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.