BEFORE THE

ILLINOIS POLLUTION CONTROL BOARD

AMEREN ENERGY GENERATING

COMPANY,

v.

ILLINOIS

ENVIRONMENTAL

PROTECTION AGENCY

Petitioner,

)

)

)

)

)

)

)

)

)

)

Respondent. )

PCB 2009-038

(Thermal Demonstration)

PRE-FILED TESTIMONY OF ANN B. SHORTELLE, PH.D.

A.

BACKGROUND AND QUALIFICATIONS

1.

My name is Ann B. Shortelle, Ph.D. I am a Chief Scientist with MACTEC

Engineering and Consulting, Inc. ("MACTEC"). I have a Bachelor

of Science degree in biology

from Mercer University and a Doctorate degree in limnology from the University

of Notre

Dame.

2.

I have 24 years

of professional experience in limnology and lake and reservoir

management, including surface water quality monitoring and analysis.

My Curriculum Vitae is

attached hereto as Attachment

1.

B.

TESTIMONY

1.

In May 2009, Ameren Energy Generating Company ("Ameren") engaged

MACTEC to prepare a report on the conditions

of Coffeen Lake with regard to phosphorus and

mercury. MACTEC evaluated the conditions in Coffeen Lake and the potential for impacts on

phosphorus and mercury cycling from

Ameren's proposed modification to the current site-

specific thermal standards. The report is entitled "Evaluation

of Effects of Revised Thermal

Electronic Filing - Received, Clerk's Office, May 12, 2009

---

Standards on Phosphorus and Mercury Cycling in Coffeen Lake" and is provided as Attachment

2. I incorporate the evaluation as if fully set forth herein.

2.

Our report concludes that significant increases in phosphorus loading or mercury

methylation over current lake conditions will not result from higher thermal limits in May and

October under Ameren's proposed modification. In addition, our evaluation indicates that there

is no "dead zone" within Coffeen Lake. Below is a brief summary

of the report's conclusions.

Impact

on Phosphorus

3.

MACTEC evaluated whether prolonged stratification from an increase in water

temperature would result in an increase in phosphorus in Coffeen Lake. Internal phosphorus

release from sediments can serve

as a source of phosphorus in lakes. Seasonal stratification

within the water column

of a lake results in the development of an epilimnion (surface water)

and hypolimnion (bottom water). Seasonal stratification can also result in anoxic conditions in

the lower portions

of the hypolimnion and can promote the dissolution and release of sediment-

bound phosphorus. However, the mere presence

of thermal stratification does not indicate that

significant internal loading will occur. Thermal stratification without anoxia produces no more

phosphorus release from sediments than an unstratified lake. Thermal stratification with anoxia

present over a portion

of the bottom, may result in some phosphorus release from the sediments

into the hypolimnion, but not in quantities sufficient to reach the epilimnion and promote algal

blooms.

4.

Further, water quality measurements within Coffeen Lake indicate that internal

phosphorus loading is not currently contributing appreciable amounts

of total phosphorus to the

epilimnion in Coffeen Lake. Oxygenated hypolimnetic and epilimnetic waters were determined

to always be present over the deeper anoxic waters, significantly limiting internal phosphorus

2

---

loading. Thus, no observable effect from internal phosphorus loading was observed at Coffeen

Lake.

5.

MACTEC also reviewed the results of Illinois Environmental Protection

Agency's ("Agency") 2007 BATHTUB model used to develop the total maximum daily load

("TMDL") for phosphorus for Coffeen Lake. The Agency's model concluded that internal

phosphorus loading dominates Coffeen Lake.

We believe that significant modeling errors and

misapplications produced a model run that did not match known lake phosphorus concentrations

Thus, the Agency's model increased the amount

of internal phosphorus loading in Coffeen Lake

than is otherwise supported by available monitoring data.

6.

An increase in thermal limits in May and October is unlikely to result in

additional phosphorus loads from sediment release. MACTEC analyzed the potential impacts on

phosphorus loading with the increase in thermal limits in May and October in accordance with

Ameren's proposed modification. Results

of the analysis indicate that the anticipated additional

phosphorus load from the proposed modification is much lower than predicted from the

BATHTUB modeling completed by the Agency for the TMDL. Our analysis shows that any

potential sediment phosphorus release is not mixing into the epilimnion where it would be

available for algal production which could potentially degrade water quality within Coffeen

Lake. Our evaluation concludes that sediment phosphorus release is not a significant component

of total phosphorus concentrations in Coffeen Lake surface water. Rather other phosphorus

loading factors, specifically external phosphorus loading from the surrounding watershed, are

more important factors in water quality within Coffeen Lake.

3

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Impact on Mercury

7.

MACTEC also evaluated whether mercury methylation is likely to increase in

Coffeen Lake as a result

of thermal stratification from Ameren' s proposed modification to its

thermal limits. Methylmercury is more readily absorbed into the tissue

of aquatic organisms and

tends to bioaccumulate in aquatic systems. Mercury methylation is affected by multiple

parameters and is not based solely on thermal stratification.

8.

The current fish consumption advisory for Coffeen Lake is based on two

largemouth bass fish samples with mercury concentrations exceeding the Agency's designated

level

of concern. Mercury concentrations in largemouth bass in Coffeen Lake are lower than the

average largemouth bass tissue concentration in Montgomery County and nearly half the level

of

the Illinois Counties average.

9.

Our review of available data indicated that mercury concentrations appear

generally low in Coffeen Lake. In addition, conditions

do not appear favorable for the

methylation

of mercury. Ameren's proposed modification in May and October will not change

lake conditions, apart from potentially lengthening the period

of thermal stratification for a few

days on average, annually. The minor lengthening

of the period of thermal stratification will not

significantly increase hypolimnetic mercury methylation rates, and will not result in increased

mercury in the biota.

10.

In addition, Illinois regulations controlling the release of atmospheric mercury

from electric generating facilities is expected to reduce the amount

of mercury deposited in

Illinois water bodies.

It

is anticipated that fish tissue concentrations will measurably decline as a

result

of the reduction in mercury loading into Illinois water bodies from reductions in

atmospheric mercury deposition.

4

---

Attachment 1

5

---

AnnB. ShorteHe, PhD

Lhnnologist

Years of Experience: 24

Education:

• PhD, Limnology, 1985, University of Notre Dame

• BS, Biology, 1975, Mercer University

Dr. Shortelle has

24 years of professional experience in limnology, lake and reservoir management,

surface water modeling, (WASP, Bathtub, SWMM) and environmental assessments. She has managed

numerous lake and reservoir, riverine, estuarine, and wetland assessments related to eutrophication, acid

deposition, toxic effluents, biomonitoring, siting and licensing, mitigation planning, and natural resource

damage assessment. She has managed and conducted field and laboratory bioaccumulation studies and

bioassays, and has developed and verified bioaccumulation models for contaminants

in riverine systems.

Dr. Shortelle

is an experienced leader in surface water quality monitoring and analysis and has served as

an expert witness. She has experience working with both MFLs and TMDLs.

Dr. Shortelle

is currently serving on the North American Lake Management Society Board of Directors

and served on the policy advisory committee to FDEP for designated use and classification refinement for

surface waters.

Representative Experience

Feasibility Study

and Implementation of Restoration of Taum Sauk Reservoir and Associated

Black River and Tributaries, Project Principal - Initiated field and benchscale studies following an

upper reservoir dam break to determine feasible methods for reservoir and downstream restoration based

upon hydraulic calculations and field/ laboratory results. The resulting application allows for the

immediate drawdown

of the reservoir under continuously monitored conditions to prevent further

environmental damage and allow for the initiation

of restoration projects.

Taum Sauk Alum Injection Systems, AmerenUE, Project Principal- As part of the restoration of the

Taum Sauk Reservoir, oversaw the selection

of a water quality treatment, design, installation and

operation

of a system to remove turbidity in the Black River. Due to the regulatory requirements of no

environmental impacts, liquid alum was chosen to treat the water. System parameters included creating a

system with a backup to maintain river flow downstream while the flocculated fines were cleaned from

the holding area. The system included design

of a pumping system for regulated injection and line

cleansing, ease

of access for monitoring and system adjustments and dual detention areas with access for

cleaning.

City of Maitland Stormwater / Lakes Management Plan, FL, Project Manager - MACTEC updated

this central Florida City's plan to enhance water quality

in the City's 22 named lakes, including Impaired

Waters requiring TMDLs. MACTEC estimated loadings from nine urban land uses to more than 250 sub

basins and outfalls contributing runoff to these lakes, incorporating the effects

of in place BMPs, and

evaluated potential nutrient loading reductions achievable with alternative additional BMPs. MACTEC

characterized the status and trends

of water quality in all the lakes, and estimated the water quality

benefits and costs associated with more than 500 potential BMPs.

Wekiva River and Floridan Aquifer Nitrate Sourcing Study, St. Johns River Water Management

District (SJRWMD), Principal Scientist - The Wekiva is a spring-fed river with seven 2

nd

magnitude

springs that have elevated levels

of nitrate. Its basin has relatively low population density including large

natural areas and encroaching development. SJR WMD has been tasked by FDEP to develop an estimate

of the sources of nitrate to ground and surface waters in the Wekiva basin, and develop preliminary load

reduction strategies. MACTEC is responsible for the development

of basin-wide nitrate loading estimates

to groundwater and surface water. Source types that will be evaluated include municipal and industrial

wastewater (point sources), septic tanks, storm water runoff, fertilizer use (agricultural, residential, golf

Page

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Ann B. Shortelle, PhD

courses), and atmospheric deposition. Nitrate loads will be partitioned by source types and by land use.

Responsibilities include nitrate loading modeling and budgets.

City of Lakeland, Southwestern Basin of Lake Parker: BMP Alternatives Analysis, FL, Project

Manager - This project's objective is to provide engineering services to determine Lake Parker Water

Quality Improvement Project Best Management Practice (BMP) Identification, Selection, and Ranking

for the Southwestern Basin

of Lake Parker, an impaired waterbody. Tasks include water quality and

hydraulic modeling, nutrient loading estimates, and estimates

of BMP nutrient reductions, prioritization

of BMPs, conceptual design, and recommendations. Phase II includes design, permitting, and

construction management.

Hydraulic and Wetlands Restoration Projects, Pithlachascotee River Wetland Restoration Project,

SWFWMD,

Project Manager - MACTEC is developing the wetland restoration and FDOT mitigation

plans for three areas

of the Pithlachascotee River. This effort will restore hydraulic functions, wetland

functional values, wildlife habitat restoration,

as well as provide mitigation acreage and UMAM is being

used to provide "lift" documentation. Dr. Shortelle

is responsible for the engineering and environmental

monitoring analyses, design, permitting and construction services to accomplish the objectives for the

sites.

Hydraulic and Wetlands Restoration Projects, Serenova Preserve Pond and Associated Wetland

Restoration

Project, SWFWMD, Project Manager - MACTEC is developing the wetland restoration

and FDOT mitigation plans for a pond with associated wetland strands and sloughs at the Serenova

Preserve. Historic modifications

of the pond and drainage of the wetlands have altered site hydrology, and

severely impacted the wetlands. This effort will restore hydraulic functions, wetland functional values,

wildlife habitat restoration, as well as provide mitigation acreage and UWMAM

is being used to provide

"lift" documentation. Dr. Shortelle

is responsible for the engineering and environmental monitoring

analyses, design, permitting and construction services to accomplish the objectives for the sites.

Assessment of Nutrient Management Alternatives, SN Knight North, SJRWMD, FL, Project

Manager - Managing the completion of the data evaluation and review tasks for a series of lab and field

experiments to evaluate the efficacy

of various compounds for possible wide-scale use is a nutrient

management program, to include benthic invertebrate sampling and processing. Field work includes

collection

of water quality data, in situ water quality monitoring and collection of water sample.

Upper Shingle Creek Basin and Western Boggy Creek Basin Water Quality Assessment, Modeling

and Planning, Orange County, FL, Project Manager - MACTEC is developing a nutrient loading and

reduction evaluation for the management and protection

of the Upper Shingle and Western Boggy Creek

Basins. Responsibilities include monitoring and analysis

of significant pollutant inputs in to the surface

and groundwater; revision

of watershed and basin delineations; development of hydrologic and nutrient

budgets; development

of nutrient limitation water quality models; development of alternatives for water

quality improvements.

Seminole Reservation Non-point Source Management Plan, Chief Scientist - MACTEC is revising

the Seminole Reservation Non-point Source Management Plan. This plan includes identifying data gaps,

preparation

of water quality models and comparison to the Tribes Water Quality Code and the Water

Quality Guidelines. Watershed basins and land use were obtained and field verified for use

in the

modeling

of the seven reservations. The water quality models were prepared for each watershed within

the reservation to identify areas

of concern. Recommendations for filling the data gaps within the existing

sampling plan were outlined and new sample points were identified. The list

of recommended BMP's

focused on potential water quality per land use type was revised. The revised Plan focuses specifically on

each area to provide straight forward and cost effective BMP recommendations. Recommendations

in the

Plan also contain ranking BMP projects for implementation, which include cost opinions, schedules, and

community education associated with the BMP.

Seminole Reservation Numeric Nutrient Criteria Development Plan Central and South Florida,

Project

Manager - MACTEC is revising the Seminole Reservation Numeric Nutrient Criteria

Development Plan. Duties include assisting the Tribe with task by analyzing existing and newly collected

Page2of6

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Ann B. Shortelle, PhD

data for trends; utilizing statistical analysis between parameters such as total phosphorus, total nitrogen,

chlorophyll

a, total Suspended Solids, and trophic state index. Criteria will be developed to support each

of the waterbodies' designated use classifications within the respective reservations. Recommendations

will be made to the Tribe

in order to meet the EPA requirements.

Lake Conine Watershed Restoration and Stormwater Treatment Project, Principal - Modeled and

designed and permit the South Lake Conine Watershed Restoration Project on a city-owned, 34 acre,

vacant, lakefront parcel. This project includes design

of a regional stormwater pond, and storm water

treatment train to finish with a polishing wetland before cleaner water is discharged to Lake Conine, an

impaired waterbody with a nutrient TMDL. The design also specifically optimizes nutrient load

reductions to improve water quality

in the lake, and satisfy TMDL load reduction targets. MACTEC will

also provide the City with bidding services, construction services and post construction water quality

monitoring.

Limnological

I

Nutrient Investigations, Neponset Reservoir. Technical Expert - Field monitoring and

statistical analyses to evaluate whether or not phosphorus

in the reservoir sediments are above

background. Additionally, analyses were conducted to evaluate the effects

of metals and other

constituents present

in the sediments on ecological receptors. Analyses included bulk sediment and pore

water sampling,

SEMI

A VS evaluations, sediment toxicity testing, ecological risk assessment,

comparisons to other waterbodies, and nutrient loading modeling.

SFWMD Biscayne Bay Coastal Wetlands

I

Basin Restoration, FL, Project Director - Multiple site

project involving site assessments

of thousands of acres in southeast Florida that are part of the

Comprehensive Everglades Restoration Project land acquisition program. Assessments have been

performed on over

45 sites where recognized environmental concerns were noted. Dr. Shortelle is

currently directing basin wide ecological risk assessments on several parcels formerly used for

agricultural purposes

in order to determine potential impacts of pesticides and metals to aquatic organisms

and birds after the lands are re-flooded. These assessments include consultations with USFWS and

SFWMD personnel to ensure compliance with ESA and NEP

A. Remedial recommendations and remedial

costs are provided to the SFWMD to assist

in the acquisition negotiations and planning.

North Shore Restoration Area Feasibility Study SJRWMD, Lake Apopka, FL, Principal Scientist -

Responsible for technical quality and completeness of the feasibility study evaluating alternatives to

restore the NSRA

of Lake Apopka to functioning wetlands. This project focuses on technologies that may

used to mitigate the adverse impacts associated with organochlorine pesticide residues

in surficial muck

soils necessary to accomplish the restoration

of these wetlands.

Water Quality, Hydraulics, and Aquatic Biology; Pee Dee River Electrical Generating Station,

Santee Cooper,

Project Principal- MACTEC was retained by Santee Cooper to review and research a

number

of environmental topics that were needed to update an environmental assessment for a proposed

power plant located on the tidally influenced Pee Dee River. Responsibilities included surface water

assessment, which specifically dealt with establishing a baseline for surface water and sediment quality,

hydraulic and hydrologic conditions, and aquatic biota conditions. Modeling included the potential for a

dissolved oxygen sag, salinity gradient and new plant influence on the baseline salinity regime, and

mercury fate and transport.

Ocklawaha River Basin and Emeralda Marsh Nutrient Control Studies, SJRWMD, Eureka, Ocala

Areas, FL,

Project Manager - Nutrient control and floc distribution studies (including alternative

treatments for restoration

of wetlands) within Ocklawaha River Basin near Sunnyhill Farms and

Ocklawaha Prairie (wetlands), and

in Emeralda Marsh Conservation Area. Responsible as Contract

Manager and Supervising Limnologist for evaluations

of restoration alternatives, such as restoring natural

wetland hydrology to sites including Ocklawaha Prairie, Sunnyhill Long Farm, Eustis Muck Farm and

in

Emeralda Marsh Conservation Area. Sampling and analyses conducted to evaluate potential impacts to

Trustee species from restoration implementation.

Assessment of Nutrient Management Alternatives, SN Knight North, SJRWMD, FL, Project

Manager - Managing the completion of the data evaluation and review tasks for a series of lab and field

experiments to evaluate the efficacy

of various compounds for possible wide-scale use is a nutrient

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Ann B. Shortelle, PhD

management program, to include benthic invertebrate sampling and processing. Field work includes

collection

of water quality data, in situ water quality monitoring and collection of water sample.

North Shore Restoration Area Feasibility Study SJRWMD, Lake Apopka, FL, Principal Scientist -

Responsible for technical quality and completeness of the feasibility study evaluating alternatives to

restore the NSRA

of Lake Apopka to functioning wetlands. This project focused on technologies that may

used to mitigate the adverse impacts associated with pesticide residues

in surficial muck soils necessary to

accomplish the restoration

of these wetlands.

Expert Witness, Effects of Construction and Dewatering on Protected Wetland Species - Records

review and depositions to support litigation against a remediation contractor and PRP group for avoidable

impacts to protected wetland species in forested riparian wetland setting. Analysis included identification

of alternative mitigation strategies, and resulted in settlement favorable to the client.

SJRWMD, Ecological Risk Assessments, Land Acquisition and Restorations, Project Manager -

Sampling and analyses to evaluate the potential effects of flooding, water impoundment, and other water

regime manipulations associated with proposed restorations at Eustis Muck Farm, Ocklawaha Prairie,

Sunny

hill. Evaluations included potential effects to aquatic receptors such as aquatic macrophytes, fish,

and invertebrates, and effects on protected species.

Lake Tahoe Master Plan for Erosion Control and Storm Water Management, Lake Tahoe Basin,

Nevada, Senior Technical Review -

The Nevada Department of Transportation (NDOT) is proceeding

with the preparation

of storm drainage and erosion control master planning and final design documents

for roadways within the Lake Tahoe Basin that are owned and maintained by NDOT. The goal

of the

project is to identify regional and local erosion control and water conveyance and quality management

measures that will reduce discharge

of sediments and pollutants into Lake Tahoe. Approximately 38

miles

ofNDOT right-of-way within the Lake Tahoe Basin are included in the effort.

Best Management Practices for Residential Canals, Southwest Florida Water Management District,

Project Manager - Conducted an evaluation of hydrological, limnological and engineering parameters

associated with freshwater and estuarine canals to develop BMPs and design alternatives to enhance water

quality and natural wetland systems.

Watershed Fate and Effects of BTEX in Hall's Brook Pond and Wetlands, Woburn, MA, Project

Manager - Performed biodegradation tests on site sediments to determine the extent of natural processes

mitigating the transport and fate

of BTEX from groundwater to surface water in this flow way. Site

investigations included water budget, flow pathway determinations and potential fate

of benzene and

toluene in this drainage system.

Duck Lake and Tributaries Diagnostic Analysis and Remediation of Sewer Line, Robbins AFB,

Georgia, Supervising Limnologist -

Designed and implemented studies to isolate the source and

location

of high levels of fecal coliforms detected in Duck Lake. A sewer line brake was determined to

be discharging into an upstream tributary. Surface flow was diverted around the source until it could be

restored. Monitoring

of the impoundment and tributary were conducted until a recommendation could be

made to reopen the lake.

Impacts of MGP Residues on Aquatic Resources in the Nashua River, NH, Task Manager -

Conducted riverine investigations into the fate and effects of P AHs and metals on aquatic receptors,

including benthic invertebrates, macrophytes, and fish,

in the river. Investigations included hydrologic

discharges

of groundwater through sediments into the surface waters, determination of porewater

chemistries, and population studies.

Watershed Mercury Investigation, PPG Industries, Inc., Lake Charles, LA, Task Manager -

Conducted field sampling of surface water, sediments, and biological samples to evaluate the occurrence

of mercury in these media and identify approved trends or patterns thorough statistical comparisons.

Ecological and Wetlands Assessment in Big Cypress Swamp, Confidential Client, Task Manager-

Managed and evaluated the potential for adverse effects due to chloride exposure to terrestrial and aquatic

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Electronic Filing - Received, Clerk's Office, May 12, 2009

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Ann B. Shortelle, PhD

receptors via multi pathway exposure. Activities included determinations of wetland hydroperiods, and

monitoring to determine the extent

of impacts to wetland species.

Marathon Battery NPL Site, Wetlands Assessment, Vincent, Elkins, and Gould - Evaluated the

selected feasible alternative for the tidal marsh including identification

of expert witnesses, potential for

adverse environmental effects associated with dredging, and the efficiency

of the proposed marsh

revegetation in restoring wetland functional values.

Bench Scale Determination of Chemical Dosages for Eustis Muck Farm Nutrient Removal, Project

Manager, SJRWMD - Conducted laboratory experiments with site water to determine the appropriate

dosage and chemical ratio

of alum to sodium aluminate (for aluminum and buffering capacity) to

accomplish optimum nutrient removal without undue stress to the ecosystem. Testing included dosing

experiments, toxicity testing, and laboratory analyses.

UOP, Inc., NPL Site WetlandslEcological Assessment, East Rutherford, New Jersey, Task Manager

- Conducted an environmental risk assessment at a site involving significant exposure pathways,

including potentially contaminated sediments and biota,

in the Hackensack estuary and wetlands. This

work included jurisdictional boundary determinations, field studies

of floral and faunal impacts, and

ecological modeling

of affected both terrestrial and aquatic estuarine species.

Charles George Landfill Wetlands Assessment, EPA - Conducted field investigation of the fourteen

wetlands at this Superfund site to determine wetland boundaries, extent

of contamination, evaluate

potential adverse effects due to proposed remedial alternatives, and design mitigative measures for the

chosen alternative. Studies included flora, benthic invertebrate, and fish investigations.

Clean Lakes Diagnostic and Feasibility Studies, Various Sites, MA, Project Manager and

Limnologist - Developed workplans, and executed diagnostic/feasibility studies for nutrient impaired

lakes and reservoirs. Determined water budgets and sources and sinks

of nutrients, and developed

feasible alternatives for reductions

in nutrient loadings and/or surface water restoration projects.

Bioaccumulation Modeling and Site Assessment, Rocky Spring Lakes, Chambersburg, PA

Limnologist - Responsible for conducting a study of mercury cycling in aquatic plants, fish, water fowl

and abiotic media to identify and quantify the source

of episodic mercury exposure to aquatic receptors.

This evaluation included sampling and analysis

of spring flows and discharges into the Rocky Spring

watershed surface waters, and subsequent fate to the surface water impoundment.

Ripogenus Dam Relicensing Hearings, Bowater/Great Northern Paper Company, Millinocket, ME,

Expert Witness -

Testified at the ME Land Use Regulation Commission hearings in favor of the

Ripogenus Dam Relicensing plan regarding the mercury cycling issues related to plant operations

of the

impoundment and potential for adverse effects to fish and wildlife. Federal procedures for relicensing,

and additional investigations regarding mercury biogeochemical cycling

in impoundments were also

conducted.

Yaworski NPL Site on Quinebaug River, PRP Committee, Senior Scientist - Responsible for

preparing endangerment assessment review comments. Designed and conducted field investigation

of the

site associated wetlands and Quinebaug River to evaluate the potential for adverse environmental effects

and bioaccumulation

of metals and organic compounds in fish.

TCDDITCDF Risk Assessment Manual, National Council for Air and Stream Improvement

(NCASI) - Managed effort to realistically model dioxin bioaccumulation in fish exposed to contaminated

effluent. The model includes fate and transport

of dioxin in rivers, dynamics of bioaccumulation and fish

physiological and behavioral parameters, and estimation

of risk based on fish consumption. The model

was designed for use by the pulp and paper industry.

Estuarine and Riverine Fate and Transport of HCB and HCBD, PPG, Inc., Task Manager -

Conducting field investigations and modeling to determine the fates of HCB and HCBD in the Calcaseieu

estuary. Responsible for conducting the evaluation

of contaminant body burdens in a wide variety of

organisms to determine bioaccumulation factors and the evaluation of the potential risks to human and

nonhuman receptors.

PageS 0/6

Electronic Filing - Received, Clerk's Office, May 12, 2009

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Ann B. Shortelle, PhD

Expert Technical Comparison of NOAA Documents Relevant to Shortnose Sturgeon, Confidential

Client, Philadelphia, P A, Technical

Expert - Reviewed both an ecological risk assessment and the

shortnose sturgeon recovery plan for consistency, and technical relevance to existing shortnose sturgeon

resources and potential exposure to PCBs, metals, and other chemicals

in sediments from an NPL site in

the Delaware River. Evaluated watershed sources of PCBs and probable uptake scenarios for tissue

residues.

Floreffe Oil Spill Assessment, Kirkpatrick and Lockhart (Representing Ashland Oil Company),

Task Manager - Conducted field investigation and ongoing analyses of the Ohio and Monongahela

Rivers according to Natural Resource Damage Assessment procedures to determine environmental and

human health effects due to the spilling

of No. 2 diesel fuel. Responsible for directing laboratory and field

investigations, including chemical fate and transport and bioaccumulation analysis, to evaluate the

potential for adverse health effects associated with consumption

of fish possibly contaminated with

inorganic and organic substances.

Representative Publications and Presentations Available upon Request.

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Attachment 2

6

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Evaluation

 

of

 

Effects

 

of

 

Revised

 

Thermal

 

Standards

 

on

 

Phospphorus

 

and

 

Mercury

 

Cycling

 

in

 

Coffeen Lake

Prepared

 

for:

Ameren

St.

 

Louis,

 

Missouri

Prepared

 

by:

MAMACCTTEECC

 

EngineeringEngineering

 

andand

 

ConsultingConsulting,

 

IncInc.

3199

 

Riverport Tech

 

Center

 

Drive

Maryland

 

Heights,

 

Missouri

May

 

2009

---

Evaluation of Effects of Revised Thermal

Standards on Phosphorus and Mercury

Cycling in Coffeen Lake

Chief Scientis

t

Prepared for:

Ameren

St. Louis, Missouri

Prepared by:

MACTEC Engineering and Consulting, Inc.

3199

Riverport Tech Center Drive

Maryland Heights, Missouri

6 MACTEC

May 11, 2009

Wi ham Elzinga

Project Manager

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

i

Table of Contents

Section

Page

Executive Summary .............................................................................................................................. ES-1

1.0 Introduction .......................................................................................................................... 1-1

 

1.1  Purpose ...................................................................................................................................... 1-1 

1.2  Report Organization .................................................................................................................. 1-3 

2.0 Internal Phosphorus Loading ............................................................................................. 2-1

 

2.1  Relationship Between Elevated Temperature and Surface Water Phosphorus in Coffeen

Lake ........................................................................................................................................... 2-1 

2.1.1  Seasonal Changes in Phosphorus and Chlorophyll-

a

...................................................... 2-1 

2.1.2  Sediment Phosphorus Adsorption .................................................................................... 2-5 

2.1.3  Impact of External Phosphorus Loading Seasonal Changes in Phosphorus and

Chlorophyll-

a

.................................................................................................................. 2-6 

2.1.4  Internal Loading Assumptions from the TMDL BATHTUB Model ............................... 2-9 

2.1.5  Evaluation of the Spatial Extent of Anoxic Sediment and Water .................................. 2-11 

2.2  Potential Impacts of Increased Thermal Standard for May and October on Internal

Phosphorus Loading ................................................................................................................ 2-22 

2.2.1  Spatial Impacts to Lake Stratification ............................................................................ 2-22 

2.2.2  Potential Increase in Phosphorus Loading ..................................................................... 2-25 

2.2.3  Limitation of Impacts to Epilimnion Water Quality ...................................................... 2-25 

3.0 Mercury Cycling .................................................................................................................. 3-1

 

3.1  Mercury Load and Bioavailability ............................................................................................. 3-4 

3.1.1  Surface Water Data .......................................................................................................... 3-4 

3.1.2  Sediment Data .................................................................................................................. 3-4 

3.1.3  Fish Tissue Data ............................................................................................................... 3-4 

3.2  Additional Parameters Related to Methylation .......................................................................... 3-6 

3.2.1  Dissolved Oxygen ............................................................................................................ 3-8 

3.2.2  Alkalinity ......................................................................................................................... 3-9 

3.2.3  Metals .............................................................................................................................. 3-9 

3.2.4  Iron ................................................................................................................................... 3-9 

3.2.5  Organic Carbon .............................................................................................................. 3-10 

3.2.6  pH .................................................................................................................................. 3-11 

3.2.7  Seasonality and Temperature ......................................................................................... 3-11 

3.3  Summary .................................................................................................................................. 3-12 

4.0 Summary ............................................................................................................................... 4-1

 

4.1  Introduction ............................................................................................................................... 4-1 

4.2  Phosphorus................................................................................................................................. 4-1 

4.3  Mercury ..................................................................................................................................... 4-2 

5.0 References ............................................................................................................................. 5-1

 

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Table of Contents (continued)

List of Tables

Table 2-1.

Sediment Phosphorus Concentrations Between 1989-2002

Table 2-2.

Average Depth (m) Below Which DO Less Than 1 mg/L (anoxia) by Month

Table 2-4.

Area of Substrate Surface Exposed To Seasonal Anoxia (Hectares) under Existing

Conditions

Table 2-5

.

Current and Predicted Days with Anoxic Sediment Conditions

Table 2-6.

Potential Increase in Lake Substrate Surface Area Exposed To Seasonal Anoxia

(Hectares)

Table 3-1.

Average Fish Tissue Mercury Data from Montgomery and Surrounding Counties

Table 3-2

.

Summary of Various Parameters that may Influence Mercury Methylation Rates

List of Figures

Figure 1-1.

Site Location Map – Coffen Lake, Montgomery County, Illinois

Figure 2-1.

Coffeen Lake Phosphorus Comparison Between 1989 and 2008

Figure 2-2.

Coffeen Lake Seasonal Chlorophyll-

a

Concentrations Between 1989-2002

Figure 2-3.

Seasonal Phosphorus Comparison Between Greenville (a) and Coffeen Lake (b)

Figure 2-4.

Seasonal Chlorophyll-

a

Comparison Between Greenville (a) and Coffeen Lake (b)

Figure 2-6.

Total Phosphorus Concentrations at Coffeen Lake by Sampling Site

Figure 2-7.

Chlorophyll-

a

Concentrations at Coffeen Lake by Sampling Site

Figure 2-8.

Coffeen Lake Watershed Land Use and Surface Water Sampling Locations

Figure 2-9.

SIUC Depth Profile Segments for Coffeen Lake

Figure 2-10.

Coffeen Lake Anoxic Sediment Zone - May

Figure 2-11.

Coffeen Lake Anoxic Sediment Zone - June

Figure 2-12.

Coffeen Lake Anoxic Sediment Zone - July

Figure 2-13.

Coffeen Lake Anoxic Sediment Zone - August

Figure 2-14.

Coffeen Lake Anoxic Sediment Zone - September

Figure 2-15.

Coffeen Lake Anoxic Sediment Zone - October

Figure 2-16.

Coffeen Lake Cross Section Locations

Figure 2-17.

Cross-Section of Lake Bottom, Average Anoxic Water Depth, and Oxygenated Surface

Water Depth for Segments 1 and 2, May and October

Figure 2-18.

Coffeen Lake Anoxic Sediment Zone Under New Permit Conditions - May

Figure 2-19.

Coffeen Lake Anoxic Sediment Zone Under New Permit Conditions - October

Figure 2-20.

Incremental Loading Differences to Estimated Current Phosphorus Loads

Figure 3-1.

Major Transformations of Mercury in the Environment

Figure 3-2.

Illinois Largemouth Bass Mercury Concentrations

Electronic Filing - Received, Clerk's Office, May 12, 2009

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Coffeen Lake

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MACTEC Engineering and Consulting, Inc.

May 2009

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Executive Summary

MACTEC Engineering and Consulting, Inc., (MACTEC) evaluated potential for impacts on phosphorus

and mercury cycling from proposed modifications to current site-specific thermal standards in Coffeen

Lake in support that raising the thermal limits for the months of May and October will not result in

significant increases in phosphorus loading or mercury methylation over current lake conditions.

Illinois EPA claimed that Ameren failed to address the impact of the proposed thermal limits on total

phosphorus and mercury levels in Coffeen Lake, in addition to failing to address the impact on Lake

Habitat. Illinois EPA stated a concern that higher temperatures of Coffeen Lake in May and October may

result in prolonged stratification which can increase phosphorus levels and methylmercury levels.

Phosphorus is a limiting nutrient in Coffeen Lake and is therefore an important component of its long-

term water quality. Internal phosphorus release from sediments can serve as an additional source of

phosphorus loading to the lake, yet is ultimately dependent on a number of chemical and physical factors

which occur at the sediment-water interface. The mere presence of thermal stratification does not indicate

that significant internal loading will occur as a result. Despite the potential for seasonal sediment

phosphorus release from the sediments, water quality measurements within Coffeen Lake indicate that

internal phosphorus recycling is currently not contributing appreciable amounts of total phosphorus to

epilimnetic surface water. Oxygenated hypolimnetic water and epilimnetic waters (DO> 1 mg/L) were

always present overlying these deeper anoxic layers as shown by cross section for May and October. The

data and this analysis clearly show that there is no “dead zone” within the lake.

TMDL assessments for Coffeen Lake attribute elevated phosphorus concentrations to external watershed

loading, primarily due to expansive agriculture surrounding the lake. External loading as a driver of water

quality is also apparent in high phosphorus concentrations measured in the shallow northern portions of

the lake. Additionally, seasonal water quality comparisons do not show elevated phosphorus or

chlorophyll-a concentrations during summer stratification of the water column, indicating that phosphorus

is either not being released in large volumes from the sediment or is not being mixed into the epilimnion

where it may be available for algae production.

Review of the original TMDL BATHTUB (2007) model revealed significant modeling errors and

misapplications which led to the erroneous conclusion that internal phosphorus loading dominates

Coffeen Lake. These errors produced a model run which did not match known lake phosphorus

concentrations. To compensate for this “under-prediction of observed phosphorus concentrations”, the

modelers introduced an additional internal phosphorus load (the BATHTUB model already incorporates

internal loading) to force the model to calibrate. The conclusions and load reduction requirements of the

original TMDL were not revised, despite these errors and discrepancies. However, available monitoring

data do not confirm this estimated level of internal loading (see Section 2.1.1).

An evaluation of potential impacts associated with modified thermal discharge during the months of May

and October was also performed to quantify the potential for additional phosphorus release and

Electronic Filing - Received, Clerk's Office, May 12, 2009

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May 2009

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anticipated impacts to surface water quality. Results of this analysis indicate that the additional

phosphorus load which may be anticipated from the proposed modification ranges from 329.1 kg P/year

to 658.1 kg P/yr under existing permit conditions, which is much lower than predicted from the

BATHTUB modeling completed for the TMDL. Additionally, any phosphorus released from the

sediment is not expected to reach the epilimnion, and is therefore unavailable for biological production

within Coffeen Lake. Based on seasonal water quality comparisons sediment phosphorus release does not

appear to be an important component of surface water phosphorus loading within Coffeen Lake. Future

modifications to thermal discharge limits from the Ameren Power Generating Plant are unlikely to present

additional phosphorus loads from sediment release in the future, and therefore are not a threat to the

existing water quality of Coffeen Lake.

Mercury readily bioaccumulates in living tissues, and thus, fish consumption advisories are common

nationwide. Coffeen Lake is currently included in the Illinois fish consumption advisories based on two

fish tissue samples with mercury concentrations exceeding the Illinois EPA level of concern of 0.06

mg/kg. These samples consist of two composite (5 fish per composite) samples of largemouth bass filet

with concentrations of 0.08 and 0.09 mg/kg of mercury. Because largemouth bass are a top aquatic

predator in the lake, although the sample size is small, the results are conservative for the lake. Illinois

EPA’s concern for Coffeen Lake is that mercury methylation is likely based on thermal stratification

throughout the summer months.

Methylation is affected by multiple parameters and cannot be based solely on thermal stratification. There

are multiple indicator parameters that may predict whether the methylation of mercury is favorable under

certain conditions. While general trends may be observed as these indicator parameters increase or

decrease, the suite of parameters should be evaluated as a whole to predict the potential for methylation of

mercury.

Based on the available Coffeen Lake data, mercury concentrations appear to be generally low and

conditions do not appear to be favorable for methylation. Current sources of methylation may be within

the lake or occurring in the watershed, but appear low. The proposed change in the thermal standard

affecting May and October conditions does not substantially change lake conditions, although thermal

stratification may persist for more days on average, annually. This change is minor, and does not

represent a change that could or would significantly increase hypolimnetic mercury methylation rates. It

is anticipated that the change, if any, would be so small, that it would not result in increased mercury in

the biota. Fish tissue concentrations are anticipated to measurably decline, however, as a result of regional

mercury load reductions.

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1.0 Introduction

1.1

Purpose

This report provides an evaluation of the potential for impacts on phosphorus and mercury cycling from

proposed modifications to current site-specific thermal standards in Coffeen Lake. Coffeen Lake is a

384 hectare reservoir constructed as the source for steam condenser cooling water for the 945-MW

Coffeen Power Station (Coffeen or the "Station"), located in Montgomery County in central Illinois,

approximately 1 mile south of the city of Coffeen, Illinois and 50 miles northeast of St. Louis, Missouri

(Figure 1-1).

Current thermal standards for Coffeen Lake specify that the months of May and October fall within an

8-month “winter” period extending from October through May. During this 8-month period, thermal

discharges from Coffeen Power Station may not result in water temperatures that exceed:

?

89

o

F as a monthly average, or

?

94

o

F as a maximum for greater than 2 percent of the hours during that period, as measured at the

boundary of a 26-acre mixing zone.

Abnormally warm temperatures and low precipitation in recent years have resulted in instances,

particularly during late May and early October, when Coffeen Power Station has had to reduce electric

generation (derate) in order to comply with the above thermal standards. The existing limits of 89

o

F and

94

o

F were not established on the basis of definitive thermal requirements for the aquatic community and

fish populations of Coffeen Lake during these two months. Rather, they were set as assurance that thermal

limits set for the “summer” months of June through September (105

o

F mean or 112

o

F maximum for

greater than 3 percent of the hours) were not applied year-round.

The petitioner, Ameren Energy Generating Company (Ameren), proposed relief in the form of the

following revised standards for the months of May and October:

?

96

o

F as a monthly average, and

?

102

o

F as a maximum for more than 2 percent of the hours during that period.

The Illinois Environmental Protection Agency (EPA) denied the proposed revised standards in April

2009. Specifically, the Illinois EPA claimed that Ameren failed to address the impact of the proposed

thermal limits on total phosphorus and mercury levels in Coffeen Lake, in addition to failing to address

the impact on Lake Habitat. The Illinois EPA stated a concern that higher temperatures of Coffeen Lake

in May and October may result in prolonged stratification which can increase phosphorus levels and

methylmercury levels.

This report presents an evaluation of the conditions in Coffeen Lake with regard to phosphorus and

mercury supporting the conclusion that raising the thermal limits for the months of May and October will

not result in significant increases in phosphorus loading or mercury methylation over current lake

conditions.

Electronic Filing - Received, Clerk's Office, May 12, 2009

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Coffeen Lake

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MACTEC Engineering and Consulting, Inc.

May 2009

1-2

Fi gure 1.1: Site

I

L<~'""

Map.

Coffen Lake,

Montgomery County

, Illinois

I MilltS

0

2.5

5

e

IlIln o l $

0

Area of

/

Interest

t

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Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

1-3

1.2

Report Organization

In this report, the effects of phosphorus and mercury cycling of Coffeen Lake are evaluated. MACTEC

evaluated temperature and lake chemistry data collected during the SIUC and Illinois EPA studies to

evaluate the thermal environment of Coffeen Lake, specifically examining the stratification and anoxic

conditions of the lake. A general description of the thermal environment in the lake is explained in

Section 2.

MACTEC evaluated the phosphorus loading of the lake and the potential impacts of revised thermal

standards on phosphorus cycling as further explained in Section 2. Phosphorus is a limiting nutrient in

Coffeen Lake and has been evaluated by the Illinois EPA to ensure the lake meets its designated use

under the Total Maximum Daily Load (TMDL) determination (Illinois EPA, 2007; Illinois EPA, 2009a).

MACTEC evaluated the potential for increased internal loading of phosphorus as a result of increasing

water temperatures.

In Section 3, MACTEC evaluated methylmercury loading of the lake and the potential impacts of the

revised thermal standards on mercury cycling. Increased internal loading of mercury could result from

anoxic conditions. MACTEC evaluated the potential for increased internal loading of mercury as a result

of increasing water temperatures resulting in anoxic conditions.

Finally, Section 4 summarizes and integrates the multiple lines of investigation presented in the previous

sections in order to characterize the actual risk for adverse impact occurring from revisions to the thermal

standards for May and October.

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2.0 Internal Phosphorus Loading

Coffeen Lake was determined to be impaired due to excessive algal growth caused by excess phosphorus.

It has been evaluated by the Illinois EPA to ensure the lake meets its designated use by development of a

Total Maximum Daily Load (TMDL) (Illinois EPA, 2007; Illinois EPA, 2009a). To protect water quality

and provide the designated “aesthetic quality” established for the lake, the Illinois EPA has set a water

quality standard of 0.05 mg P/L as the TMDL endpoint. Concerns regarding degradation of water quality

and trophic status which may result from modification to the existing thermal limits are largely based on

internal cycling processes of phosphorus within Coffeen Lake. The Illinois EPA contends that increasing

water temperatures within the lake will result in enhanced phosphorus release from the sediments into the

water column, thereby providing an additional phosphorus load within the Lake.

2.1

Relationship Between Elevated Temperature and Surface Water Phosphorus in

Coffeen Lake

Seasonal temperature differences in productive (eutrophic) freshwater lakes and reservoirs often lead to

seasonal thermal stratification within the water column, resulting in the development of an epilimnion

(surface water) and hypolimnion (bottom water) which are separated by temperate and density gradients

which prevent mixing within the water column. The mere presence of thermal stratification does not

indicate that significant internal loading will occur as a result. Thermal stratification without anoxia

produces no more phosphorus release from sediments than an unstratified lake. Seasonal stratification can

also result in anoxic conditions in the lower portions of the hypolimnion, a condition which is generally

recognized as promoting dissolution and subsequent release of sediment-bound phosphorus, where

sediment phosphorus is loosely bound. Thermal stratification with anoxia present over a portion of the

bottom, may result in some phosphorus release from the sediments into the hypolimnion, but in

insufficient quantities to actually reach the epilimnion and fuel algal blooms. Although anoxia within the

hypolimnion has the potential to release sediment phosphorus to the water column, water quality

measurements within Coffeen Lake indicate that internal phosphorus recycling is currently not

contributing appreciable amounts of total phosphorus to epilimnetic surface water. The following analysis

also shows that the incremental difference in phosphorus that may result from the revised thermal

standard for May and October will not result in measureable adverse impact to the lake.

2.1.1 Seasonal Changes in Phosphorus and Chlorophyll-

a

Surface water temperature measurements in Coffeen Lake reveal that different segments of the lake

display seasonal stratification for a period of days to months during the months between May and October

(see Section 2.2.1). In its April 2009 Recommendation, the Illinois EPA states that “the amount of

phosphorus released from the sediments is directly related to the period of anoxia during stratification.”

Although seasonal changes in oxygen concentrations can alter the short-term uptake and release of

phosphorus from the sediments, oxygen availability at the sediment-water interface cannot control the

long-term P retention of lake sediments (Hupfer and Lewandowski, 2008), or determine the net effect of

any release on the lake. Numerous physical and chemical processes within the sediment and overlying

water column will determine the exchange capacity of phosphorus from the sediment to surface waters

such that the relationship between anoxia and sediment phosphorus release cannot be universally applied

Electronic Filing - Received, Clerk's Office, May 12, 2009

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to all lakes under varying conditions. In Coffeen Lake, phosphorus release from the sediment is modest,

and does not affect the epilimnion (see discussion below).

An evaluation of seasonal phosphorus concentrations during the warmest portion of the year (April-

October) was performed using data from the 2009 Coffeen Lake TMDL Addendum (Illinois EPA, 2009a)

as well as data used in the 2007 TMDL (Illinois EPA, 2007), which was obtained from the United States

Environmental Protection Agency (USEPA) STORET database (Illinois EPA, 2009b). No statistically

significant trends were observed for water column phosphorus concentrations within Coffeen Lake during

summer months (Figure 2-1). Additionally, chlorophyll-

a

may be used as a surrogate or response analysis

for increased phosphorus loading due to increased biological production that would result from excess

sediment phosphorus release if this phosphorus reached the epilimnion during destratification at fall

turnover. A similar comparison of chlorophyll-

a

concentrations between 1989-2002 (Figure 2-2) show no

significant increase in chlorophyll-

a

concentrations during and following turnover. The lack of a seasonal

component to phosphorus concentrations in Coffeen Lake, and the absence of a chlorophyll-

a

spike or

algal blooms at fall turnover are both strong evidence that internal phosphorus recycling is not currently a

significant contribution of the total lake phosphorus budget. Fluctuations in either phosphorus or

chlorophyll-

a

concentrations during fall turnover at Coffeen Lake would indicate that internal sediment

phosphorus release is a controlling process in seasonal nutrient concentrations within lake surface waters.

However, neither total phosphorus or chlorophyll-

a

reveal correlated trends with warmer surface water

temperatures within the lake. The lack of correlating water quality responses following seasonal

stratification and hypolimnion anoxia suggests that other phosphorus loading factors, including external

phosphorus loading from the surrounding watershed (Section 2.1.3), are more important factors in water

quality within Coffeen Lake.

By comparison, Greenville Lake, which was also evaluated under the 2007 TMDL (Illinois EPA, 2007),

shows distinct differences in seasonal phosphorus (Figure 2-3) and chlorophyll-

a

(Figure 2-4)

concentrations resulting from sediment phosphorus release to the water column during fall turnover.

Phosphorus in Greenville Lake shows peak concentrations occurring in the fall, with increasing

phosphorus loads entering surface waters towards the end of the summer. Chlorophyll-

a

concentrations in

Greenville Lake show a similar pattern of increasing concentrations in the late fall, and this seasonal

pattern is typical for a lake or reservoir where internal phosphorus loading is a significant portion of the

loading. Neither phosphorus or chlorophyll-

a

in Coffeen Lake show similar patterns of increasing

concentrations in late summer into fall, indicating that any potential sediment phosphorus release is not

mixing into the epilimnion where it would be available for algae production.

While thermal stratification and some deep water anoxia in the hypolimnion does appear to occur on a

seasonal basis within Coffeen Lake (Section 2.2.1), the lack of phosphorus and chlorophyll-

a

pulse during

fall overturn suggest that that a majority of the sediment phosphorus remains bound in sediments or that

whatever phosphorus is released in not reaching the epilimnion in sufficient quantities to degrade water

quality (see further discussion in Section 2.1.4).

Electronic Filing - Received, Clerk's Office, May 12, 2009

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MACTEC Engineering and Consulting, Inc.

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Figure 2-1.

Coffeen Lake Phosphorus Comparison Between 1989 and 2008

(Data Source: Illinois EPA, 2009a; Illinois EPA, 2009b).

Created by: DRD Checked by: BMJ 5/5/2009

Figure 2-2.

Coffeen Lake Seasonal Chlorophyll-

a

Concentrations Between 1989-2002

(Source: Illinois EPA, 2007)

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MACTEC Engineering and Consulting, Inc.

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Figure 2-3.

Seasonal Phosphorus Comparison Between Greenville Lake (a) and Coffeen Lake (b)

(Source: Illinois EPA, 2007)

a - Greenville Lake

b - Coffeen Lake

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MACTEC Engineering and Consulting, Inc.

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Figure 2-4.

Seasonal Chlorophyll-

a

Comparison Between Greenville Lake (a) and Coffeen Lake (b)

(Source: Illinois EPA, 2007)

2.1.2

Sediment Phosphorus Adsorption

Inorganic phosphorus is highly particle reactive and will vary in its sorption and exchange capacities with

different physical and chemical sediment characteristics, including iron, aluminum, and organic matter

content (Detenbeck and Brezonik, 1991). Speciation of phosphorus into saloid-bound (NH

4

Cl-P

i

), iron-

bound (NaOH-P

i

), and aluminum-bound (NH

4

F-P

i

) phosphorus (Chang and Jackson, 1957) is often

characterized to evaluate the proportion of phosphorus which may be released into the water column

under changing environmental conditions at the sediment-water interface. Saloid-bound phosphorus

a - Greenville Lake

b - Coffeen Lake

Electronic Filing - Received, Clerk's Office, May 12, 2009

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Coffeen Lake

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represents the portion of phosphorus which is highly soluble and is therefore considered readily available

for release from the sediments into the water column. Iron-bound phosphorus, however, is generally

considered stable under oxidizing conditions in the sediment, but becomes unstable under anoxic

(reducing) conditions, allowing the iron-bound phosphorus to separate from the sediment for release into

the water column. Phosphorus bound by aluminum in the sediments is considered inert under both

oxidizing and reducing conditions, and is therefore considered unavailable for release back into the water

column.

An analysis of total phosphorus concentrations in Coffeen Lake sediments indicate large variations

between sampling locations and annual sampling events, with an overall mean concentration of

769 mg/kg and a standard deviation of 268 mg/kg (Table 2-1). While no phosphorus speciation data exists

for Coffeen Lake sediments, available iron concentrations (Table 2-1) were determined to have no

correlation to total phosphorus sediment concentrations within the eight individual samples (R

2

=0.328).

Although a portion of available phosphorus within the sediments is likely iron-bound, the lack of

increased surface water phosphorus concentrations suggest that other phosphorus species may remain

permanently bound to sediments despite enhanced redox potential associated with bottom water anoxia.

Table 2-1.

Sediment Phosphorus Concentrations Between 1989-2002

Monitoring

Location

Date Sampled

Iron (mg/kg)

Phosphorus (mg/kg)

ROG-1

4/27/1989

26,500

297

ROG-1

7/8/1993

40,000

1,034

ROG-1

7/1/1997

30,000

1,156

ROG-1

7/22/2002

24,000

814

ROG-3

4/27/1989

23,500

648

ROG-3

7/8/1993

30,000

842

ROG-3

7/1/1997

24,000

780

ROG-3

7/22/2002

17,000

577

Mean Concentration (mg/kg)

26,875

769

(Data Source: Illinois EPA, 2009b).

Created by: BMJ Checked by: KAR 5/5/2009

2.1.3

Impact of External Phosphorus Loading Seasonal Changes in Phosphorus and

Chlorophyll-

a

Segmentation of Coffeen Lake for sampling and analysis in the 2007 TMDL (Illinois EPA, 2007)

provided a comparative assessment of deep and shallow portions of the lake, as well as a comparison of

regional watershed characteristics which contribute to the total phosphorus load within the Lake. Sample

locations ROG-1 and ROG-2 (Figure 2-5) were taken closest to the Coffeen Power Generating Station,

and are representative of the deeper locations within the Coffeen reservoir. Sample location ROG-3 is the

northernmost sampling location, and represents the shallowest portion of Coffeen Lake monitored during

both the 2007 (Illinois EPA, 2007) and 2009 (Illinois EPA, 2009a) TMDL evaluations.

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Figure 2-5.

Illinois EPA Sampling Locations at Coffeen Lake

(Source: Illinois EPA, 2007)

Phosphorus concentrations by sampling location (Figure 2-6) were taken from the Illinois EPA TMDL

assessment for Coffeen Lake (Illinois EPA, 2007). Mean phosphorus concentrations at ROG-3 are

elevated compared to ROG-1 and ROG-2, with a greater maximum range of phosphorus concentrations

sampled. Similarly, Chlorophyll-

a

results (Figure 2-7) show greater mean concentrations at ROG-3 than

the other sampling locations. These data confirm that external loading (from the tributary and watershed)

rather than internal loading are dominant in this reservoir. Further, the shallow depth of this upper region

of the reservoir has been caused by sedimentation, another indicator of the extent to which the watershed

is contributing to the eutrophication and impairment of the lake. Elevated phosphorus and chlorophyll-

a

concentrations at shallow portions of the lake indicate that external loading is the dominant factor in

Coffeen Lake phosphorus concentrations. The Coffeen Lake watershed is largely dominated by

agricultural land use, which accounts for 66.5% of the total watershed area (Illinois EPA, 2007). The

2007 TMDL report (Illinois EPA, 2007) recognizes row crop agriculture as a common source of sediment

and nutrient loads which are prevalent within the Coffeen Lake watershed. Water quality modeling used

in the 2009 Coffeen Lake TMDL addendum (Illinois EPA, 2009a) also attributes elevated phosphorus

concentrations to the dominant agricultural land use found in the watershed. Fertilizers commonly used

within the watershed include anhydrous ammonia, ammonium phosphate, and potash, which are

frequently applied in the fall and spring (Illinois EPA, 2007).

ROG-3 is located in the northernmost portion of Coffeen Lake, where a majority of runoff from

agricultural operations to the north enter the lake (Figure 2-8). The high range of phosphorus

concentrations recorded at this site (Figure 2-6) suggest that period runoff entering the lake, particularly

in the shallower northern portions, is controlling the total available phosphorus load for algae production

in surface waters. Sediment phosphorus release is unlikely to contribute to the total phosphorus load at

ROG-3 due to infrequent occurrences of anoxia in shallow bottom waters (Section 2.2.1), leaving external

phosphorus loads as the primary mechanism for phosphorus loading and water quality within Coffeen

Lake.

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May 2009

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Figure 2-6.

Total Phosphorus Concentrations at Coffeen Lake by Sampling Site

(Source: Illinois EPA, 2007)

Figure 2-7.

Chlorophyll-

a

Concentrations at Coffeen Lake by Sampling Site

(Source: Illinois EPA, 2007)

Electronic Filing - Received, Clerk's Office, May 12, 2009

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Figure 2-8.

Coffeen Lake Watershed Land Use and Surface Water Sampling Locations

(Source: Illinois EPA, 2007)

2.1.4

Internal Loading Assumptions from the TMDL BATHTUB Model

The available phosphorus and chlorophyll-

a

data for Coffeen Lake are indicative of a eutrophic

waterbody with high external (watershed) phosphorus loading. There is no observable effect from internal

phosphorus loading. This contradicts the TMDL BATHTUB model results (Illinois EPA, 2007, Illinois

EPA, 2009a). Review of the original (2007) model revealed significant modeling errors and

misapplications which led to the erroneous conclusion that internal phosphorus loading dominates

Coffeen Lake. A non-exhaustive list of errors includes (but is not limited to):

?

Use of the approximate maximum depth instead of the mean depth, resulting in a gross overestimate

of the lake volume and phosphorus mass,

?

Approximately a four fold increase in hydraulic retention time over either the Stage 1 or TMDL

addendum assumptions,

?

Underestimate of tributary (watershed) phosphorus concentrations.

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These errors produced a model run which did not match known lake phosphorus concentrations. To

compensate for this “under-prediction of observed phosphorus concentrations”, the modelers introduced

an additional internal phosphorus load (the BATHTUB model already incorporates internal loading) to

force the model to calibrate.

The BATHTUB model was produced by the United States Army Corp of Engineers. The guidance for

this model explicitly states (USACE, 2004):

Internal Loading Rates reflect nutrient recycling from bottom sediments. Rates are normally set to

0, since the pre-calibrated nutrient retention models already account for nutrient recycling that

would normally occur (at least in the collection of reservoirs used for model calibration).

Nonzero values should be specified with caution and only if independent estimates or

measurements are available.

In some studies, internal loading rates have been estimated from measured phosphorus

accumulation in the hypolimnion during the stratified period. This procedure should not be

followed unless there is evidence the accumulated phosphorus is transported to the mixed layer

during the growing season.

Specification of a fixed internal loading rate may be unrealistic for evaluating response to

changes in external load. Because they reflect recycling of phosphorus that originally entered the

reservoir from the watershed, internal loading rates would be expected to vary with external load.

This option is included at the request of model users but is not endorsed by the author. In

situations where monitoring data indicate relatively high internal recycling rates to the mixed

layer during the growing season, a preferred approach would generally be to calibrate the

phosphorus sedimentation rate (specify calibration factors< 1). There is some risk that apparent

internal loads actually reflect under-estimation of external loads (USACE, 2004).

The forcing of this model through the use of an internal loading factor, as noted above, is not

recommended or endorsed by the model developers, and may lead to erroneous conclusions about the

phosphorus sources in the waterbody. In this case, the model produced the following estimate of

phosphorus mass sources for Coffeen Lake:

External sources of phosphorus (watershed, precipitation, point sources) (kg/yr):

329.7

Internal phosphorus load (kg/yr):

3,495.8

Total phosphorus load (kg/yr):

3,825.2

Many of the above errors were eliminated in the BATHTUB modeling conducted for the TMDL

addendum, however, this model was assembled in a simpler framework. Based upon discussion with the

modelers, the updated model was kept consistent with the original modeling where possible, except for

the correction of significant errors. The update did include additional data for watershed loading and

Electronic Filing - Received, Clerk's Office, May 12, 2009

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-11

water budget information that led to model improvements, but lake morphometry was not updated.

Sediment transport to the lake from the watershed has reduced the effective lake volume, and this factor,

for example, was not addressed in the modeling. Reduction in lake volume would have resulted in better

agreement between predicted and observed values of phosphorus concentration in the lake without the use

of a “correction factor”. The baseline case for the TMDL addendum modeling estimated 9054.8 kg P/yr

total phosphorus loading, with the majority of this attributable to McDavid Branch (an inflowing tributary

from the watershed). However, an internal loading factor was still applied, and resulted in an estimate of

approximately 39% internal loading. The conclusions and load reduction requirements of the original

TMDL were not revised, despite these errors and discrepancies. However, available monitoring data do

not confirm this estimated level of internal loading (see Section 2.1.1).

2.1.5

Evaluation of the Spatial Extent of Anoxic Sediment and Water

Historic surface water depth profiles of temperature and dissolved oxygen were evaluated from the

Southern Illinois University at Carbondale (SIUC) annual monitoring reports (SIUC, 2006 ; SIUC, 2007,

etc.). Depth profiles used in this analysis were collected between 2001 and 2006; however no data were

available from 2002. Four segments were identified by SIUC for Coffeen Lake Depth profiles

(Figure 2-9). Nearly all depth profiles collected at segments one and two, which represent the deepest

portions of the lake, displayed thermal stratification between the months of May-September. Thermal

stratification of surface water at segments three and four were less consistent during the warm summer

months, showing less frequent stratification and periodic mixing in shallower portions of the lake.

Although stratification is frequently present, the presence of a thermocline and hypolimnion does not

indicate anoxia (DO < 1mg/L) at the surface of the sediments or in the deeper hypolimnetic waters.

Anoxic conditions, if and when they form, develop more slowly, over time, compared to thermal

stratification.

Figure 2-9.

SIUC Depth Profile Segments for Coffeen Lake

(Source: SIUC, 2007)

Electronic Filing - Received, Clerk's Office, May 12, 2009

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Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-12

In order to determine the depth within each segment of Coffee Lake which experiences seasonal

stratification and anoxia, all vertical profiles provided by SIUC (2007, and others) between 2001 and

2006 were visually analyzed to record the total depth to bottom, depth to the thermocline, if present, and

the depth to anoxic conditions (defined as a dissolved oxygen concentration <1 mg/L). The total depth in

which anoxic conditions were present was calculated by subtracting the depth to anoxia from the depth to

bottom of the lake. Each segment was then separated by month and year to determine an average depth

below which anoxic conditions were observed within the recorded depth profiles. Once an average depth

had been determined by segment for each month and year, a final average of the depth to anoxic

conditions was calculated for each segment between 2001 and 2006 (Table 2-2).

Table 2-2.

Average Depth (m) Below Which DO Less Than 1 mg/L (Anoxia) by Month

MAY

JUN

JUL

AUG

SEP

OCT

Segment 1

8.19

4.97

5.72

5.73

6.33

7.00

Segment 2

9.07

8.31

7.36

7.69

8.07

10.50

Segment 3

7.17

6.58

5.67

5.92

7.25

--

Segment 4

--

6.67

6.33

6.17

7.75

--

-- No anoxia observed within the segment between 2001 and 2006

(Data Source: SIUC, 2007)

Created by: KAR Checked by: BMJ 5/5/2009

The presence and extent of seasonal anoxia within Coffeen Lake due to stratification of the water column

during summer months was also evaluated. Similar to the procedure used to determine the mean depth of

anoxic conditions (Table 2-2), the total number of days during which anoxic conditions were observed

was also determined for each segment and month between 2001 and 2006. The date at which vertical

depth profiles were measured by SIUC (2007, and others) was compared to the dissolved oxygen profiles

to determine the total length of time within each month that anoxic conditions at the sediment water

interface, and the depth of oxygen depleted hypolimnetic waters, were observed. A conservative estimate

of the total length of time anoxia was observed was made between sample events. Each segment was then

separated by month and year to determine an average number of days per month for which anoxic

conditions were observed. Once an average number of days had been determined by segment for each

month and year, a final average of the number of days anoxic conditions were observed was calculated for

each segment between 2001 and 2006 (Table 2-3).

Similar to monthly patterns of thermal stratification, anoxic bottom waters are most frequently observed

during July and August in segments one and two, with decreasing frequency resulting from increased

mixing during the months of May, June, and September (Table 2-3). Less frequent hypolimnion anoxia

was observed in segments three and four, which frequently mix and rarely remain stratified for all

summer months.

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-13

Table 2-3.

Summary of Average Monthly Anoxic Days (Percentage of the Month)

MAY

JUN

JUL

AUG

SEP

OCT

Segment 1

18 (58%)

23 (77%)

31 (100%)

31 (100%)

26 (84%)

1 (3%)

Segment 2

17 (55%)

25 (83%)

31 (100%)

31 (100%)

21 (68%)

1 (3%)

Segment 3

9 (29%)

4 (13%)

5 (16%)

4 (13%)

1 (3%)

0 (0%)

Segment 4

0 (0%)

8 (27%)

4 (13%)

4 (13%)

1 (3%)

0 (0%)

(Data Source: SIUC, 2007, and others)

Created by: BMJ Checked by: KR5/6/2009

The depth to anoxic water (Table 2-2) was used to estimate the area of potential internal phosphorus

loading. Depths in each segment were analyzed spatially (GIS) by applying the depth intervals to existing

bathymetry for the lake (Illinois DNR, 2006). Figures 2-10 through 2-15 depict the areas of anoxic

sediment and deep hypolimnetic waters for existing conditions (May through October). Oxygenated

hypolimnetic water and epilimnetic waters (DO> 1 mg/L) were always present overlying these deeper

anoxic layers as shown by cross section for May and October (Figures 2-16 and 2-17). The data and this

analysis clearly show that there is no “dead zone” within the lake. Anoxic conditions were not present in

other areas, as estimated from the available data. Existing conditions within Coffeen Lake show that the

greatest spatial area exposed to anoxic conditions is found in the deepest portions of the lake at

segments 1 and 2 (Table 2-4). The spatial extent of seasonal anoxia is greatest during the months of July

and August when temperatures are warmest, the same period of time in which segments one and two

exhibit continual stratification and anoxia (Table 2-3).

Table 2-4.

Area of Substrate Surface Exposed To Seasonal Anoxia (Hectares) under Existing Conditions

MAY

JUN

JUL

AUG

SEP

OCT

Segment 1

25.3

41.8

38.2

38.2

29.7

28.1

Segment 2

72.7

77.2

83.4

81.0

78.6

52.3

Segment 3

6.4

6.8

9.6

8.9

6.3

0.0

Segment 4

0.0

13.3

14.0

14.3

11.3

0.0

(Data Source: SIUC, 2007, and others)

Created by: CGS Checked by: BMJ 5/7/2009

Using these areas and representative flux rates (Haggard

et al

, 2005; Illinois EPA, 2009a) estimates of

phosphorus flux into the hypolimnion were made. This estimate ranges from 329.1 kg P/year to 658.1 kg

P/yr under existing permit conditions. This estimate is much lower than predicted from the BATHTUB

modeling completed for the TMDL, but is consistent with available site data.

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-14

-

,,: ,i ~T-'-_

"

.

-

--I

/

-

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\

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,

,

.,

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,

f

2-10:Coffeen Lake

Anoxic Sediment

Zone -

May

Legend

-

Segment Boundary

10 It Contour

•

Aerobic Sediment

•

Anoxic Sedimen

t

"

0,

25

Created by: CGS

Checked by: WJE

Appmv&d by: ASS

May 5, 2009

I

Mles

"'

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-15

-

,,: ,i ~T-'-_

"

.

-

--I

/

-

\'

\

,

,

,

.,

,

,

f

2-11 :Coffeen Lake

Ano xic Sedi

ment

Zone - June

Legend

-

Segment Boundary

10 It Contour

•

Aerobic Sediment

•

Anoxic Sediment

"

0,

25

Created by: CGS

Checked by: WJE

Appmv&d by: ASS

May 5

, 2009

I

Mles

"'

Electronic Filing - Received, Clerk's Office, May 12, 2009

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-16

-

,,: ,i ~T-'-"'.

-

--I

/

-

\'

\

,

,

,

.,

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f

2-12:Coffeen Lake

Ano xic Sediment

Zone - J uly

Legend

-

Segment Boundary

10 It Contour

•

Aerobic Sediment

•

Anoxic Sediment

"

0,

25

Created by: CGS

Checked by: WJE

Appmv&d by: ASS

May 5, 2009

I Mles

"'

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-17

-

,,: ,i ~T-'-_

"

.

-

--I

/

-

\'

\

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,

,

.,

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2-13:Coffeen Lake

Ano xic Sediment

Zone - August

Legend

-

Segment Boundary

10 It Contour

•

Aerobic Sediment

•

Anoxic Sediment

"

0,

25

Created by: CGS

Checked by: WJE

Appmv&d by: ASS

May 5

, 2009

I Mles

"'

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-18

-

,,: ,i ~T-'-_

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.

-

--I

/

-

\'

\

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,

,

.,

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2-14:Coffeen Lake

Anoxic Sediment

Zone - September

Legend

-

Segment Boundary

10 It Contour

•

Aerobic Sediment

•

Anoxic Sedimen

t

"

0,

25

Created by: CGS

Checked by: WJE

Appmv&d by: ASS

May 5

, 2009

I Mles

"'

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-19

-

,,: ,i ~T-'-_

"

.

-

--I

/

-

\'

\

,

,

,

.,

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,

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2-1S:Coffeen Lake

Anoxic Sediment

Zone - October

Legend

-

Segment Boundary

10 It Contour

•

Aerobic Sediment

•

Anoxic Sediment

"

0,

25

Created by: CGS

Checked

by: WJE

Appmv&d by: ASS

May 5

, 2009

I Mles

"'

Electronic Filing - Received, Clerk's Office, May 12, 2009

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-20

"

" ,

1 ---

,

1/

.I

"

"

,

-

"

,

,

,

,

+

'

,

,

1

,-

,

,

,

1"9W" ;, . ,,, Coffeen lake

Section Locations

l i'; :e 9' ''"'

n' ' ~

U=

L

egend

Segment

1

Cr

oss Secti

on

S

egment 2

-

Cr

oss Secti

on

o

Crea

ted by: CGS

Checked by: WJE

Approvo;d by: A6S

May 5

, 2009

• . >

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-21

Figu r e 2- 17. Cro s s- Section of La ke Bottom , Av erage Ano xic Water Dep t h , and Oxygenated

Su rfac e Wat er Depth fo r Seg ments 1 and 2, Ma y and Oc tob er

Segment 1 Cros

s Section - M aV

m

I

g

!

=

~'T

!

~

53%

-

,

,

,

,

,

,

•

,~

=

=

-

~

~

=

~

~

H.,.~_.!

Oh ..... Ih)

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ros

s Section - O

ctober

m

I

,

=

rC2~c

,

l

~

~

7.71 0

~

,

•

,=

=

=

~

~

=

=

~

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o lhl

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m

•

~

i

=

!

•

,=

=

=

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=

=

=

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egment 2 Cross Section - October

m

g

=

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-

SUtf_E .... tlotI

- -~

_

W

o""t_

,

=

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-22

2.2

Potential Impacts of Increased Thermal Standard for May and October on Internal

Phosphorus Loading

Although internal phosphorus cycling does not appear to be a primary driver of surface water quality in

Coffeeen Lake, potential impacts to lake water quality following modification of the existing thermal

standard were evaluated. Changes to seasonal temperature and oxygen stratification were estimated for

May and October to evaluate the potential for incremental effect on internal phosphorus loading resulting

from changes to seasonal anoxia in Coffeen Lake bottom waters.

2.2.1

Spatial Impacts to Lake Stratification

The proposed change in the thermal discharge during May and October could potentially result in a small

increase in lake substrate surface area that will experience seasonal anoxia as a result of increased

discharge temperatures. Existing data were reviewed and evaluated to estimate potential changes during

May and October (Table 2-5). These estimates reflect May conditions that are expected to resemble

current June conditions once ambient temperatures sustain stratification, and October conditions that

resemble late September. In October, the plant will be able to operate more frequently, but ambient

conditions will be cooling, and aerated waters from Segments 3 and 4 are likely to contribute to general

contraction of the anoxic areas, although stratification may remain stable through at least a portion of

October.

Table 2-5

. Current and Predicted Days with Anoxic Sediment Conditions

Existing MAY

Proposed MAY

Existing OCT

Proposed Oct

Segment 1

18

23

1

13

Segment 2

17

25

1

11

Segment 3

9

9

0

0

Segment 4

0

0

0

0

Based on Coffeen Lake bathymetry, and existing May and October data, only Segments 1 and 2 will have

additional sediment surface area exposed to potential anoxic conditions during May (Figure 2-18) and

October (Figure 2-19). The resultant increase in exposed surface area for the entire lake is 21.1 hectares in

May and 11.1 hectares in October, resulting in an 8% increase in sediment surface exposed to anoxia

during that time period within Coffeen Lake (Table 2-6). Although increased thermal discharge may

expose additional sediment surface area to seasonal periods of anoxia, the frequency and duration of

stratification and anaerobic activity within the hypolimnion during the months of May and October is

significantly lower than the rest of the summer months, and will likely not expose the additional surface

area to prolonged anaerobic activity such that a measurable increase in surface water phosphorus

concentrations will be observed.

Electronic Filing - Received, Clerk's Office, May 12, 2009

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-23

,

-._j •• -

,

I--~

/-

/'

"

-

"

'(

,

,

,

,

•

c

_

, ,

,

1

,

,

,

2.18:Coffeen Lake

10 fI Contour

Aerobic Sedime

nt

Added Ano

x ic Sediment

~

~~~~~t~

,

0.

25

Created

by:

CGS

Checked by: WJE

Appwvo;d by: ASS

M

ay 5, 2009

I

Miles

"

Electronic Filing - Received, Clerk's Office, May 12, 2009

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-24

:'

r

,

,

,

l

"

-

\

,

\

,

,

+

'

,

,

•

i

,

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-

,

,

,

,-

2.19

:Coffeen Lake

i Sediment Zone

Under New Permit

Condilions - October

1

--

'''g , ~ct

Boundary

10

ft

Contour

Aerobic Sedi

ment

Added Anoxic Sedimen

t

1--

-

~""-

.....

~

AJ10xfc Sedimen

t

o

0.

25

Cr"~ted

by: CGS

Check

ed by: WJE

Approv&d by: ASS

May 5, 2009

I

Miles

"

"\

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

2-25

Table 2-6.

Potential Increase in Lake Substrate Surface Area Exposed To Seasonal Anoxia (Hectares)

May

October

Segment 1

16.5

0.8

Segment 2

4.5

10.3

Total:

21.1

11.1

(O

2

Profile Data Source: SIUC, 2007)

Created by: BMJ Checked by: ABS 5/7/2009

2.2.2

Potential Increase in Phosphorus Loading

Using these areas and representative flux rates (Haggard

et al

, 2005; Illinois EPA, 2009a), estimates of

the incremental difference in phosphorus flux into the hypolimnion were made. This estimate ranges from

48.08 kg P/year to 96.17 kg P/yr under the new permit conditions.

2.2.3

Limitation of Impacts to Epilimnion Water Quality

The incremental difference in phosphorus loading is a 0.5% to 1.1 % increase of the TMDL addendum

predicted internal loading (Illinois EPA, 2009a), and a 1.5% predicted increase if the internal loading

estimate in this analysis (see Section 2.2.1) is accurate (Figure 2-20). In any case, the incremental increase

is

de minimus

, and poses no harm to the lake, as this phosphorus is not expected to reach the epilimnion

or change current in-lake conditions with respect to phosphorus.

Figure 2-20.

Incremental Loading Differences to Estimated Current Phosphorus Loads

(Data Source: Illinois EPA, 2009a).

Created by: BMJ Checked by: KAR 5/11/2009

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

3-1

3.0 Mercury Cycling

Coffeen Lake is currently listed on the Illinois EPA 303(d) list of impaired water for mercury. Illinois

EPA states their concerns as follows: “During periods of stratification and low dissolved oxygen, more

methylmercury is produced. Methylmercury bioaccumulates and is typically found in predatory fish. If

the temperature of the Lake is higher in May and October, and the period of stratification is lengthened,

the levels of mercury in the fish may also increase.” This chapter discusses the complexity of mercury

methylation, the current understanding of mercury and mercury dynamics in Coffeen Lake, and the

incremental effect of the change in the thermal standard for May and October on mercury cycling in the

lake.

Current Illinois fish consumption advisories include waters containing at least one fish tissue where the

mercury level 0.06 mg/kg (Illinois EPA, 2008). Mercury readily bioaccumulates in living tissues, and

thus, fish consumption advisories are common nationwide. Coffeen Lake is included in this advisory

based on fish tissue samples from collections in 2002. These samples consist of two composite (5 fish per

composite) samples of largemouth bass filet. Because largemouth bass are a top aquatic predator in the

lake, although the sample size is small, the results are conservative for the lake. Illinois EPA’s concern for

Coffeen Lake is that mercury methylation is likely based on thermal stratification throughout the summer

months. Methylation is affected by multiple parameters and cannot be based solely thermal stratification.

Mercury in the environment is constantly cycled through a biogeochemical cycle, and its presence is the

result of natural (e.g., geothermal activity) and anthropogenic activities. Two main types of reactions in

the mercury cycle convert mercury through its various forms: oxidation-reduction and methylation-

demethylation. In oxidation-reduction reactions, mercury is either oxidized to a higher valence state (e.g.,

Hg

0

to Hg

2+

) or reduced to a lower valence state. In methylation-demethylation reactions, mercury is

transformed into methylmercury when the oxidized mercury (i.e., Hg

2+

, or mercuric species) gains a

methyl group (CH

3

) (Environment Canada, 2007). Chemical speciation is an important variable in

determining mercury toxicity (Eisler, 2006). Mercury compounds in aqueous systems are complex, and,

depending on various physical and chemical parameters, a variety of chemical species may be formed

(Figure 3-1) (Eisler, 2006). Methylmercury is the biologically active form of mercury and bioaccumulates

up the food chain.

Mercury may be methylated through biological processes, chemical processes, or both in aquatic systems.

Mercury methylation in ecosystems depends on mercury loadings, nutrient content, pH, oxidation-

reduction conditions, bacterial activity, and other variables (Eisler, 2006). Changes in biological or

chemical parameters can result in increased or decreased methylation and demethylation rates in aquatic

systems (Eisler, 2006), however external mercury loading is a dominant variable in fish tissue mercury

concentrations. This section summarizes available research on the factors that affect methylation of

mercury and how it relates to Coffeen Lake. The parameters discussed in the following subsections are

indicator parameters that may indicate whether the methylation of mercury is favorable or unfavorable

under certain conditions. While general trends may be observed as individual indicator parameters

Electronic Filing - Received, Clerk's Office, May 12, 2009

---

Figure 3-1 Major transformations of mercury in the environment. (Eisler, 2006

)

CH

4

C

2

H

6

Hg

2+

AIR

CH

3

Hg

+

(CH

3

)

2

Hg

Hg

0

WWAATERTER AND

AND BENTHBENTHICIC REGIONREGION

(CH

3

)

2

Hg

DIMETHYL

Hg

0

.

ELEMENTAL

FISH

CH

3

Hg

+

CH

3

SHgCH

3

METHYL

Hg

2+

MERCURIC

Hg

2

2+

C

OS

METHYL

MERCURIC

Inorganic and Organic Complexes

SHELLFISH

MERCUROUS

HgS

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

3-3

increase or decrease, the suite of parameters should be evaluated as a whole to indicate the potential for

methylation of mercury.

Mercury may be methylated in a variety of areas and under various conditions throughout the Coffeen

Lake watershed. Within the Coffeen Lake watershed, various land use activities are present, totaling

12,278.4 acres surrounding Coffeen Lake (Illinois EPA, 2007). Certain types of land use may attribute to

methylation of mercury in and around Coffeen Lake and other nearby waterbodies. According to Illinois

EPA (2007) 8,170.70 acres in the Coffeen Lake watershed are used for various forms of agricultural

farming, such as soybeans, corn, grasslands and other small grains and hay. During times of harvest and

planting runoff from various types of agricultural fields can lead to deposition of sediments, suspended

solids and sources of organic carbon into Coffeen Lake and nearby waterbodies. Along with sediment

deposition suspended solids and sources of organic carbon as well as various other contaminants may also

enter the water systems due to runoff. Contaminants may include pesticides, herbicides, large sediment

loads and animal and plant waste materials (as a source of organic carbon). Over 600 acres of the lake’s

watershed are wetlands. Wetlands are another land use type where mercury methylation is commonly

favored. Wetland areas may also be an area of high rates of methylation. This is true because the highest

rates of mercury methylation are often observed in surface sediments where microbial activity is

relatively high due to input of fresh organic matter. As a result, systems with high organic matter

production (e.g., wetlands, reservoirs) may exhibit extremely high rates of methylmercury production

(Benoit

et al

., 2003). Mercury methylation may be occurring in a variety of areas throughout the

watershed, depending upon site-specific conditions. East Fork Shoal Creek Gate Structure project

proposes to pump water from East Fork Shoal Creek in order to provide additional water to Coffeen Lake.

The creation of new floodplain and wetland areas may provide additional areas for potential methylation

of mercury to Coffeen Lake due to inundation of areas not previously covered with water. This

environment may encourage certain bacteria to anaerobically metabolize available mercury, resulting in

methylmercury as a byproduct. However, the annual flooding frequency for the area will not increase, and

thus, methylation rates may not be affected by this action.

Methylation can occur in a variety of situations, most notably in surficial sediments at the oxic-anoxic

interface (Park and Bartha, 1998), however it may also occur in surrounding areas inundated with water

for various amounts of time, forcing bacteria to switch from aerobic respiration to anaerobic respiration.

Runoff from agricultural land use may attribute to the amount of sediment deposition, organic carbon, and

chemical depositions occurring in Coffeen Lake and in surrounding waterbodies. Methylation rates may

increase as sediment loads increase, organic carbon enters a waterbody or dissolved oxygen becomes

depleted as a result of nutrient loading. Along with sediment, organic carbon and DO depletion, pH may

also play a role in changing methylation rates of mercury. As low pH (acidic conditions) may not favor

methylation, higher pHs may favor methylation. Some types of nutrient runoff from agricultural areas

may contain chemicals which can raise or lower pH values.

3,464.2 acres of the Coffeen Lake watershed are forested, wetland areas or urbanized and not used for

agricultural land use activities. Of the 3,464.2 acres not used for agriculture, 343.2 acres are urbanized.

---

Coffeen Lake

Ameren

MACTEC Engineering and Consulting, Inc.

May 2009

3-4

Due to impervious surface, urbanized areas may also contribute runoff and various forms of potential

pollutants to Coffeen Lake and surrounding waterbodies.

3.1

Mercury Load and Bioavailability

The presence of mercury in environmental media, the availability of that mercury for methylation, and the

bioavailability of methylmercury, are important for understanding potential risks to receptors. The

relationship between mercury load (i.e., mercury concentration) and mercury methylation is logarithmic

so that the rates of mercury load and methylation are proportional at relatively low mercury levels.

Methylation rates become asymptotic at relatively high levels (Krabbenhoft

et al

., 1999). The greatest

potential for mercury methylation occurs in surficial sediment (Korthals and Winfrey, 1987) at the oxic-

anoxic interface in sediments (Pak and Bartha, 1998).

3.1.1

Surface Water Data

In 2007, the USEPA conducted mercury sampling in Illinois lakes as part of the National Lakes Survey.

Survey locations were chosen based on waterbody acreage and included a subset of lakes included in the

1972 USEPA National Lake Eutrophication Study. Approximately 50 Illinois lakes were sampled, the

average total mercury concentration was 2.24 ng/L, and the average methylmercury concentration was

0.07 ng/L (Krabbenhoft,

et al

., 2008).

Based on readily available Illinois EPA data, Coffeen Lake surface water was not analyzed for mercury.

3.1.2

Sediment Data

Mercury concentrations from Segments 1 and 3 in Coffeen Lake (Figure 3.-2) sediments collected in 2002

were below the Illinois EPA detection limit. Sediment mercury concentrations from samples collected

between 1989 and 1997 ranged from 0.03 to 0.51 mg/kg (average 0.21 mg/kg) in Segment 1 and ranged

from 0.0005 to 0.10 mg/kg (average 0.07 mg/kg) in Segment 3 (Illinois EPA, 2009b).

3.1.3

Fish Tissue Data

Coffeen Lake is located in Montgomery County, southwestern Illinois. The Illinois Contaminant

Monitoring Program sampling (1985-2004) and USEPA Lake Fish Tissue Study sampling (1999-2003)

included composite fish tissue analysis for Montgomery County and surrounding counties of Bond,

Christian, Fayette, Macoupin, Madison, Sangamon, and Shelby Counties. A total of 54 fish were sampled

from Montgomery County, including largemouth bass (

Micropterus salmoides

), bluegill (

Lepomis

macrochirus

), and white crappie (

Pomoxis annularis

). The average mercury concentration in

Montgomery County was 0.13 mg/kg with concentrations ranging from 0.08 to 0.22 mg/kg. Fish species

collected from surrounding counties included, largemouth bass, bluegill, carp (

Cyprinus carpio

), channel

catfish (

Ictalurus punctatus

), smallmouth buffalo (

Ictiobus bubalus

), walleye (

Sander vitreus

), black

crappie (

P. nigromaculatus

), and spotted bass (

M. punctulatus

). The average mercury concentration in

fish tissues from the surrounding counties was 0.14 mg/kg, with a sample range from 0.01 mg/kg to

---

Figure 3-2 Illinois Largemouth Bass Mercury Concentrations

0.90

1.00

Figure 3-2 Illinois Largemouth Bass Mercury Concentrations

Knox County Average

Hg Concentration

2.97 mg/kg

0.70

0.80

)

National Average

Largemouth Bass

Hg Concentration

0.50

0.52 mg/kg

0.60

e

ntration (mg/kg

)

Coffeen Lake

Average Hg Concentration

0.085 mg/kg

0.52 mg/kg

0 30

0.40

Mercury Conc

e

Montgomery

0.20

0.30

Montgomery

County

Average Hg

Concentration

0.13 mg/kg

0.00

0.10

ond

o

wn

oun

t

ian

C

la

y

n

ton

o

les

ook

and

k

alb

W

itt

ag

e

dg

ar

h

am

e

tte

k

lin

l

ton

a

tin

ndy

nry

son

son

se

y

k

ee

nox

a

ke

a

lle

L

ee

s

ton

con

u

pin

son

r

ion

h

all

nry

e

an

r

cer

m

ery

g

an

o

ria

e

rry

P

ike

ope

a

ski

olph

and

and

l

ine

mon

y

ler

e

lb

y

lair

w

ell

l

ion

g

ton

yne

h

ite

s

ide

W

ill

son

f

ord

Bo

Br

o

Calh

o

Chris

t

C

Cli

n

Co

Co

Cumberl

a

De

k

De

W

DuP

a

Ed

Effing

h

Fay

e

Fran

k

Fu

l

Gall

a

Gru

n

He

n

Jack

s

Jeffer

s

Jer

Kanka

k

Kn

La

LaS

a

L

Livin

gs

Ma

c

Maco

u

Madi

s

Ma

r

Mars

h

McHe

n

Mcl

e

Me

r

Montgo

m

Mor

g

Pe

o

Pe

P

Po

Pul

a

Rand

o

Richl

a

Rock Isl

a

Sa

l

Sangam

Schu

y

Sh

e

St.C

Taze

w

Vermi

l

Washin

g

Wa

y

Wh

White

s

W

William

s

Wood

f

Sources: Illinois Fish Contaminant Monitoring Program Database 1985-2004

Prepared by/Date: AES 5/7/09

USEPA National Survey of Cioncentrations in Fish Database 1999-2003

Checked by/Date: MBR 5/7/09

Electronic Filing - Received, Clerk's Office, May 12, 2009

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0.51 mg/kg. Average mercury concentrations from fish collected in Montgomery and surrounding

counties is presented in Table 3-1.

Jenkins (2007) assessed the Illinois Fish Mercury Monitoring Program, which included samples collected

between 1974 and 1998. Sample locations were divided by watersheds. Montgomery County is in the

Kaskaskia watershed, which comprised 77% of Jenkins’ dataset. Other nearby counties in this watershed

are Bond, Fayette, Madison, and Shelby Counties. The median tissue mercury concentration from

Jenkins’ entire fish dataset (>2300 samples, 18 species, 149 lakes) was 0.10 mg/kg.

3.1.3.1 Largemouth Bass

The largemouth bass is the top predatory fish species in Coffeen Lake. Available fish tissue mercury data

for Coffeen Lake is limited to two largemouth bass samples, comprised of 5 composited filets each,

collected October 22, 1990 and October 21, 1991 (Illinois EPA, 2009c; ; USEPA, 2009). Mercury

concentrations of these samples were 0.08 and 0.09 mg/kg, respectively. Using the maximum observed

mercury concentration (0.09 mg/kg) in Coffeen Lake largemouth bass, a 33% reduction in mercury

loading would be necessary to reach 0.06 mg/kg. Over time, this reduction in fish tissue concentration can

be expected to be achieved by regional mercury load reductions. Montgomery County average

largemouth bass tissue concentration (0.13 mg/kg) was nearly half than the Illinois Counties average

(0.22 mg/kg) (Illinois EPA, 2009c). Figure 3-2 presents the average Illinois largemouth bass mercury

concentrations as compared to the national average concentration of 0.52 mg/kg (USEPA, 2001).

3.1.3.2 Wildlife

Some animals, such as bald eagles and wading birds, within the watershed may prey on fish from Coffeen

Lake. Mercury levels in fish of concern to wildlife are higher than the benchmark of 0.06 mg mercury/kg

adopted by Illinois EPA for protection of human health. Given the current and anticipated low levels of

mercury in fish (with the largemouth bass samples representing the upper end of mercury concentrations

in fish), wildlife are not at risk from mercury in fish from Coffeen Lake.

3.2

Additional Parameters Related to Methylation

In addition to the mercury load, acid volatile sulfide (AVS)/simultaneously extracted metals (SEM) ratios,

changes in water levels, dissolved oxygen (DO), hardness and alkalinity, metals, molybdate, organic

carbon, oxidation-reduction potential (ORP), pH, salinity, seasonality and temperature, sulfate and

sulfide, water levels, and the microbial community structure are factors that affect methylation. Readily

available Coffeen Lake analyte data are not available for each of these parameters; however, data are

available for DO, alkalinity, iron, manganese, pH, organic carbon, and temperature. A summary of these

parameters and their expected influence on mercury methylation are listed below. The parameters with

Coffeen Lake data are discussed further in the following sections.

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County

Waterbody

No. of

Samples

No. of Fish

Sampled

Species

Ave Hg Conc (mg/kg)

Bond

Greenville New Lake

1

5

LMB

0.100

Bond

Patriots Park Lake

2

10

LMB

0.360

Christian

Sangchris Lake

5

22

LMB

0.118

Christian

Taylorville Lake

3

14

LMB

0.090

Fayette

Kaskaskia river

4

17

C, CC, LMB, SMB, WE

0.125

Fayette

Vandalia Lake

1

5

LMB

0.070

Macoupin

Beaver Dam Lake

1

5

LMB

0.140

Macoupin

Bunn Lake

2

10

BG, LMB

0.140

Macoupin

Mt. Olive New Lake

2

10

LMB

0.215

Macoupin

Mt. Olive Old Lake

1

5

LMB

0.260

Macoupin

Otter Lake¹

5

25

C, LMB

0.166

Macoupin

Staunton City Lake

2

10

LMB

0.175

Madison

Highland-Silver Lake

1

5

LMB

0.240

Madison

Horseshoe Lake

3

15

BG, LMB

0.100

Madison

Mississippi River - S. Central

3

12

LMB, WB

0.110

Madison

Pine Lake

4

13

BC, BG, LMB

0.100

Montgomery

Coffeen Lake

2

10

LMB

0.085

Montgomery

Glenn Shoals Lake

2

10

LMB

0.140

Montgomery

Lou Yaeger Lake

8

34

BG, LMB, WC

0.138

Sangamon

Springfield Lake

5

25

LMB

0.072

Shelby

Kaskaskia river

2

6

LMB, WE

0.100

Shelby

Little Wabash River

4

15

C, LMB, SB

0.238

Shelby

Shelbyville Lake

6

30

LMB, WC, WE

0.085

Notes:

Samples comprised of composite filets collected between 1985 and 2004 as part of the Illionois Contaminant Monitoring Program.

¹Includes four composited filet samples collected in 2001 as part of the US EPA Lake Fish Tissue Study.

Species Codes:

BC = Black Crappie

SB = Spotted Bass

BG = Bluegill

SMB - Smallmouth Buffalo

C = Carp

WB = White Bass

CC = Channel Catfish

WC = White Crappie

Hg = Mercury

WE = Walleye

LMB = Largemouth Bass

Source:

Illinois Fish Contaminent Monitoring Program database (1985-2004);

Prepared by/Date: MBR 5/5/09

USEPA National Survey of Concentrations in Fish database (1999-2003).

Checked by/Date: AES 5/6/09

Table 3-1. Average Fish Tissue Mercury Data from Montgomery and Surrounding Counties

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Table 3-2.

Summary of Various Parameters that may Influence Mercury Methylation Rates

Mercury Methylation

Parameter

General Effect on Methylation of Mercury

AVS/SEM

AVS/SEM ratios greater than 1 tend to inhibit methylation.

DO/ORP

Oxic and oxidizing environments do not favor methylation.

Hardness/Alkalinity

Increased hardness and alkalinity reduce metal toxicity and reduce uptake of metals.

Iron/Manganese

May favor or inhibit methylation depending on concentration and chemistry.

pH

Acidic conditions in sediment may not favor methylation.

Salinity

As salinity increases, methylation of mercury decreases.

Sulfate

Reduction of sulfate by sulfate reducing bacteria (SRB) may enhance methylation of

mercury.

Sulfide

The presence of sulfide may reduce methylation of mercury and bioavailability of

methylmercury.

Temperature

Increasing temperature increases methylation of mercury.

Organic Carbon

DOC in the water column may enhance methylation but may also bind

methylmercury; TOC in sediment may enhance methylation.

3.2.1

Dissolved Oxygen

DO plays a role in mercury methylation. When oxic conditions exist in the water column and in sediments

(i.e., DO >1 milligrams per liter [mg/L]), bacteria respire aerobically, which means that they use oxygen

as the terminal electron receptor during metabolism. When anoxic conditions are present in the water

column or in sediments, bacteria will respire anaerobically, which means they will use another molecule

besides oxygen as the terminal electron receptor during metabolism. The molecule used depends on the

types of bacteria present. Mercury can be methylated to produce methylmercury as a byproduct of these

metabolic reactions. Several studies have concluded that the formation of methylmercury from mercury in

lakes and reservoirs is favored under low DO conditions; the rate of mercury methylation is lower in the

presence of oxygen; and methylmercury may be formed primarily in anoxic waters and sediments but is

demethylated under aerobic conditions (Ramlal

et al

., 1986; Korthals and Winfrey, 1987; Bloom and

Effler, 1990; Oremland

et al

., 1991; Gilmour

et al

., 1992; Watras

et al

., 1995; Herrin

et al

., 1998). Pak

and Bartha (1998) discovered that the most important location of methylation is at the oxic-anoxic

interface in sediments. However, the mere absence of oxygen does not demonstrate that rates of mercury

methylation are high.

Based on Coffeen Lake bottom conditions between 2001 and 2006 (see Section 2), anoxic conditions are

present over a portion of the lake bottom and in the hypolimnion (at depth) in waters overlying these

sediments during a portion of the six month period from May to October. Mercury (whether methylated

or not) is quite low in Coffeen Lake, compared to many other lakes in Illinois, based upon the available

largemouth bass data. Changes to the thermal standard for Coffeen Lake during May and October will not

increase the overall mass of mercury in the lake. The marginal changes in anoxia in these two months

attributable to these changes (see Figures 2-18 and 2-19 in Section 2), compared to the current operating

conditions, leads to the conclusion that any effect on mercury methylation rates that may occur would be

very minor, and likely not result in measureable changes in fish mercury concentrations.

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3.2.2

Alkalinity

Total alkalinity (i.e., carbonate and bicarbonate) can also regulate metal content in surface water by

precipitating toxic metals out of solution. Total alkalinity is also an indication of the buffering capacity of

the surface water system or the ability of a water body to resist changes in pH. The pH level also plays a

role in the methylation of mercury and is discussed in Section 2.10. Buffering capacity of a water body is

geologically dependent, but, in general, total alkalinity levels less than or equal to 10 mg/L indicate a

poorly buffered system that is susceptible to changes in pH (Wilkes University, 2007). Higher alkalinity

levels have also been correlated with reduced bioaccumulation rates (Barkay

et al

., 1997).

Total alkalinity concentrations in Coffeen Lake Segment 1 ranged from 80 to 140 mg/L. Segment 2

concentrations ranged from 50 to 120 mg/L. Segment 3 concentrations ranged from 60 to 110 mg/L.

Based on these results, total alkalinity concentrations indicate potentially reduced bioaccumulation rates

within Coffeen Lake.

3.2.3

Metals

Substrates other than oxygen act as the terminal electron receptor for bacterial metabolism under anoxic

conditions. Depending on the species of bacteria present and the physico-chemical environment, metals

such as iron and manganese can be used as terminal electron receptors. The production of methylmercury

can be a byproduct of these metabolic reactions. In addition, non-microbial methylation of mercury was

documented to be stimulated by the presence of certain metals, such as iron and manganese (Stokes and

Wren, 1987). Iron and manganese can also inhibit the methylation of mercury through mineralization.

Selenium has been shown to decrease bioaccumulation rates of methylmercury. Research on each metal is

presented in the following sections.

3.2.4

Iron

Iron can potentially stimulate or inhibit methylmercury production depending on concentration and

speciation. Iron reduction by bacteria may be responsible for some amount of in situ mercury methylation

(Kerin

et al

., 2006). Depending on iron speciation, iron can stimulate iron-reducing bacteria to methylate

mercury, and these bacteria can do so at a rate equivalent to SRB in some circumstances (Fleming and

Nelson, 2006) (see Section 1.14). As a result, the presence of iron, which can be used as a terminal

electron receptor in metabolism for certain bacterial populations, can increase methylation rates. Warner

et al

. (2003) found measurable methylation in sediments where iron was the dominant terminal electron

acceptor, although methylation rates were lower than those observed in sulfate-reducing or methanogenic

sediments. In sediments from Clear Lake, California, where microbial iron reduction was occurring,

inhibition of sulfate reduction did not result in complete inhibition of mercury methylation, suggesting

that iron reduction may have been responsible for some amount of in situ mercury methylation (Fleming

et al

., 2006). Jackson found that iron-coated clays counter depression of both methylation and

demethylation (Jackson, 1989). Ferric oxyhydroxide addition was documented to increase methylation

rates in certain lacustrine (lake) sediments (Fleming

et al

., 2006).

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While iron may stimulate methylmercury production under certain conditions, it may also inhibit

methylmercury production. In a study of estuarine wetland sediment slurries from San Francisco Bay,

California, Mehrotra and Sedlak (2005) observed decreases in mercury methylation rates with the

addition of 30 millimolar (mM) ferric iron; they believe that this effect was caused by decreases in

dissolved mercury and sulfide due to complexation with iron. The addition of ferrous iron may also

decrease the net rate of methylmercury production by reducing the concentration of dissolved sulfide.

Complexation with iron could also reduce mercury bioavailability.

Coffeen Lake iron concentrations in sediments in Segment 1 ranged from 26,500 to 40,000 mg/kg at

Segment 1 and from 17,000 to 30,000 mg/kg at Segment 3. At these concentrations, the mercury may be

complexed with iron and not available to iron-reducing bacteria for methylation, as noted in research by

Mehrotra and Sedlak above.

3.2.4.1 Manganese

Manganese, like iron, may complex with mercury and reduce bioavailability. The role of clays in

reducing methylation was dependent on their surface coatings in research involving clay minerals and

oxides on methylation and demethylation of mercury (Jackson, 1989). Manganese oxide coatings

sometimes promoted methylation, but larger amounts of manganese oxide suppressed methylation

(Jackson, 1989).

Coffeen Lake manganese concentrations in Segment 1 ranged from 712 to 1,600 mg/kg at Segment 1 and

from 290 to 521 mg/kg at Segment 3. At these concentrations, the mercury present in Lake sediments

may be complexed with manganese and, therefore, may not be bioavailable.

3.2.5

Organic Carbon

Two types of organic carbon, DOC and total organic carbon (TOC), can affect the methylation of

mercury. Both mercury and methylmercury will complex strongly with DOC and, as a result, can both

decrease and increase bioaccumulation (Brumbaugh

et al

., 2001). Organic complexation can increase the

amount of mercury substrate for methylation in the water column, but the binding of methylmercury by

DOC in the water column can result in lower fish bioconcentration factors (Watras

et al.,

1995). DOC

associations may decrease the bioaccumulation of mercury in aquatic food webs by lowering the

bioavailability of mercury to methylating organisms (Barkay

et al.,

1997; Haitzer

et al.,

2003).

TOC has also been shown to have opposing effects on the methylation of mercury and its bioavailability.

TOC can enhance mercury methylation by acting as a food source and thereby increasing the metabolism

of heterotrophic microorganisms (Furutani and Rudd, 1980; Stokes and Wren, 1987); however, mercury

methylation may also be inhibited through formation of mercury complexes with organic ligands

(Robinson and Tuovinen, 1984; Gilmour

et al.,

1992; Macalady

et al.,

2000; Han

et al.,

2007). The

highest rates of mercury methylation are often observed in surface sediments where microbial activity is

greatest due to the input of fresh organic matter. As a result, systems with high organic matter production

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(wetlands, reservoirs) may exhibit extremely high rates of methylmercury production (Benoit

et al

.,

2003).

Illinois EPA 1997 Coffeen Lake samples had concentrations of 0.58 and 0.82 percent TOC, which may

suggest conditions do not appear to favor methylation. Krabbenhoft,

et al.

(2008) correlated DOC levels

with total and methyl mercury, stating “proximity to sources and DOC levels are the most significant

drivers.” Coffeen Lake DOC levels are not available; however, Illinois DOC averaged 7.1 mg/L. As

discussed in Section 2.1.1, total mercury average concentration in Illinois was 2.24 ng/L and methyl

mercury concentrations averaged 0.07 ng/L.

3.2.6

pH

The level of pH also plays a role in the methylation of mercury. Acidic pH generally favors the

methylation of mercury to a point. The pH level may also affect the bioavailability of methylmercury to

higher trophic level organisms. Low pH (usually less than 5) is frequently associated with high mercury

concentrations in fish tissue (Stokes and Wren, 1987; Watras

et al

., 1995; Barkay

et al

., 1997;

Brumbaugh

et al

., 2001). Low pH favors both the direct uptake of methylmercury through the gills of fish

and dietary uptake due to increased mercury accumulation by organisms in lower trophic levels (WHO,

1990). In some systems, surface water pH has been identified as the most important factor controlling

mercury bioaccumulation in fish (Moore

et al

., 2003).

Coffeen Lake surface waters are neutral or circum-neutral, which does not favor methylation. Data for pH

are not available for Coffeen Lake sediment samples, but are also likely to be circum-neutral.

3.2.7

Seasonality and Temperature

Seasonality resulting from temperature changes affects the methylation of mercury. The potential for

mercury methylation varies at different times of the year, with the greatest potential generally occurring in

the summer from mid-July to September (Korthals and Winfrey, 1987). Lacustrine environments (i.e.,

lakes and ponds) with a significant depth profile and low water flows may thermally stratify in the

summer and in the winter. The stratification generally disappears during the spring and fall during what is

known as turnover events. The ratio of methylmercury to mercury in thermally stratified lakes is generally

greater in the hypolimnion (bottom layer), especially if the hypolimnion is anoxic, than in the epilimnion

(upper layer) (Bloom and Effler, 1990; Mason and Sveinsdottir, 2003; Eckley

et al

., 2005). The increase

in methylmercury in the hypolimnion appears to be related to the anaerobic conditions and the inability of

DO to penetrate the thermocline (region between the epilimnion and hypolimnion that exhibits a marked

temperature gradient equal to or exceeding 1

˚

C per meter) until a turnover event. Korthals and Winfrey

(1987) discovered that the seasonal peak in mercury methylation in profundal (deep, bottom-water area

beyond the depth of effective light penetration) surficial sediments coincided with a depletion of DO in

the lower hypolimnion, and the decrease in mercury methylation corresponded with the reaeration of the

hypolimnion during fall turnover. Several mechanisms have been proposed to explain the seasonal

changes of mercury methylation rates in anoxic hypolimnia. These potential mechanisms include the

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diffusion of methylmercury from sediment to surface water during anoxic conditions, methylation

occurring in anoxic water column, and sedimentation of particulate methylmercury (Eckley

et al.,

2005).

Herrin

et al

. (1998) observed pronounced increases in mercury body burdens of zooplankton and juvenile

bass at the time of thermal destratification of a seasonally anoxic reservoir. Methylmercury stored in the

anoxic hypolimnion during the summer stratified period became available to lake biota during the fall

turnover and remained available for a short time after complete turnover (Herrin

et al

., 1998).

Increasing temperature also promotes methylation (Shanley

et al

., 2005). It also appears that mercury

methylation can be stimulated in the late spring by the high supply of fresh organic matter after the spring

plankton bloom (Choe

et al.,

2004). These increases are difficult to isolate, as other parameters, such as

input of fresh organic matter, coincide with temperature changes.

Based on Coffeen Lake bottom conditions between 2001 and 2006 (see Section 2), anoxic conditions are

present over a portion of the lake bottom and in the hypolimnion (at depth) in waters overlying these

sediments during a portion of the six month period from May to October. Mercury (whether methylated

or not) is quite low in Coffeen Lake, compared to many other lakes in Illinois, based upon the available

largemouth bass data. Changes to the thermal standard for Coffeen Lake during May and October will not

increase the overall mass of mercury in the lake. The marginal changes in anoxia in these two months

attributable to these changes (see Figures 2-18 and 2-19 in Section 2), compared to the current operating

conditions, leads to the conclusion that any effect on mercury methylation rates that may occur would be

very minor and likely not result in measureable changes in fish mercury concentrations.

3.3

Summary

Several geochemical factors that may affect the methylation of mercury were discussed in the previous

sections. The parameters discussed in the previous subsections are indicator parameters that may

generally predict whether the methylation of mercury is favorable under certain conditions. While general

trends may be observed as these indicator parameters increase or decrease, the suite of parameters should

be evaluated as a whole to predict the potential for methylation of mercury.

Flooding of terrestrial and wetland environments may or may not play a role in the methylation of

mercury. Current research on flooding or re-wetting of sediments or soils and methylation rates is

contradictory and appears largely dependent on site characteristics. While it may not be possible to

manipulate all parameters to reduce mercury methylation or methylmercury bioavailability, it may be

possible to manipulate some parameters. The effectiveness of manipulating any particular parameter

depends on various site-specific conditions. Recent research indicates that the most important parameter

that affects the methylation of mercury may be its mineralization with various other compounds in the

environment.

Based on the available Coffeen Lake data, mercury concentrations appear to be generally low and

conditions do not appear to be favorable for methylation. Current sources of methylation may be within

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lake or occurring in the watershed, but appear low. The proposed change in the thermal standard affecting

May and October conditions do not substantially change the lake conditions, although thermal

stratification may persist for more days on average, annually. This change is minor, and does not

represent a change that could or would significantly increase hypolimnetic mercury methylation rates. It

is anticipated that the change, if any, would be so small that it would not result in increased mercury in

the biota. Fish tissue concentrations are anticipated to measurably decline, however, as a result of regional

mercury load reductions

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4.0 Summary

4.1

Introduction

MACTEC evaluated potential for impacts on phosphorus and mercury cycling from proposed

modifications to current site-specific thermal standards in Coffeen Lake in support that raising the thermal

limits for the months of May and October will not result in significant increases in phosphorus loading or

mercury methylation over current lake conditions.

Illinois EPA claimed that Ameren failed to address the impact of the proposed thermal limits on total

phosphorus and mercury levels in Coffeen Lake, in addition to failing to address the impact on Lake

Habitat. Illinois EPA stated a concern that higher temperatures of Coffeen Lake in May and October may

result in prolonged stratification which can increase phosphorus levels and methylmercury levels.

4.2

Phosphorus

Phosphorus is a limiting nutrient in Coffeen Lake and is therefore an important component of its long-

term water quality. Internal phosphorus release from sediments can serve as an additional source of

phosphorus loading to the lake, yet is ultimately dependent on a number of chemical and physical factors

which occur at the sediment-water interface. The mere presence of thermal stratification does not indicate

that significant internal loading will occur as a result. Despite the potential for seasonal sediment

phosphorus release from the sediments, water quality measurements within Coffeen Lake indicate that

internal phosphorus recycling is currently not contributing appreciable amounts of total phosphorus to

epilimnetic surface water. Oxygenated hypolimnetic water and epilimnetic waters (DO> 1 mg/L) were

always present overlying these deeper anoxic layers as shown by cross section for May and October. The

data and this analysis clearly show that there is no “dead zone” within the lake.

TMDL assessments for Coffeen Lake attribute elevated phosphorus concentrations to external watershed

loading, primarily due to expansive agriculture surrounding the lake. External loading as a driver of water

quality is also apparent in high phosphorus concentrations measured in the shallow northern portions of

the lake. Additionally, seasonal water quality comparisons do not show elevated phosphorus or

chlorophyll-a concentrations during summer stratification of the water column, indicating that phosphorus

is either not being released in large volumes from the sediment or is not being mixed into the epilimnion

where it may be available for algae production.

Review of the original TMDL BATHTUB (2007) model revealed significant modeling errors and

misapplications which led to the erroneous conclusion that internal phosphorus loading dominates

Coffeen Lake. These errors produced a model run which did not match known lake phosphorus

concentrations. To compensate for this “under-prediction of observed phosphorus concentrations”, the

modelers introduced an additional internal phosphorus load (the BATHTUB model already incorporates

internal loading) to force the model to calibrate. The conclusions and load reduction requirements of the

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original TMDL were not revised, despite these errors and discrepancies. However, available monitoring

data do not confirm this estimated level of internal loading (see Section 2.1.1).

An evaluation of potential impacts associated with modified thermal discharge during the months of May

and October was also performed to quantify the potential for additional phosphorus release and

anticipated impacts to surface water quality. Results of this analysis indicate that the additional

phosphorus load which may be anticipated from the proposed modification ranges from 329.1 kg P/year

to 658.1 kg P/yr under existing permit conditions, which is much lower than predicted from the

BATHTUB modeling completed for the TMDL. Additionally, any phosphorus released from the

sediment is not expected to reach the epilimnion, and is therefore unavailable for biological production

within Coffeen Lake. Based on seasonal water quality comparisons sediment phosphorus release does not

appear to be an important component of surface water phosphorus loading within Coffeen Lake. Future

modifications to thermal discharge limits from the Ameren Power Generating Plant are unlikely to present

additional phosphorus loads from sediment release in the future, and therefore are not a threat to the

existing water quality of Coffeen Lake.

4.3

Mercury

Mercury readily bioaccumulates in living tissues, and thus, fish consumption advisories are common

nationwide. Coffeen Lake is currently included in the Illinois fish consumption advisories based on two

fish tissue samples with mercury concentrations exceeding the Illinois EPA level of concern of 0.06

mg/kg. These samples consist of two composite (5 fish per composite) samples of largemouth bass filet

with concentrations of 0.08 and 0.09 mg/kg of mercury. Because largemouth bass are a top aquatic

predator in the lake, although the sample size is small, the results are conservative for the lake. Illinois

EPA’s concern for Coffeen Lake is that mercury methylation is likely based on thermal stratification

throughout the summer months.

Methylation is affected by multiple parameters and cannot be based solely on thermal stratification. There

are multiple indicator parameters that may predict whether the methylation of mercury is favorable under

certain conditions. While general trends may be observed as these indicator parameters increase or

decrease, the suite of parameters should be evaluated as a whole to predict the potential for methylation of

mercury.

Based on the available Coffeen Lake data, mercury concentrations appear to be generally low and

conditions do not appear to be favorable for methylation. Current sources of methylation may be within

the lake or occurring in the watershed, but appear low. The proposed change in the thermal standard

affecting May and October conditions does not substantially change lake conditions, although thermal

stratification may persist for more days on average, annually. This change is minor, and does not

represent a change that could or would significantly increase hypolimnetic mercury methylation rates. It

is anticipated that the change, if any, would be so small, that it would not result in increased mercury in

the biota. Fish tissue concentrations are anticipated to measurably decline, however, as a result of regional

mercury load reductions.

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