TSD

000331

---

Prepared

for:

Ameren

Services

St.

Louis,

MO

Hutsonville

Power

Pond

D

-

Human

Health

Ecological

Risk

Assessment

AECOM.

Inc.

April

2009

Document

No.:

10418-003

---

AECOM

Contents

1.0

Introduction............................................................................................................................................

1-1

1.1

Purpose............................................................................................................................................

1-1

1.2

Human

health risk

assessment

(HHRA).........................................................................................

1-1

1.3

Ecological

risk

assessment

(ERA)..................................................................................................

1-1

1.4

Report

organization.........................................................................................................................

1-1

2.0

Conceptual

site

model..........................................................................................................................

2-1

2.1

Setting..............................................................................................................................................

2-1

2.2

Site

geology

and

hydrogeology.......................................................................................................

2-1

2.3

Potential

sources.............................................................................................................................

2-1

2.4

Groundwater

monitoring

and

modeling...........................................................................................

2-2

2.5

Groundwater

use.............................................................................................................................

2-2

2.6

HHRA

CSM......................................................................................................................................

2-3

2.7

ERA

CSM.........................................................................................................................................

2-4

3.0

Data

evaluation.......................................................................................................................................

3-1

4.0 Human

health risk

assessment...........................................................................................................

4-1

4.1

Hazard

identification........................................................................................................................

4-1

4.1.1

Essential

nutrients

.............................................................................................................4-2

4.1.2

Comparison

to

Applicable

Standards and/or

Screening

Levels..—..................................

4-3

4.2

Dose-response

assessment............................................................................................................

4-4

4.2.1

Sources

of

toxicity

values..................................................................................................

4-5

4.2.2

Noncarcinogenic

toxicity

assessment...............................................................................

4-5

4.3

Exposure

Assessment.....................................................................................................................

4-6

4.3.1

Human

Health

Conceptual

Site

Model..............................................................................

4-7

4.3.2

Quantification of

potential

exposures................................................................................

4-7

4.3.3

Receptor-specific

exposure

parameters...........................................................................

4-9

4.3.4

Exposure

point

concentrations........................................................................................

4-10

4.4

Risk

characterization.....................................................................................................................

4-11

4.4.1

Noncarcinogenic

risk

characterization

methods.............................................................

4-12

4.4.2

Risk

characterization

results

...........................................................................................

4-12

4.4.3

Evaluation of

the

Selection

of Constituents of Potential

Concern..................................

4-13

5.0

Ecological

risk

assessment..................................................................................................................

5-1

5.1

Problem formulation

........................................................................................................................

5-1

J

April

2009

TSD

000333

---

AECOM

Environment

5.1.1

Definition

of

risk

assessment

objectives...........................................................................

5-2

5.1.2

Site

characterization and

definition

of the

geographic

area

to

be

considered.................

5-2

5.1.3

Selection

of

specific ecological

receptors

and

exposure

pathways.................................

5-2

5.1.4

Selection of

assessment

and

measurement

endpoints...................................................

5-2

5.1.5

Selection of

COPCs.....................:.....................................................................................

5-3

5.1.6

Conceptual

site

model.......................................................................................................

5-3

5.2

Risk

analysis....................................................................................................................................

5-3

5.2.1

Aquatic

assessment

endpoint...........................................................................................

5-3

5.2.2

Agricultural

crop assessment

endpoint.............................................................................

5-4

5.3

Risk

characterization.......................................................................................................................

5-5

6.0 Conclusions.

7.0

References...

.6-1

.7-1

II

April

2009

TSD

000334

---

AECOM

List

of

Appendices

Appendix

A

Consumer

Confidence

Report (CCR)

for

Hutsonville,

IL

Appendix

B

Groundwater

Use

Restriction

Appendix

C

Downgradient

Groundwater

Data:

2002-2008

Appendix

D

Manganese

in

the

Deep

Alluvial

Aquifer

Appendix

E

Derivation of

Dilution

Factor

for the

Wabash

River

Appendix

F

Risk

Calculation

Spreadsheets

Appendix

G

Leachate

Data

Evaluation

Appendix

H

Potable

Well

Search

April

2009

TSD

000335

---

AECOM

List

of Tables

Table 3-1

Summary

of Available

Data

for

Downgradient

Wells

Table

3-2

Summary

Statistics

for

Downgradient

Wells

-

Upper

Migration

Zone

and

Deep

Alluvial

Aquifer

Table

4-1

Comparison

of

Maximum

Detected Concentrations

in

Downgradient

Wells to

Human

Health

Screening

Levels

Table

4-2

Comparison

of

Maximum

Detected

Concentrations

in

Extraction

Wells to

Human

Health

Screening

Levels

Table

4-3

Dose-Response

Information for

COPC

with

Potential

Noncarcinogenic

Effects

from Chronic

Exposure

through

the

Oral

Route

Table

4-4

Potential Receptors,

Exposure

Media,

and

Exposure

Pathways

Table

4-5

Dermal

Permeability

Constants

for

Groundwater and Surface

Water

Table

4-6

Summary

of Potential

Exposure

Assumptions

-

Future

Construction

Worker

Table

4-7

Summary

of

Potential

Exposure

Assumptions

-

Current

and Future Recreational

Swimming

Child

Table

4-8

Summary

of Potential

Exposure

Assumptions

-

Current and Future Recreational

Swimming

Teenager

Table

4-9

Summary

of

Potential

Exposure

Assumptions

-

Current and

Future Recreational

Fisher

Table

4-10

Exposure

Point

Concentrations

Table

4-11

Summary

of

Potential

Hazard Indices

Table

4-12

Total Potential

Hazard

Indices

Table

5-1

Comparison

of

Estimated

Surface

Water

Concentrations

to

Ecological

Screening Levels

for

Surface

Water

Table

5-2

Comparison

of

Concentrations

in

Downgradient

Wells to

Irrigation

Screening Levels

Table

5-3

Boron

Concentrations

in

Downgradient

Deep

Alluvial

Aquifer

List

of

Figures

Figure

2-1

Site

Location

Map

Figure

2-2

Site Plan

Figure

4-1

Human

Health

Conceptual

Site

Model

Figure

5-1

Ecological

Conceptual

Site

Model

IV

April

2009

TSD

000336

---

AECOM

List

of

Acronyms

Al

Adequate Intake

AWQC

Ambient

Water

Quality

Criteria

bgs

below

ground

surface

CADD

Chronic

Average

Daily

Dose

CAS

Chemical Abstracts Service

COPC

Constituent

of

Potential

Concern

CSM

Conceptual

Site

Model

CTE

Central

Tendency

Exposure

EAR

Estimated

Average

Requirement

EFH

Exposure

Factors

Handbook

EPC

Exposure

Point

Concentration

ERA

Ecological

Risk

Assessment

ERAGS

Ecological

Risk

Assessment

Guidance for

Superfund

HHRA

Human

Health

Risk

Assessment

HI

Hazard

Index

HQ

Hazard

Quotient

IEPA

Illinois

Environmental

Protection

Agency

IRIS

Integrated

Risk

Information

System

kg

kilogram

LOAEL

Lowest Observed Adverse

Effect

Level

MCL

Maximum Contaminant Level

mL

milliliters

NHANES

National

Health

and

Nutrition

Examination

Survey

NOAEL

No

Observed

Adverse

Effect

Level

OSWER

Office

of

Solid

Waste

and

Emergency

Response

RfD

Reference

Dose

RME

Reasonable Maximum

Exposure

RO

Remediation

Objective

SERA

Screening

Level

Ecological

Risk

Assessment

SL

Screening

Level

SMCL

Secondary Maximum Contaminant Level

SMDP

Scientific/Management

Decision

Point

TACO

Tiered

Approach

to

Corrective

Action

Objectives

USEPA

U.S.

Environmental

Protection

Agency

WQS

Water

Quality

Standard

April

2009

TSD

000337

---

AECOM

Executive

Summary

This

report

presents

a

human

health

risk

assessment

(HHRA)

and

an

ecological

risk

assessment

(ERA)

in

support

of

the

closure

of

Pond

D,

a

former

coal ash

impoundment,

at

the

Ameren

Energy

Generating

Company's

Hutsonville

Power

Station

(Station).

Ameren

is

requesting

that

the

Illinois

Pollution

Control

Board

(Board) adopt a

site-specific regulation

for

the

closure

of Pond

D.

The

closure,

detailed

more

fully in

the

Pond

D

Closure

Alternatives

Report (NRT,

2009a),

includes

capping

of Pond

D

with

a

geo-synthetic

membrane,

and

installing

a

groundwater

collection trench

along

the

southern

Station

property

boundary.

The

purpose

of the

HHRA

and

ERA

presented

in this

report

is

to

confirm

that the

closure

plan/activities

for

Pond

D

are

protective

of

human

health

and

the

environment

under

current

and

reasonably

foreseeable

future

conditions

and

land

use.

Illinois

regulations

do

not

require

the

performance

of

a

risk

assessment

in

evaluating

the

proper

closure

of

surface

impoundments such

as

Pond

D.

The

risk

assessments

have been conducted

consistent

with

state

and federal

guidance

for

site

remediations,

and based

on

a

site-specific

conceptual

site

model

(CSM),

presented

below.

The results

of

the

risk

assessment

are

then

presented.

The

risk

assessments

have been

conducted

based

on

the

current

environmental

and

land

use

conditions

associated

with

Pond

D,

in

the

absence

of additional

closure

activities

(e.g.,

capping,

trench

installation).

The

results determined

that

current

conditions

are

protective

of

human

health

and

the

environment

under current

and

reasonably

foreseeable future

conditions

and

land

use.

Therefore,

as

the

proposed

closure

activities

will

result

in

groundwater

meeting

Illinois

Class

I

groundwater

quality

standards

at the

Station

property

boundary

in

the

future

(NRT,

2009b),

the

closure

plan/activities

for

Pond

D

are

also

protective

of

human

health

and

the

environment.

Conceptual

Site Model

(CSM)

Setting.

The

Hutsonville

Power

Station

is

located

on

approximately

205

acres

in

Crawford

County,

Illinois

on

the

west

bank

of the

Wabash

River between

the

towns

of Hutsonville and

York (SW1/4,

Section

17,

Township

8N,

Range

11W).

Figure

2-1

presents

the

location and

environs

of

the

Station.

In

1968

the

company

constructed Pond

D

as an

unlined

water

pollution

treatment

facility

for

coal combustion

wastes

and related

waste

generated

at

the

Station.

Pond

D

was

taken out

of

service

in

2000, and

dewatered

shortly

thereafter.

Pond

D

is

located

on

the

western

bank

of

the

Wabash

River,

and

is

bounded

to the

south

by

agricultural

land.

The land

use

for

the Station is

classified

industrial,

and the

agricultural

land to

the south

of

Pond

D

is

classified

agricultural.

These

land

uses

are

expected

to

continue for

the

reasonably foreseeable

future.

The

closest

residence

is

approximately one-half

mile

from

the

Station.

Geology/hydrogeology.

There

are

two

water

bearing

units

of interest

in

the

vicinity

of

Pond

D

(NRT,

2009a).

•

The

upper

migration

zone

•

The

deep

alluvial

aquifer

A

confining

layer

is

present

that restricts vertical

migration

of

groundwater between

the

upper

migration

zone

and

deep

alluvial

aquifer.

Groundwater

flow direction

in

both

the

upper

migration

zone

and

the

deep

alluvial

aquifer

is

eastward,

toward

the

Wabash

River.

Sources.

As

an

unlined

former

coal

ash

impoundment,

with

ash

present

below

the

water table,

constituents

may

leach from Pond

D

and impact

groundwater.

Boron and sulfate

are

constituents

that

can

leach

from

coal

ash and

are

mobile

in

groundwater,

and

are common

indicators

of

coal

ash

impacts

to

groundwater.

Groundwater

monitoring

of Pond

D

has

indicated that

boron

and

sulfate

are

present

at

some

locations

in

the

ES-1

.

April

2009

TSD

000338

---

AECOM

Environment

•,

'"^

upper

migration

zone

at

concentrations

above

Illinois

Class

I

Groundwater

Quality

Standards.

The

locations

of

these

results

suggest

the

potential

for

off-site

migration

in

the

upper

migration

zone,

south

of Pond

D.

While

boron

and

sulfate

have

been

detected

at

an

elevated

level

in

one

well

in

the

deep

alluvial

aquifer

compared

to

other

deep

alluvial

aquifer

wells,

the

concentrations

are

below

the

Illinois

Class

I

Groundwater

Quality

Standard.

Groundwater

use.

The

upper

migration

zone

is

not

used

for

potable

or

irrigation

water

supplies

at

or

downgradient

of the

Station.

This

zone

does

not

yield

sufficient

quantities

of

water

to

constitute

a

productive

aquifer

for

power

plant

operational

uses

or

agricultural irrigation

purposes.

Only

the

deep

alluvial

aquifer

at

depth

in

the

Wabash River bedrock

valley

has

sufficient

thickness

and

hydraulic conductivity

to

yield

adequate

groundwater

supplies

for

power

plant

and

agricultural

irrigation

purposes.

There

are

six

supply

wells

within

%

mile of

the

Station,

as shown

in

Appendix

H.

All

are

finished

in

the

deep

alluvial

aquifer.

Two

wells

are

located

directly

east

of

Pond

D

and

are

used

by

the

Station

for

potable

and

production

water

(plant

extraction

wells

EW-1

and

EW-2).

Four

wells

are

located

south

and/or west

of Pond

D

and

are

used

for irrigation

water.

The

nearest

public

water

supply

is in

Hutsonville,

which

draws water

from

the

deep

alluvial

aquifer

near

the

Wabash River

approximately

a

mile

to

the

south

of

the

Station

(see

Appendix

H).

As

the

only

off-site

groundwater

impacts

are

limited

to the

upper

migration

zone,

groundwater

from

Pond

D is

not

expected

to

impact

the Hutsonville supply

well

(NRT,

2009a).

As

noted,

the

upper

migration

zone

does

not

yield

sufficient

quantities

of

water

to

constitute

a

productive

aquifer

for

power

plant

or

irrigation

purposes;

however,

this aquifer

is

capable

of

supporting

residential

water

use.

While

no

potable

wells

exist

within

the

upper

migration

zone

within

the

area

that

may

be

impacted

by

Pond

D

(NRT,

2009a;

Appendix

H), the

landowner

adjacent

to the

southern

border

of

the

Station,

and

^

downgradient

of Pond

D,

has

agreed

to

groundwater

use

restrictions

to

ensure

that

no

small-scale

domestic

6

j

supplies

are

withdrawn

from

this

aquifer

within

the

impacted

area

(see

Appendix

B).

Potential

receptors

and

exposure pathways.

Based

on

the

presence

of

coal ash-related

constituents

in

the

upper

migration

zone

and

the

deep

alluvial

aquifer,

potential

exposures

to

these media

are

addressed

in

the

risk

assessments,

as

described

below.

Human

health

risk

assessment

(HHRA)

The HHRA

evaluated

potential

exposure

to

constituents

present

in

groundwater associated

with

Pond

D

to

determine whether

the

closure

plan/activities

for

Pond

D

are

protective

of

human

health

under

current and

reasonably

foreseeable

future

conditions

and

land

use.

The

HHRA

evaluates

potential

human

health

effects

using

the

four

step

paradigm

as

identified

by

the

USEPA

(USEPA, 1989).

The

steps

are:

•

Hazard

Identification

•

Dose-Response Assessment

•

Exposure Assessment

•

Risk

Characterization

Constituents

of

potential

concern

(COPCs)

were

identified

for

quantitative

evaluation

in

the

risk

assessment

based

on

a

comparison

of

the

maximum

detected

constituent

concentrations

in

each water-bearing

zone

to

conservative

drinking

water

screening

levels.

Boron

and

manganese were

identified

as

COPCs

in

the

upper

migration

zone;

no

COPCs

were

identified

in

the

deep

alluvial

aquifer.

Dose-response

values

available

from

current

USEPA

sources were

used

in

the

evaluation.

ES-2

April

2009

TSD

000339

---

AECOM

Environment

Exposure

scenarios

considered

for evaluation

in

the HHRA included direct

exposure

to

constituents

in

groundwater

either

by

use as

drinking

water

or

by

direct contact

with

groundwater exposed

in

an

excavation

trench

under

a

construction/utility

worker

scenario.

As

groundwater

discharges

to

the

Wabash

River,

recreational

users

of

the

river

were

also

evaluated.

The

HHRA

was

conducted

based

on

the

assumption

that

upper

migration

zone

groundwater

in

the

area

is

not

used

as

a

drinking

water

source

and

that

a

use

restriction

will

prevent

such

use

in

the

future.

The

deep

alluvial

aquifer

on-site

is

used

for

plant potable

and

production

water;

groundwater

immediately

downgradient

of Pond

D

is

not

currently

used

as an

off-site

drinking

water source,

though

it

could

be used

in

the

future

in

the

unlikely

event

that the

agricultural

land

use

would

change.

However,

no

COPCs

were

identified

in

the

deep

alluvial

aquifer

based

on

the

use

of

conservative

drinking

water screening

levels. Therefore,

a drinking

water pathway

was

not

quantitatively

included

in

the

HHRA.

The

water

table

can

occur

at

3

to

33

feet

below

ground

surface

(bgs).

It

is

assumed

that

a

future

construction/utility

worker

may

be

required

to

work

in

excavations

up

to

a

depth

of

15

feet

bgs.

Therefore,

a

future

construction/utility

worker

was

evaluated

for

direct

exposure

to COPCs

in

groundwater

in

the

upper

migration

zone

via

incidental

ingestion

and

dermal

contact

during

excavation.

Surface

water

concentrations

in

the

Wabash

River

were

estimated

from

the

maximum

detected

concentrations

of

constituents

in

groundwater

in

both

the

deep

alluvial

aquifer

and

the

upper

migration

zone.

Three

recreational

receptors

were

evaluated

for

potential

exposure

to

COPCs

that

may

have

migrated

to

the

Wabash

River.

A

recreational

child

and

a

recreational

teenager

were

evaluated

for

potential

exposure

to

COPCs

in

surface

water

while

swimming

via incidental

ingestion

and dermal

contact.

A

recreational

fisher

(adult)

was

evaluated

for

potential

exposure

to COPCs

in

surface

water

while

wading

via

incidental

ingestion

and dermal

contact and

for

potential

exposure

to

COPCs

via

ingestion

of

fish

caught

in

the

river.

The

results

of

the

HHRA indicate

that

predicted

risks

are

orders

of

magnitude below regulatory target

risk

levels

and,

therefore,

no

adverse

health effects

are

expected

for

any

of the

receptors

evaluated

based

on

the

assumptions

of

the

HHRA.

Ecological

risk

assessment

(ERA)

The

screening

level

ERA

evaluated

potential

exposure

by

ecological

receptors

to

constituents

present

in

groundwater

associated

with

Pond

D

to

determine whether

the

closure

plan/activities

for Pond

D

are

protective

of

the

environment

under current and

reasonably

foreseeable future

conditions

and

land

use.

The

screening

level

ERA

is

organized

into the

three

following

major

sections

suggested

by EPA's

Framework

for

Ecological

Risk

Assessment (USEPA,

1992);

these

are:

•

Problem Formulation

•

Risk

Analysis

•

Risk

Characterization

Exposure

scenarios

considered for

evaluation

in

the

ERA

included

use

of

the

deep

alluvial

aquifer

for

irrigation,

and

as

groundwater

discharges

to the

Wabash

River,

aquatic

receptors

in

the river

were

also

evaluated.

To

evaluate

the

use

of

groundwater

as

a

source

of

irrigation

water,

which

is

used

as

a

supplement

to

rainwater,

the

average

constituent

concentrations

in

the

deep

alluvial

aquifer

were

compared

to

ecological

risk

based

screening

levels

and

short

term

agricultural

water

quality

levels. Based

on

this

comparison,

it

is

not

expected

that

groundwater

used

for

irrigation

will

adversely impact

crops.

ES-3

April 2009

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---

AECOM

Environment

A

screening

level

ERA

was

conducted

to

determine

whether

exposure

to

constituents

in

groundwater

discharging

to

the

Wabash

River

posed a

risk

to

ecological

receptors.

Surface

water

concentrations

in

the

Wabash

River

were

estimated

from

the

maximum

detected

concentrations

of

constituents

in

groundwater

in

both the

deep alluvial

aquifer

and

the

upper

migration

zone.

The

maximum

estimated

surface

water

concentrations

were

then

compared

to

Illinois

Water

Quality

Standards

(WQS)

and

federal Ambient

Water

Quality

Criteria

(AWQC)

derived

to

be

protective

of

aquatic

life.

Estimated

concentrations

of

the

detected

constituents

were

well below

the

screening

levels

indicating

that

groundwater

discharging

into

the

Wabash

River

is unlikely

to

pose

a

risk

to

aquatic

receptors

in

the

river

in

the

vicinity

of

the

Station.

The results of

the

ERA

indicate

no

potential

for

ecological

risks

associated

with

the

Pond

D

closure

plan/activities,

and

no

further

ecological

evaluation

is

warranted.

Summary

The

human

health

and ecological

risk

assessments

presented

in this

report have

demonstrated

that

the

current

environmental

conditions associated

with

Pond

D

are

protective

of

human

health

and

the

environment

under

current

and

reasonably foreseeable

future conditions

and

land

use.

Closure

plan/activities

for

Pond

D

are

expected

to

result

in

groundwater meeting

Illinois

Class

I

groundwater

quality

standards at

the

Station

property

boundary

in

the

future

(NRT,

2009b).

Therefore,

the

closure

plan/activities

for

Pond

D

are

also

protective

of

human

health

and

the

environment.

ES-4

April

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1.0

Introduction

This

report

presents

a

human

health

risk

assessment

(HHRA)

and

an

ecological risk

assessment

(ERA) in

support of

the

closure

of

Pond

D,

a

former

coal

ash

impoundment,

at

the

Ameren

Energy

Generating

Company's

Hutsonville

Power

Station

(Station).

Ameren

is

requesting

that the

Illinois

Pollution

Control Board

(Board)

adopt

a

site-specific regulation regulating

the

closure

of

Pond

D.

The

closure,

detailed

more

fully in

NRT,

2009a,

includes

capping

of

Pond

D

with a

geo-synthetic

membrane,

and

installing

a

groundwater

collection trench

along

the

southern

Station property

boundary.

1.1

Purpose

The

purpose

of

the

HHRA

and

ERA

presented

in

this report

is

to

determine

if

the

closure

plan/activities

for

Pond

D

are

protective

of

human

health

and

the

environment under

current

and

reasonably

foreseeable future

conditions

and

land

use.

This

is accomplished

by

evaluating potential

human

health

and

ecological

effects of

potential

exposures

to

constituents

detected

in

samples

of

groundwater

from the

upper

migration

zone

and

the

deep

alluvial

aquifer

associated

with

Pond

D

(see

Section

2).

1.2

Human

health

risk

assessment

(HHRA)

The

HHRA

was

conducted

to

be consistent

with

United States

Environmental

Protection

Agency

(USEPA)

guidance

for

conducting

a

risk

assessment

(see

Section

4)

as

well

as

the

Illinois

Environmental Protection

Agency

(IEPA)

Tiered

Approach

to Corrective

Action

Objectives (TACO)

(IEPA,

2007).

The

HHRA

has

been

conducted

in

accordance

with

the

four-step

paradigm

for

human

health

risk

assessments

developed

by

~\

USEPA

(USEPA,

1989);

these steps are:

•

Data

Evaluation and Hazard

Identification

•

Toxicity

Assessment

•

Exposure

Assessment

•

Risk

Characterization

1.3

Ecological

risk

assessment

(ERA)

The

ERA

was

conducted

to

be consistent

with

USEPA

guidance

for

conducting

a risk

assessment.

The

ERA

is

organized

into the

three

following

major sections suggested

by EPA's

Framework

for

Ecological

Risk

Assessment

(USEPA,

1992);

these

sections

are:

•

Problem

Formulation

•

Risk

Analysis

•

Risk

Characterization

1.4

Report organization

The

information

presented

in

each

section

of the

report

follows.

•

Section

2.0

-

Conceptual Site

Model.

This

section discusses

the study

area

and

its

environs,

describes

source

areas,

potential migration

pathways,

and

potentially

impacted

media.

•

Section

3.0

-

Data

Evaluation.

This

section

presents

a

summary

of

the

data

for

use

in

the

HHRA

and

ERA.

1-1

April

2009

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Environment

•

Section

4.0

-

Human

Health

Risk

Assessment.

This

section

presents

the

HI-IRA

methods

and

results.

•

Section

5.0

-

Ecological Risk

Assessment.

This

section

presents

the ERA

methods and

results.

•

Section

6.0

-

Conclusions.

This

section

summarizes

the

conclusions

of

the

HHRA

and

ERA.

•

Section

7.0

-

References.

This

section

presents

the

references

used

in

the

text.

Tables and

figures

are

provided

after

Section

7.

Note

that

table

and

figure

numbers

are

based

on

the

appropriate

section.

1-2

April

2009

TSD

000343

---

AECOM

2.0

Conceptual

site

model

This

section

presents

the

conceptual

site

model

(CSM)

for Pond

D.

A

CSM

describes

the

system

in

which

a

site

is

located,

and includes information about

the

setting,

land

use,

geology

and

hydrogeology,

potential

sources,

groundwater

monitoring

and

modeling,

and

groundwater

use.

CSMs

specific

to the

HHRA

and

the

ERA

are

also

provided

that

present

potential

receptors,

and

potential

pathways

to

receptors.

The

conceptual

model

is

the

foundation

for

the

development

of the

risk

assessments.

2.1

Setting

The Hutsonville

Power

Station

is

located

in

Crawford

County,

Illinois

on

the

west

bank

of

the

Wabash

River

between

the

towns

of

Hutsonville

and

York (SW1/4,

Section

17,

Township

8N,

Range

11W),

on

approximately

205

acres.

Figure

2-1

presents

the location

and

environs

of

the

Station.

The

Station

consists

of

a

coal-fired

electrical

generating

plant

and

a

wastewater

disposal

system

for

management

of

coal-combustion

wastes,

including

fly

ash.

The coal-fired

power

plant

has

operated

since

the

1940's.

The

wastewater

disposal

system

consists

of

five

surface impoundments,

denominated

Pond

A,

Pond

B,

Pond

C,

Pond

D,

and

the

bottom

ash

pond.

The

impoundments accept

only

coal

combustion

waste

(fly

ash

and

bottom

ash) and

low-volume

waste

from

the

Hutsonville

facility.

In

1968

Pond

D

was

constructed

as an

unlined

water

pollution

treatment

facility

for

coal

combustion

and

related

wastes

generated

at

the

Station.

Pond

D

has

an

area

of

approximately

22

acres,

is

located

on

the

west

bank

of

the

Wabash

River,

and

is

as

dose as

one

hundred

(100)

feet

to the

river.

Pond

D

no

longer

('

^i

receives

coal combustion

by-products,

and

sluice

waters

from the

power

station

are

no

longer

routed

through

v

the

impoundment.

Ameren

estimates

that

during

its

30

years

of

active

operation,

Pond

D

accumulated

approximately 950,000

cubic

yards

of

ash and

approximately 280,000

cubic

yards

lies

below

the

water

table.

The

land

use

for

the

Station

is

classified

as

industrial. The

Wabash River forms

its

eastern

border

while

farmland

comprises

the

southern

and western

borders.

The northern

border

is

undeveloped

wooded

land.

The

closest residence

is

approximately

one-half

mile

from

the

Station.

2.2

Site

geology

and hydrogeology

There

are

two

water

bearing

units of interest

in

the

vicinity

of

Pond

D

(NRT,

2009a).

•

The

"upper

migration

zone,"

which

is

unconfined

with

the

depth

to

water

ranging

from

3

to

20

feet

below

ground surface,

depending

on location.

•

The

"deep

alluvial

aquifer,"

which is

confined,

with

depth

to

the

top

of

this

aquifer

ranging

from

22

to

24

feet

on

the

plant

property.

A

confining

layer

is

present

that

restricts vertical

migration

of

groundwater

between

the

upper

migration

zone

and

deep

alluvial

aquifer.

Groundwater

flow

direction

in both

the

upper

migration

zone

and

the

deep

alluvial

aquifer

is

eastward,

toward

the Wabash

River.

2.3

Potential

sources

As

an

unlined

former

(now

dewatered) coal ash

impoundment,

with

ash

present

below

the

water

table,

constituents

may

leach

from

Pond

D

and

impact

groundwater.

Boron

and

sulfate

are

constituents

that

can

leach

from

coal ash and

are

mobile

in

groundwater.

Groundwater

monitoring

of

Pond

D

has

indicated

that

2-1

April

2009

TSD

000344

---

AECOM

Environment

boron

and sulfate

are

present

at

some

locations

in

groundwater

at

concentrations above

Illinois

Class

I

Groundwater

Quality

Standards,

as

discussed

in

more

detail

below

and

in

Section

3.

2.4

Groundwater

monitoring and

modeling

Ameren

has maintained

a

monitoring

well

network

at

the

Station

and has

sampled

wells

periodically

since

1984.

Monitoring

wells

associated

with

Pond

D

are

shown

on Figure

2-2.

Pond

D

is

underlain

by

two

water

bearing

units

(the

upper

migration

zone

and

the

deep

alluvial

aquifer)

that

are

separated

by

materials

that

have

low

hydraulic conductivity (shale

bedrock

or

silts

and

clays).

Wells installed

to

monitor

groundwater

quality

associated

with

Pond

D

(see

Section

3)

have

indicated that

elevated

concentrations

of boron and sulfate

(two

common

indicators

of

coal ash

impacts)

are

present

in

Pond

D

monitoring

wells

screened

in

the

upper

migration

zone

(NRT,

1999).

Groundwater

samples

from

wells

MW6

and

MW11R,

which

are

screened

in

the

upper

migration

zone

near

the

south

property

boundary,

show

elevated

boron

and

sulfate

concentrations,

suggesting

the

potential

for

off-site

migration.

Ameren

investigated

the

extent

of

off-site

impact

by

obtaining direct-push

samples

approximately

1,300

feet

in

the

actively

farmed

agricultural field

immediately

south

of

the

property line

and

determined

that

the

upper

migration

zone was

not impacted

at

these

locations

(NRT,

1999). To

further

delineate

the

extent

of

offsite

impacts,

Ameren

used

a

calibrated

numerical groundwater

flow

and

transport

model

which

calculated

the

extent

of

such impacts

in

the

upper

migration

zone

to be

approximately

500

feet

from

the

Station's

southern

property line

(NRT,

2009b).

As

suggested

by

the

groundwater

modeling

conducted

by

NRT,

the

past

dewatering,

together

with

the future

capping

of the

unlined Pond

D,

and

the installation

of

a

groundwater

collection

trench,

will

result

in

groundwater

meeting

Class

I

groundwater

standards

in

the

future

at

the property

boundary.

Groundwater

in

the

deep

alluvial

aquifer

has

also been

monitored.

The results

indicate

highly

localized,

low-

level

(i.e.,

lower

than Class

I

standards)

coal ash

impacts

at

MW14.

The

efficacy

of

the

confining

layer

to

limit

migration

is

supported

by

these concentration

data

because,

as

explained

by

NRT

(2009a),

the

concentrations

are

much lower

than

in

the

upper

migration

zone,

despite

the fact that

Pond

D

was

fist

placed

in

service

more

than

40

years

ago.

2.5

Groundwater

use

The

upper

migration

zone

currently

is

not

used

at

or

downgradient

of

the

Station.

This

zone

does

not

yield

sufficient

quantities

of

water

to constitute

a

productive

aquifer

for

power

plant

operational

uses or

agricultural

irrigation

purposes.

Only

the

deep

alluvial

aquifer

at

depth

in

the

Wabash

River

bedrock

valley

has

sufficient

thickness

and

hydraulic conductivity

to

yield

adequate groundwater

supplies

for

power

plant

and

agricultural

irrigation

purposes.

There

are

six

supply

wells

within

Vt

mile of

the

Station,

as

shown

in

Appendix

H.

All

are

finished in

the

deep

alluvial

aquifer.

Two

wells

are

located

directly

east

of

Pond

D

and

are

used

by

the Station

for

plant

water

(plant

extraction wells EW-1

and EW-2). Four

wells

are

located south

of

Pond

D

and

are

used

by

the

adjacent

landowners

for

irrigation

water.

The

nearest

public

water

supply

is

in

Hutsonville,

which

draws

water

from

the

deep

alluvial

aquifer

near

the

Wabash

River

approximately

a

mile

to

the

south of

the

Station

(Appendix

H).

Since

groundwater

flow

is

toward

the

east (NRT,

2009a),

there

is

no reason

to

expect

that

groundwater

from

Pond

D

can

impact

the

Hutsonville

supply

well. Appendix

A

presents

the

Consumer

Confidence

Report

(CCR)

for

the

Hutsonville

water

supply.

As

can