U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2019–1001

Prepared in cooperation with the U.S. Environmental Protection Agency

Coagulant and Sorbent Efficacy in Removing Mercury from 

Surface Waters in the Cache Creek Watershed, California

Coagulant and Sorbent Efficacy in 

Removing Mercury from Surface Waters in 

the Cache Creek Watershed, California

By Erica R. De Parsia, Jacob A. Fleck, David P. Krabbenhoft, Kim Hoang, 

David Roth, and Paul Randall

Prepared in cooperation with the U.S. Environmental Protection Agency

Open-File Report 2019–1001

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DAVID BERNHARDT, Acting Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2019

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Suggested citation:

De Parsia, E.R., Fleck, J.A., Krabbenhoft, D.P., Hoang, K., Roth, D., and Randall, P., 2019, Coagulant and sorbent 

efficacy in removing mercury from surface waters in the Cache Creek watershed, California: U.S. Geological Survey 

Open-File Report 2019–1001, 46 p., https://doi.org/10.3133/ofr20191001.

ISSN 2331-1258 (online)
iii

Acknowledgments

We thank our colleagues at the U.S. Environmental Protection Agency, Region IX, especially 

Wilson Yee, John Hillenbrand, Matthew Small, Joseph Eidelberg, Eugenia McNaughton, and 

Larry Bradfish for their assistance in the development of project scope, site selection, and 

logistical support. We are grateful to Todd Muelhoefer at Kinder Morgan, Inc., and J.R. Flanders 

at EHS Support, LLC, for the Harley Gulch area site information, guidance, and access. We thank 

our colleagues at the U.S. Geological Survey, California Water Science Center (USGS), especially 

Angela Hansen, Joan Lopez, and Nicholas Graham for assistance in field and laboratory 

activities and Charlie Alpers, Peter Bennett, Tamara Kraus, and Liz Stumpner for constructive 

insights and valuable information contributing to the successful execution of the project. We 

thank Shane Kiley, Phil Bachand, and Mathew Tinker for valuable information about materials 

and operations for coagulation and sorbent techniques. We also extend our appreciation 

to John DeWild at the USGS Wisconsin Mercury Research Laboratory for assistance with 

laboratory analyses and data quality. 
iv

Contents

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

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

Purpose and Scope .......................................................................................................................................2

Methods and Materials.................................................................................................................................2

Site Selection.........................................................................................................................................2

Coagulant and Sorbent Selection ......................................................................................................6

Procedures.............................................................................................................................................6

Part 1: High-Particulate Sample Mercury Removal........................................................................8

Sample Collection........................................................................................................................8

Coagulation Jar Tests..................................................................................................................8

Part 2: Low-Particulate Sample Mercury Removal.......................................................................10

Sample Collection......................................................................................................................10

Coagulation Jar Tests................................................................................................................10

Sorbent Experiments.................................................................................................................10

Analytical Methods.............................................................................................................................11

Total Mercury and Methylmercury Concentration Analysis ..............................................11

Dissolved Organic Carbon Concentration and Optical Characterization of 

Dissolved Substances .................................................................................................12

Trace-Metal Concentration Analysis......................................................................................12

Grain-Size Distribution Analysis..............................................................................................12

Coagulant and Sorbent Efficacy in Mercury Removal ..........................................................................12

Part 1: Particulate-Dominated Source ............................................................................................12

Coagulation Test Run.................................................................................................................12

Coagulation Full Experiment ....................................................................................................12

Mercury Removal.......................................................................................................................13

Turbidity .......................................................................................................................................13

Flocculant Size and Physical Stability....................................................................................16

Dissolved Organic Matter ........................................................................................................16

Other Effects...............................................................................................................................21

Part 2: Low-Particulate Mercury Samples .....................................................................................25

Initial Sample Characterization ...............................................................................................25

Coagulation Test.........................................................................................................................25

Sorbent Experiments: Methods and Statistics .....................................................................25

Sorbent-Modeling Results .......................................................................................................25

Discussion............................................................................................................................................29

Summary........................................................................................................................................................32

References Cited .........................................................................................................................................33

Appendix Tables...........................................................................................................................................37
v

Figures

1. Map showing the Cache Creek watershed showing locations of important 

mining features, and the Cache Creek Settling Basin and its connection to the 

Sacramento–San Joaquin Delta via the Yolo Bypass ............................................................3

2. Hydrograph showing flow conditions at the time when the high-particulate 

samples were collected relative to the flows over the hydrologic year.............................8

3. Photograph showing the bottles from the coagulant dosing series for ChitoVanTM

after 20 minutes of settling........................................................................................................10

4. Photographs showing Turkey Creek downstream from the geothermal spring 

exiting the Turkey Run mine adit and the Connate Spring...................................................11

5. Graph showing ChitoVanTM dose-rate turbidity response curve for the initial 

coagulation test run, using a storm-runoff sample...............................................................13

6. Graphs showing decrease in methylmercury concentrations and total mercury 

concentrations for different dose rates during the coagulation full experiment.............14

7. Graphs showing coagulant dose-rate turbidity-response curves for three 

coagulants: ChitoVanTM; FerralyteTM; UltrionTM over time; and turbidity for all three.......15

8. Graph showing grain-size distribution curves for the settled materials from the 

coagulation full experiment and for sediment in non-treated (raw) surface water........16

9. Graphs showing dose-rate response curves for optical measurements of 

dissolved organic carbon; specific absorbance at 254 nanometers; fluorescence 

index; and relative fluorescence efficiency...........................................................................17

10. Graphs showing effect of the coagulants on the ultraviolet absorbance spectra..........18

11. Graphs showing effects of coagulants on the fluorescence spectra ...............................19

12. Graphs showing intensity of excitation emission matrices for samples treated 

with the ChitoVanTM coagulant, and blank water..................................................................20

13. Graphs showing intensity of excitation emission matrices for samples treated 

with the FerralyteTM coagulant and blank water ...................................................................22

14. Graphs showing intensity of excitation emission matrices for samples treated 

with the UltrionTM coagulant, and blank water ......................................................................23

15. Graphs showing coagulant dose-rate response curves for pH and 

specific conductance ................................................................................................................24

16. Graph showing absorbance spectra for the low-particulate source waters ..................27

17. Graphs showing excitation-emission matrix plots showing the differences in 

fluorescence spectra of the three samples from each of the two source waters 

used in the sorbent experiment May 4–5, 2016 .....................................................................28

18. Boxplot showing least squares mean (plus or minus standard error) for total 

mercury removed using a linear fixed effects model including water source, 

sorbent type, and flow rate as fixed effects...........................................................................29

19. Graphs showing amount of total mercury removed from surface water passing 

through sorbents tested at the 0.1-liter per minute 

flow rate for the Connate Spring and Turkey Creek..............................................................30
vi

Tables

1. Selected trace metals found in whole-water samples ..........................................................4

2. Field water-chemistry data, laboratory mercury, and dissolved organic-carbon 

data for candidate sources in the Cache Creek watershed, California ..............................5

3. Site characteristics affecting the effectiveness of coagulants and sorbents...................7

4. Summary table listing the coagulants and sorbents used in this experiment. 

Source samples tested, dose amounts, and flow rates used with each coagulant 

and sorbent also are shown .......................................................................................................9

5. Summary of grain-size classifications and statistics for settled materials from 

coagulation treatments and for sediment in non-treated (raw) surface water...............17

6. Field surface-water-quality measurements for sampling sites in the Harley Gulch 

area collected in November 2015 and May 2016...................................................................26

7. Summary of results from the coagulant and sorbent experiment......................................32

1–1. Mercury and dissolved organic-carbon concentration data, and optical data 

from samples and blanks collected during the ‘clean’ portion of the coagulation 

full experiment.............................................................................................................................37

2–1. Mercury concentrations and dissolved organic-carbon concentrations for 

samples and blanks collected during the sorbent experiment...........................................38

3–1. Selected water-quality measurements collected during the coagulation test run 

and the coagulation full experiment, by elapsed settling time ...........................................40

4–1. Data for least squares means for total mercury removed using a linear fixed 

effects model including source water, sorbent type, and flow rate as fixed effects......43

5–1. Data for amount of total mercury removed at the 0.1 liters per minute flow rate for 

samples collected during the sorbent experiment ...............................................................43

6–1. Trace metal concentrations for sorbent experiment samples and source waters .........44
vii

Conversion Factors

International System of Units to U.S. customary units

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

kilometer (km) 0.5400 mile, nautical (nmi) 

meter (m) 1.094 yard (yd) 

nanometer (nm) 3.937e-8 inch (in.)

micrometer (μm) 3.937e-5 inch (in.)

Volume

cubic meter (m3) 6.290 barrel (petroleum, 1 barrel = 42 gal)

liter per minute (L/min) 1.05669 quart per minute (qt/min)

liter (L) 33.81402 ounce, fluid (fl. oz)

liter (L) 2.113 pint (pt)

liter (L) 1.057 quart (qt)

liter (L) 0.2642 gallon (gal)

milliliter (mL) 0.033814 ounce, fluid (fl. oz)

milliliter (mL) 0.00211338 pint (pt)

milliliter (mL) 0.00105669 quart (qt)

milliliter (mL) 0.000264172 gallon (gal)

microliter (μL) 3.3814e-5 ounce, fluid (fl. oz)

microliter (μL) 2.11338e-6 pint (pt)

microliter (μL) 1.05669e-6 quart (qt)

microliter (μL) 2.64172e-7 gallon (gal)

cubic meter (m3) 264.2 gallon (gal) 

liter (L) 61.02 cubic inch (in3) 

Flow rate

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

Mass

gram 0.03527 ounce avoirdupois

nanogram 3.527e-11 ounce avoirdupois

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

°F = (1.8 × °C) + 32.
viii

Datum

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

Supplemental Information

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

25 °C).

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

or micrograms per liter (μg/L), or nanograms per liter (ng/L). 

Abbreviations

CCSB Cache Creek Settling Basin

DI deionized

DOC dissolved organic carbon

DOM dissolved organic matter

EEMs excitation emission matrices

EPA U.S. Environmental Protection Agency

F Statistical test metric

FNU Formazin Nephelometric Units 

HDPE high density polyethylene

Hg mercury

Hg(II) inorganic divalent mercury

IOPs inherent optical properties

MeHg methylmercury

NWIS National Water Information System

p Statistical significance of the model

PETG polyethylene terephthalate copolyester glycol modified

QSE quinine sulfate equivalent

RFU relative fluorescence units

RPM revolutions per minute

THg total mercury

TMDL total maximum daily load

USGS U.S. Geological Survey
Coagulant and Sorbent Efficacy in Removing Mercury from 

Surface Waters in the Cache Creek Watershed, California

By Erica R. De Parsia, Jacob A. Fleck, David P. Krabbenhoft, Kim Hoang, David Roth, and Paul Randall 

Abstract

Cache Creek drains part of northern California’s Coast 

Ranges and is an important source of mercury (Hg) to the 

Sacramento–San Joaquin Delta. Cache Creek is contaminated 

with Hg from several sources, including historical Hg 

and gold mines, native Hg in the soils, and active mineral 

springs. In laboratory experiments in a study conducted 

by the U.S. Geological Survey, in cooperation with the 

U.S. Environmental Protection Agency, the use of coagulants 

and sorbents to immobilize Hg in water samples from highconcentration sources in the Cache Creek watershed was 

investigated. Three sites were selected for the collection of 

surface-water samples containing high and low concentrations 

of particulate-associated Hg. The high-particulate Hg samples 

were collected from Cache Creek Settling Basin during 

stormflow conditions. The low-particulate Hg samples were 

collected from two geochemically contrasting sites during 

base-flow conditions (downstream from a geothermal spring 

and at the emergence point of a connate-water spring). 

Three coagulants were chosen for laboratory testing with the 

high-particulate sample— (1) ChitoVanTM HV 1.5 percent 

(shell based), (2) FerralyteTM 8131 (ferric sulfate based), and 

(3) UltrionTM 8186 (aluminum based). Each coagulant was 

tested at various dose amounts to determine the optimum 

dose rate for the high-particulate sample. The low-particulate 

source samples were passed through three sorbents— 

(1) chitosan flakes, (2) coconut shell-based activated carbon, 

and (3) coal-based activated carbon. In-line columns were 

packed with each material, and the untreated sample was 

passed through each column at three different flow rates (0.1, 

0.5, and 1.0 liter per minute, L/min).

For dose rates used in this study, ChitoVanTM reduced 

turbidity of the particulate sample by 85–91 percent, 

FerralyteTM reduced turbidity by 54–93 percent, and UltrionTM

reduced turbidity by greater than 90 percent. At the lowest 

dose rate, ChitoVanTM achieved a 59- to 61-percent reduction 

in whole-water methylmercury (MeHg) concentrations and 

a 71- to 75-percent decrease in whole-water total mercury 

(THg) concentrations. FerralyteTM achieved a 37- to 48-percent 

decrease in whole-water MeHg concentrations and a 37- to 

48-percent reduction in whole-water THg concentrations. 

UltrionTM achieved a greater than 90-percent decrease in 

whole-water MeHg and THg concentrations. 

Mercury removal from the low-particulate samples 

was less efficient for the sorbent materials compared to 

the coagulants; less than 30 percent of THg was removed 

from any 500-milliliter aliquot using sorbent materials. The 

coal-based sorbent was the most versatile of the sorbents, 

removing THg to a similar extent from both low-particulate 

source waters. The chitosan sorbent was the most effective at 

removing THg from the low-particulate stream sample, but 

less effective for the low-particulate connate-spring sample. 

The Hg removal efficiency of the coconut sorbent decreased 

quickly compared to the other two sorbents, indicating that 

sorption may be limited by the short contact times evaluated in 

this study. 

Introduction

Mercury (Hg) is a potent neurotoxin that affects the 

reproductive success, neurological development, and survival 

rates of a wide variety of life forms (Morel and others, 1998; 

Wiener and others, 2003). Methylmercury (MeHg) is the 

form of Hg that biomagnifies through aquatic food chains 

and thus poses a health risk to wildlife and humans (Wiener 

and others, 2003). Inorganic divalent mercury [Hg(II)] can 

be transformed into MeHg by sulfate- and iron-reducing 

bacteria that inhabit aquatic sediment and wetlands (Gilmour 

and others, 1992; Fleming and others, 2006; Kerin and others, 

2006). Aquatic environments, especially wetlands, typically 

have biogeochemical conditions that are conducive to MeHg 

production (Hurley and others, 1995; St. Louis and others, 

2004; Hall and others, 2008). Thus, aquatic environments 

worldwide are an important nexus between the occurrence of 

Hg(II) and MeHg exposure to humans and wildlife (Driscoll 

and others, 2013).
2 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

Because Hg(II) methylation occurs in specific aquatic 

habitats, the transport of Hg(II) to these habitats is important 

to the effective management of the MeHg threat to humans 

and wildlife. Mercury contamination of aquatic ecosystems 

is globally extensive because of natural and anthropogenic 

Hg emissions and transport through the atmosphere (Driscoll 

and others, 2013). At more localized scales, hydrologic or 

atmospheric transport of Hg from legacy mining sources, 

such as waste rock and tailings piles, mine adit drainage, and 

processing equipment, can increase localized Hg loadings 

and MeHg concentrations in local and downstream food webs 

(Gray and others, 2000; Rytuba, 2000; Gray, 2003; Alpers and 

others, 2016; Fleck and others, 2016). 

The Cache Creek watershed in northern California’s 

inner Coast Ranges provides a model watershed for studying 

the control of Hg mobilization in a catchment with extensive 

areas of sensitive habitats downstream (fig. 1). The high 

levels of Hg in the watershed sediment are from natural 

background geologic sources that could have been exacerbated 

by mining activities. Mercury transport from the watershed 

affects a diverse range of habitats from riverine floodplains 

in the Yolo Bypass to estuarine and coastal wetland habitats 

in the Sacramento–San Joaquin Delta and San Francisco 

Bay. The characteristics of the Cache Creek watershed are 

representative of many mining-affected watersheds across the 

western United States and throughout the world where gold 

and Hg mining have occurred, making it a prime candidate for 

studies aimed at controlling the transport of Hg downstream. 

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

U.S. Environmental Protection Agency (EPA), conducted 

a study of the use of coagulants and sorbents to control Hg 

in surface water, specifically in the Cache Creek watershed. 

The purpose of this study was to demonstrate the utility of 

coagulants and sorbents by removing Hg from the waters with 

high-Hg levels in the Cache Creek watershed. Mercury-source 

types evaluated in this study included (1) particulate Hg(II) 

associated with fine-grained sediment and (2) filter-passed 

Hg(II) bound up in the dissolved and colloidal fractions. 

Purpose and Scope

The purpose of this report is to summarize the results 

of laboratory experiments investigating the efficacy of 

coagulation and sorbent techniques in removing Hg from 

surface waters. Data in this report characterize sourcewater and post-treatment samples. Primary analytes include 

total mercury (THg), methylmercury (MeHg), and trace 

metals (table 1) in non-filtered water; standard water-quality 

measurements taken in the field at the time of sample 

collection and during the laboratory experiments (pH, specific 

conductance, and turbidity); dissolved organic carbon (DOC); 

and selected inherent optical properties (IOPs). 

The scope of the study is limited to laboratory 

evaluations of the potential for the removal of Hg from 

Cache Creek surface water using selected materials as a 

proof of concept and prioritization for future research; and 

ultimately the application could be tested in a field-based 

setting. The USGS recently investigated the use of coagulation 

techniques in high-DOC waters on Twitchell Island in the 

Sacramento–San Joaquin Delta. Results indicate that effective 

Hg removal could be achieved in the low-particulate samples 

using low-dose, in situ treatment techniques (Ackerman and 

others, 2015; Stumpner and others, 2015). The coagulationremoval strategy is effective because it has been shown that 

Hg(II) and MeHg in surface waters of freshwater ecosystems 

are predominantly associated with dissolved and particulate 

organic matter (Henneberry and others, 2011). Thus, by 

injecting a coagulant that effectively removes much of the 

organic matter from water, the associated Hg species also are 

removed. However, little is known about the effectiveness 

of coagulation for the removal of Hg from waters with 

characteristics of either elevated particulate Hg or elevated 

dissolved and colloidal Hg from geothermal sources and 

groundwater-seepage sources. This study reflects the first 

step in addressing these unknowns at the bench scale before 

moving forward with more expansive field-scale efforts. 

Methods and Materials

Methods presented in this report describe the use of 

coagulants and sorbents as a means of removing Hg from 

areas of high-Hg concentration in the Cache Creek watershed. 

In this section we describe the selection of sampling sites, 

coagulants, and sorbents tested; the collection of samples; and 

sample processing. 

Site Selection

The Cache Creek watershed has concentrations of Hg 

elevated above background conditions that are derived from 

several sources, including historical Hg mines, historical 

gold mines where Hg was used for amalgamation, soils with 

a high natural background of Hg from hydrothermal activity, 

and active mineral springs (Rytuba, 2000; Churchill and 

Clinkenbeard, 2003; Domagalski and others, 2003, 2004a, 

2004b; Rytuba and others, 2011). Sampling locations of 

source waters in the Cache Creek watershed were selected 

through a review of the literature and existing data concerning 

Hg contamination and associated surface-water chemistry 

for the watershed, pH, specific conductance, and other 

chemical characteristics that define different sources and 

reactivity (table 2). 
Methods and Materials 3

Base modified from U.S. Geological Survey and other 

Federal and State digital data,various scales; 

Albers Equal-Area Conic projection, standard parallels are

29° 30'N and 45° 30'N; North American Datum of 1983

Woodland

Sacramento

Capay

Guinda

Rumsey

Lake 

Berryessa

Indian

Valley

Clear Reservoir

Lake

0 10 20 KILOMETERS

0 10 20 MILES

Verona

39°

38°

30'

123° 122°

HARLEY GULCH AND 

TURKEY CREEK 

SAMPLING SITES

ABBOTT AND TURKEY 

RUN MINE COMPLEX

Prospect

Slough

Yolo

Yolo Bypass

CACHE CREEK

SETTLING BASIN

EXPLANATION

Cache Creek Watershed

Major mercury point source

Midd l e Creek

Putah Creek

Cache Creek

Elk Slough

San

Francisco Bay

SacramentoSan Joaquin

Delta Region

Cache Creek

Watershed CALIFORNIA

San Francisco

Sacramento

Valley

Sacramento River

Basin Sierra Nevada

Coast Ranges

Sacramento River

Sacramento River

Figure 1. Cache Creek watershed showing locations of important mining features, and the Cache Creek Settling Basin and its 

connection to the Sacramento–San Joaquin Delta via the Yolo Bypass (modified from Domagalski and others, 2004b). Sampling sites 

shown in the figure represent sites used during the Domagalski and others (2004b) study. 
4 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

Table 1. Selected trace metals found in whole-water samples.

Name Abbreviation

Aluminum Al

Arsenic As

Boron B

Barium Ba

Beryllium Be

Bismuth Bi

Calcium Ca

Cadmium Cd

Cerium Ce

Cobalt Co

Chromium Cr

Copper Cu

Dysprosium Dy

Erbium Er

Europium Eu

Iron Fe

Gallium Ga

Gadolinium Gd

Holmium Ho

Potassium K

Lanthanum La

Lithium Li

Lutetium Lu

Magnesium Mg

Manganese Mn

Molybdenum Mo

Name Abbreviation

Sodium Na

Niobium Nd

Nickle Ni

Phosphorus P

Lead Pb

Praseodymium Pr

Rubidium Rb

Sulfur S

Antimony Sb

Selenium Se

Silicon SiO2

Samarium Sm

Strontium Sr

Terbium Tb

Tellurium Te

Thorium Th

Titanium Ti

Thallium Tl

Thulium Tm

Uranium U

Vanadium V

Yttrium Y

Ytterbium Yb

Zinc Zn

Zirconium Zr
Table 2. Field water-chemistry data, laboratory mercury, and dissolved organic-carbon data for candidate sources in the Cache Creek watershed, C[Sites labeled as “This study” were sampled to determine their candidacy for use in the coagulant and sorbent experiments. Sites 11452600 and 11452900 were sampled by the Cproject and used in the coagulation full experiment. Data from the U.S. Geological Survey stations are available from the National Water Information System (NWIS, https://waAbbreviations: C, creek; DOC, dissolved organic carbon; FNU, Formazin Nephelometric Turbidity; fTHg, filter-passed total mercury; ID, identification; mg/L, milligrams per lyear; N/A, not applicable; ng/L, nanograms per liter; nr, near; pTHg, particulate total mercury; Trib, tributary; USGS, U.S. Geological Survey; uTHg, unfiltered total mercury; *carbon; —, no data exist; [], USGS parameter code; ~, approximately; ^, estimated from field fluorescence measurements; `, North American Datum of 1983 (NAD83) coordinaper centimeter; <, less than]

Source Sampled (mm/dd/yyyy) USGS station ID Latitude Longitude pH Specific conductance (μS/cm) Turbidity (FNU) DOC (mg/L) uTHg (ng/L) fTHg (ng/L) 

Cache C Inflow to Settling 

Basin nr Yolo CA

03/17/2016 11452600 38.726015` –121.729963` 8.1 

[00400]

391 

[00095]

480 

[63680]

— — 1.9

Cache C Outflow from 

Settling Basin nr Woodland CA

03/17/2016 11452900 38.678515` –121.672739` 7.92 

[00400]

384 

[00095]

210 

[63680]

— — 2.8

Connate Spring A 

Unnamed Trib nr Wilbur Springs CA

11/16/2015 390041122260401 39.011317` –122.434350` 8.01

[00400]

6,820 

[00095]

1 

[63680]

~15^ 131 — 

Turkey C nr Wilbur 

Springs CA

11/16/2015 390057122262501 39.015789` –122.440267` 8.37 

[00400]

8,250 

[00095]

3 

[63680]

~5^ 113 — 

Turkey Creek 05/24/1994 N/A 39.016058 –122.439412 8.3 — — 16* — 1,100 Turkey Creek 02/14/2000 N/A 39.016589 –122.440076 — — — — 404 — Turkey Creek 02/21/2001 N/A 39.016589 –122.440076 — — — — 87 — Turkey Run Geothermal 

Spring nr Wilbur Springs CA

11/16/2015 390101122262501 39.016922` –122.440234` 6.7 

[00400]

8,560 

[00095]

15 

[63680]

~5^ 3.1 

Turkey Run Geothermal 

Spring 

05/24/1994 N/A 39.017489 –122.439444 6.5 — — <2* — <200 

Turkey Run Geothermal 

Spring

02/14/2000 N/A 39.017108 –122.440201 — — — — 4 — 

Turkey Run Geothermal 

Spring

02/21/2001 N/A 39.017108 –122.440201 — — — — 6 — 

Downstream from Turkey 

Run

06/16/2010 N/A 39.0154 –122.44023 8.06 7,820 — 2.7 825 — 

Downstream from Turkey 

Run

05/25/2011 N/A 39.01627 –122.44001 8.2 2,270 — 9.23 624 — 

Middle of Harley Gulch 

Wetland 

05/25/2011 N/A 39.01402 –122.43709 8.26 5,560 — 4.66 2,300 — 
6 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

Four sites were selected and sampled for the experiments 

described in the following subsections of this report. Two 

locations in the Cache Creek Settling Basin (CCSB) were 

selected for the particulate-dominated Hg sample (Cache 

Creek Inflow to Settling Basin near Yolo, CA; 11452600 and 

Cache Creek Outflow from Settling Basin near Woodland, 

CA; 11452900). The CCSB is a sedimentation basin located 

where Cache Creek empties into the Yolo Bypass en route to 

the San Francisco Bay (fig. 1). The water entering the CCSB is 

an integration of all the upstream sources, and the Hg transport 

is dominated by suspended sediment from mine-affected and 

natural landscapes across the watershed (Cooke and others, 

2004; Foe and Bosworth, 2008; C.N. Alpers, U.S. Geological 

Survey, written commun., 2017). Two locations in the Harley 

Gulch area downstream of the Abbott and Turkey Run Mine 

complex (fig. 1) were selected for the low-particulate Hg 

sampling. One site (Turkey Creek near Wilbur Springs, 

CA; 390057122262501) is approximately 100 meters (m) 

downstream of a geothermal spring. The other site (Connate 

Spring at Unnamed Tributary near Wilbur Springs, CA; 

390041122260401) is at the emergence point of a connatewater spring. The low-particulate samples have sources 

and chemical characteristics like those collected by Rytuba 

and others (2011). The two low-particulate sites selected 

for this study (390041122260401 and 390057122262501) 

had similarly high-Hg concentrations but differed in other 

chemical characteristics (table 2), with mercury most likely 

existing in the dissolved and colloidal forms. 

Coagulant and Sorbent Selection

The selection of coagulants and sorbents for the 

laboratory experiments was accomplished through literature 

review and consultation with coagulant manufacturers and 

stormwater-treatment professionals. The effectiveness of 

coagulant and sorbent types is dependent on the physical 

and chemical characteristics of the water to be treated 

(table 3). Three coagulants were selected for testing the highparticulate samples. ChitoVanTM HV 1.5 percent (Dungeness 

Environmental Solutions Inc., Bothell, Washington) is a 

liquid form of chitosan acetate (proprietary blend) derived 

from natural source materials (crab and shrimp shells) used 

commonly in stormwater treatment. It has been extensively 

tested for release into the environment (Macpherson, 2004) 

and has been used as a plant growth enhancer (Freepons, 

1997). FerralyteTM 8131 (NALCO, Naperville, Illinois) 

is a ferric sulfate (proprietary blend) based solution used 

primarily in wastewater and raw-water clarification, odor 

control (hydrogen sulfide), and phosphate removal. UltrionTM

8186 (NALCO, Naperville, Ill.) is a high activity, highmolecular weight, aluminum-based (proprietary blend) 

cationic coagulant used for paper, wastewater, and drinkingwater processing. UltrionTM is available in high and low 

concentrations; the low concentration was used for this study. 

Coagulants selected for the low-particulate Hg sources 

were the same as for the high-particulate source except for 

the ChitoVanTM coagulant. Preliminary tests indicated the 

ChitoVanTM coagulant was unlikely to be effective on the 

low-particulate sources, so a metal scavenging co-precipitant 

(MetClearTM 2405; GE Water and Process Technologies, 

Trevose, Pennsylvania) was selected as a replacement for 

ChitoVanTM. This metal scavenger is less environmentally 

friendly than the coagulants but may be effective in a 

more actively managed system for the mercury speciation 

encountered in these systems. 

Sorbents also were selected for the low-particulate Hg 

sources because there was uncertainty that the coagulation 

process would be successful in removing Hg not associated 

with dissolved organic matter (DOM) or particles (Henneberry 

and others, 2011). The selected sorbents included two forms 

of activated carbon, one made from charred coconut husks 

and one derived from mined coal (Carbon Activated Corp., 

Compton, California), and the third sorbent is made from 

solid-phase chitosan flakes (Dungeness Environmental 

Solutions Inc., Bothell, Wash.). All sorbents were sieved (less 

than 1 millimeter [mm]). Sorbents were not evaluated for the 

high-particulate source samples.

Procedures

The experiments focused on two types of Hg-source 

samples: (1) high-particulate, with Hg predominately 

bound up in fine-grained suspended sediment (C.N. Alpers, 

U.S. Geological Survey, oral commun., 2017), and (2) lowparticulate, with Hg predominantly present in the dissolved 

and colloidal fractions that pass through a 0.45-micron filter 

(Rytuba and others, 2011). The coagulation experiment 

was done in two phases to maximize success because the 

experiment demanded large volumes of water to do the testing, 

and the streaming current detector was out of operation during 

the critical wet, raining period when sampling was required. 

A streaming current detector is a device that measures the 

stability of coagulant particles in water (Sibiya, 2014). The 

first phase involved a coagulation “test run” in which a 

large volume (605–609 milliliters, mL) of a turbid sample 

was dosed with ChitoVanTM to determine the approximate 

scale of optimal dose for all three coagulants using turbidity 

as an analog for Hg removal. The second phase used the 

results from the first phase to complete the coagulation “full 

experiment” on a freshly collected large-volume sample. 

Coagulants were tested on both sample types. 
Table 3. Site characteristics affecting the effectiveness of coagulants and sorbents.[Ca2+, calcium; DOC, dissolved organic carbon; Hg, mercury; mg/L, milligram per liter; mmol, millimole; nmol, nanomole; ° C, degrees Celsius; >, greater than; <, less than; —

Site characteristic Effect on coagulation and sorption treatments Notes 

pH Changes in pH may negatively affect coagulation efficiency as it 

can result in unintentional shifts in the coagulation-flocculation mechanism, potentially causing charge reversal and resuspension of particles. Also, with redox status, affects chemical speciation and stability. 

Acceptable ranges for floc formation: –5.5 to 7.5 = alum optimal range –5.0 to 8.5 = ferric salts optimal range pH> 8.5 = ferric salts or other highly acidic coagulants 

recommended 

Alkalinity/salinity/

ionic strength/condictivity

LOW: <50 mg/L alkalinity is too low for salt-based coagulants; 

adding lime, soda, ash or caustic as an aid is recommended. 

HIGH: Halogen-dominated and high cation (Ca2+) systems affect 

Hg-binding and may make the coagulant ineffective. 

Coagulation aids for LOW alkalinity conditions may raise the p

of the water; pH adjustment may be needed to obtain proper flformation.

Temperature Coagulation becomes less efficient in cold temperatures. Higher 

coagulant doses must be used to compensate. 

Temperature <5 °C = alum and ferric salts may not provide prop

floc formation at low temperatures (<5 °C)

Particle 

concentration

LOW: difficult to coagulate due to the difficulty of inducing 

collision between the colloids. 

HIGH: dose requirement becomes challenging to meet. 

— 

Particle type Clays and negatively charged colloids respond well to metal saltbased coagulants. The types of particles affect dose requirements, though not in a linear manner. DOC concentration DOC consumes coagulant. May reduce effectiveness of particulate 

removal or enhance removal of dissolved species. 

— 

DOC - Hg ratio High Hg = DOC have lower binding strength which may lower 

coagulant effectiveness.

Ratios <120 nmol Hg:mmol DOC are strong binding sides Ratios >120 nmol Hg:mmol DOC are weaker binding sites

Redox conditions If applies to environment in situ, redox status may be important 

to both the coagulation process and floc stability. Effects are complex and dependent on coagulant type and other environmental variables coupled with the redox state. 

Strongly reducing conditions may inhibit coagulation and floc 

formation using iron-based flocs if the iron is converted to a mobile, soluble phase, or it may enhance floc stability and limHg bioavailability if insoluble, solid-phase iron species form.

Total metals/cation 

concentration

High concentrations of cations may compete with the binding/

adsorption of the target mercury species and require more coagulant or more sorbent surface area to be effective. 

— 

Delivery/mixing Poor site characteristics that limit sufficient transport, or inadequate 

mixing, will result in a variety of problems.

— 
8 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

Part 1: High-Particulate Sample Mercury 

Removal

Sample Collection

Two large volume samples were collected from the 

CCSB during March 2016— (1) one for an initial test of 

the coagulants and (2) one for a full experimental run with 

the coagulants (fig. 2)—following mercury clean-sampling 

protocols (U.S. Geological Survey, 2012). The first sample 

was collected at the inlet to the CCSB (11452600) during the 

first storm on March 6, 2016, which exceeded the targeted 

3,000 cubic feet per second (ft3/s) threshold at Cache Creek 

at Yolo (fig. 2). A total of 20 liters (L) of high-turbidity 

water at 1,308 Formazin Nephelometric Units (FNU) were 

collected in two TeflonTM-lined 12-L jerricans at the inlet of 

the CCSB, in coordination with ongoing Hg sampling at this 

location (C.N. Alpers, U.S. Geological Survey, oral commun., 

2017). The sample was collected on the rising limb of the 

hydrograph and used for the initial test run of the coagulants. 

The second sample was collected on March 17, 2016, at the 

inlet and outlet (11452600 and 11452900, respectively) of 

the CCSB on the falling limbs of the hydrographs and used 

for the coagulation full experiment one week later. Two 

10-L samples were collected at each site for a total of 40 L. 

Turbidity at the inlet (11452600) was 500 FNU, and turbidity 

at the outlet (11452900) was 238 FNU, which represent 

much lower turbidity values compared to the value for the 

original test sample (1,308 FNU). Because of a forecast for an 

extended drought, it was likely that no further samples would 

be collected for the experiment, so the samples from the two 

sites were composited to create a single, homogenous turbid 

sample for the coagulation experiment rather than being tested 

as two independent samples. The composited sample used in 

the full experiment had an average laboratory turbidity value 

of 342 FNU. 

Coagulation Jar Tests

For the coagulation test run, the initial dosing rates were 

determined by literature review, suggestions from experienced 

stormwater technicians, and the “test run.” The initial dose 

rates were then adjusted through experimentation before being 

used on the coagulation full experiment. A dose range from 20 

to 120 microliters (μL) of a 1.5-percent solution of ChitoVanTM

was selected for the experimental run to cover the range of 

greatest change in turbidity encountered in the test runs. The 

experimental dose range was selected to determine the optimal 

dose rate, which is the rate with the greatest turbidity decrease 

per unit of dose material on the dose-response curve. Dose 

amounts lower than 20 μL were not tested because of accuracy 

limits of the dosing equipment used in the experimental set up. 

1,000

0

2,000

3,000

4,000

5,000

6,000

Discharge, in cubic feet per second

2015 2016

Sept. 3 Oct. 23 Dec. 12 Jan. 31 Mar. 21 May 10 June 29 Aug. 18 Oct. 7 Nov. 26

EXPLANATION

Dates where high-particulate samples

were collected for the coagulation test 

run, and the coagulation full experiment

Flow measured at 15-minute intervals

Cache Creek at Yolo

Figure 2. Flow conditions at the time when the high-particulate samples were collected relative to the flows over the hydrologic 

year. The targeted flow rate for sample collection was greater than 3,000 cubic feet per second. Flow data were obtained from the 

U.S. Geological Survey real-time monitoring station, Cache Creek at Yolo, California (https://waterdata.usgs.gov/nwis/uv?11452500), 

which is approximately 13 kilometers upstream of the sampling location, Cache Creek Inflow to Settling Basin near Yolo CA (11452500).
Methods and Materials 9

The coagulation full experiment was done in two stages: 

(1) a “dirty” run in glass beakers, allowing for collection of 

ancillary (non-Hg) water-quality measurements and (2) a 

“clean” run, enforcing Hg clean techniques and allowing for 

Hg-specific sample collection. The three coagulants were 

tested in the following order (1) ChitoVanTM, (2) FerralyteTM, 

and (3) UltrionTM. Four 12-L TeflonTM-lined jerricans of 

samples were collected at the locations described above. One 

jerrican from each site was composited into a 20-L TeflonTM-

lined churn. Jerricans were vigorously shaken before emptying 

into the churn. After completion of the first coagulant test, 5 L 

from each of the two remaining jerricans was composited into 

the same churn to ensure that enough volume was present to 

complete testing of the second coagulant. The third coagulant 

was tested 4 days after the first test, and the remaining sample 

in each jerrican was agitated and composited into a clean 20-L 

TeflonTM-lined churn. 

For the “dirty” stage of the experiment, six clean 

glass beakers were labeled with the coagulant used and the 

corresponding dose amount. Each beaker was tared and 

filled with 966–1,000 mL of the sample. The beakers were 

re-weighed to determine the exact amount of water added 

and placed on a magnetic stir plate set to 600 revolutions per 

minute (RPM). Before the coagulant addition, turbidity, pH, 

fluorescent DOM, and specific conductance measurements 

were collected from each jar using a YSI EXO2 water-quality 

sonde (YSI, Yellow Springs, Ohio); total water-column depth 

also was measured. Each beaker was dosed with the specified 

amount of coagulant (table 4). ChitoVanTM and FerralyteTM

were mixed for 2 minutes. However, upon further inspection 

it was determined that 2 minutes was not enough mixing time 

for the full amount of flocculant to form, so mixing time was 

increased to 5 minutes for the “dirty” stage of UltrionTM and 

the “clean” stage for all three coagulants. After mixing, the 

beakers were removed from the stir plates and beaker-specific 

timers were started to record the flocculant settling time. 

Measurements of the above listed characteristics were taken 

after 5, 10, 20, and 30 minutes of settling. At each time point, 

the visual depth of the overlying water column was recorded, 

and the clarity of the overlying water column was visually 

noted. Once the 30-minute measurements were completed, 

the overlying water of the coagulant-amended beakers was 

gently poured off to minimize disturbance, and the remaining 

flocculant was composited and poured off into 20-mL 

scintillation vials that were subsequently used for grain-size 

distribution analysis or were archived (frozen).

The “clean” experiment was repeated with six 1-L 

polyethylene terephthalate copolyester glycol modified 

(PETG; Thermo Fisher Scientific, Waltham, Massachusetts) 

bottles; four bottles received a specified dose (table 4) across 

the range determined from the “dirty” dosing curve, one 

control bottle received no dose, and one bottle was filled 

with organic-free water as the blank (fig. 3). Each bottle 

was labeled with the coagulant used and corresponding dose 

amount, and then tared and filled with approximately 1-L of 

sample water. The bottles were re-weighed to determine the 

exact amount of water added and placed on a magnetic stir 

plate set to 600 RPM. Each bottle was dosed with the specified 

amount of coagulant and allowed to mix for 5 minutes. After 

5 minutes of mixing, the bottles were removed from the 

stir plates and bottle-specific timers were started to record 

flocculant settling time. The visual depth of the clarified water 

column was measured every 5 minutes up to 25 minutes and 

then again at 40 minutes (fig. 3). A MasterflexTM peristaltic 

pump and TeflonTM sampling line were used to pump the 

overlying clarified water into 1-L PETG bottles without 

disturbing the flocculated materials. The water sample was 

then homogenized by shaking immediately before pouring the 

sub-sample splits identified below. 

Each 1-L sample was split into two 125-mL PETG 

bottles for MeHg and THg analysis, one 250-mL highdensity polyethylene (HDPE) bottle for trace-metal analysis 

(if needed), and one 125-mL amber-glass bottle for optical 

properties and DOC analysis; the remaining volume went 

into a glass scintillation vial for analysis on a benchtop 

turbidity meter (Hach 2100AN IS Turbidimeter, Loveland, 

Colorado) using the shake and pour method. Mercury samples 

were preserved to 1 percent by volume with concentrated 

hydrochloric acid. Trace-metal samples were preserved with 

2 mL of quartz-distilled nitric acid. Optical property samples 

were poured into TeflonTM filter towers and vacuum filtered 

through pre-combusted 0.3-micron glass-fiber filters (GF75 

47 mm; Advantec MFS, Inc., Dublin, Calif.) and collected 

in 125-mL amber-glass bottles. Optical-property analyses 

were performed within 2 days of sample collection and 

filtration. Dissolved organic carbon samples were poured off 

from the amber-glass bottles, acidified to less than 2 pH with 

concentrated sulfuric acid, and refrigerated for no more than 

28 days before DOC analysis.

Table 4. Summary table listing the coagulants and sorbents used 

in this experiment. Source samples tested, dose amounts, and 

flow rates used with each coagulant and sorbent also are shown.

[Coagulation “test run” information is not shown. Abbreviations: L, liters; 

L/min, liters per minute; TM, trademark; μL, microliters; %, percent]

Coagulants 

selected

Source 

sample tested

Dose 

amounts tested 

(μL)

ChitoVanTM HV 1.5% high-particulate, 

low-particulate

20, 30, 50, 120

FerralyteTM 8131 high-particulate, 

low-particulate

20, 40, 60, 100

UltrionTM 8186 high-particulate, 

low-particulate

20, 40, 60, 100

Sorbents 

selected

Source 

sample tested

Flow 

rates tested 

(L/min)

Total amount 

of water tested 

per flow rate 

(L)

chitosan (shellbased)low-particulate 0.1, 0.5, 1.0 3

coconut-based 

activated carbon

low-particulate 0.1, 0.5, 1.0 3

coal-based 

activated carbon

low-particulate 0.1, 0.5, 1.0 3
10 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

Figure 3. Bottles from the coagulant dosing series for ChitoVanTM after 20 minutes of settling. Coagulant amendment amounts increase 

from left to right; the blank at the right end.

Part 2: Low-Particulate Sample Mercury 

Removal

Sample Collection

The removal of Hg species (MeHg and THg) by 

coagulation and sorption was tested on samples collected 

during base-flow conditions from two locations in the Harley 

Gulch area (390041122260401; 390057122262501) as 

described previously; site 390057122262501 was sampled 

during low-flow conditions. At each site, on May 3, 2016, a 

large volume of water was collected into a 10-L TeflonTM-

lined jerrican following trace-metal sampling protocols 

(U.S. Geological Survey, 2012). The samples were collected 

at the surface, and the contribution of dissolved gaseous Hg is 

assumed to be negligible.

Coagulation Jar Tests

Coagulants and the metal scavenging agent were tested 

on water samples from each site, following methods like those 

for the high-particulate Hg samples from the CCSB with slight 

modifications. Sequential coagulant dosing of unfiltered-water 

samples from the Turkey Creek site (390057122262501) 

was used during the test run instead of separate bottles for 

each coagulant dosing level. Visual inspection of flocculant 

material production was used as a measurement of success, 

rather than measuring the loss of turbidity. Because visible 

flocculant material was not produced for the non-filtered water 

sample, three sorbents were tested as an alternate approach to 

Hg removal. An aliquot was collected from each sample for 

determination of optical properties and for DOC analysis to 

characterize differences in the dissolved phase between the 

two source waters before treatment. Optical property samples 

were poured into TeflonTM filter towers, gravity filtered 

through pre-combusted 0.3-micron glass-fiber filters (GF75 

47 mm; Advantec MFS, Inc., Dublin, Calif.), and collected in 

125-mL amber-glass bottles. All samples were placed on ice 

in a dark cooler until delivered to the laboratory where they 

were transferred to a refrigerator. Optical-property analyses 

were performed within 2 days of sample collection and 

filtration. Dissolved organic carbon samples were poured off 

from the amber-glass bottles, acidified to less than 2 pH with 

concentrated sulfuric acid, and refrigerated for no more than 

28 days before DOC analysis. 

Sorbent Experiments

The three selected sorbents were tested over the course of 

2 days in the following order (1) chitosan flake, (2) coconutbased activated carbon, and (3) coal-based activated carbon. 

Sample water was collected from the two Harley Gulch area 

sites (390041122260401; 390057122262501) via a peristaltic 

pump into TeflonTM-lined jerricans using Hg clean techniques 

(Wilde and others, 2004). The chitosan flake and coconutbased activated carbon sorbents were tested on May 4, 2016, 

and the coal-based activated carbon sorbent was tested on 

May 5, 2016. 
Methods and Materials 11

A B

Figure 4. A, Turkey Creek downstream from the geothermal spring exiting the Turkey Run mine adit and B, the Connate Spring.

Testing of the sorbents was done on site in a mobile field 

laboratory (fig. 4). Each sorbent was thoroughly rinsed with 

deionized (DI) water in a 1-mm mesh sieve to ensure the 

particle size was greater than 1 mm and to remove any excess 

dust. Sorbent materials were prepared and packed before 

transportation to the field site. TeflonTM in-line filter columns 

were packed to the brim with each type of sorbent, and DI 

water was added to each packed column to ensure the sorbent 

was evenly distributed in the filter column. Sample water 

was pumped from the jerrican through the sorbent-packed 

columns using TeflonTM tubing. Three different flow rates were 

selected to be tested with each sorbent (0.1, 0.5, and 1 liter 

per minute [L/min]), which corresponded to contact times 

between sample and sorbent of approximately 10 seconds, 

2 seconds, and 1 second, respectively (table 4); new columns 

were used for each flow rate. After passing through the in-line 

filter, water was collected in 500-mL increments until 3 L had 

passed through each sorbent filter at the three designated flow 

rates. A method blank also was tested by passing organic-free 

water through acid-cleaned glass beads. 

From each 500-mL aliquot, sample splits were shaken 

to homogenize and poured off into 250-mL HDPE bottles for 

trace-metal analysis, and then into 125-mL PETG bottles for 

MeHg and THg analysis. Mercury samples were preserved 

to 1 percent by volume with concentrated hydrochloric 

acid. Trace-metal samples were preserved with 2 mL of 

quartz-distilled nitric acid. Both sets of samples were then 

stored in ambient temperature in the dark until further 

processing.

Analytical Methods

The analytical methods presented in this report were used 

to obtain results for samples collected during the coagulation 

and sorption experiment. Analytical methods used to obtain 

optical results and DOC, trace-metal, MeHg, and THg 

concentrations are detailed below. 

Total Mercury and Methylmercury Concentration 

Analysis

Total mercury and MeHg concentrations were 

measured by methods like those used by Stumpner and 

others (2015) at the USGS Mercury Research Laboratory in 

Middleton, Wisconsin (appendices 1, 2). Whole-water THg 

concentrations were measured according to EPA Method 1631 

(U.S. Environmental Protection Agency, 1999). Whole-water 

MeHg concentrations were measured using distillation/

ethylation and gas-phase separation with cold vapor atomic 

fluorescence spectrometry as described by DeWild and 

others (2002). Method detection limits for MeHg and THg 

concentrations in whole-water samples were 0.04 nanogram 

per liter (ng/L). 
12 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

Dissolved Organic Carbon Concentration 

and Optical Characterization of Dissolved 

Substances

Dissolved organic matter concentration and IOPs 

were analyzed at the USGS Organic Matter Research 

Laboratory in Sacramento, Calif. Dissolved organic matter 

was measured using a high-temperature combustion total 

organic carbon analyzer (Model TOC-VCHS; Shimadzu 

Scientific Instruments, Columbia, Maryland) according to 

EPA Method 415.3 (U.S. Environmental Protection Agency, 

2005). Characterization of IOPs (spectral absorbance and 

fluorescence) was done with an Aqualog® Spectrofluorometer 

(Horiba Scientific, Edison, New Jersey) using methods 

outlined in Hansen and others (2016). 

Trace-Metal Concentration Analysis

Whole-water trace-metal concentrations were measured 

via inductively coupled plasma mass spectrometry at the 

USGS National Research Program Trace Metals Research 

Laboratory in Boulder, Colo. Methods used were like those of 

Taylor and others (2012). 

Grain-Size Distribution Analysis

Particle-size distribution was measured on a composite 

sample of the settled material from all six doses for each 

coagulant using a Beckman Coulter LSTM 13–320 Laser 

Diffraction Particle Size Analyzer (Beckman, Brea, Calif.) 

equipped with an Aqueous Liquid Module, employing 

sonication and autodilution at the USGS Hydrologic Research 

Laboratory in Sacramento, Calif. Analyses were performed 

according to the instrument user’s manual (Beckman Coulter, 

2011), and data were processed according to Marineau and 

Wright (2017). To avoid chemically altering the size of the 

flocculant particles, sample bottles were shaken vigorously 

to re-suspend the settled material and run on the instrument 

without the aid of any dispersant material; however, the 

samples were sonicated during analysis to measure only 

physically stable particles. Coagulated materials were run 

in replicate, whereas raw-water samples had limited settled 

material and thus were run only once. 

Coagulant and Sorbent Efficacy in 

Mercury Removal

Results from the high-particulate and low-particulate 

Hg-removal experiments are summarized independently to 

focus on the specific objectives of each water source and 

experimental approach. For the particulate-enriched water 

source, we focused on the coagulation experiments, whereas 

the sorbent experiments measured Hg removal from both the 

dissolved and colloidal phases. 

Part 1: Particulate-Dominated Source

Coagulation Test Run

The highly turbid sample responded to the addition of 

the ChitoVanTM (fig. 5; appendix table 3–1). The untreated 

sample had a turbidity of approximately 1,300 FNU. Turbidity 

removal followed a curvilinear response to the dose rate, 

with turbidity decreasing in value as the dose rate increased. 

There was an 81-percent decrease in turbidity in the first 

5 minutes of settling for the lowest dose rate (33 μL/L). After 

10 minutes of settling, the turbidity was lowered by 85 percent 

and after 20 minutes, by 87 percent. For the second lowest 

dose rate (99 μL/L), turbidity was lowered by 97 percent after 

5 minutes of settling, by 98 percent after 10 minutes, and 

by 98 percent after 20 minutes. Settling time had little effect 

on the percentage of turbidity removal; minor differences 

occurred after 5 minutes. The largest decrease in turbidity 

was at the 30-μL/L dose rate; little improvement occurred 

from additional dosing beyond 100 μL/L. The apparent 

optimal dose rate was determined to be less than 100 μL/L and 

possibly less than 30 μL/L; therefore, the full experiment was 

designed to bracket this range.

Coagulation Full Experiment

The coagulation full experiment was focused on the 

removal of MeHg and THg in a particulate-dominated sample 

but revealed marked differences in coagulant effectiveness 

with respect to the removal of particulate and dissolved 

constituents. In addition, ancillary measurements of water 

quality and particle character help to explain observed 

differences in MeHg and THg removal efficiency and the 

stability of the formed flocs in the environment.
Coagulant and Sorbent Efficacy in Mercury Removal 13

0 50 100 150 200 250 300 350

Dose rate, in microliters per liter

200

0

400

600

800

1,000

1,200

1,400

Turbidity, in Formazin Nephelometric Units

EXPLANATION

5

10 30

20

Field turbidity (FNU)

Minutes settling

Figure 5. ChitoVanTM dose-rate turbidity response curve for the initial coagulation test run, using a storm-runoff sample. Turbidity 

values for each settling time were collected in the laboratory.

Mercury Removal

All coagulants effectively removed MeHg and THg from 

suspension in the high-particulate sample (fig. 6; appendix 

table 1–1). ChitoVanTM lowered the THg mean concentration 

by 82 percent from 37 to 6.5 ng/L at the highest dose tested 

(120 μL/L). The removal of MeHg, mean concentration 

reduced from 0.38 to 0.11 ng/L at the highest ChitoVanTM

dose, was slightly less (71 percent) than THg removal. 

However, most of the removal of MeHg and THg occurred 

in the lowest dose rate tested (20 μL/L), accounting for 

greater than 90 percent of the removal at the 120-μL/L dose. 

FerralyteTM efficacy was like that of ChitoVanTM at the highest 

dose amount (100 μL), removing 87 and 74 percent of MeHg 

and THg, respectively (fig. 6). FerralyteTM was less effective 

than ChitoVanTM at lower dose rates, removing only 43 percent 

of MeHg and THg at the lowest dose rate (20 μL/L). 

UltrionTM was the most effective at lowering MeHg and THg 

concentrations, achieving a greater than 90-percent decrease 

in MeHg species at the second lowest dose (40 μL/L), and a 

greater than 90-percent decrease in THg at the lowest dose 

(20 μL). At the lowest dose, 90-percent MeHg removal was 

achieved for one sample, but only 45 percent for the replicate 

sample. Given that this dose rate achieved 90-percent removal 

of both turbidity and THg in replicate, the replicate sample 

for MeHg is likely a result of error or contamination. An 

increase in the UltrionTM dose rate did improve removal of 

MeHg, although that result could have been affected by MeHg 

measurements being very near the method detection limit.

Turbidity

ChitoVanTM was effective at decreasing the turbidity 

of the solution even at low-dose rates (fig. 7A; appendix 

table 3–1). The ChitoVanTM optimal dose rate appears to be 

between 20 and 50 μL/L for the 342 FNU sample, whereas the 

optimal dose rate is between 30 and 100 μL/L for the greater 

than 1,000 FNU sample associated with the test run. Turbidity 

decreased with an increase in dose rate and time after the dose. 

There was a 54-percent decrease in turbidity at the lowest dose 

rate (20 μL/L) after 5 minutes of settling, but the decrease 

increased to 73 percent after 30 minutes. Higher dose rates 

were less affected by the settling time. A dose rate of 30 μL/L 

led to a 71-percent decrease in turbidity after only 5 minutes 

of settling and increased to 78 percent after 30 minutes. 

Additional turbidity removal obtained from dose rates greater 

than 30 μL/L did not increase removal rates, indicating that 

these dose rates were above the optimal dose (figs. 7A, 7D).
14 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

Dose rate, in microliters per liter

0 20 40 60 80 100 120 140

0

5

10

15

20

25

30

35

40

45

50

Total mercury, in nanograms per liter

B

EXPLANATION

ChitoVanTM

FerralyteTM

UltrionTM

Methyl

mercury, in nanograms per liter

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

A 0.45

Dose rate, in microliters per liter

0 20 40 60 80 100 120 140

EXPLANATION

ChitoVanTM

FerralyteTM

UltrionTM

Figure 6. Decrease in A, methylmercury concentrations and B, total mercury concentrations for different dose rates during the 

coagulation full experiment.
Coagulant and Sorbent Efficacy in Mercury Removal 15

D

0

50

100

150

200

250

300

350

0 20 40 60 80 100 120 140

Hach turbidity,

in Formazin Nephelometric Units

Dose rate, in microliters per liter

UltrionTM

ChitoVanTM

FerralyteTM

EXPLANATION

C

0

50

100

150

200

250

300

350

0 20 40 60 80 100 120 140

Turbidity, in Formazin Nephelometric Units

UltrionTM dose rate, in microliters per liter

Minutes settling

5

10

20

30

EXPLANATION

B

Minutes settling

5

10

20

30

EXPLANATION

0

50

100

150

200

250

300

350

Turbidity, in Formazin Nephelometric UnitsTurbidity, in Formazin Nephelometric Units

0 20 40 60 80 100 120 140

FerralyteTM dose rate, in microliters per liter

0

50

100

150

200

300

350

A

0 20 40 60 80 100 120 140

ChitoVanTM dose rate, in microliters per liter

Minutes settling

5

10

20

30

EXPLANATION

250

Figure 7. Coagulant dose-rate turbidity-response curves for three coagulants: A, ChitoVanTM; B, FerralyteTM; C, UltrionTM over time; and 

D, turbidity for all three, were measured using a Hach Turbidimeter at the end of the “clean” stage of each experiment.

FerralyteTM required a higher dose rate than ChitoVanTM 

to lower the turbidity to less than 50 FNU; the optimal dose 

was in the range of 60–100 μL/L (fig. 7B). There was a 

44-percent decrease in turbidity at the lowest dose amount 

(20 μL) after 5 minutes of settling, and a 77-percent decrease 

in turbidity after 30 minutes. At the 60-μL/L and higher dose 

rates, turbidity removal was greater than 80 percent, and the 

speed at which the flocs settled increased (fig. 7B). 

UltrionTM was most effective at decreasing turbidity at 

low-dose rates (fig. 7C). At the lowest dose rate (20 μL/L), 

there was a 97-percent decrease in turbidity after 5 minutes 

of settling. The optimal dose rate is less than or equal to 

the lowest dose rate (20 μL/L). There was some indication 

that decreasing turbidity was less effective (89–93 percent 

decrease) at the mid-range dose rates (30–80 μL/L), but 

the difference was within the error of measurement. The 

effectiveness at the highest dose rate (100 μL/L) was like that 

at the lowest dose rate (20 μL/L). 

Measurements from the end of each experiment (fig. 7D) 

illustrate the differences among the coagulant efficacies in 

decreasing turbidity, and parallel the trends seen in MeHg 

and THg removal. UltrionTM was most effective at lowering 

turbidity at the lowest dose rates. FerralyteTM required the 

highest dose rate to lower turbidity to the 50 FNU level, and 

ChitoVanTM required a medium dose rate between FerralyteTM

and UltrionTM at dose rates up to 50 uL/L. The turbidity 

response curve for FerralyteTM was more incremental than for 

the other coagulants. 
16 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

Flocculant Size and Physical Stability

The particle-size distribution of the settled material in 

the coagulation full experiment differed among the coagulants 

tested (fig. 8). The particle size of the materials treated with 

UltrionTM showed the greatest difference in particle-size 

distribution compared to that of the raw-water materials and 

was dominated by medium-to-coarse silt with an average 

median particle size of 21 micrometers (μm; table 5). The 

UltrionTM coagulant also appeared to be the most effective at 

aggregating the smallest particles, raising the 10th percentile 

of the particle size from less than 1.5 to 5 μm, and lowering 

the fraction as clay to less than 9 percent (fig. 8; table 5). 

In contrast, the FerralyteTM and ChitoVanTM coagulants 

experienced a loss of particles in the 2- to 5-μm range and 

concomitant increase of particles in the 6- to 20-μm range, 

but ultimately these had a relatively small effect on the overall 

distribution (fig. 8). The changes in particle-size distribution 

despite the marked increase in settled materials likely reflects 

the production of unstable particles that disaggregated upon 

sonication. The variability in the percent of sand-size particles 

was attributed to the variability inherent in subsampling of the 

material and the inclusion of aggregates when a dispersant is 

not used (Beckman Coulter Inc., 2011). 

Dissolved Organic Matter

Coagulants can remove DOM and the MeHg and THg 

associated with specific types of DOM from the water column 

(Henneberry and others, 2011). Changes in the optical 

character of the samples were assessed to better understand 

the differences observed in the removal of MeHg and THg 

associated with DOM for the different coagulants.

ChitoVanTM had little effect on DOM concentration 

or optical properties (figs. 9–12). ChitoVanTM caused DOC 

concentrations to increase slightly with each increase in 

dose rate, which could be attributed to the coagulant being 

an organic-based compound (fig. 9A) and had a minor effect 

on IOPs related to DOM character (figs. 9B–D). The full 

absorbance scans show a consistent non-linear decrease in the 

total absorbance of the sample with increasing wavelength 

(from 240 to 540 nanometers, nm) and a small overall 

decrease in absorbance in ChitoVanTM amended samples 

compared to that in untreated raw water (fig. 10A). There was 

no discernable effect from the addition of ChitoVanTM across 

the fluorescence spectra (figs. 11, 12).

0

10

20

30

40

50

60

70

80

90

100

0.0001 0.001 0.01 0.1 1

Percentage finer

Grain size, in micrometers

Clay Silt Sand

Median

UltrionTM

ChitoVanTM

FerralyteTM

Raw water 1

Raw water 2

EXPLANATION

Figure 8. Grain-size distribution curves for the settled materials from the coagulation full experiment and for sediment in non-treated 

(raw) surface water. The raw water 1 and 2 samples were collected during the coagulation full experiment from the large batch of 

samples collected on March 17, 2017. Size classifications according to Poppe and others (2000). 
Coagulant and Sorbent Efficacy in Mercury Removal 17

Table 5. Summary of grain-size classifications and statistics for settled materials from coagulation treatments and for sediment in nontreated (raw) surface water.

[All grain size distribution analysis performed at the U.S. Geological Survey California Water Science Center Hydrologic Research Laboratory. 

Abbreviations: n, number; TM, trademark; μm, micrometer]

Treatment Sand 

(percent)

Silt 

(percent)

Clay 

(percent)

Average 

median 

(μm)

Average 

10th percentile 

(μm)

Average 

10th percentile 

(n)

UltrionTM 5.0 86.3 8.8 20.9 4.9 2

ChitoVanTM 5.0 70.3 24.7 8.4 1.5 2

FerralyteTM 6.2 66.2 27.7 7.4 1.4 2

Raw water 1 3.0 61.3 36.0 6.2 1.1 1

Raw water 2 9.2 58.5 32.3 7.6 1.2 1

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0 20 40 60 80 100 120 140

Dissolved organic carbon, in milligrams per liter 

Dose rate, in microliters per liter

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 20 40 60 80 100 120 140

Specific ultraviolet absorbance at 254

nanometers, in liters of milligram of carbon per meter

Dose rate, in microliters per liter

1.60

1.65

1.70

1.75

1.80

1.85

1.90

0 20 40 60 80 100 120 140

Fluorescence index

Dose rate, in microliters per liter

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

0 20 40 60 80 100 120 140

Relative fluorescence efficiency

Dose rate, in microliters per liter

A

C

B

D

EXPLANATION

ChitoVanTM

FerralyteTM

UltrionTM

EXPLANATION

ChitoVanTM

FerralyteTM

UltrionTM

EXPLANATION

ChitoVanTM

FerralyteTM

UltrionTM

EXPLANATION

ChitoVanTM

FerralyteTM

UltrionTM

Figure 9. Dose-rate response curves for optical measurements of A, dissolved organic carbon; B, specific absorbance at 

254 nanometers; C, fluorescence index; and D, relative fluorescence efficiency.
18 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

0

20

40

60

80

100

120

240 280 320 360 400 440 480 520

Percentage of absorbance remaining after each dose

ChitoVanTM dosing series ChitoVanTM dosing series

20

40

60

80

100

120

240 280 320 360 400 440 480 520

Percentage of absorbance remaining after each dose

FerralyteTM dosing series

0

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

240 280 320 360 400 440 480 520

Absorbance, in absorbance units per centimeter

0

20

40

60

80

100

120

240 280 320 360 400 440 480 520

Percentage of absorbance remaining after each dose

Wavelength, in nanometers Wavelength, in nanometers

UltrionTM dosing series UltrionTM dosing series

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

240 280 320 360 400 440 480 520

Absorbance, in absorbance units per centimeter

C

D

B FerralyteTM dosing series E

F

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

240 280 320 360 400 440 480 520

Absorbance, in absorbance units per centimeter

A

Raw

Raw replicate

21

31

50

121

Blank

Practical quantitation

Dose rate, microliters 

per liter (μL/L)

EXPLANATION

Raw

Dose rate, microliters 

per liter (μL/L)

Dose rate, microliters 

per liter (μL/L)

Dose rate, microliters per liter (μL/L)

EXPLANATION

Dose rate, microliters 

per liter (μL/L)

EXPLANATION

Raw

Raw replicate

20

40

60

101

Blank

EXPLANATION

Dose rate, microliters 

per liter (μL/L)

EXPLANATION

Raw

Raw replicate

20

40

60

101

Blank

Raw

20

40

60

101

Blank

EXPLANATION

Raw

Raw replicate

21

31

50

121

Blank

20

40

60

100

Blank

Figure 10. Effect of the coagulants on the ultraviolet absorbance spectra (left-side figures show absorbance measurements for 

each dose rate; right-side figures show the percent absorbance remaining across the spectra for each coagulant and dose rate). 

Measurements at wavelengths longer than 540 nanometers were predominantly below the practical quantitative limit and have 

been omitted.
Coagulant and Sorbent Efficacy in Mercury Removal 19

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

ChitoVanTM–Raw FerralyteTM–Raw 

ChitoVanTM–50 microliters per liter (μL/L)

UltrionTM–60 μL/L

UltrionTM–Raw

FerralyteTM–60 μL/L

<0.10

Intensity, in relative fluorescence units

<0.20

<0.30

<0.40

<0.50

<0.60

<0.70

<0.80

<0.90

<1.00

<1.10

<1.20

<1.30

<1.40

<1.50

≥1.50

<, less than; ≥, greater than or equal to

EXPLANATION

Peak A: Carbon-normalized 

fluorescence

intensity at ex260em450

Peak B: Carbon-normalized 

fluorescence

intensity at ex270em305

Peak C: Carbon-normalized 

fluorescence

intensity at ex340em440

Peak D: Carbon-normalized 

fluorescence

intensity at ex390em510

Peak M: Carbon-normalized 

fluorescence

intensity at ex300em390

Peak N: Carbon-normalized 

fluorescence

intensity at ex280em370

Peak T: Carbon-normalized 

fluorescence

intensity at ex270em340

Peak Z: Carbon-normalized 

fluorescence

intensity at ex420em460

fDOM: Carbon-normalized 

fluorescence

intensity at ex370em460

HIX: Humification index

FI: Fluorescence index

ex370em520/ex370em480

β/α: Freshness index

Definitions: 

Figure 11. Effects of coagulants on the fluorescence spectra. The first three figures show the excitation emission matrices (EEMs) 

intensity for the raw-water sample with no coagulant added for each experimental run. The last three figures show the EEMs intensity 

for the second highest dose rate for each coagulant in the experimental run. Peak intensity is measured in Relative Fluorescence Units 

(RFU) for all graphs. 
20 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

<0

<10

<20

<30

<40

<50

<60

<70

<80

<90

<100

≥100

Dose/raw

Percentage of excitation emission

matrices, intensity relative to the

non-treated sample for ChitoVanTM

<, less than; ≥, greater than or equal to

EXPLANATION

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

21 microliters per liter (μL/L) 31 μL/L

50 μL/L 121 μL/L

Blank

Figure 12. Intensity of excitation emission matrices (EEMs) for samples treated with the ChitoVanTM coagulant, and blank water. Red 

indicates 100 percent of the initial EEMs intensity, whereas blue indicates less than 10 percent of the initial EEMs intensity remains. The 

blank shows the EEMs intensity relative to the raw-water sample. Peak intensity is measured in Relative Fluorescence Units (RFU) for 

all graphs. 
Coagulant and Sorbent Efficacy in Mercury Removal 21

In contrast, the addition of FerralyteTM lowered DOM 

concentrations and affected optical indicators of DOM 

character. FerralyteTM decreased DOC concentrations 

by 30 percent at the highest dose (fig. 9A). The addition 

of FerralyteTM decreased total absorbance (fig. 10) and 

fluorescence (fig. 11) across the measured spectra. The effects 

of FerralyteTM dose rates on the optical character were linear 

over much of the spectral field, indicating that additional 

dosing would remove additional DOM. However, the loss 

of fluorescence was in the area of the excitation-emission 

matrices (EEMs) associated with humic and fulvic acids, 

whereas the region associated with algal and microbial 

source (Chen and others, 2003) was unaffected (fig. 13). This 

preferential removal of humic DOM is consistent with that 

observed previously (Henneberry and others, 2011).

The addition of UltrionTM had a response like that of 

FerralyteTM, but the effect was more pronounced for UltrionTM 

at lower dose rates. DOC concentration was decreased by 

30 percent at the lowest dose rate, did not change markedly 

with increasing dose rates, and even increased at the highest 

dose (fig. 9A). Indices of DOC character were most affected 

by UltrionTM (figs. 9B–D). Most of the decrease in DOC 

concentration, absorbance, and fluorescence was at the 

lowest dose rate (20 μL/L), with less additional decreases at 

higher dose rates. A large loss of absorbance and fluorescence 

occurred at the lowest dose rate, but the optical signals 

were enhanced at higher dose rates, increasing to more than 

60-percent removal for the highest dose rate for some areas of 

the measured spectra—even in the algal and microbial region 

of the spectra (figs. 10, 11, 14). The highest dose rate appeared 

to release some DOM back into the solution, indicating 

that overdosing could have a negative effect on coagulant 

performance.

Other Effects

Other environmentally relevant water-quality 

characteristics that may be affected by coagulation are specific 

conductance and pH; these properties are relevant because 

they affect biogeochemical processes and wildlife health. Few 

effects of coagulant dosing on the pH or specific conductance 

were observed. Very little change occurred in pH values for 

ChitoVanTM between each dose, which ranged from 7.86 to 

7.98 (fig. 15A). A decrease in pH was caused by the addition 

of FerralyteTM, which lowered the pH at a rate of 0.21 pH units 

for each 25-μL/L dose added. This pH response was quite 

large given the small-dose volumes, indicating that the source 

samples were poorly buffered for the addition of the iron (II) 

sulfate-based coagulant. ChitoVanTM caused very little change 

in specific conductance between each dose rate; conductivity 

ranged from 367 to 378 microsiemens per centimeter at 

25 degrees Celsius (μS/cm at 25 oC; fig. 15B). Similarly for 

FerralyteTM, no systematic change in specific conductance 

was observed across the range of dose rates tested, but the 

conductivity range of 357–387 μS/cm at 25 oC was wider than 

for other coagulants. 
22 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

20 microliters per liter (μL/L) 40 μL/L

100 μL/L

Blank

60 μL/L

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

<0

<10

<20

<30

<40

<50

<60

<70

<80

<90

<100

≥100

Dose/raw

Percentage of excitation emission

matrices, intensity relative to the

non-treated sample for FerralyteTM

<, less than; ≥, greater than or equal to

EXPLANATION

Figure 13. Intensity of excitation emission matrices (EEMs) for samples treated with the FerralyteTM coagulant and blank water. Red 

indicates 100 percent of the initial EEMs intensity, whereas blue indicates less than 10 percent of the initial EEMs intensity remains. The 

blank shows the EEMs intensity relative to the raw-water sample. Peak intensity is measured in Relative Fluorescence Units (RFU) for 

all graphs.
Coagulant and Sorbent Efficacy in Mercury Removal 23

20 microliters per liter (μL/L)

HIX

FI

C A

B

T

M

D

N

Z

β/α

40 μL/L

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

60 μL/L

HIX

FI

C A

B

T

M

D

N

Z

β/α

Blank

HIX

FI

C A

B

T

M

D

N

Z

β/α

100 μL/L

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

fDOM fDOM

fDOM

<0

<10

<20

<30

<40

<50

<60

<70

<80

<90

<100

≥100

Dose/raw

Percentage of excitation emission

matrices, intensity relative to the

non-treated sample for UltrionTM

<, less than; ≥, greater than or equal to

EXPLANATION

Peak A: Carbon-normalized 

fluorescence

intensity at ex260em450

Peak B: Carbon-normalized 

fluorescence

intensity at ex270em305

Peak C: Carbon-normalized 

fluorescence

intensity at ex340em440

Peak D: Carbon-normalized 

fluorescence

intensity at ex390em510

Peak M: Carbon-normalized 

fluorescence

intensity at ex300em390

Peak N: Carbon-normalized 

fluorescence

intensity at ex280em370

Peak T: Carbon-normalized 

fluorescence

intensity at ex270em340

Peak Z: Carbon-normalized 

fluorescence

intensity at ex420em460

fDOM: Carbon-normalized 

fluorescence

intensity at ex370em460

HIX: Humification index

FI: Fluorescence index

ex370em520/ex370em480

β/α: Freshness index

Definitions: 240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

Figure 14. Intensity of excitation emission matrices (EEMs) for samples treated with the UltrionTM coagulant, and blank water. Red 

indicates 100 percent of the initial EEMs intensity, whereas blue indicates less than 10 percent of the initial EEMs intensity remains. The 

blank shows the EEMs intensity relative to the raw-water sample. Peak intensity is measured in Relative Fluorescence Units (RFU) for 

all graphs.
24 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

7.0

7.2

7.4

7.6

7.8

8.0

8.2

0 20 40 60 80 100 120 140

pH 320

330

340

350

360

370

380

390

400

0 20 40 60 80 100 120 140

Specific conductivity, in microSiemens per centimiter

Dose rate, in microliters per liter

Dose rate, in microliters per liter

A

B

EXPLANATION

ChitoVanTM

FerralyteTM

UltrionTM

EXPLANATION

ChitoVanTM

FerralyteTM

UltrionTM

Figure 15. Coagulant dose-rate response curves for A, pH and B, specific conductance.
Coagulant and Sorbent Efficacy in Mercury Removal 25

Part 2: Low-Particulate Mercury Samples

The two sample types collected from the Harley Gulch 

area varied in origin and composition. To effectively evaluate 

the potential for coagulation and sorbent treatment approaches, 

the original source-water character of these representative 

sites was assessed and compared with respect to trace metals 

and a suite of standard water-quality metrics to provide 

further context as to the effectiveness of coagulant and sorbent 

experiments. 

Initial Sample Characterization

Water quality of the two low-particulate Harley Gulch 

source waters (Turkey Creek, 390041122260401; Connate 

Spring, 390057122262501) used in the sorbent experiments 

differed markedly. Mercury concentrations, pH, and specific 

conductance measurements resembled values reported in the 

literature and for reconnaissance sampling (table 6), indicating 

consistent concentrations for the water sources. The THg 

concentrations were similar for the two sources, ranging from 

159 to 186 ng/L despite otherwise markedly different chemical 

characteristics (appendix table 2–1). The specific conductance 

of the Connate-Spring source was higher in November 

compared to samples collected in May and values previously 

reported in the literature. The Turkey Creek samples generally 

had warmer temperatures, were more enriched in chlorophyll 

and dissolved oxygen, less enriched in dissolved organic 

matter, and during the May 2016 experimental run, had 

higher specific conductance than the connate-spring samples, 

(approximately 8,400 and 5,000 μS/cm, respectively; table 6). 

The trace-metal concentrations differed between the source 

samples; uranium and nickel were higher in the connate-spring 

samples, whereas sodium and manganese were markedly 

higher in the Turkey Creek samples (appendix table 6–1). 

The characterization of water sources using IOPs 

revealed the unique signatures of these two sources. There 

were distinct differences in the absorbance and fluorescence 

spectra of the water sources (figs. 16, 17). The IOPs for 

the Turkey Creek and Connate Spring samples revealed 

by the EEMs indicate a different water chemistry between 

the two sites. Spectral slopes were markedly higher in the 

Connate Spring samples than in the Turkey Creek samples, 

except for wavelengths shorter than 256 nm. The Connate 

Spring samples had higher overall absorbance, between 

245 and 400 nm, than the Turkey Creek samples. Turkey 

Creek samples had the highest fluorescence intensities in the 

excitation/emission (ex/em) area of ex240:em390, in a spectral 

region that has not been well documented and extends out 

toward the “peak M” region (fig. 17). In contrast, the Connate 

Spring samples had fluorescence signatures like those of DOM 

in natural surface waters with the highest intensities in the 

“peak A” region (fig. 17).

Coagulation Test

Despite evidence of different organic-matter 

concentrations in samples from the two low-particulate sites 

(390041122260401; 390057122262501; table 6), the addition 

of coagulants failed to produce any flocculant material in any 

samples processed. Dosing with the MetClearTM solution, 

which is designed to remove metals via co-precipitation, 

caused a minimal response observed as a slight production of 

neutrally buoyant white flakes that resulted in a slightly cloudy 

sample. As a result, the coagulants and the MetClearTM were 

eliminated from further experimentation with waters from 

the two low-turbidity sites, and the focus shifted to the use of 

sorbents to remove dissolved Hg species. 

Sorbent Experiments: Methods and Statistics

We constructed a linear fixed-effects model to determine 

the influence of the experimental variables on the amount 

of THg removed from the water after passage through the 

sorbents (appendix tables 4–1, 5–1). “Nanograms (ng) of 

mercury removed” was the dependent variable (Y) that was 

calculated as the difference between the THg concentration 

of the untreated sample (in nanograms per liter) and the 

concentration of the treated aliquot multiplied by the sample 

volume (0.5 L). The water sources (390041122260401; 

390057122262501), sorbent type (chitosan, coal, or coconut), 

flow rate (0.1, 0.5, or 1.0 L/min), and total volume passed 

(0–3 L in increments of 0.5 L) were the fixed effects (x 

variables). Two-way interactions between flow rate and water 

source, flow rate and sorbent type, and flow rate and volume 

passed were included. A single 3-way interaction between 

water source, sorbent, and flow rate also was included. All 

statistical analyses were performed using JMP (v12; Cary, 

North Carolina).

Sorbent-Modeling Results

We observed differences in the removal of THg by 

sorbent type (F 2,31 = 9.77, F is the F-ratio or statistical test 

metric that is used when reporting analysis of covariance 

results; p = 0.0005, p is statistical significance), flow rate 

(F2,31 = 47.6, p < 0.0001), and total volume passed (F1,31 = 13.9, 

p = 0.0008), but not by water source (F1,31 = 0.422, p = 0.5205; 

fig. 18; appendix table 4–1). However, there were several 

significant interactions including source by flow rate 

(F2,31 = 19.8, p < 0.0001), source by sorbent type (F2,31 = 4.464, 

p = 0.0198), and the 3-way interaction of source by sorbent 

by flow rate (F4,31 = 6.33, p = 0.0008), indicating that the 

effects of the variables on the THg removal from these waters 

are complicated and require a reduction in the total number 

of model variables for better interpretation of individual 

variable effects. 
Table 6. Field surface-water-quality measurements for sampling sites in the Harley Gulch area collected in November 2015 and May 2016. [C, creek; fDOM, fluorescent dissolved organic matter; FNU, Formazin Nephelometric Unit; ID, identification; hh:mm, hour:minute; mg/L, milligrams per liter; mm/dd/yyyy, mmillimeters of mercury; nr, near; PDT, Pacific Daylight Time; QSU, quinine sulfate unit; Trib, tributary; USGS, U.S. Geological Survey; —, no data exists; [], USGS parameter μg/L, micrograms per liter; μS/cm, microsiemens per centimeter] Field ID USGS station ID Date (mm/dd/yyyy) Time (PDT) (hh:mm) Temperature (°C) [00010] Specific conductivity (μS/cm) [00095] Dissolved oxygen (mg/L) [00300] Dissolved oxygen (percent) [00301] Barometric pressure (mmHg) [00025] pH [00400] Tur

(F

[63

Connate Spring A Unnamed Trib nr Wilbur Springs CA 390041122260401 11/16/2015 12:30 14.8 6,820 9.34 94.5 725.9 8.01 Connate Spring A Unnamed Trib nr Wilbur Springs CA 390041122260401 05/03/2016 11:40 14.2 5,041 9.05 89 719.6 8.16 Connate Spring A Unnamed Trib nr Wilbur Springs CA 390041122260401 05/04/2016 15:30 14.2 5,078 8.85 87.6 714.8 8.16 Connate Spring A Unnamed Trib nr Wilbur Springs CA 390041122260401 05/04/2016 17:30 14.2 5,050 9.07 — 714.7 8.18 Connate Spring A Unnamed Trib nr Wilbur Springs CA 390041122260401 05/05/2016 12:30 13.9 5,046 8.98 88.4 715.6 8.2 Turkey C nr Wilbur Springs CA 390057122262501 11/16/2015 14:30 15.5 8,250 9.7 100 723.2 8.37 Turkey C nr Wilbur Springs CA 390057122262501 05/03/2016 10:30 23.3 8,412 9.7 117 717.4 8.4 Turkey C nr Wilbur Springs CA 390057122262501 05/04/2016 9:10 20.1 8,379 7.99 90.6 713.8 8.36 Turkey C nr Wilbur Springs CA 390057122262501 05/04/2016 11:40 23.6 8,404 10.49 127.1 714 8.41 Turkey C nr Wilbur Springs CA 390057122262501 05/04/2016 13:40 26.8 8,433 11.4 147.1 713.1 8.42 Turkey C nr Wilbur Springs CA 390057122262501 05/05/2016 9:40 18.6 8,390 7.75 85.2 713.4 8.38 
Coagulant and Sorbent Efficacy in Mercury Removal 27

0.00

0.05

0.10

0.15

0.20

0.25

0.30

240 280 320 360 400 440 480 520 560 600

Absorbance, in absorbance units per centimeter

Wavelength, in nanometers

Turkey Creek Connate Spring

Turkey Creek Connate Spring Blank

Turkey Creek Connate Spring

EXPLANATION

Figure 16. Absorbance spectra for the low-particulate source waters. Three samples were collected from each site between May 4 

and 5, 2016. The results for blank water are provided for reference. 
28 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

fDOM

HIX

FI

C A

B

T

M

D

N

Z

β/α

<0.5

<1.0

<1.5

<2.0

<2.5

<3.0

<3.5

<4.0

<4.5

≥4.5

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

Turkey Creek

5/4/16, AM

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

Turkey Creek

5/4/16, PM

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

Turkey Creek

5/5/16, AM

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

Connate Spring

5/4/16, AM

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

Connate Spring

5/4/16, PM

240 260 280 300 320 340 360 380 400 420 440

300

320

340

360

380

400

420

440

600

580

560

540

520

500

480

460

Excitation wavelength, in nanometers

Emission wavelength, in nanometers

Connate Spring

5/5/16, AM

<, less than; ≥, greater than or equal to

EXPLANATION

Peak A: Carbon-normalized 

fluorescence

intensity at ex260em450

Peak B: Carbon-normalized 

fluorescence

intensity at ex270em305

Peak C: Carbon-normalized 

fluorescence

intensity at ex340em440

Peak D: Carbon-normalized 

fluorescence

intensity at ex390em510

Peak M: Carbon-normalized 

fluorescence

intensity at ex300em390

Peak N: Carbon-normalized 

fluorescence

intensity at ex280em370

Peak T: Carbon-normalized 

fluorescence

intensity at ex270em340

Peak Z: Carbon-normalized 

fluorescence

intensity at ex420em460

fDOM: Carbon-normalized 

fluorescence

intensity at ex370em460

HIX: Humification index

FI: Fluorescence index

ex370em520/ex370em480

β/α: Freshness index

Definitions: 

Intensity, in relative fluorescence units

Figure 17. Excitation-emission matrix (EEM) plots showing the differences in fluorescence spectra of the three samples from each of 

the two source waters used in the sorbent experiment May 4–5, 2016. The fluorescent signature of each water source was consistent 

across sample collections. Peak intensity is measured in percent Relative Fluorescence Units (RFU) for all graphs. 
Coagulant and Sorbent Efficacy in Mercury Removal 29

–25

–20

–15

–10

–5

0

5

10

15

20

25

(0.1 L/min) (0.5 L/min) (1.0 L/min) (0.1 L/min) (0.5 L/min) (1.0 L/min) (0.1 L/min) (0.5 L/min) (1.0 L/min)

Mercury removed, in nanograms

Chitosan Coal Coconut

Turkey Creek

Connate Spring

L/min, liters per minute

EXPLANATION

Figure 18. Least squares mean (plus or minus standard error) for total mercury (THg) removed using a linear fixed effects model 

including water source, sorbent type, and flow rate as fixed effects (r2 = 0.86; p < 0.0001). 

We focused further evaluation on the flow rate where 

we had the greatest response and the greatest number of 

observations, the 0.1-L/min flow rate (appendix table 5–1). 

The coal sorbent is the most versatile of the sorbents, 

effectively removing THg from both water sources and 

showing only a small decrease in the THg removal rate as 

the total-volume passed increased (figs. 18, 19). In contrast, 

the effectiveness of the coconut sorbent appears to decrease 

relatively quickly compared to that of the other sorbents 

tested, perhaps indicating a lower binding capacity for Hg(II). 

The chitosan sorbent was more effective at removing THg 

from the Turkey Creek sample compared to the ConnateSpring sample, but its effectiveness was not decreased 

markedly as more water passed, indicating that it may be more 

of a kinetic effect than an inhibition of binding.

Dissolved trace-metal concentrations did not change 

markedly after the water passed through any of the tested 

sorbents (appendix table 6–1). Trace-metal concentrations in 

treated water samples were in the same ranges as those in the 

non-treated water samples. Blank samples had trace-metal 

concentrations that were variable for the concentration ranges 

measured in the samples, limiting the ability to observe any 

trends.

Discussion

Active- and passive-treatment approaches to control the 

mobilization of Hg may prove feasible with widely available 

technologies and materials. The use of coagulants to sequester 

MeHg and THg from surface water was highly effective in 

laboratory experiments, removing as much as 90 percent of 

the THg in suspension with the addition of only one unit of the 

UltrionTM coagulant (1.5-percent solution) per 50,000 units of 

source water (1:50,000 ratio). UltrionTM also is available as a 

3-percent solution, meaning dose rates could readily be halved 

with products currently on the market. The other coagulants 

also removed substantial amounts of the MeHg and THg 

in suspension at dose ratios of 1:10,000–1:30,000, but the 

UltrionTM coagulant was the only one that lowered the MeHg 

concentration to less than the Sacramento–San Joaquin Delta 

MeHg TMDL implementation goal of 0.06 ng/L (Wood and 

others, 2010). UltrionTM also produced the largest and most 

physically stable aggregates. UltrionTM may have performed 

better because it was used on the remaining high-particulate 

samples, had been refrigerated for 11 days after the collection 

date, and natural coagulation may have occurred.

Dose ratios of this scale make large-scale applications a 

realistic possibility for management challenges such as that 

of the CCSB where stormflows that carry large quantities of 

MeHg and THg downstream to sensitive habitats can reach 

into the millions of liters per minute (Cooke and others, 2004; 

C.N. Alpers, U.S. Geological Survey, oral commun., 2017). 

Coagulation-based systems are typically applied to flow rates 

of a few to dozens of cubic meters per second. Addressing the 

scale of these treatment systems is essential to the feasibility 

of future implementation at a site such as the CCSB. For 

instance, applying a dose rate of 20 μL/L of water at a daily 

average flow of 57 m3

/s requires approximately 100,000 L of 

coagulant per day. Although challenging, a passive system 

employing a silo-fed coagulant storage and delivery system 

could operate unattended for a week before needing to 

be refilled. 
30 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

0

20

40

60

80

100

120

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Total mercury (THg) removed, in nanograms

Volume of water passed, in liters

Turkey Creek

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Total mercury (THg) removed, in nanograms

0

20

40

60

80

100

120

Volume of water passed, in liters

B Connate Spring

A

EXPLANATION

Coconut

Coal

Chitosan

Trend lines

EXPLANATION

Coconut

Coal

Chitosan

Trend lines

Figure 19. Amount of total mercury (THg) removed from surface water passing through sorbents tested at the 0.1-liter per minute 

(L/min) flow rate for the A, Connate Spring and B, Turkey Creek.
Coagulant and Sorbent Efficacy in Mercury Removal 31

Although it may not be feasible to fully treat the entire 

volume of water entering the CCSB throughout the winter, 

targeted approaches could substantially lower the amount of 

MeHg and THg transported downstream to the Sacramento–

San Joaquin Delta and San Francisco Bay. For instance, an 

approach that targets treatment of only the highest flows that 

carry the greatest amounts of Hg could be achieved for a short 

period of time. In systems like the CCSB, a single large storm 

can transport most of the MeHg and THg loads for the entire 

winter (C.N. Alpers, U.S. Geological Survey, oral commun., 

2017). Alternatively, a more traditional scaled-dosing system 

(less than 12,000 L/min) could treat portions of the stormflows 

in a subbasin, thus avoiding the challenges associated with 

excessively high dosing rates and supply requirements for 

large storm peaks in these watersheds. Although outside of 

the scope of this project, a full economic analysis is warranted 

to evaluate this technically feasible approach, especially 

when comparing this approach to landscape-scale alternatives 

employed to control Hg and MeHg transport (Randall and 

Chattopadhyay, 2013).

Although promising, the use of coagulants to reduce 

MeHg and THg in surface water, especially in a passivedosing approach that allows the resulting flocculants to settle 

in the natural environment, will require further assessments 

with respect to their stability and potential for toxicity to 

plants and wildlife. ChitoVanTM is the only coagulant that has 

been reported to be non-toxic in the environment and has been 

used to enhance plant growth (Freepons, 1997). However, 

fish and wildlife have survived in previous field-based studies 

using metal salt-based in-situ coagulation systems (Stumpner 

and others, 2015; Liang, 2016), and one previous study even 

showed lower Hg bioaccumulation in fish inhabiting wetlands 

receiving salt-based coagulant doses (Ackerman and others, 

2015). The use of FerralyteTM would add more sulfate to the 

system, potentially stimulating methylation. However, the 

addition of iron has been shown to impede methylation in 

laboratory- and field-based mesocosm studies (Mehrotra and 

others, 2003; Ulrich and Sedlak, 2010). Despite these positive 

anecdotes, to our knowledge, no formal testing of metal saltbased coagulants on biotic diversity and ecosystem health has 

been performed. 

The mechanisms by which MeHg and THg are removed 

via coagulation indicate that any adverse effects from the Hg 

accumulated in sediments are unlikely, although further study 

is necessary to confirm effects. In the case of particulatedominated Hg transport, the coagulant serves merely as a 

bridge or charge neutralizer that promotes the aggregation 

of fine particles into larger and denser particles that settle 

more quickly (Ghernaout and Ghernaout, 2012). These 

aggregates also can physically sequester Hg from interacting 

with biological processes by creating large particles, thus 

effectively lowering the Hg potential for further transformation 

and bioaccumulation. Enhanced nucleation and aggregation 

of colloids also would effectively lower bioavailability 

of Hg(II) to methylating bacteria (Graham and others, 

2012; Hsu‐Kim and others, 2013). The decrease in specific 

ultraviolet absorbance at 254 nanometers (SUVA254) associated 

with coagulant addition is consistent with a preferential 

removal of large molecular-weight, aromatic-DOM structures 

(Henneberry and others, 2011). This hypothesis is further 

supported by fluorescence indicators of dissolved organic 

matter character (fluorescence index; relative fluorescence 

efficiency) measured in this study (fig. 9). 

Sorbents proved to be less effective than coagulation 

under the experimental conditions tested, with more effective 

THg removal at the 0.1-L/min flow rate (10-second contact) 

than at other rates (appendix table 2–1). The chitosan sorbent 

was the most effective at removing THg from the Turkey 

Creek source water. The amounts of THg removed at the 0.1- 

and 0.5-L/min flow rates (10- and 2-second contact times, 

respectively) were nearly identical, indicating that chitosan 

can handle a higher flow rate than other sorbents. At high flow 

rates, the chitosan and coconut sorbents showed an increase 

in THg concentrations (fig. 18), which could be attributed 

to “stripping” of Hg from the sorbent materials that was 

present originally, or not enough contact time between the 

sorbents and the sample water. The conditions of the sorbent 

experiments were established with affordability and feasibility 

in mind. The sorbent materials used in this study were not 

modified in any way, and the flake form of chitosan used was 

fairly effective at the lowest flow rate. More effective Hg 

removal could potentially be achieved through two scenarios: 

(1) using the same materials used in this study but increasing 

the size of the sorbent system or (2) enhancing the sorbent 

materials used. An increase in the size of the trapping system 

could increase Hg removal. This size increase could come 

with additional costs. However, the amount of sorbent needed 

to achieve more Hg removal may not be feasible to maintain 

over a long period of time. Longevity or capacity of the 

sorbents was not tested. 

Increased Hg removal could be achieved by enhancement 

of the sorbent materials. Modified chitosan and its derivatives 

have been extensively studied as materials to aid in heavymetal removal because of their relatively low cost and 

high availability (Miretzky and Cirelli, 2009; Lui and Bai, 

2014). Chitosan beads linked with organic compounds were 

reported to be effective in removing copper from solution 

(Osifo and others, 2009). Chitosan coalesced with activated 

carbon also have shown promising results in removing dyes 

from wastewater (Auta and Hameed, 2013). There have 

been recent advances in using other materials as potential 

sorbents. One study by Chavan and others (2016) used 

coffee grounds combined with silicone polymers to create a 

foam to trap heavy metals from wastewater. The foams were 

reported to be effective at removing lead and Hg, and the foam 

structure made for easy handling and disposal. Gilmour and 

others (2013) demonstrated that adding activated carbon to 

sediments contaminated with Hg reduced bioaccumulation in 

local organisms in the sediment, which indicates a promising 

method for addressing Hg-contaminated soils. Studies using 

different materials to remove Hg from aqueous solutions have 

been ongoing for years. Knocke and Hemphill (1981) showed 

that ground vulcanized rubber was effective at removing Hg 

from solutions. 
32 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

During low-flow conditions typically seen in the summer 

in the Sacramento Valley, the use of sorbents would be a 

feasible approach to removing dissolved Hg from waters 

entering sensitive habitats like wetlands. During high-flow 

storm conditions in the Cache Creek watershed, however, 

sorbents would be overwhelmed by particulate-rich water and 

would be unable to accommodate removal of dissolved or 

colloidal Hg during high-flow rates. Under such conditions, 

the focus could shift to particulate removal with coagulants. 

Targeted approaches of coagulant dosing in the Cache Creek 

watershed could substantially decrease the amount of Hg 

entering the Sacramento–San Joaquin Delta.

Summary

Coagulants and sorbents were investigated by 

the U.S. Geological Survey, in cooperation with the 

U.S. Environmental Protection Agency, as a means of 

immobilizing and removing mercury (Hg) from water 

collected from sites with high levels of Hg in the Cache 

Creek watershed. The Cache Creek watershed, in the northern 

California inner Coast Ranges, provides a model watershed 

for studying the control of Hg contamination and mobilization 

in a catchment with extensive areas of sensitive habitats 

downstream. The high levels of Hg in the watershed sediment 

are from natural background geologic sources that could have 

been exacerbated by mining activities.

Both particulate-dominant and dissolved-dominant Hg 

source waters were selected for sampling and laboratory 

experimentation. The high-particulate samples were collected 

in March 2016 from the Cache Creek Settling Basin (CCSB), 

whereas the low-particulate Hg samples were collected May 3, 

2016, from two locations in the Harley Gulch area. One site 

in the Harley Gulch area is approximately 100 meters (m) 

downstream from a geothermal spring, and the second site is 

at the emergence point of a connate-water spring. The lowparticulate samples selected for sorbent testing were chosen 

because of high, naturally present Hg levels and a replenishing 

source that could potentially allow for a field setting for testing 

of the sorbents. The particulate-dominant sample was treated 

with varying doses of three coagulants— (1) ChitoVanTM HV 

1.5 percent (shell based), (2) FerralyteTM 8131 (ferric sulfate 

based), and (3) UltrionTM 8186 (aluminum based)—then mixed 

on a stir plate and allowed to settle for 40 minutes. The lowparticulate Hg sample was passed through exchange columns 

packed with three different sorbents— (1) solid-phase chitosan 

flakes, (2) charred coconut husks, and (3) coal pellets. For the 

particulate-dominant source, samples of a settled flocculant 

were collected during a “clean” experimental run in which 

Hg clean techniques were enforced. For the low-particulate 

Hg samples, water was passed through the packed exchange 

columns at three different flow rates (1.0, 0.5, and 0.1 liter 

per minute), representing realistic contact times for passive 

exchange bed applications (1–10 seconds, respectively), and 

then collected into bottles for Hg analysis. 

Coagulation was effective at removing particulate Hg 

(table 7). At the lowest dose amounts, ChitoVanTM achieved 

a 59- to 61-percent decrease in methylmercury (MeHg) 

concentrations and a 71- to 75-percent decrease in total 

mercury (THg) concentrations. FerralyteTM achieved a 

37- to 48-percent decrease in MeHg concentrations and a 

37- to 48-percent decrease in THg concentrations. UltrionTM

achieved a greater than 90-percent decrease in MeHg and THg 

concentrations at the lowest dose (20 μL). 

The use of sorbents was effective at removing Hg from 

the filter-passing phase, but sorbents were less effective 

than coagulation for the flow rates and water:sorbent ratios 

tested (table 7). Less than 30 percent of the filter-passed 

THg was removed, even at the lowest flow rate (10-second 

contact time). Coal-based activated carbon appears to be 

the most versatile of the three sorbent materials, but overall 

filter-passing THg removal was less effective than expected. 

Conditions of the experiment were established with simple 

design, logistical feasibility, and affordability in mind, and 

more effective removal of Hg may be achieved through 

increasing the amount of sorbent per unit of source water 

and increasing contact time. Further research is needed to 

determine the sorption capacity and stability of the sorbents.

Table 7. Summary of results from the coagulant and sorbent 

experiment.

[Percent removal is shown for the lowest dose amounts of each coagulant. 

Turbidity measurements were collected from the Hach turbidometer and 

represent turbidity values for all dose amounts. Abbreviations: TM, 

trademark; >, greater than; %, percent]

Coagulants selected

Methylmercury 

reduction 

(percent)

Total 

mercury 

reduction 

(percent)

Turbidity 

reduction 

(percent)

ChitoVanTM HV 1.5% 59–61 71–75 85–91

FerralyteTM 8131 37–48 37–48 54–93

UltrionTM 8186 >90 >90 99

Sorbents selected Efficiency of mercury removal

Chitosan 

(shell-based)

More effective at removing mercury from 

Turkey Creek than Connate Spring, 

removed the highest amount of mercury 

overall for the Turkey Creek source sample.

Coconut-based 

activated carbon

Quick decrease in the effectiveness of 

mercury removal for both source waters, 

removed the highest amount of mercury 

overall for the Connate Spring source 

water.

Coal-based 

activated carbon

Most versatile, removed mercury at all three 

flow rates, but did not achieve the highest 

amounts of removal overall.
References Cited 33

Our results compare well with those of Henneberry and 

others (2011) and Stumpner and others (2015) where the 

effectiveness of using coagulants to lower MeHg and THg was 

demonstrated in experimental wetlands. The use of coagulants 

to sequester MeHg and THg from surface water was highly 

effective in these laboratory experiments, removing as much 

as 90 percent of the THg in suspension with the addition 

of only one unit of UltrionTM coagulant per 50,000 units of 

source water (1:50,000 ratio). Dose ratios of this scale make 

large-scale applications a realistic possibility for management 

challenges such as that of the CCSB where stormflows that 

carry large quantities of MeHg and THg downstream to 

sensitive habitats can reach millions of liters per minute. 

Although it may not be feasible to fully treat the entire 

volume of water entering the CCSB throughout winter storms, 

targeted approaches could substantially lower the amount of 

Hg transported downstream to the San Francisco Bay and 

Sacramento–San Joaquin Delta. 

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Appendix Tables 37

Appendix Tables

Table 1–1. Mercury and dissolved organic-carbon concentration data, and optical data from samples and blanks collected during the 

‘clean’ portion of the coagulation full experiment.

[All mercury analysis performed at the U.S. Geological Survey (USGS) Wisconsion Mercury Research Laboratory. Each sample was analyzed twice, both 

results are reported. All optical and dissolved organic carbon (DOC) analysis performed at the USGS California Water Science Center Organic Matter Research 

Laboratory. Numbers at the end of each sample ID note the dose amount. Blank samples were selected at random to be tested and noted with lowercase letters. 

Abbreviations: A254, absorbance at 254 nanometers; nm, nanometers; FI, flourescence index; ID, identification; L mg C–1 m–1, liters per milligram of carbon 

per meter; MeHg, methylmercury; mg/L, milligrams per liter; mm/dd/yyyy, month/day/year; N/A, not applicable; ng/L, nanograms per liter; RFE, relative 

fluorescent efficiency; RU, Raman units; SUVA254, specific ultraviolet absorbance at 254 nanometers; THg, total mercury; TM, trademark; <, less than]

Sample ID Date 

(mm/dd/yyyy)

Methyl mercury 

(ng/L)

Total mercury 

(ng/L) A254

(nm)

DOC 

(mg/L)

SUVA254

(L mg C–1 m–1)

RFE 

(RU) FI

MeHg - 1 MeHg - 2 THg - 1 THg - 2

ChitoVanTM

Hg clean_control 03/24/2016 0.38 0.37 33.20 41.50 0.14 4.78 3.01 18.47 1.63

Hg clean_20 03/24/2016 0.15 0.15 9.69 10.40 0.13 4.88 2.71 22.10 1.65

Hg clean_30 03/24/2016 0.15 0.14 9.43 9.85 0.13 4.94 2.69 22.20 1.64

Hg clean_50 03/24/2016 0.13 0.14 7.42 8.22 0.13 5.03 2.60 22.91 1.64

Hg clean_120 03/24/2016 0.11 0.11 6.32 6.74 0.13 5.31 2.46 22.69 1.64

FerralyteTM

Hg clean_control 03/24/2016 0.40 0.30 42.80 36.60 0.14 4.77 3.00 18.70 1.62

Hg clean_20 03/24/2016 0.21 0.19 22.40 22.90 0.12 4.40 2.74 20.85 1.67

Hg clean_40 03/24/2016 0.16 0.15 15.00 13.20 0.11 4.05 2.64 22.03 1.68

Hg clean_60 03/24/2016 0.12 0.13 7.26 7.58 0.09 3.72 2.35 25.91 1.71

Hg clean_100 03/24/2016 0.09 0.09 5.29 5.08 0.07 3.34 2.12 28.96 1.73

UltrionTM

Hg clean_control 03/28/2016 0.40 0.41 45.40 41.40 0.15 4.79 3.12 16.48 1.64

Hg clean_20 03/28/2016 0.22 0.04 2.37 2.12 0.07 3.42 2.01 35.83 1.81

Hg clean_40 03/28/2016 <0.04 <0.04 3.14 4.10 0.05 2.89 1.78 38.43 1.85

Hg clean_60 03/28/2016 0.05 0.05 4.03 4.06 0.05 2.66 1.72 39.69 1.88

Hg clean_100 03/28/2016 <0.04 0.04 2.80 2.68 0.05 3.30 1.52 28.74 1.83

Coagulation experiment blanks

Hg clean_Blank_chitovan 03/24/2016 <0.04 <0.04 0.30 0.22 N/A 0.19 N/A N/A N/A

Hg clean_Blank_ferralyte 03/24/2016 <0.04 <0.04 0.43 0.44 N/A 0.14 N/A N/A N/A

Hg clean_Blank_ultrion 03/28/2016 <0.04 <0.04 0.61 0.65 N/A 0.20 N/A N/A N/A
38 Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California

Table 2–1. Mercury concentrations and dissolved organic-carbon concentrations for samples and blanks collected during the 

sorbent experiment.

[All mercury analysis performed at the U.S. Geological Survey (USGS) Wisconsin Water Science Center Mercury Research Laboratory. All dissolved organic 

carbon (DOC) analysis performed at the USGS California Water Science Center Organic Matter Research Laboratory. Letters assigned to each sample represent 

the total amount of water that passed through the Teflon in-line filter: 500 mL (A), 1500 mL (C), and 3000 mL (F), blank samples were selected at random to 

be tested and noted with lowercase letters. Abbreviations: L/min, liters per minute; mg/L, milligrams per liter; mL, milliliter; mm/dd/yyyy, month/day/year; 

N/A, not applicable; ng/L, nanograms per liter; OFW, organic-free water; <, less than; —, no sample data exists]

Source Sorbent Rate 

(L/min) Run Collection date (mm/dd/yyyy)

Methyl mercury 

(ng/L)

Total mercury 

(ng/L)

DOC 

(mg/L)

Chitosan

Turkey Creek chitosan 0.1 A 05/04/2016 — 133 —

Turkey Creek chitosan 0.1 B 05/04/2016 — 127 —

Turkey Creek chitosan 0.1 C 05/04/2016 — 138 —

Turkey Creek chitosan 0.1 E 05/04/2016 — 129 —

Turkey Creek chitosan 0.1 F 05/04/2016 — 151 —

Turkey Creek chitosan 0.5 A 05/04/2016 — 136 —

Turkey Creek chitosan 0.5 F 05/04/2016 — 134 —

Turkey Creek chitosan 1 A 05/04/2016 — 187 —

Turkey Creek chitosan 1 F 05/04/2016 — 196 —

Connate Spring chitosan 0.1 A 05/04/2016 — 160 —

Connate Spring chitosan 0.1 B 05/04/2016 — 157 —

Connate Spring chitosan 0.1 C 05/04/2016 — 163 —

Connate Spring chitosan 0.1 E 05/04/2016 — 158 —

Connate Spring chitosan 0.1 F 05/04/2016 — 170 —

Connate Spring chitosan 0.5 A 05/04/2016 — 192 —

Connate Spring chitosan 0.5 F 05/04/2016 — 202 —

Connate Spring chitosan 1 A 05/04/2016 — 181 —

Connate Spring chitosan 1 F 05/04/2016 — 174 —

Coconut

Turkey Creek coconut 0.1 A 05/04/2016 — 146 —

Turkey Creek coconut 0.1 B 05/04/2016 — 141 —

Turkey Creek coconut 0.1 C 05/04/2016 — 159 —

Turkey Creek coconut 0.1 E 05/04/2016 — 153 —

Turkey Creek coconut 0.1 F 05/04/2016 — 183 —

Turkey Creek coconut 0.5 A 05/04/2016 — 147 —

Turkey Creek coconut 1 F 05/04/2016 — 382 —

Connate Spring coconut 0.1 A 05/04/2016 — 136 —

Connate Spring coconut 0.1 B 05/04/2016 — 140 —

Connate Spring coconut 0.1 C 05/04/2016 — 165 —

Connate Spring coconut 0.1 E 05/04/2016 — 148 —

Connate Spring coconut 0.1 F 05/04/2016 — 165 —

Connate Spring coconut 0.5 A 05/04/2016 — 204 —

Connate Spring coconut 0.5 F 05/04/2016 — 222 —

Connate Spring coconut 1 A 05/04/2016 — 161 —

Connate Spring coconut 1 F 05/04/2016 — 210 —
Appendix Tables 39

Table 2–1. Mercury concentrations and dissolved organic-carbon concentrations for samples and blanks collected during the 

sorbent experiment.—Continued

[All mercury analysis performed at the U.S. Geological Survey (USGS) Wisconsin Water Science Center Mercury Research Laboratory. All dissolved organic 

carbon (DOC) analysis performed at the USGS California Water Science Center Organic Matter Research Laboratory. Letters assigned to each sample represent 

the total amount of water that passed through the Teflon in-line filter: 500 mL (A), 1500 mL (C), and 3000 mL (F), blank samples were selected at random to 

be tested and noted with lowercase letters. Abbreviations: L/min, liters per minute; mg/L, milligrams per liter; mL, milliliter; mm/dd/yyyy, month/day/year; 

N/A, not applicable; ng/L, nanograms per liter; OFW, organic-free water; <, less than; —, no sample data exists]

Source Sorbent Rate 

(L/min) Run Collection date (mm/dd/yyyy)

Methyl mercury 

(ng/L)

Total mercury 

(ng/L)

DOC 

(mg/L)

Coal

Turkey Creek coal 0.1 A 05/05/2016 — 116 —

Turkey Creek coal 0.1 B 05/05/2016 — 108 —

Turkey Creek coal 0.1 C 05/05/2016 — 119 —

Turkey Creek coal 0.1 E 05/05/2016 — 116 —

Turkey Creek coal 0.1 F 05/05/2016 — 132 —

Turkey Creek coal 0.5 A 05/05/2016 — 140 —

Turkey Creek coal 0.5 F 05/05/2016 — 150 —

Turkey Creek coal 1 A 05/05/2016 — 147 —

Turkey Creek coal 1 F 05/05/2016 — 159 —

Connate Spring coal 0.1 A 05/05/2016 — 148 —

Connate Spring coal 0.1 B 05/05/2016 — 138 —

Connate Spring coal 0.1 C 05/05/2016 — 151 —

Connate Spring coal 0.1 E 05/05/2016 — 159 —

Connate Spring coal 0.1 F 05/05/2016 — 159 —

Connate Spring coal 0.5 A 05/05/2016 — 164 —

Connate Spring coal 0.5 F 05/05/2016 — 158 —

Connate Spring coal 1 A 05/05/2016 — 171 —

Connate Spring coal 1 F 05/05/2016 — 171 —

Untreated samples

Turkey Creek none none Raw 05/04/2016 0.04 176 3.04

Turkey Creek none none Raw 05/05/2016 0.04 159 2.81

Connate Spring none none Raw 05/04/2016 0.04 325 5.41

Connate Spring none none Raw 05/05/2016 0.05 182 5.71

Sorbent experiment blanks

OFW blank none none N/A 05/05/2016 — — 0.25

Blank_glass beads none none N/A 05/05/2016 <0.04 0.26 —

Blank_glass beads none none N/A 05/05/2016 2.10 0.17 —

Blank_glass beads none none N/A 05/05/2016 <0.04 0.47 —
Table 3–1. Selected water-quality measurements collected during the coagulation test run and the coagulation full experiment, by elapsed settling t[All experiments were performed at the U.S. Geological Survey California Water Science Center. Abbreviations: cm, centimeters; fDOM, fluorescent dissolved organic matter; Units; L, liters; mL, milliliters; μS, microsiemens; N/A, not applicable; QSU, quinine sulfate units; —, no data exists; μL, microliters] Coagulant test run Sample ID Coagulant Water added (mL) Dose amount (μL) Dose rate (μL/L) Time: 5 minutes, settling Time: 10 minutes, settling Time: 20 minutes, settlin

Turbidity (FNU) Turbidity (FNU) Turbidity (FNU) 

CCSB- RAW NA — — 0.0 1,308 1,308 1,308 CCSB-A ChitoVanTM 606.4 20 33 245.2 197 176 CCSB-B ChitoVanTM 605.8 60 99 38.5 26.6 26.32 CCSB-C ChitoVanTM 605.4 100 165 28.67 21.8 7.57 CCSB-D ChitoVanTM 605.4 140 231 15.6 15.5 7 CCSB-E ChitoVanTM 609 180 296 15.64 9.8 6 

Coagulation full experiment (dirty stage) Sample ID Coagulant Water added (mL) Dose amount (μL) Dose rate (μL/L) Time: 0 minutes Time: 5 minutes settling T

pH SpC (μS/cm) Turbidity (FNU) fDOM (QSE) pH SpC (μS/cm) Turbidity (FNU) fDOM (QSE) pH 

CCSB Chitovan_”dirty” ChitoVanTM 996 1 1 8.09 388 310 12.9 8.03 382 281 13.4 7.89 CCSB Chitovan_”dirty” ChitoVanTM 978 20 20 8.03 386 300 15.4 8 382 160 25.8 7.87 CCSB Chitovan_”dirty” ChitoVanTM 988 30 30 8.04 385 330 13.6 7.94 383 100 31.25 7.98 CCSB Chitovan_”dirty” ChitoVanTM 986 40 41 8.03 386 300 10.3 7.88 379 83 35.53 7.9 CCSB Chitovan_”dirty” ChitoVanTM 978 50 51 8.05 386 330 11.1 7.92 376 72 37.15 7.89 CCSB Chitovan_”dirty” ChitoVanTM 996 60 60 8.05 386 300 14.9 7.89 382 81 35 7.87 CCSB Chitovan_”dirty” ChitoVanTM 996 120 120 — — — — 7.89 373 77 32 7.88 CCSB Ferric Sulfate_”dirty” FerralyteTM 988 1 1 7.96 379 330 11.9 8.22 388 300 13.7 8.03 CCSB Ferric Sulfate_”dirty” FerralyteTM 996 20 20 7.95 385 330 13.5 7.85 389 195 16.4 7.86 CCSB Ferric Sulfate_”dirty” FerralyteTM 998 40 40 7.96 387 320 12.8 7.71 379 132 18.7 7.71 CCSB Ferric Sulfate_”dirty” FerralyteTM 990 60 61 8.03 386 330 12.1 7.42 385 45 22.8 7.5 CCSB Ferric Sulfate_”dirty” FerralyteTM 996 80 80 8.02 386 300 12.9 7.35 365 28 19 7.35 CCSB Ferric Sulfate_”dirty” FerralyteTM 998 100 100 8.02 385 320 12.7 7.15 398 21 20.5 7.21 CCSB AlClOH_”dirty” UltrionTM 996 1 1 7.6 386 330 14.6 7.73 392 307 13.5 7.6 CCSB AlClOH_”dirty” UltrionTM 988 20 20 7.46 386 350 13.7 7.78 374 9 26.5 7.71 CCSB AlClOH_”dirty” UltrionTM 990 40 40 7.7 384 330 13.3 7.56 372 27 21 7.68 CCSB AlClOH_”dirty” UltrionTM 998 60 60 7.9 385 300 13.8 7.51 375 36 22.5 7.64 CCSB AlClOH_”dirty” UltrionTM 992 80 81 7.9 384 320 12.1 7.59 380 26 25.3 7.63 CCSB AlClOH_”dirty” UltrionTM 996 100 100 7.9 386 300 13.5 7.52 389 18 24.1 7.56 
Coagulation full experiment (dirty stage)—Continued

Sample ID Coagulant

Water 

added 

(mL)

Dose 

amount 

(μL)

Dose 

rate 

(μL/L)

Time: 20 minutes settling Time: 30 m

pH SpC (μS/cm) Turbidity (FNU) fDOM (QSE) pH SpC (μS/cm) 

CCSB Chitovan_”dirty” ChitoVanTM 996 1 1 7.88 380 270 14.5 7.82 373 CCSB Chitovan_”dirty” ChitoVanTM 978 20 20 7.84 377 109 29.3 7.82 364 CCSB Chitovan_”dirty” ChitoVanTM 988 30 30 7.85 380 82 33.4 7.87 375 CCSB Chitovan_”dirty” ChitoVanTM 986 40 41 7.85 373 76 32.2 7.81 374 CCSB Chitovan_”dirty” ChitoVanTM 978 50 51 7.83 364 63 35.5 7.87 380 CCSB Chitovan_”dirty” ChitoVanTM 996 60 60 7.82 377 75 35.4 7.89 360 CCSB Chitovan_”dirty” ChitoVanTM 996 120 120 7.96 367 73 32.5 8.01 364 CCSB Ferric Sulfate_”dirty” FerralyteTM 988 1 1 7.9 384 250 13 7.8 385 CCSB Ferric Sulfate_”dirty” FerralyteTM 996 20 20 7.85 357 102 22.7 7.85 360 CCSB Ferric Sulfate_”dirty” FerralyteTM 998 40 40 7.65 374 60 23.5 7.6 372 CCSB Ferric Sulfate_”dirty” FerralyteTM 990 60 61 7.4 384 21 25 7.45 371 CCSB Ferric Sulfate_”dirty” FerralyteTM 996 80 80 7.25 374 21 18.5 7.3 378 CCSB Ferric Sulfate_”dirty” FerralyteTM 998 100 100 7.1 370 13 21.4 7.15 372 CCSB AlClOH_”dirty” UltrionTM 996 1 1 7.69 384 260 14.1 7.73 367 CCSB AlClOH_”dirty” UltrionTM 988 20 20 7.77 365 5 25.5 7.77 368 CCSB AlClOH_”dirty” UltrionTM 990 40 40 7.75 376 11 22.4 7.74 379 CCSB AlClOH_”dirty” UltrionTM 998 60 60 7.57 380 17 18.7 7.63 375 CCSB AlClOH_”dirty” UltrionTM 992 80 81 7.62 384 16 26 7.64 379 CCSB AlClOH_”dirty” UltrionTM 996 100 100 7.61 383 9 22.5 7.61 388 

Table 3–1. Selected water-quality measurements collected during the coagulation test run and the coagulation full experiment, by elapsed settling t[All experiments were performed at the U.S. Geological Survey California Water Science Center. Abbreviations: cm, centimeters; fDOM, fluorescent dissolved organic matter; Units; L, liters; mL, milliliters; μS, microsiemens; N/A, not applicable; QSU, quinine sulfate units; —, no data exists; μL, microliters]
Coagulation full experiment (clean stage) Sample ID Coagulant Water added (mL) Dose amount (μL) Dose rate (μL/L) 

CCSB Chitovan_Hg clean_control N/A 1,000 0 0 CCSB Chitovan_Hg clean_20 ChitoVanTM 974 20 21 CCSB Chitovan_Hg clean_30 ChitoVanTM 966 30 31 CCSB Chitovan_Hg clean_50 ChitoVanTM 996 50 50 CCSB Chitovan_Hg clean_120 ChitoVanTM 994 120 121 CCSB Chitovan_Hg clean_Blank N/A 984 N/A N/A CCSB Ferric Sulfate_Hg clean_control N/A 996 0 0 CCSB Ferric Sulfate_Hg clean_20 FerralyteTM 992 20 20 CCSB Ferric Sulfate_Hg clean_40 FerralyteTM 998 40 40 CCSB Ferric Sulfate_Hg clean_60 FerralyteTM 996 60 60 CCSB Ferric Sulfate_Hg clean_100 FerralyteTM 998 100 100 CCSB Ferric Sulfate_Hg clean_Blank N/A 998 N/A N/A CCSB AlClOH_Hg clean_control N/A 998 0 0 CCSB AlClOH_Hg clean_20 UltrionTM 986 20 20 CCSB AlClOH_Hg clean_40 UltrionTM 996 40 40 CCSB AlClOH_Hg clean_60 UltrionTM 1000 60 60 CCSB AlClOH_Hg clean_100 UltrionTM 992 100 101 CCSB AlClOH_Hg clean_Blank N/A 998 N/A N/A 

Table 3–1. Selected water-quality measurements collected during the coagulation test run and the coagulation full experiment, by elapsed settling t[All experiments were performed at the U.S. Geological Survey California Water Science Center. Abbreviations: cm, centimeters; fDOM, fluorescent dissolved organic matter; Units; L, liters; mL, milliliters; μS, microsiemens; N/A, not applicable; QSU, quinine sulfate units; —, no data exists; μL, microliters]
Appendix Tables 43

Table 4–1. Data for least squares means (+/– std error) for 

total mercury (THg) removed using a linear fixed effects model 

including source water, sorbent type, and flow rate as fixed 

effects (r2=0.86; p < 0.0001). 

[L/min, liters per minute; ng, nanograms; std, standard; +/-, plus or minus; 

<, less than]

Sorbent Flow rate

(L/min) Source

Least 

square mean

(ng)

Standard 

error

(ng)

Chitosan 0.1 Connate Spring 12.12 2.32

Chitosan 0.5 Connate Spring –5.46 3.66

Chitosan 1.0 Connate Spring 4.32 3.66

Coal 0.1 Connate Spring 16.72 2.32

Coal 0.5 Connate Spring 10.54 3.66

Coal 1.0 Connate Spring 5.57 3.66

Coconut 0.1 Connate Spring 17.52 2.32

Coconut 0.5 Connate Spring –13.46 3.66

Coconut 1.0 Connate Spring 0.32 3.66

Chitosan 0.1 Turkey Creek 20.90 2.61

Chitosan 0.5 Turkey Creek 20.54 3.66

Chitosan 1.0 Turkey Creek –7.68 3.66

Coal 0.1 Turkey Creek 13.32 2.32

Coal 0.5 Turkey Creek 7.04 3.66

Coal 1.0 Turkey Creek 3.07 3.66

Coconut 0.1 Turkey Creek 9.72 2.32

Coconut 0.5 Turkey Creek 10.79 3.66

Coconut 1.0 Turkey Creek –20.08 5.42

Table 5–1. Data for amount of total mercury removed at the 

0.1 liters per minute (L/min) flow rate for samples collected during 

the sorbent experiment.

[L, liters; ng, nanograms; —, no data]

Sorbent Flow rate

(L/min) Source 

Volume 

passed 

(L)

Cumulative 

mercury removed 

(ng)

Chitosan 0.1 Turkey Creek 0 —

Chitosan 0.1 Turkey Creek 0.5 —

Chitosan 0.1 Turkey Creek 1 24.5

Chitosan 0.1 Turkey Creek 1.5 43.5

Chitosan 0.1 Turkey Creek 2 60.4

Chitosan 0.1 Turkey Creek 2.5 83.9

Chitosan 0.1 Turkey Creek 3 96.4

Coconut 0.1 Turkey Creek 0 —

Coconut 0.1 Turkey Creek 0.5 15.0

Coconut 0.1 Turkey Creek 1 32.5

Coconut 0.1 Turkey Creek 1.5 41.0

Coconut 0.1 Turkey Creek 2 45.5

Coconut 0.1 Turkey Creek 2.5 57.0

Coconut 0.1 Turkey Creek 3 53.5

Coal 0.1 Turkey Creek 0 —

Coal 0.1 Turkey Creek 0.5 21.5

Coal 0.1 Turkey Creek 1 30.5

Coal 0.1 Turkey Creek 1.5 50.5

Coal 0.1 Turkey Creek 2 68.4

Coal 0.1 Turkey Creek 2.5 71.4

Coal 0.1 Turkey Creek 3 84.9

Chitosan 0.1 Connate Spring 0 —

Chitosan 0.1 Connate Spring 0.5 13.0

Chitosan 0.1 Connate Spring 1 26.0

Chitosan 0.1 Connate Spring 1.5 37.5

Chitosan 0.1 Connate Spring 2 47.8

Chitosan 0.1 Connate Spring 2.5 53.6

Chitosan 0.1 Connate Spring 3 61.6

Coconut 0.1 Connate Spring 0 —

Coconut 0.1 Connate Spring 0.5 25.0

Coconut 0.1 Connate Spring 1 44.5

Coconut 0.1 Connate Spring 1.5 55.0

Coconut 0.1 Connate Spring 2 65.5

Coconut 0.1 Connate Spring 2.5 72.9

Coconut 0.1 Connate Spring 3 83.4

Coal 0.1 Connate Spring 0 —

Coal 0.1 Connate Spring 0.5 17.0

Coal 0.1 Connate Spring 1 35.2

Coal 0.1 Connate Spring 1.5 50.7

Coal 0.1 Connate Spring 2 64.8

Coal 0.1 Connate Spring 2.5 73.1

Coal 0.1 Connate Spring 3 84.6
Table 6–1. Trace metal concentrations for sorbent experiment samples and source waters. [All trace metal analysis performed at the U.S. Geological Survey Trace Metals Research Laboratory in Boulder, CO. Abbreviations: OR, sample was above instrument calibratliter; <, less than. Letters assigned to each sample represent the total amount of water passed through the filter: 500 mL (A), 1,500 mL (C), and 3,000 mL (F), blank samples werand noted with lowercase letters.] Sample ID Collection date (mm/dd/yyyy) Al As B Ba Be Bi Ca Cd Ce Co Cr Cu Dy Er E

Untreated Source Water (μg/L) Turkey Creek 05/04/2016 44 <22 OR 79 0.009 0.31 29 0.06 0.13 1.2 6.3 4.2 0.033 0.026 0.0

Turkey Creek 05/05/2016 44 <22 OR 73 0.011 0.13 27 0.41 0.18 1.1 5.6 7.3 0.029 0.023 <0.0Connate Spring 05/04/2016 65 <22 OR 42 0.007 0.28 42 0.48 0.083 0.68 5.7 5.6 0.014 0.011 <0.0Connate Spring 05/05/2016 26 <22 OR 39 0.006 0.18 42 0.1 0.043 0.43 4.5 3.7 0.011 0.009 <0.0

Chitosan (μg/L) Turkey Creek-A 05/04/2016 39 <22 OR 81 0.009 0.05 32 0.03 0.12 1.2 6.3 5.4 0.027 0.021 <0.0

Turkey Creek-C 05/04/2016 34 <22 OR 82 0.013 0.22 34 0.12 0.1 1.3 5.6 8.6 0.029 0.022 <0.0Turkey Creek-F 05/04/2016 34 <22 OR 80 0.013 0.35 31 0.15 0.1 1.3 6.1 13 0.033 0.023 <0.0Connate Spring-A 05/04/2016 22 <22 OR 43 0.004 0.26 46 0.12 0.034 0.54 5.4 4.7 0.009 0.011 <0.0Connate Spring-C 05/04/2016 22 <22 OR 41 0.004 0.11 44 0.06 0.039 0.51 5.5 4 0.010 0.008 <0.0Connate Spring-F 05/04/2016 21 <22 OR 41 0.004 0.14 41 0.03 0.037 0.50 5.3 4.2 0.011 0.010 <0.0

Coconut (μg/L) Turkey Creek-A 05/04/2016 37 <22 OR 85 0.018 1 31 0.48 0.12 1.3 6.4 3.9 0.032 0.025 0.0

Turkey Creek-C 05/04/2016 34 <22 OR 80 0.017 0.06 30 0.06 0.11 1.2 6 4.7 0.031 0.025 <0.0Turkey Creek-F 05/04/2016 32 <22 OR 79 0.012 0.56 28 0.08 0.11 1.2 5.9 8.1 0.032 0.022 <0.0Connate Spring-A 05/04/2016 25 <22 OR 45 0.005 0.12 41 0.03 0.04 0.52 5.6 3.9 0.01 0.011 <0.0Connate Spring-C 05/04/2016 26 <22 OR 45 0.003 0.28 44 0.04 0.04 0.55 5.6 5 0.012 0.01 <0.0Connate Spring-F 05/04/2016 25 <22 OR 42 0.004 0.31 45 0.11 0.04 0.51 8.9 3.7 0.011 0.012 <0.0

Coal (μg/L) Turkey Creek-A 05/05/2016 50 <22 OR 77 0.015 0.24 33 0.15 0.17 1.1 6.5 3.9 0.05 0.046 0.0

Turkey Creek-C 05/05/2016 39 <22 OR 78 0.015 0.12 33 0.04 0.13 0.96 5.8 4.4 0.037 0.037 <0.0Turkey Creek-F 05/05/2016 37 <22 OR 76 0.017 0.15 34 0.30 0.13 1.1 6.4 4.2 0.04 0.028 <0.0Connate Spring-A 05/05/2016 36 <22 OR 42 0.004 0.13 42 0.04 0.07 0.51 6 9.1 0.019 0.018 <0.0Connate Spring-C 05/05/2016 55 <22 OR 42 0.006 0.12 43 0.64 0.06 0.55 6.3 4.7 0.016 0.014 <0.0Connate Spring-F 05/05/2016 28 <22 OR 42 0.004 0.23 43 0.30 0.06 0.54 5.9 4.5 0.014 0.014 0.0

Blanks (μg/L) Blank - a 05/05/2016 2.9 <22 <137 0.1 0.003 0.32 0.05 0.03 0.01 0.028 3 3.1 <0.0004 <0.0004 <0.0

Blank - c 05/05/2016 3.2 <22 <137 0.08 0.005 0.18 0.04 0.21 0.01 0.015 2.9 4.2 <0.0004 <0.0004 <0.0Blank - f 05/05/2016 4.8 <22 <137 0.14 <0.001 0.09 0.05 0.15 0.01 0.025 3 0.5 0.001 <0.0004 <0.0
Table 6–1. Trace metal concentrations for sorbent experiment samples and source waters.—Continued[All trace metal analysis performed at the U.S. Geological Survey Trace Metals Research Laboratory in Boulder, CO. Abbreviations: OR, sample was above instrument calibratliter; <, less than. Letters assigned to each sample represent the total amount of water passed through the filter: 500 mL (A), 1,500 mL (C), and 3,000 mL (F), blank samples werand noted with lowercase letters.]

Sample ID Collection date (mm/dd/yyyy) Ho K La Li Lu Mg Mn Mo Na Nd Ni P Pb Pr Rb 

Untreated Source Water (μg/L)

Turkey Creek 05/04/2016 0.010 47 0.042 OR 0.004 514 42 1 1,393 0.071 2.8 157 0.36 0.014 102 2

Turkey Creek 05/05/2016 0.008 43 0.076 OR 0.004 483 27 0.4 1,370 0.084 2.8 156 1.4 0.019 94 2

Connate Spring 05/04/2016 0.004 15 0.029 OR 0.002 373 4.2 3.8 749 0.035 13 91 0.51 0.008 2.8 2

Connate Spring 05/05/2016 0.004 14 0.015 OR 0.001 378 1.2 3.5 718 0.02 9.1 98 0.08 0.004 2.6 2

Chitosan (μg/L)

Turkey Creek-A 05/04/2016 0.007 47 0.036 OR 0.004 522 13 0.3 OR 0.06 2.2 164 0.27 0.012 105 2

Turkey Creek-C 05/04/2016 0.009 47 0.032 OR 0.004 582 13 0.3 OR 0.065 2.8 180 1.7 0.01 104 2

Turkey Creek-F 05/04/2016 0.009 46 0.029 OR 0.004 523 14 0.4 1,587 0.06 2.4 177 0.68 0.01 100 2

Connate Spring-A 05/04/2016 0.003 16 0.012 OR 0.001 397 1.3 3.9 802 0.013 6.9 98 0.5 0.003 2.8 3

Connate Spring-C 05/04/2016 0.003 16 0.013 OR 0.001 386 0.85 3.7 782 0.014 7.5 84 0.1 0.003 2.7 3

Connate Spring-F 05/04/2016 0.003 15 0.012 OR 0.001 351 0.91 3.8 719 0.015 7.6 79 0.12 0.003 2.7 2

Coconut (μg/L)

Turkey Creek-A 05/04/2016 0.011 49 0.044 OR 0.004 548 22 0.8 OR 0.069 2.7 365 0.24 0.013 119 2

Turkey Creek-C 05/04/2016 0.009 47 0.035 OR 0.004 514 18 1 1,422 0.059 2.4 238 0.35 0.012 106 2

Turkey Creek-F 05/04/2016 0.008 46 0.034 OR 0.004 504 16 0.7 1,502 0.059 2.4 207 1.2 0.011 103 2

Connate Spring-A 05/04/2016 0.004 17 0.015 OR 0.002 363 9.2 3.8 727 0.017 8.6 295 0.3 0.004 15 2

Connate Spring-C 05/04/2016 0.003 16 0.017 OR 0.001 382 4.2 3.7 779 0.021 9.6 172 0.47 0.004 6.7 3

Connate Spring-F 05/04/2016 0.003 16 0.015 OR 0.002 394 2.9 3.7 789 0.017 9.0 126 0.16 0.004 4.8 3

Coal (μg/L)

Turkey Creek-A 05/05/2016 0.012 44 0.059 OR 0.006 554 33 4.7 1,630 0.087 2.6 176 0.11 0.017 98 2

Turkey Creek-C 05/05/2016 0.012 46 0.043 OR 0.005 577 31 2.4 OR 0.076 2.4 165 0.12 0.014 100 2

Turkey Creek-F 05/05/2016 0.011 46 0.041 OR 0.005 556 32 1.4 OR 0.071 2.4 172 0.12 0.012 103 2

Connate Spring-A 05/05/2016 0.006 15 0.027 OR 0.003 368 2.3 6.1 733 0.032 8.9 83 1.8 0.006 3.9 2

Connate Spring-C 05/05/2016 0.005 16 0.022 OR 0.002 372 1.5 4.9 756 0.024 9.9 91 0.14 0.005 3.4 3

Connate Spring-F 05/05/2016 0.005 15 0.022 OR 0.002 360 1.2 4 780 0.025 9.8 75 0.38 0.005 3.1 3

Blanks (μg/L)

Blank - a 05/05/2016 0.000 0.04 0.003 <0.3 <0.0001 <0.4 0.37 <0.2 <1 0.002 1.50 <12 1.3 0.001 0.014 

Blank - c 05/05/2016 <0.0001 0.04 0.005 <0.3 <0.0001 <0.4 0.24 <0.2 <1 0.003 0.72 <12 0.48 0.001 0.014 

Blank - f 05/05/2016 0.000 0.05 0.005 <0.3 <0.0001 <0.4 0.29 <0.2 <1 0.004 0.85 <12 0.13 0.001 0.022 
Table 6–1. Trace metal concentrations for sorbent experiment samples and source waters.—Continued [All trace metal analysis performed at the U.S. Geological Survey Trace Metals Research Laboratory in Boulder, CO. Abbreviations: OR, sample was above instrument calibratliter; <, less than. Letters assigned to each sample represent the total amount of water passed through the filter: 500 mL (A), 1,500 mL (C), and 3,000 mL (F), blank samples werand noted with lowercase letters.] Sample ID Collection date (mm/dd/yyyy) Sm Sr Tb Te Th Ti Tl Tm U V Y 

Untreated Source Water (μg/L) Turkey Creek 05/04/2016 0.023 2,467 0.004 0.09 0.022 <0.5 0.097 0.003 0.067 1.8 0.39 

Turkey Creek 05/05/2016 0.017 2,392 0.004 0.05 0.023 <0.5 0.008 0.003 0.064 1.2 0.36 

Connate Spring 05/04/2016 0.008 1,162 0.002 0.04 0.022 <0.5 0.095 0.002 2.4 4.9 0.19 

Connate Spring 05/05/2016 0.004 1,156 0.002 0.02 0.01 <0.5 0.092 0.001 2.3 4.4 0.17 

Chitosan (μg/L) Turkey Creek-A 05/04/2016 0.013 2,625 0.004 0.11 0.021 <0.5 <0.005 0.003 0.081 1.9 0.37 

Turkey Creek-C 05/04/2016 0.017 2,810 0.005 0.09 0.017 <0.5 <0.005 0.003 0.068 1.6 0.39 

Turkey Creek-F 05/04/2016 0.016 2,576 0.005 0.08 0.009 <0.5 0.012 0.003 0.056 1.3 0.38 

Connate Spring-A 05/04/2016 0.004 1,240 0.002 0.04 0.022 <0.5 0.097 0.002 2.6 4.7 0.17 

Connate Spring-C 05/04/2016 0.004 1,213 0.001 0.04 0.02 <0.5 0.097 0.001 2.5 5.2 0.17 

Connate Spring-F 05/04/2016 0.005 1,141 0.002 0.04 0.02 <0.5 0.091 0.001 2.4 5 0.17 

Coconut (μg/L) Turkey Creek-A 05/04/2016 0.016 2,583 0.004 0.12 0.016 <0.5 0.023 0.004 0.07 1.4 0.39 

Turkey Creek-C 05/04/2016 0.018 2,500 0.005 0.07 0.015 <0.5 0.019 0.003 0.053 1.6 0.38 

Turkey Creek-F 05/04/2016 0.018 2,422 0.005 0.08 0.025 <0.5 0.01 0.004 0.057 1.7 0.37 

Connate Spring-A 05/04/2016 0.005 1,127 0.001 0.03 0.015 <0.5 0.036 0.001 2.5 4.9 0.16 

Connate Spring-C 05/04/2016 0.005 1,202 0.002 0.03 0.013 <0.5 0.051 0.001 2.6 5.6 0.17 

Connate Spring-F 05/04/2016 0.006 1,255 0.002 0.03 0.014 <0.5 0.06 0.001 2.5 5.2 0.17 

Coal (μg/L) Turkey Creek-A 05/05/2016 0.025 2,696 0.007 0.08 0.019 <0.5 0.008 0.006 0.29 1.7 0.65 

Turkey Creek-C 05/05/2016 0.02 2,737 0.006 0.07 0.02 <0.5 0.01 0.005 0.18 1.6 0.54 

Turkey Creek-F 05/05/2016 0.019 2,761 0.006 0.09 0.015 <0.5 0.006 0.004 0.14 1.5 0.5 

Connate Spring-A 05/05/2016 0.009 1,156 0.003 0.03 0.016 <0.5 0.054 0.003 2.5 5.3 0.3 

Connate Spring-C 05/05/2016 0.006 1,192 0.002 0.03 0.011 <0.5 0.065 0.002 2.5 5.2 0.25 

Connate Spring-F 05/05/2016 0.004 1,189 0.002 0.03 0.013 <0.5 0.071 0.002 2.5 5.3 0.23 

Blanks (μg/L) Blank - a 05/05/2016 <0.0004 <1.0 <0.0002 <0.02 <0.003 <0.5 <0.005 0.000 <0.009 <0.7 <0.001 <

Blank - c 05/05/2016 0.000 <1.0 <0.0002 <0.02 <0.003 <0.5 <0.005 0.000 <0.009 <0.7 0.001 

Blank - f 05/05/2016 0.001 <1.0 <0.0002 <0.02 <0.003 0.70 <0.005 <0.00009 0.01 <0.7 0.002 <
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https://ca.water.usgs.gov ISSN 2331-1258 (online)

https://doi.org/10.3133/ofr20191001
De Parsia and others—Coagulant and Sorbent Efficacy in Removing Mercury from Surface Waters in the Cache Creek Watershed, California—

Open-File Report 2019–1001