Case History

Sediment Redox Processes and Mercury Management

in Onondaga Lake, New York

C O

S

N

Hg

ENVE5504 – Surface Water Quality Modeling

Hennigan, R.D., 1990. America's Dirtiest Lake. Clearwaters 19: 8-13.

Testimony to the U.S. Senate has described Onondaga Lake as one of the most polluted in the country – perhaps the most polluted.

Syracuse, New York: The Salt City• 1615 – first European visitor, Samuel Champlain• 1654 – salt springs discovered, Father Simon Lemoyne• 1794 – salt industry in place, James Geddes• 1820 – local brine springs failing• 1838 – wells dug around Onondaga Lake fail to locate source• 1862 – salt industry reaches its peak

The Solvay Process

http://pubs.acs.org/subscribe/journals/tcaw/11/i02/html/02chemchron.html

In 1865, a Belgian chemist, Ernest Solvay, developed a process to produce soda ash from calcium carbonate (limestone) and sodium chloride (salt). Soda ash is used in softening water and in the manufacture of glass, soap and paper:

3 2 3 22CaCO NaCl N Ca O ClC a

Ernest Solvay

1943: wastebeds collapse flooding region with soda ash waste

Solvay Process Allied Chemical Allied Signal Honeywell

1884 soda ash production begins on west shore using locallyproduced salt brine and limestone from nearby Dewitt

1880s salt production moved to Tully Valley

1912 limestone quarries moved to Jamesville

1986 industry closes

The Chlor-Alkali Process

The mercury cell chlor-alkali process was used to produce chlorine gas and sodium hydroxide through electrolysis of a salt brine solution.

( ) 2 ( ) ( ) 2( ) 2( )2 2 2aq l aq g gNaCl H O NaOH Cl H

+ anode

Hg cathode

carbonelectrode

Cl2

26% NaCl

24% NaCl

sodium amalgum, NaHg

H2

HgH2O

50% NaOH

The Chlor-Alkali Process

There is loss of mercury through leakage and dumping as the cells are cleaned or replaced. Approximately 75,000 kg of mercury were discharged to Onondaga Lake over the period 1946-1970.

0

75m

g∙kg

DW

-1

Adapted from Atlantic States Legal Foundationhttp://www.aslf.org/ONONDAGALAKE/gallery1.html

Hg(0) – mercury can be present as elemental or metallic mercury, a form that is subject to volatilization and release to the atmosphere;

Hg(II) – mercury can be present in ionic form, associated with salts and existing in equilibrium with Hg(0);

MeHg, (Me)2Hg – mercury may be present in the mono- and dimethyl forms, readily available for biotic uptake and produced from ionic mercury by sulfate-reducing bacteria.

(0) ( )Hg Hg II MeHg

Source: Global Mercury Assessment, United Nations Environment Programmehttp://www.chem.unep.ch/mercury/Report/GMA-report-TOC.htm

Adapted from Atlantic States Legal Foundationhttp://www.aslf.org/ONONDAGALAKE/gallery1.html

0

75

mg∙kgDW-1

Superfund

Dredge and Cap: the plan includes dredging of 2.65 million cubic yards of contaminated sediment with capping of 579 acres (20%) of the lake bottom.

MSNBC, 16 October 2006

Superfund

-Closure of the Allied Signal chlor-alkali plants

-Bottom sediments and adjacent sites were assigned to the Federal Superfund National Priorities List

-Clean-up of upland sites has been completed wherein 8,500 tons of soil were treated

-Wetland restoration was completed in 2007

-Groundwater Collection System/Barrier Wall—barrier wall construction has begun and groundwater treatment is in progress

Innovative Soil Washing Technology

Sediment Remediation Plan: dredge and cap, 20%

Sediment Remediation Plan: the other 80%

EPA does not consider monitored natural recovery to be a ‘no-action’ alternative, but rather an alternative means of achieving remediation objectives (U.S. EPA 1999). Selection of this approach implies that contaminant degradation and/or sequestration will eventually lead to remediation of the sediment environment (U.S. EPA 2005) and restoration of lost beneficial uses.

Monitored Natural Recovery

The Mercury Cycle

Hg(0) me-Hg

Hg(II) Hgp

SRB

SRB

complexation - sequestration

Monitored Natural Recovery

• fully protective of human health and the environment

• objectives achieved in a reasonable time

Enhanced Natural Recovery

• where MNR guidelines are not met, consider in situ approaches to reduce risk as sediments proceed toward a new SS following source controls.

Chemical Augmentation • oxygen• nitrate

Mercury Sulfur Interactions

Methylmercury production is associated with the activities of sulfate reducing bacteria.

22 4 2 2 2( )C H O SO H S CO H O

Source: Matilainen, T. 1995. Involvement of bacteria in methylmercury formation in anaerobic lake waters. J WAS, Vol. 80.Data from Dave Matthews, Upstate Freshwater Institute (S) and Svetoslava Todorova, Syracuse University (Hg)

J A S O

mgS

2-L

-1ngM

eHgL

-1

0

5

10

15

20

0

2

4

6

8

C(H2O)

Sulfur and the Ecological Redox Series

O2

SO4

NO3

2 2CO H O

C(H2O)

Sulfur and the Ecological Redox Series

O2

SO4

NO32 2 3 2N CO HCO H O

C(H2O)

Sulfur and the Ecological Redox Series

SO4

NO3

2 2 2H S CO H O

O2

0

2

4

6

0.0

0.5

1.0

1.5

2.0

0

5

10

15

Oxygen

Nitrate

HydrogenSulfide

mgS

2-L

-1m

gN-

L-1m

gO2

L-1

A M J J A S

Redox Manifestations in Onondaga Lake

The depletion of alternate electron acceptors (oxygen and nitrate) and the accumulation of an end-product of sulfate reduction (hydrogen sulfide) in the hypolimnion of Onondaga Lake tracks the ecological redox series.

Data from Dave Matthews, Upstate Freshwater Institute

Oxygenation and Nitrate Augmentation

0

2

4

6

0.0

0.5

1.0

1.5

2.0

0

5

10

15

Oxygen

Nitrate

HydrogenSulfide

mgS

2-L

-1m

gN-

L-1m

gO2

L-1

A M J J A S

Nitrate augmentation is one means of blocking sulfate reduction and the attendant production of methylmercury.

Data from Dave Matthews, Upstate Freshwater Institute

22 2 2( )C OH O CO H O

3 232 2 2( )C H O N CO HCO H ONO

2 24 2

2( )C H O Mn COMn H O

2 23 2

2( )C H O Fe COFe H O

22 2 2 24( )C H O H S CO H OSO

42 2( ) C OC HH O C

electrondonor

electronacceptor CO2+ reduced species

end product+

various various

Mapping Diagenesis

-2

8

18

28

38

48

58

0 2 4 6 8 10

-2

8

18

28

38

48

58

0 2 4 6 8 10

Sediment Profiles

Measuring Methylmercury Flux

1. Determine the MeHg flux from the sediments with the nitrate concentration in the hypolimnion maintained at 2 mg/L.

2. Describe setup and conditions for the laboratory measurements.

3. Write the equation that will yield the desired flux and identify the source of the input terms to that equation.

J

FeedStock

Q C∙ in Q C∙

EXPERIMENTAL SET-UP

J

Measuring Methylmercury Flux

FeedStock

Q C∙ in Q C∙

EXPERIMENTAL SET-UP

J

indCV Q C Q C J Adt

0.0

0.2

0.4

0.6

0.8

1.0

0 2 4 6

Flow

(m

Lm

in∙

-1)

Days

0

1

2

3

1 2 3 4 5 6

Nitr

ate

(mgN

L∙-1 )

Days

0

2

4

6

8

10

12

1 2 3 4 5 6

Oxy

gen

(mg

O2.L

-1)

Days

Q

0.0

0.1

0.2

0.3

0.4

0 2 4 6

MeH

g (n

g.L

-1 )

Days

ssQJ CA

Css

Results

Results

0

30

60

90

120

150

Hypolimnetic Accumulation Rates

Porewater Calculations

Flow-through No/No

ng.m

-2.d

-1

Results

0

40

80

120

160

200

Hi O2 + Hi NO3

Low O2 + NO3

No/No O2 NO3

ng.m

-2.d

-1

0102030405060708090

100

0 3 6 9 12 15

Net demethylation

Sulfate Reduction and Methylmercury Production

Application