Photograph (front cover) Westward view of Cache Creek from the bridge at Rumsey, California, by 

Cathy Munday, U.S. Geological Survey.
Mercury and Methylmercury 

Concentrations and Loads in the 

Cache Creek Basin, California, 

January 2000 through May 2001

By Joseph L. Domagalski, Charles N. Alpers, Darell G. Slotton, 

Thomas H. Suchanek, and Shaun M. Ayers

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2004-5037

Prepared in cooperation with the

California Bay–Delta Authority
U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225-0286

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Domagalski, J.L., Alpers, C.N., Slotton, D.G., Suchanek, T.H., and Ayers, S.M., 2004, Mercury and Methylmercury 

Concentrations and Loads in Cache Creek Basin, California, January 2000 through May 2001: U.S. Geological Survey 

Scientific Investigations Report 2004–5037, 56 p.
iii

Contents

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

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

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

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

Description of Study area and Selection of Sampling Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Sampling and Sample Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Analytical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Mercury Concentrations and Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Chemical Signatures of Water Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Chloride-to-Sulfate Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Boron-to-Aluminum Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Boron-to-Lithium Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Boron-to-Chloride Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Boron, Chloride, and Sulfate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Stable Isotopes of Hydrogen and Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Dissolved Organic Carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Appendix 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
iv

Figures

Figure 1. Map showing study area and location of sampling sites and major mercury 

point sources, Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 2. Graphs showing daily mean discharge for Bear Creek above Holsten Chimney 

Canyon and Cache Creek at Yolo, Cache Creek Basin, California . . . . . . . . . . . . . . . 8

Figure 3. Graphs showing concentrations of total mercury at large river sites, 

Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 4. Graphs showing concentrations of total mercury at small stream sites, 

Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 5. Graphs showing methylmercury concentrations at large river sites, 

Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 6. Graphs showing methylmercury concentrations at small stream sites, 

Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 7. Graphs showing instantaneous loads of total mercury in unfiltered and 

filtered water at large river sites, Cache Creek Basin, California . . . . . . . . . . . . . . . 14

Figure 8. Graphs showing instantaneous loads of total mercury in unfiltered and 

filtered water at small stream sites, Cache Creek Basin, California . . . . . . . . . . . . . 15

Figure 9. Map showing instantaneous loads of total mercury at selected sites sampled 

February 27, 2000, through March 3, 2000, Cache Creek Basin, California. . . . . . . . 16

Figure 10. Map showing instantaneous loads of total mercury at selected sites sampled 

February 20–23, 2001, Cache Creek Basin, California. . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 11. Graphs showing relation between total mercury concentration and 

stream discharge at selected sites, Cache Creek Basin, California . . . . . . . . . . . . . 18

Figure 12. Graphs showing instantaneous loads of methylmercury in unfiltered and

filtered water at large river sites, Cache Creek Basin, California . . . . . . . . . . . . . . . 20

Figure 13. Graphs showing instantaneous loads of methylmercury in unfiltered and 

filtered water at small stream sites, Cache Creek Basin, California . . . . . . . . . . . . . 21

Figure 14. Map showing instantaneous loads of methylmercury at selected sites sampled 

February 27, 2000, through March 3, 2000, Cache Creek Basin, California. . . . . . . . 22

Figure 15. Map showing instantaneous loads of methylmercury at selected sites 

sampled February 20–23, 2001, Cache Creek Basin, California . . . . . . . . . . . . . . . . . 23

Figure 16. Graph showing total mercury in streambed sediment at selected sites 

sampled during fall of 2000, Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . 24

Figure 17. Graph showing molar ratio of chloride to sulfate at the Cache Creek 

at Rumsey site, Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 18. Graph showing ratio of boron to aluminum mass ratios at selected sites 

of the Cache Creek Basin and Yolo Bypass, California . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 19. Graph showing boron and lithium concentrations at selected sites 

within the Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 20. Graph showing boron and chloride concentrations at selected sites 

within the Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 21. Ternary plot of the molar relation between boron, chloride, and sulfate for 

selected sites within the Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 22. Graph showing ratios of stable isotopes (delta [δ] deuterium and 

δ oxygen-18) for selected sites within the Cache Creek Basin, California . . . . . . . . 31

Figure 23. Graphs showing lithium in filtered water and mercury in unfiltered water

versus delta [δ] oxygen-18 for selected sites within the 

Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 24. Graph showing methylmercury and dissolved organic carbon for selected 

sites within the Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
v

Tables

Table 1. Number, location, identification number, and name of sites sampled in 

the Cache Creek Basin, California, January 2000 through May 2001 . . . . . . . . . . . . 5

Appendix 1,Table 1. Stream discharge and concentrations of mercury in unfiltered and 

filtered water from sites in the Cache Creek Basin, California. . . . . . . . . . . . . . . . . . 37

Appendix 1,Table 2. Stream discharge and concentrations of methylmercury in unfiltered 

and filtered water from sites in the Cache Creek Basin, California . . . . . . . . . . . . . . 41

Appendix 1, Table 3. Concentrations of mercury in unfiltered and filtered water, 

in field blanks, from sites in the Cache Creek Basin, California . . . . . . . . . . . . . . . . . 45

Appendix 1, Table 4. Concentrations of methylmercury in unfiltered and filtered water, 

in field blanks, from sites in the Cache Creek Basin, California . . . . . . . . . . . . . . . . . 46

Appendix 1, Table 5. Concentrations of methylmercury in unfiltered and filtered water, 

in field blanks, from sites in the Cache Creek Basin, California . . . . . . . . . . . . . . . . . 47

Appendix 1, Table 6. Replicate concentrations of mercury in filtered water from sites

in the Cache Creek Basin, California. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Appendix 1, Table 7. Replicate concentrations of methylmercury in unfiltered water 

from sites in the Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Appendix 1, Table 8. Replicate concentrations of methylmercury in filtered water 

from sites in the Cache Creek Basin, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Appendix 1, Table 9. Stable isotopes in water from sites in the Cache Creek Basin, 

California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
vi

Conversion Factors

Multiply By To obtain

cubic meter (m3) 35.31 cubic foot (ft3) 

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

gram (g) 0.03527 ounce (oz)

gram per day (g/d) 0.03527 ounce per day (oz/d)

square kilometer (km2) 0.3861 square mile (mi2)

liter (L) 1.057 quart (qt)

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

oF=1.8 oC+32.

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). 

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

micrograms per liter (μg/L).

Acronyms and Abbreviations

Al, aluminum 

B, boron

BMSL, Battelle Marine Sciences Laboratory

Cl, chloride

CO2, carbon dioxide

DOC, dissolved organic carbon

DI, deionized

DL, detection limit

δD, delta deuterium, 2H/1H relative to Vienna Standard Mean Ocean Water

1H, hydrogen-1

2

H, hydrogen-2, deuterium

H2, elemental hydrogen

Hg, mercury

HgS, cinnabar

Hg (II), ionized, divalent mercury 

Li, lithium

16O, oxygen-16

18O, oxygen-18

δ18O, delta oxygen-18, 18O/16O relative to Vienna Standard Mean Ocean Water

p, level of significance 
vii

per mil, per thousand

ppm, parts per million

R2, coefficient of determination

RPD, relative percent difference

SO4, sulfate

UCD, University of California at Davis

USGS, U.S. Geological Survey

VSMOW, Vienna Standard Mean Ocean Water

μm, micrometer

mL, milliliter

ng, nanogram

>, greater than indicated value

<, less than indicated value
Mercury and Methylmercury Concentrations and 

Loads in the Cache Creek Basin, California, 

January 2000 through May 2001

By Joseph L. Domagalski1, Charles N. Alpers1, Darell G. Slotton2, 

Thomas H. Suchanek3 , and Shaun M. Ayers2

Abstract

Concentrations and mass loads of total mercury and 

methylmercury in streams draining abandoned mercury mines 

and near geothermal discharge in the Cache Creek Basin, 

California, were measured during a 17-month period from 

January 2000 through May 2001. Rainfall and runoff averages 

during the study period were lower than long-term averages. 

Mass loads of mercury and methylmercury from upstream 

sources to downstream receiving waters, such as San Francisco 

Bay, were generally the highest during or after winter rainfall 

events. During the study period, mass loads of mercury and 

methylmercury from geothermal sources tended to be greater 

than those from abandoned mining areas because of a lack of 

large precipitation events capable of mobilizing significant 

amounts of either mercury-laden sediment or dissolved 

mercury and methylmercury from mine waste. Streambed 

sediments of Cache Creek are a source of mercury and 

methylmercury to downstream receiving bodies of water such 

as the Delta of the San Joaquin and Sacramento Rivers. Much 

of the mercury in these sediments was deposited over the last 

150 years by erosion and stream discharge from abandoned 

mines or by continuous discharges from geothermal areas. 

Several geochemical constituents were useful as natural tracers 

for mining and geothermal areas. These constituents included 

aqueous concentrations of boron, chloride, lithium, and sulfate, 

and the stable isotopes of hydrogen and oxygen in water. Stable 

isotopes of water in areas draining geothermal discharges were 

enriched with more oxygen-18 relative to oxygen-16 than 

meteoric waters, whereas the stable isotopes of water from 

much of the runoff from abandoned mines were similar to that 

of meteoric water. Geochemical signatures from stable isotopes 

and trace-element concentrations may be useful as tracers of 

total mercury or methylmercury from specific locations; 

however, mercury and methylmercury are not conservatively 

transported. A distinct mixing trend of trace elements and 

stable isotopes of hydrogen and oxygen from geothermal 

waters was apparent in Sulphur Creek and lower Bear Creek 

(tributaries to Cache Creek), but the signals are lost upon 

mixing with Cache Creek because of dilution. 

Introduction

The Cache Creek Basin, also known as the Cache Creek 

watershed or drainage basin (fig. 1), is an important source of 

total inorganic mercury to downstream areas including the San 

Francisco Bay and the region known as the Delta of the 

Sacramento and San Joaquin Rivers (Domagalski, 1998, 2001; 

Foe and Croyle, 1999; Domagalski and Dileanis, 2000). 

Although the Cache Creek drainage basin covers only about 4 

percent of the Sacramento River Basin, the mercury transported 

downstream can be as high as 50 percent of the total annual 

load of the Sacramento River Basin (Foe and Croyle, 1999). 

Sources of mercury within the Cache Creek drainage basin 

include natural geothermal springs, and abandoned and 

inactive mercury mines (fig. 1). Sulphur Creek has several 

active geothermal springs within its drainage. 

1U.S. Geological Survey, Placer Hall, 6000 J Street, Sacramento, CA 

95819-6129. 

2Dept. of Environmental Science and Policy, University of California, One 

Shields Avenue, Davis, CA 95616.

3Dept. of Wildlife, Fish & Conservation Biology, University of California, 

One Shields Avenue, Davis, CA 95616 and U.S. Fish and Wildlife Service, 

Division of Environmental Contaminants, 2800 Cottage Way, Sacramento, 

CA 95825. 
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2 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Figure 1. Study area and location of sampling sites and major mercury point sources, Cache Creek Basin, California.

Cr., Creek; N., North; Res., Reservoir.
Introduction 3

Following the discovery in 1848 of placer gold in the 

California Sierra Nevada, mercury production was especially 

high in the Coast Ranges of California. Cenozoic-age cinnabar 

(HgS) hydrothermal mercury deposits were mined at several 

locations in the Cache Creek Basin, including areas near Clear 

Lake and within the Cache Creek and Putah Creek drainages 

(Rytuba, 1996). The Clear Lake deposits are the northernmost 

part of a group of similar deposits associated with volcanism 

and migration of a transform fault system within the central 

part of the Coast Ranges region of California (Rytuba, 1996). 

Peak production of mercury occurred in 1877 when mines of 

the California Coast Ranges produced approximately 2,776 

metric tons of elemental mercury (Bradley, 1918). This 

elemental mercury was transported out of the Cache Creek 

Basin and used to mine gold at other locations in California and 

Nevada, and around the Pacific Rim, but residues from the 

abandoned mercury mines remain a source of total mercury to 

Cache Creek and downstream receiving bodies of water 

(Domagalski, 1998; Foe and Croyle, 1999). Mining wastes 

enter streams primarily through runoff associated with rain, 

and the highest observed concentrations of total mercury in 

Cache Creek have followed rainfall events (Domagalski, 1998, 

2001). Mercury from geothermal sources enters the creeks 

year-round; however, most of the annual load of total mercury 

is transported from the Cache Creek Basin during the 4-month 

period of high rainfall (December through March) 

(Domagalski, 1998; Foe and Croyle, 1999).

The mercury transported from the Cache Creek Basin to 

receiving waters may pose a human health problem if it enters 

the aquatic food web and methylmercury eventually 

bioaccumulates in fish to levels above health guidelines. 

Although some of the inorganic or total mercury can 

bioaccumulate in fish, the organic form, methylmercury, is 

more likely to do so (Zilloux and others, 1993). Although the 

processes that produce methylmercury in a given ecosystem 

are not completely understood, one step is associated with 

bacteria in anoxic sedimentary environments, especially during 

the chemical reduction of sulfate to sulfide (Compeau and 

Bartha, 1985; Gilmour and others, 1992). Other bacteria are 

known to detoxify the methylmercury by breaking the 

chemical bond of the methyl group to the mercury ion, a 

process referred to as demethylation (Marvin-DiPasquale and 

others, 2000). Methylmercury can also be degraded by 

sunlight, a process known as photo-degradation. When the rate 

of mercury methylation exceeds the rate of demethylation, 

methylmercury may bioaccumulate. 

The potential for the mercury of the Cache Creek Basin to 

change to the methylated form, either within the Cache Creek 

Basin or when transported downstream to a receiving body of 

water such as the Delta, is largely unknown. Most of the 

mercury transported through Cache Creek is presumably in the 

form of cinnabar or metacinnabar as a suspended solid. The 

cinnabar or metacinnabar must dissolve or oxidize to liberate 

aqueous ionized mercury, Hg (II), before the mercury can be 

transformed to methylmercury. Although previous studies (Foe 

and Croyle, 1999; Domagalski, 2001) have documented the 

amount of total mercury transported from the Cache Creek 

Basin, the present study is the first to document the fraction of 

mercury present as methylmercury at different locations within 

the Basin.

Purpose and Scope

The primary purpose of this report is to present the 

concentrations and mass loads of mercury and methylmercury 

for selected surface water sites in the Cache Creek drainage 

basin during January 2000 through May 2001, to relate the 

loads to sources of mercury and methylmercury, and to explain 

the seasonal variation in concentrations and mass loads. The 

report also provides chemical data for mercury and 

methylmercury, for selected trace elements, and for stable 

isotopes of hydrogen and oxygen in water molecules within the 

Cache Creek drainage basin for the same time period. 

The report provides data and interpretations for part of a 

larger study, funded by the CALFED Bay–Delta Program, of 

the impact of mercury in the Bay–Delta drainage basin on 

ecology and human health 

(http://loer.tamug.tamu.edu/calfed/). The larger investigation 

is examining mercury bioaccumulation, the potential for mine 

remediation within the Cache Creek drainage basin to reduce 

mercury loads, and issues associated with ecosystem 

restoration within the Delta of the Sacramento and San Joaquin 

Rivers.

Acknowledgments

The authors thank the CALFED Bay–Delta Program, the 

source of funding for this research. Numerous individuals 

within the U.S. Geological Survey assisted with sample 

collection, processing, and analysis: Michelle Chao, Peter 

Dileanis, Michael Hunerlach, Mark Johnson, and Frank 

Moseanko (in Sacramento, California); Alan Mlodnosky (in 

Salinas, California); and Ronald Antweiler, Dale Peart, Terry 

(Brinton) Plowman, David Roth, and Howard Taylor (in 

Boulder, Colorado). The authors also thank Mark Stephenson 

and Max Puckett of the California Department of Fish and 

Game for their assistance with project organization and 

administration.
4 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Description of Study area and 

Selection of Sampling Sites

The Cache Creek Basin occupies approximately 3,000 

square kilometers in northern California (fig. 1). The area 

upstream of Rumsey is characterized by the low hills of the 

California Coast Ranges, whereas the area downstream of 

Rumsey is part of the Sacramento Valley. Land cover in the 

upstream portion of the basin is mainly forest and grazing land 

with minor amounts of orchards and cropland. The amount of 

land used for crops increases downstream of Rumsey. Former 

mine sites represent a relatively small amount of the total land 

cover. 

Cache Creek begins as outflow from Clear Lake. The 

largest tributary to Cache Creek, the North Fork Cache Creek, 

originates in the northern part of the basin and includes the 

Indian Valley Reservoir. Flows of the North Fork Cache Creek 

below Indian Valley Reservoir are partly controlled by 

reservoir releases. Another major tributary to Cache Creek is 

Bear Creek, which does not have a reservoir within its 

drainage area. Both Clear Lake and Indian Valley Reservoir 

are used, in part, to supply irrigation water to farmers in the 

lower parts of the Cache Creek Basin. During summer, flows 

in Cache Creek and North Fork Cache Creek are entirely 

managed for irrigation, and essentially no water reaches the 

Sacramento River until winter (Domagalski and others, 2000). 

There are numerous smaller tributaries to Cache Creek; 

some drain geothermal areas or abandoned mine sites. Harley 

Gulch (fig. 1) drains an abandoned mercury mine complex (the 

Abbott and Turkey Run Mines). Davis Creek drains an area 

including the Reed Mine, which was remediated by the 

Homestake Mining Company in conjunction with their 

development of the McLaughlin gold mine. Davis Creek 

Reservoir is a small reservoir on Davis Creek. The Sulphur 

Creek drainage includes natural sources of mercury from 

geothermal springs and some mine wastes, including wastes 

from mercury and gold mines. Sulphur Creek drains into Bear 

Creek, a tributary to Cache Creek above Rumsey.

Irrigation-period flows of Cache Creek (fig. 1) are 

managed to deliver only the amount of water purchased by 

local farmers for consumptive irrigation use. As a result, very 

little water leaves the basin during the irrigation season. Fall 

and winter flows tend to be low, at least initially, because 

releases from Clear Lake and Indian Valley Reservoir are very 

low. Seasonal rainfall causes high flows in winter. In addition, 

the level of Clear Lake or Indian Valley Reservoir is 

occasionally lowered for flood protection during the winter 

rainy season, generally December through March. Water from 

Cache Creek that leaves the basin enters a flood-control 

channel of the Sacramento River system known as the Yolo 

Bypass (fig. 1). Water from the Sacramento River also 

discharges into the Yolo Bypass through a weir when the 

Sacramento River near Verona exceeds 1,560 m3/s. The flood 

control system is designed to reduce the potential for flooding 

in downstream areas, especially in the city of Sacramento. The 

Yolo Bypass rejoins the Sacramento River downstream in the 

Delta region. The Yolo Bypass region is almost entirely crop 

land; a smaller amount is wildlife habitat.

Sampling sites were selected to assess representative 

locations of potential sources of mercury within the Cache 

Creek drainage basin. Stream sites immediately downstream of 

the dams on both Clear Lake and Indian Valley Reservoir were 

sampled to determine mercury and methylmercury 

concentrations from either the lake or the reservoir. Another 

sampling site was on the North Fork Cache Creek just 

upstream of its confluence with Cache Creek. Sites on small 

tributaries or other water bodies near mercury mines or natural 

mercury sources included two sites on Bear Creek (an upper 

site, Bear Creek above Sulphur Creek, and a lower site, Bear 

Creek above Holsten Chimney Canyon) and one site each on 

Sulphur Creek (which receives runoff from geothermal 

springs), Harley Gulch (downstream of the Abbott and Turkey 

Run Mines), and Davis Creek Reservoir at its spillway. 

Additional sites on Cache Creek included a site at Rumsey, 

which is centrally located in the Cache Creek Basin, and two 

sites just upstream of the point where Cache Creek discharges 

into the Yolo Bypass; these latter two sites surround an area 

known as the Cache Creek Settling Basin, which is designed to 

trap sediment transported out of the Cache Creek drainage 

basin. Finally, two sites were in the Yolo Bypass: one in the 

central portion of the Yolo Bypass (Yolo Bypass at Interstate 

80 near West Sacramento) and the second site (Lower Yolo 

Bypass) just upstream of where the Yolo Bypass discharges 

into the Delta region. 

Methods

Some sites, including the Yolo Bypass sites and the site 

immediately downstream of the dam on Indian Valley 

Reservoir, were sampled only by the U.S. Geological Survey 

(USGS), and some sites, such as Bear Creek above Sulphur 

Creek and Cache Creek at Highway 505, were sampled only by 

the University of California at Davis (UCD). Other sites were 

sampled by both the USGS and UCD. Sampling sites are 

shown on figure 1 and listed in table 1. The frequency at which 

sites were sampled varied either because of hydrological 

conditions (such as low discharge) or logistical problems 

(difficult access or remote location). Water sampling by UCD 

was coupled with biological sampling of invertebrates and fish 

to assess mercury bioaccumulation (Slotton and others, 2004); 

UCD samples were timed to avoid peak storm event flows to 

best approximate average seasonal biotic exposure to mercury 

and methylmercury.
Methods 5

In addition to the sites listed in table 1, the Abbott and 

Turkey Run and the Sulphur Creek mine site areas were 

sampled in more detail by a separate team from UCD. The 

locations of several sampling sites in these areas are described 

in detail by Suchanek and others (2003). Splits of the UCD 

water samples from these locations were provided to the USGS 

for the analysis of inorganic constituents, as described in the 

next section.

Sampling and Sample Processing

Water samples were collected across the stream channel 

by the USGS using a USGS D-77 sampler designed for 

collecting isokinetic samples. Sampling protocols followed 

guidelines by Edwards and Glysson (1988), Ward and Harr 

(1990), Shelton (1994), and the U.S. Geological Survey (1999). 

The water samples were collected in 3-L Teflon bottles that had 

been rigorously cleaned for the purpose of collecting water 

samples for mercury and trace metals. The bottles were 

originally cleaned by immersion in 10-percent hydrochloric 

acid at 65 degrees Celsius for 3 days. After thorough rinsing 

with ultra-clean water, the bottles were tightly capped and 

double-wrapped in plastic for transport to field sites. After 

collecting a water sample, the bottles were rinsed with ultraclean water and then cleaned in the field with a dilute detergent, 

followed by thorough rinsing with ultra-clean water, a rinse 

with 5-percent hydrochloric acid, and a final series of rinses 

with ultra-clean water. One set of sampling bottles was used 

only for sites influenced by geothermal sources or mercury 

mines expected to have high mercury concentrations, whereas 

another set was only used for downstream sites on the larger 

creeks and rivers expected to have low mercury concentrations. 

After collection, the water samples were composited in an 8-L 

Teflon-lined stainless-steel churn. The churn was cleaned by 

using dilute detergent followed by a thorough rinse with ultraclean water, a thorough rinse with 5-percent hydrochloric acid, 

and a final series of rinses with ultra-clean water. Similar to the 

procedure for the 3-L Teflon sampling bottles, one churn was 

used only for sites influenced by geothermal sources or 

mercury mines, and a second churn was used only for the sites 

on the large creeks and rivers. 

Water samples were taken from the churn for analyses of 

unfiltered water samples. Before filling the sample bottles, 

samples were churned for at least 1 minute to ensure that 

sediment was suspended uniformly. Samples were then 

collected for analysis of suspended sediment concentration, 

mercury and methylmercury in unfiltered water, trace elements 

in unfiltered water, nitrogen and phosphorus species in 

unfiltered water, measurement of pH and specific conductance, 

and oxygen and hydrogen isotope ratios in water. Samples were 

then preserved if required by the sampling protocol. A 0.45-μm 

high-capacity Gelman capsule filter was used for samples that 

were filtered as part of the sampling protocol. C-flex tubing 

(composed of a thermoplastic polymer) was used to pump the 

sample water through the filter. The tubing had been cleaned 

Table 1. Number, location, identification number, and name of sites sampled in Cache Creek Basin, California, January 2000 through May 2001 

[Latitude and longitude are in degrees (° ), minutes (′ ) , and seconds (′′ ). Site identification numbers are not available for sites that were sampled only by 

University of California at Davis; NA, not available]

Site 

number 

(see 

fig. 1)

Latitude Longitude

USGS site

identification

number

Site name (abbreviated name, if any)

1 38° 55′ 27′′ 122° 33′ 53′′ 11451000 Cache Creek near Lower Lake (Clear Lake)

2 39° 05′ 50′′ 122° 25′ 12′′ NA Bear Creek above Sulphur Creek (upper Bear Creek)

3 38° 57′ 28′′ 122° 20′ 30′′ 11451715 Bear Creek above Holsten Chimney Canyon (lower Bear Creek)

4 39° 02′ 19′′ 122° 25′ 08′′ 11451690 Sulphur Creek at Wilbur Springs (Sulphur Creek)

5 39° 00′ 33′′ 122° 26′ 04′′ 11451540 Harley Gulch near Wilbur Springs (Harley Gulch)

6 39° 04′ 50′′ 122° 32′ 07′′ 11451300 North Fork Cache Creek near Clearlake Oaks (Indian Valley 

Reservoir)

7 39° 01′ 09′′ 122° 34′ 04′′ 11451500 North Fork Cache Creek at Highway 20

8 38° 51′ 51′′ 122° 21′ 11′′ 11451600 Davis Creek Reservoir at Dam, near Knoxville

9 38° 53′ 26′′ 122° 14′ 14′′ 11451800 Cache Creek at Rumsey

10 38° 41′ 47′′ 121° 57′ 12′′ NA Cache Creek at Highway 505

11 38° 43′ 40′′ 121° 43′ 44′′ 384340121434401 Cache Creek into Settling Basin

12 38° 40′ 40′′ 121° 40′ 23′′ 384040121402301 Cache Creek out of Settling Basin

13 38° 34′ 01′′ 121° 36′ 51′′ 11453120 Yolo Bypass at Interstate 80 near West Sacramento

14 38° 14′ 27′′ 121° 40′ 49′′ 381427121404901 Lower Yolo Bypass
6 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

using detergent and rinsed with ultra-clean water. The tubing 

was then thoroughly rinsed by a peristaltic pump using 10-

percent hydrochloric acid, followed by a final rinse with ultraclean water. One set of tubing was dedicated for each site 

sampled. Before filtration, the capsule filter was rinsed by 

pumping 1 L of ultra-clean water through it. Then, a small 

amount of sample water was pumped through to displace the 

clean water. The filtration order for samples was total mercury, 

methylmercury, other trace metals, dissolved nitrogen and 

phosphorus species, and finally alkalinity. Samples to be 

analyzed (usually 50 ml) for dissolved and suspended organic 

carbon were processed using a 0.45-μm silver filter. The 

particles collected on the silver filter were analyzed for organic 

carbon to estimate suspended (particulate) organic carbon.

Water samples collected by UCD differed from those 

taken by the USGS in that the UCD samples were grab samples 

collected in the part of the river or stream judged to have the 

greatest discharge. The UCD group did not filter samples in the 

field, but rather transported the samples by overnight courier or 

ground transport to the laboratory where samples were 

immediately filtered and preserved. Samples taken for analysis 

of mercury and methylmercury were collected in 1-L prewashed glass bottles supplied by the Battelle Marine Sciences 

Laboratory (BMSL). Samples taken for trace metals, 

alkalinity, and stable isotopes were collected in 4-L 

polyethylene bottles that were cleaned using the same 

procedure as that used for the Teflon-lined churns. 

Analytical Methods

Samples collected by the USGS for the measurement of 

total mercury in water were analyzed according to the method 

of Roth (1994) at the USGS laboratory in Boulder, Colorado. 

This method uses cold vapor atomic fluorescence 

spectrometry. (Details of analytical chemical methodology are 

given by Puckett and van Buuren [2000].) Water samples 

collected by UCD also were analyzed using a cold vapor 

atomic fluorescence methodology at the BMSL in Sequim, 

Washington; complete details are given by Puckett and van 

Buuren (2000). The method is based on that of the U.S. 

Environmental Protection Agency (U.S. Environmental 

Protection Agency, 1996). Methylmercury in water was 

measured using a similar method after distillation and 

ethylation of aqueous samples (Puckett and van Buuren, 2000). 

Both the USGS and UCD used the same methodology to 

analyze methylmercury at the BMSL. Selected major cations, 

iron, and silica in water were analyzed by inductively-coupled 

plasma atomic-emission spectroscopy (Alpers and others, 

2000). Selected trace elements in water were analyzed by 

inductively-coupled plasma mass spectroscopy (Alpers and 

others, 2000). Nutrients were analyzed by the methods of 

Fishman and Friedman (1989) and Fishman (1993). Dissolved 

and suspended organic carbon were analyzed by the methods 

of Brenton and Arnett (1993). 

Quality Assurance 

A rigorous quality assurance program was adopted for 

this project. Full details of laboratory and field quality 

assurance requirements are given by Puckett and van Buuren 

(2000). Field-level quality assurance required at least one 

blank for every ten samples collected and at least one replicate 

for every ten samples. 

Seven field blanks were collected for total mercury in 

unfiltered and filtered water during the three sampling events 

completed by the USGS. The concentrations of total mercury 

in unfiltered water blanks ranged from less than detection 

(0.5 ng/L) to 1.2 ng/L. The median value was 0.6 ng/L, which 

was estimated by setting the concentrations of non-detected 

values to one half the detection limit. The concentrations of 

total mercury in filtered blank samples ranged from less than 

detection (0.5 ng/L) to 1.2 ng/L. The median value was less 

than the detection limit. The concentrations of total mercury in 

environmental samples ranged from less than the detection 

limit to 3,070 ng/L, and 98 percent of all measured 

concentrations exceeded a concentration of 1 ng/L. Because 

these levels are much higher than those in blank samples, any 

contamination of the blanks was insignificant and does not 

affect the data set.

Six field blanks were collected for methylmercury in 

unfiltered and filtered water during the three sampling events 

completed by the USGS. Most of the measurements were less 

than the detection limit of 0.02 ng/L. Two samples of 

methylmercury in unfiltered water had concentrations just 

slightly above the detection limit, and the highest 

concentration was 0.03 ng/L. Bias caused by contamination 

was not significant and, therefore, does not affect the 

measurements of methylmercury in this data set.

All samples collected for total mercury in unfiltered and 

filtered water by the USGS were taken as replicates, and each 

of the replicate samples was analyzed three times. The median 

relative percent difference (RPD) for the values of total 

mercury in unfiltered water samples was 3.5 percent, whereas 

that for filtered water samples was 6.4 percent. The higher 

median RPD for the filtered water samples may be attributed 

to the lower concentrations of total mercury in filtered water. 

Six replicates were collected by the USGS for methylmercury 

analysis. The median RPD for methylmercury in unfiltered 

water samples was 8.5 percent, whereas that in filtered water 

was 4.5 percent. The filtered water samples do not provide a 

very good estimate of reproducibility because two of six 

replicate sets had methylmercury concentrations less than the 

detection limit.
Results and Discussion 7

The UCD sampling team also collected field blanks and 

replicates according to the quality assurance requirements (one 

each for every ten samples) specified by Puckett and van 

Buuren (2000). The median concentration for unfiltered water 

blanks was 0.32 ng/L for total mercury and less than the 

detection limit of 0.02 ng/L for methylmercury. The median 

concentration for the field blanks collected by the UCD team 

and filtered at the BMSL was 0.072 ng/L for total mercury and 

below the detection limit of 0.024 ng/L for methylmercury. 

The median RPD for replicate samples of total mercury in 

unfiltered water was 8.6 percent and that for methylmercury 

was 13.3 percent. The RPD for methylmercury in filtered water 

for the replicate samples collected by UCD was 7.5 percent and 

that for methylmercury was 20.1 percent. The higher RPD for 

methylmercury in filtered water samples used for the UCD data 

relative to the RPD for samples taken by the USGS (RPD of 4.5 

percent) is probably due to more replicate pairs and to more 

replicate pairs having concentrations above the detection limit. 

Thus, the UCD data may provide a better indication of the 

replication of methylmercury in filtered water.

Additional information on quality assurance in this project 

is provided by the results of laboratory intercomparison 

studies. An intercomparison study with regard to analysis of 

total mercury in water by laboratories participating in the 

CALFED mercury project was an integral component of 

overall project quality-assurance oversight (van Buuren, 2002). 

This intercomparison study consisted of three rounds of testing 

in which participating laboratories were provided with splits of 

fresh-water and seawater samples that had been spiked with 

known concentrations of inorganic mercury. A total of three 

spiked seawater samples and four spiked fresh-water samples 

were prepared. The water samples were preserved with HCl, 

which causes a positive bias of 25 to 30 percent using the 

analytical method employed by the USGS laboratory in 

Boulder, Colorado. Without correcting for the bias introduced 

by the HCl preservative, results from the USGS laboratory 

were within a tolerance of three standard deviations (3-sigma) 

for four of the seven intercomparison samples; correcting the 

results from the USGS laboratory for the analytical bias 

introduced by the HCl preservative results in six of the seven 

samples falling within the 3-sigma tolerance. In addition, the 

USGS laboratory in Boulder has participated successfully in 

several round-robin comparisons of total mercury analysis 

conducted by the USGS Branch of Quality Assurance using 

Standard Reference Water Samples.

A separate laboratory quality assurance program was used 

to analyze oxygen and hydrogen isotope ratios for unfiltered 

water samples. Isotopic analyses of oxygen and hydrogen 

atoms in water are recorded as ratios relative to Vienna 

Standard Mean Ocean Water (VSMOW; O'Neil, 1986). Isotope 

ratios of oxygen, oxygen-18/oxygen-16 (18O/16O, expressed as 

δ18O [delta oxygen-18]), and hydrogen, hydrogen-2/hydrogen1 (2H/1H, expressed as δD [delta deuterium]), in water were 

measured using a light stable isotope ratio mass spectrometer at 

the University of California, Davis, Department of Geology. 

δ18O in carbon dioxide (CO2) was measured after equilibration 

of the water at 25 degrees Celsius. Hydrogen isotope 

measurements were made on hydrogen gas (H2) after reducing 

the water with zinc using a platinum catalyst. The calibration 

procedure used three unique standards; duplicates of each 

standard were analyzed during each run. In all cases, the 

laboratory was able to calibrate the instruments according to 

the known values of isotope ratios in the standards. 

The UCD stable isotope laboratory completed 18 

duplicate measurements of δ18O and 16 duplicate 

measurements of δD while the environmental samples from 

this study were being analyzed. The average difference 

between the replicates was 0.03 per mil for δ18O and 0.4 per mil 

for δD. Another quality assurance check was made by 

including 13 samples of DI (deionized) water from the USGS 

laboratory in Sacramento as blind replicates. The standard 

deviations for 13 measurements of the DI water were 0.07 per 

mil for δ18O and 0.8 per mil for δD. Therefore, overall 

precision of the stable isotope measurements is considered to 

be better than 0.10 per mil for δ18O and better than 1.0 per mil 

for δD.

Results and Discussion

Mercury Concentrations and Loads

Loads were determined using two approaches: (1) during 

the rainy season, samples were collected during or after storms 

because of the higher river flows and the greater potential for 

transport of mercury and methylmercury, and (2) during the dry 

season samples were collected at planned intervals. The rainy 

season in northern California is generally between November 

and March, with little or no rainfall during the remainder of the 

year. Two representative hydrographs are shown (fig. 2) for 

representative sites on a tributary (Bear Creek above Holsten 

Chimney Canyon) and on Cache Creek. At both sites, the peak 

flows occurred during the rainy season, and extremely low 

flows occurred during the spring-to-fall dry season. As noted 

earlier, flows on the main stem of Cache Creek during the dry 

season are largely controlled through releases of water from 

Clear Lake or Indian Valley Reservoir (fig. 1). These dryseason releases of water irrigate downstream farms or orchards. 

Because water is released according to accurate assessment of 

irrigation needs, the dry season flows of the Cache Creek at 

Yolo site (fig. 1) are very low, as water is diverted to farms. The 

Yolo Bypass is used as a flood control channel, and as a result, 

very little water is present in the Bypass during the dry season. 

Rainfall was below normal during this study and discharge 

from Cache Creek was relatively low compared with other 

years having historical records. The discharge for water year 

2000 (October 1, 1999, through September 30, 2000) for Cache


































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8 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Creek at Yolo was only 55 percent of the average annual 

discharge for 1903–2000 (Anderson and others, 2001). The 

previous water year (1999) had higher rainfall, and the annual 

runoff was more than twice the runoff during water year 2000. 

Discharge during water year 2001 was even less than that 

during water year 2000. Therefore, the results of this study 

reflect low-flow conditions in the Cache Creek drainage basin. 

Concentrations of mercury in unfiltered and filtered water 

samples are shown in figure 3 for the large river sites and in 

figure 4 for the small stream sites; data are given in table 1 in 

ppendix 1. As expected, the small stream sites (the mining and 

geothermal sites—Bear Creek above Holsten Chimney anyon, 

Sulphur Creek at Wilbur Springs, and Harley Gulch near 

Wilbur Springs) (figs. 1, 4) had the highest concentrations, and 

most of the mercury was associated with suspended sediment. 

Much of the mercury in the suspended sediment, especially 

that near the mine sites, is probably in the form of cinnabar or 

metacinnabar, which is very insoluble. These three small 

stream sites had higher proportions of mercury in filtered water 

than the large river sites. Mercury passing through the 0.45 μm 

capsule filter may be truly dissolved or present as very fine 

colloidal particulates. It is likely that dissolved and (or) 

colloidal mercury enters the streams near the mines or 

geothermal springs. Concentrations of mercury were lower at 

most of the downstream sites (large river sites) than at the 

mining and geothermal sites because of the greater distance of 

the downstream sites from the mercury sources and because of 

dilution by the two largest sources of water, Clear Lake and 

Indian Valley Reservoir. The ratio of mercury in filtered water 

to that in unfiltered water tended to be lower at the sites farther 

downstream (fig. 3). 

Concentrations of methylmercury in unfiltered and 

filtered water samples for selected sites are shown in figures 5

and 6. (See also table 2 in Appendix 1.) The highest 

concentrations were measured in water from Sulphur Creek at 

Wilbur Springs, Bear Creek above Holsten Chimney Canyon, 

and Harley Gulch near Wilbur Springs. Concentrations of 

methylmercury were higher in unfiltered water samples than in 

filtered samples. The proportion of methylmercury in the 

filtered water samples relatiave to the unfiltered samples was 

higher than the corresponding ratio for total mercury. The ratio 

of methylmercury in filtered water samples to that in unfiltered 

water samples ranged from approximately 0.1 to 1.0. There 

was considerable variability in this ratio at all sites. 

Figure 2. Daily mean discharge for Bear Creek above Holsten Chimney Canyon and Cache Creek at Yolo, Cache Creek Basin, California.
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Results and Discussion 9

Figure 3. Concentrations of total mercury at large river sites, Cache Creek Basin, California. 
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10 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Figure 4. Concentrations of total mercury at small stream sites, Cache Creek Basin, California.


























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Results and Discussion 11

Figure 5. Methylmercury concentrations at large river sites, Cache Creek Basin, California.

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12 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Figure 6. Methylmercury concentrations at small stream sites, Cache Creek Basin, California.

DL, detection limit.
Results and Discussion 13

Instantaneous loads of total mercury in unfiltered and 

filtered water for selected sites are shown graphically in figures 

7 and 8; instantaneous loads of total mercury are shown on 

maps in figures 9 (February and March 2000) and 10 (February 

2001). The largest loads were measured during the winter rainy 

season. For the year 2000 sampling (fig. 9), the instantaneous 

loads of total mercury were low near the mining and 

geothermal sites (sites 3, 4, and 5 on fig. 1; site names on 

table 1) relative to the downstream sites because of the lower 

discharges from the mining and geothermal sites. During the 

February to March 2000 storm, loads of total mercury 

increased downstream and exceeded the sum of the loads from 

the mining and geothermal sites. During February 2000, part of 

the increase downstream could be attributed to water 

management or hydrological factors. On February 28, 2000, 

midway during the period that samples were being collected, 

water began to be released from the Clear Lake dam to lower 

water levels of Clear Lake to reduce the risk of flooding. Water 

is periodically released after winter rains to prevent flooding of 

homes and businesses near the lakeshore. For example, during 

sampling, the discharge of Cache Creek at Rumsey and at 

downstream sites contained both storm-water runoff and water 

released from Clear Lake, whereas discharge during sampling 

at the mining and geothermal sites, as well as the sites on the 

North Fork Cache Creek, contained only storm-water runoff. 

Therefore, the higher loads at Cache Creek at Rumsey and 

downstream at Cache Creek into Settling Basin can be logically 

attributed primarily to higher flows of the released water resuspending mercury previously deposited in the bottom 

sediments. Releasing water from Indian Valley Reservoir 

would have the same effect. The load of total mercury at the 

sites farthest downstream, that is, the Yolo Bypass at Interstate 

80 near West Sacramento and the Lower Yolo Bypass, resulted 

from combined flows from Cache Creek and the Sacramento 

River. No attempt was made, nor are data available, to 

discriminate between these sources.

The mercury loads during the storm in late February 2001 

(fig. 10) were much less than those during the storm in 

February to March 2000 (fig. 9). (Note the difference in scale 

of the bars on those two figures.) As measured after the storm 

in February 2001, the sum of the loads originating from a 

mining and geothermal site (site 3 on fig. 1) approximated the 

sum of the loads measured at Cache Creek at Rumsey (site 9) 

and farther downstream. During that storm, there was very low 

discharge of water from both Clear Lake and Indian Valley 

Reservoir. As a result, the mercury loads measured 

downstream at Cache Creek originated mainly from the mining 

and geothermal sites. 

It was not possible to calculate accurate annual loads of 

mercury or water flux from all the sampling sites, or at all times 

at individual sites. Continuous records of discharge are 

available for a limited number of sampling sites. At some sites, 

instantaneous discharge was measured at the time of sampling 

and used to calculate instantaneous loads only. Discharge for 

the input to the Cache Creek Settling Basin can be estimated 

from the discharge record of the nearby gaging station Cache 

Creek at Yolo (fig. 1). Although continuous discharge of Cache 

Creek at Rumsey was recorded, the quality of hydrologic data 

from that site was considered inadequate for this study to 

calculate reliable estimates of either chemical loads or water 

flux. Continuous discharge records are available for Sulphur 

Creek at Wilbur Springs, Bear Creek above Holsten Chimney 

Canyon, Harley Gulch near Wilbur Springs, outflow from 

Clear Lake (Cache Creek near Lower Lake), the upper Yolo 

Bypass sites, and outflow from Indian Valley Reservoir (North 

Fork Cache Creek near Clearlake Oaks). 

The calculation of the water flux for the Sulphur Creek 

site shows that discharge from that location (2,784,928 m3 in 

water year 2000 and 1,834,695 m3 in water year 2001) 

accounted for approximately 1 percent of the discharge of 

Cache Creek at Yolo in water year 2000 and approximately 2 

percent of the discharge in water year 2001. It accounted for 

approximately 0.1 percent of the discharge of the Yolo Bypass 

in water year 2000 and just less than 1 percent in water year 

2001. 

Bear Creek discharged 33,270,771 m3 in water year 2000 

and 18,267,003 m3 in water year 2001, accounting for 

approximately 12 percent of the annual discharge of the Cache 

Creek at Yolo site in water year 2000, and 19 percent in water 

year 2001. The Bear Creek discharge accounted for 

approximately 1 percent of the discharge of the Yolo Bypass in 

water year 2000 and approximately 9 percent in water year 

2001. 

The discharge of Harley Gulch (395,288 m3 for water year 

2000 and 5,016 m3 for water year 2001) was less than that of 

Sulphur Creek or Bear Creek. The discharge of Harley Gulch 

accounted for approximately 0.15 percent of the discharge of 

Cache Creek at Yolo during water year 2000 and only 0.005 

percent during water year 2001. The discharge of Harley Gulch 

accounted for approximately 0.01 percent of the discharge of 

the Yolo Bypass for water year 2000, and an insignificant 

amount for water year 2001. 

The discharge of Cache Creek into the Yolo Bypass 

(268,342,149 m3 in water year 2000 and 93,931,485 m3 in 

water year 2001) accounted for approximately 8 percent of the 

discharge of the Yolo Bypass during water year 2000, but 

45 percent during water year 2001. The discharge of the Yolo 

Bypass at Interstate 80 site, estimated using the discharge data 

from the nearby Yolo Bypass at Woodland gaging station, was 

3,384,847,180 m3 in water year 2000 and 208,324,638 m3 in 

water year 2001. 

Water release from the Clear Lake dam was 

283,815,038 m3 in water year 2000 and 90,868,105 m3 in water 

year 2001. Water release from the Indian Valley Reservoir dam 

was 129,800,393 m3 in water year 2000 and 160,754,977 m3 in 

water year 2001. 








































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14 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Figure 7. Instantaneous loads of total mercury in unfiltered and filtered water at large river sites, Cache Creek Basin, California.


































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5NFILTEREDWATERMERCURYLOAD

&ILTEREDWATERMERCURYLOAD

(ARLEY'ULCHNEAR7ILBUR3PRINGS

%80,!.!4)/.

Results and Discussion 15

Figure 8. Instantaneous loads of total mercury in unfiltered and filtered water at small stream sites, Cache Creek Basin, California.
7OODLAND

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16 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Figure 9. Instantaneous loads of total mercury at selected sites sampled February 27, 2000, through March 3, 2000, Cache Creek Basin, California.

Cr., Creek; Sl., slough.
7OODLAND

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4ALLESTBARREPRESENTSANINSTANEOUSLOADOF

GRAMSOFMERCURYPERDAY

!LLOTHERBARSARESCALEDPROPORTIONALLY 


Results and Discussion 17

Figure 10. Instantaneous loads of total mercury at selected sites sampled February 20–23, 2001, Cache Creek Basin, California.

Cr., Creek; Sl., slough.
18 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

A significant relation between stream discharge and the 

concentration of a constituent is required to calculate an 

accurate annual load of any constituent in a river for which 

there is a continuous record of discharge but few 

measurements of the concentrations of the constituent. Linear 

least-squares regressions of the data for stream discharge and 

total mercury concentrations at selected tributary sites and for 

the input to the Cache Creek into Settling Basin site were low 

(figure 11). The best relation between stream discharge and 

mercury concentration was for the Cache Creek into Settling 

Basin site (R2 = 0.7, where R2 is the coefficient of 

determination), but the regression equation had poor predictive 

value and a positive y-intercept. This lack of a reliable relation 

between discharge and mercury concentration limited our 

ability to calculate annual loads of mercury for these streams. 

A crude estimate of annual mercury loads at selected sites 

may be obtained by combining estimated average mercury 

concentrations for the dry (April through Novemeber) and the 

wet (December through March) seasons with flow data for 

sites that have reliable records of discharge. For the Clear Lake 

outflow, an estimated average of 4 ng/L of mercury for the dry 

season and an estimated average of 12 ng/L of mercury for the 

wet-season were used. For the Indian Valley Reservoir, an 

estimated average of 2 ng/L of mercury for the dry season and 

5 ng/L for the wet season were used. For Harley Gulch, an 

estimated average of 169 ng/L for the dry season and 279 ng/L 

for the wet season were used. For Bear Creek, concentrations 

of 38 ng/L and 131 ng/L were used. For Sulphur Creek, values 

of 758 ng/L and 1,095 ng/L were used. For the Cache Creek 

Settling Basin, concentrations of 1.3 ng/L and 51.3 ng/L were 

used. 

















3TREAMDISCHARGEINCUBICMETERSPERSECOND

3TREAMDISCHARGEINCUBICMETERSPERSECOND

3TREAMDISCHARGEINCUBICMETERSPERSECOND

3TREAMDISCHARGEINCUBICMETERSPERSECOND

2

2 

















      

"EAR#REEKABOVE(OLSTEN#HIMNEY#ANYON 3ULPHUR#REEKAT7ILBUR3PRINGS

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4OTALMERCURYUNFILTEREDWATER

4OTALMERCURYFILTERED WATER

2

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2

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-ERCURYCONCENTRATIONSINNANOGRAMSPERLITER

         

       

%80,!.!4)/.

Figure 11. Relation between total mercury concentration and stream discharge at selected sites, Cache Creek Basin, California.

R2 is the coefficient of determination.
Results and Discussion 19

The estimated annual loads of mercury in unfiltered water 

at the Clear Lake outflow were 1,660 g in water year 2000 and 

370 g in water year 2001. The estimated annual loads for the 

outflow from Indian Valley Reservoir were 320 g for both 

water year 2000 and water year 2001. The estimated annual 

loads for Bear Creek were 3,670 g for water year 2000 and 

1,960 g for water year 2001. The estimated annual loads 

obtained for Sulphur Creek were 2,850 g for water year 2000 

and 1,660 g for water year 2001. The estimated annual load for 

Harley Gulch was 100 g for water year 2000, but was negligible 

for water year 2001 because of very low discharge. In both 

years, the loads from Sulphur Creek, the geothermal source, 

were greater than those from Harley Gulch, the mining source. 

The estimated annual loads for the Cache Creek Settling Basin 

were 12,300 g for water year 2000 and 4,580 g for water year 

2001. Annual loads, either estimated or otherwise, for North 

Fork Cache Creek at Highway 20 and Cache Creek at Rumsey 

could not be calculated because of incomplete, inaccurate, or 

poorly documented hydrological records. Estimated annual 

loads for Yolo Bypass at Interstate 80 near West Sacramento 

were calculated using the average wet-season value of 23.5 

ng/L. The estimated annual loads were 70,370 g in water year 

2000 and 4,900 g in water year 2001. 

Instantaneous loads of methylmercury in unfiltered and 

filtered water for selected sites are represented on graphs in 

figures 12 and 13; instantaneous loads of methylmercury in 

unfiltered water are represented on maps in figure 14 for 

February to March 2000 and in figure 15 for February 2001. 

The upstream loads of unfiltered methylmercury during the 

February to March 2000 sampling were lower than the 

downstream loads. During the March 2001 sampling, 

however, the highest load of total methylmercury was at the 

Cache Creek at Rumsey site (site 9 on fig. 1); two upstream 

sites, Bear Creek above Holsten Chimney Canyon (site 3) and 

the North Fork Cache Creek at Highway 20 (site 7), were 

apparently the main contributors to this load.

Concentrations (dry weight) of total mercury in streambed 

sediment collected during the late fall of 2000 are shown on 

figure 16. As expected, concentrations were considerably 

higher in the sediments from the mining or geothermal sites 

(sites 3, 4, and 5 on fig. 1) than in the sediments at the sites 

downstream on Cache Creek or from the North Fork Cache 

Creek site. Much of the mercury in the bed sediment 

downstream of the mines is probably in the form of cinnabar or 

metacinnabar. Mercury concentrations in sediment have been 

measured previously in samples from the Cache Creek at 

Rumsey site and at the Yolo Bypass (Domagalski, 2001). The 

concentration of mercury in streambed sediment collected from 

Cache Creek at Rumsey in 1995 was 150 ng/g of dry sediment, 

whereas the sample collected in 1997 contained 450 ng/g of dry 

sediment, and the sample collected in 2000 contained 613 ng/g 

of dry sediment. Streambed sediments at the Yolo Bypass at 

Interstate 80 site were also sampled in 1997. The concentration 

of mercury measured in that sample was 310 ng/g of dry 

sediment, and the sample collected in 2000 contained 288 ng/g 

of dry sediment. 

Mercury mining began more than 150 years ago in the 

Cache Creek Basin, and abandoned mines continue to 

contribute waste in the form of mercury-contaminated 

sediment to locations downstream. It is difficult to estimate the 

baseline concentration of mercury in streambed sediment had 

there been no mining. Mercury concentrations were 100 ng/g of 

dry sediment in streambed sediment collected just below Clear 

Lake and 87 ng/g of dry sediment in North Fork Cache Creek 

at Highway 20. These values may approximate the 

concentrations of mercury in sediment uncontaminated by 

mining waste; however, the sediments below Clear Lake likely 

show some influence from historical mining activity at the 

Sulphur Bank Mine (fig. 1), an Environmental Protection 

Agency Superfund site located in the Oaks Arm of Clear Lake. 

Mercury concentrations in sediment from the Cache Creek at 

Rumsey site are expected to be higher than those upstream at 

the Clear Lake site (site 1 on fig. 1) because of runoff from 

geothermal sources and because of naturally occurring mercury 

in upstream soils. Although no pre-mining background 

concentration of mercury in sediment could be derived for the 

Cache Creek at Rumsey site, the present concentrations 

probably have been influenced by human activities for more 

than 150 years and almost certainly exceed the pre-mining 

levels. Because of the anthropogenic influences, the streambed 

sediments along Cache Creek can be considered as an 

additional source of mercury to downstream areas.

Chemical Signatures of Water Sources

The water chemistry at different locations within the 

Cache Creek Basin can vary because of chemical differences 

between the inflowing waters from different sources. These 

variations in water chemistry, related to water source, may be 

useful in determining the sources of mercury or methylmercury 

at downstream locations if the water associated with each 

mercury source has a distinguishable geochemical signature. 

Constituents that may be useful as chemical tracers of sources 

include the aqueous concentrations of chloride (Cl), sulfate 

(SO4), boron (B), lithium (Li), and organic carbon; the amounts 

of dissolved relative to suspended mercury; and the stable 

isotopes of hydrogen and oxygen in water. 




























































































-ETHYLMERCURYLOADSINGRAMSPERDAY

#ACHE#REEKNEAR,OWER,AKE .ORTH&ORK#ACHE#REEKAT(IGHWAY

#ACHE#REEKAT2UMSEY































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4OTALMETHYLMERCURYLOAD

&ILTEREDWATERMETHYLMERCURYLOAD

9OLO"YPASS3ITES

%80,!.!4)/.

20 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Figure 12. Instantaneous loads of methylmercury in unfiltered and filtered water at large river sites, Cache Creek Basin, California.






























"EAR#REEKABOVE3ULPHUR#REEK









































3ULPHUR#REEKAT7ILBUR3PRINGS





































-ETHYLMERCURYLOADSINGRAMSPERDAY

"EAR#REEKABOVE(OLSTEN#HIMNEY#ANYON































4OTALMETHYLMERCURYLOAD

&ILTEREDWATERMETHYLMERCURYLOAD

(ARLEY'ULCHNEAR7ILBUR3PRINGS

%80,!.!4)/.

Results and Discussion 21

Figure 13. Instantaneous loads of methylmercury in unfiltered and filtered water at small stream sites, Cache Creek Basin, California.
7OODLAND

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GRAMSOFMETHYLMERCURYPERDAY

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22 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Figure 14. Instantaneous loads of methylmercury at selected sites sampled February 27, 2000, through March 3, 2000, Cache Creek Basin, California. 

Cr., Creek; Sl., Slough
7OODLAND

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Results and Discussion 23

Figure 15. Instantaneous loads of methylmercury at selected sites sampled February 20–23, 2001, Cache Creek Basin, California.

Cr., Creek; Sl., Slough
24 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Chloride-to-Sulfate Ratios

#ACHE#REEKNEAR,OWERLAKE	

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4OTALMERCURYINSTREAMBEDSEDIMENT

INNANOGRAMSPERGRAMDRYWEIGHT



An example of chemical signatures for the Cache Creek at 

Rumsey site is the ratio of aqueous chloride to sulfate (Cl/SO4). 

A 2-year profile of Cl-to-SO4 is shown in figure 17

(Domagalski and others, 2000). The Cl-to-SO4 ratio for Cache 

Creek water depends on the principal source of water to the 

creek. The Indian Valley Reservoir has a Cl-to-SO4 ratio of 3, 

whereas ratios for Clear Lake are between 1 and 2. Harley 

Gulch has a relatively low range of Cl-to-SO4 ratios (0.7–1.25), 

but Sulphur Creek and Bear Creek have relatively high ratios 

(28–122 for Sulphur Creek and 14–53 for Bear Creek). The 

Cl-to-SO4 ratio for the Cache Creek at Rumsey site depends 

mostly on whether Clear Lake or the Indian Valley Reservoir is 

the primary source of water (typically during the irrigation 

period and wet period), or whether Bear and Sulphur Creeks 

dominate the flow (typically during the dry period, late fall to 

early winter). Because of the higher Cl content in the 

geothermal springs within the Sulphur Creek drainage, the 

Cl-to-SO4 ratio increases as the percentage of water from 

Sulphur Creek increases. The Harley Gulch samples have low 

Cl-to-SO4 ratios because of their higher concentrations of 

sulfate, which is probably derived from the mine waste; 

retorting (roasting) cinnabar to recover elemental mercury left 

behind sulfate minerals in the mine waste (Kim and others, 

2002), some of which could readily dissolve. The Cl-to-SO4

ratio for winter storm water runoff indicates a mixed source. 

The water chemistry, and therefore the Cl-to-SO4 ratio, 

changes significantly in the fall. As the irrigation period ends 

and flows from Clear Lake and Indian Valley Reservoir are 

decreased, the percentage of water in Cache Creek from 

Sulphur and Bear Creeks increases. As water containing high 

concentrations of the Cl ion enter the Bear Creek, the Cl-toSO4 ratio increases, and the reduced discharge from either 

Clear Lake or Indian Valley Reservoir causes the chemistry of 

Cache Creek to become increasingly similar to that of Sulphur 

and Bear Creeks.

Figure 16. Total mercury in streambed sediment at selected sites sampled 

during fall of 2000, Cache Creek Basin, California. 

Site numbers are in parentheses; locations are on table 1.
Results and Discussion 25

Systematic changes in water chemistry throughout the 

year, as indicated by the changing Cl-to-SO4 ratio, suggest that 

differences in other elemental ratios might be useful as tracers 

to indicate which locations (abandoned mines or geothermal 

springs) are important sources of mercury or methylmercury to 

downstream locations. Erosion of geologic material at the 

mine or geothermal sites, for example, might differ from that 

of the surrounding geologic material such that runoff from the 

mine or geothermal sites would have characteristic signatures 

with respect to element ratios. This is true, as discussed, for 

Cl/SO4. To determine if other elements are useful, an analysis 

of unfiltered water samples was completed by computing the 

ratios of the amounts of various elements in unfiltered water 

samples to the amount of aluminum. Aluminum has low 

solubility, but is a major constituent of the rock types in the 

Cache Creek Basin. Therefore, normalizing element 

concentrations in unfiltered water samples to that of aluminum 

might provide a useful tracer. 

Boron-to-Aluminum Ratios 



































#HLORIDESULFATE

Boron concentrations differed at several locations 

throughout the Cache Creek Basin. A graph of the ratios of 

boron to aluminum (B/Al) for mining and other sites within the 

Cache Creek Basin and at the Yolo Bypass is shown in 

figure 18. Many of the mining and geothermal sites (such as 

those of the Abbott and Turkey Run Mines), the Sulphur Creek 

Mines, sites that are downstream of mines (such as Harley 

Gulch), and sites downstream of geothermal streams (such as 

Sulphur Creek at Wilbur Springs) have generally higher 

B-to-Al ratios than other non-mining or non-geothermal sites. 

Outflows from the Clear Lake (Cache Creek near Lower Lake) 

and the upper Bear Creek (Bear Creek above Sulphur Creek) 

sites have relatively low B-to-Al ratios. The median values of 

the B-to-Al ratios for outflows from these sites did not differ 

statistically, according to the Mann-Whitney non-parametric 

test. The ratios for the upper Bear Creek and the lower Bear 

Creek (Bear Creek above Holsten Chimney Canyon) sites did 

differ (p = 0.0001, where p is the level of significance) 

according to the Mann-Whitney non-parametric test. Water 

from Sulphur Creek probably has the greatest impact on the 

B-to-Al ratio at the lower Bear Creek site. The B-to-Al ratios 

for this site and the Sulphur Creek at Wilbur Springs site are 

similar and are much higher than that for the upper Bear Creek 

site. 

Figure 17. Molar ratio of chloride to sulfate at the Cache Creek at Rumsey site, Cache Creek Basin, California. 
#ACHE#REEKNEAR,OWER,AKE

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"ORON
TO
ALUMINUMRATIOINUNFILTEREDWATER

THPERCENTILE

THPERCENTILE

THPERCENTILE

THPERCENTILE

THPERCENTILE

26 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

The B-to-Al ratios were statistically similar (p > 0.05) for 

Sulphur Creek, the Sulphur Creek mines, the Bear Creek above 

Holsten Chimney Canyon and the Harley Gulch near Wilbur 

Springs sites, and the Abbott and Turkey Run mine sites. The 

B-to-Al ratio for Indian Valley Reservoir outflow (North Fork 

Cache Creek near Clearlake Oaks) was higher than that for 

Clear Lake (Cache Creek near Lower Lake), and that 

influenced the chemistry of the Cache Creek at Rumsey site. 

The few water samples collected at the outlet of Indian Valley 

Reservoir (North Fork Cache Creek near Clearlake Oaks) were 

not sufficient to yield a high confidence level, but those 

analyzed indicated a higher B-to-Al ratio than that for Clear 

Lake outflow (Cache Creek near Lower Lake); this higher ratio 

probably caused an increase in the B-to-Al ratio downstream at 

the Cache Creek sites near Highway 505 and Rumsey. 

However, the B-to-Al ratio for the Cache Creek into Settling 

Basin site, farther downstream, was much lower and similar to 

that for Clear Lake. Therefore, the mine and geothermal 

chemical signature of the B-to-Al ratio was distinctive in the 

upper part of the drainage basin, but was lost before Cache 

Creek discharged into the Yolo Bypass, at least during the 

present study.

Figure 18. Boron-to-aluminum mass ratios at selected sites of the Cache Creek Basin and Yolo Bypass, California.
Results and Discussion 27

Boron-to-Lithium Ratios

Although the B-to-Al ratios for water were similar at the 

geothermal and the mining sites, B and lithium (Li) might covary and the concentrations of both B and Li might be highest 

in geothermal water (Goff and others, 1993a,b). A graph of B 

and Li concentrations in water from the study sites is shown in 

figure 19. There is a very good relation between these two 

elements and the coefficient of determination (R2) for all sites 

is 0.987. As expected, the concentrations of B and Li were 

highest in water from the Sulphur Creek at Wilbur Springs and 

nearby Sulphur Creek mine sites. There was considerable 

overlap in ranges of concentrations in water from Sulphur 

Creek and the Abbott and Turkey Run mine sites and in water 

from the Harley Gulch site. Because of the discharge of 

Sulphur Creek into Bear Creek, the B and Li concentrations in 

the Bear Creek above Holsten Chimney Canyon water samples 

partially overlapped those of Sulphur Creek and nearby mine 

sites. The samples from Bear Creek upstream of its confluence 

with Sulphur Creek (Bear Creek above Sulphur Creek) had the 

lowest concentrations of B and Li. As was true for the Cl and 

SO4 concentrations, the concentrations of B and Li were low in 

water from Clear Lake and Indian Valley Reservoir, which 

partially dilutes the concentrations from mine waste or 

geothermal water in Cache Creek. Concentrations of B and Li 

at the Cache Creek at Rumsey site were elevated relative to 

those at the Clear Lake outflow or at North Fork Cache Creek, 

but it is unclear whether the source of B and Li is the 

geothermal water or the mine sites. 













    

,ITHIUMINMICROGRAMSPERLITER

!BBOTTAND4URKEY2UNMINESITES

"EAR#REEKABOVE(OLSTEN#HIMNEY#ANYON

#ACHE#REEKAT2UMSEY

#ACHE#REEKNEAR(IGHWAY

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(ARLEY'ULCHNEAR7ILBUR3PRINGS

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.ORTH&ORK#ACHE#REEKNEAR#LEAR,AKE/AKS

)NDIAN6ALLEY2ESERVOIR	

3ULPHUR#REEKAT7ILBUR3PRINGSAND

NEARBYMINESITES

"EAR#REEKABOVE3ULPHUR#REEK

9OLO"YPASSAT)NTERSTATE

NEAR7EST3ACRAMENTO

"ORONINMICROGRAMSPERLITER

2



 

Figure 19. Boron and lithium concentrations at selected sites within the Cache Creek Basin, California.

R2 is the coefficient of determination).
28 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Boron-to-Chloride Ratios

Plots of B and Cl concentrations also indicate the 

signatures of geothermal waters in the Cache Creek Basin 

(Donnelly-Nolan and others, 1993; Goff and others, 1993a,b) 

(fig. 20). As in the case of B and Li, concentrations of B and 

Cl are strongly correlated; the coefficient of determination 

(R2) is 0.98. Measurements of B and Cl concentrations for 

samples from Sulphur Creek and Sulphur Creek mine sites 

overlapped those for samples from the Abbott and Turkey Run 

Mines and Harley Gulch. Cl and B concentrations were highest 

in samples from Sulphur Creek and the Sulphur Creek Mines. 

Goff and others (1993b) showed that the high Cl 

concentrations in Sulphur Creek water can be attributed to 

relict seawater in the geothermal springs. Figure 20 shows a 

line of equal B and Cl concentrations. All samples collected 

during this study plot below this line. Samples from 

geothermal springs located closer to the Clear Lake volcanic 

area (Sulphur Bank Mine area, fig. 1) plot on the line of equal 

B and Cl concentrations (fig. 20), providing a signature 

different from that for geothermal water from Sulphur Creek 

(Goff and others, 1993b). The Sulphur Bank geothermal 

waters differed from those of Sulphur Creek because the 

waters were near the metamorphic environment near the Clear 

Lake volcanic area (Goff and others, 1993b). Water having 

high concentrations of B and Cl in Sulphur Creek mixed with 

water in Bear Creek resulting in concentrations much higher at 

Bear Creek above Holsten Chimney Canyon (lower Bear 

Creek) than at Bear Creek above Sulphur Creek; 

concentrations at lower Bear Creek overlapped those in 

Sulphur Creek and at the Sulphur Creek mine sites. Water from 

locations farther downstream, such as Cache Creek at Rumsey, 

Cache Creek at Highway 505, and Cache Creek Settling Basin, 

showed the diluting effect (lower Cl and B concentrations) of 

Clear Lake outflow and North Fork Cache Creek. 















   

#HLORIDECONCENTRATIONINMILLIGRAMSPERLITER

!BBOTTAND4URKEY2UN-INESITES

"EAR#REEKABOVE(OLSTEN

#HIMNEY#ANYON

#ACHE#REEKAT2UMSEY

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7ILBUR3PRINGS

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CHLORIDE 2



"ORONCONCENTRATIONINMILLIGRAMSPERLITER

 

Figure 20. Boron and chloride concentrations at selected sites within the Cache Creek Basin, California.

R2 is the coefficient of determination.
Results and Discussion 29

Boron, Chloride, and Sulfate

The molar relation among B, Cl, and SO4 is shown using 

a ternary plot (figure 21). A mixing relation of water from 

Sulphur Creek, the Bear Creek at Holsten Chimney Canyon 

site, and, in some cases, the Cache Creek at Rumsey and the 

Cache Creek at Highway 505 sites, is apparent from the plot. 

The water at Cache Creek at Rumsey has a chemistry similar to 

that of Sulphur and Bear Creeks in fall when outflows are low 

after the irrigation season and before the rainfall/runoff season. 

At other times of the year, the water at Cache Creek at Rumsey 

is more similar to that of Indian Valley Reservoir or Clear 

Lake. The water at Cache Creek at Rumsey generally had less 

boron, or more Cl, than water in Indian Valley Reservoir or 

Clear Lake. The Abbott and Turkey Run Mines, and Harley 

Gulch water samples plot along a wide range of Cl and SO4

levels. It is not possible to distinguish mixing trends of the 

Abbott and Turkey Run Mines and Harley Gulch waters with 

downstream sites on Cache Creek using these constituents. 

Stable Isotopes of Hydrogen and Oxygen

Another useful signature is the stable isotopic 

composition of water. Stable isotope data for hydrogen and 

oxygen in water are given in table 9 of Appendix 1. Hydrogen 

and oxygen isotope ratios were derived from samples collected 

from most of the sites of this study (fig. 22). Stable isotope 

signatures of the geothermal waters also have been previously 

reported (Goff and others, 1993a,b; 2001). Stable isotope ratios 

of 18O/16O and 2H/1H in rain become progressively smaller as 

air masses leave the ocean and move inland and towards the 

poles. By definition, ocean water (VSMOW) has values of 

δ18O and δD equal to 0.0. Rain and snow (meteoric water) 

having the smallest values of δ18O and δD are at the north and 

south poles (Drever, 1982). Water that plots away from the 

global meteoric water line usually indicates some type of 

isotopic fractionation such as may occur during evaporation or 

certain types of water-rock interactions (Drever, 1982). 

Many of the water samples collected during this study had 

isotopic distributions that plot away from the global meteoric 

water line (fig. 22), which is based on worldwide stable isotope 

patterns (δ18O and δD) in rainfall. In this study, the waters from 

the Sulphur Creek and the Sulphur Creek mine sites deviated 

the most from the global meteoric water line. The samples from 

the Sulphur Creek mine sites had some of the largest values of 

δ18O, which generated a regression line that deviated the most 

from the global meteoric water line. The samples from Bear 

Creek above Holsten Chimney Canyon plotted along an 

implied mixing line from the Sulphur Creek waters. The large 

deviation from the global meteoric water line was a unique 

geochemical signature for the waters of this study. In contrast, 

the waters from the Abbott and Turkey Run Mines and those 

from Harley Gulch were more depleted in 18O and plotted 

closer to the global meteoric water line. The runoff from the 

Abbott and Turkey Run Mines and the water in Harley Gulch 

are generally not affected by geothermal discharge and 

therefore their isotopic distribution is more similar to that of 

rain. 

A second prominent feature of the isotope plot shown in 

figure 22 is the regression line for the Clear Lake outflow 

(Cache Creek near Lower Lake). The isotopic signature for that 

site was similar to those for Cache Creek at Rumsey, Cache 

Creek at Highway 505, and Cache Creek into Settling Basin. 

The Clear Lake outflow regression line indicates the isotopic 

composition of Clear Lake water, which is due to evaporation 

and local geothermal input over geologic time. The water most 

depleted in the heavier isotopes is that of the Yolo Bypass. That 

water plots on or just below the global meteoric water line. 

Much of the water in the Yolo Bypass originated from the 

Sacramento River, which is depleted in the heavier isotopes 

and also plots on the global meteoric water line (Domagalski 

and others, 2001). Therefore, the isotopic patterns of the 

geothermal waters are very distinct in the small streams in the 

upper part of the Cache Creek Basin, but the signature of Clear 

Lake water dominates at locations on Cache Creek downstream 

of the mining and geothermal sites.

Plots of chemical constituents and stable isotopes of water 

molecules can be used to show mixing relations and to evaluate 

whether or not constituent transport is conservative. Plots of Li 

versus δ18O and total mercury versus δ18O for sites along a 

flow path from Sulphur Creek to Bear Creek to Cache Creek 

are shown in figure 23. The water from Sulphur Creek had the 

highest enrichment in 18O as a the result of a high percentage 

of geothermal discharge into Sulphur Creek. Elevated 

concentrations of both Li and mercury in Sulphur Creek water 

spanned a wide range of oxygen isotope values. The plot for 

dissolved Li indicates a continuous mixing line from the 

Sulphur Creek Mines to the Sulphur Creek at Wilbur Springs 

waters for the samples that are most enriched in 18O 

(δ18O > –2). In contrast, the plot for mercury does not suggest 

a continuous mixing line from the Sulphur Creek Mines to 

Sulphur Creek at Wilbur Springs to Bear Creek above Holsten 

Chimney Canyon. Dissolved mercury in mine or geothermal 

waters, originating from locations along Sulphur Creek, 

probably sorbs to suspended sediment particles and settles to 

the streambed. Li is probably transported conservatively in 

these waters because it is dissolved and does not precipitate as 

a mineral along this flow path or become adsorbed to other 

sediment particles. 




































#HLORIDE

3ULFATE

"ORON

!BBOTTAND4URKEY2UNMINESITES

"EAR#REEKABOVE

(OLSTEN#HIMNEY#ANYON

#ACHE#REEKAT2UMSEY

#ACHE#REEKAT(IGHWAY

#ACHE#REEKINTO

3ETTLING"ASIN

#ACHE#REEKNEAR,OWER,AKE

(ARLEY'ULCHNEAR7ILBUR3PRINGS

,OWER9OLO"YPASS

.ORTH&ORK#ACHE#REEKAT(IGHWAY

3ULPHUR#REEKAT7ILBUR3PRINGSAND

NEARBYMINESITES

"EAR#REEKABOVE3ULPHUR#REEK

%80,!.!4)/.

30 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Figure 21. Ternary plot of the molar relation between boron, chloride, and sulfate for selected sites within the Cache Creek Basin, California.
DEUTERIUMINPERMIL D 

D OXYGEN
INPERMIL

!BBOTTAND4URKEY2UNMINESITES"EAR#REEKABOVE(OLSTEN#HIMNEY#ANYON#ACHE#REEKAT2UMSEY#ACHE#REEKAT(IGHWAY#ACHE#REEKINTO3ETTLING"ASIN#ACHE#REEKOUTOF3ETTING"ASIN#ACHE#REEKNEAR,OWER,AKE(ARLEY'ULCHNEAR7ILBUR3PRINGS.ORTH&ORK#ACHE#REEKAT(IGHWAY

.ORTH&ORK#ACHE#REEKNEAR#LEARLAKE/AKS3ULPHUR#REEKAT7ILBUR3PRINGS"EAR#REEKABOVE3ULPHUR#REEK

9OLO"YPASSAT)
NEAR7EST3ACRAMENTO$AVIS#REEK2ESERVOIRAT$AMNEAR+NOXVILLE,OWER9OLO"YPASS3ULPHUR#REEKMINES'LOBAL-ETEORIC7ATER,INE

2EGRESSIONLINEFOR#ACHE#REEKNEAR,OWER,AKE#LEAR,AKE	

2EGRESSION,INEFOR3ULPHUR#REEK-INES

6IENNA3TANDARD-EAN/CEAN7ATER

Results and Discussion 31

Figure 22. Ratios of stable isotopes (delta [δ] deuterium and δ oxygen-18) for selected sites within the Cache Creek Basin, California.













 
 
 
 
     

-ERCURYCONCENTRATIONINUNFILTEREDWATERINNANOGRAMSPERLITER













,ITHIUMCONCENTRATIONINFILTEREDWATERINMICROGRAMSPERLITER

3ULPHUR#REEKAT7ILBUR

3PRINGS

"EAR#REEKABOVE(OLSTEN

#HIMNEY#ANYON

#ACHE#REEKAT2UMSEY

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3ULPHUR#REEKMINES

DOXYGEN
INPERMIL

32 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Figure 23. Lithium in filtered water and and mercury in unfiltered water versus delta [δ] oxygen-18 for selected sites within the Cache Creek 

Basin, California.
Results and Discussion 33

Dissolved Organic Carbon

Another chemical relation to consider is that between 

DOC (dissolved organic carbon) and methylmercury. The 

Cache Creek at Rumsey site has higher levels of DOC than 

many other stream sites within the Sacramento River Basin 

(Domagalski and Dileanis, 2000). Some of the higher levels of 

DOC can be attributed to outflow from Clear Lake, which is 

eutrophic. A graph of concentrations of methylmercury and 

DOC is shown in figure 24. Although higher levels of 

methylmercury generally correspond to higher levels of DOC, 

the relation is weak (R2 = 0.13) and, therefore, is a poor 

predictor. Prior studies within the Sacramento River Basin also 

have shown that methylmercury concentrations are not 

correlated with DOC (Domagalski, 2001), even though organic 

carbon is considered an essential ingredient in the microbially 

mediated methylation of mercury.















-ETHYLMERCURYINUNFILTEREDWATERINNANOGRAMSPERLITER

$ISSOLVEDORGANICCARBONINMILLIGRAMSPERLITERASCARBON

"EAR#REEKABOVE3ULPHUR#REEK

"EAR#REEKABOVE(OLSTEN

#HIMNEY#ANYON

3ULPHUR#REEKAT7ILBUR3PRINGS

(ARLEY'ULCHNEAR7ILBUR3PRINGS

.ORTH&ORK#ACHE#REEKAT

(IGHWAY

#ACHE#REEKAT2UMSEY

$AVIS#REEK2ESERVOIRAT$AM

NEAR+NOXVILLE

#ACHE#REEKNEAR,OWER,AKE

.ORTH&ORK#ACHE#REEKNEAR

#LEARLAKE/AKS

#ACHE#REEKINTO3ETTLING"ASIN

#ACHE#REEKOUTOF3ETTLING"ASIN

9OLO"YPASSAT)NTERSTATENEAR

7EST3ACRAMENTO

           ,OWER9OLO"YPASS

Figure 24. Methylmercury and dissolved organic carbon for selected sites within the Cache Creek Basin, California.
34 Mercury and Methylmercury Concentrations and Loads in the Cache Creek Basin, California, January 2000 through May 2001

Summary and Conclusions

A 17-month study of mercury and methylmercury 

concentrations and loads was completed in the Cache Creek 

drainage basin. Tributaries to Cache Creek located 

downstream of abandoned mercury mines and near geothermal 

discharges were sampled for mercury and methylmercury and 

other aqueous constituents. Other major tributaries to Cache 

Creek and Cache Creek itself also were sampled at several 

locations, as was the Yolo Bypass, which receives water from 

Cache Creek and the Sacramento River during flood 

conditions. Because of relatively low rainfall during the study 

period, the stream discharge in this drainage basin was low 

compared with that noted in historical records. Consequently, 

observed loads of mercury and methylmercury were probably 

less than those during years of normal or above-normal 

precipitation. The largest instantaneous loads of mercury and 

methylmercury were measured during the winter rainy season. 

Release of water from either Clear Lake or Indian Valley 

Reservoir, for the purpose of flood control or to supply 

irrigation water to downstream farms, also may increase the 

loads of mercury and methylmercury by re-suspending 

previously deposited streambed sediment containing elevated 

concentrations of mercury. Loads of mercury and 

methylmercury were generally low in the summer months 

because of low stream discharge. Although the loads of 

mercury and methylmercury can be low during the dry season, 

concentrations can be high at any other time of the year.

During the study period, January 2000 through May 2001, 

loads from geothermal sources of mercury and methylmercury 

were greater than those from abandoned mining sources. This 

can be partly attributable to weather patterns that failed to 

produce large stream flow and erosion from mining waste. 

Therefore, loads from geothermal sources may not exceed 

those from abandoned mines during periods of normal or 

above-normal rainfall. The streambed sediments of the larger 

streams, such as Cache Creek, also are a significant source of 

mercury. Re-suspension of Cache Creek streambed sediment 

and its associated mercury results in the transport of the load 

downstream. That was especially apparent during the first 

winter of this study when water was released from Clear Lake 

to lower the lake level. Therefore, the higher loads at Cache 

Creek at Rumsey and downstream at Cache Creek into Settling 

Basin can be logically attributed primarily to higher flows of 

the released water re-suspending mercury previously 

deposited in the bottom sediments. 

Water from the geothermal and mining locations had 

different geochemical signatures, especially for stable isotopes 

of water and other aqueous constituents such as boron, 

chloride, sulfate, and lithium. The discharges from Clear Lake 

and Sulphur Creek have distinct stable isotope signatures 

caused by evaporation and the interaction of water and rock, 

but these signatures are lost by dilution in lower Cache Creek. 

The ratio of chloride to sulfate in water samples from Cache 

Creek at Rumsey shows strong seasonal variations that can be 

attributed to different sources of water in the drainage basin. 

The aqueous constituents also are useful as tracers for 

geothermal sources of water and for evaluating the extent to 

which mercury is transported conservatively. Concentrations 

of lithium correlate well with oxygen isotopes along a mixing 

and dilution flow path from Sulphur Creek to Bear Creek to 

Cache Creek, indicating that all of these constituents are 

transported conservatively. In contrast, total mercury in 

unfiltered water does not correlate well with oxygen isotopes 

or the other aqueous constituents, indicating that mercury 

transport is not conservative. It is hypothesized that dissolved 

mercury from the geothermal sources is largely adsorbed onto 

fine-grained sediments in Sulphur Creek and lower Bear 

Creek. Mercury transport in the tributaries dominated by 

geothermal sources is highly episodic; much of the transport is 

related to the re-suspension of previously deposited sediment. 

Mercury transport in tributaries dominated by mining sources 

such as Harley Gulch is also related to sediment transport 

mechanisms, as the main form of mercury is hypothesized to 

be particles of mercury sulfide (cinnabar and metacinnabar).

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Appendix 1. Table 1. 37

Appendix 1. Table 1. Stream discharge and concentrations of mercury in unfiltered and filtered water from sites in the Cache Creek Basin, California

[m3/s, cubic meter per second; NA, not available; ng/L, nanogram per liter; —, not measured]

Site Date

Daily mean

stream

discharge, 

in m3

/s

Instantaneous

stream 

discharge, 

in m3

/s

Mercury in

unfiltered

water,

in ng/L

Mercury in

filtered water,

in ng/L

Bear Creek above Holsten Chimney Canyon 1/31/2000 4.00 — 125 33

Cache Creek at Rumsey 1/31/2000 — 5.40 273 10.6

Cache Creek into Settling Basin 1/31/2000 5.00 — 5.38 2.17

Cache Creek near Lower Lake 1/31/2000 0.15 — 7.48 5.31

Harley Gulch near Wilbur Springs 1/31/2000 0.13 — 831 71.3

North Fork Cache Creek at Highway 20 1/31/2000 — 4.40 149 4.77

Sulphur Creek at Wilbur Springs 1/31/2000 0.62 — 1,560 399

Bear Creek above Holsten Chimney Canyon 2/27/2000 16.60 — 195 13.4

Harley Gulch near Wilbur Springs 2/27/2000 0.21 — 243 60

Sulphur Creek at Wilbur Springs 2/27/2000 1.02 — 542 328

Cache Creek at Rumsey 2/28/2000 — 60.71 40.6 3.75

Davis Creek Reservoir at Dam 2/28/2000 1.90 — 33 6.60

North Fork Cache Creek at Highway 20 2/28/2000 — 63.01 23.7 1.90

Cache Creek near Lower Lake 2/29/2000 51.80 — 17.5 13.40

North Fork Cache Creek near Clearlake Oaks 2/29/2000 65.40 — 5.2 1.85

Cache Creek into Settling Basin 3/1/2000 139.00 — 209 4.10

Cache Creek out of Settling Basin 3/1/2000 139.00 — 161 4.70

Bear Creek above Holsten Chimney Canyon 3/2/2000 5.60 — 48.4 9.13

Bear Creek above Sulphur Creek 3/2/2000 — 4.20 5.38 2.04

Cache Creek at Rumsey 3/2/2000 — 116.70 40 1.48

Cache Creek into Settling Basin 3/2/2000 129.70 — 151 2.11

Cache Creek near Lower Lake 3/2/2000 52.70 — 10.9 1.35

Harley Gulch near Wilbur Springs 3/2/2000 0.04 — 101 39.1

North Fork Cache Creek at Highway 20 3/2/2000 — 75.50 16.7 1.40

Sulphur Creek at Wilbur Springs 3/2/2000 0.42 — 376 135

Yolo Bypass at Interstate 80 near West Sacramento 3/2/2000 1,283.26 — 20.5 2.05

Lower Yolo Bypass 3/3/2000 1,283.26 — 13.5 3.35

Davis Creek Reservoir at Dam 3/10/2000 1.36 — 29.8 5.38

Bear Creek above Holsten Chimney Canyon 3/15/2000 2.60 — 32.7 12.4

Harley Gulch near Wilbur Springs 3/15/2000 0.02 — 144 69.5

Sulphur Creek at Wilbur Springs 3/15/2000 0.18 — 528 342

Cache Creek at Rumsey 3/16/2000 — 43.72 10.6 1.75

Cache Creek at Rumsey 3/16/2000 — 43.20 8.28 1.02

Cache Creek at Highway 505 3/16/2000 — 51.00 16.6 1.05

Davis Creek Reservoir at Dam 3/16/2000 0.54 — 9.65 3.95

North Fork Cache Creek at Highway 20 3/16/2000 — 12.72 5.05 0.85

North Fork Cache Creek at Highway 20 3/16/2000 — 12.70 4.13 0.88

Cache Creek near Lower Lake 3/17/2000 5.90 — 25.6 2.95

North Fork Cache Creek near Clearlake Oaks 3/17/2000 7.70 — 3.5 3.05

Cache Creek into Settling Basin 3/18/2000 26.60 — 24.3 1.50
38 Mercury and Methylmercury Concentrations and Loads, Cache Creek Basin, California, January 2000 through May 2001

Site Date

Daily mean

stream

discharge, 

in m3/s

Instantaneous

stream 

discharge, 

in m3/s

Mercury in

unfiltered

water,

in ng/L

Mercury in

filtered water,

in ng/L

Cache Creek out of Settling Basin 3/18/2000 26.60 — 11.2 1.60

Yolo Bypass at Interstate 80 near West Sacramento 3/18/2000 96.32 — 15.7 1.65

Lower Yolo Bypass 3/22/2000 96.32 — 39.2 1.75

Bear Creek above Holsten Chimney Canyon 4/17/2000 2.12 — 72.4 23.3

Cache Creek at Rumsey 4/17/2000 — 54.40 43.3 1.62

Cache Creek into Settling Basin 4/17/2000 16.80 154 1.51

Cache Creek at Highway 505 4/17/2000 — 42.50 43.4 1.72

Cache Creek near Lower Lake 4/17/2000 28.30 — 6.91 1.42

Harley Gulch near Wilbur Springs 4/17/2000 0.05 — 140 63.6

North Fork Cache Creek at Highway 20 4/17/2000 — 4.10 3.45 1.21

Sulphur Creek at Wilbur Springs 4/17/2000 0.26 — 430 99.3

Cache Creek near Lower Lake 6/13/2000 19.70 — 3.49 0.63

Davis Creek above Davis Creek Reservoir 6/13/2000 0.01 — 49.9 8.95

Davis Creek below Davis Creek Reservoir 6/13/2000 0.00 — 6.31 4.73

Harley Gulch near Wilbur Springs 6/13/2000 0.00 — 197 89.6

North Fork Cache Creek at Highway 20 6/13/2000 0.85 1.84 0.83

Bear Creek above Holsten Chimney Canyon 6/14/2000 0.09 — 26.5 11.3

Bear Creek above Sulphur Creek 6/14/2000 — 0.07 0.65 1.20

Cache Creek at Rumsey 6/14/2000 — 34.55 5.61 1.17

Cache Creek into Settling Basin 6/14/2000 1.70 — 17.7 1.71

Cache Creek at Highway 505 6/14/2000 — 0.85 11.2 1.62

Sulphur Creek at Wilbur Springs 6/14/2000 0.01 — 676 125

Bear Creek above Holsten Chimney Canyon 8/10/2000 0.04 — 17.3 8.40

Cache Creek at Rumsey 8/10/2000 — 14.70 5.64 0.73

Cache Creek into Settling Basin 8/10/2000 0.88 — 10.6 1.14

Cache Creek at Highway 505 8/10/2000 — 0.30 2.38 1.99

Cache Creek near Lower Lake 8/10/2000 15.60 — 7.57 0.47

Davis Creek above Davis Creek Reservoir 8/10/2000 0.00 — 114 8.26

North Fork Cache Creek at Highway 20 8/10/2000 — 0.30 2.17 1.05

Sulphur Creek at Wilbur Springs 8/10/2000 0.00 — 690 63.3

Bear Creek above Holsten Chimney Canyon 10/11/2000 0.10 — 24.6 10.5

Bear Creek above Sulphur Creek 10/11/2000 0.09 — 0.62 0.39

Cache Creek at Rumsey 10/11/2000 — 9.60 5.67 0.45

Cache Creek into Settling Basin 10/11/2000 2.40 — 5.51 0.85

Cache Creek at Highway 505 10/11/2000 1.00 — 2.19 0.80

Cache Creek near Lower Lake 10/11/2000 7.70 — 4.38 0.24

North Fork Cache Creek at Highway 20 10/11/2000 — 0.20 2.64 0.87

Sulphur Creek at Wilbur Springs 10/11/2000 0.01 — 676 216

Davis Creek above Davis Creek Reservoir 11/6/2000 0.00 — 52.6 7.60

Davis Creek below Davis Creek Reservoir 11/6/2000 — 0.00 5.90 3.50

Bear Creek above Holsten Chimney Canyon 11/7/2000 0.09 — 47.4 25.7

Appendix 1. Table 1. Stream discharge and concentrations of mercury in unfiltered and filtered water from sites in the Cache Creek Basin, California—

Continued
Appendix 1. Table 1. 39

Site Date

Daily mean

stream

discharge, 

in m3

/s

Instantaneous

stream 

discharge, 

in m3

/s

Mercury in

unfiltered

water,

in ng/L

Mercury in

filtered water,

in ng/L

Bear Creek above Sulphur Creek 11/7/2000 — 0.09 0.80 0.70

Cache Creek at Rumsey 11/7/2000 — 0.57 2.40 1.70

Cache Creek into Settling Basin 11/7/2000 0.48 1.80 1.30

Cache Creek at Highway 505 11/7/2000 0.71 1.20 1.10

Cache Creek near Lower Lake 11/7/2000 0.13 0.30 0.30

North Fork Cache Creek at Highway 20 11/7/2000 0.23 1.80 1.60

Sulphur Creek at Wilbur Springs 11/7/2000 0.02 — 1,320 219

Bear Creek above Holsten Chimney Canyon 12/11/2000 0.11 — 46.5 24.5

Bear Creek above Sulphur Creek 12/11/2000 — 0.07 0.70 0.50

Cache Creek at Rumsey 12/11/2000 — 0.85 2.30 1.50

Cache Creek at Highway 505 12/11/2000 — 0.99 1.40 0.80

Cache Creek near Lower Lake 12/11/2000 0.11 — 0.30 0.30

North Fork Cache Creek at Highway 20 12/11/2000 0.28 1.80 0.60

Bear Creek above Holsten Chimney Canyon 1/11/2001 2.40 — 310 39.2

Bear Creek above Sulphur Creek 1/11/2001 — 0.28 3.80 0.90

Cache Creek at Rumsey 1/11/2001 — 7.08 24.9 2.90

Cache Creek at Highway 505 1/11/2001 — 1.93 5.20 1.20

Cache Creek near Lower Lake 1/11/2001 0.14 — 7.60 1.00

Harley Gulch near Wilbur Springs 1/11/2001 0.00 — 366 186

North Fork Cache Creek at Highway 20 1/11/2001 — 0.25 9.50 2.10

Sulphur Creek at Wilbur Springs 1/11/2001 0.37 — 3,070 318

Bear Creek above Holsten Chimney Canyon 2/13/2001 1.42 — 144 64.5

Bear Creek above Sulphur Creek 2/13/2001 — 0.11 1.70 1.00

Cache Creek near Lower Lake 2/13/2001 0.11 — 3.50 1.70

Cache Creek at Rumsey 2/13/2001 — 4.70 37.5 11.5

Cache Creek at Highway 505 2/13/2001 — NA 19.9 4.40

Harley Gulch near Wilbur Springs 2/13/2001 0.00 — 169 92.8

North Fork Cache Creek at Highway 20 2/13/2001 — 0.91 2.6 1.60

Sulphur Creek at Wilbur Springs 2/13/2001 0.13 — 906 317

Bear Creek above Holsten Chimney Canyon 2/20/2001 5.18 — 150 43.5

Cache Creek near Lower Lake 2/20/2001 0.13 — 13.9 6.65

Harley Gulch near Wilbur Springs 2/20/2001 0.00 — 100 65.5

North Fork Cache Creek near Clearlake Oaks 2/20/2001 0.34 — 3.85 2.55

Sulphur Creek at Wilbur Springs 2/20/2001 0.59 — 685 310

Cache Creek at Rumsey 2/21/2001 — 28.60 60.5 11.1

North Fork Cache Creek at Highway 20 2/21/2001 — 7.93 17.4 7.15

Cache Creek out of Settling Basin 2/22/2001 26.40 — 53.5 12.2

Cache Creek Into Settling Basin 2/22/2001 26.40 — 58.5 9.45

Yolo Bypass at Interstate 80 near West Sacramento 2/22/2001 40.21 — 34.3 6.40

Lower Yolo Bypass 2/23/2001 40.21 — 36.8 4.70

Cache Creek at Rumsey 3/23/2001 4.02 — 5.25 2.16

Bear Creek above Holsten Chimney Canyon 3/23/2001 0.91 — 31.4 16

Bear Creek above Sulphur Creek 3/23/2001 NA — 1.42 0.81

Appendix 1. Table 1. Stream discharge and concentrations of mercury in unfiltered and filtered water from sites in the Cache Creek Basin, California—

Continued
40 Mercury and Methylmercury Concentrations and Loads, Cache Creek Basin, California, January 2000 through May 2001

Site Date

Daily mean

stream

discharge, 

in m3/s

Instantaneous

stream 

discharge, 

in m3/s

Mercury in

unfiltered

water,

in ng/L

Mercury in

filtered water,

in ng/L

Cache Creek near Lower Lake 3/23/2001 0.18 — 8.82 2.25

North Fork Cache Creek at Highway 20 3/23/2001 1.48 — 2.31 1.22

Bear Creek above Holsten Chimney Canyon 5/3/2001 0.31 — 35.5 17.9

Bear Creek above Sulphur Creek 5/3/2001 NA — 0.98 0.54

Cache Creek near Lower Lake 5/3/2001 0.31 — 2.53 0.63

Cache Creek at Rumsey 5/3/2001 NA — 10 1.12

Harley Gulch near Wilbur Springs 5/3/2001 0.00 — 265 106

North Fork Cache Creek at Highway 20 5/3/2001 NA — 5.09 0.80

Sulphur Creek at Wilbur Springs 5/3/2001 0.03 — 557 124

Appendix 1. Table 1. Stream discharge and concentrations of mercury in unfiltered and filtered water from sites in the Cache Creek Basin, California—

Continued
Appendix 1. Table 2. 41

Appendix 1. Table 2. Stream discharge and concentrations of methylmercury in unfiltered and filtered water from sites in the Cache Creek Basin, California

[m3/s, cubic meter per second; NA, not available; ng/L, nanogram per liter; —, not measured; <, less than indicated value]

Site Date

Daily mean 

stream 

discharge, in 

m3/s

Instantaneous 

stream 

discharge, in 

m3/s

Methylmercury in 

unfiltered water, 

in ng/L

Methylmercury in 

filtered water, in 

ng/L

Bear Creek above Holsten Chimney Canyon 1/31/2000 4.00 — 0.58 0.48

Cache Creek at Rumsey 1/31/2000 — 5.40 0.78 0.23

Cache Creek into Settling Basin 1/31/2000 5.00 — 0.18 0.09

Cache Creek near Lower Lake 1/31/2000 0.15 — 0.11 0.11

Harley Gulch near Wilbur Springs 1/31/2000 0.13 — 0.98 0.63

North Fork Cache Creek at Highway 20 1/31/2000 — 4.40 0.17 0.22

Sulphur Creek at Wilbur Springs 1/31/2000 0.62 — 2.46 0.30

Bear Creek above Holsten Chimney Canyon 2/27/2000 16.60 — 0.30 0.18

Harley Gulch near Wilbur Springs 2/27/2000 0.21 — 0.07 0.12

Sulphur Creek at Wilbur Springs 2/27/2000 1.02 — 0.33 0.29

Cache Creek at Rumsey 2/28/2000 — 60.71 0.13 < 0.024

Davis Creek Reservoir at Dam 2/28/2000 1.90 — 0.33 0.16

North Fork Cache Creek at Highway 20 2/28/2000 — 63.01 0.08 < 0.023

Cache Creek near Lower Lake 2/29/2000 51.80 — 0.13 < 0.023

North Fork Cache Creek near Clearlake Oaks 2/29/2000 65.40 — 0.03 < 0.023

Cache Creek into Settling Basin 3/1/2000 139.00 — 0.58 < 0.023

Cache Creek out of Settling Basin 3/1/2000 139.00 — 0.44 < 0.023

Bear Creek above Holsten Chimney Canyon 3/2/2000 5.60 — 0.26 0.14

Bear Creek above Sulphur Creek 3/2/2000 — 4.20 0.10 0.02

Cache Creek at Rumsey 3/2/2000 — 116.70 0.22 0.02

Cache Creek into Settling Basin 3/2/2000 129.70 — 0.35 0.05

Cache Creek near Lower Lake 3/2/2000 52.70 — 0.15 0.07

Harley Gulch near Wilbur Springs 3/2/2000 0.04 — 0.12 0.10

North Fork Cache Creek at Highway 20 3/2/2000 — 75.50 0.07 0.02

Sulphur Creek at Wilbur Springs 3/2/2000 0.42 — 0.22 0.11

Yolo Bypass at Interstate 80 near West Sacramento 3/2/2000 1,283.26 — 0.20 0.03

Lower Yolo Bypass 3/3/2000 1,283.26 — 0.16 0.16

Davis Creek Reservoir at Dam 3/10/2000 1.36 — 0.27 0.10

Bear Creek above Holsten Chimney Canyon 3/15/2000 2.60 — 0.15 0.09

Harley Gulch near Wilbur Springs 3/15/2000 0.02 — 0.09 0.07

Sulphur Creek at Wilbur Springs 3/15/2000 0.18 — 0.06 < 0.023

Cache Creek at Rumsey 3/16/2000 — 43.72 0.07 < 0.023

Cache Creek at Rumsey 3/16/2000 — 43.20 0.10 0.07

Cache Creek at Highway 505 3/16/2000 — 51.00 0.15 0.07

Davis Creek Reservoir at Dam 3/16/2000 0.54 — 0.22 0.08

North Fork Cache Creek at Highway 20 3/16/2000 — 12.72 < 0.024 < 0.024

North Fork Cache Creek at Highway 20 3/16/2000 — 12.70 0.05 0.06

Cache Creek near Lower Lake 3/17/2000 5.90 — 0.05 < 0.023

North Fork Cache Creek near Clearlake Oaks 3/17/2000 7.70 — < 0.023 < 0.023

Cache Creek into Settling Basin 3/18/2000 26.60 — 0.09 < 0.022

Cache Creek out of Settling Basin 3/18/2000 26.60 — 0.20 0.06

Yolo Bypass at Interstate 80 near West Sacramento 3/18/2000 96.32 — 0.48 0.17

Lower Yolo Bypass 3/22/2000 96.32 — 0.69 0.31

Bear Creek above Holsten Chimney Canyon 4/17/2000 2.12 — 0.35 0.16
42 Mercury and Methylmercury Concentrations and Loads, Cache Creek Basin, California, January 2000 through May 2001

Cache Creek at Rumsey 4/17/2000 — 54.40 0.41 0.04

Cache Creek into Settling Basin 4/17/2000 16.80 — 0.51 0.02

Cache Creek at Highway 505 4/17/2000 — 42.50 1.08 0.11

Cache Creek near Lower Lake 4/17/2000 28.30 — 0.47 0.13

Harley Gulch near Wilbur Springs 4/17/2000 0.05 — 0.45 0.41

North Fork Cache Creek at Highway 20 4/17/2000 — 4.10 0.02 0.02

Sulphur Creek at Wilbur Springs 4/17/2000 0.26 — 0.66 0.38

Cache Creek near Lower Lake 6/13/2000 19.70 — 0.12 0.03

Davis Ck above Davis Creek Reservoir 6/13/2000 0.01 — 0.36 0.18

Davis Creek Reservoir at Dam 6/13/2000 0.00 — 0.74 0.61

Harley Gulch near Wilbur Springs 6/13/2000 0.00 — 7.76 1.57

North Fork Cache Creek at Highway 20 6/13/2000 — 0.85 0.08 0.02

Bear Creek above Holsten Chimney Canyon 6/14/2000 0.09 — 0.17 0.13

Bear Creek above Sulphur Creek 6/14/2000 — 0.07 0.21 0.09

Cache Creek at Rumsey 6/14/2000 — 34.55 0.20 0.13

Cache Creek into Settling Basin 6/14/2000 1.70 — 0.26 0.09

Cache Creek at Highway 505 6/14/2000 — 0.85 0.27 0.08

Sulphur Creek at Wilbur Springs 6/14/2000 0.01 — 0.76 0.21

Bear Creek above Holsten Chimney Canyon 8/10/2000 0.04 — 1.09 0.15

Cache Creek at Rumsey 8/10/2000 — 14.70 0.23 0.10

Cache Creek into Settling Basin 8/10/2000 0.88 — 0.48 0.09

Cache Creek at Highway 505 8/10/2000 — 0.30 0.14 0.82

Cache Creek near Lower Lake 8/10/2000 15.60 — 0.18 0.02

Davis Ck above Davis Creek Reservoir 8/10/2000 0.00 — 0.24 0.17

North Fork Cache Creek at Highway 20 8/10/2000 — 0.30 0.19 0.03

Sulphur Creek at Wilbur Springs 8/10/2000 0.00 — 4.04 0.07

Bear Creek above Holsten Chimney Canyon 10/11/2000 0.10 — 0.13 0.13

Bear Creek above Sulphur Creek 10/11/2000 0.09 — 0.09 0.02

Cache Creek at Rumsey 10/11/2000 — 9.60 0.11 0.03

Cache Creek into Settling Basin 10/11/2000 2.40 — 0.18 0.07

Cache Creek at Highway 505 10/11/2000 1.00 — 0.19 0.05

Cache Creek near Lower Lake 10/11/2000 7.70 — 0.03 0.03

North Fork Cache Creek at Highway 20 10/11/2000 — 0.20 0.04 0.03

Sulphur Creek at Wilbur Springs 10/11/2000 0.01 ó 1.57 1.02

Bear Creek above Holsten Chimney Canyon 11/7/2000 — 0.09 0.32 0.28

Bear Creek above Sulphur Creek 11/7/2000 0.00 — 0.05 0.05

Cache Creek at Rumsey 11/7/2000 0.02 — 0.05 0.03

Cache Creek into Settling Basin 11/7/2000 — 0.57 0.09 0.04

Cache Creek at Highway 505 11/7/2000 0.09 — 0.07 0.03

Cache Creek near Lower Lake 11/7/2000 0.13 — 0.02 0.03

North Fork Cache Creek at Highway 20 11/7/2000 — 0.23 0.02 0.04

Sulphur Creek at Wilbur Springs 11/7/2000 — 0.00 1.30 1.31

Appendix 1. Table 2. Stream discharge and concentrations of methylmercury in unfiltered and filtered water from sites in the Cache Creek Basin, California—

Continued

Site Date

Daily mean 

stream 

discharge, in 

m3/s

Instantaneous 

stream 

discharge, in 

m3/s

Methylmercury in 

unfiltered water, 

in ng/L

Methylmercury in 

filtered water, in 

ng/L
Appendix 1. Table 2. 43

Bear Creek above Holsten Chimney Canyon 12/11/2000 — 0.28 0.22 0.12

Bear Creek above Sulphur Creek 12/11/2000 0.11 — 0.07 0.03

Cache Creek at Rumsey 12/11/2000 — 0.07 0.04 0.04

Cache Creek at Highway 505 12/11/2000 0.11 — 0.09 0.03

Cache Creek near Lower Lake 12/11/2000 0.48 — 0.02 0.03

North Fork Cache Creek at Highway 20 12/11/2000 — — 0.03 0.03

Bear Creek above Holsten Chimney Canyon 1/11/2001 — 0.28 0.47 0.13

Bear Creek above Sulphur Creek 1/11/2001 — 0.25 0.18 0.06

Cache Creek at Rumsey 1/11/2001 0.37 — 0.04 0.03

Cache Creek at Highway 505 1/11/2001 2.40 — 0.09 0.06

Cache Creek near Lower Lake 1/11/2001 — 0.99 0.05 0.02

Harley Gulch near Wilbur Springs 1/11/2001 0.14 — 1.09 0.45

North Fork Cache Creek at Highway 20 1/11/2001 — — 0.06 0.04

Sulphur Creek at Wilbur Springs 1/11/2001 0.00 — 0.92 0.09

Bear Creek above Holsten Chimney Canyon 2/13/2001 — 0.11 0.71 0.53

Bear Creek above Sulphur Creek 2/13/2001 — 0.91 0.05 0.03

Cache Creek at Rumsey 2/13/2001 0.13 — 0.28 0.12

Cache Creek at Highway 505 2/13/2001 1.42 — 0.23 0.09

Cache Creek near Lower Lake 2/13/2001 — 1.93 0.09 0.05

Harley Gulch near Wilbur Springs 2/13/2001 0.11 — 0.66 0.39

North Fork Cache Creek at Highway 20 2/13/2001 — — 0.05 0.05

Sulphur Creek at Wilbur Springs 2/13/2001 0.00 — 0.41 0.13

Bear Creek above Holsten Chimney Canyon 2/20/2001 — NA 0.67 0.44

Cache Creek near Lower Lake 2/20/2001 0.34 — 0.09 0.05

Harley Gulch near Wilbur Springs Cr 2/20/2001 — — 0.39 0.29

North Fork. Cache Creek near Clearlake Oaks 2/20/2001 5.18 — < 0.013 0.02

Sulphur Creek at Wilbur Springs 2/20/2001 0.00 — 0.49 0.43

Cache Creek at Rumsey 2/21/2001 — 7.93 0.59 0.13

North Fork Cache Creek at Highway 20 2/21/2001 0.59 — 0.17 0.07

Cache Creek out of Settling Basin 2/22/2001 40.21 — 0.33 0.17

Cache Creek into Settling Basin 2/22/2001 40.21 — 0.49 0.15

Cache Creek into Settling Basin (replicate) 2/22/2001 — 28.60 0.46 0.12

Yolo Bypass at Interstate 80 near West Sacramento 2/22/2001 26.40 — 0.35 0.11

Lower Yolo Bypass 2/23/2001 0.13 — 0.21 0.11

North Fork Cache Creek at Highway 20 3/15/2001 NA — 0.07 0.02

Cache Creek at Rumsey 3/19/2001 1.48 — 0.10 0.02

Bear Creek above Holsten Chimney Canyon 3/23/2001 NA — 0.30 0.09

Bear Creek above Sulphur Creek 3/23/2001 — — 0.07 0.03

Cache Creek near Lower Lake 3/23/2001 0.91 — 0.15 0.03

North Fork Cache Creek at Highway 20 3/23/2001 0.18 — 0.09 0.04

Bear Creek above Holsten Chimney Canyon 5/3/2001 0.31 — 0.10 0.02

Appendix 1. Table 2. Stream discharge and concentrations of methylmercury in unfiltered and filtered water from sites in the Cache Creek Basin, California—

Continued

Site Date

Daily mean 

stream 

discharge, in 

m3/s

Instantaneous 

stream 

discharge, in 

m3/s

Methylmercury in 

unfiltered water, 

in ng/L

Methylmercury in 

filtered water, in 

ng/L
44 Mercury and Methylmercury Concentrations and Loads, Cache Creek Basin, California, January 2000 through May 2001

Bear Creek above Sulphur Creek 5/3/2001 NA — 0.06 0.04

Cache Creek near Lower Lake 5/3/2001 0.31 — 0.26 0.08

Cache Creek at Rumsey 5/3/2001 NA — 0.30 0.05

Harley Gulch near Wilbur Springs 5/3/2001 0.00 — 8.26 7.05

Sulphur Creek at Wilbur Springs 5/3/2001 0.03 — 0.15 0.81

Appendix 1. Table 2. Stream discharge and concentrations of methylmercury in unfiltered and filtered water from sites in the Cache Creek Basin, California—

Continued

Site Date

Daily mean 

stream 

discharge, in 

m3/s

Instantaneous 

stream 

discharge, in 

m3/s

Methylmercury in 

unfiltered water, 

in ng/L

Methylmercury in 

filtered water, in 

ng/L
Appendix 1. Table 3. Concentrations of mercury in unfiltered and filtered water, in field blanks, from sites in the Cache Creek Basin, California

[ng/L, nanogram per liter; <, less than indicated value]

Site Date Mercury in unfiltered water, 

in ng/L

Mercury in filtered water, 

in ng/L

Sulphur Creek at Wilbur Springs 2/27/2000 < 0.5 < 0.5

North Fork Cache Creek at 

Highway 20

2/28/2000 1.1 < 0.4

Harley Gulch near Wilbur Springs 2/27/2000 0.6 < 0.4

Sulphur Creek at Wilbur Springs 3/14/2000 < 0.5 < 0.5

Cache Creek at Rumsey 3/16/2000 < 0.5 < 0.5

North Fork Cache Creek at 

Highway 20

3/18/2000 0.6 0.7

Sulphur Creek at Wilbur Springs 2/20/2001 0.6 0.3

North Fork Cache Creek at 

Highway 20

2/21/2001 1.2 1.2

Appendix 1. Table 3. 45
Appendix 1. Table 4. Concentrations of methylmercury in unfiltered and filtered water, in field blanks, from sites in the Cache Creek Basin, California

[ng/L, nanogram per liter; < , less than indicated value]

Site Date

Methylmercury in 

unfiltered water, 

in ng/L

Methylmercury in 

filtered water,

in ng/L

Sulphur Creek at Wilbur Springs 2/27/2000 < 0.021 < 0.023

North Fork Cache Creek at Highway 20 2/28/2000 0.022 0.020

Cache Creek near Lower Lake 3/17/2000 < 0.023 < 0.023

Cache Creek into Settling Basin 3/18/2000 < 0.022 < 0.023

Sulphur Creek at Wilbur Springs 2/20/2001 0.042 0.020

North Fork Cache Creek at Highway 20 2/21/2001 0.032 < 0.013

46 Mercury and Methylmercury Concentrations and Loads, Cache Creek Basin, California, January 2000 through May 2001
Appendix 1. Table 5. 47

Appendix 1. Table 5. Replicate concentrations of mercury in unfiltered water from sites in the Cache Creek Basin, California

[ng/L, nanogram per liter]

Site Date Time Replicate Mercury in unfiltered 

water, in ng/L

Bear Creek above Holsten Chimney Canyon 2/27/2000 1115 1 of 2 217

Bear Creek above Holsten Chimney Canyon 2/27/2000 1115 2 of 2 172

Sulphur Creek at Wilbur Springs 2/27/2000 1400 1 of 2 547

Sulphur Creek at Wilbur Springs 2/27/2000 1400 2 of 2 537

Harley Gulch near Wilbur Springs 2/27/2000 1600 1 of 2 237

Harley Gulch near Wilbur Springs 2/27/2000 1600 2 of 2 249

North Fork Cache Creek at Highway 20 2/28/2000 945 1 of 2 24.3

North Fork Cache Creek at Highway 20 2/28/2000 945 2 of 2 23.1

Cache Creek at Rumsey 2/28/2000 1425 1 of 2 40.5

Cache Creek at Rumsey 2/28/2000 1425 2 of 2 40.7

Davis Creek Reservoir at Dam, near Knoxville 2/28/2000 1600 1 of 2 34.3

Davis Creek Reservoir at Dam, near Knoxville 2/28/2000 1600 2 of 2 31.7

Cache Creek near Lower Lake 2/29/2000 920 1 of 2 17.8

Cache Creek near Lower Lake 2/29/2000 920 2 of 2 17.2

North Fork Cache Creek near Clearlake Oaks 2/29/2000 1350 1 of 2 6.3

North Fork Cache Creek near Clearlake Oaks 2/29/2000 1350 2 of 2 4.1

Cache Creek into Settling Basin 3/1/2000 930 1 of 2 220

Cache Creek into Settling Basin 3/1/2000 930 2 of 2 197

Cache Creek out of Settling Basin 3/1/2000 1140 1 of 2 155

Cache Creek out of Settling Basin 3/1/2000 1140 2 of 2 166

Yolo Bypass at Interstate 80 near West Sacramento 3/2/2000 1200 1 of 2 20.6

Yolo Bypass at Interstate 80 near West Sacramento 3/2/2000 1200 2 of 2 20.3

Lower Yolo Bypass 3/3/2000 1350 1 of 2 14.4

Lower Yolo Bypass 3/3/2000 1550 2 of 2 12.7

Bear Creek above Holsten Chimney Canyon 3/15/2000 1220 1 of 2 32.0

Bear Creek above Holsten Chimney Canyon 3/15/2000 1220 2 of 2 33.5

Sulphur Creek at Wilbur Springs 3/15/2000 1550 1 of 2 536

Sulphur Creek at Wilbur Springs 3/15/2000 1550 2 of 2 520

Harley Gulch near Wilbur Springs 3/15/2000 1750 1 of 2 142

Harley Gulch near Wilbur Springs 3/15/2000 1750 2 of 2 146

North Fork Cache Creek at Highway 20 3/16/2000 1030 1 of 2 5.0

North Fork Cache Creek at Highway 20 3/16/2000 1030 2 of 2 5.1

Davis Creek Reservoir at Dam, near Knoxville 3/16/2000 1630 1 of 2 9.1

Davis Creek Reservoir at Dam, near Knoxville 3/16/2000 1630 2 of 2 10.2

North Fork Cache Creek near Clearlake Oaks 3/17/2000 1400 1 of 2 3.9

North Fork Cache Creek near Clearlake Oaks 3/17/2000 1400 2 of 2 3.0

Cache Creek into Settling Basin 3/18/2000 830 1 of 2 24.3

Cache Creek into Settling Basin 3/18/2000 830 2 of 2 24.2

Cache Creek out of Settling Basin 3/18/2000 1050 1 of 2 11.2

Cache Creek out of Settling Basin 3/18/2000 1050 2 of 2 11.2

Yolo Bypass at Interstate 80 near West Sacramento 3/18/2000 1300 1 of 2 15.5

Yolo Bypass at Interstate 80 near West Sacramento 3/18/2000 1300 2 of 2 15.9

Lower Yolo Bypass 3/22/2000 1110 1 of 2 39.4
48 Mercury and Methylmercury Concentrations and Loads, Cache Creek Basin, California, January 2000 through May 2001

Lower Yolo Bypass 3/22/2000 1110 2 of 2 38.9

Bear Creek above Holsten Chimney Canyon 2/20/2001 1200 1 of 2 150

Bear Creek above Holsten Chimney Canyon 2/20/2001 1200 2 of 2 150

Harley Gulch near Wilbur Springs 2/20/2001 1340 2 of 2 100

Harley Gulch near Wilbur Springs 2/20/2001 1340 1 of 2 100

North Fork Cache Creek near Clearlake Oaks 2/20/2001 1400 1 of 2 3.9

North Fork Cache Creek near Clearlake Oaks 2/20/2001 1400 2 of 2 3.8

Sulphur Creek at Wilbur Springs 2/20/2001 1500 1 of 2 700

Sulphur Creek at Wilbur Springs 2/20/2001 1500 2 of 2 670

Cache Creek near Lower Lake 2/20/2001 1600 1 of 2 13.8

Cache Creek near Lower Lake 2/20/2001 1600 2 of 2 13.9

North Fork Cache Creek at Highway 20 2/21/2001 930 1 of 2 16.5

North Fork Cache Creek at Highway 20 2/21/2001 930 2 of 2 18.2

Cache Creek at Rumsey 2/21/2001 1220 1 of 2 63

Cache Creek at Rumsey 2/21/2001 1220 2 of 2 58

Cache Creek into Setting Basin 2/22/2001 1020 1 of 2 58

Cache Creek into Settling Basin 2/22/2001 1020 2 of 2 59

Cache Creek out of Setting Basin 2/22/2001 1050 1 of 2 48

Cache Creek out of Settling Basin 2/22/2001 1050 2 of 2 59

Yolo Bypass at Interstate 80 near West Sacramento 2/22/2001 1240 1 of 2 34.1

Yolo Bypass at Interstate 80 near West Sacramento 2/22/2001 1240 2 of 2 34.5

Lower Yolo Bypass 2/23/2001 1100 1 of 2 18.2

Lower Yolo bypass 2/23/2001 1100 2 of 2 55.3

Appendix 1. Table 5. Replicate concentrations of mercury in unfiltered water from sites in the Cache Creek Basin, California—Continued

[ng/L, nanogram per liter]

Site Date Time Replicate Mercury in unfiltered 

water, in ng/L
Appendix 1. Table 6. 49

Appendix 1. Table 6. Replicate concentrations of mercury in filtered water from sites in the Cache Creek Basin, California

[ng/L, nanogram per liter]

Site Date Time Replicate

Mercury in

filtered water,

in ng/L

Sulphur Creek at Wilbur Springs 2/27/2000 1400 1 of 2 316

Sulphur Creek at Wilbur Springs 2/27/2000 1400 2 of 2 334

Sulphur Creek at Wilbur Springs 2/27/2000 1401 1 of 2 322

Sulphur Creek at Wilbur Springs 2/27/2000 1401 2 of 2 258

Harley Gulch near Wilbur Springs 2/27/2000 1600 1 of 2 58

Harley Gulch near Wilbur Springs 2/27/2000 1600 2 of 2 62

Bear Creek above Holsten Chimney Canyon 2/27/2000 1115 1 of 2 22.4

Bear Creek above Holsten Chimney Canyon 2/27/2000 1115 2 of 2 24.1

North Fork Cache Creek at Highway 20 2/28/2000 945 1 of 2 2.1

North Fork Cache Creek at Highway 20 2/28/2000 945 2 of 2 1.7

Cache Creek at Rumsey 2/28/2000 1425 1 of 2 4.1

Cache Creek at Rumsey 2/28/2000 1425 2 of 2 3.4

Cache Creek at Rumsey 2/28/2000 1426 1 of 2 3.2

Cache Creek at Rumsey 2/28/2000 1426 2 of 2 3.5

Davis Creek Reservoir at Dam, near Knoxville 2/28/2000 1600 1 of 2 6.5

Davis Creek Reservoir at Dam, near Knoxville 2/28/2000 1600 2 of 2 6.7

North Fork Cache Creek near Clearlake Oaks 2/29/2000 1350 1 of 2 1.9

North Fork Cache Creek near Clearlake Oaks 2/29/2000 1350 2 of 2 1.8

Cache Creek out of Settling basin 3/1/2000 1140 1 of 2 5.0

Cache Creek out of Settling basin 3/1/2000 1140 2 of 2 4.4

Yolo Bypass at Interstate 80 near West Sacramento 3/2/2000 1200 1 of 2 1.9

Yolo Bypass at Interstate 80 near West Sacramento 3/2/2000 1200 2 of 2 2.2

Lower Yolo Bypass 3/3/2000 1350 1 of 2 3.4

Lower Yolo Bypass 3/3/2000 1350 2 of 2 3.3

Sulphur Creek at Wilbur Springs 3/15/2000 1550 1 of 2 353

Sulphur Creek at Wilbur Springs 3/15/2000 1550 2 of 2 331

Harley Gulch near Wilbur Springs 3/15/2000 1750 1 of 2 69

Harley Gulch near Wilbur Springs 3/15/2000 1750 2 of 2 70

Bear Creek above Holsten Chimney Canyon 3/15/2000 1220 1 of 2 12.3

Bear Creek above Holsten Chimney Canyon 3/15/2000 1220 2 of 2 12.5

North Fork Cache Creek at Highway 20 3/16/2000 1030 1 of 2 0.9

North Fork Cache Creek at Highway 20 3/16/2000 1030 2 0f 2 0.8

Cache Creek at Rumsey 3/16/2000 1350 1 of 2 2.0

Cache Creek at Rumsey 3/16/2000 1350 2 of 2 1.5

Davis Creek Reservoir at Dam, near Knoxville 3/16/2000 1630 1 of 2 4.2

Davis Creek Reservoir at Dam, near Knoxville 3/16/2000 1630 2 of 2 3.7

North Fork Cache Creek near Clearlake Oaks 3/17/2000 1400 1 of 2 2.0

North Fork Cache Creek near Clearlake Oaks 3/17/2000 1400 2 of 2 4.1

Cache Creek near Lower Lake 3/17/2000 940 1 of 2 2.5

Cache Creek near Lower Lake 3/17/2000 940 2 of 2 3.4

Cache Creek into Settling Basin 3/18/2000 830 1 of 2 1.5
50 Mercury and Methylmercury Concentrations and Loads, Cache Creek Basin, California, January 2000 through May 2001

Cache Creek into Settling Basin 3/18/2000 830 2 of 2 1.5

Cache Creek out of Settling Basin 3/18/2000 1050 1 of 2 1.6

Cache Creek out of Settling Basin 3/18/2000 1050 2 of 2 1.6

Yolo Bypass at Interstate 80 near West Sacramento 3/18/2000 1300 1 of 2 1.5

Yolo Bypass at Interstate 80 near West Sacramento 3/18/2000 1300 2 of 2 1.8

Lower Yolo Bypass 3/22/2000 1110 1 of 2 1.8

Lower Yolo Bypass 3/22/2000 1110 2 of 2 1.7

Bear Creek above Holsten Chimney Canyon 2/20/2001 1200 1 of 2 42

Bear Creek above Holsten Chimney Canyon 2/20/2001 1200 2 of 2 45

Harley Gulch near Wilbur Springs 2/20/2001 1340 1 of 2 67

Harley Gulch near Wilbur Springs 2/20/2001 1340 2 of 2 64

North Fork Cache Creek near Clearlake Oaks 2/20/2001 1400 2 of 2 2.6

North Fork Cache Creek near Clearlake Oaks 2/20/2001 1400 1 of 2 2.5

Sulphur Creek at Wilbur Springs 2/20/2001 1500 1 of 2 290

Sulphur Creek at Wilbur Springs 2/20/2001 1500 2 of 2 330

Cache Creek near Lower Lake 2/20/2001 1600 1 of 2 6.5

Cache Creek near Lower Lake 2/20/2001 1600 2 of 2 6.8

Cache Creek at Rumsey 2/21/2001 1220 1 of 2 11.5

Cache Creek at Rumsey 2/21/2001 1220 2 of 2 10.7

North Fork Cache Creek at Highway 20 2/21/2001 930 2 of 2 7.1

North Fork Cache Creek at Highway 20 2/21/2001 930 1 of 2 7.2

Cache Creek into Settling Basin 2/21/2001 1020 1 of 2 9.5

Cache Creek into Settling Basin 2/21/2201 1020 2 of 2 9.4

Cache Creek out of Settling Basin 2/21/2001 1050 1 of 2 11.8

Cache Creek out of Settling Basin 2/21/2201 1050 2 of 2 12.5

Yolo Bypass at Interstate 80 near West Sacramento 2/22/2001 1240 1 of 2 6.5

Yolo Bypass at Interstate 80 near West Sacramento 2/22/2001 1240 2 of 2 6.3

Lower Yolo Bypass 2/23/2001 1100 1 of 2 4.6

Lower Yolo Bypass 2/23/2001 1100 2 of 2 4.8

Appendix 1. Table 6. Replicate concentrations of mercury in filtered water from sites in the Cache Creek Basin, California—Continued

[ng/L, nanogram per liter]

Site Date Time Replicate

Mercury in

filtered water,

in ng/L
Appendix 1. Table 7. Replicate concentrations of methylmercury in unfiltered water from sites in the Cache Creek Basin, California

[ng/L, nanogram per liter]

Site Date Time Replicate

Methylmercury in

unfiltered water,

in ng/L

Cache Creek at Rumsey 2/28/2000 1425 1 of 2 0.14

Cache Creek at Rumsey 2/28/2000 1425 2 of 2 0.13

Sulphur Creek at Wilbur Springs 2/29/2000 1400 1 of 2 0.33

Sulphur Creek at Wilbur Springs 2/29/2000 1400 2 of 2 0.30

Bear Creek near Holsten Chimney Canyon 3/15/2000 1220 1 of 2 0.15

Bear Creek near Holsten Chimney Canyon 3/15/2000 1220 2 of 2 0.19

Cache Creek near Lower Lake 3/17/2000 940 1 of 2 0.048

Cache Creek near Lower Lake 3/17/2000 940 2 of 2 0.049

North Fork Cache Creek at Highway 20 2/21/2001 930 1 of 2 0.17

North Fork Cache Creek at Highway 20 2/21/2001 930 2 of 2 0.14

Cache Creek into Settling Basin 2/22/2001 1020 1 of 2 0.49

Cache Creek into Settling Basin 2/22/2001 1020 2 of 2 0.46

Appendix 1. Table 7. 51
Appendix 1. Table 8. Replicate concentrations of methylmercury in filtered water from sites in the Cache Creek Basin, California

[ng/L, nanogram per liter; <, less than indicated value]

Site Date Time Replicate

Methylmercury in 

filtered water, 

in ng/L

Cache Creek at Rumsey 2/28/2000 1425 1 of 2 < 0.024

Cache Creek at Rumsey 2/28/2000 1425 2 of 2 < 0.024

Sulphur Creek at Wilbur Springs 2/29/2000 1400 1 of 2 0.29

Sulphur Creek at Wilbur Springs 2/29/2000 1400 2 of 2 0.30

Bear Creek near Holsten Chimney Canyon 3/15/2000 1220 1 of 2 0.095

Bear Creek near Holsten Chimney Canyon 3/15/2000 1220 2 of 2 0.19

Cache Creek near Lower Lake 3/17/2000 940 1 of 2 < 0.023

Cache Creek near Lower Lake 3/17/2000 940 2 of 2 < 0.023

North Fork Cache Creek at Highway 20 2/21/2001 930 1 of 2 0.073

North Fork Cache Creek at Highway 20 2/21/2001 930 2 of 2 0.078

Cache Creek into Settling Basin 2/22/2001 1020 1 of 2 0.15

Cache Creek into Settling Basin 2/22/2001 1020 2 of 2 0.12

52 Mercury and Methylmercury Concentrations and Loads, Cache Creek Basin, California, January 2000 through May 2001
Appendix 1. Table 9. 53

9

Appendix 1. Table 9. Stable isotopes in water from sites in Cache Creek Basin, California

[δ18O, delta oxygen−18; δD, delta deuterium; per mil, per thousand; VSMOW, Vienna Standard Mean Ocean Water; NA, not available; ]

Date Time Site δ18O

(per mil, VSMOW)

δD 

(per mil, VSMOW)

7/21/1999 1230 Cache Creek at Rumsey −5.84 −45.8

8/18/1999 1100 Cache Creek at Rumsey −4.27 −38.3

2/27/2000 1115 Bear Creek above Holsten Chimney Canyon −9.38 −68.9

2/27/2000 1400 Sulfur Creek at Wilbur Springs −9.43 −69.3

2/27/2000 1600 Harley Gulch near Wilbur Springs −9.30 −69.1

2/28/2000 945 North Fork Cache Creek at Highway 20 −7.93 −57.7

2/28/2000 1425 Cache Creek at Rumsey −8.18 −59.8

2/28/2000 1600 Davis Creek Reservoir at Dam, near Knoxville −6.55 −51.4

2/29/2000 920 Cache Creek near Lower Lake −7.02 −54.8

2/29/2000 1350 North Fork Cache Creek at Highway 20 −7.42 −56.0

3/1/2000 930 Cache Creek into Settling Basin −7.68 −57.5

3/1/2000 1140 Cache Creek out of Settling Basin −7.72 −57.8

3/2/2000 1200 Yolo Bypass at Interstate 80 near West Sacramento −10.41 −76.7

3/3/2000 1350 Lower Yolo Bypass −11.04 −78.7

3/15/2000 1220 Bear Creek above Holsten Chimney Canyon −8.56 −63.4

3/15/2000 1550 Sulfur Creek at Wilbur Springs −7.84 −60.9

3/15/2000 1750 Harley Gulch near Wilbur Springs −8.14 −61.8

3/16/2000 1030 North Fork Cache Creek at Highway 20 −7.91 −57.6

3/16/2000 1350 Cache Creek at Rumsey −6.29 −49.4

3/17/2000 940 Cache Creek near Lower Lake −4.42 −38.2

3/17/2000 1400 North Fork Cache Creek near Clearlake Oaks −7.52 −56.4

3/18/2000 830 Cache Creek into Settling Basin −6.82 −51.3

3/18/2000 1050 Cache Creek out of Settling Basin −6.24 −47.5

3/18/2000 1300 Yolo Bypass at Interstate 80 near West Sacramento −8.78 −67.2

3/22/2000 1110 Lower Yolo Bypass −7.86 −60.4

4/17/2000 1200 Cache Creek near Lower Lake −4.88 −42.4

4/17/2000 1200 Cache Creek into Settling Basin −7.44 −57.1

4/17/2000 1200 Cache Creek at Rumsey −6.01 −47.1

4/17/2000 1200 Bear Creek above Holsten Chimney Canyon −8.07 −61.8

4/17/2000 1200 North Fork Cache Creek at Highway 20 −8.40 −59.7

4/17/2000 1200 Harley Gulch near Wilbur Springs −8.18 −60.4

6/13/2000 1200 Cache Creek near Lower Lake −4.25 −35.7

6/13/2000 1200 Davis Creek Reservoir at Dam, near Knoxville −7.58 −53.3

6/13/2000 1200 North Fork Cache Creek at Highway 20 −7.67 −56.5

6/13/2000 1200 Harley Gulch near Wilbur Springs −6.94 −56.2

6/14/2000 1200 Cache Creek at Rumsey −4.81 −40.2

6/14/2000 1200 Bear Creek above Holsten Chimney Canyon −6.87 −56.6

6/14/2000 1200 Bear Creek above Sulphur Creek −7.74 −58.8

6/14/2000 1200 Sulfur Creek at Wilbur Springs −2.33 −40.4

6/14/2000 1200 Cache Creek into Settling Basin −4.70 −41.2
54 Mercury and Methylmercury Concentrations and Loads, Cache Creek Basin, California, January 2000 through May 2001

6/14/2000 1200 Cache Creek at Highway 505 −4.75 −43.1

8/10/2000 1040 Davis Creek Reservoir at Dam, near Knoxville −7.42 −53.2

8/10/2000 1155 Cache Creek near Lower Lake −3.75 −35.3

8/10/2000 1240 North Fork Cache Creek at Highway 20 −7.27 −54.8

8/10/2000 1325 Sulfur Creek at Wilbur Springs 4.00 −20.7

8/10/2000 1350 Bear Creek above Holsten Chimney Canyon −4.73 −48.0

8/10/2000 1430 Cache Creek at Rumsey −3.70 −35.6

8/10/2000 1530 Cache Creek at Highway 505 −5.07 −43.4

8/10/2000 1610 Cache Creek into Settling Basin −4.11 −38.7

10/11/2000 1445 Cache Creek near Lower Lake −3.16 −33.1

10/11/2000 1230 North Fork Cache Creek at Highway 20 −7.32 −54.7

10/11/2000 1320 Bear Creek above Sulphur Creek −7.78 −60.2

10/11/2000 1420 Bear Creek above Holsten Chimney Canyon −5.90 −52.3

10/11/2000 1500 Cache Creek at Rumsey −3.34 −32.3

10/11/2000 1605 Cache Creek at Highway 505 −3.80 −33.9

10/11/2000 1645 Cache Creek into Settling Basin −3.83 −33.2

10/11/2000 1200 Sulfur Creek at Wilbur Springs 1.94 −28.4

11/6/2000 1400 Davis Creek below Davis Creek Reservoir −5.66 −46.1

11/6/2000 1500 Davis Creek Reservoir at Dam, near Knoxville −7.49 −53.4

11/7/2000 1000 Cache Creek near Lower Lake −3.01 −33.8

11/7/2000 1115 North Fork Cache Creek at Highway 20 −7.49 −57.1

11/7/2000 1210 Bear Creek above Sulphur Creek −7.78 −59.2

11/7/2000 1245 Sulfur Creek at Wilbur Springs −0.07 −33.7

11/7/2000 1315 Bear Creek above Holsten Chimney Canyon −6.31 −53.5

11/7/2000 1355 Cache Creek at Rumsey −6.00 −49.1

11/7/2000 1500 Cache Creek at Highway 505 −5.16 −44.3

11/7/2000 1600 Cache Creek into Settling Basin −5.12 −44.4

12/11/2000 1100 Cache Creek near Lower Lake −3.12 −33.0

12/11/2000 1215 North Fork Cache Creek at Highway 20 −7.48 −54.3

12/11/2000 1310 Bear Creek above Sulphur Creek −8.01 −59.6

12/11/2000 1200 Bear Creek above Holsten Chimney Canyon −6.62 −56.6

12/11/2000 1200 Cache Creek at Highway 505 −5.37 −45.6

12/11/2000 1200 Cache Creek at Rumsey −6.26 −51.0

1/11/2001 1055 Cache Creek near Lower Lake −4.20 −40.2

1/11/2001 1205 North Fork Cache Creek at Highway 20 −7.88 −59.2

1/11/2001 1245 Harley Gulch near Wilbur Springs −7.40 −56.7

1/11/2001 1320 Bear Creek above Sulphur Creek −6.88 −61.7

1/11/2001 1405 Sulfur Creek at Wilbur Springs −6.96 −56.4

1/11/2001 1445 Bear Creek above Holsten Chimney Canyon −8.01 −60.1

1/11/2001 1525 Cache Creek at Rumsey −7.07 −52.0

Appendix 1. Table 9. Stable isotopes in water from sites in Cache Creek Basin, California—Continued

[δ18O, delta oxygen−18; δD, delta deuterium; per mil, per thousand; VSMOW, Vienna Standard Mean Ocean Water; NA, not available; ]

Date Time Site δ18O

(per mil, VSMOW)

δD 

(per mil, VSMOW)
Appendix 1. Table 9. 55

1/11/2001 1625 Cache Creek at Highway 505 −6.09 −49.7

2/13/2001 925 Cache Creek at Highway 505 −8.15 −59.5

2/13/2001 1200 North Fork Cache Creek at Highway 20 −8.05 −60.0

2/13/2001 1140 Cache Creek near Lower Lake −6.00 −46.8

2/13/2001 1400 Cache Creek at Rumsey −8.60 −62.1

2/13/2001 1410 Harley Gulch near Wilbur Springs −8.35 −61.6

2/13/2001 1445 Bear Creek above Sulphur Creek −8.82 −63.7

2/13/2001 1505 Sulfur Creek at Wilbur Springs −7.24 −59.3

2/13/2001 1535 Bear Creek above Holsten Chimney Canyon −9.07 −67.0

2/13/2001 1600 Cache Creek at Rumsey −8.61 −62.6

2/20/2001 1200 Bear Creek above Holsten Chimney Canyon −8.88 −63.6

2/20/2001 1340 Harley Gulch near Wilbur Springs −8.84 −62.4

2/20/2001 14;00 North Fork Cache Creek near Clear Lake Oak −6.85 −53.9

2/20/2001 1500 Sulfur Creek at Wilbur Springs −8.74 −62.9

2/20/2001 1600 Cache Creek near Lower Lake −7.04 −51.3

2/21/2001 930 North Fork Cache Creek at Highway 20 −9.05 −62.2

2/21/2001 1220 Cache Creek at Rumsey −8.86 −60.3

2/22/2001 1016 Sulfur Creek at Wilbur Springs −8.27 −58.4

2/22/2001 1020 Cache Creek into Settling Basin −8.53 −58.5

2/22/2001 1040 Sulfur Creek Mine −8.05 −59.2

2/22/2001 1050 Cache Creek out of Settling Basin −8.46 −59.1

2/22/2001 1145 Sulfur Creek Mine 4.79 −21.9

2/22/2001 1155 Sulfur Creek Mine 4.78 −20.9

2/22/2001 1215 Sulfur Creek Mine 4.66 −19.4

2/22/2001 1240 Yolo Bypass at Interstate 80 near West Sacramento −7.72 −56.8

2/22/2001 1318 Sulfur Creek Mine −8.55 −59.5

2/22/2001 1335 Sulfur Creek Mine 6.17 −14.1

2/22/2001 1455 Abbott and Turkey Run Mines −8.91 −64.1

2/22/2001 1503 Sulfur Creek Mine −5.60 −50.7

2/22/2001 1520 Sulfur Creek Mine −8.26 −57.9

2/22/2001 1613 Sulfur Creek Mine −8.74 −59.9

2/23/2001 1100 Lower Yolo Bypass −8.47 −63.2

3/22/2001 1045 Cache Creek near Lower Lake −8.69 −61.1

3/22/2001 1145 North Fork Cache Creek at Highway 20 −8.58 −59.7

3/22/2001 1245 Bear Creek above Sulphur Creek −8.81 −64.4

3/22/2001 1415 Bear Creek above Holsten Chimney Canyon −8.31 −61.2

3/22/2001 NA Cache Creek at Rumsey −8.22 −61.6

5/3/2001 1140 North Fork Cache Creek at Highway 20 −7.07 −53.5

5/3/2001 1205 Harley Gulch near Wilbur Springs −7.12 −55.0

5/3/2001 1245 Bear Creek above Sulphur Creek −7.78 −57.7

5/3/2001 1340 Sulfur Creek at Wilbur Springs −2.77 −42.9

5/3/2001 1410 Bear Creek above Holsten Chimney Canyon −6.61 −54.8

Appendix 1. Table 9. Stable isotopes in water from sites in Cache Creek Basin, California—Continued

[δ18O, delta oxygen−18; δD, delta deuterium; per mil, per thousand; VSMOW, Vienna Standard Mean Ocean Water; NA, not available; ]

Date Time Site δ18O

(per mil, VSMOW)

δD 

(per mil, VSMOW)
56 Mercury and Methylmercury Concentrations and Loads, Cache Creek Basin, California, January 2000 through May 2001

5/3/2001 1545 Cache Creek at Rumsey −7.02 −53.4

2/21/2001 1050 Abbott and Turkey Run Mines −8.77 −50.8

2/21/2001 1107 Abbott and Turkey Run Mines −7.73 −50.8

2/21/2001 1305 Abbott and Turkey Run Mines −5.91 −50.8

2/21/2001 1345 Abbott and Turkey Run Mines −8.56 −50.8

2/21/2001 1100 Davis Creek Resrvoir at Dam, near Knoxville −6.86 −50.8

Appendix 1. Table 9. Stable isotopes in water from sites in Cache Creek Basin, California—Continued

[δ18O, delta oxygen−18; δD, delta deuterium; per mil, per thousand; VSMOW, Vienna Standard Mean Ocean Water; NA, not available; ]

Date Time Site δ18O

(per mil, VSMOW)

δD 

(per mil, VSMOW)