5. Wastewater Treatment Plant Updates
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Incorporated 1892
Telephone (406) 758-7700
Douglas Rauthe
FAX (406) 758-7758
Mayor
Post Office Box 1997
Zip 59903-1997
Bruce Williams
City Manager
City Council
Members:
TO: Mayor Rauthe and All City Council Members
Gary W. Nystul
Ward
FROM: Bruce Williams
Cliff Collins
DATE: November 8, 1995
Ward I
Barbara Moses
RE.: Repairs to Gravity Thickener
Wardll
Dale Haarr
Attached to this cover note is a memo from John Wilson dated
Wardll
November 2, 1995. John's memo briefly explains the type of
Jim Atkinson
problem we are experiencing with our Gravity Thickener. This
Ward III
old information will be updated for you Monday night
concerning what we have learned since November 5, 1995.
Lauren Granmo
Ward III
Pamela B. Kennedy
Ward IV
M. Duane Larson
Ward IV
Telephone (406) 758-7700
FAX (406) 758-7758
Post Office Box 1997
Zip 59903-1997
Incorporated 1892
Memorandum
Date: November 2, 1995
To: Bruce Williams, City Manager
From: John Wilson, Assistant City EngineeP__L'_0
Re: WWTP - Emergency Repairs to Gravity Thickener
This memo is a request for authorization to proceed with the design and implementation
of emergency repairs to the wastewater treatment plant's fermenter thickener. Although
the design for repairs will involve more research, the cost of options currently under
consideration is estimated at $70,000 to $80,000. Obviously, we have not budgeted this
amount. We will also look into the cost of replacing the facility.
Our problem is the premature failure of a corrosion resistant coating for the roof beams,
roof panels, side walls and bottom of this 85 foot diameter concrete tank. Emergency
repairs are necrssary to prevent further deterioration of critical structural members.
As part of the new plant construction, the existing gravity thickener was refitted and
incorporated into the fermenter system. The fermenter enhances the production of
volatile fatty acids and is essential to the phosphorus removal process. Because of
strong odors, the exiting tank was refitted with a low concrete roof. The odor causing
gas, hydrogen sulfide, also reacts with moisture in the air to produce sulfuric acid.
Concrete is particularly vulnerable to the corrosive effects of sulfuric acid, so the design
provided for a protective bituminous coal tar coating. Unfortunately this material has
not performed well and has peeled away from about 25% of the concrete above the
water line. The coating is also starting to fail below the water line.
The thickener is currently off line and we are using alum, at a cost of around $1000 per
week, to maintain phosphorus removal. Our preference is to put the tank back in
service, knowing that we can return to make extensive repairs as soon as design work
and scheduling will allow. Our general plan is to sand blast the interior and recoat the
surfaces with another material. The options for "coatings" include a gunnite (spray -on)
type grout, a fiberglass liner, or other materials, similar to a tar coating, which could be
brushed or sprayed on.
We have contacted Stanley Engineering, who was the process engineer for our plant.
They tell us that the plant in Penticton, B.C. is having similar problems in their fermenter.
Douglas Rauthe
Mayor
Bruce Williams
City Manager
City Council
Members:
Gary W. Nystul
Ward I
Cliff Collins
Ward I
Barbara Moses
Ward II
Dale Haarr
Ward 11
Jim Atkinson
Ward III
Lauren Granmo
Ward III
Pamela B. Kennedy
Ward IV
M. Duane Larson
Ward IV
Telephone (406) 758-7700
FAX (406) 758-7758
Post Office Box 1997
Zip 59903-1997
Incorporated 1892
Memorandum
Date: November 9, 1995
To: Bruce Williams, City Manager
From: John Wilson, Assistant City Engineer--60
Re: WWTP - Gravity Thickener Repairs
This memo is a request for authorization to solicit contractor's proposals for the
installation of inspection ports and recoating of the gravity thickener. Our updated
estimate for the project is $50,000.
Over the past week we have evaluated the corrosive environment of the gravity thickener
and researched various methods of corrosion protection. Based on that analysis, we
have chosen to sandblast the remaining tar coating from the walls and roof of the tank
and apply a new glass flake epoxy coating. This material will be applied with an airless
sprayer, much like house paint. But given the confined working environment and special
techniques associated Arith epoxy materials, the cost is estimated to be considerably
higher that the average paint job.
Three or four local contractors will be asked to submit proposals by November 27, when
I will be back in the office. We intend to order materials and proceed with repairs by
mid -December.
The contractor's proposals will include the installation of a series of inspection ports.
These will provide much needed access for future maintenance and inspection. The
proposals will also provide for sandblasting and preparation; scaffolding, heating and
ventilation as required; equipment and labor to apply the new coating; and cleanup. We
will order and provide the inspection ports and epoxy coating materials.
We have reasonably firm costs on sandblasting and materials, but it's hard to predict how
contractors will respond to the requirements of working with special materials in a
confined space.
Douglas Rauthe
Mayor
Bruce Williams
City Manager
City Council
Members:
Gary W. Nystul
Ward I
Cliff Collins
Ward 1
Barbara Moses
Ward II
Dale Haarr
Ward II
Jim Atkinson
Ward III
Lauren Granmo
Ward III
Pamela B. Kennedy
Ward IV
M. Duane Larson
Ward IV