Chapter

6

TSD000175

---

AMEREN

HYDROGEOLOGIC

ASSESSMENT

HUTSONVILLE

POWER

CRAWFORD

COUNTY,

PROJECT

NO:

Resource

Technology

TSD

000176

---

Resource

Technology,

Inc.

N

R

T

HUTSONVILLE

POWER

STATION

HUTSONVILLE,

ILLINOIS

HYDROGEOLOGIC

ASSESSMENT

FINAL REPORT

Project

No:

1375

Prepared

For:

Ameren

Services

One

Ameren Plaza

1901

Chouteau

Avenue

St.

Louis,

Missouri

Prepared

By:

Natural

Resource Technology,

Inc.

23713

W.

Paul

Road,

Suite

D

Pewaukee,

WI

53072

August

19,1999

Spires

s

L.

L.

Fafalios,

Fafalios.

P.E.

P.E."

^l/

,<^-

Environmental

Engineer

6rucelE{.

Hensel,P.G.

Senior

Hydrogeologist

23713

W.

Paul

Road.

Unit

D

•

Pewaukee,

WI

53072

.

(262)

523-9000

<

Fax

(262)

523-9001

www.naturalrt.com

---

TABLE

OF

CONTENTS

EXECUTIVE

SUMMARY..................................................................................

ES-1

1

INTRODUCTION......................................................................................................

1-1

2

FIELD

PROCEDURES

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

2-1

2.1 Direct-Push

Sampling......................................................................................

2-1

2.1.1

Laboratory

Samples

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

2-2

2.1.2

Probe

Hole

Abandonment....................................................................

2-3

2.2

Installation

of

New

Monitoring

Wells................................................................

2-3

2.2.1

Rationale..............................................................................................

2-3

2.2.2

Drilling...................................................................................................

2-4

2.2.3

Construction

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

2-4

2.2.4

Development........................................................................................

2-5

2.2.5

Hydraulic

Testing..................................................................................

2-6

2.3

Decontamination..............................................................................................

2-6

2.4

Waste

Handling...............................................................................................

2-7

3

RESULTS OF

FIELD

INVESTIGATION

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

3-1

3.1

Site

Geology....................................................................................................

3-1

3.1.1

Stratigraphic

Units................................................................................

3-1

3-1.2

Subsurface

Ash/Coal

Distribution.........................................................

3-2

3.1.3

Bedrock

Topography............................................................................

3-4

3.2

Site

Hydrogeology...........................................................................................

3-5

3.2.1

Hydraulic

Conductivity..........................................................................

3-5

3.2.2

Groundwater

Flow................................................................................

3-5

3.2.3

Elevation

of

Groundwater

Relative to

Ash............................................

3-7

3.3

Nearby

Groundwater

Users.............................................................................

3-8

hutsonville

hydrogeologic

assessment.doc

Natural

Resource

Technology

TSD

000178

---

TABLE

OF CONTENTS

4

GROUNDWATER QUALITY

IN

DIRECT-PUSH SAMPLES

...................................4-1

4.1

Parameters

of

Concern

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

4-1

4.2

Direct-Push

Leachate

Samples.......................................................................

4-1

4.3

Direct-Push

Groundwater

Samples.................................................................

4-2

5

GROUNDWATER

QUALITY

IN

MONITORING

WELLS..........................................

5-1

5.1

Parameters

of

Concern

...................................................................................5-1

5.2

Groundwater

Results.......................................................................................

5-1

5.3

Surface

Water

Results.....................................................................................

5-3

5.4

Source

Area

and

Receptor

Analysis................................................................

5-4

6

CONCLUSIONS.......................................................................................................

FIGURES

Figure

9:

Figure

10:

Figure

11:

Figure

12:

Figure

13:

Figure

14:

Figure

15:

Figure

16:

Figure

17:

Site

Plan

(1375-1-B01)

Elevation

of well

screens,

ground

surface,

bedrock

surface,

and

groundwater

Geologic

cross-sections

(1375-1-B12)

Bedrock

elevation

contours

(1375-1-B11)

Water

table

elevation

contours,

November

16-18,1998

(1375-1-B09)

Water

table

elevation

contours,

April

29-30,1999

(1375-1-B10)

Historical

groundwater.

elevations

at

MW-2

and

MW-3

Historical

groundwater

elevations at

nested

wells

(MW-3/3D,

MW-7/7D,

MW-10/10D)

Site

location

map

(1375-A01)

Total

boron

in

groundwater

(1375-1-B02)

Historical

total

boron

concentrations

in

MW-2

and

MW-3

Sulfate

in

groundwater

(1375-1-B07)

Total

maganese

in

groundwater

(1375-1-B03)

Total iron

in

groundwater

(1375-1-B05)

Total

nickel

in

groundwater

(1375-1-B04)

Field

pH

in

groundwater

(1375-1-B06)

Total

dissolved

solids

in

groundwater

(1375-1-B08)

hutsonviHe

hydrogeologic

assessment.doc

Natural

u

Resource

Technology

TSD

000179

---

TABLE OF

TABLES

Table

1:

Direct-Push

Sampling

Data

Table

2:

Water

Sample

Parameters

and

Analytical

Methods

Table

3:

Monitoring

Well

Locations,

Elevations,

Depth

to

Bedrock,

and

Screened

Formation

Table

4:

Monitoring

Well

Completion

Details

Table

5:

Monitoring

WeU

Slug

Test Results

Table

6:

Leachate

and

Groundwater

Concentration

Results

from Direct-Push

Samples

Compared

to Ash

and

Coal Thickness

Table

7:

Groundwater

Concentration

Results

from

Monitoring

Wells

Compared

to

Ash

and

Coal

Thickness

Table

8:

Source

APPENDICES

Appendix A:

Boring/Monitoring

Well

Construction

Logs

Appendix

B:

Slug-Test

Data

Appendix

C:

Direct-Push

Water Quality

Results

Appendix

D:

Water

Well

Logs

hutsonville

hydrogeologic

assessment.doc

ill

Natural

.

Resource

Technology

TSD000180

---

EXECUTIVE

SUMMARY

This

hydrogeologic

assessment

describes

hydrogeology, groundwater

flow,

and

groundwater

quality

near

the

AmerenQPS

Hutsonville

Power

Station ash

impoundments.

There

are two

impoundments

at

this site,

an

unlined

impoundment

that

has

been

in

operation

since

1968

and

a

hned

impoundment

that

has been

in

operation

since

1986.

This

assessment

was

prompted by

concentrations

of boron

and

sulfate

at

several

monitoring

wells

near

these

impoundments

that

exceeded

Illinois

Class

I

groundwater

standards.

Boron

and

sulfate

are

indicator

parameters

for

coal

ash leachate

in

groundwater.

Two

rounds

of

field

work

were

performed.

From

August

25-28,

1998,

soil,

leachate,

and

groundwater samples

were

collected

at

23

locations across

the

site

using

direct-push

sampling

methods.

In

addition,

two

temporary

well

points

were

installed

and

sampled

in

the

lined

ash

impoundment.

From

October

5-10,

1998,

seven

monitoring

wells

were

installed

to

augment

the

existing network

of

nine

monitoring

Results

of

Field

Investigation

Coal

ash

is

found

predominantly

in

three

areas

of

the

plant

site:

the

two

impoundments

and

an

ash

laydown area

that

is

between

the

two

impoundments.

Ash

thickness

in

the

unlined

impoundment

ranged

from

about

12

feet at

the

north

end

of

the

impoundment

to

31

feet in the

central

portion

of

the

impoundment.

Ash

thickness

in

the

laydown

area

is

as much

as

12

feet.

There

is

also

a

coal

pile

near

the

impoundments,

and

some

boreholes

outside

the

coal

pile

area

encountered

thin

seams

of

spilled

coal

near

the

surface.

The

stratigraphy

encountered

at

the

Hutsonville

Power

Plant

consisted

of

a

relatively

thin

veneer

of

unlithified

deposits

overlying bedrock. Over most

of

the

site,

the unlithified

units

are

sandy

and

less

than

20

feet

thick;

however,

thickness

abruptly

increases

to at

least

90

feet

near

the

Wabash

River,

where

there

is

a

bedrock

valley.

Silt

was

found

in

the

upper

portion

of

the

hutsonville

hydrogeologic

assessment.doc

Natural

ES-1

Resource

Technology

TSD000181

---

EXECUTIVE SUMMARY

bedrock

valley,

and

sand and

gravel

occurs

in

the

lower

portions

of

the

valley.

The

underlying

bedrock

is

comprised

mainly ofPennsylvanian-age

sandstone and

shale.

The

groundwater

surface

throughout

most

of

the

plant

site

occurs

within sand and

gravel.

However,

near

the

river,

it

occurs

within alluvial

silt

and

clay

deposits,

and

near

the

southern

portion

of

the

unlined

impoundment

the

groundwater

surface

occurs

within

ash.

Groundwater

flow

through

the

sand

is

east

toward

the

Wabash

River.

Horizontal

groundwater

flow

velocity

varies

with

hydraulic gradient

and

hydraulic

conductivity,

and

was

estimated

to

range

from

150 ft/yr

to

240

ft/yr

in

the

sand.

and

gravel

Groundwater

and

Leachate Quality

The Hutsonville

work

plan

identified

boron,

sulfate,

manganese,

pH,

and

IDS

as

parameters

of

concern

(POCs)

because

they

had

concentrations

in

groundwater

near

the

impoundments

that

exceeded

Ulinois

Class

I

groundwater

standards.

Boron

and

sulfate

are

indicator

parameters

of

coal

ash

leachate,

while

the

other

POCs

are

not necessarily indicators.

Iron

and

nickel

were

also

included

in

this

assessment

because

these

parameters

sometimes

have

high

concentrations

in

groundwater

near

coal

piles.

Most

ash

leachate

samples

bad

boron,

sulfate,

and

TDS

concentrations

that

exceeded

the

Class

I

groundwater standard-

Manganese

exceeded

the

standard

in

leachate

from

the

unlined ash

impoundment

and

from

the

former

ash

laydown

area,

but

not

in

the

lined

ash

impoundment

(lowest

concentrations

on

site);

thereby

exhibiting

its

unreliability

as

an

ash

indicator

parameter.

Iron

was

below

the

standard

in

all

leachate

samples

from

the

impoundments,

but

exceeded

the

standard

in

the

leachate

sample from

the

former

ash

laydown

area.

Nickel

was

below

the

standard

in

all

leachate

samples.

The

pH

of

the

leachate

samples

was

neutral,

except

in

the

lined

impoundment

where

it

was

alkaline.

Direct-push

groundwater

samples

showed

concentrations of

boron,

manganese,

sulfate,

and TDS

higher

than

Class

I

standards

in

most samples

near

the

impoundments

and

the

ash

laydown

area.

hutsonville

hydrogeologic assessment.doc

.

Natural

ES-2

Resource

Technology

TSD

000182

---

EXECUTIVE SUMMARY

Groundwater

samples

extracted

near

the

coal

pile

typically had

high

concentrations,

relative

to

standards,

of

iron,

nickel,

sulfate,

IDS,

and

manganese.

Acidic pH

values

were

recorded

in

groundwater

samples

throughout

the

coal

pile

area,

and

values

were

typically

lower

than

the

lower

Class

I

standard.

There

was

only

one

standard

exceedance

(manganese)

in

groundwater

sampled

south

of

the

site.

Groundwater

samples from

several

monitoring

wells

near

the

ash

laydown

area

and

unlined

ash

impoundment

had

high

concentrations,

relative

to Class

I

standards,

of

boron,

manganese,

sulfate,

and

TDS.

There

were

also

two

wells

with

high

nickel and

low

pH,

and

both

of

these

wells

were

in

areas

where

coal

had

been

spilled.

I

Overall,

there

is

a

correlation between

groundwater

quality

and

potential

leachate

sources.

Groundwater

near

the

unlined

coal

ash

impoundment

and

ash

laydown

area

had

high

boron

and

sulfate

concentrations.

Groundwater

near

the

coal

pile

and

coal

spill

areas

typically had

high

nickel,

iron,

and

sulfate

concentrations.

Groundwater

near

the

coal

pile

also

had

very

low

h

Conclusions

i

Groundwater

samples

from

some

on-site monitoring

wells

and

direct-push

locations

had

'.

concentrations

of

boron,

manganese,

sulfate,

TDS,

iron,

and

nickel

higher

than Class

I

standards.

j

High

iron

and

nickel

concentrations

were

found

in

locations

where

coal

was

present.

These

observations

indicated

two general

sources

for

groundwater

quality impacts:

1)

the

coal

pile

and

h

coal

spill

areas,

and

2)

the ash

laydown

area

and

unlined

ash

impoundment.

There

is

no

evidence

that

iron

and

nickel

from

the

coal

pile

and

coal

spill

areas

is

migrating

beyond those

areas.

However,

boron

and

sulfate

are

migrating east

toward

the

Wabash

River.

There are

no

groundwater

extraction

wells

in the

shallow

sediments

between

the

unlined

ash

impoundment

and

the

Wabash

River.

There

are

four extraction

wells

within

%

mile

of

the

site,

all

finished in

deep

sand

and

gravel

in

the

Wabash

River

valley.

Two

wells

are

directly

east

of

hutsonville

hydrogeologic assessment.doc

Natural

ES-3

Resource

Technology

TSD000183

---

EXECUTIVE

SUMMARY

the

unlined

impoundment

and

are

used

for

plant

water,

and

two

wells

are

southeast

of

the

impoundment

and used

for

irrigation

water.

Groundwater

quality

data

from

monitoring

well

MW-7D,

which

is

directly

downgradient of

the

unlined

ash

impoundment

and

is

the deepest

on-

site

monitoring

well

in

the

Wabash

River

valley,

indicates

no

evidence

of

ash

impoundment

or

coal

pile impacts

at

that depth.

hutsonvillc

hydrogeologic

assessment.doc

Natural

ES-4

Resource

.

Technology

TSD000184

---

1

INTRODUCTION

AmerenCIPS

operates

the

Hutsonville

Power

Station

in

Crawford

County

Illinois. The

Power

Station

is

located

on

the

west

bank of

the

Wabash

River

between

the

towns

of Hutsooville

and

York

(SW

%,

Section

17,

Township

8N,

Range 11W).

The

coal-fired

power

plant

has

been

in

operation

since

the

1940's.

There

are currently two

units

operating

at

the

plant,

completed

in

|

1953

(unit

3)

and

1954

(unit

4),

with

a

combined

generating

capacity

of

156

MW.

Fly

ash

from

^

the

operating

units

is

collected

by

an

electrostatic

precipitator

and sluiced to

a

lined

ash

I.

I

impoundment.

Bottom

ash

is

sluiced

to

a

separate

pond

and

eventually

recycled.

Sluice

water

,

from

both

the

bottom

ash

pond

and

lined

fly

ash

impoundment

is

routed

through

an

unlined

ash

I

impoundment,

before

discharge

to

the

Wabash

River

via

an

NPDES

permitted

outfall.

The

lined

I

ash

impoundment

was

constructed

in

1986, and

has

an

area

of

about

12

acres.

The

unlined

'.

impoundment

was

constructed

in

1968,

and

has

an

area

of

about

17

acres.

Groundwater

quality

has

been

monitored

at

this

facility

since

1984.

Concentrations of

boron

and

j-

sulfate

at

several

monitoring

wells

exceed

Blinois

Class

I

groundwater standards.

Boron

and

sulfate

are

indicator

parameters

for

coal

ash

leachate in

groundwater.

In

response

to these

f

findings,

Ameren

Services

contracted Science

&

Technology

Management

Inc.

(STMI) and

'

Natural Resource

Technology

Inc.

(NRT)

to

perform

a

hydrogeologic

assessment

that

will

[

characterize

hydrogeology,

groundwater

flow,

and

groundwater

quality

at

this

facility.'

1

Science

&

Technology

Management

Inc.

(STMI)

ceased

operations

on

January

31,1999.

At

that

time,

the

STMI

project

manager

overseeing

this

investigation

took

a position

at

Natural

Resource

Technology,

Inc.

(NRT).

NRT

developed

this

report

based

on

information

in

STMI's

files

and

on

the

project

managers

past

involvement

with

this

project.

hutsonville

hydrogeologic

assessment.doc

1-1

Natural

Resource

Technology

TSD000185

---

2

FIELD

PROCEDURES

Two

rounds

of

field

work

were

scheduled

and

completed.

From

August

25-28,

1998,

soil and

groundwater

samples

were

collected

at

23

locations

across

the site

(Figure

1) using

direct-push

sampling

methods.

In

addition,

two

temporary

well

points

were

installed

and

sampled

in

the

lined

ash

impoundment.

From

October

5-10,

1998,

seven

monitoring

wells

were

installed to

augment

the

existing

network

of nine

monitoring

wells.

The

monitoring

wells

were

installed

in a

manner

consistent

with

specifications

in

Section

811.318(d)

of

the

Illinois

Waste

Management

Rules.

In

addition,

hydraulic

conductivity

tests

were

performed

on

selected

new

and

existing

monitoring

wells.

Drilling

was

performed

by

American

Environmental

Corporation

of

Indianapolis,

IN,

under

subcontract

to

STMI.

Field

geology

and

hydraulic

testing

were

performed

by

STMI.

Water

quality analyses

were

performed

by

AmerenCIPS central

i

2.1

Direct-Push Sampling

,

—A-truek-mounted,-GeoProbe™-direct-push

sampling

system-was

used to

collect coal

ash,

soil,

and

groundwater

samples from

23

locations

across

the

Hutsonville

plant

site

(Figure

1).

The

direct-

I

push

sampling

was

conducted

to

survey groundwater

quality

around

the

site,

to

estimate

the

depth

of

ash

and

obtain

leachate

samples

in

the

old

impoundment,

to

log

the

type

and

extent

of

geologic

and

fill

materials,

and

to estimate

depth

to

bedrock.

Table

1

lists

direct-push

sampling

data;

boring logs

are

provided

in

Appendix

A.

\

•

A

Macro-Core®

Soil Sampler,

consisting

of

a

52-inch

long

by

2.2-inch

O.D.

split-barrel

sampler

fitted with

a

replaceable

plastic

liner, was

used

to

collect

a

continuous

sequence

of

soil

and

ash

core

at

each

probe

hole

location.

The

probe

holes

were

advanced

to

bedrock,

typically

encountered

at

depths

of

9.5

feet to

36.5

feet.

Bedrock

was

not

encountered

at

locations

GP-14

(total depth

40

feet)

and

GP-19

(total depth

32

feet)

southeast of

the

plant

site.

After

a

probe

hole

was

geologically

logged,

a

Screen

Point

15

Groundwater

Sampler®

was

connected to

the

direct-push

rod

and

driven

into

the

ground

to

the

target

sampling

depth.

The

water

sample

was

hutsonville

hydrogeologic

asscssment.doc

2-1

Natural

Resource

Technology

TSD000186

---

2

FIELD

PROCEDURES

collected

by

retracting

the

rod

several

feet

to

expose

the

sampler's

stainless

steel

screen,

then

inserting

a

section

of

disposable

polyethylene

tubing

and

slowly

extracting

the

sample

using a

peristaltic

pump

connected

to the

tubing.

Water

samples

were

not

collected at locations

GP-1,

GP-19,

and

GP-22

because

of

low

water

yield

from

the

screened materials.

No

water

sample

was

collected

at

probe

hole

GP-8,

which

was

used

only

to

log

geology

near

the

southwest

comer

of

the

lined

ash

impoundment.

Concurrent

with

direct-push

sampling,

two

temporary

well

points

were

installed

at

depths

of

seven

to

eight

feet

in

the

lined ash

impoundment

to collect

leachate

samples

(Figure

1,

LP

locations).

Each

well

point

was

constructed

of

1.25-inch

I.D.,

polyvinyl

chloride

(PVC)

pipe

flush-threaded to

a

four-foot long

section

of

0.01-inch factory-slotted

PVC

screen

covered

by

a

filter

sock.

Because

the

lined

impoundment

was

too

soft

for truck

access,

the

well

points

were

hand-driven

into

the

ash.

The

leachate

samples

were

collected

by

hand

pumping

a

section

of

disposable

high-density polyethylene

(HDPE)

tubing

connected

to

a

stainless

steel

foot-valve.

After

sampling,

the

temporary

well

points

were

completely

removed

and

the

holes

were

allowed

2.1.1

Laboratory Samples

All

direct-push

water

samples

were

collected

in

laboratory

transfer

containers

and

transported

to

the

Hutsonville plant's

on-site

laboratory

for

measurement

of

temperature,

electrical

conductivity,

pH,

dissolved

oxygen,

and

oxidation-reduction

potential.

Samples

for

metals

analysis

were

then

passed

through

a

0.45

micron

cellulose

nitrate

filter

membrane

(one

per

sample)

into

250-ml

polyethylene

containers and

preserved

with

concentrated

nitric

acid.

The

remaining

sample

volume was

transferred into

1000-ml

polyethylene

containers

(without

preservatives).

All

sample

aliquots

were

stored

at

a

temperature

below

39°F

(4°C)

prior

to

analysis

at

AmerenCIPS

laboratory.

Parameters analyzed

and

analytical

methods

used

are

listed

in Table

2.

hutsonville

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2.1.2

Probe Hole

Abandonment

Upon

completion

of

sampling,

probe

holes that

encountered

coal

or

coal

ash

were

backfilled

with

bentonite

grout

that

was

injected

as

the probe

or

sampler

was

withdrawn,

while

probe

holes

that

did

not

encounter

ash

were

backfilled

with granular

bentonite.

Pump

tubing

was

discarded

after

collection

of

each

water

sample

and all

reusable

direct-push

sampling

equipment

was

decontaminated

to

prevent cross-contamination

between

sampling

2.2

Installation

of

New Monitoring

Wells

•*

2.2.1

Rationale

Seven

new

groundwater

monitoring wells

were

installed

at

locations determined

after

analysis

of

:

previous

groundwater sampling

and

the

direct-push

sampling.

Well

location, elevation,

and

-

completion

details

are

listed

in

Tables

3

and

4.

Boring

logs

and

well

completion

reports

are

provided

in

Appendix

A.

:

Four"

shallow wells

were

installed.

One

shallow

well

(MW-10)

was

installed to

provide

additional

background

groundwater

quality

data.

Three shallow

wells

(MW-11,

MW-12,

and

MW-13)

were

installed

to

characterize

aquifer properties

and

groundwater

flow

at the

site,

and

to

delineate

the

extent

of

groundwater

impacts

associated with the

ash

impoundments.

Wells

MW-10,

MW-12,

and

MW-13

were

screened

predominantly

in

unlithified

materials,

although

MW-10

extended

into

the

very

shallow

bedrock

(Figure

2).

Shallow

monitoring

well

MW-11

I

was

screened

mostly

within

shallow

bedrock, where

the

water

table

was

encountered.

Three

deep

wells

were

installed.

Deep

well

MW-7D

was

nested

with

existing

well

MW-7

to

evaluate

the

vertical

groundwater

quality

distribution

and

vertical flow conditions

between

the

unlined

ash

impoundment

and

the

Wabash

River.

Wells

MW-3D

and

MW-10D

were

installed

completely

within

bedrock

to

measure

hydraulic

properties

and

groundwater

quality

in

the

sandstone.

The

two

wells

were

nested

with

existing

shallow wells

to

determine

vertical

gradient

hutsonville

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between

the

sandstone

and

the

overlying unlithified sediments,

and

to evaluate

whether

the

sandstone

is

a

potential

pathway

for

solute

transport.

2.2.2

Drilling

A

truck-mounted

drill

rig

with

4^-inch

inside

diameter

(I.D.)

hollow-stem

augers

was

used

to

advance

eight-inch

diameter

borings

into

the unlithified

materials.

Hollow-stem

augers

were

also

used

to

advance

the

boreholes

for

MW-3D,

MW-10/10D,

and

MW-11

into bedrock.

At

MW-3D,

the

augers

were

used

to

drill

the

upper

five

feet

of

bedrock.

A

rotary

air-hammer

was

then used

to

extend

the

bedrock

borehole,

at

a

four-inch diameter,

to

the

depth

of

completion.

At

MW-10D,

fine-grained

materials

in the

bedrock

caused

the

rotary

air-hammer

to

bind internally,

therefore,

the

augers

were

used

to advance

the

borehole

until

bedrock

composition

baited

further

augering.

During drilling,

the

unlithified

materials

were

sampled

with

a

split-spoon

and

described

in

the

field

by

STMI's

geologist.

The

split-spoon

samples

were

collected at

five-foot

intervals

in

previously

investigated

areas

(near

existing

wells

or

direct-push

borings)

and

were

collected

at

two-foot

intervals

in

newly

drilled

areas.

Bedrock

was

characterized

by

examining

drill

cuttings.

2.2.3

Construction

All

new

well boreholes

were

drilled

to

their intended

screen

depths

-

except

MW-7D,

which

was

drilled

five

feet

deeper

than

originally

proposed

to

provide

15

feet

of vertical

offset

from

nested

well

MW-7.

The

new

monitoring

wells

were

constructed

with

two-inch

I.D.,

schedule

40

PVC

pipe

flush-threaded

to

a

section

of

0.01-inch,

factory-slotted

PVC

screen.

The

four

shallow

wells,

which

were

screened

across

the

water

table,

were

constructed with

either

five-foot

or ten-

foot

screens,

depending

on

water

table

and

bedrock

depths.

The

deep

monitoring

wells

were

constructed

with

five-foot

screens.

From

bottom to

top,

the

annulus

for

wells

MW-3D,

MW-10D,

MW-12,

and

MW-13

was

filled

with:

1)

filter

pack

consisting

of

uniform

silica

(#5)

sand to

at least

one-half

foot

above

the

hutsonville hydrogeologic

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screen;

2)

about

one

to three feet

of

fine

(#7) sand; 3)

about

one

foot

of

bentonite

chips;

and

4)

a

Portland

cement-bentonite

(5:1 weight

ratio)

grout

mixture

to

near

ground

surface.

Wells

MW-10

and

MW-11

were

completed

in

a

similar

manner,

except

that

fine

sand

was

not

used in

order

to

maximize

the

annular

(bentonite)

seal

thickness.

Conversely,

because

of

the

depth

of

water

in

the

MW-7D

borehole,

three

feet

of

fine sand

was

installed

(in

lieu

of

bentonite

chips)

to

separate

the

filter

pack

and

grout

seal.

The

bentonite

chips had a

tendency

to swell

and

bridge

inside

the

auger

instead

of

settling

to

the

top

of

the

filter

pack.

The

grout

was

pumped

into

the

boreholes,

using

a

tremie hose

inserted to

the

base

of

the

hollow-

stem

augers.

The

tremie hose

was

then

removed

from

the

augers,

and

the

augers

were

gradually

withdrawn

from

the

borehole,

allowing

the

grout

to

settle.

The

grout

was

brought

up

to

a depth

of

three

feet

to allow for construction of

concrete

well

pads,

or

up

to

the

ground

surface at

shallow well

locations

to

maximize

the

annular

seal.

After

grouting,

all

of

the

new

monitoring

wells

were

finished with

a

stick-up

style,

locking

steel

well

protector,

surrounded

by

a

set

of

two

to three steel

bumper

posts for

additional

protection.

The

steel

protectors

for

MW-3D, MW-7D,

and

MW-13

were

set

in

three

feet

of

concrete,

and

the

protectors for

the

other

four wells

were

set into

the

bentonite-cement

grout

that

was

brought

up

to

the

ground

surface

and

topped

with

native

soil.

2.2.4

Development

New

wells

were

developed

to

remove

sediment

from

within

the

wells

and

to

restore

the

natural

flow

of

groundwater

around

the

wells.

Except for

MW-11,

development

was

accomplished

using

a

surge

and

pump

technique

(using

a

Geosquirt™

pump)

until

extracted

water

achieved

visual

clarity

and at least

1.5

borehole

volumes

(defined

as

the

volume

of

water

in

the

well

and

filter

pack)

were

removed

(Table

4).

Monitoring

well

MW-11

readily

bailed

dry

and

continued

to

produce

turbid,

silly

water

after

removal

of

22

gallons

of

water (2.7

borehole

volumes)

over

a

two-day

period.

The

well

borehole

was

augered

into sandstone bedrock

that has

a high

silt/fine

hutsonvi'Ile

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assessmcnt.doc

2-5

Natural

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FIELD

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sand

content,

and

substantial

amounts of

these materials

may

continue

to

pass

through

the

filter

pack.

2.2.5

Hydraulic Testing

Single

well

recovery

tests

were

performed

per

STMI

standard

operating

procedure

(see

Hutsonville

Work Plan,

STMI/249/98-01)

using a

five-foot

long

by

one-inch

diameter

solid

PVC

slug,

which

has

a

displacement

volume

of 0.027

ft3

(0.20

gallons).

An

m-Situ

Troll™

SP4000

pressure

transducer

with

on-board

datalogger

was

used to

monitor

groundwater

levels

during

the

':

testing.

The tests

were

programmed

utilizing

a portable

PC

loaded

with

software

designed

for

the

Troll™

unit.

After

measuring

static

water

level,

the

Troll™

was

inserted

into

the

well

to

approximately

one

foot

above

the

bottom,

and

the

water

level

was

allowed to

return

to static

level.

For

wells

with

screen

and

filter

pack

completely below

the

water

table,

the Troll™

was

activated

from

a

portable

PC

and

the

PVC

slug

was

quickly

lowered

below

the

water

level

in

the

well.

For

-

wells_screened .across

the

water

table,_the slug

was

lowered

below

the.water

level

at

the.

same

time

the Troll™

was

positioned.

After

the

water

level stabilized,

the

test

was

initiated

and

the

slug was