Tanks, Structures and Components

Tanks, Structures and Components
New prestressed tank accommodates expected growth

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New prestressed tank accommodates expected growth

Problem
The influx of new residents, businesses and recreational users to the City of Pocatello, Idaho, made additional water storage necessary. The city wanted to take advantage of federal grant money to build a 1-million-gallon prestressed concrete water storage tank.

Solution
The city chose a prestressed concrete tank design from DN Tanks as the most cost-effective solution for an underground water storage lifeline facility. With an inside diameter of 85 feet and a wall height of 26 feet, the tank was built using a poured-in-place corewall and a flat concrete slab roof supported by 21 concrete columns, each 24 inches in diameter. All joints incorporated PVC waterstops to ensure a watertight structure. The 10-inch-thick corewall was circumferentially and vertically prestressed using fully automated equipment. Located in the foothills south of town, the tank was unique in being fully buried so it would not detract from the natural scenery.

Result
Upon completion, the project gave the community safe, reliable water storage to accommodate recent and future growth. It will help facilitate new development expected in the area. 800/227-8181; www.dntanks.com.

Tight space adds challenge to water tank replacement

Problem
The Watuppa Water Board of Fall River, Mass., needed to replace a water storage tank with a new 1-million-gallon tank. The confined site was close to a large cellphone tower and in the middle of a suburban neighborhood, raising concerns about construction traffic, equipment, noise, environmental issues and overall safety.

Solution
The city and the Fay, Spofford and Thorndike (FST) engineering firm devised a plan for demolition of the existing tank. Fisher Tank Company worked with FST to fabricate and construct the replacement tank, and to develop a construction plan to minimize impact on the neighborhood. They carefully planned for materials delivery and lay-down and for placement of a large crane for setting the tank’s AWWA D-100 knuckle umbrella roof in place.

Result
Fisher worked with a local paint contractor to make sure surrounding homes and property would not be affected by the painting of the tank’s exterior. The replacement tank was installed without incident. 610/494-7200; www.fishertank.com.

Covers provide algae and odor control

Problem
The Penitencia Water Treatment Plant in San Jose, Calif., was replacing chlorine with ozone for primary disinfection. The plan was to reduce or eliminate chlorine feed at the head of the plant and so reduce formation of disinfection byproducts. Past attempts to reduce chlorine feed led to algae growth on the basins walls, launders and tube settlers, at times creating taste and odor issues. However, if prechlorination were continued at the same rate to control algae, the benefits of ozonation would be reduced.

Solution
District staff chose to cover the tube settler basins because the cost could be recovered through hypochlorite reduction. Geomembrane Technologies provided its retractable, structurally supported covers over the tube settler basins. The cover system consists of a durable NSF 61-approved coated fabric cover tensioned over a series of low-profile aluminum arches. The covers block sunlight and can be quickly disconnected and retracted to access tank internals for maintenance or inspection. Rainwater drains off the covers automatically.

Result
The covers met the plant’s requirements. Algae growth was controlled and hypochlorite feed reduced. Tube settler cleaning was significantly reduced. The covers were installed on budget while the basins remained in service. 506/449-0993; www.gticovers.com.

Town cuts THMs in potable water with removal system

Problem
The Town of York, N.Y., (population 1,000) purchases its water from a neighboring town, which chlorinates lake water and stores it in concrete ponds. The water as received can be high in trihalomethanes (THM) due to chlorine reacting with the water’s natural organic material. To meet the U.S. EPA THM limit of 80 ug/L throughout the distribution system, York officials needed to treat the water to eliminate the THMs created at the disinfection point.

Solution
After consulting with their engineer, town officials decided that the GridBee THM removal system from Medora Corporation could provide the greatest percentage reduction at the tank, no matter what came in from the supplier. The system combines mixing and air-stripping technologies to remove THMs from the water and purge them through a venting system. A submersible pump pushes water through the spray nozzles, where THMs are volatilized and removed through rooftop vents. A GridBee GS-12 submersible mixer ensures that the water exiting the spray nozzles is well mixed with the remaining water in the tank.

Result
York’s twin tanks (east and west) measured the same amount of THMs in inflow water. The west tank, without the GridBee system, had no change in THM level in the outflow water. The GridBee-equipped east tank measured a 62 percent reduction in THMs in outflow water, meeting the EPA rule. 866/437-8076; www.medoraco.com.

Epoxy lining refurbished an iconic water standpipe

Problem
Restoration of the iconic standpipe and carillon at the University at Albany (N.Y.) was challenging given its location within a reflecting pool at the center of the busy campus. The project involved removal of lead-based exterior paint in accord with health and safety regulations. The project also required replacement of the interior lining system with a lining specified to meet state health department regulations governing volatile organic compounds (VOCs) in drinking water.

Solution
Scaffolding enclosed in plastic sheeting contained sandblasting debris during interior and exterior renovation of the 251-foot high standpipe. Sandblasting equipment used low-decibel compressors, minimizing the disruption of students and faculty. The 320,000-gallon tank was drained, rusted steel sections replaced, and the interior coated with Series FC22 Epoxoline from Tnemec Company, a 100 percent solids epoxy lining certified under NSF/ANSI Standard 61. The interior coating included a zinc-rich urethane prime coat for an extended maintenance cycle. Low-VOC white and metallic fluoropolymer coatings provided exterior steel with UV light resistance and high color and gloss retention.

Result
VOCs were undetectable in water samples taken from the finished tank. The standpipe returned to service in September 2013. 800/863-6321; www.tnemec.com.

Water treatment plant restored using repair mortar

Problem
The Raccoon Creek Water Treatment Plant in Summerville, Ga., was badly deteriorated. A thorough engineering study sought to determine whether the plant could be repaired while in continuous operation or had to be replaced.

Solution
The study found that the plant could be repaired to optimal working condition using Megamix II from Xypex. The construction schedule was divided into three phases, allowing work to proceed while water treatment continued. More than 306,000 pounds of Megamix II was used on the flocculation tanks and sedimentation basins.

Result
The plant was restored while remaining in service, saving millions of dollars for the communities that depend on its output. 800/961-4477; www.xypex.com.

Inclined plate technology utilized for turbidity removal

Problem
Meota, Saskatchewan, on the southwest shore of Jackfish Lake, is surrounded by recreational communities. The lake’s water poses challenges to communities that would like to use it for drinking water. Under normal conditions the water is turbid from organic and inorganic compounds. Three new shallow infiltration wells were drilled nearby to take advantage of the soil’s natural filtration. However, the new water source contained high amounts of iron, manganese and TOC.

Solution
The Unitized Treatment System from Tonka Water with inclined plate technology (UTS-P) was installed. Coagulant is added to the raw water before it enters the UTS-P unit. As the water flows by gravity through the unit, it undergoes flocculation, sedimentation and media filtration. The water then travels to the sedimentation compartment and upward through stainless steel inclined plate settlers. The settlers offer high solids separation efficiency and deliver clarified water to the Simul-Wash filtration component. The efficiency of the plates allows for a smaller sedimentation compartment and a lower overall equipment footprint and cost. Solids in the sedimentation compartment are periodically cleared out through a sludge removal system.

Result
Meota now has a highly efficient plant producing high-quality water with minimal operator involvement. Before treatment, turbidity levels were 23 NTU; current levels are 0.063 NTU. 763/559-2837; www.tonkawater.com.



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