value]

Water-Quality Data

U.S. Department of the Interior 4

U.S. Geological Survey

November 2010

storm, the alkalinity values were initially 

about the same at both sites. Dissolved 

oxygen ranged from 10 to 11.6 mg/L 

in the urban area; no measurement of 

dissolved oxygen was made in the rural 

area. pH values in storm samples in the 

urban area ranged from 7.6 to 8.5 units, 

and pH values in the rural area were 7.8 

and 7.7 units. Both ranges of pH values 

were significantly below residential ash 

and burned soil values (12.5 to 13 units) 

obtained from a 5-minute leach test 

(Hageman, 2007). pH values for storm 

runoff from the urban area were similar 

to those for wildland burned soil from 

a 5-minute leach test (Hageman, 2007), 

but most samples had lower alkalinity. pH values for storm runoff from 

the rural area were less than pH values 

for ash and soil from the mobile home 

park that burned, 12.5 and 10.6 units, 

respectively (site Harris 07; Plumlee and 

others, 2007), but were similar to those 

for local burned soil samples (site Harris 

06; Hageman and others, 2008). Turbidity values for the rural area (15,700 to 

22,700 nephelometric turbidity ratio 

units [NTRU]) were orders of magnitude 

greater than those for the urban area (9.7 

to 154 NTRU).

Nitrate concentrations in stormflow 

samples at all sites were less than a quarter of the maximum contaminant level 

of 10 mg/L as nitrogen, as set by the 

U.S. Environ-mental Protection Agency 

(2006). Nitrate concentrations at all sites 

were highest during stormflow recession. 

Phosphorus concentrations in filtered 

samples were twice as high in the rural 

area as in the urban area. Phosphorus 

concentrations in unfiltered samples were 

two magnitudes greater in the rural area 

than in the urban area.

Suspended Sediment 

The highest suspended-sediment 

concentrations were in the rural area, and 

93 to 100 percent of this sediment was 

finer than 0.062 millimeter (mm). In the 

urban area, 70 to 84 percent of the suspended sediment in the storm drain was 

fine-grained (less than 0.062 mm) and 56 

to 92 percent of the suspended sediment 

in the drainage ditch was fine-grained. 

Total-suspended-sediment concentrations in the urban area were lower than 

those in the rural area, possibly because 

hay rolls were used in burned areas to 

minimize erosion. 

Organic Carbon

Ten samples were analyzed for 

DOC (from filtered water samples) and 

for total organic carbon (TOC) (for 

unfiltered water samples) (table 1, fig. 

7). DOC concentrations were 180 and 

280 mg/L in the rural area and ranged 

from 7 to 22 mg/L in the urban area. The 

median concentration of DOC in the 

urban area was 11.8 mg/L. TOC concentrations were 198 and 2,870 mg/L in 

the rural area, and ranged from 12.8 to 

30.5 mg/L in the urban area. Both DOC 

and TOC concentrations were greater in 

samples from the rural area than from the 

urban area (fig. 7). High organic carbon 

concentrations in the rural area are not 

surprising because water samples from 

this area were almost black with ash; 

bottles. Sediment samples were collected in separate bottles by using the 

EWI method and analyzed using methods described by Guy (1969).

Nutrients, organic carbon, UV 

absorbance at 254 nm, and metals were 

analyzed at the USGS National Water 

Quality Laboratory in Denver, Colorado, 

by using methods described by Fishman and Friedman (1989), Brenton and 

Arnett (1993), Fishman (1993), Standard 

Methods, 19th Edition (1995), Garbarino 

and Struzeski (1998), Patton and Truitt 

(2000), Garbarino and Damrau (2001), 

and Garbarino and others (2006). Fullspectrum optical-property measurements 

of UV absorbance were made by the 

USGS laboratory in San Diego, California. UV absorbance was measured from 

190 to 400 nm using a UV/VIS spectrophotometer with a 1 cm path-length cell. 

Water-Quality Data 

Selected water-quality data and field 

parameters for ten samples are listed in 

table 1. The highest alkalinity was in the 

rural area. During the first storm in the 

urban area, the alkalinity in the storm 

drain was about three times the alkalinity 

in the drainage ditch; during the second 
11/30

at

1825

11/30

at

2145

11/30

at

1900

12/07

at

0600

12/07

at

0910

12/07

at

1200

11/30

at

1140

11/30

at

1430

11/30

at

1900

12/07

at

0900

1

10

100

1,000

10,000

Dissolved organic carbon (filtered)

Total organic carbon (unfiltered)

LOCATION

DATE AND TIME OF SAMPLE (24 HOUR)

ORGANIC CARBON, IN MILLIGRAMS PER LITER

Cottonwood

Creek

Rancho Bernardo

ditch

Rancho Bernardo

storm drain

Figure 7. Graph of organic carbon from stormflow samples collected in Cottonwood 

Creek and Rancho Bernardo, California.

Phosphorus, 

unfi ltered 

(milligrams 

per liter)

Residue on 

evaporation @ 

180 degrees Celsius (milligrams 

per liter)

Silica, 

fi ltered 

(milligrams 

per liter)

Silica, 

unfi ltered 

(milligrams 

per liter)

Specifi c 

conductance, 

fi eld (microsiemens per 

centimeter) 

Suspended 

sediment 

concentration 

(milligrams 

per liter)

Suspended 

sediment, sieve 

>0.0625 mm 

(percent)

Turbidity 

(NTRU)

Water 

temperature, fi eld 

(degrees 

Celsius)

0.484 113 2.59 18.4 269 120 91.9 71.4 16.7

0.555 93 2.36 24.5 142 268 81.0 118 na

na 456 9.94 14.3 691 50 56.4 na 17.1

0.389 100 4.00 26.3 182 na na 154 14.2

0.409 2,220 27.3 28.0 na 7 70.2 22.6 16.2

0.518 123 2.88 23.3 215 349 77.0 104 14.1

0.450 246 5.33 11.2 660 79 84.2 46.1 14.3

0.398 1,410 31.3 32.4 1,940 na na 9.7 16.6

25.3 586 6.61 275 579 64,800 93.1 15,700 na

65.5 969 6.90 392 990 36,800 99.6 22,700 15.7

OFR 2010-1234

U.S. Department of the Interior 5

U.S. Geological Survey

November 2010

even after filtering, the samples were 

dark brown.

Knowing the source and composition of organic carbon is important 

because of environmental concerns 

associated with DOC having the potential to increase disinfection by-product 

formation during chlorination of drinking water. Many disinfection byproducts 

have been shown to cause cancer and 

developmental effects in laboratory 

animals (U.S. Environmental Protection 

Agency, 2006). Since storm runoff at the 

study sites was not sampled before the 

two post-fire storms, pre-fire DOC values 

for unburned conditions at these sites are 

unknown; however, concentrations of 3 

to 5 mg/L are typical for surface water 

in arid regions (Thurman, 1986). For 

comparison, DOC concentrations from 

the Santa Ana River (in Orange County) 

ranged from 3 to 15 mg/L, with a median 

concentration of 6.7 mg/L (Izbicki and 

others, 2004).

Ultraviolet Absorbance

A simplified approach to characterize the composition of DOC is to utilize 

changes in optical properties of water. 

Exposure to specific wavelengths of light 

can result in the absorbance and fluorescence of energy that is related to the 

presence of specific functional groups 

within complex carbon molecules. Optical properties of DOC are useful for 

identification of aromatic (benzene-like 

ring structures) and aliphatic (carbon 

compounds not containing benzene ring 

structures) compounds. Interpretation 

of UV absorbance data does not provide quantitative analysis of DOC; 

however, a change in UV absorbance 

can indicate a change in composition of 

DOC (California Department of Water 

Resources, 1994; Izbicki and others, 

2007). DOC absorbance within the UV 

range of 220−800 nm is associated with 

unsaturated molecules, such as those 

containing carbon-carbon double bonds 

or carbon-oxygen double bonds (Gutsche 

and Pasto, 1975). Carbon-carbon double 

bonds within aromatic ring structures 

generally absorb near 254 nm, and 

carbon-oxygen double bonds generally 

absorb near 285 nm. The exact absorbance wavelength, however, varies with 

the length and complexity of associated 

carbon molecules and other structures 

(Izbicki and others, 2004). Ring-structure 

bonds cause smooth curves instead of 

peaks at wavelengths corresponding to 

specific functional groups (figs. 8A,B).

Although UV absorbance was measured from 190 to 400 nm (figs. 8A,B), 

analyses were conducted on data collected at 254 nm. UV absorbance at 254 

nm (UV254) in samples from the urban 

area ranged from 0.145 to 0.782 cm-1, 

with a median absorbance of 0.300 cm-1. 

UV254 data collected from storm runoff 

in this study were similar to UV254 data 

collected from storm runoff on the Santa 

Ana River (Izbicki and others, 2004). 

Data from two samples collected at the 

same time from the urban area during 

the first storm (November 30, 2007 at 

1900 hours) indicate there was about 25 

percent more DOC coming through the 

storm drain than through the drainage 

ditch across the street. During the second 

storm, the DOC in the drainage ditch 

was about the same as that of the DOC 

in the storm drain.

Nitrate and iron absorb in lower UV 

ranges (190–230 nm), which may have 

caused the large differences in individual 

samples in this range. Within the range 

230 to 400 nm, more variability for the 

two storms is observed in the storm 

drain than in the drainage ditch. UV 

absorbance at 254 nm was compared to 

DOC concentrations (fig. 9) in order to 

identify differences between samples or 

between storms. The strong correlation 

for all samples in both storms (R2 = 0.98) 
UV ABSORBANCE AT 254 NANOMETERS

DISSOLVED ORGANIC CARBON, IN MILLIGRAMS PER LITER

0

5

10

15

20

25

R2 = 0.98

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

November storm

December storm

Linear (all data)

Drainage ditch

Storm drain

Drainage ditch

Storm drain

Figure 9. Dissolved organic carbon (DOC) as 

a function of UV254 from stormflow samples 

collected in Rancho Bernardo, California

Water-Quality Data

U.S. Department of the Interior 6

U.S. Geological Survey

November 2010

WAVE LENGTH, IN NANOMETERS

ABSORBANCE

B

0

1

2

3

4

5

0

1

2

3

4

5

190 240 290 340 390 190 240 290 340 390

254 285 254

Time (24 hr)

December 7, 2007

Drainage ditch

Time (24 hr)

December 7, 2007

Storm drain

0430

0700

0800

0900

1000

1100

1300

1400

1500

1600

1700

1800

1900

1930

285

0500

0700

1100

1300

1500

1700

1900

Figure 8. Full-spectrum ultraviolet (UV) 

absorbance scans for filtered stormflow 

samples collected in Rancho Bernardo, 

California drainage ditch for storms of (A) 

November 30, 2007, and (B) December 7, 

2007. [UV Absorbance was analyzed at U.S. 

Geological Survey Water Quality Laboratory in San 

Diego, California.] ABSORBANCE

A

0

1

2

3

4

5

0

1

2

3

4

5

254 285 254

1140

1200

1400

1430

1900

Time (24 hr)

November 30, 2007

Drainage ditch

1230

1300

1500

1600

1700

1800

1900

285

November 30, 2007

Storm drain

Time (24 hr)

suggests that the composition of DOC 

remained substantially the same. 

 Metals and Major Ions

Metals (including trace elements) 

and major ions were analyzed for in 

filtered and unfiltered water samples 

(table 2). Metals occur naturally in 

the environment, but when metals are 

released into the environment in higher 

than natural concentrations, they can 

be problematic because colloidal and 

dissolved metals may influence the rates 

and mechanisms of metal bioaccumulation (the accumulation of an environmental compound into an organism). 

Two aquatic-life criteria that are intended 

to be protective of the vast majority of 

the aquatic communities in the United 

States (U.S. Environmental Protection 

Agency, 2005) are listed in table 2. Criteria Maximum Concentration (CMC) is 

an estimate of the highest concentration 

of a material in surface water to which 

an aquatic community can be exposed 

briefly without resulting in an unacceptable effect. The Criterion Continuous 

Concentration (CCC) is an estimate of 

the highest concentration of a material in 

surface water to which an aquatic community can be exposed indefinitely without resulting in an unacceptable effect. 

Aquatic-life criteria are established for 

about half of the metals and ions listed 

in table 2. No concentrations for arsenic 

or mercury were detected above either 

CMC or CCC. In the urban area, most 

concentrations of aluminum, iron, and 

lead exceeded both aquatic-life criteria. 
OFR 2010-1234

U.S. Department of the Interior 7

U.S. Geological Survey

November 2010

Table 2. Metal (including trace elements) and major-ion concentrations in stormflow samples collected at Rancho Bernardo and Barrett 

Junction, California. [Analyzed at the U.S. Geological Survey National Water Quality Laboratory in Denver, Colorado. E, estimated value. Shaded columns 

represent major ions; μg/L, microgram per liter] 

Station name Station number

Date 

(yyyymmdd)

Sample 

time 

Aluminum, 

fi ltered 

(micrograms 

per liter)

Aluminum, 

unfi ltered 

(micrograms 

per liter)

Antimony, 

unfi ltered 

(micrograms 

per liter)

Arsenic, 

fi ltered 

(micrograms 

per liter)

Arsenic, 

unfi ltered 

(micrograms 

per liter)

Cadmium, 

fi ltered 

(micrograms 

per liter)

Cadmium, 

unfi ltered 

(micrograms 

per liter)

Criteria Maximum Concentration, (μg/L) 750 340 2.0

Criteria Continuous Concentration, (μg/L) 87 150 0.25

Drainage ditch on West Bernardo Drive at 

Rancho Bernardo

330226117044001 20071130 1140 20.0 3,710 2.01 1.06 1.93 0.063 0.215

20071130 1430 21.7 4,980 1.42 1.07 2.21 E.034 0.258

20071130 1900 10.1 994 2.10 2.15 2.44 0.095 0.141

20071207 0900 11.2 4,820 1.71 1.21 1.98 E.034 0.163

Storm drain on West Bernardo Drive at 

Rancho Bernardo

330225117044101 20071130 1900 8.4 130 0.852 2.61 2.87 0.129 0.181

20071207 0600 17.2 5,210 3.22 1.37 3.54 E.026 0.442

20071207 0910 18.3 1,470 2.54 2.13 2.67 0.055 0.290

20071207 1200 13.7 434 2.21 5.11 5.39 0.101 0.119

Cottonwood Creek at Highway 94 bridge 

at Barrett Junction

323631116420201 20071130 1825 105 451,000 0.750 2.10 33.1 E.038 8.89

20071130 2145 64.3 21,900 1.54 2.67 36.5 0.067 10.2

Station name Station number

Calcium, 

fi ltered 

(milligrams 

per liter)

Chloride, 

fi ltered 

(milligrams 

per liter)

Chromium, 

unfi ltered 

(micrograms 

per liter)

Copper, 

fi ltered 

(micrograms 

per liter)

Copper, 

unfi ltered 

(micrograms 

per liter)

Iron, 

fi ltered 

(micrograms 

per liter)

Iron, 

unfi ltered 

(micrograms 

per liter)

Lead, 

fi ltered 

(micrograms 

per liter)

Lead, 

unfi ltered 

(micrograms 

per liter)

Criteria Maximum Concentration, (μg/L) 860 na 65

Criteria Continuous Concentration, (μg/L) 230 1,000 2.5

Drainage ditch on West Bernardo Drive at 

Rancho Bernardo

330226117044001 12.8 15.5 5.43 8.01 24.2 30.5 4,430 0.304 7.51

11.1 13.2 7.33 8.99 35.2 26.9 6,930 0.279 9.82

45.8 98.7 2.99 9.37 15.3 19.7 1,040 0.177 3.00

13.6 12.5 9.40 6.50 25.1 18.2 7,350 0.197 10.5

Storm drain on West Bernardo Drive at 

Rancho Bernardo

330225117044101 195 646 1.38 7.97 9.1 17.4 143 E.170 0.616

15.8 13.7 8.41 5.58 70.4 16.1 6,990 0.185 16.7

31.6 41.4 3.40 7.42 28.1 16.5 1,840 0.386 11.7

126 268 2.90 12.1 19.4 36.1 551 0.227 2.10

Cottonwood Creek at Highway 94 bridge 

at Barrett Junction

323631116420201 71.0 30.1 80.3 6.05 104 110 236,000 0.145 1,030

132 63.9 42.9 6.90 322 89.5 238,000 0.148 286

Station name Station number

Magnesium, 

fi ltered 

(milligrams 

per liter)

Manganese, 

fi ltered 

(micrograms 

per liter)

Manganese, 

unfi ltered 

(micrograms 

per liter)

Mercury, 

unfi ltered 

(micrograms 

per liter)

Potassium, 

fi ltered 

(milligrams 

per liter)

Sodium, 

fi ltered 

(milligrams 

per liter)

Sulfate, 

fi ltered 

(milligrams 

per liter)

Zinc, 

fi ltered 

(micrograms 

per liter)

Zinc, 

unfi ltered 

(micrograms 

per liter)

Criteria Maximum Concentration, (μg/L) 1.4 120

Criteria Continuous Concentration, (μg/L) 0.77 120

Drainage Ditch on West Bernardo Drive at 

Rancho Bernardo

330226117044001 3.59 28.4 158 0.017 3.21 13.0 22.8 22.8 88.1

2.72 21.9 221 0.025 3.00 10.6 20.2 17.2 114

20.3 76.1 112 0.015 5.80 68.5 130 31.2 49.0

3.41 29.8 210 0.017 2.63 12.9 20.1 8.03 69.4

Storm Drain on West Bernardo Drive at 

Rancho Bernardo

330225117044101 114 47.5 67.4 0.013 11.5 353 597 17.4 18.5

2.98 15.0 212 0.067 2.67 12.7 34.3 8.69 200

7.20 27.7 84.0 0.018 4.28 33.2 74.4 17.3 66.5

63.5 82.8 97.3 0.024 7.40 223 484 25.8 33.0

Cottonwood Creek at Highway 94 bridge 

at Barrett Junction

323631116420201 18.2 637 3,480 < .010 21.0 19.7 60.6 5.37 862

32.6 426 1,180 < .010 24.5 35.6 135 4.56 1,790

Chloride concentrations in the storm 

drain exceeded CCC during the recession of both storms. In the rural area, 

aluminum, cadmium, iron, lead, and zinc 

exceeded both aquatic-life criteria.

 Concentrations of metals in 

unfiltered water samples from the first 

storm at the urban sites were highest in 

the middle sample, but concentrations 

decreased throughout the second storm. 

Concentrations of most trace metals in 

unfiltered water samples from the storm 

drain decreased throughout the second 

storm, whereas the filtered water sample 

had the highest concentrations in the last 

sample. At all sites, ion concentrations 

increased during storm sampling. The 

rural site had higher concentrations in 

unfiltered water samples than the urban 

sites for all metals and ions analyzed 

except for antimony and mercury. The 

rural site had higher concentrations of 

aluminum and manganese in filteredwater samples for than the urban sites. 

These high concentrations in water 

samples may be the result of the composition of debris from the upstream mobile 

home park that burned.

Conclusions

Following extensive wildfires in 

San Diego County in October 2007, 

water-quality samples were collected in 

runoff from burned areas, which could 

have been sources of contamination to 

waterways or reservoirs. The sampling 
8

sites were chosen within the two largest 

burned areas in San Diego County and 

represented an urban area (two residential sites in Rancho Bernardo: a drainage 

ditch and a storm drain that were affected 

by the Witch Fire) and a rural area (Cottonwood Creek, which was downstream 

of a mobile home park destroyed in the 

Harris Fire). Samples were collected 

from runoff during the first two storms 

following the fires. 

Nitrate concentration in stormflow 

samples were less than a quarter of the 

maximum contaminant level of 10 mg/L, 

as nitrogen (U.S. Environmental Protection Agency, 2006). Nitrate values were 

highest during the recession of the storm. 

Phosphorus concentrations were twice as 

high in filtered samples and two magnitudes larger in unfiltered samples from 

the rural site than from the two urban 

sites. Total sediment concentrations at 

the residential sites ranged from 7 to 

349 mg/L; the percentage of fines ranged 

from 56 to 92. Total sediment concentrations at the rural site were 64,800 and 

36,800 mg/L, of which 93–100 percent 

was fines. Turbidity concentrations in the 

rural area were hundreds or thousands of 

times greater than those in the urban area.

DOC concentrations and UV absorbance values were lower in the residential 

area than in the rural area. DOC concentrations in stormflow samples ranged 

from 7.0 to 22 mg/L at the urban sites 

and from 180 to 280 mg/L at the rural 

site. UV absorbance at 254 nm (UV254) 

in samples from the residential sites 

ranged from 0.145 to 0.782 cm-1 and at 

the rural site were 0.703 and 0.497 cm-1. 

UV-absorbance data indicated that the 

composition of DOC remained substantially the same during both storms. 

 Selected metals analyzed for this 

study had lower concentrations in water 

from the urban sites than from the rural 

site. No concentrations of arsenic or 

mercury were detected above aquatic-life 

criteria. In the urban area, most concentrations of aluminum, iron, and lead 

exceeded both aquatic-life criteria. In 

the rural area, aluminum, cadmium, iron, 

lead, and zinc exceeded both aquatic-life 

criteria. Concentrations of aluminum 

and iron were two orders of magnitude 

greater in the rural area than the urban 

area. At all sites, ion concentrations 

increased with time.

U.S. Department of the Interior

U.S. Geological Survey November 2010

Water-Quality Data

For additional information on this report 

contact

Greg Mendez

4165 Spruance Road, Suite 200

San Diego, CA 92101

(619) 225-6176

e-mail: gomendez@usgs.gov

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