As home to the University of Iowa, Iowa City lays claim to
many "big city" attributes: thriving arts, good hospitals, enviable
educational resources, and flourishing businesses and industry.
Its primary water source is the Iowa River, on the banks of
which a new $26 million water treatment plant recently began operations --
built to meet the expanded needs of this modern Midwestern city.
Iowa City's population fluctuates regularly due to the
arrival and departure of its college students -- some 30,000 in number --
during the year. As a result, water consumption and treatment fluctuate.
Ten years in planning, the new water plant went online 100
percent on March 7, 2003, designed to better serve Iowa City's growing
population. It is also designed to meet ever-increasing state and federal
drinking water quality standards, and to improve the taste and odor of the
water supply for the area's Hawkeye State citizens.
The previous treatment plant, which the new facility has
replaced, was nearly 100 years old. By enlisting the services of engineering
firm Howard R. Green Company, the city sought to create a structure that would
meet its immediate and future requirements for the next 50 to 100 years.
The selection of protective coating systems was a critical
consideration of Howard R. Green Company to ensure long-term corrosion
protection and chemical resistance. In addition, the protective coating systems
for this project were also intended to enhance operation and maintenance
efficiency.
The new plant was constructed with concrete and houses
several steel and fiberglass processing tanks and storage vessels. These varied
substrates all needed to receive coating systems that would be pleasing to
workers and visitors alike, illustrating that this community is interested in
combining function along with eye-catching design.
Because construction was scheduled to take place during
winter months, some of the coatings applied had to be tolerant of low
temperatures.
New facility exceeds water quality standards
As part of a $100 million capital improvement program that
also includes modern water and sewer mains, the new lime-softening water
treatment facility has a 20 million gallons per day (20 mgd) capacity.
State-of-the-art process equipment at the plant includes
three Clari-Cone(TM) lime-softening tanks (a CB&I design),
granular-activated carbon (GAC) filters, and a chlorine contact tank designed
to be retrofitted for ozonation if new disinfection requirements are
introduced.
The plant uses a combination of surface and ground water
sources for better overall water quality. The majority of water comes from four
horizontal collector wells with direct intake from the Iowa River. Water is
also supplied by four shallow alluvial aquifer wells and one deep well that
penetrates the bedrock of the Jordan aquifer.
This aquifer covers nearly all of the state of Iowa and is
used by many communities as a major water supply source. A man-made lake
located on the plant site will provide a supplementary source of water.
"Using multiple water sources, we have much more
flexibility in terms of the quality of the water supply," says Mark Duben,
project manager with Howard R. Green Company. "We have a range of water
capabilities. By taking a combination of water from the river and the aquifers,
we are protected against potential contamination from any one source."
Among the regulations that created the need for new plant
construction were lower maximum contamination levels (MCLs) on inorganic
chemicals, organic byproducts, and radionuclides, according to Shaun Bradbury,
special projects manager of Iowa City.
"Most notably, we are well below all MCLs for our
drinking water," says Bradbury. "We've also reduced the presence of
hydrogen sulfide, which gives off an odor; and we are raising the parameters
for water taste. Improving taste and odor was a goal to improve the aesthetic
quality of our water."
Concrete substrates dominate plant
The new plant's compact design and significant use of
concrete construction, including two two-million-gallon storage reservoirs,
distinguish the Iowa City water treatment facility.
More than 13,000 yards of cast-in-place concrete were
utilized in the plant's construction. For long-term corrosion protection, and
the ability to maintain the plant's "clean" appearance, high
performance epoxy coatings from Sherwin-Williams were selected for these
surfaces.
"This is a high humidity environment that required
substrates that are less subject to deterioration," says Duben. "In
turn, we identified several long-life concrete coatings for their protective
nature that would allow us to minimize the time between recoat and repair."
Before the treatment plant was closed in, some initial
painting occurred during the coldest months of the year in Iowa City. Daytime
winter temperatures in Iowa City are routinely in the 30s, but may plummet
after dark, so low temperature tolerance was another important factor in
product selection.
For the majority of the concrete walls and ceilings
surfaces, Sherwin-Williams Dura-Plate 235 Multi-Purpose Epoxy was recommended.
"With the painting moving into January and February and
the subsequent weather conditions, cold weather curing capability became a real
issue," says Cliff Mohling, president of Cedar Rapids-based Pospisil
Painting. "Dura-Plate 235 allows painting to be done year-round because it
has the ability to cure out to zero degrees."
Dura-Plate 235 is an epoxy phenalkamine formulated
specifically for service in industrial and marine environments. This coating is
formulated to provide optimal performance in corrosive environments and can be
applied at temperatures as low as 0º Fahrenheit.
It also is suitable for use in USDA-inspected facilities.
This was particularly helpful on this project, because city officials
emphasized the importance of cleanliness and maintenance efficiency as they
likened their plant requirements to the strict standards typical of food
processing environments.
"We demand a clean plant. If you can keep the facility
cleaner, it's much easier to maintain the quality of the water. We needed
something that was low-maintenance and easy to wash down," says Bradbury.
"In addition, we'll have many tours going through here and we want the
facility to shine."
Dura-Plate 235 was submitted and approved, according to Dave
Kelchen, Sherwin-Williams Industrial and Marine Coatings specialist, because
the product is specifically engineered and formulated to control corrosion and
provide maximum durability and resistance to frequent water washdowns, chemical
solvents, and abrasives.
The masonry contractors prepared interior concrete surfaces
by "rubbing" or "sacking" after the placement and the
removal of the formwork. Rubbing a concrete surface with additional concrete or
grout is done to prevent the formation of holes and voids.
This process provides a dense, uniform surface that is
rougher than that provided by steel troweling and ready to paint immediately
after drying and curing.
After the surface was prepared, two coats of the
multi-purpose epoxy were applied at 4 - 6 mils dry film thickness (DFT) per
coat on interior concrete walls and ceilings as well as steel columns, beams,
and stair stringers. According to Mohling, the epoxy's low temperature
properties allowed his crew to work unhindered despite the temperature, and to
obtain the required film build and spread rate.
As weather and temperature conditions improved, Dura-Plate
235 continued to be used on interior PVC piping, ductwork, conduit and other
galvanized and concrete surfaces throughout the water treatment facility. On
lightly sanded exterior PVC and FRP items, the 235 was applied followed by one
coat of Sherwin-Williams Acrolon 218 HS.
Acrolon 218 HS is a two-component, low VOC, acrylic
polyurethane coating designed for high performance protection when maximum
exterior gloss and color retention is needed. The heavy duty coating provides
good resistance to corrosion due to weathering and, when used as a system,
conforms to AWWA D102-97 Outside Coating Systems #5 & #6. All coating
systems maintained a DFT between 6 - 10 mils.
Specialty coating required in containment areas
In areas where even greater chemical protection was
required, Sherwin-Williams Shelcote II was specified, according to Duben.
"On cast-in-place concrete floors and walls in the
liquid coagulant and fluoride chemical containment storage areas, we needed a
more specialized, chemical-resistant coating in case of a spill," he said.
Duben specified Shelcote II -- a high-solids, amine cured
epoxy coating designed for resistance to a broad range of aqueous and
petroleum-based chemicals including MTBE. Concrete in secondary containment
areas was prepared in accordance with SSPC-SP 13. Two coats of this high
performance epoxy were then applied to a 5 to 6 mil, DFT per coat.
With its greater water treatment capacity, the new facility
is another tool for attracting to the Iowa City area companies requiring large
amounts of water.
This is in addition, of course, to fulfilling the facility's
primary aim: providing residents with a safe, clean and abundant water supply.
For further information, phone 800-524-5979.
