ILLINOIS

POLLUTION

CONTROL

BOARD

August

15~

1985

CITY

OF

DIXON,

An

IrL~nois

Municipal

Corporation

)

Petitioner,

)

V.

)

PCB

85—47

T~LIC’~OIS

ENVIRONMENTAL

)

~QfE~TfON

AGENCY,

Respondent.

C’INIO~

AND

ORDER

OF

THE

BOARD

~hy

R.

C~.

Flemal):

Thi$

matter

comes

before

the

Board

upon

a

petition

for

~artce

~iled

by

the

City

of

Dixon

(1’D:Lxon”)

on

April

16,

~

Pursuant

to

the

Boardts

request

for

additional

n~ornation,

Dixon

filed

an

amended

petition

on

May

9,

1985.

The

rclief

requested by Dixon consists

of

v~riancr~until

October

30,

~6,

from

35 Iii.

Adm. Code

304.120(b)

a~.reflected in NPDES

j~rmit

number 1L0026450,

which presently limits

the discharge of

~ ~e

day

biochemical oxygen demand

(BOD)

to

20 milligrams per

~er

(mg/i)

on

a

monthly average,

and 40 mg,’i on

a weekly

average,

and

of

total

suspended

solids

(TSS)

to

25

mg/i

on

a

~ont.h~y

average,

and

45

mg/i

on

a

weekly

average.

The

Illinois

Environmental

Protection

Agency

(“Agency”)

E~Q itS

recommendation

in

this

matter

on

June

1,

1985,

~mending

that

variance

be

granted

with

conditions.

No

~b:E

ion

or

comment

was

received

by

the

Agency

in

response

to

‘egal

notices

published

on

its

behalf.

Dixon

waived

its

right

to

r~earing~,

and

none

was

held.

Dixon.,

which

is

an

Illinois

Municipal

Corporation

located

in

~ee

County,

owns

and

operates

a

Municipal

Wastewater

Treatment

r;:LciL~t.y

which

serves

the

Dixon

community

consisting

of

~

18,147

residents

and

numerous

commercial

and

industrial

establishments.

The

treatment

plant

is

located

on

the

~

o

~he

Rock

River,

into

which

discharge

occurs.

Facilities

e!~i~1e

raw

sewage

pumps,

comminutors,

grit

removal,

primary

~c~diinentation,

aeration

tanks,

final

sedimentation,

disinfection

(chlorination),

anaerobic

digestion,

sludge

storage,

drying

beds,

and

assorted

appurtenant

facilities,

The

plant

has

a

design

~a~ze

flow

of

3.5

million

gallons

per

day

(mgd)

and

a

design

naximum

flow

of

8.4

mgd.

Present

treatment

volumes

average

aç~rox

rru~tely

300

mgd

T~scharge

Monitoring

Reports

filed

with

the

Agency

have

sh~n

Jiat

the

effluent

from

the

Dixon

treatment

plant

has

commonly

experienced

excursions

heond

the

limits

specified

in

cr~.cive

!IPFES

permit,

number

1L0026450,

with respect to

---

-2-

both BOD and TSS.

The Agency provides data indicating

that

during the twelve month period April 1984 to March 1985 the NPDES

perrntt

limit of 20 mg/i BOD on a monthly average was exceeded

during

eight

months

and

the

TSS

limit of 25 mg/i on a monthly

average

was

exceeded

during

six

months.

Data provided by

Petitioner (Exhibit C) ±ndicatethat during the longer 26 month

perinci from January 1983 through February 1985 there were

18

excurssons

beyond

the monthly average

DOD

limit and 17 excursions

3eyoitd

the

monthly

average

TSS

limIt.

The

Exhibit

C

data

proviced

by

Petitioner

suggest

similar

rates

of

excursion

for

the

NPDSS-specif led

‘nekly

average

concentrations:

the

40

mg/i

BOO

I

itt

was

excev~c

in

17

of

the

26

months and the

45

ng/i

TSS

t.imi:

was

exceed...

in

21

of

the

26

months.

Dixon

contends,

and

the

Agency

agrees,

that

failure

to

meet

.he

extsttng

standards

is

a

result

of

two

problems,

namely

very

inadequate

existing

final

settling

capacity

and

the

need

for

increased aeration capacity for the activated sludge process.

The

existing

final

settling

capacity

is

only half of that needed

to

comply

with the current design criteria.

This results in

exeeasive velocities and turbulence in the settling tanks, poor

ettting of solids and

a

carryover

of

solids

over

the

tank

weirs

to

the

plant

discharge.

The

existing

aerators

are

not

sized

to

provide

sufficient

oxygen

transfer

to

satisfy the oxygen uptake

rates of

the

existing

toads

and

can

not

maintain an adequate

dissolved oxygen concentration in the process basins.

The

resulting sludges additionally tend to be bulky and difficult to

settte.

Dixon

has

commenced

a

project

to

address

these

two

principal

system

deficiencies,

with

the

goal

of

providing

the

treatment

necessary

to

achieve

the

NPDES

permit

effluent

standards.

SpeciE

tcslly

Dixon

intends

to:

1.

Construct

a

new

third

final

clarifier

equal

in

area

to

the

combined

areas

of

the

two

existing

final

clarifers,

and

thus

increase

the

present

capacity

by

1002.

2.

Replace

four

of

the

existing

aerators

with

larger

aerators

of

increased

aeration

and

mixing

capacity.

Preliaiinary

engineering

and

estimating

has

been

completed,

the

project

financing

has

been

developed,

and

construction

is

estimated

to

be

completed

and

the

new

facilities

in

full

operation

by

October,

1986.

Total

project

costs,

which

include

some

lesser-scale

improvements

than

those

specified

above,

are

estimated

at

$600,000.

By

Order

of

April

18,

1985

the

Board

requested

that

Dixon

discuss

the

posrble

use

of

stIlling

wells

or

cantilevered

weirs

in

r.he

f i.nat

ct

sr

.fiers

as

a

crnnpl

lance

alternative

•

This

Dixon

did

in

ics

Ame:;:i~t:., Petition.

Di.

ton

contends

65456

---

—3—

Since the existing final clarifiers are the tangential inlet

“Spira-Flo’ type, stilling wells, as used in center feed

clarifjets, are not viable or practicable means of improving

settling characteristics and achieving compliance.

Also, the

use of cantilevered weirs, as used for center feed or

rectangular clarifiers, is not a practicable means of

achieving compliance for these “Spira-Flo” clarifiers

•

The

operator is attempting to use baffles behind the inlet

circular

skirt

to

decrease

tank

spin”

with

limited success,

but the overall very

high

hydraulic rate in these clarifiers

makes

compliance

with

the

effluent

criteria

impracticable,

until

the new third clarifier is built and operational.

The

Agency

agrees

with

this

assessment

and

is

of

the

opinion

that

stilling

wells

or

cantilivered

weirs

would

not

resolve

the

particular

problems

faced

by

Dixon.

Dixon’s

intent

in

the

instant

case

to

seek

variance

from

the

NPDES

limitations

during

the

period

when

the

system

improvements

are

in

progress

•

Dixon

asserts

that

the

present

level

of

treatment can be maintained during construction, and that the

utilization

of

good

construction methods will assure against

the

introduction

of

extraneous

construction

debris

into

the

effluent.

Thus,

there

would

be

no

change

in

the

effluent

from

the

status

quo

during

the

pendency

of

the

variance.

The

specific

limitations

requested

by

Dixon

for

the

term

of

the

variance

are

30

and

45

mgfl

of

BOD

as

monthly

and

weekly

averages,

respectively,

and

40

and

60

mg/l

of

TSS

as

monthly

and

weekly

averages,

respectively.

Dixon

believes

these

to

be

reasonable

limitations

besed

on

past

plant

performance

and

on

existing

plant

capacity.

The

Agency

recommendation

agrees

with

the

reasonableness

of

the

monthly

average

limitations,

but

leaves

the

matter

of

the

weekly

averages

unaddressed.

Petitioner

addresses

the

issue

of

environmental

impact

by

noting

that

the

Rock

River

at

and

below

the

point

of

discharge

“is

a

wide,

shallow,

fast-flowing

stream

that

would

have

optimum

reaeration

and

assimilative

capabilities”

(Petition,

p.

4).

The

Agency

agrees

with this

assessment.

Dixon

further

notes

that

the

7-day

10-year

low

flow

at

Dixon

is

1144

cfs

(739

mgd),

which

provides

a

minimal

low

flow

dilution

factor

of

246:1

for

the

3.0

mgd

average

plant

discharge;

under

normal

river

flows

the

dilution

would

be

considerably

greater.

On

this

basis

Dixon

contends

that

no

measurable

effect

on

th.

stream

water

quality,

the

environment,

or

aquatic

life

is

expected.

During

Water

Year

1983,

the

Agency

collected

water

quality

samples

of

the

Rock

River

at

Grand

Detour,

which

is

about

12

miles

upstream

of

Petitioner’s

outfall,

and

at

Como,

which

is

about

18

miles

downstream.

Analysis

of

the

sampling

for

dissolved

oxygen

and

ammonia

nitrogen

(un-ionized)

indicated

to

the

Agency

that

the

Rock

River

is

essentially

unaffected

by

Petitioner’s discharge.

On this basis the Agency concludes “that

85-257

---

—&,—

the

requestec

variance

would

have

little

effect

on

the

water

quality

of

the

Rock

River” (Recommendation,

9).

En addressing the issue of hardship, Petitioner believes

that immediate compliance with its existing NPDES permit effluent

limitations for BOD and TSS

imposes

an

arbitrary

or

unreasonable

hardship because the existing noncompliance is due to physical

constraints of the treatment plant process units.

These

constraints, it is argued, can not be instantaneoulsy addressed,

but rather require the system improvements specified in

Petitioner’s c~w’plianceplan.

The system improvements, in turn,

will require

:r.c~.lOctober 30,

1986 to carry out

•

The Agency

agrees

with

.‘.

analysis,

consIders

the

construction

timetable

to

be

expeth::

.,is, and accordingly believes that an arbitrary or

unreasonable :‘cdship would result

if

the

variance

were

denied.

Based on c~ieforegoing, the Board finds that requiring

immediate coc~.iancewould constitute an unreasonable or

arbitrary hnë::~ip,considering the limited environmental

impact.

Accc.’~ingly,

the

requested

variance

is

hereby

granted,

subject to co3~iltions.

This Opin-on constitutes the Board’s findings of fact and

conclusions of law in this matter.

ORDER

The

City

of Dixon is hereby granted variance beginning this

day

from

35 111.

Adin.

Code 304.120(b) for

Outfall

001 of NPDES

Permit

110026450

with

the

following

conditions;

1.

The

variance

shall

be terminated on October 30, 1986, or

1

month

subsequent

to

the

completion

of

the

proposed

improvements, whichever occurs first.

2.

The interim effluent limitations shall be 30 mg/l BOD and

40 mg/l

TSS

on monthly averages, and 45

mg/i

BOD

and

60

mg/l TSS on weekly averages.

3.

Petitioner shall continue to sample and analyze its

effluent

at

the

frequency

specified

in

its

NPDES

permit

and

shall

comply

with all other effluent limitations and

conditions

thereof.

4.

Petitioner

shall

submit

a

progress

report

with

each

monthly D~scharge Monitoring Report outlining

construction efforts during the month.

5.

Within

‘.5 days of this

3rder, Petitioner shall execute

and submit to the Agency a Certificate of Acceptance in

the following form:

65-288

---

CERTIFICATION

We,

the

City

of

Dixon,

hereby

accept

and

agree to

be

bound

by

all

terms

and

conditions

of

the

Opinion

and

Order

of

the

Pollution

Control

Board

in

PCB

85~47~

City

of

Dixon.

By: Authorized Agent

Title

Date

The Certification shall be sent to the following address:

Illinois Environmental Protection

Agency

Division of Water

Pollution

Control

Compliance Assurance Section

2200 Churchill

Road

Springfield,

IL

62706

Attention:

James

Frost

IT

IS SO

ORDERED.

I,

Dorothy N. Gunn,

Clerk

of

the Illinois Pollution Control

Board, hereby certify that

the above Opinion

and

Order

was

ado ted

on

the

~

day of

~hy.unn,erk

Illinois Pollution

Control Board

8~259