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Primary Clarifier RehabilitationCase Study

MWEA Annual Conference

TJ Bates – Donohue & Associates, Inc.June 25, 2019

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Outline

What’s so Complicated?

Holland WRF Background

Clarifier Condition Assessment

Alternative Evaluation

Construction Update

Lessons Learned

My Advice

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What’s so Complicated?

Primary

Effluent

Primary Clarifier

Sludge

RW

W

SCUM

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What’s so Complicated?

Circular

66

What’s so Complicated?

Squircles

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What’s so Complicated?

Rectangular

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What’s so Complicated?

Covered

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What’s so Complicated?

Not all Primary Clarifiers are created equal

Primary clarifier repair shouldn’t be a standard detail

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Holland WRF Background

Average day flow: 9 MGD

Design capacity: 12 MGD

Four covered primary clarifiers:

Two 7-ft deep, constructed in 1960

Two 14-ft deep, constructed in 1980

Odor control covers added in 1995

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Centralized influent distributed to all four clarifiers

Holland WRF Background

1

2

3

4

Splitter

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Weir modifications to better control distribution

Holland WRF Background

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2

3

4

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Effluent conditions vary

Holland WRF Background

1

2

3

4

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Holland WRF Background

Covers and odor control to address complaints

Corrosive gassed trapped below cover

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Holland WRF Background

Bridge creates air dam, making uniform air flow difficult

Concrete and steel are exposed and unprotected

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Clarifier Condition Assessment

Significant corrosion to steel components above the water line

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Clarifier Condition Assessment

Corrosion on the steel walking surface

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Clarifier Condition Assessment

Conditions even worse than expected once portion of the cover was removed

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Clarifier Condition Assessment

Iron oxide buildup

Holes in steel members

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Clarifier Condition Assessment

Concrete deterioration

Most notable on outside face of the launder

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Clarifier Condition Assessment

Exposed aggregate

“Soft” areas

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Alternative Analysis

Design a repair that fits the existing conditions

Corrosion and concrete protection only where required

Corrosion and concrete deterioration require oxygen

Can existing conditions be made better

Remove corrosive gasses below cover

Improve odor control efficiency

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Corrosion Protection – Only Where Required

Clarifier Mechanism

SS components were corrosion potential is high

Coated components where corrosion potential is low

Alternative Analysis

PC Mechanism Prices Based on Varying Materials

Construction Material Total Cost Cost Increase

Coated Steel $ 456,000 --

Partial Coated Steel,

Partial 304 SS$ 527,000 71,500

304 SS $ 612,000 156,000

316 SS $ 736,000 280,000

Prices from Nov 2017

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Alternative Analysis

Corrosion Protection – Only Where Required

Concrete Repair

Epoxy coating

Applied only where necessary

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Alternative Analysis

Remove gasses from below the cover

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Alternative Evaluation

Odor Control Efficiency

Majority of odors are generated as the water falls over the weir

Capture odors at the source

Minimize volume the odor control system protects

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Alternative Evaluation

Image Source: NEFCO

Launder Covers

Cover launder, weir, and baffle

Can be connect to odor control

Limit algae growth

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Alternative Evaluation

Launder cover on final clarifier

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Alternative Evaluation

Individual access hatches

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Alternative Evaluation

Accessible for routine OM checks

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Alternative Evaluation

Alternative 1

Remove cover

Coated steel mechanism

Install launder covers with odor control

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Alternative Evaluation

Alternative 2

316SS above water line

Coated steel below waterline

Isolate steel bridge from corrosive environment

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Alternative 2 Bridge Design

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Alternative Evaluation

Bid Results

Elected to proceed with Alternate 2

Alternative Cost

Alternate 1:

Launder Covers

Coated mechanism

$2.24M

Alternate 2:

Exist Aluminum Cover

SS/Coated Mechanism

$2.04M

Prices from July 2018

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Construction Update

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Construction Update

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Construction Update

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Construction Update

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Construction Update

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Construction Update

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Construction Update

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Construction Update

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Construction Update

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Lessons Learned

Varying outlet conditions require a variable plan

Dedicated effluent box

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Lessons Learned

Junction structure effluent box

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Lessons Learned

Be selective with approving you’re coatings!

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Lessons Learned

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Lessons Learned

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Lessons Learned

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My Advice

Be aware of “simple” projects

When spending millions of $$

Tailor every solution to the problem

Bidding markets are complex

Alternatives can be helpful

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Thank You!

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