Construction crews in Chattanooga are building a $14.2 million residuals centrifuge facility at the Tennessee American Water Plant that will process solid materials remaining from treating the water drawn from the Tennessee River. The project includes two centrifuges that will minimize the amount of the solid material, which then must be hauled off-site for land application or other disposal methods.
“There are multiple activities going on,” said Rosemary Carswell, manager of engineering of Tennessee American Water. “Concrete is being poured, rebar is being tied, form work is being placed, piping is being laid and there is potholing being done to locate existing utilities underground. There’s a lot of movement going on around the plant site. There are more than 30 extra people and personal vehicles on-site moving around on a daily basis. This is in addition to the 100 Tennessee American Water employees.”
Tennessee American Water’s current discharge permit to the city of Chattanooga’s wastewater treatment plant expires in April 2015, prompting the new construction.
“Current EPA standards now require that we minimize the amount of zinc in the discharge and, therefore, we must have an alternative discharge for our residuals,” said Carswell. “Although the zinc is a naturally occurring element in the raw water withdrawn from the Tennessee River, Tennessee American Water must assure removal of the zinc to meet the EPA standards and be in compliance with our discharge permit.
“The residuals centrifuge facility will eliminate the need for Tennessee American Water to send any solid residuals to the city of Chattanooga’s wastewater treatment plant. This will allow all parties to be in compliance with EPA requirements as they relate to the Clean Water Act. The Clean Water Act establishes the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters.”
The process wastewater improvements upgrades will include modifying the existing thickener #1 one to improve settling and solids retention performance, and installing a thickened sludge transfer pump station to draw thickened sludge from thickener #1 and deliver to the new thickened residuals holding tank. Crews also will install a thickened sludge holding tank to receive sludge from thickener #1, add a second thickener, construct a flow splitter box to split sedimentation basin residuals between the two thickeners and add a filter backwash equalization tank.
Crews will construct a dewatering building and system that will include a thickened residuals feed pump station, centrifuges, polymer storage and feed system and dewatered residuals conveyance and truck loading area. The hole created for the dewatering building, equalization tank, thickener #2 and residuals holding tank is approximately 18 ft. (5.5 m) deep. Equipment being used on the project includes excavators, bulldozers, rollers, dump trucks and flatbeds trucks.
“The solids that come from the filters and the sedimentation basins will be transferred to the existing thickener #1, or to the new thickener #2,” said Carswell. “The new thickened residuals transfer pump station will be used to draw thickened residuals out of either thickener and deliver it to the new thickened residuals holding tank. The new dewatering facilities will include thickened residuals feed pumps, two dewatering centrifuges, a polymer feed system and a cake solids conveyor. The centrifuges will be installed on concrete supports to allow for the discharge of cake solids from the bottom of the centrifuges onto a shaftless screw conveyor to transport dewatered cake to a loading point for transfer to trailers for offsite disposal.”
Challenges include working on an existing water treatment plant site where there are numerous utilities, such as piping, telephone, gas, electric and Internet. Maintaining access to the plant while large equipment is moving around is another concern.
“This is not only a working site to provide clean water to our customers, but a construction site,” Carswell said. “We have to assure we can maintain at all times the main core of our business, which is providing clean, reliable, affordable water to our customers.
“Bowen has done an excellent job in maintaining not only a safe site, but a clean site amid all the construction activities of moving and hauling dirt and gravel, receiving and storing materials on-site and constructing the facilities.”
Bowen Engineering Corporation of Indianapolis is serving as contractor on the project. According to Bowen project manager Michael Doenges, demolition of the existing buried clearwater basin has already taken place, with approximately 1,750 cu. yds. (1,337.9 cu m) of concrete and stone removed. Workers have excavated and hauled off approximately 17,000 cu. yds. (12,997.4 cu m) of dirt. Crews also started laying process piping throughout the job site, have begun placing concrete for building foundations and are performing backfilling and layout for backwash tank foundations.
Still to be carried out is the installation of 6,400 ft. (1,950.7 m) of underground pipe and 1,100 ft. (335.3 m) of exposed pipe. Crews must place the remaining concrete for dewatering building foundations, walls and slabs, place concrete for the backwash tank slab and walls, place concrete for the thickener bottom and walls and place concrete for the residuals holding tank slab and walls. Manholes, lift stations and other precast vaults also must be installed, along with masonry and roof for the dewatering building, handrail, steps and support steel for equipment.
Workers will install centrifuges, a polymer system, a thickener mechanism, pumps and other process equipment. Crews also are responsible for pave drives and site restoration, the installation of electrical and instrumentation and control equipment throughout site, along with dewatering building plumbing, HVAC and building finishes.
Process Equipment includes submersible mixers, a polymer system, weir gates, submersible pumps, rotary lobe pumps, decanters, centrifuges, a thickener mechanism and a monorail and hoist. Excavators, a backhoe, a bulldozer and roller have been required for excavation, backfill and pipe laying. A crane also has been necessary for moving concrete forms, process equipment and large structural components.
Materials needed for the project include 2,300 cu. yds. (1,758.4 cu m) of concrete, 7,500 ft. (2,286 m) of ductile iron pipe and PVC pipe, 19,000 sq. ft. (1,765.4 sq m) of masonry, 310 tons (281 t) of rebar, 5,000 sq. ft. (464.6 sq m) of asphalt paving, 25,000 tons (22, 679.6 t) of stone and 8,000 sq. ft. (743.2 sq m) of precast concrete roof.
“The continuous operation of this plant is critical to the water company and its customers,” said Doenges. “All parties have been working diligently and with great care to ensure that the impact to plant operations is minimized, so the level of water to supply 370,000 people every day continues.
“The excavation and demolition of the existing clearwater basin was the primary focus for the first portion of the project. Now that this part of the project is complete, there will be numerous areas of focus that will occur at the same time and with equal importance.
“Working in a plant with a long history has created several challenges while trying to excavate and make room for the new structures and utilities. The project team has encountered numerous abandoned pipe lines that required thorough research and planning to ensure they could be safely removed without interrupting plant operations. American Water, CDM Smith, CTI and Bowen have worked cohesively as a team to identify these lines and safely remove them so that construction could progress.”
Security remains a top priority at the water treatment facility. The plant is secured at all times, and all construction personnel and deliveries are required to check in with a guard positioned at the main gate.
The site experienced a fair amount of rain during the fall months. Preparations will be made to work as efficiently as possible throughout the winter, so that crews can meet their deadline. Work began in 2014 and should be completed next year.
Since 1887, Tennessee American has served as Chattanooga’s water provider. Originally a steam-generated pump station fueled by coal, high tech motors now run Tennessee American Water Co. The city’s very first water pipes were laid in 1850, and the city’s first water company — Chattanooga Water Corp. — was established in 1856. The water system was later sold to the American Water Co. and the water plant was relocated to its current site along Amnicola Highway. The location is known as the home of Phillip D. Glass, the company’s iconic figure who sits on a roadside water tower, tilting his hat to those who pass by.
American Water is the largest publicly traded water and wastewater utility company in the country, serving an estimated 14 million people in more than 40 states, and parts of Canada. American Water provides services to homes, businesses and municipalities through regulated and market-based businesses. Its primary business involves the ownership of water and wastewater utilities that provide water and wastewater services to residential, commercial and industrial customers, treating and delivering more than one billion gallons of water per day.
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